IS_0846-18th Young Researchers Conf Proceedings

Transcription

18
6 April 2016
Sponsors:
British Group
British Group
18
6 April 2016
The Institution of Structural Engineers | Proceedings of the 18th Young Researchers’ Conference | 6 April 2016
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Contents
Conference sponsors
3
Welcome4
Keynote Speaker
5
Conference team
6
Research Panel
7
Panel members
8
Programme12
Poster presentations
2
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13
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Rwayda Al Hamd - Finite element modelling of concrete slab-column connections under eccentric loads
14
2
Sherwan Albrifkani - Investigation of progressive collapse mechanisms of reinforced concrete frames in fire
16
3
Marco Baiguera - Experimental validation of a novel seismic-resistant steel frame for damage minimisation
18
4
Konstantinos-Nikolaos Bakis - Aeroelastic control of long-span bridges with controllable winglets
20
5
Bogdan Balan - Stronger and ductile float glass-GFRP hybrid beams
22
6
Shanshan Cheng - A new design method for side wall buckling of equal-width RHS truss X-joints
24
7
Giuseppe Marcantonio Del Gobbo - Improving the non-structural seismic performance of conventional multi-storey buildings
using viscous fluid dampers
26
8
Evelyne El Masri - A vibration-based NDT technique for civil engineering structures
28
9
Sami Elshafie - Would basalt fibre concrete reduce cracking in light rail embedded track slab?
30
10 Alfred Kofi Gand - Demountable spacelink truss - design evolution of PFRP joints and performance integrity testing 32
11 Mohamed Kiari - New design of a FRP-reinforced concrete beam system for fire performance
34
12 Matthew Kidd - On the robustness of ‘simple’ and/or ‘semi-rigid’ structural steel connections when subjected to blast loading
36
13 Jalil Kwad - Estimating fatigue life of details in steel bridges using continuous response monitoring
38
14 Pinelopi Kyvelou - Composite flooring systems comprising cold-formed steel beams and wood-based particle boards
40
15 Robin Malloy - Hybrid testing of buckling-restrained braces 42
16 Karl Micallef - A study on punching shear failure induced by impact loading on reinforced concrete flat slabs 44
17 Conan O’Ceallaigh - Long-term deformation in unreinforced and reinforced Sitka Spruce glulam
46
18 Ucheowaji Ogbologugo - Prospective view of cement based (GEM-TECH) material as a structural material
48
19 Caoimhe O’Neill - Glued-in BFRP rods as moment connections in indigenous low grade timber
50
20 Naveed Rehman - Deconstructable composite floor system with metal profiled decking
52
21 Razvan Sencu - Multiscale stochastic fracture mechanics modelling of composites informed by in-situ X-ray CT tests
54
22 Adeayo Sotayo - Experimental investigation of recycled carpet composites for barrier structures 56
23 Petia Tzokova - Tall modular buildings: height limits of stacked steel modules
58
24 Jean Paul Vella - Development of novel connection methods between precast concrete panels
60
25 Jie Wang - Design of hot-finished high strength steel tubular members
62
26 Yan Xu - Detecting long-span bridge displacement from fusion of GPS and accelerometer signals
64
27 Panayioiti Yianni - A modelling approach to railway bridge asset management
66
28 Dimitrios K. Zimos - Dynamic non-linear analysis of sub-standard reinforced concrete frames accounting for shear failure localisation
68
Conference sponsors
Elsevier
products and services. The company works in partnership with the global science and
health communities to publish more than 2,000 journals, including The Lancet, Cell, and
Structures, the Research Journal of the Institution of Structural Engineers.
www.elsevier.com
Ramboll
Ramboll is a leading engineering, design, environmental and consultancy company
countries, Ramboll combines local experience with a global knowledgebase, constantly
striving to achieve inspiring and exacting solutions that make a genuine difference to our
customers, end-users and society as a whole.
www.ramboll.co.uk
Flint & Neill
Flint & Neill is an engineering consultancy specialising in the design of unique and
innovative bridges and structures. The practice has been involved in the high quality
complex projects, large and small, all over the world and is currently leading the detailed
design of Mersey Gateway Bridge Project.
IABSE
IABSE (International Association for Bridge and Structural Engineering) is a long
established and well-respected international association dedicated to developing, sharing
and disseminating structural engineering knowledge and expertise among its members.
The British Group comprises those members currently working in the UK and organises a
variety of events and meetings in the UK.
British Group
British Groupwww.iabse.org and www.iabse.org.uk
Oasys
Oasys is a leading developer of structural and geotechnical engineering software, with a
long-standing reputation for providing high-quality solutions and unrivalled support.
Established in 1976 as part of Arup, Oasys software is used by leading engineering
organisations and reputable research and teaching Universities across the globe. Our
extensive product range includes heavily discounted University bundles for structural and
geotechnical engineers - helping to develop the future of engineering.
www.oasys-software.com
The Institution of Structural Engineers Research Fund
Research Fund
The Institution of Structural Engineers Research Fund supports the Undergraduate
Research Grant Scheme, the MSc Research Grant Scheme, the Young Researchers’
Conference and the Institution of Structural Engineers’ Research Award. The fund
occasionally awards other research grants. Details of all these schemes are available on
our website.
www.istructe.org/research-fund
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Welcome
Welcome to The Institution of Structural Engineers’ Young
Researchers’ Conference. This institution represents and
supports structural engineers worldwide, and all those
involved in ensuring the safety, stability and serviceability of
our buildings and bridges. Our members do extraordinary
things, daily, to create economic, efficient and elegant
structures all over the world.
The profession of structural engineering, like any modern
profession, relies on keeping up to date with developments
in our understanding of structural behaviour and in the
application of new materials and technologies, among
other things. The Institution of Structural Engineers is
central to ensuring that vibrant research continues to
underpin our members’ professional development and
ability to innovate.
The Young Researchers’ Conference is now in its 18th year,
and its success simply multiplies year on year. It celebrates
the research being conducted by the future leaders of our
profession, and it suggests important paths which could
lead to successful innovation. Today you will experience
first-hand some research of potentially great significance
and impact to structural engineering.
And what a wonderful way to enter this profession!
Conducting research at the limits of our knowledge is both
exciting and crucial. Your work is vital to the continuing
development of structural engineering technology and
to the ability of the institution’s members to remain up to
date. Thank you for wanting to tell our profession about
your research. This is a deep responsibility, and we all look
forward immensely to hearing your stories.
It might be that after your research degree you become
an academic, thereby helping to lead future generations
of researchers in structural engineering. Or it might be that
you enter practice, and become a highly-skilled member
of a design or construction team. Whatever you end
up doing, the skills which you acquire as an inquisitive,
rigorous researcher will ensure that you have an extremely
rewarding and successful career. And of course, the
biggest winner will be structural engineering, and those
who use, occupy and experience the structures which our
members create daily.
Ian Firth
Senior Vice-President of
The Institution of Structural Engineers
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Keynote Speaker
Professor Ian Kinloch
Professor of Materials Science at the University of Manchester
Ian Kinloch currently holds an ESPRC Challenging
Engineering Fellowship on Delivering Graphene as an
Engineering Material. He previously held an EPSRC/
RAEng Research Fellowship and won the IOM3 Rosenhain
Medal. His research covers the production, processing and
applications of nanomaterials. His work on manufacture
of nanotubes has been commercialised by Thomas Swan
and Co Ltd and his electrochemical exfoliation of graphene
is currently being scaled in a joint project with Morgan
Advanced Materials. His application studies focus on
composite materials and energy storage.
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Conference team
Chairman:
Oral judges:
Ian Firth
FREng CEng FIStructE FICE
Chris Walker - Chair of oral presentation judges
Senior Vice-President of the Institution
Dr Keerthi Ranasinghe
Susan Giahi-Broadbent
Carl Brookes
& Neill, a member of the COWI Group of companies. His
work mainly involves bridge design and engineering and
he has worked on many major bridges worldwide including
several long-span crossings. He has also been responsible
for many award-winning pedestrian bridge designs,
including the aluminium Lockmeadow footbridge in Kent,
the cable stayed Sail Bridge in Swansea and the little
Bridge of Aspiration in London’s Covent Garden.
Ian is one of the UK’s leading bridge designers and directs
the designs, checks and structural assessments of bridges
around the world. He frequently works with leading bridge
architects on the conceptual design of bridges and is a
regular speaker on the subject of elegance and aesthetics
in structural design. He directs building structures projects
and acts as expert witness in connection with claims
and litigation and is also Chairman of the British Group
of the International Association for Bridge and Structural
Engineering.
Poster judges:
Team A
Professor Dennis Lam - Team leader and Chair of poster
judges
Dr Roger Escofet
Steve Matthews
Team B
Steve Denton
Dr Pete Winslow
Professor John Forth
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Research Panel
The Institution of Structural Engineers’ Research Panel comprises members from both industry and academia, and has
the primary role of supporting, facilitating and directing research in Structural Engineering. The Research Panel, through its
members and sponsors, as well as through its links with the local regional groups of the Institution and Institution Liaison
Officers in Universities, aims to promote the effective dissemination and application of research, attract young people to
research careers and liaise with other organisations with an interest in research. The Research Panel also engages with
‘Structures’, the Research Journal of the Institution of Structural Engineers, by judging papers for awards.
Through its Research Fund, the Panel are responsible for a number of research grant and award schemes, including the
assessment of applications, the assignment of funds, the judging of deliverables and the award of prizes. The research
grant and award schemes are as follows:
•
Undergraduate Research Grant scheme (www.istructe.org/ug-research-grants).
•
MSc research Grant scheme (www.istructe.org/msc-research-grants).
•
Research Award scheme (www.istructe.org/research-award).
Recently the Research Panel has introduced the Industry Focussed Research Challenge which means that research
funding available through the institution’s established schemes can be focussed on research that is well aligned with the
current challenges faced by the profession. Applications through the established schemes that address the priorities of the
industry focussed research challenge receive additional credit in the initial selection of grant winners however, grants can
still be awarded to high quality applications on other topics.
The challenge is built around research themes that aim to encourage and facilitate collaboration between industry and
researchers and to raise awareness of the industry needs. The themes are given below:
Construction materials
—— Advanced engineering materials;
—— Durable materials considering life-cycle issues;
—— New materials and materials used in other industries;
—— Reflections on ‘old materials’.
Loading on buildings
—— Imposed loading on floors;
—— Assessment of actual loading on structures;
—— Designing buildings for being adaptable to load levels;
—— Combinations of loading and a review/evaluation of international practice.
More information on the Research Fund can be found at: www.istructe.org/research-fund.
The Young Researchers’ Conference was instigated by the Research Panel to provide PhD students with an opportunity to
present their work to an audience of peers and industry professionals, and to exchange ideas and experiences with fellow
researchers. The Panel assesses the applications submitted to the conference and judges the presentations on the day.
Professor Leroy Gardner
Research Panel Chair
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Panel members
Professor Leroy Gardner (Chairman)
Alan Burr
CEng MICE FIStructE
BSc MSc DIC CEng MIStructE PE
Leroy is Professor of Structural
Engineering at Imperial College
London. He is engaged in teaching at
both undergraduate and postgraduate
level, specialist advisory work and
leading an active research group
in the area of steel structures. His
principal research interests, in respect
of which he has co-authored four textbooks and some
200 papers, lie in the areas of structural testing, numerical
modelling and the development of design guidance for
steel structures. He is a member of the European and BSI
Committees responsible for Eurocode 3 and Fellow of both
the Institutions of Civil (FICE) and Structural (FIStructE)
Engineers. He is also Chair of the Research Panel and
Editor-in-Chief of the new Research Journal of the
Institution of Structural Engineers - Structures.
Alan is a principal of the firm of Murphy
Burr Curry, Structural Engineers in
San Francisco, which he co-founded
in 1997. He and his firm specialized
in structural engineering services and
building design, including commercial,
retail, residential and educational
facilities, with an emphasis on seismic
design and retrofit. Before moving to San Francisco in
1991, Alan worked in London, Cardiff and Hong Kong
for Ove Arup and Partners. Alan has a Master’s Degree
from Imperial College London and is a licensed Structural
Engineer in California and Hawaii, as well as a member of
the Institution of Structural Engineers.
Chris Walker (Vice-Chairman)
CEng MIStructE
Chris is a Principal Engineer at Flint
& Neill Limited which he joined after
graduation in 2004 and his experience
to date reflects the capability of Flint &
Neill to tackle complex and technically
ambitious structural engineering
projects. Chris holds Master’s degrees
from the University of Cambridge and
Imperial College and his recent projects include detailed
design of the cable systems for the 3,300m bridge across
the Messina Strait between Italy and Sicily (2010-2011) and
deck design for the 1,550m Izmit Bay suspension bridge,
due for completion in 2016. He is currently leading a team
working on erection engineering for the transformation of
the London 2012 Olympic Stadium.
Susan Giahi-Broadbent
MSc(Eng) CEng FIStructE MICEL MCIHT
Susan has over 25 years experience
in Civil and Structural Engineering
Projects (Rail, Highways and Building)
involving Management, Design and
Construction in the UK and Overseas.
As a Structures Project Manager,
a Discipline Lead and coordinator
she has wide experience on highly
prestigious projects. She has been an active member of
the Institution since2007. This involvement has included
Member of Council, Board, Membership Committee,
Research Panel, Health & Safety Panel and Chair for
Midland Counties Region.
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Professor John Forth
PhD CEng MIStructE
John is the Chair of Concrete
Engineering and Structures in the
School of Civil Engineering at the
University of Leeds. He was awarded
his first degree, a BEng (Hons) in Civil
and Structural Engineering from the
University of Sheffield. He received
his PhD from the University of Leeds.
A chartered member of The Institution of Structural
Engineers, he is on several Technical Committees (i.e.
Eurocodes, fib, RILEM) in the European Union. His
research interests include serviceability, durability and the
dynamic performance of reinforced concrete and masonry
structures.
Professor Costas Georgopoulos
MEng MSc CEng FHEA FCS FIStructE FICE
Costas is Chair in Structural
Engineering Practice at Kingston
University London, he has a unique
multi-sector experience comprising
Consulting Engineering, Academia
and Professional Bodies in the UK
and overseas. Costas has particular
expertise on concrete (manager of
education for The Concrete Centre), earthquake-resistant
structures (tutor of the ICE 1-day CPD course on Seismic
Design to EC8 for practising engineers) and sustainability
(author of the book ‘Sustainable Concrete Solutions’ by
Wiley). Prof Georgopoulos’ contribution to the IStructE
has included: chairman of the Southern Branch, member
of Academic Qualifications Panel & Research Panel and
member of the Council.
Tim Hetherington
Dr David M Martin
MEng CEng MIStructE
BSc PhD CEng FIStructE FIMechE
Tim graduated from Leeds in 1992
and worked for Mott MacDonald
on land regeneration and general
structures/civils projects before
focussing fully on progressively more
advanced structural engineering at
Bison Structures, Buro Happold, then
at special structures company Fenton
Holloway. In 2004 he moved to Edinburgh and worked on
taller steel and concrete buildings at Upton McGougan
before moving to SKM Anthony Hunts as senior engineer
then structural lead, where he was responsible for several
award winning cultural, educational and sports facilities
up to £25M. Tim now runs his own expanding practice
Applied Engineering Design, with offices in Edinburgh and
Glasgow.
David is a graduate of the Universities
Glasgow and Dundee. He has worked
in the construction and engineering
industries for over 30 years and has
particular experience in managing
large multidisciplinary design and
engineering teams for major capital
projects. David is a Chief Engineer
with ATKINS and is accountable for the quality of design
and engineering work undertaken across a broad range
of projects in two highly regulated, high hazard market
sectors.
Professor Jason Ingham
Toby heads civil engineering at in
the School of Engineering at The
University of Warwick. He is a member
in the Midland Counties Region and
a past chairman. He is internationally
known for his structural engineering
research with fibre reinforced polymer
shapes and systems, often directed to
inform the writing of design standards or codes of practice.
His teaching includes interdisciplinary design projects,
steel structures, civil engineering materials and forensic
engineering for undergraduates to ‘learn from failures’.
BE(Hons) ME(Dist) PhD MBA F.IPENZ
Jason is a professor of structural
engineering at the. He obtained his
PhD from the University of California
San Diego and an MBA from the
University of Auckland, and his
research interests primarily focus
on the seismic assessment and
improvement of existing masonry
and concrete buildings. Jason also undertakes research
on the seismic response of precast concrete components
and concrete materials technology. Recently Jason’s
primary focus has been associated with the performance
of masonry buildings in the Canterbury earthquakes
and the development of a detailed seismic assessment
methodology for unreinforced masonry buildings.
Professor Dennis Lam
BEng(Hons) MPhil PhD CEng FIStructE MICE MIMgt
Dennis is the Chair of Structural
Engineering and the Director of
Bradford Centre for Sustainable
Environments at the University of
Bradford. He is a Chartered Engineer,
Fellow of the Institution of Structural
Engineers and Member of the
Institution of Civil Engineers. Before
joining the academia, he has spent more than ten years
in engineering practices and had extensive experience in
structural design, especially in schools and public buildings
using steel, concrete and composite frames. He holds
visiting professorships at Tsinghua University, China and
Hong Kong Polytechnic University and is a member of the
European Committee on Standardization (CEN) responsible
for the development of the Eurocode 4.
Professor J Toby Mottram
DSc CEng FIStructE
Professor Messaoud Saidani
BEng PhD HEA PgCertLT CEng MIStructE
After completing his first degree in Civil
Engineering, Messaoud embarked
on a PhD in Structural Engineering at
The University of Nottingham, which
he successfully completed in 1991.
He then stayed on as a post-doc
research fellow working with Professor
David Nethercot on a number of
pan-European and UK projects. In 1995, he jointed
Coventry University as a lecturer, where he is currently
a Reader in Structural Engineering. Research interests
include: materials engineering and novel materials
for construction, sustainability in construction, concrete,
steel and timber structures. Current research activities
include carrying out an investigation into the material and
structural properties of a novel cementitious material called
GEM-Tech. Messaoud published of over 80 journal and
conference papers, and technical documents.
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Dr. Keerthi Ranasinghe
Professor Ahmer Wadee
BSc PhD
BEng PhD MSc DIC ACGI
Keerthi is the Principal Structural
Engineer & Eurocodes Consultant for
BM TRADA. He is the author of the
Eurocode 5 version of the popular
TRADA publication, Span Tables
and is also the developer behind the
TRADA Eurocode 5 online software
suite. Keerthi sits on BSI committees
B/525/5 (Timber), B/525/1 (Actions) and B/525/-/32 (Fire).
He also sits on the European Committee CEN/TC250/
SC 5 (Timber) and the Working Group 4 (Fire). He is also
the current expert commentator for Eurocode 5 on the
BSI Eurocodes Online website. Keerthi has served the
Research Panel at the institution for the last two years.
Ahmer is currently Reader in
Nonlinear Mechanics in the Structural
Engineering Section at Imperial
College London. He is a leading expert
on structural stability having published
over 100 articles in international
journals and conference proceedings.
In 2014, he was listed as one of
the UK’s top 100 practising scientists by The Science
Council and was also a co-editor of the book “50 Visions
of Mathematics” published by Oxford University Press.
He is a Chartered Mathematician and Scientist, a Fellow
of the Institute of Mathematics and its Applications and a
Graduate Member of the Institution of Structural Engineers
Dr Robin Sham
Professor Chien Ming Wang
BSc PhD DIC FCGI CEng FICE FIHT FHKIE
BEng(Hons) MEngSc PhD FIStructE FIES
Robin has an illustrious career that
spans nearly four decades and
several continents. He is a leading
international authority in bridge
engineering, whose pioneering
contributions have helped realized
the largest and the most complicated
bridges in the world. He is a Gold
Medallist of the Institution of Civil Engineers, and a Fellow
of the City and Guilds of London Institute. He is the Global
Long Span and Specialty Bridges Director of AECOM. His
recent projects included the Taizhou Bridge, which received
the Institution of Structural Engineers 2013 Structural
Award in the Highway or Railway category, and also the
Supreme Award
Chien is the Director of the Engineering
Science Programme, National
University of Singapore. He is a Fellow
of Academy of Engineering Singapore,
a Fellow of Institution of Engineers
Singapore, a Fellow of Institution of
Structural Engineers and Chairman
of IStructE Singapore Regional
Group. He is also Adjunct Professor in Monash University,
Australia. His research interests are in the areas of
structural stability, vibration, optimization, nanostructures,
plated structures and Mega Floats. He has published over
400 papers and authored several books. He is the Editor
in Chief of International Journal of Structural Stability and
Dynamics and IES Journal Part A: Civil and Structural
Engineering and an Editorial Board Member of several
journals. His awards include Lewis Kent Award, Keith
Eaton Award, IES Prestigious Engineering Achievement
Award, and IES/IStructE Best Structural Paper Award.
Dr Roger Singleton Escofet
Roger is currently Portfolio Manager at
EPSRC; having previously completed
a PhD in Biology at UCL and a degree
in Biochemistry. His role involves
managing research in civil engineering
which gives him a privileged position
in understanding the future trends
and challenges within Structural
engineering research.
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Dr Pete Winslow
PhD CEng MIStructE
Following the completion of his PhD
on longspan, free-form structures,
Pete joined Expedition Engineering
whereupon he played key roles in
designing the pioneering ferrocement
solar canopy for the Stavros Niarchos
Cultural Centre in Athens and the
Stockton Infinity footbridge. He was in
the engineering team for the award-winning London 2012
Velodrome, and is currently working on range of unusual
structures including refurbishment of a historic building,
a tensegrity sculpture and the acoustically-sculpted
Soundforms shells. Pete is also responsible for Expedition’s
R&D programs, working with universities and industry to
explore advanced materials, pedestrian induced vibrations
and prototyping adaptive structures.
Professor Siu Lai Chan
PhD CEng MIStructE FHKIE
Siu Lai is currently the Chair
Professor in Computational Structural
Engineering at the Department of Civil
and Environmental Engineering of The
Hong Kong Polytechnic University.
He has been involved in teaching at
undergraduate and postgraduate level
and research in non-linear structural
analysis, design of steel and composite structures and
second-order direct analysis of structures for which
his developed program “Nida” is widely used in Hong
Kong and the region for education and practical design.
He is the chief editor of the journal “Advanced Steel
Construction” and regional editor of “Applied Mechanics
and Engineering”.
Dr Diana Petkova
MSc PhD
Dr Diana Petkova is a Senior Lecturer in
the Department of Civil Engineering at
Kingston University. She received her PhD
from Kingston University London in 2011
and since has been teaching at
undergraduate and postgraduate level. Her
research interests include the use of FRP
as internal reinforcement and for
strengthening, the effects of elevated and high temperatures
on reinforced concrete and steel structures and the behaviour
of hybrid elements.
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Programme
09.30
10.00
Welcome by conference chairman Ian Firth – Senior Vice President of the Institution of Structural Engineers
10.10
Research matters
10.15
Keynote address by Professor Ian Kinloch – University of Manchester
10.45
Chairman’s introduction
10.55
Session 1
10.55
Improving the non-structural seismic performance of conventional multi-storey buildings (Abstract No. 7)
Giuseppe Del Gobbo – University of Oxford
11.10
Aeroelastic control of long-span bridges with controllable winglets (Abstract No. 4)
Konstantinos Bakis – University of Oxford
11.25
Discussion
11.35
12.00
Session 2
12.00
Long-term deformation in unreinforced and reinforced Sitka Spruce glulam (Abstract No. 17)
Conan O’Ceallaigh – National University of Ireland, Galway
12.15
Glued-in BFRP rods as moment connections in indigenous low grade timber (Abstract No.19)
Caoimhe O’Neill – Queen’s University Belfast
12.30
Discussion
12.40
Key research challenges from an industrial perspective
13.00
Lunch
13.45
Poster presentation
14.20
Session 3
14.20
Composite flooring systems comprising cold-formed steel beams and wood-based particle boards (Abstract No. 14)
Pinelopi Kyvelou – Imperial College London
14.35
Deconstructable composite floor system with metal profiled decking (Abstract No. 20)
Naveed Rehman – University of Bradford
14.50
Development of novel connection methods between precast concrete panels (Abstract No. 24)
Jean Paul Vella – Imperial College London
15.05
Demountable spacelink truss - design evolution of PFRP joints and performance integrity testing (Abstract No. 10)
Alfred Kofi Gand – University of Warwick
15.20
Discussion
15.40
Tea & judging
16.05
Membership matters
16.15
Prize giving & closing remarks
16.30
Close
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Poster presentations
Finite element modelling of concrete slab-column connections under eccentric loads (Abstract No. 1)
Rwayda Al Hamd – University of Manchester
Investigation of progressive collapse mechanisms of reinforced concrete frames in fire (Abstract No. 2)
Sherwan Albrifkani – University of Manchester
Experimental validation of a novel seismic-resistant steel frame for damage minimisation (Abstract No. 3)
Marco Baiguera – Heriot-Watt University
Stronger and ductile float glass-GFRP hybrid beams (Abstract No. 5)
Bogdan Balan – University of Southampton
A new design method for side wall buckling of equal-width RHS truss X-joints (Abstract No. 6)
Shanshan Cheng – University of Sheffield
New design of a FRP-reinforced concrete beam system for fire performance (Abstract No. 11)
Mohamed Kiari – University of Edinburgh
On the robustness of ‘simple’ and/or ‘semi-rigid’ structural steel connections when subjected to blast loading (Abstract
No. 12)
Matthew Kidd – University of Liverpool
Estimating fatigue life of details in steel bridges using continuous response monitoring (Abstract No. 13)
Jalil Kwad – University of Exeter
Hybrid testing of buckling-restrained braces (Abstract No. 15)
Robin Malloy – University of Oxford
A study on punching shear failure induced by impact loading on reinforced concrete flat slabs (Abstract No. 16)
Karl Micallef – University of Surrey
Multi-scale stochastic fracture mechanics of composites informed by in-situ x-ray CT tests (Abstract No. 21)
Razvan Sencu – University of Manchester
Experimental investigation of recycled carpet composites for barrier structures (Abstract No. 22)
Adeayo Sotayo – Lancaster University
Tall modular buildings: height limits of stacked steel modules (Abstract No. 23)
Petia Tzokova – University of Cambridge
Design of hot-finished high strength steel tubular members (Abstract No. 25)
Jie Wang – Imperial College London
A modelling approach to railway bridge asset management (Abstract No. 27)
Panayioti Yianni – University of Nottingham
Dynamic non-linear analysis of sub-standard reinforced concrete frames accounting for shear failure localisation (Abstract
No. 28)
Dimitrios Zimos – City University London
This booklet contains synopses from researchers taking part in the 18th Young Researchers’ Conference, organised by the Institution of Structural
Engineers. The Institution bears no responsibility for the presentation or technical accuracy of the content in these synopses.
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Finite element modelling of concrete slab-column
connections under eccentric loads
Poster presenter
01
Rwayda Al Hamd
University of Manchester
Abstract
Flat plate concrete structures are an economical type
of building frame commonly used for offices and similar
structures. They are easy to construct, offer flexible column
arrangements and are relatively cheap to build. However,
they are susceptible to a type of failure known as “punching
shear”, where columns pierce the floor slabs leading to
collapse. This is a particularly dangerous type of failure as it
occurs suddenly and without and warning. Punching shear
occurs in the case of pure axial loads on columns but it
might be even more dangerous if there is a moment applied
to the structural connection as well, such as might occur in
columns at the edge of structure or during a building fire.
This condition has not been extensively studied previously
and is the topic of this project. Finite element models were
developed and validated based on the author’s previous
tests. The failure mechanics were examined and the model
gave a good agreement with the experimental results
considering the correct crack pattern and the failure loads.
With the modelling approach validated, it was possible to
examine a range of further load cases numerically and gain
insights into the failure patterns and loads that might be
expected. This information will be of use to designers and
result in safer buildings.
Project objectives and goals
–
Develop a finite element models that can capture
punching shear behaviour.
–
Investigate the structural performance of flat platecolumn
connections under eccentric loads i.e. loads
that produce both shears and moments in the slab
column connections.
–
Compare the results with relevant codes.
Description of method and results
Previously completed experimental work (Al Hamd et al.
2015) was simulated using the finite element package
Abaqus. The models used 8-noded hexahedral solid
elements with reduced integration for all concrete parts
of test specimens, together with truss (axial forces only)
elements to represent the reinforcement. Full bond between
the two materials was assumed.
Concrete was represented using the damaged plasticity
model provided with Abaqus (Lubliner et al. 1989; Lee &
Fenves 1998; Anon 2013) with the uniaxial compressive
stress-strain relationship taken from (Eurocode 2 2004).
Uniaxial tension behaviour was taken from Wang and Hus
(Wang & Hsu 2001), after a validation study (below). The
main parameters used for the damage plasticity model
were taken from (Lubliner et al. 1989) (Lee & Fenves 1998).
Steel behaviour was taken from measured behaviour in
coupon tests and modelled using a von Mises yield criterion.
The concrete damage plasticity parameters were chosen
14
|
according to relevant literature where the dilatation angle for
concrete should be between (15°- 40°), the shape factor
of the yield surface (K) is between (1-2/3), the eccentricity
of the dilation of concrete related to wide range confining
pressure and in this case was taking as 0.1 and f b /f c0
stress ratio should be between (1.12-1.16)(Anon 2013;
Chaudhari 2012; Genikomsou & Polak 2015; Lubliner et al.
1989)
Abaqus offers two numerical methods to analyse unstable
nonlinear models: a general static analysis and a Riks static
analysis (Anon 2013). Both types of analysis were used to
validate the numerical model against experimental results.
Both produced good comparisons but due to the numerical
scheme, the general static results were not able to capture
structural softening behaviour that resulted from concrete
cracking and reinforcement rupture. Despite this advantage,
in the following results, the general static approach is
adopted as it has the advantage of being applicable to
heating behaviour, unlike the Riks method.
Potential for application of results
After validating the modelling approach, several models
were produced to compare the results with the Eurocode
design predictions. It was found that the Eurocode is not
conservative without the partial safety factor being present.
This is a serious concern as safety factors are not intended
to account for shortcomings in design methods.
References
Anon (2013). ABAQUS, User’s Manual, Version 6.13.
Dassault Systémes Simulia Corp., Providence, Rhode.
Chaudhari, S. V. (2012). Modeling of Concrete for Nonlinear
Analysis Using Finite Element Code ABAQUS. , 44(7),
pp.14–18.
Eurocode 2 (2004). Design of Concrete Structures, Part 1-1:
General Rules and Rules for Buildings,
Genikomsou, A.S. & Polak, M.A., 2015. Finite Element
Analysis of Punching Shear of Concrete Slabs Using
Damaged Plasticity Model in ABAQUS. Engineering
Structures, 98(2015), pp.38–48. Available at: http://
linkinghub.elsevier.com/retrieve/pii/S0141029615002643
[Accessed May 26, 2015].
Al Hamd, R.K.S. et al. (2015). Punching Shear – Eccentric
Load and Fire Conditions. In CONFAB 2015 Conference
Proceedings. Glasgow, United Kingdom: ASRANet Ltd, pp.
201–209.
Lee, J. & Fenves, G.L. (1998). Plastic-Damage Model
for Cyclic Loading of Concrete Structures. Journal of
Engineering Mechanics, 124(8), pp.892–900.
Lubliner, J. et al. (1989). A Plastic-Damage Model for
Concrete. International Journal of Solids and Structures,
25(3), pp.299–326.
Wang, T. & Hsu, T. (2001). Nonlinear Finite Element Analysis
of Concrete Structures Using New Constitutive Models.
Computers & Structures, 79, pp.2781–2791.
Further information
Rwayda Al Hamd (E: [email protected])
Dr Martin Gillie (E: [email protected])
Table 1. Comparing the results with Eurocodes
Slab
d
(mm)
fc
(MPa)
0mm
Eccentricity
(kN)
60mm
Eccentricity
(kN)
120mm
Eccentricity
(kN)
Euro code
Euro code
with safety
factor
Experimental
65
26
74
71.5
65.8
95.4
73.4
Validated
models 80mm
65
26
69.4
65.5
61.8
95.4
73.4
Numerical
60mm
45
26
56.4
54.8
48.5
77.7
59.7
Numerical
100mm
85
26
81.6
80.4
75.8
108.9
83.8
Numerical
120mm
105
26
101.5
90.7
82.8
122.2
94
Numerical
35MPa
65
35
80.8
71.8
70.1
105.6
81.3
Numerical
45MPa
65
45
93.8
80.9
72.1
114.8
88.3
|
15
Investigation of progressive collapse mechanisms of
reinforced concrete frames in fire
Poster presenter
02
Sherwan Albrifkani
Introduction
The study of robustness of building structures has received
extensive attention from researchers following a few high
profile structural collapses. This research focuses on
understanding the mechanism of progressive collapse and
improving the robustness of reinforced concrete structures in
fire. A particular emphasis of this research is catenary action
which can develop in axially restrained beams after the
conventional flexural bending action, and can significantly
enhance the beam survival time compared to the fire
resistance estimated based on bending resistance. There is
a lack of research on catenary action of reinforced concrete
beams in fire and a general lack of study on the robustness
of reinforced concrete (RC) structures in fire. The aim of the
current PhD research work is to address these knowledge
gaps. It includes the development of efficient and effective
numerical simulation schemes to model the large deflection
behaviour of RC structures in fire and to use the validated
numerical model to further investigate methods of improving
the robustness of RC structures in fire.
Finite element model and validation
Faithful numerical simulation of the structural behaviour
of RC members presents serious challenges due to the
material failures that can occur, including concrete cracking,
crushing and reinforcement fracture (which may cause
temporary loss of equilibrium of the structure and dynamic
behaviour), and very severe geometrical nonlinearities at
very large deflections. In this study, the explicit modelling
approach is employed to prevent problems of convergence.
When using this algorithm, the time increment has to be
very small which is problematic for fire-related problems
because fire exposure has long durations. However, either
load factoring or mass scaling techniques may be used to
speed up the simulation process. Minimum ratios of loading
duration and mass scaling factors to be used to achieve
a quasi-static solution were determined. The developed
3D model was verified by tests on axially restrained beams
at ambient temperatures under column removal scenario
by Yu and Tan (2013) and at elevated temperatures by
Dwaikat and Kodur (2009). The good agreement observed
between predicted and measured results demonstrated the
applicability of the developed model to accurately predict
detailed structural behaviour and follow temporary failures.
The main objectives of this PhD research project study are:
––
To develop and validate efficient and effective FE
models using ABAQUS to trace the large deflection
behaviour of RC structures in fire.
––
To investigate the effects of some influential parameters
on the fire resistance of restrained RC beams under
catenary action.
––
To develop simple calculation methods to predict
catenary action behaviour of RC beams in fire
––
To investigate methods of enhancing RC beam-column
connections that give prolonged fire resistance of
beams from catenary action.
––
To assess frame robustness of framed RC building
structures under fire conditions.
16
|
Large deflection behaviour of restrained RC beams in fire
The developed FE model is used to study the fire response
of axially and rotationally restrained RC beams at large
deflections. Figure 1 shows the mid-span deflection and
the beam axial force-fire exposure time relationships for a
typical RC beam. As the beam approaches its bending limit,
it undergoes accelerated rate of deflection until the activation
of catenary action. This stage of behaviour corresponds to
the transition of the axial force from compression to tension.
Afterwards, the beam enters a stage of stable behaviour
when the rate of deflection is steady and the applied load
on the beam is mainly resisted by tensile catenary action.
The tensile catenary force is withstood by the longitudinal
steel bars. It is possible to use catenary action to significantly
prolong the survival time of reinforced concrete beams. The
FE model successfully predicted the quasi-static behaviour
as the ratio of the kinetic energy to the internal energy
remains bounded and is close to zero in the stable periods.
Further studies are being conducted to investigate different
parameters. Also, simplified hand calculation methods
are being derived for design objectives accounting for the
catenary action.
Robustness of framed RC structures in fire
The final stage of the research is to assess the robustness
of framed RC building structures in fire. To obtain
computationally efficient solutions based on the same
proposed modelling methodology described above, a mixed
element approach is adopted. Critical frame members that
are subjected to fire with huge anticipated deformations
are modelled using solid elements, while members that are
away from the fire action are modelled using beam elements.
Figure 2 is an example of fire attacking the ground floor
using this approach when (i) the fire is contained within the
fire compartment of origin (Figure 2 (b)) and (ii) fire spread
to adjacent fire compartments (Figure 2(c)). In future work,
frame robustness will be evaluated considering different
fire scenarios. The key role of beam-column connections
to distribute internal forces due to alternative load path and
catenary action will be studied leading to recommendations
of improving the robustness of RC frames in fire.
References
Dwaikat, M., and Kodur, V. (2009). Response of restrained
concrete beams under design fire exposure, Journal of
Structural Engineering 135:11, 1408-1417.
Yu, J., and Tan, K. (2013). Structural behaviour of RC beamcolumn subassemblages under a middle column removal
scenario, Journal of Structural Engineering 139: 2, 233-250.
Further information
Sherwan Albrifkani (E: sherwan.albrifkani@postgrad.
manchester.ac.uk)
Prof Yong Wang (E: [email protected])
This PhD research is mainly concerned with understanding
the mechanisms of progressive collapse, and investigating
methods of improving the robustness of reinforced concrete
frames in fire. It has developed an efficient and effective
method of numerically modelling the large deflection
behaviour of RC structures in fire.
Figure 1 . General behaviour of axially restrained RC beam
Figure 2
|
17
Experimental validation of a novel seismic-resistant steel
frame for damage minimisation
Poster presenter
03
Marco Baiguera
Heriot-Watt University
Conventional steel frames designed according to current
seismic provisions prevent collapse and ensure life
safety under the design earthquake. However, two major
drawbacks of conventional systems are that they experience
significant inelastic deformations (i.e. damage) in main
structural members and residual storey drifts after a major
seismic event (Bruneau et al., 2011). Socio-economic losses
associated with repairing damage in structural members
include high repair costs and excessive disruption to
building use or occupation (ARUP, 2013). Residual storey
drifts may pose further complications: a recent study on the
economic impact of residual drifts showed that direct and
indirect repair costs are not financially viable when residual
drifts are greater than 0.5% (McCormick et al., 2008). As
modern societies demand for a rapid return to occupancy
after an earthquake, this research project aims to develop an
innovative resilient system that uses simple structural details
to minimize damage and thus disruptions and downtime.
A 6-storey steel prototype building is chosen to compare the
seismic response of the proposed frame with a conventional
steel system with buckling-restrained braces. Performancebased seismic design criteria and appropriate capacity
design rules are used to design the seismic-resistant frames
located along the perimeter of the building.
Providing high post-yield stiffness is recognized as one of
the most effective approaches to reduce damage following
a major earthquake (Pettinga et al., 2008). This project
proposes and develops a dual seismic-resistant steel frame,
which consists of a moment-resisting frame equipped with
concentric braces. High post-yield stiffness is provided by
replaceable hourglass shape pins made of duplex stainless
steel, which are installed in series with the braces (Figure
1). The hourglass shape promotes a constant curvature
profile and a uniform distribution of plastic deformations to
delay fracture and increase energy dissipation, where the
properties of the duplex stainless steel material provide
high post-yield stiffness (Baiguera et al., 2016). In addition,
replaceable fuses are introduced at the locations of the
beams of the moment frame where plastic hinges are
expected to develop at large drifts. The ductile elements
installed in braces and beams are detailed to dissipate
the seismic energy and to accommodate large inelastic
deformations, while preserving the integrity of the main
structural components.
This project examines the seismic behaviour of the proposed
frame by means of numerical analyses, which are calibrated
using experimental results from full-component tests on
the stainless steel pins. A comparison with a conventional
seismic-resistant steel system is presented to highlight the
advantages of the dual frame in terms of structural and nonstructural damage minimization under severe earthquakes
and collapse potential.
18
|
Full-scale component tests on the prototype steel pins
(Figure 2) are conducted under several cyclic loading
protocols up to fracture. The load histories are representative
of earthquake loadings. The results show that pins made of
duplex stainless steel have stable hysteretic behaviour and
high fracture capacity, along with high post-yield stiffness.
The seismic performance of the system is then evaluated
with numerical simulations using the commercial software
Abaqus. A simplified finite element model (FEM) of the
dual frame using beam elements for the main structural
members, nonlinear connector elements for the steel
pins and solid elements for the beam fuses, is found to
provide a similar level of accuracy with a detailed FEM
model using shell and solid elements (Figure 1). Nonlinear
static monotonic and cyclic analyses performed using
the detailed FEM model show that the proposed design
methodology and capacity design rules guarantee that
inelastic deformations are concentrated only in the steel pins
and beam fuses, whereas the main structural components
are essentially elastic even for drifts expected under the
maximum considered earthquake (MCE). Nonlinear dynamic
analyses results show that the proposed and conventional
frames experience comparable peak storey drifts. However,
the combined effects of the high post-yield stiffness and the
appreciable elastic displacement capacity of the momentresisting frame drastically reduce the maximum residual
drift of the dual frame. The maximum residual drift of the
proposed frame is negligible under the FOE, has a mean
value of 0.06% under the design basis earthquake (DBE)
and a mean value of 0.12% under the very rare MCE, well
below the assumed reparability limit of 0.5% The maximum
residual drift experienced by the conventional frame is five
times larger under the DBE and nearly four times larger
under the MCE.
Fracture models will be calibrated against the experimental
results and incorporated into advanced numerical models
for realistic seismic collapse simulations. Following the
collapse assessment, the construction of fragility curves for
the proposed frame will provide a prediction of the extent of
probable damage and economic implications in the repair
process.
The results of the numerical analyses from models validated
against full-scale component tests indicate a superior
residual storey drift performance compared to conventional
steel frames, and highlight the potential of the proposed
frame to help steel buildings to return to service within
an acceptable short time in the aftermath of a strong
earthquake. Loss estimation studies will be conducted to
evaluate the economic impact of the innovative dual system,
which is a key aspect for its practical application.
References
ARUP (2013). Resilience-based earthquake design initiative
for the next generation of buildings, REDi Rating System,
San Francisco, CA.
Figure 1. View of the detailed FEM model representing the
proposed frame
Baiguera, M., Vasdravellis, G., and Karavasilis, T.L. (2016).
Seismic-resistant steel frame with high post-yield stiffness
braces for residual drift reduction, Journal of Constructional
Steel Research, under review.
Bruneau, M., Uang, C.M., and Sabelli, R. (2011). Ductile
design of steel structures, McGraw-Hill, New York, NY.
McCormick, J., Aburano, H., Ikenaga, M., and Nakashima,
M. (2008). Permissible residual deformation levels for building
structures considering both safety and human elements.
14th World Conference on Earthquake Engineering. Beijing,
China.
Further information
Marco Baiguera (E: [email protected])
Dr George Vasdravellis (E: [email protected])
Figure 2. Experimental test on a prototype steel pin made of
duplex stainless steel
|
19
Aeroelastic control of long-span bridges with controllable
winglets
Oral presenter
04
Konstantinos-Nikolaos Bakis
University of Oxford
The now iconic Tacoma Narrows bridge disaster (1940)
was caused by a gradual growth, over a period of
approximately 45 minutes, of an unstable torsional oscillation
that resulted from fluid-structure interaction, see Figure 1.
This disaster fuelled the interest in aeroelastic problems
in civil engineering. The presented research relates to the
modelling, control and dynamic stabilization of long-span
suspension bridges. By employing leading and trailing-edge
flaps in combination, we demonstrate that the critical wind
speeds for flutter and torsional divergence can be increased
significantly.
A successful outcome of this research will allow for a more
economical and elegant design of long span suspension
bridges and might also push the boundaries of feasible
span length. Increasing span lengths pose a challenge to
aeroelastic stability and experience gained from record span
projects such as the Akashi Kaikyo Bridge and Great Belt
Bridge showed that classic aerodynamic design either in
the form of deep truss girders (Akashi Bridge) or the more
modern flat box girder solution (Humber, Bosporus, Great
Belt) reaches its limit for spans approaching 2000m. The
proposed countermeasures traditionally have focused on
a more conservative approach which is based on altering
the shape of the deck for reducing aerodynamic forces.
This work is focused on the use of actively or passively
controlled devices which generate stabilizing forces against
aerodynamic loading. This approach can also be used as
a temporary solution during the erection stage of the main
span when suspension bridges show great vulnerability to
aeroelastic instabilities.
We commence the control design study by focusing on a
structurally simplified flexible bridge model that interacts
with a constant velocity airstream. Two different strategies
are considered separately and in combination. The first
one makes use of trailing and leading flaps adjacent to the
bridge deck, the motion of which is triggered by the deck’s
movement through a combination of springs, dampers
and inerters at the hinged connection, see Figure 2.
Emphasis is placed on the effect of the flap hinge location
and an optimization procedure is used for determining the
compensator parameters that result in optimum system
dynamics in terms of favourable aeroelastic properties. The
second approach aims at combining the flap aerodynamic
stabilizing effect with a driving force provided by a tuned
mass inside the deck section. The tuned mass in this
case also functions as a fictitious cable, which senses the
deck's motion and controls accordingly the flap rotations.
In this work special attention is given to ensuring that
the passive control systems attains optimum robustness
properties or in other words maximizing the tolerance
to system uncertainties. Uncertainties are quantified in a
series of simulations which aim at providing insight on how
the alteration of the bridge's natural frequencies affect
the stability of the closed loop system. The two strategies
investigated in this work exploit favourable aerodynamic
configurations for increasing the flutter and divergence
limit. It is shown that good robustness properties can also
be attained and it is possible to overcome most of the
shortcomings of previous proposed models. A preliminary
experimental investigation of the bridge-flap model was also
performed in the Imperial College wind tunnel facilities and
results show the effectiveness of the proposed system.
References
Bakis, K.N., Massaro, M., Limebeer, D.J.N., Williams, M.S.,
“Passive Aeroelastic Control of a Suspension Bridge during
Erection” International Journal of Numerical Methods in
Engineering (under Review).
Bakis, K.N., Massaro, M., Williams, M.S., Limebeer, D.J.N.,
“Aeroelastic Control of Long-Span Suspension Bridges with
Controllable Winglets” Journal of Structural Control and
Health Monitoring (under review).
Bakis, K.N., Massaro, M., Williams, M.S., Graham, M.J.R.,
“Passive Control of Wind-Induced Instabilities by Tuned
Mass Dampers and Movable Flaps” Journal of Engineering
Mechanics (under review).
Massaro, M., Bakis, K.N., Graham, M.J.R. (2015). Flutter
and Buffeting of Long Span Suspension Bridges in Fully
Erected and Partially Erected Conditions, International Forum
on Aeroelasticity and Structural Dynamics, Saint Petersburg,
Russia.
Bakis, K.N., Massaro, M., Williams, M.S., Limebeer, D.J.N.
(2015). Aeroelastic Control of a Full Long-Span Suspension
Bridges during erection, IABSE conference in Elegance in
Structures, Nara, Japan.
Bakis, K., Limebeer, D.J.N., Williams, M.S. (2014). Dynamic
and Aeroelastic Modelling of Long-Span Suspension
Bridges, 6th International Symposium on Computational
Wind Engineering, Hamburg, Germany.
20
|
Funding body
Further information
This work has been partially funded by the IKY State
scholarship by means of the ESPA European fund 20072013.
Konstantinos-Nikolaos Bakis (E: konstantinos-nikolaos
.
[email protected])
Figure 1. Tacoma Narrows failure mechanism.
Figure 2.
|
21
Poster presenter
05
Bogdan Balan
University of Southampton
Background
Using glass, with its unique characteristics, as a main
structural material can help to make buildings more energy
efficient. Despite its great potential, glass has a brittle
behaviour which causes major challenges to structural
engineers when designing load-bearing elements. In order
to avoid these brittle failures, the current industrial designs
mostly over-dimension the glass elements (IStructE, 2014).
A way to eliminate brittle failure of glass elements is to use
a second material such as steel timber of fiber reinforced
polymers as reinforcement in glass. The present abstract
presents an innovative technique of improving strength and
ductility of glass elements by exploiting the higher strength
of Glass Fibre Reinforced Polymer (GFRP). Lightweight
and semi-transparent, GFRP has ar geat potential as a
reinforcing material in hybrid glass beam, taking the tensile
force after the glass in tension shattered. High strength and
ductile pre-stress float glass elements can be achieved by
initially pre-tensioning the GFRP reinforcement.
–
Using GFRP interlayer to increase the strength and
ductility of glass elements.
–
Mechanical pre-stressing for improved glass elements.
It is known that compressive pre-stresses generated into
the surface of float glass can subsequently help to avoid
shattering. Inspired by the technique used in pre-stressing
concrete elements, the compressive pre-stress in the glass
beams was provided by adhesively bonding a pre-tensioned
GFRP layer between two float glass sheets.
Glass-GFRP beams, were fabricated from two sheets of 6
mm thick float glass (600 x 40 mm) and adhesively bonded
to a pre-cured GFRP sheet (650 x 40 x 1.35 mm) in between
the glass layers. For the pre-stressed beams, the GFRP
layer was initially tensioned to a pre-determined load while
the glass sheets were bonded. Using special connections,
to ensure the pre-stressing level of 10 MPa in glass was
reached until the adhesive cured, the glass and GFRP were
mechanically joined. The initial induced stress value in the
hybrid Glass-GFRP beams was checked using a
scatteredlight-polariscope. The flexural capacity of the beams
wastested using four-point bending experiments. Single layer
glass beams (6 mm thick) and adhesively bonded 2-layer
beams, made from 6 mm thick float glass layers were also
tested as reference specimens. To quantify the ductility of
each beam, the ductility index defined in Eqn 1 was used.
Ductility index (DI) =
22
|
(1)
The study was completed by 3D finite element (FE) models
of the beams, created to investigate the stress evolution in
the glass elements during loading. Particular attention was
paid to modelling the effect of existing residual stresses in
glass using eigenstrains (Achintha and Balan, 2015). The
results obtained from the experiments and FE models are
presented in Table 1. The average load and deflection at
the appearance of the first crack for each beam are shown,
along with the respective ductility index. The experimental
results showed a variance of ~ 30%, value which is common
in glass tests due to the existence of surface flaws (Veer et
al, 2008).
The findings show that glass beams incorporating GFRP
reinforcement have a ductile behaviour (DI > 6.2) once
the first crack appears, as can be seen in Figure 1. Initial
calculations show that the provision of pre-compressive
stress in the beams do not have a great influence in
deflection, less than 10 % when compared with beams with
no initial pre-stress. The major benefit of providing a 10 MPa
compressive pre-stress in the beams was that it enhanced
the strength of the beams by ~ 25 % over the beams with
no initial pre-stress. Moreover an elastic recovery of the
hybrid beams was observed once unloaded (Figure 1 & 2).
It was noticed that although the adhesive layer increased
the strength of the beams, this did not offered any ductile
behaviour after cracking (DI = 0). The FE results match
relatively well (~ 10 % difference) with the experimental ones.
The FE beams models show to have an increased stiffness
than the tested beams, this being related to the assumption
of a full interaction between the adhesive and the glass layer.
–
Glass elements with increased performance. The
findings show a practical solution for strengthening
critical parts of glass structures such as joints.
–
Development of a new way for designing of glass
element. Similar design criterions as for more traditional
materials can be developed to design glass elements.
–
Correct prediction of failure. As structural engineers
rely more on computer models, correct prediction of
glass failure can be determined using the knowledge of
residual stresses (Achintha and Balan, 2015).
–
Cheaper glass elements, due to cheap and readily
available materials.
–
Safer post-breakage behaviour of glass structural
elements.
–
Aid for designing against extreme loads such as blast.
Summary
The pre-stressed float Glass-GFRP hybrid beams show
an improved load carrying capacity over traditional glass
beams with a safe failure behaviour. The experiments show
the viability of using composite Glass-GFRP hybrid beams
for structural use. The numerical models allow to predict
the stress evolution in the glass elements during loading,
enabling for a safe and sustainable design.
Funding body
References
Dr Mithila Achintha (E: [email protected])
University of Southampton, The Institution of Structural
Engineers (Research Award 2012)
Further information
Bogdan Balan (E: [email protected])
Achintha, M. and Balan, BA. (2015). An experimentally
validated contour method/eigenstrains hybrid model to
incorporate residual stresses in glass designs, Journal of
Strain Analysis for Engineering Design, 50:8, 614-627.
IStructE. (2014). Structural use of glass in buildings. The
Institution of Structural Engineers, London, U.K.
Veer, FA., Louter, PC. and Bos, FP. (2009) The strength
of annealed, heat-strengthened and fully tempered float
glass. Fatigue and Fracture of Engineering Materials and
Structures, 32:1, 18-25.
Table 1
Experiments
Beam type
(kN)
FE models
Ductility index (DI)
(kN)
Glass-GFRP
3.3
2.9
> 6.9
3
2.6
(10 MPa pre-stress)
Glass-GFRP
3.6
2.4
> 6.2
3.1
2.2
(0 MPa pre-stress)
Adhesively bonded
3.8
1.7
0
3.3
1.7
Single layer
6.7
0.5
0
6.6
0.45
Figure 1. Load-Deflection curves of the tested beams
Figure 2. Elastic recovery of GFRP beams after unloading.
|
23
A new design method for side wall buckling of equal-width
RHS truss X-joints
Poster presenter
06
Shanshan Cheng
Steel hollow sections have been widely used in engineering
structures due to its structural efficiency and aesthetic
features. When the RHS X-joints with equal width of chord
and brace members are under brace compression, the side
wall buckling of the chord members is the critical failure
mode. In CIDECT design rules, it is designed by isolating
a vertical strip in the chord side wall and considering it as
a column (Packer et al., 2009). While defendable because
of its simplicity, this approach obviously ignores the twodimensional character of the side wall buckling as a plate.
Therefore, it has been known that the current CIDECT
design rules are quite conservative, and more so for larger
chord wall slenderness h0/t0 (Becque and Wilkinson, 2015).
Besides, the side wall buckling load is determined as the
minimum of the peak load or the load corresponding to the
3%b0 deformation limit from a connection test. However,
any argument that buckling of the side wall will lead to
a rapid increase in side wall deformations and therefore
the load corresponding to a deformation of 3%b0 will be
somewhat representative of the buckling load, is quickly
invalidated by experimental evidence (Becque and Wilkinson,
2015). Therefore the aim of this project is to present an
alternative design equation for chord side wall buckling,
equally simple in its application, but founded on a rational
plate buckling model and verified against experimental data.
Theoretical model
The chord side wall (see Figure 1) is idealized as an infnitely
long plate, simply supported along both longitudinal edges
and subject to a uniform localized load 1 (originating from
the brace members) and a longitudinal compressive stress
(from the chord pre-load).
2
The critical buckling stress of the chord side wall is obtained
using a Rayleigh-Ritz approach (Cheng and Becque, 2016):
1
2
3
Experimental model
Although numerous experimental results on RHS X-joints
is available in literature, the recorded data typically includes
the peak load and/or the load corresponding to 3%b0
deformation limit, while the buckling load of the side wall
remains unreported. Five equal-width SHS X-joints, all made
of S355, with varying chord wall slenderness h0/t0 were
tested at the University of Sheffield (Becque and Wilkinson,
2015). The limited database was augmented with another
four experiments reported by Becque and Wilkinson (2011)
|
FE modelling
There is a profound lack of experimental data of RHS
X-joints under compressive chord pre-load. Therefore, FEM
was adopted to investigate the effect of a chord pre-load
on the side wall buckling of equal-width X-joints. The finite
element model was developed in Abaqus and was first
benchmarked against nine experimental results. A total of
36 models were analysed. The exact point of buckling is
not always easy to pinpoint, especially when buckling takes
place in the inelastic range. However, the buckling load
Pb could be determined by the divergence point between
a geometric non-linear analysis and a linear analysis
(both including material non-linearity) in the load vs. axial
shortening diagram (Cheng and Becque, 2016).
Proposed design method
The proposed design is aligned with the current CIDECT
practice of referring, in the design for side wall buckling, to
the code specifications for column buckling (EN1993 -1 -1,
2005):
4
with the squashed load
24
on equal width X-joints, made of C450 cold formed steel
tube. The resulting database contains a more balanced mix
of geometries and material properties. See test results in
(Becque and Wilkinson, 2015).
y
= 1.2 x 2fyh1t = 2.4fyh1t
5
The factor 1.2 thereby takes into account that some of the
load follows an alternative load path through the chord top
and bottom faces and then spreads out into the chord side
walls. The definition of the non-dimensional slenderness
λ, the reduction factor of buckling were adopted from
EN1993-1-1 (2006). The elastic critical buckling load Pcr
obtained from the theoretical model is used in the definition
of λ, while the imperfection factor α was determined to be
0.08 by conservatively fitting a lower bound curve to the
numerical data (see Figure 2).
The ratios of the design prediction by the proposed design
equation and CIDECT to the numerical results were
assessed. An average ratio of 0.87 was obtained with a
COV of 0.14 for the proposed design model. It strongly
outperforms the current CIDECT design rule for side wall
buckling, which over the same data set features an average
ratio of 0.57 with a COV of 0.28. Importantly, it is also seen
that the CIDECT rule does not offer a consistent margin of
safety, but is more conservative for side walls with high h0/t0
values.
The proposed design equation has a great potential in
improving the design of RHS X-joints failed by side wall
buckling, since it was derived based on a rational analysis
of plate buckling, which avoids the arbitrary assumption of
Further information
3%b0 deformation limit. As it follows the format of buckling
curve in Eurocode, it could be easily embedded in Eurocode
design.
Dr Shanshan Cheng (E: shanshan.cheng@sheffield.ac.uk)
References
Dr Jurgen Becque (E: j.becque@sheffield.ac.uk)
Becque, J., & Wilkinson, T. (2015). A new design equation
for side wall buckling of RHS truss X-joints. Tubular
Structures XV, 419-426.
Becque, J., & Wilkinson, T. (2011). Experimental investigation
of the static capacity of grade C450 RHS T and X truss
joints. Tubular structures XIV: CRC Press.
BSI. (2005). Eurocode 3: Design of steel structures Part 1-1:
General rules and rules for buildings.
Cheng, S., & Becque, J. (2016). Design of equal-width RHS
truss X-joints for side wall buckling in the presence of chord
pre-load. Submitted to SDSS 2016, 30th May to 2nd June,
2016, Romania.
Packer, J. A., Wardenier, J., Zhao, X. L., Vegte, G. J. v. d.,
& Kurobane, Y. (2009). Design guide for rectangular hollow
section (RHS) joints under predominantly loading.
Figure 1. Idealised model of the chord side wall
Figure 2. Proposed design curve
|
25
Improving the non-structural seismic performance of
conventional multi-storey buildings using viscous fluid
dampers
Oral presenter
07
Giuseppe Marcantonio Del Gobbo
Description of method
Buildings designed to modern standards are able to
withstand earthquakes while undergoing only minimal
structural damage. Although this suggests that a quick
recovery may be possible, this outcome is not always
achieved. Recent earthquakes such as the 2010
Canterbury earthquake and the 2010 Chile earthquake have
demonstrated that conventional seismic design philosophy
allows for undesirable levels of non-structural damage.
Inadequate non-structural seismic performance has led to
extensive repair costs and lengthy functional disruptions,
as non-structural systems comprise the majority of building
investments and are essential to building operations. Nonstructural damage accounted for billions of dollars of losses
in 2010 alone (Fierro et al., 2011).
A 16 storey steel building design was created to be
representative of modern seismically designed structures.
The lateral load resisting system consists of concentric
braced frames located around the perimeter of the structure.
Seismic design was conducted through modal response
spectrum analysis in SAP2000. The Eurocode compliant
design allowed the seismic performance of conventional
structures to be evaluated and set as a benchmark for
alternative designs incorporating viscous fluid dampers.
Attaining a target level of seismic performance mandates the
harmonization of structural and non-structural performance
levels. However, both analytical and experimental research
on non-structural systems have been scarce compared
to primary structural systems. This study investigates the
capability of viscous fluid dampers to enhance the nonstructural seismic performance of conventional multi-storey
buildings and to contribute to the achievement of resilient
structures.
Despite having the potential to be effective and economically
viable solutions (Dicleli and Mehta, 2007; Pavlou and
Constantinou, 2006; Wanitkorkul and Filiatrault, 2008),
research focusing on viscous fluid damper applications
for non-structural enhancement has been limited. Studies
have concentrated on applications in low-rise and mid-rise
buildings at the expense of high-rise structures. There have
also been minimal attempts to maximize non-structural
performance using viscous fluid dampers. Parametric
studies on nonlinear viscous damper coefficients and
examinations on the optimization of damper placement have
been restricted to structural objectives.
This project examines the effect of damper properties and
damper placement on non-structural response. Expected
non-structural damage from retrofitted designs is compared
to code conforming buildings. Several non-structural
configurations and earthquake intensities are considered.
The final aim of the project is to develop a viscous fluid
damper placement strategy that minimizes non-structural
repair costs and service disruptions.
26
|
The structure was modelled in the finite element program
OpenSees. Nonlinear time history analyses were performed
using ground motion suites representing the ultimate limit
state (ULS) and the serviceability limit state (SLS). Structural
response parameters used to characterise demands on
non-structural systems such as absolute acceleration and
interstorey drift ratios were recorded.
The FEMA P-58 performance assessment procedure (ATC,
2012) was used to evaluate the seismic performance of the
conventional building. Non-structural normative quantities
corresponding to a commercial office building were
considered along with all structural components. Structural
response parameters from the ULS and SLS analyses were
used to determine repair costs and downtime.
Following the completion of the benchmark examination,
viscous fluid dampers were incorporated into the building
model. The capability of viscous fluid dampers to improve
non-structural seismic performance was measured by
comparing the performance assessment results to the
conventional benchmark results. Damper placement
optimization will then be explored. The enhanced placement
procedure will be verified through testing in both the office
building model and several other representative structures.
Results and potential for application
The seismic performance assessment of the conventional
design determined that drift-sensitive and accelerationsensitive non-structural systems would experience
substantial damage. The results indicate that significant
repair costs and downtime can be expected in modern
multi-storey structures following an earthquake. Large repair
costs were observed for both the SLS and ULS scenarios.
The high level of repair costs was particularly concerning for
the SLS scenario, as damage should be limited during this
more frequent event. This suggests that modern building
standards still do not accomplish resilience, the ability
of a community to quickly recover after an earthquake.
Limitations of the Eurocode damage mitigation methodology
were revealed as the prescribed interstorey drift ratio limits
did not prevent non-structural damage. These results
highlight the need for design procedures which enhance
non-structural seismic performance.
The results of this analysis also provide a benchmark on
which to compare the effectiveness of alternative designs
in improving non-structural seismic performance. This
benchmark is valuable when evaluating retrofit alternatives
for an existing building or when selecting design options for
new structures. The application of viscous fluid dampers is
currently being explored using the benchmark. Expectations
are shifting in modern earthquake engineering, as clients are
requesting that a rapid return to occupancy be possible after
an earthquake event (May, 2007). This research contributes
towards meeting these new expectations.
References
Dicleli, M. and Mehta, A. (2007). Seismic performance
of chevron braced steel frames with and without viscous
fluid dampers as a function of ground motion and damper
characteristics, Journal of Constructional Steel Research
63:8, 1102-1115.
Fierro, E.A., Miranda, E. and Perry, C.L. (2011). Behaviour
of non-structural components in recent earthquakes,
Proceedings of the 2011 Architectural Engineering
Conference, Oakland, U.S.A., 369-377.
May, P.J. (2007). Societal Implications of Performance-Based
Earthquake Engineering, PEER Report 2006/12, University
of California Berkeley, U.S.A.
Pavlou, E. and Constantinou, M.C. (2006). Response of nonstructural components in structures with damping systems,
Journal of Structural Engineering 132:7, 1108-1117.
Wanitkorkul. A. and Filiatrault, A. (2008). Influence of passive
supplemental damping systems on structural and nonstructural seismic fragilities of a steel building, Engineering
Structures 30:3, 675-682.
Applied Technology Council (ATC) (2012). FEMA P-58
Seismic Performance Assessment of Buildings, Federal
Emergency Management Agency, Washington, D.C.
Funding body
The Clarendon Fund, Natural Sciences and Engineering
Research Council of Canada (NSERC)
Further information
Giuseppe Del Gobbo (E: [email protected])
Dr Martin Williams (E: [email protected])
Dr Tony Blakeborough (E: [email protected])
|
27
A vibration-based NDT technique for civil engineering
structures
08
Evelyne El Masri
Repair of concrete structures is essential, to increase their
lifetime and remain serviceable. One major step before the
repair is to investigate the potential damage to the structure
and to decide upon a proper procedure. By practical testing
and laboratory observations, it has been shown that the
majority of cracking in concrete and premature failures are
dominated by corrosion of reinforcement rebars. The loss
of structural strength is due to delamination of its concrete
cover.
The majority of non-destructive techniques (NDT) require
knowledge of the existence of the deterioration. Thus,
vibration based methods have been developed as global
and local approaches to detect damages. All the modal
based techniques are dependent on the boundary
conditions of the structure since it involves resonances
and reflections of the waveguide. In reinforced concrete
structures, all the structural members like beams and
columns are not completely fixed nor completely pinned.
That is why the use of modal based techniques for damage
detection is not very accurate since the boundary conditions
are not well categorised and assumptions should be
made. In contrast to modal based techniques, wave based
techniques are independent of the boundary condition of
the structure and therefore they are more feasible to detect
damage in reinforced concrete structures with different
boundary conditions.
By tracking the changes in wave characteristics throughout
the waveguide, or by comparing waves propagating
features, damage can be detected using wave-based
methods. These wave characteristics can be related to
wavenumber, phase and group velocities, reflection and
transmission coefficients and frequency response functions.
These methods are known as physical based techniques
and compared to other methods, propose more precise
and even an early term detection of steel corrosion.
Ultrasonic guided wave (UGW) was among the proposed
physical based techniques (Lei and Zheng, 2013). All the
UGWs experiments in reinforced concrete are based on
the configurations where the transmitter and receiver of
longitudinal guided waves are attached to the exposed
ends of steel reinforcement that offset from the sides of the
concrete beam (Li et al., 2012), (Miller et al., 2012), (Zheng et
al., 2014).
As a result, the experimental configuration in the current
UGWs used for corrosion detection in reinforced concrete
is only feasible in laboratory conditions, where longitudinal
guided waves are induced in the reinforcement steel by
directly attaching the transducers to the offset part of the
rebar. Thus, an alternative solution is needed where all these
structural limitations are considered. Finally, this project
will adopt vibration based techniques and more precisely
guided waves in detecting corrosion in steel reinforcement
embedded in concrete beams. The challenge is to develop
28
|
these methods to be adapted to reinforced concrete
beams without direct contact between transmitter and steel
reinforcement.
The knowledge of wave characteristics is essential within a
specified waveguide. That is why the Wave Finite Element
method (WFE) had been used as an efficient path to predict
free and forced response of waveguides. In addition it had
been applied to different structures such as laminated plates,
thin–walled structures, fluid-filled pipes (D. Duhamel, August
2003), (B.R. Mace, 2005). In this project, WFE is applied to
reinforced concrete section waveguide as shown in Figure 1
using ANSYS software. WFE concept relies on the notion of
predicting the wave characteristics of a repetitive structure
through analysing the wave propagation within a periodic
element. By taking a short section of the waveguide, and by
expressing the continuity of displacements and equilibrium
of forces between the boundaries, an eigenvalue problem is
posed in terms of a transfer function. By solving this problem
at each specified frequency, the eigenvalues are related to
the wavenumbers of the waveguide that relate the variables
to the right and left side of the section, and the eigenvectors
are associated with the displacement and forces at this
section.
Waves characteristics are defined and dispersion curves
and mode shapes are plotted. Different reinforced section
waveguides with different damage scenarios are modelled.
Their modelling waves are then analysed and compared
where specific features are identified. Subsequently,
numerical results are presented and the identified features
show the potential of the principal wave components
that comprise sensitivity to steel reinforcement corrosion.
In addition, WFE solution as eigensolutions are used to
couple damaged and undamaged waveguides to predict
the reflection and transmission coefficients due to defect
(Ichchou et al., 2009). WFE is used to construct a numerical
database of reflection coefficients by varying the damage in
the reinforced bars as reduction of the effective cross section
area as shown in Figure 2.
––
Define a detecting algorithm methodologies based on
the reflection coefficients due to damage.
––
Recognise material properties and geometric
parameters of a specimen suitable for physical
experiment. Design a suitable test specimen or
specimens.
––
Validate the defined theoretical criteria on the physical
specimen(s).
––
Evaluation of the limitations and adaptations of these
methods.
References
Funding body
B.R. Mace, D.D., M.J. Brennan, L. Hinke (2005) Finite
element prediction of wave motion in structural waveguides.
Journal of the Acoustical Society of America 117 (5), 28352843.
D. Duhamel, B.R.M.a.M.J.B. (August 2003) Finite Element
Analysis of the Vibrations of Waveguides and Periodic
Structures. ISVR Technical Memorandum 922.
Further information
Evelyne El Masri (E: [email protected])
Dr. Neil Ferguson (E: [email protected])
Dr. Timothy Waters (E: [email protected])
Ichchou, M.N., Mencik, J.M. and Zhou, W. (2009) Wave finite
elements for low and mid-frequency description of coupled
structures with damage. Computer Methods in Applied
Mechanics and Engineering, 198 (15-16), 1311-1326.
Lei, Y. and Zheng, Z.-P. (2013) Review of Physical Based
Monitoring Techniques for Condition Assessment of
Corrosion in Reinforced Concrete. Mathematical Problems in
Engineering, 2013, 1-14.
Li, D., Ruan, T. and Yuan, J. (2012) Inspection of reinforced
concrete interface delamination using ultrasonic guided wave
non-destructive test technique. Science China Technological
Sciences, 55 (10), 2893-2901.
Miller, T.H., Kundu, T., Huang, J. and Grill, J.Y. (2012) A new
guided wave-based technique for corrosion monitoring in
reinforced concrete. Structural Health Monitoring, 12 (1),
35-47.
Zheng, Z., Lei, Y. and Xue, X. (2014) Numerical simulation
of monitoring corrosion in reinforced concrete based on
ultrasonic guided waves. Scientific World Journal, 2014,
Article ID 752494, 9 pages.
Figure 1. Modelling of undamaged reinforced concrete
section in ANSYS
Figure 2
|
29
Would basalt fibre concrete reduce cracking in light rail
embedded track slab?
09
Sami Elshafie
University of Bolton
1.
0% Basalt fibre
This ongoing research looks into the issues surrounding
concrete cracking in light rail embedded track slab and
possible solutions to minimise the development of cracks by
using basalt fibres within the concrete mix.
2.
0.15% Basalt fibre
3.
0.25% Basalt fibre
4.
0.35% Basalt fibre
The research is specifically related to problems encountered
during extension works to the Metrolink light rail transit
system in Greater Manchester, U.K. and in particular
development and propagation of cracks in the third stage
embedded track slab laid in Oldham town centre.
The addition of basalt fibres within concrete will be
investigated to assess whether it is a suitable and feasible
additive to resolve the crack width issues experienced
by sections of embedded track slab on the Manchester
Metrolink.
The main objectives of this research are:
––
To investigate the chemical and thermal resistance
of basalt fibres to several acidic, alkaline and thermal
environments representative of in-service environmental
conditions.
––
To research the feasibility of whether basalt fibres are
capable of reducing concrete cracks.
––
To determine the trackslabs failure limits after being
reinforced with basalt fibres.
––
To identify the best basalt fibre content that has
influence on reducing concrete cracks.
––
To provide recommendations for the future application
of fibre reinforcement in embedded track slabs.
To ascertain the performance of the basalt fibres against
different chemical and thermal environments, basalt fibers
were immersed in different strong and weak alkaline and
acid chemicals containing different pH levels, as well as
heated at several thermal degrees. Followed by measuring
tensile strengths of the fibres, and carrying out S.E.M. and
E.D.S. analyses.
Studies have found that the optimum basalt fibre ratio is
0.25%. In order to verify the findings and also improve the
accuracy of the findings, smaller increments (0.5%) will
be applied either side of the optimum ratio. The samples
were cast in an identical shape and size to the third stage
embedded track slab section which was subjected to
cracking. The greatest load (265kN) applied to the trackslab
is at the centre of the carriage acting over four wheel in total.
As a result, it is logical to divide this load by four as the load
will be transferred through the wheel, in which each wheel
would receive a loading of around 66kN. Cyclic loading
tests were performed on the samples which simulated
the in-service tram load effects. The cracks formed and
deflection are then measured as can be seen from Figure
1. Static loading tests were also performed which failed the
specimens as exemplified by Figure 2.
This research is considered to be distinct from other
research work as it fills the literature gap by presenting new
unknown facts and also adds new knowledge. For example,
it evaluates the efficiency of basalt fibres in resisting different
strong and weak alkaline and acid chemicals containing
different pH levels, and also evaluates the capability of
basalt fibres to resist several thermal degrees. It measures
the deflection ratio on light rail embedded track slab and
provides advice on how to reduce the deflection ratio. It
determines the crack length and widths on slabs generated
by trams and explained the effect of using basalt fibres in
different proportions on reducing cracks on the embedded
concrete slabs. It identifies the best basalt fibre content
that demonstrates an improvement in the concrete
strength. It also provided recommendations to Manchester
Metrolink authority in relation to the application of basalt
fibre reinforcement in embedded track slabs. Hence, this
research is considered to add new knowledge to the current
literature, and have a potential effect on reducing slab cracks
in the construction industry.
To undertake this feasibility study on crack mitigation four
concrete slab specimens reinforced with different basalt fibre
proportions were tested. As well as the control mix (1), which
was modeled on the mix design used within the actual
in-situ track slabs in Oldham town centre, there are several
adjusted mixes with different proportions of basalt fibres (2)
(3) (4):
30
|
Further information
Sami Elshafie (E: [email protected])
Gareth Whittelston (E: [email protected])
Figure 1. 0.15% Basalt fibre slab time vs crack width
Figure 2. Slab Failure of specimen (4) (0.35% Basalt fibre)
|
31
Demountable spacelink truss - design evolution of PFRP
joints and performance integrity testing
Oral presenter
10
Alfred
Gand
University of Warwick
Fibre Reinforced Polymer (FRP) structural profiles are
increasingly becoming a choice of material over steel,
concrete, masonry and timber for the design, repair,
construction and delivery of civil infrastructure. Pultruded
E-Glass Fibre Reinforced Polymer (GFRP) profiles are
preferred owning to their excellent material property portfolio
including lightweight and rust resistant. To be able to provide
long span and open spaces, truss elements and space
frames are adopted as efficient structural forms. Pultrusion
is a relatively simple method of manufacturing the profiles. It
involves pulling continuous E-glass fibre reinforcement which
comes in the form of alternate layers of randomly oriented
mat and layers of unidirectional roving bundles through a
resin impregnator and subsequently through a heated die.
The process consolidates the material and forms the cured
shape. The pultruded profiles have their highest modulus of
elasticity and axial strength in the direction of the material
with the highest volume fraction of aligned (continuous)
fibres. This property makes pultruded profiles to be ideal
for applications where uni-axial forces are predominant. For
applications such as truss element and space frames, the
connection of the various geometrical elements poses an
interesting challenge. Most times, the connections depend
on the size, shape, type and load of the structure to be
used. This paper presents the work of recent feasibility
studies on the concept development and integrity proof
testing of novel joints made from GFRP box profiles. The
joints would constitute the truss nodal points that are subject
to tensile stresses.
the range of applications. By continuous refinement of
the joint configurations, the most efficient configuration
was developed which sustained pull out forces averaging
between 35kN and 45kN. Further proof testing of an
optimised joint configuration resulted in pull out forces
in excess of 60kN being recorded. Test results showed
joint failures predominantly characterised by punching
shearing. A total of six different joint configurations were
developed and fabricated. For each configuration, at least
five specimens were proof tested to failure. Figure 1 shows
the load-displacement plots for typical joint configured with
76×76×6.35mm thick GFRP square hollow section. Figure
2 shows a prototype Pratt truss assembled and being
transported for physical testing.
Potential for application of results and impact on industry
FRP materials have material properties that are sustainable
and makes them ideal and attractive candidates in new
build construction (Mottram 2011). The GFRP structural
profiles are lightweight, and rust resistant, thus offering a
durable and cost efficient alternative to structural steel. The
range of applications of the Spacelink truss system include
supporting long span roof structures, pedestrian and light
vehicular and military bridges, and for electrification of the
railway including the HS2 scheme. Following the feasibility
studies, a number of stake holders have expressed keen
interest in the outcome which optimistically will open up
numerous application opportunities in structural engineering.
References
This project aimed to explore and undertake design
feasibility and investigate by integrity proof testing various
joint configurations that would facilitate the assembly of
truss elements and space frames quickly and efficiently.
The study aims to establish the feasibility of the novel truss,
through design optimization and integrity static testing.
The success of the studies will enable the development
and construction of lightweight modular trusses for wide
range of structural applications including long span roofing,
domestic flooring, light vehicular bridges and foot bridges,
infrastructure gantries as well as temporary demountable
structures. The scheme seeks to introduce a cost effective
alternative to steel and aluminium trusses and lattice beams
with potential advantages over both. In this paper the results
of a comprehensive array of integrity static testing of various
joint assemblies are presented. The development, assembly
and integrity proof testing of a prototype truss are also
presented.
Mottram, J. T., (2011). “Does performance based design
with fibre reinforced polymer components and structures
provide any new benefits and challenges?” The Structural
Engineer, 89 (6), 23-27.
Dr Tak-Ming Chan (E: [email protected])
Funding body
Innovate UK
Further information
Alfred Kofi Gand (E: [email protected] or a.gand@
coventry.ac.uk)
Mark Singleton (E: [email protected])
Professor James Toby Mottram (E: Toby.Mottram@warwick.
ac.uk)
In order to achieve the aims of the current research,
feasibility studies were undertaken with the view to exploring
the range of applications of the truss. The exercise enabled
probable static loading to be established with expected
joint forces. The process informed the research testing
regime on the probable joint pull out forces feasible for
32
|
Figure 1. Load-displacement plots for joint configured from 76x76x6.35mm PFRP box section.
Figure 2. Prototype PFRP Pratt truss (5m span and 400mm deep) being transported for
physical testing – truss weighs just 41kg.
|
33
New design of a FRP-reinforced concrete beam system for
Poster presenter
11
Mohamed Kiari
University of Edinburgh
This research project investigates a new arrangement of fibre
reinforced polymer (FRP) internal reinforcement intended to
enhance the fire performance of FRP-reinforced concrete.
Instead of using straight separate FRP bars (an arrangement
that has been copied from steel-reinforced concrete design),
the longitudinal reinforcement is made from closed FRP
loops, which are filament wound from long continuous fibres.
This design exploits the fact that the FRP fibres are capable
of sustaining a large proportion of their original strength at
high temperatures. This synopsis provides a summary of
the results of a series of four-point bending tests, which
demonstrate that the proposed design achieved four times
fire resistance time than traditional method.
A series of four-point bending tests were used to investigate
the performance of the new design of FRP reinforcement
at ambient and elevated temperatures. Twenty-eight beam
specimens were manufactured and tested under sustained
monotonic loading and transient localized heating in their
midspan region. The beam specimens include beams
reinforced with either CFRP loops, splice CFRP Straight bars
or continuous CFRP bars for comparison (Figure 2). Fire load
was applied by means of radiant panels.
Previous research
Force transfer between concrete and FRP is a vital aspect
of concrete-FRP composite performance, and has been
the focus of much research. However, very little of this
work covers the bond behaviour of FRP bars at high
temperature. The limited previous studies show that at
elevated temperatures (180-200°C) a severe reduction
in bond strength (up to 90%) occurs. Research has also
shown (Bisby et al. 2005) that structural collapse of concrete
members reinforced with FRP in fire typically occurs due
to loss of bond at temperatures exceeding glass transition
temperature of resin.
FRP Loop Manufacturing Process
Closed FRP loops were produced by wrapping a continuous
carbon fibre tow around a mould. Each loop was made of
25 carbon tows. The resulting fibre volume fraction of the
5×5mm cross-section reinforcement was 44%. Fyfe Tyfo-S
epoxy resin was used to saturate the fibres to form the
matrix of the composite. The straight CFRP reinforcement
was manufactured in the same manner as loops. However,
longer loops were made, so that the straight portions of
reinforcement could be cut out, Figure 1.
Testing results clearly demonstrate the feasibility of FRP loop
reinforced concrete for carrying load at fire temperatures
(Figure 2). Specimens reinforced with CFRP achieved fire
resistance time four times longer than traditional method.
Moreover, unlike the case or straight bars where failure
occurred due to pull out, CFRP loops achieved their ultimate
strength in fire and failed by rupture.
This new technology will allow FRP reinforced concrete to
be used in situations where its fire performance is important.
It could consequently remove the last obstacle to its
widespread use in buildings, brining substantial benefits for
sustainable construction.
References
Bisby, L. A., Green, M., et al. (2005). "Response to fire
of concrete structures that incorporate FRP." Progress in
Structural Engineering and Materials 7(3): 136-149.
Kiari, M., Stratford, T., and Bisby, L. (2015). “New Design of
Beam FRP reinforcement for Fire Performance” Response of
Structures under Extreme Loading, USA.
Further information
Mohamed Kiari (E: [email protected])
Tim Stratford (E: [email protected])
34
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Figure 1. CFRP loops after de-moulding
Figure 2. Fire resistance time and failure mode for different reinforcement shapes.
|
35
On the robustness of ‘simple’ and/or ‘semi-rigid’ structural
steel connections when subjected to blast loading
Poster presenter
12
Matthew Kidd
University of Liverpool
Introduction
The resilience and robustness of structures, to the
unforeseen, has become a very real and necessary design
consideration in recent years. This is mostly due to the
turbulent natural and geo-political environment we live
in. Within steel framed structures, failure of the primary
connections or loss of structural elements is what is
most likely to trigger a collapse. In the UK, steel framed
structures (with the exception of portal frames) are generally
constructed with simple and/or semi-rigid connections,
and rely on independent bracing systems to provide lateral
stability. Design guidance on the dynamic behaviour of
simple and/or semi-rigid connections is currently nonexistent.
Steel designers instead revert to the prescriptive
tie-force method (as outlined in SCI P391 (Way, 2011)) as a
means of providing some level of structural robustness to a
building. This, in most cases, may act as a safety net against
collapse but it overlooks the true dynamic behaviour of the
connections and nature of the collapse motion. The current
research being carried out at the Blast and Impact Research
Centre, within the University of Liverpool, in addition to
existing studies relating to the topic may help contribute
towards the development of guidance for simple/semi-rigid
connection design that incorporates dynamic effects such
as strain rate and inertia.
There are two distinct blast loading scenarios that this study
has in mind. The first refers to the ‘sudden column loss
scenario’ whereby the blast pressure from an explosion
eliminates a primary supporting column at a distance away
from the connections. The consequence of this is a sudden
dynamic rotation through the connections resulting from the
almost instantaneous development of catenary action in the
steel frame above the lost column (Figure 1) and the second
refers to the direct blast pressure scenario. In this situation
the transient pressure from an explosion in the vicinity of a
connection is applied directly to the beam (and connection),
or floor slab it supports (Figure 2).
The objective of this study is to enable the development of a
set of formal design guidelines to achieve dynamic resilience
in standard simple/semi-rigid connections. To do this, the
following have been identified as research goals for the PhD
study:
–
quantification of all existing research and key findings
on the topic.
–
understanding the role that the sub-grade of steel plays
in the level of strain rate sensitivity.
–
developing the parameters of the Johnson-Cook
constitutive relation for S275 and S355 steel.
–
investigation of the dynamic behaviour of connections
into the web of the supporting column or beam.
36
|
–
investigation of the response of such connections to
direct blast scenarios.
–
investigation into the effects that the stresses resulting
from the gravity loads has on the connection’s
performance under direct blast loading.
The above objectives are to be investigated using high
fidelity physics based numerical models coupled with
experimental validation. To derive the Johnson-Cook
constitutive parameters for S275 and S355 steel, a series
of quasi-static and dynamic tensile tests on dog bone
specimens machined from steel flats is to be undertaken.
The strain rate sensitivity of both grades of steel will be
observed over strain rates from quasi-static up to 50/s
which relates to the strain rates covered by UFC 3-340-02,
Structures to Resist the effects of Accidental Explosions
(US DoD, 2014). Numerical simulations will be run for
each individual tensile test. The validation of the numerical
analyses will enable an iterative process to be carried out
to calibrate the Johnson-Cook constitutive parameters for
S275 & S355 steel. The Johnson-Cook constitutive relation
is as (1):
σeq = [ A + B εneq,p ][1 + C lnε• *eq,p ]
(1)
In which σeq is the equivalent Von Mises flow stress.
Parameter ‘A’ is the yield stress. ‘B’ and ‘n’ represent the
effects of strain hardening. Parameter ‘C’ is the strain rate
constant. The term ε• *eq,p is the dimensionless plastic strain
rate represented as ε*eq,p = ε• p / ε• o,p and ε• o,p is the effective
plastic strain rate of the quasi-static test used to determine
parameter ‘A’. The terms ε• eq,p and ε• p are the known plastic
strain and plastic strain rate respectively. The JohnsonCook constitutive relation has been chosen rather than the
traditional Cowper-Symonds relation because the JohnsonCook relation explicitly accounts for strain hardening
whereas the Cowper Symonds relation assumes a strain
hardening function of unity.
Once the Johnson-Cook parameters have been derived, an
experimental programme for full scale connection testing
is to be undertaken. This will incorporate dynamic testing
of fin plate, partial depth end plate and full depth end plate
connections. Numerical simulations are to be run for the
experimental tests that, once validation is achieved, will be
used to aid the development of component models that
will in turn be used to carry out parametric studies for the
standardised connection details as set out in SCI P358,
more commonly referred to as the ‘Green Book’ (BCSA,
2014).
The research findings will ultimately aid the development of
formal design guidance for the design of the standard simple
and/or connection details when blast loading is a necessary
consideration. These guidelines would be in a similar format
to SCI P358 (BCSA, 2014) for industry to use. Findings
from the research will all be disseminated via journal and
conference papers as well as a presentation at an IStructE
regional group meeting.
References
Way A. G. J. SCI P391: Structural Robustness of Steel
Framed Buildings. Ascot, UK: The Steel Construction
Institute; 2011.
US Department of Defense. UFC 3-340-02: Structures to
Resist The Effects of Accidental Explosions, US Department
of Defense, Washington D.C. 2014.
Figure 1. Illustration of ‘sudden column loss’ scenario
BCSA, SCI, Tata Steel. SCI P358 Joints in Steel
Construction: Simple Joints to Eurocode 3, 2014 Re-print
ed. Ascot, UK: The Steel Construction Institute & The British
Constructional Steelwork Association Limited; 2011.
Funding body
Engineering and Physical Sciences Research Council
(EPSRC), IStructE Research Award
Further information
Mr Matthew Kidd (E: [email protected])
Dr Ryan Judge (E: [email protected])
Dr Steve Jones (E: [email protected])
Figure 2. Illustration of connection subjected to direct blast
loading
|
37
Estimating fatigue life of details in steel bridges using
continuous response monitoring
Poster presenter
13
Jalil Kwad
University of Exeter
Metallic bridges of all ages, including those that are
approaching or have exceeded their design life and those
that are relatively new having been built over the last few
decades, are vulnerable to fatigue damage. The risk is
particularly higher for older bridges due to a combination of
much greater traffic volumes in recent years and significant
age-related deterioration (Zhou, 2006). A recent mapping
of the age profile of existing steel railway bridges in Europe
(Olofsson and Elfgren, 2004) shows that more than 70%
of these bridges are over 50 years old, and about 30%
of them are over 100 years old. In the UK, there are more
than 6000 metallic bridges, which are over 100 years old
(Adasooriya & Siriwardana, 2014). For these structures,
fatigue is highlighted as the major risk to bridge safety. Thus,
the assessment of the remaining fatigue life of steel bridges
is of great importance both nationally and internationally for
making decisions regarding rehabilitation and replacement of
existing bridges.
Significant amount of research effort has been directed
towards the development of approaches for accurate
fatigue life evaluation. However, due to the uncertain nature
of the input load conditions, such as traffic volumes, axle
loads and position of vehicles, existing theoretical methods
fail to reliably evaluate the remaining fatigue life of bridges.
Recent developments in sensing technology can enable a
fundamentally different approach to fatigue life evaluation
that is based on measured and therefore potentially reliable
data on real-life structural behaviour and loading. This
study aims to harness the potential of these technological
advances in a fatigue monitoring system that is capable of
tracking fatigue life of components in real-time based on insitu measurements of deformations in structures.
The main aspect of the research methodology is to integrate
response measurements and numerical modelling to
predict fatigue life of steel connections. It will feed field
strain measurements to high-resolution numerical models of
fatigue-prone connections to evaluate the fatigue damage,
and thereby the remaining service life of bridge-girders.
Measuring strain histories for this purpose requires a modern
data acquisition system with large storage capacity, rapid
sampling rate, and the capability to provide a continuous
record of strain profiles near various fatigue-prone structural
components. While technologies that offer these capabilities
are now widely available, there is no reliable approach to
analysis of the data for evaluating fatigue life. This research
will provide that missing link. The strain profiles are first
analysed to determine the forces experienced by the
components. This step requires a systematic consideration
of the effects of the various loads on the structure including
the static and dynamic effects of vehicular passage,
temperature and other ambient conditions such as wind.
The inferred forces are then applied to a detailed numerical
38
|
model of the component (e.g. connection) to find the
stresses at critical details such as a weld or a rivet. Stress
predictions from the model are used to arrive at an estimate
of the fatigue life of the component, i.e. the time remaining
before the component or structure could be expected to fail
by fatigue based on the current loading conditions.
The methodology in detail is described in Figure 1. This
research will implement and test the methodology for a
full-scale bridge near Exeter. In the first step, a numerical
model of a steel bridge is created and analysed to get
an initial indicator about the most fatigue critical bridge
components. Figure 2 shows a numerical model of a typical
bridge connection with rivets and welds, often designed
at the intersection of main-girder and cross-beams. All
the connection parts of the main-girder and cross beam
are modelled by using 8-noded brick elements using the
commercial finite element code (ANSYS).
The project is currently preparing the instrumentation
required for strain data collection. A bridge in Exeter has also
been identified for the case study. In the coming months, a
specific connection in the bridge will be instrumented with
strain gauges and thermocouples for collecting data to
validate the methodology. The real internal forces transferred
by the main-girder and the cross-beam will be evaluated
based on strain history data from field measurement. These
forces will then be directly applied to the numerical model
of the connection to determine the stress history at the
weld. Modal analysis of the bridge will also be performed
subsequently to evaluate if global measurements can then
be used to predict the fatigue performance of other details
without instrumenting all connections.
The main area of application is for bridge management.
Asset owners and operators will be able to track fatigue life
of components in real-time and then plan interventions in an
optimal, cost-effective manner for their bridge portfolio. The
research group is working with Devon County Council and
other UK bridge owners.
References
Adasooriya, N. D., & Siriwardane, S. C. (2014). Remaining
fatigue life estimation of corroded bridge members. Fatigue
& Fracture of Engineering Materials & Structures, vol.37
no.6, p. 603–622.
Olofsson, I. and Elfgren, L. (2004). Sustainable BridgesAssessment for Future Traffic Demands and Longer Lives;
Taylor & Francis: Oxford, UK, 2004; p. 369.
Zhou, Y. E. (2006). Assessment of Bridge Remaining Fatigue
Life through Field Strain Measurement. Journal of Bridge
Engineering (ASCE), 11, 737–744.
Funding body
The Higher Committee for Education Development in Iraq
(HCED- Iraq)
Further information
Jalil E. Kwad (E: [email protected])
Prakash Kripakaran (E: [email protected])
Figure 1. Research methodology
Figure 2. Main girder and cross beam connected by means of plate
and rivets, at the level of the webs of the beams
|
39
beams and wood-based particle boards
Oral presenter
14
Pinelopi Kyvelou
Imperial College London
Lightweight systems comprising cold-formed steel joists
and wood-based flooring provide economical and durable
solutions for building floors. However, their eficiency would
be improved if the potential for composite action between
the joists and the panels could be mobilised. Although
the benefits of composite construction are well-known
for hot-rolled steel members and concrete slabs, current
design methods for lightweight floors ignore the potential
for composite action between cold-formed steel beams and
the associated panels. Hence, this study aims to:
–
Assess the extent of composite action present within
such a system, when employing typical fastening
arrangement.
–
Investigate the potential to increase composite action
through changes to fastening arrangements.
–
Quantify the derived benefits and provide design
guidance for lightweight flooring systems that recognise
the beneficial effect of composite behaviour.
A flooring system of current practice, comprising coldformed steel beams and wood-based floorboards, was
chosen for the experimental investigation (Kyvelou et
al., 2015). A series of 4-point bending tests have been
conducted on systems with different degrees of partial
shear connection, achieved through different shear transfer
mechanisms: self-drilling screws with varying spacing and
structural adhesive. The bare steel system was also tested
to provide a reference response. A description of the tested
specimens as well as the measured values of flexural
stiffness EI and ultimate moment capacity Mult normalised
against the stiffness and capacity of the bare steel system is
given in Table 1; the experimental setup is shown in Figure 1.
The usual failure mode, illustrated in Figure 2, was
distortional buckling between fixings in the constant moment
area; only for specimen No.5 did local buckling develop in
the web and top flange. For specimen 2 to 5, progressively
increased composite action resulted in reduced distortional
bucking wavelengths and, eventually, a different mode of
failure.
It was found that the spacing of self-drilling screws as well
as the application of structural adhesive at the beam-board
interface has a significant influence on the moment capacity
of the system, while the application of wood adhesive at
the board joints leads to a further increase in the system’s
flexural stiffness. As expected, the best overall behaviour
was exhibited by specimen No.5, with 100% increase in
moment capacity and 42% increase in stiffness, when
compared to the bare steel system. The attained degree
of shear connection η was calculated for all specimens
40
|
according to Clause 3.2.1.3(3) of BSEN 1994-1-1(2004):
η=
NC
NC,f
(1)
where NC is the measured compressive force in the board
and NCf is the compressive force in the board for an
equivalent system with full shear connection, assuming a
plastic distribution of stresses. Current practice systems
were found to provide just 4% partial shear connection,
while 68% shear connection was achieved for the best
performing of the rest of the tests (specimen No. 5).
A finite element simuation using ABAQUS (2013), modelling
the examined slooring system, has been developed in order
to increase the number and range of results available as
the basis for a predictive formula for the attained degree
of shear connection η as a function of the characteristics
of the flooring and connection system. Shell elements
are employed for the modelling of the steel beams; solid
elements are used to replicate the floorboards while the
fasteners are modelled with nonlinear springs. To investigate
the load-slip response at the beam-board interface and
assign it to the nonlinear springs, push-out tests have
been conducted. Finally, for the accurate determination
of the material characteristics of the steel beam and the
wood-based board, material tests have been carried out on
coupons extracted from the tested steel joists and flooring
panels.
The developed finite element model has been validated
against the experimental data, giving accurate predictions
of the moment capacity, flexural stiffness, attained degree of
shear connection and failure mode for all five tests. Current
research involves parametric studies, the results from which
will permit the establishment of the predictive formula for the
degree of shear connection η.
The composite action that can potentially arise within a
cold-formed steel flooring system is not currently taken into
consideration by designers. However, once the predictive
formula for the attained degree of shear connection η is
determined, the moment capacity and flexural stiffness
of flooring systems may be calculated through a design
method following the established approach for composite
construction. Findings from the experimental programme
completed thus far show that, with little change in practice,
there is potential for significant improvements in the overall
performance of a cold-formed steel flooring system, with a
100% increase in moment capacity and a 42% increase in
flexural stiffness having already been achieved.
References
Funding bodies
ABAQUS. (2013). ABAQUS Version 6.13. Pawtucket, USA:
Hibbitt, Karlsson & Sorensen, Inc.
Ayrshire Metal Products (AMP)
BS EN 1994-1-1. (2004). Eurocode 4: Design of composite
steel and concrete structures – Part 1-1: General rules and
rules for buildings. CEN.
Kyvelou, P., Gardner, L. & Nethercot, D.A. (2015).
‘Composite Action Between Cold Formed Steel Beams and
Wood Based Floorboards’. International Journal of Structural
Stability and Dynamics, 15(08), p. 1540029.
Further information
Pinelopi Kyvelou (E: [email protected])
Professor Leroy Gardner (E: [email protected])
Professor David A. Nethercot (E: [email protected])
Table 1. Summary of 4-point bending tests
Specimen No.
Type of shear connection
Screw spacing
Mult / Mult,bare
EI / EIbare
1
n/a (bare steel)
n/a
1.00
1.00
2
Self-drilling screws
600 mm
1.05
1.07
3
Self-drilling screws
150 mm
1.45
1.14
4
Self-drilling screws,
wood adhesive at board joints
150 mm
1.50
1.41
5
Self-drilling screws, wood adhesive at
board joints, epoxy resin at the beam-board
interface
100 mm
1.99
1.42
Figure 1. Experimental setup
Figure 2. Typical failure mode
|
41
Hybrid testing of buckling-restrained braces
Poster presenter
15
Robin Malloy
Seismic dampers can significantly improve the response
of a building to an earthquake through increased energy
dissipation. One such device is the buckling-restrained brace
(BRB), consisting of a steel core encased in a concrete-filled
steel tube. The steel core carries the applied axial loads while
the debonded surrounding concrete provides confinement
to prevent buckling of the core. The BRB dissipates energy
as the steel core yields in both tension and compression due
to the prevention of buckling (Black et al., 2004).
To use dampers effectively and with confidence designers
require methods of adequately modelling the seismic
response of structures fitted with dampers. Hybrid testing (or
real-time substructure testing) is a procedure for modelling
the dynamic response of a complex structural system
whereby part of the system is tested physically at full-scale,
while the rest is modelled numerically on a computer (Darby
et al., 1999). A feedback system is created whereby the
displacements calculated in the numerical substructure are
applied to the physical specimen by hydraulic actuators
and the resulting force is measured and fed back to the
numerical substructure. This project focuses on the seismic
response of a structure fitted with a BRB, the BRB forming
the physical substructure, with the rest of the structure
modelled numerically. BRBs are a prime candidate for hybrid
testing due to their non-linear hysteretic response.
The aim of this research is to develop a hybrid testing set-up
and to carry out hybrid tests on sample BRBs. On the one
hand, this will demonstrate the effect of BRBs on seismic
response and provide information that can be used in the
development of computational models of BRBs. At the same
time it will provide validation of the performance of the hybrid
testing procedure developed.
The test rig used for the physical part of the hybrid testing
is shown in Figure 1. The BRB sample lies horizontally
with a 250kN servo-hydraulic Instron® actuator on either
side. All three are fixed to a stiff reaction plate at one end
(top-left of figure) and a stiff end beam at the other, which
is free to move back and forth. Each actuator includes a
load cell and a linear variable displacement transducer. In
addition, a linear displacement encoder is fitted across the
BRB. The actuators are controlled by the Instron® 8800
controller and RS Plus software. Transducer data is read by
the data acquisition dSPACE board, and recorded using the
ControlDesk® software. The data processing (including the
numerical substructure) is programmed in Simulink® and
compiled prior to testing.
substructure consists of a single-degree-of-freedom system
having mass m, stiffness k and dampening coefficient c. It is
therefore modelled by eqn 1, where u(t) is the displacement
of the structure which is applied to the specimen and FD(t) is
the resulting force.
c
k
u(t) = -xg(t) - m u(t) - m u(t) -
|
(1)
Eqn 1 represents the simplest possible structural model,
which was used for initial small amplitude tests, but this
will be extended to incorporate more structural degreesoffreedom and/or non-linear structural behaviour in future
tests. The desired displacement of the BRB xd is increased
by an amount equal to the estimated deflection of the rig
(computed from the measured BRB force Fm and the prei
determined rig stiffness krig) to obtain the target displacement
of the actuators xt . Actuation delays are inevitable, so
a delay compensator is included to minimise errors by
predicting ahead and advancing the command signal uc by
a time equal to the estimated delay. Inner-loop control of
each actuator is provided by a PID controller built into the
proprietary control system.
Any delay or amplitude error between the target
displacement xt and the measured displacement xm will
result in inaccuracy, so robust delay compensation is
required. Testing showed the Adaptive Time Series (ATS)
Compensator (Chae et al., 2013) to be the best candidate
as it is able to automatically react to variations in delay and
amplitude error during the test. An improvement on the
system is proposed using a recursive formulation that can
reduce the computational demand (allowing the use of
smaller timesteps). In tests of the bare actuators (under zero
load), ATS compensation reduced the normalised root mean
square displacement errors from 3.5% to 0.37%.
While the concept of hybrid testing is reasonably
straightforward, it can take many months to set up a test if
each aspect has to be designed and validated from scratch,
which is a barrier to the use of hybrid testing. It is intended
for the procedure developed in this research to be adaptable
to different types of hybrid test so that future hybrid tests can
be set up in less time and with a less daunting learning curve
for the operator.
The results of the BRB tests will be informative for designers
considering using BRBs in their structures, and can be used
to develop and validate computational models of BRBs,
which will be useful when tackling the problem of the sizing
and placement of dampers.
Figure 2 shows a simplified schematic representation of the
hybrid testing procedure. The input to the system is a scaled
earthquake acceleration time history, xg(t). The numerical
42
FD(t)
m
References
Funding body
Black, C. J., Makris, N., and Aiken, I. (2004). Component
testing, seismic evaluation and characterisation of bucklingrestrained braces, Journal of Structural Engineering 130:6,
880-894.
Engineering and Physical Science Research Council
(EPSRC)
Chae, Y., Kazemibidokhti, K. and Rickles, J. (2013). Adaptive
time series compensator for delay compensation of servohydraulic actuator systems for real-time hybrid simulation,
Earthquake Engineering and Structural Dynamics 42, 16971715.
Robin Malloy (E: [email protected])
Further information
Dr Martin Williams (E: [email protected])
Dr Tony Blakeborough (E: [email protected])
Darby, A., Blakeborough, A., and Williams, M. (1999). Realtime substructure tests using hydraulic actuator, Journal of
Engineering Mechanics 125:10, 1133-1139.
Figure 1. BRB Test Rig
Figure 2. Simplified schematic of hybrid testing procedure
|
43
A study on punching shear failure induced by impact loading
Poster presenter
16
Karl Micallef
Skidmore, Owings and Merrill Inc., London
Project goals and objectives
strain-rate of 100Hz. Further details can be found in Micallef
et al. (2014).
The design of reinforced concrete (RC) flat slab structures,
used extensively in construction due to its economic
and functional advantages, is associated with adequate
provisions for punching shear. Traditionally, design for
punching shear has been carried out using empirical
formulae (e.g. BS 8110, EN 1992, ACI 318). The critical
shear crack theory (CSCT) proposed by Muttoni (2008) and
Fernández Ruiz and Muttoni (2009) provides a more rational,
mechanically-based formulation to predict punching shear
strength for slabs without and with shear reinforcement
respectively.
However, both code methods and the CSCT are only
applicable to static loads (e.g. gravity loading). In the cases
of slabs subjected to dynamic loads (e.g. impact loading),
it has been observed that such slabs exhibit an increase in
strength with increasing loading (or strain) rate. Thus, the aim
of this research was to:
–
Assess the influence of dynamic loading on RC slabs
–
Provide a method of calculating the dynamic punching
shear strength of such slabs
–
Use the method to assess whether punching shear
failure occurs in RC slabs subjected to impact loading
and obtain the slab deformation at/close to failure
Dynamic punching shear strength
The initial stage in the research project was to determine
the dynamic punching shear strength of a RC slab. This
was done by extending the CSCT, which provides punching
shear capacity VR (in N) as a function of normalised slab
rotation ψ (to which the shear crack is assumed to be
proportional). The CSCT assumes that the punching shear
strength is derived from the concrete’s residual tensile
strength after cracking (i.e. fracture energy, which is a
function of the concrete’s compressive strength fck ) and from
aggregate interlock (also a function of fck ). The CSCT failure
criterion is described by Eqn 1 and is a function of the slab
geometry (the slab’s effective depth d and control perimeter
b, both in mm) and concrete material characteristics (f ck in
MPa and maximum aggregate size dg in mm).
VR
0.75
=
bd fck
1 + 15Ψd
16 + dg
(1)
Using the variation of f ck with strain-rate as given in MC2010
and using a discrete crack model in line with the original
formulation of the CSCT, a dynamic punching shear strength
based on the strain-rate was derived, by considering the
effects of strain-rate on aggregate interlock and fracture
energy. The punching shear strength was found to increase
by 7% for modest strain-rates of 10Hz and up to 33% for a
44
|
Dynamic response of RC slab
The next stage was to formulate a method by which the
structural response of a RC slab subjected to an impact load
could be obtained from a set of given inputs (i.e. impactor
mass and drop height) and slab characteristics, i.e., the
slab mass and stiffness, the contact stiffness (derived from
the Hertz contact law) and damping which ranges from 5 to
10%. The slab stiffness is derived using an effective reduced
span due to inertial effects (which leads to an increase in
stiffness).
A simplified mass-spring-dashpot model was used to obtain
the slab’s response (i.e. displacement, from which the slab
rotation could then be obtained). This is done by numerically
solving the equation of motion considering two phases: the
contact phase (when the impactor is in contact with the RC
slab) and the post-contact phase (which is the subsequent
behaviour using results from the end of the contact phase
as initial conditions for this phase). The impact force and
contact time of the impact event were evaluated using the
Petry formula.
A method for estimating the strain-rate was also derived.
Using this strain-rate, the slab’s dynamic punching shear
capacity could be derived, as described above. Further
details and the complete model formulation can also
be found in Micallef et al. (2014). Knowing the loaddisplacement (hence rotation) response, this could then be
compared with the dynamic punching shear capacity, which
is a function of rotation, to assess whether failure occurs.
The proposed model was used to assess slabs subjected
to impact loading e.g. a 12x4.8x0.28m slab impacted by
a 450kg mass dropped from a height of 30m tested by
Delhomme et al. (2007). The proposed model predicted that
the slab would undergo severe deformation but punching
shear failure does not occur, which was observed in the test,
as shown in Figure 1. The advantage of using the CSCT
is that the method allows distinction between the strength
contribution from the concrete alone and the reinforcement
and also provides information on the slab’s rotation at failure,
which is often considered to be a measure of its ductility.
This is also very useful for seismic and robustness design.
This research work presents an analytical model based on
the CSCT which can be applied to RC slabs subjected to
dynamic loading. This model is particularly useful for cases
such as falling slabs from above, rock-fall arrest systems
and flat slab-column connections subjected to an impulsive
axial load in the column. The novelty of the method is that
it encapsulates both the dynamic punching capacity and
also the dynamic shear demand, both in terms of the slab
rotation.
Funding body
The proposed method is currently being extended to
investigate the behaviour of RC slabs subjected to blast
loading with respect to punching shear failure. Further
research carried out at University of Surrey is looking at how
the model is applied to investigate progressive collapse of
flat slab structures (including column-removal scenarios)
in which the behaviour of the slab-column connection is
critical.
This research is part of a post-doctoral research
program carried out at the University of Surrey under the
supervision of Dr. Juan Sagaseta in collaboration with Dr.
Miguel Fernández Ruiz and Prof. Aurelio Muttoni of ÉPFL
(Switzerland) and funded by EPSRC (grant reference EP/
K008153/1).
References
Further information
Delhomme, F., Mommessin, M., Mougin, J.P. and Perrotin, P.
(2007). Simulation of a block impacting a reinforced concrete
slab with a finite element model and a mass-spring system.
Engineering Structures, 29:11, 844-852.
Dr. Karl Micallef (E: [email protected])
Dr. Juan Sagaseta (E: [email protected])
Muttoni, A. (2008). Punching shear strength of reinforced
concrete slabs without transverse reinforcement. ACI
Structural Journal, 105:3, 440-450.
Fernández Ruiz, M. and Muttoni, A. (2009). Applications of
critical shear crack theory to punching of reinforced concrete
slabs with transverse reinforcement. ACI Structural Journal,
106:4, 485-494.
MC2010 - Model Code for Concrete Structures. (2013).
CEB/fib.
Micallef, K., Sagaseta, J., Fernández Ruiz, M. and Muttoni,
A. (2014). Assessing punching shear failure in reinforced
concrete flat slabs subjected to localised impact loading,
International Journal of Impact Engineering, 71, 13-33.
Figure 1. Load-rotation response and failure criterion
|
45
Long-term deformation in unreinforced and reinforced Sitka
Spruce glulam
Oral presenter
17
Conan O’Ceallaigh
National University of Ireland, Galway
The focus of this research is to investigate the potential
of fast-grown Sitka spruce as a suitable material in the
manufacture of engineered wood products. The most
common structural grade achieved by this timber is C16
Grade, which is generally limited to low load applications.
However, the capacity of this softwood timber may be
greatly increased when used in glued laminated beams.
Glued laminated beams generally outperform solid timber
beams of the same grade and dimensions due to defects
such as knots being limited to one laminate within a
combined beam. The performance of glued laminated
beams may be further enhanced with the addition of fibre
reinforced polymer (FRP) reinforcement. It has been seen
that the addition of modest reinforcement ratios can delay
tension failure in glued laminated elements. The additional
reinforcement utilises the additional capacity of the timber
in the compression zone resulting in much more consistent
behaviour as well as a significant increase in flexural stiffness
(Gilfillan et al. 2001; Raftery & Harte 2011).
A significant body of research has been carried out on the
short-term behaviour of reinforced timber beams. However,
the long-term performance of these beams has received
little attention. This study aims to quantify the long-term
creep effects in both unreinforced and reinforced beams.
The creep of timber is known to be greatly increased in the
presence of a variable climate, commonly referred to as the
mechano-sorptive effect. To account for this EC5 (CEN,
2004), assigns a modification factor, which accounts for the
in-service environment, in calculating the final deflection. In
order to determine the influence of the reinforcement on the
creep behaviour, unreinforced and reinforced beams, are
subjected to long-term creep testing in both constant and
variable climates.
Forty glued laminated beams were manufactured from
individual C16 Grade laminates, graded with the use of
a mechanical grader at the National University of Ireland,
Galway. The grading results aided in the design and
manufacture of beams with similar flexural stiffness so that
the influence of the timber variability was minimised. Twenty
of these beams were reinforced with two 12 mm diameter
basalt fibre reinforced polymer (BFRP) rods. The rods were
housed in two circular grooves, routed the entire length of
the soffit and bonded using a two-component structural
epoxy adhesive.
The beams were subjected to short-term flexural testing in
accordance to EN 408 (CEN 2014). The reinforced beams
were tested in both their unreinforced and reinforced state
allowing for the increase in bending stiffness due to the
addition of reinforcement to be determined. The results
of the short-term tests were used to create four matched
46
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groups for comparative studies of the long-term deflection
of unreinforced and reinforced beams in a constant and
variable climate.
The beams were then loaded in four-point bending as seen
in Figure 1. Each beam was subjected a constant load,
which would result in a maximum compressive stress of
8 MPa on the top surface. This led to higher loads on the
reinforced beams to achieve the same stress. In a constant
climate chamber, unreinforced and reinforced beams were
subjected to long-term testing at a constant relative humidity
(RH) of 65% ± 5% and a temperature of 20°C ± 2°C. In a
variable climate chamber, unreinforced and reinforced beams
were subjected to long-term testing in an environment where
the RH changed from 65 ± 5% to 90% ± 5% in an 8 week
cycle allowing the moisture content to change similar to that
experienced in external sheltered climates.
The results of the short-term testing show a mean increase
in bending stiffness of 16.3% for a modest percentage
reinforcement ratio of 1.85%. This large increase is due
to the high stiffness of the reinforcement relative to the
timber. The results of the creep testing are shown if Figure
2. The creep response is described in terms of relative
creep, which is defined as the deflection at time, t, divided
by the initial elastic deflection. The lower two lines on the
graph shown the response in the constant climate. No
significant difference in relative creep was found between
unreinforced and reinforced beams indicating that the
addition of reinforcement did not reduce the viscoelastic
creep. The upper two lines show the response in the variable
climate. The relative creep is seen to be significantly greater
than in the constant climate, highlighting the importance of
accounting for the service conditions in design. Also, there
is a significant difference in the creep response of the two
types of beams in a variable climate. After 40 weeks of
repeated cycling, there is an average reduction of 9.94% in
relative creep due to the reinforcement.
The long-term deflection of structural elements is of
importance to structural design engineers, especially when
dealing with timber elements. This hygroscopic material
is adversely affected by variable climates, which must
be accounted for in design. The use of reinforcement to
increase the flexural performance has been shown to
improve the short-term stiffness and relative creep deflection
of glued laminated beams in variable climates. Currently,
design codes do not allow for the possible advantages
which can result from reinforced timber elements. This
research will provide data that will allow for the beneficial
effect of reinforcement to be accounted for in future revisions
to the design code.
References
Funding body
CEN (2004) EN 1995-1-1. Eurocode 5. Design oftimber
structures. Part 1-1
This research is funded by the Department of Agriculture,
Food and the Marine of the Republic of Ireland under the
FIRM/RSF/COFORD scheme as part of ‘Innovation in Irish
timber Usage’ (project ref. 11/C/207).
CEN (2014) EN 408. Timber structures - Structural timber
and glued laminated timber - Determination of some physical
and mechanical properties.
Gilfillan, J.R., Gilbert, S.G. & Patrick, G.R.H. (2001) The
Improved Performance of Home Grown Timber Glulam
Beams Using Fibre Reinforcement. Journal of the Institute of
Wood Science, 15(6).
Further information
Conan O’Ceallaigh (E: [email protected])
Dr Annette Harte (E: [email protected])
Raftery, G. & Harte, A. (2011) Low-grade glued laminated
timber reinforced with FRP plate. Composites Part B:
Engineering, 42(4), pp.724–735.
Figure 1. Creep Test Rig
Figure 2. Mechano-sorptive creep results
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47
Prospective view of cement based (GEM-TECH) material as a
structural material
18
Ucheowaji Ogbologugo
Coventry University
Introduction
With the advancement in the construction industry in recent
years, there has been a revolution in the construction
industry and construction materials with steel and concrete
being the two leading materials used. Concrete being the
most dominant structural material used, has been criticised
for its weight especially when used in the construction of
mega structures resulting in expensive foundations to carry
them when constructed on areas that have weak soils and
could be a problem in earthquake prone areas.
Several lightweight materials have been developed to solve
the issue of excessive weight by replacing coarse gravel
with other lightweight aggregates such as scoria (Yasar, Atis
and Kilic 2003), expanded clay (Li, Chen and Zhao 2011), oil
palm shell (Shafigh et al 2014) etc. However, most of these
materials have been limited to non-structural applications
and some others have limited use as these lightweight
aggregates may not be found in some part of the world.
GEM-TECH Technology has come up with the GEM-TECH
material that is made up of simple materials such as sand,
cement, water and the GEM-SOL catalyst. This material
is free flowing, self-compacting, highly workable and
consistent with a good strength to weight ratio. What makes
the GEM-TECH unique is the GEM-TECH mixing screw and
the GEM-SOL catalyst, the former being a patented mixing
screw system based on precision engineering to accurate
mix constituent materials in specific proportions resulting
in a consistent mix whereas the latter is the surfactant that
generates the air bubbles and also acts as a glue around
these bubbles preventing them from breaking down during
the rigorous mixing process.
This research aims at delivering an experimental study of the
mechanical properties of the GEM-TECH material so as to
determine its suitability for use as a structural material when
reinforced with steel. This study will tend to
–
Experimentally quantify the mechanical properties of the
GEM-TECH material cured in air
–
Study the relationship between these mechanical
properties and compare them to that from literatures
and standard codes that has been established for
conventional concretes.
–
Establish benchmarks for use of the GEM-TECH
material as structural material.
Description of methods and results
latter adopted for comparison. The target densities were
obtained from adjusting the foam volumes injected into the
mix as foam volume would have more effect on the density
of lightweight ‘foamed’ concrete than varying the sandcement mix (Nambiar and Ramamurthy 2006). The samples
were cured in air and tested for their mechanical properties
such as the compressive strength, flexural strength, elastic
modulus, tensile split strength after 7, 14, 28, 56 and 90
days and a 4 point loading test of reinforced beam made of
the material was also carried out.
A summary of results gotten from tests on the mechanical
properties of the GEM-TECH material is shown in Table 1. As
expected, there was a reduction in the wet density over time
tending towards the designed density. This is due to the loss
of moisture during the period of curing and hydration. There
was also a growth in compressive strength with the material
gaining up to 25 MPa for a designed target density of 1600
kg/m3 which makes it ideal to considered for structural
application. At 28 days the material had achieved up to
76% of its 90 days compressive strength which is similar
to the range of 80% to 85% given by Bing et al (2012). The
relationship between properties of the GEM-TECH material
such as that between its compressive strength and elastic
modulus is similar to the predictive model developed by
Jones and McCarthy (2005) as seen in Eqn 1.
E=0.42f c1.18
The material showed good flexural strength properties
of about 15% percent of its compressive strength which
depicts a similarity with that of conventional concrete which
ranges between 10 to 20% of their compressive strengths
(NRMCA 2000). The GEM-SOL catalyst tends to contribute
to the strength of the material in addition to holding the
bubbles together and this to an extent explains why the
samples with higher foam volume (Target density of 1600
kg/m3) showed better mechanical properties than those with
lower foam volume (Target density of 1810 kg/m3).
Results from the tests for mechanical properties and the
relationship between these properties shows that the GEMTECH material can be used as structural load carrying
member. Further tests carried out on beams reinforced
with steel loaded for bending showed good load carrying
capabilities despite its light weight. This research is ongoing
and positive outcome to the research would birth a
lightweight structural material that is made from simple raw
materials that can be gotten from every part of the world.
The material is also cheap, workable, possess a good
strength to weight ratio and to an appreciable extent can
replace conventional concretes in the construction industry.
Two sets of mixes of the GEM-TECH material were prepared
based on target densities of 1810 kg/m3 and 1600 kg/m3,
with the former regarded as the limit of density to which a
material can be referred to as a lightweight material and the
48
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(1)
References
Further information
Bing, C., Zhen, W., and Ning, L. (2012). Experimental
Research on Properties of High-Strength Foamed Concrete.
Journal of Materials in Civil Engineering 24:1, 113-118
Ucheowaji Ogbologugo (E: [email protected])
Dr Messaoud Saidani (E: [email protected])
Li, C. Y., Chen, H., and Zhao, S. B. (2011). Mechanical
Properties of Steel Fiber Reinforced Lightweight Aggregate
Concrete. AMR 366, 12-15
Nambiar, E.,K.K. and Ramamurthy, K. (2006). Models
Relating Mixture Composition to the Density and Strength
of Foam Concrete using Response Surface Methodology.
Cement & Concrete Composites 28, 752-760
NRMCA (2003). Concrete in Practise. What, why & how?
CIP 16- Flexural Strength Concrete. USA: National Ready
Mix Concrete Association
Shafigh, P., Mahmud, H. B., Jumaat, M. Z. B., Ahmmad,
R., and Bahri, S. (2014). Structural Lightweight Aggregate
Concrete using Two Types of Waste from the Palm Oil
Industry as Aggregate. Journal of Cleaner Production 80,
187-196
Yasar, E., Atis, C. D., and Kilic, A. (2003). High Strength
Lightweight Concrete made with Ternary Mixtures of
Cement-Fly Ash-Silica Fume and Scoria as Aggregate.
Turkish J.Eng.Env.Sci 28, 95-100
Table 1. Summary of results from mechanical testing of GEM TECH material.
Target Density
(kg/m3)
Age (Days)
Density (kg/m3)
Average
Compressive
Strength (MPa)
1600
7
1825.92
11.81
1600
14
1800.06
15.68
1600
28
1722.08
1600
56
1600
Elastic Modulus
(GPa)
Flexural
Strength (MPa)
Tensile Split
Strength (MPa)
19.36
13.58
2.08
1.08
1704.36
23.63
16.41
3.55
1.24
90
1739.25
25.36
18.01
3.68
1.51
1810
7
1926.12
12.46
1810
14
1963.60
16.30
1810
28
1804.87
17.96
8.43
1.92
0.68
1810
56
1823.60
19.85
11.17
2.74
1.15
1810
90
1797.53
20.40
13.65
4.65
1.16
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49
Glued-in BFRP rods as moment connections in indigenous
low grade timber
Oral presenter
19
Caoimhe O’Neill
Queen’s University Belfast
Glued-in rods present a viable alternative to traditional
timber connection methods, including mechanical fasteners,
adhesives or carpentry connections. Suitable for use in a
moment-resisting connection, glued-in rods transfer forces
from timber to timber through the timber/adhesive and rod/
adhesive interfaces. As well as their use in new build, gluedin rods have been used successfully for reinforcement and
restoration of timber structures, for example in the renovation
of roof and floor beams in buildings subject to decay. This
repair method is favoured for renovation of historic structures
in particular as it enables a stiff and strong hidden repair and
allows the maximum possible portion of the original timber to
be retained.
No universal standard exists for the design of glued-in rods
despite many research projects being commissioned on
their use since the 1980s. There had been an informative
annex in the pre-standard PrENV 1995-2 (1997) which
provided limited coverage of the design of glued-in rods
using steel rods however this document was replaced by
BS EN 1995-2:2004 and no guidance is included in this
current document. It is expected that guidelines on the
design of glued-in rods will be included in the next revision of
Eurocode 5.
The majority of research done in this area to date comprises
steel rods glued-in to glued laminated (glulam) elements
with lamellae of a high strength class timber. However other
researchers have investigated the behaviour of glued-in
rods in lower grade timber and with some fibre reinforced
polymer (FRP) materials in place of the standard steel rods
with the merits of these materials being reported in a recent
state of the art report on the use of glued-in rods (Steiger et
al, 2015). This research investigates the behaviour of Basalt
Fibre Reinforced Polymer (BFRP) rods glued-in to indigenous
Sitka Spruce which has relatively poor strength and is of a
low classification, typically C16. Optimum embedded length
of the rod and edge distance was determined through pullout testing before durability performance was investigated.
The research will conclude with glued-in rods being used as
moment connections in full-scale frame corners, the testing
of which will be used to validate the theoretical design
developed.
Pull-out capacity can be used as a measure of the strength
of a glued-in rod. In order to represent the combination of
axial and bending effects on a glued-in rod a pull-bending
set-up was used to evaluate the influence of embedded
length on pull-out capacity, see Figure 1. Results showed
a clear increase in pull-out strength with an increase in
embedded length with a 213% increase in capacity between
the longest embedded length of 600mm and the shortest
of 80mm. The most prevalent failure mode observed
was a failure in shear of the timber with the majority of all
specimens failing solely in this manner. Several specimens
50
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exhibited splitting along their tension face as a result of
the build-up of stresses around the glueline before failure.
Specimens where splitting occurred generally had a lower
pull-out capacity as a result. As a means of preventing
splitting edge distance was increased in steps of 1 rod
diameter, an optimum edge distance of 3.5dr was identified
where pull-out strength remained at an optimum and
splitting was less likely to occur.
Two ageing methods were used to assess the durability
of the glued-in BFRP rods. A vacuum-pressure regime
was used to simulate the deteriorative effects of long term
moisture ingress. Specimens were soaked in a pressure
vessel to saturation, dried and tested to failure where a
22% decrease in strength was observed after ageing. From
observation of the failed specimens it was clear that some
delamination had occurred by debonding of the epoxy and
the BFRP bar. This vacuum-pressure regime is an extreme
form of moisture cycling giving a worst case scenario
representation. The second ageing method represented a
more realistic exposure condition for structures designed
for service classes 1 and 2. This was achieved by cycling
relative humidity in a moisture chamber to mimic a typical
Northern European annual relative humidity cycle. After three
full cycles, when compared with similar specimens tested
in ambient conditions no significant loss of strength was
observed. Aged specimens had average failure strength of
74.47kN whereas non-aged specimens failed at an average
of 75.44kN. Variation within the samples sets was similar
confirming that ageing for a short time period does not have
a detrimental impact on the bond strength.
Frame corner tests were designed to validate theoretical
design guidelines that have been developed. These tests
consisted of 600mm deep box beams connected to a post
via glued-in rods on the back face embedded in to the post,
see Figure 2. Specimens were loaded in 1kN increments
to failure with ultimate failure load and failure mode being
recorded. At the time of writing results from these tests are
being analysed and will be available in future publications by
the author.
The ultimate results from this research include a design
method for glued-in rod moment connections. Looking
towards the next edition of Eurocode 5, expected in 2020,
the research presented here can provide information on the
behaviour of Basalt Fibre Reinforced Polymer as a viable rod
material and the design thereof.
References
Further information
RILEM TC, 1994, “RC 5 Bond test for reinforcement steel.
1. Beam test, 1982,” in RILEM Recommendations for the
Testing and Use of Constructions Materials, RILEM, Ed. E &
FN SPON, pp. 213 – 217.
Caoimhe O’Neill (E: [email protected])
Steiger R., Serrano, E., Stepinac M., Rajčić V., O’Neill C.,
McPolin, D., Widmann, R.; 2015; Strengthening of timber
structures with glued-in rods, Construction and Building
Materials, Vol 97, pp. 90-105
Dr Danny McPolin (E: [email protected])
Prof. Su Taylor (E: [email protected])
Funding body
This research is funded by the Department of Agriculture,
Food and the Marine of the Republic of Ireland under the
FIRM/RSF/COFORD scheme as part of ‘Innovation in
Irish timber Usage’ (project ref. 11/C/207). Experimental
work on durability was carried out as part of two
COST FP1101 - funded Short Term Scientific Missions
(ECOST-STSM-FP1101-281014-050275; ECOST-STSMFP1101-020815-063100).
Figure 2. Frame corner test
Figure 1. Pull-bending test
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51
decking
Oral presenter
20
Naveed Rehman
University of Bradford
Introduction
In recent years, much emphasis has been given to
sustainability, deconstructability, reducing waste in
the construction industry and carbon emissions by
reusing structural parts (materials) without going into the
recycling process. The use of steel beams with a metal
profiled decking concrete slab is very common in current
construction practice, as it is a very cost effective and
efficient construction system. The metal profiled decking
concrete slab is attached to steel beams through welded
shear studs to achieve the composite action. These shear
studs are welded to the steel beam flange and embedded in
the concrete slab, making deconstruction almost impossible.
The steel beams cannot be reused straightaway after
dismantling the composite floors system as it has to go
through a recycling process. This project will explore the
strength and stiffness of a new form of demountable shear
connector used in a composite beam instead of welded
shear studs. This new form of demountable shear connector
would allow the steel beams to be reused after dismantling
the composite floor structure.
Dai et al. (2014) investigated the use of demountable shear
connectors in solid RC slabs while Ataei and Bradford,
(2015) used precast solid concrete slabs and pretension
high strength bolts for demountable frame system. Moyniah
and Allwood, (2014) have recently reported beam tests
using M20 Gr8.8 bolts shear connectors with embedded
nuts and concluded that the results are comparable with
the Eurocode 4 prediction for welded studs. In this research
Nelson studs are used as demountable shear connectors for
the composite floor system.
This research aims to investigate the failure characteristics
of a composite beam with demountable shear connectors
subjected to static and cyclic loading. Secondly to
investigate the load slip behaviour of demountable shear
connectors. Testing will also include crack analysis in
concrete slab, measurements of strain, end slip, slip
between steel beam and profile decking, mid span deflection
and to measure the moment capacity of a composite beam
with demountable shear connectors.
slip between the steel beam and the composite slabs, mid
span deflection and slip of connectors against the load.
Strain gauges were used to measure the values of strain in
the concrete and steel beam.
This form of composite floor design will make this steelconcrete composite construction more sustainable by
enabling deconstruction and reuse of the material. The
test results show that this type of composite floor system
has similar moment capacity as compared in Figure 2 with
welded shear stud specimen. The test results indicate the
potential of demountable shear connectors as an alternative
to welded studs. Nuts of the demountable shear connectors
can be unfasten easily from the steel beam after testing
and the concrete slab with metal profiled decking can be
lifted from steel beam. The test results also highlight the
applicability of reusing the steel beam without recycling.
This deconstruction will in turn help to reduce the carbon
emissions and save on the consumption of new steel.
References
Dai, X., Lam, D., and Saveri, E. (2015). Effect of concrete
Strength and Stud Collar Size to Shear Capacity of
Demountable Shear Connectors. Journal of Structural
Engineering.
Antaei, A. and Bradford M A (2014). FE Analysis of
sustainable and deconstructable semi-rigid beam-to-column
composite joints. ICCM2014 28-30th July, Cambridge,
England
Moynihan, M. C. and Allwood, J. M. (2014). Viability and
performance of demountable composite connectors,
Journal of Constructional Steel Research, 99, 47-56
Funding Body
Engineering and Physical Science Research Council
(EPSRC)
Further information
Description of method
Mr Naveed Rehman (E: [email protected])
In this study experimental investigation was carried out on
a composite beam under cyclic and static load. The vertical
downward load was applied using a hydraulic jack through
the spreader beam. Load was applied using a two points
loading system on the simply supported composite beam
as shown in Figure 1 to evaluate the strength and stiffness
of the composite floor system with demountable shear
connectors. LVDTs were used for the measurement of end
Professor Dennis Lam (E: [email protected])
52
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Dr Xi Dai (E: [email protected])
Professor Ashraf Ashour (E: [email protected])
Figure 1. Composite beam test set up
Figure 2. Comparison of demountable shear connector specimen
with welded shear stud specimen
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53
Multiscale stochastic fracture mechanics modelling of
composites informed by in-situ X-ray CT tests
Poster presenter
21
Razvan Sencu
The aim of this PhD research project is to develop a
new multiscale stochastic fracture mechanics modelling
framework informed by in-situ X-ray Computed Tomography
(X-ray CT) tests. The specific objectives of the project are:
–
To extend the cohesive interface crack model to multiphase composites in both 2D and 3D,
–
To develop a new in-house loading rig to support in-situ
X-ray CT tests,
–
To develop a reconstruction technique to convert low
quality phase-contrast X-ray CT image datasets of
carbon fibre composites to FE mesh models,
–
To integrate the X-ray CT image-based FE mesh
models into detailed crack propagation modelling,
–
To validate the image-based multiscale stochastic
modelling method by direct comparison with in-situ
X-ray CT tensile test results.
In-situ X-ray CT experiments
During this research project, an innovative in-situ X-ray CT
testing method with advanced micro-loading control was
specially designed and made to support the detection of
multiple scale cracks that start at fibre scale and grow to
influence composite mechanics at component level. In-situ
X-ray CT tests were carried out using the Henry Moseley
X-ray imaging facility at the University of Manchester and the
Diamond-Manchester Imaging Branchline I13-2 at Diamond
Light Source (see Figure 1).
The specifically designed and manufactured micro-loading
device was necessary to overcome important limitations
that existed in available commercial rigs. The rig consists
of a mechanical, an automation and a data acquisition
system. This allows both compression and tension loading
with continuous, cyclic or in-situ stepped loading histories.
Other innovative features of the device include multipurpose
loading modes, sample setups, fast sample mounting,
fully autonomous motion control, real-time data acquisition
and flexibility in carrying out various in-situ micro-loading
programmes.
In-situ X-ray CT imaging of damage and fracture in cross-ply
composites and reconstruction
Figure 1 shows example results of the X-ray CT scan of
crack formation in a carbon fibre composite sample. The
visualisation was prepared in the software Avizo (FEI/Avizo)
using the volrenGreen tool. The sample was subjected to
uniaxial tension and crack growth in this case started from
54
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a notched ply at 90 degrees and propagated to other fibre
plies of different orientations. The conducted X-ray CT tests
reveal that the fibre scale can now be more clearly inspected
for carbon fibre reinforced polymers (CFRP). This contributes
to better understanding of complicated composite fracture
mechanics and provides important information about
damage progression and fracture.
The X-ray CT scan images are converted, using a specially
developed reconstruction method, to FE meshes. This
reconstruction method is able to track long and tortuous
fibres in complex/non-linear laminae and caters for poor
phase-contrast images that arise in high volume fraction
datasets. Figure 2 (f, g) shows an example of the converted
FE mesh, corresponding to the X-ray CT image. The FE
meshes are implemented in the general FE package to
simulate multiscale crack propagation, explained in the next
section. The multiscale modelling tools were developed
using multiple programming languages and packages
including Matlab, Python, Java, C++, ImageJ and Abaqus.
Advantage was taken of the high performance computing
(HPC) facility at University of Manchester. The use of object
oriented programs and HPC considerably reduced the
numerical modelling time.
Multiscale modelling of damage and fracture in cross-ply
composites
The first step of the new multiscale modelling method is to
simulate crack propagation in meso-scale elements (MeEs).
To avoid ambiguity, special boundary conditions and unique
overlapped sampling were used in a comprehensive 2D
numerical validation study that links the meso-scale fracture
behaviour of separate MeE simulations to global scale.
The 2D model allows material anisotropy and conserves
fracture energy and crack path locations in scale transfer.
Due to numerical challenges, the global damage and
fracture modelling validation in 3D, is conducted by direct
comparison with in-situ X-ray CT test results. Although the
field-of-view of the X-ray CT scans was smaller than sample
dimensions, the imaging and mechanical measurements
are used as reference to all new modelling tools that are
developed in the following way: (1) converted FE meshes are
used to obtain meso-scale behaviour (stress-strain, fracture
energy, crack formation); (2) meso-scale results above are
used to establish a model for macro-modelling; (3) macromodelling
results of load-deflection/crack propagation
are compared with measurements for validation. Figure
2 shows a few numerical case studies conducted on: 2D
crack simulations (a, b), X-ray CT testing using cone (c) &
synchrotron (d, e, f) sources, segmentation & reconstruction
tools (c, d, e, f) image-based fracture modelling (f, g, h) and
detailing of the global multiscale stochastic model used in
validation (i).
Funding body
A new multiscale stochastic fracture mechanics modelling
method has been developed in this PhD project. This
model is informed by in-situ X-ray CT images, in which the
FE mesh is constructed from X-ray CT images and the
synchrotron in-situ X-ray CT images provide multiscale crack
propagation information for validation. The new method is
capable of modelling quasi-brittle behaviour in composites
containing multiple phases, various degrees of bonding and
feature distributions. This in-situ image informed multiscale
modelling method opens up a new way for designing and
assessment of fibre composite materials.
This study is funded by U.S. Air Force EOARD grant (No
FA8655-12-1-2100) and EPSRC grant (No EP/J019763/1)
at University of Manchester.
Further information
Razvan M Sencu (E: [email protected])
Zhenjun Yang (E: [email protected])
Yong C Wang (E: [email protected])
References
FEI/Avizo. Software Version Avizo 8 Fire - Educational
License at University of Manchester.
Figure 1. In-situ X-ray CT experiment under synchrotron radiation conducted at Diamond Light Source.
Figure 2. Challenges versus numerical results in carbon fibre composites using latest X-ray CT characterisation
technique, image-segmentation/ reconstruction tools and cohesive crack modelling results.
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55
Experimental investigation of recycled carpet composites for
barrier structures
Poster presenter
22
Adeayo Sotayo
Lancaster University
In the UK, approximately 400 000 tonnes of carpet waste
are sent to landfill annually (Bird, 2014). However, the
landfill option is becoming increasingly impractical due to
environmental impact considerations, reduced availability,
and increasing cost (Sotayo et al. 2015). Furthermore, carpet
textiles are non-biodegradable, and their disposal to landfill
results in the release of methane (CH4) and carbon dioxide
(CO2) to the atmosphere, and methane emissions are more
harmful (by a factor of 20) than CO2 emissions (United
Nations Environment Programme, 2002).
The results obtained so far from the analysis and testing
demonstrate the potential of the carpet composite as a
potential alternative to some common materials used in
fencing applications, such as timber and PVC. Furthermore,
the successful outcome of the research currently underway
offers the prospect of a viable remediation pathway for
carpet waste, bringing both economic and environmental
benefits.
Increasing recycling is a major goal of the current
environmental agenda. The study described herein
contributes towards this goal via the development of
a waste carpet structural composite material, and the
characterisation of its mechanics/physical properties. It is
anticipated that such materials can replace other common
materials (e.g. timber, PVC etc) in fencing or other barriertype
applications. Consequently, the study also includes
an investigation of the load-deformation response of a post
and rail barrier/fence structure fabricated from carpet-based
composite material, and seeks to evaluate its stiffness
characteristics relative to those of a similar timber fence
(benchmark data).
Bird L. (2014). Carpet recycling UK conference, [online].
Available from http://www.carpetrecyclinguk.com/
downloads/27_percent_landfill_diversion_how_the_UK_
exceeded its_targets_two_years_early_Laurance_Bird_and_
Jane_Gardner_Carpet_Recycling_UK.pdf [accessed 26 July
2014].
Description of methods and results
Structural analysis and testing
Carpet-based composites have been fabricated into
rectangular cross-section beams and tested in three-point
bending and compared with similar tests on timber and PVC
beams (benchmark materials). The flecural moduli obtained
from these tests are listed in Table 1.
The elastic properties of timber were used to analyse a
two-bay post and rail fence (a benchmark structure) using
ANSYS FE software (see Figure 1). The results of the
timber FE model were validated by means of static loaddeformation tests carried out on a full-scale timber fence
(see Figure 2). Using the elastic properties of the carpet
waste composite material in the FE model, the loaddeformation response of a similar composite fence was
investigated. In addition, the research will undertake design
optimisation of the carpet composite sections and the overall
geometry of the structure to enable it to achieve a loaddeformation response similar to that of the timber fence.
56
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References
Sotayo, A., Green, S. & Turvey, G. (2015). Carpet recycling:
A review of recycled carpets for structural composites,
Environmental Technology & Innovation 3, 97 – 107
United Nations Environment Programme. (2002). Gas
emissions from waste disposal, [online]. Available from http://
www.grid.unep.ch/waste/html_file/42-43_climate_change.
html [accessed 31 July 2014].
Funding body
Centre for Global Eco-Innovation (CGE), Lancaster University
Engineering Department.
Further information
Adeayo Sotayo (E: [email protected])
Dr Sarah Green (E: [email protected])
Dr Geoffrey Turvey (E: [email protected])
Table 1. Flexural moduli of carpet-based composite, timber and PVC materials
Material
Flexural modulus (GPa)
Recycled carpet-based composite
2.6
Timber
10
PVC
2.5
Figure 1. Contour plot showing the deflections of the two-bay timber fence due to an out-of-plane load of 1400 N at the top
of the middle post
Figure 2. Image showing the load-deformation test setup of the twobay timber fence
|
57
Tall modular buildings: height limits of stacked steel modules
Poster presenter
23
Petia Tzokova
University of Cambridge
Introduction
Population and urban density in cities is rising, therefore
many new homes are required (Miles and Whitehouse,
2013). Modular buildings are constructed from roomsized
compartments (or modules) made in a factory and
assembled on site. Advantages include fast construction,
high quality control and economies of scale due to the
repeatability of modules (Lawson, 2007). The off-site nature
of modular buildings can help with the mentioned issues
above, if these buildings can be extended to high-rise.
Maximum heights of modular buildings made from stacked
modules in current practice are about 10 storeys (Lawson,
2007). Lawson and Richards (2010) investigated the
possibility of extending the typical current designs of modular
buildings to 12 storeys. The authors imposed this 12 storey
limit from the outset, however, and did not consider whether
going taller would be possible.
It was clear from the literature studied that the definitive
height limit of modular buildings has not previously been
investigated in depth, giving the following main objectives of
this project:
−
To find the structural height limit of the simplest,
stacked form of modular buildings.
−
To find the variation of these height limits between
different types of module.
Perfectly connected stacked modules of the same type
(‘modular towers’) were considered. Different steel module
types were investigated – thin walled boxes, unbraced
frames and braced frames, also including sub-types of
each of these. Both vertical and horizontal loads were
considered, as shown in Figure 1 with a 10 storey modular
tower as an example. Failure due to material strength and
buckling (ultimate limit state) and horizontal deflection limits
of the towers (serviceability limit state) were considered.
Analytical equations were derived and solved for the height
of tower at which each limit state is exceeded for many
different modules of each type, each made up of different
commercially available sections. The results of this analysis
were plotted in the style of an Ashby chart (Ashby, 2005)
where maximum achievable heights could be found and
patterns could be observed between different modular
towers.
58
|
Figure 2 shows the final Ashby chart, combining ultimate
and serviceability limit state results. The chart has logarithmic
axes, showing maximum number of storeys against weight
of a module in each modular tower. Each point on the chart
is a different modular tower; the colours are indicated in
the legend and show the different types and sub-types of
module. Three clusters of module sub-types have been
highlighted using ovals to show emerging patterns (others
have been omitted for clarity of the plot). The purple cluster
(thin walled boxes with corrugated steel walls) gives light
modules, but poor modular tower height. The pink cluster
(thin walled boxes with cold formed section walls) gives quite
light modules, with decent height. Finally, the green cluster
(unbraced frames with hot rolled sections) gives heavier
modules, with a large range of heights but also the tallest
modular tower at 78 storeys (labelled in Figure 2). This is an
unintuitive result – the unbraced frames greatly outperform
the braced frames (maximum height 36 storeys) as well as
the thin walled boxes (maximum height 38 storeys). This is
thought to be because an unbraced frame with moment
connections and large sections works well in bending and
hence may give a smaller lateral deflection than if the same
sections are pinned and braced with a smaller section.
Potential for application of results & further research
The height limit results found were much greater than the
height limits of current typical modular buildings, therefore
the results of this project will hopefully cause the current
height limits to be reconsidered in research and industry. The
research and results presented here formed a preliminary
project to a PhD in the form of a Master of Research (MRes).
Further research in the main PhD project will focus on
dynamics of tall modular buildings, in particular control and
hence mitigation of excessive lateral displacements due to
extreme events such as earthquakes or strong winds.
References
Miles, J. and Whitehouse, N. (2013) Offsite Housing Review,
Construction Industry Council, London.
Lawson, R. M. (2007) P348: Building Design Using Modules,
Steel Construction Institute, Ascot.
Lawson, R. M. and Richards, J. (2010) Modular design for
high-rise buildings, Proceedings of the Institution of Civil
Engineers – Structures and Buildings 163:3, 151-164.
Ashby, M. F. (2005). Materials selection in mechanical
design, Butterworth-Heinemann, Boston.
Funding body
Engineering and Physical Sciences Research Council
(EPSRC)
Further information
Petia Tzokova (E: [email protected])
Dr Janet Lees (E: [email protected])
Dr Keith Seffen (E: [email protected])
Figure 1. 10 storey modular tower, showing the
location of applied loads at each storey
Figure 2. Final Ashby chart with three module clusters highlighted; the
highest storey modular tower is labelled
|
59
Development of novel connection methods between precast
concrete panels
Oral presenter
24
Jean Paul Vella
In precast concrete construction, particular attention should
be given to connections between separate precast elements
as these are required to transfer static and dynamic loads,
whilst ensuring the overall strength and robustness of the
structure (Elliot, 2002).
In collaboration with BRE and Arup, Laing O’Rourke
have developed and patented a novel form of connection
between precast concrete panels utilising lapped headed
bars, known as the “E6 joint”. Headed reinforcement bars
protrude from adjacent faces of precast lightweight concrete
panels, such that a reduced lap length can be used in the
cast-in-situ concrete joint region, thereby decreasing the
joint width, when compared to straight bar lap splices.
Confining reinforcement in the form of vertical shear studs
and transverse bars is also installed in the joint (Figure 1).
The aim of this research is to study the mechanical
behaviour of this novel form of connection, at the
serviceability and ultimate limit states, by means of numerical
analysis, experimental testing and reliability analysis. The
experimental results are used to validate a three dimensional
non-linear finite element (NLFEA) model of the joint. A
simplified design method is also being developed which will
be validated against the experimental results and NLFEA
simulations with parameters not considered in the laboratory
tests.
The tensile strength of the joint is investigated by studying
the specimen shown in Figure 2 which comprises two
headed bars lapped with a central headed bar. The
specimen geometry was chosen for convenience of
laboratory testing, ease of interpretation of test results
and relative simplicity of numerical modelling. Transverse
bars and shear studs are provided in the test specimens,
as would be the case in joints between precast units. The
specimen response is investigated with three dimensional
NLFEA, using ATENA, and experimentally. Parameters
considered in the NLFEA include, amongst others; concrete
strength, diameter and arrangement of transverse bars
and the presence or absence of shear studs. Results from
preliminary analyses, were used to develop the experimental
program which is subsequently used to refine and validate
the NLFEA.
Previous studies on similar joints with lapped headed bars,
or U-bars, have used a variety of analytical approaches to
determine joint strength, such as; combined models for head
bearing and bond (Thompson et al. 2006), strut-and-tie
models (STM) (Ma et al. 2012, He et al. 2013), and plasticity
based models (Joergensen and Hoang, 2013). Currently, a
STM developed by Laing O’Rourke, and reviewed by Arup,
is used to determine the E6 design joint strength. Analysis
shows that the STM gives conservative results compared
with experimental results whilst not fully capturing the
observed behaviour of the joint. In particular, NLFEA and
experimental studies show that the bending stiffness of the
transverse bars contributes significantly to joint strength,
whilst only their axial contribution is considered in the STM.
Table 1 compares test results with corresponding unfactored
STM and preliminary NLFEA predictions. Maximum loads, N,
are limited to 258kN, corresponding to the yield strength of
the loaded headed bar. On average, the STM predictions are
30% lower than test results, whereas the NLFEA predictions
are 7% higher than test results. STMs are typically used
in much larger scale elements such as deep beams, and
certain assumptions considered in these structures, such
as neglect of dowel action, do not seem applicable to such
small scale joints. Table 1 therefore shows that the NLFEA
gives much better estimates of joint strength than the
STM which will be refined to more accurately simulate the
numerical results and laboratory tests. Alternative design
approaches will also be considered.
Improved understanding of joint behaviour gained through
experimental testing and NLFEA will enable the joint
design to be optimised and facilitate the development of
an improved simplified design method. Designers would
also gain more confidence in the system, encouraging
them to apply it in their designs. A more widespread use
of this system would lead to improvements in buildability,
sustainability and health and safety of concrete structures,
including; reduced construction time, reduced material
waste, high quality control and reduced on-site labour
resulting in safer construction sites.
Numerous strain gauges are used in the test specimens to
determine the reinforcement axial and bending forces. A
digital image correlation (DIC) system is also used to gather
data concerning displacements, concrete surface strains
and crack propagation. Additionally, four slab specimens
will be tested under four-point bending to determine the
generality of the conclusions drawn from the tension tests.
60
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References
Funding body
Elliot, K. S. (2002). Precast Concrete Structures,
Butterworth-Heinemann, Oxford, U.K.
Laing O’Rourke Centre for Systems Engineering and
Innovation at Imperial College London
He, Z., Ma, Z. J., Chapman, C. E. and Liu, Z. (2012).
Longitudinal Joints with Accelerated Construction
Features in Decked Bulb-Tee Girder Bridges:
Strut-and-Tie Model and Design Guidelines, Journal
of Bridge Engineering 18:3, 372-379.
Further information
Jean Paul Vella (E: [email protected])
Dr. Robert L. Vollum (E: [email protected])
Joergensen, H. B. and Hoang, L. C. (2013). Tests and Limit
Analysis of Loop Connections between Precast Concrete
Elements Loaded in Tension, Engineering Structures, 52,
558-569.
Ma, Z. J., Lewis, S., Cao, Q., He, Z., Burdette, E. G. and
French, C. E. W. (2012). Transverse Joint Details with Tight
Bend Diameter U-Bars for Accelerated Bridge Construction,
Journal of Structural Engineering, 138:6, 697-707.
Thompson, M. K., Ledesma, A., Jirsa, J. O. and Breen,
J. E. (2006). Lap Splices Anchored by Headed Bars, ACI
Structural Journal 103:S29, 271-279.
Table 1. Comparison between STM and test results
Test #
1.1
1.2
1.5
2.1
2.2
2.5
3.1
3.2
3.5
NNLFEA
172
232
242
123
181
207
236
258
258
NSTM
129
129
191
99
126
139
160
160
160
NTest
149
232
242
123
181
207
236
258
258
NNLFEA/NTest
1.15
0.93
1.02
1.32
1.12
1.13
0.97
1.00
1.00
NSTM/NTest
0.87
0.56
0.79
0.80
0.70
0.67
0.68
0.62
0.62
Figure 1. Typical two-layer E6 joint arrangement
Figure 2. Typical NLFEA and tension test specimen
|
61
Poster presenter
25
Jie Wang
High strength steels (HSS), with yield strengths over 460
MPa, are attracting increasing attention from structural
engineers in recent years owing to their potential to
enable lighter structures while being more sustainable
and economic. Compared to conventional carbon steels,
the structural application of HSS is still rather rare, which
could be attributed to the lack of understanding and limited
research into structural HSS. The only available design
code that was proposed specifically for these structures,
the European standard EN 1993-1-12 (2007), is conceived
as a simple extension to the traditional design rules for
ordinary carbon steels (EN 1993-1-1, 2005). Consequently,
the potential of HSS is limited by the use of design criteria
that are not optimised for the characteristics of the material.
Towards this end, previous research work by Rasmussen
and Hancock (1992), Rasmussen and Hancock (1995)
and IABSE (2005) based on limited experimental tests
and analytical calculations, observed notable differences
between the response of HSS and ordinary steels.
Cross-sectional level: The cross-sectional behaviour of HSS
has been studied by means of stub column tests, 3- and
4-point in-plane bending tests and combined axial-bending
tests. Rigorous FE models have been developed and
validated against the experiments to extend the scope of
the test results. Based on the stub column and in-plane
bending test results, the slenderness limits for HSS internal
elements under compression in the EC3 cross-sectional
classification have been examined. Interestingly, the results
fit well with the revised slenderness limits for conventional
carbon steel design in Taras et al. (2013), which are therefore
recommended in HSS. The combined loading tests have
been performed on three SHS sizes, and the results verified
that the EC3 design envelope (EN 1993-1-1, 2005) for SHS/
RHS under combined axial-bending applies safely to the
tested HSS specimens.
The scope of this project is to provide a better understanding
of the structural response of HSS and contribute towards
the development of optimum design criteria for these
structures. To this end, a comprehensive testing programme
on hot-finished S460 and S690 tubular members has
been carried out. Different aspects from the material level
to the cross-sectional level and the member level have
been studied, and the corresponding design regulations in
EN 1993-1-1 (2005) and EN 1993-1-12 (2007) have been
evaluated based on the test results.
Member level: The structural behaviour of the HSS
specimens has been examined by long column tests, where
five cross-section sizes and eight column slendernesses
were considered. Prior to testing, the initial imperfection was
adjusted in all the specimens to reach Lcr/1000, where Lcr
is the buckling length of the member. The test results are
plotted against the codified design curve a0 in EN 1993-1-1
(2005) in Figure 1. HSS columns outperform lower grade
carbon steels, which becomes clear by comparing the
S690 with the S460 members. This result can be explained
by the reduced sensitivity of HSS to initial imperfections
and residual stresses, which echoes the findings of IABSE
(2005). Moreover, buckling curve a0 can be safely applied to
the S690 members, while overestimating the capacity of the
S460 members.
The experimental programme was designed to cover
different structural aspects of HSS, including material
coupon tests, stub column tests, in-plane bending tests,
combined axial-bending tests and long column tests on a
total of eleven square and rectangular hollow section sizes
(SHS/RHS). The results and conclusions associated with
each test at the different structural levels are summarised as
follows:
This study presents an extensive experimental and numerical
study to shed some light on the design of structures with
HSS and to promote the general application of this material.
The assessment of the current EC3 design rules at material,
cross-sectional and member levels contributes towards the
improvement of the accuracy and safety of HSS structural
design. The comprehensive testing program significantly
increases the available experimental data on HSS members,
which is of a great importance for the future development of
the next generation of design codes for structural steels.
Material level: Tensile and compressive material coupon
tests have been performed for each cross-section size.
The engineering stress-strain response of the specimens
presents a yield plateau that is very similar to that of
conventional carbon steels, but with lower strain hardening
and ductility. Even so, the codified ductility requirements (fy/
fu, εf and εu) in EN 1993-1-12 (2007) are satisfied for the
majority of the tested hot-finished S460 and S690 materials
with only some S690 corner coupons failing to meet the fy/fu
and εu requirements.
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References
Funding body
IABSE (2005). In Use and application of high-performance
steels for steel structures. International Association for
Bridge and Structural Engineering, Switzerland
The Research Fund for Coal and Steel (RFCS)
EN 1993-1-1: 2005. Design of steel structures – Part 1-1:
General rules and rules for buildings. 2005
Jie Wang (E: [email protected])
EN 1993-1-12: 2007. Design of steel structures – Part 1-12:
Additional rules for the extension of EN 1993 up to steel
grades S 700. 2007
Further information
Professor Leroy Gardner (E: [email protected])
Dr Sheida Afshan (E: [email protected])
Rasmussen, K. J. R. and Hancock, G. J. (1992). ‘Plate
slenderness limits for high strength steel sections’. Journal of
Constructional Steel Research, 23, pp73–96
Rasmussen, K. J. R. and Hancock, G. J. (1995). ’Test of
high strength steel columns’. Journal of Constructional Steel
Research, 34, pp27–52
Taras, A., Greiner, R. and Unterweger, H. (2013). Technical
report: Proposal for amended rules for member buckling and
semi-compact cross-section design. Consolidated version of
documents of the same title submitted to the SC3 Evolution
Group 1993-1-1, Paris
Figure 1. Assessment of buckling curve a0 in EC3 with HSS column test
results
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63
Detecting long-span bridge displacement from fusion of GPS
and accelerometer signals
26
Yan Xu
University of Exeter
Displacement measurement of structures under dynamic
excitations enables the evaluation of bridge performance
and serviceability. Currently it remains an open question how
best to detect the dynamic displacement with an adequate
level of precision (Erol, 2010). RTK-GPS survey technique
has been widely used in structural monitoring activities
(Ogaja, 2007). However, due to a few system limitations
like multipath effect and dependence on satellite coverage,
GPS observation allows centimetre accuracy to be achieved
which remains insufficient.
Using an additional sensor to supply redundant information
of structural movement is an ideal method to improve the
precision level. GPS observation usually has lower sampling
rate with limited dynamic characteristics. By contrast,
accelerometers can easily detect wide range of frequencies
and give stabilise sampling rate. This study is an exercise
of applying multi-rate Kalman filtering and expectationmaximisation algorithm to merge GPS and accelerometer
signals which obtained from a long-span bridge.
The Kalman filter algorithm has actively been applied in the
navigation field. It is merging the measured acceleration
and displacement data to track the specific object motion.
Smyth and Wu (2007) proposed a multi-rate Kalman filtering
approach with smoothing technique to estimate the velocity
and displacement based on measurements (acceleration
and displacement). These measurements were sampled
at different sampling rates. Chang and Xiao (2010) applied
this method to merge the acceleration and videogrammetric
displacement from some experimental examples.
During the implementation of Kalman filtering, four
parameters including the covariance of process noise Qd,
the covariance of measurement noise Rd, the initial state of
state variables X1, and the initial covariance of state variables
V1, are latent variables. They are required to be determined
before estimation and have direct influence on the estimation
accuracy. However, the latent variables determination was
seldom mentioned in the previous study. Li and Chang
(2012) proposed an adaptive subspace technique to quantify
noise variances embedded in measurement signals. This
physical-based method is built on the assumption that the
number of measurement signals is larger than the number
of identifiable structural modes from these signals. From this
point of view, the method is inapplicable to predict the noise
variance using the single-channel signal of acceleration or
displacement. In this project, the expectation–maximisation
(EM) algorithm is applied to solve this problem.
64
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The EM iteration alternates between performing an
expectation (E) and a maximisation (M) step (Ghahramani
and Hinton, 1996) and the procedure is shown in Figure 1.
The expectation (E) creates a function for the expectation of
the log-likelihood using the current estimation. Otherwise,
the maximisation (M) step computes parameters maximising
the expected log-likelihood that found on the E step. In the
state space model, four unobserved parameters (Qd , Rd , X1
and V1) are considered. The EM algorithm is guaranteed to
increase the likelihood at each iterating cycle until to reach
stationary process.
This method is firstly validated by a numerical example of a
swept-sine signal with linear trend and then applied to the
monitoring of Humber Bridge in the UK. In current bridge
SHM system, two GPS rover receivers are installed in two
sides of mid-span with the sampling rate of 1 Hz. Three
accelerometers are installed inside the deck at mid-span
with the sampling rate of 20 Hz. The estimated displacement
has the sampling rate of 20 Hz shown in Figure 2. The
variation between GPS measurement and Kalman
estimation is predicted as noise of GPS. The predicted noise
is in the range of -13.20mm and 16.64 mm, which matches
with the reality (RTK GPS sensors provide the centimetre
precision level).
The multi-rate Kalman filtering with expectation maximisation
algorithm has been investigated to estimate the
displacement from contaminated noise measurements of
acceleration and displacement in the bridge. The first denefit
is to increase the frequency bandwidth of displacement
which allows us to capture more dynamic information.
In addition, using EM algorithm to determine the latent
variables makes the estimation result more reliable. The
proposed data fusion method can be extended to other
displacement measurement devices.
Kalman filtering algorithm is an on-line prediction tool. In this
study, fix-point smoothing and expectation-maximisation
(EM) algorithm were applied to improve estimation accuracy,
but leading to the loss of on-line feature. However, realtime monitoring is sometimes required rather than postprocessing results. The accuracy of real-time estimation
using Kalman filtering algorithm will deserve further
investigation.
References
Funding body
Chang, C. C., and Xiao, X. H. (2010). An integrated visualinertial technique for structural displacement and velocity
measurement. Smart Structures and Systems, 6:9, 10251039.
EMPS, University of Exeter
Erol, B. (2010). Evaluation of high-precision sensors in
structural monitoring. Sensors, 10:12, 10803-10827.
Further information
Yan Xu (E: [email protected])
Prof. James Brownjohn (E: [email protected])
Ghahramani, Z., and Hinton, G. E. (1996). Parameter
estimation for linear dynamical systems. Technical Report
CRG-TR-96-2, University of Toronto, Dept. of Computer
Science.
Li, Z., and Chang, C. C. (2012). Adaptive Quantification
of Noise Variance Using Subspace Technique. Journal of
engineering mechanics, 139:4, 469-478.
Ogaja, C., Li, X., and Rizos, C. (2007). Advances in structural
monitoring with global positioning system technology:
1997–2006. Journal of Applied Geodesy, 1:3, 171-179.
Smyth, A., and Wu, M. (2007). Multi-rate Kalman filtering for
the data fusion of displacement and acceleration response
measurements in dynamic system monitoring. Mechanical
Systems and Signal Processing, 21:2, 706-723.
Figure 2. Measured and estimated displacement time history
Figure 1. Flowchart of EM algorithm
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65
A modelling approach to railway bridge asset management
Poster presenter
27
Panayioiti Yianni
University of Nottingham
Introduction
Management of a large portfolio of structures can be
complex and demanding for infrastructure agencies. The UK
railway system plays a vital role in national transportation and
the structures that support the railway system are integral.
The structures in this study are railway bridges. With the
introduction of moving block signalling and greater pressure
from commuters to have more railway throughput, the
stresses imposed on the supporting structures is only set to
increase.
The model that has been developed is able to predict the
deterioration of bridges, when maintenance will be required,
what type of maintenance it will be and the associated
cost with that maintenance. This allows the model to
output whole life cost estimated over the lifetime of the
simulation, an example of this can be seen in Figure 2. This
is a revolutionary insight which would help bridge portfolio
managers maximise budget performance. Although the
study was limited to railway bridges, the methodology
and modelling techniques can also be applied to highway
bridges.
An additional complexity arises from the fact that portfolio
management is often performed by large organisations.
These organisations often have departmentalised systems
with little cross-department collaboration. This can lead to
situations where different teams are responsible for different
aspects of the same assets: a maintenance team, an
inspection team, a safety team, etc. This disjointed system
often means that no one team knows exactly what the
condition of the asset is.
The aim of the project is to provide a decision making tool
which uses a stochastic modelling technique. Each of the
aspects of bridge management have been scrutinised and
the resulting model strikes a balance between modelling
simplicity and true-to-life processes. The modelling approach
used is called Petri-Nets and this modelling technique
affords a great deal of flexibility which means that the model
can be enhanced with complex procedures to make it trueto-life.
Additionally, the model has scope for optimisation which
means that optimised schedules can be suggested to keep
the condition of the structure at a satisfactory level whilst
minimising the whole life cost. This would allow portfolio
managers to predict the work items, keeping a stable
amount of work items for the inspection/maintenance teams
whilst being able to predict budget performance. The benefit
for a tool such as this has wide-reaching implications.
Funding body
Network Rail, Engineering and Physical Sciences Research
Council (EPSRC) grant reference EP/L50502X
Further information
Panayioti Yianni (E: [email protected])
Luis C. Neves (E: [email protected])
Additionally, the model will be enhanced with Local
Environmental Factors which are calculated from historical
data. A bridge population totalling 17,000 has been used
to calibrate the deterioration module which can closely
match the real world deterioration of structures. This has
been further enhanced with key factors that affect the
deterioration profile.
The methodology follows common reliability analysis. To
calibrate the deterioration profile, Mean-Time-To-Failure
(MTTF) was calculated for each of the condition states from
historical data. In total, over 400,000 element inspections
were used for this calibration. A similar approach was used
with the Local Environmental Factors where the data was
split up into the various attributes and the MTTFs were then
calibrated accordingly. These can then be directly fed into
the Petri-Net model which performs Monte Carlo simulation.
An example of the deterioration profile can be seen in Figure
1 which shows the probability of being in different conditions
over time.
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Figure 1. A demonstration of the deterioration module with the probability of being in
different condition states over time.
Figure 2. Graph to show the nominal and cumulative cost per year of interventions
and inspections.
|
67
Dynamic non-linear analysis of sub-standard reinforced
concrete frames accounting for shear failure localisation
Poster presenter
28
Dimitrios K. Zimos
City University London
Reinforced concrete (R/C) buildings designed according
to older seismic codes (or even without adhering to any
code) represent a large part of the total building stock
worldwide. Transverse reinforcement in their structural
elements is typically inadequate, rendering them vulnerable
to shear failure subsequent, or even prior, to yielding of
their longitudinal reinforcement. This can eventually lead
to loss of axial load capacity of vertical elements and
initiate progressive collapse of buildings. Previous studies
attempting to model the full hysteretic behaviour of shearcritical elements following a macro-modelling approach are
typically based on quite a limited amount of experimental
results, especially with respect to the post-peak part of their
response, and make use of simplifying assumptions that are
not always valid (e.g. Baradaran-Shoraka and Elwood, 2013;
LeBorgne and Ghannoum, 2013; Wibowo et al., 2014).
A rather large database of experimental results of
rectangular shear and flexure-shear critical R/C columns
(150 specimens) has been compiled (Zimos et al., 2015).
Statistical analysis of this dataset has been carried out, in
order to develop empirical models of the post-peak shear
force – shear deformation response and the angle of the
shear failure plane defining the “shear critical length”, by
using non-linear least-squares regression analysis.
The development of a new member-type model for the
full-range response of substandard elements is put forward
herein, with a view to accurately and efficiently capturing
the response of shear-deficient elements and structures.
It is based on a previously established flexibility-based
spread-inelasticity model that accounts for shear-flexure
interaction (Mergos and Kappos 2012). Its novelty lies in the
consideration of localisation of shear strains, after the onset
of shear failure, in a critical length defined by a diagonal
failure plane (Zimos et al., 2015), herein termed “shear failure
localisation”.
In addition, empirical models have been developed for
the key parameters defining the post-peak response of
shear critical RC column members, i.e. the angle of the
failure plane defining the critical length, the shear strength
degradation after the onset of shear failure, taking into
account both cyclic and in-cycle degradation, as well as
the onset of axial failure (Zimos et al., 2015). The latter
constitutes a vital aspect of the non-linear response of the
entire structure, since it signals the initiation of a process
of loss of an individual vertical R/C element’s axial capacity
simultaneously with the redistribution of vertical loads to its
neighbouring ones, potentially initiating vertical progressive
collapse.
68
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The beam-column model shown in Figure 1 has been
implemented in IDARC2D software (Valles et al., 1996;
Reinhorn et al., 2009). It is composed of flexural, shear
and bond-slip sub-elements connected in series. After the
onset of shear failure, the shear sub-element dominates the
hysteretic response by following the post-peak shear forceshear strain relationship defined by regression analyses.
Shear failure localisation is taken into account by setting,
after the onset of shear failure, the inelastic zone of the shear
sub-element equal to the shear critical length. Pinching,
in-cycle and cyclic strength degradation as well as unloading
and reloading stiffness deterioration are accounted for.
Figure 2 shows an application of the model in the case of
the quasi-static cyclic experiment of Specimen-1 (Sezen and
Moehle, 2006) failing in shear after yielding in flexure. The
comparison of the predicted response with the experimental
results shows a good agreement. The model is capable of
predicting the cyclic response of this flexure-shear critical
specimen, predicting reasonably its shear strength, its prepeak as well as post-peak hysteretic response and energy
dissipation.
The versatility of this model makes it an ideal tool to be used
in any R/C structure analysis for assessment purposes. Its
aforementioned advantages make it suitable even for the
special and challenging case of shear-dominated elements
in sub-standard old R/C structures.
References
Funding body
Baradaran-Shoraka, M. and Elwood, K.J., (2013).
Mechanical Model for Non Ductile Reinforced Concrete
Columns, Journal of Earthquake Engineering 17:7, 937–957.
City University, London
LeBorgne, M.R. and Ghannoum, W.M., (2013). Analytical
Element for Simulating Lateral-Strength Degradation in
Reinforced Concrete Columns and Other Frame Members,
Journal of Structural Engineering 140:7, 04014038.
Dimitrios K. Zimos (E: [email protected])
Mergos, P.E. and Kappos, A.J., (2012). A gradual spread
inelasticity model for R/C beam–columns, accounting for
flexure, shear and anchorage slip, Engineering Structures
44, 94–106.
Further information
Prof Andreas J. Kappos (E: [email protected])
Dr Panagiotis E. Mergos (E: Panagiotis.Mergos.1@city.
ac.uk)
Reinhorn, A., Roh, H., Sivaselvan, M., Kunnath, S.K., Valles,
R., Madan, A., Li, C., Lobo, R. & Park, Y.J., 2009. IDARC2D
Version 7.0: A Program for the Inelastic Damage Analysis of
Structues. Technical Report MCEER-09-0006.
Sezen, H. and Moehle, J., (2006). Seismic tests of concrete
columns with light transverse reinforcement, ACI structural
journal 103:6, 842–849.
Valles, R., Reinhorn, A., Kunnath, S., Li, C. & Madan, A.,
1996. IDARC2D, version 4.0: A computer program for the
inelastic damage analysis of buildings. Technical Report
NCEER-96-0010.
Wibowo, A., Wilson, J.L., Lam, N.T.K. and Gad, E.F., (2014).
Drift performance of lightly reinforced concrete columns,
Engineering Structures 59, 522–535.
Zimos, D.K., Mergos, P.E. and Kappos, A.J., (2015).
Shear Hysteresis Model for Reinforced Concrete Elements
Including the Post-Peak Range, In COMPDYN 2015,
Hersonissos, Crete.
Figure 1 Proposed finite element model: (a) geometry of a
flexure-shear critical R/C cantilever column with a diagonal
failure plane at the bottom (shear critical length, Lcr, shown
in red); (b) flexural sub-element with inelastic zone at the end;
(c) shear sub-element with bottom inelastic zone equal to
the shear critical length; (d) anchorage slip sub-element.
Figure 2. Comparison of the experimental hysteretic loops
(shear strength against total lateral displacement) with the
analytical prediction by the model in the case of Specimen-1
(Sezen & Moehle, 2006).
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18
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IS_0846-18th Young Researchers Conf Proceedings

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