curtainwall

Transcription

curtainwall

WILSON Curtain Wall Consultant (HK) Limited
Websites: www.curtainwall.com.hk & www.curtainwall.com.cn
An Introduction
to
The Design and Inspection of Curtain Walls
By Dr. Wilson ZHOU
Definition of a Curtain Wall
• A building façade hung on the structure of a building
• A building façade to protect the building users against; wind (air),
water (rain, moisture), dirt (dust), heat/ coldness (sun, hot/cold air),
noise, & light (sunshine).
As a result, the water (rain water or moisture condensation
water) at one floor may ravel down to the floors below
Curtain Wall Systems
• Stick system (standard system)
elements for the curtain wall are installed piece-by piece on site
• Semi-unitized system
main frames installed on site (usually mullions and transoms)
glass glazed in factory and fixed to main frame on site
• Unitized curtain wall system
i) Glass glazed to aluminum
ii) Aluminum fabricated into units
iii) Units installed to brackets and embeds on site
• Stick system (standard system)
elements for the curtain wall are installed piece-by piece on site
• Semi-unitized system
main frames installed on site (usually mullions and transoms)
glass glazed in factory and fixed to main frame on site
• Unitized curtain wall system
i) Glass glazed to aluminum
ii) Aluminum and Glass fabricated into units
iii) Units installed to brackets and embeds on site
A curtain wall unit – of a unitized curtain wall
• Usually of one bay wide, one floor high.
• To form units
a) Mullions are split.
b) Transoms for the top / bottom of the unit are split (stack joint)
The fire resistance requirements for
curtain walls
• 2-hour fire resistance between floors
• Use only non-combustible materials (Building
(construction) regulations – clause 39)
•
Non-combustible: - Pass the test to BS 476 part 4
• No requirement for fire resistance for curtain walls if
neighbor building is more than 900mm away.
» 2-hour fire
insulation to
protect the
brackets
Specials for stack joints
• Lower part of the stack joint is the top of a unit
• The stack joint is a gutter where water may store. Therefore
a)
Need weep holes [2 No. holes to balance (equalizing) the
air pressure]
b) Need a “Gutter” or a stiffener across the top of two
neighboring units.
c) The bottom of the gutter should be better sloped outward
to drain water (most design allowed it to be horizontal)
d) The level of the weep hole be the same as the gutter
bottom (A contractor designed a huge weep hole – airborn noise, traffic noise, and excessive air leakage)
Unitized Curtain Wall:
Extra effort for using unitized curtain wall system
• More detailed design to ensure the minimum site
works.
• Prevent water leakage through the gap between
four neighboring units which cannot be avoided.
(one contractor used sealant to seal the gap
between the split mullion on site)
Pressure equalization (weep holes)
•
•
•
Water leakage is caused by all of the following:
– water
– leaking cracks, joints or openings that would also leak air
– positive pressure (force that will drive the water inward)
Pressure equalization, because:
– It is hard to keep air-tight forever
– Water (from rain) is unavoidable
– It is easier to equal the pressure to cancel the driving force
To be noted for weep holes
– Pressure-equalized space should be dry
– Weep holes should face downward
Gutter
A hole between gap units
The gap closed by a “Gutter”
leaving a hole underneath
The gap is sealed with sealant
Top of the stack joint (when
Gutter is not installed
The stack joint (after the “Gutter”
is installed
A sponge at
the cross-joint
Stack joint
Side of a male mullion section
Bracket
Stack joint
Sealed at the cross joint
serrated
The hole is sealed
A channel
The hole between 4
neighboring units is sealed
A typical bracket fixing system for a unitized curtain wall
outside
The gutter crossed two units
inside
(top at the units)
Photo 2 A typical stack joint
The hole at the cross-joint formed by four (4)
neighboring units
• This joint is often the water leakage source for unitized system
• Proper sealing requires the use of sealant and gaskets on site
(the only sealant applied on site for unitized system)
• Proper use of pressure-equalization (the first sealing line
between split mullions to be in the front of the first “sealing line”
in the stack joint
Unit #1
#2
#3
#4
Huge weep hole
Photo 3 Stack joint at a corner
Condensation in curtain wall
• Condensation on external side (inside air-conditioned)
• For single glazing
a)
b)
Moisture condensed on external face of the glass
Usually no complaint as water is the same as rain water on glass
• For spandrel area
– mostly on either the exterior face of the thermal insulation or the front of
the spandrel glass (ventilation in mullions may not be necessary)
• For double glazing
a)
No condensation on the glass faces in the air space if the air space is
desiccated and well-sealed
b)
Condensation on the external face of the interior glass panel if
moisture get into the air space and the desiccant is saturated
Two Methods to avoid condensation in the space you do not
wish to have
• Total-seal
a)
Seal the space thoroughly like the air space in double
glazing units
• Ventilation
a)
With the space ventilated so that the moisture in the
space is reduced, then the dew point will be decreased,
and the surface temperature is increased
Defect 11 Coping panel deformed (SAM_2171)
Defect 12 Rusted steel washer and nut (SAM_2185)
Defect 13 The steel C-channel was seriously corroded (SAM_2183)
Coping panel deformed (SAM_2171)
Rusted steel washer and nut (SAM_2185)
The steel C-channel was seriously corroded (SAM_2183)
Defect 7 Moulds grown in a Norton tape (SAM_1272)
Defect 8 Glass edge chipped (SAM_1280)
Defect 9 Dirty stuff on glass surface (SAM_1257)
Defect 1 Sealant detached from Aluminum
Defect 2 Sealant detached from Glass (SAM_1185)
Defect 3 Sealant cracked (SAM_1188)
How to prevent bi-metal effect
• Two metals in direct contact, and/or connected by a
medium (usually water) (worse if it is salted water)
There is bi-metal effect (electricity generated, the electrical current
will increase the corrosion to one of the two metals)
• To prevent:
a)
b)
Isolate the metals (if in direct contact) with a non-metal material
(gasket, sealant, bitumen paint)
Seal one of the two metals to avoid water to get into the space
between the metals (if both metals are soaked in water but not
in direct-contact.
Design for the brackets
• Loads from mullion on the brackets should be as in align with
the support to the bracket as possible, to minimized the moment
in the bracket
• Easy for installation on site
• Minimize the localized stress in the mullion.
• Allow the tolerance in concrete (±25mm along 3-directions)
Typical fixing for the curtain wall
» 2-hour fire
insulation to
protect the
brackets
Stack joint
Sealed at the cross joint
serrated
The hole is sealed
A channel
The hole between 4
neighboring units is sealed
A typical bracket fixing system for a unitized curtain wall
Design Using Glass
Glass is an amorphous solid
•
•
•
•
•
Transparent
Hard (Solid) at ordinary temperature
Soft at elevated temperature (easy for shaping)
Chemically stable
Breaks without warning
Production of annealed glass
•
Float glass production on a line
Mechanical and physical properties of glass
•
•
•
•
•
•
•
Specific weight: 25kN / m3
Thermal expansion coefficient: 8.5 x 10-6 m/m oC
Elastic modulus: 72000MPa (N/mm2)
Softening point: 720 to 730 oC
Melting point: 1500 oC
Ultimate tensile/bending stress (FOS = 2.5 for allowable):
– σtu = 50MPa (annealed);
– σtu = 90 to 140MPa (Heat Strengthened);
– σtu =120 to 260MPa (tempered).
Ultimate compressive stress: σcu = 820 to 1000MPa
Allowable Stresses for glass
Load condition
Glass type
Short term /
central area
Short term /
Edge
Long term /
central area
Long term /
edge area
Tempered
75MPa
50MPa
50MPa
35MPa
Heatstrengthene
d
40MPa
27MPa
24MPa
16MPa
Annealed
20MPa
18MPa
12MPa
9MPa
Allowable Deflections for glass
Standard
Deflection limit
Notes
BS 6262
L/125 for single glass
L/175 for double glazing
Allowable for edge supports
to the glass
AS 12881994
L/60, L is the short span
2-side, 3-side or 4-side
supported
ASD General 25mm under 50% design
Specification load
s
2-side, 3-side or 4-side
supported
BD PNAP235 50mm under worst
combination of the loads
(imposed load and wind
load)
Free-standing glass as barrier
•
Tempering of glass
•
•
•
•
•
Glass heat to 650 C
Cooled down quickly
Surface cooled first (contraction)
Internal cooled further (further contraction on the surface)
Surface compression may be visualized by polarized light
For tempered glass
Compression on surface
Tension in middle
•
Causes to glass breakage
•
Nickel sulfide inclusion
– Induce spontaneous breakage
– Happens to only tempered glass (some times heat strengthened glass treated at
higher temperature)
Supported at wrong place
– Corners, edges, using hard bearing material, holes drilled near edge or corner
Improper storage
– Supporting material is hard with sharp edges
– Layers glass not supported at the same locations, or supports are not aligned
Thermal stress
– Temperature difference (a part of the glass is under sunshine and the other in
shadow).
– Not enough clearance. Thermal expansion is restricted
Glass with defects (chipped edge)
Calculation mistakes
Vibration during transportation
•
•
•
•
•
•
• Spontaneous breakage to tempered glass
• Nickel sulfide inclusion
– Induce spontaneous breakage
– Happens to only tempered glass (some times heat
strengthened glass treated at higher temperature)
– Happens in the tension part of the tempered glass
– “Butterfly pattern”
Heat Soak Test
• For only tempered glass;
• To APP-37 & BS EN14179-1
Safety Glass to human impacts
Definition:
• Any glass or glazing materials satisfies the
safety requirements when tested to BS 6202
to the relevant classes (A, B and C)
What kind of glass can be Safety glass (class A)?
• Tempered glass;
• Laminated glass (annealed, heat-strengthened or
tempered)
• Wired (annealed) glass;
• Annealed glass of 19mm (or more) thick
• Heat-strengthened glass of 15mm (or more) thick
Where should safety glass be used?
• Anywhere at or below 1.1m above floor level (and
barrier in front of the glass does not exist)
Thermal stress causes glass breakage
• Happen only to Annealed glass
• Increase the thickness does not help
• Defects with glass edge and closed space and dark edge
covers (or spandrel areas)
• Temperature difference.
Photo 15
Photo 16
Photo 17
Supported at a wrong place
• Glass is usually weaker at its edges.
• Glass in contact with a hard material (say
steel, or broken glass piece) – stress
concentration.
• Extra force on the glass.
Load from the scaffolding
Hard stuff beneath
Photo 1 - 22mm thick annealed glass
Photo 2 - 22mm thick annealed glass
Source of
breakage
Photo 11 – 25mm thick annealed glass
Source of breakage
Photo 12 – 25mm thick annealed glass
Butterfly pattern of breakage
Photo 5
Photo 18
Source of breakage
(19mm thick tempered glass improper fixing)
Photo 3
Photo 14
De-lamination of laminated glass
•
•
•
•
Spring back effect of tempered glass
Improper support to the glass (on one layer only)
Direct contact with the silicone sealant
Exposed PVB to the weather
What we will do:
• Generate elevations for the curtain wall & canopies. Mark a unique number
for every panel.
• Prepare an inspection procedure, testing proposals.
• Generate forms for inspections.
• Carry out inspection.
• Retrieve design drawings from the BD where available.
• Conduct coating thickness test, Conduct sealant tests (peeling on site, tests
in our lab.)
• Test reports
• Inspection report (with remedial proposal)
Presented by:
Dr. Wilson ZHOU
Wilson Curtain Wall Consultant (HK) Limited
What to be checked
• Curtain walls
– Sealant, (crack, detachment, penetration, change of
colour etc)
– Glass (crack, chipped edge, displacement, coating
damage etc)
– Aluminum (visual damage, corrosion, scratching on
coating, coating thickness-optional)
– Screws, rivets, bolts etc (corrosion to aluminum,
loosened screws, missing screws)
– Gasket (hardening, missing, detachment)
– Sashes (malfunctioning, lock fails, hinges stuck,
corroded, fixing screws missing, loose)
– Sign of leakage, complaints from the users.
Defect 1
Sealant at the joint between transom and the mullion is
detached -- see Photos 1a, 29
Defect 2
There is a hole in the sealant at the joint between the
transom and the mullion
Defect 3
Gasket is aged and detached from glass(at the joint between
glass and aluminium)
Defect
4
Defect 5
Gasket detached from aluminium (at the joint between glass
and aluminium)
Defect
6
Defect
7
Defect 8
Sealant at the joint between glass and aluminium or at the butt
joint between glass panels cracked -- see photos 4,6 and 8
Defect 9
Sealant at the expansion joint detached, cracked/missing -see photos 1c, 15, 17, 19, 21 & 37
A hole in the Sealant (at the joint between glass and/or
aluminium) -- see photos 1b, 1c & 5
All the screws fixing the rail for Gondola to the Mullion are
found not sealed with sealant
Sealant is missing -- see photos 1d, 1e & 10
Gasket cracked (due to aging) -- see photo 1f
Defect
10
at the joint between aluminium coping panels
Defect 11 Sealant
detached -- see photos 1g & 32
Defect 12 A hole in the gaskets -- see photos 1h & 2
Defect 13 Screws in a mullion is missing -- see photos 1i, 27 & 33
Defect 14 A hole in the sealant at the expansion joint -- see photo 3
Defect 15 Gasket is missing -- see photos 7 & 28
Defect 16 Top of the mullion is not well sealed -- see photo 25
A gap between the gasket for mullion and the horizontal
Defect
sealant joint between glass -- see photo 30
17
Defect 18 A gap between a louver and the aluminium frame -- see
photo 35
Defect 19 Sealant was cut off below a louver systems -- see photo 36
An extending segment to a mullion (not well sealed) -- see
Defect 20 photo 38
Defect 11 Coping panel deformed (SAM_2171)
Defect 12 Rusted steel washer and nut (SAM_2185)
Defect 13 The steel C-channel was seriously corroded (SAM_2183)
Defect 1 Sealant detached from Aluminum (CIMG0990)
Defect 2 Sealant detached from Glass (CIMG0999)
Defect 2a Caulking sealant detached from concrete (CIMG1027)
Windows pushed outward
• Appears like curtain wall;
• Water behind tiles may travel to inside.
Water at joint H (Fig. 6)
Water stain at the meeting joint
between the top transoms
Photo 1
Fig. 8
Fig. 8a
Hole in sealant
Sealant detached form tiles
Cement in missing at the cement joint
Sealant cracked
Fig. 8a
Fig. 9
between the top transoms
Between the top transoms at a corner
Water seeped to inside from the joint
Between the ceiling and the top transom
Water seeped in at joint H (Fig. 6)
Option 1 – facial sealant replaced
Works: cut off the existing sealant and replace all with new silicone
sealant.
Advantage:
lowest cost.
Disadvantage:
a) one barrier system;
b) sealant ages,
c) workman ship is not perfect.
d) the current sealant does not seem to be so aged.
e) the existing water leakage problem will not be totally solved
f) the rusting to the steel will further develop.
Fig.1 Peeling Test
Coating Thickness Test
Defect 10b Reflective coating on the glass is missing (CIMG0941)
There is no reflective coating in
this area
Defect 12 Glass surface scratched (CIMG1058)
Defect 15 Aluminum panel deformed (P30656)
The inspection on a sash
–
–
–
–
Hinges
Screws (sealant in screw holes)
Lock points
Keepers
• Locking screws
– Hooks
– Stops
Fig. 6
Fig. 6a
Fig. 6b

curtainwall

Transcription

Similar documents

party for a living

Innovative glazing system shines light on hospital research

curtainwall - Wausau Window and Wall Systems

O`hare South Air Traffic Control Tower

VISIONWALL Project Profile

Design and implementation of Curtain Wall System

Insulated glass with integral cord-free louvers