Collapse Simulation of Non-Ductile RC Column under Lateral Load

Comments

Transcription

Collapse Simulation of Non-Ductile RC Column under Lateral Load
12/15/2016
Collapse Simulation of Non-Ductile RC
Column under Lateral Load
Sashi K. Kunnath
University of California at Davis
Andrea Lucchini, Paolo Franchin
Sapienza University, Rome, Italy
Background and Objectives
• Nonlinear analysis of non-ductile reinforced
concrete components to enable development
of collapse fragilities of older RC buildings
• Evaluate ability of existing FE software to
simulate complex failure modes
– Brittle failure of poorly confined concrete
– Buckling of longitudinal reinforcing bars due to:
• lack of inadequate transverse reinforcement, or
• opening of stirrups after spalling of cover concrete
– Bond failure
1
12/15/2016
Background and Objectives
• SOFTWARE: LS-DYNA
• Validation of simulation model
– Available experiments in literature
– Biaxial versus uniaxial tests
• Avoid “tuning” of parameters to match a
single experiment, rather focus on accurate
modeling based on available material
properties and specimen configuration
• Use validated model in parametric studies to
enable development of simpler models
SELECTED SPECIMEN FOR MODEL VALIDATION
Sezen and Moehle (2000)
2
12/15/2016
SELECTED SPECIMEN FOR MODEL VALIDATION
Specimen Details
3
12/15/2016
LS-DYNA: Concrete model
• 8-node solid element (constant stress, viscous hour-glass
control, based on Flanagan-Belytschko approach)
• yield surface formulated in terms of three stress invariants
(I1, J2, and J3, respectively)
• a hardening cap that expands and contracts
• a damage-based formulation for describing the softening
behavior
• regularization technique adopted for reducing mesh-size
dependence of the softening response
Constitutive modeling - concrete
•
Softening behavior
– Compression: does not converge as the mesh is refined
– Tension: size independent
4
12/15/2016
Constitutive modeling – reinforcing steel
• MAT_174 (works with Hughes-Liu beam elements with crosssection integration)
• Monotonic: parabolic after plateau up to ultimate stress
• Cyclic: Ramberg-Osgood model, includes Bauschinger effect
CONCRETE-STEEL interface modeling
• Concrete & reinforcement
•
Connections between nodes
– dir 1
• Core & Bar: springs
• Core & Cover: constrain
– dir 2
3
• Core & Cover: constrain
– dir 3
• Core & Cover & Bar: constrain
2
•
dir 1
Cover
Core
Contacts between parts
– dir 2
• Bar & Core
• Bar & Cover
5
12/15/2016
CONCRETE-STEEL interface modeling
• At intersection of longitudinal & transverse
reinforcement
•
Connection between nodes
– dir 1
• Core & Bar: springs
• Core & Cover: constrain
– dir 2
3
• Core & Cover: constrain
– dir 3
• Core & Cover: constrain
• Core & Bar: springs
2
•
dir 1
– dir 2
• Bar & Core
• Bar & Cover
Core
Cover
Contact between parts
CONCRETE-STEEL interface modeling
• Intersection between Longitudinal & transverse
reinforcement at corners
Core
•
Cover
Connections between nodes
– dir 1
• Core & Bar: springs
• Core & Cover: constrain
– dir 2
• Core & Cover: constrain
– dir 3
• Core & Cover: constrain
•
3
2
Contacts between parts
– dir 2 & 3
• Bar & Core
• Bar & Cover
dir 1
6
12/15/2016
CONCRETE-STEEL interface modeling
• Stirrup opening
•
Connection between nodes
– dir 1
• Core & Bar (node 1): springs
• Core & Cover: constrain
– dir 2
• Cover & Bar (node 2): constrain
– dir 3
• Cover & Bar (node 3): constrain
•
Contact between parts
– dir 2 & 3
• Bar & Core
• Bar & Cover
Bond-slip relationship
• Two coincident zero-length springs acting in the two opposite
directions of slip are employed
• Each spring element is oriented (using the command
*DEFINE_SD_ORIENTATION) in the axial direction of one of the two
beam elements of the rebar that is connected to the node.
• The constitutive behavior of the spring is defined with the material
model *MAT_SPRING_INELASTIC, using a (monotonic) bond-slip law
calibrated based on Eurocode model
7
12/15/2016
Complete
FE model
Overall simulation of lateral response
8
12/15/2016
Experiment vs. simulation
Experiment versus simulation
9
12/15/2016
Experiment vs. simulation
400
lateral force [kN]
200
yielding bar Pos.18
opening T1 stirrup Pos.7
yielding T2 stirrup Pos.9
0
-200
Test
Simulation
-400
-50
0
50
100
lateral disp [mm]
150
200
Experiment vs. simulation
10
12/15/2016
Conclusions & Future work
•
•
•
•
•
A strategy for 3D finite element modeling of older reinforced
concrete columns with non-ductile details is presented.
Interaction between concrete, longitudinal and transverse
reinforcement is explicitly modeled
Local phenomena such as confinement effects on concrete due
to transverse reinforcement, buckling of longitudinal bars,
opening of stirrups, and bond effects, can be simulated
It was shown that the finite element model adequately
simulates the global response, as well as the damage pattern
and failure mechanism observed in the test. Success in
modeling other failure modes depends largely on gaining proper
insight into the failure process itself.
Future work will focus on other failure modes, biaxial loading
and advanced computing (parallel & distributed computing)
Thank you!
11

Similar documents