The 5th Tongji-UBC Symposium on Earthquake Engineering “Facing Earthquake
Challenges Together” May 4-8 2015, Tongji University Shanghai, China
Seismic Behavior & Modeling of Reinforced
Concrete Flat Slab-Column Connections
Omar AlHarras
[Dr. Tony Yang’s Tall Buildings Research Group]
BEng (Hons) + DIS | Loughborough University, England (2013)
MASc Student | The University of British Columbia, Canada (2013 - Present)
Structural System


Flat Slabs + Columns
Shear Walls
Typical Floor Plan
[Gravity Framing]
[LFRS]
Typical Construction Scheme
Reinforced Concrete Flat Slabs
Design Procedure
[Two-way slabs without beams in accordance with CSA A23.3-14]

Analysis under gravity load combinations :
◦ Equivalent frames method
◦ Finite element analysis

Determine required flexural reinforcement & spacing in both directions.

Check punching shear capacity in the vicinity of concentrated loads or
reactions (e.g. : columns):
◦ Provide shear reinforcement if necessary: stud rails, shear bands, lattice
reinforcement, or stirrups.

Re-check punching shear for seismic drift demands:
◦ Reduced punching shear capacity shall exceed direct punching shear stresses.
 0.005 
RE  

 i 
0.85
 1.0
i 
Inter-storey drift ratio
Seismic Behaviour of Flat Slabs
Dominant Modes of Failure in Slab-Column Connections


Punching shear [Brittle]
Yielding of longitudinal reinforcement
[Relatively ductile]
(Hwang & Moehle, 2000)
[Courtesy of Wolverhampton, UK]
Proposed Modeling Technique
Flat Slab-Column Assembly
Proposed Modeling Technique
Equilibrium When Subjected to an Unbalanced Moment
γ- factors are dependent on the column’s geometry and orientation.
Proposed Modeling Technique
Flexural & Shear Hinges
The two types of hinges simulate the two dominant modes of failure:Capacity of one could be exhausted before the other, or both at the same time!
Proposed Modeling Technique
Estimating Punching Shear Capacity
 Mfe
vf 
 v 

bo d
J


1
v  1
2 b1
1
3 b2
Vf
vr  vc 2 
f 'c
6
or
e
cd
2
vr  vc 2  vs 

Vu 
J
M unb   vc 2  vs 

b
d
cd 
o 

v 

 2 
M unb
Vp 
(c  d )
f 'c
2
[MPa]
Proposed Modeling Technique
Flexural & Shear Hinges
Proposed Modeling Technique
When is punching shear expected to happen?
(Kang & Wallace, 2007)


Based on data from a spectrum of experimental studies.
Approach adopted and drift limits are enforced by ACI 318 &
ACI 352.1R
Proposed Modeling Technique
Deriving ΔP :
0.07
0.06
0.05
θp
0.04
0.03
0.02
0.01
0
0
0.2
0.4
Vg/ϕVc
p 
 p (c  d )
2
0.6
0.8
1
Proposed Modeling Technique
Flexural & Shear Hinges
Proposed Modeling Technique
Estimating Flexural Capacity

Based on bending width of (c2+3h)
M y ,unb 
My
f
u  l p .(u   y )
M n,unb 
Mu
f
lp  d
Proposed Modeling Technique
Flexural & Shear Hinges
PT Concrete Slabs
Backbone from 3D FEM

Equivalent static forces for prestressing not a good assumption.

Two-tendon technique with thermal properties.
[Models produced by Omar AlHarras & Omar Alcazar]
Proposed Modeling Technique
Hysteretic Models in OpenSees
Standard Hysteretic Material
Pinching4 Material
Proposed Modeling Technique
Developing a New Hysteretic Model

Better capturing of the cyclic behaviour.

Less theoretical parameters enabling minimal variations:

e.g. pinchX, pinchY, damage1, damage2, beta – OpenSees Hysteretic Material.
Proposed Modeling Technique
Elastic Lateral Stiffness
[Effective Beam Approach]
[Illustration by Choi et al. (2012)]

Verified by several experimental
tests including large-scale tests
and shake-table tests.

α –factor to account for
effective elastic width.

β –factor to account for
cracking.

Recommended values:
◦ Pan & Moehle (1988)
◦ Hwang & Moehle (1993)
◦ Grossman (1997)
◦ Luo & Durrani (1995,1996)
◦ Kang & Wallace (2009)
[Illustration by Wallace (2010)]
Proposed Modeling Technique
Verification

Predicting the cyclic behaviour of slab-column subassemblies that have been
experimentally tested.
(Kang et al., 2006)
Proposed Modeling Technique
Examples

Three specimens tested by Park et al. (2012):
Proposed Modeling Technique
Verification
[Specimen 1]
Proposed Modeling Technique
Verification
[Specimen 2]
Proposed Modeling Technique
Verification
[Specimen 3]
Concluding Remarks

Behaviour of high-rise buildings & estimating demands on LFRS.

A more accurate force distribution between the gravity framing elements.

Detection of local failures in flat slabs.
◦ No need for manually checking each connection after time-history analysis.
◦ Hinges account for limit-states
Thank you!
Special thanks to:
Dr.Tony Yang
Lisa Tobber
Yuanjie Li & Jeremy Atkinson
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