Prof. Khalid Mosalam
University of California, Berkeley
NUMERICAL SIMULATION OF URM
INFILL WALLS in RC FRAMES:
CRITICAL MODELING ASPECTS
KHALID M. MOSALAM
UNIVERSITY OF CALIFORNIA,
BERKELEY
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
Motivation
URM Infill Walls in RC Buildings
 Benefits



Significant effects on functionality
Contribute to lateral force resisting capacity & damping up to a certain hazard level
Increase the overall stiffness – may have benefits for certain cases
 Detrimental Effects





Sudden brittle failure: High potential to form a soft story during shaking
Interaction with the frame: Shear failure of columns
In plane/out of plane interaction: Reduced capacity in both directions
In plane/out of plane interaction: Debris from out of plane failure, life safety concerns
Torsional effects due to asymmetric wall arrangement in plan
Quantification of detrimental effects requires proper modeling
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
3
Motivation
Soft Story:
Kocaeli EQ, Turkey, 1999 (left)
Haiti EQ, 2010 (right)
In-plane /out-of-plane
interaction:
Wenchuan EQ, China, 2008
Frame-URM interaction:
L’Aquila EQ, Italy, 2009
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
4
Critical Modeling Aspects
In-plane/Out-of-plane Interaction: General modeling
Beam-column elements (frame members)
Inelastic fiber section
Elastic section
beamWithhinges & midspan node
with OOP mass
elements
Y
Infill wall model
Z
X
Beam-column elements (frame members)
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
5
Critical Modeling Aspects
In-plane/Out-of-plane Interaction: Section discretization
Note: fiber areas and
y (local)
locations are symmetric
th
with respect to the y-axis i fiber with area Ai
i=1
Fiber 1
z (local)
zi
Mi+1-Mi
P
i=2
i
Pi-Pi+1
i+1
PNA 1
PNA 2
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
i = Npts
M
6
Critical Modeling Aspects
URM infill removal upon failure
Integration
time step i-1
IP displacement
Integration
time step i
@Integration
time step i
Displacement history
OOP displacement
Failure Curve (symmetric
about x and y axes)
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
7
Critical Modeling Aspects
URM wall removal upon failure: Algorithm
Obtain OOP displacement from
the analysis (OOP analysis)
Obtain the IP displacement
from the analysis (IP analysis)
Calculate the IP displacement from the
interaction curve corresponding to the
absolute value of OOP analysis (IP limit)
Check |IP analysis|  IP limit
No
Yes
Do not activate
removal
IP displacement
Activate removal for the infill wall (Remove
beam-column elements and the middle node)
Displacement history
OOP displacement
Failure Curve (symmetric
about x and y axes)
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
8
Critical Modeling Aspects
Shear failure of columns
$nodetop
$ele2
Shear springs with
nonlinear force
displacement relationship
$ele1
$nodemid
$nodebot
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
9
Numerical Simulations For Retrofit
Rocking spine retrofit
Courtesy of
Tipping Mar,
Berkeley
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
10
Numerical Simulations For Retrofit
Rocking spine retrofit
Courtesy of
Tipping Mar,
Berkeley
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
11
Numerical Simulations For Retrofit
Rocking spine retrofit: Dynamic analysis with critical modeling aspects
9
As-built
Retrofit
8
7
Story #
6
5
4
3
2
1
0
0
0.01
0.02
0.03
Interstory Drift Ratio
0.04
0.05
Maximum inter-story drift profile
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
12
Numerical Simulations For Retrofit
Rocking spine retrofit: Dynamic analysis with critical modeling aspects
1
IDR = 0.01 As-built
IDR = 0.01 Retrofit
IDR = 0.02 As-built
IDR = 0.02 Retrofit
IDR = 0.03 As-built
IDR = 0.03 Retrofit
Probability of exceedance
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.25
0.5
0.75
PSa (g)
1
1.25
1.5
Fragility curves
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
13
Thank you
15WCEE, Lisbon, Portugal, September 24-28, 2012
Special Session 24.1 Seismic Retrofit of Masonry Structures. Monday, 24 September 2012
14