George E. Brown, Jr. Network for Earthquake Engineering Simulation
NEESR-SG
Seismic Performance Assessment and
Retrofit of Non-Ductile RC Frames
with Infill Walls
P. Benson Shing, Jose Restrepo, and Andreas Stavridis
University of California, San Diego
Kaspar Willam, Sivaselvan Mettupalayam, and Ben Blackard
University of Colorado, Boulder
Sarah Billington and Marios Kyriakides
Stanford University
July 21-23, 2006
NEES Annual Meeting
1
Performance Issues
2000 Kocaeli, Turkey Earthquake (EERI)
• Non-uniform infill –
open bottom story
• Asymmetric stiffening
introducing torsion
July 21-23, 2006
NEES Annual Meeting
2
Beneficial Influence of Infill
Negro et al. (1996)
Bare Frame
Infilled
Frame
July 21-23, 2006
NEES Annual Meeting
3
Main Issue


Brittle shear failure of columns
Strength degradation of infill and
columns leading to soft story
mechanism
Soft Story
July 21-23, 2006
NEES Annual Meeting
4
Questions to be Answered


What is the threshold ground motion level
beyond which an infilled frame will have
undesirable performance?
How can we raise this threshold with costeffective strengthening?
July 21-23, 2006
NEES Annual Meeting
5
State of the Practice



Lack of reliable analysis tools for sound
engineering decisions
Contribution of infill walls to seismic
resistance difficult to assess
Lack of proven cost-effective strengthening
methods for infill walls
July 21-23, 2006
NEES Annual Meeting
6
Complicated Failure
Mechanisms
July 21-23, 2006
NEES Annual Meeting
7
Frame-Panel Interaction
Frames Tested by
Mehrabi et al. (1994)
Strong Infill
Weak Infill
July 21-23, 2006
NEES Annual Meeting
8
Project Deliverables



Improved analysis methods for
performance assessment
Rational assessment procedure
considering contribution of infill walls
Validated cost-effective strengthening
methods to enhance system-level
performance
July 21-23, 2006
NEES Annual Meeting
9
Research Approach
Assessment of Existing
Modeling Methods
Improved Analysis
Methods
Small-Scale Tests on
Strengthening Methods
Medium-Scale Tests on
Single-Story Frames
Component Performance
Large-Scale Tests on
Multi-Story Frames
System Performance
Retrofit Methods
July 21-23, 2006
NEES Annual Meeting
10
Performance Assessment
Rational Assessment Procedure
Does the building need
strengthening considering the
contribution of infill walls?
Done
Yes
Can it be economically and
adequately strengthened without
additional load resisting systems?
Yes
Infill and/or column
strengthening
July 21-23, 2006
No
No
Addition of new loading
resisting systems
NEES Annual Meeting
11
Retrofit Methods

Engineered Cementitious Composites
(ECC) for infill strengthening

FRP overlay or spray

Infill wall-to-beam connection

Column strengthening
July 21-23, 2006
NEES Annual Meeting
12
ECC Overlay (Stanford U.)
A
ECC
Shear
connector
A-A
A
July 21-23, 2006
NEES Annual Meeting
13
Small-Scale Tests at Stanford
In-plane Wall Tests
Prism Tests
Flexural Tests
July 21-23, 2006
NEES Annual Meeting
14
2/3-Scale Single-Story Frame Tests
(Colorado NEES Site)
July 21-23, 2006
NEES Annual Meeting
15
Tentative Test Matrix for SingleStory Specimens
Specimen
Infill
Wall
Wall
Openings
Column
Retrofit
Wall Retrofit
1
Y
N
N
N
2
Y
N
N
ECC/Connectors
3
Y
Y
N
N
4
Y
Y
N
ECC
5
Y
Y
N
FRP or Spray
FRP
6
Y
N
Y
HPFRCC, FRP
or Spray FRP
July 21-23, 2006
NEES Annual Meeting
16
Full-Scale Shake Table Tests
(UCSD NEES Site)
• Frame with solid
infill.
• Frame with solid
infill and retrofit.
• Frame with infill
openings and
retrofit.
July 21-23, 2006
NEES Annual Meeting
17
Analysis Methods



Advanced computational models for detailed
analysis (CU-Boulder)
Limit analysis methods accounting for
multiple failure scenarios
Simplified strut models for time histories
analysis
July 21-23, 2006
NEES Annual Meeting
18
Evaluation of Existing Models
Tests by Mehrabi et al. (1994)
Effect of Infill
70
Load, kips
60
Bareframe
Frame w/ Infill
50
40
30
20
10
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Displacement, in
July 21-23, 2006
NEES Annual Meeting
19
Comparison of Programs
100
FEAP
80
Stanford: DIANA
Colorado: ABAQUS
UCSD: FEAP
Lateral Load (kips)
30
60
Crack and Crushing
40
25
20
20
15
0
STANFORD
COLORADO
UCSD
Experimental
10
5
0
0
0
0.5
1
1.5
2
2.5
3
20
DIANA
40
60
80
100
120
Principal
Tensile Strain
Lateral Displacement (in)
July 21-23, 2006
NEES Annual Meeting
20
Infill Joint Modeling with FEAP
Element
Axial Compression
Shear
Failure Surface
July 21-23, 2006
NEES Annual Meeting
21
Infilled Frame Analysis (FEAP)
Single Story Single Bay Concrete Frame with Infill
60
Finite Element Model
Experiment
Force, Kips
40
20
0
-20
-40
-60
-1.5
July 21-23, 2006
-1
-0.5
0
Displacement, in
NEES Annual Meeting
0.5
1
1.5
22
Additional Modeling Work




Parametric studies to examine influence of
model parameters
Calibration of simplified analytical models
Predictive analysis and assessment with new
experimental results
Model improvement
July 21-23, 2006
NEES Annual Meeting
23
Project Team
Benson Shing
Jose Restrepo
Andreas Stavridis
Sarah Billington
Marios Kyriakides
July 21-23, 2006
Kaspar Willam
Sivaselvan Mettupalayam
Ben Blackard
Rutherford & Chekene
Joe Maffei
Bill Holmes
Bret Lizundia
NEES Annual Meeting
24
Professional Advisory Panel







Joe Maffei, R&C (Chair)
Dave Brieholz, BQE
John Kariotis, K&A
Ron Mayes, SGH
Paul Murray, PSDG
Mike Valley, MKA
Greg Kingsley, KLA
Ron Hamburger, SGH
July 21-23, 2006
NEES Annual Meeting
25
Thank You
July 21-23, 2006
NEES Annual Meeting
26