NEES-Soft: Seismic Risk Reduction
for Soft-Story Woodframe
Buildings
John W. van de Lindt, University of Alabama
Michael D. Symans, Rensselaer Polytechnic Institute
Xiaoyun Shao, Western Michigan University
Weichiang Pang, Clemson University
Mikhail Gershfeld, Cal Poly Pomona
2012 Quake Summit and NSF CMMI Awardees Conference
Boston, MA; July 2012
The NEES-Soft Project Team
University of Alabama:
Prof John W. van de Lindt; Pouria
Bahmani, Ph.D. Student
Clemson University:
Prof WeiChiang Pang; Ershad Ziaei,
Ph.D. Student
Western Michigan University:
Prof Xiaoyun Shao; Chelsea Griffith,
M.S. Student
Rensselaer Polytechnic Institute: Prof Michael D. Symans, Prof David V.
Rosowsky; Jingjing Tian, Ph.D.
Student
Cal Poly – Pomona:
Prof Mikhail Gershfeld; Robert
McDougal. M.S. Student; Nathan
Summerville, B.S. Student
SUNY at Buffalo:
Prof Andre Filiatrault
Structural Solutions Inc.:
Gary Mochizuki
U.S. Forest Products Lab.:
Douglas Rammer
Tipping Mar:
David Mar
South Dakota State University: Prof Shiling Pei
Cal Poly – SLO:
Charles Chadwell
The NEES-Soft Practitioner Advisory Committee (PAC)
Laurence Kornfield
Kelly Cobeen
Steve Pryor
Tom Van Dorpe
Doug Thompson
Doug Taylor
Janielle Maffeti
Rose Grant
City of San Francisco - CAPSS
WJE
Simpson Strong Tie
VanDorpe Chou Associates, Inc.
STB Structural Engineers
Taylor Devices
California Earthquake Authority
State Farm Research
Motivation for NEES-Soft
Community Action Plan for Seismic
Safety (CAPSS)
43 to 80 percent of the multi-story woodframe buildings will be deemed unsafe
after a magnitude 7.2 earthquake
25% of these buildings would be expected
to collapse
Thousands of these buildings exist, many
of them multi-family rentals
ATC 71.1 Project
Develop seismic retrofit requirements for
soft-story wood-frame buildings in
seismically active regions of the United
States
Focusing primarily on Northern and
Southern California and the Pacific
Northwest
NEES-Soft Project Summary
NEES-Soft: Seismic Risk Reduction for SoftStory Woodframe Buildings
Five-university-industry National Science
Foundation-funded collaboration
Develop a better understanding the
behavior of soft-story woodframe buildings
under seismic loads through numerical
analyses and experimental testing
Provide experimental validation of ATC 71.1
concepts and PBSR approaches
Characterize the improvement in seismic
performance for an array of force-based
and performance-based retrofit techniques
Develop improved models of woodframe
collapse mechanisms to better estimate the
margin against collapse.
NEES-Soft Retrofit Testing
NEES@UB Rxn Wall
7 months beginning April 2013
Full-scale slow pseudodynamic test
Six actuators (6 DOF)
One 2-bedroom apartment per
floor
Level 1 – two-car garage and
storage space
Floor Plans
First Floor
H: Horizontal Wood Sheathing
G: Gypsum Wallboard
Ground Floor Plan
3'-0"
8'-0"
3'-0"
NEES-Soft (11.19.2011)
10'-8"
3'-4"
H,G
H,G
4"
1
Rev. 4-2
H,G
G,G
H,G
EQx
G,G
H,G
H,G
3
8'-0"
EQx
8'-0"
24'-0"
2
H,G
H,G
H,G
H,G
H,G
4
7'-0" 1'-6"
1'-6"
1'-6" 7'-0"
10'-0"
10'-0"
Y
X
A
B
C
Floor Plans
Typical Floor
H: Horizontal Wood Sheathing
G: Gypsum Wallboard
Typical Floor Plan
3'-0"
Rev. 4-2
14'-0"
3'-0"
3'-112"
H,G
Bdrm 2
9'-2"
G,G
3'-0"
3'-0"
2
9'-4"
G,G
6'-0"
5'-6"
8'-0"
EQx
G,G
4"
7'-0"
H,G
Kitchen
H,G
G,G
G,G
3'-0"
6'-4"
5'-6"
8'-0"
Bath
Living Room
H,G
H,G
G,G
7'-0" 1'-0"
G,G
3
2'-0"
4'-8"
8'-0"
24'-0"
G,G
Bdrm 1
G,G
4'-0"
4
1'-6"
EQx
3'-0" 1'-10"
H,G
H,G
1
NEES-Soft (11.19.2011)
H,G
H,G
1'-6"
7'-0"
3'-0"
10'-0"
H,G
7'-0"
1'-6"
10'-0"
20'-0"
Y
X
A
B
C
Seismic Retrofits for the NEES-Soft Building
Phase 1– steel base frame
Retrofit Type
Target Verification
Steel Special Moment Frame (SSMF) ATC 71.1
or Inverted Moment Frame (IMF)
Wood Shear Walls
SSMF/IMF and Wood Shear Walls
Cross Laminated Timber (CLT)
Performance-Based Seismic Retrofit
Dampers
Phase 2 – first story constructed
Retrofit Type
Steel Special Moment Frame (SSMF)
or Inverted Moment Frame (IMF)
SSMF/IMF and Wood Shear Walls
Knee-brace
Target Verification
ATC 71.1
Performance-Based Seismic Retrofit
Other (only a limited numerical
prediction being performed)
NEES-Soft PSD and Real-time tests @UA
Test Objectives:
– to verify the developed psudodynamic (PSD) testing
and hybrid testing methods and their application to
wood frame structures for eventual expansion to full
buildings at NEES@UB (completed)
The first time hybrid testing of a wood frame structure.
– to characterize the highly nonlinear seismic behavior
of woodframe construction (underway)
– to evaluate in real earthquake rate the enhanced
seismic behavior of woodframe installed with viscous
dampers (underway)
NEES-Soft PSD hybrid and Real-time tests @UA
– Cyclic Tests: full CUREE protocol
– Open Loop Hybrid Tests
• to determine slow testing rate: 20 times slower was selected
• to verify the developed continuous loading method
– Closed Loop Hybrid Tests
• Specimen 1: Loma Prieta Capitola (Completed)
– Test 1: 72 year
– Test 2: 2500 year
– Test 3: mass x 3 and 2500 year
• Specimen 2: Northridge-Beverly Hills (to be complete by
Shao @ WMU remote control UA hybrid testing controller)
Test Setup - Slow Pseudo Dynamic and Real-time
Cyclic test (CUREE Protocol) - Photos
Slow Pseudo Dynamic test
UA Hybrid Testing Results
First Floor Wall HysteresisSlow Hybrid Test
10
Test 3, 2500yr x3 mass
Test 2, 2500yr
Test 1, 72yr
8
6
Force(kip)
4
2
0
-2
-4
-6
-8
-10
-6
-5
-4
-3
-2
-1
Displacement(in)
0
1
2
3
Slow PSD hybrid test @UB NEES
Objective : to develop an increased understanding of
–
–
–
–
the effects of first floor (soft-story) retrofits on the
upper stories
Specimen: 3-dimensional (near) full scale model with
and without retrofit
Numerical substructure: existing first story with
various retrofits
Physical substructure: upper stories, full
representation with construction details
Use six actuators to consider rotation
Conceptual plot of PSD hybrid test @ UB
Performance-Based Retrofit using
Energy Dissipation System
•Performance-Based Retrofit
• Increase damping in first story (and possibly stiffness)
• May increase force transmitted to upper stories (imposes
limit on magnitude of damping in first story)
• Expected performance level for design earthquake:
Fully Operational (FO) to Immediate Occupancy (IO)
• Energy Dissipation System
• Linear fluid viscous dampers
• Peak force out-of-phase with peak displacement
• Previously tested in wood structures
• Location of Dampers
• First story only
• Along perimeter walls to provide contribution to torsional resistance
• Along both stiff and flexible wall lines
• Displacement amplification system employed (scissor-jack)
Parametric Study of One-Story Inelastic
Structure with Energy Dissipation System
- Two-way asymmetric w/rigid diaphragm
- Biaxial ground motion
- CR and CM are fixed
- CSD varied
EQ-Y
EQ-X
EQ Motions
- Canoga Park Station
(moderate far-field)
- Far-field EQ records from ATC-63
- Stronger component applied in
X-direction
- 4 walls (one on each side)
- Wall materials:
Exterior: Horiz. wood sheathing
Interior: Gypsum wall board
- 2 dampers along X- direction,
(one each on north and south sides)
- 2 dampers along Y- direction,
(one each on west and east sides)
SAWS Shear Wall Model:
Hysteretic response
of conventional
structure (no dampers)
subjected to bi-axial
Canoga Park motion.
CM = Center of Mass
CR = Center of Rigidity (located at ex / a  0.2 and ey / d  0.2 ; similar
to location for NEES-Soft test specimen)
CSD = Center of Supplemental Damping (location varies in X- and Y-direction).
20
Effect of Damper Location (CSD)
on Max. Inter-Story Drift
- One-story inelastic structure (Tnx = Tny = 0.5 sec)
- Biaxial ground motion (CP106+CP196)
- Fixed total damping magnitude: Damping
coefficient along each direction is 5 kips-sec/in
Conventional
0.77
(0.2,-0.2)
Moving CSD from CR towards, and beyond, CM:
- The maximum structural responses generally decreases (reducing translation AND torsion).
- Damper location (plan-wise distribution) has strong influence on structure response.
- For a range of ground motions, the optimized CSD location is approximately at the
coordinate (0.2, -0.2), which is symmetric with CR about CM.
21
DDD from previous work
Pang et al, 2010
CM & CR
CM & CR
Z
Y
X
DDD with Torsion
Procedure:
Linear system (i.e. stiffness of lateral load resisting system element does not change during the analysis)
Decoupling torsional modes from translational modes
Modal analysis for decoupled modes
Combining modes to obtain the total displacement
Using spectral displacement to find the design stiffness of each lateral load resisting element
Nonlinear system
Using equivalent secant stiffness and damping ratio using method proposed by Filiatrault and Folz
Regular building with Large in-plane Eccentricities
Stiffness ratio over the height:
K3 = 1.75 K;
K1 / K2 = 1.11
K2 = 2.25 K;
K2 / K3 = 1.29
K1 = 2.5 K;
Eccentricity ratio:
ex = 4.82 ft ; Lx = 30 ft  ex / Lx = 16.1%
ey = 4.29 ft; Ly = 20 ft  ey / Ly = 21.4%
er = 6.45 ft
CM
ey
CR
Unit weight for each floor: 30 psf
Earthquakes at MCE level (San Francisco)
EQ forces applied in X-direction
Target Drift = 2% for Prob. of NonExceedance of 50%
Tn = 0.577 sec.  Sa = 1.44g
Probability of Exceedance
ex
1st Story
Target = 2.0%
Error (%) = 2.5%
2.05%
Inter-story Drift Ratio (%)
Soft-story Building with Irregularity over the height and in-plane
Stiffness ratio over the height:
K3 = 1.8 K;
K1 / K2 = 0.77
K2 = 2.6 K;
K2 / K3 = 1.44
K1 = 2.0 K;
Eccentricity ratio for all stories:
ex = 3.75 ft ; Lx = 30 ft  ex / Lx = 12.5%
ey = 3.33 ft ; Ly = 20 ft  ey / Ly = 16.7%
er = 5.02 ft
CM
CR
ey
ex
Earthquakes at MCE level (San Francisco)
EQ forces applied in X-direction
Target Drift = 2% for Prob. of NonExceedance of 50%
Tn = 0.489 sec.  Sa = 1.5g
Probability of Exceedance
Unit weight for each floor: 30 psf
1st Story
1.93%
Error (%) = 3.5%
Target = 2.0%
Inter-story Drift Ratio (%)
Summary
Eccentricity
Fundamental
ex/Lx ey/Ly Period (sec) Sa @ MCE
(%) (%)
Regular Building with Large in-plane Eccentricity 16.1 21.4
0.577
1.44g
Building
Soft-story Building with in-plane Eccentricity
12.5 16.7
0.489
1.5g
Drift (%)
Error (%)
Target Performance
CDF Curve
2% / 50% NE
2.05
2.5
2% / 50% NE
1.93
3.50
3D Model for Collapse Analysis
Frame Element
Task
1. Hybrid Testing of Soft-Story Woodframe Building
2. 3-D Collapse Model Development
3. PBR Method for Soft Story
4. Evaluation of ATC-71.1 Retrofit Guidelines
5. Seismic Protection Systems for Higher Performance
6. Performance-Based Retrofit Guidelines
7. Project Advisory Committee
8. System Level Verification of Retrofit Procedures
9. Education, Outreach, and Technology Transfer
10. NEES Awardee Meetings (every 18 months)
• 3D Model
• Based on large deformation
theory
• Co-rotation
• Geometric Nonlinearity
• P-Delta Effect
Year 1
Year 2
Year 3
1.1
1.2
F2F Element
2.1
3.1
3.2
3.3
4.1
5.1
5.2
4.2
5.3
Soft Story
6.1
(a)
7.1
8.1,2,3
9.1
10
6 - DOF Node
12 - DOF Frame Element
(u pper floor diaphragm)
Slave
Node
6 - DOF Link Element
12 - DOF Frame Element
(Shear Wall)
(lower floor diaphragm)
Slave Node
(b)
Incremental Dynamic Analysis (IDA)
FEMA P-695 Far Field Ground Motions
ID Num
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
ATC-63 / FEMA P-695 Far Field Ground motions
M
Year
EQ Name
Station Name
6.7
1994
Northridge
Beverly Hills
6.7
1994
Northridge
Canyon Country-WLC
7.1
1999
Duzce,
Turkey Bolu
7.1
1999
Hector
Mine Hector
6.5
1979
Imperial
Valley Delta
6.5
1979
Imperial
Valley EI
6.9
1995
Kobe,
Japan Nishi-Akashi
6.9
1995
Kobe,
Japan Shin-Osaka
7.5
1999
Kocaeli,
Turkey Duzce
7.5
1999
Kocaeli,
Turkey Arcelik
7.3
1992
Landers
Yermo Fire
7.3
1992
Landers
Coolwater SCE
6.9
1989
Loma
Prieta Capitola
6.9
1989
Loma
Prieta Gilroy
7.4
1990
Manjil,
Iran Abbar
6.5
1987
Superstition
Hills El
6.5
1987
Superstition
Hills Poe
7
1992
Cape
Mendocino Rio
7.6
1999
Chi-Chi
Taiwan, CHY101
7.6
1999
Chi-Chi
Taiwan, TCU045
6.6
1971
San Fernando
LA
6.5
1976
Friuli
Italy, Tolmezzo
Y
Bi-axial ground motions
X
Torsion
Torsion
EQ ID 21,
1971 San Fernando Earthquake
Roof Drift in Y direction - node#1&4 - EQ17
0.05
node#4
node#1
0.04
0.03
400
Node 4
0.02
z
Y Roof Drift
300
0.01
0
-0.01
Node 1
200
100
-0.02
0
-100
torsion
-0.03
6
0
400
100
-0.04
200
200
0
300
-0.05
0
5
10
15
Time(s)
20
25
400
-200
x
Soft-story drift and torsion are observed
y
IDA Curves
IDA curves
Maximum resultant Inter-Story Drift
3.5
x   y
2
a
Median S at Natural Period (g)
3

2
h
2.5
EQs g=0o
EQs g=90o
16%
median
84%
2
1.5
1
0.5
0
0
5
10
Max. Resultant Interstory Drift (%)
15
Collapse Fragility Curves
maximum resultant inter-story drift
Collapse Diagram - Max Resultant Inter-Story Drift
0.9
0.8
0.7
Collapse Probability
0.6
0.5
0.4
Median Collapse
drift 12~13%?
0.3
0.2
0.1
0
0
2
4
6
8
10
12
14
Max. Resultant Interstory Drift (%)
16
18
20
IEBC
ASCE 41
ATC 71-1
DDD
a.
b.
c.
d.
e.
f.
?
1.25
?
1.5
2.5%
?
Force Based
Entire
Structure
6.5
2%/50yr
Collapse
Prevention
1.0
1.25
1.5
2.5%
2%/50yr
Collapse
Prevention
n/a
3%
2%/50yr
n/a
Life Safety
n/a
2%
Entire
10%/50yr Performance
Basedb
Structure
n/a
Immediate
Occupancy
n/a
1%
20%/50yr
n/a
Collapse
Prevention
n/a
4%c
1.25%d
2%/50yre
Collapse
Prevention
n/a
4%
Life Safety
n/a
Immediate
Occupancy
n/a
Ground
Force Based
Level
2
0.154
6.9a
16.5a
0.192
8.7a
20.6a
0.231
10.4a
24.7a
0.375
0.469
0.563
32.5p
40.7p
48.8p
77.2p
96.4p
115.7p
-
-
-
-
-
-
Dynamic
Analysis
Base Shear
(kips)n
R
Retrofit
Extent
Design
Approach
Hazard Level
Target Drift
10%/50yr
Base Shear
(kips)m
ASCE 7-10
1.0
Seismic
Response
Coefficient
Life Safety
Importance
Factor
Performance
Level
Code/
Methodology
Summary of Current Methods
n/a
1.920f
2.657g
0.870h
1.129k
17-24
25-42
2%/50yr
n/a
1.527m
1.527n
45.6p
108.7p
2%
Entire
10%/50yr Performance
Basedb
Structure
n/a
0.342m
0.356n
10.2p
25.3p
1%
50%/50yr
n/a
0.148m
0.154n
4.4p
11.0p
Performance Ground
Basedb
Level
Value includes ρ = 1.3
Story drift displacement performance
ground level target drift
upper levels target drift
Maximum Considered Earthquake (MCE)
Strength Coefficient based on ground story strength in the X-direction (W = 35 kips)
g. Strength Coefficient based on second story strength in the X-direction (W = 35 kips)
h. Strength Coefficient based on second story strength in the X-direction (W = 82 kips
k. Strength Coefficient based on second story strength in the X-direction (W = 82 kips)
m.Based on total weight W = 35 kips
n. Based on total weight W = 82 kips
p. Vmax(Ultimate Capacity)
EOT – Educational Outreach
NEES Academy
30 minute on-line modules under development
NS 10 – Classification, typical construction and
behavior of soft story wood frame
buildings
NS 20 – Understanding of design options for
retrofit of weak/soft story buildings
NS 30 - Design example of weak/soft story
retrofit using ATC 71.1
NS 40 - Design example of weak/soft story
retrofit using direct displacement design
methodology
EOT – Educational Outreach
NEES Academy - EOT Modules
Stand alone educational content
Could be incorporated into undergraduate and
graduate online or hybrid courses.
Moodle - NEES supported LMS (Learning
Management System
Modules allow for quicker and more efficient
dissemination of information to various
audience.
Additional modules could be developed as
needed
NEES-Soft Validation Testing
NEES @ UCSD Shake Table
2 months beginning Fall 2013
4-story full-scale
Retrofit order
PBSR
ATC 71.1
Remove retrofits and collapse
Retrofit types
SMF
Cantilevered column (IMF)
Dampers
Design just underway
Next Steps for NEES-Soft
NEES-Soft Retrofit building tests at UB
Construction phase in April 2013
Test phase May – Oct 2013
DDD with torsion
Completed June 2012
PBSD for soft-story
Completed August 2012
UC San Diego Testing
August-Sept 2013
Update presentations
WCTE – Auckland, New Zealand; July
2012; next week
WCEE – Lisbon, Portugal; Sept 2012
Thank you!
Professor John W. van de Lindt
Email: jwvandelindt@eng.ua.edu
Or jwv@engr.colostate.edu
This material is based upon work supported by
the National Science Foundation under Grant
No. CMMI-1041631 (NEES Research) and
NEES Operations. Any opinions, findings,
and conclusions or recommendations
expressed in this material are those of the
investigators and do not necessarily reflect the
views of the National Science Foundation.
½” scale model constructed by Prof Mikhail
Gershfeld and students at Cal Poly Pomona.