Development of Self-Centering
Steel Plate Shear Walls
(SC-SPSW)
Jeff Berman
Assistant Professor
University of Washington
NEESR-SG: Steel Plate Shear Wall
Research
Larry Fahnestock
K.C. Tsai
Jeff Berman and
Laura Lowes
Graduate Students:
UW: Patricia Clayton, David Webster
UIUC: Dan Borello, Alvaro Quinonez
UB: Dan Dowden
Sponsored by NSF through the
George E. Brown NEESR Program
Material Donations from AISC
Michel Bruneau
Rafael Sabelli
Project Overview
Resilient
SPSW
Analysis and Verification
of Performance
Fill Critical
Knowledge
Gaps
Subassemblage
Testing
Shake Table
Testing
Full-Scale
Testing
a
~43°
Cyclic Inelastic Tension
Field Action
SPSW Damage States
and Fragilities
Coupled SPSW
Testing (MUST-SIM)
Motivation
• Current U.S. seismic design codes
– Life Safety and Collapse Prevention
– Maximum Considered Earthquake (MCE)
• U.S. Earthquakes since 19701:
– Only 2 people per year die due to structural collapse
– $2 billion per year in economic loss
1
ATC-69 (2008)
US Northridge Earthquake (1994)
Haiti Earthquake (2010)
Resilient SPSWs:
Motivation
• Steel Plate Shear Walls (SPSWs):
–
–
–
–
–
Thin web plates: tension field action
High initial stiffness
Ductile
Distributed yielding
Replaceable “fuses” (web plates)
• However,
– Damage in HBEs and VBEs
not as easy to repair/replace
How can we limit damage to HBEs
and VBEs to provide a quicker return
to occupancy following an
earthquake?
(Vian and Bruneau 2005)
Resilient SPSW: SPSW+ PT Frame
VPT
VSPSW
D
D
VR-SPSW
Unloading
Plate yields
Connection
Decompression
Plates Unloaded
Connection
Recompression
Previous PT Connection Work: Garlcok et
al. 2002, Christopoulos et al., 2002
D
1st Cycle
2nd Cycle
SC-SPSW Research Overview
Analytical
Research
System Behavior
Performance-Based
Design Procedure
Analysis and Verification
of Performance
Experimental
Research
Subassembly Testing
(U. of Washington)
Shake Table Testing
(U. at Buffalo)
Full-scale Testing
(NCREE, Taiwan)
R-SPSW Mechanics
• Distributed loads
on frame from
web plates
• Compression of
HBE from three
components:
– PT
– Web plate loads
on VBE
– Web plate loads
on HBE
Performance-Based Design
REPAIR OF
PLATES ONLY
V
V2/50
V10/50 NO REPAIR
V50/50
Vwind
COLLAPSE
PREVENTION
First occurrence of:
 PT yielding
 Frame yielding
 Residual drift > 0.2%
Plate
yielding
First occurrence of:
 PT rupture
 Excessive PT yielding
 Excessive frame yielding
 Excessive story drifts
Connection
decompression
D50/50
D10/50
D2/50
D
Analytical Model
• Nonlinear model in OpenSees
• SPSW modeled using strip method:
• Tension-only strips with pinched hysteresis
• Strips oriented in direction of tension field
Analytical Model (cont.)
• PT connection model:
Rocking about HBE flanges
Shear transfer
Compression-only springs
at HBE flanges
Diagonal springs
HBE
VBE
PT tendons
Truss elements with
initial stress (Steel02)
Rigid offsets
Physical Model
Analytical Model
Dynamic Analyses
• 3 and 9 story prototypes based on SAC buildings: 4-6 SPSW bays
• Each model subjected to 60 LA SAC ground motions representing
3 seismic hazard levels
• 50% in 50 year
• 10% in 50 year
• 2% in 50 year
• Used OpenSeesMP to run ground motions in parallel on
TeraGrid machines
Ranger
Analytical Summary
• Results for typical 9-story SC-SPSW
– designed WITHOUT optional 50% in 50 year “No repair” performance obj.
• Performance Objectives:
– No plate repair (Story drift < 0.5%) in 50/50
– Recentering (Residual Drift < 0.2%) in 10/50
– Story drift < 2.0% in 10/50 (represents DBE)
– Limited PT, HBE, and VBE yielding in 2/50
V
NO
V2/50
V10/50 REPAIR
V50/50
REPAIR OF COLLAPSE
PLATES ONLYPREVENTION
Vwind
D50/50
All performance objectives met !!!
D10/50
D2/50
D
UW Component Tests
Reaction Blocks
Target Deformation
of Specimen
Subassemblage
Roller to Allow Gap
Opening
Pin to Allow VBE
Rotation
Laboratory
Configuration
Development of
tension field
R-SPSW Testing
Connection
decompression
Flag-shaped
hysteresis
Residual web plate
deformation after test
Comparison of Parameters
Change in number of PT strands
Change in web plate thickness
Kr
• Affects recompression stiffness, Kr,
due to change in PT stiffness
• Affects system strength and energy
dissipation
• Affects decompression moment
• Affects post-decompression
stiffness
Comparison with Idealized Response
VSC-SPSW
Unloading
Plate yields
Connection
Decompression
Plates Unloaded
Connection D
Recompression
1st Cycle
2nd Cycle
• More energy dissipation
than assumed
• Some “compressive”
resistance due to geometric
stiffening
Web Plate Behavior Study
FE modeling
Residual Load
Experimental testing
Pins
(Webster 2011)
~25% of yield
strength
Comparison with Models
• OpenSees model
• With and without compressive resistance in strips
• Future improvements
to strip model:
– Modify strain
hardening rules to
account for cyclic
yielding
– Quantify compression
in SPSW strip model
Frame Expansion
• As PT connection decompresses, VBEs spread apart
Garlock (2002)
• Can cause floor damage or increase
frame demands if beam growth is
restrained, especially at 1st floor beam
Kim and Christopoulos (2008)
Accommodation of Frame Expansion
• Flexible collector beams connecting PT
frame and composite slab
– Applies additional point loads along beam
– Damage to collector beams
Garlock (2007)
• Sliding interface
between slab and beams
– Eliminates slab
restraint
Kim and Christopoulos (2008)
Elimination of Frame Expansion
• Rocking about HBE centerline (Pin)
• NewZ-BREAKSS
– Rocking about top flange only
Testing at NEES@Buffalo
• Quasi-Static tests
• 1/3 scale, 3-story
• Various PT connection details
• Full plate and Strips
N ew Z -B R E A K S S C onn.
F lange R ocking
C enterline R ocking
Comparison of Behavior
• Flange rocking provides better
re-centering because of
decompression moment
• NewZ-BREAKSS prevents floor
damage due to frame expansion.
N ew Z -B R E A K S S C onn.
F lange R ocking
UB Shake Table Tests
• 6 degree-of-freedom shake table
• Same specimens as quasi-static tests
• Scheduled for completion in fall 2012
System-level Testing
• National Center for
Earthquake Engineering
(NCREE) in Taiwan
– 2-story, full scale SC-SPSW
– Single actuator
– Quasi-static loading
– Summer 2012
NCREE Specimens
• PT column base
– Column can rock about its flanges
NCREE Specimens
• PT column base
– Column can rock about its flanges
• 2 specimens
– Flange rocking HBEs
– NewZ-BREAKSS Connection
(Top flange rocking HBEs)
Conclusions
• Performance-based design procedure developed for SCSPSW:
– Elastic behavior during frequent events
– Web plate yielding and recentering during DBE events
– Collapse prevention during MCE events
• Analytical studies show SC-SPSWs are capable of
meeting proposed performance objectives
• Experimental subassembly tests show ‘simple’ models
are conservative and have room for improvement
• Future testing will verify performance on system level
Thank You
Questions?
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