Development of Self-Centering Steel Plate Shear Walls

(SC-SPSW)

Jeff BermanAssistant Professor

University of Washington

NEESR-SG: Steel Plate Shear Wall Research

Jeff Berman and Laura Lowes Michel BruneauLarry Fahnestock

K.C. Tsai

Sponsored by NSF through the George E. Brown NEESR Program

Rafael Sabelli

Material Donations from AISC

Graduate Students:

UW: Patricia Clayton, David Webster UIUC: Dan Borello, Alvaro Quinonez

UB: Dan Dowden

Project Overview

Resilient SPSW

Analysis and Verification of Performance

Subassemblage Testing

Shake TableTesting

Fill Critical Knowledge

Gaps

Cyclic Inelastic Tension Field Action

SPSW Damage States and Fragilities

Coupled SPSW Testing (MUST-SIM)

a~43°

Full-Scale Testing

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) Haiti Earthquake (2010)US Northridge Earthquake (1994)

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 FrameVSPSW

D

1st Cycle2nd Cycle

VPT

D

VR-SPSW

D

Plate yields

Unloading

ConnectionDecompression

ConnectionRecompression

Plates Unloaded

Previous PT Connection Work: Garlcok et al. 2002, Christopoulos et al., 2002

SC-SPSW Research Overview

Analytical Research

Analysis and Verification of Performance

Performance-Based Design ProcedureSystem Behavior

Subassembly Testing (U. of Washington)

Experimental Research

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

V

D

V10/50

D10/50

First occurrence of:·PT yielding·Frame yielding·Residual drift > 0.2%

REPAIR OF PLATES ONLY

V2/50

D2/50

First occurrence of:·PT rupture·Excessive PT yielding·Excessive frame yielding·Excessive story drifts

COLLAPSEPREVENTION

D50/50

V50/50 Plate yielding

NO REPAIR

VwindConnection decompression

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:

HBE

VBE

Rocking about HBE flangesCompression-only springs at HBE flanges

Rigid offsets

Shear transferDiagonal springs

PT tendons Truss elements with initial stress (Steel02)

Analytical ModelPhysical 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

All performance objectives met !!!

REPAIR OF PLATES ONLY

COLLAPSEPREVENTION

NO REPAIR

V

D

V10/50

D10/50

V2/50

D2/50D50/50

V50/50

Vwind

UW Component Tests

Reaction Blocks

Roller to Allow Gap Opening

Pin to Allow VBE Rotation

Subassemblage

Target Deformation of Specimen

Laboratory Configuration

R-SPSW TestingDevelopment of tension field

Connection decompression

Residual web plate deformation after test

Flag-shaped hysteresis

Comparison of ParametersChange in number of PT strands Change in web plate thickness

• Affects recompression stiffness, Kr, due to change in PT stiffness• Affects decompression moment

Kr

• Affects system strength and energy dissipation• Affects post-decompression

stiffness

Comparison with Idealized Response

• More energy dissipation than assumed

• Some “compressive” resistance due to geometric stiffening

1st Cycle2nd Cycle

VSC-SPSW

D

Plate yields

Unloading

ConnectionDecompression

ConnectionRecompression

Plates Unloaded

Web Plate Behavior StudyFE modeling

Experimental testing

Pins

Residual Load

~25% of yield strength

(Webster 2011)

Comparison with Models

• Future improvements to strip model:– Modify strain

hardening rules to account for cyclic yielding

– Quantify compression in SPSW strip model

• OpenSees model• With and without compressive resistance in strips

Frame Expansion• As PT connection decompresses, VBEs spread apart

• Can cause floor damage or increase frame demands if beam growth is restrained, especially at 1st floor beam

Garlock (2002)

Kim and Christopoulos (2008)

Accommodation of Frame Expansion

Kim and Christopoulos (2008)

Garlock (2007)

• Flexible collector beams connecting PT frame and composite slab– Applies additional point loads along beam– Damage to collector beams

• Sliding interface between slab and beams– Eliminates slab restraint

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 NewZ-BREAKSS Conn. Flange Rocking

Centerline Rocking

Comparison of Behavior

Flange RockingNewZ-BREAKSS Conn.

• Flange rocking provides better re-centering because of decompression moment

• NewZ-BREAKSS prevents floor damage due to frame expansion.

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 SC-

SPSW:– 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

Questions?

Thank You

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