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Seismic Testing of an Isolated Scale-Model Bridge Structure with an Adaptive Passive

Negative Stiffness DeviceN. Attary and M.D. Symans

Rensselaer Polytechnic Institute

S. Nagarajaiah and D.T.R. PasalaRice University

A.M. Reinhorn, M.C. Constantinou, and A.A. SarlisUniversity at Buffalo

D. TaylorTaylor Devices, Inc.

2012 Quake Summit, Boston, MASession 4, Base Isolation/Energy Dissipation

July 11, 2012

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NEESR-SG: Development of Next Generation Adaptive Seismic Protection Systems

Satish NagarajaiahProfessor

Civil & Mechanical Eng.Rice University

Michael SymansAssociate Professor

Civil EngineeringRensselaer Polytechnic Institute

Andrei ReinhornProfessor

Civil EngineeringUniversity at Buffalo

Michael ConstantinouProfessor

Civil EngineeringUniversity at Buffalo

Jian ZhangAssistant Professor

Civil EngineeringUniv. of Calif. Los Angeles

Douglas TaylorPresident, Taylor Devices, Inc.

Mechanical EngineeringTaylor Device Inc.

Research supported by National Science Foundation CMMI Grant No. 0830391 (NEESR - Network for Earthquake Engineering Simulation Research)

Project Team

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Outline• Seismic Protection Systems for Bridges

• Concept of Negative Stiffness

• Development of Mechanical Negative Stiffness Device

• Implementation of Negative Stiffness Device within a Quarter-Scale Bridge Structure

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Advanced Seismic Protection Systems for Bridges

• Patten (1998)Semi-active control using variable-orifice fluid damping/stiffness device (implemented in highwaybridge in Oklahoma for vibration control)

• Sahasrabudhe and Nagarajaiah (2005)Semi-active control of isolated bridge using:– Magnetorheological (MR) dampers– Variable stiffness devices

Small-scale bridge model

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Improved Seismic Performance via Combined Weakening and Damping

Source: Reinhorn et. al. (2002)

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Concept of Negative Stiffness Force develops in same direction as imposed force

Positive vs. Negative StiffnessAdding Positive/Negative Stiffness to a Basic

System with Positive Stiffness

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Working Principle of Negative Stiffness and Positive Damping in Structures

Source: Nagarajaiah et. al. (2010)

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Pseudo-Negative Stiffness in BridgesSource: Iemura and Pradono (2003)

Cyclic Testing of PNS Damper

With PNS,Both Force and Displ.Reduced

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True Negative Stiffness Device

Deformed ShapeUndeformed Shape

- Device is completely passive (no external power source needed)- Device has adaptive behavior (stiffness varies with displacement

in a controllable manner)

Passive AdaptiveNSD

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Analytical Force-Displacement

Relation of NSD

Distance from spring pin to hinge pin L1 = 10 inDistance from lever pin to hinge pin L2 = 5 in

Vertical length of main spring Lp = 30 inStiffness of main spring Ks = 0.8 kips/inPre-load of main spring Pin = 4.4 kips

Fg = Force in gap-spring assembly

Values of Parameters for Bridge Model Analysis

Neglecting inertial effects, friction at pins, and flexibility of steel framing members:

11 22 2

2 1 2

2in s p pNSD s g

s

P K L L LL LF K u F

L L L L u

vAB

vBC

vCDls

l1

l2

uU( )l1

l2

FBh

FNSD

FS

FS

A

B

C

DFg

FBv

FDv

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Force-Displacement Relation in Gap-Spring Assembly

1

1 21

1 2

s gap

g s ss gap gap gap

s s

k u u dF k k

k d u d u dk k

Disp.

Forc

e

dgap

Pcomp

Kstiff

Kstiff Ksoft

Kstiff +Ksoft

Pcomp

KSoft KStiff

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NSD Force-Displacement Relation

Source: Sarlis, Pasala, Constantinou, Reinhorn, Nagarajaiah, and Taylor (2011)

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Implementing NSD's in Bridge Model

• Quarter-scale single-span highway bridge with clear span of 4.8 m and deck weight of 35.5 kips

• NSD's located under bridge deck within isolation system• Isolation system:

– Elastomeric bearings (low damping)– Elastomeric bearings + fluid viscous dampers– Elastomeric bearings + NSD's– Elastomeric bearings + fluid viscous dampers + NSD's

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Component- and System-Level Analytical Force-Displacement Relations

Bearings

Bridge with

Bearings + NSD'sBearings + NSD's

NSD's

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Cyclic Testing of NSDs

Harmonic TestAmplitude = 3"Freq. = 0.01 Hz

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Shake Table Testing of Bridge Model with NSDs Installed

SolidWorks Model

SAP2000 Model

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Building and Preparing

Bridge Model

New Bridge Deck

Torsional Restraint and NSD Force Transfer ColumnExisting Bridge Pier

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Building and Preparing Bridge Model (Cont.)

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Quarter-Scale Bridge Model on Shake Table at NEES-UB

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Sine Sweep Test of Bridge Model with NSDs

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Seismic Test of Bridge Model with NSDs: Kobe Earthquake (KJM000 – 100%)

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Summary• Conceptual Development

– Concept of weakening and damping (via negative stiffness and positive damping) offers potential for improved seismic performance by reducing both forces and displacements.

• Validation of Analytical Model via Cyclic Testing– Mechanical negative stiffness device (NSD) has been developed and cyclic tests

have been performed. Simplified analytical model captures cyclic response.

• Shake Table Testing of Bridge Model– Negative stiffness device has been implemented in a scale-model bridge

structure. Numerical simulations demonstrate potential for improved seismic performance. Shake table testing is underway.

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Acknowledgments• National Science Foundation (NSF) under Grant No. CMMI- 0830391

• Mr. John Metzger (Engineering Manager), Taylor Devices, Inc.

• Mr. Peter Fasolino, K&E Fabricating Co.

• Staff of NEES & SEESL Laboratories at University at Buffalo (listed alphabetically)– Thomas Albrechcinski (Site Operations Manager)– Myrto Anagnostopoulou, M.Sc. (Structural and Test Engineer)– Christopher Budden (Electronic/Instrumentation Specialist)– Jeffrey Cizdziel (Mechanical Technician)– Goran Josipovic (IT Service Manager)– Duane Kozlowski (Lead Mechanical Technician)– Lou Moretta (Mechanical Technician)– Mark Pitman (Technical Services Manager)– Robert Staniszewski (Mechanical Technician)– Scot Weinreber (Electronic/Instrumentation Engineer)– Shomari White (IT Specialist)