1. Seismic Testing of an Isolated Scale-Model Bridge Structure with an Adaptive Passive Negative Stiffness Device
N. Attary and M.D. Symans
Rensselaer Polytechnic Institute
S. Nagarajaiah and D.T.R. Pasala
Rice University
A.M. Reinhorn, M.C. Constantinou, and A.A. Sarlis
University at Buffalo
D. Taylor
Taylor Devices, Inc.
2012 Quake Summit, Boston, MA
Session 4, Base Isolation/Energy Dissipation
July 11, 2012

2. (NEESR - Network for Earthquake Engineering Simulation Research)
Project Team
NEESR-SG: Development of Next Generation Adaptive Seismic Protection Systems
Satish Nagarajaiah
Professor
Civil & Mechanical Eng.
Rice University
Michael Symans
Associate Professor
Civil Engineering
Rensselaer Polytechnic Institute
Andrei Reinhorn
University at Buffalo
Michael Constantinou
Jian Zhang
Assistant Professor
Univ. of Calif. Los Angeles
Douglas Taylor
President, Taylor Devices, Inc.
Mechanical Engineering
Taylor Device Inc.
Research supported by National Science Foundation CMMI Grant No
(NEESR - Network for Earthquake Engineering Simulation Research)

3. 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

4. Advanced Seismic Protection Systems for Bridges
Patten (1998) Semi-active control using variable-orifice fluid damping/stiffness device (implemented in highway bridge 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

5. Improved Seismic Performance via Combined Weakening and Damping
Source: Reinhorn et. al. (2002)

6. Concept of Negative Stiffness
Force develops in same direction as imposed force
Adding Positive/Negative Stiffness to a Basic System with Positive Stiffness
Positive vs. Negative Stiffness

7. Working Principle of Negative Stiffness and Positive Damping in Structures
Source: Nagarajaiah et. al. (2010)

8. Pseudo-Negative Stiffness in Bridges Source: Iemura and Pradono (2003)
Cyclic Testing
of PNS Damper
With PNS,
Both Force
and Displ.
Reduced

9. True Negative Stiffness Device
Undeformed Shape
Deformed Shape
- Device is completely passive (no external power source needed)
Device has adaptive behavior (stiffness varies with displacement
in a controllable manner)
Passive
Adaptive
NSD

10. Analytical Force-Displacement Relation of NSD
Neglecting inertial effects, friction at pins, and
flexibility of steel framing members: A
FNSD l2
FBh
vAB B l1
FBv
vBC C
Fg = Force in gap-spring assembly FS
Values of Parameters for
Bridge Model Analysis u
vCD ls
U( ) l1 l2
Distance from spring pin to hinge pin
L1 = 10 in
Distance from lever pin to hinge pin
L2 = 5 in
Vertical length of main spring
Lp = 30 in
Stiffness of main spring
Ks = 0.8 kips/in
Pre-load of main spring
Pin = 4.4 kips FS D Fg
FDv

11. Force-Displacement Relation in Gap-Spring Assembly
dgap
Pcomp
Kstiff
Kstiff Ksoft
Kstiff +Ksoft
Pcomp
KSoft
KStiff

12. NSD Force-Displacement Relation
Source: Sarlis, Pasala, Constantinou, Reinhorn, Nagarajaiah, and Taylor (2011)

13. 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

14. Component- and System-Level Analytical Force-Displacement Relations
Bearings
Bridge with Bearings + NSD's
Bearings + NSD's
NSD's

15. Cyclic Testing of NSDs
Harmonic Test
Amplitude = 3"
Freq. = 0.01 Hz

16. Shake Table Testing of Bridge Model with NSDs Installed
SolidWorks Model
SAP2000 Model

17. Building and Preparing Bridge Model
New Bridge Deck
Existing Bridge Pier
Torsional Restraint and NSD Force Transfer Column

18. Building and Preparing Bridge Model (Cont.)

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

21. Sine Sweep Test of Bridge Model with NSDs

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

23. 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.

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