7. testing of seismic isolators-aiken

8NCEETutorial on State of the Art Technologies

Testing of Seismic Isolators

April 17, 2006

Ian Aiken, Ph.D., P.E.SIE inc.


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Overview

• Basis for testing

• Requirements of existing codes

• Capabilities for testing

• Issues with existing approaches

• Testing and a simplified design procedure


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Basis for Testing

• Verify isolator properties used in the design– Stiffness (effective stiffness, 1st cycle stiffness)– Energy dissipation characteristics (effective damping,

hysteresis loop area)– Amplitude, frequency and/or velocity, and vertical

load dependencies

• Confirm isolator integrity / stability / durabilityunder maximum loading conditions


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Testing Requirements –Codes, Standards, Guidelines

New Buildings• International Building Code, 2003 (ASCE 7-02)• California Building Code, 2001 (UBC 1997)• FEMA-450, 2003

Retrofit

• FEMA-365, 2000 (FEMA-273, 1997)

Bridges

• AASHTO Guide Specification, 1999


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Types of Tests

• Material physical tests• Prototype

– Comprehensive testing of each type/designof isolator for a project

– may be a combination of full-size andreduced-scale (pre-prototype)

• Production– Quality control


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Prototype Tests

• Sustained compression

• Compression stiffness

• Compression-shear

• Stability

• Uplift


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1997 UBC – Prototype Test Requirements

• Two full-size specimens (or sets) of each type and size• For a vertical load of D + 0.5L (average for each type):

1. 20 cycles at the wind design force2. 3 cycles at each of 0.2DD, 0.5DD, 1.0DD, and 1.0DM

3. 3 cycles at 1.0DTM

4. (15 CVD/CVABD), but not less than 10, cycles at 1.0DTD

• If isolator is a vertical load-carrying element, then Item 2 shall be additionally performed for:

(1) 1.2D + 0.5L + |E|(2) 0.8D - |E|

• Additional tests required if isolators dependent on loading rate or bilateral load


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Test ID

No. ofCycles

Vertical Load Shear Displacement

Span (%)

Freq. (Hz)

Logger(sec.)

(kips) (MN) (in.) QA 3 950 4.226 1.0D 16 66.7% 0.0026 0.5

Note QA test to be performed on 2nd pair of Type II bearings 0708 2 20 950 4.226 Wind 1 4.2% 0.0416 0.1

3A 3 950 4.226 0.25D 4 16.7% 0.0104 0.5 3B 3 950 4.226 0.50D 8 33.3% 0.0052 0.5 3C 3 950 4.226 0.75D 12 50.0% 0.0035 0.5 3D 3 950 4.226 1.0D 16 66.7% 0.0026 0.5 4A 3 1560 6.939 0.25D 4 16.7% 0.0104 0.5 4B 3 1560 6.939 0.50D 8 33.3% 0.0052 0.5 4C 3 1560 6.939 0.75D 12 50.0% 0.0035 0.5 4D 3 1560 6.939 1.0D 16 66.7% 0.0026 0.5 5A 3 190 0.845 0.25D 4 16.7% 0.0104 0.5 5B 3 190 0.845 0.50D 8 33.3% 0.0052 0.5 5C 3 190 0.845 0.75D 12 50.0% 0.0035 0.5 5D 3 190 0.845 1.0D 16 66.7% 0.0026 0.5 6 3 (1/2) 950 4.226 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 7 3 (1/2) 1560 6.939 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 8 3 (1/2) 190 0.845 1.0DTM 0/-26 54.2% & bias 0.0032 0.5

Rotate Bearings Through 180 Degrees 6A 3 (1/2) 950 4.226 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 7A 3 (1/2) 1560 6.939 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 8A 3 (1/2) 190 0.845 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 9 18 950 4.226 1.0DT 18 75% 0.0023 0.5 10 18 1560 6.939 1.0DT 18 75% 0.0023 0.5 11 18 190 0.845 1.0DT 18 75% 0.0023 0.5

Position Bearings Offset to the Test Press Vertical Centreline (BRD 2578 sheet 3) 12 1 (1/2) 2900 12.9 1.0DTM 0/-26 54.2% & bias 0.0032 0.5

Rotate Bearings Through 180 Degrees 12A 1 (1/2) 2900 12.9 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 13 N/A Section 4.4.1.6 of spec

Position Bearings on the Press Vertical Centreline (BRD 2578 sheet 2) 14 1 (1/2) Nominal 0 1.0DTM 0/-26 54.2% & bias 0.0032 0.5

Rotate Bearings Through 180 Degrees 14A 1 (1/2) Nominal 0 1.0DTM 0/-26 54.2% & bias 0.0032 0.5 15 16

Uplift Test Refer to Test Sequence 4.5 on

17 3 1560 1.0D +16/-16 66.7% 0.0026 0.5

Example Test Matrix

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1997 UBC – Production Tests

1661.2.9 Quality control. A quality control testing program forisolator units shall be established by the engineer responsible forthe structural design.


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Production Tests

• Primary intent is quality control• Agreement with Prototype Test results• Minimum test requirements defined by the

Engineer-of-Record• Typical tests

– Sustained compression– Compression stiffness– Compression-shear

typically 3-5 fully-reversed cycles at the design displacement and average vertical load

• End result is thorough testing of all isolators for all projects


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Test Machines – Manufacturers


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Caltrans’ SRMD Test Facility, UC San Diego

• World’s largest machine fortesting seismic devices

• Built for testing bearings and dampers for the Benicia-Martinez, Richmond-San Rafael,SF-Oakland Bay Bridge andother toll crossing retrofits

• Construction cost >$15M

• Capable of bi-directional dynamic testing of full-size isolators and dampers


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Typical Results – Compression-Shear Test

-200

-150

-100

-50

0

50

100

150

200

-20 -15 -10 -5 0 5 10 15 20

Displacement (in)

Shea

r For

ce (k

ips)

-150

-100

-50

0

50

100

150

-20 -15 -10 -5 0 5 10 15 20

Displacement (in)

Shea

r For

ce (k

ips)


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Issues Associated with Testing

• Cost of prototype isolators, test program

• Time required to manufacture test specimensand perform tests

• Custom isolator designs for nearly every project has not allowed manufacturers to standardize – therefore detailed testing required for nearly all projects

• Is the current approach necessary, and beneficial/of value to projects?


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Isolator Testing and theSimplified Design Procedure

• Development of the simplified design procedure is a work in progress

• An important aspect of the final simplified approach will be to rationalize/simplify the testing requirements

• Opportunity exists to define a framework for standardized and pre-qualified isolator designs, as has been done in Japan


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Questions…

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