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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 Page 8
17 3 1560 1.0D +16/-16 66.7% 0.0026 0.5
Example Test Matrix
SIE inc.
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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…