seismic isolation design examples - an update
TRANSCRIPT
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Seismic Isolation Design Examples
- An Update
Ian Buckle
University of Nevada Reno
Technical Subcommittee for Bearings and Expansion Devices (T-2)
Annual Meeting AASHTO Subcommittee on Bridges and Structures
July 10, 2012, Austin TX
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Background
• NCHRP 20-7/Task 262 (M2): Seismic Isolation
Design Examples of Highway Bridges
• Committee sponsors: T-2 and T-3
• Program Officer: Waseem Dekelbab
• Authors:
– Ian Buckle, Moustafa Al-Ani, Eric Monzon
• Status: Completed
• Dissemination:
– Proposed inclusion as Appendix B, AASHTO Guide
Specifications Isolation Design Third Ed.
– Ballot Item 2012 Annual Meeting
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Design Examples Overview
• Two benchmark bridges
• short-span concrete bridge
• long-span steel bridge
• Six variations on each:
• seismic hazard
• site class
• pier height
• skew
• isolator type (3)
• Total number of examples = 14
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Design Examples: Benchmark No. 1
ID Description S1 Site
Class Pier height Skew Isolator type
1.0 Benchmark bridge 0.2g B Same 0 Lead-rubber bearing
1.1 Change site class 0.2g D Same 0 Lead rubber bearing
1.2 Change spectral
acceleration, S1 0.6g B Same 0 Lead rubber bearing
1.3 Change isolator to SFB 0.2g B Same 0 Spherical friction
bearing
1.4 Change isolator to EQS 0.2g B Same 0 Eradiquake bearing
1.5 Change column height 0.2g B H1=0.5 H2 0 Lead rubber bearing
1.6 Change angle of skew 0.2g B Same 450 Lead rubber bearing
Benchmark Bridge No. 1
• 3-span, 25-50-25 ft
• 6 PC continuous girders
• 3-column piers
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Design Examples: Benchmark No. 2
Benchmark Bridge No. 2
• 3-span, 105-152.5-105 ft
• 3 steel plate continuous
girders
• Single-column piers
ID Description S1 Site
Class Column height Skew Isolator type
2.0 Benchmark bridge 0.2g B Same 0 Lead-rubber bearing
2.1 Change site class 0.2g D Same 0 Lead rubber bearing
2.2 Change spectral acceleration, S1 0.6g B Same 0 Lead rubber bearing
2.3 Change isolator to SFB 0.2g B Same 0 Spherical friction
bearing
2.4 Change isolator to EQS 0.2g B Same 0 Eradiquake bearing
2.5 Change column height 0.2g B H1=0.5H2 0 Lead rubber bearing
2.6 Change angle of skew 0.2g B Same 450 Lead rubber bearing
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Design Methodology
Step A. Assemble bridge and site data; determine
performance objectives.
Step B. Analyze bridge in longitudinal direction
(i.e. find Qd and Kd to achieve required
performance using (1) simplified and (2) multi-
modal spectral analysis methods)
Step C. Analyze bridge in transverse direction as in Step B.
Step D. Combine results (100/30 rule); check performance
Step E. Design isolation hardware to provide required Qd
and Kd
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Table of Contents
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Design Example Template
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Design Example Template
GSID = Guide Specifications for Seismic Isolation Design (AASHTO 2010)
LRFD = LRFD Bridge Design Specifications (AASHTO 2008)
Sample calculation for Effective Period
Benchmark Bridge No. 1
Step number
/ generic
instructions
Step number
/ calculation
and result for
this example
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Summary of Isolator Designs: Set 1
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Summary of Isolator Designs: Set 1
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Summary of Isolator Designs: Set 2
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Thank you.