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

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

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

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

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

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

Table of Contents

Design Example Template

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

Summary of Isolator Designs: Set 1

Summary of Isolator Designs: Set 1

Summary of Isolator Designs: Set 2

Thank you.