Bridge Seismic Isolation

Some Western Canada Experience

Steve Zhu, Ph.D., P.Eng., P.E.

Buckland & Taylor Ltd.

1

Design Standards

1991 AASHTO Guide Specifications

CAN/CSA-S6-06 CHBDC (Similar to 1991 AASHTO Guide Specifications)

1999 AASHTO Guide Specifications (Including 2000 Interim Revisions)

2

Design Earthquakes

475 Year Design Earthquake

975 Year Design Earthquake

2475 Year Design Earthquake

3

Analysis Methods

Multi-Mode Response Spectral Analysis - Reduced Effective Stiffness and Increased Equivalent Viscous Damping

Nonlinear Time History Analysis – Hysteretic Behaviour of Isolation System

4

Testing

1999 AASHTO Guide Specifications

System Characterization Tests

Prototype Tests

Quality Control Tests

5

Design

Substructures to Remain Essentially Elastic (R ≤ 1.5)

Ductile Detailing for Potential Plastic Hinge Regions

Adequate Seat Length

Fuse Expansion Joints under 2475 Year Design Earthquake

6

Burrard Bridge, Vancouver, BC

7

Burrard Bridge, Vancouver, BC

8

Burrard Bridge, Vancouver, BC

9

Burrard Bridge, Vancouver, BC

10

Granville Bridge, Vancouver, BC

11

South Approach to Granville Bridge, Vancouver, BC

12

South Approach to Granville Bridge, Vancouver, BC

13

South Approach to Granville Bridge, Vancouver, BC

14

White Water Bridge, Yukon

15

Golden Ears Bridge – Main Spans

16

Golden Ears Bridge – South Approach

17

Golden Ears Bridge – South Approach

18

Testing of Seismic Isolation Bearings

19

Testing of Seismic Isolation Bearings

20

3D Computer Model

21

Nonlinear Time History Analysis

22

Bent S13 Isolation Bearing: Relative Transverse Displacement

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0 20 40 60 80 100

Time (s)

Rela

tive D

isp

lacem

en

t (m

)

Loma Prieta

Chi Chi

Design Displacement Combinations

475 Year Design Earthquake

C/S + 0.5 T + EQ

2475 Year Design Earthquake

C/S + EQ

Where

C/S = Creep and Shrinkage Effects

T = Thermal Effects

EQ = Seismic Effects

23

Issues

How to Combine with Thermal Displacements

Cold Weather Effects

Appropriate Levels of Lateral Restoring Force

Vertical Load Stability

Reliability over Time

Maintenance

How to Address Various Effects Systematically to Provide Levels of Protection Appropriate for Structure Importance and Design Earthquake Considered.

24