Seismic Design of Bridges for Prevention of Girder Pounding

By H. Hao1, N. Chouw2

1 University of Western Australia, Australia 2University of Auckland, New Zealand

Featured in: Electronic Journal of Structural Engineering (EJSE)

Poppy BrewerEast Peckham

THE PROBLEM

Introduction

• Current design regulations depend on an in-phase overall vibration to stop adjacent structures from colliding.

• However, pounding damage has still been observed in recent earthquakes.

Taiwan earthquake, 1999

The Trans European Motorway (TEM), 1999

‘Million Dollar’ truss-bridge Alaska, 1964

BAD TIMES!

THE REASSESSMENT

Reassessing the causes of pounding

• Hao and Chouw found two key areas that needed to be better considered:

1. Non-uniform vibrations

2. Soil-structure interaction (SSI)

Non-uniform vibrations

• Vibrations within a system can vary greatly!

Soil-structure interaction (SSI)

• Supporting subsoil can have vastly different properties, so the chance of vibrations being the same at all support bases of a bridge is very small.

The evidenceOriginal method of calculation gives much smaller maximum gap

requirement than the new method, which considers SSI.

AHA! A genius new design philosophy is required.

THE SOLUTION

The solution

• Taking these key aspects of bridge behaviour into account, it is evident that a wider gap is required between adjacent bridge members.

• MEJs, or modular expansion joints provide a solution.

Modular Expansion Joints (MEJs)•MEJs are already being used to combat the thermal expansion and contraction of bridges.

TA DAH!