Session 1.2 - Bridges

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Wave-passage Effect on the Seismic Response of Long Bridges

J. Wang, A.J. Carr, N. Cooke and P.J. Moss

The effect of the spatial variation of seismic ground motions on the response of bridge structures has been of concern for decades. However most of these studies focus on the elastic behaviour of the structure. In this paper, a study of the inelastic response of an irregular bridge with piers of different heights subjected to travelling seismic motion is presented. The time-history responses of bridge models were produced using a 3D computer program. Parametric analyses using different propagation velocities of the seismic waves and different natural accelerograms were conducted to assess the wave-passage effect on the response of a bridge. The response of the bridge to asynchronous input motions at different pier bases consists of two components: a dynamic component induced by the inertia forces and a so-called pseudo-static component, due to the difference between the adjacent support displacements. It was observed that the propagation velocity of the seismic waves had a significant effect on the response of the bridge. When the travelling wave velocity was low, the response was dominated by the pseudo-static component. As the travelling wave velocity increased, the pseudo-static component reduced considerably and the dynamic component increased rapidly. When the travelling wave velocity was high, the response was dominated by the dynamic component.

Paper 050: [Read][Print]

Keywords: long bridge, wave-passage effect, inelastic response, time-history

An Experimental Study into the Distribution of Earthquake Forces in Steel Plate Girder Bridges

L.P. Carden, A.M. Itani and I.G. Buckle

Recent earthquakes have resulted in damage to components of steel plate girder bridge superstructures and have highlighted the need to design these components for seismic loading. A 2/5th scale model was constructed in order to study the seismic response of a typical concrete slab-on-steel girder bridge superstructure. The initial focus was on the transverse response of the bridge superstructure, with earthquake loading simulated by pseudo static loads applied at the deck level, using twin actuators. The distribution of resulting forces was determined from experiments and supporting finite element analysis. The longitudinal load path was also studied using finite element analysis. Critical elements identified in the load path include the shear connection between the deck and steel girders, as well as the end cross frames, web stiffeners and bearings. Except for bearings, the effect of each of these components is discussed in this paper.

Paper 060: [Read][Print]

Keywords: steel bridge, superstructure, shear studs, cross frames

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