Seismic Response of Steel Bridges With Decoupled Ductile End-Cross Frames

Abstract eng:
A promising technique for improving the seismic performance of highway bridges with steel plate girder superstructures, is to dissipate energy through the inelastic deformation of the end-cross frames. Ductile response of these cross frames can reduce the shear demand on the substructure below the frames, but this reduction in base shear is accompanied by an increase in the lateral drift in the superstructure, which in turn places large deformation and force demands on the shear connectors and plate girders. Damage to these components may lead to permanent deformations in the superstructure, which could lead to reduced capacity for live load. This paper presents the development of a cross frame that is partially decoupled from the superstructure, which then permits larger drifts to occur without causing damage to elements elsewhere in the superstructure while dissipating significant levels of energy. In the proposed configuration, the shear studs are removed from the top flange of the girders between the support and the first intermediate cross frame at both ends of the span. Ductile chevron (inverted V) bracing is then used at the supports to transmit the lateral shear from the concrete deck slab directly to the lower flange of the girders above the bearings. It is shown that these decoupled frames can tolerate drifts of up to 6% without causing distress to the remainder of the superstructure. At such a drift, the base shear transmitted to the substructure is about 25% of the value when the superstructure has conventional ductile end-cross frames.

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