Simplified approach for the seismic analysis of precast girder bridges with gap

Precast girder bridges are very attractive structural systems to bridge engineers due to their construction rapidity. In their deck arrangement a gap is introduced between the precast girders and the inverted pier cross head. Under longitudinal seismic effect the gap can be closed and the superstructure movement will be locked by the web of the pier cross-head. Usually a rigorous and sensitive non-linear time history analysis will be required for this type of structures. In this paper, a simplified approach will be introduced to estimate the base shear force transmitted to the bridge substructure under seismic loading. In the present approach the modelling of the elastomeric bearing element stiffness is modified in such a way that under earthquake loading the relative displacement between top level and bottom level of bearing equals to the gap value. The seismic analysis with slight, moderate and sharp earthquake accelerations is performed based on the response spectrum analysis as presented by AASHTO LRFD.

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