Seismic Fragility Analysis of GRS Bridge Abutments Using Nonlinear Finite Element Method

Damages observed during previous earthquakes instigated the need to understand the cause of seismic failures of different lifelines and to identify the ways and means of reducing the seismic damage. In this study, the fragility curves for geosynthetic reinforced soil (GRS) bridge abutments are developed as tools for seismic vulnerability assessment. The soil is modelled with a user material subroutine in ABAQUS, a finite element (FE) software, using the hypoplastic constitutive model. The input earthquake time histories are obtained from the Pacific Earthquake Engineering Research earthquake database. The seismic acceleration time histories are scaled suitably to simulate earthquakes of different intensities. A total of twenty-five acceleration time histories are given as input, and responses of the FE model of the GRS bridge abutment are obtained to generate the seismic damage database using the Incremental Dynamic Analysis. The results of the nonlinear time history analyses are processed using probabilistic methodologies to derive probabilistic seismic demand models (PSDMs) and corresponding fragility functions, consistent with the principles of performance-based earthquake engineering. The peak ground acceleration at the ground surface under free field conditions (PGAff) is considered as the intensity measure, and the same is used in the generation of fragility curves. Using the PSDMs, the fragility curves for three damage states of the GRS bridge abutment are developed. The developed PSDMs and fragility curves serve as practical decision-making tools for designers of bridge systems.