A framework to integrate conditional simulation of multicomponent spatially varying ground motion field with seismic performance assessment and its application to medium-span bridges

The routine practice of seismic design and performance assessment employs three translational components of ground motion, but their spatial variability is rarely considered. A comprehensive framework that integrates the conditional simulation of multicomponent (three translational and three rotational) spatially varying ground motion field (accounting for the site-specific epistemic uncertainties) with the seismic performance assessment of a structure is not yet explored in the prior art. Along the same line, this paper is aimed to develop such a comprehensive framework and demonstrating its application to a medium-span reinforced concrete highway bridge. This is to offer dual objectives: i) understanding the influence of Spatially varying ground motion (SVGM) field on different engineering demand parameters (EDPs); and ii) influence of multicomponent excitation on the EDPs. Two types of bridges, namely, one simply supported and one 4-span continuous, are considered for this purpose. Probabilistic seismic hazard assessment (PSHA) employing the logic tree approach is carried out for selection and scaling of translational ground motion components. Conditional simulation of SVGM field for translational components is carried out using an evolutionary power spectral density-based framework accounting for the coherency and site-specific effects. Subsequently, the rotational components at each station are extracted using a single-station procedure. Nonlinear time history analysis of the bridge is carried out while considering various combinations of translational and rotational components of ground motion, and the results from SVGM field are compared with that computed using spatially uniform ground motion (SUGM). Overall, the nature and extent of influence contributed from the consideration of multicomponent SVGM field is contingent to the EDPs of interest as well as the structural configuration. The demand for a given EDP when subjected to SVGM field may either be amplified or deamplified depending on the structural configuration.