Focal Mechanism Influence with Azimuth Using Near-Field Simulated Ground Motion: Application to a Multispan Continuous Concrete Single-Frame Box-Girder Bridge

Abstract Bridges in earthquake-prone states like California have been studied for near-field and far-field loadings. However, there is a research gap in terms of how an earthquake of a certain strike, dip, and rake is going to influence the bridge response. Here, we focus on multispan continuous concrete single-frame box girder bridges. In this study, we simulate earthquakes of varying focal mechanisms and perform nonlinear dynamic analysis of bridges with the synthesized ground motion. Furthermore, the influence of azimuth orientation with respect to the source is studied by placing the bridge model a few kilometers from the source at certain azimuths motivated by the radiation pattern of seismic waves. Fixing a magnitude, depth, and reference focal mechanism angles determining a focal mechanism is varied to study the effect of strike, dip, and rake on the bridges. In each of these cases, the potential risk is identified, and the study underscores the need to include these focal mechanism parameters into bridge fragility computations in risk assessment platforms such as HAZUS.