Utilization of Site-Based Simulated Ground Motions for Hazard-Targeted Seismic Demand Estimation: Application for Ordinary Bridges in Southern California

Current seismic design procedures such as Caltrans Seismic Design Criteria (2013, 2019) are continuously evolving to develop methodologies for conducting seismic analysis to achieve more accurate estimations of the demands corresponding to target hazard levels. The most widely used conventional procedure to conduct seismic demand analysis is to scale recorded or simulated ground motions to achieve the intensity measure (IM) associated with the target hazard level. The scaled ground motions are then used to conduct the nonlinear time-history analysis (NLTHA) of the bridge models, and the obtained response values are then utilized to design the bridge structure. This study systematically shows how to make use of site-based synthetic ground motions for assessing the seismic demands of Caltrans ordinary bridges in the context of performance-based design. Within this framework, catalogs of synthetic ground motions representing a time-span of 100,000 years for seven sites in Southern California are generated; the ground motions are then used to conduct NLTHA of four Caltrans standard ordinary bridge structures (denoted as A, B, C, and F). Using the results of the analyses, statistical methods of Hypothesis T-Test and KL-Divergence are applied to obtain the optimal number of ground motions and ground motion intercept angles that can statistically replicate the results of simulated ground motions that naturally possess the IM of the target hazard level. Scaling relations are provided that convert engineering demand parameters (EDP) associated with IM for a target hazard level with EDPs directly representing the target hazard level.