Optimal EDPs for Post-Earthquake Damage Assessment of Extended Pile-Shaft-Supported Bridges Subjected to Transverse Spreading

During earthquakes, extended pile-shaft-supported bridges in laterally spreading ground can undergo inelastic deformations, especially in their embedded portions. Following earthquakes, it is critical to assess damage to these difficult-to-inspect portions and determine whether vehicles can safely pass bridges. This paper aims to identify optimal aboveground engineering demand parameters (EDPs) that are readily measurable after earthquakes and have high-quality probabilistic associations with post-earthquake load-carrying capacity of bridges as well as underground difficult-to-inspect EDPs. For this purpose, an experimentally validated bridge-soil-foundation model considering liquefaction-induced lateral spreading is adopted and subjected to ground-motion time histories in the transverse direction. Subsequently, pushdown analyses are performed to assess the post-earthquake vertical load-carrying capacity of bridges. Metrics such as efficiency, practicality, and measurability are established and examined for EDPs. Results show that residual column drift ratio is the optimal EDP for load-carrying capacity assessments, whereas maximum column drift ratio best predicts pile demands. Furthermore, developed probabilistic relationships between residual and maximum column drift ratios will assist in preliminary post-earthquake evaluation of bridges for damage assessment and posting decisions.