Ductile Behavior of Scoured RC Pile-Group Foundations for Bridges in Cohesionless Soils: Parametric Incremental Dynamic Analysis

Abstract

Scoured pile-group foundations (SPGFs) are susceptible to inelastic deformation during earthquakes. Hence, the ductile behavior of SPGFs has become a rising concern in academic and industrial communities. Traditionally, pushover analyses with single-point load patterns have been adopted to obtain the ductile characteristics of bridge pile-group foundations. However, this practice cannot properly account for the inertial effects from both the superstructure and the pile-cap. Accordingly, in this study, the well-known incremental dynamic analysis (IDA) was adopted to rigorously and comprehensively investigate the ductile behavior of SPGFs for the seismic design of bridges in flood-prone regions. To this end, a shake-table test on an SPGF-supported RC bridge bent model was firstly employed to validate the adopted numerical modeling technique. An in-depth parametric study was then conducted on the bridge bent with the damage potential of the SPGF embedded in cohesionless soil, considering various structural and geotechnical parameters. Based on the IDA results, the seismic failure process, structural limit states, and ductile performance indices of SPGFs were systematically investigated. It was found that the failure process of SPGFs obtained from IDA was consistent with that reported in a previous quasistatic test. Scoured pile-group foundations have a considerable displacement ductility capacity (quantified as 2.48 and 3.47, on average, for the easy-to-repair and ultimate states, respectively), as well as lateral strength enhancement capacity (i.e., the lateral strength values for the easy-to-repair and ultimate states were, on average, 1.40 and 1.46 times that of the first-yield state, respectively). The displacement ductility capacity of SPGFs can be improved by using more rows of piles, a larger pile diameter, a higher transverse confinement of the pile section, a lower longitudinal reinforcement ratio of the pile section, or a larger pile spacing. Those with a shorter aboveground pile height (scour depth), or supporting a shorter pier, exhibited a larger displacement ductility capacity.