Dynamic Analysis of Cable-Stayed Bridges Considering Soil-Structure Interaction under Near-Field Motions

This research investigates the dynamic response of cable-stayed bridges to near-field ground motions, incorporating the effects of soil-structure interaction (SSI), ground motion directionality, and ground motion characteristics. A 1/60-scale experimental model of a typical cable-stayed bridge, based on the "Twin Bridge" in China, was designed and fabricated for laboratory testing. The experimental program employed seismic records from far-field, non-pulse near-field, and pulse-type near-field events, applied in longitudinal, transverse, and diagonal directions to the bridge model. A key innovation of the experimental setup was a novel box-spring system that simulated various foundation soil stiffness conditions, enabling a detailed investigation of SSI effects. The study was conducted in two phases: a single-axis phase focusing on transverse near-field ground motions and a multi-axis phase examining pulse-type near-field ground motions applied at various incidence angles. A three-dimensional numerical model of the bridge was developed and validated against experimental results, and it was further used to analyze bridge response for additional incidence angles not tested in the laboratory. The results revealed that pulse-type near-field motions significantly amplify bridge demands, particularly when the foundation soil is more flexible. Directionality effects were also prominent, with a significant coupling between longitudinal and transverse displacements observed at angles of 45° and 135°. Additionally, the correlation between Peak Ground Velocity (PGV) and Peak Ground Acceleration (PGA) highlighted the reliability of velocity-based intensity measures as indicators of seismic performance. Predictive equations were developed to estimate dynamic displacements of the bridge deck and towers, incorporating the influence of ground motion characteristics, angle of incidence, soil flexibility, and the bridge’s dynamic properties. This comprehensive study underscores the importance of considering SSI, pulse-type ground motions, and directionality for the seismic design of cable-stayed bridges. The findings provide valuable insights for improving the safety and resilience of such structures in earthquake-prone regions.