Tsunami loads on bridge bents: pier interaction and dynamic amplification

Abstract As natural hazards continue to intensify, tsunami waves have become one of the most destructive events affecting transportation infrastructure, especially bridges. Although structural engineering research has traditionally been concentrated on seismic loading and earthquake-resistant bridge design, tsunami-induced forces can also significantly impair bridge serviceability and seismic performance, representing a serious risk to structural safety. This study examined the dynamic forces imposed by tsunami waves on bridge piers through combined hydrodynamic and structural analyses, aiming to evaluate the influence of load dynamics on the system response. The investigation first compared the total hydrodynamic forces acting on a multi-column bridge bent with those on a single-column pier using hydrodynamic simulations. The influence of column spacing on the resulting overturning moment was then assessed. In addition, the characteristics of tsunami wave loading were further investigated through structural analyses incorporating soil–structure interaction of the pier-foundation-soil system. The results demonstrated the significant influence that column pier arrangement has on the hydrodynamic forces acting on bridge bents, with the multi-column bent resulting in an increase by at least 25% in the total force transmitted to the foundation compared with the single-column pier. Furthermore, the structural analysis demonstrated that neglecting the dynamic component of tsunami-induced loading led to a significant underestimation of its damaging potential. To address this issue, a dynamic amplification factor associated with the surge Froude number was proposed, to estimate the dynamic response of bridge piers from static analysis. This enables consideration of the dynamic effects into existing hydrodynamic load formulations in design codes. The proposed amplification factor ranged from 1.0 to 2.0, highlighting its dependence on flow conditions and its significance for practical design.