Effects of tsunami wave and bathymetric parameters on hydrodynamic forces and structural fragility

Tsunamis pose serious risks to coastal regions, often causing severe structural damage and loss of life. Although current design codes prescribe simplified representations of tsunami loads, it remains uncertain whether these assumptions fully reflect the demands imposed by real events. This study examines how tsunami-induced forces and structural vulnerability are influenced by offshore wave characteristics and coastal bathymetry. Tsunami propagation was simulated with a high-resolution numerical model, and inundation depth and flow velocity were extracted at nearshore stations and converted into hydrodynamic forces using ASCE 7–22 provisions. These forces were then applied to nonlinear structural models, and fragility curves were derived under an integrated structural reliability framework. The analysis considers variations in wave period, crest amplitude, trough amplitude, and the number of wave cycles. Bathymetric parameters, including offshore and onshore slope, seafloor friction (represented by the Manning coefficient), and the distance of structures from the shoreline, are also investigated. Results show that increases in Manning coefficient, bathymetric slope, wave period, and shoreline distance are generally associated with reduced structural fragility. For example, increasing the Manning coefficient from 0.025 to 0.04 reduces maximum onshore and offshore tsunami forces by 41 % and 55 %, respectively. Steeper offshore slopes reduce fragility, with serviceability failure probability dropping from 40 % to 3 % as slope decreases from 1/75 to 1/225. Longer wave periods (20–35 min) reduce onshore force by 56 % and serviceability failure probability from 100 % to 0 %. Crest amplitude strongly amplifies vulnerability, with serviceability failures increasing from 0 % at 5.7 m to 70 % at 6.9 m, while trough amplitude has little influence. Additional wave cycles increase cumulative vulnerability, raising serviceability failure probability from 8 % (one wave) to 37 % (three waves). Structures located farther inland consistently experience reduced loading due to energy dissipation during propagation. A comparison with ASCE 7–22 highlights key discrepancies, and new normalized curves are proposed to improve tsunami force estimation. These findings provide a more comprehensive understanding of tsunami effects on structures and support evaluation of the adequacy of code-based assumptions. • Tsunami wave simulations are conducted with varying offshore wave and bathymetric parameters. • Effects of wave and bathymetric conditions on tsunami-induced forces are quantified. • Code-based and simulation-based tsunami forces are compared and assessed. • Normalized tsunami flow curves are developed to aid design improvement. • Fragility curves are generated for different wave and bathymetric scenarios.