Shoreline Distance-Based Tsunami Fragility Curves for Steel Moment-Resisting Frame Buildings

This study develops collapse fragility curves for a representative steel moment-resisting frame building exposed to idealized tsunami-loading scenarios, explicitly incorporating shoreline distance as an organizing spatial variable. Nonlinear static analyses are performed in SeismoStruct for braced and unbraced configurations, using the maximum interstory drift ratio as the engineering demand parameter. Drift-based damage states are defined according to ASCE 41-23 and FEMA 356 to interpret damage progression, while the probabilistic formulation focuses on the collapse limit state using a lognormal model with total dispersion based on FEMA P695. Triangular and rectangular tsunami-load distributions are considered to assess the influence of load-pattern assumptions. The braced model remains below global collapse within the analyzed intensity range and is retained as a comparative case, whereas the unbraced model reaches global instability and provides the collapse-response information used to construct the fragility curves. The median collapse inundation depth is approximately 14.1 m for the triangular distribution and 11.7 m for the rectangular distribution, corresponding to shoreline distances of approximately 97.5 m and 157.5 m, respectively. The results suggest that shoreline distance can support a spatial interpretation of collapse vulnerability for preliminary coastal-risk assessment, provided that the idealized and site-dependent nature of the adopted distance–depth–velocity scenarios is properly recognized.