Simplified Impact Load Model Analysis of Vehicle-to-Bridge Pier Collision

As a key member of the bridge substructure, the pier is always the most critical part under a variety of hazards, among which vehicle-induced impact is a rare but extreme load hazard that may result in significant structural damage and even the full failure of the bridge. Current design provisions, such as those in the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications, adopt a constant equivalent static force (ESF) of 600 kips to represent vehicle impact loads. However, this simplified assumption neglects key parameters—such as vehicle speed, mass, and pier geometry—that significantly influence impact behavior. This study develops and evaluates two simplified impact load estimation models to improve the accuracy and practicality of design-level assessments: a reduced-order dynamic model and a response surface model. The reduced-order dynamic model captures vehicle–pier interaction through a simplified mass–spring system, while the response surface model uses regression-based relationships derived from extensive finite element (FE) simulations conducted in LS-DYNA. Sensitivity analyses identify the most influential parameters governing impact loads, including vehicle velocity, cargo mass, pier diameter, and impact height. The results show that both models can effectively predict peak dynamic and equivalent static impact loads, providing more accurate and physically interpretable results than the current constant-load approach. The proposed frameworks offer practical tools for bridge engineers to evaluate vehicle–pier collision scenarios and can be further extended for use in truck-to-pier and ship-to-pier impact analyses.