An Improved Equivalent Static Analysis Method for Barge-Bridge Collision Design

In the United States, barge impact resistant bridge design typically involves static application of code-prescribed impact loads. However, recently conducted full-scale experimental collision tests led to the discovery of significant inertial effects not accounted for in existing design provisions. Subsequent to the experiments, a numerically efficient dynamic (time history) analysis procedure was developed to quantify transient impact loads and load effects. While this technique is capable of accurately predicting member design forces, a time-domain dynamic analysis may not be warranted for the design of certain structures, or during preliminary design iterations when detailed structural parameters cannot be adequately estimated. In this paper, common modes of dynamic pier response arising during barge impact loading are characterized for a wide range of bridge configurations. Dynamic amplifications of pier member design forces are quantified by comparing forces obtained from time-history dynamic simulations to those obtained from static analyses. As a means of capturing dynamic amplification effects, an equivalent static analysis procedure is developed that mimics pier response during dynamic barge impact events. The proposed static method is shown to produce conservative predictions of both pier and substructure design forces, relative to dynamic analysis.