Numerical Investigation of Scoured Bridge Response Under Ship Collisions

Abstract

Abstract Bridges crossing navigable waterways may be subjected to scour within their service life. Scour has complex mechanisms due to its site- and time-dependent characteristics, making it challenging to predict the scour depth accurately. Local scour alters the soil support conditions around bridge foundations, which may ultimately lead to potential structural damage and failure. Accidental ship collisions also pose threats to the overall integrity of bridges with navigable channels. However, current bridge design specifications and guidelines treat these two hazards independently, where intact bridge configurations are adopted as the design and analysis basis for ship collisions. To date, there have been limited studies investigating the dynamic behavior of bridges with scour subjected to ship collision loads. In this study, comparisons are made among four empirical prediction models for the equilibrium local scour depth around cylindrical piles. The accuracy of each prediction model is evaluated by using historical laboratory test records. Then, a four-span continuous bridge is chosen as the representative structure to study the applicability of these prediction models. The effects of key parameters such as flow depth, flow velocity, pile diameter and bed sediment size are analyzed. To study the dynamic behavior of bridges with scour under ship collisions, detailed numerical models of both the bridge and the ship bow are developed in LS-DYNA. The soil-structure interaction is modeled as a nonlinear spring system considering the pile group effect. A selection of typical scour scenarios based on the optimal scour prediction model with the least estimation error is considered. The maximum displacements at the top of bridge piers and group piles are investigated. The obtained simulation results can provide bridge engineers with not only guidance on the accuracy of different scour prediction models, but also a better understanding of the structural behavior of bridges with scour under accidental ship collisions.