Influence of Impact-Induced Relative Motion on Effective Barge Flotilla Mass

Abstract

Impact-induced loads associated with barge-to-bridge collisions frequently control the design of bridges spanning navigable waterways. To design for such loads, widely used bridge design standards use an approach in which impact loads are computed from the kinetic energy of either a single impacting barge or a multibarge flotilla. Within a flotilla, individual barges are arranged into columns and rows and are connected together with lashing elements, such as wire-rope cables. During impact these lashings elongate and may rupture, influencing the degree of overall flotilla mass that contributes to impact force generation. In this study, finite-element impact simulations are used to investigate lashing deformation and relative sliding between barge columns during flotilla impacts with bridge piers. After analytically quantifying the fraction of overall vessel mass, which contributes to impact load generation, an “effective flotilla mass” is formulated for use in bridge design. Importantly, the majority of impact simulation results indicate that the effective flotilla mass is nearly equal to total flotilla mass rather than the impacting-column mass presently assumed by bridge design standards.