Low-order model for impact load prediction on walls of navigation structures

Abstract

As commercial waterway vessels such as groups of interconnected barges (i.e., barge flotillas) traverse navigable US waterways, collision incidents may occur on nearby structures. Navigation structures such as guide walls are therefore designed to resist loads that arise during collision events. Previous studies involving full-scale experimental impact testing and high-resolution finite element (FE) impact simulations revealed that barge impact loads on wall structures are transient (dynamic) and can be influenced by: flotilla impact-speed, mass, stiffness, and configuration, as well as impacted wall mass and stiffness. Empirical load prediction equations intended for use over wide ranging wall stiffness and mass characteristics often introduce excess conservatism into the design process. Accordingly, the present study was undertaken to develop a fast-running analysis methodology capable of accurately computing impact loads for navigation wall structures with varying mass and stiffness characteristics. Typical “run-times” required by the methodology are short enough so as to facilitate probabilistic design, wherein thousands of such analyses may be required. A standalone “low-order” dynamic analysis procedure was formulated to treat flotilla-wall systems in a simplified low-resolution manner, as contrasted to computationally-expensive high-resolution finite element analysis. The low-order procedure produces time-varying impact loads and wall displacements that are sufficiently accurate for design, yet requires drastically reduced computational resources in comparison to high-order approaches. Presented herein is derivation of an equation of motion for (low-order) barge flotilla impacts on rigid and flexible wall structures. Demonstration of suitable accuracy is achieved by comparing results obtained from the low-order procedure to those obtained from high-resolution impact simulations.