Dynamic Response of a Floating Bridge to a Moving Light Rail Train

This study pertains to the vehicle–bridge interaction analysis of Homer M. Hadley Memorial Bridge located in Seattle, Washington. The bridge carries the westbound and reversible lanes of Interstate 90 across Lake Washington and is the widest and fifth-longest floating bridge in the world. Based on the proposed plan to design and construct a light rail transit system for the bridge, a detailed three dimensional finite element model of the west spans of the bridge was developed for dynamic analysis. The bridge model includes a fixed span, floating span and transition span connecting the fixed span and floating span. Two track bridge structures (one at each side of the transition span), anchors and a set of nonlinear springs to simulate variable buoyancy forces are presented. An innovative modeling approach based on bridge-vehicle coupled system was proposed to evaluate the bridge behavior under moving train loads. The light rail vehicle was separately modeled as a coupled system with rail, which includes the flexibility of the rail fasteners as well as dynamic characteristics of the vehicle. The train is a four-car consist composed of a three-section passenger vehicle with articulation joints between the bodies. The suspension system of the vehicle was modeled by nonlinear springs and dashpots. The vehicle was moved over the rail profile dynamically. Wheel reactions were extracted and applied to the rails in the bridge model. The floating bridge model was analyzed for a set of loading scenarios including different storm conditions and vehicle speeds. The vehicle accelerations, rail stresses, track bridge displacements and stresses were extracted.