SC Solutions was responsible for developing a global model of the Fruitvale Avenue Railroad Lift Bridge. The Army Corps of Engineers maintains and operates the bridge which provides a rail link between the island of Alameda and the city of Oakland. The bridge is primarily a steel latticed member truss structure with concrete foundation piers below each of the steel towers. The lift span is raised and lowered through a system of counterweights suspended on cables, which ride on guides inside the tower truss structures.
The model was developed for dynamic response spectrum analysis in the GT STRUDL program. Because the bridge is used only for rail traffic, much of the time the lift span is raised to mid-height of the towers. Sometimes, the span is also kept in a fully raised position. The only time the span is lowered is when trains are expected to cross the estuary. Therefore, the model had to accommodate these three geometric configurations, and be analyzed in all three lift span positions.
The counterweights were also modeled explicitly as were the cables from which they were suspended. Dynamic behavior of the "pendulum mode" of the counterweights and cables also had to be considered in these analyses.
