Dynamics of Cambered Rapid-Transit Bridge

Numerical solutions are presented concerning the influence of vehicle speed and roadway live load camber on the dynamic bending moments and deflections of a rapid-transit bridge traversed by a rapid-transit vehicle. The vehicle is simulated as a four-degree-of-freedom lumped parameter system, whereas the bridge is considered as a simply supported beam in dynamic flexure with inertia and equivalent distributed viscous damping in the formulation of the governing equations of motion. For the rapid-transit system considered, it is found that higher speeds produce higher maximum bending moments and deflections; camber is slightly beneficial at high cruising speeds (50 mph-60 mph) but in general it results in larger maximum and rms displacements and bending moments at low cruising speeds (20 mph-30 mph). The solutions also show that negative bending moments and deflections occur at these speeds in contrast to the static analysis (zero speed) in which the bending moments are always positive and the deflections downward.