Bridge dynamic responses due to road surface roughness and braking of vehicle

The dynamic behavior of a multi-span non-uniform continuous bridge under a moving vehicle is studied by considering the effect of interaction between the structure, the road surface roughness and the vehicle. The bridge is modeled as a multi-span continuous Benoulli-Euler beam with non-uniform cross-section on linear spring supports with large stiffness. The vehicle is modeled as a group of moving loads at a fixed spacing. Numerical simulation and laboratory tests were performed on a single-span and a two-span beam. The first span is found to exhibit smaller dynamic responses compared with the other spans for both constant speed vehicle and with vehicle braking due to the smaller initial conditions of the vehicle at entry of the span. Braking of the vehicle generates excitation forces covering a wide range of frequencies and this requires a large number of vibration modes for an accurate prediction on the responses. Since braking in one span would create response in different spans, a more correct definition of impact factor with vehicle braking should be based on a comparison of the maximum dynamic and static responses at the same span in which braking occurs.