Model Experiments for Span-Vehicle Dynamics

The transient dynamics of multiple-span beam-type bridges responding to constant speed, sprung and unsprung vehicle loads are investigated experimentally. Both instrumentation and the severe problems of dynamic modeling of realistic prototypes are considered. Scaling parameters such as vehicle mass to span mass ratio, passage frequency to bridge frequency ratio, vehicle suspension frequency ratios, and loading length to span length ratio are defined and applied to the design of a laboratory test facility. Considered are problems of data retrieval for the bridge dynamics and for the vehicle heave acceleration. The latter data, needed to design safe and comfortable vehicle suspension systems, are essential in future urban and interurban transportation systems. Span data are presented in nondimensional form, suitable for design purposes. Typical data for a six-span bridge show that the peak bending moments may exceed four times their respective static moments for a vehicle at its crawl speed.