A 12 meters long steel beam-concrete slab has been shaken under six different earthquakes and harmonic loadings. Tests are done with and without a car on top of the bridge. The six different harmonic motions applied to the system to identify the resonant frequencies of the bridge. It has been observed that the 1 ton vehicle has reduced the seismic response by 20% for the 20 tons of superstructure. Bearings have been used to isolate the superstructure from the substructure.