Experimental analysis of an asymmetric reinforced concrete bridge under vehicular loads

Dynamic response of a three span continuous bridge has been determined by full scale experiments on the bridge. In the experiments, a heavy vehicle was driven across the bridge at different speeds and along different lanes of travel and the strains were recorded at different locations. The bridge was made of reinforced concrete and was asymmetric in plan and in elevation. Frequencies and modes of vibration excited by the vehicle were determined. The dependence of the dynamic amplification on bridge location and vehicle speed was investigated and dynamic amplifications up to 1.5 were recorded, which was higher than values predicted by bridge design codes. It was evident that when this asymmetric bridge was loaded by an asymmetric forcing function, higher modes, which are lateral and/or torsional in nature, were excited. Dynamic modulus of elasticity and the support stiffness influenced the natural frequencies of the bridge, which in turn influenced the dynamic amplifications. Larger than anticipated dynamic amplification factors and the excitation of lateral and/or torsional modes should be of interest and concern to bridge engineers.