Experimental measurement of dynamic load parameters for pier pile caps of high-speed railway bridges

Train-induced dynamic responses and loads in bridge pier systems are not well understood. In this study, five different piers from two separate railway bridges were investigated experimentally. The dynamic responses and loads at the bridge beam ends, pier tops, and pile caps were measured by considering various train speeds. The frequencies of the dynamic loads on pile caps were also analyzed. The results show that the induced dynamic response decreases significantly with the descending pier height. The train-induced vertical dynamic displacements are related to the axle loads and the stiffness of the pile foundation and foundation soils. The accelerations at pier tops and pile caps are very similar but noticeably less than those at beam ends. The train-induced vertical dynamic loads on pile caps increase with the total span length. The measured change of dynamic forces (Q) is approximately 20-30% of the measured peak loads (Q). In addition, the results show that the frequency (f) varies linearly with the train speed rather than with the bridge span length.