Dynamic load allowance in different positions of the multi-span girder bridge with variable cross-section

To investigate the dynamic performance of the multi-span girder bridge under moving vehicles, based on the synthesis modal method, the program for vehicle-bridge coupled vibration analysis is completed firstly. According to the numerical simulation, the estimation formulas in current codes (China and UK) and some other references (USA) have been proved problematic. Also, the roughness and the critical speed are fully discussed. In addition, the DLA in the side span is largely different from that in the other span, and the DLA in other spans are almost the same. The DLA of middle span is little influenced by the number of spans. However, the DLA of side span will be stable only when the number of spans is not less than five. And when the number of spans is not more than five, the DLA of the three-span bridge is biggest, that of the five-span bridge is second, and that of the four-span bridge is smallest. It has been proved that the DLA in current code is not rational enough, as it does not distinguish the positions. It may provide some basis for the design and evaluation of the dynamic performance of bridges to moving vehicles.