Dynamic Loading of Bridges

Management of the aging bridge infrastructure is demanding an increased understanding of all aspects of the performance of existing bridges. Loading models are an important consideration in the risk assessment of a structure. Quantifying the actual in-service dynamic response of a structure can make a significant difference in terms of keeping a bridge in service. Code-recommended allowances for dynamic effects range between 20 and 40 percent for major elements. Higher values are sometimes recommended for local effects. It is well understood that parameters including the unevenness of the road profile, the potential of frequency matching between heavy vehicles and the bridge, vehicle speed, and heavy-vehicle load levels all contribute to the dynamic response of a bridge to a single-vehicle event. Multiple vehicles increase the complexity even further. Recent new editions of bridge codes around the world tend to have diversified the methods and allowances for dynamic effects. These methods are compared, and then they are compared with a database of experimental responses measured in a range of structures in Australia and New Zealand during recent years. The results clearly illustrate the importance of each of the above parameters and that very large dynamic responses can be achieved, particularly in short-span structures.