The dynamic response of bridges to heavy vehicles is the result of a complex interaction between the bridge, vehicles using the bridge and the road profile. The Australian Bridge Design Code, like others, uses a Dynamic Load Allowance (DLA) which is applied to the vehicle static mass to make provision for this complex interaction. The drivers for this research are the need to extend the life of an ageing bridge infrastructure by better understanding the actual bridge response to heavy vehicle traffic, and the introduction of the SM1600 loading in the proposed Australian Standard for Bridge Design. This report provides a summary of dynamic testing carried out on approximately 80 bridges in Australia and New Zealand. It compares the results of these tests with the current DLA provisions in the Australian Bridge Design Code and makes recommendations for extrapolating and modifying these provisions. As part of this project vehicle bridge interaction (VBI) software was developed to analyse the theoretical response of a bridge to vehicles with different suspensions, travelling at a range of speeds over nominated road profiles. The software was used to perform a parametric study of the critical variables including: vehicle suspension, mass and speed; road profile; and bridge span, frequency, flexibility, and damping. Many theories about vehicle bridge interaction developed from field testing of bridges have been confirmed and quantified. Principal outcomes of the parametric study were that the road profile generally was more critical than bridge characteristics for DLA, highlighting the importance of monitoring and maintaining pavements in the vicinity of bridges. DLA is also sensitive to vehicle mass, speed and suspension type. Based on the outcomes of this study, recommendations for dynamic load allowance in the new bridge code were developed. Further development of the VBI software is recommended. (Author/publisher)
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