Live load and dynamic load are important load components for highway bridges. rational load models are needed for the development oflrfd design codes. the paper summarizes the available data base andcalculation procedure. live load model is based on the truck surveys. maximum 75 year load effects are derived by extrapolation and simulations. calculations are performed for single lane and two lane bridges. for two lanes, the maximum effect is obtained for two trucks side-by-side, with fully correlated weights. for the maximum 75 yearmoment or shear, each side-by-side truck is represented by the maximum 1.5 month truck. the approach to selection of the design live load is formulated. the acceptance criterium is uniformity of the mean-to-nominal ratio for various spans. dynamic load is based on limited test data and special simulations. the major factors influencing dynamic load are the road roughness, bridge dynamics (frequency of vibrations) and vehicle dynamics (suspension system). tests and analysis indicate that dynamic load (as a fraction of live load) is reduced for heavier trucks. it is also lower for two trucks compared to a single truck. it is recommended to use a uniform dynamic load for all the span lengths larger than 20 ft. this paper appears in transportation research record no. 1290, third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 1.
Abstract