Identification of Dynamic Vehicular Axle Loads: Demonstration by a Field Study

A new identification methodology for dynamic axle loads using the superposition principle and influence surface concept was proposed in the companion paper, in which the effects of various factors such as bridge inertia force, measurement station, vehicle speed, traveling route, number of vehicles, road surface condition, and noise level were investigated through numerical simulations. In this study the proposed methodology is applied to identify the axle loads of a test truck traveling across an existing bridge. The axle load time-histories are obtained and compared to the static axle loads of the test truck. The results show that the identified dynamic axle loads are fluctuating around their static counterparts. The dynamic impact factor and load amplification factor for the axle loads under different vehicle speeds and road surface conditions are also studied. Being able to identify the real dynamic axle loads, the methodology can be applied to improve the current bridge-weigh-in-motion techniques that usually require a smooth road surface and slow vehicle movement to minimize the dynamic effects. The developed methodology will also be useful in identifying real dynamic vehicle forces on bridges, which will provide more reliable live load information for site-specific bridge fatigue assessment and performance evaluation.