Equivalent Shear Force Method for Detecting the Speed and Axles of Moving Vehicles on Bridges

Traffic monitoring, particularly on the gross vehicle weight (GVW) and axle weights (AWs) of heavy trucks, provides valuable information for the design and performance evaluation of bridges. Bridge weigh-in-motion (BWIM) is a recently developed technology that uses the bridge as a scale to estimate vehicle weights. For BWIM systems, the acquisition of vehicle speed and axle spacing (AS) is a prerequisite for accurate identification of the AWs and GVW. Traditionally, axle detectors are placed on the road surface to detect vehicle axles. However, axle detectors are not durable due to their exposure to the traffic. Also, their installation and maintenance also cause disruption to the traffic. For these reasons, the concept of the nothing-on-road (NOR) BWIM is proposed. Most existing NOR BWIM systems require additional sensors for axle detection, which limits their applicability. In this paper, a novel equivalent shear force method (ESF) is proposed to identify vehicle speed and AS by using the flexural strain signal acquired from the weighting sensors. Compared with the existing NOR BWIM systems, the proposed method does not require additional sensors for axle detection, making it desirable for commercial BWIM systems. The effectiveness and accuracy of the proposed method are demonstrated through numerical simulations and validated through an experiment using scaled model tests. Parametric studies are also conducted to investigate the effects of various factors on the accuracy of the proposed method.