Bridges

Reliable live traffic data collection is crucial for effective pavement life prediction, fatigue estimation, vibration control, maintenance, and condition assessment of the bridge structures. Bridge weigh-in-motion (BWIM) is a technology utilising a series of conventional strain gauges to characterise the traffic data including speed, number of axles, axles spacing, and gross and axle weight of the passing vehicles.

A short-span cable-stayed bridge over the Great Western Highway in the state of New South Wales in Australia is considered as a case study to test and validate the performance of the BWIM axle detection schemes. The bridge is supported by four longitudinal girders sitting on the cross beams which are connected to the bridge cables.

The bridge structure including the cables, the girders and the deck have been instrumented with several uni-axial and shear strain gauges to measure the axial, the bending and the shear strains at various locations along the bridge. Data are collected using an HBM Quantum-X data acquisition system and are transferred into a server through 4G connection for signal processing.

The purpose of this work is then to identify the sensor arrangement through which the closely-space axles can reliably be detected regardless of the vehicle’s speed, travelling direction and lateral location on the bridge. It is demonstrated that the axial strains on the cables and bending strains under the girders are unable to identify closely-spaced axles. On the contrary, it is revealed that the longitudinal strains under the deck can identify the closely-spaced axles, provided they are accurately positioned under the wheel path. Finally, it is illustrated that the shear rosettes at the end of the span are well capable of producing accurate results for closely-spaced axles irrespective of the location of the vehicle on the bridge.