This paper develops a Bridge Weigh-In-Motion (BWIM) system which uses accelerometers instead of strain gauges to estimate the Gross Vehicle Weights (GVWs) of passing vehicles. The statistical properties of vehicles at a site (such as mean GVW) tend to be consistent so these properties can be a useful indicator of bridge condition. Conventional BWIM systems using strain gauges are effective in finding traffic loads but strain gauges are not sensitive to bridge damage, except locally at the sensor location. Acceleration on the other hand, is influenced by damage at any location . For this reason, the focus of this paper is the design of a BWIM system using accelerometers. To assess the feasibility of the system, the acceleration responses of a bridge at midspan are simulated for a single quarter car axle passing over it at different weights. It is shown that the system is substantially linear, i.e., amplitude is related linearly to axle weight. The concept of BWIM is to minimise the difference between measured and theoretical responses to applied load – inferred axle weights are those that minimise the sum of squared differences. The theoretical response is calculated as a linear combination of the responses to unit axle loads. A vehicle bridge dynamic interaction analysis is carried out to simulate a population of 120 trucks crossing a typical bridge. The acceleration signals are extracted from these analyses. The BWIM algorithm is applied to infer the vehicle weights from these simulated ‘measured’ acceleration responses. The calculated axle weights are moderately accurate – classified as Class C according to the COST 323 Weigh-in-Motion classification system . The relationship between axle weights and acceleration response is influenced by the bridge condition. It is therefore concluded that any change in bridge condition will manifest itself as an incorrect change in inferred vehicle weights.
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