Bridge weigh-in motion : development of a 2-D multi-vehicle algorithm

Abstract

Road transport and the related infrastructure are clearly an integral part of the economic, political and social development of the western world. Road pavements and bridges can be greatly damaged by excessively heavy vehicles. Great economies in the cost of road pavements can thus be achieved if truck and axle weights can be maintained within legal limits. Consequently, there has been a considerable research effort at European level on technologies for weighing trucks (and axles) while they are moving. The hope is that the accuracy of these so-called weigh-in-motion systems can be enhanced to such a level that they can be used directly for enforcement purposes. Bridge Weigh-in-Motion (B-WIM) systems are based on the measurement of the deformation of an existing bridge, and the use of these measurements to estimate the attributes of passing traffic. The purpose of this research is to enhance accuracy and usability of such B-WIM systems. B-WIM accuracy is heavily dependent on exact calibration, i.e., the correct choice of influence line or influence surface. A new method of influence line inference is presented. This matrix method has been developed to provide a fully automatic and accurately calibrated influence line from measurements of the bridge response to a truck of known weight. The B-WIM algorithm is extended to allow for the variation in the transverse position of the truck on the bridge. This involves moving from an influence line to an influence surface. Various methods were employed to calculate the transverse position of the crossing calibration vehicle. The calibration procedure to find the influence surface, solely from experimentally measured data, is presented. The accuracy of existing B-WIM systems is strongly affected by the number of vehicles present on the bridge during measurement. A B-WIM algorithm has been developed to cater for multi-vehicle events, thus removing unnecessary constraints regarding the operating environment of future B-WIM systems. The developed algorithms are verified using data from two test sites in Sweden and one in Vienna, Austria. A clear trend between erroneous results and the transverse position of the crossing vehicle is noted. The study suggests that the accuracy of B-WIM systems can be significantly enhanced through the use of a 2-D algorithm, based on the use of an influence surface. Adoption of the 2-D algorithm is also shown to allow the accurate determination of vehicle weights during multi-vehicle events. A detailed Finite Element model of an instrumented bridge and calibration vehicle is constructed and combined with a program that derives the interaction forces for bridge and vehicle models. These models are validated using measured data and a number of simulations performed which confirm the suitability of the 2-D B-WIM algorithm for such bridge types.