A Study of Sources of Error in BWIM Systems using a Model Bridge

Bridge-weighing-in-motion (BWIM) uses dynamic responses of an instrumented bridge to estimate the weights of vehicles moving at normal speeds. Since working with actual bridges is relatively expensive, the intricacies of and the sources of error in a BWIM system are best explored through a scale lab model. This project describes the experimental investigation of BWIM system on a 1/10 scale model of the South Perimeter Bridge in Winnipeg, Canada. The model bridge structure was fabricated using polycarbonate (Lexan) sheets, and was designed to have natural frequencies that matched to those of the actual bridge. The model was instrumented at two different locations with piezoelectric sensors for estimating the velocity, transverse position and class of the vehicles. It was also instrumented with electrical strain gauges at three transverse sections for determining the gross vehicle weights. A video camera was also used for determining the velocity profile of the model truck, it being noted that unlike the case in actual bridges, the velocity of the model truck was not constant over the length of the bridge. The objective of this project is to identify sources of error in BWIM systems with the aid of Model Bridge. One of the objectives is to verify three methods which were tested on the case study bridge. The methods were further investigated on Model Bridge to obtain 95% confidence interval over real bridge BWIM testing.

Field measurements are very accurate in estimating fatigue loading. This project also reports a case study of the fatigue assessment on an ageing steel bridge in Winnipeg, Manitoba, which integrates a BWIM system. The identified sources of error in the fatigue evaluation using the BWIM system, if addressed properly, are expected to increase the accuracy of fatigue analysis using BWIM data.

Project Team: Ms. Sofia Faraz; Dr. Aftab Mufti; Dr. Baidar Bakht; Dr. Douglas Thomson; Dr. Karim Helmy; Dr. Basheer Algohi; Dr. Chad Klowak; Mr. Brendan Pachal