Monitoring and Assessment Program for Wabasha County Bridge

Project summary:

Several members of a truss bridge over the Mississippi River in Wabasha County, Minnesota (MnDOT Bridge No. 79000) have been observed to vibrate perceptibly during moderate and strong wind gusts. These vibrations raise questions regarding the possibility of fatigue distress and have elicited emergency measures from MnDOT. At present, measured amplitudes of vibration are available for certain wind speeds, but eyewitnesses have observed vibrations with amplitudes that are perceptibly larger than those measured. Furthermore, strains and stresses induced by wind vibrations in the various truss members need to be quantified. A research team comprising faculty, staff and students of the Department of Civil Engineering at the University of Minnesota propose a program to instrument and monitor the Wabasha County Bridge, and assess the dynamic response of the bridge and evaluate the efficacy of the retrofit strategy. In order to achieve these goals, a coordinated monitoring program is proposed. As part of this program, a remote monitoring data acquisition system will be assembled using commercially available products. This system will serve as the central repository of data for the bridge, and it will be capable of transferring data remotely. This last feature is essential for the proposed work because of the distance between the bridge and the University. Furthermore, this feature in conjunction with automatic triggering capabilities will allow the U of M team the flexibility to select the threshold wind speed or response accelerations above which data is to be collected. In addition to the acceleration and wind speed data, measurement of strains in select locations of the instrumented truss members is also necessary. And, because these are dynamic strain measurements, strains must be measured using electrical resistance strain gages.