Remote Monitoring of Distortional Fatigue in Multi-Girder Steel Bridges

Project summary:

A remote monitoring and assessment program for a multi girder steel bridge on skew supports and typical of those found throughout Minnesota is proposed to quantify the magnitude of distortional fatigue stresses in the girder webs at the connection to diaphragm plates in the negative moment region of the girder. Vulnerability to distortional fatigue in steel plate girders of multi girder bridges exists when diaphragm connection plates are attached to the girder webs but not to the flanges. The magnitude of distortional stresses is worsened by skew supports, fixity of the tension flange in the negative moment region, and stiff diaphragms. To date, instances of distortional fatigue cracking have not been reported in Minnesota, but the MnDOT Office of Bridges and Structures has ascertained that highway officials in other states have begun to observe cracks at the weld between diaphragm connection plates and web plates in skew, multi girder steel bridges. The proposed work is designed to collect representative field data on the magnitude and frequency of out of plane bending stresses at web diaphragm connections of typical interior and exterior girders in multi girder bridges on skew supports. A research team comprising faculty, staff and students of the Department of Civil Engineering at the University of Minnesota proposes a program to instrument and monitor a typical multi girder steel highway bridge on skew supports and assess the frequency and magnitude of distortional fatigue stresses in the web plates, as well as to evaluate the impact of these stresses on fatigue life. As art of the proposed study, an existing multi girder steel highway bridge which is typical of bridges throughout Minnesota will be elected for instrumentation in the Twin Cities greater metropolitan area. Field instrumentation will be used to monitor the strain changes at critical locations in the selected bridge, and an existing remote monitoring data acquisition system will be upgraded usin