ASSESSMENT OF THE FATIGUE LIFE OF A STEEL GIRDER BRIDGE

To assess the fatigue life of welded, cover plated steel girders, strain gauges were placed in critical locations on the superstructure of the Leslie Street Overpass on Highway 401, Toronto Bypass. Data were gathered for 200 hours in 12-hour continuous tape recording sessions. Analysis of the data revealed that normal traffic caused a live load stress peak of 4,000 psi (27.50 N/mm2) only once in 10 hours, which is less than 50 percent design live load stress. Available stress history data gathered by various agencies during the past few years seem to indicate that design stress does not occur at all or it occurs with such a low frequency that it precludes the development of any fatigue situation. The phenomenon is associated with the low probability of simultaneous, multiple presence of loaded commercial vehicles on a structure. The problem is therefore statistical in nature; its recognition appears to be in conflict with the prevailing concept used in fatigue consideration of highway bridges.