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A welded plate girder bridge on a main interstate highway in service for over 25 years suddenly develops a through crack in the web and flange of a fascia girder. An in-depth inspection and metallographic examination reveal the crack started in the vicinity of a welded diaphragm. The crack propagated quickly and was characteristic of a brittle fracture. Further analysis, including strain gauging and Charpy V-notch (CVN) tests, does not conclusively identify the cause for the propagation of the crack.
Fatigue analysis reveals it is very unlikely the crack could have been initiated by fatigue within the 25-year life span of the structure. The problem is traced to a 3-mm (1/8-in.) porosity defect at the root of a weld at the diaphragm connection. Propagation is attributed to out-of-plane bending in the web of the girder, high residual stresses, low toughness of steel, and cold weather.
A method for retrofitting the structure via “softening the connections” and repairing the cracked girders is selected as the course of action.
bridges, brittle fracture, fatigue, out-of-plane bending, retrofitting cracked girders
Principal, A. G. Lichtenstein & Associates, Fair Lawn, NJ