Fatigue Assessment of Bridge Members Based on In-Service Stresses interim report no. 1 August 1996 (FHWA-OK-95-07) 2196

Abstract

Construction problems involving poor welding practice occurred during widening of the U.S. 69 bridge over the South Canadian River. As a result of these problems, cc>ncerns developed regarding the remaining fatigue life of the bridge. A research project was initiated to address these concerns The first portion of the project involved instrumenting the bridge and recording strains under both known loads and normal traffic. These measured strains were used to calibrate an analytical model prepared as a second part of the project. The analytical model was then used to determine the critical location for fatigue. A third part of the project involved conducting laboratory fatigue tests on beam specimens with a welded detail similar to the detail of concern on the bridge. The results of the fatigue tests were used to construct an S-N curve for the detail. Based on the developed S-N curve and stress ranges from computations and measurements, the remaining fatigue life of the bridge is estimated. The estimate indicates that the remaining fatigue life of the bridge is infinite. The reader is cautioned against using the results of this research as justification for poor welding practice. The laboratory tests show that poor welding significantly reduces the fatigue life of a beam. The long remaining life which is estimated for this particular bridge is a result of the low stress ranges in the bridge, which compensate for the inferior quality of the welds. The same result should not be expected in every case.