Influence of Residual Damage on Fatigue Performance of Heat-Straightened Steel Bridge Girders

Damage to highway bridge members can occur when vehicles strike a bridge member. The damage, which occurs at high strain rates, results in significant plastic deformation of the member. Heat straightening along with mechanical techniques, such as jacking or pressing, of damaged members has been demonstrated to be an effective, accurate, and cost-efficient repair technique when applied correctly. Fortunately, significant research efforts over the past 20 years have led to the development of appropriate techniques to repair severely damaged members. Less certain, however, is the fatigue and fracture performance of heat-straightened members. This paper reports on the current status of NCHRP Project 10-63, Heat-Straightening Repair of Damaged Steel Bridge Girders: Fatigue and Fracture Performance. The initial results of the study suggest that there is no degradation in the fatigue resistance of damaged, heat-straightened members as long as all nicks, gouges, and other defects are removed and the beam is returned to its initial undamaged geometry. It has been found that in the presence of residual geometric damage, the live load stresses near the impact location can be significantly altered and local stresses at fatigue sensitive details may be much higher than determined through traditional nominal stress calculations. The FHWA manual of standard practice for heat-straightening repair of steel bridges does not address this issue, and its use can therefore result in unconservative estimates of remaining fatigue life in repaired girders in some instances. A preliminary method to quantify the effects of residual damage and some of the general findings of the research are presented in this paper.