Study on the load distribution factor for fatigue evaluation of steel girder bridges

Fatigue cracks have recently been reported at out-of-plane gusset welded joints in main girders of old existing steel girder highway bridges on heavy traffic routes. These cracks are potentially dangerous and may cause the main girder to break. Therefore, strategic maintenance is of particular importance in addition to periodic inspection. In this paper, a simplified method for the estimation of live load stress for fatigue evaluation is discussed on the basis of load distribution factor (LDF). The relationship between structural parameters and fatigue live load stress is investigated. The proposed method is based on 22 data sets computed by grillage analysis of 14 girder bridges with various structural parameters. Regression analyses based on these data sets are conducted and practical equations are extracted to estimate the fatigue damage caused by live load stress. Simplified equations are proposed as a function basic bridge parameters, which provide good approximate estimates for the analysis values.