Fatigue cracks have been reported at out-of-plane welded gussets in main girders of existing steel highway bridges on severe traffic routes. This paper describes a simplified method to estimate live load stress of main girder due to the passage of the F load (F load stress) for fatigue evaluation using load distribution factor (LDF). Structural dimension data were prepared through the design of 29 bridges with various parameters such as span length, girder spacing, etc., based on the past design code. F load stress data obtained by FE analyses of 29 bridges were also prepared. Regression analyses were conducted based on the data sets, and simplified equations that provide approximate estimates for the analysis values were extracted.
