Assessing remaining fatigue life of existing riveted steel bridges

Assessing the remaining fatigue life for continuing services is critical to aged riveted steel bridges, especially for decisions on structure replacement, deck replacement or other major retrofits. Experiences from engineering practices have indicated that fatigue analysis based on specification loads and distribution factors usually underestimates the remaining fatigue life of existing bridges by overestimating the live load stress ranges. Fatigue evaluation based on field measured stress range histograms under actual traffic load proves to be a more accurate and efficient method for existing bridges. This paper describes the application of such method in assessing the remaining fatigue life of riveted bridges. The special characteristics, fatigue cracking mechanisms, typical crack types, and fatigue strength of riveted members are discussed. Current provisions on fatigue evaluation of riveted bridge members from various AASHTO specifications are reviewed. Fatigue evaluation results of three major highway riveted bridges based on field strain measurements are summarized. Finally a procedure for evaluating the fatigue life of existing bridges based on case-specific field strain measurement is proposed for bridge owners and practicing engineers.