PROBABILISTIC FRACTURE MECHANICS ASSESSMENT OF SERVICE SAFETY FOR OLD STEEL BRIDGES

There are many old steel bridges on Chinese highway and railway lines. These old steel bridges are often required to carry an increasing volume of traffic, usually consisting of truck heavier than those considered in the original design. Therefore, the remaining fatigue life and service safety of old steel bridges is a topic of considerable importance, particularly for their operators. An improved method for the estimation of the actual fatigue life and safety of such structures are required in order to make their continued safe use possible while avoiding unnecessary repairs or replacements. According to the fatigue failure mechanism of riveted steel bridges, two probabilistic fatigue failure models –brittle and ductile are proposed. Moreover, the corresponding limit-state equation and the basic variables based on probabilistic fracture mechanics are identified, and the uncertainties associated with them are quantified. A single-angle probabilistic fatigue failure model(SAPFFM)of riveted bridge members is proposed. Furthermore, a reliability analysis program-SAPFF, based on Monte-Carlo method, is developed to compute the fatigue failure probability of SAPFFM. Then SAPFFM is used to predict the time fatigue reliability of main truss members of Zhejiang Road Bridge in Shanghai. Based on the assessment results, the probabilistic remaining fatigue life, inspection intervals and maintenance strategy are determined.