Abstract :
A method for the fatigue reliability assessment of post-tensioned concrete bridges is applied to a wide spectrum of highway bridges covering over the most commonly built with this technique. The objective is to obtain the fatigue performance of reinforcing bars and prestressing strands. First, bridge geometry and properties are defined, and different degrees of prestressing are considered. The reliability indices are worked out for ultimate limit state (ULS) of fatigue and bending and for heavy and light traffic conditions. In this way, a method to identify the minimum prestressing required by a given probability of fatigue-induced failure for a 100-year service life is derived. Fatigue in the steel elements and cracking are closely related, mainly in the posttensioning tendons, where the fretting fatigue effects are of concern. Thus, based on the results of the fatigue analysis, the paper identifies an objective criteria to check the serviceability limit state (SLS) of decompression. In comparison, current criteria in bridge codes seem to be overconservative. Conclusions regarding the main factors affecting bridge performances under fatigue are also drawn.
