Fatigue strength of prestressed concrete girder bridges

A model for evaluating the fatigue life of a prestressed concrete girder bridge is presented. Experimental studies indicate that fatigue is a random phenomenon. Therefore, the approach is based on probabilistic methods. The fatigue life of the prestressed concrete girder is estimated from the fatigue properties of its components, namely, the cast-in-place slab, precast beam, prestressing steel, and, if partially prestressed, the tension reinforcement. The model utilizes the available S–N curves for structural materials and Miner's rule to evaluate the fatigue life under variable amplitude loading. A model for determining the distribution function of time to first cracking is also presented. To demonstrate the developed models, a typical prestressed concrete girder bridge is analyzed. On the basis of this investigation, it is concluded that fatigue in prestressed concrete girder bridges designed according to the American Association of State Highway and Transportation Officials specifications is not a limiting design criterion. Key words: bridges, fatigue, prestressed concrete, structural reliability.