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Fatigue Reliability of Prestressed Concrete Girder Bridges (Analysis, Composite Structures, Cracking).
Rajeh Z. Al‐Zaid
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Abstract
The main objectives of this investigation were: (1) to develop a general stress-strain analysis procedure for cracked and uncracked, composite and noncomposite prestressed concrete beams, and (2) to develop a reliability-based model for the evaluation of fatigue life of prestressed concrete girder bridges. Based on equilibrium and compatibility, a new solution to the analysis of prestressed and partially prestressed composite sections in which cracking is assumed to occur under service loads is developed. The effects of shrinkage, static and cyclic creep of concrete, and relaxation of steel are efficiently incorporated in the developed model. Hence, the model is capable of predicting the stresses and strains in the constituent materials of the composite section at any time t and number of cycles N. Solutions for the special cases of uncracked composite sections, cracked and uncracked noncomposite sections as well as expressions for the cracking and decompression moments are also presented. A parametric analysis is conducted to study the effects of various parameters on the variations of stresses in the constituent materials with time. Models for the evaluation of fatigue life of prestressed concrete girder bridges are presented. Two limit states are considered, namely, the fatigue strength and cracking limit states. The fatigue strength model utilized available S-N curves derived for structural materials under constant amplitude loading and Miner's rule to evaluate the fatigue life under variable amplitude loading. The fatigue cracking model is concerned with the calculation of the probability distribution function of time to first cracking. Applications to some practical cases are considered. On the basis of this investigation, it is concluded that fatigue in prestressed concrete girder bridges designed according to the AASHTO specifications is not a limiting design criterion. Recommendations for future research needs are also presented.