Deformations and deflections of partially prestressed concrete T-beams under static and random amplitude fatigue loading.

Abstract

Structures are subjected to repeated cycles of loading and unloading during their service life. Such loadings may cause fatigue failure which must be considered in design. This is particularly true for partially prestressed concrete members in which service loads cause the opening and closing of structural cracks. The main objective of this research is to evaluate the behavior of partially prestressed concrete beams subjected to random amplitude fatigue loading and to better understand the parameters that control their fatigue life. The study comprises an experimental and an analytical part. The experimental program includes the evaluation of six control beams tested to failure under monotonically increasing load and ten beams tested in fatigue. The peak load in the fatigue tests was selected to simulate the frequency distribution of truck loadings on bridges. Tests measurements included deflections, crack widths, curvatures, strains in the reinforcing and prestressing steels as well as the increases of these measures during cyclic loading up to failure. The analytical program deals with a formulation for the unified solution of the analysis of partially prestressed beams in the cracked elastic range of behavior. It leads to the prediction of stresses, strains, curvatures and deflections in such members. The analytical model is shown to predict with reasonable accuracy the response of the static control beams tested in this study as well as beams tested by other researchers. Numerous conclusions related to each variable investigated are shown. It was found that random amplitude fatigue loading is more severe than constant amplitude fatigue loading and that the combination of stress range in the prestressing steel and crack width range in the concrete may be particularly damaging in fatigue. It is also observed that shear failure under random amplitude fatigue loading may need further investigation.