Optimum Rib Design in TMT Rebars to Enhance Fatigue Life While Retaining Bond Strength

Abstract

This paper investigates high-cycle fatigue (HCF) failure in thermomechanically treated (TMT) rebars using fractographic analysis. Most fatigue failures are found to initiate at the root of the transverse ribs, irrespective of rebar diameter. Three-dimensional finite-element (FE) analysis is used to study the effect of modifications to the rib geometry on stress concentrations at these critical locations. Modification of the ratio of the radius (r) of the root of the transverse rib to its height (h) is found to reduce stress concentrations at the rib root. A procedure combining FE analysis with ideas adapted from notch fatigue is developed to predict the fatigue life of rebars with optimum r/h ratio. The predicted fatigue life of a 16-mm-diameter rebar with optimum r/h ratio is found to be significantly higher than that of the original rebar. Pullout tests reveal that the proposed modification to the rib design does not result in any deterioration in bond strength between rebar and concrete.