Acceptable lower bound of the ductility index and serviceability state of RC continuous beams strengthened with CFRP sheets

Abstract

Although many in-situ Reinforced Concrete (RC) beams are of continuous constructions, there has been very little research on the behavior of such beams strengthened with Fiber Reinforced Polymer (FRP) laminate. Ductility is even more important for statically indeterminate structures, such as strengthened continuous beams, as it allows for moment redistribution through the rotations of plastic hinges. In addition, some aspects of the flexural condition of strengthened RC beams still need experimental and analytical investigation; furthermore, especially for serviceability checks, code provisions are lacking. This paper presents an experimental and analytical program conducted to investigate the serviceability and ultimate behavior of RC continuous beams strengthened with carbon FRP (CFRP) sheets. The program consists of four continuous (two-span) beams with overall dimensions equal to 250×150×6000 mm. Beams were strengthened by CFRP in flexure along their sagging and hogging regions. The results show that by strengthening beams, a lower rate of transition of flexural rigidity from the uncracked to the fully cracked section occurs. The crack width and deflection are acceptably predicted by an analytical model. Also the acceptable lower bound of ductility for ensuring minimum moment redistribution is 3.