EXPERIMENTAL STUDY OF DOUBLE RETROFITTED LOW AND HIGH-STRENGTH REINFORCED CONCRETE BEAMS AND SLABS USING CFRP

Abstract

During its service life, a structure may exhibit a range of deficiencies due to deterioration, construction or design errors, changes in functionality, and updates in design standards. Consequently, deficient structures need to be retrofitted to sustain their functionality. Structures that have been retrofitted once may require further strengthening during their service life. This research aims to further evaluate the behavior of retrofitted structural elements. In this study, three beams and two slabs that were retrofitted with FRP flexural reinforcement five years ago will undergo additional retrofitting. The beams will be reinforced with FRP shear reinforcement, and the slabs will receive another layer of FRP flexural reinforcement. The study evaluates two types of concrete: high-strength concrete and low-strength concrete. The main objective is to evaluate the behavior of retrofitted beams and slabs by observing their ductility, stiffness, ultimate load, mode of failure, and moment capacity. Based on the experimental results, it was found that low-strength beams still experience shear compression failure, while high-strength beams experience flexural failure with a higher ultimate load. Specifically, in high-strength beams, ductility increased significantly with the addition of FRP shear reinforcement. Both low-strength and high-strength slabs experienced shear failure due to an over-reinforced condition, exhibiting higher stiffness due to the additional layer of flexural FRP reinforcement. This study highlights the need to consider failure modes in FRP retrofitting. Shear reinforcement improves ductility in high-strength beams, while low-strength beams remain shear-critical. In slabs, excessive flexural FRP increases stiffness but risks over-reinforcement. These insights aid in optimizing structural rehabilitation.