Experimental study on the behavior of damaged CFRP and steel rebars RC columns retrofitted with externally bonded composite material

Abstract

The structural behavior of concrete columns reinforced with CFRP bars has been the focus of many researches over the past two decades. There is a dearth of comprehensive research concerning the axial compressive performance of retrofitted CFRP bars reinforced concrete (RC) columns. To fill this gap a thorough investigation was carried out to understand failure mode, load–displacement response, axial deflection, axial load-bearing strength, ductility index (DI), stiffness index (KI), and strength index (SI) of retrofitted CFRP bars RC columns. The experimental matrix comprised 14 short circular columns, seven reinforced with CFRP bars and hoops and the other seven with steel bars and hoops. Initial damage was induced through axial loading until a 35% reduction in peak axial strength was observed, after which damaged columns were repaired and retrofitted using CFRP sheets. The parameters of the study include concentric and eccentric compressions, transverse reinforcement spacing, CFRP wrapping, steel, and CFRP reinforcements. According to the findings, lowering transverse hoop spacing enhanced the utmost capacity and ductility of both types of retrofitted columns. The average peak strength and corresponding axial displacement of CFRP RC columns were 22.63% and 14.87%, and ductility (at a 20% load decrease) was 118% higher after CFRP retrofitting. The axial stiffness of damaged CFRP bars RC columns after strengthening with CFRP sheet were not fully rehabilitated and on average SI under concentric loading was 3.22% lower while DI under eccentric loading was 2.71% higher than steel RC columns.