Pre-cracked RC beam strengthening with CFRP materials

The application of CFRP materials for strengthening and rehabilitation of concrete structures has been spreading widely during the last two decades. Bonding failure of continuous fiber sheets is observed due to less adhesion with the concrete surface. Recently developed FRP strand sheet consists of individually hardened continuous fiber strands. This paper presents the shear strengthening capacity and failure modes of Pre-cracked Reinforced Concrete (RC) rectangular beams bonded externally with unidirectional Carbon Fiber Reinforced Polymer (CFRP) Composites. The study evaluates the efficiency of external strengthening of concrete members using CFRP strand sheets and compares this with the performance of continuous fiber sheets. Variables such as load vs deflection, end anchorage and number of CFRP U-strips applied (for shear retrofitting) are considered. Depending on the type of CFRP material and strengthening technique, beams strengthened for shear gave results close to or greater than control beam. Load capacity recovery of the beam specimens varied between 4–20% while deflection of the CFRP strengthened pre-cracked beam decrease by 8–23% (with respect to control beam) at ultimate load. In the ultimate loading condition mainly shear failure mode with concrete cover debonding are observed.