Impact of elevated temperature on the behavior of strengthened RC beams with CFRP

Elevated temperatures (beyond 500°C) severely deteriorate concrete structures due to vapor pressure, decomposition of cement hydration products, inhomogeneous volume changes of concrete’s ingredients. Carbon fiber-reinforced polymer (CFRP) composite materials provide the most significant retrieval of the structural performance to severely heat-damaged structural concrete members. Therefore, an experimental study investigated the influence of elevated temperatures on the flexural behavior of reinforced concrete (RC) beams strengthened externally with CFRP. For this purpose, thirty-two reinforced concrete beams were cast. Twenty-four beams were externally strengthened with CFRP, and eight beams were unanchored and left as a control. The beams then were tested under four-point bending to assess their structural performance in terms of failure modes and load-displacement relations. The experimental results have clearly shown that the control beams suffered from ductile failure. The CFRP strengthened beams failed by debonding the CFRP sheets after yielding the flexural steel reinforcement. The strengthened beams showed an increase in the ultimate load-carrying capacity accompanied by an enhancement in mid-span deflection in different percentages concerning the control beam. The CFRP sheets’ ability in the bridging of the crack increased with the increase of CFRP length by providing more development length in catching the two sides of the major flexural crack. The load-deflection curve can be divided into two stages; the first portion is nearly a straight line, and the second stage with slope experienced a slight increase in the load with a large increase in deflection. The second stage formed after the yielding of steel reinforcement and formation of the main flexural crack where the applied load was carried by the CFRP sheet. Finally, the influence of the exposure temperature on the ductility, energy absorption, and ultimate load reduction percentage increases with the increase of temperature.