| Fiber-reinforced polymer composites are increasingly used for strengthening and rehabilitation of existing reinforced concrete(RC)structures due to their superior mechanical properties.However,the FRP materials and the matching bonding adhesive have poor resistance to fire and high temperatures,which is a critical issue of safe applications that should be considered during the design process.In order to enhance the fire performance of FRP-strengthened RC members,they are usually covered by an additional fire insulation layer.Most of the existing research studies have been carried out on the beams and slabs flexurally strengthened with FRP composites,while there is lacking research on the fire performance of FRP shear-strengthened RC beams.This thesis for the first time presents the results of fire tests on FRP shear-strengthened RC beams.A finite element(FE)model was also developed for heat transfer analysis of the FRP shear-strengthened RC beams with or without fire insulation.The main contents of the thesis consist of the following three parts.Firstly,this thesis presents a state-of-the-art review on the fire performance of FRP-strengthened RC members,including the mechanical properties of FRP composites at elevated temperatures,the existing fire tests and numerical modeling as well as the fire resistance design methods,and the limitations of current research studies are also highlighted.Moreover,the thesis presents the detailed results of an experimental program on carbon FRP(CFRP)shear-strengthened RC beams.The experimental program consisted of two parts:static loading tests and fire tests.The static loading tests were conducted to investigate the effect of different layers of CFRP U-wraps on the shear strength(i.e.,load capacity)and the associated failure mode of the test specimens.The fire tests were performed to examine the fire protection of the insulation layer,as well as to study the effects of the number of layers of CFRP U-wraps and the shear span-to-depth ratio on the fire performance of CFRP shear-strengthened RC beams.The results from the fire tests indicated that the RC beam without insulation was failed due to the diagonal shear cracks and exhibited a brittle characteristic.However,the insulated CFRP shear-strengthened RC beams had small deflection responses under fire conditions,and they all had achieved satisfactory fire resistance periods of 2.5 hours.Besides,the measured temperatures of steel rebars and the inner concrete core were all lower than 150 ~oC during the entire fire exposure,mainly due to the good fire protection provided by the additional insulation layer.Therefore,the room-temperature mechanical properties of concrete and steel reinforcement were almost completely retained,leading to the excellent fire resistance performance of the insulated CFRP shear-strengthened RC beams.On the basis of the above fire tests,a finite element(FE)model for heat transfer analysis of insulated CFRP shear-strengthened RC beams was established within the framework of ABAQUS software.The FE model was verified extensively by the fire test results in this thesis and the exiting results of insulated FRP-strengthened beams and columns in the literature.The presented results in the thesis provide unique test data for future research on the fire performance of CFRP shear-strengthened RC beams,and the results of fire tests and numerical simulations can serve as a basis for the fire resistance design of CFRP shear-strengthened RC beams. |
