Seismic Performance Of RC Beam-column Joints Strengthened Using Near-surface Mounted CFRP Strip

Reinforced concrete frame is one of the most common structures, and it is very important to improve the seismic performance. Many existing RC frame joints do not satisfy current codes as they were designed based on old codes of practice without any transverse reinforcement in the joint region, which do not meet the principle of strong joint - weak member and may induce joint shear failure and even the collapse of building.Traditional techniques for retrofit of RC beam-column joints include section enlargement using RC or fiber reinforced concrete jackets, and external bonding/bolting of steel plates. In recent years, these traditional techniques have been replaced to a large extent by the technique of externally bonded FRP composites, due to their high strength-to-weight ratio, excellent corrosion resistance, and ease for installation; however, there are deficiencies for externally bonded FRP sheets, such as premature debonding and beam hinges located at the column face.To overcome the drawbacks, a novel scheme has been proposed that using near-surface mounted (NSM) FRP strips to strengthen RC beam-column joints based on the concept of relocating the plastic hinge away from the column face. And a test programme has also been carried out to validate its effectiveness. Besides, a shear strength model has also been proposed. The main work and research results are as follows:1. A total of four specimens were designed in the study, including one empty control specimen, one code-confirmed seismically specimen, and two strengthened joints using the NSM CFRP method. The main variables are the section area and distance of CFRP strips.The experimental study has also been carried out to evaluate the seismic performance of the specimens, focusing on failure modes, energy dissipation, ductility, strength and stiffness deterioration and the strain distribution and development of CFRP strips.2. The experimental results show that using near-surface mounted (NSM) FRP strips to strengthen RC beam-column joints can raising the bearing capacity of the joints, improving the ductility of the components,and deferring the degeneration of the members, and rationally arrange the CFRP strips distance even can turn joints shear failture to the beam hinge damage away from the cylinder.3. Due to the scarcity of shear strength models for beam-column joints with NSM CFRP strips, a shear strength model has also been proposed based on biaxial tension- compression failure criterion and the stress state of joint cores subjected to seismic loading. And the comparison indicated that the proposed mode is accurate and consistent.