Experimental Research On Seismic Performance Of RC Frame Joints Strengthened With The Beam-column-end-CFRP Indirectly

Beam-column joints are very important element in reinforced concrete (RC) frame structures, destruction of the joints will lead to the collapse of the whole structure. Current researches on retrofitting technology of joints mainly focus on the plane frame joint cores strengthened with carbon fiber-reinforced polymer (CFRP) directly, which are not easily to be applied to practical projects. The method of internal joints strengthened with the beam-column-end-CFRP indirectly is more suitable for practical works and also can improve the bearing capacity of the joints with orthogonal slabs. Supported by Hunan Provincial Natural Science Foundation of China and Hunan Provincial Science and Technology Program, the seismic performance of seven joints strengthened with the beam-column-end-CFRP indirectly was discussed by experimental study. The working mechanism and design formula of frame joints with lock-anchored CFRP sheets were also proposed. The main work and research results are as follows:1) The seismic performance, ductility behavior and energy dissipation capability and working mechanism of seven RC frame joints strengthened with the beam-column-end-CFRP indirectly under a low cyclic load were investigated by different anchorage methods. The methods include the through-slab CFRP closed hoops, the border-beam-slab U-CFRP anchored hoops and the bolt-plate lock-anchored CFRP hoops.2) The experiment results show that the bolt-plate lock-anchored CFRP hoops can effectively delay the debonding of the longitudinal CFRP at the end of beam, significantly increase the seismic performance of the joint.3) According to the fitting tri-linear skeleton curves and the tri-linear hysteresis circle curves by the nearly yield point and nearly limit point scatter diagram, the restoring force model of frame joints strengthened with the lock-anchor beam-column-end-CFRP indirectly was suggested with the stiffness degradation.4) The method of calculating the shear strength of frame joints strengthened with the lock-anchor beam-column-end-CFRP indirectly was suggested, and the formulae for bending and shear capacity of beam were also derived. The predictions of the proposed models were shown to be in close agreement with the test data. The formulae provide reference for the design of frame joints strengthened with the beam-column-end-CFRP indirectly.