| Abstract:It is hard to apply the retrofitting-technology of concrete frame joints strengthened with fiber-reinforced polymer (FRP) directly because of orthogonal beam and slab, and debonding of the FRP from the concrete is easy to occur due to the insufficient FRP anchorage, the strengthening effect is not satisfactory. Hence, the research about solving these problems is of great significance. The method of internal joints strengthened with the beam-column-end-CFRP indirectly can also improve the seismic performance of the joints and is more suitable for the frame joints with orthogonal slab in practical works. In this paper, the working mechanism of frame joints with the lock-anchored beam-column-end-CFRP indirectly by finite element numerical analysis of seven joints under a low cyclic load was discussed. On the basis of the finite element analysis and experimental results, the design formula of frame joints with lock-anchored beam-column-end-CFRP was also proposed. The main work and research results are as follows:1) Based on the experimental results of seven RC frame joints strengthened with the lock-anchored beam-column-end-CFRP indirectly under a low cyclic load, the finite element models of joints with lock-anchored CFRP sheets were established. The resistance capacity, failure modes, hysteretic behavior, ductility behavior, the strain law of reinforcing steel bar and CFRP of joints were then analyzed.2) According to the data of the resistance capacity, ductility behavior, strain of reinforcing steel bar and CFRP in the core area, comparative results of finite element analysis and experiment data show that the finite element model in this paper is reasonable. The working mechanism and seismic performance of joints strengthened with different anchorage methods were also investigated. The anchorage methods include the through-slab CFRP closed hoops, the border-beam-slab U-CFRP anchored hoops and the bolt-plate lock-anchored CFRP hoops.3) Comparative analysis shows that the bolt-plate lock-anchored CFRP hoops can effectively delay the debonding of the longitudinal bars and CFRP at the end of beam, significantly increase the seismic performance of the joint.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 formulae were verified by the finite element analysis results and experiment results. The formulae provide reference for the design of frame joints strengthened with beam-column-end-CFRP indirectly. |
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