| Based on the analysis and reaearch on the existing retrofitting methods for RC frame joint,a new method of retrofitting the RC beam-to-column joints with prestressed steel strips was proposed in this paper.Prestressed steel strip reinforcing technology is to exert prestressing on the steel strip around the frame joint and archor it with closed locking,so that the frame joint is subjected to larger circumferential confinement and thus aiming to improving the seismic behavior of the specimen.It could effectively overcome the problems of orthogonal beam in RC frame joint with the method of steel strips crossing through holes of the joint to retrofit the joint.Besides,it could reduce the shear lagging existing in traditional retrofitting methods and improve the performance of joint effectively.In this paper,with the aim to study the effect of the proposed retrofitting method on the seismic behavior of RC joint,following studies were carried out.Experimental study on 6 specimens retrofitted with prestressed steel strips and 1specimen without retrofitting were performed under cyclic-reserved loading.The influence of steel strips space both in the retrofitted joint core and in the beam-end,layout of the prestressed steel strips as well as the type of the joint on the feasibility and the strengthening effect of the method for retrofitting the RC beam-to-column joints with prestressed steel strips were investigated.The results demonstrated that specimens strengthened with prestressed steel strips developed higher shear resistance,and the failure mode of specimens changed from the combination of flexural failure of beams and shear failure of joints to the flexural failure of beams.Moreover,utilization of prestressed steel strips could greatly improve the seismic performance.The hysteresis behavior was better with no pinching effect,resulting in higher energy-dissipation capacity,and the ductility was improved with a gentle descending branch curve.The strength and stiffness degradation of the retrofitted specimens were obviously improved,and a stable behavior in resistance under large horizontal deformation of the column top was developed.Prestressed steel strip reinforcing technology could overcome the obstacles of orthogonal beams effectively and reinforce the space joint with effective confinement,which greatly improve the seismic performance of specimens.In addition,in order to validate the feasibility of retrofitted method with prestressed steel strips,experiments on 1 specimens retrofitted with CFRP and 1specimen retrofitted with steel casing were performed to study the seismic performance according to the equivalent strength substitution principle.The seismic performance index of specimens retrofitted with prestressed steel strips,steel casing and CFRP were analyzed and compared,including the failure mode,hysteresis behavior,skeleton curve,deformation performance,energy dissipation capacity,ductility as well as strength and stiffness degradation.Finally,the finite element model using ABAQUS was established,and the numerical analysis on RC joint was conducted.The contrastive results indicated the computation result agreed well with the experimental results.The retrofitted method with prestressed steel strips are further studied by the parameter analysis on different steel strips prestress and axial compression ratio on the basis of the accurate model,,results show that the steel strip prestress size and axial compression ratio have no obvious influence on the bearing capacity of the specimen when the specimen occurs the bending failure of the beam.With the increase of initial prestress,the shear capacity of the joint core of the specimen increases gradually when the specimen occurs the shear failure in joint core.When the steel strip prestress increases from0 MPa to 352 MPa,the shear capacity of the joint core area of the specimen increasesfrom 222.17 kN to 246.78 kN,increased by 11.08%. |
PDF Full Text Request