Research On The Seismic Behavior Of New Type Of Outsourced Enhanced Joint For RC Frame Lightweight Steel Structure

Reinforced concrete(RC)frame lightweight steel mixed structure can increase the use area without disturbing the original structure,which can effectively alleviate the contradiction between urbanization construction and land resource shortage.It has become a new trend in the development of the international construction industry.However,the disadvantages of this kind of structure,such as the vertical mass and stiffness mutation,seriously affect its application.Therefore,how to ensure the overall seismic performance of the structure after adding stories,and how to improve the cooperative working ability of the added stories and the existing structure are the key points of the seismic design of this kind of structure.Based on this,this paper puts forward a new type of outsourced enhanced joint which is used in RC frame lightweight steel mixed structure on the basis of fully considering the connection requirements of the added story and the existing structure and ensuring the embedded effect of the original structure on the added story of lightweight steel.Through the comparative quasi-static test and research with the traditional planting reinforcement joint,and with the help of ABAQUS finite element software,the mechanical performance and failure mechanism of the joint are further verified,and reasonable design suggestions are given based on the research of relevant parameters.The specific research contents are as follows:(1)Combined with the research status of lightweight steel mixed structure at home and abroad,and based on the connection construction problem of lightweight steel joints,the 1/2 scale specimen design of the new type of outsourced enhanced joint and the traditional planting reinforced joint is carried out.Through the comparative quasi-static test,the seismic performance indexes are studied in depth.The results show that the two kinds of joints are all plastic hinge failure of beam section,but the hysteretic curve of the new type of outsourced enhanced joint is fuller,and the pinching speed is slower,and the plastic hinge can be moved out,effectively protecting the core area of the joint.The energy consumption capacity indexes,plastic hinge rotation capacity and displacement ductility of the joint are all improved to different degrees compared with the traditional reinforced joint,which not only improves the bearing capacity of the joint,but also limits the development of cracks,obviously has better seismic performance.(2)With the help of ABAQUS finite element software,a new type of outsourced enhanced joint model is established.The nonlinear analysis of the joint under the action of low cycle reciprocating load is carried out.The mechanical performance and failure mechanism of each loading section are studied in depth,and the correctness of the finite element model is verified by comparing with the test results.The results show that the finite element model always shows a good integrity in the whole loading process,the upper load value is mainly transmitted downward through shear studs and encased concrete,the joint stiffness is guaranteed under the action of the internal reinforcement of column base wrapped with concrete,which effectively limits the damage of the core area,the cracks of the concrete beam body continue to develop,and then the longitudinal reinforcement enters the yield,finally,the plastic hinge failure of the beam section under the bending shear action of the normal section far away from the core area of the joint is formed;the final overall failure mode of the finite element is basically consistent with the test results,and the error of its characteristic load value and each energy consumption index are within the reasonable and controllable range,which shows that the finite element model is correct and reliable and can be used for subsequent research.(3)Study on the influence of relevant parameters on the seismic performance of new joints.By changing the axial compression ratio,the elevation height and the horizontal length of the wrapped foot,the influence of the parameter change on the seismic performance of the new type of joints is analyzed.The results show that:①With the increase of the axial compression ratio,the second-order effect of the steel column is more significant.The energy dissipation capacity,ultimate bearing capacity and initial stiffness of the specimens are all slightly improved.However,when the axial compression ratio is too large,the contact surface of steel and concrete is easy to produce large stress concentration,which accelerates the formation of fracture surface;②With the increase of the elevation height of the wrapped foot,the hysteretic curve of the specimen is more full,and the ultimate bearing capacity and initial stiffness are slightly increased,but the excessive height of the wrapped foot is likely to cause a significant increase in the horizontal load effect,which is not conducive to the development of the seismic resistance and later ductility of the specimen;③With the increase of the horizontal length of the wrapped foot,the bending rigidity of the beam body is strengthened,and the ultimate bearing capacity and initial rigidity of the test piece are improved obviously.However,if the horizontal length of the wrapped foot is too long,the stiffness ratio of the beam to the column will be inconsistent,the joint connection tends to be hinged,and the failure of the concrete in the core area will be accelerated,which is not conducive to the seismic resistance of the test piece.Based on this,the optimal parameter design range is determined,which provides technical support for the subsequent research of light steel structure.