| Since twentieth century,especially for nearly half a century,the steel structures have been widely used in all kinds of industry and civil constructions.The research shows that the key part of the design of the steel structure of the beam column joints is directly related to the seismic performance of the whole steel structure.Due to the brittle failure of traditional welded joints,the destruction of joints often results in deformation and collapse of the whole steel structure after the earthquake.Therefore,a variety of new connection methods have been put forward by scholars to the steel frame joints.The purpose is to improve the seismic performance of the steel frame.In this paper,Force-Transforming Plates outside Tubular Column's frame joints with different beam's heights is an improved joint for the engineering retrofit.The stresses are by adding force-transforming plates on the unequal hight beam flanges of tubular column.The seismic performance of the new type of joint and its space frame is studied systematically in this paper,which provides the theoretical basis and application foundation for the engineering retrofit.The following work has been carried out mainly:(1)The finite element simulation analysis of traditional joints and new joints with equal hight beam is carried out under uniaxial loading.The failure modes and load displacement curves of two joints are obtained,which are compared with experimental results to verify the correctness of finite element models.Finite element simulation analysis are used in the same way to the traditional joints and new joints with corner columns,side columns and columns under uniaxial loading,to compare their failure modes and the load displacement curves.The results show that: the failure modes of the finite element model of the traditional joints and the new type of joints are all consistent with the experiment.The bearing capacity of both of them is slightly higher than the test value,which verifies the correctness of the finite element model.Compared with the traditional joint,the uniformity of the stress distribution of the new joint with unequal hight beam's is obviously improved.The improvement degree of the middle column joint is also the most obvious.It can effectively delay the brittle failure of the connection position of the joint under uniaxial loading.(2)The von Mises stress cloud diagram,hysteretic curve,skeleton curve and stress distribution of nodal field are obtained for low load cycles of traditional nodes and new joints with unequal hight beam by using ANSYS software.The failure modes,bearing capacites,energy dissipation capacities,strength and stiffness degradation coefficiences,ductility,plastic rotation capacities and stresses path of two kinds of joints are compared and analyzed.The results show that the new joint has a plastic stress redistribution compared with the stress distribution of the traditional joints with unequal hight beam's.The stress distribution of the node is no longer concentrated at the junction of the beam and column,but is transferred to the external force.And it has better energy dissipation capacity,ductility and plastic rotation ability,and the strength and stiffness degradation are slower.The stress of the connection position of the beam and column is obviously decreased,and the peak stress is outside the force-transforming plate,which has reached the purpose of delaying the failure of the joints.(3)The comparative analysis of the fracture characteristics of traditional nodes and new joints with unequal hight beam is performed to analyze the equivalent plastic strain index of the internal partitions,the end of the beam-column joints,the force-transforming plate,and the connection region of the force-transforming plate and key points are selected for comparative analysis.The results show that the equivalent plastic strain index of the beam-column connection area is significantly reduced after the force-transforming plate is added,and the peak value is transferred to the force-transforming plate and the edge of the joint connected to the beam flange,which significantly improves the fracture characteristics of the beam-column joint.(4)The finite element software ANSYS is used to analyze the seismic performance of four parameters,such as the width of the force-transforming plate,the thickness of the cover plate,the thickness of the web of the force-transforming plate,and the distance to the tubular column.The analysis results have obtained the von Mises stress,hysteresis curves,skeleton curve and stress distribution under the change of the parameters.And then in order to make the new joint has a good seismic performance,compare the aseismic performance indexes from the above results by comparing the same parameters.The reasonable range of the width of the force-transforming plate,the thickness of the cover plate,the thickness of the web of the force-transforming plate,and the distance to the tubular column are determined.(5)Through the finite element analysis of the seismic performance of the two groups of space frames that are equal to the height of the beam and the beam height is not equal in front of the additional force-transferring plates and after the adding of the force-transferring plates.The stress cloud,hysteretic curve and skeleton curve of two groups of space frames are obtained by finite element analysis.The aseismic performance indexes of the two groups of frames are obtained by comparison and analysis from the above results.The results show that the redistribution of the plastic stress in the middle column joints of the space frame after the additional force-transferring plates is added.The stress peak,due to the appearance of the outside of the orce-transferring plates,will delay the failure of the joint.And the new frame has better energy dissipation capacity,ductility performance and plastic rotation ability,showing good seismic performance.It can provide reference for the retrofit and reconstruction of the actual projects. |
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