| China's "Standard for Steel Structure Design"(GB50017-2017)stipulates that beam-to-column connections can be constructed by bolt connection,end-plate connection and top-to-bottom angle steel connection.In the code,the design requirements of rigid connection between beam and column are given in detail.For semi-rigid connection of beam-column joints,the code only addresses that the strength checking of joints should be carried out under the action of bending moment and shear force,and never gives specific theory and method.Most of the beam-to-column joints in engineering practice are semi-rigid connections.There is a big difference between the results of the rigid connection design and the actual engineering situation.It is necessary to design the joints according to the semi-rigid connection.Therefore,this paper studies the semi-rigid connection of steel structure beam-to-column joints in the following aspects:(1)Based on the theory of semi-rigid connection of beam-column joints and the deficiency of the existing calculation model ofM-?_r curve of semi-rigid connection,this paper studies the constitutive relationship of semi-rigid connection by using BP neural network,and establishes a neural network with semi-rigid connection test data as training samples,and predicts theM-?_r curve,initial stiffness and ultimate bending moment of steel connection with double web top and bottom angles.The error of calculation results is very small,which verifies the correctness of the neural network calculation model.Compared with other computational models,the proposed neural network model is more concise and convenient.For the constitutive curves of semi-rigid connections outside the sample,the neural network also has good prediction results in the elastic stage.(2)Three-dimensional non-linear finite element analysis of semi-rigid beam-to-column joints is carried out by ANSYS.Mixed meshing method is adopted.Pyramid transition element is used between hexahedron element and tetrahedron.Considering material nonlinearity,geometric nonlinearity and state nonlinearity,displacement characteristics,stress distribution,contact distribution and moment-rotation angle of the whole joint and its components are obtained.The curve is compared with the test data to verify the correctness of the program.Finally,the influence of the parameters such as the distance from the top angle steel bolt to the flange of the beam,the thickness of the top and bottom angle steel,the section height of the beam and the thickness of the web angle steel on the semi-rigid connection is explored.(3)Linear spring and non-linear spring are used to analyze rigid connection and semi-rigid connection with different connection stiffness of plane frame and space frame.The mechanical characteristics of displacement,internal force and stress of frame are obtained.It is found that the simulation of semi-rigidity by non-linear spring element is closer to reality;the influence of semi-rigid connection on spatial frame is greater,the higher the floor is,the larger the horizontal displacement is,and the smaller the vertical displacement deviation is.Compared with rigid frame,the mid-span bending moment of semi-rigid frame beam increases,while the beam-end bending moment and Column-end bending moment decrease.Under the same load,the stress of beam-column joints of rigid frame is larger.However,the stress at the column foot of semi-rigid frame is larger than that of semi-rigid frame.The smaller the joint stiffness is,the easier the maximum inter-story displacement will appear on the top floor.Reducing the distance between the top angle steel bolt and the flange of the beam and increasing the thickness of the top and bottom angle steel can significantly reduce the relative inter-story displacement of the semi-rigid connection frame. |
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