Study On The Internal Force Calculation Methods Of Semi-rigid Steel Frames Under Vertical Loads And Ground Deformation

With the development of society and economy, the advantages of steel structure make it more and more popular and universal. As an important structure style of steel structure, the steel frame has been widely used in industrial and civil buildings.And because of its superior deformation performance, the steel frame is More and more used in the gob area and surface subsidence area. As an important part of steel frame, the connection form of beam-column joints is usually simplified as rigid or hinge connected. However it actually is in between the hinged and rigid, so that the results have a great error. So this paper mainly studies the internal force calculation methods of semi-figid frames under vertical loads and ground deformation.Firstly, based on the theoretical analysis, the function relation between semi-rigid and rigid connection frame bending moment is established under the effect of vertical loads. The simplified calculation method of the internal force of semi-rigid frame considering connecting linearity and nonlinearity is proposed, and the analysis of applicability for each method is conducted. The Kishi-Chen power function model is adopted to simulate the nonlinear behavior of nodes, and ANSYS is utilized to carry out the contractive analysis.The analysis of examples of semi-rigid frame shows the result obtained by the method of this paper is very similar to those obtained by employing the method of COMBIN39 element analog connection. When the bending moment of the node is relatively small, the meaning is the node characteristic is in the elastic stage, the characteristics of the stimulation nodes with the initial stiffness can be adopted. However, when the bending moment of the node is relatively big, this means the node characteristic is in the plastic stage and the nonlinearity of the node must be considered.Then, changing jionts stiffness, structural layers and the number of spans by using the finite element software, it studies the law of joint moment distribution for the semi-rigid frame under vertical loads.it is found that jionts stiffness of beam-column has a great influence on the internal force of frames. The jionts stiffness is more bigger more close to rigid connection, and more smaller more close to hinge.Frame layers have a little influence on the function relation of the joint αβ-; The frame spans have a great influence from single span to two span,but the influence is very small from double span to multi span.Based on the theoretical analysis,the function relation of the joint αβ- for the equal span semirigid frames is established under the effect of vertical uniform loads,and ANSYS is utilized to carry out the contrastive analysis.Besides,the function relation of the joint αβ- for the single span semi-rigid frames is established under the effect of vertical arbitrary loads.Lastly,through the theoretical analysis of transformation, The traditional calculation method is applied to the internal force and sideway calculation analysis of frame structure in mining subsidence area, and study on the performance variation law of frame structure under the action of single surface deformation and combined surface deformation. The analysis of examples shows The main effect object of vertical deformation is frame beam, and affects all floors. The main effect object of horizontal deformation is frame column, but only on the frame bottom two layers. The combined surface deformation is the combined action of horizontal and vertical deformation, the effect is much larger than the single deformation,and is the main factor of structure failure.Compared with the rigid frame, the effect law of the surface deformation to the semirigid frame is similar. At the same time the semi-rigid of joint will greatly weaken the adverse effects of the vertical deformation and combined deformation to the frame internal force.In terms of surface horizontal deformation, the semi-rigid of joint can weaken the adverse effects to the internal force of the frame beam end,but the impact on the column end can’t make much difference.