Study On Mechanical Properties Of Assembled Square Steel Tube Column-H Steel Beam Joints

The assembled structure not only solves the problems of construction waste,noise,operation time,labor demand and resource depletion,but also improves the quality of the project,and has a broader development space and development potential.Under the background of the country ’s vigorous promotion of prefabricated steel structures,the theoretical research of circular steel tubular columns is relatively mature,while the research and application of square steel tubular columns are relatively lagging behind,and the theory of square steel tubular column joints needs to be strengthened.A new type of assembled square steel tube column-H-shaped steel beam joint was proposed.The size of the reinforcing ring and the number of bolts of the joint were determined according to the current specification.The finite element software ABAQUS was used to analyze the mechanical properties of the new joint under low cyclic loading.Through the stress cloud diagram and the equivalent plastic diagram,it is determined that the yield mode of the joint does not meet the design requirements of ’ strong column and weak beam ’.In order to obtain the design parameters of the joints with better mechanical properties and yield modes that meet the requirements,the enlarged parameters of the joints are analyzed.The analysis parameters include column thickness,reinforcement ring thickness,bolt pre-tightening force,friction coefficient and width of outer reinforcement ring side,a total of 18 models.The effects of various parameters on the mechanical properties and yield modes of the joints were analyzed by finite element analysis,and two key parameters were determined.The orthogonal analysis of the key parameters is carried out to determine the optimal parameters of the joint design,and the formula for calculating the bearing capacity of the joint and determining the width of the reinforcing ring is deduced.The main conclusions are as follows :(1)According to the standard design of this kind of joint under low cyclic loading,the strengthening effect of the upper and lower rings makes the new joint better realize the plastic hinge outward,and has good ductility.Combined with the standard formula,it is found that the bending resistance,shear strength,stability and seismic bearing capacity meet the requirements.However,there are still the following problems in the joint design : stress concentration occurs in the core area of the column,the corner of the reinforcing ring and the bolt hole.The stress of the side width of the reinforcing ring which is not connected to the beam flange is basically zero during the whole loading process,and slip occurs at the joint splicing.The yield mode of the joint does not meet the design requirements of ’ strong column and weak beam ’.In order to improve the problems of the joints,five types of parameters that may affect the performance of the joints are proposed,which are : column thickness,outer edge width of the reinforcing ring,thickness of the reinforcing ring,bolt preload and friction coefficient.(2)Through the analysis of the expansion parameters of the joints,it is found that the mechanical properties of the joints increase significantly with the increase of the column thickness.Reducing the thickness of the outer reinforcing ring is beneficial to the improvement of ductility,but it will also cause the increase of stress.Changing the size of the bolt preload and the width of the outer reinforcing ring has little effect on the mechanical properties of the joints.Excessive and too small friction coefficients have adverse effects on the mechanical properties of the joints.In order to obtain the best mechanical properties of the joints,the optimal values of various parameters are as follows : the column thickness is 20 mm,the outer reinforcing ring thickness is 14 mm,the bolt preload is 190 k N,the outer reinforcing ring side width is 257 mm,and the friction coefficient is 0.45.Two key parameters that have a significant effect on the yield mode of this type of joint are determined as the column thickness and the thickness of the outer reinforcement ring.(3)Four orthogonal joint models are designed by using the two parameters of column thickness and outer reinforcing ring thickness.Through the analysis of the equivalent plastic diagram of the joints obtained by finite element calculation,it is found that increasing the column thickness can effectively improve the yield mode of the joints,while the outer reinforcing ring thickness has little effect on the yield mode.The optimal parameters of column thickness and reinforcing ring thickness are determined to be 18 mm and 14 mm respectively,and the calculation formula of bearing capacity and the design formula of outer reinforcing ring size suitable for this new type of joint are deduced.