Mechanical Properties Analysis Of Inner Sleeve Joint Between Modular Steel Frame Modules

In recent years,assembly-type modular buildings have quickly become a research hotspot of building industrialization in China with their unique advantages such as short production cycle,high degree of prefabrication,green environment protection,convenient on-site installation and reusable modules and units,and have a broad prospect for development.Finite element numerical simulation and test verification were carried out for the inner sleeve connection nodes between fabricated modular steel frame modules.The influences of the clearance between the inner sleeve and the column wall,the thickness of the inner sleeve and the length of the inner sleeve on the bearing capacity and seismic performance of the nodes were studied.The formation mechanism of the contact force between the column wall and the inner sleeve was analyzed,the formula of the contact force was derived,and the influence of the contact force on the column wall was verified.The results are compared with the finite element numerical calculation.The main research conclusions are as follows:(1)The finite element numerical calculation results were compared and verified by the seismic performance test of the spliced-joint joints between the modules of the new modular prefabricated steel frame.The test specimens and the finite element numerical simulation results had the same failure position,and plastic hinge failure occurred at the beam end.Meanwhile,the hysteresis curves were consistent with each other,and the stress path changes were consistent.Therefore,the finite element numerical calculation results have a good accuracy,which can be further carried out parameter analysis of the inner sleeve joint.(2)The reserved clearance between the inner sleeve and the column wall has a significant impact on the bearing capacity,seismic performance,stress distribution and contact force of the joint.When there is no clearance between the inner sleeve and the column wall,the stress distribution of the column wall in the joint area is more uniform,the bearing capacity is higher,and the hysteresis curve is fuller.With the increase of the reserved installation clearance,the non-uniform contact stress is formed between the inner sleeve and the column wall,and the bearing capacity of the joint decreases.At the same time,the envelope area of the hysteresis curve decreases,and the energy dissipation capacity and the joint stiffness decrease obviously.It is recommended that the reserved gap between the inner sleeve and the column wall should not exceed 4mm.(3)As the thickness of the inner sleeve increases,the yield load,ultimate bearing capacity and seismic performance of the joints increase significantly.The stress distribution of the joints tends to be uniform,the stress distribution range of the column wall is larger,and the stress concentration of the inner sleeve is alleviated.When the inner sleeve thickness is less than the column wall thickness,the innersleeve stress concentration phenomenon is obvious,and the peak stress is large,the inner sleeve local damage,joint bearing capacity decreases,hysteresis curve pinches,can not meet the design requirements of "strong junction,weak component".It is recommended that the inner sleevethickness be greater than 1～2mm column wall thickness.(4)Increasing the length of the inner sleeve can effectively reduce the stress concentration of the column wall and the stress mutation of the inner sleeve in the joint domain,so as to improve the bearing capacity and seismic performance of the joint.It is suggested that the length of the inner sleeve should not be too small when designing the joint,so as to ensure that the inner sleeve can strengthen the column wall.However,when the inner sleeve is longer,it has little influence on the yield load and ultimate bearing capacity of the joint.At the same time,the hysteresi curve did not change obviously.Therefore,in order to improve the bearing capacity of joints and save steel,it is suggested that the innersleeve should extend 30～50mm outside the upper beam flange and the lower beam flange.(5)The formula for calculating the contact force between the inner sleeve and the column wall is derived.The bending rigidity of contact force and main column,column,inner sleeve and the height of the column wall clearance,the height of the beam,and the length of the inner sleeve.The contact force can be reduced by increasing the bending stiffness of the column or appropriately increasing the gap between the innersleeve and the column wall.The influence of contact force on column wall is further checked and calculated.The ultimate bearing capacity of column wall buckling failure is related to the thickness of column wall,the width of inner sleeve and the gap between inner sleeve and column wall.Increasing the thickness of column wall or the bending stiffness of column wall can effectively improve the ultimate bearing capacity of column wall,and the greater the gap between innersleeve and column wall,the ultimate bearing capacity of column wall decreases.The results show that there is a great difference between the maximum contact force and the ultimate buckling load of the column wall,and there is a good safety reserve.(6)The calculation formula of contact force is compared and verified by the finite element numerical calculation results.The error of the two formulas is about 10%,which is in good agreement.