Study On Mechanical Behavior Of Welded Hollow Spherical Joints With H-Beams Under Axial Compression Under Fire/Post Fire

As the most extensively used joint in spatial structure,the welded hollow spherical joint has the advantages of clear force transfer,simple technology and low cost.Over the past decades,scholars have studied mechanical properties of traditional welded hollow spherical joint and compiled relevant specifications for engineering applications.In practical application,on the basis of traditional welded hollow spherical joint,joints with different cross sections of rods,like welded hollow spherical joint with H-beam,appeared.The bearing capacity characteristics,stiffness characteristics and design methods of this kind of joint are quite different from those of traditional ones,while there is a lack of relevant research.In addition,in the case of fire,mechanical properties of the joint will be greatly weakened;while after fire,it is necessary to evaluate residual mechanical properties of the joint accurately and reinforce the structure.The study of mechanical properties of joints at high temperature and after high temperature has theoretical significance and engineering application value.Therefore,experimental studies on compressive performances of welded hollow spherical joints with H-beams under and after high temperature were conducted.The axial bearing capacity and initial stiffness were analyzed by finite element software.Based on parametric analysis,formulas for the ultimate axial bearing capacity and initial stiffness of the joints under and after high temperature were proposed.The main research work is as follows:Firstly,28 welded hollow spherical joints with H-beams were designed considering temperature,sphere diameter,residual deformation,steel type and rib.Axial compression tests at high temperature were conducted to obtain the failure mode,axial bearing capacity and initial stiffness of welded hollow spherical joints with H-beams in different conditions.The influence of different parameters on the reduction coefficient of axial bearing capacity and initial stiffness were analyzed.Secondly,finite element models were established by ABAQUS,and numerical simulation was conducted for the axial compression process at high temperature to verify the accuracy of the finite element model.The influence of 7 parameters,i.e.temperature,steel type,ribbed,sphere diameter,ratio of sphere diameter to wall thickness,ratio of H-beam height to sphere diameter,ratio of H-beam width to sphere diameter,on the bearing capacity and initial stiffness of the joint was analyzed.The calculation formulas of normal temperature axial compression bearing capacity and initial stiffness of joints in relevant literature were verified.Based on theoretical analysis and parametric analysis results,the calculation formulas of axial compression bearing capacity and initial stiffness of joints at high temperature were proposed.Thirdly,the axial compression tests of welded hollow spherical joints with H-beams after high temperature were carried out to study the failure mode,strain distribution and variation rule of residual coefficients of axial compression bearing capacity and initial stiffness of joints undergoing different high temperature and residual deformation under the second axial load.The influence of different parameters on the residual coefficient of axial bearing capacity and initial stiffness were analyzed.Finally,finite element models were established by ABAQUS to simulate the axial compression process of joints after high temperature to verify the accuracy of finite element models.Considering 8 parameters,i.e.temperature,residual deformation,steel type,ribbed,sphere diameter,ratio of sphere diameter to wall thickness,ratio of H-beam height to sphere diameter,ratio of H-beam width.Based on theoretical analysis and parametric analysis results,calculation formulas of axial compression bearing capacity and initial stiffness of joints after high temperature were proposed.