Shear Performance Of External Diaphragm Connections Under Axial And Cyclic Loads

The joints between the steel tubular concrete columns(CFST)and the steel beams play an essential role in the safety and stability of the composite framed-structures.Due to its remarkable applications,it has been widely used in engineering designs of all kinds of CSFT structures.In recent years,the overall utilization rate of steel concrete columns and steel beams has been increasing extensively.Steel tubes in concrete columns usually provide constraints for concrete to make it under tri-axial stresses which result in rising of concrete strength,while the concrete core inside the tubes limits the local buckling of steel tubes.Generally speaking,joints are the most crucial zone in the framed-structures which may particularly result in the complete or partial collapse of the entire structure subjected to an extreme loading.The current study was carried out on the shear performance of the respective beam-column joints in the panel zone of CFST structures.In such a case,three reduced scale external diaphragm connections were fabricated according to the geometrical requirements.The connections were designed based on strong members and weak panel zones concept so as to ensure the joints shear failure in the penal zone.Cross-shaped samples were tested against cyclic and axial load respectively.Role of external diaphragm,in-filled concrete and steel tube were taken an account to examine the shear response in the panel zone of the proposed connections.The hysteretic loops and skeletal curves obtained using experimental data of the tested specimens were showing a sounds ductile manner as well as high seismic energy dissipation capacity.An ultimate load carrying capacity carried by the samples were140.66 kN,120 kN,and 158.9 kN respectively as well as the corresponding displacements were 56.57 mm,41.81 mm and 56.65 mm respectively.Load control before yielding point and deflection control criteria after yielding point was adopted to carry out the experimental process.Compression strut mechanism was observed in the panel zone concrete of external diaphragm connections which enhances the shear bearing capacity in the panel zone of connections.Tension field action in a diagonal way at the steel tube web during post-elastic stage took place.This composite action of the core concrete and steel tube in the panel zone has a significant effect to increase the ultimate shear bearing capacity of external diaphragm connections.A nonlinear 3-D finite element models were introduced using general static analysis,which were showing a quite unique resemblance for yielding as well as for ultimate load carrying capacity with the experimental results,which has concluded that additional parametric study can be possible on the proposed connections by changing the concrete material properties,steel grades,thickness of steel tube web and flanges as well as loading phenomena using finite element method.Based on parametric study it is concluded that increasing the thickness of tube web and using high grade of concrete in panel zone largely contribute towards shear performance of external diaphragm connections while there is no major role of width or thickness of beam flanges towards shear bearing capacity of specimens in the panel zone.