Axial Rigidity of Unstiffened Transverse Plate-to-Circular Hollow Section (CHS) Joints

To study the initial axial rigidity of transverse plate-to-circular hollow section (CHS) joint, a semicircular arch and circular ring models for the rigidity calculation of T-type and cross shaped-type plate-to-CHS joints were developed based on the analysis of force transferring mechanism and local deformation characteristics. Utilizing maclaurin series expansion and multiple nonlinear regression analysis, the complex theoretical formula was simplified to the product of an exponential function and a power function. A calculation formula for the initial axial rigidity was established by introducing the neglected influential factor, plate-to-CHS thickness ratio. The results indicate that the initial axial rigidity of joints is directly proportional to CHS diameter and elastic modulus, and it has a logarithmic relationship with plate-to-CHS thickness ratio, showing power function with CHS diameter-to-thickness ratio and exponential function with plate width-to-CHS diameter ratio. The last two ratios affect each other. The rigidity is not affected by bending and shear when the joints is under the elastic stress, and the relative errors between the theoretical rigidities calculated by the proposed formula and the finite element analysis (FEA) are less than 10%.