Calculation Model for Axial Rigidity of CHS Y-Type Joints

In order to establish a practical parameterization calculation formula for the axial rigidity of a circular hollow section (CHS) Y-type joint, a semicircular arch model for Y-type joint rigidity was developed based on the round-direction model and the relationship between local deformation of a joint and its axial rigidity, and a theoretical formula for the axial rigidity was established. With the help of the Taylor series, the complex theoretical formula was simplified to the product of an exponential function and a power function embodying the interaction effect between independent variables. In addition, the secondary influence factor, brace-to-chord thickness ratio, was omitted in the light of the single-parameter analysis result from finite element analyses (FEA). As a result, a practical formula for the axial rigidity of a Y-type joint was obtained through a multiple nonlinear regression analysis. The results show that the axial rigidity is directly proportional to elastic modulus of steel, reciprocal of sine-square of the angle between branch and chord in plane and chord diameter, brace-to-chord diameter ratio and chord diameter-to-thickness ratio have significant effects on the axial rigidity, and relative errors between axial rigidity values obtained by the practical formula and the FEA and existing test results are basically less than 8%.