Parametric analysis and design method for diaphragm-free composite beam to CCHSST column joints

Abstract

Cold-formed high-strength square steel tubes (CHSSTs) exhibit high standardization, excellent mechanical properties, and low carbon emissions. Given the critical role of joints in structural systems, the related paper proposed a novel diaphragm-free composite beam to concrete-filled cold-formed high-strength square steel tubular (CCHSST) column joint. To further investigate the key parameters and develop a seismic design method for diaphragm-free joints, the influence of the column wall thickness and the thickened area height in the joint zone on the seismic performance of the joints was systematically examined based on validated finite element models (FEMs). A total of 70 models were established for the joints with different column-to-beam linear stiffness ratios and strengthening coefficients. The results indicate that the column wall thickness in the joint zone is a critical factor affecting the seismic performance of diaphragm-free joints. To achieve the design objective of relocating the plastic hinge to the beam, the column wall thickness in the joint zone must be at least 2 times the conventional column thickness, and the thickened area height must be at least 1.1 times the beam height. When the strengthening factor is not less than 1.3, the column wall thickness can be relaxed to at least 1.5 times the conventional column thickness, but the thickened area height should be at least 1.3 times the beam height. By analyzing the different failure modes and force transfer mechanisms, the corresponding calculation formulas for their flexural bearing capacity were developed. Ultimately, a systematic design method for the diaphragm-free joints was proposed, providing a theoretical basis for engineering applications.