STUDY ON THE FAILURE MECHANISM AND STRENGTH OF LINEAR STRENGTHENED DIAPHRAGM-THROUGH JOINTS OF LWA CONCRETE-FILLED SQUARE STEEL TUBULAR SIDE COLUMNS WITH VARIABLE CROSS SECTIONS AND STEEL BOX BEAMS

Low-cycle reversed loading tests were performed on linear strengthened diaphragm-through joints of lightweight aggregate (LWA) concrete-filled square steel tubular side columns with variable cross sections and steel box beams. The effects of the linear strengthened diaphragms on the failure mode, strength, plastic rotation and ductile behavior of the joints were investigated. The distribution of the residual stress of the panel zone was measured using the blind-hole method. The numerical simulation and failure mechanism analysis of tested joints were carried out based on an elliptical fracture model coupled with an elliptical yield model of constructional steel considering the welding residual stress and a general failure model described by using quadratic functions of LWA concrete. The fracture and yield evolution of the welds in the panel zone, the butt welds of the beam flanges and the fillets of the beam webs, and the stress state of LWA concrete in the panel zone are obtained. The formulas for calculating the bending and shear strength are presented for linear strengthened diaphragm-through joints of LWA concrete-filled square steel tubular side columns with variable cross sections and steel box beams based on the numerical analysis and test results.