Research on Structure and Bearing Capacity of Stiffened X-Joints of Lightweight Aggregate Concrete-Filled High-Strength Square Steel Tubes

In order to study the structure and bearing capacity of lightweight high-strength truss joints, static loading tests were carried out on X-joints with stiffened plates and basic X-joints of lightweight aggregate (LWA) concrete-filled Q345B steel square tubes. The effects of the stiffened plates between braces and chords and the LWA concrete poured into braces and chords on the failure mode and bearing capacity of X-joints were studied. Tests results showed that the failure modes of stiffened X-joints were weld cracking between stiffened plates and braces under shear and compression, tension failure of brace flange under shear and compression by stiffened plates, and shear and compression failure at sections of braces under shear and compression near stiffened plate outer edge. The failure mode of the basic X-joints was weld cracking between braces and chords. The yield and fracture process of X-joints were delayed and the bearing capacity of X-joints increased significantly due to the stiffened plates between braces and chords. Pouring LWA concrete into braces and chords could effectively prevent buckling of square steel tubes. The weld cracking load and the bearing capacity of stiffened X-joints were 63.3% and 18.3%, respectively, which were higher than those of the basic X-joints. According to the failure modes of stiffened X-joints, the calculation models were established and the bearing capacity calculation formulas were derived considering the effects of stress transfer and diffusion of stiffened plates for fracture of fillets between stiffened plates and braces under shear and compression, flange pulling of shear-pressure braces, shear-compression failure of shear-pressure braces of stiffened X-joints of lightweight aggregate concrete-filled high-strength square steel tubes. The calculation error of the suggested bearing capacity formula for stiffened X-joints was -27.8% to +3.7%.