Tests Of Steel And Composite CHS Joints With Big Curved Chord Under Axial Compression

Circular hollow section(CHS) is the most widely used section in onshore and offshore structures due to its aesthetic appearance, uniform flexural rigidity, high fatigue and corrosion resistance. Typical applications of CHS joints, which are fabricated by welding brace members to the continuous chord members, include reticulated shell structures, long-span roof systems and marine petroleum platforms. It is worth noting that the curved chords with certain curvature radius are being used increasingly for architectural and structural purposes in recent years. Up to the authors’ knowledge, however, there is no design rule for CHS joints with curved chord, let alone concrete-filled CHS joints with curved chord.Empty and concrete-filled circular hollow section(CHS) X-joints with curved chord, T-joints with concave chord and T-joints with convex chord have been designed based on the basic X-joints and T-joints. For each type of joint, a total of 16 specimens was fabricated by hot-rolled bending the chord members into curvature with three different radii to apply axial compression force to the brace members, in which 6 specimens were tested with empty curved chord, 6 specimens were tested with concrete filled in the curved chord only, and 4 traditional empty and concrete-filled CHS joints with straight chord were also tested for comparison. The joints’ ultimate capacity, failure mode, deformability, development of stress and strain are discussed and the effects of curvature radius of chord member and concrete filled in the chord member on the joint strength and behavior were evaluated. Based on the experimental investigation, the finite element simulation of the three types of joints have been carried out, the simulative failure mode, axial load-vertical displacement curves, ultimate capacity and the plastic area were consistent with the experimental result. In addition, the parameters of the three types of empty joints were analyzed with the verified finite element model, the main research parameters are brace to chord diameter ratio β(=d1/d0), chord diameter to thickness ratio 2γ(=d0/t0) and curvature radius R. On the basis of the parameter analysis, the design equations for X-joints and T-joints in Eurocode 3 have been revised and the curvature influence coefficients have been adopted. The recommended design equations for empty circular hollow section(CHS) X-joints with curved chord, T-joints with concave chord and T-joints with convex chord have been proposed. The strengths calculated using the recommended design equations were consistent with the parameter analysis results, the recommended design equations have a certain guiding significance.