Experimental Study on Hysteretic Behavior of Double-Plate Reinforced Overlapped K-Joints

The lifetime of hollow section tubular joints frequently can be shortened owing to the occurrence of the welded cracks and the plastic deformation of chords under the cyclic loading, because of the deficient radial bearing capacity of the steel tube. To avoid such failures, this paper proposes a novel method to strengthen the chord with double plates at the intersection of the chord and braces. To further investigate the efficiency of this strengthening method on hysteretic performance and energy depletion ability of the overlapped K-joints with hollow sections, two unreinforced K-joints and two reinforced K-joints were fabricated. By loading on the braces with collaborative cyclic loading, the joints failure modes, hysteresis curve, and skeleton curve were obtained. The bearing capacity, ductility, and energy depletion of the joints were assessed and the restoring force model of joints was proposed. The results show that the failure mode of the unreinforced joint is the plastic failure of the surface of the chord. For the K-RC1 (double-plate reinforced square hollow section tubular K-joints), cracks appeared at the junction weld between the through brace and the overlapped brace. However, cracks extended along the weld at the intersection of the chord and the through brace for K-CC1 (double-plate reinforced circular hollow section tubular K-joints). There is no obvious deformation on the chord surface of reinforced joints. Experimental results reveal that the mechanical properties of the joints can be improved effectively by such reinforcement measures and that the plastic deformation of the chord can also be restrained. Meanwhile, the reinforcement measures demonstrate the ability to avoid the risk of large stress concentration of the chord in the area where the braces and chords are intersected. The bearing capacity of the joint was increased; however, the ductility of the joint was weakened.