Experimental Study on hysteretic behaviour of tubular N-joints

Tubular joints are often adopted in CHS structures due to their simple and aesthetic appearance. The ultimate load carrying capacity of this kind of joint has received lots of attention in the past 30 years. However, little research work has been carried out on their hysteretic behavior. In this paper, the hysteretic behaviour of tubular N-joints was studied experimentally. Four specimens were built and tested under quasi-static cyclic loads. They are unstiffened tubular N-joint, doubler plate reinforced tubular N-joint, tubular N-joint with concrete filled chord member and doubler plate reinforced tubular N-joint with concrete filled chord member. The failure modes of the four specimens under cyclic loads were observed during the tests. The hysteretic curves obtained for all the four specimens are plump and stable. Based on the hysteretic curves, the ductility ratio and the energy dissipation ratio were evaluated and compared for the four specimens. The ultimate load carrying capacities of the specimens determined from their skeleton curves are also discussed and compared.