Research On The Hysteretic Behaviour Of Tubular N-joint

With the advantage of simple construction and appearance, tubular joint has become an important kinds of joints for circular hollow sections (CHS) structures. Recently, lots of research has been carried out for the load capacity of tubular joints. Design equations from theoretical and experimental studies have been adopted by related codes. However, little works has been done on the hysteretic behavior of tubular joints. China is a country with frequent earthquakes. All structures in seismic zones should be designed to resist the action of earthquake. The performance of the joints under earthquake will affect the overall seismic behavior of the structures. Therefore, it is necessary to understand the seismic behavior of tubular joints through the study of their hysteretic behavior.In this study, the triangle steel truss structure of Beidaihe Train Station was taken as a case study. The hysteretic behavior of tubular N-joints was studied by experiments and finite element analysis. The hysteretic curves of the joints were determined. The effect of cover plate and in-filled concrete on the hysteretic behavior and failure modes of the joints was investigated. The load capacity ratio, the first yield displacement and force and the ductility ratio were evaluated and compared for four types of tubular N-joints. The effect of wielding on steel property and hysteretic behavior was also studied. The conclusions of the study are as the following: (1) the four types of tubular N-joints studied have good hysteretic behavior and can be used in CHS structures in seismic zone; (2) second-time welding has little effect on steel properties and the hysteretic behavior of tubular N-joints; (3) hysteretic curves determined by finite element analysis agreed very well with the experimental results, which means that finite element method is efficient and reasonable for hysteretic behavior determination of tubular N-joints; (4) cover plate and in-filled concrete restrict the development of plastic zone in the joint region and aggravate the hysteretic behavior of the joint region. However, the tubular N-joints will keep their hysteretic behavior by developing plastic zone at other location of the joints, such as the ends of braces.