Experimental study on structural performance improvement of Concrete Steel Tube joints

Abstract

Most of the defects and damages occurring in the steel bridges are caused by the use of high strength steel and the damage and breakage due to the stress concentration phenomenon acting on the discontinuity of the joint. Unlike road bridges, railway bridges are characterized by the large number of times a large load passes near the design load, which causes local damage to the joints due to the fact that the actual stress range is very large. Especially, it is necessary to consider the local damage due to the stress concentration phenomenon at the joint when designing the structure using the unreinforced hollow steel tube. Various methods of reinforce joints have been proposed to mitigate this stress concentration, and the method of Concrete Fille Steel Tube(CFT) is a effectively mitigating stress concentration while maintaining aesthetic appearance. However, existing studies on detail and reinforcement of CFT, member joints have been made mainly on joints in architectural of offshore structures. There is a difference in the design criteria of steel structure and in the international standard in terms of yield ratio and slenderness ratio. Especially, the study on complicated local behavior of steel tube joint is insufficient. As a result, the design formula is continuously revised based on many experiments and interpretations abroad. In this study, the improvement of the structural performance of the CFT joints through the stress dispersion effect was quantitatively evaluated in various fracture types. In particular, the stress dispersion effect of the CFT members was evaluated in terms of stiffness, strength, ductility and fatigue, Is expected to improve overall.