Behaviour and Calculations of Concrete-Filled Double Skin Steel Tubular (CFDST) Members Lin-Hai Han * Fei-Yu Liao * Zhong Tao ** * Department of Civil Engineering, Tsinghua University, Beijing, 100084, China ** College of Civil Engineering, Fuzhou University, Fuzhou, 350108, China Abstract This paper briefly summarises some recent research outcomes of concrete-filled double skin steel tubes (CFDST). The design approach and behaviour of CFDST members presented by the authors and their collaborators are briefly introduced. The topics covered in this paper include members subjected to static and dynamic loading, effects of long- term loading, fire performance and residual strength after exposure to fire. Future research needs are identified. Keywords: Concrete-filled double skin steel tubes (CFDST), behaviour, design, static, long-term, cyclic, fire 1. Introduction CFDST (Concrete-filled double skin steel tube) is a new type of composite construction, which consists of two concentric steel tubes with concrete sandwiched between them. CFDST members combine the advantages of the well-known concrete-filled steel tube (CFST) and the conventional hollow reinforced concrete (RC) columns. Thus, CFDST columns have a series of advantages, such as high strength and bending stiffness, good seismic and fire performance, and favorable construction ability. Figure 1 (a), (b) and (c) shows three typical profiles of the CFDST sections (designated as circular, square and rectangular CFDST respectively in this paper), where B o is the width of outer square or rectangular steel tube, B i is the width of inner rectangular steel tube, D o is the diameter of outer circular steel tube or the depth of outer rectangular steel tube, D i is the diameter of inner circular steel tube or the depth of inner rectangular steel tube, t o , and t i are the thicknesses of outer and inner steel hollow sections, respectively. CFDSTs have great potential to be used as columns or piers in structures. In the past, the behaviour of CFDST columns has been the subject of investigations (Wei et al., 1995; Yagishita et al., 2000; Lin and Tsai, 2001; Zhao and Grzebieta, 2002; Han et al.; 2004; Tao et al., 2004; Zhao and Han, 2006; Tan and Han, 2006; Han et al., 2006; Han et al., 2009a). Figure 1. CFDST cross-section configurations This paper briefly summarises some recent research outcomes of concrete-filled double skin steel tubes Sandwiched concrete D i D o t o t i Outer steel tube Inner steel tube (a) Circular t o t i Outer steel tube Sandwiched concrete Inner steel tube D i B o (b) Square (c) Rectangular t o t i Outer steel tube Sandwiched concrete Inner steel tube D o B o B i D i