Mechanical Performance of Circular Ultrahigh-Performance Concrete–Filled Double Skin High-Strength Steel Tubular Stub Columns under Axial Compression

This paper proposed a new type of stiffened circular ultra-high performance concrete-filled double skin steel tubular (UHPCFDST) column, in which stiffeners were applied to connect both inner and outer steel tubes. It efficiently delayed the local buckling of steel tubes and enhanced the integral of the section. This new type of UHPCFDST can be named multicells ultra-high performance concrete-filled double skin steel tubular (MUHPCFDST) column since the stiffener divided the sandwich space between the two steel tubes into multicells. Both the UHPCFDST and MUHPCFDST stub columns were fabricated and tested under centrally compression loading to investigate the axial mechanical behavior. The parameters considered in this study included specimen size, diameter-to-thickness ratio, the quantity of stiffener, and hollow ratio. Based on the tests, specimens' column failure mode, axial load-shortening curves, local buckling behavior, compounding strength, strength index, and ductility coefficient were obtained and discussed. Then, the authors proposed a uniaxial stress-strain function of ultra-high performance concrete under compression and established three-dimension finite-element (FE) models with this stress-strain model to simulate the axial behavior of UHPCFDST and MUHPCFDST columns. Compared with the experimental results, the average deviation of the FE analysis in predicting the column bearing capacity and corresponding axial shortening was −3% and −5.5%, respectively. Finally, parametric studies were carried out, and a calculation method was proposed. The parametric analysis results and predictions from different methods (including the proposed method and methods suggested by existing design codes) were compared. The proposed method and calculating methods provided in AIJ-2008, EC4, and AS/NZS 2327 can reasonably predict the ultimate bearing capacity of both circular UHPCFDST and circular MUHPCFDST columns.