STUDY ON N_u -M_u CORRELATION CURVES OF CONCRETE FILLED DOUBLE SKIN STEEL TUBULAR (CFDST) BEAM-COLUMNS WITH EXTERNAL STAINLESS STEEL TUBE

Concrete filled double skin steel tubular (CFDST) members with external stainless steel tubes present the merits of CFDST members and stainless steel, and have a wide application prospect in bridge piers, in offshore platforms and, in transmission towers. For this purpose, totally 225 CFDST beam-columns with outer stainless steel tubes were systematically analyzed using a fiber-based model in this work. The influences of the parameter on the typical N/N_u-M/M_u curve were investigated, and the obtained curves were compared with those of CFDST members with carbon steel. Finally, the correlation curve equation of N/N_u-M/M_u was proposed. The study results showed that: the fiber-based model program developed could well predict the compression-bending capacity and the development of N/N_u-M/M_u curve of CFDST members with external stainless steel tube; the shape of N/N_u-M/M_u curve is affected by the concrete strength, by the ratio of the diameter to the thickness of the inner steel tube, by the yield strength of steel, by the hollow ratio, by the nominal steel ratio and, by slenderness ratio; due to an obvious strain-strengthening effect of stainless steel, the N/N_u-M/M_u curves of the CFDST members with external stainless steel tubes are close to the steel members when compared to those of the CFDST members with external carbon tubes; and the characteristic-point and N/N_u-M/M_u formulas for CFDST members with outer stainless steel based on the test and parametrical results were suggested by modifying the formulas used for the companion with outer carbon steel, the calculation results by the formulas modified indicate a good agreement with the program-calculated results.