Behavior of CFDST stub columns under preload, sustained load and chloride corrosion

For a concrete-filled double skin steel tubular (CFDST) column in practice, during the construction stage, both the inner and the outer hollow tubes are subjected to the constructional load; during the service stage, the whole composite cross-section is mainly subjected to compression. If it is used in offshore structures, the outer steel tube is subjected to chloride corrosion as well. However, the information is still limited on the structural behavior of CFDST columns under the combination of preload on hollow tubes, the sustained load on the composite cross-section and chloride corrosion on the outer tube. In this study, a finite element analysis (FEA) model is developed to predict the structural behavior of CFDST stub columns with considerations of these factors, where the long-term effect for concrete under sustained load is applied. The experimental work is also conducted for CFDST stub columns subjected to corresponding loading protocols, and the test results are used to calibrate the numerical model. Discussions are made on the differences of specimens with and without considerations of these factors. It has been found that, the results from the verified FEA model have generally good agreement with measured results in all loading stages. The corrosion of outer steel tube leads to a large reduction of column strength, and the influences of the preload and long-term sustained load can be tentatively estimated by multiplying different coefficients together.