Concrete-filled Steel Tube Specimens Research Articles

Experimental behaviour of RACFST stub columns after exposed to high temperatures

The experimental studies on the behaviour of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposed to high temperatures are reported in this paper. Forty specimens, including 32 RACFST stub columns and 8 normal concrete-filled steel tube (CFST) stub columns as reference, were tested, and the failure pattern, load versus strain relation and ultimate strength of the specimens were presented and analysed. Five types of concrete were produced: one reference concrete with natural aggregates, two concrete mixes with recycled coarse aggregate (RCA) replacement ratios of 50% and 100%, and two concrete mixes with recycled fine aggregate (RFA) replacement ratios of 50% and 100%. The specimens were exposed to 300°C, 600°C and 800°C for 3h. The test results showed that, due to the existence of the recycled aggregates, the post-fire performance of RACFST stub columns was lower than the corresponding normal CFST specimens under the same maximum temperature suffered, and the RACFST specimens with RCA had a better behaviour than those with RFA under the same recycled aggregate replacement ratio.

Concrete filled steel tube (CFST) columns subjected to concentrically partial compression

This paper studies the behaviour of thin-walled concrete filled steel tube (CFST) column subjected to concentrically partial compression. A series of tests was carried out to investigate the effects of sectional type, length-to-diameter (width) ratio, partial compression area ratio and top endplate thickness on the behaviour and bearing capacity of partially loaded CFST column. Twenty-six CFST specimens were tested, and the bearing capacity, load versus deformation relation and failure mode of the specimens were obtained. It was shown that the CFST columns under concentrically partial compression generally had reasonable bearing capacity and ductility. A finite element analysis (FEA) model was developed for simulating the behaviour of CFST column subjected to concentrically partial compression, and a comparison of the performances predicted using this model showed generally good agreement with the test results. The FEA model was then used for the mechanism analysis of CFST column subjected to concentrically partial compression. Finally, a simplified model that could be used to predict the bearing capacity of the composite column under concentrically partial compression was proposed.

Compressive behavior of T-shaped concrete filled steel tubular columns

Special-shaped column structures improve residential architectural space, compared with traditional frame structures. However, in respect to applicable building height and seismic fortification intensity, traditional special-shaped reinforced concrete (RC) columns have strict limitations in seismic behavior, which hampers further generalization and application of special-shaped columns. Due to increase in constraint effect for concrete, special-shaped concrete-filled steel tube (CFST) columns are expected to behave advantages on the strength, ductility and seismic behavior over special-shaped RC columns. However, special attention should be paid to prevent the steel plates’ premature local buckling and the separation between steel tube and concrete at inner corners. The battlement-shaped bar stiffeners and tensile bar stiffeners, welded on tube surfaces, were first put forward in this paper. Experimental study of 9 stubs in three groups subjected to axial loads was conducted, and the specimens consist of 3 square stubs (including 1 non-stiffened and 2 stiffened CFST specimens) and 6 T-shaped stubs (including 1 RC specimen, 2 non-stiffened and 3 stiffened CFST specimens). Failure modes and static properties of the specimens were investigated. Experimental results reveal that: Due to the constraint effect provided by T-shaped tubes, the CFST specimens behave advantages on the RC specimen in the ascending stiffness, peak resistance and ductility (except for the battlement-shaped bar stiffened CFSTs). For square and T-shaped stiffened CFST specimens, the stiffeners improve their ductility, especially the tensile bar which gives the best performance in ductility and improves the peak resistance substantially. The stiffeners postpone the buckling of tubes, and even upgrade the classification of composite sections, without thickening the tubes.

Experimental Studies on Concrete Filled Steel Tubes under High Strain Rate Loading

A split Hopkinson pressure bar equipment was used to perform high strain rate compressive tests on concrete filled steel tubes (CFT) along with benchmark plain concrete cylinders for comparison. This paper reports the results of dynamic compressive strength, ultimate strain, residual strength and the secant stiffness. The dynamic increase factor (DIF) of CFT strength upon the increase of strain rate was obtained based on the logarithm linear fitting of the test results. The DIF of the CFT specimens can be relatively well estimated with conservatism using the simple superposition of dynamic uniaxial strength of concrete and steel. The confinement stress and the confinement coefficient under high strain rate loading are also discussed based on assumptions similar to those used for the static loading cases.