Experimental Study on the Behavior of a Novel Stiffened Hexagonal CFDST Stub Column under Axial Load

Abstract

A concrete-filled double skin tube (CFDST) consists of an outer steel tube, an inner steel tube, and the space between them filled with concrete. Existing studies have shown that the buckling of steel tubes can be significant in noncircular CFDST for nonuniform confinement or a large width-thickness ratio. Stiffening of the steel tubes is necessary to fully utilize the strength and improve the load-carrying capacity of CFDST. Against this background, the author proposed a novel stiffened hexagonal CFDST column with steel strips welded on both the inner tube and outer tube to form several closed cavities. This paper presents an experimental study on the axial compressive behavior of this new type of CFDST column. The experimental program consisted of five stiffened hexagonal CFDST specimens and two reference specimens for comparison, and the test variables were the hollow ratio and rib width. The test results showed that the ultimate bearing capacity and ductility of the CFDST specimens were greatly enhanced by the steel strips and ribs. Moreover, the finite-element (FE) method was used to develop a three-dimensional model of the CFDST column subjected to axial loading and validated against the experiment. The average error of the FE analysis when predicting the column bearing capacity was 0.029 compared with experimental results. Based on the FE model, a parametric study was conducted to analyze further the effect of each parameter on the axial behavior. Furthermore, a strength design formula was developed to estimate the compressive strength of the novel hexagonal CFDST column.