Search

CFST-RC column is modified from CFST laced column in which CFST members are connected with RC web instead of steel bracings. The CFST-RC column has excellent static and earthquake resistant properties, such as high strength, high ductility and large energy absorption capacity. The failure of CFST laced column is ductile; the cracks initiate from RC-web and the column fails due to the formation of plastic hinge at bottom of CFST limbs. Lateral load carrying capacity increases with the increase in the diameter of steel tubes and the thickness of RC-web. Ductility increases with increase in the diameter of steel tubes and decreases with increase in the thickness of RC-web. Under cyclic loading, the hysteretic performance of CFST-RC columns, such as failure modes, ductility, load displacement hysteretic curves, energy absorption capacity, strength, stiffness degradation and load strain curves are studied in this paper.

This paper presents the first study of its kind on the torsional moment behavior of a new dumbbell-shape concrete-filled steel tube (DCFST) system. Experiments were conducted to investigate the effect of the dimensions of the web connecting the two circular CFSTs, in terms of its width-to-diameter (b/D) and its minimum depth-to-diameter (h/D) ratios, on torsional strength (Tu). Torsion tests were also conducted on circular CFSTs (CCFSTs), on hollow tubes and on plain concrete, as control specimens. It was shown that Tu of DCFSTs ranged from 1.3 to 2.2 that of the CCFST, depending on (b/D) and (h/D) ratios. Increasing (b/D) from 0.31 to 0.54 resulted in only 7% increase in Tu. However, a further increase from 0.54 to 1.0 resulted in an additional 31% increase in Tu. The effect of (h/D) on Tu was more pronounced at higher (b/D) ratios. In general, increasing the web width appears to be more effective than web height. A rigorous nonlinear finite element model was developed and a simple mechanics-based design equation have been proposed to predict Tu of CCFSTs and DCFSTs and resulted in an average predicted-to-experimental Tu of 0.98.

In general, the calculation of ultimate load capacity (UL) of a concrete-filled steel tubular (CFST) column is based on the assumption that the load is resisted by both the steel tube and the concrete core simultaneously as a composite member. However, steel tubes of CFST columns are preloaded due to self-weight, wet concrete weight as well as temporary construction loads before the composite action is formed. There is still no consensus on how the preload affects the loading resistance of CFST columns and how to quantify the effect of preload on the ultimate strength. The paper reported an experimental study on circular CFST columns subjected to preload. The testing results showed that the preloading effect increased with the increase of slenderness, decreased the ultimate load capacity and increased the deformation significantly at high preloading ratio, but did not have much influence on the ultimate load capacity at light preload. Then, a parametric analysis of coupled effects of preloading ratio with other parameters, such as slenderness ratio, eccentric ratio, as well as material properties, is presented. Finally, a simplified method is proposed to predict the ultimate load capacity of CFST columns with preload. The preloading reduction factor of simplified methods of UL based on regressive analysis can be used to evaluate the UL of CFST columns with preload after verified by overall comparison of total preloading tests.

This paper describes an experimental study on the flexural and eccentric compressive behavior of concrete-filled square steel tube (CFSST) beam-columns stiffened with PBL stiffeners. Three types of CFSST beam-columns were fabricated and tested under the flexural moment and eccentric compressive load. Among the three types of columns, the two types of columns were strengthened with the PBL and steel plate stiffeners; the other type of columns was not strengthened. In addition, extensive finite element analyses (FEA) were carried out to evaluate the stress distribution. Flexural test results show that failure modes of specimens without stiffeners were different from specimens with the PBL or steel plate stiffeners. The results also demonstrate the distribution of cracks in the concrete was affected by stiffeners and the columns with the PBL stiffeners have the most uniformed crack distributions. The capacity improved by the PBL stiffeners was insignificant. However, the flexural stiffness of the specimen stiffened with the PBL stiffeners was about 20% larger than the unstiffened specimen. Eccentric compressive load test results show the capacity of specimen with the PBL stiffeners was 6.95% larger than the unstiffened specimen. The eccentric compressive capacity decreased with the increase of the eccentricity ratio or slenderness ratio. FEA results show that stiffeners can effectively improve the mechanical behavior of CFSST specimens under bending and eccentric compressive loads.