Double-skin Tubular Stub Columns Research Articles

Axial compressive behavior and modeling of fiber-reinforced polymer-concrete-steel double-skin tubular stub columns with a rectangular outer tube and an elliptical inner tube

This paper presents the experimental results of monotonic axial compression tests on eighteen glass fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular stub columns (DSTCs) with a rectangular outer glass FRP tube and an elliptical/rectangular inner steel tube, as well as eight rectangular glass FRP-confined hollow stub columns (FCHCs) with an elliptical inner void. The effects of cross-sectional aspect ratio, FRP thickness, void area ratio and the shape of inner steel tube (i.e., elliptical and rectangular) on the axial compressive behavior of confined concrete core in rectangular DSTCs are considered and analyzed. The test results demonstrate that rectangular DSTCs possess excellent bearing capacity and ductility. Additionally, the axial stress-strain curves of confined concrete core in rectangular DSTCs are approximately trilinear and show obvious post-peak softening phenomenon because of the non-uniform and insufficient confinement. Furthermore, the larger aspect ratio, the thicker FRP tube, the higher void area ratio, as well as elliptical inner steel tube (compared with rectangular) have positive confinement effect on the axial compressive behavior of confined concrete core in rectangular DSTCs. Based on the analysis of experimental data, a design-oriented three-stage stress-strain model (considering post-peak softening behavior) of confined concrete in rectangular DSTCs with elliptical inner steel tube is proposed. Through the comparison, it is found that the predictions calculated by the proposed model accord well with the experimental results.

Compressive behavior of double-skin tubular stub columns with recycled aggregate concrete and a PET FRP jacket

This paper presents an experimental study on the compressive behavior of hybrid fiber reinforced polymer (FRP)-concrete-steel double-skin tubular stub columns (DSTSCs) with recycled aggregate concrete (RAC) and a polyethylene terephthalate (PET) FRP jacket. RAC is a green, sustainable alternative to natural aggregate concrete (NAC), while its mechanical properties are generally inferior to NAC. Polyethylene terephthalate (PET) FRP is manufactured from recycled plastics and has a large rupture strain (LRS) value of more than 7% compared to pure polyethylene FRP. In this study, a total of 20 DSTSC specimens were tested under axial compression. The main parameters studied were the RAC replacement percent (0, 50 and 100%), the FRP jacket thickness, and steel tube thicknesses (3 and 5 mm). Test results indicated that the compressive behavior of DSTSC specimens with RAC and PET FRP is similar to that of specimens with NAC and PET FRP, and both types of columns exhibit highly ductile compressive behavior. It is also observed that the compressive behavior of DSTSCs is primarily influenced by the confinement stiffness of the FRP jacket and the steel tube, and the replacement percent of RAC has marginal effect. The increase of the FRP jacket or steel tube stiffness can counterbalance the replacement percent effect of RAC on the axial compressive behavior of DSTSCs. Finally, the suitability of the existing ultimate condition models of different types of DSTSCs was investigated based on the experimental results of this study.

08.29: Experimental investigation of concrete‐filled double skin tubular stub columns with ferritic stainless steel outer tubes

ABSTRACTAn experimental investigation of concrete‐filled double skin tubular (CFDST) stub columns with ferritic stainless steel outer tubes and carbon steel inner tubes is presented in this paper. A total of 14 tests was carried out to study the axial compressive behaviour and strengths of CFDST specimens. The outer tubes were cold‐formed from ferritic stainless steel material (grade 1.4003) into rectangular hollow sections (RHS) with depth‐to‐thickness ratios ranging from 26.1 to 42.1, while the inner tubes were cold‐formed from carbon steel (grade S235) into square hollow sections (SHS) with width‐to‐thickness ratios ranging from 7.5 to 13.5. The gaps between the outer and inner tubes were filled by concrete with three different nominal cylinder strengths of 40, 80 and 120 MPa. The columns had different lengths so that the length‐to‐depth ratio remained at a constant value of 2.5. The CFDST specimens were subjected to uniform axial compression. The column strengths, load‐axial strain relationships and failure modes were evaluated in this paper. The test strengths were then compared with the strengths calculated from the existing design codes, where the guidance given in European Code, Australian Standard and two American Specifications for concrete‐filled columns were used. It is shown that current design rules provide conservative predictions for the resistance of CFDST stub columns with ferritic stainless steel outer tubes.

12.06: Numerical analysis of stainless steel, concrete encased and carbon steel double skin tubular stub columns

ABSTRACTThe use of stainless steel as formwork for concrete columns provides several benefits for the structure, including the high corrosion resistance, durability, fire resistance, ease of maintenance and high aesthetic value. The use of composite systems in columns has been a major breakthrough in bridges and viaducts. A particular advantage of the composite columns is the reduction of cross sectional area, speed of construction, easy maintenance and material saving when compared to conventional reinforced concrete structures. These advantages are related to the idea that the columns are concrete filled eliminating the use of forms and the need for extra steel reinforcing bars. The investigated system adopts a second carbon steel tube inside the primary stainless steel tube composing the structural system made of concrete‐filled double skin composite tube columns (CFDSCT). This study aims to develop numerical models, using the finite element method and considering geometric imperfections. The structural behaviour was assessed through a nonlinear analysis and was later compared to compressive tests performed in the laboratory. After the completion of the numerical models calibration, a parametric analysis was performed to investigate the influence of parameters like the diameter, thickness and height of the stainless steel tube (outer) while its results were also compared to predictions made by traditional design equations.

Testing of self-consolidating concrete-filled double skin tubular stub columns exposed to fire

A concrete-filled double skin tube (CFDST) is an innovative steel and concrete composite construction with the potential to be used as columns in high-rise buildings. Self-consolidating concrete (SCC) can offer convenience for construction and ensure the construction quality of CFDST columns. There is very limited knowledge about the fire performance of CFDST columns, which is a key issue in the application to high-rise buildings. This paper reports an experimental investigation into the fire behaviour of CFDST stub columns filled with SCC and fibre reinforced SCC. The study aims to obtain thermal and structural responses of the stub columns through standard fire testing. Details are given in terms of the failure mode, temperature distribution, critical or limiting temperature and fire resistance. It was found that the added fibre does not affect the temperature distribution whereas the increased concrete thickness and outer tube perimeter reduces the temperature in CFDST specimens. The added steel fibre increases the fire resistance of CFDST stub columns especially for load levels less than 0.6. The critical or limiting temperature for CFDST sections was found to be higher than for CFST (concrete-filled steel tube) or unfilled tubes.