Concrete-filled Double-skin Tubes Research Articles

Heat Transfer in Ultra-High-Performance Concrete-Filled Double-Skin Tubes Under Fire Conditions

Heat Transfer in Ultra-High-Performance Concrete-Filled Double-Skin Tubes Under Fire Conditions

Behaviour of CFDST and RCC member hybrid frames

This paper presents the results of an experimental investigation and Finite element analysis of concrete-filled double skin tubes (CFDST) using hot rolled square hollow sections having cross-section of 100 mm for outer tube and 30 mm for inner tube. The annulus between the two steel hollow sections is filled with M-25 grade of concrete. The picture frame testing procedure has been adopted for the analytical and experimental investigations. Two opposite members were provided as CFDST members, while as other two members were provided as normal reinforced cement concrete (RCC) members with equivalent amount of steel as used in CFDST members. The finite element analysis of the frame has been done using Simula Abaqus finite element package. The results were compared with the frames without the CFDST members, i.e. the CFDST members replaced with normal RCC members, which were also experimentally as well as analytically. It was found that the performance of CFDST frame is better than that the conventional RCC member frame. The load-carrying capacity of the frame with CFDST members is above 30% more with lesser deflection in horizontal as well as in vertical direction.

Experimental tests and design of rubberised concrete-filled double skin circular tubular short columns

The adequacy of rubberised concrete (RuC) for use in structural columns is, currently, investigated experimentally through the use of cold-formed double-skin circular steel tube confinement. The RuC is of particular interest because the aggregate can be sourced from recycled tyres, so it is a form of sustainable concrete, and it possesses superior mechanical properties to conventional concrete such as increased ductility and energy absorption. Rubberised concrete does have one major issue in that it has a low compressive strength compared to normal concrete, which limits its application. The aim of this study is to evaluate the effectiveness of confinement in overcoming this mechanical deficiency by using rubberised concrete-filled double-skin tubes (RuCFDST). The experimental program involves testing and measurements of key mechanical properties including compressive strength, hoop and axial strains, and compressive load-deflection curves. A total of 15 composite specimens were examined to ascertain the varying properties of single-skin, double-skin, confined, unconfined, standard and rubberised concrete. Recycled rubber particles ranging from two to seven millimeters in size were used to replace 15% and 30% of the fine and coarse concrete aggregate by weight. The rubber particles were treated with sodium hydroxide solution resulting in increased bonding strength to the concrete. Circular hollow section (CHS) configurations of different internal and external dimensions were also examined to further understand the mechanics of double-skin confinement. Confinement in RuCFDST showed significant improvements in strength and ductility properties. Experimental results proved to be in agreement with design ultimate axial strength predictions proposed by existing methods and design codes. Given the exceptional ductility, energy dissipation and improved strength of RuCFDST, this study shows the potential viability of RuCFDST as structural columns particularly in areas that are prone to seismic activity.

Finite element modelling of concrete-filled double-skin short compression members with CHS outer and SHS inner tubes

Composite steel-concrete construction utilising the benefits of both materials has extensively been used in structural engineering with the ability to be used in onshore and offshore applications. One of these elements is the concrete-filled double-skin tubes (CFDST) which is a concept that has been developed in recent years. In this column, the steel tubes can support considerable amounts of loads while providing permanent formwork to the concrete. Likewise, the steel tubes add confinement to the concrete whereas the concrete infill delays the local buckling of the steel tubes. This paper provides the behaviour of CFDST short columns under concentric compressive loads. The specimens studied consist of an outer skin, which is a circular hollow section (CHS), and an inner skin, which is a square hollow section (SHS), with the annulus filled with concrete while the inner tube is completely empty. A finite element (FE) analysis is generated in order to analyse the performance of such columns. Therefore, to assure the accuracy of the modelling of these specimens, FE models with concentric axial loads are developed and compared against results from past experiments. In view of this, different stress-strain curves for structural steel and concrete infill are identified, and those that provided the best curve fittings were selected for the parametric study. Accordingly, the best combination of the constitutive models of both the steel (suiting the cold-formed tubes) and the concrete (filled in double-skin tubes) is found based on previous research and considered herein. The study aims at examining the effect of various diameter-to-thickness (Do/to) ratios, width-to-thickness (Bi/ti) ratios and material properties such as nominal compressive strength and nominal yield strength on the fundamental behaviour of CFDST. In the parametric study, high nominal compressive strengths are tested, and the steel tubes are cold-formed from different design yield strengths. Overall, this paper provides important conclusions for current circular CFDST short columns with an inner SHS and an outer CHS.

Flexural Behavior of Concrete-Filled Double-Skin Tubes Subject to Blast Loading

AbstractLarge-scale tests on concrete-filled double-skin tubes, composed of pairs of concentric cold-formed rectangular hollow section members with the annulus between them filled with grout, are p...

Experimental study of CFDST columns infilled with UHPC under close-range blast loading

Concrete-filled double-skin tubes (CFDST) have been increasingly popular in the field of engineering in recent years. A lot of research has been carried out to investigate the behaviour of CFDST members under a variety of loading conditions. This paper presents an experimental investigation on ultra-high performance concrete infilled double-skin tube columns subjected to close-in blast loading. Two types of CFDST columns were investigated in the experiments – one with both inner and outer tubes circular and the other one with both square. The main test parameters included the explosive charge weight and the magnitude of axial load. After the blast tests, there was no visible buckling nor ruptures found on the steel tubes and only minor cracks, of no more than 1mm width, were observed in the core concrete when the outer steel tube was removed. Based on the findings of the experiments, it is evident that CFDST column has excellent blast resistance. This feature has the potential to be used in high-value structures which may be the targets of terrorist attacks, such as embassies, government buildings and critical infrastructures.

Residual axial capacity of CFDST columns infilled with UHPFRC after close-range blast loading

Concrete-filled double-skin tubes (CFDST) consist of two concentrically placed steel tubes with concrete filled in between and they have more and more commonly been used in the field of civil engineering in recent years. A number of recent researches evidenced the excellent performance of CFDST columns under a variety of loading conditions. However, very limited knowledge is known about the residual axial capacity of CFDST columns following severe blast loadings. This paper presents an experimental study on the residual behaviours of ultra-high performance concrete infilled double-skin steel tubular columns after close-in blast loading. In total, eight CFDST columns, including 3 square ones and 5 circular ones, were first tested under different blast loads with two axial load levels. After the blast tests, all CFDST columns were transported to the laboratory and each of them was then subjected to static axially compressive load until failure. It was found that the CFDST columns with smaller permanent displacement had larger peak residual axial capacity and the CFDST columns which were not subjected to axial load during the blast test exhibited more ductile behaviour than those which were axially loaded during the blast test.

Research on Bearing Capacity of Short Concrete Filled Double Skin Steel Tubes Columns under Axial Compression

The use of steel tube confined concrete columns has been the interests of many structural engineers. For investigation of the axially loading capacity of short concrete filled double skin tubes (CFDST) columns, axial compression loading experiments were carried on 9 short CFDST column samples. According to experimental results and with numerical analysis, an ultimate load estimation equation of CFDST column with one correction parameter is presented, the linear relation between the parameter and the inner-to-outer diameters ratio Di/Do is given out. The ultimate load estimation equation is validated by the test results of short CFDST column samples.

Compressive stiffness and strength of concrete filled double skin (CHS inner & CHS outer) tubes

This paper investigated the stiffness and capacity of concrete filled double skin tubes (CFDST) column under axial compression. The column has circular hollow section (CHS) as both outer skin and inner skin. Stiffness of CFDST columns under small displacement was analyzed by the energy method. The modified elastic modulus of the between concrete and steel tubes were deduced respectively to calculate the composite stiffness of the CFDST stub column. According to the unified theory of concrete filled steel tube (CFST), the bearing capacity of the stub column was predicted by presenting the equivalent confinement coefficient of CFDST. The composite modulus and ultimate strength of the stub columns were calculated in comparison with corresponding test value, and it was found that there was good agreement between theoretical and experimental results.

Double skin composite construction

AbstractThere are several types of composite construction such as reinforced concrete (RC) sections, concrete‐filled tubes (CFT), composite beams, floors and frames, steel–concrete–steel sandwich (SCSS) double skin panels and concrete‐filled double skin tubes (CFDST). This paper focuses on CFDST. It gives the background, advantages and challenges of CFDST. The behaviour of such members subjected to static and dynamic loads are described. Future research in this area is pointed out.

Tests of concrete-filled double skin CHS composite stub columns

This paper describes a series of compression tests carried out on concrete filled double skin tubes (CFDST). Both outer and inner tubes are cold-formed circular hollow sections (CHS). Six section sizes were chosen for the outer tubes with diameter-to-thickness ratio ranging from 19 to 57. Two section sizes are chosen for the inner tubes with diameter-to-thickness ratio of 17 and 33. The failure modes, strength, ductility and energy absorption of CFDST are compared with those of empty single skin tubes. Increased ductility and energy absorption have been observed for CFDST especially for those having slender outer tubes with largerrndiameter-to-thickness ratio. Predictions from several theoretical models are compared with the ultimate strength of CFDST stub columns obtained in the tests. The proposed formula was found to be in good agreement with the experimental data.

Strength and ductility of concrete filled double skin (SHS inner and SHS outer) tubes

This paper describes a series of compression and bending tests carried out on concrete filled double skin tubes (CFDST). Theoretical models developed to predict the ultimate strength of CFDST stub columns and beams are also described. Both outer and inner tubes were cold-formed C450 (450 MPa nominal yield stress) square hollow sections (SHS). Four different section sizes were chosen for the outer tubes with a width-to-thickness ratio ranging from 16.7 to 25.0. One section size was chosen for the inner tube which had a width-to-thickness ratio of 20. It was found that there is an increase in ductility for CFDST both in compression and bending when compared to empty single skin tubes. It was also shown there was good agreement between theoretical and experimental results.