Double Skin Steel Tubular Columns Research Articles

Sustainable FRP–recycled aggregate concrete–steel composite columns: Behavior of circular and square columns under axial compression

This paper presents the results of an experimental study on the behavior of fiber reinforced polymer (FRP)–recycled aggregate concrete (RAC)–steel double-skin tubular columns (DSTCs) under concentric compression. Influences of the concrete strength, DSTC cross-sectional shape, and aggregate replacement ratio were experimentally investigated through the test of 24 hollow-core circular and square DSTCs. Results indicate that the overall behavior and performance of RAC DSTCs closely resemble that of DSTCs manufactured with conventional concrete, which is highly promising for structural use of RAC in the construction industry. The aggregate replacement ratio has limited influence on the ultimate condition of DSTCs. On the other hand, the replacement ratio has some influence on the trend of the stress-strain curve of concrete in DSTCs, and this is more pronounced in square specimens than in circular specimens.

Compressive Behavior of Double-Skin Tubular Columns with High-Strength Concrete and a Filament-Wound FRP Tube

AbstractHybrid fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular columns (DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them filled with concre...

Fire performance of stiffened concrete filled double skin steel tubular columns

A major deficiency of the concrete-filled double skin steel tube (CFDST) columns in fire exposure is the inadequate steel-concrete interface bonding leading to separating concrete and steel surfaces at elevated temperatures and triggering buckling failure of the columns. To improve interface interaction as well as postpone overall buckling, it is proposed in this study to use longitudinal steel stiffeners in CFDST columns. Different patterns of stiffeners including six, four and two number of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes are considered in the analysis. A sequentially-coupled thermal-stress analysis procedure is conducted to evaluate the effects of different patterns of stiffeners on the fire performance of these columns. One of the novelties of the current study is the incorporation of the confinement effects of both inner and outer tubes on the compressive strength of concrete at elevated temperatures which gives a realistic prediction of the fire resistance behavior of the CFDST columns. From the results, it is found that among the different patterns studied, stiffeners embedded in the exterior surface of the inner tubes or interior surface of the outer tubes enhancing steel-concrete interface interaction have a determinant role in much-improving fire endurance of the columns. With increase in the load ratio fire resistance of the specimens decreases drastically. The stiffeners strength and concrete strength have minimal effect on the fire performance of the stiffened CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

Concrete-Filled Double Skin Steel Tubular Columns Exposed to ASTM E-119 Fire Curve for 60 and 90 Minutes of Fire

Concrete-filled double skin steel tubular (CFDST) columns with outer steel tubes varying in diameter and thickness were exposed to ASTM E-119 fire curve for 60 and 90 minutes. All specimens (control and heated) failed by outward local buckling of outer steel tube, crushing of concrete and outward and inward buckling of inner steel tube. Residual Strength Index (RSI), secant stiffness and Ductility Index (DI) were calculated in order to compare the performance of control and fire-damaged CFDST columns. It was found that specimens with 90 minutes of fire exposure time possessed highest RSI. Meanwhile, secant stiffness seems to decrease with increased exposure time. And finally, CFDST columns became more ductile after being heated.

Reflections on Mechanisms Affecting the Behavior of FRP-Concrete-Steel Double-Skin Tubular Columns

This paper presents the results of 20 hollow and concrete-filled double-skin tubular columns (DSTCs), which were tested as part of a comprehensive experimental program that was undertaken at The University of Adelaide on FRP-concrete steel DSTCs. The paper is aimed at providing important insights into the influence of two key parameters, namely the diameter of inner steel tube and presence/absence of a concrete-filling inside the inner steel tube, which play major roles in the column behavior through their influences on a series of interacting mechanisms that govern the complex system behavior. A detailed examination of the results yielded a number of important insights into the mechanisms that influence the compressive behavior of DSTCs.

Behavior of square fiber reinforced polymer–high-strength concrete–steel double-skin tubular columns under combined axial compression and reversed-cyclic lateral loading

This paper presents an experimental study on seismic behavior of square fiber reinforced polymer (FRP)–concrete–steel columns. Six hybrid double-skin tubular columns (DSTCs) manufactured using high-strength concrete (HSC) were tested under combined axial compression and reversed-cyclic lateral loading. The main parameters under investigation were the axial load level, size of inner steel tube, provision (or absence) of a concrete-filling inside the steel tube, and the column aspect ratio. The results indicate that, in general, square DSTCs exhibit very ductile behavior under combined axial compression and reversed-cyclic lateral loading. However, the important influence of the axial load level on the column behavior is evident, with an increase in the load level leading to a significant decrease in the lateral deformation capacity of DSTCs. The results also indicate that a DSTC with a larger inner steel tube exhibits lower lateral displacement capacity than that of a companion DSTC with a smaller inner steel tube. It is shown, however, that provision of a concrete-filling inside the inner steel tube leads to a significant increase in the lateral deformation capacity of a DSTC with a larger inner steel tube to a level that is higher than that seen in a companion DSTC with a smaller hollow inner steel tube. Experimental results are presented together with accompanying discussions on the influence of the investigated parameters on the seismic behavior of square DSTCs.

Confinement model for concrete in circular and square FRP–concrete–steel double-skin composite columns

This paper presents a new design-oriented model for predicting the ultimate failure conditions of concrete in fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular columns (DSTCs). An experimental test database consisting of all the axial compression test results for DSTCs available in the published literature is presented and used to assess the performance of four existing models to predict the compressive strength and ultimate axial strain of concrete in DSTCs. A new concrete confinement model that incorporates the failure mode of the inner steel tube is proposed. Both the strength and strain predictions of the proposed model are in close agreement with test results to an accuracy better than the existing models.

Theoretical and numerical analysis to concrete filled double skin steel tubular columns under fire conditions

As one of the recently developed steel–concrete composite structural members, concrete filled double skin tubular (CFDST) columns have been used in current construction industry due to its good structural performance. However, CFDST columns could be vulnerable under fire attack. In the current work, the fire resistance of CFDST columns has been studied. Finite element analysis (FEA) models were developed to investigate the fire resistance of unprotected CFDST columns. The FEA models were verified with experimental data from literature. Based on the developed numerical model, the failure mechanism of CFDST columns under fire conditions were studied and a parameter study was performed on the fire resistance design for CFDST columns. Based on the computational analysis, the conventional Rankine approach was extended to predict fire resistance of CFDST columns. Experimental data were used to validate the accuracy of the proposed method; it shows that the proposed method can predict the fire resistance of CFDST columns with reasonable accuracy compared with experimental data.

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.

Experimental behavior of hybrid FRP–concrete–steel double-skin tubular columns under combined axial compression and cyclic lateral loading

Hybrid FRP–concrete–steel double-skin tubular columns (DSTCs) are a new form of hybrid columns, consisting of an outer tube made of fiber reinforced polymer (FRP) and an inner tube made of steel, with the space between filled with concrete. In hybrid DSTCs, the three constituent materials are optimally combined to achieve several advantages not available with existing columns, including their excellent corrosion resistance and seismic performance. Although two existing studies have examined the seismic performance of circular hybrid DSTCs, they have been limited to normal strength concrete, small column dimensions, and small void ratios (ratios between the inner diameter and the outer diameter of the annular concrete section). Against this background, this paper presents the first experimental study on hybrid DSTCs filled with HSC subjected to axial compression in combination with cyclic lateral loading. A relatively large column section (with a diameter of 300mm) was chosen to allow reliable experimental modeling of real columns. The test results indicate that hybrid DSTCs possess excellent ductility and seismic resistance even when high strength concrete with a cylinder compressive strength of around 120MPa is used; column damage is concentrated in a small plastic hinge region near the column bottom end; and the performance of hybrid DSTCs can be enhanced by filling the inner void in the plastic hinge region. The test results provide valuable data needed for the formulation and verification of a theoretical model for the hysteric behavior of hybrid DSTCs, particularly when they are filled with HSC.

Square FRP–HSC–steel composite columns: Behavior under axial compression

This paper presents an experimental study, which investigated the compressive behavior of square fiber reinforced polymer (FRP)–concrete composite columns through the tests of 40 column specimens. 24 FRP–concrete–steel double-skin tubular columns (DSTCs), four concrete-filled FRP tubes (CFFTs), and 12 CFFTs with inner voids (H-CFFTs) were tested under axial compression. The majority of the specimens were manufactured using high-strength concrete (HSC). The key parameters examined included the influence of the strength of the concrete, cross-sectional shape (i.e. circular and square) and dimension of the inner steel tube, and presence (or absence) of a concrete filling inside the steel tube. The results of the DSTCs with circular inner steel tubes indicate that concrete-filling inner tubes results in an increase in the ultimate axial stress but a decrease in the ultimate axial strain of concrete compared to those seen in DSTCs with hollow inner steel tubes. It is observed that concrete in hollow DSTCs manufactured with square inner steel tubes develop significantly lower ultimate axial stresses and strains than concrete in companion hollow DSTCs with circular inner steel tubes. It is found, however, that the performance of these specimens improves dramatically when the square inner steel tube is filled with concrete. Comparisons of the results indicate that concrete in filled DSTCs develops larger ultimate axial stresses and strains than concrete in companion CFFTs. Finally, the results demonstrate that H-CFFTs perform significantly worse than DSTCs and CFFTs, and their performance further degrade as the diameter of the inner void increases.

Investigation of Concrete-Filled Double-Skin Steel Tubular Columns with Ultrahigh-Strength Steel

Concrete-filled steel tubular (CFT) columns have been used increasingly in building structures because of their construction efficiency and provision of high stiffness and strength. A relatively new configuration design with inserted inner steel tubes, so-called concrete-filled double-skin steel tubes (CFDSTs), has been developed in the field. To promote the seismic capability of the CFT/CFDST columns further, the authors present results from an experimental investigation of CFT and CFDST columns using ultrahigh-strength steel. Eight scaled column specimens were examined by subjecting them to combined axial and flexural cyclic loadings. The performance of the CFT and CFDST design configurations using high-strength steel was comparable and both provide large moment capacities and elastic deformation capacities. The ultimate member moment capacity could be predicted accurately using a proposed simple formulation based on the concept of the superposed strength method. Various performance parameters are evaluated and discussed, and the influence of compressive strength of the concrete core, applied axial loads, and inserted inner steel tubes on the seismic behavior of the column members is clarified by the experimental results.

Seismic Behavior of FRP-High-Strength Concrete–Steel Double-Skin Tubular Columns

AbstractThis paper reports on an experimental study on the seismic behavior of fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular (DST) columns. Nine DST and one concrete-filled FRP-tube (CFFT) columns that were made of high-strength concrete were tested under constant axial compression and reversed-cyclic lateral loading. The main parameters of the experimental study were axial load level, amount and type of FRP confinement, concrete strength, sectional shape and thickness of the inner steel tube, and provision (or absence) of a concrete filling inside the steel tube. Of primary importance, the results indicate that DST columns are capable of developing very high inelastic deformation capacities under simulated seismic loading. The results also indicate that the presence of a concrete filling inside the inner steel tube significantly and positively influences the seismic behavior of DST columns. It is found that the performance of the void-filled DST column is superior to that of a compani...

Compressive behavior of aramid FRP–HSC–steel double-skin tubular columns

This paper presents the results of an experimental study on the behavior of fiber reinforced polymer (FRP)–concrete–steel double-skin tubular columns (DSTCs) under concentric compression. Influence of column parameters was investigated experimentally through the test of 16 normal- and high-strength concrete-filled DSTCs and six concrete-filled FRP tubes (CFFTs). The column parameters examined included the thickness of FRP tube; the concrete strength; the diameter, thickness, and shape of inner steel tube. The results of the experimental study show that concrete in a DSTC system is confined effectively by FRP and steel tubes. Both the normal- and high-strength concrete DSTCs tested in the present study exhibited a highly ductile compressive behavior. The results also show that increasing the inner steel tube diameter leads to an increase in the ultimate axial stress and strain of concrete in DSTCs. It is found that, for a given nominal confinement ratio, an increase in the concrete strength results in a decrease in the ultimate axial strain of DSTCs. It is also observed that DSTCs with square inner steel tube confined concrete ineffectively. In addition, it is found that concrete in DSTCs developed similar ultimate axial stresses but higher ultimate axial strains compared to concrete in companion CFFTs. The results of the present study and those from the previously reported studies are then compared with the only existing stress–strain model proposed for DSTCs. Finally, a new design-oriented model that provides improved predictions of the ultimate conditions of concrete in DSTCs was proposed.

The Study on Bearing Capacity of Concrete-Filled Double Skin Steel Tubular Columns of Octagon Section under Axial Compression

Based on unified strength theory solution of thickness cylinder, according to the introducing concrete strength reduction factor and equivalent restriction factor, this paper deduced the axial compressive bearing capacity formula of concrete-filled double skin steel tubular columns of octagon section. Compared the results of the paper with the experiment results，both coincide in good condition. The results show that the theoretical formula are correct and viable. The theoretical formula is expected to provide a theoretical foundation to the research of concrete-filled double skin steel tubular columns of octagon section.And it provides references for the engineering design.

Experimental Study on Concrete-Filled Steel Tubular with External Octagon Steel Tube and Inner Circle PVC-U Pipe under Axial Compression

An investigation of the octagon-shaped concrete-filled double skin steel tubular columns which used PVC-U pipe to replace the steel tube as inner tube was carried out. In order to study the performances and mechanisms of the components when suffered axial load, ultimate axial bearing capacities of 9 components were tested. The cross-sectional size of the outer steel tube and inner PVC-U pipe and length of the specimen was concerned by the nominal steel ratio and the hollow ratio and slenderness ratio, respectively. The external steel tube and core concrete appeared three and four types of destruction phenomenons, respectively, but the inner PVC-U pipe did not destroy. Finally, experimental results and numerical analysis results were comparied.

Tests on stub stainless steel–concrete–carbon steel double-skin tubular (DST) columns

A new type of composite member, a stainless steel–concrete–carbon steel double-skin tubular (DST) column, is introduced in this paper. This composite member is expected to combine the advantages of all three types of materials, and have additional advantages of esthetics and resistance to corrosion that outer stainless steel offers. A series of tests are performed to investigate the performance of the composite column, and a total of 80 specimens were tested. The main parameters of the tests are the sectional type (circular, square, round-end rectangular and elliptical), the column type (straight, inclined and tapered), and the hollow ratio of the composite section (from 0.5 to 0.75). The results show that all types of columns behaved in a ductile manner, and the mechanical behavior is similar to those columns with double carbon steel tubes. A simplified model for the prediction of the stainless steel–concrete–carbon steel double-skin tubular (DST) columns cross-sectional strengths is suggested as well.

Tests on cyclic performance of FRP–concrete–steel double-skin tubular columns

Eight FRP–concrete–steel double-skin tubular columns were tested under constant axial load and cyclically increasing flexural loading. The main parameters in the tests are axial load level and number of fibre reinforced polymer (FRP) layers. The influence of those parameters on the strength, ductility, stiffness, and energy dissipation was investigated. It was found that, in general, FRP–concrete–steel double-skin tubular columns exhibit high levels of energy dissipation prior to the rupture of the longitudinal FRP, but experience a sudden drop in the lateral load capacity after that. The ductility of the specimens can be improved to some extent due to the existence of the axial compressive load in current tests.

Fire performance of self-consolidating concrete filled double skin steel tubular columns: Experiments

An investigation into the fire performance of self-consolidating concrete (SCC) filled double skin tubular columns (CFDST) during the standard fire test is reported. Six full size SCC filled CFDST columns were designed for the fire tests. Detail failure modes of overall specimens and each component in the columns as well as temperatures, deformation and fire endurance were presented. Fire performance of the CFDST columns were studied through analysis of the limiting temperature of the outer tube, composite action between steel and concrete and effect of a number of parameters on the fire endurance. It showed that the limiting temperature in the CFDST columns is significantly higher than that in concrete filled steel tubular (CFST) columns or critical temperature in steel structural components. Strong evidence was found to prove the existence of composite action between steel and concrete in the CFDST columns during fire exposure. Effect of a number of parameters on the fire endurance of the composite columns was identified. Investigation into the fire performance of the columns also reveals possible solutions to improve the fire resistance of CFDST members.

Behavior of concrete-filled double skin steel tubular columns with octagon section under axial compression

Based on some conclusions of two kinds of concrete-filled double skin steel tube (CFDSST) members with circular or square sections, a new kind of CFDSST with octagonal section, where the outer tube has an octagonal section and the inner tube has a circular section, is proposed in this paper. Behaviors of the CFDSST members with octagon section subjected to axial compression are investigated, and some curves of load-strain of steel tubes and confined concrete and the bearing capacity of members are obtained. It is indicated that the bearing capacity of the columns with octagonal section is larger than that with square section and is smaller than that with circular section, and the bearing capacity of members is related to the ratio of the straight side to the bevelled one. Based on the proper stress-strain relationship, a couple of numerical analyses are made using the finite element software named ANSYS. Finally, a simplified formula is proposed in the paper, and the numerical results agree well with the experimental results and the mathematical solutions. The results are valuable for engineers.