Concrete-filled Stainless Steel Tubular Research Articles

Experimental study of concrete-filled stainless steel tubular stub columns with circular and square cross-sections subjected to combined compression and bending

This paper presents an experimental study into the structural behaviour and strength of concrete-filled stainless steel tubular stub columns with circular and square cross-sections subjected to combined compression and bending moment. A total of sixteen concrete-filled stainless steel tubular (CFSST) stub columns were tested, including two section types (circular and square hollow sections), two grades of concrete infill (C30 and C60), two thicknesses of tube wall for each cross-section (6 and 10 mm), and five loading eccentricity ratios (0, 0.2, 0.3, 0.4 and 0.5). The CFSST stub column specimens were loaded in compression, with different loading eccentricities applied to achieve a wide range of axial load-to-bending moment ratios. This research provides a comprehensive report on the experimental methodology and subsequent observations, including the failure modes, load-deformation curves, axial load-bending moment curves, strain development at the key locations and values of ductility index. It can be observed that for circular CFSST columns, ultimate load decreased by roughly 70% with an increase in loading eccentricity ratios from 0 to 0.5, while for square columns, the reduction was about 50% under same conditions. The experimental results were used to evaluate if the existing design provisions for carbon steel-concrete composite structures is capable of designing the investigated CFSST stub columns. It was found that the mean ultimate load to predicted failure load ratios are 1.25, 1.32, and 1.36, with coefficients of variations (COV) equal to 0.08, 0.09 and 0.11, for the European, American, and Chinese codes, respectively. Consequently, the design approach specified in the Chinese code led to the most conservative and scattered strength predictions among the three codified design approaches. In contrast, the European code provides the most precise predictions of the test results, though there still remains scope for improvements in the ultimate resistance predictions of CFSST stub columns subjected to combined compression and bending.

Behavior and design of concrete filled stainless steel tubular columns under concentric and eccentric compressive loading

Concrete Filled Stainless Steel Tubular (CFSST) column is a novel type of composite columns that features excellent structural performance, corrosion resistance as well as aesthetic appearance. Owing to the differential mechanical properties between stainless steel and carbon steel, extending the current design codes of conventional CFST columns to CFSST columns may cause unreliable predictions. To this end, this paper summarizes the current state-of-art of CFSST columns and compiles the database of CFSST columns subjected to concentric compressive loading and eccentric compressive loading. Based on the analysis of current studies, the applicability of current international design codes is comprehensively evaluated, and the numerical simulation is also performed through three-dimensional Finite Element (FE) modeling and two-dimensional Fiber Section (FS) modeling technique, where the concrete confinement effect is properly incorporated. Parametric study is then conducted using the validated FS model to investigate the influence of concrete compressive strength, steel yield strength and section slenderness ratio on load-carrying capacity. Finally, a new approach is proposed to construct the axial force-bending moment interaction diagram of CFSST columns, which is simple to use and generates enhanced prediction accuracy as compared with the current design method.

Test and design of rectangular steel-reinforced concrete-filled stainless steel tubular short columns

In this study, the compressive behaviour of rectangular steel-reinforced concrete-filled stainless steel tubular (SRCFSST) short columns was investigated. Compressive tests on 10 rectangular SRCFSST stub columns and 2 rectangular concrete-filled stainless steel tubular (CFSST) counterparts were performed to study the effect of steel ratios and steel sectional shape on the compressive performance of SRCFSST short columns. Compression test results showed that the rectangular SRCFSST column has higher carrying capacity, deformability, and ductility than the rectangular CFSST column. A refined finite element (FE) model of the rectangular SRCFSST stub column was created. According to the FE study, adding carbon profiled steel to rectangular CFSST significantly improved confinement of concrete. Thus, ductility and bearing capacity of the composite column were greatly improved. The carrying capacity, peak strain, and compressive stiffness of the rectangular SRCFSST short column were evaluated using FE parametric analysis. Finally, design methods of the carrying capacity, peak strain, and compressive stiffness of the SRCFSST short column were recommended or refined.

Unified numerical model for performance analysis of various cross-sections of concrete-filled stainless-steel tubular stub columns under axial loading

This research presents a unified numerical model for analyzing the performance of concrete-filled stainless-steel tubular (CFSST) stub columns with different cross-sectional shapes. The model converts the cross-sections of the CFSST columns with various shapes into an equivalent circular column, and a new concrete constitutive relation is proposed to estimate the compressive strength of confined concrete of CFSST columns with different cross-sections. To simulate the axial load–strain curves of CFSST columns, a computer program is used that converts the various cross-sections of CFSST columns into equivalent circular columns. To validate the model, 196 tested columns with various cross-sections gathered from previous literature are used. The unified model proposed is found to be accurately predicting the performance of CFSST columns. The model is then used to investigate the effects of concrete, steel yield stress, and the depth-to-thickness ratio on the different radius ratios and aspect ratios of CFSST columns. A unified design formula is also suggested to calculate the ultimate strength of CFSST columns with various shapes, and the proposed simplified model is shown to provide a more accurate estimation when compared to existing design codes.

Behaviour of CFRP confined square concrete-filled stainless steel tubular columns under uni-axial compression

To study the behaviour of the carbon fibre-reinforced polymer (CFRP) confined square concrete-filled stainless steel tubular (CFSST) stub column, three square CFSST stub columns and nine CFRP confined square CFSST stub columns were tested under axial compression. The test parameters included the number of CFRP sheet layers and the thickness of the stainless steel tube. The test results showed that failure modes of all CFRP confined square CFSST stub columns were the fracture of CFRP sheets and the outward local buckling of the stainless steel tube at the chamfering. The typical load–displacement curves of the tested columns exhibited four stages, i.e., elastic stage, elastoplastic stage, descending stage and residual stage. CFRP sheets could restrain the local buckling of CFSST, and improve the ultimate bearing capacity and the ductility index of the columns. With the increase in the number of CFRP sheet layers and the wall thickness of the stainless steel tube, the bearing capacity of the column increased linearly. Based on the twin-shear unified strength theory, a calculation method of the ultimate bearing capacity of the square CFSST stub column was proposed. Besides, through the superposition method and regression analysis, two simplified methods to predict the ultimate bearing capacity of CFRP confined square CFSST stub column under axial compression were obtained.

A study on the compressive strengths of stiffened and unstiffened concrete-filled austenitic stainless steel tubular short columns

Concrete-filled steel tubular columns are currently used in offshore structures, through which the external steel tubes become at risk due to aggressive ocean climate. This has recently led to the introduction of the concrete-filled stainless steel tubular (CFSST) columns, which make use of stainless steel as a superior material resistant to metallic corrosion. However, concrete-filled stiffened stainless steel hollow tubular (CFSSST) columns have not received much attention, although recently they have shown great performance under compression. Accordingly, this paper is devoted to addressing the advantages of using CFSSST columns in practice. Currently, a comparison is made between CFSSST columns and CFSST columns that have the same cross-sectional areas for both the stainless steel and concrete components. A nonlinear finite element (FE) analysis is first generated, using ABAQUS software, for CFSST columns. Then, FE results for CFSST columns are compared with the available experimental results for CFSSST columns. The results show that CFSSST columns provide significantly higher strengths compared to unstiffened columns, which correlates with the significant increase in the strength of the confined concrete compared with equivalent CFSST columns. Furthermore, both strengths of the two column types are compared to EC4 predictions, the results of which appear to be suitable for CFSST columns but conservative for CFSSST columns. For the case of CFSST short columns, a modified version of the continuous strength method is suggested, where a more accurate value of the buckling factor of stainless steel plate is used when it is in contact with concrete. Additionally, a formula is proposed for the lateral confining pressure provided by the stiffened austenitic stainless steel tubes to the concrete core, and used in a suggested design model for CFSSST short columns, for the first time in the literature.

Computational analysis of axially loaded thin-walled rectangular concrete-filled stainless steel tubular short columns incorporating local buckling effects

This paper investigates the structural performance of concrete-filled stainless steel tubular (CFSST) columns composed of rectangular and square sections. A fiber-based mathematical model is developed to simulate the nonlinear performance of such columns loaded concentrically accounting for the local buckling of steel tube. An accurate lateral pressure model, as well as a strength degradation parameter are proposed based on the existing test results and incorporated in the mathematical modeling developed. A large test dataset is used to validate the accuracy of the numerical prediction. The mathematical model is employed to study the sensitivities of important column parameters on their axial behavior. The accuracy of the existing confinement model of rectangular CFST columns is evaluated in predicting the performance of CFSST short columns. Furthermore, the accuracy of the existing codified design models as well as and the simplified design model proposed in this study to quantify the ultimate compressive strength of such columns is investigated. An accurate artificial neural network (ANN) model along with the GUI feature is developed for the design engineers as a tool to predict their ultimate axial strengths.

Compact and slender box concrete-filled stainless steel tubes under compression, bending, and combined loading

An extensive investigation on the behaviour of compact and slender box concrete-filled stainless steel tubular (CFSST) members is carried out studying their response under compression, bending, and combined compression and bending, with the main aim of developing comprehensive design procedures. Under this objective, an experimental programme is first conducted comprising compact and slender CFSSTs fabricated from austenitic and lean duplex stainless steel plates. Stub columns under axial compression as well as combined compression and bending, CFSST beams under pure bending, and long CFSST columns under axial force are all included in the experiments in order to investigate both the section and member responses. Specimens with high width-to-thickness ratios, high length-to-width ratios, and those under combined compression and bending are particularly considered in the experiments as test data is very scarce for such CFSSTs in the literature. A special technique is used to estimate the loads carried individually by the stainless steel section and the concrete infill to assist with the development of design recommendations. The experiments are followed by an extensive numerical study comprising over two hundred three-dimensional nonlinear finite element simulations. Outcomes of the experimental and numerical programmes are presented, analysed, and discussed thoroughly. Comprehensive procedures are then developed for the design of compact and slender CFSSTs under compression, bending, and combined loading which incorporate the effects of local and global buckling in strength predictions. Such procedures have not yet been established for CFSSTs in international design standards. The validity of the recommendations is demonstrated through comparison with the results of the present study as well as the test data available in the literature.

Nonlinear analysis of elliptical concrete-filled stainless steel tubular short columns under axial compression

Elliptical concrete-filled stainless steel tubular (CFSST) columns are high-performance composite columns that have the enormous potentiality to be used in composite construction in the near future. However, to date, limited studies on the performance analysis of such columns under axial compression have been performed taking into account the accurate material laws of stainless steel and the confined concrete. This paper presents a mathematical model to investigate the axial performance of elliptical CFSST short columns. Accurate material laws of stainless steel and the confined concrete are incorporated in the numerical modeling to capture their true performance. Independent test results are utilized to validate the accuracy of the mathematical predictions. A parameter study is performed to study the important column parameters on their axial performance. The investigations of the accuracy of the existing design models for CFST columns in designing axially loaded elliptical CFSST columns are performed with the test and numerical predictions.

Performance of geopolymer materials concrete filled stainless steel tubular (GCFSST) column subject to axial compression

Recently, concrete-filled stainless steel tubular (CFSST) columns pay attention to the modern construction field. CFSST column provides significant advantages over the column such as greater in strength resisting capacity, larger energy dissipation and stiffness. In this research work, experimental studies are carried out to examine the behavior of geopolymer concrete mixed with ground granulated blast furnace slag (GGBS) filled stainless steel tubular (GCFSST) column and compared with geopolymer concrete mixed with GGBS filled mild steel tubular (GCFMST) column under axial compressive load. The result reveals that the GCFSST column shows a 7.05% strength enhancement in ultimate load-bearing capacity for the L/D ratio of 5.33 when compared with GCFMST column. Also, experimental values authenticated with the theoretical values calculated based on relevant code specifications show that the ultimate strength obtained is higher than the calculated theoretical values. Also, stainless steel tubes as an outer core material improve the load-bearing capacity of the GCFSST columns.

Fire Resistance Design of Concrete-Filled Steel Tube Stub Columns

This paper introduces simplified design methods for calculating the load bearing capacity of axially loaded concrete-filled carbon steel tubular (CFST) stub columns and concrete-filled stainless steel tubular (CFSST) stub columns. Refined finite element (FE) models are developed for capturing the fire performance of CFST and CFSST stub columns under ISO 834 fire. The accuracy of proposed FE models is validated by comparing with existing test data. By using the new developed FE models, the design equations suggested in Eurocode 4 for calculating the axial load bearing capacity of CFST and CFSST stub column in fire are evaluated. It is found that the Eurocode 4 generally provide an unsafe prediction due to the influence of unsuitable consideration on thermal expansion and adopted material strength values. In order to improve the equations in Eurocode 4, correction factors kc and ks for the concrete core and steel tube are defined and calibrated based on comprehensive parametric analysis, and refined equations for predicting the axial load bearing capacity of CFST and CFSST stub columns in fire are suggested. Finally, a design example based on the proposed simplified design methods is demonstrated in this paper.

Behaviour of through plate connections to concrete-filled stainless steel columns

Bond between stainless steel and concrete is not reliable for load transfer in concrete-filled stainless steel tubular (CFSST) columns. This paper proposes the use of a full-through plate for connecting the primary beam to a stainless steel composite column, whereas half-through plates are used to connect other secondary beams. In fabricating such connections, welding of through plates inside a steel tube can be avoided. This paper presents an experimental investigation of the properties of such through plate connections, and the test results are compared with those of blind-bolted endplate connections tested in our earlier research. Meanwhile, finite element models are developed with an aim to compare the behaviour of through plate connections with that of fin plate connections in terms of initial stiffness, flexural resistance and rotation capacity. It is found that the through plate connection with slab exhibits semi-rigid behaviour. Its initial stiffness and flexural resistance are lower than those of the blind-bolted endplate connection, but the rotation capacity is higher. Both the through plate and fin plate connections have similar flexural resistance, but the former has much higher initial stiffness. This study confirms that it is feasible to have a combined use of full-through and half-through plates for connecting beams to CFSST columns. This arrangement might also be suitable for normal composite columns if there is not sufficient bond to enable load transfer.

Flexural buckling of circular concrete-filled stainless steel tubular columns

Concrete-filled steel tubular (CFST) columns are currently used in offshore structures and oil and gas drilling platforms, from which the external steel tubes become at risk due to the aggressive ocean climate and/or sea water. Therefore, the CFST columns in corrosive environment lose their excellent mechanical performances and safety as the thicknesses of steel tubes decrease due to corrosion. This has recently led to the introduction of the concrete-filled stainless steel tubular (CFSST) columns, which benefit from the stainless steel as a superior metallic corrosion resistant material. Accordingly, CFSST short columns have recently attracted the scientific community. However, circular CFSST slender columns have received very little attention. Currently, this paper provides a nonlinear finite element (FE) inelastic analysis for the axially-loaded circular CFSST slender columns to substitute the lack in their behaviour; especially when the relative cheap lean duplex stainless steel material (EN 1.4162) is utilised. The FE models are firstly validated by using the available test results in literature. This validation stage is, then, followed by a parametric analysis to explore the fundamental behaviour of such columns considering the most important factors. The paper divides the slender columns into intermediate length and long columns based on the type of the overall buckling that takes place, and then the behavioural differences between both types are clearly addressed. The obtained FE axial strengths are additionally compared with those predicted by the European (EC4) and American (AISC) specifications. Based on these comparisons, a formula, based on Eurocode 4, is suggested for the routine compressive design practice of these columns, which is found to fit well with the axial strengths of current slender columns which utilise the lean duplex stainless steel material.

Performance of concrete-filled stainless steel tubular (CFSST) columns after exposure to fire

Abstract The post-fire performance of concrete-filled stainless steel tubular (CFSST) columns subjected to an entire loading–fire history, including four characteristic phases: (i) ambient temperature loading, (ii) heating, (iii) cooling with constant external loads, and (iv) post-fire loading, is investigated in this paper. Sequentially coupled thermal-stress analyses are performed using ABAQUS to establish the temperature field and structural response of CFSST columns. To improve the precision of the finite element analysis (FEA) models, the influence of moisture on the thermal conductivity and specific heat of the concrete in the heating and cooling phases is considered by using subroutines. Existing fire and post-fire test data on CFSST columns are used to validate the FEA modelling. Comparisons between FEA and test results indicate that the accuracy of the model is acceptable; the FEA model is then extended to simulate CFSST columns subjected to the four characteristic phases. The behaviour of the CFSST columns during the four characteristic phases is explained by analysis of the temperature distribution, load versus axial deformation relations, failure modes and internal force redistribution. The excellent post-fire performance of CFSST columns is examined in comparison with traditional concrete-filled carbon steel tubular (CFST) columns with the same total cross-sectional area. The residual strength index is studied with respect to a series of parametric analyses. It is found that the residual strength of CFSST columns is higher than that of CFST columns after the same fire exposure, and that the diameter of the stainless steel tube, slenderness, heating time ratio and load ratio have a significant influence on the residual strength index.

Performance of concrete-filled stainless steel tubes subjected to tension: Experimental investigation

Abstract Concrete-filled stainless steel tubular (CFSST) structures have attracted increasing attention from researchers and engineers in the past decade. CFSST members can be adopted as columns in buildings or chord members in trusses, which could be subjected to tension under some circumstances. This paper presents an experimental investigation on the mechanical behavior of concentrically and eccentrically loaded CFSST tensile members. The parameters considered in the tests included the steel type (stainless steel or carbon steel), load eccentricity (e = 0–75 mm), steel ratio of the cross section (α = 0.075 or 0.112), concrete strength (fcu = 53.4 MPa or 84.7 MPa), and steel-concrete interfacial condition (lubricated or not). The test results show the concrete infill effectively works with the outer stainless steel tube, leading to tensile strength and stiffness higher than those of the corresponding hollow stainless steel tube. All the CFSST tensile members show ductile behavior and the end rotation of the eccentrically loaded members exceeds 0.1 rad. Finally, the feasibility of existing design method to predict the tensile strength of CFSST members was also evaluated.

Investigation on structural behavior of concrete filled stainless steel tubular stub columns

Concrete filled stainless steel tubular (CFSST) Columns have the recognizing feature of high corrosion resistance so that we can directly use in the sea-sand based environments and as well as in normal environments also, we can widely use as structural application without corrosion. This paper presents the finite element analysis and behaviour of short CFSST stub columns of circular cross-sections loaded axially. A finite element model was developed in the ABQUS software and the behaviour of axially loaded s short CFSST stub columns, taking account into the concrete confinement effect and significant effect of stress strain of stainless steel. The computational method outcomes are comparatively verified with the laboratory outcomes and design formula proposed by Liang which is to predict the ultimate strength of short CFSST stub columns of circular columns.

Behavior of eccentrically loaded concrete-filled stainless steel tubular stub columns confined by CFRP composites

In this paper, experimental, numerical and analytical investigations were carried out to study the structural behavior of concrete-filled stainless steel tubular (CFSST) stub columns externally wrapped by carbon fiber reinforced polymer (CFRP) composites under eccentric compression loading. In the experimental work, twelve stub columns of 101 mm outer diameter and 2 mm thickness were tested. The main variables considered were the thickness of the CFRP wrap (tf) and the load eccentricity to the outer diameter ratio (e/D). A 3D finite element (FE) simulation was developed for the CFRP-bonded CFSST stub columns using the well-known commercial FE program ABAQUS and validated against the experimental results. The validated FE models were further utilized to generate more data with different variables. From the experimental and numerical results, it was found that the CFRP wrapping effectively improves the ultimate strength of the CFRP-bonded CFSST stub columns. Finally, an analytical axial force-bending moment (P-M) interaction model was proposed. It provided conservative predictions when compared to the experimental and FE results.

Fire performance of steel reinforced concrete-filled stainless steel tubular (CFSST) columns with square cross-sections

Concrete-filled stainless steel tubular (CFSST) columns combine the advantages of composite action seen in concrete-filled steel tubular (CFST) columns with the durability benefits associated with stainless steel. An effective means of reducing the material usage in the outer stainless steel tube in CFSST columns is to embed an inner carbon steel profile. This enables the material costs to be reduced, while achieving similar load-bearing capacity and durability, as well as enhanced fire resistance. The behaviour of such steel reinforced composite columns, i.e. concrete-filled stainless steel tubular (CFSST) columns with outer square cross-sections and embedded carbon steel profiles, under ISO 834 standard fire conditions is investigated in this study by finite element (FE) analysis. Firstly, FE models are developed and validated against relevant published experimental data on CFSST and steel reinforced CFST columns under fire conditions. Based on the validated FE models, the working mechanisms of the studied steel reinforced CFSST columns under fire conditions are investigated by analysis of the temperature field, failure modes, axial deformation versus time response and internal force distribution. The fire performance of the studied steel reinforced CFSST columns is also evaluated in comparison with CFST and CFSST columns with the same total cross-sectional area of steel or the equivalent cross-sectional load-bearing capacity at ambient temperature. Finally, with respect to fire resistance, the optimal ratio of the cross-sectional areas of the inner carbon steel profile to the outer stainless steel tube is investigated.

Analytical Behaviour of Rectangular Concrete Filled Stainless Steel Tubular Columns under Bi-axial Eccentric Compression

The aim of this paper is to numerically investigate the behavior of the rectangular concrete filled stainless steel tubular (CFSST) columns subjected to bi-axial eccentric compression. A finite element (FE) model for modelling the bi-axial eccentric compressive behaviour was established. The FE predictions were verified against the test results. Behaviour analysis was then performed to investigate the typical curves of load versus deformation, the internal force distribution, stress development and interaction of stainless steel tube and core concrete during the loading process.

Structural performance of CFRP-strengthened concrete-filled stainless steel tubular short columns

The use of concrete-filled stainless steel tubular (CFSST) members is relatively innovative and new. CFSST columns can be used for bridge piers, multi-story buildings and other supporting structures. However, a common mode of failure with these type of tubular composite columns is inelastic outward local buckling occurring at the column ends. Therefore, this paper presents the results of experimental, numerical and analytical investigations into the behavior of circular CFSST columns strengthened by carbon fiber reinforced polymer (CFRP) wrap and subjected to axial compression loading. The experimental investigation comprised three series of tests. The main variables tested were the diameter to thickness ratio of the stainless steel tube and the thickness of the CFRP wrap. 3D finite element models (FEMs) were developed for CFRP-wrapped CFSST columns using the ABAQUS software and were validated with experimental results. An extensive parametric study was carried out by using the validated FEMs. It was shown from the experimental and FEMs results that CFRP jacketing was highly effective in improving the axial load carrying capacity and axial shortening capacity of the CFSST columns. Finally, an analytical model based on the FE parametric study results was proposed to predict the axial load carrying capacity of the CFRP-wrapped CFSST columns.