Concrete-filled Stainless Steel Tubular Columns Research Articles

Eccentric compressive performances of circular steel-reinforced concrete-filled stainless steel tubular column

Steel-reinforced concrete filled stainless steel tube (SRCFSST) columns are predicted to offer excellent durability, load bearing capacity, ductility, fire resistance, impact resistance, and seismic performance. Therefore, eccentric compressive tests of 18 circular SRCFSST columns were carried out to investigate the effects of the slenderness ratio, load eccentricity, and embedment of carbon-profiled steel (CPS) on circular SRCFSST columns. The ultimate strength and ultimate deflection of the composite columns were improved significantly after the CPS was embedded. A finite element (FE) model was established and the FE analysis indicated that the CPS was proved to be an effective means of constraining concrete. Based on the FE parametric analysis, it was shown that the stability coefficient decreased with increasing concrete strength, proof strength of stainless steel, and CPS yield strength, but increased with increasing rotation radius-diameter ratio. The greater the concrete strength, the more similar the N∼M interaction curves of the SRCFSST columns and reinforced concrete columns. The higher the CPS yield strength, stainless-steel ratio, slenderness ratio, carbon steel ratio, or proof strength of stainless steel, the more similar the interaction curves of the SRCFSST columns and profiled steel columns. Finally, the simplified model was refined to forecast the carrying capability of a circular SRCFSST specimen under the eccentric compression.

Experimental study on concrete-filled stainless steel tubular stub columns under axial compression load

Axial compression tests were conducted on twenty-four concrete-filled stainless steel tubular (CFSST) stub columns with circular and square cross sections to study the performance. The failure modes, loaddisplacement curves, loadstrain curves, and the effects of stainless steel tube wall thickness and concrete compressive strength on the axial compression capacity of the specimen were investigated. The finite element (FE) models were established to study the failure mechanism of columns with different cross sections types and the restraining effect of steel tube on concrete. The results indicated that the stress development and failure mechanism of CFSST stub columns with square cross sections are more complex compared with the CFSST stub columns with circular cross sections. In addition, a formula for calculating the axial compressive bearing capacity for CFSST stub columns was proposed by regression analysis and theoretical derivation. The formula had high accuracy and its calculation results were more consistent with the experimental data.

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.

Bond Strength of Rectangular CFSST Columns after Exposed to Elevated Temperature

This article investigates the bond- behavior of Rectangular Concrete-filled stainless-steel tubular (RCFSST) columns under post-fire conditions. The main objective of this research was to obtain τ-s relationship of RCFSST columns under the combined effects of high temperature and concrete age. A total of sixteen specimens, including four reference specimens, were tested with different parameters, namely: i) temperature (600 °C, 800 °C & 1000 °C) ii) different concrete ages (30 days, 60 days, 90 days & 180 days). Analyzing the τ-s curves of the test specimens, chemical adhesion and micro-locking were the principal forces contributing to bond strength at lower concrete ages under post-fire conditions. At a higher concrete age, RCFSST specimens displayed a longer curve after the inflection point, indicating the contribution of macro-locking forces in amplifying the bond-strength. Five distinct curve types were found from the experiments. Type 1 curves with three stages, i) initial linear, ii) non-linear, and ii) final linear stage, had a higher frequency among the other types. For 90-day cured specimens, a decline in bond strength was observed at higher temperatures, but for 180 days cured specimens, a significant rise was seen under post-fire conditions. A new set of τ-s relations for RCFSST columns with different concrete ages under post-fire was established. Doi: 10.28991/CEJ-2024-010-03-019 Full Text: PDF

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.

Axial local compressive behavior of reinforced concrete-filled stainless steel tubular column piers

In offshore structures, stainless steel structures are widely used in recent years. This paper presents an experimental and numerical study on carbon steel reinforced concrete-filled stainless steel tubular columns, which is defined as CFSCT (concrete-filled stainless‑carbon tubular) stub columns, under local compression. A total of 25 specimens were tested, the effects of outer tube thickness, concrete strength, local compression ratio and shape of bearing block on the local compression performance were studied. The advantages of CFSCT specimens over conventional design schemes were discussed. FE models were established to verify the experimental results. Parametric study was conducted to consider a wider range of geometric and material properties. The results indicate that with the increase of β, the stiffness of the specimen decreases and the deformation performance increases. When local compression ratio β = 2.25, increasing outer tube thickness and concrete strength results in an improvement in bearing capacity of 21.0% and 9.6%, respectively. When β = 9, increasing the thickness and strength of inner tube proves to be more effective, resulting in the highest increasement of 81.6% and 108.7%, respectively. The shape of bearing block has little impact on the bearing capacity. Under the same steel ratio, SI values of CFSCT specimens are 28.8% and 141.7% higher than those of CFSST specimens at β = 2.25 and 9, respectively. Finally, the bearing capacity results were further compared with current design codes, and equations of evaluating local bearing capacity were proposed, which shows good agreement with experiment results.

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.

Behaviour of recycled aggregate concrete-filled stainless steel tubular columns subjected to lateral monotonic and cyclic loading

This paper presents a series of experimental research on recycled aggregate concrete-filled stainless steel tubular (RAC-FSST) columns subjected to lateral monotonic and cyclic loading. The influence of axial load level, shear span ratio, and replacement ratio of recycled coarse aggregate on the RAC-FSST members under compression-bending loads is studied. The test results indicate that the RAC-FSST columns exhibit favorable ductility and energy dissipation capacity. The P-Δ skeleton curves of the columns subjected to lateral cyclic loading are similar to those of columns under monotonic loading. It indicates that, compared with the plastic damage of the concrete, the cyclic hardening characteristics of the stainless steel have more significant influence on the bearing capacity. Considering the characteristics of material loading and unloading criteria, a FE model is established to analyze the seismic performance of RAC-FSST, with the internal force development and stress distribution discussed. Based on the parametric analysis, the modification method of bearing capacity and the hysteretic models of RAC-FSST members are proposed.

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.

Behavior of embedded steel profile ultra-high performance concrete-filled stainless steel tubular short columns under axial compression

This study investigated the behavior of ultra-high performance concrete-filled stainless steel tubular columns with embedded steel profiles (ESUHPCFSST) under axial compression. Six short columns were designed with the parameters of diameter-to-thickness ratio and embedded steel profile ratio. Axial compression tests were conducted to investigate the failure modes, failure mechanisms, and the impact of relevant parameters on the mechanical properties of the specimens. A finite element model was developed and validated against the experimental results to enable a more comprehensive parameter analysis. The results indicate that the failure of the specimens always initiates from the steel profile flange and gradually extends to the external stainless steel tube. The initial stiffness, ultimate bearing capacity, and ductility of the specimens increase with decreasing diameter-to-thickness ratio and increasing embedded steel profile ratio. The strength of the embedded steel profile positively correlates with ultimate bearing capacity and ductility. Higher concrete strength improves ultimate bearing capacity but reduces ductility. Finally, a bearing capacity prediction model for ESUHPCFSST columns is proposed based on the experimental and finite element results, which guides the engineering application of such structures.

Axial compressive behavior and model assessment of FRP-confined seawater sea-sand concrete-filled stainless steel tubular stub columns

Concrete-filled steel tubular (CFST) columns have corrosion issues in coastal/offshore constructions. Thus, a FRP-confined seawater sea-sand concrete (SSC)-filled stainless steel tubular (SST) column (FRP-SSCFSST) is proposed to mitigate corrosion problems. Meanwhile, the use of SSC can relieve the over-exploitation of river-sands. In the present study, the axial compressive behavior of FRP-SSCFSST columns was investigated through testing 12 pairs of stub columns (two duplicates in a pair) including 6 pairs of FRP-SSCFSST specimens, 4 pairs of SSCFSST specimens, and 2 pairs of unconfined concrete specimens. FRP thickness, wall thickness of stainless steel tubes, and concrete strength are the influencing parameters examined in this study. The experimental results showed that the FRP-SSCFSST specimens exhibited a strain-hardening response with the full activation segment as a second ascending line. The SST confinement was less significant, as doubling the wall thickness of SST only led to a small difference in strength index. However, both strength index and strain enhancement ratio increased almost linearly with the increase of FRP thickness. An increase in the concrete strength could result in a reduction in both strength index and axial strain enhancement ratio due to the brittleness of high strength concrete. In addition, the performances of seven load-capacity prediction models and two ultimate axial strain estimation equations were evaluated by using the test results. With minor modifications, Lam and Teng’s model had the best performance in predicting the load carrying capacities of the specimens with an average absolute error at only 3.9%.

Behavior of steel reinforced UHPC-filled stainless steel tubular columns under eccentric loads

This study was conducted to examine the behavior of steel-reinforced ultra-high performance concrete-filled stainless steel tubular (SRUHPCFSST) intermediate columns under eccentric loads. There were nine columns tested in the test program, all of which were subjected to static eccentric loading with consideration given to the effects of the eccentricity, diameter-to-thickness ratio, steel ratio, and eccentric direction. The columns were evaluated to determine their performance characteristics such as ductility, load-displacement relationships, load-strain relationships, and failure modes. The intermediate SRUHPCFSST columns demonstrated good load-carrying and deformation capacity as well as a clear instability failure under eccentric compression after reaching their maximum load. The ultimate bearing strength of the columns decreased significantly with the increase of the diameter-to-thickness ratio and eccentricity, and the increase of the steel ratio or loading in the major axis of the steel skeletons effectively improved the ultimate bearing strength and ductility of the columns. The numerical simulation of the eccentric compression on the SRUHPCFSST was carried out with the finite element software ABAQUS, and the effects of the L/D ratio, concrete strength, steel skeleton strength, and large eccentricities on its eccentric bearing strength were expanded and analyzed. The eccentric bearing strength of the SRUHPCFSST intermediate columns was calculated using a formula derived from the test data and the numerical analyses. The results of the equation correlated well with the experimental data and can serve as a reference for future research in this area.

Axial compressive behavior of built-in carbon-steel marine concrete-filled stainless steel tubular columns

To investigate the axial compressive behavior of marine concrete-filled stainless steel tubular (MCFST) columns with built- in carbon steel, a total of 10 specimens were tested under axial loads. The mechanical failure process and morphology of the specimens were observed, and the axial load-displacement curve and the strain curve of each steel were obtained. Based on the test data, the influence of various variation parameters on the ultimate bearing capacity, axial ductility, energy dissipation capacity and damage development of kinds of specimen was analyzed. The three-dimensional nonlinear finite-element (FE) models were established and verified with the experimental results. The test results indicated that the failure modes of specimens are local buckling and wrinkle of stainless steel tube and oblique shear failure of concrete. The built-in carbon steel can improve the ultimate bearing capacity, axial ductility and energy dissipation capacity of the specimen, and inhibit the damage development of the specimen. Under the condition of increasing the unit carbon steel ratio, MCFST column with built-in circular steel tube achieved the axial compression performance best. Considering the positive effect of the constraints of built-in carbon steel, the calculation methods of bearing capacity were proposed, and the calculated value reflected the measured data well.

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.

Computational simulation of nonlinear inelastic behavior of circular concrete-filled stainless-steel tubular short columns incorporating confinement effects

This paper is concerned with the computational simulation, nonlinear inelastic behavior, and structural design of circular concrete-filled stainless-steel tubular (CCFSST) short columns subjected to axial compression accounting for confinement effects. A new confinement model is proposed for confined concrete based on extensive experimental data on CCFSST columns and implemented in the computational simulation model developed for CCFSST columns. A full-range three-stage stress–strain relationship for stainless steel is incorporated in the computational model that discretizes the column cross-section into fiber elements. The accuracy of the computational model of CCFSST columns is examined by comparison of computer solutions with experimental results of 125 CCFSST short columns documented elsewhere. A comparative study of various confinement models for predicting the axial capacities of CCFSST columns is presented. The computer model is employed to investigate the nonlinear inelastic behavior of CCFSST columns loaded concentrically to failure. The applicability of existing design codes for predicting the ultimate axial capacities of CCFSST columns is evaluated. A simple formula is proposed to calculate the ultimate strength of CCFSST short columns. It is demonstrated that the developed computer model simulates well the nonlinear inelastic behavior of CCFSST columns, and the proposed confinement model yields more accurate strength predictions than existing ones. Moreover, the proposed design method provides a better estimation of the strengths of CCFSST columns than current design codes.

Size effect of square concrete-filled stainless steel tubular short columns under axial compression

Concrete-filled stainless steel tube (CFSST) members combine the advantages of stainless steel materials and concrete-filled steel tube (CFST) members. Therefore, it has a broad range of applications than CFST members in the marine environment and other scenarios requiring great durability and corrosion resistance. However, there are limited researches on the large-size CFSST members. In this paper, 40 square CFSST members with varying steel ratios (4 % ≤α≤ 10 %), widths (500 mm ≤B≤ 900 mm) and strength of concrete (fcu = 40 MPa, 50 MPa) are studied on the size effect under axial compression. The size effect on the peak axial stress, peak axial strain, composite elastic modulus and ductility coefficient are investigated. Then this paper adopted the two-way analysis of variance test (ANOVA) to analyze the data. According to the results, the peak axial strain, composite elastic modulus and ductility coefficient have size effect, but the size effect in peak axial stress does not significant. It was found that the steel ratio will also affect the size effect of CFSST members, and the size effect decreases with the increase of steel ratio. Compared with the current CFST codes, the size effect coefficient included steel ratio is introduced can better predict the ultimate bearing capacity of square CFSST short columns with low steel ratio of range of 4–10 %.

Axial compression and bond behaviour of recycled aggregate concrete-filled stainless steel tubular stub columns

This paper presents a series of axial compression and push-out tests on recycled aggregate concrete-filled stainless steel tube (RAC-FSST) stub columns. A total of 36 specimens were tested, including 18 circular columns and 18 square ones, to determine the effect of the confinement factor and the recycled aggregate replacement ratio on the axial compressive behaviour of these columns. The axial compression load versus longitudinal strain curves of tested columns demonstrated three trends as the confinement factor increased: post-peak softening, plasticity, and strengthening. Correspondingly, push-out slip tests of RAC-FSST members were conducted and formulas for bond strength were proposed. Generally, the bond strength of RAC-FSST was lower than that of CFST due to the smoother surface of the stainless steel tube and the larger shrinkage deformation of the core RAC. A finite element model was developed and verified for further analysis. Based on the experimental and numerical study, the structural behaviour of RAC-FSST was compared with that of normal CFST. The feasibility of existing formulas for axial compression strength calculation of RAC-FSST was evaluated. Based on the collected experimental results of RAC-FSST stub columns and the statistical parameters of the strength for stainless steel tube, reliability analysis was carried out. The partial factors of axial compressive strength of RAC-FSST in building structures, highway bridges, and port engineering structures were proposed.

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.

Performance of steel-reinforced square CFST stub columns loaded in axial compression: Experiments

A steel-reinforced concrete-filled steel tubular column is a type of concrete-filled steel tubular (CFST) column reinforced by embedded steel profile. The inner carbon steel tube reinforced square concrete-filled stainless steel tubular column (SR-CFSST) has not been systematically investigated. In this project, stub composite columns with various experimental parameters were tested as loaded in axial monotonic compression, considering the effects of the concrete strength, column size and wall thickness of the steel tubes. The mechanical behaviour of stub columns was analysed in terms of ultimate load-bearing capacity, strength index, ductility, and failure modes. The calculation methods in five codes, including GB 50936, DBJ/T 13–51, Eurocode 4, ANSI/AISC 360 and AIJ, which are widely used for ordinary CFST stub columns, were compared. Finally, a simplified calculation method for the SR-CFSST stub columns was proposed for predicting the ultimate bearing capacity. The predicted results agree well with test results and the simplified calculation method can be used to design SR-CFSST stub columns loaded monotonically in axial compression.

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.