Concrete-filled Stainless Steel Tube Research Articles

Eccentric compression behaviour of normal and ultra-high performance concrete-filled stainless steel tube stub columns

To investigate the mechanical properties of normal concrete-filled stainless steel tubes (CFSST) and ultra-high performance concrete-filled stainless steel tubes (UFSST) under eccentric compression, 6 axial compression specimens and 18 eccentric compression specimens were designed. The effect of different concrete strengths, eccentricity and diameter-to-thickness ratios (D/t) on the damage modes, load-displacement curves, load-strain curves, and lateral deflection distribution curves of the specimens were investigated. The test results showed that stainless steel tubes exhibited different degrees of buckling after failure. The load-displacement curve of CFSST presents a slight upward trend after the elastic-plastic phase, whereas that of the UFSST enters a slowly decreasing phase. And the increase in eccentricity leads to a decrease in the load bearing capacity, ductility, and initial stiffness of the specimen. As the D/t decreases, the load carrying capacity of the specimen increases. Additionally, parametric analysis was conducted on CFSST and UFSST specimens, including the eccentricity, concrete strength, stainless steel yield strength, and D/t. Compared with the design codes of EC 4, AISC 360, and GB/T 51446, the ultimate axial force-bending moment (Nu-Mu) curve was inaccurate. Thus, a prediction model for the Nu-Mu curve of CFSST and UFSST stub columns was proposed, and the predicted results of the proposed model were in good agreement with the experimental results.

Circular recycled aggregate concrete-filled stainless steel tube stub columns after exposure to fire: Experiments, simulations, and design

This paper presents experimental and numerical investigations into the post-fire cross-section compressive behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. Twelve stub column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating and cooling of specimens, cylinder tests and post-fire tensile coupon tests and stub column tests. The test results, including load–end shortening curves, failure loads and failure modes, were fully reported and the initial compressive stiffnesses and confinement effect were discussed. The numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Given the absence of design codes for stainless steel–recycled aggregate concrete composite structures after exposure to fire, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as set out in the European code, Australia/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to circular RACFSST stub columns after exposure to fire, based on the test and numerical data. The assessment results generally revealed that the European code and the Australian/New Zealand standard led to an acceptable level of design accuracy and consistency, while the American specification resulted in rather conservative and scattered post-fire cross-section compression resistance predictions.

Post-fire behaviour and resistances of square recycled aggregate concrete-filled stainless steel tube stub columns

Experimental and numerical studies on the cross-section compressive behaviour and residual resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns after exposure to fire are reported in this paper. An experimental programme was firstly carried out on twelve stub column specimens with three recycled coarse aggregate replacement ratios (0%, 35% and 70%) after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The test results, including load–end shortening curves, failure loads and failure modes, were presented, with the initial compressive stiffness and confinement effect analysed. The experimental programme was followed by a numerical modelling programme, where thermal and mechanical finite element models were developed and validated against the test results and afterwards used to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions. Based on the test and numerical data, the relevant design rules for square natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as specified in the European code, Australia/New Zealand standard and American specification, were evaluated, using post-fire material properties, for their applicability to square RACFSST stub columns after exposure to fire. The evaluation results generally revealed that the European code and Australian/New Zealand standard led to a good level of design accuracy, while the American specification resulted in slightly conservative post-fire cross-section compression resistance predictions.

Structural behaviour and resistances of high strength concrete-filled stainless steel tube (HCFSST) beam-columns

This paper reports experimental and numerical investigations into the structural behaviour and resistances of high strength concrete-filled stainless steel tube (HCFSST) beam-columns under combined compression and bending. An experimental investigation was conducted on sixteen HCFSST beam-columns specimens fabricated from stainless steel tubes with two cross-section sizes and high strength concretes with four material grades, and included concrete cylinder tests, tensile coupon tests, initial global geometric imperfection measurements and eccentric compression tests. The test setups and procedures were fully reported and the experimental observations were discussed and analysed in detail. It was found that the plane cross-section assumption was valid for eccentrically loaded HCFSST sections and the lateral deflection distribution patterns for HCFSST beam-columns were approximately half-sine wave shapes. The test results were used in a subsequent numerical investigation for the validation of finite element models, which were then employed to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. Based on the experimental and numerical results, the relevant design rules, as set out in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to HCFSST beam-columns. The evaluation results revealed that the European code provided accurate but scattered failure load predictions when used for HCFSST beam-columns, while the American specification and Australian/New Zealand standard resulted in conservative and scattered failure load predictions.

Finite Element Analysis and Calculation Method of Concrete-Filled Stainless Steel Tubes under Eccentric Tension

Concrete-filled stainless steel tubes (CFSST) could be used as structural members in corrosion-prone environments. A detailed numerical investigation of the mechanical performance and calculation method of CFSST members under eccentric tension is carried out in this paper. A finite element analysis (FEA) model that adopts three-dimensional elements is established, and related experimental results of CFSST and conventional concrete-filled carbon steel tubes (CFST) subjected to tension are used to validate the FEA model. Then, the calibrated FEA model is used to investigate the performance of CFSST eccentrically tensile members, especially the composite actions and stress distribution laws between the stainless steel tube and the concrete core, which play a key role in the load-carrying capacity of the composite member. To quantitatively determine the influence of different parameters on the load-carrying capacity of CFSST tensile members, a wide-range parametric analysis is performed. Finally, a calculation model is proposed to be used to predict the ultimate tensile strength of CFSST members subjected to eccentric tension, and the model-predicted values show good agreement with the FEA-computed results.

Experimental research on axial mechanical properties of circular CFSST columns after exposure to temperature and sliding

This paper presents experimental investigations on axial mechanical properties of circular concrete-filled stainless steel tube (CFSST) columns after exposure to temperature and sliding. A total of 117 CFSST specimens were tested under axial compression loading with four factors (i.e., tube thickness, temperature, duration, and concrete compressive strength) considered. Test results indicated that the initial stiffness of circular CFSST short columns was degenerated due to high-temperature sliding. Circular CFSST specimens exhibited a 50.9% lowest residual strength at 1000 ℃. The influence of high-temperature duration on the residual strength of circular CFSST short columns was limited. The residual strength of specimens was positively correlated with the thickness and concrete compressive strength. All circular CFSST columns after exposure to temperature and sliding experienced an outward local buckling under axial compression. In addition, the parameters formulae of residual strength for circular CFSST columns after exposure to temperature and sliding are proposed, which achieve sufficient accuracy. The research could offer valuable references for strengthening circular CFSST columns after fire.

Behavior of square concrete-filled stainless steel tube columns after high-temperature sliding

This paper presents herein pertains the experimental and numerical investigations on axial compressive behavior of square concrete-filled stainless steel tube (CFSST) columns after high-temperature sliding. A total of 117 CFSST specimens were tested under axial compression loading. The design variables included tube thickness, temperature, duration, and concrete compressive strength. Test results indicated that the initial stiffness of square CFSST short columns was degenerated due to high-temperature sliding. CFSST specimens exhibited a 62.7% lowest residual strength at 1000 °C. The influence of high-temperature duration on the residual strength of square CFSST short columns after high-temperature sliding was limited. The residual strength of specimens was positively correlated with the thickness and concrete strength. All square CFSST columns after high-temperature sliding experienced an outward local buckling under axial compression. Finite element models of square CFSST columns after high-temperature sliding are established and validated against the experimental results. In addition, the parameter formulae of residual strength for CFSST columns after high-temperature sliding were proposed, which achieved high accuracy. This research results could provide strengthening reference for the application of CFSST columns after high-temperature sliding.

Numerical investigation and calculation method of concrete-filled bimetallic tubes subjected to concentric tension

Concrete-filled stainless steel (outer)-carbon steel (inner) bimetallic tubes (CFBT) are potential to be applied as structural members in the corrosion-prone environments. A detailed numerical investigation on the mechanical performance and calculation method of CFBT members under concentric tension is carried out in this paper. A finite element analysis (FEA) model adopting three-dimensional elements is established, and related experimental results of conventional concrete-filled carbon steel tubes (CFST) and concrete-filled stainless steel tubes (CFSST) are used to validate the FEA model. Then, the calibrated FEA model is used to investigate the performance of CFBT tensile members, especially the composite actions and stress distribution laws between the two tube-layers and the infilled concrete, which play the key role in the load-carrying capacity of the composite member. To quantitatively determine the influence of different parameters on the load-carrying capacity of CFBT tensile members, a wide-range parametric analysis is performed. Finally, a calculation model is proposed to be used to predict the ultimate tensile strength of CFBT members subjected to concentric tension, and the model-predicted values show good agreement with the FEA-computed results.

Eccentric compressive behavior of square concrete-filled stainless steel tube (CFSST) stub columns

To study the eccentric compressive behavior and mechanism of square concrete-filled stainless steel tube (CFSST) stub columns, a total of 12 specimens with different steel ratio and load eccentricity under eccentric load was investigated. The results demonstrated that the failure modes of all square CFSST stub columns were the outward local buckling of the stainless steel tube at the compression side and two adjacent sides. The load-longitudinal deformation curve of specimens exhibited three stages, including elastic stage, elastic-plastic stage, and descending stage. The longitudinal strain distribution in the cross section at the mid-height of the specimens generally satisfied the plane-section assumption during the loading process. Increasing the steel ratio of specimens significantly improved the ultimate bearing capacity. Meanwhile, the ultimate bearing capacity of the specimens decreased with the load eccentricity, and the second-order effect became more pronounced with the increase in eccentricity. Finally, based on the existing specification, this study proposed a prediction formula for the eccentric bearing capacity of square CFSST stub columns by modifying the eccentric reduction coefficient accompanied by adopting the method of equivalent cross section. The formula was verified using an established database of eccentric compression CFST stub columns in the existing literatures.

Strengthening Behavior of Rectangular Stainless Steel Tube Beams Filled with Recycled Concrete Using Flat CFRP Sheets

Recently, the adoption of recycled concrete instead of normal concrete as infill material in tubular stainless steel members has received great attention from researchers regarding environmental improvement. However, the flexural behavior of recycled concrete-filled stainless steel tube (RCFSST) beams that have been repaired/strengthened using carbon fiber-reinforced polymer (CFRP) sheets via a partial-wrapping scheme has not yet been investigated, and is required for a variety of reasons, as with any conventional structural member. Therefore, this study experimentally tested six specimens for investigating the effects of using varied recycled aggregate content (0%, 50%, and 100%) in infill concrete material of stainless steel tube beams strengthened with CFRP sheets. Additionally, several finite element RCFSST models were built and analyzed to numerically investigate the effects of further parameters, such as the varied width-to-thickness ratios and yield strengths. Generally, the results showed that using 100% recycled aggregates in infill concrete material reduced the RCFSST beam’s bending capacity by about 15% when compared to the corresponding control specimen (0% recycled aggregate), with little difference in the failure mode behavior. Pre-damaged RCFSST beam capacity showed significant improvement (43.6%) when strengthened with three CFRP layers. The RCFST model with a lower w/t ratio showed better-strengthening performance than those with a higher ratio, where, the models with w/t ratios equal to 15 and 48 achieved a bending capacity improvement equal to about 18% and 35%, respectively, as an example. Furthermore, the results obtained from the current study are well compared by those predicted using the existing analytical methods.

Behaviour of eccentrically loaded circular recycled aggregate concrete-filled stainless steel tube stub columns

This paper presents an experimental and numerical study of eccentrically loaded circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. The testing programme was conducted on twelve specimens designed with different stainless steel tube section sizes and recycled coarse aggregate replacement ratios, and included tensile coupon tests, concrete cylinder tests and eccentric compression tests. The test results, including the failure loads and modes, load–mid-height lateral deflection curves and evolution of neutral axis, were reported and discussed. Following the testing programme, a numerical modelling programme was conducted, with finite element models developed and validated against the test results and then employed to perform parametric studies to generate further numerical data. The confinement effects were analysed based on the numerical data. The relevant design interaction curves, as set out in the European code, American specification and Australian/New Zealand standard, were assessed for their applicability to circular RACFSST stub columns under combined compression and bending. On the basis of the quantitative and graphical assessments, it has been found that (i) each set of codified design interaction curve leads to similar assessment results for eccentrically loaded circular RACFSST stub columns with different recycled coarse aggregate replacement ratios and (ii) the failure load predictions from the codified design interaction curves are conservative.

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 %.

A novel concrete-filled auxetic tube composite structure: Design and compressive characteristic study

Concrete-filled stainless steel tube (CFSST) members take advantage of the high strength and the outstanding corrosion resistance to act as an important role in civil engineering structures. However, the steel tube could not provide the perfect confinement effect for the core concrete during the initial elastic compression stage because Poisson’s ratio of the concrete is smaller than that of the stainless steel tube (SST). In this paper, a novel concrete-filled auxetic stainless steel tube (CFASST) composite structure was designed and manufactured to actively restrain the concrete, making the best use of the desirable deformation characteristics of auxetic tubular structures. The axial compressive performance of these CFASST members and their control factors were investigated experimentally and numerically. Test results were discussed in detail which included failure modes, load versus displacement curves and strain analysis. Finally, parametric analyses were conducted to further study the effects of different parameters (Poisson’s ratio, thickness of the stainless tube) on the CFSST composite structure under axial compression. It was found that CFASST composite structures possess an unusual deformation mode and an improved confinement effect.

Effect of Geometric and Material Properties on the Behavior of Axially Loaded Concrete-Filled Stainless Steel Tube Columns

Effect of Geometric and Material Properties on the Behavior of Axially Loaded Concrete-Filled Stainless Steel Tube Columns

Experimental and numerical investigations of recycled aggregate concrete-filled stainless steel tube stub columns under combined compression and bending

This paper reports experimental and numerical investigations into the behaviour and resistance of recycled aggregate concrete-filled stainless steel tube stub columns under combined compression and bending. Eccentric compression tests were conducted on twelve stub column specimens fabricated from austenitic stainless steel tubes with two cross-section sizes and concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%). The test results, including the failure loads, load–mid-height lateral deflection curves, evolution of neutral axis and confinement effect, were discussed in detail. The testing programme was followed by a numerical modelling programme, where finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Given that there are no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for natural aggregate concrete filled-carbon steel tube stub columns under combined compression and bending, as set out in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to recycled aggregate concrete filled-stainless steel tube stub columns, based on the test and numerical data. The evaluation results revealed that the European code and Australian/New Zealand standard generally provide an acceptable level of design accuracy, while the American specification yields unduly conservative failure load predictions.

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.

Cyclic Axial Compression Behavior of FRP-Confined Seawater Sea-Sand Concrete-Filled Stainless Steel Tube Stub Columns

Concrete-filled steel tube (CFST) columns have been widely used in onshore constructions. To extend its applications to coastal/offshore structures and meanwhile relieve the overexploitation on freshwater and river sand, an FRP-confined seawater sea-sand concrete-filled stainless steel tube (F-SSCFSST) column is proposed. The cyclic axial compressive behavior of this newly proposed column was investigated in this study. A total of 22 specimens (including nine pairs of specimens for cyclic compression and four individual specimens for monotonic compression) were tested. Most importantly, the influences of three loading patterns (i.e., single full unloading/reloading, repeated full unloading/reloading, and mixed of repeated full and partial unloading/reloading) were studied. The results showed that although all F-SSCFSST specimens failed from FRP rupture in the mid-height area, the FRP rupture was less fierce for specimens with repeated internal unloading/reloading cycles. Similar to the FRP-confined concrete, the envelope curve of cyclic axial load–strain response matched closely with the monotonic compression curve for a particular specimen. However, the unloading curve was less curly compared with that of a typical FRP-confined concrete. The confinement effect provided by the FRP jacket was much stronger than that by the stainless steel tube. Although Lam and Teng’s model, which is proposed for the FRP-confined concrete, could provide satisfactory estimations for strain recovery ratios and stress deterioration ratios, it underestimated the envelope plastic strains by 20%.

Study on stainless steel blind bolted T-stub to concrete-filled stainless steel tube connections

Tension zone of a bolted steel beam-to-column connection can be represented by an equivalent T-stub to column connection under tensile load as recommended in Eurocode 3. This paper presents an experimental and theoretical study on equivalent T-stub to concrete filled stainless steel tube connections (T-to-CFSST) and the basic component (CFSSTs). Both stainless steel blind bolts and normal bolts were selected for the connections. Effects of various parameters, including tube thickness, bolt layout, bolt size, bolt type and bolting method, on the performance of T-to-CFSST and CFSST were investigated. Compared to hollow tubes, filling concrete could greatly enhance the stiffness and strength of the connections. Anchorage between bolts and concrete could be improved by setting studs at bolt ends. A finite element (FE) model was developed in this study and its accuracy was validated by the experimental results. Parametrical study was conducted to investigate the effects of parameters that cannot be covered in experiments, such as material type, tube length and T-stub thickness, on the behavior of CFSST and T-to-CFSST. Based on the experimental and numerical results, theoretical models were proposed to estimate the load–displacement curves of CFSSTs and their stiffness, yield capacity and ultimate capacity. By adopting the concept of component method, formulas were also proposed to predict the stiffness, yield capacity and ultimate capacity of T-to-CFSSTs. In general, the prediction matched well with the experimental results of CFSSTs and T-to-CFSSTs.

Experimental study on the steel–concrete bond behaviour of circular concrete-filled stainless steel tubes

The paper reports an experimental investigation on the bond stress–slip relationship in concrete-filled stainless steel tube (CFSST) structures. Push-out tests were conducted on twelve specimens covering two stainless steel grades, two concrete grades, two cross-sectional dimensions and two internal ring conditions (with and without the internal ring). The effects of these factors on the bond stress–slip relationship in CFSST members were analysed and discussed. A theoretical model, based on the assumption that no restraining force from the steel tube was applied to the concrete core, was developed to predict the bond stress–slip response of CFSSTs and was evaluated against the test results. An empirical model was also proposed based on regression analysis to replicate the experimental bond stress–slip relationships, which can be used as input data for analytical and numerical simulations in future studies of CFSST structures.

Axial compressive behavior of reinforced concrete-filled stainless steel tube (RCFSST) stub columns: Experimental research

In this study, an innovative reinforced concrete-filled stainless steel tube (RCFSST) column is proposed. A total of twenty-two specimens, including eighteen RCFSST stub columns and four concrete-filled stainless steel tube (CFSST) stub columns were tested under axial compression. The primary variables included cross-section type (circular and square), spiral stirrup spacing (spiral stirrup ratio), number and strength of longitudinal reinforcing bars, and concrete strength. The failure modes, load versus deformation curves, ultimate bearing capacity, strain characteristics, local buckling stress, and ductility of the specimens were compared and discussed. Results showed that the load versus deformation curves were stable, and outward buckling was the final failure mode for all specimens. Compared with CFSST columns, RCFSST columns had higher ultimate bearing capacity and better ductility. Increasing the spiral stirrup ratio can significantly improve ultimate bearing capacity and post-peak ductility. Increasing the number and strength of longitudinal reinforcing bars can also increase ultimate bearing capacity. Higher concrete strength can improve the ultimate bearing capacity of the specimen but worsen post-peak ductility. Inserting a reinforcement cage, even a small amount, can be an economical method of significantly improving the ductility of CFSST columns with high strength concrete. Finally, design formulas for calculating the ultimate bearing capacity of RCFSST columns subjected to axial compression loading were proposed.