Concrete-filled Stainless Steel Research Articles

Post-fire bond-slip performance of concrete-filled stainless steel tube columns

Concrete-filled stainless steel tube (CFSST) structures exhibit superior strength, durability, and fire resistance. These attributes, coupled with their aesthetic appeal and corrosion resistance, make them highly suitable for a broad range of civil engineering applications, ensuring long-term performance and safety across diverse environments. This study investigates the post-fire bond-slip performance of CFSST structures to facilitate the strengthening and retrofitting of fire-damaged CFSST structures. The paper reviews the bond-slip performance and fire resistance of CFSST. A series of fire tests and push-out tests were conducted on 99 circular CFSST stub columns, considering variables such as fire duration, wall thickness of the stainless steel tube, and concrete strength. The analysis covers the slip mechanism, load-slip relationship, sliding load, ultimate displacement, and ultimate bond strength of specimens post-fire. The bonding force between interfaces transitions from cementation to mechanical interlock and ultimately to friction, with some overlap among these mechanisms. A positive correlation exists between sliding load and wall thickness when fire duration is short. For shorter fire durations, fire exposure reduces the ultimate displacement while increasing bond-slip stiffness. Finally, a formula is proposed to predict the ultimate bond strength of CFSST stub columns following exposure to ISO 834 standard fire conditions.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.