Stainless Steel Tubular Columns Research Articles

Experimental and numerical investigations of stainless steel tubular columns strengthened by CFRP composites

This paper presents experimental and numerical investigations of cold-formed circular stainless steel tubular (HSST) stub columns strengthened externally using carbon fiber reinforced polymer (CFRP) wraps. For the experimental investigation, eleven stub columns were tested under axial compression loading. The experimental variables were the CFRP thickness (tf), the CFRP arrangement (fully or partial wrapping), and the diameter-to-thickness ratio of stainless steel tubes (D/ts). The ratio of the compressive strength of wrapped specimens to that of unwrapped specimens (strengthening ratio) was employed to assess the compressive behavior of CFRP-wrapped HSST columns. Three-dimensional finite element (FE) simulation was implemented using ABAQUS software and validated against the experimental results. A parametric study was performed on the validated FE models for further investigation. The experimental results indicated that the full CFRP wrapping reasonably enhanced the ultimate compressive strength of the columns. In contrast, the partial wrapping showed no improvement in the ultimate compressive strength. The FE parametric study results showed that the strengthening ratio (i) decreases with increasing the diameter of the tubes, (ii) decreases when the failure mode changes from outward to inward local buckling (iii) is affected by the strength of the CFRP and tube materials. Based on the parametric study results, a design model was proposed to predict the ultimate strength of axially loaded CFRP-wrapped HSST stub columns.

Fire Resistance Design of Concrete-Filled Steel Tube Stub Columns

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

Design and testing of stainless steel columns filled with steel-fibre-reinforced concrete

This paper presents the design and testing of stainless steel tubular columns filled with steel-fibre-reinforced concrete. The pin-ended, axially loaded composite columns had a fixed depth-to-plate thickness ratio and various stainless steel tube cross-sections, lengths, non-dimensional slenderness, concrete strengths and steel fibre percentages. They were filled with plain and steel-fibre-reinforced concrete. The composite column strengths, load–axial shortening behaviour and failure modes were measured and observed. The investigation showed that stainless steel tubular columns filled with steel-fibre-reinforced concrete offer a considerable increase in column strength and ductility compared with plain-concrete-filled tubes. It was also shown that Eurocode 4 accurately predicted the strengths of the composite columns, but was unsafe for long tubes of circular section and those filled with plain high-strength concrete.

The Continuous Strength Method for the design of stainless steel hollow section columns

The Continuous Strength Method (CSM) provides accurate resistance predictions for both stocky and slender stainless steel cross-sections; in the case of the former, allowance is made for the beneficial effects of strain hardening, while for the latter, design is simplified by the avoidance of effective width calculations. Although the CSM strain limits can be used in conjunction with advanced analysis for the stability design of members, for hand calculations, the method is currently limited to the determination of cross-sectional resistance only, i.e. member buckling resistance is not covered. To address this limitation, extension of the CSM to the design of stainless steel tubular section columns is presented herein. The proposed approach is based on the traditional Ayrton-Perry formulation, but features enhanced CSM cross-section resistances and a generalized imperfection parameter that is a function of cross-section slenderness. The value of the imperfection parameter increases as the slenderness of the cross-section reduces to compensate for the detrimental effect of plasticity on member stability that is not directly captured in the elastic/first yield Ayrton-Perry approach. The accuracy of the proposed approach is assessed against numerical results generated in the current study and existing experimental results collected from the literature. The presented comparisons show that the CSM provides consistently more accurate member buckling resistance predictions than the current EN 1993-1-4 design rules for all stainless steel grades. The reliability of the proposed approach is demonstrated through statistical analyses performed in accordance with EN 1990. Finally, the paper presents a framework through which the proposed approach can be developed for other cross-section types and materials.

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

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

Numerical analysis of circular double-skin concrete-filled stainless steel tubular short columns under axial loading

Circular double-skin concrete-filled stainless-steel tubular (DCFSST) columns have the distinguishing feature of high resistance to corrosion so that they can be constructed by either normal concrete or seawater sea-sand based concrete without corrosion. The numerical study of circular short DCFSST columns is very limited. This paper presents the computational modeling and behavior of short DCFSST columns of circular sections loaded concentrically. A computational model is developed for simulating the structural behavior of concentrically loaded short circular DCFSST columns, taking into account the effects of the concrete confinement induced by the double stainless-steel skins and significant strain hardening of stainless steel. The accuracy of the computational modeling technique proposed herein is assessed by means of comparing computations with available experimental data. The verified computational method is utilized to investigate the significance of geometric configurations as well as material strengths on the structural performance of circular DCFSST columns. The applicability of the current design provisions for steel tubular columns filled with concrete to the design of circular DCFSST columns is evaluated by comparisons against experimental and numerical results on DCFSST columns. The comparative study shows that the present computational model and the design formula proposed by Liang predict well the ultimate strengths of short DCFSST columns composed of circular tubes. The codified design approaches in current design codes generally give conservative estimations of the strengths of circular DCFSST stub columns.

Flexural buckling of circular concrete-filled stainless steel tubular columns

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

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

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

Study on Stressing State and Failure Criterion of Concrete‐Filled Stainless Steel and Steel Tubular Column

In this paper, the mechanical characteristics of concrete‐filled stainless steel and steel tubular (CFSSAST) columns under axial and eccentric loads are analyzed by using the theory of structural stressing state. Firstly, the sum of generalized strain energy density (GSED) values of the short column at every load value (Fj) is normalized as Ej,norm to describe the structural stressing state. Then, according to Mann–Kendall (M‐K) criterion and the natural law from quantitative change to qualitative change, the transition of stressing state is distinguished, which leads to the update of failure load. Then, the corresponding finite element models are established, and the accuracy of the models is verified by the experimental data, and the stress contour maps are analyzed by simulation data. Finally, the simulation data are used to perform parameter analysis. This study explores a new method to reveal the invisible working characteristics of structures and provides a new reference for the study of similar structures.

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

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

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

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

Behavior of circular stainless steel stub columns internally strengthened by longitudinal carbon steel bars

In this paper, experimental and numerical investigations into the performance of circular unfilled and concrete filled stainless steel tubular stub columns strengthened by carbon steel bars welded to the inner surface were presented. The carbon steel bars were fabricated to be a structural component of the stub column and directly participate in supporting the axial load. Ten stub columns of 141.3 mm outer diameter and 3.4 mm thickness were tested under axial compression load for different numbers and sizes of carbon steel bars. 3D finite element models (FEMs) were carried out for the strengthened stub columns by using finite element program ABAQUS and validated with the experimental results. The validated numerical work was utilized to carry out a parametric study to assess (i) the practical configuration of the carbon steel bars, (ii) the possible reduction of stainless steel thickness, which can be compensated for by the addition of carbon steel bars, (iii) the effect of the diameter to thickness ratio (D/t) on the stub column performance. The numerical work was further utilized to generate extensive data to validate the load carrying capacity predicted by the ACI and Eurocode4 codes and the continuous strength method (CSM). The experimental and numerical results demonstrated that this strengthening technique enhanced the axial load carrying capacity for unfilled and filled stainless steel stub columns. The results from the parametric study confirmed that (i) strengthening by two carbon steel bars is the most practical configuration to minimize the welding process, (ii) a substantial reduction in stainless steel thickness can be achieved by using carbon steel bars, (iii) the ultimate load carrying capacity is inversely proportional to the D/t ratio. CSM was the most accurate method for predicting the failure load of the strengthened stainless steel tube.

Eccentrically loaded SFRC-filled stainless steel columns

An experimental investigation on eccentrically loaded stainless steel tubular columns filled with steel-fibre-reinforced concrete (SFRC) is presented in this paper. The composite columns had different depth-to-plate thickness (D/t) ratios, stainless steel tube cross-sections, lengths, non-dimensional slenderness, concrete strengths, steel fibre percentages and concrete type. The pin-ended composite columns were subjected to eccentric compressive loads with a large eccentricity of 0·25D. The composite column strengths, load–axial shortening behaviour and failure modes were measured and observed in the tests. The experimental investigation showed that eccentrically loaded SFRC-filled stainless steel tubular columns offer a considerable enhancement in column strength compared with those filled with plain concrete (PC). In addition, it was found that an increase in the steel fibre percentage enhanced the strength behaviour of the composite columns. Furthermore, the composite column test strengths were compared with design strengths predicted using Eurocode 4 for composite columns. Generally, the investigation showed that the code accurately predicted the strengths of the eccentrically loaded PC-filled stainless steel tubular columns of high concrete strength and was quite conservative in estimating the column strengths of the eccentrically loaded SFRC-filled stainless steel tubular columns.

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

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

Experimental investigation of square stainless steel tubular stub columns after elevated temperatures

The behaviour of square stainless steel tubular (SSST) stub columns after elevated temperatures under axial compression is presented in this paper. A total of sixty specimens were tested, including forty-eight SSST stub columns at elevated temperatures cooled in air, nine SSST stub columns at elevated temperatures cooled in water and three SSST stub columns at ambient temperature. A total of twelve square CFSST stub columns were carried out load-strain tests. The main parameters explored in the test include thickness (1.0 mm, 1.2 mm, 1.5 mm), high temperature duration (30 min, 60 min, 90 min, 120 min), temperature ranging from 400 °C to 1000 °C and cooling methods. This paper presents the failure modes, ultimate load-bearing capacity, load-strain curves, load versus displacement curves, initial stiffness at the elastic stage and ductility of the specimens. It was found that high temperature has the greatest influence on the ultimate load-bearing capacity of the columns, and the cooling methods also have some effect on it. As the elevated temperature specimens subjected increased, the percentage decrease in load-bearing capacity had an obvious increase, the ductility became worse and the initial compressive stiffness slightly decreased. The crack resistance of the specimens improved after elevated temperature. The axial deformation versus load curves had an obvious elastic-plastic stage as the elevated temperature duration increased to 120 min. Based on the experimental results, a formula was proposed to calculate the ultimate load-bearing capacity of SSST stub columns after elevated temperatures.

Numerical Study on Oblique Hysteresis Performance of Composite-sectioned Square Concrete-filled Stainless Steel Tubular Columns

The composite-sectioned square concrete-filled stainless steel tubular column has the characteristics of high rigidity, strong integrity, reasonable force, beautiful structure and low maintenance cost. It has good performance in marine platform and cross-sea bridge structure and urban landmark buildings with high corrosion resistance. However, there are few studies on the performance and design methods of this kind of structure, which restricts its application. In this paper, Finite-element models (FEMs) for analyzing the tangential hysteresis behavior of the composite-sectioned square concrete-filled stainless steel tubular columns were established and verified. A parametric study was conducted on the influence of axial compression ratio, internal and external tube diameter ratio, and oblique angle. The calculated results showed that, the composite-sectioned square concrete-filled stainless steel tubular column has good oblique hysteresis ability, but the larger axial pressure ratio or larger oblique angle will weaken the capacity, while the pipe diameter has little effect on it.

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

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

Analytical behaviors of concrete-filled circular stainless steel tubular (CFCSST) stub columns under axial loading

The objective of this paper is to investigate the behaviors of concrete-filled circular stainless steel tubular (CFCSST) stub columns under axial loading. A fine finite 3D solid element model was established, and the FE results revealed that the increased ultimate bearing capacity of CFCSST stub columns compared with their carbon steel counterparts was mainly due to that the confinement effect of CFCSST stub columns was stronger than that of carbon steel counterparts and the stress contribution of stainless steel was higher than that of carbon steel. The stress nephogram was simplified reasonably in accordance with the limit state of core concrete and a formula was proposed to estimate the ultimate bearing capacity of CFCSST stub columns using superposition method. Finally, the difference of the experimental and predicted results using the proposed formula and the existing codes were illustrated.

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

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

Experimental investigation on sea sand concrete-filled stainless steel tubular stub columns

This paper studies the behaviour of sea sand concrete-filled stainless steel tube (CFSST) stub columns under axial compression through experimental investigations. A total of 48 specimens were tested, including circular and square stainless steel tubes filled with three types of core concrete, including natural river sand concrete, desalted sea sand concrete and natural sea sand concrete. The effects of key parameters such as the tubular thickness of stainless steel, the cross-sectional configuration and the types of concrete infill on the behaviour of these innovative composite columns were investigated. The confinement effects of CFSST with sea sand concrete were evaluated and compared with that of CFSST with conventional river sand concrete. Testing results showed that the tested CFSST columns showed generally high strength and excellent ductility, while the confinement effect of stainless steel on the sea sand concrete is as reliable as that on the river sand concrete counterpart. Comparisons were made between the test results and the predicted ultimate sectional capacity using the existing specifications AISC360–10 (2010), EC4 (2004) and DBJ/T13-51-2010 (2010). These codes are proved reasonably conservative for predicting the sectional strength of sea sand concrete-filled stainless steel tubular stub columns.