Stainless Steel Tubular Stub Columns Research Articles

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.

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.

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%.

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.

Numerical analysis of CFRP-confined concrete-filled stainless steel tubular stub columns under axial compression

The carbon fiber-reinforced polymer (CFRP)-confined concrete-filled stainless steel tubular (CFRP-CFSST) column has the superiority in outstanding mechanical properties, corrosion resistance, and low maintenance cost needed throughout its life cycle, and therefore it has a wide application prospect. In order to study the axial compression behavior of CFRP-CFSST stub column, a numerical simulation study based on the previous test was conducted. A finite element model of CFRP-CFSST was developed and the accuracy of the model was verified by the test results of typical failure modes and load-compression curves of specimens. the stress–strain responses and the interaction between different materials, which were difficult to obtain directly during tests, were disclosed through the finite model. The parametric analyses were also conducted for the sake of the effects of stainless steel, CFRP, concrete, diameter-to-thickness ratio, and cross-section area on the mechanical behavior of CFRP-CFSST. Compared the existing ultimate bearing capacity prediction formula, and a reduction factor ϕ = 0.9 was adopted to the previous formula proposed by Ref. [1].

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.

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.

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.

Experimental investigation of square concrete filled stainless steel tubular stub columns after exposure to elevated temperatures

The behaviour of square concrete filled stainless steel tubular (CFSST) stub columns after exposure to elevated temperatures under axial compression is presented in this paper. A total of sixty-nine specimens were tested, including forty-eight square CFSST stub columns at elevated temperatures cooled in air, nine square CFSST stub columns at elevated temperatures cooled in water and twelve square CFSST stub columns left untreated 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, 2.0 mm), concrete strength (C20, C30, C40), temperatures 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 compressive stiffness at the elastic stage and ductility of the specimens. It was found that high temperature had the greatest influence on the ultimate load-bearing capacity of the columns, and the cooling methods also had some effect on it. As the elevated temperature to which the specimens were subjected increased, the percentage of the ultimate load-bearing capacity decrease had an obvious increase and the ductility of the specimens was enhanced. The initial compressive stiffness decreased evidently as the temperature increased to 800 °C. A new failure mode was identified without visible corner crack in the specimens after exposure to elevated temperatures compared with the specimens at ambient temperature. The ultimate load-bearing capacity increased and the axial deformation versus load curves had a longer elastic stage as the concrete strength increased.

Tests on seawater and sea sand concrete-filled CFRP, BFRP and stainless steel tubular stub columns

This paper presents an experimental study on concrete-filled circular tubes that consisted of seawater and sea sand concrete (SWSSC), stainless steel (SS) tube, carbon fibre reinforced polymer (CFRP) tube, and basalt fibre reinforced polymer (BFRP) tube. A total of 38 stub columns, which included 12 hollow section tubes, 12 fully SWSSC-filled tubes and 14 SWSSC-filled double-skin tubes, with four combinations of inner and outer tubes, were tested under axial compression. Tensile coupon tests and “disk-split” tests were conducted to obtain the material properties of SS, CFRP and BFRP. Ultimate strain of SWSSC-filled tubes and stress-strain curves of the confined concrete were characterised in the study. The effects of some key parameters (e.g., tube diameter-to-thickness ratio, cross-section types, outer tube types, and inner tube types) on the confinement effects were also discussed. Comparisons were made among CFRP, BFRP and glass fibre reinforced polymer (GFRP) in terms of confinement to SWSSC. The capacity prediction formulae previously proposed by the authors for SWSSC filled GFRP tubes were found to be reasonable for estimating the load carrying capacity of SWSSC filled CFRP and BFRP tubes.

Experimental study on seawater and sea sand concrete filled GFRP and stainless steel tubular stub columns

This paper presents an experimental investigation on mechanical and associated properties of seawater and sea sand concrete (SWSSC) filled glass fibre reinforced polymer (GFRP) and stainless steel (SS) circular tubes. A proper SWSSC mix was developed to achieve the target strength and desirable workability. A total of 24 stub columns, including hollow sections and SWSSC fully filled tubes or double-skin tubes, were tested under axial compression with the load applied to concrete and tubes simultaneously. The stress-strain curves of the core concrete indicate that concrete strength and ductility is enhanced due to the confinement effect. Discussion focuses on the influence of tube diameter-to-thickness ratio, outer tube types and inner tube types on concrete confinement. Capacity formulae are proposed to estimate the load carrying capacity of SWSSC fully filled SS or GFRP tubes, and that of double skin tubes with four combinations of inner and outer tubes, i.e. SS and SS, SS and GFRP, GFRP and GFRP and GFRP and SS.

Numerical modelling of concrete-filled lean duplex slender stainless steel tubular stub columns

Major technological advances in materials processing have led to the development of duplex stainless steels with exceptional mechanical properties. Duplexes have great potential for expanding future structural design possibilities, enabling a reduction in section sizes leading to lighter structures. The duplex grades offer combination of higher strength than austenitics as well as a great majority of carbon steels with similar or superior corrosion resistance. However, high nickel prices have more recently led to a demand for lean duplexes with low nickel content, such as grade EN 1.4162. Extensive work is needed to include the lean duplex grade EN 1.4162, into design standards such as EN 1993-1-4 and ENV 1994-1-1. Accordingly, finite element modelling for concrete-filled lean duplex slender stainless steel tubular stub columns of Grade EN 1.4162 is presented in this paper. The paper is predominantly concerned with two parameters: cross-section shape and concrete compressive strength, which have not yet been investigated. The non-linear displacement analysis of the columns was constructed herein based on the confined concrete model provided by Hu et al. (2003) [15]. The behaviour of the columns was investigated using a range of concrete cylinder strengths (25–100 MPa). The overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. The concrete-filled lean duplex slender stainless steel tubular columns were subjected to uniform axial compression over the concrete and stainless steel tube to force the entire section to undergo the same deformations by blocking action. The ABAQUS 6.6 program, as a finite element package, is used in the current work. The results showed that the design rules specified in the ASCE are highly conservative for square and rectangular concrete-filled lean duplex slender stainless steel stub columns while they are conservative in the case of European specifications. A new design strength is, therefore, proposed that is accurately found to represent the behaviour of concrete-filled lean duplex stainless steel tubular stub columns.

Confinement effect of stiffened and unstiffened concrete-filled stainless steel tubular stub columns

This paper presents a comparative study between stiffened and unstiffened concrete-filled stainless steel hollow tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). Finite element analysis of concrete-filled stainless steel unstiffened tubular stub columns is constructed herein based on the confined concrete model recently available in the literature. It is then compared with the experimental results of concrete-filled stainless steel stiffened tubular stub columns. The stiffened stainless steel tubular sections were fabricated by welding four lipped angles or two lipped channels at the lips. The longitudinal stiffener of the column plate was formed to avoid shrinkage of the concrete and to act as a continuous connector between the concrete core and the stainless steel tube. The behavior of the columns was investigated using two different nominal concrete cubic strengths of 30 and 60 MPa. The overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. The stiffened and unstiffened concrete-filled stainless steel tube specimens were subjected to uniform axial compression over the concrete and stainless steel tube to force the entire section to undergo the same deformations by blocking action. The ABAQUS 6.6 program, as a finite element package, is used in the current work. The results of the comparative study showed that the stainless steel tubes in stiffened concrete-filled columns offered a high average of increase in the confinement of the concrete core than that of the unstiffened concrete-filled columns.

A comparative experimental study between stiffened and unstiffened stainless steel hollow tubular stub columns

This paper presents a comparative experimental study between stiffened and unstiffened stainless steel hollow tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). Stainless steel structural shapes are becoming increasingly complex as cold-forming techniques are advancing. The unstiffened stainless steel tubular stub sections were fabricated by welding four angles or two channels tip-to-tip, whereas the stiffened sections were fabricated by welding four lipped angles or two lipped channels at the lips. Therefore, the stiffeners were formed at the mid-depth of the sections. In total, five columns without stiffeners and five columns with stiffeners were tested. Series of tests were performed to investigate the effects of cross-section shape on the behaviour and strength of stainless steel tubular stub columns. The measured average overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. Different lengths of columns were selected to fix the length-to-depth ratio to a constant value of 3. The specimens were subjected to uniform axial compression. The column strengths, load–axial strain relationships and failure modes of the columns are presented. The column strengths obtained from the experimental study were compared with the design strengths calculated using the European Code for cold-formed stainless steel structures and the ASCE Standard. The results of the experimental study showed that the design rules specified in European specifications and ASCE standard generally overestimate the column strengths of stainless steel square and rectangular hollow section stub columns fabricated by cold-forming and welding.