Outer Stainless Steel Tube Research Articles

Axial performance of concrete-filled GFRP tube columns jacketed by outer stainless steel tube and sandwiched concrete

The concrete-filled FRP tube (CFFT) column, a prevalent and crucial structural element in marine environments, requires reinforcement measures to enhance its operational performance. This paper introduces a novel strengthening technology involving sandwiched concrete and stainless steel tube jackets. By conducting axial compression tests on two CFFT columns and nine reinforced columns, the failure modes, load-axial deformation curves, and load-strain relationships were analysed in this study. Additionally, the influence of outer steel tube thickness (3.0 mm, 4.0 mm, 5.0 mm) and sandwiched concrete strength grades (C50, C60, C70) on the axial compressive performance of the reinforced columns was investigated. The findings indicated that the proposed reinforcement method effectively mitigated the brittle failure associated with the original CFFT column. The external stainless steel tube played a crucial role in restraining lateral deformation of the internal CFFT column, thereby enhancing the axial compressive bearing capacity. Through theoretical analysis on the components in reinforced columns, a calculation formula for the axial compressive capacity of the reinforced column was derived according to the unified theory and the double-shear unified strength theory.

Compressive Behavior of Stainless Steel–Concrete–Carbon Steel Double-Skin Tubular (SCCDST) Members Subjected to External Hydraulic Pressure

The new-type stainless steel–concrete–carbon steel double-skin tubular (SCCDST) members, characterized by their exceptional corrosion resistance and mechanical bearing capacity, have promising applications in ocean engineering, particularly in deep-water engineering. The external hydraulic pressure and interfacial action of various materials intensify the complexity of composite performance of SCCDST members. This paper describes an analytical investigation on the concentric compressive performance of SCCDST members under external hydraulic pressure. The full-range mechanism, including load–displacement response, bearing capacity contribution, and contact pressures, was investigated through the finite element (FE) model that was validated by the failure mode, bearing capacity, and response of axial load versus strain. Subsequently, influences of key geometric–physical parameters were analyzed, e.g., diameter-to-thickness ratios (Do/to, Di/ti), material strengths (fyo, fyi, and fc), hollow ratios (χ), and water depths (H). Typical results indicate that: the initial active confinement action derived from the hydraulic pressure can enhance the interfacial contact pressure and axial compression capacity of SCCDST members due to the tri-axial compression state; the enhancement of confinement effect is mainly from the interfacial interaction between outer stainless steel tube and concrete infill; influence of water depth on bearing capacity cannot be ignored, e.g., the bearing capacity of an SCCDST member with larger hollow ratio (χ = 0.849) is not enhanced under a higher hydraulic pressure (H = 900 m) because of the cross-sectional buckling failure risk. Finally, a modified method considering the effect of water depth was proposed and verified for SCCDST members under hydraulic pressure.

Testing, numerical analysis and design of CFDST cross-sections with square stainless steel outer tubes in bending

The structural performance and design of concrete-filled double skin tubular (CFDST) cross-sections with square stainless steel outer tubes are studied herein. A total of 17 four-point bending tests on CFDST cross-sections with varying concrete grades, together with accompanying material tests, were first conducted. The details of the test rig and procedures, as well as the key experimental results are reported. Following the physical testing, a numerical modelling campaign was carried out. A finite element (FE) model was initially validated against the tests, and then adopted to conduct a parametric study to acquire further FE data, covering a broader spectrum of material strengths and cross-section slendernesses. The obtained test and FE results were used to evaluate the applicability of the general design provisions for concrete-filled carbon steel members in the current European and American design codes. Overall, the examined design codes are shown to provide unduly conservative (less so for the higher concrete grades) and rather scattered moment resistance predictions, though some moment resistances predicted using the European code were on the unsafe side. Modifications to the European design treatment in relation to the assumed stress distribution, to take due account of the partial spread of plasticity in the outer tube, and the effective compressive strength of the concrete infill, to reflect the reduced relative effectiveness of using higher concrete grades, are proposed and shown to improve the consistency of the resistance predictions.

Simulation modeling and design of circular concrete-filled double-skin tubular slender beam-columns with outer stainless-steel tube

The stainless-steel tube has been used to construct Concrete-Filled Steel Tubular (CFST) columns because it has a high resistance to fire and corrosion, good durability, and aesthetic appearance compared to the carbon steel tube. However, there is very little published research on eccentrically loaded circular Concrete-Filled Double-skin Steel Tubular (CFDST) slender beam-columns composed of an outer stainless-steel tube and an inner carbon-steel tube. In line with this, this paper presents a fiber-based simulation model for predicting the structural performance of CFDST slender columns with external circular stainless-steel tube under eccentric compression. The simulation modeling of load-deflection curves and load-moment interaction diagrams for slender CFDST beam-columns is developed and verified by the experimental results. The verified simulation model is then used to study the effects of geometric and material properties on structural performance. The range analysis is applied to the orthogonal design to identify the relative significance of the factors that influence the structural response. The orthogonal design covers CFDST beam-columns with a hollow ratio ranging from 0.1 to 0.8. The results indicate that the column slenderness ratio is the most significant factor, followed by the loading eccentricity ratio, the outer tube thickness, stainless steel proof stress, concrete strength, and carbon steel yield strength. The accuracy of the design method specified in Australian standard AS/NZS 2327, and the proposed design methods are evaluated. The proposed equation provides accurate strength predictions of CFDST slender columns where the external skin is made of stainless steel.

Compressive behavior of CFRP-confined concrete-filled double-skin stainless-steel tube stub columns

The axial compression behavior of CFRP-confined concrete-filled double-skin stainless-steel tube (CFDSST) stub columns were investigated through experiments and FE modeling in this study. The typical failure modes, axial load–shortening curves, and strain responses of CFDSST and CFRP-confined CFDSST specimens were determined. The test results showed that CFRP could effectively restrain the local buckling and evidently enhance the compression behavior of the specimens. FE models of the CFRP-confined CFDSST stub columns were established and then validated by comparing with the experimental results. On this basis, FE modeling was used to perform parametric studies. To avoid the local buckling and yield failure of the inner steel tube prior to that of the outer stainless-steel tube, a design model was suggested to calculate the minimum thickness and yield strength of the inner tube. Furthermore, to evaluate the ultimate bearing capacity of the CFRP-confined CFDSST stub columns, a prediction model based on the superposition principle was suggested. The calculation results of the prediction model were consistent with the test and FE results.

Design of stainless steel CHS-concrete infill-carbon steel CHS double-skin stub columns

Concrete filled double-skin tubular (CFDST) stub column with outer stainless steel circular hollow section (CHS) and inner carbon steel CHS is presented in this paper. It combines the strength of stainless steel, concrete and carbon steel, and also provides the stainless steel's durability, ductility and corrosion resistance properties along with the lighter weight due to the sectional feature. Finite element analysis (FEA) is done in this paper and the developed FE models are verified with the available test results on the basis of failure modes, full load-deformation curves and ultimate strengths of the specimens. Afterward, a series of parametric analysis are conducted to investigate the structural performance of each component and the overall column as well as the confining stresses between the tubes and concrete. In addition, the effect of stainless-steel grade, concrete strength, carbon-steel strength, diameter-to-thickness ratio of outer tube, diameter-to-thickness ratio of inner tube and hollow ratio on confining stress and mechanical property of sandwiched concrete is studied. The constitutive models of sandwiched concrete and outer stainless steel tube under plane stress are proposed. Based on these proposed models, the fiber element model is used to predict the mechanical properties of this composite column and then checked with the finite element modelling (FEM) outputs. Different design methods such as ACI code, European code, continuous strength method (CSM), Han et al. method and Nie et al. method are assessed to evaluate the applicability and accuracy. Finally, a new design method for calculating the ultimate bearing capacity of the CFDST stub column is proposed, which exhibits good agreement with the results of the FEA.

Compressive behaviour of double skin sections with stainless steel outer tubes and recycled aggregate concrete

An experimental and numerical study into the behaviour of concrete-filled double skin tubular (CFDST) stub columns is presented. A total of eight axial compression tests were carried out, four utilising conventional concrete and four with recycled aggregate concrete. The stub columns were circular in cross-section and each comprised an austenitic stainless steel outer tube and a carbon steel inner tube, of varying dimensions. Accordingly, hollow ratios of 0.67 and 0.55 were considered. The recycled coarse aggregate was made by crushing test specimens from a previous research project, and a replacement ratio of 50% was adopted. During the experiments, similar structural behaviour and failure modes were observed between the specimens with conventional and recycled aggregate concrete. To investigate the behaviour further, a finite element model was developed in ABAQUS; validation of the model against the experimental results from the current work as well as data available in the literature is described. The finite element model was employed to conduct a parametric study to examine the load-bearing contributions of the constituent components of CFDST sections and to assess the influence of the hollow ratio on the structural behaviour. The experimental and numerical ultimate loads are compared with the capacity predictions determined using available design procedures. Overall, the results show that CFDST stub columns with recycled aggregate concrete can achieve similar capacities to their conventional concrete counterparts, demonstrating the potential for the wider use of recycled aggregate concrete, towards more sustainable structural solutions.

Optimizing Coaxial Sonic Spray Geometry for Generating Water Microdroplets.

Sonic spray creates a stream of neutral and charged microdroplets without application of voltage, heating, laser irradiation, or corona discharge. The solvent of interest flows through an inner capillary (usually constructed of fused silica) that is surrounded by an outer stainless-steel tube through which a nebulizing gas flows under pressure. This technique has been widely used as the interface in mass spectrometric studies for chemical analysis and for understanding microdroplet chemistry. We have used light scattering to characterize the size distribution and density for water microdroplets as a function of several parameters, such as water quality, water flow rate, nebulizing gas pressure, and sonic sprayer geometry. We find that the size distribution of the microdroplets, which is critical to many applications, depends most sensitively on the distance between the inner and outer capillary outlets and the gas flow pressure. The best performance as measured by the smallness of the microdroplet diameters is obtained when the gas flow pressure is the highest and there is no separation distance, d, between the two capillary outlets. In addition, at d = 0 mm, the microdroplet diameter distribution is nearly independent of the water flow rate, indicating that studies under these conditions can be scaled up.

Testing and numerical modelling of circular CFDST cross-sections with stainless steel outer tubes in bending

The structural performance of circular concrete-filled double skin tubular (CFDST) cross-sections with stainless steel outer tubes has been examined herein based on experiments and numerical modelling. A laboratory testing programme comprising a total of 22 four-point bending tests was performed on seven CFDST cross-sections with varying concrete grades. The details of the test rig and procedures, as well as the key test observations, including the failure moment capacities, moment–curvature curves and failure modes, are fully reported. A numerical modelling programme was then carried out; a finite element (FE) model was first established to replicate the test observations, and then adopted to conduct a parametric study to acquire further FE data over a broader spectrum of material strengths and cross-section slendernesses. Based on the combined set of test and FE results, the general design provisions for concrete-filled carbon steel members in the current European and American design codes were evaluated for their applicability to the studied CFDST cross-sections. Overall, the results revealed that both of the examined design codes yield unduly conservative (less so for the higher concrete grades) and scattered moment resistance predictions, though some moment resistances predicted from the European code were on the unsafe side. Modifications, including a concrete reduction factor η to reflect the reduced relative effectiveness of using higher concrete grades and a modified stress distribution considering the partial spread of plasticity, were proposed and shown to improve the consistency of the resistance predictions. Finally, the reliability of the current and modified design rules was demonstrated through statistical analyses.

Research on concrete-filled stainless steel tubular composite columns

Concrete-filled stainless steel tubular composite columns are used in the structures. It is important to define the structural behaviour of this type of columns. This paper presents experimental and theoretical studies of eccentrically loaded concrete-filled stainless steel tubular composite columns. The column specimens were manufactured with high strength outer stainless steel tube, in-filled concrete and inner carbon structural steel. The tubular composite column specimens were designed with plain concrete and steel fiber reinforced concrete. The column specimens were tested and the experimental load–deflection curves of columns were presented in the study. In addition, the tested plain and steel fiber concrete-filled stainless steel tube composite columns were analysed based on a theoretical method for the prediction of strength and load–deflection behaviour. It was observed that the tested tubular column specimens behaved in a ductile manner. A good degree of agreement was obtained between the experimental and theoretical load–deflection curves of concrete-filled stainless steel tubular composite columns. In addition, a parametric study was carried out to examine the influences of loading eccentricity, slenderness, plate slenderness and the concrete compressive strength on concrete-filled stainless steel tubular composite column behaviour. It was concluded from the parametric study that the strength of columns increased by increasing stainless steel wall thickness and concrete compressive strength. However, column strength decreased when the eccentricity and column length were increased.

Performance of concrete-filled stainless steel tubes subjected to concentric tension: Numerical investigation and parametric study

Concrete-filled stainless steel tube (CFSST) has great potential to be applied in the marine environment attributed to its excellent structural behavior and corrosion resistance. This paper presents numerical investigation and parametric study on the performance of CFSST members subjected to concentric tension. Firstly, a three-dimensional finite element analysis (FEA) model is established and validated against the experimental results reported in a companion paper. Secondly, the calibrated FEA model is used to investigate the tensile behavior of CFSST members, especially the composite action and stress distribution between the outer stainless steel tube and the concrete infill, which determines the load-carrying capacity of the steel–concrete composite member. Then, a wide-range parametric analysis is conducted by varying the parameters of both the stainless steel tube and concrete infill, and the influence of different parameters on the load-carrying capacity of CFSST tensile members is studied. Finally, a calculation model is proposed to be used to predict the ultimate strength of CFSST tensile members, and a good agreement is achieved between the model-predicted values and the FEA-computed ones.

Axial compressive behavior of concrete filled stainless-carbon steel tube columns: Experimental investigation

This paper investigates the axial compressive behavior of concrete-filled stainless-carbon steel tube (CFSCT) stub columns, consisting of an outer stainless steel tube, an inner carbon steel tube, and infilled concrete. A total of twenty column specimens are fabricated and tested. Test parameters include column section type, strength and wall thickness of carbon steel tube, and concrete strength. Failure modes, load versus deformation relationships, ultimate strength, residual strength, ductility, elastic and elastic-plastic local buckling stress, and strain characteristics are investigated. Results show that outward local buckling of stainless steel tubes occurs in all CFSCT column specimens, and columns fail in a ductile manner. Increasing the carbon steel tube thickness can significantly improve column ultimate strength and residual strength. Compared to conventional concrete-filled stainless steel tube (CFSST) columns, the ultimate strength of CFSCT columns improved by 10.9%, 23.1%, and 27.4% on average for columns with carbon steel tube wall thickness of 2, 4, and 6 mm, respectively. The post-peak ductility behavior is also related to carbon steel tube wall thickness, increasing wall thickness can slow down the descending branch after peak load. Concrete has significant effect on the ultimate strength, when concrete strength increases, specimen ultimate strength increases by 15.1% on average. In addition, finite element model is established and analyzed based on the experimental results. Finally, ultimate strengths are compared and evaluated according to the Eurocode 4, AIJ, ACI and GB 50936.

Numerical modeling of rectangular concrete-filled double-skin steel tubular columns with outer stainless-steel skin

Concrete-filled double-skin steel tubular (CFDST) columns composed of outer stainless-steel skin have grown increasingly popular in structural applications on account of their attractive appearance, ductility, resistance to corrosion, fire resistance and easy maintenance. However, only one numerical study of the behavior of rectangular CFDST short columns with outer stainless steel tube has been reported. This paper presents the numerical analysis and design of axially loaded rectangular CFDST short columns where the outer tube is made of stainless-steel. A finite element model is created for analyzing the responses of rectangular CFDST short columns. The numerical analysis accounts for the confinement mechanism of concrete, strain hardening of stainless steel and imperfection of steel tubes. A comparative study of numerically predicted and experimentally observed behavior is presented to gain an appreciation for the accuracy of the developed numerical model. A parametric study is undertaken, investigating the performance of a series of rectangular CFDST columns by varying the concrete strength, load distribution, cross-section shape and tube thickness. The ultimate axial strengths predicted using Australia/New Zealand Standard for composite structures are compared against experimental results. It is demonstrated that the numerical model predicts well the responses of CFDST columns where the outer skin is made of stainless steel. Australia/New Zealand Standard yields the accurate predictions of the ultimate axial strengths of rectangular CFDST columns with outer stainless-steel tube.

Axisymmetric simulation of circular concrete-filled double-skin steel tubular short columns incorporating outer stainless-steel tube

A concrete-filled double-skin steel tubular (CFDST) column incorporating an outer stainless-steel tube and a high-strength inner carbon steel tube exhibits high corrosion resistance and load-carrying capacity. This paper presents the axisymmetric analysis technique for simulating the structural response of short circular CFDST columns loaded concentrically. The double-skin confinement mechanism for modeling the sandwiched concrete is explored and implemented in the analysis. The significant strain hardening response of stainless steel in axial compression is recognized in the analysis technique. The benefits of axisymmetric analysis over the full three-dimensional simulation are highlighted for the analysis of a member which is symmetric about its rotation vertical axis. The comparison of axisymmetric analysis results is made with the experimental results given in the previous independent studies. The parametric investigation on the structural response of CFDST columns is performed by means of using the verified axisymmetric model. The analysis results indicate that the inner tube diameter-to-thickness ratio less than 40 should be selected to prevent its local buckling from occurring and the inner tube should have yield stress higher than the 0.2% proof strength of the outer stainless steel tube. The outer stainless-steel with proof stress of 195 MPa should be filled with high-strength concrete of 120 MPa to ensure the strain compatibility. Liang’s design model closely estimates the ultimate axial strengths of the CFDST columns composed of an outer stainless-steel tube and a high-strength inner carbon steel tube.

Compressive behaviour and design of CFDST cross-sections with stainless steel outer tubes

A finite element (FE) investigation into the compressive behaviour of concrete-filled double skin tubular (CFDST) cross-sections with lean duplex and ferritic stainless steel outer tubes is presented. FE models were initially developed and validated against available test results reported in the literature. Upon successful replication of the ultimate capacities, load–deformation histories and failure modes exhibited by the tested CFDST stub columns, a parametric study was undertaken to investigate the influence of key variables, including the local slendernesses of the outer and inner tubes, the concrete strength and the adopted grade of stainless steel, on the ultimate response of the studied CFDST stub columns. Based on the generated FE data pool and the available test results, the applicability of the existing European, Australian and American design provisions for composite carbon steel members to the design of the studied CFDST cross-sections was evaluated. All the examined design rules are shown to yield unduly conservative (less so for the higher concrete grades) and rather scattered capacity predictions. Modifications to the design treatment in relation to the effective area of the outer tubes, to take due account of outward-only local buckling, and the effective compressive strength of the infilled concrete, to reflect the reduced relative effectiveness of higher concrete grades, are considered. The modified design rules are shown to improve the accuracy and consistency of the design capacity predictions. Finally, statistical analyses were carried out to demonstrate the reliability of the modified design approaches.

CFDST sections with square stainless steel outer tubes under axial compression: Experimental investigation, numerical modelling and design

The use of concrete-filled double skin tubular (CFDST) cross-sections for compression members has become increasingly popular in construction. A recently proposed innovative form of CFDST cross-section, ultilising stainless steel for the outer tube, offers the combined advantages of the composite action seen in CFDST member alongside the durability and ductility associated with stainless steel. CFDST sections with stainless steel outer tubes, for which there are currently little experimental data, are the focus of the present study. A comprehensive experimental and numerical investigation into the compressive behaviour of CFDST sections with square stainless steel outer tubes is presented in this paper. A total of 19 specimens was tested under uniform axial compression, and the test observations are fully reported. The ultimate loads, load-displacement curves and failure modes from the tests were used for the validation of finite element (FE) models. Parametric finite element analyses were then performed. The combined set of experimentally and numerically derived data was employed to assess the applicability of the existing European, Australian and American design provisions for composite carbon steel members to the design of the studied CFDST cross-sections. Overall, the existing design rules are shown to provide generally safe-sided (less so for the higher concrete grades) but rather scattered capacity predictions. Modifications to the current design codes are also considered—a higher buckling coefficient k of 10.67 to consider the beneficial restraining effect of the concrete on the local buckling of the stainless steel outer tubes, as well as a reduction factor η to reflect the reduced relative effectiveness of higher concrete grades. Overall, the comparisons demonstrated that improved accuracy and consistency were achieved when the modified design rules were applied.

Performance of concrete-filled stainless steel tubes subjected to tension: Experimental investigation

Abstract Concrete-filled stainless steel tubular (CFSST) structures have attracted increasing attention from researchers and engineers in the past decade. CFSST members can be adopted as columns in buildings or chord members in trusses, which could be subjected to tension under some circumstances. This paper presents an experimental investigation on the mechanical behavior of concentrically and eccentrically loaded CFSST tensile members. The parameters considered in the tests included the steel type (stainless steel or carbon steel), load eccentricity (e = 0–75 mm), steel ratio of the cross section (α = 0.075 or 0.112), concrete strength (fcu = 53.4 MPa or 84.7 MPa), and steel-concrete interfacial condition (lubricated or not). The test results show the concrete infill effectively works with the outer stainless steel tube, leading to tensile strength and stiffness higher than those of the corresponding hollow stainless steel tube. All the CFSST tensile members show ductile behavior and the end rotation of the eccentrically loaded members exceeds 0.1 rad. Finally, the feasibility of existing design method to predict the tensile strength of CFSST members was also evaluated.

Experimental Study of Square and Rectangular CFDST Sections with Stainless Steel Outer Tubes under Axial Compression

AbstractA comprehensive experimental investigation into the axial compressive response of concrete-filled double skin tubular (CFDST) sections with stainless steel square and rectangular outer tube...

Performance of circular CFDST members with external stainless steel tube under transverse impact loading

Abstract This paper presents an experimental and numerical study on the impact performance of circular concrete-filled double skin steel tubular (CFDST) members with external stainless steel tube. Austenitic 304 stainless steel was used for all the test specimens. Taguchi approach was employed for the parametric design of the experimental program. The testing parameters were the impact height, hollowness ratio and axial load level. 18 specimens were tested under transverse impact loading to obtain the failure patterns, the time histories of impact force and mid-span deflection, as well as the strain developments in the stainless steel tube. Finite element (FE) models were then established and verified against the test results, in which the strain rate effects of the stainless steel, the carbon steel and the infilled concrete were considered. The validated FE model was then employed to investigate the whole dynamic response of CFDST members with outer stainless steel tube subjected to impact. The impact resistance of the stainless composite member was also compared with that of the CFDST member with an external carbon steel tube.

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.