Stainless Steel Cross-sections Research Articles

Ultimate behaviour of hybrid stainless steel cross-sections

Hybrid steel plate girders are used worldwide as primary structural members in steel and composite bridges, when there is a need for deeper sections with greater stiffness and bending resistance than rolled sections to carry heavy loads. With the increasing importance of sustainability and lifecycle (cost) analysis, design for maintenance has become an important consideration for infrastructure projects like bridges which have a design working life exceeding 100 years over which they need to be regularly inspected and maintained. Stainless steels are known for their excellent corrosion resistance and low maintenance costs and thus the application of hybrid plate girders in bridge designs could be explored. This paper reports a numerical study on stainless steel hybrid plate girders subjected to compression and to bending and assesses relevant recommendations for their design. Previously developed FE models validated against stub column and four-point bending tests are employed and a parametric study is conducted on hybrid I-sections over a wide range of cross-section slenderness and aspect ratios. Based on the obtained results, the EN 1993-1-4 design predictions for stainless steel cross-sections in compression and in bending are assessed and the accuracy of the codified slenderness limits for both homogeneous and hybrid stainless steel girders is discussed. Furthermore, the numerically obtained deformation capacity at ultimate load is plotted against the CSM base curve originally derived for homogeneous sections and the accuracy of the CSM predictions of the cross-section resistance is also assessed, demonstrating that the CSM can be employed to predict the cross-section resistance of hybrid girders.

Fire resistance of stainless steel slender elliptical hollow section beam-columns

PurposeStainless steel has different advantages when compared to conventional carbon steel. The corrosion resistance and aesthetic appearance are the most known; however, its better behaviour under elevated temperatures can also be important in buildings design. In spite of the initial cost, stainless-steel application as a structural material has been increasing. Elliptical hollow sections integrate the architectural attributes of the circular hollow sections and the structural advantages of the rectangular hollow sections (RHSs). Hence, the application of stainless-steel material combined with elliptical hollow profiles stands as an interesting design option. The purpose of the paper is to better understand the resistance of stainless-steel-beam columns in case of fireDesign/methodology/approachThe research presents a numerical study on the behaviour of stainless-steel members with slender elliptical hollow section (EHS) subjected to axial compression and bending about the strong axis at elevated temperatures. A parametric numerical study is presented here considering with and without out-of-plane buckling different stainless-steel grades, cross-section and member slenderness, bending moment diagrams and elevated temperatures.FindingsThe tested design methodologies proved to be inadequate for the EHS members being in some situations too conservative.Originality/valueThe safety and accuracy of Eurocode 3 (EC3) design methodology and of a recent design proposal developed for I-sections and cold-formed RHSs are analysed applying material and geometric non-linear analysis considering imperfections with the finite element software SAFIR.

Design of stainless steel cross-sections with outstand elements under stress gradients

A significant amount of research has been reported on stainless steel tubular sections, while studies on I- and C-sections remain relatively limited. This paper presents a comprehensive numerical study on the response of stainless steel I- and C-sections subjected to minor axis bending, with outstand flanges subjected to stress gradients. Numerical models are developed and validated against reported test data on austenitic stainless steel sections under minor axis bending. Subsequently, parametric studies using standardised material properties on austenitic, duplex and ferritic stainless steel grades, covering a wide variety of cross-section slendernesses, are carried out to expand the structural performance data. The results are used to assess the applicability of the Eurocode slenderness limits, revealing that the Class limit 3 for outstand flanges under stress gradient is overly conservative. Moreover, Eurocode underestimates the predicted bending strengths, whereas the level of accuracy and consistency improves for stocky sections, when the Continuous Strength Method is used. Aiming to address the lack of accuracy and consistency in the design predictions of slender sections, particular focus is placed on their performance. It is demonstrated that outstand elements under stress gradients exhibit significant inelastic behaviour after the compression flanges have locally buckled. Inelastic buckling behaviour is not considered in current design guidance, thus resulting in overly conservative and fundamentally incorrect strength predictions. An alternative design method based on the plastic effective width concept is proposed for slender stainless steel I- and C-sections in minor axis bending, which leads to more favourable and less scattered strength predictions.

Tests on stainless steel frames. Part I: Preliminary tests and experimental set-up

Austenitic stainless steel is an excellent construction material for structures required to withstand accidental loads such as seismic and/or fire events due to its appropriate mechanical properties, including high ductility, considerable strain hardening and good fire resistance. In recent years, a considerable amount of research has been devoted to the understanding of the structural performance of single isolated stainless steel members. However, new trends in the design philosophy moving from current member-based methods to direct system-based approaches will require more experimental evidence on more complex structural systems such as frames, which are currently scarce. With the aim of contributing to the advances in this field, one of the first known extensive experimental programmes on austenitic stainless steel frames is presented in this paper. The experimental programme comprised several sub-programmes, in which the performance of stainless steel structures at different levels was investigated. This paper describes a series of tests on austenitic stainless steel cross-sections and members, which were utilized in the planning and analysis of the subsequent frame tests. The paper also outlines the complex experimental set-up adopted for the stainless steel frame tests, including the implemented loading schemes, auxiliary elements and instrumentation, through a detailed explanation of the different issues encountered in the process of their definition. The knowledge gained and the experiences reported in this paper could assist researchers in planning similar experimental programmes.

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.

Progress in the Design of a Hybrid HTS-Nb3Sn-NbTi Central Solenoid for the EU DEMO

State-of-the-art high field solenoids make use of hybrid designs exploiting the superior high field performance of High Temperature Superconductors (HTS) in the innermost region. The benefits of a hybrid Central Solenoid in a pulsed tokamak like the EU DEMO can be two-fold: either to reduce its outer radius (which would result in a reduced overall size and cost of the tokamak), or to increase the generated magnetic flux (which could extend the plasma burn time and possibly increase the power plant efficiency). In the framework of the pre-conceptual design studies for DEMO coordinated by EUROfusion, a hybrid Central Solenoid is proposed based on ten layer-wound sub-coils using HTS, Nb3Sn, and Nb-Ti conductors respectively for the high, medium, and low field sections. The design exploits the flexibility of layer winding by grading both the superconductor and the stainless steel cross sections in each sub-coil, which has the potential for space and cost savings. Mechanical analyses have identified fatigue as the main design driver for the EU DEMO Central Solenoid. Possible alternatives to reduce the sensitivity of the proposed design to fatigue are currently under investigation.

Design of cold-rolled stainless steel rectangular hollow section columns

Considering the effects of cold-forming and strain hardening in the design of cold-formed stainless steel columns is an effective way to reduce construction costs. This approach has become a common trend in the revision of relevant design codes. A few studies were conducted in the past on two key aspects: (i) predicting the enhanced material properties in cold-formed stainless steel cross-sections and (ii) modifying the design methods to adapt to stainless steel material characteristics. However, in the existing literature, they had been separately studied, and integration of these two aspects to form a complete design method was rarely reported. In this study, a series of column tests were conducted on 19 stub and 32 long columns in rectangular hollow sections. The measured imperfections, material properties, load-displacement curves, and failure modes were reported. A new design method for columns was developed, which could clearly and accurately determine the column capacity over the space encompassed by member slenderness and cross-sectional slenderness values. The proposed design method and the method laid out in the Design Manual for Structural Stainless Steel were evaluated against the test data. It was demonstrated that the two design methods were both very conservative in predicting the column capacity when material properties in the annealed condition were used. However, their performances improved when the predicted enhanced material properties were used. Generally, the predictions of the proposed design method matched the test data better. Furthermore, a reliability analysis was conducted, and resistance factors were recommended for the corresponding design methods.

Test on residual stress distribution of welded S600E high-strength stainless steel sections

ABSTRACT S600E high-strength stainless steel is a new type of sorbite stainless steel with 1.5–2.2% Ni and 13–15% Cr. Compared with commonly used S30408 austenitic stainless steel, it has outstanding characteristics, e.g., a much higher yield strength and a lower price. Thus it has an obvious competitiveness in stainless steel construction. Currently, few studies have been reported on the structural behaviours of S600E high-strength stainless steel. This study focuses on the residual stresses in welded S600E high-strength stainless steel cross-sections. A total of 16 welded cross-sections were prepared, including 6 Box-sections and 10 I-sections. Tensile coupon tests were conducted to obtain the material properties. Residual stresses were measured using the sectioning method, and detailed distribution in each cross-section was provided. Test results indicate that tensile residual stresses are shown in the region around the welds with magnitudes less than the nominal yield strength, and compressive residual stresses are in the other regions. Test results were compared with the current residual stress distribution models to check their applicability. It was concluded that current residual stress distribution models could not represent test results well for the peak tension residual stress and the width of the tension-compression transition zone. Simplified residual stress distribution models were proposed for welded S600E High-strength stainless steel Box-sections and I-sections by modifying the ones in ECCS and the ones proposed by Yuan, which could better match the test results. The proposed models would contribute to researches on the behaviours of members and structures.

Design of stainless steel cross-sections for simple load cases with the O.I.C.

The present paper investigates the resistance of stainless steel I or H sections as influenced by yield extent and local stability issues. In particular, the influence of a rounded stress-strain law with large strain hardening effects on the buckling response of sections is studied. Extensive shell non-linear numerical parametric studies led to a 750+ dataset that considered various material grades, 50 different section shapes (from compact to slender) and either sections in compression or under major-axis bending. These results allow to assess the merits of a design proposal based on the Overall Interaction Concept (O.I.C.) that is shown to be both very effective and accurate while remaining simple. The various influences of section's slenderness, section shape and steel grade are studied, and comparisons with alternative design proposal and design specifications evidence an increased level of accuracy, consistency and safety.

Structural behaviour and design of high strength steel RHS X-joints

This paper aims to investigate the structural behaviour and static strength of high strength steel rectangular hollow section (RHS) X-joints under axial compression in the braces through tests and numerical analysis. Eight RHS X-joints which were composed of fabricated steel tubes with a measured yield stress of 907 MPa were tested. Extensive numerical simulations on the fabricated RHS X-joints in S460, S690 and S960 steel were conducted using finite element (FE) analysis. The FE model was validated against the test results. The investigated failure modes are chord face plastification, chord side wall failure and a combination of these two failure modes. The effects of the heat affected zones (HAZ) and suitability of the strength equations adopted by the CIDECT design guide for the fabricated RHS X-joints were examined. The deformation capacity and ductility of test specimens which failed by chord face plastification could be considered as reasonably sufficient. The effects of material strength reduction in the HAZ on the joint initial stiffness are minor, but could significantly lower the joint strength. In general, the CIDECT strength prediction is increasingly unconservative with increasing steel grade for the RHS X-joints failing by chord face plastification. However, the CIDECT strength prediction is generally conservative for the combined failure modes, and becomes increasingly conservative with increasing chord side wall slenderness for chord side wall failure. The suggested ranges of brace to chord width ratio (β) and chord width to wall thickness ratio (2γ) are 0.4 ≤ β ≤ 0.85 and 2γ ≤ 60β − 1 for the RHS X-joints failing by chord face plastification to allow for more effective use of high strength steel, and corresponding strength equations were proposed. An analytical model of plate buckling was proposed and the deformation-based continuous strength method (CSM) originally developed for designing non-slender stainless steel cross-sections was adopted for the design of chord side wall failure in the RHS X-joints with β = 1.0 and 2γ up to 50. The proposed design method is also applicable for designing chord side wall failure in equal-width RHS X-joints using cold-formed and hot-finished carbon steel and cold-formed stainless steel. A linear interpolation approach using the proposed strength equations at β = 0.85 and β = 1.0 is suggested for the RHS X-joints with 0.85 < β < 1.0 and 2γ ≤ 50 which failed by the combined failure modes. The proposed strength equations can produce much more accurate and consistent strength prediction than the CIDECT design guide, and were converted to design strength equations for the design of high strength steel RHS X-joints.

The Continuous Strength Method of Cold-formed Stainless Steel Equal-leg Angle Section Stubs

Structural stainless steel requires appropriate recognition of its beneficial properties such as material nonlinearity and significant strain hardening. The recently proposed Continuous Strength Method (CSM) exploits those benefits through a strain based approach for both stocky and slender cross-sections, and is shown to yield a higher level of accuracy and consistency, as well as design efficiency, in the capacity predictions of stainless steel cross-sections. Although there have been extensive and comprehensive studies on SHS, RHS, round tubes and H-sections stubs, but research into cold-formed stainless steel equal-leg angle section stubs remains scarce. In this paper, the scope of the CSM is extended to cover the design of cold-formed stainless steel equal-leg angle section stubs. Developed FE models included material nonlinearities as well as initial geometric imperfections. A comprehensive parametric study has been carried out covering a wide range of slenderness with different cross section geometries for the considered angle stubs. Cross-section resistances obtained from the numerical study were used to assess the performance of the current Continuous Strength Method (DSM) guidelines and EC3 when applied for stainless steel equal-leg angle section stubs; obtained comparisons showed considerable conservatism. A modified design method for cold-formed stainless steel equal-leg angle section stubs is proposed herein following CSM techniques, which provides considerably more accurate predictions for the considered cold-formed stubs. Reliability of the proposed design equations is also presented showing a good agreement with both experimentally and numerically obtained results.

Influence of fuel ashes on corrosion of surface coatings cladded by CMT method

ABSTRACT The aim of the present research was to investigate the influence of different biomasses and sewage sludge ash (at 650°C for 1000 h and 2000 h, respectively) on the surface of weld cladded (Cold Metal Transfer technique, CMT) stainless steels 309 and 310. The biomass ashes were rich in K2O, CaO, SiO2, whereas sewage sludge ash in P2O5, CaO, Fe2O3, and SiO2. Characterization of the stainless steel cross-section and surface after the corrosion process inducted by the presence of ash were carried out by scanning electron microscopy (SEM) with EDAX analysis. Phase analysis of corrosion products was made by X-ray diffraction (XRD). Chromium, nickel, and iron oxides were the main oxides which occurred after the corrosion test. It has been proved that biomass ashes have the corrosive properties (because of their chemical composition) and are more aggressive than the sewage sludge ash for that kind of materials.

The continuous strength method for the design of mono-symmetric and asymmetric stainless steel cross-sections in bending

The current codified treatment of local buckling in stainless steel cross-sections is based on the traditional cross-section classification framework and a simplified elastic, perfectly-plastic material model, providing consistency with the corresponding carbon steel design rules. However, the cross-section classification framework treats the cross-section as an assemblage of isolated plate elements without considering the beneficial element interaction effect, and the elastic, perfect-plastic material model neglects the pronounced strain hardening exhibited by stainless steels. These limitations have been generally found to result in unduly conservative and scattered resistance predictions through comparisons against previous test data. To address these shortcomings, a deformation-based continuous strength method (CSM) has been developed, which relates the strength of a cross-section to its deformation capacity and employs a bi-linear (elastic, linear hardening) material model to account for strain hardening. The CSM has been established for the design of doubly symmetric plated sections and circular hollow sections, and shown to yield a high level of design accuracy and consistency. In this paper, the scope of application of the CSM is extended to cover the design of non-doubly symmetric cross-sections in bending. Global member buckling is not investigated. The developed design methodology and comparisons with existing test data and numerical results generated herein are described. Finally, reliability analysis is performed, which demonstrates the suitability of the proposals for inclusion in structural design codes.

Element interactions of cold-formed stainless steel cross-sections subjected to combined compression and bending

A comprehensive numerical investigation of cold-formed stainless steel cross-sections subjected to combined compression and bending is presented in this paper. A non-linear finite element model (FEM) including geometric and material non-linearities was developed using the finite element package ABAQUS. Upon validation of the FEM, the model was then used for an extensive parametric study to investigate the interaction effects of constituent plate elements of cold-formed stainless steel square and rectangular hollow section beam-columns.The investigation indicates that the interaction effects of constituent plate elements on cross-section response are obvious particularly for slender sections. Current design provisions on Class 3 and Class 2 slenderness limits and effective width equations specified in American Specification, EC3 code and proposed by Gardner are not suitable for square and rectangular stainless steel hollow section beam-columns since the interaction effects of constituent plate elements are ignored. The new Class 3 and Class 2 slenderness limits and the section capacity design equations based on the whole cross-section response enable more accurate prediction of local buckling, thus allowing better utilization of material and more economic design.

DEMO Central Solenoid Design Based on the Use of HTS Sections at Highest Magnetic Field

Previous studies indicated that the use of high-temperature superconductors (HTS) in the highest field allows us achieving the required magnetic flux in the central solenoid (CS) of the European DEMO at a reduced outer diameter, which would enable a reduced overall size and cost of DEMO. The proposed winding pack design of the CS1 module is based on ten layer-wound subcoils using an HTS, react and wind Nb3Sn, and NbTi conductors in the high, medium, and low field sections, respectively. The design utilizes a stainless steel and a superconductor grading leading to different overall current densities in each of the ten subcoils. Both, the hoop stress and the vertical loads are taken into consideration for determination of the required stainless steel cross-section in the winding pack. The stainless steel grading has been found to have an even more pronounced effect on the overall subcoil current densities than the superconductor grading. A preliminary estimation of the space required for the precompression structure is also reported.

Deformation-based design of stainless steel cross-sections in shear

The continuous strength method (CSM) is a recently developed deformation-based design method for metallic structures. In this method, cross-section classification is replaced by a normalized deformation capacity, which defines the maximum strain that a cross-section can endure prior to failure. This limiting strain is used in conjunction with an elastic, linear-hardening material stress-strain model to determine cross-section capacity allowing for the influence of strain hardening. To date, the CSM has been developed for the determination of cross-section capacity under normal stresses (i.e. compression, bending and combined loading), where it has been shown to offer more accurate predictions than current codified methods. In this paper, extension of the CSM to the determination of shear resistance is described. The relationship between the normalized shear deformation capacity, referred to as the shear strain ratio, and the web slenderness is first established on the basis of experimental and numerical data. The material model and proposed resistance functions are then described. Comparisons of the developed method with the ultimate shear capacity of a series of tested stainless steel plate girders show that improved resistance predictions of test capacity over current design methods are achieved.

Moment-Curvature-Thrust Relationships for Beam-Columns

Moment–curvature–thrust relationships (M–κ–N) are a useful resource for the solution of a variety of inelastic and geometrically non-linear structural problems involving elements under combined axial load and bending. A numerical discretised cross-section method is used in this research to generate such relationships for I-sections, rectangular box-sections and circular or elliptical hollow sections. The method is strain driven, with the maximum strain limited by an a priori defined local buckling strain, which can occur above or below the yield strain depending on the local slenderness of the cross-section. The relationship between the limiting strain and the local slenderness has been given for aluminium, mild steel and stainless steel cross-sections through the base curve of the Continuous Strength Method. Moment-curvature-thrust curves are derived from axial force and bending moment interaction curves by pairing the curvatures and moments for a given axial load level. These moment–curvature–thrust curves can be transformed into various formats to solve a variety of structural problems. The gradient of the curves is used to find the materially and geometrically non-linear solution of an example beam-column, by solving numerically the moment–curvature ordinary differential equations. The results capture the importance of the second order effects, particularly with regard to the plastic hinge formation at mid-height and the post-peak unloading response.

Structural response and continuous strength method design of slender stainless steel cross-sections

In current structural stainless steel design codes, local buckling is accounted for through a cross-section classification framework, which is based on an elastic, perfectly-plastic material model, providing consistency with the corresponding treatment of carbon steel cross-sections. Hence, for non-slender cross-sections, the codified design stress is limited to the 0.2% proof stress without considering the pronounced strain hardening exhibited by stainless steels, while for slender cross-sections, the effective width method is employed without considering the beneficial effect of element interaction. Previous comparisons between test results and codified predictions have generally indicated over-conservatism and scatter. This has prompted the development of more efficient design rules, which can reflect better the actual local buckling behaviour and nonlinear material response of stainless steel cross-sections. A deformation-based design approach called the continuous strength method (CSM) has been proposed for the design of stocky cross-sections, which relates the strength of a cross-section to its deformation capacity and employs a bi-linear (elastic, linear hardening) material model to account for strain hardening. In this paper, the scope of the CSM is extended to cover the design of slender stainless steel cross-sections under compression, bending and combined loading, underpinned by and validated against 794 experimental and numerical results. The proposed approach allows for the beneficial effect of element interaction within the cross-section, and is shown to yield a higher level of accuracy and consistency, as well as design efficiency, in the capacity predictions of slender stainless steel cross-sections, compared to the effective width methods employed in the current international design standards. Non-doubly symmetric sections in bending, which may be slender, but still benefit from strain hardening, are also discussed. The reliability of the CSM proposal has been confirmed by means of statistical analyses according to EN 1990, demonstrating its suitability for incorporation into future revisions of international design codes for stainless steel structures.

The Continuous Strength Method for slender stainless steel cross-sections

This paper extends the scope of the Continuous Strength Method (CSM), which has recently been proposed for stocky sections, to include slender stainless steel sections. A new parameter called the Equivalent Elastic Deformation Capacity is introduced to tackle the significant post-buckling deformation observed in slender sections. A comprehensive finite element study was carried out to supplement limited number of available test results. Obtained FE results and available test evidences were used to propose design guidelines for compression and bending. The performance of the proposed technique was compared against EC3 guidelines, which showed good agreement with test and FE results with an acceptable level of reliability.

Behaviour and design of stainless steel slender cross-sections subjected to combined loading

The Continuous Strength Method (CSM) is a recently developed strain based design technique that produces accurate predictions for cross-section resistances for stocky sections against individual and combined actions. This paper numerically investigates the behaviour slender stainless steel cross-sections subjected to combined loading i.e. compression plus bending. Generated numerical results and available test results were used to develop CSM formulations to tackle the conservatism shown by the current international codes in predicting resistances of slender sections. Keeping the basic design philosophy in line with the current CSM design technique, interaction equations are re-calibrated herein for slender stainless steel hollow sections.