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Journal ArticleDOI

Structural performance of cold-formed lean duplex stainless steel beams at elevated temperatures

01 Aug 2018-Thin-walled Structures (Elsevier)-Vol. 129, pp 20-27

Abstract: The structural performance of cold-formed lean duplex stainless steel beams at elevated temperatures ranging from 24 to 900 °C was investigated in this study. A finite element model was developed. The numerical analysis covered the specimens of square and rectangular hollow sections. The material properties obtained from tensile coupon tests on lean duplex stainless steel at elevated temperatures were used in the finite element model. A total of 125 numerical flexural strengths were obtained from the finite element analysis. The numerical results were compared with the design values calculated by the existing design rules, including the American Specification, Australian/New Zealand Standard, European Code, direct strength method and continuous strength method. The suitability of these design rules for lean duplex stainless steel beams at elevated temperatures was assessed using reliability analysis. It was shown that the existing design rules are generally quite conservative in predicting the flexural strengths at elevated temperatures, except that the modified direct strength method provides accurate and reliable predictions. Therefore, it is recommended that the modified direct strength method be used for cold-formed lean duplex stainless steel beams at elevated temperatures.
Topics: Flexural strength (54%)

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Structural Performance of Cold-formed Lean Duplex Stainless
Steel Beams at Elevated Temperatures
Citation for published version:
Huang, Y & Young, B 2018, 'Structural Performance of Cold-formed Lean Duplex Stainless Steel Beams at
Elevated Temperatures', Thin-Walled Structures, vol. 129, pp. 20-27.
https://doi.org/10.1016/j.tws.2018.03.031
Digital Object Identifier (DOI):
10.1016/j.tws.2018.03.031
Link:
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Document Version:
Peer reviewed version
Published In:
Thin-Walled Structures
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Download date: 10. Aug. 2022

1
Structural Performance of Cold-formed Lean Duplex Stainless
Steel Beams at Elevated Temperatures
Yuner Huang
1
* and Ben Young
2
1
Institute for Infrastructure and Environment, School of Engineering, University of Edinburgh, UK
2
Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
ABSTRACT: The structural performance of cold-formed lean duplex stainless steel beams at
elevated temperatures ranging from 24 900 ºC was investigated in this study. A finite element
model was developed. The numerical analysis covered the specimens of square and rectangular
hollow sections. The material properties obtained from tensile coupon tests on lean duplex
stainless steel at elevated temperatures were used in the finite element model. A total of 125
numerical flexural strengths were obtained from the finite element analysis. The numerical
results were compared with the design values calculated by the existing design rules, including
the American Specification, Australian/New Zealand Standard, European Code, direct strength
method and continuous strength method. The suitability of these design rules for lean duplex
stainless steel beams at elevated temperatures was assessed using reliability analysis. It was
shown that the existing design rules are generally quite conservative in predicting the flexural
strengths at elevated temperatures, except that the modified direct strength method provides
accurate and reliable predictions. Therefore, it is recommended that the modified direct
strength method be used for cold-formed lean duplex stainless steel beams at elevated
temperatures.
Keywords: Beam; cold-formed; elevated temperatures; lean duplex; stainless steel; structural
design.
Corresponding author. Tel.: +44 (0) 131 650 5736; Fax: +44 (0) 131 650 6554.
E-mail address: Yuner.Huang@ed.ac.uk

2
1. Introduction
A relatively new type of cold-formed lean duplex stainless steel is becoming an attractive
choice as a construction material. Lean duplex stainless steel is characterized by a low nickel
content of around 1.5%. Thus, lean duplex stainless steel has economic advantages over the
other types of stainless steel. In addition, it is regarded as a high strength material with the
nominal yield strength (0.2% proof stress) of 450 MPa [1]. However, there has been limited
research on the structural performance and design of lean duplex stainless steel members,
especially at elevated temperatures. Therefore, research on the lean duplex stainless steel
material and structural members is required.
Lean duplex stainless steel is a relative new construction material. The previous research on
lean duplex stainless steel focused mainly on the material properties and design of structural
members at room temperature. Huang and Young [2], as well as Theofanous and Gardner [3],
conducted tensile coupon tests and stub column tests to investigate the mechanical and section
properties of cold-formed lean duplex stainless steel rectangular and square hollow sections.
Experimental and numerical investigations were carried out on cold-formed lean duplex
stainless steel columns [3, 4, 5, 6], and the test and numerical data were compared with the
predicted column strengths calculated by the existing design rules. It was shown that the
existing design rules, including design rules in the European Code, explicit approach in the
Australian/New Zealand Standard and the direct strength method, are quite conservative for
the lean duplex stainless steel. The implicit approach for column design in the American
Specification and Australian/New Zealand Standard provides accurate predictions, but the
iterative calculation procedure is tedious. Therefore, modified design rules have been proposed
for better prediction of lean duplex stainless steel structural strengths. Some research has also
been conducted for cold-formed lean duplex stainless steel beams [7, 8, 9, 10]. This research
indicated that the existing European Code and direct strength method are quite conservative
for lean duplex stainless steel flexural members, while the continuous strength method provides
a better prediction. The European Code and direct strength method were found to be suitable
for the shear design of lean duplex stainless steel rectangular hollow beams. The existing design
rules in the European Code and the Australian/New Zealand Standard are generally quite
conservative for lean duplex stainless steel beam-column members [11, 12]. The mechanical
properties of cold-formed lean duplex stainless steel at elevated temperatures have been

3
investigated in previous research [13, 14]. Huang and Young [13] conducted tensile coupon
tests on lean duplex stainless steel in both steady and transient states. The existing design rules
for predicting the reduced material properties at elevated temperatures were assessed for lean
duplex stainless steel. A modified design rule was proposed for lean duplex stainless steel
material properties at elevated temperatures. Gardner et al. [14] summarized the results of tests
on material properties of various stainless steel alloys at elevated temperatures, including the
lean duplex stainless steel material reported by Outokumpu [15]. Reduction factors of strength
and stiffness for lean duplex stainless steel were proposed according to the available data.
A search of the literature revealed a lack of research on cold-formed lean duplex stainless steel
beams at elevated temperatures. Therefore, the objective of this study was to investigate the
structural performance of cold-formed lean duplex stainless steel beams at elevated
temperatures, ranging from 24 900 ºC, using finite element analysis. The reduced mechanical
properties at elevated temperatures were used in the FEM. A total number of 125 numerical
flexural strengths were compared with the design values calculated from the existing design
rules. The applicability of the existing design rules for the lean duplex stainless steel beams
was assessed using reliability analysis. According to the comparison, recommendations for
designing cold-formed lean duplex stainless steel flexural members at elevated temperatures are
proposed based on this study.
2. Finite Element Model
The finite element model (FEM) for cold-formed lean duplex stainless steel flexural members
was developed by Huang and Young [7] using the program ABAQUS version 6.11 [16]. The
FEM has been verified with the test results of four-point bending tests at room temperature.
The moment-curvature curves and the failure modes predicted by the FEM have been found to
agree well with the test results. In this study, the FEM developed by Huang and Young [7] was
used for the finite element analysis of flexural members at elevated temperatures, except that
the materials properties at room temperature were replaced by the reduced material properties
obtained from tensile coupon tests at elevated temperatures [13]. The mechanical properties of
section 50×50×1.5 obtained from the tensile coupon tests at 24 ºC, 300 ºC, 500 ºC, 700 ºC and
900 ºC using the steady-state test method were used in the FEM. ABAQUS allows for a multi-
linear stress-strain curve to be used. Similar to the Huang and Young FEM [7], the first part of

4
the curve represents the elastic part up to the proportional limit stress with the measured
 ratio taken as 0.3. In the plastic analysis, the static stress-strain
curve obtained from tensile coupon tests was converted to true stress and logarithmic true
plastic strain curve, as described by Huang and Young [7]. The material properties adopted in
the FEM, including the modulus of elasticity, yield strength, and ultimate strength at high
temperatures ranging from 24 900 C, are summarized in Table 1. Similar to the FEM for
beams at room temperature, the local imperfection of t/10 was incorporated into the FEM,
where t is the thickness of the sections. The residual stresses in the sections were not included.
3. Parametric Study
A total of 125 cold-formed lean duplex stainless steel flexural members at elevated
temperatures, ranging from 24 900 ºC, were investigated in the parametric study. The finite
element model (FEM) in the parametric study was identical to the FEM developed by Huang
and Young [7], except that the mechanical properties obtained from the tensile coupon tests at
elevated temperatures were used. The parametric study included square hollow sections (SHS)
and rectangular hollow sections (RHS), which had one SHS of 300×300 (overall depth ×
overall width) as well as four RHS of 100×50, 50×100, 300×100 and 100×300. Five different
thicknesses were designed for each section, in order to cover a wide range of slenderness ratios,
from stocky to slender sections. The length of moment span between the two loading points
was equal to the length of shear spans between the loading points to the supports for the flexural
members. The lengths were designed carefully so that the section flexural capacity could be
reached without shear failure. The specimens with the same cross-sectional dimensions and
specimen lengths were investigated under five different temperatures in the finite element
analysis, including 24 ºC, 300 ºC, 500 ºC, 700 ºC and 900 ºC. The RHS specimens were
subjected to both major and minor axes bending. The specimens in the parametric study were
labelled such that the cross-section dimension, specimen length and the specimen temperature
could be identifid the cross-
sectional dimensions (D×B×t          was the
specimen length in millimeters        was the specimen
temperature in degrees Celsius. For example, the label 100×50×5L900T300 defined the
flexural member with cross-section (D×B×t) of 100×50×5 in millimeters, and the specimen
length of 900 mm as well as the specimen temperature of 300 ºC. The dimension of the overall

Citations
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01 Jan 1991-
Abstract: ASCE's standard Specification for the Design of Cold-Formed Stainless Steel Structural Members (ASCE 8-90) provides design criteria for the determination of the strength of stainless steel structural members and connections for use in buildings and other statically loaded structures. The members may be cold-formed to shape from annealed and cold-rolled sheet, strip, plate, or flat bar stainless steel material. Design criteria are provided for axially loaded tension or compression members, flexural members subjected to bending and shear, and members subjected to combined axial load and bending. The specification provides the design strength criteria using the load and resistance factor design (LRFD) and the allowable stress design (ASD) methods. The reasoning behind, and the justification for, various provisions of the specification are also presented. The design strength requirements of this standard are intended for use by structural engineers and those engaged in preparing and administrating local building codes.

85 citations


Journal ArticleDOI
Hai-Ting Li1, Ben Young2Institutions (2)
Abstract: The structural responses of cold-formed high strength steel (HSS) square and rectangular hollow section (SHS and RHS) beams at elevated temperatures were examined in this study. Stress-strain relationships of cold-formed HSS at elevated temperatures were proposed and verified against material test results. The proposed stress-strain relationships were then employed in a finite element (FE) analysis to study the behaviour of cold-formed HSS SHS/RHS beams at elevated temperatures up to 1000 °C. The developed FE model was verified with available test results of cold-formed HSS SHS/RHS beams; upon verification, a total of 252 numerical flexural capacities were gained from FE analyses. The numerical results were used to investigate the suitability of existing cross-section slenderness limits to the HSS tubular sections at elevated temperatures. The applicability of current flexural design provisions in the Eurocode 3, AISC and AISI specifications to the investigated HSS tubular beams at elevated temperatures was also examined. Overall, it is shown that the codified provisions can provide quite conservative predictions; an improved design rule is proposed by modifying the direct strength method (DSM) in the AISI specification. Furthermore, reliability analyses were carried out to assess reliability levels of codified and modified provisions. It has been demonstrated that the modified DSM can produce accurate and reliable design and therefore is recommended to be used for cold-formed HSS SHS/RHS beams at elevated temperatures.

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Abstract: In this paper, the elevated temperature buckling performance and design of cold-formed square, rectangular and circular hollow section columns made of stainless steel is studied through a numerical modelling investigation. The finite element analysis software Abaqus was employed to perform the simulations, where the validity of the models was established by replicating the results of flexural buckling tests at both elevated and room temperatures from literature test programmes. In total, twelve square (SHS) and rectangular (RHS) hollow section columns tested at elevated temperature and eleven circular (CHS) hollow section columns tested at room temperature were simulated. Following this, a comprehensive numerical parametric investigation was performed to systematically assess the effect of variation of the governing parameters including the grade of stainless steel (austenitic, duplex and ferritic) and the elevated temperature member slenderness ( λ ‾ θ = 0.1–2.0) for all considered cross-section shapes with the addition of the aspect ratio of the cross-section (h/b = 1.0 and 1.5) and the column axis of buckling (major and minor) for the SHS and RHS. The applicability and accuracy of the design methods recommended in EN 1993-1-2 and the Design Manual for Stainless Steel Structures were carefully assessed on the basis of the numerical flexural buckling performance results. New buckling formulations for the fire design of cold-formed stainless steel SHS/RHS and CHS columns were proposed, and their suitability was confirmed by means of reliability analysis.

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Abstract: Cold-formed steels are commonly used in construction applications. However, there is a lack of understanding on its post-fire mechanical properties. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed steels. The test specimens were cut from flat portion and corners of cold-formed channel sections, which were exposed to temperatures ranging from ambient temperature to 800 °C, and then cooled with water and air. The specimens are of grade Q235, with section thicknesses of 1 mm and 2 mm. The stress-strain curves and mechanical properties of the specimens were obtained from tensile coupon tests. Test results of post-fire mechanical properties are presented. Moreover, evolution of microstructure and fracture morphology of specimens with different cooling methods were examined. Finally, predictive equations are proposed for evaluating the post-fire mechanical properties of Q235 cold-formed steel channel sections.

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References
More filters

BookDOI
10 Dec 2002-
Abstract: Specification for the Design of Cold-Formed Stainless Steel Structural Members provides design criteria for the determination of the strength of stainless steel structural members and connections f...

276 citations


Journal ArticleDOI
Marios Theofanous1, Leroy Gardner1Institutions (1)
Abstract: Stainless steels are employed in a wide range of structural applications. The austenitic grades, particularly EN 1.4301 and EN 1.4401, and their low-carbon variants EN 1.4307 and EN 1.4404, are the most commonly used within construction, and these typically contain around 8%–11% nickel. The nickel represents a large portion of the total material cost and thus high nickel prices and price volatility have a strong bearing on both the cost and price stability of stainless steel. While austenitic stainless steel remains the most favourable material choice in many applications, greater emphasis is now being placed on the development of alternative grades with lower nickel content. In this study, the material behaviour and compressive structural response of a lean duplex stainless steel (EN 1.4162), which contains approximately 1.5% nickel, are examined. A total of eight stub column tests and twelve long column tests on lean duplex stainless steel square (SHS) and rectangular hollow sections (RHS) are reported. Precise measurements of material and geometric properties of the test specimens were also made, including the assessment of local and global geometric imperfections. The experimental studies were supplemented by finite element analysis, and parametric studies were performed to generate results over a wider range of cross-sectional and member slenderness. Both the experimental and numerical results were used to assess the applicability of the Eurocode 3: Part 1-4 provisions regarding the Class 3 slenderness limit and effective width formula for internal elements in compression and the column buckling curve for hollow sections to lean duplex structural components. Comparisons between the structural performance of lean duplex stainless steel and that of other more commonly used stainless steel grades are also presented, showing lean duplex stainless steel to be an attractive choice for structural applications.

172 citations


"Structural performance of cold-form..." refers background or methods in this paper

  • ...Huang and Young [2], as well as Theofanous and Gardner [3], conducted tensile coupon tests and stub column tests to investigate the mechanical and section properties of cold-formed lean duplex stainless steel rectangular and square hollow sections....

    [...]

  • ...Experimental and numerical investigations were carried out on cold-formed lean duplex stainless steel columns [3, 4, 5, 6], and the test and numerical data were compared with the predicted column strengths calculated by the existing design rules....

    [...]


Journal ArticleDOI
J.P. Papangelis1, Gregory J. Hancock1Institutions (1)
Abstract: The calculation of the stresses and failure modes in thin-walled structural members is a complex procedure. Structural designers will often need help in analysing these types of structures. A vehicle for providing this help is the computer program developed for the microcomputer. In this paper, a computer procedure is described for the cross-section analysis and elastic buckling analysis of thin-walled structural members. The cross-section analysis calculates the section properties, warping displacements, and the longitudinal and shear stresses for thin-walled open and closed cross-sections of any shape. The longitudinal stresses are used to perform an elastic finite strip buckling analysis of thin-walled structural members. The analysis can be done for a number of different buckle half-wavelengths of the member and the load factor and buckled shape are output for each length. The analysis is performed by the user-friendly computer program THIN-WALL, which is also described in the paper.

166 citations


Journal ArticleDOI
Abstract: Appropriate assessment of the fire resistance of structures depends largely on the ability to accurately predict the material response at elevated temperature. The material characteristics of stainless steel differ from those of carbon steel due to the high alloy content. These differences have been explored in some detail at room temperature, whilst those at elevated temperature have been less closely scrutinised. This paper presents an overview and reappraisal of previous pertinent research, together with an evaluation of existing elevated temperature stainless steel stress–strain test data and previously proposed material models. On the basis of examination of all available test data, much of which have been recently generated, revised strength and stiffness reduction factors at elevated temperatures for a range of grades of stainless steel have been proposed, including four grades not previously covered by existing structural fire design guidance. A total of eight sets of strength reduction factors are currently provided for different grades of stainless steel in EN 1993-1-2 and the Euro Inox/SCI Design Manual for Structural Stainless Steel, compared to a single set for carbon steel. A number of sets of reduction factors is appropriate for stainless steel since the elevated temperature properties can vary markedly between different grades, but this has to be justified with sufficient test data and balanced against ease of design — it has been proposed herein that the eight sets of reduction factors be rationalised on the basis of grouping grades that exhibit similar elevated temperature properties. In addition to more accurate prediction of discrete features of the elevated temperature material stress–strain response of stainless steel (i.e. strength and stiffness reduction factors), a material model for the continuous prediction of the stress–strain response by means of a modified compound Ramberg–Osgood formulation has also been proposed. The proposed model is less complex than the current provisions of EN 1993-1-2, more accurate when compared to test results, and the model parameters have a clear physical significance.

148 citations


"Structural performance of cold-form..." refers background in this paper

  • ...3 investigated in previous research [13, 14]....

    [...]

  • ...[14] summarized the results of tests on material properties of various stainless steel alloys at elevated temperatures, including the lean duplex stainless steel material reported by Outokumpu [15]....

    [...]


Journal ArticleDOI
Leroy Gardner1, Marios Theofanous1Institutions (1)
Abstract: Cross-section classification is an important concept in the design of metallic structures, as it addresses the susceptibility of a cross-section to local buckling and defines its appropriate design resistance. For structural stainless steel, test data on cross-section capacity have previously been relatively scarce. Existing design guidance has been developed based on the limited experimental results and conservative assumptions, generally leading to unduly strict slenderness limits. In recent years, available test data for stainless steel cross-sections have increased significantly, enabling these slenderness limits to be re-assessed. In this paper all available stainless steel test data have been collected and additional moment–rotation curves have been presented. The study covers both cold-formed and welded plated elements as well as CHS. Following analysis of the test results, new slenderness limits for all loading conditions have been proposed and statistically validated. In addition to re-assessment of the current slenderness limits, a new approach to the treatment of local buckling in structural elements–the Continuous Strength Method–has been outlined. The Continuous Strength Method (CSM) is based on a continuous relationship between cross-section slenderness and deformation capacity and is applied in conjunction with accurate material modelling. The method enables more rational and precise prediction of local buckling than can be achieved with the traditional cross-section classification approach, thus allowing better utilization of material and more economic design.

128 citations


"Structural performance of cold-form..." refers methods in this paper

  • ...It was shown by Huang and Young [7] that the suggested method by Gardner and Theofanous [20] provides a more accurate and less scattered prediction for lean duplex stainless steel flexural members at room temperature....

    [...]

  • ...Modified design rules by Huang and Young [7] were proposed and were shown to provide better predictions for lean duplex stainless steel flexural members at room temperature compared with the existing EC3 [19] and the design rule proposed by Gardner and Theofanous [20], as shown in Huang and Young [7]....

    [...]

  • ...compression elements was proposed, and the effective width equations were modified [20]....

    [...]

  • ...The design rules in the (1) ASCE [17], (2) AS/NZS [18], (3) modified ASCE and AS/NZS in Huang and Young [7], (4) EC3 [19], (5) suggested EC3 by Gardner and Theofanous [20], and (6) modified EC3 in Huang and Young [7] use the effective width method for the sections when local buckling occurs....

    [...]

  • ...The unfactored design strengths (nominal strength) were calculated using (1) American Specification (ASCE) [17] (Myielding,T, Minelastic,T), (2) Australian/New Zealand Standard (AS/NZS) [18] (Myielding,T, Minelastic,T), (3) modified ASCE and AS/NZS described in Huang and Young [7] (Minelastic,T), (4) European Code (EC3) [19] (MEC3,T), (5) suggested EC3 by Gardner and Theofanous [20] (MG&T,T), (6) modified EC3 in Huang and Young [7] (MEC3,T), (7) direct strength method (DSM) in AISI [21] (MDSM,T, M ^ DSM,T), (8) modified DSM in Huang and Young [7] (M # DSM,T), and (9) continuous strength method (CSM) described in Saliba and Gardner [9] (MCSM,T)....

    [...]


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