Publications
578 results found
Gardner L, 2014, Untitled, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-STRUCTURES AND BUILDINGS, Vol: 167, Pages: 79-79, ISSN: 0965-0911
Liew A, Boissonnade N, Gardner L, et al., 2014, Experimental study of hot-rolled rectangular hollow sections, Pages: 33-51
Hot-rolled structural steel hollow sections typically display largely homogeneous material properties around the cross-section with low residual stresses, due to the uniform cooling pattern associated with the production of uniform sections of constant thickness. This leads to a stress-strain response with a clearly defined yield stress and an extended yield plateau. To examine the behaviour of such members, tests were carried out on hot-rolled structural steel rectangular hollow sections, including material tests and experiments on stub columns, simply supported beams, continuous beams and propped cantilevers. Two wall thicknesses were considered which gave compact cross-sections according to AISC 360-10 (2010), yet most test specimens did not reach their designated plastic design values. Failure by local buckling occurred during the extended material yield plateau, and did not allow for the benefits from strain hardening that are implicitly assumed for the attainment of the plastic moment capacity. Tests on elements in indeterminate configurations showed that system peak loads can occur when some cross-sections are unloading, having already passed their peak moments. Plotting rotation-curvature curves at hinge locations showed that the hinge rotations from an idealised plastic collapse geometry, are proportional to curvatures only during the elastic loading phase. This proportional relationship deteriorated once cross-section yielding had occurred, as curvatures measured by post-yield strain gauges rapidly accelerated when compared to the rotations measured from inclinometers.
Kucukler M, Gardner L, Macorini L, 2014, Stiffness reduction method for the design of steel columns and beam-columns, Pages: 297-314
A stiffness reduction approach is presented in this paper, which utilises Linear Buckling Analysis (LBA) and Geometrically Nonlinear Analysis (GNA) in conjunction with developed stiffness reduction functions for the design of columns and beam-columns in steel frames. The proposed stiffness reduction approach obviates the need to model member imperfections and to make member buckling checks. While LBA with appropriate stiffness reduction provides inelastic buckling loads of columns, GNA with stiffness reduction is performed for the prediction of beam-column failure. In addition to regular members, the accuracy and practicality of the method is illustrated for irregular members. For the latter case, results indicate that the proposed stiffness reduction method provides more accurate strength predictions in comparison to traditional design approaches. The influence of moment gradient on the development of plasticity (i.e. stiffness reduction) is accounted for by incorporating simple moment gradient factors into the stiffness reduction expressions originally derived for members under uniform bending. The accuracy of the proposed stiffness reduction approach is verified against results obtained through non-linear finite element modelling for all of the considered cases.
Su MN, Young B, Gardner L, 2014, Numerical study of aluminium alloy continuous beams, Pages: 351-360
The aims of this study are to investigate the behaviour of aluminium alloy continuous beams using finite element (FE) analysis and to underpin the development of revised design methods for indeterminate structures. FE analyses of two-span continuous beams (i.e. five-point bending) of square and rectangular hollow sections (SHS and RHS) are presented. The FE model was developed using ABAQUS 6.10-1, and the ultimate loads were determined when either a plastic collapse mechanism was formed or the material fracture strain was reached on the tension flange. Upon validation of the model against available experimental results, an extensive parametric study was performed to assess the effect of key parameters such as the cross-section aspect ratio, cross-section slenderness and the moment gradient on the strength, strain hardening behaviour and moment redistribution characteristics of aluminium alloy continuous beams. A total of 40 numerical results were generated and reported in this paper. The simulated ultimate loads were found to be beyond the theoretical loads that cause the first hinge to form, as well as the theoretical loads that cause the collapse mechanism to occur. A key characteristic of aluminium alloy, namely strain hardening, receives particular attention in the numerical investigation. In addition, the numerical results were also compared to design predictions from the American, Australian/New Zealand and European design standards and the continuous strength method for indeterminate structures. The design strengths predicted by the three specifications are found to be rather conservative, while the predications of the continuous strength method are more precise and consistent. The results reveal that strain hardening at the cross-sectional level and moment redistribution at the global system level have significant influence on the performance of stocky (plastic and compact sections) aluminium alloy structures, and should therefore be accounted for in efficie
Gardner L, Law A, Buchanan C, 2014, Unified slenderness limits for structural steel circular hollow sections, Romanian Journal of Technical Sciences, Applied Mechanics, Vol: 59, Pages: 153-163
Law KH, Gardner L, 2013, Global Instability of Elliptical Hollow Section Beam-columns under Compression and Biaxial Bending, International Journal of Steel Structures, Vol: 13, Pages: 745-759, ISSN: 1598-2351
The global instability of elliptical hollow section members under combined compression plus biaxial bending is studied in this paper by means of laboratory testing and numerical simulations. A total of 9 beam-column tests were carried out under different combinations of compression and bending about both principal axes. The material properties of the tested sections were determined by means of tensile coupon tests. All tested elliptical hollow sections were EHS 150×75×5, and three nominal member lengths of 1 m, 2 m and 3 m were considered. Graphs of applied load versus mid-span bending moment, based on theoretical first and second order elastic considerations and the experimental second order inelastic response, are presented and described. Numerical models were initially validated against the experimental data using measured material and geometric properties, including imperfections. The models were subsequently employed in parametric studies to assess the influence of member slenderness and cross-sectional aspect ratio on the structural response. Finally, based on the experimental and numerical findings, design rules for hot-finished EHS beam-columns were assessed and statistically verified.
Saliba N, Real E, Gardner L, 2013, Shear design recommendations for stainless steel plate girders, Engineering Structures, Vol: 59, Pages: 220-228, ISSN: 0141-0296
The behaviour and design of stainless steel plate girders loaded in shear is investigated in this paper. A review of existing methods for the design of stainless steel plate girders, including codified provisions, is first presented. A database of thirty-four experiments carried out on austenitic, duplex and lean duplex stainless steel plate girders is then reported, and used to assess the current shear resistance design equations from Eurocode 3: Part 1.4 and Eurocode 3: Part 1.5 and the recent proposals from the literature. The comparisons clearly indicate that the design provisions of Eurocode 3: Part 1.4 are conservative and that improved results can be achieved by applying Eurocode 3: Part 1.5 and the proposed expressions of Estrada et al. However, yet further improvements are possible and, based on the available structural performance data, revised design expressions for the calculation of the ultimate shear capacity of stainless steel plate girders suitable for incorporation into future revisions of Eurocode 3: Part 1.4 have been proposed and statistically verified. Unlike the current provisions of Eurocode 3: Part 1.4, the design rules proposed herein differentiate between rigid and non-rigid end posts, and, offer enhancements in shear buckling capacity of around 10%.
Foster ASJ, Gardner L, 2013, Ultimate behaviour of steel beams with discrete lateral restraints, THIN-WALLED STRUCTURES, Vol: 72, Pages: 88-101, ISSN: 0263-8231
Through a programme of experiments, numerical modelling and parametric studies, the implications of allowing for strain-hardening in the design of laterally restrained steel beams is investigated with particular emphasis on the performance of the bracing elements. A total of twelve tests were performed on simply supported beams considering two basic scenarios: discrete rigid restraints and discrete elastic restraints of varying stiffness. In the latter case, the forces developed in the restraints were measured and compared to the design forces specified in EN 1993-1-1 (2005). Two different restraint spacings were considered in the tests to give non-dimensional lateral torsional slenderness values of 0.3 and 0.4 for the unrestrained lengths. In all tests, bending resistances in excess of the plastic moment capacity were observed, but for the considered restraint spacings, the resistances often fell short of that predicted by the deformation-based continuous strength method (CSM), which allows for strain-hardening. It was concluded that closer restraint spacing may be required to harness significant benefit from strain-hardening and to develop the full CSM bending resistance, though the forces generated in the restraints were within current code requirements.
Yang H, Liu F, Gardner L, 2013, Performance of concrete-filled RHS columns exposed to fire on 3 sides, ENGINEERING STRUCTURES, Vol: 56, Pages: 1986-2004, ISSN: 0141-0296
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Su MN, Young B, Gardner L, 2013, Continuous strength method for aluminium alloy structures, Pages: 70-75, ISSN: 1022-6680
Aluminium alloys are nonlinear metallic materials with continuous stress-strain curves that are not well represented by the simplified elastic, perfectly plastic material model used in many current design specifications. Departing from current practice, the continuous strength method (CSM) is a recently proposed design approach for non-slender aluminium alloy structures with consideration of strain hardening. The CSM is deformation based and employs a base curve to define a continuous relationship between cross-section slenderness and deformation capacity. This paper explains the background and the two key components - (1) the base curve and (2) the strain hardening material model of the continuous strength method. More than 500 test results are used to verify the continuous strength methodas an accurate and consistent design method for aluminium alloy structures. © (2013) Trans Tech Publications, Switzerland.
McCann F, Wadee MA, Gardner L, 2013, Lateral stability of imperfect discretely braced steel beams, Journal of Engineering Mechanics, Vol: 139, Pages: 1341-1349, ISSN: 0733-9399
The lateral stability of imperfect discretely braced steel beams is analyzed using Rayleigh-Ritz approximations for the lateral deflection and the angle of twist. Initially, it is assumed that these degrees of freedom can be represented by functions comprising only single harmonics; this is then compared with the more accurate representation of the displacement functions by full Fourier series. It is confirmed by linear eigenvalue analysis that the beam can realistically buckle into two separate classes of modes: a finite number of node-displacing modes, equal to the number of restraints provided, and an infinite number of single harmonic buckling modes, where the restraint nodes remain undeflected. Closed-form analytical relations are derived for the elastic critical moment of the beam, the forces induced in the restraints, and the minimum stiffness required to enforce the first internodal buckling mode. The position of the restraint above or below the shear center is shown to influence the overall buckling behavior of the beam. The analytical results for the critical moment of the beam are validated by the finite-element program LTBeam, whereas the results for the deflected shape of the beam are validated by the numerical continuation software AUTO-07p, with very close agreement between the analytical and the numerical results.
Gardner L, Macorini L, Kucukler M, 2013, The continuous strength method for steel and composite design, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-STRUCTURES AND BUILDINGS, Vol: 166, Pages: 434-443, ISSN: 0965-0911
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Gardner L, Silvestre N, 2013, Editorial: Stability and non-linear behaviour of steel structures, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-STRUCTURES AND BUILDINGS, Vol: 166, Pages: 379-380, ISSN: 0965-0911
Law KH, Gardner L, 2013, Buckling of elliptical hollow section members under combined compression and uniaxial bending, Journal of Constructional Steel Research, Vol: 86, Pages: 1-16, ISSN: 0143-974X
Experimental and numerical investigations into the behaviour of elliptical hollow section beam-columns under axial compression and uniaxial bending have been performed and described in this paper. A large-scale experimental programme, comprising a total of 10 tensile coupon tests and 24 beam-column tests, was carried out. The beam-column tests included 6 pure compression tests, 3 buckling about the major axis and 3 about the minor axis, and 18 eccentric compression tests, 9 inducing compression plus bending about the major axis and 9 inducing compression plus bending about the minor axis. All tested elliptical hollow sections were EHS 150 × 75 × 5, and three member lengths of 1 m, 2 m and 3 m were considered. The test results have been supplemented by numerically generated results based on validated FE models to assess the influence of member slenderness and cross-sectional aspect ratio. On the basis of the experimental and numerical findings, design rules covering instabilities in hot-finished EHS beam-columns have been assessed and verified by statistical analysis. The limiting length concept has also been extended to EHS beam-columns.
Gardner L, 2013, Structural stainless steel: Research and design, Ninth Conference on Steel and Composite Construction – IXCMM. 24th-25th October, 2013. (Keynote)
Afshan S, Gardner L, 2013, Experimental study of cold-formed ferritic stainless steel hollow sections, Journal of Structural Engineering, Vol: 139, Pages: 717-728, ISSN: 1943-541X
Stainless steel is gaining increasing use in construction because of its durability, favorable mechanical properties, and aesthetic appearance, with the austenitic grades being the most commonly used. Austenitic stainless steels have a high nickel content (8–11%), resulting in high initial material cost and significant price fluctuations; this, despite its desirable properties, represents a considerable disadvantage in terms of material selection. Ferritic stainless steels, having no or very low nickel content, may offer a more viable alternative for structural applications, reducing both the level and variability of the initial material cost while maintaining adequate corrosion resistance. There is currently limited information available on the structural performance of this type of stainless steel. Therefore, to overcome this limitation, a series of material, cross section, and member tests have been performed, covering both the standard EN 1.4003 grade (similar to the chromium weldable structural steel 3Cr12) and the EN 1.4509 grade (441), which has improved weldability and corrosion resistance. In total, 20 tensile coupon tests, 16 compressive coupon tests, eight stub column tests, 15 flexural buckling tests, and eight in-plane bending tests were carried out. Precise measurements of the geometric properties of the test specimens, including the local and global geometric imperfections, were also made. The experimental results are used to assess the applicability of the current European (EN 1993-1-4) and North American (SEI/ASCE-8) provisions to ferritic stainless steel structural components. In addition, the relative structural performance of ferritic stainless steel to that of more commonly used stainless steel grades is also presented, showing ferritic stainless steel to be an attractive choice for structural applications.
Afshan S, Gardner L, 2013, The continuous strength method for structural stainless steel design, Thin-Walled Structures, Vol: 68, Pages: 42-49, ISSN: 0263-8231
Current stainless steel design standards are based on elastic, perfectly plastic material behaviour providing consistency with carbon steel design expressions, but often leading to overly conservative results, particularly in the case of stocky elements. More economic design rules in accordance with the actual material response of stainless steel, which shows a rounded stress–strain curve with significant strain hardening, are required. Hence, the continuous strength method (CSM) was developed. The CSM replaces the concept of cross-section classification with a cross-section deformation capacity and replaces the assumed elastic, perfectly plastic material model with one that allows for strain hardening. This paper summarises the evolution of the method and describes its recent simplified form, which is now suitable for code inclusion. Comparison of the predicted capacities with over 140 collected test results shows that the CSM offers improved accuracy and reduced scatter relative to the current design methods. The reliability of the approach has been demonstrated by statistical analyses and the CSM is currently under consideration for inclusion in European and North American design standards for stainless steel structures.
Salih EL, Gardner L, Nethercot DA, 2013, Numerical study of stainless steel gusset plate connections, Engineering Structures, Vol: 49, Pages: 448-464, ISSN: 0141-0296
Despite fundamental differences between the mechanical behaviour of stainless steel and carbon steel, design provisions for stainless steel connections in current standards essentially follow the rules for carbon steel with some limited modifications. For the common case of angle section members connected by one leg to a gusset plate, the design rules for net section capacity from EN 1993-1-8 for carbon steel have been adopted for stainless steel connections in EN 1993-1-4 and the SCI/Euro Inox Design Manual without any modification. In this paper, an investigation into net section rupture of stainless steel single angles connected by one leg to a gusset plate with a single row of bolts is investigated. Numerical models for austenitic stainless steel have been developed and validated against existing test results. These models are then used to perform parametric studies. Finally, based on the obtained results, revised design equations for determining the net section capacity of stainless steel angles are proposed and their reliability demonstrated by means of statistical analysis.
Osofero AI, Wadee MA, Gardner L, 2013, Numerical studies on the buckling resistance of prestressed stayed columns, Advances in Structural Engineering, Vol: 16, Pages: 487-498, ISSN: 1369-4332
The structural behaviour of prestressed stayed columns is investigated through nonlinear finite element modelling. The models were developed using the commercial software ABAQUS and validated against a series of recently conducted experiments. The sensitivity of the load-carrying capacity to the geometry of the stayed column, the initially applied prestress level within the stays and the initial global imperfection is investigated through parametric studies. It is found that there is a substantial increase in load-carrying capacity with increasing cross-arm length, provided the critical buckling mode remains symmetric. Once the critical buckling mode becomes antisymmetric, mode interaction becomes significant and the load-carrying capacity reaches a plateau and the component generally becomes more sensitive to imperfections. It is also found that the relative level of initial prestress required to maximize the load-carrying capacity of a given stayed column tends to reduce with increasing cross-arm length.
Qu X, Chen Z, Nethercot DA, et al., 2013, Load-reversed push-out tests on rectangular CFST columns, Journal of Constructional Steel Research, Vol: 81, Pages: 35-43, ISSN: 0143-974X
Load-reversed push-out tests have been carried out on 6 rectangular concrete-filled steel tubular (CFST) columns with the aim of investigating the nature of the bond between the concrete infill and the steel tube, the contribution of each bond stress component (i.e. chemical adhesion, microlocking and macrolocking) and the development of macrolocking within four half-cycles of loading. The contribution of microlocking to the total bond strength was obtained from the comparison between the ultimate strength of normal specimens and lubricated specimens, which also revealed the detrimental effect of lubrication on the bond strength. The macrolocking contribution was obtained from the comparison between the ultimate strength achieved in the first half-cycle of loading τu1 and the ultimate strength achieved in the third half-cycle of loading τu3 of the non-lubricated specimens. The developed bond mechanisms were explained and details of the interface bond stress distribution were obtained from the recorded axial strain gradients in the steel tube. Finally, the concept of a critical shear force transfer length was introduced, and its implications on practical design discussed.
Afshan S, Rossi B, Gardner L, 2013, Strength enhancements in cold-formed structural sections - Part I: Material testing, Journal of Constructional Steel Research, Vol: 83, Pages: 177-188, ISSN: 1873-5983
This paper describes a material test programme carried out as part of an extensive study into the prediction of strength enhancements in cold-formed structural sections. The experiments cover a wide range of cross-section geometries – twelve Square Hollow Sections (SHS), five Rectangular Hollow Sections (RHS) and one Circular Hollow Section (CHS), and materials – austenitic (EN 1.4301, 1.4571 and 1.4404), ferritic (EN 1.4509 and 1.4003), duplex (EN 1.4462) and lean duplex (EN 1.4162) stainless steel and grade S355J2H carbon steel. The experimental techniques implemented, the generated data and the analysis methods employed are fully described. The results from the current test programme were combined with existing measured stress–strain data on cold-formed sections from the literature and following a consistent analysis of the combined data set, revised values for Young's modulus E and the Ramberg–Osgood material model parameters n, n′0.2,u and n′0.2,1.0 are recommended. A comparison between the recommended values and the codified values provided in AS/NZS 4673 (2001) [1], SEI/ASCE-8 (2002) [2] and EN 1993-1-4 (2006) [3] is also presented. The test results are also used in a companion paper Rossi et al. (submitted for publication) [4] for developing suitable predictive models to determine the strength enhancements in cold-formed structural sections that arise during the manufacturing processes.
Rossi B, Afshan S, Gardner L, 2013, Strength enhancements in cold-formed structural sections - Part II: Predictive models, Journal of Constructional Steel Research, Vol: 83, Pages: 189-196, ISSN: 1873-5983
Cold-formed structural sections are manufactured at ambient temperature and hence undergo plastic deformations, which result in an increase in yield stress and a reduction in ductility. This paper begins with a comparative study of existing models to predict this strength increase. Modifications to the existing models are then made, and an improved model is presented and statistically verified. Tensile coupon data from existing testing programmes have been gathered to supplement those generated in the companion paper and used to assess the predictive models. A series of structural section types, both cold-rolled and press-braked, and a range of structural materials, including various grades of stainless steel and carbon steel, have been considered. The proposed model is shown to offer improved mean predictions of measured strength enhancements over existing approaches, is simple to use in structural calculations and is applicable to any metallic structural sections. It is envisaged that the proposed model will be incorporated in future revisions of Eurocode 3.
Sheehan T, Chan TM, Xing JH, et al., 2013, Numerical investigation of the cyclic response of CHS braces, Pages: 253-258
The behaviour of seismic-resistant buildings relies heavily upon the inclusion of energy dissipating elements. For concentrically-braced frames, the function of energy dissipation is accomplished by diagonal bracing members, whose performance depends upon both cross-sectional properties and global slenderness. Rectangular hollow sections are traditionally preferred in such applications. However these sections are susceptible to local buckling and, particularly in the case of cold formed tubes, have high residual stresses and reduced corner ductility. Hence as an alternative, this paper focuses on the hysteresis response of hollow circular tubes under cyclic axial loading. The uniformity of the circular cross-section may provide improved performance under cyclic loading over rectangular sections. In this paper, finite element analysis and a damage assessment method are first validated against experimental data on both hot-rolled and cold formed hollow CHS members. A series of parametric investigations is then carried out to access the influence of the local slenderness, global slenderness and steel material type on the hysteresis behaviour. Predictive expressions for displacement ductility and energy dissipation, incorporating both local and global slenderness, are proposed. © 2013 Taylor & Francis Group, London, UK.
Theofanous M, Gardner L, Koltsakis E, 2013, Structural response of stainless steel cross-sections under combined compression and biaxial bending, Pages: 1453-1458
The Continuous Strength Method (CSM) was developed and calibrated against experimental and numerical results as a design approach, which allows for a rational exploitation of the significant strainhardening exhibited by stocky stainless steel cross-sections, thereby leading to more economic design. In order to extend its scope of application beyond the fundamental loading cases of concentric compression and uniaxial bending, a comprehensive numerical parametric study has been conducted and the obtained numerical results have been utilized to determine suitable interaction equations for cross-sections subjected to combined loading. This paper focuses on the ultimate response of I-sections under combined loading and complements a recent relevant study on RHS under combined loading. It is concluded that the current design guidance for stainless steel cross-sections under combined compression and biaxial bending is overly conservative and significant gains can be made if the effect of strain-hardening on ultimate capacity is taken into account. © 2013 Taylor & Francis Group, London, UK.
Afshan S, Gardner L, Baddoo NR, 2013, Buckling response of ferritic stainless steel columns at elevated temperatures, Pages: 1471-1476
This paper presents a numerical study on the buckling behaviour of ferritic stainless steel columns in fire. Finite element models were developed and validated against existing test results to predict the elevated temperature non-linear response of ferritic stainless steel columns. A total of nine austenitic and three ferritic stainless steel column tests were replicated using the finite element analysis package ABAQUS. Parametric studies were performed to investigate the effects of variation of load level and global slenderness on the elevated temperature buckling response of ferritic stainless steel columns, and to extend the range of structural performance data. Both the experimental and numerical parametric study resultswere compared with the current design rules in EN 1993-1-2 (2005) and recent proposed modifications thereof by Ng and Gardner (2007), Uppfeldt et al. (2008) and Lopes et al. (2010). © 2013 Taylor & Francis Group, London, UK.
Su M, Young B, Gardner L, 2013, Continuous beam tests on aluminium alloy SHS and RHS with internal stiffeners, Pages: 1113-1117
The aims of this study are to generate experimental data on aluminium alloy continuous beams of square and rectangular hollow section (SHS and RHS) with internal stiffeners, as well as to assess the current design approaches for indeterminate structures using this new cross-section shape. The experimental programme comprised material tests and five-point bending tests (i.e. continuous beams over three supports) with three different loading configurations. Generally, the specimens failed by the formation of a collapse mechanism comprising three plastic hinges. Comparisons of the test results with design strengths were also carried out. The design strengths predicted by the American (2010), Australian/New Zealand(1997) and European (2007) specifications are found to be rather conservative. The plastic hinge method in Annex H of Eurocode 9 (2007) provides improved results, while the Continuous Strength Method (CSM) for indeterminate structures gives the most accurate and consistent predictions. The results reveal that both strain hardening at the cross-sectional level and moment redistribution at the global system level have significant influence on the structural performance of stocky aluminium alloy structures. © 2013 Taylor & Francis Group, London, UK.
Hui C, Gardner L, Nethercot DA, 2013, Moment redistribution in cold-formed steel continuous beams, Pages: 1035-1040
Cold-formed steel purlins supporting corrugated roof sheeting are often arranged to be continuous over an internal support. Economic design should be based on failure of the system, recognising the opportunity for redistribution of moments. This paper presents the findings from a numerical investigation of the degree of moment redistribution in continuous cold-formed steel zeta-section beams subjected to a Uniformly Distributed Load (UDL). Three types of nonlinear finite element analysis were validated against reported physical tests: (1) continuous two-span beams subjected to a UDL, (2) single span beams subjected to a central point load producing a moment gradient and (3) single span beams subjected to two point load producing a central region under pure bending. The interior support moments from the continuous beam models were compared with the reference moment capacities from the three-point bending models. Based on various different sections sizes, covering a range of cross-sectional slenderness, full moment redistribution with no drop-off in moment at the interior support was found to be possible only for stocky sections but not for slender sections. In the case of slender sections, local and distortional buckling caused a reduction in interior support moment prior to failure of the system. Hence a design formula is proposed to estimate the post-peak reduction of interior support moment from its initial peak, and use this reduced moment in conjunction with the full span moment to determine the load-carrying capacity of the system. Comparisons show the proposed approach to offer accurate prediction of observed system failure loads. © 2013 Taylor & Francis Group, London, UK.
Wadee MA, Gardner L, Osofero AI, 2013, Design of prestressed stayed columns, Journal of Constructional Steel Research, Vol: 80, Pages: 287-298, ISSN: 0143-974X
General design procedures for prestressed stayed columns with a single cross-arm system are presented. The accuracy of the proposed design expressions is confirmed by comparison with the results of physical experiments and validated finite element simulations. Reliability is assessed by following the approach set out in Annex D of EN 1990. The presented resistance expressions for prestressed stayed columns are a function of the system geometry, the level of initial prestress in the cables and the global imperfection level. Worked examples are also presented to illustrate the application of the developed design approach.
McCann F, Gardner L, Wadee MA, 2013, Design of steel beams with discrete lateral restraints, Journal of Constructional Steel Research, Vol: 80, Pages: 82-90, ISSN: 0143-974X
Discrete lateral restraints offer an effective means of stabilising beams against lateral-torsional buckling. Design expressions for simply-supported beams braced regularly along their span with elastic restraints, based on analytically-derived formulae, are presented herein. These include the minimum restraint stiffness required to force the beam to buckle in between the restraint nodes and the forces induced in the restraints, along with a brief treatment of the critical moment of the beam. It is demonstrated that there is close agreement between the values obtained from the design formulae and their original analytical counterparts. These are also compared with the results from design formulae based on analogous column behaviour, an approach commonly used in design codes. It is found that the column rules used by design codes return values that, when compared with the results of the current analysis, are overly conservative for cases where the restraints are positioned at the compression flange of the beam but unsafe for restraints positioned at the shear centre.
Saliba N, Gardner L, 2012, Cross-section stability of lean duplex stainless steel welded I-sections, Journal of Constructional Steel Research, Vol: 80, Pages: 1-14, ISSN: 0143-974X
Despite growing interest in the use of stainless steel in construction and the development of a number of national and regional design codes, stainless steel is often still regarded as only suitable for specialised applications. This is partly due to the high initial material cost associated with the most commonly adopted austenitic grades. The initial material cost of stainless steel is largely controlled by the alloy content, in particular the level of nickel, which is around 8%–10% for the common austenitic grades. A recently developed grade, known as lean duplex stainless steel (EN 1.4162), has a far lower nickel content, around 1.5%, and hence lower cost. Despite the low nickel content, it possesses higher strength than the common austenitic stainless steels, along with good corrosion resistance and high temperature properties and adequate weldability and fracture toughness. The structural performance of lean duplex stainless steel remains relatively unexplored to date with only a few studies having been performed. For this reason, an experimental and analytical research programme investigating the structural characteristics of lean duplex stainless steel was initiated. The present paper summarises the laboratory tests performed on lean duplex stainless steel welded I-sections. The experiments include material testing, stub column tests and 3-point and 4-point bending tests. The experimental data were supplemented by results generated by means of a comprehensive numerical investigation including parametric studies covering a wide range of cross-sections. The obtained experimental and numerical results, together with the results of previous tests performed on lean duplex stainless steel cold-formed hollow sections are reported and used to assess the applicability of existing cross-section classification limits and the continuous strength method (CSM) to lean duplex stainless steel. Furthermore, the structural performance of lean duplex stainless steel was
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