The Experts below are selected from a list of 54351 Experts worldwide ranked by ideXlab platform
B W Schafer - One of the best experts on this subject based on the ideXlab platform.
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development and experimental validation of the direct strength method for cold Formed Steel beam columns
Journal of Structural Engineering-asce, 2018Co-Authors: Shahabeddin Torabian, B W SchaferAbstract:AbstractThe direct strength method of cold-Formed Steel member design uses local, distortional, and global cross-section elastic buckling analysis with empirically derived direct expressions to pre...
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system reliability of floor diaphragms framed from cold Formed Steel with wood sheathing
Journal of Structural Engineering-asce, 2018Co-Authors: Aritra Chatterjee, B W Schafer, Sanjay R Arwade, Cristopher D. MoenAbstract:AbstractA high-fidelity simulation-based system reliability calculation methodology was implemented for Steel floor diaphragms framed from cold-Formed Steel joists topped with wood sheathing, leadi...
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modeling seismic response of a full scale cold Formed Steel framed building
Engineering Structures, 2017Co-Authors: Jiazhen Leng, Kara D Peterman, Stephen G Buonopane, Guanbo Bian, B W SchaferAbstract:Abstract The objective of this paper is to present finite element modeling protocols and validation studies for the seismic response of a two-story cold-Formed Steel-framed building with oriented strand board sheathed shear walls. Recently, shake table testing of this building was completed by the authors. The building provides an archetype for modern details of cold-Formed Steel construction, and provides benchmarks for the seismic response of the building system, subsystem, and components. The seismic response of buildings framed from cold-Formed Steel has seen little study in comparison with efforts on isolated members and shear walls. Validated building-scale models are needed to expand our understanding of the seismic response of these systems. Finite element models corresponding to the archetype building during its various test phases are developed in OpenSees and detailed herein. For cold-Formed Steel framed buildings accurate seismic models require consideration of components beyond the isolated shear walls, e.g. the stiffness and capacity of the gravity framing is included in the model. Such decisions require model refinement beyond what is typically perFormed and details for completing this effort accurately and efficiently are described herein. In addition, nonstructural components, including exterior sheathing of the gravity framing, interior gypsum sheathing for the shear walls and gravity framing, and interior partition walls, are included in the building model based on nonlinear surrogate models that utilize experimental characterization of member-fastener-sheathing response. Comparisons between the developed models and testing for natural period, story drift, accelerations, and foundation hold-down forces validate the model. Performance of the tested archetype building is better than predicted by design or typical engineering assumptions. The model developed herein provides insights into how the building achieves its beneficial performance and will be used to further quantify the lateral resistance of each subsystem and the extent of their coupling. In addition, the protocols used to develop the model herein provide a first examination of the necessary modeling characteristics for wider archetype studies of cold-Formed Steel-framed buildings and the development and substantiation of seismic response modification coefficients.
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laser based cross section measurement of cold Formed Steel members model reconstruction and application
Thin-walled Structures, 2017Co-Authors: Xi Zhao, Mazdak Tootkaboni, B W SchaferAbstract:Abstract The objective of this paper is to present procedures for processing three-dimensional point clouds that are generated from laser-based scanning of a cold-Formed Steel member into useful measurements of cross-section dimensions and imperfections, as well as for use in finite element simulations of the as-measured geometry. The measurement data comes from a unique laser-based scanning platform developed by the authors. Multiple passes on the target cold-Formed Steel specimen using a line laser are registered with an iterative closest point algorithm to develop the initial three-dimensional point cloud. A novel feature recognition method is proposed to distinguish and extract geometric characteristics such as corners and flats in the targeted specimen. Three different applications are demonstrated herein for the three-dimensional point cloud: feature recognition for determination of nominal dimensions, deviation from nominal configuration for determination of simplified imperfection patterns, and re-mapping of the three-dimensional point cloud onto regularized grids appropriate for subsequent shell finite element modeling. The high fidelity of the measured data provides potential for new insights across all three application areas. Extensions of the algorithms to other cold-Formed Steel cross-sections, as well as built-up cold-Formed Steel cross-sections, are currently being pursued.
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seismic response and engineering of cold Formed Steel framed buildings
Structures, 2016Co-Authors: B W Schafer, D Ayhan, Kara D Peterman, Jiazhen Leng, David A Padillallano, Matthew Stehman, Stephen G Buonopane, Matthew R Eatherton, R L Madsen, B ManleyAbstract:Abstract Buildings framed from cold-Formed Steel members are becoming increasingly common. Significant research has been conducted on individual cold-Formed Steel members, but little research has been done on full buildings framed from cold-Formed Steel. In the past, testing on individual shear walls has been used to provide insights and create safe seismic designs for cold-Formed Steel buildings, but understanding and modeling of whole buildings have been out of reach. As a result, seismic performance-based design has also remained out of reach for cold-Formed Steel framed buildings. Recently, a North American effort under the abbreviated name: CFS-NEES has begun to address this challenge head on. Major deliverables in the CFS-NEES effort included: shear wall testing, characterization, and modeling; cyclic member testing, characterization, and modeling; and, whole building shake table testing, and modeling. The research provides the necessary building blocks for developing efficient nonlinear time history models of buildings framed from cold-Formed Steel. In addition, the experiments demonstrate the large difference between idealized engineering models of the seismic force-resisting system and the superior performance of the full building system.
D A Nethercot - One of the best experts on this subject based on the ideXlab platform.
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testing and analysis of composite cold Formed Steel and wood based flooring systems
Journal of Structural Engineering-asce, 2017Co-Authors: Pinelopi Kyvelou, Leroy Gardner, D A NethercotAbstract:AbstractAn experimental study was conducted into the degree of composite action that can arise between cold-Formed Steel joists and wood-based flooring panels. A series of material, push-out and 4-...
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moment redistribution in cold Formed Steel continuous beams
Thin-walled Structures, 2016Co-Authors: Chi Hui, Leroy Gardner, D A NethercotAbstract:Abstract The external envelope of Steel framed industrial buildings normally involves the use of purlins and rails spanning between the main hot-rolled frames to support the roofing/cladding. These purlins are typically light-gauge cold-Formed Steel members of complex shape for which the thin-walled nature of the material means that local instabilities will significantly influence their structural behaviour. 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 beams subjected to a downward (gravity) uniformly distributed load (UDL). Three types of nonlinear finite element analysis were validated against previously reported physical tests: (i) continuous two-span beams subjected to a UDL, (ii) single span beams subjected to a central point load producing a moment gradient and (ii) single span beams subjected to two point loads producing a central region under pure bending. The interior support moments from the continuous beam models were compared against reference moment capacities from the three-point bending models. Based on various different section 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 this reduced moment capacity is then used 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.
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finite element idealization of a cold Formed Steel portal frame
Journal of Structural Engineering-asce, 2004Co-Authors: James B.p. Lim, D A NethercotAbstract:A simple linear beam idealization of a cold-Formed Steel portal frame is presented in which beam elements are used to idealize the column and rafter members, and rotational spring elements are used to represent the rotational flexibility of the joints. In addition, the beam idealization takes into account the finite connection length of the joints. Deflections predicted using the beam idealization are shown to be comparable to deflections obtained from both a linear finite element shell idealization and full-scale laboratory tests. Using the beam idealization, deflections under rafter load are divided into three components: Deflection due to flexure of the column and rafter members, deflection due to bolt-hole elongation, and deflection due to in-plane bracket deformation. Of these deflection components, the deflection due to bolt-hole elongation is the most significant and cannot, therefore, be ignored. Using the beam idealization, engineers can analyze and design cold-Formed Steel portal frames, including making appropriate allowances for connection effects, without the need to resort to expensive finite element shell analysis.
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serviceability design of a cold Formed Steel portal frame having semi rigid joints
Steel and Composite Structures, 2003Co-Authors: James B.p. Lim, D A NethercotAbstract:Details are given of a cold-Formed Steel portal framing system that uses simple bolted momentconnections for both the eaves and apex joints. However, such joints function as semi-rigid and, as a result, the design of the proposed system will be dominated by serviceability requirements. While serviceability is a mandatory design requirement, actual deflection limits for portal frames are not prescribed in many of the national standards. In this paper, a review of the design constraints that have an effect on deflection limits is discussed, and rational values appropriate for use with cold-Formed Steel portal frames are recommended. Adopting these deflection limits, it is shown through a design example how a cold-Formed Steel portal frame having semi-rigid eaves and apex joints can be a feasible alternative to rigid-jointed frames in appropriate circumstances.
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ultimate strength design of bolted moment connections between cold Formed Steel members
Advances in Steel Structures. Proceedings of the Third International Conference on Advances in Steel StructuresHong Kong Institution of Engineers Hong, 2002Co-Authors: James B.p. Lim, D A NethercotAbstract:The behaviour and design of bolted moment-connections between cold-Formed Steel members, Formed by using brackets bolted to the webs of the section, is considered. The particular problem of the moment-capacity of such joints being lower than that of the cold-Formed Steel sections being connected because of web buckling, caused by the concentration of load transfer from the bolts, is addressed. In this paper, a combination of laboratory tests and finite element analyses is used to investigate this mode of failure. It is demonstrated that there is good agreement between the measured ultimate moment-capacity and that predicted by using the finite element method. A parametric study conducted using the finite element model shows that the moment-capacity of a practical size joint can be up to 20% lower than that of the cold-Formed Steel sections being connected. Web buckling so-caused must therefore be considered in the design of such connections.
James B.p. Lim - One of the best experts on this subject based on the ideXlab platform.
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nonlinear behaviour of back to back gapped built up cold Formed Steel channel sections under compression
Journal of Constructional Steel Research, 2018Co-Authors: Krishanu Roy, Tina Chui Huon Ting, Hieng-ho Lau, James B.p. LimAbstract:Abstract In cold-Formed Steel structures, such as trusses and portal frames, the use of back-to-back gapped built-up cold-Formed Steel channel-sections for column members are becoming increasingly popular. In such an arrangement, the lowest flexural buckling mode may not necessarily be overall buckling of the whole column. In the literature, only three test results have been previously reported for such cold-Formed Steel columns, and limited to values of non-dimensional slenderness ranging from 1.08 to 1.16. This issue is considered herein. The results of 40 experimental tests are reported, conducted on back-to-back gapped built-up cold-Formed Steel channel-sections covering the range of non-dimensional slenderness from stub to slender columns. A nonlinear finite element model is then described that shows good agreement with the experimental results. The finite element model is then used for the purposes of a study comprising 84 models. Using the experimental and finite element results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS) can be conservative by as much as 53%. However, use of a modification to the non-dimensional slenderness, that considers the gap, results in the design standards being within 5% conservative with respect to the experimental and finite element results.
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effect of screw spacing on behavior of axially loaded back to back cold Formed Steel built up channel sections
Advances in Structural Engineering, 2018Co-Authors: Tina Chui Huon Ting, Hieng-ho Lau, Krishanu Roy, James B.p. LimAbstract:In cold-Formed Steel structures, such as trusses, wall frames, and portal frames, the use of back-to-back built-up cold-Formed Steel channel sections for the column members is becoming increasingly...
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Design Optimization of Long-Span Cold-Formed Steel Portal Frames Accounting for Effect of Knee Brace Joint Configuration
MDPI AG, 2017Co-Authors: Thanh Duoc Phan, James B.p. Lim, Meheron Selowara Joo, Hieng-ho LauAbstract:The application of cold-Formed Steel channel sections for portal frames becomes more popular for industrial and residential purposes. Experimental tests showed that such structures with long-span up to 20 m can be achieved when knee brace joints are included. In this paper, the influence of knee brace configuration on the optimum design of long-span cold-Formed Steel portal frames is investigated. The cold-Formed Steel portal frames are designed using Eurocode 3 under ultimate limit states. A novel method in handling design constraints integrated with genetic algorithm is proposed for searching the optimum design of cold-Formed Steel portal frames. The result showed that the proposed routine for design optimization effectively searched the near global optimum solution with the computational time is approximate 50% faster than methods being popularly used in literature. The optimum configuration for knee brace joint can reduce the section size of rafter and so the lighter frame could be obtained especially for long-span portal frame. The minimum weight of main frame obtained from optimization process is approximate 19.72% lighter than a Benchmark Frame used in the full-scale experimental test
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Stiffness prediction for bolted moment-connections between cold-Formed Steel members
Journal of Constructional Steel Research, 2004Co-Authors: James B.p. Lim, David A. NethercotAbstract:The authors have recently described a cold-Formed Steel portal framing system in which simple bolted moment-connections, Formed through brackets, were used for the eaves and apex joints. Such connections, however, cannot be considered as rigid because of localised in-plane elongation of the bolt-holes caused by bearing against the bolt-shanks. To therefore predict the initial stiffness of such connections, it is necessary to know the initial bolt-hole elongation stiffness kb. In this paper, a finite element solid idealisation of a bolted lap-joint in shear will be described that can be used to determine kb; the results obtained are validated against experimental data. A beam idealisation of a cold-Formed Steel bolted moment-connection is then described, in which spring elements are used to idealise the rotational flexibility of the bolt-groups resulting from bolt-hole elongation. Using the value of kb in the beam idealisation, the deflections predicted are shown to be similar to those measured experimentally in laboratory tests conducted on the apex joint of a cold-Formed Steel portal frame.
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finite element idealization of a cold Formed Steel portal frame
Journal of Structural Engineering-asce, 2004Co-Authors: James B.p. Lim, D A NethercotAbstract:A simple linear beam idealization of a cold-Formed Steel portal frame is presented in which beam elements are used to idealize the column and rafter members, and rotational spring elements are used to represent the rotational flexibility of the joints. In addition, the beam idealization takes into account the finite connection length of the joints. Deflections predicted using the beam idealization are shown to be comparable to deflections obtained from both a linear finite element shell idealization and full-scale laboratory tests. Using the beam idealization, deflections under rafter load are divided into three components: Deflection due to flexure of the column and rafter members, deflection due to bolt-hole elongation, and deflection due to in-plane bracket deformation. Of these deflection components, the deflection due to bolt-hole elongation is the most significant and cannot, therefore, be ignored. Using the beam idealization, engineers can analyze and design cold-Formed Steel portal frames, including making appropriate allowances for connection effects, without the need to resort to expensive finite element shell analysis.
Ben Young - One of the best experts on this subject based on the ideXlab platform.
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structural performance of cold Formed Steel elliptical hollow section pin ended columns
Thin-walled Structures, 2019Co-Authors: Mantai Chen, Ben YoungAbstract:Abstract The structural performance of cold-Formed Steel elliptical hollow section pin-ended columns buckled about the minor axis was studied through experimental and numerical investigation. Four cross-section series with five different column lengths were designed in the test program to include a wide range of cross-section geometries and column slenderness. Finite element model was developed to replicate the key test results and to perform extensive parametric study. The validation results show that the model can accurately predict the behavior of cold-Formed Steel elliptical hollow section pin-ended columns buckled about the minor axis. Subsequently, an extensive parametric study with a wide range of cross-section geometries and a spectrum of column slenderness was perFormed. Since currently there is no codified design rule on elliptical hollow section compression members, the results of 22 column tests and 280 finite element analyses were only compared with the predicted strengths by the equivalent diameter method and equivalent rectangular hollow section approach proposed by previous researchers, the traditional design methods with equivalent diameter incorporated as well as the Direct Strength Method. Reliability analysis was conducted to examine these design methods. Among these design methods, the comparisons show that the existing Direct Strength Method offers the most suitable design provisions, though further improvement remains possible. In this study, modification is proposed on the Direct Strength Method to further improve the accuracy of design strength predictions. It is suggested to adopt the modified Direct Strength Method design equations in the nominal strength predictions of cold-Formed Steel elliptical hollow section pin-ended columns buckled about the minor axis.
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design of cold Formed Steel channels with stiffened webs subjected to bending
Thin-walled Structures, 2014Co-Authors: Liping Wang, Ben YoungAbstract:Abstract The objectives of this study are to investigate the structural behaviour and evaluate the appropriateness of the current direct strength method on the design of cold-Formed Steel stiffened cross-sections subjected to bending. The stiffeners were employed to the web of plain channel and lipped channel sections to improve the flexural strength of cold-Formed Steel sections that are prone to local buckling and distortional buckling. An experimental investigation of simply supported beams with different stiffened channel sections has been conducted. The moment capacities and observed failure modes at ultimate loads were reported. A nonlinear finite element model was developed and verified against the test results in terms of strengths, failure modes and moment–curvature curves. The calibrated model was then adopted for an extensive parametric study to investigate the moment capacities and buckling modes of cold-Formed Steel beams with various geometries of stiffened sections. The strengths and failure modes of specimens obtained from experimental and numerical results were compared with design strengths predicted using the direct strength method specified in the North American Specification for cold-Formed Steel structures. The comparison shows that the design strengths predicted by the current direct strength method (DSM) are conservative for both local buckling and distortional buckling in this study. Hence, the DSM is modified to cover the new stiffened channel sections investigated in this study. A reliability analysis was also perFormed to assess the current and modified DSM.
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design of cold Formed Steel built up closed sections with intermediate stiffeners
Journal of Structural Engineering-asce, 2008Co-Authors: Ben Young, Ju ChenAbstract:A series of column tests on cold-Formed Steel built-up closed sections with intermediate stiffeners is presented in this paper. The test specimens were first brake pressed from structural Steel sheets to form open sections with intermediate web stiffeners, then two of the open sections were connected at their flanges using self-tapping screws to form the built-up closed sections. The high strength structural Steel sheets had the measured 0.2% proof stress up to 586 MPa. Initial and overall geometric imperfections as well as material properties and residual stresses of the test specimens were measured. Tests were perFormed over a range of lengths such that column curves could be obtained. The test strengths are compared with the design strengths calculated using the direct strength method in the North American Specification and Australian/New Zealand Standard for cold-Formed Steel structures. Three different methods were used to obtain the local and distortional buckling stresses for the calculation of the direct strength method. Reliability analysis was perFormed to assess the reliability of the direct strength method on cold-Formed Steel built-up closed section columns. It is shown that the direct strength method using single section to obtain the buckling stresses is generally conservative.
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cold Formed Steel lipped channel columns at elevated temperatures
Engineering Structures, 2007Co-Authors: Ju Chen, Ben YoungAbstract:The main objective of this paper is to study the behaviour and design of cold-Formed Steel lipped channel columns at elevated temperatures using finite element analysis. The effects of initial local and overall geometrical imperfections have been taken into consideration in the analysis. Failure loads and load-shortening curves of lipped channel columns were investigated in this study. The finite element analysis was perFormed on lipped channel columns compressed between fixed ends over a range of column lengths for various temperatures. The nonlinear finite element model was verified against experimental results of lipped channel columns at normal room temperature and elevated temperatures. Three series of columns were studied using finite element analysis to investigate the strength and behaviour of lipped channel columns at elevated temperatures. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the effective width and direct strength methods by substituting the reduced material properties. It should be noted that the current effective width and direct strength methods are developed based on cold-Formed Steel structural members at normal room temperature. In this study, the suitability of the effective width and direct strength methods for cold-Formed Steel lipped channel columns at elevated temperatures is investigated. It is shown that the effective width and direct strength methods are able to predict the cold-Formed Steel lipped channel column strengths at elevated temperatures. In addition, the ratio of the failure loads of the columns at elevated temperatures to that at normal room temperature is also studied and compared with the prediction proposed by other researcher.
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experimental investigation of cold Formed Steel material at elevated temperatures
Thin-walled Structures, 2007Co-Authors: Ju Chen, Ben YoungAbstract:Abstract This paper presents the mechanical properties data for cold-Formed Steel at elevated temperatures. The deterioration of the mechanical properties of yield strength (0.2% proof stress) and elastic modulus are the primary properties in the design and analysis of cold-Formed Steel structures under fire. However, values of these properties at different temperatures are not well reported. Therefore, both steady and transient tensile coupon tests were conducted at different temperatures ranged approximately from 20 to 1000 °C for obtaining the mechanical properties of cold-Formed Steel structural material. This study included cold-Formed Steel grades G550 and G450 with plate thickness of 1.0 and 1.9 mm, respectively. Curves of elastic modulus, yield strength obtained at different strain levels, ultimate strength, ultimate strain and thermal elongation versus different temperatures are plotted and compared with the results obtained from the Australian, British, European standards and the test results predicted by other researchers. A unified equation for yield strength, elastic modulus, ultimate strength and ultimate strain of cold-Formed Steel at elevated temperatures is proposed in this paper. A full strain range expression up to the ultimate tensile strain for the stress–strain curves of cold-Formed carbon Steel at elevated temperatures is also proposed in this paper. It is shown that the proposed equation accurately predicted the test results.
Benjamin W. Schafer - One of the best experts on this subject based on the ideXlab platform.
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Direct Strength Method for Design of Cold-Formed Steel Columns with Holes
Journal of Structural Engineering-asce, 2011Co-Authors: Cristopher D. Moen, Benjamin W. SchaferAbstract:In this paper, design expressions are derived that extend the American Iron and Steel Institute (AISI) direct strength method (DSM) to cold-Formed Steel columns with holes. For elastic buckling-controlled failures, column capacity is accurately predicted by using existing DSM design equations and the cross-section and global elastic buckling properties calculated including the influence of holes. For column failures in the inelastic regime, in which strength approaches the squash load, limits are imposed to restrict column capacity to that of the net cross section at a hole. The proposed design expressions are validated with a database of existing experiments on cold-Formed Steel columns with holes, and more than 200 nonlinear finite-element simulations that evaluate the strength prediction equations across a wide range of hole sizes, hole spacings, hole shapes, and column dimensions. The recommended DSM approach is demonstrated to provide a broad improvement in prediction accuracy and generality when com...
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Distortional Buckling Tests on Cold-Formed Steel Beams
Journal of Structural Engineering, 2006Co-Authors: Benjamin W. SchaferAbstract:Failure in cold-Formed Steel beams is generally initiated by one of three instabilities: local, distortional, or lateral-torsional buckling. For cold-Formed Steel joists, purlins, or girts, when the compression flange is not restrained by attachment to sheathing or paneling, distortional buckling may be the predominant failure mode. Experimental results on cold-Formed Steel beams with unrestrained compression flanges are scarce. Therefore a series of distortional buckling tests on cold-Formed Steel C and Z sections in bending was conducted to establish the capacity in distortional buckling failures. Test details were selected to allow distortional buckling to form, but restrict lateral-torsional buckling to the extent possible. These distortional buckling tests also provide a direct comparison against the local buckling tests previously perFormed by the writers. As expected, large strength reductions are observed in the tested specimens when distortional buckling initiated the failure instead of local buckling. U.S., Canadian, and joint North American standards for design, which are known to primarily focus on local buckling, provided unconservative predictions of the observed strength. The Australian/New Zealand Standard and the direct strength method, which provide explicit methods for calculating the capacity in the distortional buckling mode, provided reasonably accurate and reliable predictions.
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Local Buckling Tests on Cold-Formed Steel Beams
Journal of Structural Engineering, 2003Co-Authors: Benjamin W. SchaferAbstract:\iC and \iZ sections are two of the most common cold-Formed Steel shapes in use today. Accurate prediction of the bending performance of these sections is important for reliable and efficient cold-Formed Steel structures. Recent analytical work has highlighted discontinuities and inconsistencies in the American Iron and Steel Institute (AISI) and Canadian Standards Association (S136) design provisions for stiffened elements under a stress gradient (i.e., the web of \iC or \iZ sections). New methods have been proposed for design, and an interim method has been adopted in the North American Specification (NAS). However, existing tests on \iC and \iZ sections do not provide a definitive evaluation of the design expressions, due primarily to incomplete restriction of the distortional buckling mode. Described in this paper is a series of flexural tests with details selected specifically to insure that local buckling is free to form, but distortional buckling and lateral-torsional buckling are restricted. The members selected for the tests provide systematic variation in the web slenderness (\Ih/t\N) while varying other relevant nondimensional parameters (i.e., \Ih/b, b/t, d/t, d/b\N). Initial analysis of the completed testing indicates that overall test-to-predicted ratios for AISI, S136, NAS, and the direct strength method are all adequate, but systematic differences are observed.
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LATERALLY BRACED COLD-Formed Steel FLEXURAL MEMBERS WITH EDGE STIFFENED FLANGES
Journal of Structural Engineering, 1999Co-Authors: Benjamin W. Schafer, Teoman PeközAbstract:The moment capacity of a laterally braced cold-Formed Steel flexural member with edge stiffened flanges (e.g., a channel or zee section) may be affected adversely by local or distortional buckling. New procedures for hand prediction of the buckling stress in the local and distortional mode are presented and verified. Numerical investigations are employed to highlight postbuckling behavior unique to the distortional mode. Compared with the local mode, the distortional mode is shown to have (1) heightened imperfection sensitivity, (2) lower postbuckling capacity, and (3) the ability to control the failure mechanism even in cases when the elastic buckling stress in the local mode is lower than in the distortional mode. Traditional design methods do not explicitly recognize distortional buckling, nor do they account for the observed phenomena in this mode. A new design method that integrates distortional buckling into the unified effective width approach, currently used in most cold-Formed Steel design specifications, is presented. For each element a local buckling stress and a reduced distortional buckling stress are compared to determine the effective width. Comparison with experimental tests shows that the new approach is more consistent and reliable than existing design methods.
