Conference Paper

Computational study of elastic buckling and post-buckling strength of steel decks in bending

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Abstract

The elastic buckling and post-buckling strength of steel decks in bending are examined computationally via finite element modeling. Nonlinear finite element models of steel deck were created in ANSYS and successfully validated against published experimental results. A parametric study comprising 472 simulations was conducted using the developed models to examine the influence of the deck cross-sectional geometry and thickness, boundary conditions, and transverse ties on the deck elastic buckling and post-buckling strength. The influence of the deck yield stress and steel constitutive models on the deck flexural strength was also investigated. The obtained local and distortional elastic buckling moments, as well as the ultimate moments for decks failing in local and distortional buckling, are discussed. It was found, in particular, that the post-buckling flexural strength of deck with flat compression flanges failing in local buckling is highly affected by the level of deck non-symmetry, in addition to the deck compression flange slenderness. The deck ultimate moments obtained in the parametric study are compared with those predicted by the AISI S100-16 direct strength and effective width methods. Design equations are proposed for predicting local elastic buckling coefficients of deck with flat compression flanges and distortional buckling coefficients of deck with intermediate stiffeners in compression flanges. Modifications of the direct strength method are proposed for better predictions of the flexural strength of deck with flat compression flanges failing in local and distortional buckling. The proposed equation predictions agree well with the numerical simulation results.

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... Still, they may also exhibit distortional buckling of flange-longitudinal stiffener junctions or web-edge flange junctions when unstiffened edge flanges are in compression. It was previously shown that the EWM might provide unconservative predictions of the deck strength governed by distortional buckling (Degtyarev 2020a). ...
... The DSM allows for predicting the CFS member strength governed by distortional buckling and the strength of the members optimized by multiple stiffeners, which the EWM cannot easily achieve. Despite its many benefits, the DSM demonstrated overly conservative strength predictions for flexural members with slender compression elements Peköz 1998, Schafer 2008), especially when the cross-sections are not symmetric with respect to the bending axis (Dudenbostel and Sputo 2016, Raebel and Gwozdz 2018, Raebel et al. 2020, Oey and Papangelis 2020, Degtyarev 2020a. Steel deck manufacturers offer profiles with non-symmetric cross-sections and slender compression elements. ...
... Advanced finite element analysis (FEA), which is capable of accurate predictions of the deck strength in bending (Degtyarev 2020a(Degtyarev , 2020b(Degtyarev , 2020c(Degtyarev , and 2020d, can be used as an alternative to the EWM and the DSM. However, it requires advanced software, modeling expertise, and substantial computational resources, which are not always available to designers. ...
Conference Paper
Accurate predictions of the elastic buckling and ultimate moments of steel decks in bending are essential for obtaining economic and safe designs. The existing design methods give accurate results for some deck profiles while producing unsafe or overly conservative predictions for others. This paper explores machine learning in the form of the Support Vector Machine regression (SVR) for estimating the elastic buckling and ultimate moments of steel decks. Eight SVR models for predicting the following properties of North American steel deck profiles were developed: plate buckling coefficient of stiffened flanges, plate buckling coefficient of unstiffened flanges, plate buckling coefficient for distortional buckling of deck flanges with a longitudinal stiffener, local elastic buckling moment of stiffened flanges, local elastic buckling moment of unstiffened flanges, distortional elastic buckling moment of a web-edge flange junction, distortional elastic buckling moment of a flange-stiffener junction, and ultimate moment. The dataset used for the model training, validation, and testing consisted of 1152 finite element simulations performed on deck models previously validated on experimental data. The developed SVR models demonstrated a good generalization ability and excellent prediction accuracy, which exceeded the accuracy of the existing design methods. The SVR models were interpreted by evaluating feature importance and feature effects using the SHapley Additive exPlanations (SHAP) method. The obtained feature importance and feature effects aligned well with the mechanics-based knowledge, confirming the abilities of the SVR models to capture and reveal the underlying physics from the data used for the model development. A web application for predicting steel deck properties in bending by the developed SVR models was created and deployed to the cloud. It can be opened and run in a browser on any device, including mobile. The application's source code, which was made available on GitHub, can be used to run the application on a local machine.
... The simulation results from the Degtyarev [7] study are plotted in Figs. 11 and 12 for deck profiles identified as 1F, 1.5B, 1.5BR, 3N, and 3NR. ...
... (22)) new DSM reflect the adjustment for unsymmetric sections (i.e., 0.74 < < 1.26) and better predict the strengths. The Degtyarev [7] study included some tests with an elastic-perfectly plastic stress-strain curve, but far more cases were run with a nonlinear stress-strain curve that increases to ultimate stress 12% to 45% above yield stress. This may contribute to the overstrength observed in these simulations. ...
... The results of numerical simulations by Degtyarev [7] of stiffened deck sections limited by distortional buckling are shown in Fig. 14. The current DSM predictions (Eq. ...
Article
The Direct Strength Method (DSM) has been an available option for the design of cold-formed steel members in the American Iron and Steel Institute (AISI) specification since 2004. The strength of flexural members unsymmetric about the bending axis presents some challenges related to post-buckling stress redistribution, which are not fully addressed in DSM today. This paper introduces generalized modifications to the DSM strength curves to improve strength prediction for these cases. Simple adjustments for stress redistribution due to both yielding and buckling are introduced and validated against a variety of section types from various published test and simulation results. An alternate solution is also developed utilizing a novel form of the strength equation which incorporates inelastic reserve strength. Both methods provide improvement to strength predictions suitable for consideration in design specifications.
... It has been used by many researchers for studying strength and structural behavior of CFS structures. The FE method was also successfully used for simulating structural response of solid and perforated steel deck through collapse [11][12][13][14]. Therefore, the FE method was employed in this work for studying the flexural strength of CFS deck with holes. ...
... More discussion about strength predictions of solid decks by EWM and DSM can be found in [14]. It should also be noted that the available research on the elastic buckling and post-buckling strength of steel deck profiles is very limited and disproportionate to the amount of steel deck used in construction worldwide. ...
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Holes in steel roof decks are often provided to allow for the passage of services. Published information on structural properties and design methods of steel deck with holes is limited. To shed light on this topic, a numerical parametric study of the flexural strength of steel decks with single square and rectangular holes was performed. This paper presents results of the study. Nonlinear finite element deck models were developed in ANSYS and validated using published test results. Flexural strengths and load-deflection curves predicted by the developed models showed good agreement with the experimental data. The following parameters were varied in the study: deck type and thickness, hole width and length-to-width ratio, hole location along and across the deck span, and load type. Ultimate moment reductions due to the holes have been presented and discussed. The ultimate moments obtained numerically were compared with those predicted by the effective width and direct strength methods. Modifications of the direct strength method were proposed to allow for better predictions of the flexural strength of steel deck with holes. A method to account for the effects of hole location along and across deck span on the ultimate moment was also presented. The design methods predicted the simulation results well when the proposed design procedures were considered. It was shown that the direct strength method predictions for distortional buckling of solid decks depend on the compression-to-tension flange width ratio. The conservatism of the DSM predictions increases when the compression-to-tension flange width ratio increases.
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Finite element simulations of structural members are a good alternative to physical testing for studying strength and structural response of the members when finite element models have been properly calibrated and validated. Published information on finite element modeling of cold-formed steel deck in bending is scarce. This paper presents the development of finite element models of corrugated steel deck in bending using a general-purpose software, ANSYS. Effects of the following parameters on elastic buckling and ultimate moments of models, as well as on their load-deflection curves, were studied: shell element types, mesh density, corner radius, number of deck corrugations, presence of transverse ties, initial geometric imperfection distribution and magnitude, deck boundary conditions, loading type, and stress-strain diagrams. Optimal parameters of the models were determined. Moment capacities, flexural stiffness, and load-deflection curves predicted by the models with the optimal parameters correlated well with test results available in literature, especially when the deck material behavior was described by nonlinear stress-strain diagrams. The developed FE models can be used for studying flexural strength and behavior of solid steel deck with various geometry under various loading types, which can be useful in development of new efficient profiles and in improving the current deck design methods. The models can also be used as a basis for the development of FE models of steel deck with openings and acoustical perforations, as well as built-up deck profiles, design methods for which are currently underdeveloped.
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Cold-formed steels are generally characterized by a rounded stress-strain response with no sharply defined yield point. It is shown herein that this material behaviour can be accurately described by a two-stage Ramberg-Osgood model provided that the values of the key input parameters can be established. The focus of the present paper is to develop predictive expressions for these key parameters to enable the full engineering stress-strain response of cold-formed steels to be represented. The predictive expressions are based on the analysis of a comprehensive set of material stress-strain data collected from the literature. In total, more than 700 experimentally-derived stress-strain curves on cold-formed steel material have been collected from around the world, covering a range of steel grades, thicknesses and cross-section types. The strength enhancement in the corner regions of cold-formed sections has also been analysed and the applicability of existing predictive models has been evaluated. Finally, standardized values of strain-hardening exponents used in the Ramberg-Osgood model have been recommended for both flat and corner material in cold-formed steel sections. The proposed stress-strain curves are suitable for use in advanced numerical simulations and parametric studies on cold-formed steel elements.
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The objective of this paper is to provide a review of the development and current progress in the Direct Strength Method for cold-formed steel member design. A brief comparison of the Direct Strength Method with the Effective Width Method is provided. The advantage of methods that integrate computational stability analysis into the design process, such as the Direct Strength Method, is highlighted. The development of the Direct Strength Method for beams and columns, including the reliability of the method is provided. Current and ongoing research to extend the Direct Strength Method is reviewed and complete references provided. The Direct Strength Method was formally adopted in North American cold-formed steel design specifications in 2004 as an alternative to the traditional Effective Width Method. The appendices of this paper provide the Direct Strength Method equations for the design of columns and beams as developed by the author and adopted in the North American Specification.
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