bluuebunny/crossref_metadata_2025 huggingface dataset:
04.10: Analysis of stiffened curved panels in compression: A preliminary numerical study for experimental tests
Authors: Piculin Sara , Sinur Franc , Može Primož
Published: September 2017

The use of different kinds of curved steel panels in bridge design has been increasing in the past few years, but the design recommendations and the knowledge in this field remain scarce. Taking in account the fact that very few experimental tests on life size curved panels have been carried out so far, an experimental study on stiffened and unstiffened curved panels in compression is planned in the near future. For this purpose, a preliminary numerical study on curved panels was conducted, in order to establish an appropriate experimental test setup. This paper deals with a parametric study on stiffened and unstiffened transversally curved steel panels subjected to pure in‐plane compression performing linear buckling analysis (LBA) and fully nonlinear analysis with geometric imperfections (GMNIA). Considering that the shell‐like structures are highly sensitive to initial imperfections, which significantly lowers their ultimate strength, a linear bifurcation analysis is performed first in order to get the buckling modes of the analysed panels. The buckling shapes are later used as equivalent geometric imperfections in the nonlinear analysis, based on the rules given by EN1993‐1‐5. Furthermore, a finite element analysis, considering geometric and material nonlinearity with initial imperfections, is conducted in ABAQUS software. Simply supported, transversally curved and longitudinally stiffened panels are analysed in order to determine their resistance to pure in‐plane compression. A large parametric study is performed to evaluate the effects of different parameters on the ultimate resistance of the panel. Panels that differ in curvature, aspect ratio and stiffness of the stiffeners are studied. Finally, the numerical results of the parametric study on all, the unstiffened, longitudinally stiffened, both curved and flat panels with the same dimensions are compared. Effects of panel curvature on the critical elastic stress and the ultimate resistance are presented.
04.11: Strength enhancement in axially compressed cylinders with stepped walls
Authors: Rotter J. Michael , Al Lawati Hussain
Published: September 2017

Metal silos and tanks are subject to loading that increases progressively from the top to the base of the cylindrical shell. Efficient design calls for progressive increases in wall thickness, but metal sheets are made in discrete thicknesses. For silos, buckling under axial compression is the dominant design condition, whilst in tanks axial compression with internal pressure may also be critical. The step increases in wall thickness mean that the most critical point on the wall is always at the base of one strake of uniform thickness, so the location of a critical buckle is expected to be at or just above a change of thickness. Until now, design rules have always ignored the effect of the thicker lower strake in restraining the axial compression buckle above it, and the requirement for buckles to have a finite size.

Whilst this effect has previously been noted [1,2], it has never been systematically studied. In this paper, a first thorough study is presented, which shows that the strength enhancement associated with a change of plate thickness can be considerable (over 40%). The presented information addresses the buckling of imperfect shells, and includes both elastic and plastic conditions. The findings are sufficient to produce a modification of the current design rules for buckling under axial compression, giving designers the freedom to extend their thin shell segments deeper in the silo or tank structure.
04.12: Analysis of silo supporting ring beams: Resting on discrete supports
Authors: Zeybek Özer , Topkaya Cem , Rotter J. Michael
Published: September 2017

Silos in the form of a cylindrical metal shell are often supported on a ring beam which rests on discrete column supports. The function of the ring beam is twofold. First, it is required to carry circumferential forces to maintain equilibrium at the transition junction between the cylinder and hopper. Second, the ring beam plays an important role in redistributing the majority of the discrete forces from the column supports into a more uniform stress state in the cylindrical wall. The Eurocode EN 1993‐4‐1 [1] only provides design equations for stress resultants produced in the isolated ring beam under uniform transverse loading. This paper explores the extent to which a practical silo shell causes these stress resultants to be reduced when the ring beam has only practical stiffness.

The behaviour of a ring beam which interacts with the silo shell is much more complex than that of an isolated ring beam. In traditional design treatments, it is assumed that the discrete support forces are redistributed entirely by the ring beam to provide circumferentially uniform axial membrane stresses in the silo shell. But this assumption is only even approximately valid if the ring beam is much stiffer than the silo shell [2]. Since the cylindrical shell is very stiff in its own plane, the ring beam that responds with both flexure and twisting must be remarkably stiff to be stiffer than the shell. A ring beam stiffness ratio was previously developed by the authors to find the requirement for the ring beam stiffness to meet this traditional role [2]. This paper presents a new study to explore the ring beam stress resultants when closed section ring beams of lower stiffness and practical dimensions are used. A finite element parametric study is undertaken to explore the stress resultants and displacements in more flexible ring beams connected to a silo shell. The results show that the level of reduction from the isolated ring beam values can be directly related to the ring beam to shell stiffness ratio.
04.16: Rethinking imperfections in tanks and silos
Authors: Knoedel Peter , Ummenhofer Thomas , Rotter J. Michael
Published: September 2017

A careful consideration of imperfections is critical to the design of shell structures to ensure that they are both adequately safe and economically built. Following the development of the Eurocode for shell structures EN 1993‐1‐6, the situation has considerably improved:

the extensive literature on the imperfection sensitivity of shells has been introduced into practical designs;

fabrication tolerance classes have been defined, which allow the designer to adjust his design to the professional efforts of the fabricator; and

numerical and experimental results have been matched by defining an axisymmetrical weld depression as a substitute imperfection in the recent amendment.

These advances seem to have established a very good position, and it might be thought that little more needs to be done. However, a closer look at some of the above items reveals the need to reconsider the management of imperfections, especially from the designers point of view. In this paper the authors attempt to make a first step to resolve the role of imperfections from different points of view. In addition, some unpublished results from researches at KIT are presented.
04.17: Cylindrical shell buckling under a hydraulic constraint: Numerical study
Authors: Sabau Gabriel , Koltsakis Efthymios , Lagerqvist Ove
Published: September 2017

Steel cylindrical shell structures are used in a large variety of civil engineering applications such as off‐ shore platforms, tanks, silos, wind turbine towers, etc. The local stability of such structures and their sensitivity to imperfections is a well‐known problem. In current engineering practice the design method is based on the selection of an imperfection class for the shell and subsequently calculating a reduction factor,χ, to the resistance of the shell. One such methodology is supplied by the EN1993‐1‐6; special conditions are given to pressurized tubes subjected to meridional compression.

Past studies have focused on the stability of cylindrical shells with internal pressure. The stability problem of a long cylinder considering the internal pressure as a simple static load was addressed. Thus, the approaches considered the fluid as compressible.

The purpose of the present work is to investigate numerically the potential benefit of using an incompressible fluid fully enclosed in a circular cylindrical shell. The constraint imposed by the presence of the liquid in the interior of a shell will be referred to as “hydraulic constraint”. As liquids are nearly incompressible, the buckling of a liquid‐filled shell has to satisfy the condition that the integral of all the displacements normal to the shell surface is equal to the volume variation of the contained liquid. The volume variation of the shell interior has to be equal to the dilation of the shell due to liquid pressure increments associated to the onset of geometrical instability. Additionally, the weight of the contained liquid causes additional circumferential tension in the cases of vertically placed cylinders.

The methodology followed is the numerical analysis of cylindrical shells by means of the ABAQUS Finite Element code and a comparison with the methods given in the Eurocode.
05.05: A flexibility‐based element for second‐order inelastic analysis using plastic hinge method
Authors: Du Zuo‐Lei , Liu Yao‐Peng , Chan Siu‐Lai , Tan Wei‐Qi
Published: September 2017

In the past decades, the stiffness‐based elements with plastic hinge method and the flexibility‐based elements with plastic zone method are widely used for second‐order inelastic analysis. The former emphasizes the computational efficiency with relatively less accurate structural responses while the later aims to precisely simulate the structural behaviour but normally needs more computer times. For the member under complex loads, several stiffness‐based elements are generally required to capture its plastic behaviour. In such case, one‐element‐per‐member for member initial imperfection required in second‐order direct analysis is violated. On the contrary, a flexibility‐based element with several integration points is sufficient for material yielding. However, the more integration points associated with fibre section the more computational efforts are needed. It is also noted that the conventional flexibility‐based type elements cannot meet the codified requirements of direct analysis due to lack of consideration of member initial imperfection. In this paper, a new flexibility‐based element equipped with plastic hinge method without huge computational time is proposed for second‐order inelastic analysis. This element is also able to take the member initial bowing into account. Thus, an innovative solution is proposed for routine design. Finally, several numerical examples are used to demonstrate the validity and accuracy of the proposed method.
05.07: Structural behaviour of simple steel beams subject to axial compression, biaxial bending moments and torsion
Authors: Walter Adrian , Herbersagen Julia , Winkler Rebekka , Knobloch Markus
Published: September 2017

European design rules provide simplified design models for steel beams subjected to biaxial bending moments and torsion (e.g. Annex A of EN 1993‐6 [1]). However, these rules do not consider axial forces. This paper presents a combined experimental and numerical study on the structural member behaviour of simple steel beams under axial compression, biaxial bending and torsion. First, an experimental study performed at Ruhr‐Universität Bochum is presented. Secondly, a numerical model is developed and validated with the results of the tests. Next, a numerical parametric study analyses the influence of the cross‐section, member slenderness ratio and ratio of internal forces on the member stability behaviour. The paper uses the results of both the numerical simulations as well as the experimental investigations for reviewing the existing simplified structural models. Finally, the paper develops and proposes a simplified model for simple steel members subjected to combined axial compressive forces, biaxial moments and torsion.
05.12: Effect of initial imperfection on elasto‐plastic behavior of SHS columns under axial force with bending moment
Authors: Mitsui Kazuya , Sato Atsushi , Aoyama Masahiro
Published: September 2017

Steel products which have various characteristic (e.g. high ductility, high yield stress, low yield stress and high weldability) are used as main structures by diversification of demanded application, and technology for steel manufacturing has developed. Because steel square tubular member is processed by cold‐forming and welding in the process of manufacturing, residual stress will exist in the products. Moreover, due to the cold‐forming process, geometrical initial imperfection, i.e., global and local, will exist. These initial imperfection are still remained even so the technology for steel manufacturing is developed. However, effect of the initial imperfection on elasto‐plastic behaviour of square hollow section columns under compressive axial force with bending moment is not clarified. In this paper, firstly, the effect of individual initial imperfection (e.g. initial global imperfection, initial local imperfection or residual stress) on elasto‐plastic performance is investigated independently; comparison between the experimental results are shown. It is shown that initial local imperfection has a significant impact on elasto‐plastic performance. Secondly, the effect of composite initial imperfections is investigated. The amplitude of the local imperfection is the most influential initial imperfection on the deformation capacity of the column, and the deformation capacity decreased with an increase of the amplitude of local imperfection. Validation of the numerical simulation were also performed and recommend values of imperfections are shown.
05.13: Efficient static and dynamic analysis of steel frames by one‐element‐per‐member models
Authors: Liu Si‐Wei , Liu Yao‐Peng , Chen Liang , Chan Siu‐Lai
Published: September 2017

This paper proposes an efficient numerical analysis technique for static and dynamic analysis of space steel frames by one‐element‐per‐member model, considering material and geometric nonlinearities including P‐Δ‐δ effects, large global deflections and member deformations. The curved arbitrarily‐located‐hinge (ALH) beam‐column element is developed for capturing members' behaviours and simulating initial imperfections. Unlike the conventional plastic hinge element requiring two and more elements to capture the locations of plastic hinge along member length, which causes certain difficulties to model member initial imperfections, one proposed element per member is sufficient. The plastic hinges are simulated as gradually softening springs and the corresponding formulae are presented. The additional degrees of freedom in the element are condensed so that it can be easily incorporated into the existing software with dramatic improvement on numerical efficiency and accuracy. The consistent element mass matrix is derived based on the Hermite interpolation function, and the Rayleigh damping model is adopted for representing the system viscosity. Verification examples are given to validate the present model in simulating inelastic yielding and dynamic behaviours of the steel frames and members under loads. One distinct feature of the research is to propose an effective analytical framework using high‐performance elements, dramatically improving the numerical efficiency and making the method being practical.
05.17: Modeling the stiffness reduction conditions of steel beam‐columns
Authors: Rosson Barry
Published: September 2017

The stiffness reduction that results from yielding of the cross‐section due to major and minor axis bending under axial compression and tension conditions is studied in detail for compact wide‐flange sections with an ECCS residual stress distribution pattern. For a given moment (m = M/Mp), axial load (p = P/Py), and residual stress ratio (cr = σr\σy), the distribution of stresses throughout the cross‐section and associated reduced stiffness (τ = EIep/EI) are evaluated using a fiber element model with 2,046 elements. Using increments of m and p of 0.01, detailed three‐dimensional m‐p‐τ surface plots for a given wide‐flange section are used to discuss the various stress states of the cross‐section and associated reduced flexural stiffness. Equations are provided for the m and p conditions around the perimeter of the 3‐D surfaces and for the various conditions at which yielding initiates in the flanges and web. For minor axis bending, figures are provided on the progression through the various stress states as m is increased from the initial yield point up to the fully plastic state for the axial compression conditions of p = 0.2 and 0.75. The m‐p‐τ surface plots are used to develop material models for direct implementation in MASTAN2. To study the effects of simplifying the 3‐D surface plots using a linear variation of stiffness between the initial yield surface and fully plastic conditions, the El‐Zanaty portal frame is modeled using MASTAN2 with p = 0.4 and 0.6 to compare the maximum lateral load and deflection results with published results. Discussion and recommendations are provided regarding the development and use of the m‐p‐τ surface plots for research and design purposes.
05.23: Optimal prestressing of triple‐bay prestressed stayed columns
Authors: Yu Jialiang , Wadee M. Ahmer
Published: September 2017

A nonlinear finite element model of the triple‐bay prestressed stayed column is developed within the commercial software ABAQUS. A linearly obtained ‘optimal prestress’ that maximizes the critical buckling load is investigated since this quantity has been demonstrated in previous work on single‐bay prestressed columns to provide a lower bound to the actual maximum load carrying capacity when compared to results from physical experiments and nonlinear modelling. The ratio of the crossarm to column length, the diameter of the cable stays and the ratio of the prestressing force to the linear optimal prestress are varied. Measures for the relative cost of the main column and the stays are defined and it is determined that the true optimal prestress is generally higher than the linearly obtained quantity but by a reduced factor when compared to an equivalent study for the single‐bay column case.
05.24: New interaction formulae for sensitive structures to the second order effects
Authors: Mercier Charlotte , Khelil Abdelouahab , Pamies Alain
Published: September 2017

Eurocode 3 Part 1‐1 [1] gives a method to calculate the design criterion of a structure without include the imperfection in the model structure. This criterion enables to take into account the imperfection mainly with the buckling coefficient χ. However, we can highlight that the results obtained with this criterion (interaction formulae for beam‐column) are overestimated compared to the results obtained when the imperfection where included in the model structure. This difference comes from the coefficient χ which is overestimated.

In order to overcome this problem, a new coefficient definition has been established in order to take into account the imperfection in the calculation without include it in the model structure. This new coefficient enables to take into account the charge level of the structure. First, vertically loaded structures have been studied. Then the study is extended to the vertically and horizontally loaded structures. The study results are more close to the actual results. Thus, this new coefficient enables to substitute for the establishment of an initial imperfection both a safe and a reasonable assessment of stress rate.
05.27: Resistance of mono‐axially bent beams of welded I‐sections: FEM verification of Eurocode's buckling curve formulation
Authors: Giżejowski Marian Antoni , Szczerba Radosław Bronisław , Gajewski Marcin Daniel
Published: September 2017

Present Eurocode's approach to design of steel I‐section beams is based on the analytical resistance evaluation yielding from the interaction resistance criteria established for beam‐columns that cover two design situations: a) the flexural in‐plane failure (second order biaxial bending and compression), and b) the flexural‐torsional out‐of‐plane failure (second order spatial bending, warping torsion and compression). The Eurocode's unified resistance ultimate limit state criteria of I‐sections are depended upon the technological aspects of steel section production via the buckling curve differentiation for the evaluation of reduction factors for buckling in compression and lateral‐torsional buckling in bending about the major axis. This paper attempts to verify the Eurocode's buckling resistance criteria in case of welded I‐section in mono‐axial bending on the basis of finite element simulations and on the separate inclusion of material and geometrical imperfections. The finite element shell model is utilized and built within the ABAQUS software. The Eurocode's resistance criteria are verified by results of FEM simulations in case of moment gradient loading conditions. Concluding remarks in relation to analytical formulations presented in Eurocode 3 are drawn.
05.29: Interaction curves for local and distortional buckling of polygonal tubes in combined torsion and axial loading
Authors: Rendall Morgan A. , Hancock Gregory J. , Rasmussen Kim J.R.
Published: September 2017

This paper investigates the interaction of uniform axial loading (compressive or tensile) and uniform torsion on the linear elastic buckling behaviour of long tubes with regular convex polygonal cross‐sections. The analyses pertain to tubes of sufficient length such that the results are independent of end boundary conditions. Using the generalised constrained finite strip method (cFSM), pure local buckling is examined for triangular through octagonal tubes. The interaction curves for pure local buckling are akin to those previously generated from the exact finite strip method and a square and octagonal tube are analysed in‐depth to assess the changes in interaction behaviour as the number of sides in the section is increased. The pure distortional buckling behaviour is examined for pentagonal through octagonal tubes using recent developments in Generalised Beam Theory (GBT) and an almost linear interaction between torsion and compression is found, as has been noted previously for circular tubes. The distortional interaction curves are essentially identical for all analysed tubes.
05.35: Extended design method for in‐plane stability of haunched sway portal frames
Authors: van Hove B.W.E.M. (Dianne) , Snijder H.H. (Bert) , Hofmeyer Herm , Altinga Noud
Published: September 2017

In current design rules the effect of a haunch on the sway in‐plane stability of a steel portal frame only takes into account the influence of the haunch dimensions on the beam‐to‐column connection strength and stiffness. The effect of the haunch dimensions on the beam behavior, and thus on the frame behavior, is not included. The paper describes the effect of this phenomenon by regarding current design methods and comparing these with analytical solutions. The validity of the methods is covered by numerical simulations.

For a vertical beam loading, the larger the span of the portal frame, the higher the compressive force in the beam becomes. In addition, the longer the span of the frame, the smaller the critical buckling load of the beam becomes. This decreases the stability of the overall frame significantly. In fact, the compressive force in the beam of a portal frame has a significant effect on the additional stiffness the haunch provides to the column. Due to the adjusted center line of the haunch causing an eccentricity, an additional first order moment is generated. This additional internal moment reduces the additional stiffness the haunch provides. For some spans this may even cause the additional stiffness of the haunch to be negligible.

The research has given more insight, also on the effect of the shift of the compressive force in the beam, which depends on the geometry of the haunch. The study resulted in two simple correction factors for the current design rules, where these correction factors cover amplification factors for the original stiffness of the beam. The factors depend on the kind of loading (point load or equally distributed load) and on the haunch to rafter ratio (with regard to the length of the haunch as well as with regard to the height of the haunch).
05.36: An efficient approach to limiting the elastic range in advanced analysis of steel structures via RPHM
Authors: Lemes Ígor José Mendes , Barros Rafael Cesário , Batelo Everton André Pimentel , da Mota Silveira Ricardo Azoubel
Published: September 2017

Over the years many research on the nonlinear behavior of steel structures has been made. The Refined Plastic Hinge Method (RPHM) is a fast and accurate alternative to simulate, in concentrated form, the plasticity of the structural systems materials. In recent studies, there was a loss of accuracy in the analysis of steel structures under minor axis bending, in the conventional method of RPHM where pseudo‐springs are used at the ends of the elements to simulate the flexural stiffness degradation. In this approach, the pseudo‐springs at the finite elements ends have infinite stiffness in elastic range, with gradual loss of stiffness in elastoplastic stage and a null stiffness in plastic range. For the methodology adjust to this issue, the fictitious springs were replaced by the tangent modulus of elasticity of the material and presented as a viable solution. In this paper, we propose the study of the interaction curves behavior for application in RPHM with pseudo‐springs, considering the bending around major and minor axes of inertia, with a greater focus to RPHM using the tangent Young's modulus. The Strain Compatibility Method (SCM) is used, which through a nonlinear procedure, the moment‐curvature relationship is defined allowing to obtain the exact point where the cross section starts the yield process. Thus, it is possible to trace the initial yield curve realistically minimizing simplifications. The residual stresses models of AISC‐LRFD e ECCS for I sections will be used. The results will be compared with numerical and experimental data available in the literature.
05.40: Warping constant equations for hot rolled steel channel sections
Authors: Zhang Ailin , Zhang Qingfang , Jiang Ziqin
Published: September 2017

The warping constant is one of the most important section properties for the buckling behaviour of structural members. The formulas for section warping constants are usually based on the middle line mode, and the flange slopes as well as the flange‐to‐web fillets are neglected. In this paper, 32 standard C shapes from the AISC manual were used as examples. They are drawn in AUTOCAD according to their real dimensions, and then the files are imported into ANSYS to calculate the sections' properties. It is found that the warping constants listed in the AISC manual are overestimated by about 26%. Taking the flange slope into account, a new expression of the warping constant for C shapes is presented. After a simple modification, the overestimated margin can be limited to about 5% using this new equation.
06.07: Comparison of Blast Performance of Steel Modular Buildings with Anchored and Sliding Foundations
Authors: Erkmen Bulent
Published: September 2017

A two‐module blast‐resistant steel building with overall dimensions of 12 m by 6 m floor plan and 3.4 m height was designed to resisted 80 kPa free field overpressure with 140 microsecond duration. The building was designed to remain within “high damage/response” level when it is anchored to its foundation. The effect of anchored and unanchored or sliding (free‐to‐slide) foundation on blast performance of structural elements on the wall and roof, foundation loads, building sliding, and building total friction and kinetic energy were investigated using nonlinear dynamic finite element analysis tools. The comparison of analyses results revealed that building foundation reactions and maximum deflection demands for structural members can significantly decrease with unanchored foundation. For unanchored foundation, several friction coefficients (i.e., 0.2, 0.5, and 0.8) for the interaction between the building and its foundation were considered. The analyses results show that the maximum relative deflections of the structural members of the building with unanchored foundation to be between 43% and 120% with an average of 80% of that for the building with anchored foundations. The most significant effect of unanchored foundation on blast performance of the building was the significant decrease in the foundation maximum horizontal reaction, which was approximately 15% to 60% of that for the building with anchored foundation. However, the unanchored foundation had negligible effect on building vertical foundation reactions. The computed maximum sliding displacements were approximately 10 m, 2 m and 0.3 m for the building with unanchored foundation for friction coefficient of 0.2, 0.5, and 0.8, respectively. For the building with unanchored and anchored foundations, both friction energy and kinetic energy versus time plots were very similar for initial stages of the blast loading. The overall results show that providing even limited permissible sliding between blast resistant structures and their foundation can significantly reduce their foundation reactions and improve blast performance of structural members. A controlled‐sliding mechanism between blast resistant structures and their foundation with steel cables is recommend to improve blast performance of the structure while limiting maximum sliding within desired permissible limits.
07.01: New developments in the Direct Strength Method (DSM) for design of cold‐formed steel sections under localised loading
Authors: Nguyen Van Vinh , Hancock Gregory J. , Pham Cao Hung
Published: September 2017

A consistent and simplified Direct Strength Method (DSM) for design of cold‐formed (or thin‐walled) sections under localised loading, which is called web crippling, is proposed. The development of this method proposes generalised equations for design of thin‐walled sections under the four different localised load cases which are the interior one‐flange (IOF), the end one‐flange (EOF), the interior two‐flange (ITF) and the end two‐flange (ETF). The same parameters are used in the DSM equations for both the IOF and EOF load cases. However, the ITF and ETF load cases require different parameters in the DSM equations to predict the capacities of structural members. The equations contain both an inelastic reserve component and a yield load component which are different from those proposed previously in this regard.

This paper briefly introduces the calculation of the buckling load and the yield load. From these two main input variables, DSM equations are used to determine the capacities of structural members under localised loading. Calibration is performed against all available experimental data to validate the accuracy of the DSM predictions.
07.02: Distortional‐global interaction in lipped channel beams: Part I: Mechanics and elastic behaviour
Authors: Martins André Dias , Camotim Dinar , Gonçalves Rodrigo , Dinis Pedro Borges
Published: September 2017

This work aims at presenting and discussing Generalised Beam Theory (GBT) numerical results concerning the elastic geometrically non‐linear behaviour of simply supported lipped channel (LC) beams under uniform major‐axis bending and experiencing distortional‐global (D‐G) interaction, making it possible to shed fresh light on the mechanics underlying this coupling phenomenon. Two LC beams geometries are considered, each exhibiting a different type of D‐G interaction, namely (i) “true D‐G interaction” (close global, McrG, and distortional, McrD, critical buckling moments), containing three critical‐mode initial geometrical imperfection shapes (two global, due to the lack of symmetry, and one distortional) and (ii) “secondary global‐bifurcation interaction – SGI” (McrD«McrG), containing a critical‐mode distortional initial imperfection. In order to clarify the surprising behaviour of the beam undergoing a SGI, an additional beam is analyzed, deemed to exhibit a “pure” distortional post‐buckling behaviour. The GBT results provide the evolution, along given equilibrium paths, of the beam deformed configuration (expressed in modal terms), relevant displacement profiles and modal participation diagrams. The knowledge acquired has visible impact on the development of rational design rules for CFS beams affected by D‐G interaction, a topic addressed in a companion paper.
07.05: Fatigue life assessment of cold‐formed steel roof battens
Authors: Kathekeyan Myuran , Mahendran Mahen
Published: September 2017

Metal roofs of low‐rise buildings are exposed to highly fluctuating and prolonged suction wind uplift pressures during cyclones. The high suction pressures on roofs lead to premature, low cycle fatigue failures of roof members. Steel roof batten made of thin, high strength cold‐formed steel (CFS) is one of the vulnerable roof members that fails prematurely during cyclones. Pull‐through failure in the vicinity of batten to rafter connection is one of its common failure modes. A preliminary study on this topic revealed that the fatigue pull‐through capacity of a commonly used industrial roof batten is 45% of its static pull‐through capacity. Therefore, in order to assess the fatigue capacity and performance of all available CFS roof battens, a series of constant amplitude cyclic tests was conducted on thin‐walled steel roof battens. Critical parameters which influence the pull‐through failure, such as the steel batten grade, thickness and screw fastener diameter, were considered in the test series. S‐N curves were developed for each combination of the selected critical parameters, and the respective fatigue limits were obtained. Test results led to a simple modification to the recently developed static pull‐through capacity equations in order to include the effects of fatigue. They also improved the understanding of the fatigue behaviour of roof battens. In addition, a series of multi‐level cyclic tests was included in this study to investigate the suitability of the currently available Low‐High‐Low (LHL) cyclic test method. This paper presents the details of this study, and the results.
07.10: Elastic buckling strength of light‐gauge built‐up member from lipped C‐section under compression
Authors: Takahashi Daimu , Ikarashi Kikuo , Kobashi Tomoki
Published: September 2017

In a cold‐formed steel structures, the plate thickness is thin. Therefore, plates can be connected by drilling tapping screws, or similar processes. Cold‐formed steel structures differs from conventional steel frames in that cold‐formed steel structures does not require welding. This construction method is simple and has excellent workability. In addition, cold‐formed steels can be used in built‐up members having various cross‐sectional shapes by connecting. In particular, built‐up members formed by lipped channel sections are widely used as vertical frame members, because they have a large bending stiffness relative to their cross‐sectional area. The built‐up member that joins the cold‐formed steels back‐to‐back with drilling tapping screws is one among them. When designing a built‐up compression member, it is important to understand the effect of spacing between interconnections and boundary conditions. However, it is not clear whether the connection interval of chord members affects the elastic buckling strength. Therefore, the spacing of connection is given an upper limit. In addition, previous studies have assumed that the cross section of the end is uniformly compressed. Accordingly, other boundary conditions have not been considered. This study considers steel with a thickness of less than 2.3 mm and discusses how spacing between interconnections and boundary conditions influence the elastic buckling strength.
07.12: On the design of cold‐formed steel beams with holes in shear using the direct strength method
Authors: Pham Song Hong , Pham Cao Hung , Hancock Gregory J.
Published: September 2017

The Direct Strength Method (DSM) design rules for cold‐formed steel members in shear have been incorporated recently into the North American Specification for the Design of Cold‐Formed Steel Structural Members (AISI S100‐12) and are being implemented in the Australian Cold‐formed steel structures standard (AS/NZS 4600:2005). Recent studies have shown that the DSM can be used for beams with web openings subjected to shear by modifying the shear load at buckling (Vcr) and shear load at yielding (Vy) to include the influence of openings. This paper presents a buckling study on cold‐formed steel beams with various aspect ratios and with a wide range of web opening locations and sizes using the Finite Element Method (FEM) in order to determine Vcr. An artificial neural network (ANN) is then applied to learn and establish the relationship between the relative geometrical dimensions of perforated members and the shear buckling coefficients (kv). As a result, a simple equation is derived to approximate kv, which is used as input to the modified DSM design equations.
07.13: On extending the direct strength method to the design of cold‐formed steel built‐up columns
Authors: Abbasi Mandana , Khezri Mani , Rasmussen Kim J. R.
Published: September 2017

This paper presents a numerical investigation of the effects of discrete fasteners on the buckling behaviour of cold‐formed steel (CFS) built‐up columns and concludes with the assessment of the applicability of the current direct strength method (DSM) to the design of these members. To this end, the compound strip method is first utilised to accurately model the buckling behaviour of CFS built‐up columns under axial compression via introducing connecting elements to represent the contribution of discrete fasteners. A series of elastic buckling analyses with different levels of composite action are carried out to obtain the “signature curves” corresponding to the considered CFS built‐up sections. The performed studies comprise of variations in cross‐sections, end boundary conditions and fastener spacing. Utilising the developed numerical techniques, the ultimate strength of the sections are estimated and an adjustment procedure is suggested to extend the current DSM equations to the design of CFS built‐up columns. The proposed adjustment is verified against the existing experimental data and shown to be capable and accurate in capturing the expected behaviour of CFS built‐up members with or without stiffeners.
07.15: Experimental and numerical investigation of cold‐formed steel built‐up stub columns
Authors: Meza Francisco , Becque Jurgen
Published: September 2017

This paper describes a numerical and experimental programme carried out at the University of Sheffield on built‐up stub columns fabricated from cold‐formed steel. A total of 20 built‐up columns with four different cross‐sectional geometries were tested between fixed end conditions. Two of the cross‐sectional geometries were assembled using M6 bolts and the other two using M5.5 self‐drilling sheet metal screws. The connector spacing was varied among specimens of the same cross‐sectional geometry. The cross‐sections were assembled from flat plate, plain channels and lipped channels with nominal thicknesses ranging from 1.2 mm to 2.4 mm. The initial geometric imperfections of each specimen were recorded prior to testing and their material properties were determined by means of tensile coupon tests. Single lap shear tests were also carried out in order to study the connector behaviour of the bolts and the screws used to assemble the specimens.

As part of the numerical part of the study, the test specimens were modelled using the commercially available ABAQUS software package. The recorded geometric imperfections, the measured material properties and the connector behaviour data obtained from the lap shear tests were incorporated into the FE models. Special attention was paid to the connector modelling in order to find an effective and simple way to represent their actual behaviour. The FE models were further used to quantify the effect of the connector behaviour on the buckling response of cold‐formed steel built‐up stub columns.
07.24: Behaviour of gypsum sheathed cold‐formed steel stud walls under lateral loadings
Authors: Selvaraj Sivaganesh , Madhavan Mahendrakumar
Published: September 2017

Gypsum board is a common sheathing material for a steel wall panel systems being used with cold‐formed steel (CFS) studs. However, the effect of sheathing material to the panel system is under study by many researchers. Therefore, an experimental investigation was carried out to investigate the behaviour of CFS wall studs studs under flexural loading. A total of 24 full scale single stud panels were tested on unsheathed and both side sheathed panels. The parameters studied were C channel dimensions, sheathing thickness and fastener spacing. The experimental results were compared with the design specifications of AISI and found to be conservative.
07.30: Ways of improving the stability design calculations of cold‐formed columns
Authors: Belyy Grigoriy , Kuznetsov Aleksei
Published: September 2017

The article presents the theoretical basis of engineering approach to the stability resistance calculation of cold‐formed columns subjected to an axial or eccentric compression. The research is based on an analytical stability solution and Eurocode provisions in terms of determining the reduced cross‐section in a combined action loading. It is demonstrated, that the reduced cross‐section, defined by the limit state of the column without reduction, in most cases has sufficient accuracy for engineering practice. Taking this assumption into account the engineering algorithm is designed for stability calculations by: flexural mode relatively the major axis; flexural‐torsional mode relatively the minor axis and overall mode. The results of stability calculations are demonstrated on examples of pin‐pin end restrained cold‐formed columns with high degree of section reduction. Stability resistance coefficients depending on column slenderness and load eccentricities are given. The degree of reduction influence on the overall stability is highlighted. The comparison with Eurocode results and authors experimental studies is also given.
07.32: The flexural strength behavior of profiled steel sheet – with hot rolled plate panel system with bolted connection
Authors: Govindan Senthil kumar , Madhavan Mahendrakumar
Published: September 2017

An investigation on a new lightweight floor system using cold‐formed steel (CFS) sheet connected to the hot rolled steel (HRS) plate by bolts were carried out in the present study. A total of 18 numbers of specimens with varying lengths (short, moderate and long), bolt spacing (L/4, L/6 and L/8) and thickness (0.45mm; 0.45mm + 0.45mm) of CFS trapezoidal sheet were studied in three‐point bending to understand the moment carrying capacity and flexural behavior (deflection, stiffness and rotation) for composite panels in two phases. Phase I was based on single trapezoidal CFS sheet whereas the phase II was based on doubling the thickness by nesting (placing one sheet on top of another) two sheets together. The test results indicate that entire phase II specimens attained 50% to 80% higher ultimate load compared to phase I specimens. Moreover, significant increase in stiffness observed in all the phase I and phase II specimens with a decrease in spacing between the bolts. In general, it can observed that moderate length (1200 mm, l/d = 29.4) specimens was attained maximum moment carrying capacity compared to shorter (700 mm, l/d =14.7) and longer (1700 mm, l/d = 44.1) specimens. In addition, the mode of failure changed from local bending to tearing of CFS sheet under the maximum moment region with increase in span length.
08.03: Mechanical model to predict the resistance of the shear connection in composite beams with deep steel decking
Authors: Odenbreit Christoph , Nellinger Sebastian
Published: September 2017

The resistance of a typical shear connection with headed shear studs in a composite beam is analysed in the normal case in accordance with EN 1994‐1‐1. The reducing effect of a trapezoidal metal decking onto the ultimate load bearing capacity is considered with empirically derived reduction factors and equations, which have been developed in the last century between the late 70th and the early 80th. The RFCS research project “DISCCO” [1] investigated the shear stud resistance with novel types of steel decking. In many cases, the shear resistance, which was predicted by EN 1994‐1‐1 [2] was not reached in tests.

In the respective experiments with composite beams and deep decking, a concrete cone failure mode was identified and not a pure shear failure of the stud. This failure mode acted in combination with the load bearing capacity of the shear stud, which formed one or two plastic hinges in the shaft – depending on the available geometry.

Based on these observations, new equations have been developed to predict the shear connection's resistance with more accurcy. The yield hinge mechanism of the shear stud, which was developed by Lungershausen [3], was extended by the above mentioned load bearing component ‘concrete cone’. The formulae consider the geometry of the stud and the steel decking, the material strength of the stud and of the concrete material. The statistical evaluation of the developed equations shows a good accordance with test results.
08.10: Experimental study of ferritic stainless steel composite slabs
Authors: Lauwens Kathleen , Douchy Jonas , Fortan Maarten , Arrayago Itsaso , Mirambell Enrique , Van Gysel Ann , Rossi Barbara
Published: September 2017

Steel‐concrete composite floors are commonly used in construction due to their favourable weight‐to‐depth ratio and erection time. Typically, concrete is poured onto a galvanised steel deck acting as formwork. However in case of floors exposed to corrosive environments, stainless steel is likely to be chosen over galvanised steel. Besides its better corrosion resistance, stainless steel also offers desirable aesthetic appearance and good mechanical properties. Composite slabs can fail in bending, vertical shear or longitudinal shear. The latter failure mode is the most common, and its prediction depends on values obtained through full‐scale tests. However, for stainless steel decks, no specific treatment exists in current design standards. This paper investigates the longitudinal shear resistance of stainless steel composite slabs through an experimental study. One short and three long span slabs, made using a Cofraplus 60 ferritic EN1.4003 stainless steel corrugated deck, are tested in accordance with Eurocode 4, annex B.3 [1]. The Partial Shear Connection (PSC) method is used to assess the longitudinal shear resistance. The experimental results together with the results provided in [2] are used to draw conclusions on the applicability of ferritic stainless steel decks in composite floors.