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This paper describes a parametric study addressing the resistance of U‐profiles (channel profiles) subject to bending and torsion to lateral torsional buckling. In case of U‐sections, the torsional moment results, in the majority of cases, from an unavoidable eccentricity of the applied load from the shear centre. The behavior and resistance of the studied members is addressed through a parametric study based on a numerical model validated with laboratory tests. This study is divided into two parts. First, U‐sections subject to bending only are studied in order to provide a method for this reference load case. In particular, the non symmetric stability behaviour of this type of section will be highlighted. Based on the numerical results an adaption of the European buckling curves is proposed. Then, the members are studied under combined bending and torsion. Existing design methods applicable to I sections are extended in order to account for the specific behaviour of U sections. [ABSTRACT FROM AUTHOR]

In practice, welded I‐members of steel buildings are usually made of flanges that are either wide hot‐rolled plates, or plates longitudinally divided using flame‐cuts. The residual stresses distributions resulting from both types of fabrication process are substantially different. However, the Eurocode 3 buckling design resistance of a welded I‐member in compression assumes hot‐rolled flanges, thus neglecting the beneficial impact of flame‐cuts. A parametric study is then performed regarding the out‐of‐plane flexural buckling of welded members made of flame‐cut flanges. 377 doubly symmetric members either with a uniform or a tapered cross‐section are studied. These numerical results are firstly employed to evaluate the safety and accuracy of the Eurocode 3 rules for such members by computing partial factors. The current rules proving overly conservative, two proposals are made for welded columns made of flame‐cut flanges. A first simple proposal suggests a more favorable buckling curve. A second proposal introduces an imperfection factor depending on the cross‐sectional height‐to‐width ratio. Partial factors computed for both proposals are satisfactory, the second proposal being more precise. [ABSTRACT FROM AUTHOR]

Eurocode 3 design rules for the lateral stability of welded I‐members are based on the assumption of hot‐rolled flanges. In practice, a large amount of welded I‐section members is made of flame cut flanges. However, residual stresses of hot‐rolled and flame‐cut flanges are quite different. The latter are more favourable with respect to out‐of‐plane buckling. The beneficial effect of flame‐cuts commonly performed at the flanges tips is then neglected in design standards. A literature review of lateraltorsional buckling tests on welded I‐members with flame‐cut flanges highlights a scarcity of results on mono‐symmetric and/or non‐uniform members. In addition, tests are generally performed on stocky cross‐sections while welded members are usually slender. Lateral‐torsional buckling tests have thus been conducted on four S355 slender welded members made of flame‐cut flanges: two uniform beams and two tapered beams. Within both couples of beams, one had a doubly symmetric cross‐section, the other one being mono‐symmetric. Experimental results highlight the impact of tapering and/or increasing the compression flange thickness whatever the beam type. These experimental tests are then modelled with shell finite elements considering imperfections, residual stresses and material laws measured experimentally. The results are in good agreement with experimental tests. Additional finite element analyses are performed varying the residual stresses distribution. A significant impact of the flange fabrication process is confirmed, flame‐cuts increasing substantially the lateral‐torsional buckling resistance. [ABSTRACT FROM AUTHOR]

In the framework of the revision of Eurocode 3, Part 1–1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow chart connecting the global analysis (first or second order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been conducted across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side. For example, a new formulation for lateral–torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3, Part 1–1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This article presents in a systematic way the new implementations in the formal vote version FprEN 1993‐1‐1 of the code. [ABSTRACT FROM AUTHOR]

In the framework of the European RFCS project ANGELHY, the resistance of built‐up members fabricated from angle sections is studied, amongst others. This paper focusses on the resistance of back‐to‐back connected angle sections. The studied built‐up members are connected through bolted packing plates. Due to the flexibility of this connection, the back‐to‐back connected members do not fully act as a single homogeneous member but the connection stiffness has to be accounted for. However, Eurocode 3 does not provide a clear and generally accepted method for the determination of the buckling resistance of back‐to‐back connected members that do not respect a limit distance of 15imin between the packing plates. This limit is very low and therefore there exists a need of a design method overcoming the limitations. Throughout this paper, a design method will be derived based on a comprehensive numerical study. The numerical model is based on solid finite elements and has been validated with physical tests. Owing to the use of solid elements, it is possible to model explicitly the bolts, the packing plates and all contact regions. [ABSTRACT FROM AUTHOR]

The residual stress distribution influences substantially the stability behavior of steel members. Its shape, directly impacted by the fabrication process, is very different in hot‐rolled and welded members. Among welded members, flame‐cut flanges and hot‐rolled flanges are commonly employed in practice. However, buckling curves of Eurocode 3 are based on experimental tests and numerical simulations performed on welded members having hot‐rolled flanges only and lead to conservative results comparatively to the previous French design standards but also to hot‐rolled members. Investigations are strongly needed to adapt the existing buckling curves to welded members using flame‐cut flanges and a first step is to estimate the residual stress distribution in such members. The results available in the literature dealing with residual stresses measurements in welded members with flame‐cut flanges investigate stocky profiles that can be far from common practice, welded members being preferably slender sections. This paper presents the results of an experimental campaign on residual stresses performed on eight slender welded members varying the flange width and thickness as well as the flange type : hot‐rolled or flame‐cut. The measurements were performed using the sectioning method. A new model for residual stress distribution in welded I‐section members with flame‐cut flanges is then proposed based on these tests results and existing data from the literature. [ABSTRACT FROM AUTHOR]

In the framework of the revision of Eurocode 3 Part 1‐1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow‐chart connecting the global analysis (1st or 2nd order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been carried out across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side. For example, a new formulation for lateral torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3 Part 1‐1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This paper presents in a systematic way the new implementations in prEN 1993‐1‐1. [ABSTRACT FROM AUTHOR]

In practice, the elastic lateral‐torsional buckling of doubly symmetric I‐section steel members is analyzed assuming free warping at supports. However, welded stiffeners, bolted end‐plate connections or column base plates maintain elastically the opposite flange out‐of‐plane rotations and thus induce substantial warping restraints. This paper proposes analytical formulations for the evaluation of the elastic critical bending moment for lateral‐torsional buckling of beams taking into account warping restraints at supports. Assuming series of displacement and rotation fields containing one or two terms, the energy method permits to derive expressions of the critical bending moment under constant and linear distribution of the bending moment. A single expression of the warping coefficient kw is proposed whatever the shape of the bending moment diagram. The factor C1 can be conveniently calculated by multiplying two coefficients that depend on the shape of the bending moment diagram and on the warping restraint stiffness, respectively. Finite Elements analyses of beams with warping restraints at supports have been performed considering a beam element model developed with LTBeamN and a shell element model created in ANSYS. The analytical model is in good agreement with the numerical results obtained by the two finite element models. [ABSTRACT FROM AUTHOR]

This paper focusses on the buckling resistance of compression members made of back‐to‐back connected angle sections. The studied built‐up members are connected through bolted packing plates. Due to the flexibility of this connection, these members generally do not fully work as a single member but the connection stiffness has to be accounted for. In Eurocode 3 Part 1‐1 it is currently admitted to neglect the effect of the connection stiffness if the packing plates possess a maximum distance of 15 imin (imin is the minimum radius of gyration of one individual angle section, also called "chord"). Elsewise the influence of the packing plates on the member resistance should be accounted for. The limit distance of 15imin appears to be much lower than the past practice, consequently leading to a more conservative design and a complexification of the fabrication. This paper therefore presents a sensitivity analysis focusing on the influence of several parameters as: the distance of packing plates, the presence of clearance in bolt holes and the influence of preloaded bolts. These parameters are studied with a numerical model based on solid finite elements. Owing to the use of solid elements, it is possible to model explicitly the bolts, the packing plates and all contact regions. [ABSTRACT FROM AUTHOR]

Lattice towers are extensively built in Europe and worldwide to serve telecommunication or power transmission purposes. The structural members of such towers are frequently made of equal leg angle sections that are often preferred to tubular sections due to their easy connection that results in a simple erection, a requirement set by most telecommunication or power providers. Angle sizes range from light to heavy sections with leg lengths up to 300 mm for towers with significant height. Towers, especially telecommunication ones, may need to be strengthened due to the fact that, during the design life, heavier or larger antennas resulting in a heavier wind loading may be installed. As an alternative to conventional methods, hybrid strengthening of tower angle members with carbon fiber reinforced polymers (CFRP) strips may be employed. The present paper provides an overview of ANGELHY, an RFCS‐funded research project that comes toward its end. The scope of the project is the establishment of analysis methods for lattice towers and the development of design rules for steel and hybrid angle sections, as well as built‐up members composed of angles. [ABSTRACT FROM AUTHOR]

This two‐part article gives an overview of the developments of the structural member verification in prEN 1993‐1‐1:2020 "Eurocode 3: Design of steel structures – part 1‐1: General rules and rules for buildings", one of the second generation of Eurocodes. These developments were undertaken by Working Group 1 (WG1) of Subcommittee CEN/TC250/SC3 and by Project Team 1 (SC3.PT1) responsible for drafting the new version of EN 1993‐1‐1. In the past, WG1 collected many topics needing improvement, and the systematic review conducted every five years also yielded topics needing further development. Based on this, the current version of EN 1993‐1‐1 has been developed into a new draft version prEN 1993‐1‐1:2020 enhancing "ease of use". The technical content of this new draft was laid down at the end of 2019. Many improvements to design rules have been established with respect to structural analysis, resistance of cross‐sections and stability of members. This two‐part article focuses on member stability design rules and deals with the basis for the calibration of partial factors, the introduction of more economic design rules for semi‐compact sections, methods for structural analysis in relation to the appropriate member stability design rules, new design rules for lateral torsional buckling plus other developments and innovations. This second part of the article is dedicated to illustrating the most relevant changes to member buckling design rules. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To study in an in vitro model of erythrocytes exposed to free radicals the effects of hyperosmolarity and hypoosmolarity on the induced potassium efflux and hemolysis. Design setting: Erythrocytes were separated from plasma and suspended in 3 different phosphate buffer solutions (HYPO, ISO, and HYPER) containing, respectively, 100, 150 and 200mmol/l of Na. Free radicals were generated from 2,2′-azobis(2-amidinopropane) hydrochloride (AAPH). Potassium efflux (flame photometry) and hemolysis (Drabkin method) were measured. Measurements were expressed in % (versus total) and area under % versus time curves were calculated (%min). An ANOVA was used for statistical analysis. Results: In presence of AAPH, hemolysis was significantly greater in HYPO (732.45±40%min) and lower in HYPER (578.97±15%min) as compared to ISO (608.30±42%min). Potassium efflux was significantly increased in HYPER (7508.04±85%min) as compared with HYPO (5308.74±62%min) and ISO (6561.39±62%min). Discussion: Our data suggest that hyperosmolarity increases the resistance of the red blood cells when exposed to free radicals as shown by the decreased hemolysis. In such conditions, the potassium efflux analysis appears to be inappropriate to evaluate the free radical effects on erythrocytes. [Copyright &y& Elsevier]