The author is grateful to Dr. Bedair for the time and effort taken to review the noted paper and his many deep and insightful comments. On the other hand, these comments help us understand why, to this day, there is no method for torsional strength analysis in the Canadian steel design standard, CSA S16 (CSA 2001) and no clearly laid plans to introduce one. The leading reason is the lack of appreciation by the standard-developing and academic community that this method is indeed necessary. It is believed that torsion in steel shall be avoided, rather than designed for, and that by following the principles of prudent design it is possible to eliminate torsion in all practical situations. The publication of this paper is the statement by the author, as a practicing design engineer, that torsional cases are widespread and important enough to justify the development of a design method. The examples of torsional loading provided in the paper are taken from real industrial projects in which the author has participated. These cases often occur in modernization projects on existing facilities where the designer may not be at liberty to place the column in the logical place to avoid torsion. Even in new facilities, the placement of miscellaneous equipment and small-bore piping may occur when the plant layout is already completed and major objects placed earlier may create an obstruction for the subsequent minor supports.
This technical note considers weak axis moment capacity of wide-flange steel members of different section classes. In CSA S16-01 Limit states design of steel structures, there is a disconnect in moment capacity of laterally supported members between Classes 2 and 3: when the section crosses the Class 2 boundary, its calculated capacity drops in the ratio of the elastic to plastic section modulus. This effect is relatively minor for strong axis bending but is rather significant for weak axis bending. A rational theory is presented that explains the phenomena on the transition of the two Classes and proves that the noted gap in the design capacity does not exist. An improved design formula is proposed to mitigate this problem.Key words: bending, class, flange, local buckling, steel beams, strong axis, weak axis.
This paper addresses the design of wide-flange steel members subjected to torsional forces as well as axial forces and moments about their strong and weak axes. The current Canadian steel design standard (CSA S16-01) gives no specific guidance on methodology with respect to torsional design. Codes of other countries (American, British, Australian) provide useful insight but are different in format from the Canadian standard and cannot be used directly in conjunction with it. Specialized second-order finite element programs have the capacity for torsional analysis, but are too complicated and costly to use in design practice. There is, therefore, a need for a practical design method that would allow engineers to account for the effects of torsion simply and accurately. This paper, written by a practicing design engineer, suggests a number of approaches that, subject to discussion and approval by experts in the field, could constitute the basis for design of steel members in torsion.Résumé : Cet article aborde la conception de membrures d'acier à semelle large soumises à des forces de torsion ainsi qu'à des forces et à des moments axiaux le long de leurs axes forts et faibles. Les présentes Règles de calcul aux états limites des charpentes en acier (CSA S16-01) ne fournissent aucune ligne directrice sur la méthode de conception contre la torsion. D'autres codes (américains, britanniques, australiens) offrent un point de vue utile mais leurs formats diffèrent des règles canadiennes et ils ne peuvent être directement utilisés avec celles-ci. Des programmes spécialisés par éléments finis du deuxième ordre peuvent faire l'analyse en torsion mais ils sont trop complexes et coûteux pour utiliser lors de la conception. Il existe donc un besoin d'avoir une méthode pratique de conception qui permettrait aux ingénieurs de tenir compte des effets de la torsion de manière simple et précise. Le présent article, écrit par un ingénieur concepteur d'exercice privé, suggère plusieurs approches qui, à la suite de discussions et de l'approbation par des experts dans le domaine, pourraient servir de base à la conception des membrures d'acier en torsion.
This technical note considers concrete pedestals bearing steel and concrete columns attached to the foundation with cast-in anchor rods. One mechanism of pedestal failure -the anchor rod breakout in tension -is considered. Uplift and shear forces and bending moments in the base cause tension in the anchor rods. Classical methods of statics and finite element analysis (FEA) are applicable to establish the anchor likely to fail first. For the design of the anchor rod embedment in the concrete, the new ''cone balancing'' method is proposed. It considers equilibrium of the pullout cone of concrete, ascertained by development of vertical reinforcing bars into the pullout cone and below the failure plane. The method allows determination of tensile force in each individual rebar and direct checking of its size and development length.Résumé : Cette note technique examine des socles en béton supportant des colonnes d'acier et de béton attachées à la fondation au moyen de tiges d'ancrages insérées sur place. Un mécanisme de défaillance des socles -par rupture de la tige d'ancrage en tension -est étudié. Les forces de soulèvement et de cisaillement ainsi que les moments de flexion à la base engendrent de la tension dans les tiges d'ancrage. Les méthodes conventionnelles d'analyse statique et d'analyse par éléments finis peuvent être utilisées pour déterminer le premier ancrage qui pourrait faire défaut. Une nouvelle méthode de conception du noyage des tiges d'ancrage dans le béton est proposée, la méthode « d'équilibre des cônes ». Elle tient compte de l'équilibre du cône d'arrachement de béton, déterminé par le placement de barres d'armature verticales dans le cône d'arrachement et sous le plan de rupture. La méthode permet de déterminer la contrainte de traction de chaque barre individuelle et de vérifier directement sa dimension et la longueur sur laquelle elle se développe.
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