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Steel multi-tiered concentrically braced frames (MT-CBFs) represent a bracing configuration where two or more concentric bracing panels are stacked between the ground and roof levels in tall single-storey buildings. A large proportion of MT-CBFs in Canada are located in low-to-moderate seismic regions (seismic category 0–3) where limited ductility CBFs are often preferred in design. Nevertheless, brace tensile yielding may not occur in all tiers of such frames. Additionally, the analysis and design procedure adopted by the 2019 Canadian steel design standard (CSA S16-19) can become tedious in tall frames with multiple panels. In this paper, the seismic behaviour of limited ductility MT-CBFs in moderate seismic regions of Canada is examined to propose a simplified design method. A set of 16 prototype MT-CBFs is designed in accordance with CSA S16-19, excluding the design requirements prescribed for MT-CBF columns. Nonlinear dynamic analyses are then performed to examine their seismic response. Finally, an efficient design method is proposed in the framework of CSA S16-19. [ABSTRACT FROM AUTHOR]

Single-storey braced steel frame buildings (SSBSFs) are currently the most widely used commercial structures, which include strip malls, power centres, warehouses, small and medium-sized industrial plants. The lateral seismic or wind forces acting on such low-rise structures are usually transferred from a metal roof-deck diaphragm to a system of vertical bracing members. Because these flexible roof diaphragms have a considerable effect on the dynamic response of SSBSFs during an earthquake, they also play an important role in the evaluation of the fundamental vibration period, a key parameter in determining the magnitude of the design seismic forces. It is therefore of utmost importance to reliably predict the fundamental period of SSBSFs. This paper presents the results of a four-year field measurement research project on the dynamic behaviour of SSBSFs. The goal of the project was to create a reliable database for the dynamic characteristics of SSBSFs (periods, mode shapes, and damping) and to find a relationship between them and the geometric parameters (height and plan dimensions). The field tests are described, along with the selected buildings and experimental setup. The measured fundamental periods are then compared to the National building code of Canada (NBCC) empirical equations. A statistical analysis of the data, based on different regression models, yielded new proposed building geometric parameters to be used in simple equations for the prediction of the fundamental period of SSBSFs. [ABSTRACT FROM AUTHOR]

This paper describes the seismic behaviour of chevron steel braced frames for 2-, 4-, 8-, and 12-storey steel building structures. Two different design approaches were considered: one that corresponds to current CSA-S16.1 seismic provisions for braced frames with nominal ductility with an R factor of 2.0, and one in which the beams are sized to develop a fraction of the yield tension capacity of the bracing members. In this second approach, an R factor of 3.0 was used for determining the seismic loads and chevron bracing with stronger beams capable of developing 100%, 80%, and 60% of the brace yield load were examined. The results show that current S16.1 provisions for chevron braced frames may lead to systems that are prone to dynamic instability for 4-storey and taller structures. Chevron bracing with stronger beams exhibits a more stable inelastic response and can be used for structures up to 8 storeys in height. For 2- and 4-storey buildings, chevron braced frames with beams designed to develop only 60% of the brace yield resistance can be used. The analyses also show that the force demand in brace connections, beams, and columns as determined from capacity design provisions agree well with that anticipated under strong ground motions.Key words: earthquakes, seismic design, steel, structures, braced frames, bracing members, beams, columns, connections.Cet article décrit le comportement sismique de contreventements en treillis avec diagonales en chevron utilisés dans la charpente d'acier de bâtiments de 2, 4, 8 et 12 étages. Deux approches de conception ont été considérées : l'une qui suit les dispositions actuelles de la norme CSA S16.1 pour les contreventements à ductilité nominale et l'autre où les poutres sont conçues pour résister aux efforts engendrés lorsque l'effort dans la diagonale tendue atteint une fraction de sa limite élastique. Pour la seconde méthode, on a considéré un coefficient R égal à 3,0 pour le calcul des charges sismiques et on a étudié des contreventements dont les poutres pouvaient reprendre des efforts correspondant à un effort dans les diagonales tendues égal à 100%, 80% et 60% de leur limite élastique. Les résultats montrent que les contreventements de 4 étages et plus peuvent subir de grandes déformations latérales et être sujets à une instabilité dynamique lorsque conçus selon la norme S16.1 actuelle. Les contreventements avec poutres pouvant soutenir la plastification des diagonales tendues ont un comportement plus stable et peuvent être utilisés dans des structures jusqu'à 8 étages. Pour des bâtiments de 2 et 4 étages, on peut utiliser des poutres conçues pour un effort dans les diagonales tendues égal à 60% de leur résistance plastique. Les analyses dynamiques démontrent également que les efforts dans les assemblages des diagonales, dans les poutres et dans les poteaux tels, qu'obtenus d'un calcul par capacité, correspondent bien aux efforts que l'on peut anticiper lors d'un séisme important.Mots clés : séismes, conception parasismique, acier, structures, contreventements en treillis, diagonales, poutres, poteaux, assemblages. [ABSTRACT FROM AUTHOR]