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This paper presents an extensive investigation of the seismic demands on acceleration-sensitive nonstructural components (NSCs) attached to reinforced concrete moment-resisting frame buildings with limited ductility and designed according to the National Building Code of Canada. A total of four benchmark structures with varying heights are considered in this study. Linear and nonlinear time-history analyses were performed using artificial ground motions compatible with Montreal site Class C uniform hazard spectra having 2% and 10% probabilities of being exceeded in 50 years. Seismic acceleration demands on NSCs were evaluated by assessing the horizontal height factor Ax, the component dynamic amplification factor Ar, and the component force factor Sp compared with various building code provisions. The overall acceleration demands of NSCs are discussed, and a corresponding optimized Sp profile is proposed to improve the estimation of the seismic force demands on NSCs at the rooftops of buildings located in moderate seismic zones. [ABSTRACT FROM AUTHOR]

Glass fibre-reinforced polymer (GFRP) with low tensile strength (hereafter referred to as low-grade GFRP) is a cost-effective alternative to other types of GFRPs with higher tensile strength. This paper investigates the prospect of retrofitting deficient and repairing damaged circular concrete columns with low-grade GFRP jackets. Two identical one-third scale models of a seismically deficient prototype bridge pier were constructed and tested under constant axial compression and quasi-static reversed cyclic loading. The first column was tested twice, first under "as-built" condition and second under repaired conditions. The second column was retrofitted prior to testing. The repaired and retrofitted columns were characterized with enhanced flexural, ductility, and energy dissipation capacities when compared to the deficient column, and were stable up to the maximum applied drift. Provisions of the Seismic Retrofitting Manual for Highway Structures were found to yield conservative estimates of the required thickness of the low-grade GFRP jacket. [ABSTRACT FROM AUTHOR]

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]

Seismic base isolation technique has been successfully used to protect structural as well as nonstructural components from the damaging effects of earthquakes by reducing floor accelerations and inter-story drifts for many decades. The level of floor acceleration is a key issue in the protection of acceleration-sensitive nonstructural components. The intensity of floor acceleration varies depending on the vibration characteristics of the structural system. Furthermore, the viscous damping devices sometimes are used to improve the performance of the superstructure as well as the base isolation system. The characteristics of the ground motions are also influential in the performance of the viscous damping devices. In this paper, the floor acceleration performance of seismically isolated buildings with different lateral load resisting systems such as moment resisting frame, dual system, moment resisting frame plus viscous wall dampers, and dual system plus viscous wall dampers is investigated under near-fault and far-fault earthquake ground motions. Moreover, the effectiveness of supplemental viscous damping devices equipped in parallel with lead-rubber-bearing isolators is studied. It is inferred from the study that the most effective way of reducing floor accelerations is to provide more rigidity to the superstructure. Utilizing supplemental viscous dampers along with lead-rubber-bearing isolators having about 20% of effective damping ratio is meaningless or harmful in relation to floor acceleration and base shear. [ABSTRACT FROM AUTHOR]

The National Research Council Canada recently developed a Semi-Quantitative Seismic Risk Screening Tool (SQST) for seismic risk screening of existing buildings in Canada. This paper presents the structural scoring system that is part of the SQST. The structural scoring methodology is based on FEMA P-154, but has been substantially modified to suit Canadian seismicity and seismic design and construction practices. Structural scores are obtained by adding structural basic scores and applicable score modifiers. For an existing building, a structural basic score is determined by calculating the probability of collapse on the basis of a number of assumptions. Then a series of score modifiers are calculated to address the effects of applicable building characteristics on the building's seismic performance. The structural score is compared with an acceptable structural threshold to determine whether the structural seismic risk is acceptable. The objective of the structural scoring system is to ensure an acceptable and consistent seismic risk in building portfolios while minimizing life safety threats. [ABSTRACT FROM AUTHOR]

Nonlinear time-history analysis conducted as part of a performance-based seismic design approach often require that the ground motion records are selected and then scaled to a specified level of seismic intensity. In such analyses, besides an adequate structural model, a set of acceleration time-series is needed as the most realistic representation of the seismic action. In this paper, the effects of scaling procedure on seismic demands of steel frames are investigated. To this, two special steel moment-resisting frames with considerable higher mode effects, and two sets of ground motions, including near-fault and far-fault motions are considered. Moreover, three scaling procedures are introduced for performing nonlinear dynamic time-history analysis of structures. Among different demands, lateral roof displacement and interstory drift are selected as seismic demands. The height-wise distribution of demands shows that the inelastic seismic demands of the near-fault pulse-like ground motions differ considerably from those of far-fault ones. These results show that the story drifts are mostly larger for far-fault motions in the upper story levels in comparison to near-fault records and in the lower floors, the reverse is true. Thus, the scaling procedures directly affect the results of seismic demands and choosing different methods would result in varying responses. Moreover, a low-cost and fairly effective procedure is proposed to estimate the target displacement demands of buildings from response-spectrum analyses, considering near-fault effects. The precision of this method is verified by nonlinear time-history analysis results, as the benchmark solution, and acceptable improvements have been achieved. [ABSTRACT FROM AUTHOR]

This paper presents a preliminary seismic risk screening tool to identify buildings whose superior structural and non-structural seismic performance in regions of low seismicity can be assessed based on several key attributes. The tool is designed to exempt buildings from detailed seismic risk assessment if key exemption criteria are met. The exemption criteria are based on: a seismic categorization system linked to anticipated building damage and seismicity; whether or not the building was designed using modern seismic design provisions; and the remaining time that the building will be occupied. The tool also provides a second list of criteria, which if satisfied, will automatically trigger further detailed seismic risk assessment. The decisions rendered by the tool regarding the expected seismic performance of a building are evaluated against the next level of seismic risk screening tool to ensure the consistency. A flowchart is presented to facilitate adoption of the tool by practicing engineers and other end-users. [ABSTRACT FROM AUTHOR]

This paper presents the results of a research project to study the seismic resistance of fibre reinforced polymer (FRP) strengthened concrete members after fire exposure. Specifically, the paper presents results of FRP strengthened reinforced concrete columns exposed to a standard fire including temperatures measured during the test and a discussion of the loads applied to the columns. Finally, the paper also presents the impact of lateral loading on structural columns after fire to assess the effectiveness of structural resistance of fire-damaged FRP strengthened building elements in case of an earthquake. Numerical models to simulate the lateral behaviour are presented and the predictions are compared to the test results. Since the FRP strengthened columns were insulated with fire protection, the lateral load resistance of the unstrengthened column was reduced by less than 5% due to fire exposure. [ABSTRACT FROM AUTHOR]

After the 2010 Haiti earthquake, which destroyed a significant part of the seismically vulnerable city of Port-au-Prince, the country's capital, a 12-storey reinforced concrete building that behaved well was investigated to understand its dynamic response. This paper completes the experimental work presented in a companion paper, in which the dynamic properties of the building were obtained from ambient vibration tests, and from which a finite-element model was updated. This paper's main objectives are: ( i) to understand the causes that led to the observed structural damage; and ( ii) to estimate the likely seismic excitation at the site of the building. Several nonlinear analyses involving various ground motion intensities were conducted and the results were compared with the damage reported during the on-site survey. The numerical models reproduced the observed damages well and helped to explain them. The overall response of the mixed stiff frame-wall structure was clearly dominated by the high stiffness of the shear walls, showing that this type of structural system helps in keeping reasonable interstorey drift levels. Overall, the building's structure seems to have responded linearly to all the ground motions investigated, but deformation demands imposed to the frame by the shear walls lead to local damages. [ABSTRACT FROM AUTHOR]

This paper presents performance of steel buildings and nonstructural elements during the 27 February 2010 Maule Earthquake in Chile. Structural steel buildings are not common in Chile, due to the relatively high cost of material. The majority of damage to steel structures was observed in industrial facilities. In general, the structural steel buildings performed well. Limited damage was observed in some of the older buildings. Extensive damage was sustained by nonstructural elements, including masonry infill walls, suspended ceilings, partition walls, and architectural features. Brick masonry partition walls, commonly used in Chilean buildings, suffered damage when used in frame buildings with little drift control. The paper presents a summary of observed damage and a comparison of Chilean and Canadian design practices for steel buildings, with lessons drawn from observed structural performance. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to first provide relevant information about the historic seismicity of the island of Haiti, the tectonic setting and the identification of the unmapped Léogâne fault which is now believed to have been the main cause of the 12 January 2010 Haiti earthquake. The paper then focuses on the state of construction in Haiti, with particular emphasis given to engineered buildings. The lack of a building code and standards for the design of structures, as well as the fact that seismic forces were not considered in the design of most buildings explains the failure of so many engineered structures. Several examples are given and arranged according to building function. Since the earthquake has occurred, interim measures have been implemented to control construction of new buildings. Some recommendations are given to improve construction practice in Haiti for the reconstruction. [ABSTRACT FROM AUTHOR]

This paper proposes a simple, relatively new elastic-plastic design method for earthquake resisting frames that enables the engineer to directly control the essential aspects of the future behavior of certain structural forms, through basic statics and imposition of predetermined modes of behavior. The method is particularly applicable to the preliminary design of low to mid-rise buildings where the fundamental period of vibrations dominates the response of the system to seismic loading. The focus of this paper is directed towards simplified but accurate manual design rather than sophisticated structural analysis. The premise of the proposed solution is that the constituent elements of the system can be selected in such a way as to cause both the elastic as well as the plastic drift functions to follow linearly varying straight line profiles during all phases of loading. Frameworks designed by this method act not only as structures of uniform response (UR), i.e., uniform strength and stiffness, where the demand/capacity ratios of its members remain the same, both before and after formation of plastic hinges, but they also result in unique solutions, satisfying the prescribed yield criteria, the boundary support, as well as the of static equilibrium conditions. [ABSTRACT FROM AUTHOR]

This is the first of two companion papers on improved intensity measures of strong seismic ground motions for use in probabilistic seismic demand analysis. It describes the formulation and the development of new intensity measures. The second paper illustrates the application of the developed intensity measures in probabilistic seismic demand analysis. The development of the intensity measures was based on investigations of the seismic responses of three reinforced concrete frame buildings (4, 10, and 16-storey high) designed for Vancouver. The buildings were subjected to a selected set of seismic motions scaled to different intensity levels. Maximum interstorey drifts obtained from nonlinear dynamic analyses were used as response parameters. Based on the results from the analyses, two intensity measures are proposed: one for short- and intermediate-period buildings, and another one for long-period buildings. The proposed intensity measures are superior compared to that represented by the spectral acceleration at the fundamental building period (Sa(T1)), which is currently the most widely used intensity measure in probabilistic seismic demand analysis. Cet article est le premier de deux articles connexes concernant l'amélioration des mesures d'intensité de grands mouvements sismiques du sol qui seront utilisées dans l'analyse probabiliste de la demande sismique. Il décrit la formulation et le développement de nouvelles mesures de l'intensité. Le deuxième article illustre l'application des mesures de l'intensité développées par l'analyse probabiliste de la demande sismique. Le développement de ces mesures de l'intensité a été basé sur les études des réponses sismiques de trois bâtiments à charpente en béton armé (4, 10 et 16 étages de haut) conçus pour Vancouver. Les bâtiments ont été soumis à un ensemble de mouvements sismiques mis à l'échelle pour différents niveaux d'intensité. Les mouvements inter-étages maximums, obtenus par analyse dynamique non linéaires, ont été utilisés comme paramètres de réponse. En se basant sur les résultats des analyses, nous proposons deux mesures de l'intensité : une pour les bâtiments de période courte et intermédiaire, et l'autre pour les bâtiments de longue période. Les mesures de l'intensité proposées étaient supérieures à celles représentées par l'accélération spectrale à la période de bâtiment fondamentale (Sa(T1)), laquelle est actuellement la mesure de l'intensité la plus utilisée dans l'analyse probabiliste de la demande sismique. [ABSTRACT FROM AUTHOR]

This is the second of two companion papers on improved intensity measures of strong seismic ground motions for use in probabilistic seismic demand analysis of reinforced concrete frame buildings. The first paper discusses the development of improved intensity measures. This paper describes the application of the developed intensity measures in probabilistic seismic demand analysis. The application is illustrated on the three reinforced concrete frame buildings (4, 10, and 16-storey high) that were used in the first paper. This involved computations of the seismic responses of the structures and the seismic hazard using the improved intensity measures. The response and the hazard results were then combined by means of probabilistic seismic demand analysis to determine the mean annual frequencies of exceeding specified response levels due to future earthquakes (i.e., the probabilistic seismic demands). For the purpose of comparison, probabilistic seismic demand analyses were also conducted by employing the spectral acceleration at the fundamental structural periods (Sa(T1)) as an intensity measure, which is currently the most used in practice. It was found that the use of the improved intensity measures results in significantly lower seismic demands relative to those corresponding to the intensity measure represented by Sa(T1), especially for long period structures. Cet article est le deuxième sur les mesures de l'intensité améliorées de grands mouvements sismiques du sol qui seront utilisées dans l'analyse probabiliste de la demande sismique des bâtiments à charpente en béton armé. Le premier article traite du développement des mesures de l'intensité améliorées. Le présent article décrit l'application des mesures de l'intensité développées par une analyse probabiliste de la demande sismique. L'application est illustrée par trois bâtiments à charpente en béton armé (4, 10 et 16 étages de haut) utilisés dans le premier article. On y traitait du calcul des réponses sismiques des structures et des dangers sismiques en utilisant les mesures de l'intensité améliorées. Les résultats de la réponse et des dangers ont été combinés au moyen de l'analyse probabiliste de la demande sismique afin de déterminer les fréquences moyennes annuelles des niveaux excédant la réponse spécifiée en raison de prochains séismes (c.-à-d. les demandes sismiques probabilistes). Aux fins de comparaison, les analyses probabilistes de la demande sismique ont été réalisées en utilisant l'accélération spectrale à la période de bâtiment fondamentale (Sa(T1)) en tant que mesure de l'intensité, qui est actuellement la mesure de l'intensité la plus utilisée dans la pratique. Il s'est avéré que l'utilisation des mesures de l'intensité améliorées engendre des demandes sismiques considérablement plus faibles que celles correspondant à la mesure de l'intensité représentée par Sa(T1), plus particulièrement pour les structures à longue période. [ABSTRACT FROM AUTHOR]

It has been observed during previous earthquakes that the damage to operational and functional components of buildings often result in more injuries, fatalities and property damage than those inflicted by structural damage. Operational and functional components of a building include architectural components, mechanical and electrical equipment, as well as building contents. A rational approach to designing these elements against seismic excitations involves the use of floor design spectra. The development of such design spectra for buildings in Canada constitutes the objective of the paper. This objective was achieved by conducting comprehensive analyses of selected reinforced concrete buildings, with different lateral force resisting systems and building heights, under code compatible earthquake records for an eastern and a western Canadian city. It was observed that the floor response was significantly amplified, especially for buildings with short periods. Generally, the higher floors showed higher amplifications with differences in spectra between the floors being more pronounced in low-rise buildings and shear wall buildings with short fundamental periods. The results provided a large volume of data to generate floor response spectra for the design of operational and functional components of buildings in Canada. The details of the approach and the design spectra are presented in the paper. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to provide a summary of the evolution of seismic design in Canada. This paper presents the significant changes to the approach taken in determining seismic hazards and seismic hazard maps, and describes the evolution of the seismic design provisions of the National building code of Canada. The introduction of important parameters in determining the seismic base shear such as the period of vibration of the structure, the influence of type of soil, and the concepts of ductility and energy dissipation capacity of elements and structures are presented. The levels of seismic design base shears, determined from different versions of the National Building Code of Canada, are compared for reinforced concrete frame and wall structures to illustrate the changes. L'objectif de cet article est de présenter un sommaire de l'évolution de la conception parasismique au Canada en se référant aux modifications des efforts sismiques prescrits par le Code National du Bâtiment du Canada. Les changements majeurs concernant l'aléa sismique et les cartes sismiques correspondantes qui ont été créées sont présentés. On présente également les paramètres importants, qui influencent le calcul sismique de l'effort tranchant à la base, tels que la période de la structure, l'influence du type de sols, les concepts de ductilité et de dissipation d'énergie. La variabilité du niveau des charges sismiques, pour les différentes versions du Code National du Bâtiment du Canada, est présentée pour les cadres en béton et les refends, afin d'illustrer ces changements. [ABSTRACT FROM AUTHOR]

The present paper describes the hydrodynamic loads on the roof of a water-filled reservoir or storage tank due to earthquake-induced sloshing. Initially, the paper summarizes available solutions for the water surface elevation in a rectangular reservoir subjected to harmonic and earthquake base motions, and as well an available formulation for the force on the roof of a rectangular reservoir. With this background, a new formulation for the force on the roof is developed, and selected results based on this are presented. A recommended design procedure is thereby proposed, and an example application is provided. The potential extension of the proposed formulation to other reservoir configurations is discussed. Although a validation of the proposed formulation based on laboratory test results is needed, it is suggested that in the interim the proposed formulation is adopted for design. [ABSTRACT FROM AUTHOR]

This paper presents the background experimental and analytical research that was carried out to develop the provisions for the seismic design of high-strength concrete structures in the 2004 Canadian standard CSA A23.3-04. It is noted that the 1994 Canadian standard CSA A23.3-94 limited the concrete compressive strength to 55 MPa for the seismic design of nominally ductile and ductile structures, while the 1995 New Zealand Standard limited the concrete compressive strength to 70 MPa. In contrast, the 2008 American Concrete Institute (ACI) code ACI 318M has no upper limit on concrete strength, even for the seismic design of ductile structural elements. This tremendous variation in these limits indicated that more experimental evidence was needed. This paper presents experimental results of reversed cyclic loading tests on large-scale structural components as well as simulated seismic loading tests of a frame structure constructed with high-strength concrete. The goal of this collaborative research program at the University of Sherbrooke and McGill University was to determine the seismic design and detailing requirements for high-strength concrete structures to achieve the desired level of ductility and energy dissipation. The experimental programs include full-scale testing of the following: columns subjected to a pure axial load (square and circular columns); columns subjected to flexure and axial loads; beam-column subassemblages (square and circular columns); coupling beams in coupled wall structures; shear walls and a two-storey, three-dimensional frame structure. The results of the responses of the high-strength concrete structural specimens are compared with the responses of companion specimens constructed with normal-strength concrete. [ABSTRACT FROM AUTHOR]

This paper evaluates the comparative and absolute in-plane seismic performance of rainscreen and nonrainscreen stucco exterior cladding systems for residential wood frame construction in British Columbia. In this study, an experimental program including quasi-static and dynamic tests was implemented, comprised of 18 (in-plane) quasi-static tests and two dynamic tests. The principal parameters investigated in this study were type of strapping, type and length of strapping fastener, and type and length of lath fastener. All rainscreen specimens were constructed with a 20 mm air space. The overall conclusion is that both rainscreen and nonrainscreen stucco comply with the code requirements addressing the permissible drifts. Therefore, both stucco systems were found to improve the structural behaviour when used as the lateral resisting system of residential wood frame buildings. This paper concludes with recommendations for seismic refinements to current construction practices. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to establish floor accelerations to be used for shake table testing of operational and functional components that are sensitive mainly to horizontal accelerations. For this purpose, two different ensembles of floor accelerations were generated from nonlinear time–history dynamic analyses of three- and six-storey building models incorporating ductile reinforced concrete cantilevered walls. The first ensemble was generated based on synthetic ground motions representative of the intraplate regions of eastern Canada, and the second ensemble was generated from synthetic ground motions representative of the crustal and subcrustal earthquakes of western Canada. The ground motions were selected based on the deaggregations of the seismic hazard for each region in terms of most likely magnitude – epicentral distance scenarios. The building models were designed in accordance with the current seismic provisions of the National Building Code of Canada applicable for each region. Application of the resulting floor accelerations in shake table testing of free-standing bookcases and interior partition walls is reported in a companion paper. [ABSTRACT FROM AUTHOR]

This paper provides a summary of the evolution of the Canadian seismic design provisions for operational and functional components in buildings. The evolution of horizontal seismic force and displacement requirements in the National Building Code of Canada is presented and significant changes and parameters are discussed. Numerical examples illustrate the seismic design force levels as stipulated in recent editions of the NBCC for architectural, mechanical and electrical components attached at different elevations to buildings located in moderate and high seismic zones in Canada. Also, the seismic design force levels, computed according to different editions of the NBCC, are compared for a mechanical component and for an architectural component attached to buildings located in Vancouver. [ABSTRACT FROM AUTHOR]

The last version of the National Building Code of Canada was issued in 2010. The next version will be issued in 2015. In the code cycle between 2010 and 2015 significant changes have taken place in the seismic design provision. The main factor that drives these changes is an improved understanding of the seismic hazard across the country. Changes have also been introduced in the site effect factors. The structural design provisions have been appropriately adjusted to respond to changes in the estimates of hazard and the new site effect factors. There are also new provisions related to design in regions of low hazard, buildings with flexible diaphragms, buildings with inclined columns, passive energy dissipation systems, base isolation, rocking foundations, glazing systems, racks, and elevators. Some of the changes are briefly discussed. The main focus of the paper is, however, on the revisions to the structural design provisions. [ABSTRACT FROM AUTHOR]

Recent research efforts have focused on the development of performance based seismic design methodologies for structures. However, the seismic design rules prescribed in the current Canadian Highway Bridge Design Code (CHBDC) is based largely on force based design principles. Although a set of performance requirements (performance objectives) for different return period earthquake events have been specified, there is no explicit requirement in the CHBDC to check the attainment of such performance objectives for the designed bridges. Also, no engineering parameters have been assigned to the specified performance objectives. This paper correlates seismic performance objectives (both qualitative and quantitative) with engineering parameters, based on the data collected from published experimental investigations and field investigation reports of recent earthquakes. A simple method has been developed and validated with experimental results for assessing the performance of bridges designed according to CHBDC. It has been found that the design rules prescribed in CHBDC do not guarantee that specified multiple seismic performance objectives can be achieved. An implicit seismic design rule in the form of performance response modification factor has been outlined for the performance based seismic design of bridges. [ABSTRACT FROM AUTHOR]

Architectural features and other irregularities in the gravity system which apply gravity-induced lateral demands to the seismic force resisting system are being incorporated in new buildings. These gravity-induced demands have raised concerns due to the perceived potential for a ratcheting effect to occur during seismic loading. This paper summarizes the results of a study to identify if there are behavioral trends not recognized within the scope of current building codes. To this end, a nonlinear, parametric study was conducted in OpenSees to investigate the inelastic response of concrete shear wall buildings with a range of design characteristics, including gravity-induced lateral demands. The results demonstrated that a seismic ratcheting effect can develop and amplify inelastic displacement demands. The effect is significantly more prevalent in coupled shear walls compared with cantilevered shear walls. An irregularity class to address buildings with gravity-induced lateral demands on the seismic force resisting system is proposed for the 2015 National Building Code of Canada. [ABSTRACT FROM AUTHOR]

This paper provides a summary of the damage to bridges in the Mw 8.8 Chile earthquake of 27 February 2010. Lessons from the different types of structural damage observed on concrete and steel bridges are discussed. The important roles played by soil liquefaction, settlement and embankment failures are highlighted. Aspects such as shear failure of steel piles, shear failure of concrete substructure elements, failures and severe buckling of steel braces, failures of shear keys and restrainers at supports, and damage to girders due to lack of diaphragms are described. Many examples of loss of superstructure support are presented. Skew supports and multi-span simply supported bridges were particularly susceptible to loss of support. Several aspects of the Chilean bridge design code are discussed and compared with North American codes (CSA S6 and AASHTO). [ABSTRACT FROM AUTHOR]

This paper provides a summary of the damage to industrial facilities in the Mw 8.8 Chile earthquake of 27 February 2010. The types of damage observed include failure of elevated tanks, collapse and cracking of concrete silos, buckling of steel silos, collapse of conveyor systems, failure of steel bins, and failure of anchor rods. Damage to industrial buildings included buckling of bracing members, failure of brace connections, shear failures of reinforced concrete columns, and shear failures of heavily loaded steel girders. Aspects of the current Chilean design code for industrial structures are reviewed and discussed. Recommendations are proposed for the development of Canadian seismic design provisions for industrial structures. [ABSTRACT FROM AUTHOR]

New technologies based on seismic isolation are gaining popularity among engineers given the savings on construction costs. The long-term advantage of these technologies preserve the serviceability of the structure after an earthquake and eliminate the cost of reconstruction. This advantage is critical for 'emergency' bridges, required to remain operational after an earthquake. The present article examines a method of isolating the foundation of existing bridges as part of a seismic retrofitting effort. This approach is supported by the increasing interest in this method, especially since its adoption by the Canadian standards and due to the fact that engineers are not too familiar with non-linear dynamic design methods. Another source of motivation is the opportunity to apply this technique to the refection of a few Quebec bridges. The steps of the antiseismic calculations as well as the results of non-linear analyses pertaining to the Madrid Bridge are presented and discussed. This paper may become a useful tool for engineers and their projects of retrofitting existing bridges. Les nouvelles technologies basées sur l'isolation sismique connaissent un intérêt grandissant parmi les ingénieurs, compte tenu de l'économie sur le coût de la construction de l'ouvrage qu'elles offrent. Elles présentent également un avantage indéniable à long terme étant donné qu'elles préservent la fonctionnalité de l'ouvrage après séisme et éliminent le coût de reconstruction. Cet avantage revêt une importance capitale pour les ponts dits de secours qui doivent demeurer en service après le séisme. Cet article présente une méthodologie relative à l'isolation de la base des ponts existants dans un contexte de mise en conformité sismique. Cette démarche est motivée par l'intérêt grandissant de cette méthode, notamment depuis son adoption par la norme canadienne d'une part et d'autre part par le fait que les ingénieurs praticiens sont moins familiers avec les méthodes dynamiques non linéaires de conception. L'opportunité offerte aux auteurs de mettre en application cette technique pour la réfection de quelques ponts au Québec est une autre source de motivation. Les étapes de calcul parasismiques sont pourvues, et les résultats des analyses non linéaires relatives au pont Madrid sont présentés et discutés. L'article est destiné aux ingénieurs praticiens qui y trouveront un outil utile pour leurs projets en réhabilitation de ponts existants. [ABSTRACT FROM AUTHOR]

It has been a Canadian code requirement for 25 years to check whether concrete gravity-load columns can tolerate the building deformations due to the design earthquake; but the way this has typically been done using linear analysis significantly underestimates the seismic demands on gravity-load columns. Concern about the safety of gravity-load columns over the plastic hinge height of concrete shear walls, particularly elongated wall-like gravity-load columns, has resulted in new design requirements in Update No. 3 of Canadian Standard Association (CSA) A23.3-04 issued in August 2009. The current paper provides the background to these new requirements. If nonlinear analysis is not done, closely spaced seismic hoops shall be provided in all columns and walls that support gravity loads, and these members shall meet the same limit on maximum compression strain depth as concrete shear walls. The results of nonlinear analyses were used to validate this simple design rule, and to investigate factors that increase seismic demands on gravity-load columns such as diagonal cracking of concrete shear walls, localized damage of columns from cover spalling and bar buckling, and larger first storey heights. Nonlinear analysis has shown that 2.4 m (8 ft) long columns can lose over 50% of their axial load carrying capacity at an inelastic drift ratio of only 1%. Une exigence du code canadien depuis 25 ans est de vérifier si les colonnes de béton chargées par gravité peuvent résister aux déformations du bâtiment causées par un séisme type. Cette vérification était normalement réalisée par analyse linéaire et sous-estimait de manière significative les demandes sismiques sur les colonnes de béton chargées par gravité. Des préoccupations concernant la sécurité des colonnes de béton chargées par gravité quant à la hauteur des charnières plastiques des murs de contreventement en béton, plus particulièrement les colonnes de béton chargées par gravité allongées, similaires à un mur, ont engendré de nouvelles exigences de conception dans la mise à jour no 3 de la norme CSA A23.3-04 émise en août 2009. Le présent article traite de l'historique de ces nouvelles exigences. Si une analyse non linéaire n'est pas réalisée, des boucles sismiques peu espacées doivent être fournies dans toutes les colonnes et tous les murs qui supportent des charges par gravité, et ces membrures doivent rencontrer la même limite de profondeur de contrainte de compression maximale que les murs de contreventement en béton. Les résultats des analyses non linéaires ont été utilisés pour valider cette simple règle de conception et examiner les facteurs qui accroissent les demandes sismiques sur les colonnes de béton chargées par gravité, tels que la fissuration diagonale des murs de contreventement en béton, les dommages localisés sur les colonnes par l'effritement des surfaces et flambement des tiges, et des hauteurs plus élevées des premiers étages. Une analyse non linéaire a indiqué que des colonnes d'une longueur de 2,4 m (8 pi) peuvent perdre plus de 50 % de leur capacité portante axiale à un rapport de mouvement inélastique de seulement 1 %. [ABSTRACT FROM AUTHOR]

In July 2009, a full-scale six-storey platform wood frame apartment building was subjected to a series of earthquakes at the world's largest shake table in Miki, Japan. Two double-midply shear wall stacks were installed in the building from the first storey through to the fifth storey. A continuous anchor tie-down system (ATS) was used to prevent overturning and allow the shear walls to develop their full lateral load capacities. This paper focuses on the behavior of the stacked double-midply shear wall in a full-scale midrise building during a series of triaxial shakes scaled for the city of Los Angeles, California. The stacked midply shear wall achieved a maximum interstorey deformation of 40.4 mm (equivalent to 1.64% drift). The uplift forces measured at the bottom storey of the stacked wall exceeded 760 kN, indicating the need for substantial tie-down systems for this type of wall when utilized in a midrise platform wood frame building. En juillet 2009, un immeuble résidentiel à charpente en bois à plateforme de six étages à plein échelle a été soumis à une série de séismes sur la plus grande table de vibration au monde à Miki, au Japon. Deux empilements de murs de contreventement à doubles contreplaqués au centre ont été installés dans l'immeuble du premier jusqu'au cinquième étage. Un système d'ancrage à fixation continue (« ATS ») a été utilisé pour prévenir le renversement et permettre aux murs de contreventement de développer leur pleine capacité de porter la charge latérale. Le présent article porte sur le comportement d'un mur de contreventement empilé à doubles contreplaqués dans un immeuble de hauteur moyenne à pleine échelle durant une série de secousses triaxiales mises à l'échelle pour la Ville de Los Angeles, Californie. Le mur empilé de contreventement à doubles contreplaqués au centre a atteint une déformation maximale de 40,4 mm entre les étages (équivalent à une dérive de 1,64 %). Les forces de soulèvement mesurées à l'étage inférieur du mur empilé ont dépassé 760 kN, indiquant le besoin d'avoir des systèmes de fixation importants pour ce type de mur lorsqu'il est utilisé dans un immeuble de hauteur moyenne à charpente de bois à plateforme. [ABSTRACT FROM AUTHOR]

This paper presents the results of parametric studies on the seismic response of concrete rectangular liquid storage tanks using the generalized single-degree-of-freedom (SDOF) system. The effects of height of liquid and width of tank on the dynamic response of liquid storage tanks are investigated. The liquid level varies from the empty condition to a full tank. Also, instead of the commonly used ratio of width of tank to liquid height, Lx/HL, the ratio of width of tank to full height of the tank wall, Lx/Hw, is used as a characteristic parameter of tanks to study the effect of tank size on the dynamic response. The trends of added mass of liquid, effective height, and natural frequencies for different sizes of tanks are established. The values of the added mass of liquid due to impulsive hydrodynamic pressure and the effective height in the relationship with the ratios Lx/Hw and HL/Hw are determined and can be used in the seismic design of liquid storage tanks. Since the natural frequencies of liquid-containing structures are within a band of frequencies between that of a full tank and that of an empty tank, the recommended frequency to be used in the design of the tank wall is the frequency that causes the maximum dynamic response . [ABSTRACT FROM AUTHOR]

This paper describes a study of the seismic behaviour of taller eccentrically braced frames (EBFs). Chevron-type EBFs with shear-critical links are designed for 14-, 20-, and 25-storey buildings in Montreal and Vancouver. For each location the importance of different design criteria is discussed and an appropriate design sequence is proposed. It was found that ductility requirements did not control design. For Vancouver, buildings member selection was mostly influenced by the inelastic inter-storey drift requirements whereas for Montreal ensuring the global frame stability was critical. The seismic response of these frames to the sets of earthquake records calibrated to match design spectra is described. The seismic performance for Vancouver frames was found to be adequate, except that in the upper storeys the inelastic link deformations and shear forces exceeded values anticipated in design. For the Montreal structures, all global and local response indicators remained well below the design limits. [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]

Canadian Wooden Dome (CWD) is an innovative orthotropic, monolithic modular sectional building system. The main frame of these structures is built using mill trim ends that are normally chipped or used for finger-jointing. The structure, in comparison to conventional wood-frame single-family housing, has a rapid manufacturing process, and quick, on-site assembly attempts to reduce overall construction time. Presented with these advantages and the uniqueness of the wooden-dome system, a technical study was initiated to investigate the structural performance of the modular wooden dome in earthquake-prone areas and to examine its load resistance to heavy snow. This paper describes the results from a series of static and dynamic load tests conducted on the CWD as part of this study. The test results generally indicated that based on the structural performance of the CWD under static and dynamic loads, the CWD could be an alternative to the conventional wood-frame construction system. The test results are then compared with those obtained from the tests conducted on conventional single-family wood-frame houses as part of the Earthquake 99 (EQ-99) Woodframe House Project at The University of British Columbia. The seismic performance of the CWD was superior to that of the nonengineered housing system and comparable to that of the engineered wood-frame housing system. Le système de construction « Canadian Wooden Domes (CWD) » est un système modulaire novateur de construction sectionnelle, monolithique et orthotrope. Le cadre principal de ces structures est bâti en utilisant des éboutures qui sont normalement mises en copeaux ou utilisées pour des aboutages. La structure, par rapport à celle des maisons unifamiliales conventionnelles à ossature de bois, se fabrique rapidement et l’assemblage rapide sur le site tend à diminuer le temps de construction global. En tenant compte de ces avantages, une étude technique a été lancée pour examiner le rendement de cette structure unique de dôme en bois modulaire dans les zones sujettes aux séismes et sa résistance à une charge de neige abondante. Le présent article décrit les résultats d’une série d’essais en charge statique et dynamique effectués sur les dômes en bois dans le cadre de cette étude. En se basant sur le rendement structural de ces dômes en bois sous des charges statiques et dynamiques, les résultats indiquent généralement que les dômes en bois pourraient être une solution de remplacement au système traditionnel de construction à ossature de bois. Ces résultats ont ensuite été comparés à ceux obtenus lors d’essais effectués sur des maisons unifamiliales à ossature de bois traditionnelles dans le cadre du projet « Earthquake 99 Woodframe House Project » réalisé antérieurement à l’Université de la Colombie-Britannique. Par rapport aux structures à ossature de bois traditionnellement mises à l’épreuve, le dôme en bois présentait un rendement sismique supérieur à celui des systèmes non techniques et un rendement sismique similaire à celui des systèmes techniques à ossature de bois. [ABSTRACT FROM AUTHOR]

Full-scale tests provide valuable information on the characteristics of building structures that can be used to evaluate design methods, to calibrate modelling techniques, and to determine damage corresponding to loading levels. These tests are scarce due to the enormous requirements in testing space and specialized testing equipment. The seismic behaviour of a full-scale, two-storey, reinforced high-performance concrete building designed with moderate ductility detailing is evaluated by pseudo-dynamic testing, during which increasing seismic loads are applied, resulting in increasing levels of permanent damage to the structure. To monitor the level of damage, a series of successive forced-vibration tests are also carried out at each step of the process and are used to track changes in the key dynamic properties of the building. The paper presents the design of the test structure according to the new edition of the CSA A23.3-04 Design of concrete structures standard, the series of pseudo-dynamic tests simulating different levels of earthquake excitation consistent with the 2005 edition of the National building code of Canada, and the evaluation of the performance of the building. It is shown that the detailing requirements of CSA A23.3-04 are more than adequate to provide the ductility and overstrength expected. Les essais à grande échelle fournissent des informations importantes sur les caractéristiques des structures pouvant être utilisées pour évaluer les méthodes de dimensionnement, pour calibrer des techniques de modélisation, et pour déterminer l'endommagement correspondant à des niveaux de chargement. La rareté de ces essais est due principalement à la nécessité de disposer de grands espaces de laboratoire et d'équipements d'essais spécialisés. Dans cet article, le comportement d'un bâtiment en vraie grandeur de deux étages est évalué par essais pseudo-dynamiques dans lesquels le bâtiment est soumis à des niveaux d'excitation sismique croissants causant des dommages de plus en plus importants à la structure. Le bâtiment est construit en béton à hautes performances pour posséder une ductilité modérée. Des essais en vibration forcée sont utilisées pour évaluer les changements dans les propriétés dynamiques de la structure. L'article présente le dimensionnement de la structure d'après la nouvelle édition de la norme CSA A23.3-04, Dimensionnement des structures en béton, la suite des essais pseudo-dynamiques simulant les différents niveaux d'excitation des tremblements de terre consistants avec le Code national du bâtiment du Canada 2005, et l'évaluation de la performance du bâtiment. On montre que les règlements de la norme CSA A23.3-04 sont tout à fait adéquats pour assurer le niveau de ductilité et de surcapacité désiré. [ABSTRACT FROM AUTHOR]

Full-scale tests provide valuable information on the characteristics of building structures that can be used to evaluate design methods, to calibrate modelling techniques, and to determine damage corresponding to loading levels. These tests are scarce due to the enormous requirements in testing space and specialized testing equipment. The seismic behaviour of a full-scale, two-storey, reinforced high-performance concrete building designed with moderate ductility detailing is evaluated by pseudo-dynamic testing, during which increasing seismic loads are applied, resulting in increasing levels of permanent damage to the structure. This paper presents the analytical predictions of the test results using a global force-displacement parameters approach and a refined approach, half-way between global modelling and finite element modelling, using force-strain parameters and damage mechanics principles. Identification of the parameters required to describe the response parameters are presented together with a description of the numerical procedures used in each approach. It is shown that the predictions are in good agreement with the test results. Advantages and disadvantages of each approach are highlighted in the context of performance-based analysis and design. Des essais à grande échelle fournissent des informations importantes sur les caractéristiques des structures qui peuvent être utilisées pour évaluer les méthodes de dimensionnement, pour calibrer des techniques de modélisation, et pour déterminer les niveaux d’endommagement correspondant à des niveaux de chargement. La raretée de ces essais est due principalement à la nécessitée de disposer d'espace de laboratoire conséquent et d’équipements d’essais spécialisés. Le comportement d’un bâtiment en vraie grandeur de deux étages a été évaluée par essais pseudo-dynamiques dans lesquels le bâtiment est soumis à des niveaux d'excitation sismique croissants causant des dommages de plus en plus important à la structure. Dans cet article les prédictions numériques des réesultats obtenus lors des essais à l’aide d’une approche globale utilisant les forces et les déplacements et d’une approche semi-globale utilisant les forces et les déformations associées aux principes de la mécanique de l’endommagement sont présentées. L’identification des paramètres nécessaires à l’analyse est décrite et les procédures numériques sont expliquées. On montre que les résultats numériques se comparent bien aux résultats expérimentaux. Les avantages et les désavantages de chaque approche sont soulignés dans le contexte d’une analyse ou d’un dimensionnement basée sur la performance. [ABSTRACT FROM AUTHOR]

Fire following an earthquake is an important factor causing damage to buildings and life-line structures. Therefore, besides satisfying structural design requirements for normal loads, such as dead and live loads including the seismic hazard, buildings should also be designed to withstand the fire following earthquakes for a certain minimum duration as required for a desired level of performance. This period of time will allow occupants to evacuate the building safely and the emergency crews to cope with the fire. Also, it is essential to reduce the post-earthquake fire (PEF) ignitions and minimize the damage to active fire protection systems as much as possible to prevent the spread of fire. This paper presents a state-of-the-art review on the PEF hazard and discusses the causes, mitigation measures, and performance of building structures under this hazard. Mitigation measures that could be developed based on the experience from the structural engineering field are identified. Both local and global approaches that should be taken to mitigate the PEF hazard, including structural and nonstructural design, various urban planning aspects, and their interactive combinations, are discussed. Based on the review, it is concluded that that there is a strong need for the development of guidelines for structural fire safety design for PEF scenarios. In addition, appropriate analysis and numerical simulation techniques for the evaluation of the structural performance under earthquake-induced fire conditions need to be developed. It is also necessary to conduct experimental studies to validate such numerical models and refine them. Les incendies suivant un séisme sont une importante cause de dommages aux bâtiments et aux structures vitales. Ainsi, en plus d’être conçus pour répondre aux exigences de conception structurale pour les charges normales telles que les charges permanentes et en mouvement, incluant le risque sismique, les bâtiments devraient être conçus pour résister aux incendies suivant les séismes pour une durée minimale requise par le niveau de rendement désiré. La durée permettra aux occupants d’évacuer le bâtiment en toute sécurité et aux équipes d’urgence de combattre l’incendie. De plus, il est essentiel de réduire l’allumage d’incendies suivant les séismes et, dans la mesure du possible, de minimiser les dommages causés aux systèmes actifs de protection contre les incendies afin de prévenir la propagation de l’incendie. Cet article présente une revue de la technologie récente sur les dangers d’incendies suivant les séismes et analyse les causes, les mesures d’atténuation et le comportement des structures de bâtiments lors de tels dangers. Les mesures d’atténuation qui peuvent être établies en se basant sur l’expérience de l’ingénierie des structures sont identifiées. Les approches locales et globales qui devraient être prises pour atténuer le danger d’incendie suivant un séisme, incluant la conception structurale et non structurale, divers aspects de la planification urbaine ainsi que leurs combinaisons interactives sont abordées. Cette revue conclut qu’il est fortement nécessaire de développer des lignes directrices de conception structurale de sécurité incendie pour les cas d’incendies suivant un séisme. De plus, il faut développer une analyse appropriée ainsi que des techniques de simulation numériques pour l’évaluation du comportement structural lors d’incendies causés par un séisme. Il est également nécessaire de réaliser des études expérimentales pour valider et raffiner de tels modèles numériques. [ABSTRACT FROM AUTHOR]

The goal of this paper is to propose input energy spectra applicable to seismic design of structures based on Iranian earthquakes. In terms of input energy, these spectra represent the load effects of a strong earthquake that a structure may encounter during its lifetime. For this purpose, from among 1800 existing earthquake records in Iran, 110 records were selected. By using these records and through dynamic response analyses, the design input energy spectra for four ground types, defined by the Iranian earthquake code of practice, have been derived. L’objectif de cet article est de proposer des spectres d’énergie induite applicables à la conception sismique de structures basée sur des séismes Iraniens. En termes d’énergie induite, ces spectres représentent les effets de charge d’un séisme fort qu'une structure pourrait subir au cours de sa durée de vie. À cet effet, parmi les 1800 enregistrements de séismes existants en Iran, 110 enregistrements ont été sélectionnés. En utilisant ces enregistrements et des analyses de réponse dynamique, les spectres d’énergie induite par conception, pour quatre types de sol, définis par le Code de la pratique des séismes Iranien, ont été dérivés. [ABSTRACT FROM AUTHOR]

Post-tensioned concrete masonry walls provide improved seismic performance, but have had limited application in seismic regions because of a lack of research pertaining to their in-plane response. Following focused research over recent years, a consortium of product suppliers has collaborated with the University of Auckland to construct New Zealand’s first post-tensioned concrete masonry house. A feature of this innovative design was that all incorporated products were commercially available, with no proprietary products being specifically developed for the prestressed masonry system used. Consequently, it is hoped that this house will be a showcase, and provide exposure for the technology in New Zealand and elsewhere. This paper provides a brief review of previous post-tensioned concrete masonry research applications, then discusses post-tensioning details and their application to house design and construction. [ABSTRACT FROM AUTHOR]

Seismic design for nuclear power facilities is generally based on a prescribed earthquake response spectrum, which defines the response of a simple oscillator of a given natural frequency to the expected motions. To develop standard designs that may be suitable in a number of possible future locations, it is useful to develop standard spectra that describe typical environments. The adequacy of the standard design for a particular location may then be judged based on comparison of the standard spectrum with a site-specific "uniform hazard spectrum" (UHS). In this paper, UHS results from selected publicly available studies are used to develop a standard spectral shape that describes moderate-seismicity sites in eastern North America, on hard-rock site conditions. Compared with a standard spectrum that has been suggested for future nuclear plants on rock sites (modified Canadian Standards Association CSA/CAN-N289.3), the spectral shape proposed herein has higher amplitudes at high frequencies and lower amplitudes at low frequencies. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental and analytical study on high-strength, reinforced-concrete (RC) columns with different levels of initial ductility enhanced with carbon fiber reinforced polymer (CFRP) wraps. Six square columns 260 mm wide and 1650 mm long were tested under constant axial load and reversed cyclic lateral load. The test specimens were divided into three groups. Groups I and II were designed and detailed according to the requirements of American Concrete Institute ACI318-02 for intermediate-moment frames. Group I was wrapped with CFRP, group II was control specimens, and group III was designed and detailed according to the requirements of ACI318-02 for special-moment frames. Each group consisted of two columns with ρsl = 1.5% and 3.0% longitudinal steel rebars, where ρsl is the ratio of area of longitudinal reinforcement to gross area of concrete. The moment–curvature is numerically calculated for sections with fiber reinforced polymer (FRP) confinement. The theoretical prediction provides conservative results compared with the test data. Based on the test results, CFRP enhanced ultimate displacement and curvature ductility by 53% and 79%, respectively, in column WI4 with four longitudinal bars and 27% and 28%, respectively, in column WI8 with eight longitudinal bars. Moreover, the performance of wrapped columns was enhanced to a level higher than that of unwrapped columns designed according to special-moment frames. [ABSTRACT FROM AUTHOR]

The purpose of the study discussed in this paper is to evaluate the seismic response of a modern building, designed according to the current building code and to extreme earthquake earthquakes from two different source mechanisms. To this end, a three-dimensional nonlinear dynamic response of a reinforced concrete high-rise building, typical of the type built in Vancouver, British Columbia, is investigated. According to current design practice, the building has been designed to resist lateral loads with a coupled shearwall system. A comparison of the responses of the building to crustal and subduction type earthquakes of similar magnitudes is presented and discussed. The ground motion records selected for this study were derived from recorded crustal and subduction events, which are both considered to be extreme, and beyond the code-based design requirements of the building. A part of this study includes an evaluation of how the dynamic properties of the building change as the building is being damaged by severe ground shaking. The results of the study show that the crustal earthquake imposes large upper levels displacements, and much plastic hinging near the base because the response of the building is governed mainly by the first mode of the "undamaged" system. The subduction earthquake results in displacements smaller than those from the crustal event and causes plastic hinging at mid-height and near the base as well as large torsional rotations, because the behaviour of the building is greatly influenced by the second mode of the "damaged" system. [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]

The article presents a discussion of the paper "Making use of brace overstrength to improve the seismic response of multistorey split-X concentrically braced steel frames." The authors point out some inconsistencies present in the paper. They note that the first series of structures studied were designed without inclusion of P-delta effects that were included in the subsequent analyses. In addition, they contend that the lower base shear forces mandated by the 2005 National Building Code of Canada (NBCC) compared with those in the 1990 NBCC make P-delta effects more critical than earlier requirements are not insignificant.