Impact of seismic retrofit and presence of terra cotta masonry walls on the dynamic properties of a hospital building in Montreal, Canada

Unreinforced masonry (URM) infill walls are widely used in structures in North America. In several "pre-code" hospital buildings constructed before the 1970s, terra cotta masonry blocks have been used extensively. Although unreinforced terra cotta infill walls play a structural role, interior partitions are generally considered as non-structural components (NSCs) and their stiffness effects on the structure are often ignored in seismic analysis and design, while their weight/mass is included as uniformly distributed load/inertia. Terra cotta infill walls interact with their bounding frame during earthquakes and increase the lateral stiffness and strength of the structure, which in turn influences the dynamic response of the building. In situ vibration measurements and observations of past earthquake-induced damage clearly demonstrate the necessity of considering the effect of infill walls on structural response, particularly for post-critical buildings such as hospitals which have to remain functional after severe design-level seismic shaking. To illustrate the structural contribution of infill terra cotta walls, two eleven-storey buildings have been selected which are two wings (Blocks #7 and #8) of CHU Sainte-Justine, a paediatric research hospital located in Montréal, Canada. This hospital campus was initially built in the late 1950s and Block #7 was seismically retrofitted in 2008 by adding a full-height reinforced concrete shear wall at its free end and connecting the other end of the building to the adjacent Block #9, using structural anchor bars at each floor slab and along the height of interfacing columns. Block #8 was not retrofitted and has remained unattached to adjacent Block 9. A detailed linear elastic finite element analysis model of each building was created where the infill unreinforced terra cotta walls have been modeled. Only linear models were created at this stage as the hospital buildings have to remain practically linear elastic to fulfill their functionality performance objectives. Two different techniques were adopted for modeling these infill walls, namely using panel elements and compression strut models. For the compression strut models, three different formulas suggested in the literature were used to calculate the effective width and properties of the strut. In parallel, in situ Ambient Vibration Measurements (AVMs) were done in both buildings and their dominant dynamic properties have been extracted using two different operational modal analysis techniques. The AVM results were used for validation and also calibration of the numerical models. The calibrated models were subjected to a set of 12 synthetic ground accelerograms compatible with the NBC Uniform Hazard Spectra (UHS) for Montréal in both principal horizontal directions independently. Selecting two floors in each block (top floor #7 and middle floor # 3), Floor Response Spectra (FRS) and Interstorey-Drift curves were developed for each record. The effects of seismic rehabilitation and presence of infill walls on the dynamic properties of the building and also on the performance of their NSCs were addressed by comparing the results of different models. Finally, a detailed study of the NSC's seismic behaviour was done using FRS and Interstorey-Drift curves provided for the two selected floors. Finally, the lateral stiffness of the rehabilitated block # 7 is significantly improved compared to block # 8 which means it is subjected to larger accelerations; for example the maximum acceleration at the 7 floor is on average three times the acceleration of the same floor in block # 8 for the twelve earthquake scenarios. The non-structural components that are sensitive to accelerations are subjected to higher forces in block 7. Since the inter-storey drifts are much reduced in block 7 to very low values justifying the linear analysis, the performance of architectural components and functional components connected at several levels is improved.Les murs en maçonnerie non armée (MNA) sont très présents dans les bâtiments nord-américains. Dans plusieurs hôpitaux « pré-code » construits avant l'adoption des normes parasismiques dans les années 1970, la maçonnerie de blocs en terra cotta a été abondamment utilisée. Bien que les murs de remplissage jouent effectivement un rôle structural dans la réponse sismique des bâtiments, les murs qui servent simplement de cloisons internes sont considérés comme des composants non-structuraux et leur influence structurale est négligée dans les analyses sismiques. Les murs de remplissage en terra cotta interagissent avec leur cadre périphérique durant les séismes et augmentent la rigidité latérale et la résistance des ossatures, ce qui influence directement leur réponse dynamique. Observations de dommages lors de séismes antérieurs ont prouvé la nécessité de tenir compte de l'influence structurale des murs de remplissage, particulièrement pour les bâtiments de protection civile comme les hôpitaux qui se doivent de rester fonctionnels suite au séisme de conception.Cette thèse illustre la contribution structurale de murs de remplissage en terra cotta à l'aide d'une étude de cas détaillée de deux bâtiments de onze étages du Centre hospitalier universitaire (CHU) Sainte-Justine – les blocs #7 et #8, un hôpital pédiatrique situé sur l'île de Montréal. Cet hôpital a été construit à la fin des années 1950 et le bloc #7 a fait l'objet d'une réhabilitation parasismique en 2008. Le bloc #8, par contre, n'a subi aucune réhabilitation parasismique et demeure non-relié à son bâtiment adjacent. Un modèle détaillé pour l'analyse par éléments finis de chacun des deux blocs a été mis au point, avec modélisation des murs de remplissage en terra cotta. Seuls des modèles linéaires élastiques ont été créés pour cette étude considérant que les bâtiments doivent rester pratiquement en mode de réponse linéaire pour satisfaire leur objectif de performance sismique. Deux techniques ont été appliquées pour la modélisation des murs de remplissage : la définition de panneaux continus et la méthode des bielles comprimées équivalentes.En parallèle avec ces études numériques, une campagne de mesures de vibrations ambiantes a été réalisée pour les deux blocs et les propriétés dynamiques dominantes des bâtiments ont été identifiées, L'analyse des mesures s'est faite à l'aide de deux techniques d'analyse modale opérationnelle en sélectionnant les pics des fonctions obtenues par décomposition des mesures dans le domaine des fréquences, soit la méthode de base(FDD) et une version dite améliorée (EFDD). Les résultats des mesures de bruit ambiant ont été utilisés pour valider et calibrer les modèles numériques. Une fois calibrés, les modèles ont été analysés sous l'effet de 12 séismes représentés par des accélérographes synthétiques. Deux étages spécifiques ont été sélectionnés: le plancher du 7e étage et le plancher du 3e étage. Les spectres de réponse de ces planchers ainsi que les historiques des déplacements inter-étages (7-8) et (3-4) ont été générés.L'étude comparative des résultats obtenus avec les différents modèles d'analyse par éléments finis (i.e. excluant et incluant les murs de remplissage) a permis d'étudier les effets de la réhabilitation parasismique du bloc #7 et l'influence de la présence des murs de remplissage dans les blocs #7 et #8 sur leurs propriétés dynamiques. Finalement, les analyses sismiques ont permis de quantifier l'influence de ces effets sur le comportement des composants non-structuraux en comparant les spectres de planchers et les déplacements inter-étages. Au final, le bloc réhabilité a considérablement amélioré sa rigidité et par le fait même subit des accélérations de beaucoup supérieures à celles du bloc 8 non réhabilité. Par contre, les déplacements inter-étages sont réduits à des valeurs très faibles, ce qui améliore la performance des composants architecturaux et des composants fonctionnels connectés à plusieurs niveaux

State-of-the-art review: Seismic response analysis of Operational and Functional Components (OFCs) in buildings

A building is composed of two main types of components: structural components (see Figure 1) and non-structural components (NSCs) also called operational and functional components (OFCs) (see Figure 2). OFCs are those components or systems housed or mounted in the buildings which are not part of the main or intended load-resisting system of the structure. Therefore, the building structure is commonly called “primary structure” or “supporting structure” and OFCs are also known by alternative names such as "non-structural elements", "building attachments", "architectural, mechanical, and electrical elements", "secondary systems", and "secondary structural elements"

New methodology to generate floor design spectra (FDS) directly from uniform hazard spectra (UHS) for seismic assessment of non-structural components (NSCs) of buildings

Experience of past earthquakes has shown that many buildings have suffered from the failure of NSCs which caused life safety hazards, costly property damages, and significantly impacted the building functionality while their structural systems have performed satisfactorily. Avoiding these undesired consequences is of tremendous importance particularly in post-disaster buildings that must remain operational during and after earthquakes. That is why the rational assessment of seismic performance of NSCs has been the focus of many researchers during the last few decades with a focus on performance. Most recent editions of building codes incorporate empirical equations for seismic design of NSCs which are, for the most part, based on past experience and engineering judgment, rather than on objective experimental and analytical results. The lack of significant advances in design code provisions may be attributed partly to the fact that the previously developed analytical methods are too cumbersome to be employed in the design of ordinary NSCs (and their connections) housed in conventional buildings. As an effective solution to these problems, an original approach is developed and introduced in this thesis to generate Floor Design Spectra (FDS) directly from Uniform Hazard Spectra (UHS) specified in building codes. Generated FDS play the same role as UHS for structural components and can be used as a simple, fast, and reliable tool for seismic assessment and analysis of NSCs particularly in existing post-critical buildings. To develop and validate the proposed method, Ambient Vibration Measurements (AVM) data pertaining to 27 existing Reinforced Concrete (RC) buildings in have been collected and studied. The procedure has been coded in MATLAB to generate elastic Floor Response Spectrum (FRS) and inter-story drift curves at every floor of the building in both orthogonal horizontal (X and Y) directions, and considering NSCs with several damping ratios (2, 5, 10, and 20 % of critical viscous damping) having a fundamental period range of [0-4] seconds with intervals of 0.02 s. (damping ratios, period range, and intervals are user-defined in the code). The validation of the proposed method has been done through the case-study of one building from a pediatric hospital campus located in Montréal, Canada. Employing the proposed method over the entire 27-building database, approximately 132,000 FRS curves have been generated. In the first phase of the study, the generated FRS for the roof level and 5% NSC damping (ξNSC=5%) have been statistically analyzed and compared with the 5% damped UHS and a method has been proposed to generate an FDS for roof level and ξNSC=5% directly from the UHS. In the second phase of the study, the effects of the NSCs damping ratio and NSC location along the building height on the FDS have been statistically studied to extend the application of the methodology. As a result, two sets of modification factors were introduced that account for NSC damping and location effects. The extended methodology is able to produce FDS directly from UHS at any selected floor and any NSC damping ratio of interest. The methodology has been formulated for RC low and medium rise buildings and a set of equations have been recommended for each building category. The proposed method offers several advantages and improvements including capturing the effects of: 1- dynamic interaction between supporting system and NSCs, 2- higher and torsional modes of the building structure, 3- NSC damping. The method enables the generation of an exclusive FDS for each existing building taking its dynamic characteristics into account (as extracted from AVM records) and the acceleration design spectrum for the site. The generated FDS is a practical, accurate, and fast tool for seismic assessment and design of acceleration-sensitive NSCs particularly in post-critical buildings.La plupart des codes du bâtiment récents proposent des équations empiriques pour le calcul des charges sismiques sur les éléments non-structuraux, basées sur la pratique et le jugement d'experts plutôt que l'étude objective des observations expérimentales et des analyses. Cette thèse propose une nouvelle approche de conception pour pallier ces problèmes avec une méthode qui permet de générer des spectres de réponse de planchers directement à partir des spectres uniformes d'aléas sismiques prescrits dans les codes du bâtiment. En fait, ces spectres de planchers sont les outils de base pour l'analyse sismique des éléments non-structuraux au même titre que les spectres d'aléas sismiques le sont pour la structure des bâtiments. Les spectres de planchers sont un outil d'analyse simple, rapide et efficace pour évaluer la performance des éléments non-structuraux, en particulier dans les bâtiments postcritiques. La méthode proposée pour générer ces spectres de réponse est basée sur des mesures de vibrations ambiantes dont l'analyse permet d'extraire les caractéristiques dynamiques essentielles des bâtiments. Dans cette étude, 27 bâtiments à ossature en béton armé situés à Montréal ont été instrumentés et étudiés pour élaborer et valider la méthode. La procédure a été codée dans une application MATLAB qui génère les spectres de réponse élastique des planchers du bâtiment de même que les courbes de déplacements inter-étages pour chaque étage et selon deux directions horizontales principales. L'outil inclut également différents niveaux d'amortissement des éléments non-structuraux (2, 5, 10, et 20 % d'amortissement visqueux critique) dans la gamme de périodes naturelles variant de [0-4] secondes à intervalle de 0.02 s. La méthode est validée en détail à l'aide d'une étude de cas de un bâtiments.L'application de la méthode à la base de données de mesures ambiantes des 27 bâtiments en béton armé a permis de générer un ensemble d'environ 132,000 spectres de planchers. Dans une première étape, les spectres de réponse ont été générés pour le toit du bâtiment (en fait le plancher structural le plus élevé) avec un amortissement interne du composant non-structural, ξ¬NSC=5%. Ces spectres de réponse ont été analysés statistiquement et comparés aux spectres d'aléa sismique pour le site désigné avec amortissement structural de 5% (standard spécifié aux normes parasismiques pour les bâtiments). Dans une deuxième étape, l'analyse statistique des spectres en considérant l'effet de l'amortissement des éléments non-structuraux ainsi que leur emplacement selon les étages du bâtiment a permis d'étendre l'application de la méthode à tous les planchers du bâtiment considéré, au moyen de deux coefficients qui ajustent les valeurs du spectre du plancher le plus élevé avec amortissement de 5% aux valeurs appropriées pour l'étage et l'amortissement spécifique cu composant. Ainsi, la méthode permet de produire des spectres de réponse de planchers pour la conception parasismique des éléments non-structuraux directement à partir des spectres d'aléas sismiques spécifiés par les codes pour le site du bâtiment.La méthode proposée offre plusieurs avantages techniques importants. Étant basée sur la mesure de vibrations ambiantes dans les bâtiments, elle permet de tenir compte de plusieurs facteurs ignorés jusqu'à présent dans les normes, à savoir: 1- l'interaction dynamique entre la structure du bâtiment et les éléments non-structuraux; 2- l'effet des modes de vibration de plus haute fréquence, y inclus les modes de vibration en torsion du bâtiment; et 3- l'effet de l'amortissement interne des éléments non-structuraux. La méthode permet de générer des spectres de conception exclusifs pour chaque plancher d'un bâtiment existant pour lequel des mesures de vibration ambiantes ont permis d'extraire les caractéristiques dynamiques de base, et ce directement à partir du spectre d'aléa sismique spécifié au site du bâtiment

Direct generation of floor design spectra (FDS) from uniform hazard spectra (UHS) — Part II: extension and application of the method

This paper extends the methodology presented in the companion paper to study the effects of non-structural components’ (NSCs) damping ratio and their location in the building on the pseudo-acceleration floor response spectra (PA-FRS) of reinforced concrete buildings, and propose equations to derive floor acceleration design spectra (FDS) directly from the uniform hazard design spectra (UHS) for Montréal, Canada. The buildings used in the study are 27 existing reinforced concrete structures with braced frames and shear walls as their lateral load resisting systems: 12 are low-rise (up to 3 stories above ground), 10 are medium-rise (4 to 7 stories), and 5 are high-rise (10 to 18 stories). Based on statistical and regression analysis of floor acceleration spectra generated from linear dynamic analysis of coupled building–NSC systems, two sets of modification factors are proposed to account for floor elevation and NSC damping, applicable to the experimentally-derived FDS for roof level and 5% NSC damping. Modification factor equations could be derived only for the low-rise and medium-rise building categories, as insufficient correlation in trends could be obtained for high-rises given their low number. The approach is illustrated in detail for two typical buildings of the database, one low-rise (Building #4) and one medium-rise (Building #18), where the proposed FDS/UHS results show agreement with those obtained from detailed dynamic analysis. The work is presented in the context of a more general methodology to show its potential general applicability to other building types and locations.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Direct generation of floor design spectra (FDS) from uniform hazard spectra (UHS) — Part I: formulation of the method

In most current building codes, seismic design of non-structural components (NSCs) is addressed through empirical equations that do not capture NSC response amplification due to tuning effects with higher and torsional modes of buildings and that neglect NSC damping. This work addresses these shortcomings and proposes a practical approach to generate acceleration NSC floor design spectra (FDS) in buildings directly from their corresponding uniform hazard spectra (UHS). The study is based on the linear seismic analysis of 27 reinforced concrete buildings located in Montréal, Canada, for which ambient vibration measurements (AVM) are used to determine their in situ three-dimensional dynamic characteristics. Pseudo acceleration floor response spectra (PA-FRS) are derived at every building floor for four different NSCs damping ratios. The calculated roof FRS are compared with the 5% damped UHS and a formulation is proposed to generate roof FDS for NSCs with 5% damping directly from the UHS.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Damage detection in Jacket type offshore platforms using modal strain energy

Structural damage detection, damage localization and severity estimation of jacket platforms, based on calculating modal strain energy is presented in this paper. In the structure, damage often causes a loss of stiffness in some elements, so modal parameters; mode shapes and natural frequencies, in the damaged structure are different from the undamaged state. Geometrical location of damage is detected by computing modal strain energy change ratio (MSECR) for each structural element, which elements with higher MSECR are suspected to be damaged. For each suspected damaged element, by computing crossmodal strain energy (CMSE), damage severity as the stiffness reduction factor -that represented the ratios between the element stiffness changes to the undamaged element stiffness- is estimated. Numerical studies are demonstrated for a three dimensional, single bay, four stories frame of the existing jacket platform, based on the synthetic data that generated from finite element model. It is observed that this method can be used for damage detection of this kind of structures

THE EFFECT OF TEMPERATURE AND MAGNESIUM SIZE ON LOW TEMPERATURE MAGNESIOTHERMIC SYNTHESIS OF NANO STRUCTURES BORON CARBIDE BY MESOPOROUS CARBON (CMK-1)

In this study, Boron carbide was synthesized using Mesoporous Carbon CMK-1, Boron oxide, and magnesiothermic reduction process. The Effects of temperature and magnesium grain size on the formation of boron carbide were studied using nano composite precurser containg mesoporous carbon. Samples were leached in 2M Hydrochloric acid to separate Mg, MgO and magnesium-borat phases. SEM, XRD and Xray map analysis were caried out on the leached samples to characterize the  boron carbide. results showed that the reaction efficiency developed in samples with weight ratio of B2O3:C:Mg = 11:1.5:12, by increasing the temperature from 550 to 650 °C and magnesium powder size from 0.3 m to 3 m