The damaging effects of strong ground motions on highway bridges have revealed the limitations of conventional design methods and emphasized the need for innovative design concepts. Although seismic isolation systems have been proven to be an effective method of improving the response of bridges during earthquakes, the performance of base-isolated structures during near-field earthquakes has been questioned in recent years. Near-field earthquakes are characterized by long period and large- velocity pulses. They amplify seismic response of the isolation system since the period of these pulses usually coincides with the period of the isolated structures. This study explores the feasibility and effectiveness of shape memory alloy (SMA)-based isolation systems in order to mitigate the response of bridge structures against near-field ground motions. SMAs have several unique properties that can be exploited in seismic control applications. In this work, uniaxial tensile tests are conducted first to evaluate the degree to which the behavior of SMAs is affected by variations in loading rate and temperature. Then, a neuro-fuzzy model is developed to simulate the superelastic behavior of SMAs. The model is capable of capturing rate- and temperature-dependent material response while it remains simple enough to carry out numerical simulations. Next, parametric studies are conducted to investigate the effectiveness of two SMA-based isolation systems, namely superelastic-friction base isolator (S-FBI) system and SMA/rubber-based (SRB) isolation system. The S-FBI system combines superelastic SMAs with a flat steel-Teflon bearing, whereas the SRB isolation system combines SMAs with a laminated rubber bearing rather than a sliding bearing. Upon evaluating the optimum design parameters for both SMA-based isolation systems, nonlinear time history analyzes with energy balance assessment are conducted to compare their performances. The results show that the S-FBI system has more favorable properties than the SRB isolation system. Next, the performance of the S-FBI systems is compared with that of traditional isolation systems used in practice. In addition, the effect of outside temperature on the seismic response of the S-FBI system is assessed. It is revealed that the S-FBI system can successfully reduce the response of bridges against near-field earthquakes and has excellent re-centering ability.

En la actualidad, existen muchas estructuras de gran importancia y funcionalidad (hospitales, colegios, entre otros) que albergan un gran número de personas y de las que se espera que ante un evento sísmico severo se mantengan operativas, sin embargo, muchas de estas edificaciones esenciales han sido construidas con códigos sísmicos antiguos, los cuales podrían no tener los requerimientos actuales de resistencia y rigidez. Por lo que podrían fallar o tener un comportamiento deficiente ante sismos moderados y/o severos. Entonces, es así como la investigación aborda como caso de estudio uno de los bloques del Hospital Luis Negreiros, en el que se desarrolla un análisis sísmico y se propone su reforzamiento con dispositivos de protección sísmica, en especial disipadores de fluido viscoso, los cuales absorben la energía de entrada del sismo y aumentan el amortiguamiento de la estructura, lo que permite lograr un buen comportamiento durante la acción de sismos leves o moderados. La investigación consta de 6 capítulos, en el primer capítulo se explica los antecedentes de la investigación, hipótesis y objetivos, en el segundo capítulo se desarrolla el marco teórico de la investigación, una compilación del estado del arte relacionado a protección sísmica, el tercer capítulo explica el modelo matemático de los dispositivos así como las configuraciones existentes, en el cuarto capítulo se desarrolla la metodología de la investigación, en el quinto capítulo se analiza el caso de estudio y se plantea una propuesta de reforzamiento. En el sexto y sétimo capítulo se desarrollan las conclusiones y recomendaciones, respectivamente. / Currently, there are many structures of great importance and functionality (hospitals, schools, among others) that are home to a large number of people and which are expected to remain operational before a severe seismic event; however, many of these essential buildings have been built with old seismic codes, which may not have the current requirements for strength and rigidity. So they could fail or have a deficient behavior against moderate and / or severe earthquakes. Thus, this is how the research deals with one of the blocks of the Luis Negreiros Hospital as a case study, in which a seismic analysis is developed and its reinforcement is proposed with seismic protection devices, especially viscous fluid dissipaters, which absorbs the input energy of the earthquake and increase the damping of the structure, which allows to achieve good behavior during the action of mild or moderate earthquakes. The research consists of 6 chapters, in the first chapter the background of the research, hypotheses and objectives is explained, in the second chapter the theoretical framework of the research is developed, a compilation of the state of the art related to seismic protection, the third chapter explains the mathematical model of the devices as well as the existing configurations, in the fourth chapter the research methodology is developed, in the fifth chapter the case study is analyzed and a reinforcement proposal is proposed. In the sixth and seventh chapter the conclusions and recommendations are developed, respectively. / Tesis

El capítulo I presenta una introducción y aspectos generales en base a los antecedentes, realidad problemática, formulación del problema; así como la definición de la hipótesis y los objetivos concluyentes. El capítulo II se realiza el estado del arte basándose en los fundamentos teóricos más importantes en base a la eficiencia de los AMS sometidos a fuerzas o movimientos armónicos en la base; así también describe generalidades en base a la clasificación general de los sistemas de protección sísmica, fundamentos del AMS, y resumen de trabajos relevantes sobre aplicaciones en edificios y otras obras de ingeniería civil. El capítulo III, IV y V se refieren al comportamiento de estructuras sin AMS frente a acciones sísmicas. En particular se analizan las edificaciones existentes reales de 7, 10 y 20 niveles en base al análisis computacional. El capítulo VI presenta los parámetros de diseño de un AMS para tres aplicaciones de edificios reales de 7, 10 y 20 niveles, concluyendo con la determinación de las características óptimas para la construcción y los efectos generados por estas. Finalmente, en el capítulo VII se presentan las principales conclusiones y recomendaciones basadas en la investigación realizada. / Chapter I presents an introduction and general aspects based on the background, problematic reality, formulation of the problem, as well as the definition of the hypothesis and the conclusive objectives. Chapter II the state of the art is made based on the most important theoretical foundations based on the efficiency of the AMS subjected to forces or harmonic movements in the base; it also describes generalities based on the general classification of seismic protection systems, foundations of the AMS, and summary of relevant works on applications in buildings and other civil engineering works. Chapter III, IV and V refers to the behavior of structures without AMS against seismic actions. In particular, the real existing buildings of 7, 10, and 20 levels are analyzed based on the computational analysis. Chapter VI presents the design parameters of an AMS for three applications of real buildings of 7, 10 and 20 levels, concluding with the determination of the optimal characteristics for the construction and the effects generated by these. Finally, Chapter VI presents the main conclusions and recommendations based on the research carried out. / Tesis

Résumé : Ce projet de maîtrise s’intéresse au comportement ultime d’une structure en acier, contrôlée sismiquement par des amortisseurs élastomères et des contreventements en chevron. Les séismes peuvent causer des dommages considérables quand les infrastructures et les bâtiments ne sont pas construits selon les normes et les techniques appropriées. Par conséquent, réduire l’impact des séismes revient particulièrement à construire des ouvrages sécuritaires en tenant compte bien entendu du paramètre économique. Ainsi Gauron, Girard, Paultre et Proulx ont étudié en 2009, un système de reprise de forces latérales, constitué uniquement de treventements en chevron montés en série avec des amortisseurs en caoutchouc naturel fibré ayant de nombreux avantages. Premièrement, le système reste élastique sous le séisme de design en réduisant les efforts sismiques linéaires par un facteur supérieur à R[indice inférieur d] = 3 par rapport à un cadre conventionnel. Deuxièmement, il est capable de contrôler les déplacements sous la limite du CNBC 2010 (Code National du Bâtiment du Canada 2010), et même de réduire ces derniers dans certains cas. Par conséquent, il permet de réduire les sections des poutres et des poteaux des cadres par rapport à une structure conventionnelle ainsi que les coûts de réparation après un séisme. Toutefois, le comportement à l’état limite ultime d’un tel système, ses limites et ses réserves de sécurité restaient à déterminer. Ainsi, l’objectif global de ce projet de recherche est de déterminer les différents mécanismes de ruine possibles de ce système, d’établir des limites et réserves de sécurité, et de préciser, après avoir formulé certaines recommandations, à quelles conditions il peut être utilisé dans le dimensionnement de nouvelles structures. Pour atteindre les objectifs fixés, deux essais quasi statiques ont été réalisés sur deux cadres en acier dimensionnés avec le système. Des essais dynamiques ont aussi été réalisés afin d’avoir les propriétés viscoélastiques des amortisseurs. Le premier essai a mis en évidence un mécanisme de ruine inattendu et prématuré qui a souligné un défaut majeur dans les connexions des diagonales avec l’amortisseur. Le second essai a révélé un des mécanismes de ruine envisagés initialement où le caoutchouc se déchire après l’initiation du flambement dans la diagonale comprimée. Les résultats expérimentaux ont montré que l’amortisseur constitue le maillon faible du système, et que des efforts parasites peuvent réduire significativement la capacité portante des structures dimensionnées avec un tel système. Dans les deux cas, les résultats ont montré que la méthode de dimensionnement du système tel qu’elle est définie actuellement mérite d’être améliorée. En ce sens, des recommandations relatives au dimensionnement des différents éléments des structures dimensionnées avec le système ont été élaborées, particulièrement en ce qui concerne le caoutchouc et les connexions. // Abstract : This thesis focuses on the ultimate behavior of steel structures, controlled seismically by elastomeric dampers and chevron bracings. Earthquakes can cause considerable damages when infrastructures and buildings are not built considering appropriate standards and technics. Therefore, mitigating the impact of earthquakes means essentially building safe structures by taking account of economic parameters too. Thus Gauron, Girard, Paultre and Proulx studied in 2009 a seismic force resisting system consisting only of chevron braces connected in series with fiber-reinforced natural rubber dampers that offers many benefits. First, the system remains elastic under the design earthquake by reducing linear seismic efforts by a factor of R[subscript d] = 3 compared to a conventional frame. Secondly, it allows to control the displacements under the limits of NBCC 2010 (National Building Code of Canada 2010), and even to reduce them in some cases. Therefore, it allows a reduction of sections of beams and columns of conventional frames and it prevents repairing costs of the structure after an earthquake. However, the ultimate limit state behavior of this system, its limitations and safety reserves have not been determined yet. Thus, the overall objective of this project is to determine the different possible failure mechanisms of the system, to set its limits and safety reserves, and to state after some recommendations, how it can be used in the design of new structures. To achieve these objectives, two quasi static tests were performed on two steel frames designed with the new system. Dynamic tests were also conducted to get the viscoelastic properties of the damping material. The first quasi static test revealed an unexpected and premature failure mechanism that pointed out a major flaw in the connections of the braces with the damper. The second test revealed one of the failure mechanisms originally expected where the rubber tears after buckling of the compression brace. The experimental results have shown that the damper is the weak element in the system, and that additional forces can significantly reduce the structural capacity of structures designed with the system. In both cases, the results have shown that the actual design method of the system should be improved. Thus, recommendations for the design of elements of structures designed with this system have been developed, particularly with regard to the rubber and brace connections.