Isolator displacements, floor accelerations, roof displacements, base shear and torsional moments are basic parameters that are considered in the design of seismically isolated structures. The aim of this study is to evaluate the effects of bidirectional earthquake excitations of near fault records on the response of base isolated structures in terms of basic parameters mentioned above. These parameters computed from nonlinear response history analysis (RHA) and they are compared with the parameters computed from equivalent lateral force procedure (ELF). Effect of asymmetry in superstructure is also examined considering mass eccentricity at each floor level. Torsional amplifications in isolator displacements, floor accelerations, roof displacements and base shear are compared for different level of eccentricities. Two buildings with different story heights are used in the analyses.The building systems are modeled in structural analysis program SAP2000. The scaling of ground motion data are taken from the study of &ldquo / Response of Isolated Structures Under Bi-directional Excitations of Near-fault ground Motions&rdquo / (Ozdemir, 2010). Each ground motion set (fault normal and fault parallel) are applied simultaneously for different range of effective damping of lead rubber bearing (LRB) and for different isolation periods.

Στην παρούσα εργασία μελετήθηκε η δυναμική συμπεριφορά μιας τυπικής σφαιρικής δεξαμενής για την εφαρμογή διάφορων συστημάτων σεισμικής προστασίας. Πέντε διαφορετικά συστήματα σεισμικής προστασίας εξετάζονται:Οι αποσβεστήρες ιξώδους απόσβεσης, οι αποσβεστήρες τριβής και οι μη-λυγίζοντες μεταλλικοί σύνδεσμοι που η λειτουργία τους βασίζεται στην κατανάλωση σεισμικής ενέργειας, και τα ελαστομερή εφέδρανα υψηλής απόσβεσης και αυτά με πυρήνα μολύβδου που η λειτουργία τους βασίζεται στην απομόνωση της βάσης της δεξαμενής. Η αριθμητική ανάλυση έγινε με την χρήση ενός λεπτομερούς μοντέλου πεπερασμένων στοιχείων που προσομοιώνει την ακριβή γεωμετρία της σφαιρικής δεξαμενής, την επίδραση του φαινομένου αλληλεπίδρασης υγρού-δεξαμενής για ενδεικτικά ποσοστά πλήρωσης, την αλληλεπίδραση εδάφους-δεξαμενής και την μη-γραμμική συμπεριφορά των συστημάτων σεισμικής προστασίας. Παρουσιάζονται αποτελέσματα της τέμνουσας δύναμης βάσης, της κατακόρυφης μετατόπισης της ελεύθερης επιφάνειας του περιεχόμενου υγρού και οριζόντιες μετατοπίσεις χαρακτηριστικών σημείων της δεξαμενής, για καθε περίπτωση συστήματος σεισμικής προστασίας υπό σεισμική διέγερση, και συγκρίνονται με τα αντίστοιχα που προκύπτουν για την σφαιρική δεξαμενή με τους συμβατούς χιαστούς συνδέσμους. / Various seismic protection systems are used to study numerically the dynamic behavior of a typical spherical liquid storage tank. Five different anti-seismic devices are investigated; nonlinear viscous dampers, buckling restrained braces and friction devices based on the passive energy dissipation technique and lead core and high damping rubber bearings based on base isolation technique. The numerical analysis is performed by means of a detailed finite element model, taking into account the exact geometry of the steel tank, the fluid-structure interaction effects for an arbitrary level of filling, the soil-structure interaction as well as the non-linearities introduced by either the dissipative bracing systems. Representative results for base shear forces, vertical displacements of the fluid content and displacements at characteristic locations of the spherical tank are presented and compared to those corresponding to a tank with a conventional bracing system.

Le projet LIGO a pour but la détection et l'étude d'ondes gravitationnelles via un réseau de détecteurs. LIGO possède deux détecteurs d'architecture et de fonctionnement identiques, situés aux États-Unis. Chaque détecteur est une version améliorée d'un interféromètre de Michelson avec des bras optiques de 4 km de long. Ces interféromètres ont observé une onde gravitationnelle pour la première fois en septembre 2015, suivi par cinq autres détections à ce jour. Ces détections marquent le début d™une nouvelle ère pour l'astrophysique, en liaison étroite avec la physique des trous noirs et des étoiles à neutrons. Depuis, un grand nombre d'activités sont en développement pour perfectionner les interféromètres. Cette thèse a pour objectif d'améliorer le temps de service des détecteurs, en répondant en particulier à deux problématiques majeures : le problème des impacts environnementaux, et notamment celui des tremblements de terre, ainsi que le problème lié à des couplages opto-mécaniques instables dans les cavités optiques, appelés instabilités paramétriques. Les stratégies de contrôle et les outils développés pour résoudre ces problématiques sont présentés. Les résultats prémilinaires montrent une réduction du temps d'arrêt généré par les tremblements de terre d'environ 40%. De plus, le dispositif ‚Acoustic Mode Damper™ développé pendant la thèse devrait complètement résoudre le problème des instabilités paramétriques pour LIGO. En conclusion, il sera démontré en quoi les problématiques résolues ont permis d'améliorer le cycle de service des détecteurs de LIGO de 4,6%, ce qui correspond à une augmentation du nombre d'ondes gravitationnelles détectées par an de 14%. / The LIGO project is a large-scale physics experiment the goal of which is to detect and study gravitational waves of astrophysical origin. It is composed of two instruments identical in design, located in the United States. The two instruments are specialized versions of a Michelson interferometer with 4km-long arms. They observed a gravitational-wave signal for the first time in September 2015 from the merger of two stellar-mass black holes. This is the first direct detection of a gravitational wave and the first direct observation of a binary black hole merger. Five more detections from binary black hole mergers and neutron stars merger have been reported to date, marking the beginning of a new era in astrophysics. As a result of these detections, many activities are in progress to improve the duty cycle and sensitivity of the detectors. This thesis addresses two major issues limiting the duty cycle of the LIGO detectors: environmental impacts, especially earthquakes, and the issue of unstable opto-mechanical couplings in the cavities, referred to as parametric instabilities. The control strategies and tools developed to tackle these issues are presented. Early results have shown a downtime reduction during earthquakes of ~40% at one of the LIGO sites. Moreover, the electro-mechanical device called ‚Acoustic Mode Damper™ designed and tested during the thesis should completely solve the issue of parametric instabilities for LIGO. In conclusion, we will show that the problems tackled in this thesis improved the overall duty cycle of LIGO by 4.6%, which corresponds to an increase of the gravitational-wave detection rate by 14%.

Se desarrolla un método de diseño utilizando el concepto de transmisibilidad relativa para la solución del problema de grandes desplazamientos de la base (displacement demand) en estructuras aisladas bajo acción de terremotos. El procedimiento se desarrolla en el dominio de la frecuencia, esto para obtener la rigidez y amortiguamiento del sistema aislante. Posteriormente, se utiliza un modelo de estructura benchmark de múltiples grados de libertad, excitado por señales de entrada sísmica reales para la evaluación del procedimiento de diseño, siendo la propuesta un control puramente pasivo. Los resultados muestran la eficacia de esta metodología, ya que los desplazamientos de la base obtenidos con un sistema netamente de control pasivo son muy cercanos a los desplazamientos alcanzados con el uso de sistemas control activo que son más complejos y costosos. / A design method is developed using the relative transmissibility concept to solve the problem of large base displacement (displacement demand) in isolated structures under the action of earthquakes. The procedure is developed in the frequency domain, this to obtain the stiffness and damping of the isolation system. Subsequently, a multiple degree of freedom benchmark structure model is used, excited by a real seismic input signals for the evaluation of the design procedure, the proposal is a purely passive control. The results show the effectiveness of this methodology, due to the fact that base displacement obtained with a purely passive control system are very close to displacement achieved with the use of active control systems that are more complex and expensive. / Tesis

No description available.

Scrap tyres provide numerous advantages from the viewpoint of civil engineering practices. Scrap tyres are light weight, have high vibration absorption, high elastic compressibility, high hydraulic conductivity, and temperature isolation potential. Scrap tyres have a thermal resistivity that is about seven times higher than soil; they produce low earth pressure and absorb vibrations. Many new techniques have emerged with time to utilize these advantageous characteristics for practical purposes in civil engineering. Though current reuse and recovery of scrap tyres has reduced the amount of landfills, but still there is a need for developing additional practices for the reuse of scrap tyres. Moreover, most of present practices do not use its vibration absorption capacity efficiently. To use the scrap tyres as individual material or mixed with soil in civil engineering applications, the systematic understanding of static and dynamic properties of sand-rubber mixtures (SRM) are of prime importance. In the present study an attempt has been made to characterize the SRM to use them as low-cost isolation material for low-to-medium rise buildings. Proposal of this isolation system using SRM is addressed in this study in four parts; in the first part, the estimation of shear strength and volumetric characteristics of the SRM were carried out. A total of seven different rubber sizes (six sizes of granulated rubber; 2 - 1 mm; 4.75 - 2 mm; 5.6 - 4.75 mm; 8 - 5.6 mm; 8 - 9.5 mm; 12.5 - 9.5 mm and one size of tyre chips; 20 - 12.5 mm) were considered for characterizing the SRM, and the rubber size which has higher shear strength characteristics is identified as optimum size for further studies. Second part deals with the effect of reinforcement on SRM with higher rubber content (50% and 75% rubber by volume). In the third part, dynamic properties of selected SRM combination with and without reinforcement were generated from experimental studies. In the last part, the numerical analysis was carried out using finite element program Strand7 to find out optimum dimension of proposed isolation scheme and reduction of spectral accelerations. In addition, the laboratory model tests were also carried out on square footing supported on unreinforced and reinforced SRM. The relative performances of reinforcement on settlement characteristics of SRM for 50% and 75% SRM have been compared with unreinforced SRM. Engineering behaviour of SRM has been studied by considering different rubber sizes and compositions by carrying out large scale direct shear test and Unconsolidated Undrained (UU) triaxial test. The shear strength characteristics such as peak shear stress, cohesion, friction angle, secant/elastic modulus, volumetric strain, failure and ultimate strength, ductility/brittleness index, and energy absorption capacity of sand and SRM were determined. The optimum percentage rubber content based on maximum shear strength and energy absorption capacity has been arrived. The granulated rubber size (12.5 - 9.5 mm) and percentage ratio, 30% by volume is found to be optimum size and content, which gives the maximum energy absorption capacity and lower brittleness index values compared to other rubber sizes. This chapter also describes the applicability of concept of Response Surface Methodology (RSM) to identify an approximate response surface model from experimental investigations on the engineering properties of sand and SRM. The experimental data were quantitatively analyzed by multiple regression models by correlating response variables with input variables in this study. To consume more tyres in SRM, rubber mix of 50 % and 75 % mixes are studied and these SRM results in lower shear strength and higher volume change when compared to 30 % SRM. To improve shear strength and reduce compressibility, geosynthetic reinforcement study has been carried out for 50% and 75% rubber by volume. Here geotextile, geogrid and geonets were used as reinforcement and number of layers and spacing between layers were varied. Finally type of reinforcement, number of layers and optimum spacing are arrived for the optimum rubber size of 12.5 - 9.5 mm for reinforced SRM. This study found that 4 layers with equal spacing of geotextile for 50 % SRM and geonet for 75 % SRM shows better strength when compared to other combinations. Further dynamic properties such as shear modulus and damping values at different strain level are estimated for red soil, sand, 30 % SRM and unreinforced and reinforced 50 % and 75 % SRM by carrying out resonant column tests and cyclic triaxial tests. The normalized shear modulus and damping ratio curves have been developed for these materials. The experimental results indicate that, shear modulus increases for 30% rubber by volume when compared to sand, thereafter the shear modulus values decreased with a further increase in rubber content in SRM. Whereas the damping ratio increases with increasing rubber content in SRM. For sand and SRM, with an increase in confining pressure shear modulus increases and damping ratio decreases. Based on the comprehensive set of experimental results, a modified hyperbolic model has been proposed. These properties are further used in the numerical analysis to find out the effectiveness of SRM as isolation material. Numerical dynamic analysis has been carried out on a 2-D finite element model of the soil-foundation-structure system. The building model has been generated considering the typical G+2 building resting on 20 m thick soil followed by rock depth and foundation is placed at 2.0 m below ground level. The beams and columns in the superstructure are modeled using 2-D frame elements. The soil column has been modeled using 4-noded 2-D plane strain plate elements. Considering the transmitting boundary condition, viscous dampers are implemented at the base of the computational soil domain in order to mitigate the reflective effects of waves. The Newmark family method (average acceleration method) has been used to calculate the displacement, velocity and acceleration vectors. Comprehensive numerical simulations have been carried out on the soil-foundation-structure system by varying rubber content in SRM (30%, 50% and 75% granulated rubber by volume), depth and thickness of SRM around footing and considering two input earthquake acceleration time history. It was found that earthquake vibrations are considerably reduced for SRM with higher rubber content. The optimum dimension of SRM giving maximum reduction in shaking level is found to be 3B below the footing and 0.75B (where B is the width of footing) on the side of the footing. Generally, the shaking levels at different floor can be reduced by 30-50%, with the use of 75% SRM. The results also indicated that the effectiveness of proposed system would depend on the characteristics of ground motion. To study the bearing capacity of square footing on SRM, laboratory model tests were carried out on square footing supported on unreinforced and reinforced SRM. The SRM combination which have been used for numerical studies are used in this model studies to know the bearing capacity and settlement characteristics. The optimum dimension of SRM around footing has been constructed. Model tests results show that, the bearing capacity decreases and settlement increases steadily with the increase in rubber content in SRM. Addition of reinforcement to SRM significantly improved the bearing capacity and reduced settlement characteristics. Reinforced SRM may be used as an effective low cost isolation scheme to reduce earthquake vibrations.

No description available.

Nuclear power plays a crucial role in energy supply in the world: around 15% of the electricity generated worldwide is provided from nuclear stations avoiding around 2.5 billion tonnes of CO2 emissions. As of January 2016, 442 reactors that generated 380+ GW were in operation and 66 new reactors were under construction. The seismic design of new nuclear power plants (NPPs) has gained much interest after the high-profile Fukushima Dai-ichi accident. In the UK, a tectonically stable continental region that possesses medium-to-low seismic activity, strong earthquakes capable of jeopardising the structural integrity of NPPs, although infrequent, can still occur. Despite that no NPP has been built in Great Britain after 1995, a New Build Programme intended to build 16 GW of new nuclear capacity by 2030 is currently under way. This PhD project provides a state-of-the-art framework for seismic probabilistic safety assessment and risk control of NPPs in Northwest Europe with particular application to the British Isles. It includes three progressive levels: (i) seismic input, (ii) seismic risk analysis, and (iii) seismic risk control. For seismic input, a suitable model to rationally define inputs in the context of risk assessments is proposed. Such a model is based on the stochastic simulation of accelerograms that are compatible with seismic scenarios defined by magnitude 4 < Mw < 6.5, epicentral distance 10 km < Repi < 100 km, and different types of soil (rock, stiff soil and soft soil). It was found to be a rational approach that streamlines the simulation of accelerograms to conduct nonlinear dynamic analyses for safety assessments. The model is a function of a few variables customarily known in structural engineering projects. In terms of PGA, PGV and spectral accelerations, the simulated accelerograms were validated by GMPEs calibrated for the UK, Europe and the Middle East, and other stable continental regions. For seismic risk analysis, a straightforward and logical approach to probabilistically assess the risk of NPPs based on the stochastic simulation of accelerograms is studied. It effectively simplifies traditional approaches: for seismic inputs, it avoids the use of selecting/scaling procedures and GMPEs; for structural outputs, it does not use Monte Carlo algorithms to simulate the damage state. However, it demands more expensive computational resources as a large number of nonlinear dynamic analyses are needed. For seismic risk control, strategies to control the risk using seismic protection systems are analysed. This is based on recent experience reported elsewhere of seismically protected nuclear reactor buildings in other areas of medium-to-low seismic activity. Finally, a scenario-based incremental dynamic analysis (IDA) is proposed aimed at the generation of surfaces for unacceptable performance of NPPs as function of earthquake magnitude and distance. It was found that viscous-based devices are more efficient than hysteretic-based devices in controlling the seismic risk of NPPs in the UK. Finally, using the proposed scenario-based IDA, it was found that when considering all controlling scenarios for a representative UK nuclear site, the risk is significantly reduced ranging from 3 to 5 orders of magnitude when using viscous-based devices.

El presente estudio de investigación evalúa la respuesta sísmica de una clínica con aislamiento símico en Lima bajo la Norma Peruana de Aislamiento Sísmico E.031. Esta será comparada con la norma la Norma Chilena de Diseño Sísmico de Edificios NCh2745 y la Norma Americana ASCE/SEI 7, dichas normas internacionales han sido diseñadas para soportar eventos sísmicos severos, presentando parámetros rigurosos, con los cuales se podrá destacar las fortalezas y debilidades frente a la nueva Norma Peruana. En los capítulos siguientes se da entendimiento a la información que se debe poseer para analizar las tres normas, conceptos básicos de sismología y dinámica estructural, dentro de cada norma se verán los alcances, factores y parámetros que intervienen en la determinación del espectro de diseño, así como el análisis sísmico dinámico que las normas proponen y el modelamiento de la estructura de la clínica en el software ETABS. Luego se comparan los resultados de la respuesta sísmica, desplazamientos laterales, derivas y fuerzas cortantes, en las que se verán las exigencias que cada norma, llegando a saber si nuestra Norma Peruana en su modificación y mejora de su contenido se proyecta a ser una de las mejores normas de diseño sismorresistente, obteniendo así una perspectiva de nuestra Norma Peruana frente a una norma internacional ya consolidada y avalada por los años frente a sismos severos. / This research study evaluates the seismic response of a clinic with simian isolation in Lima under the draft Peruvian Seismic Isolation Standard E.031. This will be compared with the North American standard ASCE SEI 7-16 and the Chilean Seismic Design Standard for Buildings 2745, these international standards have been designed to withstand severe seismic events, presenting rigorous parameters, with which we can highlight the strengths and weaknesses against the new Peruvian Standard. In the following chapters, understanding is given to the information that must be possessed to analyze the three norms, basic concepts of seismology and structural dynamics, within each norm the scope, factors and parameters that are involved in the determination of the design spectrum will be seen, as well as the dynamic seismic analysis that the standards propose and the modeling of the clinical structure in the ETABS software. Then the results of the seismic response, lateral displacements, drifts and shear forces are compared, in which the requirements of each norm will be seen, getting to know if our Peruvian Standard in its modification and improvement of its content is projected to be one of the best seismic resistant design standards, thus obtaining a perspective of our Peruvian Standard against an international standard already consolidated and endorsed by the years against severe earthquakes. / Tesis

Metamaterials are typically described as materials with ’unusual’ wave propagation properties. Originally developed for electromagnetic waves, these materials have also spread into the field of acoustic wave guiding and cloaking, with the most relevant of these ’unusual’ properties, being the so called band-gap phenomenon. A band-gap signifies a frequency region where elastic waves cannot propagate through the material, which in principle, could be used to protect buildings from earthquakes. Based on this, two relevant concepts have been proposed in the field of seismic engineering, namely: metabarriers, and metamaterial-based foundations. This thesis deals with the development of the Metafoundation, a metamaterial-based foundation system for the seismic protection of fuel storage tanks against excessive base shear and pipeline rupture. Note that storage tanks have proven to be highly sensitive to earthquakes, can trigger sever economic and environmental consequences in case of failure and were therefore chosen as a superstructure for this study. Furthermore, when tanks are protected with traditional base isolation systems, the resulting horizontal displacements, during seismic action, may become excessively large and subsequently damage connected pipelines. A novel system to protect both, tank and pipeline, could significantly augment the overall safety of industrial plants. With the tank as the primary structure of interest in mind, the Metafoundation was conceived as a locally resonant metamaterial with a band gap encompassing the tanks critical eigenfrequency. The initial design comprised a continuous concrete matrix with embedded resonators and rubber inclusions, which was later reinvented to be a column based structure with steel springs for resonator suspension. After investigating the band-gap phenomenon, a parametric study of the system specifications showed that the horizontal stiffness of the overall foundation is crucial to its functionality, while the superstructure turned out to be non-negligible when tuning the resonators. Furthermore, storage tanks are commonly connected to pipeline system, which can be damaged by the interaction between tank and pipeline during seismic events. Due to the complex and nonlinear response of pipeline systems, the coupled tank-pipeline behaviour becomes increasingly difficult to represent through numerical models, which lead to the experimental study of a foundation-tank-pipeline setup. Under the aid of a hybrid simulation, only the pipeline needed to be represented via a physical substructure, while both tank and Metafoundation were modelled as numerical substrucutres and coupled to the pipeline. The results showed that the foundation can effectively reduce the stresses in the tank and, at the same time, limit the displacements imposed on the pipeline. Leading up on this, an optimization algorithm was developed in the frequency domain, under the consideration of superstructure and ground motion spectrum. The advantages of optimizing in the frequency domain were on the one hand the reduction of computational effort, and on the other hand the consideration of the stochastic nature of the earthquake. Based on this, two different performance indices, investigating interstory drifts and energy dissipation, revealed that neither superstructure nor ground motion can be disregarded when designing a metamaterial-based foundation. Moreover, a 4 m tall optimized foundation, designed to remain elastic when verified with a response spectrum analysis at a return period of 2475 years (according to NTC 2018), reduced the tanks base shear on average by 30%. These results indicated that the foundation was feasible and functional in terms of construction practices and dynamic response, yet unpractical from an economic point of view. In order to tackle the issue of reducing the uneconomic system size, a negative stiffness mechanism was invented and implemented into the foundation as a periodic structure. This mechanism, based on a local instability, amplified the metamaterial like properties and thereby enhanced the overall system performance. Note that due to the considered instability, the device exerted a nonlinear force-displacement relationship, which had the interesting effect of reducing the band-gap instead of increasing it. Furthermore, time history analyses demonstrated that with 50% of the maximum admissible negative stiffness, the foundation could be reduced to 1/3 of its original size, while maintaining its performance. Last but not least, a study on wire ropes as resonator suspension was conducted. Their nonlinear behaviour was approximated with the Bouc Wen model, subsequently linearized by means of stochastic techniques and finally optimized with the algorithm developed earlier. The conclusion was that wire ropes could be used as a more realistic suspension mechanism, while maintaining the high damping values required by the optimized foundation layouts. In sum, a metamaterial-based foundation system is developed and studied herein, with the main findings being: (i) a structure of this type is feasible under common construction practices; (ii) the shear stiffness of the system has a fundamental impact on its functionality; (iii) the superstructure cannot be neglected when studying metamaterial-based foundations; (iv) the complete coupled system can be tuned with an optimization algorithm based on calculations in the frequency domain; (v) an experimental study suggests that the system could be advantageous to connected pipelines; (vi) wire ropes may serve as resonator suspension; and (vii) a novel negative stiffness mechanism can effectively improve the system performance.