Structural systems often show nonlinear behavior under severe excitations generated by natural hazards. In that condition, the restoring force becomes highly nonlinear showing significant hysteresis. The hereditary nature of this nonlinear restoring force indicates that the force cannot be described as a function of the instantaneous displacement and velocity. Accordingly, many hysteretic restoring force models were developed to include the time dependent nature using a set of differential equations. This survey contains a review of the past, recent developments and implementations of the Bouc-Wen model which is used extensively in modeling the hysteresis phenomenon in the dynamically excited nonlinear structures.
ResumenBasado en la idea de reducir la demanda sísmica en lugar de aumentar la capacidad resistente de las estructuras, el aislamiento sísmico es un método simple para mitigar o reducir los posibles daños producidos por los terremotos. La correcta aplicación de esta tecnología conduce a un mejor comportamiento de las estructuras, que sigue siendo esencialmente elástico durante los terremotos de gran magnitud. El núcleo de esta tecnología es el aislador. La mayoría de los aisladores sísmicos disponibles en la actualidad siguen teniendo limitaciones prácticas que impiden que funcionen según lo previsto e imponen restricciones a su uso efectivo y al nivel de protección proporcionado.En esta Tesis, se presenta un aislador sísmico avanzado llamado roll-n-cage (RNC). Se propone investigar su eficiencia a través de simulación numérica, en un intento de crear un sistema de aislamiento sísmico práctico, efectivo y económico, que tiene por objeto resolver los principales inconvenientes de los actuales sistemas de aislamiento sísmico, manteniendo sus principales ventajas. Este aislador incorpora aislamiento, disipación de energía, amortiguamiento y capacidad de fuerza recuperadora en una sola unidad. Además, ofrece una resistencia al viento significativa y una amplia gama de flexibilidad horizontal, por lo que es adecuado para proteger las estructuras de masa ligera, moderada y grande, así como para proteger equipos sensibles, hardware y / o antigüedades alojados en edificios. Por otra parte, las cuestiones relativas a la viabilidad, los costes de construcción y la disponibilidad de materiales, reducción o prevención de las respuestas de torsión y la resistencia a la elevación son abordados a fondo durante el diseño del aislador RNC.El aislador RNC propuesto es descrito en profundidad y sus principios de funcionamiento son presentados en detalle. La caracterización mecánica del dispositivo se ha llevado a cabo por medio de un código computacional sofisticado que simula la respuesta de los dispositivos como si estuvieran sujetos a 4 una máquina de pruebas reales. A través de este esquema, se consigue analizar numéricamente el comportamiento del aislador RNC bajo el efecto simultáneo de cargas horizontales y verticales, como se da típicamente en situaciones prácticas. Además, se presenta una descripción matemática de las principales características asociadas a la rodadura de los aisladores RNC. Asimismo se obtiene un modelo matemático para describir en una forma razonable y manejable la relación fuerza desplazamiento exhibida por el aislador de RNC.Para evaluar la viabilidad del aislador RNC y para comprobar su capacidad para proteger los sistemas estructurales y no estructurales de los riesgos sísmicos, el dispositivo se implementa numéricamente en una variedad de estructuras con masas ligeras y grandes, además de en equipos sensibles alojados en los pisos superiores de dichas estructuras. Para extraer conclusiones de carácter relativamente general sobre el funcionamiento del aislador RNC, se estudia una amplia gama de terr...
This paper presents the results of an extensive series of simulation tests to identify the mechanical characteristics of an innovative isolation device known as the Roll-N-Cage (RNC) isolator. The seismic performance of an RNC passive control scheme is subsequently investigated on a model of the cable-stayed bridge benchmark. Starting from different configurations studied in the laboratory for a 1/10 reduced-scale prototype, the RNC isolator stiffness and damping properties are investigated in terms of cyclic tests with different parameters. Tests at the ultimate level state consisting of monotonic shear and axial loading have been also carried out as a part of the qualification process. The goal of this study is twofold: first, to examine the main integrated mechanisms of the RNC isolator through sophisticated 3D finite element simulation models using a multi-purpose finite element code. The main result of this step is to attempt modeling the force–displacement relationship using the standard Bouc–Wen model of smooth hysteresis. The second aim of this study is the numerical assessment of the device efficiency through its implementation into a bridge model considering several ground motions as external excitations. Based on these extensive studies, it was found that the RNC isolator is promising as a reliable isotropic horizontal isolation device for bridge structures.Peer ReviewedPostprint (published version
Seismic isolation is an appreciable control strategy that reduces the vibrations of structural and nonstructural systems induced by strong ground motions. However, under near-fault (NF) ground motion, the seismic isolation devices might perform poorly because of large isolator displacements caused by long-period large velocity and\ud displacement pulses associated with such strong motion. The objective of this paper is to assess the effectiveness of a new seismic isolation device, referred to as roll-in-cage (RNC) isolator, in protecting against NF ground motions. The device is intended to achieve a balance in controlling isolator displacement demands and structural\ud accelerations. The RNC isolator provides in a single unit all the necessary functions of rigid support, horizontal flexibility with enhanced stability, and energy dissipation characteristics. Moreover, it is distinguished from other isolation devices by two unique features: (i) it has a built-in energy-absorbing buffer to limit the design displacement under strong excitation, and (ii) it has a built-in linear recentering mechanism that prevents residual displacement after earthquakes. The seismic response of multistory buildings isolated by the RNC isolator is investigated under three recorded NF earthquakes and three synthetic ground motions. The results show that the RNC isolator is a convenient isolation system in protecting against NF earthquakes.Peer ReviewedPostprint (published version
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