No description available.

No description available.

Energy usage within the world is increasing at a drastic rate. Buildings currently consume a major amount of the total energy used within the United States, and most of this energy usage supports heating and cooling. This demand shows that new passive energy management systems are needed. The use of Increased Thermal Capacitance (ITC) is proposed as a new passive energy management system. To increase thermal capacitance, a piping system is either added into a building’s walls or ceiling. In this paper, a building with ITC added is compared to a similar building without ITC using the simulation program TRNSYS. Along with a comparison between the walls and ceiling, several parameters are analyzed for their effect on the performance of the ITC. ITC was found to be effective especially when located in the ceiling, with the location, specific heat and tank size being the most important factors.

Structural engineering has progressed from design for life safety limit states to performance based engineering, in which energy dissipation systems in structural frameworks assume prime importance. A visco-hyperelastic device is a completely new type of passive energy dissipation system that not only combines the energy dissipation properties of velocity and displacement dependent devices but also provides additional stability to the structure precluding overall collapse. The device consists of a viscoelastic material placed between two steel rings. The energy dissipation in the device is due to a combination of viscoelastic dissipation from rubber and plastic dissipation due to inelastic behavior of the steel elements. The device performs well under various levels of excitation, providing an excellent means of energy dissipation. The device properties are fully controlled through modifiable parameters. An initial study was conducted on motorcycle tires to evaluate the hyperelastic behavior and energy dissipation potential of circular rubber elements, which was preceded by preliminary finite element modeling. The rubber tires provided considerable energy dissipation while displaying a nonlinear stiffening behavior. The proposed device was then developed to provide additional stiffness that was found lacking in rubber tires. Detailed finite element analyses were conducted on the proposed device using the finite element software package ABAQUS, including parametric studies to determine the effect of the various parameters of device performance. This was followed by a nonlinear dynamic response history analysis of a single-story steel frame with and without the device to study the effects of the device in controlling structural response to ground excitations. Static analyses were also done to verify the stabilizing effects of the proposed device. Results from these analyses revealed considerable energy dissipation from the device due to both viscoelastic as well as plastic energy dissipation. Detailed experimental analyses on the proposed device, finite element analyses of the device on multistory structures have been put forth as the areas of future research. It may also be worthwhile to conduct further research, as suggested, in order to evaluate the use of scrap tires which is potentially a very valuable structural engineering material. / Master of Science

Light-framed wood structures generally have satisfied the life safety objective of the current seismic design approach. The main source of energy dissipation in such structures is the inelastic behavior of the connectors connecting framing and sheathing elements. Wood framed structures when subjected to strong ground excitations experience structural and non-structural damage which may incur large repair/replacement costs or may even render the structure out of service. Thus, it is very important to apply techniques to mitigate the seismic response of the light-framed structures and avoid large monetary losses. It is proposed to use commercially available permanent magnets, incorporated in the form of passive friction dampers, to dissipate a part of input energy induced due to strong ground motions, thereby reducing the inelastic energy dissipation demand of the lateral load resisting system. The force of attraction between the permanent magnet and ferromagnetic material like steel was utilized to produce the required friction resistance. A sliding wall configuration consisting of flexible permanent magnets and steel plates sandwiched between the plywood sheets was analyzed for its effectiveness in mitigating the response of a two story wood shear wall structure. The structural analysis program SAP2000 was used to perform nonlinear dynamic analysis of the finite element models generated using the meshing algorithms incorporated into 'WoodFrameMesh'. Nonlinear link elements available in SAP2000 were used to model the friction between the flexible magnet sheet and the steel plate. The effects of various modeling parameters on the solution of the nonlinear analysis were studied so as to arrive at appropriate values to represent the friction problem. Also the friction damped structure was analyzed to study its forced and free vibration characteristics. Further, the responses of the friction damped structure and the undamped structure were compared when subjected to different ground accelerations. The response of the friction damped structure was also compared to that of the structure in which the proposed friction dampers were replaced by normal shear walls. A huge reduction in the response of the friction damped structure was observed when compared to the response of the undamped structure. The friction damped structure was also analyzed for different values of modal damping ratios. Over all about 60-80% of the input energy was dissipated by friction damping in all the cases. The slip resistance of a flexible permanent magnet sheet was also verified in the laboratory. Above all the magnetic properties of commercially available permanent magnets and the effects of strong permanent magnets on human health were also studied. / Master of Science

A new seismic protection strategy called the hybrid passive control device (HPCD) has been developed which combines typical passive energy dissipation devices. It consists of a high damping rubber (HDR) sandwich damper in series with a buckling restrained brace (BRB). The HPCD provides energy dissipation at small deformations without significantly decreasing the structural period. The significant energy dissipation capacity of a BRB is provided for significant seismic events in the second phase. The transition between these two phases consists of an increasing stiffness as the device transitions from rubber damper to BRB. The HPCD reduces deformations, forces and accelerations from seismic events. The hyperelastic or stiffening effect also prevents resonant build-up and aids in collapse prevention due to p-delta effects. The first phase of this work included characterization of high damping rubber compounds and analytical modeling of the HPCD concept. Experimental testing was completed to measure both the static and dynamic material properties of six different rubber compounds. The two most promising rubber compounds were selected for possible inclusion in the device. Analytical models of these selected materials were developed for nonlinear solid finite element analysis. The most promising configuration of the device was selected from several options. The selected configuration was analyzed using the commercial finite element program ABAQUS. These models were used to confirm the validity of the theoretical behavior of the device. Additionally these tests were used to determine which of the rubber compounds performed best. Experimental testing of a half-scale HPCD specimen was carried out in the Structures and Materials Research Laboratory at Virginia Tech. The prototype was tested under cyclic and static loads. The experimental tests confirmed the potential of the hybrid device while highlighting minor issues with the design of the prototype. The final component in the research was an analytical study using hybrid devices in a 9-story steel moment frame structure. The devices were found to provide improved response over a special steel moment frame and a moment frame combined with a buckling restrained brace frame. / Ph. D.

This thesis presents the details of a study regarding both the use of linear viscous fluid dampers in controlling the interstory drift in steel moment frames, and the use of incremental dynamic analysis as a method of visualizing the behavior of these moment frames when subjected to seismic load effects. Models of three story and nine story steel moment frames were designed to meet typical strength requirements for office buildings in Seattle, Washington. These models were intentionally designed to violate seismic interstory drift restrictions to test the ability of the linear viscous fluid dampers to reduce these drifts to the point of code compliance. Dampers were included in one bay of every story in each model. These devices were used to produce total structural damping ratios of 5%, 10%, 20%, and 30% of critical. Undamped, traditional stiffness controlled models of both three stories and nine stories were also created for comparison purposes. Incremental dynamic analysis was used to subject these models to ten ground motions, each scaled to twenty incremental levels. Two new computer applications were written to facilitate this process. The results of these analyses were studied to determine if the linear viscous fluid dampers were able to cause compliance with codified drift limits. Also, incremental dynamic analysis plots were created to examine the effects of the dampers on structural behavior as damping increased from inherent to 30% of critical. It was found that including linear viscous fluid dampers in steel moment frame design can satisfactorily control interstory drift, and incremental dynamic analysis is a beneficial tool in visualizing dynamic structural behavior. / Master of Science

No description available.

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