Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1982. / Microfiche copy available in Archives and Barker. / Includes bibliographical references. / by Peter David McQuade. / M.S.

ABSTRACT Forced Vibration Testing and Analysis of Pre- and Post- Retrofit Buildings Erica Dawn Jacobsen The primary goal of the thesis was to detect the retrofit through vibration testing of both buildings. The secondary goal focused on correctly identifying the behavior of the building through FVT, comparing that behavior to computational model predictions, and determining the necessary level of detail to include in the computational modeling. Forced vibration testing (FVT) of two stiff-wall/flexible-diaphragm buildings yielded natural frequencies and mode shapes for the two buildings. The buildings were nearly identical with the exception that one had been retrofitted. Both buildings were comprised of concrete shearwalls and steel moment frames in the north/south direction and moment frames in the east/west direction. The retrofit strengthened the moment connections and added braces to the perimeter walls in the east/west direction. The natural frequencies were found through FVT by setting a 30-lb shaker on the roof of both buildings and sweeping through a range of frequencies in both the east/west and north/south directions. Accelerometers were placed on the building to detect the accelerations. The peaks on the Fast Fourier Transform (FFT) graphs indicated the frequencies at which the structure resonated. Mode shapes were tested for by placing the shaker in a position ideal for exciting the mode and setting the shaker to the natural frequency detected from the FFT graphs. The accelerometers were placed around the roof of the building to record the mode shape. After testing, computational models were created to determine if the models could accurately predict the frequencies and mode shapes of the buildings as well as the effect of the retrofit. A series of increasingly complex computational models, ranging from hand calculations to 3D models, were created to determine the level of detail necessary to predict the building behavior. Natural frequencies were the primary criteria used to determine whether the model accurately predicted the building behavior. The mid-diaphragm deflection and base shear from spectral analysis were the final criteria used to compare these select models. It was determined that in order to properly capture the modal behavior of the building, the sawtooth framing, major beams, and the lateral-force-resisting-system (LFRS) must be modeled. Though the mode shape of the building is dominated by the flexible diaphragm, the LFRS is necessary to model to accurately predict both the natural frequency of the building as well as the diaphragm deflection.

Afin de réduire les vibrations d'une structure, on utilise des éléments piézoélectriques connectés à des circuits électriques passifs. L'objectif est de se rapprocher de l'efficacité du contrôle actif sans en supporter la complexité et la consommation. On considère d'abord l'association d'une résistance (qui a un effet similaire à un amortissement visqueux) et éventuellement d'une inductance (permettant de réaliser un oscillateur accordé) aux éléments piézoélectriques. Ces systèmes ont des propriétés intéressantes, mais sont peu efficaces à moins d'un accord très précis de l'inductance. Afin d'obtenir des performances élevées sans accord précis, on étudie un circuit à commutation, qui se ferme et s'ouvre à des instants bien précis. L'effet de la charge, qui freine la structure, s'apparente à un frottement sec. En synchronisant les commutations sur les vibrations, le système est auto-adaptatif et peut être auto-alimenté. Les fortes non-linéarités entraînent une excitation haute fréquence de la structure qui peut rendre la synchronisation problématique. Deux modèles électromécaniques (analytique et éléments finis) réduits sont proposés, permettant de décrire la dynamique du système complet de manière précise et de mettre en valeur le couplage entre un mode de vibration et le circuit électrique. Ce couplage est déterminant pour la réduction de vibrations. Une étude de l'influence de divers paramètres permet d'optimiser les éléments piézoélectriques, les circuits, et les instants de commutation. Ces résultats sont vérifiés expérimentalement. On constate un bon accord avec la théorie ; la difficulté de synchroniser correctement la commutation est aussi constatée. / In order to reduce the vibrations of a mechanical structure, one can use piezoelectric elements connected to passive electrical circuits. The goal is to achieve the same efficiency as active vibration control without the associated complexity and energy consumption. First the use of a resistor (with an effect similar to viscous damping) and eventually of an inductor (allowing the creation of a tuned resonator) for the circuit is considered. These systems have interesting properties, but are not very efficient, except in the case of a finely tuned inductor. In order to obtain good performance without requiring a precise tuning, a switching circuit is considered. The switching process is synchronized on the vibrations, and the effect of the free electric charge (similar to a dry damping) reduces the vibrations. This system is self-adaptive and can be self-powered. However, the strong non-linearities create a high frequency excitation which may disturb the switch timing. Two different reduced electromechanical models (analytical and finite element) are proposed, allowing a description of the whole system dynamics with accuracy and to emphasize the coupling between one vibration mode and the circuit. This coupling is found to be decisive for the performance in vibration reduction. A study of the influence of various parameters allow the optimisation of the piezoelectric elements, electric circuits and switch timing. These results are experimentally tested and a good agreement with the predictions is obtained ; the difficulty of switch timing is also noticed.

Studies of human response to whole-body vibration, such those encountered in heavy machinery and ground and aerial transportation, have highlighted the critical role of the head-neck posture of seated human occupants and the role of the transport system of a supine human on the severity of the transmitted vibration to the human body. Novel passive and muscle-based models are introduced in this work to predict the biodynamical response of the human under whole-body vibration in seated and supine postures. Planar and three-dimensional models representing the human head-neck system under different seated postures and fore-aft and multiple-axis whole-body vibration are first introduced. In these models, the head-neck system is represented by rigid links connected via spring-damper components representing the soft-tissue and connecting elements between the bones. Additional muscle components are added to some models. The muscle components comprise additional mass, spring, and damper elements arranged in a special order to capture the effect of changes in the displacement, velocity, acceleration, and jerk. The results show that the proposed models are able to predict the displacement and acceleration of the head under different vibration files, with the muscle-based models showing better performance than the passive models. The second set of models is introduced in this work to investigate the effect of the underlying transport system conditions on the response of supine humans under vertical and multiple-axis whole-body vibration. In these models, the supine human body is represented by three rigid links representing the head, torso/arms, and legs. The links are connected via rotational and translational joints, and therefore, it is expected that the models can capture the coupling effects between adjacent segments. The joints comprise translational and rotational spring-damper components that represent the soft tissue and the connecting elements between the segments. The contact surfaces between the supine human and the underlying transport system were modeled using spring-damper elements. Two underlying transport systems were considered, including a rigid support and a long spinal board attached to a military litter. The results showed that the proposed models were able to predict the effect of the transport systems on the human response under different vibration conditions.

O setor de mineração registrou de 2011 até 2013 o maior número de acidentes entre as indústrias extrativas, evidenciando a relevância da preocupação com os controles dos riscos e doenças ocupacionais. Atividades intrínsecas do setor, como perfuração manual, transporte de minério e estéril com caminhões ou carregadeiras, locomoção com veículos dentro do site, manutenção e amostragem com o uso de serras circulares, entre outros, são caracterizadas por presença e alta intensidade de vibração. O objetivo do trabalho consiste em avaliar a exposição ocupacional à vibração de corpo inteiro em operadores de equipamentos frequentes em minerações a céu aberto, além de comparar os resultados obtidos com a legislação brasileira vigente e apresentar sugestões para a redução dos valores de vibração de corpo inteiro (VCI) encontrados. O autor pesquisou artigos sobre vibração de corpo inteiro na mineração e em outros setores, números de casos de doenças ocupacionais associadas ao agente em território nacional, tipos de assento disponíveis no mercado e legislações nacionais e internacionais europeias e norte-americanas. Foram visitadas três pedreiras na região metropolitana de São Paulo, onde realizaram-se avaliações preliminares da exposição seguidas de levantamento quantitativo de parâmetros aren (aceleração resultante da exposição normalizada) e VDVR (valor dose de vibração resultante). Ao todo, foram analisados 22 equipamentos envolvendo caminhões fora-de-estrada, escavadeiras, pás-carregadeiras, perfuratrizes, rompedores pneumáticos e caminhões pipa. Os equipamentos estudados em sua maioria ficaram acima do nível de ação estabelecido pela NHO-09 (norma de higiene ocupacional) e alguns acima do limite de exposição. Os equipamentos com os maiores índices de Vibração de Corpo Inteiro encontrados foram as pás-carregadeiras e os menores, perfuratrizes. / The mining sector registered the greatest number of accidents among the extractive industries from 2011 to 2013, highlighting the relevance of the concern with occupational risks and diseases control. Intrinsic activities of it such as manual drilling, ore and / or waste transportation with truck or loaders, locomotion with vehicles inside the mine site, maintenance and sampling with the use of circular saws are characterized by presence and high intensity of vibration. The objective of this study is to evaluate the whole-body vibration in common open pit machinery operators, comparing values obtained with current Brazilian legislation and to suggest improvements to reduce whole-body vibration (WBV) in the studied sites. The author researched articles on whole body vibration in and out of mining, numbers of occupational diseases associated with the agent in the national territory, types of seats available in the market and international laws in Europe and the United States. Three quarries were visited in the metropolitan region of São Paulo, where preliminary exposure assessments were performed followed by a quantitative survey of aren factors (acceleration resulting from normalized exposure) and VDVR (resulting dose of vibration). Altogether, it was analyzed 22 equipment involving off-road trucks, excavators, shovel loaders, drills, breakers and water trucks. Most of the equipment studied was above the action level established by the NHO-09 (occupational hygiene standard) and some even above the exposure limit. The equipment with the highest indexes of Whole-Body Vibration found were the loader and the lowest, drills.

Lower back disorders due to whole-body vibration (WBV) are the most common injuries reported by professional drivers. Such injuries often have long-term complications leading to significant personal and societal costs. An improved mathematical model of the whole human body would contribute to a better understanding of the mechanisms of lower back injury and be valuable in injury prevention research. Current biodynamic human models reported in the literature lack detailed information for predicting the non-linearity due to vibration amplitude of transmission of vibration from seat to a human. Therefore, one of the primary objectives of this research has been to develop and validate a detailed threedimensional biodynamic human model, with special attention given to the incorporation of active trunk muscles with non-linear stiffness properties. These muscles have been incorporated into an existing spine and neck model of a MADYMO 50th percentile male occupant model. A detailed multi-body human model has been developed, called MODEL ONE. This thesis shows that incorporating non-linear stiffness functions and energy dissipation using hysteresis or damping into a human model is appropriate for predicting non-linear biodynamic responses in arbitrary excitation functions. A major advantage of MODEL ONE compared to other multi-body models and lumped mass models is its ability to predict nonlinear seat-to-human transmissibility. However MADYMO 50th male occupant models use simplified geometry and rigid bodies to represent the lower lumbar spine. These simplified spinal models have no ability to simulate the internal stresses and deformations of soft tissues, even if these are the apparent cause of lower back pain (LBP). Therefore a detailed finite element human lower lumbar spine model - with appropriate material properties and capable of simulating internal stresses⎯is necessary, in order to better understand spinal injuries under WBV. A three-dimensional finite element model of a lower lumbar spine motion segment - called MODEL TWO - has thus been developed for the present study. MODEL TWO comprises a detailed geometric description of vertebrae, nucleus pulposus, endplates, and intervertebral discs. The intervertebral discs lump together the annulus fibrosus, ground substance and ligaments. The vertebrae have been assumed to be rigid. The material properties of the intervertebral discs of MODEL TWO were obtained from test matrices and from various parameter data reported in the literature. MODEL TWO has been validated against cadaveric experiments reported in the literature. The mechanical behaviour and stress distribution within the MODEL TWO intervertebral disc agree reasonably well with the cadaveric experiments. MODEL TWO was integrated into MODEL ONE to form a new human model, called MODEL THREE, which was subsequently dynamically validated against volunteers� responses to WBV reported in the literature. MODEL THREE, as presented in this thesis, consists of a multi-body human model with detailed representation of a finite element (FE) lower lumbar spine. As far as the author is aware, MODEL THREE is the first model with detailed representation of a FE lower lumbar spine to successfully demonstrate that it is capable of simulating the stress profile of the entire intervertebral disc and endplate region due to WBV. The simulated results revealed abnormal stress concentrations in both the posterior and xviii the posterolateral annulus. The stresses increased most in the posterolateral intervertebral discs region during WBV, suggesting a possible mechanism for disc mechanical overload leading to fatigue fracture and degeneration. The results from MODEL THREE are promising and lead to a more comprehensive understanding of the behaviour of the intervertebral disc under WBV. MODEL THREE has also provided a good foundation for the development of a bio-fidelity human model. However, implementation of currently unavailable and/or inadequate in vitro and in vivo experimental studies is needed to further validate and develop MODEL THREE. A better understanding of injury mechanisms and the clinical significance of LBP will ultimately be arrived at using a combination of analytical models with in vitro and in vivo experimental data.

Dans un contexte actuel de diminution des pollutions sonores, et plus particulièrement des pollutions sonores introduites par le fonctionnement des machines électriques, nous avons développé durant cette thèse une méthode originale de réduction des vibrations dans les machines à réluctance variable. Des actionneurs piézoélectriques dimensionnés et placés de manière optimale sur la machine, et contrôlés à partir de la mesure de l'accélération vibratoire d'une ou plusieurs positions de celle-ci, permettent une diminution significative des vibrations. Durant cette thèse l'étude du dimensionnement et du placement de ces actionneurs, leurs contrôles optimaux ainsi que l'étude de l'applicabilité de la méthode de compensation ont été développés.

Ground-borne vibrations from railway systems not only pose threats to structural integrity of nearby buildings and cause annoyance on people but also contribute into environmental noise levels. It is of utmost importance to predict these vibrations at the design stage of such systems. This thesis attempts to reach this goal through finite elements analysis. Commercial software is used to develop a finite element model of an existing railway system. The model is based on the work of Forrest and Hunt [11]. It is also aimed to perform transient analysis in time domain to complement vibration information already obtained in frequency domain. The model is validated by checking maximum element size and comparing results with the infinite boundary condition case. Parametric studies are designed to investigate effects of soil type, railpad type and train speed on vibrations induced by underground train traffic. Results acquired through the finite element analysis are found to be in good harmony with the ones by existing numerical methods. The study demonstrates that the approach can be applied to predict ground-borne vibration from any configuration of railway systems.

An emerging non-pharmacological treatment for bone degenerative diseases is whole body vibration (WBV), a mechanical signal composed of low-magnitude, high-frequency (LMHF) vibrations that when applied to bone, have osteogenic and anti-resorptive effects. Currently, the cellular and molecular mechanism underlying the effect of WBV on bone is unclear. In this study, we investigated the response of osteocytes, the putative mechanosensor in bone, under LMHF vibration. As bone cells differentiate from mesenchymal stromal cells (MSCs), we also studied the osteogenic differentiation of rat MSCs in the presence of vibration loading. We found that vibrated osteocytes show gene and protein expression changes suggestive of an anti-osteoclastogenic response, and secrete soluble factors that inhibit osteoclast formation and activity. In contrast, rat MSCs showed moderate to no response to LMHF vibration during osteogenic differentiation. Our data suggest that in vivo effects of LMHF vibration are mediated through mechanosensing and biochemical responses by osteocytes.

An emerging non-pharmacological treatment for bone degenerative diseases is whole body vibration (WBV), a mechanical signal composed of low-magnitude, high-frequency (LMHF) vibrations that when applied to bone, have osteogenic and anti-resorptive effects. Currently, the cellular and molecular mechanism underlying the effect of WBV on bone is unclear. In this study, we investigated the response of osteocytes, the putative mechanosensor in bone, under LMHF vibration. As bone cells differentiate from mesenchymal stromal cells (MSCs), we also studied the osteogenic differentiation of rat MSCs in the presence of vibration loading. We found that vibrated osteocytes show gene and protein expression changes suggestive of an anti-osteoclastogenic response, and secrete soluble factors that inhibit osteoclast formation and activity. In contrast, rat MSCs showed moderate to no response to LMHF vibration during osteogenic differentiation. Our data suggest that in vivo effects of LMHF vibration are mediated through mechanosensing and biochemical responses by osteocytes.