Torres metálicas treliçadas tem sido largamente utilizadas como suporte de antenas de microondas. Devido ao baixo peso e a inexistência de terremotos significativos no Brasil, a força de vento é o fator determinante do projeto destas estruturas. Com o objetivo de determinar estas forças e seus efeitos em torres treliçadas foram realizadas investigações numéricas e experimentais. Uma torre de 100 metros foi dimensionada com base nos padrões existentes no Brasil. Examinou-se a resposta dinâmica da estrutura ao longo do vento. Investigaram-se a resposta ressonante, não ressonante e o fator resposta de rajada. Concluiu-se que a resposta ressonante não é significativa para este tipo de estrutura. Compararam-se os modelos de DAVENPORT (1993), da norma Brasileira NBR6123/88 e o processo do vento sintético de FRANCO (1993). Uma investigação experimental foi realizada para analisar os coeficientes de força em uma seção da torre estudada. Os experimentos foram realizados no “Boundary Layer Wind Tunnel Laboratory" (BLWTL) da “University of Western Ontario" (UWO), Canadá. Foram analisados o ângulo de incidência do vento; o índice de área exposta; o efeito de proteção; o fator de interferência no coeficiente de arrasto de antenas de microondas, devido à proximidade da torre e a influência da turbulência do vento. Os resultados mostraram boa concordância com os valores obtidos em diferentes normas existentes. / With today’s expanding communication systems, a large number of lattice towers to support cellular and microwave antennas are being constructed in Brazil. Due to the lightweight of these structures, wind forces are the primary concern in the design. With the objective of determining these forces and their effects upon latticed towers, a numerical and experimental investigation is accomplished. A 100-meter tower is designed based on existing patterns of latticed towers in Brazil. The along wind dynamic response is analysed. The resonant, background response and gust factor are examined. It is concluded that the resonant response is not significant for this type of structure. The DAVENPORT (1993) method, the Brazilian code NBR6123/88 and the process of the synthetic wind of FRANCO (1993) are compared. An experimental investigation is accomplished to analyse the force coefficients on a section of the lattice tower studied. The tests were performed at the Boundary Layer Wind Tunnel Laboratory, University of Western Ontario (UWO), Canada. The wind incidence angle; the tower solidity; the shielding effect; the interference factor upon the drag coefficient of the microwave antennas, due to the tower proximity and the influence of the wind turbulence are analysed. The results are ii good agreement with the values obtained in different existent codes.

This thesis addresses the experimental and numerical study of vibration-based damage detection (VBDD) techniques in structural health monitoring (SHM) of bridge superstructures. The primary goal of SHM is to ascertain the condition or health of a structure so that decisions can be made with regard to the need for remediation. VBDD techniques are global non-destructive evaluation (NDE) techniques. The principle of VBDD techniques is to detect damage using changes in the dynamic characteristics of a structure caused by the damage. The advantage of VBDD techniques over local NDE techniques is that VBDD techniques can assess the condition of an entire structure at once and are not limited to accessible components. <p>Well controlled laboratory experiments on a half-scale, simply supported steel-free bridge deck and two full-scale, simply supported prestressed concrete girders demonstrated that small scale damage at different locations can be reliably detected and located by VBDD techniques using a relatively small number of sensors (accelerometers or strain gauges) and considering changes to only the fundamental mode of vibration. The resolution of damage localization, defined as the length of the window within which damage could be located when the technique predicts it to be located at a particular point, was 70% of measurement point spacing for the deck and 82% for the girders, provided the damage was not located too close to a simple support.<p>To establish the potential of VBDD techniques in the absence of experimental uncertainty, eigenvalue analyses using finite element models of the deck and the girders were undertaken to investigate ability of five VBDD methods to predict the longitudinal location of damage. It was found that when mode shapes were well-defined with a large number of measurement points, the damage location could be determined with great accuracy using any of the five VBDD techniques investigated. The resolution of longitudinal localization of damage was 40 to 80% of the spacing between measurement points when small numbers of measurement points were used, provided the damage was not located too close to a simple support.<p>The experimental study successfully detected small scale damage under forced resonant harmonic excitation but failed in detecting damage under forced random excitation, although the use of random sources of excitation is more practical in field testing. Transient dynamic analyses on the finite element model of the steel-free bridge deck were performed to investigate the implications of using random forced vibrations to characterize mode shapes to be used to detect damage. It was found that the probability of successful damage localization depends upon the severity of the damage, the number of trials used to obtain the average mode shape, the location of damage relative to the nearest sensor, the distance between the damage and the support, and the magnitude of measurement errors. A method based on the repeatability of measured mode shapes is proposed to calculate the probability of successful damage detection and localization.<p>In summary, results of this research demonstrate that VBDD techniques are a promising tool for structural health monitoring of bridge superstructures. However, although these methods have been shown to be capable of effectively detecting small scale damage under well controlled conditions, a significant amount of challenging work remains to be done before they can be applied to real structures.

This thesis addresses the experimental and numerical study of vibration-based damage detection (VBDD) techniques in structural health monitoring (SHM) of bridge superstructures. The primary goal of SHM is to ascertain the condition or health of a structure so that decisions can be made with regard to the need for remediation. VBDD techniques are global non-destructive evaluation (NDE) techniques. The principle of VBDD techniques is to detect damage using changes in the dynamic characteristics of a structure caused by the damage. The advantage of VBDD techniques over local NDE techniques is that VBDD techniques can assess the condition of an entire structure at once and are not limited to accessible components. <p>Well controlled laboratory experiments on a half-scale, simply supported steel-free bridge deck and two full-scale, simply supported prestressed concrete girders demonstrated that small scale damage at different locations can be reliably detected and located by VBDD techniques using a relatively small number of sensors (accelerometers or strain gauges) and considering changes to only the fundamental mode of vibration. The resolution of damage localization, defined as the length of the window within which damage could be located when the technique predicts it to be located at a particular point, was 70% of measurement point spacing for the deck and 82% for the girders, provided the damage was not located too close to a simple support.<p>To establish the potential of VBDD techniques in the absence of experimental uncertainty, eigenvalue analyses using finite element models of the deck and the girders were undertaken to investigate ability of five VBDD methods to predict the longitudinal location of damage. It was found that when mode shapes were well-defined with a large number of measurement points, the damage location could be determined with great accuracy using any of the five VBDD techniques investigated. The resolution of longitudinal localization of damage was 40 to 80% of the spacing between measurement points when small numbers of measurement points were used, provided the damage was not located too close to a simple support.<p>The experimental study successfully detected small scale damage under forced resonant harmonic excitation but failed in detecting damage under forced random excitation, although the use of random sources of excitation is more practical in field testing. Transient dynamic analyses on the finite element model of the steel-free bridge deck were performed to investigate the implications of using random forced vibrations to characterize mode shapes to be used to detect damage. It was found that the probability of successful damage localization depends upon the severity of the damage, the number of trials used to obtain the average mode shape, the location of damage relative to the nearest sensor, the distance between the damage and the support, and the magnitude of measurement errors. A method based on the repeatability of measured mode shapes is proposed to calculate the probability of successful damage detection and localization.<p>In summary, results of this research demonstrate that VBDD techniques are a promising tool for structural health monitoring of bridge superstructures. However, although these methods have been shown to be capable of effectively detecting small scale damage under well controlled conditions, a significant amount of challenging work remains to be done before they can be applied to real structures.

Local soil conditions influence the characteristics of earthquake ground shaking and these effects must be taken into account when specifying ground shaking levels for seismic design. These effects are quantified via site response analysis, which involves the propagation of earthquake motions from the base rock through the overlying soil layers to the ground surface. Site response analysis provides surface acceleration-time series, surface acceleration response spectra, and/or spectral amplification factors based on the dynamic response of the local soil conditions. This dissertation investigates and compares the results from different site response methods. Specifically, equivalent-linear time series analysis, equivalent-linear random vibration theory analysis, and nonlinear time series analysis are considered. In the first portion of this study, hypothetical sites and events are used to compare the various site response methods. The use of hypothetical events at hypothetical sites allowed for the seismic evaluation process used in engineering practice to be mimicked. The hypothetical sites were modeled after sites with characteristics that are representative of sites in the Eastern and Western United States. The input motions selected to represent the hypothetical events were developed using the following methods: stochastically-simulated time series, linearly-scaled recorded time series, and spectrally-matched time series. The random vibration theory input motions were defined using: seismological source theory, averaging of the Fourier amplitude spectra computed from scaled time series, and a response spectrum compatible motion. All of the different input motions were then scaled to varying intensity levels and propagated through the sites to evaluate the relative differences between the methods and explain the differences. Data recorded from borehole arrays, which consist of instrumentation at surface and at depth within the soil deposit, are used to evaluate the absolute bias of the site response methods in the second portion of this study. Borehole array data is extremely useful as it captures both the input motion and the surface motion, and can be used to study solely the wave propagation process within the soil deposit. However, comparisons using the borehole data are complicated by the assumed wavefield at the base of the array. In this study, sites are selected based on site conditions and the availability of high intensity input motions. The site characteristics are then developed based on site specific information and data from laboratory soil testing. Comparisons between the observed and computed response are used to first assess the wavefield at the base of the array, and then to evaluate the accuracy of the site response methods. / text

Thesis (Ph.D.)--University of Melbourne, Dept. of Civil and Environmental Engineering, 2007. / Typescript. Includes bibliographical references (leaves 344-361).

Torres metálicas treliçadas tem sido largamente utilizadas como suporte de antenas de microondas. Devido ao baixo peso e a inexistência de terremotos significativos no Brasil, a força de vento é o fator determinante do projeto destas estruturas. Com o objetivo de determinar estas forças e seus efeitos em torres treliçadas foram realizadas investigações numéricas e experimentais. Uma torre de 100 metros foi dimensionada com base nos padrões existentes no Brasil. Examinou-se a resposta dinâmica da estrutura ao longo do vento. Investigaram-se a resposta ressonante, não ressonante e o fator resposta de rajada. Concluiu-se que a resposta ressonante não é significativa para este tipo de estrutura. Compararam-se os modelos de DAVENPORT (1993), da norma Brasileira NBR6123/88 e o processo do vento sintético de FRANCO (1993). Uma investigação experimental foi realizada para analisar os coeficientes de força em uma seção da torre estudada. Os experimentos foram realizados no “Boundary Layer Wind Tunnel Laboratory” (BLWTL) da “University of Western Ontario” (UWO), Canadá. Foram analisados o ângulo de incidência do vento; o índice de área exposta; o efeito de proteção; o fator de interferência no coeficiente de arrasto de antenas de microondas, devido à proximidade da torre e a influência da turbulência do vento. Os resultados mostraram boa concordância com os valores obtidos em diferentes normas existentes. / With today’s expanding communication systems, a large number of lattice towers to support cellular and microwave antennas are being constructed in Brazil. Due to the lightweight of these structures, wind forces are the primary concern in the design. With the objective of determining these forces and their effects upon latticed towers, a numerical and experimental investigation is accomplished. A 100-meter tower is designed based on existing patterns of latticed towers in Brazil. The along wind dynamic response is analysed. The resonant, background response and gust factor are examined. It is concluded that the resonant response is not significant for this type of structure. The DAVENPORT (1993) method, the Brazilian code NBR6123/88 and the process of the synthetic wind of FRANCO (1993) are compared. An experimental investigation is accomplished to analyse the force coefficients on a section of the lattice tower studied. The tests were performed at the Boundary Layer Wind Tunnel Laboratory, University of Western Ontario (UWO), Canada. The wind incidence angle; the tower solidity; the shielding effect; the interference factor upon the drag coefficient of the microwave antennas, due to the tower proximity and the influence of the wind turbulence are analysed. The results are ii good agreement with the values obtained in different existent codes.

Neste trabalho, é apresentado um modelo aperfeiçoado para gerar carregamentos dinâmicos pseudo-aleatórios para modelos estruturais sob excitação sísmica e de vento. Este é baseado no modelo de vento sintético proposto por Franco, diferindo pelo fato que usa a transformada de wavelet harmônica ao invés da série de Fourier, pois tem como objetivo descrever um comportamento não estacionário com a ajuda de uma função temporal. Para testar a qualidade do sinal desenvolvido neste trabalho, este foi comparado com sinais verdadeiro, das acelerações de sismos ocorrido na cidade de Hachinohe, no Japão e em El-centro, na Califórnia, e com um sinal gerado pelo modelo do sismo sintético de Corbani, este também baseado no modelo de vento sintético, com o uso de séries de Fourier. Em todas as análises feitas, foi mostrando que embora a geração de carregamentos com transformadas de wavelet harmônica seja mais complexa, esta possui um bom potencial para gerar carregamentos mais próximos da realidade do que métodos usuais baseados em carregamentos estacionários. / In this work is intruduced a improve model to create random loads to use in structural models under sismic and wind disturbance. The model is based on synthetic wind model intends by Franco, differing by the fact that applies harmonic wavelet transform instead of Fourier series, because it has the goal to describe a non stationary behavior with temporal function support. To test the quality from the signal developed in this work, it has been analyzed against true seismic acceleration signal that occurs from Hachinohe city in Japan and El-centro city in California, and with the synthetic seismic model developed by Corbani, that one descending on synthetic wind model, with Fourier series application. In all analysis, although loading creation with harmonic wavelet transform have been more sophisticated, that one has a great potencial to creat loading closer to the fact than usual methods based in stationary loading.

The thesis deals with a comparative analysis of strain of parts using finite element method (FEM) and measurement of the optical system Pontos. Part was used the reflector of Volkswagen Polo. The subject of comparing were the values of deviations optical shield of reflector which excitation random vibration described power spectral density. The thesis presented describes of experimental measurements to obtain the boundary conditions using optical systems. FEM analysis was performed using software ANSYS Workbench 12.

No description available.

The investment of space commerce is skyrocketing and it is predicted to be a nascent business in the future. The spacecraft demand has been growing not only for NASA and other space agency’s mission but also collaboration business between small space industries, academia, and scientific community. This glimpse brought an interest to a new investor, government, military, and manufacturing company to deliver their objectives efficiently. Nowadays, many startups compete embracing innovation and pioneering the novelty of space project beyond prodigious vision in an unprecedented way. Many players foresee that decreasing size of the rocket is an important key to survive and succeed in the space business. One of the efficient acts is lowering the launch cost. This can be achieved by designing a small size, lightweight and affordable spacecraft. Within this context, a Beyond Atlas Spacecraft which will be sent to Asteroid 2016-HO3, has achieved a wet mass of 20.85 kg with the size of 24.7 x 42.2 x 40.8 cm in stowed mode and 84 x 399 x 40.8 cm in unstowed mode. However, the drawback being light and small may lead to catastrophic failure due to resonance frequency events. According to past experience, the gyro of the Swedish national satellite was damaged during ground testing and it was suspected due to high amplification when the natural frequency coincides to the main structure resonance. Therefore, this work is focusing on a spacecraft development and a non-destructive structural analysis. The coupled-load analysis of a preliminary spacecraft design including sinusoidal, random vibration and shock analysis are calculated using FEM. This effort can reduce the risk of component destruction before laboratory testing as well as understand better the dynamic behavior of the spacecraft. The critical frequency in each orthogonal axis with base input from launch environment of the LM-3A Launch Vehicle was devised. The maximum stress, amplitude, and acceleration in accordance of qualification test criteria were evaluated and discussed. / Investeringen av rymdhandeln är skyrocketing och det förväntas bli en växande verksamhet i framtiden. Efterfrågan på rymdfarkoster har ökat inte bara för NASA och andra rymdorganisationens uppdrag utan även samarbete mellan små rymdindustrier, akademin och det vetenskapliga samfundet. Denna glimt väckte intresse för en ny investerare, regering, militär och tillverkningsföretag för att effektivt kunna leverera sina mål. Idag konkurrerar många startups om att omfatta innovation och banbrytande rymdprojektets nyhet bortom en fördärvad vision på ett aldrig tidigare skådat sätt. Många spelare förutser att minskad storlek på raketen är en viktig nyckel för att överleva och lyckas i rymdverksamheten. En av de effektiva handlingarna sänker lanseringskostnaden. Detta kan uppnås genom att utforma en liten storlek, lätt och prisvärd rymdfarkost. Inom detta sammanhang har en Beyond Atlas Spacecraft som skickas till Asteroid 2016-HO3, uppnått en våt massa på 20,85 kg med storleken 24,7 x 42,2 x 40,8 cm i stuvningsläge och 84 x 399 x 40,8 cm i ostoppat läge. Nackdelen som är ljus och liten kan emellertid leda till katastrofalt fel på grund av resonansfrekvenshändelser. Enligt tidigare erfarenhet skadades gyroen i den svenska nationella satelliten under marktestning och det misstänktes på grund av hög förstärkning när den naturliga frekvensen sammanföll med huvudstrukturen resonans. Därför fokuserar detta arbete på rymdskeppsutveckling och en icke-destruktiv strukturanalys. Den kombinerade belastningsanalysen av en preliminär rymdfarkostkonstruktion inklusive sinusformad, slumpvibration och chockanalys beräknas med användning av FEM. Denna insats kan minska risken för komponent förstörelse före laboratorietestning samt förstå bättre rymdskeppets dynamiska beteende. Den kritiska frekvensen i varje ortogonal axel med basinmatning från startmiljön för LM-3A-startkärlet utformades. Den maximala spänningen, amplituden och accelerationen i enlighet med kvalifikationstestkriterierna utvärderades och diskuterades.