• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 265
  • 123
  • 78
  • 32
  • 16
  • 15
  • 14
  • 8
  • 5
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 613
  • 363
  • 218
  • 188
  • 118
  • 109
  • 99
  • 98
  • 93
  • 88
  • 85
  • 82
  • 79
  • 79
  • 79
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
281

Dokumentation von Versuchen zur mitwirkenden Plattenbreite an Plattenbalken / Documentation of Experiments on Effective Flange Width of T-Beams

Wiese, Hans 11 July 2007 (has links) (PDF)
Als Ergänzung für die Lehrbriefe des Instituts für Massivbau der TU Dresden zu den Grundlagen des Stahlbetons (Teil 1 und 3 sowie Übungen Teil 1 bis 3) werden hier Bilder von Versuchsreihen vorgestellt, die am Lehrstuhl für Stahlbeton, Spannbeton und Massivbrücken der TH/TU Dresden, aus dem das heutige Institut für Massivbau hervorging, innerhalb verschiedener Forschungsarbeiten von 1956 bis 1965 entstanden. Neben dem Einblick in die damaligen Arbeitsweisen und Möglichkeiten sind vor allem die zahlreichen Bruchbilder geeignet, sich in das Tragverhalten des Stahlbetons hineinzudenken. Diese Überlegungen gaben den Ausschlag dafür, das vorhandene Bildmaterial noch einmal zu ordnen und mit kurzen Erläuterungen zu versehen, um es so nochmals für Lehre und Forschung nutzbar zu machen.
282

Šiluminių-optinių reiškinių plono disko ir plokščioje kompozitinėje YAG lazerio aktyviojoje terpėje modeliavimas / Simulation of thermo-optical effects in thin disk and composite slab geometry active medium laser

Gabalis, Martynas 24 February 2011 (has links)
Pirmoje šio darbo dalyje pristatomi temperatūros pasiskirstymo aktyviojoje lazerio terpėje kompiuterinio modeliavimo rezultatai. Skaičiavimai atlikti dviem aktyviosios terpės geometrijoms – plono disko ir plokščiojo kompozitinio elemento. Apžvelgiama skirtingų aktyvios terpės ir kaupinimo parametrų įtaka temperatūros pasiskirstymui. Antroje darbo dalyje pristatomi lazerio pluošto bangos fronto iškraipymų, atsirandančių dėl nevienodo temperatūros pasiskirstymo aktyvioje terpėje ir paviršiaus deformacijų, skaičiavimo rezultatai. / This work presents results of numerical simulation of temperature distribution inside laser active medium. Calculations were performed for two different active medium geometries. First one thin disk geometry and second - composite slab. Influence of different pump and active medium parameters on temperature distribution are presented. Second part of this work presents results of wave front aberrations calculations. Those aberrations were resulted by irregular temperature distribution and surface deformations.
283

Logistikos centras "Autoarena" Išradėjų g. 6, Šiauliuose / Logistics centre "Autoarena" in Išradėjų st. 6, Šiauliai

Gailius, Rolandas 01 August 2013 (has links)
Baigiamajame darbe projektuojamas logistikos centras „AUTOARENA“, kuris bus statomas Išradėjų g. 6, Šiauliuose. Pastatą sudaro trys pagrindinės funkcinės zonos: garažų, sandėlio ir administracinių patalpų. Pastato bendras plotas 2135,8 m2. Pastatas priskiriamas prie ypatingos paskirties statinių. Architektūrinėje dalyje pateikti bendri statinio rodikliai, techniniai-tūriniai sprendimai bei rekomendacijos. Konstrukcinėje dalyje pateikti 4 konstrukcijų skaičiavimai pagal standartus LST bei techninius Reglamentus STR. Technologinėje dalyje pateikti medžiagų žiniaraščiai bei savaeigio krano parinkimas. Prieduose pateikta šilumos laidumo koeficientų skaičiavimas, konstrukcinės dalies skaičiavimo kompiuterine programa, „Robot Structural Analysis Professional 2011“, ataskaitos bei lokalinė objekto sąmata, kuri suskaičiuota „ProsSama5g“ programa. / In this final work designed logistic center „AUTOARENA“, which will be build in Išradėjų st. 6, Šiauliai. The building consists of 3 main function zone: garages, store and office space. The total area of building 2135,8 m2. The building is assigned to special purpose buildings group. The architectural part presents general indicators of the structure, technical-content solutions and recommendations. Structural part consist 4 structures calculations in accordance with standards LST and technical Regalement STR. The technological part to provide material sheets and self-propelled crane selection. Annexes contain heat transfer coefficient calculation, design calculation of a computer program, "Robot Structural Analysis Professional 2011, localized estimate of building which calculated with “ProsSama5g” program.
284

Flexural strengthening of prestressed hollow-core slabs using near-surface mounted (NSM) CFRP reinforcement

Foubert, Steven 09 May 2014 (has links)
Prestressed hollow core slabs are essential components in structures such as bridges, parking garages, marine structures, and commercial and industrial buildings. Material degradation and altered functional requirements may seriously threaten the structural integrity of these reinforced concrete structures. Using FRP composites, the NSM strengthening technique presents a viable solution to these challenges. However, further investigation is required to establish comprehensive empirical design guidelines. The intent of this research project is to investigate the NSM technique in conjunction with common design concepts such as prestressed concrete, precast hollow core slabs, the complex behaviour of disturbed regions, and fiber-reinforced composite materials. An experimental program was developed, which included eleven full-scale slab specimens, subject to a four-point load configuration. The main parameters included the prestressing reinforcement ratio, CFRP strengthening ratio, and in-service opening location. Experimental results showed that prestressed concrete strengthened in flexure with NSM-CFRP is a viable technique for lower reinforcement ratios.
285

Optimal predictive control of thermal storage in hollow core ventilated slab systems

Ren, Mei Juan January 1997 (has links)
The energy crisis together with greater environmental awareness, has increased interest in the construction of low energy buildings. Fabric thermal storage systems provide a promising approach for reducing building energy use and cost, and consequently, the emission of environmental pollutants. Hollow core ventilated slab systems are a form of fabric thermal storage system that, through the coupling of the ventilation air with the mass of the slab, are effective in utilizing the building fabric as a thermal store. However, the benefit of such systems can only be realized through the effective control of the thermal storage. This thesis investigates an optimum control strategy for the hollow core ventilated slab systems, that reduces the energy cost of the system without prejudicing the building occupants thermal comfort. The controller uses the predicted ambient temperature and solar radiation, together with a model of the building, to predict the energy costs of the system and the thermal comfort conditions in the occupied space. The optimum control strategy is identified by exercising the model with a numerical optimization method, such that the energy costs are minimized without violating the building occupant's thermal comfort. The thesis describes the use of an Auto Regressive Moving Average model to predict the ambient conditions for the next 24 hours. A building dynamic lumped parameter thermal network model, is also described, together with its validation. The implementation of a Genetic Algorithm search method for optimizing the control strategy is described, and its performance in finding an optimum solution analysed. The characteristics of the optimum schedule of control setpoints are investigated for each season, from which a simplified time-stage control strategy is derived. The effects of weather prediction errors on the optimum control strategy are investigated and the performance of the optimum controller is analysed and compared to a conventional rule-based control strategy. The on-line implementation of the optimal predictive controller would require the accurate estimation of parameters for modelling the building, which could form part of future work.
286

Bayesian Methods for Genetic Association Studies

Xu, Lizhen 08 January 2013 (has links)
We develop statistical methods for tackling two important problems in genetic association studies. First, we propose a Bayesian approach to overcome the winner's curse in genetic studies. Second, we consider a Bayesian latent variable model for analyzing longitudinal family data with pleiotropic phenotypes. Winner's curse in genetic association studies refers to the estimation bias of the reported odds ratios (OR) for an associated genetic variant from the initial discovery samples. It is a consequence of the sequential procedure in which the estimated effect of an associated genetic marker must first pass a stringent significance threshold. We propose a hierarchical Bayes method in which a spike-and-slab prior is used to account for the possibility that the significant test result may be due to chance. We examine the robustness of the method using different priors corresponding to different degrees of confidence in the testing results and propose a Bayesian model averaging procedure to combine estimates produced by different models. The Bayesian estimators yield smaller variance compared to the conditional likelihood estimator and outperform the latter in the low power studies. We investigate the performance of the method with simulations and applications to four real data examples. Pleiotropy occurs when a single genetic factor influences multiple quantitative or qualitative phenotypes, and it is present in many genetic studies of complex human traits. The longitudinal family studies combine the features of longitudinal studies in individuals and cross-sectional studies in families. Therefore, they provide more information about the genetic and environmental factors associated with the trait of interest. We propose a Bayesian latent variable modeling approach to model multiple phenotypes simultaneously in order to detect the pleiotropic effect and allow for longitudinal and/or family data. An efficient MCMC algorithm is developed to obtain the posterior samples by using hierarchical centering and parameter expansion techniques. We apply spike and slab prior methods to test whether the phenotypes are significantly associated with the latent disease status. We compute Bayes factors using path sampling and discuss their application in testing the significance of factor loadings and the indirect fixed effects. We examine the performance of our methods via extensive simulations and apply them to the blood pressure data from a genetic study of type 1 diabetes (T1D) complications.
287

Bayesian Methods for Genetic Association Studies

Xu, Lizhen 08 January 2013 (has links)
We develop statistical methods for tackling two important problems in genetic association studies. First, we propose a Bayesian approach to overcome the winner's curse in genetic studies. Second, we consider a Bayesian latent variable model for analyzing longitudinal family data with pleiotropic phenotypes. Winner's curse in genetic association studies refers to the estimation bias of the reported odds ratios (OR) for an associated genetic variant from the initial discovery samples. It is a consequence of the sequential procedure in which the estimated effect of an associated genetic marker must first pass a stringent significance threshold. We propose a hierarchical Bayes method in which a spike-and-slab prior is used to account for the possibility that the significant test result may be due to chance. We examine the robustness of the method using different priors corresponding to different degrees of confidence in the testing results and propose a Bayesian model averaging procedure to combine estimates produced by different models. The Bayesian estimators yield smaller variance compared to the conditional likelihood estimator and outperform the latter in the low power studies. We investigate the performance of the method with simulations and applications to four real data examples. Pleiotropy occurs when a single genetic factor influences multiple quantitative or qualitative phenotypes, and it is present in many genetic studies of complex human traits. The longitudinal family studies combine the features of longitudinal studies in individuals and cross-sectional studies in families. Therefore, they provide more information about the genetic and environmental factors associated with the trait of interest. We propose a Bayesian latent variable modeling approach to model multiple phenotypes simultaneously in order to detect the pleiotropic effect and allow for longitudinal and/or family data. An efficient MCMC algorithm is developed to obtain the posterior samples by using hierarchical centering and parameter expansion techniques. We apply spike and slab prior methods to test whether the phenotypes are significantly associated with the latent disease status. We compute Bayes factors using path sampling and discuss their application in testing the significance of factor loadings and the indirect fixed effects. We examine the performance of our methods via extensive simulations and apply them to the blood pressure data from a genetic study of type 1 diabetes (T1D) complications.
288

Damage assessment in structures using vibration characteristics

Shih, Hoi Wai January 2009 (has links)
Changes in load characteristics, deterioration with age, environmental influences and random actions may cause local or global damage in structures, especially in bridges, which are designed for long life spans. Continuous health monitoring of structures will enable the early identification of distress and allow appropriate retrofitting in order to avoid failure or collapse of the structures. In recent times, structural health monitoring (SHM) has attracted much attention in both research and development. Local and global methods of damage assessment using the monitored information are an integral part of SHM techniques. In the local case, the assessment of the state of a structure is done either by direct visual inspection or using experimental techniques such as acoustic emission, ultrasonic, magnetic particle inspection, radiography and eddy current. A characteristic of all these techniques is that their application requires a prior localization of the damaged zones. The limitations of the local methodologies can be overcome by using vibration-based methods, which give a global damage assessment. The vibration-based damage detection methods use measured changes in dynamic characteristics to evaluate changes in physical properties that may indicate structural damage or degradation. The basic idea is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Changes in the physical properties will therefore cause changes in the modal properties. Any reduction in structural stiffness and increase in damping in the structure may indicate structural damage. This research uses the variations in vibration parameters to develop a multi-criteria method for damage assessment. It incorporates the changes in natural frequencies, modal flexibility and modal strain energy to locate damage in the main load bearing elements in bridge structures such as beams, slabs and trusses and simple bridges involving these elements. Dynamic computer simulation techniques are used to develop and apply the multi-criteria procedure under different damage scenarios. The effectiveness of the procedure is demonstrated through numerical examples. Results show that the proposed method incorporating modal flexibility and modal strain energy changes is competent in damage assessment in the structures treated herein.
289

Transfert d'un composé organo-chloré depuis une zone source localisée en zone non saturée d'un aquifère poreux vers l'interface sol-air : expérimentations et modélisations associées / Transfer of an organo-chlorinated compound from a source area located in the unsaturated zone of a porous aquifer to the soil-air interface : experiments and modelling related

Marzougui Jaafar, Salsabil 29 January 2013 (has links)
Deux expériences ont été menées sur la plate-forme expérimentale "SCERES" afin d'évaluer les concentrations et les flux de vapeurs de TCE dans SCERES en présence de deux dalles de béton fissurées installées, l'une après l'autre, à la surface de SCERES. Cet aquifère poreux est un milieu hétérogène de grande échelle (25 x 12 x 3 m3). Les résultats ont montré que le panache de vapeur de TCE couvre la plupart du bassin au bout de 3 semaines depuis la création de la zone source de TCE dans le sous sol. L'hétérogénéité du site SCERES a engendrée une distribution verticale non uniforme de la concentration de vapeurs de TCE. La simulation du panache de vapeur dans SCERES a été effectuée au moyen du code de calcul multiphasique "SIMUSCOPP". La présence sur SCERES de la dalle de béton, un milieu peu perméable et peu diffusif, a constitué une "barrière" en vue du transfert de vapeurs de TCE vers l'interface dalle/atmosphère. Afin de mieux quantifier le flux de vapeurs à travers la dalle de béton, une étude de coefficient de diffusion et de perméabilité des deux dalles a été réalisée. Un mouvement vertical ascendant du toit de la nappe a généré un fort gradient de pression motrice de l'air du sol. Ceci a engendré une forte augmentation des flux de vapeurs à l'interface sol/atmosphère. La quantification de ces flux de vapeurs a été effectuée à l'aide d'une solution semi analytique basée sur la loi de Fick et la loi de Darcy en tenant compte à la fois de l'effet de gradient de pression motrice et l'effet de densité de vapeurs sur le transfert de vapeurs vers la surface du sol. L'intrusion de vapeurs de TCE dans le bâtiment modèle, installé sur la dalle de béton, a été générée par une mise en dépression dans ce dernier. Ce qui a fait augmenter la concentration de vapeurs de TCE sous la dalle ainsi dans le bâtiment. La simulation de l'intrusion de vapeurs dans l'air intérieur de bâtiment a été réalisée par l'intermédiaire du code de calcul multiphysics "COMSOL", avec lequel nous avons démontré l'évolution de la concentration de vapeurs obtenues expérimentalement dans le bâtiment et qui dépend directement de la variation spatio-temporelle du flux massique à travers la dalle. / Two experiments were conducted on the experimental platform "SCERES" to assess the TCE vapour concentrations and fluxes in SCERES with two concrete slabs installed, one after the other, on the ground surface. This artificial aquifer is a large scale (25 x 12 x 3 m3) heterogeneous porous medium. The results showed that the TCE vapour plume covers most of the basin 3 weeks after the creation of the TCE source area in unsaturated zone. The heterogeneity of SCERES has generated a non uniform vertical distribution of the TCE vapour concentration. Simulation of vapour plume in SCERES was carried out by the multiphase code "SIMUSCOPP".The presence in SCERES of a low permeability and low diffusive medium compared to the sand in the basin,as a concrete slab, constituted a "barrier" for the transfer of TCE vapour to the interface concrete slab / atmosphere. To better quantify the TOE fluxes through the concrete slab, a study of diffusion coefficient and permeability of both concrete slabs was done. An upward vertical movement of the water table has generated a strong soil air pressure driving gradient, which led to a strong increase in the TCE vapour concentrations near the surface which has increased the vapour fluxes at the interface soil / atmosphere. Quantification of vapour fluxes at the interfaces soil / atmosphere and concrete slab / atmosphere was performed using a semi analytical approach based onFick's and Darcy's laws by taking into account both the effect of the driving pressure gradient and the effect of density vapour on the vapour transfer towards the soil surface.The intrusion of TCE vapours into the model building installed on the concrete slab was generated by creating a vacuum. The results showed that, during the TCE vapour suction from the model building, the concentration of TCE vapours under the concrete slab and in the building increases. Simulation of vapour intrusion into indoor air was done by the computational Multiphysics code "COMSOL", allowing simulation of the evolution of the vapour concentration obtained experimentally in the building. Il was shown that they depend directly on the spatial-temporal variation of the mass flux through the slab.
290

Contribuição à análise de lajes nervuradas em pavimentos de garagem / Contribution to the analysis of waffle slab in garage floors

Tenório, Daniel Almeida 29 September 2011 (has links)
This work is turned to a structural element with a large number of scientific studies, waffle slab. The aim of this study was to elucidate two recommendations of the Brazilian codes that have different values of international codes. The first concerns the accidental loading to garage floor recommended by the Brazilian code, where there is not recommending the use of concentrated loads, the same being recommended by international codes. The second is related to the different recommendations between the Brazilian code and international codes regarding the calculation of the bending of the table of waffle slabs. To meet the objectives of this work, some numerical simulations of floors containing a single waffle slab, modeled as one-way waffle slab and two-way waffle slab, were made using the finite element method and grillage analysis using specific software. The focus of structural analysis turned to determining the maximum bending moments acting on the flange of waffle slabs and arrows. The answers to these simulations showed that for garage floors, it is important to consider concentrated loads (vehicles). As utilization in structural designs of concentrated loads is a process slow and complicated, were defined values of distributed loads to provide arrows and moments in the ribs equal to those generated by the concentrated loads. On the analysis of bending on the table of waffle slabs, some recommendations were found, some of these one being equal to the Brazilian code, and other to international codes and some different compared to all codes. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Este trabalho está voltado para alguns pontos em aberto sobre verificações de serviço e dimensionamento das lajes nervuradas moldadas no local. O objetivo deste trabalho foi estudar e elucidar duas recomendações das normas brasileiras que apresentam valores diferentes das normas internacionais. A primeira diz respeito ao carregamento acidental para pavimentos garagem recomendado pela norma brasileira, onde não existe recomendação do uso de carregamentos concentrados, sendo o mesmo recomendado em normas internacionais. A segunda está relacionada às diferentes recomendações existentes entre a norma brasileira e as normas internacionais, no que tange ao cálculo da flexão da mesa das lajes nervuradas. Para atender aos objetivos deste trabalho, algumas simulações numéricas de pavimentos contendo uma única laje nervurada, lançadas como lajes nervuradas unidirecionais e bidirecionais, foram feitas, utilizando o método dos elementos finitos e grelha através de programas de análises específicos. O foco da análise estrutural, voltou-se para a determinação dos momentos fletores máximos atuantes nas mesas das lajes nervuradas e as flechas. As respostas dessas simulações mostraram que, para pavimentos garagem, considerando os carregamentos dos veículos atuais é necessária a consideração de carregamento acidental de cargas concentradas (veículos). Como a utilização em projetos estruturais dos carregamentos de cargas concentradas é um processo lento e complicado, foram definidos valores de carregamentos distribuídos que fornecessem flechas e momentos máximos nas nervuras iguais aos gerados, utilizando o carregamento acidental de cargas concentradas. Sobre as análises da flexão na mesa das lajes nervuradas, chegou-se a algumas recomendações, sendo parte destas em igualdade com a norma brasileira, outras com as normas internacionais e algumas diferentes em relação a todas as normas.

Page generated in 0.0313 seconds