Dissertations / Theses on the topic 'Limit states method'

Main goal of thesis entitled "Landslide remediation design" is - based on acquired knowledge and submitted documents about the problematic of landslides - to determine the causes of the landslides on II. class road between villages Koryčany and Jestřabice and to propose optimal redevelopment.

In an attempt to achieve more efficient designs, the technological frontier is pushed further and further. Every year science probes for a better understanding of natural phenomena, discovering new and improved methods to perform the same task more efficiently and with better results. One of the new technologies is the nonlinear analysis of structural systems using inelastic post-buckling member performance. Inelastic post-buckling member performance is defined as the constitutive relationship between axial load and displacement after the ultimate member capacity has been exceeded. A nonlinear analysis is able to predict the failure behavior of a structural system under ultimate loads more accurately than the traditionally used linear elastic analysis. Consequently, designs can be improved and become more efficient, which reduces the realization cost of a project. An improved nonlinear analysis solution algorithm has been developed, that allows the analyst to perform a nonlinear analysis using post-buckling member performances faster than previously possible. Furthermore, the original post-buckling member performance database was expanded using results obtained from physical member compression tests. Based on the experimental results, new post-buckling member performance model curves were developed to be used together with the improved nonlinear solution algorithm. In addition, a program was developed that allows the analyst to perform a valid nonlinear analysis using a finite element program (LIMIT). The program combines a numerical pre-processor, and input and output data evaluation modules based on human expertise together with the LIMIT analysis package. Extensive on-line help facilities together with graphical pre- and post-processors were also integrated into the program. The resulting analysis package essentially combines all of the necessary components required to perform a nonlinear analysis using post-buckling member performances into one complete analysis package.

Made available in DSpace on 2015-03-26T13:28:18Z (GMT). No. of bitstreams: 1 texto completo.pdf: 4478049 bytes, checksum: 71c0114233fc7284f49a0d4753d167c9 (MD5) Previous issue date: 2013-07-05
Fundação de Amparo a Pesquisa do Estado de Minas Gerais
The growth of the real estate market in Brazil, mainly for ranges middle and low income is an incentive to the use of structural masonry, due to the economy and rationality generated by the system. These factors serve as incentives to companies that are inserted in this branch to invest in research, in the use of new materials and processes for the analysis, and more sophisticated dimensioning, which allow the assessment of critical situations more quickly. In this context, the use of computer programs make it possible to obtain a rationalized design, helping to increase the accuracy and efficiency factors. Until recently, the dimensioning of structural masonry was done based on the method of Allowable Stresses. In the Brazilian current standards for structural masonry of concrete blocks (ABNT NBR 15961-1:2011) and ceramic blocks (ABNT NBR 15812-1:2010), the method of calculation used is the Method of Limit States, which has a semiprobabilistic base. This method considers that a safe structure is the one that has not reached any limit state during its lifetime. This work presents a computational tool, developed in the AutoLISP language and DCL, which is able to perform the structural analysis and dimensioning of masonry buildings by the Method of Limit States. The program also allows the determination of the efforts in structural masonry walls, subjected to vertical loads (self weight and reactions from the slabs), as well as the horizontal loads (wind and state of being out of plumb ) . For vertical actions, the program uses the method of isolated walls and wall groups , and for the horizontal actions, allows it to take into consideration whether or not the existence of flange in panels bracing. The developed tool uses the same platform used for the graphic designs in general (AutoCAD). Among other facilities, the tool allows, in an interactive way, the automatic interpretation of the structural elements of the building (walls and slabs) and the distribution of the actions. The application also allows the creation of a memorial of calculating for steps of obtaining the vertical and horizontal actions and the tensions, besides another, aside, for sizing and other checks. Is presented a comparison between manual calculation and the results generated by the program for a four-story masonry building. The differences found in the comparison were lower than 2.0%. The application developed has shown great efficiency, ease to use, and rapid evaluation of masonry designs.
O crescimento do mercado imobiliário no Brasil, principalmente para as faixas de renda média e baixa é um incentivo ao uso da alvenaria estrutural, em virtude da economia e racionalidade geradas pelo sistema. Esses fatores servem de incentivos às empresas que estão inseridas nesse ramo para investirem em pesquisas, no uso de novos materiais e em processos de análise e dimensionamento mais sofisticados, que permitam avaliar as situações críticas com maior rapidez. Neste contexto, o uso de programas computacionais possibilitam a obtenção de um projeto racionalizado, contribuindo para o incremento dos fatores precisão e eficiência. Até pouco tempo atrás, o dimensionamento da alvenaria estrutural era feito com base no Método das Tensões Admissíveis. Nas normas atuais de alvenaria estrutural de blocos de concreto (ABNT NBR 15961-1:2011) e de blocos cerâmicos (ABNT NBR 15812-1:2010), o método de cálculo utilizado é o Método dos Estados Limites, que possui base semiprobabilística. Este método considera uma estrutura segura aquela que não atinge nenhum estado limite durante a sua vida útil. Neste trabalho apresenta-se uma ferramenta computacional desenvolvida em linguagem AutoLISP e DCL capaz de realizar a análise e o dimensionamento de edifícios de alvenaria estrutural pelo método dos estados-limite. O programa permite a determinação dos esforços em paredes estruturais de alvenaria submetidas às ações verticais (peso próprio e reações das lajes), assim como às ações horizontais (vento e desaprumo). Para as ações verticais, o programa utiliza o método das Paredes isoladas e o método de Grupos de paredes, e para as ações horizontais, permite-se levar em consideração ou não a existência de abas nos painéis de contraventamento. A ferramenta desenvolvida utiliza a mesma plataforma gráfica empregada para os desenhos de projeto em geral (AutoCAD). Dentre outras facilidades, a ferramenta permite, de uma maneira interativa, a interpretação automática dos elementos estruturais da edificação (lajes e paredes) e a distribuição das ações atuantes. O aplicativo permite ainda a geração de um memorial de cálculo para as etapas de obtenção das ações verticais e horizontais e das tensões, além de outro, à parte, para o dimensionamento e as demais verificações. Para validar o módulo, é apresentada uma comparação entre o cálculo manual e os resultados gerados pelo programa para um edifício padrão de alvenaria estrutural de quatro andares. As diferenças encontradas na comparação foram menores que 2,0%. O aplicativo desenvolvido demonstrou grande eficiência, facilidade de uso e rapidez na avaliação de projetos de alvenaria estrutural.

Submitted by Franciele Moreira (francielemoreyra@gmail.com) on 2018-09-21T14:50:47Z No. of bitstreams: 2 Dissertação - Nícolas Rodrigues Moura - 2018.pdf: 4165797 bytes, checksum: 86460ffa29b4d346005f977c2f75693e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-09-24T13:21:40Z (GMT) No. of bitstreams: 2 Dissertação - Nícolas Rodrigues Moura - 2018.pdf: 4165797 bytes, checksum: 86460ffa29b4d346005f977c2f75693e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2018-09-24T13:21:40Z (GMT). No. of bitstreams: 2 Dissertação - Nícolas Rodrigues Moura - 2018.pdf: 4165797 bytes, checksum: 86460ffa29b4d346005f977c2f75693e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-08-27
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Análises de estabilidade de taludes são predominantemente realizadas em duas-dimensões (2D) por métodos de equilíbrio limite. Os métodos convencionais de equilíbrio limite são alvos de muitas críticas pelo o uso do equilíbrio estático, pressuposições de forças na análise e por possuir o mesmo fator de segurança ao longo de toda a superfície de deslizamento. Para superar essas deficiências, o método proposto por Kulhawy (1969) incorpora o comportamento tensão-deformação do solo com tensões oriundas do Método de Elementos Finitos (FEM) e tem a mesma estrutura dos métodos de equilíbrio dos métodos de equilíbrio de equilíbrio limite clássicos. É também chamado de método aperfeiçoado. Devido à existência de taludes com geometrias complexas, a abordagem tridimensional (3D) é a única capaz de incorporar todos os aspectos geométricos do problema. Esta dissertação é dividida em dois artigos com o tema de estabilidade de taludes pelo o método de Kulhawy em abordagens 2D e 3D. O objetivo primário dessa dissertação é avaliar os principais fatores que influenciam a estabilidade de taludes. O primeiro artigo propôs geometrias variando de convexo a côncavo em um conjunto de propriedades típicas de solos. Duas trajetórias de geração de tensões in- situ foram utilizadas, i.e., construção e escavação. O método GLE foi calculado para fins de comparação. A superfície de deslizamento é muito dependente do histórico de tensão e da forma da face do talude. A diferença relativa no estado de tensões inicial típico alcançou 15% nas análises 2D e 34% nas análises 3D. A análise de sensibilidade do efeito do Poisson no fator de segurança mostrou-se muito relevante. A relação entre os fatores de segurança 2D e 3D são quase lineares independente do estado de tensões, das propriedades de resistência, formato da face do talude, na ordem de 30 a 40%. O segundo artigo propõe análises em barragens construídas em vales estreitos. Três abordagens de análises foram utilizadas: redução de resistência ao cisalhamento (SSR), métodos de Kulhawy e GLE. Condições típicas de fundações são muito variáveis como topografia e deformabilidade. A análise de sensibilidade do módulo de fundação de Young no fator de segurança foi insignificante em 2D e relevantes em 3D. A relação entre o comprimento do aterro (W) e a altura () é uma variável representativa do grau de estreitamento da barragem e na estabilidade de taludes. A análise de deformações planas tende a altas relações W/H e o oposto mostra elevados efeitos 3D. A inclinação da ombreira mostrou-se relevante no fator de segurança apenas em aterros em vales estreitos. Fundações mais rígidas são mais beneficias para o fator de segurança devido à produção de altos efeitos de arqueamento neste cenário. O método de Kulhawy provou-se ser vantajoso pela a incorporação do comportamento mecânico do solo, o uso de tensões mais realísticas nas análises e avaliação da estabilidade local na superfície de deslizamento. Isso aumenta a quantidade de informações úteis e confiáveis para o profissional de engenharia no projeto de taludes. Todas as análises foram realizadas usando o software SoilVision Systems, Saskatchewan, Canadá. Os módulos utilizados foram o SVLOPE, SVSOLID e o SVFLUX (SoilVision Systems Ltd., 2018). A análise de tensão para a simulação de trajetórias de escavação e construção utilizou do solucionador de Equações Diferenciais Parcias (PDE) o FlexPDE 6 (PDE Solutions Inc., 2014).
Slope stability analyses are predominantly performed using the two-dimensional (2D) conventional limit equilibrium methods. Conventional limit equilibrium methods are targets of many criticisms for using static equilibrium, assumptions of forces in the analysis and the same factor of safety along the slip surface. In order to overcome these shortcomings, the method proposed by Kulhawy (1969) incorporates the stress-strain behavior of the soil with stresses from the Finite Element Method (FEM) with the same structure as limit equilibrium methods. It is also called enhanced method. Due to the existence of slopes with complex geometries, the three-dimensional (3D) approach is only able to incorporate all the geometric aspects of the problem. This thesis is divided into two papers with the subject of slope stability analyses by the Kulhawy’s method in 2D and 3D approaches. The primary objective of this thesis is to evaluate major factors that influence slope stability. The first paper proposed geometries ranging from convex to concave in a set of soil properties. Two stress paths were considered, i.e., construction and excavation. The GLE method was computed for comparison purposes. The slip surface is very dependent on the stress history and the shape of slope face. The relative difference in typical initial stress state reached 15% in 2D analyses and 34% in 3D analyses. Sensitivity analysis of effect of Poisson’s ratio on factor of safety was very relevant. The relationship between 2D and 3D factors of safety are nearly linear independent of stress state on order of 30 to 40%. The second paper propose analyses on embankment dams built in narrow valleys. Three approaches of slope stability were used: shear strength reduction (SSR), Kulhawy’s and GLE methods. The typical conditions of foundation sites are very variable as topography and deformability. Sensitivity analysis of Young’s modulus of foundation on factor of safety was insignificant in 2D and relevant in 3D analyses. The ratio between embankment length (W) and height (H) was very important on slope stability. The plane strain analysis tends to high W/H ratio and the opposite shows high 3D effects. The inclination of abutment showed to be relevant on factor of safety only in embankments in narrow valleys. Stiffer foundations are beneficial to the factor of safety due producing high arching effects in this scenario. The Kulhawy’s method proved to be advantageous by the incorporation of mechanical behavior of soil, more realistic stress and local stability evaluation on slip surface. It increases the amount of useful and reliable information to the engineering professional in design of slopes. All analyses were performed using SoilVision Systems suite software, Saskatchewan, Canada. The modules used were SVSLOPE, SVSOLID and SVFLUX (SoilVision Systems Ltd., 2018). The stress analysis for the simulation of excavation and construction trajectories used partial differential equation (PDE) solver, FlexPDE 6 (PDE Solutions Inc., 2014).

It is of interest to investigate extended usability of Saab’s Deployable Aircraft Maintenance facility(DAM) with respect to Eurocode standards. One of the features of the deployable hangar is that it shouldcomply with the structural strength standards for permanent buildings which requires compliance withEurocodes.Eurocodes are European standards which deals with the development of building and structural design.Compliance with Eurocodes works as a proof of requirement for mechanical strength, stability andsafety of structures. The Eurocodes were created by the European Committee for Standardization withthe intent to simplify technical obstacles and enable trade within Europe and elsewhere.The thesis has resulted in the creation of a Finite Element Model (FE-Model) of the deployable hangar,for which different loading combinations have been applied. From the FE-results, trade-off curves havebeen generated that show the effect that the different loading conditions have on the differentcomponents of the hangar. This is done for the current configuration of the hangar and for differentproduct variants. The analysis includes the effects of increased load levels.From the trade-off curves it is possible to see to what extent the hangar can withstand increased load.This is being measured with a Eurocode ratio. It has been found that the Eurocode ratio is directlydependent on increase of loads i.e. increased loads give a linear increase in Eurocode ratio for most ofthe components studied. The product variants consists of different lengths of the hangar. From the studyit has been found that adding or removing sections does not have a substantial effect on the strength ofthe hangar and the Eurocode ratio mostly remains constant. In addition the most critical componentshave been found and design suggestions have been proposed to improve the strength of the hangarwithin compliance with Eurocodes.

Thesis (Ph. D.)--Industrial and Systems Engineering, Georgia Institute of Technology, 2007.
Jiangang Dai, Committee Co-Chair ; Amy Ward, Committee Co-Chair ; Anton Kleywegt, Committee Member ; Ron Billings, Committee Member ; Mor Armony, Committee Member.

A novel concept of multiple deterministic analyses is proposed to design safer and more damage-tolerant structures, particularly when excited by dynamic including seismic loading in time domain. Since the presence of numerous sources of uncertainty cannot be avoided or overlooked, the underlying risk is estimated to compare design alternatives. To generate the implicit performance functions explicitly, the basic response surface method is significantly improved. Then, several surrogate models are proposed. The advanced factorial design and Kriging method are used as the major building blocks. Using these basic schemes, seven alternatives are proposed. Accuracies of these schemes are verified using basic Monte Carlo simulations. After verifying all seven alternatives, the capabilities of the three most desirable schemes are compared using a case study. They correctly identified and correlated damaged states of structural elements in terms of probability of failure using only few hundreds of deterministic analyses. The modified Kriging method appears to be the best technique considering both efficiency and accuracy. Estimating the probability of failure, the post-Northridge seismic design criteria are found to be appropriate. After verifying the proposed method, a Site-Specific seismic safety assessment method for nonlinear structural systems is proposed to generate a suite of ground excitation time histories. The information of risk is used to design a structure more damage-tolerant. The proposed procedure is verified and showcased by estimating risks associated with three buildings designed by professional experts in the Los Angeles area satisfying the post-Northridge design criteria for the overall lateral deflection and inter-story drift. The accuracy of the estimated risk is again verified using the Monte Carlo simulation technique. In all cases, the probabilities of collapse are found to be less than 10% when excited by the risk-targeted maximum considered earthquake ground motion satisfying the intent of the code. The spread in the reliability indexes for each building for both limit states cannot be overlooked, indicating the significance of the frequency contents. The inter story drift is found to be more critical than the overall lateral displacement. The reliability indexes for both limit states are similar only for few cases. The author believes that the proposed methodology is an alternative to the classical random vibration and simulation approaches. The proposed site-specific seismic safety assessment procedure can be used by practicing engineers for routine applications. The proposed reliability methodology is not problem-specific. It is capable of handling systems with different levels of complexity and scalability, and it is robust enough for multi-disciplinary routine applications. In order to show the multi-disciplinary application of the proposed methodology, the probability of failure of lead-free solders in Ball Grid Array 225 surface-mount packaging for a given loading cycle is estimated. The accuracy of the proposed methodology is verified with the help of Monte Carlo simulation. After the verification, probability of failure versus loading cycles profile is calculated. Such a comprehensive study of its lifetime behavior and the corresponding reliability analyses can be useful for sensitive applications.

The diploma thesis is focused on design on loadbearing reinforced concrete structure of multi-storey apartment building with shops and offices on the ground floor and underground garage. The thesis consists of the analysis and design of ceiling slabs above underground floor, supporting columns and the beam under the underground floor ceiling slab. Calculation 3D model was created to determine internal forces. All structures are designed according to EC2, ČSN EN 1992-1-1. The thesis includes elaboration of static calculation, shape drawings, drawings of reinforcement of solved structures. The rest of the project part are not analysed.

This thesis mainly deals with modeling and static analysis of the ceiling structure in the basic environment of ANSYS. The first part is focused on verifying correctness of the model most stressed parts of the structure with a simple hand-static calculation by the process of stress on a continuous beam. The main part is devoted to modeling composite structure, element types, specifying loads and boundary conditions by ANSYS FEM program. In the end, there are the results of stress and deflection presented, and the structure is evaluated at the ultimate limit state and serviceability limit state.

The master’s thesis deals with a design of a reinforced concrete foundation of multi-storey office building. The basement of the building is an underground watertight structure. The design of foundations is a combination of a concrete slab and piles. Internal forces were analysed in RFEM software based on finite element method. The structural assessment of underground construction was performed according to ultimate and serviceability limit states. Due to watertight function of construction, the reinforcement was also designed according to non-force effect in early stage.

The aim of this diploma thesis is the design of automatic tensioning device for regulating forces in driving belts of high-pressure pumps under long-term testing, in collaboration with Bosch Diesel s.r.o. in Jihlava. The paper describes the development of the mechatronic device, from the selection of components, going through the design phase of the automatic electronic device, up to mechanical design and prototype execution. An assessment is made of custom device based on the test in real operations and economic benefits for the client are evaluated in the conslusion.

Cette these est consacree a des problemes lies a l'etude de la limite semi-classique en mecanique quantique. Le premier chapitre presente une formulation geometrique qui est equivalente au principe variationnel. Elle consiste a concevoir la dynamique classique comme une projection orthogonale de la dynamique quantique sur la famille des etats coherents. L'angle de la projection nous renseigne sur la validite de l'approximation obtenue. Ces resultats sont illustres par un exemple numerique. Le deuxieme chapitre s'attache a la mecanique quantique sur le tore en tant qu'espace de phase, et en particulier a l'etude des degenerescences dans le spectre de modeles du type harper, ou harper pulse qui manifestent du chaos classique. Ce type de modeles trouve ses applications essentiellement en physique du solide, notamment pour l'effet hall quantique. Cette etude se fait d'une part a l'aide de l'indice de chern qui caracterise de facon topologique la localisation des fonctions d'ondes lorsque des conditions de periodicite sont changees, et d'autre part par la distribution de husimi permet de representer un etat quantique dans l'espace de phase. Nous discutons le role joue par les etats associes a une separatrice, par l'effet tunnel et par la nature chaotique de la dynamique

The diploma thesis deals with the design and assessment of reinforced concrete structure supporting two-storey building of the underground garage for cars. In the space above the garage is designed open area with public space. The project was designed especially outer water-impermeable construction method white bath and a base plate and a perimeter wall. The structure was designed as a comprehensive model. Computing analyzed by finite element method. All selected elements were assessed at the ultimate limit state and limit state, namely to limit state of cracking load and forced stress.

The aim of the master‘s thesis is static and structural design of polyfunctional house. The load will be determined according to ČSN EN 1990. The finite element method will be used for the calculation of internal forces. The design will be dimensioned according to ČSN EN 1992. Text part, static calculation and shape and reinforcement drawings will form the output of this work.

The aim of this diploma thesis is to design and assess highway bridge. The structure is located on the D1 motorway section bridging a wide valley between the Slovak villages Doľany a Klčov. Three variants have been created – box girder bridge with transverse overhangs, a pair of girder bridge and a pair of box girder bridges. The various proposals were compared with each other. For the most valuable option is selected prestressed box girder bridge with transverse overhangs, which are supported by prefabricated concrete struts. The selected proposal was subsequently elaborated in detail, the load-bearing structure is analyzed using Scia Engineer 16. In calculating the internal forces is adjusted for the effects of construction methods, even as time-dependent analysis TDA. When designing the load-bearing structure it is considered the action of permanent load, also loading from transport and temperature. The structure is assessed for serviceability and ultimate limit states according to current standards. The bridge deck is built by incremental launching method. The principle of this method consists of building the segments in a casting yard located behind the bridge abutment. Each segment is matchcast against the previous one and prestressed to the section of structure already built. The whole superstructure is then jacked forward a distance equal to the length of this segment. This process is repeated until the bridge deck is in its final position. Chosen method of construction is very fast and efficient, to the country in the valley isn´t damage during construction.

Subject of the dissertation is a probability analysis on creation of embankment subsoil filtration deformations. Out of the broad topic of filtration deformations, the dissertation is focused at initiation of the process. At this phase, the overlying layers downstream of levee get uplifted, and eventually get breached. The process of downstream subsoil failure probability estimation is formulated using mathematical and statistical modelling. Within the scope of parametrical study the suggested method is applied onto a test environment. Results of the probability estimation are compared with results obtained using Limit state design method. The results of stochastic modelling can be used for improvement of Limit state design method precision.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Choi, Seung-Kyum; Committee Member: Muhanna, Rafi; Committee Member: Rosen, David. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This diploma thesis deals with design and assessment of selected parts of the reinforced concrete frame of multi-storey administrative building according to the ultimate and serviceability limit state. The aim of this thesis was to design and assess the reinforced concrete structure of a slab above the first floor, one column, a foundation pad and a staircase. In addition to the static calculation, drawing documentation is included. Internal forces were obtained from the 3D model created in computational software Scia Engineer 16.1.

The diploma thesis is focused on design and assessment selected parts of the reinforced concrete structure supporting six storey office building with regard to the ultimate and serviceability limit state.This thesis contains a static calculation and technical drawings of concrete slab above first floor, staircase and two columns. For calculation of internal forces was created a 3D structural model in Scia Engineer 16. Assessment of all designed parts of the structure is done according to Eurocode 2 (ČSN EN 1992-1-1).

The work presented in this thesis comprises the assessment of existing arch bridges with overlying backfill. The main objective is to estimate the load carrying capacity in ultimate limit state analysis. A case study of the old Årsta railway bridge is presented, serving as both the initiation and a direct application of the present research. The demand from the bridge owner is to extend the service life of the bridge by 50 years and increase the allowable axle load from 22.5 to 25 metric tonnes. The performed analyses show a great scatter in estimated load carrying capacity, depending on a large number of parameters. One of the factors of main impact is the backfill material, which may result a significant increase in load carrying capacity due to the interaction with the arch barrel. Based on theoretical analyses, extensive conditional assessments and the demand from the bridge owner, it was decided that the bridge needed to be strengthened. The author, in close collaboration with both the bridge owner and the persons performing the conditional assessment, performed the development of a suitable strengthening. The analyses showed a pronounced three-dimensional behaviour, calling for a design using non-linear finite element methods. Due to demands on full operability during strengthening, a scheme was developed to attenuate any decrease in load carrying capacity. The strengthening was accepted by the bridge owner and is currently under construction. It is planned to be finalised in 2012. The application of field measurements to determine the structural manner of action under serviceability loads are presented and have shown to be successful. Measured strain of the arch barrel due to passing train has been performed, both before, during and after strengthening. The results serve as input for model calibration and verification of the developed strengthening methods. The interaction of the backfill was not readily verified on the studied bridge and the strengthening was based on the assumption that both the backfill and the spandrel walls contributed as dead weight only. The finite element models are benchmarked using available experimental results in the literature, comprising masonry arch bridges with backfill loaded until failure. Good agreement is generally found if accounting for full interaction with the backfill. Similarly, accounting for the backfill as dead weight only, often results in a decrease in load carrying capacity by a factor 2 to 3. Still, several factors show a high impact on the estimated load carrying capacity, of which many are difficult to accurately assess. This suggests a conservative approach, although partial interaction of the backfill may still increase the load carrying capacity significantly.
Arbetet i föreliggande avhandling omfattar analyser av befintliga bågbroar med ovanliggande fyllning. Huvudsyftet är att uppskatta bärförmågan i brottgränstillstånd. En fallstudie av gamla Årstabron redovisas, vilken utgör både initieringen och en direkt tillämpning av föreliggande forskning. Kravet från broförvaltaren är att öka brons livslängd med 50 år, samtidigt som axellasten ska ökas från nuvarande 22.5 ton till 25 ton. Utförda analyser visar på stor spridning i uppskattad bärförmåga, beroende på ett stort antal parametrar. En av de främsta faktorerna är fyllningens egenskaper, vilken kan resultera i en markant ökning av bärförmågan p.g.a. samverkan med bågen. Baserat på teoretiska analyser, tillståndsbedömningar och krav från broförvaltaren beslutades att bron skulle förstärkas. En förstärkningsmetod har utvecklats i nära samarbete med broförvaltaren och personer som tidigare utfört tillståndsbedömningarna. Analyserna visar ett utpräglat tredimensionellt beteende, vilket har föranlett användandet av icke-linjära finita elementmetoder. Krav på full trafik under samtliga förstärkningsarbeten har resulterat i att dessa utförs enligt en föreskriven ordning, som ska reducera minskning i bär­förmåga under samtliga etapper. Förstärkningsförslaget godkändes av Banverket och är för närvarande under byggnation. Enligt plan ska dessa slutföras under 2012. Fältmätningar har använts för att bestämma det statiska verkningssättet under brukslaster, vilket visas ge goda resultat. Resulterande töjningar från passerande tåg har uppmäts i bågen, både före, under och efter förstärkning. Resultaten har använts både för att kalibrera beräkningsmodeller och att verifiera utförda förstärkningar. Samverkan mellan båge och fyllning har inte kunnat verifierats för den aktuella bron och de utvecklade förstärkningarna baseras på en modell där både fyllning och sidomurar endast utgör yttre verkande last. De framtagna finita element modellerna har jämförts med experimentella resultat från litteraturen, omfattande tegelvalvsbroar med ovan­liggande fyllning belastade till brott. Generellt erhålls god överensstämmelse om full samverkan mellan båge och fyllning antas. Om fyllningen istället endast betraktas som yttre last, minskar lastkapaciteten ofta med en faktor 2 till 3. Fortfarande uppvisar ett antal faktorer stor inverkan på bärförmågan, vilka ofta är svåra att med säkerhet bestämma. Ett konservativt betraktningssätt rekommenderas, även om delvis sam­verkan med fyllningen fortfarande kan öka bärförmågan avsevärt.
QC 20110426

As the main topic this thesis describes the design and evaluation of selected reinforced concrete members of the prefabricated reinforced concrete industrial building with administration at ultimate limit state in accordance with applicable standards. Movable overhead crane with carrying capacity of 50 tons is the main distinction of the industrial hall. Lateral frame whit main structural parts which are roof prestressed girder, load-bearing column supporting the overhead crane and drilled pile transferring loads from the upper construction to the load bearing subsoil, is designed in particular. Furthermore, design of the Gerber beam which forms the slab construction in the administrational part of the building is elaborated. Structural design and evaluation of other structures of the building is not part of this thesis.

A new method of adaptive impulse control is developed to precisely and quickly control the position of machine components subject to friction. Friction dominates the forces affecting fine positioning dynamics. Friction can depend on payload, velocity, step size, path, initial position, temperature, and other variables. Control problems such as steady-state error and limit cycles often arise when applying conventional control techniques to the position control problem. Studies in the last few decades have shown that impulsive control can produce repeatable displacements as small as ten nanometers without limit cycles or steady-state error in machines subject to dry sliding friction. These displacements are achieved through the application of short duration, high intensity pulses. The relationship between pulse duration and displacement is seldom a simple function. The most dependable practical methods for control are self-tuning; they learn from online experience by adapting an internal control parameter until precise position control is achieved. To date, the best known adaptive pulse control methods adapt a single control parameter. While effective, the single parameter methods suffer from sub-optimal settling times and poor parameter convergence. To improve performance while maintaining the capacity for ultimate precision, a new control method referred to as Adaptive Impulse Control (AIC) has been developed. To better fit the nonlinear relationship between pulses and displacements, AIC adaptively tunes a set of parameters. Each parameter affects a different range of displacements. Online updates depend on the residual control error following each pulse, an estimate of pulse sensitivity, and a learning gain. After an update is calculated, it is distributed among the parameters that were used to calculate the most recent pulse. As the stored relationship converges to the actual relationship of the machine, pulses become more accurate and fewer pulses are needed to reach each desired destination. When fewer pulses are needed, settling time improves and efficiency increases. AIC is experimentally compared to conventional PID control and other adaptive pulse control methods on a rotary system with a position measurement resolution of 16000 encoder counts per revolution of the load wheel. The friction in the test system is nonlinear and irregular with a position dependent break-away torque that varies by a factor of more than 1.8 to 1. AIC is shown to improve settling times by as much as a factor of two when compared to other adaptive pulse control methods while maintaining precise control tolerances.

The partial safety factor method is the main safety concept applied across structural design standards. This method is also presented in EN-1990 as the basis of structural design in Europe. In the review of this code for the new generation of Eurocodes, analysis of the partial safety factor method seems necessary. The origin of the partial safety factor method is related to probabilistic methods and reliability analysis. Therefore, the latter is selected as tools for the evaluation of the partial safety factor method in the EN-1990 framework. Consequently this research begins with an explanation of the background of partial safety factor methods and reliability analysis. Different aspects of this safety concept are investigated through this study. The analysis strategy is based on the study of partial safety factor method according to the different part of EN-1990. The research is divided into two main parts, according to the basic components of limit state functions: load and resistance. Aspects related to loading are investigated first. The available load combinations and the recommended partial factors are investigated based on their reliability levels. The load combinations are compared with each other according to the sustainability of their design. An increased factor for the application of snow load is proposed to overcome safety problems related to snow load on structures. Consequently, a proposal for simplifying these load combinations is offered and verified according to reliability analysis. In the final step, regarding the load’s partial factors, a method of calibration is proposed, based on Monte Carlo reliability analysis. Afterwards, the aspects related to the resistance are analyzed. Resistances depend mostly on experimental data. Therefore, the relationship between the partial safety factor of resistance and test numbers is investigated. A probabilistic analysis based on Annex D of EN-1990 is then applied to calculate the model uncertainty partial factor and the resistance partial factor for a database from masonry shear walls. A comparison is made to show the influence of different way of partial safety factor utilization in a limit state function.:1 Introduction 2 Partial safety factor method and EN-1990 3 Reliability analysis 4 Load combinations and partial safety factors 5 Resistance partial safety factor 6 Summary and outlook

An actual design example was used to demonstrate how limit states design methods and engineering judgement can be applied to solve a non-codified engineering problem. The work was focussed on the assessment of potential buoyancy during shutdowns of the eighty-three year old Shoal Lake Aqueduct that is the sole source of potable water for Winnipeg, Manitoba. Four separate buoyancy analyses of the Shoal Lake Aqueduct were completed. Three of the analyses were conducted using limit states and reliability-based design methods. For comparative reasons a fourth analysis was completed using a traditional working stress design (WSD) method. A buoyancy model was developed and used in these analyses. The first buoyancy analysis was completed using partial safety factors developed for the Ontario Highway Bridge Design Code. Because these partial safety factors were developed for use with the design code a second analysis was completed using project-specific partial safety factors. These partial safety factors were determined using Second Moment reliability techniques and measured data for the uncertainties in the buoyancy model. A third buoyancy analysis was completed using Monte Carlo simulation techniques. A fourth buoyancy analysis was completed using WSD methods to demonstrate the potential variability in the level of safety. Engineering judgement was required to develop the buoyancy model, to interpret the data obtained for each of the parameters and to provide meaningful design values for those parameters which could not be measured. The results of the buoyancy analyses completed using limit states design and reliability-based methods were similar. Because the partial safety factors from the Ontario Highway Bridge Design Code were not based on the measured variability of different parameters, the potential for deviation from a target level of safety is significant...

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia
Neste trabalho procura-se fundamentalmente avaliar a aplicabilidade e as vantagens dos métodos numéricos na análise dos Estados Limites Últimos. Embora seja de há muito reconhecida a importância dos métodos numéricos no dimensionamento de obras geotécnicas, a inexistência de regras e orientações claras na forma como deverão ser utilizados em conformidade com os Eurocódigos estruturais, tem vindo a dificultar o seu uso generalizado na verificação dos estados limites relacionados com o colapso da estrutura ou do terreno. Encontra-se em discussão uma nova versão do Eurocódigo 7, a qual contém uma secção dedicada à aplicabilidade dos métodos numéricos na análise dos Estados Limites Últimos, pelo que se pretende analisar as sugestões e recomendações propostas nela propostas. Assim, analisa-se um caso simples correspondente a uma escavação suportada por uma cortina monoapoiada, cujo dimensionamento é feito tradicionalmente através de métodos de equilíbrio limite. Numa primeira fase, determina-se a profundidade mínima enterrada da cortina para garantia da sua estabilidade e os valores dos esforços nela e no elemento de suporte mobilizados através de métodos de equilíbrio limite, utilizando várias formas de introduzir a segurança (tradicional e EC7). Posteriormente, o mesmo caso simples é analisado através de métodos numéricos - utilizando o software PLAXIS (versão 8.6) - com base nas regras que constam na versão ainda em discussão do EC7. Comparam-se os resultados decorrentes das análises numéricas com os obtidos pelos métodos de equilíbrio limite, procurando-se aferir quais as principais diferenças entre os dois métodos. Pretendendo compreender a influência de alguns parâmetros no comportamento da estrutura e na forma de avaliar a sua segurança, é realizado um estudo paramétrico no qual se faz variar alguns parâmetros, nomeadamente as características do maciço interessado e a flexibilidade da cortina.Por fim, resumem-se as principais conclusões sobre o trabalho desenvolvido, acrescentando-se algumas propostas para desenvolvimentos futuros com o intuito de aprofundar o conhecimento nesta temática.
In this paper it is intended to evaluate the applicability and advantages of numerical methods in Ultimate Limit State analysis. Although the importance of numerical methods in the design of geotechnical works has long been recognized, the absence of clear rules and guidelines on how they should be used in accordance with the structural Eurocodes has made it difficult to use them in the verification of limit states related to structural or ground failure. A new version of Eurocode 7 is under discussion, which contains a section dedicated to the applicability of numerical methods in Ultimate Limit State analysis, and it is therefore intended to analyze the suggestions and recommendations proposed therein.Thus, a simple case corresponding to an excavation supported by a single-propped wall, whose design is traditionally done through limit equilibrium methods, is analyzed. Firstly, the embedment depth of the wall is determined in order to guarantee its stability along with the design values of structural forces, by means of limit equilibrium methods using various ways of introducing safety (traditional and EC7). Subsequently, the same simple case is analyzed using numerical methods - by means of the PLAXIS software (version 8.6) - taking in to account the rules pointed in the version still under discussion of EC7.The results of the numerical analyzes are compared with those obtained by limit equilibrium methods, trying to ascertain the main differences between the two methods.In order to understand the influence of some parameters on the behaviour of the structure and how to evaluate its safety, a parametric study is carried out in which some parameters are varied, namely the characteristics of the soil mass and the flexibility of the wall.Finally, the main conclusions about the work developed are summarized, including some proposals for future developments in order to deepen knowledge in this subject.

Yes
For composite beams with low degrees of shear connection, additional deflections occur due to slip in the shear connectors, which can be significant for beams with low degrees of shear connection. A design formula is presented for the effective stiffness of composite beams taking account of the stiffness of the shear connectors, which is compared to measured deflections of 6 symmetric beams and an 11m span composite beam of asymmetric profile. It is shown that the comparison is good when using a shear connector stiffness of 70 kN/mm for single shear connectors and 100 kN/mm for pairs of shear connectors per deck rib. Results of push tests on a range of deck profiles confirm these initial elastic stiffnesses. To ensure that the slip at the serviceability limit state does not lead to permanent deformations of the beam, it is proposed that the minimum degree of shear connection should not fall below 30% for un-propped beams and 40% for propped beams of symmetric cross-section.
European Commission

The thesis entitled "Pushing the Limits of NMR Sensitivity and Chiral Analysis: Design of New NMR Methods and Bio-molecular Tools" consists of six chapters. The research work reported in this thesis is focused on the development of novel chemical and NMR methodological approaches for enantiomeric analysis and mea- surement of residual dipolar couplings (RDCs), and the development of sensitivity enhanced slice selective NMR experiments for obtaining pure shift 1H spectra and the measurement of scalar couplings. The thesis is divided into two parts. The Part I comprises chapters 2-4, where the enantiomeric analysis is discussed, which includes newly developed chiral reagents, two new weak chiral aligning media and design of novel NMR techniques. Part II comprises chapters 5 and 6, which discusses new sensitivity enhanced slice selective NMR techniques. Chapter 1 gives a general introduction to NMR and the problems investigated in the remaining chapters of the thesis. The chapter starts with a brief discussion on the introduction, advancements and general applications of NMR, discussion is also given on the NMR approaches for enantiomeric analysis both in isotropic and anisotropic phases and the measurement of RDCs, including the benefits and limitations associated with each approach. The chapter sets the tone by discussing limitations of the existed NMR enantiomeric approaches and slice-selective techniques, and builds the bridge for the rest of the chapters by addressing these limitations. The chapter also introduces slice selective experiments, their benefits over other conventional methods and limitations. Additional introductory notes are also given on some related concepts. Part I : NMR Chiral analysis and RDCs measurements Chapter 2 discusses chiral sensing properties of RNA nucleosides and their utility as chiral derivatizing agents for the enantio-discrimination of 1o-amines using one dimensional 1H NMR. A three component protocol has been proposed for the complexation of nucleosides with amines, which is rapid, economical and provides maximum diastereomeric conversion. The chiral differentiating ability of nucleosides are examined for different amines based on the 1H NMR chemical shift differences between the diastereomers (∆δ R, S ). Enantiomeric differentiation has been observed at multiple chemically distinct proton sites. It is observed that adenosine and guanosine exhibit large chiral differentiation (∆δ R, S ) due to the presence of a purine ring. The comparison of the diastereomeric excess (de) measured by NMR with those of the gravimetrically prepared ratios are in excellent agreement with each other confirming the robustness of these RNA nucleosides in discriminating primary amines. Chapter 3 establishes the smooth connectivity with the chapter 2 by discussing the limitations of the enantiomeric discrimination using NMR in isotropic solutions. This chapter discusses two new water compatible aligning media that were developed based on self-assembling strategy of small bio-molecules. The self-assembled folic acid, and the binary mixture of 50-GMP and guanosine are introduced as two novel weak aligning media. The properties of these low ordered media have been systematically studied for their easy preparation, physical parameter dependent tunability of their degree of alignment, mesosphere sustainability over a broad range of temperature and the concentration of the ingredients, and the phase reproducibility. The applications of both these new media are demonstrated for chiral and pro-chiral discrimination and also for the measurement of RDCs. Both these liquid crystalline media could be tuned to very low degree of alignment (order parameter of the order of 10−4), which provides simple first order spectra of molecules aligned in them, the analysis provide order dependent NMR spectral parameters. The 50-GMP:guanosine orienting medium can be prepared in less than 1 hour, and has been demonstrated to be an ideal medium for the determination of RDCs that are used as restraints in the structure calculations of small molecules. Chapter 4 describes 1H NMR spectral complexity in isotropic and anisotropic phases and its consequences on enantiomeric analysis. In circumventing such problems, new NMR techniques have been developed and the spin dynamics involved in the designed sequences are discussed. The newly developed 2D 1H NMR experimental method termed as RES-TOCSY, and its applicability for resolving R and S enantiomeric or diastereomeric peaks of all the coupled proton spins in isotropic phase is discussed. The utility of the developed method is demonstrated in diverse situations, such as, for suppressing impurities peaks, resolving the severely overlapped peaks and unraveling the peaks masked due to severe line broadening when metal complexes are used as chiral auxiliaries. The advantages and limitations of the method over other methods available in the literature are discussed and the significant advantage of the present method is illustrated by spectral comparison with J-resolved experiment. The appli- cation of the method for the accurate measurement of enantiomeric excess has also been demonstrated. The chapter also introduces another NMR experimental technique developed for resolving enantiomeric peaks and complete unraveling of R and S spectra in anisotropic phase. The developed 2D NMR method is cited in the literature as CH-RES-TOCSY. In addition to spectroscopic visualization of R and S spectra, the method also yields C-H RDCs. The applicability of the new experiment has been demonstrated on a chosen example. The wide utility of the method has also been demonstrated for the assignment of symmetric cis- and trans- isomers. Part II : Sensitivity Enhancement of Slice selective NMR Experiments Chapter 5 describes applications of slice selective NMR experiments over conven tional NMR methods and their limitations as far as the sensitivity of signal detection is concerned, especially in low concentrated samples. The chapter introduces the implementation of Acceleration by Sharing Adjacent Polarization (ASAP) technique in slice selective experiments. It is convincingly demonstrated that ASAP helps in reducing inter scan relaxation delay and consequently permits acquisition of more number of scans in a given time, resulting in the gain in signal enhancement by a factor of two. The pulse sequences have been suitably designed for obtaining the pure shift 1H spectra and in G-SERF experiment for the measurement of 1H-1H couplings, both with significantly enhanced signal intensities. Chapter 6 describes new sensitivity enhanced slice selective NMR methods for mea- surement of scalar couplings. A new experiment has been developed which is named as Quick G-SERF (QG-SERF). It is a 1D NMR slice selective method developed based on real time spin manipulation technique. The method gives multiple scalar couplings of a selected spin with simplified multiplets, which is analogous to the 2D G-SERF but with considerable saving in instrument time by 1-2 orders of magnitude. The rapidness of the experiment arises due to reduced dimensionality. The spin dynamics involved in the pulse sequence and its working principle have been described. The application of the method is illustrated for the measurement of 1H-1H couplings. The sequence has been further improved to obtain the heteronuclear couplings between two abundant spins in an orchestrated manner and has been demonstrated for measurement of 1H-19F couplings. This sequence cited as HF-QG-SERF has been implemented on the molecules containing number of chemically non-equivalent fluorine atoms.

The research is motivated by the need to address two major challenges in wind power integration: how to mitigate wind power fluctuation and how to ensure stability of the farm and host grid. It is envisaged that wind farm power output fluctuation can be reduced by using a specific type of buffer, such as an energy storage system (ESS), to absorb its negative impact. The proposed solution, therefore, employs ESS to solve the problems. The key research findings include a new technique for calculating the desired power output profile, an ESS charge-discharge scheme, a novel direct-calculation (optimization-based) method for determining ESS optimal rating, and an ESS operation scheme for improving wind farm transient stability. Analysis with 14 wind farms and a compressed-air energy storage system (CAES) shows that the charge-discharge scheme and the desired output calculation technique are appropriate for ESS operation. The optimal ESSs for the 14 wind farms perform four or less switching operations daily (73.2%-85.5% of the 365 days) while regulating the farms output variation. On average, the ESSs carry out 2.5 to 3.1 switching operations per day. By using the direct-calculation method, an optimal ESS rating can be found for any wind farm with a high degree of accuracy. The method has a considerable advantage over traditional differential-based methods because it does not require knowledge of the analytical form of the objective function. For ESSs optimal rating, the improvement in wind energy integration is between 1.7% and 8%. In addition, a net increase in grid steady-state voltage stability of 8.3%-18.3% is achieved by 13 of the 14 evaluated ESSs. For improving wind farm transient stability, the proposed ESS operation scheme is effective. It exploits the use of a synchronous-machine-based ESS as a synchronous condenser to dynamically supply a wind farm with reactive power during faults. Analysis with an ESS and a 60-MW wind farm consisting of stall-regulated wind turbines shows that the ESS increases the farm critical clearing time (CCT) by 1 cycle for worst-case bolted three-phase-to-ground faults. For bolted single-phase-to-ground faults, the CCT is improved by 23.1%-52.2%.
text

Tese de doutoramento em Engenharia Civil
Um pavimento rodoviário, para além da sua importante contribuição para a cómoda e segura circulação dos utentes da via, consome grande parte dos recursos financeiros alocados à construção ou beneficiação de uma infraestrutura. A uma estrutura desta natureza, impõem-se um conjunto de características que devem perdurar ao longo do tempo. Este carácter duradouro é garantido em duas fases distintas: em fase de projeto, pelo adequado dimensionamento da estrutura e durante a execução da obra, pela qualidade dos processos e materiais de construção. O dimensionamento de um pavimento requer o conhecimento de um conjunto de fatores que permitam avaliar ações e prever a resistência mecânica das camadas envolvidas. No âmbito da tradicional engenharia de pavimentos, a quantificação destes fatores tem um carácter determinístico, optando-se por valores mais ou menos conservadores em função do julgamento e conhecimento do projetista. Embora a abordagem seja determinística, o reconhecimento da variabilidade dos fatores envolvidos é uma realidade inalterável. A espessura de uma camada varia ao longo da infraestrutura. Influenciado pela temperatura, percentagem de betume, porosidade, etc…, o módulo de rigidez de uma camada betuminosa também varia de local para local. O número de veículos que se espera solicitem o pavimento, sendo um exercício de previsão, é claramente uma variável aleatória. Neste sentido, a quantificação de cada fator envolvido traduz-se na introdução de uma probabilidade de falha, cuja avaliação é impossível de efetuar segundo a abordagem tradicional. Com este trabalho pretende abordar-se a problemática do dimensionamento de um pavimento flexível sob o ponto de vista estocástico. Com base em amostras recolhidas em nove obras, para além de um contributo para a análise probabilística de um conjunto de fatores necessários à caracterização mecânica dos materiais betuminosos, avalia-se a variabilidade do módulo de rigidez e espessura das camadas betuminosas, determinando-se os seus efeitos sobre diferentes estruturas de pavimentos. A abordagem probabilística ao dimensionamento de um pavimento flexível é feita associando a cada estrutura a competente probabilidade de ruína, cuja determinação se faz pelo método de simulação de Monte Carlo e pelos modelos aproximados do segundo momento de primeira ordem (FOSM - First Order Second Moment, na terminologia inglesa) e das estimativas pontuais.
In addition to its important contribution to the safe movement of vehicles, the pavement consumes much of the financial resources allocated to the construction or improvement of a roadway. A structure of this nature requires a set of features that must persist over time. This long-lasting character is ensured in two distinct phases: in the design phase, by the proper design of the structure and, during the construction phase, by the processes and materials quality control. The design of a pavement requires knowledge of a set of factors which are relevant to assessing loads and predict the mechanical resistance of the layers involved. Within the framework of traditional engineering, the quantification of these factors has a deterministic character, resulting in the choice of values more or less conservatives as a function of judgment and knowledge of the pavement designer. Although the approach is deterministic, recognizing the variability of the factors involved is an unalterable reality. The thickness of a layer varies along the infrastructure. Influenced by temperature, binder content, porosity, etc. ..., the stiffness modulus of a bituminous layer also varies from place to place. The number of vehicles that are expected to load the pavement, being a forecasting exercise, is clearly a random variable. In this sense, the quantification of each factor involved is reflected in the introduction of a probability of failure, the assessment of which is impossible to perform according to the traditional approach. This work aims at addressing the problem of designing a flexible pavement under the stochastic point of view. Based on samples data collected in nine roadways, in addition to an input for the probabilistic analysis of a set of factors required for the mechanical characterization of bituminous materials, the variability of the stiffness modulus and thickness of the asphalt layers is evaluated, determining its effects on different pavement structures. The probabilistic approach to the design of a flexible pavement is carried out by assigning each structure the probability of failure, the determination of which is made by the method of Monte Carlo simulation and the approximate models such as the FOSM (First Order Second Moment) and the point estimation method.