Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Tunneling in busy urban areas is becoming a common practice, caused by the everincreasing number of commuters. This causes a decline in the service level that the surface transportation systems provide in cities. Tunneling induces movement of the soil directly surrounding the tunnel. These movements are translated into surface movements, which are translated into structural displacements of the surrounding surface infrastructure. These displacements, for which the infrastructure may not have been designed, put a question mark on the infrastructure aesthetics, serviceability, as well as structural stability. Burland and Wroth (1974) proposed a simple analytical damage assessment approach (Limiting tensile strain method (LTS)) to aid in the design of tunnels with respect to the structural integrity of the affected surface infrastructure. This study is concerned with the accuracy of this approach applied to the damage assessment of laterally unconfined, solid masonry walls, subject to a sagging mode of settlement deformation with no soil to wall friction. It is also concerned with the proposal of modifications to the approach, where deemed necessary. Finite element models of solid masonry walls are built and analysed in order to determine the accuracy of the simple analytical damage assessment approach with regard to the prediction of strains in solid masonry walls subject to tunneling-induced displacements. The predictions are found to be accurate for walls ofL/H ratio equal to 2 and larger. For walls of L/H ratio smaller than 2, the predictions are found to be underestimates. The simple analytical damage assessment approach is unable to account for the stiffness of the soil directly under the foundation of the wall. The stiffness of the soil plays a major role in the stress and strain distributions in the wall. It is therefore deemed necessary to modify the simple analytical damage assessment approach by accounting for the soil to wall interaction and the effect it has on the settlement damage to solid masonry walls. The soil to wall interaction is found to reduce the number of mitigating measures originally recommended for the walls, by the simple analytical damage assessment approach, as it accounts for the bedding of the wall into the soil previously unaccounted for. This study has reached the point where it is able to accurately predict whether a laterally unconfined, solid masonry wall, subject to a sagging mode of settlement deformation with no soil to wall friction will experience magnitudes of strain surpassing the yielding strain of the material. This was fundamentally achieved by developing a better representation of the strains in solid masonry walls as well as accounting for the inherent soil to wall interaction This study is intended to pioneer the proliferation of similar studies for various other structures. A methodology, applicable for similar investigations envisaged for other structures, is hereby developed. / AFRIKAANSE OPSOMMING: Tonnels in besige stedelike gebiede is besig om 'n allerdaagse verskynsel te raak a.g.v. die skerp toename in pendelaars. Die rede hiervoor is die afname in die kwaliteit van bogrondse vervoerdienste. Tonnels veroorsaak beweging van grond direk in aanraking met die tonnel. Hierdie bewegings versprei na die oppervlak wat strukturele verplasings veroorsaak. Vir n' struktuur wat nie vir hierdie verplasings ontwerp is nie, ontstaan vrae oor die estetika, diensbaarheid asook die stabiliteit van die struktuur. Burland en Wroth (1974) het 'n eenvoudige analitiese skade-assesseringsmetode voorgestel (Limiting tensile strain method (LTS)) vir die ontwerp van tonnels m.b.t. die strukturele integriteit van die geaffekteerde oppervlak se infrastruktuur. Hierdie studie handeloor die akkuraatheid van dié benadering, toegepas op die assessering van skade op lateraalonbeperkte, soliede messelwerkmure, onderhewig aan die deurbuigings mode van versakkingsdeformasie, met geen grond tot muur wrywing. Eindige element modelle van messelwerkmure is gebou en geanaliseer om die akkuraatheid van die eenvoudige analitiese skade-assesseringsmetode te bepaal, m.b.t. die voorspelling van die vervormings in messelwerkmure onderhewig aan grondverplasings veroorsaak deur tonnels. Die voorspellings is akkuraat in mure met lengte tot hoogte (L/H) verhoudings van 2 en hoër. Vir mure met LIH verhoudings van minder as 2, word daar gevind dat die voorspellings onkonserwatief is. By die eenvoudige analitiese skade-assesseringsmetode word die styfheid van grond direk onder die fondasies van die muur nie in ag geneem nie. Die grondstyfheid speel 'n kardinale rol by die spannings- en vervormingsverdelings in die muur. Dit is daarvoor nodig om die eenvoudige analitiese skade-assesseringsmetode aan te pas om die grond tot muur interaksie in ag te neem. Die interaksie tussen die grond en die muur veroorsaak 'dat a minder of geen skade voorkomende maatreëls getref hoef te word as wat oorspronklik deur die envoudige analitiese skade-assesseringsmetode voorgestel sou word. Dit neem die inbedding van die muur in die grond in ag, wat voorheen geïgnoreer is. Die studie het 'n punt bereik waar dit akkuraat kan voorspelof 'n lateraalonbeperkte, soliede messelwerkmuur, onderhewig aan die deurbuiging mode van versakkingsdeformasie en met geen grond tot muur wrywing, vervormings hoër as die swigvervorming van die material salondervind. Dit is bereik deur 'n beter voorstelling van die vervormings in soliede messelwerkmure asook die in agneming van inhirente grond tot muur interaksie. Die studie is veronderstel om die voorganger te wees vir soortgelyke studies toegepas op verskeie ander struktuurklasse. Die sistematiese metode wat hier ontwikkel is kan toegepas word op die ander struktuurklasse.

Call number: LD2668 .T4 1986 L43 / Master of Science / Civil Engineering

This thesis has been executed in cooperation with Abetong which is a leading company in the prefabrication of concrete structures. For a prefabricated concrete building the design engineer must take into consideration the connections between the concrete elements in order to make sure that the building will possess a sufficient structural stability. Therefore the structural engineer might have to re-calculate the original structure that often has been designed as an on site-built building. The purpose of this thesis is to examine the forces between elements related to different models to see if the structural engineer has to make a re-design. To get results for this study we have used FEM-design 3D Structure. The results of forces from the program were compared with Abetongs standard forces of point connections and recess lists and showed that the structural engineer can use the original calculation up to around five stories when a prefabricated shall be erected.

[pt] Este trabalho tem como objetivo demonstrar que um difeomorfismo do círculo é Morse-Smale se, e somente se, ele é estruturalmente estável sob C(1)- perturbações, e que o conjunto dos difeomorfismos Morse-Smale é denso no conjunto de todos os difeomorfismos C (1) do cíırculo. Uma das preocupações presentes neste trabalho é a de apresentar as demonstrações e os conceitos da forma mais acessível possível, tendo como pré-requisitos apenas análise Real e noções básicas de topologia. / [en] The main goal of this dissertation is to provide a self-contained proof that circle diffeomorphisms are Morse-Smale if and only if they are structurally stable in the C (1) topology. Another interesting result proved here is that the set of Morse-Smale diffeomorphisms is dense in the set of all C (1) diffeomorphisms of the circle. The presentation of the subject and proofs requires no more background than real analysis of functions of one variable and elementary topology. Keywords

Research, tests and analysis are presented on several reinforcements placed in the asphalt overlay of a roadway built over soft organic soils. Non-destructive Evaluation (NDE) methods and statistical analysis were used to characterize the pavement before and after rehabilitative construction. Before reconstruction, falling weight deflectometer, rut and ride tests were conducted to evaluate the existing pavement and determine the statistical variability of critical site characteristics. Twenty-four 500ft. test sections were constructed on the roadway including sixteen reinforced asphalt and eight control sections at two test locations that possessed significantly different subsoil characteristics. NDE tests were repeated after reconstruction to characterize the improvements of the test sections. Test results were employed to quantify the stiffness properties of the pavement based on load-deflection data to evaluate the relative performance of the reinforced sections. Statistical analysis of the data showed the stiffness of the reinforced sections was consistently higher than the control sections. / by Daniel D. Pohly. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

O valor do momento crítico à flambagem lateral de vigas em regime elástico-linear é geralmente obtido na literatura técnica por meio de teorias aproximadas e definido apenas para alguns casos usuais. Entretanto, a utilização de modernas técnicas computacionais permite que o estudo da flambagem lateral não fique restrito apenas a esses casos. O objetivo deste trabalho é determinar o valor do momento crítico de vigas de aço em regime elástico-linear para diversos casos de carregamento e de vinculação, por meio de uma Teoria Não-Linear Geometricamente Exata. Estes resultados são comparados aos obtidos com o emprego de expressões baseadas em teorias aproximadas, em particular as normas de projeto NBR8800:1986, prAISC-LRFD:2003, prEN1993-1-1:2002 Stage 54 e prEN1999-1-1:2004 Stage 54. Com o emprego do programa de elementos finitos PEFSYS, realiza-se, para vigas tipo I bissimétricas, uma análise paramétrica que incorpora a faixa usual de utilização destas vigas em projetos usuais de edifícios. Estuda-se a influência da restrição ao empenamento e à rotação no plano ortogonal ao da flexão para quatro condições de vinculo nas extremidades da viga. Consideram-se ainda alguns casos adicionais, como carga aplicada fora do centro de torção e vínculos ao longo do vão, para mostrar o potencial do método de análise utilizado. / The elastic lateral buckling moment is generally obtained in technical literature by means of approximated theories, and defined just for some common cases. However, the use of recent computational techniques allows that lateral-torsional buckling’s study doesn’t remain restricted to this few cases. The intend of this work is to establish accurate values for the elastic critical moment of steel beams in several cases of loading and end-restraint, using a Geometrically Exact Nonlinear Theory. This results are compared with the ones derived from approximate theories, in particular, Brazilian code NBR8800:1986, American Specification prAISC-LRFD:2003, and European Prestandards prEN1993-1-1:2002 Stage 54 and prEN1999-1-1:2004 Stage 54. A parametrical analysis is performed for doubly-symmetric I-beams using the finite element program PEFSYS for usual range in conventional structures. The influence of warping and lateral rotation restraints is studied for four idealized support conditions. Some other cases, like transverse load applied above and below shear center and presence of bracings along the span, are accounted of to corroborate the validity and the powerful of this procedure.

A demanda por estruturas mais leves implica num ganho em economia, porém o aumento de esbeltez da estrutura pode tornar ela susceptível a instabilidade frente a tensões compressivas estáticas ou dinâmicas. A instabilidade acontece em várias escalas da estrutura analisada e pode interagir com outras formas de colapso como a propagação instável de fissuras, problema governado pela mecânica da fratura, pela plastificacão do material, ou por uma combinação dos efeitos citados. Neste contexto, no presente trabalho, se explora a capacidade do método dos elementos discretizados por barras (LDEM) na simulação de problemas de instabilidade estática e dinâmica devido as tensões de compressão. Este método permite simular o sólido como um arranjo de barras com rigidez equivalente ao contínuo que se quer representar. Leis constitutivas não lineares permitem modelar ruptura de forma simples. A equação de movimento resultante da discretização permite formular uma equação de movimento desacoplada que pode ser integrada no domínio do tempo com um método explícito (Método das Diferencias Finitas Centrais). O fato das barras serem rotuladas nos seus extremos e a solução do problema ser obtida de forma incremental permite capturar problemas com não linearidade geométrica, entre eles a instabilidade estrutural frente a tensões compressivas. Como último exemplo se realiza a análise de um painel sanduiche por flexão em três pontos, que é composto por um núcleo de poliuretano, com duas lâminas externas de material compósito, neste caso a instabilidade estrutural está associada a flambagem da camada da lâmina comprimida. Finalmente a potencialidade da metodologia de análise utilizada é discutida. / The demand for lighter structures implies a gain in economy, but the increase in slenderness of the structure may make it susceptible to instability against static or dynamic compressive stresses. Instability occurs at various scales of the analyzed structure and may interact with other forms of collapse such as unstable crack propagation, problem governed by fracture mechanics, plastification of the material, or a combination of the cited effects. In this context, in the present work, we explore the ability of the discrete elements methods by bars (LDEM) in the simulation of problems of static and dynamic instability due to the compression stresses. This method allows to simulate the solid as an arrangement of bars with rigidity equivalent to the continuum that one wants to represent. Constitutive non-linear laws allow simple modeling of rupture. The equation of motion resulting from the discretization allows us to formulate a decoupled motion equation that can be integrated in the time domain with an explicit method (Central Finite Differences Method). The fact that the bars are labeled at their ends and the solution of the problem is obtained in an incremental way allows to capture problems with geometric non-linearity, among them the structural instability against compressive tensions. The last example, the analysis of a sandwich panel by three-point bending, which is composed of a polyurethane core, with two external blades of composite material, in this case the structural instability is associated with buckling of the layer of the compressed blade . Finally, the potential of the analysis methodology is discussed.

Neste trabalho reunimos alguns resultados afirmativos relacionados ao closing lemma de classe C^r em variedades bidimensionais compactas. / In this work we present some partial results corcerning closing lemma for smooth flows on compact bidimensional manifolds.

The western and northern parts of South Florida have shallow layers of organic and plastic soils under existing roads. These roads often exhibit large amount of cracking and distortion in a short period of time. Traditional repairs are often not practical due to high costs and extended construction time. In an effort to develop rehabilitation strategies that could be strictly applied to the surface layer, a pilot test site was selected along the alignment of SR 15/US 98 in northwest Palm Beach County, where severe pavement distresses were observed due to the presence of thick organic layers. PaveTrac MT-1, GlasGrid 8501, PetroGrid 4582, and ARMI were used as promising asphalt reinforcing products in 24 experimental pavement sections, including 8 control sections without any reinforcement. A comprehensive field testing and monitoring program involving FWD, rut and ride quality measurements was conducted at the preconstruction, 6-month post-construction, and 18-month post-construction stages. Due to large variability in the sub-surface conditions, a statistics-based data analysis protocol was developed for performance evaluation and relative comparisons of the test sections and, in turn, reinforcing products. Post construction data from both 6 months and 18 months demonstrated that stiffness of reinforced sections were significantly higher than the control sections. Procedures were developed to identify and statistically quantify the benefits derived from the reinforcements only, so that the relative performance of various products could be monitored over time. Based on the field testing data available to date, a framework was developed in this study for the prediction of pavement life, which is essential for conducting a detailed Life Cycle Analysis / by Alex Lima-Arie. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Dynamic fracture of metals is a fascinating multiphysics-multiscale problem that often results in brittle and/or ductile fracture of structural components. Additionally, under high strain rates such as impact or blast loads, a failure phenomena known as shear banding may also occur, which is a common precursor to fracture. Both fracture and shear banding are instability processes leading to strong discontinuities and strain localization, respectively. Namely, shear bands are zones of highly localized plastic deformation, while brittle/ductile cracks are material discontinuities due to cleavage and/or void coalescence. Furthermore, while fracture events are mostly driven by triaxial tensile loading, shear bands are driven by shear heating caused by inelastic deformations and high temperature rise. In this work, fracture is modeled through a phase field formulation coupled to a set of equations that describe shear bands. While fracture is governed by a strong length scale that propagates at a fast time scale, shear bands are dominated by a weak length scale and propagate slower. These are two different failure modes with distinct spatial and temporal scales. This thesis is aimed at the development of analytical and numerical methods to determine the onset of both shear band localization and fracture. The main contribution of this thesis is the formulation of analytical criteria, based on the linear perturbation method, for the onset of fracture and shear band instabilities. We first propose a stability framework for shear bands that account for a non-constant Taylor Quinney coefficient. In addition, we apply the linear perturbation method to the phase field formulation of fracture to study the onset of unstable crack growth. The derivations lead to an analytical, energy based criterion for the phase field method in linear elastic and visco-plastic materials. The stability criterion not only recovers the critical stress value reported in the literature for simple elastic cases but also provides a criterion for visco-plastic materials with a general degradation function and fracture induced by cold-work. Finally, we analyze the physical stability of both failure modes and their interaction. The analysis provides insight into the dominant failure mode and can be used as a criterion for mesh refinement. Several numerical results with different geometries and a range of strain rate loadings demonstrate that the stability criterion predicts well the onset of failure instability in dynamic fracture applications. For the example problems considered, if a fracture instability precedes shear banding, a brittle-like failure mode is observed, while if a shear band instability is initiated significantly before fracture, a ductile-like failure mode is expected. In any case, fracture instability is stronger than a shear band instability and if initiated will dominate the response. Another contribution of this thesis is the development of numerical type stability methods based on the discretized model which can be employed within any finite element method. In this approach, a novel methodology to determine the onset of shear band localization is proposed, by casting the instability analysis as a generalized eigenvalue problem with a particular decomposition of the element Jacobian matrix. We show that this approach is attractive, as it is applicable to general rate dependent multidimensional cases and no special simplifying assumptions ought to be made. Furthermore, this technique is also applied to the fully coupled dynamic fracture problem and is shown to agree well with the analytical criteria. Finally, we propose an alternative for identifying the instability point following a generalized stability analysis concept. In this framework, a stability measure is obtained by computing the instantaneous growth rate of the vector tangent to the solution. Such an approach is more appropriate for non-orthogonal problems and is easier to generalize to difficult dynamic fracture problems.