Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study entails the appraisal of the constitutive models available for the non linear finite element analysis of reinforced concrete, using the DIANA finite element package and following generally accepted guidelines for non linear finite element analyses. The constitutive models considered are plasticity and total strain based (fixed and rotating crack) models. The appraisal consists of the analysis of various experiments performed on reinforced concrete beams that are governed by compressive, shear and tensile dominated failures. The investigation is not limited to the accuracy of the results obtained using these models but also of the consistency of the results obtained with regard to various mesh types and sizes, as well as a study of the individual influence of several material parameters. The intention of the study was to provide the reader with an indication of the performance capacity (accuracy and consistency) of the available constitutive models, where the notion of the use of the results obtained from non linear finite element analyses for design purposes is considered. The results obtained were varied. The models performed reasonably well in the compressive and tension dominated studies, with the importance of accurate material parameters being emphasized especially for the more advanced cementitious materials investigated. The total strain rotating crack model also showed a proclivity of simulating incorrect failure modes as well as exhibiting reluctance towards stress redistribution. All models used for the shear dominated study yielded mostly inaccurate and inconsistent results, but it was found that the four node quadrilateral element with selective reduced integration performed the best. The plasticity model did not capture shear failure well, and convergence was often not attained. The constant shear retention factor of the total strain fixed crack model was found to yield more detailed response curves for the smaller mesh sizes. The results of the tension dominated beams inspired more confidence in the models as quite accurate values were attained, especially by the plasticity model used. The ability of the available models to simulate realistic structural behaviour under various failure modes is very limited, as is evident from the results obtained. The development of a more advanced and robust model is required, which can provide consistently accurate results and failure modes, and even ‘anticipate’ potential failure modes not considered by the user.

As vigas mistas configuram uma atrativa solução estrutural para pequenas e grandes obras na engenharia civil. O emprego deste tipo de estruturas proporciona: melhor aproveitamento das características de cada material, maior rapidez na construção e economia. Esta pesquisa da continuidade aos trabalhos de Tamayo (2011) e Dias (2013); apresenta-se um modelo numérico que emprega o método dos elementos finitos para avaliar o comportamento de estruturas do tipo viga mista, com foco na consideração dos efeitos de longa duração do concreto: fluência e retração; e à inclusão da protensão interna do tipo aderente, aplicada sob a laje de concreto. Implementaram-se seis modelos para predição dos fenômenos de longa duração: ACI 209R-92, Bazant-Baweja B3, CEB MC90, CEB MC99, CEB MC10 e GL2000, e disponibilizou-se uma ferramenta estatística que permite sua correta comparação. O cabo de protenssão é modelado de maneira discreta dentro do elemento de concreto e posteriormente são definidas as contribuições que o mesmo faz ao elemento de casca do concreto no qual está inserido. O Software GiD foi empregado nas etapas de pré e pós processamento, customizando sua interface para a atribuição das propriedades do problema. A validação da simulação numérica foi efetuada a partir da modelagem de 14 vigas no total, os espécimenes correspondem a vigas tanto simplesmente apoiadas como contínuas. O programa desenvolvido é capaz de modelar adequadamente estruturas do tipo viga mista, com protensão aderente instalada na laje de concreto; considerando uma análise ao longo do tempo e levando em conta os efeitos da fluência e da retração que afetam o concreto. / The composite beams constitute an attractive structural solution for small and large projects in civil engineering. The use of such structures provides better use of the characteristics of each material, faster construction and economy. This research continues the work of Tamayo (2011) and Dias (2013); it presents a numerical model employing the finite element method to evaluate composite beam structures, focusing on the long-term effects of concrete: creep and shrinkage; and the inclusion of internal adherent prestressing, applied under the concrete slab. Six models were implemented for the prediction of long-term effects: ACI 209R-92, Bazant-Baweja B3, CEB MC90, CEB MC99, CEB MC10 and GL2000, and provided a statistical tool that allows the correct comparison between them. The prestressed cable is modeled discretely within the concrete element and are further defined the contributions that it makes to the concrete shell element in which it is inserted. The GiD Software was used in the stages of pre and post processing, and its interface was customized for assigning the problem properties. The validation of numerical simulation was performed by full modeling 14 beams; the specimens correspond to both simply supported as continuous beams. The developed program is able to adequately model prestressed composite beam structures; considering the long-term effects of creep and shrinkage, that affects the concrete.

No description available.

The study presents the results of an experimental and analytical investigation aimed at examining the lateral stability of rectangular reinforced concrete slender beams. In the experimental part of the investigation, a total of eleven reinforced concrete beams having a depth to width ratio between 10.20 and 12.45 and a length to width ratio between 96 and 156 were tested. Beam thickness, depth and unbraced length were 1.5 to 3.0 in., 18 to 44 in., and 12 to 39.75 ft, respectively. Each beam was subjected to a single concentrated load applied at midspan by means of a gravity load simulator that allowed the load to always remain vertical when the section displaces out of plane. The loading mechanism minimized the lateral translational and rotational restraints at the load application point to simulate the nature of gravity load. Each beam was simply-supported in and out of plane at the ends. The supports allowed warping deformations, yet prevented twisting rotations at the beam ends. In the analytical part of the study, a formula was developed for determining the critical loads of lateral torsional buckling of rectangular reinforced concrete beams free from initial geometric imperfections. The influences of shrinkage cracking and inelastic stress-strain properties of concrete and the contribution of longitudinal reinforcement to the lateral stability are accounted for in the critical load formula. The experiments showed that the limit load of a concrete beam with initial geometric imperfections can be significantly lower than the critical load corresponding to its geometrically perfect configuration. Accordingly, a second formula was developed for the estimation of limit loads of reinforced concrete beams with initial lateral imperfections, by introducing the destabilizing effect of sweep to the critical load formula. The experimental results were compared to the proposed analytical solution and to various lateral torsional buckling solutions in the literature. The formulation proposed in the present study was found to agree well with the experimental results. The incorporation of the geometric and material nonlinearities into the formula makes the proposed solution superior to the previous lateral torsional buckling solutions for rectangular reinforced concrete beams.

The spans of precast prestressed concrete bridge girders have become longer to provide more economical and safer transportation structures. As the spans have increased, so has the depth of the girders which in turn have increased the slenderness of the girders. Slenderness in a beam or girder would increase the likelihood that a stability failure would occur. Stability failures could pose a danger to construction personnel due to the sudden nature in which a stability failure would occur. Furthermore, stability failures of prestressed concrete girders during construction would cause a detrimental economic impact due to the costs associated with the failure of the girder, the ensuing construction delays, damage to construction equipment and potential closures to highways over which the bridge was being constructed. An experimental and analytical study was performed to determine the stability behavior of prestressed concrete beams. Two stability phenomenons were investigated: (1) lateral-torsional buckling and (2) global stability. An emphasis was placed on the effects of initial imperfections on the stability behavior; the effect elastomeric bearing pads and support rotational stiffness was investigated. The experimental study involved testing six rectangular prestressed concrete beams for lateral-torsional buckling, a PCI BT-54 for thermal deformations and the same PCI BT-54 for global stability. The 32-ft. long rectangular beams were 4-in. wide and 40-in. deep. The PCI BT-54 had a 100-ft. long span. A material and geometric nonlinear, incremental load analysis was performed on the six rectangular beams. The nonlinear analyses matched the experimental load versus lateral displacement and load versus rotation behavior, and the analysis predicted the experimental maximum load within an error of 2%. The nonlinear analysis was extrapolated to several different initial imperfection conditions to parametrically study the effect of initial lateral displacement and initial rotation on the inelastic lateral-torsional buckling load. A simplified expression for lateral-torsional stability of beams with initial imperfections was developed. The data from the parametric study were used to develop reduction parameters for both initial sweep and initial rotation. The rollover stability behavior of the PCI BT-54 was investigated experimentally, and it was found that support end rotations and the elastomeric bearing pads had an adverse effect on the global stability. The nonlinear analysis was employed with the addition of a bearing pad model. It was found that the behavior was sensitive to the bearing pad stiffness properties and the assumption of uniform bearing. From the research, it was apparent that rollover stability was the controlling stability phenomenon for precast prestressed concrete bridge girders, not lateral-torsional buckling.

No description available.

Bibliography: leaves 140-144. / xix, 156 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Determines the effect of partial-interaction and interfacial friction on the fatigue behaviour of composite bridge beams and develops a set of design rules for the assessment of the residual strength and performance of composite bridge beams. / Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 1999

A structure subjected to extreme load due to explosion or human error may lead to progressive collapse. One of the direct methods specified by design guidelines for assessing progressive collapse is the Alternate Load Path method which involves removal of a structural member and analysing the structure to assess its potential of bridging over the removed member without collapse. The use of this method in assessing progressive collapse therefore requires that the vertical load resistance function of the bridging beam assembly, which for a typical laterally restrained reinforced concrete (RC) beams include flexural, compressive arching action and catenary action, be accurately predicted. In this thesis, a comprehensive study on a reliable prediction of the resistance function for the bridging RC beam assemblies is conducted, with a particular focus on a) the arching effect, and b) the catenary effect considering strength degradations. A critical analysis of the effect of axial restraint, flexural reinforcement ratio and span-depth ratio on compressive arching action are evaluated in quantitative terms. A more detailed theoretical model for the prediction of load-displacement behaviour of RC beam assemblies within the compressive arching response regime is presented. The proposed model takes into account the compounding effect of bending and arching from both the deformation and force points of view. Comparisons with experimental results show good agreement. Following the compressive arching action, catenary action can develop at a much larger displacement regime, and this action could help address collapse. A complete resistance function should adequately account for the catenary action as well as the arching effect. To this end, a generic catenary model which takes into consideration the strength degradation due to local failure events (e.g. rupture of bottom rebar or fracture of a steel weld) and the eventual failure limit is proposed. The application of the model in predicting the resistance function in beam assemblies with strength degradations is discussed. The validity of the proposed model is checked against predictions from finite element model and experimental tests. The result indicate that strength degradation can be accurately captured by the model. Finally, the above developed model framework is employed in investigative studies to demonstrate the application of the resistance functions in a dynamic analysis procedure, as well as the significance of the compressive arching effect and the catenary action in the progressive collapse resistance in different designs. The importance of an accurate prediction of the arching effect and the limiting displacement for the catenary action is highlighted.

As vigas mistas configuram uma atrativa solução estrutural para pequenas e grandes obras na engenharia civil. O emprego deste tipo de estruturas proporciona: melhor aproveitamento das características de cada material, maior rapidez na construção e economia. Esta pesquisa da continuidade aos trabalhos de Tamayo (2011) e Dias (2013); apresenta-se um modelo numérico que emprega o método dos elementos finitos para avaliar o comportamento de estruturas do tipo viga mista, com foco na consideração dos efeitos de longa duração do concreto: fluência e retração; e à inclusão da protensão interna do tipo aderente, aplicada sob a laje de concreto. Implementaram-se seis modelos para predição dos fenômenos de longa duração: ACI 209R-92, Bazant-Baweja B3, CEB MC90, CEB MC99, CEB MC10 e GL2000, e disponibilizou-se uma ferramenta estatística que permite sua correta comparação. O cabo de protenssão é modelado de maneira discreta dentro do elemento de concreto e posteriormente são definidas as contribuições que o mesmo faz ao elemento de casca do concreto no qual está inserido. O Software GiD foi empregado nas etapas de pré e pós processamento, customizando sua interface para a atribuição das propriedades do problema. A validação da simulação numérica foi efetuada a partir da modelagem de 14 vigas no total, os espécimenes correspondem a vigas tanto simplesmente apoiadas como contínuas. O programa desenvolvido é capaz de modelar adequadamente estruturas do tipo viga mista, com protensão aderente instalada na laje de concreto; considerando uma análise ao longo do tempo e levando em conta os efeitos da fluência e da retração que afetam o concreto. / The composite beams constitute an attractive structural solution for small and large projects in civil engineering. The use of such structures provides better use of the characteristics of each material, faster construction and economy. This research continues the work of Tamayo (2011) and Dias (2013); it presents a numerical model employing the finite element method to evaluate composite beam structures, focusing on the long-term effects of concrete: creep and shrinkage; and the inclusion of internal adherent prestressing, applied under the concrete slab. Six models were implemented for the prediction of long-term effects: ACI 209R-92, Bazant-Baweja B3, CEB MC90, CEB MC99, CEB MC10 and GL2000, and provided a statistical tool that allows the correct comparison between them. The prestressed cable is modeled discretely within the concrete element and are further defined the contributions that it makes to the concrete shell element in which it is inserted. The GiD Software was used in the stages of pre and post processing, and its interface was customized for assigning the problem properties. The validation of numerical simulation was performed by full modeling 14 beams; the specimens correspond to both simply supported as continuous beams. The developed program is able to adequately model prestressed composite beam structures; considering the long-term effects of creep and shrinkage, that affects the concrete.

Made available in DSpace on 2014-06-11T19:25:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-01-31Bitstream added on 2014-06-13T19:47:23Z : No. of bitstreams: 1 gamino_al_me_ilha.pdf: 1439799 bytes, checksum: f5276e70048212940034e70e154a258f (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Apresenta-se como objeto desta pesquisa o estudo numérico não-linear da ductilidade de vigas de concreto armado convencional e de alto desempenho. Toda a análise numérica é efetuada no código de cálculo baseado no método dos elementos finitos CASTEM 2000, que utiliza o modelo reológico elastoplástico perfeito para o aço, o modelo de Drucker-Prager para o concreto e o método de Newton-Raphson para a solução de sistemas não-lineares. O núcleo deste trabalho concentra-se na obtenção de curvas força - deslocamento e momento - curvatura com a finalidade de quantificar respectivamente os índices de ductilidade global e local das vigas analisadas. De início, confrontam-se as respostas numéricas obtidas com resultados experimentais fornecidos pela literatura a fim de garantir confiabilidade à análise numérica realizada. Posteriormente, efetua-se a determinação da capacidade de deformação inelástica do elemento estrutural em questão, variando-se a resistência à compressão do concreto, a taxa geométrica de armadura longitudinal de tração, a tensão de escoamento das armaduras, o espaçamento entre estribos, a base da seção transversal do elemento estrutural e o efeito escala. Estes parâmetros foram avaliados para dois casos de solicitação: flexão simples tipo I e flexão simples tipo II. O primeiro caso caracteriza-se pela ação de forças simétricas aplicadas à 1/3 e 2/3 do vão e a segunda por uma força centrada no meio do vão. A linha de tendência geral observada foi de uma maior ductilização das vigas sujeitas à flexão simples tipo II, em detrimento às solicitadas por flexão simples tipo I. Quanto ao efeito escala observa-se que a ductilização das vigas é inversamente proporcional à esbeltez das mesmas. / The objective of this thesis is the study of the ductility of high and conventional strength reinforced concrete beams by non-linear numerical simulations. The numerical analysis is based on the finite element method implemented in CASTEM 2000. This program uses the constitutive elastoplastic perfect model for the steel, the Drucker-Prager model for the concrete and the Newton-Raphson for the solution of non-linear systems. This work concentrates on the determination of force - displacement and moment - curvature curves with the purpose of quantifying the global and local ductility indexes of the beams. First, the numeric responses are confronted with experimental results found in the literature in order to check the reliability of the numerical analyses. Later, a parametric study is carried on. The inelastic deformation capacity of the structural element is investigated by varying the concrete compressive strength, the longitudinal reinforcement ratio, the yield stress of the reinforcement, the spacing between stirrups, the member section dimensions and the element size. These parameters have been analyzed for two cases: simple type I and simple type II bending. The first case is characterized by the action of applied symmetrical forces to the 1/3 and 2/3 of the beam size and second for a force centered in the middle of the beam size. The general tendency observed points to a high ductilization of the beams subjected to simple type II bending in comparison to the ones subjected to simple type I bending. With respect to the element size, it is noticed that the ductility of the beams is inversely proportional to their slendernesses.