Este trabalho apresenta uma análise comparativa de diferentes sistemas estruturais para um edifício de 20 pavimentos. Cada um dos modelos foi dimensionado através dos princípios do método da análise direta, presente na ABNT NBR 8800:2008. O método da amplificação dos esforços solicitantes (MAES) foi usado para se obter de forma simplificada os esforços atuantes nos elementos do edifício considerando os efeitos locais e globais de segunda ordem. A incidência do vento foi simulada de duas formas diferentes. Na primeira, chamada de uniforme, o vento foi aplicado sem excentricidade, gerando apenas o efeito de tombamento nas estruturas. Na segunda hipótese, considerou-se uma excentricidade devida aos efeitos de vizinhança, prescrita pela ABNT NBR 6123:1988, responsável por ocasionar o tombamento e a torção dos edifícios. Todas as análises numéricas foram repetidas fazendo o uso de outro método simplificado de segunda ordem, conhecido como P-Delta. Por meio dos resultados obtidos, constatou-se que a possibilidade de se reduzir a sobrecarga para o dimensionamento de pilares proporciona uma economia de material, mas, por outro lado, tem como consequência o aumento do tempo de análise, pois exige a utilização de diferentes combinações de cálculo para o dimensionamento de vigas e pilares. A estratégia utilizada para simular os efeitos de vizinhança mostrou-se satisfatória, pois permitiu introduzir de maneira fácil e prática a torção ocasionada pela incidência excêntrica do vento. Observou-se também que esses efeitos ocasionaram o aumento dos momentos fletores e dos deslocamentos das estruturas analisadas. Em relação à avaliação dos efeitos de segunda ordem, comprovou-se que, para a classificação da deslocabilidade, a combinação de cálculo crítica é aquela que possui o maior carregamento gravitacional. Entretanto, para o dimensionamento dos elementos, foi constatado que outras hipóteses de cálculo, principalmente aquelas em que o vento é a ação variável principal, podem ser determinantes. Por fim, foi observado que os resultados obtidos pelo método P-Delta ficaram bastante semelhantes àqueles calculados pelo MAES, com desvios desprezíveis. O MAES, por sua vez, mostrou-se bastante trabalhoso, pois exige a modelagem de diferentes tipos de estruturas para a determinação dos esforços. / This work presents a comparative analysis of different structural systems for a 20-storey building. Each model has been designed using the principles of the direct analysis method (DAM), present in the ABNT NBR 8800:2008. The first-order amplification method (FOAM) was used to obtain, in a simplified manner, the forces acting on the building elements, including local and global second-order effects. The incidence of the wind was simulated in two different ways. In the first case, named uniform, the wind was applied without eccentricity, generating only structure overturning. In the second case, it was considered an eccentricity due to vicinity effects, prescribed by the ABNT NBR 6123:1988, responsible for causing twisting and building overturning. All numerical analysis were carried out a simplified second-order method known as P-Delta. From the results obtained it was found that the reduction of live loads in the design of columns provides material economy, but on the other hand, increases analysis time, since it requires different combinations for beams and columns. The strategy used to simulate the vicinity effects was satisfactory, because it allowed, in an easy and practical way, the consideration of the torsion produced by the wind eccentric impact. It was also observed that these effects increased the bending moments and the displacements of the structures. About the second-order effects, it was shown that, for sway or non-sway classification, the critical combination is one with greatest gravitational loading. However, for the design of the elements, it was observed that other loading conditions can be critical, especially those in which the wind is the main live load. Finally, the results obtained by the P-Delta method were very similar to those calculated by the first-order amplification method. The FOAM was, in turn, very laborious, because it requires the modeling of different types of structures for the determination of the forces.

Atualmente, dentre os perfis de aço formados a frio (PFF) mais utilizados em sistemas estruturais correntes, merecem destaque aqueles compostos por duas cantoneiras ligadas entre si por meio de presilhas, apresentando seção na forma de \"T\". Embora tenha utilização bastante difundida, pouco se sabe sobre o comportamento estrutural deste tipo de perfil, principalmente em relação aos modos de instabilidade a ele associados. No presente trabalho, são desenvolvidos, com base em ferramentas disponibilizadas no código computacional ANSYS, modelos numéricos em elementos finitos com a finalidade de se investigar o comportamento estrutural dos referidos perfis submetidos à compressão e, com isso, contribuir para futuras revisões nas especificações da ABNT NBR 14762:2010 referentes aos PFF compostos. Por meio de análises não-lineares, foi investigada a influência de diversos fatores na resposta estrutural dos perfis, como: a forma de introdução do carregamento (compressão centrada ou excêntrica), as condições de vinculação, a esbeltez global, as imperfeições geométricas iniciais, a espessura das cantoneiras e o número de presilhas. Os resultados numéricos indicam que os valores de força normal de compressão resistente, obtidos conforme a ABNT NBR 14762:2010, podem resultar bastantes conservadores, principalmente nos casos de menor esbeltez global. Adicionalmente, a quantidade e a distribuição das presilhas se mostram bastante influentes, tanto na capacidade resistente como nos modos de instabilidade predominantes dos perfis. Por fim, o trabalho prevê uma investigação introdutória sobre os perfis dupla cantoneira sob temperaturas elevadas, a fim de se verificar, em caráter exploratório, o seu desempenho em situação de incêndio. As análises termoestruturais realizadas apresentaram como resultado tempos de resistência ao fogo bem abaixo do valor mínimo especificado pela ABNT NBR 14432:2001, apontando à necessidade do uso de revestimento térmico nesses perfis e de estudos mais aprofundados sobre o assunto. / Nowadays, among cold-formed steel members (PFF) commonly used in current structural systems, deserve to be highlighted those composed by two angles connected through intermediate fastener (stitch-fillers) forming a \"T\" section. Although its widespread use, little is known about its structural behavior, especially in what concerns instability modes. In this study, based on tools available on the ANSYS code, numerical finite element models were developed in order to investigate the structural behavior of these profiles under compression to contribute to future revisions of the ABNT NBR 14762:2010 specifications regarding PFF compounds. By using non-linear analysis, we investigated the influence of various factors in the structural response, namely, the loading introduction (compression-centric or eccentric), the boundary conditions, the global slenderness, the geometric imperfections, the angle thickness and the number stitch-fillers. The numerical results indicated that the compression resistance, obtained according to ABNT NBR 14762:2010, it is quite conservative, especially in cases of small global slenderness. Additionally, the stitch-fillers distribution proved its great influence both in the bearing capacity as in the determination of the instability modes. Finally, the study makes an introductory research on double angle profiles under high temperatures, in order to verify its performance under fire. The thermal analysis showed fire resistance results inferior to the minimum specified by ABNT NBR 14432:2001, indicating the need of using fire protection and further studies this subject.

Aparentemente, a análise estrutural de uma cantoneira simples submetida à compressão constitui um problema elementar e, portanto, já largamente conhecido. Entretanto, as cantoneiras formadas a frio, em geral com paredes delgadas (elevadas relações largura/espessura), apresentam dois modos críticos de instabilidade: (i) modo global de flexão, no caso de barras longas, e um modo coincidente local-chapa/global de flexo-torção, que é crítico para barras de menor comprimento. Embora existam procedimentos simplificados de cálculo, recomendados pelas normas, a consideração do modo de flexo-torção é controversa entre pesquisadores. Alguns trabalhos recentes indicam que é conservador considerar o modo de flexo-torção no cálculo da força normal resistente, enquanto outros trabalhos apontam para a necessidade dessa abordagem. Nesse trabalho é investigada a resposta estrutural de cantoneiras simples e enrijecida submetidas à compressão centrada e excêntrica, por meio de análise experimental e de análise numérica não-linear via elementos finitos, sendo avaliado o efeito das imperfeições geométricas iniciais na força normal resistente; também são avaliados os resultados provenientes dos procedimentos normativos: (i) o clássico método das larguras efetivas e (ii) o método da resistência direta (MRD), em que as cantoneiras não são relacionadas como perfis pré-qualificados. Os resultados da análise experimental e da análise numérica não-linear com imperfeições geométricas iniciais indicam a necessidade da consideração do modo de flexo-torção. / Apparently, the structural analysis of a simple angle under compression is an elementary problem, therefore, already largely known. However, cold-formed steel angles, mostly with slender legs, present two critical buckling modes: (i) global-flexural mode, in cases of high length members, (ii) and a coincident local-plate/global-torsional-flexural mode, which is critical for short length members. Although simplified design procedures exist, recommended by specifications, the consideration of the torsional-flexural mode is controversial among researchers. A few recent papers indicate that considering the torsional-flexural mode is conservative, while other papers point to the necessity of this approach. This work investigates the structural response of simple and lipped angles under concentrically and eccentrically compression, by means of tests and nonlinear finite element analysis, being evaluated the effect of initial geometric imperfections; also evaluating the results from design procedures: (i) the classic effective width method and (ii) the direct strength method (DSM), where the angles are not pre-qualified shapes. The results of the experimental and nonlinear numerical analysis with initial imperfections indicate the necessity of considering the torsional-flexural mode.

Im Mittelpunkt unserer Untersuchungen steht das mehrkriterielle Optimierungsproblem, in einer beliebigen nichtleeren Menge eines halbgeordneten endlich dimensionalen Raumes. Zu dessen Lösung betrachten wir ein Dialogverfahren, in dem der Entscheidungsträger in jedem Schritt seine Wünsche äußert. Bei der Bestimmung einer Lösung, die den Entscheidungsträger zufriedenstellt, müssen wir ein im Allgemeinen nichtkonvexes und nicht triviales skalares Optimierungsproblem lösen. Zur Lösung dieses Problems haben wir zwei Klassen einparametrischer Optimierungsprobleme (Einbettungen) konstruiert. Mit Hilfe der Projektion auf den konvexen Ordungskegel haben wir gezeigt, dass diese Einbettungen wohldefiniert sind. Im Gegensatz zu der in der Literatur untersuchten Standardeinbettung, sind die in dieser Arbeit betrachteten Einbettungen durch die Skalarisierungen der Vektoroptimierungsprobleme mittels streng monotoner skalarisierender Funktionen motiviert. Diese Untersuchung wird unter dem Gesichtspunkt der Theorie der einparametrischen Optimierungsprobleme für den Fall eines beliebigen spitzen polyedrischen Ordnungskegels durchgeführt. Sie umfasst z.B. Fragestellungen nach der Art der Singularitäten, die für die verschiedenen Einbettungen auftreten können, nach den Bedingungen, unter denen eine Zusammenhangskomponente in der Menge stationärer oder verallgemeinerter kritischer Punkte mit Hilfe von Kurvenverfolgungsmethoden numerisch beschrieben werden kann und nach den hinreichenden Bedingungen für die Existenz einer Lösungskurve. Anschließend haben wir das von Guddat und Jongen eingeführte Konzept der strukturellen Stabilität eines skalaren Optimierungsproblems in der Vektoroptimierung verallgemeinert und einen Zusammenhang zur strukturellen Stabilität eines Minimaxproblems erstellt. Dieses Minimaxproblem steht in starker Beziehung zur Skalarisierungsmethode der Vektoroptimierungsprobleme. / In this work we consider the multiobjective optimization in a subset of a partially orded finite dimensional space. In order to solve this problem we use a dialogue procedure in which the decision maker has to determine in each step the aspiration and reservation level expressing his wishes (goals). This leads to an optimization problem which is not easy to solve in the nonconvex case. We solve it proposing two classes of one-parametric optimization problems (embeddings). Using the projection in the ordering cone, we show that these embeddings are well defined, i.e. the corresponding constraint sets depending on real-valued parameters are not empty. Contrary to the very known standard embedding the proposed embeddings are motivated by the use of strongly monotonically increasing functions, which play an important role by the scalarization of multiobjective optimization problems. The two classes of embeddings are investigated from the point of view of parametric optimization considering a pointed polyhedral cone. This investigation includes the determination of the kind of singularities which can appear, the conditions under which a connected component in the set of stationary or generalized critical point can be numerically described using pathfollowing methods and a solution curve may exist. Finally, we extend the concept of structural stability by Guddat and Jongen to the multiobjective optimization problems and establish a connection to the problem of Minimax type, which is related to the scalarization of multiobjective optimization problems.

Les simulations numériques ont négligé jusqu’ici l’influence du support de silice amorphe sur la structure des nanoparticules métalliques déposées car l’interaction métal-silice amorphe est faible. Toutefois les études expérimentales montrent un effet de troncature sur la structure des nanoparticules. L’idée de ce travail a donc été d’étudier l’influence de ce support sur la structure et la morphologie des nanoparticules d’argent au moyen de la modélisation moléculaire (Monte Carlo et dynamique moléculaire). L’objectif de ce travail a été tout d'abord de déterminer le potentiel interatomique permettant de décrire l’interaction argent-silice. Ce potentiel a été obtenu sur la base des données expérimentales d'angles de mouillages en phase liquide et en phase solide. D’autre part, l'intensité d'interaction argent-silice a été déterminée par calculs DFT sur la cristobalite qui est un polymorphe de la silice cristalline présentant la même densité que la silice amorphe. Les énergies d'adhésions obtenues ont ainsi permis d'ajuster les paramètres du potentiel argent-silice de type Lennard-Jones. L’étude de la stabilité structurale des nanoparticules d'argent supportées à température nulle a été effectuée pour trois degrés d'approximation du support. (1) : un support parfaitement lisse décrit par un puits carré dont la profondeur est reliée à l’énergie d’adhésion, (2) : un support atomique de silice amorphe de surface plane et (3) : un support atomique de silice amorphe présentant une rugosité de surface. L’influence de la température sur la structure a été étudiée par fusion et recristallisation des nanoparticules d’argent sur les deux supports de silice amorphe. Afin d’étudier la stabilité structurale des nanoparticules en température, le calcul d’énergie libre des nanoparticules a été abordé. / Numerical simulations have so far neglected the influence of amorphous silica substrate on the structure of metallic nanoparticles due to its relatively weak interaction with deposited nanoparticles. However, experimental studies have often shown a truncation effect on the structure of nanoparticles. The idea of this work was to study the influence of this substrate on the structure of silver nanoparticles using molecular modeling (Monte Carlo and molecular dynamics). The objective of this work was firstly to determine silver-silica interatomic potential. This was achieved using experimental data of wetting angles in solid and liquid phase. On the other hand, silver-silica interaction intensity was determined by DFT calculations on cristobalite which is a polymorph of crystalline silica having the same density as amorphous silica. The adhesions energies obtained were used to fit the Lennard-Jones parameters for the silver-silica interaction. The study of the structural stability of silver nanoparticles supported at zero temperature was performed for three levels of approximation of the support. (1): the smooth wall approximation where the support is described by a square-well whose depth is related to the adhesion energy of the nanoparticle, (2): an atomistic model of flat amorphous silica, (3): an atomistic model of rough amorphous silica. The influence of the temperature on the structure was investigated by melting and recrystallization of the silver nanoparticles deposited on the two silica supports. In order to study the temperature stability of the nanoparticles the free energy calculation of the nanoparticles was discussed.

The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nas últimas décadas, ocorreram alguns acidentes em estruturas de concreto armado, como o desabamento do Edifício Areia Branca, na Região Metropolitana do Recife, o desmoronamento parcial do Edifício Palace II, na cidade do Rio de Janeiro e o colapso do Edifício Real Class, em construção, em Belém do Pará. Mais recentemente os casos do Edifício Liberdade no Rio de Janeiro e Senador em São Bernardo, SP. Sabe-se que, com as condições usuais de projeto ocorrendo ruptura em um dos pilares de uma estrutura de concreto armado haverá a possibilidade do chamado "efeito dominó", ou seja, poderá ocorrer o colapso progressivo envolvendo todos os pavimentos. Este fato, na maioria dos casos, impossibilita a recuperação da edificação, causando prejuízos financeiros e, principalmente, risco de morte a trabalhadores ou moradores que se encontrem no local. É cada vez mais comum a construção de prédios altos e esbeltos com pequeno número de pilares. Estas características, no caso de haver ruptura brusca em um dos apoios, podem agravar a situação significativamente. Plataformas marinhas offshore de petróleo são projetadas de tal forma que havendo a ruptura de um dos elementos de apoios como estacas ou amarras os n-1 elementos remanescentes asseguram a estabilidade do conjunto, evitando o colapso da estrutura. Baseado neste conceito o presente estudo visa encontrar condições de projeto de edifícios em que a estabilidade seja assegurada em caso de perda de um dos pilares, aumentando assim a robustez, permitindo que a estrutura sobreviva a situações imprevisíveis ou não usuais. O trabalho apresenta uma aplicação ao caso de um edifício com estrutura de concreto armado, projetado de acordo com a NBR 6118:2007. É feita a análise de verificação da viabilidade técnica e financeira da solução adotada / In recent decades, some accidents occurred in reinforced concrete structures, such as the collapse of the Areia Branca Building in the Metropolitan Region of Recife, the partial collapse of the Palace II Building in the city of Rio de Janeiro and the collapse of the Real Class Building, during construction in Belém, Pará. Most recently, the Liberdade Building in Rio de Janeiro and Senador Building in São Bernardo, SP. Knows that at case of collapse of one of the columns of a reinforced concrete structure similar to "domino effect", that is will be a progressive collapse involving all floors. This fact, in most cases, precludes recovery of the building, causing financial losses and, especially, risk of death to workers or residents who are, by chance, on the site. It is increasingly common to construct tall buildings and slender with small number of columns. These characteristics, if there is a sharp break in the backups, can aggravate the situation significantly. Offshore oil platforms, are designed so that there at case of a collapse of any support, the structure do not collapse. Based on this concept, the present study aims to find conditions of design in which stability is ensured, with the loss of one of the columns, thus increasing robustness, permits the structure to survive to the unexpected or unusual situations. This work presents the application to the case of a reinforced concrete building, designed according to NBR 6118:2007. The work makes possible the verification of technical and financial feasibility of the solution

Response of flexible structures — such as cable-supported bridges and aircraft wings — is associated with a number of uncertainties in structural and flow parameters. This thesis is aimed at efficient uncertainty quantification in a few such flow and flow-induced structural response problems. First, the uncertainty quantification in the lift force exerted on a submerged body in a potential flow is considered. To this end, a new method — termed here as semi-intrusive stochastic perturbation (SISP) — is proposed. A sensitivity analysis is also performed, where for the global sensitivity analysis (GSA) the Sobol’ indices are used. The polynomial chaos expansion (PCE) is used for estimating these indices. Next, two stability problems —divergence and flutter — in the aeroelasticity are studied in the context of reliability based design optimization (RBDO). Two modifications are proposed to an existing PCE-based metamodel to reduce the computational cost, where the chaos coefficients are estimated using Gauss quadrature to gain computational speed and GSA is used to create nonuniform grid to reduce the cost even further. The proposed method is applied on a rectangular unswept cantilever wing model. Next, reliability computation in limit cycle oscillations (LCOs) is considered. While the metamodel performs poorly in this case due to bimodality in the distribution, a new simulation-based scheme proposed to this end. Accordingly, first a reduced-order model (ROM) is used to identify the critical region in the random parameter space. Then the full-scale expensive model is run only over a this critical region. This is applied to the rectangular unswept cantilever wing with cubic and fifth order stiffness terms in its equation of motion. Next, the wind speed is modeled as a spatio-temporal process, and accordingly new representations of spatio-temporal random processes are proposed based on tensor decompositions of the covariance kernel. These are applied to three problems: a heat equation, a vibration, and a readily available covariance model for wind speed. Finally, to assimilate available field measurement data on wind speed and to predict based on this assimilation, a new framework based on the tensor decompositions is proposed. The framework is successfully applied to a set of measured data on wind speed in Ireland, where the prediction based on simulation is found to be consistent with the observed data.

Atualmente, dentre os perfis de aço formados a frio (PFF) mais utilizados em sistemas estruturais correntes, merecem destaque aqueles compostos por duas cantoneiras ligadas entre si por meio de presilhas, apresentando seção na forma de \"T\". Embora tenha utilização bastante difundida, pouco se sabe sobre o comportamento estrutural deste tipo de perfil, principalmente em relação aos modos de instabilidade a ele associados. No presente trabalho, são desenvolvidos, com base em ferramentas disponibilizadas no código computacional ANSYS, modelos numéricos em elementos finitos com a finalidade de se investigar o comportamento estrutural dos referidos perfis submetidos à compressão e, com isso, contribuir para futuras revisões nas especificações da ABNT NBR 14762:2010 referentes aos PFF compostos. Por meio de análises não-lineares, foi investigada a influência de diversos fatores na resposta estrutural dos perfis, como: a forma de introdução do carregamento (compressão centrada ou excêntrica), as condições de vinculação, a esbeltez global, as imperfeições geométricas iniciais, a espessura das cantoneiras e o número de presilhas. Os resultados numéricos indicam que os valores de força normal de compressão resistente, obtidos conforme a ABNT NBR 14762:2010, podem resultar bastantes conservadores, principalmente nos casos de menor esbeltez global. Adicionalmente, a quantidade e a distribuição das presilhas se mostram bastante influentes, tanto na capacidade resistente como nos modos de instabilidade predominantes dos perfis. Por fim, o trabalho prevê uma investigação introdutória sobre os perfis dupla cantoneira sob temperaturas elevadas, a fim de se verificar, em caráter exploratório, o seu desempenho em situação de incêndio. As análises termoestruturais realizadas apresentaram como resultado tempos de resistência ao fogo bem abaixo do valor mínimo especificado pela ABNT NBR 14432:2001, apontando à necessidade do uso de revestimento térmico nesses perfis e de estudos mais aprofundados sobre o assunto. / Nowadays, among cold-formed steel members (PFF) commonly used in current structural systems, deserve to be highlighted those composed by two angles connected through intermediate fastener (stitch-fillers) forming a \"T\" section. Although its widespread use, little is known about its structural behavior, especially in what concerns instability modes. In this study, based on tools available on the ANSYS code, numerical finite element models were developed in order to investigate the structural behavior of these profiles under compression to contribute to future revisions of the ABNT NBR 14762:2010 specifications regarding PFF compounds. By using non-linear analysis, we investigated the influence of various factors in the structural response, namely, the loading introduction (compression-centric or eccentric), the boundary conditions, the global slenderness, the geometric imperfections, the angle thickness and the number stitch-fillers. The numerical results indicated that the compression resistance, obtained according to ABNT NBR 14762:2010, it is quite conservative, especially in cases of small global slenderness. Additionally, the stitch-fillers distribution proved its great influence both in the bearing capacity as in the determination of the instability modes. Finally, the study makes an introductory research on double angle profiles under high temperatures, in order to verify its performance under fire. The thermal analysis showed fire resistance results inferior to the minimum specified by ABNT NBR 14432:2001, indicating the need of using fire protection and further studies this subject.

Aparentemente, a análise estrutural de uma cantoneira simples submetida à compressão constitui um problema elementar e, portanto, já largamente conhecido. Entretanto, as cantoneiras formadas a frio, em geral com paredes delgadas (elevadas relações largura/espessura), apresentam dois modos críticos de instabilidade: (i) modo global de flexão, no caso de barras longas, e um modo coincidente local-chapa/global de flexo-torção, que é crítico para barras de menor comprimento. Embora existam procedimentos simplificados de cálculo, recomendados pelas normas, a consideração do modo de flexo-torção é controversa entre pesquisadores. Alguns trabalhos recentes indicam que é conservador considerar o modo de flexo-torção no cálculo da força normal resistente, enquanto outros trabalhos apontam para a necessidade dessa abordagem. Nesse trabalho é investigada a resposta estrutural de cantoneiras simples e enrijecida submetidas à compressão centrada e excêntrica, por meio de análise experimental e de análise numérica não-linear via elementos finitos, sendo avaliado o efeito das imperfeições geométricas iniciais na força normal resistente; também são avaliados os resultados provenientes dos procedimentos normativos: (i) o clássico método das larguras efetivas e (ii) o método da resistência direta (MRD), em que as cantoneiras não são relacionadas como perfis pré-qualificados. Os resultados da análise experimental e da análise numérica não-linear com imperfeições geométricas iniciais indicam a necessidade da consideração do modo de flexo-torção. / Apparently, the structural analysis of a simple angle under compression is an elementary problem, therefore, already largely known. However, cold-formed steel angles, mostly with slender legs, present two critical buckling modes: (i) global-flexural mode, in cases of high length members, (ii) and a coincident local-plate/global-torsional-flexural mode, which is critical for short length members. Although simplified design procedures exist, recommended by specifications, the consideration of the torsional-flexural mode is controversial among researchers. A few recent papers indicate that considering the torsional-flexural mode is conservative, while other papers point to the necessity of this approach. This work investigates the structural response of simple and lipped angles under concentrically and eccentrically compression, by means of tests and nonlinear finite element analysis, being evaluated the effect of initial geometric imperfections; also evaluating the results from design procedures: (i) the classic effective width method and (ii) the direct strength method (DSM), where the angles are not pre-qualified shapes. The results of the experimental and nonlinear numerical analysis with initial imperfections indicate the necessity of considering the torsional-flexural mode.