O presente trabalho é uma contribuição para o esclarecimento e a quantificação das influências na deformabilidade e na capacidade portante de elementos unidimensionais de concreto armado em solicitação plana, decorrentes da não-linearidade física dos materiais concreto e aço, bem como da fissuração e do enrijecimento da armadura tracionada, também na sua fase plástica. Para aplicações práticas determinam-se a rigidez à flexão e a capacidade de rotação plástica dos elementos estruturais, o que permite limitar com mais precisão e coerência a demanda de rotação plástica obtida na análise. De início, descrevem-se os comportamentos não-lineares do concreto e do aço, aplicando-se conceitos da Mecânica da Fratura, bem como a atuação conjunta destes materiais, sob os aspectos de aderência e de fissuração. O núcleo deste trabalho concentra-se na obtenção do diagrama momento-curvatura e dos seus pontos principais, e na subseqüente determinação da capacidade de rotação plástica dos mencionados elementos. Consideram-se as seções geradas a partir da seção duplo T assimétrico, com várias camadas de armadura, sujeitas à flexão composta normal. Com dados deste diagrama e através do modelo da viga equivalente simétrica, posteriormente estendido à viga equivalente assimétrica e às vigas contínuas de pórticos planos, determina-se a capacidade de rotação plástica, considerando-se nesta suas múltiplas influências. Por fim, comparam-se os resultados teóricos e experimentais da capacidade de rotação plástica, e resumem-se as principais conclusões encontradas e os pontos que exigem subseqüente desenvolvimento. / The present study is a contribution to the enlightenment and evaluation of the influences on deformability and load carrying capacity of one-dimensional elements of reinforced concrete subject to in-plane loading, arisen from the constitutive non-linearity of concrete and steel, as well as from the concrete cracking and the tension stiffening of the reinforcement, prior and after yielding. For practical applications, the flexural rigidity and the plastic rotation capacity of structural elements are determined, which makes it possible to limit, more precisely and coherently, the plastic rotation demand coming from the analysis. Firstly, the non-linear behaviors of concrete and steel are described, applying concepts of Fracture Mechanics, and then the joint action of both materials concerning bond and cracking is studied. The core of this study lies on obtaining the bending moment-curvature diagram, specially its main points, and on the subsequent determination of the plastic rotation capacity of the aforementioned elements. The cross-sections generated from an asymmetric double T cross-section are considered, with several layers of reinforcement, acted upon simple or combined bending about one principal axis. With data based on this diagram and through the model of equivalent symmetric beam, later extended to equivalent asymmetric beam and to continuous beams of plane frames, the plastic rotation capacity is determined, considering its multiple influences. Finally, theoretical and experimental results of plastic rotation capacity are compared, and the main conclusions and points in need of subsequent development are summarized.

O presente trabalho é uma contribuição para o esclarecimento e a quantificação das influências na deformabilidade e na capacidade portante de elementos unidimensionais de concreto armado em solicitação plana, decorrentes da não-linearidade física dos materiais concreto e aço, bem como da fissuração e do enrijecimento da armadura tracionada, também na sua fase plástica. Para aplicações práticas determinam-se a rigidez à flexão e a capacidade de rotação plástica dos elementos estruturais, o que permite limitar com mais precisão e coerência a demanda de rotação plástica obtida na análise. De início, descrevem-se os comportamentos não-lineares do concreto e do aço, aplicando-se conceitos da Mecânica da Fratura, bem como a atuação conjunta destes materiais, sob os aspectos de aderência e de fissuração. O núcleo deste trabalho concentra-se na obtenção do diagrama momento-curvatura e dos seus pontos principais, e na subseqüente determinação da capacidade de rotação plástica dos mencionados elementos. Consideram-se as seções geradas a partir da seção duplo T assimétrico, com várias camadas de armadura, sujeitas à flexão composta normal. Com dados deste diagrama e através do modelo da viga equivalente simétrica, posteriormente estendido à viga equivalente assimétrica e às vigas contínuas de pórticos planos, determina-se a capacidade de rotação plástica, considerando-se nesta suas múltiplas influências. Por fim, comparam-se os resultados teóricos e experimentais da capacidade de rotação plástica, e resumem-se as principais conclusões encontradas e os pontos que exigem subseqüente desenvolvimento. / The present study is a contribution to the enlightenment and evaluation of the influences on deformability and load carrying capacity of one-dimensional elements of reinforced concrete subject to in-plane loading, arisen from the constitutive non-linearity of concrete and steel, as well as from the concrete cracking and the tension stiffening of the reinforcement, prior and after yielding. For practical applications, the flexural rigidity and the plastic rotation capacity of structural elements are determined, which makes it possible to limit, more precisely and coherently, the plastic rotation demand coming from the analysis. Firstly, the non-linear behaviors of concrete and steel are described, applying concepts of Fracture Mechanics, and then the joint action of both materials concerning bond and cracking is studied. The core of this study lies on obtaining the bending moment-curvature diagram, specially its main points, and on the subsequent determination of the plastic rotation capacity of the aforementioned elements. The cross-sections generated from an asymmetric double T cross-section are considered, with several layers of reinforcement, acted upon simple or combined bending about one principal axis. With data based on this diagram and through the model of equivalent symmetric beam, later extended to equivalent asymmetric beam and to continuous beams of plane frames, the plastic rotation capacity is determined, considering its multiple influences. Finally, theoretical and experimental results of plastic rotation capacity are compared, and the main conclusions and points in need of subsequent development are summarized.

Severe seismic events in urban regions during the last two decades revealed that the structures constructed before the development of modern seismic codes are the most vulnerable to earthquakes. Sub-standard reinforced concrete buildings constitute an important part of this highly vulnerable urban building stock. There is urgent need for the development and improvement of methods for seismic performance assessment of existing reinforced concrete structures. As an alternative to current conventional force-based assessment methods, a performance evaluation procedure for structural members, mainly reinforced concrete columns is proposed in this study, by using an energy-based approach combined with the low cycle fatigue concept. An energy-based hysteresis model is further introduced for representing the inelastic response of column members under severe seismic excitations. The shape of the hysteresis loops are controlled by the dissipated cumulative energy whereas the ultimate strength is governed by the low cycle fatigue behavior. These two basic characteristics are obtained experimentally from full scale specimens tested under constant and variable amplitude displacement cycles. The first phase of the experimental program presented in the study constitutes of testing sub-standard non-conforming column specimens. The second phase of testing was conducted on standard, code compliant reinforced concrete columns. A total number of 13 specimens were tested. The behavior of these specimens was observed individually and comparatively according to the performance based objectives. The results obtained from the experiments were employed for developing relations between the energy dissipation capacity of specimens, the specimen properties as well as the imposed displacement history. Moreover, the measured rotation capacities at the plastic regions are evaluated comparatively with the limits proposed by modern displacement-based seismic design and assessment provisions.