No description available.

This research focuses on improvements and application of 1D finite elements for nonlinear dynamic analysis of reinforced concrete frames under extreme loadings. The concept of force interpolation is adopted for the element formulation and a solution scheme developed based on a total secant stiffness approach that provides good convergence characteristics. The geometrical nonlinearities including 2nd order P-Delta effects as well as catenary action are considered in the element formulation. It is shown that geometrical nonlinearities may have a significant effect on member (structure) response within extreme loading scenarios. In the analysis of structures subjected to extreme loadings, accurately modelling of the post peak response is vital and, in this respect, the objectivity of the solution with softening must be maintained. The softening of concrete under compression is taken into account, and the objectivity preserved, by adopting a nonlocal damage model for the compressive concrete. The capability of nonlocal flexibility-based formulation for capturing the post-peak response of reinforced concrete beam-columns is demonstrated by numerical examples. The 1D frame element model is extended for the modelling of 3D framed structures using a simplified torque-twist model that is developed to take account of interaction between normal and tangential forces at the section level. This simplified model can capture the variation of element torsional stiffness due to presence of axial force, bending moment and shear and is efficient and is shown to provide a reasonable degree of accuracy for the analysis of 3D reinforced concrete frames. The formulations and solution algorithms developed are tested for static and dynamic analysis of reinforced concrete framed structures with examples on impact analysis of beams, dynamic analysis of frames and progressive collapse assessment of frames taken from the literature. The verification shows that the formulation is very efficient and is capable of modelling of large scale framed structures, under extreme loads, quickly and with accuracy.

This research focuses on improvements and application of 1D finite elements for nonlinear dynamic analysis of reinforced concrete frames under extreme loadings. The concept of force interpolation is adopted for the element formulation and a solution scheme developed based on a total secant stiffness approach that provides good convergence characteristics. The geometrical nonlinearities including 2nd order P-Delta effects as well as catenary action are considered in the element formulation. It is shown that geometrical nonlinearities may have a significant effect on member (structure) response within extreme loading scenarios. In the analysis of structures subjected to extreme loadings, accurately modelling of the post peak response is vital and, in this respect, the objectivity of the solution with softening must be maintained. The softening of concrete under compression is taken into account, and the objectivity preserved, by adopting a nonlocal damage model for the compressive concrete. The capability of nonlocal flexibility-based formulation for capturing the post-peak response of reinforced concrete beam-columns is demonstrated by numerical examples. The 1D frame element model is extended for the modelling of 3D framed structures using a simplified torque-twist model that is developed to take account of interaction between normal and tangential forces at the section level. This simplified model can capture the variation of element torsional stiffness due to presence of axial force, bending moment and shear and is efficient and is shown to provide a reasonable degree of accuracy for the analysis of 3D reinforced concrete frames. The formulations and solution algorithms developed are tested for static and dynamic analysis of reinforced concrete framed structures with examples on impact analysis of beams, dynamic analysis of frames and progressive collapse assessment of frames taken from the literature. The verification shows that the formulation is very efficient and is capable of modelling of large scale framed structures, under extreme loads, quickly and with accuracy.

No description available.

No

No / Accepted for conference.

Recent tragedies involving the collapse of several large and prominent buildings have brought international attention to the subject of progressive collapse, and the field of structural engineering is actively investigating ways to better protect structures from such catastrophic failures. One focus of these investigations is the behavior and performance of shear tab connections in steel structures during progressive collapse events. The shear tab, a simple connection, is typically modeled as a perfect pin in standard design, but in progressive collapse analysis, a much more accurate model of its true behavior and limits is required. This report documents the development of a simple yet accurate shear tab model and its use in understanding the behavior and limits of shear tab connections in column removal scenarios. Particular attention is paid to the connections’ axial force limit state, an aspect of behavior that is typically unimportant in standard design. / text

No description available.

No description available.

O evento do colapso progressivo começou a ser estudado, principalmente, após o acidente do edifício Ronan Point, em 1968, na cidade de Londres. Esse acidente fez o meio técnico rever as considerações normativas, sobretudo de maneira a adicionar recomendações que visem minimizar os danos causados à estrutura quando sujeita a um dano acidental.Entretanto, tais recomendações não realizam a análise do risco da estrutura colapsar. Essas também não conseguem analisar medidas de robustez e vulnerabilidade, e nem determinar qual é o elemento chave para a estrutura. Desse modo, partindo desses questionamentos, o presente trabalho desenvolveu uma nova metodologia nomeada aqui de Risk Analysis of the Progressive Collapse (RAPC). Este procedimento fornece uma medida mais precisa dos riscos, através de uma abordagem que utiliza a Teoria da Confiabilidade Estrutural. Assim, é deduzida uma expressão para a determinação da probabilidade de colapso progressivo, bem como são definidos os coeficientes de importância e vulnerabilidade para identificar o(s) elemento(s) chave. O elemento chave é definido como o que apresenta a maior interseção entre vulnerabilidade e importância para o colapso estrutural. Essas formulações desenvolvidas na metodologia do RAPC são implementadas em Fortran. Para isso, a modelagem do edifício de alvenaria estrutural é feita utilizando o software DIANA®, no qual os esforços solicitantes são obtidos e utilizados como dados de entrada na análise de confiabilidade. Valores de probabilidades de falha individual por elemento, condicional e condicional dupla são calculados pelo First Order Reliability Method (FORM) e Importance Sampling Monte Carlo (ISMC) com auxílio do programa StRAnD. Um algoritmo em Fortran é implementado para acoplamento do DIANA® e StRAnD, além de mapear a probabilidade de falha dos elementos estruturais. Portanto, torna-se evidente que a identificação dos elementos mais vulneráveis, e do elemento chave em particular, é útil para abordagens diretas de concepção estrutural, tais como a melhoria da resistência local. Contudo, os coeficientes propostos também medem os efeitos dos procedimentos de projeto que conduzem à continuidade, ductilidade e redundância. Quando essas medidas trabalham para reduzir as probabilidades de propagação de dano ou colapso, isso se reflete nas vulnerabilidades de elementos eventualmente iniciando esses caminhos de falha. Sendo assim, conclui-se que a formulação do RAPC se mostra como uma ferramenta na determinação do risco do colapso progressivo nas estruturas. / The progressive collapse event began to be studied, mainly, after the accident of the Ronan Point building, at 1968, in the city of London. This accident caused the engineers review their normative considerations, mainly in order to add recommendations aimed at minimizing the damage to structure when subjected to abnormal loading. However, such recommendations do not perform the risk analysis of the structure to collapse. These also fail to analyze measures of robustness and vulnerability, and either determine which is the key element of the structure. Thus, leaving of these questions, the present work to develop a new methodology named here of Risk Analysis of the Progressive Collapse (RAPC). This procedure provides a more accurate measure of risks through an approach that uses Structural Reliability Theory. Thus, an expression is deduced for the determination of the probability of progressive collapse, as well as the importance and vulnerability coefficients are defined to identify the key element (or key elements). The key element is identified as the one presenting the largest intersection between vulnerability and importance to collapse.These formulations developed in the RAPC methodology are implemented in Fortran.For this, the structural masonry building modeling is done using the DIANA® software, in which the requesting efforts are obtained and used as input data in the reliability analysis. Probabilities values individual, conditional, and double conditional are calculated by the First Order Reliability Method (FORM) and Importance Sampling Monte Carlo (ISMC) using the StRAnD software. A Fortran algorithm is implemented for DIANA® and StRAnD coupling, besides mapping the probability of failure of the structural elements. Therefore, it is clear that identification of the most vulnerable elements, and of the key element in particular, is useful for direct design approaches to structural design, such as local resistance enhancements. However, the coefficients proposed herein also measure the effects of design procedures leading to continuity, ductility or redundancy. When these measures work to reduce probabilities of damage propagation or collapse, this is reflected in the vulnerabilities of elements eventually initiating these failure paths. Therefore, it is concluded that the formulation of RAPC is shown as an tool in determining the risk of progressive collapse in structures.