MARIN, M. C. Contribution in the analysis of global stability of multi-storey precast concrete framed structures. 2009. 213f. Dissertation (M

This study deals with the reduction of the stiffness in precast concrete structural elements of multi-storey buildings to analyze global stability. Having reviewed the technical literature, this paper present indications of stiffness reduction in different codes, standards, and recommendations and compare these to the values found in the present study. The structural model analyzed in this study was constructed with finite elements using ANSYS® software. Physical Non-Linearity (PNL) was considered in relation to the diagrams M x N x 1/r, and Geometric Non-Linearity (GNL) was calculated following the Newton-Raphson method. Using a typical precast concrete structure with multiple floors and a semi-rigid beam-to-column connection, expressions for a stiffness reduction coefficient are presented. The main conclusions of the study are as follows: the reduction coefficients obtained from the diagram M x N x 1/r differ from standards that use a simplified consideration of PNL; the stiffness reduction coefficient for columns in the arrangements analyzed were approximately 0.5 to 0.6; and the variation of values found for stiffness reduction coefficient in concrete beams, which were subjected to the effects of creep with linear coefficients from 0 to 3, ranged from 0.45 to 0.2 for positive bending moments and 0.3 to 0.2 for negative bending moments.

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Resumocrescente utilização do concreto pré-moldado para solução estrutural em diversas obras, como edificações industriais e comerciais, tornouse uma alternativa vantajosa e acessível, principalmente no quesito tempo de construção. Porém, quando em situação de incêndio, determinadas características que esse sistema construtivo usualmente oferece como vantagens podem tornar-se uma desvantagem. Contando com espaços amplos, com grandes vãos livres, materiais combustíveis armazenados e ventilação apropriada, torna-se um cenário ideal para a propagação de um incêndio e consequente perda da capacidade de suporte da estrutura. Neste trabalho são apresentadas as implicações de um projeto que utiliza o concreto pré-moldado em situação de incêndio, além de levantar pontos para discussões sobre possibilidades que amenizem os riscos, tendo como base referências bibliográficas nacionais e internacionais, de uso corrente no meio técnico e acadêmico. Palavras-chaves:Incêndio. Fogo. Concreto pré-moldado. Concreto pré-fabricado. AbstractThe increasing use of precast concrete as a structural solution for different types of buildings, such as industrial and commercial buildings, has become a good, accessible choice, especially regarding construction time. However, in a fire situation, certain characteristics of this construction system that are normally considered as advantages could become disadvantages. With large spaces, large open spans, good ventilation and the storage of flammable materials, these buildings provide the ideal setting for fire spreading and the consequent loss of structure carrying capacity. In this study, we present the implications of a project that uses precast concrete in a fire situation, and we raise points for discussion on alternatives to mitigate risks, based on national and international bibliographic references currently used by the technical and academic community.