Análise e dimensionamento de lajes lisas protendidas pelo método dos pórticos equivalentesanálise e dimensionamento de lajes lisas protendidas pelo método dos pórticos equivalentes

Abstract

In view of the numerous advantages provided by the addition of prestressing in concrete structures, this work aims to expand the connections obtained in the disciplines of reinforced concrete from the study of the theoretical aspects necessary for the understanding of prestressed reinforced concrete structures, including definitions, classifications, prestress losses and other peculiarities inherent to this material.In this case, we chose to analyze and design a prestressed flat slab. This model offers not only economic advantages but also aesthetic and technical advantages, such as greater flexibility in defining spaces and designing the facade due to the elimination of beams and the possibility of spans of up to 12 meters without compromising the strength and stability of the structure. The structural analysis of the slab is performed using the equivalent frame method (which considers the slab divided into strips in each direction, where each strip corresponds to a frame, said to be equivalent to that region), considering the effects of prestressing through an equivalent external load. Some construction and design recommendations for this type of slab are also presented, so that a calculation and sizing guide can be defined based on the criteria established by ABNT NBR 6118 (2014).With this accomplished, a simplified design of a prestressed flat slab with ungreased tendons for a hypothetical commercial building is developed, applying all the steps and analyses outlined throughout the theoretical framework. Finally, the deflection and moment results obtained by the adopted method are compared with those of the SAFE program. It is found that, due to the approximations inherent in the first method, the results obtained in SAFE generally present lower values (justified by the fact that it uses a more refined method, such as finite element), and the main percentage differences between the two methods occur in the efforts due to prestressing loading.