Análise dos coeficientes de redução de rigidez empregado em lajes lisas protendidas

Abstract

Prestressed concrete structures are stretching more and more its importance nationally due to their many benefits and, among them, there are large spans, low interference with beams and the simplicity in formwork assembly that this technology provides. In tall buildings, it is essential to assess the second order effects due to lateral wind forces and, therefore, the correct assessment of the structural behavior in the Ultimate Limit State increases in preponderance. Performing elastic analyzes are simpler to perform and require a lower computational effort compared to nonlinear analyses, which, despite being more accurate, require a much higher computational effort. Nonlinear analyzes also require a much longer time for the correct elaboration of the numerical model. Therefore, the use of factors that seek to approximate the analyzes in the Ultimate Limit State to the real situation under which they will be submitted in the instant before the failure are advantageous because they reduce the computational cost and facilitate the modeling by requiring only an elastic analysis. Since Brazilian standards do not include stiffness reducing factors for prestressed flat slabs, it is necessary to study for including these factors. Thus, using the finite element analysis program Abaqus (2014), a numerical model was developed where C3D8R three-dimensional elements and various contacts between model elements were applied. Validation was carried out through the results of experimental tests and later, case studies were developed through: load versus displacement curves, stress variation along the prestressing wires and cracking map. Therefore, the results were compared with the aim of proposing a more systematic form of values for stiffness reduction factors in prestressed flat slabs in the Ultimate Limit State.