bachelorThesis
Estudo da contribuição do concreto à tração no aumento da rigidez de vigas em concreto armado: efeito de tension-stiffening
Fecha
2019-12-05Registro en:
FRIGO, Gabriel. Estudo da contribuição do concreto à tração no aumento da rigidez de vigas em concreto armado: efeito de tension-stiffening. 2019. 202 f. Trabalho de Conclusão de Curso (Graduação) – Universidade Tecnológica Federal do Paraná, Guarapuava, 2019.
Autor
Frigo, Gabriel
Resumen
In the case of reinforced concrete elements, in the post-cracking section, the intact concrete between the cracks continues to carrie tensile stresses due to the transfer of bond forces between reinforcing bars and the surrounding concrete, this phenomenon is called “tension-stiffening” (TS). With the search for a more accurate modeling of the behavior of reinforced concrete elements, since the 70s, several models to describe this effect have been proposed, being approached in NBR 6118 (ABNT, 2014), in the design of serviceability state, through the equivalent inertia equation of Branson. A difficult parameter to determinate is the contribution of intact concrete between cracks in increasing the stiffness of reinforced concrete beams, in this sense, for an analysis of this characteristic and of alternative models to the Branson equation, with greater precision for the TS effect, the present work developed a study concerning the contribution of tensile concrete in increasing the stiffness of reinforced concrete beams. Three models were implemented for the consideration of the effect: Collins and Mitchell (1987), Bentz (2005) and Stramandinoli and La Rovere (2008), comparing the results of each model with those obtained without considering the model. It was considered cross sections with bases of 15cm and 25cm, heights of 50cm and 70cm, classes C30 and C70 of concrete strength, diameters of longitudinal reinforcement of 12.5mm and 20mm for different reinforcement arrangements, with a total of 38 beam models calculated. The results showed that the tension-stiffening effect provides a considerable increase in the stiffness of the elements, which emphasizes the range of deformations before the start of the steel yielding level. It was verified that the TS effect is more significant for the cases with the lowest reinforcement rate in relation to the area effectively bonded to the bars. It was also analyzed, in the dimensioning of the flexural reinforcement (without considering the tensile concrete), the difference of results obtained as a function of two distinct equations for the concrete when subjected to compression: the simplified rectangular diagram and the integration of the concrete parabola-rectangle diagram, where the results present a small variation of values, with very small differences in the dimensioning of the steel area of the longitudinal reinforcement.