Análise da influência do tempo de exposição do concreto armado a altas temperaturas nas propriedades mecânicas do aço

Abstract

Reinforced concrete structures are widely used in civil construction due to their high strenght to external stresses. However, it is known that when subjected to high temperatures, they lose part of their mechanical strength. Despite withstanding considerable compressive stresses, concrete does not perform well when subjected to tension, requiring a higher performance of the reinforcement to maintain the stability of the structural element. In fire situations, steel experiences excessive creep and expansion effects and suffers a reduction in its elasticity modulus, compromising its strength. To minimize the occurrence of these phenomena, it is possible to use concrete as a protective barrier for the steel bars. In order to evaluate the behavior of these structures, tests were conducted to determine the influence of the protection given to the steel, by the concrete, in relation to the temperature and the exposure time of these elements. The tests were carried out on reinforced concrete specimens and also on free bars, in order to make a comparative analysis between them. The exposure time varied between 60, 90 and 120 minutes and the temperatures used were 400°C and 600°C. For the first heating value, the tests generated qualitative results indicating an increase in the ultimate strength of the steel bars and a low variation in the modulus of elasticity. On the other hand, the tests performed at 600°C, based on quantitative analysis, showed a reduction of 2.26% to 13.49% in the modulus of elasticity, depending on the test situation.