Dimensionamento em situação de Incêndio de perfis em aço estruturais convencionais e aços resistentes a fogo

Abstract

Steel elements used in construction lose much of their strength and stiffiness with the rise of the temperature. Therefore, in fire situations, in order to the structural elements of a steel building resist to a loading, the use of thermal insulating materials on these elements is needed. However, fire protection can turn steel buildings very costly or evennot viable economically. In the late 80s, in Japan, fire resistant steels were first to be developed. The essential particularity of these steels is to keep, at high temperatures, higher mechanical strength than other conventional steels used so far. With these characteristics, the fire resistant steel allow a reduction in the use of fire protection materials and, in some uses, it is not necessary to employ these materials. Recently, USIMINAS has developed two fire resistant steels, being them called USI FIRE 300 and USI FIRE 350. This work compares, by the analysis of three different steelbuildings, the performance between fire resistant steel USI FIRE 300 and two usual steels, being them USI SAC 250 and USI SAC 300. A fire resistance required time of 30 or 60 minutes was considered in the design as well as the application, isolated orcombined, of two fire protection materials (cementitious fireproofing and intumescent coat). The design was performed in accordance with the Brazilian codes NBR 14323 and NBR 8800. Besides, the mechanical properties of the referred steels used in the design were obtained experimentally, both at room and fire temperature, or specified bycodes or maker. This research aims to determine the economic gain of the use of fire resistant steels by the reduction in the consumption of the fire protection material. For all of the studied situations, fire resistant steel allowed a considerable reduction in the consumption and cost with protection. The cost with fire protection materials fell up to 37% in some situations. It was determined the maximum cost of the fire resistant steelstructure that turned out to be economically viable when compared with a conventional steel structure. Depending on the considered situation, it was concluded that the fire resistant steel could have a cost of 2 to 23% more than the conventional steel.