Sectional model for the fire evaluation of reinforced concrete columns subjected to biaxial bending

Influence of exposure temperature variability on concrete degradation as a function of compressive strength and ultrasonic wave propagation velocity

“…Due to the thermal treatment time adopted, during each firing stage it was possible to observe temperature variability inside the oven, and, consequently, in the concrete specimens, as occurs with the structural elements of buildings in fire situations, where, due to greater exposure to heat, some elements, or part of them, are more degraded [16], [17], [19], [20]. At each stage of exposure to fire, temperature readings were taken in at least six specimens, resulting in the mean temperatures and standard deviations shown as follows: for the target temperature of 200 °C the average temperature was 188 °C and the standard deviation was 58 °C; for the target temperature of 450 °C they were 401 °C and 52 °C, respectively; for the target temperature of 800 °C they were 778 °C and 156°C, respectively.…”

“…This thermal gradient mentioned above causes these transformations in the material to vary according to the depth of the surface exposed to fire [1], [9], [10], as shown in the curves by Ongah et al [16]. As concrete is not a good thermal conductor, the heat propagation process inside it is slow [1], [9], [10], [17], [18].…”

“…Studies involving concrete in fire situations are carried out considering external thermal actions with heat flow by convection or radiation from the hot gases of the burning environment [1], [3], [17], [18]. Fire curves are standardized for use in fire resistance studies with building materials and serve as a parameter in structural designs.…”

“…The most widely adopted curve in Brazil for simulating concrete fire scenarios is ISO 834 [1], [3], [19]. For design purposes, it is common practice to admit that the temperature of the burning environment reaches its maximum value and that there is a uniform temperature distribution in the room [3], [17]. However, in a real fire, there is the variability of exposure to fire in structural elements [17], [20], [21], due to the greater or lesser amount of heat absorbed from fire or smoke [18], [20], [21], which results in the variation of degradation of the structures of concrete and structural elements [20], [21].…”