Concrete beams fire design using graphs

Abstract

The most expeditious method for the design of concrete beams under fire situation is the tabular method, presented by the Brazilian standard ABNT NBR 15200:2012. Albeit simple, this method constrains the engineer's work, as it prevents him to seek alternative solutions to the few tabulated values. Yet, the Brazilian standard allows employing more advanced methods. Hence, the purpose of this work was to perform a thermal and structural analysis of beams with several widths, heights, covers and diameters/layouts of steel reinforcement (upper and lower). From those results, graphs were constructed, associating the ratio between the applied bending moment in fire over the resistance bending moment at ambient temperature, for the fire resisting time of each situation. These graphs also allow taking into account the redistribution of moments from positive to negative, which will lead to savings in the solution found.

Evaluation of the TRF of reinforced concrete beams through thermal and thermostructural analysis

“…The tabular method is widely accepted by the technical-scientific community because it is safe and practical, not requiring thermal or structural analysis of the elements, since safety is guaranteed by meeting minimum dimensions (Costa, 2008). The main disadvantage of this method is that it results in shorter fire resistance times than more complex methods (e Silva and Moreira, 2021;Albuquerque and Silva, 2013). This is because, usually, the tabulated methods do not take into account the real conditions of loading, design and behavior of the structure and can produce less economical results concerning more refined methods (Bolina et al, 2018).…”