Analysis and design of RC columns in framed RC buildings under the standard fire, according to the EC2
Purpose - RC columns are very susceptible to fire, as besides the detrimental effects due to this action, second-order effects play a significant role. In this work, the aim is to consider the ISO834 standard fire, and the focus is put on checking the proper use of a simplified method suggested on Annex B.3 of EC2 to account for the second-order effects in RC columns. Design/methodology/approach - The use of Annex B.3 of EC2 is obscure in what concerns the peak strain to be considered at the most deformed cross-section concrete fibres, and this affects the evaluation of the second-order moment installed in the RC column during the fire. Two hypotheses are analysed in the paper, and validated against the calculations from the advanced code SAM: the one where the classical limit of 3.5 parts per thousand is assumed for the peak concrete strain in compression, and a more refined compatibility of the section total strains. Findings - The simulations demonstrate that using the simplified method with hypothesis HI leads to unsafe conclusions. Conversely, hypothesis H2 compares much better with SAFIR predictions, and it can be rather easily adopted in real applications. Originality/value - The indications provided here for the proper application of the simplified method are very useful for practical use. They overcome an unclear aspect on its implementation, not yet previously addressed.
rc columns frames standard fire fire second-order effects reinforced concrete