Steel columns encased in concrete are much safer than the conservative official standards placed on them, according to newly published research.
A team at ISISE, the Institute for Sustainability and Innovation in Structural Engineering at the University of Coimbra in Portugal, carried out experimental research on composite columns under fire conditions.
They found several quite reasonable factors that affect performance; for example, increasing the amount of concrete encasing the steel extends its critical time.
Conversely, a higher initial load decreased the critical time of the steel columns tested – and like concrete cover, was found to have “a big influence”.
But significantly, the team’s article in the Journal of Constructional Steel Research notes that “the EN 1994-1-2 tabulated method is extremely conservative for these types of columns”.
The article’s authors argued that the standards are “very conservative and on the safe side” compared to their own findings.
It could be that the official standards are based on steel columns that were not subject to thermal restraining, they add, whereas their own investigation’s real-world experimental testing found the steel columns to have critical times in excess of 180 minutes.