Post-fire mechanical properties of carbon steel and safety factors for the reinstatement of steel structures

Abstract

This paper provides guidance on the post-fire material properties and associated safety factors for structural carbon steel which are required for the assessment and retrofitting of existing steel buildings which have suffered and survived a fire. Nowadays, there is a discrepancy between the methodology which is used in the design stage of a building (mostly based on the partial factor method) and the verification methods used after a fire. In the past decade, a number of researchers have published test data and there is more information available on the mechanical properties of steel following a fire. Nevertheless, a statistical evaluation of these results has yet to be conducted although design codes generally adopt a reliability-based approach for the analysis and assessment of buildings. To fill this gap of knowledge, the current article includes a statistical evaluation of the mechanical data from 718 tests collected from 19 peer-reviewed articles and doctoral theses. The study is done for hot-rolled steel, cold-formed steel as well as wrought or cast iron. By focusing on the effect of a fire on the mechanical properties after cooling, which is mostly related to how the coefficient of variation of their distribution increases, adjusted safety factors are proposed together with a reduced reliability index based on economic and social considerations. It is contended that by following this method, possible misunderstandings can be avoided and decisions on the salvage and rehabilitation of structures can be based on performance data and technical analysis, thus reducing the need for individual judgement.