Quantification of the impact of fire design on the interest of using "high yield strength" steels

Abstract

This work is a complement to the work on the interest of high yield strength steels in steel structures, which was carried out at ambient temperature. The main objective of this work is to study the economic interest of high yield strength steels compared to the standard grade S355 under fire conditions.

Using high yield strength steels allows the element to have a reduction in cross-section for the same load, which is obviously of great interest. However, when fire conditions are introduced, the mechanical properties of the steel are degraded. The consideration of instabilities will be more unfavourable than at ambient temperature. This is due to the use of a specific buckling curve, an increased slenderness to account for the higher temperature and a stricter classification of the sections. This work therefore provides an indication of the extent to which these unfavourable conditions will influence the interest in using high yield strength steels in fire conditions.

In addition to this study of the economic interest of high yield strength steel grades, a study of the dimensioning design will be carried out and will determine which design, between the design at ambient or elevated temperature, will govern the choice of the optimal profile. Indeed, fire design is indissociable from ambient temperature design, as both are complementary.

This work will be based on the development of appropriate calculation methods incorporating fire resistance at 30 minutes exposure in the process of selecting the optimal profile. These codes will take into account different situations such as whether the element is protected by intumescent paint or not, and whether it is subjected to tension or compression.