Behaviour of steel frames under fire conditions

A state-of-the-art review of the behaviour of steel frame structures in fire is presented. Results from differentstudies indicate that the behaviour of a complete structure is different from that of a single structural member under fire conditions from the point of view of fire resistance. Earlier studies also show that analysis and design of steel structures against fire based on their overall behaviour could lead to a reduction or the elimination of applied fire protection to certain structural members. The effects of continuity, restraint conditions, and load ratio on the fire resistance of frame structures are discussed. The beneficial aspects derived from considering overall structural rather than single-member behaviour in fire are illustrated through the analysis on two one-bay, one-storey, unprotected steel portal frames, a column, and a beam. Also comparison is made between the performance of a beam with different end restraints in fire. Results from the analyses indicate that the fire resistance of a member is increased when it is considered as part of a structure compared with when it is considered as a single member.Cette article pr\ue9sente la pointe de la technologie en mati\ue8re de comportement de structures \ue0 charpentes enacier expos\ue9es au feu. Les r\ue9sultats de diff\ue9rentes \ue9tudes indiquent que le comportement d'une structure compl\ue8te est diff\ue9rent de celui d'un membre structurel unique, du point de vue de la r\ue9sistance au feu. Des \ue9tudes pr\ue9c\ue9dentes d\ue9montrent \ue9galement que l'analyse et la conception de structures en acier contre le feu, bas\ue9es sur le comportement de l'ensemble, peuvent aboutir \ue0 une r\ue9duction ou \ue0 l'\ue9limination de la protection contre le feu, appliqu\ue9e \ue0 certains membres structurels. Les effets de la continuit\ue9, de conditions de restriction et du rapport de charge, sur la r\ue9sistance au feu des structures \ue0 charpentes sont discut\ue9s. Consid\ue9rer le comportement structurel de l'ensemble au lieu d'un membre unique expos\ue9 au feu, pr\ue9sente des avantages. Ces avantages sont illustr\ue9s par l'analyse de deux charpentes portales non-prot\ue9g\ue9es, \ue0 une baie et \ue0 un seul \ue9tage, une colonne et une poutre. Une comparaison est \ue9galement faite entre la performance d'une poutre avec diff\ue9rentes restrictions en bouts, expos\ue9e au feu. Les r\ue9sultats des analysesindiquent que la r\ue9sistance au feu d'un membre est augment\ue9, lorsqu'il est consider\ue9 en tant que partie d'une structure, plut\uf4t qu'en tant que membre unique.Peer reviewed: YesNRC publication: Ye