La sécurité incendie dans les bâtiments à structure métallique

When a fire occurs, the collapse of a steel framed building can be a greater hazard than the conflagration itself: eg a steel beam or girder which can support 24 kg per mm² of section at 20°C will only support half this weight if it is subjected to a temperature of 540°C. In this context, the author lays particular emphasis on the use of self-supporting structures and thermal barriers to prevent the steel framework reaching temperatures which will create distortion. An unprotected steel structure will attain a temperature of 936°C after an hour in a heavy fire. Various materials can be employed to reduce the temperature of the steel and from a listing given in the report, boxing the framework in plaster facings 15 mm thick will limit the temperature of the steel to 80°C in the presence of a heavy fire, it being assumed that the insulation is of non-inflammable material.Another important recommendation is that in the laying out of large volume cold rooms, it is absolutely necessary that the structures are independent of each other by using fire-break walls, such that a structural collapse in one room can be contained.Some interesting graphs have been prepared by the author, but in two of them (Fig. 1, the influence of the quantity of combustible material on the development of a fire and Fig. 2, the influence of the influence of the ventilation area on the development of a fire) the curve established by ISO conflicts totally with those produced by the author as regards progression.

Résumé

Les structures métalliques non protégées se comportent mal au feu: elles s'échauffent vite et se déforment, quelquefois de façon considérable.Bien que des techniques aient été mises au point pour pallier ces inconvénients (en particulier augmentation de la durée pendant laquelle la structure résiste au feu), il faut néanmoins déterminer si ces améliorations permettent de garantir la sécurité des personnes et des biens. En ce qui concerne les bâtiments industriels de stockage, il est évident que les dommages subis par les structures ne sont pas la cause des risques en cours d'incendie; en conséquence la sécurité donnée par ce type de structure peut être considéree comme satisfaisante.