Challenging Issues on Fire-Resistance of Steel Buildings.

Steel buildings may be seriously damaged in fire due to the significantly reduction of steel strength at elevated temperatures. The traditional approach for fire-resistance of steel building structures is simply relied on the fire-resistance of isolated structural members subjected to standard flash-over fire exposure. However, flash-over fire will not happen in large space buildings, and the large space enclosure fire will be localized and its effects on steel structures are completely different from that of flash-over fire. In addition, the exposed steel structures of large space buildings usually use intumescent coatings for fire protection for aesthetic appearance. The variation of intumescent coatings in material properties and thickness make its thermal resistant parameter changing during fire and making quantification of thermal-resistance of intumescent coatings extremely difficult. Moreover, steel members in actual building structures are often axially restrained, and the additional internal forces will be created in such members due to thermal deformation induced by temperature variation during fire, which results in the fire-resistance of restrained steel members being different from that of isolated ones. For settling the hereinabove challenging issues, the modellings of fire effects on steel structures in large space buildings are presented. A constant effective thermal conductivity of intumescent coatings is proposed, which can be determined with a simple steel plate sample exposed to the flash-over standard fire and used for easily predicting the temperature elevation of the steel members protected with intumescent coatings exposed to fire. The variation of restrained steel members subjected to fire are investigated and the practical principals of fire- resistance of restrained steel bending members and compressed members are proposed. Finally, the practical fire-resistance evaluation and fire protection design of steel structures with intumescent coatings employed in special building projects are implemented and presented relying on solution of the challenging issues.