Numerical assessment of post-earthquake fire response of steel buildings

Accidental actions such as fires and earthquakes are generally referred to as high consequence, low probability events. Current national building regulations consider accidental events as completely independent; therefore, the concurrent or chain occurrence of earthquakes and fires is not accounted for in standard design practice. However, in numerous instances, fires have been observed to develop as a consequence of damage sustained during an earthquake and have resulted in structural failures and loss of human lives. The performance of buildings subjected to post-earthquake fires is a major concern that poses on-going challenges to both fire safety professionals as well as structural engineers, whilst representing a high risk for fire and rescue service personnel.

The aim of this study was to assess and attempt to quantify the potential impact of an earthquake on the fire resistance of a moment-resisting steel frame, resulting from the permanent deformations (also referred to as residual drifts) of the members or from the damage sustained by the passive fire protection material during peak deformations. Multiple finite element numerical analyses have been carried out on a 5-storey and a 10-storey internal frame of a building, which have been investigated assuming both the cases of fire protected and uninsulated members. The effect of the earthquake on the fire resistance of the structures has been quantified by directly comparing the time until failure when the frames are subjected to the sole action of fire and when they are exposed to the same fire action after having been subjected to an earthquake.

The results indicated that the effect of an earthquake on the fire resistance of uninsulated steel frames is negligible irrespective of the frame height. On the other hand, a significant reduction of the fire resistance was observed in case of protected steel frames, which is directly related to the extent of insulation damage. Furthermore, the collapse mode of the frames changes in a detrimental way, if the damage of the insulation is large enough. While the reduced time until failure may directly affect the safety of the occupants, the collapse mode of a building has implications on the safety of the fire brigades and rescue service, as well as people and properties in the vicinity of the building.