The Behavior of Steel Perimeter Columns in a Fire

This study investigates the thermal and structural effects of fire protection, the slab, and the connection fixity on the thermal and structural behavior of perimeter columns in a common steel-framed high-rise building exposed to fire. A model is developed based on a tall steel building (of common construction) that was subject to conflagration in the last decade. The progression of the fire from floor to floor as it moved up the building is considered in developing the time-temperature curves for the analyses. Structural analyses therefore consider that some floors are cooling down while others are heating up. Results show that the beams framing into perimeter columns expand significantly and induce large moments in the perimeter columns, which may lead to the development of plastic hinges. The development of many plastic hinges in a frame could lead to overall structural instability. This phenomenon is essentially independent of the beam-to-column connection fixity and the presence/absence of a slab; therefore fire protection designs for perimeter columns should consider the beams framing into them, which are integral to structural stability.