Beam-columns are defined as members that are subject to axial load (P) plus bending moment (M). In a fire, perimeter columns act as beam-columns even though they may not have been designed to resist moment. Perimeter columns are found on the perimeter of a building or adjacent to an opening (e.g., shaft) in the floor system. These columns are braced and exposed to fire on three sides only. When exposed to fire, the beams that frame into them expand and laterally displace the column. This induced displacement causes large bending moments in the perimeter columns and increased axial stress in the beams themselves. When these fire-induced reactions develop, both the perimeter column and the beam are subject to a combination P plus M and therefore act as beam-columns. It is important to understand that these columns may not have been designed to resist any moment. Our group developed simple tools and design guidelines that enable practicing engineers to predict the capacity and behavior (i.e., demand) of steel perimeter columns in a fire.

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