Engineering Structures 30 (2008) 3276–3284 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct A closed-form analysis of perimeter member behavior in a steel building frame subject to fire Spencer E. Quiel ∗ , Maria E.M. Garlock Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, 08544, USA article info Article history: Received 8 August 2007 Received in revised form 12 February 2008 Accepted 1 May 2008 Available online 13 June 2008 Keywords: Fire Steel Performance-based analysis Perimeter column Subassembly frame abstract This paper outlines a closed-form methodology that can be used to predict the increase in demand experienced by the perimeter columns that are part of a fire-exposed steel building frame. The two- dimensional elevation-view subassembly considered for this study includes a two-storey length of the perimeter column and the floor beam framing into the column in the direction perpendicular to the building’s exterior. When heated, this beam will expand and induce bending moment and lateral deflection in the column as well as increased axial force in the beam itself. Our proposed approach has two primary components: (1) a material model that approximates nonlinearity and considers temperature effects, and (2) a mechanical model that represents the perimeter column and beam interaction. These models are used to develop a simplified closed-form solution for beam axial force and perimeter column bending moment that may be used as part of a performance-based design for fire exposure. The simplified model solutions are compared to the results of a more complex and detailed multi-story finite element analysis model. A comparison of these results shows that the simplified model results give good estimations of structural behavior. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction The current state of practice in the US commonly uses a prescriptive approach for designing structures to resist fire. Prescriptive codes state how a building is to be constructed to resist exposure to unwanted fire. Although this standard has been used by the building industry for nearly a century, the furnace- test methodology on which it is based is principally a thermal test, not a structural one, and it considers individual member behavior without consideration of how the member interacts with the surrounding structure. Recent reports by the National Institute of Standards and Technology (NIST) [1] in the US and the British-based Institution of Structural Engineers (IStructE) [2] have called for the development of performance-based standards and code provisions as an alternative to current prescriptive methods. Performance-based provisions state how the structure is to perform when subjected to a wide range of fire conditions and scenarios. Specifically, both of these reports have recommended the development of a structural design methodology based on the performance of the structural frame as a whole rather than the individual components. This research addresses the recommendations of these reports specifically for the behavior of steel perimeter columns exposed to fire. ∗ Corresponding author. Tel.: +1 609 258 5427; fax: +1 609 258 1563. E-mail address: squiel@Princeton.EDU (S.E. Quiel). The perimeter column in a building is typically laterally braced by one beam in the plane perpendicular to the exterior wall or a shaft opening. The fire-induced structural response of this beam that frames into the perimeter column directly affects the perimeter column’s behavior and the structural integrity of the frame as a whole. Previous research by the authors examined the fire response of a tall moment-resisting steel frame composed of wide-flange sections [3]. The analysis results indicated that the thermal expansion of the beams that frame into the perimeter column induce column lateral deformations (Δ) as well as bending moments (M c ) that can reach the plastic moment capacity of the perimeter columns. Since these beams are partially restrained from expanding by the column, large axial forces (P b ) develop in them. This interaction between the floor beams and the perimeter column in a frame with one perimeter compartment on fire is shown in Fig. 1. If these beams, which brace the perimeter column in one plane, fail, the stability of the column, and the structure as a whole, may be compromised. Recent fire-induced structural collapses have shown the importance of predicting individual member behavior based on the interaction with the adjoining structure. For example, the interaction of perimeter columns and floor systems when exposed to fire has been identified as a contributor to the collapse of multiple perimeter bays of the Windsor Tower in Madrid [4] and to the collapse of the World Trade Center (WTC) Twin Towers [1]. These events have shown us that the perimeter columns are important to the stability of a structure under fire, and it 0141-0296/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2008.05.006