Fire design rules for load bearing cold-formed steel frame walls exposed to realistic design fire curves

• Design rules developed for standard fires were investigated for LSF walls exposed to realistic design fires.
• Design rule predictions were verified with eight fire test results for three LSF wall configurations.
• Fire performance results of LSF walls exposed to 48 realistic design fire curves are presented.
• Developed a simplified design method to predict the fire resistance ratings of LSF walls exposed to realistic design fires.

Light gauge Steel Frame (LSF) walls are extensively used in the building industry due to the many advantages they provide over other wall systems. Although LSF walls have been used widely, fire design of LSF walls is based on approximate prescriptive methods based on limited fire tests. Also these fire tests were conducted using the standard fire curve (ISO 834-1, 1999 [1]) and the applicability of available design rules to realistic design fire curves has not been verified. This paper investigates the accuracy of existing fire design rules in the current cold-formed steel standards and the modifications proposed by previous researchers. Of these the recently developed design rules by Gunalan and Mahendran (2013) [2] based on Eurocode 3 Part 1.3 (EN 1993-1-3, 2006 [3]) and AS/NZS 4600 (Standards Australia (SA), 2005 [4]) for standard fire exposure (ISO 834-1, 1999 [1]) were investigated in detail to determine their applicability to predict the axial compression strengths and fire resistance ratings of LSF walls exposed to realistic design fire curves. This paper also presents the fire performance results of LSF walls exposed to a range of realistic fire curves obtained using a finite element analysis based parametric study. The results from the parametric study were used to develop a simplified design method based on the critical hot flange temperature to predict the fire resistance ratings of LSF walls exposed to realistic fire curves. Finally, the stud failure times (fire resistance rating) obtained from the fire design rules and the simplified design method were compared with parametric study results for LSF walls lined with single and double plasterboards, and externally insulated with rock fibres under realistic fire curves.