The potential for loadbearing walls to be exposed to fire on two sides was identified in cross-report 1116. This condition only applies to loadbearing walls within a fire compartment. Nonetheless, a method for the design of such walls was required.
Loadbearing light steel frame walls are used in the construction of various types of multi-storey buildings where the walls are typically fire protected using layers of gypsum-based boards. The fire resistance of the walls is demonstrated by fire testing of loaded walls exposed to fire from each side separately in accordance with BS EN 1365-1.
Compartment walls at the boundary of a fire compartment are only exposed to fire from one side at a time because design is based on the principle that a fire is contained within the fire compartment and does not spread to other compartments within the defined period of fire resistance. However, walls within a fire compartment could be exposed to fire on two sides simultaneously unless there are measures in place to prevent the spread of fire within a fire compartment.
The behaviour of loadbearing light steel walls exposed to fire on two sides was investigated by SCI, supported by members of the Light Steel Forum. As there is no standard for fire testing loadbearing walls exposed on two sides, a series of ad-hoc two-sided fire tests were conducted. The tests followed BS EN 1635-1 as closely as possible adapted for two-sided fire exposure and were supported by: Construction Metal Forming, Frameclad, Fusion Steel Framing, Hadley Group, Kingspan Steel Building Solutions, Metek, Saint-Gobain, Etex Remagin, and voestalpine Metsec.
Using their experience and expertise in the behaviour of light steel framing in fire, SCI carried out detailed analysis of the test data accompanied by thermal finite element analysis to develop a design method. The design method requires single sided fire test data for the wall and calibrated numerical thermal modelling to determine the temperatures of the light steel sections when the wall is exposed to fire on two sides. The design method is published in SCI publication P442 'Design of Loadbearing Light Steel Walls Exposed to Fire on Two Sides', this publication is a supplement to SCI publication P424 which provides comprehensive design guidance on the more general topic of fire resistance of light steel framing. As well as a detailed explanation of the design process and the technical background, P442 includes a full example design calculation for a typical loadbearing light steel framed wall exposed to fire on two sides.
The prospect of using alternative fire scenarios are discussed in SCI-P442. These include the consideration of parametric or natural fires in the two-sided fire case and the potential delay of a fire spreading from one side to the other.
The SCI would like to thank the members of the SCI's Light Steel Forum who have supported the development of the publication, and provided technical expertise, which is gratefully acknowledged.
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