BS5950 Part 8: Code of Practice for Fire Resistant Design
BS5950 Part 8, Figure 33 shown below, was first published in 1990 and redrafted in 2003.
It brings together in one document all of the methods of achieving fire resistance for structural steelwork. Although it is based on evaluation of performance of structural steel members in the BS476 Part 20 standard fire (see Steelwork fire resistance), it may also be used in fire engineering assessments when natural fire temperatures are derived by calculation (see Structural fire engineering).
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BS5950 Part 8 also includes design information and guidance for design of portal frames, hollow sections, external steelwork, composite slabs and beams and calculation of protection thicknesses based on limiting temperatures. The code contains two basic approaches to assessment of fire resistance either by test or by calculation.
From Tests - in accordance with BS476 Part 21.
By Calculation - in accordance with either:
- the limiting temperature method
- the moment capacity method
A commentary to the standard giving more detailed information and worked examples has been published by the Steel Construction Institute, Figure 34 shown below.
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Fire resistance derived from tests
All approved protection materials have been tested in accordance with BS476 and the required thickness of each product has been evaluated with regard to fire resistance period and section factor.
Limiting temperature method
The limiting temperature method allows the designer to assess the need, or otherwise, for fire protection by comparing the temperature at which the member will fail (the limiting temperature) with the temperature of the hottest part of the section at the required fire resistance time (the design temperature).
Moment capacity method
This calculation method allows the designer the opportunity to assess the fire resistance of a beam by calculating its moment capacity using the temperature profile at the required fire resistance time.
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