External steelwork

A number of modern steel buildings have been constructed with the steel skeleton on the outside of the structure, Figure 47 and 48, shown below.

Since an external structural frame will only be heated by flames emanating from windows or other openings in the building facade, the fire that the steelwork experiences may be less severe than in an orthodox design. 

It may be possible to design the frame members to remain unprotected or to have reduced protection if they are positioned so that they not be engulfed by flames and hot gases issuing from facade openings. Assessment can be carried out in accordance with The Steel Construction Institute publication Fire Safety of Bare External Structural Steel, Figure 49 shown below. 

This describes a method to define the design temperature of the structural members from consideration of their location in relation to the openings, their distance from the facade, the fire load and ventilation characteristics of the compartments and the potential effects of wind.

Comparison of the calculated design temperature with the limiting temperature of members calculated from BS5950 Part 8 will indicate whether or not protection is necessary.

Clearly consideration must be given to suitable corrosion protection methods and guidance can be found in the appropriate Corus design guide. In addition design against brittle fracture should also be considered and design guidance is given in BS5950 Part 1.