Building Construction Handbook, Eighth Edition

Fire Resistance of Structural Steelwork ~ although steel is a non-

combustible material with negligible surface spread of flame

properties it does not behave very well under fire conditions.

During the initial stages of a fire the steel will actually gain in

strength but this reduces to normal at a steel temperature range

of 250 to 400°C and continues to decrease until the steel

temperature reaches 550°C when it has lost most of its strength.

Since the temperature rise during a fire is rapid, most structural

steelwork will need protection to give it a specific degree of fire

resistance in terms of time. Part B of the Building Regulations sets

out the minimum requirements related to building usage and size,

BRE Report 128 `Guidelines for the construction of fire resisting

structural elements' gives acceptable methods.

Typical Examples for 120 minutes Fire Resistance ~

25 mm minimum cover

of concrete over steel

1.6 mm wire binding

at 100 mm pitch

steel column

with section

factor 90...140

25 mm firecheck plasterboard

15 mm firecheck

plasterboard

(^25) min.
steel column
with section
factor 90...140
non-loadbearing
concrete not
leaner than a
1:2:4 mix with
natural aggregates
2.3 mm wire
binding at
150 mm pitch
SOLID PROTECTION
SOLID PROTECTION
compartment floor slab
steel beam with section
factor 90...140
non-loadbearing concrete
not leaner than a 1: 2: 4
mix with natural aggs.
metal
lathing
20 mm thick perlite-
gypsum plaster
2.3 mm
wire binding
at 150 mm
pitch
minimum cover of concrete
over steel 25 mm
HOLLOW PROTECTION
HOLLOW PROTECTION
For section factor calculations see next page.
Structural Steelwork---Fire Protection