Civil Engineering Reference
In-Depth Information
benefit for additional protection such as gypsum plaster. Attention
is also drawn to the fact that the fire resistance of the whole struc-
ture may be greater than that ascribed to individual elements.
Reinforcement of cold worked steel shows a rapid decrease in
strength after 300°C. In well designed and constructed concrete
this should be adequately protected from fire by the cover pro-
vided to the reinforcement. For those involved in repair and/or
refurbishment, reference to
Table 14.4
will give a guide to stand-
ards current before the 1990s and possibly some beyond that date.
For a detailed account of structural fire engineering methods see
Chapter 12:
Structural fire engineering design
.
The approach to fire resistance has changed radically in
recent times and reference to www.structuralfiresafety.org
provides a one stop appraisal of Fire Protection Engineering.
absorbs damaging carbon dioxide. The original limitation of
usable length related to the size of tree has largely disappeared
with the development of high strength and durable adhesives.
These permit the manufacture of long span structural elem-
ents (such as Glulam beams) and also a wide range of boards
such as:
Plywoods, including weather-resistant marine ply, blockboard and
■
laminboard.
Particle boards including chipboard and cement particle-board.
■
Fibre building boards (including MDF - medium density
■
fibreboard).
The UK only produces about 20% of the timber used in the
country so much of its supply has to be imported from else-
where in Europe and beyond.
Wood is a cellular material and anisotropic (different proper-
ties in different directions). In addition to natural defects such
as knots, shakes and wane, timber may be adversely affected
by rot. This occurs in two manifestations: dry rot (caused by
the fungus
Serpula lacrymans
and which is more prevalent in
14.7 Timber
14.7.1 Introduction
Timber is ubiquitous; it is sustainable, it has a strength/weight
ratio that is better than mild steel when loaded in its strong
direction, and, in forests, it is beneficial to the climate as it
Minimum dimensions (mm), excluding any finish, for a fire
resistance of
Nature of construction and materials
½ h
1 h
1½ h
2 h
3 h
4 h
1
Reinforced concrete (simply supported)
(a) Normal weight concrete
thickness
width
cover
70
75
15
90
90
25
105
110
35
115
125
45
135
150
55
150
175
65
(b) Lightweight concrete
thickness
width
cover
70
60
15
85
75
25
95
85
30
100
100
35
115
125
45
130
150
55
2
Reinforced concrete (continuous)
(a) Normal weight concrete
thickness
width
cover
70
75
15
90
80
20
105
90
25
115
110
35
135
125
45
150
150
55
(b) Lightweight concrete
thickness
width
cover
70
70
15
85
75
20
95
80
25
100
90
30
115
100
35
130
125
45
1
thickness
150
150
175
200
-
-
Less than 0.4% steel Normal-weight aggregate
2
1% steel Normal weight aggregate (concrete
density 2400 kg/m
3
)
thickness
cover
100
25
120
25
140
25
160
25
200
25
240
25
3
More than 1% steel Normal weight aggregate
(concrete density 2400 kg/m
3
)
thickness
cover
75
15
75
15
100
20
100
20
150
25
180
25
4
Lightweight aggregate (concrete density
1200 kg/m
3
)
(Note: intermediate densities may be interpolated)
thickness
cover
100
10
100
20
115
20
130
25
160
25
190
25
Table 14.4
Fire resistance of reinforced concrete (IStructE, 1991) © The Institution of Structural Engineers, 1991
