Chapter 6
Timber structures
6.1 Introduction
Timber is a structural material with a useful
combination of physical properties. Although
its strength is not high (typical design stress
values are in the range 5 to 20 N/mm^2
compared to equivalent values for steel of 150
to 250 N/mm^2 ), timber is, like steel, more-or-
less equally strong in tension and compres-
sion. It can therefore withstand bending and
can be used to make every kind of structural
element. Due to the origin and nature of the
material, timber is available normally in the
form of slender, linear elements and this
favours its use in framework arrangements.
The ratio of strength to weight of timber is
high, and is comparable with that of steel, with
the result that, although, for a given size of
cross-section, timber elements are not so
strong as those of steel, they are much lighter.
Timber is therefore a lightweight material,
capable of providing structural elements which
are of low dead weight, but which are never-
theless reasonably strong and tough.
One of the problems associated with the
structural use of timber is that due to its
arboreal origins individual elements are
relatively small. The construction of large
Fig. 6.1 Timber
houses with skeleton-
frame structures in
which the principal
elements are A-frames
of plywood box-
section. A characteris-
tic of timber skeleton
frameworks is that the
primary structural
elements are normally
fairly large and must
be incorporated into
the aesthetic scheme
of the building [Photo:
Finnish Birch Plywood
Association].
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