Structural Design for Architecture
16
elements must be maintained at modest
levels. Spans are therefore normally kept small
and in modern practice loadbearing masonry
buildings are usually fairly small in scale. (This
is in contrast to the very large-scale masonry
structures of previous ages which were
achieved by the use of masonry vaults and
domes as the horizontal spanning elements -
see Section 5.2. and Fig. 5.1.)
Although modest in scale, modern loadbear-
ing masonry structures exhibit very good
combinations of properties and produce build-
ings which are durable and fireproof and which
have walls which perform extremely well in
respect of thermal and acoustic insulation.
They are therefore ideal for all kinds of living
accommodation.
Timber is a structural material which has
similar properties to steel and reinforced
concrete in the sense that it can carry both
tension and compression with almost equal
facility. It is therefore capable of resisting
bending-type load and may be used for all
types of structural element. It is significantly
less strong than either steel or reinforced
concrete, however, with the result that larger
cross-sections are required to carry equivalent
amounts of load. In practice, large cross-
sections are rarely practicable and timber
elements must therefore normally be used in
situations where the internal forces in the
structural elements are low, that is in buildings
of small size, and, in particular, short spans.
A significant advantage which timber has
over other structural materials is that it is very
light, due to its fibrous internal structure and
the low atomic weights of its constituent
chemical elements. This results in a high ratio
of strength to weight. Other advantageous
properties are good durability and, despite
being combustible, relatively good perform-
ance in fire.
Timber is commonly used for the horizontal
floor and roof elements in loadbearing
masonry structures (Fig. 6.39). Loadbearing-
wall 'panel' construction, in which the struc-
ture of a building is made entirely of timber, is
another common configuration (Fig. 1.19). Wall
panels consist of closely spaced timber posts
Fig. 1.19 Timber loadbearing-wall structure. Everything
here is structural. The wall and floor structures consist of
closely spaced timber elements. Temporary bracing
elements, which provide stability until non-loadbearing
cross-walls are inserted, are also visible. [Photo: A.
Macdonald]