STRUCTURAL DESIGN FOR ARCHITECTURE

Fig. 5.27 Cross-wall arrangement with roof carried on

purlins.

and for internal walls to be solid. In low-rise
buildings of four storeys or less, the external
walls will normally consist of two leaves which
are one half-brick-length thick or its equivalent
in blockwork (i.e. approximately 100 mm)
separated by a 60 mm wide cavity to give a
total wall thickness of approximately 260 mm.
Normally only one of the leaves is loadbearing
(usually the inner leaf), and frequently brick-
work is used for the outer leaf and blockwork
for the inner leaf. Interior walls can be one
half-brick-length thick or its equivalent in
blockwork unless, for reasons of appearance, a
bond which requires headers is used. For high-
rise buildings the inner, loadbearing leaf of
external walls and the solid internal walls must
usually be one brick-length thick or its equiva-
lent in blockwork (i.e. approximately 200 mm).

5.3.2.3 Resistance to buckling
Masonry walls, being compression elements,
are susceptible to buckling failure and the
plans of masonry buildings have to be
arranged so as to avoid the creation of walls
which are excessively slender. The slenderness
ratio of a wall is defined as the ratio of its
effective length or its effective height to its
width, whichever is the smaller (Fig. 5.28) and
the British Standard for Loadbearing Masonry,
BS 5628, requires that this should never be

Fig. 5.28 The slenderness of masonry walls, which is

determined by the distance between locations at which the

wall is provided with lateral support, must be limited to

control buckling. Lateral support can be provided either by

buttresses or orthogonal walls, in which case the slender-

ness is determined by the horizontal distance between

these, or by floor structures or horizontal-plane bracing

girders, in which case the slenderness is determined by the

vertical distance between these. In either case the measure

of slenderness is simply the distance between the

locations of lateral restraint divided by the thickness of the

wall. The need to limit slenderness can sometimes affect

the internal planning of buildings by requiring that

buttresses or bracing walls be located in particular

positions. 169

Masonry structures