Structural Design for Architecture
similar properties to those of reinforced
concrete and allows the walls themselves to
act as beams spanning across the voids at
ground level.
Where reinforced concrete floors are used
they will normally be strong enough to support
any non-loadbearing walls which are provided
for space-planning purposes. There is therefore
no structural requirement for non-loadbearing
walls to be positioned vertically above one
another and this makes possible minor vari-
ations in the plan between levels. Where
timber floors are used, these will not normally
be capable of supporting the weight of non-
loadbearing masonry walls and it is therefore
necessary that the plans at different levels
should be more-or-less the same. Where minor
variations occur, provision must be made to
transfer the weight of non-continuous walls to
the loadbearing walls on steel or reinforced
concrete beams.
Roof structures are usually capable of longer
spans than floor structures, especially if
trusses or trussed rafters are used. In multi-
storey structures the strategy which is adopted
for supporting the roof is therefore frequently
different from that for the floors in the same
building. For example, in spine-wall construc-
tion the roof is often made to span between
the external walls of the building and does not
require support from the spine-wall (Fig. 5.26).
The same system of supporting the roof on the
external walls is frequently used when the
floors span between cross-walls; the roof span
is then at right angles to the span of the floors.
Alternatively a purlin system can be used to
support the roof as well as the floors on the
cross-walls (Fig. 5.27). This relieves the exter-
nal walls of any load-carrying function, which
can be an advantage if large areas of glazing
are required.
The thickness of the walls which are required
in masonry structures depends on the indi-
vidual circumstances of the building concerned
and, in particular, on the load which each wall
must carry. Any special requirements with
regard to bond will also affect this. It is normal
practice to specify cavity construction for the
exterior walls, to prevent damp penetration,Fig. 5.25 Where large open-plan areas are required on
the ground floor of a building in which the upper floors are
multicellular, this can be achieved by the provision of a
frame structure of steel or reinforced concrete to act as the
base of a loadbearing-wall building.Fig. 5.26 Typical cross-section of a small spine-wall
building in which the roof structure spans between
168 the external walls.
Roof truss spans between
external walls3m3m4.5 m 4.5 m