STRUCTURAL DESIGN FOR ARCHITECTURE

Fig. 5.39 Tall single-storey building. A roof structure of

timber or steel girders is supported on high masonry walls.

Such buildings are the modern equivalent of the vaulted

hall (see Section 5.2.1).

a roof structure of steel or timber-truss primary

elements (Fig. 5.39). Typical depths for various

types of roof structure are given in Table 5.2.

The strategy which is normally adopted to

resist horizontal load is fairly standard.

Vertical-plane bracing is provided by the walls

which are parallel to the direction of the lateral

load and these are linked to all other parts of

the building through horizontal-plane bracing

(Fig. 5.40). In the case of these single-storey

buildings the horizontal-plane bracing must

normally be provided by incorporating a wind-

girder into the plane of the roof.

External walls which are exposed to out-of-

plane wind pressure span vertically between

the wind girder and the foundations and, as

the walls are high, the resulting bending action

can be large (Fig. 5.40). Because the compres-

sive stress due to gravitational load in the roof

will be only moderate in a single-storey build-

ing, it is necessary that the tensile bending

stress should not be high. The latter is

controlled by the expedient of increasing the

second moment of area of the wall cross-

section, and this is a factor which can have a

major effect on the planning of the building.

If the wall is relatively low (say around 3 m),

normal cavity construction, with perhaps a

thicker than normal loadbearing leaf or with

pier stiffening of the loadbearing leaf (Fig.

5.41a), is usually sufficient to prevent the

bending stress from being excessive, but if it is

higher, then relatively sophisticated systems

must be used. In the range 4 m to 5 m one of

the most economical forms of construction is

the fin-wall (Fig. 5.41b) in which one of the

leaves is stiffened with very large piers. The

wall then behaves as a series of T-beams in

response to lateral load. Fins are normally

one-half to two brick-lengths wide and four to

eight brick-lengths deep and are spaced 3 m to

5 m apart. For wall heights in the range 5 m to

10 m a form of construction called diaphragm

walling is necessary (Fig. 5.41c). This involves

separating the leaves of the wall by a gap

which is much larger than is used in normal

cavity construction, that is by one or two brick-

lengths, and providing a shear connection

between the leaves in the form of diaphragms

at closely spaced intervals (1 m to 1.5 m). The

wall then acts as a box-beam in response to

176

Structural Design for Architecture

Table 5.2 Spans and dimensions for roof

elements in tall single-storey masonry structures

Beam Beam depth (mm)

Span

(m) Universal Castellated Parallel Laminated

beam beam chord truss timber

(hot-rolled beam

elements)

10 450 500 1000 700

15 600 700 1250 900

20 700 800 1500 1200

25 800 900 1750

30 900 1200 2000

35 - 1300 2250

40 - 1300 2500