STRUCTURAL DESIGN FOR ARCHITECTURE

(3.5 m to 6 m). Element sizes for two versions
of this type of frame are given in Table 6.14.
Where timber is used for multi-storey skele-
ton-frame structures and must carry floor
loading, the spans must be kept small -
around 2 m to 3 m if simple sawn-timber
elements are used for floor beams. Longer
spans are possible with built-up-beam
elements, such as laminated timber or plyweb
beams, but the depths of these will be very
large compared to equivalent steel or
reinforced concrete structures (Fig. 6.1).
In multi-storey frames very simple grids,
with columns at all grid points, are adopted
where solid timber elements are used, so as to
minimise the loads which individual beams
carry (Fig. 6.56). Spaced beams are frequently
adopted to increase the strength of individual
elements and this allows longer spans to be
achieved. Where built-up-beams are used,
more complex primary/secondary-beam
arrangements are possible. In all cases the
beam depths must be checked at an early
stage in the design as these are likely to be
critical.
Another feature which is likely to be critical
in skeleton-frame design is the geometry of the

Fig. 6.56 An example of a beam layout which is suitable

for a multi-storey skeleton frame in timber. Primary

elements are spaced beams (double elements) and are

confined to short spans.

beam-to-column connections and some

thought must normally be devoted to this

when the design is at a preliminary stage.

Simple lap joints with bolted connections are 227

Table 6.14 Span range and dimensions of principal elements in

timber trusses in single-storey skeleton frameworks

Span Truss Roof Approximate member size (mm)

spacing pitch

(m) (m) Rafter Ceiling tie

10 2 20° 1 X 50 X 150S 1 X 50 X 100S

30° 1 X 50 X 125S 1 X 50 X 75S

15 3 20° 1 X 75 X 200S 1 X 75 X 150S

30° 1 X 75 X 150S 1 X 75 X 150S

20 4 20° 2 X 75 X 225S 1 X 75 X 225S

30° 2 X 75 X 175S 1 X 75 X 150S

30 6 20° 4 X 75 X 200S 3 X 75 X 200S

30° 3 X 75 X 125S 2 X 75 X 200S

40 6 20° 1 X150X 300L Steel tie rod

30° 1 X 150 X 250L Steel tie rod

50 6 20° 1 X 150 X 330L Steel tie rod

30° 1 X 150 x 300L Steel tie rod

60 6 20° 1 X 150 X 400L Steel tie rod

30° 1 X 150 X 330L Steel tie rod

Timber structures

S = sawn timber

L = laminated timber

Square

cross-section

column

Doubled sawn-timber

primary beam

Sawn-timber joists

2m

4m