STRUCTURAL DESIGN FOR ARCHITECTURE

Structural Design for Architecture

structures therefore involves the joining

together of many separate components. Joints

and connections are therefore an important

aspect of the technology of structural timber.

6.2 Timber and architecture

6.2.1 Introduction

Of the four principal structural materials,

timber is one which is not directly associated

with a major architectural style or movement

in the Western architectural tradition, although

significant timber building traditions (for

example, the 'stick' and 'shingle' styles of

North America) have occurred. Other architec-

tural traditions, such as those of China or

Japan, have, however, produced significant

timber styles.

Although no major Western architectural

style is associated with timber, the contribu-

tion of the material to the development of

Western architecture has nevertheless been

considerable. Its principal structural use has

been as the horizontally-spanning elements in

post-and-beam structures in which the vertical

elements were of masonry. As in the case of

structures constructed entirely of masonry, it

will be necessary here to consider historic

examples in order to review the full contribu-

tion which timber has made to architectural

expression.

Before considering the architectural qualities

of timber it is necessary to say something of

the range of structural arrangements for which

it is suitable. Although there is considerable

variation in the forms and layouts which have

been created, almost all timber floor and roof

structures conform to a similar basic layout.

The roof or floor covering of boards, slates,

tiles, etc. is normally supported on a series of

closely spaced parallel elements. The timber

beam floor (Fig. 6.2) is perhaps the simplest

example of this. The modern trussed-rafter roof

is a more sophisticated version of it (Fig. 6.27).

The common characteristic of these arrange-

ments is that the individual elements, be they

beams or trussed rafters, carry relatively small

areas of floor or roof and are therefore lightly

loaded. They span one way between parallel

supports which may be loadbearing walls or

may be primary beams in a skeleton frame.

The spacing of the structural elements in

this type of arrangement is close and is deter-

mined principally by the span capability of the

material which the timber elements support

(floor or roof boarding) but also by the need to

maintain the load carried by each timber

element at a suitably low level.

Where large spans are involved and the sizes

of the main elements are therefore large it

becomes uneconomic for the spacing of these

to be close. For large spans, therefore, a hierar-

chical arrangement of primary, secondary and

even tertiary elements provides a better

solution. An example of this is the purlin roof

(Figs 6.44 and 6.45). In the arrangement shown

in Fig. 6.44 the primary elements, which span

Fig. 6.2 In this typical timber floor structure the

elements are at close spacings and each carries a relatively

180 small amount of load.

Wall support

(masonry or

timber framing)

Beam support

(timber or steel)