STRUCTURAL DESIGN FOR ARCHITECTURE

studs are positioned at the same spacing as

the floor joists so as to minimise eccentricity

in the transfer of load. The advantages of the

platform frame are that long timber elements

are not required and that the system lends

itself to prefabrication. This is due to the

relative independence of the floors from the

walls and to the fact that none of the panels is

very large and difficult to transport. The fact

that studs and floor joists are aligned is also

an advantage because it eases the construc-

tional planning by allowing a grid system to be

used. The principal disadvantages of the

platform frame are that the building does not

become a weathertight shell until the construc-

tion is at a fairly advanced stage, and that the

structure is slightly less rigid than alternative

forms.

In balloon frames (Fig. 6.49) the wallframes

are two storeys in height (this is normally the

full height of the building) and the floor joists

are attached individually to wall studs by lap

joints. The advantage of this system is that it

allows the roof to be completed at an early

stage in the construction process, before the

floors are in position, to provide a weathertight

shell. It also provides a structure which is more

rigid than the platform frame. Its disadvan-

tages are that it requires very long elements for

the wall stud, that it does not lend itself to

prefabrication and that the joists and studs are

not aligned.

Two other types of wallframe are the

'modified' frame and the 'independent' frame

(Figs 6.50 and 6.51). Both have wall panels

which are one storey high. In the modified

frame the ground- and first-floor wall panels

are attached directly to each other and the

floor joists are then attached directly to wall

studs, as in the balloon frame. In the indepen-

dent frame the same arrangement for wall

panels is used but the floor is supported by a

steel angle or other element attached to the

edge of the lower panel and does not

penetrate the thickness of the wall. The

modified and independent frames are intended

to combine the good features of the platform

and balloon frames. They achieve something of

the structural continuity of the latter without

Fig. 6.52 Typical plan-form of a small-scale timber

wallframe building. The arrangement conforms to the

parallel-wall format of all loadbearing-wall forms of

construction.

(traditional tongued-and-grooved boarding

does not provide good racking resistance due

to the possibility of individual boards slipping

relative to each other) or by incorporating

diagonal bracing (tensioned steel wire or

timber) into the wall and floor panels.

A number of different wall configurations are

used in timber loadbearing-wall structures. The

traditional methods are the 'platform' frame or

the 'balloon' frame. In platform frames (Fig.

6.48) the wall and floor panels are more-or-less

independent entities and the wall panels are of

single-storey height. Each wall is built on top

of the platform which is formed by the floor

below it and the floor panels therefore

penetrate through the structural part of the

224 wall to the inner side of the cladding. The wall

Structural Design for Architecture

First-floor plan

Ground-floor plan

9.5 m

7.0 m

Stairwell