Structural Design for Architecture
2.3.3 The effect of cost example by columns. There have, of course,
Another factor which influences the choice of been exceptions to this, the 'prairie houses' of
structure type for a particular span is cost. Frank Lloyd Wright being good examples of
Structural efficiency is achieved by structural interiors with free flowing internal spaces
complexity which is costly to produce. The being accommodated within loadbearing-wall
builder of the long-span structure has no structures. These buildings are of relatively
choice but to use an expensive, complex type small scale, however, and the free-flowing
of structure. The builder of the short-span spaces exist within patterns of walls which are
structure does have a choice: both complex fairly regular (Fig. 2.7).
and simple types will be feasible, but the The degree of regularity of a plan affects the
complex structure will be more expensive. The preferred type of structure. As is mentioned
use of the latter, in the cost-conscious environ- above, loadbearing-wall structures must
ment of the late twentieth century, would normally be given a regular arrangement (see
therefore normally have to be justified on Chapter 5) and the same is true of frames,
some other grounds such as a particular which perform best if based on a regular
requirement for a lightweight structure. The column grid. If the pattern of vertical support
reason for choosing a complex form might, of is not regular, this is best accommodated by
course, be simply a desire for the appearance the adoption of a system for the horizontal
of complexity or extravagance. Depending on structure which has the capability to span in
the priorities of the client, therefore, cost more than one direction. For floor structures
might or might not be a significant factor in the simplest element of this type is the two-
determining the structural form which is way-spanning slab of in-silu reinforced
adopted. concrete. For roof structures it is the fully
triangulated space deck.
2.3.4 Internal planning Although both of these structural types work
The nature of the plan which is intended for a best when provided with a regular pattern of
building will normally influence the choice of vertical support they can, due to their statical
structure. The principal factors which affect indeterminacy,^16 be supported on irregular
this are the degree to which the interior is arrangements of columns or loadbearing walls,
subdivided, the degree of regularity required in The greater the degree of irregularity the
the internal planning and the degree of en- stronger, and therefore deeper, must these
closure which is envisaged. elements be.
The extent to which a building will be If the irregularity of the design of a building
compartmentalised normally has a consider- extends to a variation in plan between different
able influence on the choice of structure type. floor levels, this is best accommodated by the
Multi-cellular buildings lend themselves to adoption of a frame-type structure. The walls
loadbearing-wall-type structures, subject to the which subdivide the interior are then non-
provisos that the individual compartments are loadbearing partitions which are simply carried
not too large, that a reasonably regular pattern by the floors and whose location in the plan
of walls can be adopted and, in multi-storey can be varied between levels. If the variation in
buildings, that the plan is more or less the plan between levels is such that the continuity
same at all levels. If any of these conditions of columns through different levels is not16 See Macdonald, Structure and Architecture, Appendix 1 for
a discussion of statical indeterminacy in relation to
structural design.cannot be met, then a frame structure will
normally be required even if the plan is
compartmentalised.
If the interior of a building is to consist of
large areas of open space a frame structure will
normally be required even if the space can be
38 interrupted by some vertical structure - for