STRUCTURAL DESIGN FOR ARCHITECTURE

Fig. 1.6 Force system in a

building's structure. The gravi-

tational load on the roof is

conducted, via the roof truss

and the walls, to the founda-

tions where it is balanced by

reactions from the substrata.

The same is true of loads

imposed on the floors which

are transmitted by the floor

structural elements and walls

to the foundations. The roof

truss, wall and floor elements

must be strong enough to

carry the internal forces gener-

ated by the load.

Structure and architecture

an essential aspect of this process and are
required both to determine the magnitudes of
the forces in the individual elements - an
activity known as structural analysis - and then
to calculate the required sizes of the element
cross-sections.
A fourth property which a structure must
possess, in addition to the requirements of
equilibrium, stability, and strength, is
adequate rigidity. All structural materials
deform in response to load and it is necessary
that the overall deflection of a structure should
not be excessive. As with strength, the rigidity
of the structure depends on the properties of
the material and the sizes of the cross-
sections, which must be large enough to
ensure that excessive deflection does not
occur. Like strength, rigidity is checked and
controlled through the medium of calculations.
To summarise, the basic requirements of the
structure (the firmness element of the archi-

tectural shopping list of 'firmness', 'commod-

ity' and 'delight') are the ability to achieve

equilibrium under all possible load conditions,

geometric stability, adequate strength and

adequate rigidity. Equilibrium requires that the

structural elements be properly configured,

stability is ensured by the provision of a

bracing system; and adequate strength and

rigidity are provided by the specification of

structural elements which are of sufficient size,

given the strengths of the constituent

materials.

1.3 Structure types

1.3.1 Post-and-beam structures

Most architectural structures are of the post-

and-beam type and consist of horizontal

spanning elements supported on vertical

columns or walls. A characteristic of this type 5

Non-loadbearing

partition wall