Structural Design for Architecture
high). It is ideally suited to the form of skeleton
frameworks, where the principal alternative in
multi-storey buildings is reinforced concrete. Its
high ratio of strength to weight also makes it
suitable for lightweight frameworks such as are
used in roof structures. In this application the
principal alternative is timber. The advantages
and disadvantages of steel in relation to these
materials is reviewed briefly here.3.2.2.2 Advantages of steel
Strength
The high strength of steel, and its high ratio of
strength to weight, makes it suitable for use in
single- and multi-storey skeleton frames, over
a large range of spans and building heights.
The material therefore offers the advantages of
skeleton-frame construction in all of its
manifestations. In addition to freedom from
the restrictions of loadbearing walls in the
planning of both the interior and the exterior
of the building, as mentioned above, these
include the subsequent flexibility to alter plans
and elevations when required.
Considerable flexibility is also possible in
the planning of the building services and in
their subsequent maintenance and replace-
ment when this becomes necessary. These
advantages are, of course, also present with
reinforced concrete frameworks but because
the structural elements in steel frames are
more slender and less obtrusive than those in
equivalent reinforced concrete frames, the use
of steel allows interiors with lighter and more
open aspects to be created.Ratio of strength to weight
Steel frames are lighter than reinforced
concrete frames of equivalent strength, partic-
ularly if efficient types of element such as
triangulated girders are used. This makes them
more suitable than reinforced concrete frames
for use in single-storey buildings and the roof
structures of multi-storey buildings. In this role
the principal alternative to steel is timber.Quality control
Steel is manufactured under conditions of
strict quality control and its properties can berelied upon to be within narrow specified
limits; this allows relatively small factors of
safety to be adopted in the structural design
calculations and is a further reason why light
and slender elements are possible.Appearance
Due to the strict quality control which is
exercised during its manufacture and to the
methods which are used in the final shaping of
steel components, the finished structure has a
distinctive appearance which is characterised
by slender elements, smooth surfaces and
straight, sharp edges.Prefabrication
Steel structures are assembled from prefabri-
cated components which are produced off-site
and this allows their dimensions and general
quality to be carefully controlled. It also results
in fast erection of the structure on site and
enables a relatively simple erection process to
be adopted, even on difficult sites.
Prefabrication with site-jointing also means
that it is relatively easy for the designer to
exercise control over whether or not the struc-
ture is statically determinate.3.2.2.3 Disadvantages of steel
Intractability
Steel is a very tough material which is difficult
to work and shape in the solid form and this
has a number of consequences. It means that,
in most steelwork design, it is necessary to
specify elements from a standard range of
components which are produced by steel
manufacturers and to carry out the minimum
amount of modification to these. The standard
elements, which are produced by a hot-rolling
or cold-forming process (see Section 3.4), are
straight and parallel sided with the result that
steel frameworks must normally have a regular,
rectilinear, or at least straight-edged geometry.
The production of 'tailor-made' cross-
sections, or of geometries which are curvilin-
ear, is difficult and the use of steelwork tends
therefore to place more restrictions on the
overall forms of structures than does the use of60 reinforced concrete. Also, the final adjustment