STRUCTURAL DESIGN FOR ARCHITECTURE

Steel structures

Secondary beam

Primary beam

Steel frames can therefore be thought of as
either 'simple' frames, that is frames in which
the majority of the joints are of the hinge type,
or as 'rigid' frames, in which case the joints are
rigid. Most frames are of the 'simple' type and
therefore require bracing systems for stability
(see Sections 3.6.2 and 3.6.3).
As with other types of structure, the config-
uration which is adopted for a steel frame is
influenced by the principal types of load which
it will carry and, in particular, by the characteris-
tics of whichever of the applied loads is
dominant. In the descriptions which follow
frames are subdivided into three categories
depending on the dominant type of applied
load. The three main types of applied load on
architectural structures are imposed roof load,
imposed floor load and wind load. The three
resulting categories are single-storey frames, in
which imposed roof loading is the dominant
load, low- and medium-rise multi-storey frames,
in which imposed floor load is the dominant
form of load, and high-rise multi-storey frames,
in which wind load is a significant structural
factor in the design. A very large number of
different geometries and configurations is
possible within each category. Only the most
basic forms are actually described here.

3.6.2 Single-storey frames

3.6.2.1 Introduction
The variety of different possible arrangements
for single-storey frames is very large and they
are placed here into the two broad categories
of one-way- and two-way-spanning systems.
Each of these categories is then further sub-
divided.

3.6.2.2 One-way-spanning systems
There are two basic types of one-way-spanning
single-storey frame, the main difference
between them being that in one the principal
elements are spaced close together and carry
the roof cladding directly, and in the other they
are located at a fairly wide spacing and are
linked by a secondary system of elements to
which the cladding is attached. The second of
these arrangements is more versatile and the

Fig. 3.25 This is a typical layout for a single-storey frame

in which lightweight steel elements are used. In the

primary-secondary beam system illustrated, closely spaced

triangulated joists are arranged parallel to one another

and are supported by primary beams, which are in turn

supported by columns. The column grid is rectangular with

the secondary beams running parallel to the long side of

the rectangle.

majority of single-storey steel frames are in

this category.

Figure 3.25 shows a typical arrangement of

elements in the first type of frame. It is normal

for only every third or fourth element to be

supported directly on a column with the

remaining elements being carried on beams

running at right angles to the principal direc-

tion to produce a rectangular column grid. The

roof geometry can be given a wide variety of

elevational forms including flat, mono-pitch,

duo-pitch and curved, but a regular-plan

geometry consisting of equally spaced parallel

elements is normally adhered to.

The principal elements in this type of frame

carry relatively small areas of roof and are

therefore lightly loaded. This favours the use of

light, efficient types of structural element such

as proprietary lightweight lattice joists, based

on cold-formed sections (Figs 3.20 and 3.26).

'Improved' hot-rolled sections, such as castel-

lated beams (Figs 3.16 and 3.27), are also

suitable but the use of standard hot-rolled

sections such as the universal beam is rarely

economic. 75