STRUCTURAL DESIGN FOR ARCHITECTURE

Fig. 3.16 The castellated beam is a modified universal
I-section beam. It is more efficient in resisting bending
than the parent beam because a higher bending moment
can be resisted by the same area of cross-section and
therefore volume of material.

Steel structures

Fig. 3.18 I-section girder assembled by welding from flat

plate. These are used when the required size of cross-

section is larger than the largest available in the standard

range.

non-standard sections can be built up from the

standard sections. The 'castellating' process,

by which universal beam sections are modified

(Fig. 3.16), is one such process and provides a

range of beam sections which are lighter than

the standard hot-rolled sections (Tables 3.2

and 3.3). Light beam sections can also be

manufactured from combinations of channel

and angle sections (Fig. 3.17). Where very

heavy cross-sections are required, these can be

built up from flat plate as welded plate girders

(Fig. 3.18).

3.4.3 Cold-formed sections

Cold-formed sections are fabricated from thin

sheet steel (strip) by rolling or by folding

(press braking), both of which are types of

forging. As with hot-rolled sections, manufac-

turers produce standard ranges, such as

angles, channels and l-sections, which are

intended to be generally useful for a variety of

structural purposes. The capital cost of the

equipment required to produce these sections

is less than that for hot-rolled products and

the ranges which are readily available are

much wider. The ease with which steel sheet

can be bent into complicated shapes allows 69

Fig. 3.17 Composite beams, built up by bolting or

welding standard sections together, are used where no

suitable standard section is available.

The structural sections described above are

the basic components from which steel struc-

tures are assembled. Elements for particular

applications are normally selected from the

standard ranges; it is not considered economic

to produce 'tailor made' cross-sections by the

hot-rolling process due to the high capital cost

of the special rolling-mill equipment which

would be required. If none of the standard

sections is suitable for a particular application