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284 Barry’s Advanced Construction of Buildings
Channel
section
Angle
section
T-section
Box channel
section
Omega
section
Z-section
Figure 5.7 Cold roll-formed sections.
connections, recommend their use. These sections are also much used in the fabrication
of railings, balustrades, gates and fences with welded connections for the neat, robust
appearance of the material. Prefabricated sections can be hot dip galvanised to inhibit
rusting prior to painting.
Cold roll-formed steel sections
Cold roll-formed structural steel sections are made from hot-rolled steel strip, which is
passed through a series of rollers. Each pair of rollers progressively takes part in gradually
shaping the strip to the required shape. As the strip is cold formed, it has to be passed
through a series of rollers to avoid the thin material being torn or sheared in the forming
process, which produces sections with slightly rounded angles to this end. There is no theoretical
limit to the length of steel strip that can be formed. The thickness of steel strip commonly
used is from 0.3 to 0.8 mm and the width of strip up to about 1 m. A very wide range
of sections is possible with cold-rolled forming, some of which are illustrated in Figure 5.7.
The advantage of cold-rolled forming is that any shape can be produced to the exact
dimensions to suit a particular use or design. Figure 5.8 is an illustration of cold-formed
sections, spot welded back to back to form structural steel beam sections, and sections
welded together to form box form column sections. Connections of cold-formed sections
are made by welding self-tapping screws or bolts to plate cleats welded to one section.
Because of the comparatively thin material from which the sections are formed, it is necessary
to use some coating that will inhibit corrosion and some form of casing as protection
against early damage by fire where regulations so require. Cold-formed steel sections are
extensively used in the manufacture of roof trusses and lattice beams and frames. The
fabricated sections are protected with a galvanised coating where practical. Cold-formed,
pressed steel sections are much used for floor and roof decking for the floors of framed
buildings and also for metal doors, frames and metal trim such as skirtings.
5.4 Structural steel frames
The earliest structural steel frame was erected in Chicago in 1883 for the Home Insurance
building. A skeleton of steel columns and beams carried the whole of the load of floors,
and solid masonry or brick walls were used for weather protection and appearance. Since
then the steel frame has been one of the principal methods of constructing multi-storey
buildings (Photograph 5.1).