Fig. 3.15 Hot-rolled steel sections. These mass-produced
elements are formed by a rolling process which results in
the characteristic parallel-sided arrangement with constant
cross-section. The thickness of the metal is relatively high
and results in correspondingly high load-carrying capacity.
producing only one cross-section-, some can be
adjusted within narrow limits to produce a
small range of cross-section weights within a
particular overall cross-section size (serial
size).
Steel manufacturers produce a limited range
of cross-sectional shapes by this process; the
principal ones are as follows:
I-sections
These are typified by the UK universal beam
series (Table 3.2); they have cross-sectional
shapes with a high second moment of area^9
about one principal axis and a much lower
second moment of area about the other princi-
pal axis. They are intended for use as beam
elements, which are normally subjected to
bending in one plane only. The finishing rollers
which are used to produce universal beams
9 See Macdonald, Structure and Architecture, Appendix 2, for
an explanation of this term.consist of a complex arrangement of two pairs
of rollers, one with horizontal and one with
vertical axes. This allows the thickness of the
flanges and webs to be varied within small
limits and accounts for the different weights of
section which are produced within each serial
size.H-sections
These are typified by the UK universal column
range (Table 3.3) and have more-or-less the
same second moment of area about both
principal axes. They are designed to resist axial
compression, which requires a cross-section
with more-or-less equal rigidity about all axes
to prevent buckling.Channel and angle sections
These are much smaller than the I and H
ranges and are used mainly for secondary
elements, such as purlins (secondary elements
in roof structures), and for the sub-elements of
steel trusses and built-up cross-sections.Hollow sections
These ranges are produced in circular, square
and rectangular form. The lighter sections are
used mainly for trusses and space frames.
Heavier sections are used as beams and
columns.
Flat plate
This is available in thicknesses from 5 mm to
65 mm and is used for elements with built-up
cross-sections (plate girders and compound
beams) and for jointing components.
Strip
This is produced in the form of thin flat sheet.
Its principal use in structural engineering is as
the raw material for cold-formed sections.
Wire, rope and cable
Steel wire is manufactured by drawing solid
bar through a series of small diameter dies
accompanied by heat treatment. Wires (usually
around 50) are spun into strands. A rope
consists of a number of strands (usually 6)
spun around a core of steel or fibre. A cable is
made up of six ropes. The largest ropes are
100 mm in diameter and cables may be up to
250 mm in diameter.Steel structures65