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Structural Steel Frames 283
no stronger than the beam from which it was cut but will suffer less deflection under load.
The increase in cost due to fabrication and the reduction in weight of the beam as compared
to a solid web beam of the same depth and section justify the use of these beams for longspan,
lightly loaded beams particularly for roofs. The voids in the web of these beams are
convenient for housing runs of electrical and heating services.
Steel tubes
A range of seamless and welded seam steel tubes is manufactured for use as columns, struts
and ties. The use of these tubes as columns is limited by the difficulty of making beam
connections to a round section column. These round sections are the most efficient and
compact structural sections available and are extensively used in the fabrication of lattice
girders, columns, frames, roof decks and trusses for economy, appearance and comparative
freedom from dust traps. Connections are generally made by scribing the ends of the tube
to fit around the round sections to which they are welded. For long-span members such
as roof trusses, bolted plate connections are made at mid-span for convenience in transporting
and erecting long-span members in sections.
Hollow rectangular and square sections
Hollow rectangular and square steel sections are made from hollow round sections of steel
tube, which are heated until they are sufficiently malleable to be deformed. The heated tubes
are passed through a series of rollers, which progressively change the shape of the tube to
square or rectangular sections with rounded edges, as illustrated in Figure 5.6. To provide
different wall thicknesses, the heated tube can be gradually stretched. The advantage of these
sections is that they are ideal for use as columns as the material is uniformly disposed
around the long axis, and the square or rectangular section facilitates beam connections.
Hollow square and rectangular sections are much used as the members of lattice roof
trusses and lightly loaded framed structures with the square sections for columns and the
rectangular sections as beams. The economy in material and the neat appearance of
the sections, which with welded connections have a more elegant appearance than angle
Circular hollow sections
from 21.3 to 457 mm
outside diameter
Figure 5.6 Hollow steel sections.
Square hollow sections
from 20 × 22 to
400 × 400 mm
Rectangular hollow
sections from 50 × 30
to 450 × 250 mm