Steel Construction Vol 40 No 1 - Architecturally Exposed Steel | Page 29

SAISC SUBSIDIARIES: ASTPM

STRUCTURAL HOLLOW SECTIONS
an attractive alternative for your structures
By Franco Mordini, Committee Member ASTPM

Structural Hollow Section remains very
popular especially for aesthetically pleasing
structures, bracing members and slender
compression members that are typically
used for elevated canopies. In many other
cases the structural tube remains the
preferred material of choice for
applications where tube is subjected to biaxial bending and high compression loads.
Examples are frames to support industrial
equipment, highly loaded mechanical
applications, poles, satellite dishes etc.
Tubular steel continues to be the material
of choice in many architectural
applications such as atriums, facades,
pedestrian bridges, trusses and other
exposed steelwork. Recent successful
examples of these structures are the
Standard Bank Head office in Rosebank,
Multichoice City (DSTV) head office in
Randburg, Sandton City refurbishment, the
new elevated bridge/ walkway at
Kirstenbosch garden etc. where the clean

Tubular steel continues to be popular in many architectural applications
such as atriums, facades, pedestrian bridges, trusses and other exposed steelwork.
lines and slender tubular sections make
these structures very efficient and
aesthetically pleasing.
A suggestion to specifiers: Keep to standard
sizes recommended by the SAISC’s Red
Book. The section sizes are chosen to come
directly out of a mother tube without the
need for further cold working which, when
badly done, has led to cracking of corners of
squares and rectangles. In most cases this
will avoid unnecessary costs and provide the
users with good quality products. It is always
recommended to check availability with the
tube manufacturers to ensure timeous
execution of the fabrication.
Where quantities are high enough for a
specific product (by size), mills can run
special lengths that will avoid the high cost
of off-cuts or shop welded splices to
reduce waste. For high quantities of same
sizes it is key to discuss other alternatives
with the tube manufacturers. In order to

minimise costs, where possible, rationalise
the design by reducing number of different
sizes specified. Try to avoid same
dimensional sizes with different
thicknesses as they could in error be
interchanged during the fabrication
process leading to possible failure.
The standard grade of steel for structural
tube remains 355 (guaranteed minimum
yield strength of the steel). The grade of 355
is readily available in circular hollow sections
(CHS - Rounds) up to 356mm diameter and
also in derivatives in squares and rectangles
formed from these circular hollow sections.
Some South African producers will identify
the material as such on the tube. If in doubt
request a material certificate to ensure that
the correct grade of steel has been supplied.
Where possible avoid the use of
commercial quality grade (generally 60
diameter and smaller with 2.5mm wall
thickness and thinner but also some

imported sections) and use a grade with
guaranteed properties or at the very least
with controlled chemistry.
Another positive development in tubular
fabrication is the availability of various tube
laser services in the industry. These
specialised machines make tubular
fabrication easy. In many instances of CHS to
CHS connections, development of the end
cuts can be very tricky to produce. For these
specialised machines it is a walk in the park.
The primary benefits are high accuracy,
speed and repeatability. The analogy of
cutting through steel like a knife through the
proverbial butter holds very true for this
service. Check what your friendly tube and
pipe maker can offer you in this regard.
In order to offer your customer attractive
cost effective solutions always consider the
benefits of tube when designing and
building your structures. You may well be
pleasantly surprised.
Steel Construction Vol. 40 No. 1 2016

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