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Steel Designers' Manual - 6th Edition (2003)
Economy is generally linked to the use of standard rolled sections but, with the
advent of automated cutting and welding equipment, special fabricated sections are
becoming economic if there is sufficient repetition.
The development of efficient, automated, cold-sawing techniques and punching
and drilling machines has led to the fabrication of building frameworks with bolted
assemblies. Welded connections involve a greater amount of handling in the fabrication
shop, with consequent increases in labour and cost.
Site-welded connections require special access, weather protection, inspection
and temporary erection supports. By comparison, on-site bolted connections enable
the components to be erected rapidly and simply into the frame and require no
further handling.
The total weight of steel used in continuous frames is less than in semicontinuous
or simple frames, but the connections for continuous frames are more
complex and costly to fabricate and erect. On balance, the cost of a continuous frame
structure is greater, but there may be other considerations which offset this cost
differential. For example, in general the overall structural depth of continuous
frames is less.This may reduce the height of the building or improve the distribution
of building services, both of which could reduce the overall cost of the building.
Corrosion protection to internal building elements is an expensive and timeconsuming
activity. Experience has shown that it is unnecessary for most internal
locations and consequently only steelwork in risk areas should require any protection.
Factory-applied coatings of intumescent fire protection can be cost-effective
and time-saving by removing the operation from the critical path.
Construction
Factors influencing choice of form 55
Fig. 2.10 Structural costs: (a) economic and (b) uneconomic layouts
A period of around 8–12 weeks is usual between placing a steel order and the arrival
of the first steel components on site. Site preparation and foundation construction
generally take a similar or longer period (see Fig. 2.11). Hence, by progressing fabrication
in parallel with site preparation, significant on-site construction time may
be saved, as commencement of shop fabrication is equivalent to start-on-site for an
in situ concrete-framed building. By manufacturing the frame in a factory, the risks