Civil Engineering Reference
In-Depth Information
Figure 18.18 Structure-free floor depth adjacent to main vertical
service riser on the right, to suit large ducts emerging into ceiling
space
Figure 18.20 This truss was suspended two floors off a centre tie as
the ground floor column was omitted. Requiring minimal deflection
for compatibility with columns and too heavy for the fabricator to
make in one piece, 2 no HSFG splices were used at each end
are issues of
manufacture
,
transport
,
erection
and
connecting
on
site, a separate set of parameters to be considered. The details
are refined following mathematical validation of the adjustments
needed to the designer's structure. The process then iterates in a
'virtuous circle' of design, analysis and detail design.
18.6 Design parameters (cost, construction)
18.6.1 Overall cost
The typical cost build-up of a main frame based on standard
rolled sections would be:
Materials
30%
■
Figure 18.19
21+ m long roof beams
Steelwork contractor's detailing/design
5%
■
Fabrication
35%
■
Architectural elevations that cannot accommodate braced frames
■
Priming
8%
■
leading to a rigid frame concept.
21+ m long roof beams being transported to site with, lengths and
Delivery + erection
22%
■
■
internal exposed joints designed to be within economical transport
limits (see
Figures 18.19
and
18.21
).
Large or heavy members that need splicing in the fabrication works
Pricing by tonne is highly dependent on market conditions;
however, there are price sensitive factors that can be assumed
by the designer whatever the market conditions.
■
or on site depending on craneage.
Figure 18.20
shows a truss that
exceeded the lifting capacity of the fabrication shop cranes so
high strength friction grip (HSFG) splices were provided for site
assembly. In this case, site craneage capacity was adequate to lift
the site-assembled member to the third storey level.
Heavily serviced longer floor span buildings that have localised
18.6.2 Material cost
A factor in material selection is the use of members built up
from plate. Automated welding machinery, available in most
modern fabrication shops, means built up components are
widely available and specified with confidence. Fabsec and
Cellform beams and even the traditional castellated beam sec-
tions are available (see
Figure 18.22
).
At first glance, there is a bewildering range of rolled and fab-
ricated steel sections. In some construction markets, fabricated
sections are the norm. Where rolled sections are available, these
are likely to be the commonly used shallower sections and, if
■
concentrations of services that eliminate down stand beams adja-
cent to a primary services riser, where services congestion normally
occurs.
18.5.2 Design, analysis, detail design - final design
In summary, details are major parameters affecting engineering
decisions and, in the case of any structure made off site there
