Civil Engineering Reference
In-Depth Information
18.4.3 Industry guidance
Traditionally UK codes provided a mix of design and prac-
tice guidance. As Eurocode use becomes more common, good
practice guidance produced by the steel industry will be relied
upon. Not only in the UK but also worldwide there is an ongoing
effort to encourage an orderly definition of roles, for example,
in the advice from CASE reproduced in Section 18.1.4 above.
In 1995/7, a 'Eureka' project (SCI, 1995 and 1997) aimed to
raise awareness of the influence design decisions have on the
overall buildability and cost of a steel framed building and how
to avoid conflict in the design and construction process, redu-
cing the likelihood of expensive remedial site work. Six points
were identified that the designer 'must address':
Decisions on framing, beam and column section sizes are
driven by the physical material, its shape and building inter-
face details, manufacture, transport and joining concepts. It is
useful to contrast many modern details with the elegance of
the majority of early iron and steel structures. Regular com-
plaints from steelwork contractors about the construction dif-
ficulties leading on from designers' less than practical designs
are often linked back to a focus on computer analysis and the
'minimum weight' option in software. In conceiving a steel
design, the designer needs to have made conscious decisions
on the buildability aspects of the design. Practical experience
and buildability advice are often not readily accessible when
a structural concept is developed. Adoption of some simple
approaches to design/detailing and communication and obser-
vation of steelwork construction improves the chances of suc-
cessful steel construction and photographs of the good and bad
are provided below.
As the concept gets nearer to validation as acceptable in
all aspects of design, iteration occurs in the virtuous circle of
design, analysis, and detail design.
Recognise the complexity of the design process.
■
Establish an appropriate design team.
■
■
Agree information and programme.
Coordinate contributions.
■
Manage the interfaces.
■
■
Control design development.
18.5.1 Design, analysis, detail design - implementation
Common practice in steel construction is for the designer/over-
all designer to conceive the design and the steelwork contractor
to detail and manufacture the structural 'joining' details, i.e. the
main structural connections. In some building forms, notably
single-storey buildings there may only be a steelwork design
and construct contractor responsible for overall design. In this
case the contractor is responsible for overall stability. By virtue
of steel material sections being high strength and dimensionally
small in relation to concrete, by necessity the connections of
an assembly of beams and columns are compact. Their config-
uration and behaviour under load directly influences analysis
modelling of member assemblies.
Whatever the structural material, whether formed on site or
manufactured and assembled on site, at the initial stage there
is the idea, the concept. It may use bespoke and/or proprietary
components but whatever the concept, 'joining' details are an
intrinsic part of the concept. Some structural detail configura-
tions will be essential for the framework to behave as predicted
by mathematical models. There are usually 'key' details that
drive concept decisions.
Examples are in this chapter include:
There is no substitute for the steelwork designer to prepare
a project-specific interpretation addressing the duties sum-
marised above, perhaps by way of a project execution plan
or notes. In summary, the designer must address commercial
requirements to achieve a successful design in steelwork.
18.5 Design, analysis, detail design -
a virtuous circle
Perhaps a way to describe the complex transition of concept
through to construction is in terms of a 'virtuous circle' of
design, analysis and detail design. Detail considerations pre-
cede analysis and involve key interface requirements on the
structure. Architectural, building services and secondary struc-
tural details are reflected in the way the model is imagined and
analysed, whether by computer or traditional hand-calculated
model approximations. Analysis and modelling tools are in
general use and guidance on 3D framing arrangements and
standard cross-sections for floor, wall and roof constructions
are widely available.
However, modern steel construction practice tends to com-
partmentalise steelwork contractors and consultant designers.
Steel detailing neglected by consultant designers and left to
the steelwork contractor to detail for manufacture and erection,
means that member arrangements may be derived that do not
exploit the geometrical characteristics of steel material to bene-
fit fabrication and buildability on site. Made in a factory, using
sections delivered from a steel mill and erected at a probable
rate of 80-100 tonnes a week a modest frame can be erected
in a month. The designer may go to site but it is likely that the
designer has never been inside a fabrication shop and is even
less likely to have seen the manufacture and rolling process.
Paired 152 UC providing flush internal wall finishes by embed-
■
ding in walls (see
Figures 18.4
,
18.5
,
18.6
,
18.8
and
18.9
). The net
to gross floor areas were not compromised by structural 'design
development' in frame or cladding connections.
Internal exposed soffits that dictate slab and frame construction
■
with no down stand beams to meet M&E designer's wish for clear
soffits (see
Figures 18.7(a,b)
,
18.9
,
18.10(a,b)
, and
18.11
).
Down stand beams with 50% web material removed for M&E
■
services (see
Figure 18.6
).
