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Steel Designers' Manual - 6th Edition (2003)
known and whose loading has been evaluated and is considered separately as dead
load. Further advice on both these problems is given in section 3.3.2.
The structural steelwork designer must take an open-minded approach to the
loading information. It must be appreciated that early information from the plant
designers will represent only estimated loadings, and an uncertainty allowance may
well already be included in the values supplied, so that further allowances may be
unnecessary. However, it frequently turns out that many secondary plant items are
added at a later stage in the information process. The loadings from these should
be satisfactorily absorbed into an initial uniformly distributed loading allowance
provided that a logical scheme for dealing with loading is established at an early
stage.
3.3.2 Process plant and equipment
Loading 115
The most important advice to the structural designer of steelwork for an industrial
purpose is to ensure reasonable familiarity with the entire process or operation
involved. Existing facilities can be visited, and the plant designers and operators will
normally be more than willing to give a briefing which provides the opportunity to
describe the form of structure envisaged to the plant designer at an early stage so
avoiding later misunderstandings.
Some attempt should also be made to understand the jargon of the industry in
question in order to gain the confidence of the plant designers and to allow effective
intercommunication.
Particular examples of structural requirements which are not easily recognized as
important by plant designers, and which should therefore be fully explained, are as
follows:
(1) The physical space requirements of bracing members and the fact that they
cannot be moved locally to give clearances.
(2) The actual size of finished steelwork taking account of splice plates, bolt heads
and fittings projecting from the section sizes noted on drawings.
(3) The fact that a steel structure is not 100% stiff and that all loads cause
deflections.
(4) The fact that a steel structure may interact with a dynamic loading and that
dynamic overload multipliers calculated or allowed on the assumption of a fully
rigid or infinite mass support are not always appropriate.
The basis of loading information for plant and equipment must be critically examined.
Frequently loadings are given as a single all-up value, the components of which
may not all act together or have only a very small probability of so doing. Alternatively,
the maximum loadings may represent a peak testing condition or a fault, overload
condition, whereas normal operating loadings may be considerably less in
value. Worthwhile and justifiable savings in steelwork can be made if a statistically