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Steel Designers' Manual - 6th Edition (2003)
922 Tolerances
The most obvious case is a splice between two components of the same nominal
size, where packs may be needed before the flange splice plates fit properly, unless
the components are carefully matched. Similarly variations in the depths of adjacent
crane girders or runway beams may necessitate the provision of packs, unless
the members are carefully matched.
Less obviously, if the sizes of columns vary, the lengths of beams connected
between them will need some form of adjustment, even if the columns are accurately
located and the beams are exactly to length.
31.3.2 Attachment of non-structural components
It is good practice to ensure that all other items attached to the steel frame have
adequate provision for adjustment in their fixings to cater for the effects of all steelwork
tolerances, plus an allowance for deviations in their own dimensions. Where
necessary, further allowances may be needed to cater for structural movements
under load and for differential expansion due to temperature changes.
Where possible, the number of fixing points should be limited to three or four,
only one of which should be positive with all the others having slotted holes or other
means of adjustment.
31.3.3 Building envelope
It must be appreciated that erection tolerances, including variation in the position
of the site grid lines, will affect the exact location of the external building envelope
relative to other buildings or to site boundaries, and there may be legal constraints
to be respected which will have to be taken into account at the planning and preliminary
stages of design.
These effects also need to be taken into account where a building is intended to
have provision for future extension or where the project is an extension of an existing
building, in which case deviations in the actual dimensions have to be catered
for at the interface.
In the case of tall multi-storey buildings, the building envelope deviates increasingly
with height compared to the location at ground level, even though permitted
deviations for column lean generally reduce with height. Unless there are step-backs
or other features with a similar effect, it may be necessary to impose particular tolerance
limits on the outward deviations of the columns.