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Steel Designers' Manual - 6th Edition (2003)
918 Tolerances
Table 31.1 Reasons for specifying tolerances
Structural safety Dimensions (particularly of cross-sections, straightness, etc.) associated
with structural resistance and safety of the structure.
Assembly requirements Tolerances necessary to enable fabricated parts to be put together.
Fit-up Requirements for fixing non-structural components, such as cladding
panels, to the structure.
Interference Tolerances to ensure that the structure does not foul with walls, door or
window openings or service runs, etc.
Clearances Clearances necessary between structures and moving parts, such as
overhead travelling cranes, elevators, etc. or for rail tracks, and also
between the structure and fixed or moving plant items.
Site boundaries Boundaries of sites to be respected for legal reasons. Besides plan
position, this can include limits on the inclination of outer faces of tall
buildings.
Serviceability Floors must be sufficiently flat and even, and crane gantry tracks etc.
must be accurately aligned, to enable the structure to fulfil its function.
Appearance The appearance of a building may impose limits on verticality,
straightness, flatness and alignment, though generally the tolerance limits
required for other reasons will already be sufficient.
Table. 31.2 Definitions – deviations and tolerances
Deviation The difference between a specified value and the actual measured value,
expressed vectorially (i.e. as a positive or negative value).
Permitted deviation The vectorial limit specified for a particular deviation.
Tolerance range The sum of the absolute values of the permitted deviations each side of a
specified value.
Tolerance limits The permitted deviations each side of a specified value, e.g. ±3.5 mm or
+5 mm -0 mm.
Table 31.3 Classes of tolerances
Normal tolerances Those which are generally necessary for all buildings. They include those
normally required for structural safety, together with normal structural
assembly tolerances.
Particular tolerances Tolerances which are closer than normal tolerances, but which apply only to
certain components or only to certain dimensions. They may be necessary
in specific cases for reasons of fit-up or interference or in order to respect
clearances or boundaries.
Special tolerances Tolerances which are closer than normal tolerances, and which apply to a
complete structure or project. They may be necessary in specific cases for
reasons of serviceability or appearance, or possibly for special structural
reasons (such as dynamic or cyclic loading or critical design criteria), or for
special assembly requirements (such as interchangeability or speed of
assembly).