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Steel Designers' Manual - 6th Edition (2003)
928 Tolerances
31.4.3.5 Smoothness
In the light of the findings of the flatness tests, it can be appreciated that if absolute
local flatness is not in fact needed, absolute smoothness is irrelevant also.
The best description of the smoothness that is needed is the smoothness of a
surface produced by a good-quality modern saw in proper working order. This
degree of smoothness is indeed very good.
Where sawing is not possible, ending machines (i.e. special end-milling machines)
can be used for correcting the squareness (or flatness) of ends of built-up (fabricated)
columns, such as box columns or other welded-up constructions.Where baseplates
are not flat and are too thick to be pressed flat, either they are milled locally
in the contact zone or else planing machines are used.
However, it cannot be overemphasized that the normal preparation for a rolled
section column required to transmit compression by full contact in bearing is by saw
cutting square to the axis of the member.
It is, of course, unnecessary to flatten the undersides of baseplates supported on
concrete foundations.
31.4.4 Other compression joints
Compression joints, transferring compression through end plates in simple bearing,
also need to have their ends square to the axis. If, after the members have been
firmly drawn together, a gap remains which would introduce eccentricity into the
joint, it should be skimmed.
31.4.5 Lap joints
Steel packs should be used where necessary to limit the maximum step between
adjacent surfaces in a lap joint (see Fig. 31.3) to 2 mm with ordinary bolts or 1 mm
(before tightening the bolts) where preloaded HSFG bolts are used.
H-H
Fig. 31.3 Maximum step between adjacent surfaces
4