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Steel Designers' Manual - 6th Edition (2003)
854 Bearings and joints
capability (possibly more than a continuous structure could accommodate) to
remove it.
In bearings subjected to dynamic loadings such as machine foundations, it is necessary
to ensure that the fixings are vibration-proof.
28.2.3.3 Effect on the structure
The elements of the structure above and below the bearing are affected by the type
of bearing, which can be classified as:
(1) fixed – not permitting movement in any horizontal direction,
(2) guided – movement, constrained by guides of some form, to be in one horizontal
direction only,
(3) free – movement permitted in all horizontal directions,
(4) elastomeric, which may be laminated or not. These bearings can be ‘fixed’ by
means of steel dowels passing through them but are more often used ‘free’ in
all directions and their capability to generate forces when shearing takes place
is utilized to withstand horizontal loadings. If the whole structure is supported
on such bearings it effectively ‘floats’, with all horizontal loads shared by all
bearings. (See also section 28.2.4.2.)
If the bearings are fixed or guided, the neighbouring structure must be designed
for the forces arising from the restraints. Even when the bearing is free in a particular
direction and movement is permitted, some forces are developed – either from
friction effects at the movement interfaces of a sliding mechanical bearing, or from
shearing deformation in the case of an elastomeric bearing (see Fig. 28.7(a)).
In addition to forces developed laterally, the effects of the eccentricities produced
by the movement must be allowed for, and also the rotation capability of the bearing
in the transverse direction (see Figs 28.7(b), (c) and (d)). It is possible to control
the extent of the additional eccentricity effects on a steel superstructure by use of
a sliding bearing inverted which transfers the eccentricity to the substructure, where
it may be more easily accommodated. In this case however care should be taken to
protect the sliding surfaces against falling dust, debris, etc. by use of a flexible skirt
enclosure.
28.2.3.4 Installation
Bearings must be correctly installed into the structure. The procedure will depend
upon the form of the structure above and below the bearing, and the type of bearing,
but in general care should be taken not to load the bearing significantly before
bedding materials between the bearing and the structure have fully cured, or to load