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Steel Designers' Manual - 6th Edition (2003)
850 Bearings and joints
Fig. 28.4 Two types of elastomeric bearing: (a) fixed, (b) free
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bonded. The characteristics of the bearings can be varied considerably by alteration
of the size, shape and disposition of the layers as well as the usual parameters
of bearing plan area and thickness. Generally, these bearings are either
‘fixed’ for translation by means of a steel dowel passing through the bearing
layers (Fig. 28.4(a)) or ‘free’ bearings which permit translation and rotation by
deformation of the bearing (see Fig. 28.4(b)). This type of bearing is capable of
carrying quite substantial loadings and movements and has the benefit of being
cheaper than mechanical bearings.
28.2.2.3 Mechanical bearings
(1) Roller (Fig. 28.5(a)). The earlier and more traditional forms of bearing comprised
single or multiple steel rollers sandwiched between upper and lower steel
plates. Single rollers will allow for longitudinal movement and rotation about
the axis of the roller, while at the same time carrying comparatively high
vertical loads, hut will not permit transverse rotation or movement. Bearings of
very large capacity have been produced by use of special alloy steels to form
the contact surfaces. Note that bearings which utilize multiple rollers will not
allow rotation about an axis parallel to the axis of the rollers. Rollers are sometimes
used enclosed in an oil bath or grease box to exclude deleterious matter.
Other forms of bearing have, to a large extent, supplanted the use of rollers for
the most common applications.
(2) Rocker (Fig. 28.5(b)). Rocker bearings will not permit translational movement.
The bearings may be cylindrical or spherical on one surface with the other
surface flat or curved. In the cylindrical form there is no provision for transverse
rotation, which may have consequences for design of the structures above
and below the unit. Rocker bearings usually incorporate a pin or shear key
between the two surfaces to maintain relative position.