Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 211

Figure 3.43 Deformations of elastomeric bridge bearings.
cylindrical surface between which a PTFE sheet and the mating material
form a curved sliding surface. Cylindrical PTFE bearings are also used in
combination with flat sliding elements and guides to form free or guided
bearings. On the other hand, spherical PTFE bearing consist of a backing
plate with a convex spherical surface (rotational element) and a backing plate
with a concave spherical surface between which a PTFE sheet and the mat-
ing material form a curved sliding surface. Spherical bearings allow three-
dimensional movements. They are designed for very high vertical, horizon-
tal, and lateral loads and also for large rotational displacements. Like pot
bearings, they can be fixed, free sliding, or guided sliding depending on
the design. Spherical bearings have been structurally improved and designed
for use as incremental launch bearing, which is applicable for bridge con-
struction by launching system; force measuring bearing, which can be used
for measuring and monitoring forces acting on the structure electronically;
and uplift protection bearing, which can be used to accommodate high
uplift loads encountered during construction or service life of a struc-
ture. Figure 3.44 shows an example of spherical bearings.
3.11.3 Examples of Steel-Fabricated Bearings
Steel-fabricated bearings are the oldest types of bearing. The most common
types of steel bearings are the roller/rocker bearings, which may be hinged
or expansion bearings. Roller/rocker bearings can support high loads and
can be used where pot, spherical, and other high-capacity bearings cannot
be used due to limited space. Roller/rocker bearings are applicable for con-
ditions where only longitudinal movement is allowed and where transverse
movement is to be prevented. They operate by the movement of a roller/
rocker in between a sole plate and a lower bearing plate (see Figure 3.45 ). As
an example of fabricated steel hinged bearing, Figure 3.46 shows fabricated
line rocker bearings. The bearings provide a very economic solution in that
they can be supplied by the steelwork fabricator and ensure a good match
between hole positions in bearings, upper bearing plates, and girder flanges.