In the majority of large concrete and steel structures an allowance has to be made for relevant movement between structural components in order to steer clear of the possible build up of potentially dangerous stresses. There can be a number of reasons for this movement, including:

•  Thermal expansion and contraction
•  Permanent creep and shrinkage
•  Post tensioning strain
•  Live load deflections (from wind or traffic)
•  Earth movement

It is usually desirable to minimise the resistance forces and moments resulting from these movements and this is the primary function of structural bearings. This allowance for movement is achieved by the utilization of pot bearings, which, depending on their design, may allow for longitudinal movements, constrain transversal movements while at the same time bearing horizontal transverse loads.

Pot bearings allow rotational motions by elastic deformation of the enclosed rubber part. They also have a polytetrafluoroethylene (PTFE) molded plate as a slide on the bearing plate. The upper shoe moves on this slide to provide for horizontal motions. The advantages of pot bearings are freedom from vertical contraction and low cost. These features have been revaluated, and pot bearings have been increasingly utilized as terminal supports for continuous girders, although their use declined temporarily after the 1995 Great Hanshin-Awaji Earthquake.

A typical pot bearing may consist of:

A pot steel ring and base plate

•  An elastomer pad.
•  An internal sealing ring – often a double gasket brass ring
•  A steel piston
•  An external sealing ring – often of neoprene
•  A steel guide
•  A layer of PTFE often with silicone grease
•  A top plate of steel lined underneath with polished stainless steel

The whole device may be enclosed in an anti-dust skirt to prevent dust from getting to the sliding parts.