Nearly all large structures that are made out of concrete and steel suffer from movement caused by external means. Some sort of allowance has to be made in the design and construction of such structures for:
Thermal expansion and contraction
Permanent creep and shrinkage
Post tensioning strain
Live load deflections
each of which can cause a build up of dangerous stresses in materials if not allowed for. One of the ways of doing this that is found in most bridges is the use of line rocker bearings. The main feature of line rocker bearings is that they can provide relatively large amounts of rotation about the transverse axis of a bridge while at the same tome restricting the rotation of the structure about its longitudinal axis.
Line rocker bearings are relatively narrow in the longitudinal direction and wide in the transverse direction. In other words it permits movement similar to that of a rocking chair. This feature makes them particularly useful for cast beam type constructions because of their intrinsic transverse stability during erection. Bearing Technologies’ range of line rocker bearings make use of the unique low-friction sliding properties of polytetrafluoroethylene (PTFE) and a simple line contact rocker for rotation. The coefficient of friction of this material is as low as 0.01, and is lowest at higher pressures, making it ideal for structural bearings. At the same time side restraints are comprised of a composite material of PTFE impregnated into a metallic structure. If you would like any further information on line rocker bearings please call us at +27 11 605 2434