During the installation of bridge bearings the size of the upper plates is reduced to save the material costs. This process is known as preset.
Generally the upper bearing plate comprises of the following components:
- Length of bearing
- 2 x irreversible movement.
- 2 x reversible movement.
The bearing initially is placed right in the middle point of the upper bearing plate. No directional effects of irreversible movement is considered. But since the irreversible movement usually takes place in one direction only the displaced direction is placed away from the midpoint. In such cases the length of the upper plate is equal to the length of the length of the bearing + irreversible movement + 2 x reversible movement.
