Role of bridge bearings
Bridge bearings are connections that transfer forces between the bridge superstructure (deck) and the substructures (pier, viaduct or abutment). Temperature difference such as increase in temperature causes the bridge structure to expand/elongate along its length, thereby causing movements in the bridge structure and vice versa, decrease in temperature causes the bridge to reduce in length. During seismic occurrence the bridge foundations take up forces and transfer to the entire bridge structure causing rigorous vibration and movements of the bridge. The bridge structure also vibrates and moves in reaction to forces from heavy traffic (trains, vehicles etc.). Creep, shrinkage and elastic deformation all result in movement of the bridge structure.
Functions of bridge bearings
- Connects the bridge superstructure to the substructure.
- Accommodates and transfers dynamic forces and vibrations without causing wear or destruction to the substructure.
- Enables movement (translational, vertical or rotational) of the bridge structure in reactions to loads.
- Controls the movement in bridge structure; direction and degree wise.
- Ensures that deformations, which occur in the superstructure of the bridge, do not lead to large forces and moments in the substructure.
- Can be used to adjust the dynamic properties of the bridge.
- Bearings reduce shear on the head of the piers, viaducts or abutments.
- Recent bridge bearings are designed to act as seismic protectors that arrest and dissipate energy during earthquakes and other seismic activities.
Classification of Structural Bearings
a) According to support principle
- Fixed or clamped bearing; permits rotation but no transverse or longitudinal movement
- Hinge or pin; permits rotational movement while at the same time preventing longitudinal movement
- Movable bearing; permits both rotational and translational movements
- Guided bearing; permits only translational movements
b) According to material
- Steel bearing
- Rocker/Linear bearing
- Roller bearing
- Sliding plate bearing
- Combined roller and rocker bearing
- Rubber and combined bearing
- Laminated elastomeric bearing
- Plain elastomeric bearing
- Lead rubber bearing
c) According to design
- Pot bearings
- Spherical bearings
- Elastomeric bearings
- Disc bearings
- ILM (incremental launch) bearings
- Lifting and measuring bearings
- Deformation bearings
- Special bearings
d) Seismic isolation bearings
- Friction pendulum bearings
- Lead rubber bearings
- High damping rubber bearings
Structural Bearings Application
Provides up to 4 hours rating on structural steel columns, beams, joists, trusses, floor and roof deck assemblies in commercial construction. Designed for use to exceed the 430 psf (20.6 kpa) requirement for high rise construction.
The durable surface and Portland cement based formulation of the product make it well suited for application in areas which may be subjected to high levels of abuse and such as mechanical rooms, perimeter steel structures, and parking garages.