Bridge bearings are used to transfer forces from the deck to the foundation without damage. They are found in bridges, roadways, docks, airports, and other structures. There are three basic forms of bridge support: elastomeric, plain, and roller bearings. Each type works best with a certain type of strength and is determined by the expected load and usage of the facility.
A bridge bearing is a construction method that allows a bridge to transfer forces from the deck to the foundation without damage. These bearings are used in bridges, but similar layers can be found on roadways, docks, airports, and other structures where large, heavy objects must operate safely. Basically, the surface of the structure and the foundation of the structure have a layer between them that absorbs and transfers energy. When the surface is under pressure or hit by a large force, it will transfer the energy into the bearing layer of the bridge, which then sends it to the foundation to dissipate.
Bridge bearing is usually easy to find when looking at the structure of a bridge. Most bridges will have a solid road surface and a series of supports underneath it. Between these two sections are the bearings. These bearings will have a wide range of appearances, but are usually disproportionately small, much smaller than the road surface and usually smaller than the mount it sits on.
The small size of the bearing allows the forces of the road deck to converge into a very small point. When that energy descends into the foundation, it travels as a very compact line of force. Since only a small part of the foundation moves the energy, the rest of the system supports it as the energy moves. This reduces the shear force on the foundation and makes failure during transfer less likely.
There are three basic forms of bridge support but countless variations of each type. Each of these shapes works best with a certain type of strength, so it’s not uncommon to find a single structure with more than one style. Typically, the type and size of a bearing is determined by the expected load and usage of the facility.
An elastomeric bearing is essentially a layer of strong elastic polymer. These layers are great at absorbing energy and resisting movement. They are the most general of bridge bearings and are common in nearly every major structure. On the other hand, they deny very little energy.
Plain bearings are made using two metal plates with a low friction polymer between them. These structures do not absorb energy very well, but they almost cancel out the longitudinal forces applied to them. When energy hits the polymer layer, the plate slides, transferring the energy into motion. This drastically reduces the energy moved into the bottom plate.
Roller bearings are round ball bearings or rolling pin-shaped cylinders. These layers cancel out forces in at least two directions and, due to their thickness, absorb and transfer the remaining energy well. However, they absorb less than an elastomeric support and cancel less than a sliding bridge support.
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