Puget Sound Link Light Rail, Seattle, Washington.
Since their US introduction in the 1950’s, elastomeric bearing pads have become the standard for both steel and concrete bridge structures throughout North America. They are reliable, inexpensive, and maintenance-free with a service life that typically exceeds that of the bridge superstructure itself.
Simply put, the bearing transfers vertical loads from the superstructure to the substructure while allowing limited horizontal movement (for thermal expansion and contraction of the bridge’s structural girders), as well as rotational movement of the supported members.
In the US, most bearing pads are made of either natural rubber or polychloroprene (Neoprene). Both of these compounds have been time-proven over several decades. With the addition of internal steel reinforcement layers, the load capacity of the bearing increases dramatically. Bridge design engineers can specify the size and configuration of a bearing to accommodate the specific load, shear, and rotational requirements at each point.
Bearings with a large number of steel shims relative to the overall volume of rubber can handle higher loads and shear forces. By contrast, bearings with wider spacing of the steel shims can provide excellent vibration isolation characteristics, and are often used in theaters and concert halls. By manipulating a small number of variables, engineers can design an elastomeric bearing to suit most any application.