When bridges aren’t suspended, they sit on piers or abutments. But between the bridge deck and the pier sits this tiny little contraption called a bridge bearing. Think of bridge bearings like shock absorbers on your car or bike. When there is lateral or vertical movement, the shocks absorb most of the impact so that your bike frame isn’t destroyed and your ride is more comfortable. The same concept applies to bridges – bearings absorb lateral and vertical forces so that the bridge frame (steel stringers and concrete piers) doesn’t crack and vibrations on the deck are minimized.
Older bridge bearings used a “rocker” to control movement on the deck.
But newer bridge bearings utilize vulcanized elastomeric pads – “rubber” pads reinforced with steel sheeted plates that are designed to take vertical and horizontal loads. They’re specially engineered for “bulge factors” and temperature so that the vulcanized rubber doesn’t shear.
When bridge inspectors find corrosion on older bearings (like the “rocker” types), bridge owners find low-bid contractors to replace them. One of the ways to replace these bearings is by using pneumatic jacks to temporarily lift the bridge deck so that the older bearing can be removed safely under live loads.