Which statement best describes the function and common types of bridge deck bearings and how they accommodate movement?

• A. Bearings only carry vertical load and prevent any horizontal movement.
• B. Bearings primarily transfer torsional moments between deck and girders.
• C. Bearings transmit vertical reactions while allowing horizontal movement and rotation; common types are elastomeric, pot (spherical), rocker, and sliding/pad.
• D. Bearings are used to connect girders together and carry all bending moments.

Answer: (C)

Bearings are there to carry the vertical load from the deck into the supports while allowing the deck to move horizontally and rotate slightly. This movement comes from temperature changes, live loads, uneven settlements, and seismic effects, and without space for this movement the structure would develop large stresses.

Elastomeric bearings use bonded rubber pads between steel plates. The rubber compresses and shears to take the vertical load while permitting horizontal movement and rotation, giving a degree of flexibility without transmitting big horizontal forces.

Pot (spherical) bearings have a steel ball seated in a pot. The spherical contact allows the deck to rotate and move horizontally relative to the pier, while still carrying vertical reactions.

Rocker bearings consist of steel plates on a curved rocker element, enabling rotation and limited horizontal translation as the deck shifts.

Sliding or pad bearings provide a low-friction sliding interface (often PTFE-based) that lets the bearing slide horizontally under vertical load, with rotation accommodated by the pivoting of the bearing assembly.

In short, bearings transmit vertical reactions and accommodate horizontal movement and rotation; they are not meant to carry bending moments or torsional loads between deck and girders, which is why the described movement-allowing and vertical-load-transfer behavior is the correct description.