What is the main operational difference between fixed and expansion bearings in a bridge?

The main operational difference between fixed and expansion bearings in a bridge is that fixed bearings restrain movement in all directions, while expansion bearings allow for longitudinal movement of the bridge deck. Fixed bearings, also known as pinned bearings, are designed to prevent both horizontal and vertical movement at their location, providing stability and resisting forces in all directions. Expansion bearings, on the other hand, are designed to accommodate the thermal expansion and contraction of the bridge deck by allowing it to move longitudinally, parallel to the bridge's length. This movement prevents the build-up of excessive stresses in the bridge structure due to temperature changes. Both types of bearings support the vertical loads from the bridge deck, but their ability to accommodate movement is what distinguishes them.