What part of the bridge permits longitudinal expansion and contraction?

The part of the bridge that permits longitudinal expansion and contraction is the expansion joint. Expansion joints are critical components that allow for movement in the structure caused by changes in temperature, traffic load, and other factors. They are designed to absorb the stresses caused by thermal expansion and contraction, ensuring the structural integrity of the bridge while preventing damage to other components.

The deck, while an essential part of the bridge, does not facilitate the necessary movement; instead, it serves as the surface for vehicles and pedestrians. The bearing supports and transfers the load from the superstructure to the substructure but does not allow for the necessary movement associated with thermal changes. The substructure, which includes the piers and abutments, primarily provides support for the bridge above and does not facilitate expansion and contraction.

Understanding the role of the expansion joint is crucial in bridge design and maintenance, as proper functioning of this component is necessary for the longevity and safety of the bridge.