Which component rests directly on top of the cap to provide support?

The component that rests directly on top of the cap to provide support is the beam seats. Beam seats are specifically designed to hold and support the beams of a bridge or structure at the point where they rest on the cap. The cap itself is a structural element located on top of the columns or piers that carries the loads above it and distributes them effectively.

In bridge construction, beams transfer loads from the deck to the cap. For the structure to remain stable and effective, the beam seats ensure that the beams are properly positioned and secured atop the cap, allowing for the efficient load transfer from the beams down to the supporting structures below. This relationship is crucial for the overall integrity and stability of any bridge or elevated structure.

Other components mentioned in the choices have different roles. For instance, the deck is the surface of the bridge where traffic travels, piers provide vertical support for the structure but do not rest on the cap, and struts typically serve to resist compression and may be part of the bracing system, none of which directly rest on the cap as a means of support for the beams.