In this structure, the culvert material itself provides the needed stiffness to resist other loads.

• A. Frame Culverts
• B. Cast-in-place Concrete
• C. Embankment
• D. Rigid Culvert

Answer: (D)

The concept being tested is how stiffness to resist loads is provided by the culvert structure itself. A rigid culvert is designed so that the culvert wall and cross-section are stiff enough to carry the vertical and lateral loads from backfill and traffic without needing the surrounding soil or separate framing to provide most of that support. In this type, the culvert acts as a solid, continuous structure—often a reinforced concrete box or other rigid form—that distributes loads directly to its supports.

This differs from other culvert types where stiffness comes mainly from outside influence: embankment relies on the surrounding soil to carry and distribute loads; frame culverts depend on frames or arches to transfer loads to the ground; and cast-in-place concrete refers to the material and construction method, not the structural behavior by itself. So when the statement says the culvert material itself provides the needed stiffness to resist other loads, it points to the rigid culvert design where the culvert’s own rigidity handles the load transfer.