Which bridge type uses triangular truss units and is among the oldest modern bridge designs?

• A. Arch Bridge
• B. Suspension Bridge
• C. Truss Bridge
• D. Cantilever Bridge

Answer: (C)

Triangular truss units provide a rigid, lightweight framework because a triangle maintains its shape unless a side length changes, so loads are carried mainly by axial forces in the members rather than bending. This makes truss bridges highly efficient for spanning distances with less material. The triangular lattice distributes load through interconnected triangles, giving stability and the ability to use relatively slender members.

This approach was adopted early in metal bridge construction, making truss bridges among the oldest modern bridge designs. An arch bridge relies on a curved arch to push forces into the supports, not on a lattice of triangles. A suspension bridge transfers loads mainly through cables in tension, with a deck hung from towers rather than triangulated truss members. A cantilever bridge uses projecting arms that balance loads, and while some variants may include trusses, they aren’t defined by triangular truss units the way a truss bridge is.