What is the function of cap beams in a steel multi-girder bridge?

• A. Cap beams help to distribute wind loads across deck.
• B. Cap beams do not carry any load and are only decorative.
• C. Cap beams connect girders and transfer loads to piers, helping distribute moments and provide bearing surfaces.
• D. Cap beams are used only for aesthetics.

Answer: (C)

Cap beams act as the rigid tie that binds the ends of all the girders over a pier, creating a single, continuous load path from the deck down to the piers. They collect vertical forces from the deck and girders, transfer those loads to the piers, and spread the bending moments among the connected girders. By tying the girder ends together, the cap beam helps control differential movement and keeps the girders in proper alignment, while providing a stable bearing surface for the girter ends and bearings. This makes the structure behave more like a unified frame under loads. They are not decorative, and their primary role is not to distribute wind loads across the deck, but to transfer and distribute loads and moments from the girders into the piers and bearings.