What is the relationship of the walls and deck in a rigid frame bridge?

• A. They work together as a single U-shaped rigid frame
• B. The deck bears all loads independently
• C. Walls primarily resist wind
• D. There is no interaction between components

Answer: (A)

In a rigid frame bridge, the deck and the vertical walls are connected by moment-resisting joints so they behave as one continuous rigid frame. This means the deck isn’t carrying loads in isolation; when vehicles load the deck, bending moments flow into the walls and the walls, in turn, reinforce the deck. The whole U-shaped assembly acts together to resist both vertical and lateral forces, distributing stresses through the connected members rather than letting one component carry everything on its own. Walls don’t just resist wind by themselves in this setup; they participate in the frame’s overall stiffness and load path. There is clear interaction between the deck and the walls, since the integrity of the structure depends on how these components work together. So the correct description is that the walls and deck work together as a single U-shaped rigid frame.