Civil Engineering Professional Engineer Practice Exam

How do beam bridges primarily support their decks?

1. Using curved members

2. With trusses arranged in triangles

3. Through concrete or steel beams

4. By using cantilevers

The correct answer is: Through concrete or steel beams

Beam bridges primarily support their decks through the use of concrete or steel beams. These beams run horizontally across the bridge, transferring the loads applied to the deck down to the supports at each end. The construction of beam bridges relies on the strength and stiffness of the beams, allowing them to resist bending moments and shear forces resulting from traffic loads and other forces acting on the structure. The design of beam bridges typically involves either a single beam or multiple beams to provide the necessary structural support. Concrete beams are often used for their durability and ability to withstand compression, while steel beams offer high strength-to-weight ratios, making them versatile for various spans. The key function of these beams is to keep the bridge deck stable and support the weight of vehicles and pedestrians efficiently. Other options involve different structural concepts. Curved members are more associated with arches, which distribute loads differently, while trusses use a series of interconnected members to form triangular shapes that also create stability, suited for longer spans. Cantilevers represent a different design approach involving projecting beams that extend without external support at one end. In the context of beam bridges, the straight, horizontal beams are the critical element that enables the bridge to function effectively.