Civil Engineering Professional Engineer Practice Exam

The correct choice, which identifies the type of members used in an arch bridge to support the deck, highlights that curved members play a crucial role in the structure's integrity and function. In an arch bridge, the primary load-bearing elements are indeed the arches themselves, which are designed to handle compression forces effectively. The curvature of these members allows them to transfer the weight of the deck and any loads above it down into the supports at either end of the bridge.

This design is fundamental to the stability of arch bridges, as the curved shape allows for the distribution of forces in a way that enhances the bridge's strength and durability. By utilizing the properties of arches, these bridges can span significant distances without needing excessive vertical supports, thus benefiting both aesthetics and functionality.

In contrast, the other choices refer to structural components that are not typically used to support the deck of an arch bridge. Vertical beams are more associated with structures that need to resist bending, while trussed supports and steel girders are features found in different bridge types, such as truss bridges or girder bridges, where straight members are utilized for load-bearing. Understanding the specific structural components and their purposes is essential for grasping the principles of bridge design and engineering.