In a new era of technology and engineering, the longest bridge in the world is over a hundred miles long! A bridge is a structure built to span physical obstacles such as a body of water, a valley or a road. There are many different bridge designs created to suit different purposes. Bridge designs vary depending on the function of the bridge, the land on which the bridge is built and anchored, the money available to build the bridge, and the materials used to make it. Based on these criteria, an engineer can decide whether to build a truss, girder, or arch bridge. When evaluating bridge designs based on their load-bearing capacity, truss bridges are the most structurally durable because triangles are the strongest building form. The simplest and most common bridge design is the girder bridge. Girder bridges are horizontal beams supported at each end by substructural foundations and can be either supported only when the beams connect over a single span, or continuous when the beams are connected over two or more spans ("Basics of Girders"). bridges"). When there are several sp...