Figure 1-43 shows the structural framework of a single-span truss bridge. As with all bridges, the floor and traffic loads of the truss bridge are carried by the stringers. In the truss bridge, however, the stringers are supported by transverse beams rather than by the bridge abutments (and intermediate supports when needed). As seen in the figure, these transverse beams are supported by the structural framework of the two trusses. Finally, the entire bridge structure plus any traffic loads are transmitted through the end pedestals and bearing plates to the supporting abutments. As you will note, the nomenclature of the truss members is the same as discussed in the preceding section; however, the

diagonal end members, adjacent to the abutments, are normally called end posts.

The truss framework and the manner in which the trusses are used may differ depending upon the design of the truss bridge. Figure 1-44 shows three examples. View A shows a through truss span. In it, the traverse beams are connected to the bottom chord of the trusses, and the top chords are braced by a lateral bracing system under which traffic passes. In the deck truss span, view B, the traverse beams are carried by the top chord

Again, a lateral bracing system is used between the trusses. The pony truss span is the same as that discussed in the preceding paragragh. Because of the small depth of the trusses, no top lateral bracing is used.

Towers are framework structures designed to provide vertical support. They may be used to support another structure, such as a bridge, or they may be used to support a piece of equipment, such as a communication antenna. Since the prime purpose of a tower is to provide vertical support for a load applied at the top, the compression members providing this support are the only ones that require high-structural strength. The rest of the structure is designed to stiffen the vertical members and to prevent bending under load. Primarily, the bracing members are designed to take loads in tension and are based on a series of diagonals. A typical trestle tower used in bridge construction is shown in figure 1-45.