SUPERSTRUCTURE

Figure 1-5.—Typical pile pier. The pile pier (fig. 1-5) is composed of two or more pile bents. In this figure, notice the common cap. The cap transmits the bridge load to the corbels, which in turn, transmit the combined load to the individual bent caps. Piers are usually provided with cross bracing that ties the bents together and provides rigidity in the longitudinal direction. SUPERSTRUCTURE The superstructure of a bridge consists of the stringers, flooring (decking and treads), curbing, walks, handrails, and other items that form the part of the bridge above the substructure. Figure 1-6 is an illustration of a superstructure. As seen in the figure, those structural members resting on and spanning the distance between the intermediate supports or abutments are called stringers. The stringers are the mainload-carrying members of the superstructure. They receive the load from the flooring and transmit it to the substructure. Although the figure shows both steel and timber stringers, in practice only one type would normally be used. The flooring system includes the deck; the wearing surface, or tread, that protects the deck; and the curb and handrail system. The plank deck is the simplest to design and construct, and it provides considerable savings in time compared to other types of decks. Plank decking is normally placed perpendicular to the bridge center line (direction of traffic) for ease and speed of construction. A better arrangement, however, is provided if the decking is placed at about a 30- to 60-degree skew to 1-4