ABUTMENTS

Figure 1-2.—Types of fixed-bridge abutments. ABUTMENTS There are different types of fixed bridge abutments. First, let us discuss the footing-type abutment. In figure 1-2, views A and C show two types of footing abutments. View A shows a timber-sill abutment, and view C shows a timber-bent abutment. By studying both of these views, you should see that there are three elements that are common to a footing-type abutment. Each type has a footing, a sill, and an end dam. If you will notice, the timber-sill abutment shown in figure 1-2, view A, is the same footing-type abutment that is shown for the bridge in figure 1-1. In this type of abutment, loads are transmitted from the bridge stringers to the sill, which, in turn, distributes the load to the footing. The footing then distributes the combined load over a sufficient area to keep the support from sinking into the ground. The end dam is a wall of planks that keeps the approach-road backfill from caving in between the stringers. The timber-sill abutment should not be more than 3 feet high. It can be used to support spans up to 25 feet long. The timber-bent abutment shown in figure 1-2, view C, can be used with timber or steel stringers on bridges with spans up to 30 feet. The deadman is used to provide horizontal stability. These abutments do not exceed 6 feet in height. Other types of fixed-bridge abutments are pile abutments and concrete abutments. Timber- or steel-pile abutments can support spans of any length, can be used with steel or timber stringers, and can reach a maximum height of 10 feet. A timber-pile abutment is shown in figure 1-2, view B. Concrete abutments are the most permanent type. They may be mass or reinforced concrete, can be used with spans of any length, and can be as high as 20 feet. They may be used with either steel or timber stringers. 1-2