Figure 1-2.—Types of fixed-bridge abutments.ABUTMENTSThere are different types of fixed bridge abutments.First, let us discuss the footing-type abutment. In figure1-2, views A and C show two types of footing abutments.View A shows a timber-sill abutment, and view C showsa timber-bent abutment. By studying both of theseviews, you should see that there are three elements thatare common to a footing-type abutment. Each type hasa footing, a sill, and an end dam.If you will notice, the timber-sill abutment shownin figure 1-2, view A, is the same footing-type abutmentthat is shown for the bridge in figure 1-1. In this type ofabutment, loads are transmitted from the bridgestringers to the sill, which, in turn, distributes the loadto the footing. The footing then distributes the combinedload over a sufficient area to keep the support fromsinking into the ground. The end dam is a wall of planksthat keeps the approach-road backfill from caving inbetween the stringers. The timber-sill abutment shouldnot be more than 3 feet high. It can be used to supportspans up to 25 feet long.The timber-bent abutment shown in figure 1-2, viewC, can be used with timber or steel stringers on bridgeswith spans up to 30 feet. The deadman is used toprovide horizontal stability. These abutments do notexceed 6 feet in height.Other types of fixed-bridge abutments are pileabutments and concrete abutments. Timber- orsteel-pile abutments can support spans of any length,can be used with steel or timber stringers, and can reacha maximum height of 10 feet. A timber-pile abutment isshown in figure 1-2, view B. Concrete abutments are themost permanent type. They may be mass or reinforcedconcrete, can be used with spans of any length, and canbe as high as 20 feet. They may be used with either steelor timber stringers.1-2
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