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INTERMEDIATE SUPPORTS Bents and piers provide support for the bridge superstructure at points other than the bank ends. A bent consists of a single row of posts or piles, while a pier consists of two or more rows of posts or piles. The following text discusses some of the different types of bents and piers.The pile bent shown in figure 1-3 consists of the bent cap, which provides a bearing surface for the bridge stringers, and the piles, which transmit the load to the soil. The support for the loads may be derived either from column action when the tip of the pile bears on firm stratum, such as rock or hard clay, or from friction between the pile and the soil into which it is driven. In both cases, earth pressure must provide some lateral support, but traverse bracing is often used to brace the bent laterally.A timber pile bent consists of a single row of piles with a pile cap. It should be braced to the next bent or to an abutment to reduce the unbraced length and to provide stability. This bent will support a combined span length of 50 feet The trestle bent shown in figure 1-4 is similar to the pile bent except that the posts, taking the place of the piles, transmit the load from the cap to the sill. The sill transmits the load to the footings, and the footings transmit the load to the soil. Timber trestle bents are normally constructed in dry, shallow gaps in which the soil is firm. They are not suitable for use in soft soil or swift or deep streams. The bent can support a combined span length of up to 30 feet and can be 12 feet high.
Figure 1-4.Timber trestle bent.
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 |
 
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