The type of bridge and the span layouts are interdependent. Bridge type cannot be selected without regard to the length of spans, the ratio of adjacent span lengths, and whether spans are to be made continuous.
Table 4.2 lists common types of bridges and the maximum span lengths below which they may be an economical choice. The maximum spans tabulated are approximate, and are presented as a guide only. They are subject to increase as technology advances. Similarly, increases in specified live load may tend to reduce the maximum span. The economic competitiveness of a particular bridge type varies with regional availability and workload of fabricators and specialty contractors, yearly fluctuations of labor and material costs, and other factors. Thus, it is usually desirable to seek and permit bids on alternative bridge types.
Characteristics of some of the more common bridge types for short and intermediate spans and considerations in their selection are discussed in the following articles.
