In orthotropic-plate construction, a steel-plate deck is used instead of concrete. The plate is topped with a wearing surface that may or may not be concrete. The steel-plate deck serves the usual deck function of distributing loads to main carrying members, but it also acts as the top flange of those members (Art. 11.20). Because the deck provides a large area, orthotropic-plate construction is very efficient in resisting bending. With a lightweight wearing surface, furthermore, bridges of this type have relatively low dead load, a characteristic particularly important for keeping down the costs of long spans. Figure 12.57 shows some examples of cross sections that have been used for orthotropic-plate bridges.
These examples indicate that orthotropic plates often are used with box girders. In addition to low dead weight, this type of construction offers many of the advantages of composite box girders discussed in Art. 12.12. The examples, however, are all long-span bridges.
It may also be economical for medium spans to use orthotropic plates with girders with inverted-T shapes.
For relatively simple types of orthotropic-plate bridges, such as those with the type of cross section shown in Fig. 12.58, approximate analyses by the Pelikan Esslinger method or similar methods give sufficiently accurate results for practical purposes. For more complex types, more accurate analyses may be desirable. These can be executed with the aid of computers. Special attention should be given to the stability of deep webs and wide flanges and to the effect of shear lag on wide decks.
(T. G. Galambos, ‘‘Guide to Stability Design Criteria for Metal Structures,’’ John Wiley & Sons, Inc., New York.)