ABSTRACT
History was made when Abraham Darby III (1750-1791) built during 1776-1779 the world’s Œrst iron bridge atCoalbrookdale, England. This nearly semicircular arch bridge (Figure 6.1) with approximately 100 ft main span is still in service, albeit limited to only pedestrian trafŒc. In the United States, the Œrst cast-iron bridge was an 80-ft span structure made up of Œve tubular arch ribs; it was built in 1836 by Richard DelaŒeld (1798-1873) of the US Engineers Corps (Steinman and Watson 1957). However, the modern era in bridge building began in the United States with the construction (1868-1874) of the famed double-deck Eads Bridge (Figure 2.4) over the Mississippi in St. Louis, Missouri, which marked the Œrst extensive use of structural steel in bridges. Steel bridges then became the most common type of highway structures built in the United States, and steel continuedto dominate bridge construction until the advent of reinforced concrete and, later, prestressed concrete. The Œrst major prestressed concrete bridge-the three-span (74, 160, 74 ft), cast-in-place, posttensioned Walnut Lane Memorial Bridge, Philadelphia, Pennsylvania-was built in 1951.
