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Knight's Mechanical Encyclopedia (ed. Knight), W. (search)
Among the various forms of bridge-truss employed in the United States may be cited those of Town, Long, Burr, Howe, and McCallum. Town's lattice-truss (Fig. 7321) has been employed for spans up to 150 feet. The roadway a rests upon sleepers b, whvertical iron tensionrods were used instead of posts. Fig. 7325 represents what is known as the improved Howe truss. McCallum's inflexible arched truss. McCallum's inflexible arched truss (Fig. 7326) has braces and counter-braces; the spaces McCallum's inflexible arched truss (Fig. 7326) has braces and counter-braces; the spaces between the posts are diminished toward the ends of the spans, and diagonal braces, tending from the piers and abutments toward the middle portion of the upper arched beam, tend to reduce the tension upon the lower chord. Bridge-building was one of the arts brought to the greatest state of perfection during the late civil war. General McCallum states that the Rappahannock River bridge, 625 feet long and 35 feet high, was rebuilt in nineteen working hours; Potomac Creek bridge, 414 feet long a