GENERAL DESCRIPTION.
CLASSIFICATION.
Highway bridges shall be divided into three classes, viz., Class A, which includes those that are subject to the continued application of heavy loads; Class B, which includes those that are subject to the occasional application of heavy loads; and Class C, which includes those for ordinary, light traffic.
In general it may be stated that bridges of Class A are for densely populated cities; those of Class B for smaller cities and manufacturing districts; and those of Class C for country roads.
MATERIALS.
All parts of the structure, excepting the flooring or paving, shall, for all spans of ordinary lengths, be of medium steel, excepting only that rivets and bolts are to be of soft steel, and adjustable members of either soft steel or wrought iron. For very long spans high steel may be used for top chords, inclined end posts, pins, and eye-bars in bottom chords and in main diagonals of panels where there is no reversion of stress when impact is included. Cast iron will not be allowed to be used in the superstructure of any highway bridge or trestle, except for purely ornamental work, cast steel being employed wherever important castings are necessary.
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