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plate girder[′plāt ‚gərd·ər]
A beam built up of steel plates and shapes which may be welded or bolted together to form a deep beam larger than can be produced by a rolling mill (see illustration). As such, it is capable of supporting greater loads on longer spans. The typical welded plate girder consists of flange plates welded to a deep web plate. A bolted configuration consists of flanges built of angles and cover plates bolted to the web plate. Both types may have vertical stiffeners connected to the web plate, and both may have additional cover plates on the flanges to increase the load capacity of the member. Box girders consist of common flanges connected to two web plates, forming a closed section.
In general, the depth of plate girders is one-tenth to one-twelfth of the span length, varying slightly for heavier or lighter loads. On occasion, the depth may be controlled by architectural considerations.
Stiffeners, plates or angles, may be attached to the girder web by welding or bolting to increase the buckling resistance of the web. Stiffeners are also required to transfer the concentrated forces of applied loads and reactions to the web without producing local buckling.
Splices are required for webs and flanges when full lengths of plates are not available from the mills or when shorter lengths are more readily fabricated. Splices provide the necessary continuity required in the web and flanges.