15 August 2002
Girder flanges should be combination tee and wide-angle sections and, for
computing stresses from girder action, include all adjacent hull plating.
Members of safety and top decks must resist local loads introduced by
secondary framing and deck plating at those locations.
Webs at the girder ends are longitudinally stiffened plating for required
Weather decks should be cambered to provide drainage and designed for
specified uniform live loadings and concentrated vehicular loads normal to
the girder plane.
Design safety decks for water pressures, machinery loads, and air
pressure if the caisson is air operated.
. Make shell plate stringers
of serrated channels
angles running horizontally. At keel, provide web plate stiffeners in a vertical direction,
spaced about 0.6 m (2 ft) on centers, between vertical frames. Design stringers as
continuous beams to resist local water pressure transmitted by plating. Stringers for
both weather and safety decks should run in the long direction of the caisson, and
should consist of serrated channels. Design them as continuous beams.
Plating. Stresses in shell plating are biaxial, due to bending in two
directions. Determine maximum stresses in plating by combining stresses from overall
bending and twisting of the caisson and bending stresses from local water pressure
loading. Assume twisting moments resisted only by shearing stresses in the plating.
Determine principal stresses by combining shear resulting from twisting, stresses
produced by bending in both vertical and horizontal directions, and stresses due to local
bending. Increase the design plate thicknesses by 1.59 mm (1/16 in) to allow for
Stems and Keels. Stems and keels distribute hydrostatic pressures on
caissons to the masonry of drydock seats. Keels are to be filled solid with concrete
ballast, and stiffened with diaphragm plates.
Gaskets and Seats. The bearing of caisson ends and keel is taken
through special molded, steel reinforced, rubber seals set on both faces of caisson keel
and stem. Contact Naval Facilities Engineering Service Center for details. See Figure
Graving Drydock Seats. For cruiser, auxiliary and carrier docks, build
recesses into the drydock entrance floor 0.6 m (2 ft) and into the drydock entrance side
walls 0.76 m (2 ft 6 in), to form docking seats. For destroyer and submarine docks,
these depths may be decreased respectively 152.4 mm (6 in.)