15 August 2002
Approximate Analysis. For approximate determinations of principal
moments, shears, and reactions, assume the design length as a mean of the top and
keel lengths and apply elastic theory for a rectangular plate supported on three sides.
Determine also the distribution of shears and moments in individual frames and girders,
stiffeners, and plating.
. Main framing should consist
of a series
of vertical trusses
frames attached to horizontal girders or frames at panel points. Make a bulkhead frame
near each end watertight for trim tanks. Only the safety and weather deck horizontal
girders are made watertight. Space vertical frames about 2.44 m (8 ft) on centers, with
spacing of horizontal girders preferably not exceeding 3.05 m (10 ft). Place short
intermediate horizontal girders, usually called breasthooks, in the upper half near the
caisson ends, for better distribution of shears and end reactions.
Vertical Frames. For construction details, see Figure 9-1.
Design as follows:
Design vertical frames to resist caisson shears and bending moments in
vertical directions and local bending between girders. The part of the total
vertical caisson bending moment applicable to a frame is determined from
the approximate analysis (refer to section 9-3.3.1). Chord stresses are
determined by beam analysis.
Local bending moments between girders on the outboard side result from
water pressure loads brought to the vertical frames by hull plating and
Web member stresses are found by assuming the distributed vertical
pressure loadings to be concentrated at panel points and computing the
Design for stresses caused by internal air pressure in air
Diagonal web members should preferably be tee sections; horizontal strut
members angle sections; and chord members wide angle sections formed
by bent plates or a web plate with a welded flange.
Web member connections should be fillet welded.
Horizontal Girders. See Figure 9-2 for details of a typical girder. Design
Design horizontal girders similarly to vertical frames. In general, they are
the same type of construction.