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 MIL-HDBK-1038
adjacent inner section. Individual boom sections support pivoting lighting
fixtures, deflector sheaves, and rollers or rubbing blocks to preclude wire rope
contact with the boom structure.
4.1.11.1 Struts. Struts (also called floating masts) are structural frames that
support the outboard luffing hoist sheave nest and deflector sheaves of the hook
hoist reeving systems. They pivot on hinges similar to those of the boom, and are
connected to the boom by means of wire rope pendants. In operation, they control
the movements of the boom. The varying geometry between the A-frame, boom, and
strut on any given crane, may impose both tensile and compressive loads on the
strut, as it pivots through its range of motion. Access must be provided to all
sheaves.
(Struts have been incorporated in the designs of some newer portal cranes
to support (and eliminate the sag of) the luffing sheaves that were removed from
the boom to minimize lubrication drip on clean areas underneath the hooks. Figure
6 depicts a portal crane design with a strut.)
4.1.12
Container Crane Booms. These booms are the luffing extensions of the
main beams. In their horizontal position, they function as cantilevered girders
with trolley rails on their lower flanges. The boom girders are supported by
stays at the outer ends and are hinged at the feet so that they can be raised to
clear the ship's superstructure during travel or for storage. The boom girders
have box cross sections which are braced at their upper flanges and at the ends.
The lower flanges are widened on one side to support a trolley rail. The boom
girders' cross sections are sufficiently large to permit entry into their interior
and are reinforced with open diaphragms to permit full access for inspection or
repair. The access hatches are normally located in the upper flanges and are
reinforced around the perimeter to maintain the cross sectional properties and
preclude entry of rainwater. These boom girders are one-piece weldments.
One boom girder supports a full-length walkway arranged to permit
emergency egress from the cab anywhere along the walkway. The upper flange of the
boom girder may serve as the walkway or a separate walkway structure may be
cantilevered off the side of the boom girder.
4.1.12.1 Boom and Main Beam Stays. The booms are supported in their horizontal
operating position by stays from the top of the gantry. These stays are rigid
structural members, double-hinged near the center to allow them to fold when the
boom is raised by the boom hoist. The main beam stays differ only in the deletion
of the center hinge.
4.1.13
Container Crane Main Beams. The main beams may be considered as
extensions of the (luffing) boom and are of the same cross section and
construction as the boom girders. They are rigidly built into the gantry in line
with the boom girders and extend backwards through the gantry as cantilevers to
permit trolley travel past the land-side rail. The main beams also serve as
foundations for the hoist machinery house and the diesel engine-electric generator
room.
One of the main beams includes a walkway which matches the boom walkway
and extends to the very end of the main beam. This walkway also must permit
emergency egress from the cab at any location. The other main beam is required to
have a short
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