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 MIL-HDBK-1038
Particular care is required in the arrangement of the transit point between
rotating and stationary structures to preclude any possibility of injuring of
maintenance personnel. In general, design details of the ladders, walkways,
platforms are governed by OSHA 29 CFR 1910 criteria.
4.1.27
Structural Pins. Structural pins are defined as those in
connections/joints where no motion is intended to take place on their surface
during normal crane operation. Examples of such pins are A-frame connections
between its members and the machinery deck, and container crane main beam (but not
boom) stay-to-gantry connections. (Container crane boom stay hinge pins and
gantry connections, which are stationary during normal crane operation, but are
subjected to a substantial arc of rotation whenever the boom is elevated, are
seated in lubricated bushings and are considered to be mechanical components.)
All structural pins should be solid forgings; hollow pins (heavy wall
tubes) may be used only with NCC approval. Pinned joints must be designed to put
the pin into double shear. These pinned joints do not require provisions for
lubrication.
The pins are normally installed directly into the bored holes (without
bushings) of the connected components and are retained on one end or both ends.
The smaller pins are usually machined with a head (shoulder) on one end and a
straight slot or circumferential groove, for a keeper bar, on the other end. The
larger pins are usually straight, with chamfered ends, and a keeper bar slot on
one or both ends. If only one end is retained with the keeper bar, then the pin
length should be sufficient to allow the straight section (excluding the chamfer)
of the free end to protrude beyond the face of the structure by at least 1/8 of
the bore diameter. Large pins may have a tapped hole on one or both ends for
temporary installation of an eye-bolt for handling and extraction of the pin.
Welded bars on the end of pins, intended to function as both head and keeper bar,
are prohibited because of the tendency of the weld to crack.
4.1.28
Maintenance Support Items. Two of the most common items for maintenance
support of portal cranes are the boom stand and the upperworks lifting fixture.
The boom stand is a simple portable structure, usually a tubular
section with a wide base and an upper bracket to match the boom lower main chords.
The height is selected to support the boom in a horizontal position. The boom
stand is equipped with lifting eyes. Normally no provisions for accessibility
from ground level are provided.
Floating cranes always include a boom rest as an integral component of
the deck structure. The boom rest is a more elaborate structure than the portable
boom stand often incorporating within its structure a pilothouse and some crew
accommodations.
Portal and floating cranes which utilize a rotate bearing may be provided
with a specially designed lifting fixture for "undecking" either for
assembly/disassembly or for bearing replacement. The lifting fixtures are
designed to maintain the lifted upperworks in a horizontal position, and include a
hook eye at the top and pendants for connection to the upperworks. The lifting
fixture is most useful when the original upperworks design includes the lifting
connections. Depending on the weight of the upperworks, the boom and
counterweight may have to be removed prior to undecking the crane by means of the
lifting fixture.
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