MIL-HDBK-1038
design requirements when a fictitious load of 150 percent of rated load is placed
on the main hoist hook at maximum radius. For cranes with variable rating, 150
percent of the maximum operating moment is applied.
5.2.5.1
Trunnion Mounting. Trunnion mounting of the king pin is recommended, but
is mandatory only when specified. The upper end of the king pin is connected to a
horizontal pin whose ends are seated in the trunnion bores. The trunnion bores
may include bushings and grease lubrication, but these features are not mandatory.
The entire trunnion assembly and its mounting fasteners must be sized to comply
with the mechanical design requirements for the fictitious 150 percent load
described above. Both ends of the horizontal pin must be secured with keeper
bars.
5.2.5.2
Locking Nuts. The lower end of the king pin is threaded for the locking
nut that is intended to prevent separation of the upperworks from the portal base
or tub in case of unintentional overload on the load hooks. In normal service,
within the crane's entire operating range, the gap above the locking nut should
never close to allow the locking nut to contact the lower center steadiment
section. The locking nut must have provisions for securing it against rotation
and the gap dimension under a particular load condition must be recorded. The
threads must be sized to comply with the mechanical design requirements for the
fictitious 150 percent load described above.
5.2.6
Roller Paths. Upper and lower roller paths must be mounted on supporting
structure (in the form of circular or octagonal girders) with intermediate
circular steel shim plates for continuous support of the roller path segments.
The shim plates should be wider than the roller path segment flanges and
continuously welded to the supporting structure. The shim plates are intended to
serve as surfaces for machining to obtain a level mounting surface for the roller
path segments. The machined mounting surface is required to be level within 1/32
inch (plus or minus) in 12 linear feet. The entire supporting structure
arrangement must be of high and relatively uniform rigidity. Roller path
segments, either in the form of bent rail or machined castings, must be secured
against rotation or shifting in any direction with welded rail clips, welded
studs, or through bolts. Rail clips should be standard commercial items and
should be welded directly to the shim plates in accordance with the manufacturer's
instructions. The welded studs must be installed on the supporting structure
(through enlarged holes or gaps in the shim plates) per the applicable criteria of
AWS D1.1; likewise, their nuts must be torqued to the values given in AWS D1.1.
Through bolts must be installed in accordance with the AISC Manual of Steel
Construction.
Alternatively, if the roller path segments are cast, they may be embedded
in an epoxy resin which is poured between the roller path segments and the support
structure. Using this method, the shim plates are omitted; instead, the machined
running surfaces of the roller path segments are used for accurate leveling prior
to pouring the epoxy resin. The selected epoxy resin must be poured (installed)
in accordance with all recommendations of its manufacturer. Typical installations
require metal dams inside and outside the roller path and temporary rods through
the bolt holes. The width of the roller path segment base and the compressive
strength/creep characteristics of the epoxy resin must be matched, considering
maximum roller loads and tension in the mounting studs or bolts. In this case,
studs and bolts should be tensioned according to the epoxy resin manufacturer's
recommendations, since the epoxy resin possesses substantial bonding strength but
does not have the compressive strength of steel.
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