MIL-HDBK-1038
fittings. The wire rope may be either improved or extra-improved plow steel,
bright (non-galvanized) or coated (galvanized), regular lay, with an independent
wire rope core, and in all other respects in full compliance with Federal
Specification RR-W-410 or Wire Rope Users Manual. (This specification has been
accepted by the wire rope manufacturers as the industry standard.) Galvanized
wire ropes are well suited for non-flexing applications and the mildly corrosive
conditions of outdoor environments, but their breaking strength will be reduced by
up to 10 percent compared to that of the bright wire rope of the same diameter.
The required minimum design factor for wire rope pendant assemblies is 4.0, based
on the wire rope nominal breaking strength, and the dead and rated loads.
5.2.14.1 Pendant End Fittings. The end fittings must be installed as described in
detail in paragraph 5.3.13.2. Ends of old galvanized wire rope, however, must be
treated with muriatic acid long enough to remove the zinc coating. Swaged
fittings are preferred on pendants because the wire rope cross section, although
compressed, retains its original construction inside the fitting and is more
resistant to severe impact and fatigue effects than the poured socket connection.
NCC policy is to require the open, clevis style of fitting end
connections on new cranes. Their accurately machined holes and fitted pins or
bolts provide a solid attachment to the structure. Two-part pendants should be
made with an intermediate short steel link between the adjoining end connections.
Closed end style of end connections must engage the largest diameter pin or bolt
that can be fitted to avoid introducing significant bending loads into the loop.
5.2.15
Fasteners and Connections. The design or sizing of fasteners and
connections at structural-mechanical interfaces is governed by the less stringent
of the two applicable criteria.
Example 1: The fasteners securing the hoist drive foundation to the
machinery deck main beams are treated as structural connections.
Example 2: The pivot joints of the double-hinged folding stays of
container crane booms are treated as structural connections with the hinge pins or
bolts in double shear.
5.3
Mechanical. Crane industry standards CMAA #70 and #74 prescribe
mechanical design criteria for bridge cranes, and that criteria apply to
corresponding components of cantilever, gantry, and semi-gantry cranes. Some
elements of those design criteria are recommendations ("should" statements).
However, NCC policy is to consider them as mandatory. CMAA #70 and #74 establish
the design criteria for the following mechanical components of the above crane
types:
Open gearing
Shafting
Drum pitch diameters, grooving, and fleet angles
Sheave pitch diameters and fleet angles
Travel wheels (top running) and rails
Travel wheels (under running) for wide flange and I-beams
Bumpers
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