Travel truck drives are required to be removable (as a unit) from
the travel truck frames. The preferred connection to the wheel axle is by means
of a compression sleeve or a spline. If the wheel axle is pressed and keyed into
a hollow output shaft of a gear reducer, the assembly must include provisions for
pressing out the wheel axle.
Roof walkways and hand railings are required to be terminated at the
lines of separation of the roof sections, and each is to be removable (by
unbolting) from its roof section.
Interiors of large closed structural sections such as portal
bases, machinery decks, gantries, and container crane main beams or boom girders
are required to be accessible for inspection and maintenance. These accessibility
provisions must include ladders, platforms, and lighting. Access hatches must be
weathertight, openable from both sides, and with shielded grills for ventilation.
Structural-Mechanical. There are no industry standards for structural-
mechanical components. The following criteria have evolved from successful crane
designs administered by NCC. Deviations from these criteria are prohibited,
unless approved by NCC. The connections at interfaces of structural and
mechanical components are governed by the less stringent criteria of the two.
(For example, sheave and equalizer pins must comply with the mechanical design
criteria, but their seats and supports on the boom may follow the structural
design criteria. On either side of the interface, the appropriate design criteria
of Section 5.1 or Section 5.3 applies.)
Additional design criteria for unique structural-mechanical components
are given below.
Equalizer Bars and Bar Frames. Equalizer bars and bar frames (for
equalizer bars and sheaves) are designed according to the structural criteria; the
pivot pins and their bushings, including lubrication and retention provisions, are
designed according the mechanical criteria.
Wire rope fitting connections (padeyes) are designed to fit the pin and
clevis opening, without any bushings. The external dimensions of the padeye are
governed by the mechanical design criteria.
Boom Hinges. Boom hinges are arranged to allow the boom to be lowered to
its horizontal (maintenance) position and are designed to withstand the lateral
loads imposed on the boom by side pulls, wind, and rotational acceleration and
deceleration of the upperworks. Older crane designs traditionally spaced the two
boom hinges at 1/12 of the boom length to limit the loads on the boom hinges and
the boom structure. Newer crane designs, utilizing advanced stress analyses,
generally use a lesser spacing with a high degree of confidence in the validity of
the obtained load and stresses.
Accurate alignment of the boom hinges is of critical importance. The
boom assembly, machining techniques, and its installation on the machinery deck
must ensure that the two hinge assemblies are aligned on a common centerline. The
bushings may be pressed into the boom foot structure or into the support padeyes.
Bushing flanges or separate thrust washers are required between the boom feet and
the padeyes. Grease grooves are machined in the bushing bores in a pattern that
ensures delivery of grease to the heavily loaded locations with the boom at any