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MIL-HDBK-1038
The booms on these cranes are always in the form of a single-web girder
with an underrunning hoist/trolley unit.  The individual motions may be
electrically driven and controlled from a pendent pushbutton station or manually
operated.
2.3.1.2
Traveling.  These cranes travel along the wall on a runway comprised of a
single rail designed for the vertical loads and two widely separated moment-
carrying rails or other form of running surfaces along the wall.  The design of
the single rail end truck (carriage) is similar to that of an OET crane.  The
moment-carrying members of the runway can use either of two design options two
standard rails (oriented for opposed horizontal loads); or two single web
structural sections.  In the case of the rail option, the moment-carrying end
trucks are similar to those of an OET crane.  In the case of single web sections,
the upper end trucks are designed to pull on the flanges in the same manner as the
underrunning rigid end trucks with wheels on fixed axles in pinned brackets for
load equalization; the lower end truck is designed with crowned rollers to run on
the outer surface of the runway flange.  The running surfaces of the structural
sections can be upgraded by the addition of welded-on machined medium-carbon steel
strips.
The booms may be single beam type (either structural section or patented
track) mounting an underrunning hoist/trolley unit or a twin beam design with a
top running trolley.  The booms are supported with tie rods or knee braces, as
best suited for the particular application.  Figure 4 shows two types of traveling
wall cranes.
Wall cranes are usually electrically powered on all motions and may be
controlled from an operator's cab or a pendent pushbutton station.  Electric power
is transferred from a fixed location near the runway to the traveling vertical
frame by means of collector shoes sliding along rigid conductors parallel to the
wall.  Light duty cranes may have manually operated hoist and trolley drives of
the types available for underrunning cranes.
2.3.2
Distinctive Features.  The moments that these cranes impose on the
support structure or the runway limit their capacity and reach.  However, with the
availability of virtually all key components off-the-shelf and with many design
options, cantilever cranes can be selected or customized to suit virtually any low
capacity application.
2.3.3
Industry Standards.  There are no industry standards for this specific
category of cranes.  Various portions of the design are included in the standards
of OET (CMAA Specification #70) and underrunning cranes (CMAA Specification #74).
The safety aspects of the design and operation are addressed in ANSI/ASME B30.2,
Overhead and Gantry Cranes (Top Running Bridge, Single or Multiple Girder, Top
Running Trolley Hoist) and ANSI/ASME B30.11, Monorails and Underhung Cranes;
published by the American Society of Mechanical Engineers.
2.4
Portal Cranes.  Portal cranes derive their name from the opening (portal)
between the legs of the structure (gantry) which permits the passage of vehicles
in the congested environment of wharves and piers.  They are also popularly called
revolving gantry, dockside, or Whirley cranes.  These cranes run on two widely
spaced rails (18 to 60 foot gauge) at ground level close to the edge of the
wharves and piers that they service.  The gantry mounts a rotating superstructure
(upperworks) with a luffing boom.  The standard clearance under the gantry cap is
22 feet.
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