Access holes may be cut in the low stress areas of webs for bolt or nut
installation and torquing. Such access holes should be closed with cover plates.
Trolley Frames for OET Cranes. Trolley side frames are built-up box
sections of flat plates, channel shapes and flat plates, or rectangular structural
tubing. The side frames are joined by cross members at the ends and by
intermediate load girts which support the hoists and the upper block sheaves.
Steel floor plating, with slots for wire ropes, is often installed over the entire
trolley frame. Trolleys are normally supported on four travel wheels.
On smaller cranes, especially those with standard commercial packaged
hoists, trolley frame construction varies. It is common practice to omit the
Bridge Girders for Underrunning Cranes. The preferred bridge girder
design is the "patented track". The girder cross section has an upper T-section
of structural steel and a lower, smaller inverted T-section accurately machined
from hard, high-carbon steel. The two T-sections are joined with continuous (but
not necessarily full-penetration) groove welds. The lower T-section is available
in three standard sizes and is designed to accommodate either flanged or
flangeless wheels. It is machined on all sides-presenting smooth side surfaces
for guide rollers and a machined bottom surface for traction wheels. The ends of
the bridge girders are normally coped and reinforced with gussets and doublers for
full strength connection to the end trucks. Bridge girders are normally available
in lengths up to about 70 feet and normally are not cambered.
A less costly alternative to the patented track is a rolled structural
steel section either I-beam or wide flange. The drawbacks are the less durable
wear surfaces and wider dimensional, straightness, and warpage tolerances.
Outrigger Beams. The outrigger beams (if used) may be of any standard
structural section which is of adequate strength to mount the electric power
conductors and the single-motor bridge drive. The outrigger beam may be used to
form a horizontal truss by means of diagonal lacing to the upper flange of the
bridge girder. The ends of the outrigger beams are connected to the end trucks or
End Trucks. The underrunning end trucks may be of rigid or flexible
design. The rigid end trucks include wheel axle seats at each end; the flexible
end trucks are supported by swiveling load bars or carrier yokes. The rigid end
trucks are weldments of steel plate or channel sections which are joined and
reinforced at each end by U-shaped steel plates against wheel spreading forces and
are additionally reinforced with gussets and doublers at the wheel axle seats.
The flexible end trucks have the connecting bars as their main structural
components. Figure 14 illustrates typical arrangements of both types of end
trucks. Underrunning end trucks are usually standard commercial components.
Runways for Underrunning Cranes. The runways are designed with the same
patented track sections as the bridge girders. The length of the runways often
requires splices between the sections. (The standard track sections are normally