MIL-HDBK-1038
5.1.2.5
Floating Cranes. Structural design criteria for the upperworks of
floating cranes are established entirely by the NCC and parallel those of portal
cranes. For this reason, the major structural components of a floating crane
upperworks (the boom, A-frame, strut, and machinery deck) should be designed in
the same manner as a portal crane upperworks, as discussed in section 5.1.2.4.
The structural design of the barge hull is governed by the standards of the ABS
"Rules for Building and Classing of Steel Barges."
The tub (or pedestal) of a floating crane is affected by the radius of
the boom. The tub supporting structure in the barge is affected by the radius of
the boom, and by the orientation of the boom axis to the barge axis. Several
orientations of the boom axis should be considered in order to find the maximum
load on each of the supporting members (usually bulkheads) in the barge. Each of
these boom axis orientations should be analyzed for two boom radii: the radius
which produces maximum overturning moment on the tub, and the radius which
produces maximum axial load on the tub (unless they occur at the same radius).
The following paragraphs prescribe the design load combinations and
maximum allowable stresses for each structural component of a floating crane. The
maximum stress levels listed below represent the percentage of the AISC allowable
value for the particular material.
a)
Boom, A-frame, Machinery Deck, Tub and Hoist Foundations.
Five load
cases are considered:
1) Dead load, main hoist rated load with a vertical impact factor,
horizontal side load, and 40 mph wind. The maximum stresses are limited to 85
percent of AISC allowable values.
2) Dead load, 80 mph wind, and simultaneous maximum list and trim.
This load case must be applied to the boom at minimum operating radius and the
wind from the front or rear, boom at minimum radius and the wind from the side,
the boom at maximum radius and the wind from the side. The maximum stresses are
limited to 100 percent of AISC allowable values.
3) Dead load, 145 mph wind, and dynamic effects due to pitch, roll,
and heave. For this load case, the crane is assumed to be fully tied down (if
tie-downs are provided), with the rotate locking device engaged and the boom
secured in the boom rest. The maximum stresses are limited to 133 percent of AISC
allowable values.
4) Dead load, 150 percent main hoist rated load with a vertical
impact factor. The crane is assumed to be level. This load case is applied only
to the analyses of the king pin or hook rollers (if applicable) on roller path
type cranes. The maximum stresses are limited to 133 percent of AISC allowable
values.
5) For fatigue analyses, use the portal crane load case described
in paragraph 5.1.2.4 a) (3). The maximum allowable stress range is limited to 100
percent of AISC allowable values for Loading Condition 2 (that is, 100,000 to
500,000 cycles).
b)
Boom Stops (and A-Frame).
One load case is considered:
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