PORTAL CRANE TRACK CURVE ALIGNMENT
Apply design procedure outlined in this section to:
All new curved portal crane track projects.
Curved extensions to existing crane trackage.
c) Rehabilitation projects where new track foundations are
required throughout a curve.
Rehabilitation design for curved trackage on existing foundations will have
different methods of calculation than are outlined in this section. Some of
the criteria specified for new track cannot be applied to rehabilitation
projects because of the need to fit the track on the existing foundation while
meeting gage reduction requirements; however, wherever possible, the
definitions and objectives of this section should be utilized for replacement
design. Criteria for rehabilitation design of curved track on existing
foundations are specified in Section 4 of this Chapter.
Problem Description. The track gage must be reduced on curves
because of the nonradial position of the ends of the crane (See Figure 4).
Some form of transition is required between the tangent track and the
short-radius curved track.
(Note: A computer program TRACKS, (available from NAVFACENGCOM Headquarters)
can be used to calculate the gage reduction. The program requires the crane
float, curve radius and gage.)
Reduced Gage. Actual gage reduction for a given radius may be
computed precisely, but as the crane frame covers or "straddles" a number of
radii in traversing the transition curve, the gradual reduction between the
tangent gage and the gage at the end of the transition curve is an
approximation. The shorter the radius the greater the gage reduction
required. Gage reduction on curves with a radius greater than 300 feet is
normally not required, as it is well within the float capability of most
Crane Equivalent Length. Equivalent length is the length of a
theoretical crane that has its corners riding over the centerline of the rails
when all the wheels of the actual crane are on the rails of the curve. See
Figures 4 and 5
Lateral Float. Lateral float is the amount of transverse movement
possible on the gudgeon pins of the crane (See Figure 6). No transition from
tangent to curve or vice versa has been designed to eliminate the necessity
for providing some lateral floating action in cranes.
Radius. The floating action (transverse movement) provided in
cranes permits a crane to traverse a large radius curve without any gage