RC = Rmin + 3.00 ft.
Unless extreme space limitations dictate otherwise, it is desirable that
neither Rmin nor Rc be less than 80 feet.
Selection of Radius. The following are suggested methods for
selecting Rmin and Rc for use in the design procedure, Table 1.
a) For a symmetrical curve with ) = 180E (i.e. parallel tangents
forming a "horse-shoe" curve), a first approximation of Rmin should be:
Rmin = 0.93M
The radius of the main circular curve is:
M - YC
b) For 90E < ) < 180E, a recommended first approximation of Rmin
would be a value equal to one half the distance from PC to PT.
Note: The choice of Rmin in this case is strictly an approximation.
amount of trial and error is involved in the final choice of Rmin.
c) For ) < 90E, it is recommended that the first trial should be
based upon historical data of a similar curve if available. Otherwise,
estimate and refine by trial and error.
), M, YC and 2 = (See Table 4).
Complete Curve Combination. A complete curve combination consists
of a minimum of two switch curves and two abutting transition curves, or a
maximum of two switch curves and two transition curves, separated by one main
circular curve (See Figure 7).
Transition Curve. When the main intersection angle ( ) ) is 90
degrees or less, the curve may be made transitional throughout. When the
curves are transitional throughout, the inner transition curves abut, but the
outer transition curves are separated by a tangent of 2t length.
Tangent Length. Tangent length between curves of opposite
direction shall be at least equal to the equivalent length of the crane.
Under no circumstances shall the commonly called
"reverse curve" be used.
Transition Curve (Outside). This curve is a series of compounding
circular arcs which are not concentric with the corresponding arcs of the
inside transition curve. The first 20 feet of curvature of all transition