Figure 11-16.Algebraic differences of grades. - 14071_252
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ELEMENTS OF VERTICAL CURVES - 14071_251
Symmetrical Vertical Curves - 14071_253
Engineering Aid 2 - Intermediate Structural engineering guide book
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G
L
The
algebraic difference
of the grades:
G = g
_{2 }
-g,,
wherein plus values are assigned to uphill
grades and minus values to downhill grades;
examples of various algebraic differences are
shown later in this section.
Length of the curve; the
horizontal
length
measured in 100-foot stations from the
PVC
to
the PVT. This length may be computed using
the formula
L = G/r,
where
r
is the rate of
change (usually given in the design criteria).
When the rate of change is not given,
L
(in
stations) can be computed as follows: for a
summit curve,
L = 125
x G/4; for a sag curve,
L = 100
x G/4. If
L
does not come out to a whole
number of stations using these formulas, then
it is usually extended to the nearest whole
number. You should note that these formulas
for length are for road design only, NOT
railway.
1]
Horizontal length of the portion of the
PVC
to the
PVI;
measured in feet.
12
Horizontal length of the portion of the curve
form the
PVI
to the
PVT;
measured in feet.
e
Vertical (external) distance from the
PVI
to the
curve, measured in feet. This distance is
computed using the formula e
= LG/8,
where
L
is the total length in stations and G is the
algebraic difference of the grades in percent.
Figure 11-16.
—Algebraic differences of grades.
11-14
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