Field Notes - 14070_247
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Simple Curve Layout - 14070_246
VERTICAL CURVES - 14070_248
Engineering Aid 1 - Advanced Structural engineering guide book
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the remainder of the stations in the same way as you
would if the transit was set over the
PC.
If the setup
in the curve has been made but the next stake cannot
be set because of obstructions, the curve can be backed
in. To back in a curve, occupy the
PT.
Sight on the
PI
and set one half of the
I
angle of the plates. The transit
is now oriented so that, if the
PC
is observed, the plates
will read zero, which is the deflection angle shown in
the notes for that station. The curve stakes can then be
set in the same order shown in the notes or in the
reverse order. Remember to use the deflection angles
and chords from the top of the column or from the
bottom of the column. Although the back-in method
has been set up as a way to avoid obstructions, it is
also very widely used as a method for laying out
curves. The method is to proceed to the approximate
midpoint of the curve by laying out the deflection
angles and chords from the
PC
and then laying out the
remainder of the curve from the
PT.
If this method is
used, any error in the curve is in the center where it is
less noticeable.
So far in our discussions, we have begun staking
out curves by setting up the transit at the
PI.
But what
do you do if the
PI
is inaccessible? This condition is
illustrated in
figure 11-11
. In this situation, you locate
the curve elements using the following steps:
1. As shown in
figure 11-11,
mark two intervisible
points
A
and
B
on the tangents so that line
AB
clears the
obstacle.
2. Measure angles
a
and
b
by setting up at both
A
and
B.
3. Measure the distance
AB.
4. Compute inaccessible distance
AV
and
BV
using
the formulas given in
figure 11-11
.
5. Determine the tangent distance from the
PI
to
the
PC
on the basis of the
degree of curve
or other given
limiting factor.
6. Locate the
PC
at a distance
T
minus
AV
from the
point
A
and the
PT
at a distance
T
minus
BV
from point
B.
Field Notes
Figure 11-12
shows field notes for the curve we
solved and staked out above. By now you should be
Figure 11-12.
—Field notes for laying out a simple curve.
11-11
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