and BN from the offset stakes S and U. Check the
forms by measuring the equal diagonals MC and ND.
Mark points denoting elevation directly on the forms
and give the data to the petty officer in charge of the
construction project.
After the bridge seat is poured, mark point O.
After the rear wall has been poured, mark points
defining the girder center lines: a, b, c, d, e, and f.
These points will be used for the accurate location of
the bearing plates that will support the girders.
Abutment Wing Walls.— Figure 10-16 illus-
trates the stakeout of abutment wing walls. A typical
procedure is as follows:
1. Set up the instrument at B; turn the wing angle
from G; set reference stakes H and I; measure distances
BH and BI. Set up at A and repeat this procedure to
establish J and K. Use reference lines FG, BH, and AJ
to set temporary stakes marking the corners of the
excavation for the foundation. Then the method
described earlier for abutments is followed. If abutment
or wing-wall faces are battered (inclined, rather than
vertical), lines are established for both top and bottom.
2. To stake out wing walls for askew abutments to
the center line of a bridge, follow the procedure
described for askew abutments. Set up the instrument
over N (fig. 10-15); sight on R; turn the wing angles; set
reference stakes to establish the wing line from N.
Establish the wing line from M in the same manner.
Piers.— After the center line of the bridge is es-
tablished, locate the piers by chaining if possible. If
chaining is impracticable, locate the piers by triangu-
lation. Set stakes establishing the center line on each
side of the river. Lay out CD and EF approximately at
right angles to the center line, as shown in figure
10-17. For well-proportioned triangles, the length of
the base lines should equal at least one-half CE. To
Figure 10-16.—Staking out abutment wing walls.
Figure 10-17.—Method of locating piers.
locate piers at A and B, you may use the following
procedure:
1. Establish base lines CD and EF and carefully
reference them.
2. Measure the length of each base line with a
degree of accuracy suitable for the required accuracy of
the line CE.
3. Measure all angles of the triangles CDE and
EFC.
4. Compute the distance CE from the triangle CDE
and check against the same distance computed from
triangle EFC. The difference in computed lengths must
be within the prescribed limits of error.
5. Compute angles BDC, ADC, BFE, and AFE.
6. Draw a triangulation diagram, showing
computed angles and distances and measured angles
and distances.
7. Turn the computed angles BDC, ADC, BFE, and
AFE.
8. Set targets DA and DB on the far shore and FB
and FA on the near shore so that the intersecting lines
can be reestablished without turning angles. Carefully
reference these points.
9. Use two instruments to position piers. Occupy
two points, such as C and D, simultaneously, using the
intersection of sights CE and DA to locate the pier.
Check the locations of points A and B if they are within
the limits of error by sighting along the center line, CE.
10-18
