and BN from the offset stakesS and U. Check theforms by measuring the equal diagonals MC and ND.Mark points denoting elevation directly on the formsand give the data to the petty officer in charge of theconstruction project.After the bridge seat is poured, mark point O.After the rear wall has been poured, mark pointsdefining the girder center lines: a, b, c, d, e, and f.These points will be used for the accurate location ofthe bearing plates that will support the girders.Abutment Wing Walls.— Figure 10-16 illus-trates the stakeout of abutment wing walls. A typicalprocedure is as follows:1. Set up the instrument at B; turn the wing anglefrom G; set reference stakes H and I; measure distancesBH and BI. Set up at A and repeat this procedure toestablish J and K. Use reference linesFG, BH, and AJto set temporary stakes marking the corners of theexcavation for the foundation. Then the methoddescribed earlier for abutments is followed. If abutmentor wing-wall faces are battered (inclined, rather thanvertical), lines are established for both top and bottom.2. To stake out wing walls for askew abutments tothe center line of a bridge, follow the proceduredescribed for askew abutments. Set up the instrumentover N (fig. 10-15); sight on R; turn the wing angles; setreference 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. Ifchaining is impracticable, locate the piers by triangu-lation. Set stakes establishing the center line on eachside of the river. Lay out CD and EF approximately atright angles to the center line, as shown in figure10-17. For well-proportioned triangles, the length ofthe base lines should equal at least one-half CE. ToFigure 10-16.—Staking out abutment wing walls.Figure 10-17.—Method of locating piers.locate piers at A and B, you may use the followingprocedure:1. Establish base lines CD and EF and carefullyreference them.2. Measure the length of each base line with adegree of accuracy suitable for the required accuracy ofthe line CE.3. Measure all angles of the triangles CDE andEFC.4. Compute the distance CE from the triangle CDEand check against the same distance computed fromtriangle EFC. The difference in computed lengths mustbe within the prescribed limits of error.5. Compute angles BDC, ADC, BFE, and AFE.6. Draw a triangulation diagram, showingcomputed angles and distances and measured anglesand distances.7. Turn the computed angles BDC, ADC, BFE, andAFE.8. Set targets DA and DB on the far shore and FBand FA on the near shore so that the intersecting linescan be reestablished without turning angles. Carefullyreference these points.9. Use two instruments to position piers. Occupytwo points, such as C and D, simultaneously, using theintersection of sights CE and DA to locate the pier.Check the locations of pointsA and B if they are withinthe limits of error by sighting along the center line, CE.10-18

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