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CHECKING THE COMPUTATION BY PLOTTING - 14071_257
QUESTIONS - 14071_259

Engineering Aid 2 - Intermediate Structural engineering guide book
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vertical  scale;  that  is,  with  the  vertical  scale  perhaps 10 times the horizontal scale. After the POVCs have been plotted, you should be able to draw a smooth parabolic curve through the points with the help of a ship’s curve or some other type of irregular curve; if you can’t, check your computations. USING A PROFILE WORK SHEET After you have had some experience computing curves  using  a  table  as  shown  in  the  foregoing examples, you may wish to eliminate the table and write your computations directly on a working print of the profile. The engineer will set the grades and indicate the length of the vertical curves. You may then scale the  PVI elevations  and  compute  the  grades if  the  engineer  has  not  done  so.  Then,  using  a calculator,   compute   the   POVT  elevations   at   the selected stations. You can store the computations in some  calculators.  That  allows  you  access  to  the grades, the stations, and the elevations stored in the calculator from one end of the profile to the other. You can then check the calculator at each previously set PVI elevation.  Write  the  tangent  elevation  at  each station on the work sheet. Then compute each vertical offset: mentally note the  x/ 1 ratio; then square it and multiply by e on your calculator. Write the offset on the work print opposite the tangent elevation. Next, add or subtract the offsets from the tangent elevations (either mentally or on the calculator) to get the curve elevations; then record them on the work sheet. Plot the POVC elevations and draw in the curve. Last, put the necessary information on the original tracing. The information   generally   shown   includes   grades; finished elevations; length of curve; location of PVC, PVI, PVT, and the e. Figure 11-21 shows a portion of a  typical  work  sheet  completed  up  to  the  point  of drawing  the  curve. FIELD STAKEOUT OF VERTICAL CURVES The stakeout of a vertical curve consists basically of marking the finished elevations in the field to guide the construction personnel. The method of setting a grade stake is the same whether it is on a tangent or on a  curve,  so  a  vertical  curve  introduces  no  special problem. As indicated before, stakes are sometimes set closer together on a curve than on a tangent. But that will usually have been foreseen, and the plans will show the finished grade elevations at the required stations.  If,  however,  the  field  conditions  do  require  a stake at an odd plus on a curve, you may compute the needed  POVC  elevation  in  the  field  using given on the plans and the computational explained in this chapter. the  data methods Figure 11-21.—Profile  work  sheet. 11-20







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