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RECORDING   NOTES   FOR   SLOPE Chaining
Identifying Chaining Mistakes and Errors

Engineering Aid 3 - Beginning Structural engineering guide book
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corrections should be added as indicated by the plus signs. To  the  right  of  the  “Temp.  Corr.”  column is  the  “Slope  Corr.”  column.  Its  entries  are  to be  subtracted  as  indicated.  Use  the  following equation  to  compute  the  slope  correction. For the first taped interval, we have an h of 6.0 ft  and  an  s  of  100  ft. Therefore The  slope  correction  is  computed  as  follows: Next to the column for slope correction comes the “Total  Corr.”  column,  containing  the  algebraic sum  of  the  three  corrections  for  each  taped interval.  Finally,  in  the  “Horiz.  Dist.”  column, each value is determined by subtracting the total correction  for  each  interval  from  the  measured slope  distance  for  that  interval.  (This  example used in figure 12-17 happens to be all negative.) At  the  bottom  of  this  column,  the  sum  of  the horizontal   distances   appears.   This   is   the horizontal  distance  from  station  K  to  station  L. Solving Surveying Problems by Tape Before   the   modern   instruments   used   to measure  angles  directly  in  the  field  were  devised, the  tape  (or  rather,  its  equivalent,  the  Gunter’s chain) was often used. This tape was used not only for  measuring  linear  distances  but  also  for measuring  angles  more  accurately  than  was possible  with  a  compass. LAYING   OUT   A   RIGHT   ANGLE.—   In laying  out  a  right  angle  (or  erecting  a  perpendicu- lar)  by  tape,  you  apply  the  basic  trigonometric theory  that  a  triangle  with  sides  in  the  ratio  of 3:4:5 is always a right triangle. Assume that on the line AB shown in figure 12-18, you want to use a 100-ft tape to run a line from  C  perpendicular  to  AB.  If  a  triangle  with sides in the ratio of 3:4:5 is a right triangle, then one  with  sides  in  the  ratio  of  30:40:50  is  also  a right  triangle.  From  C,  measure  off  DC,  30  ft Figure 12-18.-Laying out a right angle using a 100-foot tape. long. Set the zero-foot end of the tape on D and the 100-ft end on C. Have a person hold the 50-ft and 60-ft marks on the tape together and run out the bight. When the tape becomes taut, the 40-ft length  from  C  will  be  perpendicular  to  AB. MEASURING   AN   ANGLE   BY   TAPE.— There  are  two  methods  commonly  used  to determine   the   size   of   an   angle   by   tape:   the CHORD  method  and  the  TANGENT  method. The  chord  method  can  be  applied,  using  the example  shown  in  figure  12-19.  Suppose  you  want to  determine  the  size  of  angle  A.  Measure  off equal  distances  from  A  (80.0  ft),  and  establish points  B  and  C.  Measure  BC;  assume  that  it measures  39.5  ft,  as  shown.  You  can  now determine  the  size  of  angle  A  by  applying  the following   equation: in which Figure 12-19.-Determining the size of an angle by the chord method. 12-21







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