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Reconnaissance - 14070_366
Computations - 14070_368

Engineering Aid 1 - Advanced Structural engineering guide book
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Figure 15-26.—Field notes for base line measurement. Base  Line  Measurement tensiometer (spring balance). When the proper tension The accuracy of all directions and distances in a system  depends  directly  upon  the  accuracy  with which   the   length   of   the   base   line   is   measured. Therefore, base line measurement is vitally important. A transit must be used to give precise alignment while measuring a base line. For third-order triangulation measurement with a steel tape, you are required to incorporate all the tape corrections described in the EA3  TRAMAN.  For  measurement  over  rough  terrain, end supports for the tape must be provided by posts driven  in  the  ground  or  by  portable  tripods.  These supports  are  usually  called  chaining bucks.  The  slope between   bucks   is   determined   by   measuring   the difference in elevation between the tops of the bucks with a level and rod. On the top of each buck, a sheet of copper or zinc is tacked down, which provides a surface on which tape lengths can be marked Bucks are setup along the base line  at  intervals  of  one-tape  length.  The  tape,  with thermometers fastened at each end, is stretched between the  supports  and  brought  to  standard  tension  by  a is indicated, the position of the forward end is marked on the metal strip with a marking awl or some other needle-pointed   marker.   At   the   same   time,   the thermometer readings are taken. If stakes, driven at tape-length intervals, are used as tape supporters, the end of the tape may begin to lie slightly off the metal marking strip on the buck after a few tape intervals have been laid off. To take care of this situation, the head chairman carries a finely divided (to 0.001 ft) pocket scale. With this scale he measures the distance that the tape must be  set back or set forward to bring the end again on the marking strip. The set back or set forward is entered in the field notes and deducted from or added to the tape length for that particular interval. Figure  15-26  shows  field  notes  for  a  base  line measurement.  In  this  case  the  tape  was  supported  on stakes, driven at full-tape, 100-foot intervals. With the exception of the interval between stakes 5 and 6, the amounts to the standard tape length (with the tape supported at both ends, and with standard tension 15-33







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