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CORRECTING   FOR   TEMPERATURE Variation
Preparing Chaining Notes

Engineering Aid 3 - Beginning Structural engineering guide book
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tensions for tapes supported at only the ends as follows: For  100-ft  tapes,  from  20  to  30  lb angle, A, or the difference in elevation h between the taped stations. When the vertical angle is used, the formula for  slope  correction  is  as  follows: For  150-ft  tapes,  from  25  to  30  lb For  200-ft  tapes,  from  30  to  40  lb Generally,  for  a  heavy  100-ft  tape  weighing about   3   lb   that   was   standardized,   whether supported  throughout  or  at  the  ends  only,  the systematic error per tape length caused by sag is as  follows: 10-lb  tension  =  0.37  ft 20-lb  tension  =  0.09  ft 30-lb  tension  =  0.04  ft For   the   Engineering   Aid’s   survey   work, measurements are normally in the lower order of precision. The correction for sag varies with the cube of the unsupported length; for short spans, it is often negligible. CORRECTING  FOR  SLOPE.—  When  you take a measurement with a tape along an inclined plane  (along  the  natural  slope  of  the  ground), obviously, the taped distance is greater than the horizontal   distance.   This   taped   distance   is represented by s in figure 12-15. The  difference  between  the  slope  distance  and the horizontal distance (s – d) is called the slope correction.  This  correction  is  always  subtracted from the slope distance. To compute for the slope correction,  you  should  know  either  the  vertical Figure  12-15.-Correction  for  slope  distance. When the difference in elevation is used, the approximate   formula   derived   by   Pythagorean theorem  of  a  right  triangle  (fig.  12-15)  for  the slope  correction  is  as  follows: But  for  a  small  slope,  d  is  approximately  equal to  s;  therefore, For  slopes  greater  than  5  percent,  a  closer approximation  of  Ch  can  be  determined  by expanding  the  above  formula  to  this  form. 12-18







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