Correction Due to Pull or Tension | Taping Corrections | Surveying
If the tension in the tape is greater or less than standard the tape will stretch or become shorter. Tension applied without the aid of a spring balance or tension handle may vary from length to length, resulting in random error. Tensioning equipment containing error would produce a systematic error proportional to the number of tape lengths. The effect of this error is greater on a light tape having a small cross-sectional area than on a heavy tape.
𝐶_𝑃=(𝑃_𝑚−𝑃_𝑠 )𝐿/𝐴𝐸
where:
𝑃_𝑚=the pull/tension during measurement or laying out
𝑃_𝑠=the pull/tension during standardization
𝐿=measured/laid out/nominal length
𝐴=cross-sectional area of the tape
𝐸=modulus of elasticity
𝐶_𝑃=(𝑃_𝑚−𝑃_𝑠 )𝐿/𝐴𝐸
where:
𝐴=𝑊/𝛾𝐿
W=weight of the tape
𝛾=unit weight of the tape
𝐿=nominal length
Ex 1. A 30 m steel tape weighing 1.45 kg is of standard length under a pull of 5 kg, supported for full length. The tape was used in measuring a line 938.55 m long on smooth level ground under a steady pull of 10 kg. Assuming 𝐸=2×10^6 kg/cm² and the unit weight of the steel to be 7.9×10^(−3) kg/cm³. Determine the following:
a) cross-sectional area of the tape
b) Correction due to pull for one tape length, and the total correction due to pull
c) Correct length of the measured line