Chapter 3

• Taping Corrections


  Adjustments made to account for various factors when measuring horizontal distances using a tape
• Measurement of Horizontal Distances: Taping Corrections

  1. Correction due to Slope

  2. Correction due to Alignment

  3. Correction due to Temperature

  4. Correction due to Tension

  5. Correction due to Sag

  6. Correction due to Wind

  7. Normal Tension
• Slope correction (gentle slope)


  𝐶ℎ= ℎ2/2𝑠
• Slope correction (steep slope)


  𝐶ℎ = ℎ2/2𝑠 + ℎ4/8𝑠3
• Slope correction (very steep slope)


  𝐶ℎ = 𝑠(1 − 𝑐𝑜𝑠𝜃)
• Correction due to Alignment

  Error due to alignment is generally the least important among the different errors encountered in taping
• Correction due to Temperature


  𝐶𝑡 = 𝐶𝐿 (𝑇 − 𝑇𝑠)
• Correction due to Tension


  �� = 𝑈��𝑖𝑡 𝑆𝑡𝑟𝑒𝑠𝑠/𝐸𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 𝑝𝑒𝑟 𝑈𝑛𝑖𝑡 𝐿𝑒𝑛𝑔𝑡ℎ

  𝐶𝑝 = 𝑃𝑚 − 𝑃𝑠 𝐿/𝐴𝐸

  𝐿1 = 𝐿 ± 𝐶𝑝
• Correction due to Sag

  𝐶𝑠 = 𝜔2𝐿3/24𝑃2 (tape supported at ends)

  𝐶𝑠 = ��2𝐿/24𝑃2 (tape supported at ends and mid-point)
• L'


  Correct length of line. The correction is added since tape is too long
• Correction due to Sag

  1. Tape attains its correct length when it is fully supported and subjected to the pull for which it was standardized

  2. If the support is only at its ends or at the two points measured, it will sag even if the standard pull is maintained because of its own weight
• Tape support configurations


  • Tape Supported at End Points
  • Tape Supported at Ends and Mid-Point
  • Tape Supported at Ends and Two Intermediate Points
  • Tape Supported at Ends and Every Quarter Point
• Correction due to sag

  The difference in length between the arc formed by the tape and the subtending chord
• Cs


  Correction due to sag or the difference between the tape reading and the horizontal distance between supports (m)
• ω


  Weight of tape per unit length (kg/m)
• W


  Total weight of tape between supports or the unsupported length of tape (m)
• L


  Interval between supports or the unsupported length of tape (m)
• P


  Tension or pull applied on the tape (kg)
• A strong wind blowing perpendicular to the direction of taping will move the middle and the unsupported portion of the tape to one side of the line measured
• To avoid wind-induced error, it is preferable not to undertake any taping work during windy days
• Correction to Normal Tension

  1. Stretch the tape on a concrete pavement (or level ground) by applying its prescribed standard pull, and mark its ends on the pavement

  2. Hold the tape above the ground by supporting it only at its ends, then, pull the tape until the ends coincide with the marked points on the pavement
• PN


  Normal tension or the pull which will eliminate the effect of sag (kg)
• A


  Cross-sectional area of tape (cm^3)
• E


  Modulus of elasticity of tape material (kg/cm^3)
• Ps


  Standard pull for the tape (kg)