This standard provides guidance on the field monitoring of movements in structures, such as cracks or joints, using a portable tape extensometer. It covers the required equipment, installation of measuring points, measurement procedures, and the necessary calculations for temperature and sag corrections.
Code of practice for field monitoring of movement of structures using tape extensometer
Quick Reference Values
Standard tape tension100 N (or as specified by manufacturer)
Typical accuracy of dial gauge unit0.002 mm to 0.01 mm
Invar tape thermal coefficient (approx)1.2 x 10^-6 per °C
Steel tape thermal coefficient (approx)11.6 x 10^-6 per °C
Typical anchor typeGroutable or swage-type stainless steel studs
Key Formulas
L_corr = L_m [1 + α(T_m - T_s)] - C_sag — Corrected length calculation where α is thermal coeff, T is temp, C is sag correction
Practical Notes
Ensure consistent tension application during all readings, as it is a primary source of error.
Measure the temperature of the tape itself, not just ambient air, for accurate thermal correction, especially in direct sunlight.
Regular calibration of the tape and tensioning device is essential for long-term monitoring projects.