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IS 12023:1987 is the Indian Standard (BIS) for field monitoring of movement of structures using tape extensometer. 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
ISO 18649:2018International Organization for Standardization (ISO), Switzerland
HighCurrent
Geotechnical investigation and testing — Field testing — Monitoring of displacements in rock masses by extensometers
Both cover monitoring displacements using extensometers, with ISO focusing on rock masses, a key application of IS 12023.
ASTM D4403 / D4403M - 19ASTM International, USA
HighCurrent
Standard Test Method for Extensometers Used in Rock
Both detail methods for using tape extensometers for monitoring movements in rock, common in tunnels and large excavations.
BS EN ISO 18649:2018BSI Group (British Standards Institution), UK
HighCurrent
Geotechnical investigation and testing. Field testing. Monitoring of displacements in rock masses by extensometers
Identical in technical content to ISO 18649, providing guidance on monitoring rock mass displacement with extensometers.
Key Differences
≠IS 12023 has a broader stated scope, covering 'structures or rock masses', whereas standards like ISO 18649 and ASTM D4403 are more specifically focused on geotechnical applications in rock.
≠IS 12023 is more prescriptive, specifying a standard tension of 100 N (10 kgf), while modern international standards are more performance-based, allowing for manufacturer-specified procedures while detailing the required principles and corrections.
≠Being an older standard (1987), IS 12023 does not explicitly discuss modern variations like digital readouts or place as strong an emphasis on comprehensive uncertainty analysis as newer standards like ISO 18649:2018.
≠While IS 12023 acknowledges sag as an error, it provides no correction formula, implying it is negligible. ASTM D4403/M explicitly discusses the catenary effect and the need for sag correction, especially on longer spans.
Key Similarities
≈All standards are based on the same fundamental principle of measuring the change in distance between two fixed reference points using a tensioned tape or wire.
≈The basic apparatus described is consistent across all standards: a graduated tape, a tensioning device, a reading head (micrometer/vernier), and fixed anchor points.
≈All standards universally recognize that thermal expansion/contraction of the measuring tape is a primary source of error and mandate that readings be corrected for temperature changes.
≈The primary intended application is the same: monitoring convergence or divergence in large-scale civil engineering and mining structures like tunnels, dam galleries, and large excavations.
Parameter Comparison
Parameter
IS Value
International
Source
Applied Tape Tension
Specifies a standard tension of 100 N (10 kgf).
Typically 100 N, but allows for manufacturer's specified tension, which must be kept constant.
ISO 18649:2018
Tape Material
Primarily refers to steel tapes for which correction is provided.
Explicitly discusses both steel and Invar tapes, noting Invar's low thermal coefficient for high-precision work.
ASTM D4403 / D4403M - 19
System Measurement Precision
States expected precision is of the order of 0.1 mm to 0.5 mm.
Requires that the precision of the system be evaluated and stated, with achievable precision being similar (e.g., ±0.1 mm over 10 m).
ISO 18649:2018
Typical Span Length
Implied for spans up to 30 m.
Notes applications for spans up to 50 m (150 ft), with increasing emphasis on sag correction for longer distances.
ASTM D4403 / D4403M - 19
Coefficient of Thermal Expansion (Steel)
Provides a value of 11.7 x 10⁻⁶ per °C for steel tape.
Uses typical values for steel (e.g., 11.2 x 10⁻⁶/°C or 6.2 x 10⁻⁶/°F) and emphasizes using the manufacturer's certified value.
ASTM D4403 / D4403M - 19
Calibration
Recommends periodic calibration against a reference bar or standard tape, with no fixed interval.
Requires calibration before first use and at regular intervals defined by the project's quality plan or when damage is suspected.
ISO 18649:2018
⚠ Verify details from original standards before use
Key Values5
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
Tables & Referenced Sections
Key Tables
Table 1 - Coefficients of Linear Thermal Expansion
Key Clauses
Clause 3 - Equipment
Clause 4 - Installation of Measuring Points
Clause 5 - Measurement Procedure
Clause 6 - Calculations and Corrections
Clause 7 - Presentation of Results
Frequently Asked Questions4
What is a tape extensometer used for?+
To measure the change in distance between two fixed points on a structure to monitor cracks, joint movements, convergence in tunnels, or deformation of slopes.
Why is temperature correction important in these measurements?+
The steel or invar tape expands and contracts with temperature. This change must be calculated and removed from the reading to isolate the actual structural movement (Clause 6.2).
What is the difference between using a steel tape and an invar tape?+
Invar tapes have a much lower coefficient of thermal expansion, making them less sensitive to temperature changes and thus more accurate for high-precision work.
How are the reference points installed?+
Stainless steel anchors or studs are typically grouted or epoxied into holes drilled on either side of the feature being monitored (Clause 4).