Code of practice for field monitoring of movement of structures using tape extensometer

IS 12023 - Scope: Key Specifications & Tables

Scope Summary (Clause 3.1.4 & 3.2)

• Tape Extensometer System Components:

  • a) Tape extensometer unit (Fig. 1A)
  • b) Portable calibration frame (Fig. 1B)
  • c) Replaceable steel tape (Fig. 1C)
  • d) Replaceable dial gauge (Fig. 1D)
  • e) Tape adapter hook (Fig. 1E & 1F)

• Permanent Reference Studs/Hooks:

  • a) Permanent reference stud hook (Fig. 2A)
  • b) Protective plug/cap (Fig. 2B & 2C)

Calibration & Convergence Measurement Formula

[ \text{Relative Convergence} = (A1 - C1) - (A2 - C2) ]

Where:

Units (SI Units)

Notes

• Final test results shall be rounded as per IS 2:1960.
• Use permanent reference studs/hooks for accurate convergence monitoring.
• Calibration is critical for reliable measurements.

flowchart LR
    A[Tape Extensometer Unit] --> B[Calibration Frame]
    A --> C[Steel Tape]
    A --> D[Dial Gauge]
    A --> E[Tape Adaptor Hook]
    F[Permanent Reference Stud] --> G[Protective Plug/Cap]

This summary provides the essential scope, components, calibration formula, and units from IS 12023 for tape extensometer usage in convergence measurement.

Tape Extensometer and Accessories (IS 12023)

Description (Clause 3.1 & 3.1.4)

A tape extensometer measures displacement between two points on a structure, useful for monitoring movement in slopes, tunnels, bridges, etc.

Components:

• Tape extensometer unit (Fig. 1A)
• Portable calibration frame (Fig. 1B)
• Replaceable steel tape (Fig. 1C)
• Replaceable dial gauge (Fig. 1D)
• Tape adopter hook (Fig. 1E & IF)

Key Specifications:

• Steel tape: Durable, replaceable, calibrated for precise length measurement.
• Dial gauge: Measures tape elongation or contraction with fine resolution.
• Calibration frame: Ensures accuracy by providing a known length for calibration.

Usage (Clause 6.1):

• Fix tape adopter hooks at measurement points.
• Attach tape extensometer unit between hooks.
• Read dial gauge for displacement.
• Calibrate regularly using the portable frame.

Typical Formula:

Displacement, ( \Delta L = L_{final} - L_{initial} )

Where:

• ( L_{initial} ) = initial tape length between points
• ( L_{final} ) = tape length after movement

flowchart LR
    A[Measurement Points] --> B[Tape Adopter Hooks]
    B --> C[Tape Extensometer Unit]
    C --> D[Dial Gauge Reading]
    D --> E[Displacement Calculation]

This setup provides accurate monitoring of structural movements as per IS 12023.

IS 12023: Installation of Reference Studs and Hooks

Key Specifications & Installation Guidelines

• Permanent Reference Stud/Hook (Clause 3.2a):

  • Use the Permanent Reference Stud Hook as per Fig. 2A.
  • Dimensions are provided in millimeters in the code figures.

• Protective Plug/Cap (Clause 3.2b):

  • Use protective plugs/caps (Fig. 2B & 2C) to safeguard studs/hooks.

• Pattern of Installation (Clause 5.1):

  • Install studs/hooks in predetermined patterns:
    • Radial grid or
    • Triangular grid
  • This arrangement is essential for monitoring lining convergence (see Fig. 3).

• Tape Extensometer Setup (Clause 6.1.2):

  • Stretch the free end of the steel tape to the second reference stud/hook to measure displacement accurately.

• Error Minimization (Clause 8.1):

  • Avoid loose connections of studs/hooks and anchor rods.
  • Ensure perfect alignment of tape and instrument with reference holes.
  • Maintain proper tension in the spring to prevent measurement errors.

Typical Installation Pattern (Radial Grid)

graph TD
    A[Central Point] --> B[Stud 1]
    A --> C[Stud 2]
    A --> D[Stud 3]
    B --> E[Stud 4]
    C --> F[Stud 5]
    D --> G[Stud 6]

Summary Table: Reference Stud/Hook Installation

Note: Follow the exact dimensions and figures (Fig. 2A-C, Fig. 3) in IS 12023 for precise installation and calibration.

IS 12023: Measurement Procedure for Tape Extensometer (Clause 7.1 & Appendix A)

Key Formulas:

• Relative Convergence (Movement) between two reference studs:

[ \text{Convergence} = (A1 - C1) - (A2 - C2) ]

Where:

• (A1) = Initial dial reading
• (C1) = Initial dial gauge reading
• (A2) = Final tape reading
• (C2) = Final dial gauge reading

Measurement Procedure:

• Use the Tape Extensometer Unit comprising:

  • Tape extensometer (Fig. 1A)
  • Portable calibration frame (Fig. 1B)
  • Replaceable steel tape (Fig. 1C)
  • Replaceable dial gauge (Fig. 1D)
  • Tape adopter hook (Fig. 1E & IF)

• Take readings by:

  1. Noting the visible pinhole position on the tape at the instrument nose.
  2. Recording the dial gauge reading.

Record of Observations Table (Proforma):

Units & Symbols (SI Units):

• Length: metre (m)
• Force: newton (N) = 1 kg·m/s²
• Pressure: pascal (Pa) = 1 N/m²

Rounding:

• Final values must be rounded per IS 2-1960, maintaining significant figures consistent with the standard.

flowchart LR
    A[Tape Extensometer Unit] --> B[Take Initial Readings (A1, C1)]
    B --> C[Take Final Readings (A2, C2)]
    C --> D[Calculate Convergence: (A1-C1) - (A2-C2)]
    D --> E[Record & Analyze Results]

This ensures accurate convergence monitoring in structural foundations per IS 12023.

IS 12023 - Field Observation and Recording (Clause 7.1 & Appendix A)

Key Specifications:

• Observations of tape extensometer (convergence readings) must be recorded using the proforma in Appendix A.
• The proforma captures initial and final readings from dial gauges and tape, calculating relative convergence.

Proforma Table Columns:

Key Formula:

[ \text{Relative Convergence} = (A1 - C1) - (A2 - C2) ]

• A1, C1: Initial readings from dial and gauge.
• A2, C2: Final readings.
• This calculates movement between two reference studs.

Units (SI Units as per IS 12023):

• Length: metre (m)
• Force: newton (N)
• Pressure/Stress: pascal (Pa)
• Time: second (s)

Summary:

• Use the proforma for systematic, error-minimized recording.
• Calculate convergence to monitor structural movement.
• Maintain SI units for consistency.

flowchart LR
    A[Initial Dial Reading (A1)] --> D[Calculate A1 - C1]
    B[Initial Gauge Reading (C1)] --> D
    C[Final Tape Reading (A2)] --> E[Calculate A2 - C2]
    F[Final Gauge Reading (C2)] --> E
    D --> G[Calculate Relative Convergence: (A1-C1)-(A2-C2)]
    E --> G
    G --> H[Record in Proforma]

This ensures accurate field monitoring per IS 12023 standards.

IS 12023: Sources of Error & Precautions in Tape Extensometer Observations

Key Sources of Error (Clause 8.1)

• Loose connections of reference studs/hooks and anchor rods.
• Misalignment of tape and instrument due to improper matching of points and reference holes.
• Loose tensioning spring affecting tape tension.
• Environmental factors and improper calibration.

Precautions

• Ensure firm and secure fixing of reference studs/hooks.
• Maintain perfect alignment of tape and instrument.
• Use proper tension on the tape (avoid slack).
• Calibrate instruments regularly; apply correction factor (k) from calibration.
• Record observations in the proforma (Appendix A) for consistency.

Observation Proforma (Appendix A)

Important Formula

Relative Convergence (ΔL):

[ \Delta L = (A1 - C1) - (A2 - C2) ]

Where:

• (A1, A2) = Dial readings initially and finally
• (C1, C2) = Gauge readings initially and finally

Calibration Correction

Apply correction factor (k) from calibration results to adjust readings.

Summary Diagram of Error Sources

graph LR
A[Loose Connections] --> E[Measurement Error]
B[Misalignment of Tape] --> E
C[Loose Tension Spring] --> E
D[Environmental Factors] --> E
E --> F[Inaccurate Convergence Reading]

Ensure careful setup and calibration to minimize errors and obtain reliable convergence monitoring.

Maintenance of Tape Extensometer (IS 12023)

Key Points from IS 12023:

• Purpose: Measures displacement/movement between two points on structures (slopes, tunnels, bridges, etc.).
• Operation (Clause 6.1): Use carefully to avoid damage; ensure proper calibration.
• Maintenance (Clause 7.1 & Appendix A): Regular checks, calibration, and record-keeping are essential.

Important Formula for Relative Movement Calculation

[ \text{Relative Movement} = (A1 - C1) - (A2 - C2) ]

Where:

• A1 = Initial dial reading
• C1 = Initial dial gauge reading
• A2 = Final tape reading
• C2 = Final dial gauge reading

Maintenance Checklist (Table 9, Clause 7.1)

• Clean tape and dial gauge regularly.
• Check for tape elongation or damage.
• Calibrate instrument using known reference studs.
• Record observations systematically using the proforma.

Proforma for Observation Record (Appendix A)

Units Reference (SI Units)

• Length: metre (m)
• Force: newton (N) = kg·m/s²
• Pressure/Stress: pascal (Pa) = N/m²

flowchart LR
    A[Start Measurement] --> B[Record Initial Readings (A1, C1)]
    B --> C[Measure Final Readings (A2, C2)]
    C --> D[Calculate Relative Movement: (A1-C1)-(A2-C2)]
    D --> E[Log Data in Proforma]
    E --> F[Check & Maintain Instrument]
    F --> G[Repeat for Next Observation]

Summary: Maintain tape extensometer by cleaning, calibrating, and recording data using the formula above, ensuring reliable

IS 12023: Proforma for Record of Observations (Tape Extensometer Convergence Readings)

Key Specifications (Appendix A, Clause 7.1)

Observation Table Format

• Relative Convergence = (A1 - C1) - (A2 - C2)

Measurement Notes (Clause 6.1.5)

• Reading = Position of visible pinhole on tape + dial gauge reading.

Units (SI Units)

• Length: metre (m)
• Force: newton (N) = 1 kg·m/s²
• Pressure: pascal (Pa) = 1 N/m²

Rounding (IS 2-1960)

• Final values must be rounded off with the same significant digits as specified in the standard.

flowchart TD
    Start[Start Observation]
    InitDate[Record Initial Date]
    ObsBy[Record Observer]
    Readings[Take Initial Readings (A1, C1)]
    FinalDate[Record Final Date]
    FinalReadings[Take Final Readings (A2, C2)]
    Calculate[Calculate Relative Convergence: (A1-C1)-(A2-C2)]
    Remarks[Add Remarks]
    End[Complete Record]

    Start --> InitDate --> ObsBy --> Readings --> FinalDate --> FinalReadings --> Calculate --> Remarks --> End

This proforma ensures standardized, accurate recording of convergence measurements using tape extensometers as per IS 12023.