Code of Practice for Use of Structural Steel In Overhead Transmission Line Towers, Part 3 Testing

Scope of IS 802 Part 3: Testing of Steel Transmission Line Towers

• Purpose: Specifies procedures for testing steel transmission line towers, focusing on load application, measurement, and reporting.

• Key Points:

  • Testing covers verification of structural performance under specified loads (Clause 12.1).
  • Loads, permissible stresses, and design requirements are detailed in Part I of IS 802 (Clause 1.1.1).
  • Test reports must include:
    • Tower type, manufacturer, client details.
    • Test dates, location, personnel.
    • Assembly drawings and load diagrams.
    • Rigging arrangements and test facility details.
    • Load tables per test step and deflection records.
    • Failure analysis if applicable (max load, failure mode, element details).
    • Photographic evidence of structure and failures (Clause 12.1).

• Rounding Off: Test results rounded per IS 2-1960, matching significant figures of specified values (Clause 0.4).

• References: Practices align with ASCE Guide and IEC draft on overhead line tower loading tests (Clause 0.3).

Summary Table: Test Report Contents (Clause 12.1)

This scope ensures comprehensive, standardized testing and documentation for steel transmission towers.

IS 802 Part 3 — General Testing Guidelines Summary

The code emphasizes detailed documentation and accuracy in testing overhead transmission line towers:

Key Reporting Requirements (Clause 12.1)

• Tower & Manufacturer Details: Type, manufacturer, client info.
• Test Details: Dates, location, personnel present.
• Drawings & Diagrams: Assembly/shop drawings, dimensioned line diagram with load points/directions.
• Load Application: Rigging arrangement diagram.
• Test Facility: Description including load transducers (number, location, range, calibration, accuracy).
• Load & Deflection Tables: Separate tables per test for applied loads and recorded deflections.
• Failure Reporting: Max load before collapse, failure description, failed elements’ mechanical/dimensional data.
• Photographs: Overall structure and failure details.

Rounding Off (Clause 0.4)

• Final test results must be rounded per IS 2-1960, maintaining the same significant figures as specified values.

Typical Test Load Table Format (Example)

Deflection Table Format (Example)

flowchart LR
    A[Test Setup] --> B[Load Application]
    B --> C[Measurement of Loads & Deflections]
    C --> D[Data Recording & Tabulation]
    D --> E[Failure Analysis (if any)]
    E --> F[Report Compilation]

This structured approach ensures clarity, repeatability, and compliance with IS 802 Part 3 testing requirements.

Calibration of Instruments as per IS 802 Part 3

• Plumb Tolerance: The test tower must be erected within a tolerance of 1 in 360 (Clause 2.3).

• Calibration Procedure (Clause 3.1):

  • Use standard weights for systematic calibration of all measuring instruments.
  • Calibration must cover the full anticipated load range before testing each tower.
  • Develop calibration curves to correct test load readings during actual tests.

• Load Application & Measurement Accuracy:

  • Graduated scales on towers should be about 1 meter long with markings accurate to ±5 mm (Clause 8.2).
  • Final test results must be rounded off as per IS 2-1960, maintaining the same significant figures as specified values.

Calibration Curve Concept

Use this table to plot the calibration curve and adjust readings accordingly.

graph LR
A[Standard Weights] --> B[Instrument Calibration]
B --> C[Calibration Curve]
C --> D[Load Correction]
D --> E[Accurate Test Results]

Summary: Calibrate instruments with standard weights up to max test load, plot correction curves, ensure tower plumb within 1:360, and use precise scales for reliable load measurements.

IS 802 Part 3 - Method of Load Application: Key Points

1. Calibration of Instruments (Clause 3.1)

• Instruments must be calibrated systematically using standard weights.
• Calibration up to maximum anticipated test load before starting.
• Calibration curves drawn to correct test loads.

2. Loading Cases (Clause 4.3)

• Load values, directions, and points of application are provided by the client.

3. Load Application Steps (Clause 6.2)

• Loads applied gradually up to ultimate design load = Design Load × Factor of Safety (F.O.S).
• Steps for loading and unloading:
  • 25%, 50%, 75%, 90%, 95%, 100%

4. Load Application Method (Clause 4.1)

• Loads applied via rigging diagram through:
  • Normal wire attachments
  • Angles or bent plates
  • U bolts, D shackles, or swinging brackets (if purchaser agrees)
• Rigging must be safe and satisfactory.

Summary Table: Load Application Steps

flowchart LR
    A[Start Calibration] --> B[Calibrate Instruments up to Max Load]
    B --> C[Draw Calibration Curves]
    C --> D[Apply Loads Gradually]
    D --> E[Load Steps: 25%, 50%, 75%, 90%, 95%, 100%]
    E --> F[Use Rigging Diagram for Load Application]
    F --> G[Ensure Safe Rigging]
    G --> H[Complete Test]

This ensures accurate, safe, and systematic load application during tower testing as per IS 802 Part 3.

IS 802 Part 3: Load and Deflection Measurement Summary

Key Specifications

• Loading Cases (Clause 4.3):

  • Defined by client: load values, directions, and points of application.

• Load Measurement (Clause 5.1):

  • Use strain devices or calibrated weights.
  • Ensure pulley friction is eliminated or measured and corrected.

• Deflection Measurement (Clause 5.2 & 8.1):

  • Measure tower deflections at top cross arm level on front sides of transverse and longitudinal faces.
  • Record deflections for:
    • Before load
    • Load on
    • Load off
  • Use theodolite and graduated scales for precise deflection readings at all test stages.

Typical Deflection Measurement Procedure

Important Notes

• Deflection readings help verify structural performance under load.
• Correct load measurement is critical to avoid errors due to friction or misplacement.
• Deflection limits depend on tower design and client specifications (refer to IS 802 Part 3 for limits).

flowchart LR
    A[Load Application] --> B[Load Measurement]
    B --> C{Pulley Friction?}
    C -- Yes --> D[Measure & Correct]
    C -- No --> E[Record Load]
    E --> F[Apply Load to Tower]
    F --> G[Deflection Measurement]
    G --> H[Before Load, Load On, Load Off]
    H --> I[Analyze Deflection]

For detailed deflection limits and load cases, refer to client specifications and IS 802 Part 3 annexures.

IS 802 Part 3 - Normal Load / Broken Wire Load Tests

Key Specifications (Clauses 6.2, 7.1, 7.2, 9.3)

• Load Application Steps:
  Gradually apply loads as percentages of ultimate design load (Design Load × F.O.S):
  • 25%, 50%, 75%, 90%, 95%, 100%
• Observation Periods:
  • For loads up to 95%: observe for 2 minutes at each step (excluding load adjustment time).
  • At 100% load: observe for 5 minutes.
• Destruction Test:
  • After 100% ultimate load, increase load in 5% increments until failure.
  • All normal/broken wire test provisions apply.

Load Application & Observation Summary

Formula for Ultimate Design Load

[ \text{Ultimate Design Load} = \text{Design Load} \times \text{Factor of Safety (F.O.S.)} ]

Notes

• Loads are applied and released gradually in the same steps.
• Monitor tower for any signs of failure during and after loading.
• Mechanical strength checks per Clause 10 must be ensured.

flowchart TD
    A[Start Load Test] --> B{Apply Load Steps}
    B -->|25%, 50%, 75%, 90%, 95%| C[Observe 2 min each]
    C --> D[Apply 100% Load]
    D --> E[Observe 5 min]
    E --> F{Destruction Test?}
    F -->|Yes| G[Increase load by 5% steps]
    G --> H[Observe until failure]
    F -->|No| I[End Test]

This ensures safe, gradual loading and reliable verification of tower strength per IS 802 Part 3.

IS 802 Part 3 - Observation Periods & Testing Key Points

Observation Periods (Clause 7)

• The standard does not specify explicit observation periods during load tests.
• Final test results must be rounded off per IS 2-1960, keeping the same significant figures as specified values.

Load Application Steps (Clause 6.2)

Loads are applied gradually to the ultimate design load (Design Load × Factor of Safety) in steps:

Loads must be applied and released gradually in the same sequence.

Test Reporting Requirements (Clause 12.1)

Reports must include:

• Tower type, manufacturer, client info
• Test dates, location, and personnel
• Assembly/shop drawings & modifications
• Dimensioned tower diagrams with load points & directions
• Rigging arrangement diagrams
• Test facility description & calibration data of load transducers
• Load tables for each test step
• Deflection tables
• Failure details (if any) including max loads, failure description, and failed element specs
• Photographs of the structure and failures

Summary Diagram of Load Steps

graph LR
    A[0% Load] --> B[25% Load]
    B --> C[50% Load]
    C --> D[75% Load]
    D --> E[90% Load]
    E --> F[95% Load]
    F --> G[100% Load]
    G --> F
    F --> E
    E --> D
    D --> C
    C --> B
    B --> A

Note: Observation duration at each load step is typically defined by project specifications or test procedures, as IS 802 Part 3 does not specify it explicitly.

Deflection Recording per IS 802 Part 3

• Measurement Points (Clause 5.2):
  Deflections are to be recorded at the top cross arm level on the front sides of transverse and longitudinal faces or front & rear sides of transverse faces.

• Load Conditions (Clause 5.2):
  Record deflections at three stages:

  • Before load
  • Load applied
  • Load removed

• Instrumentation & Calibration (Clause 3.1):

  • Use calibrated theodolite and graduated scales.
  • Calibrate instruments with standard weights up to max test load.
  • Draw calibration curves to correct test loads.

• Load Cases (Clause 4.3):
  Client provides load values, directions, and points of application.

Typical Deflection Recording Procedure:

Key Notes:

• Deflection Δ can be calculated as:
  [ \Delta = L_{loaded} - L_{unloaded} ] where (L) is the measured length or displacement from a fixed reference.

• Use theodolite for angular displacement converted to linear deflection via geometry.

flowchart LR
    A[Start: Tower Setup] --> B[Calibrate Instruments]
    B --> C[Apply Load as per Client Specs]
    C --> D[Measure Deflection at Top Cross Arm]
    D --> E[Record Deflection: Before Load, Load On, Load Off]
    E --> F[Analyze & Correct Data Using Calibration Curves]
    F --> G[Complete Test]

This ensures accurate deflection monitoring for structural safety verification during load tests.

IS 802 Part 3 – Destruction Test Key Points

• Clause 9.1: Destruction test is optional, performed if purchaser desires.
• Clause 9.2: Test can be under normal or broken wire conditions (agreed upon).
• Clause 9.3:
  • Follow all normal/broken wire load test provisions.
  • After reaching ultimate design load, increase loads in 5% increments until failure.

Important Specifications:

Summary of Load Application for Destruction Test

graph LR
A[Start with Ultimate Design Load] --> B{Increase Load by 5% Steps?}
B -- Yes --> C[Apply Load Increment]
C --> D{Structure Fails?}
D -- No --> B
D -- Yes --> E[Test Ends]

Note: This test ensures the tower's mechanical strength beyond design loads, validating safety margins.

IS 802 Part 3: Mechanical Strength Check of Tower

Key Points and Specifications:

• Ultimate Load Testing (Clause 9.3 & 2.1.1):

  • Apply ultimate design loads incrementally.
  • Increase loads in 5% steps beyond ultimate design load until failure or test completion.
  • Tower must withstand 100% ultimate load without failure.

• Load Application (Clause 4.1):

  • Loads applied via rigging diagram.
  • Use normal wire attachments, angles, bent plates.
  • U-bolts, D-shackles, or hangers allowed if rigging is safe.

• Failure & Replacement (Clause 11.1):

  • If failure occurs, replace failed part with stronger one.
  • Retest structure at 100% ultimate load.

Typical Load Increment Formula:

[ P_{n} = P_u \times (1 + 0.05 \times n) ]

• (P_u) = Ultimate design load
• (n) = Number of 5% increments after ultimate load reached

Summary Table for Load Steps:

flowchart TD
    A[Start Load Test] --> B[Apply Load up to 100% Ultimate Load]
    B --> C{Load Held?}
    C -- Yes --> D[Increase Load by 5%]
    D --> E{Load > Failure?}
    E -- No --> C
    E -- Yes --> F[Test Ends]
    C -- No --> G[Replace Failed Part]
    G --> H[Retest at 100% Ultimate Load]
    H --> F

Summary: IS 802 Part 3 mandates incremental load testing beyond ultimate design load in 5% steps, safe rigging, and retesting after part replacement to ensure mechanical strength of towers.

IS 802 Part 3: Remedial Measures for Premature Failure

Key Clauses:

• Clause 11.1:

  • Replace failed parts with members of greater mechanical strength.
  • Modified tower must pass ultimate load test at 100% specified load again.

• Clause 10.3:

  • Coupons may be cut from test members for laboratory material testing if requested.

• Clause 10.2:

  • Ovalization of holes and permanent bolt deformation are not considered failures.

Test Report Requirements (Clause 12.1):

• Detailed documentation including:
  • Tower type, manufacturer, client, test dates & location.
  • Assembly/shop drawings and modifications.
  • Load diagrams, rigging arrangement, and test facility details.
  • Load and deflection tables per test step.
  • Failure description, max load before collapse, failed element details.
  • Photographs showing structure and failure details.

Summary Table for Remedial Action:

flowchart TD
    A[Premature Failure Detected] --> B[Identify Failed Part]
    B --> C[Replace with Stronger Member]
    C --> D[Retest at 100% Ultimate Load]
    D -->|Pass| E[Approve Structure]
    D -->|Fail| B
    E --> F[Prepare Detailed Test Report]

Note: Always ensure material properties meet or exceed original specifications to prevent repeat failure.

IS 802 Part 3 — Test Report Key Requirements (Clause 12.1 & 12.2)

The Test Report for tower testing must include:

• Tower Details: Type, manufacturer, client, test dates & location.
• Personnel: Names of persons present during tests.
• Drawings: Assembly/shop drawings list with modifications.
• Diagrams:
  • Dimensioned line diagram showing load points & directions.
  • Rigging arrangement diagram for load application.
• Test Facility: Description including load transducers (number, location, range, calibration, accuracy).
• Load Tables: For each test, loads at various points & loading steps.
• Deflection Tables: Recorded deflections per test.
• Failure Data (if any):
  • Max loads before collapse.
  • Failure description.
  • Dimensional & mechanical properties of failed elements.
• Photographs: Full structure and failure details.

Additional Notes:

• Replacement members after failure must have higher strength and pass ultimate load tests (Clause 11.1).
• Certified steel producer and physical test reports for members must be furnished (Clause 12.2).
• Values must be rounded per IS 2-1960 rules, matching significant figures of specified values.

Example Table Format for Load & Deflection

flowchart TD
    A[Test Setup] --> B[Load Application]
    B --> C[Measurement of Loads & Deflections]
    C --> D[Data Recording]
    D --> E[Test Report Compilation]
    E --> F[Review & Certification]

This ensures clarity, traceability, and compliance with IS 802 Part 3 standards.