Method of test for the determination of tensile strength by indirect tests on rock specimens

IS 10082: Scope & Key Calculation References

IS 10082 covers the design and construction of steel tubular poles for overhead power lines.

Scope Highlights (Clause 2.0)

• Applies to steel tubular poles used for electrical distribution and transmission.
• Covers design, fabrication, and erection requirements.
• Ensures poles withstand mechanical loads like wind, conductor tension, and weight.

Key Calculation Clauses:

• Clause 4.4 & 5.3: Calculation of loads and stresses on poles.
• Clause 6.3: Detailed structural analysis including moment, shear, and axial forces.

Typical Formulas (per IS 10082 & structural principles):

Typical Tables (from IS 10082):

• Wind pressure values for different wind speeds.
• Section properties of tubular poles (diameter, thickness, moment of inertia).
• Load factors for safety and design.

flowchart TD
    A[Loads on Pole] --> B{Types}
    B --> C[Axial Loads]
    B --> D[Bending Moments]
    B --> E[Shear Forces]
    C --> F[Weight of conductors]
    D --> G[Wind Load]
    E --> H[Support reactions]
    F & G & H --> I[Calculate Stresses]
    I --> J[Check against allowable limits]

Summary: IS 10082 defines steel tubular pole design scope, focusing on mechanical load calculations (axial, bending, wind) with formulas and tables for safe structural design.

IS 10082: Definitions & Key Calculation References

• Clause 2.0 (Definitions): Establishes terminology specific to the standard, e.g., load types, structural elements, and material properties. Precise definitions ensure uniform understanding.

• Clauses 4.4, 5.3, 6.3 (Calculations): These sections provide formulas and procedures for structural calculations such as load analysis, design forces, and stability checks.

Key Formulas (Typical for IS 10082 context)

Typical Specifications:

• Material Properties: Use values as per IS 456 or relevant codes.
• Load Factors: As per IS 875 for dead/live loads.
• Safety Factors: Refer IS 1893 for seismic considerations.

flowchart TD
    A[Definitions - Clause 2.0] --> B[Calculation Procedures]
    B --> C[Load Calculation - Clause 4.4]
    B --> D[Design Forces - Clause 5.3]
    B --> E[Stability Checks - Clause 6.3]

For detailed tables and exact values, refer directly to IS 10082 clauses mentioned.

IS 10082: Preparation of Rock Samples – Key Points

Sample Preparation (Clause 3.1 & 3.9)

• Specimens must represent the true average of the rock type.
• Preparation follows IS 9179-1979.
• Minimum 10 specimens per rock type for statistical validity.

Loading Jaws Specifications (Clause 4.1.1)

• Two steel curved jaws contact the disc specimen at diametrically opposite surfaces over an arc of ~10°.
• Radius of curvature of jaws = 1.5 × specimen radius
• Jaw width = 1.1 × specimen thickness
• Guide pins allow relative jaw rotation of 4 × 10⁻³ radians (~0.23°).
• Upper jaw has a 25 mm diameter half ball bearing spherical seating.
• Guide pin clearance: 0.1 mm for 25 mm penetration.

Calculation (Clause 6.3)

• Calculations relate to stress at failure, typically using the Brazilian test formula:

[ \sigma_t = \frac{2P}{\pi Dt} ]

Where:

• (\sigma_t) = tensile strength (MPa)
• (P) = load at failure (N)
• (D) = specimen diameter (mm)
• (t) = specimen thickness (mm)

Summary Table for Jaw Dimensions

flowchart LR
    A[Rock Sample] --> B[Disc Shape Specimen]
    B --> C[Steel Curved Jaws]
    C --> D[Contact at 10° arc]
    D --> E[Load applied]
    E --> F[Failure Load (P)]
    F --> G[Calculate Tensile Strength σt]

This ensures standardized sample preparation and testing for reliable tensile strength results.

IS 10082: Apparatus and Procedure — Key Points

Apparatus (Clause 5.1)

• Standard Testing Machine: Capable of applying required loads smoothly.
• Measuring Devices: Dial gauges, proving rings with required accuracy.
• Specimen Molds: As per dimensions specified in the standard.
• Curing Tanks: For maintaining temperature and humidity.

Testing Procedure (Clauses 4.2, 6.2, 7.2)

• Specimen Preparation: Cast specimens as per dimensions and curing conditions.
• Loading Rate: Apply load at a uniform rate (e.g., 140 kg/cm²/min for compressive tests).
• Measurement: Record load at failure or specified deformation.
• Repeatability: Minimum 3 specimens tested; average value reported.

Typical Formula for Compressive Strength:

[ f_c = \frac{P}{A} ] where,

• ( f_c ) = compressive strength (N/mm²)
• ( P ) = maximum load at failure (N)
• ( A ) = cross-sectional area of specimen (mm²)

Summary Table: Loading Rates and Specimen Sizes

flowchart TD
    A[Specimen Preparation] --> B[Curing]
    B --> C[Testing Apparatus Setup]
    C --> D[Apply Load at Uniform Rate]
    D --> E[Record Load at Failure]
    E --> F[Calculate Strength]

This summarizes the apparatus and procedure essentials from IS 10082 for testing concrete specimens.

IS 10082: Brazilian Test Key Points

Specimen Dimensions (Clauses 3.4, 3.11)

• Disc diameter (D): ≥ 45 mm
• Thickness (t): ≈ 0.5 × D (half the diameter)
• Thickness measured at or near the center to nearest 0.1 mm.

Test Setup (Clauses 4.1.3, 5.1.1)

• Use a compressive load machine capable of controlled load application rate.
• Load applied diametrically via half-round bearing strips (half ball bearing or dowel with clearance).
• Apparatus per Fig.1 in IS 10082.

Key Formula: Tensile Strength from Brazilian Test

The indirect tensile strength (σ_t) is calculated by:

[ \sigma_t = \frac{2P}{\pi D t} ]

Where:

• P = maximum applied load (N)
• D = diameter of the disc (mm)
• t = thickness of the disc (mm)

Summary Table

flowchart LR
    A[Load Application] --> B[Disc Specimen]
    B --> C[Load P applied diametrically]
    C --> D[Measure max load P]
    D --> E[Calculate σ_t = 2P / (π D t)]

This test provides indirect tensile strength of concrete or rock specimens using standard dimensions and loading conditions per IS 10082.

IS 10082: Key Formulas & Specifications for Ring Test and Line Load Test

1. Ring Test (Clause 5.3.1)

• Tensile strength formula:

[ q_t = \frac{2P}{T D t} \left[ 6 + 38 \left(\frac{D_o}{D}\right)^2 \right] ]

Where:

• (q_t) = tensile strength of rock (MPa)

• (P) = failure load (N)

• (D) = outer diameter of ring (mm)

• (D_o) = inner diameter of ring (mm)

• (T) = thickness of ring (mm)

• (t) = length of specimen (mm)

• Purpose: Initiates fracture from specimen center, better for fracture mechanics.

2. Line Load Test (Clause 1.1)

• Used for rock prisms (not cylindrical specimens).
• Provides indirect tensile strength similar to point load test.
• Preferable to use one test method consistently for project uniformity.

Notes:

• Ring test avoids wedge failure seen in Brazilian test (Clause 4.3.2).
• Tensile strength values vary with test type and specimen size.
• Use consistent specimen dimensions and test methods for reliable comparison.

flowchart LR
    A[Rock Specimen] --> B{Test Type}
    B -->|Ring Test| C[Ring Specimen: Cylindrical Ring]
    B -->|Line Load Test| D[Rock Prism]
    C --> E[Apply Load P]
    D --> F[Apply Line Load]
    E --> G[Calculate \( q_t \) using formula]
    F --> H[Determine tensile strength indirectly]

Summary: Use the ring test formula above for cylindrical rings; line load test applies to prisms. Both are indirect tensile strength tests standardized in IS 10082.

IS 10082: Point Load Test Key Details

1. Specimen Dimensions (Clause 3.8)

• Core diameter: 12 mm ≤ d ≤ 35 mm
• Core length: Length > Diameter
• Rock-prism length > width
• Irregular specimens: roughly egg-shaped, largest to shortest diameter ≈ 1.5:1
• Volume ≈ 100 cm³
• Mass variation between specimens < 2%

2. Test Apparatus (Clause 7.1.1)

• Use apparatus as per IS 8764-1978

3. Point Load Strength Index (Is) Calculation

• Point load strength index, ( I_s ), is calculated as:

[ I_s = \frac{P}{D_e^2} ]

Where:

• ( P ) = failure load (N)
• ( D_e ) = equivalent diameter (mm), for core specimens usually the diameter ( d )

4. Equivalent Diameter for Irregular Specimens

[ D_e = \sqrt{\frac{4A}{\pi}} ]

Where ( A ) is the cross-sectional area at failure plane.

Summary Diagram of Point Load Test Setup

flowchart LR
    A[Rock Core Specimen] --> B[Placed Between Two Conical Platens]
    B --> C[Load Applied Axially]
    C --> D[Failure Load Recorded (P)]
    D --> E[Calculate Point Load Strength Index Is = P/De²]

For detailed tensile strength from line load test, refer to Clause 6.3.1 and Fig. 4 in IS 10082.

IS 10082: Reporting of Test Results - Key Points

1. Rounding Off Results

• Follow IS 2-1960 for rounding off final observed or calculated values.

2. Test Report Must Include (Clause 8.1):

• Lithologic description of rock.
• Orientation of loading axis relative to anisotropy (e.g., bedding planes).
• Sample source: geographic location, depth, orientation, sampling/storage method.
• Type of indirect tensile strength test used.
• Number of specimens tested.
• Specimen dimensions: diameter and height.
• Water content and saturation at test time.
• Test duration and stress rate.
• Date and type of testing machine.
• Failure mode.
• Additional observations: specific gravity, porosity, permeability with test methods.

3. Key Formulas for Tensile Strength (Clause 7.3):

• (D) = distance between loading points (mm)
• (V) = specimen volume (mm³)
• (W) = width (lesser base dimension, mm)
• (P) = applied load (N)

flowchart TD
    A[Test Specimen] --> B[Measure Dimensions]
    B --> C[Conduct Tensile Test]
    C --> D[Record Load P]
    D --> E[Calculate Tensile Strength]
    E --> F[Prepare Test Report]
    F --> G[Include All Required Details]

This ensures standardized, clear, and comprehensive reporting as per IS 10082.