Methods of test for determination of strength properties of natural building stones, Part IV: Shear strength
1974 Edition

Overview of IS 1121 Part 4 Scope

Scope:
This part of IS 1121 (1974) establishes the standardized procedures and apparatus specifications for assessing the shear strength of natural building stones. It details the dimensions and assembly instructions for testing devices, emphasizing the Dutton Punching Shear Device used for evaluating stone shear properties.

Key Device Details from Clause 51.00

• Hole and Post Dimensions:

  • Hole diameter: 51.00 mm (fits plunger with sliding clearance)
  • Lower member: two holes fitting 24 mm diameter posts
  • Upper member: posts of 25 mm diameter fitting into holes

• Specimen Dimensions:

  • Specimen size and shape as per Clause 6.5 (commonly cylindrical or prismatic)

Important Points:

• All measurements are specified in millimeters.
• The device assembly includes precise hole and post fittings to ensure alignment.
• Detailed illustrations (e.g., Fig. 2) are provided within the standard for device construction.

Common Specimen Dimensions (per IS 1121 general provisions):

Assembly Diagram of Dutton Punching Shear Device

graph LR
A[Upper Component] -->|25 mm Diameter Posts| B[Lower Component]
B -->|24 mm Diameter Posts| C[Specimen]
A -->|51 mm Diameter Holes| C

For full procedural details and device schematics, consult the official IS 1121 Part 4 (1974) documentation.

IS 1121 Part 4 – Guidelines for Selecting Samples for Shear Strength Testing of Natural Stones

Essential Requirements:

• Clause 2.1: Samples must accurately represent the average characteristics of the stone type or grade.
• Clause 2.2: Samples should be sourced from:
  • Quarried stone or
  • Natural rock formations (refer to Clauses 2.2.1 and 2.2.2 for details).
• Sample quantity must be sufficient to prepare the required number of test specimens.
• Clause 3.1: Specimens should be cut exclusively with saws; the use of chisels or hand tools is prohibited to prevent specimen damage.

Additional Considerations:

• The sample size depends on the number of specimens needed (generally a minimum of three).
• Proper sample selection is crucial for obtaining representative shear strength data.
• Exact specimen dimensions and test procedures are detailed elsewhere in IS 1121 Part 4.

Sample Selection Summary Table:

flowchart LR
    A[Choose Stone Sample] --> B{Is Stone Quarried?}
    B -- Yes --> C[Collect Sample from Quarry]
    B -- No --> D[Collect Sample from Natural Rock]
    C & D --> E[Ensure Adequate Size for Specimens]
    E --> F[Saw Cut Test Specimens]
    F --> G[Prepare Specimens for Shear Testing]

This approach guarantees precise and reliable shear strength outcomes in line with IS 1121 Part 4.

IS 1121 Part 4: Preparation and Conditioning of Test Specimens

Key Provisions:

• Sample Selection (Clause 2.3):
  Multiple samples should be selected to encompass variations in stone quality for comprehensive property assessment.

• Specimen Dimensions (Clause 6.5):
  The size and shape of specimens must be clearly specified prior to testing.

Conditioning Protocols:

Testing Orientation:

• Tests are performed with load applied both parallel and perpendicular to the stone's natural rift planes.

Conditioning Summary Table:

flowchart LR
    A[Select Specimens] --> B[Choose Size & Shape]
    B --> C{Conditioning Method}
    C --> D[Dry: Oven 105±5°C, 24h + Desiccator]
    C --> E[Saturated: Water immersion 20–30°C, 72h]
    D --> F[Test Load Parallel & Perpendicular to Rift]
    E --> F

These procedures ensure uniform and comparable testing outcomes as per IS 1121 Part 4.

IS 1121 Part 4 - Equipment for Conducting Shear Tests

Primary Devices:

• Modified Johnson Shear Tool (illustrated in Fig. 1)
• Dutton Punching Shear Device (illustrated in Fig. 2A & 2B)

Both instruments are intended to be used with a standard testing machine that has sufficient load capacity.

Dutton Punching Shear Device Dimensions (Clause 51.00):

All sizes are specified in millimeters.

Specimen Requirements:

• Size and shape must be indicated clearly in accordance with Clause 6.5.

Equipment Setup Diagram:

graph LR
    A[Testing Machine] --> B[Modified Johnson Shear Tool]
    A --> C[Dutton Punching Shear Device]
    C --> D[Plunger (51 mm Diameter)]
    C --> E[Lower Member with Two Holes (Sliding Fit)]
    C --> F[Posts (24 mm & 25 mm Diameter)]

Note: For precise assembly and use, consult the detailed figures and specifications in IS 1121 Part 4 (1974).

IS 1121 Part 4 — Summary of Testing Procedure

Specimen Details (Clause 6.5)

• The shape and size of the test piece must be explicitly specified.
• Typical specimen size is 50 mm × 50 mm (refer to Figs. 1 & 2).

Setup Instructions (Clause 5.2)

• Employ the Dutton Punching Shear Device.
• Mark central alignment lines on the specimen surface.
• Measure specimen thickness at three points spaced around a 50 mm diameter circle with ±0.2 mm precision.
• Position the specimen centrally between the upper and lower plates; align the plunger accordingly.
• Apply loading using the testing machine at a maximum rate of 1 mm/min.
• Maintain the testing machine beam in a free-floating condition during the load application.

Critical Dimensions (from figures)

Execution of Test

• Conduct tests on a minimum of three specimens (Clause 3.6).
• Ensure precise alignment and gradual load application.
• Record load versus displacement until specimen failure.

Test Setup Schematic

flowchart TD
    A[50x50 mm Specimen] --> B[Dutton Punching Shear Device]
    B --> C[Upper Plate with Plunger]
    B --> D[Lower Plate with Posts]
    C --> E[Load Applied at ≤ 1 mm/min]
    D --> F[Specimen Centered and Supported]

This testing process guarantees consistent measurement of punching shear strength in compliance with IS 1121 Part 4 (1974).

IS 1121 Part 4: Interpretation and Reporting of Test Outcomes (Clause 6)

Key Considerations:

• Specimen Size and Shape (Clause 6.5): Must be clearly documented in test reports.
• Measurement Precision (Clause 5.2):
  • Thickness of the specimen is measured to the nearest ±0.2 mm at three equally spaced points around a 50 mm diameter circle near the center.
  • Specimen must be centered accurately between the plates of the punching shear device.
• Testing Setup:
  • Employ the Dutton Punching Shear Device with specified hole and post sizes (e.g., 51 mm diameter hole, 24 mm and 25 mm diameter posts).
  • Load is applied at a speed not exceeding 1 mm per minute.
  • The testing machine beam remains in a floating state during the test.
• Rounding Off Results: Follow IS 2-1960 for rounding the final shear strength values.

Formula for Shear Strength (C4):

[ \tau = \frac{P}{A} ]

Where:

• (P) = Maximum load at failure (in Newtons)
• (A) = Shear area of the specimen surface (in square millimeters), depending on specimen geometry

Reporting Requirements Checklist:

• Dimensions and shape of the specimen
• Details of the test apparatus used (e.g., Dutton Device)
• Load application rate and procedure
• Thickness measurement and specimen centering method
• Final shear strength value with rounding according to IS 2-1960

flowchart TD
    A[Prepare Specimen] --> B[Measure Thickness at 3 Points (±0.2 mm)]
    B --> C[Set Up Dutton Punching Shear Device]
    C --> D[Center Specimen and Device in Testing Machine]
    D --> E[Apply Load at ≤ 1 mm/min]
    E --> F[Record Maximum Load at Failure]
    F --> G[Calculate Shear Strength (\u03C4 = P/A)]
    G --> H[Round Off per IS 2-1960]
    H --> I[Compile Test Report with Details]

Refer to Clause 51.00 and Fig. 2 in IS 1121 Part 4 for detailed device dimensions and assembly.