Method of testing timber connector joints

IS 4907 Scope - Key Points & Formulas

IS 4907 covers the design, testing, and use of connector joints in timber structures. It specifies:

1. Scope Overview

• Applies to timber connectors, their sizes, bolt diameters, washer sizes.
• Includes testing procedures, data sheets, and allowable load calculations.
• Covers edge distances, end distances, spacing, and load inclinations.

2. Key Formulas

• Maximum connector spacing (R) for any load angle (θ):

[ R = \frac{A B}{\sqrt{A^2 \sin^2 \theta + B^2 \cos^2 \theta}} ]

Where:

• (A) = minimum spacing for 0° loading

• (B) = minimum spacing for 90° loading

• (\theta) = angle of loading relative to grain

• Allowable Load Calculation:

[ \text{Allowable Load} = \text{Connector Factor} \times n \times m \times \text{Working Load} ]

Where:

• (n) = number of connectors per contact face
• (m) = number of contact faces

3. Tables & Charts (Annex B)

• Edge-distance charts (load % vs edge distance)
• End-distance charts (compression & tension)
• Spacing charts for multiple connectors

4. Testing Data Sheet (Annex A)

• Records load, slip, moisture content, connector type, thickness, edge & end distances, inclination, etc.

graph LR
A[Load Angle θ] -->|Input| B[Calculate R]
B --> C{Use formula}
C --> D[Determine connector spacing]

Summary: IS 4907 provides detailed design and testing guidelines for timber connectors including spacing, load factors, and test data recording to ensure safe and efficient joint design.

IS 4907: Definitions & Key Specifications for Connectors

1. Definitions:

• Refer IS 707:1976 for timber technology terms.
• Connector joint parameters include:
  • Number of connectors (n) per contact face.
  • Number of contact faces (m).
  • Thickness of central and side members.
  • Edge and end distances (loaded/unloaded).
  • Inclination of central member to side members (0°, 90°, others).
  • Maximum load, load at proportional limit, load at specified slip.
  • Connector factor = (average joint factor) / (n × m).

2. Connector Factor Calculation: [ \text{Connector factor} = \frac{\text{Average joint factor}}{n \times m} ]

• Joint factor: % load developed relative to full load.
• For 0°, use max load and load at proportional limit.
• For 90° and other angles, use load at proportional limit only.

3. Connector Spacing (R) for multiple connectors: [ R = \frac{ \sqrt{A^2 \sin^2 \theta + B^2 \cos^2 \theta} }{AB} ]

• (A) = minimum spacing for 0° loading.
• (B) = minimum spacing for 90° loading.
• (\theta) = angle of loading.

4. Edge and End Distance Charts:

• Graphical charts show % full load vs. edge/end distances at various load-to-grain angles.
• Used to evaluate permissible edge/end distances for tension and compression.

5. Allowable Load Calculation: [ \text{Allowable Load} = \text{Connector factor} \times n \times m \times \text{Working load} ]

• Reductions apply for reduced edge/end distances or spacing but are not additive.
• Thickness reductions and distance reductions cannot be combined without further load reduction.

flowchart TD
    A[Connector Data] --> B[Joint Parameters]
    B --> C{Calculate Connector Factor}
    C --> D[Use Load at Proportional Limit]
    C --> E[Use Max Load (0° only)]
    B --> F[Determine Spacing R]
    F --> G[Apply Spacing Formula]
    B --> H[Consult Edge & End Distance Charts]
    H -->

IS 4907: Testing Procedures for Connector Joints

Key Specifications & Data Sheet (Clause 3 & Annex A)

• Parameters to record:
  • Consignment No., Laboratory No., Room Temperature, Average Moisture Content
  • Speed of Testing Machine, Telescope Reading (Load vs. Displacement)
  • Connector size/type, Number of connectors per contact face (n), Number of contact faces (m)
  • Thickness of central and side members
  • Edge and end distances (loaded/unloaded)
  • Inclination of central member (0°, 90°, or other angles)

Important Formulas & Factors

Testing Notes

• Load vs. telescope reading plotted for slip/load behavior.
• Strength tests both parallel and perpendicular to grain (see Fig.4).
• Rounding off results per IS 2:1960.

flowchart LR
    A[Prepare Test Setup] --> B[Record Initial Parameters]
    B --> C[Apply Load Slowly]
    C --> D[Measure Telescope Reading & Load]
    D --> E[Plot Load vs Slip Graph]
    E --> F[Calculate Joint & Connector Factors]
    F --> G[Report Results per IS 2:1960]

This ensures standardized evaluation of connector joint performance under load.

IS 4907: Strength Test Parallel to Grain – Key Points

Dimensions (from Clauses 1.75 & 1.1)

• a = 3c
• b < 2x
• c ≤ 1.75x (or c = 1.1b per Clause 1.1)
• d = 2e
• e < t (thickness)
• f = 2c

Testing Procedure (Clause 3.5)

• Minimum 5 specimens tested separately for:
  • Parallel to grain (Fig. 4A)
  • Perpendicular to grain (Fig. 4B)
• Tests may be done at intermediate angles using jigs.
• Test joints soon after assembly.

Data Sheet Parameters (Annex A, Clauses 2.10 & 3.7)

• Consignment No., Lab No., Room Temp., Moisture Content
• Connector size/type, No. of connectors (n), No. of contact faces (m)
• Thickness of central and side members
• Edge and end distances
• Inclination angle of members
• Load readings: Max load, Load at proportional limit, Load at specified slip
• Connector factor: Average joint factor / (n × m)

Important Notes:

• For 0°, use max load and load at proportional limit.
• For 90° and other angles, use load at proportional limit only.
• Connector factors apply only for two connectors, three-member joints.

Summary Table of Dimensions

flowchart LR
    A[Specimen Preparation] --> B[Set Dimensions (a,b,c,d,e,f)]
    B --> C[Test Setup Parallel to Grain]
    C --> D[Load Application]
    D --> E[Record Load at Max, Proportional Limit, Slip]
    E --> F[Calculate Connector Factor]
    F --> G[Evaluate Joint Strength]

This concise framework

IS 4907: Strength Test Perpendicular to Grain – Key Points

Dimensions & Setup (Clause 1.1 & 1.75)

• a = 3c
• b < 2x
• c ≤ 1.75x
• d = 2e
• e < t (thickness)
• f = 2c
  (Refer Fig. 4B for test setup perpendicular to grain)

Testing Procedure (Clause 3.5)

• Minimum 5 specimens tested separately for parallel and perpendicular grain directions.
• Tests done ASAP after assembly.
• Intermediate angle tests possible with suitable jigs.

Data Sheet Parameters (Clause 2.10, Annex A)

Connector Factor Calculation

[ \text{Connector Factor} = \frac{\text{Average Joint Factor}}{n \times m} ]

• For 0°, use max load and load at proportional limit.
• For 90° and other angles, use load at proportional limit only.
• Applicable mainly for two connectors, three-member joints.

Summary Diagram of Test Setup (Perpendicular to Grain)

flowchart LR
    A[Central Member] -->|Thickness t| B[Side Members]
    B -->|Edge distance e| C[Load Application]
    C -->|Load Perpendicular to Grain| D[Load Cell]
    style A fill:#f9f,stroke:#333,stroke-width

IS 4907: Data Sheet for Testing Connector Joints (Annex A, Clauses 2.10 & 3.7)

Key Data to Record:

• Consignment No., Laboratory No., Room Temp., Avg. Moisture Content
• Connector Details:
  • Size & type
  • Number of connectors per contact face (n)
  • Number of contact faces (m)
  • Distinguishing notations
• Member Dimensions:
  • Thickness of central member (t_central)
  • Thickness of side members (t_side)
  • Edge distance (loaded/unloaded)
  • End distances (compression/tension)
  • Inclination of central member to side members (0°, 90°, or other)
• Load and Slip Measurements:
  • Load at proportional limit (P_pl)
  • Maximum load (P_max)
  • Load at specified slip
  • Percentage load developed to full load (joint factor)
  • Connector factor = (average joint factor) / (n × m) (only for 2 connectors, 3-member joints)

Important Specifications (Clause 3.4):

• Three-member joints with two similar connectors
• Side member thickness:
  • Normally half the central member thickness
  • For split rings: 2/3 the central member thickness
• Central member depth (width) ≥ 2 × connector depth

Testing Procedure (Clause 3.7):

• Initial load: ~200 kg, then release to settle connectors
• Apply load at intervals ensuring constant strain rate
• Measure slip with dial gauge (accuracy 0.02 mm) at load intervals
• Plot Load vs Slip curve to find proportional limit and max load
• Record all data in the data sheet with sketches of connector and failure mode

Formula Summary:

IS 4907: Additional Data Regarding Connectors

Key Specifications (Clause 2.5)

• Connector dimensions: Recommended sizes for bolts, bolt holes, washers.
• Minimum timber sizes: To ensure proper embedment and load transfer.
• Bolt & hole diameters: Standardized to maintain strength and avoid splitting.
• Washer sizes: To distribute load and prevent timber crushing.

Connector Testing Data Sheet (Annex A, Clauses 2.10 & 3.7)

Notes on Connector Factor (Clause 2.10)

• For 0° inclination, use max load and load at proportional limit.
• For 90° and other angles, use load at proportional limit only.
• Connector factors apply only to specific joint configurations.

Testing of Multiple Connectors (Clause 3.9)

• Follow Annex C provisions for multiple connector testing.

Summary Table: Connector Parameters

flowchart LR
    A[Connector Dimensions] --> B[Minimum Timber

IS 4907: Notes for Using Connectors in Various Structures

Key Specifications & Formulas

1. Connector Testing (Clause 2.10, Annex A)

• Test on 3-member joints with 2 similar connectors.
• Thickness: Side members = ½ thickness of central member (except split rings: 2/3 thickness).
• Central member depth ≥ 2 × connector width.
• Parameters recorded: Load (max, proportional limit), edge/end distances, inclination, connector factor.

2. Connector Data (Clause 2.5)

• Specifies minimum timber sizes, bolt/bolt-hole diameters, washer sizes, connector dimensions.

3. Allowable Loads (Annex C-1)

[ \text{Allowable Load} = \text{Connector Factor} \times n \times \text{Working Load} ]

• (n) = number of connectors per contact face.
• Connector factor from tests (average joint factor / (n \times m)).

4. Load Reduction Factors (Annex C-2)

• Reductions for edge distance, end distance, spacing are not additive, lowest value governs.
• Thickness reductions and edge/end distance reductions are mutually exclusive.

5. Multiple Connectors (Annex C-3)

• Max connectors per face: 3 (for more, use 1/3 allowable load per extra connector).
• Connectors must be symmetrical with minimum edge/end distances.
• Load angle > 45° to grain for best performance.
• Connector spacing (R) at angle (\theta): [ R = \frac{AB}{\sqrt{A^2 \sin^2 \theta + B^2 \cos^2 \theta}} ]
• (A) = min spacing at 0°, (B) = min spacing at 90°.

Summary Table: Connector Spacing

Diagram: Connector Location (Fig. 5 Concept)

graph LR
    A[Direction of Grain] -->|Axis A| Ellipse((