Code of practice for nail-jointed timber construction

IS 2366: Scope (Clause 2.0 & 3.1.1 Summary)

Scope:
IS 2366 covers the design and detailing of steel tubular structures, focusing on stresses due to dead, imposed, and wind loads.

Key Specifications & Definitions (Clause 2.0)

• Defines members and loading conditions for tubular structures.
• Applies to structural steel tubular members under various loads.

Stress Table (Clause 3.1.1 - Table 4 excerpt)

• Stresses are tabulated for Dead Load (DL), Imposed Load (IL), and Wind Load (WL).
• Resultant stresses combine DL + IL and wind pressure or suction.
• Design stresses consider maximum resultant stresses with safety factors.

Important Notes:

• Stress values are in kgf/cm².
• Lengths are in cm.
• Final values rounded per IS 2-1960.
• Wind load cases consider both windward and lee ward sides with suction and pressure.

Formula for Combined Stresses (Conceptual):

[ \sigma_{resultant} = \sigma_{dead} + \sigma_{imposed} \pm \sigma_{wind} ]

Where:

• (\sigma_{dead}) = Stress due to dead load
• (\sigma_{imposed}) = Stress due to imposed load
• (\sigma_{wind}) = Stress due to wind pressure or suction

This scope and stress data guide design checks for tubular members under combined loads per IS 2366.

IS 2366: Types of Joints - Key Points

1. Types of Joints (Clauses 2.6 to 2.8)

• Monochord Type Lap Joint (Clause 2.6, Fig. 2):
  Single member joint used for lengthening members by overlapping.

• Split-Chord Type Butt Joint (Clause 2.7, Fig. 3):
  Multiple member joint where chord members are split to accommodate web members.

• Split-Chord Type Lap Joint (Clause 2.8, Fig. 4):
  Multiple member joint with overlapping split chord members.

2. Node Joints (Clause 5.7.2)

• Nail Spacing for Node Joints:
  • At right angles (Fig. 7)
  • At inclined angles other than 90° (Fig. 8)
  • For reversible stresses (Fig. 9)

3. Nail Spacing Guidelines (Typical from IS 2366)

4. General Recommendations:

• The length of lap should be sufficient to transfer stresses.
• Nails should be arranged to avoid splitting and ensure load transfer.
• For reversible stresses, symmetrical nailing patterns are recommended.

graph TD
    A[Monochord Lap Joint] --> B[Lengthening Member]
    C[Split-Chord Butt Joint] --> D[Multiple Members]
    E[Split-Chord Lap Joint] --> F[Overlapping Chords]
    G[Node Joints] --> H[Nail Spacing at 90°]
    G --> I[Nail Spacing at Inclined Angles]
    G --> J[Reversible Stress Joints]

Summary: Use appropriate joint type based on member configuration. Follow nail spacing rules from IS 2366 Fig. 7-9 for node joints to ensure structural integrity.

IS 2366: Materials & Timber Species - Key Specifications & Tables

1. Strength of Nailed Joints (Clause 5.00, 19.5, 3.55)

• Strength per nail varies by species and joint type (Lengthening / Node Joints).
• Values given in kgf × 10² for permanent and temporary structures.
• Some species require no preboring for nail penetration (marked with *).

(Refer to full tables in Clauses 5.00, 19.5, 3.55 for all species)

2. Design Considerations (Clause 3.1)

• Confirm:
  • Timber species & grading
  • Moisture content
  • Pretreatment details
  • Design data (strength values, nail sizes)

Summary Table Format Example (Permanent Construction)

flowchart TD
    A[Timber Species] --> B{Nail Joint Strength}
    B --> C[Lengthening Joints]
    B --> D[Node Joints]
    C --> E[Permanent Structures]
    C --> F[Temporary Structures]
    D --> E
    D --> F

Use these tables and species-specific values for accurate nail joint design in timber structures as per IS 2366.

IS 2366: Design Requirements - Key Formulas & Tables

1. Stress Calculations (Clause 3.1.1 & Table 4)

• Stresses considered: Dead Load (DL), Imposed Load (IL), Wind Load (WL)
• Resultant stresses combine DL + IL and wind pressure/suction.
• Design stresses are maximum resultant stresses from combined loads.

2. Long Column Design (Clause 2.5)

• For slenderness ratio ( L/d > K_{10} ), design as long column.
• Constant: ( K_{10} = 0.702 \sqrt{2.5 E f_{op}} ) (Refer IS 883:1970)
• Permissible compressive stress:

[ f_o = P/A = 0.329 \times E \times \left(\frac{2.5}{L/d}\right)^2 ]

Where:

• ( E ) = Modulus of elasticity (e.g., 103,000 kgf/cm² for Bijasal timber)
• ( L/d ) = Slenderness ratio (length/least lateral dimension)

3. Timber Properties (Refer IS 883:1970)

• Modulus of Elasticity: 103,000 kgf/cm²
• Compression parallel to grain: ~1945 kgf/cm² (permissible)
• Minimum section for top chord: Twin 3 cm × 12.5 cm to accommodate nails (Clause 12.5)

Summary Diagram: Stress Combination & Design Flow

flowchart TD
    A[Load Types] --> B

Nail Specifications & Spacing (IS 2366)

Nail Spacing (Clauses 5.7.1.2 & 5.7.1.4)

• Along grain:
  • Pure tension: ≥ 10 d
  • Pure compression: ≥ 5 d
• Perpendicular to grain: ≥ 5 d

where d = nail shank diameter

Prebore Diameter for Nails (Clause 6.2.2.1, Table 3)

Key Notes (Clause 6.2)

• Nail distances marked on jigs/templates and transferred to splice plates.
• Nails loaded laterally should not be driven slant, except where no stress reversal occurs and slant tightens the joint.
• Preboring is essential to avoid wood splitting.

flowchart LR
    A[Mark Nail Distances on Jig] --> B[Transfer to Splice Plate]
    B --> C[Prebore Holes as per Table]
    C --> D[Place Members in Position]
    D --> E[Drive Nails Vertically (No Slant)]

This ensures proper nail placement and joint strength per IS 2366.

IS 2366: Web and Chord Member Design - Key Points

1. Web Members Design (Clause 3.1.3)

• Nailing: Minimum 2 nails per node joint.
• Web width: ≥ 10d (where d = nail diameter, here 5 mm).
• Edge distance: Minimum 5 cm.
• Nail size: 5 mm diameter, 150 mm length.
• Stress increase: Web member stresses can be increased by 33.3% to account for eccentricity due to web axis shifting.

2. Web Members in Compression

3. Chord Members

• Top chord size: Designed as 3 × 10 cm, but 3 × 12.5 cm used to accommodate nails (Clause 12.5).
• Solid section adopted: 3.5 × 8.5 cm (Clause 3.5).

4. Stress and Design Checks

• Constant (K_{10}) (from IS 883:1970):

  [ K_{10} = 0.702 \times V \times 2.5 \times 10^3 \times E \times f_{op} ]

• Permissible compressive stress (f_o):

  [ f_o = \frac{P}{A} = 0.329 \times E \times \left(\frac{2.5}{L/d}\right)^3 ]

• Tension members: Design web members with higher tensile stresses as tension members (e.g., member 17-18 with max tensile stress +745 kgf).

Summary Table for Web Member Design

IS 2366: Load Considerations — Key Formulas & Tables

1. Stress Table (Clause 3.1.1, Table 4)

• Provides stresses on members due to Dead Load (DL), Imposed Load (IL), and Wind Load (WL).
• Resultant stresses combine DL + IL and wind suction/pressure.
• Design stresses are checked against maximum resultant stresses.

2. Nail Strength (Clause 1.5, Fig. 11)

• For permanent construction, safe load is the lesser of:
  • Load after FS 3 on yield load
  • Load at restricted slip (0.4 mm)
• For temporary construction, safe load is load after FS 3 on ultimate load.

3. Column Design (Clause 2.5)

• Constant ( K_{10} = 0.702 \sqrt{2.5 E f_{op}} )
• If slenderness ratio ( L/d > K_{10} ), design as a long column.
• Permissible compressive stress:

[ f_o = 0.329 \times E \times 2.

Cambering of Timber Trusses (IS 2366: Clause 5.8.1)

The initial upward camber at the center of the lower chord of nail-jointed timber trusses is given by:

Where:

• L = Effective span of the truss (in meters)
• Camber is the vertical rise at mid-span (in meters)

Additional Notes from IS 2366:

• Effective span example: 12 m (Clause 5.9, Appendix B)
• Camber for permanent structure: ( \frac{12}{600} = 0.02 , m = 20 , mm )
• Camber for temporary structure: ( \frac{12}{300} = 0.04 , m = 40 , mm )

Design and Dimensions Reference:

• Depth of top chord = ( \frac{3 \times \text{Area}}{58.8} \approx 10 , cm ) (Clause 58.8)
• Top chord size adjusted to 3 cm × 12.5 cm to accommodate nail spacing (Clause 12.5)

graph LR
A[Effective Span (L)] --> B[Calculate Camber]
B --> C{Structure Type}
C -->|Permanent| D[Camber = L/600]
C -->|Temporary| E[Camber = L/300]
D --> F[Provide upward camber at mid-span]
E --> F

Summary: Use camber = L/600 for seasoned timber trusses and L/300 for unseasoned, ensuring proper uplift to counteract deflection and maintain structural integrity.

IS 2366: Inspection and Maintenance Key Points

1. Inspection & Maintenance Frequency

• Properly designed and fabricated nail-jointed timber structures require very little maintenance (Clause 9.2).
• Regular inspection should focus on moisture content and joint integrity.

2. Moisture Content Check (Clause 2.3)

• Use a Hydromat (moisture meter).
• Acceptable moisture content: 15-16% of oven-dry weight.
• Excess moisture can degrade nail joints and timber strength.

3. Stress & Load Checks (Clause 3.1.1, Table 4)

• Inspect stresses due to:
  • Dead loads
  • Imposed loads
  • Wind loads (pressure and suction)
• Compare resultant stresses with design stresses to ensure safety.

4. Joint Nail Requirements (Clause 1.33)

• Nail count depends on joint type and stress.
• Example: Heel joint requires 2 nails for given stress.
• Nail numbers increase with load and stress factors (e.g., 33% increase for axis change).

Summary Table for Moisture & Maintenance

flowchart TD
    A[Inspection] --> B[Moisture Measurement]
    B --> C{Moisture > 16%?}
    C -- Yes --> D[Dry or Repair]
    C -- No --> E[Check Joint Nails]
    E --> F{Nail Count Adequate?}
    F -- No --> G[Re-nail or Repair Joint]
    F -- Yes --> H[Check Stress Levels]
    H --> I{Stress < Design Stress?}
    I -- No --> J[Structural Assessment]
    I

Finishing of Nail-Jointed Timber Work (IS 2366 Key Points)

1. Prebore Diameter for Nails (Clause 6.2.2.1, Table 3)

Prebore diameter depends on timber hardness to avoid splitting.

2. Nail Spacing in Node Joints (Figures 7, 8, 9)

• Minimum spacing = 5d (d = nail shank diameter)
• Can be increased to 10d if member width permits.
• Spacing varies for compression, tension, double shear, and reversible stresses.

3. Strength of Nailed Joints (Clause 5.00, Table 5.6)

• Strength per nail varies by wood species and joint type.
• Example (Permanent Construction, Node Joints):

4. **Additional Specifications

IS 2366: Testing Methods for Nail-Jointed Timber Trusses

Key Specifications & Formulas

• Nail Diameter (d): Shank diameter of nails used in joints.
• Nail Length (l): Length of nails in the joint.
• Specimen Size for Compression Parallel to Grain:
  • Each specimen: 35d × 25d × l mm
  • Central piece projects 10d beyond side pieces.
• Nail Arrangement in Specimen:
  • 8 nails, 3.55 mm diameter, 75 mm long, arranged in 4 rows (2 nails per row).
  • Nails spaced 10d from ends, horizontal rows spaced 5d apart.
  • Nails driven alternately from opposite sides, at 5d from edges.

Nail Spacing in Node Joints (Figures 7, 8, 9)

Testing Methods

• Part 1: Destructive Test (IS: 4925 Part 1 - 1968)
• Part 2: Proof Test (IS: 4925 Part 2 - 1968)

Special Considerations

• Stiffness determination per IS: 4924 (Parts 1 & 2) - 1968.
• Nail spacing may be increased up to 10d if the designed width of the member allows.

Nail Spacing Illustration (Simplified)

flowchart LR
    A[Side Member] -->|Nails spaced 5d from edges| B[Nail rows]
    B --> C{Rows spaced 5d horizontally}
    C --> D[Central Member projecting 10d]
    D --> E[Nails driven alternately from opposite sides]

Summary:
Use nail spacing based on

IS 2366 - Preboring for Nails (Clause 6.2.2.1 & Table 3)

Purpose of Preboring:

• Facilitates easy nail driving without splitting timber.
• Ensures straight nail penetration.
• Reduces internal damage, preserving lateral strength.

Recommended Prebore Diameters (Table 3):

Key Notes:

• Prebore diameter < nail diameter to ensure tight fit.
• Preboring depth should be at least equal to nail penetration length.
• Nail distances and prebore locations must be accurately marked using templates/jigs (Clause 6.2).

flowchart TD
    A[Mark Nail Distances on Jig] --> B[Transfer to Splice Plates]
    B --> C[Mark Nail Positions on Timber]
    C --> D[Preboring at Marked Positions]
    D --> E[Drive Nails Straight]
    E --> F[Finished Nail-Jointed Timber Work]

This ensures structural integrity and prevents timber splitting during nailing.

Strength of Nailed Joints (IS 2366 - Clause 5.6)

Key Load Values (From Clause 1.5, Table A-5.3)

• Safe Load per Nail: 153 kg (per nail for permanent construction)
• Number of Nails Used: 8 nails (example)

Nail Strength per Species (Clause 5.00, Table 5.6 excerpt)

Values are strength per nail in kgf.

Nail Spacing (Figures 7, 8, 9)

• Minimum spacing = 5d to 10d (d = shank diameter of nail), depending on member width.
• For node joints subjected to compression, tension, or double shear, follow spacing guidelines:
  • Compression/Tension: 5d + 5d + 45° length + 5d
  • Double Shear: Similar spacing with attention to shear planes.

Summary Formula for Nail Joint Strength:

[ \text{Joint Strength} = n \times \text{Strength per Nail} ] where

• ( n ) = number of nails
• Strength per nail depends on wood species and joint type (see table above).

IS 2366 - Clenching Techniques Summary

Definition (Clause 2.9)

• Clenching: Bending the projecting nail end over so it lies flush with the timber surface.
• Increases nail holding power and withdrawal resistance.
• Clenching perpendicular to grain > clenching parallel to grain (see Fig. 5).

Nail Finishing Preference (Clause 6.2.3)

1. Clenched across grain (best strength)
2. Clenched along grain
3. Protruding nail end
4. Cut flush with surface (least preferred)

Nail Strength & Load (Clause 1.5 & Fig. 11)

Prebore Recommendations (Clause 6.2.2.1, Table 3)

IS 2366: Key Appendices & Reference Tables Summary

1. Stress Table (Clause 3.1.1, Table 4)

• Provides stresses (kgf) on various members due to:
  • Dead Loads (DL)
  • Imposed Loads (IL)
  • Wind Loads (pressure & suction)
• Resultant stresses combine these effects for design evaluation.
• Lengths of members are given in cm.
• Design stresses are max resultant stresses with safety factors.

Example format:

2. Strength of Nailed Joints (Clause 5.00, Table 5.6)

• Lists nail strength per nail (kgf × 10²) for different wood species.
• Separate values for:
  • Lengthening joints
  • Node joints
• Different strengths for permanent and temporary structures.

Sample:

3. Appendix B: Example Design of Nail-Jointed Timber Truss (Clause 5.9)

• Illustrates design steps for a 12 m effective span truss.
• Applies clauses 5.1 to 5.8 for nailed joint design.
• Useful for practical understanding of joint detailing and load calculations.

Summary Diagram: Load Combination for Member Stress

graph LR
DL[Dead Load] --> RS