Code of practice for design and construction of bolt-jointed timber construction

IS 11096: Scope & Key Design Formulas for Bolted Timber Joints

Scope (Clause 1.1):
Covers design, fabrication, finishing, and maintenance of bolted timber joints for structural use.

Key Formulas for Allowable Load on One Bolt (Appendix A, Clause 4.4.4)

Parameters:

• ( f_{o1} ), ( f_{o2} ): Permissible unit stresses parallel and perpendicular to grain (N/mm²)
• ( a = t \times d ): Projected bolt area in main member (mm²)
• ( t ): Thickness of main member (mm)
• ( d ): Bolt diameter (mm)
• ( d_a, d_e ): Diameter factors for perpendicular load
• ( M_1 ): Percentage factor for ( t/d ) ratio parallel to grain
• ( \theta ): Angle between load and grain direction

Maintenance (Clause 6.3):

• Bolts to be tightened 1 year after completion, then every 2-3 years.

Units (SI):

• Force: Newton (N) = 1 kg·m/s²
• Stress: Pascal (Pa) = 1 N/m²
• Length: mm, m

flowchart LR
    A[Load on Bolt] -->|Parallel to Grain| B[P = fo1 × a × M1]
    A -->|Perpendicular to Grain| C[Q = fo2 × a × da × de]
    A -->|At Angle θ| D[F = P sin²θ + Q cos²θ

IS 11096: Materials and Components – Key Formulas & Tables

1. Allowable Load on One Bolt in Wooden Splice Plates (Appendix A, Clause 4.4.4)

• Load parallel to grain (P):
  [ P = f_{on} \times a \times A_1 ]
• Load perpendicular to grain (Q):
  [ Q = f_{oi} \times a \times A_2 ]
• Load at an angle θ to grain (Hankinson's formula):
  [ F = P \sin^2 \theta + Q \cos^2 \theta ]

Where:

• ( f_{on} ) = permissible compression stress parallel to grain (N/mm²)
• ( f_{oi} ) = permissible compression stress perpendicular to grain (N/mm²)
• ( a = t \times d ) = projected bolt area (mm²)
• ( t ) = thickness of main member (mm)
• ( d ) = bolt diameter (mm)
• ( A_1, A_2 ) = correction factors for ( t/d ) ratio

2. Stress Percentage Factors for ( t/d ) Ratio (Clause 4.4.2, Table 4.4.3.1)

3. Bolt Tightening Maintenance (Clause 6.3)

• Tighten bolts **1 year after

IS 11096: Necessary Information & Key Design Data for Bolted Timber Joints

1. Necessary Information (Clause 3.1)

Collect before design:

• Species and grading of timber
• Design data (loads, stresses)
• Moisture content of timber
• Details of treatment (preservative, fire-retardant, etc.)

2. Allowable Load on One Bolt (Appendix A, Clause 4.4.4)

• (t): thickness of main member (mm)
• (d): bolt diameter (mm)
• (M_1, d_a, d_e): correction factors based on geometry and timber properties

3. Bolt Spacing & Stress Percentage (Clause 4.4.2, Table 4.4.3.1)

Stress reduces with increasing t/d ratio.

4. Maintenance (Clause 6.3)

• Tighten bolts 1 year after completion, then

Design Considerations for Bolt Jointed Timber Units (IS 11096)

Key Inputs (Clause 3.1):

• Timber species & grading
• Design data (loads per IS 875)
• Moisture content
• Treatment details

Allowable Load on One Bolt (Appendix A, Clause 4.4.4)

• (t) = thickness of timber (mm)
• (d) = bolt diameter (mm)
• (n) = number of bolts in joint

Maintenance (Clause 6.3)

• Tighten bolts 1 year after completion, then every 2-3 years.

Load Calculation

• Use IS 875 for load combinations.
• Consider worst-case load location.
• Wind & seismic loads not simultaneous.

Units (SI)

flowchart TD
    A[Collect Data: Species, Grading, Moisture, Treatment] --> B[Calculate Loads (IS 875)]
    B --> C[Determine Bolt Load Components]
    C --> D{Load Direction}
    D -->|Parallel| E[Calculate P = f_on * a * M1]
    D -->|Perpendicular| F[Calculate Q = f_oi * a * d_a * d_e]
    D -->|Angle θ| G[

IS 11096: Fabrication and Finishing – Key Points & Formulas

1. Pre-camber Requirement (Clause 4.4.4.5)

• A minimum pre-camber of 100 mm must be provided at the center of the bottom chord of bolt-jointed timber trusses.

2. Painting & Finishing (Clause 5.3)

• Structural units after fabrication shall be painted as per IS 2338 (Parts 1 & 2)-1967 (Code of Practice for finishing wood).

3. Bolt Maintenance (Clause 6.3)

• Bolts must be tightened after 1 year of structure completion, then every 2-3 years.

4. Allowable Load on Bolts (Appendix A)

• For bolts in timber joints, allowable load depends on load direction relative to grain:

• Variables:
  • (a = t \times d) (projected bolt area, mm²)
  • (t) = thickness of main member (mm)
  • (d) = bolt diameter (mm)
  • (M_1, d_a, d_e) = factors based on thickness/diameter ratio and grain direction

Summary Table of Allowable Bolt Load

IS 11096: Maintenance & Design of Bolted Timber Joints

Maintenance (Clause 6.3)

• Bolt tightening schedule:
  • After 1 year of structure completion.
  • Subsequently every 2 to 3 years.

Design of Bolted Joints (Appendix A, Clause 4.4.4)

Allowable load on one bolt in wooden splice plates:

Bolt Spacing & Thickness to Diameter Ratio (Clause 4.4.2)

Stress percentage reduces with increasing t/d ratio.

Key Symbols

Load Calculations - IS 11096 (Summary)

1. Load Calculation Reference:

• Loads to be calculated as per IS 875-1964.
• Consider worst load combination and location.
• Wind and seismic loads not simultaneous.

2. Allowable Load on One Bolt (Clause 4.4.4):
For bolted joints with wooden splice plates:

3. Bolt Spacing & Stress Percentage (Clause 4.4.2, Table 4.4.3.1):

Stress decreases with increasing thickness-to-diameter ratio.

4. Service Condition Adjustment (Clause 4.4.4.2):

• For wet conditions, allowable bolt load = 1/3rd of dry condition value.

Units (SI):

graph TD
    A[Load on Bolt] -->|Parallel| P[

Key Formulas & Specifications for Bolt Spacing and Arrangement (IS 11096)

1. Bolt Spacing (Clause 4.4.3 & Table 4.4.2)

• Minimum spacing between bolts in a row:

  [ \text{Min spacing} = \max\left[(r - 4)d, , 2.5d\right] ]

  Where:

  • ( d ) = bolt diameter
  • ( r ) = number of bolts in the row

• Spacing between rows of bolts:

  [ \text{Min spacing} = \max\left[1.5d, , \frac{\text{distance between rows}}{2}\right] ]

• Edge and end distances:

  [ \text{Min edge/end distance} = \max\left[(n - 4)d, , 2.5d\right] ]

  Where ( n ) = total number of bolts in the joint.

2. Thickness to Diameter Ratio (( t/d )) Influence on Stress

Refer to full table in Clause 4.4.2 for intermediate values.

3. Typical Bolt Spacing for Joint Types (Fig. 1)

• Lengthening joints:

  • For ( t/d = 2 ), spacing = ( 2.5d )
  • For ( t/d = 6 ), spacing = ( 5d )

• Node joints (loaded perpendicular to grain):

  • Follow spacing as per Fig. 1 with minimum edge and end distances.

Summary

• Maintain minimum bolt spacing as per formulas above.
• Adjust spacing based on thickness-to-diameter ratio ( t/d ) to control stress distribution.
• Ensure **edge and end

IS 11096 - Allowable Stresses and Strength: Key Formulas & Tables

1. Allowable Stresses Reference

• Timber allowable stresses are as per IS 883:1970 (Clause 4.2).

2. Allowable Load on Bolt in Timber Joints (Appendix A, Clause 4.4.4)

3. Bolt Diameter Factor (Table 2 - Clause 4.4.2.1)

(Refer full table in Clause 4.4.2)

4. Bolt Maintenance (Clause 6.3)

• Tighten bolts 1 year after completion, then every 2-3 years.

Summary:

• Calculate bolt load capacity using compression stresses parallel

IS 11096 - Shear Load Analysis for Bolted Timber Joints

1. Single and Multiple Shear (Clause 4.4.4.4)

• Single Shear Load:
  [ P_{single} = \frac{1}{2} P_{double} ] Where (P_{double}) = allowable load for a 3-member joint with main member twice the thickness of thinner member.

• Multiple Shear Load:
  [ P_{multiple} = n \times P_{single} ] Where (n) = number of shear planes.

2. Bolt Bearing Strength (Clause 4.4.2 & Table 4.4.3.1)

• Allowable load for bolt in single shear = half of that in double shear for same (t/d) ratio.
• Safe working compressive stress % varies with (t/d) ratio and grain direction:

(Refer full table for intermediate values)

3. Design Formulas (Appendix A)

• Load parallel to grain:
  [ P = f_{on} \times a ]

• Load perpendicular to grain:
  [ Q = f_{oi} \times a ]

• Load at angle (\theta) to grain (Hankinson's formula):
  [ F = P \sin^2 \theta + Q \cos^2 \theta ]

Where:

• (f_{on}), (f_{oi}) = permissible compressive stresses (parallel/perpendicular)
• (a = t \times d) (projected bolt area

Protective Coatings as per IS 11096

Key Specifications:

• Painting after fabrication:
  Structural units must be painted following IS 2338 (Parts 1 & 2) - 1967, which covers finishing of wood and wood-based materials (operations, workmanship, and schedules).

• Maintenance Painting Intervals:

  • Non-weather exposed structures: Repaint every 5 years (Clause 6.1)
  • Weather-exposed structures: Enamel painting every 2 years (Clause 6.2)

• Bolt Maintenance:
  Bolts should be tightened 1 year after completion and then every 2-3 years (Clause 6.3).

Summary Table: Maintenance Painting Intervals

Reference for Painting

• IS 2338 (Parts 1 & 2) - 1967
  Details operations and workmanship for protective coatings on wood.

If you need bolt design or load capacity formulas, refer to Appendix A for bolted joints with wooden splice plates.

flowchart TD
    A[Fabrication Completed] --> B[Painting as per IS 2338]
    B --> C{Exposure Type?}
    C -->|Weather Exposed| D[Enamel Paint Every 2 Years]
    C -->|Not Exposed| E[Paint Every 5 Years]
    F[Bolts] --> G[Tighten after 1 Year]
    G --> H[Tighten every 2-3 Years]

Note: Always use the latest editions of IS codes for compliance.

Pre-cambering of Timber Trusses (IS 11096)

• Pre-camber requirement:
  As per Clause 4.4.4.5, provide a minimum pre-camber of 100 mm at the center of the bottom chord of bolt-jointed timber trusses.
  This compensates for deflections under load and ensures the truss remains level.

Key Specifications:

Design Considerations:

• Use timber species with known compressive stress values (e.g., Hardwickia Binala).
• Factor in moisture content and treatment details for durability.
• Pre-camber helps counteract dead load and live load deflections.

Summary Formula for Pre-camber:

[ \text{Pre-camber} \geq 100 \text{ mm (minimum)} ]

graph LR
A[Start: Fabricate Timber Truss] --> B[Apply Pre-camber ≥ 100 mm at Bottom Chord Center]
B --> C[Assemble Bolt Jointed Timber Units]
C --> D[Ensure Timber Species & Grading per IS 3629]
D --> E[Check Moisture Content per IS 287]
E --> F[Final Inspection and Installation]

This ensures structural integrity and serviceability of timber trusses under load.