Code of Practice for Design and Construction of Nailed Laminated Timber Beams

IS 4983: Scope - Key Data & Formulas

Scope Summary (Clause 2.1 & A-2.1)

• Timber: Kokko (Albizia lebbeck)
• Modulus of Elasticity, E: 112 tonnes/cm² = 112,000 kg/cm²
• Live Load (IS 875-1964): 75 kg/m²
• Dead Load (timber beams/planks): 640 kg/m³
• Safe Working Stresses (Kokko timber, IS 883-1966):
  • Bending & Tension, ( f_b ) = 134 kg/cm²
  • Compression parallel to grain, ( f_c ) = 88 kg/cm²
  • Horizontal Shear, ( f_s ) = 11 kg/cm²

Key Formulas

• Deflection for Simply Supported Beam (Clause 4.3):

[ \delta = \frac{384 \times W \times L^3}{E \times b \times d^3} ]

Where:

• ( \delta ) = deflection
• ( W ) = total load
• ( L ) = span length
• ( E ) = modulus of elasticity
• ( b, d ) = beam width and depth

Nail Specifications (Clause 4.6.2.2)

• Minimum 4 nails spaced at 75 mm to resist horizontal shear & maintain plank integrity.
• Nails near joints spaced at 50 mm.

Summary Table: Safe Stresses for Kokko Timber

This data helps design nailed laminated timber beams per IS 4983, ensuring strength and serviceability.

IS 4983: Materials and Timber Species - Key Data

1. Nail Specifications (Clause 3.75 & Table 6.3)

• Nail Diameter & Length:
  • 3.75 & 4 mm dia: 75 & 100 mm long
  • 5 mm dia: 125 & 150 mm long
• Minimum Beam Depth:
  • 3.75 & 4 mm dia nails: ≥ 10 cm
  • 5 mm dia nails: ≥ 12.5 cm

2. Shear Strength per Nail (kg) for Various Timber Species (Table 2)

*Species marked with * require no preboring for nail penetration.

3. Design Data (Appendix A)

• Modulus of Elasticity (E): 112,000 kg/cm²
• Safe Working Stresses for 'kokko' timber:
  • Bending/Tension (f_b): 134 kg/cm²
  • Compression parallel to grain (f_c): 88 kg/cm²
  • Horizontal shear (f_s): 11 kg

IS 4983: Nail Specifications and Spacing for Nailed Laminated Timber Beams

1. Nail Diameter & Minimum Beam Depth (Clause 6.3.5)

• 3.75 mm & 4 mm dia nails: Minimum beam depth = 10 cm
• 5 mm dia nails: Minimum beam depth = 12.5 cm

2. Nail Spacing (Clause 6.3.2)

• Nails must be spaced horizontally at a standard spacing (refer Fig. 2 in IS 4983).
• Minimum 4 nails per row within a distance equal to the beam depth.
• Nail rows are placed to resist shear at critical beam sections.

3. Shear Strength per Nail (Table 2, Clause 5.4)

Note: Shear strength for 5 mm dia nails is approx. 45% higher than 3.75/4 mm nails.

4. Design Formula for Number of Nails (Clause 6.3.2)

[ N = \frac{V}{F_n} ] Where:

• (N) = number of nails required at a section
• (V) = shear force at the section (kg)
• (F

IS 4983: Size of Planks and Beams for Nailed Laminated Beams

Key Specifications:

• Max plank depth: 25 cm
• Max plank length: 200 cm
• Standard plank thicknesses: 2.0, 2.5, 3.0 cm
• Nail pre-boring: Required for hardwoods and some softwoods
  • Prebore diameter = Nail diameter - (0.5 to 1.5 mm depending on wood hardness)

Table 1: Number & Size of Planks and Nails

Nail Prebore Diameter Guidelines:

flowchart TD
    A[Select Beam Thickness] --> B[Determine No. of Planks & Thickness]
    B --> C[Choose Nail Size]
    C --> D[Check Wood

IS 4983: Design Considerations for Nailed Laminated Timber Beams

Key Design Data (Clause 2.1 & A-2)

• Modulus of Elasticity (E): 112 tonnes/cm² (112,000 kg/cm²)
• Live Load Intensity: 75 kg/m² (per IS 875-1964)
• Dead Load Intensity: 640 kg/m³ (timber beams/planks)
• Safe Working Stresses for Kokko Timber (IS 883-1966):
  • Bending & Tension, ( f_b ) = 134 kg/cm²
  • Compression parallel to grain, ( f_c ) = 88 kg/cm²
  • Horizontal Shear, ( f_s ) = 11 kg/cm²

Basic Formulas for Design (Clause 5 & A-3)

• Bending Stress: [ f_b = \frac{M}{Z} \leq 134 \text{ kg/cm}^2 ] where ( M ) = bending moment, ( Z ) = section modulus

• Shear Stress: [ f_s = \frac{V}{A} \leq 11 \text{ kg/cm}^2 ] where ( V ) = shear force, ( A ) = cross-sectional area

• Compression Stress: [ f_c = \frac{P}{A} \leq 88 \text{ kg/cm}^2 ]

Design Steps (Summary from Clause 5.5 & Appendix A)

• Determine loads (dead + live) on beam.
• Calculate bending moment and shear force.
• Choose beam cross-section to satisfy stresses.
• Use nailed laminated planks with thickness limits per note.
• Check deflection and serviceability.

Typical Section Dimensions

• Span: 4.0 m
• Floorboard thickness: 25 mm
• Plank thickness: variable, adhering to min/max limits
• Nail size: 5 mm dia, 150 mm long

flowchart TD
    A[Determine Loads] --> B[Calculate Moments & Shear]
    B --> C[Select Beam Section]
    C --> D[Check Stresses (bending, shear, compression)]

IS 4983: Load and Deflection Criteria for Timber Beams

Key Formulas

• Maximum deflection for simply supported beam under uniform load:

[ \delta = \frac{384 \times w \times l^4}{E \times I} ]

Where:

• (\delta) = max deflection (cm)
• (w) = load per cm length (kg/cm)
• (l) = span length (cm)
• (E) = modulus of elasticity (kg/cm²)
• (I) = moment of inertia (cm⁴)

Design Data (Clause 2.1)

Deflection Limits (Clause 5.2)

Example Load Calculation (Clause 5.3.6.1)

[ w = 2 \times 0.28 + 0.56 = 1.12 \text{ kg/cm} ]

Summary

• Use the deflection formula to check (\delta) under combined dead + live loads.
• Ensure (\delta) does not exceed limits per member type.
• Use modulus and stresses from Clause 2.1 for design checks.

flowchart TD
    A[Load Calculation] --> B[Calculate w (kg/cm)]
    B --> C[

IS 4983 Key Formulas & Specifications for Shear and Bending Stress Checks

1. Maximum Bending Moment (Clause 4.4)

[ M_{max} = w_1 \times l^2 / 8 ]

• (w_1): Load per cm length (N/cm)
• Example: (M_{max} = 400 \times 400 \times 0.84) (units N·cm)

2. Permissible Deflection (Clause 4.3)

For simply supported beam: [ \delta = \frac{5 w l^4}{384 E I} ]

• (w): Load per unit length
• (l): Span length
• (E): Modulus of elasticity
• (I): Moment of inertia

3. Shear Stress Check at Joints (Clause 4.5.2)

• Check shear at 40 cm from support due to joint placement.
• Calculate total shear force at this section and ensure it does not exceed permissible shear stress.

4. Nailing Specifications (Clause 4.6.2.2)

• Minimum 4 nails spaced at 75 mm apart for horizontal shear.
• Nails near joints at 50 mm spacing.
• Ensures integrity and stiffness of planks.

Summary Table for Nail Spacing

flowchart LR
    A[Load on Beam] --> B[Calculate Max Bending Moment]
    B --> C[Check Bending Stress ≤ Permissible]
    A --> D[Calculate Shear at 40 cm Joint]
    D --> E[Check Shear Stress ≤ Permissible]
    F[Nail Placement] --> G[4 Nails @ 75 mm]
    F --> H[Nails near Joints @ 50 mm]
    G & H --> I[Ensure Structural Integrity]

Note: Use IS 4983 tables for permissible stresses and nail sizes as per material specifications.

IS 4983: Fabrication and Construction Practices - Key Points

1. Nail Specifications & Spacing (Clause 4.6.2.2)

• Minimum 4 nails spaced at 75 mm apart to resist horizontal shear and maintain plank integrity.
• Nails near joints spaced at 50 mm.
• Ensures combined strength and stiffness within permissible limits.

2. Size of Planks and Nails for Nailed Laminated Beams (Clause 4.3, Table 1)

3. Additional Notes

• Protruding nails must be cut off or clenched across grains.
• Nail spacing and size directly affect beam strength and stiffness.

flowchart LR
    A[Planks] --> B[Nails]
    B --> C{Spacing}
    C -->|Near Joints| D[50 mm]
    C -->|Elsewhere| E[75 mm]
    B --> F[Nail Size & Length]
    F --> G[Depends on Beam Thickness]

This summary ensures compliance with IS 4983 for safe

IS 4983: Effective Span & Support Conditions

1. Effective Span (Clause 5.3)

• Freely Supported Beam (5.3.1):
  [ \text{Effective span} = \min \left( \text{distance between centres of supports}, \quad \text{clear span} + d \right) ]
  where ( d ) = effective depth of the beam.

• Continuous Beam (5.3.2):
  Define ( b_s ) = width of support, ( l_c ) = clear span

  • If ( b_s < \frac{l_c}{12} ), use 5.3.1 formula.
  • If ( b_s \geq \min\left(\frac{l_c}{12}, 600,mm\right) ):
    • (a) End span with one end fixed & other continuous, or intermediate spans:
      [ \text{Effective span} = \text{clear span between supports} ]
    • (b) End span with one end free & other continuous:
      [ \text{Effective span} = \text{clear span} + \min\left(\frac{d}{2}, \frac{b_s}{2}\right) ]

2. Support Conditions Summary

3. Deflection Formula (Clause 4.3)

For simply supported beams, maximum deflection ( \delta ):

[ \delta = \frac{5 w l^4}{384 E I} ]

where:

• ( w ) = uniform load
• ( l ) = span length
• ( E ) = modulus of elasticity
• ( I ) = moment of inertia

flowchart TD
    A[Beam Type] -->|Fre

Worked Design Example for Nailed Laminated Beam (IS 4983: Appendix A)

Design Data (Clause A-2.1)

• Modulus of Elasticity, E = 112 tonnes/cm² = 112,000 kg/cm²
• Live Load Intensity = 75 kg/m² (IS 875-1964)
• Dead Load Intensity (timber) = 640 kg/m³
• Safe Working Stresses for 'Kokko' Timber (IS 883-1966):
  • Bending & Tension, ( f_b ) = 134 kg/cm²
  • Compression parallel to grain, ( f_c ) = 88 kg/cm²
  • Horizontal Shear, ( f_s ) = 11 kg/cm²

Stepwise Calculation Highlights (Clause A-4.3)

• Span, ( L ) = 4.0 m
• Section spacing = 1 m
• Floor board thickness = 25 mm

Deflection Check (Simply Supported Beam)

[ \delta = \frac{5 w L^4}{384 E I} ]

Where:

• ( \delta ) = deflection
• ( w ) = uniform load per unit length
• ( L ) = span length
• ( E ) = modulus of elasticity
• ( I ) = moment of inertia of the beam section

Summary of Procedure:

1. Calculate loads (dead + live) on the beam.
2. Select a trial section and compute moment of inertia ( I ).
3. Calculate maximum bending moment ( M = \frac{wL^2}{8} ).
4. Check bending stress: ( \sigma = \frac{M c}{I} \leq f_b ).
5. Check shear stress: ( \tau = \frac{V}{b d} \leq f_s ).
6. Verify deflection using above formula.
7. Adjust section if any criteria fail.

flowchart TD
    A[Start: Given Span & Loads] --> B[Calculate Loads on Beam]
    B --> C[Select Trial Section]
    C --> D[Calculate Moment of Inertia (I)]
    D --> E[Calculate

IS 4983: Key Formulas, Tables & Specifications from Appendices

1. Design Data (Appendix A-2.1)

• Modulus of Elasticity, E = 112 tonnes/cm² = 112,000 kg/cm²
• Live Load Intensity = 75 kg/m² (as per IS 875-1964)
• Dead Load Intensity (timber) = 640 kg/m³
• Safe Working Stresses for 'Kokko' Timber (IS 883-1966):
  • Bending & Tension, ( f_b ) = 134 kg/cm²
  • Compression parallel to grain, ( f_c ) = 88 kg/cm²
  • Horizontal Shear, ( f_s ) = 11 kg/cm²

2. Nailing Specifications (Clause 4.6.2.2)

• Minimum 4 nails spaced at 75 mm apart for horizontal shear and plank integrity.
• Nails near joints spaced at 50 mm.
• Ensures strength & stiffness within permissible limits.

3. Deflection Formula (Appendix A-4.3)

For simply supported beams:

[ \delta = \frac{384 \times W \times L^3}{E \times b \times d^3} ]

Where:

• ( \delta ) = Deflection
• ( W ) = Load
• ( L ) = Span length
• ( E ) = Modulus of elasticity
• ( b ) = Breadth of beam
• ( d ) = Depth of beam

4. Worked Example

• Appendix A contains a detailed worked example for the design of nailed laminated beams.

Summary Table: Safe Stresses for Kokko Timber

This concise data helps in timber beam design per IS 4983 guidelines.