Methods of presentation of data on physical and mechanical properties of timber

IS 8745 - Scope & Key Specifications Summary

Scope (Clause 1.1.1):

• Covers timber testing data presentation, excluding methods of computation of timber testing data.
• Adjunct standards for timber terminology and testing methods:
  • IS 707: Glossary of timber terms
  • IS 1708 (Parts 1-18): Testing small clear specimens
  • IS 2455: Sampling model trees and logs
  • IS 8720: Sampling timber scantlings

Key Tables & Presentation (Clause 4.2, 4.3)

Tables 1, 1A, 2:

• Must have clear headings and be self-explanatory with conditions/limitations.

Table 3: Units & Rounding Scheme for Dry Condition Data

Notes:

• Units primarily in N/mm² (MP

IS 8745 - Key References for Tables and Data Presentation

1. Table Headings & Conditions (Clause 4.2)

• Tables 1, 1A, 2 must have clear headings.
• They should be self-explanatory and indicate conditions/limitations of results.

2. Table Details (Clause 4.3)

• Tables 1, 1A, and 2 include details per Clauses 4.3.1 to 4.3.5.

3. Units & Rounding Scheme (Clause 4.3.2, Table 3)

4. Important Notes

• Units are primarily N/mm² (MPa) and percent.
• Rounding ensures consistency and precision in reporting.
• Values like modulus of elasticity and stresses have specific rounding to balance accuracy and usability.

Summary Diagram of Data Presentation Flow

flowchart TD
    A[Tables 1, 1A, 2] --> B[Proper Headings

IS 8745 - Definitions: Key Specifications & Data Presentation

1. Reference Definitions:

   • Definitions as per IS 707:1976 and IS 2455:1990 apply (Clause 3.1).

2. Tables & Presentation (Clauses 4.2 & 4.3):

   • Tables 1, 1A, 2 must be self-explanatory with headings and conditions.
   • Tables include details from Clauses 4.3.1 to 4.3.5.

3. Units & Rounding Off (Table 3, Clause 4.3.2):

4. Additional Properties:
   • Hardness (Radial, Tangential, End): Nearest integral figure.
   • Cleavage resistance, torsion

IS 8745: Presentation of Data in Green Condition - Key Points

1. Physical & Mechanical Properties (Clause 4.3, Table 1)

• Properties are presented for Green (G) and Air Dry (AD) conditions.
• Typical properties include:
  • Specific Gravity (based on oven-dry mass and green volume)
  • Shrinkage Percent (Green to Oven-Dry)
  • Modulus of Rupture (Bending Strength)
  • Impact Bending Strength
  • Compression Parallel to Grain
  • Compression Perpendicular to Grain
  • Hardness Load (N)
  • Shear Parallel to Grain
  • Tension Perpendicular to Grain
  • Cleavage Resistance
  • Tension Parallel to Grain
  • Torsion Strength

2. Measure of Variability (Clause 4.3.5)

• Variability in timber test data must be reported.
• Use the recommended scheme in Table 4 (not fully shown) for statistical measures like:
  • Standard Deviation
  • Coefficient of Variation (%)

3. Presentation Guidelines (Clause 4.2)

• Tables must be self-explanatory with:
  • Clear headings
  • Conditions (Green or Dry)
  • Limitations of results

Example: Specific Gravity Calculation (Green Condition)

[ \text{Specific Gravity} = \frac{\text{Oven-dry Mass}}{\text{Green Volume} \times \text{Water Density}} ]

flowchart LR
    A[Timber Sample] --> B[Measure Green Volume]
    A --> C[Oven-dry Mass]
    B & C --> D[Calculate Specific Gravity]
    D --> E[Report in Table with Other Properties]

Summary: IS 8745 emphasizes standardized presentation of timber properties in green condition, including key mechanical properties and variability measures, ensuring clarity and comparability.

IS 8745: Presentation of Data Under Dry Condition

Key Points from Clause 4.3 & Table 3 (Units and Rounding Off)

Adjustment of Strength Values to 12% Moisture Content (IS 8745)

Key Formula (Clause 5.1)

To adjust strength from observed moisture content ( d % ) to 12% moisture content:

[ S_{12} = S_a \times \frac{f - 12}{f - d} ]

Where:

• ( S_{12} ) = Strength at 12% moisture content
• ( S_a ) = Strength at observed moisture content ( d % ) (dry condition, below fibre saturation)
• ( f ) = Fibre saturation point (%)
• ( d ) = Observed moisture content (%)

When Fibre Saturation Point is Unknown (Clause 5.2)

[ S_{12} = S_a \times \frac{12}{d} ]

Provided (|12 - d| \leq 2%).

Important Notes:

• Impact bending values (Clause 5.3) are not adjusted; they are averaged and reported at 12% moisture content.
• Fibre saturation point ( f ) is typically around 30% for most timbers.
• Use Table 1 (Clause 4.3) for species-specific physical & mechanical properties in green and air-dry conditions.

Summary Table for Adjustment

This ensures strength values are standardized at 12% moisture content for design consistency.

IS 8745: Measures of Variability & Data Presentation

1. Measure of Variability (Clause 4.3.5)

• All timber testing data must include a measure of variability.
• Recommended scheme for reporting variability is given in Table 4 (not fully provided in context).
• Typically, variability is expressed via:
  • Standard Deviation (σ)
  • Coefficient of Variation (COV) = (σ / Mean) × 100%

2. Presentation of Data Under Dry Condition (Clause 4.2, 4.3, 4.3.2)

• Tables 1, 1A, and 2 must be self-explanatory with proper headings.
• Include details per Clauses 4.3.1 to 4.3.5.
• Numerical values should follow the rounding scheme in Table 3:

According to IS 8745 Clause 4.3.2 and referencing IS 2:1960, the rounding off of numerical values for test results must follow the scheme in Table 3 of IS 8745. The number of significant figures retained should match the specified values in the standard.

Key Rounding Off Scheme (Table 3 Summary)

IS 8745: Nail and Screw Withdrawal Resistance Reporting

Key Points from Clause 4.3 & Tables:

• Withdrawal resistance is reported under 3 conditions:

  • Condition A: Driven in green timber, pulled immediately.
  • Condition B: Driven in green timber, pulled after drying.
  • Condition C: Driven and pulled in dry condition.

• Resistance values are given for:

  • Nails and Screws
  • Directions: Radial, Tangential, and End grain

Table 1 (Summary Format for Withdrawal Resistance N (kgf)):

Values include Average, Maximum, and Minimum from tests.

Units & Rounding (Table 3):

Additional Notes:

• Scantlings for testing are per IS 8720:1970.
• Withdrawal resistance depends on moisture content and grain direction.
• Data presentation includes average, maximum, and minimum values for reliability.
• Physical and mechanical timber properties (density, modulus, etc.) accompany withdrawal data for comprehensive assessment.

flowchart LR
    A[Timber Sample] --> B{Condition}
    B -->|A: Green, pull immediately| C[Nail/Screw driven]
    B -->|B: Green, dry then pull| C
    B -->|C: Dry, pull immediately| C
    C --> D{Direction}
    D -->|Radial| E[Measure Withdrawal Resistance]
    D -->|Tangential| E
    D -->|End Grain| E
    E --> F[Report Average, Max, Min]

Summary: IS 8745 mandates reporting nail and screw withdrawal resistance in kgf for radial, tangential, and end grain directions under three moisture conditions, with results rounded to the nearest integer for clarity and consistency.

IS 8745 Key Points on Tree, Scantling & Species Averages

1. Definitions (Clause 4.3.1):

   • Tree Average: Average of all sticks in a single tree or bolt.
   • Scantling Average: Average of all sticks in a scantling.
   • Species Average: Average of all tree or scantling averages of a species from a locality.

2. Use:

   • Species averages are reported in Tables 1, 1A, and 2 for different moisture conditions (green, kiln-dry, air-dry).

3. Key Tables:

   • Table 1(A): Nail and screw withdrawal resistance values (N or kgf) under three conditions:
     • Condition A: Driven green, pulled immediately.
     • Condition B: Driven green, pulled dry.
     • Condition C: Driven dry, pulled immediately.
   • Table 2: Physical and mechanical properties including:
     • Specific gravity, shrinkage, modulus of elasticity, modulus of rupture.
     • Compression parallel & perpendicular to grain.
     • Hardness, shear, tension, cleavage resistance.
     • Nail and screw withdrawal resistance.

4. Important Notes:

   • Scantlings are selected per IS 8720:1970.
   • Moisture content affects mechanical properties; values are given for different moisture states.
   • Cleavage resistance (splitting) and withdrawal resistance are included in the revised tables.

Summary Table Format Example (Nail Withdrawal Resistance)

Conceptual Flow of Averages

flowchart TD
    A[Individual Sticks in Tree] --> B[Tree Average]
    C[All Trees in Scantling] --> D[Scantling Average]
    B & D --> E[Species Average of Locality]

**Use these averages for design values

Improvement Factor from Green to Dry Condition (IS 8745)

Definition (Clause 5.6)

• The Improvement Factor (IF) is the average percentage increase in strength when timber dries from green (fresh) condition to dry condition at 12% moisture content.

Key Formula (Clause 5.1)

To adjust strength values to 12% moisture content:

[ S_{12} = S_a \times \frac{12 - f}{d - f} ]

Where:

• ( S_{12} ) = strength at 12% moisture content
• ( S_a ) = strength at observed moisture content ( d ) (below fiber saturation point)
• ( f ) = fiber saturation point (usually ~30%)
• ( d ) = observed moisture content in dry condition

Improvement Factor Calculation

[ IF = \frac{S_{12} - S_g}{S_g} \times 100% ]

Where:

• ( S_g ) = strength in green condition
• ( S_{12} ) = strength at 12% moisture content (dry condition)

Reference Table (Clause 4.3, Table 1)

• Provides physical and mechanical properties of timber species in green and air-dry conditions (including specific gravity, bending strength, compression, shear, tension, hardness).
• Use this data to compute ( S_g ) and ( S_a ) values for respective species.

Summary

• Measure or obtain green strength ( S_g ) and dry strength ( S_a ).
• Adjust dry strength to 12% moisture content using the formula.
• Calculate improvement factor as percentage increase from green to dry condition.

flowchart LR
    A[Green Strength \(S_g\)]
    B[Dry Strength at moisture \(d\) \(S_a\)]
    C[Adjust \(S_a\) to 12% moisture \(S_{12}\)]
    D[Calculate Improvement Factor \(IF\)]

    A --> D
    B --> C --> D

This factor helps in understanding strength gain due to drying, critical for design and grading of timber.

Composition of the Technical Committee (IS 8745 - Annex A)

The Timber Sectional Committee, CED 9 comprises representatives from government, industry, research institutes, and experts in timber and related fields.

Key Notes on Data Presentation (Clause 4.3.5)

Formulas:

• Standard Deviation (SD):
  [ SD = \sqrt{\frac{1}{n-1} \sum_{i=1}^n (x_i - \bar{x})^2} ]

• Coefficient of Variation (CoV):
  [ CoV = \frac{SD}{\bar{x}} \times 100% ]

flowchart TD
    A[Data Source] --> B{Type of Data}
    B -->|Lot of sticks| C[Report lot average]
    C --> D[Measure variability: Range (max-min)]
    B -->|Locality data| E[Report species average of locality]
    E --> F{Samples ≥5