The 1994 edition of IS 8745 outlines standardized procedures for displaying timber's physical and mechanical property data, enabling uniform comparison and adjustment of strength values across varying moisture levels. This standard is vital for professionals engaged in timber evaluation, design, and application, ensuring precise reporting of characteristics like strength, shrinkage, hardness, and withdrawal resistance under both green and dry states.
Overview
The 1994 edition of IS 8745 outlines standardized procedures for displaying timber's physical and mechanical property data, enabling uniform comparison and adjustment of strength values across varying moisture levels. This standard is vital for professionals engaged in timber evaluation, design, and application, ensuring precise reporting of characteristics like strength, shrinkage, hardness, and withdrawal resistance under both green and dry states.
Audience
Contents
Structure
Frequently Asked
IS 8745 Clause 5.1 specifies that to normalize timber strength values measured at a moisture content ( d % ) (below the fibre saturation point ( f )), the following formula is applied to adjust them to a standard 12% moisture content:
[ S_{12} = S_a \times \frac{f - 12}{f - d} ]
Here, ( S_{12} ) represents the strength at 12% moisture content, ( S_a ) is the measured strength at moisture content ( d ), and ( f ) is the fibre saturation point, commonly around 30%. Impact bending strengths are not adjusted but averaged at the test moisture content. This adjustment ensures consistent strength values for design purposes.
The standard covers essential timber properties crucial for design and industrial use, including physical characteristics such as density, moisture content, shrinkage in various directions, and cleavage resistance. Mechanical properties addressed include modulus of elasticity, modulus of rupture, compression strength parallel and perpendicular to grain, shear strength, and nail and screw withdrawal resistance. These properties are derived from tests on small clear specimens and structural-size samples according to relevant IS codes, ensuring comprehensive and reliable data.
As per Clause 4.3.5, variability in timber testing results must be quantitatively reported using measures like standard deviation (σ) and coefficient of variation (COV), reflecting the spread and relative variability of data. Sampling should be representative, involving multiple trees and logs. Test values should be rounded following specified schemes to maintain clarity and comparability. This approach ensures transparent presentation of data variability across species and properties.
Following Clause 4.3.2 and Table 3 of IS 8745, numerical results must be rounded as follows: average log diameters to the nearest whole millimeter; specific gravity to three decimal places; moisture content and shrinkage percentages to one decimal place; mechanical stresses mostly to the nearest integer; and modulus of elasticity values to one decimal place. This standardization supports consistent and precise reporting of timber properties.
According to Clause 4.3 and Table 1(A), withdrawal resistance for nails and screws is reported under three conditions: (A) driven in green timber and pulled immediately, (B) driven in green timber and pulled after drying, and (C) driven and pulled in dry timber. Values are given for radial, tangential, and end grain directions, including average, maximum, and minimum measurements in Newtons or kilograms-force. These are rounded to the nearest whole number to ensure clarity and facilitate design decisions.
Ask AI about any clause, requirement, or provision in IS 8745. Get instant, clause-cited responses powered by our indexed library.
Free tier includes 150 queries (50 AI + 100 Reference) · No credit card required