HOW TO CLASSIFY TIMBER ON THE BASIS OF GRADING? (IS-6534-1971)

The terms timber and timber are often used synonymously, but they have different meanings in the building industry. Wood is the hard, fibrous material that forms the tree under the bark, while wood can be defined as wood that retains its natural physical composition and chemical composition and is suitable for various engineering tasks. The following is the classification of timber as per IS: 6534.

Classification of Timber Based on Grading

Clearly differentiated between all grading specifications structural or Tension grading, and professional or Utility Grading based on Indian Standard Classification.

structural grading

it is also known as Tension Grading However, there is a small difference between the two. Structural grading refers to the principle by which materials are classified on the basis of visible defects, which have a known effect on the strength properties of the material.

Stress grading refers to the principle by which a material is classified by considering the maximum principle stresses to which it can be subjected.

Structural grading is further divided into:

  1. Grading based on known effects of defects and estimation of cumulative value.
  2. machine grading.

commercial grading

it is also known as Yard grading or Utility Grading refers to the principle by which materials are classified by considering the usefulness and value factors of the material. Commercial grading is further divided into the following sections:

grade A: It is based purely, and sometimes arbitrarily, on dimensions and general appearance. The dimensions of length and circumference for logs, or the length, width and thickness of the converted material, are measured in accordance with specified methods. This system is prevalent in Kerala and Mysore. Under these classifications, teak is placed into four grades and each grade has two sub-classes. In the case of other hardwoods, Mysore (Coorg) has four grades in common, but the dimensions are fixed separately for each species. In Kerala, there seem to be only two grades of hardwood

grade B: It is based on the best end use of the log or changed material. Such a system is prevalent mostly in Andhra Pradesh and parts of Tamil Nadu, and seems to be one of the fastest systems of grading and marking. Logs are classified into grades on the best possible use for beams, planks, scuttling, etc., and each grade is further divided into ‘A’, ‘B’ and ‘C’ classes to indicate the occurrence of defects. Is. Only two lengths are recognized; ‘Tall’ (ie 5 m and above) and ‘Short’ (ie less than 5 m). Thus each log is quickly stamped with the first letter of the grade classification, the subclass, and ‘L’ or ‘S’ for ‘Long’ and ‘Short’, for example, BAL and PBS’ respectively. Indicates beam. A-class, long’ and ‘planks, B-class, short’. Sometimes another letter is also added to indicate the species, for example, ‘T’ for teak.

Grade C: This classification is based on a qualitative assessment of defects and a rough estimate of usable material out-turns. It is popular in Madhya Pradesh.


Grade D: It is based purely on evaluating ‘units of defects’ and fixing the number of units allowed for a standard quantity in each grade. Such practices are common in the Bombay region; Sometimes an estimated out-turn is also indicated in each grade. Generally three grades are distinguished for different grades of logs and lumber. The size and other dimensions are also fixed in some cases differently for different species and different depots in the same kingdom. This system is increasingly being adopted in the Indian Standards Institute specifications and international grading specifications. This system has a distinct advantage of evaluating the cumulative effect of defects in a particular grade.

Reference

IS – 6534 – 1971


Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.