HOW TO CLASSIFY TIMBER ON THE BASIS OF POSITION AND DURABILITY (IS: 399)

CLASSIFICATION OF TIMBER

POSITION BASIS:

• Standing Timber : It means that the living tree.

• Rough Timber : Form a part of felled tree.

• Lumber : lumber are the logs of timber sown into planks, posts.

MODULUS OF ELASTICITY BASIS:

The species of timber recommended for constructional

purpose are classified as:-

Group A

Modulus of elasticity in bending above 12.5 kN/mm2

Group B 

Modulus of elasticity in bending above 9.8 kN/mm2 and below 12.5 kN/mm2

Group C

Modulus of elasticity in bending above 5.6 kN/mm2 and below 9.8 kN/mm2.

AVAILABILITY BASIS:

According to availability, timber can be of three 

grades, namely X, Y and Z.

Grade X

Most common, 1415 m3 or more per year

Grade Y
Common, 355 m3 to 1415 m3 per year

Grade Z
Less common, below 355 m3 per year

This is based upon the figures supplied by the forest departments.

DURABILITY BASIS:

Test specimens of size 600 × 50 × 50 mm are buried in the ground to half their lengths. The condition of the specimen at various intervals of time are noted and from these observations their average life is calculated. Timbers are classified based upon such observations as of:

a) High Durability:  Average life of 120 months and

over.

b)Modrate Durability: Average life of less than 120

months but of 60 months or more.

c)Low Durability: Average life of less than 60

months.

SEASONING CHARACTERISTICS BASIS:

Timbers are classified depending upon their behaviour

to cracking and splitting during normal air-seasoning

practice under three categories.

a) High Refractory: are slow and difficult to season

free from defects.

b) Moderate Refractory: protection is given against

rapid drying.

c) Low Refractory: These can be rapidly seasoned

free from defects.

TREATABILITY BASIS:

This classification is based upon the resistance offered by the heartwood of a species to preservatives under a working pressure of 1.05 N/mm2 as:

(a) Easily treatable.
(b) Treatable but complete preservation not easily

obtained.

(c) Only partially treatable.

(d) Refractory to treatment.

(e) Very refractory to treatment, penetration of

preservative being practically nil from the

sides and ends.