4.1 Species of Timber
The species of timber recommended for structural purposes are given in Table 1.
4.1.1 Grouping
Species of timber recommended for constructional purposes are classified in three groups on the basis of their strength properties, namely, modulus of elasticity and extreme fibre stress in bending-tension .
The characteristics of these groups are as given below:
a) Group A — E above 12.6 kN/mm² and above 18.0 N/mm².
b) Group B — E above 9.8 kN/mm² and up to 12.6 kN/mm² and above 12.0 N/mm² and up to 18.0 N/mm².
c) Group C — E above 5.6 kN/mm² and up to 9.8 kN/mm² and above 8.5 N/mm² and up to 12.0 N/mm².
NOTE — Modulus of elasticity given above is applicable for all locations and extreme fibre stress in bending is for inside location.
4.1.2 Timber species may be identified in accordance with good practice [6-3A(3)].
4.2 The general characteristics like durability, treatability and seasoning of the species are also given in Table 1. Species of timber other than those recommended in Table 1 may be used, provided the basic strength properties are determined and found in accordance with 4.1.1.
NOTE — For obtaining basic stress figures of the unlisted species, reference may be made to the Forest Research Institute, Dehra Dun.
4.3 The permissible lateral strength (in double shear) of mild steel common wire nail shall be as given in Table 2 and Table 3 for different species of timber.