Comments related to MoE & MoR values

Sub: Comments related to MoE & MoR values in respect to IS-303 (BWR & BWP) and IS-710 & IS-4990

Dear Shri Pradeep Singh Shekhawat,

We appreciate the steps taken during preparation of draft of IS 303,710 & 4990 with respect to MoE & MoR value. In the proposed draft, values along the grain direction has been reduced to 15% followed by a raise of 15% in across the grain. Purpose of changing those values have been done to pay attention to the request raised by the plywood manufacturing industries on the pretext that the present raw material availability are from only plantation based harvested at about 3 to 4 years of interval.

a) In this short rotation harvest period lignin contents which provide basic strength to timber are very less (consisting mostly juvenile wood) weaker in strength in comparisons to long rotation forest based species.

b) Earlier face veneer thickness used to be more than 1 mm however present practice is that at least 75% reduction in thickness are being followed by most of the industries in India due to dependence on imports.

On account of reduction of face veneer thickness, the cumulative sum of across the grain direction stands higher with the cumulative sum of along the grain direction. Let us demonstrate with an example say for 19 mm thick plywood, say we use veneer of thickness 2mm consist of 13 layers including faces therefore cumulative sum of across the direction : 2mm x 6 lines = 12 mm, whereas cumulative sum along the direction : 2mm x 5 lines + 0.25mm x 2 (face) = 10.5 mm.

From the above it is clear that across the grain MOE & MOR will be about 15 % higher than along the grain direction.

It is further pointed out that the construction of plywood in terms of the number of layers of veneers to be used and thickness of veneers vary from industry to industry. It is left to the industry how many number of layers and what veneer thickness they are going to use keeping in mind that thickness of any veneer shall not exceed twice the thickness of any other veneer in the same board.

To give freedom to the industry and keeping in view application of plywood by users the following proposal is suggested.

Industry who do not conform the MoE & MoR values set in table of related Indian Specification can still conform their product if following criteria are meet as below:

To
The Member Secretary
CED-20, BIS
Civil Engineering Department, BIS
9, Bahadur Shah Zafar Marg, New Delhi – 110002