Wood Incising Factor (C_i)

Incising Factor Explained:

In order for sawn lumber to be used in outdoor conditions, it requires a preservative treatment to prevent decay in the wood. This process includes permeating the wood with chemical preservatives to prevent decay-causing fungus to enter the wood. In most cases, this is possible by a pressure treatment, but certain species of wood must be incised (small slits into the wood), to receive the chemicals more readily.

From the Forest Products Journal^[1], Incising is a pretreatment process in which small incisions, or slits, are punched into the wood surface.This increases the amount of exposed end- and side-grain surface area, which increases chemical preservative penetration and retention.

Note: If the wood is not incised, then this factor can be ignored, or taken as unity (1.0).

Incised Wood Factors ^[2]

The loss of the area, and section modulus from the small incisions of a wood member will require certain reduction factors to be used. If the wood is incised parallel to the grain a max. depth of 0.4" (10.2mm), a maximum length of 3/8" (9.5mm), and a density of incisions up to but not exceeding 1100 incisions/sq. ft the following table may be used:

Note: If incising patterns exceed the above limits, then factors should be determined by testing or by calculation using reduced section properties.

References:

1. Forest Products Journal (Vol 55, No. 9), "Evaluation of a reduced section modulus model for determining effects of incising on bending strength and stiffness of structural lumber", 2005
   • http://www.fpl.fs.fed.us/documnts/pdf2005/fpl_2005_hernandez001.pdf
2. American Forest and Paper Association, "National Design Specification for Wood Construction", 2005