CHAPTER IX. 

 QUALITY AND KIND OF TIMBER USED. 



In order to obtain proper service from mill construction 

 buildings, it is most essential that a good quality of timber be 

 used. The special requirements for timbers which constitute 

 good quality deal with their strength and lasting power. The 

 strength of any timber will be determined by its weight or 

 density; the size, quality and distribution of knots, and the 

 presence or absence of defects. The density or dry weight of 

 wood may be regarded as a measure of its strength. Taking 

 timbers of yellow pine or Douglas fir as types, it should be 

 noted that "each annual growth ring is composed of a band of 

 dense, heavy, dark summerwood and a band of lighter, softer 

 springwood. The greater the proportion of summerwood, the 

 greater the weight and strength of the timber. The principle, 

 referring to the number of growth rings and the proportion of 

 summerwood as a measure of density and hence of strength, 

 applies to all woods in which there is a marked contrast between 

 the character of the springwood and the summerwood."* 



As a result of extensive investigation made by the United 

 States Government and the American Society for Testing Ma- 

 terials, a rule was adopted in 1915 which clearly specifies the 

 manner for determining two classes of structural yellow pine 

 timbers, one a high-grade quality called "dense pine" and the 

 other grade of lower strength value called "sound pine." The 

 specifications for these classesj will be found in a booklet issued 

 by the Southern Pine Association, New Orleans, La., entitled, 

 "Southern Yellow Pine Timbers Including Definition of the 

 Density Rule." A similar rule is now being prepared for Doug- 

 las fir, and in the absence of any accepted standard for Douglas 

 fir, it will be safe to use the rule as drawn up for yellow pine. 



^Building Code recommended by the National Board of Fire Under- 

 writers, page 282, 1915. 



$NOTE: These classes of timber are defined in the 1915 Yearbook of the 

 American Society for Testing Materials, pages 431 and 432, and were adopted 

 by this Society August, 1915, and by the American Railway Engineering 

 Association March, 1916. 



Page forty-eight 



