60 



STANDARD SPECIFICATIONS 



where in the piece. It shall be free from knots 1 in. in diameter 

 and over. 



When used for other purposes it shall be square edged, free 

 from knots 2^ in. in diameter and over, and wanes not extend- 

 ing over 5 per cent of the surface area may be allowed in 5 per 

 cent of the total number of pieces irr any one size. 



274. Dimension Timber. Dimension timber, when used as 

 beams, bridge joists, or stringers, caps, and sills in trestles and 

 posts, shall show not less than 75 per cent heart on each of the 

 four sides, measured across each side anywhere in the length 

 of the piece. No loose knots, or knots greater than 2J in. in 

 diameter or over one-quarter (J) the width of the face of the 

 stick in which they occur, will be allowed. Knots must not be in 

 groups, or be located within 3 in. of the edges. 



When used for other purposes it shall be square edged, except 

 it may have 1 in. wane on one corner and ring shakes must not 

 extend over one-eighth () of the length of the piece. 



UNIT STRESSES 



275. Timber in Buildings and Highway Bridges. The 



maximum stresses due to the combined effect of dead, snow, 

 wind, and live loads, including bending and impact, if any, shall 

 not exceed the following values in pounds per square inch: 



For columns whose length does not exceed 15d the above 

 values, given for " Compression under 15 diameters/' may be 

 used. 



