Change List for this Rule

 

General Order 95

 

Section IV

 

Strength Requirements for All Classes of Lines


Table 5 Wood Strengths

Species

Modulus of Rupture Bending (a)

Sawed Rectangular Poles, Crossarms, Etc. (b)

Round Poles

Cedar, western red   

4,700 lbs per square inch

6,000 lbs per square inch

Douglas fir, dense

6,300 lbs per square inch

6,800 (c) lbs per square inch

Douglas fir, not dense     

5,800 lbs per square inch   

6,800 (c) lbs per square inch

Fir, white or red, local       

4,700 lbs per square inch

5,600 lbs per square inch

Pine, southern yellow, dense 

6,300 lbs per square inch     

6,800 (c) lbs per square inch

Pine, southern yellow, not dense   

5,800 lbs per square inch

6,800 (c) lbs per square inch

Redwood, virgin     

5,300 lbs per square inch   

6,200 lbs per square inch

Redwood, second growth     

3,900 lbs per square inch   

6,200 lbs per square inch

 

(a)         Modulus of rupture in bending is based on the values for green wood as determined by the criteria and referenced standards in the United States Department of Agriculture (USDA) Wood Handbook: Wood as an Engineering Material (Forest Service Agricultural Handbook 72). Green wood is defined as freshly sawed or undried (unseasoned) wood. For woods not specifically listed in the table, other references, such as the USDA Tropical Timbers of the World (Forest Service Agriculture Handbook 607) may be used as long as the methods of testing meet or exceed the criteria and referenced standards specified in the USDA Handbook 72.
 

(b)         Figures given are for select structural grade of material under short time loading with the neutral plane parallel to a side. Multiply the values    shown by 1.4 where the neutral plane is on the diagonal of a square. Multiply the given values by 0.55 where the loading being considered is a long time loading (continuous load for one year or more). Also, sawed rectangular poles, crossarms, etc. must be derated by a factor based on how “dense” or “not dense” the wood is, and whether the wood comes from second growth. This is known as the density rule, which uses the percentage of latewood and number of growth rings per inch of radius (rate of growth). Typical factors are about 0.925 for “dense” wood and 0.85 for “not dense” wood. However, the appropriate factor must be determined for each species of wood used taking into account the locations and the conditions in which the trees were grown.

(c)          Where poles meet specifications of American National Standards Institute, Inc., 05.1–1992 for Wood poles, this value may be increased to not more than 8,000 lbs. per square inch. Such poles shall be given suitable preservative treatment.

 

Note:      Revised April 26, 1965 by Decision No. 68835 March 9, 1988 by Resolution E–3076 and October 9, 1996 by Resolution SU–40.