SPIRAL GRAIN- -A CAUSE OF POLE TWISTING 



Charles A. Wellner and David P. Lowery 



I 



■ Pole producers and pole users have contended witli spiral grain in poles and the twisting 

 poles that have been in service for a number of years without fully appreciating the cause - 

 and-effect relation between the two. Pole producers have rejected poles because the slope of 

 grain failed to meet specification requirements, and pole users have had to pay for costly pole 

 replacement or line repairs because poles twisted in place. It has been generally believed that 

 twisting or misalignment of crossarms was caused either by uneven pull on the wires by line 

 crews during construction or repair work, by heavy icing, or by wires broken by falling trees. 

 Although the effect of grain deviations on the warping of boards and tim±)ers has long been 

 understood, the influence on wood used in the round has not been as apparent or as obvious. 



The present American Standards Association specification for poles limits, among other 

 things, the slope of grain that can be tolerated on the pole's surface. The specification states 

 that for a pole 30 feet or shorter the maximum spiral grain permitted shall be one complete 

 spiral in any 10 feet; for poles 35 to 45 feet inclusive, one complete spiral in any 16 feet; and 

 for poles 50 feet or longer, one complete spiral in any 20 feet. 



This paper describes research""" on the occurrence of spiral grain and the effect of spiral 

 grain on the stability of poles in service. 



SURVEY OF LITERATURE 



Spiral grain in trees has been noted and reported upon rather extensively. Excellent sum- 

 maries of the literature have been prepared by Noskowiak (13), Nicholls (10), Northcott (12), 

 and Bannon (2) . 



Spiral grain is a common feature of tree growth and has been reported in nearly 200 

 species of hardwoods and softwoods. There is some evidence to indicate that spiral grain is a 

 genetic characteristic that may be transmitted from parents to offspring (4, 5, 6). So common 

 is the occurrence of spiral grain that Northcott (11) has advanced the hypothesis that spirality 

 is the normal growth pattern and that straight grain is a transitory phase of spiral grain. Ru- 

 dinsky and Vite (15) classified the water -conducting systems in trees into five groups, four of 

 which contain spiral grain. 



Because severe spiral grain has a profound influence on the strength and workability 

 of timber (1, 14, 17), it is of great interest to forest managers and wood technologists. Two 

 investigators have reported on the interrelationship of spiral grain and pole twisting. 

 Krogh's (9) studies in South Africa were designed to show the relation between spiral grain 

 and the amount of twisting that takes place in poles due to weather changes and the effect of 



The authors express their appreciation to the following men who assisted in planning or 

 conduct of fieldwork: I. V. Anderson, Frank T. Bailey, Jr., Henry H. Webster, and Peter F. 

 Stickney. They also express their gratitude and thanks to the cooperating companies for finan- 

 cial assistance, frequent suggestions and ideas, and many courtesies and other help given 

 during conduct of the various studies. 



^ Underlined numbers in parentheses refer to Literature Cited at the end of this report. 



