Solid Wood Products 2687 



broad classes are recognized: comer or brace posts, and line posts. Comer or 

 brace posts are commonly 8 feet long, sometimes longer. Line posts are sold in 

 three lengths: 6, 6.5, and 7 feet. Comer and brace posts are graded according to 

 even-inch diameter classes: 3-4, 5-6, 6-7, and 7-8 inches. Standard grades for 

 diameters of line posts do not exist, but the most popular treated posts are only 

 about 3 inches in diameter (Worrell and Todd 1955). 



Species preference and durability. — Historically black locust (Robinia 

 pseudoacacia L.) has been the preferred species for untreated fence posts, with 

 white oak, post oak, and eastem red cedar (Juniperus virginiana L.) also much 

 used. In recent years treated southem pine posts predominate, but, as discussed 

 in section 21-4, many pine-site hardwoods can be effectively treated with preser- 

 vatives for use as fence posts. Natural durability of southem woods employed as 

 fence posts varies widely; estimates of useful life (years) by the Tennessee 

 Valley Authority (1964) and Worrell and Todd (1955) follow (see also table 21- 

 18): 



Species TV A Worrell and Todd 



Black locust 15 17 (heartwood) 



Eastem red cedar 18 17 (heartwood) 



Sassafras {Sassafras albidum (Nutt.) Nees) 11 10 (heartwood) 



Mulberry (Moras rubra L.) — 10 (heartwood) 



White oak 11 8 (incl. post oak) 



Chestnut oak 4.8 — 



Hickory 4.7 — 



Red maple 4.0 — 



Black tupelo 3.4 — 



Red oaks 2.8 (black oak) 3 



Sweetgum — 3 



Yellow-poplar 2.8 — 



Life of treated fence posts is summarized in tables 21-17 and 21-19. 



Strength of hickory, oali, and pine fence posts. — Table 22-26 affords the 

 following comparison of creosote-treated roundwood posts measuring 3 inches 

 in diameter: 



Statistic Hickory Oak Virginia pine 



Modulus of rupture (psi) 14,120 8,930 7,140 



Modulus of elasticity (psi) 2,130,000 1,140,000 1,180,000 



Impact energy (inch-pounds) 46,200 41 ,000 1 1 ,000 



Machine-driving offence posts. — Neetzel and Christopherson (1964) found 

 that for maximum post firmness and straightness, with minimum expenditure of 

 driving energy, machine driven fence posts should be pointed on the large (butt) 

 end. Blunt-ended posts could, however, be satisfactorily machine driven. In 

 their evaluation, they used 3-inch-diameter, creosote-treated, southem pine 

 posts driven to a 24-inch depth in deep loam soil (both wet and dry), with a 200- 

 pound hammer. Fourteen to 22 hammer blows were generally required. 



