FORESTRY, 217 



ported for an indefinite time by a 10" X 12" block of white 

 oak ? Red oak ? Yellow pine ? Poplar ? 



784. What should be the area of the cross section of 

 a yellow pine post which is to carry indefinitely a load 

 of 18.000 pounds? What would be the length of a side 

 if this is a square post? What is the diameter if circular? 



785. What should be the side of a square hickory post 

 which is to carry an 18.000-pound load? 



(2) Beams — bending. When used as a beam the 

 amount of the safe working load will depend upon the 

 way in which the beam is supported and the way in which 

 the load is applied as well as upon the dimensions of the 

 beam and the safe working strength of the wood. 



786. What is the safe working load that may be placed 

 at the middle point of a yellow pine joist which is sup- 

 ported at the ends and which is 20 feet long, 2 inches 

 broad, and 10 inches deep? 



Process : Multiply the square of the depth in inches by the 

 breadth in inches and tliis product by the safe working strength, 

 as given in the table above, and divide by 18 times the length in 

 feet; i. e., 



d' X b X s 



P — — 



18 XL 



10 X 10 X 2 X 700 



. = 390 Pounds 



18 X 20 



787. W^hat would be the load under the same condi- 

 tions as in the preceding problem, except that the depth 

 is 12 inches? 8 inches? How many times stronger is the 

 12-inch than the 8-inch? 



788. Show that th'^ beam in problem 786 would have 

 a safe working load of less than 100 pounds if placed on 

 the side with the 2-inch side vertical. 



Note. — A man could walk over this beam, however, without 



