HOLDING POWER OF BOLTS IN TIMBER. 



383 



After the bolts were withdrawn the timber was split, and 

 the condition of the wood round the hole examined. From this 

 it appeared that in holes larger than \\ inch, only the corners 

 of the bolts held effectively. 



Extensive arrangements made by the United States Govern- 

 ment, brought out the following important facts. 1 



The resistance of all drift-bolts increases with age, being 10 

 per cent, more at seven months after driving than if drawn at once. 



The resistance to drawing a bolt through the hole is only 60 

 per cent, of that required to draw it out. 



Smooth bolts were found to have much greater holding 

 power than ragged bolts. In fact, the resistance is diminished 

 by ragging from 25 to 50 per cent. 



As regards the size of the hole, it appears that the holding 

 power of an inch rod is greater when driven into a -J-^-inch hole 

 than when driven into any larger hole. 



With a |-inch round bolt, the resistance is greater in a 

 jg-inch hole, than either a T 9 g or an ^-inch hole. 



A round bolt is, weight for weight, 25 per cent, more efficient 

 than a square bolt. 



With a 1-inch round bolt driven into a ^-inch hole in white 

 pine, the holding power was found to be 10,000 Ibs. per lineal 

 foot of bolt. In Norway pine, the resistance of a similar bolt 

 was 9000 Ibs. per foot lineal. 



Experiments made in connection with the Brooklyn Bridge, 

 on the same subject, gave the following results : 



The holding power of a 1-inch bolt driven into a ] jUinch hole 

 in Georgia pine, was 12,000 Ibs. per lineal foot, which was 

 increased to 15,000 Ibs. per lineal foot, when the hole was made 

 } j of an inch. With lighter timber containing less pitch, the 

 holding power was 20 per cent, less, and in very dense timber 

 containing more pitch, the resistance was about 10 per cent. more. 



1 Extract from "Engineering News," in Engineering, vol. li. p. 314. 



