Page:Timber and Timber Trees, Native and Foreign.djvu/84

64 In these tables are recorded the results of 108 experiments on the crushing strains applied to specimens of English Oak timber, varying from small pieces with only 1 inch of base, and 1 inch in height, carrying 7,978 lbs., to larger pieces with no inches of base, and 21 inches in height, carrying 734,272 lbs., or 327 tons 16 cwt., before breaking. The intermediate sizes include some pieces with 36 inches of base and 36 inches in height, this being the greatest length upon which I have been able to bring the crushing force to bear.

It is to be regretted that these experiments could only be carried on with pieces of inconsiderable length, owing to the difficulty experienced in keeping the centres perfectly straight with the line of pressure. Still, enough has, I hope, been done to afford a fair guide for determining the scantlings for pillars to beams, &c., although, perhaps, there is not even yet sufficient data to construct a formula upon.

M. Rondelet ascertained that it took a force of 5,000 to 6,000 lbs. to crush a piece of Oak having 1 inch of base; and Mr. Rennie gives 3,860 lbs. as the force required to crush a similar piece 1 inch in height. These two statements vary considerably from each other, and also from my own experience, inasmuch as I found it required a force of 7,978 lbs., or 3.562 tons weight, to crush a 1-inch cube of seasoned Oak; vide Table XVI.

In a trial, however, of six pieces of unseasoned Oak of the same dimensions, it was found that it took upon an average only 5,367 lbs., or 2.396 tons—one piece requiring only 4,480lbs., or 2 tons, to crush it; vide Table XV.

The experiments upon seasoned cubes of Oak, of 2, 3, and 4 inches (Table XVI.) show that the force