PRINCIPLES OF RURAL ARCHITECTURE, 



CHAPTEK XVI. 

 STRENGTH OF MATERIALS. 



A knowledge of the principles governing the strength of 

 materials is helpful along many lines of farm practice and 

 particularly in the construction of farm buildings. 



398. A Stress. When a post is placed upon a foundation 



and a load of two thousand pounds set upon it the post is 

 undergoing or opposing a stress of two thousand pounds. 

 When a rope is supporting a load of one thousand pounds 

 in a condition of rest it is subject to a stress of one thou- 

 sand pounds. The joists under a mow of hay are subjected 

 to a stress measured by the tons of hay which they carry. 



399. Kinds of Stress. Solid bodies may be subjected to 

 three kinds of stress which tend to break them and will 

 do so if the stress is great enough. These are: 



1. A crushing stress, where the load tends to crowd the 

 molecules closer together, as when kernels of corn are 

 crushed between the teeth of an animal. 



2. A stretching stress, as where a cord is broken by a 

 load hung upon it. 



3. A twisting stress, as where a screw is broken by 

 trying to force it into hard wood with a screw-driver. 



400. Strength of Moderately Seasoned White and Yellow 

 Pine Pillars. Mr. Clias. Shaler Smith has deduced, from 

 experiments conducted by himself, the following rule for 



