408 



AGRICULTURAL ENGINEERING 



If placed on the flat, 



_ bd 2 



T 



4X(2X2) 16 



or just one-half of the value previously obtained. 



The Modulus of Rupture. The modulus of rupture is a 

 measure of the strength of the material to resist transverse 

 or bending stresses. Thus oak is stronger than pine. The 

 modulus of rupture is obtained by test. The following table 

 furnishes the values of the modulus of rupture quite generally 



used. All of the values are per square inch of cross-section. 

 White pine ...................................... 7,900 



Yellow pine ..................................... 10,000 



Oak ............................................ 13,000 



Hickory ......................................... 15,000 



Cast-iron ....................................... 45,000 



Mild steel ....................................... 55,000 



Formula for Beams. The general formula for beams may 

 now be stated as follows: 



modulus of selection X rupture modulus 

 Bending moment = - : - ; - - 



factor of safety 



This formula may be used in calculating the strength of 

 beams, but it is given here principally to explain how the 

 strength of beams varies. The following tables give the 

 strength of columns or posts and of beams. 



Safe Strength of White Pine Beams. The following 

 table gives the safe loads for horizontal, rectangular beams 



Depth of 



Span in feet 



