408 



AGRICULTURAL ENGINEERING 



If placed on the flat, 



bd 2 4X(2X2) 16 



M S = — = =— - 



6 6 6 



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 









Span in 



feet 







Depth of 















beam 

















6 



8 



10 



12 



14 



16 



6 



720 



540 



432 



360 



308 





7 



980 



735 



588 



490 



420 





8 



1280 



960 



768 



640 



548 



480 



10 



2000 



1500 



1200 



1000 



857 



750 



12 



2880 



2160 



1728 



1440 



1234 



1080 



14 



3920 



2940 



2352 



1960 



1680 



1470 



