OF IRON BEAMS. 



457 



The beam twisted a little before breaking: this 

 however was not usually the case in the other 

 beams from the same model. 



Form of fracture as in figure, tr =± ftt^ 



8270 



Hence strength per inch of section = -^ 

 = 2584lbs. 



y. EXPERIMENT. 

 This casting had its top rib a parabolic arch and 

 the, top and bottom ribs; nearly equal in section, 

 with equidistant ordinates only between them. 

 Dist. between supports and depth of beam as before. « 



Dimensions of ribs in inches. 



Area of top rib = 2.2 x .56 = 1.23. 



Area of bottom rib= 2.2 x .5S = 1.17. 



Weight of casting = 41} lbs. 



Breaking weight = 5528 lbs. or less : see next expt. 



This weight however is but ~- of what was borne 



by, the common beam in the last experiment. 



It broke by separating, near the first ordinate, 

 3ii 



