660 



PROCEEDINGS OF SECTION H. 



break tte beam of full section as of truncated section ; that the former 

 is stronger than its calculated modulus would imply ; and that distinctly 

 before it receives its full breaking load it will have its tensile corner 

 cracked down some 10 per cent, of its total depth. If, however, as 

 many consider, the ordinary beam theory is little more than an ap- 

 proximation to the truth in the case of a beam upon the point of fracture, 

 when, owing to mutual lateral support, there is produced to a large 

 extent an equalisation of stress over a great part of the section inde- 

 pendent of distance from the neutral axis, then one would certainly 

 expect a greater strength from the beam of full section than from that 

 with part of the section removed. It was therefore considered of 

 interest to make experiments upon such cast-iron beams of full square 

 section and of the truncated section, i.e., with metal removed from the 

 tension corner, in order to ascertain their comparative resisting strengths. 

 Six specimen bars, 22in. long, were obtained, all cast from the 

 same ladle to ensure as great similarity of constitution as possible. 

 Each was machined all over to approximately fin. side, about \m. 

 metal being removed from each face to eliminate errors due to the 

 skin. On each specimen were cast three bearing lugs, about ^in. 

 wide, carefully faced at 45° to the sides of the beam, to take the bearing 

 edges of the testing machine. Then from each of three of the bars the 

 tension corner was machined off to a depth of |in., being approximately 

 one-tenth of the total depth of the section. 



n 



V 



Full section as figure. 



Truncated section machined off along dotted line. 



The specimens were finally broken in a hydraulic testing machine, 

 with the results shown by the following table : — 



Mean strength of full sectioned bar, l,0831bs. Of truncated section, I,L131bs., 

 i.e., 2-8 per cent, higher than the full section. 



