84 



BROOMALL : 



ends of the elementary "block" of material lying above or 

 beyond the element of length under consideration. 



3. Passing from the middle towards the ends along any 

 level line, the above horizontal forces are all "spilled off" 

 in the shape of horizontal shear, becoming reduced to zero at 

 the ends. The horizontal forces become less and less by reg- 

 ular decrements or subtractions from a previous value. The 

 horizontal shear usually increases towards the ends, but not 

 by additions to a previous value. 



4. The horizontal shear may be regarded as the physical 

 lever-arm of the couples in the upper and lower part of the 

 beam. Without this shear the parts of the beam would not 

 work together as a harmonious " resisting moment." 



5. In the I Beam the compression in the right-hand edge 

 of the upper flange, for instance, must work in conjunction 

 with its most remote comrade, the tension in the left-hand 

 edge of the lower flange. This can only be through the 

 medium of some kind of shear. Hence we must assume the 

 existence of horizontal shear in the flange as well as in the 

 web. The horizontal shear in the flanges, however, has its 

 shearing planes vertically disposed, while in the web the 

 shearing planes are horizontal, Figure i. 



niiiiL i i i i ii i 



irmnrfYTTTm 



FIGURE 1 



As a definite problem for the application of these and 

 other principles to beams of unsymmetrical cross section, let 



