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BROOMALL 



cal shear, and (c) by a secondary right-angled horizontal 

 shear necessary to equilibrate the vertical shear. These 

 forces are indicated to the left in Figure i . 



Figure 1 



If these forces are resolved for maximum values in the 

 usual way, lines of maximum stress will be found after the 

 fashion indicated in Figure i, solid lines indicating direct 

 stress and dotted lines shear. A complete diagram of lines 

 of internal stress may be found in the article already men- 

 tioned. 



Let us look further into the group of applied forces (2) 

 which is the keynote to an understanding of the theory of 

 internal stress. At any point these forces produce primarily 

 vertical shear and direct stress, and secondarily horizontal 

 shear. The direct stresses will be of large value near the 

 middle of the beam and zero at the supports. The shears, on 

 the contrary, have their maximum value at the supports, and 

 become zero at the middle. The variation of these forces is 

 interesting, and in Figure 2 the attempt is made to show the 

 varying values of the forces acting on a finite, rectangular 

 portion or block of the material at various points. It will be 

 noted that the sum of the horizontal forces acting on the 

 block is greater on the side toward the middle of the beam 



