THE I BEAM. 



49 



than on the other. It is this difference between the horizon- 

 tal forces which produces the horizontal shear along the 

 bottom of the block, the value of which can be calculated in 

 the ordinary way. In this calculation it is usual to assume 

 the block of infinitesimal length in order to avoid the consid- 

 eration of the direct load on top of it. This is a matter of 

 convenience only, and for simplicity we will assume in what 

 follows that the block is sufficiently small to neglect conside- 

 ration of any direct load effect. 



If we consider points at the same level beginning at the 

 middle and moving towards the support, it is seen that the 



L 

 \ 

 \ 



\- 



FlGURE 2 



decrements of horizontal stresses measure the value of the 

 horizontal shear. When the end of the beam is reached the 

 horizontal stresses will have all been "spilled off" in the 

 shape of horizontal shear, the latter having now reached its 

 maximum value. This effect appears at all points in the 

 beam, the difference of horizontal stresses on the block under 

 consideration producing the total horizontal shear on the 

 bottom of the block. If desired we may also consider the 

 block as situate below the level under consideration, and find 

 the shear along the top of the block. Naturally, the value 

 will be the same in either case. 



