40 REINFORCED CONCRETE CONSTRUCTION 



point in the cross-section is given by the following formula: 



,_My 

 J " I 

 in which /= fiber stress at distance y from neutral axis. 



M external bending moment at section in inch-pounds. 

 y = distance in inches from neutral axis to any fiber. 

 1 = moment of inertia of the cross-section about the 



neutral axis. 



5. The general formula which gives the longitudinal shear per 

 square inch (v) at any desired point in the cross-section is 



v = 



VQ 

 IV 



in which V = total shear at the section in pounds. 



Q = statical moment about the neutral axis of that 

 portion of the cross-section lying either above or 

 below (depending upon whether the point .in 

 question is above or below the neutral axis) an 

 axis drawn through the point in question parallel 

 to the neutral axis. 

 1 = as before. 

 V = width of beam at the given point. 



c 

 Nedtral axis 



"J Area of 

 ^ cross -halrhed 

 ; portion A 1 



b H 



FIG. 12. 



In the above formula, by the term statical moment is meant the 

 product of the area mentioned by the distance between its center 

 of gravity and the neutral axis. For example, the longitudinal 

 shearing intensity at a point c in a rectangular beam, Fig. 12,may 

 be expressed as follows: 



VA'r 



v = 



Ib 



For rectangular beams and all beams of uniform width, the 

 largest value of v for any given section will occur at the neutral 



