EXTERNAL FORCES 



15 



line of the triangle being merely a closing line. There is no bend- 

 ing moment at D. 



At (c) is drawn the shear diagram. The load being concen- 

 trated at the end, the shear of course is constant from the point 

 of application of the 



0) 



' T 



*1 



load to the support. 

 The shear may be 

 found at any point by 

 measuring a vertical 

 line at the point across 

 the shear diagram. 



Relation between 



Shear and Moment 



Diagram 



Assume line C f C n to 

 be dropped across the 

 shear diagram. Then 

 the area of the shear 

 diagram to the right of 

 the line, that is to the 

 free end, gives the 

 bending moment at C. 

 Similarly, the area of 

 the shear diagram to 

 the right of line B,,B, 

 gives the bending mo- 

 ment at B. The area 

 is in foot pounds be- 

 cause the vertical di- 

 mension is expressed in 



Shear Diagram 

 Fig. 4 Several Loads on a Beam 



The relation is true 



pounds and the horizontal dimension in feet, 

 in all cases and must not be forgotten. 



In Fig. 4 is shown the case of several loads on a beam. The bend- 

 ing moment at D - 0. The bending moment at C - 8 X 600, and 

 this is plotted as line CC f . The bending moment at B - (15 X 600) 

 + (7 x 400), and this is plotted as line BB,. The bending mo- 

 ment at A - (19 X 600) + (11 x 400) + (4 x 200), and this is 

 plotted as line AA,. 



The shear diagram, at (c), shows the shear at the right end 



