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MECHANICS 



680X5-500X3= + 1,900 ft.-lb., and that about the point 

 10 ft. from the left-hand end is 680X10-500X8-800X5 

 = -1,200 ft.-lb. It is thus seen that the greater of the 

 two maximum bending moments occurs about the point 

 5 ft. from the left-hand end. 



Bending-Moment Diagrams. The bending moments that 

 act at various points of a loaded beam may be repre- 

 sented graphically in the same manner in which the shear- 

 ing forces were shown. For example, a beam 50 ft. long 



supports two concentrated loads of the magnitudes and in 

 the positions indicated in Fig. 17. Now, assuming that 

 Fig. 17 (a) is drawn to scale, draw the horizontal line ab and 

 produce the lines indicating the reactions and concentrated 

 loads until they intersect line ab at a, c, d, and b. By cal- 

 culating the moments about the left-hand reaction, the 

 moment for the load Wi is found to be 10,000 X 10 = 100,000 

 ft.-lb. and that for W 2 , 6,000X25 = 150,000 ft.-lb. The 



100,000X150,000 

 reaction R 2 is therefore = 5,000 lb., and 



reaction #1 is 10,000 + 6,000-5,000 = 11,000 lb. 



