GRAPHIC STATICS 



219 



equilibrium polygon must begin at one reaction line and close on 

 the other. The two ends are connected by the line oo. This line 



is transferred to the polar dia- 

 gram, as shown by the dotted 

 line. The distance on the load 

 line from the top to an inter- 

 section with the closing line oo, 

 is the amount of the left reac- 

 tion and from the point o, on 

 the load line, to the bottom 

 of the load line, is the right 

 reaction, all as shown at (c). 

 The polar distance, H, at 

 (c) is measured with the scale 

 used in setting off the loads, 

 for it is a force. The vertical 

 Fig. 134. Moment, Shear and Re- distances on the equilibrium 

 actions for Beam. ,. , u , r 



polygon, from the closing line 



to the broken bottom line, are measured with the scale used in 

 drawing the beam. The vertical depth of the equilibrium poly- 

 gon, at any point, multiplied by the polar distance gives the 

 bending moment at that point. If the vertical distance is in feet 

 and the polar distance is in pounds, the moment is in pound feet. 

 At (d) is shown the shear diagram, for which it is believed no 

 explanation is necessary. 



Fig. 135. Roof Truss Unequally Loaded. 



In Fig. 135 is shown a roof truss having unequal loads on the 

 panel points. A polar diagram is drawn first, to obtain the reac- 



