OA' STKA1N. 8; 



ity of such a structure graphically, lay off, by scale, a figure 

 20 x 1 20, denoting its centre of gravity G. Draw the hori- 

 zontal line GW to any convenient scale, representing the 

 estimated force of the wind in tons. By the same scale, draw 

 a vertical line, GV, showing the direction and amount of the 

 vertical forces due to the weight of the structure. Complete 

 the parallelogram of forces as shown, and the diagonal, GR, 

 will represent the direction and extent of the combined action 

 of the vertical and horizontal forces, and, if produced, falls 

 without the figure or beyond its base. Here the structure 

 can not stand. 



Wind 



FIG 90. 



In order to secure the equilibrium of the structure it is 

 evident that some form of anchorage must be provided. Con- 

 sidering the wind-stress to which the tank may be subjected, the 

 moment of this force M, is 72,000 Ibs. multiplied by the leverage 

 in inches, 720, or 51,840,000 pounds-inches. 



The area of the tank cross-section in inches being 45,239, 



