196 TOWERS AND TANKS FOR WATER-WORKS. 





required for connection, make this a most excellent section for 

 supporting columns of a water-tower. 



Six-inch columns are manufactured from 12 to 30 feet long; 

 8-inch are from 18 to 40 feet in length, and 12-, 14-, 16-, 18-, and 

 20-inch columns are made as long as 50 feet. In the tower design, 

 where junctions are made between lengths, horizontal struts are 

 introduced between columns, and are sometimes inserted radially, 

 the latter rather for the purpose of stiffening the tower than 

 calculated as of theoretical value in transmitting stresses. There 

 is also usually inserted at the foot of the tower a strut or tie. 

 When this is omitted, as is sometimes the case, the foundation 

 loads are not vertical, there being a horizontal component. This 

 point should be taken into consideration in the design of the 

 foundations, making the resultant of the loads on the foundation 

 come in the centre of the bearing surface and thus avoid the 

 liability of unequal settlement. 



Horizontal members of the tower are subject to similar stress 

 as the vertical columns, but it is to be -noted that in particularly 

 long lengths, the weight of the strut itself produces deflections 

 that should be given consideration. 



In water-tower design, such horizontal struts are generally 

 formed of four angles back to back, and riveted either to a central 

 web plate or to lattice bars, but where the span and load is con- 

 siderable, the double-latticed channels are preferable. 



Columns and struts generally fail under the stress produced 

 by combined compression and bending. 



The investigation of a column under a given load consists 

 in computing the unit stress from formulas and then comparing 

 this with the ultimate strength and elastic limit of the material, 

 taking into consideration such conditions as the effect of a steady, 

 variable, or sudden load with further reference as to how the 

 column ends are secured. 



When the length of the column and load to be carried by it 

 Is given, the design consists in selecting suitable materials and 



