DESIGNING. 165 



intends to construct his stand-pipe of plate advancing 

 32ds, l6ths, or 8ths of an inch. Usually the thickness of the 

 plates to be used in the ascending sections or rings are de- 

 creased by i6ths; but, in close calculations, the scale is taken 

 at 32ds, and in which case the value of any subdivision would 

 be one thirty-second on the horizontal line. 



The value given to equal subdivisions of the vertical line 

 H'H can be taken at decimals of 100 ft., and represent the 

 height of each panel or ring taken in the clear that is, between 

 laps. The height of the rings is generally uniform, but is 

 entirely arbitrary, the limiting height being determined by 

 cost and convenience of handling; thus, a stand-pipe with 

 a greater number of shorter rings would require a greater 

 number of connecting joints, with increased cost of rivets, 

 punching, and driving, as well as decreased efficiency in the 

 general strength of the structure, than one with greater height 

 of ring and fewer joints; but the larger the plate which is to 

 be used in the construction of the ring, the more difficult it 

 becomes to handle, both on account of the increased weight 

 and the trouble given by the wind catching the broad expanse 

 of plate metal, swinging and swaying it in the most trouble- 

 some manner as it is being hoisted into place. 



It has been found from practice, both in shop- and field- 

 work, that a 5 -ft. segment is a very convenient height, and 

 therefore the practice of making the rings 5 ft. in the clear 

 seems to be in general use. Assuming that this height will 

 be adopted, the value of the subdivisions of the vertical scale 

 would be 5 ft. 



The increasing height on the vertical scale, in multiples of 

 five, is usually indicated as shown on the strain-sheet, as is 

 also the increasing thickness on the horizontal scale, advancing 

 by i6ths, 32ds, etc., as may be determined in advance. 



Application of Mechanical Principles. The formula for 

 arriving at the theoretical thickness of plates is explained on 



