26 TOWERS AND TANKS FOR WATER-WORKS. 



to severe criticism in that its metal has probably been subjected 

 to as much as 17,500 Ibs. per square inch under daily service, 

 which represents a factor of safety of less than 3.5 as compared 

 with the ultimate strength of 60,000 Ibs.; or if compared with 

 the elastic strength of say 30,000 Ibs. per square inch, a " co- 

 efficient of security" of 1.7 or so. The latter is the more correct 

 basis of judgment of the safety of a stand-pipe, since total failure 

 is almost certain to follow the opening up of the rivet-holes, 

 about which cracks or defects are most likely to occur. 



The Elgin stand-pipe is, of course, open to the sweeping 

 criticism which may be directed against the large number of 

 stand-pipes which have no protection from the elements, espe- 

 cially those in icy latitudes. If, as must be conceded, intelligent 

 design provides against a dangerous condition, which is certain 

 to exist, then the Elgin stand-pipe was defective in design in 

 that ice could form within it in dangerous quantities. Beside 

 the fall of the ice, other possible dangers from the action of ice 

 have been taken into consideration. One of these is the increased 

 rivet shear due to the possible suspension of 800,000 Ibs. of ice 

 from the top rim, which would amount to about 1800 Ibs. per 

 rivet. Still another danger was in the formation of the ice-cap 

 by which the rivet shear might be very greatly increased from the 

 atmospheric pressure as the water was drawn off, or the stand- 

 pipe might be overstrained by the sudden starting of the pumps. 

 Should a perfect vacuum form beneath the ice-cap, the increased 

 vertical shear would be about 3300 Ibs. per rivet, which, added 

 to that due to the suspended ice, would produce a rivet shear 

 of say 5000 Ibs. per rivet above 'that considered in tin- design. 

 Still another danger from ice is suggested by the existence of 

 the water film due to thaw against the plates. In case the ice 

 shell had a water-tight connection with the bed-plate, as might 

 appear possible from the low temperature of the supply, and 

 be free from cracks so as to isolate the film from the main body 

 of water, the dangers would be much the same as those which 



