ANCIENT AND MODERN WORKS. 2$ 



of cracks about the rivet-holes, indicating damage in punching 

 brittle plate. Physical tests of samples of the plate were made 

 at Purdue University, as was also a test to determine percentage 

 of phosphorus, with the following results: 



Original area in sq. ins 5625 -57^4 



Elongation in 8, in per cent 22.5 23.5 



Reduction of area, per cent 47-7 4-5 



Elastic limit, per sq. in., Ibs 37,020 



Ultimate strength per sq. in., Ibs 58,490 5596o 



Character of fracture, coarse, silky; laminated. 



The test for phosphorus was made upon a sample which ap- 

 peared unusually brittle and had an especially poor fracture. 

 The analysis showed .091% phosphorus. 



Examining the list of plate thickness, it appears that the 

 Elgin stand-pipe was designed with a safety factor of 4, assuming 

 70% joint efficiency with 6o,ooo-lb. steel plate. The spacing 

 and diameter of rivets as found in the lower rings was not such 

 as to give the assumed 70% efficiency. In the fourth ring the 

 rivets had a pitch of about 2\ ins. with i-in. rivet-holes, which 

 would reduce the efficiency of the joints to 60% and increase 

 the working stress with a full tank from 15,000 to 17,500 Ibs. 

 per square inch in the net section. With the water at the 72-ft. 

 level at the time of the accident the stress due to hydrostatic 

 pressure alone was perhaps 13,000 Ibs. per square inch in the 

 rings near the base, where the failure occurred. The quite general 

 practice of using a safety factor of 4 in stand-pipe design has 

 doubtless been based upon the assumption of quiescence in 

 the loading, as in building construction. In the case of a stand- 

 pipe properly encased from the action of the ice and wind 

 this assumption is doubtless consistent, although the prevailing 

 practice in good bridgework of using low working stresses for 

 loads frequently applied might warrant the use, even in the 

 protected stand-pipe, of safer unit loads than those obtained 

 with a factor of 4. In any event, the Elgin stand-pipe is open 



