1864.] of Impact, ^c, on WroughUlron Girder s» 



Experiment IV, 



125 





Number of 



Date. 



changes 





of Load. 



1861, 











November 18.,. 



126,000 



December 18... 



237,000 



1862. 





313,000 



Deflection, 

 in inches. 



0"20 

 0'20 

 0-20 



Permanent 



set, 

 in inches. 



Kemarks. 



Broke by tension across the 

 bottom web. 



Collecting the foregoing series of experiments, we obtain the following 

 summary of results. 



Summary of Results. 





Date. 



Weight 

 on mid- 

 dle of the 



Number 

 of 



Strain 

 per sq. 

 inch 



Strain 

 per sq. 



inch 

 on top. 



Deflec- 

 tion, in 

 inches. 



Eemarks. 



No.o 





beam, in 

 tons. 



changes 

 of Load. 



on bot- 

 tom. 





I 



From March 



















21 to May 







596,790 



4-62 



2-58 



•17 







14, i860... 

















2 



From May 



















14 to June 





■ 3'5o 



403,210 



5-46 



3*05 



•23 







26, i860... 

















3 



From J uly 















Broke by tension a short 





25 to July 





. 4-68 



5,175 



7-31 



4-08 





distance from the cen- 





28, i860... 















tre of the beam. 



Beam repaired. 



4 



Aug. 9, i860 



4-68 



158 



7-31 



4-08 





The apparatus was acci- 



5 



Aug. II & 12 



3-58 



25,742 



3*59 



3-12 



■22 



dentally set in motion. 



6 



From Aug. 



















13, i860 to 

 Oct. 16, 1 86 1 





■ ^'96 



3,124,100 



4*62 



2-58 



•18 

















7 



From Oct. 18, 

 1861 to Jan. 

 9j 1862 ... 





^ 4-00 



313,00c 



6-25 



3-48 



•20 1^ 



Broke by tension as be- 

 fore, close to the plate 

 riveted over the pre- 

 vious fracture. 



From these experiments it is evident that wrought-iron girders of ordi- 

 nary construction are not safe when submitted to violent disturbances 

 equivalent to one-third the weight that would break them. They, however, 

 exhibit wonderful tenacity'- when subjected to the same treatment with one- 

 fourth the load ; and assuming therefore that an iron girder bridge will bear 

 with this load 12,000,000 changes without injury, it is clear that it would 

 require 328 years at the rate of 100 changes per day before its security 

 was affected. It would, however, be dangerous to risk a load of one-third 



