" LE PONT VIERENDEEL. LXI. 



favour of the latter. It may, however, be noted that were the 

 two bridges designed to withstand the same range of stress, 

 primary and secondary, the comparison in favour of the 

 Professor's bridge would be much more marked ; also, that one 

 girder as designed by the Professor would be 3^ tons lighter 

 than one of the girders in the other design as erected, the former 

 containing 51 more rivets than the latter. 



The engineers who superintended the test of the ^ierendeel 

 bridge report that the elastic limit was reached when the load 

 (surcharge) was 358^ tons — thus the coefficient of security was 

 2*1 — and that the stress at that moment was about 10 tons per 

 square inch. Actual rupture took place under a surcharge of 

 396 tons. The Professor, however, taking into consideration the 

 difference in the weights of the deck as constructed to receive 

 the test load and the deck for which the truss was designed, 

 arrives at a factor of 2*52, and the maximum stress at that 

 moment was 9 '56 tons per square inch. 



As there can be no doubt that the statement of Professor 

 Vierendeel to the effect that stresses arrived at, no matter by 

 what means, which start on a false hypothesis must be incorrect, 

 is absolutely true, perhaps it would be as well to ascertain what 

 has been done by Continental engineers in this matter. 



The Dutch Government tested three railway bridges on the 

 Amsterdam-Rotterdam -Utrecht lines, of respective spans of 211 

 feet, 262 feet, and 324 feet, by means of the well-known apparatus 

 of Manet-Rabut and Fraenkel, in order to arrive at the actual 

 stress of various portions of these trusses under working 

 conditions. 



These trusses were of the same type, and may be roughly 

 described as right line lower boom, polygonal upper boom, with 

 counterbracing in each and every bay. The cross girders were 

 not rivetted to the main girders, but so articulated that any 

 bending in the former due to live load would have no influence 

 on the stresses in trellis bars. 



The principal results arrived at were as follows : — The 

 recorded stress exceeded the calculated stress by as much as 110 



