,LXII. J. I. HAYCROFT. 



per cen*\ in the case of the verticals, by 26 per cent, in 

 the compression diagonals, and 52 per cent, in the tension 

 -diagonals. 



The Dutch Administration have decided, as a result of these 

 tests, that the erection of redundant trusses, such as those 

 tested, was not the practical solution of providing for the 

 secondary stresses, and have reverted to the simple triangular 

 trusses calculated as articulated, but adding 100 per cent, to the 

 calculated stresses in the lattice bars, in order to provide for 

 the effect of the calculated primary and unknown secondary 

 stresses. 



French engineers have only investigated this question within 

 the past six years, having tested a double line railway bridge 

 over the Loire, of 14 independent spans, each 190 feet long, the 

 trusses being N trellis, with the cross girders riveted to the 

 verticals. The results were as follows : — An increase of 130 per 

 cent, over calculated stress in the verticals due to secondary 

 stresses, of 70 per cent, in the diagonals, of 93 per cent, in the 

 upper flange. 



The conclusion arrived at from these tests was that the best 

 type was the close-lattice girder. 



As regards Switzerland, it will be remembered that in June, 

 1891, the bridge at Monchenstein, on the Jura-Simplon Line, 

 collapsed, under ordinary working conditions, after a life of 16 

 years. The Swiss Government ordered an investigation to be 

 made as to the cause of collapse by Professor Collignon and A. 

 Hamer, Engineer-in-Chief of the Roads and Bridges in France. 

 These experts reported, inter alia, that the defect was not due 

 sto any defect in design or execution, or to quality of the iron ; 

 the cause was, in fact, abnormal, and probably due to some 

 hidden defect in the metal, which, however, when tested, showed 

 no sign of fatigue, the results being as follows : — Breaking 

 weight in 1874, 24 tons per square inch, whilst in 1891 it 

 reached 24f tons per square inch, the elongation in 1874 being 

 7*46 per cent., whilst in 1891 it was 8 per cent. 



