XL. J. I. HAYCROFT. 



2nd. Technical advantage, that the longitudinals are 

 stronger, less sensible to dynamic effects, less exposed to the 

 action of rust, and less subject to dislocations than trellis 

 girders ; all these tend to greater durability. 



3rd. Commercial advantage, which the Professor states may 

 reach 25% reduction of cost over a trellis Bridge equally strong. 



Some of the disadvantages which the Professor states pin- 

 connected trusses suffer under, and from which his design of 

 Bridge is free, are as follows : — 



Complications in carrying out the articulations, the 

 adjusting and arrangement of the pieces, at least 4, at each 

 intersection ; complications connected with the cross-girders 

 and wind bracing, due to the fact that they should be fixed on 

 the vertical central line of the articulations in a rigid manner, 

 and so as not to interfere with the articulations ; the insecurity 

 which results from the use of forged pieces (an operation which 

 always debases the metal), or from welded joints, which even the 

 most experienced operator can neither verify or guarantee the 

 results of ; the wear, which after a lapse of time, is produced in 

 the articulation, and the resulting mobility in the entire frame- 

 work, by which the dynamic effects of the line load is greatly 

 increased. 



The writer, whilst endorsing the Professor's criticisims of 

 rivetted trusses, does not agree with his strictures on American 

 trusses, as though such strictures may have been justifiable in 

 former years, nowadays such objections are only theoretic. 



The writer is also surprised at the practice of Continental 

 engineers using redundant members in Bridge trusses, though 

 aware such were employed in other structures, notably the Eiffel 

 Tower. 



Let Fig. 1 represent the side elevation of portion of a girder 

 with parallel flanges. Throughout the description H is taken as 

 the vertical distance between the centres of gravity of the 

 flanges, and D is the distance between the axes of the verticals. 



Cross girders are fixed on the centre line of each vertical, 

 either on top or bottom. 



