Polytechnic Association Proceedings. §33 



at Frankfort, which he passed over in the year 1852. It had been 

 built some years previously, but precisely when, or by whom, he 

 was unable to ascertain. It is possible that it was built before 

 Seguin's structure. Besides this, it had also no stays. The spans 

 of this stiffened suspension bridge were one hundred, two hundred 

 and sixty-one, and two hundred feet, the lattice girder was six feet 

 high, the distances of suspension rods, and likewise of the cross- 

 bearers, equal to three feet, and floor with girders had the calcu- 

 lated weight of nine hundred and thirty pounds per lineal foot. 



lu the year 1842, the Austiian engineer, Schnirch, who built the 

 well-known suspension bridge at Prague, proposed a new system 

 of suspension bridges, the curves consisting of two pairs of parallel 

 chains, one above the other, and both connected by triangular 

 . trussings. At these bridges the chains themselves represent a stiff 

 inverted arch, and are to be calculated only as such. A bridge of 

 this kind, before Schnirch had occasion to introduce hLs system in 

 practice, was carried out in Switzerland, across the river Aar, near 

 Aaruu, but the distance of the chains was too small to be considered 

 as sufficient. 



Schnirch's plan was carried out for two tracks in Vienna, in the 

 year 1861, to bridge a canal of the Danube river. As Schnirch's 

 plan is of so old origin, and an ingenious invention; and, as the 

 euspensiou railroad bridge in Vienna is, until this day, the best, 

 though not the longest stiffened suspension bridge, I will proceed 

 to describe it. 



Two parallel chains on each side, consisting of alternately eight 

 and nine iink-plates each, are placed at a distance apart of 4.1 feet. 

 The trussing consists of a single triangular system, the diagonals 

 being 6.4 feet long, the links of the chains are ten feet long, and 

 six by 1.35 inch, and six by 1.16 inch, respectively; two pairs of 

 chains, in a distance of thirty-one feet from center to center, limit 

 the floor sideways; four longitudinal trusses of wrought iron, con- 

 sisting of uprights and crossing diagonals, are made to stiffen the 

 floor and to offer suitable points of attachments to the suspension 

 rods, at distances of about five feet. The suspension rods them- 

 selves are made adjustable. The longitudinal trusses are 2.5 feet 

 high, and represent likewise the chords for a horizontal trussing, 

 the uprights of which are the cross-bearers, iron girders of 2.5 feet 

 height, and the diagonals are strong iron bars, fastened by rivets. 



The span is two hundred and fifty-two feet; anchorage, archi- 

 tecture of piers, and performance are entirely successful. 



(Inst.] 53 



