The Works Of Messrs. Schneider And Co.

.142 MESSES. SCHNEIDER AND CO.’S WORKS. stream and in a groin 30 metres (98 ft.) in length on the right bank, to which the current takes all boats and float- ing material after passing under the Concorde Bridge. For the sake of economy, it was intended to build a roller bridge adapted for erecting one rib at a time ; but this idea had to be abandoned, owing to the risk that would be incurred in leaving the first rib, even when firmly secured, and proceeding with the second. down after the érection of each group of ribs. They do not rest direct on the piles, but on a string-piece placed on the top, so as to distribute the load over a set of six piles. These arrangements, which seem out of proportion to the vertical load carried (a series of twelve piles can easily bear a load of 300 tons) are rendered necessary by the force of the wind, which displaces in a marked degree the resultant line of efforts applied to the intermediate bearing frame. The roller bridge, which it was decided should be employée! in the construction of the bridge, consista of two straight lattice girders, 120 metres (394 ft.) long between 1 end verticals, and 7.50 metres (24 ft. 6 in.) high. The j transverse distance between these girders is 5.714 metres i (18 ft. 8 in.). The frames consist of plain I-bars, the lattice work being double. The vertical uprights are | placed at such a distance apart as to be equal to the length of the horizontal projections of the arch voussoirs, namely, । 3.625 metres (11 ft. 11 in.). In the centre of the bridge the three spaces that correspond to the bridge key have been reduced, owing to the lesser length of the key voussoirs. The two girders are joined together by a series of | frames consisting of two vertical uprights, united at the I middle of their height by a horizontal stay ; this stay and ; the inside surfaces of the uprights carry brackets, on which are placed a rail track for the trucks that serve in the érection of the arches. Above the stay the frames are further strengthened by horizontal bars, level with the top trusses. Below the stay-bar a space has been left free for the carrying of the pieces forming the arches. In the lateral spåns the lower part of the vertical uprights is inclined so as to rest on the frame soleplates. In the central span, on the contrary, the lower part of these uprights, as well as that of the track bracket supporting frames, is arranged so as to be fitted with suspension-rods level with the lower soleplates of the frame. The framework thus formed would not have sufficient strength to resist the force of the wind, which is consider- j able, owing to the surface exposed, not only by the roller bridge, but also by the superstructure and the arches under ; érection. It has, therefore, been stiffened by a lattice girder, placed horizontally at the middle of the height, the j framing of which, made of I bars, unites the uprights at ! the joints of the lattice work. The end frames of the j bridge are stayed by inclined cross-braces for the whole of their length. To relieve the bridge during the érection of the arches, ; and to reduce the vibrations caused by tbe wind, and which ' On the banks the bridge bearings are carried on triple beams, laid parallel to the river. These form the top edge of the trestie. Below, in a line with each of the bearings, are six uprights which divide the load on the truck body above the truck rollers of the bridge. These standards are 5.85 metres (19 ft. 2 in.) high ; the track is 4-metre (13 ft. 1 in.) gauge, the distance between the end rollers of one series being 11.50 metres (37 ft. 9 in.). The rollers are ten in number, the centre set of each series being fitted to the ends of the two standards. The roller truck is stayed with bars placed in a line with each pair of rollers. The whole is further stiffened by two other sets of stays, one uniting the standards at half their length and forming a horizontal bed around the trestie, the other joining the middle of the trimmer to the middle of the trunk frames. The roller-bridge framework is made throughout of rolied steel bars, while all bearing parts are of cast steel. The tests prescribed for the rolied steel are the same as those for that used in the construction of permanent bridges, namely, 42 kilogrammes, tensile strength per square millimétré (26.67 tons per square inch), and 22 per cent, elong-ation. The weight of the material employed in the construc- tion of the roller bridge is divided as follows : Tons Roller bridge proper, with bearings ... ... 238.5 Bank trestles ... ........ ............ 47.0 Winch platform, pulley carrying beams, ties, swing trees ... ... ... ... ... 25.5 Two steam winches ... ... ... ... 14.0 Total of movable part ... ... ... ... 325.0 River piles ... ... ... ... ... ... 58.5 Total ......... 383.5 To the weight of the movable part should be added, during érection, the weight of the wood flooring, 10 tons. Stability of Roller Bridge. The roller bridge has been désignée! to withstand not only vertical loads, but also a horizontal wind pressure of 120 kilogrammes per square metre ; it has been reckoned that the strain on the steel would have caused great trouble in the adjustment of the j voussoirs, intermediate bearings have been provided, the outside series of outer centre piles being employed for this, j the piles having been strengthened for that purpose. The bearings are placed on triple-ribbed beams, laid parallel with the bridge and carried on a trestie of iron posts, the uprights of which are direetly above the series of piles. The tresties are placed in the space adjoining tliat of two arches in course of érection ; they are taken might reach 12 kilogrammes per square millimétré (7.62 tons per square inch) of gross section under the action of vertical loads, and 13 kilogrammes (8.25 tons) under that of the wind. It is under the action of its own weight, inereased in the middle by the weight of the centres, that the moment of flexure is at a maximum, and the coefficient of 12 kilo- grammes per square millimétré (7.62 tons per square incli) of gross section is reached. It should be remarked that