The Works Of Messrs. Schneider And Co.

THE ALEXANDER III. BRIDGE. 139 piers are made with pointed cut-waters up stream, and carry columns formed of Scotch pink granité. The spring- ings of the arches rest on large stone Blocks of great résistance ; these are carried on stone masonry made parallel to the ends of the arches and the abutments. The roadway is paved with wood Blocks for lightness. Each spån consista of eight ribs 2.600 metres (8 ft. 6g- in.) distant from centre to centre under the roadway and 8.300 metres (10 ft. 10 in.) under the pavements. The ribs are built up of plates and angles, and are box-shaped, with double vertical webs ; the flanges are .800 metre (31 j in.) wide ; the ribs are divided in 26 sections in the central spån and into 24 parts in the end spåns. They are united by beams and stiffening bars. Opposite each division the ribs carry vertical uprights which enlarge at the top so as to form a series of small arches; these are surmounted by the string piece that carries the iron superstructure. The ends of the ribs bear on the piers and abutments through the intermediary of three curved sockets, placecl in the middle above each flange of the ribs, so that the effort is always received between two of the hinges in the varions combinations of surcharges and temperature. The ends of the ribs were carefully planed, and they rest against steel plates 77 millimétrés (3 in.) thick, which are grooved for taking the three bearings. The pressure is transmitted to the masonry through a first course of cast- iron plates. The spåns were constructed and wedged on the bearing hinges at an average temperature ; the end hinges were wedged after completion of the bridge, also at a temperature approaching normal. The steel used in the construction of the Morand bridge has a breaking strain of 47 kilogrammes per square milli- métré (29.84 tons per square inch), with a maximum élonga- tion of 24 per cent. For erecting the ribs, Messrs. Schneider and Co. built a continuons centring, which rested on piles driven in the river. Two portable crânes lifted the pieces for each half of the bridge. The railway at both ends served for the carriage of the pieces. The érection began on the upstream half of the bridge : the ribs were forwarded from the Chalon Works in sections corresponding to two divisions ; these were placed on wood bearings and fitted together in their final positions. The réduction in pitch which the permanent load was calculated to produce being 40 millimétrés (lT9ë in.), the keys were heightened by 60 millimétrés (2-^- in.) to compensate for the tightening of joints, and bearings and flattening of the lead, placed between the first-course plates and bearing Blocks. When the érection of the upstream half of the bridge was commenced, the ribs were placed by careful levelling in the exact position they had to occupy, taking into account the temperature at which the centring was to be taken down. They were lifted by means of jacks, and the wood wedges were tightened more or less. When this was effected, each rib rested on five wedges placed at top, on the sides, and at the springlag, and which corresponded approximately to the tresties of the staging. After the adjustment of the work was complété, the centre pins were hammered tight on the wliole three arches ; in passing from one rib to the otlier, care had to be taken tliat the tightening should be uniform ; with this view, it was completed by one single gang of workmen. The middle, and then the sides of the ribs, were lifted by means of jacks, and the wedges that held up the ribs were removed, the work being carried out as before, on three ribs of the same longitudinal series the wedges placed near the first courses were then destroyed with axes. The total time taken up by the striking of the centres did not exceed three hours. When the centring had been taken down, it was removed to the down-stream half of the bridge, wliere the system was repeated with equal success. The Alexander III. Bridge.—(Figs. 399 and 400, and Figs. 401 to 463, Plates LXXXVI. to XCII., and Fig. 464). —Among the conspicuous engineering feat'ures which will distinguish the Paris Exhibition of 1900, the new and permanent bridge over the Seine, to be known as the Pont Alexander IIL, will be of leading interest to engi- neers because of its bold construction and correct detail, and to the general public because of its beauty of design. The Alexander III. Bridge will survive the ephemeral splendour of the Exhibition, and will form a permanent attraction in the marvellous Seine perspective, which constitutes one of the striking beauties of Paris. Before giving a brief description of the work and of the processes adopted in its érection, we should mention that the designs of the bridge are due to the eminent engineers, MM. Résal and Alby. The Administration des Ponts est Chaussées entrusted the préparation of detailed drawings of the bridge, jointly to Messrs. Schneider and Go., of Creusot, and the Fives-Lille Company. In accordance with a contract made between these two firms, Messrs. Schneider and Co. have especially in their charge the work of erecting the bridge, including the design, construction, and érection of all the temporary work required. It is scarcely too much to say that this part of the undertaking has involved more skili in design, and ingenuity, than the permanent bridge itself. All that part of the work undertaken by Messrs. Schneider and Co., including érection, was entrusted to their Chalon yard. General Description of the Work.—In the scheine of the engineers, to whom is due the general arrangement, as well as the details, of the Exhibition, the Alexander III. Bridge figurée! essentially as a monumental and décorative work, designed to fulfil the following conditions : 1. The bridge was not to mask the view of the Inva- lides, which is to be brought out conapicuously by the new avenue between the Champs-Elysées Fine Art palaces, and the axis of which, as well as that of the bridge, coïncides with the centre of the Esplanade des Invalides. 2. It was not to interfère with the beautiful view of the Seine, as seen from the Place de la Concorde bridge, a