The Works Of Messrs. Schneider And Co.

THE RIO MALLECO VIADUCT. 135 The problem was solved in a most satisfactory männer, and the superstructure was erected witliout it having been necessary to stay the top of the piers. Mild steel of 45 kilogrammes per square millimétré (28.57 tons per square inch) and 25 percent, élongation was used throughout in the construction. The main girders are 7 metres (23 ft.) high, and are 4.500 metres (14 ft. 9 in.) distant from centre to centre. The top and bottom flanges are single webbed, and are fitted to the soleplates by angles. The trellis work consists of a quadruple system of bars placed at an angle of 45 deg., the diagonal of the squares thus formed is 3.400 metres (11 ft. 2 in.) and all the bars being u shape, the strength of the construction is considérable. The trellis is made wide and open, in order to offer a comparatively small sur- face to the action of the wind. The U section was the most practical one to use for this work, on account of the process of érection Messrs. Schneider and Co. intended to The girders are strengthened in the following manner : 1. By a double set of horizontal cross-bars placed at the top and at the bottom of the main girders, underneath the beams. They form cross-stays, the length of which is equal to the distance between the girder upriglits. 2. By vertical transverse cross-bars, which unité the girders together opposite each upright. They form cross- stays, separated by a middle horizontal cross-bar. Thus constructed, the superstructure possesses ample stiffness, and can resist all actions which tend to deform it, whether they be produced by the force of the wind or the weiglit of the load carried. Piers.—The superstructure is carried on four piers of varions heights ; the two end piers are 43.700 metres (143 ft. 4 in.) high from the masonry base to the top of the pier. One of the middle piers, on the right bank of the Malleco River, is 67.700 metres (222 ft.) high, Details of Viaduct over the Rio Malleco, Chili. follow, and during which. the bars undergo alternate efforts of tension and compression. The top and bottom members of the girders are United by verticals 3.400 metres (11 ft. 2 in.) apart, which hold all the elements together. These uprights consist of a web stiffened on the outside by four angles. The varions ties of the trellis bars and uprights are divided over the frames in such a manner as to reduce, as much as possible, the distance between two consecutive ties. This is an advantageous arrangement, as it largely reduces local and temporary strains that arise in the lower ribs, owing to the action of the rollers in the erecting operations. The girders are made with steel plate pannels on the lengths above the piers ; these pannels are 1.500 metres (4 ft. 11 in.) wide between the two uprights, and are strengthened by a third vertical placed over the centre of the bearing. The girders are joined at the top by beams placed above each upright ; two lines of longitudinal sleepers, 1.800 metre (5 ft. 11 in.) distant from each. other, rest on the lower side of the beam angles. They carry the oak ties on which the rails are fixed. and the other 75.700 metres (248 ft. 4 in.). The piers are firmly set in the masonry bases, and the volume of these bases is such that the work has a perfect stability, and cannot be overturned by the force of the wind. In the calculations this force was reckoned at 270 kilogrammes per square metre (55 Ib. per square foot) vvlien the bridge is empty, and at 170 kilogrammes per square metre (34.800 Ib. per square foot) when it carries a moving train. This last figure is a maximum in this case, as the force it represents is capable of overturning empty wagons and preventing all circulation on the line. Though these forces are exceptional, the piers have been so calculated that the strains of the metal do not exceed in any part, 10 kilogrammes per square millimétré (6.35 tons per square inch.) under the weights of the loads or the force of the wind. The piers are formed of four posts, placed in the shape of a pyramid and directed to one point ; they are consequently of a very neat architectural appearance. The dimensions at the top are the same for all the piers, namely, 4.500 metres (14 ft. 9 in.) from centre to centre of