feet lengths. They are formed of three plates and four angle-irons, with a lacing on the fourth side, so that the interior of the column is accessible for painting. The angles are all 4x4x inches, and the plates are all 16 inches wide; the thickness of the side plates being varied to provide for the increased strains in the lower sections. The ends of the several lengths are squared and faced, and they rest directly upon one another without jointboxes; the upper end of each length is fitted with two projecting plates which form a tenon; the length above fits over the tenon-plates, and is secured to the lower length by a turned pin of 1 inches diameter passing through carefully bored holes; this same pin serves for the attachment of the longitudinal rods. A second pin at right angles to this one forms the attachment for the transverse strut and ties. The diagonal ties are everywhere in pairs. The longitudinal strut, which is nearly 50 feet long, is built in the form of a light lattice truss, is 2 feet deep and I foot wide, with the ends squared and butting against the side of the column. "The towers were raised with no other false-work than that actually used in handling the material of each successive section. Before beginning to raise a tower a floor of long timbers reaching from pier to pier and loose boards was laid at the site of the tower; on this floor was erected a framework 30 feet high, and composed of two bents, one on each side of the tower; each bent consisted simply of two posts 48 feet apart and a cap 55 feet long, braced with planks across the corners. The lower lengths of the columns were then lifted into position, the transverse and longitudinal struts put in place, and the diagonal ties put on. A gin-pole 55 feet high was then lashed to each column, and these ginpoles were used to transfer the floor and frame to the top of the now completed lower section of tower. The same operation was then repeated with the second FIG. 49.-Iron Viaduct over the Genesee River, N. Y., on the New York, Lake Erie, and Western R. R. lengths of columns, which were placed over the tenon- | end of each long truss is bolted to the iron capital of plates of the lower length and secured by the pins. When the second section of the tower was completed, the frame was used to raise the gin-poles; the floor and frame were then raised again, and the process repeated till the tower attained its full height. The last tower raised, weighing 277,000 pounds, was entirely erected in eleven days, one day only having been previously spent in preparing the staging for the first section. "To erect the long spans combination Pratt trusses were built, the top chords of which were made of four pieces of pine 4x 10 inches, packed in pairs, and sprung about 4 feet apart in the centre; the bottom chord was of straight parallel eye-bars and the posts V-shaped. The form of the top chord made the truss stiff without lateral bracing. These trusses were put together below, and raised by block and falls to the bottom of the upper section of the towers, where they were placed, resting upon the transverse struts, two being used for each span. A suitable staging was then erected on them, and the permanent truss was put together, the materials being run out from the end of the bridge. "The trusses are of the simple Pratt pattern. One the column, and the other is placed on rollers, but connected with the next truss by iron loops passing over the end pins of each span, and allowing only the amount of motion needed for expansion. The short spans over the truss are bolted to the capitals at both ends. The end pins of the 50-feet spans are placed 6 inches from the centre of the column, and those of the long spans only 3 inches, so that under a full load the centre of weight comes directly in the line of the centre of the column." The Verrugas Viaduct (fig. 50), completed in 1873, under the supervision of Mr. C. H. Latrobe, C. E., with Mr. W. W. Evans of New York as consulting engineer, is situated on the Oroyo Railroad in Peru, It crosses the valley of the Agua de Verrugas at a height of 5478 feet above sea-level. The structure is composed of three iron piers connected by Fink trusses, and is remarkable for the rapidity and cheapness of its construction. The piers are respectively 145, 252, and 177 feet high, and each 50 feet long by 15 feet wide at top, having a batter of . Three of the spans are 100 feet long in the clear, the remaining one being FIG. 50.-Verrugas Viaduct, Oroyo R. R., South America. plished by stretching wire ropes across the chasm, from | Chords strained in tension, per sq. in. of which a scaffold was suspended. An extensive iron viaduct has just been completed on the Galveston, Harrisburg, and San Antonio Railroad over the Rio Pecos in Texas, having an extreme height of 302 feet and length of 1662 feet. But the most recent, as well as most remarkable, construction of this class is the Kinzua Viaduct, which is said to be the highest viaduct in the world. It forms part of a branch of the Erie Railway into the coal-fields of Elk co., Pa., and its construction was found to be the most economical way of crossing the Kinzua Gorge, a long-time obstacle in the way of railroad construction. Surveys and investigations leading to the conception of this work were made by Mr. O. W. Barnes, chief engineer of the road before it passed into the hands of the Erie Railway. It was built according to Erie Railroad specifications by Messrs. Clarke, Reeves & Co., under Mr. O. Chanute, chief engineer. It contains 3,500,000 pounds of iron, and cost $275,000. The foundations consist of one hundred and twelve sandstone piers laid upon rock, shale, and gravel. The few below the level of the stream are founded on timber cribs. The following data will give a good idea of the magnitude and strength of this viaduct: 2052 ft. 301" 20 16 ft. net section... 8,000 lbs. 7,000 Chords strained in compression, per sq. in. 66 66 5000 lbs. WIND-PRESSURE. Maximum compression, structure loaded: Maximum tension, structure unloaded Pressure assumed at top of each bent............. the length used (16 to 33 feet), with an Maximum compression from live load, per sq. inch..... Maximum compression from wind-pressure, 66 66 strains on struts.. tension on anchor-bolts........ 20,000 lbs. 1,980 : 15,000 3,300 35,000 7,000 46 The cost of erecting large bridges over treacherous streams has been a serious obstacle to the opening of important avenues of communication; but modern skill and science have overcome this objection in a great measure by devices which no longer render it necessary to construct an auxiliary bridge upon which the permanent structure may rest during erection. The various methods of erection are-1st, by use of staging; 2d, by lifting bodily; 3d, by protrusion or rolling over; and 4th, 10 ft.+ of height by building out. The railway bridge over the Weser near Bremen (1867), and the great bridge at Moerdyk in Holland, and upon which the entire bridge is assembled. Occa- feet. A light iron lattice supported on clusters of piles was used in the erection of the railroad bridge over the Inn at Königswart in Bavaria, with three spans of 227 feet; but the intermediate piles of the middle span were swept away by a flood, necessitating the substitution of a temporary wrought-iron framework, erected by overhang; its panels advancing from the piers at each side and meeting midway. The first digression from the method involving staging was introduced at the Britannia tubular bridge in 1848. The four tubes were constructed on shore upon a platform 2200 feet long built on piles spaced 27 feet apart. On the completion of the first tube, 472 feet long, six pontoons, each being 98 X 25X8 feet, were placed beneath it, so that the rising tide should lift the tube clear of its bearings. By means of capstans the tube was then swung into the vertical plane between the piers, in which grooves had been left to receive it. When adjusted in line, water was let into the barges and the tube lowered upon its masonry bearings. Heavy chains having links of 6 feet, equal to the stroke of the rams, were then attached, and the tube raised that height whilst the masonry was laid up under it. The crosssection of the chain was 276 square inches. The maximum strain, 8-3 tons per square inch. It required from thirty to forty-five minutes for each 6-foot lift, but only one lift was made each day, and about a month was consumed in elevating each tube to the full height of 100 feet and fixing it in place. The cost of erecting the tubes, weighing in all 11,647 tons, was $316,900, or about $27.25 per ton, whilst the cost of the tubes themselves was, for material and workmanship, about $162 per ton. (See fig. 51.) The bridge at Saltash designed by Brunel was erected in 1859 in a similar manner. The two larger spans are each 455 feet, and the height of the roadway is 100 FIG. 51.-Erection of Britannia Tubular Bridge, Wales. having fourteen spans of 328 feet each, were also completed in this manner. FIG. 52.-Floating Staging used at the International Bridge over the Niagara River, U. S. A. The superstructure of the International bridge over the Niagara River, comprising a large number of spans varying from 197 to 248 feet, was placed in position by the aid of a floating staging carried by five pontoons. (See fig. 52.) having caused a delay of not more than two hours. The general elevation of the plant, omitting the engine, is shown in fig. 53. The reverse of this method of erection was illustrated in the placing of James Millholland's bridge, previously described. When completed, this bridge was coupled at each end to a railway-car, and was slung by chains to a temporary timber truss. It was then taken nineteen miles from Baltimore by rail, run exactly over the place it was intended to occupy; the existing timber bridge was cut away, and the girder lowered with the permanent way ready for traffic, the whole operation FIG. 53.-Lowering of a Tubular Bridge into place (1847). Erection by rolling over requires a predetermination of the strains, not only for the completed girder, but for its various intermediate positions as a cantilever, and requires the highest attainments of science and art. The principle seems to have been first applied in the placing of the Sarine Railway viaduct at Freiburg, where the roadway was constructed on the hill behind one of the abutments, and was pushed bodily forward upon rollers placed on piers over successive openings of 160 feet. This method, however, is applicable only to continuous girders, or to the replacing of old bridges by new ones built alongside and rolled over laterally. It was used at the St. Just road-bridge over the Ardèche, spans of 152 feet, in erecting the temporary staging for the arched wrought-iron ribs. Erection by Building Out.-The famous steel arched bridge spanning the Mississippi River at St. Louis (opened 1874) furnishes a striking instance of this method of construction (fig. 54). This bridge was built by the Keystone Bridge Co. under the direction of Capt. James B. Eads and his assistants, Col. Henry Flad, Charles Pfeifer, and Walter Katté. The twenty-four arches were made of chrome steel, mannfactured by the Midvale Steel Works at Philadelphia. Each arch is composed of straight sections of tubes about 12 feet long, having an exterior diameter of 18 inches and at the crown. The ends of the sections are bevelled and a thickness varying from 24 inches at the springing to 1 joined by steel or wrought-iron, sleeve-couplings, through which steel pins are passed to receive the feet of the main brace-bars. The lowest sections are screwed into wroughtiron skew-backs, which rest on heavy cast-iron bed-plates anchored to the masonry. About 2200 tons of steel and span is 504'07 feet; the east, 50484 feet; and the centre 3400 tons of iron are used in the whole bridge. The west span, 522-39 feet, measured on a line through the centre of the lower skew-back pins. The upper roadway is 54 feet wide. The original intention of the contractors was to erect by the aid of guys depending from the masonry and by cables passing over temporary towers. Capt. Eads urged the use of catenary cables extending over towers placed on the piers and abutments and anchored at the approaches. Investigations showed that this method would be expensive and uncertain. The difficulty of maintaining these cables FIG. 54.-Illinois and St. Louis Highway and Railroad Bridge. in the assumed curve, when supporting the constantly varying weight of the arches as they progressed from the abutments and piers, led Mr. Linville to propose, early in 1871, in his instructions to Walter Katté, engineer in charge, the use of direct guys and back-stays depending from temporary towers. These suggestions embraced the leading principles of erection adopted, securing direct support to the arches at a certain number of fixed points. It was subsequently suggested by Col. Flad to use guys passing over towers, the guys or cables being made adjustable by means of hydraulic rams placed on the summit of the towers, to compensate for changes of temperature. The officers of the Keystone Bridge Co., fearing accidents to the rams and difficulty in repairing the same, substituted movable towers supported on the rams, which were placed on the masonry. The scaffolding on top of the arches was used in erecting the cables and for the purpose of maintaining them in straight lines. The erection was commenced at the west abutment and at each side of the first pier. The cantilevers on opposite sides of the pier balanced each other. The sections of the arches were hoisted from boats, and added in succession until the semi-spans met, and were made self-supporting by the insertion of the closing tubes. During the entire erection the rams were operated automatically by means of a balance-gauge and proportional weights, to compensate for variations in the lengths of the cables due to strains and thermal changes. The bridge is pronounced by all to be the finest mechanical specimen of work in the world. The method of erect ing these immense steel tubes, without any of the usual appliances of scaffolding or support from below, is shown in the illustration, copied from a photograph. All the adjustments were made with the greatest accuracy, and the arches were all closed in the centres of the spans by the use of "extension "-tubes capable of being lengthened or shortened by means of solid wrought-iron cylinders filling the interior of the tubes and furnished with right- and left-handed screws. The bridge was publicly opened on July 4, 1874, and the cost, including a large amount of interest and commission accounts, was not far from $10,000,000. It is worthy of note incidentally that as early as 1833, Maj. Ellett proposed a wire suspension bridge for this site at an estimated cost of $600,000, but his proposal was rejected because of the "immense cost." The Douro bridge, near Oporto, Portugal (fig. 55), also furnishes a remarkable instance of the mode of erection by building out, as well as novelty in design of long-span bridges. The foundations for the iron piers were built of granite quarried on the spot. On these were erected the iron piers, composed of four corner posts with the usual sway-bracing. The lattice truss proper was then built on the plateau by additions to the shore ends, and pushed out across their apices as a continuous girder until it overhung the channel-span 105 feet on either side, when the FIG. 55.-Railway Bridge across the River Douro, near Oporto, Portugal. structure. The ends of the arch are hinged on the skewbacks. The guy-ropes were moved out as the work progressed, and continued to support the arch until the lower ribs met in the centre. On the completion of the arch two short iron piers were erected on its haunches to support the truss over the spandrels, and over these the lattice was extended to the crown. The iron was manufactured in Paris. The total length of the bridge is 1150 feet; span of arch, 520 feet; height from low water to crown, 198 feet. The time required to complete the structure was a little more than two years, and it was opened for travel in Nov., 1877, by the king of Portugal. One of the most remarkable instances of rapid and bold erection is to be found in the construction of the Kinzua viaduct, already mentioned (figs. 56, 57). The 1750 net tons of iron were distributed and erected between May 5 and Aug. 29, 1882, or in less than four months, by a gang averaging about 125 men, aided by two steam-hoists and about twenty-five miles of rope. No scaffolding was used, but the girders were put in position by a travelling crane moving over the completed portions of the structure. In setting up the towers four masts 60 feet long were placed at the corners, by the aid of which the first story of 33 feet was completed. Four gin-poles, each 60 feet long, were then braced to these corner-posts about halfway up, and the posts and braces of the second story hoisted and bolted in place. This operation was repeated until the last story was reached, which was raised and swung in place in two pieces by an overhanging travelling crane, which also handled the 61-foot girders, weighing 6 tons each. The workmen climbed the diagonal rods, which were in pairs, and then walked the horizontal struts with perfect freedom, and even recklessness. There were no serious accidents during the erection, and it was not necessary to use a punch or chisel on any part of the work, so perfectly had the parts been fitted in the shops. On one of the highest towers it required just three hours to hoist the last section, 287 feet, into place, swing out a 61-foot girder, go back 1000 feet for the second girder, put it in position, make connections, and put in the transverse bracing, all with a gang of twelve men. About one day was required to raise and connect one story and put the Before final adjustment the towers came to centre-line within half an inch. gin-poles in position for the next one. at a height of 150 FIG. 56.-Erection of the Kinzua Viaduct, on the New feet. The time required to complete the entire structure from the laying of the foundations was about eight and a half months, whilst that required for the Göltzsch Valley masonry viaduct was five years and two and a half months. York, Lake Erie, and Western R. R. The iron received one coat of paint in the shop and two in the field. The composition of the paint was |