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feet lengths. They are formed of three plates and four is 2 feet deep and 1 foot wide, with the ends squared and angle-irons, with a lacing on the fourth side, so that the butting against the side of the column. interior of the column is accessible for painting. The “The towers were raised with no other false-work than angles are all 4x4x} inches, and the plates are all 16 that actually used in handling the material of each sucinches wide; the thickness of the side plates being varied cessive section. Before beginning to raise a tower a to provide for the increased strains in the lower sections. floor of long timbers reaching from pier to pier and The ends of the several lengths are squared and faced, loose boards was laid at the site of the tower; on this and they rest directly upon one another without joint- floor was erected a framework 30 feet high, and comboxes; the upper end of each length is fitted with two posed of two bents, one on each side of the tower; each projecting plates which form a tenon; the length above bent consisted simply of two posts 48 feet apart and a fits over the tenon-plates, and is secured to the lower cap 55 feet long, braced with planks across the corners. length by a turned pin of 14 inches diameter passing The lower lengths of the columns were then lifted into through carefully bored holes; this same pin serves for position, the transverse and longitudinal struts put in the attachment of the longitudinal rods. A second pin place, and the diagonal ties put on. A gin-pole 55 feet at right angles to this one forms the attachment for the high was then lashed to each column, and these gintransverse strut and ties. The diagonal ties are every- poles were used to transfer the floor and frame to the where in pairs. The longitudinal strut, which is nearly top of the now completed lower section of tower. The 50 feet long, is built in the form of a light lattice truss, 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 Westeru 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. the column, and the other is placed on rollers, but conWhen the second section of the tower was completed, nected with the next truss by iron loops passing over the frame was used to raise the gin-poles; the floor and the end pins of each span, and allowing only the frame were then raised again, and the process repeated amount of motion needed for expansion. The short till the tower attained its full height. The last tower spans over the truss are bolted to the capitals at both raised, weighing 277,000 pounds, was entirely erected ends. The end pins of the 50-feet spans are placed in eleven days, one day only having been previously 6 inches from the centre of the column, and those of spent in preparing the staging for the first section. the long spans only 3 inches, so that under a full load
"To erect the long spans combination Pratt trusses the centre of weight comes directly in the line of the were built, the top chords of which were made of four centre of the column.'' pieces of pine 4x 10 inches, packed in pairs, and sprung The Verrugas Viaduct (fig. 50), completed in 1873, about 4 feet apart in the centre; the bottom chord was under the supervision of Mr. C. H. Latrobe, C. E., of straight parallel eye-bars and the posts V-shaped. with Mr. W. W. Evans of New York as consulting The form of the top chord made the truss stiff with engineer, is situated on the Oroyo Railroad in Peru, out lateral bracing. These trusses were put together It crosses the valley of the Agua de Verrugas at a below, and raised by block and falls to the bottom height of 5478 feet above sea-level. The structure is of the upper section of the towers, where they were composed of three iron piers connected by Fink trusses, placed, resting upon the transverse struts, two being and is remarkable for the rapidity and cheapness of used for each span. A suitable staging was then erected its construction. The piers are respectively 145, 252, on them, and the permanent truss was put together, the and 177 feet high, and each 50 feet long by 15 feet materials being run out from the end of the bridge. wide at top, having a batter of Y. Three of the spans
“The trusses are of the simple Pratt pattern. One are 100 feet long in the clear, the remaining one being 125 feet, making the total length of the bridge, with slightest accident to any of the men. The grade on piers, 575. The erection of the iron-work was begun the bridge is 158 feet per mile, and trains pass from Sept. 17, 1872, and completed before the first of the a curve of 350 feet radius directly on to the viaduct. year, or in eighty-eight working days, without the The total cost was $164,640. The erection was acwm.
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
8,000 lbs which a scaffold was suspended.
net section... An extensive iron viaduct has just been completed Chords strained in compression, per sq. in.
7,000 on the Galveston, Harrisburg, and San Antonio Rail- Diagonals
, strained per sq. in. from 5000 to 7000 lbs. road over the Rio Pecos in Texas, having an extreme Rivets,
5000 lbs. height of 302} feet and length of 1662 feet. But the most recent, as well as most remarkable, con
WIND-PRESSURE. struction of this class is the Kinzua Viaduct, which is
Maximum compression, structure loaded : said to be the highest viaduct in the world. It forms Pressure assumed at the top of each bent...... 20,000 lbs part of a branch of the Erie Railway into the coal-fields Additional pressure at each story of tower... 1,980 of Elk co., Pa., and its construction was found to be the
Maximum tension, structure unloaded : inost economical way of crossing the Kinzua Gorge, a Pressure assumed at top of each bent....... 15,000 long-time obstacle in the way of railroad construction. Additional pressure at each story of tower... 3,300 Surveys and investigations leading to the conception of Strains allowed on “Phænix” columns, of this work were made by Mr. O. W. Barnes, chief engi
the length used (16 to 33 feet), with an 35,000 neer of the road before it passed into the hands of the Maximum compression from live load, per
ultimate strength per sq. in. of........... Erie Railway. It was built according to Erie Railroad sq. inch.......
7,000 specifications by Messrs. Clarke, Reeves & Co., under Maximum compression from wind-pressure, Mr. 0. Chanute, chief engineer. It contains 3,500,000
per sq. inch..
10,000 pounds of iron, and cost $275,000. The foundations Greatest strain for combined loads.. consist of one hundred and twelve sandstone piers laid Maximum tension on diagonals (rods)........
strains on struts..
2 to 3000 upon rock, shale, and gravel. The few below the level
tension on anchor-bolts....... of the stream are founded on timber cribs.
12,000 The following data will give a good idea of the
ERECTION. magnitude and strength of this viaduct:
The cost of erecting large bridges over treacherous Total length.......
2052 ft. streams has been a serious obstacle to the opening of Height of rail above stream .......................
important avenues of communication; but modern skill Number of towers..
20 and science have overcome this objection in a great Height of iron-work of lowest towers.......... 16 ft. measure by devices which no longer render it necessary highest
278'3''. Length of girders over towers...
to construct an auxiliary bridge upon which the perma
nent structure may rest during erection. The various clear)..............
methods of erection arest, by use of staging; 2d, bę Width of towers at top......
lifting bodily; 3d, by protrusion or rolling over; and 4th, bottom.
10 ft.+3 of height by building out. Live load “Consolidation" engines in any
In the first and most common method for iron or position : Equal on each column of tower at top....
wooden trusses (in fact, the only one in use up to 1848)
76,500 lbs. foundations are formed by driving piles, either in rows Dead load on top of each column..........
22,950 each story per column, about...
or clusters, to a sufficiently hard substratum, and carGirders, calculated for a train of “Consolida
ping them with a temporary scaffold or staging, which tion" engines :
is “ blocked up” to the grade of the lower string-piece,
8,000 5 15,000
and upon which the entire bridge is assembled. Occa- feet. The railway bridge over the Weser near Bremen sionally the foundation for the staging may be upon (1867), and the great bridge at Moerdyk in Holland, temporary "cribs,” which are sunk in the river, and upon which the trestles are placed; or the staging may consist of a light iron or wooden truss supported by chains, as in the erection in 1866 of the bridge at El Kantara, in Algeria.
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 25 X 8 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, 83 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.)
FIG. 51.- Erection of Britannia Tubular Bridge, Wales. The bridge at Saltash designed by Brunel was erected in 1859 in a similar manner. The two larger spans are having fourteen spans of 328 feet each, were also comeach 455 feet, and the height of the roadway is 100 | pleted 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 having caused a delay of not more than two hours. the Niagara River, comprising a large number of spans The general elevation of the plant, omitting the engine, varying from 197 to 248 feet, was placed in position by is shown in fig. 53. the aid of a floating staging carried by five pontoons. (See fig. 52.)
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 Fig. 53.—Lowering of a Tubular Bridge into place (1847). bridge was cut away, and the girder lowered with the Erection by rolling over requires a predetermination permanent way ready for traffic, the whole operation of the strains, not only for the completed girder, but for its various intermediate positions as a cantilever, The twenty-four arches were made of chrome steel, mangand requires the highest attainments of science and factured by the Midvale Steel Works at Philadelphia. art. The principle seems to have been first applied in Each arch is composed of straight sections of tubes about the placing of the Sarine Railway viaduct at Freiburg, 12 feet long, having an exterior diameter of 18 inches and where the roadway was constructed on the hill behinà a thickness varying from 24 inches at the springing to 17
at the crown. The ends of the sections are hevelled and one of the abutments, and was pushed bodily forward joined by steel or wrought-iron sleeve-couplings, through upon rollers placed on piers over successive openings of which steel pins are passed to receive the feet of the main 160 feet. This method, however, is applicable only brace-bars. The lowest sections are screwed into wroughtto continuous girders
, or to the replacing of old bridges iron skew-backs, which rest on heavy cast-iron bed-plates by new ones built
alongside and rolled over laterally. It anchored to the masonry. About 2200 tons of steel and was used at the St. Just road-bridge over the Ardèche, span is 504:07 feet; the east, 504.84 feet; and the centre spans of 152 feet, in erecting the temporary staging for span, 522-39 feet, measured on a line through the centre of the arched wrought-iron ribs.
the lower skew-back pins. The upper roadway is 54 feet Erection by Building Out.—The famous steel arched wide. bridge spanning the Mississippi River at St. Louis The original intention of the contractors was to erect by (opened 1874) furnishes a striking instance of this the aid of guys depending from the masonry and by cables method of construction (fig. 54).
passing over temporary towers. Capt. Eads urged the use
of catenary cables extending over towers placed on the This bridge was built by the Keystone Bridge Co. under piers and abutments and anchored at the approaches. Inthe direction of Capt. James B. Eads and his assistants, vestigations showed that this method would be expensive Col. Henry Flad, Charles Pfeifer, and Walter Katté. / 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 | ing these immense steel tubes, without any of the usual varying weight of the arches as they progressed from the appliances of scaffolding or support from below, is shown abutments and piers, led Mr. Linville to propose, early in in the illustration, copied from a photograph. 1871, in his instructions to Walter Katté, engineer in charge, All the adjustments were made with the greatest accuthe use of direct guys and back-stays depending from tem- racy, and the arches were all closed in the centres of the porary towers. These suggestions embraced the leading spans by the use of “extension"-tubes capable of being principles of erection adopted, securing direct support to lengthened or shortened by means of solid wrought-iron the arches at a certain number of fixed points. It was cylinders filling the interior of the tubes and furnished subsequently suggested by Col. Flad to use guys passing with right- and left-handed screws. The bridge was pubover towers, the guys or cables being made adjustable by licly opened on July 4, 1874, and the cost, including a large means of hydraulic rams placed on the summit of the amount of interest and commission accounts, was not far towers, to compensate for changes of temperature. The from $10,000,000. officers of the Keystone Bridge Co., fearing accidents to the It is worthy of note incidentally that as early as 1833, rams and difficulty in repairing the same, substituted mov- Maj. Ellett proposed a wire suspension bridge for this site able towers supported on the rams, which were placed on the at an estimated cost of $600,000, but his proposal was masonry. The scaffolding on top of the arches was used in rejected because of the "immense cost.” erecting the cables and for the purpose of maintaining them in straight lines. The erection was commenced at The Douro bridge, near Oporto, Portugal (fig. 55), the west abutment and at each side of the first pier. The also furnishes a remarkable instance of the mode of cantilevers on opposite sides of the pier balanced each erection by building out, as well as novelty in design other. The sections of the arches were hoisted from boats, of long-span bridges. and added in succession until the semi-spans met, and were made self-supporting by the insertion of the closing tubes. The foundations for the iron piers were built of granDuring the entire erection the rams were operated auto- ite quarried on the spot. On these were erected the matically by means of a balance-gauge and proportional iron piers, composed of four corner posts with the usual weights, to compensate for variations in the lengths of the sway-bracing. The lattice truss proper was then built on cables due to strains and thermal changes.
the plateau by additions to the shore ends, and pushed The bridge is pronounced by all to be the finest mechan- out across their apices as a continuous girder until it overical specimen of work in the world. The method of erect- I hung the channel-span 105 feet on either side, when the
erection of the arch was begun at the springing lines, and four heavy cast-iron plates securely bolted to the masonry; continued up and out, panel by panel, by tying up to the and the two at either end are so placed that the distance cantilevers projecting overhead by means of wire ropes between them is double that between the girders on the passing over the piers. The skew-backs of the arch are crown of the arch, thus adding to the lateral stiffness of the
FIG. 55.—Railway Bridge across the River Douro, near Oporto, Portugal. structure. The ends of the arch are hinged on the skew- | Before final adjustment the towers came to centre-line backs. The guy-ropes were moved out as the work pro- within half an inch. gressed, 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 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
York, Lake Erie, and Western R. R. from the laying of the foundations was about eight and a half months, whilst that required for the Göltzsch Valley The iron received one coat of paint in the shop and two masonry viaduct was five years and two and a half months. in the field. The composition of the paint was,