BRIDGES. being formed by two circular arcs of sixty degrees each. The up-stream edge or nose of each main channel pier is sloped back at an angle of about thirty degrees from the perpendicular, the better to enable them to resist, break up or turn aside masses of ice or other floating bodies. The pivot pier has guards, constructed of stone in the same manner as itself, placed up and down stream at the proper distances to receive the ends of the draw when swung open, and connected with the pivot pier by timber crib-work filled with loose stone. Superstructure.--The superstructure, designed ultimately to be of iron, and to carry a double track, at present consists of a single-track timber bridge, all except the draw spans being on the Howe plan. The trusses of the long spans are twenty-four feet high, and those of the short spans nine feet high. The clear width between the trusses is fifteen feet. The draw, designed by Col. J. W. Adams, is the "arch brace plan," the peculiarity of which consists in having the main supporting braces radiate from the ends of the lower chords to different points in the length of the upper chords, thereby transmitting the weight of the bridge and load directly to the abutments. The ends of the draw when swinging are supported by eight chains composed of iron bars 5x1 inches, extending from the top of a central tower sixty feet high to the ends of the lower chords of the trusses. The turn-table of the draw consists essentially of a series of seventy rollers, placed between two circular tracks, one being fastened to the masonry of a pivot pier, and the other to the under side of the bridge. The faces of the tracks, which are nine inches broad, are accurately planed, so as to present no obstacle to the movement of the rollers, which are turned true and smooth. The rollers are twelve inches in diameter, and nine inches long on the face. They are placed in the annular space between two concentric iron rings, and kept at the proper distance by radial bars, which connect the inner ring with a collar fitted to and revolving around a central pivot-pin six inches in diameter. The Cincinnati Suspension Bridge.-This bridge was designed and built by John A. Roebling, Esq. The total length of this bridge, including the approaches from Front Street, Cincinnati, and Second Street, Covington, is 2,252 feet; length of main span from centre to centre of the towers, 1,057 feet; length of each land suspension, 281 feet; width of bridge in the clear, 36 feet; its height above low water, 100 feet; height of towers from foundation, without turrets, 200 feet; height of turrets, 30 feet; number of cables, 2; diameter of cables, 124 inches; strands in each cable, 7; wires in each strand, 740; wires in both cables, 10,360; weight of wire, 500 tons; deflection of cables, 88 feet; strength of structure, 16,800 tons; masonry in each tower, 32,000 perches; ma sonry in each anchorage, 13,000 perches; tctal The Connecticut River Bridge.-The Connecticut River Bridge, erected on the line of the New Haven, Hartford, and Springfield Railroad, where it crosses the Connecticut River, has been replaced by an iron bridge on the same line as the old wooden structure, without interrupting the traffic of the road. The difficulty of this undertaking will be appreciated, when it is considered that twenty-two regular trains, and from two to four extra trains, pass over the bridge daily, and mostly during working hours. The new bridge was designed and erected under the direction of James Laurie, Esq. The iron work was contracted for by William Fairbairn & Co., and the London Engineering and Iron Ship-Building Company. The several spans were constructed from the plans by the above firms, put together with bolts, and every part fitted and adjusted before being shipped. The rivet-holes were all drilled or punched, and such parts as could be permanently put together without being too cumbersome, were riveted by machinery. In arranging the spans of the new bridge all the old piers and abutments were made use of, with the necessary alterations and additions to bring them up to the proper height for the new girders. In the middle of each of the 177-feet spans across the river, with the exception of the middle or channel span, a new pier was built, like the old ones, so as to divide the seven river spans of the old bridge into twelve of 88 feet each, with one of 177 feet in the centre. For convenience in building the new piers, a temporary track was laid inside the old bridge, supported by the lower chords, over which the stone for the lower part of the piers was hauled, and lowered to its place. The general form of girder is that of a truss composed of rolled plate, angle and iron. The posts or compression bars are vertical, and the ties or tension bars are at an angle of about 45° with the chords, the several parts being all firmly riveted together. There are three distinct varieties of this general form adopted for the different lengths of spans, by which the use of bars beyond a cor 70 BRIDGES. tain size is avoided in the longer spans, as rolled bars of a much greater width than nine inches cannot be depended upon for such uniform strength and tenacity as the smaller bars. The difference consists in the arrangement of the tie bars. In the channel span of 177 feet, the ties cross three of the panels formed by the vertical posts; in the 140 feet and 881feet spans they cross two panels, while in the 76 feet span they cross but one panel. When the ties cross three panels diagonally, as in the channel span, the truss partakes somewhat of the character of a lattice; and the principle is capable of being extended still farther for longer spans by making the ties cross four or more panels according to the length of the girder. The work of erecting the bridge was commenced the last week in June, 1865, and progressed without interruption until the whole of the iron work was finished, on the 1st of February, 1866. Before commencing the iron work of the several trusses, a series of blocks were laid across longitudinal timbers placed under the position to be occupied by each girder, for the purpose of supporting it during construction. These blocks were of the proper height to give the required camber to the girders, and were placed under each post. Upon these were first placed the plates of the lower chord, which were then riveted together in their proper places. Next, the posts were placed in position and riveted to the plates of the lower chord. The top chord was then put on, first the side piates and angle irons, then the horizontal plates and covers. After the plates were all riveted, the camber blocks upon which the girders were built were removed by striking the wedges upon which they rested, leaving the girders supported by the ends. During the construction of the bridge, as The channel span, however, was subjected to 10/ 16 on The cost of the iron, delivered in New York, was $241.55 per ton, in United States currency, $117.18 of which was premium paid upon gold. The total cost of the iron work of the bridge erected and completed was $277.41 per ton, or 12 cents per pound. 33 100 The Susquehanna Bridge.-This bridge, de- The draw span is 175 feet long in the clear. The piers are all of solid granite masonry, sheathed from the bottom to the height of extreme high water (eleven feet above ordinary high water) with plate iron. The masonry above water is cut to joints of one-eighth of an inch, and where exposed to lateral pressure is clamped in the courses vertically and horizonare eight feet wide, and their sides batter to tally. At the top of the sheathing the piers the bottom at the rate of five-eighths of an inch to the vertical foot. They terminate at each end in triangular starlings seven feet long on the top, which have a double sheathing of wrought iron. They do not project like the ordinary ploughshare-shaped ice-breakers of American bridges, but have a concave outline at their salient edge; not being exposed to the planes, this modification of the ordinary form momentum of the ice-fields moving down long seemed necessary; as these piers have only to meet, when subjected to their greatest strain, a steady crushing pressure, resistance to which cannot be much aided by any mechanical contrivance, but which must be met in the main by simple inertia and irrefragibility. An uncommon degree of inertia (proportioned to bulk) is ing, and also by the extraordinary density of given to these structures by their iron sheaththe stone of which they are composed; the latter being Port Deposit granite, weighing more than one hundred and sixty-five pounds to the cubic foot. They are 35 feet 4 inches seat. The draw pier is circular, 24 feet 8 inches long, and 7 feet 4 inches wide at the bridgo in diameter at the top of the iron sheathing. The abutments are of solid masonry of the same character as that of the piers, but not iron cased below the water line. Above high-water line they are hollow, and contain offices and appliances necessary for the uses of the bridge and the railroad. Their upper story is of iron, corresponding in architectural character with flank. the covering of the superstructure, which they The easterly abutment and the six easterly piers rest upon pile foundations. The western abutment, and all the other piers, rest upon solid rock. The eastern abutment was built within an old embankment of earth where the water stood at about the level of the foundation piles; and the abutment on the western shore was built in water seventeen feet deep. The depth of water at the several piers is as follows: at pier one, 21 feet 2 inches, and successively 19 feet 2 inches, 38 feet 5 inches, 7 feet 5 inches, 9 feet 10 inches, 31 feet 6 inches, 30 feet 8 inches, 31 feet 4 inches, 25 feet, 22 feet, 17 feet 6 inches, and 11 feet. Coffer-dams could not have been used upon the foundations of this bridge with any chance of success, except where the water is shallow, or rather where it is of ordinary depth, for it is nowhere of much less depth than the St. Lawrence, where it is the deepest at the site of the Victoria Bridge; nor could pneumatic piles have been used here but in exceptional cases. It would have been hazardous in the extreme also to have attempted to use the method adopted by Mr. Brunel at the Salrash Bridge. The ruder and more unscientific methods, dependent more or less upon chance for their efficacy, which are sometimes resorted to by engineers in difficult situations, were altogether The unavailable here, for various reasons. means actually employed, therefore, for effect ing the under-water work were necessarily somewhat different from the ordinary, and consisted mainly in the use of portable iron caissons sunk upon prepared foundations, partly by the use of screws, and partly by means of guide piles only. Where the foundations were of piles, these were driven as far as was possible with a ram weighing 2,200 pounds, and were sawed off at a level as much below the river bed as was practicable. The sawing was effected by a very simple machine, which accurately did its work in depths of water exceed ing forty-two feet, at the rate sometimes of sixty piles per day. At one of the piers where the water was thirty-nine feet above the foundation piles, a construction wharf was built around the site in the manner shown in the accompanying drawing. The caisson of this pier was E Б B FIG. 2. fastened to a timber platform, four feet thick. within guides attached to these constructed The platform was made to move vertically wharves. Three arms projected from each side of the platform. Screws of three and a half inches in diameter and fifty-six feet long, secured to simple turning-gear erected upon the deck of the wharves, were passed vertically through nuts contained in these arms. Upon the screws turning horizontally, and having no other movements, the pier was made to descend, or, if required by any exigency, to move excellently well illustrated by the elevators in the opposite direction. This movement is used at hotels. The caisson was designed to be water-tight. The boiler-plate iron used was three-eighths of an inch thick from the bottom and elsewhere one-quarter of an inch thick. to within ten feet of the surface of the water, It was made rigid by angle iron attached to the sides and ends in rows about seven feet apart. During the process of lowering, it was heavily braced inside with oak timber, to strengthen it against the pressure of the water outside, which at some points in the descent was sixteen pounds to the square inch. The superstructure of this bridge has some peculiarities. It was originally designed to be of iron, but when the time came for its erection that material could not be procured of the requisite quality with that promptness which the emergency required, and, though with great reluctance on the part of the engineer, timber was employed as a substitute. The chords of the trusses vary in their dimen tain size is avoided in the longer spans, as rolled bars of a much greater width than nine inches cannot be depended upon for such uniform strength and tenacity as the smaller bars. The difference consists in the arrangement of the tie bars. In the channel span of 177 feet, the ties cross three of the panels formed by the vertical posts; in the 140 feet and 883feet spans they cross two panels, while in the 76 feet span they cross but one panel. When the ties cross three panels diagonally, as in the channel span, the truss partakes somewhat of the character of a lattice; and the principle is capable of being extended still farther for longer spans by making the ties cross four or more panels according to the length of the girder. The work of erecting the bridge was commenced the last week in June, 1865, and progressed without interruption until the whole of the iron work was finished, on the 1st of February, 1866. Before commencing the iron work of the several trusses, a series of blocks were laid across longitudinal timbers placed under the position to be occupied by each girder, for the purpose of supporting it during construction. These blocks were of the proper height to give the required camber to the girders, and were placed under each post. Upon these were first placed the plates of the lower chord, which were then riveted together in their proper places. Next, the posts were placed in position and riveted to the plates of the lower chord. The top chord was then put on, first the side piates and angle irons, then the horizontal plates and covers. After the plates were all riveted, the camber blocks upon which the girders were built were removed by striking the wedges upon which they rested, leaving the girders supported by the ends. During the construction of the bridge, as soon as any part was finished and the track placed upon it, heavy trains, weighing about one ton to the foot, were run over it to test its safety. These loads were not so heavy as it was designed ultimately to subject the bridge to as a test, on account of the rest of the bridge, where the iron work was not completed, not being in a condition to bear the extra strain. The channel span, however, was subjected to a severe test by loading it with railroad bars, in addition to a heavy train of four cars loaded with iron, with the engine and tender; in all, about 220 tons. This would be about 1 tons to the foot. With this load the deflection of the girders was 18 on one side, and 9" on the other. When the load was removed there was a permanent deflection of only on one side and none on the other. 16 The cost of the iron, delivered in New York, was $241.55 per ton, in United States currency, $117.18 of which was premium paid upon gold. The total cost of the iron work of the bridge erected and completed was $277.41 per ton, or 123 cents per pound. The Susquehanna Bridge.-This bridge, designed and executed under the direction of George A. Parker, Esq., is situated nearly one mile above the mouth of the Susquehanna River, and four miles below the head of navigation and tide-water, and has been built by the Philadelphia, Wilmington, and Baltimore Railroad Company, at an expense of nearly $2,000,000. The engineering difficulties involved in building it were, principally, the unusual depth of water, the unstable nature of the bottom at certain points, and the more than common violence of the ice freshets peculiar to its locality. It is composed of thirteen spans, seven of 250 feet 9 inches each in the clear, east of the draw, and five of nearly the same dimensions, west of the draw. The draw span is 175 feet long in the clear. The whole length of the superstructure of the bridge, including the draw, from abutment to abutment, is 3,273 feet 9 inches. Its height is 25 feet, and its width 22 feet 6 inches. The piers are all of solid granite masonry, sheathed from the bottom to the height of extreme high water (eleven feet above ordinary high water) with plate iron. The masonry above water is cut to joints of one-eighth of an inch, and where exposed to lateral pressure is clamped in the courses vertically and horizontally. At the top of the sheathing the piers are eight feet wide, and their sides batter to the bottom at the rate of five-eighths of an inch to the vertical foot. They terminate at each end in triangular starlings seven feet long on the top, which have a double sheathing of wrought iron. They do not project like the ordinary ploughshare-shaped ice-breakers of American bridges, but have a concave outline at their salient edge; not being exposed to the momentum of the ice-fields moving down long planes, this modification of the ordinary form seemed necessary; as these piers have only to meet, when subjected to their greatest strain, a steady crushing pressure, resistance to which cannot be much aided by any mechanical contrivance, but which must be met in the main by simple inertia and irrefragibility. An uncommon degree of inertia (proportioned to bulk) is given to these structures by their iron sheathing, and also by the extraordinary density of the stone of which they are composed; the latter being Port Deposit granite, weighing more than one hundred and sixty-five pounds to the cubic foot. They are 35 feet 4 inches long, and 7 feet 4 inches wide at the bridgo seat. The draw pier is circular, 24 feet 8 inches in diameter at the top of the iron sheathing. The abutments are of solid masonry of the same character as that of the piers, but not iron cased below the water line. Above high-water line they are hollow, and contain offices and appliances necessary for the uses of the bridge and the railroad. Their upper story is of iron, corresponding in architectural character with the covering of the superstructure, which they flank. BRIDGES. The easterly abutment and the six easterly piers rest upon pile foundations. The western abutment, and all the other piers, rest upon solid rock. The eastern abutment was built within an old embankment of earth where the water stood at about the level of the foundation piles; and the abutment on the western shore was built in water seventeen feet deep. The depth of water at the several piers is as follows: at pier one, 21 feet 2 inches, and successively 19 feet 2 inches, 38 feet 5 inches, 7 feet 5 inches, 9 feet 10 inches, 31 feet 6 inches, 30 feet 8 inches, 31 feet 4 inches, 25 feet, 22 feet, 17 feet 6 inches, and 11 feet. Coffer-dams could not have been used upon the foundations of this bridge with any chance of success, except where the water is shallow, or rather where it is of ordinary depth, for it is nowhere of much less depth than the St. Lawrence, where it is the deepest at the site of the Victoria Bridge; nor could pneumatic piles have been used here but in exceptional cases. It would have been hazardous in the extreme also to have attempted to use the method adopted by Mr. Brunel at the Salrash Bridge. The ruder and more unscientific methods, dependent more or less upon chance for their efficacy, which are sometimes resorted to by engineers in difficult situations, were altogether unavailable here, for various reasons. means actually employed, therefore, for effect ing the under-water work were necessarily somewhat different from the ordinary, and consisted mainly in the use of portable iron caissons sunk upon prepared foundations, partly by the use of screws, and partly by means of guide piles only. Where the foundations were of piles, these were driven as far as was possible with a ram weighing 2,200 pounds, and were sawed off at a level as much below the river bed as was practicable. The sawing was effected by a very simple machine, which accurately did its work in depths of water exceed ing forty-two feet, at the rate sometimes of The sixty piles per day. At one of the piers where the water was thirty-nine feet above the foundation piles, a construction wharf was built around the site in the manner shown in the accompanying drawing. The caisson of this pier was 15 FIG. 2. fastened to a timber platform, four feet thick. The platform was made to move vertically within guides attached to these constructed wharves. Three arms projected from each side of the platform. Screws of three and a half inches in diameter and fifty-six feet long, secured to simple turning-gear erected upon the deck of the wharves, were passed vertically through nuts contained in these arms. Upon the screws turning horizontally, and having no other movements, the pier was made to descend, or, if required by any exigency, to move in the opposite direction. This movement is excellently well illustrated by the elevators used at hotels. The caisson was designed to be water-tight. The boiler-plate iron used was three-eighths of an inch thick from the bottom to within ten feet of the surface of the water, and elsewhere one-quarter of an inch thick. MODE OF SINKING PIERS AT SUSQUEHANNA BRIDGE. C FIG. 1. It was made rigid by angle iron attached to the sides and ends in rows about seven feet apart. During the process of lowering, it was heavily braced inside with oak timber, to strengthen it against the pressure of the water outside, which at some points in the descent was sixteen pounds to the square inch. The superstructure of this bridge has some peculiarities. It was originally designed to be of iron, but when the time came for its erection that material could not be procured of the requisite quality with that promptness which the emergency required, and, though with great reluctance on the part of the engineer, timber was employed as a substitute. The chords of the trusses vary in their dimen |