BRIDGES. 



69 



being formed by two circular arcs of sixty <le- 

 1'iicli. The up-stroarn edge or nose of 

 each main channel pier is sloped back at an 

 anjrle <it' about thirty deTives from the perpen- 

 dicular, tlio bettor to enable them to n-i-t, 

 break up or turn ;iMle masses of ico or other 

 floating bodies. The- pivot pier has guards, 

 constructed of stem- in the same manner as 

 its> IT, placed up and down stream at the proper 

 distances to receive tlio ends of the draw when 

 Kwung open, and connected with the pivot pier 

 bv timber crib-work filled with loose stone. 



rstruct ure. The superstructure, designed 

 ultimately to be of iron, and to carry a double 

 track, at present consists of a single-track tim- 

 ber 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 

 lii.irh. 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 6x1 

 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 essen- 

 tially of a series of seventy rollers, placed be- 

 tween 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 be- 

 tween two concentric iron rings, and kept at 

 the proper distance by radial bars, which con- 

 nect 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. 

 I ',( uMing, 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 tlio 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, 

 12 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 la each anchorage, 18,000 perches; fctal 

 amount of masonry, 90,000 perches. Size of 

 towers at base, 80 by 52 feet; by 40 



f-'.-t. The wrought-iron floor beams (the '. 

 of two of which makes the width of the 1 ; 

 are each 19 feet long by 5 inches wide ; nnd 

 there will be two joined in every five feet of 

 the bridge one to each suspender. The weight 

 is 20 pounds per foot. Two iron trusses 10 

 feet high separate the foot road-ways, one on 

 each side, from the carriage-ways ; and flat-iron 

 tracks, of accommodating width, are laid for 

 wheels to run upon. The wrought-iron girders, 

 80 feet long and 12 inches wide, will run the 

 entire length, under the middle of the bridge. 

 The estimated total cost of this bridge is about 

 $1,750,000. . 



The Connecticut River Bridge. The Con- 

 necticut River Bridge, erected on the line of 

 the New Haven, Hartford, and Springfield Rail- 

 road, 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 diffi- 

 culty 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 work- 

 ing hours. 



The new bridge was designed and erected un- 

 der the direction of James Laurie. Esq. The 

 iron work was contracted for by William Fair- 

 bairn & 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 perma- 

 nently put together without being too cumber- 

 some, 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 mid- 

 dle 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 88J 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 chord?, the several parts being all 

 firmly riveted together. 



There are three distinct varieties of this gen- 

 eral form adopted for the different lengths of 

 spans, by which tbe use of bars beyond a cor- 



