126 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[April 



The price of (lie'fiiiilwr for tlie Troy Bridge, iiii'liuling every thing 

 but pninling, is lS-25 ilolUirs per foot. The |)iiMs ;ire of fine bhie 

 limestone. The flooring is 30 feet above low water. The Tuscaloosa 

 briilgi' is fonr spans of 220ft. each over the black Warrior River. Tiie 

 lieight of the trellis is Kift. anil it cost (MUU/. It was opened in De- 

 cember 1^3-1; ami has stood well ag;iinst the trallic wbieli has passed 

 o\n, particularly large herds of cattle. Anotiier bridge of the same 

 conslrncticn of large span is at Nashua, in New llampsliire, thrown 

 over I lie Merriuack, The bridge across the great Conestogo to I'arry 

 the iMnladelphia aiid C'ulumbia railway, as it formerly stood was 1-U2 

 feet long, and in nine s]ians of 1 JO feet. Its breadlli was 22 feet, and 

 the flooring rested oii the string piece. Tliis bridge was nuich too 

 weak, Ihe trains could run but slowly on if, and the trusses were only 2 

 inches thick, so that it has recently been obliged to be rebuilt. 



Mr. Kobinson prefers trellis bridges, and the many railways he has 

 constructed to those of any other construction, and has introduced con- 

 siderable improvements into them. That atKichiiiond is the most re- 

 markalile which he has built, and is distinguished as a first rate piece 

 of carpentry, even in America where this mode of construction is car- 

 ried to such jierfecfion. This bridge stands without the town of Rich- 

 mond, on the railway from that town to I'etersbiirgh, forming part of the 

 grand line from nortli to south thrmigb New York, I'liiladi-ipbia, Bal- 

 timore, Washington, Fredricksburgh, Richmond, I'etersburgh, Raleigh, 

 and Charleston. 



Bridge oveh the James River at Richmo.nd in Virginia, 



United States. 



This bridge was commenced in December 1S3G, and finished 5th 

 September 1838, it was built by Mr. Sandford, nnder the directions of 

 Mr. Robinson the engineer. It was erected a little below the magni- 

 ficent cataract of the James River at Richmond, where the rive*- is 

 very broad, but not very deep (lowing over the bare rock which forms 

 an excellent foundation for the piers. The banks on each side of the 

 river are very steep, which rendered it necessary to erect the bridge 

 at a great height above the water. 



The bridge is 2,841 feet long between the abutments, and contains 

 10 openings, wdiich vary in their sjians, one span is 130 feet, four 140 

 feet, four laO feet, and ten 153 feet s])an from centre to centre of pier. 

 The superstructure is entirely of timber, erected on the top of piers 

 built of solid granite, rough scabbled on the face, and with rustic 

 grooves at the joints; these piers are only 7 feet tj inches thick by 21 

 feet long, on a level with the low water-mark, they batter all 

 round to the top, which is 4 feet thick by IS feet long on the plan; 

 the height is 10 feet above low water-mark, and to the top of the rails 

 is 20 feet more, making a total height of GO feet. 



Plate VII, fig. 1, is an elevation of the centre arches drawn to a very 

 small scale. 



Fig. 2 is an enlarged vievr of different parts of the elevation, showing 

 the details of construction. 



Fig. .3 is a transverse section of the carpentry. 



Fig. 4 is a horizontal )ilan of the carpentry, one part exhibits the 

 rails and floor, another part the joists, girders and wind braces. 



Fig. .1 is a hurizontil plan of the lower girders ami wind braces, to- 

 gether with one of the almtinenfs, and also the top of one of the piers. 



The carpentry of the superstructure consists of a continuous double 

 trellis work, lait. bin. high on each side, and running from one end of 

 the bridge to the other, with a triple string at the fo|) and bottom, and 

 another above the lower girders, each consists of two 3iii. planks 

 12 inches deep. The trellis work is formed of 3in. planks 1 1 iiichi's 

 wide crossing each other and pinned together witli two |iins at each 

 crossing, and with 4 pins at to]) and bottom to the stringjiieces. The 

 whole tliickness of the trellis work including the string jiieces is 2ft. 

 Oin. and the width between, nnder tlie roadway, is 12ft. r>in making a 

 total width of 17ft. bin. from outside to outside of the trellis work. 



(^n the lower string jiieces are placed transverse girders (tie beams") 

 )«, )fl, 14 by 10 inches, and 17ft. (iiu. long and IGft. ajiart from centre 

 to centre; on the top of the trellis work are placrMl similar girders 

 g, g, 22ft. (iiii. long; the extremities of which are notched or caulked 

 down to the top of the trellis work ; upon the girders the joists are 

 laid longitudinally, upon which is the flooring of planks inclined 

 from the centre to the sides, the wdiole breadth of the top of the bridge 

 is 23ft, 4 in. 



U|)on the to)) of the floor are placed tlie rails, r, r, for two lines, they 

 are of timber, 5 inclies sijuare, capped with an iron bar 2 indies wide 

 by i inch thick, and for the the security of the trains, each rail is pro- 

 vided with a guard rail of a similar scantling, the guardrail at the 

 bottinn is in close contact with the rail, but at the top there is a spacp 

 formed for the wheel, the width between the rails is ti feet. 



Between the upper and lower girders are fixed horizontal diagonal 

 wind braces, 1 1 whicli arc morticed into tlieni, tlieve are also vertical 



diagonal braces, between the top and bottom girders, which render the 

 whoh' of the bridge very stiff. 



On the top of each ))ier are two capping stones 12 inches thick and 

 Tl feet long by 3 feet (i inches wide, which project over the ])ier G 

 inches, on these stones are templates of timber to carry the trellis 

 \vork. 



The whole quantity of iron introduced in the bridge is less than a 

 ton weiirht. 



The following table of scantlings will explain together with the 

 references and the drawings, the general construction of the bridge. 



PRACTICAL ILLUSTRATIONS OF THE METHOD OF INDI- 

 CATING THE POWER EXERTED BY STEAM-ENGINES 

 IN FACTORIES. 



Sir, — In pursuance of this subject, perhaps I cannot do belter than 

 give detailed examples of cases in actual practice, as more likely to 

 be of interest to practical men. With this view I have recently been 

 furnished by a friend* with the amiexed diagrams (Figs. 1 and 2), 



Fig. 1. 



11.0 12 8 12 C 12.'; 12 3 12 ll-fi 10 8 97 75 

 Avcra^;i' 1 1 28 lbs. per circular inc-h. 



' A correspondent of your Journal, Mr. Da\id \V. Boivman, a young 

 engineer of great promise, now on his way to South America. 



