A description of the patent Chain Bridge; invented by James Finley; of Fayette County, Pennsylvania. With data and remarks, illustrative of the power, cost, durability, and comparative superiority of this mode of bridging. THE general satisfaction that this invention has given to all concerned, since its first introduction, in point of safety, simplicity, economy and duration, has animated me in this attempt to diffuse the knowledge of its principles; and perceiving the rapid strides it has lately made towards a general adoption, I am not without hopes of a patient hearing before a candid public; and that this project may yet materially subserve the internal interest of our country. JAMES FINLEY. DESCRIPTION. THE bridge is solely supported by two iron chains, one on each side, the ends being well secured in the ground, and the chains raised over piers of a sufficient height erected on the abutments at each side, extended so slack as to describe a curve, so that the two middle joists of the lower tier may rest on the chains. The other joists of the same tier, are attached to the chains by iron pendants of different lengths so as to form a level of the whole. In order that the chain may support as much weight as it could bear, when hung with the weight attached to the end of it, the piers must be so high as to give the chain a sinking or curve of the one full seventh of the span. The ends of the chains must descend from the tops of the piers with the same inclination that they take inwards, until each end reaches the bottom of a digging, large enough to contain stones and other materials sufficient to counterbalance the weight of the bridge and what may chance to be thereon. The chains, if only one to a side, must be made with four branches at each end, to be let down through as many ŝtones, and to be bolted below. These stones are laid flat on the bottom of the digging: other flat stones may be placed thercon, to bind and connect the whole, that they may have the same effect as a platform of one piece; four or more joists will be necessary for the upper tier-to extend from end to end of the bridge-each will consist of more than one piece; the pieces had best pass each other side by side, so that the ends may rest on different joists on the lower tier. The splice will then extend from one joist to another of the lower tier, and must be bolted together by one bolt at each end of the splice. The plank flooring is laid on this tier. It will be probably found most convenient that the chains be made with links as long as the space between the joists: every other suspender must attach to a link of the chain edge upwards, perhaps this may best be done by a clevis to go through the upper link of the suspender, and embrace the link of the chain and receive a key above-the other suspenders will come up through the flat links of the chain and receive a key above-the lower end of the lower link of the suspender may be made so wide as to receive the end of the lower tier of joists. In the year 1801, I erected the first bridge on this construction over Jacob's creek, on a contract with Fayette and Westmoreland counties, to build a bridge of seventy feet span, twelve and a half feet wide, and warrant it for fifty years (all but the flooring) for the consideration of six hundred dollars. Nothing further of the kind was attempted for six years. The exclusive right was secured by patent in the year 1808. There are eight of these bridges erected now; the largest of which is that at the Falls of Schuylkill, 306 feet span, aided by an intermediate pier; the passage eighteen feet wide, supported by two chains of inch and half square bar. berland (Maryland) supported by two bar, span 130, width 15 feet. There is also one at Cumchains of inch and quarter Another over the Potomack above the Federal city, of nearly the same dimensions as that at Cumberland. This season, one has been thrown over the Brandywine, at Wilmington, 145 feet span, supported by four chains of inch and ths square bar, breadth 30 feet, it has two carriage ways, and one or two foot passages. There are two erected near Brownsville, in Fayette county, the spans 120 and 112 feet-inch and quarter iron, breadth 18 and 15 feet. There was one built last season over the Neshamany, in Buck's county, near 200 feet span, one pier. An incorporated company at Frankfort, have begun to build one over the Kentucky river, span 334 feet, with one pier. Another incorporated company at Pauling's Ford, on Schuylkill, are taking measures to erect one this summer at that place near 200 feet span, without any pier. The following particulars it is thought will enable any person to make a rough estimate for any particular case. A bridge of 300 feet span and 30 feet wide, with two or more passages, so arranged that one may undergo repairs while the others are in use. To support such a bridge with four chains of inch and half square bar, would require about twenty tons of iron, and would be equal in strength to eighteen bars of iron one inch square-a strength capable of bearing 540 tons weight. And supposing the timbers to be of pine or other light wood, the whole materials will not amount to 140 tons; consequently the bridge will have an excess of power of at least 400 tons beyond its own weight. A bridge of the same span fifteen feet wide would be supported by two such chains. One of 150 feet span and 15 feet wide, would require about five tons of iron-the chains being one half the length of those in the first case stated, and the materials only one fourth of the weight. But in order to possess that strength on which these calculations are made, the chains must be allowed a sinking or curvature of nearly one sixth of the span; and when this proportion is adhered to, the strength will be the same, whether extended to three feet, or to three hundred. |