US174510A - Improvement in the construction of bridges - Google Patents

Description

T. C. FIDLER.

CONSTRUCTION oF BRIDGES.

Patented March 7,1876.

STAT-Es IMPROVEMENTIN THE CONSTRUCTION OF BRIDGES.

Specification forming part of Letters Patent No. l 74,5 l0, dated March I7, l87ti application tiled f December 12, 1874.

To all whom it may concern:

. Be it known that I, THOMAS CLAXTON FID- LER, 'ot' Emberton, .in the county ot' Bucks, England, civil engineer, have invented Improvements in the Construction of Suspension- Bridges and Iron Arches, of which the following is a specilcation My said4 invention consists in a method ot' constructingl suspension-bridges whereby the chains are so arranged and braced as to afford an inexible support to the roadway, and to carry a passing load without distortion; and in order that my said invention maybe fully understood I shall now proceed more particularly to describe the same, and for that pur- 4pose shall refer tothe several figures on the annexed sheet of drawings, the same letters of reference indicating corresponding parts in all the corresponding figures.l

a Figure l of my drawings is an elevation of a suspension -bridge constructed according to my said invention.

a a are the piers, and b b the land-ties. In the place of a single chain from c to h, I employ two chains, (represented by the lines c d e fg h and c z' kfm 7L,) which are attached together, or to the same saddle,'at"`c and h, and cross each other at f.' The line c i kf is a parabolic curve, and the line f m his `a straight line, whiwch forms a tangent to that curve va'afrIn like manner the chain f g h lies ip a paraboliccurve, and the chain c d e f in a straight line, which forms a tangent to that ycurve at the point f. The chains are united by the vertical struts d t' e 7s, 8vo., and by the diagonal braces d k 'i e, 85o. The roadway r r is attached to the chains by the rods i r k fr, &c. If the half-span cj' is uniformly loaded the load is carried by the chaine i kf m h, which forms aline of equilibrium for that load quite independently of what, load there may beA upon the other half-span.V In like manner the'chain c d cfg h is in equilibrium under any uniform load upon the half-span f v h, so that eachchain is under a uniform horizontal tension throughout its length so long asthe two half-spans are uniformly loaded, though the load on one halt may be greater than the load on' the other half, and the braces have no strain upon them.

When either half -span is only partially bow-string rib. "Ihe bracing acting in this way4 increases the strain in certain parts of the chains, and lessens itin otherparts, and I make the sectional area of the chains proportional to the secant of the angle o'f inclination at its different parts, just as inA an' ordinary suspension-chain, because the greatest horizontal strain is the same for every bar of the lower chain, and is nearly equal to the horizontal strain of the upper chain at f, but less than the greatest horizontal strain in the upper chains at cfandh. 1

In bridges of large span, Where the live load bears a small proportion to the dead load,

thejgminution ot'-V tension caused by an irregular loading of either half-.span is not great, and I construct the chains of such bridges in any ordinary method, as shown in Fig. 2, which is a cross-section of the inverted bowstring rib formed by one-half of the bridge. a is the upper chain b, the lower'chain, and c is a vertical strut braced to resist compression.

1 In bridges where the live load bears a great proportion to the dead load the upper chain may at certain points be thrown into compression. Therefore, in small bridges, I substitute a rigid plate structure in place of the upper-chain, as shown in the cross-section, Fig. 3, where the upper chain is replaced by the plates ct and angle-irons b, which are capable of resisting either tension or compression. d is the lower chain, and c is a vertical strut built of plate and angle irons. The difterences of strain caused by the said irregular loading are less when the upper chain is straight than when ithangs in a curve; therefore I construct all suspension-bridges with the upper chain straight. a

In building arched structures on the same principle the two half-ribs, as seen in Fig. 4, are hinged at the abutments a and c, and hinged together lat the crown b. Each halt'- rib has an upper llange, a d b, sharply curved,

. and a lower tia-nge, a e b, less sharply curved,

or straight. The lianges meet at a and at b, and are united in the middle by a plate or lattice-web h, and the flanges are so arranged PATENT rFIo-n 'iiange a e b into tension; but, as this is of no consequence, the lower flange may be curved, and not straight.

Fig. 5 is a cross section ot' an arch-rib of wrought-iron, the upper flange a b and the lower ange d e being built of plate and angle iron united by the plate or lattice-web c. Fig.

. 6 is across-section of an arch-rib of cast-iron,

in which the flanges a and b and the web c are cast in one piece. The suspension bridge may also have the cross-section shown in Figs. 5 or 6, and may be constructed exactly as the arch inverted.

The half-ribs ot' the suspension-bridge are in any case either actually or virtually hinged to the piers at c and h, Fig. l, and hinged together atf. The upper and lower chains or ijanges may be actually hinged together and with the saddle ath, or the two chains may be separa tcly attached to the saddle, as shown in Fig. 7, in which a d is a' bar otl the upper chain; b c. a bar otf the lower chain, attached by the pins a and b to the saddle-plates e. The pins a and b are placed in the line of the bar b c, so that a small angular motion ofthe whole half-rib would produce no sensible strain upon either bar. In the same way the two half-ribs may be actually hinged together at j', Fig. l, or the two chains may cross each other, the ilat links of one chain passing between those ot' the other chain; or the upper and lower chain otl each half-rib may be sep-.

arately attached to junction-plates, as shown in Fig. 8, in which p is the junction-plate, to which are attached the chains a b and e f of the left half-rib, and the upper chain g h n and lower chain c d o of the right half-rib, the centers b, c, f, and g being arranged in the lines of the bars, or nearly so, in the same way as in Fig. 7. iis a vertical strut in the right half-rib, and 7c 7i. the diagonal braces, cottered up to an adjusting-plate, m.

I do not desire to claim, broadly, a suspension-bridge constructed with two chains attached to the same piers and crossing each other at the center; but

1. A suspended or arched structure, in which two half-ribs are jointed together' at the center ot' the span, each half-rib consisting of a straight member and a curved member, so arranged that the straight member of one haltrib torms a tangent to, ora direct continuation ot', the curved member ot' the other half-rib, substantially as described.

2. lIhe two half-ribs, constructed of plate and angle iron, substantially as described, and hinged to each other and to the piers or saddles, as set forth.

In witness whereof I have signed my name to this specification in t-he presence of two subscribing witnesses.

T. C. FIDLER.

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