US142381A - Improvement in iron bridges - Google Patents

Description

- l. B. EADS. Iron Bridges. N0; l42,38l, Patented'SeptemberZ,1873.

, ATTEST: INVENTORI UNITED STATES A;IENT FFIGE.

JAMES B. EADS, OF ST. LOUIS, MISSOURI.

IMPROVEMENT in IRON BRIDGES.

Specification forming part of Letters Patent No. 142,381, dated September 2, 1873; application filed June 11, 1873.

To all whom it may concern:

Be it known that I, JAMES B. EADs, of St.

Louis, St. Louis county, Missouri, have in-- vented an Improvement in. Bridges, of which the following is a specification:

' My invention consists in stiffening or trussing the arches of a bridge by attaching to each arch of the span two inverted or counter arches, one under'each halt of the arch, as shown in the drawings in Figs. 1 and 4. Another part of my invention consists in forming the abutments of solid or hollow columns, inclined together in pairs, and joined together at their upper ends, like the two sides of the letter A, with proper bracing between them, so that the thrust of the arch may be received at the point of junction of the two columns, and will a be resisted by one column in compression, and allow the weight of the other to be availed of to resist the overturning of the columns or piers thus formed.

- In the drawings, Figure 1 is a side view of the bridge with the piers shown in vertical section. Fig. 2 is a top view. Fig. 3 is an end view.

The above figures all show a throughbridge.

Fig. 4 is a side view of a deck-bridge of my improved construction, and shows the striding abutmentrolumns extending down to the natural foundation. Fig. 5 is a top view, showing a portion of the end of the arch arch A at their ends, and connected between the ends by suitable brace-work O. The arch A, with its two counter-arches B B, constitutes one rib of. the bridge. There should be in one span of the bridge two or more of these ribs, according to the strength and width required.

When a partial load is on one end of the arch, the counter-arch, under the loaded end, is strained by tension, as the weight is transmitted to it by the vertical bracing between the main and counter arches on that side. The counter-arch on the unloaded end is at this time under compression, and forms, with the unloaded half of the main arch, an inclined strut between the center of the arch and the abutment, which transmits the pressure caused by the load to the abutment at the unloaded end. The unloaded counter-arch, by its compressive strength and vertical attachment to the unloaded half of the main arch, prevents that part of the main arch from rising up and losing its proper curvz t ire. The counter-arches are under no strains whatever when the entire span is equally loaded throughout, or when it is entirely unloaded, if the main arch be of parabolic form. The counter-arches simply truss the main arch against unequal loading.

The joint a connects the end of the arch A to a diagonal brace, D, extending in the direction of the thrust of the arch, the other end of this brace being seen-red to the apex of the abutment structure. This brace D really constitutes an extension of the arch A. The abutment structure has two inclined pillars or supports, E E, for each rib or arch, which pillars are securely joined together at the top,.and spread out downward, like the two sides of the letter A. These pillars or legs E may be secured to vertical pillars E supported in masonry F, and having collars e to give a firmer hold upon the masonry; or the legs E may extend down to the solid rock or other foundation G, as shown in Fig. 4. The legs E, especially in the latter form, should have suitable bracing e to keep themin proper relative position. These pairs of A- shaped colunins are to be supported against the current, or 'other lateral force, by bracing between each two or more pairs, forming a pier or abutment. H are vertical struts extending from the joints to tothe abutment or pier to prevent the joint to from moving ver tically. I are horizontal struts extending from the joint a of one arch to the same joint of the arch next adjoining, or to other fixed part of the abutment, to prevent horizontal movement of the joint a. The vertical struts H and horizontal ones I may be omitted by securing the arch A directly to the apex of the abutment; but in this case the clear span between the opposite ends of the arch will be lessened by the amount of space occupied by the stride of the abutment-columns at the waterline. K is a transverse beam attached to the struts H to sustain the end of the roadway L. The roadway is not attached to the beam K, but, if made of metal, is free to slide thereon, as its length is increased or diminished by change of temperature. The roadway L does not assist in any manner in the support of the arches, but is connected therewith only by vertical suspension-rods M, as in Fig. 1, why struts M, as in Fig. 4. When arranged as a deck-bridge, as in Fig. 4, the roadway should be directly attached to the center jointa of the arch, or to the arch near the center, so as to insure itequal extension and contraction at each end of the arch.

In Fig. 4 L is a section of the roadway inserted over the piers, and between the main parts L over the spans, the parts L being connected to those of L by a slotted joint, or its equivalent. The section L may be stiffened by a truss, Z. If the roadway is placed above and secured at the central joint at, its expansion and contraction will be easily accommodated by the slight alteration in the vertical position of the struts M, as it will expand and contract in each direction from that joint, and thii will be accommodated by the slotted joint at If the roadway be suspended below, the suspension-rods will adjust themselves readily to these alterations in the length of the roadway, excepting at each end of the span, where they may be too short, and where the movement of the roadway caused by the change of temperature will be most excessive. At these points the suspenders should be arranged in Stirrup form to allow the roadway to slide back and forth through them. Although this movement will, even in long spans, be only the fraction of an inch, or at most a few inches, it is important to accommodateit in the way suggested, or in the manner that trusses are allowed to move longitudinally on the tops of the bridge-piers, so-as toavoid all strains from temperature in the superstructure, as well as to avoid the horizontal force that would otherwise exert itself to overturn the piers or abutments, and which force, if not thus accommodated, would require the piers and abutments to be so much stronger. If the longitudinal parts of the roadway are made of timber these provisions for expansion will be needless.

Any suitable system of lateral bracing to preserve the relative position of the arches in their proper planes, and to resist wind-pressure, may be used between the arches. The roadway may also be provided with windbracing.

When the roadway is suspended, of course a portion of the wind-bracing between the arches must be omitted at each end of the span for head room, unless the road be suspended some distance below.

The widening of the ribs at the abutments will allow of the introduction of inside stays from the abutments to the points of the upright ribs of the arch where the wind-bracing commences. This is shown at 0 in Figs. 2, 3, and 5.

With the roadway above (see Fig. vit) the stays 0 would be unnecessary, as the windbracing between the ribs might be'continuous from end to end. The object of these stays is to preserve the arches in their proper planes where the necessity of head room for the suspended roadway makes it necessary to omit the bracing between the arches at each end of the span. The appearance of the span in Fig. 2 very much resembles the bow-string girder; but it is essentially different, as the thrust of the arch has no chord to resist it, but is taken solely on the abutments. The roadway L in Fig. 1 gives the appearance of a chord and causes this resemblance.

In the girder the string or chord would re-' quire to have almost the same section as the arch. The counter-arches required in a span of five hundred feet to carry two thousand five hundred pounds per foot are found by careful investigation to need but two-elevenths of the section of the supporting-arches; hence the weight of the arches and counter-arches of this system would be to the arches and chords of the bow-string girder of equal versed sine and strength as thirteen is to twenty-two, while the vertical'bracing in this system would also be less than that in the bow-string girder. The value of this feature of my invention is shown by this comparison, the estimate having been made for steel arches with one-eighth versed sine. Twenty thousand pounds per square inch was themaximum strain allowed. It constitutes, in addition, the simplest and cheapest system yet devised for trussing or stiffening the arches of bridges.

In constructing the arches thegreatest econ-' omy will be attained by making all the mem bers straight between the points of attachmentof the vertical bracing.

I would recommend the counter=arches be of similar curvature to the main arch. By lessening the radius of the counter-arch (viz., increasing its versed sine) the strains in it will be reduced, but the lengths of the vertical bracing will be increased.

I claim as my invention---- 1. The within-described method of trussin g or stiffening the upright arches of a bridge by securing to each arch ofthe bridge by suit- 2. The bridgepier composed of columns ab1e vertical bracing, two inverted counter- E, inclined and joinedtogether in pairs, the arches of half the'span, the inner ends of the planes of said pairs being located in the line counter-arches being fastened at the center of of 0r-para1le1 with the thrust of the arch.

the main arch, and their outer ends secured to JAS. B. EADS. the ends of the main arch at or near the abutments, in such manner as to enable the conn- Witnesses:

ter-arches to resist tensile and compressive SAML. KNIGHT,

strains in the direction of said counter-arches. GEO. O. FABIAN.

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