US309171A - Chaeles l - Google Patents

Description

(No Model.)

C. L. STROBEL.

BRIDGE TRUSS OR GIRDER.

No. 309,171. Patented Deo. 9, 1884.

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lInTTnn STrTTre iPaTinyT @erica CHARLES L. STROBEL, 0F PITTSBURG, FEXXSYLVANIA.

BRIDGE TRUSS @R GBRDER.

SPECIFICATION forming part of Letters Patent No. 309,171, dated December 9, 1884.

Application tiled February 11, 1884.

To a/ZZ 107mm t may concern:

Be it known that I, CHARLES L. STROBBL, a citizen of the United States, residing at Pittsburg, county of Allegheny, State of Fenu` Sylvania, have invented or discovered a new and useful Improvement in Bridge Trusses or Girders; and I do hereby declare the following to be a full, clear, concise, and exact description thereof, reference being had to the accompanying drawings, making a part of this specitioation, in which-like letters indieating like parts- Figure 1 is a diagrammatic side view in elevtation of a bridge, illustrating the combination of curved members as employed in my invention; Figs. 2 and 3, similar views of bridges embodying my invention, illustrating, respectively, different arrangem-ents of chord members in the end spans, Fig. 4, a similar view illustrating the action of the chord members in maintaining the pier-posts in position; Fig. 5, a similar view illustrating a moditication in the end spans; Fig. 6, a similar view showing single chord members in each span, and Fig. 7 a similar view showing the application of my invention in a bridge having both deck7 and through spans.

The object of my invention is to provide a truss or girder for bridges, the employment of which shall ettect, among other advantages, those of enabling the erection of the bridge to be facilitated and economized, the strains sustained to be accurately determined and provided for, and those of temperature eliminated, a reduction in the cost of superstructure and masonry, simplicity of construction, and a light and graceful appearance.

To these ends my improvement, generally stated, consists in atruss for the intermediate span or spans ofa bridge, in which are combined acatenary and arch member and a chord member or members connecting the pier-posts ofthe truss, and also in the combination, with one or more intermediate spans, as stated, of end spans continuous therewith, and having anchorages adapted to admit of expansion and contraction ofthe trusses due to changes of temperature.

The improve-ments claimed are-hereinafter fully set forth.

(No model.)

In the practice of my invention I form the intermediate span or spans of a bridge having three or more spans or bays of lenticular trusses, T 3 9 10, Figs. 1 to 3, each composed of two curved members, one of which is downwardly curved substantially as a catena-ry, and the other is an upwardly-curved arch. Said curved members are connected at their intersections 7, 8, 9, and 10, which constitute points of contradexure, and are thence extended and connected to pier posts or supports 2 22 3 23 4 24, &c. The curved members of each span are connected together by any suitable system of struts and ties inserted in the ordinary manner in the spaces between them, and the pierposts are connected one to the other and to the ends of the bridge by chord members, which are substantially straight, the connections being made either at the lower ends only of the pier-posts by chord members 12 13 14 15, or at both their lower and their upper ends by chord members 12 13 14 15 and 16 17 18 19. In the end spans ofthe bridgea semicatenary is combined with an arch', said members connecting at points 6 11, located at their intersections nearest the pier-posts 2 22 and 4 24 of the adjacent intermediate spans, and at their opposite ends uniting in common points 1 5 at the extreme ends of the bridge.. Vhere upperchord members are employed in the end spans, as in Figs. 2 and 3, they may either extend from the upper ends, 2 4, of the pier-posts to the end connections, 1 5, of the curved members, as shown in Fig. 2, or from the pier-posts to points 2O 21 in the arch members, as shown in Fig. 3, the strains being thence transmitted through the arch members to the points 1 The truss above described partakes, as will be seen, of the nature of a continuous girder, with points of contratlexure fixed in position.

rlhe parts which are merely accessory, and not essential to the truss, are shown in the several figures in dotted lines. The deck or :door supports 'of the center span are thus in- 9 dicated in Fig. 5, and in a construction similar to that'shown in Fig. 7 it will be advisable to introduce vertical posts, as in the dotted lines, to support the chords at each panel point, said posts also carrying the floor-beams.

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In Figs. 2, 3, and 4 the non-essentialmem bers are wholly omitted, for greater clearness ot' illustration.

I have not herein illustrated or described the specific constructive details of the several members, as the same do not, per se, constitute part of my present invention, and are, further, familiar to those skilled in thevart of bridge construction. It will, moreover, be obvious that it is not essential that the arch members should be of any prescribed regularity, nor that the downwardly-curved members should be necessarily in catenary form. Said members may be circular arcs, or may be parabolic, elliptic, or irregular, as deemed in particular cases most convenient or desirable, and will, in practice, be made up of Vstraight lines between panel-points, the succession of said lines approximating to the form of curve desired. The strains in the catenary being tensile and those in the arch compressive, said members are to be constructed in the usual manner proper to receive and transmit strains of such character, the tension member being formed, preferably, of eye-bars, and the compression member of plates and angles. The action of the chord members in holding the pier-posts in position is exemplified in Fig. 5. The upper chord-line may be made a tension member, in which case the lower chord-line will be a compression member; or the character of the chord-lines maybe reversed, the upper then being a compression and the lower a tension member.

Assuming the bridge to be composed of four spans, as indicated in Figs. 1, 2, and 3, and the points of contratlexure, G 7 8 9 10 1l, to be located at equal distances, measured horizontally, on cach side ofthe supports or pierposts, and that the lenticular trusses formed in each span by thc before-described combination of catenary and arch members are of the same span length, (measured by projection on a horizontal line,) there will then, for equal loads, be such balance of forces that equilibrium would be maintained without the necessity of employing other or further truss members than thoseindieatcd. At the points 1 and 5 the thrust ofthe arch will be counteracted by the pull of the catenary, and there will be no strain in the direction of the line 1 5. The bridge will exert upon its supports at 1 22 28 24 5 vertical pressures only, and

may, therefore, beplaced upon rollers, so as to be free to expand and contract under the effects of temperature. No tempera-ture strains, consequently, require to be provided for. v

In order to render each span capable of carrying unequal loads, or loads covering a portion only of the span, as is requisite in bridges, especially those of railways, it is necessary to provide the strut and tie bracing between the curved members and the chords connecting the ends of the pier-posts with each other and with the ends of the bridge,as before specified. The chord members prevent the pierposts from cantingover longitudinally in consequence of the application of a heavier load to one span than to others, and the bracing` between the curved members forms, in connection therewith, rigid trusses between points of contraleXurc.

Under the conditions assumed as to the position of the points of contraflexure relatively to each other and to the pier-supports the chords 16 17 1S 19 15 14 13 12, Figs. 2 and 3, are without strain in two cases-to wit, when the spans are unloaded and when they are uniformly loaded. Initial strains may, however, be introduced in these members, if found desirable, by raising or lowering the ends of the trusses at 1 and This it willl be advisable to do for very large bridges, in order to reduce the deflection of the points of contraflexure, which would otherwise be considerable. Vhere the spans are not as described above, for which there is a complete balancing of the vertical forces at the points of contra-fiexure around the pier-supports, the chords will be strained for the two cases mentioned. There the end span is not of such (length and weight as to resist by its own inertia the upward force at 1 due t0 the maximum load applied at 9, as indicated by the arrows, Fig. 4, the end 1 and, correspondingly, the opposite end, 5, are to be anchored to the masonry by means of vertical anchor-bars 25 26, so arranged as to permit longitudinal expansion and contraction ofthe superstructure from temperature without impediment, while preventing vertical movement. This may be effected in any suitable manner, as by causing the anchor-bars to bear against 'sliding plates or rollers placed on top of the lower chords at these points. \Vhere three spans only are used, as in Fig. 5, the chord members described may be dispensed with, as stability is attained without them, and it may, further, be found advantageous to depart from the construction of end spans shown in Figs. 2 and 3,

eliminating the curved members and substi-V tuting a straight-line truss or other form, as shown in Fig. 5, continuous with the middle span and anchored, as before specified.

Fig. (5 illustrates a construction in which, in addition to the modication of the end-span trusses by dispensing with arch members therein, the upper chord members are wholly omitted. rlhe strains allotted to said members are in this case taken by the curved members'and pass through the points of eontratlexure. The construction shown is specially adaptable to highway-bridges, both on account of the more graceful appearance of the structure and for the reason that the strains to be taken by the chords are light, as the moving loads are seldom very unequally distributed.

Various structural modifications, which will be apparent to the skilled engineer, may be made, as necessary or desirable in'special cases, without departing from the principle of my invention, as hereinbefore described,

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and I have shown in Fig. 7, representing a combined deck and through bridge, the facility with which my improvements may be adapted to different conditions of span lengths and position of grade on bridge.

Among the advantages 'afforded by the employment of my invention are the following: First. The bridge can be erected either entirely or partially without false works, at low cost,

` with minimum of risk, and without obstructing the channel to passing vessels. The structure shown in Fig. 2 would be put fin place by first erecting the two end or shore spans (which are usually at a comparatively low level above ground) upon false works, then putting up posts over the piers and holding them by guy-lines, then erecting the catenary members in the manner of the cables in suspension-brid ges, by ii rst stretching a wire rope across the stream or chasm and following up with the heavier material. After the catenary is in place the other members of the truss can be readily put up by means of a traveler, the catenary forming the support for this work'. It will be seen that by this mode of erection no additional material is required for erection strains, as is the casein the ordi nary cantalevcr bridge.

Second. In constructions under my improvement no ambiguityor uncertainty exists as to the strains, as in cantalever bridges of the usual type, where more than `one system of web-bracing is employed, and as is the ease in the different forms of suspension'bridges herctofore constructed.

rIhird. No temperature strains are to be provided i'or, as in elastic arch and suspension bridges, and by the elimination ot' said strains an important economy of material in thc su pcrstructurc is etlectcd over ordinary arch and suspension bridges, as well as a still greater economy in masonry and foundations, inasmuch as vertical pressures only are sustained by the masonry.

Fourth. A material saving is clccted as compared with the ordinary cantalevcrt-rnss, not only because thc curved members are favorable for economy, but also by the more favorable position ot' the points ot' contratlexure, which can be located nearer to the supports than in the cantalever-truss, in which regard for erection strains docs not permit the central portion between the points of contraflexurc to be made of any considerable length.

Fifth. As compared with the'lenticular or Paulitrus's of equal span length, my improved truss affords twice the effective depth without greater weight of web-bracing, and the saving on this account more than balances the cost of extra material required for the chord members, which are not employed in the Pauli truss.

Sixth. Theappearauceofabridgeconstructed with my improved trusses is light and graceful.

I am aware that the combination of a catenary and an arch intersecting in the manner hereinbcforc described has been heretofore proposed in ln-idge-trusscs, but in such case the means adopted to obtain stability against forces induced by the loading of one span sin gly (to prevent cant-ing over of pierposts) was to build the piers encastr with the superstructure-that is to say, to unite them with the superstructure to a solidarity, causing them t-o resist said forces by their transverse or bending strength. I therefore disclaim the combination, per se, of said curved members.

I claim herein as my inventionn l. In a truss or girder for an 'intermediate span of a bridge consisting of three or more continuous spans, the combination, substantially as set forth, of a downwardly-curved member and an upwardly-curved member interscct-iug in two points of contraiicxure between pier -snpports, and a straightchord member connecting said piersupports, the curved members being connected by a system of web-bracing with each other, but not with the straight chord member.

2. In a truss-bridge having three cr more continuous spans, the combination, substantially as set forth, of an intermediate-span truss having a downwardly-curved member and an upwardly-curved member intersecting in two points of contratlexure between piersupports, and a straight chord member connecting said supports one with the other and with the ends ot' the bridge, said curved menibcrs in the intermediatespan truss being connected by a system of web-bracing with each other, but not with the straight chord members.

In a trusslbridge having three or more continuous spans, the combination, substantially as set forth, ot' an intermediate span. truss having a downwardly-curved member and an upwardly-curved member intersecting in two points oi' contratiexure between pierf supports, and connected by a system of webbracing, an end-span truss, and a vertical anchor-bar secured to a foundation and bearing at top on said end-span truss in such manner as to allow of a sliding or rolling longitudinal motion ot' said span, thereby permitting longitudinal expansion and contraction of the structure, while preventing vertical movement thereof'.

il. In a truss-bridge having three or more continuous spans, the combination, substantially as set forth, of an intermediate span truss having a downwardly-curved member and an upward]y-curved member intersecting in two points ot' contra'tlexure between pierL supports, a straight chord member connecting said pier-supports,and an endspan truss having a downwardly curved member and a straight chord member, which are connected one to the other at the outer end of the end span.

5. In a trussbridge having three spans, the combination, substantially as set forth, of a middle-span truss composed of adownwardly curved member andan upwardly-curved mem=Y IOO IIO

above und below the trusses, and chord mem'- hers connecting the outer end supports adja- `@eut to the eud spans with the ends of thev bridge.

In testimony whereof I have hereunto s'et niy hand. v

CHARLES L. STROBEL. w'itnesses:

J. SNowDnN BELL, C. C. LEE.

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