USRE3758E - Improved bridge - Google Patents

Description

SMITH, LATROBE PATENT OIEIcEo a oo., orl BALTIMORE, MARYLAND, AssIGNEEs or FREDERICK H. SMITH.

IMPROVED BRIDGE.

Specification forming part of Letters Patent No. 96,278, dated October 2G, 1869; Reissuc'No. 3,758, dated December 7, 1869. i

To all whom it may concern:

Be it known that FREDERICK H. SMT'III, of the city of Baltimore, county of Baltimore, and State of Maryland, has invented certain new and useful Improvements in the Construction of Bridges and other Truss-Frames; and we hereby declare that the following is a full, clear, and exact description of the same, ret'- erence being had to the accompanying drawings, making part of this specification, in which- Figure 1 is a side elevation of that form of suspension-truss known as FinhsJ Fig. 2 is a side elevation of a beam-truss of the quad rangular type. Fig. 3 is a side elevation of a beamtruss of thetriangular type. Figsa, 5, and 6 are side view, section, and rear view of the roller-bed, foot-box, and pin-joint at the end of beam trusses, showing the attachment of the lateral bracing and bottom chord to the pin. Figs. 7 and 8 are side view and longitudinal section of the top chord at the joint, showing connection of chord, strut, and lateral system at the pin. Figs. 9 and 1() are end views and cross-section through thel top chord at the junction of lateral and vertical systems on lthe pin. Figs. 11 and 12 are top view and chord, exhibiting the'conneetious of lateral, vertical, and longitudinal systems. Figs. 13 and 14 are side views of bottom chord and adjusting-loop and foot-box, showing connection of lateral bracing systems to pins, and showing the method of riveting fianges upon the edges of the chord-bars. Figs. 15 and 16 are end views and cross-section through bottom chord, showing angcs riveted to chord-bars, and also connection of lateral systems. Figs. 17 and 18 are cross-sections of bottom chords, showing chord-bars simply stift'ened by blocks, and also where the flanges are rolled upon the chord-bar instead of being riveted on. Figs.

y19 and 20 are top view and horizontal section of bottom chord, showing connection of pin and laterals. Figs. 21, 22, and 23are side elevations of the same representative forms of truss, substituting wood for iron in top chord. Figs. 24, 2,5, and 26 are sideelevations of the representative trusses with all compressive strains taken up in wooden struts and top chords, tensonistrains in iron. Figs. 27, 28,

horizontal section through the top 29, and 30 are views, on an enlarged scale, of the adjusting-loops and foot-box.

rlhis invention consistsvin, first, a noveland useful method of adjusting beam-trusses by' the use of adjusting devices applied directly to the foot of`the strut or post, instead of to the tie, as heretofore has been done, and at the same time securing perfect freedom of action in the truss by using the pin-joint throughout; second, a novel construction of bottom chordbars, in which no enlargement of ends for eyes is required, as the bars are rolled the full width required for the eye, and then stit'ened so as to utilize, for the transverse strain of the load, all of what would otherwise be surplus metal in the bar, the sti'ening process also furnishing a perfect bearing for theooring; third, a novel attachment of thelateral bracing systems to the joint-pins by means of a bolt which passes through vthe strap-loops nclosing 'the nuts of the lateral ties, through the strut which ts over the end of the pin, and through thc end ot' the pin itself,-thus securing facility of attachment, adjnstablity, compactness, a hinged joint in the lateral planes ofthe bridge,

` and freedom from welds in any of the connections; fourth, a novel device for adjusting trusses of all kinds by means of loops or yokes bent over the pins, and having adjusting-nuts upon each fork of the loops, upon which nuts the bottom plate of the strut is supported'at its corners, thus virtually allowing .the use of the squareend formula for columns, and giv ing extreme facility of adjustment and total absence of welds in the manufacture of the loops. ,l

To enable those skilled in the art to make and use this invention, we will describethe manner in which the same is or may be carried into effect. t

In a truss composed entirely of wrought iron economy is secured by concentrating the preponderance of strain in tension, where the materialis worth abouttwelve thousand pounds to every square inch of section, instead of taking it up in compression, where the material is only worth about seven thousand pounds per inch. This fact indicates at once that the struts should be inclined, thus throwing the heaviest strains into the bottom chord, and also shows that the economical angle and con= the top chord, and not square'box inserted into the recess, as is some.

sequent reach ol' the ties are much greater than those ot`tlie struts. If the truss is to be raised or lowered by elongatng or shortening the tie, as is the usual custom, it is obvious that the resistance to be overcome will be much greater in the greatly inclined tie than in the slightly inclined strut, and the 'tie is 'therefore abandoned and the adjustment is applied to the strut, the means ot' adjustment being directly applied to the base or fool: of the strut, thus admitting of the arrangement ofthe struts not onlyin a vertical position, but at any desired inclination, as shown in Fig. 3, which would not be practicable were the adjustingdevicrsapplied not directly to the strut, but through the liooring system or other intermediary. This at once avoids the necessity ot' using screws upon the ends ofthe main tics, thus permitting the use of the pin-joint, com'- bin'ed with complete adjustability throughout the bridge.

The necessity of a pin-joint is seen in the passage of a llull-weight train across a threeliumlrcdfert-span beam-truss, during which the heads ot' the end struts are drawn about halt' an inch toward the span centerby the contraction ol' the top chord, while the feet of the same struts are thrown about one inch away from the span .center by the elongation oli the bottom chord, thus inclin'ing the strut about one and one-half inch from the perpendicular or other original position. This distortionof ligure must Vsooner or later cause the i crystallization ofthe iron, unless a hinge-joint is'used. In lnanybridges the pin-jointis used, but with no adjustment, and the lopsided or n sagging condition of most of these structures f is the best argument to prove the positive nccessity ofan adjustment. In this arrangement the chords S are pierced at the joints for the pins a to enter, and both struts and ties take hold directly upon the pins, the top chord be! i ing recessed, as shown in Figs. 7 and 9, to permit these members to reach upto the pins, which in turn transfer their strain directly to to the cheeks ot' the times done. 'The bottoms of the strutsB have slotted holes bin them, (see Fig. 14,) or are oth erwise forked over the pins of the lower chord, and are supported squarely and firmly upon the nuts of adjusting-loops A A. The adjustment is e'ected by turning these nuts, thus f drawing the pin upward or downward in the i slotted hole, and thereby increasing or decreas-A ing the distance between the pins at the dif.

ferentends of the strut, and virtually making the strut longer or shorteiggas may be required. The ties C also take hold of the pins of the bottom chord, and in common with the strut have full liberty to turn upon the pin. Y In constructing the bottom chords of bridges the method usually followed is to use flat bars with enlarged ends to receive the pins, this en- Y largement being a very expensive process and liable to insecurity fromwelds, unless the up- Aand single bars, I between the ends ofthe former, and each three put the line ot' lateral bracing below the center y line of the cord, and leaves the structure liable `to great vibration. In the arrangement herein shownl the tension-bars D are not really eyebars, but are simply rectangular bars of the full width ofthe eye. The pin-hole is drilled out, and the available section thus left is applied to resist tension-strains in the chord, while the reniainingscction in the body of the bar,which would otherwise be surplus metal,'s used to resist the transverse strain arising from the passage of the load, the bars being stil'ened between the points of support in order to resist this strain more eifectually, and also to afford a broader support to the cross-tiesE than would be o'ered by the simple edge ot the bar. This stifteuiug is done by rivetingtlanges d to the upper or both edges of the bar, or by insertingpacking-blocks between the bars,with bolts or rivets through them, and placing the cross-ties upon them. The lianges can be rolled upon the original bars, as seen in Fig. 1S, instead ot' being riveted to them, if desired.

In long spans, where the chord-strains are very heavy, the amountot'surplus metal would be much more than could be utilized were all the bars rolled full width, and in these cases a sufficient number ot wide bars is used, and the remainder ofthe requisite section for tension is made up by placing ordinary eye-bars upon the pin. This arrangement brings the point ot' application ot' the transverse load as nearly as possible to the center line of the chord, thus reducing vibration.

It will further be noticed that the tension or chord bars .D are arranged alternately in pairs the ends of the latter litting ends which thus meet being jointed upon the pins a. The bars which are in pairs have an angle or stilfening iron inserted between them, while the single bars have the stil'ening-irons on each side. The chord is thus made completely adjustable at any desired point, while at the same time it preserves the strength requisite for the purpose for which it is designed. Heavy guardst-ringers F are notched over and bolted down to the cross-ties to perform the double duty 'of preventing displacement of ties during accidents, and also to distribute the load fore and aft. The pins in both top and bottom chords have screws and substantial '.nutsf upon their outer ends, and their inner ends projectseveral inches beyond the chords,

&c. The lateral struts G lit over the projecting ends of the pins. The lateral ties H have screwsaud nuts upon their ends and pass into straps 01 loops which fork over the ends of the lateral struts. A bolt, g, passes through the loops, strut, and pin, and the whole combination is then drawn up to a tight and compact joint by the nut f upon the outer end of pin. The bolt gives freedom of motion for expansion and contraction in sympathy with the motion ofthe chord, and the lateral ties H are adjusted by means of the nuts upon their ends within the loops.

In order to show the adaptation of the foot adjustment, as used in this arrangement for the beam truss to a suspension -truss, the points of difference between the loop herein shown and the other devices that have been used in the feet of suspension-trusses will be noted. In the bridge patented and built by Bollman there is a link which closely resembles in appearance the one herein shown, but differs very essentially in the fact that it is ``composed of a single eye-bar with a screw upon the end, this screw supporting the post directly under its center line, and necessitating the use of the formula for columns with roundedends. The wedge system used by the patentee of the Fink truss is also open to the same objection, as it supports its load above the pin, and is also liable to fatal displacement of parts by sudden shocks. The loop herein described supports the post at the four corners ot' the foot-plate entirely below the pin, and the loop itself is simply a bar bent over the pin, requiring no welding, as does the Bollinan lnlr.-A In cases where the diameter of the strut is very great a collar is placed around the pill in order to spread the two arms of the loop apart, and thus obtain the widest possible basev of support.

The adjusting-loop and foot-box are represented on an enlarged scale in Figs. 27, 28, 29,

and 30. The pin a is set in the slotted footbox of the strut B, and carries on each side the ties C. The loops A lit over the pin, and their lower screw-threaded ends pass down through the base of the foot-box, and are provided with nuts c c, by turning which the working length ofthe strut may be increased or diminished, as before specified.

While preferring the use of the adjusting devicesjdeseribcd, other means may be employed for the purpose, they being, however, applied directly to the foot ofthe strut in all cases.

The construction of the lateral struts may also be varied, the only requisite being that they sha-ll have the jointed connection with the pin, as above specified.

So far as relates to that portion of our claim -viz., the second clause-which embraces the construction of the adjusting devices, we are aware that means resembling in some respects those herein described have been used-as, for instance, in addition to the other'cases above named, an adjusting device has been made et" a bar, to which the bolt which serves as the pin and the rods which act in some measure as the loops have been firmly secured or welded. We lay no claim to such instrumentalities, but desire to secure only the loops and pin when constructed and combined as above set forth.

Having now described this invention and the manner in which the same is or may be carried into effect, what we claim, and desire to secure by Letters Patent, ifsl. The combination, in a'beatntruss, ofthe strut or post, with the adjusting devices here* in described, or their mechanical equivalent, applied directly to the foot or base Vof said pest` for the purpose of contracting or elongating its working length, substantially as set forth.

Y 2. The hereindescribed construction and combination of the loops and pin constituting an adjusting device applied to the foot of the post in either beam or suspension trusses, subsfantiallyf'as shown and set forth.

3. The arrangement of the chord-bars, provided at their upper edge or edges with flanges or stiifening-irons, for the purpose specified, and jointed to the pins upon which their ends are supported, substantially as shown and set forth.

4. rIhe attachment of the lateral bracing systems to the joint-pins by means of the bolt, which at once combines the pin, strut, loops, and adjustable ties into ak hinged joint in the lateral plane of the truss, substantially as shown and specified.

5. The combination, with the feet ef the struts or posts, ofthe adjusting-loops andjointpins, with which thelateral-bracing system is connected, substantially as herein shown and set forth. f

In witness whereof we have hereunto set our hands in the presence of two subscribing witf nesses.

SMITH, LATROBE Sz CO.-

Witnesses:

A. PoLLoK, NV. FINLEY.

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