US242396A - Bridge-truss - Google Patents

Description

(No Model.)

B. TEACHER.

Bridge Truss. I No; 242,396. Patented May 31,1881.

INVBNTOR %a 0M WITNESSES: AQWWJJZW ATTORNEYS.

UNITED STATES PATENT OFFICE.

EDWIN TEACHER, OF PITTSBURG, PENNSYLVANIA.

BRlDGE-TRUSS.

SPECIFICATION forming part of Letters Patent No. 242,396, dated May 31, 1881.

Application filed July 16, 1880.

To all whom in? may concern:

Be it known that I, EDWIN THAoHER, a citizen of the United States, residing at Pittsburg, Allegheny county, in the State of Pennsylvania, have invented useful Improvements in Combination and All-Iron Bridge-Trusses, of which the following is a specification.

By combination-truss is meant one in which the top chord and end struts are wood, the bottom chord, ties, and suspenders iron, and the intermediate struts either wood or iron.

The object of my invention is to overcome the defects common to a greater or less extent in all forms of triangular or quadrangular truss now in use, of which the following may be named:

First. In all combination quadrangular trusses (trusses containing quadrangles the sides of which are all connected with each other and with diagonals that cross each other and join opposite angles) both main ties and counter-ties are affected by temperature, the latter frequently to the extent of half their breaking strength.

Second. In double and triple intersection trusses there is ambiguity of strain-that is to say, there are no means of finding what the actual strain on a member is. This is also true of any truss in which a weight can find its way in more than one direction to the masonry or points of support.

Third. Counter-ties are liable to be overstrained in adjustment by unskilled workmen.

Fourth. Triangular trusses have sometimes tension and at other times compression on braces near the center. When the greater of these strains is compression, a wooden brace with iron tensile connections is generally used in combination-trusses. If, on the other hand, tension is much the greater strain to which the brace is subjected, flat bars connected with zigzag bracing are generally used. Both of these expedients are objectionable, the former owing to strains by temperature 011 the connections and the latter to frequency of damage by handling.

Fifth. Both quadrangular and triangular trusses as usually constructed have each end of the floor-beam 0r cross-girder on which the track or flooring rests supported by two suspenders, which are short links or bars con- (No model.)

nectin g the endof the floor-beam to joint above. These suspenders are generally a considerable distance apart, in combination triangular, two feet six inches being. not uncommon. The reason of this is, that each joint is made up strut,

.tie, chord, and floor-beam suspender. The

thrust coming down the strut from other parts of the truss, together with the weight suspended at the floor-beam, is taken by the tie and carried on toward the support. Now, in order to avoid a very large pin at the joint or excessive bending strain upon it, it is necessary that the connection of floor-beam susponder on the pin be made near or in contact with that of the tie, the latter being in pairs, and from the nature of the truss cannot be brought close together. The deflection of a floor-beam when the load comes upon itcauses an excess of weight to be thrown upon thein- 'ner suspender, and relieves the outer one to a corresponding extent. This unequal strain is conveyed by the suspender through the pin on which it hangs to the various members of the truss, whose unequal extension or compression gives rise to distortion and crossstrains.

Sixth. Adjustable counterties in quadrangular trusses and trussed ties in triangular trusses are "cry expensive in workmanship.

Seventh. The large variation in top-chord sections in the different panels of most combi nation-trusses renders iron packing difficult and expensivethat is to say, the strain on the chordincreases rapidly toward the center, where a much larger section of timber is required than at the ends and as the chord, as a whole, is always made of uniform width and depth from endto end, the variation in section can only be made by allowing much larger spaces between the sticks composing the chord at the end than at the center. make these sticks act together and about the axis of the chord as a whole, it is necessary to connect them by keys or packing, by which any strain on one stick will be transmitted through the keys to all the other sticks of which the section is composed; otherwise each stick will bend about its own axis and its strength he thereby much diminished. If the spaces between the sticks are small, the required connection can be easily and cheaply made by In order tomeans of lightcast-iron keys but if the spaces are large the keys become massive, and their effectiveness at bestis much impaired. WVooden keys are generally used in these bridges, but at the expense of greatly-reduced durability, for it is a well-known fact that wood in contact with wood soon decays, but that wood in contact with iron is not thus affected.

Eighth. In quadrangular trusses the sudden change of strain from counter-tie to opposite main tie, or the reverse, as a train passes over, and the consequent racking of parts, is very in urious.

My improved truss can be made free from the foregoing objections.

Itconsists of a primary triangular truss composed of top and bottom chords, together with a web of struts and ties, arranged in the form of triangles, free to change figure from the effects of temperature. The center ties extend each over a greater number of panels than any strut, ovcrnot less than two, and over not more than the number in halt-span less one. The panel-points intermediate between the tops of the center ties, and not at joints of the primary truss, are supported by vertical suspenders, or partially supported by pairs of inclined suspenders, from the top of the center strut, and the balance supported from the outermost limits ofsuspension. The inclined suspenders are connected with each other, but have no fixed connection with the bottom chord, nor with the center ties at intermediate points of intersection.

Figures 1 to 5, inclusive, represent side ele-' vations of bridge-trusses embodying my invention; and Fig. 6 represents, in detail, a side elevation of intermediate panel-point, D.

In Figs. 1, 2, and 3 the top and bottom chords, together with the members F A, AB, and B G,constitute the primary truss. In Figs. 4 and 5 it consists of the same members, with the addition of the two diagonals between A F and the end of span.

All parts not specified above as belonging to the primary truss are suspended from it or used to supportintermediate panel-points. A A may be called the limit of suspension.

A B are the center ties, connected with the top chord at A and with the bottom chord at B.

O B is the center strut, either vertical, as in Figs. 1 and 3, or sloping toward the end, as in Figs. 2 and 4, or toward the center, as in Fi 5. The struts may be vertical or inclined, as best fulfills the requirements of any particular case.

In Figs. 1, 2, 3, and 4 the center ties meet in the bottom chord. In Fig. 5 the center struts meet in'the top chord.

E E are intermediate panel-points, supported by the vertical suspenders O E from the top of the center strut, G B.

D D are intermediate panel-points, supported by inclined suspenders directly or indirectly from the points A and C of the primary truss.

These suspenders are in pairs, connected with each other at D but they have no fixed connection with the center ties, A B, nor with the bottom chord. In Fig. 6 the broken bar below D is the chord, supported, as shown by the suspenders, by means of a stirrup attached to the pin above. It may,however, be done, if desired, by means of a seat on the floor-beam below; but whatever method is adopted, the joint at D must be left free to move longitudinally unrestrained by the chord. These panelpoints may each be supported by pairs of inclined suspenders A D and D (J, leading directlyfrom them to the points A and O of the primary truss, as shown orsome of them may be thus supported and others of them as before described.

If the length of span permits, the center ties may each extend over four or more panels, and a greater numberof intermediate panel-points be suspended. A A are the limits between which intermediate suspended panel points aid in overeomin g reversed strains in the center braces, and the center ties may always extend over a suflicient number of panels to accomplish this object when desired.

The weight at any intermediate panel-point, D, is conveyed by the inclined suspenders to the joints A and O of theprimary truss in pro portions inversely as its horizontal distance from thosejoints. Thepart going toO increases the compression in the center strut, O B, as does also the weight from any intermediate panel-point, E,conveyed through vertical suspenders to the same point. Any compression in the center strut due to intermediate suspended panel-weights gives tension on the center ties on both sides of the center, and opposes reversed strains in the center braces due to partial rolling loads. The only panel-points on which rolling load either side of the center can tend to produce reversed strains in the center ties are those at A, or between those points and the truss-supports. The compression in the center strut and tension in the center tie increases as the points A are moved toward the end of span, and the distance between these points can, if desired, always be made sufficient to overcome all reversed strains in the center braces. Any panel load produces compression in the top chord and tension in the bottom chord.

In Figs. 1 and 3 the maximum strain in either chord, which occurs when all joints are loaded, is uniform throughout its length, and in all the trusses the maximum strains in the different panels of the top chord are so nearly uniform that in combination-bridges the section could be made uniform without material increased cost.

The bottom lateral system may consist oflongitudinal and diagonal tension-rods connected with transverse floor-beams, which act as the struts of the system; or it may consist of transverse struts and diagonal tension-rods connected with longitudinal floor-beams sus' pended from the panel-points.

From the preceding description it will be understood how the advantages which my truss possesses over the prevailing styles previously claimed, but not described, are gained.

As there are no confined quadraugles, and as no wooden braces having iron tensile connections need be used, temperature strains can be avoided.

As the suspenders act independent of the chord at D, the weight at those points can reach the joints A and O of the primary truss in no other way or manner than as described, and as the primary truss consists of a single system of triangular figures, a weight at any joint of it can go in but one way to either point of support; consequently there can be no ambiguity.

As thelength of any one or more of the members of the primary truss or of the suspenders can be changed and the work still come together as readily as before, adjustments are not called for.

As the pairs of inclined suspenders at D and of center ties at B can be placed as near together as desired and in contact with the floor-beam suspender between them, the latter can be made of a single bar at the center of pin without increase of cost.

The vertical suspenders O E can be made a single bar passing through the floor-beam it the latter is of wood, or in pairs connected by pin at E, with a single loop-suspender between them connected with the floor-beam, if an iron floor-beam with asingle web is used.

As in all the figures a top chord of uniform section would be used in combination-bridges, and the spaces between the chord-sticks he made uniform and as small as desired, packing blocks or keys of iron can be used at a minimum expense.

My improved truss is more economical in workmanship than others, owing to the shorter and smaller pins, the absence of sleeve-nuts or adjustments of anykind, and its freedom from zigzag bracing. It is also fully as economical 4 5 in material as any of the prevailing styles.

As there are no adjustments to get out of order, it requires little or no superintendence after it is once erected, and as every part is strained under all conditions of load, and as no distortion can change this relation of parts, less repairs will be required and a longer life insured than in counterbraced forms. It has all the advantages without the disadvantages found in most of the trusses now in use.

I claim as new and desire to secure by Letters Patent- 1. A bridge-truss consisting of a primary triangular truss, composed of top and bottom chords, and a web of struts and ties arranged in the form of triangles free to change figure from the effects of temperature, substantially as set forth, the center ties extending each over a greater number of panels than any strut,

over not less than two, and over a number not exceedingthe number in half-s pan less one, the panel-points intermediate between the tops of the. center ties, and not at joints of the primary truss, being supported by vertical suspenders, or partially supported by pairs of inclined sus- 7o penders, from the top of the center strut, and the balance from the outermost limits of suspension, said inclined suspenders being also connected with each other, but having no fixed connection with the bottom chord, nor with the 7 5 center ties at intermediate points of intersection.

2. Inclined suspenders in combination with a triangular truss having a bottom chord always in tension, which support the weight of that chord without having any fixed connection with it by means of a stirrup attached to the pin above, substantially as set forth and described.

EDWIN THAOHER. Witnesses:

NATHANIEL GREEN, 0. A. JACKSON.

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