USRE2070E - Improvement in truss-bridges - Google Patents

Description

UNITED STATES ALBERT D. BRIGGS, OF SPRINGFIELD, MASSACHUSETTS.

IMPROVEMENT IN TRUSS-BRIDGES.

Specification forming part of Letters Patent No. 20,987, dated .Iuly 27, 1858.; Reissue No.

2,070, dated September 12, 1865.

To all whom it may concern:

Be it known that I, ALBERT D. BRIGGS, of Springfield, Hampden county,Gommonwealth of Massachusetts, have invented certain new and useful Improvements in Truss-Frames for Bridges and other Structures; and I do hereby declare that the following is a full, clear, and exact description of the same, reference being had to the accompanying drawings, and to letters of reference marked thereon.

`In the drawings, Figure l is a side elevation of a truss-frame constructed according to my invention. Fig. 2 is a side view of a section of the sameion an enlarged scale. Fig. 3 is a perspective view ofa section of the same trussfraine. Fig. et is a perspective view of part of the lower chord or stringer, showing the manner of placing packing keys or blocks between the chord-sticks and between the bearing-blocks ofthe braces which constitute one part ot' my invention.

Similar letters of reference indicate correspondin g parts in the several igures.

This invention consists in a certain method of increasing the bearing-surface for the bearing-blocks against which the braces abutV in truss-frames.

To enable others skilled in the art to make and use my invention, I will now proceed to describe the manner in which it is applied to practice.

A A is the top chord or s tringer, and B B the bottom chord or stringcr. These I usufally make each of three or more pieces or sticks ot' timber, which sticks are kept apart by means of the keys c @,which pass vertically through the openings in the chords into which they are notched to prevent the chord-sticks from slipping past each other. Upon the upper side of the bottom chord and the under side of the top are placed bearing-blocks or angle-pieces d d, against which the main braces 7c lr, which are arranged in pairs, and the counter-braces i fi, which are arranged singly, abut. These braces, forming the panels of the bridge, are shown in the drawings so arranged that the bearing-blocks d d ofthe top chord are in vertical planes which pass through or near the centers of the spaces between bearing-blocks of the bottom chord, and that the bearingblocks of the bottom chord are in vertical planes which pass through or near the centers I of spaces between the bearing-blocks of the top chord, which makes the panels of or nearly of the form of a series of isosceles triangles; but I do not consider this arrangement essential, as the bearing-blocks may bein any other the outside bearing-blocks or angle-pieces c c,

as shown at s s in Figs. 1, 2, and 3. Between each pair of main braces k k (excepting the end pairs, where it is not necessary) there is a counter tensionrod, o o', which, like the tension-rods ff, pass through the bearing-blocks d and c, and are screwed at their ends and fitted with nuts, which screw up against the outer bearing-blocks, e e, as represented at m m in Figs. l and 2.

When the tension-rods ff are screwed up with the braces 7c 7c and counter-braces i i in their proper places to keep the chords apart and the counter-tension rods 0 o, tightened up -to prevent vertical vlbration, a truss-frame is formed which cannot be affected by the passing of a variable load which is within its capacity to sustain.

The method of increasing the bearingsun face for the bearing-blocks d and e is as follows: I make the said bearing-blocks to extend beyond the sides of the chords, as shown at g g in Figs. 3 and 4, and between the corresponding bearingblocks d e d e of each chord I fit blocks la h and blocks or keys c c, of hard wood, to keep the bearing-blocks apart and prevent the crushing of the chord-timbers by the screwing up of the nuts of the tensionrods, the blocks h h being placed between the ends of the bearing-blocks, which extend beyond the sides of the chords, and a block-or key, c', being fitted tightly into each opening between the chord-sticks. The tension-rodsj' f pass through the above-described blocks c c.

The bearing-blocks e c of the lower chord,

with the exception of those at the ends the ot' frame, are held up to their places by the tension and counter tension rods, but the bearingblocks next the end ofthe frame are supported by the bolsters or corbels u u, which project laterally beyond the sides of the chord sticks for the purpose of sustaining the blocks h h, at theV points ot' bearing over the abutments and piers.

The wooden blocks c c and h h areintended to have substantially the ,same ei'ect as thev metallic sockets which constitute part of the subject of NVm. Howes patent oflStG-viz., to

` prevent the crushing of the soft timber of the chords by the bearing blocks-but the side blocks, c c and li h, are also intended to obviate some of the objections to the use of said metallic sockets, which may be briefly enumerated as follows: First, the cost of the heavy cast-iron. bearing-blocks with the sockets attached; second, the liability to breakage; third, the socket must be of a certain length, and, as the timber is usually framed in an unseasoned condition, the chords must, in framing therefor, be left so deep that they will when seasoned correspond with the depth ot' the socket, or if they are cut to the depth ot1 the socket when framed, the timber shrinks away from the casting and leaves a loosejoint, which is prejudicial to the durability of the structure.

My method of providing for a bearing-surface for the blocks d e by the employment ot'v the blocks h h and c c obviate all the above diiiculties, and said blocks serve to keep the bearing-blocks from crushing the chords in a manner far more e'ective than the iron sockets, as the blocks c e can be fitted tightly beentirely ll up the spaces between the chordsticks, and providing blocks h h outside of the chords, a very much greater amount of bearlgurface for the blocks d e is obtained than is provided for by the cast-iron sockets, and it is this characteristic that constitutes the important feature ot' this part of my invention for iron.

I do not claim separately any oi' the parts ot' the truss-frame; but

What l do claim as my invention, and de sire to secure by Letters Patent, isn l. The method of increasing the bearingsurfaces for the blocks d d e e by the employment of the blocks or keys c c fitted, between the chordsticks and between the bearingblocks d d e e, substantially as described.

2. The employment of the blocks h h, iitted between the bearingblocks d cl e e on the ontside of the chord-sticks, substantially as herein set forth.

' A. D. BRIGGS. Witnesses:

J. B. GARDINER, J. R. SMITH.

tween the chord-sticks while the truss is bei ing framed, and by making said blocks c c and makes it not merely a substitute of wood

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