US121374A - Improvement in iron girders - Google Patents

Description

Patented Nov. 28,1871

4PETER H. JACKSON. Improvement in Iron Girde'rs.

Mmm

redraw" extended across the chord of the arc.

UNITED PETER H. JACKSON,

STATES PATENT CEEICE.

OF NEW YORK, N. Y.

IMPROVEMENT |`N IRON GIRDERS.

To all whom it may concern:

Be it known that l, PETER H. JAcKsoN, of the city of New York, in the county and State of New York, have invented a new and useful Improvement in Girders; and I do hereby declare that the following is a full, clear, and eX- act description of the same, reference being had to the accompanying drawing` and to the letters of reference marked thereon which form a part of this specification.

The invention relates to certain provisions for insuring that the cast-iron shall be subjected to a compressive strain alone, and not at any point subjected to a tensile strain. I have succeeded in constructing` the cast-iron portion in separate pieces with certain provisions for distributing pressure uniformly von the abutting surfaces in producing a very complete and eiiicient girder possessing marked advantages over any before known to me. The girder is of the variety known as bowstring, where a slightly-arched casting is tied by one or more wrought-iron bars Such girders have been long known and widely approved. As ordinarily constructed, the arch or casting is made in one piece, with grooves in the bottom at the ends to receive the tie-rods, and the latter, being made a little shorter, are eX- panded by heat, placed inv position in 'the casting, and allowed to contract in cooling and tie the bottom of the casting. It is diflicult in practice to secure a proper adjustment of the strain on the parts. If the tie-rod is too long, it does not receive its full proportion of the strain until 'the cast-iron has so far straightened itself' that its lower edge is subjected to a severe tensile strain, which cast-iron is very feeble to resist.

If, as is more frequently the case, the tie-rod is made too short, it is subjected to a severe initial strain, which is added to the strain proper induced by the load to induce fracture. In my improved construction of girder I subject the tie-rod or rods simply to the tensile strain due to the load. I impose upon it or upon the casting no initial strain due to the mutual action of the parts, but only the strain due to the load. My girder is a simple arch tie. There may be more than one of the ties, and there may be more than two pieces in the cast-iron portion; but I will proceed to describe what I consider the best means of carrying out the invent-ion by aid of the accompanying drawing, which forms a part of this specification.

\ Figure lis a side elevation of an entire girder made according to one of the best forms or modifications of my invention. Fig. 2 is a cross section on the line S S in Fig. l. Fig. 8 is a crosssection on the line T T in the same gure. The remaining ii gures represent only the central parts of the girder in several different modifications of the form of the abutting faces. There is understood to be one or more ties under each at a little distance from the casting. All the forms are intended to carry the masonry with the lower coruse or courses constructed archwise, and thus giving strength to the Work, the abutments being formed by skew-backs, as shown in Fig. 1.

Similar letters of reference indicate like parts in all the figures.

A1 A2 indicate the main cast-iron portions of the girders. They are formed with skew-backs a, near the ends, presenting a fair surface for the arched brick-Work, which is to be laid immediately above. The main body of the girder is formed with a broad flange at its upper edge and a narrower one at its lower edge, connected by a Web, the section being of the ordinary chargirder in proportion to its length may be varied shown. I have endeavored to represent what I consider the best patterns for ordinary practice in this city. In making heavy girders for twentyve feet spans I prefer to employ the tie-metal in two rods rather than one, but this is not essential. In transporting my girders, one or more rods with heads forged thereon forming the tie B, the castings may be transported separately. It is, under some circumstances, a very important advantage that my girders may be moved with greater facility( in consequence of there being less Weight to transport in any single mass. The parts are applied together in putting them in place in the building. A small Washer of tin, or of an alloy of lead with tin or I esteem it especially important to put a thin plate of lead between the abutting surfaces of the castings at the center. The soft metal by yielding slightly adapts itself to the inequalities in the iron and distributes the bearing over the whole surface. The construction of the abutting acter for the bovvstring girder. The depth of the one way or the other from the proportions here zinc, may be placed under the head of each tie.

ends at the center is important. I form one a concave, al, and the other. with a partially cylindrical surface, c2, adapted to match therein and form one part, A2, with a lip, a2, on each side, matching closely against the face of the other casting A1. The cylindrical swell a2, and the concave al adapted to receive it, serve as a joint to keep the parts exactly in the right position as the arch yields downward slightly under a load. The lips a3 prevent the gushing' out ofthe soft lead interposed in the joint. The leadas used in my joint performs two functions: The yielding of its particles serves as a stili" but none the less real lubricant in the slight turning m0- tion of the joint, and its capacity for filling all indentations and matching to all the prominences allows it to distribute the bearing as above suggested. The lips a3 perform import vant functions in this connection in preventing the escape of any considerable quantity of the lead under any load however severe. I propose to iind by trial how much these girders will yield downward under any given loads, and to carefully adapt the construction thereto, so as to secure the proper height of the girder when loaded.

Many modications may be made in the details of the construction without entirely defeating the ends attained by the invention. A portion of the advantage may be secured by the use of pa-rts of the invention without the whole. Amon g other modiications, a central casting may be interposed between the parts Al and A2. The abutting surfaces may, in such case, be formed with the cylindrical swell on one surface and the corresponding concave on the other. I have not deemed it necessary to represent these parts. Fig. 10 shows the abutting-surfaces principally plane, but with a projection on one fitting into a recess or mortise in the other. This construction is less perfectly adapted to allow the rolling motion analogous to that of a rule joint, which is performed by the swell and concave in the first or main plan, but is particularly advantageous in guarding against any possible displacement of thel abutting parts laterally' as well as vertically upon each other. Vhere the rolling joint or convex and concave surfaces are presented to each other, as in the main plan, Fig. l, I prefer to provide some plane surface above and below. Fig. 4 shows two beads or small convex swells on one portion, matching into corresponding concavities on the other. Fig. 5 shows the same after the girder has been depressed. In any construction the soft metal,

guarded by the lips, as described, tends greatly to diffuse and distribute the pressure 5 but my girder may be applied with some successwithout this important feature. In any construction I consider it important to so form the parts that,

on applying the castings together in place, the

lower edges bear the hardest when unloaded. As the load is applied and the castings spring downward the distribution of force becomes equal over the whole abutting ends. I propose in some cases to dispense with the soft metal in the form of the joint in Fig. l, but consider it almost indispensable to the best use of the invention in the forms shown in Figs. 8, 9, l0, and 11. Instead of lead I ca-n use alloy of lead and harder metal, so as to get just a proper consistency and hardness to move slightly, but be easily re strained by the lips from gushing outward. 4In cases where the joint is much open at the upper side while unloaded, as indicated in Figs. S and 10, I propose to sometimes apply the soft metal in the form of a melted filling, allowing it to liow in and take the form of the surfaces, and be afterward compressed by the sinking of the girder to act as above described for the thin sheet. Although the figures show the parts of the girder with the broadest part of the upper edge, it will be evident that the invention will also serve with the broadest part at the lower edge, so as to carry the masonry with its base at a lower level, if desired. It is only necessary in such case to take care to provide suflicient metal for a good and iirm resistance to the compressive force of the upper edge.

I claim as my inventionl. The within-described girder, formed of separate castings Al A2, with a tie or ties, B, con structed and combined substantially as herein specified.

2. The separate castings A] A2, in combination Awith each other and the tie B, with soft metal contined between the abutting surfaces and serving therewith, as specified.

3. In an iron girder having a tie-rod, B, to receive the tensile strain, and two separate castings, Al A2, to receive the compressive strain, the partiallycylindrical form a2 of one abutting surface, and the corresponding concave form al of the opposite abutting surface, adapted to yield downward and relieve one casting from most of the transverse strain while keeping each other firmly abutted and supporting lthe incumbent masonry, as speciied.

In testimony whereof I have hereunto set my name in presence of two subscribing witnesses. Witnesses: PETER H. JACKSON.

THOMAS D. STnTsoN, ARNOLD HOERMANN. (21)

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