US3094813A - Bar joist - Google Patents

Description

'June 25, 1963 VAN RENSSELAER P. SAXE 3,094,813

BAR JOIST Filed April 7, 1961 INVENTOR ATTORNEY United States Patent 3,094,813 BAR JOIST Van Rensselaer P. Saxe, 1701 St. Paul St., Baltimore, Md. Filed Apr. 7, 1961, Ser. No. 101,453 1 Claim. (Cl. 50-406 This invention relates to an improvement in bar joists used in concrete and steel building construction.

Bar joist is widely used in steel frame building construction work as the support for floors placed between steel beams which are a part of the basic structural steel construction. After these bar joists are erected by placing them on seats on the top of the beams, they are covered by a heavy wire mesh laid on top of the joist and spanmng between the joists. This is a close woven mesh on top of which is placed a very dry concrete mix which is troweled smooth to form the floor. Bar joists are also covered with sheets of corrugated metal laid on top of and running crosswise of the joist to act as forms on which to place concrete of normal consistency which forms the floor over the joist. This method of using sheets produces less waste of concrete material which occurs due to the sag of wire mesh when it is used. After the concrete floor has been put in place, then a plaster ceiling is usually put on the bottom of the joists to hide them from view and give a good finished appearance to the rooms under the bar joist supported concrete floor.

Because of the use of plates or seats attached to the bar joists as bearing ends between the joist ends and the beams, the overall height of a building is increased. The general efifect of this greater height of the bar joist type of building is to increase the material required for every vertical type of material used to make a completed building. Items under this heading would be more brick wall work, more partition work, more vertical piping, more steel columns, etc., all of which cumulative costs ofiset much of the saving made in using bar joists with structural frame construction. In other words, while the flat slab bar joist concrete floor job is estimated to cost less because it can be much more rapidly erected, as for example, a one or two-story building or an apartment project where early rental dates are a first consideration, nevertheless it is actually more expensive in the long run than it should be because of the total cost of extra materials used in multi-story buildings, though there are some offsets to this height increase due to the fact that pipes, ventilating and air conditioning ducts, etc., can be run through the bar joists above the ceiling and are thus hidden from view.

The bar joist type of constructionhas one principal .type of competition, namely what is known as flat slab reinforced concrete floors using reinforced concrete columns to support the concrete slabs. While this construc- 'tion is slow compared with bar joist, it is also of generally higher dollar cost than the bar joist type of floor supported on steel beams. However, as an ofiset to this greater structural cost, it has one advantage over bar joists in that the'concrete flat slab can be designed so that it produces a floor of considerably less thickness than can be secured by the use of bar joists as presently made and sold. The net result of this difference in floor thickness, which may be from 5" to 8", is that in a ten-story building a bar joist building will be 50 to 80 higher than the same building constructed with flat slab concrete construction.

Accordingly, one of the objects of this invention is to provide a solution to the problem of reducing the height of a building and consequently its cost by making bar joists in a manner to retain and augment its structural and economic features, while reducing the height of the top chord of the joist above the plane of the supporting beams. 'In'that connection it is proposed to eliminate bearing 3,094,813 Patented June 25., 1963 plates, shims, saddles or the like that are built as hearing ends on the bar joists between the top of the beam and the joist bearing support and secure the top chord of the bar joist directly to the beam, and, at the same time, preserve a safe hearing from an engineering standpoint and save the vertical material otherwise contributing to more costly construction, while also saving placing of forms for concrete as an extra item of work material cost and time required to install the concrete floor covering.

Another object of the invention is to use corrugated sheet metal as top chord of the joist so these sheets of corrugated metal with the corrugations disposed parallel to the web of the joist with the ends of the corrugated sheet resting directly on the beams and welded thereto and provide the least possible depth or projection above the building beam while said sheets have slots punched in them so that serpentine-bar web peaks may be secured in slots above the top surface of the corrugated sheet to be included in the slab, while the lower valley portion of the web have rods or other shapes welded on opposite sides thereof to provide the bottom chord. Because of the added lateral stiffness imparted to the top chord by the corrugated sheets, as compared with angles, for example, the resistance to compressive forces is better distributed and the rods for the bottom chord are in relatively the same tension. However, the corrugated sheets provide better support for the concrete floor material and prevent the usual material waste incident to the use of mesh or crosswise placed corrugated sheets.

Moreover, the corrugated sheets having considerable stifiness in themselves, when placed with the corrugations parallel to and acting as a compression chord for the bottom tension members can form a beam unit of any designed strength. In such a beam the top flange corrugated sheet acts as a floor or form on which to place the concrete floor so by the act of placing one of this type joist on top of the steel supporting beam, you have in the same act provided a steel floor form on which to place the concrete forming the finished floor. V A further object is to provide a bar joist wherein the edges of the corrugated sheet metal at either side of the sinuous web provide support for additional strips of sheet metal to complete the span between joists.

With the above and other objects in view which will appear as the nature of the invention is better understood, the invention consists in the novel construction, combination, and arrangement of .parts, hereinafter more fully described, illustrated, and claimed.

A preferred and practical embodiment of the invention is shown in the accompanying drawings, in which:

FIGURE 1 is a diagrammatic vertical cross sectional view of a concrete floor supported on the bar joist of the present invention.

FIGURE 2 is .a detail cross-sectional view taken on the line 2-2 of FIGURE 1, illustrating the preferred form of the invention wherein two bar joists are attached to the same sheet.

FIGURE 3 is an enlarged fragmentary perspective view emphasizing that the corrugated sheet forming the top chord of the bar joist rests directly upon the supporting beam.

FIGURE 4 illustrates .a modification of the invention wherein a single bar joist of FIGURES 2 and 3 may be attached to a single sheet iandthe adjacent edges of the sheets overlap.

Similar reference characters designate corresponding parts throughout the several figures of the drawings.

The usual beams which support the bar joist are designated as A, while the prefabricated bar joist assembly of the present invention is designated generally as B. This new bar joist assembly includes a shallow top chord C, serpentine web W, and bottom chord C.

Corrugated sheet as disclosed herein is to be understood as conforming to its dictionary definition, namely, sheet iron bent into series of alternate ridges and grooves in parallel lines, and when resting directly on the building beams provide lowaprofile bearing portions.

As indicated at the preface of this specification, the distinctive feature of the present invention resides in providing a bar joist wherein the corrugated sheet forming the top chord has its corrugations disposed at right angles to the beam A and parallel to the web W as clearly shown in FIGURE 3. Thus the corrugated sheet forming the top chord of the bar joist rests directly upon the upper surface of the beam A thereby eliminating height increasing plates, shims, chairs, or similar elements which have a tendency to increase the height of the floor in the general overall height of the building, and to have the corrugated sheet metal top chord act as a form for placing of concrete.

"Referring more in detail to the bar joist assembly, it will be observed that the same includes strips of corrugated sheet metal 1 whose end portions 2 may be directly welded as at 3 to the top surface of the beam A. Only part of one sheet is shown in FIG. 3 as resting on top of the beam, but it will be understood that the end of another sheet may substantially abut with the adjacent end of the related sheet shown, and, the end of the last sheet referred to will also be welded to the beam top.

There is an accepted theory in the use of concrete slabs or floor-s built on a steel beam of any character that, if you can, by mechanical means, firmly attach the concrete slab to the top flange of the steel beam, the quantity of steel required can be materially reduced in the top flange of such beam as much as sixty percent, and, through this mechanical attachment, the concrete slab will take the stress that the beam top flange would take if it were full size.

Thus, by substantially flushly anchoring the top chords C to the beam and also locking the concrete slab thereto by a portion of the sinuous web of the bar joist, not only is a stronger and more practical construction provided, but additional economies are effected in the quantity of metal used in the bar joist.

As has been described, this use of a corrugated sheet top and which acts as a form for placing and acting as a unit with its bottom chord, has suflicient strength to support the dead weight due to placing concrete on its corrugated sheet top chord. When this concrete placed on the corrugated top chord sheet hardens, it adds strength by acting as a part of the top chord attached to the bottom chord through the sinuous members making up the complete joist.

The hardened concrete slabs add additional strength to the joist to carry live and other loads which may be placed on the concrete floor and the bottom chord tension bars of the joist are designed to support this additional live load as well as the original dead load due to placing of concrete on the corrugated sheet forming the top chord.

As will be seen from FIG. 2, the top chord C of the bar joist comprises a single corrugated sheet 1 with two sinuous webs W attached thereto. These sheets are pro vided at appropriate intervals with suitable openings or slots 4 formed by subjecting the sheets to dies which punch all sides of the metal to one side of the sheet to provide end flanges 5 and side flanges 6 to snugly receive an inverted U-shaped peak 7 of the web- W. In the case of the truncated end 8 of peak 7, this will be welded to the top of beam A. Also, the top portions 7 of the sinuous bar constituting the web-truss W of the bar joist are welded to the flanges 5 and 6 of the corrugated sheet forming the compression flange of the joist.

The punching of the openings 4 to form the flanges 5 and 6, because of the shape of the corrugated sheet 1, provides, when the U-shaped peaks 77 are welded to said flanges 5, 6, an unusually stiff and strong connection between the corrugated sheet 1 and the inverted U- shaped peaks 77 due to the stiffness of the ribs and the arching effect caused by the corrugations of sheet 1 because of the effect of stress at these points, 5 and 6, is transferred through the corrugated sheet 1 without local bending or distortion of the sheet at said points as would be the case in the use of a flat uncorrugated sheet.

The projection of the peaks 7 above the general plane of the corrugated strips 1 is sufficient to enable the concrete to key into the arches beneath the peaks 7 and also to cover the peak heads to a depth sufficient to provide the floor slab: S of adequate depth so that this concrete slab on hardening will become a permanent and integral part of the bar joist which supports the concrete until set.

The web W of the bar joist, formed by the sinuous bar has its lower valleys 9 connected to rods 10' welded to either side of the stock forming the sinuous web. These bars 10 which form the bottom chord C of the bar joist may be of relatively light stock.

Suitable rods 11 may be laid transversely of the corrugations and preferably within and welded to the arched portions 7 of the sinuous web, with their ends bent down and welded as at l1 to the top of the sheets 1. Thus, these rods will give additional stiffness to the corrugated sheets constituting the top chord and at the same time, after the concrete has been placed on thecorrugated sheets or plates, said rods will help to provide a better anchorage for the loops 7 where they project up into the concrete slab and also provides additional strength for the completed slab once the concrete has hardened.

In the preferred form of the invention shown in FIG- URE 2, certain valuable advantages accrue. For eX- ample, by using two truss elements or webs for a single corrugated sheet, it is possible to more fully utilize the compression value of a standard sheet. Moreover, by connecting spaced truss members to a single sheet, fabrication at the mill is facilitated and units thus constructed may be easily stacked and transported. By providing a pair of web-truss elements inwardly of the edges of the single sheet, proper overlap of adjacent units may be readily effected, and it will be safer for men and equipment to travel over the units assembled on a beam.

It will, or" course, be understood that the invention is not limited to the use of a single sheet with the pair of web-truss elements as above described because, in FIG- URE 4 it is shown that the invention can be fully utilized where the single sheet 1 has only a single web-truss attached thereto. This arrangement aside from the fact that it is less convenient to handle and stack does not fully and economically utilize all of the compression value of the corrugated sheet.

Regardless of the specific embodiment of the invention as shown in FIGURES 2 and 4, it will be understood that the sinuous web is welded to the corrugated sheets and the latter are Welded to the tops of the beams while the edges of the corrugated sheets of one uni-t will overlap those of another to provide a combined top chord and complete slab form.

Since the edges of the corrugated sheets are welded to the top of the beam, and, likewise, the ends of the peaks of the top chord C are welded to the beam, and said peaks forming anchoring keys for the concrete, it will now be seen that the ultimately formed concrete slab S is directly tied to and connected with the supporting beam A to accomplish the important engineering requirement previously set forth.

I claim:

A prefabricated bar joist having low profile bearing ends to rest on related supporting beams of a building, comprising, in combination,

a top chord constituting the upper compression member of the bar joist andcomprising at least one sheet of corrugated metal continuous from end to end and having the corrugations manifested in the form of alternate ridges and grooves disposed parallel to the side edges of the sheet and also exposed at the ends of the sheet, whereby, said alternate ridges of the corrugations are adapted to rest directly on the building beams,

said corrugated sheet having slots with edge flanges,

a serpentine Web member disposed in a plane parallel to the corrugations and having peaks projecting through the slots and Welded to said flanges to provide high resistance to bending lengthwise of the sheet,

cross rods passing through and welded to said peaks of the serpentine web member projecting above the corrugated sheet and also welded at their ends to the edges of the sheet to prevent deflection thereof,

and a bottom tension chord member secured to the bottom portions of the serpentine Web.

References Cited in the file of this patent UNITED STATES PATENTS Evers Sept. 11, Wilson Aug. 3, Stewart Sept. 16, Tashjian Feb. 4, Tashjian May 5, Birdsey Oct. 16, Braden Nov. 8, Fro-mson July 3, Hammitt et a1. Dec. 4, Colbath Feb. 9,

FOREIGN PATENTS Germany July 4,

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