Composite floor system - Patent Review 4454695

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DESCRIPTION OF THE INVENTION

This invention relates to a composite floor construction, and more particularly to a composite open-web steel joist and concrete floor construction for use in the construction of buildings.

In the past, floor construction has used open-web steel joists placed in position spanning structural supports and a concrete slab poured on decking supported by the joists. Generally, an open-web steel joist is a joist in the form of a truss having horizontal top and bottom chords joined by a web comprising tension and compression members triangulating the space between the top and bottom chords.

While the chords may be of many shapes, typically, the top and bottom chords each comprise a pair of steel angle bars, the top chord angle bars being arranged with one leg of each bar extending horizontally outward at the top of the truss, and the other leg of each bar extending downwardly on opposite sides of the web. The bottom chord angle bars are arranged with one leg of each bottom chord angle bar extending horizontally laterally outward at the bottom of the truss, and the other leg of each bottom chord angle bar extending vertically upward on the opposite sides of the web. Decking for supporting the concrete slab is laid on and fastened to the horizontal leg of the top chord angle bars at the top of the joist, and a concrete slab poured on the decking. In this typical construction, there is no structural integration of the concrete slab and joist since there is no anchoring of the concrete slab to the joists, and the slab and joists function as separate entities with the slab constituting dead load on the joists without contributing materially to the strength of the overall structure.

In another construction, the upper ends of the web members project upwardly above the upper horizontal legs of the top chord angle bar for anchorage in the concrete slab to form a composite slab and joist construction in which the slab may, to some extent, become a compression member sharing part of the load. It has been found that this type of construction does not obtain the full potential of a composite slab and joist construction, and has certain disadvantages, for example, the effective anchorage is between the slab and the upper ends of the web members so that transfer of stress between the joists and the slab occurs only at the upper ends of the web members. Furthermore, the slab is necessarily placed above the level of the supporting structure for the joists.

In addition, the decking is formed with slots to enable the web member to protrude into the concrete forming the composite section. One problem in this method is that the slots must be exactly aligned along the length of the building and the joist must also be perfectly aligned. If the slots are not perfectly aligned as the material is placed as construction proceeds, the offset between the slots increases.

One attempt to remedy the problems associated with composite floor constructions is disclosed in U.S. Pat. No. 3,362,121, which describes an open-web steel joist in the form of a truss having a web, a top chord and a bottom chord. The top chord comprises a pair of steel angle bars arranged with one leg of each of the bars extending horizontally outward from a position on the truss below the top of the truss, and the other leg of each bar extending upwardly to the same height on opposite sides of the web and terminating below the top of the web. Decking is laid on the horizontal legs of the top chord, and concrete is poured on the decking to embed the vertical legs of the top chord angle bars and the upper ends of the web in the concrete slab to create a composite floor structure.

In both of these constructions, the top chord is below the top of the web member. This construction is weaker in design than the standard joist construction wherein the top of the top chord is aligned with the top of the web. Accordingly, these constructions require heavier members.

Accordingly, an object of this invention is to provide an improved composite floor system which is easy and fast to erect, economical, and which provides improved load carrying capacity.

Still further, it is an object of the invention to provide a composite floor system using a joist in which the upper chord of the joist insures composite action with the concrete deck with a high safety margin.

Still further, it is an object of the invention to provide a composite floor system having less deflection, bounce, vibration and sound transmission as compared with prior floor systems.

It is still another object of the invention to provide a composite floor system having increased lateral diaphragm action.

In accordance with the invention, a joist used in forming a composite concrete floor system comprises a truss which has a top chord, a bottom chord and a web, including tension and compression members in the space between the top and bottom chords secured to the top and bottom chords. The top chord has a pair of metal bars, each having an angle shape in cross section and each having a vertical leg and a horizontal leg. The vertical leg of the first bar extends to a height above the vertical leg of the second bar, and the top of the web extends to a point below the top of the vertical leg of the second metal bar. The vertical legs of the top chord are spaced from one another to permit concrete when poured, to form the composite floor system, to flow between the vertical legs. This joist construction permits internal bonding between the concrete slab and joist.

In accordance with another aspect of the invention, a composite floor system comprises a plurality of metal joists, the joists being in the form of an open-web truss having a top chord and a bottom chord and a web comprising tension and compression members in the space between the top and the bottom chords. The top chord includes first and second metal bars each of angle shape in cross section, and each having a vertical leg and a horizontal leg. The vertical leg of the first bar extends to a height above the vertical leg of the second bar, and the top of the web extends to a point above the top of the vertical leg of the second metal bar and below the top of the leg of the first metal bar. The vertical legs of the chords are spaced from one another by the width of the web which is held between them. Decking material is supported between the horizontal legs of the top chords of adjacent trusses, and a concrete slab is formed over the top of the decking and truss so that the top chord and the top of the web become embedded in the slab, and the concrete, when poured, flows between the inner faces of the vertical legs of the top chord to provide strong interlocking between the concrete slab, decking, top chord and web. Means are provided, which project between the lower surfaces of the horizontal legs of the top chord metal bars, to close the space between the horizontal legs of the bars of the top chord to prevent concrete from leaking out from between the vertical legs.

These and other objects and features of the invention will become apparent to a worker skilled in the art when taken in conjunction with the drawings, in which:

FIG. 1 is a perspective view of a portion of the floor system showing two joists supporting steel decking between the laterally-extending top chords and overlaid with a poured concrete slab, the steel decking and poured concrete slab being partially broken away in the rear to expose portions of the joists;

FIG. 2 is a front elevation view of the portion of the floor system shown in FIG. 1;

FIG. 3 is a section taken along lines 3--3 of FIG. 2 and looking in the direction of the arrows; and

FIG. 4 is an enlarged view of a portion of the joist of FIG. 1 before the concrete slab is poured showing the vertical legs of the top chord angle bars and the top portion of the web between the vertical legs of the top chord.

Referring to FIG. 1, there is shown a portion of a composite floor system including a pair of identical joists 10, 12, each having a top chord 14, a bottom chord 16, and a web 18 comprising tension and compression members in the space between the top and bottom chords. Bottom chord 16 includes two metal bars 20, 22 having an angle shape, each having a vertical leg 24 and a horizontal leg 26; the height of the vertical legs 24 preferably being the same. The vertical legs 24 of the two bars in the bottom chord are spaced apart by the width of web 18 which is secured between the vertical legs 24.

The top chord 14 includes two metal bars 28, 30 having an angle shape. Metal bar 28 has a horizontal leg 32 and a vertical leg 34, and metal bar 30 has a horizontal leg 36 and a vertical leg 38. The top of vertical leg 38 extends above the top of vertical leg 34. Vertical legs 34 and 38 are spaced from one another by the width of web 18 which is secured to the top chord between vertical legs 34 and 38. As best seen in FIGS. 2, 3 and 4, the top 40 of each leg of web 18 extends to a point below the top of vertical leg 38 and above the top of vertical leg 34. Preferably, the top of web 18 is aligned with the top of vertical leg 38.

To form a composite floor system, a plurality of spaced open joists span the open spaces between two building supports with the lower surfaces of opposite ends of horizontal chords 32 positioned on the supports as is well known in the art. Metal decking 42, which is preferably corrugated, as shown, is supported between the horizontal legs 36 of adjacent joists 10, 12. A concrete slab 44 which may have reinforcing material 46 is poured over the metal decking. The poured concrete flows between the vertical legs 34, 38 of the top chord 14 of each joist to produce an intimate bond between the top chord 14, the web 18 and the metal decking 42. Tape 48, or other conventional material, seals the bottom of the opening between the vertical legs 34, 38 of top chord 14 to prevent concrete from flowing out between the vertical legs 14.

The unequal height of the vertical legs of the top chord provides a continuous high chair permitting the reinforcing material to be draped over the supports, thereby allowing a greater proportion of the top chord to be encased with concrete, thereby reducing the possibility of cracks forming along the supports.

In one particular embodiment of the invention, all joists are designed in accordance with the American Institute of Steel Construction. The top and bottom chord members are formed of hot-rolled angles preferably having a minimum yield stress of steel of 50,000 psi. All web members are designed to equal or exceed Steel Joist Institute specifications. The top chord consists of two angles, one being typically 21/2 by 2 inches and the other being typically 11/2 by 2 inches. In forming the composite floor system, the joists are typicaly placed on 5-foot centers. The length of the joists typically range from 5 to 30 feet or more, and are welded or bolted to the building supporting members before the metal deck is placed. The metal decking should be high tensile, uncoated or galvanized steel with the gauge of the steel dependent upon the spacing of the joists. For joists spaced on five-foot centers, 24 gauged steel decking can be used. The metal decking is fastened or placed to the horizontal legs of the upper chord, for example, by welding. Typically, the reinforcing material should be welded wire fabric or rectangular mesh with an equal cross section.

While there has been described a specific preferred embodiment of the invention, those skilled in the art will realize that modifications and changes can be made while still coming within the scope of the invention, which is set forth in the appended claims. For example, an additional shear connector can be welded to the top chord between the web members to provide increased composite action.

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