US2510958A - Composite floor of metal and concrete - Google Patents

Description

June 13, 1950 L. coFF I COMPOSITE FLOOR 0F METAL AND CONCRETE 3 vSheets-Sheet l Filed Feb. 20, 1946 WITNESSES INVENTOR 72m ma@ June 13, 1950 L. coFF 2,510,958

couposm: FLooR oF METAL AND CONCRETE Filed Feb. 2o. 194e :s sheets-sheet 2 Fig. 4

w/TNEssEs Y BY W ia i l /NvE/vTo'R June 13', 195o L. COFF 2,510,958

COMPOSITE FLOOR 0F METAL AND CONCRETE Filed Feb. 20, 1946 l 3 Sheets-Sheet 3 Fig. 5a

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-wllvEssEs BY @124mg mvENToR Patented June 13, 1950 UNITED STATES PATENT OFFICE COMPOSITE FLOOR OF METAL AND CONCRETE Leo Coil, New York, N. Y.

Application February zo, 1946, seria1No.'s49,o1o In Great Britain July 4, 1945 (Cl. 'l2-70) 12 Claims.

The present invention relates toimprovements in the construction of composite structures, and

more particularly to such composite structures away from the concrete layer as the shearing stresses will readily overcome the bond between the two construction elements. This condition is extremely undesirable since the concrete slab will not bear its proper share oi' the load.

Various remedies have been devised in the form of auxiliary bonding elements, such as spirals, angles, stirrups, and the like, which are welded to the steel shape and mechanically engage the concrete. These devices are suiilciently effective after the concrete slab has hardened, provided that they have adequate strength to withstand the considerable shear of the loaded structure. The latter requirement tends to increase their first cost, particularly since the bonding devices must be designed for ample safety margin under maximum load conditions. being completely imbedded in the concrete and therefore not subsequently accessible for inspection, adjustment, or replacement. A further disadvantage is that the steel shape will be prestressed as it sags under the weight of the concrete being poured, should conditions make it impractical to support the structure at intermediate points during the hardening process.

A principal object of the invention is to provide, in a structure of the above kind, simple and effective means assuring cooperation between the concrete slab and the metallic support, whereby new forces are introduced to counteract the shearing stresses; this to such an extent that the bond between concrete and steel, enhanced by a slight anchorage such as roughening (knurling) of the upper ange surface, should sumce to prevent displacement oi the slab relative to its support.

Another object of the invention is to provide shear-controlling means adjustable to diierent lpeak loads, permitting of prefabrlcation and convenient on-the-spot adaptation to prevailing conditions.

A further object is to provide shear-controlling means that is readily accessible for purposes of reinforcement. replacement, or readjustment.

Still another object is to provide a method o1' manufacturing composite structures of the kind described whereby prestressing of the supporting shape is avoided, even in cases where it is not feasible to support the steel member during the hardening process; this to assure cooperation of the slab with the beam for dead load as well as live load.

Additional objects will become apparent as the description proceeds with reference to the accompanying drawing, in which several embodiments of the invention are illustrated by way of example.

In the drawing- Figs. 1 and 1a show, in longitudinal elevation and in cross section respectively, an I-section steel girder according to normal practice:

Figs. 2 and 2a show, in longitudinal elevation and in end view respectively, an embodiment of the invention as applied to such a composite structure;

Figs. 3 and 3a, in views similar to those of the preceding figures, show a modification;

Figs. 4 and 4a are longitudinal and cross-sectional respectively of a construction according to the invention, embodying another modification;

Fig. 5 is an end view of a pair of beams similar to the one of Fig. 2, supporting a common layer of concrete, the structure having been prestressed according to a method shown in detail in Figs. 7 and 7a;

Fig. 5a is a longitudinal sectional view illustrating a modification of the method for prestressing the tension wires before laying the concrete;

Fig. 6 is a cross-sectional view of a pair of beams supporting a common layer of concrete. the structure having been prestressed according to another modiiication of the method indicated 1n Fis. 5:

Fig. 6a is a fragmentary section along line A-A of Fig. 6;

Figs. 7 and 'Ia show respectively, on a larger scale, an end view and a fragmentary side elevation of a beam as illustrated in Fig. 5.

Figures 1 and 1a show a steel or other metal rolled section or girder I, constituting a beam having its ends resting freely on supports S of any kind. 2 indicates a slab or layer of concrete supported by the upper flange 3 of section I. The weight of the concrete layer 2 and any additional load thereon will cause a deflection of the structure which will progressively increase from the top surface of concrete slab 2 to the lower surface of section I. Horizontal shear stresses 4 and vertical shear stresses 5 will come into play and by reason of the former relative movement will occur between concrete layer 2 and nange 3 in longitudinal direction oi' shape I. These are the conditions which apply to normal structures comprising concrete slabs supported by metal beams or girders wherein the bond between the concrete and the metal surfaces is not sufficient to counteract effectively the horizontal shear that arises.

As already indicated, the main object of the invention is to introduce new forces acting against the horizontal shear stresses. According to the invention, this result is accomplished by the provision of a metallic tie as illustrated in Figs. 2 and 2a.

We shall assume, for the moment, that the shape I can be supported at intermediate points by shores S' and S". Vertical plates 6a are inserted above one or more of these points between the two flanges of the shape and serve as an anchor for a transverse brace, such as the pin 6. Generally, the number of transverse braces 6 will depend on the length of the structure. Beneath the pins 6 pass tension' wires 1 of high yield point which are anchored at their ends to angle plates 8 by means of nuts I1. These nuts can also be used for applying tension to the wires 1 before the concrete is laid, thereby lifting the beam I from the shores S'. If this tension is just sufficient to counterbalance the weight of the slab 2, pouring of the concrete will bring the beam I back into its original position without letting the structure sag after the shores S' have been removed. Loading of the structure will further tension the wire tie 1; this tension has a horizontal component 9, acting upon the layer 2 through angle plates 8, and a vertical component I0, acting upon the girder I through pins 6. Whereas the forces 9 will tend to increase the deflection of the slab 2, forces I will simultaneously limit the downward movement of the shape I; thus contact between layer 2 and flange 3 will be maintained under varying load conditions.

The wires 1 must be free to slide longitudinally throughout their length; if the steel shape I is to be encased in concrete, housings must be provided around the pins 8, and the wires either coated or sheathed so that they are not bonded to the concrete.

As an alternative to stressing the wire tie before the concrete is poured, this may also be done after the dead weight has been applied; tensioning of the wires will then correct the deflection of the composite structure. Again the tension may be adjusted to such a value that the composite section is deflected upward when not loaded, to an extent equal to the deflection produced by the maximum load expected. Thus the structure receives an initial camber which is wholly or partly absorbed by the load. In this case, no break of bond is required between the wires 1 and the concrete encasement, if any, of girder' I, provided the concrete of such encasement was allowed to harden while maxlmum stress was applied to the wire tie (e. g., by loading the structure).

It is obvious that in the absence of deection there is no shear between the concrete slab and the steel shape; hence the closer We are to this condition, the less bond is required in the contact plane for securing full cooperation. On the other hand, it should be observed that the initial camberA must not be driven beyond a certain limit, as otherwise the eilect of the forces 9 will be reversed. Thus, under certain load conditions, the composite structure of Fig. 2 may be advantageously replaced by the modification shown in Figs. 3 and 3a.

Instead of bearing a slab of uniform thickness, steel shape I in Fig. 3 supports a concrete layer II of arched or strongly haunched form. The wires 1 are anchored to the plates 0a between the rises of adjacent arches II' and II". This construction allows the use of shallower girders I for the same over-all depth, since deflection can be accurately regulated by the tension of the tie 1. Moreover it enables the anchorages 8a for that tie to be disposed at a more convenient level as compared with the angle plates 8 of Fig. 2, a fact that results in additional leeway in the distribution of deflectioncontrolling forces. A further advantage is that stressing of the concrete layer through tensioning of the wires need not impart compression to the steel shape, which may be important especially when the latter is not encased.

It will be appreciated that tension of the wires 1 can be adjusted in all instances so as to compensate for volume changes due to shrinkage and plastic flow of the concrete; such adjustment may be made either prior or subsequent to the hardening of the concrete layer.

The invention is not limited to such cases where the concrete terminates at the ends of the individual beam or girder, but may be readily adapted to composite structures having continuous layers extending over several spans. This is illustrated in Figs. 4 and 4a. The junction point of two adjacent beams I rests on a support S which may consist of a similar beam transversely arranged. It will be noted that angle plates 8 have been omitted; instead, supporting elements I2 are xed to the upper flanges of girders I, having a, function similar to that of pins 6 in serving as a bearing for the wires 1. 'I'he wire ties 1 of adjacent girders are joined together by means of a turnbuckle I3 which can also be used to provide adequate tension, in a manner analogous to that of screws I1. As before, if the structure is not to be prestressed, the

wires 1 must be coated or sheathed and will receive their tension from the loads. The portion of the wires extending between the supporting elements I2 constitutes the negative tension flange; a compression flange may be provided beneath the ends of adjacent girders I, e. g. by a concrete layer I4 cast between the girder flanges, if the latter are not strong enough or not adequately connected to transfer compression.

In many instances, as in the case-of roof purlins, it will not be convenient to support the structure at intermediate points during hardening of the concrete. The remaining figures illustrate a method of erecting the aforedescribed composite sections under such conditions. This method consists in providing a load or reaction, temporary or otherwise, to counteract the increasing pull of the wires during concreting. If the wires are to be prestressed, the reaction must be provided even before the dead load is on the .structure. If the reaction is to be temporary, it will be removed after the concrete has hardened, resulting in a transfer of the stress to the concrete layer.

A temporary load or reaction is illustrated in Fig. 5 and again, on a larger scale, in Figs. 7 and 7a. It consists of a round bar or tube I8, projecting through the bore I9 of brackets I 9a and bearing with its ends against removable plates 23 that span the slotted or recessed angle plates I5. This bar I8 should be coated or sheathed to permit its removal after the surrounding concrete has set. Before the concrete is poured, or before the hardening process is completed, the wire tie 1 is adjusted to the desired stress, thus imparting compression to the member I8 which will act as a reaction in substitution for the concrete slab. After the bar I8 has been withdrawn, the plates 23 may be reinserted to help transfer the stress of the wires I to the concrete layer 2.

In Fig. 5a, the temporary reaction is formed by tension means. A tension member is provided between brackets 20a mounted on the lower flange of the girder I, and the applied tension is adjusted by turnbuckle 2| until the desired load can be carried without undue deflection.

A permanent reaction is shown in Figs. 6 and 6a, consisting of a row of pre-cast blocks 24 which are disposed along the girder Il between side plates which also serve to support the ends of pins E. The blocks 24.are scored or indented `on their surfaces and are provided with recesses 22, for mechanical engagement with the concrete that is subsequently poured over them. This concrete may form an arched layer II similar to the one shown in Figs. 3 and 3a. An effective bond will result if the blocks 24 are thoroughly wetted before the layer II is cast.

Alternatively to pre-cast blocks 24', the permanent reaction or load producing member may consist of a horizontal column of wood, plywood, asbestos bricks, hollow tiles, or the like. If precast concrete is used, it may have a strength of 8,000 to 10,000 p. s. i. Since this reaction member will be permanently embodied in the concrete slab or arch, the proportions of the compressive force which will be respectively absorbed by that member and by the concrete layer will be a function of the are-as and of the moduli of elasticity, comparab'y to a reinforced concrete column.

It is to be understood that the invention is not to be construed as limited to the embodiments described, and that it is on the contrary capable of numerous adaptations and modifications without departing from its scope as defined in the appended claims.

What is claimed is:

1. A composite metal and concrete structure, comprising a concrete layer, a metallic support having a substantially fiat, horizontal bearing surface, said layer resting on said bearing surface, at least one metallic tie member extending underneath said layer and longitudinally of said support, anchor means bearing endwise on said layer, said anchor means being in engagement with respective ends of said tie member and keeping the latter under tension, thereby applying pressure from said tie member to said layer, and bracing means secured to an intermediate portion of said supportand engaged by said tie member, said bracing means applying a generally upward acting force to said portion.

2. -A composite mtal and concrete structure, comprising a concrete slab, a metallic shape having a, substantially horizontal flange supporting said slab and a substantially vertical web holding up said flange, a plurality of substantially horizontal projections extending from said web at points spaced longitudinally of said shape, anchor plates bearing on the ends of said slab, and a pair of wires under tension interconnecting said anchor plates and extending underneath said slab at opposite sides of said web, thereby exerting pressure upon said slab, said wires engaging said projections and applying a generally uplward force to said shape at said longitudinally spaced points.

3. A structure according to claim 2, wherein said horizontal flange has a knurled surface cooperating mechanically with saidconcrete slab.

4. A structure according to claim 2, wherein said projections comprise pins extending through said web and projecting from both sides thereof.

5. A composite metal and concrete structure. comprising a plurality of longitudinally adjacent metal beams each having a substantially flat, horizontal bearing surface, a concrete layer resting on all of said bearing surfaces, bracing means fastened at intervals to said beams, supporting elements mounted on either side of the junction point of adjoining beams, wire means bridging the junction between adjoining beams, said wire means extending underneath said bracing means and passing through the concrete layer above said supporting elements, anchor means securing the ends of said wire means to the structure, and tensioning means maintaining said Wire means under tension, thereby tending to raise portions of said structure adjacent said bracing means relative to said supporting elements. 6. A structure according to claim 5, wherein a portion of said layer extending above the junction point of adjacent beams surrounds part of said wire means, said wire means being adapted to slide freely in said portion of said layer.

7. A structure according to claim 6, further comprising sheathing means embedded in said portion of said layer and surrounding said wire neans to facilitate sliding movement of the lat- 8. A structure according to claim 5, wherein said tensioning means include at least one turnbuckle inserted in said wire means intermediate two of said supporting elements, said wire means being adapted to slide freely in the vconcrete layer above said elements.

9. A method of erecting composite metal and concrete structures wherein a layer of concrete is supported by a metallic shape, comprising the steps of horizontally supporting said metallic shape, subjecting said shape to upward deflection by stressing same, pouring said layer, allowing said layer to harden, anchoring an elastic tie member under tension endwise to said hardened layer, and supporting at least one intermediate point of said shape on said tie member to counteract the weight of said layer.

10. A method according to claim 9, wherein the step of stressing said shape includes arranging a substantially non-compressible column longitudinally of said shape, anchoring said tie transferred from said column to said layer after 5 the latter has hardened.

11. A method according to claim 10, further comprising the step of removing said column after said layer has hardened.

12. A method according to claim 9, wherein the step of stressing said shape includes placing the lower face of a said shape under compression by a temporary force before the layer is poured, and releasing the temporary force effecting said compression after the layer has hardened.

LEO COFF.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 520,491 McCarthy AMay 29, 1894 960,305 Gilbreth June 7, 1910 1,000,088 Haas Aug. 8, 1911 1,813,338 Batel July 7, 1931 2,016,616 Schaub Oct. 8, 1935 2,153,741 Cobi Apr. 11, 1939 2,382,139 Cueni Aug. 14, 1945 FOREIGN PATENTS Number Country Date 464,361 Great Britain Apr. 16, 1937 117,344 Great Britain -..July 18, 1918

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