Shear Connectors

Abstract

A shear fastener for securing concrete decking relative to a supporting structure in a laminar building structure. The fastener includes a stud, an enlarged means at one end, and a spacer adapted to enclose the stud shank and isolate it in spaced relation from the encapsulating concrete to permit bending moments to be applied to the stud shank rather than a straight shear stress when the decking shifts relative to the supporting structure.

Description

BACKGROUND

Current building practices for offices, industrial and multiple dwelling construction have gravitated strongly to various modifications of concrete structures. Many involve a sequential fabrication of floor after floor of reinforced concrete, wherein wooden forms are sequentially erected for each floor and its supporting columns with steel wire and rod being utilized to absorb certain stresses which normally would result in a failure of the concrete. Another type involves the use of prestressed concrete members which are fabricated either on-site or off-site and erected in building block style with appropriate connection means.

The type of concrete construction that the present invention is primarily concerned with is related to the first type mentioned above except that the basic loads are carried by beams or joists, generally, the steel bar joist being the preferable form because of its low weight to load carrying ratio. A corrugated sheet material which may be steel, reinforce d asbestos type or of other suitable material is laid transversely to the beam or joist with the troughs and ridges of the corrugations generally being laid perpendicular to the beams or joists. A fastener is applied to secure the sheet to the supporting structure and concrete is then poured onto the sheet material, which serves as a permanent form, and encapsulates the fastener which normally projects upwardly from the sheet material. Fasteners previously utilized for such assemblies have taken the form of either weld studs or screws. In the case of weld studs it has been found that the welding operation is complicated by the fact that most steel corrugated sheet material is galvanized and this results in a difficult welding operation plus destruction of the galvanized coating thereby leading to possible corrosion of the sheeting and joint. The other blind application joints, utilizing screws, normally must be predrilled and tapped or alternatively a thread-forming screw used to form its on threads or a nut applied to the blind end of the screw.

In both forms of fastening, mentioned above, the stud is totally encapsulated or rigidly captured in concrete from its juncture with the sheeting to its enlarged head spaced from said juncture. Thus, during wind loading, seismic shock or any other form of stress directed to a structure utilizing such fastenings, there is a force applied which tends to laterally shift the concrete deck. Such a movement of the concrete transfers a shear load to the stud at its juncture with the supporting structure and the return of the structure to its initial position applies a shear load in the reverse direction. While it is thought that there is some tendency during such a shifting for a tensile load to be applied to some fasteners, such tensile loading is minor in comparison to the shear load.

SUMMARY

The present invention contemplates a shear fastener for use in laminar building structures subjected to transverse forces by wind loading, seismic shock and other external stresses where floor and roof decking has a tendency to shift when the structure is stressed. Where the prior art rigidly encapsulated the fastening means used to secure the various strata of the laminate, the present invention provides means to isolate the stud fastener from the concrete at least at the juncture of the stud with the supporting structure and for a substantial portion of its axial extent whereby shifting of the concrete deck results in the application of a bending moment to the stud rather than the application of a shear load.

The invention also contemplates the use of such a fastener assembly of a stud and spacer or isolating means in a system which includes a supporting beam or joist, a permanent corrugated decking form and a concrete deck for use as a floor or roof component in a building structure.

DESCRIPTION OF DRAWINGS

FIG. 1 is an elevational view in partial section showing system utilizing a fastener incorporating the teachings of the present invention;

FIG. 2 is an enlarged elevational view in partial section of a portion of the system shown in FIG. 1;

FIG. 3 is an elevational view in partial section of a fastening means of the type contemplated by the present invention;

FIG. 4 is an elevational view in partial section of a preassembled fastening means;

FIG. 5 is an elevational view in partial section of a modified form of the teachings of the present invention;

FIG. 6 is an elevational view in partial section of another embodiment of the present invention;

FIG. 7, 8 and 9 are elevational sectional views of three modifications to the fastening means wherein stop means are included;

FIG. 10 is a further modification of the head of the fastening means of the present invention;

FIGS. 11 and 12 are partial sectional elevational view illustrating modifications to the spacer means of the present invention;

FIGS. 13 and 14 are elevational views in partial section showing nonblind type applications of the present invention; and

FIGS. 15, 16 and 17 are elevational views in partial section showing modifications to the stud element utilized in the present invention.

DESCRIPTION

Referring now to the drawing wherein similar parts are designated by similar numerals throughout the description, a laminar construction of the type contemplated by the present invention generally includes a supporting structure 20 having a beam 22 and corrugated sheeting 24; fastening means 26 and a concrete deck 28.

The supporting structure 20 utilizes a beam 22 which can take the form of an I-beam, a wood beam or preferably a bar joist which includes an upper and lower runner and connecting bar structure which because of its geometric relationship to the runner forms a truss-type structure. It is generally chosen because of its low weight to load-carrying ratio. The secondary element of the supporting structure is corrugated sheeting 24 which normally has its valleys 30 and crests 32 running transverse to the axis of the beam 22. The corrugated material can be fabricated from galvanized steel or may also be constructed of a reinforced asbestos type of material. Other materials will be apparent to those skilled in the art so long as the material chosen has a fireproof quality since in this form of construction the supporting structure comprising the beam and sheeting remains in place throughout the life of the building and must have this quality of being fireproof.

The fastening means 26 generally includes a stud 40, an enlarged means or head 42 at one end of the stud 40, means for fastening the stud to the supporting structure, and an isolating or spacer means 44. In the preferred embodiment shown in FIG. 3 the stud 40 is provided with threads 46 through a substantial portion of its length and a washer base 48 on a hex head to provide a maximum laterally extending engaging means, for purposes best set forth hereinafter. To facilitate assembly of this screw with the supporting structure a drill point 48 is provided at the opposite extremity of the screw. Surrounding a substantial portion of the axial extent of the threaded shank 46 is an isolating or spacer means 44. In this preferred embodiments the spacer includes a substantially frustoconical portion 50 and a cylindrical portion 52 integral with the minor diameter of the conical portion 50. The internal diameter of the cylindrical portion is equal to or slightly less than the crest diameter of the thread 46 so that the stud 40 can be preassembled by an interference fit with the spacer means 44. The spacer 44 can be a drawn member or in the case of the present embodiment a rolled split member with the edges of the split being maintained in abutting relationship. In the present embodiment a power tool is applied to the hex faces of the head 42 and the drill point 48 is brought into contact with a valley 30 of the corrugated sheeting 24 when it is positioned in superposed relation to a beam 22. The rotation of the fastener results in the drill point 48 creating an aperture through the sheeting 24 and the beam 22 with the threaded portion 46 forming its own thread. The fastener assembly 26 progresses axially until such time as the bottom or major end of the conical portion 50 is brought into engagement with the upper surface, as viewed in the drawing, of the valley 30 with the flange 46 being brought into intimate relationship with the cylindrical portion 52. At this point the driver torques-out and ceases driving. Thus, the threaded shank 46 is isolated from its surrounding environment by the spacer means 44 through a substantial portion of its axial extent. The screw is thus sealed at the juncture of the cone 50 with the valley 30 and the cylindrical portion 52 with the flange 46. Concrete of a suitable mixture is then poured on top of the supporting structure and encapsulates the fastening means 26 as well filling the valley 30 and covering the crest 32. Preferably the fastening means 26 has an axial extent such that the enlarged head 42 is positioned adjacent to or above a plane passing through the crest 32 of the corrugated sheet 24 thereby insuring captivation of the enlarged head 42 within the concrete at or above a shear line falling in the plane passing through the crest 32. In this fashion any movement in a vertical direction, as viewed in the drawings, will apply a tensile load to the fastener stud 40 through the head 42.

Thus, when a transverse load is applied to the concrete deck 28 the fastening means 26 can bend at its juncture with the supporting structure as represented by the sheet of material 24 and the beam or joist 22. As has been previously pointed out the prior approach was to totally encapsulate the stud and thereby create a pure shear force to be applied to the fastener at is juncture with the supporting structure. As can be recognized a bending moment can be repeated a great number of times without resulting in total fatigue of the fastener as when compared with the direct application of a shear load.

It will be recognized that other forms of studs can be utilized for the fastening means. For example, the sheet and beam can be predrilled or can be drilled at the site and a thread-forming screw be utilized as the fastening means. A weld stud can be spot welded to the joist 22 with a suitable bead weld being provided around an aperture that is predrilled in the corrugated material 24 to thereby retain the stud in the position. Still another form could be a drive stud where a hydraulic or explosive force is applied to the stud to pierce the corrugated material and the joist with the spacer or isolating means 44 limiting the axial position of the stud. Still other forms will be hereinafter described.

Referring now to FIGS. 4 through 17 various forms of isolater or spacing means 44 will be described in conjunction with stud forms. While the preferred embodiment disclosed an interference fit between the cylindrical section 52 and the threaded shank 46 for preassembly purposes it may be desirable to provide a mechanical interlock which would restrain the axial relative movement between the spacer means and the stud while permitting rotative movement between the two. FIG. 4 discloses a threaded shank 46a having an unthreaded portion 60 adjacent the head adapted to accept an inwardly directed flange 62 for preassembly of the screw and spacer. While a frustoconical form was previously described to isolate the stud from its surrounding environment it would be totally feasible to utilize a cylindrical form of spacer 64, as shown in phantom in FIG. 4, with a plurality of laterally extending flange means 66 for purposes of engagement with the concrete to provide attachment therewith and to accept a tensile load.

FIG. 5 discloses a threaded screw 46b having an increased diameter 70 which is greater than the crest diameter of the threads of the screw to form a shoulder 72 adapted to bear on top of the crest 32b whereby the enlarged head 42b with its flange 46b can be captivated within the concrete for fastening purposes. In this case the corrugated sheeting 24b with its associated crest 32b serves as the isolating means for the screw 46b which is driven directly through the crest 32b into the beam 22b.

A further modification of the present invention can be seen in FIG. 6 wherein the valley 30c has a portion of its horizontal extent dimpled or cupped upwardly to form an integral spacer means 44c to provide a conical portion 50c and a cylindrical portion 52c which isolates the stud 40c from the encapsulation by the concrete, not shown.

As was previously mentioned, the spacer means 44 can be fabricated at a split sleeve-type member. It will be recognized that if an excessive axial force is applied to the sleeve the split will tend to circumferentially open and thereby permit the ingress of concrete to the screw. To eliminate this possibility one of the forms shown in FIGS. 7 through 9 can be utilized. In FIG. 7 the spacer means 44a is provided with an axially extending cylindrical portion 80 which is a reversely bending extension of the upper cylindrical portion 52d. It will be noted that the lower extremity of the tubular member 80 is spaced a small amount from the lower extremity of the conical portion 50d whereby the portion 50d can be sprung out to provide resilient takeup before the extremity of 80 will contact the corrugated sheet 24 and stop the axial progression of the stud 40d. The modification shown in FIG. 8 utilizes a separate cylindrical member 82 which is substantially coextensive with the spacer means 44e and which will serve as a stop when it contacts the sheet. The modification shown in FIG. 9 employs basically the same technique except that the stop means instead of being a part of the spacer 44f is an enlarged shank portion 70f forming a shoulder 72f at its juncture with the threaded shank 46f. The shoulder 72f forms a stop which limits the axial extent to which the screw shank 46f can be driven into the supporting structure 20f thereby limiting the axial stress placed on the spacer member 44f.

To facilitate bending of the stud 46g it may be desirable in certain instances, to provide a conical or slightly spherically clamping surface 86 adjacent the washer face 46g. whereby the head 42g can be shifted relative to the spacer means 44g. Such a fastener is shown in FIG. 10.

To increase the strength of thinner materials a laterally extending flange 90 can be provided on a spacer 44h, as seen in FIG. 11. The flange 90 provides a certain degree of hoop strength to the spacer and also provides a shoulder or foot for contact with the surface of the corrugated material to provide frictional resistance against spreading or splitting of the spacer 44h, if it is a split member. A similar strengthening means is the inwardly rolled lip 92 at the lower end of the spacer means 44j, as seen in FIG. 12. Such a rolled rim increases the hoop strength and provides a line contact for sealing purposes with corrugated material.

While each of the previously illustrated embodiments have shown the use of a self-drilling screw it is contemplated as being within the purview of this invention to make use of other forms of mechanical fasteners. In FIGS. 13 and 14 the beams 22k and 22m as well as their associated sheets 24k and 24m respectively are predrilled to accept a screw-threaded member 100 and 100m which are inserted from the blind side by axial telescoping through the beam and then the sheet, as the reverse of the techniques mentioned heretofore. In FIG. 13 the spacer means 44k is provided with internal threads 102 in the cylindrical portion 52k which are complementary to the threads of the screw 100. A laterally extending flange 104 is provided for purposes of encapsulation and tensile engagement with the concrete to be poured around the fastener. The modification of of FIG. 14 shows the use of a separate washer face nut element 106 for maintaining the spacer unit 44m in intimate contact with the corrugated material 24m. The function of both of these is substantially identical to previously disclosed embodiments in that they tensilely engage the concrete while permitting bending moments to be applied to the screws 100 and 100m respectively.

In FIG. 15 the stud 40n is welded as at 110 to the beam 22n. The enlarged head 42n in this embodiment is in the form of a sphere. It is contemplated that when the cement encapsulates the enlarged head it will provide a ball and socket type joint between the enlarged head and the cement and permit free bending of the stud 40n under extreme conditions of movement between the various strata of the laminar structure.

FIG. 16 discloses a weld stud 40p which has its free extremity welded, as at 110p and has its enlarged head 42p in the form of a truss head. The function of such a head is similar to the spherical head to provide a broad face for engagement with the concrete for tensile purposes. The last embodiment shown in FIG. 17 utilizes a drive stud 40q having a bullet nose point 120 which when moved axially under great force, either hydraulic or explosive, will penetrate the sheet material 24q and the beam 22q with the spacer 44q serving as a stop means to limit the axial movement of the stud 40q to a point where the head 42q has engaged the upper end of the spacer and the spacer is in engagement with the sheet material 44q for sealing for isolating purposes, as set forth hereinbefore.

In many of the embodiments in the disclosure hereinabove a self-drilling screw is utilized as the stud in the fastening means assembly. Such a screw fastening normally provides a tight fit between the structures which are drilled and in which a thread is formed by the screw. It should be recognized, in the present environment, that such a screw to be functional must be a hardened screw. Conversely, the corrugated sheet material 24 is a thin soft material. Thus, when the various strata of the laminar structure shift relative to one another, the hardened screw which is isolated by the spacer 44 from the surrounding concrete will tend to teardrop or tear the soft thin sheet forming the corrugated material 24, thereby eliminating any shear stresses bought to bear against the stud at its juncture with the supporting structure and permit its bending within the confines of the spacer.

Additionally, the stud 40 can be provided with limited case hardening adjacent its tip or free end which normally is utilized at its point of fastening to the supporting structure with the balance of the axial extent being left in a soft or natural condition which will provide easier bending through greater ductility when it is in the soft condition. This will facilitate the desired end result.

Thus, the principle of this invention permits a small diameter, hardened fastener with a highly tensile value to match the crushing load of concrete by offering a large cross section via the spacer 44. This distributes the crushing force on the concrete over a wide area which can be sustained by the concrete whereas when the axial force is concentrated on a small diameter fastener there is a positive tendency for the concrete to crush and crumble. Further, the method of creating a void around the shank of the fastener can take several shapes, for example, by an axial extension of the cylindrical portion 52 and a foreshortening of the conical portion 50 it is possible to "tune" the fastener and control the degree of load deflection by selection of the void configuration. It should be recognized that while most of the embodiments are indicated as having a cylindrical portion at the top flaring into a frustoconical bottom portion, the spacer could be frustoconical all the way from the top to the bottom with the amount of void created around the shank being contoured so as to control the deflection available in the fastener and thereby bringing about the "tuning" effect.

Other embodiments will be apparent to those skilled in the art but it is the broad intent of the present invention to provide a spacer means for purposes of isolating a stud at its juncture with the supporting structure whereby the stud, as a part of a laminar structure, can be deflected to meet the load-deflection requirements as the strata of the structure moves with wind, seismic and other types of loads. The fastener also, as has been indicated, provides a large area of contact to preclude crushing of the concrete and to balance the high tensile strength of the hardened fastener with the crush rating of the concrete. It is felt that the various embodiments set forth hereinabove accomplish this goal and it is our intent to be limited only by the appended claims.

Claims

We claim:

1. A fastening means for use in a laminar building assembly which includes a supporting structure and a concrete deck superpositioned thereon wherein the fastener means is arranged to secure the concrete deck to the supporting structure, said fastener means comprising associated stud and spacer elements, said stud element having one end adapted to be secured to the supporting structure and enlarged means at the opposite end of the stud element adapted to be embedded in the concrete deck, said spacer element having integral circumferentially uninterrupted cylindrical and frustoconical portions both of which surround the stud element, the cylindrical portion of the spacer element engaging the stud element adjacent the enlarged means over a predetermined axial height which is sufficient to continuously center the stud element relative to the spacer element, the frustoconical portion of the spacer element diverging outwardly from the cylindrical portion in a direction away from the enlarged means of the stud element and terminating in a free end which is adapted to contact the supporting structure, said frustoconical portion having a predetermined axial height substantially greater than the cylindrical portion and having its inner wall surface laterally spaced from the stud element over its entire axial height by progressively increasing radial dimensions as the frustoconical portion diverges away from the enlarged means of the stud element, the spacing of the frustoconical portion form the stud element in planes taken perpendicular to the axis of the stud element being substantially equal throughout the entire circumferential extent of the frustoconical portion, thereby providing an isolated chamber for the stud element enabling bending thereof relative to the one end which is secured to the supporting structure when the concrete deck is shifted relative to the supporting structure.

2. A fastener of the type claimed in claim 1 wherein said stud and spacer element includes means for preassembly, said preassembly means including radially inwardly directed flange means extending from said spacer and protuberance means on said stud adapted to cooperate with said radially directed flange means on said spacer to accomplish axial preassembly of said stud with said spacer but to permit rotation of said stud relative to said spacer.

3. A fastener of the type claimed in claim 1 wherein said supporting structure is apertured and said stud is a screw capable of creating a mating thread in an initially unthreaded aperture in said supporting structure.

4. A fastener of the type claimed in claim 1 wherein said stud includes a threaded portion of a predetermined diameter and an unthreaded portion of a substantial extent adjacent said enlarged means acting as said cylindrical portion, said spacer including a radially inwardly directed flange presenting opposed surfaces acceptable by said unthreaded portion and axially restrained by said threaded portion whereby said stud is rotatable relative to said spacer but axially restrained relative thereto.

5. A fastener of the type claimed in claim 1 wherein said stud is a self-piercing stud adapted to be driven into said supporting structure and having the axial movement restrained by said spacer means.

6. A fastener of the type claimed in claim 1 wherein the free end of said stud spaced from said supporting structure is provided with screw threads, said enlarged means including nut means complementary to said screw and mounted thereon for securing said spacer means in juxtaposition to said supporting member.

7. A fastener of the type claimed in claim 6 wherein said spacer means includes a threaded portion in the cylindrical portion integral with its reduced dimension adjacent the upper extremity for engaging said screw while said opposite enlarged end portion of said spacer engages said supporting structure, flange means extending laterally from said cylindrical portion forming said enlarged means for embedment in said concrete.

8. A fastener of the type claimed in claim 1 wherein said stud and spacer assembly includes rigid means for contacting said supporting structure to control the axial compressive stress exerted by said stud on said spacer.

9. A fastener of the type claimed in claim 8 wherein said means for contacting said supporting structure includes a laterally extending shoulder intermediate the axial extremities of said stud to control the penetration of said stud through said supporting structure.

10. A fastener of the type claimed in claim 8 wherein said means for contacting supporting structure includes an axially disposed rigid element from the smaller dimension of said spacer to a point adjacent to a plane passing through the free end of its enlarged portion.

11. A fastener of the type claimed in claim 1 wherein said spacer includes a laterally extending bearing element at the end of the enlarged portion of said spacer.

12. A fastener of the type claimed in claim 11 wherein said spacing element includes radially outwardly extending flange adapted to bear on said supporting structure.

13. A fastener of the type claimed in claim 11 wherein said bearing element includes a radially inwardly rolled lip adapted to strengthen the hoop characteristics of said spacer when subjected to axially disposed compressive forces.

14. A laminar building assembly comprising s supporting structure, a concrete deck superpositioned thereon and fastening means extending outwardly from the supporting structure, securing the concrete deck to the supporting structure, said fastening means including associated stud and spacer elements, said stud element having one end secured to the supporting structure and enlarged means at the opposite end of said stud element embedded in said concrete deck, said spacer element having integral circumferentially continuous cylindrical and frustoconical portions which surround the stud element, the cylindrical portion of the spacer element engaging the stud element at least at a position axially spaced from the supporting structure for centering the stud element relative to the spacer element, the frustoconical portion of the spacer element diverging outwardly from the cylindrical portion of said spacer element and terminating in a free end which contacts the supporting structure, said spacer element at least at said frustoconical portion being laterally spaced from the stud element for a predetermined axial distance away from the supporting structure providing an isolated chamber for the stud element enabling bending thereof relative to the supporting structure when the concrete deck is shifted relative to the supporting structure.

15. A system of the type claimed in claim 1 wherein said supporting includes a transverse structural member and corrugated sheeting disposed substantially perpendicularly to said member, said stud traversing said sheeting and securing same to said member, said spacer means and said enlarged means projecting upwardly from said sheeting a substantial distance to insure encapsulation by said concrete deck.

16. A system of the type claimed in claim 15 wherein said corrugated sheeting includes ridges and valleys, certain of said valleys including spaced apertures and having axially extending integral tapered hubs serving as said spacer means surrounding said apertures and of such a size as to accept said studs in spaced relation thereto.

17. A system of the type claimed in claim 15 wherein said stud element is a screw which includes a drilling point capable of forming the aperture in said supporting structure at random locations and forming a mating thread in the aperture so formed.