Girder supported reinforced concrete slab building structures with shearing connectors

Abstract: Reinforced concrete slab and girder building structures incorporate shearing connectors with lengthwise support parts to which lengthwisely spaced, transversely extending, rigid load transfer plates affix. A girder structure having one or more lengthwisely extending girders is provided and the shear connectors are fixed to the girders near their support walls below a deck for supporting the slab, the shearing connectors being positioned so that portions of the load transfer plates and support parts project above the girder structure and deck to receive compression forces in the slab which are transferred by the connectors to the girders. The lengthwisely extending connector support parts have connections for carrying a series of lengthwisely spaced rebar rods which embed in the slab when it is poured and transfer compressive load forces to the transfer plates.

Description: This invention relates to reinforced concrete slab building structures wherein shearing connectors are used to transfer compression loads from the slab directly to an underlying girder structure. Coupling induced bending stresses are countered in the system to be described and vertical disengagement of the concrete slab from the girder system is resisted. While my novel connector system is particularly suited to transferring compression forces in the concrete slab due to the load of the slab itself, as well as those imposed by loads which are placed upon the slab, to underlying wood beam girders, a second structural system is also disclosed wherein the underlying girder structure employs steel I-beams. U.S. Patent 4,628,654 is directed to a so-called composite floor structure, wherein underlying, upwardly open steel channel beams are employed which are filled with concrete when the slab is poured, and wherein a series of spaced apart transverse connector plates are employed at spaced intervals over the length of the channel beams. The disclosure in this patent relates to what is termed a reinforced concrete floor slab formed integrally with a plurality of horizontally disposed concrete filled and concrete encapsulated steel channel members. Other prior constructions, referenced in the aforesaid patent No. 4,628,654, mention a structure with I-beam girders in which the upper flanges of the I-beam girders are embedded in the concrete slab, and another construction in which the I-beams are provided along their tops with a series of shear resisting members which are spaced longitudinally along the length of the I-beam and secured thereto. Prior art patent 4,628,654 does not consider nor seek to solve the problems which are encountered when the underlying girder structure consists of wood beams. EP-A-0 717 149 discloses a reinforced concrete slab and girder building structure incorporating shearing connectors. The present invention is concerned with a girder supported, reinforced concrete slab building structure incorporating shearing connectors. Such concrete floors are cast or poured, and cured, on decks resting upon spaced apart girders which span the vertical building support walls. The building walls may be studded wood frame walls or masonry walls, for example, and the wood girders contemplated may be solid timber beams or glued laminated beams to which the wood decking is secured. The wood decking may be tongue and groove boards or plywood decking, or fashioned from other suitable material and, normally, a parting layer, such as a plastic sheet, is used on top of the decking between the decking and the slab. Novel shearing connectors are used to transfer the compressive load forces present in the concrete slab directly to the underlying support girders or beams, and these are provided at the ends of the beams and do not extend the full length of the girder beams. Typically, the particular shearing connectors used depend upon the compressive forces which need to be transferred from the reinforced slab into the girder or beams, keeping in mind that the shearing connectors of the present invention are used near the supported sections of the girders or beams to resist shearing forces and counter bending moments. The excellent results obtained are possible whether wood beams or steel beams are employed in the girder system or assembly. It is to be understood that the invention to be described was developed in the first place for wood girder beams. A steel beam girder structure is also secondarily disclosed which utilizes a related shearing connector system which secures to the upper flange of an I-beam girder and, similarly, extends through the upper decking and the plastic parting layer to embed within the concrete slab. In each instance, connections or passages for the rebar rods are provided in the shearing connectors such that the rebars transfer compressive stresses to the connectors for transmission to the girder beams. These connections are uniformly spaced lengthwisely along the connectors and are disclosed as constituting openings of a size to snugly receive the rebar rods which extend transversely in the slab crosswisely of the connectors. One of the prime objects of the present invention is to provide a building construction incorporating shearing connectors between the slab and girders which accommodate reinforcing rods in a manner such that load is transferred from the rods to the transversely disposed end plates of the connectors, which then impose the load crosswisely to the girder beam length. Still another object of the invention is to provide a building structure of the character described in which the shearing connectors transfer the bending stresses directly to the wood beam girder structure disclosed crosswisely to the grain of the wood. Still another object of the invention is to provide a building structure of the character disclosed wherein the connectors which transfer the load are embedded in the concrete slab, and are so constituted as to provide compression load resistant enclosures in the slab which are filled with concrete during the pouring of the slab. Still another object of the invention is to provide a building structure of the character described wherein a composite flooring structure functions to very efficiently and reliably transfer slab compression loads directly to the underlying girder system. Still another further object of the invention is to provide a building structure of the type described which is relatively economical to construct using shearing connectors which can be factory assembled, and need not be fabricated on the job. These and other objects, advantages and features of the present invention will become more apparent from the following detailed description when taken together with the accompanying drawings. Figure 1 is a schematic fragmentary, sectional perspective plan view of the building structure with various components broken away to illustrate underlying elements of the structure; Figure 2 is a similar fragmentary schematic view of the underlying girder structure with the shearing connectors shown fixed in position, the view being of the underlying girder and support wall system only; Figure 3 is an isometric view of a shearing connector which is used in a one bay frame; Figure 4 is an enlarged front elevational view thereof; Figure 5 is a top plan view of the connector shown in Figure 4; Figure 6 is an end elevational view of the shearing connector shown in Figure 4; Figure 7 is a schematic, fragmentary, sectional, elevational view of one end of a building structure having a wood beam girder system, the arrows illustrating force application and force resistance; Figure 8 is an enlarged perspective partly exploded plan view schematically showing shearing connector applied to an underlying wood beam girder; Figure 9 is a reduced scale perspective plan view illustrating the application of wood decking to the girder system; Figure 10 is a side elevational view depicting a more elongate shearing connector which is used in two bay frame structures; Figure 11 is a similar side elevational view showing the still more elongated shearing connector which is used in three bay frame structures; Figure 12 is a schematic sectional elevational view showing shearing connectors in use in a two span girder system; Figure 13 is a schematic load system view illustrating the load forces applied; Figure 13a is a graphical illustration the bending moment for a simple girder; Figure 13b is a bending moment graphical illustration for the present invention; Figure 13c is a similar view for a girder with forces applied in accordance with the present system; Figure 13d is a graphical representation of compressive forces in the slot. Figure 14 is a schematic, perspective, elevational view of a related building structure in which I-beams are used in the girder system in place of the formerly used wood beams; Figure 15 is a similar fragmentary view on a slightly enlarged scale; Figure 16 is a similar view with the concrete slab removed; Figure 17 is a schematic, fragmentary perspective view showing one of the girders with the connector fixed to the upper surface of the I-beam girder; Figure 18 is a similar isometric view showing the connectors fixed in position on the I-beams; and Figure 19 is a similar perspective elevational view in which wood decking has been partially applied to the underlying I-beam girder system. Referring now, more particularly, to the accompanying drawings and in the first instance to Figures 1-12 wherein I have illustrated a construction in which the underlying girder supports are wood beams, a letter W indicates vertical supporting walls forming a part of the building structure which I have generally designated BS. The wood beams which make up the underlying girder system or assembly, generally designated GS, include wood beams 10 (Figure 2) connecting the wood beams 11 which extend from one wall W to the other wall W. In Figure 2, the wood beams 10 and 11 are shown as received in cutouts or recesses 12 provided in the walls W. The support walls W can be wood or masonry walls, or poured concrete walls, or made up of any other desired material. The beams 10 and 11 may be solid timber beams or adhesively joined laminated or other wood beams. In Figure 1, the reinforced concrete slab, generally designated S, is shown as covering a wood deck or decking, generally designated D, which may be made up of side by side, preferably tongue and groove connected boards 13. Other materials may alternately be used, but the wood boards or planks 13 preferentially nail readily to the underlying beams 10 and 11. The concrete slab S is a reinforced concrete slab in which there is a wire reinforcement mesh 14 formed of suitable rebar steel rods welded in mesh configuration. As Figure 13 indicates, the concrete slab S, which typically is on the order of typically four to six inches in thickness, is subjected to a dead load, which is the weight of the concrete, and a live load, which is variable dependent upon the weights which are borne by the slab S. These dead and applied loads create compressive stresses in the concrete slab S which need to be relieved by transferring them to the underlying girder system GS, without imposing them on the decking D. This is accomplished by using specially formed shearing connectors, generally designated 15, which extend upwardly from the beams 10 and 11 through slotted openings 16 provided in the wood decking D and become embedded in the concrete slab S when the latter is poured or cast. In Figure 13a, the bending moment for a single girder 11 of length L between walls W, whether it be of wood or steel construction, is portrayed. Figure 13c indicates the reduced amplitude configuration of the bending moment when shearing connectors 15 are used in the matter disclosed in Figures 1 and 2, for example. With the shearing connectors provided at (i.e. adjacent) the wall supported ends or portions of the beams, as shown, the better results achieved with the use of the shearing connectors 15 to be described are evident from a comparison of Figures 13a and 13c by comparing the amplitudes of the bending moments or shear stresses along the girder or beam. The maximum amplitude at bending line 1 in Figure 13a is greatly reduced to the magnitude of line 2 in Figure 13c when connectors 15 are used. Diagrams 13, 13b, 13d and 13e are load diagrams which contemplate load application at the connector 15 locations. The shearing connectors 15, which are specially formed, rigid metal devices, i.e. welded steel elements, will be available in different sizes or configurations depending on the shear forces which need to be transferred from the reinforced slab to the underlying girders. Referring now, more particularly, to Figures 3-6, a one bay shearing connector includes a lengthwisely extending, horizontal frame or frame component, member or element, generally designated 17, which as shown comprises transversely spaced apart side plates 18. While the plates 18 are preferred, other possibilities are the use of a channel or annular or polygonal members, either tubular or solid. The plate system 18 is preferred because it can be readily provided with transversely aligned reinforcing rod or rebar openings 19 in lengthwisely spaced relation, and, when the concrete slab is cast, the enclosure, generally designated E, formed between the plates 18, will fill with concrete to capture and encapsulate the reinforcement rods or rebars which extend snugly through openings 19 and function to further reinforce the concrete slab S. Welded or otherwise securely fixed to the sideplates 18, are shear load transfer web or end plates 20 which are inset from the ends of the plates 18 as shown to form the end walls of enclosure E, and which have portions or sections 20a projecting below the plates 18. The side plates 18 also have downwardly projecting portions or sections 21 which project with the plates 20 and, it will noted, that there are bottoms or bottom walls or plates 22 which span the projecting side plates portions 21 and the projecting web plate sections 20a and fix thereto, as for example, by welding them in position. The plates 21, 22, and 20-20a form open ended end compartments, as Figure 3 illustrates. The bottoms 22 are provided with fastener openings 23 for receiving fasteners 25 which may typically comprise a wood screw or a bolt. With reference now, more particularly, to Figure 7, it will be noted that pockets 24 are provided in the wood beam or girder 10 or 11, as the case may be, to receive the downwardly projecting portions of the connector provided by members 21, 22 and 20a. When the end downward compartment projections, generally designated P, are received within the pockets 24, the plates 18 extend along the upper surface of the beam 11 as shown in Figure 8, for example, and the fasteners 25 are fixed in the beam 11 to resist any tendency of the shearing connector 15 to raise, and to counter the couple formed as illustrated in Figure 7 by the arrows F2 and F3. Generally a polyethylene or other plastic parting sheet PS is used between the decking D and the concrete slab S, and this plastic sheet will have cutouts corresponding to the cutouts 16 in deck D. Once the pockets 24 have been cut in the beam 10 or 11, as the case may be, to the configuration of the projections P of the shearing connector 15, and the downwardly projecting end portions P snugly inserted in the pockets 24 and securely fastened by the fasteners 25, the pockets 24 are filled with a cementitious grout compatible with the concrete used in the slab so as to bond thereto. The expanding grout employed is compression force resistent when cured, and does not shrink or swell in its cured state so that its installed volume does not change. The grout is one which can be purchased and mixed on-site, and, for example, may be the grout designated 1000-1 marketed by Quick-mix Sonderprodukt GmbH & Co. in Germany. A generally cementitious product of this type is preferred over other possible resinous alternatives such as epoxy products. With the shearing connectors 15 all in place, as shown in Figure 8, the wood decking D may be nailed in position in the manner indicated in Figure 1, and the slab S then poured, after the parting sheet PS is also positioned. The concrete slab, generally designated S, is made up of surrounding portions 27 which embed the side plates 18 in the slab, as well as the portions 28 which fill the connector end compartments above the grout portions 26, and the portions 29, which are received in the central enclosures E of each connector 15 between the side plates 18 and web or end plates 20. The reinforcement rods 30, may preferably include generally U-shaped portions, as shown in Figure 1, or may be linear. The steel reinforcing rods 30 are sized and configured to the shape of the openings 19 in the plates 18 so as to be snugly received therein and to embed within the concrete portions 29, as well as in the slab portions 27. They maybe formed in the U-shaped configuration shown in Figure 1. The ends of the reinforcements bars 30 pass through the openings 19 and are received within the concrete portions 29 of the slab S to be rigidly held in position. As particularly shown in Figure 7, the compressive forces P1 transfer from the slab S to the transversely disposed load transfer plates or webs 20 which are rigid or what might be termed "bending stiff", so that they are not bent under the stress of the forces P1. The dimensions indicated in Figures 4-6 will, for example, provide this rigidity. The reinforcement rods 30 also transfer compressive stresses to the left end plate 20 in Figure 7 in view of their snug reception in the openings 19. From the plates 20, the shearing forces P1 due to compression load transfer through the grout 26 in pockets 24 to impose their forces, without slippage, by end grain compression on the girder 10 or 11 as the case may be and subject the girder to tension forces. The bending moment out of the eccentric points of load application is taken up by the force couple, F2 and F3, indicated in Figure 7. As Figure 2 illustrates the compression resistant concrete slab S connects to the tension resistant girders 10 and 11 only at selected locations adjacent to the wall W supports and the two materials, concrete and wood, are not connected between these shearing connections. Thus the two materials act completely separately in this context. Typically, for a thirty foot girder the pockets 24 will be cut in the beam 10 or 11 a distance of about 2 feet (L-1) from each end of the beam, the next one then being cut a distance of 2L(L-2)+1 inch from each end of the beam. Figures 10 and 11 illustrate related appropriate distances for the longer connectors with additional downward projections P, as will be noted. In Figure 7 the wood beam 11 typically will be one foot in height and one half foot in length and a single shearing connector 15 may typically transfer a 200,000 pound compression force to the beam from a slab S which typically may have a depth of 4 inches. Because plates 18 rest on the beam 11 the degree and level of interfacing embedment of the discontinuous connectors 15 in slab S is controlled. The compressive forces are concentrated by the connectors 15 and applied perpendicularly to the grain of the wood beams. Figures 10 and 11 designate shearing connectors which are used for two bay and three bay frames, respectively, and it will be noted that the parts remain the same and function in the same way, except that in Figure 10, three web plates 20 and three downwardly projecting projections P are disclosed, whereas in Figure 11 four web plates 20 and four downwardly projecting projections P are disclosed. With particular reference to Figure 2, it is to be understood that the compressive forces transferred to each end of the beam 11 are applied in opposite directions from the center of the beams where the shear stress is greatest and the forces are exerted outwardly toward the walls W or locations of support. In Figure 12, a so-called continuous beam system is illustrated wherein wood girder beam 11 is supported by three walls W. In this construction, shearing connectors 15, 15a, 15c, and 15d are provided adjacent the locations of support as previously. In Figure 12, the compressive forces applied to shearing connector 15a is applied in an opposite direction to the forces applied to connector 15b and, likewise, the forces applied to connector 15c are applied in a direction opposite to the compressive forces applied to connector 15d. In Figures 14-19, I have shown a construction in which the wood beams 10 and 11 are replaced by steel I-beams 31. As Figure 17 particularly illustrates, the shearing connectors, now generally designated 15', are formed of the same side plates 18 and transverse load applying web plates 20. There are no projections P, however, which extend downwardly and the plates 18 and 20 are simply welded or otherwise suitably secured to the top surface of the upper flanges of the beams 31. The side plates 18 are provided with the same openings 19 for capturing the ends of the rods 30 and embedding them in the concrete portions 29. Except as indicated, the component parts of the building structure BS are all the same and have been accorded the same identifying letters and numerals. The plates 20 do not apply the shearing forces by end grain compression, as particularly illustrated in Figure 7, but do transfer shearing forces to the steel beams 31 otherwise in the same general manner. It is to be understood that other embodiments of the invention, which accomplish the same function, are incorporated herein within the scope of any ultimately allowed patent claims.

Claims: Shear connector (15, 15') for partial embedment in a concrete slab (S) and for use to transfer compression loads in said concrete slab (S) supported by an underlying girder structure (10, 11, 31) directly to the girder structure through a deck (D) supported by the girder structure, comprising: a. a pair of lengthwisely extending side plates (18) with a pair of load transfer plates (20) transversely spanning and rigidly affixed to the side plates (18); and b. connections (19) on said side plates (18) at lengthwisely spaced intervals for carrying rebars (30) thereon in transversely spaced relation at a level to embed in said slab (S). Shear connector as claimed in claim 1 in which said connections for the rebar rods (30) are aligned openings (19) in said side plates (18), and said elongate rebar rods (30) extend through said aligned openings (19) and project outwardly from said side plates (18). Reinforced concrete slab and girder building structure (BS) incorporating shearing connectors, including a concrete slab (S) of predetermined width and length; a deck (D) beneath said slab; and at least one slab support girder (10,11,31) for supporting said deck and slab and to receive compressive load forces applied to said slab; characterized in that a shearing connector (15, 15') for each end of said girder having at least a pair of transversely extending, lengthwisely spaced, rigid load transfer web plates (20) is secured between upstanding, lengthwisely spaced, side plate members (18), said load transfer web plates (20) and side plate members (18) forming an enclosure (E) closed at its sides and ends and fixed by said girder (11,31) to project upwardly from said girder through said deck, the enclosure (E) being embedded in said slab (S), and the slab (S) having a concrete portion (29) filling said enclosure (E). Building structure as claimed in claim 3, wherein said side plate members (18) have lengthwisely spaced openings (19) of a size and shape to snugly accommodate rebars (30) which extend through said openings (19) and embed in said slab (S). Building structure as claimed in claim 3 wherein said load transfer web plates (20) are end plates inset from the ends of said side plate members (18) and have web sections (20a) projecting below the ends of said side plate members, said side plate members also having downwardly projecting portions (21) to function with the said web sections (20a) to form lengthwisely outwardly facing compartments (P); said one girder being a wood beam (10,11) having pockets (24) in its upper face snugly receiving said downwardly projecting web sections (20a) and downwardly projecting side plate portions (21); and a compression resistant, settable and hardenable material which does not shrink or expand filling said outwardly facing compartments (P) and transferring the shear load imparted by said end plates (20) longitudinally to the grain of said beam without slippage. Building structure as claimed in claim 5 wherein said compartments (P) have a bottom member (22) fixed to said web sections (20a) to form the bottoms of said compartments. Building structure as claimed in claim 5 wherein said settable and hardenable material is a grout. Building structure as claimed in claim 6 wherein vertically extending fasteners (25) extend from said bottom members (22) into said wood beam (10, 11) to counter the bending couple set up by the forces applied. Building structure as claimed in claim 3 wherein said deck (D) is cut out to accommodate said connector web plates (20) and side plates (18), which protrude above said deck. Building structure as claimed in claim 3 wherein said girder is a steel beam (15') and said web plates (20) and side plate members (18) are fixed to the top of said steel beam.

Inventors: BERTSCHE PETER, BERTSCHE, PETER
Applicants: BERTSCHE PETER, WRIGHT KEITH M, BERTSCHE, PETER, WRIGHT, KEITH M.
Application year: 1998
Main classification: E04B5
IPC codes: E04B5, E04C5