SHEAR CONNECTORS

Abstract: The present invention is concerned with the forming of concrete floors by pouring concrete onto corrugated shuttering (18) supported on a steel beam (10). Shear forces between the concrete (24) and the beam (10) are resisted by shear connectors (20) which are strips of corrugated material fixed to the beam, e.g. by pins (22), and which are so shaped and so dimensioned that the corrugations of the shear connectors fit into the corrugations of the shuttering (18) and key into the concrete (24).

Description: SHEAR CONNECTORS The present invention relates to shear connectors; shear connectors are used in the fabrication of composite steel and concrete structures, e.g. bridges and buildings, to transfer shear forces between steel beams and a body of concrete, thus limiting relative movement (or slip) at the steel/concrete interface so that the system acts as a unit that resists longitudinal bending and prevents uplift between the steel and the concrete. Known shear connectors are metal plates or studs that are welded to the beam prior to casting of the concrete; when the concrete is cast, the shear connectors are embedded in concrete and as a result prevent lateral movement between the concrete and the beam. It is a time-consuming and awkward task to arrange these shear connectors on the beam and to weld them in place. It has been proposed to use flanged plates as shear connectors and to fasten them to the steel beam using explosive pins that penetrate through the flange of the connector into the steel beam. Whereas the use of such pins to fix the plates to the beams is much quicker than welding, it is still a time-consuming task to arrange individual plates on a beam and fix them in place. The aim of the present invention is to provide a method of constructing a concrete structure using a novel shear connector that is quicker and easier to secure to steel beams than known shear connectors; the present invention also provides the novel shear connector itself and an assembly including both the novel shear connector and shuttering. According to the present invention, there is provided a shear connector for use in connection with commercially-available corrugated sheet shuttering of dimensions commonly used in the building art, characterised in that the shear connector comprises an elongate strip of corrugated material having corrugations extending transverse to its length, wherein the distance between adjacent corrugations of the shear connector strip is identical to the distance between adjacent corrugations of the said shuttering, wherein the shear connector corrugations have a height that exceeds the height of the corrugations of the shuttering by at least 25 mm, wherein each shear connector corrugation has a base matched in shape to the shape of the bases of the corrugations of the shuttering and wherein the base of each shear connector corrugation has a width (when viewed in longitudinal section) that is less than the width of the bases of the shuttering corrugations. The width of the shear connector strip is preferably less than the width of the base of each corrugation of the shuttering so that the strip can be located in, and extend along the length of, a single corrugation of the shuttering; more preferably, the width of the strip is smaller by at least 10 mm than the width of the base of a shuttering corrugation. Corrugated profiled steel shuttering commonly used in the art at the present time have dimensions as follows (in mm): distance between adjacent corrugations: 150 150 150 150 183 280 corrugation base width: 62 137 137 114 87 110 corrugation height: 55 38 51 58 75 80 The shear connector of the present invention preferably has one or more ribs on the shoulders of the corrugations to reinforce the strip. If the bases of the shuttering corrugations have ribs, then the bases of the shear connector corrugations should also be provided with such ribs to match those of the shuttering. Preferably, the width of the shear connector strip (i.e. the width of the shear connector taken in transverse section) is in the range of from 30 to 110mm, more preferably 35 to 100mm, e.g.40 to 90mm; typically, the width will be approximately 50 to 80mm. The length of the shear connector is indeterminate since it will depend on the length of the beam used; the shear connector need not extend along the whole length of the beam. The shear connector of the present invention is preferably made of sheet steel having a thickness of at least 1.2mm, e.g about 2mm and preferably having the following specification: BS 2989 sheet Z28 G275 N steel (normal spangle-finish zinc coating of 275 g/m 2 total mass on both sides, the steel having a minimum yield strength of 280 N/mm 2 ). In order to cast a concrete floor on a framework of steel beams in a partly-constructed building or other structure, areas of corrugated sheet shuttering are placed on top of the structural beams that will support the floor so that the -shuttering covers all the area that the floor is intended to occupy. Two orientations between the shuttering and a beam will generally arise: - Case 1, where the corrugations in the shuttering extend perpendicularly to the length of the beam, and - Case 2, where the corrugations of the shuttering extend parallel to the length of the supporting beam. Shear connector strips are then arranged on the shuttering above the various beams with each strip extending parallel to a respective beam so that in case 1, the corrugations of the shear connectors fit into respective corrugations of the shuttering while in case 2, the shear connectors are located in, and extend along, individual corrugations of the shuttering. The shear connectors are then fixed to the underlying beams by welding or by means of explosive pins (as described above) or indeed by any other suitable means. Reinforcing rods or mesh are placed on the resulting structure and concrete is poured onto the shuttering so that it covers the shear connectors; concrete will flow into the gaps between the shuttering and the shear connectors and thereby embed the connectors into the concrete. As will be appreciated, it is considerably simpler to use a single strip as a shear connector in place of a large number of individual plates or studs which are used currently; hitherto it has been common practice to use from one to three individual plates or studs as shear connectors in each corrugation of the sheet shuttering (depending on the design calculations), each of which had to be individually located and fixed. According to a second aspect of the present invention, there is provided a method of constructing a concrete structure, which structure is supported by or otherwise in contact with a structural beam, which method comprises laying corrugated shuttering against the beam, placing a shear connector on the shuttering so that it overlies the beam, securing the shear connector to the beam and casting a body of concrete on the shuttering so that the shear connector is embedded in the concrete when set, characterised in that the shear connector is a corrugated strip which is either located in and extends along a single corrugation in the shuttering or the troughs of the corrugations in the shear connector strip are located in respective troughs of the corrugations of the shuttering. According to a third aspect of the present invention, there is provided an assembly comprising a beam having fixed thereto a sheet of corrugated shuttering and a shear connector, characterised in that the shear connector is an elongate corrugated strip extending along the length of the beam and either (a) the corrugations of the shuttering extend along the length of the beam and the shear connector strip is located in and extends along a corrugation in the shuttering or (b) the corrugations of the shuttering extend transversely across the beam and the troughs of the shear connector corrugations are located in respective troughs of the shuttering corrugations. It is preferred that the difference in height between the peaks of the shear connectors and the peaks of the shuttering is at least 50 mm. The present invention will now be described in further detail, by way of example only, with aid of the following drawings in which: Fig. 1 is an end view, which is partly cut away, of part of a cast concrete floor and shows a beam, a sheet of corrugated shuttering whose corrugations extend across the beam, a shear connector, a reinforcing steel mesh and a layer of cast concrete, Fig. la is a cross sectional view along line la-la in Fig 1, Fig.2 is an axisonometric view of the arrangement of the beam, the corrugated sheet shuttering and the shear connector shown in Fig.l. Fig. 3 is an end view, which is partly cut away, of a cast concrete floor and shows a beam, a sheet of corrugated shuttering whose corrugations extend along the beam, a shear connector and a layer of concrete. Fig.4 shows, in section, several forms of commercially available corrugated sheet shuttering and shear connectors for use with such shuttering. One method of building bridges or buildings etc. involves the constuction of a framework consisting of steel beams. Floors are formed between the beams by laying sheets of corrugated shuttering (or decks) between the beams and pouring a layer of concrete onto the shuttering which, when set, constitutes the floor; as in standard practice in cast concrete, reinforcing material (mesh or bars) is incorporated into the concrete floor. In order to limit slip at the interface between the concrete and the beam so that the steel beam/concrete system acts as a unit to resist longitudinal bending and to prevent uplift between the steel beam and the concrete slab, shear connectors are fixed to the beam and extend into, and are therefore embedded in, the concrete layer. A cast concrete floor using a shear connector of the present invention is shown in Fig.l while Fig. 2 shows only the beam, the sheet shuttering and the shear connector. Referring to these two Figures, an I-section steel beam 10, which has a top flange 12 joined by a web 14 to a bottom flange 16, forms part of the framework of a building. Sheets 18 of corrugated metal shuttering are laid between the beams of a floor to form a continuous base or deck on which concrete can be poured; Fig. 2, for ease of illustration, shows a relatively narrow section of sheet shuttering 18 but it will be appreciated that the shuttering extends further both in the lateral direction (shown by arrows A) and in the longitudinal direction (shown by arrows B). The shear connector of the present invention is a strip of corrugated steel 20 which is placed on the sheet shuttering 18 with its corrugations fitting into the corrugations of the sheet shuttering; as can be seen in Fig. 1 and 2, the shear connector 20 overlies the beam 10 and is fixed to the flange 12 of the beam 10 by explosive pins 22 of a type that are available commercially from Hilti AG of Switzerland. Alternatively, the shear connector 20 may be fixed to the beam by any other means that enables the shear connector 20 to withstand horizontally-acting forces. In Figs. 1 and 2, the corrugations of the shuttering run perpendicular to the beam 10. Obviously there are other beams forming the framework which extend perpendicular to the beam shown in Figs. 1 and 2 and consequently the corrugations of the shuttering run parallel with these other beams; the arrangement of securing shear connectors to such beams is shown in Fig. 3: the connector 20, which is identical to that shown in Figs.1 and 2, is located in, and extends along, one corrugation of the shuttering 18. It is fixed to the flange 12' of beam 10' by means of explosive pins 22, two pins being used in each corrugation of the strip. As will be seen from Fig.3, the width of the shear connector strip W3 must be smaller than the width W-^ of the base of the corrugatons. A reinforcing steel mesh 23 (shown in Figs. 1 and 3) is then laid over the shuttering 18 and concrete is poured onto the shuttering to a thickness of approximately 130-150 mms (although the precise thickness will have to be calculated on standard engineering principles, depending on the forces that the floor will have to encounter). The concrete is shown shaded in parts of Figs. 1 and 3 and is indicated by the reference numeral 24 while the top level of the concrete is indicated at 26. As is apparent, the concrete penetrates into the space 28 (see Fig. 1) between the peaks of the corrugations of shuttering 18 and the peaks of the corrugations of shear connector 20 thereby embedding the shear connector in the concrete; in the Fig.3 arrangement, the concrete totally engulfs the shear connector 20. Because the shear connectors are fixed to beam 10 and 10' by pins 22, the body of concrete is prevented by the shear connectors from moving horizontally with respect to beam 10, 10'. The dimensions of the shear connector 20 depend on the type of shuttering 18 that is used; the criteria for the dimensions of the shear connector are as follows: (1) the period P of the shear connector, i.e. the distance between adjacent peaks of the corrugations, must be substantially identical to the period of the corrugations in the shuttering 18 in order that the corrugations of the shear connector can fit into those of the shuttering, (2) the width W2 of the base of each trough of the shear connector must be smaller than the width W2 of the base of each troug in the shuttering; again this is necessary to allow the shear connector to fit into the corrugations of the shuttering and to provide a gap 30 between the side walls of the shuttering and the side walls of the shear connector, (3) the height £_2 of the shear connector must be sufficiently large to provide a gap 28 of height H-^ between the peaks of the shuttering 18 and the peaks of the shear connector 20. Height H^ must allow the concrete to penetrate into the gap and generally must be at least 25 mm and more typically at least 35 mm; if the concrete does not penetrate into gap 28, the keying of the shear connector into the concrete will be impaired and, as is apparent, this will reduce its effectiveness, (4) the width 3 of the shear connector strip 20 must be smaller (preferaby by at least 10 mm) than the width W-* ^ of the base of the corrugations of the shuttering. It is apparent that one design Of connector could be used for the arrangement shown in Figs. 1 and 2 and a different design could be used for the arrangement shown in Fig. 3 but it is more convenient to use a single design of connector for both arrangements. The I-beam 10, 10' and the sheet shuttering 18 are standard commercial products and will not be described in further detail. The shear connector is made of type BS 2989 sheet Z 28 G 275 N steel having a thickness of 1 to 3 mm, e.g. 1.2 to 2 mm, and which has been cold formed into the shape shown in Figs. 1, 2 an 4. The shear connector may have reinforced ribs 30 pressed into the shoulders of its corrugations as shown on one of the corrugations in Fig.1 and in more detail in Fig. la. Fig.4 shows cross-sections of six types of sheet shuttering 18 and associated shear connectors 20. The dimensions of the shear connectors are given below. It will be seen that a single size of shear connector (type 1) can be used with any of the first four forms of sheet shuttering illustrated while shear connector types 2 and 3 are used for the fifth and sixth forms of shuttering; the shear connectors have the following dimensions, in mm: overall height (dimension H^ in Figs. 1 and 4): 105 105 105 width of the corrugation trough (dimension 2 in Figs. 1 and 4): 35 55 55 width of corrugation peak (dimension W4 in Fig 4): 55 55 55 distance between corrugations (dimension P in Fig. 4): 150 183 280 width of shear connector strip (dimension 3 in Fig. 3): 50 75 80

Claims: CLAIMS 1. A method of constructing a concrete structure, which structur is supported by or otherwise in contact with a structural beam, whic method comprises laying corrugated shuttering against the beam, placing a shear connector on the shuttering so that it overlies th beam, securing the shear connector to the beam and casting a body of concrete on the shuttering so that the shear connector is embedded in the concrete when set, characterised in that the shear connector is a corrugated strip which is either located in and extends along a single corrugation in the shuttering or the troughs of the corrugations in the shear connector strip are located in respective troughs of the corrugations of the shuttering. 2. A method as claimed in claim 1, wherein the corrugations of the shear connector strip are taller than the corrugations of the shuttering by at least 25 mm. 3. A method as claimed in claim 2, wherein the corrugations of the strip are taller than those of the shuttering by at least 50 mm. 4. An assembly comprising a beam having fixed thereto a sheet of corrugated shuttering and a shear connector, characterised in that the shear connector is an elongate corrugated strip extending along the length of the beam and either (a) the corrugations of the shuttering extend along the length of the beam and the shear connector strip is located in and extends along a corrugation in the shuttering or (b) the corrugations of the shuttering extend transversely across the beam and the troughs of the shear connector corrugations are located in respective troughs of the shuttering corrugations. 5. An assembly as claimed in claim 4, wherein the corrugations of the shear connector strip are taller than the corrugations of the shuttering by at least 25 mm. 6. An assembly as claimed in claim 5, wherein the corrugations of the strip are taller than those of the shuttering by at least 50 πrn. 7. A shear connector for use in connection with commercially- available corrugated sheet shuttering of dimensions commonly used in the building art, characterised in that the shear connector comprises an elongate strip of corrugated material having corrugations extending transverse to its length, wherein the distance between adjacent corrugations of the shear connector strip is identical to the distance between adjacent corrugations of the said shuttering, wherein the shear connector corrugations have a height that exceeds the height of the corrugations of the shuttering by at least 25 mm, wherein each shear connector corrugation has a base matched in shape to the shape of the bases of the corrugations of the shuttering and wherein the base of each shear connector corrugation has a width (when viewed in longitudinal section) that is less than the width of the bases of the shuttering corrugations. 8. A shear connector as claimed in claim 7, wherein the height of the corrugations of the shear connector exceeds the height of the corrugations of the shuttering by at least 50 mm. 9. A shear connector as claimed in claim 7, wherein the width of the shear connector strip is less than the width of the base of each corrugation of the shuttering. 10. A shear connector as claimed in claim 9, wherein the width of the shear connector strip is less than the width of the base of each corrugation of the shuttering by at least 10 mm. 11. A shear connector as claimed in claim 7, wherein the width of the shear connector strip is 35 to 100 mm. 12. A shear connector as claimed in claim 11, wherein said width is 40 to 90 mm. 13. A shear connector as claimed in claim 11, wherein said width is 50 to 80 m. ' 14. A shear connector as claimed in claim 11, wherein said width is selected from 50 mm, 75 mm and 80 mm. 15. A shear connector as claimed in claim 7, wherein the corrugations of the shear connector includes shoulders intermediate between the bases of the corrugations and peaks of the corrugations, which shoulders have one or more reinforcing ribs. 16. A shear connector as claimed in claim 7, which is made of sheet material and wherein the thickness of the shear connector material is at least 1.2 mm. 17. A shear connector as claimed in claim 7, wherein the distance between adjacent corrugations of the shear connector is selected from 150 mm, 183 mm and 280 mm. 18. A shear connector as claimed in claim 7, wherein the height of the said corrugations of the shear connector is approximately 105 mm. 19. A shear connector as claimed in claim 7, wherein the width of the base of the corrugations of the shear connector (when viewed in longitudinal section) is 30 to 60 mm. 20. A shear connector as claimed in claim 19, wherein the said width is selected from 35 and 55 mm. 21. A shear connector as claimed in claim 7, in combination with said shuttering.

Inventors: SHANIT GILI, SHANIT, GILI
Applicants: SAFFERSON LTD, SHANIT GILI, SAFFERSON LIMITED, SHANIT, GILI
Application year: 1988
Main classification: E04B5
IPC codes: E04B5