EP0414485B1 - Shearhead reinforcement - Google Patents
Shearhead reinforcement Download PDFInfo
- Publication number
- EP0414485B1 EP0414485B1 EP90309138A EP90309138A EP0414485B1 EP 0414485 B1 EP0414485 B1 EP 0414485B1 EP 90309138 A EP90309138 A EP 90309138A EP 90309138 A EP90309138 A EP 90309138A EP 0414485 B1 EP0414485 B1 EP 0414485B1
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- EP
- European Patent Office
- Prior art keywords
- shearhead
- hoop
- shear
- slab
- column
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B5/00—Floors; Floor construction with regard to insulation; Connections specially adapted therefor
- E04B5/43—Floor structures of extraordinary design; Features relating to the elastic stability; Floor structures specially designed for resting on columns only, e.g. mushroom floors
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
- E04C5/06—Reinforcing elements of metal, e.g. with non-structural coatings of high bending resistance, i.e. of essentially three-dimensional extent, e.g. lattice girders
- E04C5/0645—Shear reinforcements, e.g. shearheads for floor slabs
Definitions
- This invention relates to the design of shearheads in the reinforcement of junctions between for example, vertical columns and horizontal floors, where at least the floor is formed in reinforced concrete.
- a shearhead is a separately definable structure embodied in the concrete at the junction which serves to spread the load of the floor on the respective column and thereby reduce the effect of the vertical forces; ie, reduce the stress in the slab concrete by increasing the critical shear perimeter around the column.
- shearhead design is based essentially on the premise that shear failure of the laterally extending slab occurs along a shear failure plane on a perimeter, around the head of the respective column. If this shear perimeter can be enlarged; i.e., spaced from the column axis, then the shear forces acting on the slab at a particular point on the perimeter will be reduced.
- shearheads have been designed as reinforcing structures which are placed directly on a column and extend laterally outward therefrom to define a shear perimeter significantly spaced from the column axis.
- elements are introduced into the slab to provide more local shear reinforcement, effectively to a radius from the column at which the slab can be sufficiently self-supporting. Such local reinforcement can be interconnected to form a linked unit.
- the present invention is directed at the second of these options.
- Known forms of shear head of this type may be seen, for example, in DE-A-3410419, GB-A-1396780, and also as shown on Page 390 of the publication C.E. Reynolds and J.C.
- the present invention provides a shearhead for casting within the body of a laterally extending reinforced concrete slab to reinforce a junction between the slab and a supporting concrete column comprising a plurality of shear legs attached to, depending from and spaced along at least one horizontal closed hoop bar which is arranged to extend around or in the vicinity of the column, characterised in that the hoop bar is arranged to contain the horizontal forces radially extending from the column when the floor is loaded and in that the shearhead is equipped with suspension means for suspending it from the floor slab upper reinforcement mesh comprising a portion of each shear leg which extends above the hoop bar and is provided with a hook for coupling to the said mesh.
- the hoop bar in shearheads according to the invention may be divided into discrete sections which can be installed separately in the shearhead assembly.
- Each section embodying this aspect of the invention comprises an upper bar from which a plurality of shear legs depend, if desired, to a lower bar to form a readily handleable unit.
- Such a unit can be suitably supported in the shearhead assembly at the desired location or locations prior to casting the concrete slab thereover.
- a substantially continuous hoop bar, or interconnected such sections is necessary as the effective encircling of the column by substantially continuous length of bar structurally strengthens the function against shear forces. The reason for this is that in the region of concrete confined within the bar, cracking of the concrete is inhibited.
- each hook extends substantially horizontally when installed on a column. This facilitates the coupling to reinforcement in the slab, as the reinforcement can be readily slid under the hooks, or vice versa. If the shear legs are to be coupled to only one set of reinforcement rods in the slab, then all the distal ends of the hooks can be made parallel. If the shear legs are to be coupled to reinforcement rods extending in different directions, then the orientation of the hooks can be similarly varied. Typically, different sets of hooks are oriented to extend in different, normally orthogonal directions. As the reinforcement in the slab will normally comprise rods extending in one direction at one level and in another direction at another level, then again the height of one set of hooks relative to the hoop bar can be different from that of another.
- Shearheads according to the invention may be embodied in circular form. However, as the principal forces acting in a shearhead assembly can be resolved along perpendicular axes, preferred embodiments of the invention are in substantially square or rectangular form. This also facilitates the division of the hoop bar into sections and/or the hooks of the shear legs into sets as described above for coupling to perpendicularly oriented reinforcement rods in the slab. It should be noted though, that the attachment of the shearhead to reinforcement in the slab is not essential. Preferably though, it extends above the reinforcement to prevent the creation of a shear failure plane below the reinforcement. Such attachment does of course, additionally provide a convenient means by which the shearhead can be located prior to the slab being cast.
- Shearheads according to the invention can include an additional bar to which the shear legs are attached at their lower ends. This is though, not essential, but provides a convenient means by which the shearhead and the orientation of the shear legs thereof may be set.
- Such a lower hoop bar or mesh can also provide an alternative means by which the shearhead is located in the slab; ie, on shuttering against which the slab is cast. It can be supported on separate spacers, or props attached to the lower hoop bar or mesh, or on props attached directly to at least some of the shear legs. This last option is of course available when a lower hoop bar or mesh is not used.
- each shear leg comprises a single length of rod shaped to form the hook at its upper end.
- the hook forms an upper anchorage point in the subsequently cast slab, and a lower anchorage point is normally also formed; for example by shaping its lower end into a second hook which can extend around a lower slab reinforcement rod.
- Preferred shear legs however, each comprise a single length of rod which extends to form a loop below the hoop bar with both ends extending above the hoop bar to a hook. The loop thus forms a lower anchorage point in the cast slab.
- the shape of the loop may vary, but a preferred shape is broadly U-shaped, with two leg sections downwards from each hook to a link section thereby minimising bearing stresses.
- the shape of the loop may be broadly triangular, with two leg sections converging downwardly to a single bend. Each leg is attached to the hoop bar adjacent each hook.
- each shear leg is in the form of a closed or substantially closed curve through which the slab reinforcement passes where the coupling is made.
- the preferred shape in these embodiments is square or rectangular, although other shapes can be used, with particular benefit in certain applications.
- the shear legs will depend vertically from the upper hoop bar. However, different applications may require different orientations of the legs. For example they might depend downwardly and outwardly from the hoop bar, relative to the column.
- the depth to which the shear legs extend from the upper bar will also affect the reinforcement they provide.
- the shear legs should extend as far as possible towards the lower surface of the slab, i.e., to but not into the cover layer. Generally, this means to or to just below the level of the lower layer of reinforcement in the slab and the legs may be attached to such lower reinforcement, for example by extending around rods thereof.
- shearheads or hoop bar sections thereof according to the invention can be dropped or lowered into place after all the lower slab reinforcement has been put in place.
- a shearhead of the invention can be lowered into place by allowing the depending sections to pass through openings in the slab reinforcement.
- the lower slab reinforcement comprises welded mesh reinforcement, and not separate reinforcement bars. It is preferred in all embodiments of the invention where the slab has upper and lower layers of reinforcement that the shear legs extend fully between the layers to prevent the creation of shear failure planes in this region.
- a shearhead assembly embodying the invention will have the shearhead and slab reinforcement suitably supported on shuttering prior to the concrete slab being cast. Further, in some embodiments two or more shearheads extending around the same column may be employed, the second being disposed outside the first, but surrounding it generally in the same plane. Concentric square, rectangular or circular shearheads according to the invention may be used in this way.
- Shearheads according to the invention can be used on columns of any suitable construction. Typically, suitable columns are of reinforced concrete or steel. Shearheads of the invention can also be used in conjunction with shearheads of other types. As the shearheads of this invention extend around or spaced from the column axis, they are particularly suited as auxiliaries to other types of shearheads disposed on or around the column axis. In this connection reference is directed to our co-pending Application filed today under our Agent's reference EH 34198. It will be appreciated that shearheads of this invention may interdigitate with laterally extending beams or arms of such other shearhead types to more closely define the shear perimeter thereof.
- Shearhead structures broadly of the kind disclosed herein can also be useful at the periphery of such an area; in other words with at least one boundary of the shearhead coinciding with the column at the periphery of the area.
- a shearhead structure comprising a hoop bar with a plurality of shear legs attached thereto and depending therefrom can be cast within the body of a laterally extending slab at the periphery of the area thereof with a part of the hoop bar at the perimeter of the shearhead being cast within a supporting column also disposed at the periphery of the area.
- This can most conveniently be accomplished where the shearhead is of square or rectangular planar shape such that a straight edge thereof can be laid against the periphery of the area to be cast.
- shearheads Two or more such shearheads can be used adjacent each other if desired, and if the point on the periphery of the area to be cast is at a corner with an angle of greater than 180°, a plurality of shearheads can be disposed around the corner.
- Shearheads used in these variants will normally comprise at least two and normally a greater plurality of concentric hoop bars with depending shear legs.
- a shearhead embodying the invention can comprise for example a hoop bar extending around three sides of a column between two points on the periphery of the area to be cast, with shear legs depending therefrom.
- an upper and a lower hoop bar are preferably used, which bars are linked by vertical section at the periphery of the area to be cast.
- This arrangement can result in the creation of a torsion box in the region of the junction, which extends horizontally on either side of the column to limits defined by the hoop bars. If a plurality of concentric hoop bars are used, as is preferred, then the horizontal length of this torsion box can be considerable, and provide effective reinforcement into the body of the slab.
- the shearhead shown in Figure 1 comprises a single hoop bar 2 disposed over the top of a column 4, and surrounding the axis thereof.
- the hoop bar 2 is of generally square form with its respective sides aligned parallel to the sides of the column 4 which is also of square cross-section. Attached to the hoop bar 2 is a plurality of shear legs 6, 8 as indicated on the respective sides of the hoop bar.
- shuttering also not shown
- reinforcement rods 10,12 are suitably supported thereon.
- the rods 10 are laid first, with the rods 12 laid thereover either supported by the rods 10 or by some other means.
- Each shear leg 6, 8 has a hook at the top thereof which is disposed above the hoop bar 2, and at least some of these hooks are used to suspend the hoop bar 2 and all the shear legs 6, 8 from the reinforcing rods 10, 12.
- the hooks on the shear legs 6 are disposed closer to the hoop bar 2 than those on the shear legs 8. In this way, the hooks on the shear legs 6 may be attached to the rods 10, and the hooks on the shear legs 8 to the rods 12, while retaining the hoop bar 2 substantially horizontal.
- each leg 6 is attached to the hoop bar 2, typically by a spot weld, and a portion of each leg extends above the bar 2 to form a hook 14.
- the distal end 16 of the hook 14 extends substantially horizontally, and parallel to the plane of the hoop bar 2. This enables the hook 14 to be readily slid over the reinforcing rod 10 or alternatively, if the shearhead is located before the slab reinforcement, enables the rod 10 to be readily slid under the hook 14.
- the transverse reinforcing rod 12 is supported directly on the rods 10, but not in the vicinity of the hook 14.
- the shear legs 8 are formed in a similar shape to the shear legs 6, but with the respective hook 14 and distal end 16 further spaced from the hoop bar 2.
- the distal end 16 would again extend substantially parallel to the adjacent length of hoop bar 2, but of course perpendicular to the ends of the shear legs 6 as the respective legs 8 will be attached to a perpendicular section of hoop bar 2.
- shear legs 6, 8 on the hoop bar 2 can of course be varied to suit the structure within the concrete slab upon which the shearhoop is to be suspended.
- orientation of the hooks 14 can of course be preserved even if the hoop bar is of different; eg, circular form.
- a square or rectangular form is preferred, as is a perpendicular orientation of respective shear legs as this simplifies the attachment of the hooks to slab reinforcement, which is normally arranged in two perpendicular directions along which the internal forces in the structure can be readily resolved.
- FIG 3 and 4 show an alternative shearhead construction in which shear legs 18 are attached to two generally concentric hoop bars 20, 22.
- Hoop bar 22 surrounds hoop bar 20, and both are arranged around the top of a column 24.
- spacers 26 supporting the lower ends of the shear legs 18.
- each shear leg 18 forms a pair of hooks 28.
- the shape of each hook is broadly similar to that described with reference to Figure 2 above, and because all the hooks are oriented in the same direction, they are uniformly spaced above the respective hoop bars 20 and 22.
- Each shear leg 18 forms a loop below the hoop bar to which it is secured, and it is the base of the loop which is supported by a spacer 26. It will be noted from Figure 3 that the loops are respectively in planes parallel to the length of hoop bar to which they are attached while the hooks are all oriented in the same direction.
- each shear leg 18 below the hoop bar 20 is of generally triangular configuration.
- a leg section 30 depends from each hook 28, converging towards another section depending from an adjacent hook.
- the sections 30 merge in a smooth bend 32 which forms a lower anchorage point in the slab 34.
- Each hook is coupled to an upper slab reinforcment rod 10 (see Figure 1) and the bends 32 are substantially at the level of the lower reinforcement rods 36.
- Figure 5 shows an alternative and preferred form of shear leg which also defines a loop.
- the leg sections 30 are parallel, and connected at their lower ends by link section 38.
- This form of shear leg may be substituted directly for the legs of the Figure 4 embodiment.
- the link section 38 provides a convenient means by which the shear leg may be supported, either on a spacer as shown at 26 in Figure 4, or on a lower reinforcement rod 36.
- the two rods 36 shown in Figure 5 are arranged orthogonally in the slab such that the link section 38 extends adjacent one rod while resting on the other.
- Shearheads with shear legs of the kind shown in Figures 4 and 5 are particularly suited for installation after placement of the lower slab reinforcement. As shown in Figure 4, the shearhead is lowered into positon after placement of the lower reinforcement rods 36, but before location of the upper rods 10, 12.
- a steel mesh may be used in place of the spacers 26, having components intersecting within the body of the column 24 which support the shearhead. It will be appreciated from the description of Figure 1 above, that such a mesh may be supported at the top of the column 24 prior to casting the slab and the overlaying column length. However, the mesh can of course be supported directly on the shuttering for the slab if preferred.
- the shearhead a detail of which is shown in Figure 6, comprises an upper hoop bar 42 and a lower hoop bar 44 to which a shear leg 56 is welded at 48.
- the shear leg 56 is of generally rectangular shape, but which does not complete a closed curve and is open at one corner of the "rectangle". In this way, the shearhead as a whole can be supported on the slab reinforcement. Further slab reinforcement can also be threaded through the lower portion of the shear leg or on either side thereof as indicated at 54. Reinforcement will also be disposed below this slab reinforcement 54 as indicated at 52.
- the shear leg 56 will normally extend below the lowermost slab reinforcement 52, although without of course reducing the cover factor to an unacceptable level.
- the lower hoop bar 44 may be dispensed with in some circumstances.
- the shearhead illustrated in Figures 7 to 9 is shown comprising three hoop bars 62, each extending around three sides of a column 58.
- Each hoop bar 62 has an upper and lower portion linked by a vertical section 64.
- the hoop bars 62 are arranged generally concentrically around the column 58 in the slab 60, and shear legs 66 (only one is shown in Figure 7) extend from above the upper hoop bar section to below the lower hoop bar section as does the shear leg described above with reference to Figure 6. It will be appreciated that shear legs of any suitable form can be used.
- the hoop bars 62 form a torsion box which extends generally horizontally through the column 58 at the periphery of the area being cast.
- Figure 9 in addition shows the column reinforcement 68 and additional reinforcement 70 around which the link portions 64 extend between the upper and lower portions of the hoop bar 62.
- the hoop bar 62 In combination with the shear legs 66 mounted as shown, the hoop bar 62 combines with the reinforcement 70 to form a torsion box which effectively reinforces the slab around the column.
- Figures 10 to 13 show how square or rectangular shearheads can also be put to good effect at the periphery of the area to be cast.
- Figure 10 shows two shearheads 72 arranged side by side against the periphery of the cast area, with adjacent corners cast within the body of a pillar or column 74.
- Figure 11 shows a single shearhead 72 with the cross-section of a column 76 extending generally perpendicularly into one side thereof.
- Figure 12 shows how a shearhead 72 can be fitted into a corner with a corner thereof cast into a vertical column 78.
- Figure 13 shows how three shearheads can be fitted around an obtuse corner, each coupled to a part of a vertical column 80.
- Shearheads described herein in relation to the accompanying drawings are normally formed in steel and as noted above, are preferably of square or rectangular form.
- the inner hoop bar of Figure 3 might be 60cm square, with the outer bar being 90cm square.
- Each hoop bar would typically be of 12mm diameter steel, with the shear legs being in 8mm steel for attachment to reinforcing rods of 16mm steel in a slab having a 25mm cover.
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Abstract
Description
- This invention relates to the design of shearheads in the reinforcement of junctions between for example, vertical columns and horizontal floors, where at least the floor is formed in reinforced concrete. A shearhead is a separately definable structure embodied in the concrete at the junction which serves to spread the load of the floor on the respective column and thereby reduce the effect of the vertical forces; ie, reduce the stress in the slab concrete by increasing the critical shear perimeter around the column.
- It has long been recognised that supporting an horizontally extending body or slab on one or more vertical columns imposes bending and shear forces on the slab at the junctions with the columns which must be withstood by the structure of the slab or resisted by specific design features at the respective junction. Traditionally, the cross-section of the columns has been enlarged at least at the junction either wholly or locally at the junction by the introduction of flared column heads. Alternatively or additionally, the depth of the slab has been increased in the vicinity of the column to reduce the stresses arising particularly from the local shear forces. However, in modern building design it has become desirable to eliminate such obstructions or modifications to the slab, and provide clear substantially perpendicular junctions between each column and the lower uniform surface of the slab. It is also desirable to be able to use columns of smaller cross-section for a given slab loading or to increase the span of the slab for a given column size or cross-section. A number of shearhead designs have been proposed to these ends, and examples of such proposals are disclosed in European Patent Specification Nos. 0079413 and 0128994. This subject has also been considered in the following papers published by the American Concrete Institute:
- 1. Corley, W.G., and Hawkins, N.M., "Shearhead Reinforcement for Slabs," ACl Journal, Proceedings V.65, No. 10, October 1968, pp. 811-824.
- 2. Hawkins, N.M., and Corley, W.G., "Moment Transfer to Columns in Slabs with Shearhead Reinforcement", Shear in Reinforced Concrete, Special Publication SP-42, American Concrete Institute, Detroit, 1974, pp. 847-879. Also, Research and Development Bulletin RD 037.01D, Portland Cement Association.
- Research into shearhead design is based essentially on the premise that shear failure of the laterally extending slab occurs along a shear failure plane on a perimeter, around the head of the respective column. If this shear perimeter can be enlarged; i.e., spaced from the column axis, then the shear forces acting on the slab at a particular point on the perimeter will be reduced.
- Research into the above problem has followed two distinct paths. In the first, shearheads have been designed as reinforcing structures which are placed directly on a column and extend laterally outward therefrom to define a shear perimeter significantly spaced from the column axis. In the second, elements are introduced into the slab to provide more local shear reinforcement, effectively to a radius from the column at which the slab can be sufficiently self-supporting. Such local reinforcement can be interconnected to form a linked unit. The present invention is directed at the second of these options. Known forms of shear head of this type may be seen, for example, in DE-A-3410419, GB-A-1396780, and also as shown on Page 390 of the publication C.E. Reynolds and J.C. Steedman "Reinforced Concrete Designer's Handbook" 9th Edition, 1981, Cement and Concrete Association, Slough. A plurality of shear legs are shown attached to and spaced around spiral or circumferential supporting wires which serve to position them around the column so as to enlarge the shear perimeter. Such devices are normally stood on formwork prior to pouring the concrete and rely upon the latter for their anchorages.
- The present invention provides a shearhead for casting within the body of a laterally extending reinforced concrete slab to reinforce a junction between the slab and a supporting concrete column comprising a plurality of shear legs attached to, depending from and spaced along at least one horizontal closed hoop bar which is arranged to extend around or in the vicinity of the column, characterised in that the hoop bar is arranged to contain the horizontal forces radially extending from the column when the floor is loaded and in that the shearhead is equipped with suspension means for suspending it from the floor slab upper reinforcement mesh comprising a portion of each shear leg which extends above the hoop bar and is provided with a hook for coupling to the said mesh.
- The hoop bar in shearheads according to the invention may be divided into discrete sections which can be installed separately in the shearhead assembly. Each section embodying this aspect of the invention comprises an upper bar from which a plurality of shear legs depend, if desired, to a lower bar to form a readily handleable unit. Such a unit can be suitably supported in the shearhead assembly at the desired location or locations prior to casting the concrete slab thereover. However, a substantially continuous hoop bar, or interconnected such sections, is necessary as the effective encircling of the column by substantially continuous length of bar structurally strengthens the function against shear forces. The reason for this is that in the region of concrete confined within the bar, cracking of the concrete is inhibited.
- In preferred embodiments of the invention, the distal end of each hook extends substantially horizontally when installed on a column. This facilitates the coupling to reinforcement in the slab, as the reinforcement can be readily slid under the hooks, or vice versa. If the shear legs are to be coupled to only one set of reinforcement rods in the slab, then all the distal ends of the hooks can be made parallel. If the shear legs are to be coupled to reinforcement rods extending in different directions, then the orientation of the hooks can be similarly varied. Typically, different sets of hooks are oriented to extend in different, normally orthogonal directions. As the reinforcement in the slab will normally comprise rods extending in one direction at one level and in another direction at another level, then again the height of one set of hooks relative to the hoop bar can be different from that of another.
- Shearheads according to the invention may be embodied in circular form. However, as the principal forces acting in a shearhead assembly can be resolved along perpendicular axes, preferred embodiments of the invention are in substantially square or rectangular form. This also facilitates the division of the hoop bar into sections and/or the hooks of the shear legs into sets as described above for coupling to perpendicularly oriented reinforcement rods in the slab. It should be noted though, that the attachment of the shearhead to reinforcement in the slab is not essential. Preferably though, it extends above the reinforcement to prevent the creation of a shear failure plane below the reinforcement. Such attachment does of course, additionally provide a convenient means by which the shearhead can be located prior to the slab being cast.
- Shearheads according to the invention can include an additional bar to which the shear legs are attached at their lower ends. This is though, not essential, but provides a convenient means by which the shearhead and the orientation of the shear legs thereof may be set. A light steel mesh suitably disposed relative to the upper hoop bar and the shear legs can be equally effective. Such a lower hoop bar or mesh can also provide an alternative means by which the shearhead is located in the slab; ie, on shuttering against which the slab is cast. It can be supported on separate spacers, or props attached to the lower hoop bar or mesh, or on props attached directly to at least some of the shear legs. This last option is of course available when a lower hoop bar or mesh is not used.
- The shear legs of shearheads according to the invention may take a number of different forms. Most simply, each shear leg comprises a single length of rod shaped to form the hook at its upper end. The hook forms an upper anchorage point in the subsequently cast slab, and a lower anchorage point is normally also formed; for example by shaping its lower end into a second hook which can extend around a lower slab reinforcement rod. Preferred shear legs however, each comprise a single length of rod which extends to form a loop below the hoop bar with both ends extending above the hoop bar to a hook. The loop thus forms a lower anchorage point in the cast slab. The shape of the loop may vary, but a preferred shape is broadly U-shaped, with two leg sections downwards from each hook to a link section thereby minimising bearing stresses. In another form, the shape of the loop may be broadly triangular, with two leg sections converging downwardly to a single bend. Each leg is attached to the hoop bar adjacent each hook. In some embodiments each shear leg is in the form of a closed or substantially closed curve through which the slab reinforcement passes where the coupling is made. The preferred shape in these embodiments is square or rectangular, although other shapes can be used, with particular benefit in certain applications.
- For some applications, the shear legs will depend vertically from the upper hoop bar. However, different applications may require different orientations of the legs. For example they might depend downwardly and outwardly from the hoop bar, relative to the column. The depth to which the shear legs extend from the upper bar will also affect the reinforcement they provide. Generally, the shear legs should extend as far as possible towards the lower surface of the slab, i.e., to but not into the cover layer. Generally, this means to or to just below the level of the lower layer of reinforcement in the slab and the legs may be attached to such lower reinforcement, for example by extending around rods thereof. However, we have found that an equivalent effect can be acheived if the shear legs merely extend to this level between lengths of the lower reinforcement without such attachment. This is of particular benefit as shearheads or hoop bar sections thereof according to the invention can be dropped or lowered into place after all the lower slab reinforcement has been put in place. Thus, a shearhead of the invention can be lowered into place by allowing the depending sections to pass through openings in the slab reinforcement. This is particularly advantageous when the lower slab reinforcement comprises welded mesh reinforcement, and not separate reinforcement bars. It is preferred in all embodiments of the invention where the slab has upper and lower layers of reinforcement that the shear legs extend fully between the layers to prevent the creation of shear failure planes in this region.
- A shearhead assembly embodying the invention will have the shearhead and slab reinforcement suitably supported on shuttering prior to the concrete slab being cast. Further, in some embodiments two or more shearheads extending around the same column may be employed, the second being disposed outside the first, but surrounding it generally in the same plane. Concentric square, rectangular or circular shearheads according to the invention may be used in this way.
- Shearheads according to the invention can be used on columns of any suitable construction. Typically, suitable columns are of reinforced concrete or steel. Shearheads of the invention can also be used in conjunction with shearheads of other types. As the shearheads of this invention extend around or spaced from the column axis, they are particularly suited as auxiliaries to other types of shearheads disposed on or around the column axis. In this connection reference is directed to our co-pending Application filed today under our Agent's reference EH 34198. It will be appreciated that shearheads of this invention may interdigitate with laterally extending beams or arms of such other shearhead types to more closely define the shear perimeter thereof.
- The above discussion is concerned primarily with shearheads disposed within a horizontal area of cast concrete, in which the hoop bar extends around the column in a generally symmetrical fashion. Shearhead structures broadly of the kind disclosed herein can also be useful at the periphery of such an area; in other words with at least one boundary of the shearhead coinciding with the column at the periphery of the area. Thus, a shearhead structure comprising a hoop bar with a plurality of shear legs attached thereto and depending therefrom can be cast within the body of a laterally extending slab at the periphery of the area thereof with a part of the hoop bar at the perimeter of the shearhead being cast within a supporting column also disposed at the periphery of the area. This can most conveniently be accomplished where the shearhead is of square or rectangular planar shape such that a straight edge thereof can be laid against the periphery of the area to be cast. Two or more such shearheads can be used adjacent each other if desired, and if the point on the periphery of the area to be cast is at a corner with an angle of greater than 180°, a plurality of shearheads can be disposed around the corner. Shearheads used in these variants will normally comprise at least two and normally a greater plurality of concentric hoop bars with depending shear legs.
- We have also found that shearheads of the kind described above in which the hoop bar does not wholly surround the column can provide effective reinforcement of the junction. Thus, a shearhead embodying the invention can comprise for example a hoop bar extending around three sides of a column between two points on the periphery of the area to be cast, with shear legs depending therefrom. In this variant, an upper and a lower hoop bar are preferably used, which bars are linked by vertical section at the periphery of the area to be cast. This arrangement can result in the creation of a torsion box in the region of the junction, which extends horizontally on either side of the column to limits defined by the hoop bars. If a plurality of concentric hoop bars are used, as is preferred, then the horizontal length of this torsion box can be considerable, and provide effective reinforcement into the body of the slab.
- The invention will now be described by way of example, and with reference to the accompanying schematic drawings wherein:
- Figure 1 is a perspective view showing the installation of a shearhead according to a first embodiment of the invention at the top of a column;
- Figure 2 is a detail view indicated by arrow A in Figure 1 showing a part of the shearhead and the slab reinforcement;
- Figure 3 is a plan view of a second embodiment of the invention in which two shearheads are disposed around a column;
- Figure 4 is an enlarged front elevation of part of the two shearheads shown in Figure 3;
- Figure 5 illustrates an alternative form of shear leg for use in the embodiment of Figures 3 and 4;
- Figure 6 is a schematic detailed view showing a shear leg supported on a shearhead according to a third embodiment of the invention;
- Figure 7 is a schematic perspective view of a shearhead according to a fourth embodiment of the invention disposed against a peripheral pillar or column;
- Figure 8 is a schematic plan view of the arrangement of Figure 7;
- Figure 9 is a schematic elevation of the arrangement shown in Figure 7; and
- Figures 10 to 13 show how shearheads according to the invention can be used at the periphery of an area to be cast.
- The shearhead shown in Figure 1 comprises a
single hoop bar 2 disposed over the top of acolumn 4, and surrounding the axis thereof. Thehoop bar 2 is of generally square form with its respective sides aligned parallel to the sides of thecolumn 4 which is also of square cross-section. Attached to thehoop bar 2 is a plurality ofshear legs 6, 8 as indicated on the respective sides of the hoop bar. In casting a substantially horizontal reinforced concrete slab (not shown) at the top of thevertical column 4, shuttering (also not shown) is appropriately located at the top of thecolumn 4, andreinforcement rods rods 10 are laid first, with therods 12 laid thereover either supported by therods 10 or by some other means. Eachshear leg 6, 8 has a hook at the top thereof which is disposed above thehoop bar 2, and at least some of these hooks are used to suspend thehoop bar 2 and all theshear legs 6, 8 from the reinforcingrods shear legs 6 are disposed closer to thehoop bar 2 than those on the shear legs 8. In this way, the hooks on theshear legs 6 may be attached to therods 10, and the hooks on the shear legs 8 to therods 12, while retaining thehoop bar 2 substantially horizontal. - The coupling of the shear legs to the reinforcing
rods leg 6 is attached to thehoop bar 2, typically by a spot weld, and a portion of each leg extends above thebar 2 to form ahook 14. Thedistal end 16 of thehook 14 extends substantially horizontally, and parallel to the plane of thehoop bar 2. This enables thehook 14 to be readily slid over the reinforcingrod 10 or alternatively, if the shearhead is located before the slab reinforcement, enables therod 10 to be readily slid under thehook 14. - As shown in Figure 2, the transverse reinforcing
rod 12 is supported directly on therods 10, but not in the vicinity of thehook 14. To enable the shearhead to be to be coupled to therods 12 as well as to therods 10, the shear legs 8 are formed in a similar shape to theshear legs 6, but with therespective hook 14 anddistal end 16 further spaced from thehoop bar 2. Thedistal end 16 would again extend substantially parallel to the adjacent length ofhoop bar 2, but of course perpendicular to the ends of theshear legs 6 as the respective legs 8 will be attached to a perpendicular section ofhoop bar 2. - The above described arrangement and orientation of
shear legs 6, 8 on thehoop bar 2 can of course be varied to suit the structure within the concrete slab upon which the shearhoop is to be suspended. Particularly, it should be noted that the orientation of thehooks 14 can of course be preserved even if the hoop bar is of different; eg, circular form. However, a square or rectangular form is preferred, as is a perpendicular orientation of respective shear legs as this simplifies the attachment of the hooks to slab reinforcement, which is normally arranged in two perpendicular directions along which the internal forces in the structure can be readily resolved. - Figure 3 and 4 show an alternative shearhead construction in which shear
legs 18 are attached to two generally concentric hoop bars 20, 22.Hoop bar 22 surroundshoop bar 20, and both are arranged around the top of acolumn 24. Also shown in Figure 4 arespacers 26 supporting the lower ends of theshear legs 18. - In the embodiment of Figures 3 and 4, each
shear leg 18 forms a pair ofhooks 28. The shape of each hook is broadly similar to that described with reference to Figure 2 above, and because all the hooks are oriented in the same direction, they are uniformly spaced above the respective hoop bars 20 and 22. Eachshear leg 18 forms a loop below the hoop bar to which it is secured, and it is the base of the loop which is supported by aspacer 26. It will be noted from Figure 3 that the loops are respectively in planes parallel to the length of hoop bar to which they are attached while the hooks are all oriented in the same direction. - As is apparent from Figure 4, the loop formed by each
shear leg 18 below thehoop bar 20 is of generally triangular configuration. Aleg section 30 depends from eachhook 28, converging towards another section depending from an adjacent hook. Thesections 30 merge in asmooth bend 32 which forms a lower anchorage point in theslab 34. Each hook is coupled to an upper slab reinforcment rod 10 (see Figure 1) and thebends 32 are substantially at the level of thelower reinforcement rods 36. - Figure 5 shows an alternative and preferred form of shear leg which also defines a loop. Here, the
leg sections 30 are parallel, and connected at their lower ends bylink section 38. This form of shear leg may be substituted directly for the legs of the Figure 4 embodiment. As can be seen, thelink section 38 provides a convenient means by which the shear leg may be supported, either on a spacer as shown at 26 in Figure 4, or on alower reinforcement rod 36. The tworods 36 shown in Figure 5 are arranged orthogonally in the slab such that thelink section 38 extends adjacent one rod while resting on the other. - Shearheads with shear legs of the kind shown in Figures 4 and 5 are particularly suited for installation after placement of the lower slab reinforcement. As shown in Figure 4, the shearhead is lowered into positon after placement of the
lower reinforcement rods 36, but before location of theupper rods - A steel mesh may be used in place of the
spacers 26, having components intersecting within the body of thecolumn 24 which support the shearhead. It will be appreciated from the description of Figure 1 above, that such a mesh may be supported at the top of thecolumn 24 prior to casting the slab and the overlaying column length. However, the mesh can of course be supported directly on the shuttering for the slab if preferred. - The shearhead, a detail of which is shown in Figure 6, comprises an
upper hoop bar 42 and alower hoop bar 44 to which ashear leg 56 is welded at 48. Theshear leg 56 is of generally rectangular shape, but which does not complete a closed curve and is open at one corner of the "rectangle". In this way, the shearhead as a whole can be supported on the slab reinforcement. Further slab reinforcement can also be threaded through the lower portion of the shear leg or on either side thereof as indicated at 54. Reinforcement will also be disposed below thisslab reinforcement 54 as indicated at 52. Theshear leg 56 will normally extend below thelowermost slab reinforcement 52, although without of course reducing the cover factor to an unacceptable level. Thelower hoop bar 44 may be dispensed with in some circumstances. - The shearhead illustrated in Figures 7 to 9 is shown comprising three
hoop bars 62, each extending around three sides of acolumn 58. Eachhoop bar 62 has an upper and lower portion linked by avertical section 64. The hoop bars 62 are arranged generally concentrically around thecolumn 58 in theslab 60, and shear legs 66 (only one is shown in Figure 7) extend from above the upper hoop bar section to below the lower hoop bar section as does the shear leg described above with reference to Figure 6. It will be appreciated that shear legs of any suitable form can be used. - Referring particularly to Figures 7 to 9, it can be seen how the hoop bars 62 form a torsion box which extends generally horizontally through the
column 58 at the periphery of the area being cast. Figure 9 in addition shows thecolumn reinforcement 68 andadditional reinforcement 70 around which thelink portions 64 extend between the upper and lower portions of thehoop bar 62. In combination with theshear legs 66 mounted as shown, thehoop bar 62 combines with thereinforcement 70 to form a torsion box which effectively reinforces the slab around the column. - Figures 10 to 13 show how square or rectangular shearheads can also be put to good effect at the periphery of the area to be cast. Figure 10 shows two
shearheads 72 arranged side by side against the periphery of the cast area, with adjacent corners cast within the body of a pillar orcolumn 74. Figure 11 shows asingle shearhead 72 with the cross-section of acolumn 76 extending generally perpendicularly into one side thereof. Figure 12 shows how ashearhead 72 can be fitted into a corner with a corner thereof cast into avertical column 78. Figure 13 shows how three shearheads can be fitted around an obtuse corner, each coupled to a part of avertical column 80. - Shearheads described herein in relation to the accompanying drawings are normally formed in steel and as noted above, are preferably of square or rectangular form. By way of example, for the mounting of a slab with a depth of 22cm on a column 40cm square, the inner hoop bar of Figure 3 might be 60cm square, with the outer bar being 90cm square. Each hoop bar would typically be of 12mm diameter steel, with the shear legs being in 8mm steel for attachment to reinforcing rods of 16mm steel in a slab having a 25mm cover.
Claims (14)
- A shearhead for casting within the body of a laterally extending reinforced concrete slab (34) to reinforce a junction between the slab and a supporting concrete column (41) comprising a plurality of shear legs (6, 8) attached to, depending from and spaced along at least one horizontal closed hoop bar (2) which is arranged to extend around or in the vicinity of the column, characterised in that the hoop bar is arranged to contain the horizontal forces radially extending from the column when the floor is loaded and in that the shearhead is equipped with suspension means for suspending it from the floor slab upper reinforcement mesh (10, 12) comprising a portion of each shear leg which extends above the hoop bar and is provided with a hook (14, 28) for coupling to the said mesh.
- A shearhead according to Claim 1 wherein each shear leg (6, 8) is a length of rod, one end of which forms the hook (14, 28).
- A shearhead according to Claim 1 wherein each shear head (6, 8) is a length of rod (30) extending in a loop (38) below the hoop (2) with both ends of the rod having each a portion extending above the hoop to form a said hook (14, 28).
- A shearhead according to any preceding claim wherein the hoop (2) extends substantially in one plane and the distal end (16) of each hook (14) comprises a portion of the respective shear leg which extends substantially parallel to the plane of the hoop.
- A shearhead according to Claim 4 wherein the distal ends of all the hooks are parallel.
- A shearhead according to Claim 4 wherein the distal ends of a first set of the hooks extend in a first common direction, and the distal ends of a second set of the hooks extend in a second common direction perpendicular to said first direction.
- A shearhead according to Claim 6 wherein the first set of hooks are disposed further above the hoop than the second set of hooks.
- A shearhead according to any preceding claim wherein the hoop (2) is substantially rectangular or square.
- A shearhead according to Claim 8 when dependent upon Claim 7 wherein the first set of hooks are part of the shear legs on two parallel sides of the hoop and the second set of hooks are part of the shear legs on the other two parallel sides of the hoop.
- A shearhead according to any preceding claim including an additional hoop (44) to which the shear legs are attached at the lower ends thereof.
- A shearhead assembly having a shearhead according to any preceding claim supporting a laterally extending concrete slab on a column wherein the shearhead is cast within the slab around the column with at least some of the hooks of the shearhead extending over horizontal reinforcement of the slab.
- A shearhead assembly according to Claim 11 including an additional shearhead (20, 22) cast within the slab and surrounding both the column and the first-mentioned shearhead, wherein the additional shearhead comprises a hoop for extending around the column with a plurality of shear legs attached thereto and depending therefrom, each shear leg including a portion extending above the hoop, which portion forms a hook for coupling to reinforcement in the slab.
- A shearhead assembly according to Claim 11 including an additional shearhead comprising beams effectively coupled directly to the column, with the first-mentioned shearhead co-operating with said additional shearhead to reinforce the assembly.
- A shearhead assembly according to Claim 13 wherein the shear legs of the first-mentioned shearhead depend between the beams of the additional shearhead.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT90309138T ATE96489T1 (en) | 1989-08-21 | 1990-08-21 | SHEAR REINFORCEMENT FOR COLUMN HEAD. |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8919009 | 1989-08-21 | ||
GB898919009A GB8919009D0 (en) | 1989-08-21 | 1989-08-21 | Shearhead reinforcement |
GB909001755A GB9001755D0 (en) | 1990-01-25 | 1990-01-25 | Shearhead reinforcement |
GB9001755 | 1990-01-25 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0414485A2 EP0414485A2 (en) | 1991-02-27 |
EP0414485A3 EP0414485A3 (en) | 1991-05-15 |
EP0414485B1 true EP0414485B1 (en) | 1993-10-27 |
Family
ID=26295796
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP90309138A Expired - Lifetime EP0414485B1 (en) | 1989-08-21 | 1990-08-21 | Shearhead reinforcement |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0414485B1 (en) |
AT (1) | ATE96489T1 (en) |
DE (1) | DE69004193T2 (en) |
DK (1) | DK0414485T3 (en) |
GB (1) | GB2235226B (en) |
Families Citing this family (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2328455A (en) * | 1996-08-21 | 1999-02-24 | Jubin Motamed | Concrete slab shear reinforcement |
DE29812891U1 (en) * | 1998-07-20 | 1999-01-14 | Frisch, Hans, 89343 Jettingen-Scheppach | Shear reinforcement in the column area |
DE19924418A1 (en) * | 1999-05-27 | 2000-11-30 | Schoeck Bauteile Gmbh | Shear reinforcement component |
DE29912526U1 (en) * | 1999-07-19 | 1999-09-23 | Filigran Trägersysteme GmbH & Co KG, 31633 Leese | Punching shear reinforcement for flat slabs |
DE19937414A1 (en) * | 1999-08-07 | 2001-03-15 | Heinz Pape | Construction component for producing recesses in support area of flat ceilings of reinforced- and stressed concrete involves stresses taken up and dissipated by round tube with all-round torus at each end |
ES2246619B1 (en) * | 2003-01-13 | 2007-01-01 | Olatz Isabel Merino Garay | FERRALLA ARMOR FOR THE CONSTRUCTION OF UNIDIRECTIONAL AND BIDIRECTIONAL FORGES OF ARMED CONCRETE. |
DE202005019077U1 (en) * | 2005-12-06 | 2007-04-19 | nolasoft Ingenieurgemeinschaft Ozbolt Mayer GbR (vertretungsberechtigter Gesellschafter: Dr.-Ing. Utz Mayer, 70178 Stuttgart) | Reinforcement element for structures made of reinforced concrete, prestressed concrete or the like. |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR964234A (en) * | 1950-08-08 | |||
FR964257A (en) * | 1948-04-06 | 1950-08-09 | ||
FR59986E (en) * | 1950-01-31 | 1954-09-22 | Special device of beams and ribs for floors, economical installation of ceilings | |
GB1396780A (en) * | 1972-05-02 | 1975-06-04 | British Reinforced Concrete Eng Co Ltd | Reinforced concrete |
AT378217B (en) * | 1983-03-21 | 1985-07-10 | Avi Alpenlaendische Vered | REINFORCEMENT ELEMENT |
FR2568916B1 (en) * | 1984-08-10 | 1986-09-05 | Selam Sa | IMPROVEMENT IN METAL FRAMEWORK FOR PREFABRICATED CONSTRUCTION ELEMENTS |
EP0184995B1 (en) * | 1984-12-12 | 1991-07-31 | Ulisse C. Aschwanden | Reinforcement system preventing shearing |
-
1990
- 1990-08-21 GB GB9018326A patent/GB2235226B/en not_active Expired - Fee Related
- 1990-08-21 EP EP90309138A patent/EP0414485B1/en not_active Expired - Lifetime
- 1990-08-21 DE DE90309138T patent/DE69004193T2/en not_active Expired - Fee Related
- 1990-08-21 AT AT90309138T patent/ATE96489T1/en active
- 1990-08-21 DK DK90309138.7T patent/DK0414485T3/en active
Non-Patent Citations (1)
Title |
---|
Reynolds & Steedman "Reinforced Concrete Designer's Handbook" p. 390 * |
Also Published As
Publication number | Publication date |
---|---|
GB9018326D0 (en) | 1990-10-03 |
ATE96489T1 (en) | 1993-11-15 |
GB2235226B (en) | 1993-08-18 |
EP0414485A2 (en) | 1991-02-27 |
DE69004193T2 (en) | 1994-04-07 |
DE69004193D1 (en) | 1993-12-02 |
EP0414485A3 (en) | 1991-05-15 |
GB2235226A (en) | 1991-02-27 |
DK0414485T3 (en) | 1993-12-20 |
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