Title of Invention	A METHOD OF CONSTRUCTING A REINFORCED STRUCTURAL ELEMENT AND A REINFORCED STRUCTURAL ELEMENT PRODUCED THEREBY
Abstract	A method of constructing a reinforced structural element (1), comprising : a) providing spaced first and second reinforcing structures (2,3;4,5) disposed substantially perpendicular with respect to a first direction, each structure comprising reinforcing elements formed as a network having gaps between the reinforcing elements; b) providing thin elongate strips (6) of undulating form having at least one peak and a trough on either side; c) anchoring the strips around the reinforcing elements of the first structure by engagement of said peak with an element thereof; and d) casting structural material around both the reinforcing structures and around the strips to embed said structures and strips in the material; characterised by :- e) disposing the strips in the first and second reinforcing structures from a direction opposite said first direction and from one side of the first reinforcing structure; f) said anchoring being without additional structural connection of the strips to said elements, said troughs passing through said gaps in the first reinforcing structure so as to lie adjacent the second reinforcing structure; and g) the strips being of high stiffness material and forming shear reinforcement for the structural element.

Title of Invention

A METHOD OF CONSTRUCTING A REINFORCED STRUCTURAL ELEMENT AND A REINFORCED STRUCTURAL ELEMENT PRODUCED THEREBY

Abstract

A method of constructing a reinforced structural element (1), comprising : a) providing spaced first and second reinforcing structures (2,3;4,5) disposed substantially perpendicular with respect to a first direction, each structure comprising reinforcing elements formed as a network having gaps between the reinforcing elements; b) providing thin elongate strips (6) of undulating form having at least one peak and a trough on either side; c) anchoring the strips around the reinforcing elements of the first structure by engagement of said peak with an element thereof; and d) casting structural material around both the reinforcing structures and around the strips to embed said structures and strips in the material; characterised by :- e) disposing the strips in the first and second reinforcing structures from a direction opposite said first direction and from one side of the first reinforcing structure; f) said anchoring being without additional structural connection of the strips to said elements, said troughs passing through said gaps in the first reinforcing structure so as to lie adjacent the second reinforcing structure; and g) the strips being of high stiffness material and forming shear reinforcement for the structural element.

Full Text	This invention relates to a method of constructing a reinfored structural element, and a reinforced structural element produced thereby and more particularly to a reinforced concrete structural element having improved resistance to shear failure and to a method of providing shear reinforcement for a reinforced concrete structural element. BACKGROUND TO THE INVENTION Thin reinforced concrete elements, for example flat concrete slabs, provide an elegant form of construction, which simplifies and speeds up site operations, allows easy and flexible partitioning of space and reduces the overall height of buildings. Reinforced concrete flat slab construction also provides large uninterrupted floor areas within a minimum construction depth, and is used extensively for a wide range of buildings such as office blocks, warehouses and car parks. One design problem associated with this form of construction is punching failure, which occurs as a result of high point loads or high shear stresses around the supporting columns. In punching failure, the failed surface of the slab forms a truncated cone or pyramid. This problem has in the past often lead to the use of mushroom heads or local thickening of the slab, but these solutions increase costs and slow down the rate of construction.As the spans become larger and the slabs become thinner the increased stresses around the critical shear perimeter have created even greater problems for the structural engineer. A variety of design solutions have been proposed, of which the mast commonly used are as follows: 1. Conventional shear reinforcement This solution is very labour-intensive and requires extra work both in the design and on site. 2. Use of a larger column and/or a thicker conerets slab These solutions increase the deadload of the building and reduce the available space. 3 . Use of a column head This requires more complicated formwork, slows down the rate of construction, and interferes with the installation of building services. 4. Use of slab drops These are a modified form of column head. Shear reinforcement, when required, is normally accomplished by providing reinforcing members either at an angle or laterally to the main flexural reinforcement. In thin structural elements, such as flat slabs, anchoring of short lengths of shear reinforcement is a major design problem. The problem is aggravated by the fact that normal shear reinforcement cannot be placed above the top layer of flexural reinforcement without reducing either the durability, or the efficiency, of the flexural reinforcement. In addition, there is the practical problem of supporting the shear reinforcement during the construction stages. Recently a new system has been introduced by Square Grip Limited, designated the Shearhoop system, which consists of an assembly of specially shaped links (shear leg bobs) and hoop reinforcing bars. The hoops are available in a range of sizes and can be combined to form a complete system extending outwards from the column to the zone where the shear resistance of the concrete slab alone is adequate. In the construction of a slab using Shearhoops, bars B1, B2 for the bottom layer of reinforcement are first laid down and the Shearhoops placed over them in the appropriate location. Top reinforcement T2 is then positioned on chairs and the bars overlapping the Shearhoops fully located under the ends of the shear leg bobs extending from the Shearhoops. Finally the top reinforcement T1 is placed over the entire structure. Whilst the Shearhoops are an improvement on previous arrangements, they still cannot be anchored above the top layer of reinforcement T1 and thus do not provide the best possible shear reinforcement. From the above, it is apparent that, although much effort has gone into the design of reinforcing systems that address some of the above mentioned problems, none of them provide a complete solution. Although prepackaged reinforced systems offer some time savings over the in-situ steel fixing solutions, they are nevertheless more expensive in terms of materials and other resources, such as labour and crane time. Sxane of the other prior art proposals are also of questionable effectiveness, or produce an unquantifiable increase in flexural capacity. There is a need, therefore, for an improved reinforcing system to impart better shear resistance, without increasing the thickness of the slab. An additional advantage would be to provide a shear reinforcement system enabling thinner slabs to be used. US 4854106 described foundations for buildings and like . structures employing steel reinforcement. A hook leg has an elongate member bifurcated at each end longitudinally of the member to form a pair of extensions with a slot therebetween, the distal portion of the extensions being bent into a curved form extending transversely of the member to form hooks adapted to resiliently engage a pair of reinforcing rods in the reinforcement, the slots in the unbent portions of the extensions being adapted to receive a second pair of reinforcing rods extending transversely of the first pair, whereby to fix the rods in spaced alignment. There is no mention of shear reinforcement. US 4472331 described a reinforcing framework for a concrete building structure in which column and beam reinforcing bars are inserted into holes in reinforcement frames disposed at predetermined intervals. Shearing reinforcement bands, formed by bending a steel strip into a rectangular frame shape, are disposed between adjacent reinforcement frames and secured to wooden sheathing boards by nailS. The construction requires access to all sides of the column or beam, and the protruding nails would give rise to potential corrosion problems. DE 3331276 describes shear reinforcement elements for column supported flat slabs or beams of reinforced or prestressed concrete, which consist of flat steel strips which are undulating in at least two dimensions and transverse to the main surface of the flat slab or beams. The shear reinforcement elements are used in place of conventional round reinforcing bars. SUMMARY OF THE INVENTION The present invention provides a shear failure reinforcing system for structural elements, in which thin elongate strips of high stiffness material are anchored around a layer of conventional reinforcement, and/or are anchored around a plurality of layers of conventional reinforcement, such that the strips tie the structural element and improve its resistance to shear failure. In preferred embodiments, the strips are enchored around the outermost reinforcing members of a layer or layers of reinforcement, to give improved shear resistance. Accordingly, the present invention provides a method of constructing a reinforced structural element, said element being, in use, potentially subject to concentrated forces in a first direction, said forces resulting in shear stresses in the element, said method comprising : a) providing spaced first and second reinforcing structures disposed substantially perpendicular with respect to said first direction, each structure comprising reinforcing elements formed as a network having gaps between said reinforcing elements; b) providing a plurality of thin elongate strips said strips being undulating so as to have at least one peak having a trough on either side; c) anchoring the strips around the reinforcing elements of said first reinforcing structure by- engagement of said peak with an element thereof; and d) casting structural material around said first and second reinforcing structures and around said strips to embed said structures and strips in said material; characterised in that the method further comprises :- e) disposing said strips in the first and second reinforcing structures from a direction opposite said first direction and from one side of said first reinforcing structure; f) said anchoring being without additional structural connection of said strips to said elements, said troughs passing through said gaps in the first reinforcing structure so as to lie adjacent said second reinforcing structure; and g) said strips being of high stiffness material and being arranged to provide shear reinforcement for the structural element in the event of the clement being subject to such concentrated shear-resulting forces in said first direction. This invention also provides a reinforced structural element produced by the above method, said element being, in use, potentially subject to concentrated forces in a first direction, said forces resulting in shear in the structural element, said structural element comprising : a) spaced first and second reinforcing structures disposed substantially perpendicular with respect to said first direction, each structure comprising reinforcing elements formed as a network having gaps between said reinforcing elements; b) a plurality of thin elongate strips, said strips being undulating so as to have at least one peak having a trough on either side; c) the strips being anchored around the reinforcing elements of said first reinforcing structure by engagement of said peak with an element thereof; and d) structural material embedding said first and second reinforcing structures and said strips; characterised in that e) said strips are disposed in the first and second reinforcing structures from a direction opposite said first direction and from one side of said first reinforcing structure; f) said anchoring is without additional structural connection of said strips to said elements, said troughs passing through said gaps in the first reinforcing structure so as to lie adjacent said second reinforcing structure; and g) said strips being of high stiffness material and being arranged to provide shear reinforcement for the structural element in the event of the element being subject to such concentrated shear-resulting forces in said first direction. DETAILED DESCRIPTION OF THB INVENTION The reinforced structural element may be cast in situ or precast, and may be provided with any suitable longitudinal reinforcement comprising elongate reinforcing members, which may be initially unstressed, pre-stressed, or post-tensioned. The invention finds particular application where the reinforced structural element is a slab structure especially a flat slab, although it can also be a waffle or ribbed slab, a slab with downstands, a foundation slab Or footing, or a staircase slab Other possible uses may be in a wall, a wide band beam, or normal beam, a normal or extended column, a box or other hollow shape, or a shell or other three dimensional shape. The element may be with or without openings, as desired. The reinforced structural element may have any suitable thickness, depending upon the application. Henceforth the invention will be more particularly described with reference to thin reinforced concrete structural elements, for example flat slabs, having a thickness of from 10 to 80cms, more particularly from 10 to 30cms, but it is to be understood that although the invention has particular advantages when applied to such structures, it is not limited thereto. The thin reinforced concrete structural element may have any desired length and width, but reinforced flat slabs used in conventional building construction are often of a size of from 1 to 10 metres in length and from 1 to 10 metres in width. The reinforcing members will usually be elongate rods or bars embedded in the structural element and lying parallel to the major surfaces of the element. The reinforcing members can have any suitable cross-section, for example round, square, or rectangular. Typically, the reinforcing members lie adjacent one or more of the major surfaces of the structural element, and comprise series of reinforcing bars laid at right angles to each other. The major surfaces of the structural element will normally be the top and bottom surfaces, where the element is a slab, but they could also be the side surfaces of a wall. The material of the reinforced concrete structural element may be normal concrete, high strength concrete, light weight concrete, concrete with special cements and aggregates, polymer modified concrete, special cement mortar, special polymer mortar. Elements formed from other suitable materials able to be cast which require strengthening in shear, such as, for example, fibre reinforced plastics and ceremics can also be used. The thin elongate strip of high stiffness material preferably has dimensions such that it will not radically change the overall thickness of the structural members to which it is anchored, and such that it will not break when bent to the required shape, which could be around tight corners. Preferably the strip has a thickness of from 0.5 to 1.0mm and a width of from 10 to 30mm. The material of the strip is preferably a high tensile, high stiffness material, such as, for example, high tensile steel, although other high stiffness materials, for example structural polymers such as polypropylene and fibre reinforced plastics comprising, for example, carbon fibre, glass fibre and aramids, are not excluded. The material is required to have high stiffness in order to be able to arrest the development of shear cracks at low strains, and, for example, a material of stiffness of from 100KN/mm2 to 210KN/mm2 is preferred. High strength material is preferred for the strips because a lower volume of strip material can be used. A typical strength for a high tensile steel used for the strip can be, for example, from 460N/mm2 to 1500N/mm2. Special hardness strips may be useful when dealing with walls in safe areas. The durability of the strip may be improved by adequate cover, by special surface protection, or by using non- corrosive materials such as stainless steel, or fibre reinforced plastics. Where the strip is metallic, it may also be eharged to provide cathodic protection. Punched holes, embossments and indentations in the strip, as well as spedial bending, twisting or surface treatment of the strip, can help the overall bond characteristics of the strip to the material of the structural element, although a right angle bend may be sufficient to anchor the strip where concrete is used as the material for the reinforced structural element. In use, the strip may be disposed in a vertical, horizontal, or inclined direction, and may be bent or clipped around the reinforcing member to which it is anchored, or tied thereto. In a preferred aspect of the invention, the strip is anchored around one or more of the outermost reinforcing members, that is, those members closest to the major surfaces of the structural element. Since the reinforcing bars are often of significant thickness, for example around 20mm diameter, this provides shear reinforcement to a point closer to the surface than has been possible hitherto. Bending and shaping of the strips to the desired shape may be readily accomplished by hand, or by the use of specialised automated or semi-automated equipment, the strips may be preformed before conveying to the site, and use, if desired. The strips may be anchored in the material of the structural element by providing an appropriate extra strip length beyond a bend around a structural element, or alternatively ends of the strip may be secured together by metal clips, rivets or other fixing means. It is particularly pref erred for the strip to be so shaped that it can be positioned from one side of the structural element, without the need to obtain all round access. The strip can, for example, be bent into a zigzag shape, a castellated shape, a sine wave curved shape, or other repeating straight sided or curved shaped and then dropped into position on the reinforcing members. This greatly facilitates assembly, where it is often difficult to obtain all round accesss to the structural element. Preferably the strips are arranged such that they are totally enclosed within and not exposed at. any point on the surface of the structural element, and are not connected to any metal fixing, for example, a nail or screw, which is exposed on the structural element surface. This is to avoid the risk of corrosion or deterioration of the strips in service. Structural elements reinforced by the method of the invention can have improved strength and substantially improved ductility, imparting improved resistance to shear failure. In addition, structural elements reinforced in accordance with the invention can have a thinner section than those hitherto specified because of their improved resistance to shear failure. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS In order that the invention may be better understood, preferred embodiments thereof will now be described in detail, by way of example only, with reference to the accbmanying Drawings in which: Figure 1A shows schematically a section side elevation of a reinforced flat structural element according to the invention; Figure 1B shows a sectional side elevation of a reinforced curved structural element according to the invention; Figure 1C shows a sectional side elevation of a reinforced • flat structural element according to the invention in which the strip is anchored to both top and bottom reinforcing members; Figure 1D shows a sectional side elevation of a reinforced flat structural element according to the invention reinforced with single spacing inclined strip; Figure 1E shows a sectional side elevation of an inclined reinforced structural element according to the invention; Figure 1F shows a sectional side elevation of a vertical reinforced structural element according to the invention; Figure 2 shows examples of punched and pre-formed steel strips for use in the invention; Figure 3A shows a perspective view from the top and one side of the reinforcing formwork of a flat reinforced concrete structural slab in accordance with the invention, reinforced with inclined metal strips with punched holes; Figure 3B shows a perspective view from the top and one side of the reinforcing formwork of a reinforced flat concrete structural slab in accordance with the invention, having inclined metal strip shear reinforcement, but without punched holes in the strips; Figure 3C shows a perspective view from the top and one side of the reinforcing formwork for a reinforced flat concrete slab in accordance with the invention, having shear reinforcement comprising vertically arranged metal strips with punched holes; Figure 4A shows the load versus deflection curves for the slabs of figures 3A to 3C (PPSB to PPSD} in comparison with an unreinforced control slab (PPSA); and Figure 4B shows the load versus strain in the flexural reinforcement for the slabs of figures 3A to 3C {PPSB to. PPSD) in comparison with an unreinforced control slab (PPSA). Referring now to figure 1, in figure 1A there is shown a flat element 1, supported on a column 7 about a centre line C , having upper reinforcing bars, 2, 3, arranged at right L angles to each other, and lower reinforcing bars 4, 5 similarly arranged. U-shaped strips 6 of thin, elongate high stiffness steel are arranged between the upper and lower reinforcing bars in order to provide double spaced vertical shear reinforcement. In figure 1B there is shown a curved reinforced concrete element 10, supported on columns 16, having upper reinforcing bars 11, 12 and a lower reinforcing bar 13. A thin strip of 14 of high stiffness steel is bent around the upper reinforcing bars 12 and the lower reinforcing bar 13 to provide single spacinq vertlaal Strip shear reinforcement. The strip 14 is bent at its ends 15 around the lower reinforcfing bar 13, leaving a substantial length of the strip for anchoring in the concrete. Figure 1C shows a flat concrete structural slab 20, supported on a column 21 about a centre line C , and having upper reinforcing bars 22, 23, and lower reinforcing bars 24, 25. In this case the thin, high stiffness metal strip 26 is bent around both upper, and lower reinforcing bars. In figure 1D there is shown a flat reinforced concrete slab 30, supported upon a column 31, and provided with upper reinforcing bars 32, 33 and lower reinforcing bars 34, 35. Shear reinforcement is provided by the metal strip 36 which is bent around upper and lower reinforcing bars so as to provide inclined shear reinforcement. Figure 1E shows an inclined concrete reinforcing slab 40, supported on a column 41, and provided with upper reinforcing bars 42, 43 and lower reinforcing bars 44, 45. Shear reinforcement is provided by the high stiffness metal strip'46 which is bent around both upper and lower reinforcing bars to form a. single spaced shear reinforcement. Figure 1F shows a vertical concrete structural slab 50 having right side reinforcing bars 51, 52 and left side reinforcing bars 53, 54. Shear reinforcement is provided by the high stiffness metal strip 55 which is bent around both left and right side reinforcing bars to provide inclined shear reinforcement. The invention will now be illustrated, by the following examples : Example 1 This example describeds the enhancement of shear capacity of a flat slab with inclined metal strip reinforcement having punched holes. Steel strips are produced having a series of punched holes as shown in figure 2, and are preformed to the castellated shape shown therein. The strips are arranged in the formwork for a concrete slab in locations determined by using British Standard BS8110 (1985), as illustrated in figure 3A. It will be noted that it is only necessary to have access to the top side of the formwork in order to place the strips in position. Concrete is then poured to produce a slab of thichness 175mm which is below the 200mm limit imposed by BS8110 on the thickness of flat slabs. The slab (B) was tested with an eight-point load arrangement, simulating loading typical of flat slabs in buildings of conventional construction. The load versus deflection curves and the load versus strain in the flexural reinforcement curves for this slab and others tested for comparison are shown in figures 4A and 4B respectively. Slab (A) was unreinforced and failed in abrupt punching shear mode at a load of 460kN. Slab (B) deflected considerably more, developed very large strains in the longitudinal reinforcement and failed in a ductile mode at a maximum load of 560kN in the fashion desired in practirce by structural engineers. Example 2 -This example demonstrates the increase in load and ductility of a flat slab reinforced with inclined steel strip. Steel strips without the punched holes are preformed as shown in figure 2 and arranged in the metal formwork for a concrete slab in locations determined by using BS8110 (1985) as illustrated in figure 3B. Concrete is then poured to produce a slab of thichness 175mm. The slab (C) was tested with an eight-point load arrangement, making extra allowance for anchoring the strip at its ends. The load versus deflection curves and the load versus strain in the flexural reinforcement curves for this slab and others tested for comparison are shown in figures 4A and 4B respectively. Slab (C) deflected considerably more than slab (A), and developed very large strains in the longitudinal reinforcement, failing in' a ductile mode at a maximum load of 560kN. Example 3. This example demonstrates the increase in load and ductility of a flat slab reinforced with vertical steel strip reinforcement anchoring both layers of longitudinal reinforcement. Steel strips, punched and pre-formed as shown in figure 2, are inserfed into the form form work of a concrete slab as shown in figure 3C and anchored to the upper and lower layers of longitudinal reinforcing bars. The strips are arranged in locations determined by using BS8110 (1985 ). Concrete is then poured to produce a slab of thickness 175mm. The slab (D) was tested with an eight-point load arrangement, simulating loading typical on flat slabs in buildings. Extra allowance was made for anchoring the strip at its ends. The load versus deflection curves and the load versus strain in the fiexural reinforcement curves for this slab and others tested for comparison is shown in figures 4A and 4B respectively. Slab (D) deflecting considerably more than slab (A) , developed very large strains in the longitudinal reinforcement, and failed in a ductile mode at a maximum load of 560kN. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstrct and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutally exclusive. Each feature disclosed in this specification (including any accompanying claims abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of the generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. We Claims : 1. A method of constructing a reinforced structural element (1), said element being, in use, potentially subject to concentrated forces in a first direction, said forces resulting in shear stresses in the element, said method comprising: a) providing spaced first and second reinforcing structures (2, 3;4,5) disposed substantially- perpendicular with respect to said first direction, each structure comprising reinforcing elements formed as a network having gaps between said reinforcing elements; b) providing a plurality of thin elongate strips (6), said strips being undulating so as to have at least one peak having a trough on either side; c) anchoring the strips around the reinforcing elements of said first reinforcing structure by engagement of said peak with an element thereof; and d) casting structural material around said first and second reinforcing structures and around said strips to embed said structures and strips in said material; characterised in that the method further comprises :- e) disposing said strips in the first and second reinforcing structures from a direction opposite said first direction and from one side of said first reinforcing- structure; f) said anchoring being, without additional structural connection of said strips to said elements, said troughs passing-through said gaps in the first reinforcing structure so as to lie adjacent said second reinforcing structure; and g) fsaid strips being of high stiffness material and being arranged to provide shear reinforcement for the structural element in the event of the element being subject to such concentrated shear-resulting forces in said first direction. 2. A method as claimed in claim 1, wherein the reinforced structural element is a flat slab. 3. A method as claimed in claim 1 or 2, wherein the structural element is a reinforced concrete element. 4. A method as claimed in any of claims 1 to 3, wherein the structural element has a thickness of from 10 to 30cms. 5. A method as claimed in any preceding claim, wherein the structural element has a length of from 1 to 10m and a width of from 1 to 10m. 6. A method as claimed any preceding claim, wherein the reinforcing elements comprise a series of reinforcing bars laid at right angles to each other. 7. A method as claimed in any preceding claim, wherein the elongate strips of high stiffness material have a thickness of from 0.5 to 1.0mm and a width of from 10 to 30mm. 8. A method as claimed in any preceding claim, wherein the material of the elongate strips comprises high tensile steel. 9. A method as claimed in any preceding claim, wherein the material of the strips has a stiffness of from 100KN/mm2 to 210KN/mm2 and a strength of from 460N/mm2 to 1500N/mm2. 10. A method as claimed in any preceding claim, wherein the elongate strips are provided with holes along the lengths thereof to assist the overall bond characteristics of the strips to the material of the structural element. 11. A method as claimed in any preceding claim, wherein the ends of the elongate strips are bent or clipped around reinforcing elements of the second reinforcing structure. 12. A method as claimed in claim 11, wherein the strips are preformed into a castellates shape. 13. A method as claimed in any preceding claim, wherein the elongate strips are anchored in the material of the structural element by providing an appropriate extra strip length beyond a bend around a structural element. 14. A method as claimed in any preceding claim, wherein the elongate strips are totally enclosed within the structural element and are not connected to any exposed metal fixing. 15. A method as claimed in any preceding claim, wherein the elongate strips are tied to elements of the reinforcing structure. 16. A method as claimed in any preceding claim, wherein ends of the elongate strips are secured to each other by metal clips, rivets or other fixing means. 17. A method of constructing a reinforced structural element (l) substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 18. A reinforced structural element (1) produced by a method as claimed in any preceding claim, said element being, in use, potentially subject to concentrated forces in a first direction, said forces resulting in shear in the structural element, said structural element comprising : a) spaced first and second reinforcing structures (2,3,-4,5) disposed substantially perpendicular with respect to said first direction, each structure comprising reinforcing elements formed as a network having gaps between said reinforcing elements; b) a plurality of thin elongate strips (6), said strips being undulating so as to have at least one peak having a trough on either side; c) the strips being anchored around the reinforcing elements of said first reinforcing structure by engagement of said peak with an element thereof; and d) structural material embedding said first and second reinforcing structures and said stirps; characterised in that e) said strips are disposed in the first and second reinforcing structures from a direction opposite said first direction and from one side of said first reinforcing structure; f) said anchoring is. without additional structural connection of said strips to said elements, said troughs passing through said gaps in the first reinforcing structure so as to lie adjacent said second reinforcing structure; and g) said strips being of high stiffness material and being arranged to provide shear reinforcement for the structural element in the event of the element being subject to such concentrated shear-resulting forces in said first direction. 19. A reinforced structural element substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. Dated this 6th day of May, 1996.

Full Text

This invention relates to a method of constructing a
reinfored structural element, and a reinforced structural
element produced thereby and more particularly to a
reinforced concrete structural element having improved
resistance to shear failure and to a method of providing
shear reinforcement for a reinforced concrete structural
element.
BACKGROUND TO THE INVENTION
Thin reinforced concrete elements, for example flat
concrete slabs, provide an elegant form of construction,
which simplifies and speeds up site operations, allows easy
and flexible partitioning of space and reduces the overall
height of buildings. Reinforced concrete flat slab
construction also provides large uninterrupted floor areas
within a minimum construction depth, and is used extensively
for a wide range of buildings such as office blocks,
warehouses and car parks.
One design problem associated with this form of
construction is punching failure, which occurs as a result of
high point loads or high shear stresses around the supporting
columns. In punching failure, the failed surface of the slab
forms a truncated cone or pyramid. This problem has in the
past often lead to the use of mushroom heads or local
thickening of the slab, but these solutions increase costs
and slow down the rate of construction.As the spans become
larger and the slabs become thinner the increased stresses
around the critical shear perimeter have created even greater

problems for the structural engineer. A variety of design
solutions have been proposed, of which the mast commonly used
are as follows:
1. Conventional shear reinforcement
This solution is very labour-intensive and requires
extra work both in the design and on site.
2. Use of a larger column and/or a thicker conerets slab
These solutions increase the deadload of the
building and reduce the available space.
3 . Use of a column head
This requires more complicated formwork, slows down
the rate of construction, and interferes with the
installation of building services.
4. Use of slab drops
These are a modified form of column head.
Shear reinforcement, when required, is normally
accomplished by providing reinforcing members either at an
angle or laterally to the main flexural reinforcement. In
thin structural elements, such as flat slabs, anchoring of
short lengths of shear reinforcement is a major design
problem. The problem is aggravated by the fact that normal
shear reinforcement cannot be placed above the top layer of
flexural reinforcement without reducing either the
durability, or the efficiency, of the flexural reinforcement.
In addition, there is the practical problem of supporting the
shear reinforcement during the construction stages.

Recently a new system has been introduced by Square Grip
Limited, designated the Shearhoop system, which consists of
an assembly of specially shaped links (shear leg bobs) and
hoop reinforcing bars. The hoops are available in a range of
sizes and can be combined to form a complete system
extending outwards from the column to the zone where the
shear resistance of the concrete slab alone is adequate.
In the construction of a slab using Shearhoops, bars B1,
B2 for the bottom layer of reinforcement are first laid down
and the Shearhoops placed over them in the appropriate
location. Top reinforcement T2 is then positioned on chairs
and the bars overlapping the Shearhoops fully located under
the ends of the shear leg bobs extending from the Shearhoops.
Finally the top reinforcement T1 is placed over the entire
structure.
Whilst the Shearhoops are an improvement on previous
arrangements, they still cannot be anchored above the top
layer of reinforcement T1 and thus do not provide the best
possible shear reinforcement.
From the above, it is apparent that, although much
effort has gone into the design of reinforcing systems that
address some of the above mentioned problems, none of them
provide a complete solution. Although prepackaged reinforced
systems offer some time savings over the in-situ steel fixing
solutions, they are nevertheless more expensive in terms of
materials and other resources, such as labour and crane time.
Sxane of the other prior art proposals are also of

questionable effectiveness, or produce an unquantifiable
increase in flexural capacity.
There is a need, therefore, for an improved reinforcing
system to impart better shear resistance, without increasing
the thickness of the slab. An additional advantage would be
to provide a shear reinforcement system enabling thinner
slabs to be used.
US 4854106 described foundations for buildings and like .
structures employing steel reinforcement. A hook leg has an
elongate member bifurcated at each end longitudinally of the
member to form a pair of extensions with a slot therebetween,
the distal portion of the extensions being bent into a curved
form extending transversely of the member to form hooks
adapted to resiliently engage a pair of reinforcing rods in
the reinforcement, the slots in the unbent portions of the
extensions being adapted to receive a second pair of
reinforcing rods extending transversely of the first pair,
whereby to fix the rods in spaced alignment. There is no
mention of shear reinforcement.
US 4472331 described a reinforcing framework for a
concrete building structure in which column and beam
reinforcing bars are inserted into holes in reinforcement
frames disposed at predetermined intervals. Shearing
reinforcement bands, formed by bending a steel strip into a
rectangular frame shape, are disposed between adjacent
reinforcement frames and secured to wooden sheathing boards
by nailS. The construction requires access to all sides of

the column or beam, and the protruding nails would give rise
to potential corrosion problems.
DE 3331276 describes shear reinforcement elements for
column supported flat slabs or beams of reinforced or
prestressed concrete, which consist of flat steel strips
which are undulating in at least two dimensions and
transverse to the main surface of the flat slab or beams.
The shear reinforcement elements are used in place of
conventional round reinforcing bars.
SUMMARY OF THE INVENTION
The present invention provides a shear failure
reinforcing system for structural elements, in which thin
elongate strips of high stiffness material are anchored
around a layer of conventional reinforcement, and/or are
anchored around a plurality of layers of conventional
reinforcement, such that the strips tie the structural
element and improve its resistance to shear failure. In
preferred embodiments, the strips are enchored around the
outermost reinforcing members of a layer or layers of
reinforcement, to give improved shear resistance.
Accordingly, the present invention provides a method of
constructing a reinforced structural element, said element
being, in use, potentially subject to concentrated forces in
a first direction, said forces resulting in shear stresses in
the element, said method comprising :
a) providing spaced first and second reinforcing
structures disposed substantially perpendicular
with respect to said first direction, each

structure comprising reinforcing elements formed
as a network having gaps between said reinforcing
elements;
b) providing a plurality of thin elongate strips said
strips being undulating so as to have at least one
peak having a trough on either side;
c) anchoring the strips around the reinforcing
elements of said first reinforcing structure by-
engagement of said peak with an element thereof;
and
d) casting structural material around said first and
second reinforcing structures and around said
strips to embed said structures and strips in said
material;
characterised in that the method further comprises :-
e) disposing said strips in the first and second
reinforcing structures from a direction opposite
said first direction and from one side of said
first reinforcing structure;
f) said anchoring being without additional structural
connection of said strips to said elements, said
troughs passing through said gaps in the first
reinforcing structure so as to lie adjacent said
second reinforcing structure; and
g) said strips being of high stiffness material and
being arranged to provide shear reinforcement for
the structural element in the event of the clement

being subject to such concentrated shear-resulting
forces in said first direction.
This invention also provides a reinforced structural
element produced by the above method, said element being, in
use, potentially subject to concentrated forces in a first
direction, said forces resulting in shear in the structural
element, said structural element comprising :
a) spaced first and second reinforcing structures
disposed substantially perpendicular with respect
to said first direction, each structure comprising
reinforcing elements formed as a network having
gaps between said reinforcing elements;
b) a plurality of thin elongate strips, said strips
being undulating so as to have at least one peak
having a trough on either side;
c) the strips being anchored around the reinforcing
elements of said first reinforcing structure by
engagement of said peak with an element thereof;
and
d) structural material embedding said first and second
reinforcing structures and said strips;
characterised in that
e) said strips are disposed in the first and second
reinforcing structures from a direction opposite
said first direction and from one side of said
first reinforcing structure;
f) said anchoring is without additional structural

connection of said strips to said elements, said
troughs passing through said gaps in the first
reinforcing structure so as to lie adjacent said
second reinforcing structure; and
g) said strips being of high stiffness material and
being arranged to provide shear reinforcement for
the structural element in the event of the element
being subject to such concentrated shear-resulting
forces in said first direction.
DETAILED DESCRIPTION OF THB INVENTION
The reinforced structural element may be cast in situ or
precast, and may be provided with any suitable longitudinal
reinforcement comprising elongate reinforcing members, which
may be initially unstressed, pre-stressed, or post-tensioned.
The invention finds particular application where the
reinforced structural element is a slab structure especially
a flat slab, although it can also be a waffle or ribbed slab,
a slab with downstands, a foundation slab Or footing, or a
staircase slab Other possible uses may be in a wall, a wide
band beam, or normal beam, a normal or extended column, a box
or other hollow shape, or a shell or other three dimensional
shape. The element may be with or without openings, as
desired. The reinforced structural element may have
any suitable thickness, depending upon the application.
Henceforth the invention will be more particularly described
with reference to thin reinforced concrete structural
elements, for example flat slabs, having a thickness of from

10 to 80cms, more particularly from 10 to 30cms, but it is to
be understood that although the invention has particular
advantages when applied to such structures, it is not limited
thereto.
The thin reinforced concrete structural element may have
any desired length and width, but reinforced flat slabs used
in conventional building construction are often of a size of
from 1 to 10 metres in length and from 1 to 10 metres in
width.
The reinforcing members will usually be elongate rods or
bars embedded in the structural element and lying parallel to
the major surfaces of the element. The reinforcing members
can have any suitable cross-section, for example round,
square, or rectangular. Typically, the reinforcing members
lie adjacent one or more of the major surfaces of the
structural element, and comprise series of reinforcing bars
laid at right angles to each other.
The major surfaces of the structural element will
normally be the top and bottom surfaces, where the element is
a slab, but they could also be the side surfaces of a wall.
The material of the reinforced concrete structural
element may be normal concrete, high strength concrete, light
weight concrete, concrete with special cements and
aggregates, polymer modified concrete, special cement mortar,
special polymer mortar. Elements formed from other suitable
materials able to be cast which require strengthening in
shear, such as, for example, fibre reinforced plastics and

ceremics can also be used.
The thin elongate strip of high stiffness material
preferably has dimensions such that it will not radically
change the overall thickness of the structural members to
which it is anchored, and such that it will not break when
bent to the required shape, which could be around tight
corners. Preferably the strip has a thickness of from 0.5 to
1.0mm and a width of from 10 to 30mm. The material of the
strip is preferably a high tensile, high stiffness material,
such as, for example, high tensile steel, although other high
stiffness materials, for example structural polymers such as
polypropylene and fibre reinforced plastics comprising, for
example, carbon fibre, glass fibre and aramids, are not
excluded. The material is required to have high stiffness in
order to be able to arrest the development of shear cracks at
low strains, and, for example, a material of stiffness of
from 100KN/mm2 to 210KN/mm2 is preferred. High strength
material is preferred for the strips because a lower volume
of strip material can be used. A typical strength for a high
tensile steel used for the strip can be, for example, from
460N/mm2 to 1500N/mm2. Special hardness strips may be useful
when dealing with walls in safe areas.
The durability of the strip may be improved by adequate
cover, by special surface protection, or by using non-
corrosive materials such as stainless steel, or fibre
reinforced plastics. Where the strip is metallic, it may also
be eharged to provide cathodic protection.

Punched holes, embossments and indentations in the
strip, as well as spedial bending, twisting or surface
treatment of the strip, can help the overall bond
characteristics of the strip to the material of the
structural element, although a right angle bend may be
sufficient to anchor the strip where concrete is used as the
material for the reinforced structural element.
In use, the strip may be disposed in a vertical,
horizontal, or inclined direction, and may be bent or clipped
around the reinforcing member to which it is anchored, or
tied thereto. In a preferred aspect of the invention, the
strip is anchored around one or more of the outermost
reinforcing members, that is, those members closest to the
major surfaces of the structural element. Since the
reinforcing bars are often of significant thickness, for
example around 20mm diameter, this provides shear
reinforcement to a point closer to the surface than has been
possible hitherto.
Bending and shaping of the strips to the desired shape
may be readily accomplished by hand, or by the use of
specialised automated or semi-automated equipment, the strips
may be preformed before conveying to the site, and use, if
desired.
The strips may be anchored in the material of the
structural element by providing an appropriate extra strip
length beyond a bend around a structural element, or
alternatively ends of the strip may be secured together by

metal clips, rivets or other fixing means. It is particularly
pref erred for the strip to be so shaped that it can be
positioned from one side of the structural element, without
the need to obtain all round access. The strip can, for
example, be bent into a zigzag shape, a castellated shape, a
sine wave curved shape, or other repeating straight sided or
curved shaped and then dropped into position on the
reinforcing members. This greatly facilitates assembly, where
it is often difficult to obtain all round accesss to the
structural element.
Preferably the strips are arranged such that they are
totally enclosed within and not exposed at. any point on the
surface of the structural element, and are not connected to
any metal fixing, for example, a nail or screw, which is
exposed on the structural element surface. This is to avoid
the risk of corrosion or deterioration of the strips in
service.
Structural elements reinforced by the method of the
invention can have improved strength and substantially
improved ductility, imparting improved resistance to shear
failure. In addition, structural elements reinforced in
accordance with the invention can have a thinner section than
those hitherto specified because of their improved resistance
to shear failure.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In order that the invention may be better understood,
preferred embodiments thereof will now be described in

detail, by way of example only, with reference to the
accbmanying Drawings in which:
Figure 1A shows schematically a section side elevation of a
reinforced flat structural element according to the
invention;
Figure 1B shows a sectional side elevation of a reinforced
curved structural element according to the invention;
Figure 1C shows a sectional side elevation of a reinforced •
flat structural element according to the invention in which
the strip is anchored to both top and bottom reinforcing
members;
Figure 1D shows a sectional side elevation of a reinforced
flat structural element according to the invention reinforced
with single spacing inclined strip;
Figure 1E shows a sectional side elevation of an inclined
reinforced structural element according to the invention;
Figure 1F shows a sectional side elevation of a vertical
reinforced structural element according to the invention;
Figure 2 shows examples of punched and pre-formed steel
strips for use in the invention;
Figure 3A shows a perspective view from the top and one side
of the reinforcing formwork of a flat reinforced concrete
structural slab in accordance with the invention, reinforced
with inclined metal strips with punched holes;
Figure 3B shows a perspective view from the top and one side
of the reinforcing formwork of a reinforced flat concrete
structural slab in accordance with the invention, having

inclined metal strip shear reinforcement, but without punched
holes in the strips;
Figure 3C shows a perspective view from the top and one side
of the reinforcing formwork for a reinforced flat concrete
slab in accordance with the invention, having shear
reinforcement comprising vertically arranged metal strips
with punched holes;
Figure 4A shows the load versus deflection curves for the
slabs of figures 3A to 3C (PPSB to PPSD} in comparison with
an unreinforced control slab (PPSA); and
Figure 4B shows the load versus strain in the flexural
reinforcement for the slabs of figures 3A to 3C {PPSB to.
PPSD) in comparison with an unreinforced control slab (PPSA).
Referring now to figure 1, in figure 1A there is shown a
flat element 1, supported on a column 7 about a centre line
C , having upper reinforcing bars, 2, 3, arranged at right
L
angles to each other, and lower reinforcing bars 4, 5
similarly arranged. U-shaped strips 6 of thin, elongate high
stiffness steel are arranged between the upper and lower
reinforcing bars in order to provide double spaced vertical
shear reinforcement.
In figure 1B there is shown a curved reinforced concrete
element 10, supported on columns 16, having upper reinforcing
bars 11, 12 and a lower reinforcing bar 13. A thin strip of
14 of high stiffness steel is bent around the upper
reinforcing bars 12 and the lower reinforcing bar 13 to
provide single spacinq vertlaal Strip shear reinforcement.

The strip 14 is bent at its ends 15 around the lower
reinforcfing bar 13, leaving a substantial length of the strip
for anchoring in the concrete.
Figure 1C shows a flat concrete structural slab 20,
supported on a column 21 about a centre line C , and having
upper reinforcing bars 22, 23, and lower reinforcing bars 24,
25. In this case the thin, high stiffness metal strip 26 is
bent around both upper, and lower reinforcing bars.
In figure 1D there is shown a flat reinforced concrete
slab 30, supported upon a column 31, and provided with upper
reinforcing bars 32, 33 and lower reinforcing bars 34, 35.
Shear reinforcement is provided by the metal strip 36 which
is bent around upper and lower reinforcing bars so as to
provide inclined shear reinforcement.
Figure 1E shows an inclined concrete reinforcing slab
40, supported on a column 41, and provided with upper
reinforcing bars 42, 43 and lower reinforcing bars 44, 45.
Shear reinforcement is provided by the high stiffness metal
strip'46 which is bent around both upper and lower
reinforcing bars to form a. single spaced shear reinforcement.
Figure 1F shows a vertical concrete structural slab 50
having right side reinforcing bars 51, 52 and left side
reinforcing bars 53, 54. Shear reinforcement is provided by
the high stiffness metal strip 55 which is bent around both
left and right side reinforcing bars to provide inclined
shear reinforcement.

The invention will now be illustrated, by the following
examples :
Example 1
This example describeds the enhancement of shear
capacity of a flat slab with inclined metal strip
reinforcement having punched holes.
Steel strips are produced having a series of punched
holes as shown in figure 2, and are preformed to the
castellated shape shown therein. The strips are arranged in
the formwork for a concrete slab in locations determined by
using British Standard BS8110 (1985), as illustrated in
figure 3A. It will be noted that it is only necessary to have
access to the top side of the formwork in order to place the
strips in position. Concrete is then poured to produce a slab
of thichness 175mm which is below the 200mm limit imposed by
BS8110 on the thickness of flat slabs.
The slab (B) was tested with an eight-point load
arrangement, simulating loading typical of flat slabs in
buildings of conventional construction. The load versus
deflection curves and the load versus strain in the flexural
reinforcement curves for this slab and others tested for
comparison are shown in figures 4A and 4B respectively.
Slab (A) was unreinforced and failed in abrupt punching
shear mode at a load of 460kN. Slab (B) deflected
considerably more, developed very large strains in the
longitudinal reinforcement and failed in a ductile mode at a
maximum load of 560kN in the fashion desired in practirce by

structural engineers.
Example 2
-This example demonstrates the increase in load and
ductility of a flat slab reinforced with inclined steel
strip.
Steel strips without the punched holes are preformed as
shown in figure 2 and arranged in the metal formwork for a
concrete slab in locations determined by using BS8110 (1985)
as illustrated in figure 3B. Concrete is then poured to
produce a slab of thichness 175mm.
The slab (C) was tested with an eight-point load
arrangement, making extra allowance for anchoring the strip
at its ends. The load versus deflection curves and the load
versus strain in the flexural reinforcement curves for this
slab and others tested for comparison are shown in figures 4A
and 4B respectively.
Slab (C) deflected considerably more than slab (A), and
developed very large strains in the longitudinal
reinforcement, failing in' a ductile mode at a maximum load of
560kN.
Example 3.
This example demonstrates the increase in load and
ductility of a flat slab reinforced with vertical steel strip
reinforcement anchoring both layers of longitudinal
reinforcement.
Steel strips, punched and pre-formed as shown in figure
2, are inserfed into the form form work of a concrete slab as

shown in figure 3C and anchored to the upper and lower layers
of longitudinal reinforcing bars. The strips are arranged in
locations determined by using BS8110 (1985 ). Concrete is then
poured to produce a slab of thickness 175mm.
The slab (D) was tested with an eight-point load
arrangement, simulating loading typical on flat slabs in
buildings. Extra allowance was made for anchoring the strip
at its ends. The load versus deflection curves and the load
versus strain in the fiexural reinforcement curves for this
slab and others tested for comparison is shown in figures 4A
and 4B respectively.
Slab (D) deflecting considerably more than slab (A) ,
developed very large strains in the longitudinal
reinforcement, and failed in a ductile mode at a maximum load
of 560kN.
The reader's attention is directed to all papers and
documents which are filed concurrently with or previous to
this specification in connection with this application and
which are open to public inspection with this specification,
and the contents of all such papers and documents are
incorporated herein by reference.
All of the features disclosed in this specification
(including any accompanying claims, abstrct and drawings),
and/or all of the steps of any method or process so
disclosed, may be combined in any combination, except
combinations where at least some of such features and/or
steps are mutally exclusive.

Each feature disclosed in this specification (including
any accompanying claims abstract and drawings), may be
replaced by alternative features serving the same, equivalent
or similar purpose, unless expressly stated otherwise. Thus,
unless expressly stated otherwise, each feature disclosed is
one example only of the generic series of equivalent or
similar features.
The invention is not restricted to the details of the
foregoing embodiments. The invention extends to any novel
one, or any novel combination, of the features disclosed in
this specification (including any accompanying claims,
abstract and drawings), or to any novel one, or any novel
combination, of the steps of any method or process so
disclosed.

We Claims :
1. A method of constructing a reinforced structural element
(1), said element being, in use, potentially subject to
concentrated forces in a first direction, said forces
resulting in shear stresses in the element, said method
comprising:
a) providing spaced first and second reinforcing
structures (2, 3;4,5) disposed substantially-
perpendicular with respect to said first direction, each
structure comprising reinforcing elements formed as a
network having gaps between said reinforcing elements;
b) providing a plurality of thin elongate strips (6),
said strips being undulating so as to have at least one
peak having a trough on either side;
c) anchoring the strips around the reinforcing
elements of said first reinforcing structure by
engagement of said peak with an element thereof; and
d) casting structural material around said first and
second reinforcing structures and around said strips to
embed said structures and strips in said material;
characterised in that the method further comprises :-
e) disposing said strips in the first and second
reinforcing structures from a direction opposite
said first direction and from one side of said
first reinforcing- structure;

f) said anchoring being, without additional structural
connection of said strips to said elements, said
troughs passing-through said gaps in the first
reinforcing structure so as to lie adjacent said
second reinforcing structure; and
g) fsaid strips being of high stiffness material and
being arranged to provide shear reinforcement for
the structural element in the event of the element
being subject to such concentrated shear-resulting
forces in said first direction.
2. A method as claimed in claim 1, wherein the reinforced
structural element is a flat slab.
3. A method as claimed in claim 1 or 2, wherein the
structural element is a reinforced concrete element.
4. A method as claimed in any of claims 1 to 3, wherein the
structural element has a thickness of from 10 to 30cms.
5. A method as claimed in any preceding claim, wherein the
structural element has a length of from 1 to 10m and a
width of from 1 to 10m.
6. A method as claimed any preceding claim, wherein the
reinforcing elements comprise a series of reinforcing
bars laid at right angles to each other.
7. A method as claimed in any preceding claim, wherein the
elongate strips of high stiffness material have a
thickness of from 0.5 to 1.0mm and a width of from 10
to 30mm.

8. A method as claimed in any preceding claim, wherein the
material of the elongate strips comprises high tensile
steel.
9. A method as claimed in any preceding claim, wherein the
material of the strips has a stiffness of from 100KN/mm2
to 210KN/mm2 and a strength of from 460N/mm2 to
1500N/mm2.
10. A method as claimed in any preceding claim, wherein the
elongate strips are provided with holes along the
lengths thereof to assist the overall bond
characteristics of the strips to the material of the
structural element.
11. A method as claimed in any preceding claim, wherein the
ends of the elongate strips are bent or clipped around
reinforcing elements of the second reinforcing
structure.
12. A method as claimed in claim 11, wherein the strips are
preformed into a castellates shape.
13. A method as claimed in any preceding claim, wherein the
elongate strips are anchored in the material of the
structural element by providing an appropriate extra
strip length beyond a bend around a structural element.
14. A method as claimed in any preceding claim, wherein the
elongate strips are totally enclosed within the
structural element and are not connected to any exposed
metal fixing.

15. A method as claimed in any preceding claim, wherein the
elongate strips are tied to elements of the reinforcing
structure.
16. A method as claimed in any preceding claim, wherein ends
of the elongate strips are secured to each other by
metal clips, rivets or other fixing means.
17. A method of constructing a reinforced structural element
(l) substantially as hereinbefore described with
reference to and as illustrated in the accompanying
drawings.
18. A reinforced structural element (1) produced by a method
as claimed in any preceding claim, said element being,
in use, potentially subject to concentrated forces in a
first direction, said forces resulting in shear in the
structural element, said structural element comprising :
a) spaced first and second reinforcing structures
(2,3,-4,5) disposed substantially perpendicular with
respect to said first direction, each structure
comprising reinforcing elements formed as a network
having gaps between said reinforcing elements;
b) a plurality of thin elongate strips (6), said
strips being undulating so as to have at least one peak
having a trough on either side;
c) the strips being anchored around the reinforcing
elements of said first reinforcing structure by
engagement of said peak with an element thereof; and

d) structural material embedding said first and second
reinforcing structures and said stirps;
characterised in that
e) said strips are disposed in the first and second
reinforcing structures from a direction opposite
said first direction and from one side of said
first reinforcing structure;
f) said anchoring is. without additional structural
connection of said strips to said elements, said
troughs passing through said gaps in the first
reinforcing structure so as to lie adjacent said
second reinforcing structure; and
g) said strips being of high stiffness material and
being arranged to provide shear reinforcement for
the structural element in the event of the element
being subject to such concentrated shear-resulting
forces in said first direction.
19. A reinforced structural element substantially as
hereinbefore described with reference to and as
illustrated in the accompanying drawings.
Dated this 6th day of May, 1996.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=h+xSZHgFcZF/lZvlpBnNoQ==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

270192

Indian Patent Application Number

821/CAL/1996

PG Journal Number

49/2015

Publication Date

04-Dec-2015

Grant Date

30-Nov-2015

Date of Filing

06-May-1996

Name of Patentee

CONTEQUE LTD.

Applicant Address

THE INNOVATION CENTRE, 217 PORTOBELLO, SHEFFIELD S1 4DP, UNITED KINGDOM

Inventors:

#	Inventor's Name	Inventor's Address
1	KYPROS PILAKOUTAS	26 FOUNTSIDE,OAKDALE ROAD,SHEFFIELD,S7 1SN, UNITED KINGDOM

PCT International Classification Number

E04B1/58

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	9509115.3	1995-05-04	U.K.