GB2569186A

GB2569186A - Method for the reinforcement of masonry structures

Info

Publication number: GB2569186A
Application number: GB1720584.0A
Authority: GB
Inventors: George Edscer William
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-12-11
Filing date: 2017-12-11
Publication date: 2019-06-12
Anticipated expiration: 2037-12-11
Also published as: GB2569186B; GB201720584D0

Abstract

A method for the reinforcement of masonry structures comprises: conducting a structural analysis of the masonry structure to identify stress lines corresponding to actual or potential fracture in the masonry structure, and identifying from that structural analysis the desired tensile strength and precise position of reinforcement tie bars to be incorporated into the masonry structure. A second step in the method is, wherever two such stress lines cross in close proximity, to create by machining or by 3D printing a tie connecting knuckle joint which comprises a base unit (1) formed from a single block or from two or more interconnected blocks of a rigid corrosion-resistant material, the base unit having two or more non-interconnecting bores extending partially or completely therethrough, and received in and extending from each bore a screw-threaded tie bar (2a, 2b, 2c) of a high tensile corrosion resistant material, anchored to the base unit (1) by screw means (3, 4). The bores are aligned in planes and at mutual angles calculated so that the tie bars (2a, 2b, 2c) extending from the base unit (1) can lie along the stress lines identified in the masonry structure. A third step in the method comprises bonding the tie bar connecting joint or joints to the masonry structure to be reinforced, with the tie bars (2a, 2b, 2c) received in grooves or bores created in the masonry structure and aligned to coincide with the identified stress lines in the masonry structure to be reinforced.

Description

METHOD FOR THE REINFORCEMENT OF MASONRY STRUCTURES

TECHNICAL FIELD

The present invention relates to the reinforcement of masonry structures. By “masonry structures” there is meant structures made from brick, stone or concrete either with or without internal reinforcement.

TECHNICAL BACKGROUND

All masonry exhibits strong resistance to compressive loads but has a lower resistance to tensile stresses. It is commonplace to reinforce concrete structures with internal steel reinforcement, but even such steel reinforced concrete may prove inadequate for its function and may require further repair or reinforcement to increase its resistance to failure under tensile stress.

By way of example, consider the potential failure of a masonry arch such as a bridge. It is known to reinforce the face of the bridge or the underside of the arch barrel of the bridge by cutting a groove into the masonry and bonding a reinforcing steel bar securely in the recess using a grout of cement or resin. Alternatively a tie bar may be inserted through a hole drilled through the masonry and used to support a pair of pattress units on opposite outer faces of the masonry. Screw threads formed at opposite ends of the tie bar may be used to draw together the pattress units putting the tie bar under tension to hold together the masonry structure. Similar tie bars connecting together pattress units are commonly used to resist outward forces on masonry panels, solid walls or the outer skins of cavity walls, and it is commonplace to see visible pattress units on the outside of such reinforced walls where they are visible as large X or S shaped or circular metal plates. All such basic repairs, whether to a masonry arch bridge or to a masonry wall, provide reinforcement in a single plane only. Often however a masonry arch bridge suffers damage which requires reinforcement in more than one plane. For example excessive traffic movement above or below the bridge, heavy loads and general traffic-induced vibration can cause side walls of an arch bridge to detach from the arch barrel and fall away outwardly, and such a deterioration of the bridge structure

-2can pull apart some of the underlying arch barrel. To reinforce such an arch bridge it is necessary to connect together two or more tie bars lying in different planes, the angle between the planes being a function of the shape of the bridge and of the extent of the repair or reinforcement being addressed. Each of the interconnected tie bars is then received in grooves or bores in the masonry and bonded to the masonry structure. Similar multi-directional reinforcement tie bar assemblies have been proposed in order to improve the ability of other masonry structures to resist earth tremors, earthquakes, ground movement and/or increased loads, or in response to new legislative safety requirements, or to support additional attachments to be fixed to the external face or within a masonry structure. Such additional attachments may include monitoring devices, brackets, reinforcement, girders, panels, mesh, curtain walling and other materials.

It has been proposed to fasten together two or more tie bars, to create such a multidirectional reinforcement tie bar assembly, by welding or by the use of adhesive materials. However such multi-directional reinforcement tie bar assemblies have proved inadequate to withstand the forces which are likely to be imposed on the tie bar assemblies in use. Also, in the case where the tie bars are interconnected by welding, the accuracy of the angle between the interconnected tie bars can be inadequate, since it is dependent on the skill of the welder. It is therefore an object of the invention to provide a method for the repair or reinforcement of a masonry structure, which is strong enough to permit a satisfactory repair or reinforcement and which enables the angles between two or more interconnected tie bars to be accurately controlled to match a detailed stress analysis of the masonry structure to be repaired or reinforced.

SUMMARY OF THE INVENTION

The invention provides a method for the reinforcement of a masonry structure according to claim 1.

The method of the invention uses a knuckle joint which links together the two or more tie bars to create a multi-directional reinforcement tie bar assembly in which the tie bars

-3extend from the base unit at angles which can be precisely controlled in accordance with a calculated stress pattern specific to the masonry structure to be repaired or reinforced. Moreover the tie bar assembly is extremely strong, and because the base unit of the knuckle joint is created from a single block of material or from two or more interconnected blocks of material, it avoids the inherent weakness and reliance on human expertise and accuracy in assembly which is a characteristic of the welded or adhesive joints of previously proposed tie bar assemblies.

The base unit is preferably made from stainless steel, from a fibre-reinforced resin or from graphene or from bronze. It may be formed from a single block of such material or from a plurality of blocks of such material which have an interfitting structure which enables them to be interconnected into a composite accurately created shape. The interfitting structure may include cooperating faces such as dovetail joints or may comprise parts interconnected by bolts. For ease of accurately aligning the bores at angles and in planes dictated by the structure to be repaired or reinforced, the base unit is preferably prismatic in shape, for example with a rectangular or circular section. The tie bars are preferably made from stainless steel, from galvanized steel, from sherardized steel or from carbon fibre-reinforced resin, and may be solid or hollow in section.

In use, the tie bars are received in recesses or bores cut into the masonry structure that is being repaired or reinforced and are secured in place by a grout of a resin or mortarbased cement which bonds them to the masonry. If desired, the grout anchoring the tie bars to the masonry of the structure may be received in a flexible and expansible sleeve surrounding each tie bar. The sleeve is expanded by injecting the grout under pressure into the sleeves prior to setting or curing the grout. Preferably the sleeve is supported and held spaced apart from the tie bar which it surrounds by spacers which are carried on the tie bar and which hold the sleeve away from the tie bar whilst permitting injected grout to flow along the length of the tie bar. In addition, the base unit itself may be received in a recess cut into the masonry structure, where it may be concealed by a grout fill or repair mortar which encases the base unit. If a pattress plate is secured to

-4the base unit, then it too may be received in the same recess and if desired concealed by a grout fill which encases both the base unit and the pattress plate.

In the method of the invention, a stress analysis of the masonry structure to be repaired or reinforced is first carried out by a structural engineer. Such a stress analysis maps out the stress lines and potential or actual fracture lines inherent in the masonry structure, and provides detailed assessment of the tensile strength that is necessary in the tie bars used in the repair or reinforcement as well as the precise geometrical positioning of those tie bars needed in the final reinforced structure in order to meet a specified set of strength characteristics. That stress analysis may be to meet new statutory stress limits for an existing undamaged structure or to meet strength characteristics set down for the repair of a failed structure. The stress analysis enables the structural engineer to prescribe tensile strength requirements for the tie bars to be incorporated into the structure as well as the specific three-dimensional positioning of the tie bars when so incorporated. A tie connecting knuckle joint can then be designed and constructed meeting that precise specification. It is then incorporated into the masonry structure by placing the tie bars of the knuckle joint in grooves or bores formed in the masonry structure and bonding them in place using a grout of a resin or mortarbased cement. The placing of the individual tie bars into the grooves or bores may be one at a time, for example by anchoring one of the tie bars to the base unit and then inserting that tie bar into its groove or bore before anchoring in place a second tie bar, and later optionally a third tie bar or subsequent tie bars, to the same base unit so as to extend therefrom at the predetermined angle or angles consistent with the original stress pattern specification before securing the entire tie connecting knuckle joint, with its tie bars extending from the base unit at the precise specified angles, to the masonry structure using a grout of resin or mortar-based cement.

-5BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by the drawings of which:

Figure 1 is a perspective view of a welded knuckle joint base unit as proposed and used prior to this invention;

Figure 2 is a perspective view of a tie connecting knuckle joint to be used in a method according to the invention;

Figure 3 is a perspective view of another tie connecting knuckle joint to be used in a method according to the invention;

Figures 3a to 3d are perspective views of alternative shapes for the base unit of Figure 2 or Figure 3;

Figure 4a is a perspective view of the tie connecting knuckle joint of Figure 2 together with other ancillary components;

Figures 4b and 4c are perspective views of alternative shapes for the pattress of Figure 4a;

Figure 5 is another perspective view of the tie connecting knuckle joint of Figure 2 together with other ancillary components;

Figure 6a is a side view of a wire spacer used to support and locate a sleeve such as one of the sleeves of Figure 5;

Figure 6b is a perspective view of an alternative wire spacer used to locate a tie rod of Figure 2; and

Figure 7 is a photograph of a masonry barrel arch reinforced by a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will now be described by way of example only and with reference to the accompanying drawings.

Referring first to Figure 1, there is shown a known tie connecting knuckle joint base unit comprising two metal anchorages welded together at a specified angle, in this case approximately 90°. Each metal anchorage is an internally screw-threaded tube for

-6receiving an end of a threaded metal tie rod, and the two anchorages are mitre-cut before welding. In use it has been found that the weld is liable to fracture under stress unless the weld has been very competently completed; and also the angle between the anchorages is liable to be inaccurate, depending on the skill of the welder. The knuckle joint is therefore unreliable for use in the repair or reinforcement of any masonry structures which demand a guarantee of structural integrity following that repair or reinforcement.

Figures 2 and 3 illustrate two variants of a tie connecting knuckle joint to be used in a method according to the invention. Each joint comprises a base unit 1 comprising a single block of material through which have been created three internal bores each extending completely through the base unit. The bores are internally screw-threaded, and they receive three tie bars 2a, 2b and 2c. The bores are mutually offset from one another so that they do not interconnect, and the tie bars do not touch within the base unit. Lock nuts 3 prevent the tie bars from rotation relative to the base unit 1. However if the bores were to be unthreaded and the tie bars were received as a sliding fit in their respective bores, then load nuts threaded to the tie bars at the opposite sides of the base unit would serve to secure the tie bars to the base unit 1. Figure 4a shows two such load nuts 4. If desired lock nuts 3 may still be used to prevent slackening of the load nuts 4.

Figures 3a to 3d show a number of alternative shapes for the base unit 1 of Figures 2 and 3. Figures 3a and 3b illustrate two different prismatic shapes, whereas Figures 3c and 3d illustrate two alternative shapes of base unit which can be created from a pair of tubular blocks screw-threaded together at an appropriate angle.

The three tie bars 2a, 2b and 2c in Figures 2 to 4a may be of any tensile strength and of any length as dictated by the masonry reinforcement to be achieved using the tie connecting knuckle joint according to the invention, and Figures 2 and 3 show the extended lengths of the tie bars schematically as broken sections of each tie bar.

-7Clearly such extended lengths can be repeated at both sides of the base unit 1 for each tie bar whenever the specific repair demands it.

The strength of the tie bars is carefully chosen in accordance with the original stress analysis of the masonry structure to be repaired or reinforced. Preferably the screw threads formed in metal tie bars are created by rolling rather than cutting, since the rolling process does not detract from the inherent tensile strength of the tie bar rod, as opposed to a thread cutting process. The screw thread need not extend for the entire length of the tie bar, although any non-threaded portions of the tie bar are preferably shaped to anchor the tie bar securely to the grout used to bond it to the masonry structure. For example, a tie bar may be created starting from a length of a standard deformed steel reinforcing bar, and rolling a screw thread into one or both end portions of that bar to create a screw threaded portion or portions for securing to the base unit or to two base units.

Moreover the angle between the tie bars is infinitely variable, to be specified by the precise demands of the structure to be repaired or reinforced. The fact that Figures 2 to 4a show three tie bars 2a, 2b and 2c in mutually perpendicular planes is merely an illustration of one such specified geometry. Also there may be only two tie bars associated with each base unit 1, or more than three. The actual angle between the bores, which dictates the precise angle between the tie bars, can be very precisely controlled during machining or during the 3D printing manufacture of the base unit 1 and can therefore be under computer control as opposed to the purely manual assembly of the welded knuckle joint illustrated in Figure 1. For holding the base unit accurately during a machining formation of the bores, it is preferred that the base unit is prismatic in shape. The section of the prism may be rectangular as in Figure 2 or circular as in Figure 3, but other shapes for the base unit are also possible as illustrated in Figures 3a and 3b, as long as the base unit can be securely and accurately held during CNC machining of the bores.

-8Although the tie bar connecting knuckle joint to be used in a method according to the invention is intended to incorporate tie bars at predetermined angles to one another and lying in mutually inclined planes, it is possible within the scope of the invention to have several tie bars extending from the base unit which are mutually parallel to each other as well as another or others in an inclined plane or inclined planes at a predetermined angle or predetermined angles to the set of parallel tie bars. The number of tie bars, and their positioning and orientation relative to each other and relative to the base unit, is all as specified by a structural analysis of the stress loadings on the actual masonry structure.

Figure 4a shows some additional elements that can be used with the knuckle joint of Figure 2. A disc-shaped pattress plate 5 is shown. Typically that disc would be threaded onto one of the tie bars such as the tie bar 2a, and if necessary held fast to the base unit 1 using another load nut and/or lock nut. That would be useful if another pattress plate were threaded to another end of the tie bar 2a. The pattress plate 5 shown in Figure 4 has an array of six bores or recesses arranged around its central bore. Those may be used as a key for a spanner or similar tool if the pattress plate 5 is screw-threaded onto the tie bar 2a, but may be omitted if the pattress plate 5 is not itself screw-threaded and is simply held against the base unit 12 by a load nut and lock nut. If the pattress plate 5 is screw-threaded onto the tie rod 2a then it may be prevented from unscrewing by a lock nut. Of course if the base unit 1 is designed to have several tie bars extending therefrom parallel to one another as well as others inclined at a specified angle, then the parallel tie bars may pass through an array of holes in a multibore pattress plate such as that illustrated in Figure 4a.

Figures 4b and 4c illustrate alternative shapes for the pattress plate 5 of Figure 4a.

The base unit 1 is made from a single piece of a strong corrosion-resistant material, preferably stainless steel. It may however be made from a material other than stainless steel, such as carbon-fibre-reinforced resin or graphene or bronze. The tie bars 2a, 2b and 2c are also made from corrosion-resistant material, such as stainless steel,

-9galvanized steel, sherardized steel or a carbon-fibre-reinforced resin. Each tie bar may be of solid or tubular construction.

Figure 4a also shows how an external restraint rail 6 may be supported by one of the tie bars, in this case by the tie bar 2c shown in Figure 4. The external restraint rail is mounted on the tie bar 2c by means of a restraint rail support 7 which is screw-threaded onto the tie bar 2c, and its spacing from the base unit 1 is adjustable to suit the masonry structure to be repaired or reinforced. One possible use of such restraint rails is in the reinforcement or repair of concrete cladding panels for multi-storey tower block buildings. The tie connecting knuckle joint may be used to repair or reinforce the actual concrete cladding panels and secure them to the core part of the tower block building while the restraint rails may be used to support fire retardant and/or insulating panels between the concrete cladding panels and the core part of the tower block building.

Figure 5 shows three flexible fabric sleeves 8 around the tie bars 1a, 1b and 1c. The use of those sleeves 8 is to facilitate the grouting of the tie bars into grooves or bores into the masonry structure to be repaired or reinforced. A grout of resinous or mortarbased cement is injected into each sleeve 8 under pressure when the tie connecting knuckle joint is in position with the tie bars received in grooves or bores in the masonry structure. The grout injection is preferably through an injection tube inserted down each sleeve 8 to its closed end, and the injection tube is slowly withdrawn as the grout is injected, to fill the sleeve 8 from the end remote from the base unit. That ensures complete filling of the bore or recess. The sleeve 8 ensures that the grout is in consistently good contact with the tie bar along the whole of its length, and where there are large voids in the masonry structure the sleeve 8 is designed to expand to its maximum size within the void and in doing so prevents the filling of those large voids and wastage of grout or other injection material. Elsewhere the sleeve 8 expands against the masonry under the pressure of the injected grout and seepage of the grout through the fabric of the sleeve 8 and into contact with the masonry is sufficient to ensure a strong bond between the grout and the masonry of the structure being repaired or reinforced.

-10Figure 6a shows one example of a wire spacer 9 that may be used to help support and locate the sleeve 8 on the tie bar 2a, 2b or 2c. The tie bar is shown as a cross section illustrated in broken line numbered 2 in Figure 6a, and the spacer 9 has an inner arcuate portion which is clipped around the tie bar 2 to hold the spacer on the tie bar, and an outer arcuate portion which holds the sleeve (not shown in Figure 6) away from the tie bar. The use of a series of such spacers along the length of the tie bar 2 covered by the sleeve 8 holds the sleeve 8 apart from the tie bar 2 even before the grout is injected and ensures that on completion of the repair the grout is in good adhesive contact with the tie bar 2 along the whole of its length. Figure 6b shows another example of a wire spacer 9b, being one as described and claimed in GB 2313822 A, which positions the tie bar 2a, 2b or 2c centrally in its bore. The wire spacer 9b of Figure 6b may be used whether or not the tie bar is surrounded by a sleeve 8.

Figure 7 shows an example of a masonry bridge repaired and reinforced using a pair of tie connecting knuckle joints in a method according to the invention. The first step in the method is a structural analysis of the masonry bridge structure, to analyse all lines of necessary reinforcement to counter structural defects or failures in the case of a repair, or any potential fracture lines in the case of a reinforcement. That structural analysis identifies the preferred lines of reinforcement and the tensile strength of all reinforcing bars to be incorporated into the masonry structure along those lines of necessary reinforcement or potential fracture lines. From that structural analysis a precise geometry and tensile strength of the necessary tie bars is calculated, and wherever two of those tie bars cross in close proximity to one another the geometry of a tie bar connecting knuckle joint can be precisely defined. Such a tie bar knuckle joint can then be created by machining or by 3D printing from one or more pieces of a suitable material, such as stainless steel. The designed knuckle joint may for example be that shown in any of Figures 2 to 6. If the knuckle joint is made from more than one block of material, then those pieces should be interconnected to form a single integral body by interfitting machined portions (such as dovetail jointed portions) of the separate blocks locking the blocks together into a single integral body or by bolting together separate

-11 blocks with surfaces defining a precise geometry between the interfitting and locked together blocks. Once the tie bar knuckle joint has been designed and manufactured, it is used in the method of the invention to connect together two or more tie bars which have the tensile strengths dictated by the structural analysis and which lie along the precise lines of necessary reinforcement identified in the masonry structure. Typically one such tie bar would be connected to the knuckle joint and inserted into a bore or groove lying along one such line of necessary reinforcement in the masonry structure, and then a second such tie bar would be connected to the same knuckle joint and inserted in a second bore or groove lying along another such line of necessary reinforcement in the masonry structure, and then a third if needed, and so on until all identified lines of necessary reinforcement have their counterpart tie bars in position. Each tie bar is cemented in place as previously described herein, and finally the or each knuckle joint is grouted in place.

In Figure 7 the ends of two tie bars are visible in shallow recesses made in the masonry of the bridge. Each tie bar would typically extend completely through a bore drilled through the barrel arch wall of the bridge and would terminate in a pattress plate at each end of the tie bar. Circular pattress plates are shown in Figure 7, one in each recess. When the pattress plates are tightened using their interconnecting tie bars, they provide reinforcement to resist the movement apart of the masonry walls at opposite ends of the barrel arch. Although not yet shown in Figure 7, the recesses would in use be filled with a mortar cement to conceal their presence. Also not visible in Figure 7 is a connecting tie bar grouted into a groove formed in the masonry and fastening together the base units of the two knuckle joints. In use that connecting tie bar would be for example the tie bar 2b of Figure 2 or 3, with the two visible tie bar ends shown in Figure 7 corresponding to the tie bar 2a (one for each of the two interconnected knuckle joints) of Figure 2 or 3. The resulting repair to the bridge is a structural reinforcement in more than one plane.

Figure 7 also illustrates the support, by the tie connecting knuckle joint, of external restraint rails such as that shown in Figure 4, supported by a restraint rail support held

-12 against the underside of the barrel arch of the bridge by a third tie bar forming part of one of the knuckle joints.

Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

Claims

1. A method for the reinforcement of a masonry structure comprising:

conducting a structural analysis of the masonry structure to identify stress lines corresponding to actual or potential fracture in the masonry structure, and identifying from that structural analysis the desired tensile strength and precise position of reinforcement tie bars to be incorporated into the masonry structure;

and wherever two such stress lines cross in close proximity, creating by machining or by building using a 3D printer a tie connecting knuckle joint which comprises:

a base unit formed from a single block or from two or more interconnected blocks of a rigid corrosion-resistant material, the base unit having two or more interconnecting or noninterconnecting bores extending partially or completely therethrough, and received in and extending axially from each bore a screwthreaded tie bar of a high tensile corrosion resistant material, anchored to the base unit by screw means;

the bores being aligned in planes and at mutual angles calculated so that the tie bars extending from the base unit can lie along the stress lines identified in the masonry structure;

and bonding the tie bar connecting joint or joints to the masonry structure to be reinforced, with the tie bars received in grooves or bores created in the masonry structure and aligned to coincide with the identified stress lines in the masonry structure to be reinforced.

2. A method according to claim 1, wherein for the or each tie connecting knuckle joint the screw means comprises a screw thread formed internally of each bore for screw threaded engagement with the screw thread of its associated tie bar, and a lock nut for each tie bar, for tightening against the base unit to lock the tie bar against rotation relative to the bore in which it is received.

3. A method according to claim 2, wherein for the or each tie connecting knuckle joint at least one of the bores extends only partially through the base unit.

4. A method according to any preceding claim, wherein for the or each tie connecting knuckle joint at least one of the bores extends completely through the base unit, and for each tie bar extending from such a bore the screw means comprises a load nut on the said tie bar tightened against the base unit and a locking nut on the said tie bar tightened against the load nut to lock the tie bar against rotation relative to the bore in which it is received.

5. A method according to any preceding claim, wherein for the or each tie connecting knuckle joint the tie rods are screw threaded over the whole of their length.

6. A method according to any preceding claim, wherein the or each tie connecting knuckle joint further comprises a pattress plate for securing to a face of the base unit.

7. A method according to claim 6, wherein the pattress plate is provided with a screw-threaded bore for threaded engagement with the screw thread of one of the tie bars and is securable to the base unit by screw-threaded engagement with that tie bar.

8. A method according to any preceding claim, wherein there are three such bores in the base unit and three tie bars, one for each bore.

9. A method according to any preceding claim, wherein the or each base unit is made from stainless steel.

10. A method according to any of claims 1 to 8, wherein the or each base unit is made from a carbon fibre-reinforced resin or from graphene or from bronze.

11. A method according to any preceding claim, wherein the or each base unit is prismatic in shape with a rectangular section.

12. A method according to any of claims 1 to 10, wherein the or each base unit is prismatic in shape with a circular section.

13. A method according to any preceding claim, wherein at least one of the tie bars is of hollow section.

14. A method according to any preceding claim, wherein the tie bars are made from stainless steel, galvanized steel, sherardized steel or carbon fibre-reinforced resin.

15. A method according to any preceding claim, wherein the tie bars are bonded to the masonry with a grout of resin or mortar-based cement.

16. A method according to claim 15, in which the base unit of the or each tie connecting knuckle joint is received in a recess created in a face of the masonry structure.

17. A method according to claim 16, wherein the or each recess created in the face of the masonry structure is filled with a grout of cement to encase the base unit.

18. A method according to claim 16, wherein the or each tie connecting knuckle joint includes a pattress plate as specified in claim 6 or claim 7, and the pattress plate is also received in the recess created in a face of the masonry structure.

19. A method according to claim 18, wherein the recess created in a face of the masonry structure is filled with a grout of cement to encase the base unit and pattress plate.

20. A method according to any of claims 15 to 19, wherein the grout bonding the tie bars to the masonry of the structure is received in a flexible and expansible sleeve surrounding each tie bar.

21. A method according to claim 20, wherein the grout is injected under pressure into the sleeves, prior to setting or curing the resin or mortar-based cement, to expand the sleeves and bond the tie bars to the masonry of the structure.