WO1995007400A1

WO1995007400A1 - Method for reinforcing a cavity wall

Info

Publication number: WO1995007400A1
Application number: PCT/GB1994/001968
Authority: WO
Inventors: William George Edscer
Original assignee: William George Edscer
Priority date: 1993-09-09
Filing date: 1994-09-09
Publication date: 1995-03-16
Also published as: AU7618494A

Abstract

A method of reinforcing a double skin wall including the step of raking out a bed joint (11) in an outer skin (10) of the wall and grouting a flat bar (13) preferably of deformed or apertured austenitic steel into the joint (11) to form a reinforced beam. An aperture is made below the beam formed, to permit access to the inner skin (12) of the wall so that a flat reinforcing bar (24) may be similarly incorporated into the inner skin. Additional reinforcement bars may be incorporated at lower points in the outer and inner skins respectively. A reinforced concrete beam may be formed in the aperture formed in the outer skin (10), and a damp proof course or cavity tray may be incorporated into the wall.

Description

METHOD FOR REINFORCING A CAVITY WALL

This invention relates to a method of reinforcing walls such as cavity walls of brick, masonry or concrete.

Buildings may suffer from a variety of structural- failures both above and below ground level, for example lintel failure, subsidence, thermal movement, differential movement and design faults. Since underpinning and partial rebuilding are both very expensive solutions to such problems, there is a need for less radical but nonetheless effective ways of preventing or remedying structural failures .

There have been a number of proposals for repairing walls which involve raking out a bed joint in a wall, inserting a reinforcing steel rod or the like and regrouting and repointing the wall. Such methods are normally limited to the reinforcement of solid walls or the outer skins of cavity walls, and involve reinforcing the wall at a single level only. Such a method is disclosed in patent specification EP 0 494 099. According to the present invention there is provided a method of reinforcing and/or reparing a cavity wall having inner and outer skins, which comprises the steps of:

raking out a bed joint in the outer skin;

inserting a reinforcing bar in the joint and regrouting the joint to link a plurality of bricks or blocks and form a beam resistant to vertical loads;

forming an aperture below the beam thus formed to gain access to the inner skin;

similarly inserting a reinforcing bar into a raked out bed joint of the inner skin, and

filling in the said aperture.

When the inner skin has been reinforced and its bed joint regrouted, the aperture below the beam originally formed can be closed off and the outer skin repointed so as to leave almost no visible sign of a repair.

Using the above method relating to a cavity wall, the bar or bars inserted into the outer skin can allow apertures up to 4 metres in length to be formed below the beam for access to the inner skin. In the event of an aperture of over 4 metres being required, additional support systems such as temporary jacks may be used. The method can be easily adapted to be applied to any configuration of double skin wall. The method may also include the step of forming a reinforced support (such as a reinforced concrete support) in the aperture formed below the beam. The support may extend into the inner skin so as to support both skins of the wall. The reinforced concrete support may extend entirely round a walled structure to form a ring beam.

Preferably the bars are of flat cross section, and can thus be inserted into narrower joints than the round bars previously used and also enable the bed joint to be adequately reinforced by means of a single bar. The flat form of the bar will facilitate the even distribution of grout or other fixing material around the bar, allow it to be positioned centrally within the joint and provide a bar having a higher surface area to volume ratio than round reinforcing bars customarily used in building construction. The reinforcing bars are preferably made from a metal such as steel, typically deformed auεtenitic stainless steel. High tensile plastic such as polyethylene may also be used. The width of the bar is preferably at least four times the thickness of the bar so as to provide a large enough surface area to volume ratio.

The bars may be machined and or provided with some form of surface roughening treatment in order to increase adhesion between the grout and the bar. Surface roughening includes blasting with granular material such as sand. Machining may include deforming parts of the bar out of its substantially flat form eg by forming dimples therein or may involve forming the bar with a slight undulating form along its length. The machining may alternatively include through apertures in the form of circular or elongate holes. Such apertures provide a convenient means by which one bar may be joined to another to form a lap joint, by passing fixing bolts through a pair of overlapping bars. A selection of straight and/or angled joining bars may be provided with a variety of inter-hole spacings so as to permit a wide variety of joint configurations. Bars may however be joined by riveting or welding. Alternatively or in addition to providing apertures in the bar, the edges of the bar may be notched. In order to improve stress distribution in a bar when in use such notches are preferably longitudinally offset from through apertures in bars .

The or each reinforcing bar may be part of a reinforcing arrangment comprising a reinforcing bar connected to one or more supplementary reinforcing members at least one of which is positioned substantially perpendicularly to the reinforcing bar and others which may be positioned substantially parallel to and spaced from the reinforcing bar. The reinforcing bar and some of the supplementary reinforcing members may advantageously be of the type described above. Such a reinforcing arrangement may advantageously be used in one of the methods discussed above in order to link one bed joint in a wall with adjacent vertical joints. Where one of the supplementary reinforcing members is substantially parallel and spaced from the reinforcing bar the reinforcing arrangement may be used to link two vertically spaced (normally adjacent) bed joints. The reinforcing bars and reinforcing arrangements discussed above provide a particularly efficient transfer of load between the structure of the wall and the reinforcement used and are considered to constitute inventions independent Of the inventive method described above. - ι_n particular flat bars suitably dimensioned to fit in a bed joint as discussed above may be designed to have a specific surface (surface per unit volume) up to 50% greater than round section bars having an equivalent cross sectional area. The efficiency of the bond is increased still further when the bars are deformed, apertured, notched or surface roughened.

Preferred embodiments of the intention will now be described with references to the accompanying drawings wherein:

Figure 1 shows in cross section a part of a cavity wall to which the method according to the invention is being applied;

Figure 2 is a perspective view of part of a cavity wall reinforced by means of the methods according to the invention;

Figure 3 is a cross sectional view through the cavity wall of Figure 2;

Figure 3a shows a cross sectional view through a cavity wall reinforced by means of the method according to the invention showing how a damp proof membrane or damp proof course can be inserted as part of the method; Figures 4 to 6 show reinforcing bars suitable for use in the method according to the invention;

Figure 7 is a vertical cross section through a wall in a region where two overlapping reinforcing bars are joined together;

Figure 8 is a perspective view showing how two bars may be joined end to end;

Figure 9 is a perspective view showing how two bars may be joined at a corner of a building;

Figures 10 to 12 show various forms of reinforcing arrangement suitable for use in the method according to the invention;

Figures 13 and 14 are two vertical cross-sections through cavity walls which have been reinforced by the method according to the invention in which an extra reinforcing support has been incorporated into the wall;

Referring to Figure 1, a cavity wall comprises an outer skin 10 of bricks and inner skin 12 of breeze blocks or the like, with a cavity 19 between them.

To reinforce the wall in accordance with the first aspect of the invention, firstly a bed joint 11 between two courses of bricks is first raked out to a predetermined depth, typically 5 to 8cm in the case of standard size bricks.

A reinforcing bar 13, which may be a substantially flat bar of crimped austenitic stainless steel having a width of 1 to 10cm and a thickness of 1 to 10mm, typically having a rectangular cross section of 25 x 3mm, is inserted centrally into the gap formed by raking out the bed joint, preferably after insertion of some new grout. With the reinforcing bar in position, the bed joint is regrouted, preferably with an expanding cementitious grout 14. Alternatively, a resinous grout such as an epoxy resin can be used.

The insertion of the reinforcing bar 13 binds the courses of bricks above and below it into a beam of high rigidity capable of withstanding of considerable vertical loads and the resulting stresses. A course of bricks below the reinforcement can thus be removed, leaving a longitudinal gap 15 which may be 4 metres or greater in length although it may be desirable to leave one or two bricks of this course in position or insert jacks depending on the length of gap needed to carry out the next stage of the process . Through the gap 15 a bed joint 16 of the inner skin can be raked out in the same way as in the outer skin. Another reinforcing bar 24 is then inserted into the gap 18 thus formed, and this gap also can then be regrouted. The aperture 15 can then be closed off, to leave a substantially invisible repair.

Referring to Figure 2 a typical repair pattern is illustrated. Two reinforcing bars are incorporated into each of the inner and outer skins 10, 12. First, a reinforcing bar 13 is inserted as described in connection with Figure 1, below an upper course of bricks 25. This reinforcement could well extend over the whole length of wall shown in Figure 2, or indeed over a greater length.

With the reinforcing bar 13 in position, bricks can be removed below it to give access to the inner skin, for the purpose of inserting reinforcing bars 24 and 26. In the course of closing of the outer skin, a further reinforcinq bar 22, can be inserted. The reinforcing bars 20,- 22 form between them a very substantial and rigid beam, which has considerable resistance to vertical stresses, and thus greatly strengthens the wall against subsidence and the like. The inner skin 12 is similarly strengthened, without the need for any opening up on the inside of the building, and when the outer skin has been repointed there need be no external sign of any repair having been carried out at all. The repair shown in Figure .2 is shown to an enlarged scale, and in more detail, in Figure 3. Figure 3a shows how a damp proof membrane 30, suitably of plastics or metal, can be inserted below one of the lower courses of bricks in the outer skin. The membrane shown is in the form of a longitudinally folded strip of which one half forms a membrane between two courses of bricks in the outer skin 10 while the other half forms a cavity tray 32.

The invention thus provides a simple method for reinforcing cavity walls involving no disturbance to the interior of the building or its occupants, which can be carried out by removing only a minimum of the existing structure and following which only a minimum of making good is required to render the repair invisible.

The reinforcing bars used may be machined or otherwise formed with a pattern of grooves extending transversely of the bar on either of its sides . The reinforcing bars may alternatively have short rods welded so as to extend substantially perpendicularly therefrom. Such bars have been found useful in the process according to the invention. Such a configuration of the bar increases the bond between the grout and the bar. Alternatively the reinforcing bars may be made of austenitic stainless steel, and crimped in alternating directions at intervals of 2 to 4cm, so that each side of the bar has alternating humps and recesses formed centrally along the length of the bar. The crimping imparts greater rigidity to the bar, enables the bars to be held more firmly by the expanding ce entitious grout, and allows the interlocking of overlapped ends of adjacent bars to form a continuous reinforcement. Figures 4 to 6 show a variety of alternative reinforcing bars 62 to 64 suitable for use in the method according to the invention. Each bar has regularly spaced through holes 72 to 76. The function of the holes is to allow easy joining of the bars by means of appropriate fasteners such as bolts, rivets or studs and also to provide a good bond between the bar and grout or similar material used to fix the bar in the bed joint of -a wall. Bars 62 and 63 shown in Figures 4 and 5 respectively have regularly spaced edge notches. The purpose of these notches is to control the distribution of stress in the bar when the bar has been incorporated in a wall using the method described above. Stress concentrations will occur where grout (or similar material) passes through a hole or notch in the bar. All of the bars shown in Figures 4 to 6 have a width 77 of 25mm and a thickness of 3mm.

The bar 64 shown in Figure 6 has been found to be of a particularly advantageous design. The spacing of holes provides particularly adaptable joining means . The holes 75 and 76 etc... occupy approximately 13% of the area of the bar. This provides an optimum transfer of load between the bar 64 and the grout (or similar material) for a bar having the dimension as described above.

The bars 62 to 64 are all made of austenitic steel so as to reduce adverse reaction with the wall into which they are incorporated. The surfaces of the bar are cold worked in order to increase the strength' of the bar and roughen the surface to improve the bond between the bar and the material used to fix the bar. Straight and angled joins between the reinforcing bars of the general type shown in Figures 4 to 6 may be affected as shown in Figures 7, 8 and 9. A straight joining bar 84 or an angle joining bar 86 both of which include regularly spaced taped holes 92, may be bolted to straight reinforcing bars 88 in overlapping relationship. Fixing bolts 82 are passed through aligned holes to fix the straight reinforcing bars 88 to the joining bars. _A selection of joining bars 84 and 86 will be provided with different hole spacings at the locations identified by letters X, Y and Z in order to provide adjustability in the way in which the straight reinforcing bars are joined. Where such a joint is formed it will be necessary to form an enlarged portion 80 in the raked out joint as shown in Figure 7.

Reinforcing arrangements 94 to 96 suitable for use in the method according to the invention are shown in Figures 10 to 12 respectively. All of these arrangements permit a reinforcing bar to be securely linked to portions of a wall above or below a joint in which the bar is located.

In the reinforcing arrangement shown in Figure 10, supplementary angled members 99 are bolted to a straight reinforcing member 100 with bolts 97. The advantage of such an arrangement is that legs 98 of the angled members which project outwardly from the reinforcing member 100 may be grouted into raked out vertical joints between bricks or into vertical slots cut into a wall. A selection of angled members 99, each with a different dimension W, as shown in Figure 10, will be provided to allow an upstanding leg 98 to be provided at any location along the reinforcing member 100.

In the reinforcing arrangement shown in Figure 11 two reinforcing bars 102 and 104 are vertically separated by the distance between two adjacent bed joints in a wall and joined at regular intervals by supplementary reinforcing members in the form of vertical rods 105 (only one shown). Nuts 106 located on either side of each reinforcing bar hold the arrangement rigid . As in the embodiment shown in Figure 10 the rods 105 may be grouted into raked out vertical joints between bricks or blocks or into vertical slots cut into the wall. When the arrangement 95 has been grouted into a wall with the bars 102 and 104 located in vertically adjacent bed joints and- rods 105 located in vertical joint or slots, a rigid beam will be formed, which is capable of supporting a very high vertical load. Where the reinforcing arrangement is incorporated into a double skin wall a third reinforcing bar 102a may be connected to the reinforcing bar 102 by means of adjoining member 105a. When each bar 102 and 102a are incorporated into outer and inner skins of a double skin wall, lateral as well as vertical support of the wall skins will be provided.

Figure 12 shows four examples of supplementary reinforcing members which can be connected to a reinforcing bar 96. The supplementary reinforcing member may be in the form of a sinuous hanger 110 engageable in a hole 114 in the reinforcing bar 112 and able to depend therefrom. The hangers may be grouted into vertical joints between bricks or blocks or into vertical slots cut into the wall. This will connect the reinforcing bar 96 to its underlying course of bricks or blocks more securely. Three other examples of supplementary reinforcing members 110a, 110b, 110c, are also shown in Figure 12. Member 110a will be bolted to the bar 96 and comprises a C shaped body. From the back of the body, projections llOd are provided which can be grouted into joints between facing bricks attached to the outer surface of a wall being repaired. Member 110b includes a hooked bar for engagement with the bar 96 and a plate connected perpendicularly to a lower end of the bar. The plate can act to support an item located below the courses of bricks or blocks being reinforced. Finally member 110c comprises an open loop reinforcing bar which may depend from the bar 96 and be grouted into a vertical joint or slot in the same way as the legs 98 of the angled members 99.

Figures 13 and 14 show three ways in which a cavity wall strengthened by the method according to the •the invention (described with reference to Figures 1 to 3 ) may be further strengthened by the incorporation of a reinforcing support member 122 or 124 into the wall. The incorporation of these support members is a relatively straight forward task when included in the reinforcing method described above. In each case the reinforcing member will be formed below the reinforcing bars -27 to 130 once they have been securely grouted in place. By reinforcing a wall in discrete 3m to 4m sections and subsequently joining adjacent reinforcing members a complete ring beam extending around a structure may be formed .

In the embodiment shown in Figure.14 the reinforcing member is constituted by a concrete body 133 accommodating steel reinforcing bars 13S_«

The reinforcing member is cast in the customary manner. The reinforcing member may support only one skin of the wall or may extend across and support both skins as shown in Figure 14. Any space 136 between the skins and below the reinforcing member 124, as shown in Figure 14, is preferably filled with concrete before the reinforcing support member is formed. This will obviate the necessity of providing a soffit shutter for the casting of the reinforcing member 124. Figure 13 shows an alternative form of reinforcing member 122. Horizontal reinforcing bars 138 link reinforcing bars 128 and 146 in the inner skin 150 with reinforcing bars 139 and 148 in the outer skin, by bolts or any other suitable means. A shaped member 140 which is positioned in the gap between the skins is bolted with vertically disposed bolts (not shown) to the horizontal reinforcing members 138. An expanded polystyrene layer 142 is located between the shaped member 140 and the inner skin 150. The gap between the shaped member 140 and the outer- skin 152 is filled with grout, preferably by injecting grout after the outer skin 152 has been bricked up.

A reinforced concrete support installed as described above may be connected by rods to adjacent floor joists. Facing bricks may be used to cover the aperture in which the beam is formed so as to obscure the fact that any remedial work has taken place. A layer of expanded polystyrene may be incorporated next to each support beam so as to isolate it from one of the skins of the wall or the facing bricks. Above or below the support beam a cavity tray 207 may be incorporated into the wall.

The reinforcing bars may have a round instead of a flat cross section.

Claims

CLAIMS :

1. A method of reinforcing and/or repairing a cavity wall having inner and outer skins, which comprises the steps of:

raking out a bed joint in the outer skin;

inserting a reinforcing bar in the joint and regrouting the joint to link a plurality of bricks or blocks to form a beam resistant to vertical loads;

filling in the said aperture.

2 A method according to claim 1 wherein the reinforcing bars are of flat cross section and the width of each bar is at least 4 times its thickness.

3. A method according to claim 2 wherein the reinforcing bars have a width of 1 to 10cm and a thickness of 1 to 10mm.

4. A method according to any preceding claim wherein the reinforcing bars are embedded in an expanding cementitious grout.

5. A method according to any preceding claim wherein the reinforcing bars are deformed or apertured such that the apertures represent between 10 and 40% of the transverse cross sectional area of the bars.

6. A method according to any preceding claim wherein the reinforcing bars have notched edges .

7. A method according to any preceding claim wherein at least one of the reinforcing bars is part of a reinforcing arrangement including supplementary reinforcing members extending substantially perpendicularly to the said reinforcing bar.

8. A method according to claim 7 wherein the reinforcing arrangement includes two interconnected substantially parallel reinforcing bars spaced apart so as to be insertable into vertically spaced bed joints in a skin of the wall.

9. A method according to any preceding claim further comprising the steps of incorporating into the cavity wall an additional reinforcing support member which supports one or both of the skins of the wall below upper reinforcing bar or bars in the inner and outer skins .

10. A method according to claim 9 wherein the additional support member comprises reinforced concrete and extends round an entire structure so as to form a ring beam.