GB2173536A - Repairing buildings - Google Patents

Abstract

The present invention relates to a method for repairing a building comprising a series of substantially upright load bearing column members 1 erected upon a foundation member and having panel members 6 extending between adjacent columns, said columns carrying the load of an overlying structure, which method comprises removing the panels between adjacent column members, forming a basal load-spreading member extending around substantially the whole of the periphery of the structure and adjacent the feet of the column members, said load-spreading member being formed from a series of co-operating pre-cast plinth members 7 incorporating a plurality of re-inforcing members 9, linking the plinth members and the basal portions of any remaining columns together by applying a grouting composition to the interfaces therebetween so as to form a unitary construction, and erecting a load-bearing wall upon the load-spreading member to the level of the head of the columns whereby the wall carries at least part of the load of the overlying structure. <IMAGE>

Description

SPECIFICATION Repairing buildings The present invention relates to a method for repairing buildings.

In someforms of houses and other buildings, a main-load-bearing structure is constructed from up rightpre-castconcretecolumns having steel or other reinforcing therein with concrete panels spanning the gaps between the columns to form the walls of the building. However, with time, the acidity in the air neutralisesthe alkalinity in the concrete leading to structural breakdown ofthe concrete columns and panels.

In orderto remedy defects in such structures, it has been proposed to cast new concrete plinth members encasing the base of the affected columns from which the more adversely affected portions have been cut away. However, this method is time consuming and costly and can involve evacuation of the building to permit access to the structure. As a result, some local authorities have chosen to demolish affected buildings ratherthan incurthecostanddisruption of carrying outthe repairs. In our British Patent Number 2114640 B we have proposed a method using a precast plinth which reduces the above problems.

However, that method of repairing damaged structures does not compensate for subsequentfailure of the column.

We have now devised a method for repairing such structures which reduces the above problems.

Accordingly, the present invention provides a method for repairing a building comprising a series of substantially upright load bearing column members erected upon a foundation memberand having panel members extending between adjacent columns, said columns carrying the load of an overlying structure, which method comprises removing the panels between adjacent column members, forming a basal load-spreading member extending around substantiallythe whole ofthe periphery ofthe structure and adjacentthefeetofthe column members, said load-spreading member being formed from a series of co-operating pre-cast plinth members incorporating a plurality of re-inforcing members, linking the plinth members and the basal portions of any remaining columns together by applying a grouting composition to the interfaces therebetween so asto form a unitary construction, and erecting a load-bearing wall upon the load-spreading membertothe level ofthe head of the columns whereby the wall carries at least part of the load of the overlying structure.

Preferably, substantially all of the load of the overlying structure is carried by the load-bearing wall by removing substantially all ofthe columns and panels and replacing them by the load bearing wall. It is especially preferred to carry this out by relieving the load on the columns over a section of the circumference ofthe building by means of temporary support members, removing the columns and panels within that section to permit the formation of the loadspreading member and load bearing wall to carry the load of the overlying structure; and repeating this procedure at successive sections around the circumference ofthe building.Such a method enables the unsound structures of the house to be eliminated in stages and replaced by newstructureswhichwill carry the load of the overlying structure from outside the buidling, thus minimising inconvenience and disruption ofthe occupants ofthe building.The new structure carries the load ofthe overlying structure and spreads it aroundthe circumference ofthe building with little deviation from the original load distribution, thus reducing the risk of relative movement between sections of the building.

The present invention can be applied to pre-cast concrete types of structure incorporating columns which carry the load of an overlying structure such as a roof or a second storeyto a house, for example barns, garages and other sectionally built houses.

However, the invention is of especial use in the repair ofthattype of house structure known as a Cornish unit type of house. For convenience the invention will be described with resectto the repair of that type of house and with resectto the accompanying drawings in which Figure lisa vertical section through the basal portion of the structure of a house with the loadspreading member in position; Figure 2 is a horizontal section through the structure of Figure 1; and Figure 3 is a vertical cross-section through a repaired wall using the method of Figure 1.

The house is builtfrom a series of generally upright pre-cast concrete columns 1 set on a suitablefounda- tion 2 and damp-proof course. The columns are usually re-inforced with one or more steel tubes or rods encased within the concrete of the column. The columns 1 are provided with peripheral vertical grooves 4 or ribs into which concrete or other panels 5 engage to provide the external cladding to the building. The columns 1 usuaily also carry plasterboard or other panels 6to provide the internal finish.

Typically, the columns 1 have an outer, a median and an inner web extending laterally from the column as shown to form the grooves into which the panels 5 and 6 locate. However, these panels are not cemented into the grooves and do not provide any load-bearing structure. The cavity between the inner and outer skins of the wall can contain fibrous or other insulating material.

Due to the action of water and chemicals, the concrete of the structure becomes unsound. In the method of the invention, the ribs orwebs holding the panels5in placeare removedto permitthe panelsto be separated from the structure. Thus, the basal portion of the outer web can be removed, as shown dotted in Figure 2, to permitthe bottom panelto be removed and to allowthe other panels to be dropped and then removed. Aiternatively, the whole ofthe height of the outerweb can be removed so that all the panels can be lifted forward and clear ofthe column.

The removal ofthepanelsexposestheinner structure for repair and treatment. lfdesired, insulation and water proofing can be carried outwhilstthe structure isexposedwherethe original construction is defective in these respects. Where only a small section ofthe building is to be repaired, it may be sufficientto cut back unsound concrete in the column to sound material. With the form of spreader plinth shown in Figure 1, it is necessary to remove sufficient material from-theexteriorface ofthe column to enable the reinforcing rods to be put into placetoform a continuously re-inforced spreader beam, as described below.

Wherethe re-inforcing ofthe column is exposed, it should be cleaned to provide a good surfaceforthe grouting to key onto, e.g. using a wire brush. If desired, the cleaned re-inforcing rods ortubes can be given an anti-corrosive treatment, e.g. with a phosphate. In some cases it may be necessary to cut away the foot of a re-inforcing tube where this is badly corroded. The foot ofthe resultant shortened tube should be supported, e.g. by inserting a bolt into the end ofthetube and screwing a nut on the boltup hard againstthetube, so thatthe bolt acts as a simple screw jack.

In the particularly preferred method of the invention, substantially all ofthe columns and panels are successively removed and replaced with new load bearing walls supported on a load-bearing member running around substa ntiallythe whoie ofthe circumference ofthe building. In this way all the load of the overlying structure is carried by new structure and the- risk of failure of one or more ofthe original columns is avoided. Furthermore, that load is sup ported during repair with little redistribution during the repair work and hence there is reduced risk of movement of sections of the building relative to one another.

In the preferred method,one or more temporary supports are erected adjacent that section ofthe outer wall ofthe house wall to be worked on. Typically, the supports will be hydraulic orscrewjacks. These serve to supportthe load of the overlying structure whilst the columns, panels and foundation member are removed from the section.

When the required number of panels and either material from the columns orthe columns themselves has been removed, a series of precast plinth members 7 are positioned atthefootofthe column orin place of part or all of the underlying foundation member. The plinth members can be located between the columns as shown in Figure2; can encompass the foot of one column 1 and extend to either side thereof to co-operate with the plinth members of adjacent columns; or can be laid on the existing foundation member, which can have been cut back to sound material,wherea newsection of load bearing wall is to be erected without retaining the original columns.

We preferthat, where some ofthe original columns are to be retained in the repaired structure, each plinth member7 has 3 stepped plan shapeto its ends so that it lies between adjacent columns and provides a portion extending acrossthe cut backface of column 1 as shown in Figure 2.

With the present invention, the plinth members are inserted around substantially the entire periphery of the building, exceptforthe door openings. Such a structure provides, when grouted or otherwise fixed in position and tied to any remaining columns, a unitary construction tie-ing the whole ofthe baseof the building together and acting to spread the loads imposed on it through the remaining columns and the load-bearing walls builtdirectly upon it.

The plinth members preferably have two or more longitudinal bores or slots 8therein which are to receive reinforcing rods 9. The bores or slots 8 in adjacentplinth membersarein registerwithone anothersothata continuous length of rod can be passed through a series of the plinths to tie them together. The bores can have any suitable crosssection and this need not be the circular shape shown in Figure I. The plinth members 7 can be provided with additional bores or slotsto those shown in the drawings and each plinth can also be provided with individuai internai reinforcement 10 if desired.A transverse bore or bores 11 can also be provided to link bore 8with an outerface, preferablythetop face, ofthe plinth so thatgrouting medium can be fed to bore 8.

When the plinth members and the reinforcing rods 9, have been put into position to form the load-spreading memberaroundthe peripheryofthe building, a grouting medium, e.g. cement, is fed into slots or bores 8 via bore 11 and into gaps between remaining columns 1 and plinth 7 to form a unified structure incorporating the foot of the remaining columns 1,the plinth 7 and the rods 9. The re-inforcementtubes in the columns can have holes through the walls thereof, notably when they have been shortened and a bolt inserted to supportthe foot ofthe tube as described above. The holes allow groutto enterthe tubes and aids formation of a unified structure.Such a structure provides a unitary base to the structure which accepts loads directly from the wall to be built upon it as described below, and also will accept indirect loads fromthecolumn 1. The unitary member spreads the loads comparatively uniformlyoverthe underlying foundations and reduces point loads and the risk of redistribution of loads.

As indicated above, the spaces between adjacent remaining columnsorformed by the removal ofthe original columns and panels around the circumference ofthe building are filled with load-bearing wall sections built up on the unitary ioad-spreading member to receivethe load from the overlying structure. The wall can be builtfrom bricks orfrom structural blocks using conventional methods and can be provided with an external cladding orfinish, eg. a thermally insulating layer and rendered finish, if desired.

The wall is built up to the height ofthe original columnsto pick up and supportthe load ofthe overlying structure, eg. of a rooforthefloorbeams or slabs of a second storeyto the building. However, the method ofthe invention allows sections ofthe wall to be builtonly partwayto thefull height,forexample where there is a window opening. Thewall can be stopped atcill height to accommodate an existing window structure or can permittheformation of new orwiderwindow openings.Aswith conventional building practice, the load ofthe overlying structure at such new window or other openings can be carried by any remaining-columns or can be transferred to load-bearing wall adjacent the new window opening bymeansoflintolsacrossthe head of the opening and/or by building a load-bearing pierto each side of the window opening to support the load directly onto the underlying wall structure. In this way the method ofthe invention allows flexibility in reconstruction of thefenestration of the house during repairtothe main structure ofthe house.

The wall sections extend to the full height ofthe original columns and are grouted or otherwise packed at their upper extremities using conventional techniquesto ensure that the overlying structure bears onto the upper course ofthe wall, thus providing direct reliefto the load originally borne by the column. If desired, an upper load-bearing circumferential mem ber or beam can be installed to sread point loads from the overlying structure, eg. from floor or roof beams, overthethe new wall sections.

The method ofthe invention provides a means for repairing existing structures so as to ensure that even if any original columns retained in the repaired structurefail afterthe repair, the remaining load is carried by the load-bearing walls and the building will not collapse. Since the main structural loads can be spread around the building, the method ofthe invention gives the builder scope for modification of the appearance ofthe building and allows him the modify door and window openingsto accommodate modern sized and styled casements in place ofthe Imperial and superceded casements in the original design with reduced risk ofvarying the distribution of the loads around the building during the repairwork.

The new wall sections can incorporate modern standards of insulation and weather-proofing sothat the repair not only overcomes a structural defect but may also reduce cold and condensation problems within the building.

Claims (6)

1. A method for repairing a building comprising a series of substantially upright load bearing column members erected upon a foundation member and having panel members extending between adjacent columns, said columns carrying the load of an overlying structure, which method comprises removing the panels between adjacent column members, forming a basal load-spreading member extending around substantially the whole of the periphery ofthe structure and adjacentthe feet of the column members, said load-spreading member being formed from a series of co-operating pre-cast plinth members incorporating a plurality of re-inforcing members, linking the plinth members and the basal portions of any remaining columns together by applying a grouting composition to the interfaces therebetween so as to form a unitary construction, and erecting a load-bearing wall upon the load-spreading member to the level ofthe head of the columns whereby the wall carries at least part ofthe load of the overlying structure.

2. A method as claimed in claim 1 wherein substantially all ofthe load of the overlying structure in the repaired structure is carried by the load-bearing wall by removing substantially all ofthe original columns and panels and replacing them by the load bearing wall.

3. A method as claimed in claim 2 wherein the load ofthe overlying structure on the columns over a section ofthe circumference ofthe building is relieved by means oftemporary support members, the columns and panels within that section are removed to permittheformation of the load-spreading member and load bearing wall to carrythe load ofthe overlying structural; and repeating this procedure at successive sections around the circumference of the building.

4. A method as claimed in any one of the preceding claims wherein the building is a pre-cast concrete domestic dwelling of the Cornish type.

5. A method for repairing buildingssubstantiaLly;: as hereinbefore described.

6. A building when repaired accordingtoamethod as claimed in any one of the preceding claims.