WO2015118372A1

WO2015118372A1 - Process for reinforcing a building with masonry walls

Info

Publication number: WO2015118372A1
Application number: PCT/IB2014/002640
Authority: WO
Inventors: Stefano SACRATO; Giovanni Plizzari
Original assignee: Tri Srl
Priority date: 2014-02-05
Filing date: 2014-12-03
Publication date: 2015-08-13
Also published as: EP3102756A1

Abstract

The process for reinforcing a building with masonry walls having an inner surface and an opposite outer surface comprises the steps of: - preparing the outer surface of all of the walls, with removal of possible pre-existing plaster; - providing anchors in the outer surface of all of the walls, said provision in turn comprising: - forming holes in the walls, - inserting and fixing connectors in the holes; - applying a layer of plaster on the outer surface of all of the walls. In this way, an excellent reinforcement of the building is obtained. The plaster, clinging firmly to the walls thanks to the connectors, gives the masonry building greater strength, effectively opposing the disintegration of the individual elements (bricks or similar) that form the walls.

Description

Process for reinforcing a building with masonry walls

DESCRIPTION

The present invention concerns the reinforcement of buildings with masonry walls. In the present description and in the attached claims, the term "masonry" is to be taken in the most general sense, i.e. comprising a wall construction based on bricks, stone, unfired clay, or mixed, bound together dry or through cementitious material. In the present description and in the attached claims, by the term "reinforcement" an improvement is meant of the characteristics of structural strength of the building, also against seismic activity. This improvement can be the result of a preventive intervention, to make the wall stronger with respect to possible seismic stresses, or the result of a recovery intervention, to restore the necessary structural solidity to a building that has been damaged, for example due to seismic activity.

By the term "building" a complete construction or a portion of construction is meant, which comprises at least a series of masonry walls connected together. It should be understood that such a building can be a house, a block formed by adjacent houses, a portion of a house or something else.

Construction in seismic risk areas has always had to deal both with defending against possible damage caused by an earthquake and with restoration of buildings that have suffered damage due to an earthquake, obviously unless complete demolition of the building is inevitable.

In the first case, relative to newly built buildings, the prevailing approach, particularly in seismic high-risk areas, is to build buildings the structure of which contains elements capable of withstanding the action of the earthquake; in this way, in the case of a seismic shock within the foreseen limits, the building deforms but ensures the safety of human life. In order to obtain these characteristics, in the structure metallic and concrete building materials are widely used, while masonry, i.e. the construction of walls with bricks or similar (solid bricks, perforated bricks, brickwork slabs, prefabricated concrete blocks, stones, etc.) bound together by mortar, is usually avoided.

In the second case, i.e. for existing constructions, the interventions are often based on the connection of the different masonry walls and/or on the addition of elements capable of withstanding seismic activity. The walls possibly damaged by a quake are normally reconstituted or replaced, as a function of the degree of damage. These additional elements can, for example, be a layer of suitable cementitious material applied to the walls, in which material it is possible to incorporate a metallic reinforcement, normally a mesh.

It should be noted that both seismic protection and recovery of buildings damaged by seismic shocks are both particularly important and particularly difficult for historical masonry buildings. Indeed, the cultural value of these buildings requires a very conservative approach, so that their nature - also artistic - is not altered by a reinforcement intervention, either preventive or on an already damaged building. Moreover, ancient building materials often have little strength and therefore make historical buildings more vulnerable and subject to greater damage due to seismic shocks.

CN 202925925 U describes the anti-seismic reinforcement of a masonry wall. The reinforcement is obtained by inserting short steel bars in the masonry wall - at the vertical joints between adjacent bricks - said bars passing through the wall, protruding from both faces thereof; the two faces of the wall with the bars projecting from them are also coated with a fibre-reinforced concrete, which covers the entire wall. This reinforcement is thus based on obtaining a sort of strong capsule that encases the wall and takes care of bearing the stresses of a possible seismic shock; therefore, it cannot be used where one of the two faces of the wall is not accessible and cannot therefore be coated with fibre-reinforced plaster. The invention appears to refer to the construction of new buildings, since it foresees very precise positioning of the bars with respect to the single bricks, an operation that is only possible while building a wall.

JP 2008231869 A describes anti-seismic reinforcement of a masonry or concrete wall. The reinforcement is obtained by applying sheets of fibre on the wall, with the help of anchors fixed to the wall, and then applying a material that penetrates into the sheet of fibre incorporating it. This reinforcement thus forms a mesh-type strong structure, coupled with the wall and embedded in the plaster, said structure taking care of bearing the stresses of a possible seismic shock; therefore, it cannot be used in a historical building, where the application of such a mesh-type structure would be unacceptable in terms of the conservation of the building. The material applied over the mesh of fibre only has a clinging function and gives no contribution to the seismic resistance of the invention.

The Applicant has realised that there is a need to have materials and processes that allow the protection of buildings with masonry walls from seismic damage, and/or the restoration of such buildings even when already damaged by seismic shocks. Therefore, the present invention refers in a first aspect thereof to a process according to claim 1 . Preferred characteristics are defined in the dependent claims 2-16.

More specifically, the process comprises the steps of:

- preparing the outer surface of the walls, with removal of possible preexisting plaster;

providing anchors in the outer surface of the walls, said provision in turn comprising:

forming holes in the walls,

- inserting and fixing connectors in the holes;

applying a layer of fibre-reinforced plaster on the outer surface of the walls.

By "fibre-reinforced plaster" a plaster is meant in which dispersed fibres of another material are incorporated, to give better mechanical properties (greater resistance to traction, bending, shearing and/or twisting, elasticity, toughness, ductility, etc.).

It has been found that in this way an excellent reinforcement of the building is obtained. The fibre-reinforced plaster, clinging firmly to the walls, gives the masonry building greater strength. Indeed, the whole of all of the walls of the building thus reinforced forms a single reinforced structure, in which the plaster applied to each wall makes a sort of reinforcing shell that surrounds the entire building, making it suitable for withstanding seismic activity much better.

If it is possible to access the inner surfaces of the walls of the building, it will be possible to further improve the strength of the building by treating the whole of all of the inner surfaces in the same way.

This effect makes it possible to use the process on an undamaged building thus obtaining greater resistance also to seismic activity.

Moreover, it has been found that the process can be advantageously applied to a building damaged by an earthquake, provided of course that the damage is not excessive (building partially collapsed). In particular, it has been found that, by applying the process to a building with damaged masonry walls, in most cases a reinforcement of the building is obtained such as to allow the load- bearing function to be completely restored and to improve the characteristics of shear strength, avoiding having to destroy and subsequently rebuild the building.

The process is particularly suitable for historical buildings, since it is simply in the form of the application of new plaster. The only slightly destructive interventions (the formation of the holes) are very small and normally acceptable even in historical buildings, since they are then covered and hidden from view by the plaster and do not pass right through.

Preferably, the connectors have an enlarged head, incorporated in the plaster; in this way, a more effective reinforcement is obtained since the plaster clings very firmly to the walls of the building thanks to the enlarged heads.

Preferably, the holes are non-through holes and, more preferably, are evenly distributed over the surface of the wall, with density of 2-12 holes/m²

Preferably, the plaster used in the process of the invention is formed with a material having the following mechanical characteristics:

flexural tensile strength; 0.5-30 MPa (UNI EN 1015-1 1 ; 2007);

compressive strength: 5-120 MPa (UNI EN 1015-1 1 ; 2007);

adhesion to the support: 0.2-8 MPa (UNI EN 1015-12; 2002)

fibre-reinforced flexural tensile strength: fi_ = 1 -15 MPa; fRi=1 -20 MPa and f_R3=1 -20 MPa (UNI EN 14651 ; 2007)

these characteristics being measured according to the indicated standards.

Preferably, the average thickness of the layer of plaster is 5-80 mm. Smaller thicknesses indeed give a small reinforcing effect that may be insufficient whereas larger thicknesses can become too rigid and difficult to apply.

Preferably, the connectors have a conical, cylindrical or prismatic stem with bulk (diameter) of about 4-12 mm and head having a width of 4-100 mm. By the term width here the maximum bulk of the head in a plane perpendicular to the stem is meant. The head can have a simple shape, for example square, rectangular or circular, or even a more complex shape, for example cross-shaped, with two or more perpendicular bands that cross over at the stem. The head can have both two or three-dimensional development.

It is recommended that, in general, the thickness of the plaster, the width of the head and the density of the holes on the walls be selected in a coordinated manner: if the thickness is high, it is considered suitable for the width of the head and the density to also be high, and vice-versa.

Preferably, the plaster is formed with a hydraulic binder material.

Preferably, the fibre-reinforced plaster comprises steel fibres. The steel fibres give the plaster high mechanical strength, particularly to traction and shearing, whilst being relatively cost-effective.

Preferably, the steel fibres have a length of 3-65 mm and preferably a thickness of 0.01 -4 mm. Preferably, the steel fibres are helical, wavy, sawtooth shaped, hook-shaped or a combination thereof. These configurations promote anchoring of the fibres in the plaster, thus allowing tensile strength, in particular, to be improved.

Preferably, the steel fibres are made from high strength steel; even more preferably, they are made from stainless steel, so as to be suitable even for applications in situations of high humidity. By "high strength steel" a steel is meant having better mechanical characteristics than those of ordinary steel used for concrete reinforcement.

Preferably, the plaster comprises components aggregated in a binding matrix. The aggregated components can have a globular and/or acicular macromolecular structure.

Further characteristics and advantages of the present invention will become clearer from the following description of a preferred embodiment thereof, made with reference to the attached drawings. In such drawings:

- fig. 1 schematically shows a building to be reinforced;

fig. 2 schematically shows the outer surface of a wall of the building of fig. 1 ;

figs. 3 and 4 show the wall of fig. 2 in successive steps during the reinforcement process;

- fig. 5 shows the wall of fig. 2 at the end of the reinforcement process.

Figure 1 very schematically shows a building 10 to be reinforced; the building 10 in particular can comprise doors, windows and other architectural elements, not relevant for the purposes of the present invention and therefore not highlighted in fig. 1 . The building 10 can be a building already damaged by a seismic shock or a building still intact; in particular, the building 10 can be a historical building.

The building 10 comprises a plurality of masonry walls 11 , each having an outer surface 12 and an inner surface 13, with reference to the building 10.

Figures 2 to 4 show one of the walls 1 1 , seen from the side of its outer surface 12. In figures 2 to 4, it is not highlighted whether the wall 1 1 is an intact wall or a wall that has been damaged - but not destroyed - by a seismic shock or by another event; in any case, the process according to the invention applies to all of the walls 1 1 of the building 10, irrespective of whether the building is damaged or not; however, if on the surface 12 there is pre-existing plaster, this must be preliminarily removed. If the walls 1 1 are intact, with the reinforcement process the building 10 will be made more resistant to seismic activity; if, on the other hand, the walls 1 1 are already damaged, the previous functionality of the building 10 will also be restored.

In accordance with the process of the invention, on the surface 12 of every wall 1 1 a plurality of holes 14 are made, see fig. 3. The holes 14 are evenly distributed over the surface 12 with a density comprised between 2 and 12 holes/m² The holes 14 are non-through holes, i.e. they are blind, so that they do not create routes for the passage of air and/or humidity between the two surfaces 12 and 13 of the walls 1 1 .

Now with reference to figure 4, the holes 14 have connectors 15 (for example screws), preferably having enlarged heads 16, inserted and fixed in them (in a forced or glued manner). The insertion and fixing of the connectors 15 can be obtained for example with expansion plugs, or with the direct screwing of the connectors 15 in the holes 14, or through anchor chemicals. The connectors 15 have a bulk (diameter) of the stem of about 4-12 mm, whereas the width of the enlarged head 16 is comprised between 4 and 100 mm. In figure 4, the heads 16 are shown having a square shape. The connectors 15 in the holes 14 form anchor points in the surface 12 of the walls 1 1 of the building 10.

Now with reference to figure 5, on the surface 12 of the walls 1 1 provided with the holes 14 and the connectors 15 with the possibly enlarged heads 16, a layer of fibre-reinforced plaster 17 is applied, so that it incorporates the connectors 15 and their possible enlarged heads 16 in it, which are thus no longer visible. The average thickness of the layer of plaster 7 is 5-80 mm.

The plaster 17 is formed with a material having the following mechanical characteristics:

- flexural tensile strength; 0.5-30 MPa (UNI EN 1015-1 1 ; 2007);

compressive strength: 5-120 MPa (UNI EN 1015-1 1 ; 2007);

adhesion to the support: 0.2-8 MPa (UNI EN 1015-12; 2002)

these characteristics being measured according to the indicated standards.

The plaster 17 is formed with a hydraulic binder material, fibre-reinforced with high strength stainless steel fibres having a helical, wavy, sawtooth, hook-shape or a combination thereof, length of 3-65 mm and thickness of 0,01 -4 mm. The plaster 17 comprises inert components having a globular and/or acicular macromolecular structure in a binding matrix. The fibres, their shape characteristics and the inert components are not visible in the figures.

Once the plaster 17 is applied according to the process described above, once the time possibly necessary for the hydration and complete clinging thereof, the building 10 is reinforced. In other words, the structural strength of the whole of the walls 1 1 of the building 10 is greater than that of the building 10 prior to the process, suitable for withstanding even the stresses of an earthquake.

If the building 10 was a building already damaged by an earthquake, with the reinforcement obtained with the process according to the invention, the building 10 will have recovered its mechanical characteristics of structural strength, necessary for example to make it habitable once again. The building 10 thus reinforced is also suitable for withstanding the stresses of another earthquake.

The process according to the invention, described above and shown in the figures as used on the outer surface 12 of the walls 1 1 , can also be used on the inner surface 13 of the walls 1 1 , not visible in the figures.

It should be noted that with the process of the invention the walls 1 1 of the building 10 do not undergo any substantial transformation but at the end are simply coated with plaster, since the screws 15 and their heads 16 are not visible at the end of the process. Therefore, the process is highly suitable for restoration and/or reinforcement interventions of historical buildings.

If later on - for whatever reason - it is wished to restore the state of the building prior to the reinforcement intervention, all that is needed it to remove the plaster 17 and the connectors 15, possibly filling the holes 14. Of course, by doing so the reinforcement effect will be lost.

It is worth noting the simplicity with which the process of the invention is carried out, which makes its application easy and inexpensive, without the need for extensive construction work.

Claims

1 . Process for reinforcing a building (10) with masonry walls (1 1 ) having an outer surface (12) and an opposite inner surface (13), comprising the steps of: preparing the outer surface (12) of the walls (1 1 ), with removal of possible pre-existing plaster;

providing anchors (14, 15) in the outer surface (12) of the walls (1 1 ), said provision in turn comprising:

forming holes (14) in the walls (1 1 ),

inserting and fixing connectors (15) in the holes (14);

- applying a layer of fibre-reinforced plaster (17) on the outer surface (12) of the walls.

2. Process according to claim 1 , wherein the building (10) is an existing building.

3. Process according to claim 1 , wherein the building (10) is a historical building.

4. Process according to any of the previous claims, wherein the connectors (15) have an enlarged head (16), incorporated in the plaster (17).

5. Process according to any of the previous claims, wherein the holes (14) are non-through holes, preferably evenly distributed over the surface of the walls (1 1 ), with a density of 2-12 holes/m²

6. Process according to any of the previous claims, wherein the plaster (17) is formed with a material having the following mechanical characteristics:

flexural tensile strength; 0.5-30 MPa (UNI EN 1015-1 1 ; 2007);

compressive strength: 5-120 MPa (UNI EN 1015-1 1 ; 2007);

- adhesion to the support: 0.2-8 MPa (UNI EN 1015-12; 2002)

these characteristics being measured according to the indicated standards.

7. Process according to any of the previous claims, wherein the average thickness of the layer of plaster (17) is 5-80 mm.

8. Process according to any of the previous claims, wherein the plaster (17) is formed with a hydraulic binder material.

9. Process according to claim 1 , wherein the fibre-reinforced plaster comprises steel fibres.

10. Process according to claim 9, wherein the steel fibres have a length of 3- 65 mm and thickness of 0.01 -4 mm.

1 1 . Process according to any of claims 9 to 10, wherein the steel fibres are helical, wavy, sawtooth shaped, hook-shaped or a combination thereof.

12. Process according to any of claims 9 to 1 1 , wherein the steel fibres are made from high-strength steel, preferably stainless steel.

13. Process according to any of the previous claims, wherein the plaster (17) comprises components aggregated in a binding matrix.

14. Process according to claim 13, wherein the aggregated components have a globular and/or acicular macromolecular structure.