EP1170440B1

EP1170440B1 - Process of strenghthening masonry walls

Info

Publication number: EP1170440B1
Application number: EP00670005A
Authority: EP
Inventors: Vitor Manuel Bravo Coias E Silva
Original assignee: Stap-Representacao Consolidacao E Modificacao De Estruturas Sa
Current assignee: Stap-Representacao Consolidacao E Modificacao De Estruturas Sa
Priority date: 2000-07-05
Filing date: 2000-07-05
Publication date: 2009-04-01
Anticipated expiration: 2020-07-05
Also published as: ATE427395T1; EP1170440B8; EP1170440A1; DE60041913D1; ES2323261T3

Abstract

The present invention refers to a process of strengthening a stone or brick masonry wall, degraded (or not) by weathering or by seismic activity and that consists in simultaneously applying the following elements to the wall: a) confining ties (10) that pass through the thickness of the wall preferentially along a previously cleaned joint. They are made from an elongated cylindrical tie-rod (14) that is threaded at one or both ends and that fastens two circular anchoring and strength distribution plates (12), each one possessing a cylindrical casing (13) for the housing of the tie-rod's head or of a tightening nut; b) a laminate superficial strengthening membrane (20), made of a composite material of glass or carbon fibres soaked in an epoxy resin, and made from an adhesive gauze (22), a distribution element (23), and a covering web (24), is applied to one or both surfaces of the wall. In simpler cases it is possible to eliminate the confinement ties. When the opposed walls of a construction can be braced by adequately designed members, the composite laminate can be applied only on the external faces. The present invention can be especially used in the repair of buildings, with the aim of giving them an adequate resistance, especially to seismic activity. <IMAGE>

Description

The present invention refers to a process of strengthening a regular or irregular masonry wall, preferentially of stone or brick, in order to increase its resistance to compression or bending efforts applied perpendicularly to or in the same direction as the wall face.
Other reinforcing devices and methods have been already disclosed. For example, the document DE 19620029 discloses a reinforcing device for buildings to be used especially in ceilings, which comprises two main parts, an anchor part and a harness part, both of which extend from a different plate element. These two parts can be fixed together, so that a tensile force will transfer between the two plates which are arranged above and below the building structure. The document US 5640825 discloses the strengthening of wall surfaces by first cleaning them and by providing a plurality of straps of flexible non-metallic fiber composite material and fixedly attaching the straps of non-metallic fiber composite material to the wall portion along at least lengthwise portions of the straps and opposite end portions thereof by epoxy bonding the straps onto the surface. The document DE 4213839 discloses a reinforcement carried out by securing a strong fibre compound to at least one side of the constructional component.
The process is especially designed to enable the rehabilitation of old masonry buildings having an architectural significance that have been relatively degraded or not by the effects of weather and/or seismic activity to which the resistance to bending of the perpendicular plane is highly critical. However, the resistance of walls in inhabited buildings can also be increased reducing any inconvenience and disturbance for the inhabitants as the repair work can be carried out without the need for relocation.
Fundamentally, the process of strengthening masonry walls in need of rehabilitation in accordance with this invention involves the application of two characteristically different elements:

a) laminates of composite material whose purpose is to resist the tensile and compressive strains that act at the surface of the walls when these are exposed to lateral actions.
b) confinement elements that pass through the thickness of the wall and whose purpose is to restrain and hold the wythes of the stone or brickwork wall in position, also called confinement tie.

The combined use of these two elements enables the co-operation of a traditional material having a relatively low resistance but high inertia - the masonry, with an advanced material of high resistance and stiffness but with a low inertia - the composite.
When the strengthened wall is exposed to a bending effort perpendicular to its vertical plane, the laminate remains under tensile and compressive strains. The resistance to the tensile strain is not a problem and alleviates the brickwork. Under the influence of the compressive strains, the laminate will tend to slide in relation to the wall surface and warp. However this effect can be reduced or fought due to the presence of the confinement ties between the wall faces.
In cases where opposed walls of the same construction can be braced by adequately designed members, the composite laminate can be applied only on the external faces.
The present description is based on the following figures that show respectively the preferred means of execution.
Consequently,

Figure 1: shows a schematic transversal section of a masonry wall by a vertical plane and strengthened in accordance with the process described in the present invention;
Figure 2: shows a schematic enlarged view of the confinement ties and composite laminate fixing detail to the masonry wall;
Figure 3: shows an enlarged view of this fixing detail;
Figure 4: (a) shows an enlarged side elevation view of a dimple formed in the brickwork;
Figure 5: shows an enlarged sectional view that details the constitution of the composite laminate elements;
Figure 6: shows a schematic view of the first phase of the process involving the removal of plaster, the cleaning of the joints and the marking of places of drill holes;
Figure 7: shows a schematic view of the respective second phase of the process involving drilling the holes for the tie-rods and the execution of the cavities;
Figure 8: (a) shows a schematic view of the third phase involving placing an adhesive membrane or web, in the shape of strips aligned in two directions, and the creation of the dimples;
Figure 9: shows a schematic view of the fourth phase involving placing distribution elements, covering web, and the introduction of the rod-ties and injection and furthermore, if necessary, the placing and tightening the ties; and

The process to which this invention refers can be considered innovative, as there is no evidence that these types of materials have been previously used. Furthermore, it explores the combination of composite materials having high mechanical resistance and low inertia with materials having high inertia but low mechanical resistance, where the union between masonry and laminate is merely mechanical based on the joint action of the dimples with the confining ties.
Compared to the traditional methods of wall strengthening there are advantages, certainly not entirely worthless, of which the following can be presented as non-exhaustive examples: lower disturbance of residents, particularly relevant when concerning residential buildings; lower disturbance of the original structure which is especially relevant in the case of buildings having architectural or cultural importance; totally unnoticeable after the application of the finishing plaster; irrelevant increase in wall thickness, of the order of millimetres and which can be compensated by the thickness of the rendering; easy reversibility, which is of special relevance in the case of buildings of architectural importance, because the distributing plates, if injected, can be loosened and disassembled, the tie-rods can be drilled out and the laminates can be subsequently cut with a vulgar cutting tool and removed if necessary.
These advantages can be increased by the use of advanced equipment completed with debris suction and storage systems, and adequate guidance and motion systems.
Figure 1 shows a schematic design of the system of repairing and strengthening masonry walls in degraded buildings in accordance with the present invention.
As previously mentioned, the process involves the application and even distribution over the surface of the wall of two strengthening elements with different characteristics.

1) Confinement Ties (10)

These elements totally pass through the wall along one of the joints and are essentially made of two circular anchorage and strain distribution plates (12) connected by a steel tie-rod threaded at one or both ends (14).
The plates are provided with a cylindrical casing (13) which is used for housing a tightening nut that serves as support for the tie-rod.
The tie-rod can be solid or, if necessary, it can be tubular with one or two sleeves for later injection, achieved through the holes in the tube wall (15).

2) Superficial Strengthening Laminates (20)

They are made of a composite material having high strength fibres, polyester, glass or carbon, previously soaked with an epoxy resin, and destined to withstand tensile and compressive strains, the mobilisation of their resistance being insured by the combined effect of the confinement ties and the dimples. The laminates can be made as follows:

a) They can be made of three types of associated elements, destined to work together forming a resistant membrane applied to one or both sides of the wall, and which are: an adhesive membrane or web (22), a distribution element (23); and a covering web (24) (fig 2 to 5).
The adhesive membrane or web (22) is made from strips of the composite material having a width, as a rule, from 1 to several decimetres. These strips are generally placed diagonally on the wall surface and accompany any irregularities, particularly the ruts that appear in the brick or stone joints that are previously raked and cleaned.
b) Alternatively, the strengthening laminate layers can be made up by spraying the polyester or epoxy resin simultaneously, incorporated chipped fibres. In this alternative process, the wall face can be previously treated with a debonding agent so as to insure that shear pieces are transmitted preferably by the mechanical connection provided by the joint effect of the confining ties and the dimples, thus insuring the reversibility of the system.

The said strips pass over the cavities destined to the confinement ties anchoring plates (Fig. 2 and 4).
The existing cavities in these strips that correspond to the ruts in the joints are filled with the appropriately formulated epoxy resin mortar, so as to form small dimples (25) (Fig 1, 2, and 4).
The distribution elements made from circular or polygonal shaped composite material (23) are then placed on top of the adhesive web (22). They are pasted to the strips of the adhesive web (22) and accompany the cavity where the anchorage plates (12) are fitted, below which they are then tightened. They are provided with only an applied finishing destined for future pasting to the part of the surface that is to be placed between the first and last layers; the surface that is to be overlapped with the anchorage plates (12) is not subject to treatment.
The covering web (24) is made from strips similar to those used for the adhesive web (22). These strips are then pasted over the adhesive web strips and may be treated on the outside surface so as to improve their mechanical connection and on the inner surface so as to enable easy bonding to the contact layer.
After the polymerisation, the three layers of a laminate having high resistance and stiffness are tightly fastened by the confinement ties to the wall surface, which are bonded to it through the dimples.
When the wall is exposed to out of plane bending, the sliding of the plate is prevented by three mechanisms:

shear resistance of dimples;
shear resistance of tie-rods and rods;
mechanical connection and friction created by the sand grains, bonded to the laminate surface, in contact with the masonry.

When the wall is exposed merely to an additional compression, the resistance of the laminate is mobilised immediately due to its greater stiffness and the wall tendency to yield is counteracted by the force of the ties. The high inertia of walls counteracts any tendency to warping of the laminate which would be significantly higher should it be isolated, due to the degree of slenderness it would present in that case.

The practical realisation of the present process consists of the series of tasks carried out in the order as indicated in the following table and schematically shown in figs. 6 to 9.

TABLE

Summary of Works
Work	DESCRIPTION	OBSERVATION
1	Removal of wall plaster, cleaning joints and marking the places of drill holes.	Use of equipment having suction and debris collection capability.
2	Execution of transversal drill holes (for the ties) and respective enlargements using specific equipment (if applicable).	Use of mobile equipment pre fixed to the structure in the span areas by tracks and with capabilities for debris and suction collection.
3	Fixing of the composite strips membranes or webs and creation of dimples.	Vacuum equipment should be used in order to achieve a good bonding to the masonry surface. Curing equipment for the previously impregnated composite material should also be used. Alternatively, spraying equipment may be used to form the composite strips.
4	Instalation of the confinement ties and distributing plates.
5	Rendering or fire protection	Prefabricated dismountable finishing boards may be used.

Claims

Strenghtening process for deteriorated, even and uneven masonry walls, preferably stone or brick, in order to increase their resistance to tension or compression forces, characterised by applying to the aforementioned walls a combination consisting of:
a) a laminate membrane for the surface reinforcement (20) made of highly-resistant composite fibre material, e.g. polyester, glass or carbon, pre-impregnated with epoxy resin, applied to one or both sides of the wall, successively consisting of an adhesive fabric (22), a distribution element (23) and a covering fabric (24);

b) one or more confinement elements (10) that transversally penetrate the thickness of the wall preferably along a joint and which essentially consist of an elongated, cylindrical tie-rod (14), whether solid or tubular, having one or two threaded ends, which interconnect two anchoring and force-distributing circular plates (12), each equipped with a small cylindrical box (13) used to house a tightening nut and support the ends of the tie-rod.
Process according to claim 1 characterised by the fact that the above-mentioned laminate membrane for surface reinforcement (20) is formed by bands which are diagonally fixed to the wall being reinforced in the mentioned order.
Process according to claims 1 and 2, characterised by the fact that the adhesive fabric (22) is adapted to the grooves of the joints between the stone rows of the wall being reinforced, thus penetrating inside them and the resulting cavities being filled with epoxy resin mortar in order to form small dimples (25) which prevent the reinforcement laminate from slipping.
Process according to claims 1 to 3, characterised by the fact that the adhesive fabric (22) is treated on the back to improve its mechanical connection to the wall surface.