Patent Publication Number: US-11028604-B2

Title: Reinforced masonry wall

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a reinforced masonry wall and to a method of reinforcing a masonry wall, in particular for increasing its resistance against earthquakes. A masonry wall is built from individual units laid in and bound together by mortar. Brick and concrete block are the most common types of masonry units, but stone, marble, granite, travertine, limestone, cast stone, glass block, stucco, tile, and cob are also common. The walls may be either weight-bearing or a veneer. Although masonry is generally a highly durable form of construction and masonry has high compressive strength under vertical loads, it has low tensile strength (against twisting or stretching) unless reinforced. Unreinforced masonry buildings are highly vulnerable to damage during earthquakes, due to their high mass, limited ductility and low tensile strength. 
     “ FRP Composites for Masonry Retrofitting ” Tumilian et al., Structure magazine, May 2009, p. 12-14 describes reinforcing existing masonry with fibre reinforced plastic (FRP) strips. According to this document, strengthening of masonry walls for seismic and wind loads may require FRP placement on both sides of the wall, to provide flexural resistance against both inward and outward loads. It is also contemplated that, for some exterior walls that are part of the building envelope, placing FRP on both sides may not be possible due to field constraints (e.g. presence of the backup wall of a cavity wall system) and that similar constraints may exist for brick walls in historical buildings. In this case, even though both wall sides are accessible, the exterior side may be “untouchable” because the FRP would disrupt the facade appearance unless outside-face bars are concealed in the bed joints. 
     In “ Earthquake Protection of Masonry Shear Walls Using Fibre Reinforced Polymer Strengthening ”, K. M. C. Konthesingha, PhD-thesis, School of Engineering, The University of Newcastle, Australia, 2012, cyclic loading was used to investigate the cyclic bond behaviour of FRP to solid clay brick masonry. For instance, pull test specimens, each consisting a four brick high stack bonded prism reinforced with 15 mm wide unidirectional pultruded carbon fibre reinforced plastic (CFRP) strips inserted in vertical slots cut into the brick units using a brick cutting saw. The FRP strips were then glued into the slots with a two-part epoxy adhesive. The cross section of the vertical slots was 20 mm deep and 6 mm wide. The strengthening reinforcement was applied only on one side of the wall because in practice it is usually not possible to access both sides of an existing wall. 
     Reinforcing walls with FRP strips is also disclosed in U.S. Pat. No. 5,894,003 and Korean patents 101240283, 1004432318 and 101057667. 
     European patent application 1 170 440 discloses strengthening a stone or brick masonry wall, especially with regard to seismic activity, by applying a laminate superficial strengthening membrane made of a composite material of glass or carbon fibres soaked in an epoxy resin, and made from an adhesive gauze, a distribution element, and a covering web, to one or both surfaces of the wall. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a solution that allows reinforcing a wall of masonry, in particular in an existing building, to increase the resistance of the wall against earthquakes, without access to or leaving traces on one wall surface of the wall. 
     According to the invention, this object is achieved by providing a wall of a building, wherein: 
     the wall is a masonry wall built from individual units laid in and bound together by mortar; 
     the wall has first and second wall surfaces on opposite first and second sides of the wall and a midplane centrally between and parallel to the opposite wall surfaces; 
     a plurality of passageways is provided in the wall, the passageways each being elongated in a longitudinal direction; 
     at least one reinforcement member is provided in each of the passageways, the reinforcement members being elongated in the longitudinal direction of the passageways; 
     the reinforcement members include a first group of reinforcement members each having a centre line on the first side of the midplane and a second group of reinforcement members each having a centre line on the second side of the midplane; 
     the passageways include slots; 
     the slots are open horizontally to the first side of the wall only; 
     the second group of reinforcement members are arranged in passageways located spaced from the second wall surface; and
         the reinforcement members in the passageways are each embedded in an adhesive substance, the adhesive substance being bonded to each of the reinforcement members and to an inner surface of the passageway in which the reinforcement member is provided.       

     Because in such a wall, also passageways on a second side of a midplane of the wall are located spaced from the second wall surface opposite of the first wall surface, reinforcements can be provided also on the second side of the neutral midplane of the wall, without requiring access to or through the wall surface on the second side of the wall and can accordingly be made without leaving any traces on the second side of the wall and also if the second side of the wall is inaccessible, for instance because it is in a cavity of a cavity wall. 
     The invention can also be embodied in a method of reinforcing a masonry wall of a building, the wall being built from individual units laid in and bound together by mortar and having first and second wall surfaces on opposite first and second sides of the wall and a midplane centrally between and parallel to the opposite wall surfaces, the method including: 
     making a plurality of passageways in the wall by removing wall material, the passageways each being elongated in a longitudinal direction, the passageways including slots, wherein the slots are open horizontally to the first side of the wall only; 
     arranging at least one reinforcement member in each of the passageways, the reinforcement members being elongated in the longitudinal direction of the passageways, the reinforcement members including a first group of reinforcement members each having a centre line on the first side of the midplane and a second group of reinforcement members each having a centre line on the second side of the midplane, the second group of reinforcement members being arranged in passageways located spaced from the second wall surface; and 
     embedding the reinforcement members in the passageways in an adhesive substance injected in the passageways, the adhesive substance bonding to each of the reinforcement members and to an inner surface of the passageway in which the reinforcement member is provided. 
     According to another aspect of the invention, a wall of a building is provided, wherein: 
     the wall is a masonry wall built from individual units laid in and bound together by mortar; 
     a plurality of passageways is provided in the wall, the passageways each being elongated in a longitudinal direction; 
     at least one reinforcement member is provided in each of the passageways, the reinforcement members being elongated in the longitudinal direction of the passageways; 
     the reinforcement members in the passageways are each embedded in an adhesive substance, the adhesive substance being bonded to each of the reinforcement members and to an inner surface of the passageway in which the reinforcement member is provided; and
         the adhesive substance has an elongation at break of at least 40% and preferably at least 50% (DIN 53544) and a hardness at room temperature of at most 100 and preferably at most 90 Shore A.       

     Because the adhesive substance is relatively soft and has a large elongation at break, it can accommodate relatively large deformations of the wall, without causing cracking of masonry along the reinforcing members. Thus, even if the wall deforms to an extent that some cracking occurs, the reinforcing members effectively hold the wall together so that complete collapse of the wall is counteracted. Such a failure mode in which complete collapse or other failure of a wall occurs only at loads much larger than loads at which first cracks occur is of particular advantage for avoiding casualties in the event of an earthquake. 
     According to yet another aspect of the invention, a masonry wall of a building is provided, which wall is built from individual units laid in and bound together by mortar, the wall further including a stabilizing layer covering a vertical surface of the wall, the stabilizing layer being composed of a matrix material and fibres embedded in the matrix material, the matrix material adhering to the first wall surface, wherein the matrix material has an elongation at break of at least 250% and preferably at least 300% at 24° C. (ASTM D412) and a hardness of at most 120 and preferably at most 110 Shore A or at most 60 and preferably at most 50 Shore D (ASTM D2240). 
     Because the matrix material of a composite layer covering a surface of the wall is relatively soft and has a large elongation at break, it can accommodate relatively large deformations of the wall, without debonding from the masonry. Thus, even if the wall deforms to an extent that some cracking occurs, the composite layer effectively holds the wall together so that complete collapse of the wall is counteracted. Such a failure mode in which complete collapse or other failure of a wall occurs only at loads much larger than loads at which first cracks occur is of particular advantage for avoiding casualties in the event of an earthquake. 
     Optional features of the invention are set forth in the dependent claims. Further features, effects and details of the invention are described in the detailed description with reference to examples of walls according to the invention shown in the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a horizontal cross-sectional view of a portion of a first example of a wall according to the invention; 
         FIG. 2  is a horizontal cross-sectional view of a portion of a second example of a wall according to the invention; and 
         FIG. 3  is a horizontal cross-sectional view of a portion of a third example of a wall according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is first described with reference to a first example of a wall according to the invention shown in  FIG. 1 . 
     In  FIG. 1 , a cavity wall  1  including a load bearing inner wall  2 , a veneer wall  3  and a cavity  4  filled with insulating foam is shown. In this example, the load bearing inner wall  2  is an example of a reinforced wall according to the invention. 
     The inner wall  2  is a masonry wall built from individual bricks  5  laid in and bound together by mortar  6 . The inner wall  2  has first and second wall surfaces  7 ,  8  on opposite first and second sides of the inner wall  2  and a midplane  9  centrally between and parallel to the opposite wall surfaces  7 ,  8 . 
     Passageways  10 ,  11  are provided in the inner wall  2 . The passageways  10 ,  11  are each elongated in a longitudinal direction. The longitudinal direction is preferably oriented substantially vertically. Vertical reinforcement has been shown to provide greater increases in strength and ductility in walls subjected to in-plane shear loading and to be most effective for strengthening against out of plane bending. In the present example, the passageways  10 ,  11  are in the form of slots. Such slots can be provided quickly, efficiently and accurately by sawing, e.g. using a diamond saw. 
     A reinforcement member  12 ,  13  is provided in each of the passageways  10 ,  11 . The reinforcement members  12 ,  13  are elongated in the longitudinal direction of the passageways  10 ,  11 . In this and other embodiments, the reinforcement members  12 ,  13  preferably each extend over the entire length of the passageway  10 ,  11  in which they are arranged. However, due to manufacturing tolerances, availability of reinforcement members in a limited number of pre-cut sizes, reinforcement members  12 ,  13  will typically be slightly to substantially (up to 1, 5, 10 or 20 cm) shorter than the length of the passageway  10 ,  11  in which they are arranged. 
     In this and other embodiments, the passageways  10 ,  11  are preferably of a length extending from one end of the wall to the opposite end (e.g. from the top to the bottom) so that the wall  2  is reinforced over its entire height (or width). The passageways may end at a small distance (e.g. up to 5, 10 or 20 cm) of the ends of the wall, for instance to avoid cutting into the floor or the ceiling or if cutting equipment is unable to reach into corners between the wall and a ceiling or floor. 
     The reinforcement members include a first group of reinforcement members  12  each having a centre line (i.e. line in longitudinal direction of the reinforcement member intersecting centres of the reinforcement member cross-sections) on the first side of the midplane  9  and a second group of reinforcement members  13  each having a centre line on the second side of the midplane  9 . Thus, reinforcement members  12 ,  13  are provided on both sides of the midplane  9  of the inner wall  2 , so that reinforcement members  12 ,  13  can be loaded with tensile loads transferred thereto on both sides of the midplane  9 . This is particularly advantageous in the event of earthquakes oscillating with a substantial directional component in a direction transverse to the wall  1 , which causes the walls  2 ,  3  to be subjected to oscillating bending loads. 
     The passageways  10 ,  11  are open (disregarding items and substances inserted therein) horizontally to the first side  7  of the inner wall  2  only and the second group of reinforcement members  13  are arranged in passageways  11  that are located spaced from the second wall surface  8 . Thus, the slots  10 ,  11  can be made even if, as in the present example, the second surface of the wall  2  is not accessible because it bounds a cavity of a cavity wall. There may also be other reasons why making passageways from the side of the second wall surface  8  is preferably avoided or impossible. The second wall surface may for instance be difficult to reach due to a location high above the ground or due to implements such as stairs or a kitchen mounted thereto. Also restoring the outer appearance of the second wall surface after cutting passageways therein may be difficult, expensive or even impossible (e.g. in a historic building). 
     The reinforcement members  12 ,  13  in the passageways  10 ,  11  are each embedded in an adhesive substance  16  (adhesive substance in the passageways  10  holding reinforcement members  12  of the first group not shown). The adhesive substance  16  is bonded to each of the reinforcement members  12 ,  13  and to an inner surface of the passageway  10 ,  11  in which the reinforcement member  12 ,  13  is provided. Thus loads exerted onto the inner wall  2  that would cause deformation of the inner wall  2  are effectively transferred to the reinforcement members  12 ,  13 , which thus counteract deformation of the inner wall  2 . In particular tensile loads are thus absorbed particularly effectively by the reinforcement members  12 ,  13 , so that the masonry is effectively protected from being damaged when subjected to tensile loads, for instance as a result of bending loads caused by oscillations of the ground in an earthquake. Also the failure mode of the wall in the event of damage exhibits a much wider load range between initial damage (e.g. cracks) and full collapse of the wall, which is of particular importance for avoiding casualties due to suddenly falling floors and roofing in the event of an earthquake. 
     In this and other embodiments, the adhesive substance preferably has an elongation at break of at least 40% and preferably at least 50% (DIN 53544) and a hardness at room temperature of at most 100 and preferably at most 90 Shore A and at least 50 to 60 Shore. Because the adhesive substance is relatively soft and has a large elongation at break, it can accommodate relatively large deformations of the wall, without causing cracking of masonry along the reinforcing members. Thus, even if the wall deforms to an extent that some cracking occurs, the reinforcing members effectively hold the wall together so that complete collapse of the wall is counteracted. Such a failure mode in which complete collapse or other failure of a wall occurs only at loads much larger than loads at which first cracks occur is of particular advantage for avoiding casualties in the event of an earthquake. Adhesion of the adhesive substance is preferably greater than 1 N/mm 2  (DIN 52455) and tensile strength is preferably greater than 2 N/mm 2  (DIN 52455). Adhesive substances fulfilling these specifications are commercially available. It is noted that although using such an adhesive substance is particularly advantageous in the relatively deep passageways for holding the reinforcement members of the second group, an adhesive substance that is relatively soft and has a large elongation at break is also advantageous if passageways are provided on the first side of the midplane only. 
     If, as in the present example, the reinforcement members  13  of the second group are also arranged in slots  11  that are open horizontally to the first wall surface  7 , the slots  11  having a depth extending from the first wall surface  7  to beyond the midplane  9  and the reinforcement members  13  of the second group are arranged adjacent to a side of the slots  11  most remote from the first wall surface  17 , the passageways  11  for holding the reinforcement members  13  on the second side of the midplane  9  can be made easily and by making incisions through the same first wall surface  7  in which also the slots  10  for holding the reinforcement members  12  on the first side of the midplane  9  are cut. The slots  10 ,  11  for receiving the reinforcement members  12 ,  13  of the first and second groups can in principle be made using the same cutting tools. 
     The reinforcement members  12  of the first group are arranged in a first group of slots  10  having a first depth and the slots  11  in which the reinforcement members  13  of the second group are arranged are slots  11  of a second group having a second depth larger than the first depth. Thus, the slots  10 ,  11  for receiving the reinforcement members  12 ,  13  of the first and second groups can simply be made by for instance alternatingly cutting deep and shallow grooves in the first surface of the inner wall  2 . 
     Because the space in the slots  10 ,  11  remaining after the reinforcement members  12 ,  13  have been inserted is filled with the adhesive substance, weakening of the wall  2  due to the interruption of masonry by the slots  10 ,  11  is at least counteracted. Also, the reinforcement members  12 ,  13  in the slots reduce deformation of the wall  2  in particular in the area of the slots  10 ,  11 , so that failure by cracking along the slots  10 ,  11  occurs at very high shock loads only. 
     A stabilizing layer  20  covers the first wall surface  7 . The stabilizing layer  20  is composed of a matrix material and fibres such as glass fibres in a woven or non-woven pattern embedded in the matrix material. The matrix material adheres to the first wall surface  7 . The stabilizing layer  20  is particularly effective for counteracting the formation of cracks along the reinforcement members of the first group  12  when the wall  2  is heavily loaded with tensile stress on the first side of the midplane  9 , e.g. during bending loads with the first side  7  located on the outside of the induced bend. If cracks do occur, the stabilizing layer effectively holds the wall  2  together so that complete collapse of the wall is counteracted. Another advantage of the stabilizing layer is that it constitutes a bridging interconnecting and mutually fixing wall portions on opposite sides of the slots  10 ,  11  containing the reinforcement members  12 ,  13  thereby further reducing the resistance against cracking along the slots  10 ,  11 , also along the relatively deep slots  11 . 
     The matrix material of the covering layer  20  preferably has an elongation at break of at least 250% and more preferably of at least 300% at 24° C. (ASTM D412) and a hardness of at least 60 or 70 and at most 120 and more preferably at most 110 Shore A or at least 25 or 30 and at most 60 and preferably at most 50 Shore D (ASTM D2240). The composite material may for instance be an elastomeric substance of aromatic isocyanate resin reacted with amine prepolymers having a tensile strength of at least 12 MPa at 24° C. (ASTM D412). 
     Because the matrix material of a composite layer covering a surface of the wall is relatively soft and has a large elongation at break, it can accommodate relatively large deformations of the wall, without debonding from the masonry. Thus, even if the wall deforms to an extent that some cracking occurs, the composite layer effectively holds the wall together so that complete collapse of the wall is counteracted. Such a failure mode in which complete collapse or other failure of a wall occurs only at loads much larger than loads at which first cracks occur is of particular advantage for avoiding casualties in the event of an earthquake. It is noted that although providing such a covering layer is particularly advantageous when covering deep passageways that are open on the side of a wall surface, a covering layer with a matrix material that is relatively soft and has a large elongation at break is also advantageous if no passageways are provided or if passageways are provided on the first side of the midplane only. 
     In  FIG. 2 , a second example of a wall according to the invention is shown in the form of a different reinforcement of an otherwise identical cavity wall  51  with an inner wall  52 . 
     In this example, the reinforcement members  62  of the first group are each arranged in a slot  60  in which also a reinforcement member  63  of the second group is arranged. The reinforcement members  62  of the first group are arranged closer to an open side of the respective slot  60  than the reinforcement members  63  of the second group arranged in the respective slots  60 . This allows arranging a reinforcement member  62  of the first group and a reinforcement member  63  of the second group in each slot  60 , so that no separate slots have to be cut for each reinforcement member. Accordingly, the reinforcement can be applied with less cutting and less adhesive substance has to be inserted into the slots. 
     The slots  60  each have a first portion  64  on the first side of the midplane  59  having a first width and a second portion  65  on the second side of the midplane  59  having a second width, the first width being larger than the second width and the reinforcement members  62  of the first group arranged in the slots  60  each have a width larger than the second width. This reliably prevents the reinforcement members  62  of the first group from being inserted into the slots  60  too deeply. 
     Also in this example a composite covering layer  70  has been provided which mutually fixes wall portions on opposite sides of the deep slots  60 , so that it counteracts cracking along the slots  60 . 
     In  FIG. 3 , an example of a single wall  102  according to the invention is shown. This may for instance be a load bearing internal wall to the second wall surface  108  of which implements like a kitchen and or bathroom equipment and tiles (not shown) are applied. As the walls according to the previously described examples, also this wall has reinforcement members  112  on a first side of a midplane  109 , which are arranged in slots  110  that are open on the side of the first wall surface  107 . The reinforcement members  113  of the second group on the second side of the midplane  109  are arranged in passageways in the form of bores  111 . The bores  111  have been drilled approximately parallel to the second wall surface  108 . This requires the top or bottom (or lateral side if the bores are oriented horizontally) of the wall  102  to be accessible for drilling. Accordingly, reinforcement in accordance with this example may for instance be provided when building a new building, the holes  111  and reinforcement members  113  of the second group being provided preferably prior to positioning a floor or roof panel on top of the wall  102 . However, reinforcement according to this example may also be installed by drilling through a floor or roof panel resting on top of the wall  102  or if for instance local portions of roofing above the wall  102  can be removed temporarily to provide access to the top of the wall. An advantage of providing the passageways  111  for holding the reinforcement members  113  on the second side of the midplane  109  in the form of bores  111  is that no joints over the full height or almost the full height of the wall  102  are made, which is advantageous for maintaining the structural integrity of the wall  102 . While the passageways  111  for holding the reinforcement members  113  on the second side of the midplane  109  in the form of bores  111 , the passageways  110  for holding the reinforcement members  112  on the first side of the midplane  109  are provided in the form of slots  110 , which are easier to make than bores and can therefore be provided at lower costs. 
     The reinforcement members are preferably of fibre reinforced plastic, with fibres predominantly oriented in the longitudinal direction. Such reinforcement members are flexible slats, battens or rod having some stiffness which facilitates handling and installation in the passageways, in particular if the passageways are provided in the form of bores into which the reinforcement members have to be inserted in axial direction. Also, such fibre reinforced plastic members can be combined with a relatively pasty adhesive substance, because impregnation of the fibres by the adhesive substance is not required. Filling the remaining space in the passageways with a pasty substance facilitates filling the remaining space in the passageways. It is however also possible to provide the reinforcement members in the form of fibre material that is introduced into the passageways, where it is combined with matrix material to form a composite reinforcement member or to provide the reinforcement members in the form of prepregs of which the matrix material is cured after installation in the passageways. These options do for instance allow the fibre material to be inserted from a roll. 
     In the present examples, at least some of the reinforcement members  12 ,  13 ,  62 ,  63 ,  112  are battens, having a batten thickness in a batten thickness direction and a batten width in a batten width direction perpendicular to the batten thickness direction. The batten thickness is smaller than the batten width and the battens are arranged in the slots with the batten width direction oriented in a slot depth direction perpendicular to the first wall surface  7 ,  57 ,  107 , so that only relatively narrow slots have to be cut. This is particularly advantageous for the slots  11 ,  61  extending from the first wall surface  7 ,  57  to the second side of the midplane  9 ,  59 . Also, the surface area of the reinforcement members facing opposite slot wall surfaces is relatively large, so that a strong adherence of the reinforcement members  12 ,  13 ,  62 ,  63 ,  112  relative to the masonry material of the wall  2 ,  52 ,  102  is achieved. 
     For obtaining a particularly effective reinforcement of a wall against oscillating bending loads, it is preferred that the reinforcement members of the first group are each arranged fully on the first side of the midplane and the reinforcement members of the second group of reinforcement members group are each arranged fully on the second side of the midplane. 
     The invention allows reinforcing a masonry wall of an existing building or of a building under construction in a particularly simple and low cost manner and particularly suitable to be applied to buildings risking to be subjected to earthquakes as a result of human intervention, such as extraction of oil and gas with or without fracking. In such areas, buildings are typically not constructed to withstand earthquakes because historically, such earthquakes have not occurred in these areas, but an urgent need has arisen to reinforce a large number of buildings in a relatively short span of time, to reduce the risk of casualties and irreparable damage, in particular to historic buildings. 
     Reinforcing a wall in accordance with the invention only involves making a plurality of passageways in the wall by removing wall material, the passageways including slots, which are easy to cut and the slots are open horizontally to the first side of the wall only. Thus, the wall needs to be accessible from one side only and after completing the reinforcement, restoring the external appearance of the wall only has to be carried out on the wall surface on one side of the wall. 
     Because the reinforcement members include a first group of reinforcement members each having a centre line on the first side of the midplane and a second group of reinforcement members each having a centre line on the second side of the midplane, a particularly effective reinforcement against oscillating bending loads is achieved. Nevertheless, because the second group of reinforcement members is arranged in passageways located spaced from the second wall surface, the second wall surface does not have to be accessible and is left unaffected by installing the reinforcement, so that finishing of the second wall surface after installing the reinforcement is not necessary. 
     Embedding the reinforcement members in the passageways is achieved in a simple manner by injecting an adhesive substance into the passageways, the adhesive substance bonding to each of the reinforcement members and to an inner surface of the passageway in which the reinforcement member is provided. 
     Several features have been described as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention also includes embodiments having combinations of all or some of these features other than the specific combinations of features embodied in the examples.