Patent Publication Number: US-6662516-B2

Title: Reinforced wall structures and methods

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of patent application Ser. No. 09/781,933, filed Feb. 12, 2001. 
    
    
     FIELD 
     The present invention relates to methods for providing structural reinforcement to preexisting wall structures using an adhesive material. 
     BACKGROUND 
     There are countless older buildings located in earthquake-prone regions of the world whose walls are susceptible to seismically induced damage. During an earthquake, the ground upon which the building rests moves laterally and/or vertically. These ground motions are transmitted through the building foundation to the building walls. The walls may crack as a result of the ground motions or, if the motions are sufficiently severe, the walls may fail completely and collapse. Damage caused by seismically induced forces is exacerbated in buildings with walls made from weak or brittle materials, such as clay tile, which are susceptible to failure even in the event of a relatively minor earthquake. 
     Accordingly, it is desirable to reinforce such building walls with bracing to resist the forces created by seismic activity. A common method for retrofitting a preexisting wall structure  6  is illustrated in FIG.  1 . In this method, metal studs  12  are secured to the outside surface of each wall portion  8  of the double wall structure  6 . The studs  12  extend vertically in a parallel array and are securely mounted to the outside surface of each wall portion  8  with suitable masonry ties  14 , such as Helifix screws. An outer wall  16  may be mounted to the metal studs  12  to provide a conventional wall surface and hide the studs. 
     Although this method is adequate for its intended purpose, that is, for strengthening the wall structure to resist seismic forces, it is a costly and labor-intensive process. Moreover, stud walls added to the inside walls of a building can be intrusive and reduce usable space. In the case of a school, for example, not only would adding the stud walls reduce corridor and classroom space, it would generate the associated costs of removing or replacing items such as chalkboards, lockers, shelving, artwork and cabling. 
     Conventional wisdom presents obstacles for solving this problem. The cavity between the preexisting walls typically is not easily accessible and some times is enclosed even from the top. The cavity itself usually contains dust, dirt or other contaminants on the wall surfaces which are difficult to clean. 
     The present invention is directed toward new and nonobvious aspects of methods for retrofitting preexisting wall structures to better resist damage caused by seismic or other forces, as set forth in the claims below. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a cross sectional view of a preexisting double wall structure that is retrofitted with metal stud walls according to a known method. 
     FIGS. 2A-2C are cross sectional views illustrating a method for retrofitting a preexisting double wall structure according to the invention. FIG. 2A shows the positioning of a nozzle before adhesive material is introduced into the cavity of the wall structure. FIG. 2B shows the wall structure after an initial layer of an adhesive material has been formed in the cavity. FIG. 2C shows the wall structure after the cavity has been filled with plural layers of the adhesive material. 
     FIG. 3 is a cross sectional view of a preexisting single wall structure without seismic reinforcements. 
     FIG. 4 is a cross sectional view of the wall structure of FIG. 4 after it has been retrofitted according to the invention. 
     FIG. 5 is a cross sectional view of the wall structure of FIG. 5 taken along line  6 — 6 . 
     FIG. 6 is a perspective view of a preexisting single wall structure retrofitted with seismic reinforcements according to another embodiment, with portions of the outer form, the structural members, the sheathing layer, and the adhesive material broken away for clarity. 
     FIG. 7 is a vertical cross sectional view of the wall structure of FIG.  6 . 
     FIG. 8 is a horizontal cross sectional view of the wall structure of FIG. 7 taken along line  8 — 8  of FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     The present invention seeks to overcome the problems of the prior art by providing an improved method for strengthening preexisting wall structures. The present invention seeks to provide a method and structure for reinforcing preexisting walls which is not labor intensive, has a relatively low construction cost and preferably does not sacrifice usable building space. 
     According to one embodiment, a method for retrofitting a double wall structure having at least one preexisting wall portion comprises introducing successive layers of a foamable, adhesive material as necessary to fill the cavity between the two wall portions. The amount of adhesive material in each layer is such that the expansion force of the adhesive material does not exceed the lateral strength of the wall portions. The layer of adhesive material is allowed to substantially cure, after which at least one additional layer of adhesive material typically is formed on top of the previously formed layer. The layering process is then repeated until the cavity is filled with plural layers of adhesive material bonding together the wall portions such that the strength of the preexisting wall is increased to more effectively resist seismic activity. The amount of adhesive material used to form each additional layer is substantially the same amount that is used for the initial, bottommost layer. 
     If needed, a camera may be used to provide a visual image of the interior of the cavity as the layers are being formed. A light source may also be provided to illuminate the interior of the cavity. 
     According to another embodiment, a method for retrofitting a preexisting single wall comprises mounting plural, horizontally spaced, vertically extending metal studs to the floor and ceiling adjacent to one of the surfaces of the preexisting wall. An outer form is mounted to the metal studs so as to form a cavity between the preexisting wall and the outer form. Layers of a foamable, adhesive material are introduced successively to fill the cavity. The layer of adhesive material is allowed to substantially cure, after which at least one additional layer of adhesive material is formed on top of the previously formed layer. The layering process is then repeated until the cavity is filled with plural layers of adhesive material, bonding together the preexisting wall and the outer form to strengthen the preexisting wall. 
     According to yet another embodiment, a method for strengthening a wall comprises spacing an inner form, or sheathing layer, from one surface of the wall so as to define a cavity therebetween. A plurality of structural members are positioned outside of the cavity so as to support the inner form. In one specific implementation, the structural members comprise horizontally spaced, vertically extending wooden or metal studs, which can be mounted to the floor and the ceiling adjacent the inner form. 
     A foamable, adhesive material is introduced into the cavity to bond together the inner form and the wall. Desirably, although not necessarily, the adhesive material is introduced into the cavity as successively formed layers. Each layer desirably is allowed to substantially cure before the next uppermost layer is added to the previously formed layer. If desired, a camera may be used to provide a visual image of the interior of the cavity as adhesive material is introduced into the cavity. A light source may also be provided to illuminate the interior of the cavity. 
     Finally, an optional outer form may be positioned adjacent to the structural members opposite the sheathing layer to cover the structural members. The outer form desirably comprises a building material conventionally used to form the interior walls of a building, such as wallboard. In an alternative approach, an outer form is not used and the structural members are left exposed. 
     According to another embodiment, a reinforced wall structure comprises a wall, which may comprise a preexisting wall or a newly constructed wall, and a sheathing layer spaced from the wall so as to define a cavity therebetween. The sheathing layer has first and second major surfaces, with one of the first and second major surfaces serving as an interior surface of the cavity. A plurality of structural members are positioned adjacent to the other major surface of the sheathing layer outside of the cavity. An adhesive material is disposed in the cavity to bond together the wall and the sheathing layer. An outer wall, such as conventional wallboard, may be used to cover the exposed structural members. 
     More specifically, and with reference to FIGS. 2A-2C, there is shown a method for retrofitting a preexisting double wall structure  20  according to one embodiment of the invention. The double wall structure  20  includes first and second wall portions  22  horizontally spaced to form a cavity  24  therebetween. In the illustrated embodiment, the wall portions  22  are brick walls, although it is to be understood that the method can be used to retrofit walls of any type of construction to which the cavity filling material will adhere. For example, the method may be applied to cement or concrete walls made of either masonry construction (i.e., blocks joined by mortar) or poured construction; clay tile walls; stone or rock walls; and walls made from other suitable materials, such as earth, adobe, compositions which are cement-like but may not be within a strict definition of the term cement, and the like. Also, the wall portions  22  may contain an internal structure, such as a wooden frame or steel reinforcing bars. 
     According to the present embodiment, plural layers of a foamable, adhesive material  26  are formed in the cavity  24  to bond together the wall portions  22 , thereby providing a more integral construction. Desirably, the adhesive material  26  has the following characteristics: high adhesion to provide a strong bond between the wall portions  22 ; high compressive, tensile, and shear strength; and low expansion. The adhesive material  26  also should be sufficiently elastic to adsorb energy transmitted to the wall structure  20  caused by seismic activity, have a minimal set up or cure time, and produce minimal off gases harmful to those handling the adhesive material. The adhesive material  26  also may be selected to provide some measure of waterproofing for the wall structure to which the adhesive material is applied. Some examples of adhesive material that can be used include, without limitation, open or closed cell polyurethane foam, or other suitable materials. Closed cell foams are most desirable in that they are substantially impervious to water. A suitable polyurethane foam is the HSF-118 closed cell polyurethane foam manufactured by Hydroseal Polymers, Inc. of Riverside, Calif. The adhesive material  26  desirably has a density from about 1 lb./ft 3  to 10 lbs./ft 3 , and even more desirably from about 2 lbs./ft 3  to 10 lbs./ft 3 . 
     With reference to FIG. 2A, the adhesive material  26  is formed by mixing a resin base material stored in a container  42  with a conventional activating agent stored in a container  50 . In one example, the base material and blowing agent are mixed in a one-to-one ratio. To form a polyurethane foam, such as described above, the base material would be a polyurethane resin. The base material may contain surfactants, fire retardants, a blowing agent and other additives. The density of the adhesive material  26  introduced into the cavity  24  can be varied by starting with a base material of a different formulation, typically by varying the amount of blowing agent in the formulation. 
     Pumps (not shown) in containers  42  and  50  pump the resin base material and activating agent, respectively, through hoses  44  and  48  into a proportioning unit  46 . The proportioning unit  46  pumps the base material and the activating agent at about 1000 psi through hoses  40  and  49 , respectively, to a spray gun  28  wherein the base material is mixed with the activating agent. The proportioning unit  46  and the hoses  44 ,  48 ,  40  and  49  preferably have heating coils to preheat the base material and activating agent to about 120° F. When the materials mix in the spray gun  28 , the activating agent triggers an exothermic chemical reaction, the product of which is the adhesive foam material  26  typically having an initial temperature of about 140° F. During this early exothermic stage, the foam is in a viscous seam-like state and can be poured into the cavity. Once in the cavity the foam flows and expands to fill the cavity. 
     More specifically, the foam enters the cavity through a nozzle  30  inserted through a longitudinally extending slot  32  formed in one of the wall portions  22  to introduce adhesive material into the cavity  24  (as shown in FIGS.  2 A and  2 B). If needed, a camera  38 , such as a fiber optic camera, may be inserted through an aperture defined in one of the wall portions  22  to provide a visual image of the cavity  24  on a monitor or television screen (not shown) outside the wall structure  20 . A light source  41  may be inserted through another aperture defined in one of the wall portions  22  to illuminate the cavity, or alternatively, the camera  38  may be provided with its own light source (not shown). Of course, if the top of the double wall structure is open, the adhesive material  26  can be introduced through the open top of the wall structure and the camera may not be necessary. 
     The formation of layers of adhesive material  26  within the cavity  24  may be accomplished in the following manner. As shown in FIG. 2A, the end  36  of the nozzle  30  is desirably positioned at a point proximate the bottom of the cavity  24  to ensure an even layer of adhesive material is formed on the bottom of the cavity  24 . The adhesive material  26  is sprayed on the bottom of the cavity  24  as the nozzle  30  is moved longitudinally of the cavity (i.e., perpendicular to the plane of the page) so as to form a bottommost layer  34  of adhesive material  26  having a height H after the adhesive material has expanded (as shown in FIG.  2 B). The camera  38  and light source  41  may be removed from their respective apertures and inserted into different apertures along the length of the cavity  24  so as to follow the gun  28 /nozzle  30  as the layer of adhesive material is being formed. In this manner the “pour area” can be kept in view by the operator. 
     Since the adhesive material  26  expands to some extent when expelled from the nozzles as it cures, the amount of adhesive material  26  used to form layer  34  should be such that the expansion force of the adhesive material does not exceed the lateral strength of the wall portions  22  and thereby damage the wall portions. It will be appreciated that the adhesive material is free to expand upwardly with relatively little resistance, lessening the outward lateral load exerted on the wall portions by the adhesive material. However, if an excessive amount of adhesive material is introduced into a short section of the cavity over a relatively short duration, the weight of the adhesive material can reduce its ability to expand upwardly and cause excessive expansion forces to be applied laterally outwardly to walls. The rate at which material can be introduced into a given section of the cavity of course will depend on a number of factors including the width of the cavity, rate of expansion of the material as it contacts the air, density of the material, wall strength, and cure time. 
     After the adhesive material is sprayed into the cavity to form the bottommost layer  34 , the end  36  of the nozzle  30  is raised a sufficient distance so as to avoid contact with the expanding adhesive material, which is allowed to cure before another layer of adhesive material is formed on the bottommost layer  34 . Preferably, the adhesive material is cured until it expands at only a minimal rate (e.g., the adhesive material has expanded to about 99 percent of its expanded state), or more even preferably, to a point where the adhesive material no longer expands. The cure time is a function of the foam density. For example, the cure time for a foam density of 2 lbs./ft 3  is about 4 minutes while the cure time for a foam density of 10 lbs./ft 3  may be longer. Once the adhesive material has substantially cured, the end of the nozzle  30  is positioned at a point just above the previously formed, bottommost layer  34  and adhesive material is sprayed on top of the bottommost layer  34  as the nozzle  30  is moved longitudinally of the cavity so as to form an additional layer of adhesive material. The layering process is then repeated until the cavity  24  is filled with layers having substantially the same height H (as illustrated in FIG.  2 C). 
     As explained above with reference to forming the bottommost layer  34 , the amount of adhesive material used to form each additional layer within the cavity  24  also should be an amount that does not generate excessive lateral expansion forces that could damage the wall portions  22 . Using substantially the same amount of adhesive material for each additional layer as was used to form the bottommost layer  34  should ensure that the expansion forces do not exceed the lateral strength of the wall portions. 
     When reinforcing clay tile walls, it has been found that for certain applications the height H of each layer should be about 24 inches for a polyurethane foam having a density of about 2 lbs./ft 3 . For a polyurethane foam having a density of about 10 lbs./ft 3  one would expect the preferred layer height H to be less, such as 12 to 16 inches, due to the added weight of the foam. 
     In an alternative embodiment to the method described above, the cavity  24  of the double wall structure  20  may be completely filled with an adhesive material  26  without forming successive layers, as described above, if the wall portions  22  are strong enough to withstand the expansion forces of the adhesive material  26  injected into the cavity  24  in such a manner. This may be the case, for example, if the wall portions are not particularly high. 
     The layers of adhesive material  26  bond together the wall portions  22  to reinforce and strengthen the wall portions  22 . Surprisingly, the adhesive material  26  will adhere to the inside surfaces of the wall portions  22 , regardless of any imperfections, dirt, dust, or other contaminates on those surfaces. Accordingly, cleaning and/or preparation of the inside surfaces of the wall portions  22  is not required prior to forming the layers of adhesive material in the cavity  24 . 
     The invention enjoys several advantages over known methods for retrofitting preexisting wall structures. First, since expensive hardware, such as metal studs and masonry ties, is not required, the material costs for upgrading a building are substantially reduced. Additionally, labor costs are reduced because the method can be accomplished in significantly less time than that required for a conventional method. Moreover, the interior space of a building that is retrofitted according to the present method is not affected and items supported on or located near the inner walls of the building do not have to be disturbed, as is the case when using conventional bracing or metal stud walls. Finally, the invention has been found to be particularly advantageous in retrofitting certain masonry walls, such as clay tile walls, which are especially susceptible to failure even in the event of a minor earthquake. In such cases, the adhesive material bonds together the clay tile walls to more effectively resist cracking or complete collapse of the clay tile walls should an earthquake occur. 
     According to another embodiment of the invention, a method for retrofitting a preexisting single wall structure  60  (shown in FIG. 3 without any seismic reinforcements) is provided. In this method, plural, horizontally spaced, vertically extending metal studs  62  are mounted to the floor and ceiling, in close, preferably abutting, relationship to the wall  60  (as shown in FIG.  5 ). An outer form or wall  64  is mounted to the metal studs so as to form a cavity  66  between the preexisting wall  60  and the outer form  64 . In this sense, the preexisting wall  60  and the outer form  64  together form a double wall structure having a single preexisting wall portion. The outer form  64  may comprise, for example, plywood, composition board, or metal siding. 
     As shown in FIG. 4, plural layers of a foamable, adhesive material  26  are formed in the cavity  66  to bond together the preexisting wall  60  and the outer form  64  so that the preexisting wall  60  is strong enough to better resist seismic forces. The adhesive material also bonds the metal studs  62  to the preexisting wall  60 . Consequently, Helifix screws or equivalent masonry ties are not required to secure the metal studs  62  to the wall  60 . 
     In a working embodiment, the layers of adhesive material  26  are formed in the cavity  66  in the manner described above with respect to the double wall structure  40  shown in FIGS. 2A-2C. However, it should be understood that the layers of adhesive material may be formed in any suitable manner, or alternatively, the cavity  66  may be completely filled with an adhesive material without forming successive layers if the wall  60  and outer form  64  are strong enough to withstand the expansion forces of the adhesive material injected into the cavity in such a manner. 
     FIGS. 6-8, illustrate another approach for strengthening a single wall  100 . This approach (as well as the other strengthening methods described herein) has particular applicability for strengthening a preexisting wall structure, although it may also be used to strengthen wall structures in new construction. As shown, an inner form, or sheathing layer  102 , having first and second major surfaces  104 ,  106 , respectively, is spaced from a surface  101  of the wall  100  so as to define a cavity therebetween for receiving adhesive material  26 . Although not required, spacers (not shown), having a thickness equal to the desired width of the cavity, may be positioned along the surface  101  of the wall  100  to facilitate positioning of the sheathing layer  102 . Desirably, the sheathing layer  102  is selected to have sufficient strength to withstand the expansion forces of adhesive material  26  introduced into the cavity. Without limitation, the sheathing layer  102  may comprise, for example, plywood, composition board, OSB, hardy board, metal siding, or other forms of structural boarding made of any of various materials. 
     Suitable structural members are positioned adjacent the second major surface  106  of the sheathing layer  102  outside of the cavity for supporting the sheathing layer  102 . In the illustrated embodiment, for example, the structural members comprise a plurality of horizontally spaced, vertically extending metal studs  108 , which can be mounted to the floor  110  and the ceiling  112  adjacent the sheathing layer  102 . The sheathing layer  102  may be mounted to the studs  108  with screws or other suitable fasteners. The metal studs  108  desirably have a C-shaped cross sectional, although studs having other cross sectional shapes also may be used. For example, studs having I-shaped cross sections (i.e., I-beams) can be used. In addition, other forms of structural members also may be used. For example, conventional wooden studs may be used in lieu of metal studs. Further, it is not a requirement that the structural members be oriented in a vertically upright position. For example, the structural members may extend horizontally or diagonally across the second major surface  106  of the sheathing layer  102 . 
     Like the embodiment of FIGS. 4 and 5, plural layers of the foamable, adhesive material  26  desirably are formed in the cavity to bond together the wall  100  and the sheathing layer  102  so that the wall  100  is strong enough to better resist seismic forces. An elongated slot (not shown) may be provided in the sheathing layer  102 , through which the nozzle  30  of a spray gun  28  (FIGS. 2A and 2B) may be inserted for introducing the adhesive material  26  into the cavity. Desirably, the layers of adhesive material  26  are formed in the cavity in the manner described above with respect to the double wall structure  40  shown in FIGS. 2A-2C. However, it should be understood that the layers of adhesive material may be formed in any suitable manner, or alternatively, the cavity may be completely filled with an adhesive material without forming successive layers if the wall  100  and the sheathing layer  102  are strong enough to withstand the expansion forces of the adhesive material injected into the cavity in such a manner. Still alternatively, in some applications, it may be sufficient to partially fill, rather than completely fill, the cavity with adhesive material. This may be the case, for example, if the wall  100  is not particularly brittle or weak but nonetheless needs to be upgraded to better resist seismic or other forces. 
     If desired, as described above in connection with FIGS. 2A and 2B, a camera (not shown) may be used to provide a visual image of the interior of the cavity as the adhesive material  26  is introduced into the cavity. A light source (not shown) may also be provided to illuminate the interior of the cavity. 
     An optional outer form, or wall  114  may be positioned adjacent the studs  108 , opposite the sheathing layer  102 , to cover the exposed studs  108  and provide a convention wall surface. The outer form  114  may be mounted to the studs  108  with screws or other suitable fasteners. The outer form  114  may comprise any suitable material. For example, in applications where the wall  100  is strengthened from the interior of the building (i.e., the adhesive material  26 , the sheathing layer  102 , and the studs  108  are added to the interior surface of the wall  100 ), then building material conventionally used to form the interior walls of a building, such as wallboard (also called drywall or sheet rock), may be used to cover the studs  108 . However, other conventional building materials, such as plywood, composition board, OSB, hardy board, or metal siding or any of other various materials also may be used. 
     The strengthening method of FIGS. 6-8 provides additional advantages when compared to the method of FIGS. 4 and 5. By positioning the studs  108  outside of the cavity in the method of FIGS. 6-8, rather than inside of the cavity as in the method of FIGS. 4 and 5, the width of the cavity can be reduced. Thus, less adhesive material  26  is required to fill the cavity in FIGS. 6-8. 
     The present invention has been shown in the described embodiments for illustrative purposes only. The present invention may be subject to many modifications and changes without departing from the spirit or essential characteristics thereof. We therefore claim as our invention all such modifications as come within the spirit and scope of the following claims.