Abstract:
Cost-effective reinforcement system for frames walls helps support against failure from violent lateral forces. Strips of resin-impregnated textile in crossed pairs are attached to frame members. Attachment of ends of strips is ductile due to use of multiple fiber anchors.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to building methods, and more particularly to a method of reinforcing structures against lateral forces that is well suited to retrofit of existing wood-framed buildings. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many modern buildings, including most residences, are supported by a framework consisting of an array of vertical support members connected at top and bottom by horizontal connecting members. The most familiar example of this type of construction in the United States is the wooden frame house with 2×4 wooden studs connected by a wooden bottom plate at the bottom and a wooden top plate at the top. 
         [0003]    The bottom plate connects the frame to the foundation and the top plate connects to the roof. The studs are typically attached to the top and bottom plates by stiff attachment means such as nails or screws. The wooden framework provides the compressive strength sufficient to support the weight of the walls and roof. However, a conventional wooden framework does not have much resistance to the lateral forces that may result from earthquake or high wind. 
         [0004]    Typically, a degree of shear bracing is added in the form of some diagonal “let-in” braces added between vertical studs. The braces are to prevent twisting of the framed structure, such as could be caused by warping of the studs or plates as the wood reacts to varying temperature and humidity conditions. Horizontal blocking members are attached between studs for various reasons, such as to increase the stiffness of a wall where cabinets will be attached or to maintain lengthy studs parallel to each other. 
         [0005]    The sheathing of the walls, such as plywood or gypsum board attached over the framework, adds to the resistance to lateral forces. Modern experience in major earthquakes and more sophisticated modeling and testing techniques have shown that, in the past, the role of wall sheathing in providing shear strength may have been over-estimated. In many regions throughout the world, building codes have been made stricter and new buildings are more resistant to lateral forces. 
         [0006]    It is well known that a framed wall does not typically have good resistance to forces normal to the plane defined by the wall. Frequently, especially in older structures, a framed wall is supported against normal forces mainly by the attachment of other walls. Structures that have experienced strong lateral forces, such as from earthquake or wind, are often flattened except for corners where multiple walls joined. Persons warned of high wind, such as from a hurricane, may take advantage of this effect by sheltering in an interior corner of a building. However, other disasters such as a tornado or earthquake may not allow time for a person to find the strongest location within a structure. 
         [0007]    Unfortunately, a great many framed structures that were built in compliance with less stringent codes are still in use and are not expected to be replaced for many years. Such structures include single family houses, multiple family residences, office buildings, and public structures. Occupants of such structures are endangered during a disaster such as earthquake or tornado by walls being knocked over and the roof subsequently falling down into the structure. 
         [0008]    There is a worldwide need for methods to retrofit such structures to withstand better the forces from earthquakes and high winds. In some cases, even a degree of resistance to explosive or other sudden forces is desired. 
         [0009]    At one time, it was believed that the most effective way to reinforce a structure that was not strong enough was to increase the stiffness of the structure such as by thickening certain members, adding stronger attachment means at strategic points of the structure, or adding more diagonal bracing. 
         [0010]    It has been found that a more effective strategy for reinforcing a structure is to increase its ductility. Ductile reinforcement allows a structure to deform and recover in response to unusual forces. 
         [0011]    If ductile reinforcement is stressed beyond its capacity, it typically fails in a gradual manner, allowing minutes or even hours for evacuation of the reinforced structure. A stiff structure frequently fails suddenly and catastrophically, crushing or trapping occupants. 
         [0012]    One type of connector for reinforcing a structure in a ductile manner is a fiber anchor, as disclosed in U.S. Pat. No. 7,207,149 of Fyfe, et al., issued Apr. 24, 2007. It has been used to connect many structural elements, such as to reinforce the connection among masonry blocks that make up a wall. 
         [0013]    When designing a ductile reinforcement system for a structure, it would be expected that ductile connectors such as taught in the Fyfe, et al. patent should be utilized instead of more traditional rigid connecting means such as nails, screws, or metal brackets. Other ductile materials should also be considered to replace traditional bracing or thickening of support elements. 
         [0014]    A method for retrofitting a structure that is in use would preferably be one that can be implemented with minimal disruption of the occupants. It is preferable that it not be necessary to partially dismantle or cut into the structure, and that the floor or adjacent grounds not need to be dug up. For example, cables have been used to tie structures laterally to the ground or other physical features. However, a cable support system typically requires the structure to be attached to vacant ground or another feature and may require excavation to install. 
         [0015]    Further, a retrofit method is preferably quickly installed with a minimum of noise, dust, and other disturbance of the occupants or neighbors. 
         [0016]    There is a need for wall reinforcing or a retrofit method that is relatively inexpensive and thrifty with materials. There is further a need for a method to strengthen even historical structures without spoiling the original aesthetic design of the structure. 
         [0017]    There is a need for a method of reinforcing an existing or new structure to resist lateral forces in order to avoid injury or death of the occupants and persons adjacent the structure, as well as to minimize property damage and to allow normal routines to carry on after a disaster. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention is a system for reinforcing structures against earthquake, wind, and other strong lateral forces. The system increases the ductility of the structure and strengthens the structure against sudden forces in several directions. 
         [0019]    The reinforcement system is attached to existing members of a framed structure or may be incorporated into a structure being newly built. The reinforcement system of the present invention generally includes a plurality of pairs of strips with high tensile strength attached to junction points between vertical and horizontal framing members, with anchor plates reinforcing the attachment of strips to the junctions of framing members. 
         [0020]    The strips with high tensile strength are lengths of resin-impregnated textile made of fibers or filaments of materials such as fiberglass, graphite carbon, nylon, polyaramid, or materials of similar tensile strength and ductility. The fibers may be all one material or a mixture of materials of slightly different strength or ductility. 
         [0021]    The ends of the strips are connected to the anchor plates with a plurality of fiber anchors that spread forces and prevent tearing out of the strips. The fiber anchors are lengths of roving that pass through boreholes in the anchor plates and the framing members and are attached with adhesive. The adhered ends of the roving are splayed out to cover a larger area of the plate in order to spread applied forces and prevent tearing out of the anchors. 
         [0022]    The strips are preferably used in pairs, with each pair roughly resembling the letter “X,” having each of the four ends of the X attached to a anchor plate that is in turn attached to a junction of a stud with a top or bottom plate. 
         [0023]    The system is quickly applied to an existing wall and requires minimal disruption of the room itself. The materials used are relatively light in weight and do not require special machining or design. The components of the system are applied in an efficient manner that maximizes the reinforcement value of a minimal quantity of materials. The system requires little special equipment and training, thus is suited for use in most countries or regions. 
         [0024]    The components of the reinforcement system are thin and do not unduly affect the appearance or design of the structure being reinforced. Because the reinforcing system can be completely covered by appropriate wall sheathing or finish, even historical structures retain their integrity. 
         [0025]    The system of the present invention greatly increases the resistance of a building to earthquake forces. Use of the reinforcement system also includes the following benefits: increases the ductility of the structure, uses a minimal amount of relatively low-cost and lightweight materials, is appropriate for use in most regions of the world, can be quickly retrofitted in existing buildings with minimum disturbance of occupants and neighbors, and does not spoil the appearance or design of a existing structure. 
         [0026]    The features and advantages of the invention will be readily understood when the detailed description thereof is read in conjunction with the drawings wherein like reference numerals refer to like parts throughout. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is an environmental front elevation view of the reinforcement system of the present invention, attached to a conventional framed wall. 
           [0028]      FIG. 2  is an enlargement of the upper right corner portion of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 1  is an environmental front elevation view of reinforcement system  10  of the present invention, attached to a conventional framed wall  100 . Framed wall  100  consists generally of frame members  101  (shown in phantom) and wall sheathing  110  for covering frame members  101 . 
         [0030]    Frame members  101  typically include vertical support members  102 , such as first vertical support member  103  and second vertical support member  104 . First and second vertical support members  103 , 104  for a single family house are typically “studs” of soft wood that are nominally 2 inches by 4 inches cross-section and of any needed length, frequently 8 feet. 
         [0031]    Support members  103 , 104  are parallel and spaced apart from one another. The maximum spacing is usually specified by relevant building code for the region and the type of structure.  FIG. 1  indicates an additional support member  102  between first support member  103  and second support member  104 . 
         [0032]    Vertical support members  102  must have sufficient compressive strength, in array, to support the weight of the structure. However, vertical support members  102  do not necessarily have sufficient rigidity to support themselves perfectly upright and parallel against gravity or twisting forces that arise from fluctuating temperature and humidity conditions. To maintain vertical support members  102  in parallel relationship, horizontal connecting members  105 , including top connecting member  106  and bottom connecting member  107 , tie together the top ends and bottom ends of vertical support members  102 . 
         [0033]    Bottom connecting member  107  connects the bottom ends of vertical support members  102  and also connects them to foundation  120 . Top connecting member  106  connects the tops of vertical support members  102  and also connects them to the roof and ceiling (not shown). 
         [0034]    Vertical support members  102  and horizontal connecting members  105  are typically connected together where they abut with rigid attachment means, such as nails, screws, or metal brackets (not shown). Herein, a “junction  109 ” is meant to describe the portions of a vertical support member  102  and a horizontal connecting member  105  within a few inches of the area where the two members  102 , 105  abut. 
         [0035]    Frame members  101  for one wall typically are rigidly joined so as to form a structural element that has good compressive strength and good flatness, but does not typically have good resistance to forces normal to the plane defined by the wall. Frequently, especially in older structures, a framed wall is supported against normal forces mainly by the attachment of other, non-parallel walls. The framed wall may not have sufficient integrity to remain upright when stressed by a large lateral force and the main section will frequently tear apart from the rigidly attached corners. 
         [0036]    Reinforcement system  10  of the present invention increases the ductility of the framed wall and spreads forces throughout the framed wall. This allows the framed wall to retain integrity along its entire length when stressed laterally and to remain connected to adjacent walls, foundation  120 , and roof. 
         [0037]    Reinforcement system  10  includes a pair of elongate strips  11 , of a material with good ductility and good tensile strength. A preferred material for strips  11  is resin-impregnated textile  12 , also known as fiber-reinforced plastic (“FRP”). Resin-impregnated textile  12  is typically composed of a textile stock that is woven or knitted from filaments, fibers, or yarns of high-strength fiberglass, graphite, polyaramid. The textile stock is impregnated with a suitable hardening resin such as an epoxy or ester. Other suitable materials may, of course, be employed. 
         [0038]    Each FRP strip  12  includes a first end  13 , a second end  14 , and a middle portion  15  between ends  13 , 14 . Each FRP strip  12  further includes an inner face  17  that is attached to wall  100  and an exposed face  18 , opposite inner face  17 , and which faces away from wall  100 . 
         [0039]    FRP strips  12  are attached in pairs, forming an “X” upon a section of framed wall  100 . FRP strips  12  may be attached over existing wall sheathing  110  or directly on bare framing members  101  in a structure being built or remodeled. 
         [0040]    It has been found through experimentation that reinforcement system  10  is strongest if FRP strips  12  are attached such that the longitudinal axis of one strip  12  of a pair is at an angle of nominally 90° to the longitudinal axis of the other strip  12  of the pair. Thus, the horizontal width of the “X” should be about equal to the vertical distance from bottom connecting member  107  to top connecting member  106 . 
         [0041]    Because ends  13 , 14  of FRP strips  12  are attached over a junction  109 , that is, to both a vertical support member  102  and a horizontal connecting member  105 , the width of the “X” will actually be a multiple of the spacing of support members  102 . For this reason, FRP strips  12  cannot always be at a 90° angle to each other, but care should be taken to set up reinforcement system  10  to come as close as possible to the preferred angle of 90°. 
         [0042]    FRP strips  12  may be precut to a length determined to yield a “X” of appropriate dimensions, or FRP strips  12  may be cut as they are used from a length or roll of FRP material  12 . 
         [0043]    It is convenient to attach ends  13 , 14  to frame members  101  initially with some temporary means, such as staples. Then ends  13 , 14  are attached permanently by ductile attachment means  30 , such as a plurality of fiber anchors  32 . 
         [0044]    Each end  13 , 14  is attached to both a vertical support member  102  and a horizontal connecting member  105 . To accomplish this, end  13 , 14  is attached so as to generally cover junction  109  where a vertical support member  102  and a horizontal connecting member  105  abut. 
         [0045]    For example, in  FIG. 1 , first end  13  of first strip  12   a  is attached to both first vertical support  103  and top connecting member  106 . First end  13  partially covers junction  109  surrounding the area where first vertical support  103  and top connecting member  106  contact each other. 
         [0046]    To create each fiber anchor  32 , a borehole  34  is created, which passes through an end  13  or  14  of FRP strip  12  and into a frame member  101 , underneath end  13  or  14 . Precut FRP strips  12  may include pre-punched holes at appropriate locations in ends  13 , 14 . In this case, an electric drill would be inserted into a punched hole and borehole  34  finished by drilling about an inch into the wood of frame member  101 . Alternatively, borehole  34  may be drilled directly through end  13  or  14  and into frame member  101 . 
         [0047]    A length of roving  35  is inserted into borehole  34 . Roving  35  is typically a hank of fibers or filaments loosely twisted together. The fibers are of a suitable material such as high-strength fiberglass, graphite, polyaramid, or nylon. Roving  35  may desirably include a mixture of fibers of different materials. 
         [0048]    Roving  35  may be pre-cut into lengths or each piece of roving  35  may be cut as needed. Each length of roving  35  is inserted into borehole  34  such that one end of roving  35  is at or very close to the bottom of borehole  34  and the free end  37  of roving  35  protrudes from borehole  34 , such as by 0.5 to 2 inches. 
         [0049]    If the diameter of roving  35  is substantially less than the diameter of borehole  34 , it may be desirable to fold roving  35  in half and insert the folded end into borehole  34 . This is conveniently done by pressing the folded end of roving  35  into borehole  34  with a tool such as a screwdriver. In this case, obviously, roving  35  must be cut into lengths that are twice the depth of borehole  34  plus 0.5 to 2 inches. 
         [0050]    Borehole  34  with the inserted roving  35  is then backfilled with a suitable backfill material  36  such as a hardening adhesive resin, which may be epoxy, silicone, acrylic, or other suitable material that has high cohesive strength and good adhesion to wood and roving  35 . Backfill material  36 , after hardening, anchors roving  35  into borehole  34   
         [0051]    Roving  35  is inserted into borehole  34  such that free end  37  protrudes by a slight amount, such as 0.5 to 2 inches. After borehole  34  is backfilled, free end  37  is attached to a surface of framed wall  100 , such as existing wall sheathing  110 . Free end  37  is attached in a two-step process. First, free end  37  is splayed apart so that the individual fibers or filaments that compose roving  35  are spread over an area at least two or three times wider than the initial diameter of roving  35 . 
         [0052]    In the second step of attaching free end  37 , the splayed out free end  37  is attached to outer face  18  of FRP strip  12  with an adhesive, such as a hardening adhesive resin. The preferable qualities of the adhesive for attaching free end  37  are similar to the preferable qualities of backfill material  36 . Therefore, the same resin is typically used for both purposes. 
         [0053]    A typical method for backfilling borehole  34  and attaching free end  37  is to first provide a syringe (not shown) filled with a suitable backfill material  36  and having a blunt needle tip with a length about the same as the depth of borehole  34 . Next, free end  37  is splayed apart by working it in the hands. The tip of the syringe is used to press roving  35  into borehole  34 , then backfill material  36  is expressed as the syringe is withdrawn, to fill borehole  34  with backfill material  36 . Additional backfill material  36  is deposited over free end  37 . Free end  37  and the adhesive covering it may then be flattened and spread over outer face  18  near borehole  34  with a suitable tool, such as a plastic putty knife (not shown). 
         [0054]    The purpose of splaying apart and attaching free end  37  to outer face  18  is to spread the lateral forces that may be applied by a earthquake or other event, so that fiber anchor  32  does not pull or tear apart from borehole  34  or FRP strips  12 . 
         [0055]    Each fiber anchor  32  so created attaches end  13 , 14  to one of the underlying frame members,  102 , 105 . Each end  13 , 14  is preferably attached with a plurality of fiber anchors  32 . Fiber anchors  32  are disposed such that some anchors  32  attach a given end  13 ,  14  to vertical support member  102  and some anchors  32  attach the same end  13 ,  14  to the horizontal connecting member  105  near junction  109  where the two frame members  102 , 105  abut. Thus, the plurality of fiber anchors  32  ductilely attach each end  13  or  14  to both a vertical support member  102  and a horizontal connecting member  105 , and indirectly reinforce the attachment of the two members  102 , 105  to each other. 
         [0056]    Middle portion  15  of each FRP strip  12  is attached to wall sheathing  110  by adhesive means, such as the resin that impregnates FRP strip  12 . This resin may be a partially cured (“gelled” or “B-staged”) resin that is supplied as a component of FRP strip  12 , or liquid resin that is applied at the worksite, such as by dipping a strip  11  into a container of resin, or by rolling or brushing resin over strip  11  that has been attached to wall  100  by temporary means or with ductile attachment. 
         [0057]    The most preferred manner of practicing the reinforcement system  10  of the present invention, as illustrated in the drawings, is to further attach an anchor plate  20  to each junction of vertical support member  102  and horizontal connecting member  105  to which first end  13  or second end  14  will be attached. 
         [0058]    Referring especially now to  FIG. 1 , anchor plates  20  are generally square plates, such as of wood or plastic. For use in a single-family house, typical dimensions are 12 by 12 inches with a thickness of about 0.25 inch. 
         [0059]    The purpose of anchor plates  20  is to spread out forces. Because each anchor plate  20  is connected to both a vertical support member  102  and a horizontal connecting member  105 , each fiber anchor  32  is effectively connected to both members  102 , 105  as well. Anchor plate  20  helps stabilize fiber anchors  32  such that each fiber anchor  32  helps reinforce against forces from any direction. Anchor plate  20  also helps ensure that fiber anchor  32  will not pull out under especially violent forces. 
         [0060]    To begin the method of the present invention, a first anchor plate  20   a  is attached to the junction of first vertical support  103  with top connecting member  106 . Preferably, a section of wall sheathing  110 , of the same dimensions as anchor plate  20 , is cut out from the existing wall  100  so that anchor plate  20  will end up flush with the outer face of wall sheathing  110 . 
         [0061]    Known attachment means such as nails, screws, bracket, or adhesives are used to attach first anchor plate  20   a  to both frame members  101 . Second anchor plate  20   b  is attached to top connecting member  106  and second vertical support  104  in a similar manner. Third anchor plate  20   c  is attached to both bottom connecting member  107  and first vertical support  103 . Lastly, fourth anchor plate  20   d  is attached to both bottom connecting member  107  and second vertical support  104 . 
         [0062]    Next, the other steps discussed above are followed: temporary attachment of strips  12 , creation of boreholes  34  that pierce strips  12 , anchor plates  20 , and end in a framing member  101 , insertion of roving  35  into borehole  34 , then splaying out free end  37  and adhering free end  37  to anchor plate  20 . 
         [0063]    After all reinforcements  10  have been installed, wall  100  may be finished decoratively as desired. Paint or other wall finish such as paper may be applied directly over reinforcement system  10 , or reinforcement system  10  may be covered with decorative paneling. 
         [0064]    The invention has been discussed herein as a reinforcement system for a wood framed wall having sheathing such as wood or gypsum board (drywall). The method of the invention may be practiced in a similar manner for structures of other materials and construction, including but not limited to lath and plaster, cement board, or metal I-beam construction. 
         [0065]    Although particular embodiments of the invention have been illustrated and described, various changes may be made in the form, composition, construction, and arrangement of the parts herein without sacrificing any of its advantages. Therefore, it is to be understood that all matter herein is to be interpreted as illustrative and not in any limiting sense, and it is intended to cover in the appended claims such modifications as come within the true spirit and scope of the invention.