A wall panel has elongate members connected together to form a rectangular frame having a top, a bottom and opposite sides, a sheathing extending over the rectangular frame; and connectors providing a connection between the sheathing and the rectangular frame. The connectors are varied so that the strength of the connection increases from the top and bottom towards the middles of the opposite sides of the frame.

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the construction of wood frame walls for buildings.  
           [0003]    2. Description of the Related Art  
           [0004]    It is known in the art to construct a building diaphragm consisting of a skin and a frame that are attached to each other by means of connectors (nails, screws, staples, etc.). A building diaphragm is subject to lateral forces as in roofs and floors, where wind and seismic forces are transferred to side walls and by the side walls to the ground. Walls that transfer horizontal loads in the plane of the walls are called shear walls. Shear walls resist horizontal loads imposed by shear and moment forces, i.e. the wall is subject to shear forces and rotated by an overturning moment. Shear forces and overturning moments are resisted at the wall-to-ground interface by tie-downs and anchors driven through bottom members of the frame walls into foundations.  
           [0005]    Shear walls and roof and floor diaphragms are subject to two design considerations, namely ultimate load and allowable deformation.  
           [0006]    In a shear wall, the frame is usually made from 2×4 or 2×6 lumber framing members at 16″ or 20″ spacings, and provided with a skin is made from 4′×8′ particle board or plywood sheathing. In floor or roof diaphragms, frame members are usually joists made conventionally of 2×8 to 2×12 lumber or of engineered I-joists. The prevailing failure mode in prior art shear walls is shearing at connectors (nails) in frame corners due to rotation of the skin panels that are very stiff in that phase compared to the relatively pliant frames. Hitherto, this has been counteracted by driving more nails into the frames or by reinforcing connection zones by attaching steel strips and driving nails through the strips. While the corner nails (connectors) are sheared, all other nails are less stressed and do not contribute to the overall resistance to their full capacity.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    It is accordingly an object of the present invention to strengthen wood frame wall constructions  
           [0008]    According to one aspect to the present invention, a sheathing is attached to a wood frame by connectors (nails, screws, staples, etc.) so as to transfer shear force uniformly to all panel areas. This is achieved by strategically placed and/or selected connectors.  
           [0009]    This may be achieved by:-  
           [0010]    A. Driving stiffer nails into a control zone of the sheathing close to the centre of rotation or by driving more nails in the same zone; or  
           [0011]    B. Installing diagonal members flush to the frame and skin and driving nails (connectors) into the frame and driving nails into diagonal members provided within the frame; or  
           [0012]    C. Providing the frame with corner connectors that counteract movement of sheathing relative to the studs.  
           [0013]    According to another aspect of the present invention, there is provided a wood frame wall construction which comprises rectangular frames of e.g. lumber provided with sheathing, e.g. in the form of panels, with corner connectors connecting the corners of the rectangular frames, the corner connectors being fastened directly to the sheathing.  
           [0014]    According to a further aspect of the present invention, the corner connectors at lower ends of the rectangular frames are secured to a foundation or other support by resilient tie-down devices which allow limited resilient displacement of the corner connectors and thus of the rectangular frames relative to the foundation or support. Resiliency in the corner connectors may be achieved by two principal methods, i.e. by a combination of resilient neoprene rubber-like materials and steel inserts or by spiral, conical, flat or washer-type steel springs, or by a combination of both of these methods.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention will be more readily understood from the following description thereof taken with reference to the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1 shows a diagrammatic view in elevation of a pair of wall panels in shear;  
         [0017]    [0017]FIGS. 2 and 3 show views in front elevation of a pair of wall panels embodying the present invention;  
         [0018]    [0018]FIGS. 4 through 6 show views in front elevation of three different frame constructions for use in the panels of FIGS. 2 and 3;  
         [0019]    [0019]FIGS. 7 and 8 show, respectively, a broken-away view in front elevation and a horizontal cross-section of a further wall panel construction;  
         [0020]    [0020]FIG. 9 shows a broken away view in front elevation of a corner of a wall panel frame provided with a metal corner connector;  
         [0021]    [0021]FIGS. 10 and 11 show, respectively, a front elevational view and a plan view of a further corner connector;  
         [0022]    [0022]FIGS. 12 and 13 show a broken-away front elevational view and a broken-away plan view, respectively, of a frame corner employing the connector of FIGS. 10 and 11;  
         [0023]    [0023]FIGS. 14 and 15 show views corresponding to those of FIGS. 13 and 14 but illustrating a still further frame corner;  
         [0024]    [0024]FIGS. 16 through 21 show broken-away views in vertical cross-section of corner connectors provided with resilient tie-downs;  
         [0025]    [0025]FIGS. 22 through 26 show plan views of the corner connectors of FIGS. 17 through 21, respectively;  
         [0026]    FIGS.  27  to  29  illustrate panel under deflection:  
         [0027]    [0027]FIG. 30 shows a pair of panels subject to a shear force;  
         [0028]    [0028]FIGS. 31 through 33 each show a pair of panels connected to one another;  
         [0029]    [0029]FIGS. 34 and 35 show views in horizontal cross-section through a pair of panel connectors and wall components connected thereby;  
         [0030]    [0030]FIG. 36 shows a view in front elevation of a wall structure according to a further embodiment of the present invention; and  
         [0031]    FIGS.  37  to  41  show broken-away views, taken in front elevation, of connections between adjacent panels in further embodiments of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    [0032]FIG. 1 shows a pair of wall panels  10  of the type comprising a rectangular wooden frame provided on one side with a sheathing of plywood or other suitable material. Assume that, due to the rigid body of sheathing, the deformed shape of adjacent panels  10  of a shear wall subject to a shear load is linear as shown in broken lines in FIG. 1 and indicated by reference numeral  12 .  
         [0033]    The nail stress and shear forces in nails  14  used as connectors between sheathing and lumber frames of the panels  11  are proportional to deformation, and are maximum at the top and minimum at the centre of rotation RC.  
         [0034]    If a stiff nail has to be deformed to the same extent as a weaker one, a proportionally larger force must be used. If A=deformation, F=force and K=nail stiffness, the deformation relationship is described as A=F/K.  
         [0035]    For full utilization of the nails, with proportionally lesser deflection as one approaches the centre of rotation RC, the nail stiffness should be increased, as in Fconstant=A (reduced)×K (increased).  
         [0036]    This can be achieved by using progressively stronger nails from the top and bottom of the panel to the middle, as shown in the left-hand half of FIG. 2, which shows the use of 8 d  nails at the top and bottom sections of the panel, 10 d  nails at intermediate sections thereof and 12 d  nails at middle sections. As shown in the right-hand half of FIG. 2, this arrangement is reversed.  
         [0037]    Alternatively, as shown in the left-hand half of FIG. 3, uniform nails can be used but with spacings varying from 12″ at the top and bottom sections, through 9″ spacings at the intermediate sections to 6″ spacings at the middle sections. As shown in the right-hand half of FIG. 3, this arrangement is reversed.  
         [0038]    Another alternative is for different stiffnesses of nails to be achieved by using nails made of different quality materials and/or alloys.  
         [0039]    FIGS.  4  to  6  illustrate wall panel frames  20 ,  21  and  22  of three wall units embodying the present invention, with the sheathings of these wall units omitted. The frames  20  through  22  can be installed between conventional wall studs (not shown) or can be used as frame members in lieu of standard vertical and horizontal frame members.  
         [0040]    The frames  20  through  22  each have a top member  24 , a bottom member  26  and opposite side members  28 .  
         [0041]    The frame  20  has inclined brace members  30 , the frame  21  has brace members  32  forming triangles and the frame  22  has horizontal braces  34  and inclined braces  36  between the top and bottom members  24  and  26  and the horizontal braces  34 .  
         [0042]    In each of the wall units in which the frames  20  through  22  are provided, the sheathing, indicated by reference numeral  38  in FIGS. 7 and 8, is in face-to-face contact with one side of each of the frame members, which are all flush with one another and which are indicated by reference numerals  40  in FIGS. 7 and 8. This facilitates full contact of all frame members with the sheathing  38 . The brace members and any other members of the frames between the side members are attached along their entire lengths to the sheathing  38  by connectors, which as shown comprise nails  42  but which may alternatively comprise screws, staples, etc.  
         [0043]    The frames  20  through  32  may be replaced by the frames disclosed in my co-pending patent application Ser. No. 08/955,805, filed Oct. 22, 1997, the disclosure of which is incorporated herein by reference. Also, the present frames may have their frame members flush with wall studs and other components of wall framing so that the latter likewise contact face-to-face with the sheathing  38 .  
         [0044]    Prior art diaphragm walls (shear-walls) are built with non-direct connections between the most stressed parts. Tie-downs in such walls are usually connected to studs, which are usually connected to the sheathing. The sheathing panels are normally connected separately to the weak frames. The entire systems lack simple straightforward load-paths.  
         [0045]    Embodiments of the present invention include metal corner connectors which directly connect anchor bolts to the sheathing, by-passing the weak frames, which allows for maximum transfer of vertical force in the studs while not resisting stud rotation that is detrimental to the connections, and allows for resisting horizontal forces at the wall-foundation interfaces while allowing for sheathing rotation.  
         [0046]    In addition to this, the new corner connectors described below may be designed and utilized as energy absorption components that will act as isolators and will reduce ground motion (earthquake) effects on buildings, since most of the energy will be spent in deformation of these isolators.  
         [0047]    [0047]FIG. 9 shows a first one of such corner connectors, which is indicated generally by reference numeral  50  and which comprises an abutment portion in the form of a tube  52  of square cross-section, against which abut the ends of wood frame members  54  and  56  connected by the connector  50 .  
         [0048]    The connector  50  has flanges  58  and  60  in face-to-face contact with sides of the frame members  54  and  56 , and co-planar side flanges  62  and  64  which extend from and at right angles to the flanges  58  and  60 . The flanges  62  and  64  are formed with nail openings through which nails  66  are driven through the flanges  62  and  64  into the frame members  54  and  56  to connect the latter at the corner of a wall unit frame which may, for example, be similar to any of the above-described frames. A sheathing  68  of plywood or other suitable sheathing material, shown in chain-dot lines, is secured directly to the co-planar side flanges  62  and  64  at the outer sides of the flanges  62  and  64 , i.e. at the sides of the flanges  62  and  64  opposite from the frame members  54  and  56 , by rivets  70 , without being otherwise connected to the frame members  54  and  56 . This ensures a direct transference of shear loads from the sheathing  60  to the flanges  62  and  64  of the connector  50 , by-passing the frame members  54  and  56 . Instead of nails and rivets, other means, e.g. prongs punched out from the flanges  62  and  64 , may be provided for connecting the latter to the frame members  54  and  56  and to the sheathing  68   
         [0049]    When the frame is subjected to shear stress, the metal corner connector  50  will be deformed, as illustrated in broken lines, to allow deformation of the frame.  
         [0050]    [0050]FIGS. 10, 11,  12  and  13  show another embodiment of the corner connector, which in this case is indicated generally by reference numeral  70 , and which includes a square-sectioned abutment portion  72  in one piece with a pair of flanges  74  and  76 , which each extends from the middle of a respective side of the abutment portion  72 , at right angles thereto, between a pair of wood frame members  78 ,  80  and  81 ,  82 , respectively, (FIGS. 12 and 13), to which the flanges  74  and  76  are connected by prongs  84  punched from the flanges  74  and  76 . Co-planar side flanges  83  and  85  extend at right angles to the flanges  74  and  76  from the abutment portion  72 .  
         [0051]    A sheet  86  of plywood or other suitable sheathing material, which is shown broken-away ion FIGS. 10 and 11, is connected to the flanges  83  and  85  and the frame members  78 ,  80  and  81 ,  82  by nails  88 . which extend through the nail holes  89  in the flanges  83  and  85 .  
         [0052]    In FIGS. 14 and 15 there is shown a corner connector comprising a square-sectioned abutment portion  90  with side flanges  92  and  94  but no flanges corresponding to the flanges  74  and  76  of FIGS.  10 - 13 . The flanges  92  and  94  are secured by nails  96  to wood frame members  98 , and a sheathing panel  100  secured by nails  102  to the frame members  98 .  
         [0053]    [0053]FIGS. 16 through 26 show various tie-down devices for securing the square-sectioned abutment portions of the above-described corner connectors to a foundation (not shown). Each of these anchor devices has an energy absorbent insert which acts as a linear or non-linear spring.  
         [0054]    More particularly, FIG. 16 shows a square-sectioned abutment portion, indicated generally by reference numeral  102 , of a corner connector, which may e.g. be one of the above-described corner connectors or a modification thereof, and which is formed with an internal horizontal web  103 . An anchor bolt  104 , the lower end of which is embedded in a foundation  106 , extends through the web  103 , a washer  106  and a retaining nut  108 , with rubber blocks  110  and  112  interposed between the foundation  106  and the web  103  and between the web  103  and the washer  106 . The anchor bolt  104  extends through a circular hole  111  in the web  103  and has a diameter less than that of the hole  111  to allow the anchor bolt  104  to deflect laterally relative to the web  103 .  
         [0055]    [0055]FIGS. 17 through 26 show various modifications of the tie-down device of FIG. 16.  
         [0056]    In FIGS. 17 and 22, an anchor bolt  114  has a head embedded in a rubber ball  116 ; in FIGS. 18 and 23 rubber discs  118  are interposed between washers  120  on an anchor bolt  122  and a transverse web  124 ; in FIGS. 19 and 24 a disc  126  fixed to an anchor bolt is embedded in a rubber block  128 ; in FIGS. 20 and 25 a disc  130  on an anchor bolt is located on a rubber block  132  and in FIGS. 21 and 26 a vertical plate  132  is sandwiched between two rubber blocks  134 .  
         [0057]    By the above-described means, the ultimate load capacities and deformation under load of the frames are controlled by connectors attached directly to the sheathing or diaphragm panel and to the frame.  
         [0058]    The stiffness of the frames may be controlled by any combination of the above-described embodiments.  
         [0059]    When a frame wall comprising rectangular frames provided with sheathing in the form of sheathing panels is subject to shear stress, and if there is no relative movement between adjacent sheathing panels, the wall will have the same strength and stiffness as a single sheathing panel having the same dimensions as the entire wall. It is possible to provide sheathing panels which are larger than standard sized sheathing panels, and which may for example be 8 feet by 16 feet, 8 feet by 24 feet, 16 feet by 16 feet, et cetera. Although such large size sheathing panels would have increased strength and stiffness compared with standard sheathing panels, they are nevertheless too rigid, heavy, expensive and difficult to handle. The present invention allows for the building of a large size continuous skin from a plurality of standard sized sheathing panels. Also, the present invention provides for the flexibility in design, e.g. by varying the size and number of connectors employed to connect adjacent sheathing panels, thus retaining the benefits of small, conventionally sized sheathing panels while also achieving the benefits of large size sheathing panels.  
         [0060]    Standard shear wall design can sustain an allowable force which is limited to that producing one half inch horizontal deflection, provided that the force is less than one third of the ultimate strength of the wall unit.  
         [0061]    The allowable shear force is in the range of 275-550 pounds per linear foot. For an 8-foot sheathing panel, this translates to 2200 to 1400 pounds, approximately. If a single sheathing panel of 8 feet by 8 feet dimensions is loaded by 4400 pounds, the deflection will be given by the equation: 
         A=A panel rotation+A panel shear 
         [0062]    [0062]FIG. 27 diagrammatically illustrates, in broken lines, the deflection under shear of a wall unit, while FIG. 28 shows the deflection under rotation. The panel rotation illustrated in FIG. 28 is caused by yielding of connections at the corners A and B of the wall unit due to yielding of the nails between the sheathing panel and the studs.  
         [0063]    [0063]FIG. 29, in broken lines, the combined effects of the rotation and the deflection under shear of the wall unit.  
         [0064]    When the sheathing panel is connected directly to a corner connector as described above, the upward and downward deflections of the panel are greatly reduced due to the direct transfer of force from the sheathing panel to the corner connectors, and the remaining shear deformation is negligible, as indicated for example by the following equation:-  
         Ashear   =         6   5     ×     4400     0.5   ×   96   ×   100000         =         0.001   ''     <<     <     0.5   ''                                            
 
         [0065]    Consequently, most of the deformations of present shear walls are caused by yielding of the connectors, i.e. nails or staples, and the consequential relative movement of the sheathing panels relative to one another and to the corner connectors.  
         [0066]    The present invention proposes to counteract relative movement of adjacent sheathing panels by connecting the adjacent sheathing panels directly to one another through connectors  140 , such as those shown in FIGS.  9  to  15 , as shown in FIG. 31.  
         [0067]    In this way, it is possible to counteract relative movement of the sheathing panels within an 8-foot by 8-foot wall, between the corners of the sheathing panels and anchor bolts securing the wall to a foundation or other anchorage and between the shear wall units in order to form, for example, an 8-foot by 24-foot continuous shear wall.  
         [0068]    By increasing the number of the connectors  140 , as shown in FIG. 32, and by increasing the sizes of the connectors  140 , as shown in FIG. 33, the shear wall stiffness can be correspondingly increased.  
         [0069]    [0069]FIGS. 34 and 35 show two types of connectors which may be employed for interconnecting adjacent wall units and their sheathing panels  
         [0070]    In FIG. 34, a metal connector indicated generally by reference numeral  150  has parallel flanges  152  secured by nails  154  to a stud  156 . The flanges  152  extend from a plate  158 , to which a pair of sheathing panels  160  are secured by fasteners which, in the present embodiment, comprise rivets  162 . If required, an additional backing plate (not shown) may be provided at the sides of the sheathing panels  160  opposite from the connector  150 .  
         [0071]    In FIG. 35, there is shown a metal connector, indicated generally by reference numeral  164  which is of generally H-shaped cross section and which is secured by nails  166  to studs  168 , with sheathing panel edges  170  sandwiched between the studs  166  and the metal connector  164 .  
         [0072]    [0072]FIG. 36 shows a reinforcement structure indicated generally by reference numeral  180  provided with corner connectors such as those of FIGS. 9 through 15, indicated by reference numeral  181  installed between two studs  182 . More particularly, the modified reinforcement structure  180  comprises rectangular frames, having side members  184  and  186  and top and bottom members  188  and  190 , with sheet material diaphragms or panels  192 A-F secured to the side members  184  and  186  and the top and bottom members  188  and  190 . A window opening  194  interrupts the four central rectangular frames, and has a sill  196  and an upper board  198 .  
         [0073]    [0073]FIG. 37 shows broken-away portions of two sheathing panels  200  and  201 , which are secured to a vertical elongate wood member  202  by means of a cross-shaped metal fastener  204 , which is pressed into embedded engagement with the elongate wood member  202  and the panels  200  and  201 .  
         [0074]    In FIGS. 38 and 39, there are shown modified cruciform connectors, indicated by reference numerals  206  and  208 , respectively, which are embedded in plywood panels  200  and  201  and in the elongate wood member  202  for the same purpose.  
         [0075]    [0075]FIGS. 40 and 41 illustrate the use of generally S-shaped fasteners  210  and  212  for the same purpose. These fasteners  210  and  212  may also be used to interconnect elongate members.