Abstract:
A fastener including a body having a predetermined axial length, wherein the body includes a screw head at one axial end of the body, a threaded portion at an opposite axial end of the body and an unthreaded shank portion extending between the screw head and the threaded portion, and wherein the shank portion has an axial length in excess of at least one-third of the axial length of the fastener body.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application is a divisional application which claims priority to application Ser. No. 10/211,790 filed Aug. 2, 2002 which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/309,802, filed Aug. 3, 2001. This application is also related to co-pending U.S. patent applications Ser. No. 10/211,810 abandoned Nov. 29, 2004, U.S. Pat. No. 6,928,778 issued Aug. 16, 2005 and U.S. Pat. No. 6,907,699 issued Jun. 21, 2005 filed on even date herewith, each of which is incorporated by reference. 
     
    
     FIELD ON THE INVENTION  
       [0002]     The present invention is related to a fastener for stucco sheathings, and more particularly, to a screw for retrofitting existing stucco, which is attached to the exterior of a building frame, to improve the resistance of the stucco to shearing forces caused by seismic and hurricane lateral loading.  
         [0003]     Therefore there is a need for a device and method of improving the strength of existing stucco sheathing against intense lateral forces, which is inexpensive and easily retrofitted to existing stucco sheathings.  
       BACKGROUND  
       [0004]     As observed, reported and learned from nine California earthquakes since 1951, existing Portland cement-based exterior plaster (stucco) of wooden-framed structures has had little success in surviving intense lateral loads caused by earthquake, as well as hurricane forces. For example, the shaking intensity during the 1994 Northridge Earthquake, which in some locations reached magnitudes of 8 and 9 Modified Mercalli Intensity (MMI), was enough to detach stucco sheathings from the wooden frame of many one and two story single family residences and apartment buildings. Such detachment of the stucco sheathings from the wood framing resulted in heavy interior damage, uninhabitable structures and required the removal and replacement of the stucco sheathings.  
         [0005]     A primary reason for the detachment of the stucco from the wood framing was the Uniform Building Code&#39;s approval of staples, since 1957, for attaching a reinforcing wire mesh to  
         [0006]     A primary reason for the detachment of the stucco from the wood framing was the Uniform Building Code&#39;s approval of staples, since 1957, for attaching a reinforcing wire mesh to the wood framing prior to applying the stucco over the wire mesh coupled with the requirement of the Uniform Building Code in 1967 that a 26 gauge corrosion resisting continuous drip screed be installed against the mud sill plate, which is disposed along the lower portion of the wood framing. The mud sill plate has a minimum of a one inch overlap below the wood sill plate. The continuous drip screed is typically attached to the mud sill by the use of nails so that the stucco ends evenly just below the mud sill. Waterproof building paper and wire mesh or metal lath are then installed over the drip screed.  
         [0007]     The wire mesh or metal lath is normally attached to the metal drip screed by use of the Uniform Building Code&#39;s specified staples, which are typically applied by use of a staple gun. Many times, the staple legs become bent and do not penetrate the metal drip screed. Staples used to fasten the wire mesh at the drip screed are often rusted out within a few years due to moisture rusting and weakening the thin staple legs. Stucco having poor lateral attachment to the mud sill due to unattached or rusted staples, typically fails at the wood sill plate during intense lateral displacement of the wood framing generated by such forces as earthquakes and/or hurricanes. Failure of the stucco sheathing generally results in heavy structural damage, often leaving the structure uninhabitable and needing complete replacement of the exterior stucco sheathing.  
         [0008]     More recently, particularly in structures built after 1994, home builders have had limited success in improving the structural strength of the stucco sheathings by using furring nails to reinforce the wire mesh to the wood framing. Such nails are the subject of U.S. Pat. No. 1,517,035, wherein the head of the nail and a spacer concentrically disposed around the nail are configured to both retain the wire mesh and maintain the wire mesh at a distance apart from the underlying structure, or building paper, when the nail is driven into place within the framing. However, the use of such furring nails is labor intensive and cannot be retrofitted to strengthen existing stucco wall sheathings.  
         [0009]     Therefore there is a need for a device and method of improving the strength of existing stucco sheathing against intense lateral forces, which is inexpensive and easily retrofitted to existing stucco sheathings.  
       SUMMARY OF THE INVENTION  
       [0010]     An exemplary embodiment of the present invention includes a fastener comprising a body having a predetermined axial length, wherein the body comprises a screw head at one axial end of the body, a threaded portion at an opposite axial end of the body and an unthreaded shank portion extending between the screw head and the threaded portion, and wherein the shank portion has an axial length in excess of at least one-third of the axial length of the fastener body.  
         [0011]     Another exemplary embodiment of the present invention includes a building structure comprising a building frame, one or more layers of stucco sheathing and a plurality of fasteners for securing a predetermined portion of the stucco sheathing to the building frame, wherein each fastener comprises a body of a predetermined axial length having a screw head at one axial end of the body, a threaded portion at an opposite axial end of the body, and an unthreaded shank portion extending between the screw head and the threaded portion, wherein the shank portion has an axial length in excess of at least one-third of the axial length of the fastener body.  
         [0012]     A further embodiment of the present invention includes a method of improving a lateral resistance of a stucco sheathing that is attached to a building frame. The method comprises providing a building frame, providing one or more layers of stucco sheathing and drilling a plurality of holes, wherein each hole extends through the stucco sheathing and into the building frame. A corresponding fastener is provided for each drilled hole, wherein each fastener comprises a body of a predetermined axial length having a screw head at one axial end of the body, a threaded portion at an opposite axial end of the body, and an unthreaded shank portion extending between the screw head and the threaded portion, wherein the shank portion has an axial length in excess of at least one-third of the axial length of the fastener body. The plurality of fasteners are installed in each corresponding drilled hole to secure the stucco sheathing to the building frame. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:  
         [0014]      FIG. 1  is a partial perspective view of an exterior wall plate of a typical wood framing;  
         [0015]      FIG. 2  is a side view of a first embodiment of a fastener of the present invention;  
         [0016]      FIG. 3  is a side cross-sectional view of the fastener of  FIG. 2  installed into the exterior wall plate of  FIG. 1 ;  
         [0017]      FIG. 4  is a side view depiction of a stucco panel used during lateral load testing; and  
         [0018]      FIG. 5  is a side view of a second embodiment of a fastener of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     The present invention is generally related to a fastener for a stucco sheathing, which is attached to a building frame, to improve a lateral resistance of the stucco sheathing. The fastener may be used to retrofit to an existing stucco sheathing to improve lateral and shear load resistance of the existing stucco sheathing to earthquakes or other forces. As shown in  FIG. 1 , a typical building structure or structural frame  10  comprises a series studs  11 , such as 2×4 or 2×6 wooden studs, a sill plate  12 , such as a wooden sill plate, as well as window jambs and door jambs, among other structures (not shown). The frame  10  is anchored to a building foundation  13 , such as an on-grade concrete slab, by being anchored to the sill plate  12 , which is in turn anchored to the foundation  13 , by bolts. Insulation  14  is typically disposed between the studs  11  to thermally “proof” the structure  10 .  
         [0020]     Building paper  16 , such as waterproof building paper, and a metal lath or wire mesh  17  are generally attached to the frame  10  by fasteners, for example, staples or furring nails, before a stucco sheathing  18  is applied over the wire mesh  17  as an exterior finish to the frame  10 . Typically, the stucco sheathing  18  is applied over the wire mesh  17 , such that bonding occurs between stucco sheathing  18  and the wire mesh  17 . The stucco sheathing  18  may be applied in several coats, such as three coats.  
         [0021]     A drip screed  19  may be installed between the building frame  10  and stucco sheathing  18 , for example, at a base of the frame  10 . The drip screed  19  helps prevent moisture from entering the juncture of the bottom of the frame  10  and the foundation  13 .  
         [0022]     A fastening device or fastener  20 , such as a screw fastener, may be inserted through the stucco sheathing  18  and into the frame  10  to maintain the structural integrity and enhance the lateral strength of the stucco sheathing  18 . The fastener  20  may be installed to retrofit existing stucco sheathings. The fastener  20  is specially designed to transfer shearing loads from the stucco sheathing  18  to the frame  10 , which transfers the shearing forces to the sill plate  12  and the building foundation  13  during sudden intense lateral movement, such as that generated by seismic and/or hurricane forces. As a result, the stucco sheathing  18  will resist greater lateral loads and experience less lateral displacement prior to failure.  
         [0023]     In one embodiment, as shown in to  FIG. 2 , the fastener  20  is a shear screw having a screw head  24  at one axial end and a threaded portion  26  at an opposite axial end. The screw head  24  is generally tapered inwardly. For example, the screw head  24  may taper from a diameter of approximately ⅜ inches to a diameter of approximately 3/16 inches to form a countersunk screw head. However, the screw head  24  may comprise other suitable constructions as well. In one embodiment, the screw head  24  is adapted for removable engagement with a socket wrench (See  FIG. 5 ). For example, the screw head  24  may be hexagonally shaped, such that a ⅜ inch socket wrench may be removably coupled thereto. Alternatively, the screw head  24  may be slotted to receive a phillips head or slot head screw driver.  
         [0024]     In the depicted embodiment of  FIG. 2 , an unthreaded shank portion  28  is disposed between the screw head  24  and the threaded portion  26 . The shank  28  may axially extend to any suitable length so long as the axial length of the shank  28  is in excess of at least one-third of the total axial length of the fastener  20 . In one embodiment, the shank  28  axially extends approximately one-half the total axial length of the fastener  20 . For example, in one embodiment the fastener  20  is approximately 2¼ inches in axial length and the shank  28  is approximately 3/16 inches in diameter and axially extends approximately 1⅛ inches from the screw head  24 . In this embodiment, the threaded portion  26  also has a diameter of approximately 3/16 inches.  
         [0025]     The fastener  20  may be comprised of any one of a variety of suitable materials. For example, the fastener  20  may be comprised of a metal material, such as a 300 Series non-heat treated, stainless steel wire stock. The fastener  20  may also be normalized to increase the ductility of the fastener material to enable the fastener  20  to better endure the back and forth forces of the stucco sheathing  18  against the frame  10  during earthquakes and/or hurricanes. In addition, the fastener  20  may be electro-plated to galvanize the fastener  20 .  
         [0026]     In one embodiment, as shown in  FIG. 3 , the axial length of the shank  28  is such that the shank  28  extends through the stucco sheathing  18 , the wire mesh  17 , the building paper  16 , the drip screed  19  (where applicable), and at least partially into the frame  10 . This design allows the shank  28  to engage the frame  10  to transfer shear forces, such as seismic shear forces experienced by the stucco sheathing  18 , to the frame  10 , which transfers the shearing forces to the sill plate  12  and the building foundation  13 . This maintains the structural integrity of the exterior stucco sheathing  18  and interior wall sheathing during high intensity earthquake and/or hurricane forces and increases the shear resistance provided by the stucco sheathing  18  and results in less deflection of the stucco sheathing  18  prior to failure. In addition, since the shank portion  28  is not threaded, less damage is done to the stucco sheathing  18  when the stucco sheathing  18  experiences shear forces than is done by use of a threaded shank, which tends to cut into the stucco sheathing  18  when the stucco sheathing  18  experiences shear forces.  
         [0027]     A method of use of the fastener  20  comprises drilling a hole  30 , such as a countersunk pilot hole (shown in  FIGS. 3 &amp; 4 ), through the stucco sheathing  18 , the wire mesh  17 , the building paper  16 , the drip screed  19  (where applicable), and at least partially into the frame  10 . A plurality of the holes  30  may be spaced about the frame  10 . For example, the holes  30  may be uniformly spaced along the studs  11  and sill plate  12 , 8 inches on center (i.e., a distance of 8 inches from the center of one drill hole to the center of another drill hole). The pilot holes may be disposed along studs forming the base structure, the base sill plates, the door jambs, the window jambs and other edges of the wall.  
         [0028]     Ser. No. 10/211,810 abandoned Nov. 29, 2004, the disclosures of which are incorporated herein by reference. A preferred application of the fastening device of the present invention is in retrofitting existing stucco sheathings along the sills, plates, edges and jambs of exterior walls.  
         [0029]     In one embodiment, the retrofit drill provides a 3/16 inch diameter hole  30 , which extends from an outer surface of the stucco sheathing  18  and at least partially into the frame  10 . The fastener  20  likewise projects from the outer surface of the stucco sheathing  18  and at least partially into the frame  10 . For example, in one embodiment, the fastener  20  extends into the frame  10 , such that an entire axial length of the threaded portion  26  extends into the frame  10  and approximately ⅜ inch of the axial length of the shank  28  extends into the frame  10 . In another embodiment, approximately 2 inch of the axial length of the shank  28  extends into the frame  10 . When at least a portion of the shank  28  extends into the frame  10 , lateral forces experienced by the stucco sheathing  18  are transferred from the stucco sheathing  18  to the building frame  10 .  
         [0030]     After the fastener  20  is engaged with the holes  30 , the holes  30  may be filled with an epoxy enhanced stucco patch material  32 , for example caulking. In addition, the outer surface of the stucco sheathing  18  may be coated with a color coat or a finishing layer of stucco  34 . Alternatively, texture may be provided over the patch material  32  to match the finish of the outer surface of the stucco sheathing  18 .  
         [0031]     In an alternative embodiment, as shown  FIG. 5 , the fastener  20  comprises a pan-head portion  44  and a grommet  48 . The grommet  48  seals the hole  30  when the fastener  20  is engaged with the hole  30 . For example, when the hole  30  comprises a countersunk portion, the grommet  48  may be a similarly tapered, such that the grommet  48  forms a sealed section in the hole  30  when the fastener  20  is engaged with the hole  30 . In one embodiment, the grommet  48  is comprised of an elastic material, such as a synthetic rubber material, for example neoprene. In such an embodiment, the grommet  48  forms a water tight sealed section in the hole  30  when the fastener  20  is engaged with the hole  30 .  
         [0032]     In addition, a washer  50  may be disposed between the head portion  44  and the grommet  48  to provide a bearing surface for urging the grommet  48  into sealing contact with the hole  30  when the fastener  20  is engaged with the hole  30 . Although the grommet  48  has been described as used in conjunction with a pan-head screw, the grommet  48  may be used with other fasteners, such as screws having various other head configurations.  
         [0033]     It is important to note that when retrofitting the fasteners  20  to existing stucco sheathings, the existing stucco sheathings should be initially investigated to confirm that they are in good enough condition to warrant reinforcing the existing stucco sheathings with the fasteners  20  to improve the lateral resistance of the existing stucco sheathings. In addition, it is also advisable  
         [0034]     It is important to note that when retrofitting the fasteners  20  to existing stucco sheathings, the existing stucco sheathings should be initially investigated to confirm that they are in good enough condition to warrant reinforcing the existing stucco sheathings with the fasteners  20  to improve the lateral resistance of the existing stucco sheathings. In addition, it is also advisable when retrofitting the fasteners  20  to existing stucco sheathings to inspect the frame  10  for dry rot, fungus and/or termite damage or any other damage that would lessen the advantage of applying the fasteners  20  to the existing stucco sheathings.  
         [0035]     It is preferred that the fasteners  20  be installed to exterior stucco sheathing prior to color coating. By this is it meant the color coating which typically occurs every 10 to 15 years, where the outer surface of existing stucco sheathings are provided with a thin new coat of stucco, such as the layer  34  described above. Installing the fasteners  20  prior to color coating may reduce the cost of maintenance of the stucco sheathing, as fasteners  20  may be retrofitted to the existing stucco sheathing around the same time when the color coating is applied.  
         [0036]     Experimental testing to investigate the enhanced lateral strength of stucco sheathings  18  that have been reinforced with the fasteners  20  has been conducted. Referring now to  FIG. 4 , tests were conducted on a 10 foot by 8 foot high stucco panel  60  comprising a window  62  at its center. The fasteners  20  where disposed along the outer surface of the stucco panel  60  and into a framing structure as described above.  
         [0037]     In addition, the stucco panel  60  was fixed to an apparatus  66  which anchored the panel  60  along its base  68 , and provided lateral displacement (depicted by an arrow  67 ) of the panel  60  along its free standing end  70 . The test revealed that the fasteners  20  increased the resistance of the stucco panel  60  from approximately 300 pounds per foot to approximately 700 pounds per foot. In summary, the present invention provides an inexpensive device and method for improving a building structures resistance to earthquake and/or hurricane forces. This reduces structural damage to the building structures stucco sheathing, interior wall sheathing and prolongs the occupancy of wood framed residences.  
         [0038]     The preceding description has been presented with reference to certain embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of the invention. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the appended claims which are to have their fullest and fair scope.