Abstract:
A two-piece fastener plate and fastener assembly and method of securing a roof membrane to a roof deck wherein the fastener is reinforced with rigid, inflexible concentric dome-shaped ribs separated by concentric depressions or dimples. The concentric depressions or dimples are provided with pairs of barbs for gripping the roof membrane when the fastener secures the roof membrane to the roof deck.

Description:
CROSS REFERENCE TO PRIOR APPLICATION DATA  
       [0001]     This application is a continuation-in-part of copending application Ser. No. 10/357,113 filed on Feb. 3, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to fasteners employed to fasten a covering material to an underlying substrate. More particularly, the invention relates to a stress plate with a fastener for fastening a membrane, such as a roof membrane or roofing insulation, to a roof deck, a wall, concrete, stone, plaster, or wood.  
         [0004]     2. Reported Development  
         [0005]     Fasteners are conventionally employed in the building industry for fastening or clamping a flexible membrane, such as an insulation membrane to a substrate, such as a roof deck. The fasteners typically comprise a large head portion and a shank portion. In use, the shank portion is driven through the membrane into the underlying substrate to anchor the fastener thereinto, while the head portion holds the membrane against the substrate and prevent removal thereof by wind lift. The undersurface of the head portion is typically provided with gripping means so that the membrane is prevented from moving or sliding under the fastener. The gripping means are designed not to penetrate the membrane in order to prevent atmospheric moisture from entering into the substrate through the holes which tend to be made by the gripping means. It is also important that the gripping means are spread/distributed in the undersurface of the head portion of the stress plate in order prevent tearing of the membrane. Conventional fasteners are illustrated by the following references.  
         [0006]     U.S. Pat. No. 4,787,188 discloses a stress plate for securing a roof membrane to a roof deck. The stress plate is circular having a top surface and a bottom surface with a central circular opening for receiving a screw for fastening the stress plate over a roof membrane and to the roof deck. The stress plate is equipped with four gripping prongs of triangular shape which are circumferentially spaced from each other by 90°.  
         [0007]     In use a first membrane is applied to a roof deck surface, then the membrane is secured to the roof deck surface with the stress plate and the screw. A top sheet or membrane is lapped over the first membrane to cover the stress plate and welded to the first membrane. The four gripping prongs in the stress plate grip the first sheet and hold the same on top of the roof deck without tearing.  
         [0008]     U.S. Pat. No. 5,049,018 discloses a fastener for gripping a substrate material. The fastener is of a unitary piece comprising a head portion, a shaft portion, and a hook portion at the end of the shaft portion, wherein the hook portion has an outwardly and upwardly extending resilient end portion. The end portion has an end surface which provides gripping contact with a wall of a hole in a substrate into which the fastener is inserted.  
         [0009]     It is apparent that the reference invention is directed to a fastener the construction of which insures that the fastener will not be dislodged by wind uplift from the hole of the substrate.  
         [0010]     U.S. Pat. No. 5,163,798 relates to a fastener assembly which is employed to secure plies or membranes of roofing, felt and paper to prevent the materials from being blown off the base roofing material before the base material is sufficiently hardened.  
         [0011]     The assembly comprises a fastener and a retainer plate. The assembly includes a fastener plate which defines a substantially rectangular opening. The fastener includes a head and a pair of legs which are integrally hingably connected to the head. The legs have a contoured distal portion and an angular side configuration so that at least one of the legs is forced apart as the fastener is driven into the base material.  
         [0012]     U.S. Patent Application Publication No. 2003/0196398 disclose a stress plate comprising:  
         [0013]     a circular disc having a central aperture for receiving a screw fastener;  
         [0014]     concentric ribs between the central aperture and the peripheral edge of the plate for providing reinforcing and bending or flexibility characteristics; and  
         [0015]     a plurality of singly spaced downwardly extending projections to engage and hold an underlying roof membrane on the roof of a building.  
         [0016]     The stress plate has two concentrically disposed annular rib members: a first radially inner, upwardly extending rib member; and a second, radially outer upwardly extending rib member. The first rib member is larger in both radial extent and elevational height than the second rib member. The first member provides rigidity while the second member provides flexibility to the stress plate.  
         [0017]     U.S. Pat. No. 6,250,034 discloses a membrane plate for attaching a membrane to a roof comprising:  
         [0018]     an oval shaped body;  
         [0019]     an opening in the center of the oval shaped body to receive a screw member therethrough; and  
         [0020]     a plurality of spaced apart lenses joined to the oval shaped body with hinges extending downwardly from the oval shaped body.  
         [0021]     U.S. Pat. No. 5,951,225 discloses a large area washer of square, rectangular and elliptical shape comprising:  
         [0022]     a large area plate;  
         [0023]     an aperture in the center portion of the plate to receive a fastener therethrough;  
         [0024]     stiffeners in the form of beads or indentations in the plate;  
         [0025]     unreinforced corner regions outside the stiffeners which can be resiliently bent; and  
         [0026]     engaging components formed in the comer regions.  
         [0027]     We have observed that under windy conditions the prior art fasteners need improvement in securely holding a flexible membrane on a substrate without the gripping means penetrating the flexible membrane, and without tearing the flexible membrane.  
         [0028]     Accordingly, an object of the present invention is to provide a new and improved stress plate with a fastener to allow attachment of one or more flexible membranes to an underlying substrate without tearing the flexible membrane or allowing it to slip out from under the stress plate.  
       SUMMARY OF THE INVENTION  
       [0029]     The present invention comprises two non-integral components: a stress plate, and a fastener. In use the stress plate and the associated fastener attach and firmly hold a flexible membrane to an underlying substrate, such as a roof deck. The stress plate has a top surface and a bottom surface and is provided with multiple pairs of barbs extending vertically outwardly from the bottom surface and having sufficient length to grip the flexible membrane without puncturing therethrough. The stress plate further includes an opening in its central portion to allow a fastener, such as a screw, therethrough for attachment of the stress plate to the underlying substrate. The opening may be circular or rectangular.  
         [0030]     The rib members are of the same elevational height and along with the stress plate, are completely rigid, stiff and inflexible. Other descriptors that define the stress plate include unresilient, unyielding and unbending. These descriptors are relevant to the stress plate per se, and also when the stress plate is installed to secure a roof membrane to an underlying roof surface.  
         [0031]     The present invention comprises eight embodiments.  
         [0032]     In the first embodiment of the invention the stress plate is circular having an opening in its center portion and three dome-shaped concentric ribs or protuberances rising above the top surface of the stress plate for providing sufficient strength thereto. The radius of the concentric ribs increases from the center opening to the circumference of the stress plate. Separating the first and second concentric ribs there is a first concentric depression or dimple, and separating the second and third concentric ribs there is a second concentric depression or dimple. A flat surface extends between the third rib and the edge or circumference of the stress plate.  
         [0033]     The first dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly space from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0034]     In the second embodiment of the invention the stress plate is elliptical having an opening in its center portion and three dome-shaped concentric ribs or protuberances rising above the top surface of the stress plate for providing sufficient strength thereto. Separating the first and second concentric ribs there is a first concentric depression or dimple, and separating the second and third concentric ribs there is a second concentric depression or dimple. A flat surface extends between the third rib and the edge or circumference of the stress plate.  
         [0035]     The first dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly spaced from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0036]     In the third embodiment of the invention the stress plate is of square configuration having an opening in its center portion and three dome-shaped concentric ribs or protuberances running parallel to each other and to the edge of the stress plate rising above the top surface of the stress plate for providing sufficient strength thereto. Separating the first and second ribs there is a first depression or dimple, and separating the second and third ribs there is a second depression or dimple. A flat surface extends between the third rib and the edge or circumference of the stress plate.  
         [0037]     The first dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly spaced from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0038]     In the fourth embodiment of the invention the stress plate is of rectangular configuration having an opening in its center portion and three dome-shaped ribs or protuberances running parallel to each other and to the edge of the stress plate rising above the top surface of the stress plate for providing sufficient strength thereto. Separating the first and second ribs there is a first depression or dimple, and separating the second and third ribs there is a second depression or dimple. A flat surface extends between the third rib and the edge or circumference of the stress plate.  
         [0039]     The first dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly spaced from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0040]     In the fifth embodiment of the invention the stress plate is circular having an opening in its center portion and two dome-shaped concentric ribs or protuberances rising above the top surface of the stress plate for providing sufficient strength thereto. The radius of the first concentric rib close to the opening is smaller than the radius of the second concentric rib close to the circumference of the stress plate. Separating the first and second concentric ribs there is a concentric depression or dimple. A flat surface extends between the second rib and the edge or circumference of the stress plate.  
         [0041]     The first dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular pair of barbs approximately evenly space from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0042]     In the sixth embodiment of the invention the stress plate is elliptical having an opening in its center portion and two dome-shaped concentric ribs or protuberances rising above the top surface of the stress plate for providing sufficient strength thereto. Separating the first and second concentric ribs there is a first concentric depression or dimple. The edge or circumference of the stress plate terminates in a substantially flat surface.  
         [0043]     The dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly space from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0044]     In the seventh embodiment of the invention the stress plate is of square configuration having an opening in its center portion and two dome-shaped ribs or protuberances running parallel to each other and to the edge of the stress plate rising above the top surface of the stress plate for providing sufficient strength thereto. Separating the first and second ribs there is a depression or dimple. A flat surface extends between the second rib and the edge or circumference of the stress plate.  
         [0045]     The dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly space from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
         [0046]     In the eighth embodiment of the invention the stress plate is of rectangular configuration having an opening in its center portion and two dome-shaped ribs or protuberances running parallel to each other and to the edge of the stress plate rising above the top surface of the stress plate for providing sufficient strength thereto. Separating the first and second ribs there is a depression or dimple. A flat surface extends between the second rib and the edge or circumference of the stress plate.  
         [0047]     The dimple is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to eight pairs of triangular, rectangular, or semi-circular barbs approximately evenly spaced from each other. The flat surface of the stress plate adjacent to the edge is provided with a multiplicity of pairs of barbs extending 90° downward from the bottom surface of the stress plate, and preferably, four to ten pairs of triangular, rectangular, or semi-circular pairs of barbs approximately evenly spaced from each other.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0048]     The invention will be further described with respect to the accompanying drawings wherein:  
         [0049]      FIG. 1  is a top, perspective view of the circular stress plate having three ribs thereon and fastener;  
         [0050]      FIG. 2  is a side elevational view thereof;  
         [0051]      FIG. 3  is a top plan view thereof;  
         [0052]      FIG. 4  is a bottom perspective view thereof;  
         [0053]      FIG. 5  is a top perspective view of the elliptical stress plate having three ribs thereon and fastener;  
         [0054]      FIG. 6  is a side elevational view thereof;  
         [0055]      FIG. 7  is another side elevational view thereof;  
         [0056]      FIG. 8  is a top plan view thereof;  
         [0057]      FIG. 9  is a bottom perspective view thereof;  
         [0058]      FIG. 10  is a is a top perspective view of the square stress plate having three ribs thereon and fastener;  
         [0059]      FIG. 11  is a side elevational view thereof;  
         [0060]      FIG. 12  is a top plan view thereof;  
         [0061]      FIG. 13  is a bottom perspective view thereof;  
         [0062]      FIG. 14  is a top perspective view of the rectangular stress plate having three ribs thereon and fastener;  
         [0063]      FIG. 15  is a side elevational view thereof;  
         [0064]      FIG. 16  is another side elevational view thereof;  
         [0065]      FIG. 17  is a top plan view thereof;  
         [0066]      FIG. 18  is a bottom perspective view thereof;  
         [0067]      FIG. 19  is a is a top perspective view of the circular stress plate having two ribs thereon and fastener;  
         [0068]      FIG. 20  is a side elevational view thereof;  
         [0069]      FIG. 21  is a top plan view thereof;  
         [0070]      FIG. 22  is a bottom perspective view thereof;  
         [0071]      FIG. 23  is a top perspective view of the elliptical stress plate having two ribs thereon and fastener;  
         [0072]      FIG. 24  is a side elevational view thereof;  
         [0073]      FIG. 25  is another side elevational view thereof;  
         [0074]      FIG. 26  is a top plan view thereof;  
         [0075]      FIG. 27  is a bottom perspective view thereof;  
         [0076]      FIG. 28  is a is a top perspective view of the square stress plate having two ribs thereon and fastener;  
         [0077]      FIG. 29  is a side elevational view thereof;  
         [0078]      FIG. 30  is a top plan view thereof;  
         [0079]      FIG. 31  is a bottom perspective view thereof;  
         [0080]      FIG. 32  is a top perspective view of the rectangular stress plate having two ribs thereon and fastener;  
         [0081]      FIG. 33  is a side elevational view thereof;  
         [0082]      FIG. 34  is another side elevational view thereof;  
         [0083]      FIG. 35  is a top plan view thereof;  
         [0084]      FIG. 36  is a bottom perspective view thereof;  
         [0085]      FIG. 37  is an enlarged top plan view of the pair of triangular barbs;  
         [0086]      FIG. 38  is an enlarged top plan view of the pair of rectangular barbs;  
         [0087]      FIG. 39  is an enlarged top plan view of the pair of semi-circular barbs; and  
         [0088]      FIG. 40  is a cross-sectional view illustrating the use of the stress plate and the fastener for attaching a roof membrane to a roof deck.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0089]     Reference is now being made to the drawings wherein like numerals represent like parts throughout the figures showing the various embodiments of the present invention.  
         [0000]     First Embodiment—Circular with Three Ribs  
         [0090]      FIGS. 1-4  relate to the first embodiment of the present invention in which the circular stress plate is generally designated at  10  and the fastener is generally designated at  12 . The two components are non-integral and when put together, constitute the invention. The circular stress plate  10  has a round or rectangular opening  14  in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with three concentric dome-shaped ribs: rib  16  is the closest to the opening; rib  20  is farthest from the opening; and rib  18  is between ribs  16  and  20 . The ribs serve as reinforcements to the stress plate. Separating rib  16  from rib  18  there is a concentric depression or dimple  22 , and separating rib  18  from rib  20  there is another concentric depression or dimple  24 . An essentially flat surface  26  extends between rib  20  and the circumferential edge  28  of the stress plate. Dimple  22  is provided with multiple pairs of barbs  30  (six pairs are shown), and flat surface  26  is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Second Embodiment—Elliptical with Three Ribs  
         [0091]      FIGS. 5-9  relate to the second embodiment of the present invention in which the elliptical stress plate is generally designated at  10 ′ and the fastener is generally designated at  12 ′ The two components are non-integral and when put together, constitute the invention. The elliptical stress plate  10 ′ has a round or rectangular opening  14 ′ in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with three concentric dome-shaped ribs: rib  16 ′ is the closest to the opening, rib  20 ′ is farthest from the opening; and rib  18 ′ is between ribs  16 ′ and  20 ′. The ribs serve as reinforcements to the stress plate. Separating rib  16 ′ from rib  18 ′ there is a concentric depression or dimple  22 ′, and separating rib  18 ′ from rib  20 ′ there is another concentric depression or dimple  24 ′. An essentially flat surface  26 ′ extends between rib  20 ′ and the circumferential edge  28 ′ of the stress plate. Dimple  22 ′ is provided with multiple pairs of barbs  30 ′ (six pairs are shown), and flat surface  26 ′ is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Third Embodiment—Square with Three Ribs  
         [0092]      FIGS. 10-13  relate to the third embodiment of the present invention in which the square stress plate is generally designated at  40  and the fastener is generally designated at  42 . The two components are non-integral and when put together, constitute the invention. The square stress plate  40  has a round or rectangular opening  44  in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with three concentric dome-shaped ribs: rib  46  is the closest to the opening; rib  50  is farthest from the opening; and rib  48  is between ribs  46  and  50 . The ribs serve as reinforcements to the stress plate. Separating rib  46  from rib  48  there is a concentric depression or dimple  52 , and separating rib  48  from rib  50  there is another concentric depression or dimple  54 . An essentially flat surface  56  extends between rib  50  and the circumferential edge  58  of the stress plate. Dimple  52  is provided with multiple pairs of barbs  60  (eight pairs are shown), and flat surface  56  is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Frourth Embodiment—Rectangular with Three Ribs  
         [0093]      FIGS. 14-18  relate to the fourth embodiment of the present invention in which the rectangular stress plate is generally designated at  40 ′ and the fastener is generally designated at  42 ′. The two components are non-integral and when put together, constitute the invention. The rectangular stress plate  40 ′ has a round or rectangular opening  44 ′ in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with three concentric dome-shaped ribs: rib  46 ′ is the closest to the opening; rib  50 ′ is farthest from the opening; and rib  48 ′ is between ribs  46 ′ and  50 ′. The ribs serve as reinforcements to the stress plate. Separating rib  46 ′ from rib  48 ′ there is a concentric depression or dimple  52 ′, and separating rib  48 ′ from rib  50 ′ there is another concentric depression or dimple  54 ′. An essentially flat surface  56 ′ extends between rib  50 ′ and the circumferential edge  58 ′ of the stress plate. Dimple  52 ′ is provided with multiple pairs of barbs  60 ′ (ten pairs are shown), and flat surface  56 ′ is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Fifth Embodiment—Circular with Two Ribs  
         [0094]      FIGS. 19-22  relate to the fifth embodiment of the present invention in which the circular stress plate is generally designated at  70  and the fastener is generally designated at  72 . The two components are non-integral and when put together, constitute the invention. The circular stress plate  70  has a round or rectangular opening  74  in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with two concentric dome-shaped ribs: rib  76  is an inner rib close to the opening, and rib  78  is an outer rib spaced from the inner rib toward the circumferential edge  88  of the stress plate. The ribs serve as reinforcements to the stress plate. Separating rib  76  from rib  78  there is a concentric depression or dimple  82 . An essentially flat surface  86  extends between rib  78  and the circumferential edge  88  of the stress plate. Dimple  82  is provided with multiple pairs of barbs  90  (eight pairs are shown), and flat surface  86  is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Sixth Embodiment—Elliptical with Two Ribs  
         [0095]      FIGS. 23-27  relate to the sixth embodiment of the present invention in which the elliptical stress plate is generally designated at  70 ′ and the fastener is generally designated at  72 ′. The two components are non-integral and, when put together, constitute the invention. The elliptical stress plate  70 ′ has a round or rectangular opening  74 ′ in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with two concentric dome-shaped ribs: rib  76 ′ is an inner rib close to the opening, and rib  78 ′ is an outer rib spaced from the inner rib toward the circumferential edge  88 ′ of the stress plate. The ribs serve as reinforcements to the stress plate. Separating rib  76 ′ from rib  78 ′ there is a concentric depression or dimple  82 ′. An essentially flat surface  86 ′ extends between rib  78 ′ and the circumferential edge  88 ′ of the stress plate. Dimple  82 ′ is provided with multiple pairs of barbs  90 ′ (six pairs are shown), and flat surface  86 ′ is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Seventh Embodiment—Square with Two Ribs  
         [0096]      FIGS. 28-31  relate to the seventh embodiment of the present invention in which the square stress plate is generally designated at  100  and the fastener is generally designated at  102 . The two components are non-integral and, when put together, constitute the invention. The square stress plate  100  has a round or rectangular opening  104  in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with two concentric dome-shaped ribs: rib  106  is an inner rib close to the opening, and rib  108  is an outer rib spaced from the inner rib toward the circumferential edge  118  of the stress plate. The ribs serve as reinforcements to the stress plate. Separating rib  106  from rib  108  there is a concentric depression or dimple  112 . An essentially flat surface  106  extends between rib  108  and the circumferential edge  118  of the stress plate. Dimple  112  is provided with multiple pairs of barbs  120  (eight pairs are shown), and flat surface  116  is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0000]     Eighth Embodiment—Rectangular with Two Ribs  
         [0097]      FIGS. 32-36  relate to the eighth embodiment of the present invention in which the rectangular stress plate is generally designated at  100 ′ and the fastener is generally designated at  102 ′. The two components are non-integral and, when put together, constitute the invention. The rectangular stress plate  100 ′ has a round or rectangular opening  104 ′ in its center portion through which the fastener is inserted when the stress plate is employed for attaching and firmly holding a roof membrane to an underlying roof deck. The stress plate is provided with two concentric dome-shaped ribs: rib  106 ′ is an inner rib close to the opening, and rib  108 ′ is an outer rib spaced from the inner rib toward the circumferential edge  118 ′ of the stress plate. The ribs serve as reinforcements to the stress plate. Separating rib  106 ′ from rib  108 ′ there is a concentric depression or dimple  112 ′. An essentially flat surface  106 ′ extends between rib  108 ′ and the circumferential edge  118 ′ of the stress plate. Dimple  112 ′ is provided with multiple pairs of barbs  120 ′(eight pairs are shown), and flat surface  116 ′ is also provided with multiple pairs of barbs (eight pairs are shown). The pairs of barbs are either triangular (as shown), or rectangular (not shown), or semi-circular (not shown). The pairs of barbs are approximately evenly spaced from each other.  
         [0098]      FIGS. 37, 38  and  39  shows the pairs of barbs in top plan view used in the stress plate and are integral therewith.  
         [0099]      FIG. 37  shows a pair of equilateral triangles in the stress plate the sharp points of the triangles extend outwardly from the bottom surface of the stress plate.  
         [0100]      FIG. 38  shows a pair of rectangular barbs. In the stress plate the rectangular barbs extend outwardly from the bottom surface of the stress plate.  
         [0101]      FIG. 39  shows a pair of semi-circular barbs. In the stress plate the semi-circular barbs extend outwardly from the bottom surface of the stress plate.  
         [0102]     The length of the barbs may vary depending on the thickness of the roof membrane which is to be attached to the underlying roof deck. Typically, the length of the barbs would be in the range of 0.1-1.0 centimeter or more, and preferably in the range of 0.2-0.5 centimeter.  
         [0103]     The barbs are formed by cutting the same from the surface of the stress plate and bending them 90° from the surface of the stress plate.  
         [0104]     The stress plates are made of materials including galvanized carbon steel and stainless steel. Softer metals such as copper or aluminum may also be used, however, the thickness of the stress plate should be larger to provide sufficient integrity to the stress plate. The thickness of the stress plate typically is about 0.05-0.1 cm. The fastener is typically a screw of 4 to 10 cm long having thread thereon.  
         [0105]      FIG. 40  is a cross-sectional view illustrating the use of the stress plate and the fastener for attaching a roof membrane to a roof deck. Lower membrane  130  is positioned over insulation  132  which is over the roof deck surface  134 . Inserting fastener  138  through stress plate  136 , insulation  132  and into roof deck  134 . Upper membrane  140  is then lapped-over portions of the lower membrane covering the stress plate  136 . The upper membrane is secured to the lower membrane by the welded seam  142 .  
         [0000]     Wind Uplift Test  
         [0106]     Comparative wind uplift tests were conducted on the double barb stress plates of the present invention, and the single barb stress plate. The wind uplift test measures the resistance of the roofing system to high wind currents. For example, a three second burst of wind at 175 miles per hour can exert a negative pressure of 90 pounds per square foot on the roof system.  
         [0107]     The roofing system consists of: a roof deck, an insulating layer placed on the roof deck, and a roof membrane placed on the top of the insulating layer. The respective plates were then attached to the roofing system by inserting the respective fasteners through the stress plates, the roof membranes, and the insulating layer and into the roof deck and holding the roofing system at 15 pounds per square feet intervals starting at 30 pounds per square feet from sixty seconds until failure. Failure of the roofing system was measured by the membrane tearing around the stress plates.  
         [0108]     The roofing system having the double barb stress plate passed the wind uplift test at 60 seconds at 90 pounds of pressure per square feet, while the roofing system having the single barb stress plate failed at 47 seconds at 75 pounds of pressure per square feet.  
                                             First and Second Embodiments - Circular and Elliptical with Three Ribs                                    Stress plate, generally designated   10, 10′           Fastener, generally designated   12, 12′           Opening in center portion   14, 14′           Ribs   16, 16′, 18, 18′,               20, 20′           Depressions or dimples   22, 22′, 24, 24′           Flat surface of stress plate   26, 26′           Circumferential edge of stress plate   28, 28′           Pairs of barbs   30, 30′                      
 
         [0109]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Third and Fourth Embodiments - Square and Rectangular with Three Ribs 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Stress plate, generally designated 
                 40, 40′ 
               
               
                   
                 Fastener, generally designated 
                 42, 42′ 
               
               
                   
                 Opening in center portion of stress plate 
                 44, 44′ 
               
               
                   
                 Ribs 
                 46, 46′, 48, 48′, 
               
               
                   
                   
                 50, 50′ 
               
               
                   
                 Depressions or dimples 
                 52, 52′, 54, 54′ 
               
               
                   
                 Flat surface of stress plate 
                 56, 56′ 
               
               
                   
                 Circumferential edge of stress plate 
                 58, 58′ 
               
               
                   
                 Pairs of barbs 
                 60, 60′ 
               
               
                   
                   
               
             
          
         
       
     
         [0110]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Fifth and Sixth Embodiments - Circular and Elliptical with Two Ribs 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Stress plate, generally designated 
                 70, 70′ 
               
               
                   
                 Fastener, generally designated 
                 72, 72′ 
               
               
                   
                 Opening in center portion of stress plate 
                 74, 74′ 
               
               
                   
                 Ribs 
                 76, 76′, 78, 78′ 
               
               
                   
                 Depressions or dimples 
                 82, 82′ 
               
               
                   
                 Flat surface of stress plate 
                 86, 86′ 
               
               
                   
                 Circumferential edge of stress plate 
                 88, 88′ 
               
               
                   
                 Pairs of barbs 
                 90, 90′ 
               
               
                   
                   
               
             
          
         
       
     
         [0111]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Seventh and Eighth Embodiments - Square and Rectangular with Two 
               
               
                 Ribs 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Stress plate, generally designated 
                 100, 100′ 
               
               
                   
                 Fastener, generally designated 
                 102, 102′ 
               
               
                   
                 Opening in center portion of stress plate 
                 104, 104′ 
               
               
                   
                 Ribs 
                 106, 106′, 108, 
               
               
                   
                   
                 108′ 
               
               
                   
                 Depressions or dimples 
                 112, 112′ 
               
               
                   
                 Flat surface of stress plate 
                 116, 116′ 
               
               
                   
                 Circumferential edge of stress plate 
                 118, 118′ 
               
               
                   
                 Pairs of barbs 
                 120, 120′ 
               
               
                   
                   
               
             
          
         
       
     
         [0112]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Using the Stress Plate 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Lower membrane 
                 130 
               
               
                   
                 Insulation 
                 132 
               
               
                   
                 Roof deck 
                 134 
               
               
                   
                 Stress plate 
                 136 
               
               
                   
                 Fastener (screw) 
                 138 
               
               
                   
                 Upper membrane 
                 140 
               
               
                   
                 Welded seam 
                 142 
               
               
                   
                   
               
             
          
         
       
     
         [0113]     Having described the invention with reference to its preferred embodiments, it is to be understood that modifications within the scope of the invention will be apparent to those skilled in the art.