Abstract:
As ambient conditions change around a truss structure, such as a wooden truss in an attic, webs of the truss are affected by changes of moisture and temperature in the air. As the end-grain of the webs expand and contract, a contraction and expansion management (CEM) joint minimizes unwanted expansion and contraction in the truss chord. An elastic layer such as an elastomer in the CEM joint absorbs expansion while plates around the CEM joint maintain rigidity of the chord, keeping it secure to the walls. As the moisture and temperature in the attic decrease, the end-grain of the truss returns to its original state.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the inclusion of contraction and expansion management (CEM) joints in truss structures to minimize distortion, lift, and other problems encountered with expansion and contraction of the truss structure, especially relative to the structure around the truss. 
       BACKGROUND OF THE INVENTION 
       [0002]    The extensive use of trusses in modern construction enables many structural capabilities. Trusses are used in a broad range of applications ranging from steel superstructures and commercial applications to wooden roof supports for houses. 
         [0003]    Attics of modern houses typically have trusses rather than rafters and ceiling joists. Because trusses typically are constructed from several members, trusses are susceptible to deformation from expansion and contraction. For example, as a wooden truss loses moisture over time, and as the temperature and humidity of the surrounding environment fluctuates due to changing weather conditions, the spanning member of each of the various trusses used to construct a roof will flex or bow in response to these changing environmental conditions. As these conditions fluctuate and as the spanning member begins to flex or bow, the nails or like implements which are typically relied upon to secure the truss to the various plate members of the interior walls often bend, allowing a bowing or flexing action to occur. The bowing or flexing of each of the spanning members can become significant, and often results in a bulging exceeding ½″ to about ¾″ at various points. 
         [0004]    When such bowing or flexing of one or more of these spanning members occurs, wall board or dry-wall board secured to the underside of the spanning member deforms. For example, a portion of a ceiling of an interior room is typically lifted upward. When this occurs, the tape at the joints of upper side walls is pulled outward of the joint as the ceiling wall board or dry wall is lifted upward, thus causing significant damage to the finish of the corners of the interior rooms of the dwelling and further causing an unsightly and unfinished appearance. This problem is sometimes called “truss lift” or “truss uplift.” 
         [0005]    This particular problem has been known and is described in U.S. Pat. No. 6,009,681 issued to inventor L. Kozloff. The &#39;681 patent is directed to a truss bracket for securing a spanning member of a truss to a wall plate member of an interior wall of a building such as a residential house. 
         [0006]    The &#39;681 patent describes the problem of truss members bowing or flexing. It notes that wall board or dry-wall board secured to the underside of the spanning member can deform due to fluctuations in moisture and temperature. The truss bracket of the &#39;681 is designed to more securely affix the truss chord to ceiling, thereby reducing deformation. However, this solution seeks to control rather than accommodate contraction or expansion, and over time, the bracket can come loose or cause damage to the ceiling. In some cases, damage results when the bracket causes the wall to lift along with the truss. 
         [0007]    Accordingly, there is a need for an improved device to address the problem of truss lift associated with truss member expansion and contraction. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a novel solution to truss lift and other problems associated with expansion and contraction of truss members. An anti-lift contraction and expansion management (CEM) joint is provided within the truss that accommodates expansion and contraction forces without permitting deformation of the truss. Damage to the surrounding structure resulting from truss expansion and contraction is thereby avoided. 
         [0009]    A CEM joint is included within at least one member of a truss. The CEM joint has a receptacle segment and an insertion segment. The receptacle segment may have a plate extending along a cross-section of the truss member, which acts as a stop. Next to the plate stop is an elastic layer such as an elastomer gasket. Surrounding the sides of the receptacle, and extending beyond the plate and gasket, is a plate sleeve which fits around the insertion segment. The plate sleeve may have one or more holes for receiving one or more buttons located on the insertion segment which lock the insertion segment into place once the buttons are depressed, the insertion segment is placed inside the receptacle, and the buttons are raised through the holes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a front view of a king-post truss with CEM joints. 
           [0011]      FIG. 2  is a perspective view of expansion joint in a truss member. 
           [0012]      FIG. 3  is an exploded view of expansion joint attachment mechanism. 
           [0013]      FIG. 4  is a detailed perspective view of a CEM joint receptor segment. 
           [0014]      FIG. 5  is a detailed perspective view of a CEM joint insertion segment. 
           [0015]      FIG. 6  is a front view of a W-truss with CEM joints. 
           [0016]      FIG. 7  is a perspective view of a CEM joint in a truss member. 
           [0017]      FIG. 8  is a perspective view of a CEM joint in a truss member. 
           [0018]      FIG. 9  is a lateral sectional view of a CEM joint in a truss member. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The contraction and expansion management truss device of the present invention comprises a truss having a CEM joint situated in a member of the truss. The term “expansion” as used in this written description encompasses both expansion and contraction. The CEM joint of the present invention is an expansion point comprising a receptacle segment, an insertion segment, and a means for attaching the two segments. 
         [0020]    The truss of the present invention incorporates a CEM expansion joint. Such a truss has an expansion joint situated in a member of the truss, the truss comprising: (1) at least one chord member and at least one web member; (2) an expansion joint situated in a truss member, and (3) a means for attaching the insertion segment to the receptacle segment. 
         [0021]    The expansion joint comprises a receptacle segment comprising a protective layer, an elastic layer, and a sleeve secured to the receptacle segment and extending outward. 
         [0022]    The insertion segment comprises an end portion that fits into the sleeve of the receptacle segment. 
         [0023]    The truss of the present invention may be a construction truss for a roof, a structural truss, or other truss where expansion or contraction of truss members may cause distortion of the surrounding structure. Two examples of trusses embodied in the present invention are the king-post truss ( FIG. 1 ) and W-truss ( FIG. 6 ). A truss as contemplated by this invention, for example king-post truss  1  in  FIG. 1 , has at least one chord member  2 , at least one web member  3 , and at least one CEM joint  4  situated in a truss member, preferably a truss web member  3 . Trusses particularly well suited for the resent invention include wooden construction trusses having wooden web and chord members. The number and geometry of truss members may vary, and one skilled in the art would appreciate the various ways CEM joints may be utilized in various truss geometries. Thus, the location, size, and number of truss web and chord members do not limit the claimed invention. 
         [0024]    The CEM joint  4 , as illustrated in  FIG. 2 , comprises a receptacle segment  5  and an insertion segment  6 . The CEM joint  4  is connected by a suitable attachment mechanism, such as the slot  8 , button  7 , and sleeve  10  attachment means shown in  FIG. 2 . 
         [0025]      FIG. 3  illustrates an embodiment of an unattached CEM joint  4  of the present invention, showing the attachment system in further detail additionally depicting the hole  9  in the receptacle segment  5  for the button  7 . In the embodiment illustrated in  FIG. 3 , the insertion segment  6  is slidably mounted inside the sleeve  10  of the receptacle segment  5 . 
         [0026]      FIG. 4  depicts the receptacle segment  5 . The receptacle segment  5  is connected to the truss web member  3  and has an end comprising a protective layer  14  that may serve to evenly distribute force along the cross section of the truss web member  3 . The protective layer may be a metal plate protective layer, or it may be any suitable barrier that serves to shield the end of the truss in contact with the receptacle end. 
         [0027]    The receptacle segment  5  further comprises an elastic layer  12  which is positioned between the protective layer  14  and the end portion of the insertion segment  6  shown in  FIGS. 3 and 5 . According to the embodiment of the present invention in  FIG. 4 , a sleeve  10  is located at the end of the receptacle segment  5 , positioned to fit around and secure the end portion of the insertion segment  6 . 
         [0028]    The elastic layer  12  of the receptacle segment is intended to provide a flexible barrier to unwanted expansion in the CEM joint. As the truss member expands, the CEM joint experiences the force of the insertion segment impinging on receptacle segment. The elastic layer serves to absorb this force, limit deformation, and maintain the structural integrity of the web member. Thus, in one example, the elastic layer is made of an elastic material which absorbs force from truss member expansion by contracting in the center and pushing material outwards. 
         [0029]    The elastic layer  12  may be made of any suitable material capable of absorbing forces due to expansion while maintaining the structural integrity of the truss member. For example, the elastic layer could comprise a hydraulic or pneumatic piston. In the embodiment illustrated in  FIG. 4 , the elastic layer comprises a layer of elastic polymer, preferably an elastomer, and more preferably, ethylene propylene diene M-class rubber. The chemical composition of the ethylene propylene diene M-class rubber may be optimized as suitable. Preferably, the ethylene propylene diene M-class rubber has an ethylene content from 45% to 75% by weight, and more preferably 65% to 70% by weight. 
         [0030]    Preferably, the ethylene propylene diene M-class rubber has a diene content from 3% to 12% by weight, and more preferably 5.5% to 10% by weight. 
         [0031]    The CEM joint  4  of the present invention has a means for attaching the receptacle segment  5  and insertion segment  6 . In  FIG. 3  through  FIG. 5 , the means for attaching is a system of a slot  8 , button  7 , and sleeve  10 . However, any suitable means for attaching may be used, for example a telescoping friction fitting, an accordion connector, gudgeon and pintle system, or equivalent. In one embodiment of the present invention, a pin and through-holes are employed for this purpose. The present invention is not intended to be limited by the means for attaching the segments, and one skilled in the art of structural engineering would readily substitute various equivalent attaching means suitable for use in the present invention. 
         [0032]    As further shown in  FIG. 4 , the receptacle segment  5  is situated in a truss member, preferably a truss web member  3  which may have cleats  11  located on one or more surfaces. 
         [0033]    The sleeve  10  of the receptacle segment is designed to fit around the end of the insertion segment. It may serve multiple purposes, such as: (1) acting as part of the means for attaching the two segments; (2) minimizing distortion from contraction; and (3) evenly distributing force over the cross-section of the elastic layer. In one embodiment of the claimed invention, the sleeve surrounds the end portion of the insertion segment when the two segments are attached. The sleeve may be made from any suitable material, including metal or plastic. 
         [0034]    In one embodiment of the present invention, the sleeve is not rigidly secured to the receptacle segment. Rather, it is fitted around the end of the truss member adjoining the receptacle segment, but may translate over at least a portion of the length of the truss member. In this way, the sleeve may accommodate contractive force when attached to the insertion segment of the CEM joint. When the member contracts, the CEM joint experiences forces pulling the segments away from each other. A sleeve according to this embodiment is attached to the insertion segment, but may translate across the receptacle segment, thereby accommodating the contractive forces that might otherwise stress or damage the CEM joint. However, not all CEM joints of the present invention employ a sleeve of this nature. Rather, it may be preferable to have the sleeve rigidly attached to the receptacle segment. 
         [0035]      FIG. 5  illustrates one example of the insertion segment  6  of the CEM joint of the claimed invention. The insertion segment  6  embodied in this drawing has an end portion  15  that fits into the sleeve  10  of the receptacle segment  5 . A means for attaching the receptacle segment  5  and insertion segment  6  is illustrated in  FIGS. 3 ,  4 , and  5 . The means for attaching depicted comprises a hole  9  in the sleeve  10 , and a corresponding button  7  located on the end portion  15  of the insertion segment  6 . In one embodiment of the present invention, it is preferred that the end portion  15  of the insertion segment  6  is designed to fit snugly into the sleeve  10  of the receptacle segment  5 . 
         [0036]    The button  7  may be depressed and passed through a slot  8  in the sleeve  10  of the receptacle segment  5 , as shown in  FIG. 4 , and then locked into place by extending through the hole  9 , as depicted in  FIG. 3 . The end portion  15  of the insertion segment  6  may thereby be slidably mounted into sleeve  10  and attached to the receptacle segment  5 . This system functions as a means for attaching the two segments. 
         [0037]      FIG. 6  illustrates the present invention where CEM joints  4  are mounted in a W-truss,  21 . 
         [0038]      FIG. 7  shows an embodiment of the present invention where the attaching means comprises multiple slots  8  and buttons  7 . The buttons may be attached to each other to facilitate depressing and extending the buttons  7  during attachment into the sleeve  10  of the receptacle segment  5 . 
         [0039]    It is intended by the present invention that where desirable, the CEM joints may be designed to be inserted into truss web members. In this instance, an ordinary truss may be converted to a modified contraction and expansion management CEM truss by placing CEM joints into truss web members. This may be accomplished by the designing the insertion segment  6  and receptacle segment  5  to be incorporated into the truss web member  3 . For example, the ends of the segments  5  and  6  may be adhered to the cut away ends of the web member  3 . 
         [0040]    In this example of the invention, a continuous web member  3  is prepared by cutting away or otherwise removing a portion of truss web member roughly corresponding to the size of the CEM joint  4 . 
         [0041]    Another embodiment of the present invention is depicted in  FIG. 8 . This pin CEM joint  17  is similar to previously described embodiments with the additional feature of having a pin  18  located in the sleeve  10  of the receptacle segment  5 . The pin  18  runs through a hole in the receptacle segment  5  and a corresponding hole in the insertion segment  6 . Cleats  11  may be located on one or more surfaces of the segments. 
         [0042]    Another view of the pin CEM joint  17  embodiment appears in  FIG. 9 . This is a lateral sectional view of a pin CEM joint incorporated into truss member  3 . An elastic layer  12  is situated towards the end portion  15  of the insertion segment  6 . A pin  18  is located in the sleeve  10  of the receptacle segment  5 . The pin  18  runs through a hole in the receptacle segment  5  and passes through the elastic layer  12  and a corresponding hole in the insertion segment  6 . 
         [0043]    The pin  18  can be any variety of suitable members known to those of skill in the structural engineering arts. Considerations for the pin construction include rigidity, strength, surface characteristics, and means for maintaining the pin in position. Means for maintaining the pin in position include but are not limited to secondary pins, such as cotter pins, braces, ties, clips, threads, nuts, or any other suitable means. The pin may or may not be allowed to rotate in its position and may contain one or more protective layers to limit wear on the pin surface or on any contacting surface, such as that of the elastic layer  12 . 
         [0044]    The elastic layer  12  is positioned between a protective layer  14  near the end portion of the insertion segment  6 . The protective layer  14  may serve to distribute stresses on the receptacle segment  5 . 
         [0045]    The expansion joint in this example has an approximately constant cross-sectional area along the length of the expansion joint and has approximately the same cross-sectional area as the truss web. However, other embodiments of the claimed invention may have cross-sectional areas that vary substantially. 
         [0046]    The present invention may incorporate various types, sizes and shapes of trusses. Indeed, trusses for various purposes are made in various shapes, sizes and materials. In the context of residential construction, trusses are often prefabricated structural assemblies that support the roof and top floor ceilings. Trusses have been used in place of older roof framing. Most commonly, trusses are triangular and include cross members fastened with gusset plates. However, the present invention may be employed in other trusses, such as trapezoidal trusses or rectangular trusses. 
         [0047]    The many features and advantages of the present invention are apparent from the written description and thus, it is intended by the claims to cover all such features and advantages of the invention. Further, since numerous modifications and changes will readily become apparent to those skilled in the art, it is not desired to limit the invention to the exact construction and operation as illustrated or described. Hence, all suitable modifications and equivalents may be resorted to as falling within the scope of the invention.