Abstract:
A take up device for a building structure, e.g. holdown for securing the building structure to a foundation, has a housing secured by fasteners to the building structure, the housing defining a cylindrical chamber containing a piston and fluid, with a piston rod projecting from the housing. The piston rod is connected to a foundation anchor, and a fluid passage interconnects portions of the cylindrical chamber at opposite sides of the piston. The fluid passage is provided with a one-way valve, which allows the housing to move upwardly relative to the piston, to maintain the tightness of the connection to the anchor bolt, but resists opposite movement of the housing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to take up devices for use in building structures and is useful in particular, but not exclusively, holdowns for reinforcing building structures against seismic vibrations and hurricane damage.  
           [0003]    2. Description of the Related Art  
           [0004]    Holdowns are used in wood frame building structures in order to secure the structures to their concrete foundations. For this purpose, conventional holdowns are made of sheet metal and are secured by nails, bolts and other fasteners to the wooden components of the building structure and by anchor bolts to the concrete foundations of the buildings.  
           [0005]    It is found, in practice, that nuts securing the holdowns to the anchor bolts tend to become loose, after a period of time, as a consequence of wood shrinkage due to drying and, also, due to vibration of the building structure caused by seismic activity.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    It is, therefore, an object of the present invention to provide a novel and improved take up device for building structures which will counteract such loosening of the securing nuts.  
           [0007]    According to the present invention, there is provided a take up device which comprises a housing secured by fasteners to a building structure, the housing defining a cylindrical chamber containing a piston and a fluid, i.e. a liquid or a gas, with a piston rod projecting from one or both ends of the housing. One end of the piston rod is connected to a foundation anchor, and a fluid passage interconnects portions of the cylindrical chamber at opposite sides of the piston. The fluid passage is provided with a one-way valve.  
           [0008]    In use, the one-way valve allows the housing to move in one direction, i.e. toward the anchor member, relative to the piston in order to maintain a tight connection between the housing and the anchor. This tightening movement counteracts any compression of the wooden components of the building structure. However, the one-way valve counteracts flow of the fluid in the opposite direction through the fluid passage so as to prevent loosening of this connection.  
           [0009]    The present take up device may be used as a holdown or part of a holdown, e.g. for securing a building structure to a foundation, or as a take up device between e.g. horizontally or vertically adjacent building components.  
           [0010]    In a preferred embodiment of the invention, the fluid passage is formed by a clearance between the piston and the wall of the cylindrical chamber, and the one-way valve comprises an annular seal between the piston and the cylinder wall.  
           [0011]    To allow the present device to act as a dampener, e.g. for dampening seismic vibrations of the building structure, a further fluid flow passage may be provided, e.g. through the piston or bypassing the piston, to allow relaxation of the connection.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will be more readily understood from the following description of preferred embodiments thereof given, by way of example, with reference to the accompanying drawings, in which:— 
         [0013]    [0013]FIG. 1 shows an exploded view, in perspective, of a holdown according to a first embodiment of the present invention;  
         [0014]    [0014]FIG. 2 shows a view in perspective of components of the holdown of FIG. 1;  
         [0015]    [0015]FIG. 3 shows a view in perspective of a piston and an annular seal forming parts of the holdown of FIG. 1;  
         [0016]    [0016]FIG. 3A shows a view taken it in cross-section through the annular seal of FIG. 3 along the line  3 A- 3 A of FIG. 3;  
         [0017]    [0017]FIGS. 4 and 4A show views corresponding to those of FIGS. 3 and 3A, but of a modified annular seal;  
         [0018]    [0018]FIGS. 5 and 5A show views in vertical cross-section through a housing, a piston and a one-way valve forming components of the holdown of FIG. 1;  
         [0019]    [0019]FIGS. 6 and 7 show views corresponding to that of FIG. 5 but illustrating modifications of the holdown components of FIG. 5;  
         [0020]    [0020]FIG. 8 shows a view in perspective of the holdown of FIG. 1 in an assembled condition;  
         [0021]    [0021]FIGS. 9 and 9A show views corresponding to that of FIG. 8, but illustrating modifications of the holdown of FIG. 8;  
         [0022]    [0022]FIG. 10 shows a broken-away view, in perspective, of another modification of the holdown of FIG. 1;  
         [0023]    [0023]FIGS. 11 and 12 shows views in perspective of two further modifications of the holdown of FIG. 1, in a partly exploded condition;  
         [0024]    [0024]FIGS. 13 and 14 show, respectively, a view in perspective of the holdown of FIG. 1 with added components and a broken-away view in side elevation of an application of that holdown;  
         [0025]    [0025]FIGS. 15 through 22 show views corresponding to those of the FIGS. 13 and 14, but illustrating different applications of the holdown according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    As shown in FIG. 1, a holdown indicated generally by reference numeral  10  has a housing  12  provided with a housing cover  14 , which is secured to the housing  12  by screws  15 .  
         [0027]    A piston  16  on a piston rod  18  is located in a cylindrical chamber  20  (FIG. 5) in the housing.  12 . The cylindrical chamber  20  is closed at one end by the housing cover  14  and, at its opposite end, by a wall  22  of the housing. The housing cover  14  has a cylindrical recess accommodating a bushing  24 , and the wall  22  has a cylindrical recess accommodating a bushing  26 . The piston rod  18  extends in opposite directions from the piston  16  through the bushings  24  and  26 , and has opposite threaded ends  28  and  30 .  
         [0028]    The outer diameter of the piston  16  is less than the inner diameter of the cylindrical chamber  20 , so that a clearance  31  (FIGS. 5 and 5A) is provided between the periphery of the piston  16  and the cylindrical wall of the cylindrical chamber  20 . An annular seal  32  extends around the periphery of the piston  16  and provides a seal between the piston  16  and the wall of the cylindrical chamber  20 , as described in greater detail below. More particularly, and as shown in FIG. 3A, the annular seal  32  has a U-shaped cross-section comprising limbs  34  and  35  connected by an intermediate portion  36 . The limb  34 , which is the outermost limb, is normally in sealing contact with the cylindrical wall of the cylindrical chamber  20 , and the inner limb  35  is in sealing contact with the piston  16 .  
         [0029]    [0029]FIGS. 4 and 4A show a modified O-ring  38 , which has first and second limbs  39  and  40 , extending toward one side of the O-ring  38 , which are in sealing contact with the cylindrical wall and the piston  16 , respectively, and third and fourth limbs  42  and  43  extending oppositely from the limbs  39  and  40 , and sealingly contacting the cylinder wall. The O-ring  38  of FIGS. 4 and 4A is used instead of the O-ring  32  on the piston  16 , as shown in FIG. 6 and described in greater detail below.  
         [0030]    As can be seen in FIG. 5, the piston  16  has an annular intermediate surface  46 , which is cylindrical, between an annular peripheral projection  48 , forming a shoulder on the piston  16 , and a frustoconical surface  50 , which tapers convergently from the annular intermediate surface  46 . The modified annular seal  38 , as shown, in FIG. 6, extends around the annular intermediate surface  46 , with its limbs  39  and  43  in sealing contact with the annular intermediate surface  46 .  
         [0031]    Referring again to FIG. 1 of the accompanying drawings, the holdown  10  is provided with inlet openings  52  and  54  which are provided with threaded plugs  55  and through which a fluid is introduced into the cylindrical chamber  20  at opposite sides of the piston  16 . The opening  52  is provided in the housing  12 , and communicates directly with the cylindrical chamber  20 , while the opening  54  is provided in the housing cover  14  and communicates with the cylindrical chamber  20  through an axial passage  56  in the housing cover  14 .  
         [0032]    In operation of the holdown  10 , as it has so far been described, the piston is able to move along the cylinder  20  toward the housing cover  14 , e.g. in response to shrinkage of the wooden building components secured by the holdown  10  as described below, so that the housing  12  is able to move relative to the piston  16  toward the end  30  of the piston rod  18 . When this occurs, the pressure of the fluid in the portion of the cylindrical chamber  20  between the piston and the housing cover  14  causes some of the fluid to flow through the clearance  31  between the piston  16  and the wall of the cylindrical chamber  20 , thereby causing the annular seal  32  to be dislodged from the annular intermediate surface  46  to the frustoconical surface  50 , as shown in FIG. 5A. When this occurs, the annular seal  32  no longer provides a seal between the piston  16  and the wall of the cylindrical chamber  20 .  
         [0033]    When, however, the piston  16  is urged in the opposite direction, i.e. toward the end wall  22  of the housing  12 , the fluid in the portion of the cylindrical chamber  20  between the piston  16  and the wall  22  of the housing presses the annular seal  32  back onto the annular intermediate surface  46  and into sealing contact with the piston  16  and the wall of the cylindrical chamber  20 . Consequently, the displacement of the piston  16  in this direction is counteracted by the pressure of the fluid between the piston  16  and the housing wall  22 .  
         [0034]    Therefore, the annular seal  32  serves as a one-way valve, which allows the piston  16  to be displaced in one direction relative to the housing  20  but which counteracts, or even prevents, displacement of the housing  12  in the opposite direction relative to the housing  20 .  
         [0035]    The piston  16  is also formed with a further annular peripheral projection  52 , toward which the frustoconical surface  50  tapers. This further annular peripheral projection  52  serves to retain the annular seal  32  on the piston  16  when the seal is displaced, as described above, from the annular intermediate surface  46  to the frustoconical surface  50 .  
         [0036]    [0036]FIG. 6 shows a modification of the piston  16 , which is indicated by reference numeral  60 . The piston  60  differs from the piston  16  in that the piston  60 , which is otherwise the identical to the piston  16 , is formed with a boring  62  extending through the piston  60 , parallel to the longitudinal axis of the piston rod  18 . This boring  62  provides a further fluid flow passage interconnecting the portions of the cylindrical chamber  20  at opposite sides of the piston  16 , and allows a restricted flow of the fluid past the piston  16 . In this embodiment of the present invention, the annular seal  32  is replaced by the annular seal  38 .  
         [0037]    By this means, the piston  16  is enabled to move gradually toward the housing wall  22 . Consequently, when this modified piston  60  is substituted for the piston  16  in the holdown  10 , the latter acts as a dampener.  
         [0038]    [0038]FIG. 7 illustrates a further modified piston, indicated by reference numeral  64 , which is identical to the piston  60  of FIG. 6 except that the piston  64  is additionally provided with a flow control screw  66 , in the form of a grub screw, which can be screwed into a correspondingly threaded opening  68  in the piston  64 . When thus inserted into the piston  64 , the flow control screw  66  can be adjusted so as to obstruct, to a greater or lesser extent, the cross-sectional area of the boring  62  and, thus, so as to adjustably restrict the flow of fluid through this further flow passage and, thereby, to control the damping effect of the piston  64 .  
         [0039]    [0039]FIG. 8 shows a view in perspective of the holdown  10  of FIG. 1 in an assembled condition.  
         [0040]    [0040]FIG. 9 shows a view corresponding to that of FIG. 8 but illustrating a modification of the holdowns of FIGS. 6 and 7, indicated generally by reference numeral  10 A, in which the piston  16  is provided, i.e. the piston lacks the further flow passage formed by the boring  62  in the piston  60  or  64 , but in which the opposite sides of the piston  16  are instead interconnected by a further flow passage extending through a tube  70  at the exterior of the housing. The tube  70  is provided with a check valve  69  controlling flow through the tube  70 .  
         [0041]    [0041]FIG. 9A shows the holdown of FIG. 9 modified by the provision of an adjustment screw  71 , which can be screwed into the check valve  69  to a greater or lesser extent in order to correspondingly adjust the flow through the tube  70 .  
         [0042]    FIGS.  10  to  12  show further modifications  10 B,  10 C and  10 D of the holdown  10 , in which flow passages within the housings of the modified holdowns interconnect the portions of the cylindrical chambers at opposite sides of the pistons.  
         [0043]    In FIG. 10, an auxiliary chamber  72  communicates through openings  74  and  76  with opposite sides of the piston.  
         [0044]    In FIG. 11, a modified piston rod  16 C projects downwardly from the holdown  10 C but does not project upwardly through a cover  14 C of a housing  12 C. A spring (not shown) is provided between the piston  16 C and the housing  12 C. An auxiliary chamber  78 , corresponding to the chamber  72  of FIG. 10, interconnects opposite sides of piston  16 C.  
         [0045]    The holdown  10 D of FIG. 12 is similar to the holdown  10 C except that, as shown in FIG. 12, the upper end  28  of the piston rod  18  projects through housing cover  14 D.  
         [0046]    [0046]FIG. 13 shows the holdown  10  mounted on a pair of parallel elongate support blocks  100 , which are provided with through-openings  102  for receiving fasteners, for example screws (not shown). In FIG. 14, the holdown  10  of FIG. 13, together with its support blocks  100 , is shown mounted on the top of a building structure indicated generally by reference numeral  104  at the top of the building structure  105 . The fasteners (not shown) extend through the support blocks  100  so to secure the holdown  10  to the top of a plate  104 . The piston rod  18  thus extends vertically, and its lower threaded end  30  is connected through a plurality of connecting rods  106  and couplings  108  to an anchor bolt  110 , which is secured in a concrete foundation  112 .  
         [0047]    Two further holdowns  10  are shown in FIG. 14, which are interconnected between two of the couplers  108  and plates  109  on joists  111  at intermediate floors of the building structure  105 . However, these two further holdowns  10  may be omitted if not required.  
         [0048]    [0048]FIG. 15 shows the holdown  10  secured to one face of a vertical metal plate  112 , formed with bolt holes  113 , with a support block  114 , which is fixed to the plate  112 , underlying the housing  12  of the holdown  10 . A plurality of such holdowns  10 , each provided with a respective vertical plate  112 , can then be bolted to vertical studs  116  of building structure, as shown in FIG. 16, and connected between the uppermost holdown  10 , which is similar to that of FIG. 13, and the anchor bolt  110 .  
         [0049]    [0049]FIG. 17 shows the holdown  10  secured to a pair of a vertical metal plates  120 . As shown in FIG. 18, these vertical plates can then be secured by nuts  122  and bolts  123  between a pair of studs  124 , with the bolts  123  extending through bolt holes  126  in the plates  120  and through the studs  124 , the holdown  10  being connected between the anchor bolt  110  and the lower end  30  of the piston rod  18  by one of the couplers  108 . The upper end  28  of the piston rod  18  is connected by a further coupler  108  and connecting rod  106  to an overlying holdown (not shown).  
         [0050]    [0050]FIG. 19 shows the holdown  10  mounted on a conventional sheet metal holdown indicated generally by reference numeral  130 . The holdown  130  is secured to a pair of studs  132  by a pair of bolts  134 , each provided with a nut  136  and a washer  138  (FIG. 20). The holdown  10  is mounted on an intermediate portion  140  of the holdown  130  extending between opposite sidewalls  142  and is connected by coupler  108  to the anchor bolt  110 .  
         [0051]    [0051]FIG. 21 shows a further arrangement of the holdown  10 , which in this case is mounted between a pair of identical elongate rectangular plates  150 , to which the housing  12  of the holdown  10  is attached by welding or otherwise. The plates  150  are formed with circular openings  152 , which are connected through tubes  154  welded or otherwise attached to the plates  150 .  
         [0052]    As shown in FIG. 22, the holdown  10  together with the plates  150  are located between a pair of wooden studs  156 , with bolts  158  extending through the studs  156  and through the tubes  154  and secured by nuts  160 . The holdown  10  is again connected through coupler  108  to the anchor bolt  110 .  
         [0053]    The fluid provided in the holdowns according to the present invention may be hydraulic fluid or any suitable inert gas.  
         [0054]    As will be apparent to those skilled in the art, various modifications may be made in the above described invention within the scope and spirit of the accompanying claims.