Abstract:
A text fixture apparatus for testing structures with a compression testing machine. The test fixture apparatus includes a support plate assembly and a load plate assembly. The support plate assembly includes two parallel support plates and has sloped surfaces to support a first and second structures and angles of equal magnitude and opposite slope. The load plate assembly is configured to oppose the support plate assembly, includes at least one load plate, and allows the load plate assembly to apply a load to the structures in response force on the support plate assembly, load plate assembly, or a combination thereof in a direction other than perpendicular to the sloped surfaces. A vertical force applied by the assemblies results in substantially equal and opposite horizontal components of force on the first structure and the second structure. Methods of testing and of making the apparatus are provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Patent Application No. 61/671,177, filed Jul. 13, 2012, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    Embodiments disclosed herein relate generally to testing of structures, and more particularly may relate to fixtures for applying a load to structures with a compression-type machine. 
       BACKGROUND 
       [0003]    Trench drains often have a grate across their top opening that must support loads that may include heavy vehicles. Grates are currently tested to certain industry standards, such as those promulgated by the American Association of State Highway and Transportation Officials (AASHTO) in AASHTO M306 “Standard Specification for Drainage, Sewer, Utility, and Related Castings.” Current testing equipment includes proof load compression machines, also referred to as test presses, which may have a static upper platen and a vertically moveable, hydraulically driven lower platen. With such a machine, when a component is to be tested, the component is placed on the lower platen, the lower platen is raised until the component contacts the bottom surface of the top platen, and then the compression test is performed. 
         [0004]    Current testing machines and apparatus, however, generally impart only a load that is perpendicular to the surface of the tested grate, which may be a vertical load. Actual dynamic loads encountered, such as when a tire impacts the grate in use, also include a horizontal component. Thus, a need exists for a test apparatus that applies a load to a grate at an angle of other than 90 degrees to simulate actual use. 
       SUMMARY 
       [0005]    In accordance with one embodiment disclosed herein, a text fixture apparatus for testing first and second structures with a compression testing machine is provided. The test fixture apparatus includes a support plate assembly and a load plate assembly. The support plate assembly includes two spaced, parallel support plates in fixed relation and parallel to a first central longitudinal plane. The support plate assembly also has sloped surfaces associated with each support plate to support the first structure at a first angle relative to horizontal and the second structure at a second angle relative to horizontal, with the first angle and the second angle being of equal magnitude and opposite slope. The load plate assembly is configured to oppose the support plate assembly. The load plate assembly includes at least one load plate parallel to a second central longitudinal plane, and is configured to allow the load plate assembly to apply a load to the first structure and to the second structure in response to application of force to the support plate assembly, load plate assembly, or a combination thereof in a direction other than perpendicular to the sloped surfaces. 
         [0006]    In some such embodiments, the test fixture apparatus further includes a first load contact plate having a first surface and a second load contact plate having a second surface. The first load contact plate and the second load contact plate are each mounted to the at least one load plate. When the load plate assembly opposes the support plate assembly with the first and second structures disposed therebetween and the first and second central longitudinal planes are parallel and in vertical alignment, the first surface of the first load contact plate is oriented at the first angle relative to horizontal and the second surface of the second load contact plate is a oriented at the second angle relative to horizontal. In some such embodiments, the first load contact plate and the second load contact plate each have a width that is transverse to the second central longitudinal plane and that is less than the distance between the support plates. In some embodiments and in combination with any of the above embodiments, the test fixture apparatus also includes at least one buffer plate adjacent to the first surface of the first load contact plate and at least one other buffer plate adjacent to the second surface of the second load contact plate. 
         [0007]    In some embodiments and in combination with any of the above embodiments, the support plates are spaced by a distance transverse to the first central longitudinal plane that permits rails of the first structure to be received by the sloped surfaces that are at the first angle and rails of the second structure to be received by the sloped surfaces that are at the second angle. In some such embodiments, the rails of the first structure and the rails of the second structure are parallel to the support plates. 
         [0008]    In some embodiments and in combination with any of the above embodiments, the sloped surface at the first angle and the sloped surface at the second angle associated with each support plate terminate proximate to each other with a stop disposed therebetween. In some such embodiments, the stop includes a protrusion configured to separate the first structure and the second structure. 
         [0009]    In some embodiments and in combination with any of the above embodiments, the sloped surface at the first angle and sloped surface at the second angle associated with each support plate slope downward from each respective outer end of the support plate toward a central portion of the support plate to terminate proximate to each other. 
         [0010]    In some embodiments and in combination with any of the above embodiments, the sloped surfaces at the first angle and sloped surfaces at the second angle on each support plate slope upward from each respective outer end of the support plate toward a central portion of the support plate to terminate proximate to each other. 
         [0011]    In some embodiments and in combination with any of the above embodiments, when the load plate assembly opposes the support plate assembly with the first central longitudinal plane parallel and in vertical alignment with the second central longitudinal plane, and with the first structure and the second structure disposed therebetween, a vertical force applied results in substantially equal and opposite horizontal components of force on the first structure and the second structure. 
         [0012]    In some embodiments and in combination with any of the above embodiments, the at least one load plate includes two spaced, parallel support plates in fixed relation. 
         [0013]    In accordance with another embodiment disclosed herein, another test fixture apparatus for testing first and second structures with a compression testing machine is provided, The apparatus includes a support and a load assembly. The support has sloped surfaces configured to support the first structure at a first angle relative to horizontal and the second structure at a second angle relative to horizontal, the first angle and the second angle being of equal magnitude and opposite slope. The load assembly is configured to oppose the support, and includes at least one load member configured to allow the load assembly to apply a load to the first structure and to the second structure in response to application of force to the support, load assembly, or a combination thereof in a direction other than perpendicular to the sloped surfaces, and a first load applying portion having a first surface and a second load applying portion having a second surface. 
         [0014]    In some such embodiments, when the load assembly opposes the support with the first and second structures disposed therebetween, the first surface of the first load applying portion is oriented at the first angle relative to horizontal and the second surface of the second load applying portion is oriented at the second angle relative to horizontal, and a force applied in a direction that substantially bisects the angle formed by the sloped surfaces results in substantially equal and opposite horizontal components of force on the first structure and the second structure. In some such embodiments, each sloped surface at the first angle terminates proximate to a corresponding sloped surface at the second angle with a stop disposed therebetween. In some such embodiments, the stop includes a protrusion configured to separate the first structure and the second structure. 
         [0015]    In some embodiments and in combination with any of the above embodiments, the sloped surfaces are spaced by a distance that are configured to permit rails of the first structure to be received by the sloped surfaces that are at the first angle and rails of the second structure to be received by the sloped surfaces that are at the second angle, wherein the rails of the first structure and the rails of the second structure are parallel to each other. 
         [0016]    In accordance with another embodiment disclosed herein, a method of testing first and second structures using a test fixture is provided. The method includes placing the first structure on a support that supports the structure at a first angle relative to horizontal and placing the second structure on the support, the support supporting the second structure at a second angle relative to horizontal of equal magnitude and opposite slope to the first angle. A load is applied to the first structure in a first direction and to the second structure in a second direction until reaching a failure mode of at least one structure. In some such embodiments, applying the load to the first structure in a first direction includes applying a load through a first plate having a surface parallel to the first angle and applying the load to the second structure in a second direction includes applying a load through a second plate having a surface parallel to the second angle. 
         [0017]    In some embodiments and in combination with any of the above embodiments, the first structure and the second structure are grates each having a top and a bottom, each grate including parallel rails and cross-bars extending therebetween, and further including applying force in a second direction to the bottom of the rails with the support and applying force in an opposite third direction to the cross-bars. 
         [0018]    In some embodiments and in combination with any of the above embodiments, placing the first structure on a support and placing the second structure on the support includes placing the first structure and the second structure on a support plate assembly including two spaced, parallel support plates in fixed relation and parallel to a first central longitudinal plane. The support plate assembly has sloped surfaces associated with each support plate to support the first structure at a first angle relative to horizontal and the second structure at a second angle relative to horizontal, the first angle and the second angle being of equal magnitude and opposite slope. Applying a load to the first structure in a first direction and to the second structure in a second direction includes applying a load to a load plate assembly that is configured to oppose the support plate assembly. The load plate assembly includes at least one load plate parallel to a second central longitudinal plane and is configured to allow the load plate assembly to apply a load to the first structure and to the second structure in response to application of force to the support plate assembly, load plate assembly, or a combination thereof in a direction other than perpendicular to the sloped surfaces. 
         [0019]    In accordance with another embodiment disclosed herein, a method of making a test fixture for testing first and second structures is provided. The method includes assembling two support plates to be spaced, parallel, and in fixed relation, each support plate having sloped surfaces to support the first structure at a first angle relative to horizontal and the second structure at a second angle relative to horizontal, the first angle and the second angle being of equal magnitude and opposite slope. Two load plates are assembled to be spaced, parallel, and in fixed relation. A load contact plate is mounted to each load plate, with the load contact plates configured to apply a load to the first structure and to the second structure in response to application of force to the support plates, load plates, or a combination thereof in a direction other than perpendicular to the sloped surfaces. In some such embodiments, assembling the support plates includes attaching the support plates to each other with elongated threaded fasteners and nuts. In some such embodiments, assembling the load plates includes attaching the load plates to each other with elongated threaded fasteners and nuts. In some such embodiments, mounting load contact plates to the load plates includes attaching the load contact plates to the load plates with threaded fasteners. In some such embodiments, the method includes varying the spacing of the support plates and the load plates with use of varying length threaded fasteners and varying width load contact plates to accommodate varying width structures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    For a more complete understanding, reference should now be had to the embodiments shown in the accompanying drawings and described below. In the drawings: 
           [0021]      FIG. 1  shows an exemplary installation of grates on trench drains. 
           [0022]      FIG. 2  shows another exemplary installation of grates on trench drains. 
           [0023]      FIG. 3  shows a perspective view of a dynamic test fixture according to one embodiment. 
           [0024]      FIG. 4  shows a front elevation view of the dynamic test fixture of  FIG. 3 ; the rear elevation view is identical. 
           [0025]      FIG. 5  shows a top plan view of the dynamic test fixture of  FIG. 3 . 
           [0026]      FIG. 6  shows a left end elevation view of the dynamic test fixture of  FIG. 3 ; the right end elevation view is identical. 
           [0027]      FIG. 7  shows an exploded perspective view of a load plate assembly of the dynamic test fixture of  FIG. 3 . 
           [0028]      FIG. 8  shows a perspective view of separated load plate assembly and support plate assembly components of the dynamic test fixture of  FIG. 3 , with trench drain grate test structures. 
           [0029]      FIG. 9  shows a perspective view of the load plate assembly and the support plate assembly of the dynamic test fixture of  FIG. 3 , with trench drain grate test structures in place in the fixture. 
           [0030]      FIG. 10  shows a front elevation view of the dynamic test fixture of  FIG. 3  with trench drain grate test structures in place in the fixture. 
           [0031]      FIG. 11  shows a perspective view of the dynamic test fixture of  FIG. 3  positioned in a proof load compression machine. 
       
    
    
     DESCRIPTION 
       [0032]    The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments. Other embodiments having different structures and operation do not depart from the scope of the present disclosure. 
         [0033]    Certain terminology is used herein for convenience only and is not to be taken as a limitation on the embodiments described. For example, words such as “top”, “bottom”, “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” and “downward” merely describe the configuration shown in the figures. Indeed, the referenced components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. Throughout this disclosure, where a process or method is shown or described, the method may be performed in any order or simultaneously, unless it is clear from the context that the method depends on certain actions being performed first. 
         [0034]    Referring to the drawings, where like reference numerals refer to the same or similar parts,  FIG. 1  shows an example of parallel trench drains  30  with grates  32  at the top of the drains. The grates  32  have parallel rails  34  resting on support surfaces formed at the upper ends of the trench drains  30  and may have cross-bars  36  or other features between and connecting the rails  34 .  FIG. 2  shows another example of parallel trench drains and grates  32  at an airport, where large dynamic loads may be experienced by the grates  32  from aircraft and other heavy vehicles. 
         [0035]      FIGS. 3-6  show an embodiment of a dynamic test fixture  40 . The fixture  40  may include a support plate assembly  42 , or support, and a load plate assembly  44 , or load assembly. The assemblies  42 ,  44  are not connected to each other in this embodiment, but are shown in their relative positions as they may be situated on a conventional compression testing machine with grates  32 , or structures, positioned between them. The support plate assembly  42  may include parallel, spaced support plates  46 ,  48  that may also be parallel to a central longitudinal plane of the support plate assembly  42 . The support plates  46 ,  48  are secured to each other by support plate spacer rods  50 , which may be elongated threaded fasteners such as bolts, of which there are six in this embodiment of a support plate assembly  42 . The support plate spacer rods  50  hold the support plates  56 ,  58  in place with nuts  52  on each side of each support plate  46 ,  48 . The spacing of the support plates  46 ,  48  is set such that the rails  14  of the grates rest on the left and right sloped surfaces  56 ,  58  of the support plates  46 ,  48 . The support plates  46 ,  48  have a top surface that is symmetrically angled on a left sloped surface  56  and a right sloped surface  58  to be shaped substantially like a “V” such that the slopes may be equal in magnitude and have opposite slope. The left and right sloped surfaces  56 ,  58  may be at an angle θ relative to horizontal ( FIG. 3 ). 
         [0036]    At the central lower portion of the top surface, between the left and right sloped surfaces  56 ,  58 , a protrusion that is a center stop  60  may be provided. Each of the left and right sloped surfaces  56 ,  58  may be configured to receive and support a section of grate (not shown) to be tested. The grates may be placed on the left and right sloped surfaces  56 ,  58  to abut a center stop  60 . The stop  60  may extends upward from the region where the sloped surfaces  56 ,  58  would intersect absent the stop  60 , proximate to where the sloped surfaces terminate at a central portion of the support plate assembly  42 , and separates the ends of the grates  32 . 
         [0037]    Also as shown in  FIG. 7 , the load plate assembly  44  may include at least one, and in the embodiment shown, two parallel, spaced load plates  70 ,  72 , or load members, that are parallel to a central longitudinal plane of the load plate assembly  44 . Each load plate  70 ,  72  has a top surface  74  and, on angled left and right lower sides, load contact plates  80 ,  82  or load applying portions that are attached to the load plates  70 ,  72 . In one method attachment the load contact plates  80 ,  82  are attached to the respective load plates  70 ,  72  with plate-retaining screws  84 , which may be countersunk into the load contact plates  80 ,  82 . The load plates  70 ,  72  may be held together with a centered load plate clamp rod  86 , which may be an elongated threaded rod such as a bolt held in place with nuts  52  on each side of the load plates  70 ,  72 , and the attached load contact plates  80 ,  82 . The load contact plates  80 ,  82  do not necessarily contact the grates  32 , as one or more of buffer plates  90 ,  92  may be provided on and adjacent to the bottom surfaces of the respective load contact plates  80 ,  82 ; in this embodiment two are shown on each load contact plate  80 ,  82 . 
         [0038]    The bottom surfaces of the load contact plates  80 ,  82  and accordingly the bottom surfaces of the buffer plates  90 ,  92 , are configured to be parallel to the left and right sloped surfaces  56 ,  58  of the support plates  46 ,  48  when the load plate assembly  44  is positioned centered over and in longitudinal alignment with the support plate assembly  42 , as shown in  FIG. 4 , with the respective central longitudinal planes parallel and in vertical alignment. Accordingly, a first surface of the first load contact plate  80  and a second surface of the second load contact plate  82  are at angle θ relative to horizontal. As shown in  FIG. 5 , the load plate assembly  44  is narrower than the support plate assembly  42 , as necessitated by the requirement to apply a load to the grates  32  between the rails  34  as opposed to on the rails  34 . 
         [0039]    The entire fixture  40 , except for the buffer plates  90 ,  92 , may be, for example, fabricated from steel. In one embodiment where the width of a grate  12  is 12 inches or more, the load contact plates  80 ,  82  may be 9 inch by 9 inch plates. In other embodiments where the width or the grate is 12 inches or less, the load contact plate  80 ,  82  may be 75% of the trench width wide by 9 inches long. The buffer plates  90 ,  92  may be, for example, wood, and in one embodiment the buffer plates  90 ,  92  may be oriented strand board (OSB). OSB may provide distributed loading, which is desirable for simulating the load presented by a vehicle tire; other materials may be as selected by one of ordinary skill in the art. The buffer plates  90 ,  92  shown are not connected to each other or to the load contact plates  80 ,  82 , but in one embodiment could be held in place with double face tape for convenience. One purpose of the buffer plates may be to avoid high stress point contacts and to better retain a distributed load pattern on the grates, instead of converting into a double line load upon grate deflection during testing. 
         [0040]      FIGS. 8-10  show the test fixture  40  with grates  32 . Two grates  32 , which may be an embodiment of test structures or structures, may be placed on the support plate assembly  42  to allow the fixture  40  to function properly, as in this embodiment there needs to be load applied from both load contact plates  80 ,  82  and resisted on both the left and right sides of the support plate assembly  42 . The rails  14  could be parallel and continuously supported by the sloped surfaces  56 ,  58 , as shown, or in another arrangement could, for example, be positioned transverse to the sloped surfaces  56 ,  58 . In the embodiment shown, horizontal components of the force applied by the load contact plates  80 ,  82  offset, or substantially offset, each other as the horizontal component of the force applied by one load contact plate  80  is equal to or substantially equal to the horizontal component of the force applied by the other load contact plate  82  and in the opposite direction. Alternatively, one of the two grates  32  could be replaced with a blank, for example, a plate, if only one grate  32  is desired to be tested. The plate would be the same thickness as the grate  32  to provide proper load distribution. 
         [0041]    In the embodiment shown, the fixture  40  is configured to accommodate a grate that is 34 inches wide and 0.5 m long. In one embodiment, the support plates  46 ,  48 , the load plates  70 ,  72 , and the load contact plates  80 ,  82  may be 1 inch thick, and the buffer plates  90 ,  92  may be 0.875 inches total thickness, but the thicknesses and dimensions may be designed to be compatible with the grate to be tested. The support plate spacer rods  50  and the load plate clamp rod  86  may be, for example, 0.75-inch diameter. The angle θ of the left and right sloped surfaces  56 ,  58  of the support plates  46 ,  48  may vary from that shown as needed to approximate the horizontal component of force expected to be experienced at a site of use of the grate  32 . 
         [0042]    A test fixture  40  with structures  32  that are grates is shown in  FIG. 11  on a compression machine, with the fixture  40  positioned between the upper platen  100  and the lower platen  102 . An example of one procedure for use of the fixture  40  and testing of a grate  32  may be as follows. First, the support plate assembly  42  is configured to provide proper support for the grate&#39;s side rails  34 . Proper support is achieved by setting the spacing of the support plates  46 ,  48  with the support plate rods  50  to a width that accepts and will continuously support the rails  34 . Then the correct width load contact plates  80 ,  82 , as appropriate for the width of grate  32  being tested as described above, are installed in the load plate assembly  44 . The support plate assembly  42  may secured in the middle of the test press lower platen using means available with the test press, such as a clamp. Identical grates  32  are then placed on both sides of support plate assembly  42 , being the left sloped surface  46  and the right sloped surface  48 , and the grates  32  are slid longitudinally until the end of the grates  32  rest against the center stop  60 . The offsetting horizontal components of force on the grates  32  helps to maintain only a vertical force on the compression machine, which generally is not designed to withstand lateral forces. 
         [0043]    A test fixture  40  with grate test structures  32  is shown in  FIG. 11 . The load plate assembly  44  is positioned such that it contacts both grates  32  centrally and equally. The load plate assembly  44  should not be secured to the test press upper platen  100  so that the load plate assembly  44  is free to equalize under a load. A load is then applied to the grates  32  until reaching a specified failure mode using, for example, the same test parameters as used in AASHTO M306 procedures. The application of the load may be at a specified acceleration, which in the embodiment shown is 0.7 g. In some embodiments, the specified failure mode may be first failure. The test may be stopped at the first failure minimize lateral test loads on the test press. First failure may be, for example, breakage of a cross-bar  16  of the grate  32 . However, if the load plate assembly  44  has a relatively high freedom of movement or the test presses are built to better resist lateral loads, the first failure criterion would not be an important or limiting factor with respect to testing to additional failure modes. 
         [0044]    It is understood that instead of being oriented with an upper platen  100  being oriented above a lower platen  102 , the compression machine and test fixture  40  could be oriented at any angle, for example, with the force being applied through the platens horizontally rather than vertically and the test fixture  40  likewise rotated 90 degrees. 
         [0045]    Force Vector Math may be used to determine how the test load is divided into the vertical load and the horizontal load on the grate. The actual longitudinal load at failure may be calculated using trigonometric functions and based upon the fixture configuration and the applied press load. The longitudinal load is the component of the load along the direction parallel to the rails of the grate. For example, if the angle θ is 35 degrees, and the load at first failure is 100,000 lbs., then the longitudinal load at failure is calculated as 100,000 lbs.×tan 35°=70,000 lbs. 
         [0046]    Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art appreciate that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown and that the embodiments herein have other applications in other environments. For example, the fixture  40  is shown and described above as configured for applying a longitudinal load component (in the direction parallel to the rails  34  of the grates  32  along with a vertical component. However, by rotating the grate and the load and support members 90 degrees, the concept is also applicable to testing of combined transverse and vertical loads as well. Instead of the sloped surfaces  56 ,  58  substantially forming a “V” shape, they could be inverted to substantially from an upside-down “V”, which would also provide offsetting horizontal components of force. Components could be attached to each other by means other than threaded fasteners, such as by welding. This application is intended to cover any adaptations or variations of the present disclosure. The following claims are in no way intended to limit the scope of the disclosure to the specific embodiments described herein.