Abstract:
A rod detensioning unit including a gripping unit removal device that engages a gripping unit on a rod, a chair frame configured to engage a rod, a rod tensioning unit that applies tension to an external portion of the rod to remove load from the gripping unit, a load cell unit that measures a tension level applied to the rod by the tensioning unit, a plate gripping unit that engages the rod and secures the chair frame, rod tensioning unit, load cell and plate gripping unit to the rod, a drive unit that engages the gripping unit removal device, and an extension unit affixed to the external portion of the rod when the original external rod length is too short to accommodate the de-tensioning unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure claims priority to U.S. Provisional Patent App. No. 62/335,362, entitled “ROD DE-TENSIONING DEVICE AND METHODS OF OPERATING THE SAME” filed on May 12, 2016, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Post-tensioned trunnion anchor rods are used to secure large devices, such as gates on dams, to structures. To firmly secure the devices to the structure, tension is applied to the trunnion rods, and the individual rods are locked off to maintain the tension load within the rod. See, U.S. Pat. No. 2,705,871 to Kenigsberg and U.S. Pat. No. 2,871,664 to Dobson. For large structures, such as dams, a large amount of tension (typically 60% or more of its ultimate strength) is applied to the rods creating a potentially dangerous situation. At least 100-200 dams in the United States use post-tensioned trunnion rods for gate anchorages. Trunnion rods are predominately made of metal that is designed to operate at a specific tension level. Increased tension, in addition to long-term environmental stresses in the rods creates a dangerous situation where the rods may fail in a brittle and abrupt manner before the end of life expectancy date. 
         [0003]    Since 1960 many dams were built using post-tensioned trunnion rods. At the time the dams were erected, and until 2010, cost-effective and safe technology to determine the amount of tension in each rod was not available, and premature rod failures due to over-tensioning have occurred on several dams since the 1970s. Because of the importance of these trunnion rods, and the aging of the inventory of rods currently in dams, dam owners and operators are beginning to regularly test the tension in each rod and the integrity of the rods using recently-developed non-destructive techniques that are safe and cost efficient. 
         [0004]    However, even with the testing, there is currently no safe or efficient procedure to remove excess tension in trunnion rods. In a dam environment, an abrupt failure of a post-tensioned trunnion rod can result in the trunnion rod being expelled from the dam at high rate of speed. Further, the costs involved with removing and replacing trunnion rods, or otherwise reinforcing gate anchorages on dams are very high. Therefore, a need exists for a method of removing excess tension from post-tensioned trunnion rods to increase the useful life of installed trunnion rods. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    One embodiment of the present disclosure includes a rod detensioning unit including a gripping unit removal device that engages a gripping unit on a rod, a chair frame configured to engage a rod, a rod tensioning unit that applies tension to an external portion of the rod to remove load from the gripping unit, a load cell unit that measures a tension level applied to the rod by the tensioning unit, a plate gripping unit that engages the rod and secures the chair frame, rod tensioning unit, load cell and plate gripping unit to the rod, a drive unit that engages the gripping unit removal device, and an extension unit affixed to the external portion of the rod when the original external rod length is too short to accommodate the de-tensioning unit. 
         [0006]    In another embodiment, the gripping unit includes an opening sized to accommodate the rod. 
         [0007]    In another embodiment, the opening has an inner surface that includes a plurality of threads. 
         [0008]    In another embodiment, the rod detensioning unit includes a second gripping unit that is in the opening of the gripping unit. 
         [0009]    In another embodiment, the second gripping unit includes a plurality of threads that correspond to the threads in the opening. 
         [0010]    In another embodiment, the second gripping unit is positioned in the opening a predetermined distance from a trunnion. 
         [0011]    In another embodiment, the rod tensioning unit is hydraulically driven. 
         [0012]    In another embodiment, the rod detensioning unit includes a central control unit communicatively coupled to the drive unit. 
         [0013]    In another embodiment, the rod detensioning unit includes a plurality of cameras optically coupled to the central control unit. 
         [0014]    In another embodiment, at least one camera is positioned to capture an image of a side of the gripping unit. 
         [0015]    Another embodiment of the present disclosure includes a method of detensioning a rod, the method including removably attaching a gripping unit removal device on a gripping unit where the gripping unit engages a rod, positioning a chair frame on the rod over a periphery of the gripping unit, positioning a rod tensioning unit on the rod with a first end of the rod tensioning unit being in contact with a surface of the chair frame, applying a first force to the rod tensioning unit, positioning a bearing plate on the rod in contact with the rod tensioning unit, positioning a load cell in contact with the rod on the rod tensioning unit, securing a drive unit to the chair frame such that a portion of the drive unit is in contact with the rod, applying a second pressure is applied to the rod tensioning unit, actuating the drive unit, and releasing the second pressure on the rod tensioning unit. 
         [0016]    In another embodiment, the first pressure is sufficient to increase the tension in the rod. 
         [0017]    In another embodiment, the second pressure is sufficient to separate the gripping uint from a trunnion. 
         [0018]    In another embodiment, the driving unit includes a engagement portion that is in contact with the rod. 
         [0019]    In another embodiment, the drive unit actuates to move the gripping unit a predetermined distance from the trunnion. 
         [0020]    In another embodiment, the drive unit is electrically driven. 
         [0021]    In another embodiment, the method includes the step of connecting a central control unit communicatively coupled to the drive unit. 
         [0022]    In another embodiment, the method includes the step of optically connecting a plurality of cameras to the central control unit. 
         [0023]    In another embodiment, at least one camera is positioned to capture an image of a side of the gripping unit. 
         [0024]    In another embodiment, the first pressure is less than the second pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0025]      FIG. 1A  depicts a dam that includes a spillway defined between two piers; 
           [0026]      FIG. 1B  depicts a trunnion rod system used to secure structures together; 
           [0027]      FIG. 2  depicts a gripping unit installed on a rod; 
           [0028]      FIG. 3  depicts a rod de-tensioning device; 
           [0029]      FIG. 4  depicts a drive unit  400  on the chair frame; 
           [0030]      FIG. 5  depicts the gripping unit moved from an original position on the rod to a new position a distance x from the original position; 
           [0031]      FIG. 6  depicts a rod de-tensioning control unit; 
           [0032]      FIG. 7  depicts a schematic representation of the process of de-tensioning rods using the de-tensioning system; 
           [0033]      FIG. 8  depicts one embodiment of a gripping unit removal device; and 
           [0034]      FIG. 9  depicts an arresting unit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]      FIG. 1A  depicts a dam  100  that includes a spillway  110  defined between two piers  120 . Mounted between piers  120  is Tainter gate  130  comprised of a curved panel  132  supported on radial arms  134 . Radial arms  134  converge at trunnion pin  136  that is supported at a rotational pivot by trunnion girders  140 . The trunnion girders  140  are separate from the piers  120  and are secured to the piers  120  by rods  150 . Sides of curved panel  132  may slide through and engage with curved leak limiting slots  122  in side faces of piers  120 . It is to be appreciated that a water reservoir is on the convex or upstream side of curved panel  132 . When gate  130  is closed the panel is in the lower position as shown in  FIG. 1A  and water is prevented from flowing downstream over the dam by curved panel  132 . When gate  130  is opened by rotating radial arm structure  134  about trunnion pin  136 , water from the reservoir is permitted to flow under panel  132 , over spillway  110 , and downstream from dam  100 . 
         [0036]    Trunnion girders  140  may be vertically supported on ledges  124  that are formed on piers  120 . Trunnion pins  136  are journaled in trunnion girders  140 . Tension rods or anchorage tendons  150  extend in a generally upstream direction into piers  120  and are anchored in the piers by tendon anchorage plates or anchorage means  152  embedded in the concrete of the piers. Downstream ends of rods  150  are secured to trunnion girders  140  to prevent trunnion girder  140  from being pushed downstream by the water held back by gate  130 . Rods  150  typically extend through trunnions  140  to facilitate securing the trunnion girder securely to the pier  120 . A typical means of securement is provided by dry-mounted trunnion base plates  154  positioned on the downstream side of the trunnion girder. Rods  150  extend through openings in base plates  154  and gripping units  156  are tightened on the rods. In some cases, gripping units  156  are threaded and engage threaded portions of rods  150 . In other cases gripping units  156  are of the so-called Howlett grip nut type, for connection to smooth rods. In any case, nuts  156  provide a secure connection of rods  150  to trunnion girders  140  such that the rod portions between trunnions  140  and anchorage means  152  are tensioned. An untensioned or free end portion  160  of each rod  150  extends downstream of each gripping unit  156 . 
         [0037]      FIG. 1B  depicts a trunnion rod system used to secure structures together. The trunnion rod system  100  includes a plurality of post-tensioned rods  150  extending through a trunnion girder  140  that apply uniform pressure to affix the trunnion girder to the pier  120  on a dam. The trunnion girder  140  is the support that holds that dam gates  130  in place, resisting gravity of hydrodynamic forces. The rods  150  are post-tensioned and “locked off” to maintain their tension to the trunnion girder  140  by gripping units  156 . When the rods  150  are installed, they are pulled away from the trunnion girder  140 , thereby applying a tensile force to the rod  150 . As the tensile force is applied to the rod  150  the gripping unit  156  is slid down the rod  150  and tightened to secure the rod  150  to the trunnion  140  without releasing the tension in the rod  150 . 
         [0038]      FIG. 2  depicts a gripping unit installed on a rod. The gripping unit  156  includes an outer portion  202  that has an opening  204  through the center of the outer portion  202 . The opening  204  has a diameter larger than the diameter of the rod  150  such that the rod  150  can move freely through the opening  204 . The inner surfaced of the opening  204  includes a plurality of threads  206 . An inner gripping unit  208  includes threads corresponding to the threads  206  on the outer portion  202  of the gripping unit  156 . The inner gripping unit  208  has a diameter equal to or slightly larger than the rod  150  such that the inner gripping unit  208  is secured to the rod  150  when the inner gripping unit  208  engages opening  204  of the outer portion  202 . In one embodiment, the inner gripping unit  208  includes a slit (not shown) extending along one side of the inner gripping unit  208  to allow the diameter of the inner gripping unit  208  to compress when the inner gripping unit  208  is in the opening  204 . In another embodiment, the opening  204  is tapered such that the diameter of the opening is larger where the rod  150  enters the gripping unit  156  and smaller where the rod  150  exits the gripping unit  156 . 
         [0039]    The inner gripping unit  208  has a height that is smaller than the height of the outer portion  202 . The inner gripping unit  208  includes an opening  210  that is concentric with the opening  204  in the outer portion  202 . The opening  210  is sized such that the rod  150  fits into the opening  210  when the inner gripping unit  208  is not inserted into the outer portion  202  and the inner gripping unit  208  compresses onto the rod  150  when the inner gripping unit  208  is threaded into the opening  204  in the outer portion  202  and tension is applied. When installed, the inner gripping unit  208  is positioned in the portion of the outer portion  202  that is farthest from the trunnion  140 . A gap having a distance x is formed in the opening  204  below the inner gripping unit  208  in the opening  204 . When installed, the outer portion  202  can rotate in relation to the inner gripping portion  208  when a rotative force is applied to the outer portion  202 . 
         [0040]      FIG. 3  depicts a rod de-tensioning device. The rod de-tensioning device  300  includes a gripping unit removal device  302 , a chair frame  304 , a rod tensioning unit  306 , a bearing plate  308 , a load cell unit  310  and a pulling gripping unit  312 . The gripping unit removal device  302  includes an opening on an inner surface that engages the outer portion  202  of the gripping unit  156 . The gripping unit removal device  302  may be secured to the gripping unit  156  using securing units  314  such as set screws. The chair frame  304  includes four legs  316  that are connected to a top plate  318  with the top plate  318  being parallel to a top surface of the gripping unit removal device  302 . The top plate  318  includes an opening that is sized to accommodate the rod  150  such that the rod  150  passes through the opening. The rod tensioning unit  306  includes a central channel that allows the rod  150  to pass through the central channel. The rod tensioning unit  306  may be a hydraulic jack that grips the rod  150  and applies additional tension to the rod  150  or any other actuation device capable of applying a tensile force to the rod  150 . 
         [0041]    The bearing plate  308  includes an opening that allows the rod to slide through the bearing plate  308 . The bearing plate  308  is positioned on a side of the rod tensioning unit  306  furthest from the chair frame  304 . A load cell unit  310  is positioned on the bearing plate  308 . The load cell  310  determines the amount of tension being applied to the rod  150  by the rod tensioning unit using known methods. A pulling gripping unit  312  is positioned on the load cell unit  310  and is secured to the rod  150 . The load cell unit  310  may be any load cell sensor capable of measuring the tensile force in a rod including a load sensor or a strain sensor. 
         [0042]      FIG. 4  depicts a drive unit  400  on the chair frame  304 . The drive unit  400  includes a motor  402  with an engagement unit  404  connected to the motor  402 . The engagement unit  404  is configured to engage the side surface of gripping unit removal device  302 . When the motor  402  is energized, the engagement unit  404  rotates to loosen or tighten the gripping unit  156  via the gripping unit removal device  302 . As the gripping unit  156  is loosened, the gripping unit  156  moves away from the surface of the trunnion  140  along the inner gripping unit  208  that is secured to the rod  150 . By moving the gripping unit  156 , a gap x is formed between the original position of the gripping unit  156  and the new position of the gripping unit  156 . When the tension is released from the rod tensioning unit  306 , the gripping unit  156  moves down the distance x or a portion of the distance x based on the number of times the gripping unit  156  is rotated. When the rod tensioning unit lowers the tension, the gripping unit  156  moves the bearing surface, and the tension in the rod is reduced at a level relative to the distance x. 
         [0043]      FIG. 5  depicts the gripping unit  156  moved from an original positon on the rod  150  to a new position a distance x from the original position. The gripping unit  156  moves along the inner gripping unit  208  which remains stationary on the rod  150 . In one embodiment, a camera is positioned on the chair frame  304  such that the camera transmits an image representing the position of the gripping unit  156 . In another embodiment, a first camera is positioned on a side chair unit  304  to view a side view of the gripping unit  156 , and a second camera is positioned on the top of the chair unit  304  to view a top view of the gripping unit  156 . 
         [0044]      FIG. 6  depicts a rod de-tensioning control unit  600 . The rod de-tensioning control unit  600  includes a central processing unit (CPU)  602 , an input output (IO) unit  604  with the load sensor  310  connected to an input of the IO unit  604  and the drive unit  400  being connected to an output of the IO unit  604 , a secondary storage device  606  that may include, a communication unit  608  communicatively coupled to a network  610 , a memory  612 . The rod de-tensioning control unit  600  may further comprise standard input devices such as a keyboard, a mouse, a digitizer, or a speech processing means (each not illustrated). Additional sensors including temperature sensors, linear vertical differential transmitters, pressure sensors, strain sensors and any other type of sensor may be connected to the IO unit  604 . In one embodiment, video streams from image capture devices, such as a camera, are captured by the IO unit  604  for analysis to determine the amount of movement of the gripping unit  156 . Consistent with this embodiment, a video analysis unit residing in the memory  612  may analyze frames extracted from the images sent from the cameras to determine when the gripping unit  156  is moved as well as the distance the gripping unit  156  is moved. 
         [0045]    In one embodiment, the rod de-tensioning control unit  600 &#39;s memory  612  includes a Graphical User Interface (“GUI”)  614  that is used to gather information from a user via the display device  616  and I/O unit  604  as described herein. The GUI  614  includes any user interface capable of being displayed on a display device  616  including, but not limited to, a web page, a display panel in an executable program, or any other interface capable of being displayed on a computer screen. The GUI  614  may also be stored in the secondary storage unit  606 . In one embodiment consistent with the present invention, the GUI  614  is displayed using commercially available hypertext markup language (“HTML”) viewing software such as, but not limited to, Microsoft Internet Explorer, Google Chrome or any other commercially available HTML viewing software. 
         [0046]      FIG. 7  depicts a schematic representation of the process of de-tensioning rods using the de-tensioning system  300 . In step  702 , the gripping unit removal device  302  is placed on the gripping unit  156  such that an inner cavity of the gripping unit removal device  302  engages the gripping unit  156 . In step  704 , the chair frame  304  is slid over the rod  150  and placed onto the surface  154  such that the legs of the chair frame  304  are positioned around the periphery of the gripping unit  156 . In step  706 , the rod tensioning unit  306  is positioned on the rod  150  with a first end of the rod tensioning unit  306  being in contact with the top plate of the chair frame  304 . In step  708 , a small amount of hydraulic pressure is applied to the rod tensioning unit  306  to move the hydraulic to simplify the process of disassmeling the system after use. to increase the tension in the rod  150 . In step  710 , the bearing plate  308  is positioned on the rod  150  on an end of the rod tensioning unit  306  that is furthest from the chair frame  304 . In step  712 , the load cell unit  310  is positioned on the rod  150  on the rod tensioning unit  306 . In step  714 , a pulling gripping unit  312  is positioned on the rod  150  on the load cell unit  310 . In step  716 , the pulling gripping unit  312  is secured to the rod  150 . 
         [0047]    In step  718 , the drive unit  400  is secured to the chair frame  304  such that the engagement unit  404  of the drive unit  400  is positioned on the outer surface of the gripping unit removal device  302 . In step  720 , hydraulic pressure is applied to the rod tensioning unit  306  to separate the gripping unit  156  from the trunnion  140 . In one embodiment, a camera unit is positioned on the chair frame  304  to determine when the gripping unit  156  has separated from the trunnion  140 . In step  722 , the drive unit  400  is actuated to rotate the gripping unit removal device  302  causing the gripping unit  156  to rotate along the threads of the inner gripping unit  208  such that the gripping unit  156  is moved a distance x from its initial position before the drive unit  400  actuated. In step  724 , the drive motor  400  actuates until the tension in the rod  150  as measured by the theoretical distance required to reduce rod tension to the target level. In step  726 , the hydraulic pressure on the rod tensioning device is released. The process of detention the rod  150  may be performed by the rod de-tensioning control unit  600 . 
         [0048]      FIG. 8  depicts one embodiment of a gripping unit removal device. The gripping unit removal device  302  includes a central shaft  800  including an opening sized to engage the gripping unit  156 . A gear unit  802  is affixed around the periphery of the central shaft  800 . The gear unit  802  includes a plurality of teeth  804  having a pitch and spacing that are sized to accommodate the engagement unit  404  on the drive unit  400  such that the drive unit  400  rotates the gripping unit removal device  302  to tighten and loosen the gripping unit  156 . In one embodiment, the gear unit  802  is sized to accommodate the engagement unit  404  that has twenty-four teeth. In one embodiment, a heating unit (not shown) is placed on the gripping unit removal device  302  to warm the gripping unit removal device  302  before de tensioning occurs. In one embodiment, the heating unit is a heat tape wrapped around the gripping unit removal device  302 . 
         [0049]      FIG. 9  depicts an arresting unit  900 . The arresting unit  900  include a main portion  902  that includes a channel (not shown) with the channel sized to engage a rod  150 . The arresting unit  900  includes a spacer  904  that extends from one side of the main portion  904 . The spacer  904  is sized such that it can be inserted between the gripping unit removal device  302  and the rod  150  to apply a restricting force on the inner gripping unit  208  to restrain the inner gripping unit  208  from rotating around the rod  150  during the detensioning process. 
         [0050]    In one embodiment, at least one linear vertical differential transmitter (“LVDT”) unit is positioned on the gripping unit removal device  302  to determine the amount of movement made by the gripping unit removal device  302 . The LVDT unit may have a rounded end that engages the gripping unit removal device  302 . By measuring the distance the gripping unit  156  is moved from its initial position, the amount of tension to be removed from the rod  150  can be determined. If the amount of tension to be removed is less than the desired value, the gripping unit  156  may be moved an additional distance. 
         [0051]    In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
         [0052]    It should be understood that various changes and modifications to the presently preferred embodiments disclosed herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present disclosure and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.