Patent Publication Number: US-2023158585-A1

Title: Shearing apparatus and process for post tensioning tendon

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a nonprovisional application that claims priority from U.S. provisional application No. 63/007,209, filed Apr. 8, 2020, which is hereby incorporated by reference. 
     Technical Field/Field of the Disclosure 
     The present disclosure relates generally to post-tensioned, pre-stressed concrete construction. The present disclosure relates specifically to an apparatus and process for shearing a tendon for use therein. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Many structures are built using concrete, including, for instance, buildings, parking structures, apartments, condominiums, hotels, mixed-use buildings, casinos, hospitals, medical buildings, government buildings, research/academic institutions, industrial buildings, malls, bridges, pavement, tanks, reservoirs, silos, foundations, sports courts, and other structures. 
     Pre-stressed concrete is structural concrete in which internal stresses are introduced to reduce potential tensile stresses in the concrete resulting from applied loads. This can be accomplished by two methods—post-tensioned pre-stressing and pre-tensioned pre-stressing. When post tensioning concrete, the pre-stressing assembly is tensioned after the concrete has attained a specified strength. The pre-stressing assembly, commonly known as a tendon, may include for example and without limitation, anchorages, one or more strands, and sheathes or ducts. The strand is tensioned between anchors which are embedded in the concrete once the concrete has hardened. The strand may be formed from a metal or composite or any suitable material exhibiting tensile strength which can be elongated, including, for example and without limitation, reinforcing steel, single wire cable, or multi-wire cable. The strand is typically fixedly coupled to a fixed anchorage positioned at one end of the tendon, the so-called “fixed end”, and is adapted to be stressed at the other anchor, the “stressing end” of the tendon. The strand is generally held to each anchor by one or more wedges. Typically, anchors include a tapered recess which, when the strand is placed under tension, causes the wedges to further engage the strand. Wedges are typically made of metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG.  1    is a cross-sectional view of an anchor according to an embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view of an anchor according to an embodiment of the present disclosure. 
         FIG.  3    is a cross-sectional view of an anchor positioned in a holding fixture. 
         FIG.  4    is a cross-sectional view of an anchor positioned in a holding fixture. 
         FIG.  5    is a cross-sectional view of an anchor and tendon with a compression mechanism positioned adjacent an end of the tendon. 
         FIG.  6    is a cross-sectional view of an anchor, with a tendon and wedges moved into a bore of the anchor. 
         FIG.  7    is a cross-sectional view of the anchor with wedges affixed to the tendon and sheathing. 
         FIGS.  8 - 10    are views of a table shear consistent with at least embodiment of the present disclosure. 
         FIG.  11    depicts the shear hole of the table shear of  FIGS.  8 - 10   . 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
       FIG.  1    depicts anchor  100  for use in post tensioning concrete. Anchor  100  is adapted to receive and couple to strand  200  of tendon  22 . Strand  200  may be, for example and without limitation, mono-wire cable, or multi-wire cable. For the purposes of this disclosure, the axis parallel with the length of strand  200  will be referred to as the longitudinal axis of strand  200 . Anchor  100  may include anchor body  10  adapted to retain the position of anchor  100  when positioned in formed concrete. 
     Anchor  100  may couple to strand  200  by the use of one or more wedges  32 . Wedges  32  may be substantially wedge shaped and adapted to fit into tapered portion  40  formed in anchor body  10 . Tension on strand  200  may cause wedges  32  to move into tapered recess  40 , applying a gripping force on strand  200 . 
       FIG.  2    depicts anchor  100  having end  24  of strand  200  cut flush or approximately flush with anchor body  10 . In certain embodiments, cutting strand  200  is a two-step process, i.e., pushing strand  200  along the longitudinal axis of strand  200  and then cutting any excess strand  200 . It is desirable to cut end of strand  200  to be as clean and straight as possible. Dust from cutting strand  200  with a saw, for example, and uneven parts of end  24  may result in uneven placement of wedges  32 , pollutants such as dust between strand  200  and wedges  32  and between wedges  32  and anchor body  10 , and bunching strand  200  as placed in anchor body  10 . 
     In certain embodiments of the present disclosure, a table shear may be used to cut strand  200 .  FIG.  3    depicts a cross-sectional view of anchor body  10  fixed in holding fixture  12 . Holding fixture  12  holds anchor body  10  stationary. 
     Following fixing anchor body  10  in holding fixture  12 , tendon  22  may be inserted into anchor body  10 .  FIG.  4    depicts a cross-sectional view of anchor body  10  having tendon  22  inserted therein. Portion  16  of sheathing  14  is removed from end  24  of tendon  22  so as to create unsheathed portion  20  and sheathed portion  18  of tendon  22 . Portion  16  may be discarded. Sheathed portion  18  and unsheathed portion  20  extend outwardly of end  28  of anchor body  10 . 
     Following removal of portion  16 , compression mechanism  34  may be used.  FIG.  5    depicts a cross-sectional view of the anchor body  10  and tendon  22 , with wedges  32  placed on the tendon  22 , and compression mechanism  34  positioned adjacent end  24  of tendon  22 . Compression mechanism  34  may include cylindrical member  36  and plunger  38  positioned interior of cylindrical member  36 . Cylindrical member  36  is mounted over plunger  38  such that plunger  38  may translate relative to cylindrical member  36 . Interior  37  of compression mechanism  34  may be placed over end  24  of tendon  22 , which is also end  21  of unsheathed portion  20 . Wedges  32  may be placed around end  21  of unsheathed portion  20 . Cylindrical member  36  of compression mechanism  34  abuts wedges  32 . In certain embodiments, wedges  32  and cylindrical member  36  are made of a magnetic material, and wedges  32  are held around unsheathed portion  20  of tendon  22  by a magnetic force provided by cylindrical member  36  of compression mechanism  34 . 
     Compression mechanism  34  may push against end  21  of unsheathed portion  20 . End  21  of unsheathed portion  20  is positioned within interior  37  of cylindrical member  36 . Cylindrical member  36  moves toward anchor body  10  until cylindrical member  36  is adjacent end  28  of anchor body  10  (as is shown in  FIG.  5   ). Plunger  38  may push end  21  of unsheathed portion  20  toward bore  26  of anchor body  10 . 
       FIG.  6    depicts a cross-sectional view of fixed anchor body  10 , with tendon  22  and wedges  32  moved into the bore  26  of the anchor body  10  by the compression mechanism  34 . As shown in  FIG.  6   , cylindrical member  36  and plunger  38  of compression mechanism  34  are adjacent end  28  of anchor body  10 . End  21  of the unsheathed portion  20  remains within interior  37  of the cylindrical member  36 , but plunger  38  can be activated, if needed, to push end  21  of unsheathed portion  20  toward tapered portion  40  of bore  26  of anchor body  10 . Wedges  32  affix tendon  22  within tapered portion  40  of bore  26  of anchor body  10 . 
       FIG.  7    depicts a cross-sectional view of anchor body  10  having wedges  32  affixed to the tendon  22  and sheathing  14 , respectively, therein. Cylindrical member  36  and plunger  38  of compression mechanism  34  are shown retracted from end  21  of unsheathed portion  20  of tendon  22 . Plunger  38  is shown retracted into interior  37  of cylindrical member  36 . Wedges  32  are positioned within tapered portion  40  of bore  26  of anchor body  10 . 
     Compression mechanism  34  is guided along the longitudinal axis of bore  26  of anchor body  10  by holding fixture  12 . This guide prevents or retards multi-directional movement of compression mechanism  34  and anchor body  10 . 
     Following compression, sheathed portion  18  or unsheathed portion  20  of tendon  22  may be cut by table shear  300 , as depicted in  FIGS.  8 - 11   .  FIG.  10    is a cross-sectional view of table shear  300 . As shown in  FIG.  10   , tendon  22  is inserted into table shear  300  through shear blade hole  310 , as shown in  FIG.  11   . Tendon  22  is held in clamp  500 . Clamp  500  may include upper spring hold down block  320  and lower shear support block  330  which abut tendon  22 . Table shear  300  further includes upper biasing mechanism  340  and lower biasing mechanism  350 , which may be, as shown in  FIG.  11   , springs. Upper biasing mechanism  340  holds upper spring hold down block  320  in place, while lower biasing mechanism  350  holds lower shear support block  330  in place. Upper biasing mechanism  340  is held in place by upper shear block  360 , while lower biasing mechanism  350  is held in place by bottom plate  370 . Tendon  22  rests against lower support block  380 . Lower support block rests on bottom plate  370 . Bottom plate  370  may also support lower shear blade back up plate  430 . 
     Table shear includes shearing mechanism  400 . Shearing mechanism  400  may include fixed lower shear blade  410  and movable upper shear blade  420 . Fixed lower shear blade  410  may be supported by lower shear blade back up plate  430 , while movable upper shear blade  420  may be supported by upper shear blade back up plate  440 . Shear compression cylinder  450 , which may include cylinder bushing  460 , abuts upper shear blade back up plate  440 . 
     In the operation of table shear  300 , tendon  22  is inserted through shear blade hole  310  and held in place as described above. Shearing mechanism  400  shears tendon  22  by applying pressure to upper shear blade backup plate through shear compression cylinder  450 , causing movable upper shear blade  420  and fixed lower shear blade  410  to cut tendon  22 . 
     The foregoing outlines features of several embodiments so that a person of ordinary skill in the art may better understand the aspects of the present disclosure. Such features may be replaced by any one of numerous equivalent alternatives, only some of which are disclosed herein. One of ordinary skill in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. One of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.