Patent Publication Number: US-9896845-B2

Title: Spindle lock anchor for post tensioned concrete member

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a nonprovisional application that claims priority from U.S. provisional application No. 62/200,918, filed Aug. 4, 2015, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD/FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to post-tensioned, pre-stressed concrete construction. The present disclosure relates specifically to anchors for use therein. 
     BACKGROUND OF THE DISCLOSURE 
     Many structures are built using concrete, including, for instance, buildings, parking structures, apartments, condominiums, hotels, mixed-use structures, casinos, hospitals, medical buildings, government buildings, research/academic institutions, industrial buildings, malls, roads, bridges, pavement, tanks, reservoirs, silos, sports courts, and other structures. 
     Prestressed concrete is structural concrete in which internal stresses are introduced to reduce potential tensile stresses in the concrete resulting from applied loads; prestressing may be accomplished by post-tensioned prestressing or pre-tensioned prestressing. In post-tensioned prestressing, a tension member is tensioned after the concrete has attained a desired strength by use of a post-tensioning tendon. The post-tensioning tendon may include for example and without limitation, anchor assemblies, the tension member, and sheathes. Traditionally, a tension member is constructed of a material that can be elongated and may be a single or a multi-strand cable. Typically, the tension member may be formed from a metal or composite material, such as reinforced steel. The post-tensioning tendon conventionally includes an anchor assembly at each end. The post-tensioning tendon is fixedly coupled to a fixed anchor assembly positioned at one end of the post-tensioning tendon, the “fixed-end”, and stressed at the stressed anchor assembly positioned at the opposite end of the post-tensioning tendon, the “stressing-end” of the post-tensioning tendon. 
     Post-tension members are conventionally formed from a strand and a sheath. The strand is conventionally formed as a single or multi-strand metal cable. The strand is conventionally encapsulated within a polymeric sheath extruded thereabout to, for example, prevent or retard corrosion of the metal strand by protecting the metal strand from exposure to corrosive or reactive fluids. Likewise, the sheath may prevent or retard concrete from bonding to the strand and preventing or restricting movement of the sheath during post-tensioning. The sheath may be filled with grease to further limit the exposure of the metal strand and allow for increased mobility. Because the metal strand and the polymeric sheath are formed from different materials, the thermal expansion and contraction rates of the metal strand and polymeric sheath may differ. During conventional manufacturing, the sheaths are formed by hot extrusion over the metal strand. When the tension members are coiled for transport and storage, uneven thermal contraction may occur as the tendon cools. When installed as a post-tensioning tendon in a pre-stressed concrete member, cooling of the sheath may cause separation of the sheath from an anchorage, potentially exposing the metal strand to corrosive or reactive fluids. 
     SUMMARY 
     The present disclosure provides an anchor. The anchor includes an anchor body, the anchor body having an internal passage, and a lock nut, the lock nut having an internal tapered surface defining a forcing cone. The lock nut is coupled to the anchor body. The anchor also includes a spindle, the spindle positioned within the internal passage and threadedly coupled to the lock nut. The spindle has an expansion wedge. 
     The present disclosure also provides for a post-tensioning tendon. The post-tensioning tendon includes a tension member including a strand and a sheath where the sheath is positioned about the strand. The post-tensioning tendon also includes a first anchor coupled to a first end of the tension member and a second anchor coupled to a second end of the tension member. Each of the anchors include an anchor body, the anchor body having an internal passage, and a lock nut, the lock nut having an internal tapered surface defining a forcing cone. The lock nut is coupled to the anchor body. The anchors also include a spindle, the spindle positioned within the internal passage and threadedly coupled to the lock nut. The spindle has an expansion wedge, and the sheath is gripped between the expansion wedge and the forcing cone. 
     In addition, the present disclosure provides for a method of coupling a tension member to an anchor for forming a post-tensioning tendon. The method includes providing a tension member including a strand and a sheath, where the sheath is positioned about the strand. The method also includes providing an anchor. The anchor includes an anchor body, where the anchor body has an internal passage and a lock nut, the lock nut having an internal tapered surface defining a forcing cone. The lock nut is coupled to the anchor body. The anchor also includes a spindle, the spindle positioned within the internal passage and threadedly coupled to the lock nut. The spindle has an expansion wedge, and the sheath is gripped between the expansion wedge and the forcing cone. The method also includes removing a portion of a first end of the sheath from a first end of the tension member exposing a first end of the strand and inserting the first end of the tension member into the anchor. In addition, the method includes inserting the first end of the strand through the spindle and inserting the sheath between the expansion wedge and the forcing cone. The method also includes tightening the lock nut onto the spindle such that the sheath is compressed between the expansion wedge and the forcing cone and coupling the strand to the anchor. 
    
    
     
       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. 
         FIGS. 1A, 1B  depict a partial cross section of a concrete post-tensioning tendon within a concrete form consistent with embodiments of the present disclosure. 
         FIG. 2  depicts a cross section view of a post-tensioning tendon within a spindle lock anchor consistent with at least one embodiment of the present disclosure. 
         FIG. 3  depicts an enlarged view of a portion of  FIG. 2 . 
     
    
    
     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. 
     When stressing concrete member  40 , anchoring systems may be provided to hold the tension member before and after stressing. In some embodiments, as depicted in  FIGS. 1A, 1B , post-tensioning tendon  11  may be positioned within concrete form  21 . Concrete form  21  is a form into which concrete may be poured to form concrete member  40 . Post-tensioning tendon  11  may include for example and without limitation fixed end anchor  13 , tension member  15 , and stressing end anchor  17 . As depicted in  FIG. 1A , in some embodiments, fixed end anchor  13  may include fixed end anchor body  14 . Fixed-end anchor body  14  may be positioned within concrete form  21  such that fixed-end anchor body  14  will be encased in concrete  23  after concrete is poured into concrete form  21 . In some embodiments, fixed end cap  19  may be positioned at distal end  41  of fixed end anchor body  14 . Fixed end cap  19  may, in certain embodiments, protect tension member  15  from corrosion after concrete  23  is poured by preventing or retarding corrosive or reactive fluids or concrete from contacting tension member  15 . 
     Stressing end anchor  17  may include stressing end anchor body  18 , positioned within concrete form  21  such that stressing end anchor body  18  is within concrete  23 . Pocket former  25  may be positioned between the end of stressing end anchor body  18  and end wall  22  of concrete form  21 . Pocket former  25  may prevent or retard concrete  23  from filling space between stressing end anchor body  18  and concrete form edge  42  of the resultant concrete member  40  formed by concrete  23  within concrete form  21 . Pocket former  25  may allow access to tension member  15  from outside concrete member  40  once concrete member  40  is hardened and concrete form  21  is removed. 
     As used herein, stressing end anchor  17  and fixed end anchor  13  may be referred to as “first anchor” and “second anchor,” or vice versa. 
     In some embodiments, tension member  15  may include strand  27  and sheath  29 . Strand  27  may be a single or multi-strand metal cable. Sheath  29  may be tubular or generally tubular and may be positioned about strand  27 . In some embodiments, space between strand  27  and sheath  29  may be filled or partially filled with a filler such as grease. When installing tension member  15 , in some embodiments, a length of sheath  29  may be removed from first end  43  of tension member  15 , exposing strand  27 . Strand  27  may be inserted through fixed end anchor body  14  and secured thereto, for example and without limitation, by one or more wedges. After strand  27  is secured, fixed end anchor body  14  may be installed in concrete form  21 . Tension member  15  may be positioned within concrete form  21  and tension member  15  may be cut to correspond with the length of concrete form  21 . In some embodiments, a length of sheath  29  may be removed from second end  44  of tension member  15 , exposing strand  27 . Strand  27  may be inserted through stressing end anchor body  18 . After insertion of strand  27  through stressing end anchor body  18 , stressing end anchor  17  may be positioned within concrete form  21  such that pocket former  25  contacts end wall  22  of concrete form  21 . End wall  22  may include strand aperture  45  through which strand  27  may extend. 
     In some embodiments, as depicted in  FIGS. 1A, 1B, and 2 , when tension member  15  is inserted into stressing end anchor body  18  and fixed end anchor body  14 , sheath  29  may be coupled to stressing end anchor body  18  and fixed end anchor body  14  to, for example and without limitation, prevent or restrict sheath  29  from pulling away from the respective anchors and exposing strand  27  to concrete  23 . 
     In some embodiments, fixed end anchor  13  may include lock nut  101  and spindle  103 . Likewise, stressing end anchor  17  may include lock nut  101  and spindle  105 . Spindles  103 ,  105  may be tubular or generally tubular members having cylindrical or generally cylindrical inner surfaces  134  defining spindle inner passages  136  through which strand  27  may pass. Spindles  103 ,  105  may be positioned within internal passage  107  of the corresponding anchor bodies  14 ,  18 . In some embodiments, spindles  103 ,  105  may include threads  109  to threadedly couple spindles  103 ,  105  to a respective lock nut  101 . 
     In some embodiments, lock nuts  101  and spindles  103 ,  105  may grip the respective ends of sheath  29  when coupled. As best depicted in  FIG. 3 , spindles  103 ,  105  may each include an expansion wedge  111 . Expansion wedge  111  may be positioned within an expansion portion  132  at an end of sheath  29  and may expand expansion portion  132  radially outward as expansion wedge  111  is inserted. Likewise, in some embodiments, lock nuts  101  may include an internal tapered surface  130  defining a forcing cone  113  corresponding to expansion wedges  111  such that, as lock nuts  101  are tightened, expansion portion  132  of sheath  29  is gripped between forcing cone  113  and expansion wedge  111 . In some embodiments, one or both of expansion wedge  111  and forcing cone  113  may be smooth or may include a grip enhancing surface feature  127  such as teeth, grooves, or any other grip enhancing surface features known in the art. 
     In some embodiments, spindles  103 ,  105  may couple to fixed end anchor body  14  or stressing end anchor body  18  by tensile forces applied when lock nuts  101  are tightened thereonto. In some embodiments, spindles  103 ,  105  may include a retention feature. The retention feature may transfer the tensile force onto fixed end anchor body  14  or stressing end anchor body  18  and prevent or restrict spindles  103 ,  105  from being pulled through fixed end anchor body  14  or stressing end anchor body  18 . In some embodiments, the retention feature may be an edge, detent, extension, or, as depicted in  FIG. 2 , conical retaining profile  115 . 
     In some embodiments, one or more of spindles  103 ,  105  may couple fixed end anchor body  14  or stressing end anchor body  18  to end wall  22  of concrete form  21 . As depicted in  FIGS. 1A, 1B, and 2 , spindle  105  includes spindle extension  106 ; spindle extension  106  may thread through strand aperture  45  in end wall  22  through which strand  27  extends. In some embodiments, spindle extension  106  may include external threads  117 . External threads  117  may threadedly couple spindle extension  106  with spindle nut  119 . Spindle nut  119  may allow stressing end anchor body  18  to be retained to end wall  22  during concrete pouring. 
     In some embodiments, after concrete  23  is poured, spindles  103 ,  105  may be left in fixed end anchor  13 . In some embodiments, after concrete  23  is poured and set as depicted in  FIG. 1B , spindle  105  may be removed from stressing end anchor body  18  by unthreading spindle  105  from lock nut  101 . Although sheath  29  may no longer be retained between extended spindle  105  and lock nut  101  after concrete pouring, sheath  29  may be prevented from retracting from stressing end anchor body  18  by concrete  23 . As understood in the art, concrete  23  surrounding sheath  29  may conform to surface irregularities of sheath  29  and may adhere thereto, thus preventing or restricting any contraction of sheath  29 . 
     In some embodiments, one or more seals may be positioned to prevent or restrict concrete  23  from ingressing into tension member  15  that may prevent or retard the tensioning of strand  27 . In some embodiments, as depicted in  FIG. 2 , gasket  121  may be positioned between lock nut  101  and stressing end anchor body  18 . 
     Although described specifically with respect to fixed end anchor  13  and stressing end anchor  17 , a spindle such as spindles  103 ,  105  may be utilized with either a fixed end anchor or stressing end anchor. Furthermore, a spindle such as spindles  103 ,  105  may be used with an intermediate anchor. An intermediate anchor, as understood in the art, may be an anchor used between adjacent concrete members which are poured and stressed sequentially utilizing the same tension member  15 . 
     Although fixed end anchor  13  and stressing end anchor  17  are depicted as unencapsulated or bare anchors, such as those formed from ductile iron, fixed end anchor  13  and stressing end anchor  17  may be encapsulated-type anchors without deviating from the scope of this disclosure and may be formed from any material. Non-limiting examples of encapsulated anchors are disclosed in U.S. Pat. Nos. 4,896,470; 5,072,558; 5,701,707; 5,749,185; 5,755,065; 6,098,356; 6,381,912; 6,560,939; 6,761,002; 6,817,148; 6,843,031; and 8,065,845 which are incorporated herein by reference. In some embodiments, spindles  103 ,  105  may be formed from a nonconductive material such as a polymer. In some such embodiments, spindles  103 ,  105  may act to electrically insulate strand  27 , fixed end anchor  13 , and stressing end anchor  17 . This electric insulation may prevent or retard galvanic corrosion from occurring due to contact between strand  27 , fixed end anchor  13 , or stressing end anchor  17  when strand  27 , fixed end anchor  13 , and stressing end anchor  17  are formed from different metals. 
     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. Unless explicitly stated otherwise, nothing herein is intended to be a definition of any word or term as generally used by a person of ordinary skill in the art, and nothing herein is a disavowal of any scope of any word or term as generally used by a person of ordinary skill in the art.