Spindle lock anchor for post tensioned concrete member

An anchor is disclosed. The anchor may 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 may be coupled to the anchor body. The anchor may also include a spindle, the spindle positioned within the internal passage and threadedly coupled to the lock nut. The spindle may have an expansion wedge.

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

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.

DETAILED DESCRIPTION

When stressing concrete member40, anchoring systems may be provided to hold the tension member before and after stressing. In some embodiments, as depicted inFIGS. 1A, 1B, post-tensioning tendon11may be positioned within concrete form21. Concrete form21is a form into which concrete may be poured to form concrete member40. Post-tensioning tendon11may include for example and without limitation fixed end anchor13, tension member15, and stressing end anchor17. As depicted inFIG. 1A, in some embodiments, fixed end anchor13may include fixed end anchor body14. Fixed-end anchor body14may be positioned within concrete form21such that fixed-end anchor body14will be encased in concrete23after concrete is poured into concrete form21. In some embodiments, fixed end cap19may be positioned at distal end41of fixed end anchor body14. Fixed end cap19may, in certain embodiments, protect tension member15from corrosion after concrete23is poured by preventing or retarding corrosive or reactive fluids or concrete from contacting tension member15.

Stressing end anchor17may include stressing end anchor body18, positioned within concrete form21such that stressing end anchor body18is within concrete23. Pocket former25may be positioned between the end of stressing end anchor body18and end wall22of concrete form21. Pocket former25may prevent or retard concrete23from filling space between stressing end anchor body18and concrete form edge42of the resultant concrete member40formed by concrete23within concrete form21. Pocket former25may allow access to tension member15from outside concrete member40once concrete member40is hardened and concrete form21is removed.

As used herein, stressing end anchor17and fixed end anchor13may be referred to as “first anchor” and “second anchor,” or vice versa.

In some embodiments, tension member15may include strand27and sheath29. Strand27may be a single or multi-strand metal cable. Sheath29may be tubular or generally tubular and may be positioned about strand27. In some embodiments, space between strand27and sheath29may be filled or partially filled with a filler such as grease. When installing tension member15, in some embodiments, a length of sheath29may be removed from first end43of tension member15, exposing strand27. Strand27may be inserted through fixed end anchor body14and secured thereto, for example and without limitation, by one or more wedges. After strand27is secured, fixed end anchor body14may be installed in concrete form21. Tension member15may be positioned within concrete form21and tension member15may be cut to correspond with the length of concrete form21. In some embodiments, a length of sheath29may be removed from second end44of tension member15, exposing strand27. Strand27may be inserted through stressing end anchor body18. After insertion of strand27through stressing end anchor body18, stressing end anchor17may be positioned within concrete form21such that pocket former25contacts end wall22of concrete form21. End wall22may include strand aperture45through which strand27may extend.

In some embodiments, as depicted inFIGS. 1A, 1B, and 2, when tension member15is inserted into stressing end anchor body18and fixed end anchor body14, sheath29may be coupled to stressing end anchor body18and fixed end anchor body14to, for example and without limitation, prevent or restrict sheath29from pulling away from the respective anchors and exposing strand27to concrete23.

In some embodiments, fixed end anchor13may include lock nut101and spindle103. Likewise, stressing end anchor17may include lock nut101and spindle105. Spindles103,105may be tubular or generally tubular members having cylindrical or generally cylindrical inner surfaces134defining spindle inner passages136through which strand27may pass. Spindles103,105may be positioned within internal passage107of the corresponding anchor bodies14,18. In some embodiments, spindles103,105may include threads109to threadedly couple spindles103,105to a respective lock nut101.

In some embodiments, lock nuts101and spindles103,105may grip the respective ends of sheath29when coupled. As best depicted inFIG. 3, spindles103,105may each include an expansion wedge111. Expansion wedge111may be positioned within an expansion portion132at an end of sheath29and may expand expansion portion132radially outward as expansion wedge111is inserted. Likewise, in some embodiments, lock nuts101may include an internal tapered surface130defining a forcing cone113corresponding to expansion wedges111such that, as lock nuts101are tightened, expansion portion132of sheath29is gripped between forcing cone113and expansion wedge111. In some embodiments, one or both of expansion wedge111and forcing cone113may be smooth or may include a grip enhancing surface feature127such as teeth, grooves, or any other grip enhancing surface features known in the art.

In some embodiments, spindles103,105may couple to fixed end anchor body14or stressing end anchor body18by tensile forces applied when lock nuts101are tightened thereonto. In some embodiments, spindles103,105may include a retention feature. The retention feature may transfer the tensile force onto fixed end anchor body14or stressing end anchor body18and prevent or restrict spindles103,105from being pulled through fixed end anchor body14or stressing end anchor body18. In some embodiments, the retention feature may be an edge, detent, extension, or, as depicted inFIG. 2, conical retaining profile115.

In some embodiments, one or more of spindles103,105may couple fixed end anchor body14or stressing end anchor body18to end wall22of concrete form21. As depicted inFIGS. 1A, 1B, and 2, spindle105includes spindle extension106; spindle extension106may thread through strand aperture45in end wall22through which strand27extends. In some embodiments, spindle extension106may include external threads117. External threads117may threadedly couple spindle extension106with spindle nut119. Spindle nut119may allow stressing end anchor body18to be retained to end wall22during concrete pouring.

In some embodiments, after concrete23is poured, spindles103,105may be left in fixed end anchor13. In some embodiments, after concrete23is poured and set as depicted inFIG. 1B, spindle105may be removed from stressing end anchor body18by unthreading spindle105from lock nut101. Although sheath29may no longer be retained between extended spindle105and lock nut101after concrete pouring, sheath29may be prevented from retracting from stressing end anchor body18by concrete23. As understood in the art, concrete23surrounding sheath29may conform to surface irregularities of sheath29and may adhere thereto, thus preventing or restricting any contraction of sheath29.

In some embodiments, one or more seals may be positioned to prevent or restrict concrete23from ingressing into tension member15that may prevent or retard the tensioning of strand27. In some embodiments, as depicted inFIG. 2, gasket121may be positioned between lock nut101and stressing end anchor body18.

Although described specifically with respect to fixed end anchor13and stressing end anchor17, a spindle such as spindles103,105may be utilized with either a fixed end anchor or stressing end anchor. Furthermore, a spindle such as spindles103,105may 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 member15.

Although fixed end anchor13and stressing end anchor17are depicted as unencapsulated or bare anchors, such as those formed from ductile iron, fixed end anchor13and stressing end anchor17may 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, spindles103,105may be formed from a nonconductive material such as a polymer. In some such embodiments, spindles103,105may act to electrically insulate strand27, fixed end anchor13, and stressing end anchor17. This electric insulation may prevent or retard galvanic corrosion from occurring due to contact between strand27, fixed end anchor13, or stressing end anchor17when strand27, fixed end anchor13, and stressing end anchor17are formed from different metals.