Pocket former and method for reanchoring live tendons

Abstract

A method for re-tensioning a stressed tendon cast in a reinforced concrete structure includes removing concrete from the structure to expose the tendon. A pocket former is attached to the exposed tendon. The pocket former comprises two partial sections assembled to enclose the tendon. Grout is poured around the pocket former and is allowed to substantially cure. The pocket former is removed and the tendon is cut. An anchor is assembled to the tendon and the tendon is stressed.

Claims

1. A method for re-tensioning a stressed tendon cast in a reinforced concrete structure, comprising: removing set concrete from the structure to expose a stressed part of the tendon, the tendon being stressed to reinforce the structure prior to the removing set concrete; attaching a pocket former to the exposed stressed part of the tendon, the pocket former comprising two partial sections assembled to enclose the stressed part of the tendon without cutting the stressed part of the tendon; pouring grout around the pocket former; allowing the grout to substantially cure; removing the pocket former; cutting the stressed part of the tendon; assembling an anchor to the cut part of the tendon; and stressing the cut part of the tendon.

2. The method of claim 1 further comprising removing a further part of the reinforced concrete structure, wherein the further removed part comprises the stressed, cut part of the tendon.

3. The method of claim 2 wherein removing the removed part forms an opening in the concrete structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example embodiment of a concrete block out (pocket former) used to form a pocket for tendons under tension prior to affixing a new anchor.

(2) FIG. 2 shows the pocket former of FIG. 1 surrounding an encapsulated anchor.

DETAILED DESCRIPTION

(3) In a method for reworking a reinforced concrete structure according to the present disclosure, the following actions may be performed. First, based on where part of the concrete structure is to be reworked, such as to make an opening, the tendons that will require re-anchoring should be located within the concrete structure with respect to position and depth. The location of such tendons may be used to determine the best places to chip out the concrete in the concrete structure to expose the tendons.

(4) Once the places to chip out the concrete are determined, at each such location, cut a hole large enough to allow the pocket former to be installed around the stressed or “live” tendons may be created by chipping out the concrete of the concrete structure.

(5) The pocket former is installed around the live tendons to be re-anchored. A form board may be installed around the pocket former(s) to prepare for pour back with grout. Grout may then be poured into the hole having the form board in place and pocket former around the tendon(s) to be re-anchored. The pocket former and form board in combination provide that the shape of the grout after cure will provide a load bearing surface for one or more post-tension anchors.

(6) The grout may be allowed to cure to full compressive strength after pouring. The same procedure may be performed at all tendon locations to be re-anchored prior to cutting any such tendons and re-stressing. It is important to ensure that the curing of the grout is substantially complete while the tendons are still live, that is, prior to cutting for re-anchoring. This make it possible to cut only one tendon or one group of tendons and then re-stress it before repeating the procedure on subsequent tendons or groups of tendons. This enables keeping as many tendons as possible under load so as to avoid the need to re-shore the concrete structure for de-tensioning and re-stressing.

(7) Once the grout is substantially fully cured, the pocket former may be removed and the tendon(s) cut. New strand anchors may be installed over the tendon(s) in the blockout(s) formed by the pocket former. The blockout(s) are shaped so that the anchor(s) will fit within the respective blockout(s) with their load transfer surface(s) in contact with the edge of the grout and with suitable features formed in the grout to enable tensioning the tendon(s). The tendon(s) may then be tensioned to the desired force and allowed to seat in the respective anchor(s).

(8) The foregoing procedure may be repeated for each tendon and/or group of tendons. Once all tendons have been cut and re-stressed, it is then possible to cut the opening or the concrete section to be removed without the need to perform any action on tendons present in such section because any such tendons have been decoupled from the reinforcing system.

(9) A Clam Shell Blockout according to one embodiment may be in the form of a four-piece pocket former mold that can be placed around one or more live tendons. This makes possible for the live tendons to be cut and re-stressed after pouring the grout. A method for performing such cutting and restressing will be explained in more detail below.

(10) FIG. 1 shows an example embodiment of a pocket former according to the present disclosure. The pocket former 10 may comprise an anchor section comprised of two partial (e.g., half) sections 12 and a tendon section comprised of two partial sections 14. The partial sections 12, 14 may be assembled around one or more exposed, live tendons in a chipped out section of concrete structure as explained above. The anchor section will produce a pocket in the grout in which one or more anchors (FIG. 2) may be inserted for re-stressing (re-tensioning) the one or more tendons as explained above. The tendon section will produce a pocket in the grout so as to enable the tendon(s) to be accessed for affixing the anchor and re-stressing after the grout is cured.

(11) FIG. 2 shows the pocket former 10 split and disposed about an encapsulated anchor 16 to provide better understanding of how the pocket former 10 is used. The anchor 16 may be any type used in post-tension concrete reinforcement. As a non-limiting example, an encapsulated anchor such as disclosed in U.S. Pat. No. 7,275,347 issued to Hayes.

(12) Various embodiments of a pocket former may comprise shapes enabling placement of one or more anchors proximate each other to re-anchor a single tendon or a plurality of tendons depending on the structure of the reinforcing system used in any concrete structure.

(13) Using a pocket former and method according to the present disclosure, it may be possible to avoid re-shoring that is often a time consuming and expensive part of cutting out and removing post-tensioned concrete slabs.

(14) Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.