US3833706A

US3833706A - Method of forming stressed concrete

Info

Publication number: US3833706A
Application number: US00163777A
Authority: US
Inventors: H Edwards
Original assignee: Cable Covers Ltd
Current assignee: Cable Covers Ltd
Priority date: 1968-08-27
Filing date: 1971-07-19
Publication date: 1974-09-03
Anticipated expiration: 1991-09-03

Abstract

A method of forming stressed concrete articles including post tensioning of a stressing tendon and utilizing an anchorage assembly including an anchor having a hollow housing and means therein for engaging a stressing tendon passing therethrough. The assembly includes a hollow member removalby attached to the anchor housing and to the concrete formwork and fixing the relative position of the anchor housing to the formwork. The member surrounds the tendon between the anchor housing and the formwork and is adapted and arranged to be detached from the anchor housing after the concrete has set. A cavity forming spacer is provided which surrounds the member and is disposed between and seals against the anchor housing and the formwork to form a cavity in the concrete. The spacer is adapted and arranged to be removed from around the member after the concrete has set.

Description

Sept. 3, 1974, H. J. w. EDWARDS 3,833,706v

METHOD OF FORMING STRESSED CONCRETE Original Filed Aug. 27, 1968 2 Sheets-Sheet l -nj i? W6 l Y FIGA I 46.', 42

72 Fl G., 5

4 l INVENTOR. yg yf 94 2f /f/y J//ff'dwmff Fler! 42 BY l 44 ,26 M 64 GMM A TTQRNEY 542933, 1974 HJ. w. EDWARDS 3,833,706

METHOD OF FORMING STRESSED CONCRETE Original Filed Aug. 27, 1968 2 SheetsSheet 2 fsa M4 126 INVENTOR 1,34 /fa/y d. Kiowa/'afs U.s. Cl. .gt4-2s 10 claims .ABSTRACT vOF THE DISCLOSURE .-A methodiof forming stressed concrete articles including post tensioning of a stressing tendon and utilizing an anchorage assembly including an anchor having a hollow housing and means therein for engaging a stressing tendon passing therethrough.-The assembly includes a hollow member Vremovably attached to the anchor housing and to the concrete formwork and fixing the relative position o f the anchor housing to the formwork. The member surrounds the tendon between the anchor housing and the formwork and is adapted and arranged to be detached from theanchor housing after the concrete has set. A cavity; forming spacer is provided which surrounds the member and is disposed between and seals against the anchor housing yand the formwork to form a cavity in the concrete. The spacer is adapted and arranged to be removed from around the member after the concrete has set.

CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION Field of the invention This invention relates to the post-tensioning of concrete structures by means of wire or strand cables. In particular this invention concerns an anchorage device or assemblyand parts thereoffor use in anchoring a cable or cables in a concrete structure. -In greater detail the invention -pertains to anchorages for concrete stressing tendons, particularly to anchorage assemblies for use in the tensioning of such tendons positioned within concrete structures after the concrete has set or cured.

For Amany years Ymild, low strength steel reinforcing was simply imbedded in ordinary concrete and the result Iwas an improvement in the strength of the concrete and someresistance to cracking and other failures was btained. Later there was an attempt to place this reinforcement under tension so that it would have a compression effect uponthe concrete. This slightly improved the construction although the success of this effort was not great becausepthose who did it did not appreciate the fact that concrete -would flow slightly under pressure thus that tension .on the reinforcement would be reduced practically back to. zero. Also under tension, the reinforcement itself would v.suffer from s omepermanent elongation that would add tothis reduction of the tension. Accordingly, the tensioning ofthe reinforcementv was not generally considered tozbe of great importance until recently when some of the factorsintiuencingthe effectiveness of reinforcement became better known and it was found that if steel wire having a very high tensile strength was used and placed under aqvery high tension, then although a part of the tensiOll. Waslost by-plastic flow and shrinkage in the concrete and permanent elongation or creep in the wire, nevertheless *sufficient tension would remain in the wire and,suticient compression would result on the concrete to cause amajor increase -in the load-carrying ca- Patented Sept. 3, 1974 pacity of the concrete and a major increase in the resistance of the concrete to cracking and the like. This represented such a complete departure from previously Iknown facts to present completely new concept in reinforced concrete and hence this high tension wire reinforcing of concrete was probably considered to furnish a cornpletely new and different approach to reinforced concrete construction. At the time that the possibility of using hightension wire reinforcement came into being a general idea of tensioned reinforcement had long been known and considered of relatively little value. The discovery that high-tensioned wire reinforcement could produce far stronger and more durable structures than had ever before been known was a discovery that revolutionized the manufacture of reinforced concrete structures.

Description of the prior art Anchors or anchorage assemblies for use in the posttensioning of stressing tendons within concrete structures have been previously devised, such prior art devices are generally disclosed in U.S. Pat. No. 3,293,811. Applicants invention of an improved anchorage assembly disclosed herein is an improvement over such prior art anchorage devices or assemblies, as shown for example in the above mentioned patent.

SUMMARY OF THE INVENTION Therefore it is an object of the invention to provide an improved anchorage assembly for concrete stressing tendons of the type which are cast in place in such a manner that they may be tensioned after the concrete has set or `been cured.

Another object of this invention is to provide an improved anchorage assembly for concrete stressing tendons in which there is utilized a single piece, wedge receiving and constraining plate anchor housing.

Still another object of the subject invention is to provide an anchorage assembly for concrete stressing tendons which includes a cavity forming spacer initially held in being engagement with the wedge receiving anchor housing and in being engagement with the concrete formwork when anchorage is secured to the formwork such as to provide a grout receiving cavity, the spacer forming an effective seal with the wedge receiving anchor housing to exclude concrete therefrom Where the concrete is being poured and cured.

Yet another object of the instant invention is to provide means whereby a tendon anchoring housing is imbedded in the concrete at the time the concrete is poured and by which means the anchor housing is attached to the formwork, and after the concrete has set the means permitting the formwork to be released from the anchor housing.

A further object of this invention is to provide an improved anchorage assembly for concrete stressing tendons wherein portions of the anchorage assembly may be salvaged and later re-used.

Yet a further object of the invention is to provide an anchorage assembly which will permit the anchor housing thereof to be left in the concrete and which anchor housing when left in the concrete will not produce an unsightly appearance.

In general these and other objects are attained byproviding an anchorage assembly including an anchor having a hollow housing and means therein for engaging a stressing tendon passing therethrough. The anchorage assembly includes a member removably attached to said housing and to the formwork, this member fixing the relat tive position of the anchor housingy with respect to the formwork. The member is additionally adapted and ar- The concrete objects produced in accordance with the apparatus of this invention may be of any desired shape ibut are generally beams, columns, channels, slabs or other like structural members. In accordance with this invention, the concrete objects are comprised of three essential parts, namely, the concrete itself, reinforcing members or tendons and the end anchorages that transfer the load of the reinforcing tendons to the concrete.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features which are believed to be characteristie of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a side elevational view, portions thereof being in cross-section, of the improved anchorage assembly of this invention;

FIG. 2 is a left-hand end view taken along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a side view of the anchor housing shown in FIGS. 2 and 3;

FIG. 5 is a prospective view of the wedges used in the assembly of FIG. 1;

FIG. 6 is a prospective view of the reusable bayonet fitting used in the assembly of FIG.V l;

FIG. 7 is a transverse-sectional View taken along line 7 7 of FIG. 3;

FIG. S is a cross-sectional view showing a second embodiment of the anchorage assembly of the invention;

FIG. 9 is a cross-sectional View taken along line 9 9 of FIG. 8;

FIG. l is a cross-sectional View taken along line 10-10 of FIG. 8; and

FIG. 1l is a top plan view of the reusable bayonet fitting used in the assembly of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, and in particular FIG. l thereof, the anchor or anchorage assembly 10 of this invention is depicted therein retaining an appropriate strand or tendon 12 to be used in the construction of a concrete beam, column, slab or the like. Cable or tendon 12 when used with the anchorage assembly of this invention in its intended application is often of the non-bonded type. This type of cable (non-bonded) comprises the normal prestressing cable which before delivery to the site is pre-cut and coated with a special protection and lubricating compound which guards against corrosion and minimizes friction during the stressing operation. The thus coated cable is wrapped in a special heavy duty reinforcing paper 14, as in FIG. 8, or a plastic sleeve or sheathing 16 is fitted over the entire length of the stand as in FIG. 1. In both cases the strand is free to move -within the covering. When the cable arrives at the site it is simply laid out in position and appropriate anchorage assemblies, such as at 10, are located on the ends thereof interiorly of the formwork or shuttering 18. After this the concrete is placed within the form with the anchor assembly 10 being recessed therein. When the concrete has set the tendon is then stressed by jacks which bear against the back of the anchor housing.

Assembly 10 generally includes a tendon anchor or housing 20, see in particular FIGS. 2 through 4; grips or teethed Wedges 22, see in particular FIG. a recess or -pocket former or spacer 24 for recessing anchor 20 into the concrete; and a releasable bayonet tting or member 26, see in particular FIG. 6, for maintaining the assembly in assembled form and when employed in combination with a nut 28 maintaining the complete and assembled asassavms Cil - r i sembly -rmly in position with respect to the shuttering or formwork 18 at any desired location thereon. The assembly is positioned on the formwork 18 at the desired location by means of a hole or opening 30 extending therethrough the bayonet iitting 26 of the assembly vbeing positioned therethrough and securedby means of 'nutf28 being tightened on a threaded portion '32 of bayonet suing 26. l' Y v The anchor or anchor housing 20 Aof anchor assembly 10 includes a forward end portion 31 having outwardly extending lip 33, a rearward end portion 35, and a conical-shaped bore or hollow passageway 34.extending theree through and through whichstrand Yor tendon 12 passes. Bore or hollow 34 is provided with an .enlarged forward portion or passageway 36 having a forwardly'facing shoulder 38 against which sheathing 16 abuts whereby the' same bunches up within enlarged portion 36 to prevent the con-'-` crete from entering internally into the anchor assembly from this its forward end portion 31. Bore or hollow-34'y is further enlarged by cavity 40 adjacent the rearward end portion 35' of anchor 20 to form a rearwardlyfacing shoulder 42, against which the forward end portion 44 of releasable bayonet fitting abuts.'Anchor 20 further includes a rib or flange member 46 of a generally rectangular shape having roundedcorners and positioned gen erally perpendicular to the axis of conical bore 34. Rib' or flange 46 distributes the stressing forces into the con-vv crete and thus reduces the stress intensities in the anchor# age zone. Member 46 additionally provides a safety factor in the fact that any bad compaction of the concrete in' the region of the face or forward end portion 31 of anchor 20 has less effect than would be the case if anchor hous" ing 20 were not provided with this flange or rib 46. Body portion 20 further includes agenerally rectangular shaped flange 48 extending outward therefrom and positioned generally adjacent the'rearward end portion 35' thereof.v Flange member 48 distributes the stressing forces into the concrete which reduces the stress intensities in the anchorage zone. Flange member 48 is provided with a slotted opening 50 in its top portionA extending downward from its upper edge and a slotted opening 52 in its bottom portion extending upward from its lower edge, see in particular FIGS. 2 and 3. Slots 50 and 52`ar'e provided such that anchor 20 may be secured tothe shuttering or framework 18 by means of nails (not shown) if so desired, ex?

tending through slots50 and 52 and into the formwork 18. Casing or anchor housing 20 is'further provided'with a pair of reinforcing ribs or members r54'and` 56 extiende'VL ing from adjacent the rearward end portion 35 and adja-A" cent opening or cavity 40 upward to the upper outer edge of flange or plate member 48. In like manner, a second edge of flange member 48.y

Wedges or jaws 22, see in particular 'FIGS '5f' have a conical shaped outer surface to generally conform to the conical configuration of passagewayor hollow 34' within anchor housing 20. Wedges 22 are provided 'withi teeth or serrations 62 extending laterally round their inn'er opening or passageway 64 to grip and bite strand 12 pass-jing therethrough, as depicted in FIG. 1. Jaws orwedgesK 22 are split and include a lleft' 66 andV right' 68'mernber or portion to tit around strand 12 and generally' conform thereto as the jaws 22 are pulled forward 'within bore 34'.l Further, each of the jaw or wedge sections or portions 66"; and 68 are slit or provided with slotted" openings,vv re` spectively at 70 and 72 adjacent their mid portidrisjivhei j by the upper and lower portions'of eachwedge section" 66 and 68 may move vtowardeach 'otherto generally -con- 'passing' theret'hrough,A l

form to and better grasp' tendon 12 see also FIG. 3; l

ing a central bore or passageway: "74 vextendingtherethrough, with an enlarged forward end" portion "76 to per# mit bayonet fitting 26 to extend therethrough and to generally accommodate the same. Forward end portion 78 of lcavity forming spacer 24 abuts rearward end portion 35 of anchor 20 to generally seal therewith to exclude the Vcement or grout from entering the anchorage assembly at this point. `In addition, rearward end portion 80 of recess former or spacer 24 abuts and generally seals with the forward edge of formwork 18 to prevent the cement from gaining access to the interior of the anchorage assembly at'this particular location.

" Detachable and releasable bayonet fitting or hollow member 26 includes a circular elongated portion 82, a threaded outer end portion 32 and an enlarged circular forward portion 84 connected to portion 82 by a transition portion 86. Elongated portion 82 extends through opening 30 within formwork 18 and through passageway or opening 74 within pocket or recess former 24. Enlarged forward portion 84 of the bayonet fitting is positionable within the enlarged rearward portion cavity `40 of the casing or anchor housing 20 outwardly of the wedges or jaws 22 such as to not interfere with the operation of the same. The forward end portion 44 of bayonet fitting 26 which abuts rearwardly facing shoulder 42 of anchor 20 is provided with a

pair

88 and 90 of flange members or shoulders (see FIGS. 3 and 7) which respectively fits behind and engage a pair of lips or shoulders 92 and 94 provided on anchor housing 20 adjacent its rearward end portion 35 and extending inward of enlarged opening or cavity 40.

rUpon proper positioning of the forward end portion 44 of bayonet fitting 26 within cavity `40 of anchor 20 and rotation or pivoting of the fitting such that -

ffange members

88 and 90 become engaged behind lips 92 and 94, the fitting 26 becomes releasably aixed or secured to anchor 20. The pocket or recess former 24 is then positioned over bayonet fitting 26 with enlarged forward portion 84 thereof fitting within the enlarged forward portion 76 of pocket former 24. Next the threaded portion 32 of elongated portion 82 of fitting 26 is positioned through opening 30 within the formwork 18, and the nut 28 is threaded on portion 32 of bayonet fitting 26. Transition portion 86 of bayonet fitting 26 prevents jaws or wedges 22 from coming out of their proper position within bore or hollow 34 of the anchor housing 20. Nut 28 is tightened on threaded portion 32 to pull bayonet fitting 26 through formwork 18 causing the attached anchor 20 to tighten against pocket former 24 thereby forming a seal between pocket former 24 and formwork 18, and between pocket former 24 and anchor 20 to prevent cement from entering the anchorage assembly 10 at these points of adjoinment. Next the concrete is poured and placed within the formwork or shuttering. After the concrete has set, nut 28, formwork 18, pocket former 24 and bayonet fitting 26 are removed to afford access to the back of anchor body 20 and wedges or jaws 22 positioned therein, which are now recessed within the set concrete. The tendon may now be stressed by jacks which bear against the back of anchor housing 20, and jaws 22 may be tapped home to firmly and snugly grip the stressed strand 12. After stressing tendon-12, the opening in the concrete which was formed by the recess or cavity forming spacer 24 canY be grouted-in if so desired.

Withdetailed reference to FIGS. 8 through l1 now, a second embodiment of the anchorage assembly 100 is depicted therein retaining strand or tendon 12, having been. wrapped with heavy duty reinforcing paper 14, to be used in the construction of a concrete beam, column, slab or the like. Assembly 100 generally includes an anchor housing or casing 20', identical to that seen in FIG. 1 grips or teethed wedges 22', identical to those shown in FIG. 5, a recess or pocket former 102 for recessing casing or anchor housing 20 -into the concrete, a releasable and detachable bayonet fitting 104, see in particular FIG. 1l, and a split nut 106 for maintaining the assemblyfirmly in position with respectto k shuttering or formwork 18. -v

'Casing or anchor housing 20fof anchorage'assembly includes a forward end portionl', a rearwardl end -portion 35,' and a conicalI shaped borey or hollow 34' extending therebetween, through .which tendon 12 passi es. Bore 34' includes an enlarged forward portion or passageway 36 and an enlarged rearward portion orcavity 40. Anchorhousing 20 further includesl a flange-like member "46' which aids in distributing and stressing forces into the concrete to thereby reduce the stress intensities in the anchorage zone, and provides a safety factor in that any bad compaction of the concrete in the region of the forward end portion 31 of anchor 20' has less effect than would the same if the anchor housing were not provided with this fiange member 46. Anchor housing 20' further includes a pair 92 and 94' of lips or shoulders adjacent rearward end portion 35 extending inward of enlarged rearward opening or cavity 40', behind which bayonet fitting 104 is engageable, as will be explained more fully hereinbelow.

In the embodiment of the strand anchor assembly shown in FIGS. 8 through 11, a grout or cement ex'truder or bushing 108 is provided which snugly and engagingly fits within enlarged forward portion or passageway 36' of bore or hollow 34 within anchor housing 20. Cement extruder 10-8 fits closely and snugly about tendon 12 passing therethrough such as to prevent grout or cement from entering anchor assembly 100 at this forward end portion thereof.

Recess or pocket former 102 is hollow and preferably formed from a frangible material of good release properties, such as a suitable plastic. Cavity forming spacer 102 includes an outer conical shaped shell portion 110 and an inner centrally disposed, hollow cylinder portion 112, through which tendon 12 passes and which is connected to the outer conical shell portion 110I by suitable webs such as 114 and 116. Webs 114 and 16 are joined or connected at 11S adjacent their outer ends to seal pocket former 10-2. Additional webs, such as indicated by dotted lines at 119 and 120, may join outer -shell 110 and inner cylinder 112 to further strengthen and rigidify pocket or recess former 102. The rearward end of inner cylinder portion 112 of recess former 102 stops short of the formwork or shuttering 118, while the rearward edge of outer shell portion 110 of pocket former 102 extends completely to the formwork 18 to form a seal therewith when the parts of the assembly are tightened together. The inner end 122 of outer shell 110 extends outward beyond anchor 20 :and forward of rearward end portion 35' thereof to form an effective seal with anchor housing 20 to prevent cement from entering the anchorage assembly at this point. The forward end portion 123 of central hollow cylinder portion 11'2 of recess former 102 is enlarged to generally accommodate and conform to Vthe shape of bayonet fitting or member 104.

Bayonet fitting 104, which is releasable and detachable includes a circular elongated hollow portion 124 having a threaded outer end portion 126 and an enlarged c ircular forward end portion 12,8 connected to elongatedV portion 124 by a transition portion 130. Elongated portion 124 is positionable through the opening of hollow cylinder 112 of recess former 102 and through opening or passageway 30 within formwork 18'. IEnlarged forward end portion 128 of bayonet fitting' 104 is positionable within enlarged rearward portion or cavity 40 of anchor housing 20', and a pair of flanges or shoulders 132 and` 134 on forward end portion 128 of bayonet 104 are 'respectively engageable behind and with lips or shoulders 92 and 94 of anchor housing 20. Bayonet fitting or member 104 has a portion removed therefrom to form a slot or opening 136 extending over yits entire length such that fitting 104 can be slipped transversely over or` clipped on cable or strand 12, thereby eliminating the need ofthreading fitting 104 over the entire length of strandZ upto' the pointwhere itv is desired to be put to use. Additionally bayonet or hollo'w member 104` is provided with'fav" V-notchw138i' extending about its entire cirduiriferenc and positioned 'on enlarged forward end portion `128 adjacent transition'po'rtion 130. V-notch 138 permits 'iittin'g 104 'to be broken "oi 'at'this point, such as when iormworlt' 1,8 is stripped away from the hardned concrete, leaving'only the enlarged forward end por-k tion 128 with anges or shoulders'132 and 134 of bayonet 1041`n anchor housing `40'.""Alternatively fitting 104 instedofr-being'brokenoff by V-notch 138 can be removed from anchor 20' by simple rotation of and release of

anges

132 and 134 from behind lips or shoulders 92 and 94 and reused with another casing, similar to casing 20', at another point along tendon 12.

In like manner nut 106v has a portion or section removed or cut-out from its entire thickness to provide a slot or opening 140 therealong whereby the nut may be transversely slipped over or clipped on strand 12 to eliminate threading of the nut over the entire length of strand 12 up to the point where it is intended to be used.

The embodiment of strand anchor assembly 100` depicted in FIGS. 8 through l1 has particular applicability when employed along the mid-portions or sections of a particularly long strand which is to be used in the stressing of concrete. When thus employed, using the readily slottable recess former 102, slotted bayonet fitting 104 and slotted nut 106, the assembly can be readily arranged and assembled on the mid-portion of the strand or tendon without the necessity of threading these por- Vtions or parts of assembly 100 over the entire length of the strand from its end to its mid-portion. In this use pocket or recess former 102 is split at reference number 115 where webs 114 and 116y are joined together and then placed or clipped over strand 12. Next the slot so formed in recess former 102 is closed by joining webs 114 and 116 together with staples 117 or the like. Now yslotted bayonet fitting 104 is clipped over strand 12 and located and secured in cavity 40 of anchor 20'. The pocket former 102 is then pushed over fitting 104 and the whole assembly 100 is lined up in slot or opening 30in formwork 18, after which split nut 106 is clipped on strand 1-2 and tightened on threaded portion 126` of tting 102 against the outer face of formwork 18- adjacent opening 30 therein. When anchorage assembly 100 is used in the mid-portions of an extended tendon, anchor 20' is usually placed on the strand in the factory at the approximate position at which it will be used before the strand is shipped to the location for use. Once the concrete has set and cured, formwork 18 is stripped by means of leverage between the formwork and the concrete, thus breaking of bayonet tting 104 at notch 1358. Pocket former 102 is then extracted to leave anchor housing and lenlarged forward end portion 128 of bayonet fitting 104 recessed within the concrete.

While only certain preferred embodiments of this invention have been shown and described by way of illustration, many modifications Ywill occur to those skilled in the artand it is, therefore, desired that it be understood that it is;l intended in the appended claims to cover all such modifications as fall within 'the true spirit and scope of thisinvention.` l y, f

What is claimed as new and 4what it is desired to secure by Letters Patent ofthe UnitedStates is:

1.` A method for forming a stressed concrete structure including a post-stressing tendon, extending between a pair of opposed and spaced formwork members and fixed with respect to one of theformwork members and a tendon.

anchorage positioned inwardly of the` other formwork member with the tendon passing through the other form'- work member and anchorage comprising the steps of securing a means including a temporary and positive locking means anda void forming means surrounding the locking-means to the anchorage with the locking means 8 extending from the anchorage andv passing'` ai in the concrete when it is setand through thefother lfornir- Work member at a predetermined spaced position there'- fr'om, urging the anchorage toward the other trmworl'g member with the void `forming means sandwichedbetwee'n the anchorage and the other formwork'membe'b'y adjus't able means attached'to the locking means outwardly/pf and bearingly against the other form'work m mbert'ro. tix the anchorage in proper positionwith respectto the other formwork member and the tendon andto tight sealthe void forming means tothe anchorage and the o lr formwork member, pouring the concrete `withinethe formworli members and about the tendon and Athe.anc'ihorage and about the void forming means, completely removing the void forming means and locking means after the concrete has set, stressing the tendon, and setting the anchorage to grip and retain the tendon under tension. p f i 2. In the method as deiined in claim 1 wherein said void forming means comprises a spacer member separate from said locking means, said step of securing a-means including the step of inserting the spacer member tightly sandwiched between the anchorage and the other formwork member with the spacer member eXtendingabout-the locking means to form the void in the set concrete.

3. In the method as deiined in claim 1 further comprising the step of temporarily setting the anchorage .to grip the tendon prior to said step of pouring the concrete. ,v

4. The method as defined in claim 3 wherein said void forming means comprises a spacer member separate-,from said locking means, said step of securing a means ,includ-` ing the step of inserting the spacer memberbetweenthe anchorage and the other formwork member Awith the spacer member extending about the locking means to form the void in the set concrete. t

5. A method for forming a stressed concrete` structure including a post-stressing tendon extending between a pain of opposed and spaced formwork members and fixed with respect to one of the formwork members* and a tendon anchorage positioned inwardly of 'the other formworle member with the tendon passing through the other form-r- Work member and anchorage comprisingthe steps offsecuring a means including a temporary and positive locking means and a void forming means to the anchorage with the locking means passing throughthe other form# work member at a predetermined spaced Vpositirnrlthere= from, removably fastening the locking means'externally of and bearingly against the other formwork member with: the anchorage urged toward the other formwork member and with the void forming means sandwiched therebetween in sealing relation to the anchorage and thefother formwork member, pouring the concrete within the formwork members and about the tendon and the anchorageand the' void forming means, removing the void forming' means and locking means after the concrete has set, stressing the tendon, and setting the anchorage to grip -lan'dretainI the tendon under tension. :r i 1 f,-

6. In the method as defined in claim 5 wherein-'said' locking means includes an elongatedmember; and saidi void forming means comprises a-spacer membenwsaid lstep".

of securing a means including the step of insertingthe'v spacer member tightly sandwiched between the-anchorage. and the other formwork member with the jspacerimember extending about the elongated-member to form the void. in the set concrete. l

7. In the method as defined in claim S further compris- 9. A method for'forming a stressed concrete structure,

the steps prior to pouring the concrete of laying the poststressing cable in place, placing an anchorage means having an aperture about the cable inwardly of the formwork, placing a means for locking and forming a void about the cable with a portion extending through an opening in the ormwork, temporarily and positively connecting the portion to the anchorage means temporarily and positively securing the portion externally of the formwork, adjustably urging the portion externally of the forrnwork and the attached anchorage means toward the formwork thereby to hold in xed position the anchorage means by the formwork through the portion, sealing the portion by another void forming portion surrounding same between the anchorage means and formwork for preventing the seepage of concrete therebetween and to form a void in the set concrete whereby the portion may be removed.

10. In the method as dened in claim 9 wherein the portion comprises a sleeve and the void forming portion comprises a spacer, placing the spacer around the sleeve and between the anchorage means and the formwork to prevent seepage of concrete onto the sleeve and to form a void in the concrete after setting thereof whereby the spacer and sleeve may be removed after setting of the concrete and removal of the formwork.

References Cited UNITED STATES PATENTS 2,781,658 2/1957 Dobell 264-228 2,695,754 11/1954 Karig 264-228 2,029,147 1/ 1936 Anderson 249-217 3,184,219 5/1965 Simms 254-29 A ROBERT F. WHITE, Primary Examiner T. P. PAVELKO, Assistant Examiner U.S. Cl. X.R.