US3230678A

US3230678A - Hold-down anchor device for prestressed grouped cables

Info

Publication number: US3230678A
Application number: US233761A
Authority: US
Inventors: George J Eriksson; Erskine W Klyce
Original assignee: Superior Concrete Accessories Inc
Current assignee: Superior Concrete Accessories Inc
Priority date: 1962-10-29
Filing date: 1962-10-29
Publication date: 1966-01-25
Anticipated expiration: 1983-01-25

Description

3 Sheets-Sheet 1 ,fill/IV VWM Jan. 25, 1966 G. J. ERlKssoN ETAL HOLD-DOWN ANCHOR DEVICE FOR PRESTRESSED GROUPED CABLES Filed 001'.. 29, 1962 INVENTORS GEOQGE J. ERIKSSON ERSKINE W. KLYCE Jan. 25, 1966 G. J. ERlKssoN ETAL. 3,230,678

HOLD-DOWN ANCHOR DEVICE FOR PRESTRESSED GROUPED CABLES 3 Sheets-Sheet 2 Filed Oct. 29, 1962 INVENTORS GEORGE J. ERIKSSON EPSKINE W. LYCE BY m 68 w (Hwy.

Jan. 25, 1966 G. J. ERlKsscN ETAL 3,230,678

HOLD-DOWN ANCHOR DEVICE FOR PRESTRESSED GROUPED CABLES Filed Oct. 29, 1962 3 Sheets-Sheet 3 INVENTORS GEOFZGE J. ERIKSSON EQSKINE W. YCE

i? @fifi/alf.

lstraight-line fashion. .hold-down anchor devices. However, those cables kwhich United StatesPatent C) The present invention relates to la hold-down yanchor device by vmeans of swhich Athe tensioni-ng' cables which are embedded in 'aprestressed concrete girder may be Vheld under tension and Ain their proper relative positions lwithin the 'girder form during initial pouring land subsequent hardening' or setting' of the concrete so that, when 'the tension inthecables Vis relieved after the concrete has become 'set and 'the projecting' or overlapping ends of the cables'have'b'een 'severed fromithe ends of the girder, the concrete of thegirder will remain prestressed, thus providing a girder which possesses greater ystrength ythan conventional 'gir'ders vwhich lare not prestressed in this manner. Giders ofi-the type withwhichthefpresent hold-down anchor device' is` useable lmay-'assume various 'cross-sectional shapes-as,ffor example, -the sha-pe of an 'YI-beam. Although a hold-down anchor device embodying thepresent invention is useable in connection with prestressed concrete girders and other structural forms vwhich vary 'widely in *their configuration, Van VI-beam structure lends itself lwell as -an exemplary 'disclosure illustrating va typical use of the -present inventionan'd, therefore,for purposes o f discussion j=herein, -the present `invention-has been described in fconnection witha pre- `stressed girder of the KI-beam` type.`

Manufacturing specifications frequently specify 'that the tensioning cables of a prestressed concrete girder or -other structural sha-pe be'contiguous throughout certain portions of their' extent throughthe girder. Such vcables 'arereferred to as-grouped cables 'andispecial hold-down anchor devices `are employed for'holdin'gfthem in their .contiguous or abutting relationship within portions of the girder form. The presentinvenftionrelateslspecically to this type yof jgrouped-cable-hold-down anchor device.

In the manufacture -of 'arprestressed concrete girder of the `I^beam configuration, the utensioning cables of .which .there may jbe a relatively 'large Inumber are strung longitudinally through thehollow girder form in different but generally'longitudinally extending directions. Certain of the cables may-be strung linearly` and yaxially through the girder-form in straightaline yfashion, while others may deviate from such axial alignmentat various angles. For example, certain of the cables of a prestressedconcrete'girderof I-beam configurationare strung through the concrete girder form lso that Ythey will extend inwardly from the ends'o'f thegirder in the head portion thereof and will be `inclined 4downwardly and pass through the narrow webportion -of the Vgirder land .enter the girders base portion, ,after which they will extend longitudinally Vin ystraight-.line fashion through the base portion of .thegi'rden The cables are thus caused to make aso-calledfdip as they pass through the girder from one end to the other. The end regions of the cables are thus .embedded in the head portion of the girder while Vthe medial regions ofthe cables 'are embedded in the girders base portion. Certain other cables are caused to pass through the base portion of thegirder outside the transverse `contines of the web portion in These latter cables require no arestrung through the form at varying angles-do require Ice Patented Jan. 25, 1966 hold-down anchor devices so that when the usual hydraulic tensionng means is set into operation, such cables will Vbe drawn taut in their predetermined directions of exytentthrough the girder form.

As is well known in the art, there currently are employed two basic-methods of 'installing hold-down anchor devices in a girder form. These are, namely, `the pulldown method and the push-down method. The holddown anchor device of the present invention' is applicable to both of these methods and,in each case, it offers certain material advantages over conventional anchor devices. In the case of the push-down method of instalwlation,4 however, the present hold-down anchor device offers advantages over and ahovethose offered in con- 4-necticn with the two other methods.

In the pull-down method, the cables are passed loosely through the form, the anchor device -is then yapplied thereto and, finally, the device is attached to la pull-down cable -vwhich Vextends through a hole in the bottom of the concrete form and drawn downwardly by suitable hydraulic mechanism to apply tension to the various cables and pull them taut and into the proper `positionwhich they will assume when they concrete for the girder is poured. In the push-down method, a

4-guide cable'is attached to a hold-down bracketbeneath .cable is then passed upwardly through anv hydraulic jack and a third strand chuck Vis applied to the g'ui'de cable above theljack. The cableswhich are to be prestressed arethen-passed through the form and the lhold-down anchor device applied thereto as in the case of the pulldown method, after which the hydraulic jack is ex- -panded to vf-push the second strand chuck downwardly into engagement with the Aanchor device, whereupon both the chuck and anchor device are slid downwardly along -the guide-cable `to draw the various tensioning cables taut. After the'predetermined degree of tension is attained in the tensioning cables, the guide cable is burned or cut oli immediately above the second strand chuck and this chuck and the anchor device subsequently become embedded in the concrete and are thus expendable when the concrete is poured. The two other strand chucks and, of course, the hydraulic jack, are retrieved forfuture use.

The various strand chucks which are employed in connection with the pull-downl and push-down methods of=holddown anchor installations are of the two-part slidingcollet type and the cost thereof is comparatively high. When employing the push-down method of installation tothe hold-down anchor device of the present'invention, the only strand chucks which need be employed are re- 'trievable after concrete pouring and setting operations andthe only expendable item of this character is a single collet jaw-assembly, the cooperating base for .which is integrally cast with the body of the hold-down anchor device. Otherwise, the push-down equipment and the method which is involved in the use remain unchanged. vThis elimination of the -need for the use of a complete and expendable strand chuck constitutes one of the `principal objects of the present invention.

It is a further object of the invention to provide a hold-down anchor device which will more positively group the tensioning cables to which it is applied than Willa conventional device for the sameY purpose, such-positive grouping of the cables being effective regardless of which .of the two methods of installation is employed for nal cable-tensioning purposes.

A further object of the invention is to provide a holdl down anchor which, in the main, is of one-piece cast metal construction and, except for the use of an associated collet jaw, is possessed of no moving parts to the end that installation problems in the ield are simplified.

Numerous other objects and advantages of the invention, not at this time enumerated, will become readily apparent as the nature of the invention is better understood from a consideration of the following detailed description. l

In the accompanying three sheets of drawings forming a part of this specification, one illustrative form of the invention has been shown as embodied in different types of installations.

In these drawings:

FIG. 1 is a fragmentary sectional view taken substantially centrally, longitudinally and vertically through a concrete girder form showing two of the hold-down anchor devices of the present invention in operative position in the form and illustrating two different ways of applying reaction forces to the devices for holding them in position against the upward pulling force of the cables undergoing prestressing;

FIG. 2 is an enlarged fragmentary side elevational view, partly in section, showing one of the hold-down anchor devices of FIG. 1 operatively installed in a girder form according to a push-down method; l

FIG. 3 is a side elevational View of the one anchor device exclusive of its associated strand chuck;

FIG. 4 is a top plan view of the anchor device;

FIG. 5 is a bottom plan view of the anchor device;

FIG. 6 is a sectional view taken on the line 6-6 of FIG. 3;

FIG. 7 is a sectional View taken on the line 7-7 of FIG. 5; and

FIG. 8 is a side elevational view, partly in section, and schematic in its representation, illustrating one of the several methods for applying tensioning stress to the cables which are associated with a concrete girder form during installation of the improved hold-down anchor device in the form.

Referring now to the drawings in detail and in particular to FIG. 1, a prestressed concrete girder utilizing a number of the hold-down anchor devices of the present invention has been fragmentarily illustrated and is designated in its entirety by the reference number 10. The girder is shown as being in position within the form which is initially prepared to receive the concrete of the girder during pouring operations. Only the at base 12 of the form is shown in FIG. 1 and only two of the holddown anchor devices appear in this view. For purposes of description herein, it may be assumed that the girder is in the form of an I-beam and that the section represented by this view is taken longitudinally and centrally through the web portion of the girder. For a full disclosure of a prestressed concrete girder having the configuration of an I-beam and utilizing hold-down anchor devices in the web portion thereof, reference may be had to United States Patent No. 3,006,114, granted on October 31, 1961, and entitled Hold-Down Anchor Device for the Embedded Cables of Prestressed Concrete Girders.

In the illustration of FIG. 1, a plurality of tensioning cables 14 extend in a generally longitudinal direction completely through the girder 10 from end-to-end and assume various directional positions within the girder as will be described presently. The cables 14 are firmly embedded in the surrounding mass of concrete and are initially positioned in the concrete girder form by means of the aforementioned hold-down anchor devices, each of which has been designated in its entirety by the reference numeral 16. These anchor devices are of unitary one-piece cast metal construction and, insofar as their manufacture is concerned, they are identical. As will be described in greater detail subsequently, the anchor device 16 appearing at the left-hand side of FIG. l is shown as being held in position within the concrete girder form by what is commonly known as a pull-down method, whereas, the anchor device that is shown at the right hand side of this view is held in position by what is commonly referred to as a push-down method. When the pull-down method of installation is employed, the holddown anchor device 16 has welded thereto a conventional threaded nut 18 for anchoring purposes in connection with the pull-down instrumentalities. When the pushdown method of installation is employed, the device 16 has associated therewith a conventional split collet jaw assembly 19 (see also FIG. 2) for anchoring purposes in connection with the push-down instrumentalities.

Prestressed concrete girders of I-beam configuration, such as the girder which is illustrated herein, may have several groups of cables extending therethrough in a generally longitudinal direction. Certain of these cables are not deected and, therefore, they extend longitudinally through the girder in straight line fashion. Such cables usually are disposed in the I-beam iianges of the girder. The present invention is particularly concerned with tensioning cables which extend through the web portion of the girder and are deected by the hold-down anchor devices 16 in the manner shown in FIG. 1, so that they extend from the upper regions of the girder at one end thereof inwardly and downwardly on an incline in converging fashion through the web portion of the girder and into the base portion thereof where they are engaged by the hold-down anchor devices 16 and are grouped together at this region. Each anchor device is adapted to accommo-date the grouping of a plurality of the tensioning cables 14. After such grouping, the cables extend generally horizontally along the base of thegirder in contiguous relationship and, further along the girder, they diverge and are grouped together, after which they extendl upwardly on an incline in diverging fashion toward the other end region of the girder and pass into the head portion and then emerge from the girder. While any number of such cables may be employed, depending upon the height of the girder, for exemplary purposes, the group of cables 14 is shown herein as being arranged in four vertical tiers, each anchor device 16 accommodating eight of the cables, i.e., four on each side thereof. Additional groups of similarly arranged cables 14 may be disposed on opposite sides of the cables illustrated herein, in which case each group of eight cables will be accommodated by two additional anchor devices (not shown). It will be understood that a similar arrangement of prestressing cables may be employed in connection with elongated girders other than those which are specifically of I-beam construction. The specific nature of the prestressed concrete girder 10 forms no part of the invention and no claim is made herein to any novelty therein. The novelty of the present invention resides rather in the construction of the hold-down anchor devices 16 by means of which the cables are initially held in their proper directional orientation Within the concrete girder form preparatory to pouring of the concrete, and the nature of which hold-down devices will now be more fully described and subsequently claimed.

Still referring to FIG. 1, it is to be noted that, while the hold-down anchor devices y16 are substantially identical in construction, the manner in which they are maintained in position within the girder form is different in the case of the two illustrated devices. As will be described presently, after the nature of the hold-down anchor devices has been made clear and, in connection with the installation of these devices in the concrete girder form, the hold-down device sli'own at the left-hand side of FIG. 1 is pulled into position through an opening 20 in the base member 12 of the con-crete girder form, while the device 16 shown at the right-hand side of this view is pushed into position from above the form. In either instance, the cables 14 which have their ends previously anchored n position, are drawn taut during the pulling or pushing operation, as the case may be. Y

Referring now to FIGS. 2. to 8, inclusive, each anchor device 16 is in the form of a single, unitaryy metal casting which, as best shown in FIG. 3, is roughly of M-shape configuration and includes an upper bridge portion 22 from which there depend three vertical legs, namely, a central leg 24, and two

outside legs

26 and 28, the three legs extending in parallelism. The

twovoutside legs

26 and 28, in combination withithe central leg 24, define a pair of relatively deep cable-receiving

notches

30 and 32, each of the notches being adapted to receive therein four of the cables 14 in nested fashion one above the other and in contiguous or tangential relationship as indicated by the `dotted outline circles in FIG. 2. In installations where there are a larger number of cables in each tier, a correspondingly larger number of the cables will be received within the

notches

30 and 32.

The two

outside legs

26 and 28 are solid and each is formed with lateral reinforcing webs 34 on the front and rear sides thereof as best shown in FIG. 7. The central leg 24 is tubular and embodies a vertical, open ended bore 36 which is designed for sliding reception therethrough of a guide cable when a push-down installation is contemplated. Where a pull-down installation is contemplated, the bore 36 is designed for reception therethrough of a lag bolt. At the regionV where the central leg 24 joins the bridge portion 22, two reinforcing gussets 38 (see FIG. 3) are provided. Further down, the leg 24 assumes the shape illustrated in FIG. 6 wherein thickened webs 40 on opposite sides thereof give a generally elliptical appearance to the leg in horizontal cross section. The lower end s of the three legs Z4, 26 and 2S terminate in the same horizontal plane. The inside surfaces of the

outer legs

26 and 28 present obtusely arranged at faces 42 (see FIG. 7) while the ywebs 40 have rounded inner faces to assist in guiding the cables 14 as they are pulled through the

notches

36 and 32.

The bridge portion 22 is formed with an integral upstanding boss 44 of generally cylindrical design, and a frusto-conical socket 46 of small slant angle passes through the boss 44 and into the metal of the bridge portion 22 where the small end thereof communicates with the upper end of the bore 36. As will be pointed out in greater detail hereafter, the frusto-conical socket is adapted to receive therein the previously mentioned collet jaw assembly 19 of a conventional strand chuck when a push-down type of installation procedure is being carried out, to the end that the entire anchor device 16 may be slid downwardly along the guide -cable in a unidirectional manner.

When the pull-down method of installation is employed for installing the device 16 as .shown at the lefthand side of FIG. l, it is preferable that the nut 1S be welded to the upper end of the cylindrical boss 44 so that the threaded bore in the nut is in axial alignment with the axis of the internal bore 36 in the central leg 24. The cables 14 have their ends anchored to suitable reaction points adjacent toV the ends of the concrete girder so that initially these cables extend longitudinally along the concrete girder form coextensively therewith adjacent to the upper regions of the latter or slightly thereabove. The device 16 is then interposed between two adjacent vertical tiers of the cables and the latter are pushed into the two

notches

30 and 32, the cables of one tier entering the notch 3 0' and the cables of the other tier entering the notch 32. The shank of a lag bolt 54 is rst passed through a pull-down bracket 56, is then passed upwards through the bore 36 of the central leg 24 of the hold-down anchor device 16, and is finally turned into threaded relation with the nut 18 at the upper end of the boss 44. A pull-down cable 58 is then connected to the bracket 56 and suitable hydraulic or other mechanism (not shown) is employed to tension the cable S8 and pull the entire assembly, including the holddown anchor de,-

vice 16, the lag bolt 54' andl the bracket S6, downwards in order to apply tension to the various`V cables 1,4 and pull them taut into the proper positions they willv assume when the yconcrete for the gifrder'` is poured into` the'girder form. During such pull-down operations, the regions 'of the cables which passA through the twoy notches 30. and 32 slide upon one another and become adjusted in tension, finally assuming the tangential` relationship wherein they are shown in FIG. 3, as indicatedbythefdottedoutlines. The diameter of the cables is substantially equal to the 'width of the notches 30'and 32 so that crowding or bllflching of the cables in the notches is prevented. As the cables emerge from the notches 30`and 3.2, they pass in contiguous fashion horizontally throughthe base' portion of the form and enter the 'notches'S and`32 of theA hold-,down anchor device shownat the right-hand, side of, FIG. 1.y

The push-down method of installing the hold-downV anchor device 16 within'the form is illustrated at the righthand side of FIG. 1 and in BLG. 8.' when, uns married is employed, the nut 18 is( omitted. Accnrding to this method, the lower end of a lguider cable W6,41)` is passed through a hold-down bracket'62 which is connected by a pin 64 to a suitable fixed reaction member and then a conventional strand chuck 68'is applied tothe guide cable 60 to retain the same against upward movement with respect to the bracket 62,. With the lower end ,ofthey cable 60 thus xedly anchored, the cable is passed upwards through a hole 70 inthe base member 12 of the'girdler form and it isvalso passed through the bore 36 the centrall leg 24 of the hold-,down anchor device 1.6. The anchor device 16 is then applied tothe various'tiers of tensioning cables 14 in the manner previously described in connection with the pull-down'm'ethod of installation and, thereafter, the collet jaw assembly 19 of a conventional strand chuck which may be identical to the strand chuck S8 is slid onto the guide cable 'immediately abOVe the device 16 as shown in dotted lines in FIG. 8 The collet jaw assembly 19 is then slid along the cable 60 until it enters the frusto-conicalsocket 46`in the boss 44 and seats therein. A conventional hydraulic jack 74y is then positioned on the cable 60 and a strand chuck 7 6 is applied to the cable 60 immediately above the jack 74. The strand chucks 68 and'76 are of the sliding collet type and each chuck includes an outer shell and an inner split collet jaw assembly 82. Each chuck is capable of being slid in one direction along the'cable'60` but when force is applied to the shell 80 tending to force the chuck in the opposite direction, a pair of interengagingtruste-

conical surfaces

84 and 86 on the shell and collet,'respectively, establish'a binding action which causes theV collet jaws to become constricted about the cable 6,0v so that' movement in this direction is prevented.y Thesest'r'and chucks are conventional and they are simply unidirectional sliding collar assemblies which are employed to establish certain reaction points along the cable 60. The strand chuck 68 is positioned so that it is incapable of being slid downwardly along the cable 60. The strand chuck76 is positioned so that it is incapable of being slid( upwardly along the cable 60. Y

The frusto-conical surface of the socket 46 in the boss 44 of the hold-down anchor device 16 cooperates with the collet jaw assembly 19 to provide, in efectfa built-in strand chuck for the hold-down anchor device 16 asa whole. The collet jaw assembly Y19 constitutes an unmodied element of a conventional strandchuck and is capable of being purchased upon the market.v The assembly 19 and the outer shell part 80 are separately sold and, in connection with the hold-down anchordevice 16, there is no need for employing an individual shell part, the part 19, in combination with the frusto-conical surfacebf the socket 46, affording the necessary unidirectional movement to the device 16 when a push-downmet'hod of installation is conducted as described above. Briefly, the collet jaw assembly 19 is comprised of plural collet jaw sections 21 having surfaces 23 which are designed for sliding and binding contact with the frusto-conical surface 46 and are held together by a suitable garter spring or resilient O-ring such as has been` shown at 25. A complete strand chuck employing such a collet jaw assembly is shown and described in copending United States patent application Serial No. 130,222, tiled on July 3l, 1961 and entitled Sectional Hold-Down Anchor Devices for the Embedded Cables of Prestressed Concrete Girders.

It is to be noted that, in connection with both the pulldown and the push-down methods heretofore described, a major portion of the hardware which is employed for holding the device 16 in position within the form may be retrieved and only asmall portion thereof is expendable. In the case ofthe pull-down method shown at the lefthand side of FIG. l, after the concrete of the installation has hardened, the lag bolt 54, the bracket 56 and the pull-down cable 58 may be retrieved from the installation, thus leaving only the device.16 embedded in the concrete. As previously pointed out, the nut 18 may be welded to the upper end of the boss 44, but it is within the purview of the invention to use a free nut. Welding of the nut in position merely facilitates tightening of the lag bolt 54 without requiring further assistance from within the form. In the case of the push-down method illustrated at the right-hand side of FIG. l and FIG. 8, the guide cable burn-off operation which is performed after the concrete has become hardened, allows the strand chuck 76, the pin-equipped bracket 62 and the reaction member 66 to be retrieved, the strand chuck 76 and hyv draulic jack 74 having previously been severed from the installation before concrete-pouring operations.

It has been pointed out above that whether the holddown anchor device 16 be intended for use in connection with either the pull-down or the push-down method of installation, the device remains the same in structure. Neither the nut 18 nor the collet jaw assembly 19 have been treated herein as being a part of the hold-down anchor device 16 since they are 'separately purchased items. However, as elements of a combination of instrumentalities by means of which the hold-down anchor device 16 may be, made effective, the nut and collet jaw assembly are essential and in this respect they have been claimed accordingly.

It is essential in any given installation that the prestressing or tensioning cables 14 do not approach the base 12 of the concrete girder form within a certain predetermined distance, but that they do approach the base of the form to such an extent that their prestressing effect is present in the lower regions of the finished girder. A two inch spacing ofthe lowermost cable 14 above the base 12 is considered satisfactory in most installations. Therefore, the hold-down anchor devices 16 illustrated herein having

legs

22, 24 and 26 of appreciable length, are designed to accommodate a full complement of tensioning cables 14, for example, eight such cables in each of the two notches and 32. Where only four cables are installed in each of the

notches

30 and 32, this being the exemplary disclosure in FIGS.` 1 and 2, neither the pull-down nor the push-down method of installation will permit the hold-down anchor devices to be forced downwardly to such an extent that the lowermost cables 14 in the Various groups of cables may assume its proper lspacing, from the `base 12 of the form. Accordingly, it is contemplated that vfor varying installations the lengths of the legs 24, 26and 28 be varied to accommodate the required number of grouped cables. To this end, a series of indicia marks as shown at 90 in FIG. 2 is provided along the central leg 24, the marks indicating the point at which burn-off or saw-01T operations may be conducted on the three legs in order properly to shorten the structure as a whole. It is not feasible S that the devices 16 be cast in different sizes and, therefore, such devices may be manufactured in one standard size or length and cut off on order by the manufacturer, or shipped in their entirety for severance as to length by the consumer.

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construction may be resorted to without departing from the spirit of the invention. Therefore, only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

Having thus described the invention what we claim as new and desire to secure by Letters Patent is:

1. As a new article of manufacture, in combination, a hold-down anchor device for positioning the tensioning cables of a prestressed concrete girder within a girder form preparatory to concrete pouring operations, said anchor device comprising a unitary metal casting of roughly M-shape configuration and providing an upper Abridge portion from which there depend three spaced .parallel legs including a central leg and two outside legs,

the two outside legs, in combination with the central leg, deiining a pair of relatively deep downwardly opening notches designed for reception therein of respective groups of tensioning cables and for assimilation of the combined upward thrust of such cables when the same are drawn taut, said bridge portion being formed with an upwardly extending integral cylindrical boss in axial alignment with the central leg, said boss and central leg having formed therein a vertical bore adapted to receive loosely therethrough a guide cable on which the device as a whole is vertically slidable, the upper region of said bore presenting a frusto-conical inner wall surface of relatively small slant angle, and a split collet jaw assembly disposed within said bore and having collet surfaces in operative engagement with said frusto-conical inner wall surface of the bore, said collet assembly being adapted to receive said guide cable therethrough.

2. A hold-down anchor device as set forth in claim 1 and wherein said frusto-conical inner wall surface extends completely through the cylindrical boss and has its lower end regions terminating within said bridge portion.

3. A hold-down anchor device as set forth in claim 1 and wherein each of said legs is formed with a pair of oppositely disposed oppositely extending reinforcing ribs which are substantially coextensive kwith their respective leg.

4. A hold-down anchor device as set forth in claim 1 and wherein each of said legs is formed with a pair of oppositely disposed oppositely extending reinforcing ribs which are substantially coextensive with their respective leg, and each leg is joined to the bridge portion by a reinforcing gusset.

References Cited by the Examiner,-

RICHARD W. COOKE, JR., Primary Examiner.

HENRY C, SUTHERLAND, Examiner.

Claims

1. AS A NEW ARTICLE OF MANUFACTURE, IN COMBINATION, A HOLD-DOWN ANCHOR DEVICE FOR POSITIONING THE TENSIONING CABLES OF A PRESTRESSED CONCRETE GIRDER WITH A GIRDER FORM PREPARATORY TO CONCRETE POURING OPERATIONS, SAID ANCHOR DEVICE COMPRISING A UNITARY METAL CASTING OF ROUGHLY M-SHAPE CONFIGURATION AND PROVIDING AN UPPER BRIDGE PORTION FROM WHICH THERE DEPEND THREE SPACED PARALLEL LEGS INCLUDING A CENTRAL LEG AND TWO OUTSIDE LEGS, THE TWO OUTSIDE LEGS, IN COMBINATION WITH THE CENTRAL LEG, DEFINING A PAIR OF RELATIVELY DEEP DOWNWARDLY OPENING NOTCHES DESIGNED FOR RECEPTION THEREIN OF RESPECTIVE GROUPS OF TENSIONING CABLES AND FOR ASSIMILATION OF THE COMBINED UPWARD THRUST OF SUCH CABLES WHEN THE SAME ARE DRAWN TAUT, SAID BRIDGE PORTION BEING FORMED WITH AN UPWARDLY EXTENDING INTEGRAL CYLINDRICAL BOSS IN AXIAL ALIGNMENT WITH THE CENTRAL LEG SAID BOSS AND CENTRAL LEG HAVING FORMED THEREIN A VERTICAL BORE ADAPTED TO RECEIVE LOOSELY THERETHROUGH A GUIDE CABLE ON WHICH THE DEVICE AS A WHOLE IS VERTICALLY SLIDABLE, THE UPPER REGION OF SAID BORE PRESENTING A FRUSTO-CONICAL INNER WALL SURFACE OF RELATIVELY SMALL SLANT ANGLE, BORE AND HAVING COLLET SURFACES IN DISPOSED WITHIN BORE AND HAVING COLLET SURFACES IN OPERATIVE ENGAGEMENT WITH SAID FRUSTRO-CONICAL INNER WALL SURFACE OF THE BORE, SAID COLLET ASSEMBLY BEING ADAPTED TO RECEIVE SAID GUIDE CABLE THERETHROUGH.