US3605361A

US3605361A - Tendon anchorage

Info

Publication number: US3605361A
Application number: US816583A
Authority: US
Inventors: George H Howlett; James W Howlett
Original assignee: HOWLETT MACHINE WORKS
Current assignee: HOWLETT MACHINE WORKS
Priority date: 1969-04-16
Filing date: 1969-04-16
Publication date: 1971-09-20
Anticipated expiration: 1988-09-20

Abstract

A TENDON ANCHORAGE FOR USE IN PRESTRESSING CONCRETE MEMBERS WHICH PREFERABLY INCLUDES A TUBULAR MOUNTING MEANS MOUNTED TO EXTEND THROUGH A WEDGE SUPPORTING BORE IN THE ANCHORAGE IN ORDER TO SECURE THE ANCHORAGE IN FIXED SPACED RELATION TO A CONCRETE FORM FOR CASTING THE ANCHORAGE INTO THE CONCRETE MEMBER IS DISCLOSED. THE MOUNTING TUBE IS FORMED TO SECURE THE ANCHORAGE FROM THE SIDE THEREOF REMOTE TO THE CONCRETE FORM AND URGE THE ANCHORAGE AGAINST A SPACING MEANS PLACED BETWEEN THE ANCHORAGE AND THE CONCRETE FORM. BEARING PLATES MAY

SIMILARLY BE SECURED BY THE MOUNTING MEANS THROUGH A TENDON RECEIVING OPENING FROM THE REMOTE SIDE THEREOF. ANCHORAGE GROUTING APPARATUS AND TENDON CONTAINING CONDUITS MAY BE SECURED TO THE MOUNTING TUBE. AN ANCHORAGE WHEREIN THE WEDGES EXTEND FROM THE REMOTE SIDE OF THE ANCHORAGE AND ARE UNSUPPORTED AND ACHIEVE GRIPPING ACTION THROUGH CANTILEVER FORCES FROM THE ANCHORAGE IS ALSO DISCLOSED.

Description

3 Sheet eet 1 G. H. HOWLETT AL summon ANCHORAGE Sept. 20, 1971 Filed April is. 1969 INVFNTOR. George H. Home" B James W Howlw m M, M 3; Am eys sept- 1971 Filed April 16. 1969 J-IQHOWLET- 5 AL I TENDON monom 3 Sheet ..5 2

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FNVENTOR Georg Home" Attorney 3 Sheets-Sheet 5 Sept- 20, 1971 s. H-HOWLETT E'I'AL mmou .mcnomn Filed April 16, 1969 ir'l l 'r' United States Patent US. Cl. 52-223L 3 Claims ABSTRACT OF THE DISCLOSURE A tendon anchorage for use in prestressing concrete members which preferably includes a tubular mounting means mounted to extend through a wedge supporting bore in the anchorage in order to secure the anchorage in fixed spaced relation to a concrete form for casting the anchorage into the concrete member is disclosed. The mounting tube is formed to secure the anchorage from the side thereof remote to the concrete form and urge the anchorage against a spacing means placed between the anchorage and the concrete form. Bearing plates may similarly be secured by the mounting means through a tendon receiving opening from the remote side thereof. Anchorage grouting apparatus and tendon containing conduits may be secured to the mounting tube. An anchorage wherein the wedges extend from the remote side of the anchorage and are unsupported and achieve gripping action through cantilever forces from the anchorage is also disclosed.

BACKGROUND OF THE INVENTION crete construction. Typically, a plurality of tendons and tendon anchorages are placed within the concrete forms and the concrete is then poured with the tendon and anchorage being cast-in-place. The forms are then removed and the tendons are tensioned. It also has been found to be desirable in many applications to have the tendon anchorage located in a recess in the end of the concrete member, which recess is subsequently grouted so that the anchorage is completely contained within the finished prestressed concrete member. When this type of construction is used, the tendon anchorage must be located and positioned in fixed spaced relation to the concrete form by means of apparatus which, after casting of the concrete membenaflord access to the anchor age for tensioning of the tendon.

Several anchorages have been previously employed in order to provide an anchorage construction which can be cast-in-place at a position interiorly of the ends of the concrete member. One approach has been to cast the anchorage as a single member in which a bearing plate and wedge receiving housing are integrally formed, and the bearing plate is provided with a plurality of openings. A rubber spacing or block-out member is placed next to the concrete form and the anchorage held against the spacing member as nails are driven through the openings in the bearing plate into the concrete form. The nails urge the anchorage against the spacing block and hold the anchorage in fixed spaced relation to the concrete form. This type of construction is illustrated in US. Pat. No. 3,293,811.

Another approach has been to provide a unitary anchorage member which is formed with screw threads or a bayonet-type socket on the side of the anchorage facing the form. A mounting member is then screwed into the front of the anchorage and extends therefrom to and through the form. A spacing block is again used,

ice

and the mounting member is secured on the outside of the form to urge the anchorage against the spacing block. The concrete member is cast and the form, mounting :means, and spacing block removed to allow access to the anchorage.

Prior cast-in-place anchorage systems have been found to have several disadvantages. Primary among these disadvantages is the inflexibility of the system for mounting the anchorage in spaced relation to the concrete form. As will be readily understood, the prestressing requirements of various concrete members may differ considerably. For example, the depth to which a cast-in-place anchorage must be placed in the concrete member may under different construction codes vary from state to state or locality to locality. Similarly, tensioning forces may require various siezs or shapes of bearing surfaces in order to properly distribute the axial loading of the tendon or tendons. Moreover, close grouping of tendons may result in special bearing plate requirements. Still further, special wedge containing anchor members may be required for given stress conditions. Thus, prior tendon anchorages have lacked an interchangeability or flexibility of the elements in the systems which would allow the structural engineer maximum flexibility of design. In prior anchorage systems which were formed by casting as unitary anchorage members, necessary changes in anchorage design were accomplished by varying the mold for the castings in order to meet the design requirements. As will be understood, these systems could only economically accommodate a relatively small number of design variations.

Prior systems have also had other disadvantages. For example, the depth of the spacing block may be so great as to make it impractical or impossible to nail the anchorage to the form. Still further, casting the bearing plate and a wedge containing housing as a unitary piece results in a relatively bulky, heavy and inconveniently shaped anchorage which is not conveniently stored or shipped. Since bearing plates can be quite heavy and yet very easy to form, it can be quite advantageous to form the bearing plates at a location relatively close to the construction site and ship only the tendon gripping wedges and containment housing therefor as a separate item from a more remote area. Moreover, casting the Wedge receiving bore into the concrete member results in exposing that bore to rust and concrete leakage past the block-out member.

In some instances it is highly desirable or necessary to cluster tendons in close side-by-side relation. One approach to this problem is also shown in the above referred to US. Pat. No. 3,293,811 wherein the tendons must be unnaturally spread apart in order to accommodate the bearing plate portion of side-by-side discrete anchorages. It is quite advantageous, however, to have the tendons continue in side-by-side close proximity and grip them with a single anchorage. Alternatively, if the tendons are spaced apart slightly, they can be gripped by a plurality of anchor members and a single bearing plate having a. plurality of tendon receiving openings therein. Prior anchorage systems have not aiforded this flexibility.

Another aspect of prior prestressing anchorage systems has been the manner in which the tendon gripping wedges are supported. In general anchorages have been formed so that the tendon gripping wedges are relatively thin and are supported over substantially their entire length by a wedge supporting structure. More particularly, prior tendon anchorages normally include wedges which are formed so that the wedge material between the tendon gripping surface and the outside anchorage engaging surface adjacent the small diameter end. of the anchorage is very thin and incapable of supporting substantial bending forces.

These prior tendon anchorage and wedge constructions have been found to have substantial disadvantages when the anchorage is employed for general use and, more particularly, to have substantial disadvantages when the anchorage is employed as a cast-in-place anchorage. The use of relatively thin wedges and support of the wedges over their complete length has resulted in the anchorages having excess metal in the bearing plate or needing a separate wedge containing anchor member, resulting in a substantial overall increase in the anchorage cost.

Accordingly, it is an object of the concrete prestressing tendon anchorage of the present invention to provide an improved anchorage construction and method of anchorage support which afiords greater flexibility in meeting design criteria by means of allowing easy interchangeability of the parts while maintaining the characteristic of being rapidly mountable to the concrete form for easting the concrete member.

It is another object of the present invention to provide a tendon anchorage wherein the parts of the anchorage can be readily and easily formed, stored and shipped.

It is still another object of the tendon anchorage of the present invention to provide an anchorage construction which can be conveniently and easily adjusted under field condiitons and minimizes the exposure of the anchorage to damage and corrosion in the field.

Another object of the tendon anchorage of the present invention is to provide an anchorage construction wherein a multiplicity of side-by-side tendons can be conveniently and easily secured.

Still another object of the tendon anchorage of the present invention is to provide an anchorage structure wherein accessories such as grouting apparatus can be easily added to and positively secured in position relative to the anchorage and concrete form.

Still another object of the anchorage of the present invention is to provide an anchorage wherein the tendon gripping forces generated in the anchorage are distributed within the gripping wedges in a manner which insures high reliability of the anchorage, minimizes the volume and weight thereof and improves the gripping profile and adaptability of the anchor member for use in cast-inplace prestressing applications.

SUMMARY OF THE INVENTION Briefly, the tendon anchorage of the present invention includes, an anchor member having a wall defining a convergently tapered bore dimensioned at the smallest point thereof to receive a tendon. to be tensioned, and anchorage mounting means formed to extend from the remote side of the anchor member through the tendon receiving bore to a concrete form in order to position the anchor member in fixed spaced relation to the form during casting of the anchor member into the concrete member. The mounting means is preferably a tube which can be removed from the anchor member after casting of the concrete member. The anchorage is used with convergently actuating gripping means, such as segmental Wedges, and with anchor spacing means, such as a spacing block or member formed to prevent entry of concrete between the anchor member and form during casting of the concrete member. Alternatively, the tubular mounting means may extend through a bore located in a bearing plate with the bore being tapered to receive mating wedges or being formed to support a separate anchor member inserted after casting of the bearing plate into the concrete member.

The tubular mounting member is preferably dimensioned on its internal diameter to receive the tendon to be tensioned in order that the anchor member can be cast into the concrete member with the tendon in place. The mounting means is preferably threaded on the end which is secured to the anchor member in order that it may receive a nut or other fastener on the remote side of the anchor member or in order that the mounting means may be threaded directly into the small diameter 4 end of the bore in the anchor member. The mounting means is further preferably formed for securement of accessories used with the tendon anchorage, such as a grouting apparatus or a conduit to allow post tensioning of the tendon.

A tendon anchorage for use in prestressing concrete members which are cast-in-place or otherwise positioned in the concrete member is disclosed wherein the bore of the anchor member and convergently actuating wedge segments are formed and dimensioned so that the wedge segments extend from the remote side of the anchor member over a substantial unsupported distance, with the wedges gripping the tendon by cantilever action. Addition ally, the wedges may extend unsupported for a substantial distance from the ither side of the anchor member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, side elevational view, in cross section, of a tendon anchorage constructed in accordance with the present invention and secured to a concrete form for casting of the anchorage into a concrete member.

FIG. 2 is a fragmentary, side elevational view, in cross section, of the anchorage illustrated in FIG. 1 after casting of the concrete member, removal of the concrete form and tensioning of the tendon.

FIG. 3 is a fragmentary end view of the anchorage as illustrated in FIG. 2.

FIG. 4 is a fragmentary, side elevational view, in cross section, of an alternative embodiment of the tendon anchorage of the present invention suitable for anchoring a plurality of tendons.

FIG. 5 is a fragmentary, side elevational view, in cross section, of the tendon anchorage of FIG. 4 after casting of the concrete member, removal of the form and tensioning of the tendons.

FIG. 6 is an end view of the tendon anchorage as illustrated in FIG. 5.

FIG. 7 is a fragmentary, side elevational view, in cross section, of an alternative embodiment of the tendon anchorage of the present invention as secured to a concrete form.

FIG. 8 is a fragmentary, side elevational view, in cross section, of the tendon anchorage of FIG. 7 illustrating the wedge and bearing plate configuration of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 12, and 3, the anchorage of the. present invention can be seen to be comprised of a bearing plate 11, anchor member 12, mounting means 13, and spacing means 14. The anchorage is secured to extend from concrete form 16 by means of a nut 17 located on the outside of the form and a second nut 18 threadably engaging mounting means 13 on the side of the anchor member and bearing plate remote or furthest from form 16. Either or both of nuts 17 and 18 can be advanced on correspondingly threaded ends 19 and 21 of mounting means 13 in order to urge the bearing plate and anchor member against spacing means 14. Extending through mounting means 13 is tendon 22, which is here illustrated as being wrapped with a paper covering 23. Covering 23 is typically provided with a layer of grease on the inner side thereof so that the tendon may be post-tensioned within covering 23 after casting of the concrete member. Sealing of the juncture between wrapped tendon 22 and mounting means 23 is preferably accomplished by tape 24 which will bridge across the juncture and prevent flow of concrete into the end of the mounting means.

An important feature of the tendon anchorage of the present invention is to provide a construction which allows improved versatility and interchangeability of the various anchorage parts in order to accommodate variations in design of the concrete member into which the anchorage is incorporated. Accordingly, the tendon anchorage mounting structure of the present invention is constructed so as to reach or extend through the tendon receiving opening in the anchorage to the side thereof remote from the concrete form in order that the anchorage may be urged toward and secured relative to the concrete form from a position on the remote side of the anchorage. Fastening of the anchorage to the concrete form by this technique, affords several substantial advantages. For example, bearing plate 11 can be readily and easily formed to have any one of a number of possible configurations and sizes without the need of providing special openings or sockets to accommodate mounting thereof for casting. Thus, bearing plate 11 may be formed with two or more openings so that anchorages can be positioned in close side-by-side relation. Alternatively, bearing plate 11 may be selected to be of varying lateral dimensions in order to achieve any desired or required distribution of tensioning forces to the concrete member through bearing surface 26. Still further, while steel is normally employed in formation of the bearing plate, differing heat treatments and formation techniques may result in differing strengths. The structural engineer can select the desired material and strength, which will cause a variation in the thickness of bearing plate 11, when the anchorage of the present invention is employed.

The ability to interchange bearing plates in the tendon anchorage of the present invention is further important in that it affords greater flexibility in the selection of the tendon anchor member. For example, anchor member 12 may be formed as illustrated in FIG. 1 or, alternatively, a different type of tendon anchorage device could be used which has a much smaller external diameter. This type of anchorage may be dictated from the design requirement that the concrete member be able to withstand stress reversals and accordingly have an anchorage which will not allow the gripping wedges to move backwards out of the anchor member. If the anchor member 12 is of a smaller diameter than illustrated in FIG. 1, the surface area 27 between the bearing plate and anchor memher will be reduced resulting in a greater concentration of the axial tension forces on the bearing plate. This may in turn require that the bearing plate 11 be of a greater thickness in order to accommodate the greater stress concentrations caused by the anchorage. The mounting means construction of the present invention affords the ability to both change the anchor member 12 to meet particular design criteria and change the bearing plate 11 correspondingly to meet the design characteristics of the anchor member. This versatility is not found in prior devices which are characteristically cast in one piece and secured to the concrete form from the front side thereof so as to inhibit the interchangeability of parts or building up of the desired anchorage to meet exactly the structural design requirements.

Still another important feature of the tendon anchorage of the present invention is to provide an anchorage construction which can readily and easily secure the anchorage at almost any position interiorly of the concrete form while still maintaining the characteristic interchangeability of parts. It may be desirable or necessary under various local and state laws and codes to bury the tendon anchorage at various depths in the end of the concrete member. Accordingly, spacing member or block-out 14 may be formed with various depth dimensions in order that recess 28 is of sufficient depth to allow later grouting of the tendon anchorage in compliance with the state or local code. Still further, anchor member 12 may have various axial dimensions, depending upon the type of anchorage employed. Thus, bearing plate 11 may be disposed at various spaced distances from form 16, some of which are far in excess of the length of common fastening means such as nails. The tendon anchorage construction of the present invention, therefore, affords further design flexibility in the location of the tendon anchorage relative to the end of the concrete member. The mounting means can be of virtually any predetermined length and have substantial continuous adjustability from either the concrete form side of the mounting member or the anchor member side thereof. As illustrated in FIG. 1, threaded ends 19 and 21 of tubular mounting member 13 are threaded over a substantial distance and would be suitable for use in connection with spacing members 14 of variable axial length. This important feature will allow take-up of the mounting means at the anchorage which is not possible in prior art devices and can be of considerable practical importance in the field.

Another advantage of having a tendon anchorage which can be assembled in the field is that the anchorage can be more conveniently shipped and stored than anchorages which are cast as a single piece. For example, bearing plates 11 can be stacked fiat and easily transported. A plurality of anchor members 12, mounting means 13 and spacing blocks 14 can similarly be easily stacked, handled and transported. Since the bearing plates and anchor members are usually formed of high strength steels and are quite heavy, it may be advantageous to form the bearing plates, which are relatively simple, at a location adjacent to the area in which the anchorage is to be used and form the anchor member 12 and corresponding segmental wedges 31 at a manufacturing facility more remote, where somewhat more complicated forming equip ment can be employed. Bearing plate 11 is typically formed with a shear and punch or drill while anchor member 12 and mating wedges 31 may be formed on a screw machine. In addition bore 25 in bearing plate 11 may be tapped, nut 18 eliminated and mounting means 13 threadably engaging plate 11 to secure the anchorage relative to the form. When flexibility in the type of anchorage needed is required, these formation methods compare quite favorably with the prior art technique of casting, which requires a different mold for each anchorage configuration. Moreover, a cast anchorage inherently will have a lower reliability than anchorages constructed from roll-formed material.

The assembly and use of the anchorage of the present invention can be described as follows. Tendon 22 will be located in the concrete member in accordance with predetermined design criteria and will be anchored at the end opposite the end shown in FIG. 1 by any one of a number of techniques, including an oppositely facing anchorage of the type illustrated in FIG. 1. The wrapping 23 will be removed from the end of the tendon in order that it may be gripped by wedges 31 and yet cover the tendon over the length thereof exposed to concrete. The mounting means 13 with nut 18 positioned thereon may be mounted over the end of tendon 22 and bearing plate 11, anchor member 12 and spacing means 14 are mounted on member 13. Spacing block 14 is preferably provided with an axially extending bore 32 in order that it may be readily slipped over the end 19 of mounting means 13. End 19 of mounting means 13 is then inserted in bore 33 in form 16 until end 19 extends from the form and nut 17 is advanced against form 16 until the anchorage is urged against spacing block 14. Alternatively, spacing block 14 may be segmented and mounted between anchor member 12 and form 16 after insertion of end 19 of the mounting means through bore 33 in the form.

As here illustrated, anchor member 12 is provided with a frusto-conical bore 36 terminating in a small diameter end 37. The smallest point in the bore 36, namely, end 37, is preferably dimensioned to receive mounting means 13 and tendon 22 simultaneously therethrough. Once secured in place, concrete member 38 is formed by pouring concrete around the anchorage and allowing it to set up. Spacer 14 abuts anchor member 12 and prevents the entry of concrete into the bore 36 while tape 24 prevents entry into the front end of mounting means 13.

Other techniques can be used to close end 21 of mounting member 13 including rubber grommets. Alternatively, nut 18 can be provided with a plastic skirt or sleeve which is formed and dimensioned to extend from the nut to encircle and resiliently grip tendon 22 and prevent entry of concrete into the mounting means. Moreover, and very importantly, since mounting means 13 extends through the anchor member, any leakage of concrete will merely pass into the tubular mounting member and not the wedge receiving bore 36. Prior mounting devices have required much more care in closing the end of the anchorage against entry of concrete into the wedge receiving bore. Moreover leakage onto tendon 22 is not important since the tendon typically elongates 6 inches or more and the surface finally gripped is underneath the wrapping 23.

As shown in FIG. 2, the mounting means 13 and form 16 have been removed from the anchorage. This is accomplished by unscrewing nut 17 and removing form 16 and spacing block 14. Still further member 13 may be unscrewed from nut 18 which remains cast into the concrete member. This is done by gripping the mounting means 13 by end 19 (pliers or other gripping tools may be used) and may be accomplished either before or after removal of form 16 and spacing block 14. Wedges 31 are preferably formed with serrated internal gripping surfaces 39 and are held together for convenience of handling in the field by an O-ring 41. Tendon 22 is then tensioned by jacking the end thereof, causing the tendon to move relative to the paper wrapping 23. Wedges 31 will advance into bore 36 and due to the frictional. engagement of tendon 22 by serrated surface 39 will convergently grip tendon 22. Once the wedges have taken the full predetermined tension load of the tendon, the end of the tendon may be out 01f by a shearing tool or welding torch so that it is within recess 28. If the tendon is to be grouted, recess 28 will then be filled with grout (not shown). It should be noted that the thickness of wedges 31 at end 42 must be sufficient to accommodate mounting means 13. That is, when a tubular mounting means is employed, the small diameter end 37 of bore 36 is larger than would be required simply to allow tendon 22 to pass through anchor member 12. Accordingly this extra dimension will result in wedges 31 having an overall thickness which is greater than might otherwise be employed.

It should be noted further, however, that mounting means 13 need not be tubular in shape and wedges 31 can be formed of a thinner construction. This can be accomplished if the tendon 22 is not cast into the concrete member but is inserted after casting of member 38. Insertion of the tendon after casting can be accomplished if a tendon receiving conduit is cast into the concrete member. In such a configuration, member 13 could be formed as a solid rod substantially the same diameter as tendon 22 with threaded ends 19 and 21. The rod would extend through bearing plate 26 with bore 25 now being only slightly greater than the tendon diameter. End 21 of the solid member 13 would be threaded and a conduit (not shown) could screw onto the exterior threads of member 13 and have an internal dimensioned to receive tendon 22. In effect, the conduit would replace greased paper 23. In this configuration removal of mounting means 13 would be followed by insertion of tendon 22 through the conduit, which was positioned and fixed relative to the concrete form by the mounting means. Such a conduit is illustrated in FIG. 4 in which three side-by-side tendons are contained.

As above set forth, in order to reduce the number of elements in the anchorage of the present invention nut 18 can be eliminated from the anchorage construction of the present invention simply by threading internal bore 25 of the bearing plate. Thus, member 13 could be screwed into the bearing plate which would again urge the bearing plate, anchor member and spacing means against concrete form 16. This construction would similarly allow the interchangeability of various parts in order to meet a variety of design criteria. Similarly, bearing plate 11 could be formed integrally with anchor member 12 or permanently secured thereto (this could be accomplished 8 in the manufacture of the piece or in the field by spot welding) and the smallest diameter portion of bore 36, namely, end 37, could be internally threaded to receive threads on end 21 of the mounting tube. This type of construction is illustrated in the anchorage in FIGS. 7 and 8.

Referring now more particularly to the anchorage illustrated in FIGS. 4, 5 and 6, an alternative embodiment of the anchorage of the present invention may be described. Anchor member 52 and spacer 54 are mounted on tubular mounting member 53 and secured by nut 57 and frustO-conical sleeve 58 against concrete form 56. Ends 59 and 61 of member 53 are externally threaded as above described. The anchorage, as set forth in FIGS. 46, is formed to secure a plurality of tendons 62, which in this case can be seen in FIG. 6 to be three tendons. The tendons are preferably mounted inside conduit 63 which is provided with internal threads 64 in order that the conduit may be threada-bly mounted onto mounting means 53. In this configuration, it is possible to cast the concrete member 78 with tendon 62 being pulled through conduit 63 after the concrete member had been cast and the forms removed.

In this form of the tendon anchorage, anchor member 52 has an integrally formed bearing surface 66 and a separate bearing plate has been eliminated. Mounting member 53 is formed to extend through frusto-conical bore 76 in member 52 and particularly through the small diameter end 77 thereof to the remote side 66 of the anchor member. As will be set forth in detail hereinafter, anchor member 53 extends beyond surface 66 and through a funnel shaped grouting member 58 in order to secure the anchorage in fixed spaced relation to form 56.

The anchorage of FIGS. 4, 5 and 6 is used in a manner similar to that described in connection with the anchorage of FIGS. 1, 2 and 3. In this embodiment of the anchorage, however, a nut 67 is provided which is secured to end 59 of member 53 (by brazing, for example) so that it may not be either advanced or removed from member 53. This nut can then be used in rotating member 53 so as to release it from the internal threads 64 of conduit 63 and the threads of funnel member 58. When nut 67 is permanently mounted on end 5,9 of the mounting member, the anchorage may be assembled by inserting the tendons into end 61 of member 53 and then inserting end 61 through bore 73 in form 76, bore 72 in spacer 54, bore 76 in anchor member 52, and finally the bore in member 58 and the internal diameter of conduit 63. The anchorage can be adjusted into a fixed rigid position by cinching down on nut 57 and/ or advancing grouting funnel 58. As illustrated in FIGS. 4, 5 and 6, the tendon anchorage of the present invention demonstrates how mounting means 53 can be used in order to support and secure accessories which are commonly employed in prestressing concrete members. Thus, member 53 supports a grouting funnel 58 and supports a tendon containing conduit. It is an important feature of the present invention that the mounting means may be secured to the tendon conduit since this results in a fixed alignment of the tendon anchorage and the tendon. Alignment of the tendon and anchorage is extremely important and reliable since tensioning forces are very high and malalignment can result in serious detrimental stress concentrations in the concrete member and tendon.

Again the versatility of the present invention is illustrated since anchor member 52 can be formed with various configurations including bearing surfaces 66 which are of a larger or smaller area. Upon removal of the form, mounting means and spacing block, recess 68 in member 78 affords access to the anchor member for insertion of tapered segmental wedges 71. The wedge configuration suitable for gripping a plurality of side-by-side tendon 62 is best seen by reference to FIG. 6. The individual wedges are again preferably held together for convenience by an O-ring 81 and formed with internal serrated tendon gripping surfaces 79.

In order to facilitate the grouting of the anchorage of the present invention, a grouting bore 83 is formed in member 52. Grouting bore 83 terminates in an opening 84 which is disposed radially inwardly of the internal diameter of funnel 58 in order to be in communication with funnel or sleeve 58 and conduit 63. The other end of bore 83 terminates in an opening 86 which communicates with recess 68. Thus, grout may be introduced through opening 86 into funnel 58 and conduit 63 with air escaping through the other end of the tendon conduit through a vent opening or through the slotted openings 87 between opposed faces of Wedges 71.

Other forms of grouting apparatus are suitable for use with the anchorage of the present invention. For example, funnel 58 may be replaced by a T-shaped pipe and a grouting tube which extends around member 52 to an exposed end of the concrete member 78. Again, however, a T-shaped member could be internally threaded so as to be mountable on conduit 53 to urge anchor member 52 against spacer 54. Similarly, conduit 63 could threadably engage mounting member 53.

Referring now to FIGS. 7 and 8, there is illustrated an alternative embodiment of the tendon anchorage of the present invention which is particularly well suited for use as a cast-in-place type of anchorage and further useful in other prestressing applications. The anchorage is comprised of a bearing plate 111 and bearing plate locating device consisting of tubular member 113 and spacing or block-out member 114, which are urged agains tform 116 by out 117 and threads 118 at the small diameter end of bore 136 in thhe bearing plate. As above described mounting member 113 is formed with externally threaded ends 119 and 121. Tendon 122 is here illustrated as a strand type of prestressing tendon having a cable-like construction. The strand can be wrapped in paper 133 and conveniently taped or otherwise blocked by member 134 against entry of concrete into the end 121 of mountin means 113.

Bearing plate 111, which in this configuration acts as an anchor member, is provided with a bearing surface 126 facing away from the concrete form which will allow transfer of axial tensioning forces to concrete member 138. The bearing plate is also formed with a frustoconical bore 136 terminating in threads 118 at the bearing surface or remote side of the bearing plate. As above described, mounting means 113 can be inserted through

bores

132 and 133 in the spacing member and form, re-

spectively, and mounting means screwed into the teeth 118 in bearing plate 111.

It is preferable and an important advantage of the anchorage of the present invention that the mounting means be further formed in order to form a recess in the concrete on the bearing surface side of the anchorage sufiicient to accommodate axial advancement of wedges 131 beyond surface 126. Thus, the mounting apparatus of the present invention functions additionally to provide a recess into which the tendon gripping wedges may move in advancing to a position of maximum radial gripping force. 1

FIG. 8 illustrates the concrete member with the anchorage of the present invention in place. Form 116 and block-out member 114 have been removed, resulting in recess 128 allowing access to bearing plate 111. As here illustrated bearing plate 111 is formed with a frustoconical bore into which segmental wedges 131, held to gether by O-ring 141, are inserted. The segmental wedges are again preferably provided with tendon gripping serrated surfaces 139. It should be noted and it is an important feature of the present invention that end 14 2 of the wedges projects past bearing surface 126 a substantial distance. Thus, radial gripping of tendon 122 is accomplished by means of cantilever action from bearing plate 111 to ends 142 of the tendon gripping wedges.

The versatility of the anchorage of the present invention can further be illustrated in that bearing plate 111 can alternatively be formed with a cylindrical bore dimensioned to receive tendon 122. Spacing block-out member 114 can be dimensioned to have a sufficient thickness so that recess 128 is of sufficient depth to accommodate the later insertion of a wedge containing housing or anchor member of the type illustrated in FIG 1 as member 12. Thus, the mounting means would be used to locate the bearing plate and upon removal of the spacer and form an anchor member and tendon gripping wedges could be slipped over the end of tendon 122 to allow tensioning of the tendon and later grouting of recess 128. An anchorage construction wherein the anchor member is subsequently inserted as a separate unit can be highly advantageous. When this approach is used the problem of entry of small amounts of concrete around block-out member 114 into frusto-conical bore 136 is eliminated. Similarly the problem of rust forming in or corrosition of the wedge receiving bore can be controlled and eliminated since the anchor member, if not cast into the beam, can be kept in a controlled environment and properly treated to prevent rust and corrosion.

The spacing or block-out members as illustrated throughout the drawings are formed of wood. Several other materials and constructions, however, will sufiice for the apparatus of the present invention. For example, block-out members have previously been formed of r-ubber, sheet metal and plastic. Moreover, while the spacing members are preferably removable from the concrete member in order that they may be reused in the subsequent placement of anchorages, the block-out and spacing member may consist of a sleeve, as opposed to a solid member, which is permanently left in the concrete member with the interior diameter of the sleeve providing an access recess to the bearing plate or anchor member.

The tendon anchorage illustrated in FIG. 8 and particularly the combination of bearing plate 111 and wedges 131, while highly advantageously employed in a cast-inplace type of anchorage, may also be advantageously employed in other prestressing applications, such as dry mounting the anchorage on the end of a concrete member. Prior art anchorages employing convergently tapered segmental wedges have been constructed so that the front end of the wedge, corresponding to end 14 2 of wedges 131, does not project from the front of the wedge containing structure so as to be unsupported in advance of that structure. Occasionally, some wedge systems have projected forwardly for a very small distance (usually less than V the wedge length) and sometimes rearwardly of the anchorage over a short unsupported distance. Accordingly, prior anchorages and Wedge systems have been formed with the wedges being relatively thin at the front ends thereof since strength in bending is not of critical importance when the wedges are supoprted over their entire length by an anchor member.

In order to achieve the advantages of radially gripping segmental wedges while reducing the volume and weight of the bearing plate or anchor member required to house and support these wedges, the anchorage of the present invention is formed with segmental wedges which protrude and are unsupported over a substantial distance in advance of the bearing surface side of the bearing plate. In order that these wedges will attain and withstand the very high radial gripping forces necessary to secure tendons at a tension force approaching their yield strength, the segmental wedges of the present invention are formed and dimensioned to be relatively thick and preferably stress relieved in order to avoid delay failure. These relatively thick Wedges, therefore, are cantilever supported from the bearing surface side 126 of bearing plate 111.

The reduction in 'bearing plate weight and volume can be illustrated as follows. The bearing plate tapered bore 136 must have sufficient surface area so that when the bore engages the exterior surface of wedges 131 there will not be undue stress concentration in bore 136 which would result in bearing plate 1L1 permanently deforming or otherwise failing. As the diameter of bore 136 increases, however, the surface area increases with the diameter. This in turn will allow reduction in the thick ness of the bearing plate and allows wedges 131. to increase in thickness between the bearing plate and wedge gripping surfaoes 139. The increase in thickness of the wedges affords a greater ability to withstand cantilever support and projection from the bearing plate and increase in bore 136 diameter affords the ability to reduce the volume and weight of the bearing plate by decreasing its thickness. Still further, it has long been thought to be an advantage to have the radial gripping forces created by wedges 131 decrease from a maximum at the midpoint of the gripping surface to a substantially lesser value at end 142 of the wedges. Cantilever support of the wedges results in this desirable tendon gripping force profile.

Another advantage of increasing the diameter of bore 136 and thus thickness of wedges 131 is that the anchorage may more conveniently be used as a cast-in-place type of anchorage since member 113 can readily pass through the smallest diameter of the tapered bore 136, namely, at threaded end 118. This in turn will allow both the mounting member 113 and tendon 122 to be simultaneously mounted in place for casting of the concrete member.

By way of example, bearing plate 111 can be formed of C1040 steel having a Rockwell hardness of between about to about 218 on the Rockwell C scale. In order to grip a strand having a nominal diameter of 0.60 the bearing plate may be formed with a thickness of about A to 1 inch, with bore 136 having a diameter at the small end of about 1% inches and a taper of about 10. The wedge material was C1117 steel, case hardened to about 0.015 to 0.020 inch and having a Rockwell hardness of about 62 on the Rockwell C scale. The wedges were stressed relieved at 350 F. to avoid delay failure. Under these conditions, the strand could be tensioned to substantially its yield point by the anchorage without deformation of the bearing plate or failure of the wedges. Teeth 118 were tapped into the front end or small diameter end of the bearing plate, and since they diverge away from the 10 taper of the wedges, they did not interfere with the advancement of the wedges. The Wedges were 2 inches in length with approximately one-quarter of their length or /2 inch projecting forwardly of surface 126 at maximum loading thereof. The diameter of end 142 of the wedges was about 1 inches with the large diameter of the wedges being about 1% inches.

What is claimed is:

1. An anchorage assembly for casting an anchorage means into a concrete member for receipt of a tendon for formation of a prestressed concrete member, comprising:

(a) a concrete form having an opening therein to receive assembly mounting means therethrough;

(b) assembly mounting means removably mounted in said opening in saidvform and extending from an exterior side thereof through said opening and interiorly of said form a distance sufiicient to allow mounting of spacing means, anchorage member and (grouting thereon;

(c) spacing means mounted on said mounting means and positioned in abutting relation tosaid form, said spacing means being of a predetermined thickness to position an anchorage means in spaced relation to said form;

(d) anchorage means having a wall defining an axially convergently tapered bore dimensioned at the smallest point thereof to receive said assembly mounting means and a tendon to be tensioned and formed to receive convergently actuating tendon gripping means, said anchorage means including bearing plate means formed with a bearing surface to allow transfer of axial tensioning forces to said concrete member, said anchorage means being releasably mounted on said mounting means with said mounting means extending through said tapered bore and said anchorage means being positioned thereon in abutting relation to said spacing means, said spacing means further preventing the ingress of concrete into said tapered bore in said anchorage means as mounted in abutting relation therewith and being removable from said concrete member toafiord access to said tapered bore for insertion of tendon gripping means therein;

(e) securement means releasably mounted on said mounting means on the exterior side of said form; and

(f) grouting member formed to allow introduction of grout adjacent to said tendon after casting of said concrete member and releasably mounted to the inner end of said mounting means in abutting relation to said anchorage means, said securement means, grouting member and mounting means urging said assembly of said anchorage means and spacing means against said form and securing said assembly in close abutting relation thereto during the casting of said concrete member.

2. A tendon anchorage as defined in claim 1 wherein said anchorage means is formed with a grouting passageway therein terminating in a passageway opening on the remote side of said anchorage means, and said grouting member is formed as a hollow internally threaded sleeve for threadably mounting on said mounting means and formed of sufficient internal radius adjacent said anchorage means to communicate with said passageway opening.

3. An anchorage assembly as defined in claim 2, and

a conduit positioned in alignment with said mounting means and formed for receipt of a tendon therein, said conduit being threadably secured to said mounting means and being formed for communication with said grouting member for receipt of grout from said grouting means after casting of said concrete member and removal of said mounting means.

References Cited UNITED STATES PATENTS 3,293,811 12/1966 Rice 52-223 3,399,434 9/1968 Kelly 24-426 FOREIGN PATENTS 181,068 7/1954 Austria 52-230 195,081 1/1958 Austria 52r-230 794,561 7/1958 Great Britain SZP-ZSO FRANK L. ABBOTT, Primary Examiner J. L. R IDGILL, JR., Assistant Examiner U.S. Cl. X.R.