US3270471A

US3270471A - Post-tensioning apparatus for prestressing concrete

Info

Publication number: US3270471A
Application number: US144112A
Authority: US
Inventors: Karl H Middendorf
Original assignee: Prescon Corp
Current assignee: Prescon Corp
Priority date: 1954-11-15
Filing date: 1961-10-10
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06

Description

K. H. MIDDENDORF 3,270,471

Sept. 6, 1966 POS'I I'ENSVIDNING APPARATUS FOR PRESTRESSING CONCRETE Original Filed Nov. 15, 1954 5 Sheets-Sheet 1 INVENTOR. 1 421 M Moon 001M- A rog/dry p 1956 K. H. MIDDENDORF 3,270,471

POST-TENSIONING APPARATUS FOR PRESTRESSING CONCRETE Original Filed Nqv. 15, 1954 5 Sheets-Sheet 2 I N V EN TOR. fizz 1/ Mmoewooer p 6. 1966 K. H. MIDDENDORF 3,270,471

POST-TENSIONING APPARATUS FOR PRESTRESSING CONCRETE Original Filed Nov. 15, 1954 5 Sheets-Sheet 5 INVEN TOR. 1 42! Almom ooef A 'rronA/eY United States Patent 3,270,471 POST-TENSIONING APPARATUS FOR PRE- STRESSING CONCRETE Karl H. Middendorf, Costa Mesa, Califi, assignor'to The Prescon Corporation, a corporation of Texas Original application Nov. 15, 1954, Ser. No. 468,762. Divided and this application Oct. 10, 1961, Ser. No. 144,112

2 Claims. (Cl. 52-223) My invention relates to apparatus for prestressing concrete, and more particularly to a post-tensioning apparatus for prestressing concrete structures. This is a division of my application Serial No. 468,762, filed November 15, 1954, on Post-Tensioning Method and Apparatus for Prestressing Mem'bers, now Patent No. 3,029,490, patented April 17, 1962.

In the art of prestressing concrete, the means that is put under tension to accomplish the prestressing of the concrete is commonly referred to as a tendon. Such a tendon is normally composed of three parts: two ends, either stressing or dead end anchors or couplers and a high tensile strength element of varying length between the ends of said tendon. These high tensile elements may be made up of wires, bars or wire strands.

In my improved apparatus for post-tensioning concrete prestressing members, the tendons comprise a plurality of wires that are provided with clips at predetermined spaced intervals along the length thereof for holding the tension members in proper relative relationship to each other. In the form of tendon shown in the drawings, said clips hold said wires in spaced side by side relation in a row transversely of the length of the tension members, thus producing what is commonly referred to as a fiat tendon, that is, one that is of greater width than thickness.

I provide a plurality of clips that are of such a character that the tension members are kept in desired relative position, but which will only slightly grip the tension members so that the same can be readily shifted or slid longitudinally through the clips, said clips spacing the tension members transversely of the length thereof. Preferably said clips are indented between the Wires, to space the same from each other and slightly grip them. I Said .clips hold the wires aligned transversely of the tendon so as to maintain the same in a side by side spaced relation.

It is another purpose of my invention to provide a bearing and spacing plate at each end of the member that is to be prestressed for arranging the ends of the wires or other tension members so that there is sufficient concrete surrounding each wire at a predetermined distance inwardly from the base of the plate to eliminate any excessive pressure on the concrete. 50

It is a further purpose of my invention to provide new and improved stressing units that are in the form of blocklike members, which may be either threaded to engage with a suitable threaded fitting on a jack or other stressing device, or which are provided with smooth inclined faces to be gripped by the jack so as to not slip relative thereto. An advantage of the latter type of stressing unit is that this type can be made of cast material and can be made in the form of a strip or bar for stressing a group of the tension members instead of individually stressing the same, if this should be desired.

Other objects and advantages of my invention will appear as the description of the drawings proceeds. I desire to have it understood, however, that I do not intend to limit myself to the particular details shown or described, except as defined in the claims.

In the drawings:

FIG. 1 is a view in side elevation of a concrete structural member made in accordance with my invention.

FIG. 2 is a fragmentary vertical sectional view on an enlarged scale through the same at one end thereof.

FIG. 3 is a view similar to FIG. 2 of a modification.

FIG. 4 is a fragmentary vertical sectional view on an enlarged scale through the opposite end portions of the structural member shown in FIG. 1, the mid-portion thereof being broken away, showing the parts in the position which the same would assume in the second step of my method.

FIG. 5 is a horizontal sectional view through a fragmentary portion of the stressing means and a fragmentary portion of a structural member to which my invention is applied, with the stressing means in engagement with the right hand end of one of the structural members shown in FIG. 4.

FIG. 6 is a transverse sectional view on a further enlarged scale through one of the spacing members and the tension members associated therewith.

FIG. 7 is a plan view of the spacing mem'ber, showing fragmentary portions of the tension members spaced thereb FIG. 8 is an end elevation of a structural member, showing the form of the invention illustrated in FIG. 3.

FIG. 9 is an enlarged cross sectional view through one of the stressing members shown in FIGS. 2, 3 and 4.

FIG. 10 is a similar view of a modified form of stressing member.

FIG. 11 is an end elevation of the stressing member shown in FIG. 10.

FIG. 12 is a view similar to FIG. 8 of a structural member, showing the form of stressing member illustrated in FIGS. 10 and 11.

FIG. 13 is a similar view, showing a further modified form of stressing member.

FIG. 14 is a vertical sectional view through the stressing member shown in FIG. 13, on an enlarged scale, and

FIG. 15 is a view similar to FIG. 5, showing a modified form of stressing means for cooperation with a modified form of stressing member that is not threaded.

Referring in detail to the drawings, in FIG. 1 a structural member 20, which may be a beam and which has a concrete body portion, is shown as having a plurality of tension members 21 embedded therein, such as wires, that can be put under tensile stress to prestress the structural member 20. A spacing and bearing plate 22 is provided in each end of the structural member through which the members 21 pass, and in FIG. 1 said members are shown as being provided with spacing means 23 at each end thereof between said plates 22 and stressing members 24, the position of the parts shown in FIG. 1 being that of the finished prestressed beam with the tension members 21 under the full tensile stress to which these are to be put to get the desired prestressing of the member 20. The spacing means 23 may be of any desired character such as shown in either FIG. 2 or FIG. 3 and the stressing members or anchors 24 may be of various types as well be described below.

In FIG. 2 a fragmentary portion of one end of such a structural member as shown in FIG. 1 is shown, in which the members 21 are shown as being held in a predetermined spaced relation by means of the bearing plate 22, which has openings therein at 25 through which said tension members pass. Thus the tension members 21 are arranged in spaced relation in the body of concrete 26. Each of said tension members, which are preferably in the form of wires of high tensile strength, are provided with heads 27 that are formed thereon from the material of the wire. A screw-threaded block 28 serves as a stressing or anchor member for each of said tension members 21, there being an opening 29 centrally through each of said members 28 (see FIG. 9) and said member 28 being externally screw-threaded as indicated at 30 in the drawings.

In assembling the structure shown in FIG. 1, a plurality of clips, constituting clamping means for holding the tension members in side by side spaced relation are arranged at desired intervals lengthwise of the tension members 21, said clips being indicated by the numeral 31 in FIG. 1. The details of construction of said clips are shown in FIGS. 6 and 7. Each of said clips is made up of a pair of sheet metal members 32 and 33, which are each provided with a portion 34, which is reduced in width and which is adapted to be bent around the end edge 35 of the opposite end of the member cooperating therewith, as shown at 36 in FIGS. 6 and 7, to clamp the members 32 and 33 to each other. In FIG. 6 the reduced portion 34 is shown in the position that it has before being crimped over into holding position at the left of said figure, and in its crimped over position of holding position at the right thereof. The length of the clips and thus of the portions 32 and 33 thereof is dependent upon the number of tension members that are spaced thereby, the number shown in FIGS. 6 and 7 being a relatively small number of tension members that would be so connected together in transverse alignment by said clips in practice.

The clips are provided with indentations 37 that are opposite each other so as to provide adjacent portions 33 in the opposite members 32 and 33 of said clips for spacing the transversely aligned wires 21 from each other, said clips thus constituting spacing members for said wires. Said members 32 and 33 are bent toward each other at 39 adjacent the end portions 35 and reduced portions 34 to thus form pockets in which the tension members 21 are located and from which these can not move toward or away from each other when the tongues 34 are crimped around the end edges 35 in the position shown at 36 in FIGS. 6 and 7. However, the tension members 21 are not gripped tightly enough by the spacing members to prevent sliding of the tension members 21 through the spacing members lengthwise of said tension members 21.

Said tension members 21 are placed in the desired position in the form with the spacing members 31 provided thereon at the desired points along the length thereof to obtain the desired transverse alignment thereof and the spacing plates 22 are placed in the desired position in the form. The spacing plates 22 and the stressing members 24 are placed on the tension members 21 before the heads 27 are formed thereon. When the tension members 21 are placed in position in the form the stressing members, such as the members 28 shown in FIG. 2, are put in position adjacent the heads 27, and U-shaped spacing members 10 are placed in position between the members 28 and the plate 22, said spacing members being of such size that this will place the members 28 at the other ends of the tension members 21 in position against the plate 22 at the other end of the structural member that is to be prestressed.

The concrete is then poured and after it has been allowed to set a suflicient time to permit movement of the tension members 21 longitudinally of themselves therein without damage to the structural member the tension members 21 are shifted lengthwise of themselves in the concrete body portion. To do this the spacing members 44 are removed from the end of the tension members to which these have been applied, which is the left hand end as shown in FIG. 2, and the tensioning or stressing means is applied to the other end of the tension members 21, for example, in the manner illustrated in FIG. 5, at the right hand end of said members. The stressing or tension applying means is shown as being a movable member 41 of a jack having a body portion 42 that engages the plate 22 at the right hand end of the structural member 20. Said jack may be of any desired or well known character and is provided with a suitable internally screw-threaded portion 43 that is screw-threadedly engaged by the threads 30 on the member 23. Obviously the tensioning is accomplished by moving the member 41 to the right relative to the member 42 as viewed in FIG. 5. The movement of the parts is only sufficient to move the member 28 on the member 21 at the opposite end or left hand end of said structural member 20 into engagement with the plate 22 at that end thereof.

If desired spacing members 40 can then be inserted between the anchor members 23 and the bearing plate 22 at the right hand end of the structural member as viewed in FIG. 1, or the tensioning means, after having moved the tension members 21 all to the right longitudinally of themselves in the manner above described, can be engaged With the members 28 on tie tension members 21 at the opposite or left hand end of the structural member to again move the tension members 21 lengthwise of themselves in the concrete body portion of the structural member 20 and this can be repeated alternately at opposite ends of the tension members 21 as often as may be necessary to break any bond that might exist between the tension members and the concrete body portion to permit movement thereof longitudinally for the purpose of tensioning said members 21 when the post-tensioning thereof for prestressing the concrete structural member 20 is to be performed. This is not done until the concrete of the structural member has been cured sufiiciently to reach its maximum strength, whereupon the posttensioning is completed by applying the tensioning means first to one end of the structural members 21 and inserting spacing members 23 between the stressing members 28 and the plate 22 at that end of the structural members, then tensioning the members 21 at the other end thereof to the desired amount and placing spacing means 23 between said members 28 and the plate 22 at the last mentioned end of said structural member, completing the prestressing.

During the shifting of the tension members 21 lengthwise of themselves the clips 31 hold these in properly spaced side by side relation transversely of the structural member 2th and the plate 22 will hold the same in properly spread out relation at the ends thereof in the structural member, but neither of the spacing members in any manner interferes with the longitudinal shifting of the tension members 21.

Instead of using a separate U-shaped spacing member 49 between each of the stressing or anchor members 28 and the bearing plate 22 adjacent the same as shown in FIG. 2, a single U-shaped spacing member as for a group of said members 28 may be provided, as shown in FIG. 3. The member 1th is also shown as being applied to the structure to space the members 28 from the bearing plate 22 in FIG. 8. The members 40 are provided with a bend at 4% connecting a pair of parallel legs 45, thus forming a U-shaped member. The members 40 are similarly made, but the leg portions are shorter, as will be obvious from FIG. 2. Said U-shaped spacing members 46 or 40 can be very readily inserted between the anchor members 28 and the bearing plate 22 while the tensioning means comprising the

members

41 and 42 are in position, as shown in FIG. 5, by passing the same between the bearing plate 22 and the anchor member 28 through the space 4-6, as the body portion 4-2 has openings therein between the spaced legs 47 provided thereon.

In FIG. 4 the structural member is shown after the tension members 21 have been shifted lengthwise of themselves from the position shown in FIG. 2 and a spacing member 40 has been inserted between the stressing or anchor members 28 at the right hand end of said tension members 21 and the bearing plate 22. With the member 46 in the position shown in FIG. 4, or members 40 such as shown in FIG. 2, in such a position, the tensioning means can be applied to the stressing or anchor member 28 at the left hand end of the tension members 21 as shown in FIG. 4 until the desired tension has been placed on each thereof to prestress the concrete to the desired amount. Then a spacing member 40' or a plurality of spacing members 48', can be inserted between the anchor members 23 and the bearing member 22 at the left hand end of the structural member, as viewed in FIG. 4. This is the condition of the structural member illustrated in FIG. 1. This last step is, of course, not taken until the concrete body portion 26 has reached its maximum strength. The spacing members 40 or 40' are made of greater thickness between the two opposite edges thereof that are in engagement with the

members

28 and 22 than the thickness of the material from which they are made, which, however, is of sufficiently heavy gauge that it will withstand the compression that is exerted on the spacing member in use.

Instead of providing a screw-threaded stressing or anchor member, such as the member 28, a stressing or anchor member that is of a tapering character may be provided, as illustrated in FIGS. and 11. Said stressing or anchor member 48 has a body portion 49 that tapers toward the end 50 thereof and has a central opening 51 therein for the tension member 21. The one pair of opposite side faces 52 thereof taper from the larger end 53 thereof to the smaller end 50 thereof uniformly, thus forming a wedge-like body portion for the stressing or anchor member. The faces of the member 48 that extend perpendicularly to the faces 52 are perpendicular to the

ends

50 and 53 of the member 48, these faces being indicated by the numeral 54 in FIG. 11. Said stressing or anchor members 48 are shown in position on the members 21 with the heads 27 thereof in engagement with the larger ends 53 thereof in FIG. 12, and a U-shaped spacing member 40 is shown as being in position between said anchor members 48 and the bearing plate 22.

If desired, instead of using a plurality of stressing or .anchor members 48, a single stressing or anchor bar 48' can be used, which is provided with inclined or tapering sides 52' corresponding to the faces 52 of the member 48, and is provided with a plurality of openings 51 for tension members 21, said member 48 being of a bar-like character as shown so as to receive a plurality of vertically aligned tension members 21 in the manner illustrated in FIG. 13. In the use of such a stressing or anchor member as the member 48 or the member 48', the jack has to be modified to provide a movable member 41' that has inclined walls 55 with which the

inclined walls

52 or 52 of the

members

48 or 48' engage to provide for movement of the stressing

member

48 or 48 by means of the jack. The jack is otherwise constructed in the same manner as that used for the threaded members 28, as illustrated in FIG. 5.

An advantage in using a stressing or anchor member such as the member 48 or the member 48 is that it can be made by casting without any finishing being required, instead of having a member, such as the member 28, that has to be threaded.

What I claim is:

1. A post-tensioned prestressed concrete structural member having a concrete body portion having a fiat bottom face, an elongated prestressing tendon for said concrete body portion embedded therein having a transversely flat body portion consisting of a plurality of closely transversely adjacent high tensile strength steel wires extending in parallelism longitudinally of said tendon and means for holding said wires in a single straight row in close side by side adjacency with said row extending transversely of said tendon parallel to the bottom face of said concrete body portion, consisting of clamping means frictionally gripping said wires adjacent opposite ends of said main body portion of said tendon and at longitudinally spaced intervals along the same therebetween, each of said clamping means consisting of duplicate paired sheet metal members, one member of each pair extending transversely across said wires in engagement therewith on one side thereof and the other member of each pair extending transversely across said wires in engagement therewith on the other side thereof, said paired members having means for holding the same assembled with said wires to connect said wires slidably with said clamping means for movement of said wires relative to said clamping means longitudinally of said wires independently of each other.

2. A post-tensioned prestressed concrete structural member having an elongated concrete body portion having a flat bottom face, a prestressing tendon for said concrete body portion embedded therein having a transversely fiat body portion consisting of a plurality of closely transversely adjacent high tensile strength steel wires extending in parallelism longitudinally of said tendon and means for holding said wires in a single straight row in close side by side adjacency with said row extending transversely of said tendon parallel to the bottom face of said concrete body portion, consisting of clamping means frictionally gripping said wires adjacent opposite ends of said main body portion of said tendon and at longitudinally spaced intervals along the same therebetween, each of said clamping means consisting of duplicate paired sheet metal members, one member of each pair extending transversely across said wires in engagement therewith on one side thereof and the other member of each pair extending transversely across said wires in engagement therewith on the other side thereof, said members having interengaging marginal portions at opposite ends thereof holding said members in frictional engagement with said wires to connect said wires slidably with said clamping means for movement of said wires relative to said clamping means longitudinally of said wires independently of each other, and indentations on said sheet metal members extending between said wires to space the same.

References Cited by the Examiner UNITED STATES PATENTS 756,309 4/1904 Wight 52723 778,416 12/1904 Kyle 52648 875,396 12/1907 White 52708 960,305 6/1910 Gilbreth 52723 977,345 11/1910 Tidnam et al. 25131 1,001,462 8/1911 Scott 52648 1.073,931 9/1913 Royse 52693 1,304,815 5/1919 Sharp 52712 1,608,184 11/1926 Rumble 52220 X 2,404,531 7 1946 Robertson 24868 2,425,033 8/ 1947 Fletcher 24868 2,637,895 5/1953 Blaton 52228 X 2,675,695 4/1954 Coif 52225 2,804,674 9/1955 Long 52223 X 2,941,394 6/1960 Brandt 52223 2,988,794 6/1961 Gutt 52223 X FOREIGN PATENTS 183,214 9/1955 Austria.

489,515 l/1953 Canada.

345,491 10/ 1904 France. 1,223,043 1/ 1960 France.

739,480 10/1955 Great Britain.

FRANK L. ABBOTT, Primary Examiner.

WILLIAM I. MUSHAKE, HENRY C. SUTHERLAND,

RICHARD W. COOKE, JR., Examiners.

JACOB L. NACKENOFF, J. L. RIDGILL,

. Assistant Examiners.

Claims

1. A POST-TENSIONED PRESTRESSED CONCRETE STRUCTURAL MEMBER HAVING A CONCRETE BODY PORTION HAVING A FLAT BOTTOM FACE, AN ELONGATED PRESTRESSING TENDON FOR SAID CONCRETE BODY PORTION EMBEDDED THEREIN HAVING A TRANSVERSELY FLAT BODY PORTION CONSISTING OF A PLURALITY OF CLOSELY TRANSVERSELY ADJACENT HIGH TENSILE STRENGTH STEEL WIRES EXTENDING IN PARALLELISM LONGITUDINALLY OF SAID TENDON AND MEANS FOR HOLDING SAID WIRES IN A SINGLE STRAIGHT ROW IN CLOSE SIDE BY SIDE ADDJACENCY WITH SAID ROW EXTENDING TRANSVERSELY OF SAID TENDON PARALLEL TO THE BOTTOM FACE OF SAID CONCRETE BODY PORTION, CONSISTING OF CLAMPING MEANS FRICTIONALLY GRIPPING SAID WIRES ADJACENT OPPOSITE ENDS OF SAID MAIN BODY PORTION OF SAID TENDON AND AT LONGITUDINALLY SPACED INTERVALS ALONG THE SAME THEREBETWEEN, EACH OF SAID CLAMPING MEANS CONSISTING OF DUPLICATE PAIRED SHEET METAL MEMBERS, ONE MEMBER OF EACH PAIR EXTENDING TRANSVERSELY ACROSS SAID WIRES IN ENGAGEMENT THEREWITH ON ONE SIDE THEREOF AND THE OTHER MEMBER OF EACH PAIR EXTENDING TRANSVERSELY ACROSS SAID WIRES IN ENGAGEMENT THEREWITH ON THE OTHER SIDE THEREOF, SAID PAIRED MEMBERS HAVING MEANS FOR HOLDING THE SAME ASSEMBLED WITH SAID WIRES TO CONNECT SAID WIRES SLIDABLY WITH SAID CLAMPING MEANS FOR MOVEMENT OF SAID WIRES RELATIVE TO SAID CLAMPING MEANS LONGITUDINALLY OF SAID WIRES INDEPENDENTLY OF EACH OTHER.