US3399502A - Flat bar stressing tendon - Google Patents

Description

Sept. 3, 1968 E. DABNEY FLAT BAR STRESSING TENDON 5 Sheets-Sheet 1 Filed April 29, 1966 INVENTOR.

EUGENE E. DAB/VEV ATTORNEY p 1968 E. E. DABNE Y FLAT BAR STRESSING TENDON 3 Sheets-Sheet 2 Filed April 29, 1966 INVENTOR.

EUGENE E DABIVEV sept- 1968 E. E. DABNEY 3,399,502

FLAT BAR STRESSING TENDON Filed April 29, 1966 5 Sheets-Sheet 3 INVENTOR.

EUGENE E. DAB/V5) United States Patent 3,399,502 FLAT BAR STRESSING TENDON Eugene E. Dabney, Corpus Christi, T ex., assignor to The Prescon Corporation, a corporation of Texas Filed Apr. 29, 1966, Ser. No. 546,291 4 Claims. (Cl. 52224) ABSTRACT OF THE DISCLOSURE A fiat bar prestressing tendon has a major portion of uniform cross section that extends slidably through a slot in a bearing member and a slot in an anchor. A head on each end of the tendon is the width of the bar. The portion of each head that increases gradually in thickness from the thickness of the major portion of the bar to the maximum thickness of the head has concave faces and the head has a convexly curved outer end. The anchor is flat faced on the side toward the bearing member and .has a recess leading into the slot on its opposite side with convexly curved flaring wall portions conforming to the concave portion of the head so that the head seats firmly in the recess. The bearing member has a flat face directed toward the flat face of the anchor and has a boss surrounding the slot on the side opposite the flat face. A U-shaped shim is mounted between the anchor and bearing member, when the tendon is stressed. It has parallel fi-at faced legs embracing the bar and extending adjacent the opposite sides of the slots and bearing against the other side of the bearing member opposite the boss. The width of the bar extends vertically in a tank wall or similar structure.

My invention relates to means for prestressing concrete and more particularly to a fiat bar tendon for prestressing concrete by the post-tensioning method.

It is a purpose of my invention to provide means for prestressing concrete that is in the form of a flat bar of high tensile strength steel having considerably greater width than thickness. By utilizing a flat bar the advantages of a flat tendon are obtained. Such fiat tendons are particularly advantageous in a flat slab concrete construction, as such flat bar tendons make it possible to resist externally induced moments by internally created moments developed by less prestressing force than where a tendon circular in cross section is utilized, when placed with their width parallel to the fiat bottom face of the slab. This is because a flat tendon can be mounted in a concrete body in such position and obtain a longer couple arm than with a round or thick tendon and at the same time maintain the required covering of concrete over the steel prestressing member to protect it against weather and fire.

Not only is a flat bar tendon made in accordance with my invention particularly desirable for use in a slab structure as above referred to, but has the same advantages in a beam structure, if mounted with its width or major transverse dimension extending substantially parallel to the bottom face of the beam. My invention is also applicable to such structures as have vertical wall portions that are prestressed, such as tanks, reservoirs and bins, which have pressures applied thereto in a substantially radially outward direction. In such prestressed concrete structures, my improved fiat bar tendon is mounted with its major transverse dimension extending vertically and with its length extending circumferentially of the structure, such as a tank or bin, or other structure that has an endless side wall.

It is a further purpose of my invention to provide a flat bar tendon with positive anchorage means comprising enlargements on the ends thereof, that are so related to a bearing plate and an anchor member that the flat bar tendon, which is made of high tensile strength steel, can be pulled by means of the anchor member into a position such that the flat bar tendon is extended to stress it and held in such extended stressed position, so that its tendency to return to normal length will cause the concrete in which the same is imbedded, to be compressed, the pulling of the tendon and the holding of the same in extended position, being accomplished after the concrete has set, by what is commonly known as a post-tensioning method.

In order to hold the high tensile strength steel tension member in stressed condition, suitable spacing means are inserted between the bearing member and the anchor member, said spacing means being preferably in the form of a shim that can be readily inserted between the anchor member and the bearing plate and which has a good bearing on both the bearing plate and the anchor member.

It is a purpose of my invention to provide an end enlargement and a bearing plate that are so constructed that the same will readily withstand the stresses to which the same are subjected, without making the same unduly heavy or bulky. It is a further purpose of my invention to provide an anchor member of such a character that it will be engaged with the enlargement on the end of the flat bar tendon so as to distribute the stresses exerted on the anchor member, by means of said enlargement, as widely as possible over the anchor member, and to avoid any sharp angular changes in direction of the engaging surfaces of the anchor member and enlargement.

It is a further purpose of my invention to provide an anchor member that is of such a character that it can be readily engaged with pulling means for putting the tendon under stress and with pulling means that is provided with a suitable anchor member engaging portion, with which the anchor member can be readily engaged by a relative transverse sliding movement between the means on the pulling member and the anchor member.

My invention relates to means for post-tensioning a concrete structure comprising a bearing member having a slot therein, a flat high tensile strength steel bar of much greater width than thickness extending through said slot, said bar having enlargements at the ends thereof, and an anchor member mounted between an enlargement at one end of said bar and one of said bearing members, the anchor member having a slot therein through which the bar extends and a recess into which the enlargement extends.

More specifically my invention comprises a flat bar that has enlargements at the ends thereof that vary in thickness to provide an enlarged portion of maximum thickness and a portion increasing in thickness from the cross sectional thickness of the bar to said maximum thickness, the bearing member having a flat face on the side thereof toward the anchor member and said anchor member having a fiat face on the side thereof toward the bearing member, so that shims can be mounted between said bearing member and said anchor member to flatly engage therewith, the bearing member having a thickened portion surrounding the slot therein on the side thereof away from the anchor member.

It is a further purpose of my invention to provide means for spacing the anchor member from the bearing plate comprising a U-shaped shim having a pair of legs that are rectangular in cross section so as to provide flat side faces on the shim, that are adapted to engage the flat faces of the bearing member and anchor member, when the shims are inserted in position to hold the anchor member spaced from the bearing member and the fiat bar tendon under stress.

In order to provide for the ready engagement of a pulling member with the anchor member, the anchor member is provided with a formation that is adapted to cooperate with a complimental formation on the pulling member by relative sliding engagement, transversely of the direction of pull of said pulling member, with respect to said anchor member, said formation including either an offset in a pair of transverse faces of the anchor member, providing a shoulder thereon with which a shoulder on the pulling member engages, or inclined or beveled faces on said anchor member on the opposite transverse faces thereof converging toward the flat face of said anchor member, for engagement with similarly inclined faces on the pulling member.

It is an important purpose of my invention to provide end enlargements on said fiat bar tendons that are of such a character that the same can be readily formed thereon without reducing the tensile strength of the steel of the fiat bar member, either by a cold forming method or the equivalent.

Summary It is the principal purpose of my invention to provide post-tensioning means comprising a bearing member that has a flat face on one side thereof, a slot therein and a boss on the opposite side thereof providing a thickened wall portion surrounding the slot, a flat high tensile strength steel bar of much greater width than thickness extending through the slot, the major portion of the bar slidably fitting the slot, the bar having integral end enlargements varying in thickness, the thickness gradually increasing from that of the major portion of the bar to a portion of maximum thickness, the portions of gradually increasing thickness having concavely curved surfaces extending from the major portion of the bar to the portion of maximum thickness of the enlargements, an anchor member having a slot slidably receiving the major portion of the bar, the anchor member being mounted between an end enlargement and a bearing member and having a flat face on the side thereof toward the bearing member, a recess in the other side of the anchor member that has flaring wall portions conforming to the gradually thickening portion of one of the enlargements to firmly seat it therein, and a U-shaped shim member between the anchor member and the bearing member, embracing the bar and having flat side faces engaging the flat faces of the bearing member and the anchor member adjacent each side of the slots, so that the stress on the anchorage will be uniformly distributed over the enlargement and be transferred through the shim to the thickened wall portion of the bearing member surrounding the slot therein.

Other objects and advantages of my invention will appear as a 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 by the claims.

In the drawings:

FIG. 1 is a fragmentary view, partly in vertical section and partly in elevation, showing my improved flat bar tendon applied to a concrete structure, the major portion of the concrete structure being broken away.

FIG. 2 is a fragmentary view, partly in vertical section and partly in elevation of one end of my improved prestressing means, showing the position of the parts after the anchor member has been pulled to the position in which it stresses the tendon and the shim has been applied thereto for holding the anchor member in its tendon stressing position.

FIG. 3 is a fragmentary view in elevation of the end anchorage shown in FIG. 2, as viewed from the right of FIG. 2.

FIG. 4 is a fragmentary sectional view taken on the line 4-4 of FIG. 1.

FIG. 5 is a fragmentary view partly in horizontal section and partly in plan of the anchorage shown in FIG. 2.

FIG. 6 is an enlarged fragmentary view partly in section and partly in elevation of the anchor member and the enlarged end of the flat bar tendon.

FIG. 7 is a view similar to FIG. 1 of a modification.

FIG. 8 is a view similar to FIG. 2 of the modification shown in FIG. 7.

FIG. 9 is a fragmentary elevational view of the anchorage shown in FIG. 8, as viewed from the right of FIG. 8.

FIG. 10 is a fragmentary view partly in horizontal section and partly in plan of the anchorage shown in FIG. 8.

FIG. 11 is a fragmentary horizontal sectional view through a portion of a structure having a vertical wall which is preferably endless, showing my invention applied thereto.

FIG. 12 is an enlarged fragmentary horizontal sectional view thereof showing the end anchorages for the fiat bar tendons.

FIG. 13 is a fragmentary section taken on the line 13 13 of FIG. 11, and

FIG. 14 is a section taken on the line 14-44 of FIG. 12.

Referring in detail to the drawings, my improved prestressing tendon is shown as being mounted in a body of concrete 20, said tendon comprising a tensioning member 21. in the form of a bar rectangular in cross section, having much greater width than thickness as shown in FIG. 4, and having fiat, smooth top and bottom faces 22 and 23. In FIGS. 1 to 5 inclusive, the flat tension member in the form of a bar is shown as being mounted in a body of concrete 20 that has a fiat bottom face 24, such as a beam or slab, and flat end faces 25. An enlargement 26 is provided on each end of the bar 21. The bar 21 is made of high tensile strength steel and the enlargement 26 is formed on the bar 21 by a cold forming, or other suitable, method, that will not undesirably affect the high tensile strength of the steel. Said enlargement extends the full width of the bar 21 and varies in thickness so as to provide a portion of maximum thickness and a portion that gradually increases in thickness from that of the main body portion 21 to the portion of maximum thickness, the portion of gradually increasing thickness having a concavely curved surface 27 on each side of the bar, which extends to and joins a convexly curved end portion 28 of the bar in a smooth curve at the points 29 on said enlarged end portions, which points 29 are located at the maximum thickness of said end portion. The bar 21, it will be noted upon reference to FIG. 4, extends with its width, or maximum transverse dimension, parallel to the flat bottom face 24 of the concrete structure 20.

Mounted on the bar 21 are bearing members 30, said bearing members each having a flat face 31 on one side thereof and a projection or boss 32 on the other side thereof. Said bearing members are preferably rectangular in character and elongated in the direction of the width of the bar 21. The boss 32 tapers toward the outer end thereof, as will be obvious from FIGS. 1, 2 and 5, and the side of said bearing member which is opposite the flat face 31 thereof, is provided with inclined surfaces 33 and 34 extending from the marginal edges of said bearing member 30 to the base of the boss 32. A slot 35 extends through the bearing member 30 and substantially centrally through the boss 32, said slot being of such configuration as to conform substantially to the cross sectional shape of the bar 21 and slidably receives said bar. The bearing member 30 thus constitutes a rectangular bearing plate that is flat on one face and has a projection on the other face thereof that provides a thickened portion surrounding the slot 35 through which the bar 21 extends.

Mounted on said bar 21 adjacent each end thereof is an anchor member 36 in the form of a washer that is provided with a slot 37 therein, said anchor member 36 being shown as being of a rectangular character and elongated in the direction of width of the bar 21 upon which it is mounted, the slot 37 conforming to the cross sectional shape of the bar 21 and being adapted to slidably receive the bar 21. The anchor member 36 has a flat side face 38 through which the slot 37 extends, which flat side face is directed toward the fiat side face 31 of the anchor member 30, and with a side face 39 which extends through the major portion thereof parallel to the side face 38, but is recessed so as to provide a seat for the enlargement 26, said recess having convexly curved wall portions 40, which conform to the concavely curved surfaces of the enlargement 26 so as to seat the enlargement firmly in the recess which leads into the slot 37. The opposite end faces 41 of the anchor member 36 are flat and extend perpendicularly to the fiat face 38, but the transverse top and bottom faces 42 extending lengthwise of said anchor member are inclined in a transverse direction so as to converge toward the flat face 38 thereof, as shown in FIGS. 1 and 2.

The tendon is used for prestressing concrete by the posttensioning method, in which case the bearing members 30 and the high tensile strength steel bar 21 are mounted in the form so as to be embedded in the concrete when it is poured, and after the concrete has set sufficiently, the bar 21 is put under tension or stress by pulling on one or both of the anchor members 36 so as to extend the bar 21. In the arrangement shown in FIG. 1 the anchorage at the left hand end of the tendon is provided with the anchor member 36 mounted between the enlargement 26 and the bearing member 30 and positioned so as to have the flat face 38 thereof in engagement with the flat face 31 of the bearing plate 30 and with the head or enlargement 26 on the bar 21 seated in the anchor member 36 as shown in FIG. 6, and all of the pulling action takes place at the other end of the tendon. Prior to such pulling action on the part of the pulling means, which will be described below, the anchor member 36 on the right hand side of the structure, as shown in FIG. 1, is in the same position as the anchor member 36 shown on the left hand end thereof, in engagement with the bearing member 30.

The pulling member is then engaged with the anchor member 36 to pull it from a position in engagement with the bearing member 30 to the position shown at the right of FIG. 1. The pulling member usually comprises a hydraulic jack (not shown) which is provided with a pulling bar 43, which is provided with a coupling member 44 at the end thereof that is adapted to be engaged with the anchor member 36, by sliding the coupling member into engagement with the anchor member 36 transversely of the length of the bar 21. The coupling member is of a yoke-like character having a pair of arms 45, that have thickened end portions 46, that have inclined or beveled faces 47 that are complemental to the inclined surfaces 42 provided on the anchor member 36 so as to interengage therewith when the pulling member 43 is moved to the right as viewed in FIG. 1, so as to pull the member 36 also to the right.

In order to hold the anchor member 36 in the position into which it has been pulled to stress the bar 21, a shim is inserted between the anchor member 36 and the bearing member 30. Said shim is provided with a pair of parallel legs 48 connected by means of a curved bight or end portion 49, said shim thus being U-shaped in character. It is put in position with one of the legs 48 above the bar 21 and the other leg 48 below said bar 21, as shown in FIG. 2. In FIG. 2 the position of the parts shown is that thereof after the pulling member has been removed by sliding the coupling member 44 transversely or in the direction of width of the bar 21 out of engagement with the anchor member 36. It will be noted that the side faces 50 of the shim are flat, said legs 48 of said shim being rectangular in cross section, so that the said side faces of said legs 48 will engage flatly with the flat face 31 of the bearing member 30 and with the flat face 38 of the anchor member 36 to provide a solid bearing of said anchor member against said shim and of said shim against said bearing member.

Referring now to FIGS. 7 to 10, inclusive, the concrete body 20 is of the same character as previously described, having a flat bottom face 24 and the fiat end face 25, such as would be provided in either a beam or a slab. The tensioning member is a flat bar 21, which is the same in character as the flat bar previously described and the same reference numerals are applied to corresponding parts thereof in FIGS. 1 to 6 and 7 to 10. The bearing member 30 is also the same in character as previously described and the same reference numerals are applied to corresponding parts thereof in FIGS. 7 to 10, inclusive, that are applied thereto in FIGS. 1 to 6, inclusive. These parts are mounted in the concrete in the same manner as previously described.

The anchor member 36 is provided with a slot 37 therein, as previously described, and has a recess provided in the one flat face 39 thereof of the same character as previously described, said recess 40 seating the enlargement 26 on the bar 21 in the same manner as previously described. Said anchor member 36', however, instead of having the inclined top and bottom faces provided on the anchor member 36, is provided with a right angular offset or shoulder 51 in each of the top and bottom faces thereof between the main body portion 52 of the anchor member and the reduced inner end 53 thereof that has the flat face 38 facing the flat face 31 of the bearing member, as previously described.

Instead of providing the pulling member 43, a pulling member 54 is provided, which has a coupling member 55 provided thereon, that is yoke-like in character, having the arms 56 and inwardly directed flanges 57 on the ends of said arms that have inner faces 58 that extend perpendicular to the main body portions of the arms 56. Said coupling member 55 is engagea'ble with the anchor member 36' by sliding the coupling member 55 into engagement with the anchor member 36' in the direction of width of the high tensile strength steel bar 21, and disengageable therefrom in a similar manner.

The tendon is stressed in the same manner as previously described, by pulling the anchor member 36' to the right by means of the pulling member 54 after the concrete has set, and a shim is inserted between the anchor member 36' and the bar member 30 in the same manner as previously described, the shim being of the same character as described in FIGS. 1 to 6, inclusive, having a pair of legs 48 and a bight portion 49 engaging in embracing relation to the bar 21 in the same manner as in the form of the invention shown in FIGS. 1 to 6, inclusive. The legs 48 are of the same cross sectional shape as previously described and the flat side faces thereof engage flatly with the flat faces 38 and 31 of the anchor member and bearing member respectively in the same manner as described in connection with FIGS. 1 to 6, inclusive.

In FIGS. 11 to 14, inclusive, my improved flat bar tensioning member is shown as being applied to a concrete structure that has a vertical arcuate wall, which may be curved on the arc of a circle or otherwise, and which is of an endless character, such as the wall of a reservoir, tank or other similar receptacle. The vertical wall is indicated by the numeral 20 and is provided with a plurality of pi'lasters 59, which are provided at regular intervals along said wall. The tendons are shown as extending from one pilaster to the next one, each comprising a flat bar tensioning member such as previously described, which are indicated by the numerals 21, 21 and 21", all of these tensioning members being alike, but being indicated by different reference numerals to distinguish the same. Each of said tensioning members has its width or major transverse dimension extending vertically of the wall 20', the tensioning members extending around the tank or other similar structure in a generally circumferential direction.

While the tensioning members, such as the member 21', may be put under stress either by pulling on the same from one end or from both ends the same are shown as having been pulled to stress the same from only one end in FIGS. 11 to 14, inclusive. The bearing members 30 are the same in structure as previously de- 7 scribed, but have their length extending vertically instead of horizontally (see FIG. 14), with the slots 35 therein extending vertically.

Similarly the anchor members 36 are positioned on the bars 21, 21' and 21" with the length of the slots 37 therein extending vertically, said anchor members 36, shown in FIGS. 11 to 14, inclusive, being duplicates of the anchor members 36 shown in FIGS. 1 to 6, inclusive, although anuhor members 36', such as shown in FIGS. 7 to 10, inclusive, could be used in a vertical wall. The enlargements 26 on the bars 21, 21' and 21 are duplicates of the enlargement shown in detail in FIG. 6 and cooperate with the anchor members 36 in the same manner as described in connection with FIGS. 1 to 6, inclusive. The shims provided between the anchor members 36, that have been pulled to stress the tendons, and the bearing members 30 are duplicates of the shims previously described and cooperate with the bearing members 30, anchor members 36 and bars 21, 21' and 21" in the same manner as previously described, the shims being applied with the 'bight 49 upward and the legs 48 depending, as shown in FIG. 14.

The tendons each comprising a flat bar of high tensile strength steel, such as the bar 21, are placed in the form before the concrete is poured with the bearing members 30 seated in the concrete, as shown in FIGS. 11 to 13, inclusive, with the flat faces thereof exposed and with the anchor members 36 engaging therewith. After the concrete has set sufficiently the anchor members 36 at one end of the tendons are pulled to stress the tendons and the shims inserted to hold the anchor members in tendon stressing position, as shown in FIGS. 11 and 12. The vertical spacing of adjacent tendons shown in FIG. 13 is merely illustrative and may be varied as required. By

placing the fiat bar tensioning members with their width vertical all portions thereof, at any point along the length thereof, will be at the same spacing from the axial center of the curved wall, and the same can be mounted in such a position as to obtain a longer couple arm than tension members of other cross sectional shapes and yet have the required covering concrete to protect it against weather and fire.

It is to be understood that the fiat high tensile strength steel bars in all forms of the invention are provided with a suitable lubricating coating or other means to prevent the bonding of the concrete thereto, so that movement of the bars within the body of concrete can take place as the same are stressed.

What I claim is:

1. Means for post-tensioning a concrete structure comprising a bearing member having a slot therein and a fiat face on one side thereof, a flat high tensile strength steel bar of much greater width than thickness extending through said slot, the major portion of said bar being of uniform cross section substantially conforming in size and shape to, and slidably fitting in said slot and having an integral end enlargement of substantially the width of said bar thereon, said end enlargement varying in thickness to provide an end enlargement portion of maximum thickness and an end enlargement portion gradually increasing in thickness, from the thickness of said major portion of said bar to said maximum thickness, said portion of gradually increasing thickness extending from said major body portion of said bar to said portion of maximum thickness, and an anchor member mounted between said enlargement and said bearing member and having a slot therein through which said bar slidably extends, said anchor member having a flat face on the side thereof toward said bearing member and a recess into which said enlargement extends in the other side thereof leading into said slot, said recess having flaring wall portions conforming to and engaging face to face with the gradually increasing in thickness portion of said enlargement to firmly seat said enlargement in said recess.

2. The means for post-tensioning a concrete structure claimed in claim 1 in which the bearing member has a boss elongated lengthwise of said slot projecting on the other side thereof, said slot extending through said boss, to provide a thickened wall portion surrounding the slot in said bearing member, and having a U-shaped shim mounted between said anchor member and said bearing member in embracing relation to said bar, said shim having a pair of straight parallel legs having fiat side faces engaging the fiat faces of said bearing member and of said anchor member on each side of and adjacent the longitudinal side edges of the slots therein.

3. The means for post-tensioning a concrete structure claimed in claim 1 in which said portion of gradually increasing thickness has concavely curved surfaces and the gradually flaring wall portion of said slot have convexly curved walls conforming in curvature to and adapted to be engaged by said concavely curved surfaces of said enlargement, to seat said enlargement firmly in said recess.

4. In a concrete structure having an endless upstanding curved wall, means for prestressing said wall by a post-tensioning method comprising a bearing member having a vertical slot therein, a flat high tensile strength steel bar of much greater width than thickness extending through said slot and circumferentially of said wall, said bar having the width thereof extending vertically of said wall, the major portion of said bar being of uniform cross section and having an integral end enlargement of sub stantially the width of said bar thereon, and an anchor member mounted between said enlargement and said bearing member and having a slot therein through which said bar extends, said anchor member having a flat face on the side thereof toward said bearing member and a recess into which said enlargement extends in the other side thereof leading into said slot.

References Cited UNITED STATES PATENTS 2,728,978 1/ 1956 Birkenmaier et al. 52230 X 2,755,657 7/ 1956 Finsterwalder 52223 2,804,674 9/1957 Long 52223 X 2,867,884 1/1959 Brandt 52223 X 3,029,490 4/ 1962 Middendorf 52--223 X 3,099,109 7/1963 Hahn 52-223 3,255,558 6/1966 Middendorf 52223 1,350,964 8/1920 Friel 52709 X 3,039,695 6/1962 Harmsen 52704 X FOREIGN PATENTS 88,112 5/ 1958 Netherlands.

1,306,797 9/1962 France.

801,407 1/ 1951 Germany.

529,146 6/ 1955 Italy.

HENRY C. SUTHERLAND, Primary Examiner.

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