US3327380A

US3327380A - Prestressing method

Info

Publication number: US3327380A
Application number: US373464A
Authority: US
Inventors: James W Howlett
Original assignee: HOWLETT MACHINE WORKS
Current assignee: HOWLETT MACHINE WORKS
Priority date: 1964-06-08
Filing date: 1964-06-08
Publication date: 1967-06-27
Anticipated expiration: 1984-06-27

Description

June 27, 1967 J. w. HOWLETT 3,327,380

PRESTRESSING METHOD Filed June 8, 1964 3 Sheets-Sheet 1 INVENTOR.

2 James W How/err A 2 Attorney J1me 1967 J. wv HOWLETT 3,327,380

PRESTRESSING METHOD Filed June 8, 1964 6 Sheets-Sheet 2 INVENTOR.

Jam W Hwlen t a I June 27, 1967 J. w. HOWLETT 3,327,380

PRESTRESSING METHOD Filed June 8, 1964 5 Sheets-Sheet Z5 [07 W14 7 74 H3 mm I09\ 4: lunmml 11mm es W How/eh United States Patent M 3,3273% PRESIRESSING METHGD .lames W. Hewlett, Richmond Annex, Qalii, assignor to Hewlett Machine Works, a corporation of California Filed .lnne 8, 1964, Ser. No. 373,464 7 Claims. (Cl. 29-452) This invention relates generally to the method of prestressing structural materials such as concrete, steel beams and the like, and more particularly is directed to the method of using elongated tendons that are placed in a tensioned condition for applying prestressing forces.

The use of tensioned tendon members is well known in the prestressing art, it being the general practice to secure the tendons at opposite ends to a given structural material and applying compressive prestressing forces to the material by placing the tendons under tension. Prestressing tendons may be broadly classified into the two categories of wires and 'bars. Wire tendons are elongated steel members usually having a diameter of no larger than about Mr inch, and are available in continuous lengths in roll form. Wires are relatively easy to handle, may be made of higher tensile strength than bars, and can be arranged in large pluralities of coextensive tendons to provide an extremely large combined tensile strength. In comparison, bar tendons may be several inches in diameter, and have inherent limitations in their utility. Because bars are relatively inflexible, they are normally limited to lengths of about 80 feet, so that they can be transported by conventional trucks or trains. Also, the

large bulk and weight of bar tendons makes them often difficult to manipulate into their required positions.

In view of the foregoing, it is often preferable that pluralities of coextensive wire tendons be used where tensioning forces are to be applied over a relatively long distance, and where relatively high forces are required. Nevertheless, however, it may still be desirable in some situations that a single large diameter bar be secured to the material to be prestressed, rather than having to secure a large number of smaller wires. Accordingly, it is advantageous to couple a large plurality of coextensive wires to single larger diameter bars, so that the wires extend over substantially the full length of the structural material and the bars are disposed only at the ends for securance to the material.

Heretofore, wire tendons have been coupled and/or secured by means of 'buttonhead protuberances provided integrally at the ends of each tendon, the protuberances being formed by a conventional metal deformation process. The wires are extended through holes in various anchor members, with the bottonheads subsequently being formed to bear against the anchor members. Where large pluralities of coextensive wires are required, it has been the practice to assemble these wires in the shop with anchor members at each end of the wires, so that the whole assembly becomes a substantially unitary structure which must then be transported to the construction job site.

Heretofore, there has been limited versatility in the use of wire tendons with regard to the ease of fabrication and assembly in on the the job situations. Also, no ready means have been provided for coupling wire tendons together in end to end relation, or for coupling large pluralities of wires together in such a manner that further tendon extensions can readily be added. In addition to this previous limited versatility in coupling and securing wire tendons, there also has not been provided ready means for tensioning and securing the tendons at their ends, and further enabling ready coupling of additional tendons to those already mounted and tensioned.

A further limitation of preassembled pluralities of wire tendons is that the anchor member secured to 3,327,380 Patented June 27, 1967 their ends is usually of a relatively large diameter. Consequently, such assembly is limited with respect to the structures through which it must be strung by the diameter of the anchor member, and difficulties are presented where tendons must be passed through relatively small diameter openings in structural materials.

A need has arisen in view of the above for a more versatile wire tendon prestressing apparatus, with which it is not necessary to preassemble pluralities of wires but rather which readily enable individual wires to be strung as desired and then be easily secured to suitable anchoring structures on the job. Likewise, a need has existed for a wire prestressing apparatus which in general has a broader field of utility than has been heretofore afforded, and with particular regard to the ability to couple and secure wire tendons, both in pluralities of coextensive wires and as individual wires. r

Accordingly, an object of the present invention is to provide a prestressing method for utilizing wire tendons with great versatility in various tensioning arrangements, wherein such wire tendons are readily coupled or anchored to other members forming a part of the complete prestressed structure.

Another object of the invention is to facilitate the use of pluralities of cocxtensively disposed tensioned wire tendons, with particular regard to coupling and securing such pluralities to other tendons or members.

A further object is to provide a prestressing method for applying tensioning force to wire tendons in a ready and quick manner, and for readily securing the ends of wire tendons so tensioned to maintain them in the required tensioned condition.

Still another object is to provide novel and improved method for securing the end of a wire tendon which does not utilize the conventional integrally formed buttonhead protuberance, but rather which employs separate members that are readily attached to a wire tendon.

The invention possesses other objects and features of advantage, some of which of the foregoing will be set forth in the following description of the preferred form of the invention which is illustrated in the drawings ac companying and forming part of this specification. It is to be understood, however, that variations in the showing made by the said drawings and description may be adopted within the scope of the invention as set forth in the claims. 1

Referring to said drawings:

FIGURE 1 is a fragmentary plan view, partly in cross section, of a wire tendon and coupling means used in conjunction with the present invention. 1 FIGURE 2 is a fragmentary cross sectional view of two wire tendons coupled together in accordance with the present invention.

FIGURE 3 is a fragmentary cross sectional view of the instant prestressing apparatus shown with a bearing plate for transmitting tensioning forces to a concrete structure. I

FIGURE 4 is a fragmentary cross sectional View with portions broken away illustrating a plurality of wire tendons coupled to a single larger diameter tendon.

FIGURE 5 is a cross sectional view along the line 5-5 as shown in FIGURE 4.

FIGURE 6 is a cross sectional view showing a plurality of tensioned wire tendons connected to a bearing plate for applying prestressing force to a concrete structure.

FIGURE 7 is a cross sectional view depicting jacking means applying a tensioning force to a wire tendon for application to a bearing plate and concrete structure.

FIGURE 8 is a fragmentary cross sectional View depicting prestressing apparatus used in securing two concrete beams to a concrete column.

FIGURE 9 is a fragmentary cross sectional view illustrating a plurality of spliced wire tendons forming part of prestressing apparatus used in securing two concrete beams to a concrete column.

FIGURE 10 is a fragmentary cross sectional view showing a modified form of wire tendon and coupling means from that shown in FIGURE 1.

FIGURE 11 is an end view of the tendon shown in FIGURE 10.

FIGURE 12 is a fragmentary cross sectional view showing another modified form of wire tendon and coupling means.

FIGURE 13 is a fragmentary cross sectional view of a plurality of coextensive wire tendons and a single larger diameter tendon all coupled to another single tendon.

FIGURE 14 is a cross sectional view along the line 14-14 shown in FIGURE 13.

=Prestressing apparatus embodying the present invention generally comprises at least one bearing plate 11 for transmitting force to a structural material to be prestressed, such as the concrete structure 12 shown in FIG- URE 3, and tensionable tendon means secured to the bearing plate for applying tensio-ning force thereto. The tendon means includes a first elongated tendon, such as the wire tendon 13 shown in FIGURE 2; means defining a protuberance secured adjacent the end 14 of the tendon 1 3, such as the integrally formed buttonhead 16; an externally threaded tubular sleeve member 17 disposed concentrically on the tendon 13 adjacent the proturberance for abutting engagement therewith; a coupling member having an internally threaded bore threadedly engaging the sleeve member 17, such as the internally threaded tubular member 18; and a second elongated tendon 19 secured to the coupling member and disposed in general end to end relation with the tendon.

A basic element of the instant prestressing apparatus is a wire tendon 21 as shown in FIGURE 1, having protuberances such as the

integral buttonheads

22 and 23 formed at either end of the tendon. An externally threaded sleeve member 24 can be mounted on the tendon prior to formation of the buttonhead, whereby the sleeve 24 is adapted to engage the buttonhead 22 in abutting relation. In some instances it may be desirable to mount the sleeve members after the buttonhead has been formed, and for this purpose a split sleeve 26 is provided which includes half-

tubular segments

27 and 28 as shown in FIGURE 1. The split sleeve 26 is of particular utility in on the job situations Where it is necessary to couple or secure an existing buttonhead tendon that does not already have a sleeve 24. The

segments

27 and 28, when placed together on a tendon, form the equivalent of a sleeve 24.

In order to coupled together two tendons disposed in generally aligned end to end relation, the internally threaded tubular coupler shown in FIGURE 2 can be used in conjunction with a pair of tendons each having buttonhead protubenances on their confronting ends. Thus, the wire tendon 19 is provided with a buttonhead 29 and a sleeve member 31, so that the coupler 18 threadedly engages both

sleeves

17 and 31 thereby connecting the

wires

13 and 19.

Means for securing a single wire tendon in a desired tensioned condition is disclosed in FIGURE 3, and in this regard it is noted that the bearing plate 11 is provided with a hole 32 through which passes the end portion of a wire tendon 33. An elongated externally threaded sleeve member 34 is concentrically mounted on the tendon 33, and abuttingly engages a buttonhead 36 on the end of the tendon. The sleeve 34 passes through the 'hole 32, and an internally threaded member such as a nut 37 is mounted on the sleeve for axial adjustment thereon. Tensioning means to be described pull the sleeve 34 outwardly to place the tendon 33 under tension, and the nut 37 is then screwed down into abutting engagement with the bearing plate to maintain the tendon in its tensioned condition. It is noted that the other end of the tendon 33 is suitably anchored to the concrete structure 12, so that when the tendon is tensioned a compressive prestressing force is applied to the concrete. In the event that another tendon 38 is required to be coupled to the tendon 33, a tubular coupler 39 can be used in the same manner as described with regard to FIGURE 2.

In some instances as noted hereinabove it is advantageous to use a plurality of coextensive wire tendons to achieve extremely high tensile forces, as compared to a single bar tendon of relatively large diameter. As noted, wire tendons can be provided more readily in longer lengths than large diameter bars or rods, and are more readily handled. In situations to be described, it is sometimes desirable to couple a large plurality of coextensive wire tendons to a single larger diameter bar tendon, and in this regard reference is made to FIGURE 4 wherein coupling means in accordance with the present invention is provided for joining four wires 41 to a single bar tendon 42. In more detail, each of the wires 41 has a buttonhead 43 and a sleeve 44 similar to that described in FIGURE 1. A coupler member 46 is provided with a corresponding number of internally threaded bores 47 which threadedly engage the sleeves 44, thus securing the tendons 41 to the coupler 46. The bar 42 can be secured to the opposite face of the coupler 46 by any suitable means, which as shown may comprise wedge grip coupling means of the type disclosed in Patent No. 2,930,642. The bar 42, of course, may be provided with conventional threads, which would engage a complementarily threaded bore in the coupler 46.

In FIGURE 6, there is shown a prestressing apparatus somewhat similar to a conventionalsystem. A plurality of wire tendons 48, having buttonheads 49, pass through holes 51 in a bearing plate 52 which engages a concrete member 53. The wires 48 also pass through holes 54 in an anchor member 56, with the buttonheads 49' being disposed on the outer side of the anchor member. As in the conventional system, the anchor member 48 can be grasped by suitable jacking means, whereby the wires are placed under tension, and then shim members such as the two metal plates 57 are interposed between the anchor 56 and bearing plate 52. In addition to the structure as described thus far, which is conventional, the instant apparatus provides a plurality of externally threaded sleeve members 58 on each of the wires 48 for engagement with their respective buttonheads 49. Consequently, it is possible with the instant apparatus to readily couple additional wire tendons in end to end relation with the,

Wires 48, in the manner already described with regard to FIGURES 2 and 3.

A jack 61 is disclosed in FIGURE 7 for use in applying tension to individual wire tendons having buttonheads. As shown, the jack 61 includes a supporting member 62 having a pair of spider leg members 63 which extend into abutting engagement with a bearing plate 64. A conventional hydraulic means 66 is mounted on the member 62, and has a piston 67 extending axially between the legs 63 and adapted for selective reciprocating movement. A wire tendon 68 extends through the bearing plate, and has a sleeve member 69 engaging a buttonhead 71. A tubular coupler 72 has internal threads which engage the sleeve 69, and external threads on which is mounted an internally threaded stop member such as the nut 73. The piston 67 of the jack 61 is externally threaded for engagement with the coupler 72, whereby the jack can be operated to pull the wire 68 into a tensioned condition. A tubular shim member 74 is interposed between the nut 73 and the bearing plate, and when the wire is tensioned to the desired amount the nut 73 is tightened against the shim 74 to maintain the wire in its tensioned condition. It will be appreciated that the jack 61 may also be used to apply tension to the wire 33 as shown in FIGURE 3, the piston 67 engaging the coupler 39 in the same manner, as described with regard to FIGURE 7.

One use of wire tendons in accordance with the present invention is disclosed in FIGURE 8, wherein a pair of

concrete beams

76 and 77 are secured to a concrete column 78. In this structure, a plurality of wire tendons 79 are coupled to a single bar 81 by means of a coupler 82 of the type described hereinabove with reference to FIGURES 4 and 5. The beam 76 is first secured to the column 79 by extending the bar 81 through a bore 83 in the column, and then anchoring the bar by means of a temporary anchor nut 84. The nut 84 may be a wedge grip nut of the type disclosed in my copending patent application for Concrete Prestressing Apparatus, Ser. No. 302,628, filed Aug. 16, 1963. After the beam 76 and column 78 are secured as shown, the second beam 77 can be connected by means of another coupler 86 which joins the bar 81 to another plurality of wire tendons 87.

In FIGURE 9, a pair of

concrete beams

88 and 89 are secured to a column 91, by means of a plurality of spliced wire tendons 92 which are joined together by means of couplers 93 in the manner described hereinabove with reference to FIGURES 2 and 3. The individual wires can be strung through openings in the beams and columns as shown, which openings need not be any larger than necessary to accommodate only the wires. It is not necessary to pass any anchor members through these holes, since the wires can be secured to bearing plates (not shown) in the manner described above with reference to FIGURE 3. That is, the Wires can simply be passed through the holes in the bearing plates, after which the stop nuts 37 are mounted on corresponding sleeve members.

An alternative embodiment regarding the buttonhead protuberances for the wire tendons is disclosed in FIG- URES l0 and 11. In particular, instead of the integrally formed buttonhead as described hereinabove with reference to FIGURE 1, there is shown in FIGURES and 11 a separate inner tubular member 94 mounted concentrically on a wire tendon 96, and which has a tapered outer surface 97. The member 94 is adapted to apply radially inward force on the wire 96, and in this regard is provided with a longitudinal slit 98. The inner bore surface 99 of the member 94 is preferably provided with a serrated finish so that it will grip the wire and restrain relative axial movement between the wire and member 94. An externally threaded sleeve member 101 is mounted concentrically on the wire, and has a tapered inner surface 102 which complimentarily engages the tapered surface 97 of the member 94. Thus, as the sleeve 101 is urged toward the end of the wire 96, the tapered surfaces create a radially inward force on the inner member 94, which therefore securely grips the wire. In the embodiment just described the inner diameter of the member 94 is dimensioned to form a slight interference fit with the wire 96, so that there will be an initial grip between the wire and member 94. Another alternative embodiment is disclosed in FIGURE 12, similar to that of FIGURES l0 and 11, but wherein the inner member 94a is not dimensioned for an interference fit with the Wire 96. Rather, the end of the wire is peened over by a hammer or the like to provide a slight protuberance 103, which serves to create the initial grip between the member 94a and the wire.

Where large pluralities of coextensive wires are used to provide tensile forces, it has been found that prior to application of tension to the wires they,tend to sag or drape irregularly between the points at which they are supported. A somewhat better natural drape is obtained with a bar. A modified coupler 104 is disclosed in FIG-

URES

13 and 14, somewhat similar to the coupler 46 shown in FIGURE 4, but which combines the greater tensile strength of wire tendons with the improved natural drape of a bar. More particularly, a plurality of internally threaded bores 106 are disposed in circumferentially spaced relation on one end face of the coupler 104, these bores threadedly engaging sleeves on wire tendons 107 in the same manner as described with regard to FIGURE 4. A large internally threaded bore. 108 is disposed concentrically within the smaller bores 106-, and engages the threaded end 109 of a bar 111 which is of substantially larger diameter than the wires 107. An internally threaded bore 112 is provided on the opposite end of the coupler 104, and engages the threaded end of another bar 113. The combined tensile strength of the wires 107 and bar 111 is substantially equal to that of the larger diameter bar 113. The advantage of the coupled tendon structure as just described is that the center bar 111 controls the desired sag while utilizing the plurality of wires to achieve the necessary tensile strength. It should be noted that the bars 111 and 113 can be secured to the coupler 104 by means of wedge grip coupling means such as shown in FIGURE 4, instead of the conventional threaded arrangement as just described.

It will be appreciated from the foregoing that the instant prestressing apparatus affords great versatility in providing tensioning forces for prestressing structural materials. Although the multiwire coupler illustrated in FIGURE 4 shows only four coextensive wire tendons, the same basic structure has been employed to couple as many as 64 4 wires together, it being necessary to use a 2 /2" diameter bar on the other side of the coupler, whereby the combined strength of the wires was sufficient to hold 650,000 pounds of tensile force. In addition, it is a simple operation with the instant apparatus to couple wire tendons in end to end relation, thus enabling construction of new concrete or other prestressed structures in adjacent position to previously formed structures. It is furthermore possible to make on the job assemblies of the instant wire tendons, rather than having to preassemble groups of coextensive wires at the factory prior to shipment to the construction site.

An important feature of the type of coupling as illustrated in FIGURES 4 and 13 is that each end of the coupler may be designed and machined to attach the type or types of tendon or tendons to be connected thereto without regard for the type or types of tendons to be connected to the opposite end of the coupler. This greatly assists in the economic manufacture of the coupling, and the best utilization of material to attain a conpler of requisite strength in a minimum overall size.

I claim:

1. In a method for prestressing structural materials, the steps comprising, providing a pair of generally elongated tendons each having a protuberance adjacent one end thereof and an externally threaded sleeve concentrically mounted on said end for engagement with said protuberance, disposing said tendons in end to end relationship with said protuberances confronting one another, and threadedly engaging a tubular internally threaded member with said two sleeve members to couple said tendons together, and applying a tensioning force to said tendons tending to pull them apart from one another.

2. In a method for prestressing a structural material, the steps comprising, disposing a bearing plate in position for abutting engagement with a structural material to be prestressed, securing an elongated tendon to said bearing plate which tendon has a protuberance provided adjacent one end thereof and an externally threaded sleeve concentrically mounted thereon for engagement with said protuberance, disposing a second tendon in end to end relation with said first tendon which second tendon has a protuberance provided adjacent the end of said tendon confronting said first tendon and an externally threaded sleeve concentrically mounted thereon for engagement with said protuberance, and coupling said two tendons together by an internally threaded tubular coupler threadedly engaging said two externally threaded sleeve members, and applying a tensioning force to said tendons tending to pull them apart from one another.

3. In. a method for prestressing structural materials, the steps comprising, providing a first generally elongated tendon having a protuberance adjacent one end thereof and an externally threaded sleeve concentrically mounted on said end for engagement with said protuberance, providing a coupling member having threaded bores opening to opposite ends thereof, threadably engaging said sleeve in one of said bores, threadably securing a second elongated tendon in another of said bores in general end to end relationship With said first tendon, and applying a tensioning force to said tendons tending to pull them apart from one another.

4. The method as defined in claim 3 providing a plurality of first generally elongated tendons, each having a protuberance adjacent one end thereof and an externally threaded sleeve concentrically mounted thereon for engagement of said protuberance, providing said coupling member with a plurality of threaded bores equal in number to said sleeves and opening to one of said ends and threadably securing said sleeves therein, disposing said.

5. The method as defined in claim 3, and forming said sleeve for said first tendon of two separate generally half-tubular members each externally threaded and assembled to form an externally threaded sleeve concentrically on said first tendon.

6. The method as defined in claim 3, forming said protuberance by concentrically mounting on said first tendon an inner tubular member having an externally tapered surface and formed for contracting into gripping engagement with said first tendon, and forming said sleeve with an internally tapered surface complementarily engaging said externally tapered surface, and radially contracting said inner tubular member when said sleeve is moved toward the proximate end of said tendon in response to said tensioning force.

7. A method as defined in claim 6, and forming an abutment on said proximate end of said tendon to set said inner tubular member.

References Cited UNITED STATES PATENTS 2,811,773 11/1957 Baskin 29-452 3,029,490 4/1962 Middendorf 264-228 3,060,639 10/1962 Fields et al 52-473 3,216,162 ll/1965 Gerber et al. 52-230 3,225,499 12/1965 Kourkene 52230 3,255,558 6/1966 Middendorf 52223 JOHN F. CAMPBELL, Prima/y Examiner. T. H. EAGER, Assistant Examiner.

Claims

1. IN A METHOD FOR PRETRESSING STRUCTURAL MATERIALS, THE STEPS COMPRISING, PROVIDING A PAIR OF GENERALLY ELONGATED TENDONS EACH HAVING A PROTUBERANCE ADJACENT ONE END THEREOF AND AN EXTERNALLY THREADED SLEEVE CONCONTRICALLY MOUNTED ON SAID END FOR ENGAGEMENT WITH SAID PROTUBERANCE, DISPOSING SAID TENDONS IN END TO END RELATIONSHIP WITH SAID PROTUBERANCES CONFRONTING ONE ANOTHER, AND THREADEDLY ENGAGING A TUBULAR INTERNALLY THREADED MEMBER WITH SAID TWO SLEEVE MEMBERS TO COUPLE SAID TENDONS TOGETHER, AND APPLYING A TENSIONING FORCE TO SAID TENDONS TENDING TO PULL THEM APART FROM ONE ANOTHER.