US2371882A - Tensioning and anchoring of cables in concrete or similar structures - Google Patents

Description

March 20? 1945. 2,371,882

TENSIONING AND ANCHORING 0F CABLES IN CONCRETE 0R SIMILAR STRCTURE E. FREYSSINET Filed Feb. l, 1941 .rlll lllllllll.; ."5

Patented Mar. 20, 1945 TENSIONING AND ANCHORING 0F CABLES 1N CONCRETE 0R SIMILAR, STRUCTURES Eugne Freyssinet, Neullly-sur-8eine, France: vested in the Alien Property Custodian application February 1, 1941, serais. :11,041

In France October Z8, 1940 s claims.' (ci. za-5o) It is well known that the characteristics of reenforced concrete constructions are vconsiderably improved by artificially submitting the reenforcements to preliminary tensile stresses sumciently high in order that the concrete is subjected to permanent compressive strains (see my U. S. Patent No. 2,080,074). The tension may be lmparted to the reenforcements either before the setting of the concrete, or after its setting and hardening, on condition that, in the latter case, provision be made for suitable means to prevent the adhesion of the steel to the concrete, in order to allow the elongation of this steel embedded in the set and hardened concrete.

Such reenforcements are frequently constituted by means of steel wire cables having a high elastic limit. In general, the devices used for ten sioning and anchoring comprise projections exterior to the concrete to be compressed, and do not allow the compressive stresses to be increased beyond a certain maximum which is very much less than the resistance of the concrete to be compressed. f

My invention has for its object a process and a device for tensioning and anchoring cables, said device being incorporated in the concrete to be compressed without requiring any projection or addition to the concrete for the purpose of concealing the anchorings. This device allows moreover the increasing of the preliminary stresses to the yielding point of the concrete. y This process is applicable in particular to pre stressed concrete constructions in the case where the tension is imparted to the reenforcements after the setting of the concrete, although it can also be utilized in constructions other than concrete or in concrete constructions when the reenforcements are tensioned before the setting of the concrete.

In what follows, only the application of the process to concrete will be considered for the sake of simplicity, it being understood that the other applications also fall within the scope of my invention.

wires and nally the releasing of the tension exerted by the jack, the tensionof the wires is maintained bythe weding. in the female c'one. of the male cone composed of the wires and the wedgesl pressed one against the other.

'I'he anchoring arrangement comprises then essentially a tunnel-shaped cavity, the inner Surface of which is capable of withstanding the stresses of expansion imrted to it by the wedging of the male cone, and means for transferring to the concrete to be compressed that component of these stresses which is parallel ,to the cable.

It may be made up, for example, of an element of cast steel, embedded in the concrete, comprising, in the first place, a funnel-shaped cavity the inside of which is machined to obtain the desired shape and, in the second place, one or more surfaces bearing on the concrete, of sumcient ares to subject the concrete to sustainable stresses.

But the same results may be obtained more economically by having recourse to means proper to reenforced concrete. The truncated cone may be hollowed 'out in the concrete itself and the wall of this cavity rendered capable of resisting the stresses of expansion by embedding in the concrete a first reenforcement which may consist in a truncated tube or in a. coil formed by helicoid turns of steel wire, having preferably a high elastic limit, or in a combination of both means. The transmission of the strains from this first reenforcement or coil to the concrete to be compressed may be ensured by a second transverse reenforcement of the concrete in which it is embedded. This second reeniorcement con. sists, for example, of a coil of'steel wire helically wound and located at a certain distance from the rst one.

In order to ensure a better achievement of the truncated aperture or cavity, it is possible to pour in advance concrete slabs, each provided with a cavity and with the reenforcing coil or coils.

These slabs may contain one or more anchoring also a sectional view of a part of an hydraulic jack utilized in tensioning a cable.

Figures 2 to 4 are transverse sectional views along axes II-II, III-III and IV-IV of Fig. 1.

Figure 5 represents a fragmentary plan view of the device utilized for the fixation of the wires to the ,i ack.

Figure 6 shows a fragmentary sectional view showing another embodiment of an anchoring block.

Figure 7 shows diagrammatically in longitudinal section one extremity only of a pre-stressed concrete beam, provided with anchoring blocks constructed in accordance with my invention.

Figure 8 represents a sectional view of a prestressed concrete beam provided with these anchoring blocks.

spread out and pressed against the inner wall a-b of the truncated cone and between these wires steel wedges 8 are set. The sides of these wedges are provided with cylindrical grooves la corresponding to the shape of the wires, so that these wedges, inserted between the wires are maintained by the latter and form together with them a sort of male cone which comes to bear against the inner wall af--b of the female cone.

For the operation of tensioning, in the case under consideration, an hydraulic Jack is utilized, the piston 9 of which can bear against head 2. This piston is provided with slots l0 equal in number to that of the wires of the cable and In the example illustrated by the drawing, the

application of the anchoring device to the ten# sionlng of the reenforcements of a concrete construction has been presumed to occur after the setting and hardening of the concrete. Each reenforcexnent. composed of a cable. is set in a sheath I which is set in place in the molds before the pouring of the concrete and serves to insulate the said reenforcement from the concrete in order to allow the elongation of the reenforcement. l

This sheath may consist of a tube of steel or of other material, preferably thin sheet steel rolled into a cylindrical shape, and clasped by bending back the edges. It may even consist merely of a plain coating of a greasy substance or of a plastic one of low melting point, basically composed of bitumen, pitch or rubber which is applied to the wires. This coating can be protected by swathing with paper or other fibres impregnated with substances of the same nature.

Each extremity of a reenforcement or only one of the extremities, if the other be securely fastened to the concrete by any well known anchoring system, is inserted in the anchoring slab or block, which is going to be described with respect to Figures 1 to 5.

This slab or block comprises a high-resistance concrete mass 2, having therein an aperture or cavity the contour of which is generated by a complete revolution of the straight line af-b about the axis :Izx, which forms with line a-b an angle having a tangent of approximately 55, the said straight line being joined to the generant of tube I parallel to axis :cby a curve b-c.

About the wall of the orice so formed, a steel reenforcemcnt 3 is embedded in the concrete 2. This reenforcement may be composed of helicold turns of asteel wire having a high elastic limit so that the coil thus formed can resist the strains to which the wall of the cavity is subjected in operation. In the example described, the slab or block has the form of a solid of revolution composed of a head 2a and of a prolongation 2b having the shape of a. truncated cone which is joined to the extremity of sheath I by a junction Ia of tissue or of paper impregnated with a plastic substance, such as tape. About the head 2a, the concrete is reenforced by a second coil 4 which may be of soft steel.

The concrete 5 of the construction or of the piece to be built is poured about tube I and about the block taking care to allow provision for a hole 6 through which it will be possible to have access to the extremity of the cable (passing through head 2) from the exterior of the construction. The wires 1 composing this cable areused for the passage of the wires, whereas the cylinder II comprises devices for the fastening of these wires. These devices consist in trapezoidal slots I2 provided on a rim I3 of the cylinder I I and of wedges I4 which are inserted in these slots between two wires of the cable; the number of slots is consequently equal to half the number of wires, which condition requires, in this embodiment, the use of cables having an even number of wires.

In the interior of piston 9, a second piston I5 may displace itself and come to bear on the extremity of wedges 8 by means of a small plate I6 provided with slots for the passage of the wires. Piston 9 is provided with a hollow Il the diameter of which corresponds to that of the small plate.

The jack being disposed as shown in Fig. 1 and pressure being admitted in cylinder II, this cylinder draws away from piston 9 and tensions wires l. The wedges follow the movement of the wires at the start until they run against plate I6, they then leave between themselves suillcient clearance to allow the wires, pulled by cylinder I I, to slide freely.

In zone b-c of the anchoring head, the wires press against the concrete of this head and to limit their friction, this zone is lined -by a casing I8 of tinplate for example.

When the tension stress, which can be determined from the pressure in cylinder II, at-

tains the desired value, the pressure is maintained in the cylinder, and piston I5 is put under pressure. The latter obtains a compression of the wedges between the wires by expanding the male cone and by compressing it against the inner wall of the female cone.

The pressure in the two jacks may then be released, the wires withdrawn from slots I2 of the jack and the latter removed; the anchoring thus being finished. The tensioned cable. subjected no longer to any external force, wedges the male cone composed of the Wires and of the wedges in the female cone. The wires could, as a matter of fact, slip between the wedges only if the angle of friction between wedges anf wires fell below a value such that tan.

In order that the anchoring may resist it steel coil 3 appears. It must bear the stresses which make with the axis of the cone an angle which is the sum of the angle at the top of the cone and of the angle of friction steel on concrete.

Under the action of the tensioned cable, there results, finally, an equilibrium between the deformations of coils 3 and l, of the concrete 2 and that of the underlying concrete 5, an equilibrium which allows a relatively large deformation of coil 3, a relativelyv much smaller deformation of coil 4 and a triple compression stress accompanied by a plastic deformation of the concrete 2 with the production of isostatic lines such as UV, XY.

In that portion of the concrete where the head bears on the concrete 5 of the construction, this concrete may be profitably reenforced by rectanguiar reenforcements.

It is to be noted that nothing prevents the jack from being set in place for operation a second time; the wires may be tensioned again by means of the jack, the wedges loosened, the initial tension increased (or even reduced, if a means for preventing the wedges from jamming by themselves be provided). So the tensioning operations may be effected in a progressive manner, they may be rectified, in case of error, etc.

Oncethe tensioning has been completed, hole t may' be stopped up by concrete, and the extremities of projecting wires embedded in concrete which ils up a small recess provided forin the mass subjected to preliminary stresses, which process oers the advantage of an additional security by opposing the vslipping of the wires against the wedging means.

Figure 6 shows a cast steel anchoring block 2a provided with a female cone 2b, the surface 2c, 2d of which block bears on the concrete and transmits the strains developed by the tensioned cable. This anchoring block is utilized in the same manner as that described for the concrete slab.

Figure 7 shows the extremity of a beam pro- 4vided with reenforcements d set in sheaths, the

reenforcements being tensioned and anchored as has just been described. The anchoring heads e are located at the extremities of the reenforcements in the housings provided for, prior to the pouring of the concrete.

The block may have also a square or rectangu` lar cross-section and comprise anchoring devices for several cables. In this case, coils i may be replaced by rectangular. reenforcements perpen A ing the tensioning operation) and the final tension are both directed along the same axis and act on the same substance, which conditions allow the compressing of the entire surface of the concrete to a maximum stress consistent with its resistance.

The invention is not limited to the case where the tensioning is effected after hardening of the concrete.

The concrete in which the tensioned reenforcements are embedded may be poured only after the tensioning of these reenforcements, on condition that fulcrums for the anchoring blocks be available while the tensioning is in process; these fulcrums can be chosen on the molds or on a portion of the concrete of the construction in which the reenforcements are not embedded, which concrete is poured in advance and has already hardened prior to the tensioning.

For example, in the case of a beam having a cross-section as represented on Figure 8, it is possible, after setting in place reenforcements d and the anchoring blocks, to pour first the concrete represented by the hatchings in which concrete the reenforcements are embedded only at the extremities of the beam. When this concrete has hardened, those reenforcements, the anhoring blocks e of which utilize the said concrete, as fulcrum, may then be tensioned. Once the tension and anchoring operations are completed, the rest of the concrete (see the dotted lines in Fig. 8) may be poured about the tensioned reenforcements d. y

The device for tensioning and anchoring constructed according Ato my invention also odors a practical means of obtaining, by tensioned reenforcements, a uniting into a single structure of distinct concrete pieces laid out end to end for example. The tensioning of the reenforcements which will be placed for example in the holes provided in these pieces, will result in their compression one against the other.

it is obvious that the embodiments which have just been described constitute only examples and that these can be departed from without affecting the scope of the invention. The invention is applicable not only to the case where the elements of the cable to be tensioned consist in simple wires, but also to the case where these elements consist of strands or of groups of wires. In the claims hereunder, the word wire must be understood as designing not only a single wire properly speaking, but also a group of wires or a strand.

What I claim is:

l. A process for anchoring an end of an elongated reinforcement for a structural member, which reinforcement includes a group of wires, said process comprislng, providing a funnel-` shaped cavity in said structural member with its larger end facing outwardly away from the member, inserting said reinforcement wires within said member with portions adjacent the ends thereof Within said cavity, spreading out the wires in spaced relationship against the wall of the cavity, tensioning the wires by the application of an external force, and forcing wedges between each pair of adjacent wires, the force applied to the wedges being sufficient to produce enough friction between the wires and the wedges l to withstand the ,tension in the wires, after which v said external force is discontinued.

2. A process for anchoring an end of an elongated reinforcement for a concrete member, which reinforcement includes a bundle of wires, said process comprising, providing a funnelshaped cavity in said concrete member with its larger end facing outwardly away from the member, lining the wall of the larger end of the cavity with reinforcing metal inserting said reinforcement wires within said member with portions adjacent to the ends thereof disposed within 4 aaneen the larger end of said cavity, spreading out the wires in spaced relationship against lining of the larger end of the cavity, tensioning the wires by the application of an external force, and applying wedges between each pair of adjacent wires, with 'sufficient force to produce an elastic expansion in the metal lining and sufiicient friction between the wedges and wires to anchor them in place, after which said external force is discontinued.

3. A process for anchoring an end of an elongated reinforcement for a concrete member. which reinforcement includes a bundle of wires, said process comprising: enclosing said wires ad- 'jacent their ends within a hollow funnel-shaped steel member, said hollow member having its larger opening facing in the direction of said ends, pouring concrete about said hollow member, spreading out the wires in spaced relationship against the inner surface of the hollow member, placing wedges between eacn pair of adjacent wires, tensioning the wires after the' hardening of the concrete by exerting a tensile stress on their extremities which project out from the concrete using said concrete as a fulcrum, then while maintaining the tensile stress, applying the wedges toward the smaller end of said hollow member between adjacent wires with sufncient force to produce an elastic expansion of said hollow member and suincient friction between the wedges and wires to anchor them in place', after which said external tensile stress is discontinued.

4. In a concrete or similar structure, in combination, a mass of concrete or the like, a longitudinally tensioned reinforcement passing therethrough and comprising an elongated member having a divided end portion comprising a plurality of strands, the mass of concrete being provided with a conical outwardly flared cavity surrounding said strands, said strands being spread to engage the wall of the cavity in circumferentially spaced relationship, and wedges forced between each adjacent pair of strands in a, manner to hold the strands tofrictionally engage with the wall of the cavity.

5. A concrete or similar structure having means for anchoring the end portions of a bundle of tensioned wires constituting reinforcement of said structure, said means comprising, in combination, a concrete part having a funnelf shaped cavity therein, the wall of which surrounds said bundle of wires adjacent the said end portions, said cavity having its larger end facing in the direction of said end portions and away from said concrete structure, a tubular metal reinforcement embedded in said concrete part and spacedly encircling said cavity, said reinforcement being tapered oppositely to and surrounding the larger end of the cavity, said wires being spread against the surface of said larger end of the cavity, and wedges forced between each pair of adjacent wires in a manner to tension the wires around the wall of the cavity.

6. A concrete or similar structure, according to claim 5, wherein said tubular metal reinforcement consists of a helically wound hard steel wire.

7. A concrete or similar structure having means for anchoring the extremity of a bundle of tensioned wires constituting reinforcement of said structure, said means comprising, in combinaton, a concrete block embedded in said structure and provided with a funnel-shaped cavity serving as a housing for a portion of said bundle of wires adjacent to the extremity thereof, said cavity having its larger end facing in the direction of said extremity and away from said structure, a steel reinforcement lining the wall of the larger end of said cavity, a second steel reinforcement embedded in the block and spacedly surrounding said lining and located adjacent to the outer periphery of said block, bearing surfaces on said block facing said structure in a direction away from said extremity of the bundle of tensioned wires and arranged to transmit compressive strains to the structure under the in-' iuence of the tension in said wires, said wires being deected to lie along the lining( in circumferentially spaced relation, and wedges forced between each pair of adjacent wires in a manner to tension said lining.

8. A, concrete or similar structure having means for anchoring the extremity of a bundle of tensioned wires constituting reinforcement of said structure, said means comprising, in combination, a concrete block embedded in said structure and provided with a funnel-shaped cavity serving as a housing for a portion of said bundle of wires adjacent to the extremity thereof, said cavity having its larger end facing in the direction of said extremity and away from said structure, a steel reinforcement lining the wall of the larger end of said cavity, a second steel reinforcement embedded in the block and spacedly surrounding said lining and located adjacent to the outer periphery of said block, bearing surfaces on said block facing said structure in a direction away from said extremity of the bundle of tensioned wires and arranged to transmit compressive strains to the structure under the influence of the tension in said wires, said wires being deflected to lie along the lining in circumferentially spaced relation, and wedges forced between each pair of adjacent wires and forcing the wires against said lining with sufficient pressure to place said lining and the surrounding concrete .under tension.

EUGNE magasiner.

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