US2449276A - Pretensioned reinforcement - Google Patents

Description

Sept. M, 194. M. cHALos 'PRE'IENSIONED REINEORGEMENT 2 Sheets-Sheet 1 Filed July 20 1945 Sept, M, 1948. M. CHALOS ,276

' PRETENSIONE D REINFORCEMENT 7 Filed July 20, 1945 2 Sheets-Sheet 2 Patented Sept. 14, 1948 2,449,276 FF 1 C E PRETENSIONED REINFORCEMENT Marcel Chalos, Paris, France Application July 20, 1945, Serial No. 606,116 In France September 30, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires September 30, 1963 The reinforcement forming the subject-matter of the present invention is intended to be used for preconstrained constructions: it comprises two juxtaposed elements which are very long relatively to their cross section; one of said elements, of great tensile strength, is intended to be incorporated in the construction to be preconstrained; it is combined with the second element, of high resistance to longitudinal compression, so that it can be greatly tensioned by taking a bearing on the end of the latter and thus remain tensioned until the reactions balancing its tension are transferred from the second element to the construction in which the reinforcement is incorporated.

In order to obtain preconstraints the present invention makes use of a compression member which possesses in the stable state, an internal potential of forces, capable of being transferred to the construction with which it will be combined. Such a compression member, always prepared beforehand (for instance in the workshop) can be manipulated, transported, shaped according to a certain curvature, then used at any moment as an ordinary reinforcement according to classical construction methods The reinforcement can be constituted by the following elements, or by any other equivalent members:

1. A sheath having high mechanical features under traction (treated steel, glass thread, etc.).

2. A core of high resistance to compression (steel, hooped concrete, etc.).

3. splices more or less spaced apart which maintain close contact between the two preceding parts.

4. End anchorings which, before using the reinforcement, transfer the reaction of the previously tensioned or pretensioned sheath to the core, and, when it is utilised, transfer the reaction of the sheath to the material to be placed under a preconstraint.

The sheath can on the contrary be compressed and the core tensioned, and the splices can be replaced, entirely or in part, by the very elements composing the sheath if the connection of the constituent parts is intimately ensured.

Whilst remaining within the resilient scope of the materials used it appears, as shown by experiments effected by the inventor, that the pretensioned reinforcement is of extreme distortableness approximating the properties of plastic substances.

This interesting particularity, consequence of the theoretical principle regulating the equilibrium of the proposed system, is improved and intensified by the suitable assemblage of the elements of any shape and nature composing the sheath which are preferably twisted or braided. This process allows of balancing the torsion torques urging the cables placed under tension 4 Claims. (CI. 72-50) and, notwithstanding the curvatures which are imposed tothe reinforecement, of also. urging all the elements of the sheath.

Finally, if the outer sheath is tensioned the twisting or the braiding allows the elements of the latter to very economically replace all or part of the splices.

Of course, it may be sufficient in order to obtain the splicing of the sheath elements, twisted or not, to braid or plait between the latter, ac cording to a definite pitch, one or more threads of suitable nature and cross section.

According to the invention, the tensioned elements of the accumulating member will preferably be constituted by very strong hard wires, twisted or braided; the sheath obtained thus advantageously presents an apparent modulus of elasticity lower than Youngs modulus of the metal used.

However, the use of hard steel is only contem plated for an economical purpose function of the industrial possibilities and does not characterise the invention in any way, as it is possible to use the high mechanical features ofall rolled, wiredrawn or cold-drawn materials, such as natural whatever may be the system of static or dynamic loads and over-loads.

These end anchorings, the function of which is to ensure, under the marketable form of the reinforcement, the action of the internal forces of the system, can be of any nature and maintain the threads or ribbons of threads, either by locking wedges on a cap, or by beading a plastic metallic cone on a very strong olive-shaped member, or preferably by coating with a binding materiaLjfusible or not (cement mortar, various resins, metals, etc.) according to the art of capping metallic cables.

The anchorings forming part of the invention allow, when manufacturing the reinforcements, the immediate locking of the desired tensions by means of any suitable mechanical devices: flexible metallic lock, key-bolt, nut, wedges, welding, etc. They also provide the user with possibility of verifying the value of the accumulated tensions, as well as the means of modifying, if need be, said state of equilibrium, Finally,

when the construction is placed in service, saidanchorings ensure the diifusion of artificial constraints by the simultaneous, progressive and automatic unlocking of all the reinforcements used.

Whether the pretensioned reinforcements are incorporated during concreting or sealed subsequently to elements prepared beforehand, the

the invention, fluid-tightness to cement grout and cement injections of the sheath-core unit, is ensured eitherby the sheath, or by the core, or by the sheath core unit.

The various twisted elements, highly tensioned, of the sheath come close together until they constitute a tubular system similar to closed or semi-closed cables. If' the elements are braided the fluid-tightness of the sheath is obtained by using for one of the sheets of threads, ribbons having a lenticular circumscribed profile the outer threads of which are, if necessary, coated, or constituted by any suitable plastic materials.

It may be more advantageous to obtain the fluid-tightness of the system by completin the properties of the sheath by the utilisation of a core particularly devised in order to be both strong", jointed, expansible and fluid-tight. The coremust in fact transmit to the anchorings the important reactions of the sheath, have an extremely low inertia so as to conform to the curvatures, maintain in the curves a length equal to all its fibres, ensure the perfect centering" of the elements'composin'g the reinforcement and allow the core to be systematically removed from the framing whilst ensuring sufiicient fluid-tightness. These properties are ensured either by a single member, or by a combination of elements. The core'c'an beconstituted by short metallic elements of suitable profile: spherical; cylindrical, bitrun cated, etc.

The elements present at the ends thereof either two coni exities or a concavity and a convexity of spherical or cylindrical shape superposed or fitting one in the other, and in order that they can be extracted, they are rendered rigid together by an-ysuit'able means or devices: wire or cable passing in a longitudinal channel, key having a flange or a dove tail, hooking spring-sleeve, outer spiral spring, resilient hooks. etc.

The expansible' device ensuring the centering and the unframin of the core can be independent or not from the resistant body and placed in position with or before the latter; it is constituted either" by balloon springs havin adjoining blades or not, flexible'hooks. etc.

Said expansibledevice is set in action by any shortening contrivances (mechanical drawing together, expansion, resilient contraction, etc.) of the elements of the chain constituting the resistant body, contrivances which cause an important transverse swelling of the order of 1/10.

Said shortenings are obtained either by resilient distortion of elementary arcs under increasing thrusts, or by the sliding movement of a wedge-system, or by any other means producing the sameeife'ct.

In certain cases", the expansible device can re'-' of allauxiliary'means ensuring the industrial eX-' ploitat'ion of theo'ore; for instance:- devices lim I to the possibility of its re use, as it is free when,

iting' the radii of curvaure', filling of internal spaces by any suitable material: clay, grease, etc, ensuring complete fluid-tightness under the concrete or the injections, diminishing the risks of corrosion and creating the lubrication of the system.

When a reinforcement is placed in service by heating the anchorings the reactions of the core cause the fusible material to flow, then the anchoring to be torn away under the double action of the resilient return of the resistant body and of the expansible device the lubricating material of which exudes and facilitates the unframing.

According to the process of the invention, the manufacture'of the reinforcements comprises the twisting and braiding of the resistant elements constituting the sheath, the cutting of the latter into sections of sufficient length, the capping of the anchorings on the ends of said sections,the placing in position of the expansible device of the core before or after tensioning the section of sheath on a draw-bench, the compression of the resistant body by "acting or not on each anchoring, the locking of the constraints introduced into the system.

Thus treated, the pretensioned reinforcements:- can be wound on suitable drums without affecting the resilient properties thereof, and economically forwarded.

As regards their use, they are incorporated in the constructions as ordinary reinforcementsaf-t er having been subjected to any shaping solely respecting the originallength thereof and a limit of curvature function of the twisting of the ele-- ments of the sheath. When the material binding the construction has a suflicient resistance, the potentialof forces is released by unlocking the anchorin'gs, The latter and the elements constituting the core can be sent back to the workshop on the drums having served for transporting the reinforcements.

The accompanyin drawing illustratesby way of examples two embodiments of the reinforcemerit according to the invention.

Fig. 1 is a-crosssection of an embodiment of the reinforcement,- such as it is prepared in order to be subsequently used;

Fig.1 shows, in perspective view on an enlarged'scale, an end anchoring.

Fig. 3 is a longitudinal section of the complete reinforcement with its two anchorings.

Fig. 4' illustrates the anchoring in longitudinal section on an enlarged scale.

Fig. 5 shows in perspective view a second embodiment, in the zone of the anchoring thereof.-

Fig. 6 diagrammatically illustrates details of theconstitution of the core'of said reinforcement.

'InFigs; I to 4, I is the sheath, 2 the core, 3 a splice.

The cross section of the reinforcement can be of any nature: circular, square, fiat, etc.

The sheath is constituted by a tube or preferably by parallel elements adjoining or not, such.

as hard steelwires (round, square, flat, twisted,- etc.-). In the embodiment chosen in the drawing, the-sheath l is formed by steel wires such-as la. Figs. 2 to 4. r

The choice of the elements constituting the sheath is function of the general economy of the construction-and of the maximum adherence possible thereof with the preconstr'ained material.

The optimum shape of the core is solely related therea'ctions of the sheath have been transferred to the construction and it can then be extracted.

from the sheath by any suitable means (pulling, contraction, etc.).

The splices can be constituted either by adjoining turns of wire, hoops, rings or washers sufficiently resilient to maintain the elements forming the reinforcement closely clamped together, or by a continuous coiled wire the spacing apart of the turns of which, as that of the other attaching members above defined, can be calculated in function of the desired curvatures and of the strength of the elements constituting the core.

The end anchorings satisfy the following conditions:

1. In the marketable form of the reinforcement: they ensure the equilibrium of the internal system of forces.

2. When it is in service: they allow the stresses to be sufficiently distributed on the preconstrained material.

By way of example, the anchorings can correspond to the device of Fig. 2.

The elements lb of the sheath I are flared and locked in a head 4 of any kind, solid or compound, made of hooped concrete or constituted by a metallic clamping hoop. Hooks or lugs 5, rigid with head 4, arranged for instance in two pairs as seen in Fig. 2, allow a traction to be exerted on said head 4, that is to say on the sheath l, as indicated by the arrows '1', whereas a compression reaction is exerted on the core 2 by any means whatever (jack, etc.) according to the arrow C. The desired internal system of forces is then stabilized by a key-bolt 6 which locks the core on the sheath through the medium of the lugs 5. In Fig. 2, the line 6' indicates the axis according to which the keying is effected.

The placing under tension and pressure of the reinforcement can be effected by any mechanical or thermic means (jacks, screws, wedges, expansion, torsion, etc.) by acting indifferently on one or the other of the end anchorings, whereas the key-bolt previously locks the sheath and the core on the opposite anchoring.

The reinforcement thus constituted and prepared encloses an invariable known potential of forces. In order to use said reinforcement, it is incorporated in the construction as an ordinary reinforcement, then when the concrete has hardened to the required degree for instance, said potential of forces is transferred to the material to be compressed, by driving the key-bolts out of both anchorings.

The core 2 can then be extracted as above stated.

According to the second embodiment illustrated, the ends of the sheath ll, constituted by strands or threads l2, twisted and braided, are sealed by means of a fusible material I8 in the annular space comprised between a. cap l4 and a cone [5.

The core I! the resistant body of which is composed of elements I8 fitted in each other and an expansible device l9 constituted by overlapping balloon springs having curved flexible blades I9, is placed within the sheath l I and compressed by the push-piece H) by the action of a dynamometric jack. This operation produces the contact of all the elements l8 of the resistant body of the core and resiliently shortens them, by causing the transverse swelling of the expansible device I 9 by accentuating the sagging of the flexible arcs I9 and, consequently, the close centering of core I! in sheath II.

For a given tension in service, the sheath-core 6 unit is locked by the action of the nut 2|. The reinforcement is placed in service, that is to say the forces accumulated are released by the action of a heating resistance 22 fitting over the cap M.

The flowing of the fusible material and the release of the anchoring [3 are produced under the double action of heat and the resilient return of the resistant body of the core and its expansible device.

It is then possible to recover the core by extraction, owing to the important transverse play given by the flexible springs 19 which moreover render all the elements 18 of the resistant body rigid together.

What I claim as my invention and desire to secure by Letters Patent is:

1. A reinforcement for use in preconstrained structures comprising a pair of flexible juxtaposed elements of substantial length as compared to their section, one of said elements having a high tensile strength and a high elongation coeflicient for being embedded in the structure to be pre-constrained, the other element having high resistance to longitudinal compression, the first-mentioned element being tensioned strongly, while using the ends of the second-mentioned element as a bearing and remaining thus tensioned until the reactions that balance the tensile stress are transferred from the second-mentioned element to the structure in which the reinforcement has meanwhile been embedded, none of said elements exhibiting any resistance to bending, while stability to buckling is ensured as a result of practically continuous radial reactions being exerted by each element upon the other,

2. A reinforcement for use in pre-constrained structures according to claim 1 wherein. one of said elements constituted by a tube made up of intertwisted steel wires or ribbons, is transversally stable without the aid of any particular means.

3. A reinforcement for use in pre-constrained structures comprising a tubular transversally stable element of considerable length as compared to its section and having high tensile strength and high coefficient of elongation, and an inner flexible element composed of a series of short compression-resisting cores arranged end to end.

4. A reinforcement for use in pre-constrained structures as claimed in claim 3 in which the cores composing the inner element are fitted with imbricated arched spring strips connecting said cores by pairs and providing an elastic layer thereabout whose diameter, which is less than that of the tubular element in the released state of the springs so that the cores can be taken out, will increase as theinner element is more tightly compressed, for the purpose of providing for contact between the compressed element and the tensioned element in the pro-stressed reinforcement.

MARCEL CHALOS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,270,240 Freyssinet Jan. 20, 1942 2,303,394 Schorer Dec. 1, 1942 2,328,033 Schorer Aug. 31, 1943 2,371,882 Freyssinet Mar. 20, 1945 2,378,584 Schorer June 19, 1945

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