DE2040085A1 - Apparatus and method for prestressed elements - Google Patents

Description

DR. ING. E. HOFFMANN · DIPL. ING. W. EITLE DR. RER. NAT. K. HOFFMANN

PATENT LAWYERS

D-8000 MÖNCHEN 81 ARABELLASTRASSE 4 TELEPHONE (0811) 911087

HERBERT CORLISS B ¹ ISGHER, Wellesley, Mass. / V. St. A. HERBERO? CORLISS FISCHER JR., Wellesley, Mass. / V.St. A.

Apparatus and method for prestressed elements

The invention relates to new prestressed elements and methods of making them.

To obtain a component with pre-compressed properties, it has long been known that a pretensioning can be used to increase the tensile strength and flexural strength of the part. For example owns concrete or a cast stone, which is preferably made of Portland cement, an aggregate and Made of water, they have great resistance to compressions. Unfortunately, however, concrete is susceptible to this

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Tensile, which causes it to become brittle and subject to cracking and fracture formation when subjected to unexpected tensile loads, such as those often occurring during the processing and assembly of precast concrete elements before and during the construction of a building.

Two approaches have already been taken to overcome the susceptibility of concrete to tension; one way provides for reinforcement, the other for precompaction by prestressing.

Reinforcement, however, has the obvious disadvantage that it still allows the concrete to crack under tensile loading, although generally the iron insert permanently holds the broken pieces together. This is because that the iron reinforcement must stretch when receiving the load, but the elongation is greater here than that it could withstand the enveloping concrete, it breaks under the load.

Prestressing is largely a type of precompaction of the concrete element in areas where tensile loads are expected . If sufficient pre-compaction is stored in the concrete element, no tensile stresses will occur with the calculated load. Under these conditions, the concrete that is under compression loses its fragility and becomes a flexible and resilient material. A prestressed concrete element loses some of its precompaction when it receives a load, so that the actual compressive loads, as the load increases, are reacted to at least up to the calculated load.

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With other relatively solid, i.e. relatively incompressible materials, such as metal, synthetic plastics, including fiber-glass resin compositions, toughening is also known to increase tensile strengths to enlarge; this is particularly applicable insofar as it is the bending stress of individual structural parts regards.

In practice, the concrete is pre-tensioned in two ways, namely by subsequent tensioning and by pretensioning. In one case, an iron rod or rope is stretched to compact the concrete. An afterthought Tensioning is achieved in that a cavity is poured in the concrete element and after the concrete has sat down, an iron rod or rope through the opening is brought in and tensioned in order to compact the concrete? in doing so, the tensioning elements are left free standing at the ends of the cavity. When pretensioning, a The steel cable is tensioned, for example, by hydraulic winches or end anchors and the concrete is poured around the iron, while the rope is kept under tension. After drying, the concrete bonds with the iron because of the recesses in it so that the end anchors can be severed and the iron under tension remains to keep the surrounding concrete under compression and in this way prestressed.

Although the latter method of biasing has been used with considerable success for over a decade it has a number of disadvantages.

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From the standpoint of quality, especially the To control cracking in precast concrete elements, it is usually difficult to achieve an optimal degree of prestressing because the expansion of the iron is small (for example, an uncoated one expands 1.25 cm diameter rope and an A.S.T.M. Grade 7 only by 1.9 cm by 3 m with a pull of 1o 2oo kp). A Achieving the optimum degree of prestressing is also difficult because of the iron in the concrete element slips and therefore results in cracking even at lower tensile loads than anticipated. Since it is also necessary to use steel cords on the order of about 1.27 cm in diameter in order to to achieve sufficient adhesion to the concrete and to reduce the tension in the steel in terms of compressive strength To compensate for the concrete, a distribution of the prestress over the cross-sectional area of the Elements not when using multiple steel ropes except for very large elements. On top of that are the ends of the prestressed steel elements necessarily open on the outer surface of the element.

Furthermore, from the standpoint of usability, such prestressing is only possible on concrete of a relatively high level Limited strength; it can not for example, for a foam concrete with light weight and lower Strength can be used, as it is generally used in elements for building cladding. This is based on the low expansion of the steel even with high tensile loads and on the fact that the foam concrete is impossible

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borrowed with a steel rod or small diameter cable sets. This makes it impossible to use a Siahl pre-tensioned Provide element of low tension and to adjust it to concrete of low strength.

Because of the difficulties in manufacturing the elements, expensive equipment is required to produce that of steel to generate the required high tension and to maintain it during the time it takes for the concrete to dry For this reason, prestressed concrete elements can only be produced economically at central locations and brought to the building hatchets. The sizes and configurations are, however, by the cost and by the limited facilities available, especially when only a few special concrete elements are possible.

Other materials, such as synthetic, organic, plastic materials, are made in a similar manner by being enclosed in tensioned, relatively inextensible elements has been biased. However, they are all subject to the difficulties listed above, namely the practical one Difficulty in achieving optimal prestressing due to the small expansion of the elements to be prestressed, even when they are under high tension. It also follows from this that they cannot be used, in particular not with elements of low strength and especially with materials that are light in weight, such as wood and plastic.

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20A0085

It is therefore a main object of the invention to provide new pre-stressed elements and methods for their manufacture, which are not subject to the difficulties listed above. Furthermore, according to the invention, it is possible to pretension light elements of low strength as well as the tensile loads over the cross-section of the Elements, even with low strength materials. In addition, it is according to the invention possible to hide the armored ropes in the elements so that they are not exposed on the surface.

Another object according to the invention is to allow the use of elements prestressed with metal Avoid, as such elements present the well-known electrolyte and corrosion problems.

This is accomplished by having uniquely useful biasing elements with materials of a class which have long been known for other uses but have never been considered practical as biasing elements. These materials include known synthetic, organic, plastic polymers such as nylon, polypropylene and polyester, preferably in the form of highly elastic, multifilamentary, twisted or untwisted ropes of moderate tensile strength compared to steel; however, they are uniquely capable of generating high compressive forces based on their recoverable tension or elongation from 10 % to 20% upwards, and are designed for a progressive increase in tension up to their ultimate tensile stress.

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-7- 204GQ85

It has been found that such vielfasrige ropes when they are stretched to at least 5 to 1o% of their constant length in the relaxed state, as much \\ / ie 80-9-O ° / o of its elastic limit at break means a relatively solid materials , in particular light materials, such as light metal, plastic, wood, etc., can be combined that are suitable for maintaining the tensioned rope over a relatively fixed length of at least 5 to "Io % of the expansion, in particular with a further expansion to to supply uncommon, lightweight, pre-tensioned elements and articles, for example strands of such ropes may be used which are on the order of at least 700 to 1050 kg / cm

up to more than 35oo kg / cm (at the base of the strand cross-section), whereby the strands can even be equipped with a tensile strength of 4 to 10 g per denier, which is equivalent to a fiber cross-section
is ago.

2 final pulls of about 42oo to 10 500 kg / cm or spar Contrary to the general opinion that tensile forces of such a taut rope, which are used to generate the required compressive forces decrease so quickly over time that they are relatively permanent Pretensioned elements are unusable, tests have shown that after an initial voltage drop from 5 to 1o #, which occurs within a few minutes, another drop is apparently approximately constant with the logarithm over time and very

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—Ο -

remains low, so that nylon, for example, appears to retain more than two-thirds of its initial pull to produce the compressive forces even after 100 years. By pretensioning a relatively strong material through such a rope, which is at least 5 to 10 ^ elongated and preferably under a pull of at least 10 to 20 % of its ultimate tensile strength is kept at a tension of at least 55oo kg / cm (fiber basis) and preferably higher, a great variety of prestressed structural elements according to the invention can be provided.

The reported decay factor can be determined by tests in which the fibers of the material to be tested are attached to the clamps of a tension tester so that the untensioned, free length of the test piece before a force is applied is 10 inches. The test piece is then tensioned at an amount of 2.5 cm per minute in order to achieve either an increase in length to 15 % or a length which is 1 % less than the elongation at tearing, which is always less . One minute after the fibers are tensioned to the desired length, the total tension on the fibers is recorded. The fibers are then left undisturbed in the tester in the tensioned state for about 4,000 minutes. The tension value after this period is then measured and recorded.

According to the invention is a tensioning element with a relatively rigid, incompressible body and a tensioning device intended, the synthetic, organic,

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Contains plastic fibers that have a recoverable elongation of at least 5 % and a tensile strength of

contains at least 7 ° o kg / cm with the tensioning device being held at a relatively fixed length in close association with the body at least 5 % elongation and under a tension of at least 10% of the ultimate tensile strength to compress the body.

Furthermore, according to the invention, a method for supplying a tensioning element is provided, the method being characterized by a tensioning element with a synthetic, organic, plastic fiber which is stretchable to a length of at least 5 # more than the initial length in the relaxed state and tends to restore a substantial portion of such expansion by applying a force to the fibers to expand the fiber to an amount of at least 5 % more than its original relaxed length and fixing the fiber at its expanded length, - where the fiber is kept under tension in order to tension the element with a certain kiaft for a period of more than a year.

Further details emerge from the following description in conjunction with the attached drawings. Show it:

Figures 1 and 2 show a plan view and a cross section of an internally prestressed structural element according to the invention;

Figures 3 and 4 are a side view and a cross section of a externally prestressed structural element according to the invention;

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Fig. 5 shows a typical end product that the component according to Figures 5 and 4 are used;

Fig. 6 shows an internally prestressed, tubular component ^

Figures 7 and 8 are isometric and partially broken away Illustration of a solid structural element which is externally prestressed in two directions according to the invention;

Figures 9 and 10 are isometric, partially broken away Illustration and end view of a pressure vessel that is externally biased in two directions according to the invention;

Figure 11 is a cross-section of an externally pre-stressed pipe according to the invention; and

Figures 12 and 13 are end and side views, partially broken away, of an externally biased grinding wheel according to the invention.

According to the preferred exemplary embodiments according to the invention, compacted structural elements are provided as shown in the drawings, the elements made of conventional solid material, such as metal, plastic, concrete, wood, etc., being compacted by means of an inner or outer fiber tensioning cable; here, as is possible with highly elastic elongations, they can change in the order of at least 5 to 10 % relative to the material being prestressed , with a waste amount of no more than

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a third over a period of years, with such ropes having an expansion of about 5 to Ίο % compared to their basic length in the relaxed state and preferably under a pressure of at least 1o to 2o % of their ultimate tensile strength with a tension of less than

- 2nd
Set at least 55oo kg / cm (at the fiber base) and preferably higher. The material that is pretensioned is in a solid, non-yielding state, ie it is relatively incompressible when. Compaction forces are applied by the tension rope; in this case the strongly tensioned rope is in close contact with the solid body and is thereby kept at a relatively certain length so that it continuously maintains its compressive force in order to pre-tension the element with a relatively small amount of waste. The use of non-metallic fiber tensioning cables according to the invention avoids the electrolyte and corrosion problems with metal and has other advantages, as will be explained below.

A variety of elastic, organic, plastic ropes can be used according to the invention including such organic, plastic materials as nylon, Polypropylene and polyester, as well as others, preferably being multifilament, untwisted or twisted Configurations such as used in conjunction with strands or strands. Such ropes usually have high tensile strength with a high amount of elastically recoverable elongation, which remains repeated after the rope has been tensioned enough times to achieve a relatively stable length in

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tense state to achieve. For example, owns a rlylon strand, a tension rope to be prepared according to the invention

2 dung, a tensile strength of about 25oo kg / cm (at the Querschnxttsbasis of the strand) at about ^ o fo elongation beyond its fixed length; it can also be stretched to 50% of its ultimate elongation at break in order to provide a tension which can be used to generate and preload compressive forces of a magnitude of about 21,000 kg / cm at an elongation of about 4 ° ^c / o . On the basis of our tests and calculations, such a nylon cord, if it is held at a relatively firm elongation of 4-0 % by a rigid element which is pre-tensioned, will have a pre-tensioning compression force of 14oo kg / cm '"even after 100 years. Another example is a polyester multi-fiber yarn (DuPont "DACRON" Type 68) with a tear strength of

ο
9 »5 g / den (11,7oo kg / cm) at 13.7 % elongation as well

2 can be used, especially with tensions above 35 °° kg / cm; at least two thirds of the applied voltage is retained over a period of years. Such materials are very useful as prestressing elements, especially for prestressing relatively light, solid elements, such as wood, aluminum, plastic, glass, etc., as well as for hollow elements and articles, such as grinding wheels, pressure vessels, pipes, etc., which are very difficult are to be prestressed with a material such as steel, since the high tensile strength of steel makes it necessary to use extremely narrow prestressing elements, which in turn are difficult to position and control. With the much lower tensile strengths and the increased elongations of the tensioning materials according to

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of the invention can. Much larger and even easier to
controlling clamping elements are advantageously used; In contrast to steel with its maximum expansion of 1 Ms 2 % , the prestressing materials according to the invention even result in a 10? & Lge decrease in their fixed clamping length either through sliding or through deformation of the component, with only an approximate loss of the applied compression force occurring .

Polyester and polypropylene strands are slightly lower Tear strength at expansions that are "approximately the Half of NyInn; but they are still connected usable well with the invention. Other plastic materials with similar physical properties can also be used.

The exact structure of a tensioning rope according to the invention is described in U.S. Patent No. 3,208,838; the tension rope can bond to a non-rigid material such as uncured concrete or plastic ', as long as the concrete or plastic material is not set, yielding,

it.
usually being poured into a suitable mold or compacted in the mold ₉ in which the tension ropes are held. After that, the non-solid body goes into solid
State over and the tension cords then contract or allow contraction to close the element
condense. Or the tension rope is in tension
State applied externally to a fixed element ^ so that it

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together with the tensioning rope in closer contact due to the compression is tensioned, so that the tensioned reinforcing element changes in size to such Tension element due to compression.

The tension of the tension cable can be increased after the previously not solid body has sufficiently settled Temperature base. For example, as in conventional practice, the drying of pre-cast Concrete elements carried out by heating the form that contains the concrete. Using the invention a tension rope can be selected in which a larger part of its contraction at a suitable Temperature occurs below which the concrete will initially dry for actual setting and bonding with the tensioning rope can be executed and over which the tensioning rope pull together with tension and so the concrete element will compact.

Concrete made from Portland cement and together can be used in connection with the invention used with a variety of known aggregates, not just the usual sand, gravel or gravel Stone aggregates, but also light aggregates such as burnt clay, expanded blast furnace slag, Pumice stone etc., as well as air and foam concrete.

In Figs. 1 and 2, a standard concrete test element (A.S.T.M.) shown, generally designated 10 and made in accordance with the invention. In particular, one has

ρ such test pattern a cross section of 38.7 cm and one

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Length of 5? »^ Cm and is due to the inclusion of tensioning elements 12, 14, 16, 18 made in plain portland cement with a compaction strength in the range from j> 50 to 42o kg / cm, as he is generally known and, for example, in Design and Control of Concrete Mixtures, 1st Ed., published by Portland Cement Association (1952).

The tensioning elements 12, 14, 16, 10 shown in FIGS. 1 and 2 are multifilament, heat-shrinkable polyester fibers with a recoverable tension of approximately 1o $, with approximately 1o shrinkage occurring when heated to a temperature of approximately Joo ⁰ . This can be done by storing such -! Fibers! In! The form of strands, which are arranged zv / corner-wise in not set cement bodies, the cement then settling at a lower temperature than is necessary to actually shrink the polyester fibers cause. The concrete body is then heated to a temperature which is sufficiently high to cause the polyester fibers to shrink. A test specimen made in this way had a breaking strength approximately twice that of a control specimen without such fibers and exhibited very desirable crack control characteristics, eliminating the cracks that appeared prior to breakage could be achieved by relieving the sample. Shrinkable fibers other than polyester can be used as well; Such fibers can then be arranged in the form of cables as well as in the form of strands.

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Pre-compressed components can also be produced using organic, plastic multi-fiber ropes in the form of cables as described above, which have at least a 5- to 10 # stretch and an elasticity under tension of at least 1o to 2o # their ultimate breaking strength. This can be done, for example, by clamping one or more such cables to be carried out from liylon. Each of these cables is then held by suitable clamping heads 2o, as shown in Fig. 6 and described together with this figure will; the tensioned cables are then tied with concrete or some other plastic that is not tied Body potted, the cables being held under tension while the material is setting. After the concrete has set, the tension on the cables can be released to compact the concrete; can do this then the ends of the cables are severed. Nylon cables are particularly suitable for such an application, and not only because of their great extensibility and the high compression forces that can be generated by them, but also because they react chemically with the concrete, which results in a particularly strong bond.

As a further modification of an internally braced, compressed component according to FIGS. 1 and 2, a Body 1o, regardless of the solid material from which it is made, thereby tensioned according to the invention ■ Be that the cables 12, 14, 16, 18 are inserted through suitable openings and that the cables are tensioned that are at least equal to 5 to 1o # across its basic length lies in the relaxed state and which is

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are under a pressure of at least 5 to 10 % of their ultimate breaking strength. The cables can then be held at a certain length relative to the body 1 o by clamping pieces 2 o.

In H ¹ Ig. 3 and 4- an externally tensioned structural element according to the invention is shown in which a solid body 25, for example made of metal, wood or plastic, is tensioned by a tensioned rope 27 which is wound around and, for example, in the form of an endless cable, a strand or a multi-twisted "multi-fiber rope. As already described, the rope 27 made of a stretchable material is pretensioned at least 5 to 1o % beyond its basic length in the relaxed state and is under a tension of at least 1o to 2o % of its breaking stress" If it is required for an application, the rope 27 need not be looped around the body 25, but it can also protrude on one or both sides, the adjacent ends then being fastened by suitable means, for example by clamping pieces 20 ".

In Fig. 5 a typical end product is shown in which the components of Figs. 3 and 4 can be used as side rails 2 ^ ₉ 25 of a conventional ladder with rungs 26. The conductor material is hardwood, although it could just as well be aluminum rope 27 is a strand of nylon o _f 64 cm diameter, which is extended to 4-O% of its basic length in the relaxed state, erdichtungskraft a residual ¥

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—'ΊΟ—

of about i> 20 kg, taking it to a third its ultimate breaking strength is loaded and housed in a notch around the side rails is. At a preload of approximately 56.7 g (2 ounces) Nylon on each side rail broke a 6 foot ladder Length when it is supported horizontally at its ends and loaded in the middle, with a load with 53 ° kp, while compared with this a similar one Ladder without a compaction rope 27 already broke under a load of 26o kp.

In Fig. 6, a further component is shown in the form of an aluminum tube 3o, which contains a strand 32, which according to the invention is stretched and strained. This strand is passed through the inside of the tube and attached to his Ends held by known clamping elements 2o; it has a conical part 22 for receiving the open end of the multifilament strand 32 and is clamped in by cooperation with a conical closure device 25, wherein the locking device is held in a certain position within the body 22 by screw threads 24 is. The internally tensioned, tubular component 6 can be used in the most varied of ways as an end product, for example as a wide variety of supporting masts Art, as ship masts and ski poles as well as for highly tensioned and flexible elements, such as Helicopter rotor blades.

In Fig. 7 and 8, a solid component 4o is shown, which is braced in two directions, namely in the direction of the longitudinal axis and perpendicular to it in the circumferential

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direction to improve strength characteristics with improved resistance to bending deformation to be provided, whereby specially light material is used. The solid body 42, which is made of wood, Metal, plastic including those composed of fiberglass resin Materials, concrete and glass, etc., can consist, has a multitude of tensioned, longitudinally running strands 44 of high strength made of organic, plastic material, preferably made of ITylon or polyester, attached to one or more sides and with a deliming of at least 5 # below a tension of more than 25oo kp / cm held are; here are strands 46 that are tensioned over the part 42 and the strands and run in the circumferential direction wrapped, which also with an elongation of at least 5 # and a tension of more than 35o "Q kp / cnl · ^ are preferably held in a strip shape in a helical configuration. After the strands 46 are wrapped around and attached by suitable putty, the underlying, longitudinal Strands 44 released and trimmed as desired be, with their tension through the wrapped over it Strands 46 are retained. The winding of the circumferential strands can do best be accomplished by a simultaneous winding of a plurality of strands, preferably in one single layer in the form of a strip, under a fairly high tension, in order to achieve a tension of over 35oo kgf / cm in to produce the finished cords.

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BADQBiSiNAL

Components of this type also have a wide range of applications; for example, such parts, if they are reinforced in this way, are used as conductor side clips suitable; Furthermore, they are particularly suitable for heavily used objects, such as Hockey sticks or baseball bats, in which the handle part is advantageous in the described manner can be armored.

Another type of object which according to the invention can advantageously be armored in this way relate to the interior objects under pressure, such as pressure vessels, tanks, pipelines, etc.

In Fig. 9 and 1o such a pressure vessel is 5 ° shown, which consists of a hollow, cylindrical, solid body 52 with hemispherical ends, which is wrapped at the ends with a multitude of overlying, longitudinally extending strands is; the middle central longitudinal part is also provided with a multiplicity of strands running in the circumferential direction 56 wrapped around it, just like the right-angled solid structure of FIGS. 7 and 8. In the pressure vessel of FIG. and 1o are the longitudinal strands preferably distributed along the circumference and transversely to the center point of the hemispherical ends, which is the can best be seen in Fig. 1o to ensure a very good reinforcement of the ends. The body can 5 ° of any desired material, v / ie for example metal, plastic, concrete, glass, etc. consist.

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BATH ORIGINAL

Particularly beneficial results are obtained when stretched strands of synthetic organic fiber material are wrapped around the axial portion of the outer surface of a hollow cylindrical member such as a tube, each strand containing a plurality of filaments and sold commercially as yarn. As already described above, significant advantages, for example increased resistance to breakage and impact, as well as additional resistance to impact, are obtained as a result. These advantages are obtained from a tubular body made of any material, provided that it has the characteristics mentioned above so as to be able to withstand despite being severely deformed by the forces exerted on the wall of the tube by the stretched strands. In this way, unexpected results are achieved in particular with tubes made of materials which consist of a liquid slurry, ie mixtures of solid particles or fibrous materials and liquids which, after they have been processed, dry or set, such as concrete, clay, Asbestos cement or even a wood pulp »As described earlier, the synthetic strands can contain organic plastic, fibrous materials such as nylon, propylene, polyester, as well as other substances, preferably in the form of a thread or in the form of many threads of untwisted or twisted configuration, "as for example in the articles of Figure" 7 to 1o® also need to pre-established specifications ^ that such strands meiir at a placement around a pipe at least 5 ⁰ P than it IH

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rer basic length in the relaxed state corresponds to οίο
A tension of at least 500 kgf / cm ^L (fiber base) must be present in order to obtain these advantageous results.

Referring to Fig. 11, there is shown an assembled structure, designated by the numeral 60, which includes a tubular body 62 with a strand or yarn 64 circumferentially wrapped around its outer surface. Of course, the material wrapped around the tube will contain a single strand or many strands. In any event, each strand contains plastic material with a recoverable elongation of at least 5 to 10 % and with a tensile strength of over 7000 kgf / cm ^c (at the fiber base); the material was also subjected to sufficient tension when circumferentially wrapped around the tube body such that when placed around the tube it was stretched 8% longer than the basic length when relaxed . In the particular illustration, two layers of strands 64 are wound one on top of the other; it goes without saying that the number of layers of strands which are wound one on top of the other depends only on the ultimate desired values of the tube and on the amount of synthetic material in the layers. While only a part of a tube is shown in FIG. 11, it is of course not beyond the scope of the invention if the advantageous results are also obtained with similar objects by overwinding which is connected in connection with the tube.

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such as couplings, T-pieces and elbow.

The following table gives the advantageous results which can be obtained in connection with the invention as applied to the pipe. Even though special materials, pipe sizes and stretched strands have been highlighted in these examples, the stated "advantages are for illustration purposes only and in no way place a limitation on the claims dai "".

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game -24- Push Hydrosta
table
after this
Push 20A0085 at Hydro
static
no
Push kg kp / cm ^ fracture
no
Push A-C channel tube kp / cm " 18.1 1% 3 kg Al. AC duct tube
(1 layer)
AC duct tube
(3 layers) 22.5 18.1
18.1 51.3
95 1554. 5 · A-C socket 52, o
1o8 9, o7 28.8 249o B1. AC socket
CZ> layers) 56.6 9, o7 116 175o 2. PVC pipe + 116 45.4 46.4 517ο C1. PVC pipe
(1 layer) 45 45.4 1o6.5 cL PVC pipe
(3 layers) 112 45.4 2o4 5 · Concrete pipe 169 ++ 9, o7 o, 7o D1. Concrete pipe
(5 layers) 9.14 9, o7 58.7 73o 2. Clay pipe 52 3, o4 O 77I0 E1. Clay pipe
(1 layer) 11.2 3, o4 3o, 9 449 2. Clay pipe 5o, 9 3, o4 46.4 522o 55.5 7750

+ Fraction not anv / endable
++ Pipe does not tear

In Example A of the table above, the AC Duct tube consists of a 2o, 5 cm asbestos-cement pipe of the type sold by Johns-Man viii e under the trademark 2o; ^; 2 cm class I500 sewer pipe is marketed.

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In example B, the A-C socket contains a 15 * 24- cm asbestos-cement pipe socket of a type sold by Johns-Manville under the brand name 15 »24- cm Class I50 pressure pipe socket is distributed.

The PVC tube in Example C contains a polyvinyl chloride tube of the! type made by Johns-Manville under the brand name 11.2 kgf / cm 15.24 cm PVC pipe is sold.

The concrete pipe in Example D is of a type that through IT. E. Concrete Pipe Co. is sold under the brand name 2o, 52 cm Type C-14-6S.

The clay pipe in Example E is of the type sold by Broekway Pipe Co. under the trademark 20, 52 cm C-2oo ES.

In the movable examples in FIG. 11 as well as in the objects in FIG. to 10 the tube, sleeve or other item was wrapped with a polyester hank yarn of the type sold by EI Du Pont De Nemours & Company as DACRON filamentary yarn for industrial use as 68, 1300 denier, 192 high tenacity _s

2 with a breaking strength of 9j5 g / den equal to 11,7oo kp / cm (at the thread base) with an elongation at break of approximately 14 ° β> . In the examples in which the number of yarn layers is indicated, each yarn layer was represented by Wik »Kefibers of the type 68 yarn run around the entire axial area of the hollow, so that about 13 strands per centimeter in the axial direction in each layer with a radial one

1 0 8 8 1 2/1 1 E 0

are

Thickness of approximately 0.025 cm /. Each strand of yarn consisted of approximately 192 threads of polyester fiber. A pull of 8.16 kp (67 ^c Jo of breaking strength of 12.2 kp) had been applied to each strand of yarn as it was wrapped in the circumferential direction around the outer surface of each pipe or sleeve so that each strand was about 10 # more when it was stretched equal to its basic length in a relaxed state.

In the exemplary embodiment, each layer has been formed by a rotatable mounting of the tube in a lathe. When the tube was rotated, a majority of the strands of yarn had been subjected to appropriate tension so that the strands were stretched to the desired amount. The strands have been wrapped around the tube in helical lines and extend from one outer end to the other. When several layers were wrapped around the pipe, they were advantageously designed so that the direction of the helical formation was changed in the following layers. The tubes must have sufficient structural strength to withstand the forces created by the strands wrapped around them. In the examples given above, each strand was subjected to forces in excess of 7,000 kgf / cm ^ (at the fiber base) when wrapped around the bore. Although the tensile force that has been applied to the yarn is relatively different for the individual synthetic materials that are used ₉ and Depending on the amount of elongation desired, it has been found that in order to obtain the advantageous results outlined above, the tensile force is greater than or equal to kp / cm must be.

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3 Increasing the pipe strength as well as the internal one hydrostatic pressure and breaking strength are crucial and are based on the tension transition caused by the wrapping of strongly tensioned and stretched fibers is provided according to the invention in an area where small narrow areas of the tubular body which would normally be tested particularly well according to the invention are solidified / so that such flaws are no longer appear. For this reason, a pipe with defects, which would normally be considered scrap, can be used by applying the invention.

Another type of article which can be particularly advantageously prestressed according to the invention contains Emery grinding wheels in the manner of a hollow cylinder or a mug which externally according to the invention may be biased to provide improved strength so that the disks at higher speeds can also be rotated with increased security.

In the case of grinding wheels, it is known that the "grinding performance is increased in general proportionally to the speed of the disc surface, so that it it is important to turn a grinding wheel at a higher speed for maximum grinding performance. the maximum disc speed is due to the disc strength limited, since the centrifugal forces that the wheel has to withstand without breaking, increase with increasing speed of the pulley enlarge quickly.

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In earlier U.S. Patent 3,14-1,271, there are grinding wheel reinforcements in the form of pre-stressed inextensible glass fibers shown and described, in which effectively increasing the grinding wheel speed up to was possible to a certain limit; In this case, however, it was very advantageous to have additional properties of the panes provide so that pieces of the grinding wheels stick together when partial defects and breaks in the wheel have occurred so that the pane cannot break and parts of it are thrown around, as this could result in serious injuries to the operating personnel.

When the present invention is applied to cylinder or cup type grinding wheels, it not only represents an improvement due to the increased preload, which results in much higher speeds to achieve, it also represents an improvement in a simplified arrangement in existing hollow Abrasive discs. In connection with other materials, made for example from pulp-like mixtures, the grinding wheels according to the invention become very good solidified, insofar as the defects are affected.

In FIGS. 12 and 13, a grinding wheel 7 ° in the form of a hollow cylinder or a cup is shown, which consists of a conventional solid body 72, which consists of emery grains or particles in connection with a resin binder together with a strand or a yarn 74 · ^to ~

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is composed, which is in the direction of the perimeter around the outer surface is wrapped around. Like the tube in Pig. 11 the strand contains plastic material a recoverable elongation of at least 5 to

2 1o % and with a tensile strength of over 7,000 kgf / cm; when the strand was circumferentially wrapped around body 72, it was subjected to sufficient tension that when placed on the body it was stretched about 5 "to 10% more than the basic length when relaxed In the particular embodiment, the strands 74 wound over them are the same as those already described in connection with Pig.

If the advantages that can be achieved due to the invention, on hollow cylindrical or cup-shaped Grinding wheels are used that have cylindrical or frustoconical - conical outer surfaces, are wrapped with a single layer of polyester yarn and that way, as they are already in Connection to the tubes was described, especially are certain, surprisingly high surface speeds are possible, which are twice as high as those at Discs that are not reinforced according to the invention.

The great strength and recoverable elongation of strands and ropes made of synthetic, organic, plastic fibers, which are over 5 % compared to the tensile strength for nylon and over 2o % for propylene and for polyester, such as DAORON, their great ability to shorten even relatively low elongations of

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about 10 % of their relaxed length (which has also been proven by their unexpectedly low rate of decay of no more than about a third of their compressed compressive forces over a period of several years) have made them very suitable for use as prestressed elements , because their particularly high elongations are achieved with far lower stress loads than with steel or glass fiber strands. For example, a 1.27 cm nylon or DACRON rope can stretch about 10 % of its length when relaxed

α state with about 18o to 23o kp, while a 1.27 cm steel cable would require 5 times more force to stretch the steel cable by 1%. This not only makes it possible to use simpler and cheaper pre-tensioning machines, but at the same time also to produce more evenly tensioned products even with light concrete, wood or aluminum and to distribute the tension evenly over the element cross-section by using multiple strands. In connection with the high degree of elongation that is provided in such organic, plastic fiber ropes, a much lower degree of slippage of the tensioning element relative to the solid body does not represent. Problem is in contrast to low elongations in steel,

W WQ ^ even less slip the clamping effect of the steel will destroy. Any required amount of preload can be achieved according to the invention by increasing the number of organic, plastic fiber strands can be achieved; the slip can be virtually eliminated by removing the strands coated with a suitable adhesive such as epoxy resin to achieve any desired degree of adhesion to keep the tendons in close contact with the body.

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Claims (21)

Patent claims Λ J Clamped element in connection with a relatively testing, incompressible body and clamping devices, characterized in that the clamping devices contain synthetic, organic, plastic fibers (12 to 18, 27, 32, 44, 46, 54, 56, 64 or 74) having a recoverable elongation of at least 5 % and a tensile strength of at least about 700 kgf / cm- ¹ , the tightening means being of a relatively fixed length in close association with the body for at least 5% elongation and under a tension of at least Io # to be held to the utmost breaking strength in order to compress the body. 2. Clamped element according to claim 1, characterized in that the clamping means is free of bearing constraints. 3. Clamped element according to claim 1 or 2, characterized in that the clamping means is curved is. 4. Clamped element according to claim 1, 2 or 3 »thereby characterized in that the fiber means Nylon includes having a repellable elongation of at least about 50 # and a tensile strength of at least 14oo kgf / cm. 5. Clamped element according to claim 1, 2 or 3 »thereby marked η et that the fiber with 109812/1150 Tel polyester contains a recoverable elongation of at least 20 % and a tensile strength of at least 14oo kgf / cm ^£ .2 6. Tensioned element according to claim 1, 2 or 3, characterized in that the fiber medium contains polypropylene with a recoverable elongation of at least 2o % and a tensile strength of at least ρ
kp / cm. 7. Clamped element according to one of the preceding claims, characterized in that the Tensioning means after a certain period of time receives the tension to at least two thirds of the force required for elongation is required. 8. Clamped element according to one of the preceding claims, characterized in that the Body is made of concrete containing Portland cement and aggregates, or that the body is made of wood, aluminum, Plastic or a grinding wheel, which is composed of emery particles and a binding agent. 9. Clamped element according to one of the preceding claims, characterized in that the Body is tubular with inner and outer surfaces, and that the clamping means around the outer surface of the tubular body is wrapped. 10. Clamped element according to one of the preceding claims, characterized in that the tubular body is a concrete pipe, a clay pipe, a PVC pipe or an asbestos cement pipe. 109812/1150 11. Clamped element according to one of the preceding claims, characterized in that the fiber means contains a thread. 12. taut element according to one of the preceding claims 1 to 11, characterized _s that the fiber means includes a plurality of threads " 13. Tensioned element according to claim 12, characterized in that the threads are wound around the outer surface in helical form that the threads in Helical shape ranging from one outer end of the tubular body to the other end and a layer from the threads, and that several layers of the threads are wrapped around the outer surface of the tubular body are. 14 · Clamped element according to one of the preceding claims, characterized in that the Body has a longitudinal axis and that the fiber means around the body in a first layer in one direction is wound parallel to the axis and in a second layer perpendicular to the fiber centers of the first layer, 15 · Tensioned element according to claim 14, characterized in that the second layer over the first lies. 16. Method of delivery of a tensioned element, g e characterized by the tension of the element in connection with a synthetic, organic, plastic 109812/1150 see fiber means that is extensible to a length of at least 5 # more than the length when relaxed, and with a tendency to restore much of such stretch when a force is applied to the fiber means to increase the fiber means by an amount of at least Stretching 5 % more than the length in the untensioned state, and by fixing the fiber means at a stretched length, the fiber means being kept under tension in order to tension the element with a certain force for a period of more than a year. 17 · Method according to claim 16, characterized in that g e k e η η draws that the force is at least 35oo kp / cm . 18. The method according to claim 16 or 171 marked through a tubular element, through a winding of several fiber layers around the tubular element Element, and by windings extending from one outer end to the other end of the tubular element. 19 · Method according to claim 16, 17 or 18, characterized by a fixation of the fibers in the stretched state, the fibers being held under a tension of at least 10 % of their ultimate breaking strength, and by a fixation that is achieved by applying a coating over the bare Surface of the fibers is obtained. 109812/1150 _35- - 204ü085 20. The method according to any one of claims 16 to 19j thereby gekennz eichnet that the element has a longitudinal axis has a first layer of fiber around this element is wound in a direction parallel to the axis and that a second layer of fiber is wrapped around the element over the first layer is wound in a direction perpendicular to the fibers of the first layer. 21. The method according to any one of claims 16 to 2o, characterized marked that the clamping amount at least retains two thirds of the stretching force. 109812/1150