FI88819C - Tension line for concrete elements - Google Patents

Description

1 88819 Tension braid for concrete elements

The invention relates to a tendon braid for concrete elements, which braid consists of at least one central yarn and a plurality of surface yarns wound around it, the diameters of which are substantially the same, the middle yarn or yarns running substantially without a twist in the longitudinal direction of the tendon braid.

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In concrete structures, steel tendon braids are used to prestress the concrete by applying tensile stress to the braid before the concrete structure flows. Traditionally, a tendon braid consists of six individual surface yarns wound around a central yarn. The prestress of the tendon braid is of the order of 50-70% of the breaking strength. Concrete elements such as hollow core slabs are produced by sliding casting with special casting machines designed for this purpose on substrates 90-150 meters long, from which they are sawn into elements of a certain size after a rather short curing time. In prestressing, the concrete has not yet reached its final strength.

Various machines and methods are used in the casting of hollow core slabs. Traditional "Canadian" machines cast a flexible 25 mass and the mass is vibrated during casting. The mold cycle is relatively slow in this method, and then there are no problems with the adhesion of the braid to the concrete.

"Finnish" machines are different and more economical in terms of production technology: 3 0. They cast hard mass using shear compaction technology without its greater: -.1 vibration. The mold cycle is fast and smooth. ·. there are problems with its infection. Therefore, the use of these methods has shifted to a braid in which the outer wires are profiled, for example, in the same way as in conventional cold-formed reinforcing bars, and this has the best slippage controlled. However, the adhesion of the braid to the concrete mass should be further improved by keeping in mind 2 88819 e.g. concrete slabs of a more demanding fire class, where adhesion must also be maintained during the fire.

The force transfer 5 between the smooth tendon of the braid and the concrete is based on an almost pure shear stress between the surface of the braid and the concrete. The stress spreads only to a very narrow area of concrete around the tendon braid, so the failure of the infection occurs very suddenly, which is very disadvantageous. The use of a texture in the surface wires 10 somewhat expands the area to which the stress from the tendon braid in the concrete is distributed. Thus, the effect is not very good, and deepening the texture to improve the adhesion properties also faces manufacturing problems because the yarn from which the tendon braid is made must be quite hard-working-reinforced, which is difficult to further shape to deepen the texture.

Finnish patent application 873196 describes an arrangement in which the surface wires are polygonal and are wound around their longitudinal axis during or after profiling. In this case, the adhesive surface between the outer wires and the concrete is made relatively large, and at the same time the shape of the tendon braid changes in the helical direction due to twisting, making it difficult for the braid to slide in the direction of the braided line. In this case, a compressive stress is created in the concrete due to the discontinuity, which considerably enhances the adhesion of the tendon braid as it expands the range of the stress. However, the production of such a tendon braid requires very special types of surface yarn drawing machines, which are expected to have a rather slow production speed, so that the production becomes relatively expensive and may also involve many manufacturing technical problems.

U.S. Pat. the direction is opposite to the direction of the thread of the outer wires. In this solution, the changes in cross-section in the direction of the thread of the 5 outer wires are very large and the adhesion to the concrete is excellent. However, the production of such a tendon braid is considerably expensive because it requires two successive braiding steps, one for the core part and the other for the surface yarns. A corresponding double braid is also described in U.S. Pat. No. 3,032,963, albeit using a triple yarn core. Its application is not concrete, but car tire reinforcement.

In CH-595 522, the shape of a tendon braid is made to deviate from the circular cylinder by using surface wires of different thicknesses. The structure of the publication, even with yarns of different thicknesses, makes it possible to the helical slip of the braid, so that the structure of these publications does not at all meet the objectives set for a good tension braid.

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The elliptical or similar cross-section of the central wire described in SE-340 875 is cumbersome and expensive to manufacture. With an oval central wire, the period of variation of the cross-sectional area of the braid is large, with an increase of 25 braids divided by two. The long period of variation does not distribute the adhesion of the braid to the concrete evenly along the length of the braid, but results in large concrete splitting forces. If the rise in the structure of the reference publication is shortened to reduce the period of variation, the deformation of the surface wires increases too much, causing them to be damaged. The proposed structure has not been implemented.

DE-2 044 665 also describes an armored wire rope of a car tire, which consists of a multi-threaded core part 35, the wires of which run in the longitudinal direction of the wire, and of surface wires wound around this core. According to the publication, the wire may further comprise a binder wire wound around the surface wires, which prevents the braiding from unraveling.

4 8 8 812 This means that the braiding is relatively loose, so that the outer yarns remain at the level of the circle forming the curtain surface and no change in the cross-section in the direction of the thread of the outer yarns is achieved. It would obviously be of no importance in both the elastic material 5 and the rubber, but in the application in question it seems to simply aim for the largest possible surface area of the steel wire.

The object of the invention is to provide a tendon braid in which the cross-section in the direction of the helical surface wires varies considerably, thus enabling the stress transferred from the tendon braid to the concrete mass to spread over a wide area in the concrete, thus preventing the tendon braid from slipping. It is a further object of the invention to provide a tendon braid of this type which can be produced by conventional braiding machines and in one braiding step. This means that the above-mentioned change in cross-section should not be based on the separate braiding of the core part or on the special rotation of the surface wires. Since in the tendon braid the surface yarns 20 are considerably reinforced even before the braiding step and the braiding is made tight so that the surface yarns follow the shape of the core relatively closely, it is an object of the invention not to deform the surface yarns at any point in the braid.

The disadvantages described above can be eliminated and the defined objects are achieved by a tendon braid according to the invention, which is characterized by what is defined in the characterizing part of claim 1.

The main advantage of the invention is that the tendon braid can be produced in one step with conventional braiding machines, and yet a helically cross-sectional area of the braid is obtained, whereby the braid has excellent adhesion to the concrete mass. In addition, the braid can be made of a conventional and hard cross-section yarn of conventional cross-section without damaging the surface yarns during the braiding and subsequent reduction of the thermomechanical relaxation treatment.

In the following, the invention will be described in detail with reference to the accompanying figures.

Figure 1 shows a cross-section of one embodiment of a tendon braid according to the invention.

Figure 2 shows a second embodiment of a tendon braid according to the invention in cross section.

Figure 3 shows a preferred embodiment of the core part of the tendon braid according to the invention.

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Figure 4 shows another preferred embodiment of the core part of the tendon braid according to the invention.

Figures 1 and 2 show the structural principle of the tendon 20 according to the invention. The surface threads 1 of the tendon braid consist of threads whose cross-section is based on a circle, but which may contain commonly used roughenings, ridges or grooves to improve the adhesion. The surface yarns 1 are thus of the type conventionally used in tendon braids 25 and are thus not described in more detail here.

In Fig. 1, the core portion of the tendon braid consists of two separate central wires 2 and 3, which are circular in cross section 30 and of which the radius B3 of the second central wire 2 is larger than the radius C3 of the second central wire 3. These two central yarns 2, 3 of different sizes run helically in the longitudinal direction of the tendon braid 10. When the surface yarns 1 spirally run around such a core part, the respective inner surface of the surface yarns 1 closely following the surface of the central yarns, the cross-sectional surface 6 of the outer yarns of the outer yarns forms a surface combination of two cylindrical parts. This is understandable when the larger radius center wire 6 O 8 81 2 forms a cross-section of the core portion for one side of the outer surface of the braid and the smaller radius center wire 3 for the other side. Thus, the cross section consists of a combination of parts of two circles R2 and R1 of different radii and is thus not rotationally symmetrical with respect to any axis. The outer surface of the tendon braid thus consists of a first cylindrical surface Y1 with radius R1 and a second cylindrical surface Y2 with radius R2 and the distance between the center lines of these cylinder parts is the sum of the radii of the central wires, i.e. B3 + C3. The ice-.0 nepunos is thus a combination of two parallel cylindrical surfaces in the longitudinal direction, but the surface yarns run helically with respect to the cylindrical axes, whereby the cross-section changes periodically when viewed in their helical direction. In this embodiment, the radius 15 B3 of the second central wire 2 is preferably 5-15% larger than the radius C3 of the second central wire 3.

In Fig. 2, the above-described effect is obtained by three unthreaded center wires 2a, 2b and 3, two of which have a radius C4 larger than the third wire 3's radius B4. In this case, the two larger central wires 2a and 2b together effectively form the core part of the larger radius R2 cylinder and the smaller radius central wire 3 forms the core part of the smaller radius R1 cylinder. The curtain surface 6 thus again consists of a cylinder part having a radius R1 and a cylinder part having a radius R2. The difference with the embodiment of Figure 1 is that the smaller radius cylinder portion is inside the larger radius cylinder portion while in Figure 1 the smaller radius portion extends beyond the larger radius portion. When three central yarns are used, the thicknesses of the central yarns may also be different from those described above, for example one of the yarns may be thicker than the other two, whereby a tendon braid closely resembling the curtain surface of the embodiment of Figure 1 can be obtained. All three center wires may also be of different sizes from each other, although it is somewhat more difficult to define effective radii for the cylinder parts. Thus, preferably the radius of the at least one central wire is 5-30% larger or smaller than the radii of the other central wires. However, the function of such a tendon braid in concrete is 7 Π 8 81 5 always the same when choosing the dimensioning of the middle wires correctly.

However, with certain braiding machines, there are hardware problems when making two- or 5-wire cores. In addition, such a tendon braid structure limits the design of the core portion, because when two yarns are used, the distance between the yarns is definitely the sum of their radii, and in the three-wire case, respectively, always the sum of the radii of the two yarns.

10 Thus, the shape of the core portion formed by the center wires is determined when the diameters of the wires are determined. This can cause problems due to the deformation of the surface wires becoming excessive in some places, causing damage.

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Figure 3 shows a preferred single yarn variant for the core portion of the combination of center wires of Figure 1 and Figure 4 shows another preferred single yarn variant of the three-wire core portion of Figure 2. As can be seen from Figs. 20, the monofilament core portion 4, 5 has a triangular shape and preferably a substantially isosceles triangle with apex angle α or S, respectively. The rounding radii of the edges of the triangles are B1 and C1 in Fig. 3 and B2 and C2 in Fig. 4. In the case of Figure 3 in particular, it can thus be seen that the roundings of the corners of the side opposite the apex angle α coincide to form a single rounding B1. The rounding of the apex angle is 30 Cl, whereby the sides of the triangle are formed by the side times of these two circles when Cl is less than B1. These side times are straightforward in this case. Since the rounding radii B1 and C1 are of different sizes, this one central wire 4 functions in the same way to form two curtain surface circles Y1 and Y2 35 as the two central wires of Fig. 1. However, the design of this central wire 4 is considerably more flexible, because the distance SI between the centers of the circles B1 and C1 can be chosen freely and in this case is smaller than the sum of the radii. When 8 ft 8 81 S? in addition, the side surfaces 7 can be shaped not only straight as shown but also cylindrically convex or otherwise, a shape is easily obtained for the middle yarn according to the principle of the invention which produces a sufficiently large cross-sectional difference in the helical direction and at the same time a sufficiently small deformation in the surface yarn. To clarify this, a side circle with a radius A is drawn around the central wire 4. If the central wires were braided around a circular core part with a radius A, 10 would of course result in a rotationally symmetrical tendon braid. The change in the helical cross-sectional area required by the objects of the invention is thus realized by using a triangular shape, which in this case consists of two circles of different radii B1, C1, and a sufficiently small deformation of the surface wires. large enough. Both of these can also be affected by the distance SI between the centers of the circles. Said deviation D1 should be in the range of about 5-45% of the radius A of the circle drawn and preferably between 10-30% of this radius A. Excessive deformation of the surface wires is avoided by forming rounding rays B1 and C1 in the range of approximately 40% to 120% of the outer wires. radius Z and preferably in the range of 60% to 105% of the radius Z of the outer wires.

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In the case of Figure 3 described above, the apex angle α is an acute angle. As another extreme case, the apex angle β may also be an obtuse angle, as in the case of Fig. 4. In it, the edges of the side opposite the apex angle β of the triangular central wire 5 are rounded by a radius B2, the distance S2 of the centers of the corresponding circles being larger than the sums of the radii. In this case, the radius of curvature C2 of the apex angle is smaller than the radii B2. Again, the roundings B2 and C2 are in the range of 40% to 120% of the radius of the outer wires and preferably 35 to 60% to 105% of the radius Z of the outer wires. In addition, the sides of the triangular center wire 5 are curved outwards in a cylindrical manner. Deviations between 8 and 9 9 -881; D3 and D2 are made small enough not to cause excessive deformation of the outer wires. These deviations D2 and D3 are, as before, about 5% to 45% of the radius A of the circle drawn around the circle, and preferably about 10% to 30% of this radius A of the circle. and the smaller rounding C2 results in a cylindrical curtain surface core portion forming a smaller radius R1.

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It is clear that the alternatives of Figures 3 and 4 can be taken to even more extreme implementations within the limits described above, or their intermediate forms can be formed. Thus, in the case of Figure 4, the circles B2 may be even further apart or may intersect. Likewise, circle C2 may be further away from circles B2, or it may intersect both. The curvatures of sides 8 and 9 must in each case be shaped so that the dimensions D2 and D3 are within a given range. Likewise, of course, the radii B2 and C2 must simultaneously be of a defined size. Intermediate embodiments of the embodiments of Figures 3 and 4 are understandably readily available when it is imagined that the circles B2 of Figure 4 are gradually moved toward each other until they coincide, resulting in the embodiment of Figure 3. One intermediate shape is also a 25-sided triangular type shape, which may include any or any of the roundings described below. When applying one of the central wires 5 described in principle in Figure 4, it is to be understood that the circles B2, which form one of the bases of the rounding, can either intersect, sideways 30 or be separated from each other as in the figure. It is clear that even with an alternative in which the radii of the circles B2 are smaller than the radius of the circle C2, a curtain surface according to the invention is obtained for the tendon braid. This is understandable because the larger radius R2 of the curtain surface is based on the interaction of the two circles B2 and the side 8 between them, which should simply be effectively larger than the third circle C2.

Claims (7)

10 f »8 81 S A tendon braid for concrete elements, which braid (10) consists of at least one central wire (2, 3; 4; 5) and a plurality of surface wires (1) wound around it, the diameters of which are substantially the same size, the central wire or wires running substantially without a twist in the longitudinal direction of the tendon braid, characterized in that the cross-section of the central wire (4; 5) is shaped or the braid (10) comprises a plurality of parallel center wires (2, 3) so arranged and dimensioned that the cross-sectional curtain surface (6) is formed by two R1, R2) of the combination of parts of the circle (Y1, Y2) and is thus not rotationally symmetric. Tension braid according to Claim 1, characterized in that the braid contains two approximately circular central yarns (2, 3) of different diameters, and of these the radius (B3) of the second central yarn is 5-15% larger than the radius (B3) of the second central yarn. 3). 20 Tension braid according to claim 1, characterized in that the braid comprises three approximately circular cross-sectional central yarns (2a, 2b, 3), of which at least one yarn has a radius 5-30% larger or alternatively smaller than the radius of the other central yarns. Tension braid according to Claim 1, characterized in that the braid comprises a central cross-sectional yarn (4; 5) with a substantially triangular cross-section, each side surface (7; 8, 9) of which is a dimension (D1, D2, D3) inwards from a circle drawn around the yarn. ), which is about 5-45% of the radius of this circle (A) and preferably about 10-30% of the radius of this circle (A). Tension braid according to Claim 4, characterized in that the triangular shape of the central wire (4; 5) corresponds to an isosceles triangle whose apex angle (α, S) between sides of the same length is in the range from about 2 to 150 °. i 11 A8819 Tension braid according to Claim 5, characterized in that the angle (α and S, respectively) between the triangular sides of the triangular shape of the central wire (4; 5) is preferably in the range from 5 to 30 ° or alternatively in the range from 90 to 120 °. 5 Tension braid according to one of the preceding claims, characterized in that the radii of curvature (B1, C1; B2, C2) of the corners of the central wire (4; 5) and the radii (B3, C3; B4, C4) of the central wires (2, 3), respectively. 40-120% of the radius (Z) of the outer wires and preferably 60-105% of the radius (Z) of the outer wires.