EP1211350B1 - Individually protected strand, its utilisation in construction and method for its manufacture - Google Patents

Description

The present invention relates to strands individually protected used in works of civil engineering, in particular to pre-stress or suspend portions of work.

These strands include an assembly of wires metallic twisted together, which are most often number of seven. Metal wires are frequently subjected to electrochemical treatment (galvanization, galfanisation, ...) providing a certain resistance to corrosion.

Uncoated strands are commonly used, ensuring that they are not placed in a corrosive environment. These strands are set up directly in concrete, or in collective ducts filled with cement grout or grease or wax oil. Cement passivity or non-corrosivity of petroleum products strengthens protection against corrosion.

We also know strands individually protected by a plastic sheath, usually a high density polyethylene (HDPE) or an epoxy, which creates a tight barrier around the metal wires. A filler, of several types (wax, grease, polymer ...), fills the existing gaps between the metal wires and the individual sheath for reinforce the protection of the strand against corrosion.

The filling product allows either a sliding metallic wires stranded relative to their sheath individual (sheathed-greased or sheathed-waxed strand), either otherwise an adhesion to transmit efforts of shear between the sheath and the strand (coherent strand).

In the coherent strand, the filling product is typically a polymer adhered to the wires and to inside the sheath. The coherent strand is notably usable when it is necessary to transmit tangential forces from the sheath to the metal wires, this which is the case for example in cables carrying suspension bridges in which the load transmitted by each hanger causes a tangential force on the cable at the level of the hanging strap (see EP-A-0 855 471).

(a) améliorer le comportement en fatigue du toron en lubrifiant les contacts entre ses fils métalliques ;

(b) éviter que la tension à laquelle le toron est soumis engendre, compte tenu de la forme du toron, des concentrations de contrainte de cisaillement et/ou de traction dans certaines portions du toron, ce qui risque de provoquer une fissuration de la gaine et donc une perte d'étanchéité exposant le métal aux agents corrosifs ;

(c) dans certaines configurations, permettre le remplacement des torons un par un, la gaine restant en place dans la structure.

In the sheathed-greased or sheathed-waxed strand, the filling product is a lubricant, which has several advantages:

(a) improve the fatigue behavior of the strand by lubricating the contacts between its metallic wires;

(b) avoid that the tension to which the strand is subjected generates, taking into account the shape of the strand, concentrations of shear and / or tensile stress in certain portions of the strand, which risks causing cracking of the sheath and therefore a loss of tightness exposing the metal to corrosive agents;

(c) in certain configurations, allow the strands to be replaced one by one, the sheath remaining in place in the structure.

In service, the cable comprising one or more sheathed-greased or sheathed-waxed strands is subjected to voltage variations and temperature variations. These variations cause different lengths of the sheath and stranded wires since the plastic and metal generally do not have the same coefficients elasticity and thermal expansion.

In particular, the sheath usually has a coefficient of thermal expansion much higher than the sons. If we consider the case of steel and HDPE commonly used in this kind of strand there is a ratio of around 20 between the two coefficients of thermal expansion. This may result in damage sheath that gets too long in hot weather, or conversely a loss of tightness in the portions end of the cable when it is cold, the sheath is retracting too much.

US 4,623,504 describes such a strand composed of a group twisted metal strands surrounded by a sheath plastic material. An anti-corrosion product fills internal gaps located between the twisted strands. However, this product superficially covers the strands, without extending to the inside of the sheath, so that this strand does not escape the aforementioned effects related to the difference in elasticity and expansion coefficients thermal between the sheath and the strands. The object of the present invention is in particular to avoid these disadvantages while retaining at least some of the advantages of the sheathed-greased or sheathed-waxed strand.

A strand according to the invention comprises a group of twisted metal strands, a plastic sheath containing said group, and a flexible filling product filling internal gaps located between the twisted strands of the group and a peripheral gap located between the periphery of the group. and the inside of the sheath. According to the invention, said peripheral gap has, in a cross section of the strand, an area between P × e _min and 0.6 × S2, where P is the outer perimeter of the group of strands, e _min = 0.05 mm and S2 is the cumulative area of the intervals between the periphery of the grouping and the smallest circle in which the grouping is inscribed.

Thanks to these provisions it is possible to obtain "semi-adherent" strands, in which the quantity regulated flexible filling product allows keep the advantages (a) and (b) of the sheathed-greased strand while ensuring that the individual sheath follows the macroscopic deformations of the metal strands.

The helical ribs on the face inner of the sheath penetrate into the grooves formed between the adjacent peripheral strands. Cooperation between these ribs and these grooves allows the adaptation of macroscopic deformations. The amount of product from filling is adjusted so that this penetration does not is not too large, which could block the sheath on the strands by form adhesion and therefore to generate constraints in the sheath, in particular shear, likely to tear it.

In a preferred embodiment of the invention, the sheath of the strand has a thickness of at least  / 5, where  is the diameter of strands located at the periphery of the grouping of twisted strands.

Another aspect of the invention relates to a use of a strand as defined above as structural element working in traction in a construction work. The strand can in particular make part of a shroud of a structure suspension system or a prestressing cable for the structure.

• enrober un groupement de brins métalliques torsadés avec un produit souple de remplissage de façon que ledit produit comble des interstices internes situés entre les brins torsadés du groupement et déborde sur la périphérie du groupement ;
• essuyer la périphérie du groupement enrobé de façon à laisser une quantité régulée de produit de remplissage par unité de longueur du groupement, ladite quantité représentant un volume par unité de longueur compris entre S1 + (P × e_min) et S1 + (0,6 × S2), où S1 est l'aire cumulée desdits interstices internes sur une section transversale du toron, P est le périmètre extérieur du groupement de brins torsadés, e_min = 0,05 mm et S2 est l'aire cumulée des intervalles compris entre la périphérie du groupement et le plus petit cercle dans lequel s'inscrit le groupement ;
• extruder une gaine en matière plastique autour du groupement de brins enrobé de ladite quantité de produit de remplissage.

A third aspect of the invention relates to a method of manufacturing a strand, comprising the following steps:

• coating a group of twisted metal strands with a flexible filling product so that said product fills internal interstices located between the twisted strands of the group and projects beyond the periphery of the group;
• wipe the periphery of the coated group so as to leave a regulated quantity of filling product per unit length of the group, said quantity representing a volume per unit length between S1 + (P × e _min ) and S1 + (0.6 × S2), where S1 is the cumulative area of said internal interstices on a cross section of the strand, P is the outer perimeter of the group of twisted strands, e _min = 0.05 mm and S2 is the cumulative area of the intervals between the periphery of the group and the smallest circle in which the group is inscribed;
• extrude a plastic sheath around the group of strands coated with said quantity of filling product.

The wiping step is advantageously accomplished at by means of a free rotating template, through which passes the group of coated strands.

• la figure 1 est une vue en coupe transversale d'un toron selon l'invention ;
• la figure 2 est une vue en coupe transversale du groupement de brins métalliques de ce toron ;
• la figure 3 est un schéma d'une installation adaptée à la mise en oeuvre d'un procédé selon l'invention ; et
• la figure 4 est un schéma de moyens d'essuyage de l'installation de la figure 3.

Other characteristics and advantages of the invention will appear during the following description of one of its embodiments, given by way of nonlimiting example, with reference to the attached drawing, in which:

• Figure 1 is a cross-sectional view of a strand according to the invention;
• Figure 2 is a cross-sectional view of the group of metal strands of this strand;
• FIG. 3 is a diagram of an installation suitable for implementing a method according to the invention; and
• FIG. 4 is a diagram of means for wiping the installation of FIG. 3.

The strand 1 shown in Figure 1 consists of several strands 2 of steel twisted together, which are here seven in number, namely a central strand and six strands peripheral devices.

The group of twisted strands 2 is contained in an outer sheath 4 of flexible plastic which may be a polyolefin, in particular HDPE, or else a polyamide.

• des interstices internes 5 de section transversale en forme de triangle curviligne dont les côtés sont constitués par des portions de circonférence de trois brins adjacents ;
• un interstice périphérique 6 situé entre les brins périphériques du toron et la face intérieure de sa gaine 4.

A flexible filling product 3, for example an amorphous polymer, a wax or a petroleum grease, fills the interstices defined by the strands 2 inside the sheath. This product 3 advantageously has lubrication properties. The aforementioned interstices include:

• internal interstices 5 of cross section in the shape of a curvilinear triangle, the sides of which consist of circumference portions of three adjacent strands;
• a peripheral gap 6 located between the peripheral strands of the strand and the inner face of its sheath 4.

Referring to Figure 2, we denote S1 the area cumulative of the aforementioned curvilinear triangles corresponding to the internal interstices 5, which are six in number the example considered. On the other hand, we denote S2 the area cumulative, in a cross section of the strand, of intervals 7 between the periphery of the grouping of steel strands 2 and the smallest circle C in which this group is registered. These intervals 7 are also at number of six in the example considered, the circle C being tangent to the six peripheral strands of the strand. We finally note P the outer perimeter of the group of strands and  the diameter of the peripheral strands. A typical value is  = 5 mm, the central strand having a diameter slightly higher, for example 5.7 mm.

The peripheral gap 6 has, in the cross section of the strand, an area between P × e _min and 0.6 × S2, where e _min represents a minimum thickness of product 3, which is equal to 0.05 mm. The minimum thickness e of the outer sheath 4 is preferably  / 5 or more.

To make such a strand, we start from a group stranded strands obtained by conventional methods of wire drawing. These strands 2 may have been, in known manner, subjected to electrochemical treatment such as galvanization or galfanisation, aimed at improving their corrosion resistance.

Referring to Figure 3, we untwist a section of the strand before passing it through the extrusion die 10 of the plastic material of the sheath 4, in order to separate its strands 2. This can be done by tightening the ends of the section in two jaws 11 subjected to a torque relative torsion in the opposite direction of the pitch stranding. The flexible filling product is introduced by projection or injection into the untwisted section. After release of the jaws 11, the strands tighten in trapping product 3 in internal gaps 5 and by overflowing this product on the periphery of the grouping of strands. We then circulate the section thus treated in a wiping template 12 used to leave the correct quantity of product 3 on the group of twisted strands. Downstream of the template 12 is the sheath plastic injection system 16 4 then the extrusion die 10 through which the strand is pulled to define its outer shape as well as the thickness e of the sheath.

The quantity of product 3 left by the wiping template 12 represents, per unit length of strand, a volume of between S _min = S1 + (P × e _min ) and S _max = S1 + (0.6 × S2) in order to satisfy the aforementioned condition on the dimension of the peripheral gap 6.

The wiping template 12 is illustrated in FIG. 4. It is mounted on the inner ring of a ball bearing 13 so as to be free to rotate. The strand coated with the product 3 passes through an opening 14 in the template 12, the area of which is between S + S _min and S + S _max , where S is the cumulative area of the sections of the seven strands 2. The shape of this opening 14 follows that of the group of strands associated with the peripheral gap 6. Its periphery thus has six teeth 15 which are housed in the grooves existing between the peripheral strands of the strand. The free rotation of the template 12 when the strand is pulled allows these teeth 15 to follow the helical path of the grooves while maintaining the desired quantity of product 3.

The strand thus produced is adapted to form a structural element working in traction in a construction work, which meets the requirements well exposed in the introduction. It will be advantageously used in guy lines (see for example EP-A-0 323 285) or prestressing cables.

Claims (8)

1. Strand comprising a group of twisted metal wires (2), a plastic sheath (4) containing said group, and a pliant filling compound (3) which fills internal interstices (5) lying between the twisted wires of the group and a peripheral interstice (6) lying between the periphery of the group and the inner face of the sheath, characterized in that said peripheral interstice has, in a cross section of the strand, an area of between P × e_min and 0.6 × S2, where P is the external perimeter of the group of wires, e_min = 0.05 mm and S2 is the cumulative area of the gaps (7) lying between the periphery of the group and the smallest circle (C) within which the group is inscribed.
2. Strand according to Claim 1, wherein the sheath (4) has a thickness (e) of at least /5, where  is the diameter of the wires lying at the periphery of the group.
3. Use of a strand according to Claim 1 or 2 as structural element working in tension in a building structure.
4. Use according to Claim 3, wherein the strand (1) forms part of a stay cable of a suspension system for the structure.
5. Use according to Claim 3, wherein the strand (1) forms part of a pre-stressing cable of the structure.
6. Process for manufacturing a strand (1), comprising the steps of:

   coating a group of twisted metal wires (2) with a pliant filling compound (3) so that said compound fills internal interstices (5) lying between the twisted wires of the group and protrudes at the periphery of the group;

   wiping the periphery of the coated group so as to leave a regulated amount of filling compound per unit length of the group, said amount representing a volume per unit length of between S1 + (P × e_min) and S1 + (0.6 × S2), where S1 is the cumulative area of said internal interstices on a cross section of the strand, P is the external perimeter of the group of twisted wires, e_min = 0.05 mm and S2 is the cumulative area of the gaps (7) lying between the periphery of the group and the smallest circle (C) within which the group is inscribed;

   extruding a plastic sheath (4) around the group of wires coated with said amount of filling compound, so that the filling compound fills a peripheral interstice (6) lying between the periphery of the group and the inner face of the sheath.
7. Process according to Claim 6, wherein the wiping step is carried out by means of a pivotally mounted template (12), through which the coated group of wires is fed.
8. Process according to Claim 6 or 7, wherein the sheath (4) is given a thickness (e) of at least /5, where  is the diameter of the wires lying at the periphery of the group.

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