EP0855471B1 - Individually protected strand for suspended civil engineering structures, structures having such strands and method for manufacturing it - Google Patents

Abstract

The steel cable consists of strands made from twisted steel wires (7) inside an outer sleeve (9) of a flexible plastic. The wires are fitted inside the sleeve with spaces which are filled with a protective material (8). The sleeve (9) is made from a plastic selected from polyolefins and polyamides, such as high-density polyethylene, and the protective filler is an elastomer such as polybutadiene. The cable strand is made by coating the steel wires in the protective material, leaving no gaps between them. The outer surface of the protective material is coated with an agent which enables it to adhere to the outer sleeve by chemical interaction. The adhesive agent is, for example, from ethylene - acrylic ester - maleic anhydride terpolymers of polyethylenes.

Description

The invention relates to strands individually protected for suspended civil engineering works, structures comprising such strands, and methods of manufacture of these strands.

We know of individually protected strands comprising several twisted steel wires surrounded by a flexible plastic outer sheath, the twisted steel wires leaving inside this sheath of interstitial spaces which are filled by a protective material.

A sheath of an outer layer of a polymer comprising, between the polymer and the wire rope, a layer of interposed and co-extruded elastomer, is described in document EP 0 671 502 A.

These individually protected strands are usually used to make deck stays, and they have been shown to be particularly effective in protect these shrouds against corrosion.

The protective material used in these strands individually protected from the prior art is generally consisting of wax or grease, so that these individually protected strands cannot effectively transmit significant axial forces from their outer sheath to their steel wires twisted.

This is the reason why such strands individually protected cannot be used for carrying the supporting cables of suspension bridges, hanging blankets, or other hanging works, because such carrying cables must resume by friction efforts directed parallel to their axis, efforts which are transmitted by cable ties to which a civil engineering structure is suspended through lines.

In suspension bridges or suspended covers, we therefore use carrier cables formed by bundles of bare strands or strands of steel. These carrier cables are surrounded by a protective layer exterior which can be constituted by paint, bitumen or tubular sheath, but that layer protective is interrupted at the clamps, tight directly on steel.

• les colliers doivent être très fortement serrés sur les câbles porteurs, d'une part compte tenu de la médiocrité du coefficient de frottement acier sur acier et, d'autre part pour limiter les mouvements relatifs entre les brins d'acier, générateurs d'usure et de fatigue par "fretting corrosion" (également appelée "fatigue induite par petits débattements" ou "usure induite par petits débattements") : ce serrage intense nécessite des colliers très longs (par exemple jusqu'à 2 mètres) et massifs, serrés par de nombreux boulons,
• les phénomènes de fatigue par "fretting corrosion" ne sont jamais complètement évités, ce qui entraíne à la fois un desserrage des colliers et la rupture des brins constitutifs du câble porteur,
• et les phénomènes de corrosion chimique sont extrêmement fréquents.

This configuration has the following serious drawbacks:

• the collars must be very tight on the carrying cables, on the one hand taking into account the poor coefficient of friction steel on steel and, on the other hand to limit the relative movements between the steel strands, generators of wear and fatigue by "fretting corrosion" (also called "fatigue induced by small deflections" or "wear induced by small deflections"): this intense tightening requires very long collars (for example up to 2 meters) and massive, tightened by many bolts,
• the phenomena of fatigue by "fretting corrosion" are never completely avoided, which leads to both loosening of the collars and the breaking of the strands constituting the carrying cable,
• and chemical corrosion phenomena are extremely frequent.

The object of the present invention is in particular to offer an individually protected strand that is likely to be used in load-bearing cables of suspended civil engineering works, so as to avoid disadvantages mentioned above.

For this purpose, according to the invention, a strand individually protected from the genre in question is provided, as defined by the characteristics of the claim 1.

Thanks to this arrangement, effective the axial forces from the outer sheath of the stranded to its twisted steel wires, both by surface adhesion and shape adhesion of the elastomer on the outer sheath and on the twisted steel wires, and by resistance of the elastomer to shear.

In addition, when using such strands individually protected to constitute the carrying cables of a bridge or other suspended structure, it is no longer necessary to tighten the line clamps so as intense as in the prior art, because sheaths of individually protected strands have a good coefficient of friction.

In addition, the phenomena of fatigue by "fretting corrosion "are avoided since there is no more contact direct between the steel wires from one strand to another.

Finally, a carrying cable made up of strands according to the invention perfectly resists chemical corrosion.

• la matière plastique constituant la gaine est choisie parmi les polyoléfines et les polyamides,
• la matière plastique constituant la gaine est du polyéthylène haute densité,
• l'élastomère est du polybutadiène.

In preferred embodiments of the strand according to the invention, use is also made of one and / or the other of the following arrangements:

• the plastic material constituting the sheath is chosen from polyolefins and polyamides,
• the plastic material constituting the sheath is high density polyethylene,
• the elastomer is polybutadiene.

a) englober les fils d'acier torsadés dans le matériau protecteur, notamment par extrusion à chaud, sans laisser de vide entre les fils d'acier,

b) enduire la surface extérieure du matériau protecteur avec un agent de liaison capable de faire adhérer ce matériau protecteur à la matière plastique constituant la gaine, par liaison chimique,

c) et enrober le matériau protecteur dans la gaine, notamment par extrusion à chaud.

Furthermore, the subject of the invention is also a method of manufacturing an individually protected strand as defined above, this method comprising the steps consisting in:

a) include the twisted steel wires in the protective material, in particular by hot extrusion, without leaving a vacuum between the steel wires,

b) coating the outer surface of the protective material with a bonding agent capable of making this protective material adhere to the plastic material constituting the sheath, by chemical bonding,

c) and coat the protective material in the sheath, in particular by hot extrusion.

When the protective material of the strand is polybutadiene and that its sheath is made of polyethylene, the agent bonding agent can for example be chosen from terpolymers ethylene - acrylic ester - maleic anhydride and grafted polyethylenes.

Finally, the invention also relates to a suspended civil engineering structure, in particular suspension bridge or suspended cover, comprising at least two pylons, at least one carrying cable extending between two anchors on the ground and supported by the pylons, and a structure of civil engineering suspended from the carrying cable via lines which are each hung on a collar rigidly fixed to the carrying cable by tightening around this cable, characterized in that the carrying cable consists of at least one bundle of strands individually protected as defined above.

In such a civil engineering work, it can be advantageous to provide a protective jacket in material plastic interposed between the carrying cable and each necklace.

Other advantages of the invention will appear during the detailed description following of one of its embodiments, given to by way of nonlimiting example, with reference to the drawings joints.

• la figure 1 est une vue schématique générale d'un pont suspendu selon une forme de réalisation de l'invention,
• la figure 2 est une vue en coupe transversale d'un des torons individuellement protégés qui constituent le câble porteur du pont suspendu de la figure 1,
• la figure 3 est une vue en coupe transversale d'un des câbles porteurs du pont de la figure 1, avec un collier d'accrochage de suspente,
• et la figure 4 est une vue de détail de la figure 3.

In the drawings:

• FIG. 1 is a general schematic view of a suspension bridge according to an embodiment of the invention,
• FIG. 2 is a cross-sectional view of one of the individually protected strands which constitute the carrying cable of the suspension bridge of FIG. 1,
• FIG. 3 is a cross-sectional view of one of the carrying cables of the bridge in FIG. 1, with a suspension hooking collar,
• and FIG. 4 is a detailed view of FIG. 3.

The suspension bridge shown in Figure 1 conventionally comprises an apron 1, two pylons 2, two parallel carrier cables 3, only one of which is visible on the drawing, and a plurality of lines 4 which are attached to the cables 3, and which carry the apron 1.

The carrying cables 3 are stretched between two ground anchors 5 at both ends of the bridge (solid artificial anchors, rock anchors or the case anchorages at both ends of the deck if is a "self-anchored" suspension bridge), and they are supported by pylons 2.

The carrying cables 3 are preferably discontinuous in line with pylons 2, with anchoring on these pylons, for example as explained in more detail in the request French patent filed on the same day as this patent application and entitled "Improvements to suspension bridges and their construction processes ".

Each carrying cable 3 comprises one or more cylindrical bundles of strands 6 individually protected, one of which is shown in Figure 2.

Each of these strands is made up of several twisted steel wire 7, possibly galvanized, which are here seven in number, and are drowned in a elastomer 8 such as polybutadiene or the like.

Elastomer 8 is itself covered by a outer sheath 9 of flexible plastic which can be a polyolefin, especially high polyethylene density, or a polyamide.

The elastomer 8 adheres to the twisted wires 7, by surface and form adhesion, in particular when the wires 7 are degreased and free of soap drawing.

In addition, this elastomer is bonded, preferably by chemical bond, with the polyethylene sheath 9 high density.

Thus, the sheath 9 is integral with the steel wires 7, which allows in particular that the applied forces to this sheath parallel to the axis of the strand 6 are suitably transmitted to steel wires.

The efforts in question are essentially applied to the sheaths 9 by the collars 10 to which are hanging the lines 4 (see figures 3 and 4).

In fact, the lines 4 exert on the collars 10 downward pulling forces which have a tangent component to the carrying cable 3, directed in the direction of the slope of the carrying cable: this are these tangential forces which are transmitted by friction with the sheaths 9 of the strands of the carrying cable.

Each of the above-mentioned collars 10 forms a jaw made up of two metal shells 12, 13 substantially semi-cylindrical, which are tight around the cable 3 by means of bolts 14.

Preferably, the carrying cable 3 is surrounded by a plastic folder 15 to the right of each collar 10, so as to prevent the sheaths 9 of the strands components of the carrying cable are injured by the collar 10, in particular when adjusting the position of this necklace.

The shirt 15 can consist for example of two semi-cylindrical shells in high polyethylene density, and preferably interstitial spaces between the periphery of the carrying cable 3 and the shirt 15 are filled with solid material 16 in synthetic foam, especially neoprene foam, to obtain a good distribution of the clamping forces of the collar 10 on the entire carrying cable 3.

In the following, a particular example will be described of the individual strand manufacturing process protected 6.

• on englobe d'abord les fils d'acier torsadés 7 dans l'élastomère 8 par extrusion à chaud (c'est-à-dire en faisant passer la torsade de fils 7 dans une filière alimentée en élastomère à l'état fluide ou pâteux), de préférence en exerçant une certaine torsion sur l'ensemble de ces fils d'acier, de façon à les détorsader légèrement pour favoriser la pénétration de l'élastomère entre les fils 7,
• on enduit simultanément (par coextrusion) la surface extérieure de l'élastomère 8 avec un agent de liaison capable d'adhériser cet élastomère 8 à la matière plastique constituant la gaine 9, par liaison chimique,
• et on enrobe finalement le matériau protecteur 8 dans la gaine 9 par extrusion à chaud.

According to this process,

• firstly the twisted steel wires 7 are included in the elastomer 8 by hot extrusion (that is to say by passing the twisted wires 7 through a die supplied with elastomer in the fluid or pasty state ), preferably by exerting a certain twist on all of these steel wires, so as to untwist them slightly to promote the penetration of the elastomer between the wires 7,
• the outer surface of the elastomer 8 is coated simultaneously (by coextrusion) with a bonding agent capable of adhering this elastomer 8 to the plastic material constituting the sheath 9, by chemical bonding,
• and the protective material 8 is finally coated in the sheath 9 by hot extrusion.

When the protective material 8 is polybutadiene or similar and that the sheath 9 is made of polyethylene or similar, for example, it can be used as a bond an ethylene terpolymer - acrylic ester - maleic anhydride, for example that marketed by ATOCHEM (FRANCE) under the brand "LOTADER", or another grafted polyethylene, for example the one sold under the brand name "OREVAC PE" by the same company ATOCHEM, or any other suitable liaison agent.

Claims (9)

1. Individually protected strand comprising a plurality of cable-twisted steel wires (7) surrounded with an external sheath (9) made of flexible plastic material, the cable-twisted steel wires (7) leaving, in the interior of this sheath, interstitial spaces that are filled up with a protective material (8), characterized in that the protective material is an elastomer (8) adhering to the cable-twisted steel wires (7) and to the internal surface of the sheath (9).
2. Individually protected strand according to Claim 1, in which the plastic material constituting the sheath (9) is chosen from among the polyolefines and the polyamides.
3. Individually protected strand according to Claim 2, in which the plastic material constituting the sheath (9) is high density polyethylene.
4. Individually protected strand according to any one of the foregoing Claims, in which the elastomer (8) is polybutadiene.
5. Process for manufacturing an individually protected strand according to any one of the foregoing Claims, comprising steps consisting of:

   a) incorporating the cable-twisted steel wires (7) into the protective material (8) without leaving any empty space between the steel wires,

   b) coating the exterior surface of the protective material (8) with a bonding agent capable of causing the protective material (8) to adhere to the plastic material constituting the sheath (9) by chemical bonding,

   c) and enclosing the protective material (8) in the sheath (9).
6. Process according to Claim 5, in which the protective material (8) is made of polybutadiene and the sheath (9) is made of polyethylene.
7. Process according to Claim 6, in which the bonding agent is chosen from among the ethylene - acrylic ester - maleic anhydride terpolymers and the grafted polyethylenes.
8. Civil engineering structure comprising at least two pylons (2), at least one bearer cable (3) extending between two anchorage points at the ground (5) and supported by the pylons, and a civil engineering structure (1) hung from the bearer cable through the intermediary of suspensions (4) which are themselves each held in a collar (10) rigidly attached to the bearer cable (3) by clamping around this cable, characterised in that the bearer cable (3) consists of at least one bundle of individually protected strands (6) according to any one of the Claims 1 to 4.
9. Civil engineering structure according to Claim 8, in which a protective liner sleeve (15) made of plastic material is interposed between the bearer cable (3) and each collar (10).

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