NO318325B1 - Suspension device for a building structure - Google Patents

Abstract

The cable is made from a number of strands (24) enclosed in individual sleeves (25) with bulges (26) at regular intervals and filled with a self-hardening material such as a cement mortar, a polymer or resin. The bulges in the sleeves making up one cable are offset lengthwise relative to one another.

Description

The present invention relates to a suspension device for building structures, especially suspension bridges and suspension decks.

Generally speaking, suspension devices for such constructions include at least one suspension cable anchored at its two ends, and holders which are themselves connected to a ring attached around the suspension cable. The holders transfer the structural force to the suspension cable. Most often they are not at all perpendicular to the suspension cable, with the result that at least some of the hoops exert a force on the suspension cable that has a component tangential to the suspension cable, a so-called tangential force.

Usually the suspension cable is made up of a bundle of bare steel wires or strands, where the suspension cable is coated with an outer protective layer of paint or asphalt, or of a tubular jacket. This protective layer is generally interrupted in the longitudinal station for the wreaths, which are tightly attached directly to the steel of the suspension cable.

This extremely tight fastening of the wreath fulfills two main functions:

- To take up by friction the tangential force to which the ring is exposed, and on

due to the low coefficient of friction between steel elements, the attractive force of the wreath must be relatively high; and - to reduce relative movements between the tensioned strings (steel wires or strings) that make up the suspension cable. Since these strands are bare, their relative movement generates wear and fatigue by fretting corrosion (fatigue or wear induced by minor displacements), which causes both the rings to loosen and some strands to possibly wear off.

These prior art suspension structures have the following disadvantages:

- The extreme tightening of the wreaths requires very long (eg

up to two meters) and heavy wreaths, tightened with the help of numerous bolts;

- the effects of fretting corrosion are never completely prevented; and

- it is often observed that the corrosion spreads under the outer protective layer of the cable.

In EP-A-0 789 110, it is proposed to improve the homogeneity of the tightening by placing inserts of a shape adapted to fill the spaces between the strands inside the wreaths, between the layers of strands in the suspension cable. These inserts located under the hoops transmit tightening force over the entire circumference of the strings, in an almost hydrostatic manner, instead of concentrating it on their lines of mutual contact.

French Patent No. 2 739 112 describes a way to allow the tightening of the hoops of the suspension cables to be reduced: Auxiliary connecting cables connect the hoops to each other so as to compensate the static part of the tangential force due to the nominal load of the structure. The dynamic part (variable overloads depending on traffic, weather conditions and the like) is taken up by the tightening force from the rings on the suspension cable. This process requires that the successive connection cables must be tensioned in accordance with specified tension values.

A main aim of the present invention is to propose a simple and effective way to deal with the problem of the tangential force to which the suspension cable is exposed.

The invention therefore proposes a suspension device for a building structure, including at least one suspension cable and holders attached to the suspension cable by means of hoops, where the suspension cable includes a bundle of strings anchored at its ends, and tensioned by means of the structural load transferred by means of the holders, and a mantel structure that contains the strings, and on which the wreaths are mounted. According to the invention, the mantle structure, parallel to the suspension cable, has sufficient compressive strength to absorb tangential components of the forces exerted by the wreaths on the cable, due to the transfer of load by means of the holders, while essentially transferring no tightening force to the strings .

The tangential forces are taken up by means of a longitudinal compression of the mantle structure rather than by friction on the tensioned strings. The result is that the tightening of the hoops, which is not transferred to the strings, can be significantly reduced or even eliminated. A large number of disadvantages of suspension constructions due to the extreme tightening of the hoops are therefore eliminated. In particular, it is avoided to expose the tensioned strings to strong clamping forces located under the wreaths, thereby improving the durability of the cable.

It should be noted that the presence of the tensioned strings inside the mantle structure gives the latter a very good resistance to distortion. This behavior can be compared to the behavior of the jacket of a bicycle's brake cable: when the brake lever is activated, it is pressed hard together at its two ends, but the jacket has a good resistance to distortion due to the fact that it contains the tensioned cable.

A major advantage that the invention provides is that the strings are extractable and replaceable one by one without the wreaths having to be taken apart, since these strings are no longer pinched under the various wreaths. This allows; - occasional testing to be performed by extracting one or more strings and analyzing them to detect possible deterioration; and - when the suspension cable has to be replaced due to wear or corrosion of the strings, this replacement can be carried out string by string, which avoids having to install a second cable before removing the first cable. The latter installation makes replacement operations particularly complicated in cases with existing suspension structures.

In a preferred embodiment, the sheath structure of the suspension cable includes an outer tube, individual sheaths each containing one of the cable's strands and a lubricant, and a hardened filler product occupying the space between the outer tube and the individual sheaths.

The strings are often effectively protected against corrosion and against the effects of fretting corrosion. The hardened filling product forms around these a matrix that resists compression in the longitudinal direction to absorb tangential forces.

In particular embodiments are:

- The strung strings are made of metal and are coated with a grease or a wax which constitutes said lubricants, or alternatively these strings are made of greased or grown metal, and each is surrounded by a first sheath of plastic material which itself becomes the compartment in a individual mantle with position between the lubricant; - the individual sheaths of the strands have bulges arranged in the direction of the cable; - the outer tube of the cable has an inner surface provided with transverse recesses in the longitudinal station for at least some of the wreaths; - the outer tube of the cable has an outer surface provided with transverse recesses in the longitudinal station for at least some of the collars which are themselves provided with complementary recesses to be connected to the outer tube; - includes the outer tube of the cable in the longitudinal station of the wreaths, to which reference is made in one or the other of the two previous paragraphs, sections which

are provided with transverse recesses, welded to smooth sections extending between the flanges.

Other distinctive features and advantages of the present invention will emerge from the following description of non-limiting embodiments, with reference to the attached drawings, where: Figure 1 is a schematic diagram of a suspension bridge;

figure 2 is a cross-sectional view of a suspension cable and coupling ring for a holder for a device according to the invention;

Figures 3 and 4 are cross-sectional views of two examples of strings that can be used in a device according to the invention;

figure 5 is a schematic side view of strings which are usable in a device according to the invention;

figures 6 to 8 are longitudinal schematic cross-sections of a suspension cable's outer tube which can be used in a device according to the invention.

The invention is described below for use in suspension bridges, without this being limiting.

The suspension bridge shown in Figure 1 conventionally includes a deck 1, two towers 2, two parallel suspension cables 3, of which only one can be seen in the drawing, and holders 4 which are connected to the cables 3 and which support the deck 1.

The suspension cables 3 are suspended between two ground anchors 5 at the two ends of the bridges (artificial anchor blocks, anchors in the rock, or anchors at the two ends of the deck in the case of "self-anchored" suspension bridges), and they are supported by the towers 2. The suspension cables 3 are preferably interrupted in the longitudinal stations in the form of the towers 2, with anchorage on these towers.

Each suspension cable 3 includes one or more bundles of individually protected strands 6, an example of which is shown in Figure 3.

In each of the individually protected strings 6, the relevant string 7 constitutes the element which will be affected by tension. The string 7 is made up of several twisted steel wires (number seven in the example shown). The steel in the wires may have been subjected to an anti-corrosion process (galvanization, coated with Zn-Al alloy or similar). The string 7 is encased in a lubricating material 8 which is itself covered with an outer sheath 9 of flexible plastic material, for example of high-density polyethylene (HDPE). The lubricating material also protects the steel of the wires against corrosion. This is typically a fat or a wax.

The individually protected strands 6 of the suspension cable 3 are the space of an outer tube 10 which extends over the entire length of the suspension cable between its two anchored ends. A hardened filler product 12 fills the space left between the outer tube 10 and the individual sheaths 9 of the strings (Figure 2). The outer tube 10 can be made of metal or of a plastic material such as HDPE. The filling product 12 can be injection mortar, a polymer or a resin.

Each holder 4 has its lower end attached to the deck 1 of the bridge, and its upper end attached to the suspension cable 3 by means of a collar 13, each collar 13 including, for example, two semi-cylindrical bushings 13a, 13b which are bolted to each other around the suspension cable 3, where the upper end of the holder 4 is hingedly connected to one of the two bushings 13a.

The sheath structure containing the strands 7 of the suspension cable 3, made up of the individual sheaths 9 of these strands, of the matrix formed by the hardened filling product 12 and of the outer tube 10, prevents the transmission to the strands 7 of clamping forces generated by the fastening of the hoops which transfer the load to which each individual holder 4 is exposed to.

Tangential forces due to the fact that the supports 4 are perpendicular to the suspension cable 3 are absorbed by this jacket structure due to its structural strength parallel to the direction of the suspension cable. With the filling materials 12, such as injection mortar or resin, the required compressive strength, which is of the order of a few tenths of MPa, is easily achieved. Alternatively, the material 12 can be a resin slurry.

To install the suspension cable 3, it is necessary to start with the outer tube 10, in which an individually protected string has been passed through. The metal element 7 of the string 6 is anchored at both ends of the cable 3. The other individually protected strings 6 are then passed through successively by pulling them by means of a shuttle which slides alternately in both directions inside the pipe 10. After each string has been passed through, its two ends become anchored. After all the individually protected strings 6 have been passed through and anchored, the filler product 12 is injected into the pipe 10 from the lowest point of the suspension cable 3. This injection is carried out under pressure, by providing draft at the high points, i.e. in the anchoring devices mounted on the break bars 2. After the injected product 12 has hardened, the holders can begin to be connected by means of their collars 13.

The strung up strings 7 on the suspension cable can be individually replaced without dismantling the wreaths 13, for example in the following way. Initially, access is gained to a first end of string 7, which protrudes from one of the anchor blocks,

and which has previously been in use, then welding it to the end of a new string. The anchor claw is then pulled back from string 7 at the first end after noting the stretch of this string. This string becomes slack. Access is then gained to a second end of this string 7, projecting from the opposite anchor block, the anchor claw is withdrawn from it, and this other end of the string 7 is pulled until it is completely removed from its individual sheath 9 and replaced by the new string. This is then stretched using a jack to the desired tightening value, and then anchored. Lubricant 8 present inside the individual sheath 9 allows easy extraction of the strand 7. A lubricant such as a grease is placed around the new strand as it penetrates the sheath 9, to facilitate this penetration, to protect the new string against corrosion, and to facilitate its subsequent replacement.

It is therefore possible to replace each of the strings 7 in the suspension cable 3 by means of

simple operations, which do not prevent the bridge from being used as normal for traffic.

Figure 4 shows another example of an individually protected string 16 which can be used in a suspension device according to the invention. The string in question 7 is coated with a protective material 18, such as wax or grease, and is surrounded by a first sealing layer of plastic material 19 which is capable of, for example, conforming to the shape of the circumference of the string 7, as shown in figure 4. It is a lubricant 20

such as a grease between the first jacket 19 and the individual jacket 21 on the string 16.

The installation of the suspension cable 3 with an individually protected string 16 according to Figure 4 can be carried out in the previously described manner. For the replacement of a strand, the individual sheaths 21 remain in place in the matrix formed by the filling product 12, and it is the unit formed by the strand 7, the protective material 18 and the first sheath 19 that is replaced with a similar unit.

The use of the individually protected strands 16 according to Figure 4 makes it possible to ensure that the metal wires in each strand 7 installed as a replacement for a previous strand can be completely coated with a layer of protective material 18, and to prevent unwanted particles from coming into contact with these metal wires during the replacement operation.

Figure 5 schematically shows another individually protected fringe structure 24 which can be used in a device according to the invention. The individual sheath 25 on these strings 24 has bulges 25 placed in the direction of the suspension cable 3. These separately placed bulges 26 are displaced in the longitudinal direction in relation to each other when the individually protected strings 24 are placed in the outer tube 10 of the cable. They therefore provide intervals /' between the individual sheaths 25 of the strands which allow the injected filler 12 to be suitably guided between all the strands 24 to form a consistent matrix after curing.

To ensure transfer of tangential forces from the hoops to the jacket structure of the suspension cable 3, frictional forces can be used by applying moderate tightening to the hoops 13 (which are not transferred to the tensioned wires 7). It is advantageous for the inner and/or outer surface of the outer tube 10 in the cable 3 to be provided with transverse recesses in the longitudinal direction of the rings where such tangential forces are exerted. The radial tightening of the rings can then be small or zero.

Such versions of the outer tube 10 are shown in figures 6 to 8. The tube 10 is made up of smooth sections 30 which extend between the rings, and of sections 40, 50, 60 which are located in the rings 13. These sections 40, 50, 60 is welded end-to-end with the smooth sections 30. They can be formed during casting, while the smooth sections 30, on the other hand, are conventionally produced by extrusion.

In the example of Figure 4, the outer surface of the tube section 40 has circumferential grooves 41, and the inner surface of the collar 13 has complementary grooves 42 to connect to the outer tube 10 and transmit the tangential force.

In the example in Figure 7, the wall of the pipe section 50 has bellows-like grooves, which result in transverse recesses 51, 52 on its inner and outer surfaces. The tangential force exerted by the ring 13, where the inner surface has matching pits 53, is transferred almost directly to the hardened filler material inside the tube 10.

In the example in Figure 8, the tube section 60 has grooves 61 on its inner surface, which transmit tangential force to the injected and hardened material inside the tube 10. An annular projection 62 is present on the outer surface of the tube section 60, and the inner surface of the flange 13 has a complementary annular pit 63 which connects to this projection 62 to transmit tangential force.

Claims (7)

1. Suspension device for a building structure, including at least one suspension cable (3) and holders (4) attached to the suspension cable (3) by means of hoops (13), where the suspension cable (3) includes a bundle of strings (7) anchored at its ends and tensioned by means of the structural load transferred by means of the holders (4), and a casing structure (9,10,12) including the strings (7), and on which the hoops (13) are mounted, which casing structure (9,10,12) has, in parallel with the suspension cable (13), sufficient compression resistance to accommodate the tangential force components exerted by the rings (13) on the cable (3) due to the transfer of load from the supports (4), while transmitting essentially no tightening force on the strings (7), characterized in that the jacket structure includes an outer tube (10), individual jackets (9,21,25), each including a strand (7) of the cable (3) and a lubricant (8; 20), and a cured filling product (12) which occupies the space between the outer tube (10) and the indivi dueling mantles. 2. Device according to claim 1, characterized in that the strings (7) are made of metal and coated with a fat or a wax which constitutes said lubricant (8). 3. Device according to claim 1, characterized in that the strings (7) are made of greased or waxed metal, and each of which is surrounded by a first mantle (19) of plastic material which is itself housed in an individual mantle (21) with a position between the lubricant (20). 4. Device according to any one of the preceding claims, characterized in that each individual jacket (25) has bulges (26) arranged along the cable direction. 5. Device according to any one of the preceding claims, characterized in that the outer tube (10) has an inner surface provided with transverse recesses (51, 61) in the longitudinal stations for at least some of the rings (13). 6. Device according to one of the preceding claims, characterized in that the casing structure includes an outer tube (10) which has an outer surface provided with transverse recesses (41; 52; 62) in the longitudinal station for some of the rings (13) which themselves is provided with complementary recesses (42; 53; 63) to connect the outer tube. 7. Device according to claims 5 or 6, characterized in that the outer tube (10) includes sections (40, 50, 60) provided with transverse recesses (41; 51, 52; 61, 62) in the longitudinal station for said rings (13 ), which sections (40, 50, 60) are welded to smooth sections (30) extending between the rings (13).