Fire protection device for a structural cable

Abstract

A fire protection device for a structural cable is proposed including taught metal reinforcements (32) and having a first stretch (41), a second stretch (42) and a connection zone (40) of a collar (30) located between the first and second stretches. The fire protection device comprises a protective mat (34) surrounding the structural cable (16) in the first and second stretches (41, 42) and interrupted in the connection zone (40), and a thermally insulating ring (36) more rigid than the protective mat (34), arranged between the reinforcements (32) and the collar (30) in the connection zone (40) and cooperating with the protective mat in order to provide the reinforcements with a continuous thermal protection along the first stretch (41), of the connection zone (40) and of the second stretch (42).

Claims

1. A fire protection device for a structural cable of a construction work, with the structural cable comprising taught metal reinforcements and having a first stretch, a second stretch and a connection zone of a collar located between the first and second stretches, with the fire protection device including: a protective mat surrounding the structural cable at least in the first and second stretches and interrupted in the connection zone; and a thermally insulating ring more rigid than the protective mat, arranged between the reinforcements and the collar in the connection zone and cooperating with the protective mat in order to provide the reinforcements with a continuous thermal protection along the first stretch, of the connection zone and of the second stretch.

2. The fire protection device according to claim 1, wherein the insulating ring comprises several elements assembled around reinforcements, in mutual contact along surfaces lined with a firebreak seal.

3. The fire protection device according to claim 1, wherein a deviator tube made of plastic material is placed between, the insulating ring and the reinforcements in the connection zone.

4. The fire protection device according to claim 1, wherein the insulating ring is made from a fibre-reinforced concrete.

5. The fire protection device according to claim 4, wherein the fibre-reinforced concrete includes metal fibres and polypropylene fibres.

6. The fire protection device according to claim 1, wherein the protective mat is comprised of several segments arranged end-to-end in at least one of the first and second stretches of the structural cable, with an overlay mat being placed around two adjacent segments in order to pride the continuity of the thermal protection.

7. The fire protection device according to claim 1, wherein the protective mat is placed longitudinally in contact with the insulating ring on the side of the first stretch and on the side of the second stretch.

8. The fire protection device according to claim 1, wherein the protective mat has a portion that has a longitudinal overlay with the thermally insulating ring, between the reinforcements and the thermally insulating ring.

9. The fire protection device according to claim 1, wherein an intumescent material is arranged at the interface between the protective mat and the insulating ring on the side of the first stretch and on the side of the second stretch.

10. The fire protection device according to claim 1, further comprising, in at least one of the first and second stretches, a tube wherein are housed the reinforcements of the structural cable, with the protective mat being arranged around said tube.

11. The fire protection device according to claim 1, wherein the insulating ring has a rigidity at least 100 times greater than that of the protective mat.

12. A constuction work comprising at least one structural cable and a collar connected to the structural cable in a connection zone, the structural cable comprising taught metal reinforcements and having a first stretch and a second stretch on either side of the connection zone of the collar, with the construction work further comprising a fire protection device including: a protective mat surrounding the structural cable at least in the first and second stretches; and a thermally insulating ring more rigid than the protective mat, arranged between the reinforcements and the collar in the connection zone and cooperating with the protective mat in order to provide the reinforcements with a continuous thermal protection along the first stretch, from the connection zone and of the second stretch.

13. The construction work according to claim 12, wherein the structural cable further comprises an outer sheath surrounding the reinforcements and the protective mat in at least one of the first and second stretches.

14. The construction work according to claim 12, wherein the collar provides a connection of at least one damper element to the structural cable in order to dampen vibrations of the structural cable.

15. The construction work according to claim 12, comprised of a cable-stayed bridge, an extradosed bridge, a suspension bridge or a cable-stayed tower.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other particularities and advantages of this invention shall appear in the description hereinafter of a non-limiting example of an embodiment, in reference to the annexed drawings, wherein: FIG. 1 is a diagrammatical profile view of a cable-stayed bridge; FIG. 2 is an axial cross-section view of a stay cable in the vicinity of a connection collar of a damping device; and FIG. 3 is a transverse section of the stay cable on the collar.

DESCRIPTION OF EMBODIMENTS

(2) The invention is described hereinafter in its non-limiting application to cable-stayed bridges. It is understood that it can also be applied in extradosed bridges, suspension bridges or cable-stayed towers. The structural cables that are to be protected from fire can also be outer pre-stressed cables of works made of concrete.

(3) In the example of FIG. 1 the structural cables considered 16 are the stay cables of a bridge that extend between a pylon 20 of the bridge and its deck 14 in order to suspend the deck 14.

(4) One or several stay cables 16 are provided with a damping device 22 comprising an arm that extends transversally to the stay cable 16 between an attaching point P located in the vicinity of the low anchoring thereof (for example at a few % points of the total length of the stay cable) and the deck 14.

(5) To connect the arm of a damping device 22 to its stay cable 16 at point P, use is made of a collar 30 such as the one shown in FIGS. 2 and 3.

(6) A similar collar can be used to connect the structural cable to a fixed deviator (without damper) through which it bears, for example, on a stayed structure or a stay pylon. Another example of application is for a hanging collar located in the vicinity of the deck of a suspension bridge. When a hanging collar is at a height less than about 10 m, even up to 18-20 m, it can be affected by a vehicle fire, in such a way that the measurements described hereinafter can advantageously be adopted.

(7) The structural cable that forms the stay cable 16 comprises a harness of metal reinforcements 32, which are stretched between two anchoring devices (not shown) arranged at its ends, one on the deck 14 and the other on the pylon 20. The reinforcements 32 are for example strands, in particular strands that are individually sheathed and greased or waxed.

(8) In the main portion of the stay cable 16, the reinforcements 32 are protected from fire by a flexible protective mat 34, which can, for example, be formed in a similar way, in particular with the same materials as the one described in WO 2007/093703 A2. The mat 34 can extend over the entire length of the stay cable, or only over a portion of the latter if the fire protection is not required over the entire length.

(9) FIG. 2 shows the connection zone 40 of the collar 30, which is located between a first stretch 41 and a second stretch 42 of the stay cable 16. Each stretch 41, 42 extends from the connection zone 40 either to an anchoring of the stay cable, or to another singular point, or to a point of the main portion starting from which the protective mat is no longer required.

(10) The protective mat 34 surrounds the stay cable 16 in the first and second stretches 41, 42, and it is interrupted in the connection zone 40. Indeed, the flexibility of the mat 34 is not necessarily suitable for the function of the equipment connected to the stay cable 16 via the collar 30. A more rigid interaction is typically required at this level.

(11) For this, a ring 36, is more rigid than the protective mat 34 (K time more rigid with K100 for example, even K10,000), is arranged between the reinforcements 32 and the collar 30 in the connection zone 40. The rigidity of the insulating ring 36 can be greater than 10.sup.6N/m, or even 10.sup.8N/m.

(12) The ring 36 is also used to prevent the thermal bridges between the metal reinforcements of the stay cable 16 and the collar 30. It is thermally insulating and cooperates with the protective mat 34 in order to provide the reinforcements with continuous thermal protection all along the first stretch 41, of the connection zone 40 and of the second stretch 42.

(13) The insulating ring 36 can be made from a fibre-reinforced concrete, in particular a fibre-reinforced concrete with ultra-high performance (UHPC). The fibres that make up the composition of the fibre-reinforced concrete can include metal fibres and polypropylene fibres. The metal fibres improve the mechanical strength of the ring 36, while the polypropylene fibres improve the resistance thereof in the event of an increase in the temperature, by limiting weakening caused by spalling.

(14) The insulating ring 36 is manufactured in several moulded elements 36a, 36b which are then assembled around the reinforcement harness 32. In the example shown in FIG. 3, the ring 36 is comprised of two moulded half-shells 36a, 36b assembled around reinforcements 32. A firebreak seal 37 is placed on the surfaces of mutual contact of the two moulded half-shells 36a, 36b.

(15) It is desirable to prevent contact of the concrete on the metal reinforcements 32 of the stay cable. For this, a deviator tube 38 is inserted between the ring 36 and the reinforcement harness 32. The tube 38 is made of plastic material, for example a high density polyethylene (HDPE). It has a toric geometry on its inner face in order to accommodate small deviations that the reinforcement harness 32 is subjected to at the collar 30. If the reinforcement harness 32 has a polygonal transverse section (hexagonal in the case of FIG. 3), the deviator tube 38 can be formed by arranging several plates made of plastic material against the faces of the harness before setting the elements 36a, 36b of the ring 36 into place.

(16) The left portion of FIG. 2 shows that as an option, a tube 44 can be provided that contains the reinforcement harness 32 and which is surrounded by the protective mat 34. This tube 44, for example made of HDPE, adds an air gap between the reinforcements 32 and the mat 34 and, in this way, further increase the thermal protection of the reinforcements in the event of fire. Such a tube can be present in one of the stretches 41, 42, or in both.

(17) In order to cover a sufficient length along the stay cable 16, it is generally necessary to install end-to-end several segments 34a, 34b of the protective mat 34 in at least one of the stretches 41, 42 (FIG. 2). In order to ensure the continuity of the fire protection in the main portion of the stay cable, an overlay mat 35 is placed around two adjacent segments 34a, 34b in such a way as to entirely cover the existing seal between them.

(18) The mat 34 is held on the cable 16 using an adhesive or strapping strips, or a combination of these two types of means.

(19) FIG. 2 further shows that the protective mat 34 is placed longitudinally in contact with the insulating ring 36 on the side of the first stretch 41 and on the side of the second stretch 42. A few additional measurements can be taken in order to perfect the continuity of the protection between the connection zone 40 and one or the other of the stretches 41, 42.

(20) In particular, a longitudinal overlay can be arranged between the thermally insulating ring 36 and a portion of the protective mat 34 (FIG. 2). This portion as an overlay 48 of the protective mat 34 is inserted between the reinforcements 32 and the ring 36, in contact with the reinforcement harness 32.

(21) When a tube 44 is present between the reinforcements 32 and the protective mat 34, allowances of the fire protection mat 45, 46 can be added in the vicinity of the ring 36 in order to offset the thickness of the air gap and of the tube 44.

(22) In addition, it is often suitable to coat an intumescent material at the interface between the protective mat 34 and the insulating ring 36. In case of excessive heating, this material swells in order to prevent the conducting of the heat in the direction of the reinforcements 32.

(23) The flexible fire protection mat arranged on either side of the collar 30 and of the insulating ring 36 will generally not be directly exposed to the open air. It will be covered by a tubular sheath (not shown) comprised either of a steel tube, for a plastic sheath (HDPE). This sheath gives the stay cable an aerodynamic and aesthetic profile and mechanically protects the mat.

(24) The embodiments described hereinabove are a simple illustration of this invention. Various modifications can be made without leaving the scope of the invention that emerges from the annexed claims.