Bridges – Suspension – Cables and cable clamps
Reexamination Certificate
2000-02-18
2001-10-16
Pezzuto, Robert E. (Department: 3673)
Bridges
Suspension
Cables and cable clamps
C014S020000, C014S021000, C248S068100, C248S074400
Reexamination Certificate
active
06301735
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the use of cables in certain construction techniques and more specifically to the methods used to attach load-transmitting elements to a structural cable.
An important, though not exclusive, application of the invention is that of suspension bridges. In this application, hangers transmitting the load of the deck have to be attached to a bearing cable of the bridge, formed of one or more bundles of strands.
This attachment is generally performed by means of collars, each being made up of several shells which are clamped around the cable using means such as bolts, each hanger being fixed to one of the shells of its collar. The clamping force applied to the collar enables the bearing cable to absorb, by friction, the tangential components of the forces transmitted by the hangers.
French patent 2 739 113 proposes a bearing cable made from a bundle of “coherent” strands. Each coherent strand comprises a strand strictly speaking, made up of a stranded assembly of seven or more metal wires, coated with an adherent elastomer material and surrounded by an individual sheath of plastic material, whereby the strand and the elastomer material fill the interior space of the individual sheath.
This strand structure limits the force needed for the clamping action, which improves the reliability of the system.
European patent application 0 789 110 discloses the insertion of filler elements in a cable made up of individually protected strands (for example coherent strands), the filler elements being placed at the level of the attachment collars so that they fill the interstices between the individual sheaths of the assembled strands, the cross-section of said interstices being triangular in shape with curved sides.
This arrangement ensures that the clamping forces of the collars are transmitted more evenly to the strands under tension. At the level of the collars, the bearing cable is contained in a tubular envelope made of plastic material and deformable elements are inserted between the envelope and the bundle of strands. This assembly is crushed instantly when the collars are clamped and is also subjected to a delayed crushing action due to the creep of the materials, generally plastic, from which the envelope, the deformable elements and/or the filler elements are made.
In the typical example of a collar having an internal diameter of 400 mm, the delayed settling of this assembly under the effect of creep is typically in the order of 1 mm. This value may cause the collar to loosen, which could have disastrous consequences. As a result, regular maintenance work has to be carried out to check the tightness of the clamped collars and re-clamp them as required.
An object of the present invention is to improve the clamping action of the attachment collars on a structural cable.
SUMMARY OF THE INVENTION
Accordingly, the invention proposes a device for attaching a load-transmitting element to a cable, comprising a collar formed of at least two shells and means for clamping the collar around the cable, at least one of the shells having means providing a link with the load-transmitting element. The cable comprises an assembly of tensioned strands contained, at the level of the collar, in a deformable matrix filling the interstices between the strands, at least part of the matrix being in a plastic material that is susceptible to creep under the action of the clamping means. According to the invention, the clamping means comprise elongate clamping elements which transmit a clamping force to the shells of the collar and which are stressed so as to have a longitudinal elastic deformation that is substantially greater than the maximum settlement of the matrix due to creep.
The pre-stressed clamping elements provide a sort of reserve capacity for deformation, allowing any settlement of the assembly located underneath the collar due to the effect of creep to be absorbed. By making the elastic extension of these clamping elements much greater than the foreseeable settlement of the cable due to creep (typically at least five times greater), the clamping action can be guaranteed to remain at a controllable value and close to the initial value.
In preferred embodiments of the device according to the invention:
each tensioned strand of the cable consists of a strand coated with an adherent elastomer material and surrounded by an individual sheath of plastic material, whereby the strand and the elastomer material fill the interior space of the individual sheath (coherent strand);
the matrix comprises inserts having a triangular-shaped cross-section with curved sides, placed so as to fill, at the level of the collar, the interstices of matching shape located between the individual sheaths of the strands assembled in a bundle, and optionally elastomer elements arranged at the periphery of the bundled strands, and a tubular envelope made from a plastic material surrounding the elastomer elements, on which the shells of the collar bear;
the elongate clamping element is a metal rod, at least one end of which has a thread for receiving a nut used to apply stress to it, or else a tensioned cable, at least one end of which is clamped by means of anchoring jaws;
the elongate clamping element is housed in at least one bracing tube filled with a protective substance such as a petroleum wax, a grease or a resin.
A second aspect of the present invention relates to a suspension bridge, comprising at least one bearing cable anchored at its two ends and a deck suspended from the bearing cable by means of hangers, at least some of the hangers being attached to the bearing cable by means of attachment devices as defined above.
Advantageously, the attachment device has a portion which projects substantially above the bearing cable and which contains a stressed clamping element, the top end of said portion being fitted with means for fixing a hand rail to allow personnel to move along the bearing cable.
Another aspect of the present invention relates to a of attaching a load-transmitting element to a cable by means of a collar formed of at least two shells, the cable comprising an assembly of tensioned strands contained in a matrix at the level of the collar, at least part of the matrix being in a plastic material susceptible to creep under the clamping action exerted on the collar. In that method, the shells of the collar are clamped around the cable by means of elongate clamping elements which are stressed so as to have a longitudinal elastic deformation substantially greater than the maximum settlement of the matrix due to creep.
The method advantageously comprises a step of simultaneously applying the stresses to the elongate clamping elements by means of a hydraulic system, and a step of clamping the elongate clamping elements in the stressed position. This makes it possible to balance the forces exerted on all the clamping elements of a same collar and avoid subjecting the elements to individual clamping forces that would cause twisting.
In specific approaches to implementing the method:
the steps of simultaneously applying stresses and clamping in the stressed position are carried out after the collar has been fitted around the cable, as well as during subsequent monitoring and re-clamping operations.
the step of simultaneously applying stresses comprises a first phase in which the hydraulic system exerts an excessive stress followed by a second phase in which the applied stresses are reduced before proceeding with the clamping stage.
the steps during which stresses are applied simultaneously and the clamping action is applied in the stressed position are performed after the collar has been fitted around the cable, as well as subsequent checking and re-clamping operations;
the step during which stresses are applied simultaneously incorporates a first phase during which the hydraulic system exerts an excessive stress, followed by a second phase in which the stresses applied are reduced before proceeding with the clamping step.
REFERENCES:
patent: 1678292 (1928-0
Jartoux Pierre
Stubler Jérô ;me
Cantor & Colburn LLP
Freyssinet International (Stup)
Pechhold Alexandra K.
Pezzuto Robert E.
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