Method of overlocking at least one strand in an anchoring block and system for overlocking at least one strand in an anchoring block

[0001] This application claims priority to France Patent Application Serial No. FR 03 06319, filed May 26, 2003, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a method of overlocking at least one strand in an anchoring block and to a system or apparatus for overlocking at least one strand in an anchoring block.

[0003] More particularly, the subject of the invention is a method of overlocking at least one strand in an anchoring block by radially clamping the strand with a frustoconical jaw that surrounds the strand and is housed in a frustoconical recess of complementary shape formed in the anchoring block.

[0004] As generally known, a stay strand comprises a wire or a plurality of twisted wires intended to be tensioned for the purpose, in particular, of prestressing a body made of concrete or for suspending a civil engineering structure such as a bridge.

[0005] To accomplish tensioning, the stay strand is first locked or clamped in an anchoring block by means of a jaw or jaws fitted into the block to grip the strand by friction or traction with the strand and at least partly by application of an axial thrust or force against a large base of the jaw. Such axial thrust effects a radial clamping force on the strand effected typically by a frustoconical or cone jaw configuration fitted into a compatible opening in the anchor block. In order to guarantee that the strand does not slip in relation to the jaw surrounding it, a securing operation, called overlocking, guarantees that the jaw will be held around the strand during the lifetime of the civil engineering structure on which the said strand is tensioned.

[0006] This overlocking operation is currently carried out by means of hammer blows applied directly to the large base of the jaw in order to displace it by a few millimetres axially within its housing or anchoring block so as to guarantee radial prestressing force on the strand. Nevertheless, this overlocking operation, carried out by an operator using a hammer to strike blows on the jaw, does not guarantee with certainty that the displacement of the anchoring jaw within its housing or anchoring block has been sufficient for the jaw to find a so-called final position, that is to say a position that the jaw is intended to find during the maximum loading tolerated by the stay strand.

[0007] Moreover, a securing operation by means of hammer blows is not generally suitable when the anchoring jaw is difficult to access, in particular in cramped civil engineering structures.

[0008] An aim or object of the present invention is to improve prior overlocking methods so that the operator can be sure that the anchoring jaw has reached its overlocking or preferred locking position in the anchor block. To this end, according to the invention, a method of overlocking comprises the following steps:

• • [0009] an explosive cartridge device including an inertia block that is to be propelled by the explosion of a cartridge is provided;
  • [0010] a force transmission device is arranged between the inertia block of the explosive cartridge device and a frustoconical jaw; and
  • [0011] an explosive cartridge is activated to propel the inertia block against the force transmission device, which, in turn, pushes against the frustoconical jaw to drive it into the frustoconical recess in the anchoring block, thereby causing the stay strand to be overlocked by radial clamping of the frustoconical jaw.

[0012] In preferred embodiments of this method, according to the invention it is possible, where appropriate, additionally to have recourse to one or the other or both of the following steps:

• • [0013] a high-pressure gas cartridge device may be used to drive the inertia block;
  • [0014] use is made of a force transmission device which comprises:
  • [0015] a body defining an inner chamber which extends between a first orifice or opening connected to an end-piece of the explosive cartridge device, from which the inertia block is propelled, and a second orifice or opening; and
  • [0016] a percussion member which comprises a first portion at one end which is housed in the inner chamber of the body and which has a larger diameter than the second orifice or opening, the said first portion being intended to be struck by the inertia block, and a second portion at the other end connected to or integral with the first portion and mounted such that it can slide in the second orifice, the said second portion having a free end intended to interact or engage with the frustoconical jaw by impacting thereon; and
  • [0017] a compression spring is interposed between the first portion of the percussion member and the inner chamber of the body.

[0018] Moreover, another object of the invention is to provide a system for overlocking at least one strand in an anchoring block by radially clamping the strand with a generally frustoconical shape jaw which generally surrounds the strand and which is housed or positioned in a frustoconical recess of complementary shape in the block, characterized in that it comprises:

• • [0019] an explosive cartridge device comprising an inertia block intended to be propelled by the explosion of the cartridge; and
  • [0020] a force transmission device intended to interact with the inertia block of the explosive cartridge device to allow, upon the explosion of the explosive cartridge, the inertia block to be propelled against the force transmission device, which in turn pushes against the frustoconical jaw to drive it into the frustoconical recess in the anchoring block, thereby causing the strand to be overlocked by radial clamping of the frustoconical jaw.

[0021] In a preferred embodiment of the overlocking system, according to the invention it is possible, where appropriate, additionally to have recourse to one or the other or both of the following arrangements:

• • [0022] the force transmission device comprising:
  • [0023] a body defining an inner chamber which extends between a first orifice or opening connected to an end-piece of the explosive cartridge device, from which the inertia block is propelled, and a second orifice or opening, and
  • [0024] a percussion member which comprises, on the one hand, a first portion which is housed in the inner chamber of the body and which has a larger diameter than the second orifice or opening in the body, the first portion being intended to be struck by the inertia block, and, at the other end, a second portion integral with the first portion and mounted such that it can slide in the second orifice, the said second portion having a free end intended to interact with the frustoconical jaw;
  • [0025] a compression spring is interposed between the first portion of the percussion member and the inner chamber of the body; and
  • [0026] the body of the force transmission device is formed by a first casing which comprises the first orifice and by a second casing which is integral with the said first casing and comprises the second orifice.

[0031] In the various figures, the same references denote like or similar elements.

[0032] FIG. 1 depicts an overlocking mechanism or device and system 1 designed to overlock at least one stay strand 2 in an anchoring block 3 by radially clamping the strand 2 by means of an anchoring jaw 4 which generally surrounds the strand 2 and which is housed in a frustoconical recess 5 formed in the anchoring block 3. The strand 2 may be composed of a single wire or of a plurality of twisted wires.

[0033] As can be seen in more detail in FIG. 2, the anchoring jaw 4 may be formed by a split anchoring jaw or by a plurality of wedges 4a, 4b, for example two, having a substantially semi-cylindrical and frustoconical shape.

[0034] The narrowest portion of the frustoconical jaw 4, formed by the wedges 4a, 4b, is housed in the narrow end 5a of the frustoconical recess 5 made in the anchoring block 3 which the strand 2 passes right through. The larger end of the anchoring jaw 4 projects axially from the face 3a of the anchoring block 3. The free end of the strand 2 likewise extends beyond the widest portion of the anchoring jaw 4.

[0035] Radial clamping of the strand 2 by the anchoring jaw 4 is provided by a wedging action by causing this anchoring jaw 4, and therefore the wedges 4a, 4b, to be driven axially into the frustoconical recess 5. During the installation of the anchoring jaw 4 in the frustoconical recess 5 of the anchoring block 3, axial stress may be generated by the actual tension of the strand 2 on account of the friction which exists between this strand 2 and the internal face of the anchoring jaw 4, or else by axially driving this anchoring jaw 4 into the recess 5 in block 3 while the tension of the strand 2 is minimal.

[0036] In order to ensure that the strand 2 will not slip from the anchoring block 3, a securing operation, referred to as an overlocking operation, ensures that the anchoring jaw 4, and therefore the wedges 4a, 4b, will hold over the lifetime of the civil engineering structure. Overlocking ensures imposition of radial prestress on the strand 2 by driving the anchoring jaw 4 into block 3, this prestress on the strand 2 substantially corresponding to the final position of the wedges 4a, 4b, that is the position that they would assume during the maximum loading to be tolerated by the strand 2.

[0037] To this end, the overlocking system according to the invention comprises, as can be seen in FIG. 1, an explosive cartridge device 6 and also a force transmission device 7 directly arranged between the explosive cartridge device 6 and the anchoring jaw 4 that has previously been driven or positioned into the frustoconical recess 5 in the anchoring block 3 before overlocking.

[0038] The explosive cartridge device 6 may, for example, be formed by a gas discharge mechanism or an automatic gun with an automatically or manually replaceable explosive cartridge, and which comprises (FIG. 2) an inertia block 8 intended to be propelled upon the explosion of the explosive cartridge. By way of example, this explosive cartridge device 6 may be formed by an automatic cartridge gun marketed by the company HILTI, in particular under the model number DXA 40.

[0039] For its part, the force transmission device 7 is intended to interact with the inertia block 8 of the explosive cartridge device 6 to allow, upon explosion of an explosive cartridge, the inertia block 8 to be propelled against the force transmission device 7, which, in turn, pushes against the frustoconical jaw 4 in order to drive it into an overlocking position in the frustoconical recess 5 in the anchoring block 3.

[0040] To this end, this force transmission device 7 comprises a generally cylindrical body 9 formed by a first casing 10 and a second casing 11 which define between them an inner chamber 12. This inner chamber 12 of the body 9 extends between a first orifice or circular passage 13 made directly in the first casing 10 and a second orifice or circular passage 14 made directly in the second casing 11. The first orifice 13 is directly connected to an end-piece 6a in which the inertia block 8 of the explosive cartridge device 6 is housed in a sliding manner. This end-piece 6a may form a constituent element of the explosive cartridge device 6 or else form a constituent element of the force transmission device 7. End-piece 6a is directly mounted in a fixed manner in the orifice 13 in the first casing 10, for example, by means of a pin 15 which passes right through the casing 10 to interact with the end-piece 6a so as to secure them to one another.

[0041] As can be seen in FIG. 2, the second casing 11 has an end wall 11a in which the opening or orifice 14 is made, and from which extends an annular wall 11b intended to interact with an annular wall 10a of the first casing 10 to form the inner chamber 12. The first casing 10 and the second casing 11 are joined or fixed relative to one another by suitable means and in particular, for example, by screwing and/or by means of a pin 16.

[0042] The force transmission device 7 also comprises a percussion member 17 which is substantially in the form of an elongate shaft which comprises, on the one hand or at one end, a first portion or piston element 18 which is housed in the inner chamber 12 of the body 9 and which has a greater diameter than the second orifice 14 of the casing 11, and, on the other hand or end, a hollow second cylindrical portion 19 which is integral with the first portion 18 and which is mounted such that it can slide in the second orifice 14 in the casing 11. This second cylindrical portion 19 has a free end 19a intended to bear against the widest part of the wedges 4a, 4b forming the anchoring jaw 4 while surrounding the end of the strand 2 which projects beyond the said wedges 4a, 4b. The first portion 18 of the percussion member 17 also comprises a cylindrical annular wall 18a which extends in the direction of the casing 10 and which surrounds a compression spring 20 directly interposed between the casing 10 and the first portion 18 of the percussion member 17. The first portion 18 of the percussion member 17 also comprises a centering piece or element 21 for the spring 20 which is arranged facing the inertia block 8. Moreover, shock-absorbing elements such as O-rings 22, 23 are arranged on either side of the inner chamber 12 of the body 9 so as to absorb the displacement of the first portion 18 of the percussion member 17 inside the body 9.

[0043] When an operator wishes to overlock the anchoring jaw 4 in the frustoconical recess 5 in the anchoring block 3 after having previously placed and driven the said anchoring jaw 4 into the frustoconical recess 5, the operator first of all positions the overlocking system such that the free end 19a of the percussion member 17 comes into contact with the wedges 4a, 4b while surrounding the strand 2. This placing of the overlocking system 1 on the anchoring jaw 4 has the effect of bringing the annular wall 18a of the first portion 18 of the percussion member 17 into abutment with the shock-absorbing element 23, doing so against the loading exerted by the compression spring 20.

[0044] All the operator then has to do is activate the explosive cartridge device 6 by triggering the explosion of the said cartridge, which may be an explosive cartridge releasing a high-pressure gas after the explosion has been triggered, in order to propel the inertia block 8 against the centering piece 21 of the first portion 18 of the percussion member 17. This percussion member 17 then automatically transmits the impact produced by the inertia block 8 to the wedges 4a, 4b of the anchoring jaw 4 so as to bring it into an overlocking position which corresponds to a position that the anchoring jaw 4 would have adopted during the maximum loading tolerated by the strand 2, thereby ensuring that the strand 2 is radially prestressed.

[0045] This overlocking operation therefore makes it possible to dissociate the holding of the strand 2 in the anchoring and the tension of the strand 2, which may prove to be advantageous in the event of the tension of the strand 2 becoming greatly diminished or even cancelled during the actual service of the strand 2, such a situation possibly arising, for example, when an impact is received by a suspension bridge strand, where the impact may, for example, be caused by an earth tremor, by a tornado or by a heavy goods vehicle losing control.

[0046] Moreover, the choice of explosive cartridge and percussion member 17 makes it possible to adapt and choose the calibrated force transmitted to the anchoring jaw 4 in order to fix it in its so-called overlocking position. Moreover, the dimensions of the inertia block and of the percussion member 17 may be chosen so as to prevent them from buckling or deforming.

[0047] While there has been set forth a preferred embodiment of the invention, ti is to be understood that the invention is to be limited only by the following claims and equivalents thereof. The mechanism for driving the jaws 4 may, for example, be altered without departing from the spirit and scope of the invention. Such mechanism may include other means for transmitting force to the percussion member 18. Pressurized gas or mechanical means may be used. Note the disclosed design facilitates recoil action and includes elements such as cushions (or rings) 22, 23 in this regard. In any event, utilization of a source of pressure on a driving member by gas, cartridge firing or otherwise to effect overlocking of the jaws on a stay strand in a block enables application of controlled force to effect such overlocking.