EP0616079B1 - Process and apparatus for placing parallel wire strands in cable-stayed bridges - Google Patents

Abstract

In order to mount a multistrand stay cable of a cable-stayed bridge between a pillar (tower) and the deck of this bridge, one of the strands (41) intended to constitute the stay cable is fitted in its final oblique position; a guide cage is suspended from this first strand thus fitted, which cage consists of a sequence of rigid bow struts (stirrup pieces) (5) connected together by small cables (6), the said cage surrounding the said first strand as well as a traction cable (9); using the said cable, the following strands (4) are pulled in succession into the cage; at the end of the traction of each strand, it is tensioned so as to apply it laterally against the strands already fitted, and its ends are anchored, respectively on the pillar and on the deck; and all of the strands have been fitted, the guide cage is released from the finished stay cable. <IMAGE>

Description

The invention relates to guy lines intended to equip guyed bridges by connecting the pylons of these bridges to their decks, guy wires constituted by multiple strands juxtaposed side by side, each of these strands being itself preferably of the "individually protected" type. , that is to say constituted by a bundle of parallel or twisted metal wires housed in a continuous sheath with the interposition of a protective product.

It relates more particularly to the methods and devices for mounting the shrouds of the type in question in their final oblique shapes, for which they together form sheets, generally vertical, arranged on either side of each pylon.

It relates more particularly to the case where at least some of the shrouds to be mounted have a very long length, this length possibly exceeding 200 meters.

In such a case, it is no longer possible to implement the known technique consisting in manufacturing the complete shroud horizontally at the foot of the pylon which must support it, then in raising the end of this shroud arranged against the pylon, pulling this guy, since its weight is then too high.

Another known technique for mounting guy wires of the kind in question consists in pulling obliquely, in the direction of its axis, said guy cable previously manufactured, that is to say already composed of all of its constituent strands juxtaposed side by side. side, using a system like cable cars.

To this end, a carrier cable is stretched beforehand between a high point of the support pylon and the deck and a hooking member is rolled on this cable, by means of an appropriate undercarriage, to which the head or high end guy line.

The prior installation of such a carrying cable is itself a difficult and costly operation and, here again, the forces to be developed to pull the shroud become prohibitive for very long lengths.

It has also been proposed to compose each guy directly, strand by strand, in its final oblique location.

In the known embodiments of this technique, use is made of an installation comprising a platform mounted on the head of the pylon concerned, a capstan winch, idler pulleys, one of which is disposed on the platform and others on the deck of the bridge, and an endless cable guided by the pulleys and actuated by the winch, cable to which are successively hung the various strands intended to compose the stay cable (see document "Works" n ° 666, June 1991, Paris , pages 16-40).

These installations are relatively heavy and expensive.

The object of the invention is, above all, to remedy the various drawbacks of these various known techniques.

• on met en place en sa position oblique définitive l'un des torons destinés à constituer le hauban, cette phase de mise en place se terminant par la mise en tension du toron et l'ancrage de ses extrémités sur respectivement le pylône et le tablier,
• on suspend à ce premier toron ainsi mis en place une cage de guidage pour les torons suivants, cage s'étendant sur toute la longueur dudit toron et composée d'une suite d'étriers rigides reliés entre eux par des câblettes, ladite cage entourant ledit premier toron ainsi qu'un câble de traction,
• on tire successivement à l'aide dudit câble les torons suivants constitutifs du hauban, éventuellement par paires, à l'intérieur de la cage,
• à la fin de la traction de chaque toron, on met celui-ci sous tension de façon à l'appliquer latéralement contre le toron ou l'ensemble des torons déjà mis en place et l'on ancre ses extrémités respectivement sur le pylône et sur le tablier,
• et après mise en place de la totalité des torons, on dégage la cage de guidage du hauban terminé.

To this end, the mounting methods of the shrouds of the type in question according to the invention also employ a direct composition of the shrouds, strand by strand, in their final oblique locations, and they are essentially characterized by the following operations:

• one sets up in its final oblique position one of the strands intended to constitute the stay, this phase of establishment ending with the tensioning of the strand and the anchoring of its ends on the pylon and the deck respectively,
• a guide cage is suspended from this first strand thus set up for the following strands, cage extending over the entire length of said strand and composed of a series of rigid stirrups connected together by cables, said cage surrounding said first strand as well as a traction cable,
• the following strands constituting the stay, successively in pairs, are successively drawn using said cable, inside the cage,
• at the end of the traction of each strand, the latter is tensioned so as to apply it laterally against the strand or the set of strands already in place and its ends are anchored respectively on the pylon and on apron,
• and after all of the strands have been put in place, the guide shroud is released.

• pour construire les différents haubans obliques constituant une même nappe verticale ou sensiblement verticale, on commence par monter le hauban inférieur le plus court, puis on monte successivement chacun des autres haubans en progressant de proche en proche vers le haut et, pour la mise en place du premier toron de chacun des haubans autres que le hauban inférieur, on utilise la cage de guidage ayant servi à monter le hauban précédent, alors qu'elle est encore suspendue à ce dernier,
• s'il est prévu d'un même côté longitudinal d'un pylône deux nappes verticales ou sensiblement verticales de haubans obliques formant ensemble un dièdre à angle aigu, on procède simultanément au montage des deux haubans, compris respectivement par ces deux nappes, qui sont disposés au même niveau en ayant recours à un câble de traction unique s'étendant selon un circuit fermé en forme de triangle isocèle délimité par des poulies, les deux grands côtés égaux de ce triangle s'étendant selon les axes obliques des deux haubans à monter et le troisième côté s'étendant horizontalement, perpendiculairement au pont et comprenant un treuil ou analogue à sens de rotation réversible.

In preferred embodiments, use is also made of one and / or the other of the provisions following:

• to build the different oblique guy wires constituting the same vertical or substantially vertical cable, we start by mounting the shortest lower guy, then we successively mount each of the other guys while progressing step by step upwards and, for setting up the first strand of each of the shrouds other than the lower shroud, the guide cage used to mount the previous shroud is used, while it is still suspended from the latter,
• if there are provided on the same longitudinal side of a pylon two vertical or substantially vertical plies of oblique shrouds together forming a dihedral at an acute angle, the two shrouds, comprised respectively by these two plies, are simultaneously mounted, which are arranged at the same level using a single traction cable extending in a closed circuit in the form of an isosceles triangle delimited by pulleys, the two large equal sides of this triangle extending along the oblique axes of the two shrouds to be mounted and the third side extending horizontally, perpendicular to the bridge and comprising a winch or the like with reversible direction of rotation.

As regards mounting devices of the kind in question, they are essentially characterized in that they comprise a guide cage for the strands and the traction cable, composed of a succession of rigid stirrups connected together by cables, each bracket including an arch and an easily removable lower closing bar.

• la cage de guidage comprend trois câblettes parallèles, l'une étant attachée au sommet des différents arceaux et les deux autres, aux pieds de ces arceaux,
• la cage de guidage contient au moins un fil parallèle aux câblettes servant de rail de guidage pour les coulissements d'un chariot, ledit chariot étant fixé en un point intermédiaire du câble de traction et étant agencé de façon telle que les têtes des torons à mettre en place soient facilement accrochables sur lui de façon amovible,
• le chariot selon l'alinéa précédent est bordé latéralement par deux tronçons tubulaires rigides traverses respectivement par deux fils de guidage contenus dans la cage,
• chaque étrier comprend intérieurement, au voisinage de chaque pied d'arceau, deux languettes définissant avec les portions adjacentes d'arceau et de barrette un oeillet à ouverture étranglée dans lequel est logé l'un des deux fils de guidage selon l'alinéa précédent,
• le chariot ci-dessus ou chariot principal est associé à un chariot auxiliaire, lequel est fixé d'une façon facilement amovible en un point intermédiaire du câble de traction disposé un peu plus haut que le chariot principal, ce chariot auxiliaire étant en outre monté coulissant sur chaque fil de guidage d'une façon éventuellement amovible et agencé de façon telle que les têtes des torons à mettre en place soient facilement accrochables sur lui de façon amovible,
• chaque chariot est agencé de façon telle que les têtes de deux des torons à mettre en place soient facilement accrochables sur lui de façon amovible,
• la distance entre les étriers successifs de la cage est comprise entre 5 et 10 mètres.

In preferred embodiments, these devices also comprise application of one and / or the other of the following provisions:

• the guide cage comprises three parallel cables, one being attached to the top of the various arches and the other two, to the feet of these arches,
• the guide cage contains at least one wire parallel to the cables serving as a guide rail for the sliding of a carriage, said carriage being fixed at an intermediate point of the traction cable and being arranged in such a way that the heads of the strands to be laid in place are easily hooked on it removably,
• the carriage according to the preceding paragraph is bordered laterally by two rigid tubular sections traversed respectively by two guide wires contained in the cage,
• each stirrup internally comprises, in the vicinity of each hoop leg, two tongues defining with the adjacent hoop and bar portions an eyelet with a constricted opening in which one of the two guide wires is housed according to the preceding paragraph,
• the above carriage or main carriage is associated with an auxiliary carriage, which is fixed in an easily removable manner at an intermediate point of the traction cable disposed a little higher than the main carriage, this auxiliary carriage being furthermore mounted sliding on each guide wire in a possibly removable manner and arranged in such a way that the heads of the strands to be put in place are easily hooked on it in a removable manner,
• each carriage is arranged in such a way that the heads of two of the strands to be placed are easily hooked onto it in a removable manner,
• the distance between the successive stirrups of the cage is between 5 and 10 meters.

The invention includes, apart from these main provisions, certain other provisions which are preferably used at the same time and which will be more explicitly discussed below.

In the following, we will describe some modes preferred embodiments of the invention with reference to the accompanying drawings of course in a non-limiting manner.

Figure 1 of these drawings shows very schematically the general principle of mounting a guy line according to the invention.

Figure 2 shows in schematic perspective and on a larger scale a portion of the corresponding mounting device.

Figure 3 shows on an even larger scale a cross section of the same device.

Figure 4 also shows on a larger scale and in perspective view a component of this device.

FIG. 5 very schematically shows a particular phase of mounting guy lines, also in accordance with the invention.

Figure 6 schematically shows in plan a portion of a cable-stayed bridge under construction comprising a mounting device according to the invention.

This involves supporting the deck 1 of a bridge by at least one pylon or pillar 2 by means of a plurality of shrouds 3 (FIG. 5) stretched in oblique directions substantially parallel to each other between the deck and the pylon so as to form vertical or substantially vertical sheets.

Each of the shrouds 3 is constituted by a plurality of independent strands, that is to say that can be mounted and tensioned independently of each other and even, in some cases, replaced in isolation.

Each strand 3 may be constituted by a large wire, but it is preferably composed of a central core surrounded by a plurality of contiguous wires, generally six in number, wound helically around said core, each wire as well as the the core being advantageously surface protected, for example by galvanization, and the resulting twisted assembly itself being surrounded by a tight protective sheath, generally made of plastic, with possibly the interposition of a suitable protective binder such as petroleum wax.

The current portions of the "individually protected" or "self-protected" strands thus defined are juxtaposed laterally, being clamped against each other by collars not shown.

For large bridges, the number of strands 4 making up the same stay 3 is several tens.

If the length of the multiple shrouds thus composed is large, and in particular if it exceeds 200 meters, or even 300 or even 400 meters, the weight resulting from each shroud is enormous and the mounting of these shrouds on the pylons poses serious problems.

To carry out such an assembly, we proceed here as follows.

For each guy, we start by setting up one 4 ₁ of the strands constituting this guy by anchoring his head at a point A of the support pylon 2 and his foot at a second point B of the deck 1.

Such an installation is advantageously carried out in the manner which will be explained below with reference to FIG. 5.

However, it can be carried out in any other desirable manner, for example by implementing the first method mentioned above (vertical elevation of the strand head extended horizontally at the foot of the pylon) since the weight of a single strand is relatively small.

It is then this first strand 4 ₁ thus put in place which is used to support the crew used to mount the following strands, the latter then taking turns to reinforce the first strand in its role of support at the end of their implementation.

To mount each "next" strand 4, that is to say other than the first, we proceed as follows.

Is placed on the first strand 4 ₁ a light guide cage formed by a series of rigid stirrups 5 connected together by cables 6 (Figures 2,3,4).

Each stirrup 5 is constituted by a hoop 7, the base of which is closed by a horizontal bar 8 that is easily removable.

The cables 6 are preferably three in number, then being attached to each arch 7, respectively at its apex C and at its two feet D and E.

The upper cable 6, attached to the top C of the arches rests directly on the strand 4 ₁ and the tension of the cables is carried out in such a way that each stirrup is stabilized with its bar 8 arranged horizontally and at the bottom.

The distance between the successive stirrups 5 is generally between 5 and 10 meters, so that each "cage" comprises several tens of stirrups.

The cage serves to contain, on the one hand, a traction cable 9 and, on the other hand, at least one wire and preferably two wires 10 and 11 suitable for serving as guide rails for at least one carriage 12.

Each stirrup 5 internally comprises, in the vicinity of each end of the bar 8 constituting its base, two tabs 13, 14 forming with the contiguous portions of the stirrup two eyelets with a constricted opening.

Each of these eyelets is crossed by one of the wires 10,11.

The carriage 12 is delimited laterally by two tubular rings 15 each traversed by one of the wires 10 and 11 and the arrangements and respective dimensions of these rings and of the above eyelets are such that the former can easily penetrate into the latter: the respective ranges of these rings and eyelets suitable for coming axially into contact have all desirable ramps (not shown) to make possible and facilitate the introduction of the former into the latter.

The carriage 12 is fixed at an intermediate point of the traction cable 9 and the head of at least one strand 4 is hooked on said carriage in an easily detachable manner, using appropriate means, for example by its clamping between the chassis of said carriage 12 and a jaw 19 screwed onto this chassis.

As can be seen in FIG. 2, one end of each strand 4, constituting the head of this strand, projects upwards beyond the carriage 12.

• il est accroché de façon facilement amovible, à l'aide de moyens non représentés, à un point intermédiaire du câble de traction 9 disposé plus haut que le chariot 12,
• il est monté coulissant d'une façon facilement amovible, à l'aide de moyens non représentés, sur les rails 10 et 11,
• chaque tête de toron 4 est accrochée sur lui de façon facilement amovible comme pour le chariot 12.

In a preferred embodiment, a second carriage 20, or auxiliary carriage, is arranged near the upper end of each of the ends in question, a carriage having the following characteristics:

• it is hooked in an easily removable manner, using means not shown, at an intermediate point of the traction cable 9 disposed higher than the carriage 12,
• it is slidably mounted in an easily removable manner, using means not shown, on the rails 10 and 11,
• each strand head 4 is easily attached to it as for the carriage 12.

The operation of the device which has just been described is as follows.

After placing the first strand 4 ₁ and the cage 5-6 on this strand, with the cable 9 and the wires 10, 11 in this cage, we initially place the bottom of the cage, that is to say in the vicinity of point B in FIG. 1, the carriages 12 and 20 hung on said cable 9, the carriage 20 being separated by one or two meters from the carriage 12 in the direction of the pylon 2.

The head of at least one strand 4 is then hung on the carriages - the number of strands 4 considered being equal to two in the embodiment illustrated - or more precisely one end of at least one continuous cable unwound in particular from a reel 15 with a horizontal axis and capable of forming the desired strand after unwinding and cutting.

Then pull the carriages in the upward direction of arrow F using the traction cable 9.

The rings 15 of the carriages then pass through the above-defined eyelets of the stirrups 5 and the drawn strands 4 successively pass through these stirrups 5 by sliding along their lower bars 8.

During this progression, the different strand sections 4 comprised between two consecutive bars 8 are slightly curved downwards under the effect of gravity, but the vertical arrow f (FIG. 1) of each of these sections is relatively small, so that the tensile force to be exerted on the cable 9 is also relatively low.

When the head of each strand 4 thus pulled reaches the high point A, this head is removed from the upper carriage 20, this carriage 20 is detached from both the traction cable 9 and the guide rails 10,11 and the stripped end of the head considered in its anchoring device, generally constituted by a tapered jaw split itself housed in a complementary bore of an anchoring block.

Then, using the traction cable 9, the carriage 12 continues to advance upwards, which continues the introduction of the head of the strand 4 into its anchoring jaw.

When this introduction is sufficient to be able to be relayed by a usual traction cylinder, the said head of the carriage 12 is detached, the base of the strand in question is cut in the vicinity of the low point B and the two ends of this strand are anchored anyway. desirable known, in the vicinity of the anchoring zones of the upper and lower ends of the first strand 4 ₁ .

This anchoring has the effect of juxtaposing laterally each new strand 4 against the strand 4 ₁ previously put in place and tensioned, which is made possible by the fact that all the strands, including the first, are arranged inside the cage subsequently formed by the hoops 5.

It is then the bundle of strands thus juxtaposed which supports the cage as well as its accessories (see the strands grouped in the upper part of the cage in Figures 2 and 3).

Using the cable 9, the carriage 12 is then lowered back empty to the bottom of the cage, as well as the carriage 20, previously reassembled on its rails and re-attached to said cable.

Then the carriages are again hitched to the head of at least one new strand and it is put in place as for the previous ones, and so on until the last strand: the shroud is then completed.

The cage can then be recovered by sliding it along the finished stay towards the lower end of the latter, then by opening each stirrup lower by at least partial disassembly of its bar 8.

According to an interesting improvement shown diagrammatically in FIG. 5, which is applicable to the positioning of each "first strand" 4 ' ₁ constituting a "new shroud" situated just above a completed shroud or "previous shroud" , the cage which still surrounds this preceding shroud is used, just at the end of its manufacture, to ensure said positioning.

In other words, the carriage 12 is also used as above to hoist the first strand 4 ′ ₁ to the vicinity of point A relating to the “preceding shroud”, but instead of anchoring the head of this strand at said level point A, it is anchored at the higher level of point A ', to which the new stay must be anchored.

For this purpose, it suffices to raise said head from strand 4 ' ₁ of height A, A'.

This elevation does not pose a major problem, because the height A, A ′ is small and the weight of a single strand is relatively low.

Of course, the elevation in question can be carried out after releasing the cage out of the preceding shroud.

As indicated above, the clearance in question of the cage out of the finished stay is made possible by the easy removable of the bars 8: when these bars are separated, or even separated, from the corresponding arches 7, these are open downwards and can therefore be released from the shroud which they overlap by simple lifting.

Their subsequent mounting on the first strand 4 ' ₁ constituting the new shroud to be manufactured is then very easily achieved by overlapping it by said hoop 7, then closing this hoop by its bar 8 below said strand so as to form the stirrup 5 composed by this hoop and this bar.

The process which has just been described for the positioning of each "first strand" of a shroud placed above a "previous shroud" cannot of course be used for the lowest shroud of each tablecloth.

But this is not a serious drawback because, said lowest guy is generally relatively short and the level of its head is relatively low: the corresponding first strand is therefore relatively light and its assembly does not pose any major problem.

In FIG. 6, another improvement has been illustrated applicable to a cable-stayed bridge for which the oblique stay cables which connect the deck 1 to one of the faces of a pylon 2 are not in the form of a longitudinal vertical sheet. single or two such parallel sheets, but in the form of two sheets N ₁ and N ₂ vertical or substantially vertical divergent from the pylon and forming together at least approximately a dihedral with a vertical axis and small opening.

In this case, it is advantageous to manufacture the guy wires of the same level simultaneously from these two plies and the process described above is very suitable for such simultaneous manufacturing.

To this end, the traction cable 9 is made to follow a closed circuit having the shape of an isosceles triangle AB ₁ B ₂ having two large equal sides AB ₁ , AB ₂ which extend respectively along the axes of the two shrouds to be manufactured and a small side B ₁ B ₂ lower horizontal perpendicular to the large dimension of the bridge and arranged at the level of its deck.

The vertices A, B ₁ and B ₂ are materialized by three pulleys 16, 17 ₁ and 17 ₂ .

An intermediate section of the cable 9 is wound on a control winch 18 mounted on the deck 1 and capable of working alternately in both directions.

In this case, the strands constituting the two shrouds to be manufactured extend respectively on the two sides AB ₁ and AB ₂ and there is available on each of these sides a light cage composed of stirrups and cables of the kind defined above. .

The two corresponding carriages - or "double carriages" - are designated respectively in FIG. 6 by the references 12 ₁ and 12 ₂ .

We see that, for a direction of rotation of the winch 18, corresponding to the arrow F, the carriages 12 ₁ rise from point B ₁ to point A, while on the contrary the carriage 12 ₂ progresses downward along the side AB ₂ .

The opposite is observed for the other direction of rotation of the winch 18.

It is therefore possible to hoist in turn the strands constituting the two shrouds to be manufactured by means of reversals of the winch's direction of rotation 18.

As a result of what and whatever the embodiment adopted, there are finally obtained arrangements for mounting shrouds with multiple strands, the constitution, implementation and advantages of which result sufficiently from the above.

As goes without saying, and as it already follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all variants thereof, defined in the appended claims.

Claims (10)

1. A method of mounting a multiple strand stay of a stayed bridge between a tower and the deck of said bridge, wherein the stay (3) is built up directly, strand by strand, in its final oblique position,
   characterized by performing the following sequence of operations: one of the strands (4₁) for making up the stay is installed in its final oblique position, this stage of installation being terminated by putting the strand under tension and anchoring its ends respectively to the tower (2) and to the deck (1); a guide cage for the following strands is suspended from said first strand installed in this way, the cage extending over the entire length of said strand and being made up of a sequence of rigid hoops (5) interconnected by strings (6), said cage surrounding said first strand and also surrounding a traction cable (9); the subsequent strands (4) making up the stay are pulled up successively inside the cage by means of said cable; after each strand has been pulled up, it is put under tension so that it bears laterally against the already-installed strand or set of strands, and its ends are anchored respectively to the tower and to the deck; and after all of the strands have been installed, the guide cage is removed from the completed stay.
2. A method according to claim 1, for mounting the various oblique multiple-strand stays constituting a common vertical or substantially vertical sheet of a stayed bridge, the method being characterized in that the following operations are performed: initially the shortest bottom stay (3) is mounted, after which each of the other stays is mounted going progressively upwards from stay to stay and, when mounting the first strand (4'₁) of each of the stays other than the bottom stay, use is made of the guide cage (5, 6) that has served for mounting the preceding stay, while said cage is still suspended from the preceding stay.
3. A method according to any one of the preceding claims, for mounting two vertical or substantially vertical sheets (N_1, N₂) of oblique stays on the same longitudinal side of a tower of a stayed bridge, the two sheets together forming an acute dihedral angle, the method being characterized in that two stays are mounted simultaneously, one for each of the two sheets, the stays being located at the same level and a single traction cable (9) being used that extends around a closed circuit in the form of an isosceles triangle defined by pulleys (16, 17₁, 17₂), the two equal long sides (AB₁, AB₂) of said triangle extending along the oblique axes of the two stays to be mounted, and the third side (B₁B₂) extending horizontally, across to the bridge, and including a reversibly rotatable winch (18) or the like.
4. Mounting apparatus for mounting multiple strand stays by the method according to any one of the preceding claims, apparatus being characterized in that it comprises a guide cage for the strands (4) and the traction cable (9), the cage being made up of a succession of rigid hoops (5) interconnected by strings (6), each hoop comprising an arc (7) and an easily removable bottom closure bar (8).
5. Mounting apparatus according to claim 4, characterized in that the guide cage comprises three parallel strings (6), one being attached to the tops (C) of the various arcs (7), and the other two strings being attached to the feet (D, E) of said arcs.
6. Mounting apparatus according to any one of claims 4 and 5, characterized in that the guide cage contains at least one wire (10, 11) parallel to the strings (6) and serving as a guide rail for a sliding carriage (12), said carriage being fixed at an intermediate point of the traction cable (9) and being disposed in such a manner that the heads of the strands (4) to be installed are easily attachable thereto in removable manner.
7. Mounting apparatus according to claim 6, characterized in that the carriage (12) has two rigid tubular lengths (15) on either side thereof, the lengths having two respective guide wires (10, 11) passing therethrough, which wires are contained inside the cage.
8. Mounting apparatus according to any one of claims 6 and 7, characterized in that the above or "main" carriage (12) is associated with an auxiliary carriage (20) which is fixed in easily removable manner to an intermediate point of the traction cable (9) disposed a little higher than the main carriage, which auxiliary carriage is also mounted to slide on each of the guide wires (10, 11) and is organized in such a manner that the heads of the strands (4) to be installed are easily fastenable thereto in removable manner.
9. Mounting apparatus according to any one of claims 6 to 8, characterized in that each carriage (12, 20) is organized in such a manner that the heads of two strands (4) to be installed are easily fastenable thereto in removable manner.
10. Mounting apparatus according to any one of claims 4 to 9,
       characterized in that the distance between successive hoops (5) of the cage lies in the range 5 meters to 10 meters.

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