FR2642449A1 - Improvements to cable-stayed bridges and more particularly to their towers and cable stays - Google Patents

Abstract

In a cable-stayed bridge comprising a bridge floor, at least one concrete tower 2 and cable stays 3, the cable stays are composed of a plurality of independent strands 4, the tower comprises, in order to receive each cable stay, two curved tunnels 6 cut into the concrete and emerging on the one hand, at their lower end 61 on one of the side faces F, G of the tower, in a direction which is oriented obliquely downwards, and, on the other hand, at their upper end 62, horizontally facing each other so as to delimit between them a coupling chamber 7 which is accessible from the outside and the upper ends of the strands forming the two cable stay sections contained in the tunnels are connected horizontally end to end and in pairs by individual couplers 14 located in the coupling chamber.

Description

Improvements to cable-stayed and cable-stayed bridges Particularly to their pylons and stay cables
The invention relates to cable-stayed bridges comprising an apron, at least one concrete pylon and stay cables and it relates more particularly to the pylons of these bridges as well as their stay cables and to the means for anchoring these stay cables to these pylons.

 In general, in the known embodiments of said bridges, the shrouds each have an end which is anchored on a pylon using an intermediate metal structure, itself mounted beforehand on the pylon.

 This formula is expensive, difficult to implement, unattractive and it hardly lends itself to at least partial replacements of the shrouds.

 There is certainly an embodiment which eliminates certain of these drawbacks: it is that comprising a "saddle" or curved seat placed on the pylon -and suitable for receiving an intermediate section of the shroud to be supported, which extends then descending obliquely towards the apron on either side of said saddle.

 This realization is simpler, more compact and more aesthetic than the previous ones.

But it still has a number of drawbacks, and in particular the following
- to mount the shroud on the saddle which is assigned to it, it is necessary to slide half the length of this shroud on this saddle, which generates friction between the saddle and the shroud and risks damaging each of the two elements in contact mutual,
- the changes in curvature imposed on the various components of the shroud during the indicated slip can also cause serious disorders within this shroud,
- said stay cable does not lend itself more than the previous ones to at least partial replacements.

 The object of the invention is, above all, to eliminate these drawbacks.

 For this purpose, the guyed bridges of the type in question according to the invention are essentially characterized in that their guy lines are composed of a plurality of independent strands which, at least in their portion carried by the pylons, are individually protected and held transversely spaced from each other by mechanical spacers, in that their pylons comprise, to receive each stay, two curved tunnels hollowed out in the concrete constituting the pylon, respectively on both sides of the median transverse plane of the pylon, these two tunnels emerging from on the one hand, at their end remote from said plane, on one of the two transverse faces of the pylon, in a direction oriented obliquely downwards, and, on the other hand, on the side of said plane, horizontally opposite one of the other so as to delimit between them a coupling chamber accessible from the outside, and in that the upper ends of the strands composing l es two sections of guy wire contained in the tunnels are connected horizontally end to end and two by two by individual couplers arranged in the coupling chamber.

In preferred embodiments, use is also made of one and / or the other of the following arrangements.
the inner wall of each curved tunnel is lined with a prefabricated rigid tubular jacket, in particular made of metal,
each strand is coated, at least in its portion housed in a tunnel, with a protective sheath made of rigid plastic, in particular high density polyethylene,
- the volume between each strand sheath and the rigid jacket which surrounds it is filled with a mortar without shrinkage injected,
the individual couplers used to connect the different strands two by two are distributed in an equilateral mesh with several stages, in accordance with the teachings of patent FR 80 25757 of the applicant,
- the multiple coupling-according to the preceding paragraph is carried out in such a way that one third of the couplers comes into axial abutment in a first direction against a rigid plate bearing on the concrete around the mouth of one of the two tunnels in the coupling chamber, and that another third of said couplers comes into axial abutment in the opposite direction to the previous one against another rigid plate bearing against the concrete around the mouth of the other tunnel,
- the upper horizontal sections of several of the shrouds carried by the same pylon - or even of all of these shrouds - are arranged parallel side by side at the same level,
- in a bridge according to the preceding paragraph, the lower ends of the stays, anchored on the deck, are arranged in the same longitudinal vertical plane of the bridge
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 what follows, we will describe preferred embodiments of the invention with reference to the accompanying drawings in a manner of course not limiting.

 Figure 1 of these drawings schematically shows a portion of a cable-stayed bridge established according to the invention.

 FIG. 2 shows on an enlarged scale, in vertical section along II-II, FIG. 5, a portion of a pylon of said bridge supporting a stay in accordance with the invention.

 FIG. 3 shows again on a larger scale the coupling chamber visible in FIG. 2.

 Figures 4 and 5 show, respectively in vertical section along IV-IV, Figure 5, and in horizontal section along a stay, the above portion of pylon.

 FIGS. 6 and 7 very schematically show a variant of the cable-stayed pylon head according to the invention, respectively in front view and in side view.

In a manner known per se, the bridge to be equipped in each case comprises an apron 1 suspended from at least one concrete pylon or pillar 2 using guy wires 3 anchored on this pylon and on this apron and distributed across and on the other side of said pylon, preferably symmetrically with respect to its median transverse plane
T by forming inverted V's.

 In the embodiment illustrated in Figures t to 5, the shrouds 3 are distributed in a single ply contained in a median longitudinal transverse plane of the bridge or in several such parallel plies, in particular two in number, in which case they border the apron 1.

 The invention relates more particularly to the construction of the shrouds 3 and their anchoring on the pylons 2.

 Each guy consists of a plurality of independent strands 4, that is to say that can be mounted and tensioned independently of each other and even replaced individually.

 This possibility of individual replacement of the strands can prove to be very advantageous in practice, because it makes it possible to ensure such replacements without interrupting the traffic on the bridge, in fact, if each layer of shrouds extending on one side of a pylon includes twenty guy lines and that each guy line is made up of twenty strands, the load supported by each strand is only 1 / 400th of the total, proportion which is much lower than the tolerances or safety margins used for the construction of bridges.

 Each stay forms an inverted V covering a pylon or at least a portion of this pylon, it is composed of two halves extending respectively on either side of a span 5 of the pylon forming "saddle", and the ends upper of the two halves, of the stay, which rest on the saddle are connected to each other horizontally by a plurality of single-strand individual couplers used to connect each one strand to another and all arranged near the median transverse plane of the saddle, which is the T of the pylon.

 The saddle 5 or bearing surface is itself formed by two curved tunnels 6 hollowed out in the concrete constituting the pylon 3 during the casting thereof, all of these two tunnels forming a sort of arch open towards the bottom and preferably symmetrical about the vertical transverse median plane of the pylon.

 The lower ends 61 of the two tunnels 6 open respectively on the two transverse faces F and G of the pylon 2 and are oriented obliquely downwards.

 The upper ends 62 of the two tunnels 6 open horizontally opposite one another symmetrically with respect to the plane T so as to define between them a coupling chamber 7.

 It is inside this chamber 7 that the upper ends of the two halves making up the shroud 3 considered are connected together, halves of which the upper portions are themselves housed in the two tunnels 6.

 The interior walls of these tunnels 6 are delimited by prefabricated rigid tubular liners 8, preferably made of metal, which are placed in the concrete during its casting.

 The portions, of individual strands 4, which are arranged inside the tunnels 6, are individually protected by rigid sheaths 9, in particular made of high density polyethylene, and these sheaths 9 are kept transversely spaced from one another by suitable spacers 10, constituted in particular by rigid plastic grids.

 Each volume between sheaths 9 and the jacket 6 which surrounds them is closed at its lower 61 and upper 62 ends by, respectively, a sealing plug 11 and a rigid metal plate 12, and it is filled with a mortar without shrinkage 13 injected after fitting the sheaths 9 and their spacers 10.

 As regards the mutual connection of the two stay halves in the chamber 7, it is carried out strand by strand using individual couplers 14 each receiving end to end two strand ends to be connected to each other.

 To form such connections, provision is made in the concrete structure of the pylon 2 for an access recess 15 FIGS. 4 and 5) of sufficient volume to receive a fitter 16, said recess communicating directly with the chamber 7.

 To reduce the transverse size of the assembly formed by the various couplers 14, they are preferably distributed according to an equilateral triangulated mesh extending over several stages, as taught by the above-mentioned patent.

 With such a distribution, each coupler 14 is surrounded by a plurality of common portions of other strands which are housed in external grooves of said coupler, the number of these grooves being generally six.

 In addition, according to an advantageous characteristic of the present invention for which the coupling of the strands of each stay stretches in three stages each comprising a third of the couplers, one axially applies a third of these couplers against one of the metal plates 12 delimiting the chamber 7, and the other third of these couplers in the opposite direction from the previous one against the other plate 12. In this case, the plates 12 are crossed contiguously by stripped sections of the strands 4 and not by their sheaths 9 , which abut axially against these plates.

 This measure has the advantage of ensuring good resistance of the pylon 2 to the asymmetrical forces exerted horizontally on it, for example during the passage of heavy goods vehicles on the bridge successively from one side to the other of the pylon.

 Indeed, the application of such an asymmetrical force has the effect of temporarily overloading the various strands 4, the couplers 14 of which bear against one of the plates 12, strands the number of which corresponds to one third of the total, while leaving the another two thirds.

 This temporary overload is always relatively low and therefore entirely acceptable.

 In addition, the friction produced between each tensioned strand and its sheath in the curved zone of the strand increases the resistance opposed by the assembly of this strand and of the coupler corresponding to the forces exerted on said strand, so that only a very small fraction of said strands. efforts finally reaches said coupler, this fraction being even zero in most cases.

 It should also be noted that the friction reported, generally generated by the lateral support of each shroud tensioned on the saddle which it straddles, ensures an effective filtering of the variations of tension at relatively high frequency generated by the wind and by the traffic on the shrouds: as a result, these variations are practically not transmitted to the couplers1 which ensures excellent resistance to fatigue — of the shrouds and of their anchorages.

 In the sections, shrouds 3 r which are arranged outside of the pylon 2, the strands 4 constituting these shrouds are preferably juxtaposed laterally side by side, being then possibly housed, in a manner known per se, inside a common protective sheath made of any desirable material such as high density polyethylene.

We see in Figure 2
deflecting members 17 which converge the strands outward to pass them from their separated position to their laterally juxtaposed position,
- cylindrical or cylindro-conical protective sleeves 18 and 19 ensuring the connection between the outlets 61 of the tunnels and the common sheath above,
- And a partition 20 forming in the chamber 7, with the plates 12, a housing suitable for receiving the couplers 14 as well as the strands of strands emerging from these couplers, said housing being advantageously equipped with a door controlling access to the inside said housing from niche 15.

 To mount on a pylon 2 a guy 3 of the kind described above, the procedure is as follows.

 Initially, the housing 12.20 is empty and the two tunnels 6 are lined with their rigid shirts 8 which are closed at their two ends by the elements 11 and 12 and which are themselves lined with protective and guiding sleeves 9 for the strands 4, the said sheaths being guided by the grids 10, passing through the plugs II contiguously and being immobilized by the filling mortar 13.

 From a winch mounted on the top of the pylon, we pull one by one each strand 4 and, after having possibly rounded the end of this strand to give it a shell shape, we possibly thread this end into the elements annulars 17, 18 and 19 if these are formed in one piece and it is forced into the sheath 9 which is assigned to it, from an outlet 61 of the tunnel.

 For this purpose the point of each strand 4, in which the cable of the traction winch is hung, is located at a sufficient distance from the end of said strand to make possible the indicated introduction of the strand into its sheath by pushing.

 At the end of this pushing, each end of the strand comes out of its sheath in the chamber 7.

The opposite ends of these strands are then connected end to end using individual couplers 14. -
Then each strand is individually tensioned from its lower end, which is anchored on the deck 1 of the bridge or on an appropriate foundation.

 When the connections of all the strands are completed and the latter are all energized, the couplers 14 and the stripped strands of the strand 4 are coated and leave therefrom with an anti-corrosion product, such as a wax, this product being able to fill the box 12,20 which one then closes the access door.

 It should be noted that with such a method of hanging the shrouds on the pylons, it is unnecessary to slide great lengths of these shrouds against their carrying saddles, which eliminates the risks of deterioration by friction of said shrouds and saddles .

 The variant shown diagrammatically in FIGS. 6 and 7 differs from the embodiment described above by the fact that the upper horizontal sections of the different guy wires 3 carried by a mast pylon 2 are arranged parallel side by side in two horizontal layers juxtaposed vertically, inside a common coupling chamber 7.

 These upper sections are therefore offset from each other transversely, that is to say in the direction of the width of the bridge.

 But in general, and just as in the previous embodiment, the anchoring points of the lower ends of the various stay cables 3 on the bridge deck 1, points visible at P in FIG. 1, are aligned in the same longitudinal vertical plane from the bridge.

 This alignment of the lower anchor points P implies that some of the shrouds 3 are slightly inclined on the longitudinal vertical plane which contains their upper horizontal section.

 It should be noted that the construction proposed for the guiding means for the shrouds in the curved tunnels 6 is entirely compatible with the slight angular offset, which can result from this slight inclination, between the exit axis of such a tunnel. and the axis of the corresponding free shroud section: in fact said axis of the free shroud section 3 can be angularly offset, during construction, relative to said exit axis from the tunnel 6 by playing on the respective locations of the recessed holes in the plugs end 11 and, in any case, the angular play still possible between these two axes after the setting of the injection mortar 13 in the tunnel allows shifts of the order of. 1 degree, which is quite sufficient in practice.

 As a result of which, and whatever the embodiment adopted, there is finally a cable-stayed bridge whose constitution and implementation result sufficiently from the above.

This bridge has many advantages over those previously known, and in particular the following
- possibility of using guy lines with independent strands, which makes it possible to partially replace these guy lines, without the need to interrupt traffic,
- absence of degrading friction between the shrouds and saddles when mounting the shrouds on the pylons,
- effective contribution made by the mutual friction between the shrouds and the saddles which they overlap to the tensile strength of said shrouds,
- limited cost price due to the absence of a special metal hanging structure,
- aesthetic.

 As goes without saying, and as already follows from the foregoing, the invention is in no way limited to those of its modes of application and implementation which have been more especially envisaged if it embraces it, on the contrary, all the variants, in particular those where the two curved tunnels receiving the same stay would be asymmetrical with respect to the median transverse vertical plane of the corresponding pylon.

Claims (8)

 1. Cable-stayed bridge comprising an apron (1), at least one concrete pylon (2) and stay cables (3), characterized in that the stay cables (3) are composed of a plurality of independent strands (4) which , at least in their portion carried by the pylon, are held transversely apart from each other by mechanical spacers (10), in that the pylon (2) comprises, to receive each guy, two curved tunnels (6) hollowed out in the concrete constituting the pylon respectively on the two sides of the median transverse plane (T) of the pylon, these two tunnels opening on the one hand, at their distant end (61) from said plane, on one of the two transverse faces (F, G ) of the pylon, in a direction oriented obliquely downwards, and, on the other hand, on the side of said plane, horizontally opposite one another so as to delimit between them a coupling chamber (7) accessible from the exterior, and in that the upper ends of the strands (4) composing the two sections of guy wire contained in the tunnels are connected horizontally end to end and two by two by individual couplers (14) arranged in the coupling chamber (7).  2. Cable-stayed bridge according to claim 1, characterized in that the inner wall of each curved tunnel is lined with a prefabricated rigid tubular jacket (8), in particular made of metal.  3. Cable-stayed bridge according to any one of the preceding claims, characterized in that each strand (4) is coated, at least in its portion housed in a tunnel (6), by a protective sheath (9) made of plastic material rigid, especially in high density polyethylene.  4. Cable-stayed bridge according to claims 2 and 3, characterized in that the volume between each sheath (9) of strand and the rigid jacket (8) which surrounds it is filled with a mortar without shrinkage injected (13).  5. Cable-stayed bridge according to any one of the preceding claims, characterized in that the individual couplers (14) used to connect the different strands (4) two by two are distributed in an equilateral mesh with several stages.  6. Cable-stayed bridge according to claim 5, characterized in that the multiple coupling is carried out such that one third of the couplers (14) comes into axial abutment in a first direction against a rigid plate (12) bearing on the concrete around the mouth of one of the two tunnels (6) in the coupling chamber (7), and that another third of said couplers (14) comes into axial abutment in the opposite direction to the previous one against another rigid plate (12) bearing against the concrete around the mouth of the other tunnel (6).  7. Cable-stayed bridge according to any one of the preceding claims, characterized in that the upper horizontal sections of several of the stay cables (3) carried by the same pylon (2) - or even of all of these stay cables - are arranged parallel side side by side on the same level.  8. Cable-stayed bridge according to claim 7, characterized in that the lower ends (P), stay cables (3), anchored on the deck (1) are arranged in the same longitudinal vertical plane of the bridge.