EP0329517A1 - Cable-stayed bridge and method of constructing it - Google Patents

Abstract

PCT No. PCT/FR89/00040 Sec. 371 Date Dec. 10, 1990 Sec. 102(e) Date Dec. 10, 1990 PCT Filed Feb. 5, 1989 PCT Pub. No. WO89/07173 PCT Pub. Date Aug. 10, 1989.A cable-stayed bridge including at least one concrete platform consisting of an assembly of caisson elements, at least partly prefabricated, extending transversely to the bridge. Each element is composed of an upper table and a lower table separated by spaces which extend transversely to the platform, and are connected by walls at the side and the end, and with longitudinal intermediate partitions and transverse partitions. The piers of the bridge extend preferably upwards to the platform and carry both a part of the platform and the pylon.

Description

The present invention relates to cable-stayed bridges with a concrete deck, intended in particular to cross spans of the order of 80 to 250 m, and the construction of such bridges.

According to the current state of the art, the deck of such cable-stayed bridges consists of a concrete box suspended at regular intervals by guy lines which themselves transmit the load to pylons located on either side of the breach. to cross.

The shrouds can be located in the median plane of the structure, between the traffic lanes. The stability of the deck under the influence of asymmetrical loads when only one traffic lane is loaded is then ensured by the torsional resistance of the box.

In another known form, the shrouds are placed on either side of the deck in two vertical planes, or oblique and also inclined on either side of the axis of the structure to allow the shrouds to converge in a single point on the pylon head.

In the case of this double lateral suspension, recent embodiments have appeared to simplify the construction of the deck and reduce the cost thereof. When the main span is sufficiently small (of the order of 100 to 150 m maximum) the deck then consists of a simple solid concrete slab suspended along its two lateral edges. The limits of use of this solution are given by the excessive flexibility of the deck vis-à-vis the risk of general buckling or for the operation of the structure. In addition, the low transverse rigidity of the slab does not always ensure the stability of the structure vis-à-vis the wind in a satisfactory manner.

For larger spans (from 100 to 300 m for example), the deck was made up of a slab ribbed in the transverse direction and provided with longitudinal edge beams in which the shrouds are anchored.

Such aprons are in principle easier to produce than box aprons. They do not, however, have the same longitudinal rigidity in flexion and above all their torsional inertia is negligible. The effects of accidental phenomena such as exceptional wind gusts, impact of a vehicle against a shroud, therefore have much more serious consequences on these structures.

On the other hand, the decks, whether in boxes or formed of a ribbed slab, can be formed of successive prefabricated elements assembled to each other in the longitudinal direction. This less expensive method of construction does not appreciably affect the rigidity and the above remarks remain valid in this case.

The object of the present invention is to overcome the limitations or inadequacies recalled above, authorizing the production of works whose rigidity is comparable to box decks, while retaining the simplicity of form and construction of the decks in solid or ribbed slab. .

To obtain this result, the invention provides a cable-stayed bridge, comprising:
- at least one deck formed by a series of at least partially prefabricated elements, each element extending over the width of the deck and over part of its length,
- a pylon carried by a pile, and the top of which supports a series of shrouds supporting the deck, which has the particularity that each element has interior recesses elongated in the transverse direction, and has a vertical cross section which is roughly symmetrical with respect to to a horizontal plane.

Thus, the main difference with conventional deck structures lies in the fact that the bridge is made up of a series of adjoining transverse boxes, and no longer of longitudinal boxes or of flat, simple or ribbed slabs. The result, for equal weight, is a very high torsional rigidity of the apron.

The elements are joined together to constitute the deck is made by all conventional means, and in particular by longitudinal prestressing cables extending over several successive elements and / or over the entire length of the deck.

According to a first embodiment of the elements, each of these is a prefabricated one-piece element formed by a lower table and an upper table which carries the floor, separated by interior voids extending over a large part of the transverse dimension of the element, the two tables being joined together by walls and, optionally, longitudinal and transverse partitions.

According to another embodiment of the elements, each of these comprises a prefabricated part consisting of a lower table and transverse and longitudinal vertical walls or partitions, horizontal slabs resting on said walls or partitions, and a continuous upper slab the along the deck, cast on the slabs and carrying the floor.

The first embodiment provides time and productivity savings thanks to further prefabrication. The second embodiment allows easy replacement of the floor slabs if necessary, which is advantageous especially in countries with a harsh climate, where it is subjected to the attack of de-icing products.

Due to the high torsional rigidity of the deck, the corresponding forces are transmitted at a distance, in particular to the abutments and the piles. It is advantageous to give the batteries a structure which makes them capable of absorbing these forces. For this, provision can be made for the stack carrying the pylon to extend upwards to the deck and support both at least part of the deck and the pylon.

In the case where the bridge comprises a relatively wide deck or two juxtaposed decks, provision is advantageously made for each stack to carry the part of the deck or decks which is closest to the longitudinal axial plane of the bridge and the part of the decks which is the most separated from the longitudinal axial plane of the bridge is supported by additional stay cables situated approximately in a transverse vertical plane and connecting the deck to the summit area of the pylon.

One thus constitutes a triangular structure constituted by the deck, the pylon and the additional shroud. This structure is formed in a transverse plane, and is therefore perpendicular to the longitudinal triangles formed by the deck, the pylon and the conventional shrouds.

According to an interesting modality, at least one of said additional stay cables is deflected at the top of the pylon and comes to hang on the opposite edge of the deck. The fixing and tensioning of the additional shrouds is thus done at the deck, which facilitates assembly.

According to a different modality, which is particularly advantageous for the case of a very wide bridge with two decks, these are hinged together or are rigidly linked together in line with the pile, and at least one of said additional stay cables is diverted to the top of the pylon and clings to the opposite edge of the same deck, near the longitudinal axial plane of the bridge.

To further strengthen the connection between the deck and the beam, it is possible to provide, preferably in addition to the additional shrouds, oblique shoring beams, connecting the edge of the deck most distant from the stack at a point thereof located lower than the apron.

The arrangements that we have just listed are compatible with various types of bracing of bridge, in particular those where there is a single ply of shrouds in the axial longitudinal plane of the bridge, those where there are two plies of shrouds each located in an oblique plane containing the outer edge of an apron and the top of the pylon, or those where there are four layers of shrouds, two located in the oblique planes which we have just spoken and two others in almost vertical planes, connecting the top of the pylon at the parts of the decks located near the longitudinal axial plane of the bridge.

The head of the pylon is of increasing complexity with the number of layers of cables, in particular if it must support the additional cables mentioned above, and which are in planes perpendicular to these layers.

According to a first modality, the pylon head is a metallic piece which has, in its upper part, a saddle-shaped surface and on which the deck support struts resting side by side are deflected to go to two attachment points located on the apron approximately symmetrically with respect to the pylon, the middle part of said metal part having a cavity which contains the means for anchoring or deflecting the additional stays.

According to a second modality, the pylon head comprises for each cable ply, a deflection assembly situated in the plane of this ply and comprising at least one part crossed by a number of deflection passages equal to the number of shrouds, these passages being superimposed on each other, and the means for anchoring or deflecting the additional stay cables being placed between the deflection assemblies.

This modality is more complicated in construction, but it turns out to be particularly well suited to the case of bridges with four plies of shrouds, since it leads to a head of small transverse dimensions with low stresses in overhang on the pylon. In addition, all the shrouds of the same tablecloth are exactly in the same plane.

It should be noted that the two head structures are interesting even in the absence of additional shrouds.

Another point to consider is that of the hanging of the shrouds on the elements constituting the deck. This attachment must, normally, be done through a side wall of the prefabricated element. The fact that the shrouds have different inclinations from one to the other very fact that, if we provide, as in usual practice, a passage through the element, with attachment device on the underside, the prefabricated elements which carry the hooks will be different from each other, and in particular their irons reinforcement should be arranged in different ways. This is likely to complicate the work of the prefabrication site and reduce its output.

To avoid this drawback, it is advantageously provided that the means for securing a stay cable with an element of the apron comprise a plate, flat as a whole, bearing by a first face against the apron, and bearing on the second face means for anchoring the guy, means for preventing sliding of said plate on the deck, and at least one prestressing cable, or an anchoring rod, directed approximately perpendicular to the plane of said plate, this cable passing through said plate and being retained by abutment against it, and crossing the apron to be in abutment against the opposite side of the apron.

According to a first embodiment, the deck has a flat support surface for the plate, this flat surface being parallel to the stay and to the longitudinal axis of the bridge, with a central hollow part, the plate carries, on its face in contact with said bearing surface, a projection which penetrates into said hollow part and which contains the means for hooking said prestressing cable, and the prestressing cable enters the apron at the bottom of said hollow part and will hang on the transversely opposite edge of the deck.

It is understood that, according to this embodiment, the edges of the prefabricated elements all have parallel bearing surfaces, and making with the vertical the same angle as the corresponding cable ply. We can therefore have all identical prefabricated elements, the orientation of the metal anchoring part is the only difference from one prefabricated element to another, in the event that this part is put in place during casting. We can equal Put these parts in place when assembling the bridge. We will then give the plate, or at least the projection of its face facing the apron, a form of revolution, frustoconical for example.

According to another embodiment, advantageous in particular in the case of a bridge with two decks very close to each other, the plate is intended to be supported on a horizontal surface of the deck and bears on the face opposite to the deck, fittings for hanging a shroud obliquely to the horizontal, and the prestressing cable or cables or anchor rods pass through the deck down.

This embodiment saves space in the transverse direction, it facilitates assembly, control and possible replacements. However, the metal attachment parts must be individualized, unless a pivot system is used.

The bridge structure according to the invention allows a particularly advantageous construction method. According to this method, a provisional framework is put in place fixed on a part of the deck already built and supported by the shrouds, this frame advancing in cantilever beyond said already constructed part and being supported by a mounting cable. connecting the top of the pylon to the end of the provisional frame furthest from the part already built, and said provisional frame is used to put in place and fix new deck elements, the length of the mounting cable being modified when the temporary frame is moved.

This avoids subjecting the bridge part already built to abnormal stresses.

• Figure 1 est une vue en élévation d'un pont à hauban.
• Figure 2 est une coupe transversale d'un ouvrage selon la figure 1, dans sa réalisation la plus simple.
• Figure 3 est une coupe longitudinal partielle d'un tablier de pont selon l'invention.
• Figure 4 est une couple longitudinale d'un disposi­tif d'accrochage de hauban sur le tablier, et
• Figure 4a est une coupe transversale du même dis­positif selon la ligne AA de la figure 4.
• Figure 5 est une coupe transversale d'un tablier montrant deux dispositifs d'accrochage identiques à ceux de la figure 4.
• Figure 6 est une coupe transversale au droit du pylône d'une réalisation différente de celle de la figure 2.
• Figure 7 est une vue en élévation du pont au voi­sinage du pylône selon la réalisation de la figure 6.
• Figure 8 est une coupe longitudinale partielle d'un tablier suivant un mode de réalisation différent de celui de la figure 3.
• Figures 9 à 12 décrivent un dispositif d'accrocha­ge de hauban suivant une réalisation différente de celle des figures 4 et 5, la figure 9 étant une vue en éléva­tion, la figure 10 une coupe transversale, la figure 11 une coupe longitudinale, et la figure 12 une coupe perpen­diculaire à la direction du hauban.
• Figure 13 est une vue en élévation transversale de la tête d'un pylône.
• Figure 14 est une vue en élévation longitudinale de la même tête.
• Les figures 15a et 15b sont respectivement des vues en coupe transversale et en élévation partielle d'un troisième mode de réalisation selon l'invention.
• Figure 16 est une coupe transversale partielle des tabliers du pont illustré aux figures 15a et 15b.
• Figure 17 représente une variante de la zone cen­trale des tabliers de la figure 16.
• Figures 18 et 19 sont, respectivement, une vue en coupe transversale et une vue en élévation longitudinale d'une réalisation de tête de pylône différente de celle des figures 13 et 14.
• Figures 20 et 21 sont des vues schématiques mon­trant deux phases successives du procédé de construction d'un pont selon l'invention.

The invention will now be explained in more detail with the aid of practical examples illustrated with the figures among which:

• Figure 1 is an elevational view of a cable-stayed bridge.
• Figure 2 is a cross section of a structure according to Figure 1, in its simplest embodiment.
• Figure 3 is a partial longitudinal section of a bridge deck according to the invention.
• FIG. 4 is a longitudinal couple of a device for hanging a guy wire on the deck, and
• Figure 4a is a cross section of the same device along line AA of Figure 4.
• Figure 5 is a cross section of an apron showing two attachment devices identical to those of Figure 4.
• FIG. 6 is a cross section at right of the pylon of a different embodiment from that of FIG. 2.
• FIG. 7 is an elevation view of the bridge in the vicinity of the pylon according to the embodiment of FIG. 6.
• FIG. 8 is a partial longitudinal section of an apron according to an embodiment different from that of FIG. 3.
• Figures 9 to 12 describe a stay for hanging a device in a different embodiment from that of Figures 4 and 5, Figure 9 being an elevational view, Figure 10 a cross section, Figure 11 a longitudinal section, and Figure 12 a section perpendicular to the direction of the stay.
• Figure 13 is a cross-sectional view of the head of a pylon.
• Figure 14 is a longitudinal elevational view of the same head.
• Figures 15a and 15b are respectively cross-sectional views and partial elevation of a third embodiment according to the invention.
• Figure 16 is a partial cross section of the bridge decks shown in Figures 15a and 15b.
• Figure 17 shows a variant of the central area of the aprons in Figure 16.
• Figures 18 and 19 are, respectively, a cross-sectional view and a longitudinal elevation view of a pylon head embodiment different from that of FIGS. 13 and 14.
• Figures 20 and 21 are schematic views showing two successive phases of the method of building a bridge according to the invention.

Figure 1 shows a cable-stayed bridge, comprising an apron 1, resting at its ends on end piers 2, and supported in its central part by stay cables 3, which connect it to the head 4 of two pylons 5, carried by batteries 6, themselves grounded 7.

It is clear that the invention is not linked to the number of piers and pylons.

Figure 2 shows a cross section of a bridge according to the invention, according to its simplest embodiment: the bridge comprises a deck 1, arranged symmetrically with respect to the transverse axial plane XX 'of the structure. The deck is supported by two substantially vertical stay cables 3 which connect the pylon head to the deck 1 in its region closest to the axial plane XX ′. The stack 6, which rests on the ground 7 by a sole 8, extends in height up to the level of the lower part of the deck, which it supports. It also supports the pylon 5, which has a smaller transverse extension than the stack 6.

The deck 1 is formed of a series of hollow transverse structures, which gives them great rigidity in bending. The bending forces are mainly supported by the abutments, and incidentally by the piles 6 and the cables 3.

Figure 3 shows a longitudinal section of an apron element 10, the assembly of similar elements constituting the apron 1. It is a prefabricated element comprising a lower table 11 and an upper table 12, the latter supporting pavement. Tables 11 and 12 are joined by transverse walls 13, as well as by an intermediate partition 14. The number of intermediate partitions 14 is not fixed, it may depend on the dimensions of the element 10. The inter partition mediary 14 may not even exist. Between the walls 13 and the intermediate partition 14, there are voids 15, which serve to reduce the weight of the element and to improve the efficiency of its load-bearing section with respect to the longitudinal flexions of the structure. It will be observed that the section of the deck is symmetrical with respect to a horizontal plane.

The voids 15 extend transversely to the edge walls 16 (FIG. 2), being only interrupted by a central partition 17 which reinforces the rigidity of the element in the longitudinal direction. The transverse resistance of the element is ensured by reinforcements 18, which can be conventional passive reinforcements, pre-tensioned adherent prestressing reinforcements, or post-tensioned prestressing reinforcements having a layout adapted to bending stresses, or all combinations of the three types of reinforcement. Only a small number of these frames have been shown in FIG. 3. The deck elements 10 are supported on each other, and held by longitudinal prestressing cables, not shown.

In the center of FIG. 3, we see a transverse prestressing cable 19.

FIGS. 4, 4a and 5 illustrate the method of connecting the shrouds 3 with the decks 1A and 1B of FIG. 2. A hooking piece 20 comprises a support plate 21, which carries on its upper face fittings 22, 23, welded to said plate 21, and oriented obliquely so that their core is parallel to the direction of the stay 3. The fittings 22, 23 hold the stay 3 by means of a stop piece 24, which cooperates with a clamping head 25 of the shroud. On its lower face, the plate 21 carries a frustoconical projection 26, which penetrates into a cavity of the same shape provided in the longitudinal wall 16 of an apron element 10.

In addition, the plate 21 is crossed by anchor rods 27, which are put under prestressing by bearing on the underside of the deck. These tie rods are shown vertical, but can be obliques.

The forces transmitted by the stay 3 to the deck can be analyzed as comprising a vertical component, which is transmitted to the deck via the plate 21 and the tie rods 27, and a horizontal component, which is transmitted to the deck by the intermediate of the plate 21 and the projection 26, which plays the role of an anchoring key.

FIG. 5 also shows barriers 28 which separate the vehicles from the hooking devices. The spacing between these two barriers 28 determines the free space for the base of the pylon as can be seen in FIG. 2.

Figures 6 and 7 relate to another embodiment.

When the width of the deck increases (with the number of traffic lanes to be carried), as well as the main span between pylons, the torsional stresses in the deck become critical, as well as the transverse deformability under the passage of asymmetric loads (only one loaded pavement). According to this second embodiment, the suspension of the deck is ensured by two plies of guy wires 3 anchored on the banks and contained in two oblique planes whose intersection is substantially at the upper level of the pylon 4.

The entire load of the deck 1 is transmitted to the stack 6 and to the foundations by the central pylon 4, the shapes of which are chosen to have maximum longitudinal inertia at the deck and maximum transverse inertia at its top.

The shrouds 3 neighboring the pylon cooperate in the resistance of the structure vis-à-vis the horizontal forces. Special stabilizing shrouds 30 are also provided for this purpose in the transverse plane passing through the axis of the pylon. In addition, the apron is stiffened as necessary in this plane by pins or spacers 31 joining the edges of the apron to the stack 6.

FIG. 8 is a longitudinal section which shows a variant of FIG. 3.

The lower part of each deck element 10 consisting of the lower slab 18 and walls or partitions 13 to 16, which constitute cores, is prefabricated. After installation in the structure, pre-slabs 32 are laid and the upper slab 33 carrying the floor is poured in place.

The process ensures the structural continuity of the floor slabs. In harsh climates, attack by de-icing products may make it necessary to replace the paving slab. The operation is then particularly simple according to the arrangements which we have just described. On the other hand, the symmetry with respect to the median horizontal plane is less rigorous than in the case of FIG. 3.

Figures 9 to 12 relate to a device for anchoring the shrouds on the outer edges, or edges of the deck. One could use, for these anchors, devices similar to those which have been described in connection with FIGS. 4 and 5, but these have the drawback of limiting the width of the roadway. The device described in Figures 9 to 12 avoids this drawback, while obeying a similar principle. An anchoring piece 40 comprises a plate 41, of generally circular shape, which comes to bear on a circular surface 42, provided during the making of the deck elements 10. The surface 42 is oblique to the vertical and made with it has the same angle as the ply of the shrouds 3. On its outer face, the plate 41 carries fittings 43, arranged perpendicular to the plate 41 and which carry the attachment system 44 and tensioning of the shroud 3. On its underside, the plate 41 carries a frustoconical projection 45, which penetrates into a corresponding cavity of the bearing element. In the projection 45 is housed the hooking means 46 of a prestressing cable 47, also visible in Figure 8. The cable 47, which is supported on the outer longitudinal wall 16 which forms the edge of the deck, crosses it and then enters the lower slab 11, and is connected, on the opposite side of the deck, to another hooking piece 40, or to any support means on the opposite edge of the 'element. It therefore contributes, not only to the holding in place of the attachment piece 40 against the apron element 10, but also to the transverse stiffness of this element. It will be observed that it is oriented along a horizontal transverse over most of its path, and relatively slightly oblique at its ends. It can therefore easily be housed between the reinforcing bars of the element 10. The prefabricated elements 10 are identical to each other, and the part 40 is oriented at the time of casting in the direction of the corresponding shroud. It will be noted that the possible replacement of a part 40 is particularly easy.

It will also be noted that the same part can be used for attaching the particular guy lines 30 for stabilizing the pylon. In fact, these shrouds are substantially in the same oblique plane as the main shroud ply.

Figures 13 and 14 show the detail of the head 4 of the pylon 5.

The shrouds contained in the two lateral plies are arranged symmetrically with respect to the mean plane of the structure.

Each shroud 3 is in fact continuous between the central span and the shore span, the change of direction to the right of the pylon taking place on a metal saddle 50 allowing the classification of the shrouds 3 next to each other.

The special stays 30 for stabilizing the pylon are anchored to the top of the latter by known means 51, housed in a niche 52 placed below the saddle 50. A special saddle could also be provided for these particular stays.

Figures 15a and 15b and 16 relate to a third embodiment of the invention.

When the number of traffic lanes to be worn increases (for example beyond pavements of 12 m width each) the size and weight of the prefabricated elements become too large and it is easier to build two separate decks 1C and 1D.

Each deck is suspended externally from a series of 3X oblique stays and in the center from a series of 3Y vertical stays. At regular intervals, articulated connecting rods 60 bring the decks together in the horizontal direction to balance the horizontal component of the forces in the shrouds of the two edge plies. These connecting rods allow relative vertical displacements of the decks, but not their approximation.

According to an alternative embodiment illustrated in Figure 17, we can secure the two decks to the right of the central reservation by concreting 61 to form a single deck.

The arrangement described in FIGS. 15 to 16, with its four plies of shrouds, presents a difficulty as regards the head of the pylon. Indeed, housing side by side the shrouds of the four layers leads to a very large width, in the transverse direction, of this head. In this case, a different pylon head structure illustrated in FIGS. 18 and 19 has been developed. Metal parts 70 to 73, each in the form of a bar pierced with a series of successive holes, are mounted on a frame 74, to form a sort of conical fan, diverging upwards, resting on the top of the pylon 5. The cables 3X of an oblique layer pass successively through a hole in each of the parts 70 to 73, these holes draw a broken line corresponding to the desired deviation of the cable. The inclination of these parts with respect to the vertical is such that they are contained in the plane of the web of the 3X shrouds.

A second series of parts 70 to 73 is disposed in the same way to support 3X shrouds of the symmetrical oblique sheet. Other similar parts, of which only 75 is shown, are arranged in a plane about vertical longitudinal to receive the shrouds 3Y of the central layers.

As can be seen, contrary to the arrangement of FIGS. 13 and 14, the shrouds are supported one above the other, and not side by side. The pylon head thus has very small transverse dimensions, it will however be observed that the attachment means 51 of the particular stabilizing shrouds 30 find their place there without difficulty.

Figures 20 and 21 illustrate part of the deck construction.

After construction of the pier and the pylon, the deck is built by successive cantilevers symmetrically with respect to the pylon.

To limit the weight of the prefabricated elements 10, the distance between the shrouds is subdivided into two or three elements 10. A frame 80 anchored at the rear in the deck already built carries a lifting winch 81 which makes it possible to place each of the elements prefabricated and temporarily immobilized. Due to the relative flexibility of the deck, the application of the weight of these prefabricated elements before implementation of the guy line 3 may create significant temporary stresses. This situation is remedied by suspending the front part of the mounting beam from the main pylon by means of a mounting cable 82 of progressively increasing length.

After installation and adjustment of the prefabricated elements suspended from the assembly frame 80, the joints between elements 10 are poured, the longitudinal prestressing of assembly is implemented and the following permanent shroud is put in place before resuming a new cycle of operations.

FIG. 21 shows an apron element 10 being assembled, arrow 83, to be put in place.

Figure 22 shows the situation after the installation of this element. After pouring the joints between elements and setting up the prestressing and new ones shrouds 3A, the mounting cable 82 is relaxed to advance the frame 80 according to arrow 84.

Claims (16)

1. Cable-stayed bridge, comprising:
- at least one deck (1) formed of a series of hollow elements (10) at least partially prefabricated, each element extending over the width of the deck and over part of its length,
- at least one pylon (5) carried by a pile (6), and the top (4) of which supports a series of shrouds (3) supporting the deck,
characterized in that the elements (10) form transverse boxes and each element (10) has interior recesses (15) elongated in the transverse direction, and has a vertical cross section which is approximately symmetrical with respect to a horizontal plane. 2. Bridge according to claim 1, characterized in that each element is a prefabricated element in one piece formed by a lower table (11) and an upper table (12) which carries the floor, separated by voids interiors (15) extending over a large part of the transverse dimension of the element, the tables being joined by walls (16), and optionally partitions (17), longitudinal and walls (13) and, optionally partitions (14), transverse. 3. Bridge according to claim 1, characterized in that each element comprises a prefabricated part consisting of a lower table (11) and vertical transverse (13, 14) and longitudinal walls or partitions (16, 17), horizontal slabs (32) resting on said walls or partitions, and an upper slab (33) continuous along the deck being poured on the slabs and carrying the floor. 4. Bridge according to one of claims 1 to 3, characterized in that the stack (6) carrying the pylon extends upward to the deck (1) and supports both at least part of the deck ( 1) and the pylon (5). 5. Bridge according to claim 4, characterized in that each stack (6) carries the part of the deck which is closest to the longitudinal axial plane of the bridge and in that the part of the deck which is furthest from of the longitudinal axial plane (XX ′) of the bridge is supported by additional stay cables (30) situated roughly in a transverse vertical plane and connecting the deck (1) to the top zone (4) of the pylon. 6. Bridge according to claim 5, characterized in that at least one of said additional stays (30) is deflected at the top of the pylon and comes to hang on the opposite edge of the deck. 7. Bridge according to claim 5 and comprising two juxtaposed decks, characterized in that the two decks are articulated by means of transverse connecting rods (60) roughly horizontal, allowing relative vertical displacements of the decks, but not their bringing together. 8. Bridge according to claim 7, characterized in that at least one of said additional stay cables (30) is deflected at the top of the pylon and comes to hang on the opposite edge of the same deck. 9. Bridge according to claim 5 and comprising two juxtaposed decks, characterized in that the two decks are rigidly linked together to react as a single deck. 10. Bridge according to one of claims 4 to 9, characterized in that there are provided oblique shoring beams (31), connecting the edge of the deck furthest from the stack at a point thereof located lower than the apron. 11. Bridge according to one of claims 1 to 10, characterized in that the head of a pylon is a metal part having, in its upper part, a saddle-shaped surface (50) and on which the shrouds (3 ) of the support of the apron resting side by side are deflected to go to two attachment points located on the apron approximately symmetrically with respect to the pylon, the middle part of said metal part having a cavity (52) which contains the means of anchoring (51) or deflecting the additional stays (3). 12. Bridge according to one of claims 1 to 11, characterized in that the pylon head comprises for each cable ply, a deflection assembly situated in the plane of this ply and comprising at least one part (70) traversed by a number of deflection passages equal to the number of shrouds, these passages being superposed on each other, and the means for anchoring (51) or deflecting the additional shrouds (30) being placed between the deflection assemblies. 13. Bridge according to one of claims 1 to 12, characterized in that the means for securing a stay cable with an element of the deck comprise a plate (21, 41), planar as a whole, bearing by a first face against the deck, and bearing on the second face means (22 to 25, 43 to 46) for retaining the stay (3), means (26, 45) for preventing sliding of said plate on the deck, and at least one cable prestress (19), or an anchor rod (27), directed approximately perpendicular to the plane of said plate, this cable passing through said plate and being retained by abutment against it, and passing through the deck to be in abutment against the opposite side of the deck. 14. Bridge according to claim 13, characterized in that the deck has a flat surface (41) for supporting the plate, this flat surface being parallel to the stay (3) and to the longitudinal axis of the bridge, with a part central hollow, in that the plate carries, on its face in contact with said bearing surface, a projection (45) which penetrates into said hollow part and which contains the hooking means (46) of said prestressing cable (19 ), and in that the prestressing cable enters the apron at the bottom of said hollow part and will catch on the transversely opposite edge of the apron. 15. Bridge according to claim 13, characterized in that the plate (21) is intended to be in abutment on a horizontal surface of the deck and bears on the face opposite to the deck of the fittings (22, 23) for hanging a guy cable obliquely by compared to the horizontal and in that that the prestressing cable (s) or anchor rods (27) pass through the deck downwards. 16. A method of constructing a bridge according to one of claims 1 to 15, characterized in that a temporary frame (80) is put in place fixed on a part of the deck (1) already built and supported by the shrouds. , this frame advancing in overhang beyond said already built part and being supported by a mounting cable (82) connecting the top of the pylon to the end of the provisional frame furthest from the already built part , and said temporary frame is used to set up and fix new deck elements, the length of the mounting cable being modified when the protective frame is moved.

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