WO1993003228A1

WO1993003228A1 - Improved cable-stayed bridges and method of construction

Info

Publication number: WO1993003228A1
Application number: PCT/FR1992/000775
Authority: WO
Inventors: François Conversy
Original assignee: Conversy Francois
Priority date: 1991-08-07
Filing date: 1992-08-05
Publication date: 1993-02-18
Also published as: FR2680186B1; FR2680186A1

Abstract

A cable-stayed bridge comprises at least one tower (1a) and at least one continuous deck (2) having at least one cable-stayed zone with cables (12a, 13a) connecting the deck to the tower. At least one cable (22a), the tension cable, is secured at one of its ends to the deck (2) and at the other end to a ground anchor block (24a), the relative position of the point at which the tension cable (22a) is secured to the deck (2) with respect to the anchor block (24a) being such that the said tension cable (22a) exerts a traction force over at least a part of the cable-stayed zone. Used particularly to increase the span of cable-stayed bridges.

Description

"Improvements to the cable-stayed bridges and their construction process"

The present invention relates to cable-stayed bridges.

The invention also relates to their construction method. By cable-stayed bridge is meant a bridge comprising at least one pylon and the deck of which comprises at least one span supported by inclined shrouds, the lower end of which is fixed to the deck and the upper end of which is fixed to a pylon. In the remainder of the text, a guyed span means a span supported by guy lines, and a guyed area designates part of the deck supported by guy lines. The shrouds corresponding to a pylon are fixed on either side of it and stretched so that the result of the horizontal forces which they exert on said pylon is relatively small.

Generally, but not necessarily, the lower ends of all the stays are fixed to the deck, either in a guyed area of the deck, or, possibly, in a portion of the deck further supported by piles.

It follows from these provisions that the deck is strongly compressed by the inclined shrouds, mainly in the vicinity of the pylons. This strong compression conditions the design of the deck section for two reasons:

- The section must be sufficient to resist compression.

- It must have sufficient vertical and horizontal inertias to prevent buckling phenomena which particularly affect the guyed areas of the deck. The risk of buckling of the deck means that the possibilities of cable-stayed bridges of known design are lower than those of suspension bridges (by possibility one understands aptitude to cross large breaches). We can recall here that, in the case of a suspension bridge the deck is supported by substantially vertical or hanging cables, the upper end of which is fixed to one or more support cables, said support cables being supported by one or more pylons and their ends being anchored to the ground. The object of the present invention is to remedy the drawbacks of the known embodiments of cable-stayed bridges by designing them so that their possibilities are substantially the same as those of suspension bridges.

The cable-stayed bridge covered by the invention comprises at least one pylon and at least one continuous apron comprising at least one guyed zone, supported by stay cables connecting the apron to the pylon. According to the invention, at least one guy, said tension guy, is fixed by one of its ends to the deck and by the other end to an anchoring block linked to the ground, the relative positions of the point of attachment of the guy tension on the deck and the anchor block being such that said tensioning shroud exerts traction on at least part of the guyed area.

Thus, in order to oppose the buckling phenomenon, the applicant has designed a new type of cable-stayed bridge different from all known embodiments, since it offers the possibility of creating traction in the guyed areas, traction which comes in deduction of the compressions generated by the shrouds. This possibility of creating pull-ups allows:

on the one hand to produce cable-stayed bridges with spans greater than those which can be envisaged for known cable-stayed bridges,

-on the other hand, for cable-stayed bridges with usual spans, to save on the deck, less stressed than in the case of known cable-stayed bridges. According to another aspect of the invention, the method of construction of a cable-stayed bridge, in which at least one cable-stayed span is constructed in a cantilever from a pylon is characterized in that, during construction, the end of the door part is fixed at the end wrong of the guyed span, at least one strut of substantially horizontal construction and this strut is tensioned at the same time as one or more tension struts are tensioned.

Other features and advantages of the present invention will become apparent in the description below. In the appended drawings, given by way of nonlimiting examples:

FIG. 1 shows in elevation a cable-stayed bridge according to the invention, symmetrical, comprising two pylons and a single guyed span, the tensioning guy lines of which are located on either side of the guyed span,

FIG. 2 shows in perspective the cable-stayed bridge of FIG. 1,

- Figure 3 shows in elevation a section perpendicular to the deck of the cable-stayed bridge of Figure 1, - Figure 4 shows in perspective the cable-stayed bridge of Figure 1 at a certain phase of construction,

FIG. 5 shows in perspective the cable-stayed bridge of FIG. 1 at the construction phase just after the construction phase shown in FIG. 4, phase during which the construction cables are put in place,

FIG. 6 is a partial perspective view of the cable-stayed bridge in FIG. 1 during the construction phase shown in FIG. 5,

- Figure 7 shows in perspective another embodiment of cable-stayed bridge according to the invention comprising a single pylon and two guyed spans, symmetrical with respect to the pylon,

- Figure 8 is a partial perspective view of the end of the cable-stayed bridge of Figure 7, end to which the tensioning cables are fixed, - Figure 9 shows in perspective another embodiment of a cable-stayed bridge guy lines according to the invention, symmetrical, comprising two pylons, a large guyed span, located between the two pylons, framed by two guyed spans of lesser span. The cable-stayed bridge shown in FIGS. 1, 2 and 3 comprises two pylons 1a and 1b and an apron 2.

The pylons la and lb are A-shaped and each comprise two oblique bars 10a and 10b, integral at their upper part and bearing on the ground. A horizontal bar 11 connects the two oblique bars 10a and 10b.

The deck 2 is constituted by a guyed span 3, extending from the pylon la to the pylon 1b, framed by two sections 4a and 4b. The section 4a is supported on the stacks 5a, 6a, 7a, 8a and 9a. The section 4b is supported on the stacks 5b, 6b, 7b, 8b and 9b. The guyed area of the deck 2 is thus constituted by the single guyed span 3.

The cross section of the deck 2, visible in particular in FIG. 3, comprises an upper slab 14 intended to support the roadway, a lower slab 15 narrower than the upper slab 14, two oblique webs 16 which connect the edges of the lower slab 15 at the edges of the upper slab 14, and two vertical webs 17 which connect the edges of the lower slab 15 to the upper slab 14. The connection of the slab 14 to the oblique webs 16 is ensured by border beams 18a and 18b. The shrouds 12a and 12b support the guyed span 3. The shrouds 12a connect the pylon la to the guyed span 3. The guys 12b connect the pylon lb to the guyed span 3. At their upper end the guys 12a are anchored in one of the oblique bars 10a or 10b of the pylon la. At their upper end, the stays 12b are anchored in one of the oblique bars 10a or 10b of the pylon 1b. At their lower end the shrouds 12a and 12b are fixed to one or the other of the edges of the deck 2, in the border beams 18a and 18b.

The shrouds 13a connect the pylon la to the deck section 4a. The shrouds 13b connect the pylon 1b to the deck section 4b. At their upper end, the stays 13a are anchored in one of the oblique bars 10a or 10b of the pylon la. At their upper end, the stays 13b are anchored in one of the oblique bars 10a or 10b of the pylon lb. At their lower end the shrouds 13a and 13b are fixed to one or the other of the edges of the deck 2, in the border beams 18a and 18b.

In line with the pylons, the deck 2 has a spacer 19 (see Figure 3). The deck 2 is located above the horizontal bar 11 of the pylons. It is supported vertically on the latter by means of support devices 20.

Horizontally, the deck 2 is supported on the oblique bars 10a and 10b by means of bearings 21. The bearings 20 and 21 are known devices, they allow the longitudinal movements of deck 2 and s' oppose vertical and transverse displacements.

Pairs of tension shrouds 22a and 23a located below the deck section 4a connect the deck 2 respectively to the anchor blocks 24a and 25a secured to the ground. The upper ends of the stays 22a are fixed to bosses 26, visible in FIG. 3, located to the right of the pylon the. The upper ends of the stays 23a are fixed to bosses, not visible, similar to the bosses 26, located to the right of the stack 9a. The vertical components of the tensions of the tension shrouds 22a are transmitted to the pylon la via the bearings 20 and the vertical components of the tensions of the tension shrouds 23a are transmitted to the stack 9a.

Similarly, pairs of tension guy lines 22b and 23b located below the deck section 4b connect the deck 2 respectively to the anchor blocks 24b and 25b secured to the ground.

Of course the sum of the horizontal components of the forces exerted on the deck 2 by the tension shrouds 22a and 23a balances the sum of the horizontal components of the forces exerted on the deck 2 by the tension shrouds 22b and 23b and generates in the guyed span 3 a traction which subtracts from the compressions generated in this guyed span 3 by the guys 12a and 12b.

This traction opposes the phenomena of horizontal and vertical buckling of the guyed span 3, this is the main function of the tension guy lines 22a, 23a, 22b and 23b.

In the case of the cable-stayed bridge shown in FIGS. 1 to 3, the tension cables 22a, 23a, 22b and 23b have another function: They are opposed to the longitudinal movements of the deck 2 which can be due to various causes such as the action of the wind or the passage of rolling loads on the deck 2.

Note that the traction created by the tension stays 22a, 23a, 22b and 23b varies according to the temperature which acts both on the deck 2 and on the tension stays. It is therefore necessary that said tension shrouds are of sufficient length. On the other hand there is a way to make some of these more deformable shrouds.

Indeed, the variation of the longitudinal force exerted by a stay cable when the distance between its two ends varies is due, on the one hand, to the elasticity of the material which constitutes it and, on the other hand, to its change of form, the middle line of the stay being all the closer to the straight line which connects its ends the higher the tension. The impact of the shape change on the deformability of a shroud can be increased by ballasting it with additional masses mainly in its central part.

For example, in the case of the cable-stayed bridge defined by FIGS. 1 to 3, the tension cables 23a and 23b could thus be ballasted. In this hypothesis, the traction exerted by the tension stays 23a and 23b would vary little as a function of the temperature, but said tension stays 23a and 23b would participate little in the longitudinal immobilization of the deck 2, while the tension stays 22a and 22b unweighted would provide most of this immobilization function.

The cable-stayed span 3 of the cable-stayed bridge defined by FIGS. 1 to 3 can be built in cantilever from pylons la and lb as shown in FIG. 4. When the lengths of the cantilevers of the guyed span 3 becomes important, the buckling safety of the overhangs may become insufficient. To continue building under acceptable conditions of safety, it is then possible to install guy lines 27 (see Figure 5) which connect the ends of the overhangs at the same time as the guy wires are used. tension 22a and 22b. The building shrouds 27 are fixed to bosses 28, clearly visible in FIG. 6, formed under the edge beams 18a and 18b of the guyed span 3.

If necessary, at a later stage in the construction of the guyed span 3, other guy lines 27, shorter than those already in place, can be added, at the same time as, being an additional tension is applied to the tension stays 22a and 22b, or the tension stays 23a and 23b are used.

When the guyed span 3 is finished, the building guys 27 can be dismantled. We can also leave them to work. It is then desirable to secure them from far to far to the deck 2. They then have a role identical to that of prestressing reinforcements.

The cable-stayed bridge according to the invention shown in FIGS. 7 and 8 comprises a single pylon 1. Its deck 29 is constituted by two guyed spans 39a and 39b, symmetrical with respect to the pylon 1. The guyed area of the deck 29 is thus constituted by the entire deck.

The stays 30a and 30b respectively support the guyed spans 39a and 39b.

Pylon 1 is analogous to pylons 1a and 1b. The attachment of the guy wires 30a and 30b to the pylon 1 and the deck 29 is similar to that of the guy lines 12a to the pylon la and the deck 2. The connection of the deck 29 to the pylon 1 is analogous to the connections of the deck 2 to the pylons la and lb.

The end 31a of the deck 29 is embedded in an anchor block 32 which also acts as a abutment. The end 31a of the deck 29 is thus fixed longitudinally.

The end 31b of the deck 29, located above the stack 33 has a spacer 34 (see Figure 8). The deck 29 is supported on this stack 33, vertically by means of bearings 20a, horizontally by means of bearings 21a. The bearings 20a and 21a are similar to the bearings 20 and 21 already described. They are located to the right of the spacer 34. Two tension shrouds 35 connect the deck 29 to the anchor blocks 36 secured to the ground. The upper ends of the tensioning shrouds 35 are fixed to bosses 37, one of which is visible in FIG. 8. The tensioning shrouds 35 pass freely through the pile 33 through holes 38 made in this stack 33. The vertical components of the tensions of the shrouds voltage 35 are transmitted to the battery 33 through the intermediary of the bearings 20a.

The cable-stayed bridge shown in Figure 9 differs from that shown in Figures 1 to 3 in that:

- Batteries 7a, 8a, 9a, 7b, 8b and 9b are deleted.

- The tension stays 23a and 23b are replaced by the tension stays 41a, 42a, 41b and 42b, the lower ends of which are fixed respectively to the anchor blocks 43a, 44a, 43b and 44b secured to the ground and the upper ends of which are linked to the apron 40 at the top respectively of the stacks 5a, 6a, 5b and 6b.

Thus the deck 40 has a central guyed span 3 and partially guyed side spans 41a and 41b. The guyed area of the deck 40 extends from the stack 6a to the stack 6b.

The traction exerted by the tensioning shrouds is greater in the span 3 than in the lateral spans 41a and 41b which is justified by the fact that the buckling tendency is stronger in the guyed span 3 than in the lateral spans 41a and 41b. As the examples of cable-stayed bridges described are necessarily limited in number, it seems useful to supplement the above description with the following non-exhaustive remarks:

The number of tension shrouds can be any. A cable-stayed bridge according to the invention is not necessarily symmetrical.

The various drawings correspond to an embodiment in concrete of the decks 2, 29 and 40. It goes without saying that the invention applies equally well to steel decks or to steel decks over part of their length and in concrete for the rest. For example, in the case of the cable-stayed bridge defined by FIGS. 1 to 3, the central part of the cable-stayed span 3 or all of the cable-stayed span 3 could be made of steel and the other parts of the deck 2 of concrete. The section chosen for the deck is closed, the invention also applies to an open section. For example, this section would include an upper slab constituting the upper chord of a beam and a plurality of webs connected to independent lower chords.

Claims

1. Cable-stayed bridge comprising at least one pylon (la) and at least one continuous deck (2) comprising at least one cable-stayed zone supported by guy lines (12a, 13a) connecting the deck to the pylon, characterized in that at least one guy (22a), called tension guy, is fixed by one of its ends to the deck (2) and by the other end to an anchor block (24a) linked to the ground, the relative positions of the point of attachment of the guy tension (22a) on the deck (2) and the anchor block (24a) being such that said tensioning shroud (22a) exerts traction on at least part of the guyed area.

2. Cable-stayed bridge according to claim 1, characterized in that the tensioning cables are inclined (22a, 23a; 22b, 23b), their point of attachment to the bulkhead (2) being located above their point of attachment to the anchor block (24a, 25a; 2.4b, 25b) linked to the ground.

3. Cable-stayed bridge according to claim 2, the construction of which is symmetrical, characterized in that it comprises a tensioning shroud (22a, 22b) at each end of the bridge, the two shrouds exerting pulls of equal values and direction opposites

4. A method of constructing a cable-stayed bridge according to claim 1, 2 or 3, in which at least one cable-stayed span (3) is constructed in cantilever from a pylon (la), characterized in that, during construction, at least one construction guy (27) is substantially horizontal fixed to the end of the cantilevered portion of the guyed span (3) and this guy guy is tensioned (27) at the same time as one or more tensioning stays are tensioned.

5. Construction method according to claim 4, in which a cable-stayed span (3) is symmetrically constructed in the form of two overhangs each from a pylon (la, lb), characterized in that the building strut (27) is fixed at the ends opposite the two overhangs.