EP1101871B1 - Steel bridge deck and method for the construction of a bridge with such a deck - Google Patents

Abstract

The decking for a metal bridge has the longitudinal beams formed from prefabricated sections which are hollow metal tubes (10) of polygonal cross section. The tube lengths are selected for ease of transport. Adjacent sections of two adjacent beams are connected by cross members (2) also formed of metal tubes. The beams are connected at their upper faces by rigid plates (3). The beams can have a rectangular or trapezoidal sections. An Independent claim is also included for a method of assembly of the bridge.

Description

The invention applies, in a general way, to the realization of medium-span metal bridges, for example a few tens meters, but is especially suitable for bridge construction for military purposes or the rapid reconstruction of a bridge destroy.

During military operations, it is often necessary to carry out crossing works for rivers or valleys, or good to quickly rebuild destroyed bridges, at least in part.

These temporary constructions are entrusted to the engineering units. For averages of a few tens of meters, we have often temporary bridges made of easy prefabricated elements to set up by a team of some men. This type of bridge called, in France, bridge "Bailey" includes supporting elements longitudinal members made of lightweight lattice girders and elements transversal bearing a decking. Given the large number of elementary pieces, the establishment of a Bailey bridge is quite long and the result is not very aesthetic but it does not matter in the case of military operations.

However, the engineering units have, for some time, to operate in war-torn areas, to reconstruction of infrastructure, particularly crossing, which have often been destroyed. Often only the apron has been cut, abutments and batteries remaining in place.

To quickly restore communications, it seems interesting to use the temporary bridge elements available the army of the requested country but these facilities are often not provided in sufficient numbers. In addition, the bridges thus reconstructed are intended to remain in place for a long time, until complete reconstruction of the structure and it is not without interest to look after their appearance as much as possible.

In addition, the "Bailey" type bridges were designed several decades to be set up by hand by some men. However, the engineering units are currently equipped lifting equipment, the capacity of which can be example up to 4 or 5 tons, and so it is interesting to change the design of temporary bridges taking into account the possibilities current.

DE 2 812 531 A describes an apron conforming to the preamble of the claim 1.

The subject of the invention is therefore a new bridge deck which, like the dismountable bridges previously known, is constituted prefabricated elements assembled on the site but whose implementation using lifting devices can be particularly fast, such an apron may, in addition, be more important than temporary bridges known until now.

On the other hand, the bridge deck according to the invention has a external appearance similar to that of a conventionally built bridge. A temporary bridge according to the invention can therefore easily be transformed into a definitive work.

Moreover, because of its many advantages, the invention is not not limit the achievement of temporary bridges but may advantageously be applied to the realization of any work of medium range crossing.

The invention therefore applies, in a general way, to the realization of a steel bridge deck having at least one span resting on two supports, said apron comprising at least two main beams parallel to a longitudinal direction of the bridge and connected by a plurality of transverse struts spaced from each other, and a transverse decking resting on said main beams longitudinal.

According to the invention, each longitudinal beam is formed by butt-joining a series of elements prefabricated metal formed each of a tubular hollow box to polygonal cross section having at least one upper face plane, said boxes having the same section and each extending over a length compatible with the means of transport and lifting. Of moreover, the caissons of two adjacent beams are connected in pairs by a plurality of spacers each consisting of a metal tube having two ends each provided with fastening means with a side face of a box and said beams are connected to their part upper, by a plurality of rigid transverse junction elements constituting at least a part of the decking and having two ends fixed respectively on the flat upper faces of the caissons of two beams.

Advantageously, each box forming an element of longitudinal beam has a quadrangular cross section and, preferably, trapezoidal, having two horizontal faces of widths different and two side faces inclined symmetrically with respect at a vertical median plane of the box.

In a first embodiment of the invention, the elements transverse junction consist of a series of sections separated from each other and extend transversely over a length of less than the distance between two beams, said sections having each two ends respectively fixed on the upper faces planes corresponding boxes of the two beams.

Preferably, the joining profiles are separated from one constant distance corresponding to the width of a wooden cross placed between two adjacent profiles and resting on the upper faces planes of the corresponding caissons of the two longitudinal beams, one Provisional deck thus consisting of a series of sleepers next to each other.

According to another advantageous characteristic, the apron includes a series of corrugated panels extending between two beams longitudinal and resting on the upper faces of the caissons corresponding beams, said panels being joined and constituting a lost formwork for the pouring of a concrete slab forming the decking of the deck.

In the case where the temporary deck consists of sleepers placed between joining profiles, it is possible, after removal of the sleepers, to place, between the two beams, a series of panels waved on the profiles and constituting a lost formwork for the pouring of a concrete slab forming the final decking of the deck.

Advantageously, the flat upper face of each box is provided with upward projecting parts, forming connectors, intended to be embedded in the concrete slab poured onto the formwork lost, for the joining of said slab with the beams longitudinal.

In another embodiment of the invention, the elements transverse joints consist of a series of slab elements made of concrete to be laid together, one after the other, on at least two series of boxes forming at least two beams longitudinal, covering these, each element of the slab being solidarized, after laying with the corresponding boxes of the two beams, so as to form the decking of the deck.

The invention also covers a number of advantageous features which will be described in more detail by the which are the subject of the subclaims.

Moreover, the invention also covers the elements prefabricated for the construction of a bridge deck and a new method of constructing a bridge span comprising such an apron.

La figure 1 est une vue schématique générale, en perspective, d'un tablier de pont provisoire selon l'invention.

La figure 2 est une vue en coupe transversale du tablier.

La figure 3 est une vue de détail, en coupe transversale, d'un caisson, au niveau d'une entretoise.

La figure 4 est une vue de côté, selon la ligne IV, IV de la figure 3, de la liaison entre deux caissons successifs.

La figure 5 montre, en élévation, l'ensemble d'une poutre longitudinale d'un tablier de pont.

La figure 6 est une vue de dessus d'une dalle préfabriquée posée sur deux poutres longitudinales.

La figure 7 est une vue en coupe longitudinale de la jonction entre deux dalles adjacentes.

La figure 8 est une vue en perspective du montage d'une dalle d'about.

La figure 9 montre, en coupe longitudinale, la jonction entre une dalle d'about et l'extrémité d'une poutre longitudinale.

La figure 10 est une vue de détail, en coupe longitudinale, de la jonction entre deux travées successives, au niveau d'un appui.

La figure 11 est une vue schématique en perspective, d'un caisson pour la coulée d'une poutre d'appui transversale.

La figure 12 est une vue générale, en coupe transversale partielle, de l'ensemble d'une pile de pont.

La figure 13 est une vue en coupe selon XIII-XIII de la figure 12.

La figure 14 et la figure 15 illustrent deux étapes de construction d'un pont selon l'invention.

But the invention will be better understood by the following description of some particularly advantageous embodiments which are described by way of non-limiting examples and are shown in the accompanying drawings.

Figure 1 is a general schematic perspective view of a temporary bridge deck according to the invention.

Figure 2 is a cross-sectional view of the deck.

Figure 3 is a detail view, in cross section, of a box, at a spacer.

Figure 4 is a side view along the line IV, IV of Figure 3, the connection between two successive boxes.

Figure 5 shows, in elevation, the assembly of a longitudinal beam of a bridge deck.

Figure 6 is a top view of a prefabricated slab placed on two longitudinal beams.

Figure 7 is a longitudinal sectional view of the junction between two adjacent slabs.

Figure 8 is a perspective view of mounting a butt plate.

Figure 9 shows, in longitudinal section, the junction between a abutment slab and the end of a longitudinal beam.

Figure 10 is a detail view, in longitudinal section, of the junction between two successive bays, at a support.

Figure 11 is a schematic perspective view of a box for casting a transverse support beam.

Figure 12 is a general view, in partial cross-section, of the assembly of a bridge stack.

Figure 13 is a sectional view along XIII-XIII of Figure 12.

FIG. 14 and FIG. 15 illustrate two stages of construction of a bridge according to the invention.

In Figure 1, there is shown diagrammatically, in perspective, four stages of construction of a bridge deck comprising, in the example shown, two lanes A and B and which is shown in section in Figure 2. Each lane is supported by two longitudinal main beams 1, 1 'which are each consisting of a series of tubular boxes 10 fixed end to end by welding or bolting and interconnected by spacers 2.

As shown in FIG. 3, each box 10 presents a quadrangular section, preferably trapezoidal, comprising a upper planar face 11, a lower planar face 12 and two faces lateral 13a, 13b inclined symmetrically with respect to the median plane Longitudinal P1 of the box 10. Preferably, the large base of the trapezium is turned upwards, the upper face 11 having a width greater than that of the lower face 12. The thicknesses of the sheets are determined according to the forces to be supported, the lower face 12 being, normally, thicker than the upper face 11.

As indicated, the bridge deck shown in the figure 1 is specially adapted for the construction of a temporary bridge, particular by a military engineering unit and is therefore constituted entirely prefabricated elements that can be made in advance and brought to the site. For the construction of a load-bearing beam, will have, therefore, a series of boxes 10 likely to be assembled end-to-end and spacers 2 provided at their ends with fixing means on the lateral faces 13 of the boxes, the number elements depending on the span of the span to be dimensions of the caissons which are determined according to the means handling equipment available.

In general, the length (L) of each box 10 corresponds to the possibilities of transport by road and, normally, also suitable for transport by rail, air or sea. Indeed, the place of construction being, often, isolated, the last part of the transport will be, generally, by road. In practice, the caissons 10 shall not exceed 5 or 6 meters in length so that transport them on a road trailer and their handling on the road. site by a hoist of the type currently available engineering units and whose power is usually, 4 or 5 tons.

However, to allow immediate adaptation to conditions of construction, a stock will be preferred. of elements, in particular caissons 10 having at least two different lengths (L), for example 2.5 meters and 5 meters so as to to be able to realize, on the site, spans with different spans.

Likewise, it will be advantageous to have caissons made from sheets of different thicknesses depending on the loads and overloads that depend on the nature of the traffic. In particular, if caissons are made in advance it is interesting to vary the thickness (e) of the lower face 12 so as to be able to choose the advance of the caissons likely to withstand the loads applied, given the scope of the span to be achieved and the position of the box compared to the supports.

However, to be able to assemble the caissons end to end, their external dimensions, that is, their height (H) and the width (11, 12) faces, respectively upper and lower, will be, normally, the same so that, when assembled, the walls will be arranged in the extension of each other, even if their thickness, in particular that of the lower face, may vary.

In practice, for example, it will be possible to have several range of boxes for which the height (H) of the box 10 can to be, respectively, 600, 700, 800 and 900 mm. For each height, we will have 3 or 4 types of caissons for which, for example, the thickness (e) of the lower face may vary from 20 to 75 mm. So, the first range of boxes with a height of 600 mm will allow to achieve spans with a range of 10 to 20 m while the latest range, having a height of 900 mm, will achieve spans with a range of 20 to 25 m.

Of course, these dimensions will be chosen in order to optimize the possibilities using a reduced number of boxes as possible to deal with all cases of bridge construction average range, that is, normally between 10 and 30 meters.

It should be noted that the design of the span, in particular the low number of elements and their simplicity, allows them to be assembled from very simple way, for example by bolting. Because of this, it is possible dismantle the bridge to recover the elements, for example after reconstruction of a permanent bridge. In addition, a construction by bolting or riveting is easier to perform and does not require a personnel as specialized as for welding, which is particularly advantageous for military applications.

The assembly of the elements will be done conventionally in metallic construction. For example, in the example shown on the 3, each end of a spacer tube 2 is provided, in its median plane, a fixing plate 21 which is applied on a gusset 22 fixed in a transverse plane to the lateral face 13 of the casing plate 21 and the gusset 22 being provided with orifices which come in alignment for installing fixing bolts.

As shown in Figure 1, for the realization of a span of temporary bridge according to the invention, so we will bring on the site a certain number of box elements prepared in advance and which are assembled end to end to form a longitudinal beam 1, some boxes may have a length (L) different to achieve a span of desired length.

If the length of this span is not too great and corresponds to the possibilities of the lifting gear that is available, can assemble the caissons on the ground so as to constitute a beam length and lift it in block to put on the supports. In this case, two longitudinal beams 1, 1 'will be placed next to each other. the other, which are then connected by a number of spacers 2.

It should be noted that the trapezoidal section of the beam decreases the risk of spillage and thus facilitates installation.

But we can also push longitudinally the beams that slide or roll on their lower soles.

Thus, in the example shown in FIG. firstly a first span member consisting of two boxes 10, 10 ' connected by two spacers, respectively a central spacer 2a and an end spacer 2b.

Having placed this first item on a launch pad placed at the desired level, the ends of the two caissons 10, 10 'the following boxes 10a, 10'a connected by a spacer 2c. We can thus gradually build the two beams longitudinal axes 1, 1 'of the span, for example on rollers, by their lower faces 12 and are pushed longitudinally as construction progresses to achieve the entire span.

As indicated, the adjacent elements 10, 10a, be assembled end to end by bolting, which allows, subsequently, to dismantle the apron to recover the elements.

However, it is more advantageous to use the of prestressing assembly shown in Figures 3 and 4.

In this case, each box 10 forming an element of a Longitudinal beam is provided at each end with four massive 23 welded, on the outside, at the four corners of the box whose soles 11 and 12 have been extended laterally. These parts massive 23 are each drilled with a bore 24 so that the parts 23a, 23b placed respectively at the ends facing each other two adjacent beams 10a, 10b apply to one another, the bores 24a, 24b being aligned. We can then slip into these bores in line with the high-yielding prestressing bars 25 which are energized and blocked, for example, by prestress 26.

Thus, it is possible to achieve, for example on the bank of a river to cross, two longitudinal beams 10, 10 'which are between two supports, for example by means of a crane, by pushing or launching.

This first phase of assembly I was represented schematically bottom right in Figure 1.

Thus, the structure carrying a first route of A circulation and it is possible, if necessary, to build, next to this one, a second supporting structure for a second way of circulation B.

To ensure the rigidity of each supporting structure, both beams 1, 1 'are then secured by junction elements such as that profiles 3 having a length at least a little longer than the distance between the two adjacent beams 1, 1 'and whose ends are fixed on the upper faces 11, 11 'thereof.

In the case of making a temporary bridge, it is then possible to place between the profiles 3 wooden beams 40, by example of railway sleepers, which thus realize a decking provisional 4.

This phase II is shown at the top right of Figure 1. It was thus possible to realize quickly and economically a span temporary bridging using simply a lifting gear of a power of a few tons.

However, according to another advantage of the invention, the bridge Provisional so constructed can be very easily converted into a bridge final.

For this purpose, after removing the sleepers 40 forming the 4, the space is covered between two adjacent beams 1, 1 'of a series of corrugated panels 31 placed one after the other, as indicated in phase III, bottom left of Figure 1. These panels 31 are provided with transverse corrugations which fit into the profiles junction 3 fixed on the two beams 1, 1 '. We thus constitute a lost formwork for the casting of a slab 41, in a last phase of construction IV shown at the top left of Figure 1. Well heard, before the pouring of the concrete, an adequate reinforcement was put in place above the lost formwork 31.

However, as indicated, the invention is not limited to the construction of temporary bridges but can also be used to make a classic metal bridge.

In this case, the carrier structure consists of at least two longitudinal beams 1, 1 'connected by spacers 2 is covered by a concrete decking consisting of prefabricated slabs that are secured to the upper faces of the longitudinal beams 1, 1 ' in order to ensure the rigidity of the structure.

As before, each longitudinal beam 1, is consists of a series of prefabricated boxes 10 fixed end to end, by example by means of prestress bars, as shown in Figure 4.

These boxes are made in advance and it is advantageous to have several lengths assembled judiciously according to the distance between supports. For example, in the embodiment represented in FIG. 5, the beam 1 is constituted, in its most a large part of boxes 10a having a length, for example, of 3.50 meters, and is completed, by a number of more boxes short 10b, 10c having lengths of 2.5 meters and 1 meter. of the 10d, 10th abutment boxes are placed at both ends.

As indicated, the two longitudinal beams 1, 1 'are connected by spacers 2. However, as the beams are permanently attached by concrete slabs, the number spacers can be reduced and it may be sufficient, for example, to simply place a spacer at each end of the span and a or two spacers in the central part.

Moreover, it is interesting to have several types of boxes in which the thicknesses of the sheets, in particular for the lower sole 12, may vary depending on the bending moment supported which depends on the position of the box in the span. Through example, as shown in Figure 5, the boxes placed in the part center of the span may have a 12-thick bottom flange larger than for the boxes placed at the ends.

FIG. 6 shows, in plan view, a slab 5 covering two longitudinal beams 1, 1 'which is shown in section cross-section in FIG. 12. The slab 5 advantageously comprises a central portion 51 extending between the two beams 1, 1 'and extended, on both sides thereof by two lateral parts 52 on which can be mounted sidewalks 42.

FIG. 7 is a detail view, in section along line I-I of FIG. Figure 6 of the connection between two adjacent slabs. Each slab 5 is provided on its sides with recesses 53 extending over part of the height of the slab so as to leave a lower part in the form of partition 54 forming lost formwork. At the establishment of two slabs adjacent, the partitions 54a, 54b come into contact with one another in limiting a rectangular space consisting of recessed portions 53a, 53b in which extend armatures waiting 55. After laying elements, we put transverse irons 56 in the armatures 55, and the whole is embedded in concrete poured into the space 53a, 53b of to form a continuous slab.

On the other hand, each slab 5 is provided, at the level of each beam 1, 1 ', at least one recess 6 which extends over the entire height of the slab 5 so as to open on a portion 14 of the upper face 11 of the beam 1 on which have been welded a plurality of studs 61 forming connectors. Preferably, there are simply two types of slabs, respectively a running slab such as 5 and a 5 'abutment slab placed at each end of the span and shown in Figure 8. Normally, there is only one type of slab current and the length (I) covered by each slab does not correspond necessarily to the length (L) of the caissons. Therefore, time of the study of the span of bridge to be built, we will determine the location of the zones 14 of each beam 1 corresponding to the recesses 6 slabs and studs 61 will be arranged on each elementary box 10 depending on the position of the latter in the span.

Advantageously, the lower partitions 54 formed on the sides of each slab 5 will be provided, at each beam carrier 1, notches 62, the corresponding area of the face 11 of the beam 1 being provided with connector pins 61 of to ensure the joining, with the beam, of two slabs successive at their junction.

At its end facing the abutment, each beam 1 is ends with an end box 10d which is covered with a slab 5 'shown in perspective in Figure 8. This slab is about provided, on its side facing the adjacent slab, with a recess transversal 53 and, on its side facing the abutment, a beam of stiffening 57, turned down and forming acroterium. The level of box 10d, the beam 57 is provided with a recess 63 in which connector studs 61, 64, respectively welded on the upper face 11 of the box 10d and on two lateral faces 14 ' arranged at the end of the box 10d. So, using formwork concrete, it is possible to pour concrete into the recess 63 for complete the transverse beam 57 and ensure the joining of the slab element 5a with the abutment box 10d.

In the example shown in the figures, the bridge is constituted two bays resting on a stack 7 via a beam transverse 8 constituting an intermediate support.

According to another advantageous characteristic of the invention, each intermediate support beam 8 constitutes a keyway of solidarization between the ends of the two spans, which is realized in the inside of a caisson forming formwork lost and resting on the stack 7.

This box 80, shown in perspective in FIG. 11, has the shape of a trough having a bottom 81, two side walls 82 in which are formed notches 83 whose profile corresponds to that, in cross-section, of a longitudinal beam 1, and two end walls 86.

Thus, as shown in Figure 10, the 10th end caissons of two aligned beams 1a, 1b of two successive bays, penetrate through the indentations 83, inside the formwork 80. The two ends two beams 1a, 1b are provided with connector studs 61, 65 welded, respectively, on the upper face 11 of the box 10e and on a flange 15 attached to the end thereof.

The upper edges of the two lateral faces 82 of the box 80 are covered by the slabs 5a, 5b placed on the ends of the beams 1a, 1b. We can then pour concrete 16 inside the box and up to the top level of the slabs, so as to realize a beam transversal 84 which ensures the joining of the two spans and the continuity of decking.

This transverse beam 84 rests on the stack 7 by means of support members 71 which can be of any known type, for example smooth or roller bearings. Preferably, each support 71 slips, with a weak game, into an 85 profile opening corresponding, formed in the bottom 81 of the formwork 80 so that the support is done directly on the concrete. Of course, the beam cross 84 thus formed may be provided with a suitable reinforcement, particularly in its lower part, to ensure the distribution of the load on the supports 71 and in its upper part, for the junction slabs 5a, 5b.

Figures 14 and 15 schematically illustrate the embodiment of a bridge according to the invention resting on a stack 7 consisting of the shown in detail in Figures 12 and 13.

In the example shown, the bridge constitutes a structure of crossing over a two-lane highway on a platform A. After preparing the ground and realized this platform, we dig first, to the level required for the foundations, a B1 excavation for the central pier and two B2 excavations for the abutments. Yes the soil is quite resistant, the foundation of the central pile can be consisting simply of a sole C1 and possibly a sidewall D in concrete on which we put elements in place prefabricated 71 which are advantageously made of caissons superimposed, as shown in FIGS. 12 and 13. internal reinforcement ensures the joining of the whole with the cross D to the upper level 73 of the stack 7.

Similarly, each abutment may consist of elements superposed 74, resting on the sole C2. These elements 74 can have, for example, a U-shape for the maintenance of an embankment realized to the desired level.

Supports 71, 71 'are then placed respectively on the upper end 73 of the stack 7, at the upper level 73 'of each abutment 70.

The battery 7 is then equipped with consoles 75 fixed so removable and constituting a temporary support for the transverse box 80 whose bottom is wedged to the desired level on the supports 71.

During this time, we realized the four supporting beams 1 each constituted by assembly of longitudinal boxes 10 secured, for example, by prestressing.

A hoisting apparatus E, for example a mobile crane, traveling on the platform A then sets up successively the four longitudinal beams 1, each beam having an end 10d which rests on the support 71 'of the abutment 70 and an opposite end 10e which engages in a corresponding recess 83 of the box transversal 80.

As shown in Figure 15, using the hoist E, we put in place the various slabs 5 constituting the decking of the bridge and we can then pour the concrete, on the one hand in the box 80 for constitute the transverse beam 8 of support on the stack 7 and, on the other hand, in each of the transverse joints 57 between two successive slabs.

This has led to a continuous decking which may have, in section cross section, the profile shown in Figure 12. The bridge can then be completed by the establishment of sidewalks 42, and a border prefabricated 43 supporting a railing.

So we see that, by means of a small number of elements prefabricated metal, one can realize quickly and economically a span of bridge, either for a construction provisionally, as shown in Figure 1, or for a definitive construction, decking may also be constituted of prefabricated elements.

But the invention is obviously not limited to the details of embodiments that have been described as mere examples and which could be subject to variations without departing from the scope of protection described by the claims.

For example, it is particularly advantageous to carry out caisses with trapezoidal section, but other shapes could be considered.

The reference signs inserted after the characteristics techniques mentioned in the claims, have the sole purpose of facilitate the understanding of these and do not limit the scope.

Claims (21)

1. A plate for a metal bridge whereby at least one span rests on two supports, the said plate comprising at least two main girders (1, 1') parallel to the longitudinal direction of the bridge and connected by a plurality of transversal spacers (2) at a distance from one another and a transversal flooring (4) resting on the said longitudinal main girders (1, 1'),
      characterised in that each longitudinal girder (1) is built by butt-jointing of a number of prefabricated metal elements, each formed of a tubular hollow coffer (10) with polygonal transversal section with at least one plane upper face (11), whereas the said coffers (10) exhibit the same section and each extending over a length (L) compatible with the transport and lifting means, that the coffers (10, 10') of two neighbouring girders (1, 1') are connected in twos by a plurality of spacers, each composed of a metal tube (2) with two ends each fitted with fastening means (21) with one lateral face (13) of a coffer (10) and that the said girders (1, 1') are connected, at their upper part, by a plurality of rigid transversal junction elements (3) making up at least a portion of the flooring (4) and with two ends fastened respectively to the upper plane faces (11') of the coffers (10, 10') of both girders (1, 1').
2. A bridge plate according to claim 1, characterised in that each coffer (10) forming an element of a longitudinal girder (1) exhibits a quadrangular transversal section, with two horizontal faces, respectively upper (11) and lower (12) faces, connected by two lateral faces (13).
3. A bridge plate according to claim 1, characterised in that each coffer forming an element of a longitudinal girder exhibits a trapezoid section, with two horizontal faces (11, 12) of different widths and two lateral faces (13) tilted symmetrically with respect to a vertical middle plane of the coffer.
4. A bridge plate according to any of the claims 1, 2, 3, characterised in that the transversal junction elements are composed of a series of profiles (3) spaced apart from one another and extending transversally over a length at least equal to the distance between two girders (1, 1'), whereas the said profiles (3) have each two ends fastened respectively on the plane upper faces (11) of the corresponding coffers (10) of both girders (1, 1').
5. A bridge plate according to claim 4, characterised in that the junction profiles (3) are spaced apart by a constant distance corresponding to the width of a timber sleeper (40) placed between two neighbouring profiles (3) and resting on the upper plane faces (11) of the corresponding coffers (10) of both longitudinal girders (1, 1'), whereas a provisional flooring (4) is composed of a series of sleepers (40) placed beside one another.
6. A bridge plate according to any of the claims 1 to 5, characterised in that it comprises a series of undulated panels (31) extending between two longitudinal girders (1, 1') and resting on the upper faces (11) of the corresponding coffers (10) of the said girders (1, 1'), whereby the said panels (31) abut one another and compose a lost casing for casting a concrete slab (41) to build the flooring of the bridge plate.
7. A bridge plate according to claim 6, characterised in that the undulated panels (31) nest into junction profiles (3) fastened to both girders (1, 1') and constituting rigid transversal junction elements.
8. A bridge plate according to claim 5, characterised in that it comprises a series of undulated panels (31) extending between two longitudinal girders (1, 1') and laid after one another while nesting onto the junction profiles (3), after removing the timber sleepers (40), whereby the said undulated panels compose a lost casing for casting a concrete slab (41) to build the permanent flooring of the bridge plate.
9. A bridge plate according to any of the claims 6 and 8, characterised in that the upper plane face (11) of each coffer (10) is fitted with parts protruding upwards, forming connectors (61), intended to be embedded in the concrete slab (41) cast on the lost casing, for interlocking the said slab (41) with the longitudinal girders (1, 1').
10. A bridge plate according to any of the claims 1, 2, 3, characterised in that the transversal junction elements are composed of a series of concrete slab elements (5) intended to be butt-mounted, one after another, over at least two series of coffers forming at least two longitudinal girders (1, 1'), while covering the said girders, whereas each element of the slab (5) is interlocked, after assembly with the corresponding coffers (10) of both girders (1, 1'), in order to build the flooring of the bridge plate.
11. A bridge plate according to claim 10, characterised in that each slab element (5) is fitted, on each part covering a coffer (10), with at least one recess (63) into which reach, when laying the element, protruding parts constituting the connectors (61), fixed to a corresponding zone of the upper plane face (11) of the coffer (10), for interlocking the slab element (5) with the coffers (10) that it covers, by casting concrete into the said recess (63) in which the said connectors (61) are embedded.
12. A bridge plate according to any of the previous claims, characterised in that the elements of longitudinal girders (1, 1') in the form of hollow coffers (10) are interlocked in twos by welding their adjacent ends.
13. A bridge plate according to any of the previous claims, characterised in that the elements of longitudinal girders (1, 1') in the form of hollow coffers (10) are interlocked in twos by bolting their adjacent ends.
14. A bridge plate according to any of the previous claims, characterised in that each girder element in the form of a coffer (10) is fitted, at each of its ends, with massive parts (23) welded to the coffer (10) and each drilled with a bore (24) and in that, when laying the coffers (10) to abut against one another for constituting a longitudinal girder (1), the massive parts (23a, 23b) of two consecutive coffers (10a, 10b) are placed one after another in order to install a means (25) for interlocking the coffers, the means being formed by a pretensioning bar (25) going through the aligned bores (24a, 243b) and being pretensioned.
15. A bridge plate according to any of the previous claims, characterised in that, at one end of a span, the main longitudinal girders rest on a support (7) of the bridge via a transversal girder (8) composed of a coffer (80) with a bottom (81) resting on the support (7) of the bridge, two lateral walls (82) and two end walls (86) whereby the said lateral walls (82) are fitted, at each longitudinal girder (1), with a scalloping (83) exhibiting the same profile as the longitudinal girder (1) in transversal section, in order to enable an extreme part (10e) of each longitudinal girder (1) to nest into a corresponding scalloping (83) of the transversal coffer (80), while penetrating partially into the said coffer, whereas the said coffer (80) forms a lost casing that is filled, after laying all the girders, with keying concrete (16) in order to realise a transversal girder (8) interlocked with the ends of all the longitudinal girders (1).
16. A bridge plate according to claim 15, characterised in that each longitudinal girder (1) is fitted, at its end (10e) penetrating into the transversal girder (80), with protruding parts forming connectors (65), for interlocking the longitudinal girder (1) with the transversal girder (8) cast in the coffer (80).
17. A bridge plate according to claim 16, characterised in that each intermediate support (7) of the bridge carries a transversal coffer (80) with two lateral sides (82) fitted with scallopings (83) for nesting into the ends of the longitudinal girders (1) of two successive spans, in order to ensure, after casting the concrete (16) in the transversal coffer (80) interlocking of both spans extending on either side of the transversal girder (8) thus provided.
18. A method of building a bridge span resting on two supports spaced apart, characterised in that the following elements are realised in advance: a plurality of elements of longitudinal girders, each composed of a tubular coffer (10) with polygonal transversal section, with at least two parallel plane faces, respectively an upper face (11) and a lower face (12), whereas the said coffers (10) have a weight and a length (L) compatible with the lifting and transport capacities, a plurality of sleeper spacer (2) each composed of a metal tube (2) with two opposite ends; then the said coffers (10) and spacers (2) are brought to the building site, the said building site comprising at least two supports (7) realised previously, the said coffers (10) are butt-jointed by interlocking their adjacent ends in order to form at least two longitudinal girders (1, 1') each composed of a series of coffers (10), the girders thus constituted are laid in place, so that they rest, by their ends, onto supports (7, 70) spaced apart on the bridge, whereby the said longitudinal girders (1, 1') are interlocked by at least two sleeper spacers (2) that are fastened, each by two opposite ends (21), respectively on two opposite lateral faces (13) of two coffers (10, 10') located at the same level on both girders (1, 1') and a flooring (4) is made, covering the said longitudinal girders of which at least one part is composed of a plurality of rigid transversal junction elements (3, 5) distributed over the whole length of the span and extending each at least over the distance between both longitudinal girders (1, 1'), whereas each junction element (3, 5) is fastened to the upper faces (11) of both longitudinal girders (1, 1').
19. A method according to claim 18, characterised in that the junction elements are metal profiles (3) each with two ends fastened, after installation, to the upper faces (11) of two longitudinal girders (1, 1'), in that the said profiles (3) are spaced regularly by a distance substantially equal to the width of a timber girder (40) such a railway sleeper, and in that a sleeper (40) is laid in each gap between two profiles, in order to build a provisional flooring (4).
20. A method according to claim 19, characterised in that, to replace the provisional flooring (4) with a permanent flooring, the timber sleepers (40) are removed, at least the space between two longitudinal girders is covered abutment panels (31), whereas the said panels are fitted with ribs nesting into the junction profiles (3), and a concrete slab (41) is cast on the surface made by the upper faces (11) of the longitudinal girders (1, 1'), with the said panels (31), whereby the said panels form a casing for casting the slab (41).
21. A method of building a bridge plate according to claim 18, characterised in that a plurality of elements of concrete slab (5) are realised in advance, each with an elementary length (I) and comprising, at the position of each longitudinal girder (1, 1'), at least one recess (6, 63) extending over the whole length of the slab (5) in order to open onto a zone (14) of the girder (1) fitted with protruding parts forming connectors (61, 64, 65) and in that, after laying two longitudinal girders (1, 1') connected by sleepers (2), a series of elementary abutting faces (5) is placed on the upper faces (11) of both girders (1, 1') so that the recesses (6, 63) of each slab (5) cover at least one junction zone fitted with connectors (61, 64, 65) of each longitudinal girder (1), then concrete (16) is poured into the said recesses (6, 63) for interlocking each slab element (5) with both longitudinal girders (1, 1').

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