EP0203868B1 - Construction element for the building industry, method of assembly and installation to carry out this method - Google Patents

Abstract

Construction element, of the self-supporting panel type, comprising a plate (1) on which is formed at least one longitudinal girder (2) of triangular section. The convergent ends (8, 9) of the slanting walls (3, 4; 3a, 4a) of each girder (2) have, on the outside of their joining ridge (5) and over their entire length, bevelled surfaces (10) via which they are in mutual contact, whilst the divergent ends (11, 12) of the slanting walls (3, 4; 3a, 4a) possess, on at least one of the faces of the latter, longitudinal indentations (13) via which they bear on longitudinal members (14, 15) integral with the plate (1). The first advantage of this construction element is that it can be manufactured very simply with the aid of a method which consists in preassembling its various components (3, 3a, 4, 4a, 5, 14, 15, 1) after having applied adhesive to their mutual contact surfaces (6, 7, 10, 13) and in pressing the preassembly thus produced between, on the one hand, the back of the panel (1) and, on the other hand, the joining ridge or ridges (5) and the longitudinal members (14, 15), while laterally immobilising the plate (2) and the outer longitudinal members (15). Application to the construction of floors or arched roofs of large surface. <IMAGE>

Description

The present invention relates to a building element for the building industry, in accordance with the preamble of claim 1. Such a building element is known from FR-A-2 279 900.

When they are provided with several parallel boxes, construction elements of the aforementioned type constitute excellent self-supporting panels usable for the realization of the roofs or floors of large buildings such as sports halls, factories or public buildings.

These self-supporting panels have the main advantage of having very good flexural strength while being relatively light. They thus make it possible to considerably reduce the intermediate supports and even to eliminate them entirely in the case of use at medium range. They are also quick to set up on site and have a pleasant aesthetic which can be modified as desired by simple exterior fittings.

To all these advantages, there is unfortunately added a major drawback which resides in the fact that the assembly of the various components of these panels, which ends with a bonding under pressure of the latter, has not been able to date to be automated, which of course has repercussions on manufacturing costs.

Thus, in the construction element described in document FR-A-2 279 800, it is necessary, before bonding under pressure, to make a mechanical connection of some of the constituent parts, using a system interlocking with grooves and tongues, and strengthen this pre-assembly using spikes or small nails planted at all the connection zones of the various constituent parts of the building element, so that the pre-assembly thus obtained can then be maintained during the application of pressure forces. This is a very long operation to implement which greatly affects the overall yield or the productivity of the total manufacturing operation of the construction elements.

The present invention proposes to remedy this drawback and, to do this, it relates to a construction element of the type specified in advance which is as defined in the characterizing part of claim 1.

In the case of a building element, in particular a self-supporting panel, comprising several substantially parallel boxes formed on a common plate, the oblique walls facing each other of two neighboring boxes are supported, by their scribing, on a median spar common, the two external beams stopping in another flush with the longitudinal edges of the plate.

The building element thus designed can be very easily assembled by the implementation of an assembly method which is also the subject of the present invention, this method being as defined by claim 8.

This simple method of assembling the construction element according to the invention is made possible by the particular shape, defined above, of the mutual bearing surfaces of its various components, which, once the plate and the outer ongons immobilized laterally, ensures self-locking of the pre-assembly, the integrity of which is thus preserved during the application of the pressure forces.

The process according to the invention can advantageously be automated, with considerable time savings lowering manufacturing costs, by means of an installation which is also the subject of the present invention and which is as defined by claim 10.

More specifically, the pressing means comprise members for supporting the pre-assembled construction element, which extend in substantially parallel directions over the entire length of said receiving cavity and are positioned at least directly above the location of the members and beams of said element, as well as pressure members which which respectively disposed above at least some of the support members and are movable in the direction of the latter, between an inactive position and a positive action, the surfaces of 'support of some being in the same plane, while those of the others are positioned in staggered rows according to a mutual arrangement correspond to that of the members and side members on the pre-assembled construction element.

As will be easily understood, the construction element, pre-assembled and pre-glued in the desired places, can be introduced into this installation to come to rest on the support members, either by the back of its plate when these are found in the same plant, either by its members and its side members when they are staggered.

Consequently, the pressing members in the inactive position are respectively plumb with the members and the side members and, under the action of a control device acting in synchronism with the movement of introduction of the element, they are brought in their active position in which they effectively press the whole of the pre-assembled construction element against the support members, along the glued surfaces of the members and the side members.

During this pressing operation, the integrity of the pre-assembly is preserved thanks to the action of the lateral stop means which will advantageously consist of a template having a cavity in which the construction element is pre-assembled, before its introduction into the pressing installation, this cavity having the same lateral dimensions as the plate of the pre-assembled building element and a height greater than that of this plate. This template will be more particularly used in the case where the plate of the pre-assembled building element is formed of adjoining planks, extending perpendicular to the side rails and kept assembled by the latter to then simultaneously constitute a "mold" maintaining the integrity of the plate during the introduction of the pre-assembly into the pressing installation.

However, in the case where this plate is in one piece, the lateral stop means will preferably be constituted by two parallel rows of rollers with vertical axis of rotation, which are arranged on either side of said receiving cavity , at the height of the location of the plate and the outer longitudinal members of the pre-assembled construction element and which are separated by a distance equal to the width of the latter, the pre-assembled construction element then being blocked laterally , over practically the entire height of the platform and the outer beams, by these two rows of rollers.

It should be noted, however, that in the case where the support members of the pressing installation are staggered, this second embodiment of the stop means can be used even if the plate of the building element is formed of several adjoining planks, since in this case the latter rest on the top of the element and cannot therefore separate when it is introduced into the pressing installation.

To provide the pressing installation according to the invention with a high production rate, the support members will advantageously be constituted by the upper strands of a train of endless chain of rollers bearing on rails, which simultaneously constitute a means for successively introducing the pre-assembled and pre-glued construction elements into the pressing installation.

During pressing, the setting of the adhesive is also accelerated thanks to the presence inside the installation of a heating device acting on the glued areas of the building element maintained under pressure. This heating device can be constituted by a blower injecting hot air into a tunnel which envelops the building element inside the pressing installation or by microwave heating elements.

The double pressing and heating operation can be carried out in the space of a few seconds, at the end of which the pressing members are returned to their inactive position and the roller chains extract the pre-assembled building element from the installation; a new pre-glued and pre-assembled construction element is then introduced into the installation to undergo the pressing operation which has just been described.

Of course, with a view to complete automation of the pressing installation according to the invention, it is feared to provide at the outlet thereof a conveyor which successively takes up the assembled construction elements extracted by the roller chains and returns to empty, at the entrance to the installation, after going to a pre-assembly station for the construction element.

In a first embodiment, more specifically intended for manufacturing in small or medium series, each of the pressing members consists of a pressing shoe mounted to slide, by means of return springs, at the lower end d 'a rigid member secured to the installation frame, an inflatable tube connected to a blower being placed between each pressing shoe and the lower end of the member carrying it.

There is thus a pressing installation of simple and therefore inexpensive structure in which the pressing shoes are placed in their active position by inflating the tubes and are returned to their inactive position by the return springs after deflating the tubes.

In a second embodiment, which will be retained on a preferential basis, each of the pressing members consists of a number of jacks aligned in the longitudinal direction of said receiving cavity and the rods of which are integral with a common pressing shoe on which rollers rollers mounted free in rotation on an endless chain driven around the row of cylinders, in said longitudinal direction, these rollers being, in the active position of the cylinders, intended to bear against the component of the element of pre-assembled construction subjected to the action of the respective pressing member.

As will be easily understood, these arrangements allow a continuous assembly of the construction elements thanks to the endless roller chains which, while the jacks exert their pressing action, advance the construction element inside the installation. This second embodiment of the pressing installation according to the invention is therefore particularly well suited for mass production.

It should also be noted that, by virtue of the pressure bonding process which is the subject of the present invention, it is advantageous to manufacture prestressed building elements bent towards the outside of the plate, in the longitudinal direction of the box or boxes and containing cables of prestress stretched in contact with the bottom of the point of each of the boxes. To do this, it suffices to fix, before pressing, a prestressing cable in contact with the bottom of the point of each of the boxes and, during pressing, to bend uniformly towards the plate, the member (s) ) and the side members by applying bending forces appropriately distributed over the length of the latter. This result can be obtained simply with the aid of a passage installation in accordance with the invention, in which the bearing surface of each of the pressing members is curved towards the support members in the longitudinal direction of the receiving cavity. , and the support members have a concavity having the same curvature.

• la figure 1 est une vue de face d'un élément de construction conforme à l'invention;
• la figure 2 est une vue en coupe de cet élément de construction effectuée dans le plan II-II de la figure 1;
• la figure 3 est une vue de face d'un premier mode de réalisation d'une installation conforme à l'invention, pour la fabrication d'éléments de construction du type de celui représenté sur la figure 1 ;
• la figure 4 est une vue représentant à plus grande échelle un détail de la figure 3;
• la figure 5 est une vue schématique en couple longitudinal de l'installation de la figure 3;
• la figure 6 est une vue représentant à plus grande échelle, un détail de la figure 5;
• la figure 7 est une vue de face partielle, analogue à la figure 3, d'un deuxième mode de réalisation de cette installation;
• la figure 8 est une vue schématique en coupe longitudinale de l'installation conforme à ce deuxième mode de réalisation de l'invention; et
• la figure 9 est une vue de face partielle, analogue à la figure 3, d'un troisième mode de réalisation de l'installation selon l'invention.

The present invention will now be described in more detail, but only by way of non-limiting example, with reference to the appended drawings, in which:

• Figure 1 is a front view of a building element according to the invention;
• Figure 2 is a sectional view of this building element made in the plane II-II of Figure 1;
• Figure 3 is a front view of a first embodiment of an installation according to the invention, for the manufacture of building elements of the type shown in Figure 1;
• Figure 4 is a view showing on a larger scale a detail of Figure 3;
• Figure 5 is a schematic view in longitudinal couple of the installation of Figure 3;
• Figure 6 is a view showing on a larger scale, a detail of Figure 5;
• Figure 7 is a partial front view, similar to Figure 3, of a second embodiment of this installation;
• Figure 8 is a schematic view in longitudinal section of the installation according to this second embodiment of the invention; and
• Figure 9 is a partial front view, similar to Figure 3, of a third embodiment of the installation according to the invention.

The construction element according to the invention, which is exemplified in FIGS. 1 and 2, is in fact a self-supporting wooden panel constituted by a plate 1 of generally rectangular shape under which two boxes 2 of triangular section are formed, which extend in the longitudinal direction of the plate 1.

More precisely, each box 2 comprises two oblique side walls 3, 4 and 3a, 4a covering the entire length of the plate 1, these two walls diverging upward to come to be fixed to the plate 1 and converging downwards to be joined by a member 5 which also extends over the entire length of plate 1. To this end, each member 5 has, on its face opposite plate 1, two longitudinal and parallel V-shaped grooves 6, 7, in which the outer edge parts of the converging ends 8, 9 of the oblique walls are respectively housed and fixed.

According to the invention, the inner edge parts of the converging ends 8, 9 of the oblique walls of each box 2, are chamfered at 10 in the median longitudinal plane and over the entire length of the latter, and are placed in mutual contact on along their surfaces 10 thus chamfered.

Furthermore and according to another characteristic of the invention, the divergent ends 11, 12 of the oblique walls 3, 4, 3a, 4a each have over the entire length of the outer face of the latter, a notch 13 cut at right angles. By these notches 13, the oblique walls facing each other 4, 3a are supported and are fixed on the same flat central spar 14, while the external oblique walls 3, 4a are supported are fixed respectively on two external flat spars 15 which are roughly half the width of the median beam and extend flush with the longitudinal edges of the plate 1, these beams 14, 15 also being integral with the underside of the latter. It will also be noted that the non-scalloped parts of the divergent ends 11, 12 of the oblique walls are directly in contact with the plate 1 by bevelled surfaces 11a, 12a.

For manufacturing convenience, the walls 3, 3a, 4 and 4a of the boxes 2 will preferably be made of glulam, as shown in Figure 1. In addition, as can be seen in Figure 2, the tray 1 will, for the same reasons, be made up of adjoining wooden planks 1a, extending in a direction perpendicular to the longitudinal axis of the caissons 2.

Panels of the type described above have the advantage of being able to be used for the construction of large area floors or vaulted roofs with a minimum of intermediate supports. In this use, several panels will be joined side by side, along their longitudinal edges, by a fitting system 16 with complementary tongues and grooves (see FIG. 1). In addition, the panel will preferably be bent in the longitudinal direction, towards the outside of the plate 1, and prestressed by means of a cable 17 stretched in contact with the bottom of the point of each of the boxes 2, over the entire length of these, by two fixing members 18.

Among the other advantages of the self-supporting panel according to the invention, mention may be made of the great layout facilities which it offers. Thus, as shown in Figure 1, the space 19 defined between two boxes 2 can be closed by a plate 20 resting on the faces of the members 5, facing the plate 1. Thus forms sheaths which can be used in the context of air heating or can be used for the passage of electric cables or water pipes. As a variant, these sheaths can be filled with thermal and / or acoustic insulation.

However, the main advantage of this panel lies in the simplicity of its assembly which can be carried out using an installation, a first embodiment of which will now be described with reference to FIGS. 3 to 6.

As these figures show, this embodiment comprises, on the one hand, a template 22, which, as will be seen below, constitutes a support for a pre-assembly P of the panel to be manufactured and, on the other hand, a press 23 into which the template 22 carrying the pre-assembly P is intended to be introduced.

This template 22 is more precisely constituted by a rectangular metal plate 26 provided with a peripheral edge 27 which is raised over a height greater than that of the plate 1 of the panel to be manufactured and delimits with the plate 26 a rectangular cavity of the same length and of same width as this tray.

As shown in Figure 3, the various components of the panel to be manufactured, previously machined to the required shapes and dimensions and glued to their surfaces intended to come into mutual contact (indicated by dotted lines in Figure 1), are pre-assembled to the inside the template cavity 22. In this pre-assembly P, the boards 1a intended to form the plate 1 completely cover the bottom of the template and are in contact, like the external side members 15, of the edge 27.

The template 22 carrying the pre-assembly P is introduced into the press 23 by one of its short sides, using six endless parallel chains with rollers 28 which extend at the same height and over the entire length of the press in the lower part of the frame 24 thereof. Each of these chains 28 is driven around two large toothed wheels 29 and, on their upper bring, their rollers 30 roll on a support rail 31, slightly hollowed out with a regular curvature in the length direction. As best seen in Figure 6, the rollers 30 of each chain 28 are mounted free in rotation, in groups of two, on stirrups 32 fixed to the chain and each of these stirrups 32 carries, opposite the rollers 30, a block of parallelepipedal wood 33. The set of void blocks 33 located on the upper strands of the chains 28 form in combination with rollers 35 mounted freely in rotation therebetween, a bearing surface for the template 22 .

Returning now to FIGS. 3 and 4, it can be seen that at its upper part, the press 23 contains six pressing members 36a to 36f extending in the direction of introduction of the template 22, over a length somewhat greater than that of the latter and respectively plumb with the rails 31 of the roller chains 28. Each of these pressing members comprises a rigid vertical member 37 secured to the frame 24 of the press and the lower end of which carries a pressing shoe 38 provided with two side cheeks 39 which are respectively placed in sliding contact with the side faces 40 of the frame 37 and are connected to the latter by return springs 41. In addition, an inflatable tube 42, connected to a blower not shown, is interposed between each frame 37 and the pressing shoe 38 which it carries.

As shown in FIG. 3, the two central pressing members 36c and 36d are juxtaposed on either side of the median longitudinal plane X of the press 23. In addition, the group of these two pressing members 36c, 36d and the other members pressers 36a, 36b, 36e and 36f are mutually positioned at intervals corresponding to those which, on the pre-assembly P, separate the members 5 and the side members 14, 15. Finally, the members 37 of the pressing members 36a to 36f have a height such that their pressing shoes 38 are staggered so as to delimit in the raised position, a space high enough to allow the introduction of the template 22 for pre-assembly P.

Referring now to FIG. 5, it can be seen that the lower surface 43 of each of the pressing shoes 38 is curved downward, in the direction of its length and according to a curvature to that of the concavity of the support rails 31 Figures 3 and 5 also show that inside the press and all around the receiving volume of the template 22 and the pre-assembly P which it carries, extends a tunnel 44 which closes on itself outside the press 23 by a sheath 45 in the middle of which are housed a fan 46 and several electrical resistors 47 located downstream of the latter, the resistors 47 can be replaced by a water or steam heating coil. In addition, the front wall of the sheath 45 is provided with a door 48 allowing the template 22 to be inserted into the press 23, while its rear wall is provided with an outlet door 49.

The template 22 carrying the pre-assembly P is guided, when it is introduced into the press 23, between two rows of rollers 50 with vertical axes, extending respectively on the two sides of the press, in relation to symmetry with respect to the median longitudinal plane X thereof. In this way, the pressing members 36a to 36f are respectively plumb with the members 5 and the median 14 and external longitudinal members 15 of the pre-assembly P.

The press 23 is further equipped with a control device, not shown, which acts in response to the complete introduction of the template 22, to stop the movement of the roller chains 28 and put the blower into service; the latter then inflates the tubes 42 over the entire length of the pressing members 36a to 36f. It follows that the pressing shoes 38 are moved downwards, against the action of the springs 41, to come to bear on the members 5 and the side members 14, 15 which they press strongly. The pressure forces are transmitted to all the glued surfaces of the pre-assembly P which, thanks to the shape of the template, retains its integrity during pressing. In addition, the curved lower surfaces 43 of the pressing shoes 38 produce the desired longitudinal bending of the panel, in cooperation with the concavity of the rails 31 of the roller chains 28.

A short time later, the fan 46 is put into service to inject air heated by the resistors 47, inside the tunnel 44 and thus accelerate the setting of the glue in the pre-assembly P still maintained in pressure . It should be noted here that this closed hot air heating circuit can be replaced by microwave heating elements.

After a predetermined time of a few seconds, the press control device stops the fan 46 and deactivates the blower. The tubes 42 being thus deflated, the springs 41 repel the pressing shoes 38 in the high position. Then the exit door 49 of the press 23 opens and the roller chains 28 are then again set in motion to extract the template and place it on a conveyor 51 which brings it to a demolding station (not shown) where the assembled panel is removed from the template.

At the same time, a new template 22 carrying a pre-assembly P is introduced into the press 23 and undergoes the operating cycle which comes to be described. Of course, the conveyor 51 can be used for the introduction of the templates 22 into the press after passing to a station where the panels are pre-assembled in their respective template 22.

Figures 7 and 8 illustrate a second embodiment of the pressing installation according to the invention, which differs from the first only on the structure of the pressing members 36a to 36f.

Each of these pressing members is constituted by a row of jacks 52 whose bodies 53 are integral with the frame 24 of the press. In addition, the rods 54 of these jacks 52 are, in each pressing member, joined by a common pressing shoe 55, on the convex lower surface 56 from which rollers rollers 57 are mounted free in rotation on an endless chain 58 driven around the row of jacks 52 in the same direction as the lower endless chains 28; the rollers 57 have the same configuration as those of the latter and in particular carry wooden pressing blocks 59.

Thus, as soon as the template 22 carrying the pre-assembly P enters the press 23 according to this second embodiment of the invention, it is sandwiched between the blocks 33 and 59 of the rollers 30 and 57 of the two trains of lower and upper endless chains 28 and upper 58 and is thus moved without interruption over the entire length of the press 23. Simultaneously, the jacks 52 press the pre-assembly P, as described above, by means of the pressing shoes 55, rollers 57 and pressing blocks 59. It is thus possible to continuously assemble the panels according to the invention, hence a significant gain in terms of yield and manufacturing costs. For the rest, the operating cycle of the installation according to this second embodiment of the invention is identical to that of the first.

Finally, FIG. 9 shows a third embodiment of the pressing installation according to the invention, the parallel roller chains 60a to 60f of which are positioned at two levels, according to an enantiomorphic staggered arrangement of that of the pressing members of the two previous modes. and the pressure members 61, which can be indifferently those of the first or second embodiment, are arranged at the same height, respectively plumb with the six roller chains 60a to 60f.

The third embodiment of the pressing installation according to the invention is further characterized by the presence of two parallel rows of idle rollers with vertical axes 62, 63, symmetrical with respect to the median vertical plane X of the installation and separated by 'a distance equal to the width of the pre-assembly. These two rows of rollers 62, 63 are also located just below the pressing blocks 64 in the lowered position and have a height greater than that of the plate 1 of the pre-assembly P.

As will be readily understood on examining FIG. 9, the pre-glued and pre-assembled construction element P can, in this pressing installation, be introduced without upside down and undergo the pressing operation in this position, without the need to use a template, as in the previous two embodiments.

Indeed, the boards 1a which constitute the plate 1 of the pre-assembly P remain attached, because they rest on the top of the latter which is itself in support, by its members 5 and its side members 14, 15 on the blocks of wood 65 roller chains 60a to 60f. In addition, inside the pressing installation, the pre-assembly P is housed between the two rows of idle rollers 62, 63 which, by being in contact with the plate 1 and the external longitudinal members 15, play the role of the edges 27 of the template 22 of the two previous embodiments and therefore maintain the integrity of the pre-assembly during the pressing operation which is carried out as described above. As additional security, it will be good to provide, as shown in FIG. 9, two parallel rows of idle rollers with vertical axes 66, 67, on either side of each of the members 5.

Of course, in the case of continuous pressing according to the principle described with reference to FIGS. 7 and 8, the rows of idle rollers 62, 63, 66 and 67 also guide the pre-assembly P during its movement at through the pressing plant.

It will also be added that for the introduction, in the pressing installation of FIG. 9, of the pre-assembly P using the conveyor 51 described above, it will be necessary to equip it with a system guide roller extending between the pre-assembly station and the entry of the pressing installation, in alignment with the rows of rollers 62, 63, 66 and 67 thereof.

Claims (18)

1. A structural member for the construction industry, comprising a slab (1) on which is formed at least one longitudinal caisson (2) of triangular section defined by two oblique walls (3, 4; 3a, 4a), the divergent ends (11, 12) of which are each fixed in the angle formed between the near face of the slab and a longitudinal thickening (14, 15) on the slab, whilst their convergent ends are joined together by a limb (5) by being partially embedded in longitudinal grooves (6, 7) formed therein, characterized in that the grooves (6, 7) in the limb are V-shaped and the parts of the convergent ends (8, 9) of the oblique walls (3, 4; 3a, 4a) outside the grooves (6,7) have chamfered faces (10) over their entire length, butted together to provide mutual support, whilst each of the divergent ends (11, 12) of the oblique walls (3, 4; 3a, 4a) is provided on its outer corner with a longitudinal notch (13) by which it straddles a flat spar (14, 15), constituting the said thickening on the slab (1), on both sides of the longitudinal corner thereof, each of the said divergent ends having, outside the notched area, a flat bevelled surface by which it lies on the near face of the slab.

2. A structural member as in Claim 1, characterized in that the flat spars (14, 15) on the slab (1) are components applied to the latter.

3. A structural member as in Claim 1 or 2, comprising a plurality of substantially parallel caissons (2) formed on a common slab (1) characterized in that the mutually facing oblique walls (4, 3a) of adjacent pairs of caissons (2) lie with their notches (13) on a shared intermediate spar (14), the two outer spars (15) furthermore terminating flush with the longitudinal edges of the slab (1).

4. A structural member as in Claim 3, characterized in that some or all of the spaces (19) left between the caissons (2) are each closed by a panel (20) which rests on the nearer faces (21) to the slab (1) of the limbs (5) of the two caissons (2) bounding the said space.

5. A structural member as in any of Claims 2 to 4, characterized in that the slab (1) is formed of a plurality of juxtaposed ribs (1a) extending at right angles to the spars and held together by the latter.

6. A structural member as in any of Claims 1 to 5, characterized in that it is arched towards the outer face of the slab (1) in the longitudinal direction of the caisson(s) (2).

7. A structural member as in Claim 6, characterized in that a pre-stressing cable (17) extends in contact with the base of the apex of each of the caissons (2).

8. A process for the assembly of a structural member as in any of Claims 1, 2, 3 and 5 from its various components, i.e., the limb(s) (5), the oblique walls (3, 4, 3a, 4a), the spars (14, 15) and the slab (1), after they have been machined to the required shapes and sizes and adhesive has been applied to the eventual mutual contact surfaces (6, 7, 10, 13), characterized in that it consists of pre- assembling the various components into the final form the finished structural member is to assume, thereby producing a self-locking pre-assembly with no mechanical connection between its said components, and then compressing the pre-assembly thus formed between, on one side, the back slab (1) and, on the other side, the limb(s) (5) and the spars (14, 15), the slab (1) and the outer spars (15) being meanwhile laterally immobilized.

9. A process as in Claim 8, for the assembly of a structural member as in Claim 7, characterized in that it further consists in fixing, prior to compression, a pre-stressing cable (17) in contact with the tip of the apex of each of the caissons (2) and uniformly arching towards the slab, during compression, the limb(s) (5) and optionally the spars (14, 15), by the application of bending forces appropriately distributed over the length of the latter.

10. An installation for effecting the process as in Claim 8, characterized in that it comprises a jig for the pre-assembly of the structural member from its various components after they have been machined to the required shapes and sizes and adhesive has been applied to the eventual mutual contact surfaces, and a press (23) having pressing means (28, 36; 52, 55; 60, 61), which delimit a longitudinal cavity for the reception of the pre-assembled structural member (P) and are actuated on command to switch from an inert state into an active state in which they hold the latter in compression between, on the side, the back of the slab (1) and, on the other side, the limb(s) (5) and the spars (14,15), holding means (22; 62,63) being further provided for the lateral immobilization of the pre-assembled structural member along the slab and the outer spars.

11. An installation as in Claim 10, characterized in that the pressing means consist of supports (28; 60) for the pre-assembled structural member (P), which extend in substantially parallel directions over the entire length of the said reception cavity and are disposed at least plumb with the fixture for the limb(s) (5) and the spars (14, 15) of the said member (P), and pressing heads (36; 52, 55; 61), which are disposed above some at least of the supports and can be moved towards the latter, between an inert position and an active position, the working faces of some being coplanar, whereas those of others are arranged in a staggered pattern corresponding to the arrangement of the limbs and spars in the pre-assembled structural member (P).

12. An installation as in Claim 10 or 11, characterized in that the said supports consist of the upper strands of a set of endless chains (28; 60) with rollers (30) running on rails (31).

13. An installation as in any of Claims 10 to 12, characterized in that the said holding means consist of a template (22) having a cavity in which the structural member is to be pre-assembled, the said cavity having the same plan dimensions as the slab (1) of the pre-assembled structural member (P) and a depth exceeding that of the slab.

14. An installation as in any of Claims 10 to 12, characterized in that the said holding means consist of two parallel rows of rollers (62, 63) with vertical axes, which are disposed on either side of the said reception cavity, level with the slab (1) and the outer spars (15) of the pre-assembled structural member (P) and are separated by a distance equal to the breadth thereof.

15. An installation as in Claim 10 to 11, for effecting the process as in Claim 9, characterized in that the working face (43; 56) of each of the pressing heads (36a to 36f) is bellied towards the supports in the longitudinal direction of the said reception cavity, the supports having a concavity of the same curvature as the working face (43; 56).

16. An installation as in any of Claims 10 to 15, characterized in that each of the pressing heads (36a to 36f) consists of a pressing shoe (38) sliding on return springs (41) at the lower end of a rib (37) integral with the framework (24) of the installation (23), an inflatable hose (42) connected to a bellows being interposed between each pressing shoe (38) and the lower end of the rib (37) on which it is mounted.

17. An installation as in any of Claims 10 to 15, characterized in that each of the pressing heads (36a to 36f) consists of a plurality of screw-jacks (52) aligned in the longitudinal direction of the said reception cavity, the stems (54) of which are attached to a common pressing shoe (55) on which run the freely rotating rollers (57) of an endless chain (58) passing round the row of screw-jacks (52) in the said longitudinal direction, the said rollers being urged, when the screw-jacks are in action, against the component (5; 14; 15) of the pre-assembled structural member (P) subjected to the action of the pressing head in question.

18. An installation as in any of Claims 10 to 17, characterized in that heating means (44, 45, 46, 47) are provided to act on the adhesive-coated parts of the pre-assembled structural member.

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