ITMO20000228A1 - PROCEDURE FOR THE REALIZATION OF A PRE-STRETCHED COMPOSITE STRUCTURE AND PRE-STRETCHED COMPOUND STRUCTURE SO OBTAINED - Google Patents

Description

DESCRIPTION attached to the patent application for industrial invention entitled: "PROCEDURE FOR THE REALIZATION OF A PRE-STRESSED COMPOUND STRUCTURE AND PRE-SOLICITED COMPOSITE STRUCTURE SO OBTAINED".

DESCRIPTION

The present invention relates to a process for producing a pre-stressed composite structure and the pre-stressed composite structure thus obtained. Various types of pre-stressed structures are known in the art. Prestressed beams are very common; in a prestressed beam, steel reinforcements are used which, when suitably stretched, induce a normal compressive stress, bending moments and possibly shear stresses in the beam itself. Pre-flexed metal beams have less diffusion; according to the technique of preflexion in the metal beam, before it is installed, through the action of a temporary preload, which causes an inflection in the beam itself having the opposite direction to that of the inflection due to the operating loads , deformations are introduced, and therefore stresses, which are maintained over time by making special metal plates integral with the pre-loaded beam. The techniques described above have some drawbacks. For example, referring to the prestress applied to metal beams, for solid-wall (metal) beams simply inflected by loads, the normal stress due to the prestress aggravates the state of stress of the beams themselves. An object of the present invention is to provide a pre-stressed structure subject, as a result of the pre-stress, to predetermined values of the bending moment and the shear stress (having opposite signs to those of the bending moment and the shear stress due to the applied loads) and to a normal effort of substantially negligible value. Another object is to provide a pre-stressed structure such that its realization is sufficiently easy. These and other objects are achieved by the process for manufacturing a pre-stressed composite structure, object of the present invention, and by the pre-stressed composite structure thus obtained, which is also the subject of the present invention. The aforementioned procedure for the realization of a pre-stressed composite structure is characterized by the fact that it includes the following phases:

- first phase: a primary structure and one or more pre-stressing structural systems are created; each of said one or more pre-stressing structural systems, moreover, is placed in the predetermined position, in contact with said primary structure; said primary structure comprises a beam, end contrast elements joined to said beam, one or more intermediate contrast elements joined to said beam and retaining elements joined to said beam and placed, one from the other, at a distance, in the longitudinal direction, greater than the height of said beam; said beam has a straight or substantially straight axis; said beam has a closed section, so that a space inside said beam remains identified; each of said one or more pre-stressing structural systems comprises a strut, with longitudinal development, and a tie rod, with longitudinal development; at the end of said first phase of the procedure, the following occurs: in each of said one or more pre-stressing structural systems the strut is positioned outside of said beam and the tie rod has its ends anchored to the ends of said strut; in each of said one or more pre-stressing structural systems the tie rod, in correspondence with its two end portions, is positioned outside said beam and, at the remaining portion between said two end portions, is positioned at least partly, in said space inside said beam; in each of said one or more structural systems pre-stressing the tie rod, in order to be anchored to the ends of the strut, at its ends it exits outside of said beam passing through openings in said beam; each of said one or more pre-stressing structural systems is in contact only with said primary structure; more precisely, in each of said one or more pre-stressing structural systems, the strut and said primary structure are in contact at two of said end contrast elements and two or more of said retaining elements, and there is the tie rod and said primary structure are in contact at one or more of said one or more intermediate contrast elements; in each of said one or more pre-stressing structural systems, considering any section of the strut made according to a plane perpendicular to the axis of said strut, the height of said strut, except in the case of the sections relating to the end zones of said strut, is less than the distance between the axis of said strut and the axis of the tie rod measured in the plane of said section;

said primary structure and said one or more pre-stressing structural systems from the outset are designed and built to create the pre-stressed composite structure;

- second phase: in each of said one or more pre-stressing structural systems the tensioning of the tie-rod is carried out by means of means which contrast with the strut and operations are carried out for maintaining over time the states of stress introduced with said tensioning; each of said one or more pre-stressing structural systems, in correspondence of the relative end contrast elements, of the relative one or more intermediate contrast elements and of the relative retaining elements, by effect of said tensioning of the tie rod, applies to said primary structure a system of pre-stressing forces which inflects said primary structure, inducing a normal stress of substantially negligible value in said primary structure; each of the one or more pre-stress force systems relieves the stress state of said primary structure due to the loads subsequently applied to the pre-stressed composite structure; in each of said one or more pre-stressing structural systems, during said tensioning of the tie rod, said tie rod, subjected to a normal tensile stress, elongates by sliding with respect to said primary structure and the strut, subjected to a normal compressive stress, shortens sliding longitudinally with respect to said primary structure; said second step of the process is completed before said pre-stressed composite structure is put into operation; each of said one or more pre-stressing structural systems remains forever in contact only with said primary structure, more precisely it remains forever in contact with said primary structure in correspondence with the relative end contrast elements, the relative retaining elements and the relative one or more intermediate contrast elements; said primary structure remains forever in contact, as well as with each of said one or more pre-stressing structural systems, with all the external constraints which bind said pre-stressed composite structure.

The pre-stressed composite structure obtained according to the process described above (which is also the subject of the present invention) is characterized by the fact that it comprises:

- a primary structure comprising a beam, end contrast elements joined to said beam, one or more intermediate contrast elements joined to said beam and retaining elements joined to said beam and placed, one from the other, to a distance, in the longitudinal direction, greater than the height of said beam; said beam has a straight or substantially straight axis; said beam has a closed section, so that a space inside said beam remains identified; said primary structure is in contact with all the external constraints which constrain the pre-stressed composite structure; the points of application of the loads applied to said pre-stressed composite structure belong to said primary structure;

- one or more pre-stressing structural systems, each of which is in contact only with said primary structure; each of said one or more pre-stressing structural systems comprises a strut, having a longitudinal development, and a tie rod, having a longitudinal development, having its ends anchored to the ends of said strut; in each of said one or more pre-stressing structural systems the strut is placed outside of said beam; in each of said one or more pre-stressing structural systems, the tie-rod, in correspondence with its two end portions, is placed outside said beam and, in correspondence with the remaining portion between said two end portions, is placed, at least partly, in said space inside said beam; in each of said one or more structural systems pre-stressing the tie rod, in order to be anchored to the ends of the strut, at its ends it exits outside of said beam passing through openings in said beam; in each of said one or more pre-stressing structural systems, the strut and said primary structure are in contact at two of said end contrast elements and two or more of said retaining elements, and the tie rod and said primary structure are in contact at one or more of said one or more intermediate contrast elements; in each of said one or more pre-stressing structural systems, considering any section of the strut made according to a plane perpendicular to the axis of said strut, the height of said strut, except in the case of the sections relating to the end zones of said strut, is less than the distance between the axis of said strut and the axis of the tie rod measured in the plane of said section; each of said one or more pre-stressing structural systems, in correspondence of the relative end contrast elements, of the relative one or more intermediate contrast elements and of the relative retaining elements, applies forces to said primary structure which are mainly due to the tensioning of the tie rod , carried out during the construction of the pre-stressed composite structure, and to the loads applied to said pre-stressed composite structure; in particular each of said one or more pre-stressing structural systems, in correspondence of the relative end contrast elements, of the relative one or more intermediate contrast elements and of the relative retaining elements, by effect of said tensioning of the tie rod, applies to said structure primary a system of pre-stressing forces which inflects said primary structure, inducing in said primary structure a normal stress of substantially negligible value; each of the one or more systems of pre-stressing forces causes an inflection in said primary structure having the opposite direction to that of the deflection caused in said primary structure by said loads applied to said pre-stressed composite structure.

The characteristics and advantages of the present invention will be further highlighted by the following description of some embodiments illustrated purely by way of non-limiting example in the accompanying drawing tables in which:

Figure I illustrates, partly in longitudinal view and partly according to a longitudinal section, a pre-stressed composite structure obtained according to the present invention;

- figure 2 represents, on a larger scale than that of figure 1, the section (with a sectioned detail) according to the straight line I-I of figure 1;

Figure 3 illustrates, on the same scale as Figure 2, a detail of Figure 1; - Figure 4 illustrates, in the same scale as Figure 3, in plan, according to a top view, the detail illustrated in Figure 3;

Figure 5 illustrates, on a larger scale than that of Figure 3, another detail of Figure 1;

- figure 6 represents, on the same scale as figure 5, a part of the section along the line ΙΙ-ΙΙ of figure 5;

- Figure 7 illustrates, partly in longitudinal view and partly according to a longitudinal section, a pre-stressed composite structure obtained according to the present invention, according to a further embodiment;

- figure 8 represents, on a larger scale than that of figure 7, the section along the line III-ΙΙΙ of figure 7;

Figure 9 illustrates, on the same scale as Figure 8, a detail of Figure 7; Figure 10 illustrates, on a larger scale than that of Figure 8, another detail of Figure 7;

Figure 11 illustrates, on the same scale as Figure 10, a detail of Figure 8; - Figure 12 illustrates, in longitudinal view (with a sectioned detail), a pre-stressed composite structure obtained according to the present invention, according to a further embodiment;

- figure 13 represents, on a larger scale than that of figure 12, the section along the line 1V-1V of figure 12;

- Figure 14 illustrates, according to a cross section, a pre-stressed composite structure obtained according to the present invention, according to a further embodiment.

For simplicity of representation, in figures 1, 2, 3, 6, 7, 8, 11 and 13 the ordinary (steel) reinforcements and the reinforcements for prestressing have not been indicated, together with anything else connected to them, present in the pre-stressed composite structures; furthermore, the figures attached to the present description do not indicate welds and bolting; it should be noted that screws and nuts have been indicated in the figures only in cases where such screws and nuts are explicitly referred to in the text of this description. It should also be noted that in each of the figures 1, 3 and 7 the longitudinal section is performed according to a plane that is parallel to the vertical plane that contains the axis of the primary structure. In order to make the steps of the process according to the present invention easier to understand, first of all, with reference to Figures 1, 2, 3, 4, 5 and 6, a pre-stressed composite structure 1 obtained according to the present invention is described. The pre-stressed composite structure 1, which is described below when it is in operation, rests at the ends; more precisely, it is constrained with an external constraint 2, schematized with a hinge, and with an external constraint 3, schematized with a carriage sliding horizontally. The pre-stressed composite structure 1 is subjected to vertical loads 4 (facing downwards) distributed over its entire length and arranged on two parallel lines. The pre-stressed compound structure 1 includes:

- a primary structure 5 which comprises a prestressed reinforced concrete beam 5a, two end contrast elements 5b, 5c joined to the beam 5a, two intermediate contrast elements 5d joined to the beam 5a and six retaining elements 5e joined to the beam 5a and placed, one from the other, at a distance, in the longitudinal direction, greater than the height of the beam 5a (referring to the height of the cross section of the beam 5a); the beam 5a has a straight and horizontal axis; the beam 5a has a closed section (of the "caisson" type), so that a space 12 inside the beam Sa itself remains identified; the beam Sa is equipped with two head partitions 9 in reinforced concrete and two intermediate partitions 10 in reinforced concrete; the primary structure 5 is in contact with all the external constraints that constrain the pre-stressed composite structure 1; these external constraints are external constraints 2 and 3; the points of application of the loads 4 applied to the pre-stressed composite structure belong to the primary structure 5 (the loads 4 are applied at the extrados of the beam 5a);

- a pre-stressing structural system 6 which is in contact only with the primary structure 5; the pre-stressing structural system 6 comprises a strut 6a, having a longitudinal development, and a tie rod 6b, having a longitudinal development, having the ends anchored to the ends of the strut 6a; the strut 6a is placed outside the beam 5a (ie it is placed outside the space 12 and outside the concrete section of the beam 5a); the tie rod 6b, at its two end sections, is placed outside the beam 5a and, at the remaining section between the aforementioned two end sections, is placed in the space 12 inside the beam Sa; it should be noted that the tie rod 6b, in order to be anchored to the ends of the strut 6a, exits outside the beam 5a at its ends, passing through openings 13 present in the beam 5a itself; it should be noted that the openings 13 are positioned in the upper slab of the beam Sa; in the pre-stressing structural system 6, the strut 6a and the primary structure 5 are in contact at the end contrast elements 5b, 5c and the retaining elements 5e, and the tie rod 6b and the primary structure 5 are in contact at the intermediate contrast elements 5d; considering any section of the strut 6a made according to a plane perpendicular to the axis of the strut 6a itself, we have that the height of the strut 6a (we refer to the height of the cross section of the strut 6a), except in the case of relative to the end areas of the strut 6a itself, it is less than the distance between the axis of the strut 6a and the axis of the tie rod 6b measured in the plane of the aforementioned section; the pre-stressing structural system 6, in correspondence with the end contrast elements 5b, 5c, the intermediate contrast elements 5d and the retaining elements 5e, applies forces to the primary structure 5 which are due to the tensioning of the tie rod 6b, carried out during construction of the pre-stressed composite structure I, and to the loads 4 applied, in operation, to the pre-stressed composite structure 1 itself; in particular the pre-stressing structural system 6, in correspondence with the end contrast elements 5b, 5c, the intermediate contrast elements 5d and the retaining elements 5e, by effect of the aforementioned stringing of the tie rod 6b, applies to the primary structure 5 a pre-stress forces which inflicts the primary structure 5, inducing in the primary structure 5 itself a normal stress of substantially negligible value; this normal stress is due to the frictional forces present in the contact areas between the pre-stressing structural system 6 and the primary structure 5, and to the components, in the direction of the axis of the primary structure 5, of the forces applied by the tie rod 6b to the primary structure 5 itself; the aforementioned system of pre-stressing forces causes in the primary structure 5 an inflection (upwards) having the opposite direction to that of the deflection caused in the primary structure 5 itself by the loads 4 applied to the pre-stressed composite structure 1. Referring to the pre-stressed composite structure 1 , in operation, subject to loads 4, it should be noted that the normal stress induced in the primary structure 5 by the pre-stressing structural system 6 is of substantially negligible value; this normal stress is due to the frictional forces present in the contact areas between the pre-stressing structural system 6 and the primary structure 5, and to the components, in the direction of the axis of the primary structure 5, of the forces applied by the tie rod 6b to the primary structure 5 itself. The tie rod 6b is constituted by a group of strands 11 of high resistance steel (ie steel having, for example, a tensile strength higher than 1750 N / mm2); each strand 11 is greased and inserted in its own sheath of synthetic material inside which the strand 11 itself can slide; the group of strands 11 (with the relative sheaths) is inserted in a containment element, made of synthetic material (possibly divided into various sections), inside which there is also a cement-based filling material (not shown, for simplicity, in the figures). The strut 6a comprises a central element 7, with longitudinal development and a straight axis, and two terminal elements 8 which are integral with the ends of the central element 7 and which constitute the ends of the strut 6a itself; it should be noted that in the case of the strut 6a the two terminal elements 8 are made together with the central element 7. The strut 6a is positioned above the extrados of the beam 5a; it should be noted, in fact, that the central element 7 is positioned above the extrados of the upper slab of the beam 5a and that the two terminal elements 8 are also positioned above the extrados of the beam Sa, considering that the extrados of the beam 5a, in correspondence with the position in which the terminal elements 8 are placed, coincides with the extrados (upper part) of the head partitions 9. The central element 7, which has a horizontal axis, comprises two longitudinal elements 22 of suitably reinforced high-strength concrete, transversal elements 23 of suitably reinforced high-strength concrete and six support elements 14, one for each retaining element 5e; the transverse elements 23, which connect the two longitudinal elements 22, are placed in correspondence with the retaining elements 5e, in proximity to the two terminal elements 8 and in the center line of each of the portions comprised between two adjacent retaining elements 5e. Each supporting element 14, which is in contact with one of the retaining elements 5e, comprises a main steel bar 14a equipped at the ends with two threaded holes (one hole for each of the two ends), two threaded steel bars 14b which are screwed into the aforementioned two threaded holes and which are integral with the main bar 14a, two steel guide plates 14c, two steel nuts 14d screwed onto the two threaded bars 14b, two steel sliding blocks 14e, four steel plates contact 14f of synthetic material and four contact plates 14g of synthetic material; each of the two guide plates 14c is provided with a central hole in which the relative threaded bar 14b is inserted; two contact plates 14f are integral with each of the two guide plates 14c; each of the two sliding blocks 14e is provided with a central hole in which one of the two ends of the main bar 14a is inserted; two contact plates 14g are integral with each of the two sliding blocks 14e and are placed one above and one below; the main bar 14a, in its central part, is incorporated in the concrete of the two longitudinal elements 22 and of the relative transversal element 23 and is therefore integral with them. It should be noted that the support elements 14 belong to the central element 7; therefore, the strut 6a comprises the supporting elements 14 themselves. The strut 6a is in contact with the retaining elements 5e only in correspondence with the supporting elements 14. Each of the two terminal elements 8 comprises a suitably reinforced high-strength concrete block 8a, a metal anchoring element 8b (illustrated, for simplicity shown, only in figure 3) almost entirely incorporated in the concrete of the block 8a, an anchoring plate 8c of steel and two connecting elements 8d in suitably reinforced high-strength concrete; the ends of the strands 11 are anchored to the anchoring plate 8c by means of wedges; therefore, the tie rod 6b is anchored to the two terminal elements 8, and therefore to the ends of the strut 6a. The two end contrasting elements 5b, 5c and the retaining elements 5e are placed outside the beam 5a and are integral with the beam 5a itself. The two end contrasting elements 5b, 5c, which are made of steel, constitute the support and transverse retainer of the two terminal elements 8; it should be noted that the end contrast elements 5b, 5c are placed in correspondence with the openings 13 present in the upper slab of the beam 5a. The end contrast element 5c comprises a base plate 15 integral with the relative head partition 9, a support element 16 and two lateral containment elements 17; each lateral containment element 17 is equipped with a threaded sleeve and a contact screw 18 screwed inside the aforementioned threaded sleeve; the terminal element 8 placed in proximity to the external constraint 3 rests in correspondence with the support element 16 and is in contact with one of the two ends of each of the two contact screws 18. The end contrast element 5b comprises a base plate integral with the relative head partition 9, a support element and two lateral containment elements, each of which is equipped with a threaded sleeve and a contact screw screwed inside the aforesaid threaded sleeve; the terminal element 8 placed near the external constraint 2 is supported in correspondence with the aforementioned support element and is in contact with one of the two ends of each of the two aforementioned contact screws. Each of the two intermediate contrast elements 5d is integral with one of the two intermediate partitions 10; more precisely, each intermediate contrast element 5d, which deflects the strands 11 (and therefore the tie rod 6b), comprises a set of metal elements incorporated in the concrete of the relative intermediate partition 10. Each retaining element Se is made of steel and it comprises a base plate 19 which is positioned in correspondence with the extrados of the beam 5a and which is integral with the beam 5a itself, two main elements 20 integral with the base plate 19 and two closing elements 21 integral with the two main elements 20; it should be noted that the base plate 19 is connected to a metal plate, not indicated for simplicity in the figures, incorporated in the concrete of the upper slab of the beam 5a itself. Each of the two main elements 20 comprises two vertical plates 20a, a vertical plate 20b, a horizontal plate 20c, two blocks 20d and a stop element 20e integral with the horizontal plate 20c; each block 20d has a threaded hole and is integral with one of the two vertical plates 20a and with the horizontal plate 20c; each main element 20 can, in general, also comprise a plate 2 Of (used as shim), made integral with the horizontal plate 20c, and two perforated plates 20g (used as shims) placed above the blocks 20d; the aforesaid plates 20f, 20g are used to compensate for the geometric and position imperfections of the various elements which are in contact. Each of the two closing elements 21 includes a crosspiece 2 la stiffened by plates, a stop element 21 b integral with the crosspiece 2 la and two screws 21 c through which the closing element 21 itself is connected to the relative main element 20; it should be noted that the screws 21c are screwed into the threaded holes present in the blocks 20d. With reference to each retaining element 5e and to the relative supporting element 14, the following occurs: the two main elements 20 and the two closing elements 21 are in contact with the contact plates 14f, integral with the relative guide plates 14c, and with the contact plates 14g integral with the relative sliding blocks 14e; the relative longitudinal displacements between the retaining element 5e itself and the relative support element 14 are possible since the ends of the main bar 14a are inserted in the two sliding blocks Me, each of which can translate in the longitudinal direction, with the relative two plates contact 14g integral with it, sliding between the relative main element 20 and the relative closing element 21; relative transverse displacements in the horizontal plane between the retaining element 5e itself and the relative support element 14 are prevented since the guide plates 14c, to which the contact plates 14f are integral, are connected, by means of the threaded bars 14b and the nuts 14d, to the main bar 14a and are positioned in such a way as to keep the contact plates 14f themselves in contact with the stop elements 20e, 21b; it should be noted that the guide plates 14c can translate longitudinally. It is noted, then, that the contact plates 14f, 14g facilitate the longitudinal sliding of the support element 14 with respect to the relative retaining element 5e. Therefore, the retaining elements 5e, (also) in operation, allow (in addition to relative rotations) only the relative longitudinal displacements (in the direction, that is, of the axis of the beam 5a) between the primary structure 5 and the strut 6a . Between the terminal element 8 next to the external constraint 3 and the relative end contrast element 5c, (also) in operation, only relative longitudinal displacements are allowed (in addition to relative rotations); between the terminal element 8 next to the external constraint 2 and the relative end contrast element 5b, (also) in operation, neither the relative longitudinal displacements nor the relative transverse displacements are allowed. According to a further possible embodiment, not shown in the figures, in each retaining element the base plate is made integral with the upper slab of the beam by means of anchor bolts and nuts; in this case it is possible to adjust in height, by means of suitable centering nuts, the position of the base plate; in this case, moreover, there is a filling material such as compensated shrinkage cement mortar between the intrados of the base plate and the extrados of the beam. In cases where the position and size irregularities between the primary structure and the one or more struts are very small, the adjustment systems capable of compensating for these irregularities may be missing. The strut 6a is stabilized by the primary structure 5 by means of the retaining elements 5e and by the end contrast elements 5b, 5c. It should be noted that the forces that the pre-stressing structural system 6 applies to the primary structure 5 in correspondence with the retaining elements 5e have a much lower intensity than the intensity of the forces applied by the pre-stressing structural system 6 itself to the primary structure 5 in correspondence with the contrasting elements. ends 5b, 5c and in correspondence with the intermediate contrast elements 5d. It should be noted that the loads 4, represented with arrows in Figure 2, are applied by the structural elements of secondary warping that rest in correspondence with the extrados of the beam 5a; it is evident that these secondary structural elements are not placed in contact with the strut 6a.

The process according to the present invention is described below for the realization of the pre-stressed composite structure 1 which comprises the following steps:

- first phase: the primary structure 5 and the pre-stressing structural system 6 are created; the pre-stressing structural system 6, moreover, is placed in the predetermined position, in contact with the primary structure 5; at the end of the first phase of the process the following occurs: in the pre-stressing structural system 6 the strut 6a is positioned outside the beam 5a and the tie rod 6b has its ends anchored to the ends of the strut 6a; the tie rod 6b, at its two end sections, is positioned outside the beam 5a and, at the remaining section between the aforementioned two end sections, is positioned in the space 12 inside the beam 5a; the tie rod 6b, in order to be anchored to the ends of the strut 6a, at its ends exits outside the beam 5a passing through the openings 13 present in the beam 5a; the pre-stressing structural system 6 is in contact only with the primary structure 5; more precisely, the strut 6a and the primary structure 5 are in contact at the end contrast elements 5b, 5c and the retaining elements 5e, and the tie rod 6b and the primary structure 5 are in contact in correspondence of the intermediate contrast elements 5d;

the primary structure 5 and the pre-stressing structural system 6 from the outset are designed and built to create the pre-stressed composite structure 1;

- second phase: in the pre-stressing structural system 6, the tensioning of the tie rod 6b is carried out by means of a hydraulic jack, not indicated in the figures, which contrasts with the strut 6a and operations are carried out to maintain the states of stress introduced with the aforementioned stringing; the pre-stressing structural system 6, in correspondence with the end contrast elements 5b, 5c, the intermediate contrast elements 5d and the retaining elements 5e, by effect of the tensioning of the tie rod 6b, applies a system of pre-stressing forces to the primary structure 5 which inflects the primary structure 5, inducing in the primary structure 5 itself a normal effort of substantially negligible value; this normal stress is due to the frictional forces present in the contact areas between the pre-stressing structural system 6 and the primary structure 5, and to the components, in the direction of the axis of the primary structure 5, of the forces applied by the tie rod 6b to the primary structure 5 itself; the aforementioned system of pre-stressing forces relieves the state of stress of the primary structure 5 due to the loads 4 subsequently applied (i.e. applied in operation) to the pre-stressed composite structure 1; in the pre-stressing structural system 6, during the tensioning of the tie rod 6b, the tie rod 6b itself, subjected to a normal tensile stress, elongates by sliding with respect to the primary structure 5 and the strut 6a, subjected to a normal compressive stress, is shortened by sliding longitudinally with respect to the primary structure 5, guided by the retaining elements 5e and by the end contrast element 5c; the second phase of the procedure is completed before the pre-stressed composite structure 1 is put into operation; the pre-stressing structural system 6 remains forever in contact only with the primary structure 5, more precisely it remains forever in contact with the primary structure 5 in correspondence with the end contrast elements 5b, 5c, the retaining elements 5e and the intermediate contrast 5d; the primary structure 5 remains forever in contact, as well as with the pre-stressing structural system 6, with all the external constraints that bind the pre-stressed composite structure 1; these external constraints are external constraints 2 and 3.

With reference to the first phase of the procedure for the realization of the pre-stressed composite structure 1, the following is specified. The primary structure 5, the strut 6a and the tie rod 6b are made; it should be noted that the beam 5a is prestressed by means of pretended strands. It should be noted that the retaining elements 5e and the end contrasting elements 5b, 5c are applied to the outside of the beam Sa making them integral with the beam 5a itself. It is specified that some parts of the retaining elements 5e, and more precisely for each retaining element 5e the two main elements 20 integral with the relative base plate 19, are applied to the outside of the beam 5a, in correspondence with the extrados of the beam 5a itself, before positioning the strut 6a; the end contrasting elements 5b, 5c, are applied to the outside of the beam 5a, in correspondence with the extrados of the head part 9; the intermediate contrast elements 5d are already incorporated in the concrete of the lower part of the intermediate partitions 10; the strut 6a and the tie rod 6b are then placed in position; the strut 6a is positioned above the extrados of the beam 5a by resting its ends, i.e. the terminal elements 8, in correspondence with the end contrast elements 5b, 5c (and more precisely in correspondence with the support element 16 belonging to the end contrast element 5c and in correspondence with the support element belonging to the end contrast element 5b) and placing the support elements 14 in correspondence with the main elements 20 (belonging to the retaining elements 5e); the closing elements 21 are then made integral with the relative main elements 20 by screwing the screws 21c inside the relative blocks 20d; it should be noted that the assembly of the retaining elements 5e is completed once the positioning of the strut 6a has been carried out; it is then specified that, usually, the plates 20f, 20g are used to compensate for the dimensional and position imperfections present; at the end of the aforesaid operations, in each retaining element 5e the contact plates 14g, integral with the relative sliding blocks 14e, are in contact with the relative main elements 20 and with the relative closing elements 21; in each retaining element 5e, then, the two nuts 14d are screwed onto the two threaded bars 14b so that the guide plates 14c are positioned so as to place the contact plates 14f, integral with them, in contact (in the horizontal direction) with the relative stop elements 20e, 21b. The positioning of the tie rod 6b in contact with the primary structure 5 includes the following two operations: the insertion of the strands 11 (each with its own sheath) inside the containment element in synthetic material (mentioned above) , previously placed in position, and the injection of the cement-based filling material (mentioned above) inside the aforementioned containment element; it should be noted that each strand 11 remains forever sliding inside its own sheath as the aforementioned filling material is in contact with the outer surface of the aforementioned sheath. Subsequently, at a point, and more precisely at the end contrast element 5b, the relative longitudinal displacements between the pre-stressing structural system 6 and the primary structure 5 are permanently blocked; the primary structure 5, then, with the pre-stressing structural system 6 (placed in contact with it) is positioned on site (but obviously not put into operation) by supporting it in correspondence with the external constraint 2 and the external constraint 3; subsequently, a part of the loads 4 is applied to the extrados of the beam 5a.

With reference to the second phase of the procedure, the following is specified. The hydraulic jack, mentioned above, positioned at the end of the tie rod 6b close to the external constraint 3, stretches the strands 11 (i.e. the tie rod 6b) in contrast with the terminal element 8 close to the external constraint 3 and then with the strut 6a; the other end (close to the external constraint 2) of each strand 11 (and therefore of the tie rod 6b) was previously anchored, by means of wedges, to the anchoring plate 8c included in the terminal element 8 next to the external constraint 2. During the stringing of the tie rod 6b, among other things, what is written below occurs: each strand 11, subject to a normal tensile stress, stretches (substantially) free to slide along its entire length, inside its own sheath synthetic material, with respect to the primary structure 5; the strut 6a, subjected to a normal compressive stress, is shortened by sliding (longitudinally) substantially freely (the term "substantially" has been introduced as frictional forces are present), unless its end is close to the external constraint 2, with respect to to primary structure 5; it should be noted that the end of the strut 6a close to the external constraint 2 was previously locked to the end contrast element 5b; the central element 7, shortening, slides longitudinally with respect to the retaining elements 5e; the terminal element 8 next to the external constraint 3 slides longitudinally on the support element 16 belonging to the end contrast element 5c. Subsequently, after anchoring (by means of wedges) the strands 11 to the anchoring plate 8c included in the terminal element 8 close to the external constraint 3, in order (among other things) to obtain (as far as possible) a symmetrical distribution of the stresses, by means of the aforementioned hydraulic jack, which is now positioned at the other end of the tie rod 6b (close to the external constraint 2), the tensioning of the tie rod 6b is completed. Subsequently the aforesaid hydraulic jack is deactivated and definitively removed. It should be noted that, at the end of the second step of the process, the ends of the tie rod 6b are definitively anchored to the ends of the strut 6a. The system of pre-stressing forces mentioned above comprises upward-directed forces applied by the pre-stressing structural system 6 to the primary structure 5 at the intermediate contrast elements 5d, downwardly directed forces applied by the pre-stressing structural system 6 to the primary structure 5 in correspondence with the end contrast elements 5b, 5c and forces, having an intensity much lower than the intensity of the other aforementioned forces, applied by the pre-stressing structural system 6 to the primary structure 5 in correspondence with the retaining elements 5e. The procedure for the realization of the pre-stressed composite structure 1 ends with the completion of the operations described above and of other complementary operations (not described) designed, among other things, to preserve the pre-stressed structural system over time 6. Subsequently, once the procedure is completed, the pre-stressed composite structure 1 is put into operation and the remaining part of the loads 4 is applied to it. 6a (among other things) the value of the normal compressive stress is increased and in the tie rod 6b the value of the normal traction effort is increased. It should also be noted that between each part of the pre-stressing structural system 6 and the primary structure 5 the same relative displacements permitted during the second phase of the procedure are permitted in operation. It should be noted that with regard to the realization of the tie rod and the stringing phases of the tie itself it is possible, depending on the case, to carry out operations other than those indicated above even with different temporal sequences; for example, in cases other than the one illustrated, the injection of the filling material into the containment element, inside which the strands are positioned, is carried out after having carried out the stringing of the strands themselves.

With reference to figures 7, 8, 9, 10 and 11, a pre-stressed compound structure 30 is described, obtained according to the present invention according to a further embodiment. The pre-stressed composite structure 30 is supported at the ends in correspondence with an external constraint 31 and an external constraint 32, technically equivalent respectively to the external constraint 2 and to the external constraint 3, and is subjected to vertical loads 33 (facing downwards) distributed along its entire length and arranged on two parallel lines. The pre-stressed compound structure 30, which is described below when it is in operation, includes:

- a primary structure 34 which comprises a prestressed reinforced concrete beam 34a, two steel end contrast elements 34b joined to the beam 34a, two intermediate steel contrast elements 34c joined to the beam 34a and five retaining elements 34d, 34e of steel joined to the beam 34a and placed, one from the other, at a distance, in the longitudinal direction, greater than the height of the beam 34a; the beam 34a has a straight and horizontal axis; the beam 34a has a closed section (of the "caisson" type), so that a space 36 inside the beam 34a itself remains identified; each of the two end contrast elements 34b is technically equivalent to the end contrast element 5c;

- a pre-stressing structural system 35 which is in contact only with the primary structure 34; the pre-stressing structural system 35 comprises a strut 35a, having a longitudinal development, and a tie rod 35b, with a longitudinal development, having the ends anchored to the ends of the strut 35a; the strut 35a, which is made of steel, is placed outside the beam 34a; the tie rod 35b, in correspondence with its two end portions, is placed on the side of the beam 34a and, at the remaining portion between the aforementioned two end portions, is placed partly in the space 36 inside the beam 34a and partly on the outside of the beam 34a; the tie rod 35b, in order to be anchored to the ends of the strut 35a, exits at its ends at the foot of the beam 34a passing through openings present at the upper slab of the beam 34a itself; it should be noted that the tie rod 35b, near the centerline of the primary structure 34, exits outside the beam 34a passing through openings in the lower slab of the beam 34a itself. The end contrast elements 34b, the retaining elements 34d, 34e and the intermediate contrast elements 34c are placed outside the beam 34a and are integral with the high beam 34a itself. The tie rod 35b comprises a group of high strength steel strands 37. The strut 35a is positioned above the extrados of the beam 34a and comprises a central element 38, with a straight and horizontal axis, and two terminal elements 39 joined at the ends of the central element 38. The central element 38 comprises two metal profiles with “I” section connected to each other by plates and connecting profiles. The beam 34a is equipped with two reinforced concrete head septa 40 placed in an inclined position with the upper part displaced towards the center of the beam 34a itself. It is pointed out that the distance between the two end contrast elements 34b, which are located in correspondence with the top of the two head partitions 40, is less than the distance between the external constraints 31, 32; this position of the two end contrast elements 34b allows, in the second phase of the procedure, to carry out the stringing of the tie rod 35b without the hydraulic jack used for the stringing overflowing from the longitudinal dimensions of the beam 34a. Each of the five retaining elements 34d, 34e, which is made of steel, comprises a base plate 41 made integral with the beam 34a, two support elements 42 placed under the intrados of the central element 38, two vertical rods 43 (coupled ) integral with the base plate 41, a horizontal rod 44 (coupled) connected to the two rods 43, two blocks 45 integral with the two rods 43 each of which is equipped with a threaded hole, two contact screws 46 screwed inside the two blocks 45 and placed in contact with the central element 38, a block 47 (with vertical axis) which is integral with the rod 44 and which is equipped with a threaded hole, and a contact screw 48 which is screwed inside of the block 47 and which contrasts with the central element 38, in correspondence with a contact element 49 included in the central element 38 itself. According to a further embodiment, not shown in the figures, each of the retaining elements is similar to one of the retaining elements 34d and differs from the retaining element 34d itself in that, instead of the contact screws 46 and 48 (with the relative blocks 45 and 47), there are elements of reinforced neoprene integral with the rods (similar to rods 43 and 44) belonging to the retaining element itself; in this case, moreover, the support elements consist of two elements in reinforced neoprene and the contact element 49 consists of a steel plate. Between the strut 35a and each of the four retaining elements 34d, relative longitudinal displacements are permitted and, at the same time, relative transverse displacements in the horizontal plane are prevented. Between the retaining element 34e and the strut 35a, in addition to the relative horizontal transverse displacements, also the relative longitudinal displacements are prevented. It should be noted that the retaining element 34e, which is placed in correspondence with the center line of the primary structure 34, differs from the retaining elements 34d in that it comprises locking elements (not indicated in the figures) which prevent relative longitudinal displacements between the strut 35a and primary structure 34. The two end contrasting elements 34b constitute the support and transverse retaining of the terminal elements 39; between the two end contrast elements 34b and the terminal elements 39, only relative longitudinal displacements are permitted (in addition to relative rotations). It should be noted that in correspondence with the retaining element 34e there is the only point at which the relative longitudinal displacements between the pre-stressing structural system 35 and the primary structure 34 are prevented. According to another embodiment (not illustrated in the figures) each end contrast element comprises a support element in reinforced neoprene. The behavior of the pre-stressed composite structure 30 and the process for making it are technically equivalent to those already described for the pre-stressed composite structure 1. It should also be noted that in the first phase of the process, in addition to the end contrast elements 34b and the retaining elements 34d , 34e, the intermediate contrast elements 34c are also applied to the outside of the beam 34a making them integral with the beam 34a itself.

With reference to figures 12 and 13, a pre-stressed composite structure 50 is described, obtained according to the present invention, according to a further embodiment. The pre-stressed composite structure 50 is supported at the ends in correspondence with an external constraint 51 and an external constraint 52, technically equivalent respectively to the external constraint 2 and to the external constraint 3, and is subjected to loads 53 uniformly distributed over its entire length and arranged on two parallel lines. The pre-stressed compound structure 50, which is described below when it is in operation, includes:

- a primary structure 54 which comprises a prestressed reinforced concrete beam 54a, two end contrasting elements 54b, 54c of steel technically equivalent to the end contrasting elements 5b, 5c, two intermediate steel contrasting elements 54d, six steel retainer 54e technically equivalent to the retaining elements 5e; the beam 54a is equipped with two head partitions 58 and two intermediate crosspieces 59; the two intermediate contrast elements 54d are integral with the two intermediate crosspieces 59;

- a pre-stressing structural system 55 which is in contact only with the primary structure 54; the pre-stressing structural system 55 comprises a strut 55a and a tie rod 55b having the ends anchored to the ends of the strut 55a. Tie rod 55b comprises a group of high strength steel strands. The strut 55a is placed outside the beam 54a, above the extrados of the beam 54a itself; the strut 55a includes (among other things) two tubular steel elements 56 with a circular section connected to each other; the strut 55a further comprises six metal support elements 57 very similar (and technically equivalent) to the support elements 14; it is noted that the strut 55a is in contact with the retaining elements 54e only in correspondence with the supporting elements 57. A protection element 60 is applied to the beam 54a, positioned in correspondence with the intrados of the beam 54a itself, which encloses and protects the part of the tie rod 55b located below the intrados of the beam 54a and also the two intermediate contrast elements 54d; the protection element 60 is made using thin steel sheets and metal profiles. The behavior of the pre-stressed composite structure 50 and the procedure for making it are technically equivalent to those already described for the pre-stressed composite structure 1. According to other embodiments, the protection element, mentioned above, can be made of concrete reinforced with a small thickness or it can be made with the use of other suitable materials characterized by remarkable fire resistance values.

With reference to Figure 14, a pre-stressed compound structure 70 is described, resting at the ends in correspondence with two external constraints (not shown in the figures) technically equivalent to external constraint 2 and external constraint 3. The pre-stressed compound structure 70, which is hereafter described when it is in operation, it is subjected to vertical loads 71, uniformly distributed over its entire length and arranged on two parallel lines. The pre-stressed compound structure 70 includes:

- a primary structure 72 which comprises a steel beam 72a, four steel end contrast elements (not shown in the figures) joined to the beam 72a, an intermediate contrast element 72b joined to the beam 72a and eight steel retaining elements 72c joined to the beam 72a and placed, one from the other, at a distance, in the longitudinal direction, greater than the height of the beam 72a; the intermediate contrast element 72b, which is made of steel, is placed at the center line of the beam 72a; the beam 72a has a straight and horizontal axis and has a closed section (of the "caisson" type), so that a space 74 inside the beam 72a remains identified; the aforementioned end contrasting elements and the retaining elements 72c are placed outside the beam 72a and are integral with the beam 72a itself; each retaining element 72c is constituted by a set of metal elements which comprises a base plate 75, rods 76, 77 and contact elements 78a, 78b;

- two pre-stressing structural systems, each of which is in contact only with the primary structure 72; each of the two pre-stressing structural systems comprises a strut 73a, having a longitudinal development, and a tie rod 73b with a longitudinal development, having the ends anchored to the ends of the strut 73a; in each of the two aforementioned pre-stressing structural systems, the strut 73a and the primary structure 72 are in contact at two of the aforementioned end contrast elements and the eight retaining elements 72c, and the tie rod 73b and the primary structure 72 are in contact at the intermediate contrast element 72b; in each of the two aforesaid pre-stressing structural systems the tie rod 73b comprises a set of high-strength steel strands and the strut 73a comprises a tubular steel element filled with high-strength concrete; it is noted that each of the eight retaining elements 72c is in contact with the two struts 73a and that the intermediate contrast element 72b is in contact with the two tie rods 73b; each of the two aforementioned pre-stressing structural systems, in correspondence with the relative two aforementioned end contrast elements, the intermediate contrast element 72b and the eight retaining elements 72c, applies forces to the primary structure 72 which are mainly due to the tensioning of the tie rod 73b , carried out during the construction of the pre-stressed composite structure 70, and to the loads 71 applied to the pre-stressed composite structure 70 itself; in particular each of the two aforementioned pre-stressing structural systems, in correspondence with the relative two aforementioned end contrast elements, of the intermediate contrast element 72b and of the eight retaining elements 72c, by effect of the aforementioned stringing of the tie rod 73 b, applies to the structure primary 72 a system of pre-stressing forces which inflects the primary structure 72, inducing in the primary structure 72 itself a normal stress of substantially negligible value; each of the two systems of pre-stressing forces causes in the primary structure 72 an inflection having the opposite direction to that of the deflection caused in the primary structure 72 itself by the loads 71 applied to the pre-stressed composite structure 70. The behavior of the pre-stressed composite structure 70 and the procedure to achieve it they are technically equivalent to those already described for the pre-stressed composite structure 1. It should be noted that in the first step of the process the two struts 73a are placed in position after the retaining elements 72c have been made integral with the beam 72a.

In general, the process according to the present invention can sometimes comprise a third phase, subsequent to the first two phases, in which, in at least one pre-stressing structural system, relative displacements, allowed in the second phase of the process, between the primary structure are permanently blocked. and parts of the pre-stressing structural system itself; it should be noted that, for example, in this possible third phase, relative longitudinal displacements between parts of the tie rod and the primary structure and / or between parts of the strut and the primary structure can be permanently blocked; it should be noted that this possible third phase is completed before the pre-solicited composite structure is put into operation. In general, the locking of the aforesaid relative longitudinal displacements can be useful for optimizing the behavior "at break" of the pre-stressed composite structure. As a rule, in each pre-stressed composite structure obtained according to the present invention, each of the one or more pre-stressing structural systems is made with materials having a resistance higher than that of the material with which the beam included in the primary structure is made. In other cases, the choice of materials for the construction of each pre-stressing structural system is carried out with the primary objective of using materials with a cost / strength ratio lower than that relating to the material with which the primary structure is made. In general, in a pre-stressed composite structure obtained according to the present invention, (as in the case of pre-stressed composite structures I, 30, 50 and 70) each of the one or more pre-stressing structural systems induces in the primary structure a normal stress of value not zero due to the frictional forces generated between the primary structure and the pre-stressing structural system itself; moreover, a pre-stressing structural system induces in the primary structure, or in parts of the primary structure itself, a normal effort of non-zero value if the axis of the primary structure is substantially (and not "perfectly") straight (yes, this case is considered according to what is provided in the present invention), as well as in the case of a primary structure with variable section, or if the bisector of at least an angle between two consecutive sections of the tie rod is not perpendicular to the axis of the primary structure (as well as in the case of pre-stressed composite structures 1, 30 and 50); it should be noted that the normal stress due to the frictional forces and to the other aforementioned causes (if any), possibly by using suitable constructive devices, appears to be, if compared to the other stresses present in the primary structure, of substantially negligible value. In each pre-stressed compound structure obtained according to the present invention in which the process of the present invention is terminated with the completion of the second phase (of the process itself), in operation, the normal stress induced in the primary structure by one or more more pre-stressing structural systems, and therefore (a fortiori) also the grandmother stress induced in the primary structure by each of the one or more pre-stressing structural systems, is of substantially negligible value. In each pre-stressed compound structure obtained according to the present invention in which the process of the present invention is terminated with the completion of the second phase (of the process itself), there is between each part of the one or more pre-stressing structural systems and the primary structure the same relative displacements and the same relative rotations that are permitted during the second phase of the procedure are permitted in operation. In each pre-stressed composite structure obtained according to the present invention for which the third step of the process has been envisaged (and therefore implemented), in general, each of the one or more pre-stressing structural systems permanently further linked to the primary structure it can induce in the primary structure itself a normal effort of some entity. It is emphasized that, for each pre-stressed composite structure obtained according to the present invention, the process of the present invention is completed before the pre-stressed composite structure itself is put into operation. In general, according to the present invention, in addition to externally pre-stressed composite structures isostatically constrained, there can also be externally pre-stressed compound structures hyperstatically constrained, such as, for example, a pre-stressed compound structure which comprises a primary structure, having the static scheme of continuous beam with several spans, and several pre-stressing structural systems placed in correspondence with the various spans of the primary structure. It is emphasized that, in a pre-stressed compound structure obtained according to the present invention, the intermediate contrast elements can be one, or two, or more than two. In a pre-stressed compound structure obtained according to the present invention at least some parts of the end contrast elements and of the retaining elements can be made together with the beam; in particular, if the beam included in the primary structure is of prestressed reinforced concrete, certain parts of each of the retaining elements and / or certain parts of each of the end contrasting elements can be incorporated into the concrete of the aforementioned beam. With reference to the method according to the present invention, (as in the case of the pre-stressed composite structure I) at least part of the permanent loads can be applied to the pre-stressed composite structure (in which the stringing of one or more tie rods has not yet been carried out ) before the start of the second phase of the procedure itself. In a pre-stressed composite structure obtained according to the present invention, not illustrated for simplicity in the figures, in at least one of the one or more pre-stressing structural systems the strut, which is positioned outside the beam, can be placed, at least for part of its length , not above the extrados of the beam. In a pre-stressed composite structure obtained according to the present invention, the beam included in the primary structure can be made, for example, of prestressed reinforced concrete or steel or wood or laminated wood, or it can be made with the use of aluminum alloys , or with the use of other metal alloys, or with the use of synthetic materials or ceramic or composite materials, or with the use of combinations of the aforementioned materials or other suitable materials. In a pre-stressing structural system comprised in a pre-stressed composite structure obtained according to the present invention, one or more materials can be used for the construction of the strut, such as, for example, steel, aluminum alloys or other metal alloys, synthetic materials, ceramic materials, composite materials, high-strength concretes, or other suitable materials or combinations of the aforementioned materials. In each pre-stressing structural system the strut comprises one or more structural elements with longitudinal development such as, for example, sections, elements composed of welded sheets, tubular elements; suitable materials such as, for example, concrete or materials based on synthetic resins can be inserted inside the tubular elements; in particular, the strut can comprise one or more tubular steel elements filled with high-strength concrete; it should be noted that reinforcement bars can also be incorporated into the concrete. In a pre-stressing structural system comprised in a pre-stressed composite structure obtained according to the present invention, the tie rod can be made of steel or using other metal alloys, or composite materials, or other suitable materials or combinations of the aforesaid materials. In each pre-stressing structural system, the tie rod comprises one or more longitudinal elements such as, for example, strands, ropes, bars, profiles. It should be noted that in a pre-stressed composite structure obtained according to the present invention each of the one or more intermediate contrast elements can comprise a rod hinged at the ends having one end connected to the beam included in the primary structure and the other end connected to one or more more tie rods included respectively in one or more pre-stressing structural systems. It should be noted that the beam included in a primary structure (belonging to a pre-stressed composite structure obtained according to the present invention) can have a substantially rectilinear axis, as in the case of a variable section beam or in the case of a beam having a planimetrically curved axis . In a pre-stressed composite structure obtained according to the present invention, the beam comprised in the primary structure, in general, can be of the solid wall type or of the reticular type or of the Vierendeel type or even of other types. It is possible to have a pre-stressed composite structure obtained according to the present invention in which the beam included in the primary structure is of prestressed reinforced concrete and is a segmented beam. It should be noted that in a pre-stressed composite structure obtained according to the present invention, as in the case of pre-stressed composite structures 1, 30, 50 and 70, it is generally necessary to waterproof or in any case protect the upper part of the pre-stressed composite structure from atmospheric agents. itself. An advantage of the present invention consists in the fact that, as a rule, a pre-stressed composite structure obtained according to the present invention is lighter than a traditional beam, of equal performance, made of the same material with which the beam included in the primary structure is made ( included in the pre-solicited composite structure itself). A further advantage of the present invention consists in the fact that, in general, during the life of the pre-stressed composite structure, it is possible to subject to checks and maintenance the one or more pre-stressing structural systems and, in particular, the one or more struts. A further advantage consists in the fact that, during the procedure for the realization of the pre-stressed composite structure, referring to each of the one or more pre-stressing structural systems, the strut can be easily placed in position, in contact with the primary structure, being it is positioned outside the beam included in the primary structure itself. A further advantage of the present invention consists in the fact that in each pre-stressing structural system the considerable value of the distance between the axis of the strut and the axis of the tie rod is exploited.

Claims (1)

CLAIMS 1) - Procedure for the construction of a pre-stressed composite structure characterized by the fact that it includes the following phases: - first phase: a primary structure (5, 34, 54, 72) and one or more pre-stressing structural systems (6, 35, 55); each of the one or more pre-stressing structural systems (6, 35, 55), moreover, is placed in the predetermined position, in contact with the primary structure (5, 34, 54, 72); the primary structure (5, 34, 54, 72) comprises a beam (5a, 34a, 54a, 72a), end contrast elements (5b, 5c, 34b, 54b, 54c) joined to said beam, one or more elements intermediate contrast elements (5d, 34c, 54d, 72b) joined to said beam and retaining elements (5e, 34d, 34e, 54e, 72c) joined to said beam and placed, one from the other, at a distance, in longitudinal direction, greater than the height of said beam; the beam (5a, 34a, 54a, 72a) has a straight or substantially straight axis; the beam (5a, 34a, 54a, 72a) has a closed section, so that a space (12, 36, 74) inside said beam remains identified; each of the one or more pre-stressing structural systems (6, 35, 55) comprises a strut (6a, 35a, 55a, 73a), with longitudinal development, and a tie rod (6b, 35b, 55b, 73b), with longitudinal development; at the end of the first phase of the procedure the following occurs: in each of the one or more pre-stressing structural systems (6, 35, 55) the strut (6a, 35a, 55a, 73a) is positioned outside the beam (5a, 34a , 54a, 72a) and the tie rod (6b, 35b, 55b, 73b) has its ends anchored to the ends of said strut; in each of the one or more pre-stressing structural systems (6, 35, 55) the tie rod (6b, 35b, 55b, 73b), in correspondence with its two end sections, is positioned outside the beam (5a, 34a, 54a , 72a) and, in correspondence with the remaining portion between said two end portions, it is positioned, at least in part, in the space (12, 36, 74) inside said beam; in each of the one or more pre-stressing structural systems (6, 35, 55) the tie rod (6b, 35b, 55b, 73b), in order to be anchored to the ends of the strut (6a, 35a, 55a, 73a), in correspondence with its own end exits outside the beam (5a, 34a, 54a, 72a) passing through openings (13) present in said beam; each of the one or more pre-stressing structural systems (6, 35, 55) is in contact only with the primary structure (5, 34, 54, 72); more precisely in each of the one or more pre-stressing structural systems (6, 35, 55) we have that the strut (6a, 35a, 55a, 73a) and the primary structure (5, 34, 54, 72) are in contact of two of the end contrast elements (5b, 5c, 34b, 54b, 54c) and of two or more of the retaining elements (5e, 34d, 34e, 54e, 72c), and the tie rod (6b, 35b , 55b, 73b) and said primary structure are in contact at one or more of the one or more intermediate contrast elements (5d, 34c, 54d, 72b); in each of the one or more pre-stressing structural systems (6, 35, 55), considering any section of the strut (6a, 35a, 55a, 73 a) executed according to a plane perpendicular to the axis of said strut, the height of said strut, except in the case of the sections relating to the end areas of said strut, is less than the distance between the axis of said strut and the axis of the tie rod (6b, 35b, 55b, 73b) measured in the said section; the primary structure (5, 34, 54, 72) and the one or more pre-stressing structural systems (6, 35, 55) are conceived and built from the outset to create the pre-stressed composite structure (1, 30, 50, 70) ; - second phase: in each of the one or more pre-stressing structural systems (6, 35, 55) the tensioning of the tie rod (6b, 35b, 55b, 73b) is carried out by means that contrast with the strut (6a, 35a, 55a, 73a) and operations are carried out for the maintenance over time of the stress states introduced with said stringing; each of the one or more pre-stressing structural systems (6, 35, 55), in correspondence with the relative end contrast elements, the relative one or more intermediate contrast elements and the relative retaining elements, due to the effect of said tensioning of the tie rod ( 6b, 35b, 55b, 73b), applies to the primary structure (5, 34, 54, 72) a system of pre-stressing forces which inflects said primary structure, inducing in said primary structure a normal effort of substantially negligible value: each of the one or more systems of pre-stressing forces relieves the state of stress of the primary structure (5, 34, 54, 72) due to the loads (4, 33, 53, 71) subsequently applied to the pre-stressed composite structure (1, 30, 50, 70); in each of the one or more pre-stressing structural systems (6, 35, 55), during said tensioning of the tie rod (6b, 35b, 55b, 73b), said tie rod, subjected to a normal tensile stress, stretches by sliding with respect to the primary structure (5, 34, 54, 72) and the strut (6a, 35a, 55a, 73a), subjected to a normal compressive stress, shortens by sliding longitudinally with respect to said primary structure; said second step of the process is completed before the pre-stressed composite structure (1, 30, 50, 70) is put into operation; each of the one or more pre-stressing structural systems (6, 35, 55) remains forever in contact only with the primary structure (5, 34, 54, 72), more precisely it remains forever in contact with said primary structure in correspondence with the relative end contrasting elements, the relative retaining elements and the relative one or more intermediate contrasting elements; the primary structure (5, 34, 54, 72) remains forever in contact, as well as with each of the one or more pre-stressing structural systems (6, 35, 55), with all external constraints (2, 3, 31, 32 , 51, 52) that bind the pre-stressed composite structure (1, 30, 50, 70). 2) - Process according to Claim 1), characterized in that in the first phase, in each of the one or more pre-stressing structural systems (6, 35, 55), the strut (6a, 35a, 55a, 73a) is positioned beyond above the extrados of the beam (5a, 34a, 54a, 72a) included in the primary structure (5, 34, 54, 72). 3) - Process according to Claim 1), characterized in that in the first phase the retaining elements (5e, 34d, 34e, 54e, 72c) are applied to the outside of the beam (5a, 34a, 54a, 72a) making them integral to said beam. 4) - Process according to Claim 1), characterized in that in the first step the end contrast elements (5b, 5c, 34b, 54b, 54c) are applied to the outside of the beam (5a, 34a, 54a, 72a) making them integral to said beam. 5) - Process according to Claim 1), characterized in that in the first phase the one or more intermediate contrast elements (34c, 54d, 72b) are applied to the outside of the beam (34a, 54a, 72a) making them integral with said beam. 6) - Process according to Claim 1), characterized in that in the first phase certain parts of the retaining elements (5e, 34d, 34e, 54e) are applied to the outside of the beam (5a, 34a, 54a), in correspondence with the extrados of said beam, before positioning the one or more struts (6a, 35a, 55a) belonging respectively to one or more pre-stressing structural systems (6, 35, 55); the assembly of the retaining elements (5e, 34d, 34e, 54e) is completed, in said first phase of the procedure, once said positioning of the one or more struts (6a, 35a, 55a) has been carried out. 7) - Process according to Claim 1), characterized in that in the first phase, in each of the one or more pre-stressing structural systems (6, 35, 55), at a point, the relative longitudinal displacements between the pre-stressing structural system (6, 35, 55) itself and the primary structure (5, 34, 54, 72). 8) - Process according to claim 1), characterized in that it comprises a third phase, subsequent to the first two phases, in which, in at least one pre-stressing structural system, relative displacements, allowed in the second phase of said process, are permanently blocked between the primary structure and parts of the pre-stressing structural system itself; said third phase is completed before the pre-stressed composite structure is put into operation. 9) - Pre-stressed composite structure obtained according to the process of claim 1), characterized in that it comprises: - a primary structure (5, 34, 54, 72) which comprises a beam (5a, 34a, 54a, 72a), end contrast elements (5b, 5c, 34b, 54b, 54c) joined to said beam, one or more intermediate contrast elements (5d, 34c, 54d, 72b) joined to said beam and retaining elements (5e, 34d, 34e, 54e, 72c) joined to said beam and placed one from the other at a distance, in the longitudinal direction, greater than the height of said beam; the beam (5a, 34a, 54a, 72a) has a straight or substantially straight axis; the beam (5a, 34a, 54a, 72a) has a closed section, so that a space (12, 36, 74) inside said beam remains identified; the primary structure (5, 34, 54, 72) is in contact with all the external constraints (2, 3, 31, 32, 51, 52) that constrain the pre-stressed composite structure (1, 30, 50, 70); the points of application of the loads (4, 33, 53, 71) applied to the pre-stressed composite structure (1, 30, 50, 70) belong to the primary structure (5, 34, 54, 72); - one or more pre-stressing structural systems (6, 35, 55) each of which is in contact only with the primary structure (5, 34, 54, 72); each of the one or more pre-stressing structural systems (6, 35, 55) comprises a strut (6a, 35a, 55a 73a), having a longitudinal development, and a tie rod (6b, 35b, 55b, 73b), having a longitudinal development, having the ends anchored to the ends of said strut; in each of the one or more pre-stressing structural systems (6, 35, 55) the strut (6a, 35a, 55a, 73a) is placed outside the beam (5a, 34a, 54a, 72a); in each of the one or more pre-stressing structural systems (6, 35, 55) the tie rod (6b, 35b, 55b, 73 b), at its two end sections, is placed outside the beam (5a, 34a, 54a, 72a) and, in correspondence with the remaining portion comprised between said two end portions, it is placed, at least in part, in the space (12, 36, 74) inside said beam; in each of the one or more pre-stressing structural systems (6, 35, 55) the tie rod (6b, 35b, 55b, 73b), in order to be anchored to the ends of the strut (6a, 35a, 55a, 73a), in correspondence with its own end exits outside the beam (5a, 34a, 54a, 72a) passing through openings (13) present in said beam; in each of the one or more pre-stressing structural systems (6, 35, 55), the strut (6a, 35a, 55a, 73a) and the primary structure (5, 34, 54, 72) are in contact at two of the end contrast elements (5b, 5c, 34b, 54b, 54c) and of two or more of the retaining elements (5e, 34d, 34e, 54e, 72c), and the tie rod (6b, 35b, 55b , 73 b) and said primary structure are in contact at one or more of the one or more intermediate contrast elements (5d, 34c, 54d, 72b); in each of the one or more pre-stressing structural systems (6, 35, 55), considering any section of the strut (6a, 35a, 55a, 73a) executed according to a plane perpendicular to the axis of said strut, the height of said strut, except in the case of the sections relating to the end areas of said strut, is less than the distance between the axis of said strut and the axis of the tie rod (6b, 35b, 55b, 73b) measured in the plane of said strut section; each of the one or more pre-stressing structural systems (6, 35, 55), in correspondence of the relative end contrast elements, of the relative one or more intermediate contrast elements and of the relative retaining elements, applies to the primary structure (5, 34 , 54, 72) forces that are mainly due to the tensioning of the tie rod (6b, 35b, 55b, 73b), carried out during the construction of the pre-stressed composite structure (1, 30, 50, 70), and to the loads (4, 33, 53, 71) applied to said pre-solicited composite structure; in particular each of the one or more pre-stressing structural systems (6, 35, 55), in correspondence with the relative end contrast elements, the relative one or more intermediate contrast elements and the relative retaining elements, due to the effect of said stringing of the tie rod (6b, 35b, 55b, 73b), applies to the primary structure (5, 34, 54, 72) a system of pre-stressing forces which inflects said primary structure, inducing a normal stress of substantially negligible value in said primary structure; each of the one or more systems of pre-stressing forces causes in the primary structure (5, 34, 54, 72) a deflection having the opposite direction to that of the deflection caused in said primary structure by the applied loads (4, 33, 53, 71) to the pre-stressed composite structure (1, 30, 50, 70). 10) - Pre-stressed composite structure according to claim 9), characterized by the fact that, in operation, the normal stress induced in the primary structure (5, 34, 54, 72) by one or more pre-stressing structural systems (6, 35, 55) , and therefore also the normal stress induced in said primary structure by each of said one or more pre-stressing structural systems, is of substantially negligible value. 11) - Pre-stressed composite structure according to claim 9), characterized in that, between each part of the one or more pre-stressing structural systems (6, 35, 55) and the primary structure (5, 34, 54, 72) are allowed, in operation, the same relative displacements and the same relative rotations that are allowed during the second phase of the procedure. 12) - Pre-stressed composite structure according to claim 9), characterized in that, in each of the one or more pre-stressing structural systems (6, 35, 55), the strut (6a, 35a, 55a, 73a) is positioned above of the extrados of the beam (5a, 34a, 54a, 72a) included in the primary structure (5, 34, 54, 72). 13) - Pre-stressed composite structure according to claim 9), characterized in that, in each of the one or more pre-stressing structural systems (6, 55), the strut (6a, 55a) comprises supporting elements (14, 57), one for each retaining element (5e, 54e); said strut is in contact with said retaining elements only in correspondence with said support elements. 14) - Pre-stressed composite structure according to claim 9), characterized in that the retaining elements (5e, 34d, 34e, 54e, 72c) are placed outside the beam (5a, 34a, 54a, 72a) and are integral to said beam. 15) - Pre-stressed composite structure according to claim 9), characterized in that the end contrast elements (5b, 5c, 34b, 54b, 54c) are placed outside the beam (5a, 34a, 54a, 72a) and they are integral with said beam. 16) - Pre-stressed composite structure according to Claim 9), characterized in that the beam (5a, 34a, 54a) is made of prestressed reinforced concrete. 17) - Pre-stressed composite structure according to claims 9) and 16), characterized in that certain parts of each of the retaining elements are incorporated in the concrete of the beam. 18) - Pre-stressed composite structure according to claims 9) and 16), characterized in that the beam included in the primary structure is a segment beam. 19) - Pre-stressed composite structure according to claims 9) and 13), characterized in that each supporting element (14, 57) comprises a main bar (14a) equipped at the ends with two threaded holes, two threaded bars (14b ) screwed into said two threaded holes, two guide plates (14c), two nuts (14d) screwed onto the two threaded bars (14b), two sliding blocks (14e) and contact plates (14f, 14g). 20) - Pre-stressed composite structure according to claim 9), characterized in that, in at least one or more pre-stressing structural systems (6, 35, 55), the strut (6a, 35a, 55a, 73a) comprises a central element (7, 38), with longitudinal development and with a straight axis, and two terminal elements (8, 39) which are integral with the ends of said central element and which constitute the ends of said strut. 21) - Pre-stressed composite structure according to claim 9), characterized by the fact that each of the one or more pre-stressing structural systems (6, 35, 55) is made with materials having a resistance higher than that of the material with which the beam is made (5a , 34a, 54a) included in the primary structure (5, 34, 54), 22) - Pre-stressed compound structure according to claim 9) characterized in that each retaining element (5e) comprises a base plate (19) which is positioned in correspondence with the extrados of the beam (5a) and which is integral with said beam, two main elements (20) integral with said base plate and two closing elements (21) integral with said two main elements. 23) - Composite structure pre-stressed according to claim 9), characterized by the fact that a protection element (60) joined to said beam is applied to the beam (54a) which encloses and protects, in each of the one or more structural systems pre-stressing (55), the part of the tie rod (55b) located below the intrados of said beam.