WO2011012974A2

WO2011012974A2 - Method for manufacturing a precast composite steel and concrete beam and a precast composite steel and concrete beam made according to said method

Info

Publication number: WO2011012974A2
Application number: PCT/IB2010/001846
Authority: WO
Inventors: Mariano Corra'
Original assignee: Fima Cosma Silos S.P.A.
Priority date: 2009-07-29
Filing date: 2010-07-27
Publication date: 2011-02-03
Also published as: IT1401624B1; WO2011012974A3; ITVI20100206A1; ITVI20090198A1

Abstract

The invention is a method for the construction of a precast composite steel and concrete beam (1, 100) of the type comprising the following stages: the preparation of a single metal sheet (2, 102) extending mainly in the longitudinal sense; the creation of a plurality of through holes (3, 103) in the metal sheet (2, 102); the folding of the metal sheet (2, 102) to obtain an elongated shaped body (4, 104) with a substantially omega-shaped cross sectional profile; the arrangement of the open end (51, 151) of the concavity (5, 105) defined in the shaped body (4, 104) so that it faces upwards; the insertion inside the concavity (5, 105) of a plurality of rebars (6, 106) for concrete comprising longitudinal rods (61, 161); the insertion of a plurality of connecting elements (7, 107) inside the through holes (3, 103) made in the shaped body (4, 104); the casting of a concrete core (8, 108) inside the concavity (5, 105), the concrete core being completely in contact with the internal surfaces of the shaped body (4, 104), the internal surfaces defining the concavity (5, 105); the arrangement of the assembly made up of the shaped body (4, 104) and the concrete core (8, 108) so that the concavity of the shaped body (4, 104) faces downwards; the installation of the assembly made up of the shaped body (4, 104) and the concrete core (8, 108); the casting of concrete (9, 109) to complete work, in contact with at least the outer surface of the shaped body (4, 104) so as to complete the precast composite steel and concrete beam (1,100); the precast composite steel and concrete beam of the invention is constructed so that before concrete is cast in order to obtain a concrete core (8, 108) in the concavity (5, 105) a plurality of torsion resistant elements (11, 111) suited to resist the torsional stress of the precast composite steel and concrete beam (1, 100) is associated with the shaped body (4, 104).

Description

METHOD FOR MANUFACTURING A PRECAST COMPOSITE STEEL AND

CONCRETE BEAM AND A PRECAST COMPOSITE STEEL AND

CONCRETE BEAM MADE ACCORDING TO SAID METHOD.

DESCRIPTION

The present invention regards a method for the construction of a precast composite steel and concrete beam used for the construction of floors or roofs with substantially plane intrados.

The invention also regards the precast composite steel and concrete beam obtained according to the method of the invention,

In the prior art there are composite steel and concrete beams for the construction of floors/roofs, each of which comprises a steel beam and a slab of reinforced concrete structurally cooperating with the steel beam.

In the prior art there are different types of composite steel and concrete beams with their relative construction methods, used for the construction of floors or roofs with substantially plane intrados.

An advantageous feature, common to most metal beams in the prior art, is that said steel beams, when in use, are self-supporting even when they support artefacts that form the floor/roof and the concrete is cast to finish the structure.

Specifically, a first type of composite steel and concrete beams, most commonly used, comprises a metal beam with an l-shaped profile featuring a lower horizontal flange having a width greater than a corresponding upper horizontal flange, interconnected through a vertical core.

As mentioned above, said metal beams, during the installation of structures, are suitable for supporting structural elements forming the floor or the roof. Subsequently the concrete is cast to complete the structure above said metal beams.

Composite steel and concrete beams pertaining to the prior art are made in this manner.

Although at first glance the degree of difficulty in the construction and use of this particular type of composite steel and concrete beam may seem irrelevant, it has some significant drawbacks as is explained below.

A first drawback lies in that this type of composite steel and concrete beam necessarily requires that the metal beam is made by connecting specially arranged profiles and/or sheets by means of continuous welding.

Another drawback lies in that to achieve the structural cooperation between the steel beam and the concrete cast to complete the structure it is necessary to solidly fasten connectors on the surfaces of said metal beams with pre- established welding methods, said connectors being later incorporated into said concrete cast.

Consequently, it is clear that the construction of this metal beam requires considerable time and the use of specific equipment.

Another recognized disadvantage of this type of composite steel and concrete beam featuring an l-shaped profile is the need to install on the steel beam, during the assembly, the elements constituting the floor or roof according to a pre-established sequence, in order to minimize deformations and torsional stresses.

In addition, the ends of said metal beams must be firmly bound, during the assembly, to the corresponding pillars, in order to avoid, even in this case, stability problems in the transitional stage.

Therefore, the disadvantage of using said composite steel and concrete beams can be understood since problems may arise during installation and therefore special attention is required in order to avoid structural problems.

To partially overcome said problems, the prior art includes an additional method for the construction of a different kind of composite steel and concrete beam consisting of a metal beam with a closed profile featuring two flanges placed on the lower part on both sides of the central core; this closed profile is substantially trapezoidal in shape with the two side cores having a plurality of large through holes.

These through holes are intended to enable the concrete cast to complete the work to penetrate inside said metal beam.

In fact, the latter type of composite steel and concrete beam shows a significant improvement when compared to the behaviour of the beams using the l-shaped profile during installation and, in particular, during the installation of the structural elements of the floor/roof on said metal beams and during the subsequent casting of the concrete to complete the work.

However, disadvantageously, said type of metal beam poses the drawback that the portion of concrete which penetrates inside its trapezoidal section does not structurally cooperate with the beam.

In addition, even though the closed profile section of said metal beams enables the attainment of greater stiffness (torsional in particular) compared to the beams described above, also in this case, disadvantageously, the method of construction of said beams is made up of stages that are somewhat laborious, exceedingly prolonged over time and particularly expensive.

In fact, also in this case the metal beam is necessarily made by welding the suitably arranged plates that make it up in a continuous manner.

Moreover, just as with the beam described above, it is disadvantageously necessary to solidly connect special connectors to the metal beam through a pre-established welding process to achieve the coupling between the beam and the finishing concrete cast during the implementation of the work.

The present invention aims to overcome these disadvantages.

In particular, the invention is intended to identify a method for the construction of precast composite steel and concrete beams which do not need continuous welding of the different elements composing them in contrast with the composite steel and concrete beams of the prior art.

Again, the object of the present invention is to propose a method for the construction of precast composite steel and concrete beams with higher torsional resistance and stiffness, even during assembly operations, compared to composite steel and concrete beams of the prior art.

This and other objects are achieved by a construction method for precast composite steel and concrete beams and the same precast composite steel and concrete beam obtained with the above method of the invention, having the characteristics according to the main claim.

Additional features of the precast composite steel and concrete beam of the invention are described in the dependent claims.

The application of the method of the invention advantageously simplifies the production and installation process of said precast composite steel and concrete beams, achieving significant savings of time and financial resources in comparison with the techniques of the prior art.

A further advantage of the method of the invention lies in that it enables a reduction in the use of the special industrial equipment that must necessarily be used in a plant.

Consequently and advantageously, the method of the invention makes it possible to construct said precast composite steel and concrete beams in situ during work.

Another advantage is represented by the fact that the particular precast composite steel and concrete beams obtained by the method of the invention have, in general, greater fire resistance compared to the composite steel and concrete beams of the prior art.

Said objects and advantages will be better explained during the description of preferred embodiments of the invention provided below by way of non-limiting examples making reference to the attached drawings, wherein:

- Figure 1 shows an axonometric view of the sheet from which the shaped body of the precast composite steel and concrete beam of the invention is made;

- Figure 2 shows an axonometric view of the sheet from which the shaped body is made and where a plurality of through holes are provided;

- Figure 3 shows an axonometric view of the shaped body belonging to the precast composite steel and concrete beam of the invention;

- Figure 4 shows a detail of the shaped body shown in Figure 3;

- Figure 5 shows the front view of the shaped body belonging to the precast composite steel and concrete beam of the invention;

- Figure 6a shows an axonometric view of a first embodiment of the entire assembly comprised of the shaped body, the rebars for the reinforced concrete and torsion resistant elements consisting of transverse rods arranged perpendicular to the longitudinal axis of the shaped body; said shaped body is in an upside down position compared to the final position during operation;

- Figure 7a shows a detail of the shaped body shown in Figure 6a including said rebars for the reinforced concrete and said transverse rods;

- Figure 8a shows the section from a vertical axis perpendicular to the axis of said shaped body of the first embodiment of the shaped body belonging to the precast composite steel and concrete beam of the invention and comprising the rebars for the reinforced concrete and said transverse rods;

- Figures from 6b to 6e show axonometric views of some variants of the first embodiment of Figure 6a comprising different types of torsion resistant elements;

- Figures from 7b to 7e show some details of the shaped bodies illustrated respectively in Figures from 6b to 6e;

- Figures from 8b to 8e show the cross-sections, from vertical planes perpendicular to the axis of said shaped body, of some variants of the first embodiment shown in Figure 8a comprising different types of torsion resistant elements;

- Figure 9 shows an axonometric view of said first embodiment of the shaped body comprising said rebars and an inner concrete core;

- Figure 10 shows a detail of the shaped body shown in Figure 9, including said rebars and the inner concrete core;

- Figure 11 shows the section, from the vertical plane perpendicular to the axis of said shaped body, of said first embodiment of the shaped body of the precast composite steel and concrete beam of the invention and comprising the rebars and the inner concrete core;

- Figure 12 shows an axonometric view of a second embodiment of the entire assembly comprised of the shaped body and the rebars for the reinforced concrete which also include prestressing tendons;

- Figure 13 shows a detail of the shaped body shown in Figure 12 comprising said rebars for the reinforced concrete which also include prestressing tendons;

- Figure 14 shows the front view of the second embodiment of the shaped body of the precast composite steel and concrete beam of the invention comprising the rebars for the reinforced concrete which also include prestressing tendons;

- Figure 15 shows a longitudinal section from a vertical plane of said second embodiment of the shaped body of the precast composite steel and concrete beam of the invention comprising the rebars for the reinforced concrete which also include prestressing tendons;

- Figure 16 shows a section from a vertical plane perpendicular to the longitudinal axis of the second embodiment of said shaped body of the precast composite steel and concrete beam of the invention comprising the rebars for the reinforced concrete which also include prestressing tendons;

- Figure 17 shows an axonometric projection of the second embodiment of the shaped body containing rebars and an inner concrete core;

- Figure 18 shows a detail of the shaped body shown in Figure 17 containing said rebars and an inner concrete core;

- Figure 19 shows the front view of the second embodiment of the shaped body of the precast composite steel and concrete beam of the invention containing said rebars and an inner concrete core; - Figure 20 shows the section from a vertical plane perpendicular to the axis of the second embodiment of the shaped body containing said rebars and the inner concrete core and arranged so as to support the structural elements of the floor/roof;

- Figure 21 shows the section from a vertical plane perpendicular to the axis of said second embodiment of the shaped body containing said rebars and the inner concrete core, arranged so as to support the structural elements of the floor/roof and on which said concrete is cast to complete work;

- Figure 22 shows an axonometric view of the precast composite steel and concrete beam of the invention arranged on two supporting pillars; the precast composite steel and concrete beam is shown prior to the casting of concrete to complete work;

- Figure 23 shows a detail of the precast composite steel and concrete beam of the invention shown in Figure 22;

- Figure 24 shows an axonometric view of the precast composite steel and concrete beam of the invention arranged to support the elements of the floor/roof; the precast composite steel and concrete beam is shown prior to the casting of concrete to complete work;

- Figure 25 shows an axonometric view of the precast composite steel and concrete beam of the invention arranged to support the elements of the floor/roof and on which said concrete is cast to complete work.

The method for the construction of precast composite steel and concrete beams, represented as a whole in Figures 21 and 25 and indicated by 1 , includes, to begin with, the preparation of a sheet 2 extending predominantly longitudinally, as seen in Figure 1. It should be noted that it is one single sheet 2.

Said sheet 2 is sized according to the construction specifications defined in the design stage.

In the preferred embodiment described and represented herein, the method of the invention, as an essential operation, includes the execution of a plurality of through holes 3 in said sheet 2, as can be seen in Figure 2.

Said operation is followed by the bending of said sheet 2 to obtain an elongated shaped body 4, which has a substantially omega-shaped cross- sectional profile, as seen in Figure 5. In said omega-shaped profile there are a horizontally-arranged top flange 41 and two webs 42 and 43 extending from the edges of said top flange 41 and sloping away from the plane defined by said top flange, and two flanges 44 arranged horizontally, each of which is joined to one of the two webs 42, 43.

In particular, in the embodiment described herein, the side webs 42 and 43 are arranged obliquely with respect to the top flange 41 and divergent with respect to each other.

In an alternative embodiment, not described herein, it is not excluded that the last two steps just introduced can be executed in reverse order.

In particular, the bending of the sheet 2 can be performed first and then the through holes 3 can be made in the shaped body 4 thus obtained.

In any case, the execution of the bending and drilling operations on the sheet 2 is necessarily done in the plant where adequate machines such as industrial presses are available.

At this point, the implementation of the method of the invention allows the first element to be obtained, that is, the shaped body 4 shown in Figure 3 and in detail in Figure 4, a shaped body 4 which constitutes a part of the precast composite steel and concrete beam 1.

As can be seen in Figures 6 and 8, the next step of the method of the invention, in the first embodiment herein described, includes the arrangement of a plurality of rebars 6 in the concavity 5 defined by said shaped body 4, which, as is better described below, comprise longitudinal rods 61 that contribute to strengthening the entire precast composite steel and concrete beam 1.

To carry out this operation, the shaped body 4 must be placed with the open end 51 of said concavity 5 facing upwards, as seen in Figure 8.

This is because the shaped body 4 is already placed in the right position for the subsequent casting of concrete to form a concrete core 8 which completely fills said concavity 5.

As shown in Figure 6a and in the detail of Figure 7a, at this point the subsequent step is the insertion, through the holes 3 made in the upper flange 41 and the side webs 42 and 43 in proximity to the same upper flange 41, of a plurality of connecting elements 7 for the structural cooperation between the shaped metal body 4 and the concrete 8.

The connecting elements 7 comprise connecting elements 7a placed horizontally near the top flange 41 and inverted U-shaped connectors 7b placed vertically at the level of the top flange 41.

First the connecting elements 7b are inserted into the corresponding through holes 3, then the connectors 7a are inserted into the corresponding through holes 3.

Furthermore, according to the method that is the subject of the invention the shaped body 4 is associated with a plurality of torsion resistant elements 11, as shown in Figures from 6a to 6e.

Said torsion resistant elements 11 have the function to resist the torsional stress to which the precast composite beam 1 is subjected.

In this way, the use of said torsion resistant elements 11 makes it possible to achieve one of the objects of the invention, which lies in providing a precast composite steel and concrete beam 1 having higher torsional resistance and stiffness than the composite beams of the known art described above, even during assembly.

According to the method that is the subject of the invention, after the insertion of the connecting elements 7, the rebars 6 and the torsion resistant elements 11 , the concrete is cast in the concavity 5 to make the core 8 of the shaped body 4, as shown in Figures 9, 10 and 11.

Again, the concrete used for making the concrete core 8 completely fills the concavity 5 in such a way that considering the precast composite steel and concrete beam 1 in its operating position, the intrados of the concrete core 8 is located substantially on the same plane as the intrados of the flanges 44.

Moreover, said concrete core 8 is placed in full contact with the inner surfaces of the shaped body 4, in particular with the internal surfaces of the top flange 41 and side webs 42 and 43.

To prevent said concrete core 8 from coming out of the sides of the shaped body 4 when in the liquid state, suitable separators of cast concrete 10 are placed at both ends of the latter and inside the concavity 5 to allow said concavity 5 to be closed in the longitudinal sense.

Said stages of the positioning of the rebars 6, the connecting elements 7 and the torsion resistant elements 11 , as well as the casting of the concrete core 8 are preferably performed in a plant, where once the necessary time has elapsed to allow said concrete core 8 to cure adequately, the shaped body 4, comprising said concrete core 8, is temporarily stored in anticipation of its future use. Alternatively, these operations can be performed in situ at the work site.

In fact, the components of the precast composite steel and concrete beam 1 of the invention and in particular the aforementioned shaped body 4, the connecting elements 7, the rebars 6 and the torsion resistant elements 11 are easily containerized and transportable even to locations distant from the production centre of said components.

In addition, the precast composite steel and concrete beam 1 of the invention can be constructed even in the absence of specific production equipment in situ at the work site.

Indeed, given that the concrete of the concrete core 8 is cast in the shaped body 4, the latter also functions as a so-called "disposable" formwork.

In this way, advantageously, the shaped body 4 serving as "disposable" formwork avoids a number of issues related to the presence of said through holes 3, issues that would occur if traditional industrial formwork were used multiple times even for beams of different lengths.

This makes the precast composite steel and concrete beam 1 of the invention usable in many cases and in a remarkable variety of work sites and situations. In any case, once transported to the work site, the shaped body 4, adequately placed with the concavity 5 housing said concrete core 8 facing downwards, and thus in an inverted position with respect to how the same shaped body 4 was positioned during the earlier stages for the insertion of the rebars and the casting of the concrete, is placed on at least two pillars P suited to support it, as shown in Figure 22 and in the detail of Figure 23.

Afterwards, the structural elements S comprising the floor/roof are placed upon said shaped body 4, as shown in Figures 20 and 24. It is specified that said structural elements S are placed on the flanges 44.

It is emphasized that even during this assembly stage the shaped body 4 housing the concrete core 8 is torsionally constrained at the ends as shown in Figures 22 and 23; in this way the mounting of said elements of the floor/roof S is easy.

Finally, as shown in Figures 21 and 25, the method of the invention includes a further finishing casting of concrete 9 performed outside the shaped body 4 so as to complete the construction of said precast composite steel and concrete beam 1.

The concrete cast to complete work 9, once cast and properly cured, structurally cooperates with the connecting elements 7 that protrude from the shaped body 4 so as to make the connection between said shaped body 4 and said finishing concrete cast 9.

It is clear that the benefits in terms of strength and stiffness of the precast composite steel and concrete beam 1, once the finishing concrete cast 9 has been executed, are significantly greater than those achieved with the assembly composed of just the shaped body 4 and the concrete core 8.

Once the assembly made up of the shaped body 4 and the concrete core 8 has been put in place, and once the structural elements S have been placed, before casting the concrete to complete work 9, additional rebars, not shown herein, are installed in situ, said rebars being made of steel bars constituting the finishing rebar for the floor/roof and the precast composite steel and concrete beam 1 itself.

Said rebars are then encased in said finishing concrete cast 9 in situ.

In particular, it is stressed that some of said rebars are embedded in the finishing concrete cast 9 which is part of the precast composite steel and concrete beam 1 itself.

Regarding the elements of the floor/roof S, in the preferred embodiment described herein, they consist of hollow core floors/roofs. In other cases, the floor/roof elements S may consist of panels made of brick-concrete or of latticed panels or even other types of elements for floors/roofs S especially with plane intrados.

Alternatively, other types of elements for floors/roofs S can be used such as wooden floor/roof elements or floor/roof elements made of corrugated sheet metal.

It is clear that during the installation of said floor/roof elements S (that is when they are laid on the assembly constituted by the shaped body 4 and the concrete core 8 at the level of their ends), as shown in Figure 20, they may also be temporarily shored up.

The execution of the stages constituting the above method of the invention enables the construction, as noted above, of the precast composite steel and concrete beam 1 that is also part of the present invention.

This document uses the expression "precast composite steel and concrete beam" meaning that the precast beam is composite due both to the fact that it is made of steel and concrete at the time of its production in the plant, and to the fact that it is completed on site with a further finishing concrete casting. In a preferred embodiment described herein and shown in Figures 3, 4 and 5, the shaped body 4 belonging to the precast composite steel and concrete beam 1 has an elongated shape with an omega-shaped profile in which it is possible to identify a horizontally-arranged top flange 41 and two side webs 42 and 43, extending from the edges of said top flange 41 and sloping away from the plane defined by said top flange 41.

In particular, in the embodiment herein described, the side webs 42 and 43 are arranged obliquely with respect to the top flange 41 and divergent from each other.

In an alternative embodiment, not described herein, it is not excluded that both of said side webs 42 and 43 can form with said top flange 41 an angle of 90 sexagesimal degrees.

In addition, in the preferred embodiment herein described, it is stressed that along the free edge of each side web 42 and 43 it is equipped with a flange 44 projecting substantially parallel to the top flange 41 which has the function of supporting the floor/roof elements S once installed.

It is not inconceivable that, in certain embodiments of the method of the invention, a flange 44 is provided that projects towards just one of the two side webs 42 or 43.

In that case, said precast composite steel and concrete beams 1 are actually edge beams.

Preferably but not necessarily, the inner surfaces of said shaped body 4 are rough in order to favour the adhesion of the concrete core 8 to the shaped body 4 itself.

In the embodiment described herein, said roughening treatment requires a sandblasting treatment on the inner surface of the shaped body 4 and the subsequent application of a thin layer of synthetic resin; finally, said surface is dusted with quartz powder.

Once said synthetic resin has properly hardened, the aforementioned part of the inner surface of the shaped body 4 has a heavily roughened surface and therefore is particularly suitable to grip the concrete core 8.

Alternatively, according to a possible variant, the treatment to roughen a part of the inner surface of the shaped body 4 may include the sandblasting of said inner surface and the deposit of particles of steel or another suitable metal for a metallization coating process using ferrous material.

Additionally, instead of said ferrous material, other technically equivalent materials may be used.

In a different embodiment, not described herein, even the external surfaces of the same shaped body 4 may be treated by sandblasting to roughen them so as to increase adhesion between steel and concrete even in the external part of said shaped body 4.

It is not inconceivable, however, that in an alternative embodiment of the invention both the internal and external surfaces of the shaped body 4 could be left substantially smooth, losing the advantages offered by increased adhesion as described above.

In the preferred embodiment described and represented herein, the through holes 3 made in the shaped body 4 are arranged along both the top flange 41 and the side webs 42 and 43, as shown in Figure 3.

In a different embodiment said through holes 3 could be made only at the level of the top flange 41 so as to promote the connection between said top flange 41 and the finishing concrete 9 cast above it.

As already noted, in the preferred embodiment described herein, the precast composite steel and concrete beam 1 also includes a plurality of rebars 6 comprising a plurality of longitudinal rods 61 positioned inside the concavity 5 on one or more planes, according to the development plane of the precast composite steel and concrete beam 1 and incorporated in the concrete core 8 shown in Figure 9.

Regarding the connecting elements 7a and 7b inserted in the corresponding through holes 3 made in the shaped body 4 as shown in Figure 21 , they are intended to make the connection between the finishing concrete cast 9 and the shaped body 4 and between said shaped body 4 and the concrete core 8.

The adhesion between the shaped body 4 and the concrete core 8 is increased by the roughness of the inner surface of said shaped body 4, as described above.

In particular, in the preferred embodiment of the invention described and represented herein, the connecting elements 7 are made of steel rebars for reinforced concrete, part of the length of which is incorporated into the concrete core 8, while the other part protrudes from the external surfaces of the same shaped body 4 so as to be embedded in the finishing concrete cast 9, as clearly seen in Figure 21.

As regards once again the through holes 3, they have a diameter slightly larger than the diameter of the connecting elements 7, so that during the casting of the concrete core 8 in the concavity 5 of the shaped body 4, the concrete in the fluid state does not flow out of said through holes 3, thus allowing the shaped body 4 to function as formwork.

In a different embodiment not described or represented herein, said connecting elements 7, which are in any case inserted in said through holes 3 previously made in the shaped body 4, may consist of threaded rods on which locknuts are screwed to position the connecting elements 7; said threaded rods may also include U-shaped bars with the function of firmly connecting the concrete core 8, the shaped body 4 and at least a portion of the finishing concrete cast 9.

At both ends of the shaped body 4 a significant increase in the number said connection elements 7 is expected.

Said increase must be defined as a function of the different situations and different production methods that may be implemented.

Furthermore, regarding the torsion resistant elements 11, as shown in Figures 6a, 7a and 8a, in the preferred embodiment of the invention described herein they comprise transverse rods 12 perpendicular to the longitudinal axis of the shaped body and arranged in proximity to the flanges 44.

In particular, the above mentioned transverse rods 12 are inserted in the portion of holes 3 made in the side webs 42 and 43 in proximity to the above mentioned flanges 44.

The torsion resistant mechanism includes, near the lower edge of the beam, the formation of a torsion resistant lattice comprising the transverse rods 12 and concrete connection units belonging to the concrete core 8.

Preferably but not necessarily, in order to associate the transverse rods 12 integrally with the shaped body 4, said transverse rods 12 consist of threaded rods inserted in the holes 3 made in the side webs 42 and 43 in proximity to the flanges 44 and fixed to said side webs 42 and 43 by means of nuts not illustrated in the figures.

According to an alternative embodiment of the invention, it cannot be excluded that the integral association of the transverse rods 12 with the shaped body 4 can be obtained by means of a welding process or through other fixing means belonging to the known art.

In a different embodiment of the invention, as shown in Figures 6c, 7c and 8c, said torsion resistant elements 11 may comprise flat transverse elements 13 instead of said transverse rods 12.

Also in this case, the flat transverse elements would be arranged in proximity to the flanges 44 and would be fixed to them preferably through a welding operation.

According to both the variants just described above, as shown always in Figures 6a, 7a, 8a and 6c, 7c, 8c, the torsion resistant elements 11 are perpendicular to the longitudinal axis of the shaped body 4.

However, in alternative construction variants, shown respectively in Figures 6b, 7b, 8b and in Figures 6d, 7d, 8d, the torsion resistant elements 11 could be inclined with respect to the longitudinal axis of the above mentioned shaped body 4, so that the same torsion resistant elements 11 are arranged one after the other according to a profile that defines a broken line.

Said arrangement, as shown for example in Figure 6b, makes it possible to obtain a lattice configuration of the plurality of transverse rods 12.

Furthermore, according to a different construction variant of the invention, shown in Figures 6e, 7e and 8e, the above mentioned torsion resistant elements 11 may comprise closed stirrups 14 arranged inside the concavity 5, embedded in the concrete core 8 and associated with suitable longitudinal rods belonging to the plurality of longitudinal rods 61.

It should be noted, therefore, that the above mentioned longitudinal rods 61 can be present inside the concavity 5 in order to increase the bending resistance or, associated with said torsion resistant elements 11 , to increase the torsional strength.

Said closed stirrups 14 may be used in the precast composite steel and concrete beam 1 also in combination with one or both types of torsion resistant elements 11 described above.

Finally, regarding the above mentioned torsion resistant elements 11, in general, independently of the variant selected among those described above, they make it possible to achieve, as already explained, one of the objects of the present invention, that is, the object to provide a precast composite steel and concrete beam 1 having higher torsional resistance and stiffness than the composite beams of the known art described above, even during assembly. Going back to the preferred embodiment of the invention shown in Figure 8a, comprising the above mentioned transverse rods 12, here the longitudinal rods 6 are arranged within the concavity 5 on two parallel planes and are supported, via a fixing process, respectively by the connecting elements 7a and by the transverse rods 12.

According to an alternative embodiment of the invention, not illustrated and not described herein, the longitudinal rods 61 may be arranged inside the concavity 5 on a single plane parallel to the plane of development of the precast beam 1 in proximity to the flanges 44 and would be supported exclusively by the transverse rods 12.

Both of said embodiments advantageously make it possible to arrange said longitudinal rods 61 in a more precise and stable manner inside the concavity 5 for the whole length of the precast composite steel and concrete beam 1 of the invention.

Furthermore, the position of the longitudinal rods 6, in this way, is maintained stable also during the casting of the concrete core 8 inside the concavity 5, avoiding any accidental variations of their arrangement; said variations, in fact, may influence the degree of stiffness of the entire structure of the precast composite steel and concrete beam 1 of the invention.

Regarding said concrete core 8 belonging to the precast composite steel and concrete beam 1 of the invention, as noted above, it embeds parts of the connecting elements 7, the rebars 6 and the torsion resistant elements 11 which are always placed inside the concavity 5.

In addition, said concrete core 8 has the plane intrados substantially coplanar with the intrados of the shaped body 4.

As an added feature, as already mentioned during the description of the method of the invention, the inner surfaces of the two side webs 42 and 43 and the top flange 41 are placed in full contact with the outer surface of the concrete core 8.

In addition, the concrete core 8 is not just in contact with the inner surfaces of the shaped body 4, but also, as noted earlier, with suitable concrete cast separators 10 which allow said concavity 5 to be closed in the longitudinal sense and thus prevent the concrete core 8 from leaking out of its ends when the latter has not yet cured properly.

The last element of the precast composite steel and concrete beam 1 of the invention is the concrete cast to complete work 9 in situ.

In particular, in the embodiment described herein and represented in Figure 21 , the finishing concrete cast 9 is in contact with both the outer surface of the top flange 41 and the external surfaces of the two side webs 42 and 43. It is not inconceivable that in different embodiments, not described or represented herein, said finishing concrete cast 9 is in contact only with the outer surface of said top flange 41.

In this circumstance, the through holes 3 shall only be made at the level of the top flange 41 and consequently the connecting elements 7 shall be inserted only at the level of the surface of said top flange 41.

In the preferred embodiment of the precast composite steel and concrete beam 1 obtained according to the method of the invention, the concrete core 8 has different features and improvements compared to the finishing concrete cast 9.

It is not inconceivable that, in different embodiments, the two concrete casts 8 and 9 have the same characteristics.

In the structure of the precast composite steel and concrete beam 1 just described, the shaped body 4, the concrete core 8 and the finishing concrete cast 9 structurally cooperate with each other to provide stiffness and bearing capacity to the precast composite steel and concrete beam 1.

A second embodiment of the precast composite steel and concrete beam 100 of the invention, represented as a whole in Figures 17 and 19, and of the application of the method for making it includes all the characteristics of the first embodiment described so far, along with any variations, except that the rebars 106 comprise not only the longitudinal rods 161 but also prestressing tendons 110 arranged in the concavity 105 and incorporated for their entire length in the concrete core 108, as shown in Figures 12 and 15.

In particular, in this second embodiment, as in the first, the intrados of the concrete core 108 is placed substantially on the same plane as the intrados of the flanges 144.

In addition, the outer surfaces of said concrete core 108 are placed in full contact with the inner surfaces of the top flange 141 and the side webs 142 and 143.

In the embodiment currently described, said prestressing tendons 110 are anchored at their ends to anchor plates 115, shown in Figures 12, 13 and 14. In the preferred embodiment described herein and represented in Figure 12, said prestressing tendons 110 are made of high tensile steel strands 116.

In particular, each prestressing tendon 110 is made of a strand 116 which is greased and inserted in a sheath made of a synthetic material, within which said strand can slide.

Said prestressing tendons 110 which are put under stress during the construction of the precast composite steel and concrete beam 100, induce normal compression, a bending moment and shear stress in the entire precast composite steel and concrete beam 100.

Regarding the route of part of said prestressing strands 116 of the embodiment described herein, as seen in Figures 15 and 16, it is substantially straight and horizontal.

The route of the remaining strands 116 is instead curved and approximates the shape of a parabola, as shown again in Figure 15.

Regarding the method for the implementation of said second embodiment of the precast composite steel and concrete beam 100 of the invention, it is substantially equivalent to that described in relation to the precast composite steel and concrete beam 1 of the first embodiment.

The differences are that during the positioning of the longitudinal rods 161 belonging to the rebars 106 said prestressing tendons 110 are also inserted into the concavity 105 of the shaped body 104.

In particular, in the preferred embodiment described herein, each prestressing tendon 110 is supported and fastened within the concavity 105 on some of the connecting elements 107 and of the torsion resistant elements 111 , the position of which is specifically determined on the basis of the route of said prestressing tendons 110; this prevents the accidental movement of the prestressing tendons 110 during casting of the concrete core 108.

According to the method applied to this second embodiment, once the concrete core 108 has been cast and once it has cured properly, the assembly comprised of the shaped body 104 and the concrete core 108 is rotated by 180 sexagesimal degrees about the longitudinal axis of said assembly so that the top flange 141 comprises the extrados of said assembly.

Subsequently, the prestressing tendons 110 are tightened and anchored to the relevant anchor plates 115, to induce in said assembly, as mentioned earlier, normal compression, a bending moment and shear stress. As regards the tightening procedure for the prestressing tendons 110, this includes the use of a hydraulic tensioning jack, powered by a special pump which tightens said prestressing tendons 110 one at a time.

Subsequently the assembly composed of the shaped body 104 and the concrete core 108 is stored in the production facility.

Then said assembly is transported to the worksite; the elements of the floor/roof are laid on it; the concrete 109 is cast; at the end of these operations the precast composite steel and concrete beam 100 is complete.

Advantageously, the prestressing of the precast composite steel and concrete beam 100 of the invention allows a significant load bearing capacity to be achieved when in operation, limiting cracking phenomena.

The limitation of the cracking phenomenon when in operation also entails a significant increase in the durability of the precast composite steel and concrete beam 100 of the invention.

In addition, the prestressing provides the precast composite steel and concrete beam 100 a camber (upwards) which is very favourable to avoid an excessive downward inflection when it is in operation and also to prevent or limit downward inflections when the beam itself, once installed, bears the load of the floor/roof elements S and the concrete 109 is cast to complete work.

At this stage the finishing concrete cast 109 is still fluid and therefore constitutes only a load that weighs on the assembly comprised of the shaped body 104 and the concrete core 108.

This stage is transient and comprises, just like for the precast composite steel and concrete beam 1, one of the aspects to consider when sizing the entire project.

Finally, prestressing enables the increase of the load bearing capacity of the precast composite steel and concrete beam 100 making it possible, under equal conditions, to have longer spans for the precast composite steel and concrete beam itself.

In a different embodiment of the invention, not described or represented herein, the prestressing tendons 110 consist of cables, each including a plurality of strands and a sheath that contains them.

This sheath is embedded for its entire length in said concrete core 108.

In addition, once the strands have been tightened, cement grout is injected inside said sheath, to protect the prestressing tendons over time and increase their adherence to the concrete core 108.

Additionally, according to other embodiments, the prestressing tendons 110 can also be made of adherent strands pretightened through anchor heads belonging to a production line for prestressed components.

In conclusion, the precast composite steel and concrete beams 1, 100 of the invention can be used for the construction of most of the buildings built today, independently of whether they include other precast elements, or are made at the work site.

In particular, the (final) static scheme of a precast composite steel and concrete beam 1, 100 obtained by means of the invention is, in principle, hyperstatic, given that said beam is inserted in a structural context which may consist, for example, of a frame, a portal etc.

In other cases, the (final) static scheme of a beam of said type is that of a beam simply resting (in addition to being torsionally constrained).

It is obvious that the static scheme of the assembly comprising the shaped body 4, 104 and the concrete core 8, 108 when installed and when the concrete 9, 109 has not yet been cast is that of a beam simply resting (with torsional constraints).

According to the above, it is understood then that the method of the invention for the construction of a precast composite steel and concrete beam and the precast composite steel and concrete beam obtained therewith achieves all the set objects.

In particular, the invention achieves the object to identify a method for the construction of precast composite steel and concrete beams which does not require continuous welding of the different elements that make them up, differently from the composite steel and concrete beams of the prior art.

A further object achieved by the invention is the attainment of a method for the construction of precast composite steel and concrete beams with higher torsional resistance and stiffness, even during the assembly stages, compared to the composite steel and concrete beams of the prior art.

During the construction stage, the method of the invention and the composite steel and concrete beam obtained with said method may be subjected to modifications, which although not represented and not described herein shall be considered protected by this patent, provided that they fall within the scope of the claims that follow. Where technical features mentioned in any claim are followed by reference signs, those reference sings have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the protection of each element identified by way of example by such reference signs.

Claims

1) Method for manufacturing a precast composite steel and concrete beam (1 , 100) of the type comprising the following steps:

- the preparation of a single metal sheet (2, 102) extending mainly in the s longitudinal sense;

- the creation of a plurality of through holes (3, 103) in said metal sheet (2, 102);

- the folding of said metal sheet (2, 102) to obtain an elongated shaped body (4, 104) with a substantially omega-shaped cross sectional profile;

o - the arrangement of the open end (51 , 151) of the concavity (5, 105) defined in said shaped body (4, 104) so that it faces upwards;

- the insertion inside said concavity (5, 105) of a plurality of rebars (6, 106) for reinforced concrete comprising longitudinal rods (61 , 161);

- the insertion of a plurality of connecting elements (7, 107) inside said5 through holes (3, 103) in said shaped body (4, 104);

- the casting of a concrete core (8, 108) inside said concavity (5, 105), said concrete core (8, 108) being completely in contact with the internal surfaces of said shaped body (4, 104), said internal surfaces defining said concavity (5, 105);

0 - the arrangement of the assembly made up of said shaped body (4, 104) and said concrete core (8, 108) so that the concavity of said shaped body (4, 104) faces downwards;

- the installation of said assembly made up of said shaped body (4, 104) and said concrete core (8, 108);

5 - the casting of concrete (9, 109) to complete work, in contact with at least the outer surface of said shaped body (4, 104) so as to complete said precast composite steel and concrete beam (1 , 100),

characterized in that before said concrete is cast in order to obtain said concrete core (8, 108) a plurality of torsion resistant elements (11 , 111) suited0 to resist the torsional stress of said precast composite steel and concrete beam (1 , 100) is associated with said shaped body (4, 104).

2) Precast composite steel and concrete beam (1, 100) made according to the method in claim 1), of the type comprising:

- said elongated shaped body (4, 104) complete with said through holes5 (3, 103), having a substantially omega-shaped cross sectional profile, in which the following are identified:

- a horizontally-arranged top flange (41 , 141);

- two side webs (42, 43, 142, 143) extending from the edges of said top flange (41 , 141) and sloping away from the plane defined by said top flange;

- a flange (44, 144) projecting from the edge of at least one of said side webs (42, 43, 142, 143) and lying on a plane substantially parallel to that of said top flange (41, 141);

- said rebars (6, 106) comprising said longitudinal rods (61 , 161) arranged on one or more planes, according to the longitudinal development plane of said beam (1 , 100), inside said concavity (5, 105) defined by said shaped body (4, 104);

- said connecting elements (7,107) inserted through said holes (3, 103) in said shaped body (4, 104);

- said concrete core (8, 108) arranged inside said shaped body (4, 104), so that the outer surface of said concrete core (8, 108) substantially lies on the same plane as the outer surface of said at least one bottom flange (44, 144), said concrete core (8, 108) being completely in contact with the internal surfaces of said top flange (41 , 141) and said side webs (42, 43, 142, 143);

said concrete (9, 109) cast to complete work on the outside of said shaped body (4, 104), in contact with at least said top flange (41 , 141),

characterized in that it comprises said torsion resistant elements (11, 111) associated with said shaped body (4, 104).

3) Precast composite steel and concrete beam (1 , 100) according to claim 2), characterized in that said torsion resistant elements (11 , 111) are integrally associated with said shaped body (4, 104) in proximity to said flanges (44, 144).

4) Precast composite steel and concrete beam (1 , 100) according to claim 3), characterized in that said torsion resistant elements (11 , 111) comprise transverse rods (12, 112) inserted in said holes (3, 103) made in said side webs (42, 43, 142, 143) in proximity to said flanges (44, 144).

5) Precast composite steel and concrete beam (1 , 100) according to claim 4), characterized in that said transverse rods (12, 112) are threaded rods fixed to said side webs (42, 43, 142, 143) by means of nuts. 6) Precast composite steel and concrete beam (1 , 100) according to claim 4), characterized in that said transverse rods (12, 112) are fixed to said side webs (42, 43, 142, 143) through a welding operation.

7) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 4) to 6), characterized in that said longitudinal rods

(61 , 161) are arranged inside said concavity (5, 105) on two parallel planes and are supported through fixing respectively by said connecting elements (7a, 107a) and by said transverse rods (12, 112).

8) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 4) to 6), characterized in that said longitudinal rods

(61 , 161) are arranged inside said concavity (5, 105) on a single plane parallel to the plane of development of said precast composite steel and concrete beam (1) in proximity to said flanges (44, 144) and supported through fixing by said transverse rods (12, 112).

9) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 6), characterized in that said torsion resistant elements (11 , 111) comprise flat transverse elements (13, 113) fixed in proximity to said flanges (44, 144).

10) Precast composite steel and concrete beam (1, 100) according to any of the claims from 2) to 9), characterized in that said torsion resistant elements (11 , 111) are perpendicular to the longitudinal axis of said shaped body (4, 104).

11) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 9), characterized in that said torsion resistant elements (11 , 111) are inclined with respect to the longitudinal axis of said shaped body (4, 104) and arranged one after the other according to a profile that defines a broken line.

12) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 11), characterized in that said torsion resistant elements (11, 111) comprise closed stirrups (14, 114) arranged inside said concavity (5, 105) and embedded in said concrete core (8, 108).

13) Precast composite steel and concrete beam (100) according to any of the claims from 2) to 12), characterized in that said rebars (106) also comprise prestressing tendons (110) located inside said concavity (105), their full length being embedded in said concrete core (108) and anchored at the ends to corresponding anchor plates (115).

14) Precast composite steel and concrete beam (100) according to claim 13), characterized in that, inside said concavity (105), each of said prestressing tendons (110) is juxtaposed with and attached to said connecting elements (107) to prevent any unwanted displacement of the latter during the casting of said concrete core (108).

15) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 14), characterized in that said shaped body (4, 104) has roughened inner surfaces to facilitate the bonding of said concrete core (8, 108).

16) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 15), characterized in that said shaped body (4, 104) has roughened outer surfaces to facilitate the bonding of said finishing concrete cast (9, 109).

17) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 16), characterized in that said plurality of holes (3, 103) is provided in line with said top flange (41 , 141) of said shaped body (4, 104).

18) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 17), characterized in that said plurality of holes

(3, 103) is provided in line with said side webs (42, 43, 142, 143) of said shaped body (4, 104).

19) Precast composite steel and concrete beam (1 , 100) according to any of the claims from 2) to 18), characterized in that said connecting elements (7, 107) comprise steel bars for concrete reinforcement.