WO2019064211A1

WO2019064211A1 - Structural element made of reinforced concrete and method for its manufacture

Info

Publication number: WO2019064211A1
Application number: PCT/IB2018/057478
Authority: WO
Inventors: Giorgio Celeste Citterio
Original assignee: Societa' Per Azioni Fratelli Citterio
Priority date: 2017-09-29
Filing date: 2018-09-27
Publication date: 2019-04-04
Also published as: IT201700109689A1; EP3701101B1; EP3701101A1

Abstract

A structural element (10) made of reinforced concrete comprising a first reinforcement (11), which first reinforcement (11) comprises at least one first continuous elongated element (12) which is made of steel for reinforced concrete and which develops mainly along the longitudinal extension of the structural element (10), and a second reinforcement (13), which second reinforcement (13) comprises at least a second continuous elongated element (14) which develops mainly along the longitudinal extension of the structural element, in which the area subtended to the force/displacement curve of the structural element (10) or of a specimen corresponding to the structural element subjected to flexural test with force acting along a substantially orthogonal direction to the longitudinal extension of the structural element or of the specimen replicating the structural element is greater by at least 20% than the area subtended to the force/displacement curve of a reference structural element replicating the structural element or of a reference specimen (200) replicating the specimen corresponding to the structural element, but lacking the second reinforcement (13), subjected to the same flexural test, in which the increase of the area is recorded substantially after the breaking point (C1÷C7) of the at least one first continuous elongated element (12).

Description

STRUCTURAL ELEMENT MADE OF REINFORCED CONCRETE AND METHOD FOR ITS MANUFACTURE

The present invention relates to a structural element made of reinforced concrete and to a method for its manufacture.

Concrete is a material widely used in building constructions, such as for example houses, bridges and tunnels, and for works to reinforce and consolidate existing building works.

It is well known that concrete has high compressive strength (which reaches up to 150-200 MPa) , but poor tensile strength and, hence flexural strength. To overcome the latter deficiency, it is well known to reinforce concrete with steel rods or steel bars. Structural elements made of known reinforced concrete have higher tensile strength and, hence, flexural strength than similar structural elements made only of concrete; however, they do not have sufficient mechanical characteristics of "ductility" that would give them high resistance for example to seismic or explosion-related stresses.

To increase the mechanical characteristics of "ductility" of structural elements made of reinforced concrete, a known solution is to increase the quantity of steel forming the reinforcement, from the usual 100 kg/m³ to 150 kg/m³; however, this solution entails higher construction costs due to the increased quantity of material used and to the use of labour necessary to install it .

It has also been proposed to add to the concrete mix quantities variable between 0.1% and 3% of cut fibres (i.e. obtained by cutting continuous yarns) having length between 5 mm and 40 mm and being made of steely materials or of organic and inorganic polymeric materials .

This technique has made it possible to increase the cracking resistance of concrete, reducing the formation of cracks and the size of the cracks that are formed with consequent advantages in terms of a higher resistance of the steel rods forming the reinforcements to aggression by environmental agents. However, this technique does not allow to increase in a significantly useful way the resistance of concrete to tensile and, hence, flexure stresses.

By way of information, studies pertaining to fibre-reinforced concrete are provided in numerous publications, such as, for example: "II calcestruzzo fibrorinforzato: prestazioni e prescrizioni" (B. Rossi, P. M. Bianchi - Cemento&Calcestruzzo - April 2010) and "High Performance Fiber Reinforced Concrete: a review" (V. Afroughsabet , L. Biolzi, T. Ozbakkalogh - Springer Science+Business 30.03.2016).

It has also been proposed to reinforce concrete with systems formed by pultruded materials made of glass, basalt and carbon fibres; however, these systems have not yielded satisfactory results in terms of increase of the mechanical characteristics in terms of concrete ductility.

The object of the present invention is to overcome the drawbacks of the prior art.

Within this general object, an object of the present invention is to provide a structural element made of reinforced concrete that has high tensile strength and, hence, flexural strength, with behaviour that is similar to that of "ductile" material.

Another object of the present invention is to provide a structural element made of reinforced concrete that has low costs and is easy to manufacture.

These and other objects according to the present invention are achieved with a structural element made of reinforced concrete as set forth in claim 1.

These and other objects according to the present invention are achieved with a method for manufacturing a structural element made of reinforced concrete as set forth in claim 19.

Further characteristics are provided in the dependent claims.

The characteristics and the advantages of a structural element made of reinforced concrete and of a method for its manufacture according to the present invention will become more evident from the following description, provided by way of non-limiting example, referred to the accompanying schematic drawings in which:

figures 1A and IB are respectively schematic views, in axonometry and in longitudinal and normal section, of a specimen used for the execution of flexural tests according to EXAMPLE 1 (comparative); figures 1C to IE are photographs of the specimen used for the execution of flexural tests according to EXAMPLE 1 in different successive test steps;

figure IF shows an equipment used for flexural tests as set forth in the EXAMPLES from EXAMPLE 1 to EXAMPLE 2 ;

figure 1G shows the force/displacement diagram as set forth in EXAMPLE 1 ; figures 2A and 2B are respectively schematic views, in axonometry and in longitudinal and normal section, of a specimen used for the execution of flexural tests according to EXAMPLE 2 ;

figure 2C shows a normal section and a longitudinal view of a segment of one of the ropes of the specimen used for the execution of flexural tests according to EXAMPLE 2;

figures 2D to 2F are photographs of the specimen used for the execution of flexural tests according to EXAMPLE 2 in different successive test steps;

figure 2G shows the force/displacement diagram as set forth in EXAMPLE 2 ;

figures 3A and 3B are respectively schematic views, in axonometry and in longitudinal and normal section, of a specimen used for the execution of flexural tests according to EXAMPLE 3;

figure 3C shows the force/displacement diagram as set forth in EXAMPLE 3;

figures 4A, 4B and 4C are similar to figures 3A,

3B and 3C but relating to the specimen of EXAMPLE 4 ;

figures 5A, 5B and 5D are figures similar to figures 4A, 4B and 4C but relating to the specimen of EXAMPLE 5;

figure 5C shows a normal section and a longitudinal view of a segment of one of the ropes of the specimen used for the execution of flexural tests according to EXAMPLE 5;

figures 6A and 6B are respectively schematic views, in axonometry and in longitudinal and normal section, of a specimen used for the execution of flexural tests according to EXAMPLE 6; figures 6C and 6D show schemes of the test equipment of EXAMPLE 6;

figure 6E shows the force/displacement diagram as set forth in EXAMPLE 6;

figures 7A, 7B and 7C are similar to figures 6A,

6B and 6D but relating to the specimen as set forth in EXAMPLE 7;

figure 8A shows the force/displacement diagram as set forth in EXAMPLE 8 ;

figures 9A and 9B schematically show different possible normal sections of second continuous elongated elements respectively in the form of ropes and cables; figure 9C respectively shows a longitudinal view and a cross section of a second continuous elongated element in the form of cable;

figure 10 schematically shows a coupling member for coupling a second continuous elongated element and a first continuous elongated element;

figures 11A and 11B schematically show two portions of possible load-bearing structures constructed with structural elements according to the present invention;

figures 12A, 12B and 12C schematically show different possible configurations of the second continuous elongated elements in a structural element according to the present invention;

figure 13 is a chart showing the residual resistance of fibres made of different materials according to the time of immersion in alkaline solutions at pH >13 at 80°C (excerpted from Kuraray® publications) ;

figure 14 schematically shows the trend of the force-displacement chart of an element made of reinforced concrete according to the prior art;

figure 15 schematically shows the trend of the force-displacement chart of an element made of reinforced concrete according to the present invention.

The present invention relates to a structural element made of reinforced concrete comprising a first reinforcement and a second reinforcement.

The first reinforcement comprises at least one first continuous elongated element that is made of steel for reinforced concrete and that develops mainly along the longitudinal extension of the structural element and parallel to the tensile stresses acting thereon. In practice, the first continuous elongated element consists of a steel rod.

The second reinforcement comprises at least a second continuous elongated element that develops mainly along the longitudinal extension of the structural element and parallel to the tensile stresses acting thereon.

In the present description and in the appended claims, the expression whereby the first continuous elongated elements and/or the second continuous elongated elements "develop mainly along the longitudinal extension of the structural element and parallel to the tensile stresses acting thereon" is not meant to indicate solely the fact that these elements are arranged with their longitudinal axis parallel to the longitudinal axis of the structural element, which is a possible arrangement, but also the fact that they are arranged, albeit with different patterns of their longitudinal axis, for example a spiroid winding or a zig-zag pattern around the longitudinal axis of the structural element, in such a way that their arrangement extends along the longitudinal extension of the structural element.

According to the present invention the second reinforcement co-operates with the first reinforcement in such a way that the area subtended to the force/displacement curve of said structural element or of a specimen corresponding to said structural element, subjected to flexural test with force acting along a direction substantially orthogonal to the longitudinal extension of said structural element or of the specimen corresponding to said structural element, is greater by at least 20% than the area subtended to the force/displacement curve of a reference structural element replicating said structural element or of a reference specimen replicating said specimen corresponding to said structural element, but lacking said second reinforcement, subjected to said same flexural test, in which the increase of said area is recorded substantially after the breaking point of said at least one first continuous elongated element forming said first reinforcement.

This breaking point is immediately identifiable by a person skilled in the art.

Substantially, the flexural force-displacement curve of a structural element according to the present invention extends beyond the decay of the flexural force-displacement curve of a corresponding known structural element with a positive trend (with significantly higher values than the practically irrelevant values of the flexural force-displacement curve of a corresponding known structural element) along at least one corresponding non-zero displacement interval, as schematically shown in figures 14 and 15. As it is readily apparent from these figures, the structural element made of reinforced concrete according to the present invention has higher flexural strength and elongation than those of a corresponding known structural element made of reinforced concrete.

In a preferred embodiment, said flexural tests are conducted respectively on a specimen corresponding to said structural element and on a reference specimen replicating said specimen corresponding to said structural element, but lacking the second reinforcement; in particular, these flexural strength tests are conducted in accordance with the standard UNI EN 12390-5:2002 of 1 June 2002 "Prova sul calcestruzzo indurito - Resistenza a flessione dei provini" (Testing hardened concrete - Flexural strength of test specimens ) .

The expression "reference structural element replicating said structural element, but lacking the second reinforcement" means a structural element identical to the one according to the present invention, except that it does not have the second reinforcement.

The expression "specimen corresponding to said structural element" means a specimen identical to the structural element according to the present invention with the exception of the shape and/or of the dimensions which are adapted to the conditions of execution of the flexural test carried out; the flexural test can be carried out in accordance with current standards, for example the standard UNI EN 12390-5:2002 of 1 June 2002 "Prova sul calcestruzzo indurito - Resistenza a flessione del provini" (Testing hardened concrete - Flexural strength of test specimens) . In the latter case, the flexural test is executed with "concentrated load".

The expression "reference specimen replicating said specimen corresponding to said structural element, but lacking the second reinforcement" means a specimen identical to the "specimen corresponding to said structural element" except that it does not have the second reinforcement.

In any case, comparing:

- the force/displacement curves of flexural tests carried out respectively on the structural element according to the present invention and on a respective reference structural element replicating said structural element, but lacking said second reinforcement, and/or

- the force/displacement curves of flexural tests carried out respectively on a specimen corresponding to the structural element according to the present invention and on a respective reference specimen replicating said specimen corresponding to the structural element according to the present invention, but lacking said second reinforcement, an increase is recorded of at least 20% of the area subtended to the first of these curves (i.e. the one relating to the force/displacement diagram of structural elements according to the present invention or corresponding specimens) with respect to the area subtended to the second of these curves (i.e. the one relating to the force/displacement diagrams of reference structural elements or corresponding reference specimens) .

According to the present invention, the increase of the area is advantageously higher than 50% and, still more advantageously, higher than 70%.

This area increase is recorded substantially after the breaking point of the first continuous reinforcing elements. This breaking point is immediately recognisable by the person skilled in the art as the point whereat, in the force-displacement chart, at the end of the first segment corresponding to elastic behaviour and of the segment corresponding to plastic behaviour (substantially horizontal segment), a nearly vertical decay of flexural strength is recorded, in terms of the force necessary to determine a given displacement, above 50% with respect to the maximum force imparted in the plastic segment (substantially horizontal segment) .

This trend is schematically shown in the chart of figure 14.

Any changes of the area subtended to the first of these curves with respect to the area subtended to the second of these curves that are recorded before the breaking point of the first continuous elongated elements are not substantial or significant.

The first reinforcement formed by at least one first continuous elongated element made of steel is of the type known to the person skilled in the art and, for this reason, it is not described in detail. This first reinforcement consists of at least one continuous elongated element made of steel for reinforced concrete as defined by current standards. In particular, according to current Italian standards, steel for reinforced concrete, with which the first continuous elongated elements are manufactured, is of the type indicated by the code B450C which has nominal values of characteristic yield strength and of characteristic breaking strength respectively equal to 450 N/mm² (450 MPa) and 540 N/mm² (540 MPa) and ultimate elongation > 7,5%. These values were defined by Italian Ministerial Decree of 14 January 2008 "Norme tecniche per le costruzioni" (Technical Construction Standards) (Chapter 11.3.2.1) and related explanatory circular no. 617 of 2 February 2009.

Each of the first continuous elongated elements consists of one bar or rod. These first continuous elongated elements are preferably arranged so as to extend with their longitudinal axis parallel to the longitudinal extension of the structural element, i.e. parallel to the extension in length of the structural element, be it, for example, of the type of a beam or of a pillar.

The first continuous elongated elements can be joined together by transverse brackets.

Advantageously, the first continuous elongated elements in the shape of bars or rods have diameter between 8 mm and 50 mm.

The first continuous elongated elements generally have their external surface machined with ribs and/or indentations, also known and standardised, for the purpose of enhancing the mechanical adhesion of the first continuous elongated elements with the concrete.

The number and the disposition of the first continuous elongated elements forming the first reinforcement are known to the person skilled in the art and, therefore, they are not further described in detail herein.

The concrete that forms the structural element according to the present invention can be of any type.

In addition, the concrete, can also have dispersed fibres added thereto, the dispersed fibres having dimensions generally between 3 mm and 40 mm and being present in quantities between 0.1% and 3% by weight. Fibres made of organic or inorganic polymeric materials, or metal fibres, can be used as dispersed fibres .

The at least one second continuous elongated element forming the second reinforcement of the structural element according to the present invention is flexible also as a result of a stressing action applied to it manually.

In addition, it is not subject to any pre- or post- tension or pre-tensile load that is typical of pre- compression, considered to be prior art. To correctly position the second continuous elongated element in the concrete element, it is sufficient to impart manual tension .

The at least one second continuous elongated element forming the second reinforcement of the structural element according to the present invention comprises at least one rope, one cable, one net or one ribbon .

Said rope, cable, net or ribbon is made with organic and/or inorganic base yarns and/or with metal wires, alone or mixed together.

The term rope means a continuous elongated element formed by two or more strands wound and twisted together, as shown for example in figures 2C and 5C relating to a rope with three strands.

The term cable means a continuous elongated element formed by two or more strands braided together, as shown for example in figure 9C relating to a cable with three strands .

The term net means a structure formed by a plurality of ropes and/or cables and/or ribbons braided together according to known textile patterns (e.g. "warp and weft") or arranged on two or more mutually superposed planes, in which the ropes and/or cables and/or ribbons of each plane are mutually parallel and the ropes and/or cables and/or ribbons of two successive planes are mutually inclined by an angle between 0° and 90° according to known so-called "bidirectional" or "multidirectional" patterns. These textile structures can also be pre-formed.

The term ribbon means a body that is flexible, also as a result of a stressing action applied manually thereto, with a generally flat shape extended in length, consisting of a set of yarns with organic or inorganic base or of metal wires, which may be twisted together, braided to each other.

As it is readily apparent to the person skilled in the art, both the first continuous elongated elements and the second continuous elongated elements must be at least in part made of alkali-resistant material; they must not degrade, maintaining their own characteristics, in particular the mechanical ones, when embedded in the cement mix forming the concrete which, as is well known, generates a basic environment with pH > 12.

With regard to the second continuous elongated elements, as indicated above, they can be made of yarns with organic or inorganic base, advantageously organic or inorganic polymeric yarns, and/or of metallic wires.

In this regard, it has been observed that it is particularly advantageous to use organic and/or inorganic polymeric yarns that have residual resistance > 99% after immersion in aqueous solution with pH >_ 13 at a temperature of 80°C for 14 days.

Preferably, the organic polymeric yarns are selected from the group comprising:

- polyvinyl alcohol (PVA) yarns,

- polypropylene (PP) yarns,

- polyethylene (PE) yarns.

Advantageously, the second continuous elongated elements in the form of rope, cable, net or ribbon are made at least in part of yarns of polyvinyl alcohol (PVA) which, in addition to having high resistance to alkali attack, also has high interface adhesion to the cement mix forming the concrete. This characteristic contributes, as it is readily apparent for the person skilled in the art, to limit the "pull-out" or sliding of the second continuous elongated elements with respect to the concrete, in which they are embedded, when subjected to tensile stresses.

A particularly advantageous example of polyvinyl alcohol (PVA) yarns consists of yarns marketed as Kuralon KII® by Kuraray Co. LTD in particular of the 5501 type having tenacity > 5cN/dtex.

A particularly advantageous example of polyethylene yarns consists of HMWPE (High Molecular Weight Poly Ethylene) yarns marketed as Dyneema® by DSM® and Spectra® by HONEYWELL® and having tenacity > 10cN\dtex.

Advantageously, the polymeric yarns used to form the second continuous elongated elements have the following mechanical tensile characteristics:

- tenacity >_ 5 cN/dtex.

Advantageously, inorganic polymeric yarns consist of carbon yarns .

Preferably, carbon yarns have the following mechanical tensile characteristics:

- tenacity >_ 5 cN/dtex;

- elongation >_ 1%, preferably >_ 1.5%, still more preferably > 2.1%.

It should also be noted that carbon yarns maintain their mechanical characteristics even at temperatures close to 2000°C in the absence of oxygen, which makes their use advantageous for the formation of the second continuous elongated elements, which thus contribute to the reinforcement of the structural element not only in case of seismic events, but also in case of fires.

It is specified that the term "yarns with inorganic base" does not mean and thus excludes yarns obtained solely with glass fibres or with basalt fibres, which are severely attacked by basic environments, unless they are appropriately treated with adequate alkali resistant coating.

The used yarns are generally continuous yarns with count above 1000 dtex; alternatively, the yarns are obtained with stretch-broken system or with cut fibres having a length between 15 mm and 150 mm. These yarns can also be wound or twisted with twisting turns between 50 twists/m and 1000 twists/m.

Yarns with organic or inorganic base and/or the second continuous elongated elements obtained therewith can be impregnated or coated with organic or inorganic polymers in the form, for example, of solutions, pastes or powders to increase their resistance to alkalis and/or to promote their adhesion to the cement mix; in addition, they can be combined with heat fusible yarns that, as a result of a known consolidation process, can modify the flexibility characteristics of the second continuous elongated elements obtained therewith. Obviously, also the organic or inorganic polymers with which the yarns with organic or inorganic base and/or the second continuous elongated elements are impregnated must have characteristics of resistance to alkali attack.

The metal wires, as indicated above, consist of steel or steely wires.

Preferably, the steel wires have a diameter between 0.05 mm and 5 mm and the following mechanical tensile characteristics:

- breaking strength (tensile strength) > 100 MPa,

- elastic modulus > 210000 MPa,

- elongation > 4%.

The steely wires and/or the second continuous elongated elements obtained therewith can be protected with surface treatments able, for example, to increase their corrosion resistance.

The yarns and/or the wires are twisted and/or wound and/or braided to form ropes, cables, nets or ribbons with technologies that are per se known.

In a preferred embodiment, the second continuous elongated elements consist of ropes, cables, nets or ribbons made with polyvinyl alcohol (PVA) polymeric yarns mixed together with carbon yarns. In the formation of these second continuous elongated elements, it is particularly advantageous that the polymeric yarns of polyvinyl alcohol (PVA) be arranged so as to form the outermost part of the second continuous elongated elements or of the individual elements that compose them, i.e. the part in direct contact with the cement mix forming the concrete, and the carbon yarns are arranged in the innermost part . Preferably, carbon yarns are present in a variable quantity between 5% and 70% by weight, yet more preferably in a quantity equal to 50% by weight.

It is advisable that the second continuous elongated elements in the form of ropes or cables have a rough or irregular outer lateral surface, to improve its characteristics of mechanical adhesion to the concrete in which they are embedded and hence to limit their pull-out or sliding in operating conditions. This roughness or these irregularities must have dimensions in the order of magnitude of the dimensions of the aggregates forming the concrete, generally between 5 mm and 80 mm.

These irregularities are for example obtained from the same conformation of the ropes, which advantageously consist of two or more strands wound/twisted around the longitudinal axis of the rope with a number of twists advantageously between 20 and 200 per linear metre.

Each strand comprises two or more twisted yarns, with a number of twists between 50 and 100 per linear metre; each strand has a diameter between 1 mm and 20 mm .

Advantageously, the ratio R between the area AO of the circle circumscribed to a single second continuous elongated element in the form of a rope or cable and the sum of the areas An of the circles circumscribed to each strand and any core constituting said rope or said cable is > 1.1, preferably between 1.05 and 2.01, still more preferably between 1.4 and 1.6.

If the first continuous elongated elements consist of steel bars or rods and the second continuous elongated elements are in the form of rope or cable, the ratio between the diameter of the circumference circumscribed to the normal section of each rope or cable and the diameter of each bar or rod is between 0.1 and 5, preferably equal to 1.

If the first continuous elongated elements consist of steel bars or rods and the second continuous elongated elements are in the form of rope, cable or ribbons, the ratio between the number of second continuous elongated elements and the number of first continuous elongated elements is between 0.5 and 10.

It is to be noted that both the first continuous elongated elements and the second continuous elongated elements extend with continuity along at least the entire length of the structural element reinforced with them, being able to extend in structural elements contiguous thereto.

It is specified that, as is known, the bars or rods that form the first continuous elongated elements are joined together with adequate superposition length.

The use of ropes, cables, ribbons or the like as second continuous elongated elements has the advantage of making it possible, thanks to their intrinsic continuity and flexibility, to avoid having to join them and, hence, to avoid or reduce their superpositions without excluding, if necessary, connection by superposition.

In the construction of a structural element according to the present invention, first of all formwork is constructed, suitable to contain the fresh concrete casting, to ensure the formation of a structural element having a given geometry and to hold in position the first reinforcement or to facilitate its creation and, with it, the second reinforcement.

The second reinforcement can be formed and connected to the first reinforcement both during the steps of assembly of the first reinforcement, and after the installation of the first reinforcement.

To connect the second continuous elongated elements to the first continuous elongated elements, coupling members can be useful to keep in position, during the concrete casting steps, the second continuous elongated elements with respect to the first continuous elongated elements. These coupling members can be selected from the group comprising: bands, staples, spacers, steel wires or polymeric yarns.

The formwork, in which the first reinforcement and the second reinforcement were formed and/or positioned, is then filled with at least one concrete casting, which is made to cure and harden according to the prior art.

Advantageously, the second continuous elongated elements are provided with adequate concrete cover and lateral concrete cover able to protect them.

The term structural element according to the present invention also indicates a structural element made of reinforced concrete of the traditional type, already existing and subsequently reinforced with an additional reinforcement according to the present invention positioned at its exterior, even only at some segments thereof, and embedded in a layer of concrete cast all around the existing structural element and to said additional reinforcement applied thereto; where the term "additional reinforcement" means the set formed by the first reinforcement and by the second reinforcement according to the present invention.

As mentioned, the second continuous elongated elements are arranged so as to develop with continuity along the longitudinal extension of the structural element, advantageously along the entire longitudinal development of the structural element.

Advantageously, the second continuous elongated elements are arranged so that the distance relative to second continuous elongated elements and/or to first continuous elongated elements adjacent thereto is no smaller than the minimum diameter of the aggregate; for example, this distance can vary between the minimum diameter of the aggregate and ten times the maximum diameter of the aggregate.

Likewise, if the second reinforcement is formed by a net or a bidirectional or multidirectional textile structure formed by ropes, cables or ribbons, the distance between adjacent individual ropes, cables or ribbons should be greater than the minimum diameter of the aggregates forming the concrete. In this case, too, said distance can vary preferably between the minimum diameter of the aggregate and ten times the maximum diameter of the aggregate.

The second continuous elongated elements can be arranged in different ways so as to develop along the longitudinal extension of the structural element for example :

- with their longitudinal axis parallel to the first continuous elongated elements,

- with their longitudinal axis arranged with crossed zig-zag pattern along the longitudinal extension of the structural element with angles between 0° and 180° relative to the direction of the first continuous elongated elements,

- with their longitudinal axis wound in a spiral along the longitudinal extension of the structural element with "circling" effect.

The second continuous elongated elements can be arranged in proximity to the outer lateral surface of the structural element; i.e., they can be arranged in such a way as to be at a position far from the neutral axis of the structural element in proximity to the side or edge of the structural element that is more stressed so as to maximise their contribution to the increase of tensile strength of the structural element. In the case of a beam, for example, they can be advantageously arranged in proximity to the lower edge. In case of pillars, they can for example be arranged in proximity to all the faces of the pillar or in such a way as to form a spiroid circling of the pillar.

It is also possible to arrange the second continuous elongated elements in a more internal position with respect to the structural element, also in proximity to the neutral axis thereof.

In case of nodes between different concurrent structural elements (beams/pillars), advantageously the second continuous elongated elements, as a result of their continuity and flexibility, extend continuously along them, through the respective nodes.

Due to the flexibility of the second continuous elongated elements, it is possible to create load- bearing structures in which the second reinforcements of the structural elements that compose them are "closed in a box"; that is to say, the second continuous elongated elements extend continuously through the structural elements (beams/pillars) that form the load-bearing structure and the related nodes.

However, different embodiments of the structural element according to the present invention are possible .

Thus, for example, the second continuous elongated elements that form the second reinforcement can also be different from each other by nature, structure or formation and/or can have different chemical - physical - mechanical characteristics.

Otherwise, the second continuous elongated elements that form the second reinforcement can be arranged in a position that is not contiguous to the first elongated elements forming the first reinforcement .

The structural elements according to the present invention and the load-bearing structures obtained therewith have high mechanical characteristics and a substantially "ductile" behaviour to tensile/flexural stresses .

The structural elements according to the present invention and the load-bearing structures obtained therewith are particularly suitable to withstand inertial and horizontal forces that are typical of seismic or other stresses (explosions or other stresses requiring the use of dissipative capability) .

With reference to the accompanying drawings, the reference number 10 indicates a structural element according to the present invention (or a specimen corresponding thereto) provided with a first reinforcement 11, which is formed by at least one first continuous elongated element 12, and with a second reinforcement 13, which is formed by at least one second continuous elongated element 14.

If the at least one second continuous elongated element 14 consists of a rope or a cable, the reference number 140 indicates each strand that composes it and the reference number 141 indicates the possible central core that composes it (Figures 9A and 9B) and that in turn can itself consist of a strand.

Each second continuous elongated element 14 can be coupled to an adjacent first continuous elongated element 12 through connecting members, such as for example an opposed double "C" or "U" member 15 shown in figure 10, in which the two Cs or Us are joined together by a bridge and encompass respectively a second continuous elongated element 14 and a first continuous elongated element 12.

The reference number 100 indicates a load-bearing structure obtained with structural elements 10 according to the present invention, be they in the form of beams or pillars (Figures 11A and 11B) .

Figures 12A-12C show different possible arrangements of the second continuous elongated elements 14 along the longitudinal extension of a structural element 10 according to the present invention provided with both a first reinforcement 11 and a second reinforcement 13 cooperating with each other .

In figure 12A the second continuous elongated elements 14 have zig-zag pattern, in figure 12B they have crossed zig-zag pattern, in figure 12C they have spiroid pattern.

In the included figures, the reference number 200 indicates a reference specimen replicating the specimens corresponding to structural elements 10 according to the present invention, provided only with the first reinforcement 11, but lacking the second reinforcement 13, used for the execution of the examples described below.

The features and advantages of the structural elements according to the present invention are illustrated below with reference to a series of examples provided by way of illustration and not to be considered as limiting.

EXAMPLES

EXAMPLE 1 (comparative example) : Structural element made of reinforced concrete according to the prior art. A flexural strength test was conducted using as a reference the standard UNI EN 12390-5:2002 of 1 June 2002 "Prova sul calcestruzzo indurito - Resistenza a flessione dei provini" (Testing hardened concrete - Flexural strength of test specimens) . In particular, a "concentrated load" flexural strength test was conducted (three point flexural test) .

The aforesaid standard was applied except for the presentation of the related test report; to better highlight the results obtained with the present invention, it was found more significant to provide as a test report the diagram with the applied force (measured in deca Newton, daN) on the y-axis and the displacement of the point of application of the force (measured in mm) on the x-axis.

A specimen of reinforced concrete was prepared, having prismatic shape with square cross section and with dimensions dixd2xL equal to 150x150x600 (in mm) .

The specimen was prepared using pre-mixed concrete having the following characteristics:

- class C32/40 according to the standard UNI EN 206- 1:2006 of 23 March 2006 {"Calcestruzzo" , Concrete), Italian version of the standard UNI EN 206-1 of December 2000 and related revisions,

- volume mass of the hardened mix equal to 2300 - 2400 kg/m³ ,

- aggregate with maximum dimension of 10 mm,

- consistency class S4 according to the standard UNI EN 12350-2:2001 of 30 June 2001 {"Prova sul calcestruzzo fresco - Prova di abbassamento al cono" , Testing fresh concrete - slump-test), Italian version of the standard UNI EN 12350-2 of October 1999.

The concrete was reinforced with a reinforcement formed by 4 (four) bars (continuous bars or longitudinal bars) with diameter equal to 8 mm made of steel for reinforced concrete of the B450C type positioned at the vertices of a square parallelepiped joined by 2 brackets aimed at assembling the cage forming the reinforcement, with average concrete cover of 15 mm. The prepared specimen was subjected to curing and preservation in water until the execution of the test, in accordance with the reference standard UNI EN 12390- 2:2002 of 1 June 2002 ("Prove sul calcestruzzo indurito - Confezione e stagionatura dei provini per prove di resistenza" , Testing Hardened Concrete - Making and Curing Specimens For Strength Tests), Italian language version of the standard UNI EN 12390-2 of October 2000, conducting the flexural strength test 28 days after the day of manufacture.

The specimen was subjected to flexural strength test with "concentrated load" in accordance with the aforementioned reference standard UNI EN 12390-5, positioning the two support rollers at a distance L from each other equal to 3d (where d=di=d2) and hence equal to 450 mm symmetrically with respect to a median transverse plane of the specimen whereat a single force application roller was positioned. Each of the two supporting rollers is distanced from the end of the specimen that is proximate thereto by a distance li equal to 75 mm.

Figures 1A and IB schematically show respectively the dimensions di, d2 and L of the specimen and the shape and arrangement of the reinforcement as well as the arrangement of the support and force application rollers .

Figures 1C and IE are photographs that respectively show a portion of the tested specimen in different successive phases of the test: at the start of the formation of the crack, with the crack fully formed, in proximity to the terminal phase of the test with the incipient collapse.

Figure IF is a photograph that shows the test equipment in a phase of execution of the test.

Figure 1G shows the force / displacement diagram (of the point of application of the force) measured during the execution of the test.

The area subtended to the diagram was calculated in a known manner and the value Ai equal to 127375 daN*mm was obtained.

On the diagram, the point Ci was also highlighted; it is related, as is readily apparent for the person skilled in the art, to the breakage of the steel bars forming the reinforcement.

EXAMPLE 2 : Structural element made of reinforced concrete according to the present invention.

A specimen was prepared and a flexural strength test was conducted exactly as indicated in EXAMPLE 1 with the sole difference that the specimen was further reinforced with the addition of 2 (two) ropes positioned parallel to the bars of the reinforcement. In particular, the two ropes were positioned between the two bars which, in the course of the test, are positioned in the plane opposite to the plane of application of the force. The two ropes were positioned so as to be distanced one from the other and from the two bars .

Each of the two ropes used is formed by approximately 50% of carbon yarns and by approximately 50% of PVA yarns .

The carbon yarns forming the ropes have elastic modulus equal to 246 GPa, tensile strength 5.766 MPa, count 1.669 tex; in particular, they are of the type H2550-24K Tansome® by Hyosung®.

The PVA yarns forming the ropes are of the type 5501 by Kuraray Co. LTD and have the following characteristics: Count: 2000 dtex

Number of filaments : 1000

Breaking strength : 196 N

Tenacity: 9.8 cN/dtex.

Elongation at break: 6.6%

Young's modulus : 203 cN/dtex

Dry heat shrinkage: 0.6%

Specific weight: 1.30 g/cm^*3

Each of the two ropes (Figure 2C) is of the flexible type and is formed by three (3) strands 140, each with diameter φ' equal to 4.75 mm, wound with pitch P2 equal to 27 mm equivalent to 37 windings per linear metre.

The winding pitch PI of two strands is equal to 9 mm.

The diameter φ of the circumference circumscribed to the normal section of the rope is equal to 9.1 mm. The rope has linear weight 60.4 g/m (grams/linear metre), in which the carbon fibre yarns are positioned mainly at the centre of each strand.

Each of the two used ropes has an average breaking load of 19 kN.

The specimen was subjected to flexural strength test with "concentrated load" in accordance with the aforementioned reference standard UNI EN 12390—5 positioning the two support rollers at a distance L from each other equal to 3d (where d=dl=d2) and hence equal to 450 mm symmetrically with respect to a median transverse plane of the specimen whereat a single roller for application of the force was positioned. Each of the two supporting rollers is distanced from the end of the specimen that is proximate thereto by a distance li equal to 75 mm.

Figures 2A and 2B schematically illustrate respectively the dimensions di, d2 and L of the specimen (corresponding to those of EXAMPLE 1), the shape and arrangement of the reinforcement formed by 4 (four) steel bars (corresponding to that of EXAMPLE 1), the arrangement of the additional reinforcement formed by 2 (two) ropes, as well as the arrangement of the support and force application rollers (corresponding to that of EXAMPLE 1) .

Figures 2D to 2F are photographs showing respectively a portion of the tested specimen in different successive phases of the test: at the beginning of the formation of the crack (figure 2D), with the crack fully formed (figure 2E) , with the crack fully open, ropes under traction and specimen as a whole in the plastic phase (figure 2F) . With reference to figure 2F, it is evident that the structural element as a whole has a "ductile" behaviour .

Figure 2G shows the force / displacement diagram (of the point of application of the force) measured during the execution of the test.

The area subtended to the diagram was calculated in a known manner and the value A2 equal to 343917 daN*mm was obtained.

On the diagram, the point C2 was also highlighted; it is related, as is readily apparent for the person skilled in the art, to the breakage of the steel bars forming the reinforcement. From the comparison of the results of the tests conducted according to EXAMPLE 1 and EXAMPLE 2, it is observed that :

- In the elastic-plastic field until the yielding (breakage) of the reinforcement formed by the steel bars the two charts have substantially similar patterns .

- After the yielding (breakage) of the reinforcement formed by the steel bars, instead, in the diagram of EXAMPLE 1 the substantial sudden yielding (breakage) of the specimen is recorded when the displacement of the point of application of the force measures approximately 11 mm, whereas in the diagram of EXAMPLE 2, additional resistance of the specimen to the load acting thereon is recorded, with extension in the "plastic" field. Hence, the specimen shows tensile strength with greater displacements than those reached with corresponding reference specimens according to the prior art (reference is made to the patterns of the charts of Figures 1G and 2G for displacements above 20 mm) . The area A2 subtended to the diagram of EXAMPLE 2, area that is indicative of the absorbed work/energy, is greater than the area Ai subtended to the diagram of EXAMPLE 1 in a ratio A₂/Ai=2.7.

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EXAMPLE 3 (comparative example) : Structural element made of reinforced concrete according to the prior art. A test was conducted as indicated in EXAMPLE 1 on a specimen having cross section equal to that of the specimen of EXAMPLE 1 and greater length than that of the specimen of EXAMPLE 1, accordingly adapting the reference standard UNI EN 12390-2:2002 of 1 June 2002. Specifically, the specimen used has prismatic shape with square cross section and dimensions dixd2 L equal to 150x150x1150 (in mm) .

The sample was prepared using pre-mixed concrete with the same characteristics of EXAMPLE 1.

The concrete was reinforced with a reinforcement formed by 4 (four) steel bars (continuous or longitudinal bars) with the same characteristics, conformation and arrangement of EXAMPLE 1, with the exception of the greater length of the bars.

The prepared sample was subjected to a period of curing and preservation exactly like EXAMPLE 1.

The specimen was subjected to flexural strength test with "concentrated load" in accordance with the aforementioned reference standard UNI EN 12390-5 adapted to the different dimensions of the specimen positioning the two support rollers at a distance 1 from each other equal to 1050 mm symmetrically with respect to a median transverse plane of the specimen whereat a single roller for application of the force was positioned. Each of the two supporting rollers is distanced from the end of the specimen that is proximate thereto by a distance li equal to 50 mm.

Figures 3A and 3B schematically show respectively the dimensions di, d2 and L of the specimen and the shape and arrangement of the reinforcement as well as the arrangement of the support and force application rollers .

Figure 3C shows the force / displacement diagram (of the point of application of the force) measured during the execution of the test.

The area subtended to the diagram was calculated in a known manner and the value A3 equal to 122262 daN*mm was obtained.

On the diagram, the point C3 was also highlighted; it is related, as is readily apparent for the person skilled in the art, to the breakage of the steel bars forming the reinforcement.

EXAMPLE 4 : Structural element made of reinforced concrete according to the present invention.

A specimen was prepared and a flexural strength test was conducted exactly as indicated in EXAMPLE 3 with the sole difference that the specimen was further reinforced with the addition of 2 (two) ropes arranged parallel to the bars of the reinforcement, also with average concrete cover of 15 mm.

The used ropes (with the exclusion of the different length) and their arrangement correspond to those of EXAMPLE 2.

Figures 4A and 4B schematically illustrate respectively the dimensions di, d2 and L of the specimen (corresponding to those of EXAMPLE 3), the shape and arrangement of the reinforcement formed by 4 (four) steel bars (corresponding to that of EXAMPLE 3), the arrangement of the additional reinforcement formed by 2 (two) ropes, as well as the arrangement of the support roller and force application roller (corresponding to that of EXAMPLE 3) .

Figure 4C shows the force / displacement diagram (of the point of application of the force) measured during the execution of the test.

The area subtended to the diagram was calculated in a known manner and the value A₄ equal to 468121 daN*mm was obtained.

On the diagram, the point C₄ was also highlighted; it is related, as is readily apparent for the person skilled in the art, to the breakage of the steel bars forming the reinforcement.

EXAMPLE 5: Structural element made of reinforced concrete according to the present invention.

A specimen was prepared and a flexural strength test was conducted exactly as indicated in EXAMPLE 4 with the sole difference that the 2 (two) ropes used consist solely of polypropylene (PP) yarns of the POLY-ROPE® type by Rolson®, each of which is flexible and formed by three (3) strands, each with diameter φ' equal to 4.05 mm, wound around the longitudinal axis with pitch P2 equal to 30 mm equivalent to 33 windings per linear metre. The diameter φ of the circumference circumscribed to each rope is equal to 10 mm and the winding pitch PI of two strands is equal to 10 mm (see Figure 5C) .

Each of the two ropes used has an average breaking strength: 6.5 k .

Figures 5A and 5B schematically illustrate respectively the dimensions di, d2 and L of the specimen (corresponding to those of EXAMPLE 4), the shape and arrangement of the reinforcement formed by 4 (four) steel bars (corresponding to that of EXAMPLE 4), the arrangement of the additional reinforcement formed by 2 (two) ropes, which corresponds to that of EXAMPLE 4), as well as the arrangement of the support roller and force application roller (corresponding to that of EXAMPLE 4) . Figure 5D shows the force / displacement diagram (of the point of application of the force) measured during the execution of the test.

The area subtended to the diagram was calculated in a known manner and the value As equal to 257987 daN*mm was obtained.

On the diagram, the point Cs was also highlighted; it is related, as is readily apparent for the person skilled in the art, to the breakage of the steel bars forming the reinforcement.

From the comparison of the results of the tests conducted according to EXAMPLE 3 and EXAMPLES 4 and 5, it is observed that:

- After the yielding (breakage) of the reinforcement formed by the steel bars, instead, in the diagram of EXAMPLE 3 the substantial sudden yielding (breakage) of the specimen is recorded when the vertical displacement of the point of application of the force measures approximately 12 mm, while in the chart of EXAMPLES 4 and 5, additional resistance of the specimen to the load acting thereon is recorded, with extension in the "plastic" field. Hence, the specimens obtained according to the present invention show tensile strength with greater displacements than those reached with corresponding reference specimens according to the prior art (reference is made to the patterns of the charts of Figures 3C and 4C 5D and for displacements above 30 mm) . The area A4 subtended to the diagram of EXAMPLE 4, the area that is indicative of the absorbed work/energy, is in fact greater than the area A3 subtended to the diagram of EXAMPLE 1 in a ratio A₄/A₃=3.8. The area A₅ subtended to the diagram of EXAMPLE 5, which is indicative of the absorbed work/energy, is in fact greater than the area A3 subtended to the diagram of EXAMPLE 1 in a ratio A₅/A₃=2.1.

~k ~k ~k

EXAMPLE 6 (comparative example) : Structural element made of reinforced concrete according to the prior art. A test was conducted on a specimen having T-beam shape with segments of square cross section having dimensions dixd2 equal to 150x150 (in mm) and length respectively Li and L2 equal to 750 mm and 600 mm.

The concrete was armed along each segment Li and L2 of the T with a reinforcement formed by 4 (four) steel bars (continuous or longitudinal bars) with the same characteristics of those of EXAMPLE 1, with the exception of the length of the bars, their crossing at the T-junction and the number of brackets used for assembling the cage.

The sample was subjected to flexural strength test with "concentrated load" applied on both segments Li and L2 of the T; in particular, the T-beam was positioned to bear on an end of the shorter segment L2 of the T and a concentrated load respectively Fl and F2 was applied both in proximity to the free end of the longer segment Li of the T, and at the centre of the free end of the shorter segment L2 of the T, as indicated in figure 6D where the following distances are reported:

- mi = 650 mm (distance between the point of application of Fl and the T-junction)

- rri2 = 75 mm (distance between the point of application of F2 and the ends of the normal section of the shorter segment Li of the T)

- Π13 = 100 mm (distance between the point of application of Fl and the free end of the longer segment L2 of the T) .

Figures 6A and 6B schematically illustrates respectively the dimensions di, d2 and Li and L2 of the specimen, the shape and arrangement of the reinforcement as well as the arrangement of the support and of application of the force.

Figure 6E shows the force / displacement diagram (of the point of application of the force) measured during the execution of the test at the point of application of the force Fl acting on the longer branch LI (750 mm) .

The area subtended to the diagram was calculated in a known manner and the value Αε equal to 83428 daN*mm was obtained .

On the diagram, the point Οβ was also highlighted; it is related, as is readily apparent for the person skilled in the art, to the breakage of the steel bars forming the reinforcement.

EXAMPLE 7: Structural element made of reinforced concrete according to the present invention.

A specimen was prepared and a flexural strength test was conducted exactly as indicated in EXAMPLE 6 with the sole difference that the sample was further reinforced with the addition of 2 (two) ropes that, with the exclusion of the different length and of the different arrangement, are of the same type as those of EXAMPLE 2.

In particular, two continuous ropes were used which were positioned along the longer segment Li of the T (traverse segment in the course of the test) and along the branch of the shorter segment L2 of the T bearing on the ground (straight segment in the course of the test) . The two ropes were positioned parallel to each other and interposed between the bars of the reinforcement as schematically shown in figure 7B.

Figures 7A and 7B schematically illustrate respectively the dimensions di, d2 and Li and L2 of the specimen, the shape and disposition of the reinforcement formed by 4 (four) steel bars (corresponding to that of EXAMPLE 6), the arrangement of the additional reinforcement formed by 2 (two) ropes, as well as the arrangement of the support and force application (corresponding to that of EXAMPLE 6) .

Figure 7C shows the force / displacement curve (of the point of application of the force) measured during the execution of the test.

The area subtended to the diagram was calculated in a known manner and the value A₇ equal to 109981 daN*mm was obtained.

On the diagram, the point C₇ was also highlighted; it is related, as is readily apparent for the person skilled in the art by direct comparison with the diagram of EXAMPLE 6, to the breakage of the steel bars forming the reinforcement. Comparing the results of the tests conducted according to EXAMPLE 6 and EXAMPLE 7, considerations similar to those made above in relation to the comparison of the previous examples apply.

5 In particular, it is observed that the area A7 subtended to the diagram of EXAMPLE 7, area that is indicative of the absorbed work/energy, is greater than the area A6 subtended to the diagram of EXAMPLE 6 in a ratio A₇/A6=1.5.

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EXAMPLE 8 (comparative example) : Structural element made of fibre-reinforced concrete according to the prior art .

A "four point" flexural test was conducted in 15 accordance with the standard UNI EN 110396 for concrete specimens reinforced solely with RF4000® PVA fibres by Kuraray® added in quantities equal to 2% by weight with length of 40 mm, where the RF4000® PVA has the following characteristics: breaking strength equal to 20 0.9 GPa and elastic modulus equal to 23 GPa.

The results of the flexural test conducted in accordance with the aforementioned standard are expressed with the chart of Figure 8A which shows on the y-axis the total force applied (equal to the sum of 25 the two forces applied through a respective roller) and on the x-axis the average displacement of the two points of application of the two forces.

It is observed that the increase in "ductility" obtainable with the addition of cut fibres dispersed in 30 the concrete is lower by several orders of magnitude to that obtainable with the second reinforcement according to the present invention. Considering the results of the tests conducted as a whole, it is possible to conclude that the use, in a structural element made of reinforced concrete, of a second reinforcement according to the present invention allows to obtain a flexural test force-displacement curve in which the area subtended to the respective curve is at least 20% greater than the area subtended to the corresponding flexural test force/displacement diagram obtained on an identical structural element made of reinforced concrete lacking the second reinforcement according to the present invention.

The increase of the area subtended to the flexural test force/displacement curve is essentially concentrated after the breakage of the steel, i.e. of the steel bars forming the reinforcement.

The structural elements according to the present invention and the load-bearing structures obtained therewith thus have a "ductile" behaviour under tensile/flexural stresses that makes them particularly suited to withstand inertial and horizontal forces that are typical of seismic stresses or deriving from explosions or other events.

It is specified that the second reinforcement of structural elements according to the present invention and of load-bearing structures obtained therewith is embedded in concrete during the formation/production of the structural elements.

It is also possible to employ the present invention to obtain reinforcements, even merely localised, of structural elements or load-bearing structures made of reinforced concrete of a conventional type, already existing, positioning, around said existing structural elements or load- bearing structures or even around just a portion thereof, an appropriate formwork in which a first reinforcement and a second reinforcement according to the present invention are manufactured and/or positioned and the concrete casting encompassing them is formed.

The structural element made of reinforced concrete thus conceived is susceptible to many modifications and variations, without departing from the scope of the invention; furthermore, all details can be replaced by technically equivalent elements. In practice, the materials used, as well as their dimensions, can be of any type according to the technical requirements.

Claims

1) Structural element (10) made of reinforced concrete comprising:

- a first reinforcement (11), which first reinforcement (11) comprises at least one first continuous elongated element (12) which is made of steel for reinforced concrete and which develops mainly along the longitudinal extension of said structural element (10), and

- a second reinforcement (13), which second reinforcement (13) comprises at least a second continuous elongated element (14) which develops mainly along the longitudinal extension of said structural element ,

characterised in that the area subtended to the force/displacement curve of said structural element (10) or of a specimen corresponding to said structural element subjected to flexural test with force acting along a direction substantially orthogonal to the longitudinal extension of said structural element or of said specimen replicating said structural element is greater by at least 20% than the area subtended to the force/displacement curve of a reference structural element replicating said structural element or of a reference specimen (200) replicating said specimen corresponding to said structural element, but lacking said second reinforcement (13), subjected to said same flexural test, in which the increase of said area is recorded substantially after the breaking point (C1÷C7) of said at least one first continuous elongated element (12) .

2) Structural element (10) according to claim 1, wherein said flexural tests are conducted respectively on a specimen (10) corresponding to said structural element and on a reference specimen (200) replicating said specimen corresponding to said structural element, but lacking said second reinforcement (13), in accordance with the standard UNI EN 12390-2 with concentrated load.

3) Structural element (10) according to claim 1 or 2, wherein said increase of said area is greater than 50%.

4) Structural element (10) according to claim 1 or 2, wherein said increase of said area is greater than 70% .

5) Structural element (10) according to one or more of the preceding claims, characterised in that said at least one second elongated element (14) is of a flexible type.

6) Structural element (10) according to one or more of the preceding claims, characterised in that said at least one second elongated element (14) comprises at least one rope, one cable, one net or one ribbon .

7) Structural element (10) according to claim 5 or 6, characterised in that said at least one second elongated element (14) is made with yarns with organic or inorganic base, with polymeric yarns with organic and/or inorganic base and/or with metallic wires, alone or mixed together.

8) Structural element (10) according to claim 7, characterised in that said organic polymeric yarns are selected from the group comprising polyvinyl alcohol (PVA) yarns, polypropylene (PP) yarns and polyethylene ( PE ) yarns .

9) Structural element (10) according to claim 7 or 8, characterised in that said polymeric yarns have tensile tenacity > 5 cN/dtex.

10) Structural element (10) according to one or more of the claims from 7 to 9, characterised in that said inorganic polymeric yarns consist of carbon yarns.

11) Structural element (10) according to claim 10, characterised in that said carbon yarns have elongation > 1%, preferably > 1.5%, still more preferably > 2.1%.

12) Structural element (10) according to one or more of the claims from 7 to 11, characterised in that said metal wires consist of steel wires.

13) Structural element (10) according to claim 12, characterised in that said steel wires have diameters between 0.05 mm and 5 mm and the following mechanical tensile characteristics:

- breaking strength (tensile strength) > 100 MPa,

- elastic modulus > 210000 MPa,

- elongation > 4%.

14) Structural element (10) according to one or more of the claims from 6 to 13, characterised in that the ratio (R) between the area (AO) of the circle circumscribed to said at least one second continuous elongated element (14) in the form of rope or cable and the sum of the areas (An) of the circles circumscribed to each strand and a possible core constituting said rope or said cable is > 1.1, preferably between 1.1 and 2.01.

15) Structural element (10) according to one or more of the claims from 6 to 14, characterised in that said at least one first continuous elongated element (12) consists of a steel bar or rod and in that said at least one second continuous element (14) is in the form of a rope or of a cable, in which the ratio between the diameter of the circumference circumscribed to the normal section of said rope or cable and the diameter of said bar or rod is between 0.1 and 5.

16) Structural element (10) according to one or more of the preceding claims, characterised in that said at least one second continuous elongated element (14) is coupled to said at least one first continuous elongated element by means of coupling members selected from the group comprising: bands, staples, spacers, steel wires or polymeric yarns.

17) Load-bearing structure (100) made of reinforced concrete comprising pillars and beams, wherein each of said pillars and/or each of said beams consists of a structural element (10) according to one or more of the preceding claims.

18) Load-bearing structure (100) according to claim 17, wherein each of said pillars and each of said beams consists of a said structural element (10), wherein said at least one second continuous elongated element (14) of at least one of said beams extends continuously in the respective pillars.

19) Method for the manufacture of a structural element (10) according to one or more of the preceding claims, comprising the steps of:

- positioning or forming said first reinforcement (11) in a formwork,

- positioning or forming said second reinforcement (13) in said formwork and

- filling said formwork in which said first reinforcement and said second reinforcement were positioned or formed with at least one concrete casting until covering said first reinforcement (11) and said second reinforcement (13) .