EP4155476A1

EP4155476A1 - Lightening formwork for reinforced-concrete objects and modular lightening structure using said formworks

Info

Publication number: EP4155476A1
Application number: EP22197156.7A
Authority: EP
Inventors: Gianfranco Gramola
Original assignee: Poseidon Gt Srl
Current assignee: Poseidon Gt Srl
Priority date: 2021-09-23
Filing date: 2022-09-22
Publication date: 2023-03-29
Also published as: IT202100024500A1

Abstract

A lightening formwork (1) for reinforced-concrete objects, which is adapted to be fixed to a metal framework (101) for reinforced-concrete objects and which comprises: at least a first (2) and a second cup-shaped body (3), separate and independent from one another, which are mutually coupled/ couplable along the perimeter edge so as to form a closed and substantially globoidal-shaped, rigid shell (4); and a protruding wedge member (5), which extends cantilevered from the rigid shell (4) and is adapted to wedge and get stuck between a pair of metal bars (102) of said metal framework (101) .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application claims priority from Italian Patent Application No. 102021000024500 filed on September 23, 2021 .

TECHNICAL FIELD

The present invention relates to a lightening formwork for reinforced-concrete objects and a modular lightening structure for reinforced-concrete objects using such formworks.
In more detail, the present invention relates to a modular lightening formwork and a modular lightening structure to be incorporated into reinforced-concrete slabs in order to lighten the resulting object. Use to which the following disclosure will make explicit reference without thereby losing generality.

BACKGROUND ART

As is known, in the past the reinforced-concrete slabs were realised by strategically inserting, between the reinforcement metal bars/rebars, large blocks of expanded polystyrene which were permanently embedded within the reinforced-concrete object, and made it possible to reduce the amount of concrete used per unit volume, with the resulting significant reduction of the overall weight of the object.
For reasons of safety and structural reliability, in recent years the expanded polystyrene blocks mentioned above have been replaced by large lightening formworks, which are structured so as to form large air bubbles within the reinforced-concrete object.
The most sophisticated lightening formworks currently on the market consist of two large cup-shaped bodies having substantially the shape of a spherical-cap, which are made of plastic material and are mutually coupled along the perimeter edge so as to form a spheroid-shaped rigid closed shell with the two flattened polar zones.
Patent EP2516763 B1 discloses a spheroidal-shaped lightening formwork that has, in at least one of the two polar zones, a pair of large clamping clips, which jut out cantilevered from the cup-shaped body and are structured to clamp onto as many reinforcement metal rebars/bars, so that the lightening formwork is firmly clamped onto the reinforcement before and during concrete casting.
Unfortunately, these protruding clips are made of plastic in a single piece with the cup-shaped body, with the considerable moulding problems that this entails.
Furthermore, due to their particular structure the locking clips tend to break rather frequently during the arrangement of the formwork on the metal reinforcement, with all the problems that this entails.
In addition, the clamping clips thus made require a perfect alignment between the lightening formwork and the reinforcement metal rebars/bars, thus the arrangement of the formworks along the metal reinforcement is rather hard-working, with the costs that this entails.

SUMMARY OF THE INVENTION

Aim of the present invention is to realise a modular lightening formwork, which is free from the drawbacks described above and is also cheap to produce.
In accordance with these aims, according to the present invention there is provided a lightening formwork for reinforced-concrete objects as defined in Claim 1 and preferably, though not necessarily, in any one of the claims depending on it.
According to the present invention, there is also provided a modular lightening structure for reinforced-concrete objects as defined in Claim 14 and preferably, though not necessarily, in any one of the claims depending on it.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which show a non-limiting embodiment thereof, wherein:

Figure 1 is a perspective view of a section of a modular lightening structure for concrete objects, which is provided with a series of lightening formworks realised according to the teachings of the present invention;
Figure 2 is a front view of the modular lightening structure shown in Figure 1;
Figure 3 is a front view of the modular lightening structure shown in Figure 1, sectioned along the midplane of one of the lightening formworks;
Figure 4 is a perspective view of one of the lightening formworks shown in the previous Figures, sectioned along the midplane of the formwork and with parts removed for clarity's sake;
Figure 5 is an exploded perspective view of one of the lightening formworks shown in the previous Figures;
Figure 6 is a side view of a first embodiment variation of the lightening formwork shown in the previous Figures, sectioned along the midplane of the formwork and with parts removed for clarity's sake; whereas
Figure 7 is a side view of a second embodiment variant of the lightening formwork shown in the previous Figures, sectioned along the midplane of the formwork and with parts removed for clarity's sake.

DETAILED DESCRIPTION OF THE EMBODIMENTS

With reference to the attached Figures, number 1 denotes, as a whole, a lightening formwork for reinforced-concrete objects, which is specifically structured to be permanently embedded within a slab or other reinforced-concrete object, so as to reduce the amount of concrete per unit volume.
In more detail, the formwork 1 is specifically structured to be incorporated into a modular lightening structure 100 for reinforced-concrete objects, which is adapted to be permanently embedded within a reinforced-concrete slab or other object.
With reference to Figures 1, 2 and 3, the modular lightening structure 100, in particular, comprises a metal framework 101 substantially rigid and at least partially made up of rectilinear metal bars rigidly fixed to each other; and one or more lightening formworks 1 that are fixed/attached to certain metal bars of the metal framework 101.
The metal framework 101, additionally, is preferably oblong in shape, and the lightening formworks 1 are fixed on the metal framework 101 one spaced beside the other, so as to form a row of formworks preferably extending without interruption substantially along the entire length of the metal framework 101.
In more detail, the metal framework 101 has a nominal length preferably ranging between 1,5 and 6 metres, and is provided with at least one pair of substantially rigid and straight, metal support bars that are rigidly connected to each other and extend alongside and substantially parallel to one another, preferably while remaining locally substantially parallel to the framework longitudinal axis L and preferably substantially along the entire length of the metal framework 101.
The lightening formworks 1 are structured so as to be forcedly wedged/fitted between said pair of metal support bars, so as to realise a mechanical interference fit.
More specifically, the lightening formworks 1 are adapted to be forcedly fitted into the slit between the two metal support bars of the metal framework 101, and are preferably structured so as to plastically deform against said metal bars when attempting to spread/move the metal bars apart/away from each other or vice versa.
In addition, at least one and more conveniently both support metal bars preferably have a substantially circular cross-section, with a nominal diameter preferably ranging between 5 and 30 mm (millimetres).
In other words, the two metal support bars are preferably reinforced-concrete rebars.
Preferably, the nominal distance d between the two metal support bars of the metal framework 101 moroever ranges between 50 and 300 mm (millimetres).
With reference to Figures 1, 2 and 3, in addition, the metal framework 101 preferably has a cage-like or lattice-like structure and the lightening formworks 1 are preferably arranged, or better housed/enclosed/contained, within the same metal framework 101.
In more detail, the metal framework 101 preferably comprises: a bundle of longitudinal metal bars 102 preferably having an approximately circular cross-section, which extend one spaced beside the other, parallel to the framework longitudinal axis L, and are arranged approximately at the vertices of a rectangle, trapezium or other polygon; and a series of transversal stiffening brackets 103, that are distributed along the entire length of the bundle of longitudinal metal bars 102 and connect the longitudinal metal bars 102 rigidly to each other.
Preferably, each transversal bracket 103 furthermore consists of a small straight metal bar preferably with a substantially circular cross-section, which is bent so as to substantially copy the shape/perimeter of said polygon, is fitted on the bundle of metal bars 102 so as to cross and overlap the various longitudinal metal bars 102, and is finally firmly fixed to the various longitudinal metal bars 102 of the bundle preferably by welding.
The lightening formworks 1 are adapted to forcedly interlocked/wedged between the two longitudinal metal bars 102 of the metal framework 101 that are located at the ends/ vertices of a same side of the rectangle, trapezium or other polygon.
In other words, the two metal support bars are a pair of longitudinal metal bars 102 of the metal framework 101.
With reference to Figures 1, 2 and 3, in the example shown, in particular, the metal framework 101 is preferably provided with at least four longitudinal metal bars 102 which have a substantially circular cross-section, with a nominal diameter preferably ranging between 6 and 20 mm (millimetres), extend parallel to the framework longitudinal axis L and are arranged approximately at the vertices of a substantially isosceles trapezium.
In more detail, the longitudinal metal bars 102 of the metal framework 101 are preferably corrugated rebars.
Preferably, the distance d between the longitudinal metal bars 102 that are arranged at the vertices of the smaller base of the trapezoid moreover ranges between 80 and 120 mm (millimetres).
Each transversal bracket 103, on the other hand, preferably consists of a small straight metal bar which has a substantially circular cross-section, with a nominal diameter preferably between 6 and 20 mm (millimetres), is substantially horseshoe- or U- bent so as to intersect the four longitudinal metal bars 102 in succession, and is firmly fixed to the four longitudinal metal bars 102 by welding.
In more detail, each transversal bracket 103 of the metal framework 101 preferably consists of a substantially horseshoe- or U- bent, corrugated rebar.
The lightening formworks 1, in turn, are preferably wedged/stuck in a rigid and stable, though easily removable manner, between the two longitudinal metal bars 102 of the metal framework 101 that are arranged at the ends/vertices of the smaller base of the trapezium.
With reference to Figures 1 to 5, each lightening formwork 1, in particular, comprises two large cup- shaped bodies 2, 3 substantially complementary in shape, separate and distinct from each other, which are adapted to be firmly coupled to each other along the perimeter edge of the respective mouth, so as to form a substantially globoidal-shaped, rigid closed shell 4. Preferably each cup- shaped body 2, 3 moreover has a single-piece structure.
In other words, the cup- shaped bodies 2 and 3 are two substantially bowl-shaped, complementary half-shells that are selectively coupled to each other along their perimeter edge so as to form the globoidal-shaped rigid shell 4.
In addition, the cup- shaped bodies 2 and 3 are preferably made of plastic material, and are preferably provided with a snap-lock system capable of rigidly locking the cup- shaped bodies 2 and 3 to one another.
With reference to Figures 1 to 5, at least one and more conveniently each lightening formwork 1 moreover comprises at least one protruding wedge member 5, which extends cantilevered from the globoidal-shaped rigid shell 4 preferably in a substantially radial direction, and is specifically structured to be wedged and get stuck in a rigid and stable, though easily removable manner, between the two metal support bars of metal framework 101, i.e. between two longitudinal metal bars 102 of metal framework 101, while attempting to spread the same metal bars apart.
In other words, the wedge member 5 is adapted to interpose and interlock between the two metal support bars of metal framework 101.
In more detail, the wedge member 5 preferably has an elastically deformable structure that is capable elastically deforming while being fitted between the two metal support bars of metal framework 101, or rather between a pair of mutually adjacent longitudinal metal bars 102.
In addition, the wedge member 5 is preferably separate and distinct from the rigid shell 4, or rather from the cup- shaped bodies 2 and 3, and is preferably structured so as to be rigidly fixed/interlocked to the globoidal-shaped rigid shell 4.
In more detail, the wedge member 5 preferably has a monolithic structure and/or is preferably made of plastic material.
With reference to Figures 1 to 5, in addition, the rigid globoidal-shaped shell 4 formed by the cup- shaped bodies 2 and 3 is preferably flattened at the two opposite polar zones, and the wedge member 5 is preferably located at one of the two polar zones of the shell.
Preferably, the wedge member 5 furthermore extends cantilevered from the rigid shell 4 remaining substantially coaxial to a central/diameter axis A that intersects the two polar zones of rigid shell 4.
With reference to Figures 1 to 5, in addition the globoidal-shaped rigid shell 4 is preferably provided with at least one flat portion 4a preferably substantially circular in shape, and the wedge member 5 extends cantilevered from said flat portion 4a, preferably in a direction substantially perpendicular to said flat portion 4a.
In more detail, the wedge member 5 is preferably placed nearly in the centre of said flat portion 4a.
In the example shown, in particular, the rigid shell 4 is preferably provided with two flat portions 4a that are arranged at opposite sides of the rigid shell 4, at the two polar zones of the shell, are preferably substantially circular in shape, and are preferably substantially parallel to each other and/or orthogonal to the central/diametrical axis A; and the protruding wedge member 5 extends cantilevered from one of the two flat portions 4a.
Preferably each cup- shaped body 2, 3 is additionally shaped so as to form a respective polar zone of the rigid shell 4.
In other words, the cup- shaped bodies 2 and 3 are two substantially basin-shaped half-shells that have a substantially flat central portion, and are selectively coupled to each other along their perimeter edge so as to form the rigid shell 4.
With reference to Figures 3, 4 and 5, in the example shown, moreover, the cup-shaped bodies 2 and 3 are preferably both substantially spherical-cap shaped, and are preferably arranged facing each other, substantially coaxial to the central/diameter axis A.
In other words, the perimeter edge of each cup-shaped body 2, 3 preferably lies in a reference plane substantially perpendicular to the central/diameter axis A. In addition, the flat portion or portions 4a of the rigid shell 4 are preferably substantially parallel to the lying planes of the perimeter edges of the cup-shaped bodies 2 and 3.
Preferably, the reference/lying plane of the perimeter edges of the cup-shaped bodies 2 and 3 moreover roughly coincides with the equatorial plane of the rigid shell 4.
In the example shown, in particular, the nominal outer diameter of the cup-shaped bodies 2 and 3 preferably ranges between 200 and 600 mm (millimetres).
Preferably, the height h₂ of cup-shaped body 2 is moreover substantially equal to the height h₃ of cup-shaped body 3. In other words, the cup-shaped bodies 2 and 3 have substantially the same dimensions.
In more detail, the height h₂, h₃ of cup-shaped bodies 2 and 3 preferably ranges between 50 and 500 mm (millimetres) .
Obviously, in a different embodiment, the height h₂ of cup-shaped body 2 may be greater or lower than the height h₃ of cup-shaped body 3.
Preferably, the outer diameter of the flattened portion or portions 4a, in turn, ranges between 25% and 50% of the nominal outer diameter d of the cup-shaped body 2, 3.
With reference to Figures 1 to 5, in addition, the perimeter edge of the cup-shaped bodies 2 and 3 is preferably provided with a protruding perimeter flange 6, which extends cantilevered flush with the edge of the mouth of the cup-shaped body, preferably while remaining substantially perpendicular to axis A and preferably without interruption along the entire length of the perimeter edge, and the cup-shaped bodies 2 and 3 are adapted to abut one against the other at the perimeter flanges 6.
Preferably, the perimeter flanges 6 of the cup-shaped bodies 2 and 3 additionally have substantially the same width, so that they can be overlapped substantially without interruption along their entire extension.
Furthermore, the snap-lock system is preferably located on the perimeter flanges 6 of cup-shaped bodies 2 and 3.
In more detail, each cup-shaped body 2, 3 has, on its perimeter flange 6, a series of protruding anchoring tabs 7 that are suitably distributed along the perimeter flange 6 and are adapted to engage as many pass-through slots 8 specifically made on the perimeter flange 6 of the other cup-shaped body 2, 3.
With reference to Figures 3, 4 and 5, in turn, the wedge member 5 is preferably arranged substantially coaxial to the cup-shaped bodies 2 and 3, and is preferably rigidly fixed to solely the cup-shaped body 2. More specifically, the wedge member 5 is preferably firmly fixed on the rigid shell 4, or rather on the cup-shaped body 2, by means of a mechanical interference fit.
In addition, the protruding wedge member 5 is preferably provided with an annular portion, preferably substantially circular in shape and preferably with an elastically deformable structure, which has a maximum width that over-approximates the nominal distance d existing between the metal support bars, and is adapted to interpose and get stuck between the two metal support bars of the metal framework 101.
In other words, the annular portion of the wedge member 5 arranges itself substantially coaxial to the central/ diameter axis A of the globoidal-shaped rigid shell 4 when the wedge member 5 is firmly fixed on the rigid shell 4.
With reference to Figures 1, 3, 4 and 5, in particular, the protruding wedge member 5 is provided with a central axis B that preferably coincides with the central/diameter axis A of the globoidal-shaped rigid shell 4 when the wedge member 5 is firmly fixed to the rigid shell 4.
Moreover the wedge member 5 preferably comprises: a substantially plate-like support base 10 which is substantially perpendicular to axis B, and is adapted to be arranged resting on, and be rigidly locked to, the globoidal-shaped rigid shell 4, preferably substantially at the centre of the or of one of the two flattened portions 4a; and a protruding tubular collar or sleeve 11 preferably having an elastically deformable structure, which extends cantilevered from the upper face of the support base 10 parallel to axis B, and is dimensioned so as to wedge and get stuck in a rigid and stable, though easily removable manner, between the two metal support bars of the metal framework 101.
Preferably the support base 10 is moreover provided with a central through-hole that joins, preferably without interruption, with the inside of the tubular sleeve 11.
In addition, the support base 10 is preferably also substantially discoidal in shape, with an outer diameter preferably greater than the nominal distance d existing between the two metal support bars of metal framework 101, and is preferably structured so as to be firmly interlocked/ interlockable in abutment on the globoidal-shaped rigid shell 4 by means of a mechanical interference fit.
In more detail, with reference to Figures 1, 3, 4 and 5, the discoidal support base 10 is preferably provided with a series of preferably lobate-shaped, protruding ridges or appendages 12 (three ridges/ appendages in the example shown) which jut out from the periphery of the support base 10 in a substantially radial direction, and are shaped so as to get stuck on specific protuberances 13 that jut out cantilevering from the surface of the globoidal-shaped rigid shell 4.
In addition, the protruding ridges or appendages 12 are preferably substantially regularly spaced along the periphery of the support base 10, and each of them is preferably provided with a transversal spline or groove, which is adapted to be engaged by a corresponding protuberance 13 of rigid shell 4.
The protuberances 13 that jut out cantilevered from the outer surface of the globoidal-shaped rigid shell 4, on the other hand, are preferably substantially cylindrical or truncated-cone in shape, and are dimensioned so as to forcedly wedged into the transversal spline or groove of the locking ridge 12.
Clearly, in a different embodiment the support base 10 of wedge member 5 may be retained in abutment on the rigid shell 4 by means of a snap-lock system.
With reference to Figures 3, 4 and 5, the protruding tubular sleeve 11, on the other hand, is preferably substantially cylindrical or truncated-cone in shape, and is preferably made in a single piece with the support base 10.
The maximum outer diameter of tubular sleeve 11, furthermore, over-approximates the nominal distance d existing between the two metal support bars of the metal framework 101, so that the tubular sleeve 11 takes an oval shape while being fitted between the metal support bars.
Preferably, the tubular sleeve 11 finally has a height h₀ greater than the nominal diameter of the metal support bars of the metal framework 101. In more detail, the height h₀ of tubular sleeve 11 preferably ranges between 10 and 50 mm (millimetres).
Functioning of the lightening formwork 1 and of the modular lightening structure 100 is easily inferable from the above and therefore does not need further explanations.
The assembly of the modular lightening structure 100 provides, in sequence: joining the cup-shaped bodies 2 and 3 so as to form the globoidal-shaped rigid shell 4; securing the wedge member 5 on the globoidal-shaped rigid shell 4; and finally securing the lightening formwork 1 on the metal framework 101 by interlocking the wedge member 5 between the two metal support bars of the metal framework 101.
The advantages connected to the presence of the wedge member 5 are remarkable.
Firstly, the wedge member 5 eliminates the need to align the lightening formwork 1 to the two metal support bars of the metal framework 101, greatly speeding up the assembly of the modular lightening structure 100.
Moreover, the protruding wedge member 5 has a thickset and robust structure that makes the wedge member much stronger and more difficult to break than the clips disclosed in Patent EP2516763 B1 .
In addition, the protruding wedge member 5 is easier and cheaper to produce by moulding than the clips disclosed in Patent EP2516763 B1 .
Finally, the wedge member 5 cane be used also in the lightening formworks currently on the market, structuring the discoidal-shaped support base 10 so as to fit directly on the ridge or annular shoulder that usually surrounds and delimits each flat portion of the formwork.
It is finally clear that modifications and variations may be made to the lightening formwork 1 and to the modular lightening structure 100 without thereby departing from the scope of the present invention.
For example, the wedge member 5 may be made in a single piece with any one of the cup-shaped bodies 2 and 3.
With reference to Figure 6, moreover, in a more sophisticated embodiment, the top of the annular portion of the wedge member 5, or rather the top of tubular sleeve 11, is preferably provided with a small annular ridge 14 that protrudes outside of the annular portion so as to hinder/make it more difficult to extract the wedge member 5 out of the slit delimited by the two metal support bars of the metal framework 101.
With reference to Figure 7, in a different embodiment, the annular portion of wedge member 5, or rather the tubular sleeve 11, is closed at the top by a concave cap 15 that preferably joins without interruption with the same annular portion.
In other words, the wedge member 5 has a cup-shaped structure that is able to form, on the outer surface of the globoidal-shaped rigid shell 4, a small closed chamber that increases the overall volume of the lightening formwork 1, with all the advantages that this entails.

Claims

A lightening formwork (1) for reinforced-concrete objects, of the type adapted to be fixed to a metal framework (101) for reinforced-concrete objects and comprising at least a first (2) and a second (3) cup-shaped body, separate and independent from one another, which are mutually coupled/ couplable along the perimeter edge so as to form a substantially globoidal-shaped, closed rigid shell (4);
said lightening formwork being characterised by also comprising a protruding wedge member (5) that extends cantilevered from the rigid shell (4) and is adapted to wedge and get stuck between a pair of metal support bars (102) of said metal framework (101).
The lightening formwork according to Claim 1, wherein said wedge member (5) is provided with an annular portion (11) that is adapted to interpose and get stuck between said pair of metal support bars (102).
The lightening formwork according to Claim 2, wherein the annular portion (11) of said wedge member (5) is substantially circular in shape.
The lightening formwork according to claim 2 or 3, wherein the annular portion (11) of said wedge member (5) has an elastically deformable structure.
The lightening formwork according to any one of the preceding claims, wherein said wedge member (5) is separate and distinct from said first (2) and second (3) cup-shaped bodies, and is rigidly fixable on the rigid shell (4) formed by said first (2) and second (3) cup-shaped bodies.
The lightening formwork according to Claim 5, wherein said wedge member (5) comprises: a support base (10) adapted to be arranged resting on the rigid shell (4) formed by said first (2) and second (3) cup-shaped bodies; and a protruding tubular sleeve (11) that extends cantilevered from the support base (10) and, is dimensioned so as to be wedged and get stuck between said pair of metal support bars (102).
The lightening formwork according to Claim 6, wherein said protruding tubular sleeve (11) is substantially cylindrical or truncated-cone in shape and/or said support base (10) is substantially discoidal in shape.
The lightening formwork according to Claim 6 or 7, wherein said protruding tubular sleeve (11) is closed at the top by a cap (15).
The lightening formwork according to Claim 6, 7 or 8, wherein said support base (10) is adapted to interlock on the rigid shell (4) preferably by means of a mechanical interference fit.
The lightening formwork according to Claim 9, wherein said support base (10) is adapted to interlock on protuberances (13) that jut out cantilevered from surface of the rigid shell (4).
The lightening formwork according to any one of the preceding claims, wherein the rigid shell (4) formed by said first (2) and second (3) cup-shaped bodies is flattened at the polar zones, and the wedge member (5) is located at one of said polar zones.
The lightening formwork according to any one of the preceding claims, wherein the rigid shell (4) formed by said first (2) and second (3) cup-shaped bodies is provided with at least one flat portion (4a) and the wedge member (5) extends cantilevered from said flat portion (4a).
The lightening formwork according to any one of the preceding claims, wherein said first (2) and second (3) cup-shaped bodies are coupled/couplable to each other by means of a snap-lock system.
A modular lightening structure (100) for reinforced-concrete objects, of the type comprising: a metal framework (101) that is at least partially made up of metal bars (102) rigidly fixed to one another; and one or more lightening formworks (1) that are fixed to said metal bars (102);
said modular lightening structure (100) being characterised in that at least one of said lightening formworks (1) is made according to any one of Claims 1 to 13.
The modular lightening structure according to Claim 14, wherein the metal framework (101) is oblong in shape and the lightening formworks (1) are fixed on the metal framework (101) one spaced beside and aligned to the other, so as to form a row of formworks.
The modular lightening structure according to Claim 15, wherein the metal framework (101) is provided with at least one pair of metal support bars (102) that are rigidly connected to one another and extend spaced alongside and substantially parallel to one another; the lightening formworks (1) being fixed on said pair of metal support bars (102) .
The modular lightening structure according to Claim 15 or 16, wherein the metal framework (101) has a cage-like or lattice-like structure and the lightening formworks (1) are placed inside said metal framework (101).
The modular lightening structure according to Claim 17, wherein said metal framework (101) comprises: a bundle of longitudinal metal bars (102) that extend one spaced alongside the other, parallel to the framework longitudinal axis (L), and are arranged substantially at the vertices of a rectangle, trapezium or other polygon; and a series of transversal stiffening brackets (103) that are distributed along the bundle of longitudinal metal bars (102) and connect the longitudinal metal bars (102) rigidly to one another; the lightening formworks (1) being stuck between two longitudinal metal bars (102) located at the ends/vertices of a same side of the rectangle, trapezium or other polygon.