Method to produce reinforced concrete panels for prefabricated structures and relative panel

Abstract: Method to produce panels (10) made of reinforced concrete for prefabricated building structures, either horizontal or vertical, such as for example wall elements, floor elements, covering elements or otherwise, the panels (10) consisting of at least a plane body (14) obtained by means of casting concrete (15) inside a perimeter frame (11) functioning as a formwork, the perimeter frame (11) containing at least a reinforcement element (13) associated therewith, the at least one reinforcement element (13) being subjected, before the concrete (15) casting is made, to a pre-shaping which is functionally correlated to compensate for the deformations to which the reinforcement element (13) is subject during the casting of the concrete (15). Panel for prefabricated building structures produced according to the method described above.

Description: This invention concerns a method to produce panels made of reinforced concrete for prefabricated structures, as set forth in the respective main claim. The invention is employed in the prefabricated building trade to produce panels made of reinforced concrete, made in the plant and then assembled on site, constituting parts of buildings or structures in general, horizontal or vertical, such as floors, wall elements, roof elements, etc. BACKGROUND OF THE INVENTION The state of the art includes prefabricated building techniques which provide for the production in the plant of the structural and auxiliary components and their subsequent assembly on site. Plane components, such as for example floors, wall elements and covering elements, generally consist of reinforced concrete panels where the metallic reinforcement consists of at least a sheet of electrowelded mesh, closed and supported on the perimeter by sections, usually C-shaped or L-shaped, welded together and defining the framework of the panel. The use of these perimeter frames, forming a box-like containing structure, has brought a series of advantages both during the production step and also during the assembly of the panels; it has also improved their mechanical characteristics. In fact, when the panels are produced, by using a perimeter frame it is possible to simplify the operations for setting up the formworks, since the sections themselves, during the casting step, constitute the perimeter formworks of the panel. Moreover, attached to the perimeter frame we find not only the electrowelded reinforcement mesh, but also any necessary ironwork elements such as ferrules, hooks, eyelets or otherwise, which are used to lift and move the panels. It is also simpler to anchor the panels since this can be done simply by welding the adjacent perimeter frames of the panels which are to be joined; there is no need for any specific anchoring elements. The problem is, however, that when the electrowelded mesh is attached to the perimeter frame, it is deformed during the casting of the concrete. The electrowelded mesh, in fact, is deformed due to the effect of its own weight, and the pressure and weight of the concrete cast; moreover, since it is constrained at the perimeter, it tends to become rounded and swollen towards the outside, which can cause a panel of unsatisfactory quality to be obtained. In fact, if the electrowelded mesh is excessively rounded, it can cause a considerable displacement of the reinforcement, thus compromising the characteristics of mechanical resistance and load-bearing capacity of the panel and/or reducing the concrete covering thickness to values which do not meet the legal requirements or the specifications of the design. Moreover, if the electrowelded mesh comes into contact with the outer face of the panel, this may cause the appearance of anti-aesthetic visible stains, damage to the plaster, cracks or fissures. This makes it necessary to replace the panel inasmuch as, when such deformations of the mesh occur, it is impossible to solve the above-mentioned problems even by maintaining the face of the panel, and the problems recur after a short period of time. DE-C-851074 refers to a method to pre-compress structures connected to bearing connecting elements, such as bridges or similar. This invention refers to a technological improvement of known procedures for the pre-compression of structural elements which are used in the construction of suspension structures supported by girders or pillars, and does not make any reference to reinforced panels for building work. US-A-3,886,648 refers to a plate made of steel and concrete consisting of a mesh of steel bars attached to a perimeter frame by means of connecting clamps. This document describes a method to ensure an efficient connection and seal between the structural elements of which it consists. When the concrete is cast, the plate described in this document has all the disadvantages described above. US-A-3,604,174 discloses a panel comprising aggregate concrete bounded by a structural steel frame that serves as a form. The panel has an internal reinforce which comprises structural metal bar members. There are channels of less width than the frame channels and rods that extend between the other pair of frame sides to which they are secured. Rods pass with a close fit through bores in the channel webs and being welded to the channels for added strenght and rigidity. The reinforcing means comprise a wire mesh member which are flat pieces which occupy substantially all of the area enclosed by the frame. In the manufacture of such a panel, the members of the frame are secured together to form the frame, after which the reinforcing members are welded or otherwise secured in position. Thereafter, the wire mesh members are secured in position and the frame is ready to receive the concrete. When the concrete is cast, it flows through the wire mesh members and around the members so that the reinforcing means is completely surrounded and concealed from view. GB-A-290,038 discloses a method of stretching and locking the reinforcements of a concrete panel whereby the reinforcements are initially tensioned and locked to the supporting structure before the concrete infilling takes place, and, for this aim, it is used an inclined hook to stretch and lock said reinforcements to the supports. In none of these documents there is any indication or suggestion for a way to pre-shape or pre-deform the reinforcements to compensate the deflection which the reinforcements themselves will be subjected during the casting of concrete, thus obtaining, at the end of the casting process, a desired shape of the reinforcements, for example substantially flat. The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art, and to achieve further advantages. SUMMARY OF THE INVENTION The invention is set forth and characterised in the respective main claim, while the dependent claims describe variants of the idea of the main embodiment. The purpose of the invention is to provide a method which will make it possible to produce panels made of reinforced concrete equipped with perimeter frames on which the reinforcement elements are anchored; when casting is completed, the reinforcement elements have a shape and position which correspond to the design specifications and to construction legislation. Another purpose is to provide a method which will produce panels with a structure of optimum quality and which meet the necessary requirements of mechanical resistance and load-bearing capacity. The invention provides for the production of panels made of reinforced concrete by using at least one reinforcement element consisting of a metallic mesh which is pre-shaped or pre-rounded in such a way as to compensate for the deformation suffered by the mesh when the panel is cast. The word "pre-shaped" or "pre-shaping" has the meaning of "pre-deformed" or "pre-deformation" throughout the description. The reinforcement elements are welded at the perimeter to framework sections which may be C-shaped, L-shaped or any other shape. According to a first embodiment, the extent of the pre-shaping is at least a function of the specific weight of the concrete with which the panel is cast. The specific weight can be different according to the type of concrete used, for example, normal or lighter concrete. According to another embodiment, the extent of the pre-shaping is at least a function of the pressure of the concrete casting. According to a further embodiment, the pre-shaping is a function of the size of the reinforcement element. According to the invention, when the concrete is cast to form the panel, the weight of the concrete and the pressure at which it is cast cause a deformation of the reinforcement elements which cancels the pre-shaping and returns the reinforcement elements to the desired, substantially plane shape. Moreover, when the concrete is cast with the reinforcement elements arranged horizontally, the weight of the reinforcement elements themselves causes them to be deformed. In this case, each reinforcement element is pre-shaped according to the weight of the reinforcement. According to a variant, there are two or more reinforcement elements, advantageously arranged symmetrically to the neutral axis of the panel. According to a further variant, a panel is arranged at an intermediate position between two reinforcement elements, which has a heat insulation and/or sound proofing function; the panel is then drowned in the concrete casting. In this embodiment, the pre-shaped reinforcement elements are coupled during the casting step with the panel in order to contain and stabilise the latter. The reinforcement elements also have a structural function, that of absorbing the critical loads acting on the panel. Therefore, with the method according to the invention, the deformations resulting from the concrete casting are compensated by the pre-shaping given to the reinforcement elements in such a manner that the latter, when the concrete casting has been completed, substantially return to the shape and position given by the design specifications. The panels obtained are therefore of excellent quality, they meet the requirements of mechanical resistance and load-bearing capacity required and the values of their concrete covering thickness come within the norm. BRIEF DESCRIPTION OF THE DRAWINGS The attached Figures are given as a non-restrictive example and show some preferential embodiments of the invention as follows: Fig. 1 shows a three-dimensional view of a panel made of reinforced concrete for prefabricated building structures produced by means of the method according to the invention; Fig. 2 shows a transverse cross section of the reinforcement element and the frame of the panel in Fig. 1 before the concrete is cast; Fig. 3 shows a transverse cross section of the casting of the panel in Fig. 1; Fig. 4 shows a transverse cross section of the finished panel in Fig. 1; Fig. 5 shows a variant of Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the attached Figures, the reference number 10 denotes generally a reinforced concrete panel for prefabricated building structures produced using the method according to the invention. The panel 10 consists of a flat body 14 made of reinforced concrete, in this case, with a sheet of electrowelded mesh 13 placed in an intermediate position with respect to the thickness of the body 14. The panel 10 is surrounded by a metallic perimeter frame 11, which is achieved by welding together a plurality of sections 12, in this case C-shaped; the sheet of electrowelded mesh 13 is attached to the frame 11. Before the casting of the concrete 15 which causes the formation of the flat body 14, and before it is anchored to the perimeter frame 11, the sheet of electrowelded mesh 13 is subjected to a pre-shaping which gives it a rounded shape, in this case upwards (Fig. 2). The extent of the pre-shaping is defined according to the presumed deformation which the sheet of electrowelded mesh 13 is subjected to during the casting of the concrete 15. To be more exact, the pre-shaping deflection "f" of the sheet of electrowelded mesh 13 is defined according to parameters relating to the physical and dimensional characteristics of the sheet of electrowelded mesh 13, and also the type of process employed to cast the concrete 15, and also the type of concrete itself. The value of the pre-shaping deflection "f" can be defined according to the maximum size of the sheet of electrowelded mesh 13, the diameter of the round pieces 13a of which it is made, and the pitch of the round pieces 13a. The value of the pre-shaping deflection "f" can also be defined according to the weight of the cast concrete 15 which will lie on the sheet of electrowelded mesh 13 and therefore substantially according to the specific weight of the concrete and the thickness of the panel 10. Furthermore, the value of the pre-shaping deflection "f" is directly proportional to the pressure at which the concrete 15 is cast. Moreover, when the concrete 15 is cast with the sheet of electrowelded mesh 13 in a horizontal position, the value of the pre-shaping deflection "f" is defined also taking into account the weight of the sheet of electrowelded mesh 13. In fact, the sheet of electrowelded mesh 13, once it has been welded to the perimeter frame 11, tends to sink in the centre due to the effect of its own weight, thus reducing the value of the pre-shaping deflection "f" which had been defined previously. When the concrete 15 is cast (Fig. 3), the sheet of electrowelded mesh 13 is subjected to the weight and pressure of the concrete 15 casting which is contained below the formwork 16; it is therefore progressively deformed and this gradually reduces the pre-shaped roundness and returns the electrowelded mesh 13 to its substantially flat shape. The pre-shaping deflection "f" is therefore reduced until it is substantially nil when the casting is finished (Fig. 4); at this point the sheet of electrowelded mesh 13 is substantially flat and therefore it assumes its final desired shape and position. The panel 10 thus embodied has substantially optimum construction characteristics which guarantee that the panel 10 meets the requirements of mechanical resistance and the load-bearing capacities of the design and the required cover value "c". In the variant shown in Fig. 5, the reinforcement elements comprise two sheets of electrowelded mesh 13, symmetrical to the neutral axis of the panel 10 and enclosing within themselves a panel 17 with heat insulating and/or sound proofing functions. The sheets of electrowelded mesh 13, pre-shaped in advance, assume a position adjacent to the panel 17 after the concrete 15 has been cast and, apart from their structural function of stiffening the panel 10, they contain and stabilise the panel 17.

Claims: Method to produce panels (10) made of reinforced concrete for prefabricated building structures, either horizontal or vertical, such as wall elements, floor elements, covering elements, the panels (10) consisting of at least a plane body (14) obtained by means of casting concrete (15) in a perimeter frame (11) functioning as a formwork, the perimeter frame (11) containing at least a reinforcement element (13) associated therewith, the method being characterised in that at least one reinforcement element (13) is subjected, before the concrete (15) casting is made, to a pre-deformation with respect to a desired form of said reinforcement element (13), the value ("f") of said pre-deformation being defined so to compensate for the deformations to which the reinforcement element (13) will be subjected during the casting of the concrete (15) and caused by said casting of the concrete (15), so to return to said desired form of said reinforcement element (13) after the casting. Method as in claim 1, characterised in that said desired form is substantially flat. Method as in Claim 1, characterised in that the value ("f") of said pre-deformation is at least a function of the specific weight of the concrete used. Method as in Claim 1 or 2, characterised in that the value ("f") of said pre-deformation is at least a function of the thickness of the layer of concrete weighing on the at least one reinforcement element (13). Method as in any claim hereinbefore, characterised in that the value ("f") of said pre-deformation is at least a function of the pressure of the cast concrete (15). Method as in any claim hereinbefore, characterised in that the value ("f") of said pre-deformation is at least a function of the physical and dimensional characteristics of the at least one reinforcement element (13).

Inventors: DA RIO RINALDO, DA RIO, RINALDO
Applicants: BMK AUTOMATISIERUNGSTECHNIK GM, BMK AUTOMATISIERUNGSTECHNIK GMBH
Application year: 1998
Main classification: E04C2
IPC codes: E04C2, E04B7, E04C5, B28B23