Sensorized fiber-reinforced structural element with optical fiber for reinforcing concrete, as well as for consolidating, stabilizing and reinforcing the ground, and pultrusion manufacturing method therefor

Abstract

A sensorized fiber-reinforced structural element (1), comprising an elongated body (2) made of a fiber-reinforced composite material extending along a longitudinal direction (L),, and a longitudinally extending fiber optic sensor (3) arranged inside the elongated body (2) in direct and intimate contact with the fiber-reinforced composite material; the elongated body (2) made of a fiber-reinforced composite material comprises two opposite ends (21, 22) thereof, the fiber optic sensor (3) comprises at least one excess segment (31, 32) thereof extending, i n the longitudinal direction (L), beyond at least one end (21, 22) of said two ends of the elongated body (2) made of a fiber-reinforced composite material.

Description

[0001] SENSORIZED FIBER-REINFORCED STRUCTURAL ELEMENT WITH OPTICAL FIBER FOR REINFORCING CONCRETE, AS WELL AS FOR CONSOLIDATING, STABILIZING AND REINFORCING THE GROUND, AND PULTRUSION MANUFACTURING METHOD THEREFOR DESCRIPTION

[0002] Technical field

[0003] The present invention relates to the technical field of monitoring fiber optic structures.

[0004] in particular, the present invention relates to a sensorized fiber-reinforced structural element.

[0005] The present invention also relates to a method for manufacturing said sensorized fiber- reinforced structural element.

[0006] Background art

[0007] in the field of monitoring buildings or other structural elements, it is generally known to employ fiber optic sensors, such as, for example, fiber optic sensors of the Bragg grating type (i .e. , “Fiber Bragg Grating”) , because they are adapted to detect local deformations without interfering with the static and dynamic behavior of the structural element itself by vi rtue of the light weight and small size thereof. The high data acquisition speed ensured by the optical fiber allows monitoring static and dynamic strains and, when needed, temperature variations when these ari se .

[0008] The monitoring technique for outdoor application, commonly used to monitor buildings and infrastructures, consists in bonding an optical fiber onto the outer surface of the structures to be moni tored .Alternatively, a monitoring technique for indoor application where optical fibers are embedded in prefabricated concrete beams by making a fiberglass housing is also known. This technique enables both controlling quality during the production of the beam and monitoring the structural element when it is installed.

[0009] However, this technique is not free from drawbacks, and in particular, the fiberglass housing containing the optical fiber does not provide structural functions and therefore reduces the structural performance of the enti re prefabricated beam, indeed, the under-stress behavior of the fiberglass housing containing the optical fiber is different from that of concrete or material of the load-bearing structural el ement .

[0010] Techniques involving the insertion of optical fibers into pultruded profiles (“pultrusion” , i .e. , pulling extrusion) are also known , in particular, pultrusion is a production process generally used to create resin-impregnated profiles made of a composite material mainly based on fiberglass or carbon fiber. The process includes orderly arranging the fiberglass or carbon fibers side-by-side. These are immersed in a resin , which fully impregnates them. The impregnated fibers are then pulled (by means of a pulling system) through a heated mold (al so referred to as a die) defining the geometry of the pultruded profile, where the resin cures (catalyzes) , thus forming the pultruded profile. The geometry dictated by the heated mold becomes permanent following the catalysis of theresin. The residence time of the profile inside the heated mold depends on the pulling speed. The subsequent step relates to cooling and cutting the profile to the desi red length. The end profile can be subjected to further surface treatments.

[0011] A known type of pultruded profiles is the “rebar” , where an unheated mold is employed for the production thereof in place of the above-mentioned heated mold, in particular, the mold is arranged upstream of the heating system where the catalysis of the resin occurs and does not give the profile a particular shape. The end geometry is instead ensured by a winding system, such as a rotating reel , which winds and compacts the impregnated fibers by means of a wi re. The profile thus produced slides through a system of furnaces in series by actuating the pulling arranged downstream. A typical application of known fiber-reinforced composite pultruded elements resides in the manufacturing of conductors for overhead power lines. For example, prior document WO-2021-181265 shows the application of optical fibers to the outer surface of a pultruded element, for monitoring the structural integrity of the power conductor.

[0012] Furthermore, prior document WO-2019-168998 discloses a solution that includes incorporating an optical fiber together with the fiber-reinforced composite in a pultrusion apparatus. This solution, albeit advantageous from certain points of view, is not at all free of drawbacks.

[0013] indeed, the pultrusion of the fiber-reinforced composite material includes embedding both thereinforcing fibers and the monitoring optical fiber in the polymer matrix (resin) before it cures. The integration of the fiber optic sensor within the matrix body is thus ensured, even after the pultruded elements have been cured (cooled down) and cut to the desi red length. However, cutting the thus-sensorized bar does not allow identifying the optical fiber from the profile itself.

[0014] Furthermore, the known heated pultrusion dies requi re high operating temperatures that can damage the optical fiber.

[0015] The need is thus strongly felt to provide an improved solution for sensorized fiber-reinforced structural elements intended to be subjected to axial , bending and / or torsional loads when under operating conditions.

[0016] Solution

[0017] it is an object of the present invention to suggest a solution to the needs here complained with reference to the prior art.

[0018] This and other objects are achieved by a sensorized fiber-reinforced structural element according to claim 1, as well as by a method according to claim 8, as well as by an apparatus according to claim 10.

[0019] Certain advantageous embodiments are the subject of the dependent claims.

[0020] By vi rtue of the suggested solutions, there is provided a sensorized fiber-reinforced structural element which allows manufacturing sensorized infrastructural structures or works that are improved with respect to the known solutions.Brief description of the figures

[0021] Further features and advantages of the invention will become apparent from the following description of embodiments given by way of non-limiting examples, with reference to the accompanying drawings, in which: - Figure 1 is a diagrammatic view of rebar comprising a sensorized fiber-reinforced structural element, according to an embodiment;

[0022] - Figure 2 is a vertical elevational view of a sensorized fiber-reinforced structural element, according to an embodiment;

[0023] - Figure 3 is a diagrammatic sectional view of a portion of a sensorized fiber-reinforced structural element, according to an embodiment;

[0024] - Figure 4 diagrammatical ly shows a modular assembly, according to an embodiment;

[0025] Figure 5 is a block diagram of a pultrusion apparatus as well as of a manufacturing method, according to an embodiment.

[0026] Detailed description of certain embodiments

[0027] in accordance with a general embodiment, a sensorized fiber-reinforced structural element 1 (hereinafter also simply: “structural element”) is provided.

[0028] The sensorized fiber-reinforced structural element 1 can be a load-bearing structural element or a reinforcing bar.

[0029] The sensorized fiber-reinforced structural element 1 can be a component of an infrastructure work.

[0030] The structural element 1 comprises an elongated body 2 made of a fiber- reinforced composite material extending along a longitudinal di rection L, and afiber optic sensor 3, also extending longitudinally and arranged inside the elongated body 2 in di rect and intimate contact with the fiber-reinforced composite material .

[0031] The fiber optic sensor 3 preferably comprises a single optical fiber extending longitudinally into the elongated body 2.

[0032] The elongated body 2 made of a fiber-reinforced composite material comprises two opposite ends 21, 22 thereof, and the fiber optic sensor 3 comprises at least one excess segment 31, 32 thereof, extending, in the longitudinal di rection L, beyond at least one end 21, 22 of said two ends of the elongated body 2 made of a fiber-reinforced composite material .

[0033] Therefore, said at least one excess segment 31, 32 of the fiber optic sensor 3 is not impregnated by the resin of the fiber-reinforced composite material .

[0034] The at least one excess segment can extend from its relative end of the elongated body 2 to a monitoring control unit 6.

[0035] The at least one end of the elongated body can comprise an elongated body end section thereof extending transversely with respect to the longitudinal di rection, and the excess segment of the fiber optic sensor extends from said end section. in accordance with an embodiment, the fiber optic sensor 3 comprises a single excess segment extending beyond the respective end of the elongated body.

[0036] in accordance with an embodiment, as shown for example in Figure 2, the fiber optic sensor 3 comprises two opposite excess segments 31, 32, each excess segmentextending beyond the respective end 21, 22 of the elongated body 2.

[0037] The provision of such a structural element provided with at least one excess segment of fiber optic sensor readily accessible outside the elongated body simplifies the establishment of an operating connection with the fiber optic sensor itself, thus facilitating the operations of data collection from and / or interrogation of the fiber optic sensor.

[0038] The at least one excess segment 31, 32 is preferably obtained seamlessly with the rest of the fiber optic sensor 3, i .e. , the at least one excess segment 31, 32 is not added to the fiber optic sensor 3 but is an integral part thereof, preferably made in one piece therewi th .

[0039] The length of each excess segment 31, 32 is in the range of 10-50 centimeters, and preferably between 20 and 30 centimeters, in accordance with a preferred embodiment, the fiber optic sensor 3 thus extends beyond a given end 21 or 22 of the elongated body 2 by a length of about 20-30 centimeters.

[0040] The elongated body 2 of the structural element 1 can be a rod or a profile made of a fiber-reinforced composite material (e.g. , of the type: “glass fiber reinforcing polymer rebar” , or “GFRP rebar”) . However, it is apparent that the reinforcing fibers can also be different from glass fibers, such as, for example, carbon fibers, basalt fibers, aramid fibers, and / or combinations thereof.

[0041] The elongated body 2 of the structural element 1 can be made with a profiled element made of resin andreinforcing fibers, which is arranged, in the cross section, around the fiber optic sensor. Preferably, the fiber optic sensor extends along a barycentric axis of the elongated body 2. Therefore, in a given cross section of the sensorized fiber-reinforced structural element 1, the fiber optic sensor 3 is located at the section barycenter and is surrounded by the fi ber- rei nforced resin (matrix) .

[0042] The fiber-reinforced composite material can be formed from glass fibers (and / or carbon fibers, and / or basalt fibers, and / or aramid fibers) impregnated in a polymer resin (matrix) and arranged therein.

[0043] The at least one excess segment 31, 32 of the fiber optic sensor 3 can be housed inside a data connector 4, 5 thereof, in accordance with an embodiment, the structural element 1 comprises at least one data connector 4, 5 , mounted at said at least one end 21, 22 of said two ends of the elongated body 2, said at least one data connector housing said at least one excess segment 31, 32 of the fiber optic sensor 3. in accordance with an embodiment, the at least one data connector 4, 5 comprises a box-shaped body mounted at the respective end 21, 22 of the elongated body, and the respective excess segment is housed inside the box-shaped body of connector 4, 5 to expose an operating portion thereof from the connector.

[0044] in accordance with an embodiment, a sensorized fiber-reinforced structural element 1 comprises two opposite connectors 4, 5, each housing a respective excess segment 31, 32 of the fiber optic sensor 3.

[0045] The two opposite connectors 4, 5 can be compatiblewith each other, i .e. , can be adapted to form a data connection, and for example, said two opposite connectors comprise a female connector and a male connector configured to form a data connection.

[0046] Therefore, in accordance with a general embodiment, there is provided a modular assembly comprising a plurality of modular units Ml, M2 each comprising a sensorized fiber-reinforced structural element 1, according to any one of the embodiments described above, where the modular units Ml, M2 are adapted to be connected together, for example by respective connectors 4, 5.

[0047] in particular, the at least one connector 5 of the sensorized fiber-reinforced structural element of one modular unit Ml is functionally connected to a respective connector 4 of a sensorized fiber- reinforced structural element of an adjacent modular unit M2. The functional connection ensures continuity between the fiber-optic sensors 3.

[0048] The sensorized fiber-reinforced structural element 1, or profile, can be employed for consolidating, stabilizing and reinforcing the ground.

[0049] in accordance with a general embodiment, there is provided a rebar 10 for structural reinforcement, adapted to reinforce concrete. Said rebar 10 consists of a grating of reinforcing bars comprising at least one sensorized fiber-reinforced structural element 1, according to any one of the embodiments described above, as shown in Figure 1, for example, in addition to the sensorized fiber-reinforced structural element 1, the reinforcing bars can comprise rods and / orbrackets .

[0050] Rebar 10 can comprise a modular assembly, as well as form a modular unit itself.

[0051] For example, the reinforcing bar grating of rebar 10 can comprise a plurality of metal (steel) reinforcing bars and at least one sensorized fiber-reinforced structural element 1.

[0052] By vi rtue of the suggested solutions, a reinforced concrete block can be manufactured, having an exposed data connector 4, 5 from the outset.

[0053] A method for manufacturing a sensorized fiber- reinforced structural element 1 according to any one of the embodiments described above will be described bel ow.

[0054] The method comprises the steps of continuously pulling reinforcing fibers through an unheated mold 15 , and continuously pulling a fiber optic sensor 3 into the section of the unheated mold 15. in particular, the term “unheated” means that no means for heating the mold 15 are provided, although said mold does not necessarily have to always be at ambient temperature, in accordance with a preferred embodiment, the unheated mold 15 consists of an unheated hollow cylinder, such as, for example, an unheated extruder cylinder or the like.

[0055] in accordance with another embodiment, an unheated mold is provided.

[0056] The method comprises, prior to the step of continuously pulling the reinforcing fibers, the step of impregnating the reinforcing fibers with a resin so that the excess portions 31, 32 of the fiber-reinforced structural element are made by temporarily interrupting the impregnation of the reinforcing fibers with resin, without interrupting the steps of continuously pulling.

[0057] it is thus possible to obtain excess portions 31, 32 of the fiber optic sensor 3 by continuously pulling both the fiber optic sensor and the reinforcing fibers, interrupting the impregnation of the reinforcing fibers with resin. Therefore, there is obtained a segment where the reinforcing fibers are bare, i .e. , without the matrix that gives the fiber- reinforced structural element its structural strength . The method preferably comprises the step of compacting the profile exiting the unheated mold 15 by means of a compacting wi re wound around it. it is thus possible to tighten the fiber-reinforced resin body (profile) being cured with the compacting wi re.

[0058] The method then comprises the step of heating the resin profile in a heating station.

[0059] The method is carried out by a pultrusion apparatus 11, where a mold 15 of the unheated type is provided, which is arranged upstream of a heating station 17 (e.g. , comprising a plurality of furnaces) .

[0060] in particular, the pultrusion apparatus 11 comprises an impregnation tank 13 comprising resin, which can be arranged downstream of one or more creels 12 in which the reinforcing fibers are wound (e.g. , glass fibers, carbon fibers, basalt fibers, aramid fibers) . The resin impregnates the reinforcing fibers in the impregnation tank 13.

[0061] The unheated mold 15 is provided downstream of theimpregnation tank 13, and a lead-in device 14, or jig 14, is provided between the impregnation tank 13 and the unheated mold 15, which serves to place the optical fiber 3 at the desi red position inside the section of the pultruded profile without requi ring the optical fiber 3 to pass through the impregnation tank 13. in other words, the optical fiber 3 is arranged in a central position (e.g. , a barycentric position) in the section of the profile to be pultruded by vi rtue of the provision of a lead-in jig 14 arranged upstream of the unheated mold 15.

[0062] A winding system 16 for compacting the profile, such as a rotating spool or reel with a compacting wi re wound thereon, is provided downstream of the unheated mold 15. By winding the compacting wi re in a helical spi ral onto the pultruded profile, which is still soft, i .e. , deformable, it is possible to give the pultruded profile the desi red shape.

[0063] A heating station 17, such as, for example, a plurality of furnaces, for catalyzing the resin is provided downstream of the winding system 16.

[0064] Furthermore, the pulling device 18 is arranged downstream of the heating station 17.

[0065] Therefore, in accordance with a general embodiment, a pultrusion apparatus 11 comprises an impregnation tank 13 for impregnating reinforcing fibers with resin, and a heating station 17, and a pultrusion pulling device 18.

[0066] The pultrusion apparatus 11 further comprises, between the impregnation tank 13 and the heating station 17, a lead-in jig 14 and a mold 15 of the unheated type .in particular, the lead-in jig 14 is arranged upstream of mold 15 and is configured to arrange a fiber optic sensor 3 inside the section defined by the mold, avoiding the optical fiber from passing through the impregnation tank 13.

[0067] Therefore, it is possible to feed the reinforcing fibers and the fiber optic sensor to the mold 15 continuously, but separately.

[0068] By vi rtue of the features described above, provided in mutual combination or not in particular embodiments, it is possible to meet the aforementioned needs, thus achieving the aforementioned advantages, and in parti cular:

[0069] - the optical fiber is inserted during the process of producing the fi ber- rei nforced structural element, thus being an integral part thereof in a predeterminable position inside the cross section thereof;

[0070] - the excessive overheating of the optical fiber being produced is avoided;

[0071] - the impregnation of the optical fiber with resin in the excess parts 31 and 32 is simultaneously avoided; - it is possible to create a network of bars using the connectors ;

[0072] - it is possible to manufacture a sensorized fiber-reinforced structural element adapted to operate in corrosive and / or cold envi ronments;

[0073] - unprecedented ease and speed of on-site installation is achieved, which allows significantly reducing the infrastructure construction time and costs;

[0074] replacing known steel reinforcing bars isfacil itated, without complicating the on-site installation thereof, which indeed does not involve different processing and / or preparation operations from those of a conventional steel bar;

[0075] - it is possible to obtain improved reinforcing bars as well as reinforcing rebars;

[0076] - it is possible to manufacture a series of fiber- reinforced structural elements or bars or profiles conti nuously ;

[0077] - it allows a clean and non-impregnated segment of fiber optic sensor to exit from the ends of the fiber- reinforced structural element (from the bar) ;

[0078] - in particular, the optical fiber, from the storage point thereof to the entry into the catalysis zone, follows a path isolated from the reinforcing fibers so as not to become impregnated or damaged, and it joins the glass fibers only at the point immediately near the heating zone, positioning itself at the barycenter, being pul led by the glass fibers;

[0079] - the heated die of the known pultrusion apparatuses is replaced by furnaces that apply heat without contact, allowing the use of lower temperatures than the fiber damaging temperature and brief stoppages without compromising the production process;

[0080] the pultrusion manufacturing of the invention includes a targeted and ci rcumscribed interruption of fiber impregnation, for a length equal to or greater than twice the fiber requi red for the connection with connectors or monitoring systems , and at a repetition interval equal to the length of the desi red bar or profile (fiber-reinforced structural element) ;- the manufactured bar or profile (fiber-reinforced structural element) has, on both sides, the clean optical fiber not impregnated with resin or connectors that are embedded or not in the elongated body, thus allowing the connection with other bars or the monitoring system.

[0081] The present finding has been described according to preferred embodiments, but equivalent variants can be devised without departing from the scope of protection granted.

[0082] LIST OF REFERENCE SIGNS

[0083] 1 Sensorized fiber-reinforced structural element

[0084] 2 Elongated body

[0085] 3 Fiber optic sensor

[0086] 4 Data connector

[0087] 5 Data connector

[0088] 10 Rebar

[0089] 11 Apparatus

[0090] 12 Creel

[0091] 13 impregnation tank

[0092] 14 Lead-in jig

[0093] 15 unheated mold

[0094] 16 winding system

[0095] 17 Heating station

[0096]

[0097] 18 Pulling device

[0098] 21 End of the elongated body

[0099] 22 End of the elongated body

[0100] 31 Excess segment of the fiber optic sensor 32 Excess segment of the fiber optic sensor L Longitudinal di rection

[0101] Ml Modular unit

[0102] M2 Modular unit

[0103]

Claims

CLAIMS:

1. A sensorized fiber-reinforced structural element (1) comprising:- an elongated body (2) made of a fiber-reinforced composite material extending along a longitudinal di rection (L) , and- a longitudinally extending fiber optic sensor (3) arranged inside the elongated body (2) in di rect and intimate contact with the fiber-reinforced composite material ;wherei n :- the elongated body (2) made of a fiber- reinforced composite material comprises two opposite ends (21, 22) thereof,- the fiber optic sensor (3) comprises at least one excess segment (31, 32) thereof extending, in the longitudinal di rection (L) , beyond at least one end (21, 22) of said two ends of the elongated body (2) made of a fiber-reinforced composite material .

2. The sensorized fiber-reinforced structural element according to claim 1 , wherein said at least one excess segment (31, 32) of the fiber optic sensor is free from the fiber-reinforced composite material and is not impregnated with resin.

3. The sensorized fiber-reinforced structural element according to claim 1 or 2, wherein the fiber optic sensor (3) extends along the barycentric axis of the elongated body (2) made of a fiber-reinforced composite material .

4. The fi ber- rei nforced structural element according to claim 1 , 2 or 3, comprising at least onedata connector (4, 5) mounted on said at least one end (21, 22) of said two ends of the elongated body, which receives said at least one excess segment (31, 32) of the fiber optic sensor (3) .

5. A reinforced concrete block comprising at least one sensorized fiber-reinforced structural element (1) according to claim 4, wherein said at least one data connector (4, 5) is exposed outside the block.

6. A modular assembly comprising a plural ity of modular units (Ml, M2) , each comprising a sensorized fiber-reinforced structural element (1) according to claim 4, wherein:- the modular units (Ml, M2) are adapted to be connected together;- the at least one connector (4) of the sensorized fiber-reinforced structural element of one modular unit (Ml) is connected to a respective connector (5) of the sensorized fiber-reinforced structural element of another modular unit (M2) .

7. A rebar (10) for structural reinforcement, adapted to reinforce concrete , consisting of a reinforcing bar grating comprising at least one sensorized fiber-reinforced structural element (1) according to any one of claims 1 to 4.

8. A method for manufacturing a fiber-reinforced structural element (1) according to any one of claims 1 to 4 by pultrusion, comprising the steps of:- continuously pulling reinforcing fibers through an unheated mold (15) ;- continuously pulling a fiber optic sensor (3) into the section of the unheated mold (15) ;wherei nthe method comprises, prior to the step of continuously pulling the reinforcing fibers, the step of impregnating the reinforcing fibers with a resin; and whereinthe excess portions (31, 32) of the fiber-reinforced structural element (1) are made by temporarily interrupting the impregnation of the reinforcing fibers with resin, without interrupting the steps of continuously pulling.

9. The method according to claim 8, further comprising the step of compacting the profile exiting the mold (15) with a compacting wi re wound around it.

10. A pultrusion apparatus (11) comprising:an impregnation tank (13) for impregnating reinforcing fibers with a resin;- a heating station (17) ;- a pultrusion pulling device (18) ;wherein the pultrusion apparatus (11) further comprises, between the impregnation tank (13) and the heating station (17) :- a lead-in jig (14) , and- a mold (15) of the unheated type;wherei nthe lead-in jig (14) is arranged upstream of the mold (15) and is configured to arrange a fiber optic sensor inside the section defined by the mold, avoiding the fiber optic from passing through the impregnation tank (13) .

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