A relay-type large strain monitoring steel strand and its manufacturing and application methods

Abstract

This invention discloses a relay-type large strain monitoring steel strand and its manufacturing and usage methods. It is applicable to large strain monitoring of various types of steel strand components in civil engineering. By embedding corresponding fiber optic strain sensing fibers in grooves corresponding to the relaxed and tensioned states of irregularly shaped steel wires, applying adhesive and wrapping with a sheath for fixation, and then twisting them with edge wires to form a steel strand, it is possible to achieve quasi-distributed dense monitoring of large strain along the entire length of the strand itself. The strain monitoring range at each point is up to 8000με, which solves the problem of difficult monitoring of large strain along the prestressed steel strand in concrete structures. In addition, the segmented relay-type large strain monitoring steel strand structure based on weak grating sensing has its own fiber optic lead, which is convenient and quick to use and easy to promote and apply.

Description

Technical Field

[0001] This invention relates to the field of bridge health monitoring technology. More specifically, this invention relates to a relay-type high-strain monitoring steel strand and its manufacturing and usage methods. Background Technology

[0002] Long-term, reliable, and accurate monitoring of the effective stress along the friction length of prestressed steel strands can minimize structural safety issues caused by prestressing problems. As a concealed component, the prestressed steel strand is susceptible to stress reduction and uneven distribution due to a combination of factors, including material properties, pipe friction, inflection points, and uneven grouting. In practical engineering, it is difficult to effectively measure the stress distribution and changes along the friction length using conventional monitoring methods. Furthermore, the design stress level of prestressed steel strands is very high, generally around 1400 MPa. Taking a low-relaxation high-strength steel strand with a standard tensile strength of 1860 MPa and a diameter of 15.2 mm as an example, the corresponding strain can reach over 7000 με. This places high demands on the performance of monitoring elements. When the fiber optic grating is constantly under high tensile strain, even if it does not exceed its tensile strength, there is a risk of static fatigue fracture. Summary of the Invention

[0003] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0004] Another objective of this invention is to provide a relay-type large strain monitoring steel strand and its manufacturing and usage methods, so as to solve the technical problem of difficulty in monitoring large strain along the path of prestressed steel strands in concrete structures in the prior art.

[0005] To achieve these objectives and other advantages according to the present invention, in one aspect, the present invention provides a relay-type large strain monitoring steel strand, which is formed by stranding a central wire and multiple side wires. The central wire includes a shaped steel wire, and the shaped steel wire has a groove formed inward on its outer side wall. The groove is parallel to the central axis of the shaped steel wire and is of the same length as the shaped steel wire. The grooves are symmetrically distributed on the shaped steel wire. Fiber Bragg grating strain sensing fiber A and fiber Bragg grating strain sensing fiber B are respectively fixed in the grooves on both sides. The fiber Bragg grating strain sensing fiber A is in the same relaxed state as the shaped steel wire, while the fiber Bragg grating strain sensing fiber B is in a compressed state. The outer side of the shaped steel wire is covered with a sheath.

[0006] Preferably, the steel strand is segmented, and for each segment of the steel strand, fiber optic strain sensing fiber A is connected to fiber optic lead a at both ends, and fiber optic strain sensing fiber B is connected to fiber optic lead b at both ends. Fiber optic lead a and fiber optic lead b on the same side are fitted with a transition protective tube at the end that exits the groove, and the transition protective tube is anchored to the corresponding end of the steel strand.

[0007] Preferably, the hinge pitch between the center wire and the edge wire is 12 to 16 times the nominal diameter of the steel strand.

[0008] Preferably, the gratings on the fiber grating strain sensing fiber A and the fiber grating strain sensing fiber B are arranged at equal intervals, and the reflectivity of each grating is the same and less than or equal to 1%.

[0009] Preferably, the diameter of the edge wire is not greater than the diameter of the center wire.

[0010] On the other hand, the present invention provides a method for manufacturing a steel strand for relay-type large strain monitoring, comprising the following steps:

[0011] S1. Fabricate the irregularly shaped steel wire and symmetrically open the grooves on the irregularly shaped steel wire;

[0012] S2. Fix the irregular steel wire to ensure that the tension force on the irregular steel wire does not exceed 1000N, and one of the grooves is located at the top;

[0013] S3. The fiber optic strain sensing fiber A is fixedly embedded in the groove at the top;

[0014] S4. Rotate the irregular steel wire, place another groove on top, then apply tension to the irregular steel wire, maintain tension, and fix the fiber optic strain sensing fiber B into the corresponding groove.

[0015] S5. The sheath is wrapped around the shaped steel wire to ensure the stable connection of the fiber grating strain sensing fiber A and the fiber grating strain sensing fiber B, thus obtaining the center wire. Then the tension is released and the center wire is removed.

[0016] S6. The multiple edge wires are bent with the center wire of step S5 to form the steel strand;

[0017] S7. Connect the optical fiber lead a to the corresponding fiber optic strain sensing fiber A at both ends of each section of the steel strand, connect the optical fiber lead b to the corresponding fiber optic strain sensing fiber B, and install the transition protective sleeve to obtain the relay-type large strain monitoring steel strand.

[0018] Preferably, when fixing and installing the fiber Bragg grating strain sensing fiber A and the fiber Bragg grating strain sensing fiber B, adhesive is applied sequentially to the fiber Bragg grating strain sensing fiber A and the fiber Bragg grating strain sensing fiber B, with both ends of each grating located within the 0-5cm length range of the fiber, and the grating positions are not coated.

[0019] Preferably, in step S4, the applied tension force is 30% to 50% of the design load of the steel strand.

[0020] The present invention also provides a method for using a relay-type large strain monitoring steel strand. Before use, the steel strand is connected to an external demodulation device via an optical fiber lead. Then, a tension is applied to the entire steel strand. Under these conditions, the fiber grating strain sensing fiber A is used for strain monitoring in the first half of the range of 0 to 4000 με, and the fiber grating strain sensing fiber B is used for strain monitoring in the second half of the range of 4000 to 8000 με, thus forming a strain monitoring range of 0 to 8000 με.

[0021] The present invention has at least the following beneficial effects:

[0022] (1) The segmented relay type large strain monitoring steel strand structure of the present invention is based on weak grating sensing and can be applied to large strain monitoring of various types of steel strand components in civil engineering. By embedding the corresponding fiber optic strain sensing fiber in the corresponding grooves of the irregular steel wire in the relaxed and tensile states, applying glue and wrapping the sheath for fixation, and then forming the steel strand with the edge wire, it can realize quasi-distributed large strain monitoring along its entire length, which solves the problem of difficult monitoring of large strain along the prestressed steel strand in concrete structures.

[0023] (2) The segmented relay type large strain monitoring steel strand structure based on weak grating sensing of the present invention has built-in optical fiber leads, which facilitates quick connection with demodulation equipment, is convenient and quick to use, and is easy to promote and apply.

[0024] (3) When the relay-type large strain monitoring steel strand of the present invention is used, the fiber optic strain sensing fiber itself is not subjected to excessive strain, which improves the durability of the fiber optic strain sensing fiber. As the prestress in the steel strand changes, the strain can be continuously monitored by the fiber optic strain sensing fiber A and the fiber optic strain sensing fiber B in sequence, which can effectively measure the stress distribution and change along the steel strand.

[0025] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0026] Figure 1 This is a front view structural diagram of a section of the relay-type large strain monitoring steel strand of the present invention;

[0027] Figure 2 This is a side view of the steel strand for relay-type large strain monitoring according to the present invention.

[0028] Figure 3 This is a side view of the central filament of the present invention;

[0029] Figure 4 This is a flowchart illustrating a method for manufacturing a relay-type large strain monitoring steel strand according to an embodiment of the present invention.

[0030] The following are the reference numerals in the instruction manual: 1. Steel strand, 2. Center wire, 3. Edge wire, 4. Shaped steel wire, 5. Groove, 6. Fiber Bragg grating strain sensing fiber A, 7. Fiber Bragg grating strain sensing fiber B, 8. Adhesive, 9. Sheath, 10. Transition protection tube, 11. Fiber optic lead a, 12. Fiber optic lead b. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0032] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0033] like Figure 1-3 As shown, the present invention provides a relay-type large strain monitoring steel strand, which is formed by stranding a central wire 2 and multiple side wires 3. The central wire 2 includes a shaped steel wire 4, and the shaped steel wire 4 has a groove 5 formed inward on its outer side wall. The groove 5 is parallel to the central axis of the shaped steel wire 4 and is of the same length as the shaped steel wire 4. The grooves 5 are symmetrically distributed on the shaped steel wire 4. Fiber grating strain sensing fiber A6 and fiber grating strain sensing fiber B7 are respectively fixed in the grooves 5 on both sides. The fiber grating strain sensing fiber A6 is in the same relaxed state as the shaped steel wire 4, and the fiber grating strain sensing fiber B7 is in a compressed state. The outer side of the shaped steel wire 4 is covered with a sheath 9.

[0034] The steel strand 1 is made of a central wire 2 encapsulated with two fiber Bragg grating strain sensing fibers and an edge wire 3 wound around the central wire 2. The two grooves 5 of the shaped steel wire 4 are arranged along the axial length of the steel wire surface. The inflection points of the grooves 5 are rounded. The cross-sectional dimensions of the grooves 5 should be larger than the outer diameters of the fiber Bragg grating strain sensing fibers A6 and B7. The fiber Bragg grating strain sensing fibers A6 and B7 are fixed in parallel and of equal length in one of the grooves 5, and then covered with a sheath 9 to ensure that the fiber Bragg grating strain sensing fibers do not fall out of the grooves 5.

[0035] When setting up fiber Bragg grating strain sensing fiber A6 and fiber Bragg grating strain sensing fiber B7, firstly, in a naturally relaxed state, fiber Bragg grating strain sensing fiber A6 is installed and fixed, which is equivalent to the same tension state as the shaped steel wire 4. Then, the shaped steel wire 4 is tensioned within the fiber's bearing capacity, and the fiber Bragg grating strain sensing fiber A6 in the groove 5 undergoes tension deformation. Then, fiber Bragg grating strain sensing fiber B7 is installed and fixed. After the tension is released, the shaped steel wire 4 and fiber Bragg grating strain sensing fiber A6 return to their initial relaxed state, while the fiber Bragg grating strain sensing fiber B7 is compressed under the fixing and retraction action of the shaped steel wire 4.

[0036] Therefore, fiber optic strain sensing fiber A6 and fiber optic strain sensing fiber B7 achieve relay-style expansion of strain range due to the different continuity states of the synchronous steel strand 1. When the steel strand 1 experiences the first stage of strain, it is monitored by fiber optic strain sensing fiber A6, while fiber optic strain sensing fiber B7 gradually reduces its contraction. When the steel strand 1 experiences the second stage of strain and reaches the upper limit of the monitoring range of fiber optic strain sensing fiber A6, strain monitoring continues through fiber optic strain sensing fiber B7. The combination of fiber optic strain sensing fibers A6 and B7 in different installation states enables quasi-distributed large strain monitoring along its entire length, with a strain monitoring range of up to 8000με, solving the problem of difficult monitoring of large strain along the prestressed steel strand 1 within the concrete structure.

[0037] In another technical solution, such as Figure 1 As shown, the steel strand 1 is segmented. For each segment of the steel strand 1, the two ends of the fiber optic strain sensing fiber A 6 are respectively connected to fiber optic lead a 11, and the two ends of the fiber optic strain sensing fiber B 7 are respectively connected to fiber optic lead b 12. The fiber optic lead a 11 and fiber optic lead b 12 located on the same side are fitted with a transition protection tube 10 at the end that passes through the groove 5. The transition protection tube 10 is anchored to the corresponding end of the steel strand 1.

[0038] By setting up corresponding optical fiber leads, it is easy to connect with external demodulation equipment to complete the output of optical fiber signals. The transition protection tube 10 is set and anchored at both ends of the steel strand 1 to ensure that the optical fiber inside the irregular steel wire 4 is not damaged at the end.

[0039] In another technical solution, such as Figure 1 As shown, the hinge pitch between the center wire 2 and the edge wire 3 is 12 to 16 times the nominal diameter of the steel strand 1.

[0040] In another technical solution, such as Figure 1-3 As shown, the gratings on the fiber optic strain sensing fiber A 6 and the fiber optic strain sensing fiber B 7 are arranged at equal intervals, and the reflectivity of each grating is the same and less than or equal to 1%.

[0041] In another technical solution, such as Figure 1-2 As shown, the diameter of the edge wire 3 is not greater than the diameter of the center wire 2. Generally, the ratio of the number of edge wires 3 to the number of center wires 2 is 6:1, and the six edge wires 3 are arranged symmetrically and closely attached to the center wire 2 in cross-section.

[0042] This invention also provides a method for manufacturing a relay-type large strain monitoring steel strand, combined with... Figure 1-4 As shown, it includes the following steps:

[0043] S1. Make the irregular steel wire 4, and symmetrically open the grooves 5 on the irregular steel wire 4; the grooves 5 can be drawn by a special mold or mechanically ground on a round steel wire.

[0044] S2. Fix the irregular steel wire 4 to ensure that the tension force on the irregular steel wire 4 does not exceed 1000N, and one of the grooves 5 is located at the top; fix it by a tensioning platform that facilitates the application of tension force to the steel strand 1.

[0045] S3. The fiber optic strain sensing fiber A6 is fixedly embedded in the groove 5 at the top; the fiber optic strain sensing fiber A6 is completely located in the groove 5 to ensure that the routing direction is good and it is fixed well, without overflowing the groove 5.

[0046] S4. Rotate the irregularly shaped steel wire 4, place the other groove 5 on top, then apply tension to the irregularly shaped steel wire 4, maintain the tension, and fix the fiber optic strain sensing fiber B 7 into the corresponding groove 5. That is, the irregularly shaped steel wire 4 is stretched to a certain force, and the fiber optic strain sensing fiber A 6 stretches and changes synchronously with the irregularly shaped steel wire 4.

[0047] S5. The sheath 9 is wrapped around the irregular steel wire 4 to ensure the stable connection of the fiber optic strain sensing fiber A6 and the fiber optic strain sensing fiber B7, thus obtaining the center wire 2. Then the tension is released and the center wire 2 is removed.

[0048] S6. The multiple edge wires 3 and the center wire 2 of step S5 are twisted to form the steel strand 1.

[0049] S7. Connect the optical fiber lead a 11 to the corresponding fiber optic strain sensing fiber A 6 at both ends of each section of the steel strand 1, connect the optical fiber lead b 12 to the corresponding fiber optic strain sensing fiber B 7, and install the transition protective sleeve 9 to obtain the relay-type large strain monitoring steel strand 1.

[0050] The segmented relay-type large strain monitoring steel strand structure based on weak grating sensing manufactured by this invention can be applied to large strain monitoring of various types of steel strand components in civil engineering. By embedding corresponding fiber optic strain sensing fibers in the corresponding grooves of the irregularly shaped steel wire in the relaxed and tensioned states, and fixing them with adhesive and sheath wrapping, and then forming the steel strand with the edge wire, quasi-distributed large strain monitoring can be achieved throughout its entire length. This solves the problem of difficult monitoring of large strain along the prestressed steel strand in concrete structures. In addition, the segmented relay-type large strain monitoring steel strand structure based on weak grating sensing has its own optical fiber lead, which is convenient and quick to use and easy to promote and apply.

[0051] In another technical solution, such as Figure 3 As shown, when fixing and installing the fiber Bragg grating strain sensing fiber A6 and the fiber Bragg grating strain sensing fiber B7, adhesive 8 is sequentially applied to each fiber Bragg grating within a 0-5cm length range at both ends of the fiber, leaving the grating areas uncoated. Epoxy resin is selected as the adhesive 8. After each application, wait for complete curing before proceeding to the next step. A sheath 9 is used to wrap around the surface of the shaped steel wire 4 to ensure that the uncoated fiber areas do not fall out of the groove 5 and be damaged.

[0052] In another technical solution, in step S4, the applied tension force is 30% to 50% of the design load of the steel strand. The tension force is set according to the maximum tensile and compressive force that the fiber optic strain sensing fiber can withstand. Combined with the measurement range of the fiber optic strain sensing fiber itself, the measurement range can be doubled. Of course, in principle, different tension forces can be set by adding grooves 5 and corresponding monitoring fibers to the irregular steel wire 4 according to the fiber optic strain sensing fiber. The method of this invention also provides research guidance for the subsequent increase of strain range.

[0053] The present invention also provides a method for using a relay-type large strain monitoring steel strand 1. Before use, the steel strand 1 is connected to an external demodulation device via an optical fiber lead. Then, a tension is applied to the entire steel strand 1. Under this condition, the fiber optic strain sensing fiber A 6 is used to perform strain monitoring in the first half with a range of 0 to 4000 με, and the fiber optic strain sensing fiber B 7 is used to perform strain monitoring in the second half with a range of 4000 to 8000 με, thus forming a strain monitoring range of 0 to 8000 με.

[0054] Specific combination Figure 1-4 As shown, the following is a specific embodiment of the manufacture and use of the segmented relay-type large strain monitoring steel strand based on weak grating sensing of the present invention, and the operation sequence is listed below:

[0055] (1) Manufacture a shaped steel wire with a nominal diameter of 5.2 mm and a groove width and depth of 1 mm.

[0056] (2) Fix the irregular steel wire horizontally on the base, ensuring that one of its grooves is at the top and the tension does not exceed 1000N.

[0057] (3) Arrange fiber optic strain sensing fibers A with a diameter of 250μm, reflectivity of 0.6‰, grating spacing of 1m and grating length of 2cm in parallel and equal length in the groove at the top of the irregular steel wire. Then, apply epoxy resin to the fiber optic strain sensing fibers A at both ends of each grating within a 5cm length of the fiber, without applying the resin to the grating position.

[0058] (4) After the epoxy resin has fully cured for 2 hours, rotate the shaped steel wire to place its lower groove on top. Then, apply a tension of 12000N to the platform. Then, arrange the fiber optic strain sensing fiber B with a diameter of 250μm, reflectivity of 0.6‰, grating spacing of 1m, and grating length of 2cm in parallel and equal length in the groove at the top of the shaped steel wire. Then, apply epoxy resin to the fiber optic strain sensing fiber B at both ends of each grating within a 5cm length of the fiber. Do not apply epoxy resin to the grating position.

[0059] (5) After the epoxy resin has fully cured for 2 hours, wrap the surface of the irregular steel wire with transparent tape to ensure that the uncoated optical fiber does not fall out of the groove. Then, release the tension and remove the irregular steel wire.

[0060] (6) The irregular steel wire and 6 edge wires with a diameter of 5mm are twisted into a steel strand with a pitch of 228mm, corresponding to a steel strand diameter of 15.2mm.

[0061] (7) Install fiber optic lead transition protection tube, fiber optic lead a and fiber optic lead b at both ends of the steel strand to form a segmented relay type large strain monitoring steel strand structure based on weak grating sensing.

[0062] (8) The segmented relay-type large strain monitoring steel strand structure based on weak grating sensing is connected to the demodulation equipment via optical fiber leads. A tensile force is applied to it; fiber optic strain sensing fiber A is used to measure the first half (0–4000 με), and fiber optic strain sensing fiber B is used to measure the second half (4000–8000 με), accumulating to 0–8000 με, thus realizing large strain monitoring of the steel strand structure.

[0063] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A manufacturing method of a relay type large strain monitoring strand, characterized by, The steel strand is made of a central wire and multiple side wires. The central wire includes a shaped steel wire. The shaped steel wire has a groove on its outer side wall. The groove is parallel to the central axis of the shaped steel wire and is the same length as the shaped steel wire. The grooves are symmetrically distributed on the shaped steel wire. Fiber grating strain sensing fiber A and fiber grating strain sensing fiber B are fixed in the grooves on both sides, respectively. Fiber grating strain sensing fiber A is in the same relaxed state as the shaped steel wire, while fiber grating strain sensing fiber B is in a compressed state. The shaped steel wire is covered with a sheath. The manufacturing method includes the following steps: S1. Fabricate the irregularly shaped steel wire and symmetrically open the grooves on the irregularly shaped steel wire; S2. Fix the irregular steel wire to ensure that the tension force on the irregular steel wire does not exceed 1000N, and one of the grooves is located at the top; S3. The fiber optic strain sensing fiber A is fixedly embedded in the groove at the top; S4. Rotate the shaped steel wire to place another groove on top, and then apply tension to the shaped steel wire. The applied tension is 30% to 50% of the design load of the steel strand. Maintain the tension and fix the fiber optic strain sensing fiber B into the corresponding groove. When fixing and installing the fiber optic strain sensing fiber A and the fiber optic strain sensing fiber B, use adhesive to sequentially coat the fiber optic strain sensing fiber A and the fiber optic strain sensing fiber B. The two ends of each grating are located within the 0 to 5 cm length of the fiber, and the grating position is not coated. S5. The sheath is wrapped around the shaped steel wire to ensure the stable connection of the fiber grating strain sensing fiber A and the fiber grating strain sensing fiber B, thus obtaining the center wire. Then the tension is released and the center wire is removed. S6. The multiple edge wires are hinged with the center wire from step S5 to form the steel strand; the hinge pitch between the center wire and the edge wire is 12 to 16 times the nominal diameter of the steel strand; the gratings on the fiber grating strain sensing fiber A and the fiber grating strain sensing fiber B are arranged at equal intervals, and the reflectivity of each grating is the same and less than or equal to 1%. S7. The steel strand is segmented. For each segment of the steel strand, fiber optic strain sensing fiber A is connected to fiber optic lead a at both ends, and fiber optic strain sensing fiber B is connected to fiber optic lead b at both ends. Fiber optic lead a and fiber optic lead b on the same side are fitted with a transition protection tube at the end that exits the groove. The transition protection tube is anchored to the corresponding end of the steel strand. At both ends of each segment of the steel strand, fiber optic lead a is connected to the corresponding fiber optic strain sensing fiber A, and fiber optic lead b is connected to the corresponding fiber optic strain sensing fiber B. The transition protection tube is then installed to obtain the relay-type large strain monitoring steel strand. Fiber optic strain sensing fiber A is used to measure the first half (0~4000με), and fiber optic strain sensing fiber B is used to measure the second half (4000-8000με), cumulatively achieving a strain range of 0-8000με.

2. The manufacturing method of the relay-type large strain monitoring steel strand according to claim 1, characterized by, The diameter of the edge wire is not greater than the diameter of the center wire.

3. A method for using the relay-type large strain monitoring steel strand obtained by the method for manufacturing the relay-type large strain monitoring steel strand according to claim 1, characterized by, Before use, the steel strand is connected to the external demodulation device via an optical fiber lead. Then, tension is applied to the entire steel strand. Under these conditions, the fiber optic strain sensing fiber A is used to monitor the strain in the first half of the range of 0~4000με, and the fiber optic strain sensing fiber B is used to monitor the strain in the second half of the range of 4000~8000με, thus forming a strain monitoring range of 0~8000με.

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