Device for testing tensile strength of bent section of FRP (Fiber Reinforce Plastic) stirrup

Abstract

The utility model provides a device for testing the tensile strength of a bent section of an FRP (Fiber Reinforce Plastic) stirrup. The device comprises a test piece, a loading mechanism and a tensile testing machine, the test piece comprises a bonding body composed of a concrete test block, a partition plate, FRP stirrups, longitudinal steel bars, an anti-cracking mechanism and a force transmission mechanism. Wherein the partition plate is arranged between the two concrete test blocks; the FRP stirrup is fixed in the center of the first direction of the concrete test block through the partition plate; the force transmission mechanisms are symmetrically arranged on the two concrete test blocks; the loading mechanism comprises a clamping plate, a distribution plate and a force transmission plate, and is movably connected with the force transmission mechanism through a connecting piece, so that the two concrete test blocks are automatically centered. The whole device is small in size, wide in application range and low in requirement for test equipment, and automatic centering of the concrete test block in the loading process is achieved; the overall structure is simple, manufacturing is easy, cost is low, the force transmission path is scientific and reasonable, and the testing result is real and accurate.

Description

Technical Field

[0001] The utility model belongs to the technical field of building material testing, and particularly relates to a device for testing the tensile strength of the bending section of an FRP stirrup. Background Technique

[0002] As an excellent building material, steel bars are widely used in modern engineering structures. However, in recent years, the corrosion and deterioration problems of steel bars in reinforced concrete structures and steel structures have become increasingly serious, among which steel bar corrosion is the most common. Steel bar corrosion has seriously affected the bearing capacity and service performance of structures, not only reducing the service life of structures, but also causing a large number of safety and accident hazards. At the same time, the maintenance and reinforcement costs brought about are also quite expensive.

[0003] In recent years, a fiber reinforced polymer (FRP) bar has been increasingly widely used in buildings, bridges, underground projects, marine projects, tunnels and civil engineering with special requirements. FRP bars have the advantages of high tensile strength, high corrosion resistance, good durability, light weight, good electromagnetic insulation, good designability, and a thermal expansion coefficient close to that of concrete. Using FRP bars to replace steel bars and jointly form an FRP bar concrete structure with concrete can fundamentally solve the corrosion problem of traditional reinforced concrete structures and effectively extend the service life of structures.

[0004] There are great differences between FRP bars and steel bars in terms of material properties. Due to the anisotropy of FRP materials and the fiber curling in the bending section of FRP as stirrups caused by the production process, the bending section of FRP as stirrups is its inherent weak point. Research shows that the tensile strength of its bending section is only about 30%-60% of its straight section. Therefore, the strength of the bending section of FRP stirrups determines the strength of FRP bars, and it is necessary to clarify the tensile strength of its bending section through testing for engineering applications. In addition, FRP bars are prefabricated in factories and cannot be cold-bent on construction sites like steel bars. Therefore, the mechanical property testing device for FRP bars needs to adapt to their geometric dimensions.

[0005] Currently, the commonly used method for testing the strength of the bending section of FRP stirrups usually involves pouring the bending section of the FRP bar into two separate concrete blocks, and setting a jack between the two blocks to apply a load to cause the bending section of the FRP stirrup to be tensioned and fractured. This method has the following limitations:

[0006] (1) It is not applicable to small-sized FRP stirrups. In this method, the two concrete blocks need to have a certain thickness, and there also needs to be enough space between the blocks to accommodate the jack and the force sensor;

[0007] (2) The straight section of the stirrup is exposed outside the concrete block and is easily interfered by external factors;

[0008] (3) The operation is difficult. During the test, the positions of the force sensor and the jack need to be repeatedly adjusted to prevent load eccentricity. Content of the Utility Model

[0009] To solve the above technical problems, the present utility model provides a device and a method for testing the tensile strength of the bent section of an FRP stirrup. The overall device is small in size and can be applicable to the strength testing of the bent sections of FRP stirrups with various different sizes and specifications. It realizes the automatic centering of the concrete test block during the loading process, ensures the test accuracy, and improves the test efficiency; the overall structure is simple, easy to manufacture, low in cost, the force transmission path is scientific and reasonable, and the test results are true and accurate.

[0010] The technical solution adopted by the present utility model is as follows:

[0011] A device for testing the tensile strength of the bent section of an FRP stirrup, comprising a test piece, a loading mechanism, and a tensile testing machine;

[0012] The test piece includes a bonded body composed of a concrete test block, a partition board, an FRP stirrup, and a force transmission mechanism;

[0013] The partition board is arranged between the two concrete test blocks for separating the concrete test blocks and fixing the FRP stirrup in the middle of the concrete test blocks;

[0014] The force transmission mechanism is symmetrically arranged on the two concrete test blocks and is perpendicular to the FRP stirrup;

[0015] The loading mechanism is respectively connected to the force transmission mechanism and is connected to the tensile testing machine;

[0016] The loading mechanism is movably connected to the force transmission mechanism so that the two concrete test blocks are automatically centered.

[0017] Further, the positioning plate is provided with a positioning groove, and the FRP stirrup passes through the positioning groove so that the annular structure formed by enclosing the FRP stirrup is located at the center of the first direction of the concrete test block.

[0018] Further, the force transmission mechanism has a through hole arranged along the first direction, which is aligned with the center line of the concrete test block along the second direction and is located inside the annular structure.

[0019] Furthermore, the loading mechanism includes a clamping plate, a distribution plate, and a force transmission plate. The force transmission plate is vertically arranged on one side of the distribution plate. The force transmission plate is respectively parallel to the two end faces of the concrete test block arranged oppositely along the first direction, and is connected to the force transmission mechanism through a connecting piece passing through the through hole; the other side of the distribution plate is connected to the clamping plate, and the clamping plate is connected to the tensile testing machine; the force transmission plate is symmetrically arranged relative to the clamping plate.

[0020] Furthermore, the radius of the through hole is greater than the cross-sectional radius of the connecting piece.

[0021] Furthermore, a non-bonding mechanism is also arranged on one of the concrete test blocks. The non-bonding mechanism covers the straight section of the FRP stirrup and extends from the partition plate to the bending section of the FRP stirrup.

[0022] Furthermore, the concrete test block with the non-bonding mechanism is also provided with longitudinal steel bars, and the longitudinal steel bars are arranged inside the bending section along the first direction.

[0023] Furthermore, an anti-cracking mechanism is also included, which is arranged between the force transmission mechanism and the annular structure and is used to prevent the concrete test block from cracking.

[0024] Furthermore, the connecting piece is fixed to the force transmission plate through a nut.

[0025] The advantages and positive effects of the present utility model are:

[0026] (1) The force transmission mechanism and the FRP stirrups are all pre-embedded in the concrete test block. The overall device has a small volume, can be applicable to the strength tests of the bending sections of FRP stirrups with various different size specifications, has a wider application range, and has lower requirements for test equipment;

[0027] (2) The concrete test block is movably connected to the force transmission mechanism through the connecting piece, realizing automatic centering of the concrete test block during the loading process, ensuring uniform stress on the FRP stirrups in the two concrete test blocks, eliminating the work of repeatedly adjusting the experimental device for centering before the test in the prior art, ensuring the test accuracy, and improving the test efficiency;

[0028] (3) Compared with the prior art, the FRP stirrups are completely buried in the concrete test block, avoiding the influence of external factors and being beneficial to improving the accuracy of the test results;

[0029] (4) Arranging longitudinal steel bars more realistically simulates the actual stress state of the FRP stirrups in concrete members. By adding lateral constraints to the concrete test piece through the anti-cracking mechanism, it avoids the cracking and breaking of the concrete, making the test results more real and accurate;

[0030] (5) The overall structure of the device is simple, easy to manufacture, low in cost, with a scientific and reasonable force transmission path, and the test results are true and accurate, making it suitable for popularization and use. Description of the Drawings

[0031] Figure 1 is an assembly schematic diagram of a specific implementation of the present utility model;

[0032] Figure 2 is a front view of a specific embodiment of the present utility model;

[0033] Figure 3 is a front perspective view of a specific embodiment of the present utility model;

[0034] Figure 4 is a side perspective view of a specific embodiment of the present utility model;

[0035] Figure 5 is a schematic diagram of a positioning plate of a specific embodiment of the present utility model;

[0036] Figure 6 is a schematic diagram of another positioning plate structure of a specific embodiment of the present utility model;

[0037] Figure 7 is a schematic diagram of a loading mechanism of a specific embodiment of the present utility model;

[0038] Figure 8 is a schematic diagram of FRP fiber cloth of a specific embodiment of the present utility model;

[0039] Figure 9 is a schematic diagram of a confinement spiral stirrup of a specific embodiment of the present utility model.

[0040] In the figures:

[0041] 1, FRP stirrup; 2, partition plate; 21, positioning groove

[0042] 3, unbonded mechanism; 4, longitudinal reinforcement; 5, force transmission mechanism

[0043] 6, connecting piece; 7, nut; 8, loading mechanism

[0044] 81, clamping plate; 82, distribution plate; 83, force transmission plate

[0045] 9, concrete test block; 10, FRP fiber cloth; 11, confinement spiral stirrup Detailed Implementation Manner

[0046] The embodiments of the present utility model will be described below with reference to the accompanying drawings.

[0047] As Figure 1 、 Figure 2, Figure 3 , Figure 4 As shown in Figure 3 and Figure 4 , the present utility model proposes a tensile strength testing device for the bent section of FRP stirrups, which includes a test piece, a loading mechanism 8 and a tensile testing machine; the test piece includes a bonded body composed of a concrete test block 9, a partition plate 2, FRP stirrups 1 and a force transmission mechanism 5; wherein the partition plate 2 is arranged between two concrete test blocks 9 for separating the concrete test blocks 9 and fixing the FRP stirrups 1 in the middle of the concrete test blocks 9, and the partition plate 2 makes the two concrete test blocks 9 have the same size and shape; the FRP stirrups 1 are in a ring structure, divided into two symmetrical parts by the partition plate 2 and respectively embedded in the two concrete test blocks 9, and the FRP stirrups 1 in each concrete test block 9 include a straight section and a bent section; the force transmission mechanism 5 is symmetrically arranged in the two concrete test blocks 9 and is perpendicular to the FRP stirrups 1; the partition plate 2, the FRP stirrups 1 and the force transmission mechanism 5 are all embedded in the concrete during the pouring of the concrete test blocks 9 to form an integral body as the test piece; the loading mechanism 8 is respectively connected to the force transmission mechanism 5 and is connected to the tensile testing machine; at the same time, the loading mechanism 8 is movably connected to the force transmission mechanism 5, and during the loading process, the force transmission mechanism 5 drives the concrete test blocks 9 to move under the action of the applied load, so that the two concrete test blocks 9 are automatically centered, and finally the FRP stirrups 1 in the two concrete test blocks 9 are uniformly stressed during the test.

[0048] In this embodiment, the tensile testing machine transmits the tensile load to the loading mechanism 8, the loading mechanism 8 further transmits the tensile force to the force transmission mechanism 5, the force transmission mechanism 5 automatically transmits the load to the concrete between the force transmission structure and the FRP stirrups 1, and finally the concrete transmits the tensile load to the FRP stirrups 1. When the load of the tensile testing machine reaches a certain value, the bent section of the FRP stirrups 1 breaks, and this value is the tensile strength value of the bent section of the FRP stirrups 1. The force transmission path in this process is scientific and reasonable, with high accuracy, and can be applied to the strength testing of the bent sections of FRP stirrups 1 of various specifications and sizes, and has low requirements for the required test equipment.

[0049] As Figure 2 shown, in a specific embodiment, the test piece as a whole is in a cuboid structure, the partition plate 2 divides the test piece into upper and lower concrete test blocks 9, and the size of the partition plate 2 is constructed to be flush with the four end faces of the concrete test blocks 9; the concrete test blocks 9 have a first direction X, a second direction Y and a third direction Z that are perpendicular to each other; specifically, as Figure 5As shown, the partition plate 2 is provided with a positioning groove 21. The opening of the positioning groove 21 extends from one end of the positioning plate to the middle of the partition plate 2. The extending direction of the positioning groove 21 is the same as the first direction X of the concrete specimen. The FRP stirrup 1 passes through the positioning groove 21 and fits against one end of the positioning groove 21 away from the opening. By providing the positioning groove 21, the annular structure formed by enclosing the FRP stirrup 1 is located at the center of the concrete specimen 9 in the first direction X. That is to say, the distances between the FRP stirrup 1 and the two end faces of the concrete specimen 9 arranged oppositely along the first direction X are the same, so that the forces on both sides of the FRP stirrup 1 along the first direction are uniform. Since the FRP stirrup 1 is usually arranged at the center position of the structural member during actual use, the stress state of the FRP stirrup 1 during the test should be restored as much as possible to its actual use state.

[0050] Furthermore, the cross-sectional shape of the FRP stirrup can be circular or rectangular, and the FRP stirrup is in the form of a continuous and closed strip; as Figure 5 shown, in order to ensure that the FRP stirrup 1 is located at the center of the concrete specimen 9 in the first direction X, when the cross-sectional shape of the FRP stirrup 1 is rectangular, the extending length of the positioning groove 21 is half of the thickness of the concrete specimen 9 in the first direction X plus half of the cross-sectional width of the FRP stirrup 1. When the cross-sectional shape of the FRP stirrup is circular, the extending length of the positioning groove 21 is half of the thickness of the concrete specimen 9 in the first direction X plus the radius of the FRP stirrup 1; the positioning grooves 21 are symmetrically arranged at both ends of the partition plate 2, and the distance between the positioning grooves 21 is the same as the distance between the straight segments of the FRP stirrup 1; the straight segments of the FRP stirrup 1 pass through the positioning grooves 21 and fit against the positioning grooves 21, and the bent segments of the FRP stirrup 1 are arranged at one end of the concrete specimen 9 away from the partition plate 2.

[0051] In some other embodiments of the present application, the positioning groove 21 can be arranged in the middle of the partition plate 2, as Figure 6 shown, the positioning groove 21 extends along the third direction Z, and the annular structure formed by enclosing the FRP stirrup 1 vertically passes through the positioning groove 21, and the FRP stirrup 1 can also be fixed at the center of the concrete specimen 9 in the first direction X; the extending length of the positioning groove 21 is half of the difference between the length of the partition plate 2 in the second direction Y and the distance between the straight segments of the FRP stirrup 1, so that the straight segments of the FRP stirrup 1 respectively fit against the positioning groove 21.

[0052] In a specific embodiment, the force transmission mechanism 5 has a through hole arranged along the first direction X, which is aligned with the center line of the concrete test block 9 along the second direction Y and is located inside the annular structure formed by enclosing the FRP stirrup 1, so that the distances between the force transmission mechanism 5 and the two end faces of the concrete test block 9 arranged oppositely along the third direction Z are the same. The purpose of this design is to make the force transmission mechanism 5 have the same influence on the concrete on both sides along the third direction Z, ensure uniform stress on both sides of the concrete, and effectively transfer the load to the concrete between the force transmission mechanism 5 and the FRP stirrup 1.

[0053] In a specific embodiment, as Figure 1 , Figure 2 , Figure 7 shown, the loading mechanism 8 includes a clamping plate 81, a distribution plate 82 and a force transmission plate 83. The force transmission plates 83 are symmetrically arranged on one side of the distribution plate 82. The two force transmission plates 83 are parallel and are respectively located outside the two opposite end faces of the concrete test block 9. The force transmission plate 83 is connected to the force transmission mechanism 5 through a connecting piece 6 passing through the through hole; the other side of the distribution plate 82 is connected to the clamping plate 81, and the clamping plate 81 is connected to a tensile testing machine. The tensile load of the tensile testing machine is sequentially transmitted to the clamping plate 81, the distribution plate 82, the force transmission plate 83, the connecting piece 6 and the force transmission mechanism 5, and then transmitted to the concrete between the force transmission mechanism 5 and the FRP stirrup 1. During the force transmission process, the two concrete blocks are in the same stress state, and finally the bending section of the FRP stirrup 1 is subjected to tensile fracture.

[0054] During the test, it should be ensured that the two concrete test blocks 9 are in a centered state to avoid eccentric load during the force transmission process and affect the accuracy of the test results; in the prior art, it is necessary to repeatedly adjust the test device before the test to make it centered with the two concrete blocks; at the same time, the inventors of the present application found that even if the two concrete test blocks 9 are centered at the beginning of the test, due to the influence of the production of the test blocks and the test equipment, it is still difficult to avoid the mutual offset of the concrete test blocks 9 after loading. Therefore, the present application adopts that the connecting piece 6 is movably connected to the force transmission mechanism 5 to drive the concrete test block 9 to automatically center under the action of the tensile load. In a specific embodiment, the specific structure for realizing the automatic centering function is as follows:

[0055] The force transmission plates 83 are respectively located outside the opposite two end faces of the concrete test block 9. The force transmission mechanism 5 is designed in the shape of a through-hole. The connecting member 6 passes through the through-hole and is connected to the force transmission mechanism 5 at both ends. The two ends of the connecting member 6 are fixed to the force transmission plates 83 by nuts 7. At this time, the connecting member 6 and the force transmission plates 83 are connected as a whole. At the same time, the concrete test block 9 and the force transmission mechanism 5 are bonded into one body. The radius of the through-hole of the force transmission mechanism 5 is larger than the cross-sectional radius of the connecting member 6, so that the connecting member 6 can move within the through-hole. When the concrete test block 9 is not centered or shifted, the connecting member 6 moves in a direction away from each other under the action of the tensile force transmitted by the force transmission plates 83. That is to say, the connecting member 6 moves relative to the through-hole, and the moving direction is to move along the inner wall of the through-hole to the farthest distance between the two arcs of the through-hole and align with the midline of the second direction Y of the concrete test block 9. In fact, at this time, the connecting member 6 is restricted by the loading mechanism 8 and its relative position remains unchanged. Instead, the force transmission mechanism 5 drives the concrete test block 9 to move relative to the connecting member 6. When the two connecting members 6 are at the farthest distance from each other in the two through-holes, that is, when the connecting member 6 aligns with the midline of the second direction Y of the concrete test block 9, the relative movement stops, and at the same time, the concrete test block 9 realizes automatic centering. This method does not require centering before the test, but realizes automatic centering during the test. Compared with the method of manual adjustment for centering, it saves a lot of time and workload, which is beneficial to improving the accuracy and work efficiency of the test.

[0056] Preferably, the force transmission mechanism 5 is made of a steel casing, and the connecting member 6 is made of a high-strength bolt, so that it has sufficient stiffness and is easy to process and manufacture.

[0057] In a specific embodiment, such as Figure 1 、 Figure 3As shown, one of the concrete specimens 9 is also provided with a non-bonding mechanism 3. The non-bonding mechanism 3 covers the straight section of the FRP stirrup 1 and extends from the partition plate 2 to the bent section of the FRP stirrup 1. That is to say, the straight section of the FRP stirrup 1 in one of the concrete specimens 9 is provided with a non-bonding mechanism 3. The non-bonding mechanism separates the FRP stirrup 1 from the concrete, and there is a small frictional force between it and the FRP stirrup 1 to avoid the bonding force between the FRP stirrup 1 and the concrete from affecting the accuracy of the test structure. At the same time, in an ideal test environment, the two concrete specimens 9 and the force transmission mechanism 5, FRP stirrups 1 and loading mechanism 8 inside them are symmetrically arranged. When the tensile load reaches a certain value, the bent sections of the FRP stirrups 1 inside the two concrete specimens 9 should break simultaneously. However, in an actual test environment, usually the bent section of the FRP stirrup 1 in one of the concrete specimens 9 breaks first, and at this time the test ends, and the bent section of the FRP stirrup 1 in the other concrete specimen 9 has not broken yet. By setting a non-bonding mechanism 3 on the straight section of the FRP stirrup 1 inside one of the concrete specimens 9, it can be ensured that the bent section of the FRP stirrup 1 on this side breaks first, the position where the FRP stirrup 1 breaks can be controlled, and the tensile strength of the bent section of the FRP stirrup 1 can be truly reflected.

[0058] Preferably, the non-bonding mechanism 3 can adopt a non-bonding sleeve or be coated with a plastic film after applying lubricating oil on the surface of the straight section of the FRP stirrup 1.

[0059] In a specific embodiment, as Figure 3 、 Figure 4 shown, the concrete specimen 9 with the non-bonding mechanism 3 is also provided with longitudinal steel bars 4. The longitudinal steel bars 4 are arranged along the first direction X on the inner side of the bent section. The length of the longitudinal steel bars 4 is the same as the length of the concrete specimen 9 along the first direction X. The diameter and material of the longitudinal steel bars 4 are determined according to the test requirements, which are used to simulate the real relative position of the FRP stirrup 1 and the longitudinal steel bars 4 in a real concrete member, so as to simulate the stress state of the FRP stirrup 1 in a real concrete member and reflect the influence of the longitudinal steel bars 4 on the tensile strength of the bent section of the FRP stirrup 1, making the test results more real and accurate. In addition, when making the concrete specimen 9, the FRP stirrup 1 can be connected to the longitudinal steel bars 4, so that the FRP stirrup 1 is supported and fixed by the partition plate 2 in the middle and the longitudinal steel bars 4 at one end together to prevent it from shifting during the concrete pouring process.

[0060] When the cross-sectional size of the FRP stirrup 1 to be tested is large or the strength of the FRP material is high, the concrete between the force transmission mechanism 5 and the annular structure formed by the FRP stirrup 1 may crack or even be crushed due to compression, affecting the test results. To solve this problem, in a specific embodiment, as Figure 8 、 Figure 9As shown in the figure, the FRP stirrup 1 bending section strength testing device proposed in this application further includes an anti-cracking mechanism, which is arranged between the force transmission mechanism 5 and the annular structure formed by the FRP stirrup 1, and is used to prevent the concrete test block 9 from cracking.

[0061] Further, the anti-cracking mechanism can adopt FRP fiber cloth 10 or confinement spiral stirrup 11. When using FRP fiber cloth 10, it is wrapped around the outer surface of the concrete test block 9; when using confinement spiral stirrup 11, it should be pre-buried inside the concrete test block 9, between the annular structure formed by the force transmission mechanism 5 and the FRP stirrup 1; regardless of which form is adopted, the anti-cracking mechanisms of the two concrete test blocks 9 are symmetrically arranged.

[0062] A method for using a testing device for the tensile strength of the bending section of an FRP stirrup proposed in this application includes the following steps:

[0063] (1) Make a concrete mold, place the partition plate 2 at the center of the concrete mold, and divide the internal space of the concrete mold into two symmetric parts;

[0064] During installation, temporarily fix the bottom of the partition plate 2 to the concrete mold with glue, so that the partition groove of the partition plate 2 extends vertically.

[0065] (2) Apply lubricating oil to half of the length of the straight section of the FRP stirrup 1, and install the non-bonding mechanism at the lubricating oil position; specifically, use a non-bonding sleeve to sleeved on the straight section of the FRP stirrup 1.

[0066] (3) Place the FRP stirrup 1 in the positioning groove 21 of the partition plate 2, and temporarily fix the FRP stirrup 1 to the bottom of the positioning groove 21 with glue, so that the FRP stirrups 1 on both sides of the partition plate 2 are symmetrically arranged; make the non-bonding mechanism fit on one side of the partition plate 2;

[0067] Install the longitudinal steel bar 4 on the inner side of the bending section of the FRP stirrup 1 on the same side as the non-bonding mechanism, and temporarily fix both ends of the longitudinal steel bar 4 to the concrete mold with glue;

[0068] Connect the FRP stirrup 1 and the longitudinal steel bar 4. Preferably, tie the bending section of the FRP stirrup 1 and the longitudinal steel bar 4 with binding wire or tie straps.

[0069] (4) Symmetrically install the force transmission mechanism 5 on both sides of the positioning plate, and bond it to the concrete mold with glue; the force transmission mechanism 5 should be aligned with the center line of the concrete mold perpendicular to the positioning plate; specifically, the force transmission mechanism 5 adopts a steel sleeve, and the center of the through hole of the force transmission mechanism 5 is located on the center line of the concrete mold perpendicular to the positioning plate.

[0070] (5) Pour concrete into the concrete mold and cure it. Then remove the concrete mold to form a specimen in which the concrete test block 9, the partition board 2, the FRP stirrups 1 and the force transfer mechanism 5 are bonded together. The test of the specimen can be carried out only after the strength of the specimen reaches the test requirements.

[0071] (6) Install the specimen on the loading device 8 and fix it through the connecting piece 6. Specifically, place the specimen between two parallel force transfer plates 83 of the loading device 8, and pass the connecting piece 6 through the holes on one of the force transfer plates 83, the through holes of the force transfer mechanism 5 and the holes of the other force transfer plate 83 in sequence, and fix it to the force transfer plate 83 by screwing the nut 7 at the end of the connecting piece 6; install the two concrete test blocks 9 respectively by the above method; then firmly clamp the clamping plates 81 on the fixtures of the tensile testing machine.

[0072] (7) Start the loading program of the tensile testing machine, gradually increase the tensile force until the FRP stirrups 1 break, and obtain the tensile strength of the bent section of the FRP stirrups 1.

[0073] During the tensile force loading process, the two concrete test blocks 9 move away from each other and finally separate from the partition board 2.

[0074] In a specific embodiment, if the cross-sectional dimension of the FRP stirrups 1 to be tested is large or the stirrup strength is high, after the concrete curing is completed, use structural adhesive to wrap and paste the FRP fiber cloth 10 on the outer surface of the concrete test block 9. After the structural adhesive is fully cured to form an effective lateral restraint on the concrete test block 9, then install the specimen on the loading device 8.

[0075] In another specific embodiment, if the cross-sectional dimension of the FRP stirrups 1 to be tested is large or the stirrup strength is high, before the concrete pouring, install the restraint spiral stirrups 11 in the concrete mold. Specifically, holes can be opened on the side wall of the concrete mold. Pass the metal binding wire through the holes on the side wall and fix it to the restraint spiral stirrups 11. After tightening the metal binding wire, the restraint spiral stirrups 11 can be fixed at the designed position, which should be located between the annular structure formed by the force transfer mechanism 5 and the FRP stirrups 1, and the restraint spiral stirrups 11 on both sides of the partition board 2 should be symmetrically installed; in other embodiments of the present application, other forms of stirrups can also be used to replace the restraint spiral stirrups 11 to achieve the same function; after the installation is completed, carry out the concrete pouring.

[0076] The advantages and positive effects of the present utility model are:

[0077] (1) The force transfer mechanism and the FRP stirrups are all pre-embedded in the concrete test block. The overall device has a small volume, can be applied to the bending section strength tests of FRP stirrups with various different size specifications, has a wider application range, and has lower requirements for test equipment;

[0078] (2) It is movably connected to the force transmission mechanism through a connecting piece, realizing automatic centering of the concrete test block during the loading process, ensuring uniform stress on the FRP stirrups in the two concrete test blocks, eliminating the need for repeatedly adjusting the experimental device for centering before testing in the prior art, ensuring the test accuracy, and improving the test efficiency;

[0079] (3) Compared with the prior art, the FRP stirrups are completely embedded in the concrete test block, avoiding the influence of external factors and being conducive to improving the accuracy of the test results;

[0080] (4) The arrangement of longitudinal steel bars more realistically simulates the actual stress state of FRP stirrups in concrete members. By adding lateral constraints to the concrete specimen through the crack resistance mechanism, concrete cracking and crushing are avoided, making the test results more real and accurate;

[0081] (5) The overall structure of the device is simple, easy to manufacture, low in cost, with a scientific and reasonable force transmission path, and the test results are real and accurate, being suitable for popularization and use.

[0082] The above has described the embodiments of the present utility model in detail, but the content described is only the preferred embodiments of the present utility model and cannot be considered as used to limit the scope of implementation of the present utility model. All equivalent changes and improvements made according to the scope of application of the present utility model shall still fall within the scope covered by the patent of the present utility model.

Claims

1. A tensile strength test device for FRP stirrup bending section, characterized by: It includes a test piece, a loading mechanism and a tensile testing machine; The test specimen includes a bonded body consisting of a concrete test block, a partition plate, FRP stirrups and a force transmission mechanism; The partition plate is disposed between the two concrete test blocks, and is used to separate the concrete test blocks and fix the FRP stirrups in the middle of the concrete test blocks; The force transmission mechanism is symmetrically arranged on the two concrete test blocks and is perpendicular to the FRP stirrups; The loading mechanisms are respectively connected to the force transmission mechanisms and connected to the tensile testing machine; The loading mechanism is movably connected to the force transmission mechanism so that the two concrete test blocks are automatically centered.

2. The FRP stirrup bending section tensile strength testing device according to claim 1 is characterized in that: The partition plate is provided with a positioning groove, and the FRP stirrups pass through the positioning groove, so that the annular structure enclosed by the FRP stirrups is located at the center of the concrete test block in the first direction.

3. The FRP stirrup bending section tensile strength testing device according to claim 2, characterized in that: The force transmission mechanism has a through hole arranged along the first direction, is aligned with the center line of the concrete test block along the second direction, and is located inside the annular structure.

4. The FRP stirrup bending section tensile strength testing device according to claim 3 is characterized in that: The loading mechanism includes a clamping plate, a distribution plate and a force transmission plate. The force transmission plate is vertically arranged on one side of the distribution plate. The force transmission plates are respectively parallel to the two end surfaces of the concrete test block that are arranged opposite to each other along the first direction, and are connected to the force transmission mechanism through a connecting piece passing through the through hole; the other side of the distribution plate is connected to the clamping plate, and the clamping plate is connected to the tensile testing machine; the force transmission plate is symmetrically arranged relative to the clamping plate.

5. The FRP stirrup bending section tensile strength testing device according to claim 4, characterized in that: The radius of the through hole is greater than the cross-sectional radius of the connecting member.

6. The FRP stirrup bending section tensile strength testing device according to claim 3 or 5, characterized in that: One of the concrete test blocks is further provided with a non-bonded structure, which is coated on a straight section of the FRP stirrup and extends from the partition plate to a curved section of the FRP stirrup.

7. The FRP stirrup bending section tensile strength testing device according to claim 6, characterized in that: The concrete test block with the non-bonding mechanism is further provided with longitudinal steel bars, and the longitudinal steel bars are arranged inside the curved section along the first direction.

8. The FRP stirrup bending section tensile strength testing device according to claim 2, characterized in that: It also includes an anti-cracking mechanism, which is arranged between the force transmission mechanism and the annular structure and is used to prevent the concrete test block from cracking.

9. The FRP stirrup bending section tensile strength testing device according to claim 5, characterized in that: The connecting piece is fixed to the force transmission plate through a nut.

Images