A test apparatus and test method for the bond performance between FRP bars and concrete.

Abstract

This invention discloses a test apparatus and method for testing the bond performance between FRP reinforcement and concrete. The apparatus includes an integral FRP reinforcement beam-hinge specimen and a loading mechanism. The integral FRP reinforcement beam-hinge specimen includes two steel hinges, one steel hinge shaft, two concrete half-beams, and one FRP reinforcement. The upper inner sides of the two concrete half-beams each have notches. The two steel hinges are located at the notches of the two concrete half-beams, and the steel hinge shaft passes through the hinge holes of the two steel hinges. The two concrete half-beams are placed opposite each other axially. The FRP reinforcement passes through the lower part of the two concrete half-beams, connecting them together. The steel hinges, FRP reinforcement, and concrete half-beams are cast together. This invention pre-embeds a beam-hinge device inside the FRP reinforcement beam-hinge specimen, constructing an integral FRP reinforcement beam-hinge specimen, which significantly enhances the overall stress performance of the specimen. This allows it to bear external forces more evenly during loading, ensuring consistent stress distribution and effectively improving the accuracy and reliability of the test results.

Description

Technical Field

[0001] This invention relates to the field of building structure testing technology, and in particular to a test method and apparatus for testing the bond performance between FRP bars and concrete. Background Technology

[0002] Fiber-reinforced polymer (FRP) bars have gained widespread attention and application in the engineering field due to their excellent properties. Compared with traditional steel reinforcement, FRP bars have higher tensile strength, better corrosion resistance, lighter weight, and good fatigue resistance. Their excellent bond properties ensure effective stress transfer between the FRP bars and concrete, thus fully leveraging the high strength of FRP bars and improving the overall load-bearing capacity and durability of the structure.

[0003] Currently, the most commonly used method for testing bond performance is the pull-out test. The basic principle of this method is to fabricate a rectangular concrete specimen and embed the FRP (fiberglass reinforced polymer) reinforcement within it according to a predetermined bond length. By applying an axial tensile load to the FRP reinforcement, the bond strength and bond failure mode between the FRP reinforcement and the concrete are tested. Although the pull-out test method is widely used in practical engineering, it also has certain limitations, especially since the traditional pull-out test conditions differ from the actual stress conditions of the FRP reinforcement in FRP-reinforced concrete members, leading to some deviation in the experimental results. Therefore, bond strength testing methods that more closely reflect the actual stress conditions of real members are becoming a development trend in this research field.

[0004] To address the shortcomings of pull-out tests, beam-type members that better reflect actual working conditions can be used to study the bond strength between FRP reinforcement and concrete. CN109856046A proposes using two half-beam concrete sections and a continuous steel bar to form a beam member. Steel hinges are placed in two L-shaped grooves reserved on the upper part of the two half-beam concrete sections to form a beam member. A four-point loading test is conducted on the beam member through two ball hinges to test the bond performance between the steel bar and concrete. This method solves the problem that the stress state of the steel bar and concrete does not match the actual situation in the pull-out bond test, and the lever arm is clear during the loading process, which is convenient for calculating the pull-out force. However, there are also some disadvantages in this technical solution: (1) When the steel hinge is placed in the groove of the concrete specimen, there will be a certain error in the degree of contact between it and the concrete contact surface. The overall stress performance of the concrete specimen during the stress process is not good, which affects the test results. (2) Considering that the elastic modulus of FRP bars is smaller than that of steel bars, they will produce larger deformations during the tensile process. The deformation of FRP bar beam hinge specimens is large. The two fixed hinge supports in the scheme will adversely hinder the deformation of the beam members, resulting in a deviation between the stress condition of the specimen and the mechanical calculation model, which affects the accuracy of the test results.

[0005] This invention aims to propose an improved testing method and apparatus to overcome the shortcomings of existing technologies, improve the accuracy of FRP bar-concrete bond performance testing, and provide new ideas and methods for the development of building structure testing technology. Summary of the Invention

[0006] Combining current traditional methods for testing the bond between reinforcing bars and concrete, and considering the inherent mechanical properties of FRP (fiberglass reinforced plastic) reinforcing bars, this invention provides a testing device and method for the bond performance of FRP reinforcing bars and concrete. By pre-embedding beam hinges within the FRP reinforcing bar beam hinge specimen, an integral beam hinge specimen is formed, enhancing the overall stress performance of the specimen and improving the accuracy of the test. This addresses the problem of poor integrity in assembling beam hinge specimens in traditional beam hinge tests. Furthermore, by applying axial pressure only to the beam hinge axis, the loading mechanism is simplified, reducing test errors caused by the testing equipment. This solves the problem of discrepancies between the specimen's stress condition and the mechanical calculation model in traditional beam hinge tests, thus improving the accuracy of the test results.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An integral FRP-reinforced beam-hinge specimen includes two steel hinges, one steel hinge shaft, two concrete half-beams, and one FRP reinforcement. The upper inner sides of the two concrete half-beams each have notches. The two steel hinges are located at the notches of the two concrete half-beams respectively. The steel hinge shaft passes through the hinge holes of the two steel hinges. The two concrete half-beams are placed opposite each other axially. The FRP reinforcement passes through the lower part of the two concrete half-beams, connecting them together. The steel hinges, FRP reinforcement, and concrete half-beams are cast together. Plastic sleeves are fitted at both ends of the FRP reinforcement within the two concrete half-beams, separating the concrete half-beams from the FRP reinforcement.

[0009] The distance between the two concrete half-beams is 20mm.

[0010] The steel hinge includes a vertical plate, the top outer side of which is provided with an integrally formed top plate, and the top inner side is provided with an integrally formed hinge ring; one of the steel hinges has two hinge rings, located on the front and rear sides of the vertical plate respectively; the other steel hinge has one hinge ring, located in the middle of the vertical plate; the hinge rings of the two steel hinges are interlocked, and the steel hinge shaft (2) passes through the hinge hole in the center of all the hinge rings.

[0011] The vertical plate has an integrally formed steel plate shear key at the center of its outer side. The steel plate shear key is cuboid in shape and extends into the interior of the concrete half-beam.

[0012] The present invention also provides a test device for the bond performance between FRP reinforcement and concrete, comprising the above-mentioned integral FRP reinforcement beam hinge specimen and loading mechanism.

[0013] The loading mechanism includes a loading ball joint, a steel loading frame, and a steel fixed hinge support.

[0014] The loading ball hinge is placed at the center of the top surface of the steel loading frame; the steel loading frame is placed on the steel hinge shaft; there are two steel fixed hinge supports, which are respectively placed against the outer side of the bottom surface of the two concrete half beams.

[0015] The longitudinal section of the steel loading frame is inverted "U" shape.

[0016] The cross-section of the loaded ball joint is square.

[0017] The test method of the FRP bar-concrete bond performance test device of the present invention is as follows: a load is applied by a pressure testing machine, and the loading end of the pressure testing machine is located at the center of the top surface of the loading ball joint;

[0018] The compressive load is distributed equidistantly from the center of the steel hinge shaft to the two fixed steel hinge supports on the left and right sides. The tensile force on the FRP reinforcement is calculated using the following formula.

[0019]

[0020] Where T is the tensile force on the FRP reinforcement; F is the compressive force at the loading end of the steel hinge shaft; x is the distance from the center of the steel hinge shaft to the center of the fixed hinge support; and y is the distance from the center of the steel hinge shaft to the center of the FRP reinforcement.

[0021] Compared with the prior art, the outstanding effect of the present invention is as follows:

[0022] This invention pre-embeds a beam hinge device inside the FRP stiffener-beam hinge specimen, constructing an integral FRP stiffener-beam hinge specimen. This significantly enhances the overall stress performance of the specimen, enabling it to withstand external forces more evenly and with more coordinated force distribution during loading, thereby effectively improving the accuracy and reliability of the test results.

[0023] When conducting mechanical property tests on FRP-reinforced beam hinge specimens, applying pressure only to the beam hinge axis simplifies the complexity of the loading mechanism and avoids interference from unforeseen factors such as friction and constraints between the loading device and the specimen, which are present in traditional loading methods. Therefore, the stress state of the specimen is consistent with the theoretical mechanical calculation model, effectively reducing experimental errors caused by the testing equipment and improving the accuracy of the test results.

[0024] The following description, in conjunction with the accompanying drawings and specific embodiments, further illustrates the experimental apparatus and method for testing the bond performance between FRP bars and concrete according to the present invention. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of an integral FRP stiffener-beam hinge specimen.

[0026] Figure 2 This is a schematic diagram of an exploded specimen of an integral FRP (fiberglass reinforced plastic) beam-hinged structure.

[0027] Figure 3 This is a schematic diagram of a steel hinge.

[0028] Figure 4 This is a schematic diagram of the loading mechanism.

[0029] Figure 5 This is a schematic diagram of the entire wooden formwork.

[0030] Figure 6 This is a diagram of the internal structure of the wooden formwork.

[0031] Figure 7 This is a simplified diagram for mechanical calculations.

[0032] Figure 8 Construction diagram of a monolithic FRP stiffened beam hinge specimen for application example (unit: mm).

[0033] Figure 9 This is a schematic diagram of loading and data acquisition for an integral FRP stiffened beam hinge specimen used as an application example.

[0034] Figure 10 1 # The τ-S curve of the specimen.

[0035] Figure 11 2 # The τ-S curve of the specimen.

[0036] Among them, 1-steel hinge, 2-steel hinge shaft, 3-concrete half beam, 4-FRP reinforcement, 5-steel plate shear key, 6-loading end of pressure testing machine, 7-loading ball hinge, 8-steel loading frame, 9-steel fixed hinge support, 10-FRP reinforcement reserved hole, 11-steel hinge shaft reserved hole, 12-bottom formwork, 13-side formwork, 14-vertical formwork, 15-inner top formwork, 16-inner side formwork, 17-strain gauge, 18-dial gauge, 19-plastic sleeve;

[0037] 111-Top plate, 112-Vertical plate, 113-Hinge ring. Detailed Implementation

[0038] Example 1

[0039] like Figure 1-3As shown, an integral FRP-reinforced beam-hinge specimen includes two steel hinges 1, one steel hinge shaft 2, two concrete half-beams 3, and one FRP reinforcement 4. The upper inner sides of the two concrete half-beams 3 each have notches. The two steel hinges 1 are located at the notches of the two concrete half-beams 3, respectively. The steel hinge shaft 2 passes through the hinge holes of the two steel hinges 1. The two concrete half-beams 3 are placed opposite each other axially. The FRP reinforcement 4 passes through the lower part of the two concrete half-beams 3, connecting them together. The steel hinges 1, FRP reinforcement 4, and concrete half-beams 3 are cast together. Plastic sleeves 19 are fitted at both ends of the FRP reinforcement 4 within the two concrete half-beams 3. These plastic sleeves are used to separate the concrete and the FRP reinforcement. In the experiment, only the bond performance between the FRP reinforcement and the concrete in the buried section is considered; therefore, plastic sleeves are fitted on non-test sections to prevent bonding between the FRP reinforcement and the concrete in those sections.

[0040] The steel hinge 1 includes a vertical plate 112, on the outer side of the top of the vertical plate 112 is an integrally formed top plate 111, and on the inner side of the top is an integrally formed hinge ring 113; one of the steel hinges 1 has two hinge rings 113, located on the front and rear sides of the vertical plate 112 respectively; the other steel hinge 1 has one hinge ring 113, located in the middle of the vertical plate 112; the hinge rings 113 of the two steel hinges 1 are interlocked, and the steel hinge shaft 2 passes through the hinge hole in the center of all the hinge rings 113.

[0041] An integrally formed steel plate shear key 5 is provided at the center of the outer side of the upright plate 112. The steel plate shear key 5 is in the shape of a cuboid and extends into the interior of the concrete half beam 3.

[0042] The spacing between the two concrete half beams 3 is 20mm.

[0043] This monolithic FRP reinforced beam hinge specimen was made using wooden formwork, the wooden formwork structure being as follows: Figure 5-6 As shown, the system includes a bottom template 12, side templates 13 fixed to the left and right sides of the bottom template 12, and vertical templates 14 fixed to the front and rear sides of the bottom template 12. Two parallel inner side templates 16 are located in the middle of the bottom template 12, and an inner top template 15 is located on top of the two inner side templates 16. The front and rear ends of the two side templates 13, the two inner side templates 16, and the inner top template 15 are all fixedly connected to the two vertical templates 14. The distance between the outer surfaces of the two inner side templates 16 is 20mm. A steel hinge shaft pre-drilled hole 11 is provided in the upper center of the vertical template 14. FRP reinforcement pre-drilled holes 10 are provided in the lower parts of the two side templates 13 and the two inner side templates 16.

[0044] During fabrication, one steel hinge shaft 2 is passed through two steel hinges 1, and then the steel hinge shaft 2 is passed through the steel hinge shaft reserved hole 11 of the wooden template to fix the steel hinge inside the wooden template; then the FRP reinforcement 4 is passed through the FRP reinforcement reserved hole 10 and fixed inside the wooden template, and then concrete is poured inside the wooden template and cured for 28 days to complete the fabrication of the integral FRP reinforcement beam hinge specimen.

[0045] Example 2

[0046] like Figure 4 As shown, a test apparatus for the bond performance between FRP reinforcement and concrete includes the integral FRP reinforcement beam hinge specimen and loading mechanism described in Example 1. The loading mechanism includes a loading ball hinge 7, a steel loading frame 8, and steel fixed hinge supports 9. The loading ball hinge 7 is placed at the center of the top surface of the steel loading frame 8; the steel loading frame 8 is placed on the steel hinge shaft 2; there are two steel fixed hinge supports 9, which are respectively placed against the outer side of the lower bottom surface of two concrete half-beams 3. The longitudinal section of the steel loading frame 8 is inverted "U" shape. The cross-section of the loading ball hinge 7 is square.

[0047] The test method for the FRP reinforcement-concrete bond performance test apparatus is as follows:

[0048] (1) Place the two steel fixed hinge supports 9 on the base plate of the pressure testing machine and finely adjust the centering;

[0049] (2) Place the integral FRP stiffener beam hinge specimen on the steel fixed hinge support 9, adjust the position, and ensure that the fabrication position is accurate.

[0050] (3) Place the steel loading frame 4 on the steel hinge shaft 2;

[0051] (4) Place the loading ball joint 7 at the center of the top surface of the loading steel frame 8;

[0052] (5) Adjust the position of the loading mechanism so that the loading end 6 of the pressure testing machine is aligned with the loading ball joint 7, start the pressure testing machine to begin the loading test, and collect the force value data through the pressure testing machine system.

[0053] like Figure 7 As shown, the load pressure is equidistant from the center of the steel hinge shaft to the two fixed steel hinge supports on the left and right. The tensile force on the FRP reinforcement is calculated using the following formula.

[0054]

[0055] Where T is the tensile force on the FRP reinforcement; F is the compressive force at the loading end of the steel hinge shaft; x is the distance from the steel hinge shaft to the fixed hinge support; and y is the distance from the center of the steel hinge shaft to the center of the FRP reinforcement.

[0056] Application Examples

[0057] The monolithic FRP reinforced beam hinge specimen was fabricated using the method described in Example 1, such as... Figure 8 As shown, the width of the integral FRP reinforced beam hinge specimen is 100mm (i.e., the thickness of the concrete half beam 3).

[0058] A schematic diagram of loading and data acquisition for integral FRP reinforced beam hinge specimens is shown below. Figure 2 As shown. The test load F is provided by a pressure testing machine, and pressure data is collected by a pressure sensor; two dial gauges 18 are respectively set at the free ends of the FPR reinforcement, and the data of the dial gauges 18 are collected by a strain gauge. A strain gauge 17 is attached at the mid-span of the FPR reinforcement. All measurement point data are connected to a computer through a data acquisition system, and the computer automatically collects the data.

[0059] The relevant parameters of the FRP reinforcement used in this experiment are shown in Table 1.

[0060] Table 1 Geometric parameters and mechanical properties of FRP reinforcement

[0061]

[0062] The concrete strength grade of the beam hinge specimen in this experiment was C30, and the cubic compressive strength of the concrete was measured to be 42.4 MPa according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GBT50081-2019). The concrete parameters and dimensional information of the beam hinge specimen in this experiment are shown in Table 2.

[0063] Table 2 Concrete parameters and dimensions of beam hinge specimens

[0064]

[0065] 1 # and 2 # All specimens failed by slippage. The average bond stress under the ultimate load was taken as the bond strength, and its calculation formula is τ. u =F1 / πdl, where F1 is the ultimate tensile force on the GFRP bar, d is the bar diameter, and l is the bar embedment depth.

[0066] Depend on Figure 9 It can be known The experimental data are shown in Table 3.

[0067] Table 3 Experimental Data

[0068]

[0069] The mean bond stress-slip curve (τ-S curve) is as follows: Figures 10-11 As shown.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A test apparatus for the bond performance between FRP bars and concrete, characterized in that: The test specimen includes an integral FRP reinforced beam hinge specimen and a loading mechanism. The integral FRP reinforced beam hinge specimen includes two steel hinges (1), one steel hinge shaft (2), two concrete half beams (3), and one FRP reinforcement (4). The upper inner side of the two concrete half beams (3) is provided with a notch. The two steel hinges (1) are located at the notches of the two concrete half beams (3). The steel hinge shaft (2) passes through the hinge holes of the two steel hinges (1). The two concrete half beams (3) are placed opposite each other along the axial direction. The FRP reinforcement (4) passes through the lower part of the two concrete half beams (3) to connect them together. The steel hinges (1), FRP reinforcement (4), and concrete half beams (3) are cast together. Plastic sleeves (19) are provided at both ends of the FRP reinforcement (4) in the two concrete half beams (3). The plastic sleeves (19) separate the concrete half beams (3) and the FRP reinforcement (4). The loading mechanism includes a loading ball joint (7), a steel loading frame (8), and a steel fixed hinge support (9). The loading ball hinge (7) is placed at the center of the top surface of the steel loading frame (8); the steel loading frame (8) is placed on the steel hinge shaft (2); there are two steel fixed hinge supports (9), which are respectively placed against the outer side of the bottom surface of the two concrete half beams (3); when conducting the mechanical property test of the FRP reinforced beam hinge specimen, only the steel hinge shaft (2) is subjected to pressure.

2. The test apparatus for the bond performance between FRP bars and concrete according to claim 1, characterized in that: The longitudinal section of the steel loading frame (8) is inverted "U" shape.

3. The test apparatus for the bond performance between FRP bars and concrete according to claim 2, characterized in that: The cross-section of the loaded ball joint (7) is square.

4. The test apparatus for the bond performance between FRP bars and concrete according to claim 1, characterized in that: The distance between the two concrete half beams (3) is 20mm.

5. The test apparatus for the bond performance between FRP bars and concrete according to claim 1, characterized in that: The steel hinge (1) includes a vertical plate (112), the top outer side of the vertical plate (112) is provided with an integrally formed top plate (111), and the top inner side is provided with an integrally formed hinge ring (113); one of the steel hinges (1) has two hinge rings (113), which are located on the front and rear sides of the vertical plate (112) respectively; the other steel hinge (1) has one hinge ring (113), which is located in the middle of the vertical plate (112); the hinge rings (113) of the two steel hinges (1) are interlocked, and the steel hinge shaft (2) passes through the hinge hole in the center of all the hinge rings (113).

6. The test apparatus for the bond performance between FRP bars and concrete according to claim 5, characterized in that: The outer center of the vertical plate (112) is provided with an integrally formed steel plate shear key (5), which is rectangular in shape and extends into the interior of the concrete half beam (3).

7. The test method of the FRP bar-concrete bond performance test apparatus according to any one of claims 1-6, characterized in that: The load is applied using a pressure testing machine, with the loading end (6) of the pressure testing machine located at the center of the top surface of the loading ball joint (7); The compressive load is distributed equidistantly from the center of the steel hinge shaft to the two fixed steel hinge supports on the left and right sides. The tensile force on the FRP reinforcement is calculated using the following formula. ； in, T This refers to the tensile force acting on the FRP reinforcement. F The loading end pressure on the steel hinge shaft; x This is the distance from the center of the steel hinge shaft to the center of the fixed hinge support; y This is the distance from the center of the steel hinge shaft to the center of the FRP reinforcement.

Images