Testing device and testing method for bonding performance of FRP (Fiber Reinforce Plastic) rib and concrete

Abstract

The invention discloses a device and method for testing the bonding performance of an FRP rib and concrete, the device comprises an integral FRP rib beam hinge test piece and a loading mechanism, the integral FRP rib beam hinge test piece comprises two steel hinges, a steel hinge shaft, two concrete half beams and an FRP rib; notches are formed in the upper portions of the inner sides of the two concrete half beams, the two steel hinges are located at the notches of the two concrete half beams respectively, the steel hinge shaft penetrates through hinge holes of the two steel hinges, the two concrete half beams are oppositely arranged in the axial direction, the FRP rib penetrates through the lower portions of the two concrete half beams to connect the two concrete half beams together, and the steel hinges, the FRP rib and the concrete half beams are formed together in a pouring mode. The beam hinge device is pre-embedded in the FRP rib beam hinge test piece, the integral FRP rib beam hinge test piece is constructed, the integral stress performance of the test piece is remarkably enhanced, the test piece can bear external force more uniformly in the loading process, stress is coordinated and consistent, and the accuracy and reliability of a test result are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building structure test, in particular to a test method and device for the bonding performance between FRP bars and concrete. BACKGROUND

[0002] Fiber reinforced polymer (FRP) bars have been widely concerned and applied in engineering field due to their excellent performance. Compared with traditional steel bars, FRP bars have higher tensile strength, better corrosion resistance, lighter self-weight and better fatigue resistance. Good bonding performance can ensure the effective transmission of stress between FRP bars and concrete, so as to fully exert the high strength advantage of FRP bars and improve the overall bearing capacity and durability of the structure.

[0003] At present, the bonding performance test method mostly adopted is the pull-out test. The basic principle of this method is to make a cuboid concrete test block, and embed FRP bars in the test block according to the set bonding length. The bonding strength and bonding failure mode between FRP bars and concrete are tested by applying axial tensile load to the FRP bars. Although the pull-out test method has been widely applied in practical engineering, it also has certain limitations, especially the traditional pull-out test working condition is different from the actual stress state of FRP bars in FRP concrete members, and the experimental results have certain deviation. Therefore, the bonding force test method close to the actual stress state of the real member is becoming the development trend in this research field.

[0004] To solve the shortcomings of the pull-out test, a beam member more in line with the actual working condition can be used to study the bonding force between FRP bars and concrete. CN109856046A proposes to form a beam member by using two half-beam concrete and one full-length steel bar, placing a steel hinge in the two L-shaped grooves reserved on the upper part of the two half-beam concrete to form a beam member, and testing the bonding performance between the steel bar and the concrete by four-point loading test on the beam member through two spherical hinges. This method solves the problem that the stress state of the steel bar and the concrete in the pull-out bonding test does not conform to the actual situation, and the force arm is clear during the loading process, which is convenient for calculating the pull-out force. However, this technical solution also has some shortcomings: (1) The steel hinge is placed in the groove of the concrete test piece, and the fitting degree of its contact surface with the concrete will have certain error, and the overall stress performance of the concrete test piece during the stress process is poor, which affects the test results. (2) Considering that the elastic modulus of FRP bars is smaller than that of steel bars, a larger deformation will occur during the stretching process, and the deformation of the FRP bar beam hinge test piece is larger, which will hinder the deformation of the beam member and cause deviation between the stress condition of the test piece and the mechanical calculation model, affecting the accuracy of the test results.

[0005] The present application aims to provide an improved test method and device to overcome the shortcomings of the prior art, improve the accuracy of FRP bar and concrete bonding performance test, and provide new ideas and methods for the development of building structure test technology. SUMMARY

[0006] In combination with the current traditional bar and concrete bonding test method, and considering the mechanical properties of FRP bar, the present application provides a FRP bar and concrete bonding performance test device and test method. By embedding a beam hinge in the FRP bar beam hinge test piece, a monolithic beam hinge test piece is formed, the overall stress performance of the test piece is strengthened, the accuracy of the test is improved, and the problem of poor integrity of the assembled beam hinge test piece in the traditional beam hinge test is solved. By only applying axial pressure to the beam hinge shaft, the loading mechanism is simplified, the test error caused by the test equipment is reduced, the deviation between the stress condition of the test piece and the mechanical calculation model in the traditional beam hinge test is solved, and the precision of the test result is improved.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A monolithic FRP bar beam hinge test piece, comprising two steel hinges, one steel hinge shaft, two concrete half-beams and one FRP bar; the inner upper part of the two concrete half-beams is provided with a notch, the two steel hinges are respectively located at the notch of the two concrete half-beams, the steel hinge shaft passes through the hinge hole of the two steel hinges, the two concrete half-beams are placed opposite along the axial direction, the FRP bar passes through the lower part of the two concrete half-beams to connect them together, the steel hinge, the FRP bar and the concrete half-beam are cast together, the FRP bar is sleeved with a plastic sleeve at both ends in the two concrete half-beams, and the plastic sleeve separates the concrete half-beam and the FRP bar.

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

[0010] The steel hinge comprises a vertical plate, an integral top plate is arranged on the outer side of the top of the vertical plate, and an integral hinge ring is arranged on the inner side of the top; the number of hinge rings of one of the steel hinges is two, which are respectively located on the front side and the rear side of the vertical plate; the number of hinge rings of the other steel hinge is one, which is located in the middle of the vertical plate; the hinge rings of the two steel hinges are mutually inserted, and the steel hinge shaft (2) passes through the hinge holes in the centers of all the hinge rings.

[0011] The outer side of the vertical plate is provided with an integral steel plate shear key, the steel plate shear key is in the shape of a cuboid, and the steel plate shear key extends into the interior of the concrete half-beam.

[0012] The present application also provides a FRP bar and concrete bonding performance test device, which comprises the above-mentioned monolithic FRP bar beam hinge test piece and a loading mechanism.

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

[0014] The loading ball hinge is placed in the center of the top surface of the steel loading frame; the steel loading frame is placed on a steel hinge shaft; and the number of the steel fixed hinge supports is two, which are respectively tightly placed on the outer sides of the lower bottom surfaces of two concrete half-beams.

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

[0016] The cross section of the loading ball hinge is in the shape of a square.

[0017] The test method of the FRP bar and concrete bonding performance test device comprises the following steps: a pressure testing machine is used to apply a load, and the loading end of the pressure testing machine is located in the center of the top surface of the loading ball hinge;

[0018] The load pressure is equal through the distances from the center of the steel hinge shaft to the two steel fixed hinge supports, and the tension of the FRP bar is calculated through the following formula,

[0019]

[0020] Wherein, T is the tension of the FRP bar; F is the loading end pressure 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 bar.

[0021] Compared with the prior art, the FRP bar and concrete bonding performance test device and the test method have the following advantages:

[0022] The beam hinge device is pre-buried in the FRP bar and beam hinge test piece, and the overall FRP bar and beam hinge test piece is constructed, so that the overall stress performance of the test piece is significantly enhanced, the test piece can more uniformly bear external force during the loading process, the stress is more coordinated and consistent, and therefore the accuracy and reliability of the test results are effectively improved.

[0023] When the mechanical performance of the FRP bar and beam hinge test piece is tested, the complexity of the loading mechanism is simplified by applying pressure only to the beam hinge shaft, and the interference of unexpected factors such as friction and constraint between the loading device and the test piece in the traditional loading mode on the test results is avoided. Therefore, the stress state of the test piece is consistent with the theoretical mechanical calculation model, the test error caused by the test equipment is effectively reduced, and the precision of the test results is improved.

[0024] The FRP bar and concrete bonding performance test device and the test method will be further described in combination with the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0025] Figure 1 It is a structural schematic diagram of the overall FRP bar and beam hinge test piece.

[0026] Figure 2 The whole FRP bar beam hinge test piece explosion component schematic diagram.

[0027] Figure 3 The structure schematic diagram of steel hinge.

[0028] Figure 4 The loading mechanism schematic diagram.

[0029] Figure 5 The whole wood template schematic diagram.

[0030] Figure 6 The wood template internal structure diagram.

[0031] Figure 7 The mechanics calculation diagram.

[0032] Figure 8 The whole FRP bar beam hinge test piece construction diagram of application example (unit: mm).

[0033] Figure 9 The whole FRP bar beam hinge test piece loading and data collection schematic diagram of application example.

[0034] Figure 10 The 1 # The τ-S curve of test piece.

[0035] Figure 11 The 2 # The τ-S curve of test piece.

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

[0037] 111-top plate, 112-vertical plate, 113-hinge ring. DETAILED DESCRIPTION

[0038] Example 1

[0039] As Figures 1-3As shown, a whole FRP tendon beam hinge test piece includes two steel hinges 1, one steel hinge shaft 2, two concrete half-beams 3 and one FRP tendon 4; the inner upper part of the two concrete half-beams 3 is provided with a notch, the two steel hinges 1 are respectively located at the notch of the two concrete half-beams 3, the steel hinge shaft 2 passes through the hinge hole of the two steel hinges 1, the two concrete half-beams 3 are placed opposite along the axial direction, the FRP tendon 4 passes through the lower part of the two concrete half-beams 3 to connect them together, and the steel hinge 1, the FRP tendon 4 and the concrete half-beam 3 are poured and formed together. Wherein, the FRP tendon 4 is sleeved with a plastic sleeve 19 at both ends in the two concrete half-beams 3. The plastic sleeve is used to separate the concrete and the FRP tendon. In the test, only the bonding performance between the buried FRP tendon and the concrete is concerned, so the plastic sleeve is sleeved on the non-test section to avoid the bonding between the FRP tendon and the concrete.

[0040] 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; the number of hinge rings 113 of one of the steel hinges 1 is two, which are respectively located on the front side and the rear side of the vertical plate 112; the number of hinge rings 113 of the other steel hinge 1 is one, which is located in the middle of the vertical plate 112; the hinge rings 113 of the two steel hinges 1 are inserted into each other, and the steel hinge shaft 2 passes through the hinge holes in the center of all the hinge rings 113.

[0041] The outer side of the vertical plate 112 is provided with an integrally formed steel plate shear key 5, which is in the shape of a cuboid, and the steel plate shear key 5 extends into the interior of the concrete half-beam 3.

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

[0043] The whole FRP tendon beam hinge test piece is made of a wooden mold, and the structure of the wooden mold is as shown in Figures 5-6 The wooden mold includes a bottom mold plate 12, the left and right sides of the bottom mold plate 12 are respectively fixed with side mold plates 13, the front and rear sides of the bottom mold plate 12 are respectively fixed with vertical mold plates 14, the middle part of the bottom mold plate 12 is provided with two parallel inner side mold plates 16, the top part of the two inner side mold plates 16 is provided with an inner top mold plate 15, the front and rear end faces of the two side mold plates 13, the two inner side mold plates 16 and the inner top mold plate 15 are fixedly connected with the two vertical mold plates 14, and the distance between the outer side faces of the two inner side mold plates 16 is 20mm. The upper central part of the vertical mold plate 14 is provided with a steel hinge shaft reserved hole 11. The lower part of the two side mold plates 13 and the two inner side mold plates 16 are respectively provided with FRP tendon reserved holes 10.

[0044] When making, 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 wood template, and the steel hinge is fixed in the wood template; then the FRP bar 4 is passed through the FRP bar reserved hole 10 and fixed in the wood template, and then the wood template is poured with concrete, and cured for 28 days to complete the making of the integral FRP bar beam hinge test piece.

[0045] Embodiment 2

[0046] As shown in Figure 4 , a FRP bar and concrete bonding performance test device includes the integral FRP bar beam hinge test piece of embodiment 1 and a loading mechanism. The loading mechanism includes a loading ball hinge 7, a steel loading frame 8, and a steel fixed hinge support 9. The loading ball hinge 7 is placed in 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; and the number of the steel fixed hinge supports 9 is two, which are respectively placed against the outer side of the lower bottom surface of the two concrete half-beams 3. The longitudinal section of the steel loading frame 8 is in the shape of an inverted "U". The cross section of the loading ball hinge 7 is in the shape of a square.

[0047] The test method of the FRP bar and concrete bonding performance test device is as follows:

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

[0049] (2) Place the integral FRP bar beam hinge test piece on the steel fixed hinge supports 9, adjust the position, and ensure the accuracy of the making position;

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

[0051] (4) Place the loading ball hinge 7 in the center position of the top surface of the loading steel frame 8;

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

[0053] As shown in Figure 7 , the distance from the load pressure through the center of the steel hinge shaft to the two steel fixed hinge supports is equal, and the tension of the FRP bar is calculated by the following formula,

[0054]

[0055] Wherein, T is the tension of the FRP bar; F is the loading end pressure 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 bar.

[0056] Application example

[0057] The method of Example 1 was used to make the integral FRP bar beam hinge test piece, as shown in Figure 8 The width of the integral FRP bar beam hinge test piece is 100 mm (i.e. the thickness of the concrete half beam 3).

[0058] The integral FRP bar beam hinge test piece loading and data acquisition schematic is shown in Figure 2 The test load F is provided by a pressure testing machine, and pressure data is collected using a pressure sensor; two dial gauges 18 are arranged at the free end of the FPR bar, and the dial gauge 18 data is collected through a strain gauge; a strain gauge 17 is attached at the mid-span position of the FPR bar, and all the measured data points are connected to a computer through a data acquisition system, and the data is automatically collected by the computer.

[0059] The FRP bar parameters used in this test are shown in Table 1.

[0060] Table 1 FRP bar geometric parameters and mechanical performance indicators

[0061]

[0062] The concrete strength grade of the beam hinge test piece in this test is C30, and the concrete cube compressive strength is 42.4 MPa measured according to the "Standard Test Methods for Physical and Mechanical Properties of Concrete" (GBT50081-2019). The concrete parameters and size information of the beam hinge test piece in this test are shown in Table 2.

[0063] Table 2 Beam hinge test piece concrete parameters and size information

[0064]

[0065] 1 # and 2 # The test pieces all failed in slip, and the average bond stress under the ultimate load was taken as the bond strength, with the calculation formula being τ u =F1 / πdl, where F1 is the ultimate tensile force of the GFRP bar, d is the bar diameter, and l is the bar embedment depth.

[0066] It can be seen from Figure 9 that The experimental data are shown in Table 3.

[0067] Table 3 Experimental data

[0068]

[0069] The average bond stress-slip curve (τ-S curve) is shown in Figures 10-11 .

[0070] The above-described embodiments are merely intended to describe the preferred embodiments of the present application, and are not intended to limit the scope of the present application. Various modifications and improvements to the present application made by those skilled in the art are intended to fall within the scope of the present application defined in the claims.

Claims

1. A monolithic FRP tendon-beam hinge test specimen, characterized by: The application relates to a whole FRP tendon beam hinge test piece, which comprises two steel hinges (1), one steel hinge shaft (2), two concrete half-beams (3) and one FRP tendon (4), wherein the inner upper portions of the two concrete half-beams (3) are provided with notches, the two steel hinges (1) are respectively arranged at the notches of the two concrete half-beams (3), the steel hinge shaft (2) penetrates the hinge holes of the two steel hinges (1), the two concrete half-beams (3) are oppositely arranged along the axial direction, the FRP tendon (4) penetrates the lower portions of the two concrete half-beams (3) and connects the two concrete half-beams (3) together, the steel hinge (1), the FRP tendon (4) and the concrete half-beam (3) are integrally formed by pouring, plastic sleeves (19) are arranged at the two ends of the FRP tendon (4) in the two concrete half-beams (3), and the plastic sleeves (19) separate the concrete half-beams (3) and the FRP tendon (4).

2. The monolithic FRP tendon-beam hinge specimen of claim 1, wherein: The interval of the two concrete half-beams (3) is 20 mm.

3. The monolithic FRP tendon-beam hinge specimen of claim 1, wherein: The steel hinge (1) comprises a vertical plate (112), an integral top plate (111) arranged at the top outer side of the vertical plate (112) and an integral hinge ring (113) arranged at the top inner side of the vertical plate (112); the number of the hinge ring (113) of one of the steel hinges (1) is two and the two hinge rings (113) are respectively arranged at the front side and the rear side of the vertical plate (112); the number of the hinge ring (113) of the other steel hinge (1) is one and the hinge ring (113) is arranged at the middle portion of the vertical plate (112); the hinge rings (113) of the two steel hinges (1) are oppositely inserted into each other and the steel hinge shaft (2) penetrates the hinge holes in the centers of all the hinge rings (113).

4. The monolithic FRP tendon-beam hinge specimen of claim 3, wherein: An integral steel plate shear key (5) is arranged at the center of the outer side of the vertical plate (112), the steel plate shear key (5) is in the shape of a cuboid, and the steel plate shear key (5) extends into the interior of the concrete half-beam (3).

5. A device for testing the bonding performance of FRP bars to concrete, characterized by: The application also discloses a loading mechanism.

6. The FRP tendon and concrete bonding performance test device according to claim 5, characterized by: The loading mechanism comprises a loading ball hinge (7), a steel loading frame (8) and two steel fixed hinge supports (9).

7. The FRP tendon and concrete bonding performance test device according to claim 6, characterized by: The loading ball hinge (7) is arranged at the center of the top surface of the steel loading frame (8); the steel loading frame (8) is arranged on the steel hinge shaft (2); and the two steel fixed hinge supports (9) are respectively arranged against the outer sides of the lower bottom surfaces of the two concrete half-beams (3).

8. The FRP tendon and concrete bonding performance test device according to claim 7, characterized by: The longitudinal section of the steel loading frame (8) is in the shape of an inverted "U" character.

9. The FRP tendon and concrete bonding performance test device according to claim 8, characterized by: The cross section of the loading ball hinge (7) is in the shape of a square.

10. A test method for the test device for the adhesion performance of the FRP bar to concrete according to any one of claims 5 to 9, characterized in that: A pressure testing machine is used to apply a load, and the loading end (6) of the pressure testing machine is arranged at the center of the top surface of the loading ball hinge (7). The load pressure is equal through the distances from the center of the steel hinge shaft to the centers of the two steel fixed hinge supports, and the tension of the FRP tendon is calculated through the following formula, wherein T is the tension of the FRP tendon, F is the load pressure 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 tendon.

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