FRP bar-clip bearing capacity testing device and fire resistance performance testing method

Abstract

The present invention discloses a testing device for the bearing capacity of an FRP tendon-clip and a method for testing its fire resistance, comprising a pressure plate assembly, a clip assembly, and a pressure rod assembly; the pressure plate assembly has a groove for placing the clip assembly, and the clip assembly is provided with a groove for placing the FRP tendon-clip to be tested. The method for testing fire resistance comprises installing the testing device on a testing machine before the test, then performing two tests to determine the test target test temperature and the insulation time of a high temperature box, performing a steady-state test and a transient test the same as the formal test to determine the test parameters; then performing a formal test based on the test parameters obtained in the previous step, using a DIC device to observe strain throughout the process, and ending the experiment and exporting corresponding data when the FRP tendon is deformed and the upper and lower pressure plates are almost in contact, thereby sorting out the temperature / load-strain curve and the load / temperature-strain curve, and obtaining the high-temperature lateral force characteristics of the FRP tendon-clip under steady-state and transient tests.

Description

Technical Field

[0001] The invention relates to the field of civil engineering, and in particular to a testing device for the bearing capacity of an FRP bar-clip under high temperature and a method for testing its fire resistance. Background Art

[0002] Fiber reinforced polymer (FRP) has excellent mechanical, physical and chemical properties such as light weight, high strength, corrosion resistance, good creep performance, low relaxation rate, fatigue resistance and small linear expansion coefficient, so it is very suitable for being made into tension members for use in engineering structures. At present, composite bars made of high-performance fiber materials such as carbon fiber, glass fiber, aramid fiber, basalt fiber, etc. through pultrusion process have been used in space cable net structures, cable bridge structures, and geotechnical structures to replace steel bars and steel cables as load-bearing members to solve the span limitation, durability, and high maintenance cost problems of steel in actual use, and ultimately greatly improve the overall performance of the structure and reduce the life cycle cost. However, FRP bars have poor high temperature resistance, and their mechanical properties deteriorate in high temperature environments, which affects the safety of the overall structure, seriously hindering the large-scale application of FRP bars in engineering structures.

[0003] The technical code for building fire protection requires that the fire protection of the nodes in the structure should be the same as the highest fire protection requirement of the connected components. Therefore, the fire resistance of FRP tendon anchors is the key to ensuring the safety of the overall structure. Clip-type anchors are the most mature type of anchorage used in steel bars and cables. They have the advantages of small size, light weight, high anchoring efficiency, and good long-term stability. They are also very suitable for FRP tendons. However, there is a lack of test methods for testing the transverse compressive bearing capacity of FRP tendons-clips at high temperatures, and it is impossible to provide a basis for the transverse compressive bearing capacity of FRP tendons-clips at high temperatures for the fire resistance design method of FRP tendon clip-type anchors, which affects the fire resistance safety and promotion and application of FRP tendon clip-type anchors. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and to provide a testing device suitable for the transverse compressive bearing capacity of FRP tendon-clip under high temperature and a fire resistance testing method thereof. The present invention is used to test the transverse compressive bearing capacity and compression mechanical response of FRP tendon-clip under high temperature, to provide a mechanical performance basis for the research on the high temperature failure mechanism and fire resistance design method of FRP tendon-clip anchor, and to promote the research on the fire resistance design method of FRP tendon-clip anchor.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A testing device for the bearing capacity of an FRP tendon-clip comprises a pressure plate assembly, a clip assembly, and a pressure rod assembly; the pressure plate assembly comprises a pair of pressure plates arranged in a mirror image and used in pairs, an inwardly concave pressure plate groove is provided on the pressure plate surface to be fastened of the pressure plate, the pressure plate groove penetrates the pressure plate along the axial direction and has a semicircular cross-section, and is used to place the clip assembly, and a slot is provided on the end surface of the pressure plate facing a testing machine; the clip assembly comprises a pair of clips arranged in a mirror image and used in pairs, an inwardly concave clip groove is provided on the clip surface to be fastened of the clip, the clip groove penetrates the clip along the axial direction and has a semicircular cross-section, and is used to place the FRP tendon-clip to be tested.

[0007] The pressure rod assembly includes a pair of pressure rods arranged in a mirror image and used in pairs; a cylindrical protrusion is provided on the first end face of the pressure rod for inserting into the slot, the outer contour of the protrusion is adapted to the slot, and a through hole is opened on the side wall of the other end face of the pressure rod for fixing and connecting the upper joint and the lower joint of the testing machine; and the length of the pressure rod is such that one end of it can be fixed on the testing machine frame and the other end can be extended into the inner cavity of the high temperature box, the diameter is adapted to the upper joint and the lower joint of the testing machine frame, and is not less than the width of the first end face of the pressure plate of the pressure plate to ensure uniform force transmission.

[0008] When in use, the clip is embedded in the pressure plate groove of the pressure plate along the axial direction of the pressure plate groove, and the FRP rib-clip is placed in the clip groove; the end faces of the two pressure plates with pressure plate grooves are placed opposite to each other, the end faces of the clips with clip grooves are placed opposite to each other, and the end faces of the clip surface to be fastened and the pressure plate surface to be fastened are flush.

[0009] Furthermore, the pressing plate includes an upper pressing plate and a lower pressing plate; the upper pressing plate and the lower pressing plate respectively include a pressing plate surface to be fastened, a first end face of the pressing plate, a front surface of the pressing plate and a rear surface of the pressing plate, the pressing plate surface to be fastened is the end face close to each other when the upper and lower pressing plates are fastened, the first end face of the pressing plate is the face opposite to the pressing plate surface to be fastened, that is, the face connected to the pressing rod, the pressing plate front surface is the surface facing the DIC shooting device during the test, the pressing plate rear surface is the face opposite to the pressing plate front surface, and both the pressing plate front surface and the pressing plate rear surface have cross-sectional notches of the pressing plate groove; the pressing plate assembly also includes a fixed vertical positioning auxiliary assembly, and the vertical positioning auxiliary assembly includes a baffle, a U-shaped frame and screws, The same material is used as the pressure plate. The U-shaped frame is a rectangular structure with a groove on the inner surface. It is screwed to the rear surface of the pressure plate located at the lower pressure plate during installation by screws, and the inner surface of the U-shaped frame is in close contact with the rear surface of the pressure plate of the lower pressure plate; the lower end of the baffle is inserted into the groove of the U-shaped frame, and the position of the baffle is raised from bottom to top so that the baffle can be in close contact with part of the rear surface of the pressure plate of the lower pressure plate, part of the rear surface of the pressure plate of the upper pressure plate, part of the upper / lower clip and part of the FRP rib-clip, and then the middle screw is tightened, the baffle is squeezed and fixed, so that the rear surface of the upper / lower pressure plate, the rear surface of the upper / lower clip and the rear surface of the FRP rib-clip are aligned on the same vertical plane.

[0010] Furthermore, in order to make the surface of the clip to be fastened flush with the surface of the pressure plate to be fastened, a gasket made of hard metal material is placed on the left and right sides of the FRP rib-clip (in terms of DIC observation angle) between the installed surface of the clip to be fastened and the surface of the pressure plate to be fastened. With the help of the gasket, the upper and lower end faces after fastening are adjusted respectively, so that the surface of the clip to be fastened at the upper part and the surface of the pressure plate to be fastened are both flush on the same horizontal plane, and the surface of the clip to be fastened at the lower part and the surface of the pressure plate to be fastened are also flush on the same horizontal plane. A testing machine is used to apply 1 to 10 kN as a preload to the test device. After the test device is pressed and all surfaces are flush, the gasket is removed.

[0011] Furthermore, the radius of the pressure plate groove of the pressure plate is equal to the outer radius of the clip + 0.1mm, the outer radius of the clip is not less than the FRP bar-clip radius + 10mm, and the radius of the clip groove is equal to the FRP bar-clip radius + 0.1mm.

[0012] Furthermore, the pressure plate and the clamp are both cut with a thickness of 0.5-1mm along the length direction, so that a 1-2mm inter-plate gap is formed between the flush upper and lower ends of the pressure plate and the clamp, ensuring that after the combination with the FRP bar-clip, there are sufficient inter-plate gaps between the upper and lower plates of the clip and between the upper and lower plates of the pressure plate to avoid the upper and lower pressure plates contacting each other in advance before the FRP bar-clip fails during the test, ensuring that the compressive load is applied to the FRP bar-clip to be measured, avoiding invalid loading.

[0013] Furthermore, the material of the clip assembly is aluminum or copper; the material of the pressure plate assembly and the pressure rod assembly is mainly high temperature resistant steel.

[0014] The specific steps of the fire resistance performance testing method of the FRP bar-clip bearing capacity testing device are as follows:

[0015] Step 1: Before the test, open the high temperature box door and install the FRP rib-clip bearing capacity test device; install the pressure rod assembly of the test device at the upper joint and the lower joint corresponding to the test machine frame respectively, and then in the inner cavity of the high temperature box, put the lower pressure plate, the lower clamp, the FRP rib-clip, the upper clamp, and the upper pressure plate in sequence on the first end face of the pressure rod extending into the inner cavity of the high temperature box at the bottom, ensuring that the protrusion of the lower pressure rod is inserted into the slot of the lower pressure plate, the protrusion of the upper pressure rod is inserted into the slot of the upper pressure plate, the upper / lower clamps are respectively embedded in the pressure plate grooves, and the FRP rib-clip is embedded in the clamp grooves, ensuring that the front surface of the pressure plate faces the glass observation window and the entire front surface area of ​​the FRP rib-clip and the upper and lower clamps are within the field of view of the observation window;

[0016] Step 2: Preparation of test parameters

[0017] Steady-state test:

[0018] Two preliminary tests are performed before the formal test, namely the glass transition temperature test of the FRP bar and the temperature rise test of the high temperature box and the test object in the box; wherein, the glass transition temperature test of the FRP bar is used to obtain the glass transition temperature range [T1, T4], and the target test temperature is proposed according to the property change law of the FRP bar-clip before, during and after the glass transition temperature range; the target test temperature includes the room temperature proposed value, the high elastic state target test temperature value, the glass transition target test initial temperature T1', the transition state target test temperature value, the glass transition target test termination temperature T4' and the viscous state target test temperature value; wherein, T1 is the glass transition initial temperature, and T4 is the glass transition termination temperature;

[0019] The heating rate, loading rate, and DIC equipment shooting speed were set according to historical experience data, among which the heating rate was 3℃ / min-10℃ / min, the loading rate was 1mm / min-1.5mm / min, and the DIC equipment shooting speed was 1 frame / second-5 frames / second. Due to the lack of appropriate historical experience data for the holding time, it was conservatively set to 4h.

[0020] Using the test parameters proposed above, multiple groups of temperature rise tests of the high-temperature box and the test objects in the box that are consistent with the formal test steps are performed to monitor the change pattern of the ambient temperature in the box and the surface temperature of the test object over time to determine the insulation time; wherein, the target test temperature of the test selects a highest value from the multiple target test temperatures proposed; the final result takes the average value of multiple groups of test results, and the insulation time is determined by the test results, which is 30min-2h; through the research of this preliminary test, we can further understand the applicability of the various test parameters proposed based on historical experience data and this steady-state test, so as to further formulate the most appropriate test parameters.

[0021] Transient test:

[0022] The upper and lower limits of the tension control stress of the fiber composite reinforcement are obtained based on historical data to formulate the target test pressure value;

[0023] The loading rate, heating rate, and DIC equipment shooting speed are set according to historical experience data; the loading rate is 1mm / min-1.5mm / min, the heating rate is 0.5℃ / min-3℃ / min, and the DIC equipment shooting speed is ≤1 frame / second;

[0024] Step 3: Testing Phase

[0025] Steady-state test:

[0026] Input the test parameters obtained in the previous step into the control panel of the test machine, turn on the test equipment, and use the DIC equipment to observe the strain during the whole process; the high temperature box is heated to the target test temperature at the set heating rate, and the ambient temperature of the high temperature box is monitored in real time through multiple temperature sensors distributed at different positions inside the high temperature box; when the target test temperature value is reached, maintain the set insulation time; then apply pressure to the test device at the set loading rate;

[0027] When the FRP bar is deformed and the upper and lower plates are almost in contact, the loading is terminated and the data is recorded and calculated; finally, the transverse compressive bearing capacity of the FRP bar-clip and the temperature / load-strain curve of the FRP bar-clip cross section and the clip cross section under the room temperature proposed value, the high elastic state target test temperature value, the target test temperature T1', the transition state target test temperature value, the target test temperature T4' and the viscous state target test temperature value are obtained; the transverse compressive bearing capacity, load-strain curve and temperature-strain curve of the FRP bar-clip under different target test temperatures are compared to obtain the high-temperature transverse force characteristics of the FRP bar-clip under steady-state testing;

[0028] Transient test:

[0029] Input the test parameters obtained in the previous step into the control panel of the test machine, turn on the test equipment, and use the DIC device to observe the strain during the whole process; the test machine applies pressure to the test device at the set loading rate until the target test pressure is reached; when the pressure value remains stable, the high temperature box starts to heat from room temperature at the set heating rate, and the temperature of the high temperature box is monitored in real time through multiple temperature sensors distributed at different positions inside the high temperature box;

[0030] When the FRP tendon is deformed and the upper and lower pressure plates are almost in contact, the loading is terminated and the data is recorded and calculated: Finally, the critical temperature of the FRP tendon-clip under transverse compression and the load / temperature-strain curves at the FRP tendon-clip cross section and the clip cross section under each target test pressure are obtained.

[0031] Furthermore, in the steady-state test of step 3, when the FRP bars are deformed and the upper and lower plates are almost in contact, the loading is terminated and the data are recorded and calculated, including:

[0032] When the FRP bar is deformed and the upper and lower pressure plates are almost in contact, the loading is terminated and the current load value is recorded as the transverse compressive bearing capacity of the FRP bar-clip, and the load-time correspondence data is derived;

[0033] Stop DIC shooting, generate the vertical compressive strain cloud map and transverse shear strain cloud map of the FRP bar-clip cross section based on the photos taken at the FRP bar cross section and the clip cross section, and derive the vertical compressive strain-time and transverse shear strain-time corresponding data;

[0034] According to the load-time correspondence data and the strain-time correspondence data, based on the time alignment principle, the load-strain correspondence data is obtained;

[0035] Turn off the heat preservation function of the high temperature box and export the temperature-time corresponding data recorded by the temperature sensor;

[0036] Based on the time alignment principle, the temperature-strain correspondence data is sorted out through the temperature-time correspondence data and the strain-time correspondence data;

[0037] The same steps were repeated for multiple groups of tests, and the test results were calculated to obtain the transverse compressive bearing capacity of the FRP tendon-clip at the room temperature target value, the high elastic state target test temperature value, the target test temperature T1', the transition state target test temperature value, the target test temperature T4' and the viscous state target test temperature value, and the temperature / load-strain curve at the FRP tendon-clip cross section and the clip cross section; the transverse compressive bearing capacity, load-strain curve and temperature-strain curve of the FRP tendon-clip at different target test temperatures were compared to obtain the high-temperature transverse force characteristics of the FRP tendon-clip under steady-state testing.

[0038] Furthermore, in the transient test of step 3, when the FRP bars are deformed and the upper and lower plates are almost in contact, the loading is terminated and the data are recorded and calculated, including:

[0039] When the FRP bar is deformed and the upper and lower plates are almost in contact, the temperature rise is stopped and the current temperature value is recorded as the critical temperature of the FRP bar-clip transverse compression, and the data recorded by the temperature sensor is exported, that is, the temperature-time corresponding data;

[0040] Stop DIC shooting, generate vertical compressive strain cloud diagrams and transverse shear strain cloud diagrams of the FRP bar cross section and the clip cross section based on the photographs taken at the FRP bar cross section and the clip cross section, and derive the vertical compressive strain-time and transverse shear strain-time corresponding data;

[0041] According to the temperature-time correspondence data and the strain-time correspondence data, based on the time alignment principle, the temperature-strain correspondence data is sorted out;

[0042] Shut down the load-keeping function of the testing machine and export the load-time correspondence data;

[0043] Based on the time alignment principle, the load-strain correspondence data is sorted out through the load-time correspondence data and the strain-time correspondence data;

[0044] The same steps were repeated for multiple groups of tests, and the test results were calculated to obtain the critical temperature of the FRP tendon-clip under transverse compression and the cross section of the FRP tendon-clip and the load / temperature-strain curve at the cross section of the clip under each target test pressure. The critical temperature of the FRP tendon-clip under transverse compression, the temperature-strain curve and the load-strain curve under different target test pressures were compared to obtain the high-temperature transverse stress characteristics of the FRP tendon-clip under transient testing.

[0045] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0046] The high FRP tendon-clip bearing capacity test device is provided with a pressure plate assembly, a clip assembly, and a pressure rod assembly, respectively, which can simulate the transverse compression process of the FRP tendon-clip in the FRP tendon-clip anchoring system at high temperature, and ensure that the pressure plate assembly directly in contact with the FRP tendon-clip is completely exposed in the high temperature box of the testing machine and the pressure of the testing machine is not directly applied to the clip assembly; the pressure rod assembly fixes the test device and the testing machine, solving the problem of easy slippage in other fixing methods;

[0047] Through the fire resistance performance testing method of the testing device, the transverse compressive bearing capacity of FRP tendon-clip at different temperatures, the temperature / load-strain curves at the FRP tendon cross section and the clip cross section can be obtained in the steady-state test; the transverse compressive critical temperature of FRP tendon-clip under different loads, the load / temperature-strain curves at the FRP tendon cross section and the clip cross section can be obtained in the transient test; finally, the high-temperature transverse compression force characteristics of FRP tendon-clip under steady-state test and transient test can be summarized; the contact deformation law of FRP tendon-clip under high-temperature pressure environment can be summarized to improve the thermal-mechanical coupling numerical model of FRP tendon-clip anchor in the finite element software abaqus; thereby, a basis is provided for the fire resistance design research of FRP tendon-clip anchor. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a three-dimensional structural diagram of the pressure plate assembly and the clip assembly of the FRP tendon-clip bearing capacity test device;

[0049] Figure 2 It is a structural schematic diagram of the upper pressure rod;

[0050] Figure 3 It is a structural schematic diagram of the lower pressure plate;

[0051] Figure 4 is a schematic diagram of the lower clip;

[0052] Figure 5 is a schematic diagram of a test apparatus having a positioning aid component;

[0053] Figure 6 It is a schematic diagram of the test device installed on the test machine frame.

[0054] In the figure:

[0055] 1: Upper pressure rod 2: Lower pressure rod 3: Upper pressure plate

[0056] 4: Lower pressure plate 5: Upper clamp 6: Lower clamp

[0057] 7: FRP rib 8: bulge 9: round slot

[0058] 10: Baffle 11: U-shaped frame 12: Screw

[0059] 13: Platen groove 14: Clip groove 15: First end face of the pressure rod

[0060] 16: First end surface of the pressing plate 17: Rear surface of the pressing plate 18: Gap between the plates

[0061] 19: Gasket 20: Connector 21: Test machine upper joint

[0062] 22: Testing machine lower joint 23: High temperature box door 24: Glass observation window

[0063] 25: Front surface of the pressing plate 26: Surface of the pressing plate to be fastened 27: Surface of the clip to be fastened

[0064] 28: Clip side wall 29: Pressure rod side wall DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solution, beneficial effects and significant progress of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the drawings provided in the examples of the present invention. Obviously, all the described embodiments are only partial embodiments of the present invention, rather than all embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0066] A test device for the bearing capacity of FRP tendons and clips, comprising a pressure plate assembly, a clip assembly, and a pressure rod assembly. The pressure rod assembly (partially exposed to the outside of a high-temperature box that is being heated up) and the pressure plate assembly (always located inside the high-temperature box that is being heated up) are both made of GH188 high-temperature resistant steel, with a yield strength of 464MPa, an elastic modulus of 237GPa at 20°C, an elastic modulus of 213GPa at 400°C, and can work for a long time at 650°C and above; the device parts that are always exposed to the outside of the high-temperature box that is being heated up (such as the test machine connector 20, gasket 19, etc.) are made of No. 45 steel That is, the yield strength is ≥355MPa and the hardness is ≤229HB; the clip assembly (located inside the pressure plate assembly) is made of A6061-T6 aluminum alloy with a yield strength of 230MPa and an elastic modulus of 71GPa; the FRP rib is a unidirectional reinforced rib with a smooth surface made by a pultrusion process of carbon fiber (T700(12K)) and epoxy resin (CP-02A / B), and the volume content of the carbon fiber filaments in the rib is designed to be 65%, and the average density is 1.583cm3.

[0067] like Figure 1As shown, the pressure plate assembly includes a pair of upper pressure plates 3 and lower pressure plates 4 that are mirror-set and used in pairs, and the height of the upper / lower pressure plates is not less than the diameter of the FRP tendons + 40mm; the width of the upper pressure plate 3 and the lower pressure plate 4 is not less than the diameter of the FRP tendons + 40mm, and the length is equal to the length of the upper / lower clips 5, 6, which is also equal to the length of the FRP tendons. The upper and lower pressing plates 3, 4 are both rectangular structures, including a pressing plate surface 26 to be fastened, a first end face 16 of the pressing plate, a front surface 25 of the pressing plate and a rear surface 17 of the pressing plate. The pressing plate surface 26 to be fastened are two very close end faces when the upper and lower pressing plates are fastened. The first end face 16 of the pressing plate is the face opposite to the pressing plate surface 26 to be fastened, that is, the face connecting the upper / lower pressing rods 1, 2. The pressing plate front surface 25 is the face facing the DIC shooting device during testing. The pressing plate rear surface 17 is the face opposite to the pressing plate front surface 25. Both the pressing plate front surface 25 and the pressing plate rear surface 17 have cross-sectional notches of the pressing plate groove 13. The end faces 16 of the upper / lower pressing plates are respectively provided with circular slots 9 with corresponding positions. And as Figure 3 As shown, the pressing plate surface 26 of the lower pressing plate 4 is provided with an inwardly concave arc-shaped pressing plate groove 13, which passes through the lower pressing plate 4. After the two upper / lower pressing plates are buckled together, a channel is formed to accommodate the clip assembly. Since the upper pressing plate and the lower pressing plate have the same structure and are only mirror-imaged, they will not be described here. The cross-section of the pressing plate groove 13 is semicircular, and the radius is equal to the clip radius + 0.1mm. The upper and lower pressing plates 3, 4 are made of high-temperature resistant hard high-strength steel, using the same material and having the same size.

[0068] In order to make the upper / lower pressing plates 3, 4, the upper / lower clamping pieces 5, 6 and the end surfaces of both sides of the FRP rib 7 realize the following Figure 1 As shown in the flush Figure 5 As shown, a vertical positioning auxiliary component is fixedly arranged on the rear surface 17 of the lower pressing plate 4, and the vertical positioning auxiliary component includes a baffle 10, a U-shaped frame 11 and screws 12, all of which are made of the same material as the pressing plate. The U-shaped frame 11 is a rectangular structure with a groove on the inner surface, which is screwed to the rear surface 17 of the lower pressing plate 4 located at the bottom during installation through the screws 12, and the inner surface of the U-shaped frame is in close contact with the rear surface of the lower pressing plate 4; the baffle 10, the U-shaped frame 11 and the screws 12 are all made of the same material as the pressing plate. 0 is inserted into the groove of the U-shaped frame 11, and the position of the baffle is raised from bottom to top so that the baffle can be in close contact with part of the rear surface 17 of the lower pressure plate 4, part of the rear surface 17 of the upper pressure plate 3, part of the upper / lower clamping pieces 5, 6 and part of the FRP rib 7, and then the middle screw is tightened, and the baffle is squeezed and fixed, so that the rear surfaces of the upper / lower pressure plates 3, 4, the rear surfaces of the upper / lower clamping pieces 5, 6 and the rear surfaces of the FRP rib 7 are aligned on the same vertical plane.

[0069] The clip assembly includes a pair of mirror-image upper clips 5 and lower clips 6 used in pairs, the upper / lower clips 5, 6 are axially embedded in the pressing plate groove 13 of the upper / lower pressing plates 3, 4, and the surface 27 to be fastened of the upper / lower clips 5, 6 is flush with the surface 26 to be fastened of the upper / lower pressing plates. Figure 4 As shown, a semicircular clip groove 14 with a cross section is opened along the axis on one side wall 28 of the lower clip 6 for placing the FRP rib 7 to be tested. The structure of the upper clip 5 is the same as that of the upper clip 5, but it is set in a mirror image, which will not be repeated here. The outer radius of the upper / lower clips 5, 6 is not less than the FRP rib radius + 10mm, and the radius of the clip groove 14 is equal to the FRP rib radius + 0.1mm. The upper / lower clips 5, 6 are made of soft metal material, preferably aluminum or copper, and their outer contours are adapted to the pressure plate groove 13.

[0070] If the upper / lower clamping surface 27 and the upper / lower pressure plate surface 26 are not flush, a gasket 19 made of hard metal material can be placed on the left and right sides of the FRP rib (from the DIC observation angle) between the installed end faces 27 of the clamping pieces 5 and 6 and the end faces 26 of the pressure plates 3 and 4 for adjustment. The gasket 19 is used to adjust the upper and lower end faces after buckling, so that the upper end faces are flush on the same horizontal plane (the same applies to the lower end faces). The gasket 19 is in the form of a thin sheet, placed on the pressure plate surface 26, and ensures that one end can cover the clamping surface 27 and the other end extends out of the gap 18 between the plates to facilitate the corresponding adjustment and removal operations of the test personnel. The specific size is not limited.

[0071] The pressure plate and the clip are both cut with a thickness of 0.5-1mm along the length direction. According to the principle that the ratio of the FRP bar-clip cross-section contact length to the FRP bar circumference length is about 0.85, the calculated cutting thickness of the upper / lower pressure plate / clip is 0.5mm when it is less than 0.5mm, and 1mm when it is greater than 1mm.

[0072] The pressure rod assembly includes a pair of upper pressure rods 1 and lower pressure rods 2 that are arranged in mirror images and used in pairs. Figure 2As shown, the lower pressure rod 2 is a cylinder having a cylindrical side wall 29, a first end face 15 of the pressure rod and an end face opposite to the first end face of the pressure rod (the second end face of the pressure rod, not shown in the figure). A cylindrical protrusion 8 is provided on the first end face 15 of the lower pressure rod for inserting into the slot hole 9. The outer contour of the protrusion 8 is adapted to the slot hole 9, and the protrusion 8 is an integral structure with the upper / lower pressure rod. A through hole is provided on the side wall of the second end face of the lower pressure rod 2 for fixing and connecting the upper joint and the lower joint of the testing machine. The structure of the upper pressure rod 1 is the same as that of the lower pressure rod 2, but is mirror-imaged, and will not be repeated here. The length of the upper / lower pressure rod is sufficient to ensure that one end of it can be fixed on the frame of the testing machine and the other end can be extended into the inner cavity of the high-temperature box. The diameter is adapted to the upper joint 21 and the lower joint 22 of the frame of the testing machine, and is not less than the width of the first end face 16 of the pressure plate to ensure uniform force transmission. The upper and lower pressure rods 1, 2 are made of high-temperature resistant hard high-strength steel, using the same material and having the same size.

[0073] When in use, the upper and lower pressing plates are provided with pressing plate grooves 13 with pressing plate surfaces 26 to be fastened relative to each other. After the cutting process, there is a gap 18 of 1-2mm between the flush surfaces to be fastened formed by the upper pressing plate and the upper clamp 5 and the flush surfaces to be fastened formed by the lower pressing plate and the lower clamp, so as to avoid the upper and lower pressing plates contacting each other in advance before the FRP tendons fail during the test, thereby ensuring that the compressive load is applied to the FRP tendons 7 to be measured and avoiding invalid loading.

[0074] The specific steps of the fire resistance performance testing method of the FRP bar-clip bearing capacity testing device are as follows:

[0075] Step 1: Before the test, open the high temperature box door 23 and install the FRP bar-clip bearing capacity test device; specifically including:

[0076] S101: Figure 6 As shown, one end of the upper pressure rod 1 and the lower pressure rod 2 are respectively inserted into the upper joint 21 and the lower joint 22 corresponding to the test machine frame, and a connecting piece 20 (i.e., a bolt rod) is inserted into the through hole of the upper / lower joint and the through hole of the upper / lower pressure rod for fixing; the other end of the upper pressure rod 1 passes through the circular hole on the top surface of the high temperature box and extends into the inner cavity of the high temperature box, and the other end of the lower pressure rod 2 passes through the circular hole on the bottom surface of the high temperature box and extends into the inner cavity of the high temperature box;

[0077] S102: In the inner cavity of the high temperature box, the lower pressing plate 4, the lower clamping piece 6, the FRP rib 7, the upper clamping piece 5, and the upper pressing plate 3 are sequentially placed on the first end face 15 of the lower pressing rod extending into the inner cavity of the high temperature box, ensuring that the protrusion 8 of the lower pressing rod is inserted into the slot hole 9 of the lower pressing plate, the protrusion 8 of the upper pressing rod is inserted into the slot hole 9 of the upper pressing plate, the upper / lower clamping pieces 5, 6 are respectively embedded in the pressing plate groove 13, and the FRP rib 7 is embedded in the clamping piece groove 14;

[0078] S103: Set up multiple temperature sensors: fix the temperature sensors on the rod body of the upper / lower pressure rod to measure the temperature of the FRP rib surface, the clamp surface, and the pressure plate surface, and fix multiple temperature sensors at various locations in the high temperature box cavity to measure the ambient temperature of the high temperature box cavity. The temperature sensor adopts a K-type thermocouple, which is composed of a temperature measuring wire and a detection head. The temperature measuring wire is fixed on the rod body and the high temperature cavity respectively to prevent it from falling off or shifting during the test; the thermocouple relies on the contact between the detection head and the surface to be measured to capture the temperature, and feeds back to the temperature recording instrument in real time through the temperature measuring wire (multiple thermocouples are displayed together with the same paperless recorder). High-temperature resistant asbestos rope is used to bind the thermocouple temperature measuring line at a distance from the detection head. The purpose of fixation is to prevent slippage to assist in the positioning of the probe; the detection heads of some thermocouples are evenly exposed to the air in the high-temperature box to monitor the change of the ambient temperature of the inner cavity of the high-temperature box over time, and the thermocouple temperature measuring line near the detection head is adhered to the adjacent pressure plate surface with polytetrafluoroethylene tape to assist in positioning; the detection heads of another part of the thermocouples are respectively in contact with the FRP reinforcement surface, the clamp surface, and the pressure plate surface to monitor the change of the surface temperature of the test object and the pressure plate over time, and the detection heads are adhered and fixed with polytetrafluoroethylene tape.

[0079] S104: Raise the baffle 10 and tighten the screws 12 on the U-shaped frame 11 to align the upper / lower pressing plates 3, 4, the upper / lower clamping plates 5, 6 and the rear surface 17 of the pressing plate of the FRP rib 7 (such as Figure 5 After alignment, loosen the screw 12 and lower the baffle 10;

[0080] Use the gasket 19 to adjust the upper and lower end faces after buckling, so that the upper clamping surface 27 and the pressing plate surface 26 are flush on the same horizontal plane (the lower end face is treated in the same way), and use the testing machine to apply 1 to 10 kN as a preload to the test device. After the test device is pressed and all faces are flush, remove the gasket 19;

[0081] S105: Close the high temperature box door 23, use DIC (Digital Image Correlation) equipment to observe the strain through the glass observation window 24 on the high temperature box door 23, and plug the other gaps around the high temperature box with asbestos to prepare for the test, which includes steady-state test and transient test.

[0082] Step 2: Preparation of test parameters

[0083] Steady-state test:

[0084] Two preliminary tests are required before the formal test: the glass transition temperature test of FRP bars (test purpose: to measure the glass transition temperature range of the specimen to formulate the target test temperature in the steady-state test) and three groups of temperature rise tests of the test objects in the high temperature box and the box that are consistent with the formal test steps (test purpose: to monitor the change of the ambient temperature in the box and the surface temperature of the test object over time to determine the insulation time). Among them, the glass transition temperature test of FRP bars can refer to the current standard operation. Since the dynamic mechanical analysis method (DMA) is the most sensitive test method among the several commonly used test methods for testing the glass transition temperature, and is more suitable for composite materials, the glass transition temperature test of FRP bars is carried out according to GB / T40396-2021, Test method for glass transition temperature of polymer-based composite materials Dynamic mechanical analysis method (DMA) "; the temperature rise test of the high temperature box and the test object in the box is basically the same as the formal steady-state test operation. It is used as a preliminary test before the formal test to debug and verify the feasibility of each test parameter (prepared based on historical experience) and determine the actual required insulation time.

[0085] Through the glass transition temperature test of FRP bars, the initial glass transition temperature T1 (126.7°C), the end glass transition temperature T4 (191.9°C) and the glass transition temperature range [T1, T4] ([126.7°C, 191.9°C]) are obtained. According to the property change law of FRP bars before, during and after the glass transition temperature range, some suitable target test temperatures can be formulated:

[0086] Before the initial glass transition temperature T1, the FRP bars are in a high elastic state with stable performance changes, and only a few temperatures with special significance are selected: the room temperature is determined to be 20°C based on the room temperature; the high elastic state target test temperature is determined to be 80°C and 110°C based on the statistics of the highest ambient temperature in North China / global (40.8°C, 71°C) and the highest roof temperature rise caused by solar thermal radiation (37.24°C) (40.8°C + 37.24°C = 78.04°C, 71°C + 37.24°C = 108.24°C).

[0087] In the glass transition temperature range [T1, T4], the FRP bar is in a glass transition state with unstable performance. First, according to the T1 and T4 values, the glass transition target test initial temperature T1' and the glass transition target test termination temperature T4' are respectively proposed. Among them, T1' adopts the rounding method, which is not greater than T1 and is 126°C, and T4' adopts the rounding method, which is not less than T4 and is 192°C. In [T1', T4'], some transition state target test temperatures are equidistantly proposed at a temperature increase interval of 6°C (generally not more than 10°C), namely, 132°C, 138°C, 144°C, 150°C, 156°C, 162°C, 168°C, 174°C, 180°C, and 186°C.

[0088] After the glass transition termination temperature T4, the FRP bar is in a viscous state. According to a smaller temperature increase interval of 4°C (generally not exceeding 5°C) and combined with the actual test situation, some viscous state target test temperatures of 196°C, 200°C, 204°C, 208°C, 212°C, 216°C, 220°C, etc. are evenly spaced (the two conditions of reaching the upper temperature limit of the equipment and the FRP bar being greatly deformed and the upper and lower pressure plates almost in contact before loading begins can be used as termination conditions).

[0089] In the temperature rise test of the high-temperature box and the test objects in the box, the heating rate, loading rate, and DIC equipment shooting speed are all consistent with those in the formal test, and the holding time is temporarily conservatively set at 4h; a highest value is selected as the target test temperature among the target test temperatures planned in the formal test, and three groups of parallel tests are carried out at this temperature; through this preliminary test, the feasibility of each test parameter can be verified (if it does not meet the requirements, based on this preliminary test, the formal test is simulated and the parameter adjustment is analyzed in the abaqus software, and finally the appropriate test parameters are formulated); based on the average result of the obtained temperature-time curve, a suitable holding time can be determined.

[0090] During the formal test, turn on all the power supplies of the high temperature box, test machine, and DIC equipment, and pre-set the planned test parameters on the control panel as follows:

[0091] Target test temperature: room temperature is set at 20°C, high elastic state target test temperature is 80°C and 110°C, glass transition target test initial temperature T1' is 126°C, transition state target test temperature is 132°C, 138°C, 144°C, 150°C, 156°C, 162°C, 168°C, 174°C, 180°C, 186°C, glass transition target test termination temperature T4' is 192°C, viscous state target test temperature is 196°C, 200°C, 204°C, 208°C, 212°C, 216°C, 220°C, etc.; the glass transition temperature range [T1, T4] obtained from the glass transition temperature test of FRP bars is proposed;

[0092] Heating rate: 5℃ / min; in order to reduce the impact of thermal hysteresis caused by overheating on the test results and reduce the heating time cost, it is proposed to be 3℃ / min-10℃ / min after referring to historical experience data (when inputting the equipment, each group of tests can use a unified value, or they can be input separately according to the principle of using a slow heating rate for a low target temperature and a fast heating rate for a high target temperature);

[0093] Insulation time: 1h; To ensure that the temperature field inside the high temperature box and inside and outside the reinforcement is evenly distributed and the entire sample reaches the target temperature, it can be set within the range of 30min-2h (according to the temperature rise test results, when the insulation time exceeds 2h, the surface temperature of the sample increases extremely slowly);

[0094] Loading rate: 1.3mm / min; To ensure stable loading, it can be set within the range of 1mm / min-1.5mm / min;

[0095] DIC equipment shooting speed: 5 frames / second; in order to ensure the smooth operation of the observation work and reduce the equipment storage space, it can be set within the range of 1 frame / second-5 frames / second (the DIC equipment used in this experiment can be set to a minimum of 1 frame / second).

[0096] Transient test:

[0097] With the experience of steady-state testing, the transient test can select the highest target test pressure to conduct a few simple preliminary tests or use numerical simulation to verify the application effect of each test parameter formulated based on historical experience data.

[0098] During the formal test, turn on all the power supplies of the high temperature box, test machine, and DIC equipment, and pre-set the proposed test parameters on the control panel as follows:

[0099] Target test pressure: 130kN, 210kN, 290kN; According to the standard "GB / P 50608-2020, Technical Standard for Engineering Application of Fiber Reinforced Composite Materials", the lower limit of the tension control stress of fiber composite reinforcement is 0.40, and the upper limit is 0.65. The above three target test pressures are formulated by establishing a numerical model of FRP reinforcement clip anchor in abaqus software and simulating the reinforcement anchoring tension reaching its limit of 0.40, 0.65, and 0.90 (considering the situation close to failure);

[0100] Loading rate: 1.3mm / min; To ensure stable loading, it can be set within the range of 1mm / min-1.5mm / min;

[0101] Heating rate: 1.8℃ / min; To minimize the temperature difference between the inside and outside of the sample and reduce the heating time cost and DIC equipment storage space, it can be set within the range of 0.5℃ / min to 3℃ / min;

[0102] DIC equipment shooting speed: 1 frame / second; in order to ensure the smooth operation of the observation work and reduce the equipment storage space, it can be set within a range lower than or equal to 1 frame / second (the DIC equipment used in this experiment can be set to a minimum of 1 frame / second).

[0103] Step 3: Testing Phase

[0104] Steady-state test:

[0105] First, conduct the first set of tests with a target test temperature of 20°C:

[0106] The temperature in the high temperature box is raised from the actual room temperature to the first target test temperature of 20°C at a heating rate of 5°C / min (if the actual room temperature is higher than 20°C, the current temperature value is recorded as the first target test temperature). The ambient temperature of the high temperature box is monitored in real time by multiple temperature sensors distributed at different positions inside the high temperature box, and the strain is observed using a DIC device;

[0107] After maintaining the target temperature for 1 h, the actuator of the testing machine was loaded at a rate of 1.3 mm / min;

[0108] When the FRP bar is greatly deformed and the upper and lower plates are almost in contact, the loading can be terminated and the current load value can be recorded as the FRP bar-clip transverse compressive bearing capacity (f1), and the load-time (F1-t) corresponding data can be derived;

[0109] Stop DIC shooting, generate the vertical compressive strain nephogram and transverse shear strain nephogram of the FRP bar cross section based on the photos taken at the FRP bar cross section and the clip cross section, and derive the vertical compressive strain-time (ε yy1 -t1) and transverse shear strain-time (εxy1 -t1) corresponding data;

[0110] According to the load-time correspondence data and strain-time correspondence data, based on the time alignment principle, the load-strain correspondence data, namely F1-ε, is sorted out. yy1 Data and F1-ε xy1 data;

[0111] Turn off the heat preservation function of the high temperature box and export the temperature sensor recorded data, that is, the temperature-time (T1-t1) corresponding data;

[0112] Based on the principle of time alignment, the temperature-strain correspondence data, namely T1-ε, is sorted out by the temperature-time correspondence data and the strain-time correspondence data. yy1 Data and T1-ε xy1 data;

[0113] Release the pressure of the testing machine and restore the test piece to the initial position. Turn on the fan function of the high temperature box to accelerate the natural cooling of the high temperature box. When the ambient temperature in the high temperature box cools down to close to room temperature, open the box door and disassemble the test device in the reverse order of step 1 (during the cooling process, the temperature in the box can be monitored in real time through the high temperature box display screen. The pressing plate and the pressing rod are reusable devices in the test. In order to protect them from the degradation of mechanical properties caused by high temperature oxidation, avoid opening the box door when the temperature is high so that they are exposed to too much air);

[0114] Close the high temperature box door and keep it ready for the next test;

[0115] The test piece is separated from the pressing plate and bagged for recovery (due to the influence of temperature, the test piece and the pressing plate may fit tightly together and be difficult to separate. They can be disassembled by knocking on the end surface with the help of tools such as steel pipes in the laboratory). It is numbered W-20-1 (the first group of tests in the steady-state test with a target test temperature of 20°C).

[0116] The same steps are used to test W-20-2 and W-20-3, and the corresponding FRP bar-clip transverse compressive bearing capacity f2 and f3, and the load-vertical compressive strain F2-ε at the FRP bar cross section and the clip cross section are obtained. yy2 With F3-ε yy3 Data and Loads - Transverse Shear Strain F2-ε xy2 With F3-ε xy3 Data, temperature-vertical compressive strain T2-ε at the cross section of FRP bars and clips yy2 T3-ε yy3 Data and temperature - transverse shear strain T2-ε xy2 T3-ε xy3 data;

[0117] According to the three test results, the arithmetic mean is calculated according to formula (1): Calculate to three significant figures.

[0118]

[0119] Where:

[0120] X i ——The data results obtained from each test group (f i 、F i , T i , ε yyi , ε xyi );

[0121] n——Number of test groups.

[0122] Calculate the standard deviation S according to formula (2) to two significant figures.

[0123]

[0124] The symbols in the formula are the same as those in formula (1).

[0125] Calculate the dispersion coefficient C according to formula (3) to two significant figures.

[0126]

[0127] The symbols in the formula are the same as those in formula (1) and (2).

[0128] Get the average results of each data Standard Deviation and coefficient of dispersion After that, As the target test temperature of 20℃, the FRP bar-clip transverse compressive bearing capacity is obtained, and the load-strain curve is drawn at the target test temperature of 20℃. And temperature-strain curve

[0129] Next, the same steps are followed for the first, second, and third tests (W-80-1, W-80-2, and W-80-3) with a target test temperature of 80°C: the temperature inside the high-temperature box is raised from the actual room temperature to the second target test temperature of 80°C at a heating rate of 5°C / min. The temperature of the high-temperature box is monitored in real time by multiple temperature sensors located at different positions inside the high-temperature box, and the strain is observed using DIC equipment... The test steps for each subsequent set of target test temperatures are similar.

[0130] The transverse compressive bearing capacity, load-strain curve and temperature-strain curve of FRP tendon-clip under different target test temperatures were compared to explore the influence of temperature and summarize the high-temperature transverse stress characteristics of FRP tendon-clip under steady-state test.

[0131] Transient test:

[0132] The first set of tests with a target test pressure of 130kN is carried out:

[0133] The testing machine actuator loaded the specimen to the first target test pressure of 130 kN at a rate of 1.3 mm / min, and the strain was observed using the DIC device;

[0134] After the pressure stabilizes, the high temperature box is heated from room temperature at a rate of 1.8°C / min, and the temperature of the high temperature box is monitored in real time by multiple temperature sensors located at different locations inside the high temperature box;

[0135] When the FRP bar is greatly deformed and the upper and lower plates are almost in contact, the temperature rise can be stopped and the current temperature value can be recorded as the critical temperature (Tc1) of the FRP bar-clip transverse compression, and the temperature sensor recorded data can be exported, that is, the temperature-time (T1-t1) corresponding data;

[0136] Stop DIC shooting, generate the vertical compressive strain nephogram and transverse shear strain nephogram of the FRP bar cross section and the clip cross section based on the photos taken at the FRP bar cross section and the clip cross section, and derive the vertical compressive strain-time (ε yy1 -t1) and transverse shear strain-time (ε xy1 -t1) corresponding data;

[0137] According to the temperature-time correspondence data and strain-time correspondence data, based on the time alignment principle, the temperature-strain correspondence data, namely T1-ε, is sorted out. yy1 Data and T1-ε xy1 data;

[0138] Shut down the load-keeping function of the testing machine and export the corresponding data of load-time (F1-t1);

[0139] Based on the principle of time alignment, the load-strain correspondence data is sorted out through the load-time correspondence data and the strain-time correspondence data, namely F1-ε yy1 Data and F1-ε xy1 data;

[0140] Release the pressure of the testing machine and restore the test piece to the initial position. Turn on the fan function of the high temperature box to accelerate the natural cooling of the high temperature box. When the ambient temperature in the high temperature box cools down to close to room temperature, open the box door and disassemble the test device in the reverse order of step 1 (during the cooling process, the temperature in the box can be monitored in real time through the high temperature box display screen. The pressing plate and the pressing rod are reusable devices in the test. In order to protect them from the degradation of mechanical properties caused by high temperature oxidation, avoid opening the box door when the temperature is high so that they are exposed to too much air);

[0141] Close the high temperature box door and keep it ready for the next test;

[0142] The specimen is separated from the pressure plate and bagged for recovery (due to the influence of temperature, the specimen and the pressure plate may fit tightly together and be difficult to separate. They can be disassembled by knocking on the end surface with the help of tools such as steel pipes in the laboratory). It is numbered S-130-1 (the first group of tests in the transient test with a target test pressure of 130kN).

[0143] The same steps were used to test S-130-2 and S-130-3, and the corresponding FRP bar-clip transverse compression critical temperatures Tc2 and Tc3, and the temperature-vertical compressive strain T2-ε at the FRP bar cross section and the clip cross section were obtained. yy2 T3-ε yy3 Data and temperature-transverse shear strain T2-ε xy2 T3-ε xy3 Data, vertical compressive strain F2-ε at the cross section of FRP bars and clips yy2 With F3-ε yy3 Data and Loads - Transverse Shear Strain F2-ε xy2 With F3-ε xy3 data;

[0144] According to the three test results, the arithmetic mean is calculated according to formula (1): Calculate to three significant figures.

[0145]

[0146] Where:

[0147] X i ——The data results obtained from each test group (Tc i 、T i 、F i , ε yyi , ε xyi );

[0148] n——Number of test groups.

[0149] Calculate the standard deviation S according to formula (2) to two significant figures.

[0150]

[0151] The symbols in the formula are the same as those in formula (1).

[0152] Calculate the dispersion coefficient C according to formula (3) to two significant figures.

[0153]

[0154] The symbols in the formula are the same as those in formula (1) and (2).

[0155] Get the average results of each data Standard Deviation and coefficient of dispersion After that, As the critical temperature of FRP bar-clip transverse compression under the target test pressure of 130kN, the temperature-strain curve under the target test pressure of 130kN is drawn and load-strain curve

[0156] Next, the same steps are performed for the first, second, and third test groups (S-210-1, S-210-2, S-210-3) with a target test pressure of 210 kN and the first, second, and third test groups (S-290-1, S-290-2, S-290-3) with a target test pressure of 290 kN.

[0157] The critical temperature, temperature-strain curve and load-strain curve of FRP tendon-clip under different target test pressures were compared to explore the influence of pressure and summarize the high-temperature transverse stress characteristics of FRP tendon-clip under transient test.

[0158] Finally, the contact deformation law of FRP bar-clip under high temperature and pressure environment is summarized by combining the steady-state test and transient test results to improve the thermal-mechanical coupling numerical model of FRP bar clip-type anchor in the finite element software abaqus. Thus, it provides a basis for the fire-resistant design research of FRP bar clip-type anchor.

[0159] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. The non-essential improvements, adjustments or replacements made by those skilled in the art based on the contents of this specification are all within the scope of protection required by the present invention.

Claims

1. A FRP bar-clip bearing capacity testing device, characterized in that: It includes a pressure plate assembly, a clip assembly, and a pressure rod assembly; the pressure plate assembly includes a pair of upper and lower pressure plates that are mirror-imaged and used in pairs, and the pressure plate surfaces of the upper and lower pressure plates are provided with inwardly concave pressure plate grooves, which penetrate the pressure plates along the axial direction and have a semicircular cross section, and are used to place the clip assembly, and the upper and lower pressure plates have slots on their end surfaces facing the testing machine; the clip assembly includes a pair of upper and lower clips that are mirror-imaged and used in pairs, and the clip surfaces of the upper and lower clips are provided with inwardly concave clip grooves, which penetrate the clips along the axial direction and have a semicircular cross section, and are used to place the FRP tendon-clip to be tested; The pressure rod assembly includes a pair of upper pressure rods and lower pressure rods that are arranged in a mirror image and used in pairs; the first end faces of the pressure rods of the upper pressure rod and the lower pressure rod are provided with a cylindrical protrusion for inserting into the slot hole, the outer contour of the protrusion is adapted to the slot hole, and a through hole is opened on the side wall of the other end face of the pressure rod for fixing and connecting the upper joint and the lower joint of the testing machine; and the length of the pressure rod is such that one end of it is fixed on the frame of the testing machine and the other end extends into the inner cavity of the high temperature box, the diameter is adapted to the upper joint and the lower joint of the frame of the testing machine, and is not less than the width of the first end face of the pressure plate of the upper pressure plate and the lower pressure plate to ensure uniform force transmission; When in use, the upper clamp and the lower clamp are axially embedded in the pressing plate grooves of the upper and lower pressing plates, and the FRP rib-clamp is placed in the clamp groove; the end surfaces of the two pressing plates provided with the pressing plate grooves are placed opposite to each other, the end surfaces of the clamp provided with the clamp grooves are placed opposite to each other, and the end surfaces of the clamp to be fastened are flush with the end surfaces of the pressing plate to be fastened; The upper pressing plate and the lower pressing plate respectively include a pressing plate surface to be fastened, a first end surface of the pressing plate, a front surface of the pressing plate and a rear surface of the pressing plate. The pressing plate surface to be fastened is the end surface close to each other when the upper pressing plate and the lower pressing plate are fastened. The first end surface of the pressing plate is the surface opposite to the pressing plate surface to be fastened, that is, the surface connecting the upper pressing rod and the lower pressing rod. The front surface of the pressing plate is the surface facing the DIC shooting device during the test. The rear surface of the pressing plate is the surface opposite to the front surface of the pressing plate. Both the front surface and the rear surface of the pressing plate have cross-sectional notches of the pressing plate groove. The pressing plate assembly also includes a fixed vertical positioning auxiliary assembly, which includes a baffle, a U-shaped frame and screws, all of which are the same as the pressing plate. The U-shaped frame is a rectangular parallelepiped structure with a groove on the inner surface, which is screwed to the rear surface of the pressure plate located at the lower pressure plate during installation by screws, and the inner surface of the U-shaped frame is in close contact with the rear surface of the pressure plate of the lower pressure plate; the lower end of the baffle is inserted into the groove of the U-shaped frame, and the position of the baffle is raised from bottom to top so that the baffle can be in close contact with part of the rear surface of the pressure plate of the lower pressure plate, part of the rear surface of the pressure plate of the upper pressure plate, part of the upper clamp and the lower clamp, and part of the FRP rib-clamp, and then the middle screw is tightened, and the baffle is squeezed and fixed, so that the rear surfaces of the upper and lower pressure plates, the rear surfaces of the upper and lower clamps, and the rear surface of the FRP rib-clamp are aligned on the same vertical plane; In order to make the surfaces to be fastened of the upper and lower clamps flush with the surfaces to be fastened of the upper and lower pressure plates, a gasket made of hard metal material is placed on both sides of the left and right sides of the FRP rib-clip between the installed surfaces to be fastened of the clamps and the surfaces to be fastened of the pressure plates. With the help of the gaskets, the upper and lower end surfaces after fastening are adjusted respectively, so that the surfaces to be fastened of the upper clamps and the surfaces to be fastened of the pressure plates are both flush on the same horizontal plane, and the surfaces to be fastened of the lower clamps and the surfaces to be fastened of the pressure plates are also flush on the same horizontal plane. A testing machine is used to apply 1 to 10 kN as a preload to the test device. After the test device is pressed and all surfaces are flush, the gaskets are removed.

2. The FRP bar-clip bearing capacity testing device according to claim 1, characterized in that: The radius of the pressing plate groove of the pressing plate is equal to the outer radius of the clip + 0.1mm, the outer radius of the upper and lower clips is not less than the FRP bar-clip radius + 10mm, and the radius of the clip groove is equal to the FRP bar-clip radius + 0.1mm.

3. The FRP bar-clip bearing capacity testing device according to claim 1, characterized in that: The pressing plate and the clamping piece are both cut with a thickness of 0.5-1 mm along the length direction, so that a gap of 1-2 mm is formed between the flush upper and lower ends of the pressing plate and the clamping piece.

4. The FRP bar-clip bearing capacity testing device according to claim 1, characterized in that: The material of the clip assembly is aluminum or copper; the material of the pressure plate assembly and the pressure rod assembly is mainly high temperature resistant steel.

5. The method for testing the fire resistance performance of the FRP bar-clip bearing capacity testing device according to claim 1, comprising: Step 1: Before the test, open the high temperature box door and install the FRP tendon-clip bearing capacity test device; The pressure rod assembly of the test device is respectively installed at the upper joint and the lower joint corresponding to the test machine frame, and then in the inner cavity of the high temperature box, the lower pressure plate, the lower clamp, the FRP rib-clip, the upper clamp, and the upper pressure plate are sequentially placed on the first end face of the pressure rod of the pressure rod extending into the inner cavity of the high temperature box, ensuring that the protrusion of the lower pressure rod is inserted into the slot hole of the lower pressure plate, the protrusion of the upper pressure rod is inserted into the slot hole of the upper pressure plate, the upper clamp and the lower clamp are respectively embedded in the pressure plate groove, and the FRP rib-clip is embedded in the clamp groove, ensuring that the front surface of the pressure plate faces the glass observation window and the entire front surface area of ​​the FRP rib-clip and the upper clamp and the lower clamp are located within the field of view of the observation window; Step 2: Preparation of test parameters Steady-state test: Two preliminary tests are performed before the formal test, namely, the glass transition temperature test of the FRP bar-clip and the temperature rise test of the high temperature box and the test object in the box; wherein, the glass transition temperature test of the FRP bar-clip is used to obtain the glass transition temperature range [T 1 ,T 4 ], and the target test temperature is proposed according to the property change law of the FRP bar-clip before, during and after the glass transition temperature range; the target test temperature includes the room temperature proposed value, the high elastic state target test temperature value, the glass transition target test initial temperature T 1 ', the transition state target test temperature value, the glass transition target test termination temperature T 4 ' and the viscous state target test temperature value; wherein, T 1 is the glass transition initial temperature, and T 4 is the glass transition termination temperature; According to historical experience data, the heating rate, loading rate, and DIC equipment shooting speed are set respectively, among which the heating rate is 3℃ / min-10℃ / min, the loading rate is 1mm / min-1.5mm / min, and the DIC equipment shooting speed is 1 frame / second-5 frames / second; the insulation time is planned to be 4h; Using the above-proposed heating rate and loading rate, perform multiple groups of temperature rising tests on the high-temperature box and the test object in the box that are consistent with the formal test steps, so as to monitor the change of the ambient temperature in the box and the surface temperature of the test object over time, so as to determine the insulation time; wherein, the target test temperature of the test is the highest value selected from the multiple target test temperatures proposed; the final result is the average value of the multiple test results, and the insulation time is determined by the test results, and the insulation time is 30min-2h; Transient test: The upper and lower limits of the tension control stress of the fiber composite reinforcement are obtained based on historical data to formulate the target test pressure value; The loading rate, heating rate, and DIC equipment shooting speed are set according to historical experience data; the loading rate is 1mm / min-1.5mm / min, the heating rate is 0.5℃ / min-3℃ / min, and the DIC equipment shooting speed is ≤1 frame / second; Step 3: Testing Phase Input the heating rate and loading rate obtained in the previous step into the control panel of the test machine, turn on each test device, and use the DIC device to observe the strain during the whole process; the high temperature box is heated to the target test temperature at the set heating rate, and the ambient temperature of the high temperature box is monitored in real time through multiple temperature sensors distributed at different positions inside the high temperature box; when the target test temperature value is reached, maintain the set insulation time; then apply pressure to the test device at the set loading rate; When the FRP bar is deformed and the upper and lower plates are almost in contact, the loading is terminated and the data is recorded and calculated; finally, the transverse compressive bearing capacity of the FRP bar-clip and the temperature / load-strain curve of the FRP bar-clip cross section and the clip cross section under the room temperature proposed value, the high elastic state target test temperature value, the glass transition target test initial temperature T 1 ', the transition state target test temperature value, the glass transition target test termination temperature T 4 ' and the viscous state target test temperature value are obtained; the transverse compressive bearing capacity, load-strain curve and temperature-strain curve of the FRP bar-clip under different target test temperatures are compared to obtain the high-temperature transverse force characteristics of the FRP bar-clip under steady-state test; Input the heating rate and loading rate obtained in the previous step into the control panel of the test machine, start each test device, and use the DIC device to observe the strain during the whole process; the test machine applies pressure to the test device at the set loading rate until the target test pressure is reached; when the pressure value remains stable, the high temperature box starts to heat from room temperature at the set heating rate, and the temperature of the high temperature box is monitored in real time through multiple temperature sensors distributed at different positions inside the high temperature box; When the FRP tendons are deformed and the upper and lower pressure plates are almost in contact, the loading is terminated and the data are recorded and calculated; finally, the critical temperature of the FRP tendon-clip under transverse compression and the load / temperature-strain curves at the FRP tendon-clip cross section and the clip cross section under each target test pressure are obtained.

6. The fire resistance testing method according to claim 5, characterized in that: In the steady-state test of step 3, when the FRP bars are deformed and the upper and lower plates are almost in contact, the loading is terminated and the data are recorded and calculated, including: When the FRP bar is deformed and the upper and lower pressure plates are almost in contact, the loading is terminated and the current load value is recorded as the transverse compressive bearing capacity of the FRP bar-clip, and the load-time correspondence data is derived; Stop DIC shooting, generate the vertical compressive strain cloud map and transverse shear strain cloud map of the FRP bar-clip cross section based on the photos taken at the FRP bar cross section and the clip cross section, and derive the vertical compressive strain-time and transverse shear strain-time corresponding data; According to the load-time correspondence data and the strain-time correspondence data, based on the time alignment principle, the load-strain correspondence data is obtained; Turn off the heat preservation function of the high temperature box and export the temperature-time corresponding data recorded by the temperature sensor; Based on the time alignment principle, the temperature-strain correspondence data is sorted out through the temperature-time correspondence data and the strain-time correspondence data; The same steps were repeated for multiple groups of tests, and the test results were calculated to obtain the transverse compressive bearing capacity of FRP tendon-clip and the temperature / load-strain curve of the FRP tendon-clip cross section and the clip cross section at the proposed room temperature value, the target test temperature value of the high elastic state, the target test initial temperature T 1 'of the glass transition, the target test temperature value of the transition state, the target test termination temperature T 4 'of the glass transition and the target test temperature value of the viscous state; the transverse compressive bearing capacity, load-strain curve and temperature-strain curve of FRP tendon-clip at different target test temperatures were compared to obtain the high-temperature transverse force characteristics of FRP tendon-clip under steady-state test.

7. The fire resistance testing method according to claim 5, characterized in that: In the transient test of step 3, when the FRP bars are deformed and the upper and lower plates are almost in contact, the loading is terminated and the data are recorded and calculated, including: When the FRP bar is deformed and the upper and lower plates are almost in contact, the temperature rise is stopped and the current temperature value is recorded as the critical temperature of the FRP bar-clip transverse compression, and the data recorded by the temperature sensor is exported, that is, the temperature-time corresponding data; Stop DIC shooting, generate vertical compressive strain cloud diagrams and transverse shear strain cloud diagrams of the FRP bar cross section and the clip cross section based on the photographs taken at the FRP bar cross section and the clip cross section, and derive the vertical compressive strain-time and transverse shear strain-time corresponding data; According to the temperature-time correspondence data and the strain-time correspondence data, based on the time alignment principle, the temperature-strain correspondence data is sorted out; Shut down the load-keeping function of the testing machine and export the load-time correspondence data; Based on the time alignment principle, the load-strain correspondence data is sorted out through the load-time correspondence data and the strain-time correspondence data; The same steps were repeated for multiple groups of tests, and the test results were calculated to obtain the critical temperature of the FRP tendon-clip under transverse compression and the cross section of the FRP tendon-clip and the load / temperature-strain curve at the cross section of the clip under each target test pressure. The critical temperature of the FRP tendon-clip under transverse compression, the temperature-strain curve and the load-strain curve under different target test pressures were compared to obtain the high-temperature transverse stress characteristics of the FRP tendon-clip under transient testing.

Images