Variable angle shear test device for the interface between fiber reinforced composites and concrete

Abstract

The present invention discloses a variable angle shear test device for the interface of fiber reinforced composite material and concrete, which belongs to the technical field of building material testing equipment, and comprises a load-bearing rod penetrating a concrete test block, and the end of the load-bearing rod can be connected to a testing machine; FRP strips are pasted on both sides of the concrete test block, and the FRP strips include a bonding part and a free part, and the free part of the FRP strips and the bonding part form a certain angle, and the free parts of the FRP strips on both sides are arranged relatively; the free end of the FRP strips is connected to the testing machine at the other end through a clamping adjustment mechanism, and the angle between the free part of the FRP strip and the concrete test block is clamped and adjusted by the clamping adjustment mechanism. The two testing machines respectively apply tension to the concrete test block and the FRP strips on both sides thereof through the load-bearing rod and the clamping adjustment mechanism, so as to realize the shear force test of the interface of the fiber reinforced composite material and concrete at different inclination angles. The present invention has a simple structure, is easy to operate, and reduces material costs and pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of building material testing equipment, and in particular relates to a variable angle shear testing device for the interface of a fiber reinforced composite material and concrete. Background Art

[0002] As the service life of various buildings increases, affected by human and natural factors, the buildings need to be reinforced and maintained after a certain period of use. Fiber-reinforced composite materials have become a good choice for reinforcing buildings without increasing their own weight. Therefore, it is particularly important to test the performance between fiber-reinforced composite materials and concrete. Most of the relevant tests in China measure the performance between fiber-reinforced composite materials and concrete when the fiber-reinforced composite materials are flush with the concrete surface without any angle. However, in actual building structures, fiber-reinforced composite materials cannot always be pasted without any angle. Therefore, the performance between fiber-reinforced composite materials and concrete at different angles also needs to be studied. However, the existing testing devices have the defects of complex structure, large amount of materials, and cumbersome and inconvenient use. Summary of the invention

[0003] The purpose of the present invention is to provide a variable angle shear test device for the interface of fiber reinforced composite materials and concrete, aiming to solve the technical problems in the above-mentioned prior art that the test device has a complex structure, uses a lot of materials, and is cumbersome and inconvenient to use.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A variable angle shear test device for the interface of a fiber reinforced composite material and concrete, comprising a load-bearing rod penetrating a concrete test block, wherein the end of the load-bearing rod can be connected to a testing machine; FRP strips are pasted on both sides of the concrete test block, wherein the FRP strips include a bonding portion and a free portion, wherein the free portion of the FRP strip forms a certain angle with the bonding portion, and the free portions of the FRP strips on both sides are arranged opposite to each other; the free end of the FRP strip is connected to the testing machine at the other end through a force-applying rod in the middle of a clamping and adjusting mechanism, and the clamping and adjusting mechanism can clamp and adjust the inclination angle of the free portion of the FRP strip.

[0006] Preferably, the clamping and adjusting mechanism includes a connecting assembly, an angle adjustment frame, high-strength bolts and high-strength nuts, the connecting assembly includes a connecting steel plate and a steel clamping plate, the connecting steel plate is divided into an inclined portion and a straight portion, the inclined portion is consistent with the inclination direction of the free portion of the FRP cloth strip, the steel clamping plate is arranged on the side of the inclined portion, the free end of the FRP cloth strip is arranged between the inclined portion and the steel clamping plate, and is connected and fixed by a high-strength bolt and a high-strength nut; the straight portion is consistent with the side direction of the FRP cloth strip pasted on the concrete test block, and the angle adjustment frame is arranged between the straight portions on both sides and is connected thereto.

[0007] Preferably, the angle adjustment frame includes a connecting screw and an adapter, one end of the connecting screw passes through the straight part of the connecting steel plate and is fixed by a fastening nut, and the other end of the connecting screw is connected to the adapter; the middle part of the adapter is connected to the force rod, and the force rod is connected to the testing machine.

[0008] Preferably, both ends of the force-bearing rod extend to the outside of the concrete test block, one end of the force-bearing rod is connected to the testing machine, and the other end is connected to the inner end of the adapter through a sleeve, so that the central axis of the force-applying rod coincides with that of the force-bearing rod.

[0009] Preferably, a through hole for cooperating with the force-applying rod is provided in the middle of the adapter, ports for cooperating with the threaded connection screw are provided on both sides of the adapter, and the sleeve is sleeved on the outside of the ends of the force-bearing rod and the force-applying rod.

[0010] Preferably, the bonding portion of the FRP strip is adhered to the concrete test block by epoxy resin, and the free portions of the FRP strips on both sides are inclined outward relative to both sides of the concrete test block.

[0011] Preferably, the load-bearing rod and the force-applying rod are both threaded steel bars, and the threaded steel bars are made of Q235 steel with a diameter of 20 mm.

[0012] Preferably, the testing machine is a 100T universal testing machine.

[0013] The beneficial effect of adopting the above technical solution is that compared with the prior art, the present invention applies tension to the force-bearing rods penetrating the concrete test block and the force-applying rod in the middle of the clamping adjustment mechanism through two testing machines. The free part and the adhesive part of the FRP cloth strips (fiber reinforced composite material) on both sides of the concrete test block form a certain angle. With the help of the clamping adjustment mechanism, the tension of the testing machine can be transferred to the FRP cloth strips, thereby realizing the angle adjustment of the interface between the fiber reinforced composite material and the concrete and the shear force test. The present invention has the advantages of simple structure and convenient operation. The test can be completed without making concrete of the relevant angle, which reduces material costs and pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0015] Figure 1 It is a structural schematic diagram of a variable angle shear test device for the interface of a fiber reinforced composite material and concrete provided in an embodiment of the present invention;

[0016] Figure 2 yes Figure 1 Schematic diagram of the connection between the FRP strip and the concrete specimen;

[0017] Figure 3 yes Figure 1 Schematic diagram of the structure of the connecting components;

[0018] Figure 4 yes Figure 1 A schematic diagram of the structure of the middle angle adjustment frame;

[0019] In the figure: 00-testing machine, 1-load-bearing rod, 2-concrete test block, 3-FRP cloth strip, 31-bonding part, 32-and free part; 4-connecting steel plate, 41-inclined part, 42-straight part; 5-high-strength nut, 6-connecting screw, 7-adapter, 8-high-strength bolt, 9-sleeve, 10-steel splint, 11-force rod, 12-fastening nut. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] See also Figure 1 , 2 , a variable angle shear test device for the interface between fiber reinforced composite materials and concrete provided by an embodiment of the present invention comprises a load-bearing rod 1 penetrating a concrete test block 2, the end of the load-bearing rod 1 being able to be connected to a test machine 00; FRP strips 3 are pasted on both sides of the concrete test block 2, the FRP strips 3 comprising a bonding portion 31 and a free portion 32, the free portion 32 of the FRP strips 3 being at a certain angle to the bonding portion 31, and the free portions 32 of the FRP strips 3 on both sides being arranged oppositely; the free end of the FRP strips 3 is connected to the other end of the test machine 00 through a clamping adjustment mechanism and a force application rod 11 in the middle, the clamping adjustment mechanism being able to clamp and adjust the inclination angle of the free portion of the FRP strips. Among them, the FRP strips are fiber reinforced composite materials, and the test machine adopts a 100T universal testing machine, one test machine clamps the end of the load-bearing rod, and the other test machine clamps the force application rod in the middle of the clamping adjustment mechanism, and applies tension to the FRP strips pasted on both sides of the concrete test block to complete the shear test of the interface between the fiber reinforced composite material and concrete.

[0022] In a specific embodiment of the present invention, Figure 2 , 3As shown, the clamping adjustment mechanism includes a connecting assembly, an angle adjustment frame, a high-strength bolt 8 and a high-strength nut 5. The connecting assembly includes a connecting steel plate 4 and a steel clamping plate 10. The connecting steel plate 4 is divided into an inclined portion 41 and a straight portion 42. The inclined portion 41 is in the same inclination direction as the free portion 32 of the FRP cloth strip 3. The steel clamping plate 10 is arranged on the side of the inclined portion 41. The free end of the FRP cloth strip 3 is arranged between the inclined portion 41 and the steel clamping plate 10 and is connected and fixed by the high-strength bolt 8 and the high-strength nut 5. The straight portion 42 is in the same direction as the side of the concrete test block 2 to which the FRP cloth strip 3 is pasted. The angle adjustment frame is arranged between the straight portions 42 on both sides and is connected thereto. The angle of the FRP cloth strip relative to the side of the concrete test block can be changed by using the connecting steel plate. The straight part of the connecting steel plate is consistent with the direction of the tension applied by the testing machine. The inclined part of the connecting steel plate and the steel clamp clamp the free end of the FRP strip, and the tension is transmitted to the FRP strip through the inclined part, which can realize the double shear test of the interface between the FRP strip and the concrete of the fiber reinforced composite material. By changing the connecting steel plate with different bending angles, the performance of the interface between the FRP strip and the concrete at different inclined angles can be measured.

[0023] As a preferred solution, Figure 2 , 4 As shown, the angle adjustment frame includes a connecting screw 6 and an adapter 7. One end of the connecting screw 6 passes through the straight portion 42 of the connecting steel plate 4 and is fixed by a fastening nut 12. The other end of the connecting screw 6 is connected to the adapter 7. The middle part of the adapter 7 is connected to a force rod 11, and the force rod 11 is connected to the testing machine 00. By changing the position of the straight portion on the connecting screw, the distance between the connecting screws on both sides can be adjusted to adapt to the angle change between the FRP strips on both sides and the concrete test block.

[0024] In a specific embodiment of the present invention, Figure 4 As shown, both ends of the force-bearing rod 1 extend to the outside of the concrete test block 2, one end of the force-bearing rod 1 is connected to the testing machine 00, and the other end is connected to the inner end of the adapter 7 through the sleeve 9, which is used to make the force-applying rod 11 coincide with the central axis of the force-bearing rod 1. The sleeve is made of plastic material, and the sleeve can be used to center the force-applying rod, while keeping the force-bearing rod and the force-applying rod in the concrete in the same horizontal straight line, which also makes the whole device more integrated and less prone to eccentricity.

[0025] To further optimize the above technical solution, the middle of the adapter 7 is provided with a through hole for cooperating with the force-applying rod 11, and both sides of the adapter 7 are provided with ports for threadedly cooperating with the connecting screw 6, and the sleeve 9 is sleeved on the outside of the ends of the force-bearing rod 1 and the force-applying rod 11. This structure is convenient for disassembly and replacement, and the connecting screw and the force-applying rod can be connected and disassembled through the adapter.

[0026] During the specific production, the bonding portion 31 of the FRP strip 3 is adhered to the concrete test block 2 by epoxy resin, and the free portions 32 of the FRP strips 3 on both sides are inclined outward relative to the two sides of the concrete test block 2, such as Figure 2 As shown. The load-bearing rod 1 and the force-applying rod 11 are both threaded steel bars, and the threaded steel bars are made of Q235 steel with a diameter of 20 mm. The combination of the concrete test block and the threaded steel bar load-bearing rod can be completed during the concrete pouring, and it is necessary to ensure that the threaded steel bar penetrates the center of the concrete test block.

[0027] In a specific embodiment of the present invention, the specific parameters of each component are as follows:

[0028] The size of the concrete test block is 150mm*150mm*300mm; the FRP strip is 50mm*450mm; the high-strength nut is an M16 high-strength bolt, the high-strength bolt is an M16 high-strength bolt, the inclined part of the connecting steel plate is 10mm*50mm*60mm, the straight part is 10mm*50mm*50mm, and 4 bolt holes with a radius of 8mm are evenly distributed on the steel clamp and the inclined part; the force-bearing rod running through the concrete test block adopts a threaded steel bar with a radius of 10mm and a length of 550mm, and the force-applying rod at the other end adopts a threaded steel bar with a radius of 10mm and a length of 350mm; the connection screw has a radius of 10mm and a length of 150mm, and the fastening nut is an M20 high-strength nut; the adapter is made of steel, and the inner diameter of its four cylinders is 20mm; the plastic sleeve is 80mm long and has an inner diameter of 20mm. The above dimensions are not limited to the specific implementation, and the above dimensions are for reference only.

[0029] The specific implementation steps of the present invention are as follows:

[0030] The first step is to dig a hole in the center of the mold when pouring concrete and put in threaded steel bars, making sure that the threaded steel bars penetrate the center of the concrete test block.

[0031] In the second step, the poured concrete test blocks were bonded to the cut FRP cloth using epoxy resin.

[0032] The third step is to assemble the clamping and adjusting mechanism, then put the FRP cloth into the connecting steel plate and the steel clamping plate, and fasten them with high-strength bolts.

[0033] The fourth step is to conduct the test using a 100T universal testing machine.

[0034] Among them, in the first and third steps, the threaded steel bars used are Q235 steel with a diameter of 20mm. During the drawing process, the steel bars will not be damaged. The tensile bearing capacity of the threaded steel to be measured is as follows:

[0035] F t =σ t·A

[0036] Where: F t --Tensile bearing capacity of threaded steel bars;

[0037] σ t --Tensile strength of Q235 steel bars;

[0038] A--Cross-sectional area of ​​threaded steel bar.

[0039] In the third step, the 8 M16 high-strength bolts and 8 M16 high-strength nuts of the clamping adjustment mechanism are subjected to shear force during the pulling process. and the tensile force along the axis The specific formula is as follows:

[0040]

[0041] Where: --The design value of the shear bearing capacity of a high-strength bolt;

[0042] k--hole coefficient, 1.0 for standard hole; 0.85 for large round hole; 0.7 when the internal force is perpendicular to the length of the slot hole; 0.6 when the internal force is parallel to the length of the slot hole;

[0043] n f --Number of friction surfaces for force transmission;

[0044] μ--anti-slip coefficient of friction surface;

[0045] P - the pre-tension design value of a high-strength bolt;

[0046]

[0047] Where: N--axial force through the centroid of the bolt group;

[0048] n--Number of bolts;

[0049]

[0050] Where: --The design value of the tensile bearing capacity of a high-strength bolt;

[0051] P--pretension of the bolt;

[0052]

[0053] Where: N--the tension of a single bolt in the bolt group;

[0054] n--Number of bolts;

[0055] P = 0.6075f u Ae

[0056] Where: f u --Minimum tensile strength of high-strength bolts;

[0057] A e --Effective area of ​​high-strength bolts;

[0058]

[0059] Where: N v 、N t --respectively the shear force and tension borne by a certain high-strength bolt;

[0060] --The design value of shear and tensile bearing capacity of a high-strength bolt;

[0061] Under five working conditions of external loads of 100kN, 80kN, 60kN, 40kN, and 20kN, the performance grade of the high-strength bolts is calculated to be 8.8 based on the inclination of the free part of the FRP cloth relative to the bonding part of 5°, and the steel material is Q235 steel. The minimum tensile strength of Q235 steel is 370MPa, and the calculation results are shown in Table 1 below. The basic parameters are shown in Table 2.

[0062] Table 1 Calculation results

[0063]

[0064] The design requirements are met and the design value is less than the ultimate load.

[0065] Table 2 Basic parameter values

[0066]

[0067] It can be seen that the calculation results under the five working conditions are within the allowable range and far less than the allowable range, so the threaded steel bars in the shear test device provided by the present invention will not be damaged. According to the bolt group force discriminant formula in the specification "GB 50017-2017 Steel Structure Design Standard" Under the five working conditions, the stress of the high-strength bolts is within the allowable range and far less than the allowable range. In summary, the device of the present invention will not be damaged in the test.

[0068] In summary, the present invention has simple installation steps and is very convenient to operate; the clamping and adjusting mechanism is detachable and replaceable, and has good versatility; the connecting steel plates corresponding to different angles can be replaced at any time according to the angle requirements between the FRP cloth strip and the concrete test block; at the same time, the angle change between the FRP cloth and the concrete can be adapted by adjusting the position of the fastening nut and the straight part of the connecting steel plate on the connecting screw. Since the angle can be controlled by adjusting the clamping device. Therefore, there is no need to make concrete of the relevant angle, which reduces material costs and pollution. In addition, the plastic sleeve reduces eccentricity and ensures the integrity of the entire component and device.

[0069] In the above description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed above.

Claims

1. A variable angle shear test device for the interface of fiber reinforced composite materials and concrete, characterized in that: It includes a force-bearing rod that passes through the concrete test block, and the end of the force-bearing rod can be connected to the testing machine; FRP strips are pasted on both sides of the concrete test block, and the FRP strips include a bonding part and a free part. The free part of the FRP strip forms a certain angle with the bonding part, and the free parts of the FRP strips on both sides are arranged oppositely; the free end of the FRP strip is connected to the testing machine at the other end through a force-applying rod in the middle of a clamping and adjusting mechanism, and the clamping and adjusting mechanism can clamp and adjust the inclination angle of the free part of the FRP strip; The clamping adjustment mechanism includes a connecting assembly, an angle adjustment frame, high-strength bolts and high-strength nuts. The connecting assembly includes a connecting steel plate and a steel clamping plate. The connecting steel plate is divided into an inclined portion and a straight portion. The inclined portion is in the same inclination direction as the free portion of the FRP cloth strip. The steel clamping plate is arranged on the side of the inclined portion. The free end of the FRP cloth strip is arranged between the inclined portion and the steel clamping plate and is connected and fixed by a high-strength bolt and a high-strength nut. The straight portion is in the same direction as the side of the concrete test block to which the FRP cloth strip is pasted. The angle adjustment frame is arranged between the straight portions on both sides and is connected thereto. The angle adjustment frame includes a connecting screw and an adapter, one end of the connecting screw passes through the straight portion of the connecting steel plate and is fixed by a fastening nut, and the other end of the connecting screw is connected to the adapter; the middle part of the adapter is connected to a force rod, and the force rod is connected to the testing machine; Both ends of the force-bearing rod extend to the outside of the concrete test block, one end of the force-bearing rod is connected to the testing machine, and the other end is connected to the inner end of the adapter through a sleeve, so as to make the central axis of the force-applying rod coincide with that of the force-bearing rod; The middle part of the adapter is provided with a through hole for cooperating with the force-applying rod, and the two sides of the adapter are provided with ports for cooperating with the thread of the connecting screw, and the sleeve is sleeved on the outside of the ends of the force-bearing rod and the force-applying rod; The load-bearing rods and the force-applying rods are both threaded steel bars, and the threaded steel bars are made of Q235 steel with a diameter of 20 mm; The implementation steps are as follows: The first step is to dig a hole in the center of the mold when pouring concrete, put in the threaded steel bar, and ensure that the threaded steel bar runs through the center of the concrete test block; In the second step, the poured concrete test block was bonded to the cut FRP cloth using epoxy resin; The third step is to assemble the clamping adjustment mechanism, then put the FRP cloth into the connecting steel plate and the steel clamping plate, and fasten them with high-strength bolts; The fourth step is to conduct the test using a 100T universal testing machine; Calculate the tensile bearing capacity of the threaded steel bar, the specific formula is as follows: ； Where: --Tensile bearing capacity of threaded steel bars; tensile strength of steel bars; A--cross-sectional area of ​​threaded steel bar; In the third step, the 8 M16 high-strength bolts and 8 M16 high-strength nuts of the clamping adjustment mechanism are subjected to shear force during the pulling process. , and the tensile force along the axis ; The specific formula is as follows: ； Where: , --The design value of the shear bearing capacity of a high-strength bolt; k--hole coefficient, 1.0 for standard hole; 0.85 for large round hole; 0.7 when the internal force is perpendicular to the length of the slot hole; 0.6 when the internal force is parallel to the length of the slot hole; --Number of friction surfaces for force transmission; --Anti-slip coefficient of friction surface; P - the pre-tension design value of a high-strength bolt; ； Where: N--axial force through the centroid of the bolt group; n--Number of bolts; ； Where: --The design value of the tensile bearing capacity of a high-strength bolt; P--pretension of the bolt; ； Where: N--the tension of a single bolt in the bolt group; n--Number of bolts; ； Where: --Minimum tensile strength of high-strength bolts; --Effective area of ​​high-strength bolts; ； Where: , --respectively the shear force and tension borne by a certain high-strength bolt; , --The design value of shear and tensile bearing capacity of a high-strength bolt; According to the angle requirements between the FRP cloth strip and the concrete test block, the connecting steel plate corresponding to different angles can be replaced at any time; at the same time, the angle change between the FRP cloth and the concrete can be adapted by adjusting the position of the fastening nut and the straight part of the connecting steel plate on the connecting screw.

2. The variable angle shear test device for the interface of fiber reinforced composite material and concrete according to claim 1, characterized in that: The free parts of the FRP strips on both sides are inclined outward relative to the two sides of the concrete specimen.

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