CN203231963U - Beam test device for bonding strength between fiber reinforced composite bars and concrete - Google Patents

Abstract

The utility model discloses a beam test device for the bonding strength of a fiber-reinforced composite reinforcement rib material and concrete. An FRP (fiber-reinforced plastic)-concrete specimen is subjected to a performance test, wherein an FRP rib is buried inside the FRP-concrete specimen. The device comprises a first steel girder, a second steel girder, distribution girders and two pressure plates; the upper parts of two ends of the first steel girder and the second steel girder are hinged through a steel bar hinge element; meanwhile, the lower ends of the first steel girder and the second steel girder are fixedly connected through a fixed steel plate; the distribution girders are arranged on the first steel girder and the second steel girder; the central axis of the distribution girders passes through the hinge point; the two pressure plates are arranged below the second steel girder; the FRP-concrete specimen is put inside the first steel girder; the FRP rib passes through the hinge end of the first steel girder and extends into a part between the two pressure plates to be fixed. By adopting the device, the initial geometric eccentricity can be removed; the situation that the exerted tension serves as axis stretching load is ensured; the test accuracy is improved.

Description

Beam test device for bonding strength between fiber reinforced composite bars and concrete

technical field

The utility model belongs to the technical field of material performance testing in the fields of buildings, bridges, water cooling, transportation, etc., and particularly relates to a test device for the bonding performance of fiber-reinforced composite bars and concrete. the

Background technique

FRP is a new type of fiber composite material, which has the advantages of high strength, light weight, corrosion resistance, fatigue resistance and convenient construction, and has been widely used in the field of civil engineering. Replacing steel bars in reinforced concrete structures with FRP bars will greatly improve the service performance and durability of concrete structures, prolong the service life of concrete structures, and reduce building structure costs and maintenance costs. Using FRP bars instead of steel bars, under the action of external load, the key factor affecting the co-operation and coordinated deformation between FRP bars and concrete is the transfer of bond force between FRP bars and concrete. For this reason, many experts at home and abroad have conducted a large number of theoretical and experimental studies on the bonding performance of FRP bars and concrete.

The composition of the bonding force between FRP bars and concrete is similar to that of reinforced concrete structures. There are three main types of bonding force: (1) Chemical bonding force: The chemical adsorption force on the contact surface between the bar and concrete is also called bonding force. This force comes from the cement paste permeating to the surface of the reinforcement during pouring and the growth and hardening of cement crystals during the curing process, so that the cement colloid and the surface of the reinforcement produce adsorption and adhesion. This force is generally very small, and disappears when the contact surface slides relative to each other, and only works in the local non-slip section. (2) Friction resistance: After the concrete shrinks, the force generated by tightly wrapping the tendons. The greater the extrusion force between the tendon and concrete, the rougher the contact surface, and the greater the friction. For smooth FRP straight ribs, after relative sliding occurs, the bonding force mainly comes from frictional resistance. (3) Mechanical occlusal force: the force generated by the mechanical occlusal action of the uneven surface of the tendon and the concrete. For surface-deformed ribbed FRP bars, the occlusal force refers to the mechanical occlusion formed by the ribbed bars embedded in concrete. This occlusal action is often very large and is the main source of the bond between the deformed ribbed FRP bars and concrete. For smooth FRP straight ribs, because the surface is too smooth, the failure is generally dominated by sliding and pulling out. For surface-deformed ribbed FRP bars, the oblique force is generally produced by the extrusion of the deformed ribs and concrete, and the oblique force will generate tangential and radial components on the surface of the bar, and the radial component will make the concrete in the cross-section hoop tension state. When loaded to a certain load, the interfacial concrete will produce internal cracks due to the effect of hoop tensile stress. If the concrete protective layer is thin and the hoop tensile stress exceeds the concrete tensile strength, radial-longitudinal cracks will form in the specimen. This type of crack develops from the surface of the reinforcement radially to the outer surface of the specimen, and at the same time extends from the loading end to the free end, and finally leads to concrete splitting and failure. If the concrete cover is thicker or restrained by transverse stirrups, the development of radial cracks is limited, and splitting damage will not occur. However, the slippage of the tendon will increase significantly, and with the continuous weakening of the FRP rib and the continuation of slippage, the tendon will eventually be damaged by the pullout slippage. At present, the bonding tests that have been carried out at home and abroad are mostly pull-out tests, beam tests are less, the test methods are single, and the research results have certain limitations. However, in the actual building structure and bridge structure, FRP bars replace steel bars as the tension bars at the bottom of the beam, and there are differences between the pull-out test and the actual FRP bars in engineering practice. At the same time, the elastic modulus of FRP is small, which is about 25%-70% of that of ordinary steel bars, and the shear and extrusion strengths are low. During the pull-out test, the FRP bars are easy to be pinched when the ultimate tensile stress is not reached. the

It can be seen from the above that in the study of the bonding performance of FRP bars and concrete, there are many practical problems mentioned above in the pull-out test, which hinders the research on the bonding properties of FRP bars and concrete. Therefore, the development of a test device suitable for studying the bonding performance of FRP bars and concrete has important application value. It provides a scientific test instrument for the experimental research of concrete structures in which FRP bars replace steel bars as beam tension bars, and has broad application prospects. . the

Contents of the invention

Purpose of the invention: In view of the existing problems and deficiencies mentioned above, the purpose of this utility model is to provide a beam-type test device for the bond strength between fiber-reinforced composite bars and concrete. This device can eliminate the geometric eccentricity of the initial test and ensure the The tensile force is the axial tensile load, which improves the test accuracy. the

Technical solution: In order to achieve the purpose of the above invention, the utility model adopts the following technical solution: a beam-type test device for the bonding strength of fiber reinforced composite bars and concrete, and performs performance tests on FRP-concrete specimens. FRP bars are buried inside the part, including the first steel beam, the second steel beam, the distribution beam and the pressure plate. and the lower end of the second steel beam are fixed by fixed steel plates; the distribution beam is set on the first steel beam and the second steel beam, and the central axis passes through the hinge point; two A pressing plate; the FRP-concrete specimen is placed in the first steel beam, and the FRP tendon passes through the hinged end of the first steel beam, and extends between the two pressing plates for fixing. the

To improve the above technical solution, the FRP-concrete test piece is provided with self-tapping bolts corresponding to the side wall of the first steel beam, and the FRP-concrete test piece is fixed in direction finding; at the same time, the top of the FRP-concrete test piece corresponds to the first The steel beams are also provided with self-tapping bolts and are fastened to the FRP-concrete specimens. the

Further, the inner top of the first steel beam is provided with a channel-shaped steel plate, and the corresponding self-tapping bolts on the top of the FRP-concrete specimen pass through the channel-shaped steel plate. the

Further, the opposite surfaces of the two pressing plates under the second steel beam are provided with triangular slots. the

Further, the FRP bars are fixed between two pressing plates with thermoplastic. the

Further, the bottom of the distribution beam is provided with a groove-shaped support member fixed on the first steel beam and the second steel beam. the

Further, the bottoms of the first steel beam and the second steel beam are respectively provided with rolling bearings. the

Further, the ends of the two pressure plates near the hinge point are arc-shaped. the

Further, the end of the first steel beam away from the hinge point is provided with a detachable channel steel plate. the

Beneficial effect: compared with the prior art, the utility model has the following advantages:

(1) The solution to the eccentricity problem in the pull-out test: in the traditional pull-out test, it is difficult to precisely control the applied tension and the FRP bars on the same straight line. Inclined; when clamping the FRP tendon, the chuck hangs above the specimen, and the operator’s proficiency in operation will directly affect the alignment situation; in order to prevent the FRP tendon from slipping, two steel plates are placed at the clamping place of the FRP tendon loading end, and the steel plate Deviations in thickness will cause the applied tension to be out of line with the FRP tendons.

In order to ensure that the applied tensile force is the axial tensile load, the utility model uses steel plates to clamp the FRP tendons to completely fix the FRP tendons, thereby eliminating the initial geometric eccentricity. During the test, the FRP bars were tightly fixed by the steel plate, so as to ensure that the FRP bars bear the axial tensile load. the

(2) Solve the problem of pinching off FRP tendons and difficult anchorage in the pull-out test: the elastic modulus of FRP tendons is small, and the shear and extrusion strengths are low. The traditional pull-out test is easy to shear the FRP tendons at the loading end. The bond performance between FRP bars and concrete cannot be measured completely. In this experiment, a new type of steel plate is used to pour thermoplastics to anchor FRP bars, and the bond strength between thermoplastics and FRP bars is higher than that between concrete and FRP bars, which ensures that the anchorage of FRP bars does not occur before concrete and FRP bars slip. question. Moreover, the length of connection between the FRP tendon and the steel plate is sufficient, which solves the problem that the FRP tendon is easily cut due to local force in the traditional pull-out test. the

(3) The solution to the problem of the difference between the traditional central pull-out test and the actual force condition of FRP bars: In actual engineering, FRP bars replace steel bars as tension bars at the bottom of beams, while FRP bars in traditional pull-out tests belong to the central load. Pulling, there is a difference with the stress of the actual FRP tendon. This new type of experiment adopts the beam experiment, which is consistent with the actual stress of FRP bars, and is more convincing for the research on the bonding performance of concrete and FRP bars. the

(4) The beam-type test device occupies a small volume (220mm×280mm×1800mm), and the MTS servo hydraulic testing machine can be used for the test and research on the bonding performance of FRP bars and concrete, and the test operation is simple and easy. the

(5) The four-point bending test of the beam test device is more stable than the traditional pull-out test. At the same time, by controlling the distance (S) between the loading point of the steel beam and the support and the height (h) of the beam, the force (P) of the MTS servo hydraulic testing machine acting on the steel beam can be amplified, and the force (P) acting on the steel beam can be amplified, and the tension can be applied to the FRP bar. The size is (PS/2h). the

(6) The design principle of the steel beam is clear and the structure is simple. It is made of stainless steel and can be used repeatedly. By changing the cross-sectional size of the steel beam and the span of the distribution beam, multiple sets of beam-type test devices can be designed, which has a wide range of applications. the

Description of drawings

Fig. 1 is the structural representation of beam type test device described in the utility model;

Fig. 2 is the sectional view of A-A direction in Fig. 1;

Fig. 3 is the sectional view of B-B direction in Fig. 1;

Fig. 4 is the sectional view of C-C direction in Fig. 1;

Fig. 5 is the structural representation of the first steel beam described in the utility model;

Fig. 6 is the structural representation of the second steel beam described in the utility model;

Fig. 7 is the sectional view of D-D direction in Fig. 5;

Fig. 8 is the sectional view of E-E direction in Fig. 5;

Fig. 9 is a cross-sectional view of F-F direction in Fig. 6;

Fig. 10 is a cross-sectional view along G-G direction in Fig. 6 .

Among them, the first steel beam 1, the second steel beam 2, the distribution beam 3, the pressure plate 4, the steel rod hinge 5, the fixed steel plate 6, the FRP-concrete test piece 7, the FRP tendon 8, the self-tapping bolt 9, and the channel steel plate 10. Channel support 11, rolling support 12, detachable channel steel plate 13, baffle plate 14, hinge rod 15. the

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, further set forth the utility model, should be understood that these embodiments are only used for illustrating the utility model and are not intended to limit the scope of the utility model, after having read the utility model, those skilled in the art will understand this utility model The modifications of various equivalent forms of the utility model all fall within the scope defined by the appended claims of the present application. the

As shown in Figure 1, a beam-type test device for the bonding strength of fiber-reinforced composite bars and concrete includes a first steel beam, a second steel beam, a distribution beam and a pressure plate. Wherein the first steel beam and the second steel beam are connected by a steel rod hinge, the left end of the steel rod hinge is provided with a hinge hole, and a hinge rod is arranged in the hinge hole, and the steel rod hinge is connected with the first steel beam through the hinge rod; The right end of the steel rod hinge is fixedly connected with the second steel beam by a bolt. The distribution beam is located above the first steel beam and the second steel beam, and the lower end of the distribution beam is provided with a channel support piece, and the central axis of the distribution beam passes through the hinge point of the first steel beam. The lower ends of the first steel beam and the second steel beam are provided with fixed steel plates, and the fixed steel plates are respectively connected with the first steel beam and the second steel beam through two bolts. The roller bearings are respectively located under the first steel beam and the second steel beam. The left end of the first steel beam is provided with a detachable channel steel plate, the right end of the first steel beam is provided with a baffle plate with holes to enhance the lateral rigidity of the first steel beam, and a stiffener is provided on the baffle plate. The FRP-concrete specimen is pushed into the first steel beam by the left end of the first steel beam, and a steel block is placed on the FRP-concrete specimen, and fixed by self-tapping bolts, and the self-tapping bolts pass through the channel steel plate to ensure its stability . The sides of the FRP-concrete specimens were fixed by self-tapping bolts. The loading end of the FRP tendon protrudes from the hole on the right side of the first steel beam and enters under the second steel beam. There are two pressure plates with triangular slots under the second steel beam, and the loading end of the FRP tendon extends into the groove of the pressure plate. In the mouth, the upper and lower pressure plates are fixed by bolts and the second steel beam, and the left end of the pressure plate is made into an arc. the

Among them, the first steel girder is assembled by six outer steel plates and two stiffened steel plates through bolts. Firstly, eight steel plates are processed and tapped at the specified position. The baffle plate and the stiffener are respectively fixed to the inner side of the right steel plate of the first steel beam by bolts. Then the upper, lower, left, right and right side steel plates of the first steel girder are assembled by bolts. The channel-shaped steel plate on the left side of the first steel girder can be disassembled during the test, and is connected with the upper and lower steel plates of the first steel girder by upper and lower bolts. The second steel beam is composed of six outer steel plates and two transverse diaphragms assembled by bolts. First, eight steel plates are processed and tapped at designated positions to connect the front and rear side plates through the left and right side plates and the two transverse diaphragms. Then use bolts to fix the upper and lower side panels. Process the steel rod hinge, tap at the specified position, the left end of the steel rod hinge is connected to the first steel beam through the hinge hole and the hinge rod 2, and the right end is connected to the second steel beam through four bolts. The pressing plate for fixing the FRP bars can be processed according to the size and tapped at the specified position, and the pressing plate is connected with the second steel beam through eight bolts. Process the fixed steel plate. The left end of the fixed steel plate is connected to the first steel beam through two bolts, and the right end is also connected to the second steel beam through two bolts. When the test starts, the fixed steel plate is removed. the

The beam-type test device of the utility model is used to test the bonding performance of FRP bars and concrete, including the following steps: (1) device preparation stage: the first steel beam and the second steel beam are fixed by steel rod hinges and fixed steel plates, and distributed The beam is fixed on the first steel beam and the second steel beam through the channel support, and the rolling track is respectively located under the first steel beam and the second steel beam; (2) Specimen preparation stage: FRP-concrete specimen is prepared by the A steel beam is pushed into the first steel beam on the left side, and a steel block is placed directly above the FRP-concrete specimen. The side is tightened by self-tapping bolts to fix the FRP-concrete specimen from the side; the loading end of the FRP tendon protrudes from the hole on the right side of the first steel beam. The protruding FRP bars are fixed between the two slotted pressure plates at the bottom of the second steel beam with thermoplastic, and then the pressure plate and the second steel beam are fixed by eight sets of bolts. The channel steel plate is fixed to the left side of the first steel beam by bolts to ensure the overall rigidity of the first steel beam. The FRP bars in the FRP-concrete specimens are attached with strain gauges. Place a displacement meter on the right side of the first steel beam to measure the displacement of the loading end, and place a displacement meter in the first steel beam to measure the displacement of the free end of the FRP tendon. Connect the electronic strain gauges to the strain collectors to debug the instrument. (3) Test stage: Remove the fixed steel plate, and apply load to the composite beam through the distribution beam, use the built-in sensor of the MTS servo hydraulic testing machine to monitor and record the load and displacement in real time, and use the strain collector to record the full strain of the electronic strain gauge. the

Claims (9)

1. A beam-type test device for fiber-reinforced composite bars and concrete bond strength, performance testing of FRP-concrete specimens, the FRP-concrete specimens are internally embedded with FRP bars, characterized in that: comprising the first steel Beam, second steel beam, distribution beam and pressure plate, the upper parts of the two ends of the first steel beam and the second steel beam are hinged by steel bar hinges, and the lower ends of the first steel beam and the second steel beam are fixed by the fixed steel plate connected; the distribution beam is set on the first steel beam and the second steel beam, and the central axis passes through the hinge point; two pressing plates are arranged below the second steel beam; the FRP-concrete specimen is placed In the first steel beam, and the FRP bars pass through the hinged end of the first steel beam, and extend between the two pressing plates for fixing. 2. according to the beam-type test device of the described fiber-reinforced composite bar material and concrete bonding strength of claim 1, it is characterized in that: the side wall of the corresponding first steel beam of described FRP-concrete test piece is provided with self-tapping bolt, and The FRP-concrete specimen is positioned and fixed by direction finding; at the same time, the top of the FRP-concrete specimen is also equipped with self-tapping bolts corresponding to the first steel beam, and the FRP-concrete specimen is fastened. 3. according to the beam-type test device of the described fiber-reinforced composite bars and concrete bonding strength of claim 2, it is characterized in that: the inner top of the first steel beam is provided with a grooved steel plate, and the top of the FRP-concrete specimen Corresponding self-tapping bolts pass through the channel steel plate. 4. The beam-type test device for bonding strength between fiber-reinforced composite bars and concrete according to claim 1, characterized in that: the opposite surfaces of the two pressure plates below the second steel beam are provided with triangular slots. 5 . The beam-type test device for bonding strength between fiber-reinforced composite bars and concrete according to claim 4 , wherein the FRP bars are fixed between two pressure plates by thermoplastic. 6. The beam-type test device for the bond strength between fiber reinforced composite bars and concrete according to claim 1, characterized in that: the bottom of the distribution beam is provided with a grooved support to be fixed on the first steel beam and the second steel beam superior. 7. The beam-type test device for bonding strength between fiber-reinforced composite bars and concrete according to claim 1, characterized in that: the bottoms of the first steel beam and the second steel beam are respectively provided with rolling bearings. 8. The beam-type test device for bonding strength between fiber-reinforced composite bars and concrete according to claim 1, characterized in that: the ends of the two pressure plates near the hinge point are arc-shaped. 9. The beam-type test device for bonding strength between fiber-reinforced composite bars and concrete according to claim 1, characterized in that: the end of the first steel beam away from the hinge point is provided with a detachable channel-shaped steel plate.

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