Self-eccentric reinforcement UHPC component axial tension test device and loading method

Abstract

The invention discloses a self-eccentric reinforcement UHPC component axial tension test device and a loading method. The self-eccentric reinforcement UHPC component axial tension test device comprises a loading frame; the loading mechanism comprises an upper clamp, a lower clamp and a loading assembly, the lower clamp is fixed at the bottom of the loading frame, the upper clamp is detachably connected with a loading rod, the top end of the loading rod is connected with the loading assembly, the loading assembly is installed at the top of the loading frame, and the upper clamp and the lower clamp are arranged oppositely; two ends of the test piece are respectively clamped on the upper clamp and the lower clamp; the number of the positioning assemblies is two, and the two positioning assemblies are arranged on the upper clamp and the lower clamp respectively and matched with the test piece in a limiting mode; the guide assembly is installed on the loading frame, and the loading rod penetrates through the guide assembly; a sensing system; the sensing system is mounted on the loading assembly; and a leveling assembly is mounted at the bottom of the loading frame. According to the method, the strength, crack development and damage modes of the self-eccentric reinforced concrete test piece in the axial pulling process can be accurately obtained.

Description

Technical Field

[0001] The invention relates to the technical field of UHPC tensile test equipment, and in particular to an axial tensile test device and a loading method for a self-eccentrically reinforced UHPC component. Background Art

[0002] Ultra-High Performance Concrete (UHPC) is a cement-based composite material with ultra-high strength, ultra-high toughness and ultra-long durability. UHPC contains a large amount of steel fibers, which play a huge role in improving the matrix strength of UHPC and limiting crack propagation. Its excellent tensile properties (high tensile strength and strain hardening characteristics) are one of its most significant features, and it is often necessary to utilize them in design. UHPC structures often have cold (wet) joints cast in sections during the pouring process. The interface of the concrete structure at the joint is separated, and its mechanical properties and durability will greatly affect the overall stress performance of the structure. Interface treatment of wet joints can improve their crack resistance to a certain extent, but the tensile properties of wet joints cannot reach the effect of the whole cast section, so other reinforcement measures are still needed on this basis. The existing measures for strengthening components include external CFRP cloth, directional insertion of steel fibers and thickened wet joint structures. However, these methods have some defects. For example, external CFRP reinforcement has its limitations. Excessive pasting will cause the interface to fail to transmit sufficient shear stress, making the strength of CFRP unable to be fully utilized, and bonding failure is prone to occur when the component is subjected to a large load. There are restrictions and requirements on the length and volume of the interface steel fiber and the steel fiber insertion connection plate when inserting steel fibers in a directional manner in the joint. Excessive use of steel fibers will increase the project cost and is not suitable for all practical projects. Reinforcing wet joints by thickening the wet joint structure will improve the crack resistance of wet joints to a certain extent, but the structural performance of thickening the wet joint will increase the self-weight of the component. Based on existing research, setting anchor steel bars at the joint is an effective means to improve the tensile performance of wet joints.

[0003] In order to deeply explore the influence of reinforced steel bars on the tensile properties of segmentally cast ultra-high performance concrete (UHPC) specimens and provide a scientific basis for the reasonable reinforcement design at the joints, it is particularly important to carry out direct tensile tests on UHPC wet joint specimens with reinforced steel bars. In tensile tests, the eccentricity problem has always been the focus of scholars, especially how to minimize the influence of eccentricity. At present, direct tensile tests of UHPC and other concrete components usually rely on commercial universal testing machines. In the case of no initial eccentricity of the specimen, the self-balancing device of the universal testing machine can provide satisfactory tensile results. However, when the specimen has its own eccentricity, the adaptive characteristics of the universal testing machine will cause the loading device to rotate with the specimen during the test, which not only aggravates the deformation of the specimen, but also may fail to obtain the expected tensile effect.

[0004] For UHPC components with self-eccentric reinforcement, the tensile test is different from the conventional test. The key to the success of the test is to ensure that the eccentric effect of the specimen remains unchanged from the beginning to the end of loading, that is, the specimen resistance line and the external load loading line are always on the same axis. Therefore, in order to accurately conduct the axial tensile test of UHPC components with self-eccentric reinforcement and eliminate the influence of the specimen's own eccentricity on the test process, it is urgent to develop a tensile test device that can achieve forced centering. Summary of the invention

[0005] The purpose of the present invention is to provide an axial tension test device and a loading method for a self-eccentrically reinforced UHPC component, so as to solve the problems existing in the prior art.

[0006] To achieve the above object, the present invention provides the following solution: The present invention provides an axial tension test device for a self-eccentrically reinforced UHPC component, comprising:

[0007] Loading rack;

[0008] A loading mechanism, the loading mechanism comprising an upper fixture, a lower fixture and a loading assembly, the lower fixture is fixed to the bottom of the loading frame, the upper fixture is detachably connected to a loading rod, the top end of the loading rod is connected to the loading assembly, the loading assembly is installed on the top of the loading frame, the upper fixture is arranged opposite to the lower fixture, and two ends of the specimen are clamped on the upper fixture and the lower fixture respectively;

[0009] Positioning components, the positioning components are provided in two groups, the two groups of positioning components are respectively arranged on the upper fixture and the lower fixture, and cooperate with the specimen limit;

[0010] A guide assembly, wherein the guide assembly is mounted on the loading frame, and the loading rod passes through the guide assembly;

[0011] A sensor system; the sensor system is installed on the loading assembly and is used to monitor the loading force output by the loading assembly;

[0012] Wherein, a leveling component is installed at the bottom of the loading frame.

[0013] According to the axial tension test device for self-eccentrically reinforced UHPC components provided by the present invention, the loading frame comprises a top plate and a bottom plate, the top plate and the bottom plate are arranged opposite and parallel to each other, and a plurality of sets of screw rods are vertically and detachably connected between the top plate and the bottom plate;

[0014] Wherein, the lower clamp is fixed on the top surface of the base plate, the leveling assembly is installed on the bottom surface of the base plate, the loading assembly is installed on the top plate, and the guide assembly is installed on the screw rod.

[0015] According to the axial tension test device for self-eccentrically reinforced UHPC components provided by the present invention, the loading assembly includes an anchor tensioner, the anchor tensioner is installed on the top surface of the top plate, the top end of the loading rod is installed on the anchor tensioner, and the sensor system is installed on the anchor tensioner.

[0016] According to the axial tension test device for self-eccentrically reinforced UHPC components provided by the present invention, the guide assembly includes a guide plate detachably connected to the screw rod, the guide plate is located between the upper clamp and the top plate, a linear bearing is installed on the guide plate, and the loading rod passes through the guide plate, the linear bearing, the top plate and is connected to the anchor tensioner.

[0017] According to the axial tension test device for self-eccentrically reinforced UHPC components provided by the present invention, the positioning assembly includes positioning plates, and the positioning plates are provided in two groups, and the two groups of positioning plates are respectively arranged on the front and rear sides of the specimen, and the positioning plates are detachably connected to the upper clamp and the lower clamp by bolts.

[0018] According to the axial tension test device for self-eccentrically reinforced UHPC components provided by the present invention, the sensing system comprises a tension sensor, and the tension sensor is fixed on the top of the anchor tensioner through an anchor.

[0019] According to the axial tension test device for self-eccentrically reinforced UHPC components provided by the present invention, a groove is provided at the center position of the inner side of the upper clamp, the cross-sectional shape of the groove is rectangular, a connecting hole is provided on the bottom wall of the groove, the end of the loading rod passes through the connecting hole and is fixedly connected to a fixing block, and the fixing block is adapted to the groove.

[0020] According to the axial tension test device for UHPC components with self-eccentric reinforcement provided by the present invention, the leveling assembly includes a leveling nut, and the leveling nut is provided in a plurality of groups, and the plurality of groups of the leveling nuts are provided in a one-to-one correspondence with the plurality of the screw rods, and the screw rods pass through the base plate and are threadedly connected with the leveling nuts.

[0021] A method for axial tension loading of a self-eccentrically reinforced UHPC component comprises the following steps:

[0022] Step 1, assembling the loading device;

[0023] Step 2: pour concrete into the customized steel membrane that fits the upper and lower clamps, and demould after forming;

[0024] Step 3, clamping the formed test piece on the upper fixture and the lower fixture, and fixing it by the positioning assembly;

[0025] Step 4: the loading assembly outputs a loading force through a loading rod to stretch the specimen to cause it to deform;

[0026] Step 5: The loading component continuously outputs the loading force, and the specimen breaks after the tensile deformation reaches the maximum bearing capacity;

[0027] Step six, obtaining the loading force output by the loading component through the sensor system.

[0028] The present invention discloses the following technical effects:

[0029] The present invention fixes the specimen on the upper clamp and the lower clamp by a positioning assembly, applies directional load by a loading assembly, and the setting of the upper clamp and the lower clamp ensures that the eccentricity effect remains unchanged from the beginning to the end of loading, so as to eliminate the influence of the eccentricity of the specimen on the test process, and then accurately determines the axial tension performance of the self-eccentric reinforced UHPC component, including key parameters such as cracking load, ultimate load and load-tensile displacement curve; effectively reduces the eccentricity phenomenon that may occur in the reinforced concrete specimen during the test process, and improves the accuracy and reliability of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a structural schematic diagram of the axial tension test device of the self-eccentrically reinforced UHPC component of the present invention;

[0032] Figure 2It is a schematic diagram of the connection relationship between the loading rod and the upper clamp of the present invention;

[0033] Figure 3 It is a schematic diagram of the connection relationship between the test piece and the upper fixture and the lower fixture of the present invention;

[0034] Figure 4 This is a physical assembly diagram of the axial tension test device of the present invention;

[0035] Figure 5 It is a schematic diagram of reinforcement of the present invention;

[0036] Figure 6 It is a physical assembly diagram of the axial tension test device and the test piece of the present invention;

[0037] Figure 7 These are the four-sided failure diagrams of the test piece of the present invention.

[0038] Among them, 1. loading rod; 2. anchor; 3. tension sensor; 4. anchor tensioner; 5. top plate; 6. bottom plate; 7. guide plate; 8. linear bearing; 9. screw; 10. upper clamp; 11. leveling nut. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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.

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Reference Figure 1-Figure 3 The present invention provides an axial tension test device for a self-eccentrically reinforced UHPC component, comprising:

[0042] Loading rack;

[0043] The loading mechanism includes an upper fixture 10, a lower fixture and a loading assembly. The lower fixture is fixed to the bottom of the loading frame. The upper fixture 10 is detachably connected to a loading rod 1. The top of the loading rod 1 is connected to the loading assembly. The loading assembly is installed on the top of the loading frame. The upper fixture 10 and the lower fixture are arranged opposite to each other. The two ends of the specimen are clamped on the upper fixture 10 and the lower fixture respectively.

[0044] Positioning components, there are two groups of positioning components, which are respectively arranged on the upper fixture 10 and the lower fixture, and cooperate with the specimen limit;

[0045] A guide assembly, the guide assembly is mounted on the loading frame, and the loading rod 1 passes through the guide assembly;

[0046] Sensing system: The sensing system is installed on the loading assembly and is used to monitor the loading force output by the loading assembly;

[0047] Wherein, a leveling component is installed at the bottom of the loading frame.

[0048] The present invention fixes the specimen on the upper fixture 10 and the lower fixture through a positioning assembly, applies a directional load through a loading assembly, and the setting of the upper fixture 10 and the lower fixture ensures that the eccentricity effect remains unchanged from the beginning to the end of loading, so as to eliminate the influence of the specimen's own eccentricity on the test process, and then accurately measure the axial tension performance of the self-eccentric reinforced UHPC component, including key parameters such as cracking load, ultimate load and load-tensile displacement curve; effectively reduce the eccentricity phenomenon that may occur in the reinforced concrete specimen during the test process, and improve the accuracy and reliability of the test.

[0049] According to a further optimized solution, the loading frame includes a top plate 5 and a bottom plate 6, the top plate 5 and the bottom plate 6 are arranged opposite and parallel to each other, and a plurality of sets of screw rods 9 are vertically and detachably connected between the top plate 5 and the bottom plate 6;

[0050] Among them, the lower clamp is fixed on the top surface of the base plate 6, the leveling component is installed on the bottom surface of the base plate 6, the loading component is installed on the top plate 5, and the guide component is installed on the screw 9.

[0051] According to a further optimized solution, the loading assembly includes an anchor tensioner 4, which is mounted on the top surface of the top plate 5, the top end of the loading rod 1 is mounted on the anchor tensioner 4, and the sensor system is mounted on the anchor tensioner 4.

[0052] A further optimized solution is that the guide assembly includes a guide plate 7 detachably connected to the screw rod 9, the guide plate 7 is located between the upper clamp 10 and the top plate 5, a linear bearing 8 is installed on the guide plate 7, and the loading rod 1 passes through the guide plate 7, the linear bearing 8, the top plate 5 and is connected to the anchor tensioner 4.

[0053] The size of the linear bearing 8 matches the size of the loading rod 1. The linear bearing 8 can not only fix the travel path of the loading rod 1 but also effectively reduce friction.

[0054] According to a further optimized solution, the positioning assembly includes positioning plates. Two groups of positioning plates are provided. The two groups of positioning plates are respectively provided on the front and rear sides of the specimen. The positioning plates are detachably connected to the upper fixture 10 and the lower fixture by bolts.

[0055] According to a further optimized solution, the sensing system includes a tension sensor 3 , and the tension sensor 3 is fixed to the top of the anchor tensioner 4 through the anchor 2 .

[0056] A further optimized solution is that a groove is opened at the center position of the inner side of the upper clamp 10, the cross-sectional shape of the groove is rectangular, a connecting hole is opened on the bottom wall of the groove, the end of the loading rod 1 passes through the connecting hole and is fixedly connected to a fixing block, and the fixing block is adapted to the groove.

[0057] A further optimized solution is that the leveling assembly includes a leveling nut 11, and the leveling nut 11 is provided in a plurality of groups, and the plurality of groups of leveling nuts 11 are provided in a one-to-one correspondence with a plurality of screw rods 9, and the screw rods 9 pass through the base plate 6 and are threadedly connected with the leveling nut 11.

[0058] A method for axial tension loading of a self-eccentrically reinforced UHPC component comprises the following steps:

[0059] Step 1: Assemble the loading device as Figure 4 As shown;

[0060] Step 2: pour concrete into the customized steel membrane that the upper fixture 10 and the lower fixture are adapted to, and demould after forming. The test piece adopts a dog bone shape with a size of 726mm×100mm×100mm. Figure 5 As shown, a through steel bar (I) with a diameter of 12 mm is set in the middle of the specimen, and a steel bar (II) with a diameter of 12 mm and a length of 48 mm is set in the middle to supplement the reduction in tensile performance of the component caused by the wet joint;

[0061] Step 3: Place the test piece prepared in step 2 on the test piece and confirm that the length of the observation area is 280 mm. Clamp the formed test piece on the upper fixture 10 and the lower fixture and fix it by the positioning assembly. Connect the strain gauge line to the strain box, arrange the displacement gauges symmetrically (the displacement gauges on the 1st and 3rd surfaces measure the elongation deformation of the entire observation area; the displacement gauges on the 2nd and 4th surfaces measure the elongation deformation of the wet joint), and make preparations for the experiment, such as Figure 6 As shown;

[0062] Step 4: The loading component outputs the loading force through the loading rod 1. A pre-loading test is performed before the test, and the pre-loading value is 1 kN. Then, a formal loading is performed at 5 kN / level to stretch the specimen to deform it.

[0063] Step 5: The loading component continuously outputs the loading force, and the specimen breaks after the tensile deformation reaches the maximum bearing capacity;

[0064] Step six, obtaining the loading force output by the loading component through the sensor system.

[0065] The test results are shown in Figure 7 and Table 1.

[0066] Table 1 Test values ​​(1- and 3-surface displacement meter data)

[0067]

[0068]

[0069] Depend on Figure 7 It can be seen that the cracked fracture at the joint is flat and perpendicular to the length direction of the specimen and the loading direction. According to the principle that the opening direction of the Type I crack is perpendicular to the force direction, it can be seen that the structural resistance line and the loading line completely coincide during the test. In addition, according to the load-displacement test data in Table 1, the maximum difference between the two displacement gauges does not exceed 0.087 mm, which shows that even if there is reinforcement eccentricity inside the specimen, the device can largely balance and offset its eccentricity during loading.

[0070] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0071] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A self-eccentrically reinforced UHPC component axial tension test device, characterized in that: include: Loading rack; A loading mechanism, the loading mechanism comprising an upper fixture (10), a lower fixture and a loading assembly, the lower fixture being fixed to the bottom of the loading frame, the upper fixture (10) being detachably connected to a loading rod (1), the top end of the loading rod (1) being connected to the loading assembly, the loading assembly being mounted on the top of the loading frame, the upper fixture (10) being arranged opposite to the lower fixture, and two ends of the specimen being clamped on the upper fixture (10) and the lower fixture respectively; Positioning components, wherein two groups of positioning components are provided, and the two groups of positioning components are respectively provided on the upper fixture (10) and the lower fixture, and cooperate with the specimen to limit the position; A guide assembly, the guide assembly being mounted on the loading frame, and the loading rod (1) passing through the guide assembly; A sensor system; the sensor system is installed on the loading assembly and is used to monitor the loading force output by the loading assembly; Wherein, a leveling component is installed at the bottom of the loading frame.

2. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 1, characterized in that: The loading frame comprises a top plate (5) and a bottom plate (6), wherein the top plate (5) and the bottom plate (6) are arranged opposite to each other and in parallel, and a plurality of groups of screw rods (9) are vertically detachably connected between the top plate (5) and the bottom plate (6); The lower clamp is fixed on the top surface of the base plate (6), the leveling assembly is installed on the bottom surface of the base plate (6), the loading assembly is installed on the top plate (5), and the guide assembly is installed on the screw rod (9).

3. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 2, characterized in that: The loading assembly comprises an anchor tensioner (4), wherein the anchor tensioner (4) is mounted on the top surface of the top plate (5), the top end of the loading rod (1) is mounted on the anchor tensioner (4), and the sensor system is mounted on the anchor tensioner (4).

4. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 3, characterized in that: The guide assembly comprises a guide plate (7) detachably connected to the screw rod (9), the guide plate (7) being located between the upper clamp (10) and the top plate (5), a linear bearing (8) being installed on the guide plate (7), and the loading rod (1) passing through the guide plate (7), the linear bearing (8), the top plate (5) and being connected to the anchor rod tensioner (4).

5. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 1, characterized in that: The positioning assembly comprises positioning plates, and two groups of positioning plates are provided. The two groups of positioning plates are respectively arranged on the front and rear sides of the test piece, and the positioning plates are detachably connected to the upper clamp (10) and the lower clamp via bolts.

6. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 3, characterized in that: The sensing system comprises a tension sensor (3), and the tension sensor (3) is fixed on the top of the anchor tensioner (4) through an anchor (2).

7. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 1, characterized in that: A groove is provided at the center of the inner side of the upper clamp (10), the cross-sectional shape of the groove is rectangular, a connecting hole is provided on the bottom wall of the groove, the end of the loading rod (1) passes through the connecting hole and is fixedly connected to a fixing block, and the fixing block is adapted to the groove.

8. The axial tension test device for UHPC components with self-eccentric reinforcement according to claim 2, characterized in that: The leveling assembly comprises a leveling nut (11), wherein the leveling nut (11) is provided in a plurality of groups, wherein the plurality of groups of the leveling nuts (11) are provided in a one-to-one correspondence with the plurality of screw rods (9), and the screw rods (9) pass through the base plate (6) and are threadedly connected with the leveling nut (11).

9. A method for axial tension loading of a self-eccentrically reinforced UHPC component, based on the axial tension test device for a self-eccentrically reinforced UHPC component according to any one of claims 1 to 8, characterized in that: The steps include: Step 1, assembling the loading device; Step 2: pouring concrete into the customized steel membrane adapted to the upper fixture (10) and the lower fixture, and demoulding after forming; Step 3, clamping the formed test piece on the upper fixture (10) and the lower fixture, and fixing them by the positioning assembly; Step 4: the loading assembly outputs a loading force through the loading rod (1) to stretch the specimen to cause deformation; Step 5: The loading component continuously outputs the loading force, and the specimen breaks after the tensile deformation reaches the maximum bearing capacity; Step six, obtaining the loading force output by the loading component through the sensor system.

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