Method for testing fatigue shear resistance of joint surface of new and old concrete

Abstract

The invention belongs to the field of concrete performance detection, and particularly relates to a new and old concrete joint surface fatigue shear resistance testing method which comprises the following steps: S1, respectively fixing two old concrete test pieces on two steel supports; s2, pouring a new concrete test piece between the two old concrete test pieces and integrally taking the new concrete test piece as a complete test piece; s3, attaching strain gauges and dial gauges to the two sides, close to the joint surface, of the new concrete test piece; s4, arranging a steel distribution beam below the MTS loading equipment actuator; s5, carrying out a shear ultimate bearing capacity static loading test on the poured complete test piece; s6, re-manufacturing a completely poured test piece, and carrying out a fatigue dynamic loading test; and S7, acquiring strain and deflection data by using a dynamic signal acquisition and analysis system in the fatigue dynamic loading test process. The test method has the effects of calculating and prolonging the fatigue life of the joint surface and preventing the initial damage of the joint surface.

Description

Technical Field

[0001] The invention belongs to the field of concrete performance testing, and in particular relates to a method for testing fatigue shear performance of a new-old concrete bonding surface. Background Art

[0002] Nowadays, infrastructure such as long-span bridges, offshore structures, and dams are subject to repeated loads when passing vehicle traffic or wind and wave loads, and usually these infrastructures require multiple concrete pourings to form a whole. For example, during the construction of existing prefabricated hollow slab bridges, the hollow slabs need to be hoisted into place first, and then concrete is poured between the two hollow slabs to combine the two into a whole; for example, in large concrete structures involving large volumes of concrete, construction also needs to be carried out in multiple stages, resulting in a new and old concrete interface; in addition, in many structures that need to be reinforced, it is often necessary to pour concrete, which leads to gaps between continuous concrete. The bonding surface is formed, and the bonding surface of continuous concrete is often considered to be one of the weakest areas of the structure, and due to the mismatch in the elastic modulus between the two different materials on both sides, cracks are more likely to occur. The reason for this is that the damage to the bonding surface is often not caused by static loads, but by fatigue damage under the repeated action of loads. Among them, the main reason is that repetitive cyclic loads will cause permanent microstructural changes inside the material, resulting in a decrease in material strength and stiffness. Therefore, it is necessary to ensure that such structures have a sufficiently long fatigue service life. As a result, how to predict the fatigue shear performance of the bonding surface between new and old concrete is a technical problem that needs to be solved urgently.

[0003] The shear resistance method in the prior art is a static loading test. However, the fatigue load acting on the structure as a dynamic load is essentially different from the action mechanism of the static load on the structure. In addition, the test piece to be tested in the currently commonly used static loading method consists of a new specimen and an old specimen, that is, there is only one new and old concrete bonding surface. Therefore, there is bound to be a force arm between the load and the bonding surface during loading. Therefore, the bonding surface is more or less affected by the bending moment, and is not only affected by the shear force, which in turn affects the determination and prediction of the fatigue shear resistance of the new and old concrete bonding surface. Summary of the invention

[0004] The purpose of the present invention is to provide a method for testing the fatigue shear performance of the interface between new and old concrete, so as to solve the technical problem that the fatigue shear performance of the interface between new and old concrete cannot be predicted, and to achieve the purpose of predicting the fatigue shear performance of the interface between new and old concrete.

[0005] In order to solve the above technical problems, the present invention provides a method for testing fatigue shear performance of the interface between new and old concrete, comprising:

[0006] S1. Fix two prefabricated old concrete specimens on two symmetrically placed steel supports respectively;

[0007] S2. Pour a new concrete specimen between the two old concrete specimens. The two old concrete specimens and the new concrete specimen form a complete cast test specimen.

[0008] S3. On the bonding surfaces formed by the two side surfaces of the new concrete specimen and the side surfaces of the two old concrete specimens, strain gauges are pasted on both sides of the new concrete specimen near the bonding surfaces, and dial gauges are arranged on both sides of the bottom of the new concrete specimen near the bonding surfaces.

[0009] S4. A steel distribution beam is arranged under the actuator of the MTS loading device. The width of the steel distribution beam is the same as the width of the new concrete specimen and the steel distribution beam is in contact with the new concrete specimen.

[0010] S5. Conduct a static loading test on the complete cast test specimen to obtain strain and deflection data and the shear ultimate bearing capacity Pu.

[0011] S6. Remake the complete cast test specimen and conduct a fatigue dynamic loading test to fit a shear fatigue life curve, and predict the shear fatigue life of the bonding surface between the new concrete specimen and the old concrete specimen under different stress amplitudes based on this curve.

[0012] S7. During the fatigue dynamic loading test, use a dynamic signal acquisition and analysis system to collect strain and deflection data. When the bonding surface between the new concrete specimen and the old concrete specimen is misaligned, stop loading and record the number of loading times Ni. Ni is the fatigue loading times when the i-th specimen is loaded to failure.

[0013] Further, in step S6,

[0014] Conduct a fatigue dynamic loading test to obtain the fatigue failure loading times Ni. Fit a shear fatigue life curve based on the relationship between the fatigue failure loading times Ni of at least 3 remade complete cast test specimens and the calculated shear stress amplitude. The shear fatigue life curve reflects the relationship between the shear stress amplitude and the number of loading times, and predict the shear fatigue life of the bonding surface between the new and old concretes under different stress amplitudes based on this curve.

[0015] Further, the calculation formula for the shear stress amplitude is:

[0016] △σ = σmax - σmin;

[0017] From: σmin = 1.5·k1·Pu / (L2·L3);

[0018] σmax = 1.5·k2·Pu / (L2·L3);

[0019] Obtained: Δσ = 1.5·Pu(k2 - k1) / (L2·L3);

[0020] Wherein, Δσ represents the shear stress amplitude; σmin represents the lower limit of the fatigue loading force value; σmax represents the upper limit of the fatigue loading force value; in the fatigue dynamic loading test, the fatigue load adopts a sine load, the loading frequency is 2 - 4 HZ, and the range of the fatigue load value is k1·Pu to k2·Pu; k1 = 0.1; k2 takes values from 0.2 to 0.8; L1 represents the length of the new concrete specimen; L2 represents the width of the new concrete specimen; L3 represents the height of the new concrete specimen.

[0021] Furthermore, in step S1,

[0022] A steel backing plate is provided on the upper side of the old concrete specimen, and fixing bolts are provided on the steel backing plate. The fixing bolts sequentially penetrate through the steel backing plate, the old concrete specimen, and the steel support from top to bottom.

[0023] Furthermore, in step S2,

[0024] Before casting the new concrete specimen between the two old concrete specimens, roughen the bonding surfaces of the two old concrete specimens and the new concrete specimen respectively; after roughening, blow away the concrete debris with a hair dryer, rinse it with clean water and keep the bonding surface wet until casting the new concrete specimen.

[0025] Furthermore, in step S3,

[0026] The length L1, width L2, and height L3 of the new concrete specimen are respectively the same as the length, width, and height of the old concrete specimen.

[0027] Furthermore, in step S3,

[0028] The strain gauges are symmetrically arranged with the new concrete specimen as the center of symmetry; the number of strain gauges ≥ 12, and the distances between the outer edges of the strain gauges and the bonding surface of the new concrete specimen and the old concrete specimen, the distances between the outer edges of the strain gauges and the upper side edge of the new concrete specimen, and the distances between the outer edges of the strain gauges and the lower side edge of the new concrete specimen are all 0.5 - 1 cm.

[0029] Furthermore, in step S4,

[0030] The steel distribution beam contacts the new concrete specimen as follows:

[0031] The self-weight of the steel distribution beam is denoted as G1. When the steel distribution beam is separated from the new concrete specimen, the force value displayed on the actuator of the MST loading device is -G1, and the data of the force displayed on the actuator of the MST loading device is -G1+(1 / 100 to 1 / 10)G1.

[0032] Further, in step S3,

[0033] The number of dial indicators is four, and the four dial indicators are symmetrically arranged at the bottom edge of the new concrete specimen, 0.5 to 1 cm away from the joint surface.

[0034] Further, in step S5, it specifically includes the following steps:

[0035] S5-1. Perform preloading, and set the preloading force value as Pp

[0036] S5-2. Unload to zero. Denote the force value of each loading as ΔP, and repeat the slow loading at each level of ΔP until the joint surface of the new concrete specimen and the old concrete specimen undergoes dislocation, and obtain the strain and deflection data and the shear ultimate bearing capacity Pu.

[0037] The beneficial effects of the present invention are:

[0038] 1. The present invention adopts an MTS dynamic loading system and a dynamic signal acquisition and analysis system to measure the strain near the joint surface of the new concrete and the displacement of the bottom edge of the new concrete specimen near the joint surface, and can obtain the shear performance parameters of the new and old concrete joint surface under fatigue loads and the fatigue life corresponding to different fatigue loads and shear stress amplitudes.

[0039] 2. The specimen structure of the present invention is a cuboid, and the formwork and specimen production are convenient and simple. The steel backing plate, fixing bolts and steel supports can firmly anchor the old concrete specimen to ensure that the joint surface is only subjected to shear force. Loading with the actuator of the MTS loading device can obtain the fatigue life of the new and old concrete joint surface, providing an experimental basis for extending its fatigue life.

[0040] 3. The new concrete specimen of the present invention is cast after the old concrete specimen is hoisted and fixed, ensuring that initial damage to the joint surface caused by external factors such as impact during the hoisting process can be prevented when the test specimen is prefabricated in advance.

[0041] 4. The resistance strain gauge of the present invention can compare the strain data collected under fatigue loads with the strain data in the ultimate bearing capacity test, and the failure loading times can be predicted based on the variation laws of the above two.

[0042] 5. The dial indicator of the present invention can accurately measure the sliding of the new concrete specimen relative to the old concrete specimen.

[0043] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0045] Figure 1 is a schematic diagram of the arrangement of old and new concrete in the first embodiment of a method for testing the fatigue shear resistance performance of the interface between old and new concrete of the present invention;

[0046] Figure 2 is a schematic diagram of the arrangement of resistance strain gauges and deflection measurement points on the front and back surfaces of old and new concrete specimens in the first embodiment of a method for testing the fatigue shear resistance performance of the interface between old and new concrete of the present invention;

[0047] Figure 3 is a schematic diagram of the tightening method and loading position of old and new concrete specimens in the first embodiment of a method for testing the fatigue shear resistance performance of the interface between old and new concrete of the present invention;

[0048] Figure 4 is a schematic diagram of the shear fatigue life curve in the second embodiment of a method for testing the fatigue shear resistance performance of the interface between old and new concrete of the present invention.

[0049] In the figure:

[0050] 1. Old concrete specimen; 2. New concrete specimen; 3. Strain gauge; 4. Micrometer; 5. Steel backing plate; 6. Fixed bolt; 7. Steel support; 8. Steel distribution beam; 9. MTS loading equipment actuator. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0052] Embodiment:

[0053] The following is the first embodiment of the present invention:

[0054] S1. Fix two prefabricated old concrete specimens 1 on two symmetrically placed steel supports 7 respectively.

[0055] S2. Pour a new concrete specimen 2 between the two old concrete specimens 1. The two old concrete specimens 1 and the new concrete specimen 2 are used as a complete cast test specimen. As Figure 1 shown, the pouring of the new concrete specimen 2 is carried out after the hoisting and fixing of the old concrete specimens 1 are completed; the length L1, width L2 and height L3 of the new concrete specimen 2 are respectively the same as the length, width and height of the old concrete specimen 1; before pouring the new concrete specimen 2 between the two old concrete specimens 1, roughen the bonding surfaces of the two old concrete specimens 1 and the new concrete specimen 2 respectively; after roughening, blow away the concrete debris with a hair dryer, rinse it with clean water and keep the bonding surface wet until pouring the new concrete specimen 2. As attached Figure 3 shown, a steel backing plate 5 is installed on the upper side of the old concrete specimen 1, and fixing bolts 6 are installed on the steel backing plate 5. The fixing bolts 6 penetrate through the steel backing plate 5, the old concrete specimen 1 and the steel support 7 from top to bottom in sequence, and the steel backing plate 5, the old concrete specimen 1 and the steel support 7 are fixedly connected through the fixing bolts 6. Among them, there are four fixing bolts 6. Both the new concrete specimen 2 and the old concrete specimen 1 are made of plain concrete; the new concrete specimen 2 is poured using a steel formwork.

[0056] S3. At the bonding surfaces formed by the two side surfaces of the new concrete specimen 2 and the side surfaces of the two old concrete specimens 1, strain gauges 3 are pasted on both sides of the new concrete specimen close to the bonding surface. The strain gauges are used to measure the strain values at the bonding surface of the new concrete specimen during the loading process; as Figure 2 shown, the strain gauges 3 are symmetrically arranged with the new concrete specimen 2 as the symmetry center; the strain gauges 3 are used to measure the strain values at the bonding surface of the new concrete specimen 2 during the loading process; the number of strain gauges 3 ≥ 12, and the distances between the outer edges of the strain gauges 3 and the bonding surface of the new concrete specimen 2 and the old concrete specimen 1, the distances between the outer edges of the strain gauges 3 and the upper side edge of the new concrete specimen 2, and the distances between the outer edges of the strain gauges 3 and the lower side edge of the new concrete specimen 2 are all 0.5 - 1 cm. Among them, the strain gauges 3 are resistance strain gauges. Dial indicators 4 are installed on both sides of the bottom of the new concrete specimen 2 close to the bonding surface. The dial indicators 4 are used to accurately measure the sliding displacement of the new concrete specimen 2 relative to the old concrete specimen 1; there are four dial indicators 4, and the four dial indicators 4 are symmetrically arranged at 0.5 - 1 cm from the bottom edge of the new concrete specimen 2 close to the bonding surface.

[0057] S4. There is a steel distribution beam 8 installed below the actuator 9 of the MTS loading device. The width of the steel distribution beam 8 is the same as that of the new concrete specimen 2 and the steel distribution beam 8 is in contact with the new concrete specimen 2. Specifically, the self-weight of the steel distribution beam 8 is denoted as G1. When the steel distribution beam 8 is separated from the new concrete specimen 2, the force value displayed on the actuator 9 of the MST loading device is -G1. To ensure that the steel distribution beam 8 is in contact with the new concrete specimen 2, the data of the force displayed on the actuator 9 of the MST loading device is -G1+(1 / 100 - 1 / 10)G1.

[0058] S5. Conduct a static loading test on the complete cast test specimen to obtain strain and deflection data and the shear ultimate bearing capacity P u ; specifically as follows: S5-1. Conduct a preloading with a preloading force value of P p ; S5-2. Unload to zero and repeat the loading slowly in each stage of ΔP until the interface between the new concrete specimen and the old concrete specimen is displaced, and obtain the strain and deflection data and the shear ultimate bearing capacity P u .

[0059] S6. Remake the complete cast test specimen and conduct a fatigue dynamic loading test to obtain the fatigue failure loading times N i , and fit a shear fatigue life curve based on the relationship between the fatigue failure loading times N of at least 3 remade complete cast test specimens i and the calculated shear stress amplitude. The shear fatigue life curve reflects the relationship between the shear stress amplitude and the loading times, and based on this curve, predict the shear fatigue life of the interface between the new and old concretes under different stress amplitudes;

[0060] Among them, the calculation formula for the shear stress amplitude is:

[0061] △σ = σ max -σ min ;

[0062] From: σ min = 1.5·k1·P u / (L2·L3);

[0063] σ max = 1.5·k2·P u / (L2·L3);

[0064] We get: △σ = 1.5·P u (k2 - k1) / (L2·L3);

[0065] Among them, △σ represents the shear stress amplitude; σ min represents the lower limit of the fatigue loading force value; σ maxIndicates the upper limit of the fatigue loading force value; in the fatigue dynamic loading test, the fatigue load adopts a sine load, the loading frequency is 2 - 4 HZ, and the range of the fatigue load value is k1·P u ~k2·P u ; k1 = 0.1; k2 takes values from 0.2 to 0.8; L1 represents the length of the new concrete specimen 2; L2 represents the width of the new concrete specimen 2; L3 represents the height of the new concrete specimen 2;

[0066] S7. During the fatigue dynamic loading test, use a dynamic signal acquisition and analysis system to collect strain and deflection data. When the bonding surface between the new concrete specimen 2 and the old concrete specimen 1 experiences dislocation, stop loading and record the number of loading times N i , N i is the fatigue loading times when the i-th specimen is loaded to failure. Among them, the model of the dynamic signal acquisition and analysis system is DH5922.

[0067] The following is the second embodiment of the present invention:

[0068] Taking an old concrete specimen with a length of 20 cm, a width of 40 cm, and a height of 50 cm as an example, specifically as follows:

[0069] S1. Precast the old concrete specimen 1 with a length, width, and height of 20 cm, 40 cm, and 50 cm respectively.

[0070] S2. Lift the old concrete specimen 1 to the steel support 7 for positioning, and fix the old concrete specimen 1 with steel backing plates 5 and 4 fixing bolts 6; among them, the steel backing plate 5 is located above the old concrete specimen 1, and the steel support 7 is at the bottom.

[0071] S3. Use a chiseling hammer to chisel the bonding surface of 2 old concrete specimens 1, then use a hair dryer to blow away the remaining and loose concrete debris, and then rinse it clean with drinking water and keep the bonding surface moist. Set up formwork between the two old concretes, pour the new concrete specimen 2 to form a test specimen, and remove the formwork after curing. The production and installation of the test specimen A are completed.

[0072] S4. Paste 12 strain gauges 3 on the front and back surfaces of the new concrete specimen 2. The strain gauges 3 should be close to the bonding surface, and the outer edge is 0.5 cm away from the bonding surface and the upper and lower edges of the new concrete specimen 2. The strain gauges 3 are symmetrically arranged; symmetrically arrange 4 dial indicators 4 near the bonding surface at the bottom edges on both sides of the new concrete specimen 2. The pointers of the dial indicators 4 are located 0.5 cm near the bonding surface at the bottom edges on both sides. The purpose of the above measuring point arrangement is to measure the strain and deflection changes during the loading process, and the installation of the measuring instruments is completed.

[0073] S5. The width of the steel distribution beam 8 under the actuator 9 of the MTS loading device needs to be the same as the width of the new concrete specimen 2. Therefore, the steel distribution beam 8 is 40 cm wide. The purpose is to ensure that the specimen is only subjected to shear force. If the top surface of the new concrete specimen 2 is uneven, it is necessary to level it with sand. After that, the steel distribution beam 8 needs to be kept in a slightly contacting state with the new concrete specimen 2, and the preparation for the shear ultimate bearing capacity test is ready.

[0074] S6. For safety reasons, the displacement of the actuator 9 of the MTS loading device is used as the safety control value, and the control value is taken as 1.5 mm. For the ultimate bearing capacity test of the specimen, first, preloading is carried out. The load is slowly increased to 40 kN in 4 levels, 10 kN for each level and holding for 5 minutes, and then unloaded to zero. Zero the balance of the actuator 9 of the MTS loading device and enter the formal loading stage. Slowly load at a rate of 5 kN per level. When the test load reaches 214 kN, it is found that the self-protection mechanism of the MTS is triggered and the testing machine stops working. At this time, the bonding surface between the new concrete specimen and the old concrete specimen is damaged, and the relative displacement has exceeded 1.5 mm.

[0075] S7. Through the dynamic signal acquisition and analysis system, the force-displacement time history curve and the force-concrete strain time history curve of the specimen are obtained. According to the time history curve, the variation law of stress and displacement with the force value during the whole loading process and the shear ultimate bearing capacity P u = 314 kN, P u which is also the peak value of the time history curve, and the shear ultimate bearing capacity test ends here.

[0076] Remake 11 complete new concrete specimens according to the above method for fatigue tests. The fatigue load is subjected to equal-amplitude fatigue loading with a sinusoidal load, and the loading frequency is 3 Hz. The minimum and maximum values of the sinusoidal fatigue load of the specimen are taken as 0.1P u ~0.3P u 、0.1P u ~0.35P u 、0.1P u ~0.4P u 、0.1P u ~0.45P u 、0.1P u ~0.5P u 、0.1P u ~0.55P u 、0.1P u ~0.6P u 、0.1P u ~0.65P u 、0.1P u ~0.7P u 、0.1P u ~0.75Pu 、0.1P u ~0.8P u , the corresponding stress amplitudes are 0.471 MPa, 0.58875 MPa, 0.7065 MPa, 0.82425 MPa, 0.942 MPa, 1.05975 MPa, 1.1775 MPa, 1.29525 MPa, 1.413 MPa, 1.53075 MPa, 1.6485 MPa respectively. For safety considerations, the actuator 9 of the MTS loading device uses displacement as the safety control value, and the control value is taken as 1.5 mm. During this process, the DH5922 dynamic signal acquisition and analysis system is used to collect strain and deflection data. When the bonding surface between the new concrete specimen and the old concrete specimen produces dislocation, the loading is stopped. Finally, when the number of loading cycles of the 11 specimens are 1.152 million times, 0.754 million times, 0.603 million times, 0.333 million times, 0.244 million times, 0.12 million times, 0.098 million times, 0.05 million times, 0.043 million times, 0.028 million times, 0.019 million times respectively, the bonding surface fails and the fatigue test ends. Later, according to the relationship between the stress amplitude and the number of loading cycles of 3 specimens, a curve is fitted, as shown in the appendix Figure 4 shown, and the empirical formula is obtained as △σ = -0.118lnN i +0.7649. The service life of the new concrete specimen can be estimated according to the empirical formula.

[0077] All the devices selected in this application are common standard parts or components known to those skilled in the art, and their structures and principles can be known to those skilled in the art through technical manuals or obtained through conventional experimental methods.

[0078] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0079] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0080] Inspired by the above-described ideal embodiments of the present invention, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for testing the fatigue shear resistance performance of the bonding surface between new and old concrete, characterized in that Including: S1. Fix two prefabricated old concrete specimens (1) on two symmetrically placed steel supports (7) respectively; S2. Pour a new concrete specimen (2) between the two old concrete specimens (1). The two old concrete specimens (1) and the new concrete specimen (2) form a complete cast test specimen; S3. On the bonding surfaces formed by the two side surfaces of the new concrete specimen (2) and the side surfaces of the two old concrete specimens (1), strain gauges (3) are pasted on both sides of the new concrete specimen (2) near the bonding surface, and dial gauges (4) are arranged on both sides of the bottom of the new concrete specimen (2) near the bonding surface; S4. A steel distribution beam (8) is arranged below the actuator (9) of the MTS loading device. The width of the steel distribution beam (8) is the same as the width of the new concrete specimen (2) and the steel distribution beam (8) is in contact with the new concrete specimen (2); S5. Conduct a static loading test on the complete cast test specimen to obtain strain and deflection data and the shear ultimate bearing capacity Pu; S6. Remake the complete cast test specimen and conduct a fatigue dynamic loading test to fit a shear fatigue life curve, and predict the shear fatigue life of the bonding surface between the new concrete specimen (2) and the old concrete specimen (1) under different stress amplitudes according to this curve; S7. During the fatigue dynamic loading test, use a dynamic signal acquisition and analysis system to collect strain and deflection data. When the bonding surface between the new concrete specimen (2) and the old concrete specimen (1) is misaligned, stop loading and record the number of loading times Ni. Ni is the fatigue loading times when the i-th specimen is loaded to failure.

2. The fatigue shear resistance test method for the interface between new and old concrete according to claim 1, characterized in that, In step S6, Conduct a fatigue dynamic loading test to obtain the fatigue failure loading times Ni. Fit a shear fatigue life curve according to the relationship between the fatigue failure loading times Ni of at least 3 remade and completely cast test specimens and the calculated shear stress amplitude. The shear fatigue life curve reflects the relationship between the shear stress amplitude and the number of loading times, and predict the shear fatigue life of the bonding surface between the new and old concretes under different stress amplitudes according to this curve.

3. A method for testing the fatigue shear performance of the bonding surface between new and old concretes according to claim 2, characterized in that The calculation formula for the shear stress amplitude is: △σ = σmax - σmin; From: σmin = 1.5·k1·Pu / (L2·L3); σmax = 1.5·k2·Pu / (L2·L3); We get: △σ = 1.5·Pu(k2 - k1) / (L2·L3); Where, △σ represents the shear stress amplitude; σmin represents the lower limit of the fatigue loading force value; σmax represents the upper limit of the fatigue loading force value; In the fatigue dynamic loading test, the fatigue load adopts a sine load, the loading frequency is 2 - 4HZ, and the range of the fatigue load value is k1·Pu - k2·Pu; k1 = 0.1; k2 takes values from 0.2 to 0.8; L1 represents the length of the new concrete specimen (2); L2 represents the width of the new concrete specimen (2); L3 represents the height of the new concrete specimen.

4. A method for testing the fatigue shear resistance performance of the interface between new and old concrete according to claim 1, characterized in that, In step S1, A steel backing plate (5) is arranged on the upper side of the old concrete specimen (1), and a fixing bolt (6) is arranged on the steel backing plate (5). The fixing bolt (6) penetrates through the steel backing plate (5), the old concrete specimen (1) and the steel support (7) from top to bottom in sequence.

5. A method for testing the fatigue shear resistance performance of the interface between new and old concrete according to claim 1, characterized in that In step S2, Before casting the new concrete specimen (2) between the two old concrete specimens (1), the bonding surfaces of the two old concrete specimens (1) and the new concrete specimen (2) are roughened respectively; after the roughening treatment, the concrete debris is blown away by a hair dryer, rinsed with clean water and kept wet until the new concrete specimen (2) is cast.

6. The fatigue shear resistance test method for the interface between new and old concrete according to claim 1, wherein In step S3, The length L1, width L2 and height L3 of the new concrete specimen (2) are the same as the length, width and height of the old concrete specimen (1) respectively.

7. A method for testing the fatigue shear resistance performance of the interface between new and old concrete as described in claim 1, characterized in that, In step S3, The strain gauges (3) are symmetrically arranged with the new concrete specimen (2) as the symmetry center; the number of the strain gauges (3) is ≥ 12, and the distances between the outer edges of the strain gauges (3) and the bonding surface of the new concrete specimen (2) and the old concrete specimen (1), the distances between the outer edges of the strain gauges (3) and the upper side edge of the new concrete specimen (2), and the distances between the outer edges of the strain gauges (3) and the lower side edge of the new concrete specimen (2) are all 0.5 - 1 cm.

8. A method for testing the fatigue shear resistance performance of the interface between new and old concrete as described in claim 1, characterized in that, In step S4, The steel distribution beam (8) contacts the new concrete specimen (2) as follows: The self-weight of the steel distribution beam (8) is denoted as G1. When the steel distribution beam (8) is separated from the new concrete specimen (2), the acting force value displayed on the actuator of the MST loading device is -G1, and the data of the acting force displayed on the actuator of the MST loading device is -G1+(1 / 100 - 1 / 10)G1.

9. A method for testing the fatigue shear resistance performance of the bonding surface between new and old concrete according to claim 8, characterized in that, In step S3, The number of the dial gauges (4) is four, and the four dial gauges (4) are symmetrically arranged at a position 0.5 - 1 cm close to the bonding surface at the bottom edge of the new concrete specimen (2).

10. A method for testing the fatigue shear resistance performance of the interface between new and old concrete as described in claim 9, characterized in that, In step S5, it specifically includes the following steps: S5-1. Perform preloading, and set the preloading force value as Pp S5-2. Unload to zero. Denote the load force value of each loading as ΔP, and repeat to load slowly at each level of ΔP until the bonding surface between the new concrete specimen (2) and the old concrete specimen (1) is displaced, and obtain the strain and deflection data and the shear resistance ultimate bearing capacity Pu.

Images