Method for measuring shear stress-strain difference-slip relation of concrete interface and application thereof

Abstract

The invention discloses a concrete interface shear stress-strain difference-slip relation measuring method and application thereof, and the method has the advantages that: 1, the concrete interface shear stress-strain difference-slip relation provided by the scheme is more in line with physical objective laws, and in an interface elastic stress stage, the interface is more stable; the deformation difference of matrixes on the two sides of the interface is very small and is represented by a micro-scale'strain difference '; 2, in the analysis of the elastic stress stage of the reinforcing beam, the strain and stress distribution of the cross section of a component are often analyzed, and the expression of the strain difference between new and old concrete interfaces is more easily fused into an analysis dimension system of the current stage; and 3, a digital image correlation method (DIC) is introduced to monitor displacement fields of concrete on two sides of the concrete bonding interface, so that a strain field and a strain difference are calculated, and a test means is updated.

Description

Technical Field

[0001] The present invention relates to the field of concrete interface bonding behavior measurement methods, and in particular to a concrete interface shear stress-strain difference-slip relationship measurement method and application thereof. Background Art

[0002] After long-term service, concrete structures of buildings and bridges will face problems such as material strength degradation and reduced bearing capacity of components. In terms of maintenance, components can be reinforced and repaired before continuing to be used, which saves a lot of money compared to "large-scale demolition and reconstruction". Among them, the cross-section enlargement method is a conventional reinforcement method, which is to set up a formwork outside the old concrete component and pour a layer of new concrete. The new and old concrete are tightly bonded together to achieve the purpose of expanding the cross-sectional area of ​​the component and improving the bearing capacity of the component.

[0003] In the reinforcement and repair analysis, it is necessary for structural engineers to conduct a safety analysis of the stress behavior of the reinforced components, which requires the use of some basic material data relationships, and the change in the bonding behavior between the new and old concrete interfaces is one of them. For example, the document "Wu Chen, Chu Fuwei, Gong Mingzi, et al. Experimental study on the bonding performance of the interface between ultra-high performance concrete and existing concrete without steam curing [J]. Materials Guide, 2023, 37(24): 163-170." discloses that the shear stress-interface slip relationship between ultra-high performance concrete and ordinary concrete was tested by direct shear test. Based on this, several relationships need to be explained: 1. In the elastic stress stage of the component, the tight bonding force between the new and old concrete is an important factor to ensure that the two work together, and this bonding force will only be generated when and only when there is a deformation difference between the matrix on both sides of the new and old concrete interface; 2. In the elastic stress stage of the component, the deformation difference between the matrix on both sides of the new and old concrete interface is very small, and it is not appropriate to use the macro-scale "slip" to characterize it, but the micro-scale "strain difference" should be used to characterize it; 3. In the analysis of the elastic stress stage of the reinforced beam, it is often necessary to analyze the strain and stress distribution of the cross-section of the component. The strain difference expression of the new and old concrete interface is easier to integrate into the current stage of analysis dimensional system; 4. When the shear stress between the new and old concrete interface exceeds the peak value, the matrix on both sides of the interface will begin to displace. After that, it is more appropriate to use the macro-scale "slip" to characterize the dislocation between the interfaces.

[0004] In actual test measurements, the shear stress, strain difference, and slip at the interface between the new and old concrete of the test specimen are all non-uniformly distributed, so the traditional measurement method faces certain difficulties. This is completely different from the uniform distribution of longitudinal stress and strain when concrete is under compression.

[0005] Based on the above analysis and the needs in the field of structural force analysis, the present invention proposes a method for measuring the shear stress-strain difference-slip relationship of a concrete interface to solve the above problems. Summary of the invention

[0006] In view of this, based on the demand for basic material data in the field of structural force analysis, the purpose of the present invention is to propose a concrete interface shear stress-strain difference-slip relationship measurement method and its application, which can to a certain extent solve the uncertainty problem caused by the non-uniform distribution of shear stress, strain difference and slip on the interface between new and old concrete of the test specimen.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A method for measuring shear stress-strain difference-slip relationship of concrete interface, comprising:

[0009] S01. Prepare L-shaped shear specimens formed by new concrete and old concrete respectively, and then assemble them to obtain double L-shaped shear specimens;

[0010] S02. Load and pressurize the double L-shaped shear specimen according to preset parameters by using a testing device, and record output data of the testing device and test data of changes in the double L-shaped shear specimen caused by loading;

[0011] S03. Fitting the vertical displacement field of concrete on both sides of the concrete bonding interface closest to the concrete according to the output data and the test data;

[0012] S04. According to the concrete vertical displacement field, fitting the concrete vertical strain field on both sides of the concrete bonding interface;

[0013] S05. Determine the ultimate strain difference of the substrate on both sides of the concrete bonding interface during the elastic stress stage |Δε u |;

[0014] S06. Determine the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface;

[0015] S07. Determine the changing relationship between shear stress τ and interface slip |Δs| during the slip stage of the concrete bonding interface, so as to complete the measurement of the concrete interface shear stress-strain difference-slip relationship.

[0016] As a possible implementation mode, further, in the present scheme S01, a pair of L-shaped shear specimens formed by new concrete and old concrete respectively are assembled inverted to each other to form a double L-shaped shear specimen, whose outer contour specification is 150mm×200mm×400mm, wherein the L-shaped long sides of a pair of L-shaped shear specimens are in contact to form a new and old concrete bonding interface, which is set as a concrete bonding interface, and its specification is 150mm×160mm, wherein 150mm represents the width of the bonding interface, and 160mm represents the height of the bonding interface.

[0017] As a preferred implementation option, preferably, in the present solution S01, the interface where a pair of L-shaped shear specimens contact each other is also roughened or coated with an interface agent.

[0018] In addition, in the present scheme S01, the front side of the double L-shaped shear specimen is also spray-painted to form scattered spots, so as to assist the double L-shaped shear specimen in monitoring the displacement field of the concrete on both sides of the concrete bonding interface by using a digital imaging method when loading and pressurizing.

[0019] As a preferred implementation option, preferably, in S02, when testing is performed by means of a testing device, the L-shaped shear specimen located at the bottom of the double L-shaped shear specimen is supported by a pad, and the L-shaped shear specimen located at the top of the double L-shaped shear specimen is connected to the press loading head of the testing device and pressure is applied thereby; a pair of separated sides of the L-shaped shear specimens are constrained by a fixed bracket, and a baffle is also provided on the surface of the L-shaped shear specimen opposite to the fixed bracket.

[0020] As a preferred implementation option, preferably, in S02, the press loading head of the test device loads and pressurizes the double L-shaped shear specimen at a loading rate of 0.02 mm / min; at the same time, the output data of the test device, that is, the force output data of the press loading head, is recorded, and a fixed high-speed camera is used to collect the position change information of the scattered spots on the double L-shaped shear specimen until the test is loaded to the point where the double L-shaped shear specimen is destroyed, thereby generating test data.

[0021] As a preferred implementation option, preferably, S03 includes:

[0022] In the height direction of the new and old concrete bonding interface, the vertex is labeled A, the bottom end is labeled B, and a vertical coordinate axis y is established with point B as the coordinate origin; then, excluding the scattered spots across the bonding interface, the scattered spots on the left side of the bonding interface are selected and numbered from bottom to top as N1, N2, ..., N i ,…, then select the scattered spots on the right side of the nearest bonding interface and number them from bottom to top as N'1, N'2,…, N' j ,…; let each numbered spot correspond to a vertical coordinate, and the vertical coordinates on both sides of the bonding interface are expressed as

[0023] The speckle position change information in the test data recorded by the high-speed camera is processed, from which the position change information of any numbered speckle at any time t can be obtained. k The vertical displacement is Represents the Nth leftmost adjacent bonding interface i The scattered spots are k The vertical displacement at time Represents the N'th closest to the right side of the bonding interface j The scattered spots are k The vertical displacement at time t k At this moment, the N1, N2, ..., N i Vertical displacement of a point The vertical displacement values ​​of these points are fitted to the polynomial function u l (y,t k ), similarly, we can get u r (y,t k ), and complete the fitting of the concrete vertical displacement field on both sides of the concrete bonding interface.

[0024] As a preferred implementation option, preferably, S04 includes: converting the vertical displacement field u l (y,t k ),u r (y,t k ) are differentiated with respect to the variable y, and the longitudinal strain field ε is obtained: l (y,t k ), ε r (y,t k ), complete the fitting of the concrete vertical strain field on both sides of the concrete bonding interface.

[0025] As a preferred implementation option, preferably, S05 includes: based on the fact that during the test, the output of the press loading head of the test device is a process of gradually increasing and then gradually decreasing, therefore, the maximum output of the press loading head is set to F u , the corresponding time is t u , at time 0~t u , the concrete bonding interface belongs to the elastic stress stage, so let the ultimate strain difference of the matrix on both sides of the bonding interface |Δε u |=|ε l (y,t u )-ε r (y,t u )| max , y∈[0,160].

[0026] As a preferred implementation option, preferably, S06 includes: u The interval between is divided into (0, t1, t2, ..., t i ,…,t N1 ), where N1 is a positive integer, t N1 That is t u , the corresponding moment of the press loading head force output is (0, F1, F2, ..., F i , …, FN1 ), where F N1 That is F u , the maximum strain difference on the concrete bonding interface at the corresponding moment is (0, |Δε1|, |Δε2|, ..., |Δε i |,…,|Δε N1 |), where |Δε N1 | is |Δε u |; Thus, the following relationship can be obtained:

[0027] 0 <F1<F2<…<F i <… <F N1 ,0<|Δε1|<|Δε2|<…<|Δε i |<…<|Δε N1 |

[0028] At any time, the strain difference |Δε| and shear stress τ on the concrete interface are different everywhere. To simplify the calculation, the following definitions are made:

[0029] When 0<|Δε|<|Δε1|, let τ=τ1, and the length of the section on the corresponding concrete interface AB is Δy1.

[0030] When |Δε1|<|Δε|<|Δε2|, let τ=τ2, and the length of the corresponding segment on the concrete interface AB is Δy2.

[0031] …

[0032] When |Δε i-1 |<|Δε|<|Δε i |, let τ=τ i , the length of the segment on the concrete interface AB is Δy i ,

[0033] …

[0034] When |Δε N1-1 |<|Δε|<|Δε N1 |, let τ=τ N1 , the length of the segment on the concrete interface AB is Δy N1 ,

[0035] Combined with the strain field distribution at any time obtained in step S04, Δy1, Δy2, ..., Δy i …, Δy N1 , now find (0, τ1, τ2,…,τ i ,…,τ N1 ), where τ N1 =τ u Represents the ultimate shear stress of the concrete bonding interface during the elastic stress stage;

[0036] At time t1, the force on the specimen is F1, which is balanced by the shear force provided by the concrete interface. At this time, the maximum strain difference on the concrete interface is |Δε1|, and the corresponding shear stress on the concrete interface is τ1, then,

[0037] F1=τ1BL,τ1=F1 / BL

[0038] Among them, B represents the width of the specimen bonding interface, which is 150 mm; L represents the height of the specimen bonding interface, which is 160 mm;

[0039] At time t2, the force on the specimen is F2, which is balanced by the shear force provided by the concrete interface. At this time, the concrete interface AB is divided into two sections Δy1 and Δy2, where Δy1+Δy2=160mm. The concrete interface strain difference in the Δy1 section meets 0<|Δε|<|Δε1|, and the corresponding shear stress on the concrete interface is τ1. The concrete interface strain difference in the Δy2 section meets |Δε1|<|Δε|<|Δε2|, and the corresponding shear stress on the concrete interface is τ2. Then,

[0040] F2=B(τ1Δy1+τ2Δy2),

[0041]

[0042] And so on.

[0043]

[0044] Thus, we can get the following data points (0,0), (|Δε1|, τ1), (|Δε2|, τ2),…, (|Δε N1 |,τ N1 ), the next step is to select a suitable function to fit the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface.

[0045] As a preferred implementation option, preferably, S07 includes: at t u After the moment, the concrete partial bonding interface enters the slip stage, the force F loaded on the double L-type shear specimen will gradually decrease, and the maximum slip on the concrete interface will gradually increase; u The time series after time is marked as t N1+1 , t N1+2 ,…,t N1+i ,…,t N1+N2 , where N1 and N2 are both positive integers;

[0046] Among them, at any time t N1+i, the concrete interface AB will be divided into a slip zone and a non-slip zone. At the boundary point between the two types of zones, the strain difference on both sides of the concrete interface is |Δε u | or slip |Δs|=0; then at any time t N1+i ,, the force output by the press loading head on the left half of the specimen is F N1+i , the maximum slip on the interface is y∈[0,160]

[0047] According to simple force analysis, there is the following relationship:

[0048] F N1 >F N1+1 >F N1+2 >…>F N1+i >…>F N1+N2 ,

[0049] 0=|Δs| N1 <|Δs| N1+1 <|Δs| N1+2 <…<|Δs| N1+i <…<|Δs| N1+N2 ,

[0050] Because at any time, the slip |Δs| and shear stress τ on the concrete interface are different everywhere, in order to simplify the calculation, the following provisions are made:

[0051] When 0=|Δs| N1 <|Δs|<|Δs| N1+1 When τ = τ N1+1 , the length of the segment on the concrete interface AB is Δy N1+1 ,

[0052] When |Δs| N1+1 <|Δs|<|Δs| N1+2 When τ = τ N1+2 , the length of the segment on the concrete interface AB is Δy N1+2 ,

[0053] …

[0054] When |Δs| N1+N2-1 <|Δs|<|Δs| N1+N2 When τ = τ N1+N2 , the length of the segment on the concrete interface AB is Δy N1+N2 ,

[0055] In t N1+1 At this moment, the force on the specimen is F N1+1 , which is balanced by the shear force provided by the concrete interface; at this time, the concrete interface AB is divided into the following segments Δy1, Δy2, …, ΔyN1 , Δy N1+1 , then we have Δy1+Δy2+…+Δy N1 +Δy N1+1 =160mm; it is also possible that the strain difference at each location on the concrete interface is large. In this case, part of Δy i =0; then,

[0056]

[0057] By analogy, we can get:

[0058]

[0059] In this way, we can obtain a series of points (0, τ u ),(|Δs| N1+1 , τ N1+1 ),(|Δs| N1+2 , τ N1+2 ),…,(|Δs| N1+N2 , τ N1+N2 );

[0060] A function that meets the preset requirements is selected to fit the changing relationship between shear stress τ and interface slip |Δs| during the slip stage of the concrete bonding interface.

[0061] Based on the above, this solution also provides a reinforcement assessment method for building and bridge concrete structures, which is characterized by: using the above-mentioned measurement method in structural finite element analysis to determine the shear stress-strain difference-slip relationship of the concrete interface.

[0062] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: the present solution ingeniously proposes a method for measuring the shear stress-strain difference-slip relationship of the concrete interface, which has the following advantages:

[0063] 1. The concrete interface shear stress-strain difference-slip relationship provided by this scheme is more in line with the objective laws of physics. In the elastic stress stage of the interface, the deformation difference of the matrix on both sides of the interface is very small, and it is characterized by the microscopic scale "strain difference";

[0064] 2. In the analysis of the elastic stress stage of the reinforced beam, this method often needs to analyze the strain and stress distribution of the cross section of the component. The strain difference expression of the interface between the new and old concrete is easier to integrate into the analysis dimension system of the current stage;

[0065] 3. This method introduces the digital image correlation method (DIC) to monitor the displacement field of concrete on both sides of the concrete bonding interface, and then calculates the strain field and strain difference, thus updating the test method. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] 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 or the description of the prior art 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.

[0067] Figure 1 This is a schematic diagram of the evolution of shear stress, strain difference, and slip distribution on the concrete interface in the principle introduction of this method;

[0068] Figure 2 This is a diagram of the relationship between the shear stress τ and the strain difference |Δε| at the bond interface in the elastic stage of the concrete interface shear force in the principle introduction of this scheme method;

[0069] Figure 3 This is a diagram of the relationship between the shear stress τ of the bonding interface and the slip |Δs| in the slip stage in the principle introduction of this method;

[0070] Figure 4 This is a schematic diagram of the division of the slip zone and non-slip zone of the concrete interface in the principle introduction of this scheme method;

[0071] Figure 5 It is the three-view drawing of the double “L” type shear specimen mentioned in the embodiment of the method of this scheme;

[0072] Figure 6 This is a schematic diagram of speckle and specimen loading during the implementation of this method;

[0073] Figure 7 Schematic diagram of numbering the speckles on both sides of the adjacent bonding interface in the embodiment of the method of the present scheme. DETAILED DESCRIPTION

[0074] The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Similarly, the following examples are only partial embodiments of the present invention rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0075] This embodiment provides a method for measuring the shear stress-strain difference-slip relationship of a concrete interface, and its technical principle is as follows:

[0076] The construction of the shear stress-strain difference-slip relationship based on the concrete interface needs to be based on the material performance test measurement. In actual test measurements, the shear stress, strain difference, and slip on the concrete interface of the test specimen are all non-uniformly distributed. Therefore, the shear stress, strain difference, and slip in the local area cannot represent the situation of the entire interface, which is also an important reason why traditional measurements face certain difficulties. This is largely related to the fact that when concrete is compressed, its longitudinal stress and strain are uniformly distributed, which is completely different.

[0077] Based on this, the shear stress behavior of the concrete interface can be divided into two stages. The first stage is the elastic stage. The deformation difference of the matrix on both sides of the concrete interface is very small, and it is characterized by the microscopic "strain difference". In this stage, the shear stress τ on the concrete interface is related to the strain difference |Δε|. At the end of the elastic stage, the maximum shear stress (or ultimate shear stress) of the concrete interface is τ u , the corresponding limit strain difference is |Δε u |. When the deformation difference between the substrates on both sides of the concrete interface exceeds |Δε u |After that, the shear stress behavior of the concrete interface enters the second stage - the interface slip stage. In this stage, the matrix on both sides of the concrete interface begins to displace, and the macroscopic "slip" |Δs| is used to characterize this dislocation. In the second stage, the shear stress τ on the concrete interface gradually decreases with the increase of interface slip. Among them, Figure 1 The schematic diagram of the evolution of shear stress, strain difference, and slip distribution on the concrete interface shows that the shear stress, strain difference, and slip distribution on the concrete interface are all non-uniformly distributed. When the deformation difference of the matrix on both sides of the concrete interface exceeds |Δε u |After that, the concrete interface is divided into two regions. The AC and BD regions are described by slip |Δs|, and the CD region is described by strain difference |Δε u | is used to describe the deformation difference. At the dividing points C and D, |Δε| = |Δε u |.

[0078] Now we need to determine the relationship between the shear stress τ and the strain difference |Δε| at the bonding interface in the elastic stage. The deduction principle is as follows:

[0079] The loading moments in the elastic phase of the test are numbered as (0, t1, t2, ..., t N1 ), the corresponding moment of the press loading head force output is (0, F1, F2, ..., F N1 ), the corresponding maximum strain difference of the concrete interface is (0, |Δε1|, |Δε2|,…, |Δε N1 |). By Figure 2It can be seen that the interface shear stress τ increases with the increase of the strain difference |Δε|, and the specific relationship is yet to be determined. At any time, the force output by the press loading head on the left half of the specimen must be balanced with the shear stress generated on the concrete interface. According to the principle that the direction of the action force and the reaction force are opposite, the shear stress at each point on the interface acts upward on the left half of the specimen.

[0080] To simplify the calculation, it is assumed that when 0<|Δε|<|Δε1|, τ=τ1, and the length of the corresponding segment on the concrete interface AB is Δy1;

[0081] When |Δε1|<|Δε|<|Δε2|, let τ=τ2, and the length of the corresponding segment on the concrete interface AB is Δy2.

[0082] …

[0083] When |Δε i-1 |<|Δε|<|Δε i |, let τ=τ i , the length of the segment on the concrete interface AB is Δy i ,

[0084] …

[0085] When |Δε N1-1 |<|Δε|<|Δε N1 |, let τ=τ N1 , the length of the segment on the concrete interface AB is Δy N1 ,

[0086] Among them, Δy1, Δy2,…, Δy i …, Δy N1 It can be solved by the strain field distribution at any time; now find (0, τ1, τ2, ..., τ i ,…,τ N1 ), where τ N1 =τ u Represents the ultimate shear stress of the concrete bonding interface during the elastic stress stage.

[0087] At time t1, the force on the specimen is F1, which is balanced by the shear force provided by the concrete interface. At this time, the maximum strain difference on the concrete interface is |Δε1|, and the corresponding shear stress on the concrete interface is τ1, then,

[0088] F1=τ1BL,τ1=F1 / BL

[0089] Among them, B represents the width of the specimen bonding interface, which is 150 mm; L represents the height of the specimen bonding interface, which is 160 mm.

[0090] At time t2, the force on the specimen is F2, which is balanced by the shear force provided by the concrete interface. At this time, the concrete interface AB is divided into two sections Δy1 and Δy2, Δy1+Δy2=160mm. The concrete interface strain difference in the Δy1 section meets the requirement of 0<|Δε|<|Δε1|, and the corresponding shear stress on the concrete interface is τ1. The concrete interface strain difference in the Δy2 section meets the requirement of |Δε1|<|Δε|<|Δε2|, and the corresponding shear stress on the concrete interface is τ2. Then,

[0091] F2=B(τ1Δy1+τ2Δy2),

[0092]

[0093] And so on.

[0094]

[0095] The following data points can be obtained: (0,0), (|Δε1|, τ1), (|Δε2|, τ2),…, (|Δε N1 |,τ N1 ), the next step is to select a suitable function to fit the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface.

[0096] Now we need to determine the relationship between the shear stress τ of the bonding interface and the slip |Δs| in the slip stage; the deduction principle is as follows:

[0097] In t u After the moment, the concrete partial bonding interface enters the slip stage, and the concrete interface shear stress τ will gradually decrease with the increase of interface slip, such as Figure 3 As shown. u The time series after time is marked as t N1+1 , t N1+2 ,…,t N1+i ,…,t N1+N2 , N1, N2 are both positive integers. At any time t N1+i , the concrete interface AB will be divided into sliding zone AC, BD and non-slip zone CD, such as Figure 4 As shown, at the boundary points C and D of the two types of regions, the strain difference on both sides of the concrete interface is |Δε u |or slip|Δs|=0. At any time t N1+i ,, the force output by the press loading head on the left half of the specimen is F N1+i , the maximum slip on the interface is:

[0098]

[0099] According to simple force analysis, there is the following relationship:

[0100] F N1 >F N1+1 >F N1+2 >…>F N1+i >…>F N1+N2 ,

[0101] 0=|Δs| N1 <|Δs| N1+1 <|Δs| N1+2 <…<|Δs| N1+i <…<|Δs| N1+N2 ,

[0102] Because at any time, the slip |Δs| and shear stress τ on the concrete interface are different everywhere, in order to simplify the calculation, the following provisions are made:

[0103] When 0=|Δs| N1 <|Δs|<|Δs| N1+1 When τ = τ N1+1 , the length of the segment on the concrete interface AB is Δy N1+1 ,

[0104] When |Δs| N1+1 <|Δs|<|Δs| N1+2 When τ = τ N1+2 , the length of the segment on the concrete interface AB is Δy N1+2 ,

[0105] …

[0106] When |Δs| N1+N2-1 <|Δs|<|Δs| N1+N2 When τ = τ N1+N2 , the length of the segment on the concrete interface AB is Δy N1+N2 ,

[0107] In t N1+1 At this moment, the force on the specimen is F N1+1 , which is balanced by the shear force provided by the concrete interface; at this time, the concrete interface AB is divided into the following segments Δy1, Δy2, …, Δy N1 , Δy N1+1 , we have Δy1+Δy2+…+Δy N1 +Δy N1+1 =160mm; Note that it is also possible that the strain difference at each location on the concrete interface is very large. In this case, part of Δy i =0; then we can get the following formula:

[0108]

[0109] By analogy, we can get:

[0110] In this way, we can obtain a series of points (0, τ u ),(|Δs| N1+1 , τ N1+1 ),(|Δs| N1+2 , τ N1+2 ),…,(|Δs| N1+N2 , τ N1+N2 ).

[0111] The next step is to select a suitable function to fit the changing relationship between shear stress τ and interface slip |Δs| during the slip stage of the concrete bonding interface.

[0112] Based on the above, this embodiment scheme uses the following example to illustrate the concrete interface shear stress-strain difference-slip relationship measurement method, which includes the following:

[0113] S01. Prepare L-shaped shear specimens formed by new concrete and old concrete respectively, and then assemble them to obtain double L-shaped shear specimens;

[0114] Combination Figure 5 As shown, in the present scheme S01, a pair of L-shaped shear specimens 11 and 12 formed by new concrete and old concrete respectively are assembled inverted to each other to form a double L-shaped shear specimen 1, whose outer contour specification is 150mm×200mm×400mm, wherein the L-shaped long sides of a pair of L-shaped shear specimens are in contact to form a new and old concrete bonding interface, which is set as a concrete bonding interface 13, and its specification is 150mm×160mm; in addition, the interface where the pair of L-shaped shear specimens contact each other is also treated by roughening or coating with an interface agent.

[0115] In order to facilitate observation and data collection, in the present scheme S01, the front side of the double L-shaped shear specimen is also sprayed with paint to form scattered spots (such as Figure 6 As shown), it is used to assist the double L-shaped shear specimen in monitoring the displacement field of the concrete on both sides of the concrete bonding interface by using a digital imaging method (DIC) when loading and compressing.

[0116] S02. Load and pressurize the double L-shaped shear specimen according to preset parameters by using a testing device, and record output data of the testing device and test data of changes in the double L-shaped shear specimen caused by loading;

[0117] Combination Figure 6As shown, in S02, when the test is performed by the test device, the L-shaped shear specimen located at the lower part of the double L-shaped shear specimen is supported by a pad 4, and the L-shaped shear specimen located at the upper part of the double L-shaped shear specimen is connected to the press loading head 3 of the test device and pressure is applied thereto; a pair of separated sides of the L-shaped shear specimens are constrained by a fixed bracket 6, and a baffle 5 is also provided on the surface of the L-shaped shear specimen opposite to the fixed bracket 6.

[0118] In terms of parameter setting, in Scheme S02, the press loading head of the test device loads and pressurizes the double L-shaped shear specimen at a loading rate of 0.02 mm / min; at the same time, the output data of the test device, that is, the force output data of the press loading head, is recorded, and a fixed high-speed camera is used to collect the position change information of the scattered spots on the double L-shaped shear specimen until the test is loaded to the point where the double L-shaped shear specimen is destroyed, thereby generating test data.

[0119] S03. Fitting the vertical displacement field of concrete on both sides of the concrete bonding interface closest to the concrete according to the output data and the test data;

[0120] Specifically, S03 includes:

[0121] Combination Figure 7 As shown in FIG. 1 , the total height of the bonding interface between the new and old concrete is 160 mm. In the height direction of the bonding interface between the new and old concrete, the vertex is labeled A, the bottom end is labeled B, and a vertical coordinate axis y is established with point B as the origin of the coordinate. Then, excluding the scattered spots across the bonding interface, the scattered spots on the left side of the bonding interface are selected and numbered from bottom to top as N1, N2, ..., N i ,…, then select the scattered spots on the right side of the nearest bonding interface and number them from bottom to top as N'1, N'2,…, N' j ,…; let each numbered spot correspond to a vertical coordinate, and the vertical coordinates on both sides of the bonding interface are expressed as

[0122] Optecal software is used to process the speckle position change information in the test data recorded by the high-speed camera, from which the position change information of any numbered speckle at any time t can be obtained. k The vertical displacement is Represents the Nth leftmost adjacent bonding interface i The scattered spots are k The vertical displacement at time Represents the N'th closest to the right side of the bonding interface j The scattered spots are k The vertical displacement at time t k At this moment, the N1, N2, ..., Ni Vertical displacement of a point The vertical displacement values ​​of these points are fitted to the polynomial function u l (y,t k ), similarly, we can get u r (y,t k ), for example, u l (160mm,t k )=-1mm represents at t k At the moment, at the height of y=160mm of the bonding interface (i.e., the same height as point A), the vertical displacement of the concrete on the left side of the bonding interface is 1mm downward. The rest is analogous to the others, completing the fitting of the vertical displacement field of the concrete on both sides of the bonding interface.

[0123] S04, according to the concrete vertical displacement field, fitting the concrete vertical strain field on both sides of the concrete bonding interface; this step includes: the vertical displacement field u l (y,t k ),u r (y,t k ) are differentiated with respect to the variable y, and the longitudinal strain field ε is obtained: l (y,t k ), ε r (y,t k ), for example, ε l (160mm,t k ) represents the k At the moment, at the height of the bonding interface y = 160 mm (i.e., the same height as point A), the longitudinal strain of the concrete on the left side of the bonding interface is closest to the concrete. The rest is analogous to this, completing the fitting of the concrete vertical strain field on both sides of the bonding interface.

[0124] S05. Determine the ultimate strain difference of the substrate on both sides of the concrete bonding interface during the elastic stress stage |Δε u |.

[0125] This step is based on the fact that during the test, the output of the press loading head of the test device gradually increases and then gradually decreases. Therefore, the maximum output of the press loading head is set to F u , the corresponding time is t u , at time 0~t u , the concrete bonding interface belongs to the elastic stress stage, so let the ultimate strain difference of the matrix on both sides of the bonding interface |Δε u |=|ε l (y,t u )-ε r (y,t u )| max , y∈[0,160]

[0126] S06. Determine the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface;

[0127] In this step, the time from 0 to t u The interval between is divided into (0, t1, t2, ..., t i ,…,t N1 ), where N1 is a positive integer, t N1 That is t u , the corresponding moment of the press loading head force output is (0, F1, F2, ..., F i , …, F N1 ), where F N1 That is F u , the maximum strain difference on the concrete bonding interface at the corresponding moment is (0, |Δε1|, |Δε2|, ..., |Δε i |,…,|Δε N1 |), where |Δε N1 | is |Δε u |; Thus, the following relationship can be obtained:

[0128] 0 <F1<F2<…<F i <… <F N1 ,0<|Δε1|<|Δε2|<…<|Δε i |<…<|Δε N1 |

[0129] At any time, the strain difference |Δε| and shear stress τ on the concrete interface are different everywhere. To simplify the calculation, the following definitions are made:

[0130] When 0<|Δε|<|Δε1|, let τ=τ1, and the length of the section on the corresponding concrete interface AB is Δy1.

[0131] When |Δε1|<|Δε|<|Δε2|, let τ=τ2, and the length of the corresponding segment on the concrete interface AB is Δy2.

[0132] …

[0133] When |Δε i-1 |<|Δε|<|Δε i |, let τ=τ i , the length of the segment on the concrete interface AB is Δy i ,

[0134] …

[0135] When |Δε N1-1 |<|Δε|<|ΔεN1 |, let τ=τ N1 , the length of the segment on the concrete interface AB is Δy N1 ,

[0136] Combined with the strain field distribution at any time obtained in step S04, Δy1, Δy2, ..., Δy i …, Δy N1 , now find (0, τ1, τ2,…,τ i ,…,τ N1 ), where τ N1 =τ u Represents the ultimate shear stress of the concrete bonding interface during the elastic stress stage;

[0137] At time t1, the force on the specimen is F1, which is balanced by the shear force provided by the concrete interface. At this time, the maximum strain difference on the concrete interface is |Δε1|, and the corresponding shear stress on the concrete interface is τ1, then,

[0138] F1=τ1BL,τ1=F1 / BL

[0139] Among them, B represents the width of the specimen bonding interface, which is 150 mm; L represents the height of the specimen bonding interface, which is 160 mm;

[0140] At time t2, the force on the specimen is F2, which is balanced by the shear force provided by the concrete interface. At this time, the concrete interface AB is divided into two sections Δy1 and Δy2, where Δy1+Δy2=160mm. The concrete interface strain difference in the Δy1 section meets 0<|Δε|<|Δε1|, and the corresponding shear stress on the concrete interface is τ1. The concrete interface strain difference in the Δy2 section meets |Δε1|<|Δε|<|Δε2|, and the corresponding shear stress on the concrete interface is τ2. Then,

[0141] F2=B(τ1Δy1+τ2Δy2),

[0142]

[0143] And so on.

[0144]

[0145] Thus, we can get the following data points (0,0), (|Δε1|, τ1), (|Δε2|, τ2),…, (|Δε N1 |,τ N1 ), the next step is to select a suitable function to fit the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface.

[0146] S07. Determine the changing relationship between shear stress τ and interface slip |Δs| during the slip stage of the concrete bonding interface, so as to complete the measurement of the concrete interface shear stress-strain difference-slip relationship.

[0147] This step includes: u After the moment, the concrete partial bonding interface enters the slip stage, the force F loaded on the double L-type shear specimen will gradually decrease, and the maximum slip on the concrete interface will gradually increase; u The time series after time is marked as t N1+1 , t N1+2 ,…,t N1+i ,…,t N1+N2 , where N1 and N2 are both positive integers;

[0148] Among them, at any time t N1+i , the concrete interface AB will be divided into a slip zone and a non-slip zone. At the boundary point between the two types of zones, the strain difference on both sides of the concrete interface is |Δε u | or slip |Δs|=0; then at any time t N1+i ,, the force output by the press loading head on the left half of the specimen is F N1+i , the maximum slip on the interface is y∈[0,160]

[0149] According to simple force analysis, there is the following relationship:

[0150] F N1 >F N1+1 >F N1+2 >…>F N1+i >…>F N1+N2 ,

[0151] 0=|Δs| N1 <|Δs| N1+1 <|Δs| N1+2 <…<|Δs| N1+i <…<|Δs| N1+N2 ,

[0152] Because at any time, the slip |Δs| and shear stress τ on the concrete interface are different everywhere, in order to simplify the calculation, the following provisions are made:

[0153] When 0=|Δs| N1 <|Δs|<|Δs| N1+1 When τ = τ N1+1 , the length of the segment on the concrete interface AB is Δy N1+1 ,

[0154] When |Δs|N1+1 <|Δs|<|Δs| N1+2 When τ = τ N1+2 , the length of the segment on the concrete interface AB is Δy N1+2 ,

[0155] …

[0156] When |Δs| N1+N2-1 <|Δs|<|Δs| N1+N2 When τ = τ N1+N2 , the length of the segment on the concrete interface AB is Δy N1+N2 ,

[0157] In t N1+1 At this moment, the force on the specimen is F N1+1 , which is balanced by the shear force provided by the concrete interface; at this time, the concrete interface AB is divided into the following segments Δy1, Δy2, …, Δy N1 , Δy N1+1 , then we have Δy1+Δy2+…+Δy N1 +Δy N1+1 =160mm; it is also possible that the strain difference at each location on the concrete interface is large. In this case, part of Δy i =0; then,

[0158]

[0159] By analogy, we can get:

[0160]

[0161] In this way, we can obtain a series of points (0, τ u ),(|Δs| N1+1 , τ N1+1 ),(|Δs| N1+2 , τ N1+2 ),…,(|Δs| N1+N2 , τ N1+N2 );

[0162] Therefore, the next step is to fit the changing relationship between shear stress τ and interface slip |Δs| during the concrete bonding interface slip stage by selecting a function that meets the preset requirements.

[0163] by Figure 5 The example shown is an example, which is established using the finite element software ABAQUS Figure 5The double "L" shear specimen shown in the figure is then simulated in the finite element model for test loading, and the displacement information of some scattered spots on the front of the specimen adjacent to the concrete interface and the force output of the press loading head are collected, as shown in Table 1. Now it is necessary to convert the concrete interface shear stress-strain difference-slip relationship based on the data in Table 1.

[0164] Table 1 Displacement information of some scattered spots on the front of the specimen adjacent to the concrete interface and the force output of the press loading head

[0165]

[0166]

[0167] Correspondingly, the calculation process of this example is as follows:

[0168] (1) Calculate |Δε1| and τ1;

[0169] At t1 = 1s, u l (0,1s)=-0.066mm,u l (32mm,1s)=-0.071mm,u l (80mm,1s)=-0.077mm,u l (128mm,1s)=-0.085mm,u l (160mm,1s)=-0.093mm,u r (0,1s)=-0.028mm,u r (32mm,1s)=-0.036mm,u r (80mm,1s)=-0.043mm,u r (128mm,1s)=-0.049mm,u r (160mm, 1s) = -0.054mm, the displacement field is fitted, which includes the following:

[0170] u l (y,1s)=(-0.4y 2 -101.4y-66503.7)×10 -6 mm;

[0171] u r (y,1s)=(0.3y 2 -207.9y-28614.1)×10 -6 mm;

[0172] The strain field is fitted, which includes the following:

[0173]

[0174] |Δε1|=|ε l (y,1s)-ε r (y,1s)| max ,y∈[0,160]

[0175] =|-1.4y+106.5| max

[0176] =106με

[0177] τ1=F1 / BL=82000 / 150 / 160=3.42MPa

[0178] Based on the above, we can get the data point (|Δε1|,τ1) = (106με, 3.42MPa);

[0179] (2) Calculate |Δε2|, τ2;

[0180] According to the displacement data at t2=2s, the displacement field is fitted.

[0181] u l (y,2s)=(-0.7y 2 -156.3y-11086.0)×10 -6 mm;

[0182] u r (y,2s)=(0.6y 2 -364.9y-46738.9)×10 -6 mm;

[0183] Fitting the strain field,

[0184]

[0185] |Δε2|=|ε l (y,2s)-ε r (y,2s)| max ,y∈[0,160]

[0186] =|-2.6y+208.6| max

[0187] =209με

[0188] Let |-2.6y+208.6|≤|Δε1|, find y∈[40,120](mm), Δy1=120-40=80mm

[0189] Let |Δε1|≤|-2.6y+208.6|≤|Δε2|, find y∈[0,40]∪[120,160](mm), Δy2=(40-0)+(160-120)=80mm

[0190]

[0191] Thus, we can obtain the data point (|Δε2|,τ2) = (209με, 7.97MPa);

[0192] (3) Calculate |Δε3|, τ3, that is, |Δε u |,τ u ;

[0193] According to the displacement data at t3 = 3s, the displacement field is fitted.

[0194] u l (y,3s)=(-0.7y 2 -204.1y-133036.7)×10 -6 mm;

[0195] u r (y,3s)=(0.7y 2 -431.9y-56080.9)×10 -6 mm;

[0196] Fitting the strain field,

[0197]

[0198] |Δε3|=|ε l (y,3s)-ε r (y,3s)| max ,y∈[0,160]

[0199] =|-2.8y+227.8| max

[0200] =228με

[0201] Let |-2.8y+227.8|≤|Δε1|, find y∈[44,119](mm), Δy1=119-44=75mm

[0202] Let |Δε1|≤|-2.8y+227.8|≤|Δε2|, find y∈[7,44]∪[119,156](mm), Δy2=(44-7)+(156-119)=74mm

[0203] Let |Δε2|≤|-2.8y+227.8|≤|Δε3|, find y∈[0,7]∪[156,160](mm), Δy3=7+4=11mm

[0204]

[0205] Thus, we can get the data point (|Δε u |,τ u )=(228με,13.49MPa);

[0206] (4) Fitting the relationship between the shear stress τ and the strain difference |Δε| at the bonding interface in the elastic stage

[0207] According to the data points obtained above (|Δε1|,τ1)=(106με,3.42MPa), (|Δε2|,τ2)=(209με,7.97MPa), (|Δε u |,τ u )=(228με,13.49MPa), and the (0,0) data point is added to fit the relationship between the shear stress τ and the strain difference |Δε| at the bonding interface in the elastic stage;

[0208] τ=0.0002|Δε| 2 +0.0015|Δε|+0.1677

[0209] Wherein, the unit of τ is MPa, and the unit of |Δε| is με.

[0210] (5) Calculate |Δs|4, τ4

[0211] According to the displacement data at t4=4s, the displacement field is fitted.

[0212] u l (y,4s)=(-1.0y 2 -267.7y-177261.7)×10 -6 mm;

[0213] u r (y,4s)=(0.9y 2 -572.8y-75353.2)×10 -6 mm;

[0214] |Δs|4=|u l (y,4s)-u r (y,4s)| max , y∈[0,160]

[0215] =|-1.9y 2 +305.1y-101910.1|max ×10 -6 mm

[0216] =0.102mm

[0217] Fitting the strain field,

[0218]

[0219]

[0220] |Δε|=|ε l (y,4s)-ε r (y,4s)|,y∈[0,160]

[0221] =|-3.8y+305.1|

[0222] Let |-3.8y+305.1|≤|Δε1|, find y∈[53,108](mm), Δy1=108-53=55mm

[0223] Let |Δε1|≤|-3.8y+305.1|≤|Δε2|, find y∈[26,53]∪[108,135](mm), Δy2=(53-26)+(135-108)=54mm

[0224] Let |Δε2|≤|-3.8y+305.1|≤|Δε3|, find y∈[21,26]∪[135,140](mm), Δy3=5+5=10mm

[0225] Δy4=160-Δy1-Δy2-Δy3=160-55-54-10=41mm,

[0226]

[0227] Thus, we can obtain the data point (|Δs|4,τ4) = (0.102mm, 4.10MPa);

[0228] (6) Calculate |Δs|5, τ5

[0229] According to the displacement data at t5=5s, the displacement field is fitted.

[0230] u l (y,5s)=(-1.3y 2 -252.3y-207390)×10 -6 mm;

[0231] u r (y,5s)=(1.1y 2-635.2y - 80773)×10 -6 mm;

[0232] |Δs|5 = |u l (y, 5s) - u r (y, 5s)| max , y ∈ [0, 160]

[0233] = |-2.4y 2 + 382.9y - 126617| max ×10 -6 mm

[0234] = 0.126mm

[0235] The strain field is fitted,

[0236]

[0237] |Δε| = |ε l (y, 5s) - ε r (y, 5s)|, y ∈ [0, 160]

[0238] = |-4.8y + 382.9|

[0239] Let |-4.8y + 382.9| ≤ |Δε1|, and solve for y ∈ [58, 101](mm), Δy1 = 101 - 58 = 43mm

[0240] Let |Δε1| ≤ |-4.8y + 382.9| ≤ |Δε2|, and solve for y ∈ [37, 58] ∪ [101, 123](mm), Δy2 = (58 - 37) + (123 - 101) = 43mm

[0241] Let |Δε2| ≤ |-4.8y + 382.9| ≤ |Δε3|, and solve for y ∈ [34, 37] ∪ [123, 127](mm), Δy3 = 3 + 4 = 7mm

[0242] Let |-2.4y 2 + 382.9y - 126617|×10 -6 mm < |Δs|4, and y ∈ [0, 34] ∪ [127, 160](mm)

[0243] Solve for Δy4 = 0, Δy5 = 160 - Δy1 - Δy2 - Δy3 - Δy4 = 67mm

[0244]

[0245] Thus, the data point (|Δs|5, τ5) = (0.126mm, 3.25MPa) can be obtained;

[0246] (7) Fitting the relationship between the shear stress τ of the bonding interface and the slip |Δs|

[0247] According to the above data points (|Δs|4,τ4) = (0.102mm, 4.10MPa), (|Δs|5,τ5) = (0.126mm, 3.25MPa),

[0248] Add (0,τ u )=(0,13.49MPa) data point, the relationship between the shear stress τ of the bonding interface and the slip |Δs| in the slip stage is fitted;

[0249] τ=449.5|Δs| 2 -137.9|Δs|+13.49

[0250] Wherein, the unit of τ is MPa, and the unit of |Δs| is mm.

[0251] The above descriptions are only some embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent device or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for measuring the shear stress-strain difference-slip relationship of a concrete interface, characterized in that: It includes: S01. Prepare L-shaped shear specimens formed by new concrete and old concrete respectively, and then assemble them to obtain double L-shaped shear specimens; S02. Load and pressurize the double L-shaped shear specimen according to preset parameters by using a testing device, and record output data of the testing device and test data of changes in the double L-shaped shear specimen caused by loading; S03. Fitting the vertical displacement field of concrete on both sides of the concrete bonding interface closest to the concrete according to the output data and the test data; S04. According to the concrete vertical displacement field, fitting the concrete vertical strain field on both sides of the concrete bonding interface; S05. Determine the ultimate strain difference of the substrate on both sides of the concrete bonding interface during the elastic stress stage |Δε u |; S06. Determine the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface; S07. Determine the changing relationship between shear stress τ and interface slip |Δs| during the slip stage of the concrete bonding interface, so as to complete the measurement of the concrete interface shear stress-strain difference-slip relationship.

2. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 1, characterized in that: In S01, a pair of L-shaped shear specimens formed by new concrete and old concrete respectively are assembled inverted to form a double L-shaped shear specimen, and its outer contour specification is 150mm×200mm×400mm. Among them, the L-shaped long sides of a pair of L-shaped shear specimens are in contact to form a new and old concrete bonding interface, which is set as the concrete bonding interface, and its specification is 150mm×160mm.

3. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 2, characterized in that: In S01, the interface where a pair of L-shaped shear specimens contact each other is also treated by roughening or coating with an interface agent; In S01, the front side of the double L-shaped shear specimen is also spray-painted to form scattered spots, so as to assist the double L-shaped shear specimen in monitoring the displacement field of concrete on both sides of the concrete bonding interface by using a digital image method when loading and pressurizing; In S02, when the test is performed by the test device, the L-shaped shear specimen located at the lower part of the double L-shaped shear specimen is supported by a pad, and the L-shaped shear specimen located at the upper part of the double L-shaped shear specimen is connected to the press loading head of the test device and pressure is applied thereto; the two sides of a pair of L-shaped shear specimens are constrained by a fixed bracket, and a baffle is also provided on the surface of the L-shaped shear specimen opposite to the fixed bracket.

4. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 3, characterized in that: In S02, the press loading head of the test device loads and pressurizes the double L-shaped shear specimen at a loading rate of 0.02 mm / min; at the same time, the output data of the test device, that is, the force output data of the press loading head, is recorded, and a fixed high-speed camera is used to collect the position change information of the scattered spots on the double L-shaped shear specimen until the test is loaded to the point where the double L-shaped shear specimen is destroyed, thereby generating test data.

5. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 4, characterized in that: S03 includes: In the height direction of the new and old concrete bonding interface, the vertex is labeled A, the bottom end is labeled B, and a vertical coordinate axis y is established with point B as the coordinate origin; then, excluding the scattered spots across the bonding interface, the scattered spots on the left side of the bonding interface are selected and numbered from bottom to top as N1, N2, ..., N i ,…, then select the scattered spots on the right side of the nearest bonding interface and number them from bottom to top as N1', N'2,…, N' j ,…; let each numbered spot correspond to a vertical coordinate, and the vertical coordinates on both sides of the bonding interface are expressed as The speckle position change information in the test data recorded by the high-speed camera is processed, from which the position change information of any numbered speckle at any time t can be obtained. k The vertical displacement is Represents the Nth leftmost adjacent bonding interface i The scattered spots are k The vertical displacement at time Represents the N'th closest to the right side of the bonding interface j The scattered spots are k The vertical displacement at time t k At this moment, the N1, N2, ..., N i Vertical displacement of a point The vertical displacement values ​​of these points are fitted to the polynomial function u l (y,t k ), similarly, we can get u r (y,t k ), and complete the fitting of the concrete vertical displacement field on both sides of the concrete bonding interface.

6. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 5, characterized in that: S04 includes: The vertical displacement field u l (y,t k ),u r (y,t k ) are differentiated with respect to the variable y, and the longitudinal strain field ε is obtained: l (y,t k ), ε r (y,t k ), complete the fitting of the concrete vertical strain field on both sides of the concrete bonding interface.

7. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 6, characterized in that: S05 includes: Based on the fact that the output of the press loading head of the test device gradually increases and then gradually decreases during the test, the maximum output of the press loading head is assumed to be F u , the corresponding time is t u , at time 0~t u , the concrete bonding interface belongs to the elastic stress stage, so let the ultimate strain difference of the matrix on both sides of the bonding interface |Δε u |=|ε l (y,t u )-ε r (y,t u )| max , y∈[0,160].

8. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 7, characterized in that: S06 includes: Set time 0 to t u The interval between is divided into (0, t1, t2, ..., t i ,…,t N1 ), where N1 is a positive integer, t N1 That is t u , the corresponding moment of the press loading head force output is (0, F1, F2, ..., F i , …, F N1 ), where F N1 That is F u , the maximum strain difference on the concrete bonding interface at the corresponding moment is (0, |Δε1|, |Δε2|, ..., |Δε i |,…,|Δε N1 |), where |Δε N1 | is |Δε u |; Thus, the following relationship can be obtained: 0 <F1<F2<…<F i <… <F N1 ,0<|Dε1|<|Dε2|<…<|Dε i |<…<|No N1 | At any time, the strain difference |Δε| and shear stress τ on the concrete interface are different everywhere. To simplify the calculation, the following definitions are made: When 0<|Δε|<|Δε1|, let τ=τ1, and the length of the section on the corresponding concrete interface AB is Δy1. When |Δε1|<|Δε|<|Δε2|, let τ=τ2, and the length of the corresponding segment on the concrete interface AB is Δy2,… When |Δε i-1 |<|Δε|<|Δε i |, let τ=τ i , the length of the segment on the concrete interface AB is Δy i ,… When |Δε N1-1 |<|Δε|<|Δε N1 |, let τ=τ N1 , the length of the segment on the concrete interface AB is Δy N1 , Combined with the strain field distribution at any time obtained in step S04, Δy1, Δy2, ..., Δy i …, Δy N1 , now find (0, τ1, τ2,…,τ i ,…,τ N1 ), where τ N1 =τ u Represents the ultimate shear stress of the concrete bonding interface during the elastic stress stage; At time t1, the force on the specimen is F1, which is balanced by the shear force provided by the concrete interface. At this time, the maximum strain difference on the concrete interface is |Δε1|, and the corresponding shear stress on the concrete interface is τ1, then, F1=τ1BL,τ1=F1 / BL Among them, B represents the width of the specimen bonding interface, which is 150 mm; L represents the height of the specimen bonding interface, which is 160 mm; At time t2, the force on the specimen is F2, which is balanced by the shear force provided by the concrete interface. At this time, the concrete interface AB is divided into two sections Δy1 and Δy2, where Δy1+Δy2=160mm. The concrete interface strain difference in the Δy1 section meets 0<|Δε|<|Δε1|, and the corresponding shear stress on the concrete interface is τ1. The concrete interface strain difference in the Δy2 section meets |Δε1|<|Δε|<|Δε2|, and the corresponding shear stress on the concrete interface is τ2. Then, F2=B(τ1Δy1+τ2Δy2), And so on. Thus, we can get the following data points (0,0), (|Δε1|, τ1), (|Δε2|, τ2),…, (|Δε N1 |,τ N1 ), the next step is to select a suitable function to fit the relationship between the interface shear stress τ and the matrix strain difference |Δε| on both sides of the interface during the elastic stress stage of the concrete bonding interface.

9. The method for measuring the shear stress-strain difference-slip relationship of a concrete interface according to claim 1, characterized in that: S07 includes: In t u After the moment, the concrete partial bonding interface enters the slip stage, the force F loaded on the double L-type shear specimen will gradually decrease, and the maximum slip on the concrete interface will gradually increase; u The time series after time is marked as t N1+1 , t N1+2 ,…,t N1+i ,…,t N1+N2 , where N1 and N2 are both positive integers; Among them, at any time t N1+i , the concrete interface AB will be divided into a slip zone and a non-slip zone. At the boundary point between the two types of zones, the strain difference on both sides of the concrete interface is |Δε u | or slip |Δs|=0; then at any time t N1+i ,, the force output by the press loading head on the left half of the specimen is F N1+i , the maximum slip on the interface is According to simple force analysis, there is the following relationship: F N1 >F N1+1 >F N1+2 >…>F N1+i >…>F N1+N2 , 0=|Δs| N1 <|Δs| N1+1 <|Δs| N1+2 <…<|Δs| N1+i <…<|Δs| N1+N2 , Because at any time, the slip |Δs| and shear stress τ on the concrete interface are different everywhere, in order to simplify the calculation, the following provisions are made: When 0=|Δs| N1 <|Δs|<|Δs| N1+1 When τ = τ N1+1 , the length of the segment on the concrete interface AB is Δy N1+1 , When |Δs| N1+1 <|Δs|<|Δs| N1+2 When τ = τ N1+2 , the length of the segment on the concrete interface AB is Δy N1+2 , … When |Δs| N1+N2-1 <|Δs|<|Δs| N1+N2 When τ = τ N1+N2 , the length of the segment on the concrete interface AB is Δy N1+N2 , In t N1+1 At this moment, the force on the specimen is F N1+1 , which is balanced by the shear force provided by the concrete interface; at this time, the concrete interface AB is divided into the following segments Δy1, Δy2, …, Δy N1 , Δy N1+1 , then we have Δy1+Δy2+…+Δy N1 +Δy N1+1 =160mm; it is also possible that the strain difference at each location on the concrete interface is large. In this case, part of Δy i =0; then, By analogy, we can get: In this way, we can obtain a series of points (0, τ u ),(|Δs| N1+1 , τ N1+1 ),(|Δs| N1+2 , τ N1+2 ),…,(|Δs| N1+N2 , τ N1+N2 ); A function that meets the preset requirements is selected to fit the changing relationship between shear stress τ and interface slip |Δs| during the slip stage of the concrete bonding interface.

10. A method for assessing the reinforcement of concrete structures of buildings and bridges, characterized in that: The measuring method according to any one of claims 1 to 9 is used in structural finite element analysis to determine the shear stress-strain difference-slip relationship of the concrete interface.

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