Numerical implementation method and system of steel-concrete interface element under cyclic load

Abstract

The present invention discloses a numerical implementation method and system for steel-concrete interface units under cyclic loads, including: establishing and discretizing a finite element model of a steel-concrete component; inserting a layer of 8-node cohesive units and generating a solution file; batch-converting the 8-node cohesive unit information into 4-node interface unit information; defining the constitutive relationship of the interface unit under cyclic loads; numerically implementing the constitutive relationship of the interface unit in a compilation subroutine; submitting the solution file and calling the compilation subroutine for solution. The present invention realizes the rapid batch generation of steel-concrete 4-node interface unit information during the numerical simulation process, and at the same time defines and numerically implements the constitutive relationship of the interface unit under cyclic loads. The present invention reasonably reflects the bonding response of the steel bar and concrete interface under cyclic loads, significantly improving the accuracy of the numerical simulation of steel-concrete components.

Description

Technical Field

[0001] The present invention belongs to the technical field of numerical simulation methods for reinforced concrete structures, and in particular relates to a numerical realization method and system for a steel bar-concrete interface unit under reciprocating loads. Background Art

[0002] Concrete and steel structures are widely used in projects such as residential buildings, railway bridges, and tunnels due to their easy shaping, strong bearing capacity, and readily available materials and manageable costs. Ensuring good adhesion between steel and concrete is key to achieving the mechanical properties of reinforced concrete components. However, in conditions such as earthquakes and overloads, the steel bars in reinforced concrete structures may peel and slip, resulting in a decrease in the mechanical properties of the structure. Therefore, in-depth analysis of the mechanical properties of reinforced concrete structures under complex loading conditions requires careful study of the performance of the steel-concrete interface.

[0003] Finite element analysis is a rapidly developing modern computational method for structural mechanics analysis. It is widely used due to its advantages such as low cost and observable internal stresses. In the past few decades, in order to consider the bond-slip effect between steel bars and concrete, scholars have established many bond-slip numerical models. However, these results are mainly used to describe the bond-slip response under monotonic loading, and there are few studies on the bond-slip constitutive relationship under reciprocating loading, especially for fiber reinforced concrete. In addition, the cohesive force element or nonlinear spring element commonly used to simulate bond-slip behavior cannot reflect the influence of residual slip when unloading, and therefore are not suitable for reciprocating loading and repeated loading conditions. Therefore, it is necessary to propose a bond-slip constitutive relationship and its numerical implementation method that are applicable to various types of concrete and steel bars under reciprocating loading. Summary of the Invention

[0004] In order to reasonably reflect the bond response of the steel-concrete interface under cyclic loads and significantly improve the accuracy of numerical simulation of steel-concrete components, the present invention addresses the shortcomings of the existing technology and discloses a constitutive relationship of steel-concrete and a numerical implementation method.

[0005] In view of the above problems, the present invention adopts the following technical solutions:

[0006] The numerical implementation method and system of the steel-concrete interface element under cyclic loads are as follows:

[0007] Step S1: Performing a three-dimensional refined model of the reinforced concrete component in finite element software and performing mesh division to form a discrete model; inserting a layer of eight-node zero-thickness cohesive elements between the steel bar and concrete interface elements, and deleting the cohesive elements at intervals along the steel bar circumference;

[0008] Step S2: Submit the calculation job and generate a finite element solution file;

[0009] Step S3: Read the finite element solution file and batch convert the unit information of the eight-node zero-thickness cohesive element into the unit information of the four-node zero-thickness custom interface element, set the unit type, number of nodes, number of activated degrees of freedom and material property parameters of the custom interface element, and obtain a new solution file;

[0010] Step S4: setting the bond-slip constitutive relation under reciprocating load;

[0011] Step S5: compile a secondary development subroutine to numerically implement the bond-slip constitutive relationship set in step S4;

[0012] Step S6: Submit the new solution file in step S3 to the finite element software, and call the secondary development subroutine in step S5 to perform the solution.

[0013] Furthermore, the process of batch converting the unit information of the eight-node cohesive unit into the unit information of the four-node zero-thickness custom interface unit in step S3 is as follows:

[0014] Step S3.1: Read the finite element solution file and identify the element information of all eight-node cohesive elements through keyword search;

[0015] Step S3.2: Process the unit information of the eight-node cohesive unit and mark the unit number E of the eight-node cohesive unit. i and the first two node numbers (N1, N2);

[0016] Step S3.3: Obtain the three-dimensional coordinates of the first two nodes of the eight-node cohesive element respectively, and record them as (X1, Y1, Z1; X2, Y2, Z2);

[0017] Step S3.4: Determine the bonding direction of the steel bars. If the bonding direction is in a certain direction, use the coordinate values ​​in the other two directions for calculation. If the absolute value of the sum of the squares of the coordinate values ​​of node N1 in the other two directions minus the absolute value of the sum of the squares of the coordinate values ​​of node N2 in the other two directions is less than the tolerance, it is the first numbering method and proceed to step S3.5; otherwise, it is the second numbering method and proceed to step S3.6;

[0018] Step S3.5: rewrite the element information (E1, N1, N2, N3, N4, N5, N6, N7, N8) of the cohesive element into the element information (NE1, N5, N1, N4, N8) and (NE2, N6, N2, N3, N7) of two four-node interface elements, and execute step S3.7;

[0019] Step S3.6: rewrite the unit information of the cohesive unit (E1, N1, N2, N3, N4, N5, N6, N7, N8) into two four-node boundary unit information (NE1, N8, N4, N3, N7) and (NE2, N5, N1, N2, N6), and execute step S3.7;

[0020] Step S3.7: Determine whether there are cohesive elements in the solution file. If there are, repeat steps S3.2 to S3.7 until all cohesive elements are converted to four-node interface elements and a new solution file is generated.

[0021] Furthermore, in step S4, the envelope, unloading bond stiffness, bond degradation rate and residual bond stress are set.

[0022] The envelope in step S4 is set as follows:

[0023]

[0024] Unloading bond stiffness E ub and initial bond stiffness E b consistent;

[0025] The bond degradation rate is set as:

[0026] The residual bond stress is set as: τ rev =α4·τ unl

[0027] Among them, τ and s are the bond stress and slip value respectively, E b is the initial bond stiffness, Ω y is the steel bar yield reduction coefficient, a and b are the shape parameters of the envelope; α3 is the bond degradation rate, τ0 is the monotonic bond stress corresponding to a certain slip value; τ n is the bond stress of the nth loading cycle under the same slip; n is the number of cycles; τ rev is the residual bond stress, τ unl is the bonding stress at maximum slip before unloading, and α4 is the bonding stress coefficient.

[0028] Furthermore, the steel bar yield reduction factor Ω y for:

[0029]

[0030] Where ε is the steel bar strain; ε y and ε u are the yield strain and ultimate strain of the steel bar, respectively; f y and f u are the yield stress and ultimate stress of the steel bar, respectively.

[0031] Furthermore, the shape parameters of the envelope are solved by the following formula:

[0032] b=-1 / ln(τ u / E b ·s u )

[0033] Among them, τ u and s u are the peak bond stress and peak slip, respectively.

[0034] Furthermore, in step S5, the radial stiffness, axial-radial associated stiffness and torsional stiffness of the four-node zero-thickness custom interface unit are set, and the coordinate transformation matrix and residual of the four-node zero-thickness custom interface unit from the local coordinate system to the global coordinate system are set in sequence in the secondary development subroutine.

[0035] Furthermore, the steps for numerically implementing the bond-slip constitutive relationship of the steel bar-concrete interface in step S5 are as follows:

[0036] Step S5.1: Set the built-in variable PROPS(·) to read the material property parameters of the custom interface element in the solution file; calculate the slip value s, slip increment Δs, and steel strain ε between the steel bar and concrete; update the values ​​of all state variables SVARS(·); calculate the slip increment Δs of the current increment and the slip increment Δs of the previous increment pre If the product is less than zero, the number of loops n increases by 1 and step S5.2 is executed; if the product is greater than or equal to zero, the number of loops n remains unchanged and step S5.2 is executed;

[0037] Step S5.2: Determine the slip value s and the historical maximum slip value s under pressure max,c The size relationship between them, if s<s max,c , then execute step S5.3, otherwise execute step S5.4;

[0038] Step S5.3: Update s max,c The value of s max,c =s; calculate the bonding stress τ; execute step S5.13;

[0039] Step S5.4: Determine the magnitude relationship between the slip value s and 0. If s < 0, proceed to step S5.5; otherwise, proceed to step S5.8.

[0040] Step S5.5: Determine the magnitude relationship between the slip increment Δs and 0. If Δs>0, proceed to step S5.6; otherwise, proceed to step S5.7.

[0041] Step S5.6: Record the unloading point bond stress τ under compression unl,c Slip value s at unloading point unl,c , let τ unl,c =τ,s unl,c =s; Calculate the residual bond stress τ under compression res,c ; Calculate the bonding stress τ=τ unl,c +E ub ·Δs, E ub is the unloading stiffness; when τ>τ unl,c , then let τ=τ unl,c ; Execute step S5.13;

[0042] Step S5.7: Calculate the bond stress τ at the intersection of the reloading curve and the reduced envelope in the compressive state int,c and the corresponding slip value s int,c ; Updates max,c The value of s max,c =s; calculate the bonding stress τ; execute step S5.13;

[0043] Step S5.8: Determine the slip value s and the historical maximum slip value s under tension max,t The size relationship between them is, if s>s max,t , then execute step S5.9, otherwise execute step S5.10;

[0044] Step S5.9: Update s max,t The value of s max,t =s; calculate the bonding stress τ; execute step S5.13;

[0045] Step S5.10: Determine the magnitude relationship between the slip increment Δs and 0. If Δs < 0, execute step S5.11; otherwise, execute step S5.12.

[0046] Step S5.11: Record the unloading point bond stress τ in tension unl,t Slip value s at unloading point unl,t , let τ unl,t =τ,s unl,t =s; Calculate the residual bond stress τ under tension res,t ; Calculate the bonding stress τ = τ unl,c +E ub ·Δs; judge when τ<τ unnl,t , then let τ=τ unl,t ; Execute step S5.13;

[0047] Step S5.12: Calculate the bond stress τ at the intersection of the reloading curve and the reduced envelope in tension int,t and the corresponding slip value sint,t ; Updates max,t The value of s max,c =s; calculate the bonding stress τ; execute step S5.13;

[0048] Step S5.13: Calculate the axial bond stiffness k U =τ / s; save all state variables SVARS(·); assemble the unit stiffness matrix based on the radial stiffness matrix, torsional stiffness matrix, and axial-radial correlation stiffness matrix of the custom interface unit; set the coordinate transformation matrix, transform the unit stiffness matrix in the local coordinate system to the global coordinate system, and calculate the residual; enter the next increment and execute step S5.1.

[0049] Furthermore, the bonding stress τ at the intersection of the reloading curve and the reduced envelope under the compressive state is int,c , unloading point bonding stress τ under tension int,t and the corresponding slip value s int,c 、s int,t Methods for determining the value of include:

[0050] The reloading stiffness is calculated by the initial reloading point bond stress and slip value, the maximum unloading point slip value and the bond degradation rate; combined with the initial reloading point bond stress and slip value, the reduced envelope and the reloading stiffness,

[0051] By using the least squares algorithm, the bond stress and slip values ​​at the intersection of the reloading curve and the reduced envelope are returned when the error is less than the set threshold.

[0052] Furthermore, the state variable SVARS(·) includes the number of cycles n, the slip value s, the slip increment Δs, the slip increment Δs of the previous incremental step pre , the bond stress τ at the intersection of the reloading curve and the reduced envelope under compression int,c , unloading point bonding stress τ under tension int,t Slip value s at unloading point unl,c and s unl,t , residual bond stress τ res,c and τ res,t , historical maximum slip value s max,c and s max,t .

[0053] In another aspect, the present invention provides a numerical implementation system for a steel-concrete interface element under cyclic loads, comprising:

[0054] Modeling module: It is used to perform three-dimensional fine modeling of reinforced concrete components in finite element software, and perform mesh division to form a discrete model; insert a layer of eight-node zero-thickness cohesive force elements between the steel bar and concrete interface elements, and delete the cohesive force elements at intervals along the steel bar circumference;

[0055] Solution file acquisition module: It is used to submit calculation jobs and generate finite element solution files;

[0056] Solution file update module: It is used to open the finite element solution file, read and batch convert the unit information of the eight-node cohesive element into the unit information of the four-node zero-thickness custom interface element, and set the unit type, number of nodes, number of active degrees of freedom and material property parameters of the custom interface element to obtain a new solution file;

[0057] Constitutive relation setting module: It is used to set the bond-slip constitutive relation under reciprocating load;

[0058] Subroutine compilation module: It is used to compile secondary development subroutines and numerically realize the set bond-slip constitutive relationship;

[0059] Solution module: It is used to submit the new solution file in the finite element software and call the secondary development subroutine to solve.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] This method rapidly generates information about four-node steel-concrete interface elements during numerical simulation. It also defines and numerically implements the constitutive relationships for these interface elements under cyclic loading. This method is suitable for analyzing the bond characteristics of steel bars with conventional concrete, steel fiber reinforced concrete, and steel-polypropylene hybrid fiber reinforced concrete. Case studies have demonstrated that this method accurately reflects the bond response of the steel-concrete interface under cyclic loading or other complex loading paths, significantly improving the accuracy of numerical simulations of steel-concrete components. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a flow chart of the present invention.

[0063] Figure 2 It is a schematic diagram of the interface unit interval deletion of the present invention.

[0064] Figure 3 It is a unit conversion flow chart of the present invention.

[0065] Figure 4 It is a unit conversion schematic diagram of the present invention.

[0066] Figure 5It is a schematic diagram of the constitutive relationship under reciprocating load of the present invention.

[0067] Figure 6 It is a flow chart for numerical realization of the constitutive relationship of the present invention.

[0068] Figure 7 Schematic diagram of residual calculation of the present invention.

[0069] Figure 8 This is a model diagram of Example 1 of the present invention.

[0070] Figure 9 3 is a comparison diagram of the adhesion-slip curve of Example 1 of the present invention and the test.

[0071] Figure 10 Schematic diagram of the specimen size and numerical model of Example 2 of the present invention.

[0072] Figure 11 Schematic diagram of the destruction process of Example 2 of the present invention.

[0073] Figure 12 3 is a comparison diagram of the load-displacement curve of Example 2 of the present invention and the test. DETAILED DESCRIPTION

[0074] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and the present embodiment. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0075] This embodiment provides a numerical implementation method and system for a steel-concrete interface unit under reciprocating loads, specifically including the following steps: Figure 1 As shown:

[0076] Step S1: In the finite element software, perform a three-dimensional fine modeling of the reinforced concrete component and divide it into a grid to form a discrete model. Then, insert a layer of eight-node zero-thickness cohesive elements (COH3D8) between the steel bar and concrete interface elements. Use the element deletion function to delete the cohesive elements along the steel bar ring at intervals, such as Figure 2 As shown; the unit deletion is performed because one cohesive unit will be converted into two interface units. If the interval deletion is not performed, all interface units will be repeated after the conversion.

[0077] Step S2: Submit the calculation job and generate a finite element solution file;

[0078] Step S3: Open the finite element solution file, read the finite element solution file through the Python script, and further batch convert the unit information of the eight-node cohesive unit into the unit information of the four-node zero-thickness custom interface unit (in Figure 2 For example, if there are 100 cohesion elements left after batch deletion, 200 custom interface elements will be generated after subsequent batch conversion. The element type, number of nodes, number of active degrees of freedom, and material property parameters of the custom interface elements are declared to obtain a new solution file.

[0079] Among them, it needs to be further explained that the unit type is U1001, the input parameters and the number of variables in the solution process are set, and the translational degrees of freedom in the X, Y and Z directions are activated. The interface unit first defines the unit number in the INP file, and then defines the four node numbers. Among them, nodes 1 and 4 are concrete units, and nodes 2 and 3 are steel units. The material property parameters are the characteristic point parameters in the bond-slip relationship curve between steel and concrete and some model geometric parameters.

[0080] Specifically, the batch conversion process of the Python script is as follows: Figure 3 As shown:

[0081] Step S3.1: Read the solution file, search for *Element,type=COH3D8 by keyword, identify the element information of all cohesive elements, and execute step S3.2;

[0082] Step S3.2: Process the unit information of the first cohesion unit. The unit information of the cohesion unit includes the unit number and the corresponding eight node numbers, four of which are shared with the concrete unit and four with the steel unit. Mark the unit number (E1) and the first two node numbers (N1, N2), and proceed to step S3.3.

[0083] Step S3.3: In the solution file, search based on the node numbers (N1, N2) of the cohesive force unit, read the three-dimensional coordinates of the nodes, and record them as (X1, Y1, Z1; X2, Y2, Z2), and then execute step S3.4;

[0084] Step S3.4: Given that the node numbering rule for cohesive elements is from the bottom surface to the top surface in the thickness direction and in counterclockwise order in the non-thickness direction, the node numbering of the cohesive element starts at the bottom surface. However, for the four-node interface element distributed along the bonding direction after conversion, there are still two different numbering methods. Figure 4 As shown, first determine the bonding direction of the steel bars. When the bonding direction is in a certain direction (if it is the Z direction), the coordinate values ​​of the other two directions are used for calculation. If the absolute value of the sum of the squares of the coordinate values ​​of the other two directions of node N1 is subtracted from the absolute value of the sum of the squares of the coordinate values ​​of the other two directions of node N2, and the absolute value of the calculation result is less than the tolerance, that is, If it is the first numbering method, go to step S3.5; otherwise, it is the second numbering method, go to step S3.6. The tolerance is recommended to be set to 1 / 100 of the length of the interface unit in the bonding direction;

[0085] Step S3.5: Rewrite the element information of the cohesive element (E1, N1, N2, N3, N4, N5, N6, N7, N8) into the element information of two four-node interface elements (NE1, N5, N1, N4, N8) and (NE2, N6, N2, N3, N7). Execute step S3.7;

[0086] Step S3.6: Rewrite the unit information of the cohesive force unit (E1, N1, N2, N3, N4, N5, N6, N7, N8) into two four-node boundary unit information (NE1, N8, N4, N3, N7) and (NE2, N5, N1, N2, N6). NE1 and NE2 are new unit numbers that do not overlap with existing unit numbers in the solution file. If the original solution file contains 20,000 units, the interface units can be numbered starting from 30,000. Execute step S3.7;

[0087] Step S3.7: Determine whether there are cohesive force elements in the solution file. If there are, loop through steps S3.2 to S3.7 until all cohesive force elements are converted to four-node interface elements. Then, terminate the task and save the new solution file to the specified save path.

[0088] Step S4: Define and numerically implement the bond-slip constitutive relation under cyclic loading, focusing on defining the envelope, unloading bond stiffness, bond degradation rate, and residual bond stress;

[0089] The envelope is defined as follows: Given that the bond failure between the steel bar and the surrounding concrete interface is a continuous process in which damage accumulates gradually, it is defined using the damage model of formula (1). It is assumed that the evolution of the damage factor D satisfies the Weibull distribution shown in formula (2). At the same time, it is assumed that the damage begins when the slip value s0 is 0 mm, and considering the reduction of the bond stress by the yield of the steel bar, the bond stress-slip relationship under monotonic load is shown in formula (3). In formula (3), Ω y is the steel bar yield reduction coefficient, and the calculation method is shown in formula (4); a and b are both shape parameters of the envelope, and the calculation method is shown in formula (5). In formula (5), τ u and s u are the peak bonding stress and peak slip, respectively, and their calculation methods are shown in Equations (6) and (7), respectively.

[0090] It should be noted that Equation (3) is the envelope of the bond-slip constitutive relation. Equations (1) and (2) are the derivation process of Equation (3). Equations (4) to (7) are the definitions of the parameters in Equation (3).

[0091] τ=E b ·(1-D)· (1)

[0092] D=1-exp[-(s-s0) b / a] (2)

[0093]

[0094] s u =(1+α1λ sf +β1λ pf )(30 / f cu ) 0.5 (6)

[0095] τ u =13.5(1+α2λ sf +β2λ pf )(F cu / 30) 0.5 (7)

[0096] Where τ and s are the bond stress and slip value respectively; E b is the initial bond stiffness; f cu is the compressive strength of concrete cube; sf and λ pf are the characteristic parameters of steel fiber and polypropylene fiber, respectively, and are calculated as the product of fiber content and aspect ratio; ε is the steel bar strain; ε y and ε u are the yield strain and ultimate strain of the steel bar; f y and f u are the yield stress and ultimate stress of the steel bar respectively; α1 and α2 are the steel fiber reinforcement coefficients, which can be calibrated according to experimental data, or the recommended values ​​of 0.76 and 0.20 can be adopted; β1 and β2 are the polypropylene fiber reinforcement coefficients, which can be calibrated according to experimental data, or the recommended values ​​of 0.17 and 0.02 can be adopted.

[0097] Unloading bond stiffness E ub and initial bond stiffness E b consistent;

[0098] The bond degradation rate is defined as follows: The bond degradation rate can intuitively reflect the law of bond strength degradation, which is mainly related to the number of cyclic loading cycles and the historical maximum slip value, and is determined according to formula (8);

[0099]

[0100] Where τ0 is the monotonic bond stress corresponding to a certain slip value; τ n is the bond stress of the nth loading cycle under the same slip; n is the number of cycles; α3 is the bond degradation rate, which can be calibrated according to experimental data, or the recommended values ​​of 0.97 (before peak slip) and 0.80 (after peak slip) can be used.

[0101] The residual bond stress is defined as follows: the magnitude of the residual bond stress mainly depends on the bond stress at the unloading point and the friction coefficient between the steel bar and concrete, and is taken according to formula (9).

[0102] τ rev =α4·τ unl (9)

[0103] Among them, τ rev is the residual bond stress, τ unl is the bonding stress at maximum slip before unloading, and parameter α4 is the bonding stress coefficient, which can be calibrated according to experimental data, or the recommended values ​​of 0 (before peak slip) and -0.2 (after peak slip) can be used.

[0104] Step S5: Prepare a secondary development subroutine to numerically realize the bond-slip constitutive relationship defined in step S4, that is, obtain the bond stress and axial bond stiffness under the complex force path through the current slip value. On this basis, define the radial stiffness, axial-radial associated stiffness and torsional stiffness of the interface unit, then the stiffness values ​​in the four directions of axial, radial, axial-radial associated and torsional can now be determined. On this basis, substitute the three values ​​of the above stiffness, steel bar diameter and length of the interface unit in the bonding direction into the unit stiffness matrix of the four directions (each unit stiffness matrix is ​​a 3-row, 3-column matrix). Further assemble according to the global coordinate method to obtain the unit stiffness matrix (12-row, 12-column matrix) of the interface unit in the local coordinate system. Then, define the coordinate transformation matrix (12-row, 12-column matrix) and the residual (12-row, 1-column matrix) of the interface unit from the local coordinate system to the global coordinate system in the subroutine;

[0105] Among them, the bond-slip constitutive relationship of the steel-concrete interface is numerically realized as follows: Figure 5 and Figure 6 As shown, the implementation steps are as follows:

[0106] Step S5.1: Define and initialize all variables and matrices; set the built-in variable PROPS(·) and read the material constants of the interface element in the solution file; read the slip value s, slip increment Δs and steel strain ε between the steel bar and concrete; update the values ​​of all state variables SVARS(·), which is an array, in this case PROPS(1)-PROPS(11); calculate the slip increment Δs of the current increment and the slip increment Δs of the previous increment pre If the product is less than zero, the number of loops n increases by 1; and step S5.2 is executed; if the product is greater than or equal to zero, the number of loops n remains unchanged, and step S5.2 is executed;

[0107] Step S5.2: Determine the slip value s and the historical maximum slip value s under pressure max,c The size relationship between them. If s<s max,c , then execute step S5.3 (enter the compression loading stage), otherwise execute step S5.4;

[0108] Step S5.3: Update s max,c The value of s max,c =s; calculate the bonding stress τ according to formula (3); execute step S5.13;

[0109] Step S5.4: Determine the magnitude relationship between the slip value s and 0. If s < 0, execute step S5.5, otherwise execute step S5.8;

[0110] Step S5.5: Determine the magnitude relationship between the slip increment Δs and 0. If Δs>0, execute step S5.6 (enter the pressure unloading phase), otherwise execute step S5.7 (enter the pressure reloading phase);

[0111] Step S5.6: Record the unloading point bond stress τ under compression unl,c Slip value s at unloading point unl,c , let τ unl,c =τ,s unl,c =s; Calculate the residual bond stress τ under compression according to formula (9) res,c ; Calculate the bonding stress τ = τ unl,c +E ub ·Δs; judge when τ>τ unl,c , then let τ=τ unl,c ; Execute step S5.13;

[0112] Step S5.7: Calculate the bond stress τ at the intersection of the reloading curve and the reduced envelope in the compressive state int,c and the corresponding slip value s int,c ; Updates max,c The value of s max,c=s; calculate the bonding stress τ according to equations (3) and (8); execute step S5.13;

[0113] Step S5.8: Determine the slip value s and the historical maximum slip value s under tension max,t The size relationship between them. If s>s max,t , then execute step S5.9 (enter the tensile loading stage), otherwise execute step S5.10;

[0114] Step S5.9: Update s max,t The value of s max,t =s; calculate the bonding stress τ according to formula (3); execute step S5.13;

[0115] Step S5.10: Determine the magnitude relationship between the slip increment Δs and 0. If Δs < 0, execute step S5.11 (enter the tension unloading stage), otherwise execute step S5.12 (enter the tension reloading stage);

[0116] Step S5.11: Record the unloading point bond stress τ in tension unl,t Slip value s at unloading point unl,t , let τ unl,t =τ,s unl,t =s; Calculate the residual bond stress τ under tension according to formula (9) res,t ; Calculate the bonding stress τ = τ unl,c +E ub ·Δs; judge when τ<τ unl,t , then let τ=τ unl,t ; Execute step S5.13;

[0117] Step S5.12: Calculate the bond stress τ at the intersection of the reloading curve and the reduced envelope in tension int,t and the corresponding slip value s int,t ; Updates max,t The value of s max,c =s; calculate the bonding stress τ according to equations (3) and (8); execute step S5.13;

[0118] Step 5.13: Calculate the axial bond stiffness k U =τ / s; save all state variables SVARS(·), including the number of cycles n, slip value s, slip increment Δs, and slip increment Δs of the previous incremental step pre , unloading point bonding stress τ unl,c and τ unl,t Slip value s at unloading point unl,c and s unl,t , residual bond stress τ res,c and τ res,t, historical maximum slip value s max,c and s max,t ; Combine the radial stiffness matrix, torsional stiffness matrix, and axial-radial correlation stiffness matrix to assemble the element stiffness matrix; define the coordinate transformation matrix to transform the element stiffness matrix in the local coordinate system to the global coordinate system; calculate the residual R a , the residual is the key matrix to judge whether it converges, such as Figure 7 As shown; go to the next incremental step and execute step 1.

[0119] In steps S5.7 and S5.12, the bond stress τ at the intersection of the reloading curve and the reduced envelope is int,c , τ int,t and the corresponding slip value s int,c 、s int,t The numerical determination method of is as follows: first, the reloading stiffness is calculated by the bond stress and slip value at the initial reloading point, the slip value at the maximum unloading point, and the bond degradation rate; then, the bond stress and slip value at the initial reloading point, the reduced envelope, and the reloading stiffness are combined, and the bond stress and slip value at the intersection of the reloading curve and the reduced envelope are returned by the least squares algorithm when the error is less than 0.001.

[0120] Step S6: Submit the new solution file in step S3 to the finite element software, and call the secondary development subroutine in step S5 to perform the solution.

[0121] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, case analysis is conducted at the material and component levels below.

[0122] Example 1:

[0123] A steel bar center pull-out specimen was established. The concrete specimen was a cubic specimen with a side length of 150 mm, a cubic compressive strength of 50.93 MPa, a steel fiber content and an aspect ratio of 1.0% and 60, respectively, and a polypropylene fiber content and an aspect ratio of 0.15% and 167, respectively. The diameter of the steel bar was 20 mm, and the model was HRB400. The bonding end length was 60 mm, which was 3 times the diameter of the steel bar. Two rows of stirrups with a diameter of 6 mm were used, with a stirrup spacing of 30 mm, and the model was HPB235. The boundary conditions of the specimen were to constrain the translational freedom of the concrete at the loading end in the loading direction, such as Figure 8 shown.

[0124] like Figure 9 As shown in FIG, under reciprocating load, the bond-slip curve of the steel bar pull-out process is in good agreement with the test, which shows that the interface element in the present invention can well reflect the mechanical behavior of the central pull-out specimen under reciprocating load.

[0125] Example 2:

[0126] In order to verify the effect of the interface unit of the present invention on the mechanical response of reinforced concrete components under cyclic loads, the test data of steel-polypropylene hybrid fiber concrete columns were compared. The specimen consists of a column with a size of 800×200×200mm and a base with a size of 900×400×400mm. The shear span ratio is 4 and the axial compression ratio is 0.308. The concrete strength, steel fiber characteristic parameters, and polypropylene fiber characteristic parameters are 56.1MPa, 0.968, and 0.594, respectively. The detailed reinforcement diagram and numerical model of the column are shown in Figure 2. Figure 10 shown.

[0127] The failure process of reinforced concrete column numerical simulation is as follows Figure 11 As shown in Figure 2, it shows an oblique shear failure pattern, which is consistent with the test results. Figure 12 As shown, it can be seen that the interface unit proposed in the present invention can better reflect the energy dissipation capacity of reinforced concrete columns under cyclic loads.

[0128] Example 3:

[0129] This embodiment provides a numerical implementation system for a steel-concrete interface element under cyclic loads, including:

[0130] Modeling module: It is used to perform three-dimensional fine modeling of reinforced concrete components in finite element software, and perform mesh division to form a discrete model; insert a layer of eight-node zero-thickness cohesive force elements between the steel bar and concrete interface elements, and delete the cohesive force elements at intervals along the steel bar circumference;

[0131] Solution file acquisition module: It is used to submit calculation jobs and generate finite element solution files;

[0132] Solution file update module: It is used to open the finite element solution file, read and batch convert the unit information of the eight-node cohesive element into the unit information of the four-node zero-thickness custom interface element, and set the unit type, number of nodes, number of active degrees of freedom and material property parameters of the custom interface element to obtain a new solution file;

[0133] Constitutive relation setting module: It is used to set the bond-slip constitutive relation under reciprocating load;

[0134] Subroutine compilation module: It is used to compile secondary development subroutines and numerically realize the set bond-slip constitutive relationship;

[0135] Solution module: It is used to submit the new solution file in the finite element software and call the secondary development subroutine to solve.

[0136] The above is only a preferred specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in this application should be covered by the scope of protection of the present application.

[0137] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0138] It should be understood that the above description of the preferred embodiment is relatively detailed and cannot be regarded as limiting the scope of protection of the patent of the present invention. Under the guidance of the present invention, ordinary technicians in this field can also make substitutions or modifications without departing from the scope of protection of the claims of the present invention, which all fall within the scope of protection of the present invention. The scope of protection requested by the present invention shall be based on the attached claims.

Claims

1. A numerical implementation method of the steel-concrete interface element under cyclic loads, characterized in that: Here are the steps: Step S1: Performing a three-dimensional refined model of the reinforced concrete component in finite element software and performing mesh division to form a discrete model; inserting a layer of eight-node zero-thickness cohesive elements between the steel bar and concrete interface elements, and deleting the cohesive elements at intervals along the steel bar circumference; Step S2: Submit the calculation job and generate a finite element solution file; Step S3: Read the finite element solution file and batch convert the unit information of the eight-node zero-thickness cohesive element into the unit information of the four-node zero-thickness custom interface element, set the unit type, number of nodes, number of activated degrees of freedom and material property parameters of the custom interface element, and obtain a new solution file; Step S4: Set the bond-slip constitutive relationship under reciprocating load; set the envelope, unloading bond stiffness, bond degradation rate and residual bond stress, The envelope is set as follows: Unloading bond stiffness Initial bond stiffness consistent; The bond degradation rate is set as: The residual bond stress is set as: in, and are the bond stress and slip value, is the initial bond stiffness, is the steel bar yield reduction coefficient, and These are all shape parameters of the envelope; is the bond degradation rate, is the monotonic bond stress corresponding to a certain slip value; The same slip Bond stress during the ring loading cycle; is the number of cycles; is the residual bond stress, is the bonding stress at maximum slip before unloading, is the bonding stress coefficient; Step S5: compile a secondary development subroutine to numerically implement the bond-slip constitutive relationship set in step S4; Step S6: Submit the new solution file in step S3 to the finite element software, and call the secondary development subroutine in step S5 to perform the solution.

2. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 1 is characterized in that: The process of batch converting the unit information of the eight-node cohesive unit into the unit information of the four-node zero-thickness custom interface unit in step S3 is as follows: Step S3.1: Read the finite element solution file and identify the element information of all eight-node cohesive elements through keyword search; Step S3.2: Process the unit information of the eight-node cohesive unit and mark the unit number E of the eight-node cohesive unit. i and the first two node numbers (N1, N2); Step S3.3: Obtain the three-dimensional coordinates of the first two nodes of the eight-node cohesive element respectively and record them as (X1, Y1, Z1; X2, Y2, Z2); Step S3.4: Determine the bonding direction of the steel bars. If the bonding direction is in a certain direction, use the coordinate values ​​in the other two directions for calculation. If the absolute value of the sum of the squares of the coordinate values ​​of node N1 in the other two directions minus the absolute value of the sum of the squares of the coordinate values ​​of node N2 in the other two directions is less than the tolerance, it is the first numbering method and proceed to step S3.5; otherwise, it is the second numbering method and proceed to step S3.6; Step S3.5: rewrite the element information of the cohesive element (E1, N1, N2, N3, N4, N5, N6, N7, N8) into the element information of two four-node interface elements (NE1, N5, N1, N4, N8) and (NE2, N6, N2, N3, N7), and execute step S3.7; Step S3.6: Rewrite the element information of the cohesive element (E1, N1, N2, N3, N4, N5, N6, N7, N8) into two four-node boundary element information (NE1, N8, N4, N3, N7) and (NE2, N5, N1, N2, N6), and execute step S3.7 Step S3.7: Determine whether there are cohesive elements in the solution file. If there are, repeat steps S3.2 to S3.7 until all cohesive elements are converted to four-node interface elements and a new solution file is generated.

3. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 1 is characterized in that: Steel bar yield reduction factor for: in, is the steel bar strain; and are the yield strain and ultimate strain of the steel bar, respectively; and are the yield stress and ultimate stress of the steel bar, respectively.

4. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 1 is characterized in that: The shape parameters of the envelope are solved by the following formula: , in, and are the peak bond stress and peak slip, respectively.

5. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 1 is characterized in that: In step S5, the radial stiffness, axial-radial joint stiffness and torsional stiffness of the four-node zero-thickness custom interface element are set, and the coordinate transformation matrix and residual of the four-node zero-thickness custom interface element from the local coordinate system to the global coordinate system are sequentially set in the secondary development subroutine.

6. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 5 is characterized in that: The steps for numerically implementing the bond-slip constitutive relationship of the steel bar-concrete interface in step S5 are as follows: Step S5.1: Set the built-in variable PROPS (∙) to read the material property parameters of the custom interface element in the solution file; calculate the slip value between the steel bar and concrete , slip increment and steel strain ; Update all state variables Calculate the slip value increment of the current incremental step The slip value increment of the previous incremental step If the product is less than zero, then the number of cycles Increase by 1 and execute step S5.2; If the product is greater than or equal to zero, then the number of cycles Keep unchanged and execute step S5.2; Step S5.2: Determine the slip value The historical maximum slip value under compression If the size relationship between , then execute step S5.3, otherwise execute step S5.4; Step S5.3: Update The value of ; Calculate bond stress ; Execute step S5.13; Step S5.4: Determine the slip value The size relationship between and 0, if , then execute step S5.5, otherwise execute step S5.8; Step S5.5: Determine the slip increment The size relationship between and 0, if , then execute step S5.6, otherwise execute step S5.7; Step S5.6: Record the bond stress at the unloading point under compression Slip value at unloading point ,make , ; Calculation of residual bond stresses under compression ; Calculate bond stress , is the unloading stiffness; , then let ; Execute step S5.13; Step S5.7: Calculate the bond stress at the intersection of the reloading curve and the reduced envelope in compression and the corresponding slip value ;renew The value of ; Calculate the bond stress ; Execute step S5.13; Step S5.8: Determine the slip value The historical maximum slip value under tension If the size relationship between , then execute step S5.9, otherwise execute step S5.10; Step S5.9: Update The value of ; Calculate bond stress ; Execute step S5.13; Step S5.10: Determine the slip increment The size relationship between and 0, if , then execute step S5.11, otherwise execute step S5.12; Step S5.11: Record the bond stress at the unloading point in tension Slip value at unloading point ,make , ; Calculation of residual bond stress in tension ; Calculate bond stress ; judge when , then let ; Execute step S5.13; Step S5.12: Calculate the bond stress at the intersection of the reloading curve and the reduced envelope in tension and the corresponding slip value ;renew The value of ; Calculate the bond stress ; Execute step S5.13; Step S5.13: Calculate the axial bond stiffness = ; Save all state variables ; Based on the radial stiffness matrix, torsional stiffness matrix, and axial-radial correlation stiffness matrix of the custom interface unit, assemble the unit stiffness matrix; set the coordinate transformation matrix, transform the unit stiffness matrix in the local coordinate system to the global coordinate system, and calculate the residual; enter the next incremental step and execute step S5.

1.

7. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 6 is characterized in that: The bond stress at the intersection of the reloading curve and the reduced envelope under the compressive state , unloading point bonding stress under tension and the corresponding slip value 、 Methods for determining the value of include: The reloading stiffness is calculated by the initial reloading point bond stress and slip value, the maximum unloading point slip value and the bond degradation rate; combined with the initial reloading point bond stress and slip value, the reduced envelope and the reloading stiffness, By using the least squares algorithm, the bond stress and slip values ​​at the intersection of the reloading curve and the reduced envelope are returned when the error is less than the set threshold.

8. The numerical implementation method of the steel-concrete interface element under reciprocating load according to claim 6 is characterized in that: The state variable Including the number of cycles , slip value , slip increment , the slip value increment of the previous incremental step , the bond stress at the intersection of the reloading curve and the reduced envelope under compression , unloading point bonding stress under tension Slip value at unloading point and , residual bond stress and , Historical maximum slip value and .

9. Numerical realization system of steel-concrete interface element under cyclic load, characterized by: include: Modeling module: It is used to perform three-dimensional detailed modeling of reinforced concrete components in finite element software, and to perform mesh division to form a discrete model; Insert a layer of eight-node zero-thickness cohesive elements between the steel bar and concrete interface elements, and delete the cohesive elements at intervals along the steel bar hoop. Solution file acquisition module: It is used to submit calculation jobs and generate finite element solution files; Solution file update module: It is used to open the finite element solution file, read and batch convert the unit information of the eight-node cohesive element into the unit information of the four-node zero-thickness custom interface element, and set the unit type, number of nodes, number of active degrees of freedom and material property parameters of the custom interface element to obtain a new solution file; Constitutive relation setting module: It is used to set the bond-slip constitutive relation under reciprocating load; Subroutine compilation module: It is used to compile secondary development subroutines and numerically realize the set bond-slip constitutive relationship; Solution module: used to submit the new solution file in the finite element software and call the secondary development subroutine to solve; The numerical realization system of the steel bar-concrete interface unit under reciprocating load is used to execute the steps in the numerical realization method of the steel bar-concrete interface unit under reciprocating load according to any one of claims 1 to 8.

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