Simulation method for bond-slip relationship between fiber bar and concrete

Abstract

The invention relates to the technical field of building materials, in particular to a simulation method for the bond-slip relation between fiber bars and concrete, which comprises the following steps: defining unit types and material constitutions; establishing a geometric model, and dividing grids; building a bonding slip relation between the concrete and the fiber bars; establishing a constraint equation between the interface unit and the concrete unit; after the model is established, loading and solving are carried out; the method has the beneficial effects that the fiber bar nodes are copied in the concrete units, the nonlinear spring units are inserted between the copied nodes and the original fiber bar nodes in the fiber bar direction, and the degree of freedom is coupled in the other directions to achieve bonding slippage and cooperative stress between the fiber bars and concrete.

Description

Technical Field

[0001] The invention relates to the field of building materials, and in particular to a method for simulating the bonding-slip relationship between fiber reinforcement and concrete. Background Art

[0002] Fiber reinforcement is a new type of fiber composite material that replaces steel bars in the field of civil engineering. The bonding performance between fiber reinforcement and concrete is an important prerequisite for ensuring their synergistic effect in bearing loads.

[0003] However, in general, the bond strength between fiber reinforcement and ordinary concrete is relatively smaller than that between ribbed reinforcement. If the bond-slip relationship between fiber reinforcement and concrete is ignored in relevant numerical simulations, the calculated results may be significantly different from the actual situation.

[0004] Therefore, it is necessary to propose a simulation method for the bond-slip relationship between fiber reinforcement and concrete based on the Ansys finite element calculation platform to solve the problem of the interaction between fiber reinforcement and concrete. Summary of the invention

[0005] The purpose of the present invention is to provide a method for simulating the bond-slip relationship between fiber reinforcement and concrete, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for simulating the bond-slip relationship between fiber reinforcement and concrete, the method comprising the following steps:

[0007] Define unit type and material constitutive structure;

[0008] Establish geometric model and divide mesh;

[0009] Establish the bond-slip relationship between concrete and fiber reinforcement;

[0010] Establish constraint equations between the interface unit and the concrete unit;

[0011] After the model is established, it is loaded and solved.

[0012] Preferably, the specific operations of defining unit type and material constitutive structure include:

[0013] The unit types and material constitutive relations of concrete and fiber reinforcement, as well as the interface unit and bond-slip constitutive relation between concrete and fiber reinforcement are defined respectively. The deformation direction of the interface unit is set to be along the fiber reinforcement direction. The bond-slip constitutive relation between the concrete and fiber reinforcement interface is:

[0014] τ=τ(s);

[0015] Where: τ is the bond force corresponding to the interface slip between concrete and fiber reinforcement when the slip amount is s. Preferably, the specific operations of establishing the geometric model and dividing the grid include:

[0016] A three-dimensional concrete solid model and a two-dimensional fiber reinforcement line model are established, and then the meshes are divided and the corresponding unit types and material properties are assigned. When the fiber reinforcement is divided into meshes, the spacing between adjacent fiber reinforcement nodes is equal to L. The F-s relationship curve of the concrete and fiber reinforcement interface unit is: F = ALτ (D);

[0017] Where: F is the interface unit force, and A is the cross-sectional area of ​​the fiber reinforcement unit.

[0018] Preferably, the specific operation of establishing the bond-slip relationship between concrete and fiber reinforcement includes:

[0019] Nonlinear spring units are inserted between concrete units and original fiber reinforcement nodes along the fiber reinforcement direction, and the remaining directions are coupled with degrees of freedom to achieve the bond slip and coordinated force between the fiber reinforcement and concrete.

[0020] Preferably, the specific operation of establishing the bond-slip relationship between concrete and fiber reinforcement further includes:

[0021] An array a is created to hold the fiber reinforcement nodes, and the fiber reinforcement nodes are sorted and stored in the array.

[0022] Preferably, the specific operation of establishing the bond-slip relationship between concrete and fiber reinforcement further includes:

[0023] The nodes of the fiber reinforcement are copied at the original positions, an array b is established to accommodate the copied nodes, and the copied nodes are sorted and stored in the array.

[0024] Preferably, the specific operation of establishing the bond-slip relationship between concrete and fiber reinforcement further includes:

[0025] Create a new array c to store the node numbers of the copied nodes that participate in establishing the bond-slip relationship.

[0026] Preferably, the specific operation of establishing the bond-slip relationship between concrete and fiber reinforcement further includes:

[0027] Select the nodes that establish bonding relationships with the fiber reinforcement nodes one by one in the copied nodes.

[0028] Preferably, the specific operation of establishing the bond-slip relationship between concrete and fiber reinforcement further includes:

[0029] The interface bonding unit and the coupling degrees of freedom in other directions are established between the corresponding copy nodes and the fiber reinforcement nodes along the fiber reinforcement direction.

[0030] Preferably, the specific operation of establishing the constraint equation between the interface unit and the concrete unit includes:

[0031] Use the CElNTF command to connect all selected replicated nodes with the selected concrete elements to generate constraint equations.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The simulation method of the bond-slip relationship between fiber reinforcement and concrete proposed in the present invention realizes the bond-slip and coordinated force between fiber reinforcement and concrete by replicating the fiber reinforcement node inside the concrete unit, inserting a nonlinear spring unit between the replica node and the original fiber reinforcement node along the fiber reinforcement direction, and coupling the degrees of freedom in the remaining directions. When the finite element model is established by the present invention, it is not required that the concrete node and the fiber reinforcement node coincide with each other, so it is not affected by the finite element mesh division of concrete and fiber reinforcement. The two can be modeled and meshed separately, thereby significantly reducing the difficulty of modeling and improving the efficiency of modeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of mesh division of the model of the present invention;

[0035] Figure 2 It is a schematic diagram of the bonding relationship between the fiber reinforcement node and the replica node of the present invention;

[0036] Figure 3 A schematic diagram of establishing a constraint equation between a replication node and a concrete unit according to the present invention;

[0037] Figure 4 This is a schematic diagram of the basalt fiber reinforcement pulling test of the present invention;

[0038] Figure 5 It is a schematic diagram of the finite element calculation model of the present invention;

[0039] Figure 6 This is the relationship curve diagram of the interface bonding unit F-s of the present invention;

[0040] Figure 7 A schematic diagram of constraint equations is established for the present invention;

[0041] Figure 8 It is a schematic diagram comparing the simulation results and the test results of the present invention;

[0042] Fig. 9 Schematic diagram of principal strains of concrete of the present invention;

[0043] Fig.10 This is a schematic diagram of the tensile stress of the fiber anchor bar of the present invention;

[0044] Fig.11 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0045] In order to make the purpose and technical solution of the present invention clearly and completely described, and the advantages more clearly understood, the embodiments of the present invention are further described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] For example, see Figure 1-Figure 3 The present invention provides a technical solution: a method for simulating the bond-slip relationship between fiber reinforcement and concrete, the method comprising the following steps:

[0047] 1. Define unit type and material constitutive relationship. Define unit type and material constitutive relationship of concrete and fiber reinforcement, as well as interface unit and bond-slip constitutive relationship of concrete and fiber reinforcement. The deformation direction of interface unit is set to be along the fiber reinforcement direction. The bond-slip constitutive relationship of the interface between concrete and fiber reinforcement is:

[0048] τ=τ(s)

[0049] Where: τ is the bond force corresponding to the interface slip between concrete and fiber reinforcement when the slip amount is s. The specific value can be obtained through experiments.

[0050] 2. Establish geometric model and divide mesh. Establish concrete three-dimensional solid model and two-dimensional fiber reinforcement line model, and then divide mesh respectively and assign corresponding unit type and material properties. When dividing fiber reinforcement mesh, divide it evenly so that the distance between adjacent fiber reinforcement nodes is equal to L ( Figure 1 ), then the F~s relationship curve of the concrete and fiber reinforcement interface unit is

[0051] F=ALτ(D)

[0052] Where: F is the interface unit force, and A is the cross-sectional area of ​​the fiber reinforcement unit.

[0053] 3. Establish the bond-slip relationship between concrete and fiber reinforcement. Insert nonlinear spring units along the fiber reinforcement direction between the concrete unit and the original fiber reinforcement node, and couple the degrees of freedom in the remaining directions to achieve the bond-slip and coordinated force between the fiber reinforcement and concrete. The specific steps are as follows:

[0054] (1) Create an array a to hold the fiber reinforcement nodes, and sort the fiber reinforcement nodes and store them in the array. The code is written in APDL language as follows:

[0055] cmsel,s,xwnode! Select the fiber reinforcement node

[0056] *get,number1,node,0,count! Get the total number of nodes

[0057] *del,a_node! Clear the array

[0058] *dim,a_node,array,number1! Define array a

[0059] *get,a_node(1),node,0,num,min! Sort the fiber tendon nodes and store them in array a

[0060] *do,i,2,number1

[0061] a_node(i)=ndnext(a_node(i-1))

[0062] *enddo.

[0063] (2) Copy the nodes of the fiber reinforcement at the original position, create an array b to hold the copied nodes, and sort the copied nodes and store them in the array. The code is as follows:

[0064] ! Copy the fiber reinforcement node

[0065] cmsel,s,copynode! Select the copied node

[0066] *get,number2,node,0,count! Get the total number of nodes

[0067] *del,b_node! Clear the array

[0068] *dim,b_node,array,number2! Define array b

[0069] *get,b_node(1),node,0,num,min! Sort the copied nodes and store them in array b

[0070] *do,i,2,number2

[0071] b_node(i)=ndnext(b_node(i-1))

[0072] *enddo.

[0073] (3) Create a new array c to store the node numbers of the copied nodes that participate in establishing the bond-slip relationship. The code is as follows:

[0074] *del,c_node

[0075] *dim,c_node,array,number1

[0076] *do,i,1,number1

[0077] c_node(i)=0

[0078] *enddo.

[0079] (4) Select the nodes that establish a bonding relationship with the fiber reinforcement nodes one by one in the copied nodes.

[0080] The code is as follows:

[0081] cmsel,s,copynode! Select the copy node

[0082] ! Assign values ​​to array c. The number of elements in the array is the number of fiber reinforcement nodes.

[0083] *do,i,1,c_node

[0084] jj=1

[0085] j=1

[0086] ! Determine whether the nearest copy node of the fiber reinforcement has established an interface unit

[0087] *dowhile,kk! Loop condition

[0088] j=nnear(a_node(i))! Assign the node number closest to the i-th node in the fiber reinforcement to j

[0089] nsel,s,cp,,all! Select all nodes with coupled degrees of freedom

[0090] jj=nsel(k)+0.001

[0091] allsel

[0092] cmsel,s,copynode! Select the copy node

[0093] nsel,u,node,,j! Exclude the replication nodes that were previously determined to participate in the coupling

[0094] cm,copynode,node! Redefine the copy node selection set

[0095] *enddo

[0096] c_node(i)=j! Assign the judged j point number to the copy node to participate in the coupling array

[0097] *enddo.

[0098] (5) Establish interface bonding units along the fiber reinforcement direction between the corresponding replica nodes and fiber reinforcement nodes ( Figure 2 ), the remaining directions are coupled with degrees of freedom, and the code is as follows:

[0099] *do,i,1,number1

[0100] e,xw_node(i),cp_node(i)! Establish interface bonding unit

[0101] cp,next,UY,xw_node(i),cp_node(i)! Coupled Y-direction degrees of freedom

[0102] cp,next,UZ,xw_node(i),cp_node(i)! Coupled Z-direction degrees of freedom

[0103] *enddo

[0104] 4. Establish constraint equations between the interface unit and the concrete unit. Use the CElNTF command to connect all selected copy nodes with the selected concrete unit to generate constraint equations ( Figure 3 ).

[0105] 5. After the model is established, load and solve it.

[0106] Embodiment 2, refer to the attached Figure 4-Figure 11 As shown, based on the first embodiment, it is proposed to simulate the pull-out test of concrete and basalt fiber (BFRP) bars based on the Ansys finite element calculation platform. The test scheme is as follows Figure 4 The modeling method considering the bond-slip relationship between concrete and fiber reinforcement is as follows.

[0107] 1. Define the unit type and material constitutive property. Use the three-dimensional solid unit Solid 65 to simulate concrete, define the three-dimensional beam unit Beam 188 to simulate fiber reinforcement, define the interface unit Combin 39 to simulate the interface slip relationship, and set the deformation direction of the interface unit to the X direction.

[0108] The main material mechanical parameters of concrete and basalt fiber anchor are shown in Table 1. The concrete model is C30, and the fiber reinforcement diameter d is 12 mm. The multilinear isotropic strengthening model is used to simulate the compression of concrete. The stress-strain relationship curve is selected according to the "Concrete Structure Design Code". Linear elasticity is used to simulate the tensile stress-strain relationship of concrete. The William-Warnke failure criterion is used to simulate the tensile failure of concrete, and the crushing failure of concrete is not considered. The strength of the fiber reinforcement is relatively high, and linear elasticity is used to simulate its stress-strain relationship.

[0109] Table 1 Main material mechanical parameters of concrete and basalt fiber anchor

[0110] Material model Elastic modulus Poisson's ratio tensile strength Concrete C30 30GPa 0.2 2.01MPa Basalt fiber anchor Φ12 53.8GPa 0.25 1266MPa

[0111] The bond-slip relationship curve between concrete and fiber reinforcement interface is fitted according to the test results:

[0112]

[0113] τ=14.28-10.63(s-2.02),2.02≤s≤2.77

[0114] τ=6.31e -0.5569(s-2.77) +0.3209[1-e -0.5569(s-2.77) ],s>2.77

[0115] Where: τ is the bond stress between concrete and fiber reinforcement interface, MPa; s is the interface slip, mm.

[0116] 2. Establish geometric model and divide mesh. Establish concrete three-dimensional solid model and two-dimensional fiber reinforcement line model, and then divide mesh respectively and assign corresponding unit type and material properties. Figure 5 , where the fiber reinforcement unit length is controlled to be 10 mm, that is, the spacing between adjacent fiber reinforcement nodes is equal to 10 mm, then the F-s relationship curve of the Combine 39 unit at the interface between concrete and fiber reinforcement is:

[0117] F=ALτ(s)

[0118] In the formula, F is the interface unit force, A is the cross-sectional area of ​​the fiber reinforcement unit, and the F-s relationship curve of the interface bonding unit Combin 39 is obtained by substituting it into the calculation ( Figure 6 ) and enter it into the real constant of the Combin39 unit.

[0119] 3. Establish the bond-slip relationship between concrete and fiber reinforcement. Insert nonlinear spring units along the fiber reinforcement direction between the concrete unit and the original fiber reinforcement node, and couple the degrees of freedom in the remaining directions to achieve the bond-slip and coordinated force between the fiber reinforcement and concrete. The specific steps are as follows:

[0120] (1) Establish an array a to contain the fiber reinforcement nodes in the bonded section with concrete, and sort the fiber reinforcement nodes and store them in the array. The code written in APDL language is as follows:

[0121] cmsel,s,xwnode! Select the node of the fiber reinforcement bonded to the concrete

[0122] *get,number1,node,0,count! Get the total number of nodes

[0123] *del,a_node! Clear the array

[0124] *dim,a_node,array,number1! Define array a

[0125] *get,a_node(1),node,0,num,min! Sort the fiber tendon nodes and store them in array a

[0126] *do,i,2,number1

[0127] a_node(i)=ndnext(a_node(i-1))

[0128] *enddo

[0129] (2) Copy the nodes of the fiber reinforcement at the original position, create an array b to hold the copied nodes, and sort the copied nodes and store them in the array. The code is as follows:

[0130] ! Copy the fiber reinforcement node

[0131] cmsel,s,copynode! Select the copied node

[0132] *get,number2,node,0,count! Get the total number of nodes

[0133] *del,b_node! Clear the array

[0134] *dim,b_node,array,number2! Define array b

[0135] *get,b_node(1),node,0,num,min! Sort the copied nodes and store them in array b*do,i,2,number2

[0136] b_node(i)=ndnext(b_node(i-1))

[0137] *enddo

[0138] (3) Create a new array c to store the node numbers of the copied nodes that participate in establishing the bond-slip relationship. The code is as follows:

[0139] *del,c_node

[0140] *dim,c_node,array,number1

[0141] *do,i,1,number1

[0142] c_node(i)=0

[0143] *enddo

[0144] (4) Select the nodes that establish bonding relationships with the fiber reinforcement nodes one by one in the copied nodes. The code is as follows:

[0145] cmsel,s,copynode! Select the copy node

[0146] ! Assign values ​​to array c. The number of elements in the array is the number of fiber reinforcement nodes.

[0147] *do,i,1,c_node

[0148] jj=1

[0149] j=1

[0150] ! Determine whether the nearest copy node of the fiber reinforcement has established an interface unit

[0151] *dowhile,kk! Loop condition

[0152] j=nnear(a_node(i))! Assign the node number closest to the i-th node in the fiber reinforcement to j

[0153] nsel,s,cp,,all! Select all nodes with coupled degrees of freedom

[0154] jj=nsel(k)+0.001

[0155] allsel

[0156] cmsel,s,copynode! Select the copy node

[0157] nsel,u,node,,j! Exclude the replication nodes that were previously determined to participate in the coupling

[0158] cm,copynode,node! Redefine the copy node selection set

[0159] *enddo

[0160] c_node(i)=j! Assign the judged j point number to the copy node to participate in the coupling array

[0161] *enddo

[0162] (5) Establish interface bonding units along the fiber reinforcement direction between the corresponding replica nodes and fiber reinforcement nodes, and couple the degrees of freedom in the remaining directions. The code is as follows:

[0163] *do,i,1,number1

[0164] e,xw_node(i),cp_node(i)! Establish interface bonding unit,

[0165] cp,next,UY,xw_node(i),cp_node(i)! Coupled Y-direction degrees of freedom

[0166] cp,next,UZ,xw_node(i),cp_node(i)! Coupled Z-direction degrees of freedom

[0167] *enddo

[0168] 4. Establish constraint equations between the interface unit and the concrete unit. Use the CElNTF command to connect all selected copy nodes with the selected concrete unit to generate constraint equations, such as Figure 7 .

[0169] 5. After the model is established, normal constraints are applied to the concrete end surface, and gradually increasing tensile loads are applied to the ends of the basalt fiber reinforcement. The calculated slip value of the free section of the fiber reinforcement under the pulling action is compared with the test value, such as Figure 8 It can be seen that the numerical simulation results obtained by the simulation method of the bond-slip relationship between concrete and fiber reinforcement proposed in the present invention are generally close to the test results and the rules are consistent. According to the model calculation results, the stress and stress results of concrete and fiber reinforcement under different pull-out forces can be output. For example, when the pull-out forces are 30kN and 60kN respectively, the principal strain of concrete is as follows: Fig. 9 As shown in Figure 2, the tensile stress of the fiber anchor bar is Fig.10 shown.

[0170] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for simulating the bond-slip relationship between fiber reinforcement and concrete, characterized in that: The method comprises the following steps: Define unit type and material constitutive structure; Establish geometric model and divide mesh; Establish the bond-slip relationship between concrete and fiber reinforcement; Establish constraint equations between the interface unit and the concrete unit; After the model is established, it is loaded and solved.

2. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 1, characterized in that: The specific operations of defining unit type and material constitutive model include: The unit types and material constitutive relations of concrete and fiber reinforcement, as well as the interface unit and bond-slip constitutive relation between concrete and fiber reinforcement are defined respectively. The deformation direction of the interface unit is set to be along the fiber reinforcement direction. The bond-slip constitutive relation between the concrete and fiber reinforcement interface is: τ=τ(s); Where: τ is the bond force corresponding to the interface slip between concrete and fiber reinforcement when the slip amount is s.

3. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 1, characterized in that: The specific operations of establishing geometric models and dividing meshes include: A three-dimensional concrete solid model and a two-dimensional fiber reinforcement line model are established, and then the meshes are divided and the corresponding unit types and material properties are assigned. When the fiber reinforcement is divided into meshes, the spacing between adjacent fiber reinforcement nodes is equal to L. The F-s relationship curve of the concrete and fiber reinforcement interface unit is: F = ALτ (D); Where: F is the interface unit force, and A is the cross-sectional area of ​​the fiber reinforcement unit.

4. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 1, characterized in that: The specific operations to establish the bond-slip relationship between concrete and fiber reinforcement include: Nonlinear spring units are inserted between concrete units and original fiber reinforcement nodes along the fiber reinforcement direction, and the remaining directions are coupled with degrees of freedom to achieve the bond slip and coordinated force between the fiber reinforcement and concrete.

5. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 4, characterized in that: The specific operations to establish the bond-slip relationship between concrete and fiber reinforcement also include: An array a is created to hold the fiber reinforcement nodes, and the fiber reinforcement nodes are sorted and stored in the array.

6. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 5, characterized in that: The specific operations to establish the bond-slip relationship between concrete and fiber reinforcement also include: The nodes of the fiber reinforcement are copied at the original positions, an array b is established to accommodate the copied nodes, and the copied nodes are sorted and stored in the array.

7. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 6, characterized in that: The specific operations to establish the bond-slip relationship between concrete and fiber reinforcement also include: Create a new array c to store the node numbers of the copied nodes that participate in establishing the bond-slip relationship.

8. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 7, characterized in that: The specific operations to establish the bond-slip relationship between concrete and fiber reinforcement also include: Select the nodes that establish bonding relationships with the fiber reinforcement nodes one by one in the copied nodes.

9. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 8, characterized in that: The specific operations to establish the bond-slip relationship between concrete and fiber reinforcement also include: The interface bonding unit and the coupling degrees of freedom in other directions are established between the corresponding copy nodes and the fiber reinforcement nodes along the fiber reinforcement direction.

10. The method for simulating the bond-slip relationship between fiber reinforcement and concrete according to claim 1, characterized in that: The specific operations of establishing constraint equations between interface elements and concrete elements include: Use the CElNTF command to connect all selected replicated nodes with the selected concrete elements to generate constraint equations.

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