Bridge cable damping support simulation method and system based on Flac3D built-in Fish language

Abstract

The invention discloses a bridge cable damping support simulation method and system based on Flac3D built-in Fish language, and the method achieves the simulation of a bridge damping support and the simulation analysis of bridge seismic resistance in Flac3D, carries out the secondary development of an entity unit in Flac3D through the Fish language, and compiles a simulation program of a support unit through the Fish language. The shear deformation of the support unit under the earthquake action is extracted in real time, the stage of the shear deformation of the support is judged in real time, and the shear rigidity of the support unit is changed in real time, so that the shear-shear strain relation can meet the mechanical property of bilinear ideal elastoplasticity of the support unit. According to the method, simulation of the bridge inhaul cable damping support in Flac3D is achieved, the damping effect of the support can be reflected in anti-seismic analysis of the bridge in Flac3D, and the calculation result of the bridge under the earthquake effect better conforms to the actual situation.

Description

Technical Field

[0001] The invention relates to the technical field of bridge seismic analysis and calculation, and in particular to a bridge cable shock-absorbing bearing simulation method and system based on Flac3D built-in Fish language. Background Art

[0002] Generally, cable shock-absorbing bearings are installed at the connection between the bridge and the pier. The sliding of the bearing releases the seismic energy, reduces the seismic response of the structure, and effectively limits the relative displacement between the pier and the bridge through the cables to prevent the beam from falling. Under normal use loads, the cable shock-absorbing bearings are the same as ordinary bearings and can meet the requirements of the upper structure load and displacement; when the bridge structure encounters a design earthquake, the shear pins of the bearings are sheared off, and the entire system is transformed into a seismic isolation system. Subsequently, the cables are used to limit the displacement between the pier and the bridge within a controllable range. Therefore, the cable shock-absorbing bearings can improve the seismic performance of the overall bridge structure.

[0003] In the numerical analysis and calculation of the seismic resistance of bridges, it is necessary not only to establish a numerical model of the main structure of the bridge, but also to model the bearing structure and simulate the mechanical properties of the bearing unit to reflect the seismic protection effect of the bearing structure on the bridge structure. The mechanical model of the cable shock-absorbing bearing consists of two independent units, the bearing and the cable. It is necessary to simulate the mechanical properties of each unit separately, and then connect them in parallel to form a cable shock-absorbing bearing unit. The friction effect of the cable shock-absorbing bearing can be simulated by a bilinear ideal elastic-plastic spring unit.

[0004] Existing bridge numerical analysis software, such as Midas Civil, has ready-made bilinear spring units that can be used to simulate the mechanical behavior of cable-stayed shock-absorbing bearings. However, when conducting seismic analysis of bridges in Midas Civil, only the bridge structure model can be established, and the terrain below the bridge structure cannot be established, and the impact of the stability of the terrain under earthquake action on the seismic performance of the bridge structure cannot be considered. In particular, for bridges built on high and steep slopes, the stability of the high and steep slopes under earthquake action has an important impact on the seismic performance of the bridge. Therefore, for the seismic analysis of bridge structures on high and steep slopes, it is necessary to simultaneously establish the bridge structure model and its lower slope model to analyze the joint stability of the bridge-slope under earthquake action.

[0005] Flac3D is a numerical simulation software based on the continuous medium fast Lagrangian analysis method. It is widely used in the research of structural and slope stability analysis because of its mature command-driven mode and the convenience of modifying and optimizing custom models. However, the existing constitutive model in Flac3D cannot reflect the bilinear ideal elastic-plastic mechanical model of the support. In order to realize the simulation of bridge shock-absorbing supports and the simulation analysis of bridge seismic resistance in Flac3D, the mechanical behavior simulation of the support unit needs to be developed secondary. Fish language is the programming language that comes with Flac3D. Many functions that cannot be realized by program commands can be realized by programming in Fish. When Flac3D calculates, many variable values ​​are set internally. Some of these data are based on blocks, some are based on grid points, and some are based on units. Through Fish language programming, this information can be retrieved at any time. On the one hand, it can be used for secondary development, and on the other hand, it can enhance the data processing capabilities and set and modify internal variables. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a bridge cable shock-absorbing bearing simulation method based on the built-in Fish language of Flac3D. The method uses the built-in Fish language in Flac3D to perform secondary development of the bridge shock-absorbing bearing unit to achieve the simulation of the bridge shock-absorbing bearing structure.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a bridge cable shock-absorbing bearing simulation method based on the built-in Fish language of Flac3D, comprising the following steps:

[0009] S1: Establish a numerical simulation model;

[0010] S2: input model parameters;

[0011] S3: Setting boundary conditions and initial equilibrium calculation;

[0012] S4: Extract the gravity W of the upper structure borne by the support, and calculate the mechanical model of the support unit according to the support model;

[0013] S5: Input seismic load;

[0014] S6: Construct a simulation program unit for the support unit, wherein the simulation program unit is used to extract the shear deformation size of the support unit under the action of an earthquake, determine the stage of the support shear deformation in real time, and change the shear stiffness of the support unit in real time, so that the shear force-shear strain relationship can satisfy the bilinear ideal elastic-plastic mechanical properties of the support unit.

[0015] Further, the shear stiffness is set in the following manner:

[0016] The shear deformation process of the support unit is divided into different stages according to the horizontal displacement difference between nodes, and the corresponding shear stiffness is set according to different stages until the seismic load ends.

[0017] Furthermore, the stage of the shear deformation of the support is divided in the following manner. The shear deformation process of the support unit includes three stages:

[0018] The first stage: the shear pins of the support structure are subjected to shear force. During the numerical simulation, the support unit at this stage satisfies the shear force-shear strain relationship of shear stiffness G=K1;

[0019] The second stage: When the shear force gradually increases and reaches the maximum shear force F of the shear pin max When , the shear pins of the bearings are sheared off, there is no shear force transmission and interaction between the bridge and the piers, and the bridge and the piers are free to move relative to each other; at this time, the bearing unit in the numerical simulation satisfies the shear force-shear strain relationship when the shear stiffness G = 0;

[0020] The third stage: When the relative displacement between the bridge and the pier reaches the maximum allowable value u0, the cables of the support structure begin to work, bearing the shear force caused by the earthquake and limiting the relative displacement between the bridge and the pier; the shear force-shear strain relationship of the support unit satisfies the shear stiffness G = K H The linear relationship between .

[0021] Further, the numerical simulation model is established in the following manner:

[0022] A three-dimensional solid model of the bridge structure was established, and solid units were established between the transition pier and the bridge to simulate the support. The solid model was meshed and imported into Flac3D. According to the requirements of seismic calculation, the maximum mesh size of the model should be less than one tenth of the earthquake wavelength, and the mesh nodes between adjacent surfaces of various bridge components were connected to make the stress and strain between different bridge components continuous.

[0023] Further, the numerical simulation model is set in the following manner:

[0024] Determine input model parameters;

[0025] The bridge model and support unit are set as linear elastic constitutive model, and the corresponding physical and mechanical parameters are set according to the concrete grades of different bridge components;

[0026] Set boundary conditions and initial equilibrium calculations;

[0027] Apply fixed boundary conditions to the bottom of the model, set the gravity acceleration g, and perform initial equilibrium calculation. During the initial equilibrium calculation, Flac3D defaults to calculating convergence when the maximum unbalanced force of the model meets the preset conditions, completing the initial equilibrium calculation.

[0028] Extract the compressive stress σ of the support element after equilibrium n , and according to the cross-sectional area A of the support unit z Calculate the gravity of the upper structure borne by the support unit W = σ n ·A z .

[0029] Furthermore, in step S4, the gravity W of the upper structure borne by the support is extracted, and the mechanical model of the support unit is calculated according to the support model, and the specific method is as follows:

[0030] The mechanical model includes a mechanical model composed of two independent units, namely, a support and a cable. The mechanical characteristics of each unit are simulated separately, and then connected in parallel to form a cable shock-absorbing support unit.

[0031] The friction effect of the cable shock-absorbing bearing is a bilinear ideal elastic-plastic mechanical model. The mechanical model of the bearing unit is calculated according to the following formula. The specific values ​​of various parameters in the mechanical model are calculated according to the model of the cable shock-absorbing bearing:

[0032]

[0033] Where: K1 is the initial stiffness; K H — is the horizontal stiffness of the cable member of the cable shock-absorbing bearing; u0—the free travel of the cable shock-absorbing bearing; x y —Yield displacement of the movable bearing, which is the displacement of the bearing at critical sliding; F max — is the critical sliding friction force of the movable support; F— is the horizontal shear force on the support; u— is the horizontal displacement of the support;

[0034] in:

[0035] (1) Critical sliding friction force F of movable bearing max :

[0036] F max =μ d W

[0037] (2) Initial stiffness K1:

[0038]

[0039] Where: μ d — sliding friction coefficient; W—superstructure gravity borne by the support; x y —The yield displacement of the movable bearing is the displacement at the critical sliding of the bearing;

[0040] (3) Horizontal stiffness K of the cable member of the cable shock-absorbing bearing H :

[0041] K H =4·cos 2 α·K S

[0042]

[0043] Where: K S —Axial stiffness of the cable; α—Angle between the cable and the horizontal plane when the cable is tensioned; E s —Elastic modulus of the cable; A—calculated cross-sectional area of ​​the cable; L—total length of a single cable.

[0044] Furthermore, the input of the seismic load in step S5 is performed in the following manner:

[0045] According to the relevant specifications for seismic design of bridges, when using the dynamic time history method to analyze the seismic performance of bridges, it is necessary to consider the seismic loads in the longitudinal, transverse and vertical directions at the same time;

[0046] Therefore, the seismic analysis of bridges in Flac3D requires converting the acceleration time history of earthquake waves in the three directions of longitudinal, transverse and vertical directions into corresponding stress time history, and applying three-dimensional earthquake loads at the bottom of the model at the same time to analyze the seismic performance of the bridge under the three-dimensional earthquake loads.

[0047] The velocity time history v(t) of the seismic wave is obtained by integrating the acceleration time history of the seismic wave. Then the velocity time history is calculated according to formula (6) to obtain the stress time history σ(t) corresponding to the seismic wave:

[0048] σ n (t) = -2(ρC p )v n (t)

[0049] σ s (t) = -2(ρC s )v s (t)

[0050] Where: n (t)—is the longitudinal stress time history of seismic wave; σ s (t)—is the transverse stress time history of seismic waves; ρ—is the density of rock medium; Cp—is the longitudinal propagation velocity of seismic waves in the medium; Cs—is the transverse propagation velocity of seismic waves in the medium; v n (t)—longitudinal velocity time history obtained by integrating the longitudinal acceleration time history of seismic waves; v s(t) — The lateral velocity time history obtained by integrating the lateral acceleration time history of the seismic wave; t — The time when the seismic load acts:

[0051] Among them, Cp and Cs are calculated according to the following formulas:

[0052]

[0053] In the formula: E — The elastic modulus of the seismic wave propagation medium; ρ — The density of the seismic wave propagation medium; v — The Poisson's ratio.

[0054] Furthermore, the simulation program unit in step S6 is implemented using the built-in Fish language in Flac3D, and is specifically carried out according to the following steps:

[0055] S61: Traverse the unit grid nodes, and according to the numbers of the support unit grid nodes, locate the position for extracting the grid node displacement information to the nodes of the support unit;

[0056] S62: Extract the displacements d1 and d2 of the node in the horizontal direction respectively;

[0057] S63: Calculate the horizontal displacement difference between the nodes, and take the absolute value of the displacement difference, that is, Δd = |d1 - d2|;

[0058] S64: Judge the magnitude of the horizontal displacement difference Δd, and according to the mechanical model formula (1) of the support unit, obtain the judgment result in the following way:

[0059] ① If Δd < x y , then set the shear stiffness of the support unit as G = K1;

[0060] ② If x y < Δd < u0, then set the shear stiffness of the support unit as G = 0;

[0061] ③ If u0 < Δd, then set the shear stiffness of the support unit as G = K H ;

[0062] S65: Run the numerical simulation model for a preset number of cycles;

[0063] S66: Judge whether the calculation of the seismic load is completed in the following way:

[0064] ① If the calculation of the seismic load is completed, the program calculation terminates and the calculation result is saved;

[0065] ② If the calculation of the seismic load is not completed, the program returns to the above step S62 for cycling.

[0066] The bridge cable shock-absorbing bearing simulation system based on Flac3D built-in Fish language provided by the present invention includes a memory, a processor and a computer program stored in the memory and executable on the processor. The above method is implemented when the processor executes the program.

[0067] The beneficial effects of the present invention are:

[0068] The present invention provides a bridge cable shock-absorbing bearing simulation method based on the built-in Fish language of Flac3D, which realizes the simulation of the bridge shock-absorbing bearing and the simulation analysis of the bridge seismic resistance in Flac3D, conducts secondary development of the solid unit in Flac3D through the Fish language, and compiles a simulation program of the bearing unit using the Fish language. By extracting the shear deformation size of the bearing unit under the action of earthquake in real time, the stage of the shear deformation of the bearing is judged in real time and the shear stiffness of the bearing unit is changed in real time, so that the shear force-shear strain relationship can meet the bilinear ideal elastic-plastic mechanical properties of the bearing unit.

[0069] This method realizes the simulation of bridge cable shock-absorbing bearings in Flac3D. The shock-absorbing effect of the bearings can be reflected in the seismic analysis of bridges in Flac3D, making the calculation results of bridges under earthquake action more consistent with the actual situation.

[0070] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for explanation.

[0072] Figure 1 It is the mechanical model of cable-damped basin bearing.

[0073] Figure 2 Simulation flow chart for bridge shock-absorbing bearings.

[0074] Figure 3 This is a numerical simulation model of the bridge structure.

[0075] Figure 4 Schematic diagram of the support unit.

[0076] Figure 5 is the relationship between shear force and horizontal displacement of the support element. DETAILED DESCRIPTION

[0077] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0078] Example 1

[0079] The basic principle of the bridge cable shock-absorbing bearing simulation method provided in this embodiment is as follows:

[0080] The shear deformation of the cable shock-absorbing bearing when subjected to shear force shows the mechanical characteristics of bilinear ideal elastic-plasticity. The simulation of the bearing unit in the numerical analysis consists of two independent units: the bearing and the cable. However, the ready-made linear elastic-plastic constitutive model in Flac3D cannot realize the shear deformation process of the cable shock-absorbing bearing. The built-in Fish language in Flac3D can extract the built-in variable information of the model during calculation, and can bring the extracted built-in variable information into various logical operations. According to the theory of elastic mechanics, the shear deformation relationship of the linear elastic unit in Flac3D satisfies Hooke's law γ=τ / G, that is, there is a linear relationship between the shear stress τ and the shear strain γ, and its stress path is determined by the shear stiffness G. Based on this, this method uses the Fish language to extract the shear strain size of the bearing unit in real time, and performs logical operations according to the shear strain size, and changes the shear stiffness of the unit in real time, so that its shear force-shear strain relationship satisfies the bilinear ideal elastic-plastic mechanical model of the bearing unit, thereby realizing the simulation of the bridge cable shock-absorbing bearing in Flac3D.

[0081] like Figure 1 As shown, the bridge cable shock-absorbing bearing simulation method based on the built-in Fish language of Flac3D provided in this embodiment includes the following steps:

[0082] S1: Establishing a numerical simulation model

[0083] A three-dimensional solid model of the bridge structure was established, and solid units were established between the transition pier and the bridge to simulate the support. The solid model was meshed and imported into Flac3D. According to the requirements of seismic calculation, the maximum mesh size of the model should be less than one tenth of the earthquake wavelength. In addition, when modeling, the mesh nodes between the adjacent surfaces of each component of the bridge should be connected to ensure the continuity of stress and strain between different components of the bridge.

[0084] S2: Input model parameters

[0085] The bridge models all adopt linear elastic constitutive model, and set the corresponding physical and mechanical parameters according to the concrete grades of different bridge components. Before the model is input with earthquake load, the support structure only bears the upper gravity without shear force, so the support unit also adopts linear elastic constitutive model before the model is input with earthquake load.

[0086] S3: Setting boundary conditions and initial equilibrium calculation

[0087] Apply fixed boundary conditions to the bottom of the model, set the gravitational acceleration g, and perform initial equilibrium calculations. During the initial equilibrium calculation, Flac3D defaults to a maximum unbalanced force of less than 1×10 -5 When the calculation converges, the initial equilibrium calculation is completed. After equilibrium, the compressive stress σ of the support element is extracted. n , and according to the cross-sectional area A of the support unit z Calculate the gravity of the upper structure borne by the support unit W = σ n ·A z ; The preset condition is that the maximum unbalanced force is less than 1×10 -5 ;

[0088] S4: Extract the gravity W of the upper structure borne by the support, and calculate the mechanical model of the support unit according to the support model;

[0089] The mechanical model of the cable shock-absorbing bearing consists of two independent units, the bearing and the cable. The mechanical properties of each unit are simulated separately, and then connected in parallel to form the cable shock-absorbing bearing unit. The friction effect of the cable shock-absorbing bearing is a bilinear ideal elastic-plastic mechanical model that satisfies Figure 1 The mechanical response relationship is shown in , and the mechanical model of the support unit is shown in formula (1). The specific values ​​of each parameter in the mechanical model can be calculated according to the model of the cable shock-absorbing support.

[0090]

[0091] Where:

[0092] K1—initial stiffness, kN / m;

[0093] K H — is the horizontal stiffness of the cable member of the cable shock-absorbing bearing, kN / m;

[0094] u0—free travel of cable shock-absorbing bearing, m;

[0095] x y —Yield displacement of the movable bearing, which is the displacement of the bearing at critical sliding, m; F max — is the critical sliding friction force of the movable support, kN.

[0096] F—horizontal shear force on the support, kN; u—horizontal displacement of the support, m; where:

[0097] (1) Critical sliding friction force F of movable bearing max :

[0098] F max =μ d W (2)

[0099] (2) Initial stiffness K1:

[0100]

[0101] Where:

[0102] μ d — sliding friction coefficient;

[0103] W—superstructure gravity borne by the support, kN;

[0104] (3) Horizontal stiffness K of the cable member of the cable shock-absorbing bearing H :

[0105] K H =4·cos 2 α·K S (4)

[0106]

[0107] Where:

[0108] K S —Axial stiffness of the cable, kN / m;

[0109] α—Angle between the cable and the horizontal plane when the cable is tensioned, °;

[0110] E s —elastic modulus of cable, MPa;

[0111] A—Calculated cross-sectional area of ​​the cable, m2;

[0112] L—total length of a single cable, m;

[0113] S5: Input seismic loads

[0114] According to the relevant specifications for seismic design of bridges, when analyzing the seismic performance of bridges using the dynamic time history method, it is necessary to simultaneously consider the seismic loads in the three directions of longitudinal, transverse and vertical directions. Therefore, in Flac3D, the seismic analysis of bridges requires converting the acceleration time histories of seismic waves in the three directions of longitudinal, transverse and vertical directions into corresponding stress time histories, and applying three-dimensional seismic loads at the bottom of the model at the same time to analyze the seismic performance of the bridge under the three-dimensional seismic loads. The velocity time history of the seismic wave is obtained by integrating the acceleration time history of the seismic wave, and the velocity time history is calculated according to formula (6) to obtain the stress time history corresponding to the seismic wave.

[0115] σ n (t) = -2(ρC p )v n (t)

[0116] σs (t) = -2(ρC s )v s (t) (6)

[0117] Where:

[0118] σ n (t)—longitudinal stress time history of seismic wave, kPa;

[0119] σ s (t)—is the transverse stress time history of seismic waves, kPa;

[0120] ρ—density of rock medium, kg / m3;

[0121] Cp—is the longitudinal propagation velocity of seismic waves in the medium, m / s, which can be calculated according to formula (7);

[0122] Cs—is the lateral propagation velocity of seismic waves in the medium, m / s, which can be calculated according to formula (7);

[0123] v n (t)—longitudinal velocity time history obtained by integrating the longitudinal acceleration time history of seismic waves, m / s;

[0124] v s (t)—transverse velocity time history obtained by integrating the transverse acceleration time history of seismic waves, m / s;

[0125] t—is the time of earthquake load action, s.

[0126]

[0127] Where:

[0128] E—elastic modulus of the medium in which seismic waves propagate, GPa;

[0129] ρ—density of the medium in which seismic waves propagate, kg / m3;

[0130] v—is Poisson’s ratio, 1.

[0131] S6: define the Fish function to conduct secondary development on the support unit, and construct a simulation program unit of the support unit, wherein the simulation program unit is used to extract the shear deformation size of the support unit under the action of earthquake, judge the stage of the shear deformation of the support in real time, and change the shear stiffness of the support unit in real time, so that the shear force-shear strain relationship can satisfy the mechanical characteristics of the bilinear ideal elastic-plasticity of the support unit;

[0132] The shear deformation process of the support unit is divided into different stages according to the horizontal displacement difference between the nodes, and the corresponding shear stiffness is set according to the different stages until the seismic load ends;

[0133] Set two grid nodes on the support element, namely node 1 and node 2, extract the horizontal displacements d1 and d2 of the support element nodes 1 and 2, and calculate the horizontal displacement difference Δd between nodes 1 and 2;

[0134] Under the action of earthquake load, the support structure between the bridge and the pier will bear shear force, and the relationship between the horizontal shear force and horizontal displacement of the support structure satisfies Figure 1 Therefore, the shear deformation process of the support unit can be divided into three stages.

[0135] In the first stage, the shear pins of the support structure are mainly subjected to shear force. During the numerical simulation, the support unit at this stage satisfies the shear force-shear strain relationship of shear stiffness G=K1.

[0136] The second stage: As the shear force gradually increases, when the maximum shear force F of the shear pin is reached max When , the shear pins of the bearings are sheared off, there is no shear force transmission and interaction between the bridge and the piers, and the bridge and the piers are free to displace relative to each other; at this time, the bearing unit in the numerical simulation satisfies the shear force-shear strain relationship when the shear stiffness G=0.

[0137] In the third stage, after the relative displacement between the bridge and the pier reaches the maximum allowable value u0, the cables of the support structure begin to work, bearing the shear force caused by the earthquake and limiting the relative displacement between the bridge and the pier; at this time, the shear force-shear strain relationship of the support unit satisfies the shear stiffness G = K H The linear relationship between .

[0138] Therefore, when simulating the mechanical behavior of the support structure, on the basis of the linear elastic constitutive model, the shear force-shear strain relationship of the support unit can be divided into three processes with different shear stiffness G sizes according to the relative displacement between the bridge and the pier, thereby realizing the simulation of the bilinear ideal elastic-plastic mechanical model of the support unit and restoring the mechanical characteristics of the support unit during numerical simulation.

[0139] like Figure 4 As shown in the figure, node 1 and node 2 are two mesh nodes on the support unit, node 1 is connected to the bridge, and node 2 is connected to the pier. When the support unit is subjected to shear force, node 1 and node 2 will produce horizontal relative displacement (i.e., shear strain of the support unit), and the shear force-shear strain is a linear relationship with respect to the shear stiffness G.

[0140] Therefore, by monitoring the relative displacement between node 1 and node 2 of the support unit (i.e., the relative displacement between the bridge and the pier), the shear stiffness G of the support unit is changed, thereby realizing the simulation of the bilinear mechanical behavior of the support unit.

[0141] Based on this, the above process is implemented using the built-in Fish language in Flac3D. The specific process of defining the Fish function is as follows:

[0142] (1) Use the element mesh node traversal statement "loop foreach gp gp.list" in the Fish language, and according to the numbers id of the nodes 1 and 2 of the bearing element mesh, locate the positions for extracting the mesh node displacement information to nodes 1 and 2 of the bearing element. The positions of nodes 1 and 2 are as Figure 4 shown;

[0143] (2) Use the statement "gp.disp.x(gp)" to extract the displacements d1 and d2 of nodes 1 and 2 in the horizontal direction respectively;

[0144] (3) Calculate the horizontal displacement difference between nodes 1 and 2, and take the absolute value of the displacement difference, that is, Δd = |d1 - d2|;

[0145] (4) Use the "if" statement to judge the magnitude of the horizontal displacement difference Δd, and according to the mechanical model formula (1) of the bearing element, the main output has the following several judgment results:

[0146] ① If Δd < x y , then use the "command" command to make the shear stiffness G of the bearing element equal to K1;

[0147] ② If x y < Δd < u0, then use the "command" command to make the shear stiffness G of the bearing element equal to 0;

[0148] ③ If u0 < Δd, then use the "command" command to make the shear stiffness G of the bearing element equal to K H .

[0149] (5) The numerical simulation model runs for 1000 steps;

[0150] (6) Judge whether the calculation of the seismic load is completed. There are mainly two judgment results:

[0151] ① If the calculation of the seismic load is completed, the program calculation terminates and the calculation results are saved;

[0152] ② If the calculation of the seismic load is not completed, the program returns to step (2) for cycling.

[0153] In step (5), when the numerical simulation model runs for 1000 time steps, the specific number of time steps for the operation can be adjusted according to the operation speed of the model and the requirements of the test accuracy.

[0154] Example 2

[0155] As Figure 2 As shown, Figure 2 This is a flow chart of the bridge cable shock-absorbing bearing simulation method based on the built-in Fish language of Flac3D, which mainly includes the following steps:

[0156] Step 1: Build a numerical simulation model

[0157] According to the design drawings and corresponding dimensions of a bridge, the bridge is a continuous rigid frame bridge with a left and right double-track span of 85m+160m+85m. The three-dimensional solid model of the bridge structure was established using Rhino 6 software, which mainly includes four components: bridge, pier, cap and pile foundation. According to the requirements of seismic calculation, the maximum grid size of the model should be less than one tenth of the earthquake wavelength. According to this requirement, the solid model was meshed and imported into Flac3D. Figure 3 As shown in the figure, the connection between the main pier and the bridge is consolidation. When establishing the model, the grid points of the adjacent surfaces between the bridge and the main pier need to be processed as common nodes. Between the transition pier and the bridge, a solid unit with the same cross section as the pier but a height of 1m is established to simulate the support unit, as shown in the figure. Figure 4 shown.

[0158] Step 2: Enter model parameters

[0159] The bridges, piers, caps and pile foundations in the model are mainly made of reinforced concrete materials of different grades, and the linear elastic constitutive model is used for simulation. According to the concrete grades used in each component in the bridge design drawing, and according to the parameters of different grades of concrete in the "Highway Reinforced Concrete and Prestressed Concrete Bridge and Culvert Design Code", the physical and mechanical parameters of each part of the bridge are set. Before the seismic load is input into the model, the support structure only bears the upper gravity but no shear force. Therefore, before the seismic load is input into the model, the support unit also uses the linear elastic constitutive model for initial equilibrium calculation. The model material parameters are shown in Table 1.

[0160] Table 1 Physical and mechanical parameters of bridge model

[0161]

[0162] Step 3: Set boundary conditions and initial equilibrium calculation

[0163] Apply fixed boundary conditions to the bottom of the model and set the gravitational acceleration g to 9.81m / s 2 , use the "solve" command to calculate. During the initial equilibrium calculation, when the maximum unbalanced force of the model is less than 1×10 -5 When the calculation converges, the initial equilibrium calculation is completed. After equilibrium, the compressive stress σ of the support element is extracted. n , and according to the cross-sectional area A of the support unit z Calculate the gravity of the upper structure borne by the support unit W = σn ·A z .

[0164] Step 4: Calculate the theoretical mechanical model of the support element according to the support model

[0165] The bearing model used in this simulation is a bidirectional movable cable shock-absorbing basin bearing (LSPZ6000SX), and the corresponding bearing parameters are shown in Table 2.

[0166] Table 2 LSPZ6000SX type support parameter table

[0167]

[0168] The mechanical model of the cable shock-absorbing bearing consists of two independent units, the bearing and the cable. The mechanical properties of each unit are simulated separately, and then connected in parallel to form the cable shock-absorbing bearing unit. The friction effect of the cable shock-absorbing bearing is a bilinear ideal elastic-plastic mechanical model that satisfies Figure 1 The mechanical response relationship shown in the figure is shown in the formula (1). The specific values ​​of each parameter in the mechanical model can be calculated according to the model of the cable shock-absorbing bearing. The specific calculation process is as follows:

[0169] (1) Critical sliding friction force F of movable bearing max :

[0170] F max =μ d W=0.02×4127.5=82.55(kN)

[0171] Where:

[0172] μ d —Sliding friction coefficient, generally taken as 0.02;

[0173] W is the weight of the upper structure borne by the support. According to the calculation results of the initial balance, it is 4127.5 kN here;

[0174] x y —The yield displacement of the movable bearing is the displacement at the critical sliding of the bearing, generally 0.003m.

[0175] (2) Initial stiffness K1:

[0176]

[0177] (3) The support height is determined according to the LSPZ6000SX cable shock-absorbing basin support dimension table 2:

[0178]

[0179] L=(B+l)×2=(1.02+0.307)×2=2.654(m)

[0180] The cosine value of the angle α between the cable and the horizontal plane when the cable is tensioned is:

[0181] Ignoring the friction between the contact surface of the cable and the support, the relationship between the axial force of the cable and the horizontal force of the support is:

[0182]

[0183] Where, l represents the length of the cable when it is tensioned, m; h represents the cable anchorage distance, m, which is taken according to the support parameter table 2; B represents the support plate length, m, which is taken according to the support parameter table 2; P represents the support horizontal force, kN; T Z represents the ultimate axial bearing capacity of the cable, kN;

[0184] It can be seen from Table 2 that the ultimate bearing capacity of the cable component of the cable shock-absorbing basin bearing (LSPZ6000SX) is 2400kN. According to the "Design Code for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts", the steel wire rope of the cable component is a steel strand, and its ultimate strength standard value f ptk =1960MPa, elastic modulus is E s =1.10×10 5 MPa, then the cable axial stiffness K s The theoretical value is:

[0185]

[0186] Horizontal stiffness K of the cable member of the cable shock-absorbing basin bearing H :

[0187] K H =4·cos 2 α·K S =4×0.814 2 ×31168=82607(kN / m)

[0188] Finally, the above calculation results are substituted into formula (1) to obtain the theoretical mechanical model of the support unit:

[0189]

[0190] Where A represents the calculated cross-sectional area of ​​the cable, m 2 ; E S represents the elastic modulus of the cable, MPa;

[0191] Step 5: Enter seismic loads

[0192] According to the relevant specifications for seismic design of bridges, when analyzing the seismic performance of bridges using the dynamic time history method, it is necessary to simultaneously consider the seismic loads in the three directions of longitudinal, transverse and vertical directions. Therefore, in Flac3D, the seismic analysis of bridges requires converting the acceleration time histories of seismic waves in the three directions of longitudinal, transverse and vertical directions into corresponding stress time histories, and applying three-dimensional seismic loads at the bottom of the model at the same time to analyze the seismic performance of the bridge under the three-dimensional seismic loads. The velocity time history of the seismic wave is obtained by integrating the acceleration time history of the seismic wave, and the velocity time history is calculated according to formula (6) to obtain the stress time history corresponding to the seismic wave.

[0193] Step 6: Define the Fish function to perform secondary development on the support element

[0194] Under the action of earthquake load, the support structure between the bridge and the pier will bear shear force, and the relationship between the horizontal shear force and horizontal displacement of the support structure satisfies Figure 1 Therefore, the shear deformation process of the support unit can be divided into three stages.

[0195] In the first stage, the shear pins of the support structure are mainly subjected to shear force. During the numerical simulation, the support unit at this stage satisfies the shear force-shear strain relationship of shear stiffness G=K1=27516kN / m.

[0196] The second stage: As the shear force gradually increases, when the maximum shear force F of the shear pin is reached max When G=82.55kN, the shear pin of the support is sheared off, there is no shear force transmission and interaction between the bridge and the pier, and the bridge and the pier are free to displace relative to each other; at this time, the support unit in the numerical simulation satisfies the shear force-shear strain relationship when the shear stiffness G=0.

[0197] In the third stage, after the relative displacement between the bridge and the pier reaches the maximum allowable value u0 = 0.25m, the cables of the support structure begin to work, bearing the shear force caused by the earthquake and limiting the relative displacement between the bridge and the pier; at this time, the shear force-shear strain relationship of the support unit satisfies the shear stiffness G = K H =Linear relationship when 82607kN / m.

[0198] Therefore, when simulating the mechanical behavior of the support structure, on the basis of the linear elastic constitutive model, the shear force-shear strain relationship of the support unit can be divided into three processes with different shear stiffness G sizes according to the relative displacement between the bridge and the pier, thereby realizing the simulation of the bilinear ideal elastic-plastic mechanical model of the support unit and restoring the mechanical characteristics of the support unit during numerical simulation.

[0199] like Figure 4As shown in the figure, node 1 and node 2 are two mesh nodes on the support unit, node 1 is connected to the bridge, and node 2 is connected to the pier. When the support unit is subjected to shear force, node 1 and node 2 will produce horizontal relative displacement, and the shear force-horizontal displacement is a linear relationship with respect to the shear stiffness G.

[0200] Therefore, the shear stiffness G of the support unit is changed by monitoring the relative displacement between node 1 and node 2 of the support unit, thereby realizing the simulation of the bilinear mechanical behavior of the support unit.

[0201] Based on this, the built-in Fish language is used in Flac3D to implement the above process. The specific process of defining the Fish function is as follows:

[0202] (1) Using the unit grid node traversal statement "loop foreach gp gp.list" in the Fish language, and according to the ID of the support unit grid node 1 and grid node 2, the position of the grid node displacement information extraction is located on the support unit node 1 and node 2. The positions of node 1 and node 2 are as follows: Figure 4 As shown;

[0203] (2) Use the “gp.disp.x(gp)” statement to extract the horizontal displacements d1 and d2 of node 1 and node 2 respectively;

[0204] (3) Calculate the horizontal displacement difference between node 1 and node 2, and take the absolute value of the displacement difference, that is, Δd = |d1-d2|;

[0205] (4) Use the "if" statement to determine the size of the horizontal displacement difference Δd, and according to the mechanical model formula (1) of the support unit, the main outputs include the following judgment results:

[0206] ① If Δd<0.003m, use the "command" command to set the shear stiffness of the support element to G=27516kN / m;

[0207] ② If 0.003m<Δd<0.25m, use the "command" command to set the shear stiffness of the support element G=0;

[0208] ③If 0.25m<Δd, use the "command" command to set the shear stiffness of the support unit to G=82607kN / m.

[0209] (5) The numerical simulation model runs for 1000 steps;

[0210] (6) There are two main judgment results for judging whether the earthquake load calculation is completed:

[0211] ① If the earthquake load calculation is completed, the program calculation will terminate and the calculation results will be saved;

[0212] ② If the earthquake load calculation is not completed, the program returns to step (2) and loops.

[0213] In step (5), the numerical simulation model operates for 1000 time steps, and the specific number of operation steps can be adjusted according to the model operation speed and test accuracy requirements.

[0214] According to the numerical simulation model of this example, the Fish program for simulating the support unit is brought into the seismic calculation. By monitoring the shear force and shear deformation of the support unit, the relationship between the two is as follows: Figure 5 At the same time, the theoretical mechanical model of the support unit in this example is calculated according to formula (8) and then imported into Figure 5 The results are compared with the numerical simulation results. The comparison shows that the results calculated according to formula (8) are in good agreement with the mechanical response of the support unit obtained by numerical simulation, indicating that the simulation calculation results of the support unit developed using the Fish language are correct and can reflect the mechanical characteristics of the cable shock-absorbing support.

[0215] This embodiment uses the Fish statement to change the shear stiffness of the bearing in real time according to the deformation of the bearing after being subjected to shear force, so that the bearing unit can meet the bilinear ideal elastic-plastic mechanical characteristics. The simulation of the bridge cable shock-absorbing bearing is realized in Flac3D, so that the shock-absorbing effect of the bearing can be reflected in the seismic analysis of the bridge in Flac3D, and the calculation results of the bridge under earthquake are more in line with the actual situation.

[0216] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A bridge cable shock-absorbing bearing simulation method based on the built-in Fish language of Flac3D, characterized by: The following steps are involved: S1: Establish a numerical simulation model; S2: input model parameters; S3: Setting boundary conditions and initial equilibrium calculation; S4: Extract the gravity W of the upper structure borne by the support, and calculate the mechanical model of the support unit according to the support model; S5: Input seismic load; S6: Construct a simulation program unit for the support unit, wherein the simulation program unit is used to extract the shear deformation size of the support unit under the action of an earthquake, determine the stage of the support shear deformation in real time, and change the shear stiffness of the support unit in real time, so that the shear force-shear strain relationship can satisfy the bilinear ideal elastic-plastic mechanical properties of the support unit.

2. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1, characterized in that: The shear stiffness is set in the following manner: The shear deformation process of the support unit is divided into different stages according to the horizontal displacement difference between nodes, and the corresponding shear stiffness is set according to different stages until the seismic load ends.

3. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1 is characterized by: The stage of the support shear deformation is divided as follows. The shear deformation process of the support unit includes three stages: The first stage: the shear pins of the support structure are subjected to shear force. During the numerical simulation, the support unit at this stage satisfies the shear force-shear strain relationship of shear stiffness G=K1; The second stage: When the shear force gradually increases and reaches the maximum shear force F of the shear pin max When , the shear pins of the bearings are sheared off, there is no shear force transmission and interaction between the bridge and the piers, and the bridge and the piers are free to move relative to each other; at this time, the bearing unit in the numerical simulation satisfies the shear force-shear strain relationship when the shear stiffness G = 0; The third stage: When the relative displacement between the bridge and the pier reaches the maximum allowable value u0, the cables of the support structure begin to work, bearing the shear force caused by the earthquake and limiting the relative displacement between the bridge and the pier; the shear force-shear strain relationship of the support unit satisfies the shear stiffness G = K H The linear relationship between .

4. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1, characterized in that: The numerical simulation model is established in the following manner: A three-dimensional solid model of the bridge structure was established, and solid units were established between the transition pier and the bridge to simulate the support. The solid model was meshed and imported into Flac3D. According to the requirements of seismic calculation, the maximum mesh size of the model should be less than one tenth of the earthquake wavelength, and the mesh nodes between adjacent surfaces of various bridge components were connected to make the stress and strain between different bridge components continuous.

5. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1, characterized in that: The numerical simulation model is set up in the following manner: Determine input model parameters; The bridge model and support unit are set as linear elastic constitutive model, and the corresponding physical and mechanical parameters are set according to the concrete grades of different bridge components; Set boundary conditions and initial equilibrium calculations; Apply fixed boundary conditions to the bottom of the model, set the gravity acceleration g, and perform initial equilibrium calculation. During the initial equilibrium calculation, Flac3D defaults to calculating convergence when the maximum unbalanced force of the model meets the preset conditions, completing the initial equilibrium calculation. Extract the compressive stress σ of the support element after equilibrium n , and according to the cross-sectional area A of the support unit z Calculate the gravity of the upper structure borne by the support unit W = σ n ·A z .

6. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1, characterized in that: In step S4, the gravity W of the upper structure borne by the support is extracted, and the mechanical model of the support unit is calculated according to the support model, and the specific method is as follows: The mechanical model includes a mechanical model composed of two independent units, namely, a support and a cable. The mechanical characteristics of each unit are simulated separately, and then connected in parallel to form a cable shock-absorbing support unit. The friction effect of the cable shock-absorbing bearing is a bilinear ideal elastic-plastic mechanical model. The mechanical model of the bearing unit is calculated according to the following formula. The specific values ​​of various parameters in the mechanical model are calculated according to the model of the cable shock-absorbing bearing: Where: K1 is the initial stiffness; K H — is the horizontal stiffness of the cable member of the cable shock-absorbing bearing; u0—the free travel of the cable shock-absorbing bearing; x y —Yield displacement of the movable bearing, which is the displacement of the bearing at critical sliding; F max — is the critical sliding friction force of the movable support; F— is the horizontal shear force on the support; u— is the horizontal displacement of the support; in: (1) Critical sliding friction force F of movable bearing max : F max =μ d W (2) Initial stiffness K1: Where: μ d — sliding friction coefficient; W—superstructure gravity borne by the support; x y —The yield displacement of the movable bearing is the displacement at the critical sliding of the bearing; (3) Horizontal stiffness K of the cable member of the cable shock-absorbing bearing H : K H =4·cos 2 a·K S Where: K S —Axial stiffness of the cable; α—Angle between the cable and the horizontal plane when the cable is tensioned; E s —Elastic modulus of the cable; A—calculated cross-sectional area of ​​the cable; L—total length of a single cable.

7. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1 is characterized by: The input of the earthquake load in step S5 is performed in the following manner: According to the relevant specifications for seismic design of bridges, when using the dynamic time history method to analyze the seismic performance of bridges, it is necessary to consider the seismic loads in the longitudinal, transverse and vertical directions at the same time; Therefore, the seismic analysis of bridges in Flac3D requires converting the acceleration time history of earthquake waves in the three directions of longitudinal, transverse and vertical directions into corresponding stress time history, and applying three-dimensional earthquake loads at the bottom of the model at the same time to analyze the seismic performance of the bridge under the three-dimensional earthquake loads. The velocity time history v(t) of the seismic wave is obtained by integrating the acceleration time history of the seismic wave. Then the stress time history σ(t) corresponding to the seismic wave can be obtained by calculating the velocity time history according to the following formula: σ n (t)=-2(ρC p )v n (t) σ s (t)=-2(ρC s )v s (t) Where: n (t)—is the longitudinal stress time history of seismic wave; σ s (t)—is the transverse stress time history of seismic waves; ρ—is the density of rock medium; Cp—is the longitudinal propagation velocity of seismic waves in the medium; Cs—is the transverse propagation velocity of seismic waves in the medium; v n (t)—longitudinal velocity time history obtained by integrating the longitudinal acceleration time history of seismic waves; v s (t) is the lateral velocity time history obtained by integrating the lateral acceleration time history of seismic waves; t is the time of seismic load action: Among them, Cp and Cs are calculated according to the following formula: Where: E is the elastic modulus of the seismic wave propagation medium; ρ is the density of the seismic wave propagation medium; v is the Poisson's ratio.

8. The bridge cable shock-absorbing bearing simulation method based on Flac3D built-in Fish language as claimed in claim 1, characterized in that: The simulation program unit in step S6 is implemented by using the built-in Fish language in Flac3D, and is specifically performed according to the following steps: S61: traverse the unit grid nodes, and locate the position where the grid node displacement information is extracted on the node of the support unit according to the number of the support unit grid node; S62: extract the horizontal displacements d1 and d2 of the nodes respectively; S63: Calculate the horizontal displacement difference between the nodes and take the absolute value of the displacement difference, that is, Δd=|d1-d2|; S64: Determine the magnitude of the horizontal displacement difference Δd, and obtain the determination result according to the mechanical model formula (1) of the support unit in the following manner: ①If Δd <x y , then the shear stiffness of the support element is set to G = K1; ② If x y <Δd < u0, then set the shear stiffness of the bearing element to G = 0; ③If u0<Δd, set the shear stiffness of the support element to G=K H ; S65: The numerical simulation model runs a preset number of cycles; S66: Determine whether the earthquake load calculation is completed in the following manner: ① If the earthquake load calculation is completed, the program calculation will terminate and the calculation results will be saved; ② If the earthquake load calculation is not completed, the program returns to the above step S62 to loop.

9. A bridge cable shock-absorbing bearing simulation system based on Flac3D built-in Fish language, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the method according to any one of claims 1 to 8 is implemented.

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