CN112699556A - Construction method of structural yielding model of energy-absorbing anchor rod/anchor cable - Google Patents
Construction method of structural yielding model of energy-absorbing anchor rod/anchor cable Download PDFInfo
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- CN112699556A CN112699556A CN202011624531.XA CN202011624531A CN112699556A CN 112699556 A CN112699556 A CN 112699556A CN 202011624531 A CN202011624531 A CN 202011624531A CN 112699556 A CN112699556 A CN 112699556A
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Abstract
The invention discloses a method for constructing a structural yielding model of an energy-absorbing anchor rod/anchor cable, which comprises the steps of analyzing the type of the energy-absorbing anchor rod/anchor cable, determining the position of an axial force transmission point, simulating a main stressed member, deleting redundant node-grid type connection, establishing node connection between the stressed members, defining the attribute of the node connection, updating an action node of the node connection, judging and deleting failed node connection, monitoring the current yielding amount and setting the node connection attribute when yielding is finished. The method provided by the invention not only can realize simulation of real working state of the yielding anchor rod in different stress states, but also can truly reflect yielding mechanism, and has important significance for safety analysis of the anchor rod (cable) supporting structure.
Description
Technical Field
The invention relates to the field of rock engineering support structure analysis, in particular to a construction method of a structural yielding model of an energy-absorbing anchor rod/anchor cable.
Background
In rock engineering, such as mining of mineral resources, development of hydraulic energy resources, construction of railways and highways, common anchor rods (such as threaded anchor rods) are generally adopted and combined with mortar and resin anchoring agents to support surrounding rocks, and the common anchor rods are widely adopted due to simple supporting technology. However, since the conventional anchor rod has a large rigidity, the deformation amount provided when the limit load is reached is very small, and thus, in large deformation rock engineering, the conventional anchor rod may fail due to insufficient deformation of the conventional anchor rod. With the development of support concept and the updating of support technology, the structural form of anchor rod support is developed from a simple common anchor rod to an energy-absorbing anchor rod/anchor cable with a yielding functional structural form. The anchor rod generates large deformation slip under yielding load through the yielding device to regulate and control stress release, so that the anchor rod is mainly used in large deformation rock engineering.
Generally, when designing a supporting scheme of a rock engineering or analyzing a bolting structure, it is necessary to simulate a bolting using a corresponding bolting (cable) structural unit through existing numerical simulation software of the supporting structure. However, the existing simulation method for the energy-absorbing anchor rod/anchor cable only uses a linear member to perform generalized simulation on the energy-absorbing anchor rod/anchor cable and does not simulate the main structural member thereof, so that the internal structural composition of the anchor rod is only approximately replaced, the stress of the internal structure cannot be reflected naturally, and the axial bearing characteristic of the structural unit and the supporting effect on the rock-soil body can only be approximately described macroscopically.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a construction method of a structural yielding model of an energy-absorbing anchor rod/anchor cable, which can not only realize the simulation of the real working state of the yielding anchor rod in different stress states, but also truly reflect the yielding mechanism, and has important significance for the safety analysis of an anchor rod (cable) supporting structure.
In order to achieve the purpose, the invention provides a method for constructing a structural yielding model of an energy-absorbing anchor rod/anchor cable, which comprises the following steps:
(1) analyzing the structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable to obtain a yielding device of the energy-absorbing anchor rod/anchor cable, wherein the yielding device consists of an anchor rod body and an outer sleeve sleeved outside the anchor rod body, and the yielding function of the energy-absorbing anchor rod/anchor cable is realized by the relative sliding of the anchor rod body and the outer sleeve at the axial force transmission point of the energy-absorbing anchor rod/anchor cable;
(2) determining the position of the axial force transmission point of the yielding device of the energy-absorbing anchor rod/anchor cable;
(3) simulating the anchor rod body and the outer sleeve by using an existing anchor rod/anchor cable structural unit in numerical simulation software;
(4) deleting node-grid type connection of structural unit nodes which are automatically generated by numerical simulation software during simulation and correspond to the first overlapped part on the anchor rod body or the second overlapped part on the outer sleeve and coincide with the anchor rod body;
(5) establishing a node-node type connection between the structural unit node on the first overlapping portion and the structural unit node on the second overlapping portion;
(6) defining the attribute of the node-node type connection;
(7) identifying the node-node type connection and updating the structural unit node corresponding to the identified node-node type connection;
(8) judging and deleting the failed node-node type connection;
(9) respectively determining a monitoring node on the anchor rod body and the outer sleeve in advance, and calculating the change amount of the relative displacement of the two monitoring nodes to obtain the current yield;
(10 when the current yielding amount reaches the maximum yielding distance, setting the attribute of the node-node type connection at the end of yielding based on the structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable.
In detail, the position of the axial force transmission point of the yielding device of the energy-absorbing anchor rod/anchor cable is determined according to the type of the energy-absorbing anchor rod/anchor cable to be simulated and the corresponding structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable.
In detail, in the simulation process of the step (3), the anchor rod body or the outer sleeve where the non-axial force transmission point is located is subjected to fine structural unit division.
In detail, the fine structural unit division is specifically: when discretizing the anchor rod body or the outer sleeve where the non-axial force transmission points are located, the structural unit nodes arranged on the anchor rod body or the outer sleeve where the non-axial force transmission points are located are more than the structural unit nodes arranged on the outer sleeve or the anchor rod body where the axial force transmission points are located.
In detail, the step (5) is specifically as follows: determining a structural unit node on the first overlapping part or the second overlapping part where the axial force transmission point is located as a source node, searching a structural unit node which is closest to the source node on the second overlapping part or the first overlapping part where the non-axial force transmission point is located as a target node, and establishing node-node type connection between the source node and the target node.
In detail, in step (6), the attribute of the node-node type connection is specifically:
for the constant resistance yielding process, the attribute of the node-node type connection at the axial force transmission point is set as follows: the axial degree of freedom of the rod is an ideal elastic-plastic spring connection, and the other 5 degrees of freedom are fixed connections, wherein the rigidity of the ideal elastic-plastic spring takes a large value, and the yield load takes yielding load; the attribute of the node-node type connection at the non-axial force transmission point is set as follows: the axial freedom degrees of the rods are in free connection, and the other 5 freedom degrees are in fixed connection;
for the resistance increasing or resistance reducing yielding process, the attribute of the node-node type connection at the axial force transmission point is as follows: the axial degree of freedom of the rod is firstly set to be connected with an ideal elastic-plastic spring, then the functional relation between the yield load of the ideal elastic-plastic spring and the relative displacement of the source node and the target node is implanted, the yield load of the elastic-plastic spring in the yielding process is controlled, and the other 5 degrees of freedom are fixedly connected; the attribute of the node-node type connection at the non-axial force transmission point is set as follows: the axial degree of freedom of the rod is freely connected, and the other 5 degrees of freedom are fixedly connected.
In detail, the functional relation between the yield load of the ideal elastic-plastic spring and the relative displacement of the source node and the target node is obtained through a bolt tensile test.
In detail, the step (7) is specifically: after each calculation step is finished, calling all connected global table head addresses, identifying the node-node type connection, firstly calling information of source nodes and target nodes corresponding to the node-node type connection for each identified node-node type connection, searching structural unit nodes on the anchor rod body or the outer sleeve where the target nodes closest to the source nodes are located, if the searched structural unit nodes are inconsistent with the current target nodes, updating the current target nodes by the searched structural unit nodes, and keeping the attribute of the node-node type connection between the updated target nodes and the original source nodes unchanged.
In detail, the step (8) is specifically: after each calculation step is finished, judging whether two structural unit nodes corresponding to the node-node type connection are both positioned at the overlapped part of the anchor rod body and the outer sleeve for the node-node type connection at the non-axial force transmission point, and if not, deleting the node-node type connection between the two structural unit nodes.
In detail, the step (10) is specifically as follows:
under the condition that the energy-absorbing anchor rod/anchor cable is provided with a slip-resistant device, when the current yielding amount reaches the maximum yielding distance, setting the attribute of the node-node type connection at the axial force transmission point as a fixed connection, and ending yielding;
under the condition that the energy-absorbing anchor rod/anchor cable is free of the anti-slip device, when the current yielding amount reaches the maximum yielding distance, the attribute of the node-node type connection at the axial force transmission point is set to be free connection, or the spring yield strength of the node-node type connection at the axial force transmission point is set to be 0, or the node-node type connection at the axial force transmission point is directly deleted, and the yielding is finished.
The technical scheme provided by the invention has the beneficial effects that:
(1) because the construction method of the invention adopts the anchor rod/anchor cable structure units to respectively simulate the main stressed components (namely the anchor rod body and the outer sleeve) of the energy-absorbing anchor rod/anchor cable, the axial bearing characteristic of the energy-absorbing anchor rod/anchor cable can be more accurately described macroscopically, the supporting effect on the rock-soil body can be reflected, and the stressed deformation condition of each main structural component of the energy-absorbing anchor rod/anchor cable with the structure type can be more truly reflected microscopically;
(2) according to the invention, the interaction relation between two stressed components is established through the node-node type connection, so that not only can the axial stress characteristic of the energy-absorbing anchor rod/anchor cable be reflected and the constant-resistance yielding pressure be realized, but also the resistance increasing or resistance reducing yielding process can be conveniently realized by controlling the yield strength of the node-node connection, and the bending-shear resistance characteristic of the overlapped part of different stressed components of the energy-absorbing anchor rod/anchor cable can be reflected;
(3) according to the invention, through dynamically updating the structural unit nodes corresponding to the node-node type connection, the relative constant resistance slippage generated by different stressed members in the actual yielding device is simulated so as to realize yielding, the slippage yielding mechanism can be truly reflected, the simulation of the true working state of the yielding anchor rod in different stress states is realized, and the method has important significance for the safety analysis of the anchor rod (cable) supporting structure.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method for constructing a structural yielding model of an energy-absorbing anchor rod/anchor cable according to the present invention;
FIG. 2 is a flow chart of energy absorbing anchor/cable rope model building operation shown in steps 7-10 of FIG. 1;
FIG. 3 is a schematic structural view of a constant-resistance large-deformation energy-absorbing anchor rod/anchor cable with a slip resistance;
FIG. 4 is a schematic diagram of mesh dispersion and node interaction of the energy absorbing anchor/cable model shown in FIG. 3;
FIG. 5 is a model diagram of a physical experiment corresponding to a numerical pull test performed on the energy absorbing anchor rods/cables shown in FIG. 3;
FIG. 6 is a load-displacement graph obtained from a tensile experiment performed on the energy-absorbing anchor/anchor cable numerical model shown in FIG. 3 established using a construction method according to an embodiment of the present invention;
FIG. 7 is a load-displacement curve obtained by performing a numerical pull experiment on the energy-absorbing anchor/anchor cable numerical model shown in FIG. 3 established by a construction method according to an embodiment of the invention;
8a-8c are bending moment distribution diagrams obtained by performing a bending shear experiment on the energy-absorbing anchor rod/anchor cable numerical model shown in FIG. 3 established by the construction method according to one embodiment of the invention;
9a-9c are shear profiles from a bend shear experiment performed on the energy absorbing anchor/anchor cable numerical model of FIG. 3 constructed using the construction method of one embodiment of the present invention;
10a-10f are axial force profiles from a numerical tensile experiment conducted on the energy-absorbing anchor/anchor cable numerical model of FIG. 3 constructed using the construction method of one embodiment of the present invention;
11a-11f are axial force profiles obtained by performing a numerical pull experiment on the energy-absorbing anchor rod/anchor cable numerical model shown in FIG. 3 established by the construction method according to one embodiment of the invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the drawings in the embodiments of the present invention.
Referring to fig. 1-2, the method for constructing a structural yielding model of an energy-absorbing anchor rod/anchor cable provided by the invention comprises the following steps:
step 1: analyzing the structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable to obtain the yielding device of the energy-absorbing anchor rod/anchor cable, wherein the yielding device has the following two characteristics: the yielding device consists of an anchor rod body and an outer sleeve sleeved outside the anchor rod body, and the yielding function of the energy-absorbing anchor rod/anchor cable is realized by relative sliding between the anchor rod body and the outer sleeve at the axial force transmission point of the energy-absorbing anchor rod/anchor cable.
Step 2: and determining the position of an axial force transmission point of the yielding device of the energy-absorbing anchor rod/anchor cable according to the type of the energy-absorbing anchor rod/anchor cable to be simulated and the corresponding structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable.
And step 3: and simulating the anchor rod body and the outer sleeve by using the existing anchor rod/anchor cable structural unit in the numerical simulation software.
Specifically, in the simulation process, the parameters of all the anchor rod/anchor cable structural units are valued according to the corresponding parameters of the actual structural member, and the anchor rod body/outer sleeve at the non-axial force transmission point is subjected to fine structural unit division, that is, when the anchor rod body/outer sleeve at the non-axial force transmission point is discretized, the structural unit nodes arranged on the anchor rod body or the outer sleeve at the non-axial force transmission point are more than the structural unit nodes arranged on the outer sleeve/anchor rod body at the axial force transmission point. It should be noted that if the axial force transmission point is on the anchor rod body, it is the outer sleeve that interacts with the anchor rod body and vice versa. Such as modulus of elasticity, poisson's ratio, yield load, maximum tensile strain, cross-sectional area, etc.
And 4, step 4: and deleting node-grid type connection of structural unit nodes which are automatically generated by numerical simulation software and correspond to the first overlapped part during simulation for a first overlapped part of the anchor rod body and the outer sleeve or a second overlapped part of the outer sleeve and the anchor rod body.
It should be noted that the numerical simulation software is a commercial software with a numerical simulation analysis function, such as Flac3D, 3DEC, UDEC, ANSYS, and the like.
And 5: and determining the structural unit node on the first overlapping part or the second overlapping part where the axial force transmission point is located as a source node, searching a structural unit node which is closest to the source node on the second overlapping part or the first overlapping part where the non-axial force transmission point is located as a target node, and establishing node-node type connection between the source node and the target node, thereby establishing node-node type connection between the structural unit node on the overlapping part of the anchor rod body and the outer sleeve and the structural unit node on the overlapping part of the outer sleeve and the anchor rod body.
Step 6: and defining the attribute of the node-node type connection.
Specifically, the attribute of the node-node type connection is defined as:
for the constant-resistance yielding process (namely yielding load in the yielding process is kept unchanged), the attribute of the node-node type connection at the axial force transmission point is set as follows: the axial degree of freedom of the rod is an ideal elastic-plastic spring connection, and the other 5 degrees of freedom are fixed connections, wherein the rigidity of the ideal elastic-plastic spring takes a large value, and the yield load takes yielding load; the attributes of the node-node type connection at the non-axial force transfer point are set as: the axial freedom degrees of the rods are in free connection, and the other 5 freedom degrees are in fixed connection;
for the resistance increasing or resistance reducing yielding process (namely, the yielding load in the yielding process increases/decreases along with the increase of the yielding distance), the attributes of the node-node type connection at the axial force transmission point are as follows: the axial degree of freedom of the rod is firstly set to be an ideal elastic-plastic spring connection, then the function relation between the yield load of the ideal elastic-plastic spring and the relative displacement of a source node and a target node is implanted, the yield load of the elastic-plastic spring in the yielding process is controlled, and the other 5 degrees of freedom are fixedly connected; the attributes of the node-node type connection at the non-axial force transfer point are set as: the axial degrees of freedom of the rod are freely connected, the other 5 degrees of freedom are fixedly connected, and the functional relation between the yield load of the ideal elastic-plastic spring and the relative displacement of the source node and the target node is obtained through a tension test of the anchor rod.
And 7: after each calculation step is finished, calling all connected global table head addresses, identifying node-node type connection, for each identified node-node type connection, firstly calling information of a source node and a target node corresponding to the node-node type connection, searching a structural unit node on an anchor rod body/outer sleeve where the target node closest to the source node is located, if the searched structural unit node is inconsistent with the current target node, updating the current target node by using the searched structural unit node (namely using the searched structural unit node as the target node), and keeping the attribute of the node-node type connection between the updated target node and the original source node unchanged.
And 8: because the anchor rod body and the outer sleeve which interact in the yielding process can slide relatively, part of the anchor rod body which is originally positioned in the outer sleeve is pulled out of the outer sleeve, and the pulled part of the anchor rod body and the outer sleeve have no direct interaction, after each calculation step is finished, whether two structural unit nodes corresponding to the node-node type connection are positioned at the superposed part of the anchor rod body and the outer sleeve or not is judged for the node-node type connection at the non-axial force transmission point, and if not, the node-node type connection between the two structural unit nodes is deleted.
And step 9: and respectively predetermining a monitoring node on the anchor rod body and the outer sleeve, and calculating the change amount of the relative displacement of the two monitoring nodes to obtain the current yielding amount.
It should be noted that the yielding amount calculated in the step actually ignores the elastic deformation of the anchor rod structural member between the two monitoring nodes, which mainly considers that the yielding process occurs in the elastic stage of the anchor rod deformation, and can be ignored compared with the yielding displacement generated by the structure slippage.
Step 10: and when the current yielding amount reaches the maximum yielding distance, setting the attribute of node-node type connection at the end of yielding based on the structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable.
Specifically, under the condition that the energy-absorbing anchor rod/anchor cable is provided with the anti-slip device, after each calculation step is finished, whether the current yielding amount reaches the maximum yielding distance is judged, if yes, the attribute of node-node type connection at the axial force transmission point is set as fixed connection, and yielding is finished;
under the condition that the energy-absorbing anchor rod/anchor cable has no anti-slip device, after each calculation step is finished, whether the current yielding amount reaches the maximum yielding distance or not is judged, if yes, the attribute of the node-node type connection at the axial force transmission point is set to be free connection, or the spring yield strength of the node-node type connection at the axial force transmission point is set to be 0, or the node-node type connection at the axial force transmission point is directly deleted, and yielding is finished.
It should be noted that the maximum yield distance is determined by the inherent properties of the energy absorbing anchor/cable.
In the method of the present invention, the above-mentioned steps 1 to 6 are steps to be performed at the time of preprocessing, and the steps 7 to 10 are steps to be performed at the end of each calculation step. By "computational step" is meant an iteration in a numerical simulation computation.
In order to more clearly describe the construction method of the structural yielding model of the energy-absorbing anchor rod/anchor cable, the following embodiment simulates the anti-slip constant-resistance large-deformation energy-absorbing anchor rod/anchor cable shown in fig. 3 by using the construction method of the present invention. In the simulation, the numerical simulation software of this embodiment employs Flac 3D. The construction method comprises the following specific steps:
analyzing the mechanical characteristics of the anchor rod structure: the main stress structural members of the energy-absorbing anchor rod/anchor cable are an anchor rod body A and an outer sleeve B through structural mechanical characteristic analysis of the anti-slip constant-resistance large-deformation energy-absorbing anchor rod/anchor cable, the axial force transmission point of the energy-absorbing anchor rod/anchor cable is located on a sliding block C at the end part of the anchor rod body A, and the structure interacting with the anchor rod body A is the outer sleeve B.
Simulation of main stress components: the simulation of the anchor rod body A and the outer sleeve B is carried out by adopting a rock anchor structure unit (pile-rock bolt), which respectively corresponds to the pile-A and the pile-B in the figure 4, the overlapping area of the anchor rod body A and the outer sleeve B is marked as S, and the part of the anchor rod body positioned in the area of S and the part of the outer sleeve B are respectively marked as B1 and B2. As the yielding process is realized by the sliding between the sliding block C at the rod end of the anchor rod and the outer sleeve B, in order to more accurately describe the continuous change of the axial force transmission positions of the anchor rod body and the outer sleeve in the sliding process, the pile-B is subjected to relatively fine unit division. The structural units of the pile-A and the pile-B are divided as shown in FIG. 3, the dots on the straight lines in FIG. 3 represent the structural unit nodes, the two structural unit nodes and the connecting lines between the two structural unit nodes are combined to be called as the structural units, and the structural units are interacted through the structural unit nodes.
Deleting redundant node-to-zone type links: under normal conditions, the grid units are generated before the rock anchor structure units, and at the moment, Flac3D automatically generates node-to-zone type link connection for each structure unit node so as to simulate interaction between the energy-absorbing anchor rods/anchor cables and the surrounding rock body. Therefore, before the connection of the force-bearing members (i.e., the anchor rod body and the outer sleeve) is established, the node-to-zone type link connection of the rod body part of the anchor rod body inside the outer sleeve on the yielding device needs to be deleted, and specifically, the node-to-zone type link connection corresponding to the structural unit node included in the S region shown in fig. 3 needs to be deleted.
The structural unit nodes between the stress components are arranged to be connected: and for the structural unit node in each S region, searching the structural unit node which is positioned on the pile-B and is closest to the structural unit node through program control, and establishing node-node type connection (node-to-node type connection) between the two structural unit nodes. The source node of the new connection is positioned on the Pile-A (anchor rod body), and the target node is positioned on the Pile-B (outer sleeve).
Defining node-node type connection attribute: setting link attributes on a structural unit node-A1 of a sliding block C representing the axial force transmission point of a bolt rod body A and an outer sleeve B as follows: the axial degree of freedom of the rod is Nydeform, and the other 5 degrees of freedom are rigid and fixedly connected; for other newly-created links, the attributes are set as follows: the axial degree of freedom of the rod is free, and the other 5 degrees of freedom are rigid fixed connection. The properties of the Nydeform spring are set as: the area is 1, the spring stiffness k is a large value (in actual use, trial calculation can be performed at intervals of 10 times from 1e 7-1 e 15), the compressive yield strength ycomp and the tensile yield strength ytens are set as yielding loads (taking force as a unit), and the yielding loads are determined by the inherent properties of the energy-absorbing anchor rods/anchor cables.
Updating node connection function nodes: the relative displacement of the anchor rod body A and the outer sleeve B under the yielding load effect in the yielding process is simulated by plastic large deformation generated by yield of a Nydeform spring, and the force transmission point of the anchor rod body A and the force transmission point of the outer sleeve B are changed due to the relative displacement generated in the yielding process, so that the connection effect node needs to be updated when each calculation step is finished. In brief, after each calculation step is finished, a stored global connection table is called, established link connections are identified, for each identified link connection, a source node and a current target node of the link connection are called, a structural unit node which is closest to the source node and is located on the pile-B is searched, and if the searched structural unit node is inconsistent with the current target node, the target node connected with the node is updated to the searched structural unit node. The calculation step refers to a calculation step in numerical simulation.
Judging and deleting the failed node connection: as the yielding process progresses, part of the anchor rod body a will be pulled out from the outer sleeve B, and the pulled-out part of the anchor rod body will not directly act with the outer sleeve B. For the pile-A and pile-B, due to the relative axial displacement, the structural unit nodes on the pile-A at the overlapping part of the pile-A and the pile-B are away from the overlapping part in sequence. For these building block nodes, it is necessary to delete their link connections to the node on pile-B. Specifically, for the link connection of each identified node, judging whether the current target node is node-B2, if so, calculating the axial distance U1 between node-B2 and node-A1, the axial distance U2 between the source node of the link connection of the node and the node-A1 of the structural unit, judging whether U2 is greater than U1, if so, indicating that the source node is away from the overlapping part of the pile-A and the pile-B, and deleting the link connection of the node.
Monitoring the current pressure yield: in this example, the current yield is obtained by monitoring the relative displacement of node-a1 and its corresponding start connection node-B3. The starting distance U3 of the node-A1 and the node-B3 is firstly calculated, and the current distance U4 of the node-A1 and the node-B3 is calculated after each calculation step is finished, so that the current yield URY is U4-U3.
Setting node connection attributes when yielding is finished: and after each calculation step is finished, judging whether URY reaches the maximum yielding distance, if yes, setting all link connection attributes on the node-A1 as rigid fixed connection, and finishing yielding.
In order to explain the yielding function, the stress characteristic and the action mechanism of the yielding model constructed by the invention and the anchored rock mass, a numerical simulation tensile test, a bending shear test and a drawing test are respectively carried out on the anti-slip constant-resistance large-deformation energy-absorbing anchor rod/anchor cable which is built by the steps and is shown in the figure 3, and the three tests are used for testing the stress bearing characteristic of the anchor rod.
(1) In a numerical simulation tensile experiment, a physical geometric model, a corresponding numerical model and unit division of the energy absorption anchor rod/anchor cable anchor rod are shown in figures 3-4, yielding load of the energy absorption anchor rod/anchor cable is 131kN, and model boundary conditions are as follows: node-B1 is fixed and node-a2 is forced to a constant rate of-1 e-7m/step in the direction of the local coordinate system x. The axial force distribution of the anchor rod at each stage in the numerical simulation tensile experiment is shown in figures 10a-10f, and the drawing load-displacement curve is shown in figure 6.
As can be seen from fig. 10a-10f, the axial force distribution of the anchor rod can be divided into three stages:
initial elastic phase (fig. 10a, fig. 10 b): at this stage, the axial force transmission positions of the anchor rod body and the outer sleeve are kept unchanged, and the outer sleeve has a free section and does not bear load.
Constant resistance slip yielding phase (fig. 10c, fig. 10 d): at this stage, because the axial force reaches the maximum frictional resistance (yielding load) between the anchor rod body and the outer sleeve, under the action of the load, the axial force transmission positions of the anchor rod body and the outer sleeve are changed all the time, and the free section of the outer sleeve is increasingly involved in axial stress, which is particularly shown in that the node connected with the node-A1 at the end of the anchor rod is continuously updated.
Let press end segment (fig. 10e, fig. 10 f): at this stage, the yielding displacement reaches the maximum value, and yielding is finished. Because of the anti-slip type of yielding bolt, the axial force transmission position of the bolt body and the outer sleeve is maintained at the node where the last node-A1 is connected in the yielding stage, and the connection can continue to bear load without failure.
Corresponding to the anchor rod tensile load-displacement curve of fig. 6, before the axial force reaches the yielding load, the anchor rod shows elasticity, the axial force is continuously increased, and the tensile characteristic shows the tensile characteristic of the anchor rod material; when the yielding load is reached, the anchor rod generates constant-resistance sliding yielding under the action of the yielding load, the axial force is unchanged, the displacement is increased, and the tensile characteristic is expressed as the structural characteristic of the anchor rod yielding device; when the maximum yielding amount is reached, the stretching characteristic of the yielding anchor rod with the anti-slip device is expressed as the stretching characteristic of the anchor rod material.
Next, under the conditions of experiment (1), the bending shear test was performed by deleting the velocity of node-a2 in the direction of local coordinate system x ', and applying a constant velocity yvel of-1 e-7 in the direction of local coordinate system y'. The distribution of bending moment of the rod body, the outer sleeve and the whole anchor rod in the experiment is shown in figures 8a-8c, and the distribution of shearing force is shown in figures 9a-9 c. The integral bending moment and shearing force distribution of the anchor rod are obtained by adding the bending moment and shearing force distribution of each component.
The bending moment and shear distribution of the anchor rod as a whole are analyzed (fig. 8c and 9 c): since the stiffness matrix of the pile structural elements in Flac3D and the beam structural elements are identical, the overall bending moment and shear distribution is identical as a result of the normal shear loading experienced by the cantilever beam ends.
Analyzing respective bending moment and shear distribution conditions on the anchor rod body and the outer sleeve: because the anchor rod body and the outer sleeve are fixedly connected at the overlapping position in other 5 degrees of freedom except the axial direction, the deformation (the rotation angle and the tangential displacement of the node) of the anchor rod body and the outer sleeve at the overlapping position is consistent, and the respective stress conditions are calculated and obtained through consistent deformation conditions.
And finally, carrying out a numerical simulation drawing test on the constant-resistance large-deformation anti-slip internal yielding anchor rod, wherein a physical model diagram corresponding to the test is shown in fig. 5. The anchoring conditions for the experiment were: except the anchoring at the outer sleeve part, the rest is a free section. The boundary conditions of the model are as follows: and (4) applying a constant speed xvel-1 e-7m/step to the node-A2 along the direction of a local coordinate system x' on the bottom surface of the fixed node model (at the position where the overall coordinate system z is 0), and loading until the anchor rod is damaged. The axial force distribution of the anchor rod in the test is shown in figures 11a-11f, and the tensile load-displacement curve is shown in figure 7.
The bolt axial force distribution shown in fig. 11a-11f was studied: because the free section is arranged in the drawing experiment, the anchor rod body is not connected with surrounding grids in the axial degree of freedom direction of the rod body, and therefore the axial force distribution condition of the rod body is the same as the anchor rod stretching result. For the outer sleeve, the stress form is gradually changed from a tension-compression mixed type to a tension type due to the anchoring effect. The deformation of the anchoring area grid and the anchoring agent under stress is changed along with the change of the axial force on the outer sleeve of the anchor rod.
The stress deformation characteristic of the yielding anchor rod constructed by the method of the invention can also be illustrated by corresponding to the anchor rod pulling load-displacement curve of fig. 7. In effect, the yielding anchor rod constructed by the method can reflect the process that the rod body is pulled out of the outer sleeve due to the mechanical sliding action in the yielding process on one hand, and can reflect the process that the outer sleeve, the anchoring agent and the rock and soil body in the anchoring area are subjected to dynamic development of stress deformation on the other hand. Therefore, the construction method of the yielding anchor rod can describe the yielding anchor rod on the basis of the yielding mechanism.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A construction method of a structural yielding model of an energy-absorbing anchor rod/anchor cable is characterized by comprising the following steps:
(1) analyzing the structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable to obtain a yielding device of the energy-absorbing anchor rod/anchor cable, wherein the yielding device consists of an anchor rod body and an outer sleeve sleeved outside the anchor rod body, and the yielding function of the energy-absorbing anchor rod/anchor cable is realized by the relative sliding of the anchor rod body and the outer sleeve at the axial force transmission point of the energy-absorbing anchor rod/anchor cable;
(2) determining the position of the axial force transmission point of the yielding device of the energy-absorbing anchor rod/anchor cable;
(3) simulating the anchor rod body and the outer sleeve by using an existing anchor rod/anchor cable structural unit in numerical simulation software;
(4) deleting node-grid type connection of structural unit nodes which are automatically generated by numerical simulation software during simulation and correspond to the first overlapped part on the anchor rod body or the second overlapped part on the outer sleeve and coincide with the anchor rod body;
(5) establishing a node-node type connection between the structural unit node on the first overlapping portion and the structural unit node on the second overlapping portion;
(6) defining the attribute of the node-node type connection;
(7) identifying the node-node type connection and updating the structural unit node corresponding to the identified node-node type connection;
(8) judging and deleting the failed node-node type connection;
(9) respectively determining a monitoring node on the anchor rod body and the outer sleeve in advance, and calculating the change amount of the relative displacement of the two monitoring nodes to obtain the current yield;
(10) and when the current yielding amount reaches the maximum yielding distance, setting the attribute of the node-node type connection at the end of yielding based on the structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable.
2. The method for constructing the structural yielding model of the energy-absorbing anchor rod/anchor cable according to claim 1, wherein the position of the axial force transmission point of the yielding device of the energy-absorbing anchor rod/anchor cable is determined according to the type of the energy-absorbing anchor rod/anchor cable and the corresponding structural mechanical characteristics of the energy-absorbing anchor rod/anchor cable.
3. The method for constructing a structural yielding model of energy-absorbing anchor rods/anchor cables as claimed in claim 1, wherein in the simulation process of step (3), the anchor rod body or the outer sleeve at which the non-axial force transmission point is located is finely divided into structural units.
4. The method for constructing the structural yielding model of the energy-absorbing anchor rods/anchor cables as claimed in claim 3, wherein the fine structural unit is divided into: when discretizing the anchor rod body or the outer sleeve where the non-axial force transmission points are located, the structural unit nodes arranged on the anchor rod body or the outer sleeve where the non-axial force transmission points are located are more than the structural unit nodes arranged on the outer sleeve or the anchor rod body where the axial force transmission points are located.
5. The method for constructing the structural yielding model of the energy-absorbing anchor rods/cables according to claim 1, wherein the step (5) is specifically as follows:
determining a structural unit node on the first overlapping part or the second overlapping part where the axial force transmission point is located as a source node, searching a structural unit node which is closest to the source node on the second overlapping part or the first overlapping part where the non-axial force transmission point is located as a target node, and establishing node-node type connection between the source node and the target node.
6. The method for constructing the structural yielding model of the energy-absorbing anchor rods/cables according to claim 5, wherein in the step (6), the properties of the node-node type connection are as follows:
for the constant resistance yielding process, the attribute of the node-node type connection at the axial force transmission point is set as follows: the axial degree of freedom of the rod is an ideal elastic-plastic spring connection, and the other 5 degrees of freedom are fixed connections, wherein the rigidity of the ideal elastic-plastic spring takes a large value, and the yield load takes yielding load; the attribute of the node-node type connection at the non-axial force transmission point is set as follows: the axial freedom degrees of the rods are in free connection, and the other 5 freedom degrees are in fixed connection;
for the resistance increasing or resistance reducing yielding process, the attribute of the node-node type connection at the axial force transmission point is as follows: the axial degree of freedom of the rod is firstly set to be connected with an ideal elastic-plastic spring, then the functional relation between the yield load of the ideal elastic-plastic spring and the relative displacement of the source node and the target node is implanted, the yield load of the elastic-plastic spring in the yielding process is controlled, and the other 5 degrees of freedom are fixedly connected; the attribute of the node-node type connection at the non-axial force transmission point is set as follows: the axial degree of freedom of the rod is freely connected, and the other 5 degrees of freedom are fixedly connected.
7. The method for constructing a structural yield model of energy absorbing anchor/cable bolts according to claim 6, wherein the functional relationship between the yield load of an ideal elastoplastic spring and the relative displacement of the source node and the target node is obtained by a bolt tensile test.
8. The method for constructing the structural yielding model of the energy-absorbing anchor rods/cables, according to claim 5, wherein the step (7) is specifically as follows:
after each calculation step is finished, calling all connected global table head addresses, identifying the node-node type connection, firstly calling information of source nodes and target nodes corresponding to the node-node type connection for each identified node-node type connection, searching structural unit nodes on the anchor rod body or the outer sleeve where the target nodes closest to the source nodes are located, if the searched structural unit nodes are inconsistent with the current target nodes, updating the current target nodes by the searched structural unit nodes, and keeping the attribute of the node-node type connection between the updated target nodes and the original source nodes unchanged.
9. The method for constructing the structural yielding model of the energy-absorbing anchor rods/cables according to claim 1, wherein the step (8) is specifically as follows:
after each calculation step is finished, judging whether two structural unit nodes corresponding to the node-node type connection are both positioned at the overlapped part of the anchor rod body and the outer sleeve for the node-node type connection at the non-axial force transmission point, and if not, deleting the node-node type connection between the two structural unit nodes.
10. The method for constructing the structural yielding model of the energy-absorbing anchor rods/cables according to claim 1, wherein the step (10) is specifically as follows:
under the condition that the energy-absorbing anchor rod/anchor cable is provided with a slip-resistant device, when the current yielding amount reaches the maximum yielding distance, setting the attribute of the node-node type connection at the axial force transmission point as a fixed connection, and ending yielding;
under the condition that the energy-absorbing anchor rod/anchor cable is free of the anti-slip device, when the current yielding amount reaches the maximum yielding distance, the attribute of the node-node type connection at the axial force transmission point is set to be free connection, or the spring yield strength of the node-node type connection at the axial force transmission point is set to be 0, or the node-node type connection at the axial force transmission point is directly deleted, and the yielding is finished.
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