Sleeve reinforcement space grid structure overall performance analysis method based on simplified model

Abstract

The invention discloses an overall performance analysis method for a casing reinforcement space grid structure based on a simplified model, and aims to solve the problems that the casing reinforcement research is limited to a component level, the overall structure modeling efficiency is low, and the node rigidity and the initial bending defect are difficult to accurately consider. The method comprises the following steps: firstly, establishing a refined and simplified model of a casing reinforcing member, verifying the accuracy of the simplified model through a test, simulating an inner pipe and an outer pipe by using a BEAM188 beam unit, and realizing collaborative stress simulation through degree-of-freedom coupling; introducing a semi-rigid defect unit, generating a component model containing a half-wave sine initial bending defect in combination with a BSPLIN command, and rotating a local coordinate system at a random angle to simulate the randomness of an initial bending direction; and parameterized simulation analysis of structural node rigidity, initial bending defects and casing reinforcement is realized based on the model. The method can efficiently and accurately simulate the mechanical property of the casing pipe reinforced overall structure, provides a reliable numerical means for evaluating the reinforcing effect of the space grid structure, and is high in calculation efficiency and wide in application range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of space grid structure reinforcement and numerical simulation, in particular to a sleeve reinforced space grid structure overall performance analysis method based on a simplified model, which is suitable for reinforcement effect evaluation and overall mechanical performance analysis of existing space grid structures of stadiums, airports, stations and the like. BACKGROUND

[0002] Space grid structures (such as net racks and net shells) are widely used in large public buildings such as stadiums, airport terminals and station waiting halls due to their large span and high space utilization. A large number of space grid structures built in China in the late 20th century and the early 21st century have entered the "middle-aged maintenance period" and "old-age reinforcement period". These existing structures generally have problems such as low design standard, fluctuating construction quality, insufficient corrosion and fire prevention measures, or long-term overloading use, which leads to member deformation, node loosening, coating failure, and even local corrosion, resulting in serious safety hazards and shortening the service life. With the increasing demand of the public and regulatory departments for building safety, the detection, identification and reinforcement of existing space grid structures are growing rapidly.

[0003] At present, the reinforcement methods of space structure compression members mainly include two kinds of welding steel plates and sticking fiber reinforced polymer (FRP) cloth. However, these two traditional reinforcement technologies have significant limitations: welding reinforcement requires on-site operation, high temperature can cause residual stress in the base material, which is easy to cause local brittle failure, and the quality of high-altitude welding is difficult to control, for example, in the reconstruction of the Bucharest dome, welding defects greatly increase the risk of member failure; FRP reinforcement relies on the adhesive interface to transfer load, and the adhesive is prone to aging in long-term hot and humid cycle environment, and the direct contact of carbon fiber with steel can cause galvanic corrosion, and the CFRP reinforced member of a certain stadium appeared interface debonding problem only after five years of use. In addition, both methods require a large amount of surface treatment of existing members, and the construction process is complex, making it extremely difficult to implement in dense truss node areas.

[0004] As a new type of reinforcement method, the prefabricated sleeve reinforcement technology has obvious advantages compared with traditional methods: the sleeve is made of two semicircular segments in the factory, and is connected by high-strength bolts on site, avoiding the welding heat damage and the durability problem of adhesives; the stiffening design of the sleeve can improve the slenderness ratio of the member and reduce material consumption; bolt connection can adapt to small construction errors and is more suitable for complex high-altitude operations. After the net grid structure of Shanghai Expo Puxi Variety Hall was reinforced using this technology, the compression bearing capacity was increased by 35%, and the construction time was shortened by 40%. The effectiveness and feasibility of this technology have been fully confirmed through theoretical analysis, experimental verification and engineering application.

[0005] However, current sleeve reinforcement research is limited to the component level, mainly focusing on the improvement of the mechanical properties of individual components after reinforcement, while ignoring the impact of reinforcement on the overall structure mechanical properties. The core bottleneck of existing research is that the numerical modeling of the overall structure is difficult, and if a refined model is used (considering all components such as inner tube, outer tube, hoop, ring rib, etc.), it is difficult to achieve efficient simulation in the overall structure due to the limitation of computer computing power. At the same time, the existing model cannot accurately consider the influence of node semi-rigidity and component initial bending defect (common geometric defect of spatial truss structure) on the overall performance at the same time, which leads to the inability to accurately evaluate the mechanical properties of the overall structure after sleeve reinforcement, and seriously restricts the popularization and application of sleeve reinforcement technology in existing spatial grid structure reinforcement engineering. SUMMARY

[0006] OBJECTIVE

[0007] The purpose of the present application is to overcome the shortcomings of the prior art and provide a sleeve reinforced spatial grid structure overall performance analysis method based on a simplified model, which solves the following technical problems:

[0008] Existing sleeve reinforcement research is only for the component level, and there is a lack of efficient modeling method suitable for the overall structure, which cannot accurately evaluate the impact of reinforcement on the overall structure mechanical properties;

[0009] The refined model has low computational efficiency and is difficult to apply to overall structure simulation, while the traditional simplified model lacks accuracy and cannot guarantee the reliability of the analysis results;

[0010] The existing model cannot accurately consider the node semi-rigidity and component initial bending defect (including initial bending direction randomness) at the same time, resulting in large deviation of the overall performance analysis results.

[0011] The purpose of the present application is to establish an overall structure analysis method that takes into account accuracy and efficiency, to realize the coordinated simulation of sleeve reinforcement, node stiffness, and initial bending defect, to provide a reliable numerical means for the reinforcement effect evaluation of existing spatial grid structures, and to guide engineering practice.

[0012] TECHNICAL SCHEME

[0013] To achieve the above-mentioned object of the present application, the following technical solutions are adopted:

[0014] 1. Sleeve reinforced component model establishment and verification

[0015] (1) Refined model construction

[0016] The general finite element software ANSYS is used to simulate the inner tube, outer tube, hoop and ring rib of the sleeve reinforced component by shell element (such as SHELL181), to accurately define the material parameters (elastic modulus, Poisson's ratio, density) and geometric dimensions (tube diameter, wall thickness, hoop spacing, ring rib size) of each component, to simulate the interaction of the inner tube and the outer tube, the hoop and the inner tube / outer tube, the ring rib and the inner tube / outer tube by the contact element, and to build a refined finite element model.

[0017] (2) Simplified model construction

[0018] Based on the refined model, the hoop and the ring rib with low stress level and mainly synergistic effect are ignored, and only the inner tube and the outer tube are retained; the beam element BEAM188 (Euler-Bernoulli beam element suitable for linear and nonlinear analysis) is used to simulate the inner tube and the outer tube, and the cross-section parameters of the beam element are calculated according to the actual cross-section size of the inner tube and the outer tube (such as moment of inertia, cross-sectional area); the synergistic stress simulation of the inner tube and the outer tube is realized by the degree of freedom coupling command "CP" in ANSYS:

[0019] Transverse linear displacement coupling: for the corresponding nodes of the inner tube and the outer tube along the length direction of the component, the linear displacement in x, y direction (perpendicular to the axis of the component) is coupled, to ensure that the inner tube and the outer tube are stressed synchronously when deformed in the transverse direction;

[0020] Axial fixation: at one end of the sleeve (such as the left end of the component), the x, y, z direction (including the axial direction) linear freedom degrees of the nodes of the inner tube and the outer tube are coupled, to limit the relative movement of the outer sleeve along the axial direction of the component, and to simulate the axial fixation effect of the sleeve and the inner tube.

[0021] (3) Model verification

[0022] Through the axial compression test of the sleeve reinforced component, the ultimate bearing capacity, stress distribution, load-displacement curve and failure mode of the component are obtained; the calculation results of the refined model and the simplified model are compared with the test results respectively:

[0023] If the error of the ultimate bearing capacity of the simplified model is within 5%, the stress distribution trend is consistent with the test, and the load-displacement curve has high coincidence degree, then the accuracy of the simplified model is confirmed;

[0024] If the error of the ultimate bearing capacity of the simplified model is within 5%, the stress distribution trend is consistent with the test, and the load-displacement curve has high coincidence degree, then the accuracy of the simplified model is confirmed;

[0025] Semi-rigid defective element construction (node stiffness and initial bending defect simulation)

[0026] (1) Node semi-rigid simulation

[0027] Semi-rigid defect element is constructed by "double unit method": divide the component into En units along the length direction (e.g. En=20), set a double unit with length of l / En (l is the geometric length of the component) at each end of the component, the double unit adopts BEAM4 elastic unit (linear beam unit suitable for small deformation analysis), the rest of the middle units adopt BEAM188 beam unit; the inertia moment I1 of the double unit is calculated through the node stiffness parameter:

[0028] Define the ratio of node stiffness to component linear stiffness α (α = node bending stiffness / component linear stiffness), when α = 1, it is a rigid joint, 0 < α < 1, it is a semi-rigid joint, α = 0.002-0.005, it is a hinged joint;

[0029] Calculate β value: β = 1 / En (En is the total number of component division units);

[0030] According to the formula γ = αβ, calculate the value of γ, and then calculate the inertia moment I1 of the double unit through the formula I1 = γl, to realize the quantitative simulation of the semi-rigid joint.

[0031] (2) Initial bending defect simulation (half-wave sinusoidal shape)

[0032] Replace the straight line unit of the component with a curve unit by using the BSPLIN command (spline curve command) of ANSYS to simulate the initial bending defect of the component:

[0033] Establish the local coordinate system of the component: take one end of the component as the origin, the x-axis along the original axis direction of the component, and the y-axis perpendicular to the x-axis (transverse);

[0034] Define the initial bending amplitude vmo: vmo is an integer multiple of 1 / 1000 of the geometric length l of the component (e.g. vmo = l / 1000, 2l / 1000);

[0035] Define additional control points on the component: evenly set m additional control points along the length direction of the component (e.g. m = 5), calculate the y-direction (transverse) defect value of each control point according to the half-wave sinusoidal function y(x) = vmo × sin(πx / l);

[0036] Assign the defect value of the control point to the BSPLIN curve to form a half-wave sinusoidal initial bending of the component, simulating the common initial bending shape of the component in actual engineering.

[0037] (3) Initial bending direction randomness simulation

[0038] In order to consider the uncertainty of the initial bending direction, a random angle rotation local coordinate system is introduced:

[0039] Generate random angle θ: generate a random angle θ uniformly distributed in the range of 0-2π radians through the random number generation function of ANSYS;

[0040] Rotate the local coordinate system established in step (2) around the x-axis (member axis) by an angle of θ, and change the direction of the y-axis randomly;

[0041] Apply a half-wave sinusoidal initial curvature in the rotated local coordinate system, and generate a member model with random direction initial curvature defects in batches through a loop statement (such as a DO loop), to more truly reflect the randomness of the initial curvature direction in the actual structure.

[0042] 3. Overall structure model construction and parametric simulation analysis

[0043] (1) Overall model construction

[0044] According to the actual design drawings of the spatial grid structure, obtain the node coordinates, member arrangement, material parameters and boundary conditions of the structure; combine the simplified model (sleeve reinforcement) verified in step 1 with the semi-rigid defect element (node stiffness + initial curvature defect) in step 2 to construct the overall finite element model in ANSYS:

[0045] Node processing: according to the actual node type (such as bolt ball node, welded ball node), assign the corresponding α value (node stiffness parameter);

[0046] Member processing: for the members that need to be reinforced, use the simplified model to simulate the synergistic effect of the inner tube and the outer tube; for all members, use the semi-rigid defect element to simulate the initial curvature defect and the semi-rigid node;

[0047] Boundary conditions: according to the actual support conditions of the structure (such as fixed hinge support, sliding hinge support), apply the corresponding constraint conditions (such as limiting the linear displacement or rotation in x, y, z directions).

[0048] (2) Parametric simulation analysis

[0049] Set the variation range of the key parameters and perform mechanical performance simulation analysis on the overall model:

[0050] Node stiffness parameter α: set α = 0.002 (hinged), 0.1, 0.5, 1.0 (rigidly connected) to analyze the influence of node stiffness on the bearing capacity and bending moment distribution of the structure;

[0051] Initial curvature amplitude vmo: set vmo = 0 (no defect), l / 1000, 2l / 1000, 3l / 1000 to analyze the influence of initial curvature defects on the stiffness and ultimate load of the structure;

[0052] Sleeve length Lc: set Lc = l / 4, l / 2, 3l / 4, l (l is the length of the member) to analyze the stiffness adjustment effect of the sleeve length on structures with different node stiffnesses;

[0053] Ambient temperature: Set the temperature range to -20℃~60℃, simulate the influence of ambient temperature on the stress (target value ≤ 16MPa) and displacement (target value ≤ 25mm) of the reinforced component.

[0054] Calculate the load coefficient peak value, stress distribution, displacement response and failure mode of the overall structure under different parameter combinations through the solver of ANSYS (such as the static general solver, nonlinear solver), and output the parametric analysis results.

[0055] 4. Overall model reliability verification

[0056] If the error between the stress calculation value and the monitoring value is ≤8%, the error between the displacement calculation value and the monitoring value is ≤10%, and the failure mode is consistent with the actual one, the reliability of the overall model is confirmed;

[0057] If the error exceeds the preset range, adjust the model parameters (such as contact stiffness, material parameters), repeat steps 1-3 until the model accuracy meets the requirements.

[0058] Beneficial effects

[0059] Compared with the prior art, the present application has the following remarkable beneficial effects:

[0060] Balancing modeling accuracy and calculation efficiency: By simplifying the model to ignore secondary components (hoops, ring ribs), using beam elements and freedom coupling to simulate the synergistic effect of the inner tube and the outer tube, the calculation efficiency is improved by more than 60% while ensuring accuracy (error ≤5% compared with test results), solving the technical bottleneck of "difficulty in balancing accuracy and efficiency" in overall structure simulation, and quickly realizing the overall performance analysis of large space grid structures

[0061] Realize multi-factor synergistic simulation: innovatively incorporate casing reinforcement, node semi-rigidity, initial bending defect (including random direction) into the same overall model, accurately quantify the influence of each factor on the mechanical properties of the overall structure through semi-rigid defect elements and random angle rotation local coordinate system, filling the gap in existing research "only focusing on a single factor and ignoring multi-factor coupling", and the analysis results are more in line with engineering practice.

[0062] Strong parametric analysis capability: supports flexible adjustment of key parameters such as node stiffness, initial bending amplitude, casing length, ambient temperature, etc., can quickly output structure performance curves under different parameter combinations, and provides quantitative basis for engineering design - for example, through analysis, it can be determined that "when α = 0.002 (hinged), the casing length Lc takes l / 2 to achieve optimal reinforcement effect", reducing trial and error costs and improving reinforcement design efficiency.

[0063] High reliability and wide applicability: verified by actual engineering monitoring data (stress error ≤8%, displacement error ≤10%), the model precision meets the engineering requirements; applicable to various types of spatial grid structures such as net racks, net shells, etc., and can be used for existing structure reinforcement effect evaluation, new structure reinforcement scheme optimization and disaster simulation, providing technical support for the safe operation and maintenance of spatial grid structures.

[0064] Lower engineering application threshold: the model construction process is based on the general finite element software ANSYS, the operation process is standardized, the component batch generation is realized through a loop statement, and engineers are easy to master; without relying on high-end computing equipment, it can run on ordinary workstations, which is conducive to technology popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 It is a mechanical schematic diagram of a sleeve reinforcement component in the specific implementation of the application;

[0066] Figure 2 It is a schematic diagram of a simplified finite element model in the specific implementation of the application;

[0067] Figure 3 It is a schematic diagram of an initial bending defect in the specific implementation of the application;

[0068] Figure 4 It is a schematic diagram of a local coordinate system rotation in the specific implementation of the application;

[0069] Figure 5 It is a schematic diagram of a defect component considering node stiffness in the specific implementation of the application; DETAILED DESCRIPTION

[0070] Taking a certain net shell structure as an example, three sleeve reinforcement component test pieces are made, axial compression tests are carried out, the average value of the ultimate bearing capacity is 285kN, the maximum stress is 210MPa, and the load-displacement curve shows a significant downward segment (brittle failure) when the load reaches 285kN.

[0071] The ultimate bearing capacity of the refined model calculation is 278kN, with an error of 2.4% from the test value; the stress distribution trend is consistent with the test (the maximum stress in the middle of the span), confirming that the refined model is reliable.

[0072] Element type: both the inner tube and the outer tube use BEAM188 elements, and the cross-sectional parameters are calculated according to the actual size (inner tube I = 1.2*10^6 mm^4, outer tube I = 1.8*10^6 mm^4);

[0073] Coupling method: set a coupling node every 100mm along the length direction of the component, and couple the x and y direction transverse line displacements; the left end couples all line degrees of freedom.

[0074] Accuracy: The ultimate bearing capacity of the simplified model is 282 kN, with an error of 1.0% compared with the test value. The maximum stress is 208 MPa, with an error of ≤1%, meeting the accuracy requirements.

[0075] Efficiency: The calculation time of the refined model is 4.5 h, and the calculation time of the simplified model is 1.5 h, with an efficiency improvement of 66.7%, meeting the overall structure simulation requirements.

[0076] Node semi-rigid simulation

[0077] Component division: The truss structure members are divided into 20 units (En = 20), β = 1 / 20 = 0.05.

[0078] Node type: The α value of the bolt ball node is 0.1 (semi-rigid), according to the formula γ = αβ = 0.1 × 0.05 = 0.005, I1 = γl = 0.005 × l (l is the length of the member), and the double unit adopts BEAM4 unit, with the moment of inertia I1.

[0079] Initial curvature defect simulation

[0080] Initial curvature amplitude: vmo = l / 1000; Half-wave sinusoidal function: y(x) = (l / 1000) × sin(πx / l), 5 additional control points are set along the length of the member, and the defect value is assigned to generate a curve unit through the BSPLIN command.

[0081] Initial curvature direction randomness simulation

[0082] Random angle: Generate 10 groups of random angles θ between 0 and 2π (such as 0.5π, π, 1.5π, etc.).

[0083] Batch generation: Through the DO loop statement, 10 groups of member models with random direction initial curvature defects are generated for overall model analysis.

[0084] In ANSYS, APDL scripts are called to automatically generate 500 random defect conditions. The analysis shows that when the node stiffness is low, the sleeve reinforcement can improve the bearing capacity of the structure by more than 35%, and the influence of initial curvature randomness on the results is significantly weakened. The system outputs the bearing capacity curve and failure mode, guiding the site reinforcement position.

Claims

1. A method for analyzing the overall performance of a space grid structure reinforced with casings based on a simplified model, characterized by, The method comprises the following steps: (1) establishing a refined model of the casing reinforced component, the refined model simulating the interaction of the inner tube, the outer tube, the hoop and the ring rib by shell elements; obtaining mechanical property data of the casing reinforced component through tests to verify the reliability of the refined model; (2) establishing a simplified model based on the refined model, the simplified model ignoring the hoop and the ring rib and only retaining the inner tube and the outer tube, the inner tube and the outer tube being simulated by BEAM188 beam elements; coupling the transverse line displacements of the nodes of the inner tube and the outer tube by a degree-of-freedom coupling command "CP", and coupling all the line degrees of freedom at one end of the casing to fix the position of the outer casing in the axial direction of the component; comparing the calculation results of the simplified model with the test results and the calculation results of the refined model to verify the accuracy and efficiency of the simplified model; (3) constructing a semi-rigid defective element, the semi-rigid defective element simulating the semi-rigidity of the nodes at both ends of the component by double elements, the double elements being elastic elements BEAM4; defining a local coordinate system of the component, the x-axis of the local coordinate system being along the original direction of the component, and the y-axis being perpendicular to the x-axis; replacing the straight elements of the component with curved elements by a BSPLIN command, and applying an initial bending defect of a specific amplitude at the midpoint of the component, so that the curved elements form a semi-wave sinusoidal initial bending by defining additional points on the component and assigning the defect values calculated by a sine function; (4) simulating the randomness of the initial bending direction: generating a random angle θ uniformly distributed in the range of 0-2π radians, rotating the local coordinate system established in step 3 by an angle θ about the x-axis, and applying the semi-wave sinusoidal initial bending in the rotated local coordinate system, and batch generating component models containing random direction initial bending defects by a loop statement; (5) establishing an overall model of the casing reinforced spatial grid structure: combining the simplified model in step 2 with the semi-rigid defective element in steps 3-4, and constructing an overall finite element model containing node stiffness, initial bending defects and casing reinforcement according to the actual size, node type and component arrangement of the spatial grid structure; (6) performing parametric simulation analysis on the overall model: setting different node stiffness parameters (α values), initial bending amplitudes (vmo), casing lengths (Lc) and environmental temperature conditions, and calculating the mechanical properties of the overall model by a general finite element software ANSYS to obtain the load coefficient peak value, stiffness change, stress distribution and displacement response of the structure; (7) verifying the reliability of the overall model: comparing the simulation analysis results with the actual engineering monitoring data (such as component stress change and displacement change), and if the error is within the preset range, it is confirmed that the overall model can be used for overall performance evaluation of the casing reinforced spatial grid structure.

2. The method of claim 1, wherein, The degree-of-freedom coupling in step 2 is specifically: coupling the x and y direction transverse line displacements of the corresponding nodes of the inner tube and the outer tube to ensure that the inner tube and the outer tube cooperate in force when deformed in the transverse direction; coupling the x, y and z direction line degrees of freedom of the nodes of the inner tube and the outer tube at one end of the casing to limit the relative movement of the outer casing in the axial direction.

3. The method of claim 1, wherein, The moment of inertia I1 of the double unit in step 3 is calculated by formula (1): I1 = γl, wherein γ is calculated by formula (2): γ = αβ, β is the reciprocal of the number of component division units, i.e. β = 1 / En, En is the total number of component division units, and α is the ratio of node stiffness to component linear stiffness, when α = 1, it is a rigid joint, when 0 < α < 1, it is a semi-rigid joint, and when α is 0.002-0.005, it is a hinged joint.

4. The method of claim 1, wherein, The initial bending amplitude vmo in step 3 is an integer multiple of 1 / 1000 of the geometric length l of the component, i.e. vmo = k × (l / 1000), k is a positive integer.

5. The method of claim 1, wherein, The parameterized simulation analysis in step 6 includes: analyzing the influence of node stiffness α on the bearing capacity of the structure, the influence of initial bending amplitude vmo on the stiffness of the structure, the stiffness adjusting effect of sleeve length Lc on structures with different node stiffness, and the stress and displacement response of the component under environmental temperature change.

6. The method of claim 1, wherein, The actual engineering monitoring data in step 7 include stress monitoring data and displacement monitoring data after reinforcement, the maximum stress change is about 16 MPa, and the displacement change is about 25 mm.

7. A system for analyzing the overall performance of a space grid structure reinforced with a casing based on the method according to any one of claims 1 to 6, characterized in that, The method comprises a model establishment module, a defect simulation module, an overall modeling module, a simulation analysis module and a verification module; the model establishment module is used for constructing a refined model and a simplified model and verifying; the defect simulation module is used for generating a semi-rigid defect unit containing an initial bending defect; the overall modeling module is used for integrating the simplified model and the defect unit to construct an overall finite element model; the simulation analysis module is used for performing parameterized simulation calculation on the overall model; and the verification module is used for comparing the simulation results with test or monitoring data to verify the reliability of the model.

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