A safety analysis method for rammed earth brick-wrapped city wall ruins

Abstract

The present invention belongs to the technical field of ancient site protection and relates to a safety analysis method for rammed earth-brick wall ruins. The method comprises the following steps: Step 1: Obtaining simplified three-dimensional data of the rammed earth-brick wall ruins; Step 2: Creating a three-dimensional model of the rammed earth-brick wall ruins based on the three-dimensional data; Step 3: Simplifying the three-dimensional model of the rammed earth-brick wall ruins to construct a two-dimensional model; Step 4: Performing finite element analysis based on the two-dimensional model to determine the safety factor of the rammed earth-brick wall ruins. The present invention establishes a two-dimensional model of the rammed earth-brick wall ruins and uses this two-dimensional model for finite element simulation. The method analyzes the stability of the rammed earth-brick wall ruins with a small mesh size, thus saving computation time while ensuring computational accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of ancient site protection and relates to a safety analysis method for rammed earth brick-wrapped city wall sites. Background Art

[0002] The existing rammed earth-covered brick city wall ruins possess immense historical, cultural, and artistic value. However, due to their age, the materials used in the wall have gradually deteriorated due to years of exposure to wind, sun, and rain. This deterioration significantly impacts both the preservation of the wall ruins and the safety of visitors. To address this deterioration, cultural relics conservationists are repairing and protecting the wall ruins. Finite element simulations are used to analyze the wall's stability before and after restoration, helping to develop restoration plans and evaluate the results.

[0003] Existing 3D finite element analysis has played a significant role in the preservation of ancient sites. However, a problem remains: when the 3D model's mesh is small, while computational accuracy is guaranteed, the computational effort is large and computational speed is slow, resulting in a long computation time. Furthermore, when the 3D model's mesh is large, computation time is reduced but accuracy is not guaranteed, often leading to distorted results. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a safety analysis method for rammed earth brick wall ruins, which solves the problem in the prior art that the two requirements of short calculation time and high calculation accuracy of finite element analysis of three-dimensional models cannot be achieved at the same time.

[0005] The present invention provides a safety analysis method for a rammed earth brick-covered city wall site, comprising the following steps:

[0006] Step 1: Obtain simplified 3D data of the rammed earth brick wall ruins;

[0007] Step 2: Building a three-dimensional model of the rammed earth brick wall ruins based on the three-dimensional data;

[0008] Step 3: Simplify the three-dimensional model of the rammed earth brick wall ruins to construct a two-dimensional model;

[0009] Step 4: Perform finite element analysis and calculation based on the two-dimensional model to determine the safety factor of the rammed earth brick-wrapped city wall ruins.

[0010] Furthermore, the simplified three-dimensional data includes outline dimension data of the soil layer and brick layer in the rammed earth-covered brick city wall ruins.

[0011] Furthermore, ANSYS Workbench was used to simplify the cross-section of the three-dimensional model of the rammed earth and brick wall ruins described in step three.

[0012] Furthermore, ANSYS Workbench was used to perform finite element analysis on the two-dimensional model described in step 4.

[0013] Furthermore, the steps of performing finite element analysis using ANSYS Workbench are as follows:

[0014] 4.1 Establish a model based on the simplified three-dimensional data of the rammed earth brick wall ruins and input the corresponding building material properties;

[0015] 4.2 Apply loads or adjust parameters of the building material properties according to the simulation analysis content;

[0016] 4.3 Meshing the two-dimensional model;

[0017] 4.4 Finite element analysis is performed based on the divided grid to obtain the safety factor of the rammed earth brick wall ruins.

[0018] Furthermore, the grid density of the two-dimensional model division in step 4.3 is greater than the grid density of the three-dimensional model division.

[0019] Furthermore, the grid type of the two-dimensional model is quadrilateral, and the grid size is 0.1m-0.5m.

[0020] Furthermore, the building material properties include density, elastic modulus, Poisson's ratio, internal friction angle and cohesion.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention establishes a two-dimensional model of a rammed earth-brick wall ruins, performs finite element simulation through the two-dimensional model, analyzes the stability of the rammed earth-brick wall ruins when the grid division is small, and saves calculation time while ensuring the calculation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following drawings are merely provided for illustrative purposes only and are not intended to limit the scope of the present invention.

[0024] Figure 1 It is a flow chart of the safety analysis method of the rammed earth brick-wrapped city wall ruins in the present invention;

[0025] Figure 2 It is a three-dimensional model of the rammed earth and brick-covered city wall;

[0026] Figure 3 It is a simplified two-dimensional model diagram;

[0027] Figure 4 This is a schematic diagram of the mesh division of the 3D model of the rammed earth and brick wall ruins;

[0028] Figure 5 It is a schematic diagram of the mesh division of the two-dimensional model;

[0029] Figure 6 It is the horizontal deformation diagram of the three-dimensional model;

[0030] Figure 7 It is the horizontal deformation diagram of the two-dimensional model;

[0031] Figure 8 It is the vertical deformation diagram of the three-dimensional model;

[0032] Figure 9 It is the vertical deformation diagram of the two-dimensional model;

[0033] Figure 10 It is the deformation diagram of earthquake simulation analysis;

[0034] Figure 11 It is a deformation diagram of the material degradation simulation analysis of the two-dimensional model;

[0035] Figure 12 It is a deformation diagram of the 3D model material degradation simulation analysis. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution, design method and advantages of the present invention more clear, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] like Figures 1-12 As shown, the present invention provides a safety analysis method for rammed earth brick-wrapped city wall ruins, comprising the following steps:

[0038] Step 1: Simplify the 3D model of the rammed earth brick wall ruins to construct a 2D model;

[0039] The steps of simplifying the three-dimensional model of the rammed earth brick wall ruins into a two-dimensional model are as follows:

[0040] First, simplified 3D data of the rammed earth and brick wall ruins are obtained, wherein the simplified 3D data includes the outline dimension data of the soil layer and brick layer in the rammed earth and brick wall ruins;

[0041] Then: establishing a three-dimensional model of the rammed earth brick wall ruins based on the three-dimensional data;

[0042] Finally: simplify the three-dimensional model of the rammed earth brick wall ruins to construct a two-dimensional model;

[0043] ANSYS Workbench software was used to model each part using a sweeping method. In this embodiment, the contours of the Tang Dynasty earth, Ming Dynasty earth, and Ming Dynasty brick parts were swept to form their respective cross-sectional contours. The sweeping path was a rectangle enclosed by the long and wide sides of the city wall ruins. A three-dimensional model of the rammed earth and brick city wall ruins was established. A cross-section of the three-dimensional model was then cut out to create a plan view and construct a two-dimensional model.

[0044] When analyzing crowd loads on a city wall, the primary focus is on the pressure exerted by tourists on the wall itself, in order to assess its capacity as a tourist attraction. The length of the wall ruins model is much larger than the other two dimensions, and the cross-sectional shape and dimensions remain unchanged along the length. In terms of stress, the crowd load acts parallel to the cross-section of the wall ruins model, resulting in no change in the wall's longitudinal stress. Therefore, the finite element calculation of the three-dimensional model can be simplified to a plane strain problem, replacing the three-dimensional model with a two-dimensional cross-section.

[0045] Specifically, the Nanmen Wengcheng in Xi'an, Shaanxi Province is used as a reference, with side lengths of 50m and 70m respectively. The model diagrams before and after simplification of the two-dimensional model are shown as follows: Figure 2 、 Figure 3 shown.

[0046] Step 2: Build a 2D model and input building material properties;

[0047] The three-dimensional size data and building material properties of the Xi'an South Gate Wengcheng city wall ruins were obtained through physical investigation and using previous research data. The city gates, towers and other parts were not considered. Details such as battlements and stairs will increase the calculation amount but have almost no effect on the experimental conclusions. After the Xi'an South Gate Wengcheng model is simplified, its cross section can be approximately regarded as a trapezoid, such as Figure 2 、 Figure 3 As shown; the central rectangle is made of earth from the Tang Dynasty, with an outline of 6m wide and 5m high; the outer rectangles are made of earth from the Ming Dynasty, with an outline of 12m wide and 11.6m high; the outermost trapezoid is made of brick from the Ming Dynasty, with an outline of 14m at the top, 18m at the bottom, and 12m high;

[0048] The building material attribute data mainly include density, elastic modulus, Poisson's ratio, internal friction angle, cohesion, etc.

[0049] The material properties of the city wall selected for research are as follows:

[0050] Tang Dynasty soil Ming Dynasty soil Ming Dynasty bricks (unit) density 1867 1908.5 1540 kg / m^3 elastic modulus 48391000 69000000 2230000000 pa Poisson's ratio 0.392 0.347 0.1 Internal friction angle 23 21 60 ° Cohesion 25000 32000 293000 Pa

[0051] Step 3: Apply load according to the simulation analysis content;

[0052] According to different simulation analysis contents, different loads are applied or parameters of the building material property data are adjusted.

[0053] First, gravity acceleration load and bottom fixed support load are applied to the model.

[0054] Secondly, a crowd load analysis was conducted on the South Gate Wengcheng of Xi'an, applying a certain pressure to the area where tourists step on the city wall ruins. In this example, a load value of 3.5kN / m was used, which is the load value under the condition of dense crowds during peak tourist season. 2 .

[0055] Step 4: Divide the model into grids;

[0056] The two-dimensional model and the three-dimensional model are meshed; the two-dimensional model is a quadrilateral mesh with a mesh size of 0.1m, and the three-dimensional model is a tetrahedral mesh with a mesh size of 1.2m; Figure 4 As shown in the figure, the three-dimensional model of the rammed earth brick wall ruins is divided into meshes, as shown in the figure. Figure 5 As shown, the 2D model of the rammed earth brick wall ruins is divided into two grids.

[0057] The mesh quality and mesh density of the 2D model are greater than those of the 3D model. The mesh density of the 2D model is greater than the mesh divided during the 3D model calculation to improve the calculation accuracy.

[0058] Step 5: Perform finite element analysis and calculation on the two-dimensional model to determine the safety factor of the rammed earth brick-wrapped city wall ruins.

[0059] ANSYS Workbench software was used to calculate and draw the horizontal deformation diagram and vertical deformation diagram of the city wall ruins. The horizontal deformation diagram of the three-dimensional model is shown in the figure. Figure 6 As shown; the horizontal deformation diagram of the two-dimensional model is as follows Figure 7 As shown in the figure, the vertical deformation diagram of the three-dimensional model is as follows: Figure 8 As shown in the figure, the vertical deformation diagram of the two-dimensional model is as follows: Figure 9 As shown;

[0060] The calculation results of the two-dimensional model and the three-dimensional model are within the error range;

[0061] Finite element calculation problems can be solved by using a two-dimensional model instead of a three-dimensional model, as follows:

[0062] ANSYS Workbench software was used for calculations. The 3D model and 2D model were each calculated three times, and the average time was taken. The coarse mesh of the 3D model took 51 seconds, and the fine mesh of the 2D plane model took 21 seconds. The 2D model took less than half the time to calculate as the 3D model, and replacing the 3D model with a 2D cross-section model significantly reduced the calculation time.

[0063] According to the above process, in step 3, the load and material properties are modified, and earthquake simulation analysis and material degradation simulation analysis are performed on the three-dimensional model and the two-dimensional model respectively; the earthquake simulation analysis is performed using modal and response spectrum analysis methods. Apply earthquake loads, calculate and draw deformation diagrams. The results are as follows Figure 10 As shown in the figure, during earthquake simulation analysis, the 2D model took 47 seconds to calculate, while the 3D model took 6 minutes and 58 seconds to calculate. The 2D model took much less time to calculate than the 3D model.

[0064] When simulating material degradation, let the degradation damage factor be D, then the elastic modulus of the degraded material E1 = (1-D)E. Set D to 0.2, 0.4, 0.6, and 0.8 respectively, calculate the material properties after degradation, perform simulation calculations, and draw a deformation diagram. The deformation diagram of the 2D model material degradation simulation analysis is as follows: Figure 11 As shown, the deformation diagram of the 3D model material degradation simulation analysis is as follows Figure 12 As shown in the figure, during the material degradation simulation analysis, the average calculation time for the 2D model was 23 seconds, while the average calculation time for the 3D model was 52 seconds. The 2D model calculation time was less than half of the 3D model calculation time.

[0065] In terms of calculation errors, due to the complex structure of the corners of the city wall, the extreme points of the calculated values ​​of the three-dimensional model are mostly located here. After simplification of the two-dimensional model, it is equivalent to the city wall model being infinitely long and without corners. Therefore, the extreme values ​​cannot be used when calculating the error. Instead, the experimental data at the same position should be obtained using a probe.

[0066] The three-dimensional and two-dimensional calculation results and relative errors of some points are shown in the following table.

[0067] Three-dimensional 0.0018359 274970 0.0019912 0.0053656 0.012042 2D 0.0016731 281230 0.0019634 0.0055181 0.011899 error -8.87％ 2.28％ -1.40％ 2.84％ -1.19％

[0068] As can be seen from the above figure, most of the errors are kept within 5%, and a very small number of errors are greater than 5% but less than 10%, indicating that the accuracy of the calculation results is guaranteed by using this method to replace the three-dimensional model with a two-dimensional model.

[0069] In summary, a two-dimensional model of the rammed earth and brick wall ruins was established for finite element simulation. With a smaller mesh size, the stability of the rammed earth and brick wall ruins was analyzed, saving calculation time while ensuring calculation accuracy.

[0070] While various embodiments of the present invention have been described above, the above descriptions are intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or technological improvements in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A safety analysis method for rammed earth brick wall ruins, characterized in that: The following steps are involved: Step 1: Obtain simplified three-dimensional data of the rammed earth and brick wall ruins; the simplified three-dimensional data includes the outline size data of the soil layer and brick layer in the rammed earth and brick wall ruins; Step 2: Building a three-dimensional model of the rammed earth brick wall ruins based on the three-dimensional data; Step 3: Simplify the three-dimensional model of the rammed earth brick wall ruins to construct a two-dimensional model; The contours of the three parts, Tang Dynasty earth, Ming Dynasty earth, and Ming Dynasty brick, were swept as their respective cross-sectional contours. The sweeping path was a rectangle enclosed by the long and wide sides of the city wall ruins. A three-dimensional model of the rammed earth and brick city wall ruins was established. The cross-sections of the three-dimensional model were intercepted and a plan view was drawn to construct a two-dimensional model. Step 4: Perform finite element analysis based on the two-dimensional model to determine the safety factor of the rammed earth brick wall ruins: The parameters for the finite element analysis calculation of the two-dimensional model include: three-dimensional size data of the city wall ruins and building material properties; The central rectangle is made of earth from the Tang Dynasty, with dimensions of 6m wide and 5m high; the outer rectangles are made of earth from the Ming Dynasty, with dimensions of 12m wide and 11.6m high; the outermost trapezoid is made of brick from the Ming Dynasty, with dimensions of 14m high, 18m low and 12m high. The building material property data includes density, elastic modulus, Poisson's ratio, internal friction angle, and cohesion.

2. The safety analysis method for a rammed earth brick-wrapped city wall ruins according to claim 1, characterized in that: ANSYS Workbench was used to simplify the cross-section of the three-dimensional model of the rammed earth brick wall ruins described in step three.

3. The safety analysis method for a rammed earth brick-wrapped city wall ruins according to claim 1, characterized in that: Use ANSYS Workbench to perform finite element analysis on the two-dimensional model described in step 4.

4. The safety analysis method for a rammed earth brick-wrapped city wall ruins according to claim 3, characterized in that: The steps for performing finite element analysis in ANSYS Workbench are as follows: 4.1 Establish a model based on the simplified three-dimensional data of the rammed earth brick wall ruins and input the corresponding building material properties; 4.2 Apply loads or adjust parameters of the building material properties according to the simulation analysis content; 4.3 Meshing the two-dimensional model; 4.4 Finite element analysis is performed based on the divided grid to obtain the safety factor of the rammed earth brick wall ruins.

5. The safety analysis method for rammed earth brick-wrapped city wall ruins according to claim 4, characterized in that: The mesh density of the two-dimensional model in step 4.3 is greater than that of the three-dimensional model.

6. The safety analysis method for rammed earth brick-wrapped city wall ruins according to claim 5, characterized in that: The grid type of the two-dimensional model is quadrilateral, and the grid size of the two-dimensional model is 0.1m-0.5m.

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