Method for analyzing mechanical properties of single-layer spherical reticulated shell structure of reconstituted bamboo components under fire

Abstract

The application discloses a kind of analysis methods for the mechanical properties of reed bamboo component single-layer spherical reticulated shell structure under fire, comprising the following steps: according to the object and characteristics of research, establish single-layer spherical reticulated shell numerical model;The single-layer spherical reticulated shell model is introduced into fire simulation software, perfects fire information and the pyrolysis parameters and combustion parameters of reed bamboo material, and carries out simulation extraction structure temperature field;The single-layer spherical reticulated shell model and the extracted temperature field are introduced into finite element simulation software, after completing the setting of node, reed bamboo material mechanical parameter and boundary condition, carry out mechanical analysis, further analyze the mechanical properties of reed bamboo component single-layer spherical reticulated shell structure under fire.The application route is clear, operability is strong, implementation method is reasonable, is favorable for promoting the stress condition characteristics and law of reed bamboo component single-layer spherical reticulated shell structure under fire in this field, and simultaneously can speed up the research process of improving the mechanical properties of reed bamboo in building structure field.

Description

Technical Field

[0001] This invention relates to the field of mechanical calculation technology, specifically to a method for analyzing the mechanical properties of a single-layer spherical reticulated shell structure made of reconstituted bamboo under fire conditions. Background Technology

[0002] Single-layer reticulated shell structures, as a typical form of large-span spatial structures, possess advantages such as good overall performance and strong span capacity, and are widely used in airport terminals, hangars, and stadium roofs. Currently, the construction materials for single-layer reticulated shells are mostly steel and aluminum alloys, but their corrosion resistance is poor, and the carbon emissions during production are high. Reconstituted bamboo, as a new type of building material, has excellent mechanical properties and a high strength-to-weight ratio, and is considered an ideal material to replace steel, making it suitable for the construction of single-layer reticulated shell structures.

[0003] However, there is currently no research on the mechanical properties of single-layer spherical reticulated shell structures made of reconstituted bamboo under fire conditions. Similar studies in the field mainly focus on the properties of reconstituted bamboo materials or the mechanical properties of reconstituted bamboo components at room temperature or high temperature. Analysis of the overall structural stress of systems based on reconstituted bamboo components under fire conditions is still lacking. The effects of cross-sectional weakening caused by carbonization of reconstituted bamboo components under high temperatures and changes in material mechanical properties at high temperatures on the overall structural stress have not been considered. The main reasons are:

[0004] 1) Finite element modeling simulation based on solid elements can only be used for the analysis of mechanical properties at the component level. Due to the complex overall form of single-layer spherical reticulated shell structures, numerous connection nodes, and complex connection structures, the workload of solid modeling calculation is too large, making it difficult to perform overall mechanical property analysis of the structure.

[0005] 2) The establishment of semi-rigid node models to simulate real connection nodes in mechanical analysis, the selection of the appropriate number of rod elements considering computational accuracy and efficiency, and the method of temperature field input are still unclear.

[0006] 3) In fire simulation, FDS software requires setting relevant parameters and rationally arranging temperature measurement points for extracting the structural temperature field in order to obtain the temperature field distribution of the reconstituted bamboo single-layer spherical reticulated shell structure under real fire conditions as accurately as possible. However, there is a lack of complete systematic research on the arrangement of these measurement points and parameter settings, and there is relatively little reference material available.

[0007] 4) The impact of carbonization and material property degradation of reconstituted bamboo components under high temperatures during a fire on their overall mechanical properties was not adequately considered. At high temperatures, carbonization of the reconstituted bamboo renders some sections unusable, completely losing their load-bearing capacity, and the material properties of the remaining sections also deteriorate. Ignoring the carbonization effect would lead to an overestimation of the component's performance under high fire temperatures during calculations, resulting in a lower safety factor for the overall structural stress calculation and insufficient structural safety. However, because the properties of reconstituted bamboo are significantly affected by the raw materials, and its high-temperature carbonization model is complex, it has not been observed to be applied to the overall structural calculations. Summary of the Invention

[0008] To address the above problems, this invention provides a method for analyzing the mechanical properties of a single-layer spherical reticulated shell structure made of reconstituted bamboo under fire conditions.

[0009] The present invention adopts the following technical solution:

[0010] A method for analyzing the mechanical properties of a single-layer spherical reticulated shell structure made of reconstituted bamboo components under fire conditions includes the following steps:

[0011] S1. First, establish a numerical model of a single-layer spherical reticulated shell;

[0012] S2. Import the numerical model of the single-layer spherical reticulated shell from step S1 into the fire simulation software to establish a fire field model of the single-layer spherical reticulated shell structure for fire simulation and extract the spatial temperature field.

[0013] S3. Import the numerical model of the single-layer spherical reticulated shell from step S1 into the finite element simulation software Abaqus to establish a single-layer spherical reticulated shell structure model for mechanical performance analysis under fire conditions.

[0014] S4. Set the mechanical property values ​​of the reconstituted bamboo component material at different temperatures, and apply the spatial temperature field extracted in step S1 to the single-layer spherical reticulated shell structure model of the reconstituted bamboo component in step S3 to complete the calculation and analysis of the mechanical properties of the single-layer spherical reticulated shell structure of the reconstituted bamboo component under fire.

[0015] S5. Based on the calculation and analysis of the mechanical properties under fire, and combined with the Abaqus visualization module, the displacement and stress cloud diagrams of the single-layer spherical shell structure of the reconstituted bamboo component are extracted to identify the nodes or members whose deflection and internal force both exceed a certain threshold, including the nodes or members whose deflection and internal force both exceed a certain threshold as weak areas.

[0016] S6. Based on the existing weak areas and the standard limit requirements, determine whether the single-layer spherical reticulated shell of the reconstituted bamboo component has failed under the action of fire. If it has not failed, the reconstituted bamboo component reticulated shell structure is safe under fire. If it has failed, the parameters should be reset and the above steps S1 to S5 should be repeated for judgment until it is determined that the overall safety of the single-layer spherical reticulated shell structure of the reconstituted bamboo component is guaranteed under fire.

[0017] Furthermore, step S2, extracting the temperature field, includes the following steps:

[0018] S21. The temperature field is extracted using solid surface variables. Four measuring points (upper, lower, front, and rear) are arranged at the node connection, and two measuring points (upper and lower) are arranged along the length of the rod. The average value is used to simulate the actual temperature at the node.

[0019] Furthermore, in step S3, the finite element simulation software Abaqus establishes the model based on beam elements, and the steps include:

[0020] S31. Simulate a real semi-rigid connection at the node connection point, and describe the stiffness of the semi-rigid node by reasonably dividing the element length, cross-sectional shape and material elastic modulus of the node.

[0021] S32. When inputting the temperature field, the number of beam elements to be divided along the length direction is determined by comparing the calculation results of beam elements with different numbers of divisions under single-sided and three-sided fire conditions with the solid elements.

[0022] Furthermore, the number of unit divisions is 4.

[0023] Furthermore, in step S3, the influence of the carbonization model of reconstituted bamboo components under high temperature and the mechanical property change model of reconstituted bamboo components under high temperature is introduced into the finite element simulation software Abaqus. The reduction coefficient of the mechanical properties of reconstituted bamboo materials under different fire high temperatures is reasonably set to realize the material properties under the complex influence of carbonization and softening. For the simulation of the complete withdrawal of the carbonized layer section from the work, the remaining section difficulty is set in real time in Abaqus. The simulation of the section withdrawing from the work is realized by setting the mechanical property reduction coefficient of this range to 0.

[0024] Furthermore, in step S6, the specific steps for specifying the limit requirements include:

[0025] S61. When a reticulated shell structure can no longer bear the load, it is manifested by a sudden and rapid drop in the displacement-time curve. If the deflection of the reticulated shell structure exceeds a certain threshold and loses its bearing capacity at this moment, it is considered that the reticulated shell structure can no longer bear the load.

[0026] The beneficial effects of this invention are:

[0027] 1. For the first time, a single-layer spherical reticulated shell structure model of reconstituted bamboo components was constructed. A carbonization model of reconstituted bamboo components under high temperature and a mechanical property change model of reconstituted bamboo components under high temperature were introduced. Related research was carried out on the mechanical property analysis of single-layer spherical reticulated shell structure of reconstituted bamboo components under fire.

[0028] 2. All models are parametrically modeled and calculated, resulting in high computational efficiency. Adjustments can be made to simulate the single-layer reticulated shell structure, building size, and indoor fire conditions as needed.

[0029] 3. Considering the multiple effects of high temperatures on materials during a fire, the calculations are biased towards safety. The effects of high-temperature carbonization and reduced material properties of reconstituted bamboo under fire conditions are also taken into account.

[0030] 4. High operability, convenient calculation, and high accuracy. In fire simulation, it provides an appropriate method for extracting the temperature field within fire simulation software, and offers a suitable number of measuring points to improve calculation accuracy. In mechanical performance calculation simulation, it provides a modeling method based on beam elements and a recommended number of element divisions, solving the problem that beam elements, lacking thickness in three-dimensional space, make it difficult to set the temperature field along the section thickness direction.

[0031] 5. Realistic Node Simulation. The finite element software employs a semi-rigid node modeling method, which can realistically simulate the node connections and overall stress characteristics of actual buildings under such conditions. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0033] Figure 1 This is a schematic diagram of the analysis method for the mechanical properties of a single-layer reticulated shell structure made of reconstituted bamboo components under fire conditions, as described in this invention.

[0034] Figure 2 This is a graph showing the temperature change over time at the top node in the middle of the span according to an embodiment of the present invention.

[0035] Figure 3 This is a diagram showing the overall structural deformation under fire conditions at the highest fire temperature, according to an embodiment of the present invention.

[0036] Figure 4 This is a graph showing the displacement of key nodes of a single-layer spherical reticulated shell over time, according to an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0039] like Figure 1 As shown, a method for analyzing the mechanical properties of a single-layer reticulated shell structure made of reconstituted bamboo components under fire conditions includes the following steps:

[0040] Step 1: First, establish a numerical model of the reticulated shell;

[0041] Numerical modeling of a single-layer spherical reticulated shell structure was performed using the spatial structure modeling software Formian-K. After inputting relevant parameters such as the span, sag, frequency, and number of rings of the reticulated shell according to the research object, the corresponding numerical model of the single-layer spherical reticulated shell was generated.

[0042] Step 2: Import the numerical model of the single-layer spherical reticulated shell from step S1 into the fire simulation software FDS to establish a fire field model of the reticulated shell structure for fire simulation, and extract the spatial temperature field.

[0043] The extraction of the space temperature field includes the following steps:

[0044] S21. The temperature field is extracted using solid surface variables. To meet the accuracy requirements, four measuring points (upper, lower, front, and rear) are arranged at the node connection, and two measuring points (upper and lower) are arranged along the length of the rod. The average value is used to approximate the temperature at the actual node.

[0045] Step 3: Import the numerical model of the single-layer spherical reticulated shell from step S1 into the finite element simulation software Abaqus to establish a reticulated shell structure model for mechanical performance analysis under fire conditions.

[0046] In step S3, the finite element simulation software Abaqus establishes the model based on beam elements. The steps include:

[0047] S31. Simulate a real semi-rigid connection at the node connection point, and describe the stiffness of the semi-rigid node by reasonably dividing the element length, cross-sectional shape and material elastic modulus of the node.

[0048] S32. When inputting the temperature field, the number of beam elements divided along the length direction is determined by comparing the calculation results of beam elements with different numbers of divisions under single-sided and three-sided fire conditions with the solid elements. The number of element divisions is 4.

[0049] In step S3, the influence of the carbonization model and the mechanical property change model of the reconstituted bamboo component under high temperature is introduced into the finite element simulation software Abaqus. The reduction coefficients of the mechanical properties of the reconstituted bamboo material under different fire temperatures are reasonably set to account for the complex effects of carbonization and softening on material properties. For the simulation of the carbonized layer section completely exiting the working state, the remaining section is difficult to simulate in real time in Abaqus. The simulation of the section exiting the working state is achieved by setting the mechanical property reduction coefficient for this range to 0.

[0050] Step 4: Set the mechanical property values ​​of the reconstituted bamboo component material at different temperatures, and apply the spatial temperature field extracted in step S1 to the reticulated shell structure model in step S3 to complete the mechanical property calculation and analysis of the single-layer spherical reticulated shell structure of the reconstituted bamboo component under fire conditions.

[0051] Step 5: Based on the mechanical performance calculation and analysis under fire conditions, and combined with the Abaqus visualization module, extract the displacement and stress cloud map of the reticulated shell structure to identify nodes or members whose deflection and internal force both exceed a certain threshold. These nodes or members with both deflection and internal force exceeding a certain threshold are considered as weak areas.

[0052] Step Six: Based on the existing weak areas and the standard limit requirements, determine whether the single-layer spherical reticulated shell of the reconstituted bamboo component has failed under fire. If it has not failed, the reconstituted bamboo component reticulated shell structure is safe under fire. Otherwise, the parameters should be reset and the above steps S1 to S5 should be repeated for judgment until it is determined that the overall safety of the single-layer spherical reticulated shell structure of the reconstituted bamboo component is guaranteed under fire.

[0053] The specific steps for setting the standard limits include:

[0054] S61. When a reticulated shell structure can no longer bear the load, it is manifested by a sudden and rapid drop in the displacement-time curve. If the deflection of the reticulated shell structure exceeds a certain threshold and loses its bearing capacity at this moment, it is considered that the reticulated shell structure can no longer bear the load.

[0055] Example

[0056] This embodiment describes a single-layer spherical reticulated shell structure made of reconstituted bamboo, considered in its lower support structure. It is a K6 type reticulated shell with three rings, a span of 45m, and a rise of 8m. The cross-sectional dimensions of its members are 0.155*0.4m, and the material is a certain type of reconstituted bamboo based on *Cibotium barometz*. The lower support structure is 8m high, and a 4*4m ventilation opening is provided on one side of the lower wall of the reticulated shell.

[0057] Considering that the fire resistance of this reconstituted bamboo single-layer spherical reticulated shell is related to various factors, such as fire source power, fire source location, member cross-sectional dimensions, rise-to-span ratio, and roof load, the fire source location and power of the reticulated shell are set in this embodiment. The fire source location is located at the center of the building, and the maximum fire source power is taken as 20MW as the fire source condition. The analysis and simulation process is as follows:

[0058] 1. Simulate the temperature field under fire conditions using FDS software.

[0059] Based on the established model of the reconstituted bamboo single-layer spherical reticulated shell, fire parameters and fire source locations have been set. Simulation calculations yielded a curve showing the temperature change over time at the top of the mid-span of the key node of the reticulated shell. Figure 2 As can be seen, during the entire fire process, the temperature peak occurred around 1200s, reaching 367℃, located near the apex of the reticulated shell directly above the fire source. At this temperature, the cross-section of the reconstituted bamboo pole at this node would char, significantly weakening its load-bearing capacity and posing a certain risk of structural damage. As the fire continued to develop, the amount of air and combustibles inside the reticulated shell structure decreased to some extent. However, due to the presence of ventilation openings, external air could slowly enter the single-layer spherical reticulated shell of the reconstituted bamboo component along with the movement of hot smoke and gas, participating in the combustion reaction. This prevented the fire from ending quickly, but the temperature fluctuated to some extent, starting to decrease after 2400s. It should be noted that the obtained temperature field is the spatial temperature field near the surface of this node under fire conditions. When conducting mechanical performance analysis under fire conditions, this spatial temperature field must be applied as a temperature load to the model established in the corresponding finite element mechanical simulation software.

[0060] 2. Mechanical property analysis under fire conditions using Abaqus

[0061] When analyzing the mechanical properties of a single-layer spherical reticulated shell structure made of reconstituted bamboo under fire conditions, the self-weight, roof mass, and live loads (wind load, snow load, etc.) of the shell structure are first calculated, and the correct load effect combination is selected. Since the obtained load combination is a surface load, it needs to be reasonably distributed to each node of the single-layer spherical reticulated shell structure according to the projected area, and applied as a concentrated force to the main nodes for analysis. In this embodiment, the equivalent nodal load at the vertex is calculated to be 114.23 kN, the equivalent nodal load at the second ring main node is 150.84 kN, and the equivalent nodal load at the third ring main node is 146.94 kN. Subsequently, the temperature field simulated in FDS is input as a temperature load into the corresponding main node area on the reticulated shell roof according to the temperature amplitude curve, and the mechanical response of the structure is calculated.

[0062] 3. Overall Mechanical Performance Analysis of Single-Layer Spherical Reticulated Shells Made of Reconstituted Bamboo Components under Fire Conditions

[0063] Simulation calculations show that the overall structural deformation at peak temperature under this operating condition is as follows: Figure 3 As shown, the maximum displacement of the structure occurs at the main node at mid-span, approximately 1.76 × 10⁻² m. The overall displacement distribution of the structure exhibits a symmetrical trend, decreasing from the second ring main node towards both sides. The displacement variation pattern of the main nodes is as follows: Figure 4 As shown, the maximum stress in the structure occurs in the main rib members from the second to the third ring, reaching a maximum stress of 45.78 MPa. The axial force of the diagonal members near the main rib members is significantly lower than that of the main rib members. The axial force of the ring members also decreases sequentially from the second ring outwards. Under this fire condition, the overall structural stress and deformation are relatively symmetrical, with no significant localized heating, making local instability unlikely. Controlled by maximum displacement, the maximum displacement at the nodes is less than 1 / 30 of the span and also less than 1 / 400 of the allowable deflection value for single-layer reticulated shell structures specified in the "Technical Specification for Spatial Grid Structures" (JGJ 7-2010), indicating a large safety margin. This suggests that the overall load-bearing capacity of the structure has a large margin, and optimizing the plan layout and reducing the cross-sectional dimensions could enhance the structure's economic efficiency. The location of the fire source and the parameters of the fire scene can also be changed. The calculation method in this embodiment can be used to set the fire source at the edge or corner to further explore the overall mechanical properties of the reconstituted bamboo single-layer spherical mesh shell under different working conditions.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for analyzing the mechanical properties of a single-layer spherical reticulated shell structure made of reconstituted bamboo components under fire conditions, characterized in that, Includes the following steps: S1. First, establish a numerical model of a single-layer spherical reticulated shell; S2. Import the numerical model of the single-layer spherical reticulated shell from step S1 into fire simulation software to establish a fire scene model of the single-layer spherical reticulated shell structure for fire simulation, and extract the spatial temperature field; step S2, extracting the temperature field, includes the following steps: S21. The temperature field is extracted using solid surface variables. Four measuring points (upper, lower, front, and rear) are arranged at the node connection, and two measuring points (upper and lower) are arranged along the length of the rod. The average value is used to simulate the actual temperature at the node. S3. Import the numerical model of the single-layer spherical reticulated shell from step S1 into the finite element simulation software Abaqus to establish a single-layer spherical reticulated shell structure model for mechanical performance analysis under fire conditions; the steps in step S3, where the finite element simulation software Abaqus establishes the model based on beam elements, include: S31. Simulate a real semi-rigid connection at the node connection point, and describe the stiffness of the semi-rigid node by reasonably dividing the element length, cross-sectional shape and material elastic modulus of the node. S32. When inputting the temperature field, the number of beam elements to be divided along the length direction is determined by comparing the calculation results of beam elements with different numbers of divisions under single-sided and three-sided fire conditions with the solid elements. The influence of the carbonization model of reconstituted bamboo components under high temperature and the mechanical property change model of reconstituted bamboo components under high temperature was introduced into the finite element simulation software Abaqus. The reduction coefficient of the mechanical property of reconstituted bamboo materials under different fire high temperatures was reasonably set. Among them, for the simulation of the complete withdrawal of the carbonized layer section from the work, the mechanical property reduction coefficient of the temperature range was set to 0 to simulate the withdrawal of the section from the work. S4. Set the mechanical property values ​​of the reconstituted bamboo component material at different temperatures, and apply the spatial temperature field extracted in step S1 to the single-layer spherical reticulated shell structure model of the reconstituted bamboo component in step S3 to complete the calculation and analysis of the mechanical properties of the single-layer spherical reticulated shell structure of the reconstituted bamboo component under fire. S5. Based on the calculation and analysis of the mechanical properties under fire, and combined with the Abaqus visualization module, the displacement and stress cloud diagrams of the single-layer spherical shell structure of the reconstituted bamboo component are extracted to identify the nodes or members whose deflection and internal force both exceed a certain threshold, including the nodes or members whose deflection and internal force both exceed a certain threshold as weak areas. S6. Based on the existing weak areas and in accordance with the standard limits, determine whether the single-layer spherical reticulated shell of the reconstituted bamboo component has failed under fire. If it has not failed, the reconstituted bamboo reticulated shell structure is safe under fire. If it has failed, the parameters should be reset, and steps S1 to S5 above should be repeated for judgment until it is determined that the overall safety of the single-layer spherical reticulated shell structure of the reconstituted bamboo component is guaranteed under fire. The specific steps for meeting the standard limits include: S61. When a reticulated shell structure can no longer bear the load, it is manifested by a sudden and rapid drop in the displacement-time curve. If the deflection of the reticulated shell structure exceeds a certain threshold and loses its bearing capacity at this moment, it is considered that the reticulated shell structure can no longer bear the load.

2. The method for analyzing the mechanical properties of a single-layer spherical reticulated shell structure made of reconstituted bamboo under fire conditions, as described in claim 1, is characterized in that... The number of units is 4.

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