Non-bedrock site nuclear island structure seismic response assessment method and device based on seismic margin assessment

Abstract

The invention discloses a non-bedrock site nuclear island structure seismic response evaluation method based on seismic margin evaluation, and the method comprises the steps: determining a seismic oscillation index and a structural damage index according to the site condition of a nuclear power plant site selection region and the dynamic characteristics of the structures of a piled raft foundation and a nuclear island; constructing a non-bedrock site-piled raft foundation-nuclear island structure three-dimensional nonlinear dynamic interaction model which is called as a model A; determining an analysis working condition of the model A and carrying out calculation; according to the structural damage process of the piled raft foundation and the nuclear island, different limit states are defined, increment power curves of the different limit states are drawn according to different structural damage indexes, and vulnerability curves in the different damage states are obtained through a failure probability calculation algorithm; and performing seismic response safety assessment on the nuclear island structure by using the vulnerability curve and based on the seismic margin. Based on the characteristic that SSI on a non-bedrock site has obvious influence on the seismic response of the nuclear island structure, the nonlinear progress of structural system damage is described more accurately.

Description

Technical Field

[0001] This invention relates to the field of seismic engineering technology, and in particular to a method and equipment for assessing the seismic response of a nuclear island structure in a non-bedrock site based on seismic margin assessment. Background Technology

[0002] Currently, against the backdrop of rapid growth in global energy demand, nuclear power, as a clean, efficient, and low-carbon energy source, has ushered in unprecedented development opportunities. In recent years, with the continuous construction of new nuclear power projects worldwide, the number of bedrock sites available for nuclear power plant construction is decreasing, and the site selection for nuclear power plants is gradually expanding to non-bedrock sites with poor geological conditions. Given that existing nuclear power seismic design codes do not yet fully address the seismic design provisions for non-bedrock sites, particularly regarding the lack of clear provisions on the nonlinear dynamic interaction between the foundation and structure, seismic response safety assessment of nuclear island structures on non-bedrock sites is an important issue for ensuring the seismic safety of engineering projects.

[0003] To ensure structural seismic safety, early seismic design followed conservative deterministic analysis methods. This approach often resulted in low economic efficiency and failed to account for the numerous uncertainties of seismic motion. With technological advancements, probabilistic analysis methods have become widely used in seismic design, and seismic safety assessment has become a crucial aspect of nuclear power plant structure seismic response research. Currently, seismic safety assessment methods for nuclear island structures can be broadly categorized into seismic probabilistic risk assessment and seismic margin assessment, with seismic margin assessment being a more direct and effective method. However, there is limited research on seismic margin assessment for nuclear island structures on non-bedrock sites, particularly regarding pile-raft foundations. Furthermore, studies have not considered the nonlinear dynamic interactions between the foundation, substructure, and nuclear island structure. Factors such as the high-frequency scattering effect of pile foundations on seismic waves, the nonlinear effects of low-velocity soil layers, and the contact state between the foundation and substructure all influence the safety assessment results, leading to low reliability of seismic safety assessments for nuclear island structures on non-bedrock sites. Summary of the Invention

[0004] This invention provides a method and equipment for assessing the seismic response of a nuclear island structure on a non-bedrock site based on seismic margin assessment, in order to solve the technical problems existing in the prior art.

[0005] The technical solution adopted by this invention to solve the technical problems existing in the prior art is as follows:

[0006] A seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin evaluation is proposed. This method determines seismic motion and structural damage indices based on site conditions of the nuclear power plant site and the dynamic characteristics of both the pile-raft foundation and the nuclear island structure. A three-dimensional nonlinear dynamic interaction model of the non-bedrock site, pile-raft foundation, and nuclear island structure, designated as Model A, is constructed. The analysis conditions for Model A are determined and calculations are performed. Based on the failure processes of both the pile-raft foundation and the nuclear island structure, different limit states are defined, and incremental dynamic curves for different limit states are plotted for different structural damage indices. A failure probability calculation algorithm is used to obtain vulnerability curves under different damage states. Finally, the seismic response safety of the nuclear island structure is assessed using these vulnerability curves and based on the seismic margin.

[0007] Furthermore, the method includes the following steps:

[0008] Step 1: Determine the ground motion intensity index based on the site parameters and seismic zoning level of the nuclear power plant site area; and determine the structural damage index reflecting the structural bearing capacity and the integrity of the containment shielding function based on the structural characteristics of the nuclear island.

[0009] Step 2: Construct finite element models of the soil in the nuclear power plant site selection area, as well as finite element models of the pile-raft foundation and nuclear island structure. Set the contact surface parameters between the soil and the pile-raft foundation and nuclear island structure, and input triaxial ground motion at the bottom of the site to construct Model A.

[0010] Step 3: Adjust the amplitude of the ground motion intensity according to the requirements of the ground motion intensity index. Select several ground motion records and adjust their amplitudes respectively. Input the amplitude-adjusted ground motion records into model A to generate several sets of calculation conditions.

[0011] Step 4: Perform vulnerability analysis on the calculated working conditions to obtain vulnerability curves of the pile-raft foundation and the nuclear island structure under different damage states;

[0012] Step 5: Determine the seismic safety reserve factor using the vulnerability curve, further obtain the HCLPF value of the nuclear island structure, and assess the seismic safety of the nuclear island structure based on the HCLPF value.

[0013] Furthermore, step one includes the following sub-steps:

[0014] Step A1: Analyze the site conditions of the nuclear power plant site selection area and determine the seismic intensity index;

[0015] Step A2: Select structural damage indicators based on the dynamic characteristics and key physical quantities of the structural response of both the pile-raft foundation and the nuclear island.

[0016] Step A3: Based on the seismic input requirements of the "Code for Seismic Design of Nuclear Power Plants" and with reference to the site design response spectrum of nuclear power plant SL-2 level, select several seismic ground motion records that meet the conditions from the PEER seismic database.

[0017] Furthermore, step two includes the following sub-steps:

[0018] Step B1: Based on the geotechnical investigation report of the nuclear power plant site selection area, and according to the soil physical parameters at different borehole locations, the site is simplified and merged into a horizontally layered multi-layered soil mass. A finite element model of the site soil in the nuclear power plant site selection area is established using ABAQUS.

[0019] Step B2: Based on the design drawings of the pile-raft foundation and the nuclear island structure, establish the finite element model of the pile-raft foundation and the nuclear island structure;

[0020] Step B3: Model A is established by setting the contact surface parameters between the soil, the pile-raft foundation, and the nuclear island structure, and inputting triaxial ground motion at the bottom of the site.

[0021] Furthermore, in step B1, when establishing the finite element model of the soil in the nuclear power plant site selection area, soil layers with similar depth and shear wave velocity in the site are simplified and merged according to the soil mechanical parameters at different borehole locations, and the soil above the bedrock surface is approximated as a horizontally layered multi-layered soil. The soil material of the site adopts nonlinear constitutive model, and the finite element model is constructed using the Davidenkov constitutive model. In step B2, when establishing the finite element model of the pile raft foundation and the nuclear island structure, the materials of both the pile raft foundation and the nuclear island structure adopt nonlinear constitutive model, and the concrete uses the CDP constitutive model to construct the finite element model.

[0022] Furthermore, step three includes the following sub-steps:

[0023] Step C1: Based on the ground motion records and ground motion intensity index requirements, adjust the amplitude of the ground motion intensity to determine the upper and lower limits of amplitude adjustment and the amplitude adjustment interval for each ground motion.

[0024] Step C2: Amplitude modulation is performed on the several ground motion records selected in Step 3 and input into Model A in Step 2 to generate several sets of calculation conditions.

[0025] Furthermore, step four includes the following sub-steps:

[0026] Step D1: Define different limit states based on the failure process of the pile-raft foundation and the nuclear island structure;

[0027] Step D2: Extract the calculation conditions of model A, and plot the incremental dynamic curves of the nuclear island structure for different structural damage indices.

[0028] Step D3: Using the natural logarithm of the seismic intensity index as the independent variable and the natural logarithm of the structural damage index as the dependent variable, establish a Cartesian coordinate system with the independent variable as the X-axis and the dependent variable as the Y-axis. Perform linear regression analysis on the data to obtain the probabilistic seismic demand model of the nuclear island structure, and obtain the vulnerability curves under different damage states based on the failure probability expression.

[0029] Furthermore, in step D1, based on the development degree of structural concrete damage factors, concrete strain change value, and peak displacement increase value, the degree of structural damage is classified, the damage state when the structure enters the elastic-plastic stage is quantified, and the limit state corresponding to different classification boundary values ​​is defined; in step D2, the calculation results of all working conditions of the model are extracted, and for different structural damage indicators, the peak value of the time history response of the nuclear island structure under different seismic input amplitudes is plotted to generate incremental dynamic curves.

[0030] Furthermore, in step five, the earthquake safety reserve factor is determined as follows:

[0031] SMR = PGA(T1) 50% / PGA (T 1)极限安全 ;

[0032] In the formula:

[0033] SMR stands for Seismic Safety Reserve Coefficient;

[0034] PGA(T1) 50% This indicates that after 50% of the ground motion input exceeds the design reference, the structural response reaches the ground motion intensity corresponding to the nuclear island structure failure standard.

[0035] PGA (T 1)极限安全 This indicates the ground motion intensity corresponding to the ultimate safe seismic action specified in nuclear power regulations.

[0036] The present invention also provides an apparatus for a seismic response assessment method for a nuclear island structure on a non-bedrock site based on seismic margin assessment, comprising a memory and a processor, wherein the memory is used to store a computer program; and the processor is used to execute the computer program and, when executing the computer program, implement the steps of the seismic response assessment method for a nuclear island structure on a non-bedrock site based on seismic margin assessment as described above.

[0037] The advantages and positive effects of this invention are:

[0038] This invention is based on a three-dimensional nonlinear dynamic interaction model of a non-bedrock site, pile-raft foundation, and nuclear island structure. It calculates the seismic vulnerability probability of the nuclear island structure using a vulnerability statistical model, reflecting the degree of damage at different stages, and assesses the seismic safety of the nuclear island structure based on the HCLPF value. Compared to traditional methods for assessing the seismic response safety of nuclear island structures, this invention has the advantage of fully considering the significant impact of seismic instability (SSI) on the seismic response of the nuclear island structure on non-bedrock sites. It can more accurately describe the nonlinear progression of damage in the structural system, providing a scientific basis for designers to identify risks in advance during the seismic design and nuclear power operation phases. Attached Figure Description

[0039] Figure 1 This is a flowchart of a seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment, according to the present invention.

[0040] Figure 2 This is a schematic diagram showing the selection of input ground motion based on the horizontal response spectrum of the plant site design.

[0041] Figure 3 This is a schematic diagram showing the selection of input ground motion based on the vertical response spectrum of the plant site design.

[0042] Figure 4 This is a schematic diagram of a numerical analysis model for the nonlinear dynamic interaction between the site, foundation, and structure.

[0043] Figure 5 A flowchart for generating structural fragility curves.

[0044] In the picture:

[0045] LS1: First limit state, the boundary value between a structure that is basically intact and slightly damaged.

[0046] LS2: The second limit state, the boundary value between a structure in a state of slight damage and moderate damage.

[0047] LS3: The third limit state, the boundary value between moderate and severe damage states of a structure. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0049] The Chinese annotations for the English abbreviations used in this application are as follows:

[0050] IDA is an abbreviation for Incremental Dynamic Analysis.

[0051] SMA is an abbreviation for Seismic margin assessment.

[0052] SSI is an abbreviation for Soil-structure interaction.

[0053] IM is an abbreviation for Intensity Measures.

[0054] DM is an abbreviation for Damage Measures.

[0055] DM is the name of a software package developed by Komatitsch et al.

[0056] PEER is an abbreviation for Pacific Earthquake Engineering Research Center.

[0057] ABAQUS is the name of a general-purpose finite element analysis software developed by Dassault Systèmes in France.

[0058] LS is an abbreviation for Limit states.

[0059] HCLPF is an abbreviation for High confidence of low probability of failure.

[0060] The Davidenkov constitutive model is a mathematical model used to describe the nonlinear mechanical behavior of soil. It is mainly applied in geotechnical engineering, especially in earthquake engineering and soil dynamics analysis. This model reflects the strength decay and energy dissipation characteristics of soil under repeated loading through stress-strain relationship curves (such as hysteresis curves).

[0061] CDP is an abbreviation for Concrete Damage Plasticity. The CDP constitutive model is an elastoplastic damage model used to simulate the nonlinear mechanical behavior of brittle materials such as concrete, and is widely used in the finite element analysis of civil engineering structures.

[0062] Please see Figures 1 to 5This paper presents a seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin evaluation. The method determines ground motion and structural damage indices based on site conditions of the nuclear power plant site and the dynamic characteristics of both the pile-raft foundation and the nuclear island structure. A three-dimensional nonlinear dynamic interaction model of the non-bedrock site, pile-raft foundation, and nuclear island structure, designated as Model A, is constructed. The analysis conditions for Model A are determined and calculations are performed. Different limit states are defined based on the failure processes of both the pile-raft foundation and the nuclear island structure. Incremental dynamic curves for different limit states are plotted for different structural damage indices. A failure probability calculation algorithm is used to obtain vulnerability curves under different damage states. Finally, the seismic response safety of the nuclear island structure is assessed using these vulnerability curves and based on the seismic margin.

[0063] Model A refers to the three-dimensional nonlinear dynamic interaction model of non-bedrock site-pile raft foundation-nuclear island structure.

[0064] Preferably, the method may include the following steps:

[0065] Step 1: Determine the ground motion intensity index based on the site parameters and seismic zoning level of the nuclear power plant site area; and determine the structural damage index reflecting the structural bearing capacity and the integrity of the containment shielding function based on the structural characteristics of the nuclear island.

[0066] Step 2: Construct finite element models of the soil in the nuclear power plant site selection area, as well as finite element models of the pile-raft foundation and nuclear island structure. Set the contact surface parameters between the soil and the pile-raft foundation and nuclear island structure, and input triaxial ground motion at the bottom of the site to construct Model A.

[0067] Step 3: Adjust the amplitude of the ground motion intensity according to the requirements of the ground motion intensity index. Select several ground motion records and adjust their amplitudes respectively. Input the amplitude-adjusted ground motion records into model A to generate several sets of calculation conditions.

[0068] Step 4: Perform vulnerability analysis on the calculated working conditions to obtain vulnerability curves of the pile-raft foundation and the nuclear island structure under different damage states;

[0069] Step 5: Determine the seismic safety reserve factor using the vulnerability curve, further obtain the HCLPF value of the nuclear island structure, and assess the seismic safety of the nuclear island structure based on the HCLPF value.

[0070] The HCLPF value is one of the final results obtained from the SMA of a nuclear power plant, and it has two definitions: ① a capability value with a 95% confidence level on the vulnerability curve corresponding to a 5% failure probability; ② a capability value with a 1% failure probability on the average vulnerability curve.

[0071] Preferably, step one may include the following sub-steps:

[0072] Step A1: Analyze the site conditions of the nuclear power plant site selection area and determine the seismic intensity index;

[0073] Step A2: Select structural damage indicators based on the dynamic characteristics and key physical quantities of the structural response of both the pile-raft foundation and the nuclear island.

[0074] Step A3: Based on the seismic input requirements of the "Code for Seismic Design of Nuclear Power Plants" and with reference to the site design response spectrum of nuclear power plant SL-2 level, select several seismic ground motion records that meet the conditions from the PEER seismic database.

[0075] Preferably, step two may include the following sub-steps:

[0076] Step B1: Based on the geotechnical investigation report of the nuclear power plant site selection area, and according to the soil physical parameters at different borehole locations, the site is simplified and merged into a horizontally layered multi-layered soil mass. A finite element model of the site soil in the nuclear power plant site selection area is established using ABAQUS.

[0077] Step B2: Based on the design drawings of the pile-raft foundation and the nuclear island structure, establish the finite element model of the pile-raft foundation and the nuclear island structure;

[0078] Step B3: Model A is established by setting the contact surface parameters between the soil, the pile-raft foundation, and the nuclear island structure, and inputting triaxial ground motion at the bottom of the site.

[0079] Preferably, in step B1, when establishing the finite element model of the soil in the nuclear power plant site selection area, soil layers with similar depth and shear wave velocity in the site can be simplified and merged according to the soil mechanical parameters of different borehole locations, and the soil above the bedrock surface can be approximated as a horizontally layered multi-layered soil. The soil material of the site adopts a nonlinear constitutive model, and the Davidenkov constitutive model can be used to construct the finite element model. In step B2, when establishing the finite element model of the pile raft foundation and the nuclear island structure, the materials of both the pile raft foundation and the nuclear island structure can adopt a nonlinear constitutive model, and the concrete can be constructed using the CDP constitutive model.

[0080] Preferably, step three may include the following sub-steps:

[0081] Step C1: Based on the ground motion records and ground motion intensity index requirements, adjust the amplitude of the ground motion intensity to determine the upper and lower limits of amplitude adjustment and the amplitude adjustment interval for each ground motion.

[0082] Step C2: Amplitude modulation is performed on the several ground motion records selected in Step 3 and input into Model A in Step 2 to generate several sets of calculation conditions.

[0083] Preferably, step four may include the following sub-steps:

[0084] Step D1: Define different limit states based on the failure process of the pile-raft foundation and the nuclear island structure;

[0085] Step D2: Extract the calculation conditions of model A, and plot the incremental dynamic curves of the nuclear island structure for different structural damage indices.

[0086] Step D3: Using the natural logarithm of the seismic intensity index as the independent variable and the natural logarithm of the structural damage index as the dependent variable, establish a Cartesian coordinate system with the independent variable as the X-axis and the dependent variable as the Y-axis. Perform linear regression analysis on the data to obtain the probabilistic seismic demand model of the nuclear island structure, and obtain the vulnerability curves under different damage states based on the failure probability expression.

[0087] Probabilistic earthquake demand models are statistical models widely used in engineering structural design and earthquake hazard assessment. Based on seismic input and structural characteristics, they predict the response of buildings or structures under seismic loading. By considering factors such as seismic parameters, structural characteristics, and seismic site conditions, these models provide the probability of a building's or structure's response under different seismic intensities and assess the degree of structural damage.

[0088] The failure probability expression is as follows:

[0089] ;

[0090] In the formula:

[0091] P f Indicates the probability of failure;

[0092] α and β represent constants obtained from linear regression analysis;

[0093] IM stands for Seismic Intensity Index;

[0094] This represents the median value of the structure's seismic resistance.

[0095] β c The logarithmic standard deviation of the earthquake demand parameter;

[0096] β d The logarithmic standard deviation of the seismic resistance parameters of a structure;

[0097] Φ represents the standard normal distribution function.

[0098] Preferably, in step D1, the degree of structural damage can be classified based on the development degree of structural concrete damage factors, concrete strain change value, and peak displacement increase value, quantifying the damage state when the structure enters the elastic-plastic stage, and defining the limit state corresponding to different classification boundary values; in step D2, the calculation results of all working conditions of the model are extracted, and for different structural damage indicators, the peak value of the time history response of the nuclear island structure under different seismic input amplitudes is plotted to generate incremental dynamic curves.

[0099] Preferably, in step five, the earthquake safety reserve coefficient can be determined according to the following method:

[0100] SMR = PGA(T1) 50% / PGA (T 1)极限安全 ;

[0101] In the formula:

[0102] SMR stands for Seismic Safety Reserve Coefficient;

[0103] PGA(T1) 50% This indicates that after 50% of the ground motion input exceeds the design reference, the structural response reaches the ground motion intensity corresponding to the nuclear island structure failure standard.

[0104] PGA (T 1)极限安全 This indicates the ground motion intensity corresponding to the ultimate safe seismic action specified in nuclear power regulations.

[0105] The present invention also provides an apparatus for a seismic response assessment method for a nuclear island structure on a non-bedrock site based on seismic margin assessment, comprising a memory and a processor, wherein the memory is used to store a computer program; and the processor is used to execute the computer program and, when executing the computer program, implement the steps of the seismic response assessment method for a nuclear island structure on a non-bedrock site based on seismic margin assessment as described above.

[0106] The workflow and working principle of the present invention will be further illustrated below using a preferred embodiment of the present invention as an example:

[0107] A method for assessing the seismic response of a nuclear island structure in a non-bedrock site based on seismic margin evaluation, comprising the following steps:

[0108] Step 1: Select the ground motion index and structural damage index, and select the input ground motion. The specific method is as follows:

[0109] Based on the site category, non-bedrock soil thickness, soil shear wave velocity, and other site parameters of the nuclear power plant site area, as well as the seismic zoning level of the site location, the ground motion intensity index IM is determined (IM can typically be selected as peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), acceleration response spectrum value Sa, etc.). Based on the structural characteristics of the nuclear island, focusing on reflecting the structural bearing capacity and the integrity of the containment shielding function, the structural damage index DM is selected (DM can typically be selected as maximum inter-story drift angle, vertex displacement, concrete strain, steel reinforcement strain, concrete damage factor, etc.). Referring to the site design response spectrum of the ultimate safe ground motion of the nuclear power plant, ground motion records are selected in PEER based on the principle of similar response spectra as input ground motions for subsequent IDA, such as... Figure 2 , Figure 3 As shown, ensure that the selected ground motion meets the ground motion input requirements of the time history analysis method in the "Code for Seismic Design of Nuclear Power Plants".

[0110] Step 2: Establish a three-dimensional nonlinear dynamic interaction model of the non-bedrock site, pile-raft foundation, and nuclear island structure, such as... Figure 4 As shown, the specific method is as follows:

[0111] Based on the geotechnical investigation report of the plant site and the soil mechanics parameters at different borehole locations, soil layers with similar depths and shear wave velocities were simplified and merged. The soil above the bedrock surface was approximated as a horizontally layered multi-layered soil mass. A site model was established using the general-purpose finite element software ABAQUS. Based on the foundation and structural design drawings, a refined finite element model of the pile-raft foundation and superstructure was established (the structure includes materials such as concrete, ordinary steel reinforcement, prestressed steel reinforcement, and steel lining). Nonlinear constitutive models were adopted for both soil and structural materials, with the Davidenkov constitutive model used for soil, the CDP constitutive model used for concrete, and the bilinear constitutive model used for steel reinforcement. The contact between soil and structure was set, and triaxial ground motion was input at the bottom of the site to complete the establishment of a nonlinear dynamic interaction model of the non-bedrock site-pile-raft foundation-nuclear island structure.

[0112] Step 3: Determine the IDA working conditions for the three-dimensional nonlinear dynamic interaction model of the non-bedrock site-pile raft foundation-nuclear island structure and perform calculations. The specific method is as follows:

[0113] Based on the seismic ground motion records and intensity index requirements, modulate the intensity of the ground motion to determine the upper and lower limits of the amplitude modulation and the modulation interval for each ground motion in the IDA (for example, when the peak ground acceleration (PGA) is used as the intensity index requirement, the amplitude can be modulated from 0.1g to 2.0g, with each modulation increment being 0.1g or 0.2g). Based on the determined amplitude values ​​and the seismic waves selected in step 3, draw the IDA condition table, as shown in the table below:

[0114] IDA Operating Conditions Table

[0115]

[0116] Several selected ground motion records were amplitude-modulated and input into the three-dimensional nonlinear dynamic interaction model of non-bedrock site-pile raft foundation-nuclear island structure in step 2 to generate a set of calculation conditions. Numerical analysis was then carried out on all conditions.

[0117] Step 4: Vulnerability analysis is performed using the IDA results of the three-dimensional nonlinear dynamic interaction model of the non-bedrock site-pile-raft foundation-nuclear island structure. Vulnerability curves under different damage states of the structure are given, such as... Figure 5 As shown, the specific method is as follows:

[0118] Based on the development of structural concrete damage factors, changes in concrete strain, and increases in peak displacement, the degree of structural damage is classified, and the damage state when the structure enters the elastoplastic stage is quantified. Limit states corresponding to different classification thresholds are defined, such as: basically intact, slightly damaged, moderately damaged, and severely damaged. The calculation results for all working conditions of the model are extracted. For different structural damage indices, the peak values ​​of the time history response of the nuclear island structure under different seismic input amplitudes are plotted, generating incremental dynamic curves. For each structural damage index, using the natural logarithm of the seismic intensity index as the independent variable and the natural logarithm of the structural damage index as the dependent variable, a ln IM-ln DM rectangular coordinate system is established, and linear regression analysis is performed on the data to obtain the probabilistic seismic demand model of the nuclear island structure. Based on the failure probability expression, vulnerability curves under different damage states are obtained.

[0119] Step 5: Conduct a safety assessment of the nuclear island structure based on seismic margin. The specific method is as follows:

[0120] Based on the seismic vulnerability curve obtained in step 4, the seismic safety reserve factor is determined, and the seismic safety reserve factor (SMR) for nuclear power plant building systems is adopted:

[0121] SMR = PGA(T1) 50% / PGA (T 1)极限安全 ;

[0122] SMR evaluates the seismic safety performance of nuclear power plant systems, where PGA(T1) is used in the formula. 50% For a ground motion input exceeding the design reference by 50%, the structural response reaches the ground motion intensity corresponding to the above-mentioned nuclear island structural failure criteria, PGA (T 1)极限安全The ground motion intensity corresponding to the ultimate safe seismic action specified in the nuclear power code is used. The seismic vulnerability analysis (SFA) method in the seismic margin method is used to evaluate the seismic resistance of the nuclear island structure under the action of ground motion above the design reference. The high confidence low failure probability (HCLPF) value of the nuclear island structure is calculated by formula, which means that when the ground acceleration is at this level, there is a 95% confidence that the failure probability of the nuclear power plant SSC (systems and equipment and their associated structures) is less than 5%.

[0123] The High Confidence Low Failure Probability (HCLPF) value of the nuclear island structure is calculated using the following formula:

[0124] HCLPF=A m exp[-1.645(β R +β U )] ;

[0125] In the formula:

[0126] A m This represents the median ground acceleration.

[0127] β R The standard deviation represents random uncertainty;

[0128] β U The standard deviation represents cognitive uncertainty.

[0129] The working principle of this invention is as follows: First, it is necessary to select seismic motion index and structural damage index according to site conditions and structural dynamic characteristics; then, based on the site-foundation-structure nonlinear dynamic interaction analysis method, IDA considering the site-foundation-structure nonlinear dynamic interaction is carried out to establish the structural seismic vulnerability curve; finally, based on the seismic vulnerability curve, the seismic safety reserve coefficient is determined, and the result safety assessment method based on seismic margin is studied.

[0130] The embodiments described above are only used to illustrate the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The patent scope of the present invention should not be limited by these embodiments. That is, any equivalent changes or modifications made in accordance with the spirit disclosed in the present invention still fall within the patent scope of the present invention.

Claims

1. A method for assessing the seismic response of a nuclear island structure on a non-bedrock site based on seismic margin assessment, characterized in that, Based on the site conditions of the nuclear power plant site and the dynamic characteristics of the pile-raft foundation and nuclear island structures, seismic motion indicators and structural damage indicators are determined. A three-dimensional nonlinear dynamic interaction model of the non-bedrock site, pile-raft foundation, and nuclear island structure is constructed and referred to as Model A. The analysis conditions of Model A are determined and calculations are performed. Based on the failure process of the pile-raft foundation and nuclear island structures, different limit states are defined, and incremental dynamic curves for different limit states are plotted for different structural damage indicators. Through the failure probability calculation algorithm, vulnerability curves under different damage states are obtained. The seismic response safety assessment of the nuclear island structure is conducted using the vulnerability curves and based on the seismic margin.

2. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 1, characterized in that, The method includes the following steps: Step 1: Determine the ground motion intensity index based on the site parameters and seismic zoning level of the nuclear power plant site area; and determine the structural damage index reflecting the structural bearing capacity and the integrity of the containment shielding function based on the structural characteristics of the nuclear island. Step 2: Construct finite element models of the soil in the nuclear power plant site selection area, as well as finite element models of the pile-raft foundation and nuclear island structure. Set the contact surface parameters between the soil and the pile-raft foundation and nuclear island structure, and input triaxial ground motion at the bottom of the site to construct Model A. Step 3: Adjust the amplitude of the ground motion intensity according to the requirements of the ground motion intensity index. Select several ground motion records and adjust their amplitudes respectively. Input the amplitude-adjusted ground motion records into model A to generate several sets of calculation conditions. Step 4: Perform vulnerability analysis on the calculated working conditions to obtain vulnerability curves of the pile-raft foundation and the nuclear island structure under different damage states; Step 5: Determine the seismic safety reserve factor using the vulnerability curve, further obtain the HCLPF value of the nuclear island structure, and assess the seismic safety of the nuclear island structure based on the HCLPF value.

3. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 2, characterized in that, Step one includes the following sub-steps: Step A1: Analyze the site conditions of the nuclear power plant site selection area and determine the seismic intensity index; Step A2: Select structural damage indicators based on the dynamic characteristics and key physical quantities of the structural response of both the pile-raft foundation and the nuclear island. Step A3: Based on the seismic input requirements of the "Code for Seismic Design of Nuclear Power Plants" and with reference to the site design response spectrum of nuclear power plant SL-2 level, select several seismic ground motion records that meet the conditions from the PEER seismic database.

4. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 2, characterized in that, Step two includes the following sub-steps: Step B1: Based on the geotechnical investigation report of the nuclear power plant site selection area, and according to the soil physical parameters at different borehole locations, the site is simplified and merged into a horizontally layered multi-layered soil mass. A finite element model of the site soil in the nuclear power plant site selection area is established using ABAQUS. Step B2: Based on the design drawings of the pile-raft foundation and the nuclear island structure, establish the finite element model of the pile-raft foundation and the nuclear island structure; Step B3: Model A is established by setting the contact surface parameters between the soil, the pile-raft foundation, and the nuclear island structure, and inputting triaxial ground motion at the bottom of the site.

5. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 4, characterized in that, In step B1, when establishing the finite element model of the soil in the nuclear power plant site selection area, soil layers with similar depth and shear wave velocity in the site are simplified and merged according to the soil mechanical parameters of different borehole locations. The soil above the bedrock surface is approximated as a horizontally layered multi-layered soil. The soil material of the site adopts nonlinear constitutive model, and the finite element model is constructed using the Davidenkov constitutive model. In step B2, when establishing the finite element model of the pile raft foundation and the nuclear island structure, the materials of both the pile raft foundation and the nuclear island structure adopt nonlinear constitutive model, and the concrete uses the CDP constitutive model to construct the finite element model.

6. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 2, characterized in that, Step three includes the following sub-steps: Step C1: Based on the ground motion records and ground motion intensity index requirements, adjust the amplitude of the ground motion intensity to determine the upper and lower limits of amplitude adjustment and the amplitude adjustment interval for each ground motion. Step C2: Amplitude modulation is performed on the several ground motion records selected in Step 3 and input into Model A in Step 2 to generate several sets of calculation conditions.

7. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 2, characterized in that, Step four includes the following sub-steps: Step D1: Define different limit states based on the failure process of the pile-raft foundation and the nuclear island structure; Step D2: Extract the calculation conditions of model A, and plot the incremental dynamic curves of the nuclear island structure for different structural damage indices. Step D3: Using the natural logarithm of the seismic intensity index as the independent variable and the natural logarithm of the structural damage index as the dependent variable, establish a Cartesian coordinate system with the independent variable as the X-axis and the dependent variable as the Y-axis. Perform linear regression analysis on the data to obtain the probabilistic seismic demand model of the nuclear island structure, and obtain the vulnerability curves under different damage states based on the failure probability expression.

8. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 7, characterized in that, In step D1, the degree of structural damage is classified based on the development of structural concrete damage factors, concrete strain change value, and peak displacement increase value. The damage state when the structure enters the elastic-plastic stage is quantified, and the limit state corresponding to different classification boundary values ​​is defined. In step D2, the calculation results of all working conditions of the model are extracted. For different structural damage indicators, the peak value of the time history response of the nuclear island structure under different seismic input amplitudes is plotted, and incremental dynamic curves are generated.

9. The seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment according to claim 2, characterized in that, In step five, the earthquake safety reserve factor is determined as follows: SMR=PGA(T1) 50% / PGA (T 1)极限安全 ; In the formula: SMR stands for Seismic Safety Reserve Coefficient; PGA(T1) 50% This indicates that after 50% of the ground motion input exceeds the design reference, the structural response reaches the ground motion intensity corresponding to the nuclear island structure failure standard. PGA (T 1)极限安全 This indicates the ground motion intensity corresponding to the ultimate safe seismic action specified in nuclear power regulations.

10. An apparatus for assessing the seismic response of a nuclear island structure in a non-bedrock site based on seismic margin evaluation, comprising a memory and a processor, characterized in that, The memory is used to store a computer program; the processor is used to execute the computer program and, when executing the computer program, implement the steps of the seismic response assessment method for nuclear island structures in non-bedrock sites based on seismic margin assessment as described in any one of claims 1 to 9.

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