Improved seismic isolation design method for structure

Abstract

According to an embodiment of the present invention, an improved seismic isolation design method utilizing nonlinear time-history analysis based on vertical stiffness linked to horizontal displacement comprises a preliminary design stage and an analysis and review stage, wherein, in the analysis and review stage, vertical stiffness is calculated according to Equation 1 during nonlinear time-history analysis of a seismic isolation device–structure system with respect to horizontal and vertical vibrations, by considering a vertical load-resisting cross-sectional area that decreases according to horizontal displacement of a seismic isolation device, wherein, in Equation 1, Kv denotes vertical stiffness, Ec denotes a composite elastic modulus of rubber, A0 denotes the total cross-sectional area, nr denotes the number of rubber layers, tr denotes the thickness of one rubber layer, and Tr denotes the total thickness of the rubber layers.

Description

Improved seismic isolation design method for structures

[0001] The present invention relates to an improved seismic isolation design method for a structure, and more specifically, to an improved seismic isolation design method for a structure utilizing nonlinear time history analysis that utilizes vertical stiffness coupled to horizontal displacement.

[0002] Generally, to determine seismic design for structures, such as wall thickness during an earthquake, computational structural analysis (hereinafter referred to as 'nonlinear time history analysis') is performed to calculate the displacement and load of the structure, and seismic isolation design is carried out by installing seismic isolation devices1) between the structure and the ground to reduce the seismic load applied to the superstructure.

[0003] In nonlinear time history analysis, to calculate the accurate vertical load response of the superstructure to external forces (seismic loads), the accurate vertical stiffness of the seismic isolation device must be input, and the vertical stiffness of the seismic isolation device is influenced by the cross-sectional area resisting the vertical load.

[0004] As shown in Fig. 1, the general seismic isolation design method according to the Korean Building Code - Structural (hereinafter KBC2016), which was newly revised and published in 2016 (notified by the Ministry of Land, Infrastructure and Transport), calculates the vertical stiffness of the seismic isolation device as a constant vertical stiffness by considering the total cross-sectional area (A0) according to Equation 1 in nonlinear time history analysis. However, as shown in Fig. 2, in reality, the vertical stiffness also changes because the cross-sectional area of ​​the vertical resistance of the seismic isolation device changes according to the horizontal displacement.

[0005]

[0006] Equation 1 :

[0007] Here, K v is vertical stiffness, E c is the composite elastic modulus of rubber, A 0 is the total cross-sectional area, n r The number of rubber layers, t r The thickness of one layer of silver rubber, T rrepresents the total thickness of the rubber layer.

[0008] Figure 2 is a diagram illustrating the vertical resistance cross-sectional area of ​​a rubber-steel plate seismic isolation device.

[0009] A method is applied to calculate the average horizontal displacement by averaging the absolute horizontal displacements of the seismic isolation device over time, and to determine the corresponding vertical resistance cross-sectional area and vertical stiffness.

[0010] Among seismic isolation devices, the rubber-steel plate laminated seismic isolation device is composed of a structure in which rubber and steel plates are alternately laminated, as shown in (a) of Fig. 2.

[0011] As shown in FIG. 2(b), when a vertical load is applied, the steel plate restrains the deformation of the rubber, so the vertical deformation and change in cross-sectional area are small.

[0012] In contrast, as shown in (c) of Fig. 2, under horizontal loads, the rubber is not restrained by the steel plate, causing large horizontal displacement, and as a result, the cross-sectional area resisting vertical loads is significantly reduced.

[0013] Therefore, in order to achieve seismic isolation design that accurately reflects the structural response, a procedure must be presented in the seismic isolation design process that incorporates the vertical stiffness calculated using the cross-sectional area (A′) changed (reduced) according to horizontal displacement into the nonlinear time history analysis.

[0014] The present invention has been devised to solve these problems, and the objective of the present invention is to provide an improved seismic isolation design method for a structure that can achieve a seismic isolation design reflecting the accurate response of the structure by considering the vertical stiffness calculated with the cross-sectional area (A′) that has changed (decreased) according to horizontal displacement in the seismic isolation design procedure and reflecting it in a non-linear time history analysis.

[0015] An improved seismic isolation design method utilizing a nonlinear time history analysis of vertical stiffness linked to horizontal displacement according to an embodiment of the present invention includes a preliminary design stage and an analysis and review stage, wherein the analysis and review stage calculates vertical stiffness by Equation 1 by considering the vertical load resistance cross-sectional area that decreases according to the horizontal displacement of the seismic isolation device during a nonlinear time history analysis of a seismic isolation device-structure system for horizontal and vertical vibrations.

[0016] Equation 1 :

[0017] Here, K v is vertical stiffness, E c is the composite elastic modulus of rubber, A 0 is the total cross-sectional area, n r The number of rubber layers, t r The thickness of one layer of silver rubber, T r It is characterized by representing the total thickness of the rubber layer.

[0018] The step of calculating the vertical stiffness includes calculating the average horizontal displacement by averaging the absolute horizontal displacements of the seismic isolation device to reflect the horizontal shear strain of the seismic isolation device based on the horizontal acceleration-time history of the seismic isolation device changing over time, and calculating the vertical resistance cross-sectional area and vertical stiffness corresponding to the average horizontal displacement.

[0019] The step of calculating the average horizontal displacement above uses the average value of the root-sum-squares displacement for the two horizontal directions when the seismic load is applied in two horizontal directions, and

[0020] The step of calculating the vertical stiffness includes a step of repeating a procedure to compare the assumed value of the vertical resistance cross-sectional area related to the horizontal displacement with the result value obtained from the nonlinear time history analysis in order to review the validity of the average horizontal displacement used in calculating the vertical resistance cross-sectional area.

[0021] The step of calculating the vertical stiffness comprises: a step of assuming the vertical resistance cross-sectional area; a step of calculating the average horizontal displacement result and the vertical resistance cross-sectional area result corresponding to the average horizontal displacement result by performing the nonlinear time history analysis; a step of comparing the assumed vertical resistance cross-sectional area with the vertical resistance cross-sectional area result calculated by performing the nonlinear time history analysis; and if the assumed vertical resistance cross-sectional area and the vertical resistance cross-sectional area result calculated by performing the nonlinear time history analysis exceed an appropriate error range, repeating the step of assuming the vertical resistance cross-sectional area and the step of comparing.

[0022] The present invention is a seismic isolation structure analysis method that can satisfy the requirement of “consideration of the correlation between horizontal-vertical load-displacement relationships” as required in Section 7.2.3 of the “Report on Technical Considerations for Seismic Isolation Application in Nuclear Power Plant Facilities” published by the US NRC, a benchmarking organization for the establishment of licensing regulations and guidelines by domestic regulatory agencies. This can increase the licensing feasibility of the domestic nuclear industry and the actual applicability thereof.

[0023] Since the load and behavior of seismic isolation devices can vary depending on their placement on the upper structure or under the equipment, they must be modeled as a structure-seismic isolation device system rather than as individual seismic isolation devices in detail, which is very complex. However, if the method according to the present invention is applied, a simple model can be utilized without the need to model multiple seismic isolation devices in detail, thereby reducing analysis time and cost.

[0024] The proposed methodology of the present invention includes a process of comparing and verifying assumptions related to vertical deformation with the results, thereby increasing the reliability of the final seismic isolation design results for the structure-seismic isolation device system.

[0025] Figure 1 is a flowchart showing the design procedure for a seismic isolation structure according to the KBC 2016 standard, and

[0026] Figure 2 is a figure showing the structure of a rubber-folded sheet metal laminated seismic isolation device and the vertical resistance cross-sectional area during vertical and horizontal deformation, and

[0027] FIG. 3 is a flowchart illustrating an improved seismic isolation design method utilizing a nonlinear time history analysis of horizontal displacement-linked vertical stiffness according to an embodiment of the present invention, and

[0028] Figure 4 is a flowchart illustrating the method for calculating vertical stiffness coupled to horizontal displacement and nonlinear time history analysis of Figure 3.

[0029] The present invention will be described in more detail below with reference to the drawings. The drawings presented below are provided as examples to ensure that the concept of the present invention is sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms. Furthermore, throughout the specification, the same reference numerals indicate the same components. It should be noted that the same components in the drawings are indicated by the same reference numerals wherever possible. Additionally, unless otherwise defined, technical and scientific terms used have the meaning commonly understood by those skilled in the art to which this invention pertains, and descriptions of known functions and configurations that could unnecessarily obscure the essence of the present invention are omitted in the following description and the accompanying drawings.

[0030] Large structures, such as nuclear power plants, are designed with seismic isolation to reduce damage caused by earthquakes. Seismic isolation is a method of mitigating damage and controlling structural response by separating the structure from the ground; it involves dispersing and reducing the horizontal inertial seismic forces transmitted to the substructure by separating the upper structure from the lower structure. In other words, seismic isolation refers to a design that separates the lower and upper structures by placing multiple seismic isolation devices between them. This involves devising measures to reduce the impact of seismic loads by increasing the structure's natural period or damping, significantly reducing the response acceleration instead of increasing the response displacement to decrease the magnitude of seismic forces, and ensuring serviceability by controlling any excessive displacements that occur within a ductile range using appropriate control devices.

[0031] Now, with reference to FIGS. 3 and 4, an improved seismic isolation design method utilizing a nonlinear time history analysis of horizontal displacement-linked vertical stiffness according to one embodiment of the present invention will be described in detail.

[0032] FIG. 3 is a flowchart illustrating an improved seismic isolation design method utilizing a nonlinear time history analysis of horizontal displacement-linked vertical stiffness according to an embodiment of the present invention, and FIG. 4 is a flowchart illustrating the method of calculating horizontal displacement-linked vertical stiffness and nonlinear time history analysis of FIG. 3.

[0033] As illustrated in FIG. 3, an improved seismic isolation design method utilizing a nonlinear time history analysis of horizontal displacement-linked vertical stiffness according to one embodiment of the present invention can be broadly divided into a preliminary design stage and an analysis and review stage.

[0034] In the preliminary design phase, the cross-sectional assumptions of the superstructure, seismic isolation system, and substructure of the seismic isolation structure are made using the ASCE 7 design method.

[0035] ASCE stands for American Society of Civil Engineers, and the title of ASCE 7 is "Minimum Design Loads for buildings and other structures." It concerns minimum design loads for structures and other structures and is a guide on the definitions of loads used in architecture and civil engineering and their combinations.

[0036] The design standards for seismic isolation structures included in KBC2016 are similar to the U.S. ASCE 7. However,

[0037] ASCE 7 allows elastic analysis that does not include the nonlinear behavior of the isolation device in the analysis model when determining the seismic performance of seismic isolation structures. On the other hand, KBC 2016 differs in that it requires establishing an analysis model capable of directly implementing the nonlinear behavior of the isolation device and verifying whether the seismic response obtained through nonlinear time history analysis using seismic waves satisfies the allowable criteria.

[0038] In the analysis and review stage, the seismic response is obtained through an analysis model that considers the nonlinearity of the seismic isolation device, compared with the values ​​assumed in the preliminary design stage, and the suitability of the assumed cross-section is reviewed.

[0039] More specifically, the preliminary design phase includes the design requirements of KBC2016 that must be verified at each design stage, and determines the structural shape and weight in accordance with the basic design requirements of 0306.12.21 (S10), and the basic design variables, wind load, and seismic load (S DS, S D1, S MS, S MN Calculate ) (S20), and damping coefficient (B Dy , B M Assuming ) (S30), target vibration period (T Dy , T M Assuming ) (S40), the effective stiffness (K) of the seismic isolation device Dy , K M) is calculated (S50). The effective stiffness (K) of the calculated seismic isolation device Dy , K M A seismic isolation layer is configured and a seismic isolation device is placed according to ) (S60).

[0040] Subsequently, in accordance with the seismic isolation system requirements of 0306.12.21, the design displacement (M) of a seismic isolation system including a structure and a seismic isolation device Dy , M M ) checks whether it satisfies 0306.12.3.6 minimum lateral displacement (S70).

[0041] At this time, the design displacement (M of the seismic isolation system) Dy , M M If ) does not satisfy 0306.12.3.6 minimum lateral displacement (NO), target isolation period (T Dy , T M Step (S40) assuming ) and the effective stiffness (K) of the seismic isolation device Dy , K M The step of calculating ) (S50) and the step of configuring the seismic isolation layer and placing the seismic isolation device accordingly (S60) are repeated.

[0042] Design displacement of the seismic isolation system (M Dy , M M If ) satisfies 0306.12.3.6 Minimum Lateral Displacement (YES), the upper and lower shear force (V) of the seismic isolation system Dy , V M ) checks whether the minimum seismic force 0306.12.3.7 is satisfied (S80).

[0043] At this time, the upper and lower shear force (V) of the seismic isolation system Dy , V M If ) does not satisfy the minimum seismic force of 0306.12.3.7, the target seismic isolation period (T Dy , T M Return to the step (S40) assuming ) and the target phase period (T Dy , T M Re-assuming ), the effective stiffness (K) of the seismic isolation device Dy , K MA step of calculating ) (S50), a step of configuring a seismic isolation layer and arranging a seismic isolation device accordingly (S60), and the design displacement (M) of the seismic isolation system Dy , M M A step (S70) for examining whether ) satisfies the minimum lateral displacement specified in 0306.12.3.6, and the upper and lower shear force (V) of the seismic isolation system Dy , V M ) sequentially proceeds with the step (S80) of reviewing whether the minimum seismic force satisfies 0306.12.3.7.

[0044] Upper and lower shear force (V) of the seismic isolation system Dy , V M If the minimum seismic force specified in 0306.12.3.7 is satisfied, the upper and lower structures of the seismic isolation system can be designed and the load-bearing capacity reviewed (S90).

[0045] The analysis and review stage establishes an analysis model of the seismic isolation structure and performs support plate scaling (S110), calculates the vertical stiffness coupled with horizontal displacement and analyzes the nonlinear time history (S120), and verifies whether the effective period, effective design displacement, and effective damping coefficient are valid (S130).

[0046] At this time, if not the effective period, effective design displacement, or effective damping factor, the damping factor of the preliminary design stage (B Dy , B M You can return to the step (S30) assuming ).

[0047] If the effective period, effective design displacement, and effective damping coefficient are present, the design seismic force can be calculated (S140), and the design of the upper and lower structures of the seismic isolation system can be reviewed.

[0048] When reviewing the upper and lower structural design of the seismic isolation system, if the upper and lower structural design of the seismic isolation system does not satisfy the calculated design seismic force (NO), the process can be re-examined by returning to the preliminary design stage of the seismic isolation system upper and lower structural design and load-bearing capacity review stage (S90).

[0049] When reviewing the upper and lower structural design of the seismic isolation system, if the upper and lower structural design of the seismic isolation system satisfies the calculated design seismic force (YES), the design is completed through the experiment and result review stage of the seismic isolation device (S150) (S160).

[0050] The reason for undergoing the experiment and results review stage (S150) of the seismic isolation device is that, since the seismic performance of a seismic isolation structure depends on the structural characteristics of the seismic isolation device, the performance of the seismic isolation device used to establish the analysis model must be verified through prototype testing, and the performance of all seismic isolation devices to be installed in the structure must be proven through product testing.

[0051] Even if a problem occurs (NO) during the experiment and results review stage (S150) of the seismic isolation device, the damping coefficient (B) of the preliminary design stage Dy , B M You can return to the step (S30) assuming ).

[0052] In the improved seismic isolation design method for a structure according to the present invention, the damping coefficient (B) in the preliminary design stage Dy , B M Assuming ) (S30), target vibration period (T Dy , T M The effective period of the analysis and review step (S40) and the design displacement damping coefficient verification step (S130) are repeated until the allowable value is satisfied, thereby determining the seismic response of the design earthquake and the maximum earthquake.

[0053] As with ASCE 7, the improved seismic isolation design method of the present invention includes various assumptions, so a design formula may be proposed to conservatively evaluate the seismic response.

[0054] Now, with reference to FIG. 4, a method for calculating horizontal displacement-coupled vertical stiffness and analyzing nonlinear time history in the improved seismic isolation design method of the structure of the present invention will be described in detail.

[0055] KBC2016 mandates that nonlinear time history analysis be performed to evaluate the response of seismic isolation structures to the corresponding seismic intensity.

[0056] The design standards for seismic isolation structures are included in Chapter 0306.12 of KBC2016 and consist of a total of five sections, including general matters, design requirements, analysis procedures, design review, and seismic isolation device testing.

[0057] Among these, the general provisions of Section 0306.12.1 specify that all seismic isolation structures and their components must be designed and constructed in accordance with Chapter 0306.12, and that the analysis of seismic isolation structures must consider changes in the material properties of the isolation devices that will occur over the life cycle of the structure. Sections 0306.12.2 through 0306.12.5 contain content related to the design and construction of seismic isolation structures.

[0058] As illustrated in FIG. 4, an improved seismic isolation design method for a structure according to one embodiment of the present invention is characterized by calculating vertical stiffness using the vertical load resistance cross-sectional area that is reduced according to the horizontal deformation of the seismic isolation device.

[0059] As illustrated in FIG. 4, an improved seismic isolation design method for a structure according to one embodiment of the present invention uses the vertical stiffness (K) of the seismic isolation device with respect to the vertical resistance cross-sectional area (A) of the seismic isolation device. vi ) is calculated (S121), a nonlinear time history analysis is performed, and the average horizontal displacement (Davg) is calculated (S122). The vertical storage cross-sectional area (A') corresponding to the average horizontal displacement (Davg) is calculated, and the vertical stiffness (K) corresponding to the average horizontal displacement (Davg) is calculated. vi+1 By recalculating ) the vertical stiffness (K) of the seismic isolation device with respect to the vertical resistance cross-sectional area (A) vi ) and the vertical stiffness (K) corresponding to the average horizontal displacement (Davg) vi+1 It is determined whether the difference of ) is within the allowable value, that is, the allowable appropriate error range (S124).

[0060] Vertical stiffness (K) of the seismic isolation device with respect to the vertical resistance cross-sectional area (A) vi) and the vertical stiffness (K) corresponding to the average horizontal displacement (Davg) vi+1 If the difference is not within the appropriate error range, the vertical stiffness (K) of the seismic isolation device relative to the vertical resistance cross-sectional area (A) of the seismic isolation device vi Return to the step of calculating ) (S121),

[0061] In this way, the vertical stiffness (K) of the seismic isolation device with respect to the vertical resistance cross-sectional area (A) vi ) and the vertical stiffness (K) corresponding to the average horizontal displacement (Davg) vi+1 If the difference is not within the appropriate error range, the vertical stiffness (K) of the seismic isolation device relative to the vertical resistance cross-sectional area (A) of the seismic isolation device vi By returning to the step (S121) of calculating ) and repeating steps S121 through S124, the validity of the average horizontal displacement used to calculate the vertical resistance cross-sectional area can be reviewed.

[0062] In other words, the validity of the average horizontal displacement used to calculate the vertical resistance cross-sectional area can be reviewed by repeating the procedure of comparing the assumed value of the vertical resistance cross-sectional area related to horizontal displacement with the cross-sectional area based on the analysis results.

[0063] Vertical stiffness (K) of the seismic isolation device with respect to the average vertical resistance cross-sectional area (A) vi ) and the vertical stiffness (K) corresponding to the average horizontal displacement (Davg) vi+1 If the difference is within an appropriate error range, the process can proceed to the step (S130) of verifying the effective period, effective design displacement, and damping coefficient.

[0064] In an improved seismic isolation design method for a structure according to one embodiment of the present invention, when performing a nonlinear time history analysis of a seismic isolation device-structure system for horizontal and vertical vibrations, the vertical stiffness is calculated using Equation 1 by considering the vertical load resistance cross-sectional area that decreases with horizontal displacement in order to calculate realistic vertical deformation and load, thereby allowing for the calculation of realistic vertical characteristics of the seismic isolation device.

[0065] A method can be applied to calculate the average horizontal displacement by averaging the absolute horizontal displacements of the seismic isolation device over time through the step (S122) of performing a nonlinear time history analysis and calculating the average horizontal displacement (Davg), and to calculate the corresponding vertical resistance cross-sectional area and vertical stiffness.

[0066]

[0067] The present invention is not limited to the embodiments described above, and its scope of application is diverse. Furthermore, it is understood that various modifications are possible without departing from the essence of the invention as claimed in the claims.

Claims

1. In an improved seismic isolation design method utilizing nonlinear time history analysis of horizontal displacement-coupled vertical stiffness, The preliminary design phase and, It includes interpretation and review stages, The above analysis and review step calculates the vertical stiffness by Equation 1 by considering the vertical load resistance cross-sectional area that decreases according to the horizontal displacement of the seismic isolation device during the nonlinear time history analysis of the seismic isolation device-structure system for horizontal and vertical vibrations. Equation 1 : Here, K v is vertical stiffness, E c is the composite elastic modulus of rubber, A 0 is the total cross-sectional area, n r The number of rubber layers, t r The thickness of one layer of silver rubber, T r A seismic isolation design method representing the total thickness of the rubber layer.

2. In Paragraph 1, A seismic isolation design method comprising the step of calculating the vertical stiffness above, which includes the step of calculating the average horizontal displacement by averaging the absolute horizontal displacements of the seismic isolation device to reflect the horizontal shear strain of the seismic isolation device by the horizontal acceleration-time history of the seismic isolation device changing over time, and the step of calculating the vertical resistance cross-sectional area and vertical stiffness corresponding to the average horizontal displacement.

3. In Paragraph 2, The step of calculating the above average horizontal displacement is a seismic isolation design method that uses the average value of the root-square-squares displacement for the two horizontal directions when a seismic load is applied in two horizontal directions.

4. In Paragraph 2, The step of calculating the vertical stiffness is a seismic isolation design method that repeats the procedure of comparing the assumed value of the vertical resistance cross-sectional area related to the horizontal displacement with the result value obtained by the nonlinear time history analysis in order to verify the validity of the average horizontal displacement used in calculating the vertical resistance cross-sectional area.

5. In Paragraph 4, The step of calculating the above vertical stiffness The step of assuming the above vertical resistance cross-sectional area, and A step of calculating an average horizontal displacement result and a vertical resistance cross-sectional area result corresponding to the average horizontal displacement result by performing the above nonlinear time history analysis, and A step of comparing the assumed vertical resistance cross-sectional area with the result value of the vertical resistance cross-sectional area calculated by performing the above nonlinear time history analysis, and A seismic isolation design method that repeats the step of assuming the vertical resistance cross-sectional area or the step of comparing the result of performing the above nonlinear time history analysis when the above assumed vertical resistance cross-sectional area and the result of the above calculated vertical resistance cross-sectional area exceed an appropriate error range.

6. In Paragraph 5, A seismic isolation design method comprising the above preliminary design stage, a step of determining the structural shape and weight of the seismic isolation device-structure system, a step of calculating basic design variables, wind load and seismic load, a step of assuming damping coefficients and target seismic isolation periods, a step of calculating the effective stiffness of the seismic isolation device, a step of configuring the seismic isolation layer and arranging the seismic isolation device, a step of reviewing the design displacement of the seismic isolation device-structure system, and a step of reviewing the upper and lower shear forces of the seismic isolation device-structure system.

7. In Paragraph 6, The above analysis and review step is a seismic isolation design method comprising, if the assumed vertical resistance cross-sectional area and the result of the vertical resistance cross-sectional area calculated by performing the above nonlinear time history analysis are within an appropriate error range, a step of verifying the effective period, design displacement, and damping coefficient, a step of calculating the design seismic force, a step of reviewing the upper and lower structural design of the seismic isolation system, and a step of testing the seismic isolation device and reviewing the results.

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