A design method for base isolation technology

Abstract

The present invention belongs to a design method of foundation isolation technology in the field of building structure engineering. The present invention is applicable to a structure whose height before isolation is less than 40m; and the structure before isolation is mainly shear deformation and the mass and stiffness are evenly distributed along the height. The design method of the present invention is a simplified method based on the design response spectrum curve, and the design response spectrum curve includes a seismic influence coefficient curve and a displacement response spectrum curve. The present invention provides a method for calculating the shock absorption coefficient and the displacement response through the changes of the equivalent stiffness and the equivalent damping ratio of the structure before and after isolation on the design response spectrum curve. It simplifies the existing design method and avoids the cumbersome calculation of the time-history analysis method.

Description

Technical Field

[0001] The invention belongs to the field of building structure engineering, and in particular relates to a simplified design method of base seismic isolation technology. Background Art

[0002] At present, the design of building structures using base isolation technology is mainly based on the Code for Seismic Design of Buildings (GB 50011-2010) (hereinafter referred to as the Code for Seismic Design of Buildings). The Code for Seismic Design of Buildings stipulates that, under normal circumstances, the time history analysis method should be used for calculation and design. The Code for Seismic Design of Buildings stipulates that the time history analysis method should be used for complex or conventional seismic isolation buildings. The calculation is relatively cumbersome and requires multiple trial calculations, which is not conducive to the mastery of designers and the promotion of seismic isolation technology.

[0003] It is now proposed that for structures with a height of less than 40m, which are mainly shear deformed and have uniform mass and stiffness distribution along the height, as well as base-isolated structures that are approximately single-mass systems, a simplified design method can be used to avoid the tedious calculations of the time-history analysis method. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a design method for base isolation technology, which is completely different from the existing time-history analysis method and provides a simplified design method for base isolation technology with simple calculation and clear theoretical principles.

[0005] The technical solution of the present invention is applicable to the case where the height of the pre-isolation structure is less than 40m; and the pre-isolation structure is mainly shear deformation, and the mass and stiffness are evenly distributed along the height. The design steps are:

[0006] Step 1: Determine the seismic influence coefficient curve of the structure before isolation;

[0007] Step 2: Determine the horizontal equivalent stiffness and equivalent viscous damping ratio of the structure after seismic isolation; use the equivalent viscous damping ratio to correct

[0008] And determine the seismic influence coefficient curve of the seismic isolation structure and the displacement response spectrum curve of the seismic isolation structure;

[0009] Step 3: Determine the natural period T1 of the structure before seismic isolation; calculate the natural period T2 of the structure after seismic isolation based on the horizontal equivalent stiffness of the structure after seismic isolation;

[0010] Step 4: Determine the first seismic influence coefficient A1 on the seismic influence coefficient curve of the structure before seismic isolation according to the natural period T1 of the structure before seismic isolation; determine the second seismic influence coefficient A2 on the seismic influence coefficient curve of the structure after seismic isolation according to the natural period T2 of the structure after seismic isolation; divide the second seismic influence coefficient A2 by the first seismic influence coefficient A1 to obtain the shock absorption coefficient;

[0011] Step 5: Find the displacement response D2 of the post-isolation structure corresponding to the natural period T2 of the post-isolation structure on the displacement response spectrum curve of the post-isolation structure.

[0012] Compared with the existing design method, the present invention has the following advantages and beneficial effects:

[0013] (1) The present invention proposes a simplified design method for base isolation technology, which can directly determine the second earthquake influence coefficient A2 and the displacement response D2 of the structure after isolation, avoiding the cumbersome calculation method of time history analysis specified in the "Anti-seismic Code".

[0014] (2) The second seismic influence coefficient A2 and displacement response D2 of the seismic isolation structure are calculated by determining the horizontal equivalent stiffness and equivalent viscous damping ratio of the seismic isolation structure. The calculation method is simple and has sufficient theoretical basis. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the seismic influence coefficient curve of the structure before and after isolation.

[0016] Figure 2 It is the displacement response spectrum curve of the structure before and after isolation. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with the accompanying drawings and the Anti-corrosion Regulations, but the implementation method of the present invention is not limited thereto.

[0018] Step 1: Determine the seismic influence coefficient curve of the structure before isolation

[0019] The design response spectrum is the basis of the simplified seismic isolation design method. The "Anti-seismic Code" stipulates that the seismic influence coefficient curve of the building structure should be calculated based on the earthquake intensity, site characteristics and structural damping ratio.

[0020] The earthquake influence coefficient curve is related to the following factors: 1) Intensity. The higher the design intensity, the greater the earthquake influence coefficient. 2) Damping ratio. The greater the damping, the smaller the earthquake influence coefficient. 3) Site conditions. The thicker the site cover and the softer the soil, the longer the ground acceleration response spectrum platform. 4) Design earthquake grouping. Design earthquake grouping mainly reflects the impact of the distance of the earthquake source, and the degree of influence is not as great as the site category.

[0021] The seismic influence coefficient curve is a pseudo-acceleration response spectrum. Considering that the displacement response spectrum curve is very useful for studying the displacement response of the isolation layer, the displacement response spectrum will be introduced according to the following relationship.

[0022]

[0023] A- is the acceleration response of a single degree of freedom system with a natural period of T under the action of earthquake ground motion;

[0024] D- is the displacement response of a single degree of freedom system with a natural period of T under the action of earthquake ground motion.

[0025] Step 2: Determine the horizontal equivalent stiffness and equivalent viscous damping ratio of the seismic isolation structure; use the equivalent viscous damping ratio to correct and determine the seismic influence coefficient curve 3 of the seismic isolation structure and the displacement response spectrum curve 4 of the seismic isolation structure.

[0026] 2.1 Determine the horizontal equivalent stiffness and equivalent viscous damping ratio of the structure after seismic isolation

[0027] 2.1.1 Based on the conventional calculation assumptions of existing seismic isolation theory

[0028] 1) The seismically isolated structure basically moves in translation during an earthquake, and the seismically isolated structural system is approximately a single-mass point system;

[0029] 2) The horizontal equivalent stiffness and equivalent viscous damping ratio of the isolation layer are used as the stiffness and damping of the entire isolation structure;

[0030] 2.1.2 Calculation method based on the Anti-corrosion Code

[0031] According to Article 12.2.4 of the Anti-seismic Code, the calculation formulas for the equivalent horizontal stiffness and equivalent viscous damping ratio of the seismic isolation layer are as follows:

[0032] K h =∑K j

[0033] ζ eq =∑K j ζ j K h

[0034] Where:

[0035] ζ eq -Equivalent viscous damping ratio of the isolation layer;

[0036] K h -Horizontal equivalent stiffness of the isolation layer;

[0037] ζ j -j The equivalent viscous damping ratio of the seismic isolation bearing is determined by test. When setting the damping device, the corresponding damping ratio should be included;

[0038] K j -j horizontal stiffness of the bearing determined by experiment.

[0039] The Anti-seismic Code has other provisions. For the calculation of horizontal seismic absorption coefficient, the horizontal equivalent stiffness and equivalent viscous damping ratio at 100% shear deformation should be taken. For verification of rare earthquakes, the horizontal equivalent stiffness and equivalent viscous damping ratio at 250% shear deformation should be adopted. When the diameter of the seismic isolation bearing is large, the horizontal equivalent stiffness and equivalent viscous damping ratio at 100% shear deformation can be adopted.

[0040] 2.2 Use the equivalent viscous damping ratio to correct and determine the seismic influence coefficient curve 3 of the seismic isolation structure and the displacement response spectrum curve 4 of the seismic isolation structure.

[0041] The Anti-seismic Code stipulates that the damping ratio of the seismic influence coefficient curve is 0.05. When the damping ratio of the seismic isolation structure increases, the damping adjustment coefficient and shape parameters of the seismic influence coefficient curve and the displacement response spectrum curve should comply with the following regulations.

[0042] 1) The attenuation index of the descending section of the curve should be determined according to the following formula:

[0043]

[0044] In the formula: γ---attenuation index of the descending section of the curve;

[0045] ζ---damping ratio;

[0046] 2) The downward slope adjustment coefficient of the straight-line downward section should be determined according to the following formula:

[0047]

[0048] Where: η1---the downward slope adjustment coefficient of the straight line downward segment, which is taken as 0 when it is less than 0.

[0049] 3) The damping adjustment coefficient should be determined according to the following formula:

[0050]

[0051] In the formula: η2---damping adjustment coefficient, when it is less than 0.55, it should be taken as 0.55.

[0052] Step 3: Determine the natural period T1 of the pre-isolation structure before isolation; calculate the natural period T2 of the post-isolation structure after isolation according to the horizontal equivalent stiffness of the post-isolation structure, and the calculation formula is as follows:

[0053]

[0054] Where:

[0055] M-total mass of the structure after seismic isolation;

[0056] K h -Horizontal equivalent stiffness of the isolation layer;

[0057] Step 4: If Figure 1 As shown, according to the natural period T1 of the structure before isolation, the seismic influence coefficient of the structure before isolation

[0058] Curve 1 determines the first earthquake influence coefficient A1; according to the natural period T2 of the seismic isolation structure, the seismic isolation structure

[0059] The second earthquake influence coefficient A2 is determined on the structural earthquake influence coefficient curve 3; the second earthquake influence coefficient A2 is divided by the first earthquake

[0060] The influence coefficient A1 gives the damping coefficient;

[0061] Step 5: If Figure 2 As shown, the inherent displacement response spectrum curve 4 of the seismic isolation structure is found.

[0062] The displacement response of the isolated structure corresponding to period T2 is D2. As a comparison, Figure 2 The displacement response spectrum of the structure before isolation is retained

[0063] Curve 2 shows the displacement response D1 of the structure after isolation corresponding to the natural period T1 of the structure before isolation.

[0064] The above is a detailed introduction to the implementation scheme of the present invention. For those skilled in the art, according to the idea of ​​the embodiment of the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation of the present invention, and any changes made according to the design idea of ​​the present invention are within the protection scope of the present invention.

Claims

1. A design method for base isolation technology, applicable to a pre-isolation structure with a height of less than 40m; the pre-isolation structure is mainly shear-deformed and has a uniform mass and stiffness distribution along the height, characterized in that: Step 1: Determine the seismic influence coefficient curve of the structure before isolation (1); Step 2: Determine the horizontal equivalent stiffness and equivalent viscous damping ratio of the seismic isolation structure; use the equivalent viscous damping ratio to correct and determine the seismic influence coefficient curve (3) and the displacement response spectrum curve (4) of the seismic isolation structure; Step 3: determining the natural period T1 of the structure before seismic isolation; calculating the natural period T2 of the structure after seismic isolation according to the horizontal equivalent stiffness of the structure after seismic isolation; Step 4: according to the natural period T1 of the structure before seismic isolation, the first seismic influence coefficient A1 is determined on the seismic influence coefficient curve (1) of the structure before seismic isolation; according to the natural period T2 of the structure after seismic isolation, the second seismic influence coefficient A2 is determined on the seismic influence coefficient curve (3) of the structure after seismic isolation; the second seismic influence coefficient A2 is divided by the first seismic influence coefficient A1 to obtain the shock absorption coefficient; Step 5: Find the displacement response D2 of the seismically isolated structure corresponding to the natural period T2 of the seismically isolated structure on the displacement response spectrum curve (4) of the seismically isolated structure.

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