Seismic isolation device

Abstract

To restrain vibration such as an earthquake from being transmitted to a structure while maintaining high damping characteristics.SOLUTION: A base isolation device 1 of this invention includes a laminate structure body 3 in which a plurality of hard material layers 4 and a plurality of soft material layers 5 are respectively stacked alternately in a vertical direction. The plurality of soft material layers 5 each include a first soft material layer 51 which is formed of a first soft material having a first equivalent damping coefficient, and a second soft material layer 52 which is formed of a second soft material having a second equivalent damping coefficient. The second equivalent damping coefficient when the maximum shear strain is ±270% is 50% or less of the first equivalent damping coefficient when the maximum shear strain is ±270%.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a seismic isolation device. [Background technology]

[0002] Some conventional seismic isolation devices have a laminated structure in which multiple hard plates and multiple soft plates are alternately laminated, with soft plate A and soft plate B having different elastic moduli (see, for example, Patent Document 1). According to the seismic isolation device described in Patent Document 1, in the low strain range, the elastic modulus of soft plate A is lower than that of soft plate B, and in the high strain range, the elastic modulus of soft plate A is higher than that of soft plate B, making it possible to combine a damping effect against minute vibrations with a spring effect and a damper effect against large deformation during an earthquake. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 190847 / 1999 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the seismic isolation device described in Patent Document 1 does not have a long natural period due to the inclusion of a soft material layer with high damping properties, and therefore may not be able to sufficiently suppress the transmission of earthquake vibrations to the structure placed on the seismic isolation device. This may result in a large impact on the upper structure placed on the seismic isolation device, i.e., a decrease in seismic isolation performance.

[0005] An object of the present invention is to provide a seismic isolation device that can sufficiently suppress the transmission of vibrations caused by earthquakes and the like to a structure while maintaining high damping characteristics. [Means for solving the problem]

[0006] The seismic isolation device according to the present invention comprises: A seismic isolation device comprising a laminated structure in which a plurality of hard material layers and a plurality of soft material layers are alternately laminated in a vertical direction, The plurality of soft material layers include a first soft material layer formed of a first soft material having a first equivalent damping constant, and a second soft material layer formed of a second soft material having a second equivalent damping constant, The second equivalent damping constant when the maximum shear strain is ±270% is 50% or less of the first equivalent damping constant when the maximum shear strain is ±270%. The seismic isolation device according to the present invention can sufficiently suppress the transmission of vibrations caused by earthquakes or the like to a structure while maintaining high damping characteristics.

[0007] In the seismic isolation device according to the present invention, It is preferable that the second equivalent damping constant when the maximum shear strain is ±270% is 30% or less of the first equivalent damping constant when the maximum shear strain is ±270%. This makes it possible to more sufficiently suppress the transmission of vibrations caused by earthquakes and the like to structures while maintaining high damping characteristics.

[0008] In the seismic isolation device according to the present invention, It is preferable that the second equivalent damping constant when the maximum shear strain is ±270% is 15% or more and 25% or less of the first equivalent damping constant when the maximum shear strain is ±270%. This makes it possible to more sufficiently suppress the transmission of vibrations caused by earthquakes and the like to structures while maintaining high damping characteristics.

[0009] In the seismic isolation device according to the present invention, In a hysteresis loop of each of the first soft material and the second soft material in a coordinate system with the horizontal axis representing shear strain and the vertical axis representing stress, when the slope of the tangent on the post-unloading side at the maximum shear strain of the first soft material and the slope of the tangent on the post-unloading side at the maximum shear strain of the second soft material are defined as a first post-unloading tangent stiffness and a second post-unloading tangent stiffness, respectively: It is preferable that the first post-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270% is greater than the second post-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270%. This makes it possible to more sufficiently suppress the transmission of vibrations caused by earthquakes and the like to structures while maintaining high damping characteristics.

[0010] In the seismic isolation device according to the present invention, In the hysteresis curves of the first soft material and the second soft material in a coordinate system with shear strain on the horizontal axis and stress on the vertical axis, when the slope of the tangent before unloading at the maximum shear strain of the first soft material and the slope of the tangent before unloading at the maximum shear strain of the second soft material are defined as the first pre-unloading tangent stiffness and the second pre-unloading tangent stiffness, respectively, it is preferable that the first pre-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270% is smaller than the second pre-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270%. This makes it possible to increase the strain at the time of breakage of the laminated structure, that is, to make it possible to prevent breakage unless a larger strain is applied.

[0011] In the seismic isolation device according to the present invention, It is preferable that the first soft material layer is disposed at the uppermost and lowermost of the soft material layers in the laminated structure in the vertical direction. This makes it possible to suppress distortion of the laminated structure due to torsional stress generated when a moment acts on the laminated structure, thereby improving the durability of the laminated structure and, ultimately, the seismic isolation device.

[0012] In the seismic isolation device according to the present invention, It is preferable that the first soft material layer is arranged only in an end region of the laminated structure, including the top and bottom, located on the end side of the laminated structure in the vertical direction, and the second soft material layer is arranged only in a central region of the laminated structure, located closer to the center than the end regions in the vertical direction. This makes it possible to better suppress distortion of the laminated structure due to torsional stress generated when a moment acts on the laminated structure, thereby further improving the durability of the laminated structure and, ultimately, the seismic isolation device.

[0013] In the seismic isolation device according to the present invention, it is preferable that the first soft material layers and the second soft material layers are arranged alternately in the vertical direction. This makes it possible to suppress changes in the characteristics of the first soft material constituting the first soft material layer due to heat generation caused by absorbing the energy of the vibration force. Effect of the Invention

[0014] According to the present invention, it is possible to provide a seismic isolation device that can sufficiently suppress the transmission of vibrations caused by earthquakes or the like to a structure while maintaining high damping characteristics. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a seismic isolation device according to one embodiment of the present invention, taken along a cross section including a central axis line. [Diagram 2] FIG. 2 is a perspective view of the seismic isolation device of FIG. 1. [Diagram 3] FIG. 2 is a schematic diagram for explaining an equivalent damping constant. [Figure 4] 2 is an image diagram showing an example of a hysteresis curve of a soft material forming a soft material layer of a laminated structure included in the seismic isolation device of FIG. 1, and of the laminated structure. [Diagram 5] 1. FIG. 4 is an image diagram showing another example of a hysteresis curve of the soft material forming the soft material layer of the laminated structure included in the seismic isolation device of FIG. 1, and of the laminated structure. [Figure 6]FIG. 2 is a cross-sectional view corresponding to FIG. 1, showing another example of a seismic isolation device, the cross section including the central axis. [Figure 7] FIG. 7 is a perspective view of the seismic isolation device of FIG. 6. [Figure 8] 4 is an image diagram showing an example of a hysteresis loop of a soft material forming a soft material layer of a laminated structure and the laminated structure in an embodiment of the present invention. FIG. [Figure 9] FIG. 4 is a diagram showing a laminate equivalent damping constant ratio of a laminate structure. [Figure 10] FIG. 13 is a diagram showing the rigidity ratio of a laminated structure. [Figure 11] FIG. 4 is a diagram showing the natural period ratio of a laminated structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The seismic isolation device of the present invention is suitable when placed between the superstructure and substructure of a structure (e.g., buildings such as buildings, condominiums, detached houses, warehouses, and bridges) in order to prevent vibrations from earthquakes and the like from being transmitted to the structure.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a seismic isolation device according to the present invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals.

[0018] 1 and 2 are diagrams for explaining a seismic isolation device 1 according to one embodiment of the present invention. Fig. 1 is an axial cross-sectional view (a cross-sectional view showing a cross section including a central axis line AX of the seismic isolation device 1; the same applies below) showing the seismic isolation device 1 according to this embodiment in a state where no deformation occurs. Fig. 2 is a perspective view of the seismic isolation device 1 shown in Fig. 1.

[0019] As shown in FIG. 1, the seismic isolation device 1 of the embodiment includes a pair of upper and lower flange plates 21, 22 (hereinafter also referred to as the “upper flange plate 21” and the “lower flange plate 22”, respectively) and a laminated structure 3.

[0020] In this specification, the central axis AX of the seismic isolation device 1 is the central axis of the laminated structure 3. The central axis AX of the seismic isolation device 1 is oriented so as to extend in the vertical direction. In this specification, the "axial direction" of the seismic isolation device 1 refers to a direction parallel to the central axis AX of the seismic isolation device 1, and since the central axis AX is oriented so as to extend in the vertical direction, the "axial direction" of the seismic isolation device 1 corresponds to the vertical direction of the seismic isolation device 1. The "axial direction" is a direction perpendicular to the axial direction. Additionally, "upper" and "lower" refer to "upper" and "lower", respectively, in the axial direction.

[0021] The upper flange plate 21 is configured to be connected to a superstructure (such as a building body) of a structure (for example, a building, an apartment, a detached house, a warehouse, or a bridge) when the superstructure is placed on the upper flange plate 21. The lower flange plate 22 is disposed below the upper flange plate 21 and configured to be connected to a substructure (such as a foundation) of the structure. The upper flange plate 21 and the lower flange plate 22 are preferably made of metal, and more preferably made of steel. As shown in FIG. 2, in this embodiment, the upper flange plate 21 and the lower flange plate 22 have a circular outer edge shape in a cross section perpendicular to the axis. However, the upper flange plate 21 and the lower flange plate 22 may have any outer edge shape, such as a polygonal shape (such as a square shape), in a cross section perpendicular to the axis.

[0022] The laminated structure 3 is disposed between an upper flange plate 21 and a lower flange plate 22. In this embodiment, the laminated structure 3 has a circular outer edge shape in a cross section perpendicular to the axis. However, the laminated structure 3 may have any outer edge shape, such as a polygonal shape (e.g., a square shape), in a cross section perpendicular to the axis.

[0023] The laminated structure 3 includes a plurality of hard material layers 4, a plurality of soft material layers 5, and a coating layer 6. The plurality of hard material layers 4 and the plurality of soft material layers 5 are alternately laminated in the vertical direction. The hard material layers 4 and the soft material layers 5 have a circular outer edge shape in a cross section perpendicular to the axis. However, the hard material layers 4 and the soft material layers 5 may have any outer edge shape, such as a polygonal shape (e.g., a square shape), in a cross section perpendicular to the axis.

[0024] In this specification, the "outer diameter" of each of the laminated structure 3, the hard material layer 4, the soft material layer 5, and the coating layer 6 refers to the diameter of the circumscribing circle of each of these in the cross section perpendicular to the axis when they have a non-circular outer edge shape in the cross section perpendicular to the axis.

[0025] Each hard material layer 4 and each soft material layer 5 are disposed coaxially with the upper flange plate 21 and the lower flange plate 22. In other words, the central axes of the upper flange plate 21, the lower flange plate 22, each hard material layer 4, and each soft material layer 5 are positioned on the central axis AX of the seismic isolation device 1.

[0026] Soft material layers 5 are disposed on both the upper and lower ends of the laminated structure 3. The pair of soft material layers 5 disposed on both the upper and lower ends of the laminated structure 3 are fixed to an upper flange plate 21 and a lower flange plate 22, respectively.

[0027] The hard material layer 4 is formed of a hard material. As the hard material forming the hard material layer 4, metal is preferable, and steel is more preferable. As in the example of FIG. 1, it is preferable that the axial distance between the hard material layers 4 is the same. Here, the "axial distance between the hard material layers 4" refers to the axial distance between the axial centers of a pair of adjacent hard material layers 4. In addition, as in the example of FIG. 1, it is preferable that the thickness of each hard material layer 4 is the same.

[0028] The soft material layer 5 is formed of a soft material having a lower rigidity than the hard material forming the hard material layer 4. The multiple soft material layers 5 include a first soft material layer 51 formed of a first soft material having a first equivalent damping constant Heq (soft 1), and a second soft material layer 52 formed of a second soft material having a second equivalent damping constant Heq (soft 2).

[0029] Here, the original purpose of providing a seismic isolation device under a structure (such as a building) is to sufficiently suppress strong vibrations transmitted to the structure by lengthening the natural period of the structure including the seismic isolation device through the provision of the seismic isolation device. Therefore, in the present invention, the second equivalent damping constant Heq (soft 2) when the maximum shear strain is ±270% is 50% or less of the first equivalent damping constant Heq (soft 1) when the maximum shear strain is ±270%. Here, "shear strain 270%" refers to a ratio of the displacement in the stress direction (horizontal direction) to the thickness (vertical length) of the soft material layer 5 being 270%. In addition, the equivalent damping constant "when the maximum shear strain is ±270%" means an equivalent damping constant calculated based on a hysteresis curve when the maximum shear strain is ±270%, which will be described later. In addition, in the present invention, the equivalent damping constant "when the maximum shear strain is ±270%" is used because the maximum shear strain expected in a normal large earthquake is about 270%. If the second equivalent damping constant Heq(soft2) exceeds 50% of the first equivalent damping constant Heq(soft1), the effect of using two types of soft material layers with different equivalent damping constants cannot be fully obtained, that is, it is not possible to sufficiently suppress the transmission of earthquake vibrations to the structure while maintaining high damping characteristics. The second equivalent damping constant Heq(soft2) may be 5% or more of the first equivalent damping constant Heq(soft1).

[0030] The equivalent damping constant is ΔW / 2πW, which is the total energy per unit volume absorbed by the seismic isolation bearing made up of the member (soft material or laminated structure), divided by 2πW, which is the elastic shear strain energy per unit volume W multiplied by 2π. The first equivalent damping constant Heq(soft1) of the first soft material and the second equivalent damping constant Heq(soft2) of the second soft material indicate the damping performance determined by the characteristics of the material (not dependent on the size and number of material layers formed by the material). Here, the energy per unit volume absorbed by the seismic isolation bearing made up of the member is a value equivalent to the area surrounded by the hysteresis curve Lss (the part hatched with a solid line in FIG. 3) in a coordinate system with the shear strain ε on the horizontal axis and the stress σ on the vertical axis, as shown in FIG. 3.

[0031] The hysteresis curve Lss is a curve showing the relationship between the shear strain ε and stress σ of a member in the process of applying an excitation force in one direction (hereinafter referred to as the positive direction) to the member until the shear strain becomes the positive maximum shear strain, then removing the excitation force, reversing the direction of the excitation force, and applying an excitation force in the opposite direction (hereinafter referred to as the negative direction) to the member until the shear strain becomes the negative maximum shear strain, and then removing the excitation force again, reversing the direction of the excitation force, and applying a positive excitation force to the member until the shear strain becomes the positive maximum shear strain. The positive maximum shear strain is the maximum shear strain of the member in the positive direction. The negative maximum shear strain is the maximum shear strain of the member in the negative direction.

[0032] The elastic shear strain energy W per unit volume is the energy stored when an external force does work, and is a value equivalent to the area enclosed by the line segment L1 connecting point ST+, where the shear strain is the maximum positive shear strain, and point ST-, where the shear strain is the maximum negative shear strain, on the hysteresis curve Lss, line segment L2 drawn perpendicular to the horizontal axis from each of points ST+ and ST-, and the horizontal axis of the above coordinate system (the area hatched with dashed lines in Figure 3).

[0033] The soft material forming the first soft material layer 51 is preferably an elastic body, more preferably a synthetic rubber (high damping rubber, etc.). The soft material forming the second soft material layer 52 is preferably an elastic body, more preferably a natural rubber or a rubber mainly composed of natural rubber. Either the first soft material layer 51 or the second soft material layer 52 is disposed between a pair of adjacent hard material layers 4, on the upper side of the uppermost hard material layer 4 (between the hard material layer 4 and the upper flange plate 21) and on the lower side of the lowermost hard material layer 4 (between the hard material layer 4 and the lower flange plate 22). As in the example of FIG. 1, it is preferable that the thicknesses of the soft material layers 5 are the same as each other.

[0034] Here, in a coordinate system with the horizontal axis representing shear strain ε and the vertical axis representing stress σ, hysteresis curves Ls11, Ls12, and Ls13 of a laminated structure 3 including a first soft material, a second soft material, and a first soft material layer 51 and a second soft material layer 52 formed of the first soft material and the second soft material, respectively, with a maximum shear strain (absolute value) of 270% will be described with reference to Fig. 4. In Fig. 4, the hysteresis curve Ls11 of the first soft material is shown by a dashed line, the hysteresis curve Ls12 of the second soft material is shown by a dashed line, and the hysteresis curve Ls13 of the laminated structure 3 including both of them is shown by a solid line. In this example, in order to generate shear strain and stress in each of the first soft material, the second soft material, and the laminated structure 3, an excitation force is applied to each of them so as to vibrate them in the horizontal direction with a triangular wave of 0.33 Hz. In the example of Fig. 4, the first soft material is high damping rubber, and the second soft material is natural rubber whose second equivalent damping constant Heq (soft 2) when the maximum shear strain (absolute value) is 270% is 50% or less of the first equivalent damping constant Heq (soft 1) of the first soft material when the maximum shear strain (absolute value) is 270%.

[0035] First, the hysteresis curve Ls11 of the first soft material with the maximum shear strain (absolute value) set to 270% will be described. In the example of Fig. 4, when an excitation force is applied to the first soft material in a positive direction from a state where no excitation force is applied to the first soft material (origin O), the shear strain of the first soft material increases as shown by the dashed line (a1), and a stress greater than the stress of the second soft material, which will be described in detail later, occurs with respect to the shear strain. The rate of change of the stress with respect to the shear strain of the first soft material is maximum at the point when the shear strain begins to occur due to the application of the excitation force, and decreases as the shear strain increases.

[0036] When the shear strain of the first soft material reaches +270% (point A in FIG. 4), the excitation force applied in the positive direction is removed and the direction of the excitation force is reversed, i.e., the direction in which the excitation force is applied changes from the positive direction to the negative direction, the shear strain of the first soft material decreases as shown by the dashed line (b1), and the stress of the first soft material relative to the shear strain begins to rapidly become smaller than the stress of the second soft material. When the excitation force continues to be applied in the negative direction, the stress of the first soft material becomes 0 and then increases in the negative direction. Furthermore, when the excitation force continues to be applied in the negative direction, the shear strain of the first soft material becomes 0 and then increases in the negative direction, and the stress of the first soft material becomes even greater in the negative direction. In the example of Figure 4, the rate of change of stress with respect to shear strain for the first soft material is maximum when the excitation force is removed, the direction of the excitation force is reversed, and the shear strain begins to decrease, and then decreases as the shear strain continues to decrease, becomes zero, and then increases in the negative direction.

[0037] When the shear strain of the first soft material becomes -270% (point B in FIG. 4), the excitation force applied in the negative direction is removed and the direction of the excitation force is reversed, that is, when the direction in which the excitation force is applied changes from the negative direction to the positive direction, the shear strain of the first soft material becomes smaller in the negative direction, and the stress of the first soft material relative to the shear strain begins to become smaller in the negative direction more rapidly than the stress of the second soft material (part indicated by dashed line (c1)). Note that "becoming smaller in the negative direction" means that the value is negative and its absolute value becomes smaller. When the excitation force continues to be applied in the positive direction, the stress of the first soft material becomes 0 and then becomes larger in the positive direction. Furthermore, when the excitation force continues to be applied in the positive direction, the shear strain of the first soft material becomes 0 and then becomes larger in the positive direction, and the stress of the first soft material becomes even larger in the positive direction. The rate of change of stress with respect to shear strain of the first soft material is greatest when the excitation force is removed, the direction of the excitation force is reversed, and the shear strain begins to decrease in the negative direction, and then decreases as the shear strain continues to decrease in the negative direction, becomes zero, and then increases in the positive direction.

[0038] Then, after the shear strain of the first soft material reaches +270% again (point A in FIG. 4), the above-mentioned changes in shear strain and stress in the first soft material are repeated.

[0039] Next, the hysteresis curve Ls12 of the second soft material with the maximum shear strain (absolute value) set to 270% will be described. In the example of FIG. 4, as shown by the dashed line, when an excitation force is applied to the second soft material in a positive direction from a state where no excitation force is applied to the second soft material (origin O), the shear strain of the second soft material increases, and a stress approximately proportional to the shear strain of the second soft material is generated (part shown by the dashed line (d1)). As described above, the second equivalent damping constant Heq (soft 2) when the maximum shear strain is ±270% is 50% or less of the first equivalent damping constant Heq (soft 1) when the maximum shear strain is ±270%, so that the stress of the second soft material is smaller than the stress of the first soft material from the start of the excitation force being applied in the positive direction until just before the excitation force is removed. Also, in the example of Figure 4, the stress in the second soft material when the shear strain reaches the maximum shear strain of +270% is the same as the stress in the first soft material when the shear strain reaches the maximum shear strain of +270%.

[0040] When the shear strain of the second soft material reaches +270% (point A in Figure 4), and the excitation force that was applied in the positive direction is removed and the direction of the excitation force is reversed, i.e., when the direction in which the excitation force is applied changes from the positive direction to the negative direction, the shear strain of the second soft material decreases, and the stress of the second soft material decreases approximately proportional to the shear strain (part indicated by dashed dotted line (e1)). When the excitation force continues to be applied in the negative direction, the shear strain of the second soft material becomes 0 and then increases in the negative direction, and the stress of the second soft material increases in the negative direction approximately proportional to the shear strain. As described above, the second equivalent damping constant Heq(soft2) when the maximum shear strain is ±270% is 50% or less of the first equivalent damping constant Heq(soft1) when the maximum shear strain is ±270%, so the stress of the second soft material is greater than the stress of the first soft material from the time when the excitation force starts to be applied in the negative direction until just before the excitation force is removed. Also, in the example of Fig. 4, the stress of the second soft material when the shear strain becomes -270%, which is the maximum shear strain in the negative direction (point B in Fig. 4), is the same as the stress of the first soft material when the shear strain becomes -270%, which is the maximum shear strain in the negative direction.

[0041] When the shear strain of the second soft material becomes -270% (point B in Fig. 4), the excitation force that was applied in the negative direction is removed and the direction of the excitation force is reversed, i.e., when the direction in which the excitation force is applied changes from the negative direction to the positive direction, the shear strain of the second soft material decreases in the negative direction, and the stress of the second soft material decreases in the negative direction approximately proportional to the shear strain. If the excitation force continues to be applied in the positive direction, the shear strain of the second soft material becomes 0, and then increases in the positive direction, and the stress of the second soft material increases in the positive direction approximately proportional to the shear strain. As described above, the second equivalent damping constant Heq(soft 2) when the maximum shear strain is ±270% is less than 50% of the first equivalent damping constant Heq(soft 1) when the maximum shear strain is ±270%, so from the time when the excitation force begins to be applied in the positive direction until just before the excitation force is removed, the stress of the second soft material is smaller than the stress of the first soft material.

[0042] Then, after the shear strain of the second soft material reaches +270% again (point A in FIG. 4), the above-mentioned changes in shear strain and stress in the second soft material are repeated.

[0043] We will now explain the hysteresis curve Ls13 of the laminated structure 3, which includes the first soft material layer 51 and the second soft material layer 52, which are respectively formed from the first soft material and the second soft material having such characteristics, and which has a maximum shear strain (absolute value) of 270%.

[0044] In the example of FIG. 4, as shown by the solid line, when a vibration force is applied to the laminated structure 3 in a positive direction from a state where no vibration force is applied to the laminated structure 3 (origin O), the shear strain of the laminated structure 3 increases, and a stress is generated against the shear strain that is smaller than the stress of the first soft material and larger than the stress of the second soft material (part shown by solid line (f1)). Furthermore, the rate of change of the stress of the laminated structure 3 against the shear strain is maximum at the time when the shear strain starts to be generated by the application of the vibration force, and decreases as the shear strain increases. Furthermore, from immediately after the vibration force starts to be applied until immediately before the vibration force is removed, the stress of the laminated structure 3 against the shear strain is smaller than the stress of the first soft material and larger than the stress of the second soft material. In the example of Figure 4, the stress of the laminated structure 3 when the shear strain reaches the maximum shear strain of +270% is the same as the stress of the first soft material when the shear strain reaches the maximum shear strain of +270% and the stress of the second soft material when the shear strain reaches the maximum shear strain of +270%.

[0045] When the shear strain of the laminated structure 3 reaches +270% (point A in Figure 4), the excitation force that was applied in the positive direction is removed and the direction of the excitation force is reversed, i.e., the direction in which the excitation force is applied changes from the positive direction to the negative direction, the shear strain of the laminated structure 3 decreases, and the stress of the laminated structure 3 begins to decrease with respect to the shear strain more gradually than the stress of the first soft material and more rapidly than the stress of the second soft material (part shown by solid line (g1)). When the excitation force continues to be applied in the negative direction, the stress of the laminated structure 3 becomes 0 and then increases in the negative direction. Furthermore, when the excitation force continues to be applied in the negative direction, the shear strain of the laminated structure 3 becomes 0 and then increases in the negative direction, and the stress of the laminated structure 3 increases even more in the negative direction. The rate of change of the stress of the laminated structure 3 with respect to the shear strain is maximum when the excitation force is removed, the direction of the excitation force is reversed, and the shear strain starts to decrease, and decreases as the shear strain further decreases, becomes 0, and then increases in the negative direction. Also, from immediately after the excitation force starts to be applied in the negative direction until immediately before the excitation force is removed, the stress of the laminated structure 3 with respect to the shear strain is greater than the stress of the first soft material and less than the stress of the second soft material. Also, in the example of FIG. 4, the stress of the laminated structure 3 when the shear strain of the laminated structure 3 becomes -270% is the same as the stress when the shear strain of the first soft material becomes -270% and the stress when the shear strain of the second soft material becomes -270%.

[0046] When the shear strain of the laminated structure 3 reaches -270% (point B in Figure 4), the vibration force that was applied in the negative direction is removed and the direction of the vibration force is reversed, i.e., the direction in which the vibration force is applied changes from the negative direction to the positive direction, the shear strain of the laminated structure 3 decreases in the negative direction, and the stress of the laminated structure 3 begins to increase more gradually than the stress of the first soft material and more rapidly than the stress of the second soft material with respect to the shear strain (part indicated by solid line (h1)). When the vibration force continues to be applied in the positive direction, the stress of the laminated structure 3 becomes 0 and then increases in the positive direction. Furthermore, when the vibration force continues to be applied in the positive direction, the shear strain of the laminated structure 3 becomes 0 and then increases in the positive direction, and the stress of the laminated structure 3 increases even more in the positive direction. The rate of change of stress in the laminated structure 3 with respect to shear strain is maximum when the excitation force is removed, the direction of the excitation force is reversed, and the shear strain begins to decrease in the negative direction, and decreases as the shear strain further decreases in the negative direction, becomes 0, and then increases in the positive direction. In addition, from immediately after the excitation force begins to be applied in the positive direction until immediately before the excitation force is removed, the stress in the laminated structure 3 with respect to shear strain is smaller than the stress of the first soft material and larger than the stress of the second soft material.

[0047] Then, after the shear strain of the laminated structure 3 reaches +270% again (point A in FIG. 4), the above-described changes in shear strain and stress in the laminated structure 3 are repeated.

[0048] In this way, the laminated structure 3 includes the first soft material layer 51 and the second soft material layer 52 formed by the first soft material and the second soft material, respectively, and thus can maintain high damping characteristics and can lengthen the natural period (immediately after unloading) compared to the case where only the second soft material layer 52 is included. Therefore, the seismic isolation device 1 including the laminated structure 3 including the first soft material layer 51 and the second soft material layer 52 can sufficiently suppress the transmission of vibrations such as earthquakes to the structure while maintaining high damping characteristics, since the natural period is long. This can mitigate the impact caused by unloading the excitation force that the structure placed on the seismic isolation device 1 receives, and can improve the seismic isolation performance of the seismic isolation device 1.

[0049] Furthermore, in this embodiment, in the hysteresis curves Ls11 and Ls12 of the first soft material and the second soft material, respectively, in a coordinate system with shear strain on the horizontal axis and stress on the vertical axis, when the slope of the tangent on the post-unloading side at the maximum shear strain of the first soft material and the slope of the tangent on the post-unloading side at the maximum shear strain of the second soft material are defined as the first post-unloading tangent stiffness and the second post-unloading tangent stiffness, respectively, it is preferable that the first post-unloading tangent stiffness in the hysteresis curve Ls11 when the maximum shear strain is ±270% is greater than the second post-unloading tangent stiffness in the hysteresis curve Ls12 when the maximum shear strain is ±270%.

[0050] In the example of Fig. 4, the above "tangent to the post-unloading side at the maximum shear strain of the first soft material" is represented by a tangent to the above-mentioned dashed line (b1) portion of the hysteresis curve Ls11 of the first soft material at point A where the shear strain of the first soft material is 270% of the maximum shear strain (i.e., a tangent drawn from the dashed line (b1) portion at point A, which is the post-unloading side). The above "tangent to the post-unloading side at the maximum shear strain of the second soft material" is represented by a tangent to the above-mentioned dashed line (e1) portion of the hysteresis curve Ls12 of the second soft material at point A where the shear strain of the second soft material is 270% of the maximum shear strain (i.e., a tangent drawn from the dashed line (e1) portion at point A, which is the post-unloading side).

[0051] The laminated structure 3 includes a first soft material layer 51 formed from a first soft material, and a second soft material layer 52 formed from a second soft material. For this reason, when the gradient of the tangent (Lg1 in FIG. 4) on the post-unloading side at the time of maximum shear strain in the hysteresis curve Ls13 of the laminated structure 3 in a coordinate system with the horizontal axis representing strain and the vertical axis representing stress is defined as the third post-unloading tangent stiffness, the third post-unloading tangent stiffness has a value between the first post-unloading tangent stiffness and the second post-unloading tangent stiffness. Therefore, as described above, if the tangent stiffness after the first unloading on the hysteresis curve Ls11 when the maximum shear strain is ±270% is greater than the tangent stiffness after the second unloading on the hysteresis curve Ls12 when the maximum shear strain is ±270%, the tangent stiffness after the third unloading on the hysteresis curve Ls13 when the maximum shear strain is ±270% is smaller than the tangent stiffness after the first unloading. Therefore, immediately after the shear strain of the laminated structure 3 becomes the maximum shear strain, the stiffness of the laminated structure 3 is smaller than the stiffness of the laminated structure 3 including only the first soft material layer 51 formed of the first soft material and not including the second soft material layer 52 formed of the second soft material.

[0052] Therefore, the laminated structure 3 can mitigate a sudden change in stress immediately after the shear strain of the laminated structure 3 reaches the maximum shear strain. Therefore, immediately after the shear strain of the laminated structure 3 reaches the maximum shear strain, the impact received by the structure placed on the seismic isolation device 1 including the laminated structure 3 can be further mitigated, and the seismic isolation performance can be further improved.

[0053] Furthermore, in the hysteresis curves Ls11 and Ls12 of the first soft material and the second soft material, respectively, in a coordinate system with shear strain on the horizontal axis and stress on the vertical axis, when the slope of the tangent before unloading at the maximum shear strain of the first soft material and the slope of the tangent before unloading at the maximum shear strain of the second soft material are defined as the first pre-unloading tangent stiffness and the second pre-unloading tangent stiffness, respectively, it is preferable that the first pre-unloading tangent stiffness in the hysteresis curve Ls11 when the maximum shear strain is ±270% is smaller than the second pre-unloading tangent stiffness in the hysteresis curve Ls12 when the maximum shear strain is ±270%.

[0054] In the example of Fig. 4, the above "tangent before unloading at the time of maximum shear strain of the first soft material" is represented by a tangent to the above-mentioned dashed line (a1) portion of the hysteresis curve Ls11 of the first soft material at point A where the shear strain of the first soft material is 270% of the maximum shear strain (i.e., a tangent drawn from the dashed line (a1) portion at point A, which is the pre-unloading side). The above "tangent before unloading at the time of maximum shear strain of the second soft material" is represented by a tangent to the above-mentioned dashed line (d1) portion of the hysteresis curve Ls12 of the second soft material at point A where the shear strain of the second soft material is 270% of the maximum shear strain (i.e., a tangent drawn from the dashed line (d1) portion at point A, which is the pre-unloading side).

[0055] The laminated structure 3 includes a first soft material layer 51 formed from a first soft material, and a second soft material layer 52 formed from a second soft material. For this reason, when the gradient of the tangent (Lf1 in FIG. 4) on the pre-unloading side at the time of maximum shear strain in the hysteresis curve Ls13 of the laminated structure 3 in a coordinate system with the horizontal axis representing strain and the vertical axis representing stress is defined as the third pre-unloading tangent stiffness, the third pre-unloading tangent stiffness has a value between the first pre-unloading tangent stiffness and the second pre-unloading tangent stiffness. Therefore, as described above, if the first unloading pretangent stiffness in the hysteresis curve Ls11 when the maximum shear strain is ±270% is smaller than the second unloading pretangent stiffness in the hysteresis curve Ls12 when the maximum shear strain is ±270%, the third unloading pretangent stiffness in the hysteresis curve Ls13 when the maximum shear strain is ±270% is larger than the first unloading pretangent stiffness. Therefore, just before the shear strain of the laminated structure 3 becomes the maximum shear strain, the stiffness of the laminated structure 3 is larger than the case where it includes only the first soft material layer 51 formed of the first soft material and does not include the second soft material layer 52 formed of the second soft material.

[0056] Therefore, the laminated structure 3 can mitigate the increase in shear strain caused by the increase in stress immediately before the shear strain of the laminated structure 3 reaches the maximum shear strain, thereby making it possible to increase the strain at the time of breakage of the laminated structure 3, that is, to prevent breakage unless the laminated structure 3 is subjected to a larger strain.

[0057] Furthermore, the tangent stiffness after the first unloading in the hysteresis curve when the maximum shear strain is ±270% is greater than the tangent stiffness after the second unloading in the hysteresis curve when the maximum shear strain is ±270% and the tangent stiffness before the first unloading in the hysteresis curve when the maximum shear strain is ±270% is smaller than the tangent stiffness before the second unloading in the hysteresis curve when the maximum shear strain is ±270%. This makes it possible to make the strain in the first soft material and the strain in the second soft material approximately the same, and makes the strain at break of the laminated structure 3 having the first and second soft materials larger, in other words, makes it possible to prevent breakage unless the laminated structure is subjected to an even larger strain.

[0058] In the example of Fig. 4, the stress of the second soft material when the shear strain reaches the maximum shear strain of +270% is the same as the stress of the first soft material when the shear strain reaches the maximum shear strain of +270%, but this is not limited to the above. For example, as shown in Fig. 5, the stress of the second soft material when the shear strain reaches the maximum shear strain of +270% may be different from the stress of the first soft material when the shear strain reaches the maximum shear strain of +270%.

[0059] In FIG. 5, the hysteresis curve Ls11 of the first soft material is shown by a dashed line, the hysteresis curve Ls12 of the second soft material is shown by a dashed line, and the hysteresis curve Ls13 of the laminated structure 3 is shown by a solid line.

[0060] In the example of Fig. 5, the stress of the laminated structure 3 when the shear strain becomes +270% is a value between the stress of the first soft material when the shear strain becomes +270% and the stress of the second soft material when the shear strain becomes +270%. Also, the stress of the laminated structure 3 when the shear strain becomes -270% is a value between the stress of the first soft material when the shear strain becomes -270% and the stress of the second soft material when the shear strain becomes -270%. In other respects, the example of Fig. 5 is the same as the example of Fig. 4 described above.

[0061] As shown in FIG. 1, in this embodiment, the laminated structure 3 has a diameter-changing laminated portion 31 and a diameter-constant laminated portion 32.

[0062] The diameter-changing laminated portion 31 is located at least at one end (both ends in the example of FIG. 1) in the axial direction of the laminated structure 3. As shown in FIG. 1, the outer diameter of the diameter-changing laminated portion 31 becomes smaller from the end toward the center of the laminated structure 3 in the axial direction. The outer diameters of the multiple hard material layers 4 included in the diameter-changing laminated portion 31 become smaller from the end toward the center of the laminated structure 3 in the axial direction.

[0063] The constant diameter laminated portion 32 is located axially adjacent to the diameter varying laminated portion 31 toward the center, and includes the vertical center of the laminated structure 3. The outer diameter of the constant diameter laminated portion 32 is approximately constant in the axial direction. The outer diameter of the constant diameter laminated portion 32 is the same as the smallest outer diameter of the outer diameters of the diameter varying laminated portions 31. The outer diameter of the hard material layer 4 included in the constant diameter laminated portion 32 is smaller than the outer diameter of the hard material layer 4 included in the diameter varying laminated portion 31. The outer diameters of the multiple hard material layers 4 included in the constant diameter laminated portion 32 can be the same as each other.

[0064] In this way, by making the outer diameter of the hard material layer 4 included in the constant diameter laminated portion 32 located on the central side in the axial direction smaller than the outer diameter of the hard material layer 4 included in the diameter variable laminated portion 31 located on the end side in the axial direction, it is possible to lengthen the natural period of the structure placed on the seismic isolation device 1, and thus improve the seismic isolation performance. Even when the laminated structure 3 is suddenly elastically deformed, the diameter variable laminated portion 31, which has an outer diameter larger than that of the constant diameter laminated portion 32, supports the constant diameter laminated portion 32, thereby suppressing the concentration of local stress generated in the end portion, which causes the laminated structure 3 to buckle.

[0065] In this embodiment, the soft material layer 5 is divided into two imaginary regions: an end region E and a central region C.

[0066] The end region E may be composed of only at least a portion of the diameter changing laminated section 31 on the flange plate 21, 22 side in the axial direction, or may be composed of the entire diameter changing laminated section 31 and a portion of the constant diameter laminated section 32 on the diameter changing laminated section 31 side in the axial direction (in the example of Figure 1, the upper end region EU is composed of the entire upper diameter changing laminated section 31 and a portion of the constant diameter laminated section 32 on the upper diameter changing laminated section 31 side in the axial direction, and the lower end region EB is composed of the entire lower diameter changing laminated section 31 and a portion of the constant diameter laminated section 32 on the lower diameter changing laminated section 31 side in the axial direction).

[0067] When the end region E is composed of at least a portion of the diameter changing laminated portion 31 on the flange plate 21 side in the axial direction, the central region C is composed of the remaining portion of the diameter changing laminated portion 31 and the entirety of the constant diameter laminated portion 32. When the end region E is composed of the entirety of the diameter changing laminated portion 31 and a portion of the constant diameter laminated portion 32 on the diameter changing laminated portion 31 side in the axial direction, the central region C is composed of the portion of the constant diameter laminated portion 32 that does not constitute the end region E. (In the example of FIG. 1, the central region C is composed of only a portion of the constant diameter laminated portion 32.)

[0068] In the present embodiment, the first soft material layer 51 and the second soft material layer 52 may be arranged alternately in the vertical direction. When the first soft material layer 51 and the second soft material layer 52 are arranged alternately in the vertical direction, when a vibration force is repeatedly applied, it is possible to suppress a change in the characteristics of the first soft material constituting the first soft material layer 51 due to heat generation caused by absorbing the energy of the vibration force.

[0069] In this embodiment, the first soft material layer 51 may be disposed at the uppermost and lowermost portions of the soft material layers 5 in the laminated structure 3 in the vertical direction. In the example of FIG. 1, the first soft material layer 51 is disposed at the uppermost and lowermost portions of the soft material layers 5 in the laminated structure 3. When a horizontal vibration force is applied to the laminated structure 3, a torsional stress is generated by a moment acting on the laminated structure 3 in a state in which shear strain is generated by the application of the horizontal vibration force to the laminated structure 3. At this time, by arranging the first soft material layers 51 at the uppermost and lowermost of the soft material layers in the laminated structure 3, it is possible to suppress the strain of the laminated structure 3 associated with the torsional stress generated by the moment acting on the laminated structure 3, and therefore the durability of the laminated structure 3 and, in turn, the seismic isolation device 1 can be improved.

[0070] In the present embodiment, the first soft material layer 51 may be disposed only in an end region E including the uppermost and lowermost parts of the soft material layer 5 of the laminated structure 3, which is located on the end side of the laminated structure 3 in the vertical direction, and the second soft material layer 52 may be disposed only in a central region C of the laminated structure 3, which is located closer to the center than the end region E in the vertical direction. In the example of Fig. 1, the first soft material layer 51 is disposed only in an upper end region EU including the uppermost part and a lower end region EB including the lowermost part, and the second soft material layer 52 is disposed only in the central region C. When a horizontal vibration force is applied to the laminated structure 3, causing shear strain, a moment acts on the laminated structure 3, generating torsional stress. At this time, if the second soft material layer 52 having a small equivalent damping constant is arranged in the end region E, torsional deformation occurs in the second soft material layer 52. On the other hand, since the second soft material layer 52 is arranged in the central region C, torsional deformation is unlikely to occur in the second soft material layer 52. This makes it possible to suppress local strain in the second soft material layer 52, and thereby improve the durability of the laminated structure 3 and the seismic isolation device 1.

[0071] Alternatively, the second soft material layer 52 may be disposed in the edge region E, and the first soft material layer 51 may be disposed in the central region C. Furthermore, the first soft material layer 51 and the second soft material layer 52 may be disposed in a random order in the vertical direction.

[0072] 1, the laminated structure 3 has a coating layer 6, which covers the outer peripheral surfaces of the hard material layer 4 and the soft material layer 5. In this embodiment, the coating layer 6 is integral with the soft material layer 5.

[0073] In this embodiment, the coating layer 6 covers the entire outer peripheral surfaces of the hard material layer 4 and the soft material layer 5, and thus constitutes the entire outer peripheral surface of the laminated structure 3. However, the coating layer 6 may cover only a part of the outer peripheral surfaces of the hard material layer 4 and the soft material layer 5, and thus constitute only a part of the outer peripheral surface of the laminated structure 3. Moreover, the coating layer 6 does not have to be provided, and in that case, the outer peripheral surface of the laminated structure 3 is constituted only by the outer peripheral surfaces of the hard material layer 4 and the soft material layer 5.

[0074] The material constituting the coating layer 6 can be the same as the soft material constituting any part of the soft material layer 5. For example, the material of each part of the coating layer 6 in the vertical direction may be the same as the material of the soft material layer 5 when that part is adjacent to the soft material layer 5 in the axial direction. The material of each part of the coating layer 6 in the vertical direction may be the same as the material of the part of the coating layer 6 adjacent to that part in the axial direction when that part is not adjacent to the soft material layer 5 in the axial direction (i.e., when it is adjacent to the hard material layer 4, for example).

[0075] However, the material constituting the coating layer 6 may be different from the soft material constituting each portion in the vertical direction of the soft material layer 5. The material of each portion in the vertical direction of the coating layer 6 may be different from the material of the portion of the coating layer 6 adjacent to that portion in the axial direction when that portion is not adjacent to the soft material layer 5 in the axial direction (i.e., when it is adjacent to the hard material layer 4, for example). The entire material constituting the coating layer 6 may be different from all of the soft materials constituting the soft material layer 5, or the entire material constituting the coating layer 6 may be the same as the soft material constituting any portion of the soft material layer 5.

[0076] The outer diameter of the laminated structure 3 at each position in the axial direction may be arbitrary. Another example of the outer diameter of the laminated structure 3 at each position in the axial direction will be described with reference to Figs. 6 and 7. Fig. 6 is an axial cross-sectional view showing a seismic isolation device 10 according to another example of the seismic isolation device 1 shown in Fig. 1 in a state where no deformation occurs. Fig. 7 is a perspective view of the seismic isolation device 10 shown in Fig. 6.

[0077] In the examples of Fig. 6 and Fig. 7, the laminated structure 3 does not include a diameter-changing laminated portion 31, the outer diameter of the laminated structure 3 is constant, the outer diameters of the multiple hard material layers 4 are the same, and the outer diameters of the multiple soft material layers 5 are the same. If the outer diameters of the multiple hard material layers 4 are the same, the hard material layers 4 can be more easily procured than if the outer diameters of the multiple hard material layers 4 are different from each other, so the laminated structure 3 can be manufactured more easily. If the outer diameters of the multiple soft material layers 5 are the same, the soft material layers 5 can be more easily procured than if the outer diameters of the multiple soft material layers 5 are different from each other, so the laminated structure 3 can be manufactured more easily.

[0078] In another example, the laminated structure 3 may include a plurality of constant diameter laminated sections 32 having different diameters, or may include three or more variable diameter laminated sections 31.

[0079] In this embodiment, the laminated structure 3 is configured to include the first soft material layer 51 and the second soft material layer 52 formed of the first soft material and the second soft material, respectively, in which the second equivalent damping constant Heq (soft 2) when the maximum shear strain is ±270% is 50% or less of the first equivalent damping constant Heq (soft 1) when the maximum shear strain is ±270%. This allows the seismic isolation device 1 and the seismic isolation device 10 to be appropriately configured according to the shear strain of the laminated structure 3 assumed when a large earthquake occurs. Note that the characteristics of the laminated structure 3 according to the equivalent damping constant ratio R, which is the ratio of the second equivalent damping constant Heq (soft 2) when the maximum shear strain is ±270% to the first equivalent damping constant Heq (soft 1) when the maximum shear strain is ±270%, will be described in detail later.

[0080] Furthermore, in the first soft material and the second soft material, it is preferable that the second equivalent damping constant Heq(soft 2) when the maximum shear strain (absolute value) is set to a predetermined value greater than 270% is also 50% or less of the first equivalent damping constant Heq(soft 1) when the maximum shear strain (absolute value) is set to the predetermined value. The predetermined value is preferably greater than 270%, and more preferably greater than 400%. This allows the seismic isolation device 1 and the seismic isolation device 10 to be appropriately configured in accordance with the shear strain when an earthquake larger than the anticipated major earthquake occurs.

[0081] As described above, according to an embodiment of the present invention, it is possible to sufficiently suppress the transmission of shaking caused by earthquakes and the like to a structure while maintaining high damping characteristics, thereby providing a seismic isolation device with improved seismic isolation performance.

[0082] (Example) Here, an embodiment of the present invention will be described with reference to Fig. 6. However, the present invention is not limited to this embodiment. The laminated structure 3 in this embodiment includes two first soft material layers 51 arranged in the upper end region EU, four second soft material layers 52 arranged in the central region C, and two first soft material layers 51 arranged in the lower end region EB. The first soft material layers 51 and the second soft material layers 52 have a circular outer edge shape in a cross section perpendicular to the axis. The first soft material layer 51 has a thickness of 26.8 mm and an outer diameter of 1000 mm. The second soft material layer 52 has a thickness of 26.8 mm and an outer diameter of 1000 mm. In this embodiment, the first equivalent damping constant Heq(soft 1) is 0.159, and the second equivalent damping constant Heq(soft 2) is 0.032. That is, the second equivalent damping constant Heq(soft 2) when the maximum shear strain is ±270% is 20% of the first equivalent damping constant Heq(soft 1) when the maximum shear strain is ±270%.

[0083] FIG. 8 is an image diagram showing the results of a simulation in which an excitation force is applied to the first soft material forming the first soft material layer 51 included in the laminated structure 3 of this embodiment, the second soft material forming the second soft material layer 52 included in the laminated structure 3 of this embodiment, and the laminated structure 3 of this embodiment so as to cause a sine wave vibration of 0.33 Hz in the horizontal direction. In Figure 8, the hysteresis curve Ls21 when the maximum shear strain of the first soft material forming the first soft material layer 51 of this embodiment is 270% (absolute value) is shown by a dashed line, the hysteresis curve Ls22 when the maximum shear strain (absolute value) of the second soft material forming the second soft material layer 52 of this embodiment is 270% is shown by a dotted line, and the hysteresis curve Ls23 when the maximum shear strain (absolute value) of the laminated structure 3 of this embodiment is 270% is shown by a solid line.

[0084] In the first soft material layer 51 included in the laminate structure 3 of this embodiment, as shown by the hysteresis curve Ls21 in which the maximum shear strain (absolute value) of the first soft material forming the first soft material layer 51 is set to 270%, the shear strain of the first soft material changes due to vibration, generating stress, as in the example described with reference to Figure 4 (the parts indicated by dashed lines (a2), (b2), and (c2)). However, in this embodiment, the hysteresis curve of the portion indicated by the dashed line (b2) is not symmetrical with respect to the perpendicular bisector Lv of the line segment having two end points, point A where the shear strain of the first soft material is +270% and point B where the shear strain of the first soft material is -270%, unlike the hysteresis curve of the portion indicated by the dashed line (b1) in the example shown in Fig. 4. Specifically, as shown in Fig. 8, the slope of the tangent to the hysteresis curve of the portion indicated by the dashed line (b2) for the first soft material of this embodiment (the rate of change of stress σ with respect to shear strain ε) is greater than 1 in the range greater than shear strain ε1 and greater than shear strain ε2 at the intersection of the perpendicular bisector Lv and the hysteresis curve of the portion indicated by the dashed line (b2), and is smaller than the slope of the tangent to the hysteresis curve in the range greater than shear strain ε2 in the range less than the shear strain ε2. That is, in this embodiment, the stress decreases at a rate greater than 1 as the shear strain decreases from +270% to ε2, and decreases at a rate smaller than the rate of change from ε2 to -270% as the shear strain decreases from ε2 to -270%. In this embodiment, the hysteresis curve of the portion indicated by the broken line (c2) is not symmetrical with respect to the perpendicular bisector Lv, unlike the hysteresis curve of the portion indicated by the broken line (c1) in the example shown in Fig. 4. Specifically, the slope of the tangent to the hysteresis curve of the portion indicated by the broken line (c2) is greater than 1 in the range of shear strains smaller than ε3 and smaller than ε4 at the intersection of the perpendicular bisector Lv and the hysteresis curve of the portion indicated by the broken line (c2), and is smaller than the slope of the tangent to the hysteresis curve in the range of shear strains larger than ε4 in the range of shear strains larger than ε4. That is, in this embodiment, the stress increases at a rate of change greater than 1 as the shear strain increases from -270% to ε4, and increases at a rate of change smaller than the rate of change from -270% to ε4 as the shear strain increases from ε4 to +270%.

[0085] In the second soft material layer 52 included in the laminate structure 3 of this embodiment, as shown by the hysteresis curve Ls22 in which the maximum shear strain (absolute value) of the second soft material forming the second soft material layer 52 is set to 270%, the shear strain ε of the second soft material changes due to vibration, generating stress (parts indicated by dashed lines (d2) and (e2)), as in the example described with reference to Figure 4.

[0086] In the laminated structure 3 including the first soft material layer 51 and the second soft material layer 52 formed respectively from the first soft material and the second soft material having such characteristics, as shown by the hysteresis curve Ls23 of the laminated structure 3 with the maximum shear strain (absolute value) set to 270%, vibration causes the shear strain of the laminated structure 3 to change and stress is generated, similar to the example described with reference to Figure 4 (parts shown by solid lines (f2), (g2), and (h2)). However, in this embodiment, the hysteresis curve of the portion indicated by the solid line (g2) is not symmetrical with respect to the perpendicular bisector Lv, unlike the hysteresis curve of the portion indicated by the solid line (g1) in the example shown in Fig. 4. Specifically, as shown in Fig. 8, the slope of the tangent of the hysteresis curve of the portion indicated by the solid line (g2) of the laminated structure 3 of this embodiment is greater than 1 in the range of greater than the shear strain ε5 and greater than the shear strain ε6 at the intersection of the perpendicular bisector Lv and the hysteresis curve of the portion indicated by the solid line (g2), and is smaller than the slope of the tangent of the hysteresis curve in the range of greater than the shear strain ε6 in the range of less than the shear strain ε6. That is, in this embodiment, the stress decreases at a rate of change greater than 1 as the shear strain decreases from +270% to ε6, and decreases at a rate of change smaller than the rate of change from +270% to ε6 as the shear strain decreases from ε6 to -270%. In this embodiment, the hysteresis curve of the portion indicated by the solid line (h2) is not symmetrical with respect to the perpendicular bisector Lv, unlike the hysteresis curve of the portion indicated by the solid line (h1) in the example shown in Fig. 4. Specifically, the slope of the tangent to the hysteresis curve of the portion indicated by the solid line (h2) is greater than 1 in the range of shear strains smaller than ε7 and smaller than ε8 at the intersection of the perpendicular bisector and the hysteresis curve of the portion indicated by the solid line (h2), and is smaller than the slope of the tangent to the hysteresis curve in the range of shear strains larger than ε8 in the range of shear strains larger than ε8. That is, in this embodiment, the stress increases at a rate of change greater than 1 as the shear strain increases from -270% to ε8, and increases at a rate of change smaller than the rate of change from -270% to ε8 as the shear strain increases from ε8 to +270%.

[0087] The damping characteristics, stiffness, and natural period of the laminated structure 3 according to the equivalent damping constant ratio R will be described with reference to Fig. 9 to Fig. 11. Fig. 9 to Fig. 11 show the results of a simulation performed by vibrating a plurality of laminated structures 3 having different equivalent damping constant ratios R, which is the ratio of the second equivalent damping constant Heq (soft 2) when the maximum shear strain (absolute value) is 270% to the first equivalent damping constant Heq (soft 1) when the maximum shear strain (absolute value) is 270%. The damping characteristics, stiffness, and natural period of the laminated structure 3 each depend on the ratio of the total thickness of the second soft material layer 52 to the total thickness of the first soft material layer 51. In the laminated structure 3 vibrated in this simulation, the ratio of the total thickness of the second soft material layer 52 to the total thickness of the first soft material layer 51 is 100% (i.e., the total thickness of the second soft material layer 52 and the total thickness of the first soft material layer 51 are the same). In this simulation, the multiple laminated structures 3 include two first soft material layers 51 arranged in the upper end region EU, four second soft material layers 52 arranged in the central region C, and two first soft material layers 51 arranged in the lower end region EB. The first soft material layers 51 and the second soft material layers 52 have a circular outer edge shape in a cross section perpendicular to the axis. The first soft material layer 51 has a thickness of 26.8 mm and an outer diameter of 1000 mm. The second soft material layer 52 has a thickness of 26.8 mm and an outer diameter of 1000 mm.

[0088] FIG. 9 shows the equivalent damping constant Heq (product) of the laminated structure 3 when the equivalent damping constant ratio R is 100% (i.e., when the laminated structure 3 does not include the second soft material layer 52 as a soft material layer and is composed only of the first soft material layer 51). 100 The laminate equivalent damping constant ratio Heq (product) / Heq 100 The "equivalent damping constant Heq (product)" refers to the equivalent damping constant of the entire laminated structure 3 made up of a plurality of soft material layers (in this embodiment, the first soft material layer 51 and the second soft material layer 52). The laminate equivalent damping constant ratio Heq (product) / Heq 100 The higher the value, the higher the damping characteristic of the laminated structure 3. As shown in Fig. 9, the laminate equivalent damping constant ratio Heq (product) / Heq 100 decreases approximately linearly as the equivalent damping constant ratio R decreases. That is, the lower the equivalent damping constant ratio R, the lower the damping characteristic of the laminated structure 3 becomes.

[0089] FIG. 10 shows the rigidity modulus G immediately after unloading of the laminated structure 3 (i.e., after unloading at the maximum strain) when the equivalent damping constant ratio R is 100% (i.e., when the laminated structure 3 does not include the second soft material layer 52 as a soft material layer and is composed only of the first soft material layer 51). 100 The stiffness ratio G / G 100 The figure shows the stiffness ratio G / G 100 The higher the value, the higher the rigidity of the laminated structure 3. As shown in Fig. 10, the lower the equivalent damping constant ratio R, the lower the stiffness ratio G / G 100 That is, the lower the equivalent damping constant ratio R, the lower the rigidity of the laminated structure 3.

[0090] FIG. 11 shows the natural period T calculated from the rigidity modulus G immediately after unloading of the laminated structure 3 when the equivalent damping constant ratio R is 100% (i.e., when the laminated structure 3 does not include the second soft material layer 52 as the soft material layer 5 and is composed only of the first soft material layer 51). 100 The ratio of the natural period to the natural period T / T 100 1 is a diagram showing the natural period T of the laminated structure 3, which is a period in the free vibration of the laminated structure 3. The natural period T is proportional to the square root of 1 / k, where k is a spring constant (shear elastic modulus) equivalent to the rigidity modulus G. In other words, the higher the rigidity modulus G, the shorter the natural period T. Furthermore, the longer the natural period T of the laminated structure 3, the longer the natural period of the structure in which the seismic isolation device 1 equipped with the laminated structure 3 is arranged, thereby suppressing the transmission of vibrations such as earthquakes to the structure.

[0091] As shown in Fig. 11, the lower the equivalent damping constant ratio R, the lower the natural period ratio T / T 100 That is, the lower the equivalent damping constant ratio R, the longer the natural period of the laminated structure 3, and accordingly, the transmission of vibrations such as earthquakes to the structure is suppressed. In particular, in the range where the equivalent damping ratio R is 50% or less, the natural period ratio T / T 100 That is, in the range where the equivalent damping constant ratio R is 50% or less, the natural period of the laminated structure 3 becomes longer abruptly as the equivalent damping constant ratio R becomes lower, and accordingly, the transmission of vibrations such as earthquakes to the structure is better suppressed. Furthermore, in the range where the equivalent damping constant ratio R is 15% or more and 25% or less, the natural period ratio T / T 100 In other words, in the range where the equivalent damping constant ratio R is 15% or more and 25% or less, the natural period of the laminated structure 3 becomes longer more abruptly as the equivalent damping constant ratio R becomes lower, and accordingly, the transmission of vibrations such as earthquakes to the structure is further suppressed.

[0092] Considering the simulation results of Fig. 9 and Fig. 11 together, in the range where the equivalent damping constant ratio R is 50% or less, the lower the equivalent damping constant ratio R, the smaller the laminate equivalent damping constant ratio Heq (product) / Heq 100 decreases almost linearly, but the natural period ratio T / T 100 Therefore, the seismic isolation device 1 having the laminated structure 3 with the equivalent damping constant ratio R of 50% or less can effectively suppress the transmission of earthquake and other vibrations to the structure while maintaining high damping characteristics. In addition, when the equivalent damping constant ratio R is in the range of 30% or less, the natural period ratio T / T 100 is higher and can better prevent vibrations from earthquakes, etc. from being transmitted to structures. Furthermore, in the range where the equivalent damping ratio R is 15% or more and 25% or less, the natural period ratio T / T 100 Therefore, the seismic isolation device 1 having the laminated structure 3 with the equivalent damping constant ratio R of 15% or more and 25% or less can better suppress the transmission of earthquake and other vibrations to the structure while maintaining high damping characteristics. In the laminated structure 3 used in this embodiment, the first soft material layer 51 is arranged in the upper end region EU, and the second soft material layer 52 is arranged in the central region C. However, it has been confirmed that similar results can be obtained in terms of damping characteristics, rigidity, and natural period even if this arrangement is changed. In addition, in the laminated structure 3 vibrated in this simulation, the ratio of the total thickness of the second soft material layer 52 to the total thickness of the first soft material layer 51 is 100%, but even if the ratio is different from this (in other words, even if it is fixed to a different ratio), it has been confirmed that the damping characteristics, rigidity, and natural period change similarly with respect to the equivalent damping constant ratio R. For ease of design, it is preferable that the total thickness of the second soft material layer 52 and the total thickness of the first soft material layer 51 are approximately equal. More specifically, the ratio of the total thickness of the second soft material layer 52 to the total thickness of the first soft material layer 51 is preferably 70 to 130%, more preferably 80 to 120%, and most preferably 100% as in this simulation.

[0093] The above description merely discloses some embodiments of the present invention, and various modifications are possible within the scope of the claims. The various configurations employed in the above-described embodiments can be appropriately replaced or combined with each other.

[0094] The seismic isolation device of the present invention is suitable for placement between the superstructure and substructure of a structure (e.g., buildings such as buildings, condominiums, detached houses, warehouses, and bridges) in order to prevent shaking from earthquakes and the like from being transmitted to the structure. [Explanation of symbols]

[0095] 1 Seismic isolation device, 21: upper flange plate; 22: lower flange plate; 3: laminated structure, 31: diameter-varying laminated portion, 32: diameter-constant laminated portion, 4: Hard material layer, 5: soft material layer, 51: first soft material layer, 52: second soft material layer, 6: Covering layer, AX: central axis, C: Central area, E: Edge area, EU: Upper edge area, EB: Lower edge area, La1, Lb1, Ld1, Le1, Lf1, Lg1: Tangent, La2, Lb2, Ld2, Le2, Lf2, Lg2: Tangent, Lss: hysteresis curve, Ls11: hysteresis curve of the first soft material, Ls12: hysteresis curve of the second soft material, Ls13: hysteresis curve of the laminated structure, Ls21: hysteresis curve of the first soft material of the embodiment, Ls22: hysteresis curve of the second soft material of the embodiment, Ls23: hysteresis curve of the laminated structure of the embodiment, L1: A line segment on a hysteresis curve connecting the point where the shear strain is the maximum positive shear strain and the point where the shear strain is the maximum negative shear strain. L2: A line segment drawn perpendicular to the horizontal axis from the point where the shear strain is the maximum positive shear strain and the point where the shear strain is the maximum negative shear strain on the hysteresis loop. Lv: Perpendicular bisector ST+: The point on the hysteresis loop where the shear strain is the maximum positive shear strain. ST-: The point on the hysteresis loop where the shear strain is the negative maximum shear strain

Claims

1. A seismic isolation device comprising a laminated structure in which a plurality of hard material layers and a plurality of soft material layers are alternately laminated in a vertical direction, The plurality of soft material layers include a first soft material layer formed of a first soft material having a first equivalent damping constant, and a second soft material layer formed of a second soft material having a second equivalent damping constant, A seismic isolation device, wherein the second equivalent damping constant when the maximum shear strain is ±270% is 50% or less of the first equivalent damping constant when the maximum shear strain is ±270%.

2. The seismic isolation device according to claim 1, wherein the second equivalent damping constant when the maximum shear strain is ±270% is 30% or less of the first equivalent damping constant when the maximum shear strain is ±270%.

3. The seismic isolation device of claim 2, wherein the second equivalent damping constant when the maximum shear strain is ±270% is greater than or equal to 15% and less than or equal to 25% of the first equivalent damping constant when the maximum shear strain is ±270%.

4. In a hysteresis loop of each of the first soft material and the second soft material in a coordinate system with the horizontal axis representing shear strain and the vertical axis representing stress, when the slope of the tangent on the post-unloading side at the maximum shear strain of the first soft material and the slope of the tangent on the post-unloading side at the maximum shear strain of the second soft material are defined as a first post-unloading tangent stiffness and a second post-unloading tangent stiffness, respectively: A seismic isolation device as described in any one of claims 1 to 3, wherein the first post-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270% is greater than the second post-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270%.

5. In a hysteresis loop of each of the first soft material and the second soft material in a coordinate system with the horizontal axis representing shear strain and the vertical axis representing stress, when the slope of the tangent before unloading at the maximum shear strain of the first soft material and the slope of the tangent before unloading at the maximum shear strain of the second soft material are defined as a first pre-unloading tangent stiffness and a second pre-unloading tangent stiffness, respectively: A seismic isolation device as described in any one of claims 1 to 4, wherein the first pre-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270% is smaller than the second pre-unloading tangent stiffness in the hysteresis curve when the maximum shear strain is ±270%.

6. The seismic isolation device according to claim 1 , wherein the first soft material layer is disposed at the top and bottom of the soft material layers in the laminated structure in the vertical direction.

7. The seismic isolation device described in claim 6, wherein the first soft material layer is arranged only in an end region of the laminated structure, including the top and bottom, located on the end side of the laminated structure in the vertical direction, and the second soft material layer is arranged only in a central region of the laminated structure, located closer to the center than the end region in the vertical direction.

8. The seismic isolation device according to claim 1 , wherein the first soft material layers and the second soft material layers are arranged alternately in the vertical direction.

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