JPH0585700B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a seismic isolation device that protects a structure from earthquakes by reducing vibration energy transmitted to the structure from its foundation. In order to reduce the seismic input transmitted from the ground to a building in the event of an earthquake, a laminate of elastic plates and metal plates (hereinafter referred to as a seismic isolation device) is placed on the foundation, similar to when a building is placed. A seismic isolation construction method has been developed for installation. As shown in FIGS. 1a and 1b, this seismic isolation device consists of one or more elastic plates 1 and a plurality of metal plates 2 alternately laminated and fixed together by vulcanization adhesive or the like. Due to this structure, this seismic isolation device 3 has a large vertical spring coefficient K _v and a small horizontal spring coefficient K _h . A large loading capacity for the building is ensured, and the natural vibration period (hereinafter simply referred to as period T) of the entire system of the building in the horizontal direction can be increased. The effect of increasing the period T of the system will be explained. The maximum periodic component of a typical seismic input is 0.1 to 1.0 seconds. Period T of reinforced concrete buildings
is generally about 0.1 second per floor, and for example, in the case of a three-story building, the period is about 0.3 seconds, so it is within the range of the maximum periodic component of the earthquake input.
For this reason, general reinforced concrete buildings exhibit acceleration characteristics several times higher than earthquake input due to resonance phenomena and are susceptible to earthquake damage. Therefore, by using the above seismic isolation device, the period T of the system can be reduced to 2.
If the time can be changed from seconds to 4 seconds or more, the period will be outside the range of the maximum periodic component of earthquake input, and the structure will be flexible against earthquakes and seismic isolation will be possible. In other words, the seismic isolation device increases the period T of the building system to 2 seconds to 4 seconds or more by using a particularly small horizontal spring coefficient K _h , thereby reducing the acceleration characteristics of the structure in response to earthquake input, and at the same time The structure is designed to absorb the input energy of an earthquake by making it perform a translational motion that is almost like a rigid body. In order to increase the period T of the building system in this way, it is necessary to use a soft material (such as a rubber plate) for the elastic plate 1. However, if a soft elastic plate is used, there is a risk of buckling due to loss of horizontal restoring force against large horizontal displacement. Therefore, the present invention defines a general range of the shear spring coefficient G of the elastic board material that can make the period T of the building system a value of 2 seconds or more, which is sufficient for seismic isolation, and in which buckling does not occur. The purpose is to determine the shape and dimensions of the elastic plate 1. First, the general range of the shear spring coefficient G of the elastic board material is determined. Here, the shear spring modulus G of the elastic board material means that the elastic board only has this material.
Since it is manufactured from a uniform material, it has the same meaning as the shear spring coefficient G of an elastic plate, and will be used in this sense hereinafter. The period T of the building system is

It is expressed as [Formula]. However, M: mass of the building M=W (weight)/g (weight acceleration) ΣK _h : total horizontal spring coefficient of the seismic isolation device ΣK _h = A・G/L _c A: total horizontal spring coefficient of the seismic isolation device Total pressure-receiving area G: Shear spring coefficient of the elastic plate material Lc: Total thickness of the elastic plate in the vertical direction. Therefore, the period T is

It is represented by [ ]. In this equation, the period T is proportional to the product of W/A and Lc divided by G. Therefore, in order to determine the general conditions for G that allow the period T to be 2 seconds or more for buildings in general, W/
This is because it is sufficient to consider general combinations of A and Lc and determine G that allows the period T to be 2 seconds or more for these combinations. Here, W/A (vertical load per unit area)
is generally used in the range of 30 to 300 Kg/cm ² to provide stable vertical support capacity. On the other hand, Lc (the total vertical thickness of the elastic plate) is limited by the installation space (vertical spacing) of the seismic isolation device between the building and its foundation, and the practical range is from several centimeters to several tens of centimeters. be. Therefore, by using relatively small values W/A = 30Kg/cm ² and Lc = 20cm as representative values and substituting them together with T = 2 (seconds) in the above formula, G = 6Kg/cm 2 and Lc = 20cm.
cm ² is found. Therefore, the general condition for G is to be smaller than this value. The significance of the above-mentioned G determination is that it defines a range in which the necessary period T can be easily given to seismic isolation devices used in general structures, and W/A and
There are countless possible combinations of Lc values. For example, G=6Kg/cm ² , W/A=90Kg/cm ² , Lc=
Assuming a combination of 6.6cm and G=3.0Kg/cm ² ,
Any combination such as W/A=30Kg/cm ² and Lc=10cm can be designed. Next, we will apply the above general range of G to the numerical value of an actual building and verify it. This numerical example is
Among buildings that require seismic isolation, two- or three-story reinforced concrete buildings are used because they are relatively light in weight and it is difficult to increase the period T. A two- or three-story reinforced concrete building typically weighs between 150 and 360 tons.
Since the width of the foundation beam is 250 to 300 mm, the diameter of the seismic isolation device that can be installed is 130 mm to 300 mm. In addition, one seismic isolation device shall be installed under each pillar of the building. Considering the above construction conditions, three design examples are listed below. If 27 seismic isolation devices made of elastic plates with a diameter of 130 mmφ are installed in a building weighing 150 TON, the weight will be
If 10 seismic isolation devices made of elastic plates with a diameter of 130 mmφ are installed in a 150 TON building, the weight will be
The third example in C is when six seismic isolation devices made of elastic plates with a diameter of 300 mmφ are installed in a 180 TON building. In order to give the elastic plate 1 a stable vertical support capacity, the vertical load W/A per unit area is determined in the range of 40 to 120 kg/ ^cm2 , and the Assuming that the installation space is relatively narrow, the total vertical thickness Lc of the elastic plate 1 is
It is set to 6cm. In each of these three examples, the period T is either 2 seconds or 4 seconds.
The shear spring coefficient G of the elastic board material required to give the second speed is calculated based on the above formula as shown in the following table.

[Table] Based on the above results, reduce the shear spring coefficient G of the elastic plate material used for the seismic isolation device (use soft rubber)
Therefore, it can be seen that the period T can be increased as necessary, and that the value of the shear spring coefficient G of the elastic board material should be 6 kg/cm ² or less in order to obtain a sufficient seismic isolation effect. As the elastic board material that provides this value, natural rubber, synthetic rubber, or a plastic having rubber elasticity mixed with a reinforcing agent, a softening agent, a hardening agent, an anti-aging agent, etc. can be used. Rubber with a JIS standard hardness of 50 has a spring modulus of 7 to 9 Kg/cm ² for natural rubber and 6 to 7 Kg/cm ² for synthetic rubber ^. In order to give the spring coefficient G, it is sufficient to use rubber with a hardness of 50 or less. However, if a rubber with a small (soft) shear spring coefficient G is used as described above, the vertical spring coefficient _Kv of the seismic isolation device will naturally decrease, and the seismic isolation device will likely buckle under the compressive load due to the weight of the building. It may cause severe deformation and become unusable. In order to prevent this, it is necessary to reduce the shear spring coefficient G while increasing the spring ratio (vertical spring coefficient _Kv /horizontal spring coefficient _Kh ) as large as possible (approximately 300 to 400 or more). In view of the above circumstances, the present invention solves this problem. In other words, the present invention uses an elastic plate material for the seismic isolation device that has a small shear spring coefficient (6 kg/cm ² or less) as described above.
When using an elastic plate (rubber plate)
Limiting the thickness t of the elastic plate to a small value (6 mm or less) (Evaluated by the shape factor, which is the ratio of the thickness t to the diameter D of the elastic plate, D/t≧25, a sufficiently large spring ratio K _v / K _h . Below, the reason why the thickness t of the elastic plate was limited to the above value (6 mm or less) will be explained based on experimental data. Figure 2 shows the elastic plate ( Rubber with a hardness of 37 that gives a shear spring coefficient of 3.3 Kg/cm ² is used for a material of 150 mmφ), and the rubber thickness t is varied in the range of 10 mm to 2.5 mm, and the spring ratio (vertical spring coefficient K _v /horizontal spring This figure shows experimental data obtained by measuring the spring ratio K _v /K _h.The spring ratio K v /K _h was measured by applying a vertical compressive stress (F) of 31 Kg/cm ² as shown in Figure 3. , horizontal distortion (δ) 100%
(Horizontal strain δ/elastic plate thickness t=1). In addition, in this experiment, the number of layers of elastic plates was varied so that the total thickness of the elastic plates (rubber plates) was kept constant at 6 cm, for example, 12 layers for 5 mm thickness and 10 layers for 6 mm thickness. I have to.
In addition, the display of each point in Fig. 2, for example, 150×
2.5-24 indicates that 24 elastic plates (rubber plates) with a diameter of 150 mmφ and a thickness of 2.5 mm are laminated alternately with metal plates. As can be seen from this example, by setting the thickness t of each elastic plate to 6 mm, a spring ratio K _v /K _h = 270, which is a condition that does not cause buckling, can be obtained, and the point at this thickness of 6 mm is obtained. However, this becomes an inflection point in the characteristic of elastic plate thickness-spring ratio, and when the thickness becomes smaller than 6 mm, and becomes 5 mm, it increases rapidly. Especially 4
When the value is less than mm, the increase rate becomes large, and a spring ratio K _v /K _h of 450 or more gives a very good value. In addition, if the seismic isolation device is not subject to any restrictions on installation work, and its height may be small, the number of laminated elastic plates can be determined under the condition that the thickness t of one elastic plate is 6 mm or less. You can do less. As an example of this, FIG. 4 shows the spring ratio K _v /K _h when only one elastic plate is used and its thickness is varied. The diameter of the elastic plate is 150mmφ, and the vertical direction
Apply 6TON compressive stress and horizontal strain is 100%
(Horizontal strain δ/elastic plate thickness t = 1).The display of each point, for example 150 x 5-1, is the same as in the case of Fig. 2, where the elastic plate has a diameter of 150 mmφ and a thickness of 5 mm ( rubber plate) represents one layer. The data in parentheses is the hardness 37 which gives the shear spring coefficient G = 3.8Kg/cm ²
The data in parentheses shows the case when a rubber with a hardness of 19 giving a shear spring coefficient G=1.5 Kg/cm ² is used. The data using this single-layer elastic plate also showed the same change in spring ratio as when using a multi-layer elastic plate,
When the thickness t of the elastic plate is 6 mm, the spring ratio K _v /K _h is ()
290 is obtained in the case of (), and 250 is obtained in the case of (), and it can be seen that the spring ratio K _v /K _h increases rapidly as the thickness t becomes smaller. In other words, in order to obtain the required spring ratio K _v /K _h (approximately 300 to 400 or more) in the seismic isolation device of the present invention, the thickness t of the elastic plates should be 6 mm or less, regardless of the number of layers of elastic plates. I know it's good. When a seismic isolation device with a larger elastic plate diameter was prototyped within the above-mentioned limit range of the seismic isolation device of the present invention, an extremely large spring ratio K _v /K _h was obtained as shown below. In other words, the diameter of the elastic plate is 250mmφ, the thickness t of each elastic plate is 5mm, the number of laminated layers of the elastic plate is 12, and the material of the elastic plate is 100% natural rubber, 10% carbon, 3% anti-aging agent, and 3% additive. When we manufactured a seismic isolation device using a device with a spring coefficient of 3.5 Kg/cm ² by adding sulfurizing agent 3, the spring ratio K _v /K _h was extremely large at 700. In addition, in each of the above experimental data, the required spring ratio
As a condition for obtaining K _v /K _h , we investigated the thickness t per elastic plate, which can be calculated using the shape factor (diameter D of elastic plate/thickness t per elastic plate) shown in Figure 3. When considered, it can be obtained under the following conditions. In other words, the shape factor (D/t) in the data at each point shown in Figures 2 and 4 is that the diameter of the elastic plate is /50mmφ, so the thickness t of the elastic plate is 10mm.
Shape factor (D/t) when changing the range of ~2.5mm
varies from 15 to 60. Here the spring ratio K _v /K _h is 300
Considering the shape factor (D/t) of a seismic isolation device that gives about 400 or more, the shape factor (D/t) can be determined to be 25 or more corresponding to a thickness of 6 mm or less. It is clear from FIG. 4 that this point of shape factor 25 is an inflection point, and as the shape factor becomes larger than this point, the spring ratio K _v ·K _h increases rapidly. The shape factor (D/t) of the seismic isolation device using the elastic plate with a diameter of 250 mm and a thickness of 5 mm is calculated to be 50, and considering that the spring ratio was 700 as mentioned above, this was calculated as Diameter of the elastic plate shown in the figure
When applied to the data for 150mmφ, it can be seen that the shape factor is approximately 50 for a spring ratio of 700.If the shape factor is used as a standard in addition to the thickness of the elastic plate 1, the conditions for not buckling (the required It can be seen that the spring size ratio) can be determined more reliably. In addition, the present invention has a shear spring coefficient of 6 for the elastic plate material.
By limiting the horizontal spring coefficient K _h of the seismic isolation device to Kg/cm ² or less, the thickness of the elastic board material is 6 mm or less, and its shape factor (D/t) is 25
By limiting the above, the spring ratio _{K v} /K _h is ensured to be larger than the predetermined value. The elastic plate (rubber plate)
Since it is inversely proportional to the total vertical thickness L _c , the elastic plate (rubber plate)
By appropriately selecting the diameter and number of layers,
It is possible to obtain a structure whose performance is adapted to the building. In the above embodiment, a circular elastic plate is used, but the elastic plate may have any shape such as a rectangular shape. In this case, the shape factor is the diameter D of a circular elastic plate with the same cross-sectional area as its horizontal cross-sectional area.
Calculated using As explained above, according to the present invention, the elastic plate of the seismic isolation device has a shear spring coefficient of 6 kg/cm or less,
By using an elastic plate with a thickness of 6 mm or less (and D/t≧25 when evaluated by shape factor), the spring ratio (vertical spring The coefficient K _v /horizontal spring coefficient K _h ) is approximately 300 to 400 or more, and the small horizontal spring coefficient K _h allows buildings, etc. to have a natural vibration period T of 2 seconds or more necessary for seismic isolation. It is possible to manufacture seismic isolation devices that provide Note that the elastic plate (rubber plate) specified in the present invention with a thickness of 6 mm or less has not been used in the past (generally, there have been only use cases or research reports of a thickness of several cm or more). , the claimed invention particularly includes:
It is significant that practical value has been found in the thin region of the elastic plate (rubber plate).

[Brief explanation of the drawing]

Figure 1a is a side view showing the structure of the seismic isolation device;
Figure b is a plan view of the same, Figure 2 is a characteristic diagram showing the change in spring ratio K _v /K _h with respect to elastic plate thickness t in a seismic isolation device in which multiple elastic plates are laminated, and Figure 3 explains shear strain. Figure 4 shows the spring ratio K _v /K _h for the elastic plate thickness in a single-layer seismic isolation device.
FIG. 1... Elastic plate, 2... Metal plate, 3... Seismic isolation device, G... Shear spring coefficient of elastic plate material, K _v /
K _h ... Spring ratio, T... Natural vibration period, t... Thickness of elastic plate.

Claims (1)

[Claims] 1. It is constructed by alternately laminating and fixing at least one elastic plate and a plurality of metal plates, and is sandwiched between the structure and its foundation, and has the following formula [Formula] ΣKh =A・G/Lc However, ΣKh: Total horizontal spring coefficient of the base isolation structure M: Amount of building material A: Total pressure receiving area of the elastic plates (rubber plates) of the total base isolation device G: Shear spring coefficient of the elastic plate material Lc: Natural vibration period T in the horizontal direction of the structure expressed by the total vertical thickness of the elastic plate (rubber plate)
However, in a seismic isolation device that is set for 2 seconds or more, the shear spring coefficient G of the elastic plate material should be 6 kg/cm ² or less, the thickness t of each elastic plate should be 6 mm or less, and the diameter D of the elastic plate should be 6 mm or less. A seismic isolation device characterized in that the shape factor (D/t), which is the ratio of the thickness t to the thickness t, is 25 or more.