JPH035450B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention prevents vibrations from being transmitted to the surrounding ground from the foundation on which mechanical devices that generate vibrations, such as large shaking tables, are installed and causing vibration damage to nearby buildings and facilities. In order to prevent earthquake waves from being transmitted from the external ground to the foundations on which important equipment such as nuclear power plants that require particularly strict seismic resistance are installed, destroying such important equipment and causing serious damage. , relates to the structure of a vibration insulating foundation that effectively isolates vibration between the foundation and the ground.

In recent years, regulations for seismic design for nuclear power plants, thermal power plants, chemical plants, etc. have become increasingly strict, and as a result, it has become necessary to demonstrate the seismic performance of buildings and equipment used in these plants. For this purpose, rigorous vibration experiments using large shaking tables have begun to be carried out.

Due to the specifications of this type of shaking table, it is necessary to generate an extremely large excitation force, and this excitation force is transmitted to the surrounding ground through the foundation, vibrating nearby buildings, etc., and causing residents to There are quite a few examples of damage caused and problems. As one of the countermeasures against such a case, it is well known that an effective method is to elastically support the foundation of the shaking table against the ground using a suitable spring device to provide so-called vibration isolation.

By the way, in this type of shaking table, the foundation is also inevitably vibrated by the reaction force from the shaking table, so in order to maintain good vibration characteristics of the shaking table,
The weight of the foundation must be sufficiently large compared to the weight of the shaking table. Therefore, it is generally considered desirable that the weight of the foundation be at least 40 to 50 times the maximum weight of the shaking table including the loaded items. When the foundation weight increases in this way, a large number of spring devices are required to elastically support it, which poses a problem in that the cost increases.

To explain the above numerically using an actual example, the maximum weight of the shaking table including the loaded items is, for example,
In the case of 50t, it is desirable that the foundation weight be at least 2000t. There are metal springs, anti-vibration rubber, air springs, etc. as springs for elastically supporting this foundation, but when the target is a vibration table like this example, the load-bearing force can be varied over a wide range, and the support Air springs are ideal because the height can be freely adjusted and controlled. Therefore, we decided to use an air spring with a maximum static load of 16 tons, which is used in vehicles.
The required number of air springs is (2000+50)/16=128, or 128.

On the other hand, in the case of the vibration insulating foundation of the present invention, a water tank sufficient to accommodate the foundation is constructed in advance, the foundation is immersed in the water, and the buoyancy of the acting water is utilized. The load on the support springs of the foundation can be significantly reduced. For example, if the foundation is a regular prism with a side of 16 m and the drainage is 6.5 m, the buoyant force acting on the foundation will be 16 x 16 x 6.5 x 1 = 1664 t, so the excess weight of 2050 - 1664 = 386 t will be the same as above. If it is supported by air springs, 386/16=24 In other words, the number of air springs in this case is only 24. Of course, in this case, if the submerged volume of the foundation is increased, the number of air springs can be further reduced, and when the buoyancy is exactly balanced with the weight of the foundation, the foundation will be completely floating in the water tank. , the support spring may not be needed.
However, in practice it is necessary to place a suitable small number of air springs so that the foundation can be fixed or elastically supported at will.

Now, the foundation in the above state is isolated from the surrounding ground by a layer of water of a certain thickness, but if the foundation continues to vibrate in this state,
The vibrations become pressure waves that propagate through the water and are eventually transmitted to the ground. Therefore, in order to reduce this vibration transmission, in the present invention, a large number of air chambers are provided in the water-contacted portions of the side and bottom surfaces of the foundation. Due to the spring action of the air in the air chamber, the vibration transmission through the water is effectively reduced. Regarding the shape and size of these air chambers,
As will be shown in the examples described below, in short, as long as the total volume of the air chamber is made sufficiently large, this underwater vibration transmission can be reduced as much as possible. Therefore, in the vibration-isolating foundation according to the present invention, the transmission of the vibrations of the foundation to the surrounding ground is mostly carried out through a very small number of support springs, and is therefore very small, resulting in a very successful result. This results in a vibration isolation effect.

Furthermore, the vibration-isolating foundation according to the invention is also economically advantageous in that relatively expensive spring devices are largely saved. However, regarding economic efficiency, in the case of the present invention, extra costs are required for constructing the water tank, water supply equipment, and providing an air chamber and air supply device on the foundation, so this point must be taken into consideration when making a comprehensive judgment. Must be. However, generally speaking, as the weight of the foundation increases, the effect of saving on spring equipment becomes more prominent, so for large foundations above a certain level, the method of the present invention is more economical than the ordinary simple spring support method. It will also be advantageous.

Next, we will discuss issues related to seismic design of nuclear power plants, etc. As mentioned above, as the seismic design requirements for these plants have become increasingly strict in recent years, so-called seismic isolation structure methods have been attempted as an active countermeasure against this. This is done by elastically supporting the important equipment in these plants along with their foundations against the ground, insulating the transmission of seismic waves from the external ground, and
This is intended to create a seismically isolated state. For example, in the example already in use at nuclear power plants in France, Iran, etc., the foundation is supported by many large laminated, square vibration-proof rubbers, and the relatively flexible shear elasticity of the foundations is used to support horizontal There is a method to measure directional vibration isolation. Calculations show that this method provides superior seismic isolation against horizontal motion. However, this method
Due to the characteristics of the vibration isolating rubber mentioned above, it is impossible to have sufficient flexibility in the vertical direction, so not only is it not expected to have a seismic isolation effect against vertical motion, but it may even amplify vertical motion. This remains a major problem in that it is possible.

In theory, the above problem can be easily solved by using a spring device that uses an air spring or a metal spring in combination with a suitable damper instead of the anti-vibration rubber, but in practice, the foundation weight in this case is Due to its large size, a huge number of spring devices are required, making this method extremely difficult to implement. All these difficulties are completely solved by applying the vibration isolation basis of the present invention.

According to an actual example, in a 500,000 KW class nuclear power plant, the total weight of the foundation containing the reactor body, containment vessel, peripheral equipment, and the building that houses them is approximately 160,000 tons. If you try to support this foundation with just a normal spring device, even if you use a large air spring with a normal static load of 50 tons, which is possible with current technology,
A large quantity of 3200 pieces will be required. In contrast, in the case of the present invention, most of the 160,000 tons of foundation weight can be balanced by immersing the foundation in a water tank to create buoyancy, so the remaining weight can be reduced. Only a small number of spring devices are needed for support. For example, the dimensions of the foundation are horizontal cross-sectional area ^of 6000m2,
If the buoyancy is 25 m, the buoyancy will be 150,000 tons, so if the remaining weight of 10,000 tons is supported by the same air springs as above, only 200 will be needed. Of course, this number can be reduced by selecting the dimensions of the foundation, but as a practical matter,
An appropriate number is required, taking into account conditions such as increasing the stability of the foundation and imparting damping properties.

The reason why the vibration insulation property of the foundation of the present invention against seismic waves, that is, the seismic isolation property, is much superior to that of a method in which the foundation is directly supported only by ordinary spring devices is due to the same reason as stated in the previous example. explained in.

Embodiments of the present invention will be described below based on the accompanying drawings.

1, 2, and 3 show the structure of a foundation when the present invention is applied to the foundation of a large-sized shaking table. FIG. 1 is a plan view of the foundation, FIG. 2 is a view in the direction of the - arrow in FIG. 1, and FIG. 3 is a view in the direction of the - arrow in FIG. In these figures, a foundation 1 is housed in a water tank 3 constructed by excavating the ground 2, and the water tank 3 is filled with water 4 up to the water level 5. As a result, the foundation 1 receives a buoyant force corresponding to the weight of the same amount of water as the foundation volume below the water surface. The remaining weight after subtracting this buoyancy from the total weight of the foundation including the loaded objects is the weight of a total of 24 spring devices 8 (in this example supported by air springs).

In the water-contact parts of the side and bottom surfaces of the foundation 1, there are a side air chamber 9 and a bottom air chamber 1 divided into a large number of sections.
0 is set. The side air chamber is the top plate 9.1,
Surrounded by a back plate 9.2, a top plate 9.3 and a side plate 9.4, the surrounding water 4 enters the air chamber through an opening 9.5 made at the bottom of the top plate 9.1 and enters the air chamber. It is in contact with the air at the water surface 11. Also, bottom air chamber 1
0 is surrounded by a top plate 10.1 and a side plate 10.2, and the air in the room is in contact with the water 4 in the tank at the water surface 12 at the bottom of the room. The number of air chambers is, in this example,
Side air chambers 9 have 3 layers and 8 compartments per side, totaling 24
There are 96 chambers in total on each side, and the bottom air chambers 10 are arranged in 8 rows and 8 columns, for a total of 64 chambers.

The reason why the air chamber is divided into a large number of sections is to prevent the stability of the foundation from being affected by the free water surface in the air chamber and to ensure sufficient stability of the foundation. However, at the same time, this is to help prevent unnecessary disturbances caused by ripples occurring on the free water surface in the air chamber due to vibrations in the foundation.

Reference numeral 13 in FIGS. 1 and 2 is a vibration table, which is connected to the foundation 1 by a vertical support and vibration device 14 and a horizontal support and vibration device 15. Reference numeral 16 denotes a test specimen mounted on the shaking table 13. Note that water supply equipment for the water tank and air supply equipment for the air chamber of the foundation are required, but these are omitted in the figure.

FIG. 4 is a conceptual diagram when the present invention is applied to the foundation of an entire building housing a nuclear reactor, its containment vessel, and its peripheral equipment, and shows a cross section of the building and foundation. The configurations of the support spring device of the foundation and the air chamber of the foundation in this case are completely the same in principle as in the previous example shown in FIGS. 1 to 3, except for the size and number. Explaining based on FIG. 4, the foundation 1 containing the reactor building 17 is housed in a water tank 3 constructed by excavating the ground 2.
is filled with water 4 up to the water level 5. The weight remaining after subtracting the buoyancy of the water from the weight of the foundation 1 is supported by the spring device 8. A side air chamber 9 and a bottom air chamber 10 are provided in the water-contacted part of the foundation 1, and the air inside the side air chamber 9 is in contact with the water 4 of the aquarium entering and exiting through the opening 9.5 at the water surface 11. On the other hand, the air inside the bottom air chamber 10 is in contact with the water 4 of the aquarium at the water surface 12 below. The number of these air chambers in this example is that the side air chambers 9 have 9 layers and 16 sections per side, for a total of 144 chambers, and a total of 576 on each side.
The bottom air chambers are arranged in 16 rows and 16 columns, for a total of 256 rooms.

Next, the operation of the present invention will be described. For convenience,
Consider the case of horizontal vibration as an example. Referring to Figure 2, if the foundation is now slightly displaced to the right,
The water on the right side of the foundation is pushed, and part of it enters the air chamber through the opening 9.5 of the side air chamber 9, and the other part goes around to the front and rear sides and bottom and flows to the left. , it ended up coming around to the left side. The water entering the right side air chamber pushes up the water level 11 in the room and compresses the air in the room. At this time, a spring action of air occurs. Then, the air pressure in the room increases, and this pressure increase becomes water pressure and is transmitted to the right tank wall.
On the other hand, the water on the left side of the foundation is drawn in the opposite direction, so the water level in the left side air chamber falls, the air in the room expands, and the air pressure decreases. This pressure reduction is transmitted via water pressure to the left aquarium wall. In this way, the horizontal displacement of the foundation causes a variation in the air pressure in the side air chambers, which exerts a force on the aquarium wall via water pressure. In addition, as mentioned above, the water flowing from the left and right sides through the front and rear sides and the bottom produces the effect of so-called virtual mass due to the vibration of the foundation.

As is clear from the above description, in the case of the present invention,
The excitation force on the foundation is transmitted to the ground through the support springs around the foundation, and the air pressure in the air chamber on the side of the foundation (for horizontal vibration) or the air chamber at the bottom (for vertical vibration) becomes water pressure. This is done by acting on the aquarium wall.

FIG. 5 shows an example of calculation results of the transmission rate of horizontal vibration to the ground (ratio of the above-mentioned transmission force to the excitation force) in the present invention shown in FIGS. 1 to 3. n on the horizontal axis of the figure is the frequency (Hz) of the excitation force. The solid line in the figure represents the case of the present invention, and the broken line represents the case of simple support with 128 air springs as described above. In the case of simple spring support, there is a resonance point at n=0.83Hz, whereas in the case of the present invention, there are two resonance points at n=0.17Hz and 0.72Hz. This is because the vibration system in the case of the simple spring support method is a one-degree-of-freedom system consisting of the support spring and the base mass, whereas in the case of the present invention, this base mass is connected to the base mass via the spring provided by the side air chamber. Furthermore, the water around the foundation is combined as a virtual mass, resulting in a two-degree-of-freedom system. The vibration at n=0.17Hz is mainly a mode in which the virtual mass vibrates, and the one at n=0.72Hz is a mode in which the foundation mainly vibrates.

As is clear from Figure 5, the transmissibility of the shaking table foundation in this calculation example is n
At n≒1.2Hz or more, the value is less than 1, which shows the vibration isolation effect.However, in the case of the present invention, the vibration insulation is even better, and the transmissibility is less than 1 at n≒1Hz or more, and at about 5Hz or more, it becomes a simple spring. Approximately for support method
This is a 40% decrease. In this embodiment, there is no need to further reduce the transmissibility, so the difference between the two methods remains at this level, but if necessary, in the case of the present invention, the volume of the base side or bottom air chamber can be increased. As mentioned before, if this is done, the transmission rate can be further reduced.

In the above example, n=0.17Hz and 0.72Hz
Resonance can be easily avoided by actually operating the shaking table by following the steps below. That is n=1.2Hz
Below, the supporting air springs are deflated and the foundation is placed directly on the ground, effectively keeping it stationary. Even if this is done, the excitation force generated from the vibration table is extremely small in this low frequency range, so there is no problem. When n=1.2Hz or higher, air is sent to the air spring to lift the foundation and return it to its normal state.

The purpose of the foundation for a nuclear power plant according to the present invention shown in Fig. 4 is to insulate the transmission of seismic waves from the external ground, but the concept of transmissibility described above is still applicable to this case as well. be done. That is, the transmissibility in this case can be considered as the ratio of the vibration amplitude of the foundation to the vibration amplitude of the external ground. Therefore, as can be easily inferred from the trends in Figure 5,
In the case of the foundation shown in Fig. 4, an extremely superior vibration isolation effect or seismic isolation effect can be obtained for vibration frequencies around 2.5 to 6 Hz, where acceleration is particularly large during horizontal motion due to earthquakes.

It should be noted here that in the horizontal motion of an earthquake,
Sometimes there are vibration components with particularly long periods and large amplitudes. Therefore, in the case of seismic isolation foundations, it is necessary to prevent the low frequency resonance that appears below 1 Hz in Figure 5 from occurring. However, it is possible to prevent sloshing of water in the aquarium by simple measures such as placing suitable baffles in the water around the foundation, and also by installing suitable dampers in the supporting spring system of the foundation, especially by simply installing suitable baffles in the water. The resonance of the foundation at low frequencies can be easily suppressed by methods such as installing a friction damper with a unique structure.

In the case of horizontal vibration, strictly speaking, the tilt vibration of the entire foundation is coupled to some extent, so the vibration degree of freedom is 3, and as a result, the natural frequency of the foundation, and therefore the number of resonance points, is 3. However, as a practical matter,
Since the influence of this tilt vibration is small, no essential errors occur even in the analysis of the two-degree-of-freedom system as described above. Of course, in this case, if the height of the center of gravity of the entire foundation is matched with the horizontal spring center plane by combining the spring actions of the support springs of the foundation and the side air chambers, the tilting vibration of the foundation becomes independent. , the above-mentioned horizontal vibration analysis holds true as is.

As is clear from the above explanation, according to the present invention, (1) it can be applied to foundations on which machines and devices that generate vibrations, such as large-scale shaking tables, are mounted, and can be applied to foundations on which vibration-generating machines and devices such as large-scale vibration tables are mounted, and can achieve an extremely excellent vibration isolation effect at a relatively low cost; can be demonstrated.

(2) It can be applied to the foundations of facilities that require especially strict seismic resistance, such as nuclear power plants, to provide extremely effective seismic isolation in both vertical and horizontal directions, which is difficult to achieve with other methods, through relatively easy construction. can be demonstrated effectively.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment in which the present invention is applied to the foundation of a large shaking table, and is a plan view of the foundation, Fig. 2 is a view taken along the - line in Fig. 1, and Fig. 3 is - in Fig. 1.
4 is a conceptual diagram when the present invention is applied to the foundation of important equipment such as a nuclear reactor, and FIG. 5 is a cross-sectional view of the reactor building and foundation, and FIG. 2 is a graph showing an example of calculation results of the transmissibility of horizontal vibration in the vibration isolation foundation of the present invention shown in FIG. In these diagrams, 1 is the foundation, 2 is the ground, and 3
is the water tank, 4 is the water in the tank, 5 is the water surface of the tank, 6 is the periphery of the foundation, 7 is the outer edge of the tank, 8 is the spring device, 9 is the side air chamber of the foundation, 9.1 is the side air chamber 9.2 is its back plate, 9.3 is its top plate, 9.4 is its side plate, 9.5 is its opening, 10
is the bottom air chamber of the foundation, 10.1 is the upper plate, 1
0.2 is the side plate, 11 is the water surface in the side air chamber,
12 is the water surface in the bottom air chamber, 13 is the vibration table, 14
15 indicates its vertical support and vibration device, 15 indicates its horizontal support and vibration device, 16 indicates the vibration test body, and 17 indicates the reactor building.

Claims (1)

[Claims] 1. A foundation on which mechanical equipment or equipment, etc. is installed is housed in a water tank, and the weight of most of the entire foundation, including the equipment or equipment, is balanced by the buoyancy of the water in the tank, and the remaining weight is It is supported by a spring device installed between the periphery of the foundation and the vicinity of the outer edge of the water tank, and the water-contact part of the foundation is provided with an air chamber partitioned into many parts, and the air chamber has a lower surface that absorbs the air in the air chamber. A structure of a vibration insulating foundation, characterized in that it is configured so that it comes into contact with water in an aquarium.