Patent Publication Number: US-6336296-B1

Title: System floor and construction method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related and claims priority, under 35 U.S.C. §119, to Japanese Patent Application No. 10-373989 filed on Dec. 28, 1998 and Japanese Patent Application No. 10-373990 filed on Dec. 28, 1998, the entire contents of which two Japanese Patent Applications are hereby incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a floor system built on a base floor so that cables, such as power cables or signal cables, can be laid in a space between a bottom of the floor surface of the floor system and the base floor, wherein the cables are connected to various electronic devices installed on the floor surface in an office and more particularly, to a structure of a floor system having a seismic isolation structure. 
     2. Discussion of Background 
     A floor system, used for a floor of an office where various electronic devices are installed, is constructed in such a manner that a plurality of floor panel units are supported by supports distributed on a base floor, and a space, formed between the bottom of the panel units and the top of the base floor, may house cables connected to the electronic device. 
     Such a floor system, as described immediately above, has low safety against an earthquake due to its structure. In fact, even during an earthquake having a medium magnitude on the Richter scale and wherein no buildings collapse, the floor system would most likely be extremely affected, and various office equipment, such as electronic devices, information devices, conmmunication devices, and office desks, all of which are usually installed on a floor system, would most likely be heavily damaged. Therefore, there are increasing requests for an anti-earthquake or seismic isolation design of a floor system itself in addition to the anti-earthquake design of a building. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a floor system, of a seismic isolation type, having a simple structure, and which can be produced and constructed at a low cost. 
     Another object of the present invention is to provide a floor system having a most suitable seismic isolation characteristic according to a building or a floor of the building. 
     Still another object of the present invention is to provide a floor system whose seismic isolation characteristic can be easily adjusted according to circumstances. 
     A further object of the present invention is to provide a floor system for easily replacing an existing floor system of a non-seismic isolation type with a floor system of a seismic isolation type. 
     To accomplish the above objects, the floor system, according to a first embodiment of the present invention, provides a space for laying cables between the bottom of the floor surface of the floor system and a base floor on which the floor system is built. The floor system includes: a sliding surface formed on at least a part of the base floor; a plurality of supports arranged on the sliding surface so as to freely slide; and a plurality of panels, which are mutually connected to each other having ends thereof fixed to the plurality of supports, and which form a floor surface with a space between the bottoms of the plurality of panels and the top of the base floor on which the floor system is built, wherein the floor system is characterized in that the coefficient of friction between the bottoms of the plurality of supports and the sliding surface is within the range from 0.09 to 0.25. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the sliding surface is composed of any one of the following: a non-ferrous metal, such as a stainless steel sheet or a hard plated steel sheet; a plastic coated plate wherein the coating includes polytetrafluoroethylene sold under the trademark “Teflon”; and a plastic plate including polytetrafluoroethylene. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the bottoms of the plurality of supports are composed of any one of a group consisting of plastic, brass, iron, or hard plated iron. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the bottoms of the plurality of supports are attached to a support leg, wherein the support leg has a surface in contact with the sliding surface, and the surface of the support leg is composed of any one of a group consisting of any one of plastic, brass, iron, or hard plated iron. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the hard plating, of both the hard plated steel sheet and the hard plated iron mentioned above, includes chromium. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the plastics are any one of a group consisting of plastics made entirely of polytetrafluoroethylene, plastics made of some polytetrafluoroethylene, plastics made of some oil and carbon, and plastics made of some of a solid lubricant. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the sliding surface has a sufficient area so that the plurality of supports can slide by a distance of at least ±10 cm or more. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that at least a part of the cables (i.e., that part which is in contact with the sliding surface) is made of a member for reducing the frictional resistance, wherein the member is made of some of a material for reducing frictional resistance, such as polytetrafluoroethylene. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the cables, which are laid in the space between the bottom of the plurality of panels and the top of the base floor, have enough slack so that a sliding operation of the plurality of supports is not restricted. 
     The floor system, according to the first embodiment of the present invention, is also characterized in that the plurality of panels are made of approximately square plates having corners which are fixed to the plurality of supports. 
     A floor system, according to a second embodiment of the present invention, provides a space for laying cables between a bottom of a plurality of panels of the floor system and a top of a base floor on which the floor system is built. The floor system includes: a plurality of sliding plates arranged on the base floor; a plurality of supports arranged on the sliding plates so as to freely slide; and a plurality of panels, which are mutually connected to each other by having ends thereof fixed to the plurality of supports, and which forms a floor surface with a space between the bottoms of the plurality of panels and top of the base floor on which the floor system is built. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the sliding plates are composed of any one of a group consisting of: a non-ferrous metal, such as a stainless steel sheet or a hard plated steel sheet; a plastic coated plate having a coating made of some polytetrafluoroethylene sold under the trademark “Teflon”; and a plastic plate made of some polytetrafluoroethylene. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the bottoms of the plurality of supports are composed of any one of a group consisting of plastic, brass, iron, and hard plated iron. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the bottoms of the plurality of supports are attached to a support leg, wherein the support leg has a surface in contact with the sliding plates, and the surface of the support leg which is in contact with the sliding plates being composed of any one of a group consisting of plastics, brass, iron, and hard plated iron. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the hard plating, of both the hard plated steel sheet and the hard plated iron mentioned above, is composed chromium. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the plastic is any one of a group consisting of plastic made entirely of polytetrafluoroethylene, plastic composed of some polytetrafluoroethylene, plastic made of some oil and carbon, and plastic made of some solid lubricant. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that each of the sliding plates has a sufficient area to allow the plurality of supports to slide a distance of at least ±10 cm or more. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that at least a part of the cables (i.e., that part which is in contact with the sliding plates) is made of a member for reducing frictional resistance, wherein the member is composed of some of a material for reducing frictional resistance, such as polytetrafluoroethylene. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the cables, which are laid in the space between the plurality of panels and the base floor, have enough slack so that a sliding operation of the plurality of supports is not restricted. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that either the sliding surface/plate) or the bottoms of the plurality of supports/support legs are made of any one of a group consisting of: a non-ferrous metal, such as a stainless steel sheet or a hard plated steel sheet; a plastic coated plate having a coating at least partially made of polytetrafluoroethylene sold under the trademark “Teflon”; and a plastic plate made of at least some polytetrafluoroethylene. 
     The floor system, according to the second embodiment of the present invention, is also characterized in that the plastic is any one of a group consisting of: plastic made entirely of polytetrafluoroethylene; plastic made of some polytetrafluoroethylene; plastic made of some oil and carbon; and plastic made of some solid lubricant. 
     A method for constructing a floor system, according to a third embodiment of the present invention, includes the steps of: forming a space for laying cables between bottoms of a plurality of panels of the floor system and a top of a base floor on which the floor system is built; forming a sliding surface on at least a part of the base floor; arranging a plurality of supports, each having pedestals and a bottom, on the sliding surface so that the bottom of each support is in contact with the sliding surface; and forming a floor surface by mutually connecting the plurality of panels to each other by having the ends thereof fixed to the pedestals of the each support of the plurality of supports, wherein the sliding surface and the bottoms of the plurality of supports are made of materials having a coefficient of friction within a range of from 0.09 to 0.25. 
     A method for constructing a floor system for forming a space, in which cables can be laid, between a bottom of a floor surface of the floor system and a top of a base floor on which the floor system is built, according to a fourth embodiment of the present invention, includes the steps of: arranging a plurality of sliding plates on the base floor; arranging a plurality of supports, each support of the plurality of supports having a pedestal and a bottom, on the sliding plates so that the bottom of each support is in contact with the sliding plates; and forming the floor surface by mutually connecting a plurality of panels to each other by having the ends thereof fixed to the pedestals of the plurality of supports. 
     A method for constructing a floor system for forming a space for laying cables between a bottom of the floor surface of the floor system and a top of a base floor on which the floor system is built, wherein the floor system is built on different floors of a building, according to a fifth embodiment of the present invention, and includes the steps of: forming a sliding surface on at least a part of the base floor of each floor; arranging a plurality of supports, wherein each support of the plurality of supports has a pedestal and a bottom on the sliding surface, so that each support of the plurality of supports is arranged in a manner that the bottom of each support is in contact with the sliding surface; and forming a floor surface by mutually connecting a plurality of panels to each other by fixing the ends thereof to the pedestal of each support of the plurality of supports, and wherein the sliding plates and bottoms of the plurality of supports are made of materials having a coefficient of friction which is within the range from 0.09 to 0.25, and wherein the coefficient of friction on a lower floor is selected to be smaller than the coefficient of friction on a higher floor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a part of a floor system according to an embodiment of the present invention. 
     FIG. 2 is an enlarged view of a support shown in FIG.  1 . 
     FIG. 3 is a partial cross-sectional view showing a structure of a support leg attached to a bottom of the support shown in FIGS. 1 and 2. 
     FIG. 4 is an exploded perspective view of the structure of the support leg attached to the bottom of the support shown in FIG.  3 . 
     FIG. 5 is a perspective view showing another embodiment of the support leg used in the floor system according to the present invention. 
     FIG. 6 is a graph and tables showing the results of the static load test under a friction condition for the floor system according to the present invention. 
     FIG. 7 is also a graph and tables showing the results of the static load test under a maximum friction condition for the floor system according to the present invention. 
     FIG. 8 is a graph and table showing the results of the vibration test under a maximum friction condition for the floor system according to the present invention. 
     FIG. 9 is also a graph and table showing the results of the vibration test under a maximum friction condition for the floor system according to the present invention. 
     FIG. 10 is a graph showing the analytical results of the seismic isolation effects under various friction conditions when a floor system, according to the present invention, is installed in a building having a plurality of floors. 
     FIG. 11 is also a graph showing the analytical results of another seismic isolation effect under various friction conditions when the floor system, according to the present invention, is installed in the building having a plurality of floors. 
     FIG. 12 is a perspective view showing another embodiment of the support used in the floor system according to the present invention. 
     FIG. 13 is a perspective view showing still another embodiment of the support used in the floor system according to the present invention. 
     FIG. 14 is a schematic perspective view showing a cable laid in the floor system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be explained hereunder with reference to the accompanying drawings. 
     FIG. 1 is a perspective view showing a part of a floor system according to an embodiment of the present invention. In FIG. 1, approximately square sliding plates  11 , preferably made of stainless steel, are arranged at equal intervals and fixed to the base floor  10  of a building by a mechanical fixing method, such as an adhesive or bolts. The sliding plates  11  may be made of various materials such that the sliding plates  11  may be a stainless steel sheet, a chromium or other rigid metal plated steel sheet, a plastic coated sheet, wherein the plastic of the coating includes some polytetrafluoroethylene (sold under the trademark “Teflon”), or a plastic sheet including some polytetrafluoroethylene. Surfaces of the sliding plates  11  are ground and made smooth to reduce the coefficient of friction with respect to support legs, which will be described later. 
     Each of the supports  12  are mounted approximately at the center of each sliding plate  11  one by one so as to freely slide. Each of the supports  12  has a pedestal  20  formed at each of the four sides of the support  12  on the top portion of the support  12 . A plurality of approximately square panels  14  are supported by a plurality of supports  12 . In other words, corners of each of four panels  14  are mounted on the pedestal  20  of one of the supports  12  with each corner of a panel  14  being cut off or chamfered (i.e., a triangle cut off of the square or ninety-degree corner). The supports  12  are made of a light and rigid material, such as aluminum die casting, zinc aluminum alloy, or plastic. 
     The panels  14  are laid over the top of the base floor so as to form an entire floor surface. Under the entirety of the floor surface formed by the panels  14 , a space is provided between the bottom surface of the plurality of panels  14  and the top of the base floor and bounded on the sides by the walls, pillars or a fixed floor provided along the walls of the room. In this manner, the entirety of the floor system is allowed to slide horizontally. 
     The panels  14  are approximately square having a size, for example, of 500 mm×500 mm. However, a rectangular panel of 500 mm×1000 mm formed by joining two square panels may also be used. In the case of rectangular panels, a triangular notch may be formed at the middle of each long side of the rectangular panel for engaging the edge of the panel to the pedestal  20  of the support  12 . 
     On the other hand, the sliding plates  11  are approximately square having a size, for example, of 400 mm×400 mm. In consideration of the anti-earthquake structure of a general building, the size of the sliding plates  11  is determined so as to allow the sliding displacement of the supports  12  to be at least ±10 cm. As the area of the sliding plates  11  becomes smaller, the cost will be reduced. However, needless to say, sliding plates  11  having an area larger than that shown above may be used. Accordingly, the maximum area of the sliding plates  11  is reached when gaps between the adjacent sliding plates  11  become zero thus, forming a sheet of sliding plate covering the entirety of the base floor  10 . In this case, an increase in the cost of the sliding plate  11  may become a concern. However, by grinding the surface of the base floor  10  to form a sliding surface, the sliding plate  11  may be omitted. 
     FIG. 2 is an enlarged view of the support  12  shown in FIG. 1. A pedestal  20  is formed on the support  12  at approximately the four outer sides of a square frame  19  on which the corners of the panels  14  are placed in order to be fixed thereto. The four corners of the pedestal  20  extend downwardly and horizontal bottoms  22  are formed at the lower ends. Support legs  21  are attached to the bottoms  22  of the supports  12 , preferably using nuts and bolts. A cover  23  is provided on the opening of the frame  19  and the top of the cover  23  is located in approximately the same plane as the plane containing the upper surfaces of the panels  14  placed on the pedestal  20 . In place of the cover  23  on the opening of the frame  19 , plug sockets or cable-drawn parts, used for laying cables in offices, may be fit and installed. The portion in which the plug sockets and cable-drawn parts are provided is not limited to the opening of the frame  19 . They may be provided at notches formed at a periphery of each of the panels  14 . 
     The four corners of each panel  14  are cut off or chamfered (i.e., a triangular shape cut off of the square or ninety-degree corner) as shown in FIG.  1 . The edges, being chamfered or having a triangular shape cut off, are placed on the pedestal  20  and fixed by bolts  24  thereto. Therefore, the plurality of panels  14  are connected to each other by the support  12  so that the connected panels  14  together move horizontally along the base floor  10 . However, different structures and methods for fixing the panels  14 , from those described above, may be applied. Since the panels  14  are connected to each other by the supports  12  as described above, the entirety of the floor system slides together as a unit. The panels  14  are fixed to the pedestals  20  of the supports  12  so that the panels  14  may move to a certain extent in the vertical direction, but the panels  14  may also be rigidly fixed so as to restrict any movement in the horizontal direction. With the above-described structure, a level and uniform load may be kept on the surface of the floor system. 
     In operation, the above-described structure allows all of the panels  14 , mounted on the pedestal  20  of the supports  12 , to be connected to each other by the supports  12  at the four corners of the panels  14 . In this manner, a space is formed between the plurality of panels  14  and the base floor  10 . Cables, such as power cables and signal cables, can be laid in the space between the bottom of the plurality of panels  14  and the top of the base floor  10 . 
     At least a portion of the cables, which are laid in the space between the plurality of panels  14  and the base floor  10 , may be in contact with the sliding plate  11 . It is preferable if the portion of the cable, that is in contact with the sliding plate  11 , be made of a material having a small coefficient of friction. Alternatively, a substance having a small coefficient of friction, for example, a polytetrafluoroethylene sheet or tape, may be wound around the cable, as shown in FIG.  14 . Thus, the sliding effect of the cables is improved. 
     Particularly, when the entire floor system slides during an earthquake, it is desirable that movement of the floor system not be restricted or obstructed by friction of cables laid in the space between the bottom of the plurality of panels of the floor system and the top of the base floor. To prevent the restriction or obstruction of movement of the floor system due to cables laid in the space between the plurality of panels of the floor system and the base floor, it is necessary to give the cables some slack and thus, allow the floor system to be able to achieve a maximum sliding displacement. 
     FIG. 3 is a partial cross-sectional view showing a structure for attaching the support leg  21 , shown in FIG. 2, to the bottom  22  of the support  12 . FIG. 4 shows the same structure as that in FIG. 3, but with the parts disassembled. 
     A hole  220  is bored at the center of the bottom  22  of each support  12  and a shaft  210 , of the support leg  21 , is inserted into the hole  220 . The support leg  21  has a disk  230 , with a diameter of about 30 mm and a thickness of about 12 mm, at the lower end of the shaft  210 . At the bottom of the disk  230 , a sliding surface is formed. The sliding surface, at the bottom of the disk  230 , is in contact with the sliding plate  11 , shown in FIG. 1, and the sliding surface slides freely on the sliding plate  11 . An elastic rubber pad  30  is inserted between the top of the disk  230  of the support leg  21  and the bottoms  22  of the supports  12 . The rubber pad  30  makes a load of each of the supports  12  uniform and provides a cushion effect for preventing a vertical movement of the panels  14 . The rubber pad  30  is required to be somewhat soft and therefore, the rubber pad  30  may be made of a material, such as a natural rubber, a synthetic rubber, a urethane rubber, or a silicone rubber. 
     The upper end of the shaft  210  of the support leg  21  has male threads thereon which mate with female threads on the inner surface of a nut  32  in order to tightly fix the rubber pad  30  to the bottom  22  of the support  12 . A ring  31  is interposed between the bottom  22  of the support  12  and the nut  32 . However, the means for fixing the rubber pad  30  to the bottom  22  of the support  12  is not limited to being a screw and nut  32 , and any fixing means may be used, as long as it is not easily disengageable. It is desirable that the a fixing means restricts movement in the horizontal direction, but allows a slight movement in the vertical direction as is the case with the panels  14 . 
     It is desirable that the material of the support legs  21  be one of a group consisting of brass, iron, or hard plated (for example, chromium plated) iron. In the case where the support legs  21  are made of brass, iron, or hard plated iron, if the periphery of each surface, which is in contact with the sliding plate  11 , is inclined (i.e., chamfered) or curved, smoother sliding can be achieved. Since the support leg  21  can be easily mounted and dismounted from the bottom  22  of the support  12 , the coefficient of friction with respect to the sliding plate  11  can be adjusted easily by replacing the support leg  21  with a different material. 
     FIG. 5 shows another embodiment of the support leg  21 . The support leg  21  is made of a material, such as plastics, iron, or hard plated iron. A friction member  50  is affixed to the bottom of the disk  230 . The friction member  50  is preferably made of any one of the following: polytetrafluoroethylene; a plastic being made of some polytetrafluoroethylene; a plastic being made of some oil and carbon; or a plastic being made of some solid lubricant. By simply affixing the friction member  50  to the bottom of the support leg  21 , the coefficient of friction with respect to the sliding plate  11  can be adjusted easily at a low cost. Therefore, it is easy to replace an existing floor with a seismic isolation floor system at a low cost by using the support leg according to the embodiment. 
     Slightly inclining (i.e. chamfering) or curving the periphery of the surface of the friction member  50  (i.e., the surface which is in contact with the sliding plate  11 ) can achieve the effect of smoother sliding. 
     When an earthquake occurs and a building provided with the floor system according to the present invention vibrates horizontally, the supports  12  for panels  14  slide horizontally on the sliding plates  11  and hence the entire floor system moves back and forth horizontally. Therefore, the horizontal vibration of the floor system caused by the earthquake is absorbed and relieved and equipment, such as various electronic devices and desks on the floor system, can be prevented from falling down and being damaged. 
     Meanwhile, it is important that the floor system slides within a proper range to fully utilize such seismic isolation ability. Namely, if the sliding range is too small, the equipment on the floor system collapses or collides with each other, resulting in damage since the floor system does not slide sufficiently in the horizontal direction and hence the horizontal vibration due to an earthquake is not absorbed sufficiently. On the contrary, if the sliding range is too large, the horizontal movement of the floor system increases and collides with the wall of the room, and thus the equipment on the floor collides with each other and is damaged. 
     As the sliding range of the floor system depends on the dynamic coefficient of friction between the sliding plates  11  and the contact bottoms  22  of the supports  12 , it is important to select the dynamic coefficient of friction having a proper value. The inventors of the present invention have conducted various experiments, which will be described later, using a model of the floor system and found as a result that the dynamic coefficient of friction between the sliding plates  11  and the contact bottoms  22  of the supports  12  (in the case of FIG. 4, the dynamic coefficient of friction between the sliding plates  11  and the contact bottoms  22  of the sliding support legs  21  and in the case of FIG. 5, the dynamic coefficient of friction between the sliding plates  11  and the friction member  50  affixed to the bottoms of the sliding support legs  21 ) is most effective for the floor system according to the present invention when it is within the range of from 0.09 to 0.25. 
     The tests conducted for selecting of the dynamic coefficient of friction will be explained hereunder. Firstly, a model of the floor system shown in FIG. 1 is constructed using four square panels  14  with a side length of 500 mm, four square sliding plates  11  with a side length of 400 mm, and nine supports  12 . The static load test is conducted using the model. In the static load test, force in the positive and negative directions is applied to the floor section of the model in one direction by the hydraulic actuator so as to generate a reciprocating sliding movement and the dynamic coefficient of friction, between the bottoms  22  of the supports  12  and the sliding plates  11  during the sliding movement, is measured. The force in the positive direction and negative direction is applied to the floor section repeatedly four times and sliding, within the range of ±50 mm, is generated. The moving speed of the panels  14  at this time is selected to be 0.5 mm/s. 
     FIG. 6 shows a table and a graph indicating the results of the test. For the test, a polytetrafluoroethylene friction member is used for the bottoms  22  of the supports  12  and a stainless steel sheet is used as the sliding plates  11 . A test body, having a long side of 560 mm, a short side of 450 mm, and a height of 1200 mm, is put on the floor, and a load of 193.5 kg, including the weight of the four panels  14 , is applied to the nine supports  12 . The sliding movement is generated in a direction parallel with the short side of the metal case. 
     The mean values of dynamic friction force and dynamic coefficients of friction, measured within the range of ±10 cm of the sliding displacement, are indicated in the table as the results of measurement. A curve indicates the relationship between the dynamic friction force and the sliding displacement at this time. In the table, {circumflex over ( 1 )} to {circumflex over ( 4 )} are shown to indicate the loading count in the positive direction or negative direction. For example, positive direction {circumflex over ( 1 )} means the first loading in the positive direction. The static load test showed that the dynamic coefficient of friction of the aforementioned floor system model is about 0.09. 
     FIG. 7 shows a table and a graph indicating the results of the static load test similar to the test shown in FIG. 6, except having some different test conditions. Namely, in FIG. 7, brass is used for the friction member  50  at the bottoms  22  of the support legs  21 . Chromium plated steel sheets are used for the sliding plates  11  and a weight load is put on the floor with a total load being 60.3 kg. The test showed that the dynamic coefficient of friction under the above conditions is 0.25. The dynamic coefficient of friction obtained here is almost equal to that with the metal case put on the floor system. 
     FIG. 8 shows a table and a graph indicating the results of the vibration test for measuring the seismic isolation characteristic of the floor system model according to the present invention shown in FIG.  6 . In this test, the floor system model of the present invention is fixed to the exciting device including the base floor therefore ( 10  shown in FIG.  1 ) and the maximum response acceleration of a specific part on the floor at the time of vibration for 20 cycles of sinusoidal wave by the exciting device is measured. In FIG. 8, the horizontal axis indicates the input maximum acceleration and the vertical axis indicates the response acceleration of a specific part on the floor. A line formed by connecting the black circular outlines (i.e., ∘) plotted on the graph indicate the response acceleration at the top of the metal case and a line formed by connecting black triangular outlines (i.e., Δ) plotted on the graph indicate the response acceleration at the center of the floor surface. A line formed by connecting the solid black circles (i.e., ) plotted on the graph indicate a response acceleration at the top of the test body when, as a comparison example, an ordinary floor system to which the present invention is not applied, that is, a non-seismic isolation floor system, is used. 
     FIG. 9 shows a table and a graph indicating the measured results of the seismic isolation characteristic of the floor system according to the present invention shown in FIG. 7 in the same vibration test. 
     As FIGS. 8 and 9 show, in the case of a floor system of a non-seismic isolation structure, it is ascertained that when the input acceleration exceeds about 4 m/s 2 , sudden response acceleration is indicated and the frame, installed on the floor system, fell down. On the other hand, in the case of the floor system of the seismic isolation structure, even if the input acceleration exceeds 4 m/s 2 , the response acceleration is not amplified greatly and is kept at almost constant response acceleration and the seismic isolation effect thereof is clear. 
     Furthermore, the inventors have ascertained, with a simulation using the earthquake response analysis method, that the dynamic coefficient of friction of the floor system, according to the present invention, within the range of from 0.09 to 0.25, is a most effective value. In this simulation, an analytical model was used in combination of a seven-storied building model and a floor system model of the present invention installed on each floor of the building. Applying great earthquake waveforms actually measured in the past at various places in the world to this analytical model, the earthquake response analysis is carried out. In this case, as a dynamic coefficient of friction of the floor system according to the present invention, 0.05, 0.1, 0.15, 0.2, and 0.25 are selected and the analysis is carried out using them as parameters. As an earthquake waveform, the acceleration waveforms of the El Centro earthquake and Taft earthquake, which occurred in the United States of America, and the Tokachi-Oki earthquake and Hyogo-ken Nambu earthquake, which occurred in Japan, are used. 
     FIGS. 10 and 11 are graphs showing the analytical results using the El Centro earthquake waveform having a maximum speed of 2.5 m/s 2 , wherein the horizontal axis indicates floors of the building and the vertical axis indicates the maximum displacement and maximum acceleration of the floor system on each floor using the dynamic coefficient of friction as a parameter. 
     In FIG. 10, when the dynamic coefficient of friction is 0.05, the maximum displacement of the floor system on the third floor is 10 cm which is within the design range of ±10 cm for the floor system according to the present invention. However, on the floors higher than the third floor, the maximum displacement is greatly beyond the design range. When the dynamic coefficient of friction is 0.1 or more on the sixth floor and on the higher floors, the maximum displacement is more than the design range, although it can be understood that the maximum displacement is applicable as a whole. 
     In FIG. 11, when the dynamic coefficient of friction increases, the response acceleration of the floor system increases. When the dynamic coefficient of friction reaches 0.25, the response acceleration of the floor system reaches 2.5 m/s 2 , which is an allowable acceleration, decided as an anti-earthquake reference of a computer in Japan. Therefore, it can be understood that a dynamic coefficient of friction of 0.25 or more is desirable. Even when another is used, it is ascertained that almost the same result can be obtained if the maximum acceleration of the earthquake waveform is 2.5 m/s 2 . 
     As mentioned above, the simulation result shows that a value of the dynamic coefficient of friction within the range from 0.09 to 0.25 is a most effective value. 
     Next, FIG. 12 is a perspective view showing another embodiment of the supports used in the present invention. A support  60  has a shape that is obtained by cutting the support  12 , shown in FIG. 2, in half in the direction of the diagonal line. Namely, the support  60  has three support legs  61  and three support bottoms  62 . When two supports  60  are united, the same structure as that of the support  12 , shown in FIG. 2, is formed. In the embodiment, a combination ring  63  is fit onto the top of the supports  60  to prevent the two supports  60  from being separated. A cover (equivalent to  23  shown in FIG. 2) is provided on the ring  63 . 
     FIG. 13 is a perspective view showing still another embodiment of the supports applied to the present invention. A support  70  has a cylindrical body  71  at the upper end and lower end. Disks  72  and  73 , having an area larger than the horizontal section of the body  71 , are fixed horizontally to the upper and lower ends of the cylindrical body  71  of the support  70 . On the top of the upper disk  72 , four strip-shaped projections  74  extend in the radial direction from the center of the disk  72  and are positioned so as to be on orthogonally intersecting lines. On the top of the disk  72 , between two adjacent strip-shaped projections  74 , a cylindrical projection  75  is attached. Between two adjacent strip-shaped projections  74 , as shown by a dashed line, the corner of the panel  14  is mounted and the cylindrical projection  75  is fit into a fixing hole  76  bored in the panel  14  to fix the panel  14  so as to prevent horizontal movement thereof. On the other hand, in the lower disk  73  of the support  70 , a plurality of holes  77  are bored and the support legs  21 , shown in FIG. 4 or  5 , are attached via the support legs  21  being placed through the holes  77  and having nuts attached to the threads at the top of the support legs  21 . These supports  70 , as shown in FIG. 1, may then be mounted on the sliding plates  11  provided on the base floor. Using this type of support  70 , according to the present invention, a conventional type floor system can be easily refashioned into a seismic isolation type floor system. 
     Next, an embodiment when the floor system, according to the present invention, is provided on each floor of a building having many floors will be explained. 
     Although the coefficient of friction for the floor systems is selected as one of the values within the range of from 0.09 to 0.25 when the present invention is applied to a building having many stories, a different coefficient of friction is selected depending on what level of the building the floor is at. 
     Namely, as mentioned previously, the maximum relative displacement of the floor system, when an earthquake occurs, is small on the lower floor levels of the building and as the floor level increases, the maximum relative displacement increases. On the other hand, when the dynamic coefficient of friction between the supports of the floor system and the sliding plates is a small value, the sliding displacement is large and when the dynamic coefficient of friction between the supports of the floor system and the sliding plates is a large value, the sliding displacement is small. Therefore, on the lower floor levels of the building, a value close to 0.09 is applied. On the middle floor levels of the building, a coefficient of friction of almost a medium value, between 0.09 and 0.25, is used. On the upper floor levels, a comparatively large coefficient of friction close to 0.25 is used so as to decrease the sliding distance. 
     As already explained, the seismic isolation effect of the floor system according to the present invention can be produced more surely by using different materials having a different coefficient of friction on the support side. For example, polytetrafluoroethylene is used as a material having a comparatively small coefficient of friction. A plastic being made of some polytetrafluoroethylene and carbon is used as a material having a medium coefficient of friction. Brass is used as a material having a high coefficient of friction. 
     The embodiments of the present invention are explained above in detail, but the present invention is not limited to the aforementioned embodiments and various modifications are available. For example, according to the aforementioned embodiments, the support legs  21  are fixed to the bottoms  22  of the supports  20  or the bottoms of the supports  70 . However, as a material for the supports themselves, when a material having a dynamic coefficient of friction within the range of from 0.09 to 0.25 is used between the supports and the sliding plates  11  or the sliding surfaces, the support legs  21  can be omitted. In this case, when the friction member  50 , made of a material having a dynamic coefficient of friction within the range of 0.09 to 0.25 is adhered to the support bottoms, the supports  20  and  70  having a necessary dynamic coefficient of friction can be obtained, unless a material having a special dynamic coefficient of friction is used for the supports themselves. When the rubber pad  30 , shown in FIG. 3, is directly adhered to the bottom  22  of each support  20 , without using the support leg  21 , and polytetrafluoroethylene solid lubricant or plastic made up of some polytetrafluoroethylene is coated on the bottom of the rubber pad  30  so as to be sheet-shaped or integratedly formed, a support leg having a simple structure can be obtained. 
     Therefore, in the explanation of the present invention, the “support leg” means a member which is additionally fixed to the bottom of the support so as to adjust the dynamic coefficient of friction between the support leg and the sliding plate and is not always limited to the structure shown in FIG. 4 or  5 . 
     The materials constituting the sliding plates  11  and the support legs  21  can be mutually exchanged. Namely, according to the present invention, the dynamic coefficient of friction between the two may be within the aforementioned predetermined range, so that it is possible to make the support legs  21  using the material for the sliding plates  11  explained in the aforementioned embodiments and to make the sliding plates  11  using the material for the support legs  21  explained in the above embodiments. 
     According to the present invention, with a simple structure and at a low cost, a floor system having a seismic isolation structure can be realized. Namely, the floor system according to the present invention absorbs the shock by allowing the entire floor system to properly slide and displace its position for the vibration due to the occurrence of an earthquake. As a result, it is possible to prevent the panels, forming the floor surface, from colliding with each other, being pushed up, and being destroyed. Equipment, such as office desks, document cases, and electronic information processing devices, installed on the floor, can be prevented from falling down and being damaged. 
     With the seismic isolation floor structure according to the present invention, which can be constructed easily at a low cost, the system is applied with high satisfaction not only to a new construction but also to refashion a previously non-anti-earthquake floor system. Furthermore, even in a comparatively high building, a seismic isolation floor can be realized by simply changing the value of dynamic coefficient of friction depending on the floor level on which the floor system is provided.