Fail-safe mechanism of the jack device

Abstract

To provide a fail-safe mechanism of a jack device capable of preventing damage of the jack device even when an earthquake occurs during jack up.SOLUTION: A fail-safe mechanism of a jack device comprises a cylindrical part 3 provided on the outer periphery of a jack device 2 provided on a base isolation layer 11 and fixed to a lower skeleton 12 below the base isolation layer 11, and a bolt 5 bonded to the cylindrical part 3 via a spring part 4 that can extend the jack device 2 in the vertical direction. The cylindrical part 3 is brought into contact with an outer peripheral surface 211 of a cylinder part 21 (outer peripheral part of the jack device) at least at two different heights. The bolt 5 is preloaded with a tensile force corresponding to the vertical strength of the jack device 2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fail-safe mechanism for a jack device. [Background technology]

[0002] When replacing a seismic isolation device in a seismically isolated building, a commonly known method is to insert a temporary jack device into the seismic isolation layer, jack up the upper structure above the seismic isolation layer slightly, and then use the gap between the upper structure and the lower structure below the seismic isolation layer to remove and insert the seismic isolation device (see, for example, Patent Document 1). Another method is to permanently install a jack device in the seismic isolation layer in advance as a permanent device to facilitate replacement of the seismic isolation device. Furthermore, it is also possible to add a locking function by providing a friction material on the top of the jack device and abutting the friction material against the sliding plate on the underside of the upper structure to restrain horizontal displacement of the seismic isolation layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-16011 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, in terms of safety against earthquakes that may occur when replacing seismic isolation devices, the "Guidelines for the Safety of Buildings During Seismic Isolation Material Replacement and Renovation Work" (Ministry of Land, Infrastructure, Transport and Tourism, 2015) and other documents prescribe required standards for damage to the building itself, but do not prescribe required standards for damage to the jacking device. In fact, no consideration has been given to the fail-safe of the jacking device against forced behavior such as the following, and the reality is that no measures for this exist. (1) When jacking up, forced vertical displacement due to earthquake motion acts on the jacking device. (2) When jacking up, horizontal force caused by earthquake motion acts on the piston part of the jack device.

[0005] Regarding (1) above, the oil flow inside the jacking device may suddenly reverse (normally, oil is supplied from the pump to the jacking device, but instead, the oil is forced back from the jacking device to the pump), causing excessive internal pressure and the risk of high-pressure oil spraying out from the packing or other parts (release into the atmosphere). Regarding (2) above, the allowable horizontal force acting on the piston part of the jacking device is generally specified for each product, but this value is small, and depending on the vertical force acting on the jacking device and the contact conditions between the jacking device and the upper structure (friction coefficient, etc.), there is a risk of a force exceeding this allowable horizontal force acting, raising concerns about damage to the jacking device. There is also the risk that the entire jacking device may rotate like a rigid body, causing it to tip over due to horizontal displacement of the seismic isolation layer. In particular, if the jack device is permanently installed in the seismic isolation layer as a permanent device, if the jack device is damaged, it will be necessary to replace the jack device because it is not easy to restore it.

[0006] Therefore, an object of the present invention is to provide a fail-safe mechanism for a jack device that can prevent damage to the jack device even if an earthquake occurs during jacking up. [Means for solving the problem]

[0007] The fail-safe mechanism of the jack device of the present invention comprises a tubular portion provided on the outer periphery of the jack device provided in the seismic isolation layer and fixed to a lower body below the seismic isolation layer, and a bolt that connects the jack device to the tubular portion via a spring portion that can expand and contract in the vertical direction, wherein the tubular portion contacts the outer periphery of the jack device at at least two different heights, and a tensile preload equivalent to the vertical strength of the jack device is applied to the bolt.

[0008] In the present invention, the cylindrical portion contacts the outer periphery of the jack device at at least two different heights. This allows the shear force acting on the jack device to be transmitted to the cylindrical portion and prevents the jack device from rotating in a direction that tilts relative to the axis. Therefore, only vertical axial force acts on the bolt. If an earthquake occurs during jacking up using the jacking device and a jack compressive force acts on the jacking device, the jack compressive force up to the preload applied to the bolts is transmitted from the jacking device to the tubular portion without the jacking device descending relative to the tubular portion. The preload applied to the bolts is a tensile force equivalent to the vertical bearing capacity of the jacking device. If the jack compressive force exceeds the preload applied to the multiple bolts, the spring portion is compressed, causing the bolts and jacking device to descend relative to the tubular portion, and the jack compressive force transmitted to the tubular portion increases slightly by the increase in spring reaction force. This prevents excessive reaction force from being generated even if an earthquake occurs during jacking up and the jacking device is forced to displace due to vertical seismic motion. As a result, reverse operation of the oil inside the jacking device and excessive pressure buildup can be prevented, preventing damage to the jacking device.

[0009] In addition, in the fail-safe mechanism of the jack device of the present invention, the cylindrical portion has a cylindrical body provided on the outer periphery of the jack device and fixed to the lower body, and a flange portion protruding inward from the inner periphery of the cylindrical body and contacting the outer periphery of the jack device, and the bolt may be joined to the flange portion via a spring portion that can expand and contract the jack device in the vertical direction.

[0010] With this configuration, the cylindrical portion can be brought into contact with the outer periphery of the jack device, and the jack device and the cylindrical portion can be easily joined together.

[0011] In the fail-safe mechanism of the jack device of the present invention, the cylindrical portion has a plate portion that protrudes inward from the inner circumference of the cylindrical body and contacts the outer periphery of the jack device at a height different from that of the flange portion.

[0012] With this configuration, the outer periphery of the jack device and the cylindrical portion can be brought into contact at two different heights.

[0013] In addition, the fail-safe mechanism of the jack device according to the present invention includes a cylindrical portion provided on the outer periphery of the jack device provided on the seismic isolation layer and fixed to a lower structure below the seismic isolation layer, and a bolt that joins the jack device to the lower structure via a spring portion that can expand and contract in the vertical direction, wherein the cylindrical portion contacts the outer periphery of the jack device at at least two different heights, and the spring portion may be preloaded with a compressive force equivalent to the vertical strength of the jack device.

[0014] In the present invention, the cylindrical portion contacts the outer periphery of the jack device at at least two different heights. This allows the shear force acting on the jack device to be transmitted to the cylindrical portion, while preventing the jack device from rotating in a direction that tilts relative to the axis. Therefore, only vertical axial force acts on the bolt. If an earthquake occurs while the jack is being jacked up and a compressive force acts on the jack, the jack compressive force up to the preload applied to the spring is transmitted from the jack to the lower body without the jack descending relative to the lower body. The preload applied to the spring is a compressive force equivalent to the vertical bearing capacity of the jack. When the jack compressive force exceeds the sum of the preloads applied to the multiple springs (total preload), the springs are compressed, the jack device descends, and the jack compressive force transmitted to the lower body increases slightly by the increase in spring reaction force.When the jack compressive force exceeds the preload applied to the springs, the jack device descends by the displacement calculated by dividing the exceeded load (increase in spring reaction force) by the spring stiffness. This prevents excessive reaction force even if an earthquake occurs during jacking and the jack device is forced to displace due to vertical seismic motion, preventing reverse action of the oil inside the jack device and excessive pressure buildup, and preventing damage to the jack device.

[0015] In addition, in the fail-safe mechanism of the jack device of the present invention, the cylindrical portion may have a cylindrical body provided on the outer periphery of the jack device and fixed to the lower body, and a plate portion protruding inward from the inner periphery of the cylindrical body and contacting the outer periphery of the jack device.

[0016] With this configuration, even if there is a difference between the inner diameter of the cylindrical portion and the outer diameter of the jack device, the outer periphery of the jack device and the cylindrical portion can be brought into contact at two different heights. [Effects of the Invention]

[0017] According to the present invention, even if an earthquake occurs during jacking up, damage to the jack device can be prevented. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a plan view of a fail-safe mechanism of the jack device according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 10 is a plan view of a fail-safe mechanism of the jack device according to the second embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along line BB in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0019] (First embodiment) A fail-safe mechanism of a jack device according to an embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1 , a fail-safe mechanism 1 of a jacking device according to this embodiment is provided in a jacking device 2 installed in a seismic isolation layer 11 of a seismic isolated building. The structure below the seismic isolation layer 11 is referred to as a lower structure 12, and the structure above the seismic isolation layer 11 is referred to as an upper structure 13. The jacking device 2 is provided to jack up the upper structure 13 when replacing a seismic isolation device installed in the seismic isolation layer 11. The jacking device fail-safe mechanism 1 prevents excessive reaction force from being generated in the jacking device 2 when an earthquake occurs during jacking up by the jacking device 2, narrowing the gap between the lower structure 12 and the upper structure 13 and causing a vertical compressive force to act on the jacking device 2. The vertical compressive force acting on the jacking device 2 during an earthquake is referred to as a jack compressive force.

[0020] The jack device 2 is, for example, a hydraulic jack. The jack device 2 is fixed to the lower body 12 via a jack device fail-safe mechanism 1. The jack device 2 is displaceable relative to the upper body 13. The jack device 2 has a cylinder portion 21, a piston portion 22, and a fixed flange portion 23. The cylinder portion 21 is cylindrical and is arranged with its axial direction oriented in the vertical direction. The piston portion 22 is columnar and is arranged coaxially inside the cylinder portion 21. The cylinder portion 21 and the piston portion 22 are displaceable relative to each other in the vertical direction.

[0021] The jack device 2 of this embodiment also has a locking function that restrains horizontal displacement of the seismic isolation layer 11. A friction material 221 is provided on the upper surface of the piston portion 22. The friction material 221 comes into contact with a sliding plate provided on the lower surface 131 of the upper body 13 when jacking up.

[0022] The fixed flange portion 23 protrudes radially outward from the lower edge of the cylinder portion 21. The fixed flange portion 23 is in the shape of an annular plate, and the plate surface is a horizontal plane. The fixed flange portion 23 has a plurality of holes 231 that penetrate in the up-down direction and are spaced apart in the circumferential direction. The jack device 2 is permanently installed in the seismic isolation layer 11 as a permanent device.

[0023] The fail-safe mechanism 1 of the jack device has a tubular portion 3 provided on the outer periphery of the jack device 2, and a bolt 5 that joins the jack device 2 to the tubular portion 3 via a spring portion 4 that is expandable and contractible in the vertical direction. The tubular portion 3 has a cylindrical body 31, an inner flange portion 32 that protrudes inward from the tubular body 31, an outer flange portion 33 that protrudes outward from the tubular body 31, and a plate portion 6 attached to the tubular body 31. The tubular portion 3 is oriented such that the axial direction of the tubular body 31 is the vertical direction.

[0024] The inner flange portion 32 protrudes radially inward from the vertical middle portion of the cylindrical body 31. The inner flange portion 32 is annular plate-shaped, and its plate surface is horizontal. The inner flange portion 32 has a plurality of holes 321 that penetrate in the vertical direction and are spaced apart in the circumferential direction. The outer flange portion 33 protrudes radially outward from the lower edge of the cylindrical body 31. The outer flange portion 33 is annular plate-shaped, and its plate surface is horizontal. The outer flange portion 33 has a plurality of holes 331 that penetrate in the vertical direction and are spaced apart in the circumferential direction.

[0025] The jack device 2 is disposed inside the cylindrical body 31 of the cylindrical portion 3, the fixing flange portion 23 is joined to the inner flange portion 32, and the outer flange portion 33 is fixed to the lower body 12. Fixing devices 332 such as bolts or pins are inserted into holes 331 of the outer flange portion 33 to fix the outer flange portion 33 to the lower body 12. The lower surface of the outer flange portion 33 is in contact with the upper surface 121 of the lower body 12.

[0026] The inner flange portion 32 is disposed so as to overlap the fixed flange portion 23. The planar shape of the inner flange portion 32 as viewed from the top-bottom direction is substantially the same as the planar shape of the fixed flange portion 23. The inner peripheral edge portion 322 of the inner flange portion 32 is in contact with the outer peripheral surface 211 of the cylinder portion 21 of the jack device 2. The inner peripheral edge portion 322 of the inner flange portion 32 is the radially inner edge portion of the inner flange portion 32. In addition to the above, the outer peripheral edge 232 of the fixing flange portion 23 may be in contact with the inner peripheral surface 311 of the cylindrical body 31. The outer peripheral edge 232 of the fixing flange portion 23 is the edge portion on the radially outer side of the fixing flange portion 23.

[0027] The inner flange portion 32 and the fixed flange portion 23 are fixed by bolts 5 via spring portions 4. The plurality of holes 321 in the inner flange portion 32 and the plurality of holes 231 in the fixed flange portion 23 are arranged one above the other in the vertical direction. The spring portions 4 are disc springs. The spring portions 4 are arranged on the inner flange portion 32 coaxially with the holes 321 in the inner flange portion 32. The spring portions 4 may be compression coil springs instead of disc springs.

[0028] The bolt 5 is oriented with its head 51 facing downward and its threaded portion 52 facing upward, and the threaded portion 52 is inserted from below through the hole 231 of the fixed flange 23, the hole 321 of the inner flange 32, and the hole of the disc spring of the spring portion 4. The head 51 of the bolt 5 is disposed below the fixed flange 23. A nut 53 is fastened to the threaded portion 52 at the top of the spring portion 4. The inner diameters of the hole 231 of the fixed flange 23, the hole 321 of the inner flange 32, and the hole of the disc spring of the spring portion 4 are larger than the diameter of the threaded portion 52. The fixed flange 23, the inner flange 32, and the spring portion 4 are capable of vertical displacement relative to the bolt 5 within a height range in which the spring portion 4 can expand and contract between the head 51 of the bolt 5 and the nut 53.

[0029] A plurality of bolts 5 are provided corresponding to the number of holes 321 in the inner flange portion 32 and the number of holes 231 in the fixing flange portion 23 . A preload of a tensile force equivalent in total to the vertical bearing capacity of the jack device 2 is applied to the plurality of bolts 5. The bolts 5 are tension-joined with the pre-tension force.

[0030] The plate portion 6 is an annular plate-shaped member whose outer diameter is approximately the same as the outer diameter of the cylindrical body 31 and whose inner diameter is smaller than the inner diameter of the cylindrical body 31. The plate portion 6 is coaxially attached to the upper end of the cylindrical body 31. An inner peripheral edge portion 61 of the plate portion 6 protrudes radially inward beyond the inner peripheral surface 311 of the cylindrical body 31. The inner peripheral edge portion 61 of the plate portion 6 is in contact with the outer peripheral surface 211 of the cylinder portion 21.

[0031] The outer peripheral surface 211 of the cylinder portion 21 is in contact with the inner peripheral edge 322 of the inner flange portion 32 and the inner peripheral edge 61 of the plate portion 6, which are at different heights. In other words, the cylindrical portion 3 is in contact with the outer peripheral portion of the jack device 2 at at least two different heights. This allows the shear force acting on the jack device 2 to be transmitted to the cylindrical portion 3, and prevents the jack device 2 from rotating in a direction that tilts relative to the axis. Therefore, only vertical axial force acts on the bolt 5. The lower surface of the outer flange portion 33 has an area large enough to prevent lift-up due to the overturning behavior caused by the shear force transmitted from the jack device 2.

[0032] In the fail-safe mechanism 1 of the jack device according to this embodiment, if an earthquake occurs during jacking up by the jack device 2 and a jack compressive force acts on the jack device 2, the jack compressive force up to the preload applied to the plurality of bolts 5 is transmitted from the jack device 2 to the tubular portion 3 without the jack device 2 descending relative to the tubular portion 3. As described above, the preload applied to the plurality of bolts 5 is a tensile force equivalent to the vertical bearing capacity of the jack device 2. When the jack compressive force exceeds the preload applied to the multiple bolts 5, the spring portion 4 is compressed and shortened, causing the bolts 5 and jack device 2 to descend relative to the cylindrical portion 3, and the jack compressive force transmitted to the cylindrical portion 3 increases slightly by the increase in the spring reaction force. As a result, even if an earthquake occurs during jacking up and forced displacement of the jack device 2 occurs due to vertical seismic motion, excessive reaction force will not be generated. In other words, the jack device fail-safe mechanism 1 limits the reaction force applied to the jack device 2 during an earthquake. As a result, reverse operation of the oil inside the jack device 2 and excessive pressure buildup can be prevented, and damage to the jack device 2 can be prevented. Furthermore, it is possible to avoid adverse effects on building behavior and ensure the safety of surrounding workers, making it possible to build a safe and reliable system. It is also effective for wind-resistant locking mechanisms that require the jack device 2 to be permanently installed as a permanent device.

[0033] The fail-safe mechanism 1 of the jack device according to this embodiment has a cylindrical portion 3 and an inner flange portion 32 that protrudes inward from the inner peripheral portion of the cylindrical body 31. This allows the inner peripheral edge portion 322 of the inner flange portion 32 to come into contact with the outer peripheral surface 211 of the cylinder portion 21, and by placing the cylindrical portion 3 over the jack device 2 with a bolt passing through the flange portion 23, the two can be easily joined together with a tension bolt.

[0034] In the fail-safe mechanism of the jack device according to this embodiment, a plate portion 6 is attached to the upper end of the cylindrical portion 3. This allows the outer peripheral surface 211 of the cylinder portion 21 to come into contact with the cylindrical portion 3 at two different heights.

[0035] (Second embodiment) Next, the second embodiment will be described based on the attached drawings. Components and parts that are the same as or similar to those in the first embodiment described above will be designated by the same reference numerals, and their explanation will be omitted. Only configurations that differ from the first embodiment will be described. As shown in FIGS. 3 and 4, in the fail-safe mechanism 1B of the jack device according to the second embodiment, the fixing flange portion 23 of the jack device 2 is fixed to the lower body 12 with bolts 5B without using a cylindrical portion 3B. A spring portion 4B is interposed between the fixing flange portion 23 and the lower body 12. The cylindrical portion 3B of the second embodiment has a cylindrical body 31, an outer flange portion 33 protruding outward from the cylindrical body 31, and a plate portion 6 attached to the cylindrical body 31. The cylindrical portion 3B is arranged such that the axial direction of the cylindrical body 31 is the up-down direction. The cylindrical portion 3B of the second embodiment does not have the inner flange portion 32 that was provided on the cylindrical portion 3B of the first embodiment.

[0036] The bolt 5B of the second embodiment is an anchor bolt with a cap nut, and includes a cap nut 54 fixed to the lower body 12, a threaded portion 55 that threads onto the cap nut 54, and a nut 56 that threads onto the threaded portion 55. The axis of the bolt 5B faces the vertical direction. The cap nut 54 is embedded in the lower body 12. The lower side of the threaded portion 55 that threads onto the cap nut 54 is inserted into the lower body 12, and the upper side protrudes above the lower body 12. The upper side of the threaded portion 55 is inserted into the disc spring of the spring portion 4B and the hole 231 in the fixed flange portion 23 of the jack device 2. The spring portion 4B is disposed between the upper surface of the lower body 12 and the lower surface of the fixed flange portion 23. A nut 56 is fastened to the threaded portion 55 above the fixed flange portion 23. A plurality of bolts 5B and a plurality of spring portions 4B are provided.

[0037] The cylindrical portion 3B is provided on the outer periphery of the jack device 2. The inner peripheral edge portion 61 of the plate portion 6 is in contact with the outer peripheral surface 211 of the cylinder portion 21. The inner peripheral surface 311 of the cylindrical body 31 is in contact with the outer peripheral edge portion 232 of the fixing flange portion 23. The jack device 2 is in contact with the inner peripheral edge portion 61 of the plate portion 6 and the inner peripheral surface 311 of the cylindrical body 31 at different heights. As a result, in the second embodiment as in the first embodiment, shear force acting on the jack device 2 is transmitted to the cylindrical portion 3B, and rotational behavior of the jack device 2 in a direction tilting relative to the axis is prevented.

[0038] In the fail-safe mechanism 1B of the jack device according to this embodiment, if an earthquake occurs during jacking up by the jack device 2 and a jack compressive force acts on the jack device 2, the jack compressive force up to the preload applied to the plurality of spring portions 4B is transmitted from the jack device 2 to the lower body 12 without the jack device 2 descending relative to the lower body 12. As described above, the preload applied to the plurality of spring portions 4B is a compressive preload equivalent to the vertical bearing capacity of the jack device 2. When the jack compressive force exceeds the sum of the preloads (total preload) applied to the multiple spring portions 4B, the spring portions 4B are compressed, the jack device 2 descends, and the jack compressive force transmitted to the lower body 12 increases slightly by the increase in spring reaction force. When the jack compressive force exceeds the sum of the preloads applied to the multiple spring portions 4B, the jack device 2 descends by a displacement calculated by dividing the excess load by the spring stiffness. As a result, even if an earthquake occurs during jacking up and forced displacement of the jack device 2 occurs due to vertical seismic motion, excessive reaction force will not be generated. In other words, the jack device fail-safe mechanism 1B limits the reaction force to the jack device 2 during an earthquake. As a result, reverse operation of the oil inside the jack device 2 and excessive pressure buildup can be prevented, and damage to the jack device 2 can be prevented. Furthermore, it is possible to avoid adverse effects on building behavior and ensure the safety of surrounding workers, making it possible to build a safe and highly reliable system.

[0039] The above describes an embodiment of the fail-safe mechanism of the jack device according to the present invention, but the present invention is not limited to the above embodiment and can be modified as appropriate within the scope of the spirit of the present invention. For example, in the first embodiment described above, the fixed flange portion 23 of the jack device 2 is joined to the inner flange portion 32 of the tubular portion 3 by a bolt 5 via a spring portion 4, but the location where the tubular portion 3 and the fixed flange portion 23 are joined by the bolt 5 via the spring portion 4 may be other than the above.

[0040] In the first embodiment described above, the outer peripheral surface 211 of the cylinder portion 21 is in contact with the inner peripheral edge portion 322 of the inner flange portion 32 and the inner peripheral edge portion 61 of the plate portion 6, which are at different heights. However, the two or more portions at different heights where the jack device 2 and the cylindrical portion 3 are in contact with each other may be at locations other than those described above. In the second embodiment described above, the outer peripheral surface 211 of the cylinder portion 21 is in contact with the inner peripheral surface 311 of the cylindrical body 31, which are at different heights, and the inner peripheral edge portion 61 of the plate portion 6. However, the two or more portions at different heights where the jack device 2 and the cylindrical portion 3B are in contact with each other may be other than those described above. In the above embodiment, the plate portion 6 is attached to the upper end portion of the cylindrical body 31, but it may be provided integrally with the cylindrical body 31. It may also be attached to a portion other than the upper end portion of the cylindrical body 31.

[0041] In the above embodiment, the jack device 2 is a hydraulic jack and has a configuration including a cylinder portion 21 and a piston portion 22, but it may have a configuration other than the above as long as it is capable of jacking up the upper body 13.

[0042] In the above embodiment, the jack device 2 is permanently installed on the seismic isolation layer 11 as a permanent device, but it may also be a temporary device that is installed when the upper structure 13 is jacked up. Furthermore, when the jack device 2 is permanently installed as a permanent device in a wind-resistant locking mechanism or the like, the fail-safe mechanisms 1, 1B of the jack device may be employed. [Explanation of symbols]

[0043] 1,1B Fail-safe mechanism of jack device 2 Jacking device 3,3B Cylindrical part 4,4B Spring part 5.5B bolt 6 Plate section 11 Seismic isolation layer 12 Lower structure 31 Cylindrical body 32 Inner flange (flange) 211 Outer surface (outer periphery)

Claims

1. a cylindrical portion provided on the outer periphery of a jack device provided in the seismic isolation layer and fixed to a lower body below the seismic isolation layer; a bolt that connects the jack device to the cylindrical portion via a spring portion that is expandable and contractible in the vertical direction, the cylindrical portion contacts the outer periphery of the jack device at at least two different heights; A fail-safe mechanism for a jack device, in which a preload of a tensile force equivalent to the vertical strength of the jack device is applied to the bolt.

2. The cylindrical portion is a cylindrical body provided on the outer periphery of the jack device and fixed to the lower body; a flange portion that protrudes inward from the inner peripheral portion of the cylindrical body and contacts the outer peripheral portion of the jack device, 2. The fail-safe mechanism of claim 1, wherein the bolt connects the jack device to the flange portion via a spring portion that is expandable and contractible in the vertical direction.

3. The cylindrical portion is 3. The fail-safe mechanism of claim 2, further comprising a plate portion that protrudes inward from the inner periphery of the cylindrical body and contacts the outer periphery of the jack device at a height different from that of the flange portion.

4. a cylindrical portion provided on the outer periphery of a jack device provided in the seismic isolation layer and fixed to a lower body below the seismic isolation layer; a bolt that connects the jack device to the lower body via a spring portion that is expandable and contractible in the vertical direction, the cylindrical portion contacts the outer periphery of the jack device at at least two different heights; A fail-safe mechanism for a jack device, in which a compressive force preload equivalent to the vertical strength of the jack device is applied to the spring portion.

5. The cylindrical portion is a cylindrical body provided on the outer periphery of the jack device and fixed to the lower body; 5. The fail-safe mechanism of claim 4, further comprising a plate portion that protrudes inward from the inner periphery of the cylindrical body and contacts the outer periphery of the jack device.

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