Static structures (e.g. – buildings) – Means compensating earth-transmitted force – Relative motion means between a structure and its foundation
Reexamination Certificate
2000-07-07
2001-09-18
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Means compensating earth-transmitted force
Relative motion means between a structure and its foundation
C052S167400, C052S167700
Reexamination Certificate
active
06289640
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a seismic isolation sliding support bearing system with low friction.
2. Description of the Related Art
Seismic isolation sliding support bearing systems are widely used in general constructions including buildings and bridges, a variety of industrial products and industrial plants. A seismic isolation sliding support bearing system is provided between a superstructure of, for example, a building and a substructure corresponding to the foundation, and includes a pair of sliding bearings opposing and in contact with each other. When an earthquake occurs, these sliding bearings are displaced relatively to each other in spontaneous directions, so as to absorb the horizontal load. The seismic isolation sliding support bearing system functions in accordance with the following mechanism: When an earthquake occurs, a horizontal load is applied to the substructure. The horizontal load is reduced by the sliding function of the sliding bearings and transferred to the superstructure. The value of the horizontal load transferred to the superstructure can be obtained by multiplying the movable load of the superstructure with the coefficient of friction of the sliding bearings. Accordingly, it is desired that the sliding bearings have a low coefficient of friction.
Therefore, various propositions have been made for reducing the coefficient of friction between the sliding bearings of the seismic isolation sliding support bearing system. For example, one method that has been suggested is reducing the friction between the sliding bearings by applying a lubricant, such as grease and fluorinated oil, between the upper and lower sliding bearings. In the case where the lubricant is simply applied, however, the lubricant is soon lost from the space between the sliding bearings, and hence, the effect of the lubricant lasts for only a short period of time.
In order to overcome this disadvantage, fixation of the lubricant onto the surface of a metallic base plate of the sliding bearing has been proposed. For example, Japanese Laid-Open Patent Publication No. 11-124591 describes a seismic isolation sliding support bearing system using a sliding bearing made from a material obtained by causing a reaction, through heating, between polytetrafluoro ethylene resin (hereinafter referred to as PTFE), an epoxy resin and a reactive silicone oil having an epoxy group on a side chain.
Under application of a large load, however, the sliding bearing described in this publication poses the problem that a lubricating film fixed onto the metallic base plate by the functional group is eliminated from the sliding bearing through the sliding against the underlying PTFE at an early stage of the sliding. In addition, once the lubricating film is eliminated from the sliding bearing, it is necessary to form the film again, which disadvantageously requires a major operation such as jacking up the seismic isolation sliding support bearing system.
PTFE, which has low frictionality and good chemical stability, is preferably used as the material for sliding bearings, and can be used for providing a sliding bearing with promisingly low friction if the aforementioned problems can be solved. In the case where a sliding bearing made of PTFE including no filler is employed for the seismic isolation sliding support bearing system, sufficient seismic isolation cannot be attained in a multistoried building, a bridge or a three-storied house having a large movable load in which a surface pressure of, for example, 300 kgf/cm
2
or more is applied. This is because PTFE itself cannot attain high mechanical strength. In order to attain sufficient seismic isolation in such constructions having a large movable load, it generally accepted that the mechanical strength for attaining a compression elastic modulus of 900 MPa or more is necessary.
Moreover, the seismic isolation sliding support bearing system is desired to have a coefficient of friction that is low and stable for a long period of time as described above. In particular, if a permanent displacement is caused by an earthquake or the like, the shifting load required for restoration is smaller when coefficient of friction is lower. According to a test carried out by the present inventors, the coefficient of friction between sliding bearings made from PTFE including no filler is generally 0.05 through 0.15. When sliding is caused between these sliding bearings under application of a large surface pressure of 300 kgf/cm
2
, the mechanical strength of the sliding bearings is so insufficient that the sliding bearings tend to degrade in a short period of time and loose their smooth sliding function.
Accordingly, there is a demand for a seismic isolation sliding support bearing system having high mechanical strength for attaining a compression elastic modulus of 900 MPa or more and a low coefficient of friction of 0.05 or less, which can be maintained for a long period of time.
SUMMARY OF THE INVENTION
The present invention relates to a seismic isolation sliding support bearing system comprising a pair of sliding bearings relatively movably opposing and in contact with each other between a superstructure and a substructure,
wherein at least one of the sliding bearings is a sliding bearing (a) made from a molding, having a porous structure including plural voids, of a composition including PTFE as a main component and including aromatic polyester resin in a ratio of 14 through 35 wt %, and the molding includes, in a surface portion thereof, a lubricant holding layer where a flowable lubricant is held.
In a preferred embodiment, the composition used for forming the sliding bearing (a) includes at least one filler selected from the group consisting of graphite, glass fiber, molybdenum disulfide, potassium titanate and bronze.
In a preferred embodiment, the lubricant is a flowable polysiloxane.
In yet another preferred embodiment, the pair of sliding bearings are the sliding bearing (a) and a sliding bearing (b) made from a metallic base plate including, on a surface thereof, a resin film of a composition including tetrafluoroethylene as a main component, and the resin film of the sliding bearing (b) includes micropores having a diameter of 10 through 100 &mgr;m in an area ratio of 10 through 50%, and includes, in a surface portion thereof, a lubricant holding layer where a flowable lubricant is held.
In a more preferred embodiment, one of the pair of sliding bearings has a diameter smaller than the other.
In a further preferred embodiment, the sliding bearing (a) is smaller than the sliding bearing (b).
In a preferred embodiment, the seismic isolation sliding support bearing system has a coefficient of friction of 0.02 or less under a surface pressure of 200 kgf/m
2
.
In this manner, according to the seismic isolation sliding support bearing system of this invention, owing to the sliding bearing (a) made from a molding or the like including PTFE having a porous structure and a high compression elastic modulus, a low coefficient of friction can be maintained for a medium or long period of time. As a result, the present seismic isolation sliding support bearing system can be suitably used in a wide range of fields including a seismic isolation sliding support bearing system for structures with a large load such as buildings and bridges.
In particular, when the diameter of the sliding bearing (a) made from the porous PTFE is smaller than the diameter of the other opposing sliding bearing, a sliding bearing (b) made from a metallic base plate having a porous PTFE film or a sliding bearing (c) made from a metallic base plate having a PTFE film, the seismic isolation sliding support bearing system can be free from a sliding failure, and early degradation and damage of the sliding bearings.
REFERENCES:
patent: 4121393 (1978-10-01), Renault et al.
patent: 4152799 (1979-05-01), Koster et al.
patent: 4320549 (1982-03-01), Greb
patent: 4553792 (1985-11-01), Reeve
patent: 4554767 (1985-11-01), Ikonomou
patent: 4644714 (1
Kawai Toshinao
Taguchi Wakao
Ueda Sakae
Glessner Brian E.
Nippon Pillar Packing Co. Ltd.
Stephan Beth A.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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