JP3870371B2 - Floating structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a floating body type seismic isolation structure, and more particularly to a floating body type base isolation structure in which a box foundation is floated in a pool capable of flowing in and out of groundwater and is insulated from surrounding ground.
[0002]
[Prior art]
As a concept of the seismic isolation structure built into the building foundation, an isolation type seismic isolation structure has been proposed in which the input seismic force from the ground is not transmitted to the structure. As an example of this insulation type seismic isolation structure, there is a method of obtaining a seismic isolation effect by a floating type seismic isolation structure in which a structure body or a base portion is floated in a fluid having an open liquid surface. This type of floating seismic isolation structure can be expected to have a high seismic isolation effect especially for horizontal input seismic waves. FIG. 7 shows a model diagram of an example of the floating body type seismic isolation structure 50. As shown in the figure, the floating type seismic isolation structure 50 is in a state where a watertight box 51 is immersed and floated in a pool (water tank) 53 filled with a liquid 52 such as water.
[0003]
In addition, the box 51 restricts the occurrence of excessive displacement with respect to a long-period horizontal force caused by wind or the like, and maintains its position through a known fender 54 made of rubber or the like. The mooring column 55 is elastically supported. Such mooring is sufficiently softer than the mass of the box 51 (the mooring spring constant is smaller than the mass), so that the natural period can be set to a period considerably longer than the seismic period band. Therefore, the response displacement of the box 51 due to the seismic force is extremely small.
[0004]
FIG. 8 is a longitudinal sectional view showing an example in which the floating body type seismic isolation structure 50 is applied to the pier foundation of the continuous bridge 60. As shown in the figure, for example, a pool 53 of a predetermined scale is constructed at a pier foundation position. The pool 53 is filled with a liquid 52 such as water to a predetermined depth, and a box base 51 serving as a footing is immersed in the pool 53. By adopting such a bridge foundation structure, it is expected that the seismic isolation structure will be applied to the foundation structure of continuous bridges.
[0005]
[Problems to be solved by the invention]
However, in the above-mentioned floating body type seismic isolation structure, the container structure constituting the pool has a bottom slab thickness that can resist the water pressure acting on the bottom surface in a state where the box is floated at all times. It is necessary to design a strong seismic structure with certain water tightness so that it does not occur. Moreover, it is considered that water filled in the pool evaporates with time. In that case, in order to maintain the water level in the pool, it is necessary to provide ancillary facilities such as water level observation means and pump facilities.
[0006]
Thus, in the conventional floating body type seismic isolation structure, the pool that supports the seismic isolation structure portion must be made a strong earthquake resistant structure or provided with watering equipment, which increases the construction cost. Moreover, it is necessary to operate the water supply equipment regularly, and high running costs and maintenance costs are expected.
[0007]
Further, in the case of the pier foundation of the continuous bridge 60 shown in FIG. 8, it is necessary to match the height of the saddle at the upper part of the pier 61 erected on each box foundation 50. As a countermeasure for this, it is necessary to connect the communication pipe 62 between the pools 53 as shown in the figure, and to control the water level in each pool 53, and an accompanying operation facility is required.
[0008]
Therefore, an object of the present invention is to solve the problems of the conventional techniques described above, and to provide a floating type seismic isolation structure that is configured with a pool that can be constructed at low cost and that requires almost no maintenance equipment.
[0009]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention provides a water-permeable wall body by digging a high groundwater level ground, and changes the groundwater level in a pool storing groundwater communicating with the groundwater in the surrounding groundwater aquifer. It is characterized in that the box foundation moored to a part of the surrounding ground is dipped and floated in a form that can be lifted up and down.
[0010]
It is preferable that the box foundation is moored to a part of the surrounding ground of the pool via an elastically deformable mooring member.
[0011]
The water-permeable wall body is preferably a precast concrete sheet pile in which a plurality of openings are formed or a screen member filled with a filler with a high porosity.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a floating body type seismic isolation structure of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a model diagram showing the concept of the floating body type seismic isolation structure 10. In the model of the floating body type seismic isolation structure 10, only the box part is shown, but this box part is used as a foundation part corresponding to footing (hereinafter referred to as a box foundation) and a structure such as a pier. Is assumed to be part of FIG. 2 shows an example in which the following box foundation 11 is used as the footing 3 of the pier foundation 2 of the continuous bridge 1, and the floating seismic isolation structure 10 is applied to each pier foundation 2.
[0013]
As shown in FIGS. 1 and 2, the box base 11 of the present invention has the same configuration as that of the conventional floating type seismic isolation structure 10 shown in FIG. In the present embodiment, an internal steel frame (not shown) is composed of a highly rigid box covered with a shell steel plate. The steel frame is composed of a framed ramen structure or a cell structure composed of a composite structure such as a shape steel or steel concrete. The outer shell steel plates are joined to each other so as to maintain watertightness, and are attached to a steel frame. The box foundation 11 is designed assuming a standing pier, an upper work load, and an external water pressure in a floating state. Moreover, the height of the box foundation 11 is determined to be a freezer that can ensure stability of the floating body when the box foundation 11 is immersed in a pool (described later) while the box foundation 11 is subjected to its own weight and the box foundation 11 is subjected to a vertical load. It has a height that can be secured, and the depth of the pool is designed in consideration of the draft of the box foundation 11. The box foundation 11 can be constructed as a composite structure such as reinforced concrete, steel reinforced concrete, ferrocement or the like if a predetermined buoyancy can be ensured.
[0014]
Furthermore, in this invention, the container structure 14 which consists of the baseplate 15 and the wall body 16 is comprised by the water-permeable structure so that the pool 13 in which the box foundation 11 is immersed may be comprised. Here, as shown in the figure, the water-permeable structure is such that, in a high groundwater level ground where the groundwater free water surface is located near the ground surface, the water level of the pool 13 is completely changed according to the fluctuation of the groundwater level of the surrounding ground. A structure with sufficient water permeability to follow, and there is almost no difference in water level between the water level in the container structure and the groundwater level of the surrounding ground.
[0015]
In the ground model of FIG. 1, when the aquifer reaches a position deeper than the bottom plate 15 of the container structure 14 constituting the pool 13, the bottom plate 15 also has a water flow structure so that the surrounding ground in the pool 13 is obtained. The water level difference between the ground water level in the surrounding ground and the water level in the pool 13 can be reliably eliminated.
[0016]
Moreover, in order to ensure the underground space as a pool 13 part, the wall body 16 of the container structure 14 needs to be provided with the mountain retaining function which resists the soil water pressure of a back ground. Therefore, a wall structure having water permeability and a predetermined rigidity is adopted. In the present embodiment, the precast concrete sheet pile 16 shown in FIG. 3 is used as the water-permeable wall body. A large number of circular holes 17 are formed on the surface of the precast concrete sheet pile 16 at predetermined intervals in the vertical and horizontal directions, and the water permeability of the ground water inside and outside the wall is ensured, so that the water pressure of the back ground can be resisted. Compared with the conventional construction method in which is not secured, rigidity is low. The circular hole 17 has a filter function so that soil particles on the back ground do not pass.
[0017]
FIG. 4 shows a modification in which the screen member 20 is used as a wall body that places importance on water flow performance in a gravel layer with relatively high self-supporting properties. In the modification shown in the figure, a saddle-shaped steel frame body 21 having a predetermined rigidity is installed along the excavation wall surface, and a coarse aggregate 22 having a predetermined particle diameter or more is filled therein as a filler. A predetermined air permeability can be obtained by securing a gap. In addition, as a filler, you may use what consists of artificial materials, such as a resin member of a predetermined diameter. As an additional maintenance device, it is also preferable to prevent the clogging by installing the blower tube 23 to a predetermined depth in order to improve clogging between the fillers.
[0018]
Moreover, depending on the scale of the box foundation 11, a water-permeable earth retaining wall such as a parent pile sheet pile can be used as the main structure. In this case, it is preferable to use a precast concrete plate or the like in consideration of durability for the lateral sheet pile or the like.
[0019]
Further, a permeable concrete wall may be applied as the wall body, and in this case, the above-described blower pipe can be provided as necessary to prevent clogging.
[0020]
The box foundation 11 described above moves up and down completely following the change in the groundwater level at all times. For this reason, it is necessary to provide a mooring system that can realize smooth raising and lowering of the box foundation 11. Since this mooring device has a soft spring effect in the horizontal direction, the natural period of horizontal movement is much longer than that of seismic waves. Therefore, the box hardly vibrates against the seismic force. However, when an external force containing a long-cycle component acts like wind, the box tries to move slowly and horizontally. It is necessary to limit the horizontal movement of the box foundation 11 at this time within a specified displacement amount. Therefore, a mooring member 30 for securely holding the box foundation 11 in the pool 13 is provided (FIG. 1). In the present embodiment, as shown in FIG. 5, the fender 32 that can be elastically deformed with respect to the support column 31 standing on the ground of the pool 13 is used as a mooring member, and the position of the box base 11 is determined. Is retained. As this type of fender 32, synthetic rubber fenders having various known shapes can be used. In addition, as shown in FIG. 6, a fender 33 having a structure in which a synthetic rubber processing member having a curved cross-sectional outer shape is attached and fixed so as to span between the ground side and the box base 11 side may be used. The fender 33 may be attached so as to surround the entire outer periphery of the box foundation 11 or may be partially attached at a position where no eccentricity of the box foundation 11 occurs.
[0021]
Although the above-described pool 13 has a structure in which the water surface is exposed to the air, if the evaporation of water is significant, it is preferable to install an evaporation preventing film on the water surface of the pool 13 as necessary. As the evaporation preventing film, a synthetic fiber sheet and a synthetic rubber sheet having buoyancy and water tightness are suitable. It is preferable to completely follow the water level change by completely covering the water surface by floating the sheet on the water surface between the box body 11 and the water-permeable wall.
[0022]
【The invention's effect】
As described above, the box foundation that bears the load of the superstructure is immersed in a pool that has a water-permeable container structure that allows groundwater from the surrounding ground to flow in and out through the water-permeable wall. As a result, it is possible to expect an effective seismic isolation effect with a simple structure on the box foundation.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing an embodiment of a floating type seismic isolation structure according to the present invention.
FIG. 2 is a longitudinal sectional view showing an example in which the floating seismic isolation structure of FIG. 1 is applied to a pier of a continuous bridge.
FIG. 3 is a partial perspective view showing an example of a precast concrete water-permeable wall body.
FIG. 4 is a partial perspective view showing an example of a water-permeable wall body of a screen member filled with a filler.
FIG. 5 is a partial cross-sectional view showing an embodiment of a mooring member.
FIG. 6 is a partial cross-sectional view showing a modified example of a mooring member.
FIG. 7 is a partial cross-sectional view showing an example of a conventional floating body type seismic isolation structure.
FIG. 8 is a longitudinal sectional view showing an example in which the floating seismic isolation structure of FIG. 7 is applied to a pier of a continuous bridge.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Floating type seismic isolation structure 11 Box base 13 Pool 14 Container structure 16 Water permeability wall 20 Screen member 30 Mooring member 32 Fender

Claims (4)

High groundwater level ground is dug to establish a water-permeable wall body, and it is moored to a part of the surrounding ground so that it can move up and down following the fluctuation of the groundwater level in a pool that stores groundwater communicating with the groundwater of the surrounding ground. Floating type seismic isolation structure, characterized by immersing and lifting the box foundation. The floating body type seismic isolation structure according to claim 1, wherein the box base is moored to a part of the ground surrounding the pool via an elastically deformable mooring member. 2. The floating type seismic isolation structure according to claim 1, wherein the water-permeable wall body is a precast concrete sheet pile in which a plurality of openings are formed. 2. The floating body seismic isolation structure according to claim 1, wherein the water-permeable wall body is a screen member filled with a filler with a high porosity.

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