JPH0739662B2 - Sliding base isolation type offshore structure and its construction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applied to a marine structure constructed by a dry dock or the like, towed and then sunk, and then installed.
Specific examples of the structure include an offshore oil development platform, an offshore leisure facility, and an industrial plant barge for power generation, methanol, pulp, and the like.

[Conventional technology]

The general procedure for constructing offshore structures, such as offshore oil development platforms, consists of the following steps.

 Construct the structure body in the dry dock.

Inject it into the dry dock and leave the structure body in a floating state to equip the equipment.

 Towing a floating structure to the site.

 The structure is sunk and installed.

After pouring water against horizontal external forces such as waves, tidal currents, wind, earthquakes, ice pressure, etc. so that it will not slip, add weight by adding sand ballast, placing concrete ballast, etc. to increase sliding resistance.

The procedure may be performed in the dry dock.

[Problems to be Solved by the Invention]

When constructing the gravity type offshore structure as described above in the coastal or offshore sea in an earthquake area such as Japan, there are the following problems.

(A) In the conventional method, since weight is added so as not to slide against an earthquake, the seismic inertial force increases, and it is difficult to secure a sufficient sliding safety factor.

(B) Offshore structures are more buoyant than land structures, and in the event of an earthquake, they are also subject to hydrodynamic pressure from surrounding seawater, making it difficult to ensure a safety factor for sliding.

(C) When the seabed is soft, not only the construction cost for ground improvement but also the construction of a gravity type offshore structure may be impossible.

The present invention is intended to solve the above-mentioned problems in the prior art.

[Means for Solving the Problems]

The sliding seismic isolation type offshore structure of the present invention is designed according to the following criteria in the gravity type offshore structure.

(1) The weight of the structure including the ballast is reduced. However, with respect to waves, tidal currents, and winds that occur frequently, the sliding resistance due to gravity does not cause slippage.

(2) Sliding is allowed for design earthquakes (earthquakes that are designed so that the stress of the structure is below the yield point or below the short-term allowable stress).

(3) Sliding is allowed for the accident load (accident load such as the largest earthquake that can be considered historically and geologically or collision of ships), and at the same time, the structure does not lead to fatal destruction. To design.

In order to make the above possible, in the present invention, the basic bottom slab portion of the structure has a double bottom slab structure so as to slide between the two bottom slabs to control the sliding resistance.

That is, the sliding seismic isolation type offshore structure of the present invention is a gravity type offshore structure installed on the sea bottom due to the weight of the ballast inside the structure body, etc., and the bottom slab is divided into the foundation side bottom plate and the body side bottom plate. It is configured to separate and allow sliding on the contact surface between the base side slab and the main body side slab against horizontal external forces above a predetermined level such as the above-mentioned design earthquake. The contact surface between the foundation side bottom slab and the main body side bottom slab is a smooth finished surface of metal, plastic, tile, stone, st mortar, concrete, etc. to grasp the sliding resistance coefficient and predict the sliding behavior. Analysis can be facilitated.

In addition, for the accident load described above, a rising wall is provided in the peripheral portion of the foundation side slab to form a predetermined gap with the main body of the structure, and an anti-defense device made of rubber or wood is used as necessary. By installing or designing the structural strength of the rising wall to be weaker than the structure body, even if there is a local breakage, by restraining the displacement of the sliding structure body to some extent and absorbing kinetic energy, A structure to prevent fatal destruction on the main body side is conceivable.

As a construction method of an offshore structure when the slab portion is separated into a foundation side slab and a body side slab, for example, a state in which the foundation side slab of an offshore structure built in a dry dock is tightly connected to the body side slab with tension bolts. Then, it is possible to use a method in which the material is suspended by pouring water into the dry dock, towed, and then submerged on the sea floor at a predetermined position. The sliding resistance is given by the weight of the ballast, etc., like the conventional gravity type offshore structure, but for horizontal external force beyond the design earthquake, it allows the structure body to slide on the foundation side slab, The weight of the ballast can be reduced, and the weight of the structure can be reduced accordingly.

〔Example〕

 Next, the illustrated embodiment will be described.

FIG. 1 and FIG. 2 show a case where the present invention is applied to an offshore oil development platform as an example.

As shown in the figure, the lower bottom slab of the hollow structure body 1 is separated into a base side slab 2 and a body side slab 3. The structure body 1 has a dry section 4 in the center, and water ballast 5 and sand ballast 6 are injected or thrown into the outer side of the dry section 4, and as a gravity type structure, against waves, tidal currents, winds and small and medium earthquakes, It does not slip. In addition, the structure body 1
On-board equipment 7, such as living facilities and work equipment, is built on the top.

Fig. 2 shows the details of the bottom slab.
On the contact surface between the main body side bottom plate 3 and the main body side bottom plate 3, a base side base plate 2a and a main body side sliding plate 3a, which are made of stainless steel plate or Teflon processed steel plate, respectively, are integrated on the concrete surface. For example, when the design earthquake mentioned above acts, the structure main body 1 slides with respect to the foundation side bottom slab 2.

In addition, in the present embodiment, in the peripheral portion of the foundation side slab 2,
A downward facing basic skirt portion 8 and an upward facing rising wall 9 are formed. The base skirt portion 8 penetrates into the sea bottom surface 10 to fix the base side bottom slab 2 to the sea bottom surface 10.
The rising wall 9 restricts sliding when the structure body 1 slides due to a design earthquake or accident load, and an anti-defense device 11 is provided on the opposing surface on the structure body 1 side with a play δ. Has been. The impact protection device 11 in the present embodiment uses a cylindrical rubber fender made of synthetic rubber or the like. With respect to the design earthquake, it slides within the range of play δ, and the defense device 11 does not work. That is, the anti-ballistic device 11 operates effectively only for accident loads or destructive earthquakes and absorbs part of the kinetic energy. In order to protect the anti-ballistic device 11, a gap 12 between the structure body 1 and the rising wall 9 is filled with a filler 12 such as styrofoam that does not restrain sliding, and a sealing material 13 for preventing foreign matter from entering the upper surface thereof. Is installed.

In the figure, 14 is a tension bolt for tightly connecting the foundation-side bottom slab 2 to the structure body 1 at the time of towing, as will be described later. Reference numerals 15 and 15a are audit corridors used when the tension bolt 14 is removed later.

FIG. 3 shows another embodiment of the anti-defense device 11. In addition to the main defense device 11a, a small sub-defense device 11b is provided in the play part between the foundation side bottom plate 2 and the rising wall 9. It is provided.
Uses a sub-defense device 11b that is softer than the main-defense device 11a,
Only the sub-defense device 11b is deformed during a design earthquake. The sub-defense device 11b is crushed (may be crushed) against the accident load, and the main defensive device 11a operates. In this embodiment, after the design earthquake, if the water ballast is removed to lighten the structure body, the residual displacement due to the sliding is corrected by the restoring force of the sub-defense device 11b, and the structure body is returned to its original position. be able to.

FIG. 4 shows another embodiment of the anti-impact device 11, in which a rubber gasket is used as the sub-impact device 11b. For this rubber gasket, a gasket made of soft rubber, which is used in the box joint portion of the submerged box (submerged tunnel), is used, and it functions like the sub-defense device 11b in the embodiment of FIG. be able to.

Next, a method of integrating the structure main body 1 and the foundation side slab 2 at the time of building and towing a marine structure in the present invention will be described.

FIG. 5 shows a specific example of the tightened portion by the tension bolt 14 described above. The lower end of the tension bolt 14 is anchored in the bottom plate 2 on the foundation side, and the base plate on the foundation side.
2a, the main body side sliding plate 3a and the main body side bottom plate 3 are penetrated, and the tightening nut 21 is tightened to integrate the base side bottom plate 2 and the main body side bottom plate 3. A sleeve 22 is embedded in the bottom plate 3 on the main body side in advance.
A rubber packing 23 is attached between 14 and. Also, around the binding nut 21, donut type packing
A waterproof lid 24 is attached by bolts 26 via 25.

When the tension bolts 14 are sheared by an earthquake, the ballast water is drained to levitate the marine structure body for towing and reuse.

When it becomes necessary to relocate the tension bolt 14 without being sheared, the structure body is levitated by the following procedure.

Loosen the waterproof cover binding bolt 26 and remove the waterproof cover 24.

 Remove the tightening nut 21 of the tension bolt 14.

 Attach the waterproof lid 24 again.

 Drain ballast water from the structure body.

The tension bolts 14 are attached to a dry section or an inspection corridor that is in contact with the bottom plate 3 on the main body side so that a worker can approach the tension bolts.

〔The invention's effect〕

(1) As for the design earthquake, the main body of the offshore structure slides on the foundation side slab to absorb the earthquake energy,
Demonstrate seismic isolation.

(2) In case of accident load, the kinetic energy is absorbed by sliding, and at the same time, a rising wall is provided in the peripheral part of the foundation side slab, and the kinetic energy is generated in the form of strain energy due to the impact protection device or deformation of the rising wall. Absorbs energy,
It is possible to prevent harmful displacement to the main body of the offshore structure and prevent fatal destruction to the main body at the same time.

(3) The sliding surface between the foundation-side bottom plate and the body-side bottom plate is metal,
Since it is a smooth finished surface of plastic, tile, stone, cement mortar, concrete, etc., the sliding resistance coefficient can be easily grasped and the predictive analysis of sliding behavior can be facilitated.

(4) The tension bolt functions to bond the foundation side slab to the offshore structure body during floating towing. After installation on site, it can be removed or left as it is.

(5) The base side slab has a "layered structure" to resist bending moments in cooperation with the main body side slab.

(6) When sliding due to an earthquake load or the like, it is possible to correct the position by reducing the contact pressure between the bottom slabs by ballast adjustment and re-floating.

(7) It is possible to re-float, dock in for repair, or relocate to another point by adjusting the ballast.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional view showing an embodiment in which the sliding seismic isolation type offshore structure of the present invention is applied to a platform.
The figure is an enlarged view of the main part, FIG. 3 and FIG. 4 are vertical cross-sectional views showing modified examples of the barrier material, and FIG. 5 is a vertical cross-sectional view showing a concrete example of the integration of the foundation slab with tension bolts. It is a figure. DESCRIPTION OF SYMBOLS 1 ... Structure main body, 2 ... Foundation side bottom plate, 2a ... Base side base plate, 3 ... Main body side bottom plate, 3a ... Main body side sliding plate, 4
… Dry compartment, 5… Water ballast, 6… Sand ballast, 7…
Overlay equipment, 8 ... Foundation skirt, 9 ... Rise wall, 10 ... Sea bottom, 11 ... Impact protection device, 12 ... Filling material, 13 ... Sealing material, 14 ...
Tension bolt, 15 ... Auditorium, 21 ... Tightening nut, 22 ...
Sleeve, 23 ... Rubber packing, 24 ... Waterproof lid, 25 ... Packing, 26 ... Bolt,

Claims (5)

[Claims] 1. A gravity type offshore structure installed on a seabed, wherein a bottom plate portion of the offshore structure is separated into a foundation side bottom plate and a body side bottom plate, and the foundation side bottom plate and the body side bottom plate are brought into contact with each other. By smoothing the surface and controlling the sliding resistance by the weight of the ballast in the structure body, it is possible to use the foundation side slab for the design earthquake where the stress of the structure is below the yield point or below the short-term allowable stress. Historically by configuring to allow sliding on the contact surface with the main body side slab and providing a rising wall in the peripheral part of the foundation side slab and forming a predetermined gap with the structure main body, historically Further, it is characterized in that it is configured to absorb the kinetic energy while restraining the displacement of the structure body sliding by the rising wall against the accident load such as the largest geologically conceivable earthquake or the collision of ships. Sliding seismic isolation Marine structures. 2. The sliding seismic isolation type offshore structure according to claim 1, wherein a base side base plate and a main body side base plate having smooth surfaces are respectively integrated with contact surfaces of the base side bottom plate and the main body side bottom plate. 3. The sliding disengagement according to claim 1 or 2, wherein an anti-shock device is provided in a gap portion between the rising wall and the structure body to restrict relative movement between the rising wall and the structure body. Seismic offshore structure. 4. The structural strength of the rising wall is weaker than that of the structure main body, and while restraining displacement of the structure main body due to accident load to some extent, kinetic energy is absorbed by local destruction of the rising wall. The sliding seismic isolation type offshore structure according to claim 3. 5. The foundation side slab is tightly connected to the main body side slab with tension bolts, towed to the installation site in a floating state, sunk on a predetermined sea floor, and then given a predetermined sliding resistance by a ballast. The method for constructing a sliding seismic isolation type offshore structure according to claim 1, 2, 3 or 4.