JP4058433B2 - Seismic isolation structure of pile foundation - Google Patents

Description

  The present invention relates to a pile foundation in which a footing fixed to a structure such as a building or a bridge and embedded in an underground ground is pin-supported to the head of a foundation pile having a hollow cross-sectional structure placed in the underground ground. Regarding seismic isolation bearing structure.

  As this type of pile foundation seismic isolation structure, for example, there is a structure as shown in FIG. 5 (see, for example, Patent Document 1). The pile foundation seismic isolation structure shown in FIG. 5 is such that a metal pile head end plate 21 is fixed to the head of a foundation pile 20 having a hollow cross-sectional structure (cylindrical structure) placed in the underground ground 26. The metal convex lower bar 22 is fixed by welding to the upper surface of the pile head end plate 21, while the annular concave upper bar 24 is fixed to the lower part of the footing 23, and the convex part of the convex lower bar 22 is recessed. A pin support is adopted in which the concave portion of the upper collar 24 is fitted through the annular rubber sheet 25.

  According to this pin support, when seismic force is applied, the stress is released by the relative rotational displacement between the head of the foundation pile 20 and the footing 23 through the thickness change (elastic deformation) of the annular rubber sheet 25, Bending moment can be prevented from occurring in the concave / convex fitting portion between the convex lower bar 22 and the concave upper bar 24, and it is sufficient to prevent damage and breakage of the foundation pile 20 and footing 23 even when excessive external force is applied. It is possible to secure a seismic performance and seismic isolation performance.

JP 2003-105780 A

  However, in the above-mentioned seismic isolation structure of the pile foundation, it is necessary to weld and fix the metal convex lower bar 22 to the upper surface of the pile head end plate 21. However, the welding work cannot be performed in the rain, and the construction period is delayed. In addition, it is disadvantageous in terms of weather and on-site construction, such as requiring a power source for welding work, and the welded part between the convex lower barb 22 and the pile head end plate 21 causes rusting and breaks over time. There is sorrow. Further, the metal convex lower bar 22 such as a steel casting is heavy, so that the total weight of the pin support components is bulky. This also makes installation workability difficult and further requires the convex lower bar 22. There were problems such as high costs.

  The present invention has been made to solve such problems, and the object of the present invention is to eliminate the need for a convex lower arm as a pin bearing component such as the conventional seismic isolation bearing structure described above. To provide a seismic isolation bearing structure for pile foundations that can eliminate the welding process of this convex lower arm, reduce the number of pin bearing components, reduce the number of installation steps, reduce the total weight, and improve workability. It is in.

In order to achieve the above object, the pile-base seismic isolation structure according to the present invention is a foundation pile having a hollow cross-sectional structure in which a pile head end plate made of metal is overlapped and fixed on the upper surface of the head. And an inner annular boss which is fixed to the lower surface side of the footing and whose outer peripheral surface is on a cylindrical surface concentric with the foundation pile and an outer annular boss whose inner peripheral surface is on a cylindrical surface concentric with the foundation pile. And a flange having a circular groove corresponding to the shape of the head including the pile head end plate of the foundation pile between the inner annular boss and the outer annular boss, and the foundation pile Of the head including the pile head end plate of the foundation pile is fitted into the annular groove of the saddle via an annular rubber elastic plate . between the outer periphery of the inner annular bosses, and the pile head end plate of the foundation pile between an inner periphery of the outer annular boss periphery and shoe seat of the head, including a pile head end plate of the foundation pile Together to form an annular gap for allowing relative rotational displacement between the non-head and shoe seat, the rubber-like elastic plate, the head including a pile head end plate of the foundation pile inner and shoe seat Prevents the annular gap between the outer circumference of the inner annular boss and the annular gap between the outer circumference of the head including the pile head end plate of the foundation pile and the inner circumference of the outer annular boss of the saddle. In the seismic isolation bearing structure of the pile foundation in which the inner seal ring and the outer seal ring are respectively fitted and held on the inner and outer circumferences of the lower surface of the rubber-like elastic plate ,
The depth E of the annular groove from the lower surface of the rubber-like elastic plate is the rubber shape obtained by (D / 2) × tan θ, where D is the outer diameter of the foundation pile and θ is the rotation amount of the foundation pile. The thickness of the pile head end plate is equal to or greater than the dimension obtained by adding the thickness change amount ± T of the elastic plate to the thickness t of the pile head end plate and four times the thickness change amount ± T of the rubber elastic plate. It is characterized in that it is set to be equal to or smaller than the dimension obtained by adding the thickness t .

  As one suitable aspect, when the said foundation pile is a product made from concrete, it is preferable that the reinforcement band is integrally wound around the outer periphery of the head of this foundation pile.

  According to the seismic isolation bearing structure of a pile foundation having the above-described configuration, the head including the pile head end plate of the foundation pile is inserted through an annular rubber-like elastic plate in an annular groove of a saddle fixed to the lower surface side of the footing. Therefore, when seismic force is applied, the stress is released by the relative rotation of the foundation pile head and the footing via the change in thickness of the rubber elastic plate, and the foundation pile head and Bending moment can be prevented from occurring at the mating part with the seat, and even when excessive external force is applied, damage and breakage of the foundation pile and footing can be prevented, and sufficient seismic performance and seismic isolation performance can be exhibited. .

  Installation work of pin bearing components by simply fitting the annular groove formed on the underside of the saddle to the head including the pile head end plate of the foundation pile via a rubber elastic plate without welding the saddle Can be completed. Therefore, the work can be performed even in rainy weather, the work period is not delayed, and no power source is required unlike welding work. In addition, since only two members, a saddle and a rubber-like elastic plate, are required as the pin support components, a convex shape compared to the conventional base-isolated support structure that required a pair of upper and lower ridges and an annular rubber sheet. It is light and easy to handle as much as it does not require a lower arm, and can reduce not only the number of members but also the number of construction steps, thereby improving workability and reducing construction costs. Therefore, it is extremely advantageous in terms of workability, installation cost, and member cost.

  By wrapping a reinforcing band integrally around the outer periphery of the foundation pile head made of concrete, the reinforcement pile can suppress the swelling of the outer periphery of the foundation pile head during hardening after concrete molding of the foundation pile, so that the annular groove in the saddle It is advantageous that the corresponding dimensional accuracy can be obtained and the foundation pile head can be reinforced.

  A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a seismic isolation structure for a pile foundation according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view taken along line AA in FIG.

  The base isolation structure of the pile foundation of the present invention has a hollow cross section such as a centrifugal reinforced concrete pile, a pretension centrifugal high strength prestressed concrete pile (PHC pile), an SC pile, an ST pile, etc. An annular pile head end plate 4 made of metal is superposed on the upper surface of the head 2a of the foundation pile 2 which is a ready-made pile having a structure (cylindrical structure). The ready-made foundation pile 2 shown in FIGS. 1 and 2 is made of concrete, and a pile head end plate 4 is superposed and fixed to the upper surface of the head 2 by using the upper end portion of the PC steel rod 3. A metal reinforcing band 5 is integrally wound around the outer periphery of the head 2 a of the foundation pile 2. By winding the reinforcing band 5, it is possible to suppress bulging of the outer periphery of the head 2a of the foundation pile 2 at the time of hardening of the foundation pile 2 after concrete molding, and to improve the dimensional accuracy. Can be reinforced.

  After the foundation pile 2 is placed on the ground 1, the pin seat 6 and the rubber elastic plate 7 are installed on the pile head end plate 4 of the foundation pile 2. The saddle 6 is made of a metal such as a steel casting, and has a circular outer ring part 61 having a slightly larger diameter than the foundation pile 2, a center part 62, and an arm part 63 that connects the outer ring part 61 and the center part 62, An inner annular boss 64 and an outer annular boss 65 are formed on the lower surface of the outer ring portion 61, and the head including the pile head end plate 4 of the foundation pile 2 between the inner annular boss 64 and the outer annular boss 65. An annular groove 66 corresponding to the shape of 2a is formed. On the upper surface of the outer ring portion 61, a plurality of ribs 67 are arranged on the same circumference in a divided arrangement state and upwards, respectively, for increasing the strength and the bonding force with the lower surface of a concrete footing (structure foundation) 13 described later. It protrudes to. The rubber-like elastic plate 7 is formed of an elastomer, synthetic rubber, natural rubber or the like in an annular shape corresponding to the annular groove 66 of the saddle 6.

  In order to install the saddle 6 on the head 2 a of the foundation pile 2, the foundation pile 2 so that the annular groove 66 of the saddle 6 is fitted to the head 2 a of the foundation pile 2 via the rubber elastic plate 7. Is placed on the pile head end plate 4. At that time, man-hours which are less required in the installation procedure in which the rubber-like elastic plate 7 is fitted in the annular groove 66 of the saddle 6 in advance and the saddle 6 is placed on the pile head end plate 4 of the foundation pile 2. However, instead of this, the rubber-like elastic plate 7 is first placed on the pile head end plate 4 of the foundation pile 2, and then the saddle 6 is mounted on the pile head end plate of the foundation pile 2. 4 can also be placed.

  In the annular groove 66 of the saddle 6, between the inner periphery of the head 2 a including the pile head end plate 4 of the foundation pile 2 and the outer periphery of the inner annular boss 64, and between the outer periphery of the head 2 a and the outer annular boss 65. In order to form an annular gap c1, c2 necessary and sufficient to allow relative rotational displacement between the head 2a of the foundation pile 2 and the saddle 6 in the event of an earthquake or typhoon, respectively. The inner diameter of the head 2a of the second pile is set to be a predetermined amount larger than the inner diameter of the annular groove 66 (the outer diameter of the inner annular boss 64), and the outer diameter of the head 2a of the foundation pile 2 is the outer diameter (outer side of the annular groove 66). The inner diameter of the annular boss 65 is set to be smaller by a predetermined amount.

  The total depth of the annular groove 66 of the saddle 6 is such that the pull-out force due to the seismic force is applied to the fitting portion between the head 2 a of the foundation pile 2 and the annular groove 66 of the saddle 6. It is set to such an extent that the combined state is not released (the head 2a of the foundation pile 2 is not pulled out from the annular groove 66 of the saddle 6).

The depth E (see FIG. 1) of the annular groove 66 from the lower surface 7a of the rubber elastic plate 7 is the amount of change in the thickness of the rubber elastic plate 7 accompanying the rotation of the foundation pile 2 during an earthquake or typhoon. On the other hand, the depth dimension is set so that the horizontal force can be transmitted. Since the transmission of the horizontal force is performed by the thickness of the pile head end plate 4, the depth dimension E is equal to or greater than the dimension obtained by adding the thickness of the pile head end plate 4 to the thickness change amount of the rubber-like elastic plate 7. It is desirable. Therefore, now, if the thickness of the pile head end plate 4 is t, the amount of change in thickness of the rubber elastic plate 7 is ± T, and the margin is s,
E = t + (± T) · s (1)
Here, with respect to the thickness variation ± T of the rubber-like elastic plate, FIG. 3 (a) (vertical front view of the seismic isolation bearing structure in normal state), FIG. 3 (b) (in the state where the foundation pile is rotated during the earthquake) When shown with reference to the longitudinal front view of the seismic isolation bearing structure, the following relational expression is obtained.
Amount of change in thickness of rubber elastic plate ± T = (D / 2) × tan θ (2)
Where D: outer diameter of foundation pile θ °: amount of rotation of foundation pile ± T: amount of change in thickness of rubber elastic plate
(-T: compression side of rubber-like elastic plate, + T: tension side of rubber-like elastic plate)
On the other hand, if the margin s is higher than 4 times, the foundation pile 2 comes into contact with the inside of the annular groove 66 by rotation, and therefore, the predetermined amount of rotation of the foundation pile 2 is obstructed. Since the pile head end plate 4 protrudes from the inside of the concave groove 66, the horizontal force may not be transmitted. Therefore, the margin s is 1 to 4 times, more preferably 1 to 1.5 times.

For example, if the outer diameter D of the foundation pile is 600 mm, the rotation amount θ ° of the foundation pile is 2 °, the thickness t of the pile head end plate 4 is 16 mm, and the margin s is 50%, the above formula (1) (2 From)
Thickness variation of rubber-like elastic plate 7 ± T = 600/2 (mm) × tan 2 ° = 10.5 (mm) Depth dimension E = 16 (mm) +10.5 (mm) × 1. 5 = 31.75 (mm)
Therefore, the depth dimension E of the annular groove 66 of the saddle 6 is set to 31.75 mm so that a horizontal force can be transmitted with respect to the thickness variation 10.5 mm of the rubber-like elastic plate 7. Become.

  As shown in FIG. 2, when the pile head end plate 4 of the foundation pile 2 has a dent 8 due to a PC steel rod mounting hole or the like, or the notch 9 is present on the outer periphery of the pile head end plate 4, a rubber-like elastic plate Prior to mounting the saddle 6 on the pile head end plate 4 of the foundation pile 2, the recess 8 and the notch 9 are epoxy. The top surface of the pile head end plate 4 is flattened by filling with a filler 10 such as resin or high fluidity mortar.

  The rubber-like elastic plate 7 includes a gap c1 between the inner periphery of the head 2a including the pile head end plate 4 of the foundation pile 2 and the outer periphery of the inner annular boss 64 of the saddle 6, and the outer periphery and the flange of the head 2a. Inner seal made of fluororesin such as PFA, PTFE, etc. that has excellent heat resistance and chemical resistance and has a small friction coefficient in order to prevent it from protruding into the gap c2 between the outer periphery of the outer annular boss 65 of the seat 6 The ring 11 and the outer seal ring 12 are fitted and held on the inner and outer circumferences of the lower surface 7a of the rubber-like elastic plate 7, respectively.

  Thus, as shown in FIG. 2, the saddle 6 installed on the head 2 a of the foundation pile 2 is on the lower surface side of the footing 13 formed by placing concrete on the underground ground 1. The concrete is fixed at the same time as the concrete is placed. At that time, the covering material 14 such as plywood is placed on the arm portion 63 prior to the concrete placement so that the cast concrete does not flow into the through hole 68 between the arm portions 63 and 63 of the saddle 6. The hole 68 (see FIG. 1) is closed.

  As described above, the base-isolated bearing structure of the pile foundation in which the annular groove 66 of the saddle 6 fixed to the lower surface side of the footing 13 is fitted to the head 2a of the foundation pile 2 via the rubber elastic plate 7. In the case of an earthquake or typhoon, the energy due to the seismic force is effectively absorbed by the relative rotational displacement between the head 2a of the foundation pile 2 and the footing 13 through the thickness change (elastic deformation) of the rubber-like elastic plate 7. Will be alleviated. Therefore, since the stress concentration on the fitting part between the head 2a of the foundation pile 2 and the footing 13 when the seismic force is applied is significantly reduced, the cross section of the foundation pile 2 and the footing 13 is reduced to the minimum necessary in terms of strength. Even when an excessive horizontal force is applied, the damage and breakage of the head 2a and footing 13 of the foundation pile 2 can be achieved while reducing the amount of bar arrangement and facilitating construction and reducing costs. This makes it possible to exhibit excellent seismic performance and seismic isolation performance.

  Moreover, the installation work of the pin support component can be completed only by fitting the annular groove 66 of the saddle 6 to the head 2a including the pile head end plate 4 of the foundation pile 2 via the rubber elastic plate 7, Since welding work that depends on the weather is not required, the construction can be carried out without being influenced by the weather, and the construction period can be shortened. In addition, since only two members of the pin support 6 and the rubber elastic plate 7 are sufficient as the pin support component, it is lightweight and easy to handle, and the number of members as well as the number of construction steps can be reduced. The construction cost can be reduced.

  FIG. 4 shows an embodiment in which the ready-made foundation pile 2 is a steel pipe pile. In this embodiment, the pile head end plate 4 is superposed and fixed to the upper surface of the head portion 2a of the foundation pile 2 by welding or the like, and other configurations and operations are the same as those of the above embodiment. In the figure, reference numeral 19 denotes a sand / crushed stone layer formed on the upper surface of the underground ground 1 around the head 2 a of the foundation pile 2.

It is a top view of the seismic isolation bearing structure of the pile foundation which shows one Example of this invention. It is an AA line expanded sectional view in FIG. (A) is a longitudinal front view of the base-isolated bearing structure in a normal state, and (b) is a longitudinal front view of the base-isolated bearing structure in a state where the foundation pile is rotated during the earthquake. It is sectional drawing which shows the seismic isolation bearing structure of the pile foundation of another Example corresponding to FIG. It is a longitudinal front view of the seismic isolation bearing structure of the pile foundation of a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Underground 2 Foundation pile 2a Head 4 Pile head end plate 5 Reinforcement band 6 Scorpio 7 Rubber elastic plate 13 Footing 66 Annular groove

Claims (2)

A foundation pile with a hollow cross-section structure that is placed on the ground, and has a metal pile head end plate superimposed on the top surface of the head, and fixed to the bottom side of the footing, and the outer peripheral surface is concentric with the foundation pile. An inner annular boss on the cylindrical surface and an outer annular boss whose inner peripheral surface is on a cylindrical surface concentric with the foundation pile are formed, and the pile head of the foundation pile is formed between the inner annular boss and the outer annular boss. And a saddle having a shape with an annular groove corresponding to the shape of the head including the end plate, and the head including the pile head end plate of the foundation pile is annular in the annular groove of the saddle Between the inner circumference of the head including the pile head end plate of the foundation pile and the outer circumference of the inner annular boss of the saddle, and the head including the pile head end plate of the foundation pile. form an annular gap for allowing relative rotational displacement between the head and the shoe seat including pile end plate of the foundation pile between an inner periphery of the outer annular boss periphery and shoe seat parts Together are the rubber-like elastic plate, the annular gap, and pile head end of the foundation pile between an outer periphery of the inner annular boss of the inner periphery and the shoe seat of the head, including a pile head end plate of the foundation pile An inner seal ring and an outer seal ring for preventing the outer elastic ring from protruding into the annular gap between the outer periphery of the head including the plate and the inner periphery of the outer annular boss of the saddle are provided on the inner and outer periphery of the lower surface of the rubber-like elastic plate. In the seismic isolation bearing structure of pile foundations that are held together ,
The depth E of the annular groove from the lower surface of the rubber-like elastic plate is the rubber shape obtained by (D / 2) × tan θ, where D is the outer diameter of the foundation pile and θ is the rotation amount of the foundation pile. The thickness of the pile head end plate is equal to or greater than the dimension obtained by adding the thickness change amount ± T of the elastic plate to the thickness t of the pile head end plate and four times the thickness change amount ± T of the rubber elastic plate. A seismic isolation structure for pile foundations, characterized in that it is set to a dimension equal to or less than the dimension added with t .   The seismic isolation bearing structure for a pile foundation according to claim 1, wherein the foundation pile is made of concrete, and a reinforcing band is integrally wound around an outer periphery of a head of the foundation pile.

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