JP2007297865A - Steel pipe pile structure and its construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe pile structure that is rational and structurally stable when a large axial force or bending moment is applied, and a construction method that improves the construction efficiency of the steel pipe pile structure.
SOLUTION: Concrete 2 is placed in a section of 3-5D (D is the outer diameter of the steel pipe) where the bending moment generated by the horizontal force acting on the steel pipe pile from the pile head of the steel pipe 1 constituting the steel pipe pile converges small. Fill. A protrusion 3 is provided on the inner surface of the steel pipe 2 near the lower end position of the concrete 2 filling section, and the axial force shared by the concrete 2 is transmitted to the steel pipe 1 through the protrusion 3.
[Selection] Figure 2

Description

  The present invention relates to a structure of a foundation pile in the field of civil engineering and architecture, and more particularly to a structure of a steel pipe pile filled with concrete as a pile that receives a large horizontal force due to an earthquake or the like, and a construction method thereof.

  A vertical load (axial force) and a horizontal load such as an earthquake or wind act on the steel pipe pile, and a bending moment is generated by the horizontal load. In the design of steel pipe piles, the diameter and thickness of the steel pipe are set to withstand axial forces and bending moments.

  In recent years, the axial force on the pile diameter has increased, such as providing wings (blades) with steel plates at the pile tip, or building root bulbs with soil cement solidified bodies. Along with this, the steel pipe thickness required for design increases, and this is particularly noticeable for upper piles where moments generated in piles often increase.

  Generally, steel pipe piles use spiral steel pipes manufactured by hot-rolled coils, but spiral steel pipes can only be manufactured to a thickness of about 25MM or less due to manufacturing restrictions. However, there is a problem that the manufacturing cost increases because a sheet-wound steel pipe, a UOE steel pipe, or the like to be used must be used.

  As an invention corresponding to such a situation, there are inventions described in Patent Document 1, Patent Document 2, and Patent Document 3.

JP 2001-214440 A JP 2002-302941 A JP 2002-180460 A

  The invention described in Patent Document 1 is to reduce the plate thickness by increasing the steel pipe diameter of the upper pile part by 1.15 to 1.6 times that of the lower pile. However, since different steel pipe diameters must be joined, the structure of the joint becomes complicated, the manufacturing cost increases, and the penetration resistance from the ground at the time of construction increases, so the workability decreases. There is a problem.

  The inventions described in Patent Literature 2 and Patent Literature 3 are for filling concrete into a portion where the bending moment generated in the steel pipe pile is large. However, when the steel pipe concrete structure is bent, the steel pipe and concrete need to behave as one unit in order to exert the composite effect of the composite member. There is a problem that the load transmission for doing so is not guaranteed.

  Even when a large axial force and bending moment are applied to a steel pipe pile, the present invention does not require an increase in the steel pipe diameter of the upper pile part, and does not require a thick plate, and can be accommodated in the manufacturing range of the spiral steel pipe. The present invention provides a steel pipe pile structure that is rational and structurally stable, and a construction method that improves the construction efficiency of the steel pipe pile structure.

  The invention according to claim 1 of the present application is a steel pipe pile structure in which a part of the length of the steel pipe pile is filled with concrete, and the section filled with the concrete is transferred from the pile head to the steel pipe pile. The bending moment generated by the acting horizontal force is made sufficiently small compared to the bending moment generated at the pile head, and the concrete is shared by the inner surface of the steel pipe constituting the steel pipe pile near the lower end position of the section filled with the concrete. A projection for transmitting the axial force to the steel pipe is provided.

  That is, when a steel pipe pile receives a horizontal force due to an earthquake or the like, a bending moment is generated in the pile body, but the present invention is a portion where the generated bending moment converges from the pile head to a hollow portion of the steel pipe pile. Concrete is filled up to this point, and the axial force shared by the concrete is transmitted to the steel pipe by a protrusion around the lower end of the concrete filling range.

  Since the bending moment generated in the steel pipe pile is larger on the pile head side (upper pile) than on the pile tip side (lower pile), the plate thickness of the upper pile is often the largest. Therefore, by filling the concrete from the pile head to a portion where the bending moment is small and converges, a composite effect of the steel pipe and the concrete can be obtained, and rationalization such as suppressing an increase in the thickness of the steel pipe can be achieved.

  The concrete in the present invention means concrete in a broad concept including mortar, cement milk and the like, and is not particularly limited as long as the steel pipe pile can be reinforced by filling and hardening the hollow part of the steel pipe pile. . Moreover, the reinforced concrete reinforced with the reinforcement etc. is also included.

  However, in order to obtain the above composite effect, it is premised that both the steel pipe and the concrete behave as one body. Therefore, in the concrete filling section, substantially all of the axial force borne by the concrete is transferred to the steel pipe. It is necessary to communicate. Therefore, in the present invention, a protrusion as a load transmitting element is provided around the lower end of the concrete filling section. In addition, the shape, shape, material, etc. of the protrusions are not particularly limited, such as those integrally formed on the steel pipe, stud gibber, and other shear connectors.

  In the present invention, the position of the protrusion is set near the lower end position of the concrete filling section. The pile section changes suddenly at the lower end position of the concrete filling section. By placing this sudden change position in the part where the bending moment is small and converging, the effect of the change in the cross section is suppressed and transition is made by providing a protrusion in this part. As a zone, the load can be transmitted smoothly from concrete to steel pipe.

  Moreover, when it is going to provide a protrusion discretely over the concrete filling section full length, it will become difficult to install a protrusion so that it may go into the back from a steel pipe end part, and manufacturing efficiency will fall, but it provides a protrusion in the limited part in the present invention. Thus, the manufacturing efficiency can be improved.

  According to a second aspect of the present invention, in the steel pipe pile structure according to the first aspect, the thickness of the steel pipe in the section filled with the concrete is equal to or greater than the thickness of the steel pipe immediately below the section.

  Since the axial force borne by the concrete is transmitted from the protrusions around the lower end position of the concrete filling range to the steel pipe, the steel pipe at the lowest end of the range shares all the axial force. Accordingly, the thickness of the section is preferably equal to or greater than the thickness immediately below the section.

  Claim 3 is the steel pipe pile structure according to claim 1 or 2, wherein the concrete filling section is set to be not less than 3 times and not more than 5 times the outer diameter D of the steel pipe constituting the steel pipe pile from the pile head. Is.

  Generally, the joint between the pile head and the footing is rigid, but in this case, the bending moment generated in the steel pipe pile is the largest at the pile head and converges as the depth increases. If the concrete filling section is made too short, the cross section will be changed suddenly at the depth where a large bending moment is generated, resulting in lack of structural stability. Factors affecting the bending moment distribution include the ground, steel pipe diameter, and plate thickness.

  Conventionally, it has been customary that the bending moment converges at a depth of about 5D from the pile head, but from the examination results of the inventors, the bending moment almost converges in the depth range of 3-5D from the pile head to the ground. I understood that.

FIG. 1 shows an example of the result. The figure shows the ratio between the generated moment Mo at the pile head and the generated moment M at each depth when the steel pipe diameter is 1000 mm, the plate thickness is 25 mm, and the horizontal ground reaction force coefficient kh = 4430 kN / m ² , 8850 kN / m ² , 17710 kN / m ^2. The depth distribution (non-dimensionalized notation with pile diameter D) is shown.

The generated moment was calculated as an elastic bearing beam when steel pipe piles have a constant ground reaction force coefficient. The ground reaction force coefficient is a value corresponding to N = 2.5, 5, 10 when assuming that the ground deformation coefficient Eo = 700 N (kN / m ² ) [N is an N value].

  From the figure, it can be seen that the bending moment converges in the range of 3 to 5D from the pile head, and the same tendency was observed under other conditions. This is thought to be because the bending moment converges at a shallow depth because steel pipe piles have lower bending stiffness at the same strength than cast-in-place piles and precast concrete piles. Therefore, if the concrete is filled in the range of 3 to 5D from the pile head, the structural stability can be ensured.

  A fourth aspect of the present invention is the steel pipe pile structure according to the first, second or third aspect, wherein a lid for damming the concrete is provided at the lowest end position of the section filled with the concrete.

  If the concrete filling section is lengthened, the necessary concrete volume increases and the workability deteriorates, which is uneconomical. The function of the present invention can be obtained by filling concrete with only a necessary part, and this lid does not need to have a structural function, so it is only required to withstand the dead weight of the concrete to be placed.

  In the case of digging piles that are constructed by inserting a rod in the steel pipe, the lid is dropped after the steel pipe pile is buried. It can also be installed in place before construction.

  The invention according to claim 5 is the construction method of the steel pipe pile structure according to claim 1, 2, 3 or 4, and when the steel pipe constituting the steel pipe pile is built in the ground, the projection of the projection is previously provided in the steel pipe. A protective device for preventing contact between the peripheral portion and the earth and sand is attached and built, and after removing the earth and sand in the steel pipe, the protective device is removed and concrete is filled. .

  When a pile with a tip wing (rotating pile) has an opening at the tip of the pile, or when a steel pipe is submerged by excavating the ground by inserting a rod into the steel pipe like an inside digging pile, the concrete in the steel pipe during construction It is assumed that earth and sand and muddy water will enter the section filled with.

  If there are deposits on the projections on the inner surface of the steel pipe, there is a concern that it may interfere with the load transmission from the concrete to the steel pipe. Therefore, deposits on the periphery of the projections after removing earth and sand and before placing concrete It must be cleaned so that there is no.

  According to the invention which concerns on Claim 5, the cleaning work process of a protrusion peripheral part becomes unnecessary or can be simplified.

  According to the steel pipe pile structure of the present invention, by filling the concrete from the pile head to the part where the bending moment is small and converged, the composite effect of the steel pipe and concrete can be obtained, and the increase in the plate thickness of the steel pipe can be suppressed. Rationalization is possible.

  Further, in the present invention, by placing the protrusion at the lower end position of the concrete filling section where the section of the pile suddenly changes in the portion where the bending moment converges with a small bending moment, by providing the protrusion at this portion, the transition is made. As a zone, the load can be transmitted smoothly from concrete to steel pipe.

  According to the construction method of the steel pipe pile structure of the present invention, when it is assumed that earth and sand or muddy water enters the section filled with concrete in the steel pipe at the time of construction, is the cleaning work step around the protrusion unnecessary? Or it can be simplified.

  FIG. 2 shows the depth direction distribution of the bending moment M generated in the steel pipe pile and the embodiment of the present invention (only the upper part). When a horizontal force Q acts on a steel pipe pile due to an earthquake or the like, a large bending moment acts near the pile head as shown in Fig. 2 (a), and it converges as it deepens.

  FIGS. 2 (b), (c), and (d) show the embodiments of the present invention, respectively. In these examples, concrete 2 is filled from the pile head to a depth L = 5D. . The bending moment is converged in the range of 3 to 5D. However, when the protrusion 3 is installed on the inner surface of the steel pipe 1, the production efficiency decreases as the steel pipe 1 enters the back from the lower end of the steel pipe 1 at the time of production (in-situ circumferential welding position). Therefore, the concrete filling length is set to 5D in order to provide the protrusion 3 at a position close to the position of the on-site circumferential weld 4 where the steel pipes 1 are welded together.

  Here, the position of the protrusion 3 is determined from the position of the circumferential welding 4 on the site, but it is also conceivable to determine the position from the factory circumferential welding position.

The number of protrusions 3 may be set as many as the axial force shared by the concrete 2 can be transmitted to the steel pipe 1, for example,
P: axial force,
Ps: axial force generated in the steel pipe in the concrete filling section,
Pc: axial force generated in concrete,
Pb: Transmittable load by protrusion,
As: sectional area of steel pipe,
Ac: Cross section of concrete,
Es: elastic coefficient of steel pipe,
Ec: elastic modulus of concrete,
εs: Steel pipe generated strain,
εc: Generated strain of concrete,
n: number of protrusions,
Ab: projected area per protrusion
σc: compressive strength of concrete,
α: coefficient,
And can be set as follows.

The schematic diagram of the load transmission mechanism to a pile body is shown in FIG. As shown in the figure, the axial force P generated in the steel pipe pile from the upper structure or the like is shared by Ps and Pc, and the value is expressed by the following equation.
P = Ps + Pc = Es · εs · As + Ec · εc · Ac (1)

Since the steel pipe 1 and concrete 2 are integrated by the footing 5 on the upper part and the protrusion 3 on the inner surface of the steel pipe, both parts are equistrained (εs = εc). Indicated.
Pc = P × Ec · Ac / (Es · As + Ec · Ac) (2)

On the other hand, the load Pb that can be transmitted from the concrete 2 to the steel pipe 1 by the protrusion 3 can be expressed by the following equation. In applying the following equation, it is necessary to set the ratio of the projection height h to the pitch P to P / h ≧ 10 to 15 or more from past tests and the like.
Pb = α · n · Ab · σc (3)

  The coefficient α here is a coefficient that takes into account that the bearing area (n × Ab) is expanded by constraining the concrete 2 by the steel pipe 1 and can be obtained by a structural test or the like.

Therefore, in order to transmit all Pc to the steel pipe 1 by the protrusions 3 on the inner surface of the steel pipe 1, it is sufficient to install a number n satisfying the following expression from the expressions (2) and (3).
From Pb ≧ Pc n ≧ P × Ec · Ac / [(Es · As + Ec · Ac) · α · Ab · σc] (4)

  In the example of FIG. 2, the thickness of the steel pipe 1 in the section filled with the concrete 2 is the same as the thickness immediately below it. As shown in FIG. 3, since Pc is transmitted to the steel pipe 1 by the protrusion 3, P (= Ps + Pc) acts on the steel pipe 1 in the A-A 'cross section at the lower end filled with the concrete 2.

  Therefore, the plate thickness immediately above the A-A ′ cross section needs to be equal to or greater than the plate thickness immediately below the cross section.

  FIG. 2 (b) shows a case where a lid 6 is installed at a predetermined position for damming the concrete 2 after the steel pipe 1 pile is buried. A lid stopper 7 is attached to the lower side (tip side) of the concrete 2 filling section before construction, and the lid 6 is dropped into the steel pipe 1 after construction.

  In the case of a pile that is constructed by inserting a rod in the steel pipe 1 like an inside digging pile, the lid 6 is dropped afterwards so as not to obstruct the construction. Can also be attached.

  In addition, as shown in FIG. 2 (c), when the earth and sand 8 is put into the steel pipe 1 by construction, or the residual soil from the root cutting etc. is discarded in the steel pipe 1, the inside of the steel pipe 1 can be closed to a predetermined position. The lid does not have to be dropped.

  FIG. 2 (d) shows the concrete 2 filling portion of FIG. 2 (b) made of reinforced concrete. Depending on the required yield strength, the reinforcing bars 9 may be inserted into the concrete 2 filling portion.

  FIG. 4 shows a method for manufacturing the built-up protrusion. In order to install protrusions on the inner surface of the steel pipe, it is conceivable to use a steel pipe with an inner rib at the corresponding part, or to weld flat steel or round steel. In the former, the height of the protrusion is low, so it is not very reasonable because the axial force shared by the concrete needs to be applied to a long range to transmit it to the steel pipe, and the cost is high compared to the flat steel pipe. Absent.

  Moreover, in order to install protrusions with flat steel or round steel, a process of bending a steel material first, temporarily attaching it to a steel pipe, and then attaching it by welding is required. In comparison, the build-up protrusion shown in the figure can be completed in one step, which is reasonable.

  By projecting the boom 12 from the welding apparatus 11, attaching a welding torch 13 to the tip of the boom 12, fixing the welding torch 13, and rotating the steel pipe 1, an annular built-up projection can be manufactured.

  At that time, as shown in FIG. 5, if a pair of contact plates 15 are arranged with the welding torch 13 interposed therebetween and manufactured while forming the build-up protrusion, the protrusion is formed high and the load per protrusion Transmission performance is improved and the number of protrusions can be reduced.

  However, if the protrusions are too high, concrete filling to the lower side (tip side) of the protrusions may be incomplete, so a height of about 5 to 15 mm is recommended.

  FIG. 6 shows the case of a pile with a tip wing (rotating pile) as an example of the construction procedure of the steel pipe pile structure of the present invention. FIG. 6 (a) shows the construction status of the lower pile 1a, and it penetrates into the ground with the propulsive force of the tip wing 21 generated by rotating the steel pipe pile. Although not shown here, the rotational force to the steel pipe pile is applied using an all-round rotating machine or a three-point pile driving machine.

  FIG. 6 (b) shows the situation where construction has been completed up to the upper pile 1b (the middle part is omitted). In the middle of the upper pile, a load transmitting projection 3 and a lid stopper 7 having a larger protruding width are provided.

  In consideration of the distribution of the bending moment, the circumferential weld 4 position of the steel pipe 1, especially the weld build-up projection, the filling range of the concrete 2 takes into account the manufacturable position where the boom with the welded torch 4 position and the weld torch arrives. It is reasonable to keep it as short as possible.

  FIG. 6 (c) shows a situation in which the lid 6 for damming the concrete 2 is installed and the concrete 2 is placed. The concrete 2 is filled into the steel pipe 1 from the pump car via the tremy pipe. FIG. 6D is a completed drawing.

  FIG. 7 shows the case of an underground digging pile as another example of the construction procedure of the steel pipe pile structure of the present invention. FIG. 7 (a) shows the construction status of the lower pile 1a. The rod 31 is inserted into the steel pipe and the ground is excavated to sink the steel pipe. The rod 31 may be rotated by a three-point pile driver and may or may not be rotated depending on the ground conditions.

  FIG. 7 (b) shows a state where the construction has been completed up to the upper pile 1b, and a root bulb 32 is built by a soil cement solidified body at the tip of the pile. It is also assumed that earth and sand or mud is contained in the section filled with concrete in the steel pipe 1 by construction.

  In that case, as shown in FIG. 7 (c), it is necessary to remove earth and sand or water with an underwater pump or a clamshell (not shown) and to clean the periphery of the protrusion with high-pressure water or a brush 33. This is because there is a concern that the load transmission from the concrete 2 to the steel pipe 1 may be incomplete if the periphery of the protrusion is soiled with earth and sand. Subsequent operations are the same as those shown in FIGS. 6C and 6D.

  FIG. 8 shows an embodiment of the construction method according to claim 5. In FIG. 7 (c), when the steel pipe is sunk, when the earth and sand or muddy water enters the steel pipe, the periphery of the protrusion 3 is cleaned. However, the cleaning work of the periphery of the protrusion 3 is not performed. In order to make it easy or simple, a protector 41 as shown in FIG. 8 (a) is applied in advance to the periphery of the protrusion 3 before the steel pipe 1 is set, and is removed after the earth and sand 8 are removed.

  As the protector 41 in FIG. 8 (a), a thin steel plate or a water-impervious sheet can be used, and is attached to the inner surface of the steel pipe 1 so as to cover the projection 3 part. After removing the earth and sand 8 and before placing concrete, the protector 41 collects the connected wire 42 by lifting it with a crane or the like.

  FIG. 8 (b) shows another example of the protective device 43, but the function is the same as FIG. 8 (a). As shown in the figure, a casing having a diameter smaller than that of the steel pipe pile as the protector 43 is placed in the steel pipe 1 in advance, and collected after removing the earth and sand 8.

  In piles where earth and sand and water enter the steel pipe, the efficiency of the construction can be improved by the method shown in FIG.

It is the graph which showed the depth distribution of the ratio of the pile head generation | occurrence | production moment Mo and the generation | occurrence | production moment M in each depth (Pile diameter D represents non-dimensionalization). (a) is the figure of the depth direction distribution of the bending moment M which arises in a steel pipe pile, (b), (c), (d) showed each embodiment of the present invention corresponding to the figure of (a), respectively. It is a vertical sectional view. It is a schematic diagram which shows the load transmission mechanism to the pile body in this invention. It is sectional drawing which showed roughly the manufacturing method of the processus | protrusion by welding overlay. FIG. 5 is a perspective view schematically showing a method for forming a build-up protrusion high in the protrusion manufacturing method of FIG. 4. It is the vertical sectional view showing the case of the pile with a tip wing (rotary pile) as an example of the construction procedure of the steel pipe pile structure of the present invention. It is the vertical sectional view which showed the case of the digging pile as another example of the construction procedure of the steel pipe pile structure of this invention. (a), (b) is a vertical sectional view showing an embodiment of the construction method according to claim 5, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Steel pipe, 2 ... Concrete, 3 ... Protrusion, 4 ... Welding, 5 ... Footing, 6 ... Lid, 7 ... Lid fitting, 8 ... Earth and sand, 9 ... Rebar,
DESCRIPTION OF SYMBOLS 11 ... Welding apparatus, 12 ... Boom, 13 ... Welding torch, 14 ... Welding wire, 15 ... Contact plate,
21 ... tip wing, 31 ... rod, 32 ... consolidating bulb, 33 ... brush, 34 ... tremy tube,
41 ... Protective equipment, 42 ... Wire, 43 ... Protective equipment.

Claims (5)

  A steel pipe pile structure in which a part of the length of a steel pipe pile is filled with concrete, and a bending moment generated by a horizontal force acting on the steel pipe pile from the pile head is generated in the section filled with the concrete. In order to transmit the axial force shared by the concrete to the inner surface of the steel pipe constituting the steel pipe pile in the vicinity of the lower end position of the section where the concrete is filled, to a part sufficiently smaller than the bending moment generated in the part A steel pipe pile structure characterized by being provided with protrusions.   The steel pipe pile structure according to claim 1, wherein a thickness of the steel pipe in the section filled with the concrete is equal to or greater than a thickness of the steel pipe immediately below the section.   The steel pipe pile structure according to claim 1 or 2, wherein the concrete-filled section is set to be not less than 3 times and not more than 5 times the outer diameter D of the steel pipe constituting the steel pipe pile from the pile head.   The concrete-filled steel pipe pile structure according to claim 1, 2, or 3, wherein a lid for damming the concrete is provided at a lowermost position of a section in which the concrete is filled.   When the steel pipe constituting the steel pipe pile is built in the ground, the steel pipe is installed with a protective device for preventing contact between the peripheral portion of the protrusion and the earth and sand, and the earth and sand in the steel pipe is removed. 5. The method for constructing a steel pipe pile structure according to claim 1, wherein the protective equipment is removed and the concrete is filled.

Images