JP2015221965A - Steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe having a recess specification of not reducing compressive performance in the pipe axis direction, by also avoiding reduction in sticking performance between sediment and concrete in the ground.SOLUTION: The present invention relates to a steel pipe 1 for forming a recess part 2 on a steel pipe outer peripheral surface 1a. The steel pipe 1 of applying the present invention comprises a straight pipe part 3 formed in a substantially straight pipe shape by extending in the pipe axis direction Y and the recess part 2 formed in a recess shape toward the inside in the pipe axis orthogonal direction X. The recess part 2 has substantially the same plate thickness as the straight pipe part 3, and the recess depth (a) formed in a more recessed shape than an outer peripheral surface 3a of the straight pipe part 3, satisfies the predetermined relationship in the relationship between a steel pipe outer diameter D and a steel pipe plate thickness (t).

Description

  The present invention relates to a steel pipe in which a hollow portion is formed on the outer peripheral surface of the steel pipe. For example, the steel pipe is embedded in the ground and provided as a foundation pile or ground reinforcement.

  Conventionally, as a steel pipe pile with a dent having a recess in the circumferential direction of the steel pipe, or a steel pipe pile with a dent formed so that a plurality of dent parts form a row along the steel pipe axial direction on the outer peripheral surface, Patent Documents 1 and 2 The steel pipe pile disclosed in is proposed.

  The steel pipe pile disclosed in Patent Document 1 has a steel pipe wall thickness of 2 mm or more, a steel pipe outer diameter (D) of 50 mm or more, a recess depth of 0.005D to 0.2D, and a recess width of 0.015D to 2D. Sometimes, the relationship between the width (B) of the recess and the depth (H) of the recess is B / H = 3 to 20, and the ratio between the width of the recess and the depth of the recess is defined.

  The steel pipe pile disclosed in Patent Document 2 is formed such that a columnar recess along the steel pipe axis direction is formed inside each of the hollow parts and deeper than the bottom surface of the hollow part, and along the steel pipe axis. In any position, the total ratio of the lengths of the respective recessed portions in the circumferential length of the steel pipe in the circumferential direction of the steel pipe is set to 50% or less.

JP 2008-175055 A Japanese Patent No. 5085809

  In the steel pipe piles disclosed in Patent Documents 1 and 2, a hollow steel pipe pile is embedded in the ground or concrete, and the earth and sand, concrete, etc. in the ground and the hollow steel pipe pile are integrated. At this time, the steel pipe pile disclosed in Patent Documents 1 and 2 resists earth and sand, concrete, etc. in the ground at the concave portion and the hollow portion of the steel pipe pile, and gives a predetermined adhesion strength to the hollow steel pipe pile. It is necessary to maintain sufficient adhesion performance in the ground or in concrete.

  For this reason, the steel pipe pile disclosed by patent document 1 aims at improving the adhesion performance of the recessed part of a steel pipe pile, concrete, etc. by making the ratio of the width | variety of a recessed part and the depth of a recessed part into a predetermined thing. It has become. However, although the steel pipe pile disclosed by patent document 1 has a possibility that the rigidity of the steel pipe pile axial direction may fall by forming a recessed part in the outer peripheral surface of a steel pipe pile, the steel pipe of a steel pipe pile The compression performance for resisting the compressive load acting in the axial direction is not taken into consideration.

  On the other hand, the steel pipe pile disclosed by patent document 2 is set to 50% or less because the ratio of the sum total of the length of the steel pipe circumferential direction of each hollow part which occupies for the steel pipe whole circumference length is set to several or less. It can avoid that the compression performance of a steel pipe pile falls by forming a hollow part. However, in the steel pipe pile disclosed in Patent Document 2, an upper limit of 50% is set to the total ratio of the length of each hollow portion in the circumferential direction of the steel pipe to the total circumference of the steel pipe. The range in which the part is formed is very limited, and the adhesion performance with concrete or the like may be naturally reduced.

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to avoid a decrease in adhesion performance with earth and sand or concrete in the ground, and at the same time, in the direction of the pipe axis. An object of the present invention is to provide a steel pipe having a hollow specification that does not deteriorate the compression performance.

  The steel pipe which concerns on 1st invention is a steel pipe by which the hollow part was formed in the steel pipe outer peripheral surface, Comprising: The straight pipe part extended in the pipe-axis direction and formed in the substantially straight tube shape, and toward the inner side of a pipe-axis orthogonal direction A recess formed in a concave shape, the recess having substantially the same plate thickness as the straight tube portion, and a recess depth formed in a recess shape than the straight tube outer peripheral surface of the straight tube portion. The relationship between the outer diameter of the steel pipe and the thickness of the steel pipe satisfies the relationship defined by the following formula (1).

ここで、ａ_max：前記窪み部の窪み深さの最大値、Ｄ：鋼管外径、ｔ：鋼管板厚とする。

Here, a _{max is} the maximum value of the depth of the recess, D is the outer diameter of the steel pipe, and t is the thickness of the steel pipe.

  The steel pipe according to a second aspect of the present invention is characterized in that, in the first aspect, the hollow portion is formed to extend in the pipe circumferential direction with only a part of the entire circumferential length of the steel pipe in the pipe circumferential direction.

  A steel pipe according to a third aspect of the present invention is the first or second aspect of the present invention, wherein the indented portion is one or more in the pipe circumferential direction so that the ratio of the hollow portion to the total circumferential length of the steel pipe is 50% or more. A plurality are formed.

  A steel pipe according to a fourth invention is characterized in that, in any one of the first to third inventions, a plurality of the recessed portions are intermittently formed at a predetermined interval in the pipe axis direction.

  The steel pipe according to a fifth aspect of the present invention is the steel pipe according to any one of the first to fourth aspects, wherein the concave portion has a concave height formed more convex than the straight pipe inner peripheral surface of the straight pipe portion. And the relationship defined by the following equation (2) in relation to the steel pipe plate thickness.

ここで、ｂ_max：前記窪み部の窪み高さの最大値、Ｄ：鋼管外径、ｔ：鋼管板厚とする。

Here, b _{max is} the maximum value of the dent height of the dent part, D is the outer diameter of the steel pipe, and t is the steel pipe plate thickness.

  According to 1st invention-5th invention, when the hollow depth a of a hollow part satisfies the relationship prescribed | regulated by the said (1) type | formula, without reducing the compression yield strength of a steel pipe, it is solid on the outer side of a steel pipe. Predetermined adhesion performance can be ensured between the binder and the like. Moreover, according to 1st invention-5th invention, when the hollow height b of a hollow part satisfies the relationship prescribed | regulated by the said (2) Formula, without reducing the compression yield strength of a steel pipe, it is a steel pipe inner side. It is possible to ensure a predetermined adhesion performance between the solidifying material and the fixing material.

  In particular, according to the third invention, by setting the dent ratio λ to be 50% or more, the dent extension of the dent portion extending in the tube circumferential direction can be made sufficiently long, so that the consolidation material or the fixing material can be obtained. It is possible to improve the adhesion performance with the like.

  Thereby, according to 1st invention-5th invention, at the same time avoiding the fall of adhesion performance with the earth and sand in a ground, a time-hardening material, etc., without reducing the compressive yield strength of a steel pipe, it is compression in the direction of a pipe axis. It is possible to provide a steel pipe having a hollow specification that does not deteriorate the performance.

It is a perspective view which shows the steel pipe to which this invention is applied. (A) is a top view which shows the steel pipe to which this invention is applied, (b) is the front view. (A) is a partially broken enlarged front view showing a hollow normal steel pipe, and (b) is a partially broken enlarged front view showing a steel pipe to which the present invention is applied. (A) is an enlarged front view which shows the steel pipe to which this invention is applied, (b) is the FF line longitudinal cross-sectional view. (A) is the GG line cross-sectional view of the steel pipe to which this invention shown in FIG. 4 is applied, (b) is the HH line cross-sectional view. (A) is a cross-sectional view which shows the state in which the hollow part was formed in three places in the steel pipe to which this invention is applied, (b) is the cross section which shows the state in which the hollow part was formed in one place. FIG. (A) is an enlarged front view which shows the state by which the vertically long hollow part was formed in the steel pipe to which this invention is applied, (b) is the GG line cross-sectional view. (A) is a cross-sectional view which shows the hollow depth of the hollow part of the steel pipe to which this invention is applied, (b) is a cross-sectional view which shows the hollow height of the hollow part. (A) is an expanded longitudinal cross-sectional view which shows the hollow part of the steel pipe to which this invention is applied, (b) is a model figure based on the collapse mode collapsed in the bellows shape. It is a graph which shows the ratio of the compression yield of the calculation result of the steel pipe to which this invention is applied, and the compression yield of an experimental result. (A) is a longitudinal cross-sectional view which shows the state by which the consolidated material was provided in the steel pipe outer side of the steel pipe to which this invention was applied, (b) shows the state by which the consolidated material was provided inside the steel pipe. It is a longitudinal cross-sectional view.

  Hereinafter, the form for implementing the steel pipe 1 to which this invention is applied is demonstrated in detail, referring drawings.

  The steel pipe 1 to which the present invention is applied is used for a foundation method for soft ground, a ground improvement method, or a reinforcement method for slopes and tunnels. The steel pipe 1 to which the present invention is applied is applied to a medium and small diameter steel pipe having a steel pipe outer diameter D of about 20 mm to 350 mm, for example.

  The steel pipe 1 to which the present invention is applied is, for example, provided as a foundation pile or the like embedded in the ground, and as shown in FIG. 1, a drilling hole 70 formed by excavating the ground 7 in a predetermined range. Embedded in the ground improvement range, a consolidation material 6 such as a time-curable material, a fixing material or the like is provided in the excavation hole 70 of the ground 7 by a filling operation or the like.

  The consolidation material 6 is made of, for example, a time-curable material such as a cement-based material such as mortar or concrete, or a time-curable material such as a urethane-based material, so that the outer peripheral surface 1a of the steel pipe 1 and the ground 7 are excavated. By filling the steel pipe outer side O in which a gap is formed between the hole 70 and the steel pipe inner side I formed by being surrounded by the steel pipe inner peripheral surface 1b of the steel pipe 1 with these time-curable materials and curing them. Provided.

  As shown in FIG. 2, the steel pipe 1 to which the present invention is applied has one or a plurality of hollow portions 2 formed on the outer peripheral surface 1a of the steel pipe. In the steel pipe 1 to which the present invention is applied, the outer peripheral surface 1a of the steel pipe is formed in a substantially circular shape and has a predetermined steel pipe outer diameter D in the pipe axis orthogonal direction X. Moreover, the steel pipe 1 to which the present invention is applied has a predetermined steel pipe plate thickness t in the pipe axis orthogonal direction X between the steel pipe outer peripheral surface 1a and the steel pipe inner peripheral surface 1b.

  As shown in FIG. 3A, the steel pipe 1 to which the present invention is applied is a substantially straight tubular normal steel pipe 5 extending in the pipe axis direction Y in which the steel pipe outer peripheral surface 1a is continuously formed on substantially the same surface. It is manufactured by hot working at a predetermined temperature or higher. The steel pipe 1 to which the present invention is applied is a depression in which a plurality of depressions 2 are formed on the outer peripheral surface 1a of the steel pipe, as shown in FIG. Manufactured as a steel pipe. In addition, the steel pipe 1 to which the present invention is applied may be one in which a hollow steel pipe is manufactured by hot rolling while forming the hollow portion 2 on the outer peripheral surface 1a of the steel pipe. Moreover, if the steel pipe 1 to which this invention is applied is not what cuts normally with respect to the steel pipe 5, the hollow part 2 may be formed by cold forming, for example.

  As shown in FIGS. 4 and 5, the steel pipe 1 to which the present invention is applied is directed to a straight pipe portion 3 extending in the pipe axis direction Y and formed in a substantially straight pipe shape, and a steel pipe inner side I in the pipe axis orthogonal direction X. And a recess 2 formed in a concave shape by hot working.

  As shown in FIG. 4A, the straight pipe portion 3 is formed with a straight pipe outer diameter D1 substantially the same as the steel pipe outer diameter D of the steel pipe 1, and makes the steel pipe outer peripheral surface 1a uneven in the pipe axis orthogonal direction X. Instead, the straight pipe outer peripheral surface 3a continues on substantially the same plane in the tube axis direction Y, so that a substantially straight tube extending in the tube axis direction Y is formed. Moreover, the straight pipe part 3 is formed by the straight pipe plate thickness t1 substantially the same as the steel pipe plate thickness t of the steel pipe 1, as shown in FIG.4 (b).

  A plurality of hollow portions 2 are formed at a plurality of locations in the tube axis direction Y with a predetermined interval in the tube axis direction Y by forming the steel pipe outer peripheral surface 1a in a concave shape. The plurality of depressions 2 formed in the tube axis direction Y are alternately formed with the straight tube part 3 in the tube axis direction Y, and the plurality of depressions 2 are not continuously formed in the tube axis direction Y. Are formed intermittently at predetermined intervals in the tube axis direction Y.

  The hollow portion 2 is formed by bending the outer peripheral surface 1a of the steel pipe in a concave shape toward the steel pipe inner side I in the pipe axis orthogonal direction X. In addition, the hollow part 2 is not restricted to what is formed by curving the steel pipe outer peripheral surface 1a, You may form by bending the steel pipe outer peripheral surface 1a. The hollow portion 2 is formed with a hollow plate thickness t2 that is substantially the same as the steel pipe plate thickness t of the steel pipe 1, and thus has a hollow plate thickness t2 that is substantially the same as the straight pipe plate thickness t1 of the straight pipe portion 3. .

  Here, since the hollow part 2 is formed by pressing the outer peripheral surface 1a of the steel pipe 1 or the like, although the hollow pipe thickness t2 is expected to slightly increase or decrease compared to the steel pipe plate thickness t of the steel pipe 1, Even when the hollow plate thickness t2 is slightly increased or decreased, the hollow plate thickness t2 is formed so as to have substantially the same thickness as the straight tube plate thickness t1 of the straight pipe portion 3.

  The hollow portion 2 is formed so that the outer peripheral surface 1a of the steel pipe is concave toward the inner side I of the pipe in the direction orthogonal to the pipe axis X, so that the outer peripheral surface 2a is lower than the straight pipe outer peripheral surface 3a of the straight pipe portion 3. And is formed in a concave shape in the tube axis orthogonal direction X with respect to the straight pipe outer peripheral surface 3a of the straight pipe portion 3 so as to have a predetermined depth a.

  At this time, the hollow portion 2 has a hollow plate thickness t2 that is substantially the same as the straight pipe plate thickness t1 of the straight pipe portion 3, and the steel pipe outer peripheral surface 1a is formed in a concave shape toward the steel pipe inner side I in the pipe axis orthogonal direction X. By doing so, the steel pipe inner peripheral surface 1b is formed in a convex shape toward the steel pipe inner side I in the pipe axis orthogonal direction X.

  The hollow portion 2 is formed so that the inner peripheral surface 1b of the steel pipe is convex toward the inner side I of the steel pipe in the tube axis orthogonal direction X, so that the hollow inner peripheral surface 2b is more than the straight pipe inner peripheral surface 3b of the straight pipe portion 3. It is arranged on the steel pipe inner side I, and is formed so as to have a predetermined recess height b in a convex shape in the tube axis orthogonal direction X with respect to the straight pipe inner peripheral surface 3 b of the straight pipe portion 3.

  As shown in FIG. 5, the hollow portion 2 is formed to extend in a substantially arc shape in the pipe circumferential direction W so as to be a predetermined hollow extension En in the pipe circumferential direction W of the steel pipe 1. The hollow portion 2 is only part of the circumferential length E of the steel pipe 1 in the circumferential direction W of the steel pipe 1 and is formed intermittently in the circumferential direction W without being continuous in the circumferential direction W of the steel pipe 1. At this time, the hollow part 2 is formed by only a part of the entire circumferential length E of the steel pipe in the pipe circumferential direction W of the steel pipe 1, so that the steel pipe 1 is interposed between both ends 20 of the hollow part 2 in the pipe circumferential direction W. The rib part 4 in which the hollow part 2 is not formed in the steel pipe outer peripheral surface 1a is formed.

  The rib part 4 is formed in the location where the press by the hot working is not made in the pipe circumferential direction W of the steel pipe 1. At this time, the rib portion 4 is formed with the rib plate thickness t3 substantially the same as the steel tube thickness t3 of the steel pipe 1 without causing the outer peripheral surface 1a of the steel tube to be uneven in the tube axis orthogonal direction X. Thus, the rib outer peripheral surface 4a and the rib inner peripheral surface 4b are formed continuously on substantially the same plane as the straight pipe outer peripheral surface 3a and the straight pipe inner peripheral surface 3b of the straight pipe portion 3.

  As shown in FIGS. 5 and 6, one or a plurality of the recessed portions 2 are formed in the pipe circumferential direction W of the steel pipe 1. As shown in FIG. 5A, the recess 2 is formed at two locations in the tube circumferential direction W by forming the first recess 21 and the second recess 22 at two locations in the tube circumferential direction W. Ribs 4 are formed. The first recess 21 becomes a predetermined recess extension E1 in the pipe circumferential direction W of the steel pipe 1, and the second recess 22 becomes a predetermined recess extension E2 in the pipe circumferential direction W of the steel pipe 1.

  As shown in FIG. 6A, the hollow portion 2 is formed by forming the first hollow portion 21, the second hollow portion 22, and the third hollow portion 23 at three locations in the pipe circumferential direction W. Ribs 4 are formed at three locations W. The first dent portion 21 becomes a predetermined dent extension E1 in the pipe circumferential direction W of the steel pipe 1, the second dent portion 22 becomes a predetermined dent extension E2 in the pipe circumferential direction W of the steel pipe 1, and the third The recess 23 becomes a predetermined recess extension E3 in the pipe circumferential direction W of the steel pipe 1. Further, as shown in FIG. 6B, the hollow portion 2 is formed at only one place in the pipe circumferential direction W, and a first hollow portion 21 that becomes a predetermined hollow extension E1 in the pipe circumferential direction W of the steel pipe 1 is formed. Thus, the rib portion 4 is formed at one place in the pipe circumferential direction W.

  The depressions 2 may be formed at four or more locations in the pipe circumferential direction W. For example, as shown in FIG. 7, each depression 2 has a substantially elliptical shape or the like extending in the pipe axis direction Y. It is also possible to form a vertically long portion along the tube axis direction Y of the steel pipe 1 at about 3 to 9 in the tube circumferential direction W. As shown in FIGS. 5 to 7, the hollow portion 2 is formed with a predetermined number n in the pipe circumferential direction W of the steel pipe 1, so that the total ΣEn of the hollow extensions En of the respective hollow portions 2 is set. It will be a thing.

  The hollow portion 2 is formed by only part of the circumferential length E of the steel pipe 1 in the circumferential direction W of the steel pipe 1, and the hollow of each hollow portion 2 with respect to the circumferential length E of the steel pipe in the circumferential direction W of the steel pipe 1. If the ratio occupied by the total ΣEn of the extension En is defined as the depression ratio λ, the depression ratio λ is set to be within a predetermined range. At this time, the dent part 2 is the whole or a part of the plurality of portions 10 where the dent part 2 is formed in the tube axis direction Y of the steel pipe 1, and each dent part 2 with respect to the entire circumferential length E of the steel pipe in the pipe circumferential direction W. As the ratio of the total ΣEn of the recess extension En, the recess ratio λ is set to be 50% or more and 95% or less.

  As shown in FIG. 8 (a), the recess 2 has a recess depth a formed in a concave shape with respect to the straight pipe outer peripheral surface 3a of the straight pipe 3, and the relationship between the steel pipe outer diameter D and the steel pipe thickness t. Therefore, the relationship defined by the following equation (1) is satisfied.

ここで、ａ_max：窪み部２の窪み深さａの最大値、Ｄ：鋼管外径、ｔ：鋼管板厚とする。

Here, a _{max is} the maximum value of the recess depth a of the recess 2, D is the steel pipe outer diameter, and t is the steel pipe plate thickness.

  Further, as shown in FIG. 8 (b), the hollow portion 2 is formed such that the hollow height b formed in a convex shape from the straight pipe inner peripheral surface 3b of the straight pipe portion 3 has a steel pipe outer diameter D and a steel pipe plate thickness t. Therefore, the relationship defined by the following equation (2) is satisfied.

ここで、ｂ_max：窪み部２の窪み高さｂの最大値、Ｄ：鋼管外径、ｔ：鋼管板厚とする。

Here, b _{max is} the maximum value of the recess height b of the recess 2, D is the steel pipe outer diameter, and t is the steel pipe plate thickness.

The hollow portion 2 is formed, for example, in a deepest concave shape in the tube axis orthogonal direction X at the approximate center 25 in the pipe circumferential direction W of the hollow portion 2, and has a maximum value a _max of the hollow depth a of the hollow portion 2. It becomes. Moreover, the hollow part 2 has a predetermined hollow depth am at each part m in the pipe circumferential direction W, with the hollow depth a of the hollow part 2 gradually decreasing from the substantially center 25 in the pipe circumferential direction W to both ends 20. Thus, the both end portions 20 of the hollow portion 2 in the pipe circumferential direction W have the minimum value a _min of the hollow depth a of the hollow portion 2.

For this reason, the hollow part 2 makes the average value _aave of the hollow depth am in each part m of the pipe circumferential direction W the hollow depth a of the hollow part 2, and averages the hollow depth am in each part m of the pipe circumferential direction W. By assuming that the value a _ave is about half of the maximum value a _max of the depression depth a, the depression depth a of the depression portion 2 is related to the maximum value a _max of the depression depth a as follows ( 3) It is approximated as satisfying the relationship defined by the equation. In addition, since the dent depth a of the dent part 2 is approximated by the following equation (3) in relation to the maximum value a _max of the dent depth a, each part in the pipe circumferential direction W in the actual product. It may be calculated by measuring the average value a _ave of the depression depth am at m.

Further, the recessed portion 2, like the recess depth a, at substantially the center 25 of the tube circumferential direction W of the recess portion 2, a maximum value b _max of the high depression of the depression part 2 is b, the circumferential direction of the pipe Each portion m of W has a predetermined recess height bm, and both end portions 20 of the recess portion 2 in the pipe circumferential direction W have a minimum value b _min of the recess height b of the recess portion 2.

Therefore, the recess portion 2, a tube as the circumferential direction W height b recess of each portion average height bm recess in m b _ave the recess 2 of the average height bm recess in each part m of the pipe circumferential direction W By assuming that the value b _ave is about half of the maximum value b _max of the recess height b, the recess height b of the recess portion 2 is related to the maximum value b _max of the recess height b as follows ( It is approximated as satisfying the relationship defined by the equation (4). In addition, since the dent height b of the dent part 2 is approximated by the following equation (4) in relation to the maximum value b _max of the dent height b, each part in the pipe circumferential direction W in the actual product. It may be calculated by measuring the average value b _ave of the depression height bm at m.

  Here, as for the steel pipe 1 to which this invention is applied, as shown in Fig.9 (a), the collapse mode 2 becomes a pipe axis because the compressive load P acts on the pipe-axis direction Y of the steel pipe 1. From the analysis of the compression experiment result of a similar depression shape, it was found after intensive study that it would be deformed so as to collapse in the direction Y. The steel pipe 1 is a steel pipe that resists a compressive load P acting in the pipe axis direction Y when the hollow portion 2 is formed in the entire circumferential length E of the steel pipe in the pipe circumferential direction W and the hollow ratio λ is 100%. The axial compression strength p of 1 is calculated by the following formulas (5) and (6).

ここで、π：円周率、Ｒ：鋼管半径（Ｄ／２）、σ_y：鋼管降伏強度とする。

Here, π: pi, R: steel pipe radius (D / 2), σ _y : steel pipe yield strength.

  The above formulas (5) and (6) assume that the compressive load P is applied in the tube axis direction Y of the steel pipe 1 having a recess ratio λ of 100%, as shown in FIG. By setting a model based on the collapse mode that collapses into an accordion-like shape, it was derived from the model based on this collapse mode by extreme analysis after intensive studies.

  In this limit analysis, the rotational moment Mp is dominant due to the deformation when the steel pipe 1 is crushed into a bellows shape, so that the plastic hinge 8 is formed at each of the peak portion 8a and the valley bottom point 8b of the recess portion 2. It is assumed. Each plastic hinge 8 is rotationally deformed at the rotation angle θ in the rotation direction r, so that the internal work of each plastic hinge 8 is calculated from the product (Mp × θ) of the rotation moment Mp and the rotation angle θ of the plastic hinge 8. Is calculated. At this time, the sum of internal work by each plastic hinge 8 becomes 4 × Mp × θ by forming the rotation angles θ at four locations. As a result, the axial compressive proof stress p of the steel pipe 1 is the sum of internal work (work done by the resistance of the rotational moment Mp) made by the plastic hinges 8 and the external force made by the external force when the compression load P deforms the steel pipe 1. From the balance with the sum of work (sum of work formed by the compressive load P), it is calculated as in the above formulas (5) and (6).

The steel pipe 1 to which the present invention is applied is set so that the depression ratio λ is 50% or more and 95% or less, and the depression 2 is formed in a portion where the depression 2 is formed in the pipe circumferential direction W of the steel pipe 1. A portion that is not formed is formed. Further, the recess depth a of the recess portion 2 is related to the maximum value a _max of the recess depth a and satisfies the relationship defined by the above equation (3), and the recess height b of the recess portion 2 is The relationship defined by the above equation (4) is satisfied in relation to the maximum value b _max of the recess height b.

  For this reason, as for the steel pipe 1 to which this invention is applied, the compressive proof stress p1 of the location where the hollow part 2 is formed in the pipe circumferential direction W of the steel pipe 1 is the following (7) from the said (3)-(6) formula. The relationship defined by the equation (8) is satisfied.

  Here, in the substantially straight tubular normal steel pipe 5 (the hollow ratio λ is 0%) in which the hollow portion 2 is not formed on the outer peripheral surface 1a of the steel pipe, the compressive yield strength p3 in a range in which the long buckling in the pipe axis direction Y is not generated. Depends on the steel pipe cross-sectional area A, the relationship defined by the following equation (9) is satisfied.

ここで、Ａ：鋼管断面積とする。

Here, A: steel pipe cross-sectional area.

  For this reason, in the steel pipe 1 to which the present invention is applied, the compressive proof stress p2 of the rib part 4 which is a place where the hollow part 2 is not formed in the pipe circumferential direction W of the steel pipe 1 is hollow with respect to the steel pipe cross-sectional area A of the normal steel pipe 5. By subtracting the ratio at which the portion 2 is formed, the relationship defined by the following equation (10) is satisfied from the relationship between the above equation (9) and the depression ratio λ.

  Therefore, in the steel pipe 1 to which the present invention is applied, the compression strength p1 of the portion where the hollow portion 2 is formed in the pipe circumferential direction W of the steel pipe 1 and the compression of the portion where the hollow portion 2 is not formed in the pipe circumferential direction W of the steel pipe 1. The sum of the proof stress p2 satisfies the relationship defined by the following formulas (11) to (13) in relation to the compression proof strength p3 of the generally straight tubular normal steel pipe 5 in which the hollow portion 2 is not formed on the outer peripheral surface 1a of the steel pipe. By doing so, the compression proof stress of approximately equal to or higher than that of the normal steel pipe 5 is ensured.

  Here, in the steel pipe 1 to which the present invention is applied, since the straight pipe plate thickness t1 of the straight pipe portion 3 and the hollow plate thickness t2 of the hollow portion 2 are substantially the same, as shown in FIG. Also in the part 10 in which the hollow part 2 and the rib part 4 are formed in the pipe axis direction Y of the steel pipe 1, the straight pipe part 3 is formed in the pipe axis direction Y of the steel pipe 1 as shown in FIG. As with the portion 11, the steel pipe cross-sectional area A is approximated as satisfying the relationship defined by the following equation (14).

As described above, in the steel pipe 1 to which the present invention is applied, by substituting the above equation (14) into the above equations (12) and (13), the dent depth a of the dent portion 2 is defined by the above equation (1). In addition to satisfying the relationship, the dent height b of the dent portion 2 is calculated as satisfying the relationship defined by the above equation (2). In addition, since the steel pipe 1 to which the present invention is applied approximates the cross-sectional area A of the steel pipe by the above equation (14), in the actual product, t / a _max and t / b in the above equations (1) and (2). _{The max} may be less than (D−t) / D by about 5%.

Table 1 below shows that the compression proof stress (p1 + p2) of the inventive examples 1 to 3 is larger than the compressive proof stress p3 of the normal steel pipe 5 by comparing the comparative examples 1 to 6 and the inventive examples 1 to 3. This is expressed from the experimental results. In Invention Examples 1 to 3, when t / a _max is equal to or greater than (D−t) / D, the indentation depth a of the indentation portion 2 satisfies the relationship defined by the above equation (1). On the other hand, in Comparative Examples 1 to 6, since t / a _max is less than (D−t) / D, the depth a of the recessed portion 2 is defined by the above equation (1). Will not be satisfied. Here, in Examples 1 to 3 of the present invention, the ratio (ΣEn / E) of the total ΣEn of the hollow extension En of each hollow portion 2 to the total circumferential length E of the steel pipe 1 in the pipe circumferential direction W is 9 Exceeding the percentage, the dent ratio λ is set to 90% or more.

  FIG. 10 is a plot of the compressive yield strength of the comparative example and the example of the present invention, in which “when the experimental result and the calculation result match” is indicated by a broken line, and “the linear approximation formula of the experimental result and the calculation result”. It is shown by a straight line. The fact that the broken line and the straight line substantially coincide with each other indicates that the compression strength (p1 + p2) of the steel pipe 1 with the depression calculated by the yield strength evaluation formula proposed by the inventor is the compression strength (p1 + p2) of the actual steel pipe 1 with the depression. It is clarified from the verification with the experimental results that it is estimated with high accuracy. From this experimental verification study, the compressive strength (p1 + p2) of the actual steel pipe 1 with the depression can be accurately estimated by the yield strength evaluation formula proposed by the inventor, and the above-described ( This shows the validity of the equations (1) and (2).

  As shown in FIG. 11, the steel pipe 1 to which the present invention is applied has a compression strength (p1 + p2) of the steel pipe 1 when the depth a of the recess 2 satisfies the relationship defined by the above formula (1). It is possible to ensure a predetermined adhesion performance with the consolidated material 6 or the fixing material on the outer side O of the steel pipe without lowering. Moreover, the steel pipe 1 to which the present invention is applied has no reduction in the compressive strength (p1 + p2) of the steel pipe 1 when the dent height b of the dent part 2 satisfies the relationship defined by the above equation (2). Predetermined adhesion performance can be secured between the consolidated material 6 and the fixing material on the steel pipe inner side I.

  In particular, the steel pipe 1 to which the present invention is applied is set so that the depression ratio λ is 50% or more and 95% or less, so that the sum of the depression extensions En of the respective depressions 2 extending in the pipe circumferential direction W is obtained. By making ΣEn sufficiently long, the adhesion performance with the consolidated material 6 and the fixing material can be improved. In addition, the steel pipe 1 to which the present invention is applied is not limited to the steel pipe outer side O or the steel pipe inner side I provided with the hardened material 6 of the time-curable material, and is predetermined with the earth and sand in the buried ground. The adhesion performance may be ensured.

  Thereby, the steel pipe 1 to which the present invention is applied avoids a decrease in adhesion performance with the earth and sand in the ground, a time-hardening material, and the like, and at the same time, without reducing the compression strength (p1 + p2) of the steel pipe 1. It becomes possible to provide the steel pipe 1 which has the hollow specification which does not reduce the compression performance of Y.

  In addition, as shown in FIG. 2, the steel pipe 1 to which the present invention is applied is formed such that a plurality of rib portions 4 arranged side by side in the pipe axis direction Y are arranged substantially in a line in the pipe axis direction Y. However, the present invention is not limited to this, and the positions in the pipe circumferential direction W may be different from each other so as to be substantially staggered in the pipe axis direction Y.

  As mentioned above, although the example of embodiment of this invention was demonstrated in detail, all the embodiment mentioned above showed only the example of actualization in implementing this invention, and these are the technical aspects of this invention. The range should not be construed as limiting.

  For example, the steel pipe 1 to which the present invention is applied is not limited to the above-described medium and small diameter steel pipe, and may be applied to a large diameter steel pipe having a steel pipe outer diameter D of about 350 mm to 3000 mm. In addition, as for the steel pipe 1 to which this invention is applied, it is desirable for the length B of the hollow part 2 of the pipe-axis direction Y to be set about 3 to 20 times with respect to the hollow depth a of the hollow part 2. FIG.

DESCRIPTION OF SYMBOLS 1: Steel pipe 1a: Steel pipe outer peripheral surface 1b: Steel pipe inner peripheral surface 10: The site | part in which a hollow part and a rib part are formed 11: The site | part in which a straight pipe part is formed 2: The hollow part 2a: The hollow outer peripheral surface 2b: In a hollow Circumferential surface 20: Both end portions 21 of the dent portion: First dent portion 22: Second dent portion 23: Third dent portion 25: Approximate center of the dent portion 3: Straight pipe portion 3a: Straight pipe outer peripheral surface 3b: Straight pipe inner circumference Surface 4: Rib 4a: Rib outer peripheral surface 4b: Rib inner peripheral surface 5: Normal steel pipe 6: Solidified material 7: Ground 70: Excavation hole or ground improvement range 8: Plastic hinge 8a: Mountain top 8b: Valley bottom Point W: Pipe circumferential direction X: Pipe axis orthogonal direction Y: Pipe axis direction

Claims (5)

A steel pipe in which a hollow portion is formed on the outer peripheral surface of the steel pipe,
A straight pipe portion extending in the tube axis direction and formed in a substantially straight tube shape, and a hollow portion formed in a concave shape toward the inside in the tube axis orthogonal direction,
The hollow portion has substantially the same thickness as the straight pipe portion, and the depth of the hollow formed in a concave shape than the straight pipe outer peripheral surface of the straight pipe portion is related to the steel pipe outer diameter and the steel pipe plate thickness. And satisfying the relationship defined by the following formula (1).

Here, a _{max is} the maximum value of the depth of the recess, D is the outer diameter of the steel pipe, and t is the thickness of the steel pipe. 2. The steel pipe according to claim 1, wherein the hollow portion is formed to extend in the pipe circumferential direction with only a part of the entire length of the steel pipe in the pipe circumferential direction. 3. The steel pipe according to claim 1, wherein one or a plurality of the recessed portions are formed in the pipe circumferential direction so that a ratio of the entire circumference of the steel pipe in the pipe circumferential direction is 50% or more. . The steel pipe according to any one of claims 1 to 3, wherein a plurality of the recessed portions are intermittently formed at predetermined intervals in the tube axis direction. The said hollow part has the relationship prescribed | regulated by the following (2) formula by the relationship between the hollow height formed in convex shape rather than the straight pipe inner peripheral surface of the said straight pipe part with a steel pipe outer diameter and steel pipe plate thickness. The steel pipe according to any one of claims 1 to 4, wherein the steel pipe is satisfied.

Here, b _{max is} the maximum value of the dent height of the dent part, D is the outer diameter of the steel pipe, and t is the steel pipe plate thickness.

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