Variable-section H-shaped steel piles

Abstract

This invention provides a variable-section H-shaped steel pile that is rational and economical in relation to the bending moment acting upon it. [Solution] The pile is formed from a lower H-shaped steel pile installed below the bottom of the excavation and an upper H-shaped steel pile joined to the upper end of the lower H-shaped steel pile. The upper H-shaped steel pile is formed from an H-shaped steel with a larger cross-sectional size than the lower H-shaped steel pile. The upper H-shaped steel pile is joined to the upper end of the lower H-shaped steel pile at a depth of 1.5 / β to 3.0 / β from the bottom of the excavation. β is the characteristic value of the pile (m -1 ) and can be found from equation (1). JPEG2026070391000006.jpg26169 Here, k H Horizontal ground reaction coefficient (kN / m 3 D: width or diameter of the pile (m), E: Young's modulus (kN / m 2 ), I: second moment of area (m 4 )

Description

[Technical Field]

[0001] The present invention relates to a variable-section H-shaped steel pile comprising a lower H-shaped steel pile installed below the bottom of the excavation and an upper H-shaped steel pile formed with a larger cross-sectional size than the lower H-shaped steel pile and joined to the upper end of the lower H-shaped steel pile, and provides a variable-section H-shaped steel pile that is extremely rational and economical in terms of the bending moment acting on the variable-section H-shaped steel pile by providing the joint between the lower H-shaped steel pile and the upper H-shaped steel pile in a range where the bending moment is as small as possible. [Background technology]

[0002] It is known that the bending moment acting on support piles such as foundation piles installed in the ground is not uniform along the entire length of the pile, but rather acts in a parabolic manner in the axial direction of the pile (see Figure 7).

[0003] Generally, for long piles (semi-infinite length piles), the bending moment at the pile head decreases as the degree of fixation at the pile head decreases, and reaches its maximum at a certain depth below the ground surface (maximum bending moment in the subsurface).

[0004] Then, it gradually decreases downwards, and once it reaches a certain depth, the bending moment gradually converges to zero with almost no change.

[0005] This means that if a portion of the pile has enough strength to withstand the maximum bending moment acting on it, the other portions only need to have less strength.

[0006] Incidentally, H-shaped steel piles are widely used as support piles for temporary platforms (see Figure 6), but their design is based on the maximum bending moment acting on the pile, and the cross-section of the entire pile is designed accordingly (full-strength specification), which has resulted in an extremely uneconomical design.

[0007] Furthermore, for example, Patent Document 1 discloses a support pile consisting of an upper H-shaped steel pile and a lower H-shaped steel pile with different cross-sectional sizes.

[0008] Simply put, the web and flange widths of the upper H-shaped steel pile are both larger than those of the lower H-shaped steel pile, and the web and flange thicknesses are also greater for the upper H-shaped steel pile than for the lower H-shaped steel pile.

[0009] Furthermore, a connecting plate is interposed between the upper H-shaped steel pile and the lower H-shaped steel pile, and the lower end of the upper H-shaped steel pile and the upper end of the lower H-shaped steel pile are welded to the upper and lower surfaces of the connecting plate, respectively. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2009-144424 [Patent Document 2] Utility Model Registration No. 3162263 Gazette [Patent Document 3] Patent No. 7079448 [Overview of the project] [Problems that the invention aims to solve]

[0011] However, while the support piles described in Patent Document 1 use thick-plate steel sections, i.e., steel sections with a large cross-sectional size, in the parts where large bending moments act, and relatively thin-plate steel sections, i.e., steel sections with a small cross-sectional size, in other parts, no particular measures are disclosed to address the bending moment acting at the joint between the upper H-shaped steel pile and the lower H-shaped steel pile.

[0012] The present invention was made to solve the above problems, and aims to provide a variable-section H-shaped steel pile that is extremely efficient and economical in relation to bending moments, by providing a joint between the lower H-shaped steel pile and the upper H-shaped steel pile in a range where the bending moment acting on the variable-section H-shaped steel pile is as small as possible. [Means for solving the problem]

[0013] The present invention relates to a variable-section H-shaped steel pile comprising a lower H-shaped steel pile installed below the bottom of the excavation and an upper H-shaped steel pile formed with a larger cross-sectional size than the lower H-shaped steel pile and joined to the upper end of the lower H-shaped steel pile, characterized in that the upper H-shaped steel pile is joined to the upper end of the lower H-shaped steel pile to a depth of 1.5 / β(m) or more from the base surface. Here, β is the characteristic value of the pile (m -1 ) and can be found from equation (1).

[0014]

number

[0015] Here, k H Horizontal ground reaction coefficient (kN / m 3 ) D: Width or diameter of the pile (m) E: Young's modulus (kN / m) 2 ) I: Second moment of area (m 4 )

[0016] Furthermore, if the joint between the lower H-shaped steel pile and the upper H-shaped steel pile is located at a depth of 1.5 / β(m) or more from the bottom of the excavation, there will be no particular strength issues with respect to the bending moment acting on the variable-section H-shaped steel pile.

[0017] Further, by providing the joint part within the range of 1.5 / β to 3.0 / β (m) deeper than the root cut-off bottom, it is possible to keep the upper H-shaped steel pile with a large cross-sectional size to the minimum necessary length, and it is possible to provide a very reasonable and economical variable cross-section H-shaped steel pile, which is preferable.

[0018] Further, when the influence of the bending moment acting in the strong axis direction is greater than the bending moment acting in the weak axis direction acting on the variable cross-section H-shaped steel pile, it is preferable to join the lower H-shaped steel pile and the upper H-shaped steel pile in the strong axis direction so that the joining position is within the range of 1.5 / β to 2.0 / β from the root cut-off bottom.

[0019] Further, when the influence of the bending moment acting in the weak axis direction is greater than the bending moment acting in the strong axis direction acting on the variable cross-section H-shaped steel pile, it is preferable to join the lower H-shaped steel pile and the upper H-shaped steel pile in the weak axis direction so that the joining position is within the range of 2.5 / β to 3.0 / β from the root cut-off bottom.

[0020] For example, when the variable cross-section H-shaped steel piles are arranged in multiple spans as support piles in the bridge axis direction of the temporary gantry, since the support piles are easily affected by the bending moment acting in the strong axis direction (perpendicular to the bridge axis direction), it is preferable to join the lower H-shaped steel pile and the upper H-shaped steel pile so that the joining position is within the range of 1.5 / β to 2.0 / β (m) deeper than the root cut-off bottom.

[0021] Further, when the same number of spans (for example, 1 span) of the variable cross-section H-shaped steel piles are arranged as support piles in both the bridge axis direction and the direction perpendicular to the bridge axis direction of the temporary gantry, it is only necessary to consider both the strong axis direction (perpendicular to the bridge axis direction) and the weak axis direction (bridge axis direction) and join in the disadvantageous direction. It is preferable to use H-shaped steel of the same beam composition for the lower H-shaped steel pile and the upper H-shaped steel pile.

[0022] Further, the lower H-shaped steel pile can be joined to the upper end of the upper H-shaped steel pile, for example, by upper and lower joint plates respectively attached to the upper end of the lower H-shaped steel pile and the lower end of the upper H-shaped steel pile, and a plurality of joint bolts for joining the upper and lower joint plates. However, the joining method of the lower H-shaped steel pile and the upper H-shaped steel pile is not particularly limited. Also, the joint position (range of 1.5 / β or more from the bottom of the undercut) between the lower H-shaped steel pile and the upper H-shaped steel pile can be derived by the following steps.

[0023] (1) A step of calculating the bending moment and bending resistance acting on the underground part from the bottom of the undercut of the variable cross-section H-shaped steel pile respectively. The bending moment acting on the underground part can be derived by the bending moment formula (2) of each part of the pile, and the bending resistance of the joint part between the lower H-shaped steel pile and the upper H-shaped steel pile can be derived by a full-scale bending test.

[0024]

Number

[0025] Here, H: Force perpendicular to the pile axis (kN) h: Ground height (m) where H acts β: Characteristic value of the pile (m -1 )

[0026] (2) A step of calculating the characteristic value β of the variable cross-section H-shaped steel pile. The characteristic value can be derived by formula (1).

[0027]

Number

[0028] Here, k H : Horizontal ground reaction coefficient (kN / m 3 ) D: Width or diameter of the pile (m) E: Young's modulus (kN / m 2 ) I: Second moment of area (m4 )

[0029] (3) A step of determining the position for joining the upper H-shaped steel pile to the upper end of the lower H-shaped steel pile within a depth range of 1.5 / β to 3.0 / β from the bottom of the excavation.

[0030] Furthermore, if the joint between the lower H-shaped steel pile and the upper H-shaped steel pile is located at a depth of 1.5 / β(m) or more from the bottom of the excavation, there will be no particular strength issues with respect to the bending moment acting on the variable-section H-shaped steel pile. [Effects of the Invention]

[0031] This invention provides a highly efficient and economical variable-section H-shaped steel pile in terms of bending moment by joining the lower end of the upper H-shaped steel pile to the upper end of the lower H-shaped steel pile within the range where the objectively determined bending moment is as small as possible. [Brief explanation of the drawing]

[0032] [Figure 1] Figures (a) and (b) are perspective views of the joint section of a variable-section H-shaped steel pile. [Figure 2] Figure 1 illustrates the variable-section H-shaped steel pile joint section, where Figure (a) is a cross-sectional view and Figure (b) is a side view. [Figure 3] Figure (a) is a perspective view of the joint section of a variable-section H-shaped steel pile, Figure (b) is a side view, and Figure (c) is a cross-sectional view. [Figure 4] Figure 5 is an explanatory diagram showing the preferred range for the joint between the lower H-shaped steel pile and the upper H-shaped steel pile, under the temporary platform and design conditions illustrated in the diagram. [Figure 5] This is a model drawing of a temporary platform. [Figure 6] This is a front view of the temporary platform. [Figure 7] This is a diagram showing the bending moment acting on a pile installed in the ground. [Modes for carrying out the invention]

[0033] Figures 1 and 2 illustrate one embodiment of the present invention, illustrating a variable-section H-shaped steel pile used as a support pile for a temporary platform (see Figure 6).

[0034] In Figures 1 and 2, the variable-section H-shaped steel pile 1 is formed from a lower H-shaped steel pile 2 and an upper H-shaped steel pile 3 joined to the upper end of the lower H-shaped steel pile 2.

[0035] The lower H-shaped steel pile 2 and the upper H-shaped steel pile 3 have the same beam depth (web height), and the beam width (flange width) of the lower H-shaped steel pile 2 is smaller than the beam width of the upper H-shaped steel pile 3.

[0036] Furthermore, the lower H-shaped steel pile 2 is installed at a certain depth underground below the base surface along its entire length, while the upper H-shaped steel pile 3 has a portion of its lower end installed below the ground surface, with the portion above that rising from the bottom of the excavation (see Figure 3).

[0037] Furthermore, the lower joint plate 4 and the upper joint plate 5 are attached by welding or other means to the upper end of the lower H-shaped steel pile 2 and the lower end of the upper H-shaped steel pile 3, respectively, in the underground portion below the bottom of the excavation.

[0038] The upper joint plate 5 is abutted against the lower joint plate 4 and is integrally joined by multiple joint bolts 6 that pass through the lower joint plate 4 and the upper joint plate 5.

[0039] Furthermore, reinforcing ribs 7, 7 are attached to the lower side of the lower joint plate 4 and the upper side of the upper joint plate 5, respectively, and at least four joint bolts are used for the joint bolt 6.

[0040] Figures 3(a) to 3(c) illustrate modified examples of variable-section H-shaped steel piles, particularly those in which the beam depth (web height) and beam width (flange width) of the lower H-shaped steel pile 2 are both smaller than those of the upper H-shaped steel pile 3. Except for the lower H-shaped steel pile 2 being formed from an H-shaped steel with a smaller cross-sectional size than the upper H-shaped steel pile 3, the construction is the same as in the embodiments shown in Figures 1 and 2.

[0041] In all cases, the lower H-shaped steel pile 2 and the upper H-shaped steel pile 3 are joined at a depth of 1.5 / β to 3.0 / β from the bottom of the excavation, depending on the pile diameters of the lower H-shaped steel pile 2 and the upper H-shaped steel pile 3. β is a characteristic value of the pile and is primarily used for evaluating the stiffness of the pile and calculating the spring constant perpendicular to the pile axis (pile displacement, etc.).

[0042] Figure 4 illustrates the preferred range (depth from 1.5 / β to 3.0 / β from the bottom of the excavation) for the joint between the lower H-shaped steel pile and the upper H-shaped steel pile, under the temporary platform and design conditions shown in Figure 5.

[0043] For example, Figures (a) and (b) illustrate the preferred range of joint positions for a variable-section H-shaped steel pile, where the lower H-shaped steel pile is A (section): H300 × 150 and the upper H-shaped steel pile is A: H300 × 300. Figure (a) illustrates the range of joint positions where the bending moment acts in the weak axis direction, and Figure (b) illustrates the range of joint positions where the bending moment acts in the strong axis direction.

[0044] Furthermore, Figures (c) and (d) illustrate the preferred range of joint positions for a variable-section H-shaped steel pile, where the lower H-shaped steel pile is A:H350×175 and the upper H-shaped steel pile is A:H350×350. Figure (c) illustrates the range of joint positions where the bending moment acts in the weak axis direction, and Figure (d) illustrates the range of joint positions where the bending moment acts in the strong axis direction.

[0045] Figures (e) and (f) illustrate the preferred range of joint positions for a variable-section H-shaped steel pile, where the lower H-shaped steel pile is A:H400×200 and the upper H-shaped steel pile is A:H400×400. Figure (e) illustrates the range of joint positions where the bending moment acts in the weak axis direction, and Figure (f) illustrates the range of joint positions where the bending moment acts in the strong axis direction. [Industrial applicability]

[0046] The present invention provides a variable-section H-shaped steel pile comprising a lower H-shaped steel pile installed below the bottom of the excavation and an upper H-shaped steel pile formed with a larger cross-sectional size than the lower H-shaped steel pile and joined to the upper end of the lower H-shaped steel pile, wherein the joint between the lower H-shaped steel pile and the upper H-shaped steel pile is provided in a range where the bending moment is as small as possible, thereby providing a variable-section H-shaped steel pile that is extremely rational and economical in terms of the bending moment acting on the variable-section H-shaped steel pile. [Explanation of symbols]

[0047] 1. Variable-section H-shaped steel pile 2 Lower H-shaped steel pile 3 Upper H-shaped steel pile 4. Lower joint plate 5. Upper joint plate 6. Joint bolts 7 Reinforcement ribs

Claims

1. A variable-section H-shaped steel pile comprising a lower H-shaped steel pile installed below the bottom of the excavation and an upper H-shaped steel pile formed with a larger cross-sectional size than the lower H-shaped steel pile and joined to the upper end of the lower H-shaped steel pile, characterized in that the upper H-shaped steel pile is joined to the upper end of the lower H-shaped steel pile within a range of 1.5 / β or more from the bottom of the excavation. β is the characteristic value of the pile (m -1 ) and can be obtained from equation (1). [Math 1] Here, k H Horizontal ground reaction coefficient (kN / m 3 ), D: Width or diameter of the pile (m) E: Young's modulus (kN / m) 2 ) I: Second moment of area (m 4 )

2. A variable-section H-shaped steel pile according to claim 1, characterized in that the connection position between the lower H-shaped steel pile and the upper H-shaped steel pile is in the range of 1.5 / β to 3.0 / β from the bottom of the excavation.

3. A variable-section H-shaped steel pile according to claim 2, characterized in that, when the influence of the bending moment acting in the strong-axis direction is greater than the bending moment acting in the weak-axis direction acting on the variable-section H-shaped steel pile, the connection position between the lower H-shaped steel pile and the upper H-shaped steel pile is in the range of 1.5 / β to 2.0 / β from the bottom of the excavation in the strong-axis direction.

4. A variable-section H-shaped steel pile according to claim 2, characterized in that, when the influence of the bending moment acting in the weak axis direction is greater than the bending moment acting in the strong axis direction acting on the variable-section H-shaped steel pile, the connection position between the lower H-shaped steel pile and the upper H-shaped steel pile is in the range of 2.5 / β to 3.0 / β from the bottom of the excavation in the weak axis direction.

5. A variable-section H-shaped steel pile according to any one of claims 1 to 4, characterized in that the lower H-shaped steel pile and the upper H-shaped steel pile are formed from H-shaped steel having the same beam depth.

6. A variable-section H-shaped steel pile according to any one of claims 1 to 4, characterized in that the lower H-shaped steel pile is joined to the upper end of the upper H-shaped steel pile by upper and lower joint plates attached to the upper end of the lower H-shaped steel pile and the lower end of the upper H-shaped steel pile, respectively, and by a plurality of joint bolts that join the upper and lower joint plates.

7. A method for determining the joint position between a lower H-shaped steel pile and an upper H-shaped steel pile in a variable cross-section H-shaped steel pile, comprising a lower H-shaped steel pile installed below the bottom of the excavation and an upper H-shaped steel pile formed to a larger cross-sectional size than the lower H-shaped steel pile and joined to the upper end of the lower H-shaped steel pile, characterized in that it includes the following steps. (1) A step of calculating the bending moment and bending strength acting below the excavation bottom of the H-shaped steel pile with a variable cross section. (2) A step of calculating the characteristic value β of the variable cross section H-shaped steel pile. (3) A step of determining the range of the joining position for joining the upper H-shaped steel pile to the upper end of the lower H-shaped steel pile so that it is within a range of 1.5 / β or more from the bottom of the excavation.

8. A method for determining the joint position between a lower H-shaped steel pile and an upper H-shaped steel pile according to claim 7, characterized in that the joint position between the lower H-shaped steel pile and the upper H-shaped steel pile is determined to be in the range of 1.5 / β to 3.0 / β from the bottom of the excavation.

9. A method for determining the joint position between a lower H-shaped steel pile and an upper H-shaped steel pile in a variable-section H-shaped steel pile according to claim 8, characterized in that, when the influence of the bending moment acting in the strong-axis direction is greater than the bending moment acting in the weak-axis direction acting on the variable-section H-shaped steel pile, the joint position between the lower H-shaped steel pile and the upper H-shaped steel pile is determined to be in the range of 1.5 / β to 2.0 / β from the bottom of the excavation in the strong-axis direction.

10. A method for determining the joint position between a lower H-shaped steel pile and an upper H-shaped steel pile in a variable-section H-shaped steel pile according to claim 8, characterized in that, when the influence of the bending moment acting in the weak axis direction is greater than the bending moment acting in the strong axis direction acting on the variable-section H-shaped steel pile, the joint position between the lower H-shaped steel pile and the upper H-shaped steel pile is determined to be in the range of 2.5 / β to 3.0 / β from the bottom of the excavation in the weak axis direction.

Images