JP7734650B2 - Method for evaluating shear strength of rotation prevention key, method for manufacturing steel pipe connection device, and steel pipe connection device - Google Patents

Description

The present invention relates to a steel pipe connecting device for connecting the ends of steel pipes that make up a steel pipe pile so that they cannot rotate relative to each other.

A known example of such a steel pipe connecting device is one in which a rotation prevention key is fixed with a bolt to a fitting recess provided across the outer surface of a box joint welded to the upper steel pipe and the outer surface of a pin joint welded to the lower steel pipe (Patent Document 1). When a steel pipe pile connected by the steel pipe connecting device of Patent Document 1 is installed, the rotational torque applied to the upper steel pipe is transmitted to the lower steel pipe via the box joint and pin joint, whose relative rotation is prevented by the rotation prevention key.

In manufacturing the above steel pipe connecting device, the shape parameters of the rotation restraint key are determined so that it has the shear strength required to transmit rotational torque without breaking. Conventionally, the following formula has been used to calculate the shear strength T _S :
b: Width of rotation restraint key in the lateral direction t: Thickness of rotation restraint key σ ₁ : Yield stress of rotation restraint key

Japanese Patent Application Laid-Open No. 2019-65525

However, when the inventors of this application verified the shear strength of the rotation prevention key, they found that there was a certain degree of discrepancy between the value calculated using the above formula and the actual value. Due to this discrepancy, the settings for the shape parameters of the rotation prevention key during the manufacture of the steel pipe connection device were not sufficiently appropriate, leaving room for improvement.

The present invention aims to provide a method for evaluating the shear strength of a rotation prevention key, a method for manufacturing a steel pipe connection device, and a steel pipe connection device that solves the above-mentioned problems.

To achieve the above object, the evaluation method according to the present invention comprises:
A box joint and a pin joint that can be connected to each other so as to have the same axis;
a rotation prevention key that is attached to a fitting recess provided across both the outer peripheral surface of the box joint and the outer peripheral surface of the pin joint and that prevents relative rotation between the box joint and the pin joint around the axis;
A method for evaluating the shear strength of a rotation restraint key in a steel pipe connecting device, the method comprising: inserting a bolt mounting hole with a counterbore provided in either a region of the rotation restraint key on the box joint side or a region of the pin joint side of the rotation restraint key, screwing the bolt into the box joint or the pin joint, and fixing the rotation restraint key in the fitting recess;
On the outer surface of the rotation prevention key,
a first imaginary line overlapping a boundary line between the box joint and the pin joint in the fitting recess;
a second imaginary line connecting one end of the first imaginary line and the center of the counterbore;
A third imaginary line is assumed to connect the other end of the first imaginary line and the center of the counterbore;
a distance from the one end of the first imaginary line to an intersection point between the second imaginary line and an edge of the counterbore is defined as b1;
When the distance from the other end of the first imaginary line to the intersection point between the third imaginary line and the edge of the countersink is b2,
The method includes calculating the shear strength T _S of the rotation preventing key using the following formula:
(where t is the thickness of the rotation restraint key, σ ₁ is the yield stress of the rotation restraint key, and k is a predetermined correction factor.)

When rotational torque is transmitted through a rotation restraining key, shear stress acts on the rotation restraining key. Conventionally, it was thought that shear stress acts along the width direction of the rotation restraining key. However, the inventors of the present application discovered that when the rotation restraining key is provided with a counterbore bolt mounting hole, shear stress acts from a portion of the edge of the rotation restraining key near the boundary between the box joint and the pin joint toward the counterbore. Therefore, the inventors of the present application defined the above-mentioned formula for calculating the shear strength T _S , taking into account the actual direction of shear stress.

The above formula incorporates "(b1 + b2) × t," which represents an area closer to the area of the surface on which shear stress actually acts. Furthermore, the above formula incorporates a correction coefficient k, which brings the uncorrected value closer to the actual value. Therefore, the above formula allows for a more accurate evaluation of the shear strength T _S of the rotation prevention key.

In order to achieve the above object, the manufacturing method according to the present invention comprises the steps of:
A box joint and a pin joint that can be connected to each other so as to have the same axis;
a rotation prevention key that is attached to a fitting recess provided across both the outer peripheral surface of the box joint and the outer peripheral surface of the pin joint and that prevents relative rotation between the box joint and the pin joint around the axis;
A method for manufacturing a steel pipe connecting device comprising: a bolt that is inserted through a countersunk bolt mounting hole provided in either the box joint side region or the pin joint side region of the rotation restraint key and threadedly engages with the box joint or the pin joint, and fixes the rotation restraint key in the fitting recess,
On the outer surface of the rotation prevention key,
a first imaginary line overlapping a boundary line between the box joint and the pin joint in the fitting recess;
a second imaginary line connecting one end of the first imaginary line and the center of the counterbore;
A third imaginary line is assumed to connect the other end of the first imaginary line and the center of the counterbore;
a distance from the one end of the first imaginary line to an intersection point between the second imaginary line and an edge of the counterbore is defined as b1;
When the distance from the other end of the first imaginary line to the intersection point between the third imaginary line and the edge of the countersink is b2,
Calculating the shear strength T _S of the rotation restraint key using the following formula:
(where t is the thickness of the rotation restraint key, σ ₁ is the yield stress of the rotation restraint key, and k is a predetermined correction factor.)
Setting b1, b2 and t so that the shear strength T _S is equal to or greater than a predetermined threshold value;
and manufacturing the rotation prevention key, the box joint, and the pin joint based on the set b1, b2, and t.

As described above regarding the evaluation method, the calculation formula for shear strength T _S in this invention allows for more accurate evaluation of shear strength T _S. Therefore, according to the above manufacturing method using this calculation formula for shear strength T _S , it becomes possible to more appropriately set the shape parameters of the rotation restraint key required to obtain the desired shear strength T _S , namely, the thickness t of the rotation restraint key and the distances b1 and b2 from the portion of the edge of the rotation restraint key near the boundary line between the box joint and the pin joint to the counterbore.

In the manufacturing method according to the present invention,
the rotation prevention key is substantially rectangular and has a box joint side edge portion entirely located on the box joint side, a pin joint side edge portion entirely located on the pin joint side, and two bearing edge portions spanning the box joint and the pin joint,
the rotation restraint key is arranged so that the box joint side edge portion and the pin joint side edge portion are parallel to the boundary line and the two bearing edge portions are parallel to the axis,
A fourth imaginary line is assumed to be parallel to the axis on the outer surface of the rotation prevention key;
The distance from the intersection of the fourth virtual line and the box joint side edge portion to the intersection of the fourth virtual line and the first virtual line is L1,
When the distance from the intersection of the fourth imaginary line and the pin joint side edge portion to the intersection of the fourth imaginary line and the first imaginary line is L2,
Calculating the bearing strength T _B1 of a first bearing portion located on the box joint side of each of the bearing edge portions using the following formula:
Calculating the bearing strength T _B2 of the second bearing portion located on the pin joint side of each of the bearing edge portions using the following formula:
Setting L1, L2 and t so that the bearing strength T _B1 and the bearing strength T _B2 are equal to or greater than predetermined threshold values;
adjusting at least one of L1 and L2 so that the shear strength T _S approaches one of the bearing strength T _B1 and the bearing strength T _B2 , which corresponds to the bearing strength of the region where the bolt mounting holes are not provided,
It is preferable to further consider at least one of the adjusted L1 and L2 when manufacturing the rotation restraint key, the box joint and the pin joint.

When rotational torque is transmitted through the rotation restraining key, the rotation restraining key is subjected to not only shear stress but also bearing stress. The rotation restraining key's overall strength against these stresses is determined by the minimum of the shear strength T _S against shear stress and the bearing strengths T _B1 and T _B2 against bearing stress. Therefore, the b1, b2, L1, L2, and t of the rotation restraining key are set so that the minimum of the shear strength T _S , bearing strength T _B1 , and bearing strength T _B2 is equal to or greater than a predetermined threshold value to achieve the desired overall strength. However, depending on the values of L1 and L2, the shear strength T _S may not match the bearing strength of the area without bolt mounting holes (either the bearing strength T _B1 or the bearing strength T _B2 ).

Here, adjustments to L1 and _L2 will be explained using an example in which a bolt mounting hole is provided in the area of the rotation prevention key on the pin joint side, and the shear strength T _S is the smallest value among the shear strength T _S , bearing strength T _B1 and bearing strength T B2.

As an example, L2 can be increased and L1 can be decreased so that the shear strength T _S increases and the bearing strength T _B1 decreases, or L2 can be increased without changing L1 so that the bearing strength T _B1 remains constant and the shear strength T _S increases. In this case, the overall strength of the rotation restraint key increases as the shear strength T _S , which is the minimum of the shear strength T _S , the bearing strength T _B1 , and the bearing strength T _B2 , increases. In other words, the above manufacturing method produces a rotation restraint key with a higher overall strength.

As another example, L1 can be reduced without changing L2 so that the shear strength T _S remains constant and the bearing strength T _B1 decreases. In this case, the height dimension of the rotation preventing key is reduced while the shear strength T _S , which is the minimum of the shear strength T _S , the bearing strength T _B1 , and the bearing strength T _B2 , is maintained. In other words, the above manufacturing method can produce a rotation preventing key that is smaller in size while maintaining the overall strength.

In the manufacturing method according to the present invention, it is preferable to adjust both L1 and L2 so that the sum of L1 and L2 is constant.

The manufacturing method described above allows for the production of a rotation prevention key with higher overall strength while maintaining the same height.

In the manufacturing method according to the present invention, it is preferable to adjust only one of L1 and L2.

With the above configuration, it is only necessary to adjust either L1 or L2, simplifying the settings for L1 and L2.

In the manufacturing method according to the present invention, it is preferable that the bolt mounting hole be provided in the area of the rotation prevention key on the pin joint side.

In this configuration, if L1 is adjusted to be smaller, the mating recess in the box joint where the rotation prevention key is attached will be positioned away from the groove on the inner surface of the box joint where the load transmission key is attached, which prevents the box joint and pin joint from coming loose. This increases the strength of the area between the mating recess and groove, making it less likely for cross-sectional damage to occur.

In the manufacturing method according to the present invention, it is preferable that the bolt mounting holes be positioned so that b1 = b2.

The above configuration is advantageous because it ensures uniform shear strength in the sections of the rotation prevention key located on both the left and right sides of the bolt mounting hole.

In order to achieve the above object, the steel pipe connecting device according to the present invention comprises:
A box joint and a pin joint that can be connected to each other so as to have the same axis;
a rotation prevention key that is attached to a fitting recess provided across both the outer peripheral surface of the box joint and the outer peripheral surface of the pin joint and that prevents relative rotation between the box joint and the pin joint around the axis;
a bolt that is inserted through a bolt mounting hole with a counterbore provided in one of the box joint side region and the pin joint side region of the rotation restraint key and threadedly engages with the box joint or the pin joint, thereby fixing the rotation restraint key in the fitting recess,
the rotation prevention key is substantially rectangular and has a box joint side edge portion entirely located on the box joint side, a pin joint side edge portion entirely located on the pin joint side, and two bearing edge portions spanning the box joint and the pin joint,
the rotation prevention key is arranged so that the box joint side edge portion and the pin joint side edge portion are parallel to the boundary line between the box joint and the pin joint in the fitting recess, and so that the two bearing edge portions are parallel to the axis,
On the outer surface of the rotation prevention key,
a first imaginary line that overlaps the boundary line;
a second imaginary line connecting one end of the first imaginary line and the center of the counterbore;
a third imaginary line connecting the other end of the first imaginary line and the center of the counterbore;
a fourth imaginary line parallel to the axis;
a distance from the one end of the first imaginary line to an intersection point between the second imaginary line and an edge of the counterbore is defined as b1;
a distance from the other end of the first imaginary line to an intersection point between the third imaginary line and an edge of the countersink is defined as b2;
The distance from the intersection of the fourth virtual line and the box joint side edge portion to the intersection of the fourth virtual line and the first virtual line is L1,
When the distance from the intersection of the fourth imaginary line and the pin joint side edge portion to the intersection of the fourth imaginary line and the first imaginary line is L2,
The shear strength T _S of the rotation prevention key is expressed by the following formula:
The bearing strength T _B1 of the first bearing portion located on the box joint side among the bearing edge portions is expressed by the following formula:
The bearing strength T _B2 of the second bearing portion located on the pin joint side of each of the bearing edge portions is expressed by the following formula:
where t is the thickness of the rotation restraint key, σ ₁ is the yield stress of the rotation restraint key, and k is a predetermined correction factor.
The shear strength T _S , the bearing strength T _B1 and the bearing strength T _B2 are equal to or greater than predetermined threshold values, and
L1, L2, b1, b2 and t are set so that the shear strength T _S is substantially equal to one of the bearing strength T _B1 and the bearing strength T _B2 , which corresponds to the bearing strength of the region where the bolt mounting holes are not provided.

The above configuration results in a steel pipe connection device equipped with a rotation prevention key that has higher overall strength.

1 is a partial cross-sectional view showing a steel pipe pile equipped with a steel pipe connecting device according to the present invention. FIG. FIG. 10 is a diagram schematically illustrating the strain distribution of a rotation prevention key. 10 is a graph showing the relationship between the engagement length of the rotation prevention key and the bearing strength of the rotation prevention key.

Embodiments of the steel pipe connecting device and the related evaluation and manufacturing methods of the present invention will be described below with reference to the drawings.

[Steel pipe connection device]
FIG. 1 shows a steel pipe pile 10 constructed by connecting the opposing ends of vertically adjacent steel pipes 11 using a steel pipe connecting device 12. The steel pipe connecting device 12 is equipped with a female box joint 13 welded to the lower end of the upper steel pipe 11A and a male pin joint 14 welded to the upper end of the lower steel pipe 11B. The upper steel pipe 11A and the lower steel pipe 11B can be connected to each other via the box joint 13 and the pin joint 14 so as to have the same axis X. Specifically, after inserting the pin joint 14 into the box joint 13, a load transmission key 15 incorporated in an inward groove 131 formed on the inner circumferential surface of the box joint 13 is pushed out by operating a set bolt 16 to a position spanning an outward groove 141 formed on the outer circumferential surface of the pin joint 14 so as to face the inward groove 131. This secures the upper steel pipe 11A and the lower steel pipe 11B in a non-detachable state.

As shown in Figure 2, a downward notch 17 is provided on the lower edge of the outer peripheral surface of the box joint 13. An upward notch 18 is provided on the upper edge of the outer peripheral surface of the pin joint 14 at a position corresponding to the downward notch 17. When the pin joint 14 is inserted into the box joint 13, the downward notch 17 and the upward notch 18 form a mating recess 19 that is generally rectangular in front view and cross-section.

The upper steel pipe 11A and the lower steel pipe 11B are prevented from rotating relative to each other around the axis X by fitting a rotation prevention key 20 into the fitting recess 19. The rotation prevention key 20 has a generally rectangular shape in front view and cross section, and includes a box joint side edge 201 located entirely on the box joint 13 side, a pin joint side edge 202 located entirely on the pin joint 14 side, and two support edges 203 that straddle the box joint 13 and pin joint 14. In this embodiment, the rotation prevention key 20 is positioned so that the box joint side edge 201 and the pin joint side edge 202 are parallel to the boundary line B between the box joint 13 and the pin joint 14 in the fitting recess 19, and the two support edges 203 are parallel to the axis X.

The rotation prevention key 20 is fixed in the mating recess 19 by a bolt 21. The rotation prevention key 20 is provided with a bolt mounting hole 22 having a through hole 221 through which the shank 211 of the bolt 21 is inserted and a counterbore 222 into which the head 212 of the bolt 21 is accommodated. In this embodiment, the bolt mounting hole 22 is provided in the area of the rotation prevention key 20 on the pin joint 14 side so that the rotation prevention key 20 can be fixed to the pin joint 14. The bolt 21 is threaded into a bolt hole 142 provided in an upward notch 18 provided in the pin joint 14.

[Evaluation of the resistance of the rotation prevention key]
In the steel pipe pile 10 configured as described above, when a rotational torque is applied to the upper steel pipe 11A, the downward notch 17 of the box joint 13 abuts against the first support portion 203A located on the box joint 13 side of the support edge portion 203 of one side of the rotation prevention key 20 (the right side in the example of Figure 2), thereby transmitting the rotational torque from the upper steel pipe 11A to the rotation prevention key 20 via the box joint 13; and the second support portion 203B located on the pin joint 14 side of the support edge portion 203 of the other side of the rotation prevention key 20 (the left side in the example of Figure 2) abuts against the upward notch 18 of the pin joint 14, thereby transmitting the rotational torque from the rotation prevention key 20 to the lower steel pipe 11B via the pin joint 14.

When rotational torque is transmitted through the rotation restraint key 20 as described above, compressive loads and shear loads are applied to the rotation restraint key 20, causing shear stress and bearing stress to act on the rotation restraint key 20. The overall strength _Ta of the rotation restraint key 20 against these stresses can be expressed, as an example, by the following equation (1):
Here, T _S is the shear strength, T _B1 is the bearing strength of the first bearing portion 203A, and T _B2 is the bearing strength of the second bearing portion 203B. D is the diameter of the steel pipe 11. N is the number of rotation restraint keys 20. γ _ex is an execution surcharge coefficient, which can be set to 1.5, for example. γ _s is a safety factor, which can be set to 1.7, for example.

Hereinafter, the methods for determining the bearing strength T _B1 , bearing strength T _B2 and shear strength T _S will be described.

<Shear strength T _S >
As described above, when rotational torque is transmitted through the rotation restraining key 20, shear stress acts on the rotation restraining key 20, and it is known that the magnitude of the shear resistance of the rotation restraining key 20 against this shear stress is determined mainly by the area of the surface on which the shear stress acts and the yield strength of the rotation restraining key 20. Therefore, in the past, it was assumed that the shear stress acts along a surface of the rotation restraining key 20 that is parallel to the boundary line B and at the same height as the boundary line B, and the formula for calculating the shear resistance T _S of the rotation restraining key 20 was defined as follows:
b: width of rotation restraining key 20 t: thickness of rotation restraining key 20 σ ₁ : yield stress of rotation restraining key

Incidentally, the inventors of the present application analyzed the strain distribution when a rotational torque was applied to the rotation prevention key 20 using a digital image correlation method, and obtained the strain distribution shown in Figure 3. As shown in Figure 3, a relatively large strain was generated from the portion of the bearing edge 203 near the boundary line B to the counterbore 222 of the bolt mounting hole 22. This shows that shear stress was acting from the portion of the bearing edge 203 near the boundary line B toward the counterbore 222. As such, there is a discrepancy between the area of the surface on which the shear stress actually acts and the area used in the conventional formula, and therefore it is thought that the shear strength T _S calculated using the conventional formula will differ to some extent from the actual value.

Therefore, the inventors of the present application have come up with a new definition of the calculation formula for shear strength T _S that takes into account the actual direction of shear stress, as follows:
That is, as shown in FIG.
a first imaginary line V1 on the outer surface of the rotation preventing key 20, which overlaps with the boundary line B between the box joint 13 and the pin joint 14 in the fitting recess 19;
a second imaginary line V2 connecting one end of the first imaginary line V1 and the center C of the counterbore 222;
A third imaginary line V3 is assumed to connect the other end of the first imaginary line V1 and the center C of the counterbore 222,
The distance from one end of the first imaginary line V1 to the intersection of the second imaginary line V2 and the edge of the counterbore 222 is defined as b1,
When the distance from the other end of the first imaginary line V1 to the intersection point between the third imaginary line V3 and the edge of the counterbore 222 is b2,
The shear strength T _S of the rotation preventing key 20 is calculated using the following formula (2).

In the above equation (2), instead of "b x t" in the conventional equation, "(b1 + b2) x t" is used, which represents an area closer to the area of the surface on which shear stress actually acts, as shown in Figure 3. Furthermore, the above equation (2) incorporates a correction coefficient k to bring the pre-correction numerical value closer to the actual numerical value. The correction coefficient k is set based on the correlation between the pre-correction numerical value and a numerical value obtained through experiments, etc. In this embodiment, k is set to 0.9, but this is not limited to this.

For verification purposes, Table 1 compares the shear strength _Ts obtained by the conventional formula, the above formula (2), and experiments for several samples of steel pipe connecting devices 12 having the above-described structure. In these samples, the bolt mounting holes 22 of the rotation prevention keys 20 are positioned so that b1 = b2. The t of the rotation prevention keys 20 was 13 mm in all cases, and _σ1 was 980 N/ ^mm2 in all cases.

In Table 1, the experimental values were obtained using the s.f. method. Specifically, the yield load is defined as the point where the slope of the load-displacement curve is one-third of the initial slope.

As can be seen from Table 1, for all samples, the values calculated using formula (2) of the present invention were closer to the experimental values than the values calculated using the conventional formula. In other words, formula (2) of the present invention makes it possible to more accurately evaluate the shear strength T _S of the rotation restraining key 20 used in the steel pipe connecting device 12 having the above-mentioned structure.

<Bearing pressure strength T _B1 , Bearing pressure strength T _B2 >
As described above, bearing stress acts on each bearing edge portion 203 of the rotation restraint key 20, and the magnitude of the bearing strength T _B1 of the first bearing portion 203A and the bearing strength T _B2 of the second bearing portion 203B against this bearing stress is determined mainly by the area of the surface on which the bearing stress acts and the yield strength of the rotation restraint key 20. Therefore, in the present invention, the bearing strength T _B1 and the bearing strength T _B2 are defined as follows:
That is, as shown in FIG.
A fourth imaginary line V4 is assumed to be parallel to the axis X on the outer surface of the rotation prevention key 20,
The distance from the intersection of the fourth imaginary line V4 and the box joint side edge 201 to the intersection of the fourth imaginary line V4 and the first imaginary line V1 (substantially the same as the engagement length of the rotation restraint key 20 with the box joint 13) is defined as L1,
When the distance from the intersection of the fourth imaginary line V4 and the pin joint side edge 202 to the intersection of the fourth imaginary line V4 and the first imaginary line V1 (substantially the same as the engagement length of the rotation restricting key 20 with the pin joint 14) is L2,
The bearing pressure strength T _B1 of the first bearing portion 203A located on the box joint 13 side of each bearing edge portion 203 is calculated using the following formula (3), and the bearing pressure strength T _B2 of the second bearing portion 203B located on the pin joint 14 side of each bearing edge portion 203 is calculated using the following formula (4).

[Method for manufacturing steel pipe connecting device]
In manufacturing the steel pipe connecting device, the overall strength _Ta of the rotation restraining key 20 must be equal to or greater than the expected rotation torque so that the rotation restraining key 20 can transmit the rotation torque without breaking.

In the above formula (1) for calculating the overall strength T _a , the threshold value for "min(T _S , T _B1 , T _B2 )" is determined according to the desired overall strength T _a , diameter D, number N, margin coefficient γ _ex and safety factor γ _s ; that is, the desired overall strength T _a can be obtained by setting the minimum value of the shear strength T _S , bearing strength T _B1 and bearing strength T _B2 to be equal to or greater than the threshold value. Note that setting the minimum value of the shear strength T _S , bearing strength T _B1 and bearing strength T _B2 to be equal to or greater than the threshold value means that all of the shear strength T _S , bearing strength T _B1 and bearing strength T _B2 are equal to or greater than the threshold value.

Therefore, in the manufacturing method of the present invention, the shear strength T _S , bearing strength T _B1 , and bearing strength T _B2 of rotation restraint key 20 are calculated using the above formulas (2), (3), and (4), and b1, b2, L1, L2, and t of rotation restraint key 20 are set so that shear strength _{T S} , bearing strength T _B1 , and bearing strength T _B2 are equal to or greater than thresholds determined according to the desired overall strength T a, etc. Then, rotation restraint key 20, box joint 13, and pin joint 14 are manufactured based on the set b1, b2, L1, L2, and t.

Furthermore, in the manufacturing method of the present invention, the L1 and L2 of the set rotation prevention key 20 may be adjusted as described below.

4 is a graph illustrating the change in bearing strength T _B1 according to the applied length L1, and the change in shear strength T _S and bearing strength T B2 according to the applied length L2, when the installation position of the bolt mounting hole 22 in the rotation prevention key ₂₀ is constant. In the example of FIG. 4, both the shear strength T _S and the bearing strength T _B2 increase as L2 increases, and when L2 is between 15 mm and 35 mm, the shear strength T _S is lower than the bearing strength T _B2 . On the other hand, the bearing strength T _B1 increases as L1 increases, and when L1 is 17.5 mm, the bearing strength T _B1 is equal to the shear strength T _S when L2 is 32.5 mm, and when L1 is 25 mm, the bearing strength _T B1 is equal to the bearing strength T _B2 when L2 is 25 mm.

As shown in Figure 4, depending on the set values of L1 and L2, the shear strength T _S and the bearing strength T _B1 of the area where the bolt mounting holes 22 are not provided (in this embodiment, the area on the box joint 13 side) may not match. In such cases, at least one of L1 and L2 is adjusted so that the two values approach each other.

Here, several examples of adjustment methods will be explained using the example where L1 and L2 are both set to 25 mm (i.e., rotation prevention keys 20 with a height of 50 mm are arranged symmetrically above and below the boundary line B) and the bearing strengths T _B1 and T _B2 are greater than the shear strength T _S. However, it goes without saying that the following methods can also be applied when L1 and L2 are set to other dimensions.

One method is to make L2 greater than 25 mm so that the shear strength T _S increases, and to make L1 less than 25 mm so that the bearing strength T _B1 decreases. By adjusting in this way, the shear strength T _S , which was the minimum value among the shear strength T S , the bearing strength T _B1 and the bearing strength T _B2 , increases, and therefore the total strength T _a of the rotation preventing key 20, which is determined according to "min(T _S , T _B1 , T _{B2 )} ," also increases.

In this method, adjustments may be made so that the sum of L1 and L2 remains constant, i.e., L1 is reduced by the amount that L2 is increased. In this case, the rotation restraint key 20 after adjustment is positioned closer to the pin joint 14 (asymmetrically positioned vertically relative to the boundary line B) while maintaining its height. This not only increases the overall strength T _a of the rotation restraint key 20, but also increases the cross-sectional area of the thin-walled portion of the box joint 13 between the downward notch 17 for installing the rotation restraint key 20 and the inward groove 131 for installing the load transmission key 15, making cross-sectional defects in the box joint 13 less likely to occur. Note that adjusting L1 and L2 so that the shear strength T _S and the bearing strength T _B1 are substantially equal (in the example of Figure 4, L1 is set to 17.5 mm and L2 is set to 32.5 mm) is more preferable because it maximizes "min(T _S , T _B1 , T _B2 )."

In another method, by reducing only L1 to less than 25 mm without changing L2, the bearing strength T _B1 is made closer to the shear strength T _S. In this case, although the height dimension of the rotation restraint key 20 after adjustment is reduced, "min(T _S , T _B1 , T _B2 )" does not decrease, so the total strength T _a remains the same as before adjustment. Therefore, with this method, the height dimension of the rotation restraint key 20 can be reduced without reducing the total strength T _a , thereby reducing production costs. Furthermore, even with this method, as described above, the cross-sectional area of the thin-walled portion between the downward notch 17 and the inward groove 131 increases, making it less likely that cross-sectional loss will occur in the box joint 13.

Conversely, by increasing only L2 beyond 25 mm without changing L1, the shear strength T _S may be adjusted to approach the bearing strength T _B1 . In this case, the shear strength T _S of the rotation restraint key 20 after adjustment increases from its minimum value, and the total strength T _a of the rotation restraint key 20, which is determined according to "min(T _S , T _B1 , T _B2 )," also increases.

The manufacturing method of the present invention takes into account at least one of the adjusted L1 and L2 when manufacturing the rotation prevention key 20, box joint 13, and pin joint 14.

The desired total strength _Ta of the rotation preventing key 20 can be determined, for example, according to the maximum rotation torque of the construction machine.

[Another embodiment]
(1) In the above-described embodiment, the method for evaluating the yield strength of the rotation restraint key 20 and the method for manufacturing the steel pipe connection device 12 were described using as an example a steel pipe connection device 12 in which the bolt mounting hole 22 is provided in the region of the rotation restraint key 20 on the pin joint 14 side, but the present invention is not limited to this. In the steel pipe connection device 12, the bolt mounting hole 22 may be provided in the region of the rotation restraint key 20 on the box joint 13 side. In this case, the bolt 21 for fixing the rotation restraint key 20 is threaded into a bolt mounting hole (not shown) provided in communication with both the box joint 13 and the pin joint 14, for example.

As described above, the method for evaluating the strength of the rotation prevention key 20 and the method for manufacturing the steel pipe connection device 12 can also be applied to the steel pipe connection device 12 of this embodiment. However, while the shear strength T _S calculated using the above formula (2) has a positive correlation with the bearing strength T _B2 in the previously described embodiment, in this embodiment it has a positive correlation with the bearing strength T _B1 . Since the region of the rotation prevention key 20 where the bolt mounting holes 22 are not provided is the region on the pin joint 14 side, in this embodiment, if the shear strength T _S does not match the bearing strength T _B2 of the region on the pin joint 14 side, at least one of L1 and L2 will be adjusted.

(2) In the above-described embodiment, the method for evaluating the strength of the rotation restraint key 20 and the method for manufacturing the steel pipe connection device 12 were described using the steel pipe connection device 12 in which the bolt mounting holes are located at positions where b1 = b2. However, the present invention is not limited to this. In the steel pipe connection device 12, the bolt mounting holes 22 may be located at positions where b1 < b2 or b1 > b2. In this case, the value of (b1 + b2) may differ from that in the above-described embodiment, and therefore the shear strength T _S calculated using the above formula (2) may also differ from that in the above-described embodiment. However, since the correlation between the bearing strength T _B1 and the bearing strength T _B2 with respect to the shear strength T _S is the same as that shown in FIG. 4 , the method for evaluating the strength of the rotation restraint key 20 and the method for manufacturing the steel pipe connection device 12 can be applied to the steel pipe connection device 12 of this embodiment as well.

DESCRIPTION OF SYMBOLS 10: Steel pipe pile 11, 11A, 11B: Steel pipe 12: Steel pipe connecting device 13: Box joint 131: Inward groove portion 14: Pin joint 141: Outward groove portion 142: Bolt hole 15: Load transmission key 16: Set bolt 17: Downward notch portion 18: Upward notch portion 19: Fitting recess 20: Rotation suppression key 201: Box joint side edge portion 202: Pin joint side edge portion 203: Bearing edge portion 203A: First bearing portion 203B: Second bearing portion 21: Bolt 211: Shank portion 212: Head portion 22: Bolt mounting hole 221: Through hole 222: Counterbore B: Boundary line C: Center V1: First virtual line V2: Second virtual line V3: Third virtual line V4 : Fourth imaginary line X : Axis center

Claims (8)

A box joint and a pin joint that can be connected to each other so as to have the same axis;
a rotation prevention key that is attached to a fitting recess provided across both the outer peripheral surface of the box joint and the outer peripheral surface of the pin joint and that prevents relative rotation between the box joint and the pin joint around the axis;
A method for evaluating the shear strength of a rotation restraint key in a steel pipe connecting device, the method comprising: inserting a bolt mounting hole with a counterbore provided in either a region of the rotation restraint key on the box joint side or a region of the pin joint side of the rotation restraint key, screwing the bolt into the box joint or the pin joint, and fixing the rotation restraint key in the fitting recess;
On the outer surface of the rotation prevention key,
a first imaginary line overlapping a boundary line between the box joint and the pin joint in the fitting recess;
a second imaginary line connecting one end of the first imaginary line and the center of the counterbore;
A third imaginary line is assumed to connect the other end of the first imaginary line and the center of the counterbore;
a distance from the one end of the first imaginary line to an intersection point between the second imaginary line and an edge of the counterbore is defined as b1;
When the distance from the other end of the first imaginary line to the intersection point between the third imaginary line and the edge of the countersink is b2,
An evaluation method including calculating the shear strength T _S of the rotation restraint key using the following formula.
(where t is the thickness of the rotation restraint key, σ ₁ is the yield stress of the rotation restraint key, and k is a predetermined correction factor.) A box joint and a pin joint that can be connected to each other so as to have the same axis;
a rotation prevention key that is attached to a fitting recess provided across both the outer peripheral surface of the box joint and the outer peripheral surface of the pin joint and that prevents relative rotation between the box joint and the pin joint around the axis;
A method for manufacturing a steel pipe connecting device comprising: a bolt that is inserted through a countersunk bolt mounting hole provided in either the box joint side region or the pin joint side region of the rotation restraint key and threadedly engages with the box joint or the pin joint, and fixes the rotation restraint key in the fitting recess,
On the outer surface of the rotation prevention key,
a first imaginary line overlapping a boundary line between the box joint and the pin joint in the fitting recess;
a second imaginary line connecting one end of the first imaginary line and the center of the counterbore;
A third imaginary line is assumed to connect the other end of the first imaginary line and the center of the counterbore;
a distance from the one end of the first imaginary line to an intersection point between the second imaginary line and an edge of the counterbore is defined as b1;
When the distance from the other end of the first imaginary line to the intersection point between the third imaginary line and the edge of the countersink is b2,
Calculating the shear strength T _S of the rotation restraint key using the following formula:
(where t is the thickness of the rotation restraint key, σ ₁ is the yield stress of the rotation restraint key, and k is a predetermined correction factor.)
Setting b1, b2 and t so that the shear strength T _S is equal to or greater than a predetermined threshold value;
and manufacturing the rotation restraining key, the box joint, and the pin joint based on the set b1, b2, and t. the rotation prevention key is substantially rectangular and has a box joint side edge portion entirely located on the box joint side, a pin joint side edge portion entirely located on the pin joint side, and two bearing edge portions spanning the box joint and the pin joint,
the rotation restraint key is arranged so that the box joint side edge portion and the pin joint side edge portion are parallel to the boundary line and the two bearing edge portions are parallel to the axis,
A fourth imaginary line is assumed to be parallel to the axis on the outer surface of the rotation prevention key;
The distance from the intersection of the fourth virtual line and the box joint side edge portion to the intersection of the fourth virtual line and the first virtual line is L1,
When the distance from the intersection of the fourth imaginary line and the pin joint side edge portion to the intersection of the fourth imaginary line and the first imaginary line is L2,
Calculating the bearing strength T _B1 of a first bearing portion located on the box joint side of each of the bearing edge portions using the following formula:
Calculating the bearing strength T _B2 of the second bearing portion located on the pin joint side of each of the bearing edge portions using the following formula:
Setting L1, L2 and t so that the bearing strength T _B1 and the bearing strength T _B2 are equal to or greater than predetermined threshold values;
adjusting at least one of L1 and L2 so that the shear strength T _S approaches one of the bearing strength T _B1 and the bearing strength T _B2 , which corresponds to the bearing strength of the region where the bolt mounting holes are not provided,
The manufacturing method according to claim 2 , further taking into consideration at least one of the adjusted L1 and L2 when manufacturing the rotation restraint key, the box joint, and the pin joint. The manufacturing method described in claim 3, wherein both L1 and L2 are adjusted so that the sum of L1 and L2 is constant. The manufacturing method described in claim 3, wherein only one of L1 and L2 is adjusted during the adjustment. The manufacturing method described in any one of claims 2 to 5, wherein the bolt mounting hole is provided in the area of the rotation prevention key on the pin joint side. The manufacturing method described in any one of claims 2 to 5, wherein the bolt mounting holes are located at positions where b1 = b2. A box joint and a pin joint that can be connected to each other so as to have the same axis;
a rotation prevention key that is attached to a fitting recess provided across both the outer peripheral surface of the box joint and the outer peripheral surface of the pin joint and that prevents relative rotation between the box joint and the pin joint around the axis;
A steel pipe connecting device comprising: a bolt that is inserted through a countersunk bolt mounting hole provided in either the box joint side region or the pin joint side region of the rotation restraint key and threadedly engages with the box joint or the pin joint, and fixes the rotation restraint key in the fitting recess,
the rotation prevention key is substantially rectangular and has a box joint side edge portion entirely located on the box joint side, a pin joint side edge portion entirely located on the pin joint side, and two bearing edge portions spanning the box joint and the pin joint,
the rotation prevention key is arranged so that the box joint side edge portion and the pin joint side edge portion are parallel to the boundary line between the box joint and the pin joint in the fitting recess, and so that the two bearing edge portions are parallel to the axis,
On the outer surface of the rotation prevention key,
a first imaginary line that overlaps the boundary line;
a second imaginary line connecting one end of the first imaginary line and the center of the counterbore;
a third imaginary line connecting the other end of the first imaginary line and the center of the counterbore;
a fourth imaginary line parallel to the axis;
a distance from the one end of the first imaginary line to an intersection point between the second imaginary line and an edge of the counterbore is defined as b1;
a distance from the other end of the first imaginary line to an intersection point between the third imaginary line and an edge of the countersink is defined as b2;
The distance from the intersection of the fourth virtual line and the box joint side edge portion to the intersection of the fourth virtual line and the first virtual line is L1,
When the distance from the intersection of the fourth imaginary line and the pin joint side edge portion to the intersection of the fourth imaginary line and the first imaginary line is L2,
The shear strength T _S of the rotation prevention key is expressed by the following formula:
The bearing strength T _B1 of the first bearing portion located on the box joint side among the bearing edge portions is expressed by the following formula:
The bearing strength T _B2 of the second bearing portion located on the pin joint side of each of the bearing edge portions is expressed by the following formula:
where t is the thickness of the rotation restraint key, σ ₁ is the yield stress of the rotation restraint key, and k is a predetermined correction factor.
The shear strength T _S , the bearing strength T _B1 and the bearing strength T _B2 are equal to or greater than predetermined threshold values, and
L1, L2, b1, b2 and t are set so that the shear strength T _S is substantially equal to one of the bearing strength T _B1 and the bearing strength T _B2 , which corresponds to the bearing strength of the region where the bolt mounting holes are not provided. A steel pipe connecting device.