JP7775149B2 - Hat-shaped steel sheet pile - Google Patents

Description

The present invention relates to hat-shaped steel sheet piles.

Hat-shaped steel sheet piles are widely used in civil engineering and construction work, driving them underground to build walls for earth retaining and watertight construction. For this reason, emphasis has traditionally been placed on the bending performance of the walls. Furthermore, to improve economy, i.e., to reduce the weight of walls, there is a trend toward wider and thinner hat-shaped steel sheet pile cross sections.

Meanwhile, as the performance and economy of hat-shaped steel sheet piles have improved, peripheral technological developments have been made, and the range of applications and uses have expanded. One example of peripheral technological development is the increase in the size of construction heavy machinery. The increase in size of construction heavy machinery aims to enable construction in harder or deeper strata, for example, and to improve construction efficiency. As construction heavy machinery increases in size in this way, not only are bending stresses applied to hat-shaped steel sheet piles after they are driven, but large axial forces also act on them during construction.

In addition, efforts are being made to expand the scope of application of hat-shaped steel sheet piles. Specifically, for example, in addition to conventional wall structures, hat-shaped steel sheet piles are increasingly being used as foundations. For example, Patent Document 1 describes technology for using steel sheet piles as foundation structures. Patent Document 2 describes technology for improving the performance of hat-shaped steel sheet piles when used as foundations by providing a blocking section only at the tip of the hat-shaped steel sheet pile to increase bearing capacity. In this way, when hat-shaped steel sheet piles are used as foundations to bear bearing capacity, there is a demand for improved performance of the hat-shaped steel sheet pile as an axial force member.

Generally, consideration must be given to buckling in axial force members. In particular, with cross sections composed of thin-walled plate materials such as hat-shaped steel sheet piles, sufficient attention must be paid to local buckling, especially in buckling. From this perspective, Patent Document 3 proposes a technology for improving the buckling strength of hat-shaped steel sheet piles by forming bent portions at the corners of the cross section. Considering the trend toward wider and thinner hat-shaped steel sheet pile cross sections as mentioned above, it is thought that improving the buckling strength of hat-shaped steel sheet piles against axial force will become increasingly necessary in the future.

Patent No. 3832845 Patent No. 4916932 Patent No. 4088041

However, while the technology described in Patent Document 3 is efficient when viewing hat-shaped steel sheet piles as axial force members, it reduces the amount of steel in the web portion, which may result in a decline in the bending performance of the wall, which is the performance originally expected of hat-shaped steel sheet piles. Furthermore, because the cross-sectional shape becomes more complex, highly advanced technology is required in the rolling manufacturing process, and it is difficult to improve manufacturing efficiency. Considering these points, it is desirable to improve the buckling strength against axial force while maintaining the basic cross-sectional shape of a hat-shaped steel sheet pile, which consists of a web, flange, and arm.

The present invention therefore aims to provide a new and improved hat-shaped steel sheet pile that can improve buckling resistance against axial force while maintaining the basic cross-sectional shape of the hat-shaped steel sheet pile.

According to one aspect of the present invention, a hat-shaped steel sheet pile includes, in a cross section perpendicular to the longitudinal direction, a web extending along the width direction on a first side in a cross-sectional height direction, a pair of flanges extending from both ends of the web in the width direction to both sides in the width direction and toward a second side in the cross-sectional height direction and forming a flange angle θ (θ≦70°) with the width direction, a pair of arms extending from each end of the pair of flanges on the second side in the cross-sectional height direction along the width direction and toward both sides in the width direction, and a pair of fitting joints formed at each end of the pair of arms opposite to the pair of flanges. The ratio of the total length of the web, the pair of flanges, and the pair of arms in the cross section to the average plate thickness of the web, the pair of flanges, and the pair of arms is 120 or more, the effective width B and effective height h in the cross section, and the flange angle θ satisfy the condition of the following formula (i) using a constant C (1.01≦C≦1.13) when the plate thickness ratio of the flange to the web is in the range of 0.6 or more and 1.0 or less, and the effective width B, the web length Bw in the cross section, the cross-sectional height H, and the flange angle θ satisfy the relationship B−Bw−2H/tan θ>0.

According to another aspect of the present invention, a hat-shaped steel sheet pile comprises, in a cross section perpendicular to the longitudinal direction, a web extending along the width direction on a first side in a cross-sectional height direction, a pair of flanges extending from both ends of the web in the width direction to both sides in the width direction and toward a second side in the cross-sectional height direction and forming a flange angle θ (θ≦70°) with the width direction, a pair of arms extending from each end of the pair of flanges on the second side in the cross-sectional height direction along the width direction and toward both sides in the width direction, and a pair of fitting joints formed at each end of the pair of arms opposite to the pair of flanges, wherein a ratio of a total length of the web, the pair of flanges, and the pair of arms in the cross section to an average plate thickness of the web, the pair of flanges, and the pair of arms is 120 or more. The effective width B and effective height h in the cross section, and the flange angle θ satisfy the condition of the following formula (i) using a constant C (1.03≦C≦1.13) when the plate thickness ratio of the flange to the web is in the range of 0.7 or more and 1.0 or less, and the effective width B, the web length Bw in the cross section, the cross-sectional height H, and the flange angle θ satisfy the relationship B−Bw−2H/tan θ>0.

The above configuration makes it possible to improve the buckling strength against axial force while maintaining the basic cross-sectional shape of the hat-shaped steel sheet pile.

FIG. 1 is a cross-sectional view of a hat-shaped steel sheet pile according to an embodiment of the present invention. 1 is a graph showing the relationship between the converted width-thickness ratio and the web width-thickness ratio in a conventional steel sheet pile product. FIG. 1 is a diagram schematically showing a cross-sectional shape of a hat-shaped steel sheet pile in a first study example. 10 is a graph showing the results of a buckling strength analysis in the first study example. 5 is a graph showing local buckling strength based on the results shown in FIG. 4. 10 is a graph showing the local buckling strength based on the results of the buckling strength analysis in the second study example. 10 is a graph showing the relationship between flange angle and aspect ratio in the third study example. 10 is a graph showing the relationship between the flange angle and the aspect ratio in the fourth study example, together with a part of the third study example. 10 is a graph showing the relationship between the flange angle and the aspect ratio in the third and fourth study examples, together with an approximate curve of the correlation for each plate thickness ratio. 10 is a graph showing the relationship between the flange angle and the aspect ratio in the third and fourth study examples, together with an approximate curve of the correlation for each plate thickness ratio.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in this specification and drawings, components that have substantially the same functional configuration will be assigned the same reference numerals, and redundant explanations will be omitted.

Figure 1 is a cross-sectional view of a hat-shaped steel sheet pile according to one embodiment of the present invention. As shown in Figure 1, the hat-shaped steel sheet pile 1 includes, in a cross section perpendicular to the longitudinal direction (z direction in the figure), a web 2 extending along the width direction (x direction in the figure) on a first side in the cross-sectional height direction (the rear side in the y direction in the figure); flanges 3A and 3B extending from both width direction ends of the web 2 to both sides in the width direction and toward a second side in the cross-sectional height direction (the front side in the y direction in the figure) and forming a flange angle θ (acute angle side) with the width direction; arms 4A and 4B extending along the width direction from the respective ends of the flanges 3A and 3B on the second side in the cross-sectional height direction and toward both sides in the width direction; and fitting joints 5A and 5B formed at the ends of the arms 4A and 4B opposite the flanges 3A and 3B.

1 shows the dimensions of each part of the hat-shaped steel sheet pile 1, specifically, the length Bw and thickness tw of the web 2, the length Bf and thickness tf of the flanges 3A and 3B, and the length Ba and thickness ta of the arms 4A and 4B. Here, the length Bw is the distance between two intersections formed between the thickness centerline of the web 2 and the thickness centerlines of the flanges 3A and 3B. Similarly, the length Bf is the distance between two intersections formed between the thickness centerline of the flange 3A and the thickness centerlines of the web 2 and the arm 4A. Furthermore, the length Ba is the distance between the intersection between the thickness centerline of the arm 4A and the thickness centerline of the flange 3A and the fitting center _EA of the fitting joint 5A. Note that the cross-sectional shape of the hat-shaped steel sheet pile 1 is symmetrical about the neutral axis in the width direction (the y-axis in the figure), so the flange 3B also has the length Bf, just like the flange 3A, and the arm 4B also has the length Ba, just like the arm 4A.

1 also shows the effective width B, cross-sectional height H, and effective height h of the hat-shaped steel sheet pile 1. Here, the effective width B is the distance between the fitting centers E _A and E _B of the fitting joints 5A and 5B. The cross-sectional height H is the height of the cross section of the hat-shaped steel sheet pile 1, including the plate thicknesses of the web 2 and arms 4A and 4B but not the overhangs of the fitting joints 5A and 5B. The effective height h is the cross-sectional height H minus half the plate thicknesses of the web 2 and arms 4A and 4B, i.e., h = H - (tw/2 + ta/2). When the shape of the hat-shaped steel sheet pile 1 shown in FIG. 1 is geometrically valid, the overall width B, web length Bw, cross-sectional height H, and flange angle θ satisfy the relationship B - Bw - 2H/tanθ > 0.

Here, for the hat-type steel sheet pile 1 according to this embodiment, the ratio B _TTL /t _AVE of the total length B _TTL to the average plate thickness t _AVE is defined as the "equivalent width-thickness ratio." As will be described later, in the hat-type steel sheet pile 1, the equivalent width-thickness ratio B _TTL /t _AVE is 120 or more, and the effective width B and effective height h in the cross section, and the flange angle θ satisfy a predetermined relationship. Here, the total length B _TTL is the sum of the lengths of the web 2, flanges 3A and 3B, and arms 4A and 4B, and is calculated by the following formula (1). The average plate thickness t _AVE is the average of the plate thicknesses of the web 2, flanges 3A and 3B, and arms 4A and 4B, and is calculated by the following formula (2).

Figure 2 is a graph showing the relationship between the converted width-thickness ratio and the web width-thickness ratio (Bw/tw) of conventional steel sheet pile products. The inventors have studied ways to improve the buckling strength against axial force while maintaining the basic cross-sectional shape of hat-shaped steel sheet piles. However, as already mentioned, this issue becomes more apparent as the cross-section of hat-shaped steel sheet piles tends to become wider and thinner. Therefore, it is reasonable to consider hat-shaped steel sheet piles that are wider or thinner than currently known hat-shaped steel sheet piles. Here, as shown in Figure 2, steel sheet piles with an converted width-thickness ratio of 120 or more have not yet been industrially realized, not only for hat-shaped steel sheet piles but also for U-shaped steel sheet piles. Therefore, the following study focuses on hat-shaped steel sheet piles with an converted width-thickness ratio of 120 or more that are wider or thinner than conventional steel sheet pile products.

In the study, buckling strength analysis (eigenvalue analysis based on elastic theory) was performed on hat-shaped steel sheet piles with an equivalent width-thickness ratio of 120 or more for various cross-sectional shapes, with changes in effective width, cross-sectional height, and plate thickness. After identifying the local buckling mode, the relationship between the buckling strength of the hat-shaped steel sheet piles and the representative elements of the cross-sectional shape was analyzed. As a result, the following findings were made.

(First study example)
First, the effective width B of the hat-shaped steel sheet pile 1 was set to 1,350 mm, and the web thickness tw, flange thickness tf, and arm thickness ta were all set to 9.0 mm. Under these conditions, multiple cross-sectional shapes were set so that the moment of inertia per meter of wall width of the steel sheet pile wall, formed by fitting multiple hat-shaped steel sheet piles 1 together with fitting joints 5A and 5B and connecting them in the width direction, would be approximately 10,000 ^cm4 /m. The effective height h (mm) and flange angle θ (degrees) of the set cross-sectional shapes are shown in Table 1, and each cross-sectional shape is schematically shown in Figure 3.

As shown in Table 1 and Figure 3, if the magnitude of the moment of inertia per meter of wall width is maintained, the effective height h increases as the flange angle θ decreases. This is because the decrease in the moment of inertia caused by a smaller flange angle θ must be compensated for by increasing the effective height h.

Figure 4 is a graph showing the results of the buckling strength analysis for the first study example. In Figure 4, the horizontal axis represents the length (longitudinal dimension) of the hat-shaped steel sheet pile, and the vertical axis represents the buckling strength of the hat-shaped steel sheet pile (elastic analysis results). In the graph in Figure 4, it can be seen that a local buckling mode occurs at the location indicated by arrow (1), resulting in a decrease in strength. In this study, the strength in this local buckling mode (local buckling strength) was treated as the result, and the local buckling strength for each cross-sectional shape was compared. Note that arrow (2) in the graph in Figure 4 indicates that the results for Example 1 (θ = 70°), Example 2 (θ = 60°), ..., Example 9 (θ = 29°) are shown at the intersection of the arrows, in order from top to bottom.

Figure 5 is a graph showing the local buckling strength based on the results shown in Figure 4. In Figure 5, the horizontal axis represents the flange angle θ for each cross-sectional shape, and the vertical axis represents the local buckling strength. The graph in Figure 5 shows that the local buckling strength increases rapidly as the flange angle θ increases from a small value, but then reaches a maximum at a certain angle and gradually decreases as the flange angle θ increases. In the example shown in Figure 5, the optimal flange angle θ at which the local buckling strength is thought to reach a maximum is 33.5°. These results suggest that the flange angle θ significantly contributes to suppressing out-of-plane deformation associated with local buckling at each portion of the hat-shaped steel sheet pile 1 (web 2, flanges 3A and 3B, and arms 4A and 4B). In other words, based on the above results, in the cross-sectional design of the hat-shaped steel sheet pile 1, an optimal solution that maximizes the local buckling strength can be obtained by appropriately determining the flange angle θ and further determining the effective height h in accordance with the relationship between the flange angle θ and the moment of inertia.

(Second study example)
Next, the effective width B of the hat-shaped steel sheet pile 1 remained at 1,350 mm, and the plate thickness was set to 10.0 mm for the web plate thickness tw and arm plate thickness ta, and 8.0 mm for the flange plate thickness tf. Under these conditions, several cross-sectional shapes were set so that the moment of inertia per 1 m of wall width of the steel sheet pile wall would be approximately 10,000 ^cm4 /m. The effective height h (mm) and flange angle θ (deg) of the set cross-sectional shapes are shown in Table 2.

Figure 6 is a graph showing the local buckling strength based on the results of the buckling strength analysis for the second study example. As with Figure 5, the graph in Figure 6 also shows that the local buckling strength varies, reaching a maximum value with respect to the flange angle θ. In the example shown in Figure 6, the optimal flange angle θ at which the local buckling strength is thought to reach a maximum value is 35.7°. According to the results shown in Figures 5 and 6, even when the plate thickness, which is a factor that has a significant impact on local buckling, is changed, an optimal solution that maximizes the local buckling strength can be obtained using the flange angle θ and the effective height h, which is determined by the relationship between the flange angle θ and the moment of inertia.

(Third Study Example)
Next, multiple cross-sectional shapes were set so that the moment of inertia per meter of wall width of the steel sheet pile wall would be approximately 9,000 cm ⁴ /m (9,000 class) to approximately 55,000 cm ⁴ /m (55,000 class) for each of the effective widths B of the hat-shaped steel sheet pile 1 of 1,100 mm, 1,300 mm, and 1,500 mm. The effective width B (mm), effective height h (mm), web thickness tw (mm), aspect ratio B/h, flange angle θ (degrees), and class of moment of inertia of the set cross-sectional shapes are shown in Tables 3 to 5.

In the example shown in Table 3, the web thickness tw and arm thickness ta are all 9.0 mm, but the flange thickness tf is thinned to 6.3 mm (the flange to web thickness ratio is 0.7). In the example shown in Table 4, the web thickness tw, flange thickness tf, and arm thickness ta are all 9.0 mm (the flange to web thickness ratio is 1.0). In the example shown in Table 5, the web thickness tw and arm thickness ta are all 12.5 mm, but the flange thickness tf is 7.5 mm (the flange to web thickness ratio is 0.6). For each example in Tables 3 to 5, a buckling strength analysis similar to the examples shown in Figures 4 to 6 was performed on the cross-sectional shape, and the optimal flange angle θ and corresponding effective height h were determined to maximize the local buckling strength.

Figure 7 is a graph showing the relationship between flange angle and aspect ratio in the third study example. In the graph in Figure 7, it can be seen that there is a correlation between the flange angle θ and the aspect ratio B/h of the hat-shaped steel sheet pile 1 that is independent of the effective width B or the moment of inertia of area when the plate thickness ratio is 1.0, 0.7, and 0.6.

(Fourth Study Example)
Next, the plate thickness was increased within a range in which the converted width-thickness ratio was 120 or more, with the same effective width B as in the third study example. The effective width B (mm), effective height h (mm), web plate thickness tw (mm), aspect ratio B/h, flange angle θ (degrees), and area second moment class of the cross-sectional shape set in this example are shown in Table 6.

In the examples shown in Table 6, the plate thickness ratio is 0.7. That is, in each example, the web plate thickness tw and the arm plate thickness ta are equal, and the flange plate thickness tf is 0.7 times the web plate thickness tw. For each example in Table 6, a buckling strength analysis was performed on the cross-sectional shape in the same way as for the examples shown in Figures 4 to 6, and the results determined the optimal flange angle θ and corresponding effective height h that are believed to maximize the local buckling strength.

Figure 8 is a graph showing the relationship between flange angle and aspect ratio in the fourth study example, along with a portion of the third study example (an example with a plate thickness ratio of 0.7 shown in Table 3). The graph in Figure 8 also shows that there is a correlation between the flange angle θ and the aspect ratio B/h of the hat-shaped steel sheet pile 1 that is independent of the effective width B or the moment of inertia. Furthermore, the graph in Figure 8 shows that, even if the web plate thickness tw is different, in each example with a common plate thickness ratio (0.7), the flange angle θ and the aspect ratio B/h show a correlation on a roughly common curve.

(Summary of the study examples)
9 and 10 are graphs showing the relationship between the flange angle and the aspect ratio in the third and fourth study examples, along with an approximation curve of the correlation for each thickness ratio. As described above, considering economic considerations and constraints such as manufacturing facilities, the thickness ratio of the hat-type steel sheet pile 1 can realistically range from approximately 0.6 to 1.0. However, the third and fourth study examples include the upper and lower limits of this thickness ratio range. Therefore, the conditions available for realistic design of the hat-type steel sheet pile 1 can be expressed by the following formula (3) using a constant C based on the two approximation curves shown in the graphs of FIGS. 9 and 10 . Here, FIG. 9 shows the case where the thickness ratio of the hat-type steel sheet pile 1 is in the range of 0.6 to 1.0, and the range of constant C is 1.01≦C≦1.13. On the other hand, FIG. 10 shows the case where the thickness ratio of the hat-type steel sheet pile 1 is in the range of 0.7 to 1.0, and the range of constant C is 1.03≦C≦1.13.

The cross-sectional shape of an actual hat-shaped steel sheet pile is not determined solely by considering the buckling strength against axial force; for example, the effective width and effective height are significantly affected by manufacturing constraints. Furthermore, the effective height of a hat-shaped steel sheet pile must be set so that the moment of inertia required for the wall design is obtained. From an economic standpoint, it is desirable to make the web and arm thicknesses thicker than the flange thickness, i.e., to make the thickness ratio mentioned above smaller than 1.0, but the range of achievable thickness ratios is limited by the constraints of manufacturing equipment and the technological level.

In contrast, the correlation between the optimal flange angle and aspect ratio that maximizes the local buckling strength found in the above study examples does not depend on the effective width or moment of inertia of the hat-shaped steel sheet pile, as shown in the third study example. Furthermore, as shown in the fourth study example, although the above correlation is affected by the plate thickness ratio, the absolute value of the plate thickness has little effect. In other words, according to the results of the above study, the cross-sectional shape conditions that maximize the local buckling strength are specified by the flange angle θ and two dimensionless quantities (the aspect ratio B/h and the plate thickness ratio tf/tw). By utilizing these conditions, it is possible to design a cross-sectional shape that maximizes the local buckling strength, taking into account the constraints of the manufacturing equipment and the required moment of inertia, etc.

The above describes in detail preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to such examples. It is clear that a person with ordinary skill in the technical field to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

1... hat-shaped steel sheet pile, 2... web, 3A, 3B... flanges, 4A, 4B... arms, 5A, 5B... fitting joints, E _A , E _B ... fitting centers.

Claims (2)

A hat-shaped steel sheet pile,
In a cross section perpendicular to the longitudinal direction, the cross section comprises: a web extending along the width direction on a first side in a cross-sectional height direction; a pair of flanges extending from both ends of the web in the width direction to both sides in the width direction and toward a second side in the cross-sectional height direction, the flanges forming a flange angle θ (θ≦70°) with the width direction; a pair of arms extending from each end of the pair of flanges on the second side in the cross-sectional height direction along the width direction and toward both sides in the width direction; and a pair of fitting joints formed at each end of the pair of arms opposite the pair of flanges,
a ratio of a total length of the web, the pair of flanges, and the pair of arms in the cross section to an average plate thickness of the web, the pair of flanges, and the pair of arms is 120 or more;
The effective width B and effective height h in the cross section, and the flange angle θ satisfy the condition of the following formula (i) using a constant C (1.01≦C≦1.13) in a range where the plate thickness ratio of the flange to the web is 0.6 or more and 1.0 or less, and the effective width B, the web length Bw in the cross section, the cross-sectional height H, and the flange angle θ satisfy the relationship of B−Bw−2H/tan θ>0,
A hat-shaped steel sheet pile that does not include a joint in the cross section.
A hat-shaped steel sheet pile,
In a cross section perpendicular to the longitudinal direction, the cross section comprises: a web extending along the width direction on a first side in a cross-sectional height direction; a pair of flanges extending from both ends of the web in the width direction to both sides in the width direction and toward a second side in the cross-sectional height direction, the flanges forming a flange angle θ (θ≦70°) with the width direction; a pair of arms extending from each end of the pair of flanges on the second side in the cross-sectional height direction along the width direction and toward both sides in the width direction; and a pair of fitting joints formed at each end of the pair of arms opposite the pair of flanges,
a ratio of a total length of the web, the pair of flanges, and the pair of arms in the cross section to an average plate thickness of the web, the pair of flanges, and the pair of arms is 120 or more;
The effective width B and effective height h in the cross section, and the flange angle θ satisfy the condition of the following formula (i) using a constant C (1.03≦C≦1.13) in a range where the plate thickness ratio of the flange to the web is 0.7 or more and 1.0 or less, and the effective width B, the web length Bw in the cross section, the cross-sectional height H, and the flange angle θ satisfy the relationship of B−Bw−2H/tan θ>0,
A hat-shaped steel sheet pile that does not include a joint in the cross section.