EP1793044A1 - Hot rolled low profile steel sheet pile - Google Patents

Abstract

Hot-rolled flat section steel sheet pile (10) has a straight bar (12) restricted at each longitudinal side by locking strip (14). The bar has a rolled-in taper designed in such a manner that the bar is plastically deformed in area of taper before malfunctioning of locking connection in a tensile test of two sample pieces from sheet pile are connected by means of locking strip.

Description

Technical area

The present invention relates to a hot rolled flat profile steel sheet pile, especially for the construction of cellular cofferdams.

State of the art

The first hot-rolled flat-profile steel sheet piles, also referred to below as flat sheet piles, were already in use at the end of the 19th century in the USA. In Europe, these flat sheet piles have been rolled since the thirties of the 20th century. They comprise a horizontal wall lying straight web, which is bounded on each longitudinal side in each case by a lock strip. By means of these lock strips, the individual flat sheet piles can be connected to a continuous sheet pile wall.

Flat sheet piles are used especially for the construction of cellular cofferdams without internal anchorage. Depending on the shape of the cells, a distinction is made between circular or flat-cell dams. In the US, so-called "open cells" are also being used (see eg US Pat. No. 6,715,964 ). These closed and open cells are designed in such a way that the loads resulting from the filling and the water overpressure stress the flat sheet piles only in the direction of the horizontal wall axis.

In sizing the flat sheet piles for such cell capture dams, the stress (e.g., the hoop tensile force determined by the "kettle formula") is contrasted with the screed resistance. This results according to the EN 1993-5, as the minimum of a failure in the castle and a flow in the bridge.

wobei:

• f_y = der Rechenwert der Fließgrenze;
• t = die Stegdicke;
• R = die vom Hersteller gewährleistete Mindestschlosszugfestigkeit (z.B. R = 5500 kN/m);
• S₁ = ein Sicherheitsbeiwert für das Fließen im Steg;
• S₂ = ein Sicherheitsbeiwert für das Versagen im Schloss;

wobei die Sicherheitsbeiwerte unterschiedlich sind für beide Versagensarten, z.B.:

• S₁ = 1,0 (Fließen im Steg);
• S₂ = 1,25 (Versagen im Schloss).

However, the steel grade for the profile is traditionally chosen by the manufacturer in such a way that the following condition is met: $$\left({\mathrm{f}}_{\mathrm{y}}\mathrm{,}\mathrm{t}\right)\mathrm{/}{\mathrm{S}}_{\mathrm{1}}\mathrm{>}\mathrm{R}\mathrm{/}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_{\mathrm{2}}\mathrm{\Rightarrow }{\mathrm{f}}_{\mathrm{y}}\mathrm{>}\left(\mathrm{R}\mathrm{,}{\mathrm{S}}_{\mathrm{1}}\right)\mathrm{/}\left(\mathrm{t}\mathrm{,}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_{\mathrm{2}}\right)$$

in which:

• f _y = the calculated value of the yield value;
• t = the web thickness;
• R = minimum lock tensile strength guaranteed by the manufacturer (eg R = 5500 kN / m);
• S ₁ = a safety factor for the flow in the web;
• S ₂ = a safety factor for the failure in the lock;

where the safety factors are different for both types of failure, eg:

• S ₁ = 1.0 (flow in the web);
• S ₂ = 1.25 (failure in the lock).

By observing the above-mentioned condition (1), it is ensured that the flow in the web never becomes decisive under tensile load of the flat sheet piles, i. that only the minimum lock tensile strength R guaranteed by the manufacturer must be observed. It also follows that a failure of a flat sheet pile connection is almost always due to a breakage of a lock connection.

Breaking a lock connection in the cell wall of a damper cell causes a discontinuity in the uptake of the ring pull forces. The result is a widening gap in the cell wall, through which the floor filling of the cradle cell is washed away. However, without adequate soil fill, the dam cradle will no longer be able to withstand the stresses resulting from the water overpressure, leading to its failure.

Almost all flat sheet piles have symmetrical lock rails of the "thumb / finger" type, which are twisted together by 180 °. If there are two locked lock strips, the two thumbs engage behind each other, whereby the fingers engage around the thumb of the opposite lock strip (see FIG. 1). A failure of such a lock connection is carried out either by tearing off the tensile load on the thumb or by opening, or break, the finger subjected to bending.

All manufacturers of flat sheet piles have for cost reasons in their standard product range only three to four flat sheet piles, which differ essentially by the thickness of their web. It comes here usually web thicknesses of 11 to 13 mm for execution. The choice of steel grades then determines the minimum tensile strength of the profile, whereby values of 2000-4000 kN / m are generally guaranteed. New high strength steels, such as The steel S 460 GP, even allow a minimum lock tensile strength of 5500 kN / m to ensure. Since an increased steel grade also leads to an increase in the yield strength in the web, it is always ensured that condition (1) remains satisfied. It should also be emphasized in this context that flat sheet piles with a thicker web usually also have a higher Mindestschlosszugfestigkeit because when rolling a thicker web and the decisive for the Schlosszugfestigkeit parts of the castle can be slightly thicker roll.

It sometimes happens that with flat sheet piles from the manufacturers' standard delivery programs the minimum lock tensile strength required for a construction project can not be achieved. For cost reasons, however, hardly any manufacturer is willing to roll special profiles for individual construction projects. In such cases, it is known to increase the Mindestschlosszugfestigkeit of profiles from the standard program in that, starting from an existing calibration, during the rolling process, the "caliber" opens wider, ie the gap between the upper and lower roll slightly larger. As a result, not only the web is slightly thicker, but also the decisive for the Schlosszugfestigkeit parts of the castle are made stronger and thus offer a higher resistance. Such a method is eg in the JP55138511 described. It should be noted that this procedure also ensures that condition (1) remains satisfied.

In order to increase the lock tensile strength, it has also been proposed to change the geometry of the lock strips (see, for example, US Pat JP56020227 ). For this, however, the manufacturer would have to invest in new rolls. Then he would then have to lead in his delivery program two different types of locks for flat sheet piles, what the logistics are not exactly simplified. For both reasons, the manufacturers of flat sheet piles are therefore hardly ready to go this way.

It has also been known for a long time that flat sheet piles in certain cofferdams can also be exposed to high dynamic loads. The cell walls are e.g. rammed by ships and are exposed to the impact of heavy flotsam in spring and storm surges. Many cofferdams are also built in earthquake-prone areas. For such dynamic load cases, flat piles would actually have to be designed completely differently than before. So, for example, Ensure that the flat sheet piles can absorb a much greater deformation energy than before, before it comes to the failure of a lock connection. However, since it has been assumed that very large investments are required for the manufacture of this completely new flat sheet pile, no manufacturer has yet brought to market a flat sheet pile, which is especially designed for the above-mentioned dynamic load cases.

The present invention is based on the surprising finding that a Flachspundbohle from the standard product range of a manufacturer can be modified with a very low cost such that it is much better suited for the absorption of dynamic stresses.

General description of the invention

According to the invention, this object is achieved by rolling in a taper in the web of the flat sheet pile, which is designed such that in a tensile test of two connected by their lock strips specimens from this sheet pile, the web deformed plastically in the region of this taper before it can lead to a failure of the lock connection. With little effort, namely the simple rolling a taper in the web, which can be done with a slightly modified set of flat sheet piles of the standard program, ie without much investment in new rolling stands, can create a sheet pile, in contrast to known flat sheet piles, has a pronounced plastic working capacity in a sheet pile wall. By this pronounced Plastic work capacity is a sheet pile with flat sheet piles invention much better suited for the absorption of dynamic stresses and can be used particularly advantageously in cofferds are exposed to the following dangers, for example: Ramming by ships, impact of heavy flotsam in storm and spring tides and earthquakes. The webs of the sheet piles according to the invention in the cell wall can absorb a not insignificant deformation energy under such loads, without causing it to break a lock connection.

In order to achieve the desired effect, the web should preferably be designed for a nominal failure load, which is less than 90% of the guaranteed minimum tensile strength of the lock strips. In a tensile test of two connected by their lock strips specimens from this sheet pile then a plastic displacement of at least 1% of the total width of the sheet pile is to be measured for the web.

The taper should preferably be formed symmetrically to the central axis of the web, so that it has an equal distance to both lock strips. It advantageously forms a central section with a width B and a constant thickness t, where t is the minimum thickness of the web. The width B is preferably between 5% and 80% of the total width W of the web. Good results are usually achieved with a width B between 30 and 100 mm. Alternatively, the thickness of the taper to the center axis of the web can steadily decrease, and the minimum thickness of the web are then achieved only on the central axis of the web.

The web has its maximum thickness advantageous in the connection area of the lock strips. It has, for example, advantageously along each lock strip on a section with a width b ₀ and a constant thickness t ₀ , where t _{0 is} the maximum thickness of the web. Normally t _{0 will be} 13 to 14 mm.

The taper advantageously has a convex cylindrical surface with a radius R ₁ to which a concave cylindrical surface with a radius R ₂ adjoins the central axis of the web, wherein R _{2 is} substantially larger than R ₁ and many times larger than the nominal width of the Sheet pile is.

Further features and advantages of the invention can be taken from the following description of a preferred embodiment of the invention and the accompanying drawings.

Brief description of the drawings

Fig. 1

ein Querschnitt durch drei verhakte Flachprofil-Stahlspundbohlen aus dem Standard-Lieferprogramm eines Herstellers ist;

Fig. 2

ein Querschnitt durch eine erfindungsgemäße Flachprofil-Stahlspundbohle ist, wobei nur die linke Hälfte der Spundbohle gezeigt ist; und

Fig. 3

ein Diagramm ist, das Last-Verschiebungskurven für eine Standard-Flachspundbohle und für zwei erfindungsgemäße Flachspundbohlen wiedergibt.

The accompanying drawings show a preferred but not exclusive embodiment of the invention wherein:

Fig. 1

is a cross section through three entangled flat-profile steel sheet piles from the standard delivery program of a manufacturer;

Fig. 2

a cross-section through a flat profile steel sheet pile according to the invention, wherein only the left half of the sheet pile is shown; and

Fig. 3

Figure 12 is a graph showing load-displacement curves for a standard flat sheet pile and for two flat sheet piles according to the invention.

Description of an embodiment of the invention with reference to the drawings

Fig. 1 shows hot rolled flat profile steel sheet piles 10 ' ₁ , 10' ₂ and 10 ' ₃ as they have been offered for decades by different manufacturers. Such a flat sheet pile 10 ' ₁ comprises a straight web 12' and two symmetrical lock strips 14 ' ₁ , 16' ₁ . The latter are of the type "thumb / finger" and limit the web 12 'on its two longitudinal sides.

The dimensions of such flat sheet pile are basically defined as shown in Fig. 1, wherein the nominal width of the Flachsundbohle 10 ' _{1 is} denoted by "L", the width of its web with "W" and the thickness of its web with "t". Flat sheet piles from the most common delivery programs of the manufacturers have, for example, a nominal width of 500 mm, a web thickness of 11 to 13 mm and a delivery length of more than 30 m.

As can be seen from Fig. 1, the flat sheet piles 10 'are arranged in a sheet pile wall alternately rotated by 180 ° and with their lock strips 14', 16 'hooked. With two hooked lock strips 14 ' ₁ , 14' ₂ , the two thumbs engage behind 18 ' _1, 18' ₂ wherein the fingers 20 ' ₁ , 20' ₂ each surround the thumb 18 ' ₂ , 18' _{1 of} the opposite lock strip.

Such flat sheet piles are used especially for the construction of cell fishing dams without internal anchoring. Depending on the shape of the cells, a distinction is made between circular or flat-cell dams. In U.S.A., so-called "open cells" are also used. Here, the flat sheet piles are claimed primarily in the direction of horizontal cell expansion to train. As already mentioned in the introduction, all known flat sheet piles are designed so that, until the manufacturer guarantees minimum lock tensile strength, i. until the failure of a lock connection, no plastic deformation of the bridge comes.

The latter comprises, as the known flat sheet piles of FIG. 1, also a substantially flat web 12 and two symmetrical lock strips of the type "thumb / fingers", which the web 12 at its two Limit longitudinal sides. The reference numeral 22 denotes the center plane of the sheet pile 10, which is also a plane of symmetry of the sheet pile 10 at the same time. The flat sheet pile 10 has the same width and the same lock strips as the flat sheet piles 10 '.

In contrast to the above-described standard flat sheet piles 10 'of FIG. 1, however, the sheet pile 10 of FIG. 2 is designed such that the nominal failure load of the web is less than 90% of the minimum tensile strength of the lock strips, so that in a tensile test of two sheet piles connected by their lock strips 14, the web deformed plastically before the lock strips 14 can yield. This is achieved in that in the web 12, a central taper 24 is rolled, so that the web 12 plastically deformed in the region of this taper 24, before it can cause a failure of a lock connection.

Design example for the new sheet pile:

The flat sheet pile shown was designed for a minimum tensile strength of R = 6000 kN / m. To achieve this relatively high minimum tensile strength, a steel grade S 460 GP with a nominal yield strength f _y = 460 MPa and a nominal failure stress of f _u = 530 MPa was chosen. Furthermore, the web thickness t ₀ in the connection area of the lock strips 14, compared to a standard flat bar with the same nominal width, slightly increased.

To ensure that the tapered web 12 plastically deforms before the lock strips 14 yield, the nominal failure load of the web has been limited to 85% of the guaranteed lock tensile strength. This results in a web thickness t in the region of the taper 24 of: $$\mathrm{t}\mathrm{>}\left(\mathrm{0}\mathrm{.}\mathrm{85}\mathrm{*}\mathrm{R}\right)\mathrm{/}{\mathrm{f}}_{\mathrm{u}}\mathrm{\Rightarrow }\mathrm{t}\mathrm{>}\mathrm{9}\mathrm{.}\mathrm{6}\mathrm{mm}$$

Finally, a minimum web thickness t of 9.5 mm was chosen for the tapered web zone.

This minimum thickness t is constant in a central web section 24 with a width B, this width B advantageously making up at least 5% of the total width W of the web 12. This central web portion 24 with the minimum thickness t takes, after exceeding the yield strength, the plastic deformation of the web. The larger the width B, the greater the plastic working capacity of the flat sheet pile, ie the more the web can expand in width before it finally fails. So that one can easily roll the slightly thickened lock strips 14 with only a slightly modified set of rolls, sufficiently wide edge edges with increased thickness t _{0 should be} left over. Furthermore, it should be noted in this connection that too great a width B can also lead to instabilities when driving in the flat sheet pile. In addition, a limitation of the plastic deformation is important to avoid damage to the secondary structure. From a defined deformation of the flat sheet pile should hereby escape further load absorption, thus initiating a relocation process. For these reasons, the width B of the central web portion 24 should therefore not be too large and in principle not greater than 80% of the total width W of the web 12. First tensile tests have also confirmed that even a width B of approximately 30-60 mm for the central web section 24 with the minimum thickness t, the plastic working capacity of the sheet pile 10 is likely to increase sufficiently for many applications. A significantly low plastic working capacity is achieved with a web whose thickness decreases steadily to the central axis 22 of the web 12, so that the web reaches its minimum thickness t only on the central axis of the web (ie B ≈0).

In the transition region from the central web portion 24 with the minimum thickness t on the thickened web edges with the thickness t ₀ , the web 12 advantageously has a convex cylindrical surface 26 with a radius R ₁ , to which a concave cylindrical surface 28 with a to the central axis of the web Radius R ₂ connects. The radius R ₂ is in this case substantially larger than the radius R ₁ and many times greater than the nominal width L of the sheet pile.

It should be noted that the flat sheet pile 10 of FIG. 2 can be rolled, with only slight changes, with the same roll stand used for rolling the standard profiles with constant web thickness. For this purpose, an existing pair of rollers, with which normally flat sheet piles of the standard program are rolled, only needs to be turned off slightly, which certainly does not require much investment.

For a further explanation of the typical properties of the flat sheet piles according to the invention, the diagram in FIG. 3 shows representative load-displacement curves for three different flat sheet piles. These curves were recorded in path-controlled tensile tests according to prEN 12048. The test candidates differed only in the shape of the web and all had a steel grade S 460 GP with a nominal yield strength f _y = 460 MPa and a nominal failure stress of f _u = 530 MPa.

The curve 1 is the load-displacement curve for a connection of two specimens from a standard flat sheet pile with a constant web thickness of 13 mm. It is noted that although this compound achieves a tensile load of more than 6000 kN / m, it begins to become unstable even at a relative displacement of 5 mm. The failure of the connection is finally by tearing the lock connection.

The curve 2 is the load-displacement curve for a connection of two specimens from a flat sheet pile in which the thickness of the web from a value of 13.5 mm in the vicinity of the lock strips, decreases steadily to the central axis of the web, and a minimum thickness of the web of 9.5 mm on the Center axis of the web is achieved. It is found that this compound achieves a maximum tensile load of 4500 kN / m, but that it becomes unstable only after a relative displacement of more than 7 mm. The failure of the connection is preceded by a pronounced plastic displacement of about 5 mm. This plastic displacement distance is thus approximately 1% of the total width of the flat sheet pile 10.

The curve 2 is the load-displacement curve for a connection of two specimens from a flat sheet pile according to FIG. 2, in which t ₀ = 13.5 mm, t = 9.5 mm and B = 40 mm. This connection also achieves a maximum tensile load of 4500 kN / m. The failure of the connection, however, is preceded by a plastic displacement of almost 10 mm, so that it can absorb relative displacements of almost 12 mm in the pulling direction, without opening the lock connection comes. The plastic displacement distance here is 2% of the total width of the flat sheet pile 10.

Due to their large plastic deformation capacity flat planks according to the invention are ideal for use in cofferdams that can be rammed by ships to withstand the impact of flotsam in spring and storm tides and / or to be built in earthquake-prone areas. The risk of tearing open a lock connection and thus the risk of leakage of the cradle cell is substantially reduced with the flat sheet piles according to the invention.

These new flat sheet piles are particularly interesting because they can be produced on an existing roll stand with a slightly modified set of rolls. The necessary investment is thus negligible compared to a new flat sheet pile with constant web thickness and modified claw geometry.

Claims (13)

Hot-rolled flat profile steel sheet pile comprising a straight web (12) which is bounded on each longitudinal side in each case by a lock strip (14);
characterized in that the web (12) has a rolled-in taper (24), which is designed such that in a tensile test of two connected by their lock strips (14) specimens from this sheet pile, the web (12) in the region of this taper (24) plastically deformed before it can come to a failure of the lock connection. Sheet pile according to claim 1, wherein a minimum tensile strength is ensured for the lock strips (14), and the web (12) has a nominal failure load which is less than 90% of the minimum tensile strength of the lock strips (14). Sheet pile according to claim 1 or 2, wherein in a tensile test of two connected by their lock strips (14) specimens from this sheet pile for the web (12) a plastic displacement distance of at least 1% of the total width of a sheet pile is measured. Sheet pile according to one of claims 1 to 3, wherein the taper (24) is formed symmetrically to the central axis of the web (12). Sheet pile according to one of claims 1 to 4, wherein the taper (24) has a central portion with a width B and a constant thickness t, and this thickness t is the minimum thickness of the web (12). A sheet pile according to claim 5, wherein the web (12) has an overall width W and the width B of the central portion is between 5% and 80% of the total width W of the web (12). Sheet pile according to claim 6, wherein the width B of the central portion has a value between 30 and 100 mm. Sheet pile according to one of claims 1 to 4, wherein the thickness of the taper (24) to the central axis (24) of the web (12) steadily decreases, and the minimum thickness of the web (12) on the central axis of the web (12) is achieved. Sheet pile according to one of claims 1 to 8, wherein the web (12) has its maximum thickness in the connection region of the lock strips (14). Sheet pile according to one of claims 1 to 9, wherein the web (12) along each lock strip (14) has a portion with a width b ₀ and a constant thickness t ₀ , and this constant thickness t _{0 is} the maximum thickness of the web (12) , Sheet pile according to one of claims 1 to 10, wherein the taper (24) has a convex cylindrical surface with a radius R ₁ , to the central axis (24) of the web (12) towards a concave cylindrical surface with a radius R ₂ connects, R _{2 is} substantially greater than R ₁ and many times greater than the nominal width L of the sheet pile. Sheet pile according to one of claims 1 to 11, which is designed such that a minimum lock tensile strength of at least 5500 KN / m is ensured. Sheet pile according to one of claims 1 to 12, wherein the lock strips (14) form symmetrical locks of the thumb-finger type (18, 20).

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