WO1999042669A1

WO1999042669A1 - Sheet piling

Info

Publication number: WO1999042669A1
Application number: PCT/GB1999/000492
Authority: WO
Inventors: Robin Dawson
Original assignee: Dawson Construction Plant Limited
Priority date: 1998-02-19
Filing date: 1999-02-17
Publication date: 1999-08-26
Also published as: GB9803535D0

Abstract

The application describes a method of forming piles comprising the steps of: i) hot rolling a steel section to form an open Z-shape with two flanges and a web, the angle between the web and the flanges being substantially less than 90°; and ii) subsequently cold reforming the section to increase the said angle so as to increase the depth of the section and thus increase the section modulus.

Description

1

SHEET PILING

The present invention concerns sheet piling, for example as used in civil engineering and large construction projects.

Sheet piles are used in civil engineering to support vertical loads and/or to resist lateral pressures. The piles are sunk or driven into the ground. Sheet piles are formed from individual piles, universally formed of steel, which individual piles are interlocked or otherwise joined together to form a "wall".

Traditionally individual piles have each been formed in either a generally "U-shape" or a generally "Z-shape", with the web of the "Z" approximately 90° to the flanges. It will thus be appreciated that when the piles are joined together, with each alternate pile facing the opposite direction, they form a sheet pile having a cross section which approximates a square wave.

Steel piles are generally formed by hot rolling, in a steel mill. The depth of the pile is determined by the depth of the grooves in the rolls, in the steel rolling mill. For the depth of the pile to become greater, then the depth of the grooves in the rolls must be increased. The traditional width of a pile was 400 mm. 2

_As will _be appreciated, the rigidity of the sheet pile is a critical parameter. The conventional indicator of rigidity is the section modulus of the steel pile or sheet pile. To increase t_he section modulus, it is desira^ble to increase the _depth o_f the pile, but as indicated a^bove it _becomes more _difficult to roll piles with a deep profile and, in_dee_d, there is in practice a maximum depth that can _be rolle_d, without the grooves in the forming rolls ^being so _deep that they tend to weaken the rolls to the point where they can break.

_At the same time as desiring a relatively higher rigi_dity, the industry is also seeking a greater construction efficiency. It will be appreciated that less work is nee_ded to construct a sheet pile if each indivi^dual pile is wider, so that there are fewer piles per unit length of the sheet pile. This factor has lead to wi^der an_d wi_der piles _being formed, although these wi^der piles are restricte_d to the same maximum depth as discusse^d a_bove. This wi_dening of the piles has created a shape m which t_he angle _between the flanges and the we^bs is significantly less than 90°. In other words, each pile is "opene_d out" to form either an "open Z-shape" or an "open U-shape" .

However, this widening of the pile shape lea^ds _directly to a _decrease in the section modulus. Thus, wⁱth the maximum _depth of pile already having been achieve^d, 3 there is a conflict between the desire on the one hand to have an increased section modulus and the desire on the other hand to have a more efficient, wider pile.

For completeness, it should be mentioned that another factor is the thickness of the steel, both at the flanges and webs and at the extreme edges. Obviously, greater stiffness can be achieved by using a thicker steel section, but this is undesirable since it leads to a heavier and more expensive section. In the above discussion, a steel section of standard thickness is being assumed.

The aim of the invention is to achieve a pile which has a relatively high width, but which does not at the same time sacrifice rigidity.

Accordingly, the invention provides a method of forming piles comprising the steps of:

i) hot rolling a steel section to form an open Z-shape with two flanges and a web, the angle between the web and the flanges being substantially less than 90°; and ii) subsequently cold reforming the section to increase the said angle so as to increase the depth of the section and thus increase the section modulus.

The invention also provides a method of forming piles comprising the steps of: 4 i) hot rolling a steel section to form an open U-shape, with two webs and a flange, the angle between the webs and the flange being substantially less than 90°; and ii) subsequently cold reforming the section to increase the said angle so as to increase the depth of the section and thus increase the section modulus.

The invention still further provides a method of forming piles comprising the steps of:

i) taking a steel section which has been hot rolled to form either an open Z-shape with two flanges and a web or an open U-shape with two webs and a flange, the angle between the web and the flange being substantially less than 90°; and ii) subsequently cold reforming the section to increase the said angle so as to increase the depth of the section and thus increase the section modulus.

The invention also provides an individual pile formed by one of the above methods and a sheet pile constructed from a plurality of such individual piles.

It can thus be seen that the invention is based on the surprising realisation that a wide pile formed of an open

Z or U-shape can be closed to an extent, to increase its depth and thus increase the section modulus, while at the same time retaining some of the advantage of the increased 5 width. The idea of cold reforming hot rolled piles goes completely against the industry standard of forming and completing the shape of steel piles within the hot rolling mill. As mentioned above, this firmly established thinking has lead to piles having a certain maximum depth, which is never exceeded.

It will be appreciated that the invention has particular application to piles which had been rolled to the maximum depth. However, because it tends to be more difficult to roll relatively deep piles than relatively shallow piles, the invention does have applicability to piles which do not have the maximum depth. In other words, even with such piles the simple approach of the present invention can be used to increase the section modulus.

The invention can be better understood from the following detailed description of preferred embodiments, which are described by example only below with reference to the drawings, in which:

Fig. 1 shows in cross section a double pile of two open Z-shaped piles, both before and after reforming;

Fig. 2 shows a double pile formed of two open U-shaped piles, both before and after reforming; and Fig. 3a and 3b show examples of how the piles may be cold reformed, to alter the relative angles.

On comparing Figs. 1 and 2, it will be appreciated 6 that two of the open Z-shaped piles of Fig. 1 are equivalent to two of the open U-shaped piles of Fig. 2, but the shapes are out of phase with one another. In other words, two of the piles of Fig. 2 are needed for each "phase" of the wave-like sheet pile to be formed, whereas one and two halves of the piles of Fig. 1 are needed per

"phase" .

In Fig. ₁ the double pile formed of two open Z-shaped piles has a width a and a depth b. After cold reforming of the piles, the double pile has a width a-, or a₂ and a depth b-_! or b₂.

For example, the width a is 1260 mm and the depth b is 460 mm (which is in fact the maximum depth which can be hot rolled in a conventional rolling mill) , and reduced width a, may be 1000 mm and increased depth b-, may be 509 mm. This dimensional change is due to an increase in the angle a between the webs and the flanges of from 63.4° to 80° (for example) . The increased angle is shown as α-, in the figures.

Typically, the width of the webs would be 14 mm an^d the thickness of the flanges would be 18 mm. Before col^d reforming, this would give a mass per square metre ^{( )} of the sheet pile of ₁₉₄ kg/m². The section modulus would be approximately ₃₆₀₀ cm³. After cold reforming, although the mass would be increased to approximately 244 kg/m , the 7 section modulus (Z) would be greatly increased to approximately 5000 cm³/m.

As mentioned above, conventionally piles were 400 mm wide, so that a double pile would be 800 mm wide. It can thus be seen that in the invention a wide pile can still be achieved while at the same time producing a very high section modulus by increasing the depth beyond that which was thought to be possible.

In the second example, a is decreased to a₂ and b is increased to b₂, where a₂ is 900 mm and b₂ is 516 mm. The angle α₂ is 83°. Weight W in this example is 271 kg/m² and the section modulus Z is increased to approximately 5600 cm³/m.

In the embodiment of Fig. 2, the angle a between the web and the flanges may be 65.6° and in the cold reforming step of the invention can be increased to 79.8° (α-,) . Where the initial width a is 1200 mm and is decreased to 1000 mm (a.,) , the depth b of 442 mm being increased to 475 mm (b-,) , the section modulus Z can thus be increased from 3200 cm³/m to 4000 cm³/m, with a weight W increase of 190 kg/m² to 228 kg/m².

In the second example of Fig. 2, a is decreased to 900 mm (a₂) and b is increased to 499 mm (b₂) . The angle α₂ is 88.8° and the weight W is 253 kg/m². The section modulus Z 8 is increased to approximately 4500 cm³/m.

As will be seen in Figs. 1 and 2, at the edges of the piles there is a "hook" shape with which each pile is intended to be interlocked with the adjacent pile. These are also known as "interlocks". The interlocking edges of the piles are not particularly relevant to the new idea of the present invention. However, it can be noted that in the embodiment of Fig. 2, with the increasing of angle α the relative angle of the web immediately adjacent the "hook" is increased also, which may orientate the hook wrongly in terms of its connection with the next pile. Thus, in practice it may be necessary to open out or "flatten" the angle between the web and the section immediately adjacent the "hook".

As indicated above, the invention finds application with hot-rolled piles where the angle (α) between the web and the flange is substantially less than 90°. By this is meant 80° or less, preferably 66° or less. It is considered that with greater angles than 80°, the relative increase in section modulus to decreased width may not be significant. It can also be noted that, in practice, the angle α in hot rolled piles would not be less than 30°, more particularly 45°.

Figs. 3a and 3b illustrate the method step for cold reforming of the hot rolled steel piles. 9

The reforming process may be done, for example, on:

a) single piles as they pass through the usual cold straightening rolls; b) single piles passing through an additional machine which could be rolling or by pressing; or c) single piles or double piles may be reformed, off the rolling mill site, either at a secondary process location or at the construction site itself.

Fig. 3a shows examples of reworking rolling arrangements which can be used to increase the angle a to angle α-, or ₂. To the left hand side of Fig. 3a, a ridged roller 10 is seen on the inside of the angle and a pair of rollers 11 and 12 are on the outside, the angle between the faces of rollers 11, 12 defining the desired angle α-, or α₂.

On the right hand side of Fig. 3a, the ridged roller

10 is again seen on the inside of the angle; in this example, the angle β is defined between the inclined faces of a grooved roller 13 , rather than two separate rollers being provided.

In the embodiment of Fig. 3b, the cold reforming working method uses, instead of rollers, a press block arrangement. A "V" block 14 is shown, the relative angle between the faces of the "V" defining the angle α-, or α₂.

A ridged blade 15 is pressed into the block 14, with the 10 angle of the pile in between, to change in the angle from α to αc, or α₂. The same operation can of course be done at the other angle of the pile.

It will be appreciated that the change in angle a to ₁ or α₂ may in some instances be done in two or more cold reforming stages.

It can be understood from the above description that embodiments of the invention enable a sheet pile with a relative high section modulus to be achieved, relative to its width and weight. As comparative examples, known piles with a section modulus similar to that obtained in the above examples of the invention can be considered.

A Larssen U-pile is known with a width of 840 mm (for a double pile) and a depth of 440 mm. Weight W is 330 kg/m² and Z is 5066 cm³/m. Using the ratio of Z to W as a measure of efficiency (E) , with this example E = 5066/330 = 15.53.

In the example of the invention where Z = 5000, W = 224, thus giving an efficiency E of 20.49. The invention thus yields an increase in efficiency of about 33%.

In another known example, W is 290 kg/m² and Z is 4200 cm³/m for a double pile of width 880 mm and an angle of 85°. This gives an efficiency E of 14.48. In the closest example of the invention above, where Z = 4000, W = 228 and 11

E is thus ₁7.₈₄. An increase of approximately 21% is achieved by the invention.

In a third known example, W is 310 kg/m² and Z is 4675 cm³/m for a width of 880 mm and an angle of 85°. This gives an efficiency E of 15.08. In the closest example of the invention given alone, Z is 4500 and W is 253, giving an efficiency E of 17.74. The invention thus achieves an increase in efficiency of about 18% over the nearest equivalent conventional pile.

The invention can also be used to enhance the section modulus of smaller and/or lighter steel sections, in order to fill the gaps between current standard sizes. Indeed, using the invention, it may be possible to reduce the number of stan_dard steel profiles and increase the section modulus as required, using the proposed cold forming, secondary process of the invention.

Claims

12CLAIMS

1. A method of forming piles comprising the steps of:

i) hot rolling a steel section to form an open Z-shape with two flanges and a web, the angle between the web and the flanges being substantially less than 90┬░; and ii) subsequently cold reforming the section to increase the said angle so as to increase the depth of the section and thus increase the section modulus.

2. A method of forming piles comprising the steps of:

i) hot rolling a steel section to form an open U-shape, with two webs and a flange, the angle between the webs and the flange being substantially less than 90┬░; and ii) subsequently cold reforming the section to increase the said angle so as to increase the depth of the section and thus increase the section modulus.

3. A method of forming piles comprising the steps of^;

i) taking a steel section which has been hot rolled to form either an open Z-shape with two flanges and a web or an open U-shape with two webs and a flange, the angle between the web and the flange being substantially less than 90┬░; and ii) subsequently cold reforming the section to increase 13 the said angle so as to increase the depth of the section and thus increase the section modulus.

4. An individual pile formed by one of the methods of claims 1 to 3.

5. A sheet pile constructed from a plurality of individual piles according to claim 4.