GB2485468A

GB2485468A - Method of manufacturing a reinforcing cage for a diaphragm wall with an aperture formed therethrough

Info

Publication number: GB2485468A
Application number: GB1119315.8A
Authority: GB
Inventors: Stephen Render
Original assignee: Romtech Ltd
Current assignee: Romtech Ltd
Priority date: 2010-11-09
Filing date: 2011-11-09
Publication date: 2012-05-16
Also published as: GB201018905D0; GB201119315D0

Abstract

The method comprises the steps of assembling a number of longitudinal bars 20 and a number of links 22, 24 into a structure having two rows of longitudinal bars, and securing a rigid frame 30 to each of the two rows of longitudinal bars. The frames each have an opening 42 which in use defines the location of the aperture. The longitudinal bars which occupy the opening are cut so as to create the aperture. The frame is intended to maintain the structural integrity of the reinforcing cage despite the cutting of certain of the longitudinal bars. The frame may be rectangular, oblong or oval and may be secured to the longitudinal bars with fillet welds. The frame may further comprise a tube secured inside the opening of the frame and filled with drillable material. The invention also provides a reinforcing cage for the diaphragm wall.

Description

METHOD OF MANUFACTURING A REINFORCING CAGE FOR A

DIAPHRAGM WALL, AND REINFORCING CAGE THEREFOR

FIELD OF THE INVENTION

This invention relates to a method of manufacturing a reinforcing cage for a diaphragm wall, and to a reinforcing cage therefor. The invention relates in particular to a diaphragm wall for use in constructing a reinforced concrete wall having an aperture through the wall.

BACKGROUND TO THE INVENTION

Reinforced concrete walls are used in many structures, particularly underground structures such as tunnel walls, underground car park walls and the like. As with other reinforced concrete structures, the walls comprise a reinforcing cage (i.e. a latticework of metal reinforcing bars) embedded within concrete.

The reinforcing cage comprises a number of longitudinal bars which are substantially vertical in use, and which provide most of the resistance to flexural loading caused by the weight of the surrounding earth. The longitudinal bars also serve to stiffen the cage for site-lifting and installation and are interconnected by links, cage formers or other metal structures which are designed to maintain the orientation and separation of the longitudinal bars during transportation and pouring of the concrete.

Several different methods of making a reinforced concrete wall are known, including for example secant or contiguous piling, where a series of reinforced concrete piles, each being substantially circular in plan view, and arranged in a row. In secant piling adjacent piles overlap whereas in contiguous piling there is a small gap between adjacent piles.

The present invention is directed to the third method of making a reinforced concrete wall, namely utilising diaphragm walls. The reinforcing cage of a diaphragm wall typically comprises two rows of longitudinal reinforcing bars, the longitudinal bars being substantially parallel and being substantially vertical in the constructed reinforced concrete wall. The longitudinal bars are interconnected by a number of links. The separation between the rows, and the separation between the longitudinal bars in each row, are determined by the diaphragm wall designer.

s Diaphragm walls have the major advantage over secant and contiguous piling in that they make better use of the metal reinforcing bars, and in particular the longitudinal bars. In secant and contiguous piling the pile cages are substantially circular and the loading of the longitudinal bars varies depending upon their position in the pile. Each of the longitudinal bars must nevertheless be designed to withstand the maximum loading so that many of the longitudinal bars are underutilised in the reinforced concrete wall. With diaphragm walls on the other hand the loading on all of the longitudinal bars can be similar.

Notwithstanding the ability of the longitudinal bars to withstand the flexural forces resulting from the weight of the surrounding earth and the stresses induced by the site-lifting of the cage, the designers of many reinforced concrete walls will require one or more ground anchors to be passed through the wall and into the surrounding earth, the ground anchors providing additional bracing for the wall and helping the wall to resist the weight of the surrounding earth.

It is not practicable to construct a reinforced concrete wall from a series of diaphragm walls and then drill through a diaphragm wall so as to insert the ground anchor. Firstly, since the size of the hole required for the ground anchor is typically larger than the spacing between adjacent reinforcing bars, this would require the drill bit to be suitable for drilling both metal and concrete. Secondly, drilling through the longitudinal bars would reduce the structural integrity of the reinforcing cage.

It is known to make a reinforcing cage for a diaphragm wall which is able to receive ground anchors by including relatively soft void formers within the reinforcing cage, each void former being positioned at the location of a ground anchor. Thus, instead of making the reinforcing structure solely from longitudinal bars and the necessary links to interconnect those longitudinal bars, the structure additionally includes one or more void formers which can be drilled out to define an aperture through which a respective ground anchor can subsequently be passed.

This method has a number of significant disadvantages, however. Firstly, during manufacture the reinforcing cage comprises a latticework of metal bars and it may be necessary to locate the void former in open space, i.e. there may be no suitable location at which to mount the void former(s) in their required positions, and no means of ensuring that the void former(s) retain their desired positions during subsequent assembly and transportation of the reinforcing cage.

Secondly, even if the void former engages a part of the reinforcing cage it is difficult to robustly connect dissimilar materials such as soft void former material and metal reinforcing bars.

Thirdly, the void former(s) will often be located in positions which would otherwise be occupied by a longitudinal bar. It is not practicable to reposition or cut the longitudinal bar without affecting the structural integrity of the reinforcing cage.

Fourthly, it is excessively expensive to build a reinforcing cage in a piecemeal fashion. A particular reinforced concrete wall will typically be constructed from a large number of similar diaphragm walls, and the manufacturer of the reinforcing cages for those diaphragm walls will wish to make all of the reinforcing cages the same so that the efficiency of the manufacturing process is maximised. The requirement to make a small proportion of reinforcing cages different from the remainder so that they can accommodate the void former(s) represents a significant penalty in terms of manufacturing complexity and therefore cost.

Fifthly, the reinforcing cage, including the void former(s), must be sufficiently rigid to be lifted. Thus, it is usually necessary to lift the assembled reinforcing cage from its assembly location, either onto a vehicle for transportation, or to another part of the factory, for the concrete to be poured therearound.

SUMMARY OF THE INVENTION

The inventor has therefore appreciated that an alternative method of making a reinforcing cage for a diaphragm wall having an aperture is required. Desirably, the method will have a minimum impact upon the manufacturing process for the reinforcing cages.

According to the invention there is provided a method of manufacturing a reinforcing cage for a diaphragm wall with at least one aperture, the method comprising the steps of: {i} providing a predetermined number of longitudinal bars for the reinforcing cage; {ii} providing a predetermined number of links for interconnecting the longitudinal bars; {iii} assembling the longitudinal bars and links together to provide a reinforcing cage comprising the predetermined number of longitudinal bars arranged in two rows, with the required spacing between the longitudinal bars in each row and the required separation between the rows; {iv} identifying the location of the aperture; {v} securing a frame to each of the two rows of longitudinal bars, the frame having an opening which defines the aperture; {vi} cutting the longitudinal bars which occupy the opening.

It will be understood that steps {iv}, {v} and {vi} can be undertaken at a dedicated facility separate from the assembly location of the reinforcing cage. Accordingly, if only one in ten of the diaphragm walls for a particular reinforced concrete wall are are required to have apertures, then all reinforcing cages can be assembled identically using the same jigs and fixtures, and one in ten of those reinforcing cages can subsequently be taken to a separate location for the fitment of the frame.

Preferably, the frame comprises a rectangular structure, preferably an oblong structure. The inventor appreciates that an aperture for a ground anchor will typically lie at an angle (so that the ground anchor can be angled downwardly into the surrounding earth); the ground anchor aperture will typically be circular in cross-section, but the circular shape of the ground anchor aperture will require an oval aperture in each surface of the diaphragm wall.

Alternatively, the shape of the frame can match the aperture. Thus, the opening in the frame can be oval if the aperture is oval for example.

Desirably, the frame is manufactured from metal plate with a cross-section having a significantly greater width than its thickness. In the assembled diaphragm wall the metal of the reinforcing cage must be kept out of the cover zone, i.e. there must be a minimum thickness of concrete surrounding the metalwork. Ideally, the thickness of the frame is less than the thickness of the links interconnecting the longitudinal bars, so that no part of the frame lies within the cover zone. In use, the width of the cross-section of the frame lies along the longitudinal bars and the s greater the width of the cross-section the longer the weld can be which secures the cut longitudinal bars to the frame. Desirably, the cross-sectional shape of the frame is an oblong with a thickness of 15-20 mm, and a width of 75-1 00 mm. It can be arranged that the ends of the longitudinal bars are secured to the frame by a pair of fillet welds, and after being cut the resistance to lifting loads of the io longitudinal bar can match or even exceed that of an uncut longitudinal bar.

The inventor has appreciated that it is desirable for the frame to be able to maintain the design strength of the longitudinal bars since the assembled reinforcing cage must retain its structural integrity as it is lifted onto a truck for s transportation to another location, or is lifted and moved to another part of the factory, for the concrete to be poured.

The method can include the additional step of: {vii} securing a tube to the frames, and perhaps also the further additional step of: {viii} filling the tube with a drillable material.

Thus, once the frames are in position the path of the drill which will form the aperture through the diaphragm waIl is defined. The concrete can be poured and allowed to set before the aperture is drilled therethrough. In such a method, the drill is required to pass through concrete only, and can therefore be adapted to such material. Alternatively, a tube corresponding to the aperture can be fixed to the rigid frames, and the tube can be filled with a relatively soft material to facilitate subsequent drilling of the ground anchor aperture. The ends of the tube can if desired be covered by a filler board, plywood casing, or the like, so that no concrete flows around the ends of the tube, and so no concrete is required to be drilled to open the aperture.

There is also provided a reinforcing cage for a reinforced concrete wall, the reinforcing cage comprising a number of longitudinal bars arranged in a predetermined array and being retained by a number of links, the reinforcing cage having at least one frame, the frame having a first part and a second part, at least one of the longitudinal bars being rigidly secured to the first part of the frame and to the second part of the frame, said one of the longitudinal bars being cut between the first part of the frame and the second part of the frame whereby to define two portions of the longitudinal bar which are interconnected by the frame.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in more detail, by way of example, with io reference to the accompanying drawings, in which: Fig.1 shows a plan view of a reinforcing cage of a diaphragm wall; Fig.2 shows a perspective view of a rigid frame for use in the method according is to the invention; and Fig.3 shows an end view of part of the reinforcing cage of Fig.1, fitted with two of the rigid frames.

DETAILED DESCRIPTION

Fig.1 shows a reinforcing cage 10 for a diaphragm wall, in plan view. The outline 12 of the concrete which is subsequently poured around the reinforcing cage 1 0 in order to make up the diaphragm wall is shown in dotted outline for ease of understanding, though it will be understood that the pouring of the concrete takes place after the reinforcing cage has been assembled, and perhaps at a different manufacturing location.

The precise form of the outline of the diaphragm wall is not relevant to the present invention, but in the embodiment shown the diaphragm wall has a key 14 which is adapted to fit into a keyway 16 of an adjacent diaphragm wall during the construction of the reinforced concrete wall. The diaphragm wall represented in Fig.1 has a width W of around 3,000 mm, and a thickness T of around 1,000 mm to around 1,800 mm (depending upon the application). The length of the diaphragm wall (i.e. the dimension running into the paper) may be around 21,000 mm to around 50,000 mm, again depending upon the application. Typically, the diaphragm wall is designed to be transported by road from the manufacturing location at which the concrete is poured to the site of use. In addition, the reinforcing cage 10 may be transported by road from its assembly location to a separate location at which the concrete is poured.

The reinforcing cage 10 comprises a predetermined number of (in this embodiment twenty two) longitudinal bars 20, arranged in two rows. Each of the longitudinal bars 20 runs the full length of the diaphragm wall, and the ends of the bars 20 may project from the concrete if it is desired to tie other structures to the diaphragm wall. The longitudinal bars 20 are substantially vertical in the is reinforced concrete wall.

The longitudinal bars 20 are interconnected by links 22 and 24. The precise form and number of the links will depend upon the application, and additional links may for example be provided as required to maintain the structural integrity of the reinforcing cage 1 0, and in particular to ensure that the reinforcing cage 10 can be lifted and transported without unwanted relative movement of any of the longitudinal bars 20. The links 22 and 24 are typically secured to the longitudinal cage bars by wire ties which surround the junction of each link and longitudinal bar. A series of links 22, 24 are located along the length of the longitudinal bars (see Fig.3), with a spacing determined by the designer of the reinforcing cage.

The reinforced concrete wall which is to be constructed will typically require a series of diaphragm walls such as that represented in Fig.1. If the designer requires the reinforced concrete wall to have at least one ground anchor then it is necessary for at least one chosen diaphragm wall to have a ground anchor aperture formed therethrough. The sides of the ground anchor aperture are represented in Fig.1 by the dashed lines 26, it being understood that a substantially circular opening will be required through the diaphragm wall for the

S

passage of the ground anchor. Clearly, the invention is applicable to any aperture in the diaphragm wall, but the provision of ground anchor apertures is expected to be the primary utilisation of the invention.

The location and orientation of the ground anchor aperture will be known to the reinforcing cage manufacturer, and as represented in Fig.1 the ground anchor aperture will typically be occupied by at least one of the longitudinal bars 20.

According to the present invention, identical reinforcing cages 10 are assembled, io regardless of whether or not the particular diaphragm wall requires an aperture.

In this way, the assembly procedure for the reinforcing cages 10 for a particular reinforced concrete wall can be commonised and the manufacturing efficiency maximised.

is Subsequent to the assembly of the reinforcing cage 10, if an aperture is required the reinforcing cage 10 can be moved to a separate manufacturing location for the fitment of rigid frames 30, such as that shown in Fig.2.

The rigid frame 30 is constructed from four beams 32, 34, 36 and 38 of flat metal (preferably steel) plate, each of the beams having a substantially identical cross-section with a thickness t and a width w. The sides of the frame 30 (which are defined by the beams 32 and 36) are longer than the top and bottom of the frame (which are defined by beams 38 and 34), the frame 30 being designed so that the beams 32 and 36 are substantially vertical in the reinforced concrete wall, and the beams 34 and 38 are substantially horizontal. The beams are secured together at their respective junctions 40 by welding. In certain embodiments the thickness t is in the range 15-20 mm, and the width w is in the range 70-1 00 mm.

It will be understood that welding together beams 32-38 of these dimensions can provide a structure which is extremely rigid, and in particular is sufficiently rigid to withstand and transmit the shear loads which are encountered by cage bars 20 of up to around thirty two millimetres in diameter, for example.

in an alternative embodiment the rigid frame may be cut (e.g. laser cut) from a single sheet of metal plate, so that no junctions are present. In such embodiments it might be preferred to make the rigid frame in an oval shape, substantially to match the shape of the ground anchor aperture.

To secure the rigid frame 30 to the reinforcing cage 10, the reinforcing cage 10 is preferably laid substantially flat, as drawn in Fig.1. The location of the aperture is identified and a rigid frame 30 is laid upon the longitudinal bar(s) 20 in that location. In the embodiment shown the location of the aperture spans a region 0 occupied by two longitudinal bars 20, but in other embodiments the location may span a region occupied by one longitudinal bar 20, or more than two longitudinal bars 20. The (horizontal) beams 34 and 38 are then welded to the underlying longitudinal bar(s) 20 (and the (vertical) beams 32 and 36 are welded to the underlying longitudinal bar(s) if they also engage a longitudinal bar). When the is rigid frame 30 has been secured to the longitudinal bars 20 the parts of the longitudinal bars which span the opening 42 of the rigid frame 30 are cut out.

A rigid frame 30 is secured to each of the rows of longitudinal bars 20, as shown in Fig.3. Fig.3 shows that the frames 30 do not encroach into the cover zone, i.e. the thickness t of the frames 30 is designed to be no more than (and preferably less than) the diameter of the links 22,24.

Fig.3 also shows the fillet welds 44 between the reinforcing bars 20 and the beams 34 and 38 of the frame 30. It will be understood that the longitudinal bars 20 are of circular cross-section and engage the flat beams 34 and 38, and a fillet weld 44 can be formed to either side of each longitudinal bar 20.

It will be understood that Fig.3 only shows the longitudinal bars 20 which span the opening 42 within the frame 30, and which longitudinal bars are therefore cut out to provide the ground anchor aperture (the top and bottom of which aperture are represented by the dashed lines 46 in Fig.3). The longitudinal bars 20 which do not span the opening 42 are not cut and are not shown in Fig.3.

in the arrangement of Fig.3 the right-hand frame 30 is located to the outside of the right-hand row of longitudinal bars 20, and the left-hand frame 30 is located to the outside of the left-hand row of longitudinal bars 20. It would, however, be possible for one (or both) of the frames to lie inside the respective row of longitudinal bars, and it would facilitate manufacture in the orientation of Fig.1 for one frame 30 to lie upon the uppermost row of longitudinal cage bars 20, and the other frame 30 to lie upon the lowermost row of longitudinal cage bars 20.

In the embodiment of Fig.3 the aperture is formed at an angle to the horizontal, as is typically the case with an aperture for a ground anchor. The vertical offset between the frames 30 matches the angle required, as does the oblong shaping of the frames 30.

Fig.3 also shows a lifting band 48, i.e. a band which interconnects some or all of is the longitudinal bars 20 and which provides a lifting point for the assembled reinforcing cage 10.

In this embodiment the frames 30 lie between adjacent links 22, 24, and the reinforcing cages will often be designed so that the links 22, 24 (and the lifting band 48) lie away from the ground anchor apertures. In other embodiments it may be necessary also to cut a link if the link spans the opening 42 of a frame 30.

Any of the links 22, 24 which span the opening 42 can also be welded to the frame 30, typically after they have been cut (it will be understood that it may be necessary to cut the links 22, 24 in order to allow the frame 30 to lie upon the longitudinal bars 20).

If desired, a tube (not shown) can be fitted to the frames 30, the tube defining the aperture in the diaphragm wall. The tube is ideally not required to maintain any of the structural integrity of the reinforcing cage 1 0. The tube can be filled with a soft material which may readily be removed by drilling after the concrete has set, and the ends of the tube can be covered by shuttering such as a filler board prior to pouring of the concrete, so that the ends of the tube do not become covered by concrete.

Claims

CLAIMS1. A method of manufacturing a reinforcing cage for a diaphragm wall, the method comprising the steps of: S {i} providing a number of longitudinal bars for the reinforcing cage; {ii} providing a number of links for interconnecting the longitudinal bars; {iii} assembling the longitudinal bars and links into a structure having two rows of longitudinal bars, with a predetermined spacing between the longitudinal bars in each row and a predetermined separation between io the rows; {iv} identifying the location of an aperture to be formed through the diaphragm wall; {v} securing a respective frame to each of the two rows of longitudinal bars, each frame having an opening which defines the location of the is aperture; {vi} cutting the longitudinal bars which occupy the opening of each frame.
2. The method according to claim 1 in which the steps {i}, {ii} and {iii} are undertaken at a first assembly location and the steps {iv}, {v} and {vi} are undertaken at a second assembly location, the second assembly location being separate from the first assembly location.
3. The method according to claim 1 or claim 2 in which each frame is rectangular.
4. The method according to claim 3 in which each frame is oblong.
5. The method according to claim 1 or claim 2 in which each frame is oval.
6. The method according to any one of claims 1-5 in which each frame is manufactured from metal plate with a cross-section having a significantly greater width than its thickness.
7. The method according to claim 6 in which the thickness of the metal plate is less than the cross-sectional dimension of the links.
8. The method according to any one of claims 1-7 in which the cross-sectional shape of the frame is oblong with a thickness in the range 15-20 mm, and a width in the range 75-100 mm.
9. The method according to any one of claims 1 -8 in which the longitudinal bar is secured to its frame by a pair of fillet welds.
10. The method according to any one of claims 1-9 including the additional step of securing a tube to the frames.
11. The method according to claim 1 0 including the further additional step of filling the tube with a drillable material.
12. A reinforcing cage for a diaphragm wall, the reinforcing cage comprising a number of longitudinal bars and a number of links, the longitudinal bars being arranged in two rows with a predetermined spacing between the rows and a predetermined spacing between the longitudinal bars in each row, the reinforcing cage having two frames, one of the frames being secured to each of the two rows of longitudinal bars, each frame having a first part and a second part, at least one of the longitudinal bars in each row being rigidly secured to the first part of the frame and to the second part of the frame, said one of the longitudinal bars being cut between the first part of the frame and the second part of the frame whereby to define two portions of the longitudinal bar which are interconnected by the frame.
13. The reinforcing cage according to claim 12 in which each frame is rectangular.
14. The reinforcing cage according to claim 13 in which each frame is oblong.
15. The reinforcing cage according to claim 12 in which each frame is oval.
16. The reinforcing cage according to any one of claims 12-15 in which each frame is manufactured from metal plate with a cross-section having a significantly greater width than its thickness.
17. The reinforcing cage according to claim 16 in which the thickness of the metal plate is less than the cross-sectional dimension of the links.
18. The reinforcing cage according to any one of claims 12-17 in which the s cross-sectional shape of the frame is oblong with a thickness in the range 15-20 mm, and a width in the range 75-100 mm.
19. A reinforcing cage constructed and arranged substantially as described in relation to Figs. 1 and 3 of the accompanying drawings.