FLEXIBLE BRIDGE ABUTMENT

Abstract

The present disclosure relates to a method and apparatus for construction of a flexible bridge abutment. In a first aspect of the disclosed technology, there is provided a flexible bridge abutment, comprising: a retaining wall operable to support an embankment; and a column operable to support a deck, fixed to a diaphragm beam; wherein the retaining wall and the column are fixed to a common foundation element, and the diaphragm beam is free to move with respect to the retaining wall.

Description

The present disclosure relates to a method and apparatus for construction of a flexible bridge abutment.

BACKGROUND

Conventional bridge construction comprises a slab sitting on beams. The ends of the beams are supported on columns or a wall. There may be an embankment on each side of the bridge that supports the running surface. This embankment needs to be retained. The end columns or wall and the embankment retaining structure are referred to as an abutment.

Since bridge structures are generally exposed to climate, they will expand and contract due to changes in temperature. This movement requires management, or else it will cause damage to the bridge structure. The longer the bridge deck, the more movement needs to be accommodated.

The examples described herein are not limited to examples which solve problems mentioned in this background section.

SUMMARY

Examples of preferred aspects and embodiments of the invention are as set out in the accompanying independent and dependent claims.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

In a first aspect of the disclosed technology, there is provided a flexible bridge abutment, comprising: a retaining wall operable to support an embankment; and a column operable to support a deck, fixed to a diaphragm beam; wherein the retaining wall and the column are fixed to a common foundation element, and the diaphragm beam is free to move with respect to the retaining wall. Optionally, the retaining wall and the column are rigidly fixed to the common foundation. A “deck” refers to deck beams and/or a deck slab. The column is fixed either rigidly or semi-rigidly to the foundation at the base of the column. If the column is fixed rigidly at the base, then it is fixed either rigidly or semi-rigidly to the diaphragm beam adjacent the top of the column. However, if the column is fixed semi-rigidly at the base, then it is fixed rigidly to the diaphragm beam adjacent the top of the column.

Bridges expand and contract due to thermal effects. To accommodate this movement, conventionally bearings have been introduced between the deck and the supporting substructure, and movement joints are introduced. This raises an issue wherein bearings and movement joints require regular inspection, maintenance and eventually replacement, which requires safe access and road closures resulting in a significant cost to the asset owner over the life of the bridge. Asset owners therefore prefer bridges without bearings and movements joints. This leads to integral bridge solutions comprised of a rigid jointed portal frame.

Due to the expansion and contraction of the bridge and the ratcheting effect on the earth behind the abutment, significant stresses can be generated in the structure which are increasingly difficult to resist, and as such integral bridges with a combined retaining wall generally have a limit of approximately 60 m in length. The longer the bridge, the greater the thermal movement and the more the potential ratcheting effect.

To create longer integral bridges, an arrangement is provided which separates the lateral earth retaining function of the abutment from the vertical bridge supports. Braking and traction loads in the bridges are resisted by the backfill behind the diaphragm beam.

Optionally, the diaphragm beam is operable to support a portion of an embankment, such as a portion of the embankment abutting the diaphragm beam.

In order to facilitate a rigid connection between the top of columns or a wall and the bridge beams, a “diaphragm” beam is cast, optionally in-situ. This also acts as a torsion beam, preventing the end of one bridge beam rotating a different amount from an adjacent bridge beam. A diaphragm in the context of construction refers to a structural element operable to transmits loads from a lateral resisting element to a vertical resisting element of a structure. A diaphragm is provided in the form of a beam, fixed to at least one bridge beam and one column.

Optionally, the diaphragm beam and the retaining wall are vertically spaced apart.

Optionally, the diaphragm beam and the retaining wall are substantially aligned on at least one side.

Optionally, the retaining wall is an open or closed section, the column being located within the section.

Optionally, the diaphragm beam is rigidly connected to at least one bridge beam.

Optionally, the column comprises concrete with at least one protruding rebar.

Optionally, the retaining wall comprises a one or more units aligned to form a substantially flat face with protrusions not exceeding 50 mm. The flat face of the retaining wall refers to any one or more faces of the or each retaining wall, for example a front face and/or a back face.

Optionally, the arrangement further comprises a capping panel adjacent the retaining wall, optionally wherein the capping panel is separated from the retaining wall by an elastically compressible seal.

Optionally, the arrangement further comprises a plurality of retaining walls and/or columns.

By spacing apart the diaphragm beam and the retaining wall, the diaphragm beam can move independently of the retaining wall. Owing to embankment movement and the embankments resistance to deck thermal expansion, the rigid connection formed by the diaphragm beam will result in axial compression in the plane of the bridge deck. This is an additional force that must be catered for in the design. However, due to said spacing apart, it is a reduced axial compression relative to what would have been present without the arrangement as described herein. The arrangement is also less prone to ratcheting. There are also high shear forces at the deck to wall connection.

In the case of an in-situ rigid joint being made between the top of a retaining wall and the deck structure, then until the concrete has achieved adequate strength it is desirable to minimise any movement between the wall top and the bridge deck. This creates a construction dependency between the completion of the bridge deck and the embankment, further adding to construction time.

The conventional method of building the retaining wall is to place formwork and cast it in-situ. Thus, the construction sequence is foundation—wall—embankment—bridge deck. Alternatively, a sequence of foundation—wall—bridge deck—embankment can be undertaken. Either way, the four main elements of conventional construction are substantially a serial operation which determines how long it takes to construct the bridge.

Further, in order to reduce the span of the bridge beams, it is generally considered desirable to build the abutment as close to the edge of a road carriageway as is deemed safe. The safe distance is reduced if the abutment presents a smooth face to the carriageway rather than, say, discrete columns. Bridge abutment systems that provide a smooth carriageway face are therefore quicker to build and more economic than those that require the face to be provided as a separate construction activity.

Bridge abutments have traditionally been constructed from in-situ reinforced concrete. Increasingly there has been interest in the use of pre-cast concrete elements to speed construction. A limiting factor with pre-cast is the weight of the elements and the sizes that can be transported.

Bridge abutments also have an aesthetic aspect to consider. Bridges are generally considered to be more than just functional necessities, but as architecturally important contributors to the enjoyment of the built environment. The colour and surface texture of the finished abutment contribute to this expression. The use of pre-cast concrete provides more options in this respect since the elements are made in a factory controlled environment.

According to a further aspect, there is provided a method of constructing a flexible bridge abutment, comprising the steps of: fixing at least one column element and at least one retaining wall element to a foundation element; and fixing a diaphragm beam to the one or more column elements, such that the diaphragm beam is free to move with respect to the one or more retaining wall elements. In some embodiments, one or more of the retaining wall element and/or the column element is rigidly fixed to the foundation element.

Optionally, the process of fixing the at least one column element and at least one retaining wall element to the foundation element comprises the steps of: placing at least a portion of the at least one column element and at least a portion of at least one retaining wall element within a foundation cage; and filling at least a portion of the foundation cage with concrete.

Cast-in-place concrete may provide improved rigidity of joints, thereby giving the bridge a structural advantage when the foundation is prepared in such a way.

Optionally, the method further comprises casting at least one column element operable to support a deck, optionally wherein the casting of the at least one column element is remote from the bridge abutment.

Optionally, the method further comprises casting at least one retaining wall element operable to support a deck, optionally wherein the casting of the at least one retaining wall element is remote from the bridge abutment.

Pre-casting elements remote from the bridge abutment can provide improved options to the construction process, as different factories may be used to provide the pre-cast elements using a greater range of tools, materials, and aesthetic considerations. Time spent on site may also be reduced, as some elements can be made concurrently and/or in advance of when actually required. This improves efficiency of construction, thereby reducing overall costs.

Optionally, the at least one column element and at least one retaining wall element are a single interconnected element. The single interconnected element may be a single pre-cast element, or a cassette formed from one or more interconnections between the at least one column element and at least one retaining wall element.

It will also be apparent to anyone of ordinary skill in the art, that some of the preferred features indicated above as preferable in the context of one of the aspects of the disclosed technology indicated may replace one or more preferred features of other ones of the preferred aspects of the disclosed technology. Such apparent combinations are not explicitly listed above under each such possible additional aspect for the sake of conciseness.

Other examples will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the disclosed technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section through a bridge abutment;

FIG. 2 shows the abutment system of FIG. 1 during an increase in temperature;

FIG. 3 shows a pressure diagram for two abutment types;

FIG. 4 shows a section through a bridge abutment wherein the stiffness of the retaining wall is increased;

FIG. 5 shows a sectional plan view through a series of shells;

FIG. 6 shows an exemplary construction sequence;

FIG. 7 shows an exemplary pocket in a foundation; and

FIG. 8 shows an exemplary capping panel arrangement;

The accompanying drawings illustrate various examples. The skilled person will appreciate that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the drawings represent one example of the boundaries. It may be that in some examples, one element may be designed as multiple elements or that multiple elements may be designed as one element. Common reference numerals are used throughout the figures, where appropriate, to indicate similar features.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating the general principles of the present technology and is not meant to limit the inventive concepts claimed herein. As will be apparent to anyone of ordinary skill in the art, one or more or all of the particular features described herein in the context of one embodiment are also present in some other embodiment(s) and/or can be used in combination with other described features in various possible combinations and permutations in some other embodiment(s).

FIG. 1 of the accompanying drawings shows a section through a bridge abutment in accordance with one embodiment of the invention. Foundation 1 supports column elements 2 and retaining wall 3. Column 2 supports beams 4 which in turn supports slab 5 and running surface 6. Wall 3 retains the earth embankment 7 which is topped with sub-base 8 and running surface 6. In this embodiment, columns 2 have a rigid or semi-rigid connection 9 to the foundation 1, retaining wall 3 has a rigid connection 10 to foundation 1. Diaphragm beam 11 rigidly connects the ends of beams 4, bridge slab 5 and columns 2. Diaphragm beam 11 is not connected to retaining wall 3.

FIG. 2 shows the same abutment system as in FIG. 1, but the bridge beams 4, slab 5 and running surface 6 have expanded owing to an increase in temperature. The result is that diaphragm beam 11 has moved to the right as shown. Since the top of column 2 is rigidly attached to diaphragm beam 11, it also moves to the right.

Also shown in FIG. 2 is the deflected shape of retaining wall 3. Under pressure arising from earth embankment 7, the top of wall 3 moves to the left. Since the top of wall 3 is not connected to diaphragm beam 11, a small relative displacement 12 will occur.

FIG. 3 shows a pressure diagram for two abutment types. FIG. 3a shows the earth pressure diagram for a conventional integral abutment. In this case the whole of the earth face is acting in passive pressure. FIG. 3b shows a construction in accordance with the invention. In this case, the part of the wall below diaphragm beam 11 is experiencing active earth pressure. Only the part of the earth embankment 7 reacting directly against diaphragm beam 11 is subject to passive pressure. The result is that axial loads generated in the deck superstructure are much smaller in magnitude. Further, the active pressure acting on wall 3 in FIG. 3b will be of lower magnitude than the passive pressure in FIG. 3a. The result is that the flexible abutment system has reduced the magnitude of loading.

With reference to FIG. 2, if running surface 6 is to remain substantially level for long periods of time, then the vertical settlement in earth bank 7 adjacent to diaphragm beam 11 must be minimised. The more wall 3 deflects, the greater the vertical settlement since the volume shown as the shaded area in FIG. 3b will be higher. It will be apparent that the stiffer wall 3 is, the less tendency there will be for vertical settlement in the earth bank 7.

FIG. 4 shows a section through an embodiment of the invention where the stiffness of the retaining wall is significantly increased. In this embodiment, the retaining wall 3 comprises tubular shells 13. It is appreciated that other arrangements of retaining wall may be provided, such as channels and/or flat panels. Column 2 is located down inside shell 13. Diaphragm beam 11 is cast to rigidly attach column 2 to bridge beam 4. There is a gap 14 so that beam 11 moves independently of shell 3, 13.

FIG. 5 shows a sectional plan view through a series of shells 13. Where a column 2 is required it is located down the centre of shell 13. Annulus 15 around the column is sized to allow for tolerances and movements resulting from column and wall deflections. Different spacings of column 2 are accommodated by using different shell sizes. By using rectangular shells, the carriageway face of the retaining wall is flat, allowing vehicles to deflect off in the event of an accident. The front face, which is the most exposed to road salts, also acts as a protective barrier to column 2 which is the main load bearing element.

The dimensions of column 2 are set by the requirements to (i) flex as bridge beams 4 expand and contract (ii) have sufficient rigidity to hold the bridge in place (e.g., under braking loads) and (iii) provide rigidity to bridge beams 4 through portal action. It will be apparent that the column section will vary with bridge beam span, bridge skew, column spacing and abutment height.

FIG. 6 shows a construction sequence in accordance with the invention. FIG. 6a shows a foundation 1 with connection pocket 15. FIG. 6b shows shell 3, 13 and column 2 during a second stage pour, in the process of being rigidly locked in place by concrete 16. FIG. 6c shows how construction can now proceed on two fronts. Beam 11 may be started at the same time as backfill 7. FIG. 6d shows a continuation of the process with beams 4 installed. A feature of the invention is that backfill 7 and associated works may continue independent of the superstructure 11, 4. Any deflection of shell 3, 13 has no impact on the superstructure works taking place. The commencement of backfill may take place before or after the beam and/or deck construction is complete, as opposed to the conventional arrangement wherein a reinforced soil retaining wall must be constructed before the deck.

FIG. 7 shows a typical pocket 15 in foundation 1. Reinforcing bars 17 projecting out of the bottom of column 2 are fixed into position using concrete or grout.

From FIG. 6 it will be apparent that to reduce construction time to a minimum, it is desirable to be able to construct diaphragm beam 11 as quickly as possible. A method of doing this is shown in FIG. 8.

FIG. 8 shows a capping panel 18 of one embodiment supported on elastically compressible seals 19. Other arrangements are possible, for example temporarily supporting the capping panel on one or more shells before being transferred to one or more columns. Alternatively, the capping panel 18 may be supported directly on one or more columns, or supported on a temporary removable structure.

The capping panel 18 of this embodiment, separated from the retaining wall by the elastically compressible seals, passes over and rests on one or more tubular shells 13. Capping panel 18 has upstands 20, 21, downstand 22, optionally cast in sockets 23, 24 and a central hole 25. The hole is sized approx. 20 mm larger than column 2 such that column 2 may subsequently be passed through it. Capping panel 18 is placed accurately on the top of shell 13. Gap 38 between down stand 23 and shell 13 is greater than the combination of thermal expansion, deflections, pre-cast manufacturing tolerances and setting out tolerances.

Column 2 with protruding rebars 26 is placed through capping panel 18. The annulus between the column and hole is filled with a compressible material 27 to effect a seal and fine adjust the column top plan position. At this stage the column bottom detail as per FIG. 7 is cast. When the concrete or grout has attained enough strength, installation of diaphragm beam 11 continues.

Levelling bar 27 is placed across the top of the column 2. Threaded bar 28 is screwed into cast in sockets 24 and passes through a slotted hole in bar 27. A nut 29 is screwed onto threaded bar 28. Capping panel 18 is raised so that it is clear of tubular shell 13. Nuts 29 are used to fine adjust the height and level of panel 18. Adjacent panels are adjusted so that they may be fixed together using additional threaded sockets 24 and connector plates with slotted holes.

When all capping panels 18 have been adjusted, concrete 30 is cast into the hollow created by the upstands on capping panel 18. This secures the capping panel 18 to the top of column 2.

Once the concrete 30 has cured, bridge beams 4 may be placed on grout bed 31. Optionally, boards 32 are shaped as appropriate and supported off strong backs 33 which are fixed to capping panel 18 using bolts 34 into the pre-fitted sockets 23. Reinforcing cage 35 is lowered over the column rebars 26. Additional rebars 36 are placed as required to complete the cage. Concrete 37 is then cast to form the completed diaphragm beam 11. Once concrete 37 has cured sufficiently, formwork 32, 33, 34 is removed.

It will be apparent that there is considerable flexibility in the sequence with which the bridge installation can proceed. It will also be apparent that a number of operations can take place in parallel. If advantage is taken of this, significant savings in overall construction time are possible.

FIG. 8 shows levelling beam 27 used to set capping panel 18. Alternative ways of achieving this are possible. If seal 19 is made of sufficiently strong material, then capping panel 18 can sit directly on top of it, though this requires very tight tolerances during pre-cast manufacture and construction. Another option is to use wedges in the gap where the seal sits. Wedges may advantageously be used with the levelling beam. In some embodiments, the wedges need to be removed before beams 4 are installed.

Wall shells 13, column 2, capping panel 18 and beams 4 are shown in the example as being made of concrete, which has optionally been pre-cast. The principles of the system apply equally if the any of these elements are made from another engineering material, e.g. steel.

The example of the invention has been shown for a bridge that is 90 degrees to what is being crossed. The principles of the system apply to bridges that are skewed, and have degrees of both longfall and crossfall. Hence, the geometry of the elements will be more complex in that they will change in 3 dimensions. However, these changes do not affect the fundamental principles of how the bridge is constructed or functions.

Any reference to “an” item refers to one or more of those items. The term “comprising” is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and an apparatus may contain additional blocks or elements and a method may contain additional operations or elements. Furthermore, the blocks, elements and operations are themselves not impliedly closed.

The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought.

Where the description has explicitly disclosed in isolation some individual features, any apparent combination of two or more such features is considered also to be disclosed, to the extent that such features or combinations are apparent and capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A flexible bridge abutment, comprising: a retaining wall operable to support an embankment; anda column operable to support a deck, fixed to a diaphragm beam; whereinthe retaining wall and the column are fixed to a common foundation element, andthe diaphragm beam is free to move with respect to the retaining wall.

2. The abutment of claim 1, wherein the diaphragm beam is operable to support a portion of an embankment.

3. The abutment of claim 1, wherein the diaphragm beam and the retaining wall are vertically spaced apart.

4. The abutment of claim 1, wherein the diaphragm beam and the retaining wall are substantially aligned on at least one side.

5. The abutment of claim 1, wherein the retaining wall is an open or closed section, the column being located within the section.

6. The abutment of claim 1, wherein the retaining wall and the column are rigidly fixed to the common foundation element.

7. The abutment of claim 1, wherein the column comprises concrete with at least one protruding rebar.

8. The abutment of claim 1, wherein the retaining wall comprises a one or more units aligned to form a substantially flat face with protrusions not exceeding 50 mm.

9. The abutment of claim 1, further comprising a capping panel adjacent the retaining wall.

10. The abutment of claim 1, comprising a plurality of retaining walls and/or columns.

11. A method of constructing a flexible bridge abutment, the method comprising: fixing at least one column element and at least one retaining wall element to a foundation element; andfixing a diaphragm beam to the one or more column elements, such that the diaphragm beam is free to move with respect to the one or more retaining wall elements.

12. The method of claim 11, wherein the process of fixing the at least one column element and at least one retaining wall element to the foundation element comprises: placing at least a portion of the at least one column element and at least a portion of at least one retaining wall element within a foundation cage; andfilling at least a portion of the foundation cage with concrete.

13. The method of claim 11, further comprising casting at least one column element operable to support a deck.

14. The method of claim 11, further comprising casting at least one retaining wall element operable to support a deck, optionally wherein the casting of the at least one retaining wall element is remote from the bridge abutment.

15. The method of claim 11, wherein the at least one column element and at least one retaining wall element are a single interconnected element.

16. The abutment of claim 9, wherein the capping panel is separated from the retaining wall by an elastically compressible seal.

17. The method of claim 13, wherein the casting of the at least one column element is remote from the bridge abutment.

18. The method of claim 14, wherein the casting of the at least one retaining wall element is remote from the bridge abutment.