GB2278384A

GB2278384A - Arch bridge constructed by initially positioning an arch former

Info

Publication number: GB2278384A
Application number: GB9409448A
Authority: GB
Inventors: Ronald Jarman Bridle
Original assignee: BULLEN AND PARTNERS
Current assignee: BULLEN AND PARTNERS
Priority date: 1993-05-13
Filing date: 1994-05-12
Publication date: 1994-11-30
Anticipated expiration: 2014-05-12
Also published as: GB2278384B; GB9409448D0

Abstract

An arch bridge is constructed by positioning an arch former (12) of polymer concrete and using this as a basis for forming a main arch (14 - 20). By forming an articulated concrete ring (16) over joint formers (14), constructing spandrel walls (18), and placing spandrel fill (20), the arch former (12) may be left in place as part of the permanent structure or removed for re-use. <IMAGE>

Description

"Arch Structures" This invention relates to a method of forming an arch and is particularly, but not exclusively, of relevance to arch bridges, either by way of new construction or as a strengthening or rebuilding of an existing bridge; and to a device for use in such method.

Arch bridges have been known from antiquity, but are little used in modern practice. This is principally because it is necessary to construct a temporary framework on which the arch is constructed, and thereafter to remove the temporary framework. This adds to the cost and the time of construction. There are however situations in which an arch form would be desirable for aesthetic or technical reasons.

The invention provides a method of constructing an arch structure comprising the steps of providing supports at either side of a desired span, positioning an arch former between said supports, the arch former comprising one or more arch former sections of polymer concrete and spanning from one support to the other, and forming a main arch of another material on top of the arch former.

Preferably the polymer concrete is more elastic than the other material.

Further according to the invention there is provided an arch structure having supports at each side of a span, an arch former of polymer concrete spanning from a support on one side of the span to a support on the other side, and a main arch of another material on top of the arch former.

In a preferred application of the invention, the arch structure is an arch bridge. The bridge may be a single arch bridge, in which case each of said supports is an abutment. Where the bridge is a multi-arch bridge, there will be one or more intermediate supports in the form of a pier.

Preferably, the arch former is used without any support other than said supports.

The arch former may be permanently included in the structure or may provide a temporary shutter which may be reusable.

Preferably, the arch former is composed of one or more arch former sections of a polyurethane/sand concrete.

The arch former section(s) may optionally be reinforced by a cast-in polymer reinforcement.

The main arch is preferably formed from conventional concrete, most suitably as an articulating ring section formed in situ, optionally within spaced joint formers.

Alternatively the main arch may be constructed of assembled blocks.

The method of the invention may be used to construct a bridge from new. It may also be used to amend a horizontal beam bridge, constructing an arch bridge by way of strengthening or incorporation within the new structure.

From another aspect, the invention provides an arch former section for use in the method of constructing an arch structure as defined above, the arch former section comprising an arcuate sheet of polymer concrete.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view, partially broken away, of a bridge constructed from new by the method of the present invention; and Fig. 2 is a cross-section illustrating the use of the present invention in modifying an existing bridge.

Referring to Fig. 1, a bridge has conventional abutments 10a, lOb formed in any suitable manner, such as in situ reinforced or mass concrete. An arch former 12 is placed on the abutments 10. The arch former is a single member formed of pre-assembled precast polymer concrete units which, being of relatively light weight, may be craned into place as a single item. In other embodiments the arch former may be constructed as a unitary structure rather than as an assembly of units.

Polymer concretes are known per se. A suitable material is a vegetable oil based polyurethane binder with a suitable filler, such as sand. Polymer concretes of this nature are available from NRG Chemical Engineering Limited of Birtley, County Durham.

Many formulations of polymer concrete are available.

In this embodiment the material has a combination of low weight and high tensile strength, about one third the density and three times the tensile strength of conventional concrete. This allows the arch former 12 to be cast off-site, and transported and craned into place.

Although a single arch former 12 is shown, where necessary a series of arch formers side by side may be used.

Once the arch former 12 is in place, it is used without additional propping as a support on which are positioned joint formers 14. Conventional concrete is cast in the joint formers 14 to form an articulating concrete ring 16. Thereafter, a spandrel wall and vehicle parapet 18 is constructed along each side of the arch, for example from precast blocks or by casting within temporary shuttering, and spandrel fill 20 is placed within the spandrel walls 18 to bring the structure to the desired roadway level. A soil reinforcement element which in this case is a polymer grid 22 attached to the articulating ring 16 may be buried in the spandrel fill 20; this increases the load bearing capacity of the ring 20. The bridge is then completed by applying any suitable cladding 24 to the side faces.

Fig. 2 illustrates the same principles applied to the repair and upgrading of an existing bridge.

The existing bridge has a flat deck 30 supported by central piers 32. The polymer concrete arch former 12 is placed under the existing bridge deck 30, and used to construct an arch ring of concrete blocks 34 cast in situ within joint formers (not shown in Fig. 2) on the arch former 12 in the same manner as in Fig. 1. Shear keys 36 are provided between the blocks 34 and the arch former 12; this helps to maintain the arch monolithic and thus to reduce the mass required. The existing piers 32 are built into the arch ring.

The space between the arch ring and the soffit of the existing deck 30 is then filled with spandrel fill 37, suitably by grouting with foamed concrete. It is preferred to break the original deck 30 in the area of the pier crosshead, as indicated at 38, so that the completed bridge acts as an arch and not as a composite beam. Finally, the original piers 32 are removed below the arch former 12.

It is possible to carry out the procedure illustrated in Fig. 2 while the original bridge remains in use.

In the example shown, the abutment 10a is a gravity abutment and the abutment 10b is secured by permanent rock anchors 10c. However, any form of abutment suitable for the site may be used.

In both of the embodiments described above, the polymer concrete arch former has sufficient strength that no temporary falsework is required, and becomes part of the completed structure which reduces the material required in the concrete ring. The entire structure can be free of ferrous materials, and there are no exposed structural joints on the underside of the arch. A long maintenance-free life can therefore be expected.

Although described principally with reference to bridges,the invention is of use also for other forms of arch structure, such as colonnade walls and domes.

In accordance with the invention, the arch former is of polymer concrete, which is extensible; that is, it is capable of resisting tensile forces produced by the loads exerted by the other material during construction of the main arch. It is also preferred that the polymer concrete is more elastic than the main arch; that is, it is of a material having a substantially lower Young's modulus. This has the effect of allowing the arch former to flex when the structure is subjected to settlement or loading of a nature which causes movement of the main arch. In a traditional arch structure formed of masonry blocks, movement of this nature causes cracking or loss of mortar from joints on the underside of the arch which may reduce the load carrying capacity but, even before the load carrying capacity is affected, the structure gives an unsafe appearance which causes concern to users. The use of a relatively flexible, permanent arch former avoids these problems.

Modifications may be made to the foregoing embodiments within the scope of the invention.

Claims

1. A method of constructing an arch structure comprising the steps of providing supports at either side of a desired span, positioning an arch former between said supports, the arch former comprising one or more arch former sections of polymer concrete and spanning from one support to the other, and forming a main arch of another material on top of the arch former.

2. A method as claimed in Claim 1, wherein the polymer concrete is more elastic than said other material.

3. A method as claimed in any Claim 1 or Claim 2, wherein the arch former is formed by pre-assembled units.

4. A method as claimed in any one of Claims 1 to 3, wherein the arch former is preformed before positioning between said supports.

5. A method as claimed in any one of the preceding claims, wherein the arch former contains reinforcement.

6. A method as claimed in any one of the preceding claims, wherein the main arch is formed as an articulating ring section.

7. A method as claimed in any one of Claims 1 to 5, wherein the main arch is formed by an assembly of blocks.

8. A method as claimed in any one of the preceding claims in the form of a single arch structure.

9. A method as claimed in any one of Claims 1 to 7 in the form of a multi-arch structure.

10. A method as claimed in any one of the preceding claims, wherein the arch former is permanently included in the structure.

11. A method of constructing an arch structure substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

12. A method of constructing an arch structure substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

13. An arch structure having supports at each side of a span, an arch former of polymer concrete spanning from a support on one side of the span to a support on the other side, and a main arch of another material on top of the arch former.

14. An arch structure substantially as hereinbefore described with reference to and as shown in Fig. 1 of the accompanying drawings.

15. An arch structure substantially as hereinbefore described with reference to and as shown in Fig. 2 of the accompanying drawings.

16. An arch structure constructed by the method claimed in any one of Claims 1 to 12.