GB2092210A - Suspension bridges - Google Patents

Abstract

In the erection of a main suspension cable 11 of a suspension bridge without the use of a preliminary footway, several preformed parallel multi-wire strands 6 from which the main cable is to be formed are drawn over and between the bridge towers by haulage ropes 12, the trailing length of each strand 6 being supported within roller-carrying spacers 15 suspended from fixed support lines 16 positioned below and to one or each side of the path to be taken by the main cable; at least one additional fixed line 20 is provided across the span to support motorised man-carrying trolleys 19 which can be driven along the span to provide manual access to strands 6 supported within the spacers 15 and to the main cable 11 itself. Subsequent erection work is carried out using a cable- supported working platform. <IMAGE>

Description

SPECIFICATION Suspension bridges This invention relates to suspension bridges and more especially to methods of erecting the cables of such bridges and to apparatus for use in such erection.

Generally, the main suspension cables for such bridges consist of a large number of parallel steel wires. Until recently, the accepted method of erection of such cables was by in situ "spinning." However, this is a long, tedious and complex labour-intensive operation requiring expensive and complicated equipment.

More recently, erection times and costs have been significantly reduced using cables made up of a number of preformed parallel wire strands.

These benefits accrue principally because of the significantly increased number of wires which can be strung across the bridge span in a single exercise with consequent increases in productivity. Hitherto, however, erection using this and other methods has required the use of an elaborate footbridge across the entire bridge span to act as staging for the labour force to assist in guiding and correctly locating the preformed strands, and subsequent banding and wrapping of the erected cable. The erection of such a footbridge is both time consuming and expensive.

The present invention sets out to provide an improved method of erecting suspension bridge cables which avoids the need for such a footbridge thereby providing substantial savings in time and cost.

According to the present invention in one aspect, there is provided a method oferecting a main suspension cable of a suspension bridge in which several preformed parallel wire strands from which the main cable is to be formed are drawn over and between towers across the span to be bridged and, as they are drawn, each strand is supported within a plurality of spacers suspended from fixed support lines positioned below and to one or each side of the path to be taken by the main cable, said method including the steps of providing at least one additional fixed line across the span in the vicinity of the main cable path and suspending from said additional line one or more trolleys which can be driven along the span to provide manual access to strands supported within the spacers and to the main cable itself.

According to the present invention in another aspect there is provided apparatus for use in the erection of the main cable of a suspension bridge such apparatus including one or more motorised trolleys operable to be supported from lines across the span to be bridged, the lines being sited to facilitate access from the motorised trolleys to the path taken by the main cable during erection.

In one embodiment of the invention the motorised trolleys consist of a man-carrying carriage driven by one or more motors connected to drive wheels which track over the trolley support lines. Pressure rollers may be provided to trap the trolley support line between said pressure rollers and the drive wheels.

According to the present invention in another aspect, there is provided apparatus for use in the erection of a suspension bridge comprising a movable working platform supported between the main cables of the suspension bridge and including two elongate structures connected to the leading or trailing edge of the platform one about each main cable and adapted to provide access to the main cables.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side view of a conventional suspension bridge; Figure 2 and 3 are respectively a sectional and a side view of one of the several parallel wire strands from which the main cables of the bridge are constructed: Figure 4 is a section taken through the several ropes and apparatus employed during erection of a main bridge cable using a method in accordance with the present invention; Figure 5 and 6 are respectively plan and side elevational views of a working platform assembly used during the erection of the suspension bridge; Figure 7 is a section to an enlarged scale taken along line VIl-VIl of figure 5; and Figure 8 and 9 are enlarged sections taken respectively along lines Vill-VIll and IX-IX of Figure 6.

As will be seen from Figure 1, the roadway 1 of a suspension bridge is suspended from hangers 2 supported from main suspension cables 3 which extend between achorages 4, across the span to be bridged and are themselves supported between towers 5 positioned along the span. Each main cable consists of a plurality of preformed parallel wire strands 6 which are conveniently hexagonal in cross-section and which, in turn, consist of a plurality of parallel wires 7. Such a strand is shown in cross-section in Figure 2 and in side elevation in Figure 3. Because of the massive nature of the main suspension cables, it is not possible to erect these merely by hauling them over the towers and across the span.

Thus, they are built up in situ from the preformed parallel wire strands which are individually hauled across the span by means of a non-twist haulage rope reeved from a reel positioned on one side of the span through a tensioner through blocks located at the top of each tower, through a puller winch positioned on the other side of the span and finally on to a reeler.

Each preformed parallel wire strand is attached to the haulage rope through a socket and the haulage rope is operated from the puller to move the strand socket with strand attached from one anchorage over and between the support towers to its anchorage on the other side of the span.

The various cables and ropes employed during erection of a main cable are illustrated in Figure 4.

The main cable is shown in broken line and bears the reference numeral 11. Located above the main cable is the haulage rope 12 with socket 1 3 and trailing preformed parallel wire strand 6 attached.

As the strand 6 is hauled across the span, its trailing length is supported within a succession of spacers 1 5 supported from anchored roller support ropes 1 6 extending across the entire span to be bridged. Each spacer 1 5 includes a convergent entry section 1 7 and a roller 1 8 rotatable about a horizontal axis. The rollers have a surface profile complementary to the crosssection of the strand 6. As shown in Figure 4, two series of spacers 1 5 are provided, one such series being positioned just below and on each side of the line to be taken by the main cable 11 , to enable two preformed strands to be simultaneously or sequentially hauled across the span.

After the preformed strand has been hauled across the span, it is tensioned to raise it from the spacers and is lifted at the towers to enable it to be moved sideways to take up its final position within the main cable. During both the haulage and the positioning stage, manual access to the strand and to the main cable along the entire length of the strand and the cable is essential. In the present invention, this access is achieved by means of one or more motorised trolleys 19 supported from anchored trolley support ropes 20.

The trolley may be driven along the support ropes 20 by any conventional means (eg. a hydraulic, petrol-driven or electric motor) located within the trolley itself. In one example, the trolley comprises four driven wheels 21 which track over the upper surface of a pair of parallel ropes.

Pressure rollers 22 may be sited below the cables to urge the ropes into contact with the respective wheel.

On completion of the haulage phase, the strand 6 is resting on the rollers 1 8 of the spacers 1 5 and on rollers located on top of each support tower.

Further, the strand end sockets are lying inside the anchorages on each side of the span and the load throughout the strand is minimal.

For the purpose of erecting each strand 6 into the main cable, split clamps are bolted onto the strand at each tower to enable the strand to be lifted, and moved sideways. Split clamps are also attached to the strand some distance from each anchorage, and tackles reeved from these clamps to the anchorage itself.

Thus, when the tackles at each end are operated to tension the strand the strand will lift out of the rollers 1 8 supported from the roller support ropes 16 and will eventually hang in free catenaries between each anchorage and the nearest tower and between the two towers, resting only on the rollers located at each anchorage and tower.

The longitudinal position of the strand in the main span relative to the towers can then be adjusted by operation of tackles at the anchorage, until survey marks 23 (see Figure 3) on one wire in the strand coincide roughly with complementary survey marks on the tower saddle. The strand is now lifted, moved sideways, and placed into the appropriate groove in the tower top saddle. Fine adjustment of the longitudinal position of the strand can be achieved by light tackle at the tower top.

Once the strand has been properly positioned within the groove, its bindings 24 (see Figure 3) are cut and removed, whereupon the wires of the strand tend to fall to the bottom of the saddle groove and form into a rectangular cross section, completelyfilling the width of the groove.

The length of the strand between the tackles at the anchorage and the end socket of the strand is only under nominal tension at this time, so the socket can be inserted into the anchorage, correctly positioned and attached to the anchorage.

As each strand 6 is erected in its correct location in the main cable 11, it is clamped in this position in each of the several formers in the line of cable.

As will be seen from Figures 5 to 9, once the several parallel wire strands have been directed into the main cables, the cables may be used to support one or more working platforms 25 from which subsequent operations such as cable compaction, erection of cable bands and suspenders, erection of deck units and cable wrapping can be effected. The working platform comprises two transverse box-section beams 26 which span between the cables and are supported on trolleys 27 which track along the cables. The platform is moved along the cables by means of anchoring clamps 28 anchored around the main cables and tackles 29. The tackles 29 act as both pullers and preventers on both cables.

Projecting from and hingedly attached to the leading edge of the platform 25 is a pair of cable encompassing travellers 30 which provide ready access to the cable lengths immediately in advance of the platform. Each traveller consists of an open steel structure and supports a pair of rails 31 over which compaction and banding machines may run. The travellers are supported on the main cables 11 by rollers 32 which track over the cables.

Jibs, winches and other machinery required may be located on the platform.

Claims (11)

1. A method of erecting a main suspension cable of a suspension bridge in which several preformed parallel wire strands from which the main cable is to be formed are drawn over and between towers across the span to be bridged and, as they are drawn, each strand is supported within a plurality of spacers suspended from fixed support lines positioned below and to one or each side of the path to be taken by the main cable, said method including the steps of providing at least one additional fixed line across the span in the vicinity of the main cable path and suspending from said additional line one or more trolleys which can be driven along the span to provide manual access to strands supported within the spacers and to the main cable itself.

2. Apparatus for use in the erection of a main cable of a suspension bridge, such apparatus including one or more motorised trolleys operable to be supported from lines across the span to be bridged, the lines being sited to facilitate access from the motorised trolleys to the path taken by the main cable during erection.

3. Apparatus as claimed in claim 2 wherein the or each trolley is driven by one or more motors connected to drive wheels which track over the trolley support lines.

4. Apparatus as claimed in claim 3 wherein pressure rollers are provided to trap the trolley support lines between the pressure rollers and the drive wheels.

5. Apparatus for use in the erection of a suspension bridge comprising a movable working platform supported between the main cables of the suspension bridge and including two elongate structures connected to the leading or trailing edge of the platform one about each main cable and adapted to provide access to the main cables.

6. Apparatus as claimed in claim 5 wherein the working platform is supported between transverse beams which span between the main cables and are supported on trolleys which track along the cables.

7. Apparatus as claimed in claim 5 or claim 6 wherein the platform is movable along the main cables by means of clamps anchored to the main cables and co-operating tackles mounted on the platform.

8. Apparatus as claimed in any one of claims 5 to 7 wherein each elongate structure comprises a steel structure including rails over which cable compaction and/or cable banding machines may run.

9. A method of erecting a main suspension cable of a suspension bridge substantially as herein described with reference to the accompanying drawings.

10. Apparatus for use in the erection of a main cable of a suspension bridge substantially as herein described with reference to the accompanying drawings.

11. Apparatus for use in the erection of a suspension bridge substantially as herein described with reference to figures 5 to 9 of the accompanying drawings.