GB2290332A - A movable ground-supported bridge - Google Patents

Abstract

A movable ground-supported bridge is constructed from a plurality of modules (15) and has a framework comprising upwardly extending members (16) interconnected by horizontally extending members (17, 18) and overlain by a deck (11). The modules (15) are linked together to form the bridge and the bridge as a whole is provided with means permitting movement of the bridge along the ground in a direction generally parallel to the longitudinal dimension of the bridge. The bridge is suitable for use in motorway repair and maintenance when repair work takes place in the space beneath the deck. <IMAGE>

Description

A Ground Supported Bridge; and a Method of Working on a Roadway Employing Such a Bridge This invention relates, in a first aspect, to a ground supported bridge particularly but not exclusively intended to facilitate repair and maintenance work on roadways such as vehicular roadways.

In a second aspect, the invention relates to a method of working on a roadway e.g. a vehicular roadway, employing such a bridge.

The invention also relates to a framework module for use in constructing a bridge as aforesaid.

In many countries, particularly those in the Western hemisphere, much effort has been devoted to the construction of efficient road networks. In particular, many countries have developed extensive motorway, autobahn or autoroute networks.

The development of such networks has speeded road travel considerably, but many of the roads constituting such networks are now typically several decades old. The age of such roads, coupled with phenomenal increases in the volumes of vehicular traffic using them, have meant that many major roads undergo maintenance, repair and widening work on a virtually constant basis.

Hitherto, when it was necessary to work on, e.g., a six lane motorway having three lanes of traffic travelling in each direction, it has often proved necessary to close at least three of the lanes even when it is only desired to carry out work on one of them.

This need has arisen primarily because of an understandable desire on the part of motorway work contractors to protect their workers against accidents involving vehicles using the motorway. It has become a common practice to provide a protection lane adjacent the lane being worked on, so that moving vehicles are separated from the workforce by at least one clear vehicular lane that remains empty. In turn, this approach has led to the widespread use of so-called "contra-flows", wherein, for example, when it is required to work on a lane in the left hand carriageway of a motorway, some or all of the traffic is routed onto the right hand carriageway which is re-configured to become a dual purpose roadway. This frees space in the left hand carriageway to allow work to be carried out and to provide a protection lane.

Virtually all known techniques for providing a safe working zone for repair and maintenance contractors on motorways are undesirable because they inevitably reduce the vehicle carrying capacity of the road and moreover induce delays at the points where it is necessary to direct traffic onto an unorthodox path. Contra-flows are particularly disadvantageous because it is necessary to dismantle a part of the central reservation of the motorway to allow traffic from one carriageway to be directed onto the other carriageway. This is time consuming to achieve, and frequently is the cause of serious road accidents because many motorists approach the switchover point of the contra-flow at too great a speed and are unable to negotiate the bend necessary to place them safely on the opposite carriageway.Furthermore, vehicles travelling in opposite directions along the contra-flow are separated from one another by only a few feet, often with only lightweight plastic lane markers between tem. Thus, the chances of accidents between vehicles travelling in opposite directions along a contra-flow are high especially Then vehicles do not observe the speed limits imposed in the region of the contra-flow.

In the UK, repair and maintenance contractors tender for motorway and dual carriageway contracts on a penalty/incentive basis, whereby they are required to estimate the number of vehicular lanes that they will have to close to complete the requisite work safely, and the number of days for which the lanes will have to be closed. The Department of Transport rents the lanes to the chosen contractor at a rate of typically 25,000 per lane per day. This rental is intended to cover the "cost" to the Department of Transport of having the contractor occupy the roadway lanes.If the contractor completes his work quicker than he anticipated he will be able to remove his men and equipment from the motorway earlier than estimated thereby saving one or more days worth of multiples of the 25,000 daily rental; and if the contractor takes longer than estimated, he will be penalised by having to rent the lanes for longer.

It will be appreciated that a roadway maintenance/repair technique that does not result in the total closure of, e.g., an entire carriageway of motorway may enable a contractor to negotiate a reduced daily rental for the lanes needing work. There is therefore a need for an apparatus and/or a method that enables work to be carried out on vehicular lanes whilst permitting traffic to travel over substantially the same route as though the lanes in question were not closed.

According to a first aspect of the invention, there is provided a ground supported bridge comprising a plurality of upwardly extending frame members interconnected by horizontally extending frame members; a deck supported above ground level on at least one of said frame members; and means permitting movement of the bridge along the ground in a direction generally parallel to the longitudinal dimension of the bridge.

The advantage of this arrangement is that the bridge can be constructed over a length of roadway to be worked on. Vehicular traffic can pass over the lanes undergoing work without having to change direction significantly (in contrast to the arrangement in a contra-flow).

Moreover, the overall number of lanes available to carry vehicles need not be reduced when it is required to work on the roadway. Therefore, the contractor's occupation of the roadway can be said to be reduced and a lower lane rental should apply.

Since vehicles are not required to change direction when approaching the bridge, the chances of accidents caused by motorists approaching the bridge too fast are reduced. Moreover, workers working on the roadway beneath the bridge are protected from accident since the vehicles do not travel at the same level as the workers. In addition, the bridge can provide shelter against bad weather (thereby enabling work to continue even during severe weather conditions) and a storage facility for the contractor's equipment; moreover, suitable lighting can be supported beneath the deck to illuminate the working area without dazzling or confusing motorists travelling over the working area on the bridge. A further advantage of the invention is that vehicles do not have to travel in opposite directions on the same carriageway, as is the case when a contra-flow is created.

When work on a particular length of roadway is completed, the bridge can be moved along the roadway to permit work to be carried out on the next adjoining length of roadway.

Conveniently, the frame members are constituted as a plurality of releasably interconnected framework modules secured in a serial relationship along the length of the bridge.

This makes the bridge easy to construct, and also enables the construction of bridges of differing lengths for different applications.

When the bridge comprises framework modules as aforesaid, the bridge may optionally include adjacent framework modules adapted to support the deck at differing heights, whereby to confer a non-horizontal gradient on at least part of the deck.

It is believed that a bridge of "hump-backed" shape is likely to provide the maximum working space beneath the deck whilst also providing a safe approach to the bridge and departure from the bridge for motor vehicles. A series of modules that provide a gradual change in gradient of the deck by supporting it at successively differing heights can advantageously achieve this result.

Preferably the upwardly extending frame members are spaced from one another in the transverse direction of the bridge and a plurality of horizontally extending frame members extend transversely of the bridge further than the lateral extent of the upwardly extending frame members, whereby a deck of greater width than the lateral spacing between the upwardly extending members may be supported.

Conveniently, the bridge includes at least one strut interconnecting an upwardly extending frame member and a horizontally extending member.

In such an embodiment, when the upwardly extending frame members are spaced laterally as aforesaid, the strut may extend transversely of the bridge in the space between adjacent upwardly extending frame members.

Alternatively, the strut may extend in the transverse direction beyond the lateral extent of the upwardly extending frame members; and in a particularly preferred embodiment, the strut is selectively securable in the first position extending transversely of the bridge in the space between the upwardly extending frame members and a second position extending in the transverse direction beyond the lateral extent of the upwardly extending frame members.

These features advantageously allow sequential working in the vicinity of the outer and inner lanes of a carriageway. In practice, the bridge will preferably include a plurality of struts interconnecting a plurality of pairs of upwardly and horizontally extending frame members whereby to confer adequate strength on the structure.

In preferred embodiments, alternate pairs of upwardly extending frame members are interconnected in the longitudinal direction of the bridge by means of bracing members. This arrangement again confers strength on the structure whilst providing spaced apertures in the upwardly extending sides of the structure whereby to permit entry and exit of contractors' vehicles and workmen.

Conveniently, each upwardly extending frame member terminates at its free end in a wheel adapted to run on or in conjunction with a groundmounted guide rail or slot. This advantageously may ensure that the bridge is moveable along a predetermined path along a roadway. Typically, the bridge will be configured to move along a kind of rail known as a bridge rail, which is of a suitable profile to support the weight of the bridge without damaging the roadway surface on which the bridge stands or moves. Nonetheless, other designs of rail and/or guide slot may optionally be employed.

As an alternative or in addition to the provision of wheels at the free ends of the upwardly extending members, each upwardly extending frame member may terminate at its free end in a ground engaging pad and/or roller. The use of such apparatus advantageously spreads the load of the bridge on a roadway, and if rollers are included it is easy to move the bridge without the need for modification of the support structure.

In preferred embodiments, the bridge includes at least one upstanding parapet extending longitudinally along the deck thereof. In practice, at least two parapets will be provided, one on either side of the deck. The parapets prevent vehicles from inadvertently driving off the edge of the deck.

When the bridge is constituted as a series of modules, the parapet may include a plurality of parapet modules each securable to a respective framework module. Thus, a framework module may be assembled with a parapet module in situ so that the parapet is formed as a continuous protective wall when the framework modules are assembled together.

Conveniently, the parapet is removable from the bridge.

In particularly preferred embodiments, as indicated above, the bridge is configured to carry e.g. motor vehicles. When so configured, the deck preferably is sufficiently wide to provide a plurality of vehicular lanes delineated side by side thereon. Suitable markings or projections can be applied to the upper surface of the deck to provide this feature.

It is also preferable that the height at which the deck (or a substantial part thereof) is supported is adjustable. It may be advantageous when the bridge is constructed as a large item perhaps more than 300 metres long to be able to lower the deck on the structure while the bridge is being moved along the roadway. This would minimise the risk of the bridge toppling over during such moving. In addition, this feature would allow the bridge to pass under eg low permanent bridges traversing a roadway. lssn general, the bridge of the invention can be sized to pass under motorway bridges of a standard height, which is greater than 5.3m in the UK, without the need for lowering.However, there may be occasions when there is a need to reduce the height of the bridge to allow it to pass under other structures.) Conveniently, the bridge includes a lead-in ramp interconnecting the deck and any ground on which the bridge stands. In practice, there will be provided a lead-in ramp at each end of the bridge whereby the approach to and exit from the bridge are constituted as gentle gradients relative to the road surface on which the bridge stands.

According to a second aspect of the invention, there is provided a framework module for use in constructing a bridge as specified hereinabove, the module comprising a plurality of upwardly extending frame members interconnected by horizontally extending frame members; a deck supported above ground level on at least one of said frame members; and means permitting movement of the bridge along the ground in a direction generally parallel to the longitudinal dimension of the bridge.

The provision of the bridge in the form of a plurality of modules ensures that the structure is advantageously versatile, and facilitates in the erection and dismantling of the bridge.

According to a third aspect of the invention, there is provided a method of repairing or otherwise working on a roadway, e.g. a vehicular roadway, comprising the steps of (i) constructing or erecting a bridge in accordance with a first aspect of the invention and/or employing a module in accordance with a second aspect extending over a length of roadway to be repaired or otherwise worked on, whereby vehicular traffic may travel over the length of roadway on the bridge; (ii) repairing or otherwise working on the length of roadway in the space beneath said bridge; and either (iii) dismantling or removing the bridge; or (iv) moving the bridge along said roadway, whereby said bridge overlies a further length of said roadway to be repaired or otherwise worked on.

A method of this kind advantageously solves the previously mentioned disadvantages of contra-flows and in addition may permit a contractor to negotiate a reduced lane rental since it is not necessary to divert vehicles to an opposite carriageway to enable the work to be carried out.

Conveniently, when the roadway includes multiple lanes and the bridge is constructed in such a manner as to permit selective securing of strut members either overlying a central portion of the roadway or outer portions of the roadway beneath the bridge, the method may advantageously be modified in that the step (ii) of repairing or otherwise working on the roadway includes the sub-steps of: (iia) repairing or otherwise working on a first lane or set of lanes spaced from one or more further lanes lying generally beneath a strut secured in its first position; (iib) releasing the strut and re-securing it in its second position, whereby to allow access by workers to said one or more further lanes; and (iic) repairing or otherwise working on said one or more further lanes.

Alternatively, the strut may optionally initially be secured in its second position and subsequently secured in its first position, thereby allowing work on the further lane or set of lanes in advance of work on the irst lane or set of lanes.

When the deck is securable at adjustable heights on the upwardly extending frame members, the step of moving the bridge along the roadway may advantageously be preceded by the step of lowering the or a part of the deck on the bridge. Of course, once the bridge is installed in a new location it would be necessary to raise the deck to its full height before vehicles can be allowed to pass onto the bridge.

There now follows a description of preferred embodiments of the invention, by way of example, with reference being made to the accompanying drawings in which: Figures 1 to 4 are schematic, side elevational views showing typical length and height considerations in bridges constructed in accordance with the invention; Figure 5 is a side elevational view of a plurality of framework modules joined together to form part of a bridge such as shown in Figures 1 to 4; Figure 6 is a top plan view of a framework module such as shown in Figure 5, when configured to allow work on the central part of a roadway beneath the bridge; Figure 7 is a view similar to Figure 6 showing the framework module converted to allow work on the outer regions of a roadway beneath the bridge; Figure 8 is an end elevational view on arrow A of Figure 6; Figure 9 is an end elevational view on arrow A of Figure 7; and Figure 10 is a side elevational view on arrow B of figure 7, showing some features of the bridge and framework module in greater detail.

Referring to the drawings, and initially to Figures 1 to 4, there is shown in schematic form a bridge 10 in accordance with the invention.

Bridge 10 includes a deck 11 that for simplicity of illustration is shown in an arcuate form. It will be appreciated that, in reality, deck 11 is more likely to be formed as a series of abutting, flat deck portions each of which is inclined at a slightly different angle to create the impression of an arcuate deck when the bridge 10 is fully erected.

Furthermore, a suitable surface cladding which preferably is flexible can be laid over the deck 11 to tend to smooth the profile of the upper surface of the bridge to an arcuate shape.

The deck 11 and the associated support structure is constructed primarily from steel, in a manner described below. At each end of deck 11, there is provided a transition ramp 12 manufactured from lightweight concrete and secured to the bridge 10. The transition ramp 12 is intended to provide a smooth lead in from the road surface 13 on which the bridge stands, and a smooth lead out onto the road surface 13 for traffic leaving the bridge 10.

Each of the embodiments shown in figures 1 to 4 has been designed with different criteria in mind.

The bridge shown in Figure 1 is designed so that the maximum height of the deck surface above the road surface 13 (i.e. dimension A in Figure 1) does not exceed 5 metres. The bridge of Figure 1 is intended to accommodate motor vehicles travelling at approximately 80.45 Km/h (50 mph). At such a speed, the minimum stoppage distance for a motor vehicle in good driving conditions is loom. Therefore, the driver of a motor vehicle must have a clear sight line of 110m at all times whilst travelling on the bridge. These two requirements lead to a bridge of the profile shown, the overall ground length B of which (including the transition ramps 12) is 332.5 metres. The angle of each transition ramp is such that the transition ramps each account for 38m of this ground distance at either end of the bridge.

The design of bridge shown in Figure 1 has a central zone identified by reference C 64m long having a clear headroom of 4 metres or greater.

The length of the zone D having a clear headroom of 3.5 metres or greater is 120m, and the length of the zone E having a clear headroom of 3m or greater is 200m. Thus, it will be seen that a bridge of this general design provides a large working area underneath the deck 11.

The bridge shown in Figure 2 was designed also to have a maximum deck height above the road surface 13 of 5m. However, the Figure 2 embodiment is intended to accommodate vehicles travelling at a maximum speed of 48.27 Km/h (30 mph) in respect of which the minimum safe sight line required is 50m. A bridge constructed according to these criteria has an overall ground length B of 169m, of which 26m at each end is constituted by the bases of the transition ramps 12.

In the embodiment of Figure 2, the central zone C having a clear headroom of 4m or greater extends for 30m about the centre of the bridge 10; the zone D having a clear headroom of 3.5m extends for 54m; and the zone E having a clear headroom of 3m extends for 71m.

Figure 3 shows a bridge design in which it is required to have a 50m length either side of the centre of the bridge in which the clear headroom exceeds 4m. The Figure 3 embodiment is intended to accommodate vehicles travelling at 8045 Km/h. The overall height A of the deck above the road sface 13 is 4.925m; the ground length B of the bridge is 330.lm of which 38m at each end is constituted by the bases of the respective transition ramps 12; and in addition to a central zone 50m long having a clear headroom of 4m, the Zone D having a clear headroom of 3.5m extends for 12m about the centre of the bridge 10 and the zone E having a clear headroom of 3m extends for 152m about the centre.

The Figure 4 embodiment is similar to the Figure 3 embodiment, except that the Figure 4 embodiment is intended to accommodate vehicles travelling at 48.27 Km/h. The overall height A of the deck of this bridge above the road surface 13 is 5.4m; the overall ground length B is 176m, of which 26m at each end is taken up by the bases of the respective transition ramps 12; in addition to the zone C 50m long having a clear headroom of 4m or greater, the zone D having a clear headroom of 5m or greater extends for 68m; and the zone E having a clear headroom of 3m or greater extends for 82m.

It will be seen from the foregoing exemplary embodiments that numerous design considerations can influence the overall profile of a bridge according to the invention, and that a great range of bridge sizes - from a few metres long to many hundreds of metres long - may readily be devised. In all the embodiments of Figures 1 to 4 there is provided significant space under the deck 11 in which large equipment such as earth moving equipment and road surfacing equipment may readily be manoeuvred and operated.

Referring now to Figure 5, there is shown a side elevational view of a portion of a bridge 10 such as shown in Figure 1 to 4. The portion shown in Figure 5 is a region of the bridge in which the gradient of the deck 11 is substantially flat.

It will be seen in Figures 5 to 7 that in preferred embodiments the bridge is constituted by a plurality of framework modules 15 mounted on a road surface 13 in a serial relationship. Each module 15 comprises a plurality (4 in the embodiment shown) of upstanding frame members 16 supporting a pair of transversely extending, generally horizontal members 17 and a plurality of longitudinally extending, generally horizontal members 18. As is shown in the Figure 5 embodiment, the upstanding and horizontal frame members are formed as I-beams fabricated, e.g., from steel. Numerous other beam profiles and materials could readily be used.

The lower, free end of each upstanding frame member 16 is secured to a ground engaging pad 20. In the embodiment shown, the pad 20 is constituted as a concrete block having the lower end of a respective upstanding frame member 16 secured thereto. However, the pads 20 can be constructed in a number of ways. For example, the pads may be of a steel or other metal construction and may optionally include rollers whereby the modules 15 may be moved along the roadway surface 13.

Instead of the pads 20, the free ends of the upstanding frame members 16 may terminate in wheels intended to ride on or in appropriate guide rails, slots or tracks. The tracks may be temporarily or permanently secured to the road surface 13 to ensure that the modules 15, when moved, travel in the desired direction.

The upstanding frame members 16 of alternate modules 15 in the series include pairs of diagonally extending cross braces 21 extending from corner to corner of the rectangle defined by the generally horizontal members 18, the upstanding members 16 and the road surface 13.

As a result of the presence of the cross braces 21, when the modules 15 are secured together to form a bridge the overall structure is of significant rigidity; however, alternate framework modules 15 are effectively open-sided, thereby allowing ready access to the underside of the bridge by workmen and equipment. Since the result of this arrangement is a plurality of open-sided modules 15, there is provided a large number of possible entry and exit points to the underside of the bridge.

Alternatively, in cases where the security of equipment stored under the bridge is important, the number of open-sided modules 15 can be reduced to a minimal number and lockable and/or removable gates provided to seal the open-sided modules 15 to prevent unauthorised removal of equipment.

A further option is for each module 15 to have cross braces 21 on one side only, such that the open-sides are provided on opposite sides of the bridge in alternate modules 15.

As is most clearly shown by the dotted outline in Figure 5, the upper edge of the deck 11 carries a pair of longitudinally extending parapets 22 that run along the outer edges of the deck 11. The parapets 22 prevent vehicles driving on the deck 11 from falling off the bridge.

It may optionally be possible to provide a further, central parapet to separate traffic travelling in opposite directions.

The modules 15 may typically be secured together by means of pin joins, bolts, spring clips or interlocking detents similar to railway clings. Numerous other arrangements would undoubtedly also occur to a worker skilled in the art.

In the embodiment shown, the approximate length of each framework module 15 is lOm. However, other lengths of module may readily be constructed and employed.

Figures 6 and 7 show plan views of typical modules such as the modules 15 of Figure 5, in two different configurations.

In the Figure 6 embodiment, which corresponds to the arrangement shown in end elevation in Figure 8, it will be seen that there are provided eight longitudinal, generally horizontally extending members 18 and the upwardly extending members 16 are secured to the undersides of the second and seventh longitudinal generally horizontal members 18 counted from the left hand side of Figures 6 and 7. The transverse horizontal members 17 are positioned to extend parallel to one another overlying the attachment points of the upstanding frame members 16.

As is best shown in Figure 8, a strut 23 extends between the lowermost end of each upstanding frame member 16 and the underside of the outermost, longitudinal members 18, to support that part of the deck that overhangs the region laterally beyond the upstanding frame members 16.

This arrangement is shown by a dotted line in Figure 6. This configuration of module 15 provides a large working area underneath the central zone thereof. Therefore, this module configuration is particularly suitable for permitting work to be carried out on, for example, the central two lanes of a four lane carriageway or the central lane plus half of each of the outer two lanes of a three lane carriageway.

The arrangement shown in Figure 7, to which Figure 9 corresponds is similar to that of Figure 6 except that the upstanding frame members 16 are secured to the undersides of the third and sixth longitudinal members 18 instead of the second and seventh such members, and the struts 23 extend from the bases of the upstanding frame members 16 towards the fourth and fifth longitudinal members 18 respectively. This arrangement permits access to, e.g., the outer two lanes of a four lane carriageway or the outer lanes plus a portion of the central lane of a three lane carriageway.

It is desirable to be able to switch the bridge modules 15 between the configuration shown in Figure 6 and the configuration shown in Figure 7. This may be achieved either by having permanently constructed examples of the respective modules of Figures 6 and 7 interchanging them as necessary when it is desired to work on different parts of the carriageway; or by providing joints between the longitudinal members 18 and the members 16, 23 connected thereto such that the members 16, 23 may readily be moved between the configurations shown in Figures 6 and 7 while the modules 15 remain in situ. In the latter case, it may be necessary to provide temporary jacks to support part of or the entire load of a module 15 while the members 16, 23 are released and re-attached in a new position.

The free ends of the longitudinal members 18 are provided with e.g.

eyes that can be brought into register with corresponding eyes in the members 18 of adjacent modules, whereby the modules may be pin jointed together. Typically, of the eight members 18 it would be expected to provide such eyes in four of them. A further pair of eyes can be provided at each end of two further members 18, whereby the module 15 may be towed when it is required to move it along the motorway.

Reference to Figure 8 shows that when the struts 23 extend outwardly of the base of the bridge, they are intended to engage and be secured to the underside of the outermost, longitudinal members 18 by means of e.g.

a tension screw arrangement as shown. However, depending on the height of the upstanding frame member 16, when the members 16, 23 are moved to adopt the configuration shown in Figures 7 and 9 the strut 23 may not coincide exactly with the fourth and fifth longitudinal members 18. In such a case, it is necessary to provide a cover plate 24 on the underside of the horizontal members 18 whereby the load borne by the struts 23 may be transmitted from the fourth and fifth longitudinal members 18. This situation arises because in the embodiment shown the first and eighth longitudinal members 18 are spaced transversely from the second and seventh such members 18 respectively by a greater distance than the spacing between the remainder of the members 18.

Referring to Figure 10, there is shown an example of a braced module 15 in greater detail. The braces 21 are secured to the remainder of the members by means of suitable tension nuts secured in appropriately shaped housings. The ends of the braces 21 are threaded to engage the tension nuts (not shown) whereby the tension in the braces may be adjusted to an appropriate level.

Figure 10 shows in more detail the deck 11, which is constituted by a steel deck plate 11a and a packing material in the form of e.g.

resilient, transversely extending members such as railway sleepers or equivalents thereto constructed from synthetic materials. Other packing materials may be used e.g. steel plates or a layer of synthetic or bituminous wear-resistant material. The upper surface of any packing material may be treated to provide a non-slip surface for vehicles.

In use of the bridge of the invention, once an appropriate size and length of bridge has been chosen for the work to be undertaken and the desired speed of travel of vehicles over the bridge, it is necessary to construct a bridge from an appropriate number of modules 15 of varying heights and/or gradients whereby the arcuate shape of the bridge may be achieved. The modules 15 are pre-fabricated away from the work site, so as to minimise assembly time which would necessitate complete closure of a road or carriageway.

The modules 15 would be manoeuvred into position on the roadway, e.g. by means of towing them on their rollers or wheels by means of cables attached to the appropriate longitudinal members 18. The final positioning of the modules could be achieved by pushing instead of towing, if insufficient space remains to tow the modules precisely into position.

Once in position, the appropriate longitudinal members 18 are pin jointed together, whereby to form a rigid, substantially continuous bridge structure. If necessary, the rollers, wheels, etc. may be locked e.g. by the application of braking mechanisms (not shown) or by driving pegs or wedges either under the pads 20 or into the ground to prevent undesirable movement in the longitudinal direction of the bridge.

Once the bridge structure is complete, it would be necessary to add packing such as packing 11b to the deck plate gila. If the modules 15 are brought onto site lacking the parapet components 22, it would be necessary in addition to secure suitable parapet modules along the edges of the deck 11 in a serial relationship as shown in the drawings.

The modules 15 would in most applications initially be configured so that, e.g., all of the struts 23 initially extend outwardly of the bases of the modules 15. This would allow continuous working on the length of the central portion of roadway beneath the bridge 10, typically over a length of some hundreds of metres.

Once the work on the central region of roadway beneath the bridge 10 is completed, and depending on the need to work on additional lanes of the carriageway, it would be necessary to move the upstanding members 16 and the struts 23 so that each module adopts generally the configuration shown in Figures 7 and 9. This would permit work to be carried out in the outermost parts of the roadway beneath the bridge 10.

Once all work is completed on a length of roadway, the bridge as a whole can be moved along the roadway if desired to enable the procedure to be repeated in respect of an adjoining length of roadway. The procedure may be repeated as many times as is necessary to complete the work on a chosen length of roadway.

The workmen operating under the bridge are fully protected against contact with vehicles travelling over their heads. In the unlikely event of a vehicle driving through the parapet 22 off the edge of the bridge 10, the vehicle would be projected clear of the sides of the bridge 10 thereby minimising the risk of injury to workers below.

The underside of the bridge 10 and/or the upstanding frame members 16 provide convenient attachment points for power outlets and lighting equipment. It is noteworthy that any lights employed under the bridge can be directed downwardly by means of appropriate shades and reflectors, thereby minimising the risk of confusion to motorists travelling overhead on the deck 11. This is in direct contrast to the situation in contraflows, where the headlights of oncoming vehicles and the proliferation of warning lamps and traffic cones frequently serve to confuse motorists at night, thereby increasing the risk of accidents in such contra-flows.

Claims (25)

1. A ground supported bridge comprising a plurality of upwardly extending frame members interconnected by horizontally extending frame members; a deck supported above ground level on at least one of the frame members; and means permitting movement of the bridge along the ground in a direction generally parallel to the longitudinal dimension of the bridge.

2. A bridge according to Claim 1 wherein the frame members are constituted as a plurality of releasably interconnectable framework modes secured in a serial relationship along the length of the bridge.

3. A bridge according to Claim 2, including adjacent framework modules adapted to support the deck at differing heights, whereby to confer a nonhorizontal gradient on at least part of the deck.

4. A bridge according to any preceding claim, wherein the upwardly extending frame members are spaced from one another in the transverse direction of the bridge and wherein a plurality of horizontally extending frame members extend transversely of the bridge further than the lateral extent of the upwardly extending frame members, whereby a deck of greater width then the lateral spacing between the upwardly extending members may be supported.

5. A bridge according to any preceding claim including a strut interconnecting an upwardly extending frame member and a horizontally extending member.

6. A bridge according to Claim 5 wherein the upwardly extending frame members are spaced from one another transversely of the bridge and wherein the strut extends in said transverse direction in the space between adjacent upwardly extending frame members.

7. A bridge according to Claim 4 and Claim 5, wherein the strut extends transversely of the bridge beyond the lateral extent of the upwardly extending frame members.

8. A bridge according to Claim 5, wherein the upwardly extending frame members are spaced from one another in the direction parallel to the transverse direction of the bridge and wherein the strut is selectively securable in a first position extending transversely of the bridge in the space between the upwardly extending frame members, and a second position extending transversely of the bridge beyond the lateral extent of the upwardly extending frame members.

9. A bridge according to any of Claims 5 to 8 including a plurality of struts interconnecting a plurality of respective pairs of upwardly and horizontally extending frame members.

10. A bridge according to any preceding claim wherein alternate pairs of upwardly extending frame members are interconnected in the longitudinal direction of the bridge by bracing members.

11. A bridge according to any preceding claim wherein each upwardly extending frame member terminates at its free end in a wheel adapted to run on or in conjunction with a ground-mounted guide rail or slot.

12. A bridge according to any preceding claim wherein each upwardly extending frame member terminates at its free end in a ground engaging pad and/or roller.

13. A bridge according to any preceding claim, including at least one upstanding parapet extending longitudinally along the deck thereof.

14. A bridge according to Claim 2 and Claim 13, wherein the parapet includes a plurality of parapet modules each securable to a respective framework module.

15. A bridge according to any preceding claim adapted to carry e.g.

motor vehicles, wherein the deck includes a plurality of vehicular lanes delineated side by side thereon.

16. A bridge according to any preceding claim including means whereby the height at which the deck, or a substantial part thereof, is supported is adjustable.

17. A bridge according to any preceding claim including a lead-in ramp interconnecting the deck and any ground on which the bridge stands.

18. A bridge generally as herein described, with reference to or as illustrated in the accompanying drawings.

19. A framework module for use in constructing a bridge according to any of Claim 2 to 18, the module comprising a plurality of upwardly extending frame members interconnected by horizontally extending frame members; a deck supported above ground level on at least one of said frame members; and means permitting movement of the bridge along the ground in a direction generally parallel to the longitudinal dimension of the bridge.

20. A framework module generally as herein described, with reference to or as illustrated in the accompanying drawings.

21. A method of repairing or otherwise working on a vehicular roadway, comprising the steps of: (i) constructing or erecting a bridge according to any of Claims 1 to 18 extending over a length of roadway to be repaired or otherwise worked on, whereby vehicular traffic may travel over the length of roadway on the bridge; (ii) repairing or otherwise working on the length of roadway in the space beneath said bridge; and either (iii) dismantling or removing the bridge; or (iv) moving the bridge along said roadway, whereby said bridge overlies a further length of said roadway to be repaired or likewise worked on.

22. A method according to Claim 1 wherein the roadway includes multiple lanes and the bridge is constructed according to Claim 8, the method being modified in that the step (ii) of repairing or otherwise working on the roadway includes the sub-steps of: (iia) repairing or otherwise working on a first lane or a set of lanes spaced from one or more further lanes lying generally beneath a strut secured in its first position; (iib) releasing the strut and re-securing it in its second position, whereby to allow access by workers to said one or more further lanes; and (iic) repairing or otherwise working on said one or more further lanes.

23. A method according to Claim 22 modified in that the strut is initially secured in its second position and subsequently secured in its first position, and in that step (iic) is replaced by step (iia) and vice versa.

24. A method according to any of Claims 21 to 23, wherein the bridge is constructed in accordance with Claim 16 and wherein the step (iv) of moving the bridge along the roadway is preceded by the step of lowering the or a part of the deck on the bridge.

25. A method generally as herein described, with reference to or as illustrated in the accompanying drawings.