Load Bearing Moulded Article

This invention relates to a load bearing reinforced moulded article. Reinforced plastics moulded articles of the type to which the invention relates may be suitable for uses as road plates, load bearing panels, barriers, partitions, walkways or roadways, or for shoreing up the sides of excavations. Further applications include bridge decking, manhole/cavity covers, temporary roadways and load spreading pads for example for use beneath the feet or cranes or the like.

Plastics road plates for positioning over excavations formed in footpaths or roadways are well known. In one known form a plastics moulded panel is provided, on one surface thereof, with a matrix of ribs, the ribs serving to inhibit or resist flexing of the panel. Such road plates perform satisfactorily under relatively low load conditions, but under higher loadings the ribs tend to deform or the intersections between ribs fail allowing the panel to flex to an unacceptable degree. Anotiber known type of road plate comprises two skins of a plastics material spaced apart from one another. A core fills the space between the skins. In use, if a load is applied to the road plate, one of the skins will be in compression, and the other in tension. A shear force is transmitted between the skins through the core, and this requires the core to be well adhered to the skins and to be of a material that will not disintegrate on repeated flexing. These constraints limit the maximum load that can be carried by the road plate. A further disadvantage associated with this type of road plate is that the manufacturing process used is typically a hand lay up process or a low pressure resin injection moulding process, and these processes are relatively slow.

It is an object of the invention to provide a moulded article in which these disadvantages are of reduced effect.

According to a first aspect of the invention there is provided a unidirectional load bearing article comprising a plastics moulded panel having integral ribs formed upon a surface thereof, elongate reinforcing members being located within the ribs.

The article is unidirectional in the sense that, when supported at two of its opposing sides it is able to bear relatively large loads, the weight bearing capacity being lower when supported only by its other two opposing sides.

The elongate reinforcing members are conveniently in the form of steel rods. The steel rods are preferably provided with a surface texture, providing a mechanical lock between the rods and the plastics material. The surface texture may comprise, for example, ribs or screw threads. Depending upon the application, it may be preferred to use elongate reinforcing members of another material, for example a suitable plastics material.

The elongate reinforcing members conveniently define a matrix. The members are preferably welded to one another. Such welding preferably occurs prior to moulding the plastics material around the reinforcing members.

The article is conveniently of generally planar form.

It will be appreciated that the location of the reinforcing members within the ribs at positions spaced from the planar part of the article results in the article bearing loads in a manner similar to an T section beam, the planar part of the article being in compression whilst the reinforcing members are under tension. Relatively large loads can be borne in this manner.

Where the moulded article comprises a road plate, it may be of square or rectangular form, and may taper adjacent at least some of the edges thereof to form ramps, reducing the formation of a trip hazard. It may taper on only two opposing sides and be designed so as to allow a plurality of individual plates to be used side-by-side. This is advantageous where a relatively long area needs to be covered, particularly if the plates are to bear heavy loads as the individual plates are easier to move than a single, large plate. Where plates are used side-by-side, conveniently, means are provided to secure the individual plates to one another. This may be achieved using, for example, bolts, appropriate formations moulded into the plates, or appropriately designed clips.

It is desirable to restrict movement of a road plate, in use, as such movement may result in the plate becoming unstable and/or incapable of bearing the necessary loads. Typically, this is achieved by bolting the plate to the surface upon which it is used, or by placing, for example, tarmac adjacent the edges of the plate. These techniques are inconvenient.

A stop device may be secured or securable to the panel, the stop device being engageable with the wall of a cavity, hole, trench or the like covered by the cover to restrict movement of the cover.

The stop device may comprise one or more stop members securable to the cover in a range of positions, for example using key-hole slots provided in a securing strip mounted to the cover, or resiliently adjustable stop arrangements. The resiliently adjustable arrangements could use, for example, springs or hydraulic means to provide the resilience. Another possibility is to provide the cover with movable stops forming the stop device, the stops being drivable by, for example, a rack and pinion type arrangement.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of the underside of a moulded article in accordance with an embodiment of the invention;

Figures 2 to 6 are sectional views along the Lines 2-2, 3-3, 4-4, 5-5 and 6-6 of Figure 1;

Figure 7 is a perspective view of an alternative embodiment;

Figures 8 and 9 illustrate a further embodiment;

Figures 10 to 20 illustrate further embodiments; and

Figure 21 illustrates another embodiment.

The moulded plastics article illustrated in Figures 1 to 6 of the accompanying drawings is a unidirectional road plate intended to cover a channel or cavity which has been dug in a road surface or walkway to permit access to underground service pipes, cables or the like. The road plate comprises a plastics moulding having a generally flat, panel-like, upper part 10 from which a series of ribs 12 depend. The ribs 12 extend both longitudinally and laterally of the road plate. As illustrated in the drawings, the upper part 10 is conveniently of slightly convex form as this improves the ability of the road plate to withstand high loadings, and may taper towards its edges to form ramps, thereby minimising the formation of a trip hazard.

As illustrated most clearly in Figures 2 and 3, most of the ribs 12 have, buried therein, an elongate reinforcing member in the form of a length of steel rod 14. Each steel rod 14 extends over substantially Hie full length/width of the road plate, terminating very slightly short of the edges of the road plate so as to be fully enclosed by the plastic material of the rib 12. The rods 14 are located close to the lowermost edge of each rib 12.

The steel rods 14 are conveniently of 10mm diameter, although it will be appreciated that rods of other diameters could be used. Further, reinforcing members of other cross-sectional shapes could be used. The rods 14 are provided with a series of

ribs which, in use, form a mechanical lock with the plastics material of the ribs 12, thus inhibiting relative axial movement of the plastics material of the ribs 12 relative to the rods 14. An additional mechanical lock is formed where the rods 14 pass over and are secured to one another.

As illustrated in Figures 1 and 5, the ribs 12 and rods 14 which extend across the width of the road plate are not equally spaced but rather are spaced in such a manner as to ensure that those parts of the road plate which require the greatest level of reinforcement are provided with rods 14 located relatively close to one another, the rods 14 being spaced apart by a greater distance where less reinforcement is required. The ribs 12 could be equally spaced if desired. The rods 14 and ribs 12 which extend along the length of the road plate may similarly be irregularly spaced, but in the illustrated embodiment are equally spaced.

Figures 1 and 4 illustrate the central rod 16 extending across the width of the road plate. The central rod 16 differs from the rod 14 in that it is of tubular form and also in that it is of larger diameter, for example 20mm. Again, a surface texture may be provided to form a mechanical lock with the plastics material. The use of a tubular member as one of the reinforcing members allows cables or the like to be carried by the road plate, if desired, and may also enhance the load bearing capacity of the road plate.

The road plate is manufactured by prefabricating a matrix comprising the rods 14 and the rod 16, by welding or otherwise securing the roads 14, 16 to one another. The matrix is located within a compression moulding press, the mould being shaped to

define channels used to form the ribs 12. The matrix is fitted into the channels of the mould. Once correctly positioned, a suitable plastics material is introduced into the mould, the plastics material being compression moulded around the matrix to fully enclose the rods 14, 16 and becoming locked thereto such that a load applied to the road plate is transmitted to the rods 14, 16.

If desired, the upper surface of the upper part 10 may be textured to reduce the risk of slipping. The texture may be applied during the moulding process.

Alternatively, a separate textured sheet may be secured to the upper part 10, for example by adhesive. Further, the road plate may be brightly coloured so as to be clearly visible.

Conveniently, during the moulding process, a fibre reinforced plastics material is used. Conveniently, the material is of the type m which the reinforcing fibres are generally aligned with one another. Consequently, the strength of the road plate in the unidirectional load bearing direction is enhanced.

The invention is advantageous in that where an article includes ribs which cross over one another, when a load is applied to such an article, there is tendency for one or more of the ribs to fail at the intersection. By providing reinforcing members in both ribs, the reinforcing members extending continuously over substantially the full length/width of the article, then the risk of such failure is reduced and even if the ribs fail, the load is transmitted along the broken ribs by the reinforcing member thus maintaining the load bearing capacity of the article.

Although not illustrated, the road plate may be provided, along an edge thereof, "with several protruding lugs, the lugs being engageable with formations provided along an edge of a second, adjacent, road plates permitting the road plates to be secured to one another using, for example, bolts. Such a connection technique can be used to ensure that loading bearing capability of a road plate assembly made of several load plates located adjacent one another is not significantly weaker at the edges of each road plate than it is at the centre of each road plate.

Figure 7 illustrates a road plate 20 of construction similar to that described hereinbefore, particularly intended for use in applications where relatively heavy loads are to be supported. The main differences between the arrangement of Figure 7 and that described hereinbefore is that the arrangement of Figure 7 is of rectangular form with only two opposing edges 22 being tapered to form ramps, the other two opposing edge walls 24 being upstanding. Although not illustrated, the upper surface 26 of the plate 20 is conveniently provided with a surface texture to reduce slipping. The plate 20 may be coloured in order to be clearly visible. Further, it may be provided with means to allow two or more plates 20 located adjacent one another to be secured to one another. One simple way of achieving this is to provide openings 28 in the walls 24 such that the openings 28 provided in adjacent plates 20 are aligned, and using bolts to secure the plates together. Alternatively, a range of clip or clamp devices could be used to achieve this function, or formations may be moulded into the plates 20 to achieve this function.

Where two or more plates 20 are located adjacent one another, the plates 20 may be of different colours to further enhance the visibility of the plates 20. An alternative

design of plate 20 may be provided for use at an end of a row of plates 20, the alternative design being ramped along its free edge to reduce the risk of tripping. The alternative design may, further, be of curved, for example substantially semi-circular form rather than rectangular in shape, if desired.

By providing plates 20 which are securable to one another, it will be appreciated that a relatively large hole, trench, opening or the like may be covered using components of weight and dimensions allowing relatively easy handling and storage thereof. The arrangement of Figure 7 is particularly advantageous in applications in which a relatively long, narrow hole or trench is formed, and in which vehicles pass over the plate in only two opposing directions, i.e. where unidirectional loads are applied. The plates 20 conveniently link together in only a single direction.

The load bearing capacity of the cover plate is designed to be greater in one direction than the other, for example by appropriate selection of the sizes of the reinforcing components, and/or by alignment of the fibres, for example glass fibres, of the moulded part of the cover, as mentioned hereinbefore.

Further, as the covers are designed to be positioned abutting one another, the design is such that the relatively weak lines which would occur if covers of the type shown in Figure 1 were placed in abutment are avoided.

Conveniently, steel plates are provided in the tapering edges of the covers. Consequently, the edges of the covers can be of reduced thickness, thereby forming less

of a trip hazard, without weakening the covers. The steel plates are conveniently secured to the reinforcing members, for example by welding. One or more handling recesses may be moulded into the covers to assist a user in being able to grip and lift a cover from, for example, a road surface.

There is a risk, with all of the arrangements that, once positioned over a hole, trench, cavity or the like, lateral movement of the road plate may occur, for example due to vehicles passing over the plate pushing the plate. If the plate were to move beyond a predetermined position, then the stability and/or load bearing capacity of the plate may be impaired. Figures 8 and 9 illustrate a road plate 30 similar to that of Figures 1 to 6 having means to resist such movement. As illustrated, a block 32 of a rigid foamed plastics material is provided, the block 32 having grooves 34 formed therein, the dimensions and spacing of the grooves 34 being such that when secured to the underside of the road plate 30, as shown hi Figure 9, the grooves 34 accommodate parts of some of the ribs 36 provided on the road plate 30 as described hereinbefore. The block 32 is conveniently retained in position using a hook and loop, Velcro-type fastening but it will be appreciated that a number of other fastening techniques may be used. For example, the block could be bolted in position using bolts passing through one or more of the ribs. Alternatively, a resilient detent mechanism may be used.

In use, the road plate 30 with the block 32 secured thereto is positioned over a hole, trench, etc, to be covered with the block 32 located within the opening. If lateral movement of the plate 30 occurs, a point will be reached at which the block 32 abuts the

side wall of the hole, restricting further movement of the plate 30, the movement being restricted before the stability or load carrying ability of the plate is reduced.

As the sideways movement of the plate 30 is restricted using the block 32 which engages the ribs 36, and so transmits its loadings directly to the ribs of the plate, it will be appreciated that no significant changes need to be made to the plate 30, and that the mechanism or technique used to secure the block in position only needs to be able to bear the weight of the block rather than being required to transmit the loads from the block to the plate.

The block 32 is provided with several grooves 34 so as to enable use with a range of plates 30.

The block 32 may be designed so as to permit other components to be secured thereto. For example, the block 32 may be designed to carry auxiliary sρacer(s) for use in the event that the opening with which the plate is used is relatively large and so even small movement of the plate may render it unstable or unable to bear the required loadings. In such arrangements, the auxiliary spacer(s) carried by the block 32 would be located between the block 32 and the edge or side wall of the opening, hole or trench and arranged to bear against the edge or side wall to prevent further movement of the plate after only a very small amount, if any, of movement of the plate has occurred.

The block 32 may be designed to accommodate an end of, for example, an expandable prop so as to allow the plate to be provided with additional support, in use.

It will be appreciated that this technique may also be used with plates of the type shown in Figure 7. If desired, the blocks 32 could incorporate at least part of the means for securing the plates to one another.

Figures 10 to 17 illustrate further techniques to prevent or restrict movement of a road plate or other device, for example being used to cover a cavity, hole, trench or the like. Figures 10 and 11 illustrate two similar arrangements in which the "underside of a cover 100 has one or more mounting strips 102 secured thereto, for example by means of bolts or other screw threaded fasteners or using other types of fastener, the strips 102 having key-hole shaped slots 104 formed therein. Stop members in the form of wedges 106 are securable to the strips 102 using the key-hole slots 104. It will be appreciated that the locations of the wedges 106 can be chosen to suit the application in which the cover is used and the size of the cavity so that, once the cover is positioned over the cavity, engagement of the wedges 106 with the walls of the cavity restrict lateral movement of the cover. Some of the key-hole slots 104 could also be used to mount connector devices for connecting adjacent plates to one another.

Figure 12 illustrates an. arrangement in which the underside of the cover is provided with a pair of hydraulic actuators 108 which can be operated to bring pads UO into engagement with the walls of a cavity to restrict movement. Figure 3 illustrates a similar arrangement, but in which the pads 110 are moved by a rack and pinion type arrangement 112.

Figure 14 illustrates an arrangement in which the cover is provided with fixed stops 114 arranged to abut one side wall of a cavity, spring means 116 engaging an opposing side wall to hold the cover in position. Rather than use spring means 116,

Figure 15 shows the use of a hydraulic type spring means 118. A ratchet mechanism could be used, if desired.

Figure 16 illustrates the use of bracing bars 120 which are adjusted to fit a cavity, a cover subsequently being provided over the bracing bars. Figure 17 illustrates an arrangement in which the bracing bars 120 are spring biased by a resilient member 122 and are arranged in a scissor-like fashion to permit automatic adjustment.

The cover device illustrated in Figures 18 to 20 comprises a plastics moulded cover 150, the underside of which is formed with a series of ribs 152 containing a matrix of reinforcing members, for example in the form of steel rods or bars. Secured to the underside of the cover 150 are a pair of socket members 154. Each socket member 154 is shaped to define a generally cylindrical opening 156 from which a pair of laterally extending recesses 158 extend. Each recess 158 opens into a groove or recess 160 defined between the socket 154 and the cover 150.

The device further comprises a pair of stop members 162, each of which is of generally cylindrical form and includes, at one end, a pair of radially extending lugs 164.

In order to secure each stop device 162 to the associated socket 154, the stop device is inserted into the opening 156 with the lugs 164 located within the recesses 158. Once fully inserted into the opening 156, the stop device is twisted about its axis to move the lugs 164 out of alignment with the recesses 158, the lugs 164 being retained within the grooves or recesses 160. It will be appreciated that such fitting of the stop devices 162 is a bayonet-type fitting.

In use, a number of sockets 154 are conveniently provided in a range of different locations. By appropriately selecting into which of the sockets 154 the stop devices are secured, it will be appreciated that the spacing of the stop devices may be chosen so as to be similar to the width of the trench, hole or cavity to be covered by the cover device. Consequently, upon positioning of the plate 150 over the hole, trench or cavity, the stop devices can engage the side walls of the hole, trench or cavity, thereby restricting lateral movement of the cover device, in use.

Figure 21 illustrates the underside of a road plate of the type described hereinbefore having ribs 36 formed thereon. A mounting plate 200 is secured to the road plate between adjustment ones of the ribs 36. Conveniently the mounting plate 200 is secured in position using, for example, bolts, but it could be secured using other techniques, for example using suitable adhesive. The plate 200 may be of metallic, for example steel, form or could, alternatively, be of a plastics material. Where of a plastics material, the plate 200 may be of injection moulded nylon form and may include integral connecting lugs or other formations.

The plate 200 is adapted to allow the temporary connection of other components, for example clamping devices to grip the sides of the trench, connecting devices to connect individual plates to one another, support or prop devices, to the plate.

The close fit of the plate 200 between the ribs 36 assists in transferring transverse loads to the road plate.

Although in the arrangements described hereinbefore, in which a plurality of road plates or covers are used side-by-side, each road plate may be provided with means to limit movement of the road plate, where the road plates are connected to one another then perhaps only a central one of the road plates, or two of the road plates, may be provided with such means.

Although the description hereinbefore is of a road plate, it will be appreciated that the invention is applicable to other moulded articles, for example panels for use in shoreing up the sides of excavated cavities, manhole covers, bridge decking or boards for use on scaffolding, temporary roadways, temporary bridges or temporary footpaths. This invention could also be used in load bearing pads for use with the feet of cranes or similar devices or many other applications. The invention is particularly applicable to generally planar load bearing panels where the load is always applied in the same direction, thus it can be ensured that the ribs 12 and the rods 14 are always under tension, in use, the panel 10 experiencing a compressive load. Panels of this type are relatively lightweight but capable of bearing high loads. Manufacture using the method described hereinbefore can be achieved quickly and economically.

Another application in which the invention can be used is in safety or security barriers of the type including a pair of uprights interconnected by one or more crossbars.

The reinforcing members may extend along the uprights, and may also be provided within one or more of the crossbars. It will be appreciated that the openings maybe formed between the crossbars, if desired.