MANHOLE COVER

Abstract: A manhole cover (1) comprising a top (2) and a base (4) which define a space therebetween, and reinforcing walls (8') which extend at least partially between the top (2) and base (4) to define voids (10, 10') within the so-defined space, wherein the reinforcing walls (8'), and hence the so-defined voids (10, 10'), radiate from the centre region of the cover.

Description: MANHOLE COVER The present invention relates to a manhole cover for closing an opening in a surface, such as a road or garage forecourt surface, the cover being receivable within a frame set in the surface to surround the opening. Manhole covers known in the art take many varied forms and have been constructed of various different materials. One known form employs glass reinforced plastics (GRP) and/or carbon fibre material. In known manhole covers employing these materials, the structure of the cover presents a dish-shaped base closed by a generally flat top, to define therebetween a space which is filled with a suitable reinforcing material, typically a foamed plastics material. Some of these know manhole covers also include a latticework structure of reinforcing walls within the space between the top and base, which provides the covers with added strength. However these known forms of manhole cover suffer from the disadvantages of being relatively heavy and expensive to manufacture and/or tend to possess insufficient strength and rigidity to withstand deformation of the top and compression of any internal reinforcing material, particularly when made of plastics materials. It is an object of the present invention to provide a manhole cover which overcomes or at least substantially reduces the foregoing disadvantages associated with known manhole covers. According to the present invention, there is provided a manhole cover comprising a top and a base which define a space therebetween, and reinforcing walls which extend at least partially between the top and base to define voids within the so-defined space, characterised in that the reinforcing walls radiate (extend radially outwardly) from the centre region of the cover. The voids defined by the radially outwardly extending (radiating) reinforcing walls, will, in the majority of cases, also extend radially outwardly (radiate) from the centre region of the cover. The top and base of the cover are preferably joined together at their peripheries and in a preferred embodiment of the inventive manhole cover, the reinforcing walls may be provided by an insert, preferably preformed, which can be corrugated by alternating crests and troughs which radiate from the centre region of the insert and between which radially extending voids are defined. In this manner, the crests and troughs of the reinforcing walls may provide alternately inverted channel sections which extend radially outwardly from the centre region of the insert and which define the radially outwardly extending voids. The corrugations provided by the alternating and radiating crests and troughs of the reinforcing walls, may be of any suitable cross-section, for example, rectangular, square or sinusoidal (arcuate) and, also, may increase in cross-section radially outwardly of the insert, such that the so-defined voids also increase in cross-section radially outwardly of the insert . The manhole cover preferably has a peripheral wall which may depend from the periphery of the top or upstand from the periphery of the base. The base may be dish-shaped to provide it, and hence the cover, with additional rigidity. Preferably, the top, base and reinforcing walls, such as the preformed insert, of the cover are formed of a glass reinforced plastics (GRP), a carbon fibre material, or any other suitable composite material or any combination thereof. Any preformed insert providing the reinforcing walls, may be of such a thickness, measured from trough to crest, that, with the troughs resting on the internal surface of the base, the crests support the internal surface of the top. Such internal surfaces of the base and tops, respectively, may be adhered, for example by a polyester adhesive, to the troughs and crests which provide the reinforcing walls of the preformed insert . The manhole cover of the present invention may take any desired shape when seen in plan view. Typically, it may be either polygonal, such as square, or circular. Thus, the reinforcing walls, and hence the voids defined therebetween, when seen in plan view, may be of generally "star" or "sunburst" shape, having a plurality of "rays" radiating from a common centre region. Although in the preferred embodiment of cover which utilises a preformed insert, any other suitable form of structure may be used for the reinforcing provided only that it affords the radially extending voids within the space between the top and base of the manhole cover. The manhole cover may have its peripheral wall shaped to be received in, and engage, an internal peripheral wall of a complementary frame, there preferably being provided on respective ones of the peripheral walls formations which can be brought into mutual retaining engagement by relative rotation between the manhole cover and frame. Preferably, the retaining formations are arranged to operate on the principle of a bayonet joint, with, say, a plurality of locking lugs projecting from the exterior peripheral wall of the manhole cover and a lip or lips, or other complementary locking lugs, on the internal peripheral wall of the frame. With the retaining formations in mutual retaining engagement, the manhole cover can be retained to the frame and may only be released therefrom by relative contra-rotation between the manhole cover and frame, in order to bring the retaining formations out of their mutual retaining engagement. Preferably, at least one stop member is provided on the manhole cover or the frame in order to limit relative rotation therebetween in the locking sense so that, when the retaining formations have been brought into full mutual retaining engagement, further relative rotation between the manhole cover and frame is prevented. A manhole cover constructed in this manner is, in plan view, preferably circular in shape and may be fitted with a circular-shaped frame. Embodiments of manhole cover in accordance with the present invention will now be described in detail by way of example only and with reference to the accompanying drawings in which: Figure 1 is a top plan view of a first embodiment of square manhole cover; Figure 2 is a side cross-sectional view of the first embodiment of manhole cover shown in Figure 1; Figure 3 is an exploded view, in perspective, of the manhole cover shown in Figures 1 and 2 , in association with a corresponding frame; Figure 4 iε a side cross-sectional view of a second embodiment of circular manhole cover; Figure 5 is a partial plan view of the manhole cover shown in Figure 4; and Figures 6A and 6B show details of the manhole cover of Figures 4 and 5. Referring firstly to Figures 1 to 3 of the drawings, a manhole cover 1 comprises a substantially flat top 2 having a slightly downturned peripheral lip 3 and a dish-shaped base 4 having a substantially flat bottom and an upstanding peripheral wall 5 terminating at its upper end in a downturned peripheral lip 6. Received within the dish-shaped base 4, and just encompassed within the overall height of its peripheral wall 5, is a preformed insert 7 formed as a unitary member having integral alternating crests 8 and troughs 9 arranged at a suitable mutual spacing and radiating from the centre 7' of the insert 7, to provide reinforcing walls 81 radiating from the centre of the insert 7. As best seen in Figure 2, bottom flat surfaces of the troughs 9 rest on the internal flat bottom surface of the base 4 and the preformed insert 7 is preferably secured in position within the base 4 by a suitable, for example polyester, adhesive applied between the bottom flat surfaces of the troughs 9 of the insert 7 and the internal bottom flat surface of the base 4. The assembly of the manhole cover 1 is completed by attachment of the top 2 , such that its peripheral lip 3 lies in superposition with the peripheral lip 6 of the base 4, and the internal flat surface of the top 2 rests upon, and is supported by, the upper flat surfaces of the crests 8 of the preformed insert 7. A suitable, for example polyester, adhesive may be applied between the peripheral lips 3, 6 and the internal flat surface of the top 2 and upper flat surfaces of the crests 8, in order to secure the top 2 in firm engagement with the base 4 and internal preformed insert 7. In such assembled condition of the manhole cover 1, the preformed insert 7 rests in the space defined between the top 2 and base 4 and the voids 10 defined between the alternating crests 8 and troughs 9 are left unfilled. Preferably, the top 2, base 4, and preformed insert 7 are formed of a glass reinforced plastics (GRP) material, a carbon fibre material, or any other suiteable comosite material or any combination thereof . As best seen in Figures 1 and 3, the manhole cover 1 is of generally square outline shape, this being determined by the outline shape of the square base 4. The preformed insert 7 formed to fit within the square base 4, has a plurality of radiating channel sections in the form of the peripherally alternating crests 8 and troughs 9 which provide upstanding reinforcing walls 8' defining therebetween spaces which, in the completed assembly of manhole cover member 1, will form respective unfilled voids 10, 10'. The radiating channel sections give the preformed insert 7 the appearance of a "star" or "sunburst" in which "rays" extend radially from a common centre. Although this is the currently preferred form of the preformed insert 7, it may, alternatively, take other forms provided that they afford radially extending reinforcing walls spaced to define the voids 10, 10' within the space defined between the top 2 and base 4 of manhole cover 1. The manhole cover member 1 need not be of square shape, as shown, but may, alternatively, be of any other suitable shape, for example circular. Irrespective of the shape of the manhole cover 1, it is constructed to cooperate, in use, with a correspondingly-shaped frame 20, as shown in Figure 3, set around an opening in a surface, for example a roadway or garage forecourt surface. In that form of the manhole cover and complementary frame which are substantially circular in shape, in plan view, there may be provided complementary formations which may be brought into mutual retaining engagement by relative rotation between the manhole cover and frame. As best seen in Figures 4 and 5, a manhole cover 1', which is constructed substantially in accordance with the present invention described above in relation to Figures 1 to 3, namely, that is has defined between its top and base a plurality of radiating reinforcing walls and voids, cooperates, in use, with a frame 20'. The manhole cover 1' has an external peripheral wall 11 and the frame 20' has a complementary shaped internal peripheral wall 21. Provided on the external peripheral wall 11 of the manhole cover 1', and projecting radially therefrom, is a plurality, here shown as three, of locking lugs 12 which are arranged to cooperate with a similar plurality of locking lugs 22 provided at appropriate positions on the internal peripheral wall 21 of the frame 20'. The locking lugs 12, 22 are arranged to operate in the manner of a bayonet joint. Thus, and as seen in Figure 5, with the manhole cover 1' resting loosely within the frame 20', rotation of the manhole cover 1' in the direction of the arrow A relative to the frame 20' will cause its locking lugs 12 to slide relative to the locking lugs 22 of the frame 20' to a position where the locking lugs 22 of the frame 20' overlie the respective locking lugs 12 of the manhole cover 1'. As best seen in the detailed views of Figures 6A and 6B, each locking lug 12 on the manhole cover 1' has an elongate main body portion arranged at a small angle to the horizontal plane P of rotation of the manhole cover 1', and an upstanding end stop member 12' which, when the position of full interengagement between the locking lugs 12, 22 has been reached, forms an abutment surface for the cooperating frame locking lug 22 and hence, affords an end stop preventing further relative rotation between the manhole cover 1' and the frame 20'. The arrangement of the main body of each locking lug 12 at a slight angle to the horizontal ensures that, upon relative rotation between the manhole cover 1' and frame 20', the corresponding pairs of lugs 12, 22 come into mutual engagement, or break free of mutual engagement, smoothly and positively. Furthermore, during rotation of the manhole cover 1' to its retained position, this slight inclination of the main body of each locking lug 12 ensures that the manhole cover 1' is pulled down slightly but firmly in relation to the frame 20' as the locking lugs 12, 22 gradually come into fuller engagement. This ensures that a proper seal is provided between the manhole cover 1' and the frame 20'. As with the first embodiment of manhole cover described above, this second embodiment of manhole cover is constructed of glass reinforced plastics (GRP), carbon fibre material or any other suitable composite material or any combination thereof. It will readily be appreciated that the provision of this simple bayonet-type joint eliminates complicated locking mechanisms, whilst affording a secure and firm retention of the manhole cover 1 to the surrounding frame 20'. Further, and as shown diagrammatically in Figure 4, the shapes of the external peripheral wall 11 and internal peripheral wall 21 of the manhole cover 1' and frame 20', respectively, are such as to minimise the possibility of ingress of dirt and moisture whereby, with the manhole cover 1' properly engaged and sealed to the frame 20', the likelihood of seizing up of the manhole cover 1' within the frame 20' is minimised. The arrangement of locking lugs interengageable by rotation, as afforded in this second embodiment, is a simple, economic, and reliable means of retaining the manhole cover 1' within the frame 20'. Whilst the present invention has been described above in detail related to the currently preferred embodiments thereof, it is to be understood that any variations or modifications such as fall within the broadest scope of the invention or inventions stated within this specification are to be regarded as falling within the scope of the present invention. Thus, for example, the preformed insert 7 of the first embodiment is not limited to the precise detailed construction illustrated in the drawings . For example also, the alternating crests and troughs of the reinforcing walls may be of arcuate, such as, sinusoidal, form rather than of square form. The peripheral wall of the manhole cover need not be a part of the base and could be formed as a separate entity or integral with the top member and the number and arrangement of locking lugs provided in the second embodiment may vary. Furthermore, it is not necessary for the retaining means comprising the complementary locking lugs 12, 22 described in the second embodiment to be combined with the manhole cover of the first aspect embodiment. Thus, manhole covers according to the present invention, afford a lightweight, yet very strong, manufacture. By virtue of the internal supports provided by the radiating reinforcing walls in whatever form, the manhole covers are stronger and less susceptible to deformation and destruction than known manhole covers in the art constructed of GRP and/or carbon fibre materials or any other composite material. The strength and rigidity of the inventive manhole covers arise primarily from the presence and form of the radiating reinforcing walls and to this extent it is usually unnecessary for any internal reinforcing filling materials, such as the foamed plastics of the prior art constructions, to be used. However, in certain circumstances, such as very heavy duty usage, at least some of the voids defined by the radiating reinforcing walls could be filled at least partially with an internal filling material, such as a foamed plastics material.

Claims: CLAIMS 1. A manhole cover comprising a top and a base which define a space therebetween, and reinforcing walls which extend at least partially between the top and base to define voids within the so-defined space, characterised in that the reinforcing walls radiate from the centre region of the cover 2. A manhole cover according to claim 1, wherein the voids defined by the radiating reinforcing walls, also radiate from the centre region of the cover. 3. A manhole cover according to claim 1 or 2, wherein the top and base of the cover are joined together at their peripheries. 4. A manhole cover according to claim 1, 2 or 3, wherein the reinforcing walls are provided by an insert. 5. A manhole cover according to claim 4, wherein the insert is preformed. 6. A manhole cover according to claim 4 or 5, wherein the insert is corrugated by alternating crests and troughs to form the reinforcing walls which extend radially from the centre region of the insert and which define the radially extending voids. 7. A manhole cover according to claim 6, wherein the corrugations formed by the alternating crests and troughs provide alternately inverted channel sections which extend radially (radiate) from the centre region of the insert and which define the radially extending 8. A manhole cover according to claim 6 or 7, wherein the corrugations formed by the alternating crests and troughs of the reinforcing walls, are of rectangular, square or sinusoidal (arcuate) cross- section. 9. A manhole cover according to claim 6, 7 or 8, wherein the radially extending corrugations increase in cross-section radially outwardly of the insert, such that the so-defined voids also increase in cross- section radially outwardly of the insert. 10. A manhole cover according to any of claims 6 to 9, wherein the troughs of the corrugated insert rest on the base and the crests support the top. 11. A manhole cover according to any preceding claim, wherein the radiating reinforcing walls are adhered, or otherwise attached, to the top and base of the cover. 12. A manhole cover according to claim 11, when dependent upon any of claims 6 to 10, wherein respective crests and troughs forming the corrugations of the insert, are adhered, or otherwise attached, to the top and base of the cover. 13. A manhole cover according to any preceding claim, wherein the base is dish-shaped. 14. A manhole cover according to any preceding claim, wherein at least the top, base and reinforcing walls are made of a glass reinforced plastics material, a carbon fibre material or any other suitable composite material or any combination thereof. 15. A manhole cover according to any preceding claim, which is generally polygonal or circular in shape. 16. A manhole cover according to any preceding claim further comprising a peripheral wall depending from the periphery of the top. 17. A manhole cover according to any of claims 1 to 15, further comprising a peripheral wall upstanding from the periphery of the base. 18. A manhole cover according to claim 16 or 17, wherein the peripheral wall is arranged to be received in, and engage, an internal peripheral wall of a complementary frame. 19. A manhole cover according to any preceding claim, wherein the voids defined by the reinforcing walls, are at least partially filled, preferably with a foamed plastics material. 20. An assembly comprising a manhole cover according to any preceding claim and a complementary frame in which the cover is received or receivable, wherein respective peripheral walls of the cover and the frame include formations which are in, or are arranged to be brought into mutual retaining engagement, with each other by relative rotation between the cover and frame. 21. An assembly according to claim 20, wherein the retaining formations of the peripheral walls of the cover and frame are arranged to operate as a bayonet joint. 22. An assembly according to claim 20 or 21 including at least one stop member on the cover or frame, arranged to limit relative rotation therebetween.

Inventors: WARDELL JEFFREY ROBERT, WARDELL, JEFFREY, ROBERT
Applicants: WARDELL JEFFREY ROBERT, WARDELL, JEFFREY, ROBERT
Application year: 1996
Main classification: E02D29
IPC codes: E02D29