WO2003069075A1

WO2003069075A1 - A manhole access cover

Info

Publication number: WO2003069075A1
Application number: PCT/IN2002/000025
Authority: WO
Inventors: Rajagopal Ramesh; Ramesh Roahan; Fitzer J. Martin
Original assignee: Devi Polymers Private Limited
Priority date: 2002-02-14
Filing date: 2002-02-14
Publication date: 2003-08-21
Also published as: AU2002238825A1

Abstract

This invention relates to a composite manhole access cover (1), comprising a top cover (6), a holding shell (11), and a grid structure between the cover (6) and shell (11). The empty space between the grid structure is filled with foam (21) to retain the grid plates (7) in the grid structure vertical, providing the necessary rigidity and strength for the top cover (6).

Description

A MANHOLE ACCESS COVER

The invention relates to a manhole access cover, comprising of a top cover, a holding shell, a grid structure between the top cover and the holding shell, and the empty space between the holding shell and the top cover filled with foam providing the necessary rigidity and strength for the top cover.

BACKGROUND OF THE INVENTION:

Manhole access covers are primarily used to give access to underground service connections such as sewerage, water., telecom and electrical. These manhole access covers have to be strong enough to withstand the traffic flow over it and should provide an easy access to service. Manhole access covers are mostly located in a frame, which is embedded in the ground or floor rigidly. The load applied on a manhole access cover is distributed through the frame to the floor. Manhole access covers are provided with provision for opening and locking to the frame. Though for certain applications, it is desirable to make manhole access covers with non-magnetic materials in order to facilitate remote sensing, in general they are made in cast iron, due to factors such as reasonable corrosion resistance, easiness to manufacture by casting, easiness to provide integral ribs to give rigidity etc., Cast iron manhole access covers can have various shapes such as circular, square, rectangular, etc., to fit the frame embedded in the floor surface. These manhole access covers have a rough surface on the outer side and is provided with sufficient thickness. They are provided with small integral ribs on the inner side to withstand the load. Some of the disadvantages in using of cast iron manhole access covers known in the art, are their heavy weight, difficulty in handling during installation, pilferage, inherent magnetic properties, and breakage during use etc. There are also environmental concerns in manufacturing them since they are made by metal casting.

Manhole access covers made of plastic or composite materials have to be provided with thick ribs in order to have the required strength. This will cause weld-lines with weak points and increase in weight. Further deep, integral ribs at close intervals makes it difficult to manufacture.

Some composite manhole access covers are made with an outer member and an inner member and a core member made of materials such as wood to provide the necessary stiffness and strength. The materials used for making the core member are difficult to process and are expensive.

OBJECT OF THE INVENTION

The invention provides a manhole access cover, which is easy to mass produce with optimum use of materials and has necessary stiffness while avoiding weak points during manufacture. They are cost effective, and address the constraints of manhole access covers known in the prior art.

DESCRIPTION OF THE INVENTION The manhole access cover according to the invention comprises a top cover with an outer surface exposed to the traffic. It can have any required shape such as circular, square, rectangular, etc., It consists of a bottom shell on which a top cover is provided with a grid structure on the inner side to distribute the load to the periphery of the manhole access cover resting on an embedded frame. Rigid foam is filled in the space between the top cover and the shell improving the rigidity of the manhole access cover. The grid structure comprises several grid plates located at suitable spacing to distribute load and the grid plates are provided with plurality of openings through which cross support members pass through. Peripheral support comprising an array of holders with corner supports for holding the ends of the cross support members are provided. The holders for the cross support members not only hold them at the extreme ends, but also help in transferring the load on the top cover to the embedded frame and the corner support transfer the load on the top cover at the unsupported ends to the embedded frame. The top cover may be in the form of a sheet of required size and shape. The outer side of the top cover preferably has a rough surface to avoid slipping. A recess may be provided on the top cover for lifting the manhole cover located on an embedded frame. The manhole access cover may preferably have locking means to lock with the embedded frame. The inner side of the top cover may be provided with ribs at intervals to locate the grid plates in position and a flange all around to locate the top cover on the bottom shell. The bottom shell have an outer dimension and thickness suitable to locate the top cover. The shell may have an outer shape to match the embedded frame provided on the floor, and an extension below the frame of a shape to contain the grid plates. Alternately, the grid plates may have the shape and size to match the bottom shell. The size and shape of the grid plates will depend upon the required size of manhole access cover. For example, the size and shape of the grid plates for a square or rectangular manhole access cover and for a round manhole access cover will be different. In a rectangular or square manhole access cover, all the cross support members can pass through all the grid plates, whereas, in a circular manhole access cover all the cross support members do not pass through all the grid plates. The grid plates may be formed with different thickness to achieve optimum use of material. Preferably the grid plates are assembled with spacers placed on the cross support members between the successive grid plates. The extreme ends of the cross support members are preferably held rigidly. In a preferred embodiment, thinner cross support members and thinner spacers may be used in the grid plates nearer to the periphery. The cross support members are supported at the extreme ends by means of an array of holders, which rest at the inner periphery of the bottom shell. The assembly of top cover and grid plates with cross support members is placed on the bottom shell, and the ends of the top cover is bonded to the bottom shell all around the periphery.

It is desirable to provide means for lifting and locking the manhole access cover before bonding the top cover to the bottom shell. The entire space between the top cover and the bottom shell is filled with a suitable foam, which is injected through an opening provided on the shell and sealed. The rigid foam and spacers help in retaining the grid plates vertical under load. The manhole access cover according to the invention can be made from metals, plastics, composites or combinations of these.

The load bearing capacity of a manhole access cover can be increased by reducing spacing between grid plates, increasing the number of grid plates, increasing the number of rows of cross support members and a combination of any of them. The spacing between the successive grid plates need not be uniform and it can be closer in the central portion and farther near the end portions to optimize the quantity of material used.

The invention is further described with reference to the accompanying drawings to illustrate a typical manhole cover of rectangular shape having round cross support members. However the manhole cover may have any suitable shape depending upon the use. Similarly it is not necessary to have round cross-section for the cross members. It can take any shape such as rectangular, square, polygonal, oval, I-section and even irregular. Therefore the description below is only for a better understanding of the invention and should not be considered as a limitation to the scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS:

Fig. 1 is an isometric view of a typical rectangular manhole access cover according to the invention.

Fig. 2 is an exploded view of fig.1.

Fig. 3 is a sectional view along XX in Fig. 1

Fig. 4 is a sectional view along YY in Fig. 1. Fig. 5 is an isometric view of the outer side of the top cover (6).

Fig. 6 is an isometric view of the inner side of the top cover (6).

Fig. 7 is a detailed view of the portion indicated by Z in figure 3.

Fig. 8 is an isometric view of a holder (23) of the peripheral support

(10).

Fig. 9 is an isometric view of corner support (24) of the peripheral support (10).

Fig. 10 is a part section showing manhole access cover according to the invention located in the floor.

DESCRIPTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:

The composite manhole cover (1) according to the invention comprises a holding shell (11) and a top cover (6) with plurality of grid plates (7) attached to the inner surface of the top cover (6). Preferably these grid plates (7) may be located on ribs (16) provided on the inner side of the top cover (6). Plurality of cross support members (9) are provided through plurality of openings (17) provided in Hie grid plates (7). The ends of these cross support members (7) may be seated on a peripheral support (10) comprising an array of holders (23) preferably having ribs (19) and slots (20) and four corner supports (24) having ribs (19) to support the corners of the top cover (6). The outer surface (14) of the top cover (6) may be an anti-skid surface and may have means (13) for lifting and locking the top cover (6). The grid plates (7) may be provided preferably with holes (18) near the periphery in order to align grid plates vertically. Preferably spacers (8) are provided between the grid plates (7) on the cross support members (9) to maintain predetermined distances between the grid plates (7). The space between the holding shell (1 1) and the top cover (6) is filled with a foam material (21). A hole (12) may be provided on the holding shell (1 1) for introducing the foaming solution after the assembly of the top cover with the grid plates and cross support members is attached to holding shell (1 1). The top cover is provided with a peripheral rib (15) to place the top cover (6) on the holding shell (11). The top cover (6) and the holding shell (1 1) are attached preferably by bonding (22) provided all around the periphery of the top cover (6) and the holding shell (11).

A part section showing the manhole access cover (1) located at the floor level (5) on concrete (4) with an embedded steel frame (3) having a support (2) for the manhole access cover (6) is shown in figure 10 illustrating the installation of the manhole access cover on the floor

The manhole access cover according to the invention is easy to manufacture in large quantities with consistent strength. It can have relatively light weight compared to manhole access covers known in the prior art and can have any desired shape for a specific size. Improved distribution of load applied on the manhole access cover is achieved by the type of structure adopted. An increase of strength can be achieved for a specific size by increasing the thickness and/or the spacing of the grid plates as well as the cross-section and/or the spacing of the cross support members. The manhole access cover made according to the invention is free of weak points and hence more durable. The manhole access cover according to the invention can be made with any suitable materials such as light metals, plastics, composites and combination of two or more of tliese materials.

Claims

WE CLAIM :

1. A manhole access cover comprising a holding shell (11), a top cover (6) with plurality of grid plates (7), on the inner side of the top cover (6), plurality of cross support members (9) passing tl rough at least some of the said grid plates (7) and a foam material (21) in the empty space between the holding shell (11) and the top cover (6).

2. The manhole access cover as claimed in claim 1, wherein at the extreme ends of the cross support members (9), a peripheral support (10) comprising an array of holders (23) with corner supports (24) is provided for holding the cross support members

(9).

3. The manhole access cover as claimed in claim 1, wherein the inner side of the top cover (6) is provided with ribs (16) for locating the grid plates (7).

4. The manhole access cover as claimed in claim 1, wherein the outer side of the top cover (6) has an anti-skid surface (14).

5. The manhole access cover as claimed in claim 1, wherein the grid plates (7) are disposed parallel to each other and perpendicular to the inner side of the top cover (6).

6. The manhole access cover as claimed in claim 1, wherein between the succusive grid plates (7), spacers (8) are provided on the cross support members (9) for maintaining the distance between the grid plates (7).

7. The manhole access cover as claimed in claim 1, wherein the cross support members (9) passing through the grid plates (7) are spaced equally and lie in a plane parallel to the inner side of the top cover (6).

8. The manhole access cover as claimed in claim 1, wherein said grid plates (7) are bonded to the inner side of the top cover (6).

9. A manhole access cover comprising a holding shell (11), a top cover (6) having an anti-skid outer side (14) and provided with plurality of ribs (16) on the inner side on which plurality of grid plates (7) are located parallel to each other, equally spaced and perpendicular to the inner side of the top cover (6), an array of equally spaced cross support members (9) passing through the grid plates (7) and located parallel to each other in a plane passing through the grid plates (7), both extreme ends of each said cross support members being held by a peripheral support (10) comprising an array of holders (23) with four corner supports (24), and the space between top cover (6) and the holding shell (11) is filled with a foam material (21).

10. The manhole access cover as claimed in claim 9, wherein the inner side of the top cover (6) is provided with peripheral ribs (15) along the periphery for locating the top cover (6) on the holding shell (11).

11. The manhole access cover as claimed in claim 9, wherein the ends of the cross support members (9) are held by slots (20) provided on the holders (23) of the cross support members (9).

12. The manhole access cover as claimed in claim 9, wherein the cross-section of said cross support members (9) are circular.

13. The manhole access cover as claimed in claim 9, wherein the cross-section of said cross support members (9) are polygonal.

14. The manhole access cover as claimed in claim 9, comprising means (17) for lifting and locking.