Manhole cover

Claim 2

Apparatus for closing the surface opening of a vertically extending passage to an underground installation, comprising: a. closure support means for disposition within the ground and defined by an annular retaining ring circumscribing said surface access opening, and an annular flange having a top surface recessed a defined depth from the top surface of said retaining ring to provide a support ledge, and b. closure means disposed within said surface access opening, said closure means comprising a top surface portion, a peripheral portion enclosing said top surface portion supported solely by the support ledge of said closure support means, and a network of transversely intersecting ribs enclosed by said peripheral portion and contiguous with said top surface portion and said peripheral portion, said network of transversely intersecting ribs providing the principal structural support for said closure means, said network further comprising a first plurality of ribs extending to a depth greater than said defined depth and a second plurality of ribs extending to a depth greater than said defined depth, said second plurality of ribs having ends integrally joined with said annular peripheral portion and respectively transversely intersecting and joined with said first plurality of ribs at locations along their length and equidistantly spaced from the center of said top surface portion.

Claim 3

The apparatus as defined in claim 1 wherein the top surface portion, peripheral enclosing portion, and the transversely intersecting rib network of said closure means are of unitary construction.

Claim 4

The apparatus as defined by claim 2 wherein said closure means is constructed from a foamed synthetic polymeric material.

Claim 5

The apparatus as defineD by claim 3 wherein said closure means is constructed from foamed polycarbonate.

Claim 6

The apparatus as defined by claim 2 wherein said network of transversely intersecting ribs is generally dome shaped with the apex of the dome generally disposed below the center of said top surface portion.

Claim 7

The apparatus as defined by claim 5 wherein said closure means is constructed from a foamed synthetic polymeric material.

Claim 8

The apparatus as defined by claim 6 wherein said closure means is constructed from foam polycarbonate.

Claim 9

The apparatus as defined by claim 5 further including means for securing said closure means to said closure support means.

Claim 10

In an assembly for closing the surface access opening to an underground installation, the assembly being of the type including closure support means disposed within the ground and formed by an annular retaining ring which circumscribes said surface access opening and has a peripheral shelf extension recessed from the top surface of said retaining ring at a first depth and closure means supported by said closure support means solely at said shelf extension for closing said surface access opening, the improvement wherein said closure means comprises: a body of synthetic polymeric material defined by a generally flat top surface portion enclosed by an annular peripheral portion dimensioned to fit within the inner periphery of said retaining ring, said annular peripheral portion having a depth substantially equal to said first depth, and a network of ribs integrally joined with said top surface portion and said annular peripheral portion for providing the principal structural support for said closure means, said network comprising a plurality of first ribs extending to a depth greater than said first depth and a plurality of second ribs integrally joined at their ends with said annular peripheral portion and respectively transversely intersecting and joined with said first plurality of ribs at locations along their length and equidistantly spaced from the center of said top surface portion.

Claim 11

In an assembly for closing the surface access opening to an underground installation, the assembly being of the type including closure support means disposed within the ground and formed by an annular retaining ring which circumscribes said surface access opening and has a peripheral shelf extension recessed from the top surface of said retaining ring at a first depth and closure means supported by said closure support means solely at said shelf extension for closing said surface access opening, the improvement wherein said closure means comprises: a body of synthetic polymeric material defined by a generally flat top surface portion enclosed by an annular peripheral portion dimensioned to fit within the inner periphery of said retaining ring, said annular peripheral portion having a depth substantially equal to said first depth, and a network of ribs integrally joined with said top surface portion and said annular peripheral portion for providing the principal structural support for said closure means, said network comprising a plurality of first ribs extending to a depth greater than said first depth and a plurality of second ribs integrally joined at their ends with said annular peripheral portion and respectively transversely intersecting and joined with said first plurality of ribs at locations along their length and equidistantly spaced from the center of said top surface portion.

Claim 12

The improvement as defined by claim 9 wherein said top surface portion, said annular peripheral portion, and said network of transversely intersecting ribs are of foamed polycarbonate.

Claim 13

The improvement as defined by claim 10 wherein recessed portions are disposed within said top surface portion and handrings are disposed within said recessed portions.

Claim 14

The improvement as defined by claim 10 wherein a plurality of circumferentially spaced locking lugs are integrally joined with said annular peripheral portion.