composite iron and concrete circular manhole cover - uses concrete filled cast iron shell which has invert projections providing shear key

摘要

The circular manhole cover is of a composite construction comprising a concave cast iron shell (1) which is filled with concrete (5). The inner surfaces of the shell (4) inc. uniformly distributed shear key (7,10) projections which ensure the composite action of the iron and concrete in flexure. The max. height of the projections corresponds to one third of the max concrete thickness, and in section the projections may be semi-circular, semi-elliptical, semi-rhomboidal or semi-cuboid. Alternatively, the projections may take the form of ribs to circular or radial lines with or without curved (10) or angular undulation.