Load bearing composite ring for manhole cover - has upper and lower cast iron rings connected with concrete ring

摘要

The frame for manhole cover and for street drain gulleys has upper and lower metal rings which enclose concrete filling. The metal and concrete rings are firmly connected. Optimum strength is ensured by using a minimum of cast iron in this support ring. The lower metal ring (3) is also held firmly over its whole surface area with the concrete ring (2). This lower metal ring is a load bearing member and it has an circumferential collar (4) which is firmly connected with concrete. The lower ring can have also internal circumferential rings or alternatively a midrib for ensuring good contact over its whole area with concrete.