Hollow inflatable formwork elements for producing concrete structures

Claim 1

A re-usable hollow formwork element, for use in concrete pipe casting and operable to be rendered pressure resistant by filling it with a fluid medium, comprising in combination, an elongated, inflatable flexible closed outer casing of predetermined shape when inflated, at least two elongated adjacent superposed closed hollow flexible bodies positioned along a substantially vertical axis whereby one hollow flexible body is positioned lower than all other hollow flexible bodies, within, and extending over the entire length of, said outer casing, whereby an elongated closed cavity is formed intermediate said outer casing and said bodies, said bodies as well as said cavity being operative to be pressurized by said fluid medium, each of said hollow bodies having at least one portion facing the respective portion of the adjoining body, and each defining an opening in said portion, the adjoining bodies intercommunicating interiorly through said openings, a first valve connected to one body operable for introducing said fluid medium thereinto for pressurizing thereby both said bodies to inflate them, a second valve connected to said outer casing adjacent said elongated cavity, operable for introducing said fluid medium into said elongated cavity for pressurizing thereby said cavity, whereby the outer casing will be inflated to its predetermined shape, and support means operable for supporting the casing when inflated where the lower of said bodies touches said casing, said support means stopping short of said elongated cavity and including a gutter-like bottom plate having two ends at an angle to each other, a part of said casing adjacent said one hollow flexible body being disposed above said bottom plate and when inflated having an external arcuate surface touching tangentially said ends of said bottom plate when inflated, whereby said inflated casing will be supported substantially only by said ends.