| 摘要 |
PROBLEM TO BE SOLVED: To provide a rib duct in which a plurality of outwardly protruded inclined ribs are provided on a constituent surface of a cylindrical duct spaced at a proper interval, the improvement being such that the inclined ribs extending from the left to the right and the inclined ribs extending from the left to the right both on the constituent surface are intersected to form diamond configuration grid ribs. SOLUTION: Inclined ribs serve as diagonal braces in building structure to be excellent in reinforcement effect, and are adapted to be ones with sleeves tucked up, particularly ones having diamond lattice shape, so that the reinforcing effect becomes further high to cause the thickness of an outer plate to be thinner and to reduce a duct weight.
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