2 thoughts on “ducts”

  1. It is part of the wall of a post-tensioned box girder, like on Spaghetti Junction. After the concrete hardens, they put high strength steel cables in the ducts and then pull them tight to hold it up. “Post-tensioned” because they tension the cables after the concrete has hardened. Once the cables are tight, they can remove the formwork and it is supposed to stand up on its own.

    I didn’t know you could comment on pictures.

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