Quote Originally Posted by walter View Post
How about encapsulating the tube in E/G? (hollow center like Zumba suggested)


EDIT:
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Dear Walter,

With hollow core precast RC slabs (the type used for floors in buildings), they create hollow cylindrical ( or rectangular) voids that run horizontally, and are centred about the neutral axis of the slab/beam. The general idea is to remove concrete that is doing very little structurally ie the concrete that is close to the neutral axis.

I would guess that the use of steel hollow sections as the formwork for creating these voids would be a waste of steel because the steel itself would be close to the neutral axis. It might be better to use cardboard rather than steel.

IMVVHO

Best wishes

Martin