Apparently, it seems that you can use hollow pipe of same diameter to economize. But, it reduces the ductility and so can quickly undergo for plastic deformation.

Theoretically one can use, if it is designed for the desired tension strength. This will lead to a bigger beam/column size to accommodate the no of such pipes and it will be overall uneconomical. This is because your concrete quantity will increase to fill the bigger size beam/column. One more thing that can happen is pipe will get damaged faster than solid rod under corrosion.

Apparently, it seems that you can use hollow pipe of same diameter to economize. But, it reduces the ductility and so can quickly undergo for plastic deformation.

I think in most cases no problem except the cost of these hollow iron pipes.

Dear Trijo:

Besides the excellent answers from Debasish, Parameshwari and Mohannad, you also need to consider the anchoring requirements, particularly if the pipe is in tension. I presume that the pipe is smooth, so anchorage and stress transfer to the concrete needs to take place through adhesion and friction. Adhesion can be easily lost, especially under repetitive or cyclic loading. You will need some form of mechanical anchor (i.e. a steel plate of a 90-degree or 180-degree bend).

I hope that this helps you.

Sincerely,

Arturo