A door frame of some design is required. No way around it. As Bucky might say, can't let in infinity.

705.04 Each of the barrel's tension hoops represents a separately operating, exclusively tensional circle with its plane parallel to, and remote from, the planes of the other, only separately acting, barrel hoops. The tension bands do not touch one another. The tension bands are only parallel to one another and act only at 90 degrees against the staves, which are also only parallel to one another. Neither the staves nor the tension hoops cross one another in such a manner as to provide intertriangulation and its concomitant structural self-stabilization. In fact, they both let infinity into the system to disintegrate it between the only parallel staves and hoops whose separate parts reach forever separately only toward infinity.
705.05 If we take a blowtorch and bum out one of the wooden staves, the whole barrel collapses because infinity floods in to provide enough space between the staves for their arch to be breached and thus collapse disintegratively. What the blowtorch does is to let infinity__or the nothingness of Universe__into the system to intrude between the discontinuous and previously only contiguously crowded together, exclusively compressional members of the system.

http://www.rwgrayprojects.com/synergetics/s07/p0000.html

Read about infinity here.

Pls advise if you got an answer to this question. I'm very much interested in knowing the solution.

Regards,

bibo