Subject: Can a ring be built at low altitude that circles the earth?

I would like to know if it is possible to build a ring that circles the 
earth at as low an altitude as possible and circles at a point that is 
roughly the widest part of the sphere. In my opinion it would be necessary 
to spin this ring around on its circumference. This would add centrifugal 
force to compensate for the gravity.  The questions that are involved with 
this are; what speed would this need to rotate? Is this possible with 
current materials? What would life be like living on it? Would it be 
possible to create a vacuum-sealed tube in the core of this ring to 
facilitate travel? And would it be possible to put a rail gun type-
launching platform in it for space expeditions without the rocket boosters?
Thanks.

Re: Can a ring be built at low altitude that circles the earth?