[xkeowner]

Three things to try and I would try them in this order.

1. Buy a small can of Liquid Wrench or the equivalent at Walmart or an auto parts store and put a few drops on each bolt. Wait 24 hours and try the sockets again.

2. If you can safely us a propane torch on the nuts without catching something nearby on fire, heat them up for a while then try the sockets again. Note that you will get some smoke initially from the Liquid Wrench burning off.

3. You can use an angle grinder to cut off the bolts but that will leave short stubs sticking up from the floor. You could grind them down once the post is removed but the risk of at least minor damage to the concrete around them is significant.

Good luck.