On Aug 12, 2:37*pm, wrote:
The lag bolts are screwed into concrete? This doesn't make sense.

Are they actually *bolts screwed into anchors that are embedded into
the concrete?

They are likely driven into expanding aluminum anchors that were
driven into holes drilled in the concrete. The galvanic reaction
between the steel lag bolts and the aluminum anchors has fused them
together permanently. They will not be coming out of there without a
fight, and then the holes will not be usable afterward.