Yes, the base plates are anchored, inside the triangles and along the outside of the triangles every 1' I did drill and use anchor bolts,with washers, Hilti brand I believe (3 1/2 ").
The buildings are not as strong if left open, But I know of one about 5 miles from mine, who hasn't enclosed his for at least 2 years, i would be worried about the elements picking it up like a parachute. It's still standing proud.
A building with the arches like mine, much smaller, something in the 20x30 range for storage of tractor and mower and gas power tools and gasoline, Would probably take me 25 - 30 days with one person (outside only), using the brackets, straps and plates I show in my postings.