The floor is down, with some extra support underneath and some strapping to tie it down. I found some stainless steel perforated banding, so I bent two long U pieces and concreted them into a suitable hole a couple of feet deep. The strapping is secured to one of the joists with 4 stainless steel screws.
I've put some polythene sheet over the floor with it hanging over the edges to help keep any rain from soaking into the cut faces. Two stud work walls are up with temporary supports made from off-cuts on the bigger wall. I've sawn the notched pieces to form the inner face of the curved beams and got one glued and screwed, the glue will cure over night. I'll have to be careful to make the second one a mirror image rather than identical.
The screw held the two pieces together nicely so that I could then handle it to get the clamps on... can never have enough clamps. It would have been a nightmare without the screws.