i just typed a whole thing about how i did something kind of like this and went to fix a spelling error and poof. it went away.
the jist of it was, we build temp walls. one on the ground sitting on a 2x8 or something then a knee wall up to the 1st level deck and a wall from 1st to 2nd level, jacked the 2nd level slightly then cut all the beams and posts out. we cut some 2x6's to hold up the 2nd floor on an angle like you see done with porch roofs before the posts are put in also (just to be sure). worked quickly to get that top beam and new posts back .
The temp wall sounds like a good way to support the upper deck, but I need to support the bottom deck, and if you can see in the pics, there is about 4' of room for the first 25 feet or so, then it goes down to about a foot of clearance between the deck and the dirt.
Sky hook.
Can you use cables and turnbuckles to tie the lower deck upward and back to the ledger of the second floor? I have never done it this way, but I have seen it done.
Wow.....That is a doozy. We've lifted quite a few houses for foundation repairs and we've fixed main beam sags but damn that seems like child's play compared to this.
You need to shorten the spans I'm assuming, to like 8'? So on top of what everyone else said add additional supports for the top deck as you go along. Or, maybe you can support it using the old beams and run new ones right on the inside of the old one.
As someone mentioned - I'd also be very concerned about how it is tied into the house.
Screw jacks and structural engineers will be your closest friends on this one. :laughing:
I second the careful with the deck to house attachment and also when you do the new beam(s) all of those posts should have knees to the beam or some other lateral resistant framing; you're in B.C. and I'm sure you're in a seismically active area, likely zone D. The attached map is of the U.S. but it's easy to see that the active zones go right on up through Canada (and continue to Alaska). The map doesn't show Canada but it's easy enough to see the west coast is active and the closer to the coast you are the more likely it's a high zone