dpb wrote:
....

For aesthetics, rather than running another joist underneath as somebody
said for the support I'd probably get another 6x and make a ledger of it
endways about 18" long or so bolted thru the post to let the deck set
on. That should then be securely tied to the rim and thru-bolted w/
steel plate.
....

Thinking some more, I think I'd stick w/ the idea but notch it to fit
the existing joists and extend below a ways. Can cut the bottom at
45-degree angle for the aesthetics was talking about.

That done, you've got it to bolt thru from both directions to tie
corners together as well as the solid rest for the outer joist to be
supported on.

Same thing could be done structurally w/ a 4" or greater angle
vertically on the inner corner; just easier working w/ the wood for
average homeowner-type.

Again, one would guess that there's nothing holding the inner corners
together, either other than either toenailed or facenailed as that end
shows it is so need similar fixup there as well...

Also, can't re-emphasize to much the need for shoring this puppy up in a
hurry and securely before even thinking about working under it. There
have been accidents around here as well from such death traps so it
ain't no joke...

If you can't get to that immediately, at least rope it off so nobody can
wander around under it, especially any of your or the neighbors' kids.

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