All the fencing and securing of perimeters isnt to keep Congress locked in it's to make sure leftists don't riot and actually storm the capitol when it turns out Trump will be President.
Why fortify DC so heavily if you are worried about Trump supporters? Shouldnt they be deployed to different state capitals where the right wingers live? DC is 95% democrat.
The Constitution is supposed to hold through all of this, so it's not clear to me how any inauguration would apply through January 20th. I believe a "transition" would still have to happen on the 20th regardless of anything else.