Good, because I don’t have time to go into the details of the fallacy of gravity.
Excellent hypothesis.
Since it appears (very provisionally) that some kind of undetected steel fatigue is to blame, I wonder if part if the problem is that trucks are much heavier now than they were at the time the bridge was designed.
I believe the concern that originated this study came under the former Governor’s administration, it was just finished & published after the new Republican Governor had taken office. The prior Transportation Commissioner (who was replaced by the Lt. Governor, who occupies both offices) has been on the news with complaints about changes made in the department.
The “timid” recommendations in the published version may be watered down from what the engineers wrote in their original version. In a recent controversy about withholding a study of an always-fatal lung disease among miners in northern Minnesota until after the election, an internal memo has come to light saying to be sure to check it with the Governor before publishing this.
Note that even the “timid” recommendations were not followed. The last inspection was 14 months ago, not the 6 months that was recommended.
I don’t see the deck staying level at all. The proximal end (relative to the camera) falls slightly ahead of its distal end. For the deck to fall level, you’d need a simultaneous failure at either end of the span, and what are the odds of that?
You’re looking along the lanes of the road, and yes one end goes down first. However, lines drawn across the lanes remain horizontal, as if all the support was suddenly removed from the end of the bridge.
If one side of the truss failed before the other, the bridge surface should have tilted sideways. It didn’t.
Hey, it’s only a theory.
Been conversing with my favorite Structural professor from engineering school. I too had questioned ‘live load’. This is what he had to say about that:
I agree with BobLibDem. Something, which is likely to be a connection contained behind one of those gusset plates, failed; which then caused failure across and through the truss as the load was shifted to other structural members which could not handle the load.
Squink, not to belabor a point, but a portion of the roadway did tilt. I’m thinking this was the first weak point to go. That end of the truss twisted, tore itself away from the truss beneath the approach span, and tossed the deck into the water. The truss beneath the approach then tilted ‘up’ (as seen in the damage photos) because the tension from the ‘waterway’ portion was suddenly gone, and it ‘sat down on its haunches’ if you will.
After the twisted portion fell, the other ‘water-side’ sections fell vertically into the river. The approach truss on that side is extremely deformed, with the steel members pulled down towards the river.
That doesn’t show on the video.
Agreed. The stills show it better. The problem I had with the slideshow was that I can’t link to individual pics. I will pick out the illustrative ones and link them one by one.
I’m not trying to be argumentative, but I think you would like to see what I see. 
Alright. This overview shows a bit of what I mean. See how on the left hand side of this photo, the remains of the truss appear to be ‘thrown out’ or away from the original position? That’s what I meant about twisting. I agree that a large portion fell vertically.
This closeup may be better.
On the opposite bank, the truss was deformed downwards and the pier is tilted riverward.
I include this prior photo for reference.
There existed a better photo in the original damage pics which began to come out last nite; I suppose it was canned for more photos of rescue (which were probably more important at the time). That photo showed a portion of the roadway which had one edge pointing to the sky and the other edge in the water.
Feel free to dis-believe me. 
I’m not trying to be a jerk, I’m just relaying my observations. I respect your opinion too.
Yup, there was some torque there. That’s the first I’ve seen of it, and if the area includes the initial point of failure, it certainly looks like BobLibDem’s on the right track.
After viewing some more photos this morning, the twisting appears to be more minor than I previously thought.
The 2 long curved beams at the bottom are key. If one breaks the other would have to take more than double the designed weight. There were no center pylons so water traffic could go under the bridge. Metal fatigue?
I think they’re going to quickly zero in on the places that they considered strengthening. From Minneapolis Star-Tribune it appears that there was some heated debate about doing some retrofit.
You’re one of those Gravitists, aren’t you?
Downerism forever!