She works for Maryland SHA. I sent her some articles on it. We discussed it. She said they used "self healing" concrete and while that is supposed to help close cracks, it also makes a weaker concrete, so has to be a bit thicker, or something to that effect.
Just looking at it, I could see a number of design flaws. It did have triangulation added between the top and bottom slabs, but looked to me it wouldn't protect strongly against sideways motions. It's also perfectly flat, whereas most walkovers have a slight arch to them, which directs force toward the foundation bulwarks at each end. It's almost 200' long too! I don't know any slab that without strong metal beams aiding it, would stretch that far on a flat slab and keep it from breaking other than ancient monolithic structures. It weighed almost 1000 tons! It's a walkover, not for heavy vehicles, and even counting for maybe many people being on it at the same time, I think a metal structure with a walk cover of 2-3" concrete, like sidewalks have, would be much better, and safer. There's one on the B&A bike/walking trail that crosses a major highway 100 here in Maryland, (main route from Annapolis to DC) built in that manner, and it's longer I think than the one that collapsed. It's been there for quite a number of years.
With snow on it.
http://saki.iwarp.com/images2016/bridgeOver100_160125.JPG
Here's google street view of it.
Here's another over highway 50 which runs from Annapolis to DC, it's 10 lanes with wider divider in middle than the collapsed one in Florida.
Uhh, did I already mention "arched"?

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