I heard the intended center support tower was not even built yet. No sign of it on the TV footage. I'm sure we will get a more complete and definitive explanation of what happened in time.
Ever watch AvE? I watch this guy all the time. He has two very interesting videos if you have time to watch them. It is my understanding from the drawings in the video that the center "support" wasn't necessary as load bearing...at least initially...though it was to be built to support the cable tower. The tensioning bolts were supposed to keep the concrete compressed to increase strength. He says in on of the photos, you can see a tension bolt that obviously broke before the collapse. The tension bolts were supposed to support the bridge completely until the tower was raised and the cable support was rigged.
I also understand that a stress test and tensioning was underway at the moment of the collapse...which lends credence to his theory.
It could have been a lot of things that led to the broken tension bolt. Human error, defective bolt, bad design, improperly cured concrete around the tension bolt anchor...we'll have to wait for the investigation to know for sure.
Videos to follow...