It was an enormous tragedy. My heart goes out to the victims. The pedestrian bridge as designed had a tower in the center, and supports at either end. I call the support to the left, the South support, and to the right the North support. The span that collapsed was the long span, from the South support to the tower. The tower had only been completed to the level of the walkway.
I can only go by the pictures as to what has happened. The picture is taken from a different perspective so north and south are reverse. The span appears to have come loose of the tower post. Video seems to show this part of the span crashing to the ground. The piece on top of the tower post is a supporting member for the canopy. The bridge collapsed on nearly every lane of the eight lane highway.
I’ve made a little sketch of the accident without the canopy as follows:
The bridge could have begun to sag in the middle, where the stress would be the greatest, and then the span connected to the tower pulled loose. Something had to give between the two posts as the bridge began to sag in the middle. All this happened extremely fast as motorists had no time to get out of the way.
The investigation has not yet begun, and will undoubtedly involve the design, the planned installation and actual installation. Certainly, the weight of the structure and the installation of the long span without a tower and stays, will be an issue.
I am certain there will be an investigation by bridge engineers, and they will provide a competent analysis of the disaster. I can only go by what is in the pictures.