It seems clear the erection schedule provided for the structure to be in place prior to installation of the mid-span column and support cables - without support at the bottom in order to facilitate auto traffic. Ergo, the design team had calculated the structure could span the gap with its dead load. One would suppose the structure could have been substantially post-tensioned while yet on the ground once the fabrication process was completed.
OTOH, what are the odds this was a Hyatt walkway type of failure?
One would suppose the structure could have been substantially post-tensioned while yet on the ground once the fabrication process was completed.
OTOH, what are the odds this was a Hyatt walkway type of failure?
I’ve been in construction basically all my life. My son is an engineer. We were watching the news reports together and i noticed the bolts on top of the center truss and said there is a structural element missing and where is the falsework at center span? This was all before seeing the rendering of the bridge or seeing the photos of the span placement over the weekend.
I agree about post-tensioning before the set. They could have cambered the deck in place and pulled tension on the tendons at that time. That said, a falsework support was still needed IMHO. Setting the span and then pulling tension without the center falsework probably contributed to the collapse again IMHO.
The bridge was only supported by the ends placing it in a catenary position (a downward parabolic position), now you pull tension and what happens? You pull the camber the wrong way. They may have been pulling above spec to try and camber the structure the proper way and instead caused the failure.
Just speculation mind you but the whole thing is a cluster and people are in deep doo doo.
I don’t think this was a Hyatt style deal. There was no live load and no dynamic live load. If you recall the Hyatt incident was precipitated by a high live dynamic load ( people at a party filling the spans and dancing).
The mechanism of failure was structure fatigue of the horizontal members at the vertical tie-ins. The vertical support members were to be continuous so each individual span was supported independently, instead the erectors hung the verticals from the flanges of the channel above, meaning the flange on the top span carried the load of all the lower spans and the flange failed. That was a failure induced by the constructors.
IMHO the Miami failure was an engineering failure. The engineering firm must have specified the methodology here and that was lacking safety margins.