Failure of the pedestrian bridge at Florida International University on March 15 is tragic, especially for the families of those who lost their lives. But it’s also sad for the concrete design and construction industry which ends up (justifiably) taking the blame. Obviously, someone screwed up—probably several someones—and one of the things everyone has heard is that the concrete was cracked. I’m not equating the lives lost with the loss of face for our industry, but a mistake like this makes us all look bad.
There’s lots of speculation about the cause, but it seems clear that the stress on a post-tensioning cable was being adjusted at the time of the collapse, since you can see the PT contractor’s truck beneath the rubble in some photos and in others an exposed cable near the failure point with a tensioning jack still attached. Why traffic was allowed under the bridge during this operation is hard to understand. Watch this dash cam view of the failure.
One point of confusion was whether this was intended to be a cable-stayed bridge--it was not, although there would eventually have been a decorative cable-stayed appearance, the span was designed to be self-supporting, as described in this Wikipedia article.
Everyone seems to have an answer, like the analysis below that I received from an architect in New Jersey. There are many other oddball guesses online about the cause. A lengthy analysis will certainly be performed and someone will get the blame. The accelerated bridge construction (ABC) method will be questioned (probably without justification) and concrete as a building material will be suspect. No one involved gets out of this without damage.
