Accelerated Arrogance: The FIU Pedestrian Bridge Collapse

I'm approximately a million hours away from being a structural engineer, but I think I could look at the cracks shown in the video at 6:49, 10:47, and 16:20 and say that maybe they shouldn't be going ahead with moving the bridge into place.

I never would have thought of the shifting forces during the movement of the bridge from its initial fabrication location, but the need to constantly restress the concrete with each move is fascinating. I would think that would require the concrete to be stressed and stressed and eventually over-stressed.

Q1. How does a prestressed precast concrete bridge beam work?

Concrete is great in compression, very strong stuff.

Concrete isn't so good in tension, however, so using any concrete slab in such a way that it will experience bending load - as a cantilever, for example, or a flooring slab with a long span - requires something to address that weakness in tension.

The most common solution is simple rebar...but then there's the prestressed option.

In the above video - the first in a series of twelve Shay Murtagh videos exploring prestressed concrete beams in great depth - explains what prestressed concrete is and why it's strong than just reinforced concrete.

In case you aren't aware of Shay Murtagh, they seem to be a company with at least 100 employees - many but not all of whom can line dance.

What is Prestressed Concrete?

"And, of course, I built a demo to show how this works" ~ Grady, 4:10 into the above video

The most wonderful part of the Practical Engineering series of videos is the models that Grady makes to illustrate his lessons.

Of course, he's clearly got a heck of a shop around his house to be able to make those models.