Florida International University Bridge Collapses, Cars Underneath

miami.cbslocal.com ^ | 03/15/2018 | Staff

[SauronOfMordor]

A stress test always involves the possibility of failure. Why was a stress test being done with traffic passing underneath?

[Freee-dame]

If there was any cosmetics involved, it might have been some type of decorative cladding on the cable stays.

How about the bridge having what looks like a very substantial cover, with triangular supports holding it up? Could this have added significantly to the weight of the bridge?

[tomkat]

No doubt it was contributory, tho what % of the total load it represented I’ve no idea.

[Ronald_Magnus]

The stays would have been attached to those triangle supports so they had to be substantial.

[tired&retired]

I saw them in the one photo, all grouped together hanging from the pillar.

One problem with the USA losing the steel industry is all the good wire rope /cable companies have closed. It’s all foreign junk, even for elevators.

[PeteB570]

You do know the bridge was under construction and not to be completed until 2019?

[dforest]

Aw, now why did you go and ask a sensible question?

[ELS]

From the article you linked: “Once it’s finished in early 2019,...” So, it wasn’t supposed to be finished, yet.

[ProtectOurFreedom]

We have ALWAYS been good at it. Canals, steamships, ironclads, steel making, railroads crossing the nation in short order, rockets, superhighways.

Liberals destroyed traditional liberal curricula decades ago and are doing the same thing to technical disciplines. High schools have dumbed down their curricula to avoid stigmatizing under-performing minorities.

I would not be surprised at all to find an honest investigation ties the failure back to the degradation of American schools. I also would not be surprised that an honest investigation finds other, different “root causes” of the failure.

[ProtectOurFreedom]

“Y??”

Hmmm...because God made X and Y?

[ProtectOurFreedom]

Weird, huh? If the truss system were properly designed to be self-supporting, what was the suspension system for? Just decoration? Or was it designed to be load-carrying? It it was to carry load, then why was the shoring removed before the suspension system was completed? What an odd construction sequence.

[Teacher317]

Did you not read the quote I posted? They opened the span to foot traffic, when it was clearly not finished.

[ProtectOurFreedom]

IIRC, inadequate cure was the root cause of the Deepwater Horizon blowout. Ignoring the required cure time was pushed by one firm against the objections of another firm.

[UNGN]

Well there’s your problem. Some idiot pulled out the supports before the cables were installed.

Probably because the supports were blocking traffic.

Suspension bridges don’t work without towers and cables and I see no tower or cables in the rubble.

[21twelve]

I was just joking about the artsy diagonals. In going through this whole thread now - it seems they installed the flat slabs (walkway and roof) and were going to attach the suspension diagonals later. You can see in the photos the grid of bolts on the roof - all nice and neat - ready to attach the diagonals to. Perhaps if they had some temporary footings underneath mid-span that may have worked - but it seems pretty obvious to me that you don’t add the necessary supports until later.

I’ve seen photos of how they build suspension bridges - it is pretty amazing. The suspension cables following behind the pavement as it is built, with the roadway hanging out in mid air.

[ProtectOurFreedom]

You wrote " uncomfortable with the idea of no support underneath or overhead". But that is the very essence of any bridge, isn't it? You have to have an open, unsupported section, otherwise it would be useless as a bridge. The concrete structure that collapsed is a self-supporting truss bridge. For some reason (esthetics? greater load carrying capacity?), a suspension design was to be added to the structure over the next months. But the truss section was obviously designed to support itself and it failed due to bad design, materials problems, or bad construction practices.

Wiki --> A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements usually forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges. A truss bridge is economical to construct because it uses materials efficiently.

As long as the concrete is in compression (which can be accomplished via pretensioning), the material can be used successfully in truss bridges.

There was a good FR article last month about the first railroad bridge to cross the Mississippi in 1856. See Bridging the Mississippi: The Railroads and Steamboats Clash at the Rock Island Bridge.

[PeteB570]

The bridge was not to open until 2019.

[UNGN]

My first thought was Chinese H1B PhD structural engineer, but this looks like a handoff FU between the delivery crew and the building crew. It is like the delivery crew said “we are leaving and taking our jacks/supports with us”.

174ft long 32 ft wide 800 ton slabs of concrete don’t do well only supported on the ends. Steel wouldn’t either and steel is stronger than concrete in bending, torsion and tension... all things that happen on a partially build bridge.

You leave the supports in until the cables are attached or the arches are complete. Bridge building 101.

[ProtectOurFreedom]

It's been done that way for quite a while.

[ProtectOurFreedom]

I do everything I possibly can to never stop my car under a bridge, especially here in Northern California. The chances of catastrophe while I’m under a bridge are extremely small, but I really don’t like the idea of being squashed like a bug under a boot.