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posted by CoolHand on Monday March 19 2018, @07:15PM   Printer-friendly

An "instant" pedestrian bridge at Florida International University in Miami collapsed on March 15, killing a number of motorists. A 174-foot, 950-ton span of the bridge was installed on Saturday, March 10 over a busy portion of Tamiami Trail called Southwest Eighth Street. The incomplete bridge suddenly collapsed on Thursday:

The bridge gave way suddenly while the traffic light for motorists on Tamiami Trail was red, so that the concrete span fell on top of a row of stopped vehicles. A woman stopped at the light who was heading westbound said the structure fell without warning. The woman, who asked that her name not be used, said it was immediately clear to her that several people were dead.

[...] The bridge crashed across six lanes of heavily traveled Tamiami Trail, crushing a still undetermined number of cars and killing a still unclear number of people. Police on the scene said at least six people could be dead.

From an earlier article:

The rapid span installation was the result of months of preparation. The bridge's main 174-foot span was assembled by the side of the Trail while support towers were built at either end. The 950-ton span was then picked up, moved and lowered into place by special gantry cranes at the intersection of Southwest 109th Avenue in an operation that lasted several hours Saturday morning.

[...] The innovative installation method significantly reduced risks to workers, pedestrians and motorists and minimized traffic disruptions, FIU said. The architecturally distinctive, cable-supported bridge is the product of a collaboration between MCM Construction and FIGG Bridge Design, the firm responsible for the iconic Sunshine Skyway Bridge over Tampa Bay.

[more...]

The news stories about the Miami Bridge follow the common pattern of containing almost no technical information and a massive focus on the horror. The comments section to the news articles are almost equally horrific. So I started looking for civil engineering forums, ran across this one: http://www.eng-tips.com/viewthread.cfm?qid=436595 and in one of the links in one of the comments, ran into a link to the proposal from MCM and FIGG: https://facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf It runs 173 pages and is a mixture of marketing and an explanation of the phases of construction. Very nice renderings

I have none of the requisite knowledge to comment on the collapse, but the reading is finally interesting. I'd be interested in other people's finds as well.

https://www.nytimes.com/2018/03/17/us/florida-bridge-collapse-crack.html

Hours before the collapse of a pedestrian bridge at Florida International University on Thursday, the engineering company for the bridge met with the construction manager and representatives from the university and the Florida Department of Transportation to discuss a crack on the structure, according to a statement from the university released early Saturday.

The engineering company, Figg Bridge Engineers, delivered a technical presentation on the crack, the statement said, and "concluded there were no safety concerns and the crack did not compromise the structural integrity of the bridge."

Six vehicles remain trapped under the bridge, with four of them very difficult to extract, Maurice Kemp, deputy mayor of Miami-Dade County, said.


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  • (Score: 5, Interesting) by Anonymous Coward on Monday March 19 2018, @07:58PM (5 children)

    by Anonymous Coward on Monday March 19 2018, @07:58PM (#655090)

    The bridge span was to have 5 pipes, each 16" in diameter, connected to a tower. This was intended to change the resonant frequencies of the bridge so that there wouldn't be a feedback loop with human leg motion. The bridge was supposed to not need those pipes for support.

    Concrete is tolerably strong in compression. For everything else, it is awful. A bit of pre-tensioned steel was supposed to make up for this.

    They were planning to do like London Bridge in the 1600s, with shops all along the bridge! WTF. If the shops didn't suck, the resulting crowds would ruin the usefulness of the bridge as a bridge.

    The bridge was required to be 20 feet wide. It was instead made 30 feet wide, but with awkward staircases that are only 15 feet wide and have right-angle turns. Most of the bridge's width was wasted.

    The concrete truss was made of sharp angles. There wasn't any stress relief at the joints.

    They really needed another support, and they could have done it. The road has a divider.

    There is an annoying power line that seems to have compromised the design. That side of the bridge lacks a tower. Moving the bridge let them avoid using a crane near the power line.

    It really should have been steel. Pure steel is great. Stone arches would have been pretty good too. Concrete sucks. Even when it isn't breaking, it's plotting to break in the future: rebar expands as it corrodes, causing modern concrete construction to fail after 50 to 100 years.

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  • (Score: 4, Interesting) by nitehawk214 on Monday March 19 2018, @08:44PM (1 child)

    by nitehawk214 (1304) on Monday March 19 2018, @08:44PM (#655113)

    Pittsburgh had a concrete bridge so shitty that they built a little bridge under it to catch all the pieces falling off.
    http://gcapgh.org/wp-content/uploads/2015/11/GB_20151122_1000x500a_rsz_phassett.jpg [gcapgh.org]

    It has since been replaced by a nice steel bridge.
    http://www.post-gazette.com/image/2017/08/31/1140x_q90_a10-7_cTC_ca106,0,2657,1700/20170831dsGreenfieldBridgeLocal01.jpg [post-gazette.com]

    --
    "Don't you ever miss the days when you used to be nostalgic?" -Loiosh
    • (Score: 1) by nitehawk214 on Monday March 19 2018, @08:56PM

      by nitehawk214 (1304) on Monday March 19 2018, @08:56PM (#655121)

      Note: In the picture the bridge was already under disassembly. The catcher bridge had been in place for over a decade at that point.

      --
      "Don't you ever miss the days when you used to be nostalgic?" -Loiosh
  • (Score: 5, Insightful) by bob_super on Monday March 19 2018, @08:57PM (1 child)

    by bob_super (1357) on Monday March 19 2018, @08:57PM (#655123)

    Humans know how to make concrete bridges that span over 300m long, supporting many highway lanes.
    This is/was a 53m pedestrian bridge, unloaded. It should have been a piece of cake from a technology standpoint. Let's not blame the materials for the incompetence of the design and execution.

    And yes, it was raw incompetence because there was obviously not enough redundancy. It's Miami, home of hurricanes and sinkholes. A bridge in Miami should be built so strong that missing half of it would not cause the rest to collapse.

    Europe and Asia have many bridges that are one or two thousand years old. Whatever happened to not cutting corners, O greatest country, headed by a builder?

    • (Score: 4, Insightful) by Freeman on Monday March 19 2018, @10:13PM

      by Freeman (732) on Monday March 19 2018, @10:13PM (#655153) Journal

      Trump was a builder like a programmer's boss is a programmer.

      --
      Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
  • (Score: 0) by Anonymous Coward on Tuesday March 20 2018, @01:54AM

    by Anonymous Coward on Tuesday March 20 2018, @01:54AM (#655223)

    I saw a thing -many- years ago on PBS about how the Greeks had used iron cleats(?)[1] inserted into matching chiseled-out voids in adjacent stones to keep the stones from pulling apart.

    [1] Like a double-ended T.

    Modern guys had come behind them and used bare iron to replace some of those and, as you say, the damned things swelled up and split the stones.
    (The original guys had dipped theirs into molten lead).

    It's sad that nobody thinks beyond next week these days.

    -- OriginalOwner_ [soylentnews.org]