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  • 1.  FIU Pedestrian Bridge Failure

    Posted 10-23-2019 11:34 AM
    Edited by Irfan Alvi 12-08-2019 05:43 PM
    ​The NTSB has completed its investigation of the failure of the FIU pedestrian bridge in Florida.  The final report will be released in the next few weeks, and meanwhile an abundance of information can be found at these links:

    Accident ID HWY18MH009 Mode Highway occurred on March 15, 2018 in Miami, FL United States Last Modified on October 22, 2019 08:10 Public Released on October 08, 2019 11:10 Total 119 document items (NTSB docket of documents released to public, including reports prepared by parties to the investigation)

    Pedestrian Bridge Collapse Over SW 8th Street, Miami, Florida, March 15, 2018 (NTSB Board Meeting documents)

    https://www.osha.gov/doc/engineering/pdf/2019_r_03.pdf (OSHA report)

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    Irfan A. Alvi, P.E., M.ASCE
    President & Chief Engineer
    Alvi Associates, Inc.
    Towson, Maryland
    www.alviassociates.com
    ialvi@...
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    ​​​​


  • 2.  RE: FIU Pedestrian Bridge Failure

    Posted 10-31-2019 10:01 PM
    Edited by Tirza Austin 11-01-2019 08:45 AM
    Thank you for sharing this information. It is relevant in my home country because we did not expect this kind of disaster to happen in the US. The information shared covers issues regarding ethics, quality control, and level of compliance with design regulations.

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    Andres Guzman Ing., M.ASCE
    Associate Professor
    UNIVERSIDAD DEL NORTE
    Barranquilla
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    Original Message


  • 3.  RE: FIU Pedestrian Bridge Failure

    Posted 11-04-2019 08:32 AM
    Edited by Irfan Alvi 12-08-2019 07:32 PM
    Andres,

    Thanks for sharing your perspective.  From my vantage point in the US, I've never assumed that structural failure rates will be substantially lower in the US than the average for the rest of the world.​  There may be a degree of 'risk compensation' involved, where greater resources and experience result in undertaking more challenging projects.  That seems to have been the case with this FIU bridge project:

    - The owner was a very large university that desired an innovative signature bridge which could be built with minimal traffic impact, and the university was a leader in research on accelerated bridge construction (ABC)

    - The designer was a leading bridge design firm which had designed many complex bridges and received hundreds of design awards

    - The reviewing state agency was a large DOT with many complex bridges in its inventory, and the DOT performed extensive review of the design and plans

    - The peer review firm and engineer also had experience with design of complex bridges (they represented themselves as prequalified to perform the review and were listed as prequalified on the DOT website, though, after the failure, the DOT indicated that they actually were not prequalified)

    These apparent and actual strong qualifications in the project team, and the extent of independent review of the design and plans, surely contributed to the decision to undertake the design and construction of a bridge of this type at this location, and may have also influenced judgments about the significance of the cracking and whether the road under the bridge needed to be closed.

    I was a member of the forensic team which investigated the spillway failures at Oroville Dam in California, which resulted in evacuation of about 188,000 people and a recovery cost over $1 billion.  Some factors similar to the FIU project influenced the judgments and decision-making on the Oroville project, as described in the forensic report: https://damsafety.org/sites/default/files/files/Independent%20Forensic%20Team%20Report%20Final%2001-05-18.pdf

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    Irfan A. Alvi, P.E., M.ASCE
    President & Chief Engineer
    Alvi Associates, Inc.
    Towson, Maryland
    www.alviassociates.com
    ialvi@...
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    Original Message


  • 4.  RE: FIU Pedestrian Bridge Failure

    Posted 11-08-2019 02:58 PM
    Very good information for a case study for future engineers and builders.  I've been following that case very closely. I have a keen interest in modular/offsite construction techniques and as a native Floridian, this is close to my heart.  Engineering New Record (ENR) seems to have a few articles each week as the case evolves.

    Two things that I ponder:
    1) Where was the salty old superintendent demanding redundancy in temporary support work? Throughout my career and on more than one occasion, I've had a salty, often grumpy, but experienced field superintendent save my behind. Call it intuition, engineering judgement, education, or whatever, but it's a like a six sense that they have when something doesn't feel right. As an example; I once had a superintendent spend less than a few minutes on the site and as he looked around he tells me he thinks something is off with the grade for the building pad. Sure enough we had the surveyors back out and quickly found that they used the wrong Datum. Thankfully no concrete was placed and it was just a matter of regrading (which the surveyors took full responsibility for) literally saving me ten's of thousands of USD. In the FIU case, I'm a little surprised that one of the senior-level field supervisors didn't independently decide to spend some money on temporary supports even though engineers were saying it wasn't needed. It wouldn't have been a substantial add to the budget.

    2) Overall, I'm a fan of private peer review. Often the government doesn't have the resources or knowledge for advanced construction methods oversight. I'd much prefer to have a field of respected engineers on contracts for peer review and inspections. It seems in this case there may have been a breakdown in that system.I'm watching very closely for the outcomes. Usually a knee-jerk reaction is to enact some rule or regulation but I think engineers are capable of self governance.

    The collapse was an unfortunate event and raises many questions.


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    Jesse Kamm PhD, PMP, A.M.ASCE
    Senior Vice President of Construction Management
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    Original Message


  • 5.  RE: FIU Pedestrian Bridge Failure

    Posted 11-12-2019 04:46 PM

    Dear Mr. Alvi and all,

    Thanks for your information and insights. 

    The Journal of Bridge Engineering (ASCE) has just published a technical paper on computational forensics of the collapse of the Pedestrian Bridge in Miami, FL, last year March.  

    A link to the full paper is available here: https://ascelibrary.org/doi/full/10.1061/%28ASCE%29BE.1943-5592.0001532

    People can download this paper for FREE by registering with ASCE LIBRARY. Registration is FREE and only requires email/country info.

    Abstract of the paper

    On March 15, 2018, a pedestrian concrete truss bridge in Miami, Florida, collapsed during construction. The failure of this bridge caused multiple casualties and raised many serious concerns regarding the design and construction of the bridge, including the emerging concept of accelerated bridge construction (ABC). The causes of failure of this bridge have not yet been comprehensively investigated. This paper used high-fidelity computational simulation to investigate the behavior of critical structural members of the bridge during construction. Four important construction stages (prestressing, transportation, relocation, and re-tensioning) were simulated to identify dominant factors that could have contributed to the failure of the bridge. A recent investigation report from the National Transportation Safety Board (NTSB) attributed the collapse to flawed design at the failed joint at the northern end of the bridge, but the specific sequence of mechanisms that led to collapse was not identified. Based on simulation and demand/capacity analysis, this work shows that the horizontal component of the re-tensioning force overcame the resistance of the joint and caused it to slide with respect to the deck. As sliding progressed, dowel action between the deck and joint became fully mobilized, crushing and damaging concrete locally within the joint and the deck. The evolving damage (to the cold joint and adjacent joint and deck concrete) prompted more sliding and led to a vicious cycle that culminated in the collapse of the entire bridge. Parametric studies investigated the effects of the coefficient of friction at the cold joint, prestressing forces in the deck, and re-tensioning forces applied to the northern diagonal member on the collapse behavior of the bridge. The results from the analysis and simulations provide important insights into the collapse mechanism and highlight lessons that could be learned for preventing similar catastrophic failures in the future.

     



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    Ran Cao S.M.ASCE
    New York NY
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    Original Message


  • 6.  RE: FIU Pedestrian Bridge Failure

    Posted 12-06-2019 11:50 PM
    In looking at the NTSB final report, I'm surprised that the report doesn't comment on, or even reference, the submissions made by the other parties to the investigation.  Those party submissions can be found in the public docket.  I especially recommend reading the party submissions by the designer and their forensic consultant:​

    https://dms.ntsb.gov/pubdms/search/document.cfm?docID=476566&docketID=62821&mkey=96877

    https://dms.ntsb.gov/pubdms/search/document.cfm?docID=476973&docketID=62821&mkey=96877

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    Irfan A. Alvi, P.E., M.ASCE
    President & Chief Engineer
    Alvi Associates, Inc.
    Towson, Maryland
    www.alviassociates.com
    ialvi@...
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    Original Message


  • 7.  RE: FIU Pedestrian Bridge Failure

    Posted 12-08-2019 02:56 PM
    ​I agree with Mr. Alvi that engineers should go and read the submissions of the other parties available at the NTSB site.  In particular, I would point people to one of the last submissions, the one by Modjeski and Masters.  At the end of their submission they discuss the possible source of the demand error made by the original designers.  It is a cautionary tale about the use and abuse of finite element analyses.

    I disagree with the applicability of the full scale tests provided in the forensic consultants report.  The full scale model tests do not include the action of the very large post-tensioning forces induced into the deck on the ends of the span.  Not only was the end diagonal trying to push itself off the deck, but the deck was trying to pull itself away from the end diagonal.  I have not seen any discussion of the post-tensioning impact on the structure.

    Another topic that has not been addressed regards the shear friction resistance of the cold joints.  It is apparent that the joint was not roughened as required.  Less apparent is that the #7 U-shaped reinforcing bars, intended to provide the tension needed to develop the shear friction resistance, were not properly developed on one side of the joint.  Below the joint the bars meet the requirements for fully developing the #7 bars in tension.  Above the joint, the projection of the U-shaped bar is significantly less than what a #7 bar hook requires for development length.  Further, the distance between the legs of the U-shaped bar seem to be less than what back to back standard #7 bar hooks require.
    ​​​​
    Neither of the two points above would change the conclusions of the NTSB report, only further support them.  I appreciate the thoroughness of the NTSB report and the availability of access to all the supporting information for engineers to make up their own minds on the event.

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    Alan D Fisher, PE
    Construction Structures Group Leader
    Cianbro Corporation
    Portland, Maine
    afisher@...
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    Original Message


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