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  1. appster

    Miami Pedestrian Bridge, Part VIII

    If any of you here ever watch the "Mayday" series which shows many types of NTSB investigations (mainly aircraft accidents but also railway, highway, bridges etc.) they always look into the human factors which may lead to an accident or make an accident worse. They will undoubtedly look into why...
  2. appster

    Miami Pedestrian Bridge, Part VIII

    To TehMightyEngineer (sorry don't know how to do quotes) To the contrary the article clearly indicates that the FDOT was represented at the morning meeting, it does not indicate if the pictures were shown at the meeting or if only a discussion was held and the FDOT rep. was in a secretarial role...
  3. appster

    Miami Pedestrian Bridge, Part VIII

    If you go to the following Miami Herald web page photos of many large cracks not revealed before can be seen. https://www.miamiherald.com/news/local/community/miami-dade/article216388430.html These photos were apparently taken on March 13 or March 14 at least one day before the collapse. This if...
  4. appster

    Miami Pedestrian Bridge, Part V

    hokie66 "appster, I think the result of the investigation will assign blame clearly enough." Actually they very seldom point out one cause or name anyone specifically because usually a number of things add up to why it happened and they usually make recommendations to prevent the same thing from...
  5. appster

    Miami Pedestrian Bridge, Part V

    If we are going to run computer models lets at least get the loads/ft correct, so in the spirit of joint effort why not use calculated numbers. Biggest room for error here is scaling the length of web members Taking the area of the canopy it is 16.29 ft2 so at 150 lb/ft3 this is 2.44 k/ft. or...
  6. appster

    Miami Pedestrian Bridge, Part V

    The NTSB will not assign blame as it is not their job; neither I believe is it the objective of this forum to assign blame but to try and uncover facts. We are trying do this with a lot of questions that may never be fully answered simply because some of the evidence may never be revealed to the...
  7. appster

    Miami Pedestrian Bridge, Part V

    In gwideman's post of 28 Mar 18 07:00 with the looped video it appears that the crane is backing up during the sequence; not sure if this is due to zooming but the car is moving forward. Also to sailkee119 I thank you for the information on the deck and canopy tendons. Appears then that the...
  8. appster

    Miami Pedestrian Bridge, Part V

    saikee119 Re strand vs PT rods No I was referring to the strands immediately either side of 12 in the deck, not in member 12 itself. The concept drawing section of the bridge shows 6 x 19 strands either side of 12 and smaller or fewer strands outboard. The smaller bundles seem to be inboard and...
  9. appster

    Miami Pedestrian Bridge, Part V

    Hold on a minute here Prof. Simon. : I calculated the stress in 11 on the pier with its axial load and assuming two PT bars at 250K tension each. Under dead load only the axial stress in 11 with a reaction of 887 kips after removing DL of 12 and half of canopy between 11 and 12 = 1508 k/ 22 X...
  10. appster

    Miami Pedestrian Bridge, Part V

    Looking at the photos in gwideman's post of 15:04 two things that I have noticed. 1) The PT strands each side of 12 appear to be smaller than originally planned, in the concept the smaller tendons were outboard of the 6-19 tendons, they appear here to be inboard, not sure number of tendons in...
  11. appster

    Miami Pedestrian Bridge, Part V

    UKJIm I was referring to the white snake going almost full length of the blister. Can only hope that the NTSB keeps a few larger pieces such as what is left of this cap and what is left of 11 and 12 to examine more closely.
  12. appster

    Miami Pedestrian Bridge, Part V

    Meerkat 007 "This confuse me. For my untrained eye looks like a PT bar but from where to where ?" I believe that it is tendon duct or utility duct from the canopy but could be wrong.
  13. appster

    Miami Pedestrian Bridge, Part V

    Do we actually know what prestress was applied to the canopy and to the bottom deck. Have the number of strands total but 1) were all of them tensioned and 2) where they all tensioned to the maximum allowed, I assume the they would be but cannot find verification anywhere. By the way I have...
  14. appster

    Miami Pedestrian Bridge, Part V

    The drawing that I have of the overall structure is stamped, dated 12/9/16 and signed by the Engineer. Not sure about US dating convention but it is either Dec. 9 of 2016 or Sept. 12 of 2016. The span is shown as 175' on this drawing; was the 11' added later than this. Here in Canada we would...
  15. appster

    Miami Pedestrian Bridge, Part V

    Quote SheerForceEng "Do we know when the PT cables in the bottom deck/chord were stressed? Were these cables stressed after the entire truss was poured or was the bottom deck poured, then stressed, then the diagonal/verticals poured and so on? If the cables in the bottom deck were stressed...
  16. appster

    Miami Pedestrian Bridge, Part IV

    Using the approximate footprint of 11 and 12 combined from the picture which is about 60" long and 22" wide the interface shear area is about 1584in2. The approximate horizontal component to the thrust in 11 is 1520 kips. Nominal shear stress then is about 1.0 KSI or 1000 psi at the web bottom...
  17. appster

    Miami Pedestrian Bridge, Part IV

    If you look at Meerkat007s latest drawing post you can see that the combined footprint of member 12 and 11 at the deck face is about double the sheer footprint of 12 alone. I have been saying from the beginning that shear is the failure mode and that the joint at no. 11 and 12 was the culprit...
  18. appster

    Miami Pedestrian Bridge, Part IV

    SheerForceEng "I must stress again that this is not a complex sturcture and indeed a truss is something we all learn in Engineering 101 at university." Totally disagree and possibly this type of off the cuff thinking is why we are now even discussing this failure. I believe that a very...
  19. appster

    Miami Pedestrian Bridge, Part IV

    I believe that the picture of the bottom deck in Incentives post above clearly shows that the tendons in the deck or the deck itself did not blow "out the back" but that section 11 and 12 sheared cleanly off at the deck due to inadequate shear capacity. Reliance mainly on shear in plain concrete...
  20. appster

    Miami Pedestrian Bridge, Part IV

    I have felt for some time that there might be other detail differences at the ends which saved the South end from failing first, or there was some difference in the PT stress or procedure at each end. Voids in the concrete due to compaction differences or areas being affected by ducts or drains...

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