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Site management has requested that we limit the length of the other thread by forming a new one. This subject may require III, IV....
Link to Part 1
Link to Part 1
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Miami Pedestrian Bridge, Part II 55
- Thread starter hokie66
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structuralengr89
Structural
When bridge consultants design cable stayed bridges for state DOTs...typically there are scale models of the bridge constructed...where the structure is put in a wind tunnel and wind analysis is performed...(you can't look up in ASCE-7 and get wind loads on something like this...I wonder if a scale model of the bridge was created (maybe at FIU?)..not only for the wind loads in Miami...but also for testing of the gravity loads... As Hokie has stated from the beginning of this thread (as he knows his stuff!) a concrete truss was a bad idea...I had never even heard of a concrete truss until this hit the news...I don't think I've ever seen one in person.
structuralengr89
Structural
I think this really opens up a can for State DOT's as well...I would say in most of the US, that pedestrian bridges are not designed by bridge engineers, but are designed by building engineers (or at least in my state). A client (hospital or school) will hire a building engineer and the building engineer submits plans to have a bridge over a DOTs right-of-way to the state. Typically, there is no secondary check from a different consultant required as there was in this case (I'm guessing that was required because federal funds were involved).
But from a liability perspective, if a state DOT looks at the plans prepared by the consultant, how much liability does he take on? Even though the state DOT is not likely not an expert in the structure being designed (and most bridge engineers aren't even familiar with ASCE 7 loading)...if a State DOT PE reviews the plans and then approves it...IMO he is taking on some liability with the structure.
Sorry...bit of a tangent
But from a liability perspective, if a state DOT looks at the plans prepared by the consultant, how much liability does he take on? Even though the state DOT is not likely not an expert in the structure being designed (and most bridge engineers aren't even familiar with ASCE 7 loading)...if a State DOT PE reviews the plans and then approves it...IMO he is taking on some liability with the structure.
Sorry...bit of a tangent
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Structuralengr89 said:
Not a tangent, but, the next phase... I'm surprised a lawsuit has not already been filed.
Moreso in the US, than in other parts of the world, the lawyer will use a 'scattergun' approach and name all parties. If the lawyer misses one that he should have included, he can be sued.
FDOT, the city, the University, the consultants, the constructor, and any of the sub-trades are fair targets...
Dik
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- #12
Just my opinion, but I think the truss was doomed to fail at the joints. At some stage, I hope we see some further information about the details, not just how the PT was arranged and anchored, but what was supposed to reinforce the joints. Based on the reporting which the NTSB released after the I35W collapse, we will eventually find out. It is ironic that Figg was the designer of the I35W bridge replacement.
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hokie66 said:
hokie66....I agree that hinges formed but it looks like those occurred first at the top of members 11/10, then at the bottom of 11 and then at the bottom of 10. But....sometimes hard to tell failure sequence in progressive collapses.
My best guess, and I assure you that's all it is, is that there was buckling or punching shear at the top of 11, rotational failure at the bottom of 11, then tension failure at the bottom of 10.
Issues such at these usually get solved by the numerous ideas posed in such conversation as we are all having. Hopefully these discussions will lead to someone reaching a logical conclusion of the failure, but as a group we don't have the benefit of the cumulative information from design and construction that will inevitably be forthcoming...either through determined analysis or the litigation process. The resolution of such failures is important to the future success of innovative design and construction, it's just unfortunate that such a high price had to be paid for this lesson.
Nobody important
Computer
Just in case anyone is interested in a rough idea of the tension / compression loading of the trusses when:
A-In transit supported underneath in 2 places mid span
B-In Situ supported at either end of the span
These are not to scale or necessarily accurate, but give a general idea. Draw your own conclusions here.
A-In transit supported underneath in 2 places mid span
B-In Situ supported at either end of the span
These are not to scale or necessarily accurate, but give a general idea. Draw your own conclusions here.
Ingenuity said:
Concur... had lumped the others under sub-contractors... Wonder if VSL were involved with stressing the cables... They've been involved with post-tensioning for decades that I'm aware of, and are very good...
tomfh said:
Shortly after it hit the ground...
Dik
Member 11 may have been a tension member during construction but it was a compression member after the temporary supports were removed. Assuming a total weight of 950 tons, the bridge reaction at each end would have been in the order of 950 kips under dead load only. Member 11 appears to be oriented at about 35o to the horizontal, so it would have been loaded to about 1650 kips, a compressive stress of 3,300 psi on a 24" x 21" section under dead load only. It did not need any prestress at that stage.
BA
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