[vtsnowedin]

By now you have heard the tragic news about this bridge collapse. As I write this they still don't have a count of how many are trapped dead or alive under the debris.
There is bound to be a lot of finger pointing about just what went wrong but I''ll be willing to guess that somebody will try to pin it on Trump.
At first glance the truss of the bridge looks a little artsy as apposed to pure utilitarian functionality. My statics and structures course was many many moon ago so I can't compute the stresses in the truss members but you can be sure they will all be computed and recomputed in the next few days.
Normally a bridge is designed with a safety factor of at least three meaning it can hold three times the anticipated load without failure. To have this one collapse under it's own weight means a major miscalculation or assembly mistake has occurred.
http://www.miamiherald.com/news/local/c ... 16174.html

[vtsnowedin]

Looking at the available pictures it looks to me like the top cord or roof failed in two places mid span and the truss members below it punched through the roof. That top cord would be under compression and the instant it failed it was all over.
http://www.miamiherald.com/news/local/c ... LAPSE-6-MI

[jedrider]

A 174-foot, 950-ton section of the bridge was hoisted into place on Saturday. When finished, the bridge would have been 289 feet long and 109 feet tall.

The bridge was being built under what is called "accelerated bridge construction" methods, which are championed at FIU. The methods basically allow larger pieces to be fabricated away from traffic, rather than assembling lots of smaller pieces above a busy road.

"FIU is about building bridges and student safety. This project accomplishes our mission beautifully," FIU President Mark Rosenberg said after the Saturday installation.

Looks to me like the students of FIU got some first hand experience of civil engineering. Someone didn't do their homework.

If you look at the structure, you have to wonder what holds it up? Now we know.

Evidently, their new construction method maybe forgot to calculate stresses at intermediate stages of their 'rapid' construction technique.

I must have a good idea of what will stand and what won't: We had an elevated freeway in Oakland collapse during the 1989 Loma Prieta earthquake and I was always afraid of driving over or under it. Couldn't anyone else see that? Then there is this New York skyscraper that always gave me the creeps, but I knew that it was completely intentional. However, it too was found to be vulnerable to collapse.

http://www.slate.com/blogs/the_eye/2014/04/17/the_citicorp_tower_design_flaw_that_could_have_wiped_out_the_skyscraper.html

[Cog]

Evidently this is designed to be a cable suspension bridge and the engineering firm was putting tension on some cables. When either the anchor point or crane failed it created a shock load on the bridge. Why anyone thought you should have traffic under it when you are doing something like this is beyond me.

From Marco Rubio twitter:

The cables that suspend the #Miami bridge had loosened & the engineering firm ordered that they be tightened. They were being tightened when it collapsed today.

I think Rubio is wrong here but there are bridges that are post-tensioned and they were doing something involving that process when it failed.

[Cog]

One more thing. The city was adamant that traffic not be blocked during the construction process. Which is why the bulk of the bridge was constructed off site and moved into place. Bad call in retrospect.

[vtsnowedin]

Yes this rapid construction process is all the rage and sometimes I think they throw in unreasonable requirements just so they can use the method and get an award or promotion. There is no glory in just putting in a temporary bridge and doing things the old fashioned way. Perhaps after this disaster they will rethink their enthusiasm for the method?
.

[yellowcanoe]

Yes this rapid construction process is all the rage and sometimes I think they throw in unreasonable requirements just so they can use the method and get an award or promotion. There is no glory in just putting in a temporary bridge and doing things the old fashioned way. Perhaps after this disaster they will rethink their enthusiasm for the method?
.

The old fashioned way involved rerouting traffic around the construction site for an extended period of time. Here in Ottawa a number of bridges on the expressway that runs through the center of the city have been replaced in recent years using a rapid bridge replacement procedure. New bridge sections (one for the east bound lanes and one for the west bound lanes) are built off site. Traffic needs to be rerouted for less than 72 hours on a long weekend in the summer to enable demolition of the old bridge sections and installation of the new bridge sections. This has worked well and is far more preferable to having many months of traffic disruption.

[vtsnowedin]

Yes this rapid construction process is all the rage and sometimes I think they throw in unreasonable requirements just so they can use the method and get an award or promotion. There is no glory in just putting in a temporary bridge and doing things the old fashioned way. Perhaps after this disaster they will rethink their enthusiasm for the method?
.

The old fashioned way involved rerouting traffic around the construction site for an extended period of time. Here in Ottawa a number of bridges on the expressway that runs through the center of the city have been replaced in recent years using a rapid bridge replacement procedure. New bridge sections (one for the east bound lanes and one for the west bound lanes) are built off site. Traffic needs to be rerouted for less than 72 hours on a long weekend in the summer to enable demolition of the old bridge sections and installation of the new bridge sections. This has worked well and is far more preferable to having many months of traffic disruption.

One of the last state jobs I worked on was a 20 million dollar upgrade to an exit with 60,000 vehicles a day and five bridges. We built widened lanes and temporary bridge widening s to provide a new lane before any old lane was closed. Much of the work on the commercial street under the interstate was done at night so all traffic was free flowing or at least as much as it would be under normal traffic light control. The costs of the temporary lanes was some two million dollars. There is more then one way to skin a cat.

[Tanada]

Yes this rapid construction process is all the rage and sometimes I think they throw in unreasonable requirements just so they can use the method and get an award or promotion. There is no glory in just putting in a temporary bridge and doing things the old fashioned way. Perhaps after this disaster they will rethink their enthusiasm for the method?
.

The old fashioned way involved rerouting traffic around the construction site for an extended period of time. Here in Ottawa a number of bridges on the expressway that runs through the center of the city have been replaced in recent years using a rapid bridge replacement procedure. New bridge sections (one for the east bound lanes and one for the west bound lanes) are built off site. Traffic needs to be rerouted for less than 72 hours on a long weekend in the summer to enable demolition of the old bridge sections and installation of the new bridge sections. This has worked well and is far more preferable to having many months of traffic disruption.

Sounds great, of course if the Florida project had followed the same approach then traffic would have been rerouted during the crucial period when the collapse took place and loss of life would have been minimal.

I see this as human error on two levels, someone screwed the pooch on the project or there would not have been a collapse is one aspect, but the government decision to not reroute traffic for a week or a few days during the crucial phase of the construction when lives were at risk was a much bigger problem because it actually lead to the loss of life of random folks where were in the wrong place at the wrong time.

[Outcast_Searcher]

When I first saw the Title of the news announcement, my first thought was "Another infrastructure failure fiasco".

So I wonder how the politics on this plays out now. So they were keeping traffic flowing as I'm sure local voters wanted, but OTOH, when the risk is you kill a number of said voters, they're probably not too impressed.

I'll probably be a wee bit more patient from now on at the time it takes to do large or complex projects, like adding lanes to an expressway, even though it does mess up the traffic for a while.

[Outcast_Searcher]

One of the last state jobs I worked on was a 20 million dollar upgrade to an exit with 60,000 vehicles a day and five bridges. We built widened lanes and temporary bridge widening s to provide a new lane before any old lane was closed. Much of the work on the commercial street under the interstate was done at night so all traffic was free flowing or at least as much as it would be under normal traffic light control. The costs of the temporary lanes was some two million dollars. There is more then one way to skin a cat.

Where I've noticed interstate bridge replacements at exits (including widening to allow for more traffic), I've noticed the method you describe. It seems to allow for safe movement of a similar number of cars while the new bridge and access to it is prepared (which can take quite a few months). Given how crowded such areas tend to be, and how few good, close options there may be, keeping that traffic moving is critical, unless they'd want to tolerate a really huge mess.

I always figured the extra lanes/work were likely somewhat expensive, but figured in a case like that, it was just a cost of doing business, given the circumstances.

Around my city, they often put up signs for days or even weeks ahead of time when there will be significant closures for road construction on major roads. That way people who drive a given route can plan an alternate route or pick another time to travel for some window the road will be fouled up. For temporary outages needed for safety, that seems like a good way to handle things.

[vtsnowedin]

Interstates usually have enough ROW (right of way) to allow building detour lanes as needed. The problem comes in urban areas where the room just isn't there. And one of the worst situations is a two lane road in a narrow valley beside a river in a rural area. No place to put the temporary lanes and no alternate routes for the traveling public. And while you are trying to solve that problem you will have to deal with a property owner with a sacred lilac bush and the governors phone number on speed dial.

[Newfie]

I had posted a news article on this bridge in the News Thread. It appears to have had some other unique features.

https://www.reuters.com/article/us-flor ... SKCN1GR3AM

A few decades ago I was deeply involved in a railroad bridge construction project in Philadelphia. It was a mutliprime job with 5 civil and two electrical contracts. I was field PM for the larger electrical. The roads crossed under the elevated railway. New railway bridges were built next to the old bridges. The old bridges were lifted out and the new ones lifted in. This obviously shut down the commuter railroad. Here is a wiki bit on that project

On November 16, 1984, the Columbia Avenue (now Cecil B. Moore Avenue) bridge near old Temple University Station was found to be unsafe, putting all four tracks out of service north of Market East Station. In December 1984, a temporary bridge opened, allowing service to resume north of Market East Station.[25] Nonetheless, the results of decades of deferred maintenance on the Reading Viaduct between the Center City Commuter Connection and Wayne Junction continued to threaten the right-of-way. In 1992, the bridge was in such poor condition that the bridge inspector actually saw the structure sag every time a train passed over the bridge; further inspection revealed that the bridge was in imminent danger of collapsing.[13]

Over the following year, SEPTA undertook a 10-month, $354 million (equivalent to $617.3 million in 2018) project to overhaul the viaduct, labeled "RailWorks."[13] The viaduct was shut down completely from April 5 to October 3, 1992, and from May 2 to September 4, 1993, with the R6 Norristown, R7 Chestnut Hill East, and R8 Fox Chase lines suspended.[13][31][32] Other Reading lines only came as far into the city as the Fern Rock Transportation Center, where riders had to transfer to the Broad Street Subway.[13] Express trackage was added to the Broad Street Line to improve travel times from Center City to Fern Rock. Nonetheless, the number of subway trains needed to carry both regular Broad Street Subway riders, as well as passengers transferring to the subway because of RailWorks, exceeded the capacity of the above-ground, two-track, stub-end Fern Rock terminus.[13][33] In 1993, SEPTA added a loop track to Fern Rock Yard, so that northbound trains did not need to use the crossovers at the station throat, somewhat ameliorating the problem.[13] During peak hours, SEPTA ran several diesel trains from the Reading side branches, along non-electrified Conrail trackage, to 30th Street Station.[13]

Meanwhile, SEPTA crews replaced several dilapidated bridges, installed new continuous welded rail and overhead catenary, constructed new rail stations at Temple University and North Broad Street, and upgraded the signals.[13] Upon the completion of RailWorks, the Reading Viaduct became the "newest" piece of railroad owned by SEPTA, although other projects have since allowed improved service on the ex-Reading side of the system.[13]

[Newfie]

C9A1BC38-B68E-4854-931F-8B9F6B7443CC.jpeg

Remember this was a PEDESTRIAN bridge.

This appears to be a photo of the installation.

https://www.gannett-cdn.com/-mm-/da14ec ... LATION.JPG

[Newfie]

Because the bridge's central tower and suspension cables were not yet installed, the Miami Herald notes that any cables being tightened were likely wires that ran through the span that fell on Thursday.

https://www.npr.org/sections/thetwo-way ... ami-bridge

I find that an incredible statement if true. Who would put up a suspension bridge BEFORE installing the cables? Incredible.

[vtsnowedin]

Because the bridge's central tower and suspension cables were not yet installed, the Miami Herald notes that any cables being tightened were likely wires that ran through the span that fell on Thursday.

https://www.npr.org/sections/thetwo-way ... ami-bridge

I find that an incredible statement if true. Who would put up a suspension bridge BEFORE installing the cables? Incredible.

I suspect that is just a reporter misunderstanding what they are being told by a politician that doesn't know what he is talking about.
The few precast modular bridges I have worked on have voids cast into them (PVC pipe usually) and once the segments are butted together steel cables are run through the voids and jacked to the design tension squeezing all the segments together. Once all the cables are jacked and tested the voids are pumped full of grout to keep water and salt from rusting the cables. All the cables holding this section together should have been in place and tight before the bridge was set in place but there might be other voids reserved to hitch on the next segment on each end.
I sure would like to get a good long look at the plans for this bridge.
Edit to add.
OK after finally looking at the link you posted I see what you mean.
If the design needs that much tower and cable stays what made them think they could just put it up there over traffic unsupported?

[Newfie]

And another thing, why would you “stress test” an unstayed suspension bridge?

What the heck do they mean by “stress test”? I think of loading it with weight and measuring deflection. But that makes zero sense to me at this point?

Not much makes any sense.

I have to believe there is something substantially wrong with the reporting. Even civil engineers aren’t that stupid.
Newfie PE ( Electrical) Ret

[vtsnowedin]

And another thing, why would you “stress test” an unstayed suspension bridge?

What the heck do they mean by “stress test”? I think of loading it with weight and measuring deflection. But that makes zero sense to me at this point?

Not much makes any sense.

I have to believe there is something substantially wrong with the reporting. Even civil engineers aren’t that stupid.
Newfie PE ( Electrical) Ret

Again they are just in the state of confusion.
As you jack a cable to put tension on the structure there is a gauge on the jack and the final tension is recorded but I would not call that a test. They were probably going from one cable to another to get them all even but why that would cause this failure is beyond what I know now.

[jedrider]

Engineer on Fla. bridge project called state to report crack days before collapse
The Florida Department of Transportation

OK, I don't have a Washington Post subscription. Something was obviously wrong, but why did the engineer have to circumvent management?

[Cog]

And another thing, why would you “stress test” an unstayed suspension bridge?

What the heck do they mean by “stress test”? I think of loading it with weight and measuring deflection. But that makes zero sense to me at this point?

Not much makes any sense.

I have to believe there is something substantially wrong with the reporting. Even civil engineers aren’t that stupid.
Newfie PE ( Electrical) Ret

Again they are just in the state of confusion.
As you jack a cable to put tension on the structure there is a gauge on the jack and the final tension is recorded but I would not call that a test. They were probably going from one cable to another to get them all even but why that would cause this failure is beyond what I know now.

Because if you are tensioning a cable and have a catastrophic failure at either the anchor point or the cable itself, you transfer all that energy back into the span beyond the design load. Or you crack the unsupported span itself by this sudden release of energy. This walkway was designed to be cable suspension bridge. At the time of the accident it wasn't supported by suspension cables. It might have well had enough strength to span that gap without the suspension cables but create a shock load and you will exceed design limits. Or at least this non-engineer is thinking that way.

Being part of more than a few large construction projects where something goes very wrong, I can understand what anyone associated with this project is thinking. Its fear you had anything to do with what happened. The blame game has already started and you want to be sure you aren't the guy that gets that blame. A lot of long nights reviewing plans and procedures is ahead of these people.