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The Florida Bridge Collapse- Interesting read
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alpa_sheth
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PostPosted: Fri Mar 30, 2018 6:52 am    Post subject: The Florida Bridge Collapse- Interesting read Reply with quote

This sentence is a very telling one: "Designed to withstand the
biggest storms nature could throw at it, the structure couldn't
withstand a perfect storm of hasty planning, managerial incompetence,
and human hubris." Lot's to learn from this. We have had no
discussions whatsoever on so many bridge collapses in our country!

Regards,
Alpa
******************************

A Prefabricated Tragedy

The collapse of a superbridge in Florida shows how an entire
philosophy of building can go wrong.

By MATTHEW N. EISLER

MARCH 18, 2018



It was to be a showcase of advanced bridge technology, a centerpiece
of urban development in Miami-Dade County. It was equipped with
titanium dioxide–impregnated self-cleaning concrete that would always
sparkle white in the Florida sun. It was designed to withstand a
Category 5 hurricane. And it was supposed to last 100 years.

But last week, the FIU-Sweetwater UniversityCity Bridge failed
catastrophically during construction, crushing rows of cars stopped at
a red light on a busy thoroughfare. Six people were killed and 10
injured.

Failures like this invoke special horror because they are so rare,
which is the only solace to be had from the tragedy. As pedestrians
and motorists, we take infrastructure reliability for granted in a way
that we don't with our consumer goods. We expect cars and computers to
crash, and conceptually, we can cope with that, even when the
consequences are dire. When bridges and tunnels implode, though, it
seems like things are truly out of our hands, the sky almost literally
falling on our heads.

So it is a tad disconcerting to learn that the technology and
techniques used in the UniversityCity Bridge may be coming to a
neighborhood near you, if they haven't already. The bridge was a
product of something called "accelerated bridge construction," or ABC,
a technique of fast-tracked prefabricated building that has strong
political backing at both the state and federal levels. More than
1,000 bridges have been built with it, and Florida International
University is one of the leading research centers in this kind of
engineering, an irony not lost on some commentators.

To be fair, the university did not design or build the bridge, as it
hastened to point out. And neither the designer nor the builder has a
spotless record. With wreckage left to be cleared, it will be a while
before the National Transportation Safety Board can pinpoint the exact
cause of the disaster.

What we can say is that when complex technological systems fail,
usually no single factor is to blame. In her study of the Challenger
Space Shuttle disaster, the sociologist Diane Vaughan noted a
phenomenon she called the "normalization of deviance," an acceptance
of assumptions and shortcuts that over time incrementally piles on
risk until, like compounding interest on debt, a kind of technological
bill suddenly becomes due.

Something like this probably happened at the UniversityCity Bridge.
And when all the rubble is removed and the reports are written, it is
likely we'll learn that the collapse had something to do with the
philosophy of accelerated construction. In a part of the country
notorious for slash-and-burn urban development, it turns out that ABC
can be much more complicated and problematic than its rather glib
acronym implies.

First, let's discuss what probably didn't cause the collapse. The FIU
bridge looked like a cable-stayed bridge, a highly reliable technology
that has been around since at least the 16th century. Cable-stayed
bridges look something like suspension bridges, but the physics are
significantly different. In suspension bridges, the load is
transmitted through two sets of cables, one set attached to the deck
that is in turn connected to two main cables loosely strung between
towers, and passes into the ground at the ends, where the cables are
anchored stoutly. As anyone who has walked or driven over one can
attest, suspension bridges are relatively flexible. They move, and
even sway, in heavy traffic, strong winds, or earthquakes.

In a cable-stayed bridge, everything is a lot stiffer. There is only
one set of cables and they are rigidly embedded into towers and the
deck, which has to be a lot more robust than a suspension-bridge deck
because the wires tend to exert strong horizontal forces. This design
is favored when ground conditions aren't suitable for the kind of
massive anchors suspension bridges require. Such bridges require fewer
materials and can be erected more quickly than their suspension
counterparts.

Cable-stayed bridges are also more flexible than suspension bridges in
terms of design and can be built in many different configurations that
play on the arrangement of cables and towers. Boosters love them for
their aesthetic potential, and some of the most prestigious recent
bridge projects are of the cable-stayed variety, including Santiago
Calatrava's Margaret Hill Hunt Bridge and Sir Norman Foster's Millau
Viaduct. Cable-stayed showcase bridges have become increasingly
popular in the U.S. and especially Florida, where they are regarded as
expressions of civic upward mobility that no self-respecting aspiring
metropolis wants to be without.

In the cable-stayed bridge, the tower is the thing. It bears all of
the load, which it transmits to the ground, and it is also the
dramatic fulcrum of the design. Suitably enough, in boat-mad Florida,
the tower in the UniversityCity design was supposed to evoke a
sailboat.

But the UniversityCity design was not actually a cable-stayed bridge.
It only looked like one. It was actually a kind of truss, also a
well-proven technology. The proposal diagrams suggest that the two
primary deck sections could be assembled prior to the erection of the
tower and cables. The main section weighed 950 tons, and was
exceptionally large and heavy for a bridge intended to accommodate
only pedestrians. It was swung into place on support pylons in a
much-publicized operation employing a huge mobile jack. And there it
sat for five days until it failed. Two days before the collapse, as
the New York Times reported, small cracks were observed at the slab's
north end, where the tower was to have been installed and where the
failure appears to have occurred. The cracks caused sufficient
disquiet that engineers were discussing the structural integrity of
the span, proclaiming it safe only hours before the collapse.

Understanding why the bridge was built and assembled in this way is a
lesson both in the politics of prefab and civic boosterism. All
first-year civil engineering students learn that concrete is good in
compression and weak in tension. Steel is good in both. But concrete
can be given tension by prestressing it—that is, by running steel
cables through it. This can be done at the time concrete is cast, in
what is known as pre-tension.

It can also be done after casting. This is known as post-tensioning
and involves tightening and locking the cables that bind a cured slab.
The UniversityCity Bridge used post-tensioned parts. In an ideal
world, cable tensioning is part of the prefab process. For bridges
that will bear heavy traffic, engineers want to achieve a slight
upward bend called a camber, which flattens out under load and gives
high carrying capacity. But sometime cables are overtightened, and
engineers would want to resolve adjustments before final assembly. It
seems that at the UniversityCity Bridge, the slab was stress-tested
not before but after it was mounted in place. In a partly assembled
structure, such a procedure is risky and has been known to end in
catastrophic failure. Reports suggest that the collapse occurred when
workers were adjusting the cables and, presumably, the camber.

Prefab assumes that all the complexities of construction can be
front-loaded into component manufacturing, so that final assembly can
take place all at once, quickly and efficiently. It has been marketed
as the scientific management of building, a triumph of logistics over
craft knowledge. Naturally, unions tend to hate prefab, seeing
componentization as a means of destroying their ability to control the
pace of construction. Managers and boosters love it for precisely
those reasons.

It looks as if a giant concrete Lego set was misassembled, with fatal results.

At UniversityCity Bridge, it looks as if one of the basic precepts of
prefabricated construction was undermined. If accelerated construction
were premised as means of simplifying project management, prefab was
surely never intended to be a complete substitute for it, as those in
charge seem to have assumed. It looks as if a giant concrete Lego set
was misassembled, with fatal results.

So what were the problems for which this application of ABC was the
solution? Ultimately, they issue from the rush to develop some of the
world's most valuable but ecologically fragile real estate. To the
pioneering activist Marjory Stoneman Douglas, the story of the
colonization of Florida was one of greed, violence, displacement, and
destruction on an epic scale, immortalized in her magisterial
Everglades: River of Grass, a classic of environmental history.

Modern boosters, including FIU's ABC center, tend to reduce Florida's
problems to traffic throughput. Western Miami-Dade was hacked out of
the Everglades, which in the wet season boils over with freshwater
that is kept at bay only with extensive public works. Foremost among
these is the Tamiami Trail, the artery that the UniversityCity Bridge
was to have spanned. Built in the 1920s to connect Florida's east and
west coasts, the road is basically a long, low dam with a highway on
top of it. It cut off the flow of freshwater from Lake Okeechobee to
the southern Everglades, drying up the wetlands and creating an
environmental catastrophe.

Today, critics regard Tamiami Trail as emblematic of Florida's
shortsighted approach to urban development, although the U.S. Army
Corps of Engineers has done remedial work to remedy the water flow
problem. Yet it remains an important east-west highway in the southern
part of the state, and so it is a strategic traffic resource. For
visitors driving in from Naples, the Tamiami is Florida's Appian Way,
and the UniversityCity Bridge was to be its triumphal arch, a gateway
to greater Miami. Construction couldn't be allowed to block traffic,
which is political plutonium in any auto-centric society, especially
South Florida. Enter accelerated construction.

The stakes here are far larger than the ambitions of one Sun Belt city
and university. The federal government has helped fund projects like
the UniversityCity Bridge through its Transportation Investment
Generating Economic Recovery initiative, a program that has drawn
criticism for privileging politics over technical merit. And federal
money has played perhaps the major role in terraforming the state, not
least through the National Flood Insurance Program, 35 percent of
which is devoted to the Sunshine State, the largest single chunk of
the program.

So it is hard not to see the tragedy of the UniversityCity Bridge as a
kind of metonym for the reckoning that Florida has long been setting
itself up for. Designed to withstand the biggest storms nature could
throw at it, the structure couldn't withstand a perfect storm of hasty
planning, managerial incompetence, and human hubris.

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PostPosted: Fri Mar 30, 2018 7:12 am    Post subject: Reply with quote

Madam, the article seems to be no more than a political rant - albeit very expressive. There's no reasoning or even speculation about the cause and mode of failure. ENR has a rather more informative article, which still cautions about theories floating around disconnected from data.

https://www.enr.com/articles/44186-theories-outrun-reliable-facts-in-florida-bridge-collapse

Regards,

Abhijeet Oundhakar
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alpa_sheth
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PostPosted: Fri Mar 30, 2018 7:53 am    Post subject: Reply with quote

Dear Er. Oundhkar:

Thanks for the link.
Neither of the two articles point to the cause of the disaster because, investigation is work in progress and quite clearly the disaster is  a cumulative set of issues.
The article I posted was interesting to me because the writer Eisler is a Professor of History. I think he is making a more philosophical point and I did not see it as a rant but as a reflection of someone who is stepping back and seeing the larger issue. We do not pay adequate attention to History in engineering and tend to miss the woods for the trees.
As engineers, we get so absorbed in looking at each dot that we do not step back to join the dots and see the picture that emerges. I think a little more training in Humanities will do all of us engineers a world of good.

best regards,
Alpa

abhio wrote:
Madam, the article seems to be no more than a political rant - albeit very expressive. There's no reasoning or even speculation about the cause and mode of failure. ENR has a rather more informative article, which still cautions about theories floating around disconnected from data.

https://www.enr.com/articles/44186-theories-outrun-reliable-facts-in-florida-bridge-collapse

Regards,

Abhijeet Oundhakar
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alpa_sheth
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PostPosted: Fri Mar 30, 2018 8:07 am    Post subject: Reply with quote

And in continuation of this thread and my contention that we as  engineers are sometimes unable to see the complete picture, here is another term I would like to share with SEFI community- "Normalization of Deviance"
********
Normalization of deviance is a term first coined by sociologist Diane Vaughan (again someone from the Humanities talking about rocket science!) when reviewing the Challenger disaster. Vaughan noted that the root cause of the Challenger disaster was related to the repeated choice of NASA officials to fly the space shuttle despite a dangerous design flaw with the O-rings. Vaughan describes this phenomenon as occurring when people within an organization become so insensitive to deviant practice that it no longer feels wrong. Insensitivity occurs insidiously and sometimes over years because disaster does not happen until other critical factors line up.


best regards,
Alpa


alpa_sheth wrote:
Dear Er. Oundhkar:

Thanks for the link.
Neither of the two articles point to the cause of the disaster because, investigation is work in progress and quite clearly the disaster is  a cumulative set of issues.
The article I posted was interesting to me because the writer Eisler is a Professor of History. I think he is making a more philosophical point and I did not see it as a rant but as a reflection of someone who is stepping back and seeing the larger issue. We do not pay adequate attention to History in engineering and tend to miss the woods for the trees.
As engineers, we get so absorbed in looking at each dot that we do not step back to join the dots and see the picture that emerges. I think a little more training in Humanities will do all of us engineers a world of good.

best regards,
Alpa

abhio wrote:
Madam, the article seems to be no more than a political rant - albeit very expressive. There's no reasoning or even speculation about the cause and mode of failure. ENR has a rather more informative article, which still cautions about theories floating around disconnected from data.

https://www.enr.com/articles/44186-theories-outrun-reliable-facts-in-florida-bridge-collapse

Regards,

Abhijeet Oundhakar
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PostPosted: Fri Mar 30, 2018 5:21 pm    Post subject: Reply with quote

Broken- Prof. Simon
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PostPosted: Fri Mar 30, 2018 5:48 pm    Post subject: Reply with quote

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PostPosted: Fri Mar 30, 2018 5:50 pm    Post subject: Reply with quote

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PostPosted: Sat Mar 31, 2018 7:07 pm    Post subject: The Florida Bridge Collapse- Interesting read Reply with quote

Thanks for the article. There can be nothing like fail proof system. This was nearly proof and human beings should realise it. 

Prof ARC


On Fri, Mar 30, 2018, 12:24 alpa_sheth <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           This sentence is a very telling one: "Designed to withstand the
biggest storms nature could throw at it, the structure couldn't
withstand a perfect storm of hasty planning, managerial incompetence,
and human hubris." Lot's to learn from this. We have had no
discussions whatsoever on so many bridge collapses in our country!

Regards,
Alpa
***************

A Prefabricated Tragedy

The collapse of a superbridge in Florida shows how an entire
philosophy of building can go wrong.

By MATTHEW N. EISLER

MARCH 18, 2018



It was to be a showcase of advanced bridge technology, a centerpiece
of urban development in Miami-Dade County. It was equipped with
titanium dioxideimpregnated self-cleaning concrete that would always
sparkle white in the Florida sun. It was designed to withstand a
Category 5 hurricane. And it was supposed to last 100 years.

But last week, the FIU-Sweetwater UniversityCity Bridge failed
catastrophically during construction, crushing rows of cars stopped at
a red light on a busy thoroughfare. Six people were killed and 10
injured.

Failures like this invoke special horror because they are so rare,
which is the only solace to be had from the tragedy. As pedestrians
and motorists, we take infrastructure reliability for granted in a way
that we don't with our consumer goods. We expect cars and computers to
crash, and conceptually, we can cope with that, even when the
consequences are dire. When bridges and tunnels implode, though, it
seems like things are truly out of our hands, the sky almost literally
falling on our heads.

So it is a tad disconcerting to learn that the technology and
techniques used in the UniversityCity Bridge may be coming to a
neighborhood near you, if they haven't already. The bridge was a
product of something called "accelerated bridge construction," or ABC,
a technique of fast-tracked prefabricated building that has strong
political backing at both the state and federal levels. More than
1,000 bridges have been built with it, and Florida International
University is one of the leading research centers in this kind of
engineering, an irony not lost on some commentators.

To be fair, the university did not design or build the bridge, as it
hastened to point out. And neither the designer nor the builder has a
spotless record. With wreckage left to be cleared, it will be a while
before the National Transportation Safety Board can pinpoint the exact
cause of the disaster.

What we can say is that when complex technological systems fail,
usually no single factor is to blame. In her study of the Challenger
Space Shuttle disaster, the sociologist Diane Vaughan noted a
phenomenon she called the "normalization of deviance," an acceptance
of assumptions and shortcuts that over time incrementally piles on
risk until, like compounding interest on debt, a kind of technological
bill suddenly becomes due.

Something like this probably happened at the UniversityCity Bridge.
And when all the rubble is removed and the reports are written, it is
likely we'll learn that the collapse had something to do with the
philosophy of accelerated construction. In a part of the country
notorious for slash-and-burn urban development, it turns out that ABC
can be much more complicated and problematic than its rather glib
acronym implies.

First, let's discuss what probably didn't cause the collapse. The FIU
bridge looked like a cable-stayed bridge, a highly reliable technology
that has been around since at least the 16th century. Cable-stayed
bridges look something like suspension bridges, but the physics are
significantly different. In suspension bridges, the load is
transmitted through two sets of cables, one set attached to the deck
that is in turn connected to two main cables loosely strung between
towers, and passes into the ground at the ends, where the cables are
anchored stoutly. As anyone who has walked or driven over one can
attest, suspension bridges are relatively flexible. They move, and
even sway, in heavy traffic, strong winds, or earthquakes.

In a cable-stayed bridge, everything is a lot stiffer. There is only
one set of cables and they are rigidly embedded into towers and the
deck, which has to be a lot more robust than a suspension-bridge deck
because the wires tend to exert strong horizontal forces. This design
is favored when ground conditions aren't suitable for the kind of
massive anchors suspension bridges require. Such bridges require fewer
materials and can be erected more quickly than their suspension
counterparts.

Cable-stayed bridges are also more flexible than suspension bridges in
terms of design and can be built in many different configurations that
play on the arrangement of cables and towers. Boosters love them for
their aesthetic potential, and some of the most prestigious recent
bridge projects are of the cable-stayed variety, including Santiago
Calatrava's Margaret Hill Hunt Bridge and Sir Norman Foster's Millau
Viaduct. Cable-stayed showcase bridges have become increasingly
popular in the U.S. and especially Florida, where they are regarded as
expressions of civic upward mobility that no self-respecting aspiring
metropolis wants to be without.

In the cable-stayed bridge, the tower is the thing. It bears all of
the load, which it transmits to the ground, and it is also the
dramatic fulcrum of the design. Suitably enough, in boat-mad Florida,
the tower in the UniversityCity design was supposed to evoke a
sailboat.

But the UniversityCity design was not actually a cable-stayed bridge.
It only looked like one. It was actually a kind of truss, also a
well-proven technology. The proposal diagrams suggest that the two
primary deck sections could be assembled prior to the erection of the
tower and cables. The main section weighed 950 tons, and was
exceptionally large and heavy for a bridge intended to accommodate
only pedestrians. It was swung into place on support pylons in a
much-publicized operation employing a huge mobile jack. And there it
sat for five days until it failed. Two days before the collapse, as
the New York Times reported, small cracks were observed at the slab's
north end, where the tower was to have been installed and where the
failure appears to have occurred. The cracks caused sufficient
disquiet that engineers were discussing the structural integrity of
the span, proclaiming it safe only hours before the collapse.

Understanding why the bridge was built and assembled in this way is a
lesson both in the politics of prefab and civic boosterism. All
first-year civil engineering students learn that concrete is good in
compression and weak in tension. Steel is good in both. But concrete
can be given tension by prestressing it—that is, by running steel
cables through it. This can be done at the time concrete is cast, in
what is known as pre-tension.

It can also be done after casting. This is known as post-tensioning
and involves tightening and locking the cables that bind a cured slab.
The UniversityCity Bridge used post-tensioned parts. In an ideal
world, cable tensioning is part of the prefab process. For bridges
that will bear heavy traffic, engineers want to achieve a slight
upward bend called a camber, which flattens out under load and gives
high carrying capacity. But sometime cables are overtightened, and
engineers would want to resolve adjustments before final assembly. It
seems that at the UniversityCity Bridge, the slab was stress-tested
not before but after it was mounted in place. In a partly assembled
structure, such a procedure is risky and has been known to end in
catastrophic failure. Reports suggest that the collapse occurred when
workers were adjusting the cables and, presumably, the camber.

Prefab assumes that all the complexities of construction can be
front-loaded into component manufacturing, so that final assembly can
take place all at once, quickly and efficiently. It has been marketed
as the scientific management of building, a triumph of logistics over
craft knowledge. Naturally, unions tend to hate prefab, seeing
componentization as a means of destroying their ability to control the
pace of construction. Managers and boosters love it for precisely
those reasons.

It looks as if a giant concrete Lego set was misassembled, with fatal results.

At UniversityCity Bridge, it looks as if one of the basic precepts of
prefabricated construction was undermined. If accelerated construction
were premised as means of simplifying project management, prefab was
surely never intended to be a complete substitute for it, as those in
charge seem to have assumed. It looks as if a giant concrete Lego set
was misassembled, with fatal results.

So what were the problems for which this application of ABC was the
solution? Ultimately, they issue from the rush to develop some of the
world's most valuable but ecologically fragile real estate. To the
pioneering activist Marjory Stoneman Douglas, the story of the
colonization of Florida was one of greed, violence, displacement, and
destruction on an epic scale, immortalized in her magisterial
Everglades: River of Grass, a classic of environmental history.

Modern boosters, including FIU's ABC center, tend to reduce Florida's
problems to traffic throughput. Western Miami-Dade was hacked out of
the Everglades, which in the wet season boils over with freshwater
that is kept at bay only with extensive public works. Foremost among
these is the Tamiami Trail, the artery that the UniversityCity Bridge
was to have spanned. Built in the 1920s to connect Florida's east and
west coasts, the road is basically a long, low dam with a highway on
top of it. It cut off the flow of freshwater from Lake Okeechobee to
the southern Everglades, drying up the wetlands and creating an
environmental catastrophe.

Today, critics regard Tamiami Trail as emblematic of Florida's
shortsighted approach to urban development, although the U.S. Army
Corps of Engineers has done remedial work to remedy the water flow
problem. Yet it remains an important east-west highway in the southern
part of the state, and so it is a strategic traffic resource. For
visitors driving in from Naples, the Tamiami is Florida's Appian Way,
and the UniversityCity Bridge was to be its triumphal arch, a gateway
to greater Miami. Construction couldn't be allowed to block traffic,
which is political plutonium in any auto-centric society, especially
South Florida. Enter accelerated construction.

The stakes here are far larger than the ambitions of one Sun Belt city
and university. The federal government has helped fund projects like
the UniversityCity Bridge through its Transportation Investment
Generating Economic Recovery initiative, a program that has drawn
criticism for privileging politics over technical merit. And federal
money has played perhaps the major role in terraforming the state, not
least through the National Flood Insurance Program, 35 percent of
which is devoted to the Sunshine State, the largest single chunk of
the program.

So it is hard not to see the tragedy of the UniversityCity Bridge as a
kind of metonym for the reckoning that Florida has long been setting
itself up for. Designed to withstand the biggest storms nature could
throw at it, the structure couldn't withstand a perfect storm of hasty
planning, managerial incompetence, and human hubris.
     



     



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PostPosted: Sat Mar 31, 2018 7:08 pm    Post subject: The Florida Bridge Collapse- Interesting read Reply with quote

Dear All,

This is an excellent piece. Very well articulated. Thanks to Alpa for posting this in SEFI.


There is a 'correction' to this article published on 20th March, which reads as follows :



"Correction, March 20, 2018: This article originally identified the FIU-Sweetwater UniversityCity Bridge as a cable-stayed bridge; it was a truss bridge. The article also said steel is weak in compression and good in tension; in fact, it is good in both. It described camber as a dangerous bend in the slab; in fact, it is a slight upward bend that is not necessarily dangerous. And it incorrectly described Tamiami Trail as the only east-west highway in South Florida."

These corrections are important to structural engineers in general and bridge engineers in particular. It is amazing how a lecturer in history can write such an informed articles where he not only dwells on the technical aspects, quite in depth, but also gives a philosophical touch to the core issue of accelerated bridge construction philosophy. No matter there are quite a few technical errors in the text, it does not in any way reduces the focus of his article.


Best Wishes


Alok Bhowmick


On Fri, Mar 30, 2018 at 12:24 PM, alpa_sheth <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           This sentence is a very telling one: "Designed to withstand the
biggest storms nature could throw at it, the structure couldn't
withstand a perfect storm of hasty planning, managerial incompetence,
and human hubris." Lot's to learn from this. We have had no
discussions whatsoever on so many bridge collapses in our country!

Regards,
Alpa
***************

A Prefabricated Tragedy

The collapse of a superbridge in Florida shows how an entire
philosophy of building can go wrong.

By MATTHEW N. EISLER

MARCH 18, 2018



It was to be a showcase of advanced bridge technology, a centerpiece
of urban development in Miami-Dade County. It was equipped with
titanium dioxideimpregnated self-cleaning concrete that would always
sparkle white in the Florida sun. It was designed to withstand a
Category 5 hurricane. And it was supposed to last 100 years.

But last week, the FIU-Sweetwater UniversityCity Bridge failed
catastrophically during construction, crushing rows of cars stopped at
a red light on a busy thoroughfare. Six people were killed and 10
injured.

Failures like this invoke special horror because they are so rare,
which is the only solace to be had from the tragedy. As pedestrians
and motorists, we take infrastructure reliability for granted in a way
that we don't with our consumer goods. We expect cars and computers to
crash, and conceptually, we can cope with that, even when the
consequences are dire. When bridges and tunnels implode, though, it
seems like things are truly out of our hands, the sky almost literally
falling on our heads.

So it is a tad disconcerting to learn that the technology and
techniques used in the UniversityCity Bridge may be coming to a
neighborhood near you, if they haven't already. The bridge was a
product of something called "accelerated bridge construction," or ABC,
a technique of fast-tracked prefabricated building that has strong
political backing at both the state and federal levels. More than
1,000 bridges have been built with it, and Florida International
University is one of the leading research centers in this kind of
engineering, an irony not lost on some commentators.

To be fair, the university did not design or build the bridge, as it
hastened to point out. And neither the designer nor the builder has a
spotless record. With wreckage left to be cleared, it will be a while
before the National Transportation Safety Board can pinpoint the exact
cause of the disaster.

What we can say is that when complex technological systems fail,
usually no single factor is to blame. In her study of the Challenger
Space Shuttle disaster, the sociologist Diane Vaughan noted a
phenomenon she called the "normalization of deviance," an acceptance
of assumptions and shortcuts that over time incrementally piles on
risk until, like compounding interest on debt, a kind of technological
bill suddenly becomes due.

Something like this probably happened at the UniversityCity Bridge.
And when all the rubble is removed and the reports are written, it is
likely we'll learn that the collapse had something to do with the
philosophy of accelerated construction. In a part of the country
notorious for slash-and-burn urban development, it turns out that ABC
can be much more complicated and problematic than its rather glib
acronym implies.

First, let's discuss what probably didn't cause the collapse. The FIU
bridge looked like a cable-stayed bridge, a highly reliable technology
that has been around since at least the 16th century. Cable-stayed
bridges look something like suspension bridges, but the physics are
significantly different. In suspension bridges, the load is
transmitted through two sets of cables, one set attached to the deck
that is in turn connected to two main cables loosely strung between
towers, and passes into the ground at the ends, where the cables are
anchored stoutly. As anyone who has walked or driven over one can
attest, suspension bridges are relatively flexible. They move, and
even sway, in heavy traffic, strong winds, or earthquakes.

In a cable-stayed bridge, everything is a lot stiffer. There is only
one set of cables and they are rigidly embedded into towers and the
deck, which has to be a lot more robust than a suspension-bridge deck
because the wires tend to exert strong horizontal forces. This design
is favored when ground conditions aren't suitable for the kind of
massive anchors suspension bridges require. Such bridges require fewer
materials and can be erected more quickly than their suspension
counterparts.

Cable-stayed bridges are also more flexible than suspension bridges in
terms of design and can be built in many different configurations that
play on the arrangement of cables and towers. Boosters love them for
their aesthetic potential, and some of the most prestigious recent
bridge projects are of the cable-stayed variety, including Santiago
Calatrava's Margaret Hill Hunt Bridge and Sir Norman Foster's Millau
Viaduct. Cable-stayed showcase bridges have become increasingly
popular in the U.S. and especially Florida, where they are regarded as
expressions of civic upward mobility that no self-respecting aspiring
metropolis wants to be without.

In the cable-stayed bridge, the tower is the thing. It bears all of
the load, which it transmits to the ground, and it is also the
dramatic fulcrum of the design. Suitably enough, in boat-mad Florida,
the tower in the UniversityCity design was supposed to evoke a
sailboat.

But the UniversityCity design was not actually a cable-stayed bridge.
It only looked like one. It was actually a kind of truss, also a
well-proven technology. The proposal diagrams suggest that the two
primary deck sections could be assembled prior to the erection of the
tower and cables. The main section weighed 950 tons, and was
exceptionally large and heavy for a bridge intended to accommodate
only pedestrians. It was swung into place on support pylons in a
much-publicized operation employing a huge mobile jack. And there it
sat for five days until it failed. Two days before the collapse, as
the New York Times reported, small cracks were observed at the slab's
north end, where the tower was to have been installed and where the
failure appears to have occurred. The cracks caused sufficient
disquiet that engineers were discussing the structural integrity of
the span, proclaiming it safe only hours before the collapse.

Understanding why the bridge was built and assembled in this way is a
lesson both in the politics of prefab and civic boosterism. All
first-year civil engineering students learn that concrete is good in
compression and weak in tension. Steel is good in both. But concrete
can be given tension by prestressing it—that is, by running steel
cables through it. This can be done at the time concrete is cast, in
what is known as pre-tension.

It can also be done after casting. This is known as post-tensioning
and involves tightening and locking the cables that bind a cured slab.
The UniversityCity Bridge used post-tensioned parts. In an ideal
world, cable tensioning is part of the prefab process. For bridges
that will bear heavy traffic, engineers want to achieve a slight
upward bend called a camber, which flattens out under load and gives
high carrying capacity. But sometime cables are overtightened, and
engineers would want to resolve adjustments before final assembly. It
seems that at the UniversityCity Bridge, the slab was stress-tested
not before but after it was mounted in place. In a partly assembled
structure, such a procedure is risky and has been known to end in
catastrophic failure. Reports suggest that the collapse occurred when
workers were adjusting the cables and, presumably, the camber.

Prefab assumes that all the complexities of construction can be
front-loaded into component manufacturing, so that final assembly can
take place all at once, quickly and efficiently. It has been marketed
as the scientific management of building, a triumph of logistics over
craft knowledge. Naturally, unions tend to hate prefab, seeing
componentization as a means of destroying their ability to control the
pace of construction. Managers and boosters love it for precisely
those reasons.

It looks as if a giant concrete Lego set was misassembled, with fatal results.

At UniversityCity Bridge, it looks as if one of the basic precepts of
prefabricated construction was undermined. If accelerated construction
were premised as means of simplifying project management, prefab was
surely never intended to be a complete substitute for it, as those in
charge seem to have assumed. It looks as if a giant concrete Lego set
was misassembled, with fatal results.

So what were the problems for which this application of ABC was the
solution? Ultimately, they issue from the rush to develop some of the
world's most valuable but ecologically fragile real estate. To the
pioneering activist Marjory Stoneman Douglas, the story of the
colonization of Florida was one of greed, violence, displacement, and
destruction on an epic scale, immortalized in her magisterial
Everglades: River of Grass, a classic of environmental history.

Modern boosters, including FIU's ABC center, tend to reduce Florida's
problems to traffic throughput. Western Miami-Dade was hacked out of
the Everglades, which in the wet season boils over with freshwater
that is kept at bay only with extensive public works. Foremost among
these is the Tamiami Trail, the artery that the UniversityCity Bridge
was to have spanned. Built in the 1920s to connect Florida's east and
west coasts, the road is basically a long, low dam with a highway on
top of it. It cut off the flow of freshwater from Lake Okeechobee to
the southern Everglades, drying up the wetlands and creating an
environmental catastrophe.

Today, critics regard Tamiami Trail as emblematic of Florida's
shortsighted approach to urban development, although the U.S. Army
Corps of Engineers has done remedial work to remedy the water flow
problem. Yet it remains an important east-west highway in the southern
part of the state, and so it is a strategic traffic resource. For
visitors driving in from Naples, the Tamiami is Florida's Appian Way,
and the UniversityCity Bridge was to be its triumphal arch, a gateway
to greater Miami. Construction couldn't be allowed to block traffic,
which is political plutonium in any auto-centric society, especially
South Florida. Enter accelerated construction.

The stakes here are far larger than the ambitions of one Sun Belt city
and university. The federal government has helped fund projects like
the UniversityCity Bridge through its Transportation Investment
Generating Economic Recovery initiative, a program that has drawn
criticism for privileging politics over technical merit. And federal
money has played perhaps the major role in terraforming the state, not
least through the National Flood Insurance Program, 35 percent of
which is devoted to the Sunshine State, the largest single chunk of
the program.

So it is hard not to see the tragedy of the UniversityCity Bridge as a
kind of metonym for the reckoning that Florida has long been setting
itself up for. Designed to withstand the biggest storms nature could
throw at it, the structure couldn't withstand a perfect storm of hasty
planning, managerial incompetence, and human hubris.
     



     



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mujkhan
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PostPosted: Sun Apr 01, 2018 12:10 pm    Post subject: The Florida Bridge Collapse- Interesting read Reply with quote

Interesting read.
While it is true that nothing can be fail safe, it is intolerable that bridge structures should fail because of hasty planning and managerial incompetence.
M M Khan






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-- Original message --
From: "prof.arc" <forum@sefindia.org>
Date: 01/04/2018 00:38 (GMT+05:30)
To: general@sefindia.org
Subject: [SEFI] Re: The Florida Bridge Collapse- Interesting read


Thanks for the article. There can be nothing like fail proof system. This was nearly proof and human beings should realise it.

Prof ARC


On Fri, Mar 30, 2018, 12:24 alpa_sheth forum@sefindia.org)> wrote:

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