FYI...one of the better discussions on the I35W bridge.

Note that so far it is still just guess work.

TMT


Metal plates examined in bridge collapse By MARTIGA LOHN, Associated
Press Writer

The metal plates that held the girders together on a failed 1960s-era
interstate bridge were originally attached with rivets, old technology
that is more likely to slip than the bolts used in bridges today.

Some of the plates, or gussets, also may have been weakened by welding
work over the years, and some may have been too thin or too small,
engineering experts said Thursday.

The National Transportation Safety Board, in a brief Wednesday
advisory to states to check such plates in bridges nationwide, cited a
"design issue" with the bridge's gussets. Engineers say that the
plates are an obvious place to start looking, but that a number of
other factors might have contributed to the Aug. 1 collapse that
killed at least seven people and left at least six still missing.

On Thursday, NTSB officials said "people have run maybe a little bit
too far" with the statement on the gussets.

"Simply by finding a piece of metal that's been sheared or twisted
doesn't necessarily mean it's a critical piece of the puzzle," said
Bruce Magladry, director of the NTSB's Office of Highway Safety. "We
see a lot of steel that's damaged because of the bridge collapse. What
we need to ferret out is what's an initial cause of damage vs. what's
a secondary cause."

Engineering experts said failure of the plates, which usually sandwich
the bridge's steel beams where they intersect, in a critical spot
could have brought down the whole bridge, although no one has
pinpointed a gusset as the cause of the failure.

"What they'll be looking for is to see whether one of the gusset
plates may have fractured," said W. Gene Corley, a forensic engineer
with the Skokie, Ill.-based engineering firm CTL Group. "If one of
those gusset plates breaks, then you have lost half the strength at
that location, and most likely the other one can't carry the load
then."

The bridge's builders in the mid-1960s riveted the plates together,
which required many more holes than bolts would have. More holes
weaken steel, said Abolhassan Astaneh-Asl, a professor of structural
engineering at the University of California-Berkeley, who compared
them to Swiss cheese.

The rivets also tend to slip more than bolts and can lead to more
cracking, Corley said. Bolts are preferred in modern bridge
construction, and were used in more recent repairs.

Welding work on some gussets - at temperatures of 2,600 degrees or
more - could also have caused tiny cracks to form as superheated steel
cooled, which may have developed fatigue cracks.

Astaneh-Asl reviewed 1965 construction drawings of the bridge that
showed varying thicknesses of the gussets. Some in key spots over the
Mississippi River were only a half-inch thick, he said, and his rough
calculation of the pressure they could withstand suggested they were
weaker than the beams they connected. A cracked gusset is visible in
photographs taken after the collapse, he said, but it's unclear what
role that might have played in the bridge's failure.

State transportation officials say damage seen on the bridge's gussets
might have been caused by the collapse.

Various problems in the bridge may simply have added up over the years
and created stresses that the designers never contemplated, Astaneh-
Asl said. For instance, at least one expansion joint locked up,
possibly pulling one of the bridge's piers out of alignment and
leading to undetermined pressures on other parts of the bridge. Such
things could have made fatigue cracks worse, he said.

Inspectors who completed the bridge's last full inspection in June
2006 noted problems - "section loss, pitting, heavy flaking rust" - on
several of the plates. They also reported loose bolts on another
gusset.

Corley, who has been invited to be part of a private investigation
into the collapse, said he saw "lots of rust" on the gussets.

"It brings the issue of load and brings the issue of fatigue there as
well as corrosion," he said.

But something could have gone wrong in design, too, Corley said. Each
plate is individually designed, and someone could have miscalculated
the load or weight-bearing capacity of an individual gusset plate, he
said.

"In design there's always the chance for a blunder," Corley said. "One
of the most common causes of collapse of any type of structure is the
blunder."

Investigators are looking closely at the weight that was on the bridge
when it fell.

Construction crews had piled up sand and gravel on the bridge as they
prepared to pave a 520-foot stretch of two southbound lanes of the
freeway, said Liz Benjamin, a construction engineer with MnDOT.
Equipment on the bridge included a cement truck, a concrete mobile
mixer, buggies to haul the concrete and personal vehicles of the
workers. Workers also were using 45-pound jackhammers to remove the
top layer of pavement.

The bridge was one of Minnesota's busiest, carrying 140,000 vehicles a
day. Mark Hallenbeck, director of the Washington State Transportation
Center at the University of Washington, said that's dramatically
higher than designers would have considered in 1965.

The traffic would have contributed to fatigue over the years, Corley
said. But the weight of truck and vehicle traffic is "pretty
insignificant" next to the weight of the bridge itself, he said.

___

Associated Press writers Patrick Condon in Minneapolis and Seth
Borenstein in Washington contributed to this report.

On Fri, 10 Aug 2007 00:33:25 -0700, Too_Many_Tools
wrote:

FYI...one of the better discussions on the I35W bridge.

Note that so far it is still just guess work.

TMT


Metal plates examined in bridge collapse By MARTIGA LOHN, Associated
Press Writer

snip
===================
It appears to be due to the design criteria.

The Romans built bridges and roads, some of which are still in
use today so it can be done.

When things are designed to be a cheap/light as possible and be
as quick to erect as possible, it means they have minimal safety
factors and little or no redundancy. As is now well known,
little to no maintenance is performed until the structure is
about to fall down because of diversion of the tax funds to other
uses.

This is a sure recipe for disaster, because any deterioration and
corrosion will reduce the already minimal safety factors to
critical levels.

The only thing that is surprising is that we have not had more
such catastrophes. Like the oil filter ad said a few years back
"pay me now or pay me [a lot more] later."

Given the extreme importance of transportation to our economic
infrastructure, and the degree such transportation is by truck
over the interstate road network, it is lunacy not to maintain
this in reasonable condition.

George, I looked up Roman Bridges in google, saw pictures, it is
totally ****ing amazing how clever builders the Romans were. These
bridges have every reason to keep standing for thousands more years.

i

In article , wrote:
It appears to be due to the design criteria.

The Romans built bridges and roads, some of which are still in
use today so it can be done.

Supposedly, under Roman law, when the construction of an arch was completed,
the architect who designed it and the foreman of the crew that built it were
required to be standing underneath the keystone when the supporting scaffold
was removed.

That probably explains why so many Roman structures are still standing after
two thousand years -- there was a powerful personal incentive to overdesign
and overbuild. Conversely, financial considerations seem paramount these days,
thus the incentive is to design and build to minimum adequacy, leaving little
room for mistakes in design, insufficiencies or defects in material, improper
maintenance, and so on. How many 20th or 21st century bridges will still be
standing in the 41st? Not many, I'll wager. And although I won't be around to
see it, I expect that some, at least, of the Roman constructions will *still*
be standing.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

On Fri, 10 Aug 2007 17:14:37 GMT, Doug Miller wrote:
maintenance, and so on. How many 20th or 21st century bridges will still be
standing in the 41st? Not many, I'll wager. And although I won't be around to
see it, I expect that some, at least, of the Roman constructions will *still*
be standing.

I am not sure if we need the 20th century bridges to stand for so
long.

That said, it seems that a lot of Roman bridges were destroyed by
retreating Germans in WWII -- otherwise a lot more of them would still
be standing. In other words, the extent to which Roman bridges were so
good, is not as apparent now due to 20th century destruction.

i

Interesting to see if rivets were the proximate cause. I thought that
the bridge dropped fairly straight, and if that's so, one plate failing
might cause a twisting force... Let's let the NTSB figure this one out.

Too_Many_Tools wrote:
interstate bridge were originally attached with rivets,

If the construction material is so heavy, why not pile it up off the
bridge and use a conveyor belt to move it? One benefit would be much
reduced heavy dump truck travel onto the bridge. Set the pile up on the
side opposite the construction, and work toward the pile, shortening the
conveyor belt as you go. Concrete might be moved via a pumping system
akin to what they already use with construction.

Dunno about asphalt, as I've not seen any other movement techniques
other than dump trucks.

Construction crews had piled up sand and gravel on the bridge as they
prepared to pave a 520-foot stretch of two southbound lanes

On Aug 10, 2:19 pm, Louis Ohland wrote:
Interesting to see if rivets were the proximate cause. I thought that
the bridge dropped fairly straight, and if that's so, one plate failing
might cause a twisting force... Let's let the NTSB figure this one out.

Too_Many_Tools wrote:
interstate bridge were originally attached with rivets,

If the construction material is so heavy, why not pile it up off the
bridge and use a conveyor belt to move it? One benefit would be much
reduced heavy dump truck travel onto the bridge. Set the pile up on the
side opposite the construction, and work toward the pile, shortening the
conveyor belt as you go. Concrete might be moved via a pumping system
akin to what they already use with construction.

Dunno about asphalt, as I've not seen any other movement techniques
other than dump trucks.

Construction crews had piled up sand and gravel on the bridge as they
prepared to pave a 520-foot stretch of two southbound lanes



Good modern bridges CAN be designed and built, ones that endure.

The first of these modern bridges is the Brooklyn Bridge in New York
city, completed in 1883 or so. It still carries as much traffic as
ever, and originally also carried railway steam trains, which are
terribly hard on bridges due to impact loading by the stem locomotive.

Other pretty old ones are the Golden Gate bridge, and the Lions Gate
bridge in Vancouver. Both of these were built in the 1930 thus
getting close to 70 years old.

The point is that having important infrastructure designed and built
by the lowest bidder can be a receipe for disaster.

It will be interesting to find out the mode of failure; looking at
the traffic camera video clip it appears like shear failure of the
beam ends since the entire structure fell horizontally and practically
intact. Agreed that a short video is not something to base any
opinion on.... I'm guessing here, admittedly.

Whether the structure is bolted or rivetted should not make any
difference in the life expectancy of any steel structure if it is
properly designed, constructed, and maintained. Big ifs when all
three are executed by the lowest bidder.

A good bridge design can be SEVERELY overloaded, under carefully
controlled condition, without impacting the safety of the bridge. The
reason is that in the design of bridges and buildings the stress level
is kept below the endurance limit so as to eliminate the onset of
fatigue cracking. The onset of fatigue cracking is difficult to
detect and expensive to eliminate in a structure since this is
generally not allowed for in the design.

Sooo, overloading the bridge once-in-a-blue-moon is ok especially if
all other traffic is stopped for the brief transit time. This was
done on the Ambassador bridge linking Windsor and Detroit when my
employer at that time moved a 90 ton weldment over that bridge in the
early 1970.

Wolfgang

On Fri, 10 Aug 2007 09:15:19 -0500, F. George McDuffee
wrote:

On Fri, 10 Aug 2007 00:33:25 -0700, Too_Many_Tools
wrote:

FYI...one of the better discussions on the I35W bridge.

Note that so far it is still just guess work.

TMT


Metal plates examined in bridge collapse By MARTIGA LOHN, Associated
Press Writer

snip
===================
It appears to be due to the design criteria.

The Romans built bridges and roads, some of which are still in
use today so it can be done.

When things are designed to be a cheap/light as possible and be
as quick to erect as possible, it means they have minimal safety
factors and little or no redundancy. As is now well known,
little to no maintenance is performed until the structure is
about to fall down because of diversion of the tax funds to other
uses.

This is a sure recipe for disaster, because any deterioration and
corrosion will reduce the already minimal safety factors to
critical levels.

Roman bridges were commissioned by the Emperor and built with slave
labor. Cost was not an issue, nor was political expediency.

Today:

inspector: "That bridge has some serious issues."
bureaucrat: "Do you assert that the bridge will fail this fiscal
year if we don't fund repairs right now?"
inspector: "No, I can't say that with certainty."
bureaucrat: "Inspect it again next year. Repair isn't in the budget."
inspector: "Get more budget. That bridge has serious issues."
bureaucrat: "You wanna get paid to inspect next year or not?"
Governor: "I ain't raisin' taxes (except for what I want.)

Not long ago, the people of Minnesota voted down a referendum for
funding maintenance and refurbishment of our aging transportation
infrastructure. In addition, schools are hurting and libraries are
being closed -- but they talk about building a new sports stadium.

Meanshile, poor people and laggards come from all over the country to
MN because our welfare is so good. They don' need no steenkin' bridge
to get their checks.

On Fri, 10 Aug 2007 12:35:55 -0500, Ignoramus22443
wrote:

On Fri, 10 Aug 2007 17:14:37 GMT, Doug Miller wrote:
maintenance, and so on. How many 20th or 21st century bridges will still be
standing in the 41st? Not many, I'll wager. And although I won't be around to
see it, I expect that some, at least, of the Roman constructions will *still*
be standing.

I am not sure if we need the 20th century bridges to stand for so
long.

That said, it seems that a lot of Roman bridges were destroyed by
retreating Germans in WWII -- otherwise a lot more of them would still
be standing. In other words, the extent to which Roman bridges were so
good, is not as apparent now due to 20th century destruction.

All this talk about what great builders the ancients were glosses over
the fact that all the evidence of their failures is long gone. We're
left only with the most startling successes, while the Roman's I-35
bridges are long forgotten.

If you're interested in seat-of-the-pants engineering in the 15th
century, this is a great book.
http://www.amazon.com/Brunelleschis-...6791985&sr=1-1

Henry Petroski's books are good essays on why **** happens in
engineering.
https://www.amazon.com/s/ref=nb_ss_/...&Go.x=0&Go.y=0

--
Ned Simmons

Ned Simmons wrote:

On Fri, 10 Aug 2007 12:35:55 -0500, Ignoramus22443
wrote:


On Fri, 10 Aug 2007 17:14:37 GMT, Doug Miller wrote:

maintenance, and so on. How many 20th or 21st century bridges will still be
standing in the 41st? Not many, I'll wager. And although I won't be around to
see it, I expect that some, at least, of the Roman constructions will *still*
be standing.

I am not sure if we need the 20th century bridges to stand for so
long.

That said, it seems that a lot of Roman bridges were destroyed by
retreating Germans in WWII -- otherwise a lot more of them would still
be standing. In other words, the extent to which Roman bridges were so
good, is not as apparent now due to 20th century destruction.


All this talk about what great builders the ancients were glosses over
the fact that all the evidence of their failures is long gone. We're
left only with the most startling successes, while the Roman's I-35
bridges are long forgotten.

http://think2020.tripod.com/photo.htm

2000+ years and still working...Whereas I-35W was 40?

On Fri, 10 Aug 2007 20:48:08 -0400, Ned Simmons wrote:
On Fri, 10 Aug 2007 12:35:55 -0500, Ignoramus22443
wrote:

On Fri, 10 Aug 2007 17:14:37 GMT, Doug Miller wrote:
maintenance, and so on. How many 20th or 21st century bridges will still be
standing in the 41st? Not many, I'll wager. And although I won't be around to
see it, I expect that some, at least, of the Roman constructions will *still*
be standing.

I am not sure if we need the 20th century bridges to stand for so
long.

That said, it seems that a lot of Roman bridges were destroyed by
retreating Germans in WWII -- otherwise a lot more of them would still
be standing. In other words, the extent to which Roman bridges were so
good, is not as apparent now due to 20th century destruction.

All this talk about what great builders the ancients were glosses over
the fact that all the evidence of their failures is long gone. We're
left only with the most startling successes, while the Roman's I-35
bridges are long forgotten.

If you're interested in seat-of-the-pants engineering in the 15th
century, this is a great book.
http://www.amazon.com/Brunelleschis-...6791985&sr=1-1

Henry Petroski's books are good essays on why **** happens in
engineering.
https://www.amazon.com/s/ref=nb_ss_/...&Go.x=0&Go.y=0


Ned, good point, but, a steel bridge is unlikely to stand for 2,000
years.

I bought the books you mentioned (one by Petroski the Renaissance
architecture). thanks

i

Tom wrote in article ...
Ned Simmons wrote:

http://think2020.tripod.com/photo.htm

2000+ years and still working...Whereas I-35W was 40?



Are you suggesting that the 2000 year-old bridge withstood dozens of
100,000 pound trucks on a daily basis througout its lifetime?

Most of today's Interstate bridges would last forever if we didn't use
them!!!!!

Apples-to-apples, please.

Don Foreman wrote in article
...
On Fri, 10 Aug 2007 09:15:19 -0500, F. George McDuffee
wrote:

On Fri, 10 Aug 2007 00:33:25 -0700, Too_Many_Tools
wrote:

FYI...one of the better discussions on the I35W bridge.

Note that so far it is still just guess work.

TMT


Metal plates examined in bridge collapse By MARTIGA LOHN, Associated
Press Writer

snip
===================
It appears to be due to the design criteria.

The Romans built bridges and roads, some of which are still in
use today so it can be done.

When things are designed to be a cheap/light as possible and be
as quick to erect as possible, it means they have minimal safety
factors and little or no redundancy. As is now well known,
little to no maintenance is performed until the structure is
about to fall down because of diversion of the tax funds to other
uses.

This is a sure recipe for disaster, because any deterioration and
corrosion will reduce the already minimal safety factors to
critical levels.

Roman bridges were commissioned by the Emperor and built with slave
labor. Cost was not an issue, nor was political expediency.

Today:

inspector: "That bridge has some serious issues."
bureaucrat: "Do you assert that the bridge will fail this fiscal
year if we don't fund repairs right now?"
inspector: "No, I can't say that with certainty."
bureaucrat: "Inspect it again next year. Repair isn't in the budget."
inspector: "Get more budget. That bridge has serious issues."
bureaucrat: "You wanna get paid to inspect next year or not?"
Governor: "I ain't raisin' taxes (except for what I want.)

Not long ago, the people of Minnesota voted down a referendum for
funding maintenance and refurbishment of our aging transportation
infrastructure. In addition, schools are hurting and libraries are
being closed -- but they talk about building a new sports stadium.

Meanshile, poor people and laggards come from all over the country to
MN because our welfare is so good. They don' need no steenkin' bridge
to get their checks.



If fewer fuel tax dollars went into pork barrels, and more went towards
their stated/intended purpose - road maintenance - we wouldn't have these
issues.......

Politics!!!!!!

* wrote:

Tom wrote in article ...

Ned Simmons wrote:

http://think2020.tripod.com/photo.htm

2000+ years and still working...Whereas I-35W was 40?




Are you suggesting that the 2000 year-old bridge withstood dozens of
100,000 pound trucks on a daily basis througout its lifetime?

Most of today's Interstate bridges would last forever if we didn't use
them!!!!!

Apples-to-apples, please.

Truly you're a star! However, your reasoning will terrify millions of
Americans as you're saying that US bridges of the "modern" era don't
have any load capacity redundancy. I notice that there is a fast growing
prevalence in the US for people to employ drivers to get them across bridges,
your doing?

As for the 2000 year bridges, they did what they were designed to do
with a safety redundancy that sees them still standing. I think there's
been odd American, John A Roebling springs to mind, who have been able
to do this.

As for 100,000lb trucks, pie in the sky? or did you just pluck that
off an apple tree? If so, it wasn't a Minnesota apple tree.

On Sun, 12 Aug 2007 08:14:44 +1200, Tom wrote:

I notice that there is a fast growing
prevalence in the US for people to employ drivers to get them across bridges,
your doing?

Where in the world did you imagine _that_ is true, Tom?

As for the 2000 year bridges, they did what they were designed to do
with a safety redundancy that sees them still standing. I think there's
been odd American, John A Roebling springs to mind, who have been able
to do this.

It depends on what your priorities are, doesn't it? A 100 year design
life for a car, would be silly. 10 years is about right, and a good
balance between cost, weight, and the realities of how a car is used.
Similar for a bridge - a 100 year design life is reasonable. 1000 year?
Why should I pay so much more for a bridge today? Does the
overengineering that would take make it any better to use, or does it
just make it last longer?

Dave Hinz wrote:

On Sun, 12 Aug 2007 08:14:44 +1200, Tom wrote:


I notice that there is a fast growing
prevalence in the US for people to employ drivers to get them across bridges,
your doing?


Where in the world did you imagine _that_ is true, Tom?

Perhaps you need to watch some current domestic news, Dave?
A news story on this from the US was screened down here yesterday.


As for the 2000 year bridges, they did what they were designed to do
with a safety redundancy that sees them still standing. I think there's
been odd American, John A Roebling springs to mind, who have been able
to do this.


It depends on what your priorities are, doesn't it? A 100 year design
life for a car, would be silly. 10 years is about right, and a good
balance between cost, weight, and the realities of how a car is used.
Similar for a bridge - a 100 year design life is reasonable. 1000 year?
Why should I pay so much more for a bridge today? Does the
overengineering that would take make it any better to use, or does it
just make it last longer?

LOL Or should I be cringing over your rationale? Hopefully you have
never been involved with anything structural, nor especially the
aircraft industry.

BTW The bridge in question didn't meet you expectations by quite a large
margin. How many more are out there of similar age and design?
I think there's a growing number of Americans, who are every day, crossing
bridges with considerable trepidation.

Tom

"Tom" wrote in message
...
Dave Hinz wrote:

On Sun, 12 Aug 2007 08:14:44 +1200, Tom wrote:


I notice that there is a fast growing
prevalence in the US for people to employ drivers to get them across
bridges,
your doing?


Where in the world did you imagine _that_ is true, Tom?

Perhaps you need to watch some current domestic news, Dave?
A news story on this from the US was screened down here yesterday.

I didn't see that news story, Tom, but I've never heard of such a thing. It
sounds like something cooked up in the newsroom. And I live near one of the
most dangerous big bridges in the USA -- the Pulaski Skyway, built in the
early 1930s.

--
Ed Huntress

Ed Huntress wrote:
"Tom" wrote in message
...

Dave Hinz wrote:


On Sun, 12 Aug 2007 08:14:44 +1200, Tom wrote:



I notice that there is a fast growing
prevalence in the US for people to employ drivers to get them across
bridges,
your doing?


Where in the world did you imagine _that_ is true, Tom?


Perhaps you need to watch some current domestic news, Dave?
A news story on this from the US was screened down here yesterday.


I didn't see that news story, Tom, but I've never heard of such a thing.

Therefore it doesn't exist? For shame Ed, I thought you had a more
open mind?

It sounds like something cooked up in the newsroom. And I live near one of the
most dangerous big bridges in the USA -- the Pulaski Skyway, built in the
early 1930s.

--
Ed Huntress


Apparently if you use Google as your friend, the phenomena started prior to
I-35W:

http://tinyurl.com/2t63ff

Tom

Tom wrote:
* wrote:

Tom wrote in article
...

Ned Simmons wrote:

http://think2020.tripod.com/photo.htm

2000+ years and still working...Whereas I-35W was 40?




Are you suggesting that the 2000 year-old bridge withstood dozens
of 100,000 pound trucks on a daily basis througout its lifetime?

Most of today's Interstate bridges would last forever if we
didn't use them!!!!!

Apples-to-apples, please.

Truly you're a star! However, your reasoning will terrify millions
of Americans as you're saying that US bridges of the "modern" era
don't have any load capacity redundancy. I notice that there is a
fast growing prevalence in the US for people to employ drivers to
get them across bridges, your doing?

Odd that you go from a single specific situation on the Chesapeake Bay
Bridge to "a fast growing prevalence in the US".

As for the 2000 year bridges, they did what they were designed to
do with a safety redundancy that sees them still standing. I think
there's been odd American, John A Roebling springs to mind, who
have been able to do this.

I don't know of any current engineer who would design a bridge for
common use that was intended for foot, horse and ox traffic as they
were 2000 years ago.

So you're saying that 2000 years ago, they built bridges that can take
the stress of many 18 wheel semi trailer trucks daily without regular
inspection and maintenance, and that there have been NO failures of
any of these bridges?

Hi Guys:

I'm going through the current topics to hopefully suggest a way to tag
valid RCM traffic.


Add RCM: on the beginning of the title line -
BEFORE the obligatory OT, OK?

Then we can filter on that tag.

Also need to add a filter for RCM: to get the reply lines.

Hang tight - keep posting.

CaveLamb

F. George McDuffee wrote:

When things are designed to be a cheap/light as possible and be
as quick to erect as possible, it means they have minimal safety
factors and little or no redundancy. As is now well known,
little to no maintenance is performed until the structure is
about to fall down because of diversion of the tax funds to other
uses.

This is a sure recipe for disaster, because any deterioration and
corrosion will reduce the already minimal safety factors to
critical levels.

This is totally insane, and the people responsible for it should
be just about taken out and shot! Our (Missouri) highway dept.
has had totally grandiose plans, building bridges and highways
all over the place. They do seem to have their eye on some of
the maintenance issues, however, and now do a low-grade
inspection of many or most highway overpasses and bridges on a
monthly basis, after some serious structural breakdowns were
detected by alert workers just by accident. One overpass had a
severely cracked and buckled main beam that was probably hours
away from total collapse when it was spotted. They are
repairing that one while in use, with some lane closures.

I really don't know whether they are doing things better here
than in MN. There was a news stock photo up for a while that
was taken last fall, and the visible orange color of the
superstructure of the I35W bridge was shocking to me. I've
never seen a major bridge in current use with that kind of
visible corrosion. It looked like they hadn't painted it in
15-25 years! Maybe the salt spray system contributed to it.

Jon

On Sun, 12 Aug 2007 21:33:00 -0500, "David R. Birch"
wrote:

So you're saying that 2000 years ago, they built bridges that can take
the stress of many 18 wheel semi trailer trucks daily without regular
inspection and maintenance, and that there have been NO failures of
any of these bridges?

In the main yes. There are no elements in tension and the stone and
bedrock they are built on have huge resistance to compressive failure.

The choice is build cheap, fast, or properly. Choose one. Some
places still have iron bridges that have been standing for over 200
years.


--

David R. Birch wrote:
Tom wrote:

* wrote:

Tom wrote in article
...

Ned Simmons wrote:

http://think2020.tripod.com/photo.htm

2000+ years and still working...Whereas I-35W was 40?




Are you suggesting that the 2000 year-old bridge withstood dozens
of 100,000 pound trucks on a daily basis througout its lifetime?

Most of today's Interstate bridges would last forever if we
didn't use them!!!!!

Apples-to-apples, please.

Truly you're a star! However, your reasoning will terrify millions
of Americans as you're saying that US bridges of the "modern" era
don't have any load capacity redundancy. I notice that there is a
fast growing prevalence in the US for people to employ drivers to
get them across bridges, your doing?


Odd that you go from a single specific situation on the Chesapeake Bay
Bridge to "a fast growing prevalence in the US".

Well, if you weren't so tired, you'd be able to find more, it's not
just a trend developing only in Chesapeake Bay.

As for the 2000 year bridges, they did what they were designed to
do with a safety redundancy that sees them still standing. I think
there's been odd American, John A Roebling springs to mind, who
have been able to do this.


I don't know of any current engineer who would design a bridge for
common use that was intended for foot, horse and ox traffic as they were
2000 years ago.

So you're saying that 2000 years ago, they built bridges that can take
the stress of many 18 wheel semi trailer trucks daily without regular
inspection and maintenance,

Well if you took your blindfold off, you'd be able to see them.

and that there have been NO failures of any of these bridges?

Don't go putting words in my mouth.