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Old 01-16-2017, 12:39 PM
Kamaski Kamaski is offline
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Modern skyscrapers are not as well built as old ones?

I'm wondering how accurate this article is
http://vincentdunn.com/wtc.html

The main point is that the modern construction methods used on the World Trade Center and other modern buildings are not nearly as good as the Empire State Building.
In the ESB all columns and floor beams were made of solid steel and then incased in concrete and masonry. The floor slabs were also made of solid concrete and masonry 8 inches thick. In the WTC only a 3 inch thick concrete slab was used and the structural steel was not encased in masonry, instead spray-on fire retardant was used which only last 5-10 minutes in a fire.
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Old 01-16-2017, 12:57 PM
Shagnasty Shagnasty is offline
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They aren't comparable because they are completely different construction methods. Older engineering principles used to throw raw materials and over-design at any problem. That is certainly durable in many cases but it isn't efficient. Both the World Trade Centers and the Empire State building worked perfectly fine for their intended purpose but neither was designed to survive the aftermath of a large aircraft impact. The Empire State building gets bonus points in that regard because it was also hit by a B-25 bomber in a freak accident in 1945 and suffered relatively little damage partially because it is so over-engineered but that wasn't an intentional part of the design.

Modern skyscrapers can be built taller because they use geometry and fairly lightweight materials rather than just throwing a bunch of steel and concrete at the problem. They also have to accommodate complex shapes, multiple elevator shafts and lots of utility conduits. Earthquake resistance is another concern that is easier to address with modern materials and lighter designs.
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Old 01-16-2017, 01:00 PM
Johnny L.A. Johnny L.A. is offline
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Old buildings certainly seem to have lasted longer than new ones.
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Old 01-16-2017, 01:06 PM
friedo friedo is offline
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Old buildings certainly seem to have lasted longer than new ones.
The old buildings that have lasted certainly have lasted longer. But that's a tautology.

The world of full of old buildings that have fallen down. There are entire cities that have been largely rebuilt after fires, earthquakes, or wars.
  #5  
Old 01-16-2017, 01:28 PM
Johnny L.A. Johnny L.A. is offline
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But that's a tautology.
That's a joke.
  #6  
Old 01-16-2017, 01:50 PM
GiantRat GiantRat is offline
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The towers at WTC were, actually, designed to withstand hits from aircraft (the Empire State Building being a lesson learned). Planes got bigger, though, and 737s are now considered puddle-jumpers. The 767 is much bigger and carries more fuel. The structural integrity of the buildings didn't fail - these were heat-induced failures. Throw a ton (actually, more than a ton) of fuel at a building full of paper - both of which burn at a steel-damaging temperature, and see what happens.

The towers were built with an innovative concept (at the time); they were core-based buildings, with the floors and exteriors being largely supported by central "shafts." That's how they got so tall, so to speak. Once doused in burning awfulness, though, the sprayed-on fire protection (which was knocked off by the collision of planes that didn't exist during their design) was inadequate.

And then bad things happened.

I was there to clean it up. Very messy, but where the structures failed (also for the other buildings) was clear. The steel failed because of heat. Several pairs of my boots failed, too.
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Old 01-16-2017, 02:41 PM
Trinopus Trinopus is offline
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Originally Posted by Shagnasty View Post
. . . Older engineering principles used to throw raw materials and over-design at any problem. . . .
Is there any truth to the urban legend that this is because they didn't have advanced mathematical modeling, but had to rely on slide rules? Today, we can do computer-simulated stress tests, and so have a more precise knowledge of structural breaking levels.

True, or just another UL?
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Old 01-16-2017, 02:47 PM
Shalmanese Shalmanese is offline
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The old buildings that have lasted certainly have lasted longer. But that's a tautology.

The world of full of old buildings that have fallen down. There are entire cities that have been largely rebuilt after fires, earthquakes, or wars.
Of all the buildings that have become the tallest in the world, only the WTC doesn't exist anymore.
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Old 01-16-2017, 04:10 PM
DrCube DrCube is offline
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Older engineering principles used to throw raw materials and over-design at any problem.
Which makes sense when we're talking about trucks and stoves and log cabins. But for something like a skyscraper or bridge, aren't they designed to last essentially forever? Maybe not until the sun goes red giant, but for hundreds of years? And in that scenario, what does "over-design" even mean?
  #10  
Old 01-16-2017, 04:22 PM
snfaulkner snfaulkner is online now
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Originally Posted by DrCube View Post
Which makes sense when we're talking about trucks and stoves and log cabins. But for something like a skyscraper or bridge, aren't they designed to last essentially forever? Maybe not until the sun goes red giant, but for hundreds of years? And in that scenario, what does "over-design" even mean?
It means when in doubt (like, because you were using a slide rule and not a server cluster for modelling) use more materials/over design the strength you think you'll need as a precaution.
  #11  
Old 01-16-2017, 04:39 PM
dofe dofe is offline
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Originally Posted by DrCube View Post
Which makes sense when we're talking about trucks and stoves and log cabins. But for something like a skyscraper or bridge, aren't they designed to last essentially forever? Maybe not until the sun goes red giant, but for hundreds of years? And in that scenario, what does "over-design" even mean?
IANAE, but a building designed to last hundreds of years is different than a building designed to survive the impact from a passenger jet (coincidentally, I raised this question once in another thread). In the context here, "over-designed" means that a building is built with redundancy over the forces it is expected to encounter. Sometimes civil engineers get their calculations wrong, and the resulting building may need reinforcements as a result -- a famous example is the Citigroup Center.

Last edited by dofe; 01-16-2017 at 04:39 PM.
  #12  
Old 01-16-2017, 09:30 PM
Magiver Magiver is online now
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Originally Posted by Trinopus View Post
Is there any truth to the urban legend that this is because they didn't have advanced mathematical modeling, but had to rely on slide rules? Today, we can do computer-simulated stress tests, and so have a more precise knowledge of structural breaking levels.

True, or just another UL?
There was nothing wrong with the structural integrity of the building. What wasn't considered in the design was the possibility of the riser being cut. 20/20 hindsight would have seen the installation of a second riser so there was water for the sprinkler system.

It's along the lines of the Fukishima nuclear power plant. they put the backup generators on the ground instead of on top of the power plant. The tsunami wiped them out and there was no power to run backup water supplies.
  #13  
Old 01-16-2017, 09:46 PM
Rick Rick is offline
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Several pairs of my boots failed, too.
[Rosie O'Donnell] Jet fuel can't melt boots! Everybody knows that [/R O'D]
  #14  
Old 01-16-2017, 09:51 PM
Francis Vaughan Francis Vaughan is offline
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The slide rule versus computer analysis issue is true. Closed form analysis of structures made from lattices of beams only really exists for 2D forms. It is well understood that if you take 2 lattices and connect them together into a 3D structure, the whole is much stronger than twice one lattice. But in order to really work out just how much stronger you need vastly more compute than mere humans are capable of. So bridges, steel frame skyscrapers, tended to be designed essentially as sets of 2D structures that were then interlinked. But where the additional strength from the interlinking of the elements was sufficiently poorly understood that it was not counted towards the design. So, by default, the structures are a lot stronger than the design requirements, but not necessarily in a consistent or efficient manner.
Look at modern bridges. They provide a wonder visual example of how 3D structural analysis allows for vastly more freedom, and designs with a lot less material.
Adding extra steel and concrete to a structure isn't really a smart answer. You have to hold up all that extra mass, so the entire thing gets much more costly and heavier, simply so it can hold itself up.

Last edited by Francis Vaughan; 01-16-2017 at 09:52 PM.
  #15  
Old 01-17-2017, 05:14 AM
Der Trihs Der Trihs is offline
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Also, at least with earthquakes mass is actually a vulnerability; it means that when the quake starts shoving the building around, its greater mass puts it under greater stress than a lower mass building would be since all that mass has greater inertia once the quake starts it moving.
  #16  
Old 01-17-2017, 08:10 AM
Atamasama Atamasama is offline
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That's a joke.
http://www.youtube.com/watch?v=joO1zz3kHTk
  #17  
Old 01-17-2017, 04:51 PM
msmith537 msmith537 is offline
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It's not an issue of "well built". A Porsche is not less well built than a Ford Explorer just because that later can crush the former in a crash.

Modern skyscrapers are essentially built as giant glass boxes around a steel frame or reinforced central concrete "core" that holds the elevator shafts, stairwells, cables and ductwork. The floors can either be cantilevered off the main core or supported by columns (hint, if you don't see massive load-bearing columns oddly space around the perimeter of your office blocking your view, the floors are cantilevered).


Old Art Deco skyscrapers like the Empire State Building, Chrysler Building, and Woolworth Building are made from steel frames supporting a lot of stonework. They are stronger and more dense than modern buildings, but also more expensive to build and don't offer the massive panoramic views.


The Great Pyramid of Giza is extremely strong, however the interior spaces lack adequate views and lighting and tend to be cramped as most of the structure is dedicated to holding itself up.


All are well designed. It's just that the modern ones are lighter, more cost effective and designed to narrower tolerances.
  #18  
Old 01-17-2017, 05:32 PM
Chronos Chronos is online now
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And I feel that I should defend the honor of slide rules, here, too. For most purposes, in trained hands, a slide rule is just as good as a modern scientific calculator, and very nearly as fast. The main benefit of the calculator is just that it's easier to learn to use it. Of course, neither one is as good as a full computer, which can do the massively-iterated calculations needed for three-dimensional stress analysis.
  #19  
Old 01-17-2017, 05:49 PM
Hari Seldon Hari Seldon is offline
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The Brooklyn bridge is something like 130 years old and seems good for another 130 (with proper maintenance). The Tappan Zee bridge and the Champlain Bridge in Montreal are decrepit after 50 years and being replaced. Overdesign? Your call.
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Old 01-17-2017, 07:33 PM
Francis Vaughan Francis Vaughan is offline
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The Tappan Zee bridge was opened in 1955. There was essentially no computer analysis available then. It was built as a traditional (slide rule) design, but its current decreptitude could be reasonably sheeted home to the very limited budget that was available for its construction. The Champlain Bridge was designed not long after, with construction starting in 1957, so no modern design either.
Maintenance is usually the key. You must be absolutely on top of the maintenance. However other things can cause you grief. The Silver Bridge disaster is a good example.

Finite element analysis tools - like Nastran were just starting out in the 60's. We see the effect of this in later designs.
  #21  
Old 01-17-2017, 08:01 PM
buddha_david buddha_david is offline
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Of all the buildings that have become the tallest in the world, only the WTC doesn't exist anymore.
Home Insurance Building, Chicago - tallest skyscraper 1884-1890. Demolished in 1931.
New York World Building - tallest skyscraper 1890-1894. Demolished in 1955.
Manhattan Life Insurance Building - tallest skyscraper 1894-1895. Demolished in 1964.
Singer Building, Manhattan - world's tallest structure 1908-1909. Demolished in 1968.
  #22  
Old 01-17-2017, 09:52 PM
Max the Immortal Max the Immortal is offline
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"Any fool can design a bridge that doesn't fall down. If you want a bridge that barely doesn't fall down, you need an engineer."
  #23  
Old 01-18-2017, 12:41 AM
Shalmanese Shalmanese is offline
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Originally Posted by buddha_david View Post
Home Insurance Building, Chicago - tallest skyscraper 1884-1890. Demolished in 1931.
New York World Building - tallest skyscraper 1890-1894. Demolished in 1955.
Manhattan Life Insurance Building - tallest skyscraper 1894-1895. Demolished in 1964.
Singer Building, Manhattan - world's tallest structure 1908-1909. Demolished in 1968.
The Ulm Minster was taller than the Home Insurance, New York World & Manhattan Life buildings. You're right about the Singer building. That's the only one other than the WTC to have ever been the tallest in the world ever demolished.
  #24  
Old 01-18-2017, 10:23 AM
Corry El Corry El is offline
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The main idea of better structural analysis has been to come up with lighter structures that are strong enough to meet anticipated design needs. So there's some truth to the common idea that they 'aren't as well built', and that can be of practical significance in some cases with regard to *un*-anticipated design needs. The (old*) WTC failed spectacularly, in an unanticipated situation, but one which arguably might have been anticipated, which older buildings might have resisted better, and which has been reflected in the design of subsequent buildings.

Bridges were also mentioned. Another category is ships. Some ships of recent decades have proved to have structures too light for all the needs of service over a long period. Improvements in structural analysis and use of higher strength steel nominally resulted in simply lighter structures equally able to meet anticipated requirements. However when the potential for corrosion and physical damage of thinner plates is factored in, and the adverse interaction of stress and corrosion, the ships were not necessarily well built practically speaking. There's been a general trend back away from high strength steel in merchant ships for that reason. Of course there's no reason to avoid continued improvements in structural analysis per se.

Also back on WTC, I worked on a high floor in that building for some years up till after the first bombing in 1993. The building would move around in high winds enough to make some people nauseous, or at least unsettled and distracted from their work. This was a less dramatic but practical drawback relative to the 'over-designed' and considerably stiffer ESB, in which I'm told the motion is not as noticeable (I've only been up there as a tourist a few times). Likewise many modern extremely tall buildings make more use of stiffer (as well as more fire resistant) steel reinforced concrete.

*the 'replacement' building is now named 'One World Trade Center', close enough to 'The World Trade Center' to potentially create confusion when using the present tense to refer to the destroyed building as at least one sentence in the thread did. I assume every reference though is to the building which existed until 2001, designed 50 yrs ago, decades after many other surviving skyscrapers but not exactly the most modern.
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Old 01-18-2017, 10:37 AM
Really Not All That Bright Really Not All That Bright is offline
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Modern skyscrapers are much more earthquake-resistant than older ones, because they're designed to flex. Not really a consideration in New York, but a Big Deal in other major cities (such as Tokyo).
Quote:
Originally Posted by Shalmanese View Post
The Ulm Minster was taller than the Home Insurance, New York World & Manhattan Life buildings. You're right about the Singer building. That's the only one other than the WTC to have ever been the tallest in the world ever demolished.
The steeple tower of Marienkirche in Germany (tallest building in the world until 1647) once fell down. True, the entire building was never demolished, but its tallest part didn't exist for a while.

Last edited by Really Not All That Bright; 01-18-2017 at 10:40 AM.
  #26  
Old 01-18-2017, 02:23 PM
msmith537 msmith537 is offline
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Originally Posted by Francis Vaughan View Post
The Tappan Zee bridge was opened in 1955. There was essentially no computer analysis available then. It was built as a traditional (slide rule) design, but its current decreptitude could be reasonably sheeted home to the very limited budget that was available for its construction. The Champlain Bridge was designed not long after, with construction starting in 1957, so no modern design either.
Maintenance is usually the key. You must be absolutely on top of the maintenance. However other things can cause you grief. The Silver Bridge disaster is a good example.
I believe there is also the issue of traffic capacity with the Tappen Zee.
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Old 01-18-2017, 02:27 PM
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I believe there is also the issue of traffic capacity with the Tappen Zee.
And the fact that it was built in a horrible location so the state of NY wouldn't lose out on toll revenue to the Port Authority.
http://www.npr.org/2014/05/14/312523...he-rivers-wide
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Old 01-19-2017, 06:52 AM
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And the fact that it was built in a horrible location so the state of NY wouldn't lose out on toll revenue to the Port Authority.
http://www.npr.org/2014/05/14/312523...he-rivers-wide
That article claims that the bridge was built "about as close as it could be" to the Port Authority's territory, a 25-mile circle centred on the Statue of Liberty. It claims it is two-tenths of a mile outside the circle, which is nonsense. Measuring on Google Maps, the closest point of the bridge is 27.2 miles from the statue.
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Old 01-19-2017, 07:43 AM
RealityChuck RealityChuck is offline
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Originally Posted by buddha_david View Post
Home Insurance Building, Chicago - tallest skyscraper 1884-1890. Demolished in 1931.
New York World Building - tallest skyscraper 1890-1894. Demolished in 1955.
Manhattan Life Insurance Building - tallest skyscraper 1894-1895. Demolished in 1964.
Singer Building, Manhattan - world's tallest structure 1908-1909. Demolished in 1968.
None of those were the tallest building at any time. The Eiffel Tower (1889) was taller than all of them. And all structures that have been the tallest in the world in recorded history are still standing -- except for the WTC.
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Old 01-19-2017, 09:56 AM
enalzi enalzi is offline
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That article claims that the bridge was built "about as close as it could be" to the Port Authority's territory, a 25-mile circle centred on the Statue of Liberty. It claims it is two-tenths of a mile outside the circle, which is nonsense. Measuring on Google Maps, the closest point of the bridge is 27.2 miles from the statue.
I think the "25 mile radius" is an approximation. It's not the actual boundary:
http://www.panynj.gov/about/facilities-services.html
  #31  
Old 01-19-2017, 11:03 AM
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None of those were the tallest building at any time. The Eiffel Tower (1889) was taller than all of them. And all structures that have been the tallest in the world in recorded history are still standing -- except for the WTC.
There's a big difference between a "structure" and a building. A tower with an observation deck is not a "building." A radio tower is not a building. See the definition in Wikipedia's history of world's tallest buildings.

Also, I believe none of these tallest buildings has ever survived a terrorist attack.

The Empire State Building did survive an aircraft crash, but that was a B-25 which has an empty weight of 19,480 lb and a max takeoff weight of 35,000 lb. Fuel capacity was something like 2000 lb.

The Boeing 767s which crashed into the weighed at least 228,000 lb at time of crash, 74,000 lb of which was fuel (source).

Last edited by scr4; 01-19-2017 at 11:07 AM.
  #32  
Old 01-19-2017, 11:09 AM
scr4 scr4 is offline
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The Boeing 767s which crashed into the weighed at least 228,000 lb at time of crash, 74,000 lb of which was fuel (source).
Sorry, that should have been 49,000 lb of fuel (for flight 175).
  #33  
Old 01-19-2017, 07:42 PM
Sleel Sleel is offline
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Modern skyscrapers are much more earthquake-resistant than older ones, because they're designed to flex. Not really a consideration in New York, but a Big Deal in other major cities (such as Tokyo).
Yep, it’s a BFD that blocks and blocks of 20–50 floor buildings not fall down in earthquakes here. There haven’t been any really big buildings put up in Tokyo (WTC towers were 100+ floors) but there are a lot of mid-height buildings, and quite a few residential towers are 15–30 floors.

For reference, that video was taken in the Tokyo area during the Tōhoku quake; local intensity readings were near the top of the scale. I was on the 9th floor of my in-laws’ 15-floor apartment in the northern suburbs of the greater metro area for some of the aftershocks. Just with mid-6 readings on that scale, there was appreciable sway. On the other hand, basically nothing fell down, though there was some damage, especially to older (1960s, 70s era) buildings.

Our apartment was on the 4th (top) floor of an old concrete building and — while nothing actually fell apart — there was visible damage to the building and everything inside the place ended up looking like Hulk was having a bad hair day. There was less shaking at my in-laws’ place than our much lower structure.

Last edited by Sleel; 01-19-2017 at 07:43 PM. Reason: corralled an errant comma
  #34  
Old 01-19-2017, 08:10 PM
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The Empire State building gets bonus points in that regard because it was also hit by a B-25 bomber in a freak accident in 1945 and suffered relatively little damage partially because it is so over-engineered but that wasn't an intentional part
Apples and oranges. A B-25 WWII Bomber is a very small aircraft compared to a modern jet. Plus the top speed of a B-25 is under 300mph. Also, the fuel capacity is no where near what a commercial jetliner carries. I suspect that the WTC building would have survived a B25 strike just fine.

Last edited by obbn; 01-19-2017 at 08:11 PM.
  #35  
Old 01-19-2017, 08:45 PM
jjakucyk jjakucyk is offline
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friedo makes a good point that only the good buildings have lasted, and the bad ones are long gone. Same for bridges, the old ones aren't necessarily better just because they're still around. In many cases they're replaced because of capacity and safety (such as narrow width or clearance) issues, not necessarily overt structural problems, but there's still issues that early designers couldn't have foreseen.

An interesting local example that so far has yet to come to a head is Cincinnati's John A. Roebling Suspension Bridge. It was the longest suspension bridge in the world when built in 1866 by the father of the later Brooklyn Bridge's engineer. Like many suspension bridges, the main cables rest on saddles atop the towers, and part of the saddle design includes rollers that allow the cable to slide due to shifting weight. So for instance, if you have a heavy load going across the middle of the bridge, it pulls down on the deck and the cables between the towers (the main span), which then lifts the cables and deck outside the towers (the approaches) so long as the cables can slide easily.

Apparently the rollers on the Roebling Bridge are frozen, either due to poor design or debris accumulation, basically fixing the cables to the towers. So with a heavy load in the middle of the bridge, it instead pulls the tops of the towers closer to each other. This gradual rocking back and forth is none too healthy for unreinforced masonry, and there's concerns about it eroding away the footing as one of the towers is not on bedrock but sunk into the compacted gravel riverbed. The addition of a second set of cables and new truss deck in 1896 for supporting electric streetcars only complicates matters.

The incredible mass of the towers and a rather low 11-ton weight limit for crossing vehicles (plus a 30-foot minimum spacing for trucks) have helped it survive, but time will tell if its able to hang on or not.
  #36  
Old 01-19-2017, 09:41 PM
Shagnasty Shagnasty is offline
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That brings up a good point. There were spectacular engineering failures as long as people have been building things. The Leaning Tower of Pisa is a famous example.

There was also the Tacoma narrows bridge disaster in 1940. It oscillated so much in a not so powerful wind-storm that it collapsed in a shocking way. There is no way you would want to be caught on that bridge when it went through complete failure conditions.

Modern engineers are not immune to incompetence though. The I-35W Mississippi River bridge in Minneapolis was extremely busy and just flat-out collapsed in 2007 without much warning killing 13 and injuring 145.

I always roll my eyes when people are anxious are about going across large bridges or to the top of large buildings. That isn't really fair though. It is completely possible that they really will just collapse and kill them.

Last edited by Shagnasty; 01-19-2017 at 09:44 PM.
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