On the other hand, World Trade Center Building 7 (WTC 7) collapsed even though it was not hit by aircraft. The 47-story office building caught fire after debris from WTC 1 fell on it, and the flames spread uncontrolled because its sprinklers also did not work—city water lines were damaged in the destruction of the Twin Towers. In the 2008 report on the breakdown of WTC 7, NIST investigators concluded the fire then caused steel floor beams and girders to expand, resulting in unexpected structural weakness and triggering a progressive collapse, the first known instance of a tall building brought down primarily by uncontrolled fires.
In light of these disasters, NIST issued 31 recommendations to improve the safety of high-rises and the emergency responses in the face of major threats. Critics did emerge against these recommendations, including from another federal agency, the General Services Administration. Concerns included the costs of these changes, "and when that happens, that's because they're not really convinced of the benefits, and I think that's because there was a lack of consensus over the results of the investigation," notes Guy Nordenson, a Princeton professor of architecture and structural engineering who runs a structural engineering firm in New York and was not involved in the NIST investigation.
Earlier NIST recommendations were received more easily. For instance, in the late 20th century, when NIST undertook a large investigation of building designs and their readiness for earthquakes, it had broad involvement from the engineering community and thus its recommendations were widely accepted by the field. "The problem many have with the World Trade Center investigation is that it wasn't as open and not adequately peer reviewed, due in part to the veil of security concerns, so lots of people can disagree with the conclusions," Nordenson says. For instance, Nordenson himself is part of litigation suggesting the collapse of WTC 7 was not inevitable, but was due to design flaws in both the fire protection and some aspects of the structure.
Sunder defended NIST's investigation, noting that the federal agency endeavored to make it as open and inclusive as possible, with numerous opportunities for the public and engineering community to review and provide input, such as public meetings, comment periods and advisory committee meetings that were open to the public. He also stood by its conclusions regarding WTC 7, saying "NIST has not seen any data or analyses from other researchers that would lead NIST to reevaluate its findings."
As to what happened with NIST's recommendations, "23 changes to the 2009 editions of the International Codes and another 17 changes to the 2012 editions, responsive to the recommendations, have been adopted," Sunder says. These building and safety codes from the International Code Council "are typically adopted by state and local authorities."
For instance, buildings taller than 420 feet are now required to include an extra exit stairwell or a specially designed elevator that occupants can use for evacuations. Also, stairwells in buildings more than 75 feet high must now have glow-in-the-dark markings that show the exit path even when lighting is out or dim. In addition, spray-applied fire-resistive materials must perform four times more effectively than current requirements in buildings 75 to 420 feet tall, and more than seven times better in buildings taller than 420 feet. "The code changes have broad implications for building safety," Sunder says.
So far, New York City has already made significant changes in response to NIST recommendations, Sunder notes, as have many new projects in the United States, such as One World Trade Center, the lead building of the new World Trade Center complex. "The speed, magnitude and scope of changes in response to the recommendations of the World Trade Center investigation have been truly remarkable," he says.
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Add CommentSci Am web site -- you're the only folks who still haven't figured out how to stop abusive "copmments" that are really only third-party sales ploys. GET YOUR FINGER OUT ALREADY and stop these
Reply | Report Abuse | Link to thisOh please, not the conspiracy theorists.
Reply | Report Abuse | Link to thisAs I watched the fire in WT1 that morning I thought it was possible that the top stories would collapse to the level where the fire was and maybe fall off the top.
Reply | Report Abuse | Link to thisIt did not come to my mind that the shock of the collapsing upper stories would buckle the columns of the underlying story and that the process would repeat all the way down.
10 years later I have not heard of an analysis of why when WT2 collapsed it did not provoke the immediate collapse of the already weakened WT1.
This study surely looked into that aspect but the story doesn't tell.
To all the conspiracy theorists who like to comment on this event.
Reply | Report Abuse | Link to thisThe USA trained and funded a bunch of very dumb, psychopathic and sociopathic lunatics, with no fear of death, from all over the Middle East, to attack the Soviet Union in Afghanistan. The ideas that the USA planted in their heads was nationalism, Islamism and pan Muslim religious nationalism. Several of the groups of fighters that the USA funded, believed in a greater Caliphate ecompassing all Muslims with a complete ban on what they called Kafir (unbelievers) in that future country.
One of the Billionaires the USA funded to achieve the aim of removing the Soviets from Afghanistan by organising funding of the Mujahadeen, was a spoilt billionaire called Osama Bin Ladin, of the Middle Easts biggest construction company. He did train in civil engineering, but was to lazy and stupid to do the job properly. (Bizzarely the USA still funds billionaires even after the results of funding Bin ladin. I assume that a form of masocism is involved in that)
Those very dumb, psychopathic and sociopathic lunatics, eventually made Afghanistan not worth having for the Soviet Union, so the Soviet Union cut its loss's and left.
At this point the USA left, breaking all its proomises to help rebuild Afghanistan after the Soviets would leave, causing massive anti-USA resentment, instead of the initial respect and loyalty to the USA that was there previously.
The very dumb, psychopathic and sociopathic lunatics were left with nothing to do, lots of weapons and in control of an entire country.
The very dumb, psychopathic and sociopathic lunatics, then started to slaughter, maim, toruture, terrorise and abuse Afghani people.
A forumer Mujahadeen fighter got fed up with all the chaos with the warlords fighting each other, so he picked up his AK47 again and started the Taliban in one small town, which quickly snowballed into a massive organisation, to try and bring order to the country. Once order was roughly secured in several areas, the Taliban was then hijacked by Osama Bin Ladin and his USA funded, very dumb, psychopathic and sociopathic lunatics.
Then USA stopped funding Bin Ladin.
The Saudi Arabian spoilt rich kid, Osama Bin Ladin got angry with the USA, when it cut of his yearly hundreds of millions of dollars, to maintain his little empire in his head.
Osama Bin Ladin plotted revenge.
Osama Bin Ladin and the USA secret Service/authorities entered at that point, into a stupidity race.
Part 2
Reply | Report Abuse | Link to thisThe USA placed troops on Saudi Arabian Soil during the first invasion of Iraq. Bin Ladin used this as an excuse to gather up support from as many stupid, dumb and idiotic supporters he could find. Eventually the level of stupidity became so great, that some of the followers were stupid enough to actually kill themselves, on Bin Ladins orders.
Due to Osama Bin Ladin being as stupid as a brick, plotting for revenge against the USA, took over a decade and several botched attempts, such as the previous bombing of the World Trade Center. However, the USA authorities tasked with preventing terrorism in the USA were more or less as stupid as Bin Ladin and his followers, with occassionally during this period the lead in stupidity switching back and forward between Bin ladin and the USA.
Then George Bush 2 became president. He replaced people in keys positions in intelligence with some of the most stupid people on the entire planet. All people appointed by Bush had to be anti-science, religious, believe in creationism and have the mind set of a member of the modern day Tea Party. Bush was not interested in intelligence reports and neither was his staff, who were all to stupid, to understand those reports anyway.
So an insane situation occurred in 2001, whereby the most stupid people in the entire Muslim world were actually more intelligent than the people in the USA tasked with stopping them from attacking the USA.
That is why the USA won that part of the present stupidity race, which it is clearly engaged in at present.
The only way to prevent future problems such as 911 and the present economic problems is to trun away from embracing stupidity and to turn towars science facts and intelligence.
The present attacks on science, facts and stability by the entire media and political estrablishment is destroying the USA from the inside and doing more damage than Osama Bin Ladin's bunch of idiots, could ever have done.
To create a more stable and defendable United States of America, it would be best to ensure that the next presidents, congress and senate are made up entirely of people with at least two PHDs in unrelated hard science subjects for the next 30 years and for all media to state that this is wonderful, with a ban on anyone holding office who has qualifications in law, banking, finance, religion or who has contacts in those areas for at least 30 years.
I am a little puzzled that the contribution of the buildings to the loss of life on 9/11 has received so little attention. It is good to see something in Scientific American on the subject. From my reading of the literature it appears that the structure of the twin towers directly contributed to their collapse, directly related to the need, in designing such tall buildings, to reduce their weight. It seems probable that the attackers were aware of these weakness and designed their attack to exploit them. (This was the second attempt to cause the buildings to collapse, the first being in 1993 when a bomb exploded in the car park under the north tower, intended to collapse that tower bringing the south tower down with it.)
Reply | Report Abuse | Link to thisThe towers consisted of a lightweight external shell of prefabricated interlocking panels (I picture it like a house of cards) tied together by light weight fabricated truss floor beams protected by a lightweight, sprayed-on fire protection coating. The fire caused by the aircraft impacts caused the trusses to buckle and collapse. Without this stabilisation for the panels in the external skin, they too collapsed.
While this explains the collapse of the buildings, the loss of life is attributable to a separate problem, evidenced by the fact that 99% of the people above the impact floors died whereas 99% of those below the impact floors survived. The reason for this loss of life is again related to the lightweight structure.
Instead of the building's core, which contained the elevators, toilets and crucially the fire stairs, being reinforced concrete as is commonly used, the WTC towers used a steel frame covered with drywall (gypsum between layers of cardboard). Needless to say, the impact of the aircraft destroyed the drywall, making all the lifts and 4 of the 5 fire stairs unusable by those above the impact floors. The fifth stair, which might have been used for escape was undamaged but not easily located, so only a few people were able to use it to escape.
It seems obvious -
Reply | Report Abuse | Link to thisThe water supply for the sprinkler system should be ABOVE
THE OTHER floors. In other if there is a swimming pool, put it on the TOP floor. Then gravity does the job for you.
The escape stairs should be on the OUTSIDE of the building, or at least exposed to the outer air. Maybe an escape ZIP LINE would be more practical? There might be a hazard to nearby aircraft though, like police helicopters.
In response to Torquemada -
Reply | Report Abuse | Link to thisWe don't vote for intelligent people. We vote for the ones that look handsome or pretty, or give good speeches.
Our method of electing good executives really sucks - - -
Re billsincl:
Reply | Report Abuse | Link to thisNot obvious, I am afraid:
Re gravity sprinklers: Sprinklers require high pressure to operate (about 50 psi (350 kPa) at the sprinkler head). Simple physics reveals that to do this by gravity would mean the tank would need to be about 115 feet (35 m) above the top floor served. That would really make buildings look interesting!
Re fire stairs on the outside of a building: Not a good idea because people escaping from above the fire affected floor must come into contact with the fire. External stairs would have been of no use in the Twin Towers. I suggest that the same hazard exists in the thousands of US buildings with external fire stairs.
Re zip lines: Not a realistic means for evacuating thousands of people.
We were in France that month, and when we ultimately learn about the catastrophic event, we were stunned.
Reply | Report Abuse | Link to thisThe first time we view the films that were taken as building went down, my father say right away as he watch films that the way the one building fell straight to ground, it resembled exactly, buildings he had seen in the past that were demolitioned. And, then we were stunned even further when there no mention made of that when it was so obvious done; particular in consideration of the unecessary loss of Americans lifes. We have decided there can be but one reason why governed leaders did not ever be compelled to investigate what was clearly a planned demolishing of building. And then we hear governed people make new laws for Americans because of tragedy, like Patriot Act which makes there freedoms less. So what we remember about the nine eleven event is that is when we saw America as changed and not the wonderful country all of Europe used to admire, because the governed leaders for some reason make this tragedy happen at the expense of all lost lifes and at expense of firemen and policemen who risked there lifes that day. We still wonder why they do it. We talk to one old real American about it, and he say sadly, this is not the America I grew up in.
Well, to make the external stairs practical, you need
Reply | Report Abuse | Link to thisto have good fire doors to keep the flames away. That also gives people inside a refuge from the fire.
Putting the stairs internally makes them impossible to use in the presence of flames and smoke. They would not be able to navigate their way around to escape, and would die from the heat and smoke inhalation before getting to safety.
Plus, as we saw, the stairs were destroyed by the impact, which made the situation even worse.
Having gravity do the job is better than NOTHING, which is what actually happened. The sprinkler pumps can be ABOVE the flames, if those are needed. According to your analysis, gravity feed would have been sufficient at the 75th floor, and all others below it.
Like I said before, a swimming pool on the top floor would be a good emergency supply of water - a health club, for example.
TRUTH & CONSPIRACY
Reply | Report Abuse | Link to thisDuring the Clinton era, the long debated truth regarding the bombing of Pearl Harbor was finally established and the issue put to bed; http://www.independent.org/newsroom/article.asp?id=103
The revelation wasn’t that our politicians are capable of public deceit and winning at any cost, it was a confirmation of government policy to hide and hold the truth of decisions and events for apparently an average of 50 years, or until the people who participated in such secret activities are either dead or too old to matter.
Given America’s adeptness at monitoring potential enemies, which was certainly the case with the Japanese (see article), the fact that Pearl Harbor could be successfully attacked without prior warning was considered impossible; and indeed it was.
Opinions at the time and after that conflicted with the official view were called ‘conspiracy theories’ or worse by politicians and the news media. And in the hysterical frenzy that accompanied Roosevelt’s push for war and the usual accompanying hyper-patriotism, those critical of the ‘official line’ were forced to bite their tongue and the matter went away for a while as events in Europe dramatically unfolded.
The lessons learned about such historical ‘state secrets’ considered expedient for the public’s safety and welfare, is that you won’t learn the truth from politicians or the media; and that those who question and suggest alternatives to the official view are always in the minority.
In its aggressive effort to keep potentially volatile information away from the public, the government has new and more challenging antagonists, in the form of Wikileaks, internet hackers and others. We will never know the complete price tag for security efforts to keep sensitive data from being leaked to taxpaying citizens. These new ‘truth foes’ mentioned above haven’t yet leaked hidden data regarding 911 and other sensitive events tied by the governments to terrorists. However, it’s an issue that you can bet is on the minds of among others, our politicians, our redundant security forces and the military.
The next time we read where politicians or the media have decided to use the ‘conspiracy card’ to discredit free-thinking individuals or groups that don’t necessarily blindly believe the official message coming from those who in the past have made a habit of hiding the truth, perhaps we should view this overworked tactic of name-calling for what it might very well be… a conspiracy theory of its own.
Always good to see some background to why things were as they were...don't know that I can fully back your suggestions to fix....Then again I don't know what they are either...
Reply | Report Abuse | Link to thismeant to say that I don't know what the answers are either....
Reply | Report Abuse | Link to thisYou watched the towering inferno
Reply | Report Abuse | Link to this<blockquote>"The greatest challenge that U.S. National Institute of Standards and Technology (NIST) investigators faced when they began in 2002 was the destruction of the main bodies of evidence that they would normally probe in such a disaster. "Most of the buildings and their contents, save the structural steel skeletons, was demolished to the point that they were unrecognizable and of no practical use in reconstructing the conditions prior to aircraft impact," says structural engineer Shyam Sunder, lead investigator of the NIST report on the World Trade Center disaster."</blockquote>
Reply | Report Abuse | Link to thisThis is a remarkable admission, as very nature of the post-collapse state of the buildings, their structural elements and their contents, WAS the primary data for recontructing the causes of building collapse they were entrusted with determining. No investigation that begins with a refusal to consider the main body of evidence, and which proceeds by allowing this evidence (the crime scene of the century) to be destroyed wholly unpreserved, uncatalogued, untested, unphotographed, unmapped, unstudied, can be said to have scientific and forensic value.
The fact that this science writer, no more than this award-winning science publication, does not see fit to question the value of such a shoddy investigation, whose conclusions, based on an outright refusal to examine the data, must of necessity be scientificaly suspect, is extremely unsettling.
The memories of those who died are sullied when scientists accept and validate such sub-standard scientific and forensic investigative methodology. Those who died deserve better. They, and everyone living in a world so utterly changed by this horrific event, deserve nothing less than a scientifically rigourous, fully resourced and totally independent enquiry into all events surrounding the attacks of September 11th.