53 comments to The astonishing ignorance of people who believe the official 9/11 story

• LJ Rolfe

  September 8th, 2011 at 8:47 pm

  OMG not this whole thing about 9/11 AGAIN! talk about Boring old samey stuff! Honestly, Why can you not except that the whole world is catagorically not a horrific place where every government is out to kill people, destroy large & Expencive buildings (some of which) belonged to them, in the 9/11 tragedy. Not forgetting that the pentagon was actually hit by a plane or something that at least looked damn well like a plane!

• LJ Rolfe

  September 9th, 2011 at 9:22 pm

  Why Did the World Trade Center Collapse? Science, Engineering, and Speculation

  The following article appears in the journal JOM,
  53
  (12) (2001), pp. 8-11.

  Feature:
  Special Report

  Why Did the World Trade Center Collapse? Science, Engineering, and Speculation

  Thomas W. Eagar and Christopher Musso

  Editor’s Note: For a more complete. updated analysis of the World Trade Center towers collapse, read “The Role of Metallurgy in the NIST Investigation of the World Trade Center Towers Collapse” in the December 2007 issue.

  OTHER ARTICLES IN THE WTC SERIES

  Why
  Did the World Trade Center Collapse? Science, Engineering, and Speculation
  by Thomas Eagar and Christopher Musso

  Better
  Materials Can Reduce the Threat from Terrorism by Toni G. Maréchaux
  An
  Initial Microstructural Analysis of A36 Steel from WTC Building 7
  by J.R. Barnett, R.R. Biederman, and R.D. Sisson, Jr.
  News
  & Update

  There have been numerous reports detailing the cause of the World Trade Center
  Tower collapse on September 11, 2001. Most have provided qualitative explanations;
  however, simple quantitative analyses show that some common conclusions are
  incorrect; for example, the steel could not melt in these flames and there was
  more structural damage than merely softening of the steel at elevated temperatures.
  Some guidelines for improvements in future structures are presented.

  INTRODUCTION

  The collapse of the World Trade Center (WTC) towers on September
  11, 2001, was as sudden as it was dramatic; the complete destruction of such
  massive buildings shocked nearly everyone. Immediately afterward and even today,
  there is widespread speculation that the buildings were structurally deficient,
  that the steel columns melted, or that the fire suppression equipment failed
  to operate. In order to separate the fact from the fiction, we have attempted
  to quantify various details of the collapse.

  The major events include the following:

  The airplane impact with damage to the columns.

  The ensuing fire with loss of steel strength and distortion (Figure
  1).

  The collapse, which generally occurred inward without significant tipping
  (Figure 2).

  Each will be discussed separately, but initially it is useful
  to review the overall design of the towers.
  THE DESIGN
  The towers were designed and built in the mid-1960s through the
  early 1970s. They represented a new approach to skyscrapers in that they were
  to be very lightweight and involved modular construction methods in order to
  accelerate the schedule and to reduce the costs.

  To a structural engineer, a skyscraper is modeled as a large cantilever vertical
  column. Each tower was 64 m square, standing 411 m above street level and 21
  m below grade. This produces a height-to-width ratio of 6.8. The total weight
  of the structure was roughly 500,000 t, but wind load, rather than the gravity
  load, dominated the design. The building is a huge sail that must resist a 225
  km/h hurricane. It was designed to resist a wind load of 2 kPa—a total
  of lateral load of 5,000 t.

  In order to make each tower capable of withstanding this wind load, the architects
  selected a lightweight “perimeter tube” design consisting of 244 exterior
  columns of 36 cm square steel box section on 100 cm centers (see Figure
  3). This permitted windows more than one-half meter wide. Inside this outer
  tube there was a 27 m × 40 m core, which was designed to support the weight
  of the tower. It also housed the elevators, the stairwells, and the mechanical
  risers and utilities. Web joists 80 cm tall connected the core to the perimeter
  at each story. Concrete slabs were poured over these joists to form the floors.
  In essence, the building is an egg-crate construction that is about 95 percent
  air, explaining why the rubble after the collapse was only a few stories high.

  Figure 1. Flames and debris exploded
  from the World Trade Center south tower immediately after the airplane’s
  impact. The black smoke indicates a fuel-rich fire (Getty
  Images).

  Figure 2. As the heat of the fire intensified,
  the joints on the most severely burned floors gave way, causing the perimeter
  wall columns to bow outward and the floors above them to fall. The buildings
  collapsed within ten seconds, hitting bottom with an estimated speed of
  200 km/h (Getty Images).

  The egg-crate construction made a redundant structure (i.e., if
  one or two columns were lost, the loads would shift into adjacent columns and
  the building would remain standing). Prior to the World Trade Center with its
  lightweight perimeter tube design, most tall buildings contained huge columns
  on 5 m centers and contained massive amounts of masonry carrying some of the
  structural load. The WTC was primarily a lightweight steel structure; however,
  its 244 perimeter columns made it “one of the most redundant and one of
  the most resilient” skyscrapers.1
  THE AIRLINE IMPACT
  The early news reports noted how well the towers withstood the
  initial impact of the aircraft; however, when one recognizes that the buildings
  had more than 1,000 times the mass of the aircraft and had been designed to
  resist steady wind loads of 30 times the weight of the aircraft, this ability
  to withstand the initial impact is hardly surprising. Furthermore, since there
  was no significant wind on September 11, the outer perimeter columns were only
  stressed before the impact to around 1/3 of their 200 MPa design allowable.

  The only individual metal component of the aircraft that is comparable in strength
  to the box perimeter columns of the WTC is the keel beam at the bottom of the
  aircraft fuselage. While the aircraft impact undoubtedly destroyed several columns
  in the WTC perimeter wall, the number of columns lost on the initial impact
  was not large and the loads were shifted to remaining columns in this highly
  redundant structure. Of equal or even greater significance during this initial
  impact was the explosion when 90,000 L gallons of jet fuel, comprising nearly
  1/3 of the aircraft’s weight, ignited. The ensuing fire was clearly the
  principal cause of the collapse (Figure 4).

  THE FIRE
  The fire is the most misunderstood part of the WTC collapse. Even
  today, the media report (and many scientists believe) that the steel melted.
  It is argued that the jet fuel burns very hot, especially with so much fuel
  present. This is not true.

  Part of the problem is that people (including engineers) often confuse temperature
  and heat. While they are related, they are not the same. Thermodynamically,
  the heat contained in a material is related to the temperature through the heat
  capacity and the density (or mass). Temperature is defined as an intensive property,
  meaning that it does not vary with the quantity of material, while the heat
  is an extensive property, which does vary with the amount of material. One way
  to distinguish the two is to note that if a second log is added to the fireplace,
  the temperature does not double; it stays roughly the same, but the size of
  the fire or the length of time the fire burns, or a combination of the two,
  doubles. Thus, the fact that there were 90,000 L of jet fuel on a few floors
  of the WTC does not mean that this was an unusually hot fire. The temperature
  of the fire at the WTC was not unusual, and it was most definitely not capable
  of melting steel.

  In combustion science, there are three basic types of flames, namely, a jet
  burner, a pre-mixed flame, and a diffuse flame. A jet burner generally involves
  mixing the fuel and the oxidant in nearly stoichiometric proportions and igniting
  the mixture in a constant-volume chamber. Since the combustion products cannot
  expand in the constant-volume chamber, they exit the chamber as a very high
  velocity, fully combusted, jet. This is what occurs in a jet engine, and this
  is the flame type that generates the most intense heat.

  In a pre-mixed flame, the same nearly stoichiometric mixture is ignited as it
  exits a nozzle, under constant pressure conditions. It does not attain the flame
  velocities of a jet burner. An oxyacetylene torch or a Bunsen burner is a pre-mixed
  flame.

  In a diffuse flame, the fuel and the oxidant are not mixed before ignition,
  but flow together in an uncontrolled manner and combust when the fuel/oxidant
  ratios reach values within the flammable range. A fireplace flame is a diffuse
  flame burning in air, as was the WTC fire.

  Diffuse flames generate the lowest heat intensities of the three flame types.

  If the fuel and the oxidant start at ambient temperature, a maximum flame temperature
  can be defined. For carbon burning in pure oxygen, the maximum is 3,200°C;
  for hydrogen it is 2,750°C. Thus, for virtually any hydrocarbons, the maximum
  flame temperature, starting at ambient temperature and using pure oxygen, is
  approximately 3,000°C.

  This maximum flame temperature is reduced by two-thirds if air is used rather
  than pure oxygen. The reason is that every molecule of oxygen releases the heat
  of formation of a molecule of carbon monoxide and a molecule of water. If pure
  oxygen is used, this heat only needs to heat two molecules (carbon monoxide
  and water), while with air, these two molecules must be heated plus four molecules
  of nitrogen. Thus, burning hydrocarbons in air produces only one-third the temperature
  increase as burning in pure oxygen because three times as many molecules must
  be heated when air is used. The maximum flame temperature increase for burning
  hydrocarbons (jet fuel) in air is, thus, about 1,000°C—hardly sufficient
  to melt steel at 1,500°C.

  Figure 3. A cutaway view of WTC structure.

  Figure 4. A graphic illustration, from
  the USA Today newspaper
  web site, of the World Trade Center points of impact. Click on the image
  above to access the actual USA
  Today feature.

  But it is very difficult to reach this maximum temperature with
  a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse
  flame are mixed in the best ratio. Typically, diffuse flames are fuel rich,
  meaning that the excess fuel molecules, which are unburned, must also be heated.
  It is known that most diffuse fires are fuel rich because blowing on a campfire
  or using a blacksmith’s bellows increases the rate of combustion by adding
  more oxygen. This fuel-rich diffuse flame can drop the temperature by up to
  a factor of two again. This is why the temperatures in a residential fire are
  usually in the 500°C to 650°C range.2,3
  It is known that the WTC fire was a fuel-rich, diffuse flame as evidenced
  by the copious black smoke. Soot is generated by incompletely burned fuel; hence,
  the WTC fire was fuel rich—hardly surprising with 90,000 L of jet fuel
  available. Factors such as flame volume and quantity of soot decrease the radiative
  heat loss in the fire, moving the temperature closer to the maximum of 1,000°C.
  However, it is highly unlikely that the steel at the WTC experienced temperatures
  above the 750–800°C range. All reports that the steel melted
  at 1,500°C are using imprecise terminology at best.

  Some reports suggest that the aluminum from the aircraft ignited, creating very
  high temperatures. While it is possible to ignite aluminum under special conditions,
  such conditions are not commonly attained in a hydrocarbon-based diffuse flame.
  In addition, the flame would be white hot, like a giant sparkler. There was
  no evidence of such aluminum ignition, which would have been visible even through
  the dense soot.

  It is known that structural steel begins to soften around 425°C and loses
  about half of its strength at 650°C.4
  This is why steel is stress relieved in this temperature range. But even a 50%
  loss of strength is still insufficient, by itself, to explain the WTC collapse.
  It was noted above that the wind load controlled the design allowables. The
  WTC, on this low-wind day, was likely not stressed more than a third of the
  design allowable, which is roughly one-fifth of the yield strength of the steel.
  Even with its strength halved, the steel could still support two to three times
  the stresses imposed by a 650°C fire.

  The additional problem was distortion of the steel in the fire. The temperature
  of the fire was not uniform everywhere, and the temperature on the outside of
  the box columns was clearly lower than on the side facing the fire. The temperature
  along the 18 m long joists was certainly not uniform. Given the thermal
  expansion of steel, a 150°C temperature difference from
  one location to another will produce yield-level residual stresses. This produced
  distortions in the slender structural steel, which resulted in buckling failures.
  Thus, the failure of the steel was due to two factors: loss of strength due
  to the temperature of the fire, and loss of structural integrity due to distortion
  of the steel from the non-uniform temperatures in the fire.
  THE COLLAPSE
  Nearly every large building has a redundant design that allows
  for loss of one primary structural member, such as a column. However, when multiple
  members fail, the shifting loads eventually overstress the adjacent members
  and the collapse occurs like a row of dominoes falling down.

  The perimeter tube design of the WTC was highly redundant. It survived the loss
  of several exterior columns due to aircraft impact, but the ensuing fire led
  to other steel failures. Many structural engineers believe that the weak points—the
  limiting factors on design allowables—were the angle clips that held the
  floor joists between the columns on the perimeter wall and the core structure
  (see Figure 5). With a 700 Pa floor design
  allowable, each floor should have been able to support approximately 1,300 t
  beyond its own weight. The total weight of each tower was about 500,000 t.

  As the joists on one or two of the most heavily burned floors gave way and the
  outer box columns began to bow outward, the floors above them also fell. The
  floor below (with its 1,300 t design capacity) could not support the roughly
  45,000 t of ten floors (or more) above crashing down on these angle clips. This
  started the domino effect that caused the buildings to collapse within ten seconds,
  hitting bottom with an estimated speed of 200 km per hour. If it had been free
  fall, with no restraint, the collapse would have only taken eight seconds and
  would have impacted at 300 km/h.1
  It has been suggested that it was fortunate that the WTC did not tip over onto
  other buildings surrounding the area. There are several points that should be
  made. First, the building is not solid; it is 95 percent air and, hence, can
  implode onto itself. Second, there is no lateral load, even the impact of a
  speeding aircraft, which is sufficient to move the center of gravity one hundred
  feet to the side such that it is not within the base footprint of the structure.
  Third, given the near free-fall collapse, there was insufficient time for portions
  to attain significant lateral velocity. To summarize all of these points, a
  500,000 t structure has too much inertia to fall in any direction other than
  nearly straight down.

  Figure 5. Unscaled schematic of WTC floor
  joints and attachment to columns.

  WAS THE WTC DEFECTIVELY DESIGNED?
  The World Trade Center was not defectively designed. No designer of the WTC
  anticipated, nor should have anticipated, a 90,000 L Molotov cocktail on one
  of the building floors. Skyscrapers are designed to support themselves for three
  hours in a fire even if the sprinkler system fails to operate. This time should
  be long enough to evacuate the occupants. The WTC towers lasted for one to two
  hours—less than the design life, but only because the fire fuel load was
  so large. No normal office fires would fill 4,000 square meters of floor space
  in the seconds in which the WTC fire developed. Usually, the fire would take
  up to an hour to spread so uniformly across the width and breadth of the building.
  This was a very large and rapidly progressing fire (very high heat but not unusually
  high temperature). Further information about the design of the WTC can be found
  on the World Wide Web.5–8
  WHERE DO WE GO FROM HERE

  The clean-up of the World Trade Center will take many months.
  After all, 1,000,000 t of rubble will require 20,000 to 30,000 truckloads to
  haul away the material. The asbestos fire insulation makes the task hazardous
  for those working nearby. Interestingly, the approximately 300,000 t of steel
  is fully recyclable and represents only one day’s production of the U.S.
  steel industry. Separation of the stone and concrete is a common matter for
  modern steel shredders. The land-filling of 700,000 t of concrete and stone
  rubble is more problematic. However, the volume is equivalent to six football
  fields, 6–9 m deep, so it is manageable.

  There will undoubtedly be a number of changes in the building codes as a result
  of the WTC catastrophe. For example, emergency communication systems need to
  be upgraded to speed up the notice for evacuation and the safest paths of egress.
  Emergency illumination systems, separate from the normal building lighting,
  are already on the drawing boards as a result of lessons learned from the WTC
  bombing in 1993. There will certainly be better fire protection of structural
  members. Protection from smoke inhalation, energy-absorbing materials, and redundant
  means of egress will all be considered.

  A basic engineering assessment of the design of the World Trade Center dispels
  many of the myths about its collapse. First, the perimeter tube design of the
  towers protected them from failing upon impact. The outer columns were engineered
  to stiffen the towers in heavy wind, and they protected the inner core, which
  held the gravity load. Removal of some of the outer columns alone could not
  bring the building down. Furthermore, because of the stiffness of the perimeter
  design, it was impossible for the aircraft impact to topple the building.

  However, the building was not able to withstand the intense heat of the jet
  fuel fire. While it was impossible for the fuel-rich, diffuse-flame fire to
  burn at a temperature high enough to melt the steel, its quick ignition and
  intense heat caused the steel to lose at least half its strength and to deform,
  causing buckling or crippling. This weakening and deformation caused a few floors
  to fall, while the weight of the stories above them crushed the floors below,
  initiating a domino collapse.

  It would be impractical to design buildings to withstand the fuel load induced
  by a burning commercial airliner. Instead of saving the building, engineers
  and officials should focus on saving the lives of those inside by designing
  better safety and evacuation systems.

  As scientists and engineers, we must not succumb to speculative thinking when
  a tragedy such as this occurs. Quantitative reasoning can help sort fact from
  fiction, and can help us learn from this unfortunate disaster. As Lord Kelvin
  said,

  “I often say . . . that when you can measure what you are speaking
  about, and express it in numbers, you know something about it; but when
  you cannot measure it, when you cannot express it in numbers, your knowledge
  is of a meager and unsatisfactory kind; it may be the beginning of knowledge,
  but you have scarcely, in your thoughts, advanced to the stage of science,
  whatever the matter may be.”

  We will move forward from the WTC tragedy and we will engineer
  better and safer buildings in the future based, in part, on the lessons learned
  at the WTC. The reason the WTC collapse stirs our emotions so deeply is because
  it was an intentional attack on innocent people. It is easier to accept natural
  or unintentional tragedies; it is the intentional loss of life that makes us
  fear that some people have lost their humanity.
  References
  1. Presentation
  on WTC Collapse, Civil Engineering Department, MIT,
  Cambridge, MA (October 3, 2001).
  2. D. Drysdale, An Introduction
  to Fire Dynamics (New York: Wiley
  Interscience, 1985), pp. 134–140.

  3. A.E. Cote, ed., Fire Protection
  Handbook 17th Edition (Quincy, MA: National
  Fire Protection Association, 1992), pp. 10–67.
  4. A.E. Cote, ed., Fire Protection
  Handbook 17th Edition (Quincy, MA: National
  Fire Protection Association, 1992), pp. 6-62 to 6-70.

  5. Steven Ashley, “When
  the Twin Towers Fell,” Scientific American Online (October 9, 2001);
  
  http://www.sciam.com/explorations/2001/100901wtc/
  6. Zdenek P. Bazant and Yong Zhou, “Why Did the World
  Trade Center Collapse?—Simple Analysis,” J.
  Engineering Mechanics ASCE, (September 28, 2001), also http://www.tam.uiuc.edu/news/200109wtc/
  

  7. Timothy Wilkinson, “World Trade Centre–New
  York—Some Engineering Aspects” (October 25, 2001), Univ.
  Sydney, Department
  of Civil Engineering; http://www.civil.usyd.edu.au/wtc.htm.

  8. G. Charles Clifton, “Collapse of the World Trade
  Centers,” CAD Headlines, tenlinks.com
  (October 8, 2001); http://www.tenlinks.com/NEWS/special/wtc/clifton/p1.htm.

  Thomas W. Eagar,
  the Thomas Lord Professor of Materials Engineering and Engineering Systems,
  and Christopher Musso, graduate research student, are at the Massachusetts
  Institute of Technology.
  For more information, contact T.W. Eagar, MIT, 77 Massachusetts
  Avenue, Room 4-136, Cambridge, Massachusetts 02139-4301; (617) 253-3229; fax
  (617) 252-1773; e-mail tweagar@mit.edu.
  

  Copyright held by The Minerals, Metals & Materials
  Society, 2001
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• Aaron atherton

  September 30th, 2012 at 11:05 pm

  I don’t really get why 9/11 is treated like the worlds biggest tragedy I mean more people died in the the blitz, Hiroshima. Nagasaki and other events why does this one in particular have to be treated more serious than other tragic events just because it was in America. I personally am not sure whether 9/11 is a conspiracy or not because I don’t see why the American government would kill there own people unless they were totally phsycho and cared only for war and possible income from oil found arises but then again I do have questions that need answered such as the pentagon and stuff

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