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Old 18th June 2012, 03:39 PM   #5543
Oystein
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A Bibliography Of Scientific Literature On The World Trade Center Collapse


Studies And Investigations

2002/05 - Federal Emergency Management Agency (FEMA) and the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE) - World Trade Center Building Performance Study - link 1, link 2
2002/05 - Massachusetts Institute of Technology (MIT) - The Towers Lost and Beyond - link
2002/09 - John D. Osteraas - World Trade Center: Assessment of Structural and Architectural Damage; The study was conducted for Exponent Failure Analysis Associates on behalf of Swiss Re and other insurers of the WTC complex.
2002/09 - Ali Reza - Damage to the WTC Complex Due to the Collapse of Only One Tower; The study was conducted for Exponent Failure Analysis Associates on behalf of Swiss Re and other insurers of the WTC complex.
2002/10 - Weidlinger Associates Inc. (WAI), LZA Technology/Thornton-Tomasetti, ARUPFire, Hughes Associates Inc., Hillman Environmental Group, RWDI, Z-Axis Corp - World Trade Center - Structural Engineering Investigation - link; The study was performed by a group of engineering firms led by WAI and was conducted on behalf of Silverstein Properties.
2005/09 - National Institute of Standards and Technology (NIST) - Federal Building and Fire Safety Investigation of the World Trade Center Disaster - link
2006/09, 2007/04 - Purdue University, Computer Graphics and Visualization Lab - High-Fidelity Visualization of Large-Scale Simulations - link 1, link 2


Journal Articles

2001
2001/12 - Thomas W. Eagar, Christopher Musso - Why Did the World Trade Center Collapse? Science, Engineering, and Speculation - JOM (Vol. 53, No. 12) - full article

2002
2002/01 - Zdenek P. Bazant, Yong Zhou - Why Did the World Trade Center Collapse? - Simple Analysis - Journal of Engineering Mechanics (Vol. 128, No. 1) - full article
2002/03 - Zdenek P. Bazant, Yong Zhou - Addendum to "Why Did the World Trade Center Collapse? - Simple Analysis"- Journal of Engineering Mechanics (Vol. 128, No. 3) - full article
2002/07 - David E. Newland, David Cebon - Could the world trade center have been modified to prevent its collapse? - Journal of Engineering Mechanics (Vol. 128, No. 7)
2002/08 - Bernard Monahan - World Trade Center Collapse - Civil Engineering Considerations - Practice Periodical On Structural Design And Construction (Vol. 7, No. 3)
2002/10 - James G. Quintiere, Marino di Marzo, Rachel Becker - A suggested cause of the fire-induced collapse of the World Trade Towers - Fire Safety Journal (Vol. 37, No. 7)

2003
2003/07 - Tomasz Wierzbicki, Xiaoqing Teng - How the airplane wing cut through the exterior columns of the World Trade Center - International Journal of Impact Engineering (Vol. 28, No. 6)
2003/10 - Asif S. Usmani, Yun Chi Chung, Jose L. Torero - How did the WTC towers collapse? A new theory - Fire Safety Journal (Vol. 38, No. 6) - full article

2005
2005/01 - Yukihiro Omika, Eiji Fukuzawa, Norihide Koshika, Hiroshi Morikawa, Ryusuke Fukuda - Structural Responses of World Trade Center under Aircraft Attacks - Journal of Structural Engineering (Vol. 131, No. 1)
2005/01 - Howard R. Baum, Ronald G. Rehm - A simple model of the World Trade Center fireball dynamics - Proceedings of the Combustion Institute (Vol. 30, No. 2) - full article
2005/06 - Asif S. Usmani - Stability of the World Trade Center Twin Towers Structural Frame in Multiple Floor Fires- Journal of Engineering Mechanics (Vol. 131, No. 6)
2005/07 - Jeremy Chang, Andrew H. Buchanan, Peter J. Moss - Effect of insulation on the fire behaviour of steel floor trusses - Fire and Materials (Vol. 29, No. 4)
2005/10 - Mohammed R. Karim, Michelle S. Hoo Fatt - Impact of the Boeing 767 Aircraft into the World Trade Center - Journal of Engineering Mechanics (Vol. 131, No. 10)

2006
2006/09 - Genady P. Cherepanov - Mechanics of the WTC collapse - International Journal of Fracture (Vol. 141, No. 1-2)

2007
2007/03 - Zdenek P. Bazant, Mathieu Verdure - Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions - Journal of Engineering Mechanics (Vol. 133, No. 3) - full article
2007/11 - Ming Wang, Peter Chang, James Quintiere, Andre Marshall - Scale Modeling of the 96th Floor of World Trade Center Tower 1 - Journal of Performance of Constructed Facilities (Vol. 21, No. 6)

2008
2008/01 - Ayhan Irfanoglu, Christoph M. Hoffmann - An Engineering Perspective of the Collapse of WTC-1 - Journal of Performance of Constructed Facilities (Vol. 22, No. 1) - full article
2008/03 - Keith A. Seffen - Progressive Collapse of the World Trade Centre: a Simple Analysis - Journal of Engineering Mechanics (Vol. 134, No. 2) - full article
2008/07 - Genady P. Cherepanov - Collapse of towers as applied to September 11 events - Fizyko-Khimichna Mekhanika Materialiv (Materials Science) (Vol. 44, No. 4)
2008/10 - Zdenek P. Bazant, Jia-Liang Le, Frank R. Greening, David B. Benson - What Did and Did not Cause Collapse of WTC Twin Towers in New York - Journal of Engineering Mechanics (Vol. 134, No. 10) - full article


Letters

2005/03 - Genady P. Cherepanov - September 11 And Fracture Mechanics - A Retrospective - International Journal of Fracture (Vol. 132, No. 2)
2007/01 - Genady P. Cherepanov, Ivan E. Esparragoza - Progressive Collapse of Towers: The Resistance Effect - International Journal of Fracture (Vol. 143, No. 2)


Conference Papers

2002/11 - Lu Xinzheng, Jiang Jianjing - Simulation for the Collapse of WTC after Aeroplane Impact - Proceedings of the International Conference on Protection of Structures Against Hazard, 14 - 15 November 2002, Singapore - full paper
2003/05 - Venkatash K. R. Kodur - Role of fire resistance issues in the collapse of the Twin Towers - Proceedings of the CIB-CTBUH International Conference on Tall Buildings, 8 - 10 May 2003, Kuala Lumpur - full paper
2003/11 - Abolhassan Astaneh-Asl - World Trade Center Collapse, Field Investigation and Analysis - Proceedings of the Ninth Arab Structural Engineering Conference, 29 November - 1 December 2003, Abu Dhabi - full paper


Articles In Science Magazines

2001/10 - Steven Ashley - When the Twin Towers Fell - Scientific American - full article
2001/10 - Zdenek P. Bazant, Yong Zhou - Why Did the World Trade Center Collapse? - Society for Industrial and Applied Mathematics News (Vol. 34, No. 8) - full article
2002/01 - Henry Petroski - The Fall of Skyscrapers - American Scientist (Vol. 90, No. 1) - full article


NIST, FEMA, & ASCE reports & critiques, WTC collapse analyses,

Articles by and about the tower engineers and investigators, progressive collapse info, engineering resources
Main 9/11 Links Page

"I am disgusted, disgusted with the structural engineers who know the truth about this and are keeping their mouth shut. There’s a special place in Hell reserved for them. And they are going to deserve it." -"Scholar for 9/11 Truth" James Fetzer

See also: Fire Safety Engineering & the Performance of Structural Steel in Fires

WTC Building 7
WTC 7 Engineering Papers, Collapse Hypotheses, Witness Accounts and Photographic Evidence

Pentagon
The ASCE Pentagon Building Performance Report (PDF) (Dead Link)

World Trade Center
NIST Answers to Frequently Asked Questions About the WTC 1&2 Collapses - August, 2006
NIST Answers to Frequently Asked Questions - December, 2007


NIST Final Reports on WTC 1 & 2
NIST NCSTAR 1 (PDF): URL="http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201.pdf"]Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Towers[/url]

NCSTAR 1-1 Design, Construction, and Maintenance of Structural and Life Safety Systems
NCSTAR 1-2 Baseline Structural Performance and Aircraft Impact Damage Analysis of the WTC Towers
NCSTAR 1-3 Mechanical and Metallurgical Analysis of Structural Steel
NCSTAR 1-4 Active Fire Protection Systems
NCSTAR 1-5 Reconstruction of the Fires in the World Trade Center Towers
NCSTAR 1-6 Structural Fire Response and Probable Collapse Sequence
NCSTAR 1-7 Occupant Behavior, Egress, and Emergency Communication
NCSTAR 1-8 The Emergency Response Operations

Alternate Collapse Hypotheses
Investigations leading to alternate tower collapse hypotheses, and critiques of NIST's WTC investigation by knowledgeable people who are not conspiracy theorists: FEMA/ASCE, Arup Fire, University of Edinburgh, Usmani, Torero, Lane, Cherepanov, Quintiere, Corbett, Mackey, Greening

Journal and Conference Papers
Peer-reviewed papers and conference papers about the WTC impacts, fires, and collapses

WTC collapse papers with Zdenek Bazant as lead author
What Did and Did not Cause Collapse of WTC Twin Towers in New York Authors Bazant, Le, Greening & Benson. Journal of Engineering Mechanics ASCE 134 (2008). Refutation of controlled demolition theory. Discusses matching of video record with progressive collapse equations, "free-fall" claims, concrete crushing (and how much TNT equivalent would be needed to do that crushing), air pressure & ejection of air, spread of dust cloud.
Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions Co-author Verdure. PDF. Journal of Engineering Mechanics ASCE 133 (2007): pp. 308-319
Excerpt (applies to link above and below): The kinetic energy of the top part of the tower impacting the floor below was found to be about 8.4x larger than the plastic energy absorption capability of the underlying story, and considerably higher than that if fracturing were taken into account (Ba=C5=BEant and Zhou 2002a). This fact, along with the fact that during the progressive collapse of underlying stories the loss of gravitational potential per story is much greater than the energy dissipated per story, was sufficient for Ba=C5=BEant and Zhou (2002a) to conclude, purely on energy grounds, that the tower was doomed once the top part of the tower dropped through the height of one story (or even 0.5 m).
Discussion and replies to June 2006 Bazant & Verdure paper: James Gourley, G. Szuladinski. Closing comments from Bazant to Gourley (after detailed rebuttal to his claims):
Although everyone is certainly entitled to express his or her opinion on any issue of concern, interested critics should realize that, to help discern the truth about an engineering problem such as the WTC collapse, it is necessary to become acquainted with the relevant material from an appropriate textbook on structural mechanics. Otherwise critics run the risk of misleading and wrongly influencing the public with incorrect information.
Bazant & Zhou, 2001-2002: Why Did the World Trade Center Collapse? - Simple Analysis J. Engineering Mechanics ASCE, Sept. 28, 2001, addendum March, 2002.

Other explanations of the tower collapses
November, 2007: Structural Engineer Keith Seffen's mathematical model of WTC tower progressive collapse (PDF. Due to appear in the Journal of Engineering Mechanics, Vol. 134, No. 2, February 2008)
BBC News article about Seffen's paper

Dr. Frank Greening's papers on the Collapses, Energy Transfer, "Tipping," Concrete Pulverization (PDFs)

Physicist Manuel Garcia's Counterpunch articles on the physics of the WTC collapses Pt.1- Pt.2- Pt.3

Why didn't the towers, or the upper portions of them, topple over?
Why didn't the upper part pivot about it's base? See Bazant & Zhou (2001) Appendix II
Eduardo Kausel (MIT): Why the Towers didn't fall like trees
Frank Greening: An analysis of the tipping of the upper section of WTC 2 (PDF)
A simple graphic explanation of why the top of the south tower didn't fall to the side.
Physicist Dave Rogers on tipping of tower tops.
Structural engineer "Newton's Bit" on "tipping"

Explanations of NIST's Investigation Methods
See also: Investigations leading to alternate collapse hypotheses.

NIST's Investigation of the Sept. 11 World Trade Center Disaster: FAQ (2002: Goals & Methods)

Ryan Mackey on how the NIST investigation works, and on "Scholars" critics
Ryan Mackey on NIST's degree of certainty, bounding cases, comparisons to other studies
Ryan Mackey on NIST altering model inputs
Ryan Mackey on NIST recovered steel and fire models
JREF Ktesibios on NIST workstation actual tests
JREF RWGuinn on testing models to failure
Ryan Mackey on NIST fuel load estimates
Physicist Dave Rogers on scaling issues with physical models of large structures


NIST's Recommendations, and the Architectural and Engineering Community's Response

NIST summary of WTC 1 & 2 investigation results & recommendations (PDF)
The AIA's Response to NIST's Draft Report and Recommendations (PDF)
The World Trade Center Collapse and its Implications for International Standards - W. Gene Corley ISO Focus, January 2004 (PDF)
"Reexamining Premises for High-Rise Design" Security Management magazine (PDF)
In this article from Security Management magazine, Dr. Gene Corley discusses lessons from the World Trade Center investigation and how they might affect future building design.
NIBS Building Code Experts: Translating WTC Recommendations into Model Building Codes
First Comprehensive Set of Model Code Changes Adopted Based on Recommendations from Commerce’s NIST World Trade Center Investigation (June, 2007)


Twin Towers' Structural Engineers on the Record

Excellent New Yorker Profile of WTC chief engineer Leslie Robertson, early speculation about collapses, many quotes from engineers, info about skyscraper design
Leslie Robertson on WTC steel core
No Tower Can Withstand Attack As Jets Get Bigger, Expert Says (Les Robertson $ NYT March 14, 2002)
"Reflections on the World Trade Center" (Robertson. PDF)
Jon Magnusson of Skilling Ward, helped design towers: "Engineers couldn't have known"


Gene Corley on FEMA/ASCE investigation lessons

"What We Learned: Building Performance Study of the WTC Collapse" (PDF) Outlines preliminary lessons learned in the FEMA/ASCE investigation of the NY World Trade Center collapse.
"Corley, ASCE Take Part in House Hearing" (PDF) On March 6, CTLGroup senior vice president Dr. Gene Corley testified before the Committee on Science of the U.S. House of Representatives. Dr. Corley was one of several members of the ASCE structural investigation team who were asked to discuss the performance of the World Trade Center in the September 11th attacks, and its implications for future building design. An article on the hearing from ASCE News.
"Looking Back on 9/11" (PDF) In this interview, Dr. Gene Corley discusses engineers' roles in the World Trade Center Building Performance Study


Abolhassan Astaneh-Asl's WTC collapse investigations

Tower Wreckage Reveals Clues - Astaneh - Jersey City Scrap Yards (later, some of these conclusions proved wrong)

Abolhassan Astaneh-Asl WTC Collapse, Field Investigations, and Analysis (Dec. 2003)

Now, as the five-year anniversary of the World Trade Center attack draws near, Astaneh-Asl finally expects to have the results of his analysis published in an academic journal. The project, requiring thousands of hours to complete, was self-funded and conducted by Astaneh-Asl, his students, and analysts from the MSC.Software Corporation, which donated the structural analysis software (MD Nastran and Dytran). Did the Building Do it? (Astaneh Study)

Testimony of Abolhassan Astaneh-Asl Before the House Committee on Science, March, 2002


Investigations involving extensive computer modeling of the towers

April, 2007: Purdue University analysis of WTC 1 collapse using LS-Dyna**More on the Purdue WTC study

"Did the Building Do It?" (Article about Abolhassan Astaneh-Asl/Cal FEA study, Sept, 2006)
Now, as the five-year anniversary of the World Trade Center attack draws near, Astaneh-Asl finally expects to have the results of his analysis published in an academic journal. The project, requiring thousands of hours to complete, was self-funded and conducted by Astaneh-Asl, his students, and analysts from the MSC.Software Corporation, which donated the structural analysis software (MD Nastran and Dytran).

NIST's SAP reference models of WTC 1&2, obtained through FOIA request

LU Xinzheng & JIANG Jianjing Simulation for the Collapse of WTC after Aeroplane Impact. Proceedings of the International Conference on the Protection of Structures Against Hazards, Nov. 2002. 57~60

Weidlinger Report Ties WTC Collapses to Column Failures (Matthys Levy). 10/25/02
The engineering team is comprised of: Weidlinger Associates Inc., led by Matthys Levy and Najib Abboud; LZA Technology/Thornton-Tomasetti Group, led by Daniel Cuoco and Gary Panariello; ARUPFire, led by Richard Custer; Hughes Associates Inc., led by Craig Beyler; SafirRosetti, led by Howard Safir; Hillman Environmental Group, led by Christopher Hillmann and John B. Glass Jr.; RWDI, led by Peter Irwin; Dr. W. Gene Corley, who led the ASCE-FEMA study; Professor Sean Ahearn; and Z-Axis Corp., led by Gary Freed and Alan Treibitz.

Weidlinger Study - Column failures

Weidlinger study refutes FEMA. Collapse inevitable due to structural damage and fires, not to WTC design defects. (NYT Oct 22, 2002)

First Tower to Fall Was hit at Higher Speed, Study Finds (NYT February 23, 2002)

Silverstein Sending Tower Data to U.S. Agency (NIST/Weidlinger/Insurance Agencies NYT Oct 1, 2002)
Even though the exterior columns all looked identical, both the grade and thickness of their steel varied from place to place, said Dr. Fahim Sadek, a researcher at the institute's building and fire research lab, who is producing a detailed structural model of the towers on a computer using the original blueprints. So there were actually more than 130 different column types, he said, each having to be accounted for in his model. From there, it gets only more intricate. One of Dr. Sadek's detailed models for a single floor -- the 96th floor of the north tower, considered typical -- contains 40,000 separate elements. A coarser representation of the entire tower contains 90,000 elements.

Swiss Re/Exponent Failure Analysis Associates WTC engineering study, Oct. 2002 (Complete copies of the FaAA study are available at Swiss Re by calling 212-317-5663.)

Ming Wang, Peter Chang, James Quintiere, and Andre Marshall "Scale Modeling of the 96th Floor of World Trade Center Tower 1" Journal of Performance of Constructed Facilities Volume 21, Issue 6, pp. 414-421 http://www.internationalskeptics.com...60#post3161860

Applied Reseach Associates NIST World Trade Center Investigations
Aircraft Impact Analysis of the World Trade Center Towers (Univ. of Tsukuba)
Jay Windley's (Jay Utah of BAUT forum) excellent explanation of Finite Element Analysis
Structure Magazine: Computer Modeling of the Collapse of the World Trade Center Towers (March, 2007)
CAD Digest article with CAD graphics (September, 2001) G. Charles Clifton
NIST's SAP reference models of WTC 1&2, obtained through FOIA request


More on WTC engineering, articles by and about engineers who worked on the buildings and on the investigations

STRUCTURAL ENGINEERS AT GROUND ZERO - NCSEA (August Domel, Nov. 2001)
The Days After, the Days Ahead: Civil engineers respond to 9/11 Attacks (Civil Engineering, Nov. 2001)
Structural engineers first in the aftermath
Civil Engineering Magazine: Dissecting the Collapses
Articles in the National Academy of Engineering's "The Bridge" Spring, 2002 (PDF):
  • Editorial: Engineering and Homeland Defense by George Bugliarello
  • World Trade Center „Bathtub": From Genesis to Armageddon by George J. Tamaro The engineer who oversaw the construction of the World Trade Center „bathtub" describes the recovery efforts.
  • A 911 Call to the Engineering Profession by Robert Prieto The events of September 11 challenged the future of our heavily engineered environment and the future of the engineering profession.


Early Structural Investigation Teams (through 5/02)

ASCE WTC Disaster Response Team
Engineer Tim Schenck on early GZ work
Multidisciplinary Center for Earthquake Engineering Research (MCEER) The World Trade Center Terrorist Attack: Damage to Critical Facilities and Crisis Response
Georgia Tech Engineering Team Will Conduct Post-Disaster Assessment at World Trade Center Attack Site
Architecture Week: Engineers Explain Collapses (5/2002)
Towers Lost and Beyond: 8 Articles by MIT researchers 2001-2002.
Civil Engineer: WTC & Pentagon Links Portal
Blog: Civil & structural engineers on WTC collapse
Forum on Technical Implications of WTC Collapses (Columbia U., November, 2001)
MIT Masters Thesis: WTC Disaster Analysis & Recommendations (June, 2005)
Designing tall buildings to Resist Earthquakes ($ NYT 2002)
Institute of Structural Engineers: Safety in tall buildings and other buildings of large occupancy ($ 2002)
9/17/01 Inferno Heat, Not Impact, Brought Down Towers, Experts Say
9/19/01: Space.com "Gravity Helped Destroy Twin Towers" concrete too heavy for core construction, walls seen buckling, seismic data
December, 2007: JOM: The Role of Metallurgy in the NIST Investigation of the Twin Tower Collapses


Others write about sensibly about the collapses

JREF Nobby Nobbs: Some basics on the physics of the collapses
Bautforum: Jay Utah's excellent explanation of Finite Element Analysis
JREF R. Mackey on Gordon Ross / Frank Greening debate
JREF R.Mackey on freefall and energy available for deformation
JREF R. Mackey on Judy Wood's "Math"
JREF Arkan on tower collapse times
JREF Myriad on kinetic energy of initial collapses
JREF rwguinn on structural steel deformation
JREF Dr. Adequate on Steven Jones' "handwaving" argument.
Physics kinetic energy Moscatelli The destructive forces unleashed
Steven Jones to Jim Fetzer: grand piano speed, damage to bathtub Judy Wood
JREF Kookbreaker on pancake collapse history
Ryan Mackey on independent validations of the NIST report.
Roberts: Were the towers as strong as they were designed to be?
JREF rwguinn: The engineers in my office thought the towers would collapse


More about the NIST & FEMA investigations

In Collapsing Towers, a Cascade of Failures ($ NYT Nov. 11, 2001)
Experts Urging Broader Inquiry In Towers' Fall (NYT Glanz, steel removal, Dec 25, 2001)
NIST to take over collapse investigation ($ NYT January 17, 2002)
Critique of FEMA WTC report by Ed Schulte in Plumbing Engineer, July, 2005 (PDF)
Learning from 9/11 (March, 2002) Hearing before the House Committee on Science: ASCE/FEMA BPAT study
Mismanagement Muddled Collapse Inquiry, House Panel Says (FEMA/NYC gov't/Fed gov't. $ NYT March 7, 2002)
At one point, Representative Anthony D. Weiner, a Democrat from New York City, asked for the official in charge to raise his hand, and two men, and then three appeared to do so. ''We have very serious problems here,'' added Representative John B. Larson, a Connecticut Democrat.

The lack of clear authority has had unfortunate consequences, the House members said. The Giuliani administration started to send World Trade Center steel off to recycling yards before investigators could examine it to determine whether it might hold crucial clues as to why the buildings fell.

The full investigative team set up by FEMA was not allowed to enter ground zero to collect other potentially critical evidence in the weeks after the attack, and it did not get a copy of the World Trade Center blueprints until early January, a delay House members found infuriating.

'The delay in the receipt of the plans did somewhat hinder the team's ability to confirm their understanding of the buildings,'' said Dr. W. Gene Corley, a structural engineer leading the investigative committee organized by FEMA.

A Port Authority spokesman defended the agency, saying that building plans had been given to federal officials within a week of the attack and that the agency was cooperating fully with the inquiry.

The federal officials who testified yesterday -- Dr. Arden L. Bement Jr., the director of the National Institute of Standards and Technology, and Robert F. Shea, the acting administrator of the Federal Emergency Management Agency's Insurance and Mitigation Administration -- repeatedly nodded their agreement.

In response to criticism from one committee member, Mr. Shea said, ''Frankly, I agree with you. There are many things in hindsight we would have done differently.''

The problem, they said, was the lack of clear authority in federal law and financing. None of the investigators, for example, had subpoena power, meaning that they could not order the city to stop sending the steel off for recycling or demand a copy of the building blueprints.

Government Orders Inquiry Into Trade Center Collapse ($ NYT March 23, 2002)
The Trade Center; Towers Fell as Intense Fire Beat Defenses, Report Says (FEMA. $ NYT March 29, 2002)
Interviews will examine why trade center collapsed -100,000 workers issued security passes
Wider Inquiry Into Towers Is Proposed ($ NYT May 2, 2002)

"In Data Trove, a Graphic Look at Towers' Fall, ($ NYT October 29, 2002)
Twin Tower Collapse Theory Challenged (Feb. 2003)
NIST Minutes of December 2-3, 2003, Meeting
New Evidence Is Reported That Floors Failed on 9/11 ($ NYT Dec. 3, 2003)
S. Shyam Sunder, who is leading the investigation for the National Institute of Standards and Technology in the Commerce Department, said, ''We are seeing evidence of floors appearing to be sagging -- or that had been damaged -- prior to collapse.'' Still, Dr. Sunder said, ''The relative role of the floors and the columns still remain to be determined in the collapse.''

NIST Not Ruling Anything Out on WTC Probe
Reliving 9/11, With Fire as Teacher (Modeling. $ NYT, Jan. 6, 2004)link
NIST Public Briefing 05/05/04

Fire Testing Is Questioned In Findings On Towers (Current testing standards for new buildings inadequate. $ NYT August 26, 2004)


WTC Twin Tower Construction Details Pertinent to Engineering Investigations
See also WTC Construction, Systems, Power and WTC Core Construction

Gregory Urich: Detailed Estimate of Mass and Potential Energy of World Trade Center Tower (pdf)
WTC 1 & 2 core column data
Report of WTC fire code compliance--1993 (pdf)


Truther Claim: the term "Progressive Collapse" is a new one and describes a phenomenon rarely or never seen before 9/11.

Jim Hoffman, whom many truthers describe as one of their best researchers:
You've heard that the Twin Towers pancaked, crushing themselves completely. The experts gave us a fancy-sounding term for this: progressive collapse. If you search with the phrase "progressive collapse" you will find numerous articles, most of them written since 9/11/01 about things like assessing and retrofitting existing structures against progressive collapse. It seems that the only examples of progressive collapse of buildings cited are the Twin Towers, Building 7, and the Murrah Federal Building in Oklahoma City.
A few examples of reality:
"As the hon. Gentleman will know, I accepted the tribunal's recommendations in respect of gas which show that once buildings are strengthened against the possibility of progressive collapse there is no reason why gas should not be used..." -Ronan Point Flats (Report), November, 1968

"New safeguards against the progressive collapse of tall buildings..." -"New Safety Law for Buildings," The Times (London), February 6, 1970

"The engineering term 'progressive collapse' - a potential calamity in high-rise structures - carries a sad double meaning throughout the evening." -'Benefactors' by Frayn, The New York Times, December 23, 1985

'It was a progressive collapse,'' Mr. Cohen said. ''What touched it off, we don't know.'' -"Collapse Inquiry Studies Bracing for New Column," The New York Times, May 1, 1987.


Some Progressive Collapse Studies & Recommendations
Thanks to JREF forum member cmcaulif for his contributions

Progressive Collapse Basics (R. Shankar Nair. 2004 North American Steel Construction Conference. PDF)
Fire Induced Progressive Collapse. (Arup. PDF) "This paper considers issues related to fire induced progressive collapse of tall buildings in extreme events."
Fire induced progressive collapse analysis of high rise buildings
NISTIR 7396 "Best Practices for Reducing the Potential for Progressive Collapse in Buildings," February 2007
Above report based on NIST/SEI workshops. Workshop presentation materials are here
Abolhassan Astaneh-Asl: Progressive collapse prevention in new and existing buildings (Includes use of catenary action of cables to resist collapse. 2003. pdf).

Practical Means for Energy-Based Analyses of Disproportionate Collapse Potential
Journal of Performance of Constructed Facilities, Volume 20, Issue 4, pp. 336-348 (November 2006)

Progressive Analysis Procedure for Progressive Collapse
Journal of Performance of Constructed Facilities, Volume 18, Issue 2, pp. 79-85 (May 2004)

Progressive Collapse of Structures: Annotated Bibliography and Comparison of Codes and Standards
Journal of Performance of Constructed Facilities, Volume 20, Issue 4, pp. 418-425 (November 2006)

Cheol-Ho Lee, Seonwoong Kim, Kyu-Hong Han, Kyungkoo Lee 2009. "Simplified nonlinear progressive collapse analysis of welded steel moment frames"
Journal of Constructional Steel Research, Volume 65, Issue 5, 1130-1137

Feng Fu, "Progressive collapse analysis of high-rise building with 3-D finite element modeling method" Journal of Constructional Steel Research, In Press, Corrected Proof, Available online 13 March 2009

A.G. Vlassis, B.A. Izzuddin, A.Y. Elghazouli, D.A. Nethercot, "Progressive collapse of multi-storey buildings due to failed floor impact" Engineering Structures, In Press, Corrected Proof, Available online 12 March 2009
Abstract excerpt: "The application of the proposed methodology is demonstrated by means of a case study, which considers the impact response of a floor plate within a typical multi-storey steel-framed composite building. ...The application study illustrates the extremely onerous conditions imposed on the impacted floor resulting in an increased vulnerability to progressive collapse for structures of this type."

B.A. Izzuddin, A.G. Vlassis, A.Y. Elghazouli, D.A. Nethercot, "Progressive collapse of multi-storey buildings due to sudden column loss - Part I: Simplified assessment framework" Engineering Structures, Volume 30, Issue 5, May 2008, Pages 1308-1318

A.G. Vlassis, B.A. Izzuddin, A.Y. Elghazouli, D.A. Nethercot, "Progressive collapse of multi-storey buildings due to sudden column loss - Part II: Application" Engineering Structures, Volume 30, Issue 5, May 2008, Pages 1424-1438

Santiago Pujol, J. Paul Smith-Pardo 2009. "A new perspective on the effects of abrupt column removal" Engineering Structures, Volume 31, Issue 4, 869-874

Hyun-Su Kim, Jinkoo Kim, Da-Woon An, "Development of integrated system for progressive collapse analysis of building structures considering dynamic effects" Advances in Engineering Software, Volume 40, Issue 1, January 2009, Pages 1-8

Jinkoo Kim, Taewan Kim, "Assessment of progressive collapse-resisting capacity of steel moment frames" Journal of Constructional Steel Research, Volume 65, Issue 1, January 2009, Pages 169-179

Jeom Kee Paik, Bong Ju Kim, "Progressive collapse analysis of thin-walled box columns" Thin-Walled Structures, Volume 46, Issue 5, May 2008, Pages 541-550


Some Engineering & physics fundamentals & calculation aids

Efunda: Engineering Fundamentals
Online scientific calculator and unit converter
Shear Force And Bending diagrams 1
Ductile fracture and fragmentation in the reconstruction of the World Trade Center Attack (Wierzbicki)
Elastic Bending Theory
JREF: PixyMIsa on truther misuse of the term "entropy"
JREF Structural Engineer Newtons Bit on DCR/dead/live loads/safety factor
Steel: Ultimate strength vs. yield strength (strength is in the geometry)
A demonstration of kinetic energy: 7 grams of plastic vs. cast aluminum block


The following individuals and groups participated in the 911 investigations, cleanup and research. Not one has come forward to support the Truther version of events.
  • 7,000+ FBI Agents who conducted a three-year 911 investigation
  • 1,500 people who worked the flight 93 crash scene
  • 40,000 people who worked the piles at Ground Zero
  • 55 FBI Evidence Response Teams at Fresh Kills in New York
  • 8,000+ people who worked the scene at the Pentagon
Notice the number of civil and structural engineers in this list
Abolhassan Astaneh-Asl, Ph.D., P.E. / Aine M. Brazil, P.E., S.E. / Alan Rosa, P.E., S.E. / Alfred D. Barcenilla, Sr., P.E. / Allan Jowsey, Ph.D. / Allyn Kilsheimer, P.E., S.E. / Amit Bandyopadhyay, S.E. / Amy Zelson Mundorff / Anamaria Bonilla, S.E. / Andre Sidler, P.E., S.E. / Andrei Reinhorn, Ph.D., P.E., S.E. / Andrew Coats, P.E., S.E. / Andrew McConnell, S.E. / Andrew Mueller-Lust, S.E. / Andrew Pontecorvo, P.E. / Andrew Whittaker, Ph.D., P.E., S.E. / Anthony Kirk US&R Structural Specialist / Anthony W. Chuliver, S.E. / Antoine E. Naaman, Ph.D. / Antranig M. Ouzoonian, P.E. / Arlan Dobson, FEMA Region 2 DAS / Arthur Schuerman, FDNY (ret.) / Asif Usmani, Ph.D., B.E. / August Domel, Ph.D., S.E., P.E. / Ayhan Irfanoglu, P.E., S.E. / Barbara Lane, Ph.D. / Bernie Denke, P.E. US&R Structural Specialist / Bill Cote / Bill Coulbourne, P.E., S.E. / Bill Crowley, special agent, FBI / Bill Daly, senior vice president, Control Risks Group / Bill Scott (Capt. USAF, Ret.), / Bill Uher, NASA Langley Research Center / Bob Gray (I.U.O.E.) / Bonnie Manley, P.E., S.E. / Boris Hayda, P.E., S.E. / Brian Lyons, Tully / Brian McElhatten, S.E. / Brian Smith (Col.), Chief Deputy Medical Examiner, Dover AFB / Brian Tokarczik, P.E., S.E. / Charles Hirsch, M.D. / Charles J. Carter, P.E., S.E. / Charles Thornton, P.E. / Charlie Vitchers / Christoph Hoffmann, Ph.D., Purdue University / Christopher E. Marrion, P.E. / Christopher M. Hewitt, AISC / Christopher N. McCowan / Chuck Guardia, S.E. / Conrad Paulson, P.E., S.E. / Curtis S.D. Massey / D. Stanton Korista, P.E., S.E. / Dan Doyle (IW 40) / Dan Eschenasy, P.E., S.E. / Dan Koch Jr. / Daniel A. Cuoco, P.E / Daniele Veneziano, P.E. / David Biggs, P.E., S.E. / David Cooper, P.E. / David Davidowitz, ConEd / David Hoy, S.E. / David J. Hammond, P.E., S.E. / David Leach, P.E. / David M. Parks, ME / David Newland Sc.D., FREng. / David Peraza, P.E., S.E. / David Ranlet / David Schomburg / David Sharp, S.E. / David T. Biggs, P.E. / Dean Koutsoubis, S.E. / Dean Tills, P.E. / Delbert Boring, P.E. / Dennis Clark (IST) / Dennis Dirkmaat, Ph.D. / Dennis Mileti, Ph.D. / Dennis Smith / Dharam Pal, M.E. / Dick Posthauer, S.E. / Donald Friedman, P.E. / Donald O. Dusenberry, P.E. / Ed Jacoby Jr., NYSEMO / Ed McGinley, P.E. / Ed Plaugher, Chief, Arlington FD / Edward A. Flynn, Arlington Police Chief / Edward M. DePaola, P.E., S.E. / Edward Stinnette, Chief, FCFD / Eiji Fukuzawa / Fahim Sadek, P.E., S.E. / Farid Alfawakhiri, Ph.D., P.E., S.E. / Frank Vallebuono, FDNY Battalion Chief / Anthony Varriale, FDNY Captain / Frank Cruthers, FDNY Chief / Frank Fellini, FDNY Chief / Joseph Callan, FDNY Chief / Daniel Nigro, FDNY Chief of Operations / Nick Visconti, FDNY Deputy Chief / Peter Hayden, FDNY Deputy Chief / Sam Melisi, FDNY Firefighter / Forman Williams, Ph.D., P.E. / Francis J. Lombardi, P.E. / Frank Gayle, Sc.D. / Frank Greening, Ph.D. / Fred E.C. Culick, Ph.D., S.B. / Fred Endrikat, FEMA USAR / Gary Keith, V.P. NFPA / Gary Steficek, S.E. / Gary Tokle, Asst. VP, NFPA / George Tamaro, P.E., S.E. / Gerald Haynes, P.E. / Gerald Wellman US&R Structural Specialist / Glenn Corbett / Graeme Flint / Guy Colonna, P.E., NFPA / Guylene Proulx, Ph.D. / H.S. Lew, P.E., S.E. / Hal Bidlack, Lt. Col. USAF (ret.), Ph.D. / Harold E. Nelson, P.E., FSFP.E. / Harry Martin, AISC / Howard R. Baum, Ph.D., M.E. / J. David Frost, Ph.D., P.E. / J. David McColskey / Jack Brown Deputy Chief Loudoun County (Va.) Fire Rescue Department / Jack Messagno, WTC project Manager (Tully) / Jack Spencer, P.E. / Jacques Grandino, P.E., S.E. / James A. Rossberg, P.E. / James Chastain US&R Structural Specialist / James H. Fahey, S.E. / James J. Cohen, P.E., S.E. / James J. Hauck, P.E., S.E. / James Lord, FSFP.E. / James Milke, Ph.D., P.E. / James Quintiere, Ph.D., P.E. / Jan Szumanski, IUOE / Jason Averill, FSFP.E. / Jeff Rienbold, NPS / Jeffrey Hartman, S.E. / Jim Abadie, Bovis / Joel Meyerowitz / John Fisher, Ph.D., P.E., / John Flynn, P.E. / John Gross, Ph.D., P.E. / John Hodgens, FDNY (ret.) / John J. Healey, Ph.D., P.E. / John J. Zils, P.E., S.E. / John L. Gross, Ph.D., P.E. / John Lekstutis, P.E. / John M. Hanson, Ph.D, P.E. / John McArdle NYPD/ESU (DTC) / John Moran, NYPD/ESU (NTC) / John O'Connell, Chief FDNY / John Odermatt (NYC OEM) / John Ruddy, P.E., S.E. / John Ryan, PAPD / John W. Fisher, P.E. / Jon Magnusson, P.E., S.E. / Jonathan Barnett, Ph.D / Joo-Eun Lee P.E., S.E. / Jos=C3=A9 Torero, Ph.D. / Joseph C. Gehlen, P.E., S.E. / Joseph Englot, P.E., S.E. / Jozef Van Dyck, P.E. / Juan Paulo Morla, S.E. / Karen Damianick, P.E. / Karl Koch III / Karl Koch IV / Kaspar Willam, P.E., S.E. / Keith A. Seffen, MA, Ph.D. / Ken Hays / Kenneth Holden / Kent Watts / Kevin Brennan, OSHA / Kevin Malley, FDNY (ret.) / Kevin Terry, S.E. / Kurt Gustafson, P.E., S.E. / Larry Keating (IW 40) / Lawrence C. Bank, Ph.D., P.E. / Lawrence Griffis, P.E. / Lawrence Novak, P.E., S.E. / Leo J. Titus, P.E. / Leonard M. Joseph, P.E. / Leslie E. Robertson, P.E., S.E. / Long T. Phan, Ph.D., P.E. / Lou Mendes, P.E., S.E. / Louis Errichiello, S.E. / Manny Velivasakis, P.E. / Mark Blair / Mark Kucera, USACE / Mark Pierepiekarz, P.E., S.E. / Mark Stahl / Mark Tamaro, P.E / Mark Volpe, IW 40 / Marty Corcoran / Matthew G. Yerkey, P.E., S.E. / Matthew McCormick, NTSB / Melbourne Garber, P.E., S.E. / Merle E. Brander, P.E. / Mete A. Sozen, Ph.D., S.E. / Michael Burton, P.E. / Michael Dallal / Michael Fagel, Ph.D., CEM / Michael Hessheimer, S.E. / Michael K. Hynes, Ed.D., ATP, CFI / Michael Tylk, P.E., S.E. / Michel Bruneau, Ph.D., P.E., S.E. / Mike Banker, FDNY Capt. (SOC) / Mike Marscio, P.E. / Miroslav Sulc,, P.E., S.E. / Mohammed Ettouney / Mohammed R. Karim, Ph.D. / Morgan Hurley, FSFP.E. / Nestor Iwankiw, Ph.D., P.E. / Nick Carcich / Norman Groner, Ph.D. / Pablo Lopez, P.E., S.E. / Patrick McNierney, P.E., S.E. / Paul A. Bosela, Ph.D., P.E. / Paul F. Mlakar, Ph.D., P.E. / Paul Sledzik / Paul Tertell, P.E. / Pete Bakersky / Peter Chipchase, S.E. / Peter Rinaldi, P.E. / Phillip Murray, P.E. / Pia Hoffman / Rajani Nair, S.E. / Ralph Castillo, P.E., F.P.E. / Ralph D'Apuzo, P.E. / Ramon Gilsanz, P.E., S.E / Randy Lawson / Raul Maestre, P.E., S.E. / Raymond F. Messer, P.E. / Raymond H.R. Tide, P.E., S.E. / Reidar Bjorhovde, Ph.D., P.E / Richard Bukowski P.E., FSFP.E. / Richard G. Gewain, P.E., S.E. / Richard Gann, Ph.D. / Richard Garlock, P.E., S.E. / Richard J. Fields, Ph.D. / Richard Kahler US&R Structural Specialist / Robert Athanas (thermal imaging specialist, FDNY) / Robert C. Sinn, P.E., S.E. / Robert Clarke, S.E. / Robert F. Duval (NFPA) / Robert Frances US&R Structural Specialist / Robert J. McNamara, P.E., S.E. / Robert L. Parker, Ph.D. / Robert Ratay, Ph.D., P.E., S.E. / Robert Shaler, M.D. / Robert Smilowitz, Ph.D., P.E / Robert Solomon, P.E. / Robert Wills, AISC / Ron Dokell, president, Demolition Consultants / Ronald Greeley, Ph.D. / Ronald Hamburger, P.E., S.E. / Ronald J. LaMere, P.E. / Ronald Rehm, Ph.D. / Ronald Spadafora, FDNY D.A.C / Ruben M. Zallen, P.E. / Russell "Rusty" Dodge Jr, Asst. Chief, Fort Belvoir FD / Ryan Mackey / S. Shyam Sunder, P.E., S.E. / Saroj Bhol, P.E. / Saw-Teen See, P.E. / Shankar Nair. P.E., S.E. / Shawn Kelly, Arlington County Fire Marshal / Skip Aldous, Lt. Col., U.S. Air Force (Ret.) / Socrates Ioannides, P.E., S.E. / Sonny Scarff / Stan Murphy, P.E. / Stephen Cauffman / Stephen W. Banovic, Ph.D. / Steve Douglass, image analysis consultant / Steve Rasweiler, FDNY B.C. (SOC) / Steve Spall, P.E., S.E. / Stuart Foltz, P.E. / Terry Sullivan, Bovis / Theodore Galambos, P.E. / Theodore Krauthammer, Ph.D., P.E. / Therese P. McAllister, Ph.D., P.E. / Thomas A. Siewert / Thomas Eagar, Sc.D., P.E. / Thomas Hawkins Jr, Chief, AFD / Thomas R. Edwards, Ph.D / Thomas Schlafly, AISC / Timothy Foecke, Ph.D. / Todd Curtis, Ph.D / Todd Ude, P.E., S.E. / Tom Scarangello, P.E. / Tom Stanton (IST) / Tomasz Wierzbicki / Tony Beale, P.E. / Valentine Junker / Van Romero, Ph.D. / Venkatesh Kodur, Ph.D., P.E. / Victor Hare, P.E. / Victoria Arbitrio, P.E. / Vincent Dunn, FDNY (ret.) / W. Gene Corley, Ph.D., P.E., S.E. / W. Lee Evey / Wallace Miller / William Baker, P.E., S.E / William E. Luecke, Ph.D. / William Grosshandler, Ph.D., ME / William Howell, P.E., S.E. / William Koplitz photo desk manager, FEMA / William McGuire, P.E. / Willie Quinlan, IW / Won-Young Kim, Ph.D / Yates Gladwell pilot, VF Corp. / Yukihiro Omika / Zdenek Bazant, Ph.D., S.E. /</div>ACE Bermuda Insurance / AEMC Construction / AIG Insurance / Air Traffic Control System Command Center in Washington / Alexandria VA Fire & Rescue / Allianz Global Risks / American Airlines / American Concrete Institute / American Institute of Steel Construction / American Red Cross / Applied Biosystems Inc. / Applied Research Associates / Arlington County Emergency Medical Services / Arlington County Fire Department / Arlington County Sheriff's Department / Arlington VA Police Department / Armed Forces Institute of Pathology / Armed Forces Institute of Technology Federal Advisory Committee / ARUP USA / Atlantic Heydt Inc. / Bechtel / Berlin Fire Department / Big Apple Wrecking / Blanford & Co. / Bode Technology Group / Bovis Inc. / Building and Construction Trades Council / Bureau of Alcohol Tobacco and Firearms / C-130H crew in D.C. & Shanksville / Cal Berkeley Engineering Dept. / California Incident Management Team / Carter Burgess Engineering / Celera Genomics / Centers for Disease Control / Central City Fire Department / Central Intelligence Agency / Cleveland Airport control tower / Columbia University Department of Civil Engineering and Engineering Mechanics / Congressional Joint Intelligence Committee / Consolidated Edison Company / Construction Technologies Laboratory / Controlled Demolitions Inc. / Council on Tall Buildings and Urban Habitat / Counterterrorism and Security Group / CTL Engineering / D.H. Griffin Wrecking Co. Inc. / DeSimone Consulting Engineers / Dewhurst MacFarlane &Partners / DiSalvo Ericson Engineering / District of Columbia Fire & Rescue / DOD Honor Guard, Pentagon / D'Onofrio Construction / E-4B National Airborne Operations Center crews / Edwards and Kelcey Engineering / Engineering Systems, Inc. / Environmental protection Agency / Exponent Failure Analysis Associates / EYP Mission CriticalFacilities / Fairfax County Fire & Rescue / Falcon 20 crew in PA / Family members who received calls from victims on the planes / FBI Evidence Recovery Teams / Federal Aviation Administration / Federal Bureau of Investigation / Federal Emergency Management Agency / Federal Insurance Co. / FEMA 68-Person Urban Search and Rescue Teams: Arizona Task Force 1, California Task Force 1, California Task Force 3, California Task Force 7, Colorado Task Force 1, Fairfax Task Force 1, Florida Task Force 1, Florida Task Force 2, Maryland Task Force 1, Massachusetts Task Force 1, Metro Dade/Miami, Nebraska Task Force 1, New Mexico Task Force 1, New York Task Force 1, Pennsylvania Task Force 1, Tennessee Task Force 1, Texas Task Force 1, Utah Task Force 1, Virginia Task Force 1, Virginia Task Force 2, Washington Task Force 1 / FEMA Disaster Field Office / FEMA Emergency Response Team / FEMA Urban Search and Rescue Incident Support Team-Advanced 3 / Fire Department of New York / Fort Myer Fire Department / French Urban Search & Rescue Task Force / Friedens Volunteer Fire Department / Gateway Demolition / Gene Code Forensics / Georgia Tech Engineering Dept. / Gilsanz Murray Steficek LLP / GMAC Financing / Goldstein Associates Consulting Engineers / Guy Nordenson Associates / HAKS Engineers / Hampton-Clarke Inc. / HHS National Medical Response Team / HLW International Engineering / Hooversville Rescue Squad. / Hooversville Volunteer Fire Department / Hoy Structural Services / Hughes Associates, Inc / Hugo Neu Schnitzer East / hundreds of ironworkers, some of whom built the WTC / Hundreds of New York City Police Department Detectives / Industrial Risk Insurers / Institute for Civil Infrastructure Systems / International Association of Fire Chiefs / International Union of Operating Engineers Locals 14 & 15 / J.R. Harris & Company / Johnstown-Cambria County Airport Authority / Karl Koch Steel Consulting Inc. / KCE Structural Engineers / Koch Skanska / Koutsoubis, Alonso Associates / Laboratory Corp. of America / Lamont-Doherty Earth Observatory / Leslie E. Robertson Associates / LIRo Engineering / Listie Volunteer Fire Company / Lockwood Consulting / M.G. McLaren Engineering / Masonry Society / Mazzocchi Wrecking Inc. / Metal Management Northeast / Metropolitan Airport Authority Fire Unit / Miami-Dade Urban Search & Rescue / Military District of Washington Search & Rescue Team / Montgomery County Fire & Rescue / Mueser Rutledge Consulting Engineers / Murray Engineering / Myriad Genetic Laboratories Inc. / National Center for Biotechnology Informatics / National Commission on Terrorist Attacks Upon the United States / National Council of Structural Engineers Associations / National Disaster Medical System / National Emergency Numbering Association / National Fire Protection Association / National Guard in D.C., New York, and Pennsylvania / National Institute of Standards and Technology (NIST) / National Institutes of Health Human Genome Research Institute / National Law Enforcement and Security Institute / National Military Command Center / National Reconnaissance Office / National Response Center / National Science Foundation Division of Civil and Mechanical Systems / National Security Agency / National Transportation Safety Board / National Wrecking / Natural Hazards Research and Applications Information Center / New Jersey State Police / New York City Department of Buildings WTC Task Force / New York City Department of Design and Construction / New York City Department of Environmental Protection / New York City Office of Emergency Management / New York City Office of the Chief Medical Examiner / New York City Police Department Aviation Unit / New York City Police Department Emergency Services Unit / New York Daily News / New York Flight Control Center / New York Newsday / New York Port Authority Construction Board / New York Port Authority Police / New York State Emergency Management Office / New York State Police Forensic Services / New York Times / North American Aerospace Defense Command / Northeast Air Defense Sector Commanders and crew / Numerous bomb-sniffing dogs / Numerous Forensic Anthropologists / Numerous Forensic Dentists / Numerous Forensic Pathologists / Numerous Forensic Radiologists / NuStats / Occupational Safety and Health Administration / Office of Emergency Preparedness / Office of Strategic Services / Orchid Cellmark / Parsons Brinckerhoff Engineering / Pennsylvania Department of Environmental Protection / Pennsylvania Department of Health and Human Services / Pennsylvania Region 13 Metropolitan Medical Response Group / Pennsylvania State Funeral Directors Association / Pennsylvania State Police / Pentagon Defense Protective Service / Pentagon Helicopter Crash Response Team / Pentagon Medical Staff / Pentagon Renovation Team / Phillips & Jordan, Inc. / Port of New York and New Jersey Authority / Pro-Safety Services / Protec / Public Entity Risk Institute / Purdue University Engineering Dept. / Robert Silman Associates Structural Engineers / Rolf Jensen & Associates, Inc / Rosenwasser/Grossman Consulting Engineers / Royal SunAlliance/Royal Indemnity / SACE Prime Power Assessment Teams / SACE Structural Safety Engineers and Debris Planning and Response Teams / Salvation Army Disaster Services / several EPA Hazmat Teams / several FBI Hazmat Teams / several Federal Disaster Medical Assistance Teams / several Federal Disaster Mortuary (DMORT) Teams / Severud Associates Consulting Engineers / Shanksville Volunteer Fire Company / Silverstein Properties / Simpson Gumpertz & Heger Engineers / Skidmore, Owings & Merrill LLP / Skilling Ward Magnusson Barkshire / Society of Fire Protection Engineers / Somerset Ambulance Association / Somerset County Coroner's Office / Somerset County Emergency Management Agency / Somerset Volunteer Fire Department / St. Paul/Travelers Insurance / State of Pennsylvania Emergency Management Agency / Stoystown Volunteer Fire Company / Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE) / Structural Engineers Association of New York / Superstructures Engineering / Swiss Re America Insurance / Telephone operators who took calls from passengers in the hijacked planes / Teng & Associates / Thornton-Tomasetti Group, Inc. / TIG Insurance / Tokio Marine & Fire / Transportation Safety Administration / Tully Construction / Twin City Fire Insurance / Tylk Gustafson Reckers Wilson Andrews Engineering / U.S. Army Corps of Engineers / Underwriters Laboratories / Union Wrecking / United Airlines / United States Air National Guard / United States Fire Administration / United States Secret Service / United Steelworkers of America / University of Sheffield Fire Engineering Research / US Army Reserves of Virginia Beach Fairfax County and Montgomery County / US Army’s Communications-Electronics Command / US Department of Defense / US Department of Justice / US Department of State / Virginia Beach Fire Department / Virginia Department of Emergency Management / Virginia State Police / Vollmer Associates Engineers / Washington Post / Weeks Marine / Weidlinger Associates / Weiskopf & Pickworth Engineering / Westmoreland County Emergency Management Agency / Whitney Contracting / Willis Group Holdings / WJE Structural Engineers / Worcester Polytechnic Institute / World Trade Center security staff / XL Insurance / Yonkers Contracting / York International / Zurich Financial / Zurich Re Risk Engineering
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