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Thursday, March 7, 2013

Watch the Movie, Sod the Facts


I pressed enter and after an ominous few seconds a notice popped up saying 'post failed, try again later'. Was the content way too long? Is there some kind of DRM embedded? Does Facebook censor any in depth discussion around 911? Are little red lights going off in a low slung building west of the Potomac River? Or, am I a victim of exactly what this blog posting is about.
Title: Watch the Movie, Sod the Facts.
I have always been fascinated by the urge that many people have to buy into conspiracy theories with a zeal that is hyper religious in nature, blind to alternative and inherently lazy. As a documentary maker I have also been interested in how production values in a movie can be mated with dubious pseudo-science and construct an emotional convincing and seemingly true narrative.
This is also a sideways look at the nature of Facebook, the realms that we can enter as parallel engagements with people we know in real life.
So it went with what started as an innocent call to sign a petition against the regulation of so called natural medicinal products by the EU. People on social media love signing petitions and there are plenty around. With the flick of a finger we can save the rain forest or, as in this case, confirm our belief in the evil nature of Big Pharma and corporate capitalism. However, if we pause and consider the actual dictates and purposes of the regulatory laws we should understand that (1) it does not affect my right to pick comfrey tea in my garden and (2) it protects me against the many dangers inherent in untested medication sold by equally profit-based entrepeneurs.
But this post is less about this than where it led to. Read on! This is all about Science V Irrational Belief.

Reprinted from Facebook:
Helge Janssen shared a link
avaaz.org
They take away herbal medicines, next minute they will be banning fruit. Sign the petition!
secure.avaaz.org
An EU directive has banned many herbal medicines, denying us safe remedies and feeding the profits of big pharma. Let's raise a massive outcry to push the Commission to fix the Directive. Let's get to 1 million voices to save herbal medicine. Add your name here:
Like ·  · 
  • 4 people like this.
  • Miriam Erasmus Thanks for the awareness, Helge, I have signed and shared 
  • John Bate Hahaha...they already tried that one Helge when, during the early '90s, the CRACKPOTS that make up the European Commission attempted to impose regulation and legislation on the acceptable level of conformity of the curvature of bananas that would make them permissible for sale within the EU...seriously....
  • Sujata Jane Metcalfe this has been going on for YEARS. 
  • Andre J Smith The sensible thing is NOT to sign this. For some bizarre reason, the same people who want to be sure that the food we buy daily is safe don't want the same standards to apply to the medicine they buy over the counter. Sadly, it is often the same people who believe that 911 was an inside job and the moonlanding was a setup. To quote: New EU rules came into force at the weekend banning hundreds of herbal remedies. The laws are aimed at protecting consumers from potentially damaging "traditional" medicines.

    Under the directive, herbal medicines will now have to be registered. Products must meet safety, quality and manufacturing standards, and come with information outlining possible side-effects.

    Herbal practitioners and manufacturers say they fear the new rules could force them out of business.he agency said it hoped to promote a more cautious approach to the use of herbal medicines after a study found that 58% of respondents believed these products were safe because they are "natural". In fact, herbal remedies can have harmful side-effects. St John's Wort can stop the contraceptive pill working, while ginkgo and ginseng are known to interfere with the blood-thinning drug warfarin. And in February the MHRA issued a warning about the herbal weight loss product Herbal Flos Lonicerae (Herbal Xenicol) Natural Weight Loss Formula, after tests showed it contained more than twice the prescribed dose of a banned substance.
  • Andre J Smith The law was sparked by cases of toxicity from over-the-counter herbal products. For example, aristolochia is a toxic plant species that is either used deliberately or can be accidentally or carelessly substituted for other plant species. It is known to cause kidney damage – even leading to kidney failure is some cases. Another herb, kava, has been linked to liver damage.

    The new EU law, which went into effect May 1, 2011, will require herbal products to be licensed, or prescribed by a licensed herbal practitioner. In order to be licensed evidence for safety of the product must be presented. It is estimated that it will cost between 80,000 and 120,000 British pounds to get an individual herbal product licensed.

    I find it interesting, and completely predictable, that sellers of herbal products are wailing that this is all a conspiracy by “Big Pharma” to crush the little guy and steal all the herbal profits for themselves, or to ban herbal products to protect their drug profits. But this is a straw man. The real question here is the balance between marketing freedom and quality control – but those who want to defend their right to sell herbs don’t want to discuss the real issues, apparently.
  • Helge Janssen Well actually it is perfectly obvious that 911 WAS an inside job. No building ON EARTH collapses like that 'naturally'. AND WHERE is ANY evidence of a PLANE crashing inot the Pentagon? And WHERE is Obama Bin? "Suddenly" buried at sea with a spurious 'photo' of him all blown up in the 'bunker'. Hahahahah! The products that you mention earlier such as ginko and St. Johns Wort are well known in the areas that you mention AND if I am not mistaken are LISTED on product information...this is no SECRET. So then paying £80 - 120K to get a product licensed is A HUGE hurdle and WILL ultimately force them out of business. People will then be forced to go via medical practitioners to obtain (and hence pay much higher prices) stuff they have been using for years without any problems. You also mention a 'banned substance' but do not mention what the banned substance is. And in fact the practitioners DO steal all the products for themselves....not 'intentionally' of course, but for the simple reason that the natural product has been 'institutionalised' out of existence. I have direct experience of it.
  • Andre J Smith Thanks for the reply. It is a worthwhile discussion to have so I will consider each point and respond.
  • Andre J Smith Meantime, a few clarifiers. I am presuming you regard the WTC 1,2 and 7 collapses as a result of controlled demolition? And...the big hole in the Pentagon wall was from a missile or a local explosive device?
  • Helge Janssen no presumption involved...
  • Andre J Smith You must hold some alternative theory and/or facts as to how the damage was caused. Either that or it was all photoshopped? What areas of NIST 1/1a do you contest?
  • Helge Janssen PHOTOSHOPPED? Read points above. Have you not watched the detailed movie, interviews: loose change?
  • Andre J Smith Yes, I have faithfully watched as many of the 911 conspiracy films as I can get my broadband around. These include 'In Plane Sight', 'Press for Truth', ' Loose Change', 'Zero', 'September Clues' and 'Truth and Lies'. It's telling that the director of ...See More
    ‎911research.wtc7.net
    My views on 911 are as dark and conspiratorial as most.  I believe that the Nati...See more
  • Helge Janssen Lol......'buildings in the real world collapse after 'airplaines' fly into them' hehehe hehehehe. from one fiction to another. next you're gonna tell me that father xmas exists in the 'real world'...hehehehe because there are pictures of him...hehehehe...See More
  • Andre J Smith I suggest you quote a few of the many pieces of the report that you find to be nonsense. Then we can interrogate the technical veracity of your query. A good staring point is to consider the absolute evidence that the collapse of the buildings starte...See More
  • Helge Janssen A building built with ammmmmerrrikkkkaannn might and steel and technology and what the fk else COLLAPSES after a mere 30 minutes? And in under 10 seconds? That's the tallest story I have ever heard....forgive the pun. And the phrase 'absolute evidence'...See More
  • Andre J Smith Thanks for the response. It was more or less what I was looking for. When I first sat down and read the almost 17000 pages of reports that were the result of an intense and complex investigation into the 911 disaster, I was humbled and realized that the search for Truth is never as easy as reading the Internet and watching a few documentaries. You may read what is below or you may choose to ignore it. If you do, it will empower you to make a more considered decision around what you feel may have been the back story to 911. Should you or any readers of this posting have any further interest I have the complete collection of reports and almost all the media made around 911. Or you can research and download it yourself, which is what I did. It is a fascinating journey that ultimately talks to us of the battle within us to leave our primitive instinctive past and embrace modernity.

    Should you choose not to read this, I will accept that you are happy to engage in the 911 issue at a shallow level and accept that we have different priorities around the search for Truth and Meaning.

    Any discussion around the veracity of claims around what happened on September 11th 2001 must be subject to a proper level of logic.

    We have many choices about how to approach this. However, as with all scientific investigation, the challenge is to remove the emotional filters and apply the best constituted research methods available.

    With the 911 debate there have been two extremely diverse approaches.

    1) The collapse of the WTC buildings 1,2 and 7 resulted from a controlled demolition as part of a secret plot by forces within the USA. I read all about it on the Internet and watched a film that convinced me. My reaction to any official report is hehehehehe.
    OR.....
    2) An official Investigation by The US National Institute of Standards and Technology, assisted by independent specialists in key technical areas is commissioned. 

    - Over 200 people partake in the investigation.
    - Tens of thousands of pages of documents are collected and reviewed.
    - Interviews are conducted with more than 1000 people intimately connected with the event of 911 or the design, maintenance and construction of the World Trade Centre.
    - 236 pieces of steel from the wreckage are analyzed, tested, and the results fed into computer simulations of the sequence of events that happened from the instant of the first plane hitting to the collapse of the towers.
    - The co-operative investigation involved the following organizations: The Port Authority of New York, Silverstein Properties (WTC administrators), The City of New York, Makers of the building components, WTC Insurers, Building Tenants, Aircraft Manufacturers,, Airlines, The Public, Families of Victims and The Media.
    - 14000 video clips and photographs from 185 photographers at least.
    - Accurate modeling of the expected performance of the buildings under normal conditions and under heightened stresses as per the disaster mitigation designs that were built in.
    - Because of the unusual nature of the source of the damage to the structures, new modeling soft and hardware was developed to simulate all the steps of the event, viz: (1) aircraft Impact (2) Primary Effects of aviation fuel fed fire (3) Evolution of multi-story fires (4) weakening of structural elements from the fires (5) Progression of structural failure leading to collapse of towers.

    As a result of this investigation, the following documents were published, available for anyone to read.

    It would seem a good idea to read them before buying into an alternative explanation that 'you read on the internet'.

    However as there are 55 reports averaging 300 pages each, you will probably not read them. So, I have provided a short summary of one of the 55 reports, being that which deals with the impact damage to the buildings 1 and 2 by the aeroplane and how this probably led to the subsequent collapse. I have also added a list of those whose expertise and time was spent on this research, so that future buildings may be designed in a way to reduce the risk of similar events.

    Final Reports released in September 2005:
    NIST NCSTAR 1: 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 Tower
    NIST NCSTAR 1-1: Design, Construction, and Maintenance of Structural and Life Safety Systems
    NIST NCSTAR 1-1A: Design and Construction of Structural Systems
    NIST NCSTAR 1-1A appendixes A-B
    NIST NCSTAR 1-1A appendixes C-G
    NIST NCSTAR 1-1B: Comparison of Building Code Structural Requirements
    NIST NCSTAR 1-1C: Maintenance and Modifications to Structural Systems
    NIST NCSTAR 1-1C appendixes
    NIST NCSTAR 1-1D: Fire Protection and Life Safety Provisions Applied to the Design and Construction of World Trade Center 1, 2, and 7 and Post-Construction Provisions Applied after Occupancy
    NIST NCSTAR 1-1E: Comparison of Codes, Standards, and Practices in Use at the Time of the Design and Construction of World Trade Center 1, 2, and 7
    NIST NCSTAR 1-1F: Comparison of the 1968 and Current (2003) New York City Building Code Provisions
    NIST NCSTAR 1-1G: Amendments to the Fire Protection and Life Safety Provisions of the New York City Building Code by Local Laws Adopted while World Trade Center 1, 2, and 7 Were in Use
    NIST NCSTAR 1-1H: Post-Construction Modification to Fire Protection and Life Safety Systems of the World Trade Center Towers
    NIST NCSTAR 1-1I: Post-Construction Modifications to Fire Protection, Life Safety, and Structural Systems of World Trade Center 7
    NIST NCSTAR 1-1J: Design, Installation, and Operation of Fuel Systems for Emergency Power in World Trade Center 7
    NIST NCSTAR 1-2: Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers
    NIST NCSTAR 1-2A: Reference Structural Models and Baseline Performance Analysis of the World Trade Center Towers
    NIST NCSTAR 1-2B: Analysis of Aircraft Impacts into the World Trade Center Towers (Chapters 1-8)
    NIST NCSTAR 1-2B: Chapters 9-11
    NIST NCSTAR 1-2B: appendixes
    NIST NCSTAR 1-3: Mechanical and Metallurgical Analysis of Structural Steel
    NIST NCSTAR 1-3A: Contemporaneous Structural Steel Specifications
    NIST NCSTAR 1-3B: Steel Inventory and Identification
    NIST NCSTAR 1-3C: Damage and Failure Modes of Structural Steel Components 
    NIST NCSTAR 1-3C: appendixes
    NIST NCSTAR 1-3D: Mechanical Properties of Structural Steels
    NIST NCSTAR 1-3E: Physical Properties of Structural Steels
    NIST NCSTAR 1-4: Active Fire Protection Systems
    NIST NCSTAR 1-4A: Post-Construction Fires prior to September 11, 2001
    NIST NCSTAR 1-4B: Fire Suppression Systems
    NIST NCSTAR 1-4C: Fire Alarm Systems
    NIST NCSTAR 1-4D: Smoke Management Systems
    NIST NCSTAR 1-5: Reconstruction of the Fires in the World Trade Center Towers
    NIST NCSTAR 1-5A: Visual Evidence, Damage Estimates, and Timeline Analysis (Chapters 1-8)
    NIST NCSTAR 1-5A: Chapters 9-appendix C
    NIST NCSTAR 1-5A: appendixes D-G
    NIST NCSTAR 1-5A: appendixes H-M
    NIST NCSTAR 1-5B: Experiments and Modeling of Structural Steel Elements Exposed to Fire
    NIST NCSTAR 1-5C: Fire Tests of Single Office Workstations
    NIST NCSTAR 1-5D: Reaction of Ceiling Tile Systems to Shocks
    NIST NCSTAR 1-5E: Experiments and Modeling of Multiple Workstations Burning in a Compartment
    NIST NCSTAR 1-5F: Computer Simulation of the Fires in the World Trade Center Towers
    NIST NCSTAR 1-5G: Fire Structure Interface and Thermal Response of the World Trade Center Towers
    NIST NCSTAR 1-6: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers
    NIST NCSTAR 1-6A: Passive Fire Protection
    NIST NCSTAR 1-6B: Fire Resistance Tests of the Floor Truss Systems
    NIST NCSTAR 1-6C: Component, Connection, and Subsystem Structural Analysis
    NIST NCSTAR 1-6D: Global Structural Analysis of the Response of the World Trade Center Towers to Impact Damage and Fire
    NIST NCSTAR 1-7: Occupant Behavior, Egress, and Emergency Communication
    NIST NCSTAR 1-7A: Analysis of Published Accounts of the World Trade Center Evacuation
    NIST NCSTAR 1-7B: Technical Documentation for Survey Administration: Questionnaires, Interviews, and Focus Groups
    NIST NCSTAR 1-8: The Emergency Response Operations
    NIST NCSTAR 1-8: Appendixes A-L 

    Final Reports released in November 2008:
    NIST NCSTAR 1A: Final Report on the Collapse of World Trade Center Building 7 *
    NIST NCSTAR 1-9: Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7, Volume 1 and 2 *
    NIST NCSTAR 1-9A: Global Structural Analysis of the Response of World Trade Center Building 7 to Fires and Debris Impact Damage *

    I have summarized just one of the above in order to give you a sense of the methodologies and attention to detail. Included is the contents list and a list of those who worked on this one of 55 reports.

    NIST NCSTAR 1-2 

    Federal Building and Fire Safety Investigation of the 
    World Trade Center Disaster 
    NIST NCSTAR 1-2 
    September 2005 
    Baseline Structural Performance and 
    Aircraft Impact Damage Analysis of 
    the World Trade Center Towers 

    Fahim Sadek 
    National Institute of Standards and Technology • Technology Administration • U.S. Department of Commerce 
    U.S. Department of Commerce 
    Carlos M. Gutierrez, Secretary 
    Technology Administration 
    Michelle O'Neill, Acting Under Secretary for Technology 
    National Institute of Standards and Technology 
    William Jeffrey, Director 

    Abstract 

    The baseline structural performance and aircraft impact damage analysis of the National Institute of 
    Standards and Technology (NIST) Investigation of the World Trade Center (WTC) disaster had two 
    primary tasks: (1) to develop reference structural models of the WTC towers and use these models to 
    establish the baseline performance of each of the towers under gravity and wind loads, and (2) to estimate 
    the damage to the towers due to aircraft impacts and establish the initial conditions for the fire dynamics 
    modeling and the thermal-structural response and collapse initiation analysis. This report provides the 
    technical approach, methodology, and results related to both tasks. 

    For the first task, the baseline performance of the WTC towers under gravity and wind loads was 
    estabhshed in order to assess the towers' abihty to withstand those loads safely and to evaluate the reserve 
    capacity of the towers to withstand unanticipated events. The baseline performance study provides a 
    measure of the behavior of the towers under design loading conditions, specifically: (1) total and inter- 
    story drift (the sway of the building under design wind loads), (2) floor deflections under gravity loads, 
    (3) the stress demand-to-capacity ratio for primary structural components of the towers such as exterior 
    walls, core columns, and floor framing, (4) performance of exterior walls under wind loading, including 
    distribution of axial stresses and presence of tensile forces, (5) performance of connections between 
    exterior columns, and (6) resistance of the towers to shear sliding and overturning at the foundation level. 

    Wind loads were a governing factor in the design of the structural components that made up the frame- 
    tube steel framing system. Wind load capacity was also a key factor in determining the overall strength 
    of the towers and was important in determining not only the ability of the towers to withstand winds but 
    also the reserve capacity of the towers to withstand unanticipated events such as major fire or impact 
    damage. Accurate estimation of the wind load on tall buildings is a challenging task, given that wind 
    engineering is still an evolving technology. For example, estimates of the wind- induced response 
    presented in two recent independent studies of the WTC towers differed from each other by about 
    40 percent. In this study, NIST developed refined estimates of wind effects by critically assessing 
    information obtained from the Cermak Peterka Peterson, Inc. (CPP) and Rowan Williams Davis and 
    Irwin, Inc. (RWDI) reports and by bringing to bear state-of-the-art considerations. Furthermore, the 
    available prescriptive codes specify wind loads on tall buildings that are significantly lower than wind 
    tunnel-based loads. This case study provided an opportunity to assess effectively current design practices 
    and various code provisions on wind loads. 

    For the purpose of establishing the baseline performance of the towers, various wind loads were 
    considered in this study, including wind loads used in the original WTC design, wind loads based on two 
    recent wind tunnel studies conducted in 2002 by CPP and RWDI for insurance litigation concerning the 
    towers, and refined wind load estimates developed by NIST. 

    In order to develop the reference models and conduct the baseline performance analyses, the following 
    steps were undertaken: 

    • Develop structural databases for the primary structural components of the WTC 1 and WTC 2 
    towers from the original computer printouts of the structural design documents. 

    NIST NCSTAR 1-2, WTC Investigation ill 
    Abstract 

    Develop reference structural analysis models that captured the intended behavior of each of 
    the two towers using the generated databases. These reference models were used to establish 
    the baseline performance of the towers and also served as a reference for more detailed 
    models for aircraft impact damage analysis and thermal-structural response and collapse 
    initiation analysis. The models included: (1) two global models (one for each tower) of the 
    major structural components and systems of the towers, and (2) floor models of a typical 
    truss-framed floor and a typical beam- framed floor. 

    Develop estimates of design gravity (dead and live loads) and wind loads on each of the two 
    towers for implementation into the reference structural models. The following three loading 
    cases were considered: 

    - Original WTC design loads case. Loads included dead and live loads as in original 
    WTC design, in conjunction with original WTC design wind loads. 

    - State-of-the-practice case. Loads included dead loads; current New York City Building 
    Code (NYCBC 2001) live loads; and wind loads from the RWDI wind tunnel study, 
    scaled in accordance with NYCBC 2001 wind speed. 

    - Refined NIST estimate case. Loads included dead loads; live loads from the American 
    Society of Civil Engineers (ASCE) 7-02 Standard (a national standard); and refined wind 
    loads developed by NIST. 

    • Perform structural analyses to establish the baseline performance of each of the two towers 
    under design gravity and wind loads. 

    For the second task related to aircraft impact, the aircraft impact damage to the exterior of the 
    WTC towers could be visibly identified from the video and photographic records. However, no visible 
    information could be obtained for the extent of damage to the interior of the towers, including the 
    structural system (floors and core columns), partition walls, and interior building contents. Such 
    information was needed for the subsequent fire dynamics simulations and post-impact structural analyses. 
    In addition, for the fire dynamics modeling, the dispersion of the jet fuel and the location of combustible 
    aircraft debris were required. The estimate of the extent of damage to the fireproofmg on the structural 
    steel in the towers due to impact was essential for the thermal and structural analyses. The aircraft impact 
    damage analyses were the primary tool by which most of the information on the tower damage could be 
    estimated. 

    The focus of the analysis was to analyze the aircraft impacts into each of the WTC towers to provide the 
    following: (1) estimates of probable damage to structural systems, including exterior walls, fioor 
    systems, and interior core columns; (2) estimates of the aircraft fuel dispersion during the impact; and (3) 
    estimates of debris damage to the building nonstructural contents, including partitions and workstations. 
    The results were to be used to estimate the damage to fireproofmg based on the predicted path of the 
    debris field inside the towers. This analysis thus estimated the condition of the two WTC towers 
    immediately following the aircraft impacts and established the initial conditions for the fire dynamics 
    modeling and the thermal-structural response and collapse initiation analysis. The impact analyses were 
    conducted at various levels of complexity including: (1) the component level, (2) the subassembly level, 
    and (3) the global level to estimate the probable damage to the towers due to aircraft impact. 

    iv NIST NCSTAR 1-2, WTC Investigation 
    Abstract 

    In order to estimate the aircraft impact damage to the WTC towers, the following steps were undertaken: 

    • Constitutive relationships were developed to describe the behavior and failure of the 
    materials under the dynamic impact conditions of the aircraft. These materials included the 
    various grades of steels used in the exterior walls, core columns, and floor trusses of the 
    towers, weldment metal, bolts, reinforced concrete, aircraft materials, and nonstructural 
    contents. 

    • Global impact models were developed for the towers and aircraft. The tower models 
    included the primary structural components of the towers in the impact zone, including 
    exterior walls, floor systems, core columns, and connections, along with nonstructural 
    building contents. A refined finite element mesh was used for the areas in the path of the 
    aircraft, and a coarser mesh was used elsewhere. The aircraft model included the aircraft 
    engines, wings, fuselage, the empennage, and landing gear, as well as nonstructural 
    components of the aircraft. The aircraft model also included a representation of the fuel, 
    using the smooth particle hydrodynamics approach. 

    • Component and subassembly impact analyses were conducted to support the development of 
    the global impact models. The primary objectives of these analyses were to (1) develop an 
    understanding of the interactive failure phenomenon of the aircraft and tower components, 
    and (2) develop the simulation techniques required for the global analysis of the aircraft 
    impacts into the WTC towers, including variations in mesh density and numerical tools for 
    modeling fluid-structure interaction for fuel impact and dispersion. The component and 
    subassembly analyses were used to determine model simplifications for reducing the overall 
    model size while maintaining fidelity in the global analyses. 

    • Initial conditions were estimated for the impact of the aircraft into the WTC towers. These 
    included the aircraft speed at impact, aircraft orientation and trajectory, and impact location 
    of the aircraft nose. The estimates also included the uncertainties associated with these 
    parameters. This step utilized the videos and photographs that captured the impact event and 
    subsequent damage to the exterior of the towers. 

    • Sensitivity analyses were conducted at the component and subassembly levels to assess the 
    effect of uncertainties on the level of damage to the towers due to impact and to determine the 
    most influential parameters that affect the damage estimates. The analyses were used to 
    reduce the number of parameters that would be varied in the global impact simulations. 

    • Analyses of aircraft impact into WTC 1 and WTC 2 were conducted using the global tower 
    and aircraft models. The analysis results included the estimation of the structural damage that 
    degraded their strength and the condition and position of nonstructural contents such as 
    partitions, workstations, aircraft fuel, and other debris that influenced the behavior of the 
    subsequent fires in the towers. The global analyses included, for each tower, a "base case" 
    based on reasonable initial estimates of all input parameters. They also provided a range of 
    damage estimates based on variations of the most influential parameters. This range included 
    more severe and less severe damage cases. 

    NISTNCSTAR 1-2, WTC Investigation 

    Abstract 
    • Approximate analyses were conducted to provide guidance to the global finite element 
    impact analyses. These included: (1) analysis of the overall aircraft impact forces and 
    assessment of the relative importance of the airframe strength and weight distribution, 
    (2) evaluation of the potential effects of the energy in the rotating engine components on the 
    calculated engine impact response, (3) influence of the static preloads in the towers on the 
    calculated impact damage and residual strength predictions, and (4) analysis of the load 
    characteristics required to damage core columns compared to the potential loading from 
    impact of aircraft components. 

    Keywords: Aircraft impact, finite element analysis, floor system, load, model, structural, truss, wind 
    loads. World Trade Center. 

    NIST NCSTAR 1-2, WTC Investigation 
    Table of Contents 

    Chapter 1 
    Introduction 1 
    1.1 Background 1 
    1.2 Reference Models and Baseline Performance Analysis 1 
    1.3 Aircraft Impact Damage Analysis 4 
    Chapter 2 
    Development of Reference Structural Models 9 
    2.1 Introduction 9 
    2.2 Development of Structural Databases 10 
    2.3 Global Models of the Towers 11 
    2.3.1 Exterior Wall Modeling 14 
    2.3.2 Core Columns Modeling 22 
    2.3.3 Hat Truss Modeling 22 
    2.3.4 Flexible and Rigid Floor Diaphragm Modeling 24 
    2.3.5 Boundary Conditions 26 
    2.4.1 Primary Trusses 31 
    2.4.2 Bridging Trusses 32 
    2.4.3 Concrete Slab and Metal Deck 33 
    2.4.4 Viscoelastic Dampers 34 
    2.4.5 Strap Anchors 34 
    2.5 Typical Beam-Framed Floor Model — Floor 75 of WTC 2 34 
    2.5.1 Composite Beams 35 

    NIST NCSTAR 1-2, WTC Investigation vii 
    Table of Contents 
    2.5.2 Horizontal Trusses 35 
    2.5.3 Concrete Slab and Metal Deck 36 
    2.5.4 Viscoelastic Dampers 36 
    2.6 Review of the Structural Databases and Reference Models of the Towers 37 
    2.6.1 Structural Databases 37 
    2.6.2 Reference Structural Models 37 
    2.7 Summary 38 
    2.8 References 39 

    Wind Loads on the WTC Towers 41 
    3.1 Introduction 41 
    3.2 Original WTC Design Wind Loads 43 
    3.3 State-of-the-Practice Wind Loads 44 
    3.4 Refined NIST Estimate of Wind Effects 45 
    3.4.1 Summary Comparison by Weidlinger Associates, Inc., of CPP and RWDI Estimates 46 
    3.4.2 Review of CPP Estimates 46 
    3.4.3 Review of RWDI Estimates 47 
    3.4.4 Comments by Third Party Reviewer (Skidmore, Owings & Merrill LLP - SOM) - 
    Appendix D 49 
    3.4.5 Summary 50 
    3.5 Comparisons of Wind Loads, Wind Speeds, and Practices 50 
    3.5.1 Wind Loads 50 
    3.5.2 Wind Speeds 53 
    3.5.3 Wind Engineering Practices Pertaining to Tall Buildings 55 
    3.6 References 57 

    Chapter 4 
    Baseline Performance of the WTC Towers 59 
    4.1 Introduction 59 
    4.2 Baseline Performance of the Global Models 59 
    4.2.1 Analysis Methodology 59 
    4.2.2 Total and Inter-Story Drift 62 
    4.2.3 Demand/Capacity Ratios 63 
    4.2.4 Exterior Columns Axial Loads and Stresses 77 
    4.2.5 Exterior Columns Splice Connection 84

    viii NIST NCSTAR 1-2, WTC Investigation 
    Table of Contents 
    4.2.6 Resistance of the Towers to Shear Shding and Overturning Moment 84 
    4.3 Basehne Performance of the Typical Floor Models 85 
    4.3.1 Typical Truss-Framed Floor 85 
    4.3.2 Typical Beam-Framed Floor 89 
    4.4 Review of Baseline Performance Analyses 90 
    4.5 Summary 90 
    4.6 References 92

    Chapter 5 
    Development of Tower and Aircraft Impact Models 93 
    5.1 Introduction 93 
    5.2 Development of Tower Impact Models 94 
    5.2.1 Exterior Wall Model Development 95 
    5.2.2 Core Columns and Floors Model Development 99 
    5.2.3 Truss Floor Model Development 102 
    5.2.4 Interior Contents Model Development 105 
    5.2.5 Global Impact Models Assembly 107 
    5.2.6 Tower Material Constitutive Models 110 
    5.3 Development of Aircraft Model 1 16 
    5.3.1 Airframe Model Development 121 
    5.3.2 Wing Section Component Model Development 125 
    5.3.3 Engine Model Development 126 
    5.3.4 Aircraft Material Constitutive Models 130 
    5.4 Component and Subassembly Level Analyses 131 
    5.4.1 Exterior Column Impacted with an Empty Wing 132 
    5.4.2 Bolted Connection Modeling 133 
    5.4.3 Floor Assembly Component Analysis 134 
    5.4.4 Modeling of Aircraft Wing Section Impact with Fuel 138 
    5.4.5 Engine Impacts Subassembly Analyses 145 
    5.5 Summary 148 
    5.6 References 150 

    Chapter 6 
    Aircraft Impact Initial Conditions 151 
    6.1 Introduction 151 
    6.2 Motion Analysis Methodology 152 

    NIST NCSTAR 1-2, WTC Investigation ix 
    Table of Contents 
    6.2.1 Videos Used in the Analysis 152 
    6.2.2 Complex Motion Analysis 153 
    6.2.3 Simplified Motion Analysis 156 
    6.3 Refinement of Aircraft Impact Conditions 158 
    6.4 Comparison with Previous Estimates of Aircraft Impact Initial Conditions 164 
    6.5 Summary 166 
    6.6 References 166 

    Chapter 7 
    Aircraft Impact Damage Results 167 
    7.1 Introduction 167 
    7.2 Analysis Methodology, Assumptions, and Limitations 167 
    7.3 WTC 1 Base Case Impact Analysis - CASE A 171 
    7.3.1 Impact Response 173 
    7.3.2 Tower Structural Damage 178 
    7.3.3 Fuel and Debris Distributions 190 
    7.4 WTC 1 More Severe Impact Analysis - CASE B 196 
    7.4.1 Impact Response 197 
    7.4.2 Tower Structural Damage 202 
    7.4.3 Fuel and Debris Distribution 212 
    7.5 WTC 1 Less Severe Impact Analysis - Brief Description 217 
    7.6 WTC 2 Base Case Impact Analysis - CASE C 217 
    7.6.1 Impact Response 218 
    7.6.2 Tower Structural Damage 224 
    7.6.3 Fuel and Debris Distributions 235 
    7.7 WTC 2 More Severe Impact Analysis - CASE D 241 
    7.7.1 Impact Response 242 
    7.7.2 Tower Structural Damage 247 
    7.7.3 Fuel and Debris Distributions 257 
    7.8 WTC 2 Less Severe Impact Analysis - Brief Description 263 
    7.9 Comparison Between WTC 1 and WTC 2 263 
    7.9.1 Exterior Wall Damage 264 
    7.9.2 Core Column Damage 264 
    7.9.3 Floor Truss Damage 267 
    7.10 Comparison with Observables 267 

    X NIST NCSTAR 1-2, WTC Investigation 
    Table of Contents 
    7.10.1 Comparison with Observables on WTC 1 268 
    7.10.2 Comparison with Observables on WTC 2 277 
    7.10.3 Summary 291 
    7.11 Comparison with Previous Studies 291 
    7.1 1.1 Comparison of Exterior Wall Damage 291 
    7.1 1.2 Comparison of Core Column Damage 295 
    7.12 Summary 296 
    7.13 References 297 

    Chapter 8 
    Findings 299 
    8.1 Baseline Performance Analysis 299 
    8.1.1 Wind Loads on the World Trade Center Towers 299 
    8.1.2 Baseline Performance of the Global Tower Models 300 
    8.1.3 Baseline Performance of the Typical Floor Models 301 
    8.2 Aircraft Impact Damage Analysis 302 
    8.2.1 Safety of the WTC Towers in Aircraft Collision 302 
    8.2.2 Preliminary Impact Analyses (Component and Subassembly Levels) 302 
    8.2.3 Aircraft Impact Damage Results 302 

    AppendxA 
    Salient Points with Regard to the Structural Design of the World Trade Center Tower ..305 
    AppencfxB 
    Estimation of Sectorial Extreme Wind Speeds 309 
    AppendxC 
    Wind Tunnel Testing and the Sector-by-Sector Approach to Wind 
    Directionality Effects 321 
    AppendxD 
    SOM Project 2, Progress Report No. 3, WTC Wind Load Estimates 329 
    AppendxE 
    Still Images of the Video Records Used in Chapter 6 339 

    NISTNCSTAR 1-2, WTC Investigation 
    Table of Contents 
    xii NIST NCSTAR 1-2, WTC Investigation 
    List of Figures 
    Figure P-1. The eight projects in the federal building and fire safety investigation of the WTC 
    disaster xxix 
    Figure 2-1. Rendered isometric views of the WTC 1 global model 12 
    Figure 2-2. Frame view of the WTC 2 model: (a) exterior wall elevation, and (b) interior section 13 
    Figure 2-3. Frame view and rendered view of the WTC 1 model (foundation to floor 9) 15 
    Figure 2^. Exterior wall tree panel (taken from Drawing Book 2, page 2-AB2-2) 16 
    Figure 2-5. Frame and rendered view of an exterior wall tree 17 
    Figure 2-6. Typical WTC tower exterior wall panel 18 
    Figure 2-7. (a), (b) Shell element, and (c) frame element models of a typical exterior wall panel 19 
    Figure 2-8. Selection of column and spandrel rigidity of typical exterior wall panel 20 
    Figure 2-9. Shell element and frame models of typical exterior wall corner panel 21 
    Figure 2-10. As-modeled plan of the WTC 1 hat truss 23 
    Figure 2-11. Rendered 3-D model of the WTC 1 hat truss 23 
    Figure 2-12. Deflection of typical beam-framed floor model due to lateral loading (exaggerated 
    scale) 25 
    Figure 2-13. Deflection of equivalent floor model due to lateral loading (exaggerated scale) 25 
    Figure 2-14. Deflections of the north and south faces of the floor for the detailed and equivalent 
    floor models 26 
    Figure 2-15. Displacement of floor 70 of WTC 2 after impact based on video analysis (NIST 

    NCSTAR1-5A) 29 
    Figure 2-16. Typical floor truss framing zones 30 
    Figure 2-17. Typical truss-framed floor model (floor 96 of WTC 1), slab not shown 31 
    Figure 2-18. Typical primary truss cross-section, as-designed and as-modeled 32 
    Figure 2-19. Typical bridging truss cross-section, as-designed and as-modeled 33 
    Figure 2-20. Strap anchors modeling, slab not shown 34 
    Figure 2-21. Typical beam-framed floor model (floor 75 of WTC 2) 35 
    Figure 2-22. Horizontal truss modeling, slab not shown 36 
    Figure 4-1. Cumulative drift diagrams for WTC 1 under the three wind loading cases 64 
    Figure 4—2. Inter-story drift diagrams for WTC 1 under the three wind loading cases 65 
    Figure 4-3. DCRs for the exterior walls of WTC 1 under original design case, (a) north elevation, 
    (b) east elevation, (c) south elevation, and (d) west elevation 71 
    NIST NCSTAR 1-2, WTC Investigation xiii 



    List of Figures 
    Figure 4^. RCRs for WTC 1 under original design loads below floor 9, (a) north elevation 72 
    Figure 4-5. DCRs for WTC 1 core columns under original design loads, (a) 500 line, and (b) 600 
    line 74 
    Figure 4-6. Distribution of normal stresses in the exterior walls of WTC 1 due to original 
    WTC wind loads only at (a) floor B6, and (b) floor 39 78 
    Figure 4-7. Three-dimensional distribution of normal stresses in the exterior walls of WTC 1 due 
    to original WTC wind loads only at floors B6 and 39 80 
    Figure 4-8. Tension force distribution (kip) in the exterior wall columns of WTC 1 under original 
    design dead and wind loads (no live loads included), (a) 100 face (north), and (b) 200 
    face (east) 82 
    Figure 4-9. DCRs for the typical beam-framed floor under original WTC design criteria loading 89 
    Figure 4-10. Beam-framed floor member groups 90 
    Figure 5-1. User interface for exterior panel generator 95 
    Figure 5-2. Impact face of the WTC 1 global model, floors 91-101 96 
    Figure 5-3. Impact face of the WTC 2 global model, floors 75-86 97 
    Figure 5-4. Model of the spandrel splice plate connection 98 
    Figure 5-5. Placement of spandrel splice plates in the exterior wall model 98 
    Figure 5-6. Model of the WTC 1 core columns and connections, floors 95-97 99 
    Figure 5-7. Detail of wide flange core columns splices 100 
    Figure 5-8. Detail of box column-to-wide flange core columns connection 100 
    Figure 5-9. Model of the core of floor 96 of WTC 1 (with and without floor slab) 101 
    Figure 5-10. Model detail of core column and beam connections 102 
    Figure 5-11. Model of the WTC 1 core, floors 94-98 102 
    Figure 5-12. Model of a truss floor segment 103 
    Figure 5-13. Simplified far field truss floor model 104 
    Figure 5-14. Truss floor connection detail at exterior wall 104 
    Figure 5-15. Truss floor connection detail at core perimeter 105 
    Figure 5-16. Detailed model of floor 96 of WTC 1 105 
    Figure 5-17. Model of floor 96 of WTC 1, including interior contents 106 
    Figure 5-18. Global impact model of the WTC 1 tower 107 
    Figure 5-19. Interior structures and contents of the WTC 1 global impact model 108 
    Figure 5-20. Nonstructural building contents in the WTC 1 global impact model 108 
    Figure 5-21. Global impact model of the WTC 2 tower 109 
    Figure 5-22. Interior structures and contents of the WTC 2 global impact model 110 
    Figure 5-23. Nonstructural building contents in the WTC 2 global impact model 110 
    xiv NIST NCSTAR 1-2, WTC Investigation 

    List of Figures 
    Figure 5-24. Finite element models of the ASTM 370 rectangular tensile specimen Ill 
    Figure 5-25. Tabular true stress-strain constitutive model curves for the tower steels 112 
    Figure 5-26. Comparison of rate effects model and test data 113 
    Figure 5-27. Finite element analysis of the unconfined compression test 114 
    Figure 5-28. Comparison of the calculated unconfined compression behavior with concrete 
    compression test data 115 
    Figure 5-29. Tabular concrete strain rate effects curve 116 
    Figure 5-30. Finite element model of the Boeing 767-200ER 119 
    Figure 5-31. Boeing 767-200ER with fuel load at time of impact 120 
    Figure 5-32. Boeing 767-200ER model wing deflections 120 
    Figure 5-33. Empennage model of the 767-200ER aircraft 121 
    Figure 5-34. Retracted landing gear components for the 767-200ER aircraft model 122 
    Figure 5-35. Underside of the 767 airframe model (skin removed) showing retracted landing gear, 
    engine, and ULDs 122 
    Figure 5-36. Complete wing structures for the 767 aircraft model 123 
    Figure 5-37. Model of fuselage interior frame and stringer construction 124 
    Figure 5-38. Integration of the fuselage and wing structures 124 
    Figure 5-39. Wing section model for component level and subassembly analyses 126 
    Figure 5-40. Pratt & Whitney PW4000 turbofan engine 127 
    Figure 5^1. PW4000 engine cross-sectional geometry and simplification 128 
    Figure 5^2. Pratt & Whitney PW4000 turbofan engine model 129 
    Figure 5^3. True stress-strain curves developed for various aircraft aluminum alloys 130 
    Figure 5^4. Tabular stress-strain curves developed for various aircraft aluminum alloys 131 
    Figure 5^5. Exterior column response comparison, showing contours of the displacement 
    magnitude (in.) 132 
    Figure 5-46. Modeling of exterior column bolted connection 133 
    Figure 5^7. Failure comparison of exterior column bolted connection treatments 134 
    Figure 5-48. Detailed model of the truss floor system 135 
    Figure 5-49. Simplified model of the truss floor system 136 
    Figure 5-50. Constitutive behavior for the combined concrete and metal decking 136 
    Figure 5-51. Floor assembly impact response with brick element concrete slab 137 
    Figure 5-52. Floor assembly impact response with shell element concrete slab 137 
    Figure 5-53. SPH and ALE fuel models in the small wing segment 138 
    Figure 5-54. Wing segment, fuel, and exterior panel configuration 139 
    Figure 5-55. Impact response of a wing section laden with fuel modeled using ALE approach 140 
    Figure 5-56. Impact response of a wing section laden with fuel modeled using SPH approach 141 
    NIST NCSTAR 1-2, WTC Investigation xv 
    List of Figures 
    Figure 5-57. Exterior panels after impact with a wing segment with fuel 142 
    Figure 5-58. Top view of structural damage and fuel dispersion at 0.04 s 143 
    Figure 5-59. Side view of structural damage and fuel dispersion at 0.04 s 144 
    Figure 5-60. Tower subassembly model 145 
    Figure 5-61. Response of the subassembly model to engine impact 146 
    Figure 5-62. Subassembly-engine impact and breakup response (side view) 147 
    Figure 5-63. Speed history for the engine subassembly impact analysis 148 
    Figure 6-1. Definition of the aircraft impact parameters 152 
    Figure 6-2. Complex motion analysis to measure object motions using multiple cameras 154 
    Figure 6-3. Simplified motion analysis procedure to determine aircraft speed 156 
    Figure 6-4. Estimated impact locations of aircraft components superimposed on the damaged face 
    ofWTC 1 159 
    Figure 6-5. Orientation and trajectory of AA 11 that matched the impact pattern (vertical 
    approach angle = 10.6°, lateral approach angle = 0°) 159 
    Figure 6-6. Estimated impact locations of aircraft components superimposed on the damaged face 
    ofWTC2 161 
    Figure 6-7. Orientation and Trajectory of UAL 175 from Video Analysis 161 
    Figure 6-8. Orientation and trajectory of UAL 175 that matches the impact pattern (vertical 
    approach angle = 6°, lateral approach angle = 13°) 162 
    Figure 6-9. Orientation and trajectory of UAL 175 that matches the impact pattern (vertical 
    approach angle = 6°, lateral approach angle = 17°) 163 
    Figure 6-10. Projected trajectory of the starboard engine of UAL 175 with an initial lateral 
    approach angle of 13° 164 
    Figure 7-1. WTC 1 global impact model 172 
    Figure 7-2. WTC 1 base case global impact analysis (side view) 174 
    Figure 7-3. WTC 1 base case global impact analysis (plan view) 176 
    Figure 7-4. Normalized aircraft momentum for the WTC 1 base case impact 178 
    Figure 7-5. Base case impact damage to the WTC 1 exterior wall 181 
    Figure 7-6. Base case impact damage to the WTC 1 core columns 182 
    Figure 7-7. Classification of damage levels in core columns 183 
    Figure 7-8. Base case impact damage to the core beams of floors 95 and 96 of WTC 1 184 
    Figure 7-9. Base case impact damage to the WTC 1 floor trusses (front view) 185 
    Figure 7-10. Base case impact damage to the trusses on floors 95 and 96 of WTC 1 (plan view) 186 
    Figure 7-11. Base Case impact damage to the slabs on floors 95 and 96 of WTC 1 (plan view) 187 
    xvi NIST NCSTAR 1-2, WTC Investigation 
    List of Figures 
    Figure 7-12. Summary of the floor-by-floor structural damage to the floors and columns of WTC 1 
    (base case) 188 
    Figure 7-13. Cumulative structural damage to the floors and columns of WTC 1 (base case) 189 
    Figure 7-14. Calculated fuel distribution in the base case WTC 1 analysis 192 
    Figure 7-15. Plan view of calculated WTC 1 building, fuel, and aircraft debris distribution for the 
    base case 193 
    Figure 7-16. Calculated floor 95 contents and fuel distribution (base case) 194 
    Figure 7-17. Calculated floor 96 contents and fuel distribution (base case) 195 
    Figure 7-18. WTC 1 more severe global impact analysis (side view) 198 
    Figure 7-19. WTC 1 more severe global impact analysis (plan view) 200 
    Figure 7-20. More severe impact damage to the WTC 1 exterior wall 203 
    Figure 7-21. More severe impact response of the WTC 1 core columns 204 
    Figure 7-22. More severe impact damage to the core beams of floors 95 and 96 of WTC 1 205 
    Figure 7-23. More severe impact damage to the WTC 1 floor trusses (front view) 207 
    Figure 7-24. More severe impact damage to the trusses on floors 95 and 96 of WTC 1 (plan view) 208 
    Figure 7-25. More severe impact damage to the slabs on floors 95 and 96 of WTC 1 (plan view) 209 
    Figure 7-26. Summary of the floor-by-floor structural damage to the floors and columns of WTC 1 
    (more severe case) 210 
    Figure 7-27. Cumulative structural damage to the floors and columns of WTC 1 (more severe 
    Figure 7-28. Calculated fuel distribution in the more severe WTC 1 analysis 213 
    Figure 7-29. Plan view of calculated WTC 1 building, fuel, and aircraft debris distribution for the 
    more severe case 214 
    Figure 7-30. Calculated more severe WTC 1 impact response of floor 95 contents 215 
    Figure 7-31. Calculated more severe WTC 1 impact response of floor 96 contents 216 
    Figure 7-32. WTC 2 global impact model 218 
    Figure 7-33. WTC 2 base case global impact analysis (side view) 220 
    Figure 7-34. WTC 2 base case global impact analysis (plan view) 222 
    Figure 7-35. Normalized aircraft momentum for the WTC 2 base case impact 224 
    Figure 7-36. Base case impact damage to the WTC 2 exterior wall 226 
    Figure 7-37. Base case impact damage to the WTC 2 core columns 227 
    Figure 7-38. Base case impact damage to the core beams of floors 80 and 81 of WTC 2 228 
    Figure 7-39. Base case impact damage to the WTC 2 floor trusses (front view) 229 
    Figure 7-40. Base case impact damage to the trusses on floors 80 and 81 of WTC 2 (plan view) 230 
    Figure 7^1. Base case impact damage to the slabs on floors 80 and 81 of WTC 2 (plan view) 231 
    NIST NCSTAR 1-2, WTC Investigation xvii 
    List of Figures 
    Figure 7-42. Summary of the floor-by-floor structural damage to the floors and columns of WTC 2 
    (base case) 233 
    Figure 7-43. Cumulative structural damage to the floors and columns of WTC 2 (base case) 235 
    Figure 7-44. Calculated fuel distribution in the base case WTC 2 analysis 237 
    Figure 7-45. Plan view of calculated WTC 2 building, fuel, and aircraft debris distribution for the 
    base case 238 
    Figure 7-46. Calculated floor 80 contents, and fuel distribution (base case) 239 
    Figure 7-47. Calculated floor 81 contents and fuel distribution (base case) 240 
    Figure 7-48. WTC 2 more severe global impact analysis (side view) 243 
    Figure 7-49. WTC 2 more severe global impact analysis (plan view) 245 
    Figure 7-50. More severe impact damage to the WTC 2 exterior wall 248 
    Figure 7-51. More severe impact damage to the WTC 2 core columns 249 
    Figure 7-52. More severe impact damage to the core beams of floors 80 and 81 of WTC 2 250 
    Figure 7-53. More severe impact damage to the WTC 2 floor trusses (front view) 252 
    Figure 7-54. More severe impact damage to the trusses on floors 80 and 81 of WTC 2 (plan view) 253 
    Figure 7-55. More severe impact damage to the WTC 2 floor slab (plan view) 254 
    Figure 7-56. Summary of the floor-by-floor structural damage to the floors and columns of WTC 2 
    (more severe case) 255 
    Figure 7-57. Cumulative structural damage to the floors and columns of WTC 2 (more severe 
    case) 257 
    Figure 7-58. Calculated fuel distribution in the more severe WTC 2 analysis 259 
    Figure 7-59. Plan view of calculated more WTC 2 building, fuel, and aircraft debris distribution 
    for the more severe case 260 
    Figure 7-60. Calculated floor 80 contents and fuel distribution (more severe case) 261 
    Figure 7-61. Calculated floor 81 contents and fuel distribution (more severe case) 262 
    Figure 7-62. Comparison of base case impact damage to the exterior walls of WTC 1 and WTC 2 265 
    Figure 7-63. Comparison of base case impact damage to the core columns of WTC 1 and WTC 2 266 
    Figure 7-64. Comparison of base case impact damage to floor trusses of WTC 1 and WTC 2 267 
    Figure 7-65. Comparison of observable and calculated base case impact damage to the north wall 
    of WTC 1 269 
    Figure 7-66. Base case aircraft debris distribution in WTC 1 270 
    Figure 7-67. More severe damage aircraft debris distribution in WTC 1 271 
    Figure 7-68. Damage to the south face of WTC 1 from the more severe damage global analysis 272 
    Figure 7-69. Landing gear found at the corner of West and Rector Streets 273 
    Figure 7-70. Landing gear found embedded in exterior panel knocked free from WTC 1 274 
    Figure 7-71. Base case stairwell disruption in WTC 1 275 
    xviii NIST NCSTAR 1-2, WTC Investigation 
    List of Figures 
    Figure 7-72. Observed and calculated WTC 1 damage (front view) 276 
    Figure 7-73. Comparison of observable and calculated base case impact damage to the south wall 
    of WTC 2 277 
    Figure 7-74. Impact damage to the northeast corner of the exterior wall of WTC 2 278 
    Figure 7-75. Documented damage to the northeast corner of floor 81 of WTC 2 279 
    Figure 7-76. Base case response on the northeast corner of floor 81 of WTC 2 280 
    Figure 7-77. Base case stairwell disruption on floor 78 in WTC 2 281 
    Figure 7-78. Base case damage aircraft debris distribution in WTC 2 282 
    Figure 7-79. Aircraft debris distribution in the more severe WTC 2 impact 283 
    Figure 7-80. Starboard engine fragment trajectory in the base case global analysis of WTC 2 285 
    Figure 7-81. Speed of the aft portion of the starboard engine 286 
    Figure 7-82. Calculated and observed engine damage 287 
    Figure 7-83. Starboard engine impact with the south face of WTC 2 in the base case global 
    analysis 288 
    Figure 7-84. Projected debris path for the WTC 2 north face cold spot 290 
    Figure 7-85. Base case WTC 2 impact orientation and trajectory (vertical approach angle = 
    6° lateral approach angle = 13°) 290 
    Figure 7-86. Comparison of impact damage to the north wall of WTC 1 293 
    Figure 7-87. Comparison of impact damage to the south wall of WTC 2 294 
    NIST NCSTAR 1-2, WTC Investigation xix 
    List of Figures 
    XX NIST NCSTAR 1-2, WTC Investigation 
    List of Tables 
    Table P-1 . Federal building and fire safety investigation of the WTC disaster xxviii 
    Table P-2. Public meetings and briefings of the WTC Investigation xxxi 
    Table 2-1. Approximate size of the reference structural models (rounded) 14 
    Table 2-2. Lateral displacement (in.) for the shell and frame models of typical exterior wall 
    panel with varied column and spandrel rigidities 21 
    Table 2-3. Calculated first six periods and frequencies without P-A effects 27 
    Table 2-4. Calculated first six periods and frequencies with P-A effects 27 
    Table 2-5. Comparison of measured and calculated natural frequencies and periods for WTC 1 28 
    Table 3-1. Approximate maximum base moments for WTC 2 induced by ASCE 7-98 standard 
    wind loads 46 
    Table 3-2. Comparison of wind load estimates for WTC 1 based on various sources 52 
    Table 3-3. Comparison of wind load estimates for WTC 2 based on various sources 53 
    Table 3-4. Base shears and base moments due to wind loads based on various building codes 53 
    Table 3-5. Comparison between various design wind speeds 55 
    Table 3-6. Comparison between the various wind studies 55 
    Table 4-1. Total drift for WTC 1 and WTC 2 under the three loading cases 62 
    Table 4-2. Statistics of DCRs for WTC 1 under original design load case 68 
    Table 4-3. Statistics of DCRs for WTC 1 under the lower estimate, state-of-the practice case 69 
    Table 4-4. Statistics of DCRs for WTC 1 under the refined NIST estimate case 70 
    Table 4-5. Statistics of DCRs for WTC 1 under the refined NIST estimate case using LRFD and 
    ASD 11 
    Table 4-6. Maximum calculated DCRs for exterior wall column splices for WTC 1 under 
    original design dead and wind load case 84 
    Table 4-7. Summary of maximum deflections for typical truss-framed floor under dead and live 
    loads for areas outside of core 86 
    Table 4-8. DCR statistics for the typical truss-framed floor under the original design load case 87 
    Table 4-9. DCR statistics for floor the typical truss-framed floor under the ASCE 7-02 loading 
    case 88 
    Table 4-10. DCR statistics for the typical beam-framed floor under the original design loading 
    NISTNCSTAR 1-2, WTC Investigation 
    List of Tables 
    Table 5-1. Summary of the size of the global impact tower models 95 
    Table 5-2. Boeing 767-200ER aircraft model parameters 118 
    Table 5-3. Density scale factors and weights for aircraft components 125 
    Table 5-4. Boeing 767 Engine Comparison 126 
    Table 5-5. Engine model parameters 129 
    Table 5-6. Exterior column component analyses comparison 133 
    Table 5-7. Truss floor assembly component analyses comparison 134 
    Table 6-1. Videos used for the analysis of aircraft impact initial conditions 153 
    Table 6-2. Measured UAL 175 impact speeds using the simplified analysis methodology 157 
    Table 6-3. Summary of measured aircraft impact conditions from video analysis 158 
    Table 6-4. Aircraft impact locations on the WTC towers 162 
    Table 6-5. Summary of refined aircraft impact conditions 162 
    Table 6-6. AA 11 (WTC 1) aircraft impact analysis comparison 165 
    Table 6-7. UAL 175 (WTC 2) aircraft impact analysis comparison 165 
    Table 7-1. Summary of core column damage for the base case WTC 1 impact 183 
    Table 7-2. Fuel and aircraft debris distribution for the base case WTC 1 impact 196 
    Table 7-3. Input parameters for the more and less severe WTC 1 impact analysis 197 
    Table 7-4. Summary of core column damage for the more severe WTC 1 impact 205 
    Table 7-5. Fuel and aircraft debris distribution for the more severe WTC 1 impact 212 
    Table 7-6. Summary of core column damage for the base case WTC 2 impact 228 
    Table 7-7. Fuel and aircraft debris distribution for the base case WTC 2 impact 241 
    Table 7-8. Input parameters for the more severe WTC 2 impact analysis 242 
    Table 7-9. Summary of core column damage for the more severe WTC 2 impact 251 
    Table 7-10. Fuel and aircraft debris distribution for the more severe WTC 2 impact 258 
    Table 7-11. Comparison of damage to core columns from various studies 296 

    Contributing Researchers and Specialist Teams

    Technical Area and Project Leader 
    Analysis of Building and Fire Codes and 
    Practices; Project Leaders: Dr. H. S. Lew 
    and Mr. Richard W. Bukowski 
    Baseline Structural Performance and 
    Aircraft Impact Damage Analysis; Project 
    Leader: Dr. Fahim H. Sadek 
    Analyze the baseline performance of WTC 1 and WTC 2 under 
    design, service, and abnormal loads, and aircraft impact damage on 
    the structural, fire protection, and egress systems. 
    Mechanical and Metallurgical Analysis of 
    Structural Steel; Project Leader: Dr. Frank 
    W. Gayle 
    Determine and analyze the mechanical and metallurgical properties 
    and quality of steel, weldments, and connections from steel 
    recovered from WTC 1, 2, and 7. 
    Investigation of Active Fire Protection 
    Systems; Project Leader: Dr. David 
    D. Evans; Dr. William Grosshandler 
    Investigate the performance of the active fire protection systems in 
    WTC 1 , 2, and 7 and their role in fire control, emergency response, 
    and fate of occupants and responders. 
    Reconstruction of Thermal and Tenability 
    Environment; Project Leader: Dr. Richard 
    G. Gann 
    Reconstruct the time-evolving temperature, thermal environment, 
    and smoke movement in WTC 1 , 2, and 7 for use in evaluating the 
    structural performance of the buildings and behavior and fate of 
    occupants and responders. 
    Structural Fire Response and Collapse 
    Analysis; Project Leaders: Dr. John 
    L. Gross and Dr. Therese P. McAllister 
    Analyze the response of the WTC towers to fires with and without 
    aircraft damage, the response of WTC 7 in fires, the performance 
    of composite steel-trussed floor systems, and determine the most 
    probable structural collapse sequence for WTC 1, 2, and 7. 
    Occupant Behavior, Egress, and Emergency 
    Communications; Project Leader: Mr. Jason 
    D. Averill 
    Analyze the behavior and fate of occupants and responders, both 
    those who survived and those who did not, and the performance of 
    the evacuation system. 
    Emergency Response Technologies and 
    Guidelines; Project Leader: Mr. J. Randall 
    Lawson 
    Document the activities of the emergency responders from the time 
    of the terrorist attacks on WTC 1 and WTC 2 until the collapse of 
    WTC 7, including practices followed and technologies used. 
    =========
    Hamins, A., A. Maranghides, K. B. McGrattan, E. Johnsson, T. J. Ohlemiller, M. Donnelly, 
    J. Yang, G. MulhoUand, K. R. Prasad, S. Kukuck, R. Anleitner and T. McAllister. 2005. Federal 
    Building and Fire Safety Investigation of the World Trade Center Disaster: Experiments and 
    Modeling of Structural Steel Elements Exposed to Fire. NIST NCSTAR 1-5B. National Institute of 
    Standards and Technology. Gaithersburg, MD, September. 
    Ohlemiller, T. J., G. W. MulhoUand, A. Maranghides, J. J. Filliben, and R. G. Gann. 2005. Federal 
    Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Tests of Single 
    Office Workstations. NIST NCSTAR 1-5C. National Institute of Standards and Technology. 
    Gaithersburg, MD, September. 
    Gann, R. G., M. A. Riley, J. M. Repp, A. S. Whittaker, A. M. Reinhorn, and P. A. Hough. 2005. 
    Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Reaction of 
    Ceiling Tile Systems to Shocks. NIST NCSTAR 1-5D. National Institute of Standards and 
    Technology. Gaithersburg, MD, September. 
    Hamins, A., A. Maranghides, K. B. McGrattan, T. J. Ohlemiller, and R. Anleitner. 2005. Federal 
    Building and Fire Safety Investigation of the World Trade Center Disaster: Experiments and 
    Modeling of Multiple Workstations Burning in a Compartment. NIST NCSTAR 1-5E. National 
    Institute of Standards and Technology. Gaithersburg, MD, September. 
    McGrattan, K. B., C. Bouldin, and G. Forney. 2005. Federal Building and Fire Safety 
    Investigation of the World Trade Center Disaster: Computer Simulation of the Fires in the World 
    Trade Center Towers. NIST NCSTAR 1-5F. National Institute of Standards and Technology. 
    Gaithersburg, MD, September. 
    Prasad, K. R., and H. R. Baum. 2005. Federal Building and Fire Safety Investigation of the World 
    Trade Center Disaster: Fire Structure Interface and Thermal Response of the World Trade Center 
    Towers. NIST NCSTAR 1-5G. National Institute of Standards and Technology. Gaithersburg, 
    MD, September. 
    Gross, J. L., and T. McAllister. 2005. Federal Building and Fire Safety Investigation of the World Trade 
    Center Disaster: Structural Fire Response and Probable Collapse Sequence of the World Trade Center 
    Towers. NIST NCSTAR 1-6. National Institute of Standards and Technology. Gaithersburg, MD, 
    September. 
    Carino, N. J., M. A. Starnes, J. L. Gross, J. C. Yang, S. Kukuck, K. R. Prasad, and R. W. Bukowski. 
    2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Passive 
    Fire Protection. NIST NCSTAR 1-6A. National Institute of Standards and Technology. 
    Gaithersburg, MD, September. 
    Gross, J., F. Hervey, M. Izydorek, J. Mammoser, and J. Treadway. 2005. Federal Building and 
    Fire Safety Investigation of the World Trade Center Disaster: Fire Resistance Tests of Floor Truss 
    Systems. NIST NCSTAR 1-6B. National Institute of Standards and Technology. Gaithersburg, 
    MD, September. 
    Zarghamee, M. S., S. Bolourchi, D. W. Eggers, O. O. Erbay, F. W. Kan, Y. Kitane, A. A. Liepins, 
    M. Mudlock, W. I. Naguib, R. P. Ojdrovic, A. T. Sarawit, P. R Barrett, J. L. Gross, and 

    NIST NCSTAR 1-2, WTC Investigation 

    T. P. McAllister. 2005. Federal Building and Fire Safety Investigation of the World Trade Center 
    Disaster: Component, Connection, and Subsystem Structural Analysis. NIST NCSTAR 1-6C. 
    National Institute of Standards and Technology. Gaithersburg, MD, September. 
    Zarghamee, M. S., Y. Kitane, O. O. Erbay, T. P. McAllister, and J. L. Gross. 2005. Federal 
    Building and Fire Safety Investigation of the World Trade Center Disaster: Global Structural 
    Analysis of the Response of the World Trade Center Towers to Impact Damage and Fire. NIST 
    NCSTAR 1-6D. National Institute of Standards and Technology. Gaithersburg, MD, September. 
    McAllister, T., R. W. Bukowski, R. G. Gann, J. L. Gross, K. B. McGrattan, H. E. Nelson, L. Phan, 
    W. M. Pitts, K. R. Prasad, F. Sadek. 2006. Federal Building and Fire Safety Investigation of the World 
    Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of World Trade 
    Center 7. (Provisional). NIST NCSTAR 1-6E. National Institute of Standards and Technology. 
    Gaithersburg, MD. 
    Gilsanz, R., V. Arbitrio, C. Anders, D. Chlebus, K. Ezzeldin, W. Guo, P. Moloney, A. Montalva, 
    J. Oh, K. Rubenacker. 2006. Federal Building and Fire Safety Investigation of the World Trade 
    Center Disaster: Structural Analysis of the Response of World Trade Center 7 to Debris Damage 
    and Fire. (Provisional). NIST NCSTAR 1-6F. National Institute of Standards and Technology. 
    Gaithersburg, MD. 
    Kim, W. 2006. Federal Building and Fire Safety Investigation of the World Trade Center 
    Disaster: Analysis of September 11, 2001, Seismogram Data. (Provisional). NIST NCSTAR 1-6G. 
    National Institute of Standards and Technology. Gaithersburg, MD. 
    Nelson, K. 2006. Federal Building and Fire Safety Investigation of the World Trade Center 
    Disaster: The Con Ed Substation in World Trade Center 7. (Provisional). NIST NCSTAR 1-6H. 
    National Institute of Standards and Technology. Gaithersburg, MD. 
    Averill, J. D., D. S. Mileti, R. D. Peacock, E. D. Kuligowski, N. Groner, G. Proulx, P. A. Reneke, and 
    H. E. Nelson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: 
    Occupant Behavior, Egress, and Emergency Communication. NIST NCSTAR 1-7. National Institute of 
    Standards and Technology. Gaithersburg, MD, September. 
    Fahy, R., and G. Proulx. 2005. Federal Building and Fire Safety Investigation of the World Trade 
    Center Disaster: Analysis of Published Accounts of the World Trade Center Evacuation. NIST 
    NCSTAR 1-7A. National Institute of Standards and Technology. Gaithersburg, MD, September. 
    Zmud, J. 2005. Federal Building and Fire Safety Investigation of the World Trade Center 
    Disaster: Technical Documentation for Survey Administration. NIST NCSTAR 1-7B. National 
    Institute of Standards and Technology. Gaithersburg, MD, September. 
    Lawson, J. R., and R. L. Vettori. 2005. Federal Building and Fire Safety Investigation of the World 
    Trade Center Disaster: The Emergency Response Operations. NIST NCSTAR 1-8. National Institute of 
    Standards and Technology. Gaithersburg, MD, September. 

    xxxvi NIST NCSTAR 1-2, WTC Investigation 

    Acknowledgments 
    The analyses presented in this report were conducted in collaboration with four contractors: 
    • A team of experts from Leslie E. Robertson Associates, whose work included the 
    development of the structural databases, the reference structural models, and the baseline 
    performance analysis of the World Trade Center (WTC) towers. The team was led by Mr. 
    William J. Faschan and Mr. Richard B. Garlock. 

    • A team of experts from Skidmore, Owings, and Merrill, who provided the third-party review 
    of the structural databases, the reference structural models, the baseline performance analysis, 
    and the refined NIST estimate of the wind loads on the towers. The team included Mr. 
    William F. Baker, Mr. John J. Zils, and Mr. Robert C. Sinn. 

    • A team of experts from Apphed Research Associates, whose work included the analysis of 
    aircraft impacts into the WTC towers. The team was led by Dr. Steven W. Kirkpatrick with 
    major contributions from Dr. Robert T. Bocchieri. 

    • Dr. David M. Parks, who provided expertise in the area of computational mechanics for the 
    aircraft impact analysis. 

    In addition. Dr. Shankar Nair of Teng & Associates provided help with the baseline analysis study. 
    Professor Daniele Veneziano of MIT provided help with the uncertainty analyses, and Professor Kaspar 
    Willam of the University of Colorado provided help with the constitutive modeling for aircraft impact. 

    The following individuals from the National Institute of Standards and Technology (NIST) made 
    contributions to this report: 

    Dr. Emil Simiu provided the wind engineering expertise required for the development of 
    Chapter 3 "Wind Loads on the WTC Towers" of this report, of which he was the primary 
    author. He was also co-author of Appendix B "Estimation of Sectorial Extreme Wind 
    Speeds." 

    Dr. Michael A. Riley and Dr. William P. Fritz assisted with preliminary stability analyses of 
    the towers that were reported in the Interim Report of June 2004. In addition. Dr. Fritz 
    participated in the wind study and was the primary author of Appendix B. 

    The mechanical and metallurgical analysis of structural steel team (Dr. Frank W. Gayle, 
    Dr. Richard J. Fields, Dr. William E. Luecke, Mr. J. David McColskey, Dr. Tim J. Foecke, 
    Dr. Stephen W. Banovic, and Dr. Thomas A. Siewert) provided the mechanical 
    characteristics of the tower steels that were used in the constitutive models for the aircraft 
    impact simulations. In addition. Dr. Foecke conducted the comparison of the calculated and 
    observed damage to the exterior walls of the towers and provided the images presented in 
    Figures 7-65 and 7-73. 

    NIST NCSTAR 1-2, WTC Investigation xxxvii 
    Acknowledgments 

    Dr. Therese P. McAllister and Dr. John L. Gross contributed to the interpretation of the 
    impact simulation results and provided the link between the impact analysis and the 
    subsequent fire-structural analyses. They also helped with the review of certain parts of this 
    report. 

    Dr. Wilham M. Pitts provided assistance in the identification of videos and photographs 
    relevant to this project, and in the interpretation of the video and photographic data collected 
    by NIST. 

    Dr. James Filliben provided guidance in the performance of the uncertainty analyses. He 
    contributed to the methodologies that allowed a large reduction in the total number of 
    analyses required. 

    NIST acknowledges the parties to an insurance litigation concerning the WTC towers for voluntarily 
    making available to NIST the Cermak Peterka Peterson, Inc. report and the Rowan Williams Davis and 
    Irwin, Inc. (RWDI) reports containing their estimates of wind loads on the towers. NIST also 
    acknowledges Dr. Najib Abboud of Weidlinger and Associates, Inc. and Dr. Peter Irwin of RWDI for 
    their cooperation in providing answers to NIST questions concerning the RWDI reports. 

    The author also acknowledges Dr. Raymond Daddazio and Mr. David K. Vaughan of Weidlinger and 
    Associates, Inc., and Professor Tomasz Wierzbicki of Massachusetts Institute of Technology for early 
    discussions on aircraft impact analysis. 
    =========================
    E.l INTRODUCTION 

    The National Institute of Standards and Technology (NIST) investigation into the collapse of the World 
    Trade Center (WTC) towers included eight interdependent projects. The Baseline Structural 
    Performance and Aircraft Impact Damage Analysis project had two primary tasks. These were: 

    1. To develop reference structural models of the towers and use these models to establish 
    the base line performance of the two towers under gravity and wind loads. 

    2 To estimate the damage to the towers due to aircraft impacts and establish the initial 
    conditions for the fire dynamics modeling and thermal-structural response and collapse 
    initiation analysis. 

    For the first task, the baseline performance of the WTC towers under gravity and wind loads was 
    estabhshed in order to assess the towers' ability to withstand those loads safely and to evaluate the reserve 
    capacity of the towers to withstand unanticipated events. The baseline performance study provided a 
    measure of the behavior of the towers under design loading conditions, specifically: (1) total and inter- 
    story drift (the sway of the building under design wind loads), (2) floor deflections under gravity loads, 
    (3) the stress demand-to-capacity ratio for primary structural components of the towers such as exterior 
    walls, core columns, and floor framing, (4) performance of exterior walls under wind loading, including 
    distribution of axial stresses and presence of tensile forces, (5) performance of connections between 
    exterior columns, and (6) resistance of the towers to shear sliding and overturning at the foundation level. 

    This task included the development of reference structural models that captured the intended behavior of 
    the towers under design loading conditions. These reference models were used to establish the baseline 
    performance of the towers and also served as a reference for more detailed models for aircraft impact 
    damage analysis and the thermal-structural response and collapse initiation analysis. The models 
    included: (1) two global models (one for each tower) of the major structural components and systems of 
    the towers, and (2) floor models of a typical truss-framed floor and a typical beam- framed floor. In the 
    towers, tenant floors were typical truss-framed floors, while the mechanical floors (floors 7, 41, 75, and 
    108) and near mechanical floors (floors 9, 43, 77, 107, 110, and roof) of both towers were typical beam- 
    framed floors. 

    For the second task, the aircraft impact damage to the exterior of the WTC towers could be visibly 
    identified from the video and photographic records collected. However, no visible information could be 
    obtained for the extent of damage to the interior of the towers, including the structural system (floors and 
    core columns), partition walls, and interior building contents. Such information was needed for the 
    subsequent fire dynamics simulations and post-impact structural analyses. In addition, for the fire 
    dynamics modeling, the dispersion of the jet fuel and the location of combustible aircraft debris were 
    required. The estimate of the extent of damage to the fireproofmg on the structural steel in the towers due 
    to impact was essential for the thermal and structural analyses. The aircraft impact damage analyses were 
    the primary tool by which most of the information about the tower damage could be estimated. 

    NISTNCSTAR 1-2, WTC Investigation 

    Executive Summary 

    The focus of this task was to analyze the aircraft impacts into each of the WTC towers to provide the 
    following: (1) estimates of probable damage to structural systems, including exterior walls, floor 
    systems, and interior core columns; (2) estimates of the aircraft fuel dispersion during the impact; and (3) 
    estimates of debris damage to the building nonstructural contents, including partitions and workstations. 
    The analysis results were used to estimate the damage to fireproofmg based on the estimated path of the 
    debris field inside the towers. This analysis thus estimated the condition of the two WTC towers 
    immediately following the aircraft impacts and established the initial conditions for the fire dynamics 
    modeling and the thermal-structural response and collapse initiation analysis. 

    DEVELOPMENT OF REFERENCE STRUCTURAL MODELS 

    The reference structural models were developed to capture the intended behavior of the WTC towers 
    under design loading conditions. The models were used: (1) to establish the baseline performance of the 
    towers under design gravity and wind loads and (2) as a reference for more detailed models used in other 
    phases of the NIST investigation, including aircraft impact analysis and thermal-structural response and 
    collapse initiation analysis. The reference models included the following: 

    • Two global models of the primary structural components and systems for each of the two 
    towers. 

    • Two models, one of a typical truss-framed floor (tenant floor) and one of a typical beam- 
    framed floor (mechanical level), within the impact and fire regions. 

    All reference models were linearly elastic and three-dimensional, and were developed using the 
    Computers and Structures, Inc. SAP2000 software. SAP2000 is a commercial finite element software 
    package that is customarily used for the analysis and design of structures. A summary of the size of the 
    global and floor models of the towers is presented in Table E-1. 

    Table E-1. Approximate size of the reference structural models (rounded). 
    ============================
    Chapter 1 

    • The WTC towers and Boeing 767 aircraft were large and complex structural systems. To 
    include all of the primary structural components and details of both the aircraft and towers 
    using refined finite element meshes in the impact models was prohibitive. As a result, 
    coarser meshes were used in the impact simulations. That presented a challenge, since a very 
    fine mesh was needed to properly capture the failure and fracture of components in these 
    analyses. A large array of impact simulations at the component level were conducted to 
    calibrate the failure and fragmentation of coarsely meshed aircraft and tower components 
    against those models with fine meshes. 

    • A significant portion of the weight of a Boeing 767 wing was from the fiiel in its integral fuel 
    tanks. Upon impact, this fuel was responsible for large distributed loads on the exterior 
    columns of the WTC towers and subsequently on interior structures, as it was dispersed 
    inside the building. Modeling of the fluid- structure interaction is complex, but was deemed 
    necessary to predict the extent of damage and the fuel dispersion within the building and to 
    help establish the initial conditions for the fire dynamics modeling. A number of modeling 
    options were investigated for possible application in the global impact simulations. 

    • The impact analyses were subject to uncertainties in the input parameters such as initial 
    impact conditions, material properties and failure criteria, aircraft mass and stiffness 
    properties, connections response, the mass and strength of nonstructural contents, and 
    modeling parameters. No information was available to determine a priori the sensitivity of 
    the damage estimates to uncertainties in these parameters. Detailed sensitivity analyses using 
    orthogonal factorial design were conducted at the component and subassembly levels to 
    determine the most infiuential parameters that affect the damage estimates. The results of 
    these analyses were used to provide a range of impact-induced damage estimates to the 
    towers using the global models. 

    The analyses of the aircraft impacts performed for this investigation are believed to be the highest-fidelity 
    simulations ever performed for this impact behavior using state-of-the art analysis methodologies. 
    Wherever possible, the models were validated against observables or supporting test data developed by 
    the WTC investigation. 

    In order to estimate the aircraft impact damage to the WTC towers, the following steps were undertaken: 

    • Constitutive relationships were developed to describe the actual behavior and failure of the 
    materials under the dynamic impact conditions of the aircraft. These materials included the 
    various grades of steels used in the exterior walls, core columns, and fioor trusses of the 
    towers, weldment metal, bolts, reinforced concrete, aircraft materials, and nonstructural 
    contents. 

    • Global impact models were developed for the towers and aircraft: The tower models 
    included the primary structural components of the towers in the impact zone, including 
    exterior walls, fioor systems, core columns, and connections, along with nonstructural 
    building contents. A refmed finite element mesh was used for the areas in the path of the 
    aircraft, and a coarser mesh was used elsewhere. The aircraft model included the aircraft 
    engines, wings, fuselage, empennage, and landing gear, as well as nonstructural components 
    of the aircraft. The aircraft model also included a representation of the fuel using the smooth 
    particle hydrodynamics approach. 

    • Component and subassembly impact analyses were conducted to support the development of 
    the global impact models: The primary objectives of these analyses were to (1) develop an 
    understanding of the interactive failure phenomenon of the aircraft and tower components, 
    and (2) develop the simulation techniques required for the global analysis of the aircraft 
    impacts into the WTC towers, including variations in mesh density and numerical tools for 
    modeling fluid-structure interaction for fuel impact and dispersion. The component and 
    subassembly analyses were used to determine model simplifications for reducing the overall 
    model size while maintaining fidelity in the global analyses. 

    • Initial conditions were estimated for the impact of the aircraft into the WTC towers: These 
    included the aircraft speed at impact, aircraft orientation and trajectory, and impact location 
    of the aircraft nose. The estimates also included the uncertainties associated with these 
    parameters. This step utilized the videos and photographs that captured the impact event and 
    subsequent damage to the exterior of the towers. 

    • Sensitivity analyses were conducted at the component and subassembly levels to assess the 
    effect of uncertainties on the level of damage to the towers due to impact and to determine the 
    most influential parameters that affect the damage estimates. The analyses were used to 
    reduce the number of parameters that would be varied in the global impact simulations. 

    • Analyses of aircraft impact into WTC 1 and WTC 2 were conducted using the global tower 
    and aircraft models: The analysis results included the estimation of the structural damage 
    that degraded the towers' strength and the condition and position of nonstructural contents 
    such as partitions, workstations, aircraft fuel, and other debris that influenced the behavior of 
    the subsequent fires in the towers. The global analyses included, for each tower, a "base 
    case" based on reasonable initial estimates of all input parameters. They also provided a 
    range of damage estimates based on variations of the most influential parameters. 

    • Approximate analyses were conducted to provide guidance to the global finite element 
    impact analyses: These included: (1) the analysis of the overall aircraft impact forces and 
    assessment of the relative importance of the airframe strength and weight distribution, (2) the 
    evaluation of the potential effects of the energy in the rotating engine components on the 
    calculated engine impact response, (3) the influence of the static preloads in the towers on the 
    calculated impact damage and residual strength predictions, and (4) the analysis of the load 
    characteristics required to damage core columns compared to the potential loading from 
    impact of aircraft components. 

    The tasks outlined above were conducted in collaboration with experts from Applied Research 
    Associates, Inc. under contract to NIST. Chapters 5 through 7 provide a summary of this study. For 
    further details, the reader is referred to NIST NCSTAR 1-2B. 

    Chapter 5 describes the global tower and aircraft impact models. The chapter provides the methodology 
    used in the development for the models and the contents of the models, including geometry, element types 
    and sizes, and boundary conditions. The chapter also includes a summary of the constitutive relationships 


    NIST NCSTAR 1-2, WTC Investigation 

    Chapter 1 

    for the various materials used in the tower and aircraft models. Finally, the chapter provides a brief 
    description of the components and subassembly models that were used to support and provide guidance to 
    the development of the global models. 

    Chapter 6 presents the methodology used to estimate the initial aircraft impact conditions. These 
    included, for each aircraft, the impact speed, horizontal and vertical angles of incidence, roll angle, and 
    impact location of the aircraft nose. Uncertainties in each of these parameters were also quantified. The 
    estimates were based on videos that captured the approach of the impacting aircraft and photographs of 
    the damage to the exterior walls of the towers. 

    Chapter 7 presents the results of the global analyses of aircraft impact into WTC 1 and WTC 2 using the 
    global tower and aircraft models. The global analyses included, for each tower, a "base case" based on 
    reasonable initial estimates of all input parameters. They also provided a range of damage estimates of 
    the towers due to aircraft impact. The chapter also provides a comparison between the simulation results 
    and observables obtained from video and photographic evidence and eyewitness interviews, and a 
    comparison of damage estimates from this study with those from prior studies. 
    ======================================
    Chapter 7 

    Plots of debris distribution and damage to tower contents at the end of the impact simulation similar to 
    those in Figure 7-46(c) and Figure 7-47(c), were used to estimate the damage to fireproofmg. The extent 
    of dislodged fireproofing was estimated by considering fireproofmg damage only to structural 
    components in the direct path of debris. For details of the methodology and the extent of fireproofmg 
    damage, see NIST NCSTAR 1-6. 

    A quantitative characterization of the fuel and aircraft debris distribution was obtained by slicing the 
    model at vertical floor locations and calculating the mass at each floor level. A summary of the floor-by- 
    floor fuel and debris distributions is given in Table 7-7. The bulk of the fuel and aircraft debris was 
    deposited in floors 78 through 80, with the greatest concentration of aircraft debris on floor 80, and the 
    largest concentration of aircraft fuel on floors 79, 81, and 82. Approximately 14,000 lb, or 5 percent, of 
    the total aircraft mass was ehminated from the debris cloud in the final state as a result of the erosion in 
    the aircraft structures due to impact and breakup. This eroded mass was maintained in the calculation but 
    eliminated from consideration in the contact algorithm. As a result, any residual momentum at the time 
    of erosion could not be subsequently transferred to the tower. 

    The calculated debris distribution included 55,800 lbs of debris and 10,600 lbs of aircraft fuel outside of 
    the tower at the end of the impact analysis, either rebounding from the impact face or passing through the 
    tower. These estimates of mass outside the tower were expected to be overestimated in the calculation 
    since the exterior walls were not modeled with windows that could contain the fuel cloud and small debris 
    inside the towers. In addition, the impact behavior of the aircraft fuel cloud did not include the ability to 
    stick to, or wet, interior components. Rather the aircraft fuel SPH particles tended to bounce off of 
    internal structures (see Section 7.3.3). 
    =======================