WTC Rubble


NIST NCSTAR 1: Federal Building and Fire Safety Investigation of
the World Trade Center Disaster


This
is the final report on the National Institute of Standards and Technology
(NIST) investigation of the collapse of the World Trade Center (WTC) towers,
conducted under the National Construction Safety Team Act. This report
describes how the aircraft impacts and subsequent fires led to the collapse of
the towers after terrorists flew jet fuel laden commercial airliners into the
buildings; whether the fatalities were low or high, including an evaluation of
the building evacuation and emergency response procedures; what procedures and
practices were used in the design, construction, operation, and maintenance of
the towers; and areas in current building and fire codes, standards, and
practices that warrant revision.


Extensive
details are found in the 42 companion reports. (The final report on the
collapse of WTC 7 will appear in a separate report.)  Also in this report
is a description of how NIST reached its conclusions. NIST complemented
in-house expertise with private sector technical experts; accumulated copious
documents, photographs, and videos of the disaster; established baseline
performance of the WTC towers; performed computer simulations of the behavior
of each tower on September 11, 2001; combined the knowledge gained into a
probable collapse sequence for each tower; conducted nearly 1,200 first-person
interviews of building occupants and emergency responders; and analyzed the
evacuation and emergency response operations in the two high-rise buildings.


The
report concludes with a list of 30 recommendations for action in the areas of
increased structural integrity, enhanced fire endurance of structures, new
methods for fire resistant design of structures, enhanced active fire
protection, improved building evacuation, improved emergency response, improved
procedures and practices, and education and training.


1.    
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


The
collapse of World Trade Center (WTC) 1, 2, and 7 resulted from structural
damage from direct and indirect effects of aircraft impact and the ensuing
fires. Thus, for collapse analyses of these buildings, knowledge of the
physical state of the structural and fire safety systems prior to the aircraft
impact is essential. To obtain information for the collapse analysis of the
buildings, National Institute of Standards and Technology reviewed design and
construction documents, correspondence, and memoranda related to the building
projects; interviewed individuals involved in the design, construction, and
maintenance of the buildings; obtained information from regulatory and
emergency services agencies of New York City; and reviewed books and published
journal and magazine articles related to the WTC building projects.


Information
obtained from various sources are synthesized and summarized in this report.
Specifically, this report presents (1) provisions used to design and construct
the structural, fire protection and egress systems of the buildings; (2) tests
performed to support the design of these systems; (3) criteria that governed
the design of the structural and fire protection systems; (4) methods used to
proportion structural members and other components of the buildings; (5)
innovative features, technologies and materials that are incorporated in design
and construction of the structural and fire protection systems; (6) details of
deviations to the contract documents granted by Port Authority of New York and
New Jersey; (7) fabrication and inspection requirements at the fabrication
yard; and (8) inspection protocols during construction.


NIST
NCSTAR 1-1: Design,
Construction, and Maintenance of Structural and Life Safety Systems


NIST
NCSTAR 1-1A: Design
and Construction of Structural Systems


1-1A
appendixes A & B


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


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


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.


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, 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 results were to be used to estimate the damage
to fireproofing 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.


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: Analysis
of Aircraft Impacts into the World Trade Center Towers (Chapters 9-11)


1-2B
appendix


NIST NCSTAR 1-3: Mechanical and Metallurgical Analysis of
Structural Steel


This
report is an overview of the results of the mechanical and metallurgical
analysis of structural steel from the World Trade Center (WTC), part of the
National Institute of Standards and Technology Investigation of the WTC
disaster of September 11, 2001.  The goal of the study was threefold:
Determine mechanical properties of WTC structural steel, Determine the quality
of the steel and if design requirements were met, and Analyze the recovered
steel to provide insight into failure mechanisms to guide and/or validate
models of building performance.  Structural steel recovered from the WTC
site was analyzed for composition, microstructure, and mechanical properties,
including room temperature properties (for modeling baseline building
performance), high temperature properties (for modeling structural response of
the building to fire), and behavior at high strain rates (for modeling airplane
impact). Failure analysis of the recovered steel, complemented by pre-collapse
photographs of the damaged building, was used to establish failure modes and
temperature excursions experienced by the steel. In addition, documents from
the construction era covering issues ranging from steel specifications to
engineering design drawings were used to help interpret the results and
supplement models of mechanical properties used in the models of building
performance.


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


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


The
National Institute of Standards and Technology investigation of active fire
protection systems in World Trade Center (WTC) 1, 2, and 7 included the design,
installation, capabilities, and performance on September 11, 2001, of the
automatic fire sprinkler, standpipe, standpipe preconnected hoses, fire alarm,
and smoke management systems. The purpose and normally expected performance of
each active fire protection system in the buildings are described, as well as
details about the systems installed in WTC 1, 2, and 7. Using fire protection
engineering methods, the capabilities of the installed systems to respond to
various fire threats from normal office fires up to and including the
extraordinary challenge of the fires ignited by the aircraft impacts on
September 11, 2001, were assessed. Information from The Fire Department of the
City of New York records was used to document the history of significant fire
events in WTC 1, 2, and 7. Findings of the investigation are presented with
regard to the fire suppression, fire alarm, and smoke management systems
installed on the day the buildings collapsed.


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


The
collapses of the World Trade Center towers on September 11, 2001, resulted from
a combination of aircraft impact damage and the ensuing fires.


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: Visual
Evidence, Damage Estimates, and Timeline Analysis (Chapters 9-Appendix C)


1-5A
appendixes D-G


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


One
of the four main objectives of the National Institute of Standards and
Technology (NIST) investigation of the collapse of the World Trade Center (WTC)
towers was to determine why and how the two towers collapsed. Events that
played a significant role in the structural performance of the towers were the
aircraft impact, the rapid ignition of fires on multiple floors, the growth and
spread of fires and the structural weakening resulting from effects of high
temperatures. The passive fire protection applied to the steel structural
components in the WTC towers was investigated to provide information on the in
place condition of the fire protection before and after aircraft impact.
Standard fire resistance tests were conducted to establish the appropriate
classification (fire resistance rating) of the original design of the WTC floor
system and to develop insight into the structural performance of the composite
steel and concrete floor system under exposure to a standard fire. Results of
simulations of the aircraft impacts were used to predict damage to the
structure, fire protection, and partition walls in the path of the debris
field. Characterization of the temperatures of the structural components,
determined from simulated WTC fires, allowed the calculation of the performance
of major subsystems constituting the structural system of the towers including
the core framing, the exterior wall (columns and spandrels), and full tenant
floors. Insights gained from these analyses were used, in turn, to formulate
and execute nonlinear, temperature-dependent finite element analyses of global
structural systems to predict the collapse sequence of each tower. The
structural analyses were guided, and where possible validated, by observations
made from the review of thousands of photographs and video recordings. This
report covers the characterization of the conditions of the WTC towers before
the attacks, their weakening due to the aircraft impacts, the response of the
structural systems to the subsequent growth and spread of fires, and the
progression of local failures that led ultimately to the total collapse of both
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


This
report describes the occupant evacuation of World Trade Center (WTC) 1 and WTC
2 on September 11, 2001. Multiple sources of information were collected and
analyzed: over 1,000 new interviews with survivors (including 803 telephone
interviews, 225 face-to-face interviews, and 5 focus groups); over 700
published interviews; 9-1-1 emergency calls; transcripts of emergency
communications, historical building design drawings, memoranda, and calculations;
formal complaints filed with the Occupational Safety and Health Administration;
and other relevant materials. The egress system, including stairwells and
elevators, was described and compared to requirement of both contemporary and
current code requirements. This report documents the emergency procedures, both
as they were designed to be implemented, as well as how they were actually
implemented on September 11, 2001.


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


The
September 11, 2001, attack on the World Trade Center (WTC) caused the deaths of
2,749 people.  Included in the group were approximately 421 emergency
responders from The Fire Department of the City of New York (FDNY), The New
York City Police Department (NYPD), the Port Authority Police Department
(PAPD), The Port Authority of New York and New Jersey (PANYNJ), from WTC
security firms, and volunteer emergency responders who were in the WTC area of
the city when the attack occurred. This report addresses the operations of
these emergency responders, the technologies used during WTC operations, and
the guidelines and practices that governed these operations. The objectives of
this study were to 1) fully document what happened during the response by the
emergency services to the attacks on the WTC, up to the time of collapse of WTC
7; (2) identify issues that need to be addressed in changes to practice,
standards, and codes; (3) identify alternative practices and/or technologies
that may address these issues; and (4) identify R&D needs that advance the
safety of the fire service in responding to massive fires in tall buildings.


NIST
NCSTAR 1-8: The
Emergency Response Operations


NIST
NCSTAR 1-8:  Appendixes
A-L


NIST NCSTAR 1A:  Final Report on the Collapse of World Trade
Center Building 7


This
is the final report on the National Institute of Standards and Technology
(NIST) investigation of the collapse of World Trade Center Building 7 (WTC 7),
conducted under the National Construction Safety Team Act.  This report
describes how the fires that followed the impact of debris from the collapse of
WTC 1 (the north tower) led to the collapse of WTC 7; an evaluation of the
building evacuation and emergency response procedures; what procedures and
practices were used in the design, construction, operation, and maintenance of
the building; and areas in current building and fire codes, standards, and
practices that warrant revision.  Extensive details are found in the
companion reports, NIST NCSTAR 1-9 and NIST NCSTAR 1-9A.


Final
Report on the Collapse of World Trade Center Building 7
* [130 Pages,
5.8MB]


NIST NCSTAR 1-9: Structural Fire Response and Probable Collapse
Sequence of World Trade Center Building 7 (two volumes)


This
is the primary technical report on the investigation of the collapse of World
Trade Center Building 7 (WTC 7), providing technical details of all aspects of
the investigation.  This report also contains five appendices, which
provide supporting background information on the Con Edison substation in WTC
7, analysis of the September 11, 2001 seismogram data recorded near the WTC
site, video analysis of WTC 7 building vibrations before its collapse, analyses
of hypothetical blast scenarios, and plasticity and creep models for WTC 7
steels.


NIST
NCSTAR 1-9:  Volumes 1
& 2
 [797 Pages, 50.3MB]



NIST NCSTAR
1-9A: Global
Structural Analysis of the Response of World Trade Center Building 7 to Fires
and Debris Impact Damage
*

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