S. Shyam Sunder, Lead Investigat

Bill Grosshandler, Associate Lead Inves

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

sunder@nist.gov

NIST Response to the World Trade Cente

World Trade Center Investigation 

April 29, 2003
Progress Outline Progress Outline

• Status of Data Collection Efforts• Interim Report on Fireproofing of WTC Floor System• Fire Model Validation Experiments and Plans for Fire Testing • Approach for Assessing the Most Probable Structural Collaps• Status of Steel and its Analysis• Photographic and Videographic Image Collection and Analys• First-Person Data on Occupant Behavior, Evacuation, and E• Selection of External Experts and Contractors
1. Status of Data Collection Efforts 1. Status of Data Collection Effort

• Solid foundation of technical evidence for rev

modeling, and testing work

• Building documents, video and photographic records, em

records, oral histories, recovered WTC steel

• NIST has received considerable cooperation 

volumes of information from a variety of orgaagencies

• Building designers, owners, leaseholders, suppliers, con

• Local NYC authorities (FDNY, NYPD, DDC, DOB, OEM)• OSHA (correspondence on evacuation experience of WT

• NIST has a number of requests for materials 

currently pending with, or not yet located andseveral organizations

• It is vital that this information be made availa
Status of Project Specifications Status of Project Specifications

• Complete set of project specifications not located: 

• Original contract specifications for WTC towers• Complete set of tenant alterations, construction l

logs for WTC 1, 2, & 7

• Specifications provided to NIST

• Procurement of materials (steel, concrete) from i

• May be possible to reconstruct project specification p

• Individual subcontract and purchase specification• Individual reports for design and fire protection e

• NIST is working to locate the complete set of project 
Status of As Status of As-Built Drawings Built Drawings

• Complete set of as-built drawings not available (WTC • NIST has original contract drawings for WTC tower str

revisions made during bid and construction

• NIST has supplementary drawings for majority of WTC 

structural modifications:

• Mostly openings to floor framing systems (WTC 1, 2, 7) t

needs

• Strengthening of core columns in upper stories of WTC t

accommodate additional gravity loads

• Repairs made to restore structural integrity of inadverten

straps that were used to brace floor system to columns
2. Interim Report: WTC Floor Fire

2. Interim Report: WTC Floor Fire

• Documents procedures and practices used in fireproofing of • Based on review of factual data in the documents reviewed b

• Few instances of conflicting data or data that need some inte• Facts presented without interpretation to maximum extent po

• Nothing in report should be taken to imply floor trusses playe

collapse of WTC towers

• Issue is a key component of ongoing investigation

• NIST continues to seek, receive, and review additional data o

• Maintenance and inspection records for WTC towers from d• Reports of critical UL tests performed for the fireproofing ma• NIST welcomes additional factual information from organiza

• NIST will review all information and update report as needed
Interim Report: WTC Floor Firepro

Interim Report: WTC Floor Firepro

• Issues covered in report:

• Applicable building codes• Building classification and fire rating requ• Fireproofing method and materials• Fireproofing thickness requirements and • Need for fire endurance testing• Fire testing of a similar floor system• Additional documents being collected and • Specific information needs to further docu

procedures and practices
3. Fire Model Validation Experime

3. Fire Model Validation Experime

Testing of WTC Floor System Testing of WTC Floor System

• NIST is using a combination of analytical, ex

numerical tools to analyze alternative collaps

• NIST is conducting experiments to provide in

analytical and numerical work, including the those results

• Fire performance of open-web bar joist syste

• NIST is reviewing previously completed t

web bar joist systems

• NIST is documenting past performance u

fire incident and insurance investigation r
Key Factors in Analyzing Collapse Hypot

Key Factors in Analyzing Collapse Hypot

• Speed, direction, orientation, and point of impact of each aircraft• Dispersion of jet fuel following the impact• Mass of steel, concrete, heavy machinery, and non-structural building 

all of which shared in absorbing the energy imparted during impact

• Effects of debris fragments on structure, fireproofing, and other buildin

load effects on structural stability

• Performance of steel components and connections, at high rates of lo

at elevated temperatures during subsequent fires, and associated failu

• Performance of fireproofing at high temperatures, and extent to which 

been missing or knocked off during impact

• Growth and spread of fire and resulting temperature of the structural s

and location

• Coupling fire dynamics and thermal-structural response analyses; fact

reconstructing fire growth and path of fire spread:

• Fire load provided by building contents, jet fuel, and fuel storage tank• Ventilation available for combustion• Inter-compartment fire spread through partitions, ceiling/floor systems
Model Validation Experiments (1) Model Validation Experiments (1)

• Mechanical properties of steel:

• High strain rates to support aircraft impact damage analy• High temperatures to support analysis of structural respo• Room temperature, quasi-static loading to: 

• compare actual properties of steel used with specificatio• analyze baseline structural performance under gravity a

• Properties of fireproofing materials

• Thermal-insulation properties as a function of temperatu• Ability of fireproofing to withstand shock and impact

• Fire tests of floor system connections and interfaces

• Floor truss-to-column connections• Load-transfer between floor truss and concrete deck
Model Validation Experiments (2) Model Validation Experiments (2)

• Fire tests to validate fire dynamics and thermal-structu

• Large compartment fires• Heat release and transfer rate to compartment gases• Heat release rate and temperature of steel

• Truss and column specimens (geometry, cross-section)

• Fireproofing: two thicknesses, no fireproofing

• Series of office work station fire tests to simulate fire d

• Based on descriptions of furnishings used in WTC office • Generate database of thermo-physical properties of the 

• Fire endurance testing of typical floor system and indiv

• Composite floor system (concrete deck, bar joist, bridgin• Fire conditions prescribed in ASTM E 119• Vary fireproofing thickness; use rods and angles
4. Assessing the Most Probable S

4. Assessing the Most Probable S

Collapse Sequence Collapse Sequence

• Several leading hypotheses postulated publicly by e

structural collapse sequence between aircraft impacWTC 1 and 2

• Little information on initial damage and source of fire • NIST considers it premature to exclude any of the p

hypotheses; NIST is analyzing these and other posssequences

• Objectives of formal approach to analyzing complex 

failure in WTC 1, 2, and 7:

• What is the most probable collapse sequence?• What confidence levels are associated with it?• What is the probability of other collapse sequences?• What parameters influence on the most probable colla
Publicly Postulated Collapse Hypothese

Publicly Postulated Collapse Hypothese

• Aircraft impact

• Damage to perimeter/interior columns, floor systems in i• Full extent of damage unknown and can only be estimat• Loads redistributed among columns (aided by hat truss)

• Hypothesis A

• Load carrying columns weakened by fires and failed, init

• No need for weakening or failure of floor system

• Hypothesis B1

• Significant portions of one or more floor systems sagged

weakened by fires

• Columns pulled inwards via connections due to sagg

• Combined compression and bending failure of colum

collapse
• Hypothesis B2

• Significant portions of one or more floor systems sagged, 

weakened by fires

• Shear failure at connections to columns• Buckling failure of columns initiated overall collapse• Load eccentricities due to partially damaged floor system

contributed additionally to column buckling

• Other factors

• Combinations of above hypotheses; other possibilities• Role of perimeter versus core columns in collapse initiatio• Difference in times for collapse of WTC 1 and WTC 2

• Details of aircraft impact (speed, height, position, orientation 

and core)

• Condition of fire protection systems (thickness and extent of 

system)

• Indicators of bias in analysis: rapid loss of stability withou

fire versus delayed loss of stability well beyond observed 

Publicly Postulated Collapse Hypothese

Publicly Postulated Collapse Hypothese
Integrated Approach to Assess Most Pro

Integrated Approach to Assess Most Pro

Structural Collapse Sequence Structural Collapse Sequence

• Developed with experts in statistical methods and probabilistic • Provides a rational, consistent approach to assess different co

combining three methods:

• Mathematical modeling methods: 

• full understanding of physics based on best available information• component, sub-system, full-scale system level analysis

• Statistical methods, using experimental design technique

• account for knowledge and random uncertainties related to collap

• identify and rank influential parameters and their relative effects o

• Probabilistic methods, using event tree and Monte Carlo t

• account for knowledge and random uncertainties related to collap

• determine probability of different collapse sequences• parameters contributing to uncertainty propagation: component to 
5. Status of Steel and its Analysis 5. Status of Steel and its Analysis

• NIST has nearly 250 pieces of WTC steel in its posse

• Vast majority of significant size (exterior column-spand

beams, wide flange, truss, channels); several smaller p

• Cataloged 235 pieces as of March 28, 2003; includes d

photographic records and member markings

• Small fraction of WTC steel examined at several salvag

cooperation with SEAoNY

• NIST has identified additional steel stored by Port Au

airport; 12 specimens are in process of being transpo

• Steel in NIST’s possession represents roughly 1/4 to 

weight of the approximately 200,000 tons of steel us
Failure at 

connection 

between floor 

system and 

exterior 

columns

Dr. John Fisher (L

WTC steel columns 

Steel from WTC Towers

Clean weld fracture of Interior columns
WTC Steel at NIST

6. Photographic and Video Image 

6. Photographic and Video Image 

and Analysis and Analysis

• Photographic and video images of damage and fires to 

• Initial conditions for modeling fires• Rates of fire spread through the building• Floors on which structural collapse may have initiated

• Many individuals contacted NIST based on news cove

2002 update. Large number of important photos and vNIST

• NIST continues to seek images; especially interested 

• close-up details of fire conditions in all three buildings• images of airplane approaching and entering• images of WTC 7, particularly on the south face• views from south and west faces of WTC towers
Collection of Visual Material Collection of Visual Material

• Assembling collection into a searchable computerized • Database now contains:

• Over 3,100 photographs taken by 66 professional or am• Over 3,400 video clips from publicly available news cove

and 25 individual videographers

• NIST has received significant visual material from Ass

York 1 News, WNBC New York

• NIST has reviewed similar materials from NYPD and F

arrangements being made to transfer materials of inte
7. Fire 7. Fire-Person Data on Occupant B

Person Data on Occupant B

Evacuation, and Emergency Respo

Evacuation, and Emergency Respo

• NIST’s study of WTC evacuation and emergency response re

collection of first-person data from:

• Survivors (occupants, first responders, others with safety respon• Families of victims who were in touch with victims after aircraft im

• Individuals with operational and command authority

• NIST believes that:

• it is possible to learn from the WTC disaster, and to improve pub

collection and analysis of first-person accounts, but

• it will need active participation of WTC employers and survivors i

and focus groups

• NIST is cooperating with complementary evacuation studies 

CDC, Columbia University, NYC Department of Health and M

• NIST developed list of tenants using information provided by Por

Properties, and identified their locations within the buildings

• April 8, 2003 public meeting in New York City to present study pl

elicit active participation of WTC employers and occupants
Purpose and Methodology for First-Per

Accounts

• To determine the behavior and fate of occupants and r

collecting and analyzing information on:

• occupant behavior• human factors• egress• emergency communications• evacuation system

• Methodology for First Person Accounts

• Face-to-Face Interviews (~750): Designed to maximize 

detail

• Telephone Interviews (~800): Designed for statistical re• Focus Groups (~15): Designed for in-depth study of spe
Face-to-Face Interviews

• Three-Step Process

• Uninterrupted description of the event• Structured discussion to elicit sequence of ac• Follow-up questions

• Participants: Occupants, First Responders, a
Telephone Interviews

• Standardized Set of Questions• Statistically representative population 

of occupants from WTC 1 and WTC 2

• Stratification Variables:

• Initial Floor Population Density

• Single/Multi-Tenant Floor• Floor Location

ZZZ
Focus Groups

• Detailed Recall of Specific Group Experien

• 5 Groups of ~10 Occupants of WTC • 10 groups of ~5 first responders ( a 

or other similar group )
8. Selection of External Experts an

8. Selection of External Experts an

Contractors Contractors

• NIST has assembled a seasoned group of in-house ex

to carry out the investigation

• Group has needed technical expertise as well as experie

prior investigations

• Over two dozen NIST experts will be involved over the c

investigation

• NIST is augmenting its in-house technical staff with ex

NIST who can contribute significantly to the goals and WTC investigation

• Contracts to provide specific deliverables on technical ta• Experts to conduct independent third-party reviews or as

methodological approach

• Bulk of the planned contract solicitations have already 

appear shortly. Several of those solicitations are now 
Statement of Work Development P

Draft SOW

by Project Leader

Review by 

Project Members

Issue Solicita

Once All Review

Complete

Review by Other

Relevant Project

Leads & Members

Review by Lead

Investigator & Associate

Lead Investigator

Review by BFRL

Director & BFRL 

Deputy Director

Review by N

Contracts Spec

& Contracting O

BFRL Director

if >$25K

NIST Director’s

Office 

if >$500K
Contract Review & Selection Proc

NIST Contracts 

Receives Proposals

Contractors Prepare

Proposals in

Response to RFQ

Technical Proposal Reviewed

by 3 Independent 

Technical Reviewers

Approved by Lead Investigator

Consensus Review by Team

of Contracts Specialist, 

Consensus Chairman &

3 Independent Technical

Reviewers

Contracting Spec

Recommends Pro

that Represen

Best Value

Award

Contract

Rating of Technical

Proposals

Review of Cost Proposal

by Consensus Review

Team (reasonable, realistic

& complete)

Approval by N

Source Selec

Authority

(Contracting O
Sole Source Award Considerations Sole Source Award Considerations

• May choose to issue a contract on a sole source basis 

federal laws and acquisition regulations

• Considered when there is only one uniquely qualified s

need is urgent and compelling

• Intent to make a sole source award is posted for 15 da

and the NIST WTC web site

• Organizations that feel they are qualified may submit a 

statement to NIST for review/consideration

• To date, NIST has awarded 2 sole source contracts in 

WTC investigation
Mitigation of Potential Conflicts of 

RFQ includes

OCI Clause &

Instructions

Offerors Disclose

Potential Conflicts and 

Submit Mitigation 

Plan with Proposal

Mitigation Plan

Approved by Contracting

Officer with Required 

Changes & Incorporated into

Terms and Conditions of Award

OCI Review Coordinated 

by Office of NIST

Counsel Prior

to Award

Organizational ConfRequirement: Offerobusiness relationshipprovide data, researcconcerning the WTC involvement in related relationship would coapparent conflict of inprovide a plan for mitThird party reviews of required to assure thawill be completely objmay include, but are ngovernment agenciesor an independent co

No contractor deliverables shall include findings, conclusion
11

2 Analysis of Aircraft Impacts into the WTC Towers 

Outside Experts for Baseline Structural Performance, Impact Analysis, Structural Response to Fire, Collapse Initiation and Probabilistic Assessment of the WTC Investigation

10 2, 5, 6

9

6 Fire Endurance Testing of the WTC Floor System 

8

7 World Trade Center Investigation First Person Accounts of Egre

7 1 Analysis of Building and Fire Codes and Practices 

Development of Structural Databases and Baseline Models for WTC Towers

6

2

WTC Investigation Survey Administration and Report Delivery: Questionnaires, Interviews and Focus Group Synopsis

5

7

4

3 Document and Evaluate the Steel Recovered from the WTC To

Media, Visual and Database Expert with Experience in ObtaininVisual Materials for the World Trade Center

3

5

2 5, 6, 7 Fire Safety Engineering Expertise 

1 7 Outside Experts for Occupant Behavior and Evacuation

Project Title 

No.

WTC No.

World Trade Center Investiga

Contract Solicitations
Thank You Thank You