Technical Conference on tBuilding and Fire Safety Inof the World Trade Center 

Session VI

Structural Fire Response 

Collapse Analysis

September 15, 2005

John L. Gross and Therese McAlliste

Building and Fire Research Labora

National Institute of Standards and Techno

U.S. Department of Commerce
Contributors and Acknowledgeme

Contributors and Acknowledgeme

 Project 6 Team

• John L. Gross• Therese P. McAllister• Monica A. Starnes• Long T. Phan• Nicholas J. Carino

 Underwriters Laboratories, Inc.

• Frederick Hervey• Mark Izydorek• John Mammoser• Joseph Treadway• William J

o

y

• Aldo Jimenez• Romuald

Bolewski
Contributors and Acknowledgeme

Contributors and Acknowledgeme

 Simpson Gumpertz & Heger Inc.

• Mehdi S. Zarghamee• Said Bolourchi• Daniel W. Eggers• Ömer

O. Erbay

• Frank W. Kan• Yasuo

Kitane

• Atis A. Liepins• Michael Mudlock• Wassim I. Naguib• Rasko

P. Ojdrovic

• Andrew T. Sarawit

 Computer Aided Engineering Ass

• Peter R. Barrett
Contributors and Acknowledgeme

Contributors and Acknowledgeme

 Technical Experts

• Prof. Kaspar Willam - University of Colora• Dr. R. Shankar Nair -

Teng Associates

• Prof. Daniele

Veneziano - MIT

 Others

• PANYNJ• Isolatek International• Laclede Steel Co• Morse Zehnter Associates• Leslie E. Robertson Assoc.
Objectives of the WTC Investigatio

Objectives of the WTC Investigatio

in Project 6 in Project 6

• Determine why and how WTC 1 and WT

collapsed following the initial impacts of 

• Determine what procedures and practice

in the design, construction, operation, anmaintenance of WTC 1 and 2, more speprocedures and practices that were used establishing the fire resistance ratings anproviding fire protection of the structural 
Information/Data Information/Data – Reference Struc

Reference Struc

• Reference global structural 

models of the WTC 1 and WTC 2 towers, and typical floor and exterior wall subsystem models

• NIST NCSTAR 1-2
Information/Data Information/Data – Aircraft Impact 

Aircraft Impact 

• Extent of damage to the structural syst

interior contents of the WTC 1 and WTresulting from aircraft impact

• NIST NCSTAR 1-2
Information/Data Information/Data – Material Propert

Material Proper

• Temperature-dependent mechanical pro

the steels, welds, and bolts used in the cof the towers, including elastic, plastic, aproperties from 20 oC to 700 oC

• NIST NCSTAR 1-3
Information/Data Information/Data – Temperature Hi

Temperature Hi

• Time-temperature histories for structu

components and connections for both fires (e.g., ASTM E 119) and actual fon fire dynamics simulations 

• NIST NCSTAR 1-5G

1

X Y

Z

0

100

200

300

400

ELEMENTSTEMPERATURESTMIN=20TMAX=924.418

1

X Y

Z

0

100

200

300

400

ELEMENTSTEMPERATURESTMIN=20TMAX=924.418
Information/Data Information/Data - Observations Observations

• Photographic and videographic record

with time stamps that documented the observed sequence of events

• NIST NCSTAR 1-5A
Critical Analysis Interdependencie

Critical Analysis Interdependencie

Collapse 

Reference Structural 

Models

Compartment Damage

Debris and Fuel 

Distribution

Fireproofing 

Damage

Structural

Damage

Gas Te

Hi

St

Tem

Hi

Aircraft Impact 

Damage Analysis

Fire D

An

Therma

Structura

and Failu

Baseline

Performance 

Analysis

Reference Model 

Conversion

Reference Model 

Conversion
Structural Analysis Progression Structural Analysis Progression

Subsystem Analyses WTC 1

• Isolated Core• South Exterior Face• Floors 93 to 99

 WTC 2

• Isolated Core• East Exterior Face• Floors 78 to 83

Component Analyses Knuckle Truss seat connections Single truss and 

concrete slab

 Full floor Column splice 

c

onnection

 Single story column Nine story column Nine story-nine column 

exterior wall p

a

n

el

Nonlinear analy

ses with 

component “simplifications” and failure mechanism “simplifications” to determine major subsy

stem behavior 

and sequential failure mechanisms.

Detailed nonlinear analy

ses to 

determine compo

nent 

behaviors and failure mechanisms
Organization of Session VI Organization of Session VI

Fire Protectio

Standard Fire 

Fire EnduranFloor Truss A
Organization of Session VI Organization of Session VI

Structural ReImpact and F

Structural and Damage due 

Probable ColSequences a

Observations 

Response