Kuldeep Prasad and Howard Baum

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

kprasad@nist.gov

Federal Building and Fire Safety Inves

of the World Trade Center Disast

Coupled Fire Dynamics and T

Response Analysis of 

WTC Towers and Bldg. 

June 22, 2004
Disclaimer Disclaimer

Certain commercial entities, equipment, producare identified in this presentation in order to desprocedure or concept adequately or to trace the procedures and practices used. Such identificaintended to imply recommendation, endorsemeimplication that the entities, products, materialsare necessarily the best available for the purpo
Objectives Objectives

• Develop an interface between the Fire Dynamic

(FDS) and the thermal response of structural elepredicting the structural performance of building

• Reconstruct the time-evolving and spatially evo

fields in the steel and concrete in World Trade C2, and 7.

• Evaluate the role of variability in fireproofing thic

damage caused by aircraft on steel temperature

• Estimate the sensitivity of model parameters.
T

O

S

Fire Dynamics

Structural Collapse, Failure

Non-linear, Coupled Fire – Thermal –Struc

Radiative Heat Transfer

Boundary Condition

Vents

Fire Growth and Spread

Load Redistribution

Coupled Analysis Coupled Analysis
Subgrid scale model for radiative heat transfer to 

50 cm
Prasad & Baum, “ Prasad & Baum, “Coupled Fire Dynamics and Thermal Response of Com

l Response of Com

Structures,” accepted for publication, ,” accepted for publication, 30th International Symposium on Com

International Symposium on Com

Grey Gas Assumption: Properties indepen

Radiative transport equation:

, integrated intensity is 

Soot particulate is dominant absorber and emitSpectral dependence of absorption coefficient 

  ⋅∇ = − I T I 4 πσ Ω κ 

Enclosures have Large Aspect Ratio.Induces a vertically stratified distribution.Hot layer that forms has spatial variations in tevary much more rapidly in the vertical than in tdirection.

Plane Layer Analysis: Two La
Pre Impact Damage to Fireproofing Pre Impact Damage to Fireproofing

• Insulation was not applied evenly over 

•What happens to insulation over 30 + years • Effect of vibrations on insulation over an ex
Finite Element Model of Steel Truss Finite Element Model of Steel Truss

• A• S• S• L• R• C• P• SAn• M• F
Thermal Analysis (K) of truss asse

Thermal Analysis (K) of truss asse

Floor 96, Tower 1 ( Time=2000 s) Floor 96, Tower 1 ( Time=2000 s) 
Temperature 

histories

Fire Simulations

CFD

Fire – Thermal Thermal – Structural Inte

Structural Inte

Structural Analysis

FEM

Write Node 

(Element) file.

Resume structural model. 

Read Body Load File.

C

Thermal Analysis

FEM

F

link

Plane Layer Analysis.

Boundary Conditions.

, , , ( , , )

2

T T L f x y t

FDS ANSYS File Transfer

u amb κ =

Fireproofing 

Damage
9 x 9 Wall Model 9 x 9 Wall Model

• Structural Model from 

Simpson, Gumpertz, & Heger, a NIST contractor: left

• Thermal Analysis & 

Mapping: right

• Floors 91-99.• Columns 150-158• Temperature in shell element. • Temperature gradient in 

beam element.
Heating of the concrete slab: Heating of the concrete slab: Full Floor Thermal Mapping : Tower A 

Te
Heavy Core Column Perimeter 

Wide 

Flange 

Columns
Core Column

• Box Shape : Heavy• 22” x 22” x 3”• A36 Steel• Insulation:

Blaze-Shield 1 1/8”

GasTemperature, Critical Temperature

C 900/538 900/600 900/700 1100/53F 1653/1000 1653/1112 1653/1292 2012/10

THICKNESS Time in hours

(INCHES/MM)0.0/0.0 0.34 0.41 0.58 00.5/12.7 5.7 7.1 10.2 1 1/8, 29.0 12.7 15.8 23.3 Damaged 6.3 7.9 11.6 
Undamaged tower Undamaged tower
Fire proofing damaged Fire proofing damaged
Fire proofing and impact damage Fire proofing and impact damage

Status: Status:

• Fire Structure Interface (FSI) - completed• Sensitivity to model parameters – completed• Thermal analysis of wall model – completed • Standard cases for evaluating collapse hypothe

• FDS-generated fires• Varied insulation thickness (0”, 0.6”, 2.2”)
Kuldeep Prasad and Howard Baum

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

kprasad@nist.gov

Federal Building and Fire Safety Inves

of the World Trade Center Disast

Coupled Fire Dynamics and T

Response Analysis of 

WTC Towers and Bldg. 

Thank you