Federal Building and Fire Safety Invest

of the World Trade Center Disast

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

Fire-Induced Thermal State

Structural Failure Analys

Dat Duthinh (Structures), Long Phan (Stru

Kuldeep Prasad (Fire), Michael A. Riley (S

Howard A. Baum (Fire), Ronald Rehm 

Emil Simiu (Structures, Lead)

Acknowledgments to: J. Gross, T. McAllister, F. Sadek
Objective Objective

• No methodology is currently available for evaluatin

redundant structural systems with fire-induced thesimulated by state-of-the-art (SOA) methods. 

• Our objective is to use SOA methods to achieve th

and realistic possible investigation of fire-thermal-one that takes full advantage of the interdisciplinarmethodology. 
Tools (Thermal) Tools (Thermal)

• Fire Dynamics Simulator – fire representations con

• Observations (NIST photographic archive).• Best estimates of initial conditions.

• Physics-based nonlinear transfer functions conver

temperatures due to fires in building interior to mea

and temperature gradients for each significant stru
Tools (Structural) Tools (Structural)

• Nonlinear FEM software (ANSYS) for structure wit

• Geometry (valid for both structural and thermal • Loads.• Temperature (mean and temperature gradient) • Section properties.• Nonlinear mechanical properties.• Thermal properties. 
Material Properties Material Properties

• Current model using bilinear

hardening rule to characterize the post-yield stress-strain relationship.

• Values of constants, e.g., 

Fy

(

T), 

E

(

T), G

(

T), Et

(

T), α(

T), and 

ν(

T), 

provided by Project #3 (Gayle, Luecke, and Fields).

• Future calculations will use Voce’s

nonlinear isotropic hardening rule.

• Material constants are currently 

being developed for 9 types of steel by Project #3.

Bilinear H

0

0.10.20.30.40.50.60.70.8

0 0.1 0.2 0.3 0.4 

Stress

E (T )

F y (T )
Possible Collapse Scenarios Possible Collapse Scenarios

1. Connection or isolated member/element failures.2. Collapse associated with floor system behavior; 

of exterior columns associated with thermally-indjoists.

3. Collapse due to damage- and thermally-induced f

columns.
Status of 2 Status of 2-D Modeling and Analys

D Modeling and Analys

• 2-D model developed to analyze sagging of joists 

column buckling, considering:

• Fire representation.• Member sizes.• Material properties.• Nonlinear analysis.

• Ongoing analysis using simplified 2-D model to:

• Evaluate role of sagging of joists and column bu

undamaged structure.

• Examine that role for a damaged structure.• Evaluate sensitivity to:

• Various types of plausible fires.• Effect of creep at high temperatures.
2

-D Structural Model and Analysis D Structural Model and Analysis
Simplified 3 Simplified 3-D Modeling and Analy

D Modeling and Analy

• 3-D models being developed to:

• Validate or improve existing results on:

• sagging of joists.• core columns failure scenario. 

• Examine effects of different fire scenarios, inclu

distribution, on global structural response.

• Examine the effects of structural damage, includ

members in the core, on global structural respon
Simplified 3 Simplified 3

-D Model D Model
Future work Future work

• Various fireproofing scenarios.• Various fire scenarios consistent with observations• Various damage scenarios.• Various sets of material property parameter values• Reliability estimates.
Summary Summary

• Our work will:

• Provide credible insights into failure scenarios b

quantitative, physics-based fire/structural analysin structural engineering.

• Use fire/structural engineering as a unified, inte• Examine various hypotheses for probability esti

• Allow NIST to monitor contractor’s work from a 

knowledge and experience.