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

Condition of Thermal Insula

Methodology

June 23, 2003

Nick Carino 

John Gross

Kuldeep Prasad

Fahim Sadek

Monica Starnes

Jiann Yang
Disclaimer Disclaimer

Certain commercial entities, equipment, promaterials are identified in this presentation describe a procedure or concept adequatelthe history of the procedures and practices identification is not intended to imply recomendorsement, or implication that the entitiesmaterials, or equipment are necessarily the for the purpose. 
Thermal Thermal-Structural Modeling Structural Modeling

• Analysis of undamaged buildings expose

fires

• Analysis of damaged buildings exposed t• Condition of fireproofing needs to be cha
Overview Overview

• Sensitivity study• In-place conditions

3⁄4 History of sprayed fire resistive material (SFR3⁄4 Measurements3⁄4 Statistical analysis

• Equivalent thickness• Thermal properties• Response to impact• Summary

Sensitivity Study Sensitivity Study

• Effects of thickness variability and “gaps” • Simplified finite-element analysis

3⁄4 1 in. thick steel plate, 60 in. long3⁄4 Average thickness: 0 to 2.0 in.3⁄4 Standard deviation: 0 to 1.0 in.3⁄4 Gap length: 0 to 30 in.

• Exposure: 1100 oC fire• Compute temperature history of steel
Model

60 in.

1 in. thick steel plate Fireproofing

12 34 
Model

• Use psuedo-random number generator to 

thickness at cross-section

3⁄4 Based on average thickness and standard de

SFRM

High conductivity 

material
Example Example

Uniform Thickness Standard 

0.5 in. 
Effect of Gap in SFRM Effect of Gap in SFRM

1234

With Gap

No Gap

Time = 50 min
Sensitivity Study Sensitivity Study

• Variability in thickness of SFRM reduces 

effectiveness

• Gap in SFRM:

3⁄4 Local heating3⁄4 Path for heat flow into member 
History of SFRM in WTC Towers History of SFRM in WTC Towers

• 1969: Decision to use 1⁄2 in. CAFCO® BLAZESHI• 1970: CAFCO® BLAZESHIELD® Type D discont

replaced with CAFCO® BLAZESHIELD® Type D

• 1994: Thickness measurements on floor trusses o

floors

• 1995: PA initiated study of SFRM thickness durin• 1999: PA established guidelines for SFRM replac• Late 90s: SFRM upgraded to 1 1⁄2 in. with CAFCO

Type II
Specified Thickness Specified Thickness

• October 30, 1969 PA Correspondence

3⁄4 Columns < 14WF228: 2 3/16 in.*3⁄4 Columns 

≥ 14WF228: 1 3/16 in.

3⁄4 Beams, spandrels, floor trusses: 1⁄2 in.

• Alcoa Drawings (Note 11)

3⁄4 3 h on spandrels 1⁄2 in. 3⁄4 4 h on columns (heavy) 1 3/16 in. 

• 1995 Upgrade Study

3⁄4 Floor trusses 1 1⁄2 in.

*CAFCO® BL**V.A. = Verm
Thickness Measurements Thickness Measurements

• 1994 measurements on 23rd and 24th floo• Analysis of photographs taken in the 199• Thickness measurements in PA Construc

Reports from late 1990s

• 1999 measurements of beams and colum

shaft 14/15
Floors 23 and 24 Trusses (1994) Floors 23 and 24 Trusses (1994)

• 16 randomly selected trusses per floor• 6 replicate measurements on “flanges an

0

0.20.40.60.8

1

1.2

22 23 

Average Thickness, in.

Floor

Grand Average = 0.74 in.St. Dev. of Avg. = 0.16 in.
Normal Probability Plots Normal Probability Plots 

• Thickness appears better described by lo

distribution

0.50.60.70.80.9

1

1.11.2

.01 .1 1 5 10 2030 50 7080 90 95 99 99.9 99.99

y = 0.74187 + 0.1607norm(x) R= 0.97209 

 Average Thickness, in.

Percent

(c)

-0.8-0.6-0.4-0.2

0

0.2

.01 .1 1 5 1

y = -0.321

Ln (Thickness)

(e)

Thickness Natural Loga
Lognormal Distribution Lognormal Distribution

0

0.10.20.30.40.50.60.70.8

0 0.5 1 1.5 2 2.5

Frequency

Thickness, in.

0

0.10.20.30.40.50.60.70.8

-2 -1.5 

Frequency
Analysis of Photographs Analysis of Photographs

• Original SFRM: WTC 1 (22, 23, 27) in mi• Upgraded SFRM, WTC 1 (below 31) in 1

Bar Radius + Fireproofing 

Thickness

Center Line

Reference 

Length
Results of Photo Analysis Results of Photo Analysis

0

0.5

1

1.5

2

2.5

.01 .1 1 5 10 2030 50 7080 90 95 99 99.9 99.99

MainBridgingStrutMain-Upgrade

Thickness, in.

Percent

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

.01 .1 1 5 1

Ln Thickness

• Original SFRM thickness distribution app

lognormal

• Upgraded SFRM thickness distribution ap

normal
Summary of Photo Analysis Summary of Photo Analysis

0.4 in. 0.2 in. 

Original Strut

1.7 in. 0.4 in. 

Upgraded Main

0.4 in. 0.25 in. 

Original Bridging

0.6 in. 0.3 in. 

Original Main

C

V

Std. Dev. Average Thickness Floor Truss
Construction Audit Reports Construction Audit Reports

• 18 data sets for WTC 1 (93, 95, 98, 99 an• 14 data sets for WTC 2 (77, 78, 88, 89, 9

1

1.5

2

2.5

3

3.5

4

4.5

5

012

Thickness, in.

Tower
Combined Measurements Combined Measurements

• Lognormal distribution appears more app• Overall average = 2.5 in.• Overall standard deviation = 0.6 in.

0.40.60.8

1

1.21.41.6

.01 .1 1 5 1

y = 0.9083

Ln (Thickness)

1

1.5

2

2.5

3

3.5

4

4.5

5

.01 .1 1 5 10 2030 50 7080 90 95 99 99.9 99.99

y = 2.5449 + 0.57398norm(x) R= 0.98583 

Thickness, in.

Percent
Core Beams and Columns Core Beams and Columns

• April 1999 measurements in shaft 14/15 o

(1st to 45th floor)

Average = 1.0 in.St. Dev. = 0.2 in.

AveragSt. Dev

0

0.5

1

1.5

2

0 10 20 30 40 50

IndividualAverage

Thickness, in.

Floor

Beams

0.75 in.

0.00.51.01.52.0

0 10 

Thickness, in.

Columns
0.2 i0.2 i

1.0 in.0.8 in.

Core BeamsCore Columns

PA Measurements

PA Truss Upgraded 2.5 in 0.6 Measurements

0.3 

0.25 

0.2 

0.4 

0.6 in.0.4 in.0.4 in.1.7 in.

Main TrussBrdg. TrussStrutMain Upgraded

Photos

PA Truss 0.7 in. 0.2 iMeasurements

St

Dev

Data Source Element Average

Summary of SFRM Thickness Summary of SFRM Thickness

*Variability of averages
Equivalent Thickness Equivalent Thickness

• Variability of thickness reduces effectiven• Not practical to include variable thickness 

modeling

• Establish “equivalent uniform thickness” t

thermal protection equivalent to variable 

• Approach

3⁄4 Bar model with variable thickness SFRM3⁄4 Compute elongation under 12,500 psi tensile 

function of time

3⁄4 Compare with elongation obtained with unifor
Cases Considered (Floor Truss) Cases Considered (Floor Truss)

• Lognormal distribution• Original SFRM: tavg = 0.75 in., st. dev. = 0• Upgraded SFRM: tavg = 2.5 in., st. dev. = • 3 sets of psuedo-random numbers• 100 elements for 60 in. bar• 5-point smoothing
5-point Smoothing point Smoothing

0.000.200.400.600.801.001.201.401.60

0 10 20 30 40 

Rough TSmooth 

Thickness, in.

Bar Position, in.
Results for Original SFRM Results for Original SFRM

0.000.200.400.600.80

0 5 10 15 20 

Rough Rough Rough SmooSmooSmoo0.4" U0.5" U0.6" U

Deformation (in)

Time (min)

Load = 9800 lbs
Results for Upgraded SFRM Results for Upgraded SFRM

0.000.200.400.600.801.00

0 20 40 60 8

Case Case Case 2.0 in. 2.2 in. 

Deformation, in.

Time, min
Fireproofing Thickness in Thermal 

Fireproofing Thickness in Thermal 

• Floor trusses (Original):

3⁄4 Main: T = 0.6 in.3⁄4 Bridging (Two-way): T = 0.6 in.3⁄4 Bridging (One-way) and struts: T = 0.3 in.3⁄4 Saddle and damper: T = 0 in.

• Floor trusses (Upgrade):

3⁄4 T = 2.2 in., except dampers T = 0 in.

• Other elements: Specified thickness

3⁄4 Average tends to exceed specified thickness3⁄4 Variability reduces effectiveness

One-w
Thermal and Physical Properties o

Thermal and Physical Properties o

• Materials

3⁄4 CAFCO® BLAZESHIELD® Type DC/F (Origin3⁄4 CAFCO® BLAZESHIELD® Type II (Upgrade)3⁄4 Monokote® MK-5® (WTC 7)

• Properties as function of temperature

3⁄4 Thermal conductivity3⁄4 Specific heat capacity3⁄4 Density3⁄4 Coefficient of thermal expansion
Example Results Example Results

0.00.10.20.30.40.50.6

0 200 400 600 800 1000 1200 1400

Monokote MK-5BLAZE-SHIELD II

Thermal Conductivity (W/mK) BLAZE-SHIELD DC/F

Temperature, oC

600800

1000120014001600

0 200 400 

Specific Heat, J/(kg 

.

 K)

Thermal Conductivity Specific 
Impact Damage Impact Damage

• SFRM was dislodged

3⁄4 Debris field3⁄4 Localized accelerations and deformations

• Estimate extent of dislodged SFRM

3⁄4 Measure static adhesive and cohesive tensile 3⁄4 Develop “failure criteria”3⁄4 Impact analysis and engineering judgment to 

dislodged SFRM
Tensile Pull Tensile Pull-off Test off Test

SFRM

Aluminum Plate

Adhesive

1⁄4 in. Steel Plate

Simple Models Simple Models

a

fb

fb

ρ t a =

t

Planar Substrate

ft

fb

4 ft (d

(do

a = 

Encased 
Impact Tests Impact Tests

• Determine acceleration to dislodge SFRM

Accelerometer

Acce

Plate Enc




Summary Summary

• Methodology for assessing condition of S

reviewed

• Variability of SFRM thickness is taken int

use of “equivalent thickness”

• Available data used to obtain rational thic

3⁄4 Floor trusses: original T = 0.6 in.3⁄4 Floor trusses: upgraded T = 2.2 in.3⁄4 Others: Specified thickness

• Temperature dependence of thermal pro

established

• Mechanical damage to be estimated on t

tests and analysis