Frank W. Gayle

Project Leader

Materials Science and Engineering L

National Institute of Standards and Tec

U.S. Department of Commerce

frank.gayle@nist.gov

Federal Building and Fire Safety Invest

of the World Trade Center Disaste

Project #3: Analysis of Structu

Update

December 2, 2003
• Task 1 - Collect and catalog physical evi

• Task 2 - Document failure mechanisms a• Task 3 - Metallurgical and mechanical pr

determination (room temperatur

temperature, high strain rate)

• Task 4 - Correlate specified properties w

properties (combined with Task 

• Task 5 - Characterize thermal excursions • Task 6 - Final report

Project 3 Tasks
• Task 1 - Collect and catalog physical evi

(99% complete)

• Structural steel 

3⁄4 236 items catalogued, report 

• Design specifications 

3⁄4 relevant structural document

report in final review

• Material specifications (ASTM, etc)• Supplier production information

3⁄4 ASTM, foreign specifications 3⁄4 Supplier documents, other 19

documents used to estimate p

3⁄4 report in final review
• Task 2 - Document failure mechanisms a

(90% complete)

• Contractor visual inspection of steel afailures completed; report drafted• Extensive analysis by NIST of steel

• failure mechanisms analyzed and • repeated patterns of fracture/failur• failures mapped on structure

• Photographic evidence enhanced and recovered steel.3⁄4 January 15, 2004 anticipated comple
91

9293949596

97

100

9899

200

157

154

151

148

145

142

139

136

133

130

127

124

121

118

115

112

109

10

102103104

1

Floor Truss Support: Perimeter Seat Damag

No se

Seat in

Seat iSeat i

Seat a

Seat in

Tab pl

Tab p

Tab p

Tab p
95th floor and below:

all attachments bent downwards or missing (components ripped off at welds)

No se

Seat in

Seat iSeat i

Seat a

Seat in

Tab pl

Tab p

Tab p

Tab p

Floor Truss Support: Perimeter Seat Damag
Paul C. Brand

April 25, 2002

© 200

Original Image
Processed Image

© 2001. Rob
© 2001. R

Enhancements added by NIST.
© 2001. Ro

Enhancements added by NIST.
© 2001. Roberto Rabanne/CORBIS

Enhancements added by NIST.
© 

2001. Roberto Rabanne/CORBIS

Enhancements added by NIST.
C40 hit by tip of tail?

Closer examination shows co

unlikely – damage occ

Direct comparison with state o

© 2001. Roberto Raban
• Task 3 - Metallurgical and mechanical properti

(room temperature, high temperature, 

Tasks

• Tensile properties determined for all perime

3⁄4 test values compared with estimated properties 3⁄4 ideal stress strain curves developed3⁄4 material parameters supplied for models

• High Strain Rate properties determined for 

perimeter columns

• Truss rod and angles characterized • Creep testing on hold:

• Possibly not necessary for WTC 1 and 2• Review needs with contractor modeling fire r• Allows earlier completion of high temp tensil
Model Stress Model Stress-Strain Curves Strain Curves

Perimeter column plates 1, 2, 4 – Preliminary test data

Best NIST

Grade estimate measured Steel source

literature mean value

FY FY FY

ksi ksi ksi

36 40 3942 57 Yawata "A 441 modified"45 57 56 Yawata "A 441 modified"50 58 58 Yawata "A 441 modified"55 62 64 Yawata "A 441 modified"60 67 66 Yawata "A 441 modified"65 73 73 Yawata WEL-TEN 60R70 78 77 Yawata WEL-TEN 6275 84 83 Yawata WEL-TEN 6280 90 95 Yawata WEL-TEN 7085 105 108 Yawata "A 514 mod" (WEL-TEN 890 105 108 Yawata "A 514 mod" (WEL-TEN 8

100 105 108 Yawata "A 514 mod" (WEL-TEN 8

56

P

Plate 4 

Mill reports used where available to estimate Fy, otherwise 1960s era literatu
Model Stress Model Stress-Strain Curves Strain Curves

Generat• Use staup to yie• Compufrom avemeasure• Model Voce’s l• Correc

σ p

Fy

(1 exp( )) 0 σ R ε R bε p = + ∞ − −

Voce’s nonlinear isotropic hardening:
0

12345

0 0.2 0.4 0.6 0.8 1 1.2

Normalized Loading, F/Fy

Strain, %

Thermal StrainElastic StrainPlastic StrainCreep Strain

012345

0 0.2 0.4 

Normal

Strain, %

Thermal StraElastic StrainPlastic StrainCreep Strain

012345

0 0.2 0.4 0.6 0.8 1 1.2

Normalized Load, F/Fy

Strain, %

Thermal StrainElastic StrainPlastic StrainCreep Strain

012345

0 0.2 0.4 

Norm

Strain, %

50 min to Tmax 100 

Tmax= 650 C Tmax= 550 C

Creep, Plastic, and Thermal Strain – Relative M

εTOTAL = 

εthermal + 

εelastic + 

εplastic + 

εcreep
For even short hold times 

at high temperature, creep strain may dominate total strain.

Time

Temperature

M

a

x

T

e

m

p (5

5

0, 6

0

0, 6

5

0...)

30 min Ramp to 550

012345

0 0.2 0

Norm

Strain, %

Plastic StrainCreep StrainElastic Strain at Thermal Strain a

30 min Ramp to 650

012345

0 0.2 

Norma

Strain, %

Creep, Plastic, and Thermal Strain – Relative M

εTOTAL = 

εthermal + 

εelastic + 

εplastic + 

εcreep
Current Status of Mechanical Test 

Impact (Charpy) 9Bolts (tensile & High Strain Rate) 5Welds 3High Strain Rate (compression) 4High Strain Rate (tensile) 6Creep (TBD) High temperature tensile tests 4RT tensile tests (quasistatic) 9

% comp
• Task 5 - Characterize thermal excursion

• Paint condition used to map upper limtemperature exposure3⁄4 Analysis completion target date Jan

• Task 6 - Final report
Finally,

Comments are welcome on:• Goals and scope of test pro• Test methods• Analysis of data• Other areas of interest

The Materials Science and Engineerin

is proud to contribute its knowledge and 

the investigation.