NIST NCSTAR 1-6B

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Fire Resistance Tests of

Floor Truss Systems

John Gross

Frederick Hervey

Mark Izydorek

John Mammoser

Joseph Treadway

National Institute of Standards and Technology • Technology Administration • U.S. Department of Commerce

NIST NCSTAR 1-6B

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Fire Resistance Tests of

Floor Truss Systems

John Gross

Building and Fire Research Laboratory

National Institute of Standards and Technology

Frederick Hervey

Mark Izydorek

John Mammoser

Joseph Treadway

Underwriters Laboratories, Inc.

September 2005

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary

Technology Administration

Michelle O'Neill, Acting Under Secretary for Technology

National Institute of Standards and Technology

William Jeffrey, Director
Disclaimer No. 1

Certain commercial entities, equipment, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication that the entities, products, materials, or equipment are necessarily the best available for the purpose. Nor does such identification imply a finding of fault or negligence by the National Institute of Standards and Technology.

Disclaimer No. 2

The policy of NIST is to use the International System of Units (metric units) in all publications. In this document,

however, units are presented in metric units or the inch-pound system, whichever is prevalent in the discipline.

Disclaimer No. 3

Pursuant to section 7 of the National Construction Safety Team Act, the NIST Director has determined that certain evidence received by NIST in the course of this Investigation is "voluntarily provided safety-related information" that is "not directly related to the building failure being investigated" and that "disclosure of that information would inhibit the

voluntary provision of that type of information" (15 USC 7306c).

In addition, a substantial portion of the evidence collected by NIST in the course of the Investigation has been

provided to NIST under nondisclosure agreements.

Disclaimer No. 4

NIST takes no position as to whether the design or construction of a WTC building was compliant with any code

since, due to the destruction of the WTC buildings, NIST could not verify the actual (or as-built) construction, the

properties and condition of the materials used, or changes to the original construction made over the life of the

buildings. In addition, NIST could not verify the interpretations of codes used by applicable authorities in determining

compliance when implementing building codes. Where an Investigation report states whether a system was

designed or installed as required by a code provision, NIST has documentary or anecdotal evidence indicating

whether the requirement was met, or NIST has independently conducted tests or analyses indicating whether the requirement was met.

Use in Legal Proceedings

No part of any report resulting from a NIST investigation into a structural failure or from an investigation under the

National Construction Safety Team Act may be used in any suit or action for damages arising out of any matter mentioned in such report (15 USC 281a; as amended by P.L. 107-231).

National Institute of Standards and Technology National Construction Safety Team Act Report 1-6B

Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-6B, 202 pages (September 2005)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 2005

For sale by the Superintendent of Documents, U.S. Government Printing Office

Internet: bookstore.gpo.gov — Phone: (202) 512-1800 —- Fax: (202) 512-2250

Mail: Stop SSOP, Washington, DC 20402-0001
Abstract

The National Institute of Standards and Technology (NIST) review of available documents related to the

design and construction of the World Trade Center (WTC) towers indicated that the fire performance of

the composite floor system of the WTC towers was an issue of concern to the building owners and

designers from the original design and throughout the service life of the buildings. However, NIST found no evidence that fire resistance tests of the WTC floor system were ever conducted. As a result, NIST

conducted a series of four standard fire resistance tests (ASTM E 119). In this series of tests, the effects of three factors were studied: (1) thickness of sprayed fire-resistive material (SFRM), (2) test restraint conditions, and (3) scale of the test. The tests were conducted by Underwriters Laboratories, Inc. under a NIST contract and represented both full-scale (35 ft span) and reduced-scale (17 ft span) floor assemblies

constructed to represent the original design as closely as practical. For three of the tests, the thickness of

the sprayed fire resistive material was 3A in. which represented the average thickness applied in the

original construction. In the fourth test, the thickness of applied SFRM was XA in. which was the

thickness specified for the original design. Tests were conducted in both the restrained and unrestrained

condition to provide bounds on the expected performance of the floor system under the standard fire exposure. The restrained full-scale floor system obtained a fire resistance rating of 1 Vi h, while the

unrestrained floor system achieved a 2 h rating. For the unrestrained test condition, specimens protected

with 3/4 in. thick sprayed fire resistive material were able to sustain the maximum design load for approximately 2 h without collapsing; in the unrestrained test, the load was maintained without collapsing

for 3'/2 h. Past experience with the ASTM E 1 19 test method would lead investigators to expect that the

unrestrained floor assembly would not perform as well as the restrained assembly, and therefore, would

receive a lower fire rating. A fire rating of 2 h was determined from the reduced-scale test with the

average applied SFRM thickness of 3/4 in., while a fire rating of 114 h was determined from the full-scale

test with the same SFRM thickness. This finding raises the question of whether or not a fire rating based on the ASTM E 1 19 performance of a 1 7 ft span floor assembly is scalable to a larger floor system such

as found in the WTC towers where spans ranged from 35 ft to 60 ft.

Keywords: ASTM E 1 19, fire testing, floor systems, sprayed fire-resistive materials, standard fire test,

steel, structural behavior, testing, trusses, World Trade Center.

NISTNCSTAR 1-6B, WTC Investigation in
Abstract

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IV NISTNCSTAR 1-6B, WTC Investigation
Table of Contents

Abstract iii

List of Figures ix

List of Tables xiii

List of Acronyms and Abbreviations xv

Preface xvii

Acknowledgments xxvii

Executive Summary xxix

Chapter 1 Introduction 1

1 . 1 Motivation for Conducting Standard Fire Tests of the WTC Floor System 1

1 .2 Purpose of the Standard Fire Tests 2

1.3 Test Variables 2

1.3.1 SFRM Thickness 2

1.3.2 Restraint Conditions 3

1.3.3 Scale 3

1.4 Test Program 3

Chapter 2 ASTM Standard Fire Test 5

2.1 General Description 5

2.2 Restraint Conditions 5

2.3 Conditions of Acceptance 5

Chapter 3 Description of WTC Floor System and SFRM 7

3.1 Composite Slab Floor System 7

3.2 Steel Trusses 7

3.3 SFRM Thickness 8

Chapter 4 Floor Test Assemblies 9

4. 1 Design of Tests 9

4.1.1 Span of Test Assembly 9

NIST NCSTAR 1-6B, WTC Investigation v
Table of Contents

4.1.2 Geometric Scaling of Floor Trusses 9

4.1.3 Concrete Slab Thickness 10

4. 1 .4 Steel Truss Sections 1

0

4.1.5 Applied Load 10

4.2 Materials of Construction 11

4.2.1 Fabrication of Trusses 11

4.2.2 Steel Grade 12

4.2.3 Truss Welds 12

4.2.4 Metal Deck 14

4.2.5 Welded Wire Fabric 21

4.2.6 Concrete 21

4.2.7 Primer 21

4.2.8 Sprayed Fire-Resistive Materials 21

4.2.9 Miscellaneous Steel 2

1

4.3 Construction of Test Assemblies 22

4.3.1 Construction of 35 Ft Assemblies 22

4.3.2 Construction of 17 Ft Assemblies 35

4.4 Loading of Test Assemblies 43

4.4. 1 Loading of 35 Ft Assemblies 43

4.4.2 Loading of 17 Ft Assemblies 44

4.5 Instrumentation 46

4.5.1 Deflection Instrumentation 46

4.5.2 Furnace Thermocouples 46

4.5.3 Radiometers 47

Chapter 5 Test Results 49

5.1 Fire Test of Assembly No. 1 49

5.1.1 Test Observations 49

5.1.2 Data 51

5.1.3 Post-Test Observations 57

5.2 Fire Test of Assembly No. 2 63

5.2. 1 Test Observations 63

5.2.2 Data .......64

5.2.3 Post-Test Observations .71

V] NISTNCSTAR 1-6B, WTC Investigation
Table of Contents

5.3 Fire Test of Assembly No. 3 73

5.3. 1 Test Observations 73

5.3.2 Data 75

5.3.3 Post-Test Observations 81

5.4 Fire Test of Assembly No. 4 83

5.4. 1 Test Observations 83

5.4.2 Data 85

5 .4.3 Post-Test Observations 91

5.5 Fire Resistance Ratings 94

5.5.1 Test Assembly No. 1 94

5.5.2 Test Assembly No. 2 94

5.5.3 Test Assembly No. 3 94

5.5.4 Test Assembly No. 4 95

5.5.5 Summary Table 95

Chapter 6

Discussion of Results 97

6. 1 Comparison of Results 97

6.1.1 Furnace Control Temperatures 97

6. 1 .2 Furnace Thermal Environment 98

6. 1 .3 Steel Temperatures 100

6. 1 .4 Unexposed Surface Temperatures 104

6.1.5 Deflections of Floor Assembly 104

6.2 Observations 105

6.3 Areas of Further Study 106

Chapter 7 References 107

Appendix A

Certified Mill Test Reports (CMTRs)

Appendix B

Primer Paint Specification

Appendix C

Construction Drawings for 35 Ft Test Assemblies

NIST NCSTAR 7-66, WTC Investigation vii
Table of Contents

Appendix D

Instrumentation for 35 Ft Test Assemblies

Appendix E

Construction Drawings for 17 Ft Test Assemblies

Appendix F Instrumentation for 17 Ft Test Assemblies

Appendix G

Truss Calculation Sheets

Appendix H

Unreliable Data

Appendix I Units Conversions

vin NISTNCSTAR 7-66, WTC Investigation
List of Figures

Figure P-l . The eight projects in the federal building and fire safety investigation of the WTC

disaster xix

Figure 3-1 . Floor system of the WTC towers 7

Figure 4-1. 35 ft main truss, column end 15

Figure 4-2. 35 ft main truss, core end 16

Figure 4-3. 1 7 ft main truss, column end 1

7

Figure 4-4. 17 ft main truss, core end 18

Figure 4-5. Bridging truss for Assemblies Nos. 1 and 2 1

9

Figure 4-6. Bridging truss for Assemblies Nos. 3 and 4 20

Figure 4-7. Structural steel frame of Assembly No. 1 23

Figure 4-8. Restrained end condition of Assembly No. 1 prior to shimming 23

Figure 4-9. Unrestrained end condition of Assembly No. 2 24

Figure 4-10. Intersection of deck support angle and main truss 25

Figure 4-1 1 . Cover plates on main truss 26

Figure 4-12. Intersection of main and bridging truss, bottom chord 26

Figure 4-13. Detail of rebar welded to end stiffener 27

Figure 4-14. Placement of steel form deck 28

Figure 4-15. Chairs for welded wire fabric 29

Figure 4-16. Welded wire fabric 29

Figure 4-17. Concrete placement 30

Figure 4-18. Sandblasted assembly 3

1

Figure 4-19. Primer on bridging truss 3

1

Figure 4-20. Peened thermocouples on truss 32

Figure 4-21. SFRM on main truss 34

Figure 4-22. Measurement of SFRM thickness on truss chord 34

Figure 4-23. Steel framing of 17 ft assembly 36

Figure 4-24. Intersection of main truss and deck support angle 37

Figure 4-25. Intersection of main and bridging truss bottom chord 37

Figure 4-26. Cover plate detail 38

Figure 4-27. Steel floor deck placement 38

NISTNCSTAR 1-6B, WTC Investigation ix
List of Figures

Figure 4-28. Chairs on steel deck 39

Figure 4-29. Welded wire fabric and rebar 40

Figure 4-30. View of radiometer and plate thermocouple 48

Figure 5-1. Assembly No. 1 - average and maximum individual temperatures on north main

truss 51

Figure 5-2. Assembly No. 1 - average and maximum individual temperatures on south main

truss 52

Figure 5-3. Assembly No. 1 - overall average and maximum individual temperatures on north

and south main trusses 52

Figure 5-4. Assembly No. 1 - average and maximum individual temperatures on west bridging

truss 53

Figure 5-5. Assembly No. 1 - average and maximum individual temperatures on east bridging

truss 53

Figure 5-6. Assembly No. 1 - average and maximum individual temperatures on unexposed

surface 54

Figure 5-7. Assembly No. 1 - average temperatures on steel deck 54

Figure 5-8. Assembly No. 1 - bottom chord deflection measurements 55

Figure 5-9. Assembly No. 1 - temperatures of bottom chord deflection rods 55

Figure 5-10. Assembly No. 1 - unexposed surface deflection measurements. 56

Figure 5-11. Assembly No. 1 - additional instrumentation through west opening 56

Figure 5-12. Assembly No. 1 - additional instrumentation through east opening 57

Figure 5-13. Unexposed surface of Assembly No. 1 after loading equipment was removed 58

Figure 5-14. Detail of spalling concrete at west end of Assembly No. 1 59

Figure 5-15. Detail of spalling concrete at east end of Assembly No. 1. 59

Figure 5-16. Close-up of spalling concrete at east end of Assembly No. 1 60

Figure 5-17. View looking east of the exposed side of Assembly No. 1- south main truss seen at right side 60

Figure 5-18. Intersection of north main and east bridging trusses on Assembly No. 1 61

Figure 5-19. View of core-end diagonal strut of south main truss on Assembly No. 1 61

Figure 5-20. Sections cut through concrete slab to confirm delamination spalling 62

Figure 5-21. Measurement of depth of delamination spalling 62

Figure 5-22. Assembly No. 2 - average and maximum individual temperatures on north main

truss 65

Figure 5-23. Assembly No. 2 - average and maximum individual temperatures on south main

truss 65

Figure 5-24. Assembly No. 2 - overall average and maximum individual temperatures on north

and south main trusses 66

x NISTNCSTAR 1-6B, WTC Investigation
List of Figures

Figure 5-25. Assembly No. 2 - average and maximum individual temperatures on west bridging

truss 66

Figure 5-26. Assembly No. 2 - average and maximum individual temperatures on east bridging

truss 67

Figure 5-27. Assembly No. 2 - average and maximum individual temperatures on unexposed

surface 67

Figure 5-28. Assembly No. - 2 average temperatures on steel deck 68

Figure 5-29. Assembly No. 2 bottom chord deflection measurements 68

Figure 5-30. Assembly No. 2 temperatures of bottom chord deflection rods 69

Figure 5-31. Assembly No. 2 - unexposed surface deflection measurements 69

Figure 5-32. Assembly No. 2 - additional instrumentation through west opening 70

Figure 5-33. Assembly No. 2 - additional instrumentation through east opening 70

Figure 5-34. Unexposed surface of Assembly No. 2 after loading equipment was removed 71

Figure 5-35. View of core end diagonal strut of north main truss on Assembly No. 2 72

Figure 5-36. South main truss of Assembly No. 2, looking east 72

Figure 5-37. Intersection of east bridging and north main trusses on Assembly No. 2 73

Figure 5-38. Assembly No. 3 - average and maximum individual temperatures on west main truss 75

Figure 5-39. Assembly No. 3 - average and maximum individual temperatures on east main truss 76

Figure 5-40. Assembly No. 3 - overall average and maximum individual temperatures on west

and east main trusses 76

Figure 5—41. Assembly No. 3 - average and maximum individual temperatures on south bridging

truss 77

Figure 5-42. Assembly No. 3 - average and maximum individual temperatures on north bridging

truss 77

Figure 5-43. Assembly No. 3 - average and maximum individual temperatures on unexposed

surface 78

Figure 5-44. Assembly No. 3 - average temperatures on steel deck 78

Figure 5-45. Assembly No. 3 - bottom chord deflection measurements 79

Figure 5^16. Assembly No. 3 - temperatures of bottom chord deflection rods 79

Figure 5^7. Assembly No. 3 - unexposed surface deflection measurements 80

Figure 5-48. Assembly No. 3 - additional instrumentation through south opening 80

Figure 5^19. Assembly No. 3 - additional instrumentation through north opening 81

Figure 5-50. Unexposed surface of Assembly No. 3 after loading equipment was removed 81

Figure 5-51. Detail of spalling concrete at north end of Assembly No. 3 82

Figure 5-52. View of column-end diagonal strut of west main truss on Assembly No. 3 82

Figure 5-53. Intersection of north bridging and west main truss on Assembly 3 83

Figure 5-54. Assembly No. 4 - average and maximum individual temperatures on west main truss 85

NIST NCSTAR 1-6B, WTC Investigation xi
List of Figures

Figure 5-55. Assembly No. 4 - average and maximum individual temperatures on east main truss 86

Figure 5-56. Assembly No. 4 - overall average and maximum individual temperatures on west

and east main trusses 86

Figure 5-57. Assembly No. 4 - average and maximum individual temperatures on south bridging

truss 87

Figure 5-58. Assembly No. 4 - average and maximum individual temperatures on south bridging

truss 87

Figure 5-59. Assembly No. 4 - average and maximum individual temperatures on unexposed

surface 88

Figure 5-60. Assembly No. 4 - average temperatures on steel deck 88

Figure 5-61 . Assembly No. 4 - bottom chord deflection measurements 89

Figure 5-62. Assembly No. 4 - temperatures of bottom chord deflection rods 89

Figure 5-63. Assembly No. 4 - unexposed surface deflection measurements 90

Figure 5-64. Assembly No. 4 - additional instrumentation through south opening 90

Figure 5-65. Assembly No. 4 - additional instrumentation through south opening 91

Figure 5-66. Unexposed surface of Assembly No. 4 after loading equipment was removed 91

Figure 5-67. Unexposed surface of Assembly No. 4, view of concrete spalling on west side of

assembly 92

Figure 5-68. Unexposed surface of Assembly No. 4, close-up of concrete spalling on west side of

assembly 92

Figure 5-69. Intersection of north bridging and west main truss on Assembly 4 93

Figure 5-70. View looking north of south bridging truss at location where concrete spalling

occurred on Assembly 4 93

Figure 6-1 . Comparison of average furnace temperatures 97

Figure 6-2. Temperatures measured at the bottom chord by the plate thermocouple in the ULC

furnace (Test No. 2) and ULN furnace (Test No. 4) 98

Figure 6-3. Temperatures measured at the underside of the metal deck by the plate thermocouple

at the ULC furnace (Test No. 2) and ULN furnace (Test No. 4) 99

Figure 6-4. Average temperatures of the bottom chord for Test Nos. 1, 2 and 3 (3/4 in. thick

SFRM) 100

Figure 6-5. Average temperature of web diagonals for Test Nos. 1, 2 and 3 (3/4 in. thick SFRM) 101

Figure 6-6. Average temperature of the top chord for Test Nos. 1, 2 and 3 (3/4 in. thick SFRM) 102

Figure 6-7. Average temperature of the bottom chord for Test No. 3 (3/4 in. thick SFRM) and

No. 4(1/2 in. thick SFRM) 103

Figure 6-8. Average temperature of the unexposed surface for all four tests 104

Figure 6-9. Deflection measured at the center of each assembly 105

Figure 6-10. Deflection measured at the center of each assembly divided by the span 105

Xll NISTNCSTAR 1-6B, WTC Investigation
List of Tables

Table P-l . Federal building and fire safety investigation of the WTC disaster xviii

Table P-2. Public meetings and briefings of the WTC Investigation xxi

Table 4-1 . Redistance Weld Data 1

3

Table 4-2. Concrete mix design per cubic yard of concrete 21

Table 4-3. General construction details 22

Table 4-4. Details of concrete placement 30

Table 4-5. SFRM Thickness measurements on Assembly No. 1 33

Table 4-6. Air dry density of spray applied fire resistive material on Assembly No. 1 33

Table 4-7. Thickness measurements on Assembly No. 2 35

Table 4-8. Air dry density of spray applied fire resistive material on Assembly No. 2 35

Table 4-9. Details of concrete 40

Table 4-10. SFRM Thickness measurements on Assembly No. 3 42

Table 4-1 1 . Air dry density of spray applied fire resistive material on Assembly No. 3 42

Table 4-12. Thickness measurements on Assembly No. 4 42

Table 4-13. Air dry density of spray applied fire resistive material on Assembly No. 4 42

Table 4-14. Summary of analysis for maximum load condition for 35 ft assembly 44

Table 4-15. Summary of analysis for maximum load condition for 17 ft assembly 45

Table 4-1 6. Summary of radiometers 47

Table 5-1 . Test observations - Assembly 1 49

Table 5-2. Test observations - Assembly No. 2 63

Table 5-3. Test observations - Assembly No. 3 74

Table 5^4. Test observations - Assembly No. 4 84

Table 5-5. Times to reach ASTM E 1 19 end-point criteria and ASTM E 1 19 hourly ratings 96

NISTNCSTAR 1-6B, WTC Investigation xiii
List of Tables

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XIV NISTNCSTAR 1-6B, WTC Investigation
List of Acronyms and Abbreviations

Acronyms

ASTM American Society for Testing and Materials, ASTM International

CMTR Certified Mill Test Report

MIG Metal Inert Gas (welding)

NIST National Institute of Standards and Technology

PANYNJ Port Authority of New York and New Jersey

SFRM sprayed fire-resistive material

STS STS Consultants, Ltd.

SMAW shielded metal arc welding

ULC Underwriters Laboratories of Canada, Toronto, Ontario, Fire Test Facility

T TT XT ULN Underwriters Laboratories, Inc., Northbrook, Illinois, Fire Test Facility

UL Underwriters Laboratories Inc. USM United States Minerals Products, Co.

WJE Wiss Janey Elstner & Associates

WTC World Trade Center

WWF welded wire fabric

Abbreviations

°C degrees Celsius (centigrade)

op degrees Fahrenheit

ft feet

in. inch

lb pound (force)

min minute

o.c. on center

pcf pounds per cubic foot ( 1 pcf = 16.03 kg/m3

)

psf pounds per square foot (1 psf = 0.0479 kN/m2

)

psi pounds per square inch (1 psi = 0.006895 N/mm2 or 0.006895 MPa)

s second

NISTNCSTAR 1-6B, WTC Investigation xv
List of Acronyms and Abbreviations

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XVI NISTNCSTAR 1-6B, WTC Investigation
Preface

Genesis of This Investigation

Immediately following the terrorist attack on the World Trade Center (WTC) on September 11, 2001, the

Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers began

planning a building performance study of the disaster. The week of October 7, as soon as the rescue and

search efforts ceased, the Building Performance Study Team went to the site and began its assessment.

This was to be a brief effort, as the study team consisted of experts who largely volunteered their time

away from their other professional commitments. The Building Performance Study Team issued its report in May 2002, fulfilling its goal "to determine probable failure mechanisms and to identify areas of

future investigation that could lead to practical measures for improving the damage resistance of buildings

against such unforeseen events."

On August 21, 2002, with funding from the U.S. Congress through FEMA, the National Institute of

Standards and Technology (NIST) announced its building and fire safety investigation of the WTC

disaster. On October 1, 2002, the National Construction Safety Team Act (Public Law 107-231), was

signed into law. The NIST WTC Investigation was conducted under the authority of the National

Construction Safety Team Act.

The goals of the investigation of the WTC disaster were:

• To investigate the building construction, the materials used, and the technical conditions that contributed to the outcome of the WTC disaster.

• To serve as the basis for: - Improvements in the way buildings are designed, constructed, maintained, and used; - Improved tools and guidance for industry and safety officials; - Recommended revisions to current codes, standards, and practices; and - Improved public safety.

The specific objectives were:

1 . Determine why and how WTC 1 and WTC 2 collapsed following the initial impacts of the

aircraft and why and how WTC 7 collapsed;

2. Determine why the injuries and fatalities were so high or low depending on location,

including all technical aspects of fire protection, occupant behavior, evacuation, and

emergency response;

3. Determine what procedures and practices were used in the design, construction, operation,

and maintenance of WTC 1, 2, and 7; and

4. Identify, as specifically as possible, areas in current building and fire codes, standards, and

practices that warrant revision.

NISTNCSTAR 7-66, WTC Investigation xvu
Preface

NIST is a nonregulatory agency of the U.S. Department of Commerce's Technology Administration. The

purpose of NIST investigations is to improve the safety and structural integrity of buildings in the United

States, and the focus is on fact finding. NIST investigative teams are authorized to assess building

performance and emergency response and evacuation procedures in the wake of any building failure that has resulted in substantial loss of life or that posed significant potential of substantial loss of life. NIST

does not have the statutory authority to make findings of fault nor negligence by individuals or

organizations. Further, no part of any report resulting from a NIST investigation into a building failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action

for damages arising out of any matter mentioned in such report (15 USC 281a, as amended by Public

Law 107-231).

Organization of the Investigation

The National Construction Safety Team for this Investigation, appointed by the then NIST Director, Dr. Arden L. Bement, Jr., was led by Dr. S. Shyam Sunder. Dr. William L. Grosshandler served as Associate Lead Investigator, Mr. Stephen A. Cauffman served as Program Manager for Administration,

and Mr. Harold E. Nelson served on the team as a private sector expert. The Investigation included eight

interdependent projects whose leaders comprised the remainder of the team. A detailed description of

each of these eight projects is available at http://wtc.nist.gov. The purpose of each project is summarized

in Table P—1, and the key interdependencies among the projects are illustrated in Fig. P-l.

Table P-1. Federal building and fire safety investigation of the WTC disaster.

Technical Area and Project Leader Project Purpose

Analysis of Building and Fire Codes and

Practices; Project Leaders: Dr. H. S. Lew

and Mr. Richard W. Bukowski

Document and analyze the code provisions, procedures, and

practices used in the design, construction, operation, and

maintenance of the structural, passive fire protection, and

emergency access and evacuation systems of WTC 1, 2, and 7. Baseline Structural Performance and

Aircraft Impact Damage Analysis; Project Leader: Dr. Fahim H. Sadek

Analyze the baseline performance of WTC 1 and WTC 2 under

design, service, and abnormal loads, and aircraft impact damage on

the structural, fire protection, and egress systems.

Mechanical and Metallurgical Analysis of

Structural Steel; Project Leader: Dr. Frank

W. Gayle

Determine and analyze the mechanical and metallurgical properties

and quality of steel, weldments, and connections from steel recovered from WTC 1, 2, and 7. Investigation of Active Fire Protection

Systems; Project Leader: Dr. David

D. Evans; Dr. William Grosshandler

Investigate the performance of the active fire protection systems in WTC 1, 2, and 7 and their role in fire control, emergency response, and fate of occupants and responders.

Reconstruction of Thermal and Tenability

Environment; Project Leader: Dr. Richard

G. Gann

Reconstruct the time-evolving temperature, thermal environment,

and smoke movement in WTC 1, 2, and 7 for use in evaluating the

structural performance of the buildings and behavior and fate of

occupants and responders.

Structural Fire Response and Collapse

Analysis; Project Leaders: Dr. John

L. Gross and Dr. Therese P. McAllister

Analyze the response of the WTC towers to fires with and without

aircraft damage, the response of WTC 7 in fires, the performance

of composite steel-trussed floor systems, and determine the most

probable structural collapse sequence for WTC 1, 2, and 7. Occupant Behavior, Egress, and Emergency

Communications; Project Leader: Mr. Jason

D. Avenll

Analyze the behavior and fate of occupants and responders, both

those who survived and those who did not, and the performance of

the evacuation system.

Emergency Response Technologies and

Guidelines; Project Leader: Mr. J. Randall

Lawson

Document the activities of the emergency responders from the time

of the terrorist attacks on WTC 1 and WTC 2 until the collapse of

WTC 7, including practices followed and technologies used.

XVlll NISTNCSTAR 1-6B, WTC Investigation
Preface

NIST WTC Investigation Projects

Nisr

Figure P-1. The eight projects in the federal building and fire safety

investigation of the WTC disaster.

National Construction Safety Team Advisory Committee

The NIST Director also established an advisory committee as mandated under the National Construction

Safety Team Act. The initial members of the committee were appointed following a public solicitation. These were:

• Paul Fitzgerald, Executive Vice President (retired) FM Global, National Construction Safety

Team Advisory Committee Chair

• John Barsom, President, Barsom Consulting, Ltd.

• John Bryan, Professor Emeritus, University of Maryland

• David Collins, President, The Preview Group, Inc.

• Glenn Corbett, Professor, John Jay College of Criminal Justice

• Philip DiNenno, President, Hughes Associates, Inc.

NIST NCSTAR 1-6B, WTC Investigation xix
Preface

• Robert Hanson, Professor Emeritus, University of Michigan

• Charles Thornton, Co-Chairman and Managing Principal, The Thornton-Tomasetti Group,

Inc.

• Kathleen Tierney, Director, Natural Hazards Research and Applications Information Center,

University of Colorado at Boulder

• Forman Williams, Director, Center for Energy Research, University of California at San

Diego

This National Construction Safety Team Advisory Committee provided technical advice during the

Investigation and commentary on drafts of the Investigation reports prior to their public release. NIST

has benefited from the work of many people in the preparation of these reports, including the National

Construction Safety Team Advisory Committee. The content of the reports and recommendations,

however, are solely the responsibility of NIST.

Public Outreach

During the course of this Investigation, NIST held public briefings and meetings (listed in Table P-2) to

solicit input from the public, present preliminary findings, and obtain comments on the direction and

progress of the Investigation from the public and the Advisory Committee.

NIST maintained a publicly accessible Web site during this Investigation at http://wtc.nist.gov. The site contained extensive information on the background and progress of the Investigation.

NIST's WTC Public-Private Response Plan

The collapse of the WTC buildings has led to broad reexamination of how tall buildings are designed,

constructed, maintained, and used, especially with regard to major events such as fires, natural disasters,

and terrorist attacks. Reflecting the enhanced interest in effecting necessary change, NIST, with support

from Congress and the Administration, has put in place a program, the goal of which is to develop and

implement the standards, technology, and practices needed for cost-effective improvements to the safety

and security of buildings and building occupants, including evacuation, emergency response procedures,

and threat mitigation.

The strategy to meet this goal is a three-part NIST-led public-private response program that includes:

• A federal building and fire safety investigation to study the most probable factors that contributed to post-aircraft impact collapse of the WTC towers and the 47-story WTC 7

building, and the associated evacuation and emergency response experience.

• A research and development (R&D) program to (a) facilitate the implementation of

recommendations resulting from the WTC Investigation, and (b) provide the technical basis

for cost-effective improvements to national building and fire codes, standards, and practices

that enhance the safety of buildings, their occupants, and emergency responders.

xx NISTNCSTAR 1-6B, WTC Investigation
Preface

Table P-2. Public meetings and briefings of the WTC Investigation.

Date Location Principal Agenda

June 24. 2002 New York City, NY Public meeting: Public comments on the Draft Plan for the pending WTC Investigation.

August 21. 2002 Gaithersburg. MD Media briefing announcing the formal start of the Investigation.

December 9. 2002 Washington, DC Media briefing on release of the Public Update and NIST request

for photographs and videos. April 8. 2003 New York City, NY Joint public forum with Columbia University on first-person interviews. April 29-30. 2003 Gaithersburg, MD NCST Advisory Committee meeting on plan for and progress on WTC Investigation with a public comment session. May 7. 2003 New York City, NY Media briefing on release of May 2003 Progress Report.

August 26-27. 2003 Gaithersburg, MD NCST Advisory Committee meeting on status of the WTC

investigation with a public comment session. September 17, 2003 New York City, NY Media and public briefing on initiation of first-person data

collection projects.

December 2-3. 2003 Gaithersburg, MD NCST Advisory Committee meeting on status and initial results and release of the Public Update with a public comment session. February 12, 2004 New York City, NY Public meeting on progress and preliminary findings with public

comments on issues to be considered in formulating final recommendations.

June 18. 2004 New York City, NY Media/public briefing on release of June 2004 Progress Report. June 22-23, 2004 Gaithersburg, MD NCST Advisory Committee meeting on the status of and

preliminary findings from the WTC Investigation with a public

comment session. August 24, 2004 Northbrook. 1L Public viewing of standard fire resistance test of WTC floor svstem at Underwriters Laboratories, Inc. October 19-20, 2004 Gaithersburg, MD NCST Advisory Committee meeting on status and near complete

set of preliminary findings with a public comment session. iMO\emoer zz, zuu-t Gaithersburg, MD NCST Advisory Committee discussion on draft annual report to Congress, a public comment session, and a closed session to discuss pre-draft recommendations for WTC Investigation.

April 5. 2005 New York City, NY Media and public briefing on release of the probable collapse sequence for the WTC towers and draft reports for the projects on

codes and practices, evacuation, and emergency response. June 23. 2005 New York City, NY Media and public briefing on release of all draft reports for the WTC towers and draft recommendations for public comment.

September 12-13.

2005

Gaithersburg, MD NCST Advisory Committee meeting on disposition of public

comments and update to draft reports for the WTC towers. September 13-15,

2005

Gaithersburg, MD WTC Technical Conference for stakeholders and technical community for dissemination of findings and recommendations

and opportunity for public to make technical comments.

• A dissemination and technical assistance program (DTAP) to (a) engage leaders of the

construction and building community in ensuring timely adoption and widespread use of

proposed changes to practices, standards, and codes resulting from the WTC Investigation

and the R&D program, and (b) provide practical guidance and tools to better prepare facility owners, contractors, architects, engineers, emergency responders, and regulatory authorities

to respond to future disasters. The desired outcomes are to make buildings, occupants, and first responders safer in future disaster events.

NISTNCSTAR 1-6B, WTC Investigation xxi
Preface

National Construction Safety Team Reports on the WTC Investigation

A final report on the collapse of the WTC towers is being issued as NIST NCSTAR 1. A companion

report on the collapse of WTC 7 is being issued as NIST NCSTAR 1 A. The present report is one of a set that provides more detailed documentation of the Investigation findings and the means by which these

technical results were achieved. As such, it is part of the archival record of this Investigation. The titles of the full set of Investigation publications are:

NIST (National Institute of Standards and Technology). 2005. Federal Building and Fire Safety

Investigation of the World Trade Center Disaster: Final Report on the Collapse ofthe World Trade

Center Towers. NIST NCSTAR 1. Gaithersburg, MD, September.

NIST (National Institute of Standards and Technology). 2006. Federal Building and Fire Safety

Investigation of the World Trade Center Disaster: Final Report on the Collapse of World Trade Center 7. NIST NCSTAR 1 A. Gaithersburg, MD.

Lew, H. S., R. W. Bukowski, and N. J. Carino. 2005. Federal Building and Fire Safety Investigation of

the World Trade Center Disaster: Design, Construction, and Maintenance ofStructural and Life Safety

Systems. NIST NCSTAR 1-1. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Fanella, D. A., A. T. Derecho, and S. K. Ghosh. 2005. Federal Building and Fire Safety

Investigation of the World Trade Center Disaster: Design and Construction ofStructural Systems.

NIST NCSTAR 1-1 A. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Ghosh, S. K., and X. Liang. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Comparison ofBuilding Code Structural Requirements. NIST

NCSTAR 1-1B. National Institute of Standards and Technology. Gaithersburg, MD, September.

Fanella, D. A., A. T. Derecho, and S. K. Ghosh. 2005. Federal Building and Fire Safety

Investigation ofthe World Trade Center Disaster: Maintenance and Modifications to Structural

Systems. NIST NCSTAR 1-1C. National Institute of Standards and Technology. Gaithersburg,

MD, September.

Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Fire Protection and Life Safety Provisions Applied to the Design and

Construction of World Trade Center 1, 2, and 7 and Post-Construction Provisions Applied after Occupancy. NIST NCSTAR 1-1D. National Institute of Standards and Technology. Gaithersburg,

MD, September.

Razza, J. C, and R. A. Grill. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Comparison ofCodes, Standards, and Practices in Use at the Time ofthe

Design and Construction of World Trade Center 1, 2, and 7. NIST NCSTAR 1-1E. National

Institute of Standards and Technology. Gaithersburg, MD, September.

Grill, R. A., D. A. Johnson, and D. A. Fanella. 2005. Federal Building and Fire Safety

Investigation ofthe World Trade Center Disaster: Comparison ofthe 1968 and Current (2003) New

xxn NIST NCSTAR 1-6B, WTC Investigation
Preface

York City Building Code Provisions. NIST NCSTAR 1- IF. National Institute of Standards and

Technology. Gaithersburg, MD, September.

Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Amendments to the Fire Protection and Life Safety Provisions ofthe New

York City Building Code by Local Laws Adopted While World Trade Center 1, 2, and 7 Were in Use. NIST NCSTAR 1-1G. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Post-Construction Modifications to Fire Protection and Life Safety Systems

of World Trade Center I and 2. NIST NCSTAR 1-1H. National Institute of Standards and

Technology. Gaithersburg, MD, September.

Grill, R. A., D. A. Johnson, and D. A. Fanella. 2005. Federal Building and Fire Safety Investigation

ofthe World Trade Center Disaster: Post-Construction Modifications to Fire Protection, Life

Safety, and Structural Systems of World Trade Center 7. NIST NCSTAR 1-11. National Institute of

Standards and Technology. Gaithersburg, MD, September.

Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Design, Installation, and Operation ofFuel System for Emergency Power in World Trade Center 7. NIST NCSTAR 1-1 J. National Institute of Standards and Technology.

Gaithersburg. MD, September.

Sadek, F. 2005. Federal Building and Fire Safety- Investigation of the World Trade Center Disaster:

Baseline Structural Performance and Aircraft Impact Damage Analysis ofthe World Trade Center

Towers. NIST NCSTAR 1-2. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Faschan, W. J., and R. B. Garlock. 2005. Federal Building and Fire Safety Investigation ofthe

World Trade Center Disaster: Reference Structural Models and Baseline Performance Analysis of

the World Trade Center Towers. NIST NCSTAR 1-2A. National Institute of Standards and

Technology. Gaithersburg, MD, September.

Kirkpatrick, S. W., R. T. Bocchieri, F. Sadek, R. A. MacNeill, S. Holmes, B. D. Peterson,

R. W. Cilke, C. Navarro. 2005. Federal Building and Fire Safety Investigation ofthe World Trade

Center Disaster: Analysis ofAircraft Impacts into the World Trade Center Towers, NIST

NCSTAR 1-2B. National Institute of Standards and Technology. Gaithersburg, MD, September.

Gayle, F. W., R. J. Fields, W. E. Luecke, S. W. Banovic, T. Foecke, C. N. McCowan, T. A. Siewert, and

J. D. McColskey. 2005. Federal Building and Fire Safety Investigation ofthe World Trade Center

Disaster: Mechanical and Metallurgical Analysis ofStructural Steel. NIST NCSTAR 1-3. National

Institute of Standards and Technology. Gaithersburg, MD, September.

Luecke, W. E., T. A. Siewert, and F. W. Gayle. 2005. Federal Building and Fire Safety

Investigation ofthe World Trade Center Disaster: Contemporaneous Structural Steel

Specifications. NIST Special Publication 1-3A. National Institute of Standards and Technology.

Gaithersburg, MD, September.

NIST NCSTAR 1-6B, WTC Investigation xxm
Preface

Banovic, S. W. 2005. Federal Building and Fire Safety Investigation ofthe World Trade Center

Disaster: Steel Inventoiy and Identification. NIST NCSTAR 1-3B. National Institute of Standards

and Technology. Gaithersburg, MD, September.

Banovic, S. W., and T. Foecke. 2005. Federal Building and Fire Safety Investigation of the World

Trade Center Disaster: Damage and Failure Modes ofStructural Steel Components. NIST

NCSTAR 1-3C. National Institute of Standards and Technology. Gaithersburg, MD, September.

Luecke, W. E., J. D. McColskey, C. N. McCowan, S. W. Banovic, R. J. Fields, T. Foecke,

T. A. Siewert, and F. W. Gayle. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Mechanical Properties ofStructural Steels. NIST NCSTAR 1 -3D.

National Institute of Standards and Technology. Gaithersburg, MD, September.

Banovic, S. W., C. N. McCowan, and W. E. Luecke. 2005. Federal Building and Fire Safety

Investigation ofthe World Trade Center Disaster: Physical Properties ofStructural Steels. NIST

NCSTAR 1-3E. National Institute of Standards and Technology. Gaithersburg, MD, September.

Evans, D. D., R. D. Peacock, E. D. Kuligowski, W. S. Dols, and W. L. Grosshandler. 2005. Federal

Building and Fire Safety Investigation ofthe World Trade Center Disaster: Active Fire Protection

Systems. NIST NCSTAR 1-4. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Kuligowski, E. D., D. D. Evans, and R. D. Peacock. 2005. Federal Building and Fire Safety

Investigation ofthe World Trade Center Disaster: Post-Construction Fires Prior to September 11,

2001. NIST NCSTAR 1-4A. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Hopkins, M., J. Schoenrock, and E. Budnick. 2005. Federal Building and Fire Safety Investigation

ofthe World Trade Center Disaster: Fire Suppression Systems. NIST NCSTAR 1-4B. National

Institute of Standards and Technology. Gaithersburg, MD, September.

Keough, R. J., and R. A. Grill. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Fire Alarm Systems. NIST NCSTAR 1-4C. National Institute of Standards

and Technology. Gaithersburg, MD, September.

Ferreira, M. J., and S. M. Strege. 2005. Federal Building and Fire Safety Investigation ofthe

World Trade Center Disaster: Smoke Management Systems. NIST NCSTAR 1-4D. National

Institute of Standards and Technology. Gaithersburg, MD, September.

Gann, R. G., A. Hamins, K. B. McGrattan, G. W. Mulholland, H. E. Nelson, T. J. Ohlemiller,

W. M. Pitts, and K. R. Prasad. 2005. Federal Building and Fire Safety Investigation ofthe World Trade

Center Disaster: Reconstruction ofthe Fires in the World Trade Center Towers. NIST NCSTAR 1-5. National Institute of Standards and Technology. Gaithersburg, MD, September.

Pitts, W. M., K. M. Butler, and V. Junker. 2005. Federal Building and Fire Safety Investigation of

the World Trade Center Disaster: Visual Evidence, Damage Estimates, and Timeline Analysis.

NIST NCSTAR 1-5A. National Institute of Standards and Technology. Gaithersburg, MD,

September.

XXIV NIST NCSTAR 1-6B, WTC Investigation
Preface

Hamins, A., A. Maranghides, K. B. McGrattan, E. Johnsson, T. J. Ohlemiller, M. Donnelly,

J. Yang, G. Mulholland, K. R. Prasad, S. Kukuck, R. Anleitner and T. McAllister. 2005. Federal

Building and Fire Safety Investigation ofthe World Trade Center Disaster: Experiments and

Modeling ofStructural Steel Elements Exposed to Fire. NIST NCSTAR 1 -5B. National Institute of

Standards and Technology. Gaithersburg, MD, September.

Ohlemiller. T. J., G. W. Mulholland, A. Maranghides, J. J. Filliben, and R. G. Gann. 2005. Federal

Building and Fire Safety Investigation ofthe World Trade Center Disaster: Fire Tests ofSingle

Office Workstations. NIST NCSTAR 1-5C. National Institute of Standards and Technology.

Gaithersburg, MD, September.

Gann, R. G., M. A. Riley, J. M. Repp, A. S. Whittaker, A. M. Reinhorn, and P. A. Hough. 2005.

Federal Building and Fire Safety Investigation ofthe World Trade Center Disaster: Reaction of

Ceiling Tile Systems to Shocks. NIST NCSTAR 1-5D. National Institute of Standards and

Technology. Gaithersburg, MD, September.

Hamins, A., A. Maranghides, K. B. McGrattan, T. J. Ohlemiller, and R. Anleitner. 2005. Federal

Building and Fire Safety Investigation ofthe World Trade Center Disaster: Experiments and

Modeling ofMultiple Workstations Burning in a Compartment. NIST NCSTAR 1-5E. National

Institute of Standards and Technology. Gaithersburg, MD, September.

McGrattan, K. B., C. Bouldin, and G. Forney. 2005. Federal Building and Fire Safety

Investigation ofthe World Trade Center Disaster: Computer Simulation of the Fires in the World

Trade Center Towers. NIST NCSTAR 1-5F. National Institute of Standards and Technology.

Gaithersburg. MD. September.

Prasad, K. R., and H. R. Baum. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Fire Structure Interface and Thermal Response ofthe World Trade Center

Towers. NIST NCSTAR 1-5G. National Institute of Standards and Technology. Gaithersburg,

MD, September.

Gross, J. L., and T. McAllister. 2005. Federal Building and Fire Safety Investigation ofthe World Trade

Center Disaster: Stmctural Fire Response and Probable Collapse Sequence ofthe World Trade Center

Towers. NIST NCSTAR 1-6. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Carino, N. J., M. A. Starnes. J. L. Gross, J. C. Yang, S. Kukuck, K. R. Prasad, and R. W. Bukowski.

2005. Federal Building and Fire Safety Investigation ofthe World Trade Center Disaster: Passive

Fire Protection. NIST NCSTAR 1-6A. National Institute of Standards and Technology.

Gaithersburg, MD, September.

Gross, J., F. Hervey, M. Izydorek, J. Mammoser, and J. Treadway. 2005. Federal Building and

Fire Safety Investigation ofthe World Trade Center Disaster: Fire Resistance Tests ofFloor Truss

Systems. NIST NCSTAR 1-6B. National Institute of Standards and Technology. Gaithersburg,

MD, September.

Zarghamee, M. S., S. Bolourchi, D. W. Eggers, O. O. Erbay, F. W. Kan, Y. Kitane, A. A. Liepins,

M. Mudlock, W. I. Naguib, R. P. Ojdrovic, A. T. Sarawit, P. R Barrett, J. L. Gross, and

NIST NCSTAR 7-66, WTC Investigation XXV
Preface

T. P. McAllister. 2005. Federal Building and Fire Safety Investigation ofthe World Trade Center

Disaster: Component, Connection, and Subsystem Structural Analysis. NIST NCSTAR 1-6C.

National Institute of Standards and Technology. Gaithersburg, MD, September.

Zarghamee, M. S., Y. Kitane, O. O. Erbay, T. P. McAllister, and J. L. Gross. 2005. Federal

Building and Fire Safety Investigation ofthe World Trade Center Disaster: Global Structural

Analysis ofthe Response ofthe World Trade Center Towers to Impact Damage and Fire. NIST

NCSTAR 1-6D. National Institute of Standards and Technology. Gaithersburg, MD, September.

McAllister, T., R. W. Bukowski, R. G. Gann, J. L. Gross, K. B. McGrattan, H. E. Nelson, L. Phan,

W. M. Pitts, K. R. Prasad, F. Sadek. 2006. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of World Trade

Center 7. (Provisional). NIST NCSTAR 1-6E. National Institute of Standards and Technology.

Gaithersburg, MD.

Gilsanz, R., V. Arbitrio, C. Anders, D. Chlebus, K. Ezzeldin, W. Guo, P. Moloney, A. Montalva,

J. Oh, K. Rubenacker. 2006. Federal Building and Fire Safety Investigation ofthe World Trade

Center Disaster: Structural Analysis ofthe Response of World Trade Center 7 to Debris Damage

and Fire. (Provisional). NIST NCSTAR 1-6F. National Institute of Standards and Technology.

Gaithersburg, MD.

Kim, W. 2006. Federal Building and Fire Safety Investigation ofthe World Trade Center

Disaster: Analysis ofSeptember 1 1, 2001, Seismogram Data. (Provisional). NIST NCSTAR 1-6G.

National Institute of Standards and Technology. Gaithersburg, MD.

Nelson, K. 2006. Federal Building and Fire Safety Investigation ofthe World Trade Center

Disaster: The Con Ed Substation in World Trade Center 7. (Provisional). NIST NCSTAR 1-6H.

National Institute of Standards and Technology. Gaithersburg, MD.

Averill, J. D., D. S. Mileti, R. D. Peacock, E. D. Kuligowski, N. Groner, G. Proulx, P. A. Reneke, and

H. E. Nelson. 2005. Federal Building and Fire Safety Investigation ofthe World Trade Center Disaster:

Occupant Behavior, Egress, and Emergency Communication. NIST NCSTAR 1-7. National Institute of

Standards and Technology. Gaithersburg, MD, September.

Fahy, R., and G. Proulx. 2005. Federal Building and Fire Safely Investigation ofthe World Trade

Center Disaster: Analysis ofPublished Accounts ofthe World Trade Center Evacuation. NIST

NCSTAR 1-7A. National Institute of Standards and Technology. Gaithersburg, MD, September.

Zmud, J. 2005. Federal Building and Fire Safety Investigation ofthe World Trade Center

Disaster: Technical Documentation for Sur\>ey Administration. NIST NCSTAR 1-7B. National

Institute of Standards and Technology. Gaithersburg, MD, September.

Lawson, J. R., and R. L. Vettori. 2005. Federal Building and Fire Safety Investigation ofthe World

Trade Center Disaster: The Emergency Response Operations. NIST NCSTAR 1-8. National Institute of

Standards and Technology. Gaithersburg, MD, September.

XXVI NIST NCSTAR 7-66, WTC Investigation
Acknowledgments

The National Institute of Standards and Technology would like to acknowledge the many individuals who

contributed substantially to the successful completion of four ASTM E 1 19 Standard Fire Tests conducted

by Underwriters Laboratories, Inc. (UL) under contract to NIST and reported herein. Specifically, the

laboratory staff at UL including William Joy, Aldo Jimenez, and Romuald Bolewski did an outstanding

and highly professional job. Colleagues at NIST who contributed both technically as well as administratively include Dr. Nicholas Carino, Dr. William Grosshandler, and Dr. Monica Starnes.

NISTNCSTAR 7-66, WTC Investigation xxvn
Acknowledgments

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xxviii NISTNCSTAR 7-66, WTC Investigation
Executive Summary

E.1 OBJECTIVES OF THE FIRE RESISTANCE TESTS

One of the objectives of the National Institute of Standards and Technology (MST) Investigation was to determine why and how the World Trade Center (WTC) towers collapsed following the initial impact of

the aircraft. A key aspect of this work was to differentiate the factors that most influenced the collapse of

the WTC towers as they may relate to normal building and fire safety considerations and those unique to the terrorist attacks of September 1 1, 2001, Another of the NIST Investigation objectives was to study

the procedures and practices that were used in the design, construction, operation, and maintenance of the

WTC buildings. As an important public safety objective, it was necessary to establish the facts regarding

the acceptance procedures for innovative materials, technologies, and systems. Past building and fire safety investigations have shown that such studies help to identify improvements to practices, standards,

and codes that may be warranted.

NIST review of available documents had indicated that the fire performance of the composite floor

system of the WTC towers was an issue of concern to the building owners and designers not only during

the original design phase but throughout the service life of the buildings. NIST found no evidence

regarding the technical basis for the selection of sprayed fire-resistive material (SFRM ) for the WTC

floor trusses and for the SFRM thickness to achieve a 2 h rating. Further, no evidence was found that fire resistance tests of the WTC floor system were conducted. Review of documents related to the WTC has

not identified a similar concern for other structural components of the WTC towers.

To address, in part, the investigation objectives cited above, NIST conducted a series of four standard fire resistance tests of the composite floor system used in the towers. The fire resistance tests were conducted

to study three factors: the effect of (1) SFRM thickness, (2) test restraint conditions, and (3) scale of the

test. The tests were conducted by Underwriters Laboratories, Inc. (UL) under contract to NIST at UL's

Northbrook (Illinois) fire testing facility and at its affiliate's, Underwriters Laboratories of Canada, fire

testing facilities in Toronto.

E.2 THE WTC FLOOR SYSTEM AND SFRM

The floor system design for the world trade center consisted of a lightweight concrete floor slab supported

by steel trusses bridging between the building's core columns and exterior wall columns. The main

composite trusses, which were used in pairs, spanned either 60 ft or 35 ft. Steel double-angles formed the

top and bottom chords of the trusses, while round bars were used for the webs. The web members

protruded above the top chord in the form of a "knuckle" which was embedded in the concrete slab to develop composite action. Additionally, the floor system included bridging trusses perpendicular to the

main trusses. In the corners of the towers, the bridging trusses acted with the main trusses to provide twoway slab action.

Passive fire protection was provided by sprayed fire-resistive materials (SFRM), commonly referred to as

"fireproofing," applied directly to the steel bars of the trusses. The Port Authority of New York and New

Jersey (PANYNY or Port Authority) specified U.S. Minerals Products Cafco BLAZE-SHIELD Type D as

NISTNCSTAR 1-6B, WTC Investigation XXIX
Executive Summary

the sprayed fire-resistive material and in a letter to the fireproofing contractor stated that "All Tower

beams, spandrels, and bar joists requiring spray-on fireproofing are to have a V2" [1/2 in] covering of

Cafco'". Measured thicknesses of the applied SFRM were found to vary between 0.52 in. and 1.17 in. with an overall average of approximately 0.75 in. These two thicknesses, Vi in. representing specified

thickness and % in. representing average applied thickness, were used in the standard fire resistance tests described here.

E.3 FIRE RESISTANCE TESTING

The fire rating of structural materials and assemblies is generally determined through testing, and in the

United States, such testing is frequently conducted in accordance with ASTM E 1 1 9, "Standard Test Methods for Fire Tests of Building Construction and Materials. " The test methods described in ASTM E 1 19 prescribe a standard fire exposure for comparing the test results of building construction

assemblies. For the tests of floors and roofs, a test assembly is structurally loaded and the standard fire exposure is applied to the underside of the specimen. The assembly is evaluated for its ability to contain

the fire by limiting flame spread (hot gasses) and heating of the unexposed surface while maintaining the

applied load. The assembly is given a rating, expressed in hours, based on these conditions of acceptance.

Since 1971, versions of the ASTM E 1 19 Standard differentiate between testing and classifying thermally

restrained and unrestrained floor assemblies. A thermally restrained specimen is "one in which expansion

at the support of a load carrying element resulting from the effects of fire is resisted by forces external to the element." In an unrestrained condition, the element is free to expand and rotate at its supports. It is customary in the United States to conduct standard fire tests of floor assemblies in the restrained

condition.

The current standard describes a means to establish restrained and unrestrained ratings for floor

assemblies from restrained test samples. For restrained ratings from restrained test samples, the

conditions of acceptance are based on limiting the passage of flame and hot gasses, limiting temperatures on the unexposed surface of the slab, and failure of the assembly to sustain the applied load. For an

unrestrained rating determined from a restrained test sample, the conditions of acceptance are based on

the same criteria and, in addition, temperature limitations are placed on the main structural members.

In addition, since 1971, the ASTM E 1 19 Standard describes a means to establish unrestrained ratings

from unrestrained test samples. For unrestrained samples, the fire resistance rating is again based on

limiting passage of flame and hot gasses, exceeding temperatures on the unexposed surface of the slab,

and failure to sustain the applied load; there are no limiting temperatures on the steel structural members

when the test sample is installed in an unrestrained condition.

Prior to 1970, there was no distinction between restraint conditions, nor were restrained and unrestrained

ratings defined in ASTM E 1 19. Fire resistance ratings were determined based upon the same

requirements as for restrained assemblies described above, and no limitations were placed on temperature

of structural steel.

1 Cafco was the manufacturer of the SFRM used for fire protection of structural steel in the WTC.

xxx NISTNCSTAR 1-6B, WTC Investigation
Executive Summary

In practice, a floor assembly such as that used in the WTC towers is neither restrained nor unrestrained

but is likely somewhere in between. Testing under both restraint conditions, then, bounds expected

performance under the standard fire exposure. In addition, it provides a comparison of unrestrained

ratings developed from both restrained and unrestrained test conditions.

The ASTM E 1 19 Standard requires that, for floor and roof assembly tests, the area exposed to fire be a minimum of 180 ft" and neither dimension of the furnace less than 12 ft. Traditionally, relatively small

scale assemblies have been tested, and results have been scaled to practical floor system spans.

The Underwriters Laboratories of Canada fire testing facility in Toronto, has a furnace with nominal

dimensions of 35 ft by 14 ft. Thus, full- or large-scale tests of floor assemblies can be tested in this furnace. Availability of the 35 ft span furnace in UL's Toronto facility, in addition to the 17 ft span

furnace its Northbrook, Illinois, facility allowed NIST to conduct tests to compare the effect of scale.

E.4 TEST PROGRAM

To limit the number of tests and obtain information of greatest value to meet the investigation objectives,

NIST conducted four tests to study the effect of three factors: SFRM thickness, scale of the test, and test restraint conditions. To this end, four tests were designed and conducted as follows:

• Test #1 : Full-scale, restrained test condition, 3A in. thick SFRM.

• Test #2: Full-scale, unrestrained test condition, 3A in. thick SFRM.

• Test #3: Reduced-scale, restrained conditions, 3A in. thick SFRM.

• Test #4: Reduced-scale, restrained conditions, lA in. thick SFRM.

The full-scale tests were conducted at the Underwriters Laboratories of Canada fire testing facility in Toronto . Loading of the floor slab with an applied load to "simulate a maximum load condition," as required by ASTM E 1 1 9, was accomplished through a combination concrete blocks and containers filled with water. The water containers were tied-off with steel cables to prevent them from falling into the

furnace and causing damage to the fire brick and instrumentation in the event of a catastrophic failure of

the floor system.

For the reduced-scale test specimens, the size of the truss members and thickness of concrete slab were

selected to allow the most information to be extracted as practicably possible considering that the

Standard Fire Resistance Test is a test of the assembly's ability to contain a fire and is based on both

thermal response (flame spread and heating of the unexposed surface) and structural response (support the

applied load) to the standard fire exposure. The sizes of the steel members, thickness of concrete slab,

and truss spacing were selected to be the same as in the full-scale tests. Otherwise, the geometry was

scaled by roughly half. This scaling required that the loading be increased by a factor of two.

NISTNCSTAR 1-6B, WTC Investigation XXXl
Executive Summary

E.5 TEST RESULTS

Results of the four tests are summarized as follows:

• The test assemblies were able to withstand standard fire conditions for between 3A h and 2 h

without exceeding the limits prescribed by ASTM E 1 19.

• Test specimens protected with 3A in. thick spray applied fire-resistive material were able to sustain the maximum design load for approximately 2 hours without collapsing; in the

unrestrained test, the load was maintained for 314 h without collapsing.

• The restrained full-scale floor system obtained a fire resistance rating of 1

lA h while the

unrestrained floor system achieved a 2 h rating. Past experience with the ASTM E 1 19 test method would lead investigators to expect that the unrestrained floor assembly would not perform as well as the restrained assembly, and therefore, would receive a lower fire rating.

• A fire rating of 2 h was determined from the reduced-scale test with the average applied

SFPvM thickness of 3A in., while a fire rating of VA h was determined from the full-scale test with the same SFRM thickness.

• The result stated above raises the question of whether or not a fire rating based on the

ASTM E 1 19 performance of a 17 ft span floor assembly is scalable to a larger floor system

such as found in the WTC towers where spans ranged from 35 ft to 60 ft.

• A fire rating of 3A h was determined from the reduced-scale test with the specified SFRM

thickness of Vi in.

The tested floor assemblies were similar, though not identical, to steel joist and concrete floor systems

that are widely used in low rise construction. The test results provide valuable insight into the behavior of

these widely used assemblies and also identify issues regarding scaling, restraint, and SFRM thickness

that require further study for floor systems and other types of structural components such as beams,

girders, columns, trusses, etc.

The NIST tests identified areas where further study related to the Standard Fire Resistance Test method

may be warranted. The issues related to the test method that NIST will consider in formulating its recommendations include:

• the scale of the test for prototype assemblies that are much larger than the tested assemblies,

• the effect of restraint conditions on test results,

• the repeatability of test results (e.g., do multiple fire resistance tests conducted under the same conditions yield the same results?),

• the effects of test scale, end restraint, and test repeatability on other types of structural components (beams, girders, columns, etc.), and

xxxn NISTNCSTAR 1-6B, WTC Investigation
Executive Summary

• the acceptance criteria to evaluate the load carrying capacity of the tested assemblies

(currently tests are stopped before the load carrying capacity of the assembly is reached

because other acceptance criteria are met or because the deflection becomes excessive and

assembly failure could damage the furnace).

NISTNCSTAR 1-6B, WTC Investigation XXXlll
Executive Summary

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xxxiv NISTNCSTAR 1-6B, WTC Investigation
Chapter 1 Introduction

The need to perform fire resistance rating tests of the floor system developed for the World Trade Center

(WTC) towers was raised several times during the design stage as well as after completion of the towers. National Institute of Standards and Technology (NIST) NCSTAR 1-6A2 contains a detailed chronicle of

the procedures and practices used for passive fire protection of the floor system of the WTC towers. The

report summarizes factual data contained in documents provided to NIST by The Port Authority of New

York and New Jersey (Port Authority) and its contractors and consultants; by Laclede Steel Company, the

firm that supplied the floor trusses for the WTC towers; and by United States Mineral Products Co.

(USM), the manufacturer of the SFRM. Review of the information collected revealed no evidence that testing was ever conducted to determine the fire endurance of the WTC floor system fireproofed with

sprayed fire-resistive materials (SFRM).

1 .1 MOTIVATION FOR CONDUCTING STANDARD FIRE TESTS OF THE WTC

FLOOR SYSTEM

The first of the four NIST investigation objectives (see Preface) was to determine why and how the WTC

towers collapsed following the initial impact of the aircraft. A key aspect of this work was to differentiate

the factors that most influenced the collapse of the WTC towers as they may relate to normal building and

fire safety considerations and those unique to the terrorist attacks of September 11, 2001.

Another of the four NIST investigation objectives was to study the procedures and practices that were

used in the design, construction, operation, and maintenance of the WTC buildings. A key aspect was to study the acceptance procedures for innovative materials, technologies, and systems. Past building and

fire safety investigations have shown that studies of procedures and practices help to identify

improvements to practices, standards, and codes that may be warranted.

A third investigation objective was to identify, as specifically as possible, areas in national building and

fire codes, standards, and practices that warrant revision.

NIST review of available documents related to the design and construction of the WTC towers indicated

that the fire performance of the composite floor system of the WTC towers was an issue of concern to the building owners and designers from the original design and throughout the service life of the buildings

(NIST NCSTAR 1-6A). NIST found no evidence to determine the technical basis for the selection of

SFRM for the WTC floor trusses and of the thickness required to achieve a 2 hour rating. Further, NIST

found no evidence that fire resistance tests of the WTC floor system were ever conducted. Review of the

documents has not identified a similar concern for other structural components of the WTC towers.

2 This reference is to one of the companion documents from this Investigation. A list of these documents appears in the Preface

to this report.

NIST NCSTAR 7-66, WTC Investigation 1
Chapter 1

1 .2 PURPOSE OF THE STANDARD FIRE TESTS

To address these three investigation objectives, NIST conducted a series of four standard fire tests as described herein. The purpose of this series of tests was as follows:

• to establish the baseline performance of the floor system of the WTC towers as they were

originally designed,

• to differentiate the factors that most influenced the collapse of the WTC towers as they may

relate to normal building and fire safety considerations and those unique to the terrorist attacks of September 1 1

, 200 1

,

• to determine whether there was an adequate technical basis for the original SFRM

specification, and

• to study the procedures and practices used to accept an innovative structural and fire protection system.

1.3 TEST VARIABLES

To obtain information of greatest value to meet the investigation objectives, while limiting the number of

tests to a practical number, NIST studied the effects of three factors: (1) SFRM thickness, (2) test restraint conditions, and (3) scale of the test. These factors are described more fully in this section.

1.3.1 SFRM Thickness

The Port Authority and its consultants sought an efficient and economical method to provide fire protection for the floor system and, by late 1965, the use of a fire-resistive material that was applied

directly to the bars of the steel trusses was selected

3

. The Port Authority specified U.S. Minerals Products

Cafco BLAZE-SHIELD Type D

4 as the sprayed fire-resistive material and, in a letter to the fireproofing contractor stated,

"All Tower beams, spandrels, and bar joists requiring spray-on fireproofing are to have a

Vt." covering of Cafco.

5

Fire protection of a truss-supported floor system using a fire-resistive material applied directly to the steel trusses was innovative and not consistent with the practice at the time. Fire resistance testing of the floor

assemblies constructed to represent as closely as practical those used in the WTC towers provides

information to evaluate the procedures and practices used to accept an innovative system and to determine

if there is a need for changes to those practices.

See NIST NCSRAT 1-6A for a detailed chronicle of the procedures and practices used for fire protection of structural steel in the WTC towers

4 This U.S. Minerals Products SFRM has been cited in WTC correspondence and documents using several designations. For

consistency with other WTC Investigation reports, it is referred to herein as BLAZE-SHIELD D.

5 Letter dated October 30, 1 969 from Robert J. Linn (Manager, Project Planning, The World Trade Center) to Mr. Louis DiBono

(Mario & DiBono Plastering Co., Inc.).

2 NISTNCSTAR 1-6B, WTC Investigation
Introduction

The BLAZE-SHIELD D product originally specified contained asbestos and its use was discontinued in 1970 at the 38th floor of WTC I. Thermal protection of the remaining floors of WTC 1 and all of WTC 2 was carried out using BLAZE-SHIELD DC/F, a product that contained mineral wool fibers in place of the

asbestos fibers.

In 1994, the Port Authority performed a series of thickness measurements of the existing SFRM

on floors 23 and 24 of WTC I. Six measurements were taken from "both flanges and web" of

each of 16 random trusses on each floor at those locations where the SFRM was not damaged or

absent. Measured average thickness varied between 0.52 in. and 1.17 in. and for the 32

measurements (16 on each floor) the overall average was 0.74 in. Four of the 32 trusses, had an

average thicknesses between 0.52 in. and 0.56 in. This limited set of data suggests that the average thickness of SFRM as originally installed (as contrasted with SFRM that was upgraded in thickness beginning in the 1990s) was approximately 0.75 in.

1.3.2 Restraint Conditions

It is customary in the United States to conduct standard fire tests of floor assemblies in the restrained

condition; that is, the condition in which expansion at the support of the floor test assembly resulting from

the effects of the exposing fire is resisted by forces external to the element. In practice, a floor assembly

such as that used in the WTC towers is neither restrained nor unrestrained, but likely its restraint condition lies somewhere in between. Testing under both restraint conditions, then, provides bounds on

the expected performance of the floor system under the standard fire exposure. In addition, it provides a comparison of unrestrained ratings developed from both restrained and unrestrained test conditions.

1.3.3 Scale

Traditionally, relatively light assemblies have been tested with spans less than 18 ft, and results have been

scaled up to practical floor system dimensions and spans. The Underwriters Laboratories of Canada fire testing facility in Toronto (ULC) has a furnace with nominal long dimension of 35 ft. Thus, full- or largescale tests of floor assemblies can be tested in this furnace. Availability of the 35 ft span furnace at ULC,

in addition to the 17 ft span furnace at UL's Northbrook, Illinois, facility (ULN) allowed NIST to conduct

comparison tests to study the effect of scale .

1.4 TEST PROGRAM

Four tests as noted above were designed and conducted as follows:

• Test No. 1: Full-scale, restrained test condition, 3A in. thick SFRM.

• Test No. 2: Full-scale, unrestrained test condition, 3A in. thick SFRM.

• Test No. 3: Reduced-scale, restrained conditions, Va in. thick SFRM.

6 ULC is used in this report to identify the fire testing facility operated by UL's affiliate, Underwriters Laboratories of Canada,

while ULN is used to identify UL's Northbrook (Illinois) fire testing facility.

NIST NCSTAR 1-6B, WTC Investigation 3
Chapter 1

• Test No. 4: Reduced-scale, restrained conditions, V2 in. thick SFRM.

The objective of the full-scale restrained test with 3A in. thick SFRM, Test 1, was to determine the

baseline fire resistance of the floor system with average as-applied SFRM thickness. This test also

demonstrated whether the fire resistance of such a system was significantly different from that of a system

with the specified SFRM thickness of 14 in.

The test conditions for Test 2, full-scale unrestrained test with lA in. thick SFRM, were the same as those

for Test 1 except that the specimen was supported to allow thermal expansion and, therefore, represented

the unrestrained test condition. Results of this test allowed a determination of the unrestrained rating by

test and, by comparing with the results of Test 1 , a comparison of unrestrained ratings from both a

restrained and unrestrained assembly test.

Test 3 was a reduced-scale test which, other than scale, was the same as Test 1. Thus, a comparison of

the results of these two tests allowed an examination of whether test results are independent of test assembly scale.

Test assemblies for Tests 1, 2 and 3 were fire protected in the same manner, with 3A in. thick SFRM

representing the average SFRM thickness in the impact and fire affected floors of WTC 2. Measurements

taken from photographs of the originally applied SFRM indicated that, while the SFRM thickness on

main the trusses was approximately % in., the thickness on the bridging trusses was approximately half

that value (see NIST NCSTAR 1-6A). Also, photographs indicated that the metal deck was sometimes

sprayed and sometimes not. For these three tests (Tests 1, 2, and 3), then, the main trusses were protected

with Va, in. thick SFRM, the bridging trusses with V» in. thick SFRM, and the metal deck was not

intentionally sprayed but was also not masked from overspray and thereby had, in most instances, at least a light covering of SFRM. These conditions best represented the thickness of the SFRM as it was

originally applied in the one-way slab areas.

The objective of the test with the lA in. SFRM (Test 4) was to determine whether or not there was

adequate technical basis for the original SFRM specification. As explained by the designer, it was not necessary to fire protect the bridging trusses in the one-way areas nor was it necessary to spray the metal

deck (see NIST NCSTAR 1-6A). Consequently, the Test 4 specimen had lA in. thick SFRM applied to the main trusses and no SFRM applied to either the bridging trusses or the underside of the metal deck.

Both the bridging trusses and metal deck were masked to prevent overspray as well. These conditions best

represented the SFRM that was necessary, in the opinion of the designer, to provide the required level of

passive fire protection.

4 NIST NCSTAR 7-66, WTC Investigation
Chapter 2

ASTM Standard Fire Test

The fire rating of structural materials and assemblies is generally determined through testing, and in the

United States, such testing is frequently conducted in accordance with the ASTM International standard,

ASTM E 1 19, "Standard Test Methods for Fire Tests of Building Construction and Materials"

(ASTM 2000). This standard was first published in 1917 as a tentative standard, ASTM C 19, and was

first adopted as ASTM E 1 19 in 1933. Since its introduction, the test method has been modified and

updated, although its essential character has remained unchanged.

2.1 GENERAL DESCRIPTION

The test methods described in ASTM E 1 1 9 prescribe a standard fire exposure for comparing the test

results of building construction assemblies. For the tests of floors and roofs, a test assembly is structurally loaded and the standard fire exposure is applied to the underside of the specimen. The

assembly is evaluated for its ability to contain a fire by limiting passage of flame or hot gasses, and

limiting heating of the unexposed surface, while maintaining the applied load. The assembly is given a

rating, expressed in hours, based on these acceptance, or end-point, criteria. Revisions to the

ASTM E 1 19 Standard in 1971. introduced the concept of fire endurance classifications based on two

conditions of support: restrained and unrestrained.

2.2 RESTRAINT CONDITIONS

According to Appendix A4 of ASTM E 1 19-73, a restrained condition is "one in which expansion at the

support of a load carrying element resulting from the effects of fire is resisted by forces external to the

element." In an unrestrained condition, the element is free to expand and rotate at its supports. The

Standard does not address how to achieve restraint at the assembly's supports, nor does it specify, in the case of floor assemblies, the stiffness characteristics of the restraining frame used to support an assembly

The current standard describes a means to establish restrained and unrestrained ratings for floor

assemblies from restrained test samples. The conditions of acceptance are based on limiting passage of

flame or hot gasses. limiting temperatures on the unexposed surface of the slab, and failure to sustain the

applied load. In addition, temperature limitations are placed on the main structural members. The

location of temperature measurements on the structural members is specified in the ASTM E 1 19

Standard.

2.3 CONDITIONS OF ACCEPTANCE

The ASTM Standard Fire Test (ASTM 2000) is conducted by exposing a specimen to a standard fire controlled to achieve specified temperatures throughout a specified time period. It is emphasized in the

Standard that the fire exposure "is not representative of all fire conditions because conditions vary with

changes in the amount, nature and distribution of fire loading, ventilation, compartment size and

configuration, and heat sink characteristics of the compartment." The conditions of acceptance relate

NISTNCSTAR 7-66, WTC Investigation 5
Chapter 2

directly to the fire by limiting passage of flame or hot gasses and heating of the unexposed surface while

maintaining the applied load. For floor and roof assemblies, the Standard provides for:

• Measurement of transmission of heat,

• Measurement of the transmission of hot gasses,

• Measurement of the load carrying ability of the test specimen during the test exposure.

Further, the Standard states specifically that it does not provide for, among other things, the following:

• Full information as to performance of assemblies constructed with components or lengths

other than those tested,

• The effect of fire endurance of conventional openings in the assembly, that is, electrical receptacle outlets, plumbing pipe, etc., unless specifically provided for in the construction.

For tests of floors and roofs, a superimposed load is applied "to simulate a maximum load condition,"

which is determined as "the maximum load condition allowed under nationally recognized structural design criteria."

Temperatures of the floor assembly are measured during the fire exposure using thermocouples located on

both the supporting steel members and top and bottom of the concrete slab.

6 NISTNCSTAR 1-6B, WTC Investigation
Chapter 3

Description of WTC Floor System and SFRM

3.1 COMPOSITE SLAB FLOOR SYSTEM

The floor system design for the World Trade Center (WTC) towers consisted of a lightweight concrete

floor slab supported by steel trusses bridging between the building's core columns and exterior wall

columns'. The main composite trusses, which were used in pairs, were spaced at 6 ft 8 in. on center (o.c.)

and had a nominal clear span of either 60 ft or 35 ft. The steel trusses were fabricated using double angles

for the top and bottom chords, and round bars for the webs. The web members protruded above the top

chord in the form of a "knuckle" which was embedded in the concrete slab to develop composite action.

Additionally, the floor system included bridging trusses (perpendicular to main trusses) spaced 13 ft 4 in.

o.c. In the corners of the towers, the bridging trusses acted with the main trusses to provide two-way slab

action, i.e.. bending moments existed in both principal directions. Figure 3-1 is a cut-away of the

composite floor system showing the main and bridging trusses, metal deck, and concrete slab.

Figure 3-1 . Floor system of the WTC towers.

3.2 STEEL TRUSSES

The steel trusses for the floor system were manufactured by Laclede Steel Co. using the resistance

welding process to join the web, generally formed by bending a single steel rod, to the double angles

forming the chord members. Resistance welding melts the two pieces being joined and fuses them to make the weld. The angles, which were produced by Laclede Steel Co., were specially rolled with a

All information and data related to the design and construction of the WTC floor system were obtained from contract drawings

provided to NIST by The Port Authority of New York and New Jersey. Refer to NIST NCSTAR 1-2A for a complete

description of the WTC structural system and index of all structural drawings.

NIST NCSTAR 1-6B, WTC Investigation 7
Chapter 3

convex protrusion on the outside surface of one leg which melted locally where the angle leg was joined

to the round bar webs.

3.3 SFRM THICKNESS

As noted in Section 1.3, the average thickness of SFRM as originally installed was approximately 3A in. The thicknesses of lA in. representing the specified thickness, and 3A in. representing average applied

thickness, were used in the standard fire resistance tests described here (see NIST NCSTAR 1-6A).

8 NIST NCSTAR 1-6B, WTC Investigation
Chapter 4

Floor Test Assemblies

4.1 DESIGN OF TESTS

For floor and roof assemblies, the ASTM E 1 19 Standard requires that the area exposed to fire be a minimum of 180 fr and that neither dimension of the furnace be less than 12 ft. Furnaces available today

(2005) in the United States for conducting standardized fire resistance tests of floor and roof assemblies

have a maximum span less than 18 ft (Beitel 2002). Traditionally, relatively light construction floor assemblies have been tested, and results have been scaled to practical floor system dimensions.

4.1.1 Span of Test Assembly

The floor system used in the World Trade Center (WTC) spanned either 35 ft or 60 ft. The Underwriters

Laboratories of Canada fire testing facility in Toronto (ULC) has a furnace with nominal dimensions of

35 ft by 14 ft, thereby allowing full-scale tests of the 35 ft span floor assemblies. For this series of tests, the floor truss designated on Laclede drawings as C32T5 was selected. This truss type was the most

common 35 ft-span truss in the floors affected by the aircraft impact and subsequent fires (see Appendix

G of NIST NCSTAR 1-2A).

As noted in Section 1.1, one of the motivations for conducting the standard fire resistance tests was to determine the technical basis for the selection of the SFRM for the WTC floor trusses and of the thickness

to achieve a 2 h rating. Since test furnaces available at the time of the initial design of the WTC towers

had a maximum span on the order of 18 ft, it would have been impractical to test a full-scale assembly

although that possibility was raised in discussions between the Port Authority, the building designer, and

steel truss fabricator (see NIST NCSTAR 1-6A). In designing a reduced-scale test, it is important to scale appropriately to capture, as nearly as practical, the conditions used for rating an assembly, namely the

transmission of heat, the transmission of hot gasses, and the load-carrying ability of the test assembly

during the period of fire exposure.

Both the thermal and mechanical properties of the materials and components used in the test assembly are important to its performance in a standard fire test. Likewise, the geometry of the test assembly,

including steel member sizes, thickness of concrete slab, and overall geometric scale are determining

factors in the thermal and structural performance of a test assembly. Finally, the magnitude of the applied

load that represents the maximum load condition affects the structural performance of the test assembly.

The fire exposure must follow the prescribed time-temperature curve given in the ASTM E 1 19 Standard.

4.1.2 Geometric Scaling of Floor Trusses

The prototype truss, designated C32T5, has an overall length of 35 ft 8 in. and a distance between

centerlines of the bolts at the end supports of 35 ft

3A in. The trusses for the "full-scale" test assembly had

an overall length of 35 ft 0 in. as determined by the inside dimension of the reaction frame at the ULC fire

test facility. The overall length of the reduced-scale specimens is 17 ft 5'/2 in., also limited by the largest

NIST NCSTAR 1-6B, WTC Investigation 9
Chapter 4

dimension of the reaction frame used at the ULN fire test facility. Thus, the span of the reduced-scale

specimen was 17.46/35.00 = 0.50, or half that of the full-scale, or prototype, span. A structural element in flexure, such as the floor system under study, carries both shear force and bending

moment. The shear force, which governs the design of the truss web diagonals, is proportional to the

magnitude of the uniform applied load on the slab multiplied by the span. If the span is reduced by one

half, then the maximum shear force is reduced by one half. The bending moment controls the design of

the truss chords and concrete slab and is proportional to the magnitude of the uniform applied load

multiplied by the square of the span. Thus, if the span is reduced by one half, the maximum moment

would be one quarter that in the prototype.

4.1.3 Concrete Slab Thickness

The heating rate of the unexposed surface of the floor assembly depends on the thermal properties of the

lightweight concrete, the thickness of the floor slab, and profile of the supporting metal deck. Since the

thermal properties of concrete are not easily changed, the slab thickness and deck must remain the same

in the scaled specimen as in the prototype, or full-scale, specimen.

4.1.4 Steel Truss Sections

The structural response of a floor assembly subjected to an exposing fire depends on the rate at which the

steel heats up since both the stiffness and strength of the steel decrease with increasing temperature. The

rate at which the steel heats up is, in turn, a function of the thermal properties of the SFRM which change

with temperature, the thickness of the applied SFRM, and the thermal conductivity of the steel. Since

both the mechanical and thermal properties of steel and the SFRM are not easily changed, to preserve the

rate at which the steel heats up and, therefore, the rate at which the steel loses its stiffness and strength,

both the size of the steel sections and thickness of SFRM must be the same in the reduced-scale specimen

as in the full-scale specimen.

4.1.5 Applied Load

The structural response of a floor assembly is also determined by the applied load, which the

ASTM E 1 19 Standard defines as the maximum load condition allowed under nationally recognized

structural design criteria. For the correct structural response to be captured, the stresses in the reducedscale test assembly resulting from the applied load should match, as closely as practical, those of the

prototype floor system. It is this principal upon which the loading for the reduced-scale tests was

calculated.

As discussed under geometric scaling, the shear force, which is a function of the applied load and the

section properties of the members, determine the stresses in the truss web diagonals. If the scale factor is one half, the applied load must be doubled to produce the same shear force. Because the section

properties are not scaled, doubling the magnitude of the applied load produces the same forces in the

diagonals of the reduced-scale assembly as in the prototype. The allowable compressive stress is governed by inelastic buckling and does not scale in exactly the same way, that is, the allowable

compressive stress for the web diagonals in the reduced-scale assembly is greater than that for the web

diagonals in the full-scale assembly.

K) NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

The stresses in the chord members and in the concrete slab are a function of the applied load and span

(bending moment) and the geometry of the assembly and geometric section properties of the structural elements. Because the bending moment is a function of the applied load and the square of the span (see

above), for a scale factor of 0.50 and an applied load approximately twice that of the prototype design

load, the bending moment is half that of the prototype. The force in the chord members is computed from

statics and is a function of the applied load and the depth of the truss. Since the moment is one half and

the depth of the floor section is approximately one half, the stresses in the truss chord members of the

reduced-scale assembly are roughly equal to those of the prototype.

The loading was calculated to satisfy design requirements of the Specification for the Design, Fabrication

& Erection ofStructural Steelfor Buildings, which were the nationally recognized structural design

criteria under which the floor system for the WTC towers was designed (AISC 1963). A complete

description of the specimen loading is presented in Section 4.4

Doubling of the applied load (expressed in force per unit length) on a composite double truss floor system

as discussed above is achievable with the loading devices available. However, if the distance between

trusses is scaled by the factor of one half, then the load per unit area would be four times that applied to the prototype full-scale assembly. Since this magnitude of loading would be difficult to achieve and the

consequences of a structural failure at elevated temperatures would be catastrophic under such a load, the

truss spacing for the reduced-scale tests was not scaled from the full-scale configuration. Since the

trusses are each loaded to their design capacity, the spacing would not be expected to influence the test results significantly.

4.2 MATERIALS OF CONSTRUCTION

Every attempt was made to duplicate conditions that existed at the time of construction of the WTC floor

system, including geometry and section properties of structural components, materials of construction,

and fabrication and construction techniques. This chapter addresses the selection of materials and

components and the level of care taken to insure faithful duplication of the floor system found in the

WTC towers. Properties of the steels, concrete, metal deck, welded wire fabric, etc. used in the

construction of all four test assemblies are documented in this section. Properties of concrete and sprayed

fire-resistive material, which varied for each test specimen, are reported in the next section.

4.2.1 Fabrication of Trusses

As will be addressed in Section 4.2.3, resistance welding, which was used in the fabrication of the WTC

trusses, was not employed in the fabrication of the test assembly trusses. Consequently, the specially

rolled angles with a convex protrusion were not necessary. Conventional hot-rolled steel angles were

used and, since unequal-leg angles were not available in the size required, equal-leg angles were cut (sheared) to the appropriate dimension.

The main and bridging trusses were fabricated by Canam Steel Co. under subcontract to Underwriters

Laboratories Inc. (UL). Dimensions were taken from Laclede Steel shop drawings and scaled for the 35 ft and 17 ft span test frames. The 35 ft long trusses, Test Specimens 1 and 2, were scaled from

35 ft 8 in., the total length of the C32T5 truss, to a length of 35 ft 5 in. to fit the dimensions of UL's test

NISTNCSTAR 1-6B, WTC Investigation I l
Chapter 4

frame in the Toronto fire test facility. The overall depth of the truss was scaled accordingly. Figures 4-1

and 4-2 show the dimensions of the full-scale test specimen main trusses.

The 17 ft trusses, Test Specimens 3 and 4, were scaled to fit the test frame in UL's Northbrook facility; that is, by the ratio of 17 ft 5Vi in. to 35 ft 8 in. The height of the knuckle was not changed since the

depth of concrete slab was the same for both full- and reduced-scale tests. All member sizes, both chord

and web, were unchanged. Figures 4-3 and 4-4 show the dimensions of the reduced-scale test specimen

main trusses.

The bridging trusses for the full-scale test assembly were scaled in the same manner as the main trusses. For the reduced-scale tests, since the truss spacing was not scaled (see Section 4.1.5) the depth of the truss was scaled per the main trusses but the length (i.e., spacing of knuckles) was not. Figures 4-5 and 4-6

show the dimensions of the full- and reduced-scale bridging trusses, respectively.

4.2.2 Steel Grade

The original C32T5 trusses in the WTC were fabricated from ASTM A242 grade steel according to WTC

contract drawings and confirmed by NIST (see N1ST NCSTAR 1-3D). Since this steel is no longer

produced, it was determined that ASTM A 572 Gr. 50 was an acceptable substitute, considering both

chemistry and mechanical properties. The truss fabricator was not able to obtain the steel used for the

web members in A572 grade steel in a time frame that would not impact the project. It was further

decided that ASTM A529 grade steel was an acceptable substitute and would be used for the truss webs

while, ASTM A572 grade steel would be used for the chord members. Chemistry, mechanical properties,

and weldability were all considered in making this determination. Certified Mill Test Reports (CMTR)

for the steel used to fabricate the main trusses and bridging trusses are shown in Appendix A.

4.2.3 Truss Welds

Most of the original WTC truss welds were made using resistance welding and the remainder using the

submerged metal arc welding (SMAW) process (see Jefferson, 1962). Resistance welding is no longer

widely used in practice, and no fabricator could be located that employed this technique. It was

determined that metal inert gas (MIG) welding (Jefferson, 1962) could be used for all welds to fabricate

the trusses.

The specification for the fabrication of the floor trusses

8 states, in section 105 Quality Control and

Inspection of Resistance Welding,

"All interior truss panel points will be connected by electronically controlled resistance

welding designed to provide a minimum of two times the strength of the connected

members at full design load."

The strength of a resistance weld is a function of the size of the pieces being joined, and parameters of the

welding process such as heat (current), applied pressure, holding time, etc. For the WTC contract,

Laclede developed 29 resistance weld designations for the various combinations of double chord angle

8 World Trade Center Contract WTC-221 .00, Fabricated Steel Floor Trusses, Bridging, Beams and Bracing for Prefabricated

floor Units for North and South Towers, dated October, 1967 (WTCI-71-I

12 NIST NCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

size and web rod size (see Table 4-1) Test Weld Strengths for many of the designations were found in a review of Laclede WTC Quality Control program documents and are also shown in Table 4-1 . Welds

designated R-22 were used for the fabrication of the C32T5 and are reported as having a Test Weld

Strength (design strength) of 24 kips. Laclede WTC Quality Control Data (load test data) were found for 20 of the 29 designations; R-22 was not among them. The test data found showed results for ten load

tests and the average load at failure is reported in Table 4-1. Dividing the failure load by the design load one obtains, in essence, a factor of safety which is also reported in the last column of Table 4-1 . The

average of these values was found to be 2.02. Thus, it could be concluded that the resistance weld

procedure used by Laclede Steel Company in the fabrication of the floor trusses, produced welds with two

times the design strength as called for in the contract specification.

Table 4- Redistance Weld Data.

Resistance

Weld

1 s t 3 I _ 1 1 tl 1 1U 11

Double ChordAngle

Size

Web Rod

Size (in.)

Test Weld

Strength (Kip)

Average

Load (Kip)

F.S.

R 1 J A Z A \J.J 1

1 1 A A^ 8 1 0 11 en

R-7 _) A Z A \J.J 1 11 .U7 ftQ A*\ oz87 1 87 1 .oz R J A Z A \J.J 1 nU.70qs £8Do R-4 _7

t. AY Z9 YA n\J.D111 fl Q7 f*1

R S 1 y 7 v n » 1 1 A AC\ 1U 77 ^ 1 QA

i\-0 R f\ jJ Ay Z? Ay nUJj11 1i .vy HQ ACt 11 6 / j .0 11 .51 8A

R 1 J1 AY Z7 vA 0V.JJ11 U. 70 32 D J .O 7 ns R 8 J

1 Av Z7 Av nU.JJ11 fi Q7 U.7Z 78zo 6.7 A 7 7"? Z.Z J

R 0 Z9 AY 11-1/Z 1 /? YA P)\J.JI ^ 7 1 1 A JO^8 67 1 1 76

IY 1 U ZA1 Y 1l -1l/ZAV/.J/ /? Y D ^7 1

1 .\jy HQ 6SUJ.O8

R-l 1 ZA?y 11I/ZAV7..J/ -1 /? y ft ^7 ft Q8 60Uv. 7/ R-12 2 x 1-1/2 x 0 37 0.92 56.9 R-13 2 x 1-1/2x0.37 0.75

R-14 2 x 1-12 x 0.31 1.14 40 66.5 1.66

R-l 5 2 x 1-1/2 x 0.31 1.09 38 65.2 1.71 R-16 2 x 1-1/2 x 0.31 0.98 30 60.1 2.00 R-17 2 x 1-1/2 x 0.31 0.92 25 56.8 2.27 R-18 2 x 1-1/2 x 0.31 0.75 40

R-19 2.x 1-1/2x0.25 1.14 40 75.4 1.88 R-20 2 x 1-1/2 x 0.25 1.09 40 73.7 1.84

R-21 2 x 1-1/2 x 0.25 0.98 29

R-22 2 x 1-1/2 x 0.25 0.92 25

R-23 2x 1-1/2x0.25 0.75

NISTNCSTAR 1-6B, WTC Investigation 13
Chapter 4

Resistance

Weld

Designation

Double ChordAngle Web Rod Test Weld Average

F.S. Size Size (in.) Strength (Kip) Load (Kip)

R-24 1-1/2 x 1-1/4x0.275 0.98 18 44.8 2.49 R-25 1-1/2 x 1-1/4x0.275 0.92 18 41.1 2.28 R-26 1-1/2 x 1-1/4x0.275 0.75

R-27 1-1/2 x 1-1/4 x 0.230 0.98 16 38.5 2.40 R-28 1-1/2 x 1-1/4x0.230 0.92 16 37.9 2.37 R-29 1-1/2 x 1-1/4x0.230 0.75 16 Average 2.02

The inherent factor of safety of welds designed in accordance with AISC, may be estimated by dividing

the nominal strength of a groove weld in shear (AISC 1999) by the allowable stress of a groove weld in shear (AISC 2001), or 0.6 Fy

/ 0.3 Fy = 2.0. To reproduce, approximately, the strengths of the resistance

welds used in the fabrication of the WTC floor trusses, NIST used metal inert gas (MIG) welds designed

to meet the strength requirements of AISC specifications (AISC 2001). The MIG process uses small

gauge wire, well suited for producing the flare-bevel groove welds joining the round web bars to the

double chord angles.

4.2.4 Metal Deck

The non-composite deck consisted of 1

lA in. No. 22 gauge galvanized sheet metal floor units. Each full panel measured 35 ft 2 in. long by 3 ft VA in. wide for Assembly Nos. 1 and 2, and 17 ft 8 in. by

3 ft 1/4 in. wide for Assembly Nos. 3 and 4. The original deck used for the floor system in the WTC

towers was custom produced specifically for the WTC buildings. The steel deck was rolled in widths that spanned between trusses without a longitudinal seam. It was not possible to obtain deck in the desired

span, and therefore, it was determined that typical Type B steel deck, seamed per the manufacturer's

recommendation, would be acceptable.

14 NISTNCSTAR 1-6B, WTC Investigation
hloor Test Assemblies

NISTNCSTAR 7-66, WTC Investigation 15
Chapter 4
Floor Test Assemblies

NISTNCSTAR 1-6B, WTC Investigation 17
Chapter 4
hloor Test Assemblies

NISTNCSTAR 1-6B, WTC Investigation 19
Chapter 4
Floor Test Assemblies

4.2.5 Welded Wire Fabric

The welded wire fabric used in the concrete was 10 in. by 4 in. W4.2/W4.3 welded steel mesh. Steel wire was supplied by Insteel Wire Products and its strength shown in Appendix A.

4.2.6 Concrete

The concrete design strength for a typical office floor of the WTC was specified to be 3,000 psi, and the

lightweight density was specified as 100 pcf The concrete for the floor slab consisted of 3A in. lightweight haydite aggregate, sand, Type I Portland cement and water. No records of actual mixture

proportions or cylinder strengths were found in NIST's review of available documents. The mix design

shown in Table 4-2 was determined by the concrete supplier to produce a 3,000 psi 28-day strength usinj

lightweight aggregate.

Table 4-2. Concrete mix design per cubic yard of concrete

Cement Havdite "C" Sand Entrained Air Water

(lb) (lb) (lb) (%) (lb) 522 940 1300 6 281*

* Includes 40 lb of water in sand

4.2.7 Primer

The trusses supplied by Laclede Steel were shop primed during production using an electro-deposition

process. The formulation for the primer was designated as Formula LREP - 10001 and was found in Laclede files (see Appendix B). The exact formulation could not be reproduced due to current environmental considerations. A stock structural steel primer, manufactured by Sherwin Williams and

designated Type B50NV1 1 (recommended by Isolatek International, the manufacturer of the sprayed

fire-resistive material used in these tests and in the original construction of the WTC towers) was

determined to be an acceptable substitute. The primer was field applied to the trusses after assembly in the ULN and ULC fire test facilities.

4.2.8 Sprayed Fire-Resistive Materials

The sprayed fire resistive material used on the test assemblies was BLAZE-SHIELD DC/F which is manufactured by Isolatek International, and is the same product as that applied during original

construction.

4.2.9 Miscellaneous Steel

Miscellaneous steel including rebar, pourstop coverplates, and support angles used during construction

are described in Section 4.3.

NISTNCSTAR 1-6B, WTC Investigation 21
Chapter 4

4.3 CONSTRUCTION OF TEST ASSEMBLIES

The construction of each assembly was conducted by UL technical staff and under the supervision of

NIST at Underwriters' Laboratories of Canada (ULC), and Underwriters Laboratories Inc. in Northbrook,

Illinois (ULN). All welds were made by certified welders and inspected by STS Consultants Ltd. (STS)

under sub-contract to UL. Table 4-3 lists the construction periods and test dates for the four assemblies

tested.

Table 4-3. General construction details.

Assembly No. Description Location Construction Dates Test Date

1 35 ft Restrained Toronto, ON, Canada 1/20/2004 - 1/27/2004 8/7/2004

2 35 ft Unrestrained Toronto, ON, Canada 1/28/2004-2/04/2004 8/11/2004

3 1 7 ft Restrained Northbrook, IL, U.S. 2/13/2004-2/22/2004 8/19/2004

4

1 7 ft Restrained w/

unprotected bridging

trusses

Northbrook, IL, U.S. 2/13/2004-2/22/2004 8/25/2004

4.3.1 Construction of 35 Ft Assemblies

Assembly No. 1 was restrained from thermal expansion. The trusses were welded to steel support angles

that were attached to the test frame, and the concrete was poured in contact with the frame. Assembly

No. 2 was unrestrained. The trusses were bolted to steel support angles having a 2

7A in. slot to allow for unrestrained thermal expansion. The concrete was poured with a 1 Vz in. gap between the concrete and the

frame. Figure 4-7 shows the assembly of the steel support system for test Assembly No. 1 . Refer to Appendix C for construction drawings.

Structural Steel Frame and Deck

The two nominal 35 ft by 14 ft floor assemblies were constructed of the same materials and in the same

manner, with the exception of the restraint condition, provided by the attachment of the main trusses to the test frame as described above. Two main trusses were symmetrically positioned in the test frame,

6 ft 8 in. o.c.

The ends of the main trusses in Test Assembly No. 1 were supported by L6x4xl structural angles 12 in. long welded to the test frame. The bearing length for each main truss was V/z in. The ends of the main

trusses were welded with a Vz in. fillet along the entire bearing length on each side of the trusses (see

Fig. 4-8). Steel plates were placed between the ends of the main trusses and the test frame, filling the gap

and, thus, preventing thermal expansion.

22 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Source: NIST. Figure 4-7. Structural steel frame of Assembly No. 1.

Source: NIST. Figure 4-8. Restrained end condition of Assembly No. 1 prior to shimming.

The ends of the main trusses in Test Assembly No. 2 were supported on L7x4xl structural angles, 14 in. long welded to the test frame. Slotted holes, 2 7/8 in. long, were provided in the steel angles, and the

NISTNCSTAR 1-6B, WTC Investigation 23
Chapter 4

centerline of each slot was located 3 in. from the edge of the angle. The edge distance of the slotted holes was VA in. The bolt holes in the truss bearing angles were 15/16 in. in diameter. The main trusses were

bolted to the support angles using two 7A in. diameter by 2/4 in. long ASTM A325 bolts with ASTM F436

washers and ASTM A563 nuts as seen in Fig. 4-9. The nuts were hand tightened to provide connection

stability without hindering thermal expansion. Also, the trusses and supports were designed so that the

bolts were installed close to the inside edge of the slot, thus allowing the maximum unrestrained outward

movement as the test specimens heated and expanded. The slots extending beyond the edge of the truss support angles are just visible in Fig. 4-13.

Source: NIST

Figure 4-9. Unrestrained end condition of Assembly No. 2.

Two bridging trusses, one located 9 ft 4 in. from the west test frame edge and one located 12 ft VA in. from the east test frame edge were installed in the assembly. The bridging trusses were welded to 6 in. long L2 1/2xl ,/2 x

l/2 angles that were welded to the bottom chord of each main truss. The top of the bridging

truss was welded to the top chord of the main truss. All welds were % in. fillets.

Three L3x2x'/4 in. steel deck support angles, one located 3 ft

3A in. from the west test frame edge, one at 16 ft 1 in. from the west test frame edge, and one at 6 ft 5 in. from the east test frame edge were welded to the bottom of the top chord of the main truss (see Fig. 4-10).

24 NISTNCSTAR 1-6B, WTC Investigation
hloor Test Assemblies

Source: NIST

Figure 4-10. Intersection of deck support angle and main truss.

At the intersection of the bridging trusses, steel deck support angles, and main trusses, a 3 in. by 3 in. by

3A in. steel plate was welded to the top side of the bottom chord of the main truss with % in. fillet on the

east and west sides of the plate. There was no steel plate welded to the bottom chord at the location of the center steel deck support angle.

Cover plates made from A3 6 steel, 7 in. wide and 0.1 16 in. thick were welded to the full length of the top

chords of the main trusses to prevent the wet concrete from passing through (Fig. 4-10). Steel cover

plates measuring 3Vi in. by 7 in. by 0.1 16 in. thick were welded under each web knuckle for the same

purpose. A 2 in. by 7 in. by % in. steel plate was welded to adjacent knuckles (Fig. 4-11) per Laclede

shop drawings. The plates were located at the knuckles immediately above the intersection of bridging

trusses and deck support angles with the main trusses (see Fig. 4-12). A 6% in. long piece of No. 8 reinforcing steel bar was welded to each end stiffener at both ends of the truss (see Fig. 4-13).

NISTNCSTAR 1-6B, WTC Investigation 25
Chapter 4

Source: NIST. Figure 4-11. Cover plates on main truss.

Source: NIST. Figure 4-12. Intersection of main and bridging truss, bottom chord.

26 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Source: NIST. Figure 4-13. Detail of rebar welded to end stiffener.

The steel floor deck was placed on the assembly in 3 ft 1/4 in. widths, 35 ft lengths, with the crests and

valleys parallel to the main trusses (Fig. 4-14). Near the east-west centerline of the assembly the deck was overlapped and secured with V% in. long self-taping hex-head screws spaced 18 in. o.c, beginning

16 in. from the east edge of the frame. At the interface of the steel deck edge and the upper chords of the

main trusses, the deck was secured to the chords with Vi in. puddle welds spaced 6 in. o.c. Where the

deck met the north and south test frame edges, 4

]A in. by 96 in. by 0.1 16 in. thick steel plate was secured

to the top of the steel deck with YA in. long by 5/32 in. shank hex-head, self-tapping screws spaced 18 in. o.c. located 114 in. from the edge of the steel plate. The steel plate was installed so that it was flush

against the test frame surface.

NIST NCSTAR 1-6B, WTC Investigation 27
Chapter 4

Source: NIST. Figure 4-14. Placement of steel form deck.

Chairs, % in. high measuring 60 in. long, with 12 legs per chair spaced 5 in. o.c. and 2% in. from each

end, were placed and taped on alternating deck crests along the full length of the assembly (see

Fig. 4-15). Welded wire fabric (WWF), 10 in. by 4 in. W4.2/W4.3, supplied in 60 in. widths, was placed on the chairs with the 4 in. dimension running the length of the assembly (east to west). The WWF was

notched to fit around the knuckles and instrumentation sleeves. Adjacent sections of WWF were

overlapped nominally 12 in. per ACI 318-63 (ACI, 1963). At the overlaps, the mesh was secured with 18

gauge wire twist-ties spaced approximately 24 in. o.c.

No. 4 (/4 in. or 13 mm diameter) steel reinforcing bar was placed on top of the first layer of welded wire

fabric, 3 in. from the east and west ends of the test frame. A second layer of welded wire fabric was

installed with overlaps and fastened with wire ties as described above for the first layer. Two lengths of

No. 5 (

5/g in. or 1 6 mm diameter) steel reinforcing bar were placed on both sides of each bridging truss over the second layer of wire fabric (Fig. 4-16). The rebar was secured to the top layer of welded wire

fabric with 18 gauge wire twist-tied approximately 24 in. o.c.

2S NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Source: NIST. Figure 4-15. Chairs for welded wire fabric.
Chapter 4

Concrete Placement

The ready-mixed concrete was poured to an average depth of 4 in. measured from the top plane of the

1/4 in. deep steel deck. Details of the concrete mix and compressive strengths are given in Table A-A. The concrete was finished to a flat, smooth surface with a wooden trowel. Placement of concrete is shown in Fig. 4-17.

Table 4-4. Detai s of concrete placement.

Assembly

No.

Concrete

Pour Date

Wet Unit

Weight*

(lb/ft

3

)

Slump*

(in.)

Air

Content*

(%)

Water

Added

(gal)

Compressive

Strength at 28 Days

(psi)

Compressive

Strength at 56 days

(psi)

1 1/27/2004 114.2/114.8 1 6/8 4.5/5.75 4 4177 4735

2 2/4/2004 109.4 lb/ft

3 7.5 8.75% 2937 3893

*Results before and after water added

Source: NIST. Figure 4-17. Concrete placement.

Curing of Concrete

The ASTM E 1 19 test standard requires the average relative humidity of the concrete slab to be

70 percent +1-5 percent. In order to accelerate the process of driving the moisture out of the concrete slab,

the assemblies were placed in a high temperature, low humidity environment following an initial 28 day

curing at ambient environment. The relative humidity of each slab was monitored regularly in accordance

with the method described in ASTM E 1 19-2000a, paragraph 12.1.3, Note 6.

30 NISTNCSTAR 1-6B, WTC Investigation
hloor Test Assemblies

Preparation of Trusses

Prior to the application of primer to the structural steel members, the steel was sand blasted (Fig. 4-18) to the Society of Protective Coatings SSPC-SP6 specification in accordance with the product specification

sheet of the primer. Following the sand blasting, the steel was primed (Fig. 4-19) with Sherwin Williams

Type B50NV1 1 at an approximate dry film thickness of 0.003 in.

Source: NIST. Figure 4-18. Sandblasted assembly.

Source: NIST. Figure 4-19. Primer on bridging truss.

NIST NCSTAR 1-6B, WTC Investigation 31
Chapter 4

Instrumentation

Prior to the concrete pour, four 18-gauge Type K thermocouples were attached to the steel form deck at each of three locations, near the center point and quarter points in the east-west direction. At each

location, a thermocouple was placed in the valley, sidewall, crest, and next adjacent valley of the deck.

Refer to Appendix D for locations of deck thermocouples.

After priming of the structural steel, 18-gauge Type K thermocouples were attached to each main and

bridging truss (see Fig. 4-20). Eight thermocouples were peened into the steel at each cross section,

located approximately at the quarter and center points on each main truss (see Appendix D for exact

locations). Additionally, 10 thermocouples were located at the intersections of each main and bridging

truss. In total, 44 thermocouples were attached to each main truss, for a total of 88 thermocouples.

On each bridging truss, four thermocouples were attached at each cross section located at the center of the

truss, at the intersections of the main and bridging trusses, and approximately halfway between the main

truss and the end of the bridging truss (see Appendix D for exact locations). In total, 16 thermocouples were attached to each bridging truss, for a total of 32 thermocouples.

Strain gauges were attached on the bottom chords of the main trusses to measure strain as each test assembly was loaded. A pre-wired 350 Q. resistance strain gauge was placed, per the manufacturer's

instructions, on the top surface and bottom surface of the bottom chord angle. The strain gauges were

symmetrically opposed, at the mid-length of the bottom chord of each main truss. Each pair of gauges was wired to a half-bridge amplifier prior to loading of the assembly. Strain gauge readings were used to confirm proper loading of the assemblies, and the wiring was cut and bridge circuit removed prior to the

start of the tests.

Source: NIST. Figure 4-20. Peened thermocouples on truss.

32 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Application of Sprayed Fire Resistive Materials

Application of the sprayed fire resistive materials was conducted by the manufacturer of the SFRM under

a sub-contract to UL and witnessed by representatives of UL and NIST. On the underside of the

assembly, the BLAZE-SHIELD DC/F sprayed fire resistive material was applied to the main and bridging

trusses in multiple coats. No attempt was made to control overspray of material onto the deck of the 35 ft test assemblies.

Thickness and density measurements were taken in accordance with ASTM E 605 Standard Test Methods

for Thickness and Density of Sprayed Fire-Resistive Material (SFRM) Applied to Structural Members

(ASTM 2000a). The average SFRM thicknesses on the trusses are shown in Table 4-5 for Test Assembly

No. 1. Figure 4-21 shows the SFRM on main trusses after achieving the desired thickness. Figure 4-22

shows SFRM thickness measurements being made on the bottom chord of a main truss.

Table 4-5. SFRM Thickness measurements on Assembly No. 1 Location Nominal

Thickness

(in.)

Final Average

Measured Thickness

(in.)

Basis: No. of

Thickness

Measurements

North Main Truss 3/4 0.756 254

South Main Truss 3/4 0.750 254

East Bridging Truss 3/8 0.385 72 West Bridging Truss 3/8 0.385 72

The air dry density of the Type DC/F sprayed fire resistive material was determined using 12 in. by 12 in. samples. The air dry densities are shown in Table 4-6 for Assembly No. 1. The average air dry density was found to be 15.73 pcf

Table 4-6. Air dry density of spray applied

fire resistive material on Assembly No. 1.

Material

Type

Nominal

Thickness

(in.)

Measured

Density

(pcf)

DC/F 3/4 17.27 DC/F 3/4 15.19 DC/F 3/4 14.73

NISTNCSTAR 1-6B, WTC Investigation 33
Source: NIST. Figure 4-21. SFRM on main truss.

Source: NIST. Figure 4-22. Measurement of SFRM thickness on truss chord.

34 NISTNCSTAR 1-6B, WTC Investigation
hloor Test Assemblies

SFRM thickness measurements for Test Assembly No. 2 are given in Table 4-7. Air dry density of spray

applied fire resistive material on Assembly No. 2 is given in Table 4-8; the average air dry density was

found to be 19.95 pcf.

Table 4-7. Thickness measurements on Assembly No. 2.

Location

Nominal

Thickness

(in.)

Final Average

Measured Thickness

(in.)

Basis: No. of

Thickness

Measurements

North Main Truss 3/4 0.756 254

South Main Truss 3/4 0.755 254

East Bridging Truss 3/8 0.393 72

West Bridging Truss 3/8 0.34 1 72

Table 4-8. Air dry density of spray applied fire resistive material on

Assembly No. 2.

Material

Type

Nominal

Thickness,

in.

Measured

Density,

pcf

DC/F 3/4 20.98

DC/F 3/4 24.01 DC/F 3/4 14.87

4.3.2 Construction of 17 Ft Assemblies

Structural Steel Frame and Deck

Assembly Nos. 3 and 4 were both restrained from thermal expansion by welding the trusses to the steel support angles that were attached to the test frame and by casting the concrete in contact with the frame.

The sprayed fire resistive material was applied to Assembly No. 3 in the same way as for Assembly

Nos. 1 and 2. Assembly No. 4 was protected with Vz in. of SFRM on the main trusses, while the bridging

trusses were left unprotected, and the deck and deck support angles were shielded from any overspray

(see Section 1.4). Refer to Appendix E for construction drawings.

The two nominal 17 ft by 14 ft floor assemblies were constructed in the test frames to fill the openings.

Both assemblies were constructed of the same materials and in the same manner. The two main trusses were symmetrically positioned in the test frame 6 ft 8 in. o.c. (see Fig. 4-23).

NISTNCSTAR 1-6B, WTC Investigation 35
Chapter 4

The ends of the main trusses were supported on structural steel support angles installed at the north and

south walls of the test frame. The resulting bearing length at each end of the main trusses was 3/4 in. The

ends of the main trusses were welded with lA in. fillets along the entire bearing length on each side of the

truss bearing angles. Steel plates were placed between the ends of the main trusses and the test frame,

filling the gap and, thus, preventing thermal expansion.

Each test assembly had two bridging trusses, one located 4 ft 9V& in. from the north test frame edge and one located 6 ft 5

5A in. from the south test frame edge. The bridging trusses were welded to 6 in. long by

VA in. by 2/4 in. by lA in. thick angles welded to the bottom chord of each main truss. The top of the

bridging truss was welded to top chord of the main truss. All welds were XA in. fillets.

Three 2 in. by 3 in. steel deck support angles, one located 1 ft 8

xAh in. from the north test frame edge, one

at 8 ft IVs in. from the north test frame edge, and one at 6 ft 5% in. from the south test frame edge, were welded to the bottom of the top chord of the main truss (see Fig. 4-24).

36 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Source: NIST. Figure 4-24. Intersection of main truss and deck support angle.

At the intersection of the bridging trusses, steel deck support angles, and main trusses, a 3 in. by 3 in. by

3/s in. steel plate was welded to the top side of the bottom chord of the main truss with V* in. fillet on the

east and west sides of the plate (see Fig. 4-25). There was no steel plate welded to the bottom chord at the location of the center steel deck support angle.

Source: NIST. Figure 4-25. Intersection of main and bridging truss bottom chord.

NIST NCSTAR 1-6B, WTC Investigation 37
Chapter 4

Cover plates made from A36 steel, 7 in. wide and 0.1 16 in. thick, were welded to the full length of the top

chords of the main trusses to prevent concrete from passing through (see Fig. 4-26). Steel cover plates

measuring 3/4 in. by 7 in. by 0.1 16 in. thick were welded under each web knuckle for the same purpose.

A 6/4 in. length of No. 8 reinforcing steel rod was welded to each end stiffener at both ends of the truss.

Source: NIST.Figure 4-26. Cover plate detail.

The steel floor deck was placed on the assembly in 3 ft 1 V2 in. widths, 18 ft lengths, with the crests and

valleys parallel to the main trusses (Fig. 4-27). At the interface of the steel deck edge and the upper

chords of the main trusses, the deck was secured to the chords with lA in. puddle welds spaced 6 in. o.c.

Source: NIST. Figure 4-27. Steel floor deck placement.

38 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Chairs, 3A in. high measuring 60 in. long, with 12 legs per chair spaced 5 in. o.c. and 2

3A in. from each

end, were placed and taped on alternating deck crests along the full 17 ft length of the assembly (see

Fig. 4-28). Welded wire fabric, 10 in. by 4 in. W4.2/W4.3, supplied in 60 in. widths, was placed on the

chairs, with the 4 in. dimension running the length of the assembly (north to south). The wire fabric was

notched to fit around the knuckles and instrumentation sleeves. Adjacent sections of WWF were

overlapped nominal 12 in. per ACI 318-63 (ACI 1963). At the overlaps, the mesh was secured with 18

gauge wire twist-ties spaced approximately 24 in. o.c.

Source: NIST. Figure 4-28. Chairs on steel deck.

No. 4 steel reinforcing bar was placed on top of the first layer of welded wire fabric, 3 in. from the east and west ends of the test frame. A second layer of welded wire fabric was installed with overlaps and

fastened with wire ties as described above for the first layer. No. 5 steel reinforcing bar was placed on

both sides of each bridging truss over the second layer of WWF (Fig. 4-29). The rebar was secured to the

top layer of welded wire fabric with 18 gauge wire twist-ties approximately 24 in. o.c.

NIST NCSTAR 1-6B, WTC Investigation 39
Chapter 4

Source: NIST. Figure 4-29. Welded wire fabric and rebar.

Concrete Placement

The ready-mixed concrete was poured to an average depth of 4 in. measured from the top plane of the

VA in. deep steel deck. The concrete was finished to a flat, smooth surface with a wooden trowel. Details

of the concrete for test Assemblies 3 and 4 are shown in Table 4—9.

Table 4-9. Details of concrete.

Wet Unit Air Water Compressive Compressive

Assembly Concrete Weight Content Added Strength at 28 Days Strength at 56 Days

No. Pour Date (lb/ft

3

) Slump(in.) (%) (gal) (psi) (psi)

3 2/20/2004 113.8 8 7 9 3370 3995

4 2/20/2004 111.6 7.5 8 0 2320 3220

Preparation of Trusses

Prior to the application of primer to the structural steel members, the steel was sand blasted to the Society

of Protective Coatings SSPC-SP6 specification in accordance with the product specification sheet of the

40 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

primer. Following the sand blasting, the steel was primed with Sherwin Williams Type B50NV1 1 at an

approximate dry film thickness of 0.003 in.

Instrumentation

Prior to the concrete pour, four 18-gauge Type K thermocouples were attached to the steel form deck at each of three locations, near the center point and quarter points in the north-south direction. At each

location, a thermocouple was placed in the valley, sidewall, crest, and next adjacent valley of the deck.

Refer to Appendix F for locations of deck thermocouples.

After priming of the structural steel, 18-gauge Type K thermocouples were installed on each main and

bridging truss. Eight thermocouples were peened into the steel at each cross section, located

approximately at the quarter and center points on each main truss (see Appendix F for exact locations).

Additionally, ten thermocouples were located at the intersections of each main and bridging truss. In

total, 44 thermocouples were installed on each main truss, for a total of 88 thermocouples.

On each bridging truss, four thermocouples were peened into the steel at each cross section located at the center of the truss, at the intersections of the main and bridging trusses, and approximately halfway

between the main truss and the end of the bridging truss (see Appendix F for exact locations). In total, 16 thermocouples were installed on each bridging truss, for a total of 32 thermocouples.

Strain gauges were attached on the bottom chord of the main trusses to measure strain as each test assembly was loaded. A pre-wired 350 Q. resistance strain gauge was placed, per the manufacturer's

instructions, on the top surface and bottom surface of the bottom chord angle. The strain gauges were

symmetrically opposed, at the mid-length of the bottom chord of each main truss. Each pair of gauges

would later be wired to a half-bridge amplifier prior to loading of the assembly. Strain gauge readings were used to confirm proper loading of the assemblies, and the circuitry was removed prior to the start of

the tests.

Application of Sprayed Fire-Resistive Materials

The application of the sprayed fire resistive materials was conducted by the manufacturer of the sprayed

fire resistive material under a sub-contract to UL and observed by representatives of UL and NIST. On

the underside of the assembly, the BLAZE-SHIELD DC/F was applied to the main and bridging trusses in multiple coats. For Test Assembly No. 3, which had 3/4 in. thick SFRM on the steel trusses, no attempt was made to control overspray on the metal deck. For Test Assembly No. 4, with lA in. thick SFRM, the

metal deck was masked to prevent overspray.

Thickness and density measurements were taken in accordance with ASTM E 605 (ASTM 2000a). The

average SFRM thicknesses on the trusses are shown in Table 4-10 for Test Assembly No. 3.

NISTNCSTAR 1-6B, WTC Investigation 4!
Chapter 4

Table 4-10. SFRM Thickness measurements on Assembly No. 3.

Location

Nominal

Thickness

fin \ (in.)

Final Average

Measured Thickness

(in.)

Basis: No. of

Thickness

Measurements

East Main Truss 3/4 0.766 128

West Main Truss 3/4 0.763 128

North Bridging Truss 3/8 0.397 66

South Bridging Truss 3/8 0.387 66

The air dry density of the BLAZE-SHIELD DC/F sprayed fire resistive material was determined using

twelve 12 in. by 12 in. samples of various thickness. The air dry densities are shown in Table 4-1 1 for Assembly No. 3. The average air dry density was found to be 20.49 pcf

Table 4-1 1 . Air dry density of spray applied fire resistive material on

Assembly No. 3.

Material

Type

Nominal

Thickness

(in.)

Measured

Density

(pcf)

DC/F 3/4 21.23

DC/F 3/4 19.76 DC/F 3/4 20.49

SFRM thickness measurements for Test Assembly No. 4 are given in Table 4-12. Air dry density of

spray applied fire resistive material on Assembly No. 4 is given in Table 4-13, and the average air dry

density was found to be 19.10 pcf. There was no sprayed fire resistive material applied to the bridging

trusses on Assembly No. 4

Table 4-12. Thickness measurements on Assembly No. 4.

Location

Nominal

Thickness

(in.)

Final Average

Measured

Thickness (in.)

Basis: No. of

Thickness

Measurements

East Main Truss 1 12 0.514 128

West Main Truss 1/2 0.512 128

Table 4-13. Air dry density of spray applied

fi re resistive material on Assembly No. 4. Material

Type

Nominal

Thickness (in.) MeasuredDensity (pcf)

DC/F 1/2 20.57

DC/F 1/2 18.90 DC/F 1/2 17.83

42 NISTNCSTAR 7-66, WTC Investigation
Floor Test Assemblies

4.4 LOADING OF TEST ASSEMBLIES

The test assemblies were loaded in accordance with ASTM E 1 19. That is, a superimposed load was

applied "to simulate a maximum load condition," which was determined as "the maximum load condition

allowed under nationally recognized structural design criteria" (ASTM 2000). In this section, the analysis

for this maximum load condition is given, and the procedures used to apply the computed loads are explained for both the full- and reduced-scale test assemblies. The structural analysis and test loading

procedure was performed by Wiss Janey Elstner & Associates (WJE) under sub-contract to Underwriters

Laboratories Inc.

4.4.1 Loading of 35 Ft Assemblies

Table 4-14 details the demand-to-capacity ratio of key elements of the trusses for Assembly Nos. 1 and 2. Demand-to-capacity ratios for the original C32-T5 truss design are given in the last column and were computed from Laclede design calculation sheets (see Appendix G). The compression web diagonal at the vertical strut was the limiting member with a demand-to-capacity ratio of 1.01. The calculations

indicate that the maximum load condition is achieved with a uniform load of 104 psf

The test load was applied to the assembly in a sequence that generally proceeded outwards from the

center. Concrete blocks, which had first been weighed, were placed between the truss lines starting at the

midspan and working symmetrically to the east and west ends of the test assembly. Next, empty water

tubs were placed symmetrically outward to the ends of the span, alternating between the truss lines from

the midspan. Finally, concrete blocks were placed between the water tubs and the longitudinal edges of

the assembly, again alternating along both edges, working symmetrically from midspan to the ends of the

assembly. The last set of blocks was placed as close as practicable to the water tubs to minimize bending

of the cantilevered deck slab. The water tubs were filled from the center of the assembly outward toward

the edges. The amount of water was calculated for each location to insure the same load was applied at each section since the weight of the concrete blocks varied slightly.

NIST NCSTAR 1-6B, WTC Investigation 43
Chapter 4

able 4-14. Summary of analysis for maximum load condition for 35 ft assembly.

Test Assembly

35 Foot Laclede WTC

P)pci (Tn

Load Case I IniTnrm III l\Jl III II.IMU n^H V_ CliV. illilt I\ >!!> Uniform Self Weight Construction Load (psf) 48 46

Additional Superimposed Load (psf) 104* 10X Top Chord Panel Point Truss Member Memher DPR Mpinhpr DPR

A: Short End of truss

B: Bearing point

#5: End Diagonal at short end n so U.JO #2A: Vertical at short end MA***

C: At vertical strut 0 Q7

#4:Compression web diagonal 1 01

D: MA***

#4A: Compression web diagonal 0 lf\

E: At bridging Truss

F:

G: Near midspan

H:

J: At bridging Truss #3A: Compression web diagonal 0

K:

#3: Compression web diagonal 0 07 U.77 0 QQ

L: At vertical strut

#2: Vertical at long end 0 87 1 00

#1: End diagonal at long end 0 88 0.99 M: Bearing point N: Long end of truss

Bottom Chord #7: Tension chord near midspan 0.63 0.81

Includes 2 psf representing weight of SFRM

The original Laclede calculations use a slope factor of 1.90, whereas the slope factor for Member 5 should be on the order of 1 .45 according to truss geometry. The original Laclede DCR of 0.76 has been adjusted as follows:0.76* 1.45/1 .90=0.58 *** Not Applicable: The Laclede calculations do not include a design for this member.

4.4.2 Loading of 17 Ft Assemblies

Table 4-15 details the demand-to-capacity ratio of key elements of the trusses for Assembly Nos. 3 and 4. The long end web diagonal at the vertical stmt was the limiting member with a demand-to-capacity ratio of 1.00. The calculations indicate that the maximum load condition is achieved with a uniform load of

293 psf and concentrated loads applied at the truss panel points averaging to 86 psf.

44 NISTNCSTAR 1-6B, WTC Investigation
Floor Test Assemblies

Table 4-1 5. Summary of analysis for maximum load condition for 1 7 ft assembly

Test Assembly

1 7 Foot Laclede WTC

Design

Load Case Uniform Load Concentrated Load Calculations

Uniform Self W eight Construction Load (psf) 48 48 46

Additional Superimposed Load (psf) 293 86* 108

Top Chord Panel

Point Truss Member Member DCR Load(lbs)

Member

DCR Member DCR

A: Short End of

truss

B: Bearing point

#5: End Diagonal at short end 0.58 0.58 0.58**

#2A: Vertical at short end 0.60 0.60

C: At vertical strut 4100 0.97 #4:Compression web

diagonal 0.46 0.38 D: 0

\1 A ***

#4A: Compression web

diagonal 0.34 0.34

E: At bridging Truss 4100

F: 0

G: Near midspan 4100

H: 0

J: At bridging Truss 3800

#3A: Compression web

diagonal 0.35 0.37

K: 0

#3: Compression web

diagonal 0.53 0.43 0.99

L: At vertical strut 3800

#2: Vertical at long end 0.55 0.55 1.00

#1 : End diagonal at long

end 1.00 1.00 0.99 M: Bearing point

N: Long end of truss

Bottom Chord

#7: Tension chord near midspan 0.70 0.64 0.81

* Includes 2 psf representing weight of SFRM

** The original Laclede calculations use a slope factor of 1 .90, whereas

of 1 .45 according to truss geometry. The original Laclede DCR of 0 *** Not Applicable: The Laclede calculations do not include a design for

the slope factor for Member 5 should be on the order 76 has been adjusted as follows:0.76* 1 .45/1 .90=0.58

this member.

NISTNCSTAR 1-6B, WTC Investigation 45
Chapter 4

The test load was applied to the assembly in a sequence that generally proceeded outward from the center of the deck. First, empty water tubs were placed between the truss lines, starting at midspan and working

symmetrically to the ends of the span. Next concrete blocks were placed, working both truss lines simultaneously from mid-span symmetrically outward to the ends of the span. After the concrete blocks were placed, the water tubs were filled to calculated depth. The hydraulic ram loads were applied last using four electric driven hydraulic pumps with pressure gauges.

4.5 INSTRUMENTATION

Prior to testing of each assembly, instrumentation was installed to measure vertical deflections of the

unexposed surface and the bottom chords of the main trusses. Instruments were also added to characterize the furnace environment as well as to measure temperature on the unexposed surface of the

test assembly.

4.5.1 Deflection Instrumentation

The deflection on the unexposed surface was measured using nine transducers, located approximately at the center and quarter points in the long span direction and center and quarter points in the short span

direction. The locations of the deflection transducers are given in Appendix D for the 35 ft test assemblies and Appendix F for the 17 ft test assemblies.

The deflection of the bottom chord of the main truss was measured at six locations by means of thin

round bars, welded at one end to the bottom chord of the main truss and protruding through sleeves in the concrete slab. Displacement transducers were attached to the rods and to a stationary frame. To account

for any thermal expansion of the round bar, 20 gauge Inconel thermocouples were attached approximately

at the midpoint of the depth of the main truss to measure temperatures throughout the duration of the test.

4.5.2 Furnace Thermocouples

The furnace temperature at UL's Toronto fire test facility was measured by means of twenty-four, 16

gauge Type K thermocouples, sheathed in Inconel pipe symmetrically located in the furnace chamber.

Sixteen furnace thermocouples, made from similar materials, were used at UL's Northbrook furnace. In addition to the furnace thermocouples required by the ASTM E 1 19 Standard, Wickstrom plate

thermocouples and aspirated thermocouples were located at the level of the bottom chord of the main

truss and at the valley of the steel form deck. The locations of the aspirated and plate thermocouples are given in Appendix D for the 35 ft test assemblies and Appendix F for the 17 ft test assemblies..

The Wickstrom plate thermocouples were made of a stainless steel sheet, on which an 1 8 gauge Type K,

Inconel sheathed thermocouple was attached to the back side. An insulating pad, approximately 4 in. by

4 in. by % in. was placed over the thermocouple. The non-insulated stainless steel side was positioned

horizontally, receiving a furnace exposure similar to the tested assembly.

The double walled aspirated thermocouple consisted of two concentric stainless steel tubes,

approximately 0.435 in. ID and 0.1875 in. ID, with an 18 gauge Type K thermocouple bead located

approximately Ys in. inside the end of the center tube. Furnace gasses were drawn through both tubes past

46 NISTNCSTAR 7-66, WTC Investigation
Floor Test Assemblies

the thermocouple bead using a Venturi air amplifier. At room temperature, air was measured at approximately 30 ft/s at the tip of the concentric tubes.

4.5.3 Radiometers

To also characterize the furnace environment, both Gardon Gauge and Schmidt-Boelter types of heat flux

gauges were mounted to the assembly (see Fig. 4-30). Table 4-16 summarizes the type of radiometer

gauges used for each test.

Table 4-16. Summary o F radiometers.

Assembly No. Location

Type: Gardon

Gauge (GG) or Schmidt-Boelter

(SB)

I Bottom Chord SB

Deck SB

2

Bottom Chord _ *

Deck _ *

3 Bottom Chord GG

Deck GG

4 Bottom Chord GG

Deck SB

Due to significant damage to the heat flux probes

during testing of Assembly l, no heat flux probes were

available at the time when testing Assembly 2

Similar to the plate and aspirated thermocouples, the heat flux probes were placed at two locations in the

furnace: at the bottom chord level of the main trusses and at the valley of the steel deck. The locations of

the sensors are given in Appendix D for the 35 ft test assemblies and Appendix F for the 17 ft test assemblies.

The Schmidt-Boelter radiometers were 1 in. diameter, 4 ft long, water and air cooled furnace probes with

Schmidt-Boelter heat flux sensors. The sensors were capable of measuring heat fluxes up to 25 BTU/ft2 -s (284 kW/m") and had a view angle of 150 degrees. An air purged zinc selenide window was attached to the sensor, blocking convective flux, thus the sensor measured only radiative flux.

Gardon Gauge sensors, used in two of the tests, were 1 in. diameter, internally water cooled, with the wire

leads air purged and insulated. The sensors were capable of measuring heat fluxes up to 15 BTU/ft2 -s (170 kW/m")andhad a view angle of 1 80 degrees. No window was attached to the sensor, thus total (radiative and convective) heat flux was measured.

NISTNCSTAR 1-6B, WTC Investigation 47
Chapter 4
Chapter 5

Test Results

The tests described herein were conducted in accordance with the Standard Test Methods for Fire Tests of

Building Construction and Materials, ASTM E 1 19-2000a. Results of all four fire resistance tests are presented in this chapter; each test is discussed separately.

5.1 FIRE TEST OF ASSEMBLY NO. 1

The fire resistance test of Assembly No. 1 was conducted at Underwriter Laboratories Toronto, Canada

facility (ULC) on August 7, 2004 under the observation of representatives of Underwriters Laboratories

Inc., Underwriters' Laboratories of Canada, and NIST.

The relative humidity of the concrete slab met the requirements prescribed in ASTM E 1 19.

5.1.1 Test Observations

Table 5-1 presents observations that were recorded during the conduct of the test. All dimensions given

are approximate since they were estimated by making observations through furnace viewports. Times

were generally recorded to the nearest minute. The term "report" is used to describe a loud sound, which

might be described as a "bang" or a "pop." Because these loud reports were often accompanied by

observed movement of the metal deck and the dislodging of SFRM, it is asumed that the reports signaled

explosive spalling of the concrete. It was not possible to ascertain the exact location and extent of any

spalling.

Table 5-1. Test observations - Assembly 1. Test Time,

Min

Exposed (E) or Unexposed (U)

Surface Observations

0.5 E There was slight discoloration of the SFRM on the west side of the assembly.

7 E The east center steel deck seam began to separate.

ll E The deck buckled west of the west bridging truss running in a north-south

direction.

14 E The east steel deck seam had a 3/8 in. opening

16 The vertical member on the east bridging truss where it intersects the south

main truss had buckled.

17 E/U Reports heard with the SFRM deck over-spray falling simultaneously.

19 E/U Same observation as 17 minutes.

19 E The east steel deck seam had a 5/8 in. opening

20 E/U Same observation as 17 minutes and could visually see deck moving

simultaneously.

21 E/U Reports becoming louder and more frequent.

21 U The concrete was spalling near the west end of the assembly.

NISTNCSTAR 1-6B, WTC Investigation 49
Chapter 5

Test Time,

Min

FVvnncpH (¥*\ or Unexposed (U)

Surface Observations

23 E/U Same observation as 2 1 minutes.

24 U The concrete continued to spall. F V J.MUU npfipptinn Utlltv LIKJH wsiq Wa3 r*Vic.prvprl UUStl VC-U in111 tnp lilt Hot L/\JIIVJ111 torn pViotHq vllvlUo of\Jx tlip lilt hnHcTino Ul lUgUlg trnccpc U U55C5.

F/l T J_// LJ Xdtnp . JiUllL UUotl ncprv:}VallUll ti r\n ti> vlJ minntpc 11111 JUIL.V 26 E Visual deflection was observed on the deck spans between the trusses.

Cpncir^tinti \\/qc nr\cpr\/pn in tnp nprK cp^m dnr\\/p tnp ppntpr HppV ci ir\r*f*rt i3CL/£il allUU Wdo UU3C1 VCU 111 U1C UCCK oCcllll ClUUVC 111C LCTHC1 UCLA SUUUU1 I angle.

iiz. / p Thp 1 lit cnnthpuct oKJ LI lilt do l mptal lilt till HppV UlL l\ cpp.mc >tillll> nipo^n Ultdll tnl\J Qpm^rfitp MUul'.lll. p \/ iciid 1 riptlpptirm \x/^»c nncpn/pn in tnp ppntpr HppV ci innnrt finrrlp Tnp \A i V IMldl UCilCCtlUll Wtlo UL/SC1 VCL1 111 L11C LLIHLI UCL.JV sUUUUl I UJ1LIC (lit OT IV1V1 was turning brown in color. 33 E The bridging trusses became more deformed. The vertical member on the west

bridging truss where it intersects the south main truss was heavily deformed.

37 E The deflection in the center deck support angle was more pronounced.

38 E/U Reports heard.

xl T^np \/pi~tir*cil mpmriprc nn qII riT trip nnnfritirt tt*iiccpc li/nprp tnp\/ mtpfcpr't tnp X 11C VClllLal [11C111UC13 Ull all Ul 111C Ul lllgXllg 11 Ui>i5Ci> W11C1C UlCy UlLCloCLl U1C main trusses were deformed.

45 E Large reports heard. 49 E/U A loud report was heard near the center of assembly and a visible drop was

observed. p (Inp ndlT r\T tnp ^F-P?N/1 nn tnp A/PT"tir*Ql mpmr\PT" nntpn dt \^ mm nQ/i TQllpn WilC Ila.lI Ul IliC OFlVivl Ull LUC VCI lltdl 111CU1UC1 11UICU al -J J 111111. UaU lallCll. I uu XLp \|a o Hrli ti r\n ct 1 tciII rvrt r\ t QPI? \^ r\n tnp nnnmnn tt*iiccpc IN U aUUIUUllal Kill Ull Ul O-TIViVl UU UIC !>1 lUUHlL: 11 USdCd. Dj XLp n p ctppl mppI/ nptw/ppn \i/pct r\t*i / i criTYfT tfi ice o

r\ tnp riP/^Lr ci i nnnr"t Qn it 1 p c 1 / / 1 11C MCC1 UCCK UCIWCCU Weal UllUUJllg 11 Uoo alJU 111C UCtK olippuil allglC Was 1/^

in. from the furnace thermocouple. The long diagonal web member on the south main truss was slightly bent. 68 E/U Large report heard. 78/ o P/i l XL/ u T OfftP rPnr»rt hpcirn i^digc rcpun ncdiu. 78 E The bottom chord of the north main truss, approximately 36 in. west of the

q c c pinnl\/ r*pntpflmp w/oc r\ PT/irm (*r\ a&sciiiujy cciiicrline, was uciuiiiicu. 87 E A 10 in. long piece of SFRM on the inner most angle of the lower chord on the n Artn tn ice \r\ m \i/pct /~\ t tnp r\Art h c i tn ppntprliriP r\t trip decPmr\ 1 \/ TP 1

norm iruss, _>o in west ui mc ijurin-suuLii cciiitiiiiie ui uic asociuuiy icu. 88 E A 7 to 10 in. long piece of SFRM on the inner most angle of the lower chord

Ull UIC 11U1 111 IIUdS, _>U 111 CdM UX UIC 11U1 111 oUULll LClllClllllC UX uic asaciiiuiy XC11. 90 E Additional SFRJVl at the area described at 87 min. peeling away but has not

fallen.

y z pXL A 10 in Innfr mppp r*"F QPI? \A i\r\ tnp ir»r\i=>r mnct ^nfrlp r\T tnp ln\*/pr pnnrn nn trip r\ 1Z 111. 1U11H UlCCC Ul OFXVlVX Ull 111C 11111C1 I11UM allele UX UIC 1UWC1 C11UI U Ull 111C south truss, 36 in west of the north-south centerline of the assembly fell. 93 E The area of fall off described at 87 min. had expanded to the three inner most

angles.

109 E/U A very large report was heard.

111 E/U A very large report was heard. 116 E/U Gas off, furnace fire extinguished.

50 NISTNCSTAR 1-6B, WTC Investigation
Test Results

5.1.2 Data

All data shown in the following figures (Figures 5-1 through 5-12) are unedited for the entire duration of

the test. However, not all data shown is reliable due to the limitations of the instrumentation, i.e. thermocouples, radiometers, and calorimeters. Data may become unreliable past the rating period when

structural events occur that can dislodge the instrumentation. Also, protective insulation of the

thermocouple wire may burn away, and the individual wires can make contact with themselves and/or

neighboring wires rendering the data unreliable. Appendix H gives a listing of the times that various

instrumentation failed to give reliable data, as determined by UL.

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004 North Main Truss

20 40 60 80 100 120 Time (minutes)

Figure 5-1. Assembly No. 1 - average and maximum individual

temperatures on north main truss.

NISTNCSTAR 1-6B, WTC Investigation 51
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004

0 -I 1

1 1 20 40 60 80 100 120 Time (minutes)

Figure 5-2. Assembly No. 1 - average and maximum individual

temperatures on south main truss.

Fire Resistance Testing of WTC Floor System

Assembly No. 1 08/07/2004

Time (minutes)

Figure 5-3. Assembly No. 1 - overall average and maximum individual

temperatures on north and south main trusses.

52 NISTNCSTAR 1-6B, WTC Investigation
Test Results

2000

1800

1600

1400

, 1200

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004 West Bridging Truss

400

200

0 60 Time (minutes)

Figure 5-4. Assembly No. 1 - average and maximum individual

temperatures on west bridging truss.

Fire Resistance Testing of WTC Floor System

Assembly No. 1 08/07/2004 East Bridging Truss

0 J 1 i 20 40 60 80 100 120 Time {minutes)

Figure 5-5. Assembly No. 1 - average and maximum individual

temperatures on east bridging truss.

NISTNCSTAR 1-6B, WTC Investigation 53
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004 Unexposed Surface Temperature

60 Time (minutes)

Figure 5-6. Assembly No. 1 - average and maximum individual

temperatures on unexposed surface.

Fire Resistance Testing of WTC Floor System

Assembly No. 1 08/07/2004

Steel Deck Temperature

©

®

©

North

Time (minutes)

Figure 5-7. Assembly No. 1 - average temperatures on steel deck.

S4 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004 Bottom Chord Deflection

_ 12.0 —.-< ) (

-CHORD 10 -CHORD 11 -CHORD 12 CHORD 13 -CHORD 14 CHORD 15

60 Time (minutes)

Figure 5-8. Assembly No. 1 - bottom chord deflection measurements.

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004 Bottom Chord Deflection Rod Temperature

60 Time (minutes)

Figure 5-9. Assembly No. 1 - temperatures of bottom chord deflection rods.

NISTNCSTAR 1-6B, WTC Investigation 55
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 1 08/07/2004 Unexposed Surface Deflection

Dtp 1

Time (minutes)

Figure 5-10. Assembly No. 1 - unexposed surface deflection measurements.

Fire Resistance Testing of WTC Floor System Assembly No. 1 8/07/2004

20 40 60 80 100 120 140 Time (Minutes)

Figure 5-11. Assembly No. 1 - additional instrumentation through west opening.

56 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Figure 5-12. Assembly No. 1 - additional instrumentation through east opening.

5.1.3 Post-Test Observations

Figure 5-13 shows the unexposed surface of the assembly after all loading equipment had been removed

(view looking east). Numbers shown at the centerline and quarter points are vertical deflections after cooling. All other numbers are reference dimensions as measured from the edge of the slab. Figures 5-14 through 5-19 are additional views of the top of the specimen, showing the cracked and

spalled concrete, and of the underside, showing bulging of the metal deck and deformations of the steel trusses after the test specimen had cooled and had been removed from the furnace. To confirm the

spalling of the bottom side of the concrete slab and to quantify the depth of spalling, sections of the slab were cut using a diamond concrete wet saw (see Fig. 5-20). The depth of the delamination spalling

varied but was on the order of 2 in. as seen in Fig. 5-21.

NISTNCSTAR 1-6B, WTC Investigation 57
Chapter 5
Test Results

Source: NIST. Figure 5-1 5. Detail of spalling concrete at east end of Assembly No. 1

.

NISTNCSTAR 1-6B, WTC Investigation 59
Chapter 5

Source: NIST. Figure 5-16. Close-up of spalling concrete at east end of Assembly No. 1.

60 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Source: NIST. Figure 5-19. View of core-end diagonal strut of

south main truss on Assembly No. 1.

NISTNCSTAR 1-6B, WTC Investigation 61
Chapter 5

Source: N1ST.

Figure 5-21. Measurement of depth of delamination spalling.

62 NISTNCSTAR 1-6B, WTC Investigation
Test Results

5.2 FIRE TEST OF ASSEMBLY NO. 2

The fire resistance test of Assembly No. 2 was conducted at the (ULC) facility on August 11, 2004 under

the observ ation of representatives of Underwriters Laboratories Inc., Underwriters Laboratories of

Canada. NIST, and a member of the National Construction Safety Team Advisory Committee.

The relative humidity of the concrete slab met the requirements prescribed in ASTM E 1 19.

5.2.1 Test Observations

Table 5-2 presents observ ations that were recorded during the conduct of the test. All dimensions given

are approximate since they were estimated by making observations through furnace viewports. Times

were generally recorded to the nearest one half minute. The term "report" is used to describe a loud

sound, which might be described as a "bang" or a "pop." Because these loud reports were often

accompanied by observ ed movement of the metal deck and the dislodging of SFRM, it is assumed that the reports signaled explosive spalling of the concrete. It was not possible to ascertain the exact location

and extent of any spalling. The reports heard during the test of Assembly No. 2 were generally not as loud as those heard during the test of Assembly No. 1.

Table 5-2. Test observations - Assembly No. 2.

1 CS I Time,

min

LAUUSCU \ r. i Ul Unexposed (U)

Surface Observations

1 E & U Faint reports heard.

1 E The SFRM began to discolor.

3 E & U A faint report was heard.

3 E SFRM over-spray on the steel deck began to fall when report was heard.

5 E The steel deck began to deform east of the east bridging truss and west of the west bridging truss.

10 E A buckle in the steel deck was observed. The buckle was located 1 ft west of

the center deck support angle and ran in a north-south direction. The length

of the buckle spanned from the north truss to the south truss.

12 E The steel deck was bowing downward between the bridging trusses and the center deck support angle.

15 E & U A faint report was heard.

16 E & U A faint report was heard.

18 E& U Reports became slightly louder. There were three reports in a row, approx. 5 seconds apart. 22 E & U Reports continued and became slightly louder. 22 E There was minor fall off of the SFRM on the top angle of the east bridging

truss. The fall off was partial and did not result in bare steel being exposed.

23 E & U Reports continued.

30 E & U Reports continued.

34 E Visual deformation of the top angles of bridging trusses was observed.

36 E There was no visual buckling of the bridging truss web members.

NISTNCSTAR 1-6B, WTC Investigation 63
Chapter 5

Test Time,

min

Exposed (E) or Unexposed (U)

Surface Observations

40 E&U A large report was heard. Pronounced deck bow at the area noted in the 10 min. observation.

43 E The web members of the bridging trusses began to deform.

46 E The steel deck continued to deform.

48 E&U Reports continued.

48.5 E&U A report was heard. 50 E&U A report was heard.

51.5 E&U A report was heard.

53 E Visual deflection of the center deck support angle was observed. 54 E&U A report was heard.

56.5 E&U A report was heard.

57 E&U Three reports in a row were heard, approx. 1 second apart.

59.5 E&U A report was heard. 60 E All SFRM remained in place besides what was previously noted on the bridging trusses.

61 E&U A report was heard.

63 E&U A report was heard. 64 E&U A report was heard.

72 E&U A report was heard. 74 E 2 1/2 ft length of SFRM fell from the top angle of the east bridging truss.

75 E&U A report was heard.

78 E&U A report was heard. 84 E&U A report was heard.

108 E All SFRM remained on the main trusses.

120 E All SFRM remained on the main trusses.

130 E&U All observations were terminated due to safety precautions.

146 E&U Gas off, fire test terminated.

5.2.2 Data

All data shown in the following figures (Figures 5-22 through 5-33) are unedited for the entire duration

of the test. However, not all of the data shown is reliable due to the limitations of the instrumentation, i.e. thermocouples, radiometers, and calorimeters. Data may become unreliable past the rating period when

structural events occur that can dislodge the instrumentation. Also, protective insulation of the

thermocouple wire may bum away, and the individual wires make contact with themselves and/or

neighboring wires rendering the data unreliable. Appendix H gives a listing of the times that instrumentation failed to give reliable data, as determined by UL.

64 NISTNCSTAR 7-66, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 2 08/11/2004 North Main Truss

20 40 60 80 100 120 140 160 Time (minutes)

Figure 5-22. Assembly No. 2 - average and maximum individual

temperatures on north main truss.

Fire Resistance Testing of WTC Floor System Assembly No. 2 08/11/2004 South Main Truss

0 J 1 20 40 60 80 100 120 140 160 Time (minutes}

Figure 5-23. Assembly No. 2 - average and maximum individual

temperatures on south main truss.

NISTNCSTAR 1-6B, WTC Investigation 65
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 2 08/11/2004 North and South Main Truss

160 Time (minutes)

Figure 5-24. Assembly No. 2 - overall average and maximum individual

temperatures on north and south main trusses.

2000

1800

1600

1400

or

Bi 1200

3 1000

I 800

I—

BOO

400

200

Fire Resistance Testing of WTC Floor System

Assembly No. 2 08/11/2004 West Bridging Truss

- SEC A AVG

- SEC C AVG

-SEC F AVG

SEC H AVG -W BRIDGE MAXIMUM INDIVIDUAL

.........

........ ) ©<>©'

North

80 100 Time (minutes)

Figure 5-25. Assembly No. 2 - average and maximum individual

temperatures on west bridging truss.

66 NISTNCSTAR 1-6B, WTC Investigation
Test Results

2000

1800

1600

1400

iTa 1200 e

3,| 1000

E 800

600

400

200

0

Fire Resistance Testing of WTC Floor System Assembly No. 2 08/11/2004 East Bridging Truss

- SEC A AVG

- SEC D AVG

-SEC E AVG

- SEC G AVG

-E BRIDGE MAXIMUM INDIVIDUAL

a 5 (!>©•©.

I1

North

60 80 100 Time (minutes)

Figure 5-26. Assembly No. 2 - average and maximum individual

temperatures on east bridging truss.

Fire Resistance Testing of WTC Floor System Assembly No. 2 08/11/2004 Unexposed Surface Temperature

80 Time (minutes)

Figure 5-27. Assembly No. 2 - average and maximum individual

temperatures on unexposed surface.

NISTNCSTAR 7-66, WTC Investigation 67
Chapter 5

Fire Resistance Testing of WTC Floor System

Assembly No. 2 08/11/2004

Steel Deck Temperature

£ 1000 ©

®

©

North

Time (minutes}

Figure 5-28. Assembly No. 2 - average temperatures on steel deck.

68 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System

Assembly No. 2 08/11/2004 „„„ Bottom Chord Deflection Rod Temperature

2000 -] -

20 40 60 80 100 120 140 160 Time (minutes)

Figure 5-30. Assembly No. 2 - temperatures of bottom chord deflection rods.

Fire Resistance Testing of WTC Floor System Assembly No. 2 08/11/2004 Unexposed Surface Deflection

60 60 Time (minutes)

Figure 5-31. Assembly No. 2 - unexposed surface deflection

measurements.

NISTNCSTAR 1-6B, WTC Investigation 69
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 2 8/11/2004 West Plate TC and Aspirated TC

Fire Resistance Testing of WTC Floor System Assembly No. 2 8/11/2004 East Plate TC and Aspirated TC

North

Figure 5-33. Assembly No. 2 - additional instrumentation through east opening.

70 NISTNCSTAR 1-6B, WTC Investigation
Test Results

5.2.3 Post-Test Observations.

Figure 5-34 shows the unexposed side of the floor assembly after all loading equipment had been

removed (view looking east). Numbers shown at the centerline and quarter points are vertical deflections

after cooling. All other numbers are reference dimensions as measured from the edge of the slab. Figures 5-35 through 5-37 are views of the underside of the test specimen, showing bulging of the metal

deck, and deformations of the steel trusses after the test specimen had cooled and had been removed from

the furnace.

Source: NIST. Figure 5-34. Unexposed surface of Assembly No. 2 after loading

equipment was removed.

NISTNCSTAR 1-6B, WTC Investigation 71
Chapter 5

Source: NIST. Figure 5-35. View of core end diagonal strut of north main truss

on Assembly No. 2.

Source: NIST. Figure 5-36. South main truss of Assembly No. 2, looking east.

72 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Source: NIST. Figure 5-37. Intersection of east bridging and north main trusses on

Assembly No. 2.

5.3 FIRE TEST OF ASSEMBLY NO. 3

The fire resistance test of Assembly No. 3 was conducted at the (ULC) facility on August 19, 2004 under

the observation of representatives of Underwriters Laboratories Inc. and NIST.

The relative humidity of the concrete slab met the requirements prescribed in ASTM E 1 19.

5.3.1 Test Observations

Table 5-3 presents observations that were recorded during the conduct of the tests. All dimensions given

are approximate since they were estimated by making observations through furnace viewports. Times

were generally recorded to the nearest one half minute. The term "report" is used to describe a loud

sound, which might be described as a "bang" or a "pop." Because these loud reports were often

accompanied by observed movement of the metal deck and the dislodging of SFRM, it is assumed that the reports signaled explosive spalling of the concrete. It was not possible to ascertain the exact location

and extent of any spalling.

NIST NCSTAR 1-6B, WTC investigation 73
Chapter 5

Table 5-3. Test observations - Assembly No. 3. Test Time,

Min

Exposed (E) or Unexposed (U)

Surface Observations

5.5 E The steel desk buckled between the south bridging truss and the center deck

support angle.

8.5 E The steel desk buckled between the north bridging truss and the center deck

support angle.

10 E The north-south deck seam between the south bridging truss and the center deck support angle began to separate.

14 E& U A minor report was hear and there was visual movement of the steel deck

with fall off of the SFRM over-spray from the steel deck.

1 0 c, The center deck support angle was twisting.

1 Q C P, 1 1 A minor report was heard.

1 1 z 1 A minor report was heard.

ZZ.J Two minor reports were heard. 23 E & U A minor report was heard. 26 E& U Three minor reports were heard. 27 E& U Two minor reports were heard. 27 E The steel deck was becoming more deformed.

31 E The third and forth vertical members north of center deck support angle on

the west main truss appear to be bent.

35 E & U A minor report was heard. 55 U Hairline cracks were observed in the concrete surface on both the east and

west sides of the assembly between the edges of the loading blocks and the edges of the test frame. The cracks were more pronounced on the east side. 59 E Visual deflection was observed on the bridging trusses. 60 E All of the SFRM remained in place.

82 E& U A very large report was heard. Pieces on concrete fell to the lower part of the furnace area were observations were being observed. 90 E All of the SFRM remained in place.

92 E The bridging trusses were becoming deformed. The deformation of the steel deck was more pronounced.

120 E No significant changes were observed besides increased deflection. All of the SFRM remained in place.

140 E The SFRM had separated from the bottom chord of the north bridging truss but had not fallen to the furnace floor.

152 E The area, approximately 8 inched long, described in the 140 min. observation

fell to the furnace floor.

180 E No significant changes were observed besides increased deflection. 210 E No significant changes were observed.

210.75 E& U Furnace fire extinguished. Fire test terminated.

74 NISTNCSTAR 7-66, WTC Investigation
Test Results

5.3.2 Data

All data shown in the following figures (Figures 5-38 through 5^49) are unedited for the entire duration

of the test. However, not all data shown is reliable due to the limitations of the instrumentation, i.e. thermocouples, radiometers, and calorimeters. Data may become unreliable past the rating period when

structural events occur that can dislodge the instrumentation. Also, protective insulation of the

thermocouple wire may burn away, and the individual wires make contact with themselves and/or

neighboring wires rendering the data unreliable. Appendix H gives a listing of the times that instrumentation failed to give reliable data, as determined by UL.

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 West Main Truss

20 40 60 80 100 120 140 160 180 200 220 Time (minutes)

Figure 5-38. Assembly No. 3 - average and maximum individual

temperatures on west main truss.

NISTNCSTAR 1-6B, WTC Investigation 75
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 East Main Truss

0 ] 1 , 20 40 60 80 100 120 140 160 180 200 220 Time (minutes)

Figure 5-39. Assembly No. 3 - average and maximum individual

temperatures on east main truss.

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 West and East Main Truss

o -J . , 1 1 20 40 60 80 100 120 140 160 180 200 220 Time (minutes}

Figure 5-40. Assembly No. 3 - overall average and maximum individual

temperatures on west and east main trusses.

76 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004

0

J 1 20 40 60 80 100 120 140 160 180 200 220 Time (minutes)

Figure 5-41. Assembly No. 3 - average and maximum individual

temperatures on south bridging truss.

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 North Bridging Truss

100 120 Time (minutes)

Figure 5-42. Assembly No. 3 - average and maximum individual

temperatures on north bridging truss.

NIST NCSTAR 1-6B, WTC investigation 77
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 Unexposed Surface Temperature

600 -, -

0 J , 1

, 1 20 40 60 80 100 120 140 160 180 200 220 Time (minutes)

Figure 5-43. Assembly No. 3 - average and maximum individual

temperatures on unexposed surface.

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004

Steel Deck Temperature

1800.0 -,

220 Time (minutes)

Figure 5-44. Assembly No. 3 - average temperatures on steel deck.

78 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 Bottom Chord Deflection

CHORD DEF 15

20 40 60 80 100 120 140 160 180 200 Time (minutes)

Figure 5-45. Assembly No. 3 - bottom chord deflection measurements.

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 Bottom Chord Deflection Rod Temperature

Time (minutes)

Figure 5-46. Assembly No. 3 - temperatures of bottom chord deflection rods.

NIST NCSTAR 1-6B, WTC Investigation 79
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 3 08/19/2004 Unexposed Surface Deflection

180 200

Figure 5-47. Assembly No. 3 - unexposed surface deflection measurements.

Fire Resistance Testing of WTC Floor System Assembly No. 3 8/19/2004 South Plate TC. Aspirated TC and Calorimiter

20 40 100 120 140 Time (Minutes)

180 200

Figure 5-48. Assembly No. 3 - additional instrumentation through south opening.

80 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 3 8/19/2004 North Plate TC, Aspirated TC and Calorimiter

-N ASPTC 148 -N PLATE TC 156 N RAD 2

100 120 Time (Minutes)180 200

Figure 5-49. Assembly No. 3 - additional instrumentation through north opening.

5.3.3 Post-Test Observations

Figure 5-50 shows the unexposed side of floor assembly No. 3 after all loading equipment had been

removed (view looking north). Numbers shown at the centerline and quarter points are vertical deflections after cooling. All other numbers are reference dimensions as measured from the edge of the

slab. Figures 5-51 through 5-53 are additional views of the post-test condition of the test specimen.

Source: NIST. Figure 5-50. Unexposed surface of Assembly No. 3 after loading

equipment was removed.

NISTNCSTAR 1-6B, WTC Investigation 81
Source: NIST. Figure 5-51. Detail of spalling concrete at north end of

Assembly No. 3.

Source: NIST. Figure 5-52. View of column-end diagonal strut of west main truss

on Assembly No. 3.

S2 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Source: NIST. Figure 5-53. Intersection of north bridging and west main truss

on Assembly 3.

5.4 FIRE TEST OF ASSEMBLY NO. 4

The fire resistance test of Assembly No. 4 was conducted at the UL Northbrook facility (ULN) on August

25, 2004 under the observation of representatives of Underwriters Laboratories Inc., and NIST.

The relative humidity of the concrete slab met the requirements prescribed in ASTM E 1 19.

5.4.1 Test Observations

Table 5^4 presents observations that were recorded during the conduct of the test. All dimensions given

are approximate since they were estimated by making observations through furnace viewports. Times

were generally recorded to the nearest one quarter minute. The term "report" is used to describe a loud

sound, which might be described as a "bang" or a "pop." Because these loud reports were often

accompanied by observed movement of the metal deck and the dislodging of SFRM, it is assumed that the reports signaled explosive spalling of the concrete. It was not possible to ascertain the exact location

and extent of any spalling. After the concrete spalling at approximately 55 minutes, ceramic fiber

insulation was placed over the opening in the concrete to protect the hydraulic loading equipment from

the heat escaping the furnace, thereby, allowing the test to continue.

NIST NCSTAR 1-6B, WTC Investigation 83
Chapter 5

Table 5-4. Test observations - Assembly No. 4. Test Time,

Min

Exposed (E) or Unexposed (U)

O --£" Surface Observations

4.25 E

pr 1.1 11" r* , i ilJI 1 J .1 1 * J * -r1 ! blight buckling oi the steel deck was observed near the bridging trusses. The

HiIHILKMIIL. i c u 1 iti ct w^c WdS mnrp nrnnni lnppH npcir trip nnrtn nrinoinrr truce 111U1C piUHUUlltCU lllcll U1C IHM III 1>I IUL1I1U 11 Uoo.

7 p Tiiprp w/nc np^\'v nppb niifKiino in 'A pnct-\x/pct Hirpptinn 1 "Ft cruitn r\T trip 1 lltl C W CIj llta V V UttR. 1 'Ut Ml J ll_ ill <x taol WCol VJllttllUll 1 11 .M'ulll Ul lilt center deck support angle.

8 E The center deck support angle was bowing towards the north.

9.5 E The finish on the bridging trusses was peeling away.

14 E/U A minor report was heard. 14.75 E/U Two minor reports were heard approximately 1 second apart.

15.5 E/U Two minor reports were heard approximately 1 second apart. 15.75 E/U A report was heard.

1 D 1 Jit ICpUlla WCit UttUJIlllJ^ 1UUUCI allU IIIUIC UCUUCllL.

1 7 ^ p (wvci l\/pr cnrQi/ spidy c\t trip n PR r\v\ trip c t pp 1 /HppL" \i/qc tq 1 1 i n rr Trnrn thp o c cprrihl \ i ui nit orrvivi un uit sicci ucck wds lcuiiiig iruiu uic aS&tiiiDiy.

p lilt [ 'Ti pk \lUp c\Y\ ptllUJU ri ("\t"*H c\\ Ul trip Hit cSUUlll 1 1 ri nnnmnrr UllUglllg, fri Ullss ice ix/qc WaS nppnm DttUIITing inn c\UtlUiIIItU. PTrMmpn

P/l l i ne reports were Becoming less irequent anu louuer. 70 S p 1 I1C MCCl UCLK UtTLalllC IlCavliy UCIOIIIICU sOUtll Ol lllC CCI11CI UCLK SUppUIl

angle.

22 E/U The reports were more frequent.

23 E/U A loud report was heard. 24.75 E The top chord of the north bridging truss was becoming deformed.

31.5 E The reports were becoming less frequent.

35.75 E The SFRM became darker in color. 41 E/U A report was heard. It was the first one since the 3 1 .5 minute observation.

Al P/l 1 CI U A loud report was heard. AA 7^ i nrec reports were nearu approximately i seconu apart. 48.5 E/U A loud report was heard.

51 E/U A very loud report was heard.

51 E Visible steel deck deflection between the center deck support angles and the bridging trusses. 54 E The bridging trusses were bowing downward near their centers. 55.25 E/U A very loud report was heard. Pieces on concrete fell to the lower part of the furnace area were observations were being observed.

56 E The center deck span west of the west main truss was bowing downward past

the lower chord of the main truss. £0 C /vii oi me or ivLvi on me main trusses remdineu in piace.

60 ? S P i ne center uecK support angle was twisting wnere it lnteriaceu witti int. main

trusses. 73 E Visual deck deflection near the center of the assembly continued.

88 E/U No reports were heard since the 55.25 minute observation.

90 E All of the SFRM on the main trusses remained in place.

110 E A minor report was heard. 120 E All of the SFRM on the main trusses remained in place. 120 E/U Furnace Fire extinguished at the request of the submitter.

S4 NISTNCSTAR 1-6B, WTC Investigation
Test Results

5.4.2 Data

All data shown in the following figures (Figures 5-54 through 5-65) are unedited for the entire duration

of the test. However, not all data shown is reliable due to the limitations of the instrumentation, i.e. thermocouples, radiometers, and calorimeters. Data may become unreliable past the rating period when

structural events occur that can dislodge the instrumentation. Also, protective insulation of the

thermocouple wire may burn away, and the individual wires make contact with themselves and/or

neighboring wires rendering the data unreliable. Appendix H gives a listing of the times that instrumentation failed to give reliable data, as determined by UL.

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 West Main Truss

2000

20 40 60 80 100 120 Time (minutes)

Figure 5-54. Assembly No. 4 - average and maximum individual

temperatures on west main truss.

NIST NCSTAR 1-6B, WTC Investigation 85
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 East Main Truss

1800 -i

'

0 -I

1

1 1 1 20 40 60 80 100 120 Time (minutes)

Figure 5-55. Assembly No. 4 - average and maximum individual

temperatures on east main truss.

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 West and East Main Truss

2000 t n

0 -I , , , , — >. 20 40 60 80 100 120 Time (minutes)

Figure 5-56. Assembly No. 4 - overall average and maximum individual

temperatures on west and east main trusses.

86 NISTNCSTAR 7-68, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 South Bridging Truss

2000 -,

20 40 60 80 100 120 Time (minutes)

Figure 5-57. Assembly No. 4 - average and maximum individual

temperatures on south bridging truss.

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 North Bridging Truss

2000 1

20 . 40 60 80 100 120 Time (minutes)

Figure 5-58. Assembly No. 4 - average and maximum individual

temperatures on south bridging truss.

NIST NCSTAR 1-6B, WTC Investigation X7
Chapter 5

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 Unexposed Surface Temperature

S

400

a.E

a> H 300

60 Time (minutes)

Figure 5-59. Assembly No. 4 - average and maximum individual

temperatures on unexposed surface.

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004

Steel Deck Temperature

©

©

60 Time (minutes)

Figure 5-60. Assembly No. 4 - average temperatures on steel deck.

88 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 Bottom Chord Deflection 1

^

• 4 * ® ©

-CHORD DEF 10 -CHORD DEF 11 -CHORD DEF 12 CHORD DEF 13 -CHORD DEF 14 CHORD DEF 15

60 Time (minutes)

Figure 5-61. Assembly No. 4- bottom chord deflection measurements.

Fire Resistance Testing of WTC Floor System Assembly No. 4

08/25/2004 Bottom Chord Deflection Rod Temperature

2000 -,

20 40 60 80 100 120 Time (minutes)

Figure 5-62. Assembly No. 4 - temperatures of bottom chord deflection rods.

NISTNCSTAR 1-6B, WTC Investigation 89
Chapter 5

Fire Resistance Testing of WTC Floor System

Assembly No. 4 08/25/2004 Unexposed Surface Deflection

60 Time (minutes)

Figure 5-63. Assembly No. 4 - unexposed surface deflection

measurements.

Fire Resistance Testing of WTC Floor System Assembly No. 4 8/25/2004

Time (Minutes)

Figure 5-64. Assembly No. 4 - additional instrumentation through south

opening.

90 NISTNCSTAR 7-66, WTC Investigation
Test Results

Fire Resistance Testing of WTC Floor System

Assembly No. 4

8/25/2004 North Plate TC, Aspirated TC and Calorimiter

20 40 60 80 100 120 Time (Minutes)

Figure 5-65. Assembly No. 4 - additional instrumentation through north opening.

5.4.3 Post-Test Observations

Figure 5-66 shows the unexposed side of the assembly after all loading equipment was removed (view

looking north). Numbers shown at the centerline and quarter points are vertical deflections after cooling.

All other numbers are reference dimensions as measured from the edge of the slab. Figures 5-67 through

5-70 are additional views of the post-test condition of the test specimen.

Source: NIST. Figure 5-66. Unexposed surface of Assembly No. 4 after loading

equipment was removed.

NISTNCSTAR 7-68, WTC Investigation 9\
Chapter 5

Source: NIST. Figure 5-67. Unexposed surface of Assembly No. 4, view of concrete

spalling on west side of assembly.

92 NISTNCSTAR 1-6B, WTC Investigation
Test Results

Source: NIST. Figure 5-69. Intersection of north bridging and west main truss

on Assembly 4.

Source: NIST. Figure 5-70. View looking north of south bridging truss at location

where concrete spalling occurred on Assembly 4.

NISTNCSTAR 1-6B, WTC Investigation 93
Chapter 5

5.5 FIRE RESISTANCE RATINGS

All four fire resistance tests were conducted for as long as practical to obtain as much information as possible. As such, the tests were not stopped when the first end-point criteria was reached. Rather, the

tests were continued until it was determined that collapse of the test specimen was imminent or until instrumentation critical to the determination of safe continuation of the test had failed to provide reliable

readings. Additionally, excessive deflection of the floor system would sometimes contact and damage

furnace instrumentation making it impractical to continue the test.

5.5.1 Test Assembly No. 1

Assembly No. 1 was fire tested on August 7, 2004 in accordance with ASTM E 119-61 and ASTM

E 1 19-00a. The test was continued for 116 minutes and terminated when collapse of the assembly was

imminent. The main trusses reached a maximum individual temperature of 1,300 °F (704 °C) (at thermocouple No. 18), as defined in Paragraph 32.1.3 of ASTM E 1 19-00a, at 62 min. The average

limiting temperature of 1,100 °F (593 °C), as defined in Paragraph 32.1.3 of ASTM E 1 19, was reached at 66 minutes at section E. The unexposed surface temperatures exceeded the maximum individual

requirement of 325 °F (163 °C) rise over ambient temperatures as defined in Paragraphs 7.4 and 32.1.2 of

ASTM E 1 19-00a at 1 1 1 minutes. For safety reasons, access to the top of the floor assembly was not permitted during the test and, consequently, testing for unexposed surface conditions that would ignite cotton waste was not done.

5.5.2 Test Assembly No. 2

Assembly No. 2 was fire tested on August 11, 2004 in accordance with ASTM E 119-61 and ASTM

E 1 19-00a. The test was continued for 146 minutes and terminated when the vertical deflection of the

assembly exceeded the capability of the instrumentation to accurately measure the deflection at the center of the test assembly. The main trusses reached maximum individual temperature of 1,300 °F (704 °C) at 62 minutes. The average limiting temperature of 1,100 °F (593 °C) was reached at 76 minutes at Section C. Neither the maximum or average unexposed surface temperatures were exceeded throughout

the duration of the fire test. As described for the test of Assembly No. 1, testing for unexposed surface

conditions that would ignite cotton waste was not done.

5.5.3 Test Assembly No. 3

Assembly No. 3 was fire tested on August 19, 2004 in accordance with ASTM E 1 19-61 and

ASTM E 1 19-00a. The test was continued for 210 minutes and terminated when the vertical deflection of

the assembly exceeded the capability of the instrumentation to accurately measure the deflection at the center of the test assembly. The main trusses reached a maximum individual temperature of 1,300 °F

(704 °C) at 80 minutes. The average limiting temperature of 1,100 °F (593 °C) was reached at 86 minutes

at Section F. The unexposed surface temperatures exceeded the maximum individual temperature

requirement of 325 °F (163 °C) rise over ambient temperature at 157 min. The average temperature of the

unexposed surface limit was reached at 180 minutes. Since the top of the floor assembly was loaded with

concrete block , water containers, and hydraulic actuators, access to most of the concrete surface was

limited and testing for unexposed surface conditions that would ignite cotton waste was not done.

94 NISTNCSTAR 7-66, WTC Investigation
Test Results

5.5.4 Test Assembly No. 4

Assembly No. 4 was fire tested on August 25, 2004 in accordance with ASTM E 1 19-61 and

ASTM E 1 19-00a. The test was continued for 120 minutes and tenninated when collapse of the assembly was imminent. The main trusses reached a maximum individual temperature of 1,300 °F (704 °C) at 58 minutes. The average limiting temperature of 1,100 °F (593 °C) was reached at 66 minutes at Section B. The unexposed surface temperatures exceeded the maximum individual requirement of 325 °F

(163 °C) rise over ambient temperatures at 58 minutes. As described for the test of Assembly No. 3, testing for unexposed surface conditions that would ignite cotton waste was not done.

5.5.5 Summary Table

Based on the results of the fire tests, assemblies 1 through 4 achieved the hourly ratings shown in Table 5-5.

NISTNCSTAR 1-6B, WTC Investigation 95
Chapter 5

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96 NIST NCSTAR 1-6B, WTC Investigation
Chapter 6

Discussion of Results

6.1 COMPARISON OF RESULTS

Results of the four fire resistance tests are compared in this section. First, it is useful to compare the fire environment for all four tests. The ASTM E 1 19 Standard requires that the prescribed time-temperature

relationship be followed as determined by the average of individual temperature measurements within the furnace. For the tests conducted here, additional instrumentation was installed to characterize the thermal

environment and. in particular, the exposure at different locations relative to the floor assembly. Lastly,

the performance of the floor assembly, as evidenced by temperatures on the unexposed side of the floor

slab, temperatures of the steel trusses, and by the deflections of the slabs and supporting steel members, is presented.

6.1.1 Furnace Control Temperatures

The average furnace temperatures during all four tests and the target time-temperature relationship

prescribed by ASTM E 1 19 are shown in Fig. 6-1. It is seen that the average furnace control

temperatures were very similar and indeed met the requirements of ASTM E 1 19.

Fire Resistance Testing of WTC Floor System

Average Furnace Control Temperature Comparison

2000

ASTM E1 19 ULC Restrained Assembly (Test 1

)

ULC Unrestrained Assembly (Test 2) UL Restrained Assembly (Test 3) UL Restrained Assembly (Test 4)

50 100 150 200 Time (minutes)

Figure 6-1. Comparison of average furnace control temperatures.

NISTNCSTAR 1-6B, WTC Investigation 97
Chapter 6

6.1.2 Furnace Thermal Environment

Additional instrumentation was included in all four tests to further characterize the thermal environment

of the exposing fire. Aspirated thermocouples, plate thermocouples and radiometers were located at the

underside of the metal deck and at the elevation of the bottom chord and recordings were made

throughout the duration of the tests.

Plate Thermocouple Measurements

Figures 6-2 and 6-3 show temperatures recorded by the plate thermocouples for Test No. 2 (ULC

furnace) and Test No. 4 (ULN furnace). Temperatures recorded at the bottom chord are presented in Fig. 6-2, and those recorded at the underside of the metal deck are shown in Fig. 6-3. These two plots

show that temperatures measured at two locations are very similar between the two furnaces. Note that the plate TC at the metal deck in Test 4 (ULN) gave unreliable data after approximately 50 min. This

time is consistent with observations of very loud report and visible steel deck deflection recorded at 51

min (see Table 5-4). This plate TC was dislodged from its initial position, relative to the metal deck, and

readings beyond 50 min cannot be interpreted.

i 800

Fire Resistance Testing of WTC Floor System

Plate Thermocouple Comparison UL Restrained Assembly (Test 4) and ULC Unrestrained Assembly (Test 2)

-Test 4 Plate TC at Bottom Chord

Test 2 Plate TC at Bottom Chord

Time (minutes)

Figure 6-2. Temperatures measured at the bottom chord by the plate thermocouple

in the ULC furnace (Test No. 2) and ULN furnace (Test No. 4).

98 NISTNCSTAR 1-6B, WTC Investigation
Discussion of Results

Fire Resistance Testing of WTC Floor System

Plate Thermocouple Comparison UL Restrained Assembly (Test 4) and ULC Unrestrained Assembly (Test 2)

0 20 40 60 80 100 120 140 160 Time (minutes)

Figure 6-3. Temperatures measured at the underside of the metal deck by the plate

thermocouple at the ULC furnace (Test No. 2) and ULN furnace (Test No. 4).

Radiometer Measurements

Thermal radiation is the dominant mode of heat transfer from the furnace to the test specimen. Hence,

heat flux measured by radiometers should provide a better indication of how quickly a specimen will heat

up than temperature of the surrounding gas as measured by furnace control thermocouples. Comparing

the radiant flux measured in the larger (ULC) furnace (see Figs. 5-1 1 and 5-12) to the radiant heat flux measured in the smaller (ULN) furnace (see Figs. 5-48, 5-49, and 5-65), one observes that smaller

furnace produced a radiant heat flux somewhat higher than the larger furnace, in spite of the fact that the

temperatures used to control both furnaces followed the ASTM E 1 19 time-temperature curve (Fig. 6-1 ). Comparison of overall average temperatures of the main trusses, protected with 3/4 in. fireproofing (see

Figs. 5-3, 5-24, and 5-40) indicates that, at 60 minutes, average steel temperatures are on the order of

700 °F to 800 °F for all three test specimens (furnace temperature at 60 min is prescribed to be 1700 °F).

The above observations are based on a limited number of measurements, and, for Test No. 2, there were no radiometer readings due to damage to the radiometers in Test No. 1 . In addition, factors such as heat

loss must also be taken into account when comparing differences in furnace exposures to assess

reproducibility of test results.

NISTNCSTAR 7-66, WTC Investigation 99
Chapter 6

6.1.3 Steel Temperatures

Steel temperatures were recorded at several locations on the main and bridging trusses. Average

temperatures of the bottom chord, web diagonal, and top chord are presented here.

Figure 6-4 shows a comparison of the average temperature of the bottom chord for the three tests in which the thickness of the SFRM was 3/4 in. Temperatures are seen to be very comparable up to about

75 min, which is around the time when SFRM began to dislodge.

Fire Resistance Testing of WTC Floor System

Bottom Chord Average Temperature Comparison

o I 1 50 100 150 200 Time (minutes)

Figure 6-4. Average temperatures of the bottom chord for Test Nos. 1, 2, and 3

(3/4 in. thick SFRM).

100 NISTNCSTAR 1-6B, WTC Investigation
Discussion of Results

Figure 6-5 presents a comparison of temperatures of the truss web diagonals for the three tests in which

the thickness of the SFRM was 3A in. The web temperatures for the two full-scale tests (35 ft span

assemblies) were greater than those for the reduced-scale test (17 ft span assembly) after about 15 min.

The reason for this difference is not clear but is possibly due to the relationship between the SFRM

thickness and scale of the steel trusses. Comparison of Figs. 5-35 and 5-53 illustrates the difference in the buildup of SFRM at the intersections of the webs and chord members between the full- and reducedscale test specimens, which may affect the rate of heating of the truss web diagonals. These results

illustrate that thermal scaling is an issue that needs to be addressed.

Fire Resistance Testing of WTC Floor System Web Average Temperature Comparison

1800

50 100 150 200 Time (minutes)

Figure 6-5. Average temperature of web diagonals for Test Nos. 1, 2, and 3

(3/4 in. thick SFRM).

NISTNCSTAR 1-6B, WTC investigation 101
Chapter 6

The average temperature of the top chord is plotted in Figure 6-6 for the three test assemblies with 3A in. of SFRM. The average top chord temperaUire for the two full-scale tests (35 ft span test assemblies) was

greater than the average temperature recorded for the reduced-scale test ( 1 7 ft span assembly) after about

50 min. Because of the comparatively abrupt changes in average temperature beginning around 50 min,

the difference may be explained by sudden changes such as the onset of spalling of concrete and attendant

loss of fire protection. However, since the steel temperatures in the reduced-scale test generally tend to be lower than in the full-scale test, this trend may be explained by a scale-related factor such as the

difference in the buildup of SFRM affecting the rate of heating of the steel as noted above. Further, it is possible that the overspray on the metal deck was greater for test Specimen No. 3 than for the other two

tests since the lower chord is closer to the metal deck. This, too, would be a geometrical scaling effect.

Fire Resistance Testing of WTC Floor System Top Chord Average Temperature Comparison

50 100 150 200 Time (minutes)

Figure 6-6. Average temperature of the top chord for Test Nos. 1, 2, and 3

(3/4 in. thick SFRM).

102 NISTNCSTAR 1-6B, WTC Investigation
Discussion of Results

Average temperature of the bottom chord at Section C (center of west truss) for Test No. 3 {

3A in. thick

SFRM) and Test No. 4 (V2 in. thick SFRM) is plotted in Fig. 6-7. As expected, the steel temperatures for the specimen with Vi in. of SFRM were higher than those for the specimen with 3A in. of SFRM. Here, the same furnace (ULN) was used for the comparison.

Fire Resistance Testing of WTC Floor System

Bottom Chord Average Temperature Comparison

0 -I 1 1—

50 100 150 200 Time (minutes)

Figure 6-7. Average temperature of the bottom chord for Test No. 3 (3/4 in. thick SFRM) and No. 4 (1/2 in. thick SFRM).

NISTNCSTAR 1-6B, WTC investigation 103
Chapter 6

6.1.4 Unexposed Surface Temperatures

The temperature of the unexposed surface of the floor assemblies is plotted in Fig 6-8. It is observed that the unexposed surface temperatures of all four test assemblies were similar prior to the onset of

significant concrete spalling at around 50 min. In Test 4, the surface-mounted TC on the west edge near

the center of the span was affected by the explosive failure of the slab and recorded hot gas temperatures.

6.1.5 Deflections of Floor Assembly

The following plots show the vertical deflection measured at the center of each assembly. Figure 6-9

shows the deflection, while Fig. 6-10 shows a plot of the deflection normalized by the span. It is seen that

test Assembly No. 1 experienced a significant increase in vertical deflection at 49 min, which corresponds

directly to a loud report and visible deflection noted in the test observations. Figure 5-13 shows the

damage to the top side of the concrete slab that occurred with the sudden increases in deflection. The

normalized curves show good agreement throughout the duration of the tests.

104 NISTNCSTAR 1-6B, WTC Investigation
Discussion of Results

Fire Resistance Testing of WTC Floor System Unexposed Surface Deflection -Center of AssemblyTime (minutes)

Figure 6-9. Deflection measured at the center of each assembly.

Fire Resistance Testing of WTC Floor System Unexposed Surface Deflection/Span

-Center of Assembly0.045 1

Time (minutes)

Figure 6-10. Deflection measured at the center of each assembly

divided by the span.

6.2 OBSERVATIONS

Several observations can be made from the results presented in Chapter 5 for each test, the summary table of hourly ratings (Table 5-5), and the comparisons discussed above.

• The test assemblies were able to withstand standard fire conditions for between % h and 2 h

without exceeding the limits prescribed by ASTM E 1 19.

NIST NCSTAR 1-6B, WTC Investigation 105
Chapter 6

• Test specimens protected with % in. thick sprayed fire-resistive material were able to sustain

the maximum design load for approximately 2 hours (the minimum was 116 min) without

collapsing; in the reduced-scale restrained test, the load was maintained for 3 Vi h (210 min)

without collapsing.

• The restrained full-scale floor system obtained a fire resistance rating of 1

lA h while the

unrestrained floor system achieved a 2 h rating. Past experience with the ASTM E 1 19 test method would lead investigators to expect that the unrestrained floor assembly would not perform as well as the restrained assembly, and therefore, would receive a lower fire rating.

• A fire rating of 2 h was determined from the reduced-scale restrained test with the average

applied SFRM thickness of 3A in., while a fire rating of 1/4 h was determined from the full- scale restrained test with the same SFRM thickness.

• The result stated above raises the question of whether or not a fire rating based on the

ASTM E 1 19 performance of a 17 ft span floor assembly is scalable to a larger floor system

such as that found in the WTC towers where spans ranged from 35 ft to 60 ft.

• A fire rating of 3A h was determined from the reduced-scale restrained test with the specified

SFRM thickness of lA in.

6.3 AREAS OF FURTHER STUDY

The NIST tests have identified areas where further study related to the Standard Fire Resistance Test method may be warranted. The issues related to the test method that NIST considered in formulating its recommendations include:

• Criteria for determining structural limit states, including failure, and means for measurement

• Scale of test assembly versus prototype application

• Effect of end restraint conditions (restrained and unrestrained) on test results, including the

influence of stiffness

• Structural connections (not currently addressed in ASTM E 1 19)

• Combination of loading and exposure (temperature profile) adequately represent expected

conditions

• Procedures to analyze and evaluate data from fire resistance tests of other building

components and assemblies to qualify an untested building element

• Repeatability of test results (single test currently defines rating for system)

• Reproducibility of heat flux environment between different furnaces and laboratories.

• Relationships between prescriptive ratings and performance of the assembly in realistic building fires.

106 NISTNCSTAR 1-6B, WTC Investigation
Chapter 7

References

AO 318-63 (1963). Building Code Requirements for Reinforced Concrete, American Concrete Institute,

Detroit, MI.

AISC 1963 (1963). Manual ofSteel Construction, Sixth Edition, American Institute of Steel Construction,

Chicago, IL.

AISC 2001 (1989). Manual ofSteel Construction: Allowable stress Design, Ninth Edition, American

Institute of Steel Construction, Chicago. IL.

AISC 2001 (2001). Manual ofSteel Construction: Load and Resistance Factor Design, Third Edition,

American Institute of Steel Construction, Chicago, IL.

ASTM (1973). Standard Test Methods for Fire Tests of Building Construction and Materials,

ASTM E 1 19-73, ASTM International, Conshohocken, PA.

ASTM (2000). Standard Test Methods for Fire Tests of Building Construction and Materials,

ASTM E 1 19-00, ASTM International, Conshohocken, PA.

ASTM (2000a). Standard Test Methods for Thickness and Density of Sprayed Fire-Resistive Material

(SFRM) Applied to Structural Members, ASTM E 605-93 (Reapproved 2000), ASTM International,

Conshohocken, PA.

Beitel, J. and Iwankiw, N. (2002). "Analysis of Needs and Existing Capabilities for Full-Scale Fire

Resistance Testing," NIST GCR 02-843, National Institute of Standards and Technology,

Gaithersburg, MD.

Jefferson, T. B. and Woods, G. (1962). Metals and How to Weld Them, Second edition, The James F. Lincoln Arc Welding Foundation, Cleveland, OH.

NISTNCSTAR 7-66, WTC Investigation 107
Chapter 7

This page intentionally left blank.

108 NISTNCSTAR 1-6B, WTC Investigation
Appendix A

Certified Mill Test Reports (CMTRs)

NISTNCSTAR 1-6B, WTC investigation
Appendix A

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
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ROANOKE ELECTRIC STEEL CORPORATION

P.O. BOX 13948 ROANOKE , VIRGINIA 24038-3948

Test and Inspection Report NO. 47405-1

ROANOKE

METALS USA P&S

50 CABOT BOULEVARD

LANGHORNE PA

LANGHORNE

19047-0000 Date 3/05/02

HEAT 1 SIZE 1 -YIELD Pt. ULTIMATE ELONG BEND GRADE

NUMBER | KSI KSI 8 IN. TEST

JD4165 ANGLES 1 1/2 X 1 1/2 X 1/4 61.7 79.2 23 .

AH36

PURCHASE ORDER NUMBER 2-YIELD PT. ULTIMATE ELONG BEND GRADE

NUMBER PIECES KSI KSI 8 IN. TEST

W6095 251 PIECES 20' 63.4 80. 7 23.

AH36

HEAT 1 SIZE 1-YIELD Pt. ULTIMATE ELONG BEND GRADE

NUMBER J MPA MPA 203mm TEST

JD4165 ANGLES 38.1 X 38.1 X 6.4 425 .4 546.23 .AH36

PURCHASE ORDER NUMBER 2-YIELD PT. ULTIMATE ELONG BEND GRADE

NUMBER PIECES MPA MPA 203mm TEST

W6095 251 PIECES 20' 437 . 1 556.4 23 . 1 AH36

C MN S P SI CR NI MO CU V NB

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MERCURY, RADIUM OR OTHER ALPHA SOURCE MATERIALS IN ANY FORM HAVE NOT BEEN USED

IN THE PRODUCTION OF THIS MATERIAL. NO WELD REPAIR HAS BEEN PERFORMED.

MATERIAL MANUFACTURED IN ACCORDANCE WITH OUR QUALITY MANUAL REVISION 9 DATED

5-1-1998, BASED UPON ISO 9002-1994, ASME SECTION III DIV I NCA3800 , ANSI-45.2 10CFR50 AND 10CFR21

Approved ABS QA Mill. Certificate No. 00NN101O8-X.

This material was melted and manufactured in the USA by basic Electric Furnace

processes to meet specification: ASTM A572-99A GR 50 TYPE 2

The tensile values stated in either inch-pound units or SI units are to be

regarded as separate as defined in the ASTM scope for this material. Unless a netric specification is ordered, this material has been tested and meets the

requirements of the inch-pound ranges.

This is to certify the above to be a true and accurate report as contained in

:he records of this company.

Engineer of Tests: Charles R. Charlton

01/07/2005 01:55PM
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ALL WIRES LISTED ABOVE MEET AST M. A-62 OR A-4 96 BEND TEST REQUIREMENTS

WELD SHEAR TESTS

WIRE SIZES: W4 2 .' 'A 4 3

Test Number 1 I 2 3 4 Break Load

2764] 2215 360B 3477

MINIMUM BREAK LOAD REQUIRED 1&05 LBS. OF FORCE

RAW MATERIALS - HEAT NUMBER INFORMATION

Longitudinal Wir»s Heat No's Code W17516 "S4S77

Transverse Wires H~a: No's Code W17S16 "64S77

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WELD SHEAR TESTS

WIRE SIZES: m 2 } W 3

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MINIMUM BREAK LOAD REQUIRED 1505 LBS. OF FORCE

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Appendix B

Primer Paint Specification

NISTNCSTAR 7-66, WTC Investigation
Appendix B

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
LACLEDE STEEL COMPANY

WTCI-32-I

September 1, 1967

Laclede Standard Steel Joist Paint

(FORMULA LREP - 10001

)

Title: Standard Protective Red Chroma te Primer No. 10001

Formulation:

Pigment

Iron Oxide

Aluminum Silicate

Strontium Chromate

Total Pigment

55.0$

4l.0$

4.0$

100.0$

28.5$

Vehicle

Unmodified Epoxy Amine 45.0$

Deionized Water and Amine 55.0$

Total Vehicle 100.0$

71.5$

100.0$

Wt/Gal

Solids

Grind

Viscosity

Bake

Weatherability

Film Thickness

Gloss

Pencil Hardness

9.3 Lbs.

52$ by wt.

#4 Hegman Gauge

3600 cps. at 77° F.

Metal temperature 20 minutes at 350° F.

ASTM B-117-64 passes 150 hrs . on specified

clean steel panel at 1 mil film thickness

unscribed

Dry 1.0 plus or minus 0.2 mils

30 - 50

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Appendix C

Construction Drawings for 35 Ft Test Assemblies

NISTNCSTAR 1-6B, WTC Investigation
Appendix C

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NISTNCSTAR 1-6B, WTC Investigation


Z1 H
Appendix C

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
Appendix D

Instrumentation for 35 Ft Test Assemblies

NISTNCSTAR 1-6B, WTC Investigation
Appendix D

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
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Appendix E

Construction Drawings for 17 Ft Test Assemblies

NISTNCSTAR 1-6B, WTC Investigation
Appendix E

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation

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Appendix F

Instrumentation for 17 Ft Test Assemblies

NISTNCSTAR 1-6B, WTC Investigation
Appendix F

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
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Appendix F

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
Appendix G

Truss Calculation Sheets

NISTNCSTAR 1-6B, WTC investigation
Appendix G

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
aclede Steel Company D105- T 5 -Sheet f_

WORLD TRADE CENTER

FLOOR GRID TRUSSES

DESIGN DATA

Truss Mk. 2C 3 2 T£> '35 Q

Truss Component Mk . c 3 2-TS-3S3

Overall Length 3$ &

Main web panels g yl\ n = 2%j±

Long End

bottom Chd. Length

Main Web

y Arc Welds

(All others controlled resistance welds)

-Bottom Chd. Length

Short End

Check

Type S End

NOTES

Main Web - Continuous uniform section throughout Member Mk. 3.

(Top chord fillers same section as Main Web - at midpoint K/DA/fT

center web panels minimum.

)

Vertical Struts Mk. 2 - Same size as main web.

End Bearing Struts - Same size as main web.

Composite Type - Webs extend above top chord 3 "

MEMBERS REQUIRED PER TRUSS COMPONENT or C

^

Member

Top Chord

Bottom Chord

Main Web

Compression Web

Vertical End Struts

Long End Diagonal

Short End Diagonal

Mk.No.

.6-8

7

3

H

" 2

5

Grade

of

Steel

a:±4!

A~3<? . A'3h

A-44\

Size

Total

Length

Member

Weight

Member

0.?Z" 0'*:

0.98" DJA.

0.9Zn otfi.

0.9Z\ DtfiO. 92." 01</>
_aclede Steel Company D105- T S -Sheet

WORLD TRADE CENTER

FLOOR GRID TRUSSES

DESIGN DATA

II

TRUSS UNIT MARKED 2CSZT^r Refer to drawings ST ioi, (*, 3 . Clearspan "L" = 54.«S 3 ft. Spacing = ft.

Applicable Total Moment = j, 9ZO, £>oo inch pounds,

v Based on 1<ST4- Ibs./sq. ft.- Total Load " w"

Applicable End Reaction = JB. OOP pounds.

Based on / £T4- lbs./sq. ft. Total Load "w".

Applicable Total Constr. Moment = <S~ Q -S~ oo o inch pounds.

Based on 4-£> lbs./sq. ft. Construction Load.

Applicable Constr. End Reaction = S4- 10 pounds.

Based on 4-L> lbs./sq. ft. Construction Load.

"V M Shear at End Panel = / 4 J qzo pounds. -ED = 3. P ft.

3/ Partial.

WEB MEMBER #1 Distance from End Panel = o. o

Applicable Shear Vx

= / 4, g

z.

o

lbs.

Slope = 2.0>S

JL = in.

ft.

v£~<3, OCO psi

fs = 3<3, & OO psi

sc psi

Reqd. Area = i .3Z sq. in. Use Z-Q.<?Z " o>* Area = 1.33 sq. in.

WEB MEMBER #2 Distance from End Panel

Applicable Shear V

x

= 14. 9 z.o lbs.

Slope = 1 .00

O.O

1- O in. sc

ft.

3L>. OOP psi

psi

//. ZOO psi

Reqd. Area = ). 32 sq. in. Use Z - Q.<?z" o<* Area = 1.33 sq. in.

WEB MEMBER if 3 Distance from End Panel = 4. & 7 ft.

Applicable Shear Vx

= 9. lbs. f

y

= 3^ OOP psi

Slope = L /6Z

Jl = 3Q. O in.

Reqd. Area = 1.3ZL sq . in.

psi

sc

Use Z - <D- 9z" pi* Area =

3. ~7<£~Z> psi

1.33 sq. in
aclede Steel Company D105- T S -Sheet 3

WEB MEMBER #4 Distance from End Panel = 3.Z1 ft. (eo= 2.0a')

Applicable Shear V XY = 12 ' 57/)^ XD5. "lbs fyr =

- c ^ SO, QQQ psi

Slope = UkZ r

= gg: Q in. f

y

s =

_. psi

'sc = Psi

Reqd. Area = I. + 7 sq. in. Use 2-<3.9fi"o„, Area = I.SI sg.ln.

WEB MEMBER ^ Distance from End Panel = O.Q f

. /fo^.^'j

Applicable Shear V = /<• oa<- ik. r _ J_ _ x —1 ^gto-a .ids • r = go, 000 psi

Slope = |. 90 rf S = 3^ (DCDQ PSi

= in.

f sc

= psi

Reqd. Area = j.q, S q. in. Use Z-O.qz"o,« Area = 1,33 sq.in.

CHORD MEMBER #6 Consists of 4 ~ Z"x I */*.- , O. Z<S

" Angles

Construction Load Design Area = 3. 6> O sq . in.

Applicable Moment = gg^, Ocgo in. lbs. f = psi

Jt = 3^76" in. fg . psi

^x " <LM_ in. fsc = /Z, 93Q psi

z = SI in. ( with fillorc in middle 60% of cpan ) r1,

r x 7^6

/? +

b m = ^.^77 less than 1

,r z F

fa

= ^T.aOQ Psi

F a = /Z. 93^ psi

fb = 7d&_ Psi

F

b

= psi

Fe

= z<s 9<S~<D psi

Use t'/z" x0.24"j{ <s Area = 3T.6<? S q. in.

CHORD MEMBER 17 Consists of 4- Z"* , <?. Z.fr" Angles

Total Load Design Area = 3. &

g

sq . ln .
Laclzz - Steel Company D105- t s- -sheet_^__

] CHORD MEMBER #7 ( CONTD . )

" Applicable Moment = ) x 9Z O, OOP in lbs. f

y

= 36, OOP psi

f s = ZZ OOP psi

D+- = 33.00 in.

5eff = &4-.QO in.

t = 4. in.

f sc

= psi

yi = Z. OO in. d 2

= 2. 4-&> \ in.

y 2 = 4.4-4- in. d-3 = ZS. C0> \ in.

y3 = 3 2, &6> in. c x = 1 in.

di = 4. go in. c

2 = Z6>. IP in.

I

s = S'^c + A c d l

2

) + ( J TCA + ATCAd 2

2

) + ^BCA + AbcA^D

_ ^ ^(Ac Yi +'AT CAy 2 + ^BCAy 3

)

y X ( A c + ATCA + aB ca) •

y = L>. ?Q in.

I s = in. ( Z^SZTsT )

T

Resisting Moment = fs x Zl = z 3QO oopln. lbs.

° 2

Use 4. - Z"* I'Al" x O. Z*£' Jj 's Area = 3. 6> O sq. in.

Composite Design Top Chord Check

Total Load Design fc= -3. OOP psi

Applicable Moment = ), qzo. POP in. lbs. f* = / , SS"P psi

fio - 3JZ psi

CHORD MEMBER #8 Consists of 4- Z"x /'/z." x a ZS " Angles

Area = 6> O sq. in.

(SAME AS MEMBER 6)
Appendix H

Unreliable Data

NISTNCSTAR 1-6B, WTC Investigation
Appendix H

This page intentionally left blank.

NISTNCSTAR 1-6B, WTC Investigation
Test 1

Test Time

Location

fmin^ \iiin if Unreliable Data

o U 1 ICAUUocU OUI IdUc TnArmA^Ai ir"\l/"» *1 Q O

1 nermocoupie loo

i

i DUILUIM OIIUIU LJc 1 ICOUUl 1 ueneciion i i

i \A/pct VVCol Inctn 1 M 0 LI UIimontcstinn 1 Icl 1 La LIUI 1 r iaie 1 nermocoupie

Olccl l_-*CUI\ TnArmA^Ai i aIa A OQ 1 nermocoupie izo

1

8

Olccl LJcUr\ TnArmAAAi i aIa "1 OC i nermocoupie izd

?n Olccl LJcUrv 1 nACmAAAl 1 aIa A OO i nermocoupie iz^i ^91i \A/oct VVCol Inctn II imontotiAn loll UI 1 Icl 1 LdllUI 1 Kaaiomexer i nermocoupie

\A/oct VvcoL Inctn 1 Mo imontotiAn U U 1 M CM Ld HUM Kauiomeier

97 Pact Ldol Inctn 1 1 montotinn 1 1 0 LI U M 1 c 1 1 Ld HUM DA/Hl ArAA^Ar 1 \~\ /~\ l"r"y\ /~\ /~s 1 i k-v 1 /^v Kdaiomeier i nermocoupie

79, Olccl L-JcOIS. oeciion QoAtiAn u-uo

0^ Olccl Ucul\ Ocuiion M-M

09 Pact Ldol Inctn imontotinn llloll UI I Icl 1 LdllUI 1 Qni^rr\ ofat Kauiomeier

ou UllcXpUocU OUIIdUc i nermocoupie 140

vvcol lllbll Ul 1 lei HdllUr 1 Aspiraxeu i nermocoupie

DO Mnrth K^'ain Tn ice InUIIII IVIdlfl 1 lUob i nermocoupie 4U

DO Mnrth ^ ^ 0 1 n Tn ice InUIIII Ivldlll 1 lUbb i nermocoupie 10 DO Mnrth ft ^ 0 1 r"^ Tn 1 0

0

IN Of III Ivldlll 1 IUbb Th^rrAaaai i »-\ 1 A Q i nermocoupie iy

KRDO InUIIII Ivldlll 1 lUbb i nermocoupie z

fiR DO Mnrth ft^oin Tn ice InUIIII Ivldlll 1 lUbb ^Th^rmnnni i aIa i ricrinoC/Oupic

RRDO Mnrth ft /1 0 1 n Tn ice InUIIII Ivldlll 1 lUbb l^h^rmnnni i a a Q i iici riiuuuupic o D3RQ Mnrth IV^oin Tn 1 0

0

InUiuI IVIdlfl 1 lUbb T^h^rmnnni i aIa <i neriiioouupic o Mnrth ft^oin Tn ice iNUllll Ivldlll 1 lUbb T^hormnnni i a a ij i iicrinuuuupic /

z

7n/ u Mnrth ft^oin Tn ice InUIIII Ivldlll 1 lUbb OcLllUll Qdrtinn A A r\~r\

1 u UllcXpUbcU OUIIdOc Thdrmnnni i aIa 11 1 ici n luuuupic ioy

79 Mnrth ft /I o i r~i Tn i o

o

InUIIII Ivldlll 1 lUbb l^hormnnni i aIa i rieririuuuupic oo

7R Mnrth ft ^ 0 1 n Tn ice InUIIII Ivldlll 1 lUbb Thormnnni i aIa 'I /

1 llcllIIUC/UUpic 1 1 7R Pact D nHninn Tn ico cidbi Diiuyiriy 1 rubb Thormnnni i aIa i iieiinuuuupic yo

74 Mnrth ft ^ 0 1 n Tn 1 0

0

InUIIII Ivldlll 1 lUbb Thcirmnnni i aIa i iiciniuuuupic OD

7fi / D Mnrth Moin Tnico iNUrill Ivldlll 1 lUbb QortiAn C— OcOUUIl El-lZ 7R/ O Rnttnm /^hnrrt l~^dflcintinn DUUUITl V^llUlU UcllcUUUIl r^£iflc»nt inn A A UcllcUUUIl 1 *+ 7R/ O Olccl UcOK Thormnnni inlo 1 Q "1

1 llcllIlUUUUpic 1 O 1 7Q Qai ith ft /1 0 i m Tn ice OUUlll Ivldlll 1 lUbb OcUUUll D-D

R9 Mnrth ft yl 0 1 n Tn i o

o

InUIIM Ivldlll 1 lUbb Thcirmnnni inl^ i iiciinuuuupic OO

R^OO vvcoi Diiuyiriy 1 rubb Thormnnni i aIa QO i iici iiiuouupic yu

RAOH ^niith r /1 0 1 n Tn 1 c

c

OUUlll ivldlll llUbo ThormnrAi i a|a *1 Q

1 1 Icl 11 lUUUUpic 1 O

Rfi OD ^nitth Mciin Tn 1 c c OUUlll Ivldlll 1 lUbb Thorrnnrni i a|a 1 i

I llcl IIIUUUUpic I I RROD OUUlll Qai ith Mum Tn ice Ivldlll IIUoo Thormnmi 1 A.

I 1 Icl 1 1 lUUUUpic It R7O 1 Qai ith f\/loin Tn ice OUUlll Ivldlll 1 lUbb Thormn^Ai mlo 1 H I Del IIIUUUUpic I O R7O / Qniith ft ^ 0 1 n Tn 1 c- 0 OUUlll Ivldlll 1 lUbb i iicriiiuuuupic i £~ R7O / Cn1 1 1 h ft /I o i r~i T" nice ouuin ividin i rubb Thnrmnnni i aIa *1 K i iicriiiuouupic ID 87 ^nuth JUU Mpin Tn 1*^0 L! 1 IVIdMI 1 IUOO Thprmorni 1 1 IUI 1 1 lUOUUUI^ idIp 101 w 89 Unexposed Surface Deflection Deflection 1 89 Unexposed Surface Deflection Deflection 3

90 South Main Truss Thermocouple 9

90 East Bridging Truss Thermocouple 94

90 Steel Deck Thermocouple 132

93 Bottom Chord Deflection Deflection 15
Test Time

(min)

Location Unreliable Data

94 North Main Truss Thermocouple 22

94 North Main Truss Thermocouple 20

95 North Main Truss Section C-C

96 Unexposed Surface Deflection Deflection 4

96 Unexposed Surface Deflection rTM\ x"i i * /"* Deflection 6

100 Bottom Chord Deflection Deflection 13

102 Steel Deck Thermocouple 121

103 North Main Truss Thermocouple 6

108 Unexposed Surface Deflection Deflection 5

108 Unexposed Surface Deflection Deflection 2

1 1South Main Truss Thermocouple 84

1 1

n XX /"""\ I I I-\ f"l X* Bottom Chord Deflection Deflection 10

1 1Bottom Chord Deflection Deflection 12

1 1Steel Deck Thermocouple 125

1 1

Unexposed Surface Thermocouple 144

1 1

Unexposed Surface Thermocouple 140

1 1Unexposed Surface Thermocouple 141

1 12 Unexposed Surface Thermocouple 138

114 Unexposed Surface Thermocouple 134
Test 2

Test Time

11 1 1 1 1 1

1

Location Unreliable Data

nu oieei uecK

=- —

Thermocouple 129

nu oieei uecK Thermocouple 123

u oieei uecK Thermocouple 124

u oieei uecK Thermocouple 131

A q+^^i r^i^/^b oieei uecK Thermocouple 121

I o oieei uecK Thermocouple 127

Z I oieei uecK Thermocouple 125

OZ South Main Truss Thermocouple 31 4U North Main Truss Thermocouple 17

40 West Bridging Truss Thermocouple 99

40 West Bridging Truss oection u-u

40 West Instrumentation Aspirated Thermocouple

40 South Main Truss Thermocouple 30

40 DOiiom unora ueiiection Deflection 15

A Q 4y oteei uecK Thermocouple 132

bo oteei Deck Thermocouple 122

f 0 oteei uecK Thermocouple 130

7/1

/ 4 Unexposed Surface Deflection Deflection 6

77/ / oteei uecK Thermocouple 128

DOOZ Unexposed Surface Deflection ueiiection i oZ Unexposed Surface Deflection uetiection z OO Bottom Chord Deflection ueiiection i i Q A 04 Unexposed Surface Deflection Deflection 5

07of North Main Truss Thermocouple 18

Q7o/ North Main Truss Thermocouple 23

Q Q OO North Main Truss Thermocouple 20

Q Q OO North Main Truss Thermocouple 24

no East Instrumentation Aspirated Thermocouple

yb West Bridging Truss Thermocouple 92

1 (Jo Bottom Chord Deflection ueiiection 14

1 L) 1 Unexposed Surface Thermocouple 137

1 no i uy South Main Truss i nermocoupie oz

1 1 n 1 1

U

iNonn iviam i russ \ ntJrrTiucuupic z i

1 1 u Unexposed Surface Deflection \\ AT AA+t A

/

uenecuon /

1 1 U Unexposed Surface Deflection ueiieciion o Unexposed Surface Deflection ueiieciion 4

1 1 Z West Bridging Truss i nermocoupie izu East Bridging Truss TnorrYiArrii ir~\lo QP\

\ nt?riTiocuupifc; c?o 110 East Bridging Truss Qnrtinn A A oeciion m-m

114 Bottom Chord Deflection ueTiecuon i o

1 1

R

I I u

P—cdoi act RriHninn di luyniy "Tn ice i i uoo Thprmnrni inlp 1 1 1 1 ICI 1 1 IUUUUUIC 1 1 VJ 119 East Bridging Truss Thermocouple 95

121 Steel Deck Thermocouple 126

122 East Bridging Truss Thermocouple 93

124 East Bridging Truss Thermocouple 103

128 North Main Truss Thermocouple 7

128 North Main Truss Thermocouple 39
Test Time

(min)

Location Unreliable Data

128 North Main Truss Thermocouple 34

128 North Main Truss Thermocouple 38

128 West Bridging Truss Thermocouple 112
Test 3

Test Time

Location

(min)

Unrpliahlp Data

0 East Main Truss Thermocouple 58

1 Steel Deck Thermocouple 126

1 Steel Deck Thermocouple 127

1 North Instrumentation Aspirated Thermocouple

2 Steel Deck Thermocouple 128

2 Steel Deck Thermocouple 125

8 Steel Deck Thermocouple 129

19 Steel Deck Thermocouple 132

71 East Main Truss Thermocouple 37

72 North Instrumentation Calorimeter

83 Unexposed Surface Deflection Deflection 7 83 Bottom Chord Deflection Deflection 14

84 Unexposed Surface Thermocouple 142

85 Steel Deck Thermocouple 121

87 Unexposed Surface Thermocouple 143

90 West Main Truss Thermocouple 13

95 West Main Truss Thermocouple 46

95 West Main Truss Thermocouple 48

96 West Main Truss Thermocouple 44

96 West Main Truss Thermocouple 42

100 West Main Truss Thermocouple45

100 West Main Truss Thermocouple 47

100 East Main Truss Thermocouple 17

101 North Bridging Truss Thermocouple 93

101 North Bridging Truss Section B-B

101 North Bridging Truss Thermocouple 96

101 North Bridging Truss Thermocouple 95

105 Unexposed Surface Thermocouple 134

107 North Bridging Truss Thermocouple 116

111 East Main Truss Thermocouple 33

111 East Main Truss Thermocouple 36

115 West Main Truss Thermocouple 59

115 East Main Truss Thermocouple 76

115 East Main Truss Section E-E

116 Unexposed Surface Thermocouple 140

132 Unexposed Surface Thermocouple 139

140 North Bridging Truss Thermocouple 104

141 North Bridging Truss Thermocouple 103

141 North Bridging Truss Section D-D

165 South Bridging Truss Thermocouple 91

165 South Bridging Truss Section A-A

167 South Bridging Truss Thermocouple 92

171 South Bridging Truss Thermocouple 99

171 South Bridging Truss Section C-C

175 South Bridging Truss Thermocouple 100

175 South Bridging Truss Thermocouple 119

181 South Bridging Truss Thermocouple 120
Test Time

/ min\ Location Unreliable Data

1 RO I OtL Noriri Bnuging i russ i nermocoupie i \ o

i y i iNonn Driaging i russ Thermocouple 94

I 3J oouin Driaging i russ i nermocoupie i

i yo oouin Driaging i russ oecuon r-r

i y4 South Bridging Truss Thermocouple 110

\A/oet ft^oir* ~T~ri ice VVtJbl Ivldlll 1 lUbb 1 1 IcI II lUOUUpic HO

196 West Main Truss Thermocouple 67

202 North Bridging Truss Section E-E

202 North Bridging Truss Thermocouple 108

206 South Bridging Truss Thermocouple 90
Test 4

Test Time

(min)

LULOIIUI 1 U 1 11 fcfl IdUlfc! L/dld

0 East Main Truss TC 58

0 East Main Truss TC 40

0 East Main Truss TC 39

0 East Main Truss TC 38

0 East Main Truss TC 37

1 East Main Truss TC 6

1 Unexposed Surface TC 143

10 South Instrumentation Radiometer

22 East Main Truss TC 51

51 Steel Deck TC 121

51 Steel Deck TC 122

51 Steel Deck TC 123

51 Steel Deck TC 124

51 Steel Deck TC 125

51 Steel Deck TC 126

51 Steel Deck TC 127

51 Steel Deck TC 128

51 Steel Deck TC 129

51 Steel Deck TC 130

51 Steel Deck TC 131

51 Steel Deck TC 132

51 South Instrumentation Aspirated Thermocouple

51 South Instrumentation Piate Thermocouple

52 Bottom Chord Deflection Deflection 12

52 Bottom Chord Deflection Deflection 1

52 Unexposed Surface Deflection Deflection 5

63 Unexposed Surface TC 144

88 East Main Truss TC 70

89 East Main Truss TC 1 97 East Main Truss TC 5
Appendix H

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NIST NCSTAR 1-6B, WTC Investigation
Appendix I Units Conversions

U.S. Customary Units to S. I. units

°F = °C x(9/5)+32

1 in. = 25.4 mm

1 in.

: = 645.2 mm2

1 ft = 0.3048 m

1 ft

2 = 0.0929 m

2

1 lb = 4.448 N

1 kip = 4.448 kN

1 fb/ft = 14.59 kN/m

1 psi = 0.006895 N/mm2 or 0.006895 MPa

1 ksi = 6.895 MPa

1 psf = 0.04788 kN/m2

lpcf - 0.1571 kN/m3

1 BTU/s = 1.055 kW

lBTU/s/ft2 - 1 1.357 kW/m2

NISTNCSTAR 1-6B, WTC Investigation
Appendix I

S. I. Units to U. S. Customary Units

°C = (°F-32) x (5/9)

1 mm = 0.0394 in.

1 m = 3.281 ft

1 MPa = 145.0 psi

1 kN/m2 - 20.88 lb/ft

2 (psf)

1 kW = 0.948 BTU/s

1 kW/m2 = 0.088 BTU/s/ft2

Table 1-1. Temperature convers ions.

°F °c

70 21 100 38

200 93

300 149

400 204

500 260

600 316

700 371

800 427

900 482

1000 538

1100 593

1200 649

1300 704

1400 760

1500 816

1600 871 1700 927

1800 982

1900 1038

2000 1093

NISTNCSTAR 1-6B, WTC Investigation