NIST NCSTAR 1-5D

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Reaction of Ceiling Tile Systems to

Shocks

Richard G. Gann

Michael A. Riley

Joshua M. Repp

Andrew S. Whittaker

Andrei M. Reinhorn

Paul A. Hough

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

NIST NCSTAR 1-5D

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Reaction of Ceiling Tile Systems to

Shocks

Richard G. Gann

Michael A. Riley

Building and Fire Research Laboratory

National Institute of Standards and Technology

Joshua M. Repp

Andrew S. Whittaker

Andrei M. Reinhorn

State University of New York at Buffalo

Paul A. Hough

Armstrong World Industries

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 1-5D

Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-5D, 146 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 degree of damage to the ceihng tile systems of the World Trade Center towers following the aircraft impacts on September 1 1

, 200 1, could have affected the rate at which the ensuing fires heated the steel- trussed concrete slab floor systems above. Accordingly, a series of shaking table tests was conducted to estimate the magnitude of distress to the ceiling tile systems that would result in substantial displacement

of ceiling tiles. Ceiling tile systems indicative of those used in the core and tenant spaces were subjected

to both single and complex impulses of varying magnitude. The systems resisted significant damage up

to about Ig applied to the test platform, corresponding to about 2.5g to 3g at the ceiling frame. The data

suggest that major system failure would occur at impulse values near 4g to 5g at the ceiling frame.

Keywords: Ceiling, ceiling tiles, shake. World Trade Center.

NISTNCSTAR 1-5D, WTC Investigation 111
Abstract

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IV NISTNCSTAR 1-5D, WTC Investigation
Table of Contents

Abstract iii

List of Figures vii

List of Tables xi

List of Acronyms and Abbreviations xiii

Metric Conversion Table xv

Preface xvii

Acknowledgments xxvii

Executive Summary xxix

Chapter 1 Introduction 1

1 . 1 Context of This Report 1

1.2 Reference 2

Chapter 2 Description of Experiments 3

2. 1 General Description 3

2.2 Test Fixture 3

2.2.1 Simulator Table 3

2.2.2 Test Frame 4

2.2.3 Instrumentation 11

2.3 Test Specimens 18

2.3.1 Suspension Systems 18

2.3.2 Tiles 27

2.3.3 Ceiling Systems 27

2.4 System Excitation Patterns 40

2.4.1 General 40

2.4.2 White Noise 40

2.4.3 Single Impulse Excitations 40

2.4.4 Multiple Impulse (Earthquake) Stimulation 49

2.5 Description of Test Series 53

2.5.1 General 53

2.5.2 Performance Criteria 53

NISTNCSTAR 1-5D, WTC Investigation v
Table of Contents

2.6 References 55

Chapters

Test Results 57

3.1 Comparison of Platfonn Simulator and Frame Responses 57

3.2 Single Impulse Tests 57

3.3 Earthquake Tests 73

Chapter 4

Summary 77

4.1 Summary of Test Results 77

4.2 Implications of Test Results 78

Appendix A

Test Histories 79

vi NISTNCSTAR 1-5D, WTC Investigation
List of Figures

Figure P-1. The eight projects in the federal building and fire safety investigation of the WTC disaster.xix

Figure 2-1 . Plan view of the base of the frame 4

Figure 2-2. Plan view of the top of the frame 5

Figure 2-3. Elevation of the east side of the frame 6

Figure 2—4. Detail A-A' frontal view of frame 7

Figure 2-5. Detail B connection of comer of the frame 7

Figure 2-6. Detail C. connection of the roof with main beams 8

Figure 2-7. Detail D, connection of the two parts of the roof along the east-west direction 8

Figure 2-8. Test frame mounted on the shaking table at the University at Buffalo 9

Figure 2-9. Connection of the roof to the main beams on the north side of the frame 10

Figure 2-10. Connection of the roof to the main beams on the west side of the frame 10

Figure 2-1 la. Locations of the accelerometers on the simulator platform 12

Figure 2-1 lb. Locations of the accelerometers on top of the testing frame 12

Figure 2-1 Ic. Locations of the accelerometers on the ceiling support grid 13

Figure 2-1 2a. Accelerometers monitoring the response of the test assembly in the center at the

top of the test frame 14

Figure 2- 12b. Accelerometers monitoring the response of the test assembly on the ceiling

support grid 14

Figure 2-1 3a. Location of displacement transducers at the base of the testing frame 16

Figure 2-1 3b. Location of displacement transducers at the top of the testing frame 16

Figure 2-14a. Displacement transducers mounted on the base of the testing frame 17

Figure 2-14b. Displacement transducers mounted on the top of the testing frame 17

Figure 2-15. Top (left) and bottom (right) CADDY fasteners in suspension system 1 19

Figure 2-16. C-clamp and top CADDY fastener in suspension system 1 20

Figure 2-17. Bottom CADDY fastener in suspension system 1 20

Figure 2-1 8. Z-bar section (left) and C- 1 5 wire clip (right) in suspension system 1 21

Figure 2-19. Channel section runner connection to Z-bar in suspension system 1 21

Figure 2-20. Channel section runner connection to edge of test frame in suspension system 1 22

Figure 2-21. Two ft (0.61 m) cross tee used in suspension system 1 22

Figure 2-22. Breather spline used in suspension system 1 23

NISTNCSTAR 1-5D, WTC Investigation vii
List of Figures

Figure 2-23. C-clamps and top CADDY clip in suspension system 2 25

Figure 2-24. CBS clip connecting channel to main runner in suspension system 2 25

Figure 2-25 . Bottom view of ceiling system CSl 29

Figure 2-26. Close-up of top view of ceiling system CSl 29

Figure 2-27. Top view of ceiling system CSl 29

Figure 2-28. 12 in. by 48 in. (0.30 m by 1.22 m) fixture with safety clip and wires in ceiling

system CSl 30

Figure 2-29. Panel perimeter spring clips in ceiling system CSl 30

Figure 2-30. Layout of main supporting members in ceiling system CSl 31

Figure 2-3 1 . Layout of splines and cross tees in ceiling system CSl 32

Figure 2-32. Top view of ceiling system CS2 33

Figure 2-33. Top view of ceiling system CS2 33

Figure 2-34. Bottom view of ceiling system CS2 34

Figure 2-35. Layout for ceiling system CS2 34

Figure 2-36. Top view of ceiling system CS3 35

Figure 2-37. Top view of ceiling system CS3 35

Figure 2-38. Layout of main supporting members in ceiling system CS3 36

Figure 2-39. Layout of splines and cross tees in ceiling system CS3 37

Figure 2-40. Bottom view of ceiling system CS4 38

Figure 2-41 . Layout for ceiling system CS4 39

Figure 2-42. White noise histories; top: horizontal direction, bottom: vertical direction 41

Figure 2-43. Fourier amplitude spectrum of horizontal and vertical white noise 41

Figure 2-44. Generic acceleration waveform 42

Figure 2-45. Estimated acceleration of airplane during impact 45

Figure 2-46. Estimated force on tower during impact 46

Figure 2-47. Estimated acceleration of tower during impact 46

Figure 2-48. Theoretical peak response of the UB seismic simulator 47

Figure 2^9. Displacement history inputs for tests 4 and 5 48

Figure 2-50. Horizontal and vertical acceleration history inputs into simulator for tests 6 through 23. ..49

Figure 2-5 1 . Required response spectra for horizontal and vertical shaking 49

Figure 2-52. RRS for horizontal and vertical shaking for Ss=1.0 51

Figure 2-53. Relationship between MCE NEHRP spectra and target qualification spectrum

{S^l.Og. Sj^OAg) 52

Figure 2-54. Relationship between NEHRP MCE and DBE spectra and target spectrum

(5^1.Og, 5/=0.4g) 52

vin NISTNCSTAR 1-5D, WTC Investigation
List of Figures

Figure 3-1. Displacement of perimeter tiles over perimeter spring clips following Test 20

for ceiling system CSl 67

Figure 3-2. Bottom view of damage to ceiling system CSl following Test 20 67

Figure 3-3. Bottom view of damage to ceiling system CSl following Test 20 68

Figure 3-4. Pemianent vertical displacements of Z-bars in the east-west direction following

Test 20 for ceiling system CS 1 68

Figure 3-5. Light fixmre swing arm support dislodged following Test 21 for ceiling system CSl 68

Figure 3-6. Dislodged Z-bar clip in ceiling system CSl following Test 21 69

Figure 3-7. Dislodged southern light fixture comer in ceiling system CS2 following Test 14 69

Figure 3-8. Stretching of Z-bar clips located at northern light fixture comer in ceiling system

CS3 following Test 20 70

Figure 3-9. Damage to the center of ceiling system CS3 following Test 20 70

Figure 3-10. Damage to the center of ceiling system CS3 following Test 23 71

Figure 3-11. Damage to the northern perimeter of ceiling system CS4 following Test 23 71

Figure 3-12. Damage to the northem perimeter of ceiling system CS4 following Test 23 72

Figure 3-13. Collapse of ceiling system CS3 after 2.5g earthquake excitation 74

Figure 3-14. Damage to north perimeter of ceiling system CS4 after 1.75g earthquake excitation 74

Figure 3-15. Damage to south perimeter of ceihng system CS4 after 1.75g earthquake excitation 75

NISTNCSTAR 1-5D, WTC Investigation ix
List of Figures

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X NISTNCSTAR 1-5D, WTC Investigation
List of Tables

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

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

Table 2-1. Dynamic properties of the frame alone 1

1

Table 2-2. Transducers used for the testing program 15

Table 2-3. Summary information on components of suspension systems 1 and 3 19

Table 2-A. Summary information on components of suspension systems 2 and 4 24

Table 2-5. Tile specifications 27

Table 2-6. Configuration of ceiling systems 27

Table 2-7. Parameters to calculate the horizontal RRS (2/77=1 .0) 50

Table 2-8. Test sequence for a set of impact experiments for a single ceiling system.'^ 54

Table 3-1 . Results from resonance search tests 58

Table 3-2. Measured acceleration values 59

Table 3-3. Observed ceiling system damage from single impulse tests 63

Table 3-4. Observed ceiling system damage from earthquake tests 73

Table 4-1 . Performance of ceiling systems 77

NIST NCSTAR 1-5D, WTC Investigation xi
List of Tables

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xu NISTNCSTAR 1-5D, WTC Investigation
List of Acronyms and Abbreviations

Acronyms

AWI Armstrong World Industries

DBE design basis earthquake

DTAP dissemination and technical assistance program

FEMA Federal Emergency Management Agency

LVDT linear variable displacement transducer

MCE maximum considered earthquake

NEHRP National Earthquake Hazards Reduction Program

NIST National Institute of Standards and Technology

R&D research and development

RRS required response spectrum

C TT" C T ShhSL Structural Engineering Earthquake Simulation Laboratory

UB University at Buffalo of the State University of New York

WTC World Trade Center

WTC 1 World Trade Center 1 (North Tower)

WTC 2 World Trade Center 2 (South Tower)

WTC 7 World Trade Center 7

Abbreviations

micrometer

°C degrees Celsius

ft foot

square foot

g acceleration (gravity) (9.81 mis', 32.2 ft/s") Hz Hertz

kg kilogram

kip a force equal to 1 ,000 pounds

kN kiloNewton

in. inch

lb pound

NISTNCSTAR 1-5D, WTC Investigation xiii
List of Acronyms and Abbreviations

m meter

min minute

mm millimeter

mph miles per hour

s second

xiv NIST NCSTAR 1-5D,WTC Investigation
Metric Conversion Table

To convert from to Multiply by

AREA AND SECOND MOMENT OF AREA

square foot (ft') square meter (m") 9.290 304 E-02

square inch (in.") square meter (m") 6.4516 E-04

square inch (in.') square centimeter (cm') 6.4516 E+00

square yard (yd") square meter (m") 8.361 274 E-01

FORCE

kilogram-force (kgf) newton (N) 9.806 65 E+00

kilopond (kilogram-force) (kp) newton (N) 9.806 65 E+00

kip (1 kip= 1,000 Ibfl newton (N) 4.448 222 E+03

kip (1 kip= 1.000 Ibf) kilonewton (kN) 4.448 222 E+00

pound-force (Ibf) newton (N) 4.448 222 E+00

FORCE Dl\ IDED BY LENGTH

pound-force per foot (Ibf'ft) newton per meter (N/m) 1 .459 390 E+01

pound-force per inch ( ibf'in.) newton per meter (N/m) 1.751 268 E+02

LENGTH

foot (ft)

inch (in)

inch (in.)

micron (m)

yard (yd)

meter (m)

meter (m)

centimeter (cm)

meter (m)

meter (m)

3.048 E-01

2.54 E-02

2.54 E+00

1 .0 E-06

9.144 E-01

MASS and MOMENT OF INERTL\

kilogram-force second squared

per meter (kgf • s"/m)

pound foot squared (lb • ft")

pound inch squared (lb in ")

ton, metric (t)

ton, short (2,000 lb)

kilogram (kg)

kilogram meter squared (kg m")

kilogram meter squared (kg m")

kilogram (kg)

kilogram (kg)

9.806 65 E+00

4.214 011 E-02

2.926 397 E-04

1.0 E+03

9.071 847 E+02

NISTNCSTAR 1-5D. WTC Investigation XV
Metric Conversion Table

10 converi iroiu lO iviuiupiy Dy

MASS UIVIULU BY AKLA

pound per square foot (Ib/fr) kilogram per square meter (kg/m") 4.882 428 E+00

pound per square inch

(no! pound force) (lb/in.') kilogram per square meter (kg/m") 7.030 696 E+02

MASS DIVIDED BY LENGTH

pound per foot (lb/ft) kilogram per meter (kg/m) 1.488 164 E+00

pound per inch (lb/in.) kilogram per meter (kg/m) 1.785 797 E+01

pound per yard (lb/yd) kilogram per meter (kg/m) 4.960 546 E-01

PRESSURE or STRESS (FORCE DIVIDED BY AREA)

kilogram-force per square centimeter (i<gf/cm") pascal (Pa) 9.806 65 E+04

kilogram-force per square meter (kgf/m") pascal (Pa) 9.806 65 E+00

kilogram-force per square millimeter (kgf/mm") pascal (Pa) 9.806 65 E+06

kip per square inch (ksi) (kip/in.') pascal (Pa) 6.894 757 E+06

kip per square inch (ksi) (kip/in.") kilopascal (kPa) 6.894 757 E+03

pound-force per square foot (Ibf/ft") pascal (Pa) 4.788 026 E+01

pound-force per square inch (psi) (Ibf/in.") pascal (Pa) 6.894 757 E+03

pound-force per square inch (psi) (Ibf/in.') kilopascal (kPa) 6.894 757 E+00

psi (pound-force per square inch) (Ibf/in.') pascal (Pa) 6.894 757 E+03

psi (pound-force per square inch) (Ibf/in.") kilopascal (kPa) 6.894 757 E+00

XVI NISTNCSTAR 1-5D, WTC Investigation
Preface

Genesis of This Investigation

Immediately following the terrorist attack on the World Trade Center (WTC) on September 1 1 , 2001, the

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

planning a building perfonnance 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 histitute 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 ser\'e 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 1-5D, 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 resuhed 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-1.

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. Biikowski

Document and analyze the code provisions, procedures, and

practices used in the design, construction, operation, and

maintenance of the stmctural, passive fire protection, and

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

Aircraft hnpact 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 detennine the most

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

Communications; Project Leader: Mr. Jason

D. Averill

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 1-5D, 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.

NISTNCSTAR 1-5D, WTC Investigation XIX
Preface

• Robert Hanson, Professor Emeritus, University of Michigan

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

Inc.

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

University of Colorado at Boulder

• Fonnan 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 cominentary on drafts of the Investigation reports prior to their public release. NIST

has benefited from the v^^ork 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 cominents on the direction and

progress of the Investigation from the public and the Advisoiy 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 reexaminafion 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 1-5D, 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 coinments on the Draft Plan for the pending WTC Investigation.

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

December 9, 2002 Washinston. 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 Pi'ogress Report.

August ''6-'^ 7 ''003 Gaithersburs. MD NCST Advisorv Committee meetmp 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

pollprtinn ^k./ll^^.llv'll nroiprt^^ Wlv.'lwx.lO- December ''-3 ""003 Gaithersburc'. MD NICST 1 T V_ O 1. iAHvi^orv a.u > 1 13 V^l Committpp mpptinp^ on statii's and inifi?il rpsults J

\ V.'llllllll.l^V' lllVvV 1111 \./ll OlCtlL^O UllVI IxxlK ICil 1 Wi3 1 Li3 and release of the Public Update with a public comment session. February 12, 2004 New York City. NY Public meeting on progress and prelimmary findings with public

rommpnt^; C\^lllIil^lllO onV^il Ts's1ip<\ lOOLlvO to\.\J HpC'Vr pnn<;irlprpH V.V.^lloidVlVB'U 111 in formiilfitintT Iv^llilUlclllllLl final lllldl recommendations.

June 1 8 ""004 New York Citv NY Media nublic briefini? on release of June ^004 Proorp^'i Rpnort June 22-23. 2004 Gaithersburg, MD NCST Advisory Committee meeting on the status of and

nrpliminarv L/l^llllllllCliy findinf^Q llllUlll^O from Ll KJlll thp UllV \VTC TV X \_- ±±l Tnvp<stiP"?itinn V ll^Cl LlWll with VV 1111 aCI niiblir LJ\AKJ11K' comment session. August 24. 2004 Northbrook, IL Public viewing of standard fire resistance test of WTC floor

sv^sfPtTi 0\>M^lli atCll 1 InHprwntpr<\ 1 1 Uv. 1 W 1 i LWl ^ T1 . ahnratnrip<s cJ. L/ V/ 1 CtLv/ll^O^ X11V>> Inr October 19-20. 2004 Gaithersburg, MD NCST Advisory Committee meeting on status and near complete

set of preliminary findings with a public comment session. iNOvember J.J., ZUU4 Gaithersburg, MD NCST Advisory Committee discussion on draft annual report to Congress, a public comment session, and a closed session to

di*;rii*;s nrp-draft rprnmmpnH?itinn«i for WTC Investigation

Apnl 5, 2005 New York City, NY Media and public briefing on release of the probable collapse

o^VJUWliL-^ (;pnnpnrp fnr l\Jl tVip W/Xf"^ VV 1 \_ tnwpr*; \.\J Wtlo dllU anH Hraft LllClll i^lJ^Jllo rpnort*; for x\Jl thp 111^ nrniprt<s Lfl \JJ^\^ Ij on\JH 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 resuhing from the WTC Investigation

and the R&D program, and (b) provide practical guidance and tools to better prepare facihty 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 fiiture disaster events.

NISTNCSTAR 1-5D, 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 I A. The present report is one of a set that provides more detailed documentation of the hivestigation 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 ofthe World Trade Center Disaster: Final Report on the Collapse of World Trade Center 7. NISTNCSTAR 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 ofthe 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-lB. 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-lC. 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 I, 2, and 7 and Post-Construction Provisions Applied after Occupancy. NIST NCSTAR 1-lD. 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 of Codes, Standards, and Practices in Use at the Time ofthe

Design and Construction of World Trade Center 1, 2, and 7. NIST NCSTAR 1-lE. 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 of the 1968 and Current (2003) New

xxn NISTNCSTAR 1-5D, WTC Investigation
Preface

York City Building Code Provisions. NIST NCSTAR 1-lF. 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 7. 2, and 7 Were in Use. NIST NCSTAR 1-lG. 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-Constniction Modifications to Fire Protection and Life Safety Systems

of World Trade Center I and 2. NIST NCSTAR 1-1 H. 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 l-ll. 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 ofthe 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 1-2 A. National Instiaite 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 1-3 A. National Instimte of Standards and Technology.

Gaithersburg, MD, September.

NIST NCSTAR 1-5D. WTC Investigation XXlll
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 ofthe 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 Instimte 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 NCSTAP. 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 1-5 A. National Institute of Standards and Technology. Gaithersburg, MD,

September.

XXIV NIST NCSTAR 1-5D, 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. Reinhom, 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 of the World Trade Center Disaster: Computer Simulation ofthe 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

Tow ers. 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: Structural 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. Stames, 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 1-5D, WTC Investigation XXV
Preface

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

Disaster: Component, Connection, and Subsystem Structural Analysis. NISTNCSTAR 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 of the 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?. (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 11, 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). NISTNCSTAR 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 Safety Investigation of the 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 Swx'ey Administration. NISTNCSTAR 1-7B. National

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

Lawson, J. R., and R. L. Vettori. 2005. Federal Building and Fire Safet\> Investigation ofthe World

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

Standards and Technology. Gaithersburg, MD, September.

XXVI NISTNCSTAR 1-5D, WTC Investigation
Acknowledgments

The Structural Engineering and Earthquake Simulation Laboratory (SEESL) staff of the State University

of New York at Buffalo performed the ceiling tile system tests. Mark Pitman, Technical Services

Manager, and Scot Weinreber, Laboratory Assistant, played pivotal roles in the development and

execution of these tests, and their support is gratefully acknou'ledged.

Armstrong World Industries (AWI) supplied the ceiling tile systems to SEESL. Thomas Fritz of AWI

provided significant contributions to the project, including information on the ceiling tile systems

installed in the World Trade Center buildings. Steven Newcomer and Barry Buhay of the Annstrong

Building Products Installation School did the lion's share of the work in installing and repairing the systems during the tests.

NIST NCSTAR 1-5D, WTC Investigation XXVll
Acknowledgments

\

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xxvni NISTNCSTAR 1-5D, WTC Investigation
Executive Summary

E.1 CONTEXT OF THIS REPORT

The collapses of the World Trade Center (WTC) towers in New York City on September 11, 2001, were a

result of damage inflicted by the aircraft and the ensuing fires within the two buildings. As seen through

the windows of the towers, the fires appeared and disappeared in various segments of the affected floors. At some point in each building, the fires burned hot enough and long enough to weaken the already

damaged structure to the point where it no longer could support itself.

The floor systems, each consisting of a concrete slab supported by a network of open web steel trusses,

would have been exposed to the flames from combustibles burning on the floor below but for the

presence of the drop ceiling system. While this ceiling system was not fire-rated, estimates indicated that they might have stayed in place for approximately 10 min to 15 min in the standard ASTM E 1 19 furnace

environment, perhaps somewhat less in the presence of a rapidly growing fire. Observations of the fires on September 11, 2001 . and computer simulations of those fires indicate that the fires did not bum more

than approximately 20 min in any location. Thus, an intact ceiling tile system could have provided an

important delay to the heating of the floor trusses.

Occupants of the towers reported that the impact of the airplanes resulted in some dislodging of ceiling

tiles and damage to the suspension system, but descriptions of the magnitude and spatial extent of the

damage were neither quantitative nor comprehensive. Thus, additional infomiation was needed in order

to estimate where the ceiling system was intact and where the heat from the fires might have impinged

unabated on the floor joist assemblies.

Accordingly, a series of tests was conducted to estimate the magnitude of distress to the ceiling tile systems that would result in substantial displacement of ceiling tiles. In addition, this study was less concerned with the accelerations on the impact floors, since flying debris would likely have damaged or destroyed most of the ceiling tiles there. Instead, the concern was for the floors just above or below the

impact zone, which were not directly damaged by the airplane, but had significant fires after the impact.

Under a contract from National Institute of Standards and Technology (NIST), these tests were performed

using the earthquake simulator ("shaking table") at the University at Buffalo of the State University of

New York (UB) from August 27 through 29, 2003. NIST and University staff provided multiple

paradigms to bracket the impulses from the airplane impacts. University staff conducted the tests. Armstrong World Industries, the supplier of the original ceiling tile systems for the WTC towers, supplied

the ceiling systems and assisted with the test program. The suspension system and tiles were close

replicates of those originally in the towers and expected to still have been in most locations on September 11, 2001.

The UB shaking table is 12 ft (3.66 m) square and has five controlled degrees of freedom (excluding the transverse translational movement). A 20 ft (6.1 m) square testing platform was located on top of the

E.2 DESCRIPTION OF EXPERIMENTS

NISTNCSTAR 1-5D, WTC Investigation XXIX
Executive Summary

simulator. The maximum payload was 85 kip (378 kN), the working frequency range was 0 to 50 Hz, and

the maximum displacement was ± 6 in. (0.15 m). The ceiling tile systems were mounted on a steel frame

fixed to the shaking table. Accelerometers and displacement transducers monitored the response of the

simulator platform, the test frame, and the ceiling support grid for each ceiling system.

Two types of ceiling tile systems were tested:

• A near replicate of that in the core areas of the towers used 12 in. (0.30 m) square tiles on a concealed suspension system.

• The original systems for the tenant spaces used 20 in. (0.51 m) square lay-in tiles on an exposed tee bar grid system. These were manufactured only for the WTC towers and were no

longer available. These tests were of a nearly identical system using 24 in. (0.61 m) tiles that might have been present in many tenant spaces on September 1 1 , 2001

.

The tile suspension systems have some directionality, i.e., they are not the same along the two orthogonal

horizontal directions; and the shaking table translates in only one horizontal direction. Thus, two

suspension systems of each type were tested, aligned parallel and perpendicular, respectively, to the

shaking table motion. Each ceiling system included two hght fixtures.

Estimation of the forces and accelerations that occurred in the WTC towers was difficult due to the large

number of unknown or poorly known parameters affecting the response, and because at the time there was little information available on the forces generated during such an impact. The project team thus

conducted tests under a variety of excitations, hypothesizing that from the test results a pattern would

emerge that would enable reasonable extrapolation to the behavior of the actual ceiling tile systems on September 11, 2001.

Each of the four ceiling tile systems was subjected to a series of single impulses that represented the

simplest formulation of the aircraft impact. These ranged from 0.1 5g to the intensity limit of the shaking

table, 1.25g. Each shake intensity was performed for a single horizontal impulse, an equal vertical

impulse, and then the biaxial combination of the two. The acceleration signals for tests with small peak

target accelerations were ramped displacement histories; the signals for tests exceeding a peak target

acceleration of 0.085g were sinusoidal-type acceleration histories, with the frequency determined from

the results of a test with white noise applied to the test fixture and ceiling tile system. The ceiling tile systems were also subjected to a standard earthquake simulation that is a sequence of complex impulses.

This was deemed germane since some tower occupants reported experiencing multiple shocks. The

earthquake tests began with a white noise excitation and continued with intensities of 0.25g, 0.50g^ 0.75g,

l.OOg, 1.25g, 1.50g, 1.75g, and 2.50g. If any distortion or damage to the system was experienced during

a given test, the system was repaired before proceeding to the next test.

The outcome of each test was verbally characterized by the extent of displacement of ceiling tiles and the

degree of damage to the suspension system. For summary purposes, the outcome was also described in terms of two limit states:

1. Loss of one or more tiles from the ceiling system.

XXX NISTNCSTAR 1-5D, WTC Investigation
Executive Summary

2. Sufficient damage to one or more components of the suspension system such that repair or replacement of part or all of the suspension system would be required.

E.3 TEST RESULTS

The performance of the different types of ceiling systems is summarized in Table E-1, where the

performance for the two limit states is given in terms of target peak acceleration of the simulator.

All four combinations of impulse and ceiling system resisted significant damage up to about Ig applied to the test platform. Since the motion of the test frame and suspension systems was considerably larger than

the motion at the base of the test frame, this corresponded to about 2.5g to 3g at the ceiling frame. Tile

motion intensified with increasing impulse strength, and significant damage occurred (or began to occur)

for relatively modest further increments in impulse strength. Analysis of this ascending effect for all systems under all the impulses suggested that gross distortion of the framing and near-complete dropping

of tiles would occur at values near 4g to 5g at the ceiling frame.

Comparison of this magnitude with the results of the impact calculations must take into account that these

tests are not exact replications of the initiating events on September 11, 2001, that the installed ceiling tile systems had been in service for up to 30 years, that the tower frames were different from the test frame,

and that the dimensions of the ceiling systems in the towers were the same size or smaller.

Table E-1. Performance of ceiling systems.

System Description Impulse

Qualification Level (g)

Limit State T Limit State 2^

East-west direction; 12 in. (305 mm) square

tiles

H >1.25 >1.25

V >1.25 >1.25

H&V >1.00 > 1.00 EO

East-west direction; 24 in. (610 mm) square

tiles

H >1.25 >1.00

V >1.25 >1.25

H&V >1.25 1.00 EO 1.75 1.75

North-south direction; 12 in. (305 mm) square

tiles

H >1.25 >1.00

V >1.25 1.00 H&V >1.25 0.75 EO 1.75 1.50

North-south direction; 24 in. (610 mm) square

tiles

H >1.25 >1.25

V >1.25 >1.25

H&V 1.25 1.25 EO 1.25 12.0

a. Limit state 1 is the loss of one or more tiles. b. Limit state 2 is sufficient damage to one or more components of the suspension system such that repair or replacement of

part or all of the suspension system would be required.

Key: EQ. earthquake; H, horizontal; V, vertical.

NISTNCSTAR 1-5D, WTC Investigation XXXI
Executive Summary

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xxxn NISTNCSTAR 1-5D, WTC Investigation
Chapter 1 Introduction

1 .1 CONTEXT OF THIS REPORT

The collapses of the World Trade Center (WTC) towers 1 and 2 in New York City on September 11, 2001. were a result of damage inflicted by the aircraft and the ensuing fires within the two

buildings. Fires in both buildings were observ ed from the times of impact of the aircraft until the

collapses occurred. These fires were not stationary. As seen through the windows of the towers, they

appeared and disappeared in \'arious segments of the affected floors. At some point in each building, the

fires burned hot enough and long enough to weaken the already damaged structure to the point where it no longer could support itself

The floors in and near the aircraft impact zones in the WTC towers were large, open spaces, affording

unobstructed views of much of New York City from nearly all locations. There were relatively few fire

barriers. Between each tenant space and the building core there were demising walls that ran from the top

of the floor slab to the bottom of the ceiling slab. A few of the floors in and near the aircraft impact zones had two tenants, and these spaces were also separated by demising walls. There were a small number of

walls interior to some of the tenant spaces, generally limited to a few perimeter offices or conference rooms. These walls ran from the top of the floor slab to just above the suspension system of the drop

ceiling. The ceiling tile suspension system was hung from the bottom of the floor joists, resulting in an

apparent room height of 8.6 ft (2.6 m) and an above-ceiling height of approximately 3.4 ft (1.0 m).

(There were two systems in the original construction, differing mainly in the size of the tiles.) In

principle, then, each tenant space appeared to a fire as two wide and long "boxes." The lower box

contained the combustibles; the upper box contained the floor joists that provided support for the concrete

floor slab above.

An intact ceiling tile system could then have played a significant role in the event of a fire. The hot gases

from a fire would have risen and formed a hot layer across the top of a room. The temperatures in this layer would have exceeded 1.000 °C, well above the threshold temperatures at which the strength of

unprotected structural steels diminishes. However, as long as the ceiling tile system remained intact, this layer would have formed below the floor joists, and the temperature in the upper "box" would have

remained relatively cool for some time interval. This delay time is most often characterized by a fire resistance rating, obtained from a standard frimace test such as ASTM E 1 19 (ASTM 2000).

The two particular ceiling tile systems originally installed in the WTC towers were not required to be fire

rated, although the tiles themselves were rated for flame spread. Nonetheless, two independent

estimates' " indicated that they might have stayed in place for approximately 10 min to 15 min in the

standard ASTM E 1 19 furnace enviromnent, perhaps somewhat less in the presence of a rapidly growing

' Fritz, T.A.. and P. A. Hough. 2002. Armstrong World Industries, Lancaster. PA, personal communication to R.G. Gann,

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

- Shipp. P. 2002. U.S. Gypsum. Northbrooi<. IL, personal communication to R.G. Gann, National Institute of Standards and

Technology, Gaithersburg, MD. December.

NISTNCSTAR 1-5D, WTC Investigation 1
Chapter 1

fire. Obsei'vations of the fires on September 1 1 and computer simulations of those fires indicated that the

fires did not bum more than approximately 20 min in any location. The comparability of these times

suggested that information regarding the integrity of the ceiling tile systems would be pivotal in assessing

the role of the floor truss assemblies in the eventual collapse of the towers.

It is clear from the accounts of building occupants that the impact of the airplanes resulted in some

dislodging of ceiling tiles and damage to the suspension system (NIST NCSTAR 1-7'^). Descriptions of

the magnitude of the damage at the observers' locations and the spatial extent of the damage were neither

quantitative nor comprehensive. Thus, additional information was needed in order to estimate where the

ceiling system was intact and where the heat from the fires might have impinged unabated on the floor

joist assemblies.

Accordingly, a series of tests was conducted to estimate the magnitude of distress to the ceiling tile systems that would result in substantial displacement of ceiling tiles. These tests were performed using

the earthquake simulator ("shaking table") at the University at Buffalo of the State University of New

York. NIST and University staff provided multiple paradigms to bracket the impulses from the airplane

impacts. University staff conducted the tests. Amistrong World Industries, the supplier of the original

ceiling tile systems for the twin towers, provided information regarding the system materials and

construction and assisted with the test program. The suspension system and tiles were close rephcates of

those originally in the towers and expected to still have been in most locations on September 11.

The NIST Investigation also included dynamic modeling of the impact of the aircraft with the tu'o WTC

towers (NIST NCSTAR 1-2). The output of the simulations included the magnitudes and time histories

of the impulses from these impacts, as felt at various locations in the buildings. The combination of those

findings with these from the present report enabled estimation of the extent of displacement of the ceiling

tiles throughout the zones where the fires were most intense. Conversely, the degree of agreement of this estimation of the locations where occupants observed extensive ceiling damage provided a further check on the accuracy of the impact modeling. This analysis is included in the report on the reconstruction of

the fires in the WTC towers (NIST NCSTAR 1 -5 ).

1.2 REFERENCE

ASTM International. 2000. Standard Test Methods for Fire Tests of Building Construction and

Materials, vol. 4.07. ASTM E 1 19-OOa, Annual Book of ASTM Standards, West Conshohocken, PA.

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

to this report.

2 NIST NCSTAR 1-5D, WTC Investigation
Chapter 2

Description of Experiments

2.1 GENERAL DESCRIPTION

The test series was conducted at the Structural Engineering Earthquake Simulation Laboratory (SEESL)

of the Unixersity at Buffalo of the State University of New York (UB), August 27 through 29, 2003.

Numerous studies related to suspended ceiling systems have been completed in recent years by the SEESL team and .Axmstrong World Industries, Inc. (Repp et al. 2003; Badillo 2003; Badillo et al. 2002,

2003a, 2003b; Kusumastuti et al. 2002). All of these studies and research programs have addressed the beha\'ior of ceiling systems under earthquake excitation. This test series is related to the previous studies,

but focuses on impact-t\'pe excitation on the response of selected ceiling systems.

The ceiling tile systems were mounted on a frame fixed to the shaking table. There were two ceiling tile systems—one indicative of the core space in the towers, the other indicative of the tenant spaces. (Both

are described in detail in Section 2.3.) The suspension systems have some directionality, i.e., they are not

the same along the two orthogonal horizontal directions; and the shaking table translates in only one

horizontal direction. Thus, two suspension systems of each system type were tested, aligned parallel and

perpendicular, respectively, to the shaking table motion. The table was shaken at an increasing range of

intensities. Each shake intensity was performed for a single horizontal impulse, an equal vertical impulse,

and then the sum of the two. The impulse shapes were based on best estimates of the airplane strikes. A

few tests were conducted using a more complex impulse sequence, indicative of an earthquake. This was deemed germane since some tower occupants reported experiencing multiple shocks. If any distortion or damage to the system was experienced during a given test, the system was repaired before proceeding to the next test.

The 12 ft (3.66 m) square simulator, or shaking table, had five controlled degrees of freedom (excluding

the transverse translational movement), a maximum payload of 1 10 kip (489 kN), and a working

frequency range of 0 Hz to 50 Hz. A composite reinforced concrete testing platform of plan dimensions

20 ft (6.1 m) by 10 ft (3.05 m) extended the useful testing area of the simulator, but limited the payload to 85 kip (378 kN). The testing platform included holes on a 1 ft square grid for attaching test specimens.

The table was capable of testing a variety of specimens up to a height of 22 ft (6.7 m). The longitudinal

(horizontal), vertical, and roll degrees of freedom were programmable with feedback control to control

displacement, velocity, and acceleration simultaneously. The performance envelope of the table was ± 6 in. (0.15 m) displacement, ± 30 in./s (0.76 m/s) velocity, and 1.1 5g acceleration at a payload of 44 kip

(197 kN) in the horizontal direction, and ± 3 in. (76 mm) displacement, ± 20 in./s (0.51 m/s) velocity, and

2.30g acceleration in the vertical direction. For a payload of 1 10 kip (489 kN), the maximum platform

accelerations were 0.55g in the horizontal direction and l.lg in the vertical direction.

2.2 TEST FIXTURE

2.2.1 Simulator Table

NISTNCSTAR 1-5D. WTC Investigation 3
Chapter 2

The frequency limit of the simulator system was determined by the natural frequency of the table and the

supporting actuator oil columns, both of which had a natural frequency of approximately 60 Hz. This

facilitated operation of the simulator over a wide band of frequencies with small error. Input or command

signals to the table could be of the following types: hannonic motions (sinusoidal, square, triangular),

random motions, earthquake histories, and blast histories. Additional software was available for the

collection and processing of data. Frequency and time-domain analysis of data were routinely perfonned.

Data could also be rapidly transferred via the Internet to other computers within the University computing

systems or to outside systems.

2.2.2 Test Frame

A 16 ft (4.88 m) by 16 ft (4.88 m) square frame of ASTM Grade 50 steel was constructed to test all four

ceiling systems. Figures 2-1 through 2-10 present detailed infonnation about the frame. Figure 2-1 is a plan view of the base of the frame. The frame was attached to the simulator platform using 1 in. (25 mm)

diameter bolts in the beams that were oriented in the east-west direction. The frame was designed and

detailed so that it could be disassembled easily.

-20'-

1 4'.2" —

.

'ng2.4

-5'-6" 5' 5'-6"-

Figure 2-1 . Plan view of the base of the frame.

4 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Figure 2-2 shows the details of the top of the frame. To facilitate rapid disassembling of the test frame,

the top of the frame was connected to the perimeter beams with 3/8 in. (10 mm) diameter bolts; the top of

the frame was divided into two equal parts along the east-west axis. Both halves of the roof were

connected with 3/8 in. (10 mm) diameter bolts as shown in the following figures.

4"X4"XT4" TS 6"X4"X1'4"TS 2" X2" X3/-B" TS

Figure 2-2. Plan view of the top of the frame.

NISTNCSTAR 1-5D, WTC Investigation
Chapter 2
Description of Experiments

Figure 2-4. Detail A-A' frontal view of frame.

U—6"—

Figure 2-5. Detail B connection of corner of the frame.

NISTNCSTAR 1-5D, WTC Investigation 7
Chapter 2

3/8" (|) bolts to

at t ach roof t o

Figure 2-6. Detail C, connection of the roof with main beams.

a (left): connection in the east-west direction, b (right): connection in the north-south

direction.

3/8" (j) bolts to

at t ach bot h part s

Figure 2-7. Detail D, connection of the two parts of the roof along the east-west

direction.

8 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Source: NIST. Figure 2-8. Test frame mounted on the shaking table at the University at Buffalo.

NISTNCSTAR 1-5D. WTC Investigation 9
Chapter 2

Source: NIST. Figure 2-10. Connection of the roof to the main beams on the west side of the frame.

10 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Table 2-1 lists the dynamic properties of the frame alone (no ceiling system installed and no suspension

grid). The modal frequencies were determined using data from the accelerometers mounted in the frame.

Table 2-1 . Dynamic properties of the frame alone.

Direction Frequency (Hz) Period (s) Damping

Horizontal 12.6 0.08 4.4 %

Vertical 9.6 0.10 0.4 %

2.2.3 Instrumentation

Accelerometers and displacement transducers were used to monitor the response of the simulator

platform, the test frame, and the ceiling support grid for each ceiling system. Accelerometers were

located in different locations of the simulator platform (Fig. 2-1 la), on top of the test frame (Figs. 2-1 lb

and 2-12a) and on the ceiling support grid (Figs. 2-1 Ic and 2-12b). Table 2-2 presents detailed

information on the characteristics and locations of the accelerometers.

The horizontal displacement was measured with linear variable displacement transducers (LVDT). The

actuators that dri\ e the simulator platform are each equipped with two transducers (one LVDT and one

accelerometer) installed in the actuator. The transducers used to measure the horizontal displacement of

the frame were located on the south side of the frame. Three LVDTs were located on the top of the

frame, one on each of the comers of the south side of the frame and the other in the center of that side of

the frame. A fourth LVDT was located in the middle of the bottom of the south side of the test frame.

Table 2-2 lists the transducers used to monitor the displacement of the test frame. Figures 2-13 and

2-14 show the location of each transducer.

NISTNCSTAR 1-5D. WTC Investigation 11
Chapter 2

1 L J

^^^Reinforced concret e plat form n\

ofsimulata \\

- - - ^

^ " """""

s Accelerometers "Abase"

(belowconcrete platfam)

@ ; y. Recording direct ion:

e

E-W

c Vertical

r X ^ X

Figure 2-1 1a. Locations of the accelerometers on the simulator platform.

v1

^ccelerd) Tieters

Fte

"Afrm"

x)rding direct ic

Ac( Blerometers

al

Rec(

y

AfrmTS"

^ding direct ion:' JStS ^' '

yfertica \

\ccelerci meters

Fte

"Afra

Dording

_Ntf

n"

direct i( n: ^X

E-l

\^rti<

V

a!

- -A

Figure 2-1 lb. Locations of the

accelerometers on top of the testing frame.

12 NIST NCSTAR 1-5D, WTC Investigation
Description of Experiments

Accelerometer

"AsideNS"

Rscxxding direction:

^^^^^^^^

Accelerometer

"Aside EW

Recording direct ion: E-W"

Accel erometers

"Agrid" ~

Recording direct ion: N-S

Vert ical

Figure 2-1 1c. Locations of the accelerometers

on the ceiling support grid.

NISTNCSTAR 1-5D, WTC Investigation 13
Chapter 2

Source: NIST. Figure 2-1 2a. Accelerometers monitoring the response of the test assembly in the

center at the top of the test frame.

Source: NIST. Figure 2-1 2b. Accelerometers monitoring the response of the test assembly on the

ceiling support grid.

14 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Table 2-2. Transducers used for the testing program.

ID

Type of

Measurement

Direction of

Recnrdino Brand 1V<1 1 1 gc VPn€ 1 i"i \' 1 f\j Location on the Test

D_\\est Displacement Horizontal N-S MTS ± 8.2 m.

(208 mm)

2.5-10-'in.

y Lllll f

West side of top of frame

Dcntr Displacement Horizontal N-S MTS

TpTTTnoQnTnp

± 8.2 in. (208 mm)2.5-10"Sn.

( f, A \ \rr[) \\J Lllil )

Center of top of frame

D_east Displacement Horizontal !s-S MTS

Temposonic

± 8.2 m.

^—Uo mm

;

2.5-10"^ m.

(D.4 jam)

East side of top of frame

Dbase Displacement Horizontal N-S MTS

Temposonic

±5.1 in. (130 mm)

1.540"^ in. (3.8 [im)

Center of the north side of

base 01 irame

Abase_NS Acceleration Horizontal N-S Sensotec ± 16.8g 0.009g Center of the simulator,

below concrete platform

Abase_\' Acceleration Vertical Sensotec ± 6.6g 0.017g Center of the simulator,

below concrete platform

Abase_EW Acceleration Horizontal

E-W

Sensotec ± 15.2g 0.036g Center of the simulator,

below concrete platform

Afram NS Acceleration Horizontal N-S Kulite ±25.5g O.Olg Center of the roof of testing rrame Afram V Acceleration Vertical Kulite ± lOg 0.004g Center of the roof of testing

frame

AframEW Acceleration Horizontal

E-W

Kulite ± 10.3g 0.003g Center of the roof of testing

frame

Table_H Acceleration Horizontal N-S Ende\ CO ±2g 6.25- 10 -'g Actuator of simulator

platform (horizontal control

acceleration)

Table_V Acceleration Vertical Endevco ±4g 1.25T0-^g Actuator of simulator

platform (vertical control

acceleration)

AfmTSNS Acceleration Horizontal N-S Kulite ± 10.2g 3.12-10-^g Middle of the south side of

top of frame

AfimTSV Acceleration Vertical Kulite ± 10.2g 3.12-lO^g Middle of the south side of

top of frame

AfrmTW'EW Acceleration Horizontal E-W Kulite ± 10.2g 3.12-10-'g Middle of the west side of

top of frame

AfrmTWV Acceleration Vertical Sensotec ± 10.2g 3.12-10-^g Middle of the west side of

top of frame

AsideNS Acceleration Horizontal N-S Square

Sensotec ± 10.2g 3.]2-10"^g Middle of intermediate angleof the south side of frame

AsideEW Acceleration Horizontal E-W Square

Sensotec ± 10.2g 3.12-10"^g Middle of intermediate angleof the west side of frame

AgridNS Acceleration Horizontal N-S Square

Sensotec ± 10.2g 3.12-lO^g Bottom of the compression

post in suspension system

Agrid_V Acceleration Vertical Square

Sensotec ± 10.2g 3.12-lO^g Bottom of the compression

post in suspension system

NISTNCSTAR 1-5D. WTC Investigation 15
Chapter 2

Figure 2-1 3b. Location of displacement transducers at the top of the testing frame.

16 NIST NCSTAR 1-5D, WTC Investigation
Description of Experiments

Source: NIST. Figure 2-14b. Displacement transducers mounted on the top of the testing frame.

NISTNCSTAR 1-5D, WTC Investigation 17
Chapter 2

2.3 TEST SPECIMENS

2.3.1 Suspension Systems

Four different suspension systems were tested. While Systems 1 and 3 are close replicates of the systems

used in the core areas of the WTC buildings, the original systems for the tenant spaces used 20 in. square

tiles. These were manufactured only for the WTC towers and are no longer available. Systems 2 and 4

are similar systems using 24 in. square tiles, and might have been present in many tenant spaces on September 11,2001.

The following subsections present the specifications and summary information for each of the four

suspension systems. These four systems had many similarities that are summarized in this introduction.

Systems 1 and 3, and 2 and 4 were identical except for differences arising from their different orientations

with respect to the horizontal (longitudinal) axis of the simulator. Systems 1 and 3 were constructed to support 12 in. (0.30 m) square tiles on a concealed suspension system; systems 2 and 4 were constructed

to support 24 in. (0.61 m) square lay-in tiles on an exposed tee bar grid system. Systems 1 and 2 had five

cold rolled channel sections spanning in the east-west direction, while systems 3 and 4 had four cold

rolled channel sections spanning in the north-south direction. The location of the pencil rods was

identical for the four suspension systems. Each of the four suspension systems was constructed to support

two light fixtures. Information on the locations of the fixtures is provided in Section 2.3.3, which

describes the ceiling systems. The sections below provide a more detailed description of the member

locations, connections, and materials used to construct the four suspension systems.

Suspension System 1

Table 2-3 presents summary information on each component of suspension system 1 . Suspension

system 1 consisted of no. 16 gauge Wi in. (38 mm) deep cold rolled channel sections spanning in the east-west direction, which were hung by % in. (6 mm) pencil rods. There were a total of five cold rolled

channels. The first channel was installed 6 in. (0.15 m) from the southern edge of the test frame. The

next three cold rolled channel sections were spaced at 4 ft ( 1 .22 m) centers. The last channel was

positioned 18 in. (0.46 m) from the northern edge of the test frame. The Z-bars were hung from the

16 gauge 1 Vi in. (38 mm) channel rumiers and spanned the north-south direction on 2 ft (0.61 m) centers. There were a total of eight Z-bars. The first Z-bar was located 6 in. (125 mm) from the western edge of

the test frame. The next six Z-bars were spaced at 2 ft (0.61 m) on center. The final Z-bar was positioned

18 in. (0.46 m) from the eastern edge of the test frame. Two ft (0.61 m) tee splines spanned in the east-west direction between the Z-bar sections and were spaced every 12 in. (0.30 m). Breather splines were installed in every tile that was supported between tee splines.

The cold rolled channel sections were hung from % in. (6 mm) pencil rods, which were connected to the

top of the test frame. There were a total of 20 pencil rods, which were spaced at 4 ft (1 .22 m) centers. Each pencil rod was connected to the top of the test fi-ame using CADDY"* fasteners as shown in Fig. 2-15. The CADDY fasteners were secured to the test frame using 4 in. (0.10 m) C-clamps as shown

in Fig. 2-16. The pencil rod was attached to the cold rolled channel main runners using a CADDY side

mount channel clamp, similar that used to connect the pencil rod to the top of the test frame, and is shown

" CADDY is a trademark of ERICO Products, Inc.

18 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

in Fig. 2-17. The Z-bar cross runners were hung from the cold rolled channel runners by C-15 wire Z-bar

clamps (Figs. 2-18 and 2-19). The cold rolled channel section runners were secured to the edge of the

test frame using XTAC clips, which were screwed to the channel and the edge of the test frame

(Figs. 2-20 and 2-21). Figure 2-22 is a photograph of a breather spline.

Table 2-3. Summary information on components of s uspension systems 1 and 3. Component Item no. Description Dimensions (in., mm) Comments

Channel

section NA Cold rolled channel

l'/2. 38 Channel runner was hung from pencil

rods.

Z-bar beams

7300

Z section runners NA Z-bar beam splices were staggered;

spanned along cold rolled channel. Two-foot tee splines

S-392

T section spline

2. 51 Spanned between Z-bar runners and

spaced at 1 ft. (305 mm) centers.

Breather

splines

7486

Spline strip

1 1 '/2. 292 Strips installed into each panels;

spanned between two-foot tee splines.

'/4 in. pencil

rod

NA

Rod suspension

support

Va X 36, 6 X 914 Supported cold rolled channel section runners; spaced at 4 ft. (1.22 m)

centers.

4 in. C-clamp

NA Adjustable

clamp

NA Connected CADDY to test frame.

V_ r\L)U I 708AB

708 A R Angle bracket support

KI A Connected top of pencil rod to test frame. CADDY

4B15LS

B15LS Side mount

channel clamp

NA Connected bottom of pencil rod to cold

rolled channel runner.

Cross-tee adapter clip

XTAC C-channel

connector NA Connected cold rolled channel section runners to edge of test frame. C-15 wire

Z-bar clamps

C15 Wire connection

bracket NA Connected cold rolled channel section runners to Z-bars.

Channel

molding

7830 Hemmed angle

molding

15/16 X 1 15/16 X 120,

13 X 49 X 3050

Hemmed angle molding with pre- finished exposed flanges.

Source: NIST

Figure 2-15. Top (left) and bottom (right) CADDY

fasteners in suspension system 1.

NISTNCSTAR 1-5D. WTC Investigation 19
Chapter 2

Source: NIST. Figure 2-16. C-clamp and top CADDY fastener in suspension system 1.

Source: NIST. Figure 2-17. Bottom CADDY fastener in suspension system 1.

20 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

NISTNCSTAR 1-5D, WTC Investigation 21
Chapter 2

Source: NIST

Figure 2-20. Channel section runner connection to edge of test frame in suspension

system 1.

Source: NIST. Figure 2-21. Two ft (0.61 m) cross tee used in suspension system 1.

22 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Source: NIST

Figure 2-22. Breather spline used in suspension system 1.

Suspension System 2

Table 2—4 presents summary information on each component of suspension system 2. Suspension

system 2 consisted of 1 Vi in. (38 mm) deep cold rolled channel sections spanning in the east-west

direction, which were hung by 'A in. (6 mm) pencil rods. There were a total of five cold rolled channels.

The first channel was installed 18 in. (0.46 m) from the southern edge of the test frame. The next three

cold rolled channel sections were spaced at 4 ft ( 1 .22 m) centers. The last channel was positioned 6 in. (0.15 m) from the northern edge of the test frame. Prelude main runners were hung from the 16 gauge

1 Vi in. (38 mm) deep cold rolled channels and spanned in the north-south direction at 4 ft (0.61 m)

centers. There were a total of four main runners. The first main runner was installed 36 in. (0.91 m) from

the western edge of the test frame. The next two main runners were spaced on 4 ft ( 1 .22 m) centers. The

final main runner was positioned 1 ft (0.305 m) from the eastern edge of the test frame. Four ft ( 1 .22 m)

cross tees spanned in the east-west direction between the main runner sections and were spaced every 2 ft (0.61 m). Two ft (0.61 m) cross tees spanned north-south between the 4 ft (1.22 m) cross tee sections and were spaced at 24 in. (0.61 m) on center.

The cold rolled channels were hung from Ya in. (6 mm) pencil rods, which were connected to the top of

the test frame. There were a total of 20 pencil rods, which were spaced at 4 ft (1.22 m) centers. The

pencil rod was connected to the top of the test frame using CADDY clips. The CADDY clips were

secured to the test frame using two 4 in. (0.10 m) C-clamps as shown in Fig. 2-23. One clamp was

positioned to fasten the CADDY clip to the test frame. The other clamp was positioned to fasten the

pencil rod to the test frame to prevent upward movement during testing. The pencil rod was attached to the cold rolled channels using a CADDY side mount channel clamp. The main runners were hung from

the cold rolled channels by CBS clips (Fig. 2-24). Cold rolled channel sections were secured to the edge

of the test frame using XTAC clips, which were screwed to the channel and the test frame edge.

NISTNCSTAR 1-5D, WTC Investigation 23
Chapter 2

Table 2-4. Summary information on components of suspension systems 2 and 4. Component Item no. Description Dimensions (in., mm) Comments

Cold rolled channels

M A In A C-channel 1 1/ 1Q 1 /2, JO Hung from pencil rods.

Main beams 7300 Heavy duty main

runner

1 5/16 X 1 11/16,

33 X 43

Double web with peaked roof top

bulb and bottom flange with pre- finished steel capping.

Main beam splices were staggered.

48 in. cross

tees XL7342 4 ft long cross

tee

48 X 15/16 X 1 3/8, 1220 X 33 X 35Double web with peaked rooftop

bulb, bottom flange with pre- finished steel cap and override at each end. 24 in. cross

tees XL7328 2 ft long cross

tee

24 X 1 5/16 X 1 3/8, 610 X 33 X 35

Double web with peaked roof top

bulb, bottom flange with pre- finished steel cap and override at each end.

'/4 in. pencil

rod

NA Rod suspension

support

% X 36,

6.4 X 914

Supported cold rolled channel

sections. Spaced at 4 ft (1.22 m)

centers. 4 in. C-clamp NA Adjustable

connection

clamp

NA Connected CADDY to test frame. Two clamps used at each

connection.

CADDY

708AB

708AB Angle bracket supportNA Connected top of pencil rod to test frame. CADDY

4B15LS

4B15LS Side mount

channel clamp

NA Connected bottom of pencil rod to cold rolled channel sections.

Cross-tee adapter clip

XTAC C-channel

connector NA Connected cold rolled channelsections to edge of test frame.

6 in. channel

beam splice

CBS6 Clip to main

runners NA Connected cold rolled channelsections to main runners.

7/8 in. wall

molding

7800 Hemmed angle

molding

7/8 X 7/8 X 144,

22 X 22 X 3660

Hemmed angle molding with pre- finished exposed flanges.

24 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Source: NIST. Figure 2-23. C-clamps and top CADDY clip in suspension system 2.

Source: NIST. Figure 2-24. CBS clip connecting channel to main runner in suspension system 2.

NISTNCSTAR 1-5D, WTC Investigation 25
Chapter 2

Suspension System 3

Suspension system 3 was similar to suspension system 1 . Suspension system 3 consisted of no. 1 6 gauge

1 Yi in. (38 mm) deep cold rolled channel sections spanning in the north-south direction. These channel

sections were hung by % in. (6 mm) pencil rods from the test frame. There were a total of four cold rolled

channel section runners. The first channel runner was located 2 ft (0.61 m) from the eastern edge of the

test frame. The next two channel runners were spaced at 4 ft ( 1 .22 m) centers. The fourth channel runner was located 2 ft (0.61 m) from the western edge of the test frame. The Z-bars were hung from the

16 gauge Wi in. (38 mm) deep channel runners and spanned in the east-west direction at 2 ft (0.61 m)

centers. There were a total of eight Z-bars. The first Z-bar was located 1.5 ft (457 mm) from the southern

edge of the test frame. The next six Z-bars were spaced at 2 ft (0.61 m) on center. The final Z-bar was

located 6 in. (0.15 m) from the northern edge of the test frame. Two ft (0.61 m) tee splines spanned in the

north-south direction between the Z-bar sections and were spaced every 1 ft (0.30 m). Breather splines were installed in every tile that was supported between tee splines.

The cold rolled channel sections were hung from % in. (6 mm) pencil rods, which were connected to the

top of the test frame. There were a total of 20 pencil rods, which were spaced at 4 ft ( 1 .22 m) centers. The pencil rod was connected to the top of the test frame using CADDY clips. The CADDY clips were

secured to the test frame using of 4 in. (0. 1 0 m) C-clamps. One clamp was positioned to fasten the

CADDY clip to the test frame. The other clamp was positioned to fasten the pencil rod to the test frame

to prevent upward movement during testing. The pencil rod was attached to the cold rolled channel main

runners using a CADDY side mount channel clamp similar to that used to connect the pencil rod to the

top of the test frame. The Z-bar cross runners were hung from the cold rolled channel runners by C-15

wire Z-bar clamps. The cold rolled channel section runners were secured to the edge of the test frame

using XTAC clips, which were screwed to the channel and the edge of the test frame. Table 2-3 presents

summaiy information on each component of suspension system 3.

Suspension System 4

Suspension system 4 was similar to suspension system 2. This suspension system consisted of 1 Vi in. (38 mm) deep cold rolled channel sections spanning in the north-south direction, which were hung from

Va in. (6 mm) pencil rods. There were a total of four cold rolled channels. The first channel was 2 ft (0.45 m) from the eastern edge of the test frame. The next two cold rolled channels were spaced on 4 ft

( 1 .22 m) centers. The last channel was positioned 2 ft (0.61 m) from the western edge of the test frame.

Prelude main runners were hung from the 16 gauge, 1 Vi in. (38 mm) deep cold rolled channels and

spanned the east-west direction on 4 ft (0.61 m) centers. There were a total of four main runners. The

first main runner was installed 3 ft (0.91 m) from the northern edge of the test frame. The next two main

runners were spaced at 4 ft (1.22 m) centers. The fourth main runner was located 1 ft (0.30 m) from the

southern edge of the test frame. Four ft ( 1.22 m) cross tees spanned in the north-south direction between

the main innner sections and were spaced at 2 ft (0.61 m) centers. Two ft (0.61 m) cross tees spanned in the east-west direction between the 4 ft (1.22 m) cross tees sections and were spaced at 2 ft (0.61 m)

centers.

The cold rolled channels were hung from % in. (6 mm) pencil rods, which were connected to the top of

the test frame. There were a total of 20 pencil rods, which were spaced at 4 ft ( 1 .22 m) centers. The

pencil rod was connected to the top of the test frame using CADDY clips. The CADDY clips were

26 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

secured to the test frame through the use of two 4 in. (0.10 m) C-clamps. One clamp was positioned to fasten the CADDY clip to the test frame. The other clamp was positioned to fasten the pencil rod to the

test frame to prex ent upward movement during testing. The pencil rod was attached to the cold rolled

channels using a CADDY side mount channel clamp. The main runners were hung from the cold rolled

channels by CBS clips. Cold rolled channel sections were secured to the edge of the test frame using

XTAC clips, which were screwed to the channel and the test frame edge. Table 2^ presents summary

information on each component of suspension system 4.

2.3.2 Tiles

Table 2-5 presents summary information on the two types of ceiling tiles examined in this study.

Table 2-5. Tile specifications.

Tile ID Panel name Description

Panel Dimensions (in., m)

Breadth, Depth, Thickness

Approximate

Weight

(Ib/ft^)

1 K4C4 Beveled edge tile (Armstrong Item No. BF 592A)

12, 12, NA,

0.305, 0.305, NA

1.00

2 Ultima Beveled

Tegular Humigard

Plus

Acoustical mineral fiber tile (Armstrong item No. 1911 A)

24, 24. 3/4, 0.61, 0.61, 0.019

1.00

2.3.3 Ceiling Systems

This section provides information on each of the four ceiling systems tested in this study. Table 2-6 lists summary information on components of each ceiling system.

Table 2-6. Configuration of ceiling systems.

Test

Series

Ceiling

System ID

Suspension

System ID'

Tile ID"Figure

No.' Comments

TSl CSl 1 1 2-25 to 2-31 System with cold rolled sections spanning in the east-west direction. Tiles were 12 in. (0.30 m) square. TS2 CS2 2 2 2-32 to 2-35 System with cold rolled sections spanning in the east-west direction. Tiles were 24 in. (0.61 m) square. TS3 CS3 3 1 2-36 to 2-41 System with cold rolled sections spanning in the north-south direction. Tiles were 12 in. (0.30 m) square. TS4 CS4 4 2 2^2 to 2-^3 System with cold rolled sections spanning in the north-south direction. Tiles were 24 in. (0.61 m) square.

a. See Section 2.3.2 for suspension system ID number.

b. See Table 2-5 for tile ID number.

c. Refers to a figure number in this report.

NISTNCSTAR 1-5D. WTC Investigation 27
Chapter 2

Ceiling System CS1

System CSl was composed of suspension system 1 and tile 1. Figures 2-25 through 2-29 are photographs of system CSl. There were 16 panels spanning in both the east-west and north-south

directions. The ceihng system was constructed flush to the edge of the test frame on all sides. Six in. (0.15 m) perimeter tiles had perimeter spring clips installed between the tile and the edge of the test frame. The total ceiling area was approximately 256 ft" (23.8 m"): 16 ft (4.87 m) in the east-west

direction by 16 ft (4.87 m) in the north-south direction. Figures 2-30 and 2-31 show the ceiling system

layout for ceiling system CSl. Two 1 ft (0.30 m) by 4 ft (1.22 m) light fixtures were installed in the

ceiling with light clips and two safety wires. The lights were supported on the grid by four swinging

amis.

Ceiling System CS2

System CS2 was composed of suspension system 2 and tile 2. Figures 2-32 through 2-34 are photographs of system CS2. There were seven full panels and two half panels spanning in both the east-west and north-south directions. The ceiling system was constructed flush to all edges of the test frame. The total ceiling area was approximately 256 ft" (23.8 m"): 16 ft (4.87 m) in the east-west direction

by 16 ft (4.87 m) in the north-south direction. Figure 2-35 shows the ceiling system layout for ceiling

system S2. Two 2 ft (0.61 m) by 4 ft ( 1 .22 m) light fixtures were installed in the ceiling with hght clips

and two safety wires.

28 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Source: NIST. Figure 2-25. Bottom view of ceiling system CS1.

Source: NIST

Figure 2-26. Close-up of top view of ceiling system CS1

.

Source: fJISTFigure 2-27. Top view of ceiling system CS1.

NIST NCSTAR 1-5D, WTC Investigation 29
Chapter 2

Source: NIST. Figure 2-28. 12 in. by 48 in. (0.30 m by 1.22 m) fixture with safety clip and wires in ceiling

system CS1.

Source: NIST. Figure 2-29. Panel perimeter spring clips in ceiling system CS1.

30 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

NISTNCSTAR 1-5D, WTC Investigation 31
Figure 2-31. Layout of splines and cross tees in ceiling system CS1.

32 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Source: NIST. Figure 2-32. Top view of ceiling system CS2.

Source: NIST. Figure 2-33. Top view of ceiling system CS2.

NISTNCSTAR 1-5D. WTC Investigation 33
Chapter 2

Source: NIST. Figure 2-34. Bottom view of ceiling system CS2.

North

Channel

runners 4 ft cross tees

2 ft cross tees

Prelude

main

runners

Pencil

rods

Simulator

horizontal

motion

2 ft X 4 ft pan lights

Figure 2-35. Layout for ceiling system CS2.

34 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Ceiling System CSS

System CSS was composed of suspension system 3 and tile 1. Ceiling system CS3 was similar to ceiling

system CSl except that this system had channel sections spanning in the north-south direction.

Figures 2-36 and 2-37 are photographs of system CS3. There were 16 panels sparming in both the east- west and north-south directions. The ceiling system was constructed flush to the edge of the test frame on

all sides. Six in. (1.52 m) perimeter tiles had perimeter spring clips installed between the tile and the edge

of the test frame. The total ceiling area was approximately 256 ft^ (23.8 m"): 16 ft (4.87 m) in the east- west direction by 16 ft (4.87 m) in the north-south direction. Figures 2-38 and 2-39 show the ceiling

system layout for ceiling system CS3. Two 1 ft (0.30 m) by 4 ft (1.22 m) light fixtures were installed in the ceiling with light clips and two safety wires. The lights were supported on the grid by four swinging

arms.

Source: NIST. Figure 2-37. Top view of ceiling system CSS.

NIST NCSTAR 1-5D, WTC Investigation 35
Chapter 2

36 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Breather

splines

2 ft cross tees

Simulator

horizontal

motion

I ft X 4 ft pan lights

Figure 2-39. Layout of splines and cross tees in ceiling system CS3.

Ceiling System 4

System CS4 was composed of suspension system 4 and tile 2. Ceiling system CS4 was similar to ceiling

system CS2 except that this system had prelude main runners spanning the east-west direction.

Figure 2-40 is a photograph of system CS4. There were seven full panels and two half panels spanning

in both the east-west and north-south directions. The ceiling system was constructed flush to all edges of

the test frame. The total ceiling area was approximately 256 ft" (23.8 m~): 16 ft (4.87 m) in the east-west

direction by 16 ft (4.87 m) in the north-south direction. Figure 2^1 shows the ceiling system layout for

ceiling system CS4. Two 2 ft (0.61 m) by 4 ft ( 1 .22 m) light fixtures were mounted with light clips and

two safety wires.

NISTNCSTAR 1-5D. WTC Investigation 37
Chapter 2

Source: NIST. Figure 2-40. Bottom view of ceiling system CS4.

38 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

North

Channel

runners

Prelude

main

runner

4 ft cross

tee

2 ft cross

tee

Pencil

rods

Simulator

horizontal

motion

2 ft X 4 ft pan lights

Figure 2-41. Layout for ceiling system CS4.

NISTNCSTAR 1-5D, WTC Investigation 39
Chapter 2

2.4 SYSTEM EXCITATION PATTERNS

2.4.1 General

Estimation of the forces and accelerations that occurred in the WTC towers was difficult due to the large

number of unknown or poorly known parameters affecting the response, and because at the time of these

tests there was little information available on the forces generated during such an impact. Limited

infomiation was available from tests involving military aircraft impacting soil or nearly rigid walls

(Attaway et al. 2003), but no infomiation was available for large aircraft impacting relatively flexible structures at high speed.

The project team thus conducted tests under a variety of excitations, hypothesizing that from the test results a pattern would emerge that would enable reasonable extrapolation to the behavior of the actual

ceiling tile systems on September 1 1 , 2001 . Each of the four ceiling tile systems was subjected to a series of single impulses or blasts, the rationale for and nature of which are described in Section 2.4.3. The

intensities of the impulses are listed Table 2-7, which appears in Section 2.5. In addition, the ceiling tile systems were subjected to a standard earthquake simulation that is a sequence of complex impulses. This

is described in Section 2.4.4. The intensities of the earthquake excitations are listed in Table 2-8, which

also appears in Section 2.5.

2.4.2 White Noise

White noise was used to find the natural frequencies of the test frame and the ceiling systems. The

natural frequencies for the horizontal and vertical directions of each test specimen were obtained by

finding the frequency associated with the peak in the acceleration transfer function (Clough and

Penzien 1993). Figures 2^2 and 2^3 show the histories and the Fourier amplitude spectrum,

respectively, of the white noise used in this study to calculate the natural frequencies of the test frame and

test assemblies. The 60 Hz peak in the Fourier spectrum is associated with oil-column resonance in the

vertical actuators of the simulator and falls well outside the testing range of interest: 1 to 33 Hz.

2.4.3 Single Impulse Excitations

Accurate estimation of the tower's motion during the airplane impact required detailed knowledge of the

geometry, weight distribution, and impact velocity of the aircraft, as well as detailed knowledge of the

geometry, weight distribution, and stnictural strength of the tower. At the time of this test series

(fall 2003), much of this infonnation was unknown, and the impact motion could only be roughly,

estimated. To allow this estimate to be made quickly, many simplifying assumptions were made

regarding the nature of the impact.

Idealized Impact Waveform

Creating the profile of building motion as a result of the airplane impact involved both simplifying

assumptions and estimation of many of the response parameters. First, a simple impact waveform was

chosen based on the limited infomiation available as of fall 2003. For simplicity, the same waveform was

used for both towers. It was anticipated that ongoing numerical studies of the airplane impact would

provide a much more accurate representation of the motion that occurred; however, the simplified

40 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

estimation described below provided a reasonable estimation that could be used for the experimental

study and with the available test facility at the time that facility was available.

0.60

so

<

0.60

10 20 30 40

Time (s)

50 60 70

Figure 2-42. White noise histories; top: horizontal direction, bottom: vertical direction.

0.1 10 100 Frequency (Hz)

Figure 2-43. Fourier amplitude spectrum of horizontal and vertical white noise.

NISTNCSTAR 1-5D, WTC Investigation 41
Chapter 2

Based on the limited information available on aircraft impact (Attaway et al. 2003) and general

information on blast loads, two possible waveforms were initially considered:

• The first waveform had a tower acceleration component that rose instantly to a maximum

value, maintained this maximum response for a short duration, and then decreased to zero over a longer duration. This waveform corresponded to a large acceleration as the nose of the

aircraft penetrated the tower, and was sustained as the forward portion of the fuselage,

landing gear, engines, and wings penetrated. The acceleration then diminished as the portion

of the aircraft within the building came to a stop and the tail penetrated the tower. While the

actual motion was certainly much more complicated, for the purpose of simplifying the

analysis, the acceleration was simplified to a constant value for the first quarter of the impact

time, followed by a steady ramp to zero over the remainder of the time history. This

waveform is shown in Figure 2-44.

• The second assumed waveform was similar except that the acceleration rose from zero to the

maximum over the short duration, and then immediately began to decrease to zero. This

waveform was simplified to an acceleration increasing with a constant slope for the first quarter of the histoiy, and then decreasing with a constant slope over the remainder of the

history.

When the two waveforms were modified for use on the UB shaking table, as described below, the

difference between them was seen to be small, and the second waveform was removed from

consideration. For this reason, the analysis with this second wavefonn is not described.

o

<

Time

Figure 2-44. Generic acceleration waveform.

42 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

Estimation of Acceleration Magnitude and Duration

Once the shape of the acceleration response was assumed, the magnitude and duration of the acceleration was estimated from basic mechanics and some simplifying assumptions regarding the tower response. Basic information about the airplane included:

• The velocity of the airplane at the start of the impact, (0) . This was assumed to be

560 mph (250 m/s). This value was based on verbal discussions with NIST investigators who

were in the process of accurately determining the aircraft velocity based on video evidence

(NIST NCSTAR 1-5A).^ This value is slightly smaller than the 590 mph (264 m/s) that was

reported by FEMA for the aircraft that hit WTC 2 (McAllister 2002).

• The mass of the airplane, . This was assumed to be to be 8,500 slugs (124 x 10"^ kg),

which was approximated by estimates of the masses of the aircraft itself, the estimated jet fuel on board, the passengers and their luggage, and the cargo. This was about 70 percent of

the maximum takeoff mass of the airplane (McAUister 2002).

• The length of the airplane. . A value of 159 ft (48.5 m) was used (Badrocke and

Gunston 1998).

One important unknown parameter that influenced the impact motion is how far the airplane traveled into

the building. The greater this distance, the longer the deceleration time would have been, which would

reduce the peak acceleration accordingly. Based on initial estimates of the internal damage, it was

assumed that the airplane penetrated through the center of the core. Some of the airplane debris would

not likely have traveled this far into the tower, while some parts of the plane and some of the fuel passed

through the building and exited the far side. It was. therefore, assumed that the center of mass of the

airplane penetrated slightly more than one-half of the tower's depth. Assuming that the center of mass of

the airplane is located at approximately the center of its length, the center of mass of the airplane would

have traveled approximately 197 ft (60 m) between when the nose impacted the face of the tower and

when the airplane remnants came to rest.

The motion of the tower was also influenced by both its mass and the distribution of that mass; however,

neither the actual mass nor its distribution is known. Based on information in the original WTC design

documents provided to NIST by Leslie E. Robertson Associates (LERA) and the Port Authority of new

York and New Jersey (PANYNJ). and baseline computer models of the WTC towers (NIST

NCSTAR 1-2), the average load per unit area (including live and dead loads) of a typical floor was

approximately 87 \h/fv (4.17 kN/m"). Based on a typical floor area of 42,200 ft^ (3,900 m"), each floor in the tower would have had a weight of approximately 3,675 kip (16,400 kN), which corresponds to a mass

of 114 X 10^ slugs (1.67 X 10^ kg).

To keep these calculations reasonably simple, the reference computer models assumed that the airplane

and towers act as lumped, rigid masses. However, the towers were quite flexible with their mass

distributed over their height. To account for this without making the analysis much more complicated.

' Subsequent analysis (NIST NCSTAR 1 -5A) estimated the impact velocities as 466 mph ± 34 mph for WTC 1 and 545 mph ± 1 8 mph for WTC 2. The difference is of little significance since, as noted in the next section, the resulting shaking

table velocity and displacement exceeded the table capability and had to be reduced.

NIST NCSTAR 1-5D. WTC Investigation 43
Chapter 2

only a portion of the tower's mass was assumed to participate. In this regard, the motion of the towers

would have been greatest at the floors of impact, with the peak accelerations decreasing with the distance

above or below the impact zone, until there would have been very little motion at the base. In addition,

this study was less concerned with the accelerations on the impact floors, since flying debris would likely

have damaged or destroyed most of the ceiling tiles there. Instead, the concern was for the floors just

above or below the impact zone, which were not directly damaged by the airplane, but had significant

fires after the impact. These floors would have Hkely seen somewhat less intense motion than the actual

impact floors. After considering the above, it was estimated that about one-sixth of the tower's floors

should be considered to be participating in the dynamic response for a lumped mass model of the

vibrations. Therefore, the participating mass of the tower, , was estimated to be 2.1 x 10*' slugs

To assess the response of the tower at the end of the impact, it was necessary to consider the kinetic

energy transfeired from the airplane to the tower. Not all of the energy from the plane would have been

transferred, but the efficiency of the impact could not be accurately estimated without extensive and

detailed analysis. It was assumed that two-thirds of the energy was transferred from the airplane to the

Based on the above assumptions, an impact magnitude and duration were calculated that were consistent

with the assumed waveform (Fig. 2-44). The transfer of energy during the impact was described as:

Here, KE^it) and KE^^{t) were the kinetic energies of the tower and airplane at time , respectively, tf

is the time of the end of the impact, and the factor 0.66 accounted for the energy lost as described above.

Expanding this equation yielded:

Here, F,(^^ ) was the velocity of the tower at the end of impact. It was assumed that at this time, both the

tower and the airplane debris were moving together at the same velocity. Inserting the values determined

above, V,{ff) was found to be 42.3 ft/s (12.9 m/s).

(31 X 10' kg).

structure.

KE, (/ , ) + KE^, (/ , ) = 0.66[KE,iO) + KE^,iO)] (2-1)

(2-2)

Given the acceleration time history of the airplane in Fig. 2^6 and defining this as A^yt), which is a

function of the acceleration magnitude, , and impact duration, tf, then:

(2-3)

and:

A,Xt)dt

(2-4)

44 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

where, x^(0 was the position of the center of mass of the airplane at time t. Given the initial and final

velocities of the airplane and the differential displacement, described above. Equations 2-3 and 2-4 were

solved to determine the acceleration parameters. The estimated peak acceleration of the airplane was

found to be -62g (-610 m/s"), and the estimated duration of the impact was found to be 0.63 s. The

resulting acceleration history is shown in Fig. 2-45.

Based on the airplane acceleration time history, the history of the impact force on the tower was

calculated, and the peak force was determined to be 17 x 10^ kip (75 x 10"^ kN). The force-time history is shown in Fig. 2^6. Figure 2^7 shows the history of the estimated tower acceleration. The peak

acceleration is 0.25g (2.46 m/s"). This acceleration history formed the basis for the modified history that was used in the experiments.

100 —

0 1-

-100

"inw -200 -

c

•2 -300 -

ro

I—

0)

0)^ -400 - <

-500 -

j -600 _

-700 —

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

Time (s)

Figure 2-45. Estimated acceleration of airplane during impact.

NISTNCSTAR 1-5D, WTC Investigation 45
Chapter 2

80.0E+3

70.0E+3

10.0E+3 -

OOO.OE+0

0.00 0.10 0.20 0.30 0.40 Time (s)

0.50 0.60 0.70

Figure 2-46. Estimated force on tower during impact.

Figure 2-47. Estimated acceleration of tower during impact.

Development of Experimental Time History

The tower acceleration time history estimated above was considered to be a reasonable, simplified

estimate of the actual tower acceleration. However, this motion had to be further refined before it could

be used on the shaking table at UB. The peak acceleration of the history was not extreme, but the

combination of the acceleration and the duration of the peak was problematic. The velocity and

displacement resulting from this time history were well in excess of the shaking table capabilities.

46 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

To understand the necessary modifications to the time history, it was useful to understand the Hmitations

of the shaking table. The specimen platform, essentially the tabletop, is driven by a series of servo- controlled hydraulic rams, which impose firm limits on the displacements, velocities, and accelerations

that the table can generate. The piston area limits the force that each ram can produce, which in turn

limits the peak acceleration that can be generated for a specimen of a particular mass. More important for the current tests is the ram stroke, which is limited to 1 ft (0.3 m) end to end. The hydraulic servovalves

that control the rams have limited flow capacity and bandwidth. This limits the peak velocity of the

shaking table to 1 ft/s (0.305 m/s) and hmits the frequency of the motion to 50 Hz and less. These are all theoretical values, and additional physical and electronic limitations, as well as signal noise and

mechanical limitations, prevent the table motion from reaching these limits. A plot describing these limitations is shown in Fig. 2^8. Note that the response envelope slopes upward

in the low frequency range, where the peak displacement limit tends to govern the response. In the

middle frequency range, where the envelope is flat, the velocity limit governs, and in the higher frequency

range, where the cur\ e slopes downward, the acceleration limits govern. The gray line at approximately

0.9 Hz indicates the natural frequency of the towers.

Figure 2-48. Theoretical peak response of the UB seismic simulator.

For the shaking table to be able to handle the impact history, three modifications had to be made to the

waveform. First, the high frequency response components that occur at sharp transitions in the response

had to be removed. Next, a deceleration component needed to be added to the history to return the

velocity to zero. Finally, the entire waveform had to be scaled so that the peak velocity and displacement

responses would remain within the table limits.

NISTNCSTAR 1-5D. WTC Investigation 47
Chapter 2

The first attempt at modifying the history consisted of filtering the signal with a low pass Butterworth

filter to remove the unwanted, high frequency components. However, the phase shifts in some prominent

frequencies, caused by filter during the removal of the high frequencies, significantly changed the nature of the history. Instead, the waveform was manually adjusted to remove the sharp transitions by replacing

the transition areas with quarter sine and cosine functions, which had frequencies within the shaking

table's response band. The result of this effort was that the two waveforms described in Section 2.4.2

converged toward a single result.

To decelerate the table before the displacement limits were reached, a pulse nearly as large and sharp as the primaiy impulse was required. This modification resulted in a history that varied significantly from

the original desired waveform, but that could be scaled for use with the shaking table. Given that the

intent was to have a single impulse approximation of the aircraft impact and that a more complex

excitation was also to be used in the testing, it was accepted that this was a sufficient rendition for the

purpose.

Acceleration signals for the simulator were then generated to produce the peak target accelerations listed

in Table 2-8 (see Section 2.5). Signals for tests with peak target accelerations of between 0.05g and

0.085g were ramped displacement histories as shown in Fig. 2-49. Signals for tests exceeding a peak

target acceleration of 0.085g were sinusoidal-type acceleration histories. The acceleration histories were

identical for vertical and horizontal excitations. The acceleration histories used for these tests is provided

in Fig. 2-50. The signals were generated and amplitude scaled using the program software STEX

(MTS 1991).

48 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

1.5

0 0.05 0.1 0.15 0.2 0.25

Time (s)

Figure 2-50. Horizontal and vertical acceleration history inputs into simulator

for tests 6 through 23.

2.4.4 Multiple Impulse (Earthquake) Stimulation

To capture the effects of the muhiple shocks reported by some of the tower occupants, ceiling systems

CS2, CS3, and CS4 were also subjected to a set of combined horizontal and vertical excitations. Since

the nature of the actual excitations is unknown, an available set was used. These were the excitations

used to qualify a ceiling system according to ICBO-AC156, Acceptance Criteria for Seismic Qualification

Testing of Nonstructural Components (ICBO 2000). The following text presents summary information on these histories, which involve both horizontal and vertical motion.

The required response spectrum (RRS) for horizontal shaking was developed using the normalized ICBO

response spectrum shown in Fig. 2-5 1

.

2/3 A,,y

Anv/15

(2/3)Ar,y/\5

Horizontal RRS

Vertical RRS

Aric

2/3 AnjG

0.1 1.3 8.3 33.3

Frequency (Hz)

Figure 2-51. Required response spectra for horizontal and vertical shaking.

NISTNCSTAR 1-5D, WTC Investigation 49
Chapter 2

The values of the parameters Ar/c and Afix that define the ordinates of the horizontal spectrum were

calculated with the following equations.

For horizontal design basis earthquake shaking, the International Building Code (ICC 2000) defines the

short period design basis earthquake acceleration response as:

^^=^^.^^5 (2-5)

where Sds is the design spectral response acceleration at short periods, F„ is the site coefficient, and is the mapped maximum earthquake spectral acceleration at short periods. Based on ICBO AC 156, the

spectral acceleration Arjg of a rigid component (assumed to have a frequency/> 33 Hz) is given by

Equation 2-6 and that of a flexible component Anx is given by Equation 2-7:

^RiG -0A-S^,{\ + 2j)<\.2-S^,

h

(2-6)

'FLX 5^,(1 + 2^)<1.6-V

h

(2-7)

where z is the height above the base of the building where the equipment or component is to be installed

and h is the height of the building. If the equipment or component is to be installed in the roof of the

building, zlh = 1.0. If the location of the equipment or component in a building is unknown, or if it is being qualified for a general use in buildings structures, it is conservative, but appropriate, to set r = /?.

Table 2-7 shows the parameters used in this study to obtain the RRS for horizontal shaking for 5 percent

damping for a mapped spectral acceleration at short period Ss equal between 0.25 and 1.75 with

1 .0 highlighted. Figure 2-52 shows the RRS in the horizontal and vertical directions for 5 percent

damping for a mapped spectral acceleration at short period, ^.s^l.Og. The ordinates of the vertical RRS

are given by ICBO as two-thirds (2/3) of those of the horizontal RRS, namely, Apix ^ 1. 01,

Arjg =0.80 for ^5= I.Og.

Table 2-7. Parameters to calculate 1the horizontal RRS (z/A7=1.0).

Ss 0.25 0.50 0.75 1.00 1.25 1.50 1.75 Fa 1.00 1.00 1.00 1.00 1. 00 1.00 1.00

Sds 0.17 0.33 0.50 0.67 0.83 1.00 1.17

Aflx 0.27 0.53 0.80 1.07 1.33 1.60 1.87

Aflx/15 0.02 0.04 0.05 0.07 0.09 0.1

1

0.12

0.20 0.40 0.60 0.80 1.00 1.20 1.40

50 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

0.1 1.0 10.0 100.0 Frequency (Hz)

Figure 2-52. RRS for horizontal and vertical shaking for Ss=1.0.

Figure 2-53 presents 2000 National Earthquake Hazards Reduction Program (NEHRP) maximum

considered earthquake (MCE) ground motion spectra and the ICBO-AC156 target qualification spectrum

for seismic qualification for ^5 = l.Og and 5/ = 0.4g. The ground motion spectra are presented for NEHRP soil t>'pes A through E. The purpose of the presentation is to relate the qualification spectral

demands that are assumed to apply anywhere in a building structure to the ground motion demands on a single degree of freedom representation of the building. The qualification spectrum envelops the MCE

spectra (for Ss = 1 .Og and Si = 0.4g) except in the short period range for site class D.

Figure 2-54 presents the 2000 NEHRP MCE and design basis earthquake (DBE) ground motion spectra

and the ICBO-AC156 target qualification spectrum for seismic qualification for ^5 = l.Og and Sj = 0.4g.

The target qualification spectrum was developed for DBE shaking, and the difference between the

NEHRP DBE spectrum and the target qualification spectrum (shown by the arrows in the figure)

represents the assumed amplification of the DBE motion by a building framing system (into which the

ceiling system would be installed).

NISTNCSTAR 1-5D. WTC Investigation 51
Chapter 2

CL) u

0.0 0.5 1.0 1.5

Period(s)

2.0 2.5 3.0

Figure 2-53. Relationship between MCE NEHRP spectra and target qualification

spectrum (Ss=1.0g, S7=0.4g).

Figure 2-54. Relationship between NEHRP MCE and DBE spectra and target spectrum

(Ss=1.0g, S;=0.4g).

52 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

2.5 DESCRIPTION OF TEST SERIES

2.5.1 General

For the purpose of performance characterization, each of the four ceiling systems was subjected to a set of

horizontal and vertical excitations. Each set included single-axis resonance search tests using white noise

excitation along each (programmable) orthogonal axis of the simulation platform. The resonance search

tests were undertaken to establish the natural frequency of the ceiling frame system. Following that, each

set of excitations included either (a) a series of individual and biaxial impulsive excitations

(Section 2.4.2) or (b) an earthquake excitation sequence (Section 2.4.3). The amplitude of the impact and

earthquake excitations was varied from a relatively mild first level (0.0 15g), perhaps representing ceiling

tiles at some distance from the airplane impact, up to the intensity limit of the shaking table (1.25g). The

result of each test was characterized by certain criteria or limit states. If any distortion or damage to the

system was experienced during a given test, the system was repaired before proceeding to the next test.

Table 2-8 lists the standard series of tests used for the impact excitations. The earthquake tests began

with a white noise excitation and continued with intensities of 0.25g, 0.50g, 0.75g, l.OOg, 1.25g, 1.50g,

1.75g, and2.50g.

2.5.2 Performance Criteria

The outcome of each test was verbally characterized by the extent of displacement of ceiling tiles and the

degree of damage to the suspension system. For summary purposes, the outcome was also described in terms of limit states.

Definitions of two limit states of response were defined in a manner similar to those adopted in past

studies using earthquake simulation (Badillo et al. 2002, 2003):

1 . Loss of one or more tiles from the ceiling system.

2. Sufficient damage to one or more components of the suspension system such that repair or replacement of part or all of the suspension system would be required.

NISTNCSTAR 1-5D, WTC Investigation 53
Chapter 2

Table 2-8. Test sequence for a set of impact experiments for a single ceiling system.^

Test No.

Test Name

Target Peak

Acceleration'' (g) Description

1 wlh White noise excitation in the horizontal (N-S) direction

2 wlv White noise excitation in the vertical direction

3 wlhv White noise excitation in the horizontal and vertical directions

4 0050h 0.050 Motion in the horizontal (N-S) direction'^

5 0085h 0.085 Motion in the horizontal (N-S) direction'

6 0150h 0.150 Motion in the horizontal (N-S) direction''

7 0150v 0.150 Motion in the vertical direction''

8 0150hv 0.150 Biaxial motion in the horizontal (N-S) and vertical directions''

9 0300h 0.300 Motion in the horizontal (N-S) direction''

10 0300v 0.300 Motion in the vertical direction''

11 0300hv 0.300 Biaxial motion in the horizontal (N-S) and vertical directions'*

12 0500h 0.500 Motion in the horizontal (N-S) direction''

13 0500v 0.500 Motion in the vertical direction''

14 0500hv' 0.500 Biaxial motion in the horizontal (N-S) and vertical directions'*

15 0750h 0.750 Motion in the horizontal (N-S) direction''

16 0750v 0.750 Motion in the vertical direction''

17 0750hv 0.750 Biaxial motion in the horizontal (N-S) and vertical directions''

18 lOOOh 1.000 Motion in the horizontal (N-S) direction''

19 lOOOv 1.000 Motion in the vertical direction''

20 lOOOhv'^ 1.000 Biaxial motion in the horizontal (N-S) and vertical directions''

21 1250h 1.250 Motion in the horizontal (N-S) direction''

22 1250v 1.250 Motion in the vertical direction''

23 1250hv' 1.250 Biaxial motion in the horizontal (N-S) and vertical directions'*

a. For actual test sequences, see Table 3-1 and Table 3-2.

b. Peak target acceleration of the simulator platfonn.

c. For input histories, see Sec. 2.4.3; Fig. 2-51 shows the input displacement histoi'y.

d. For input histories, see Sec. 2.4.3; Fig. 2-52 shows the input acceleration history.

e. Results from tests presented in Chapter 3; see Appendix A.

54 NISTNCSTAR 1-5D, WTC Investigation
Description of Experiments

2.6 REFERENCES

Attaway, S. W., J. G. Arguello, G. C. Bessette, R. G. Schmitt, P. Taylor, K. W. Gwinn, D. Crawford,

S. Tieszen, and M. Baer. 2003. Technology Ovei-view for Analysis ofAircraft Impact.

SAND2003-1952, Sandia National Laboratories, Albuquerque, NM.

Badillo, H., D. Kusumastuti, A. S. Whittaker, and A. M. Reinhom. 2002. "Seismic Qualification Tests of

Ceiling Systems", Part I, Report No. UB CSEE/SEESL-2002-01, State University of New York at Buffalo, Buffalo, NY, April.

Badillo. H.. 2003. "Seismic Fragility Testing of Suspended Ceiling Systems," M.S. Thesis, Department

of Civil, Structural, and Environmental Engineering, State University of New York at Buffalo,

Buffalo. NY, August.

Badillo, H., A. S. Whittaker, and A. M. Reinhom. 2003. "Seismic Qualification Tests of Ceiling

Systems," Part III, Report No. UB CSEE/SEESL-2003-01, State University of New York at Buffalo,

Buffalo. NY, February.

Badillo, H., A. S. Whittaker, and A. M. Reinhom. 2003a. "Seismic Qualification Tests of Ceiling

Systems," Part IV, Report No. UB CSEE/SEESL-2003-02, State University of New York at Buffalo,

Buffalo, NY, May.

Badillo, H., A. S. Whittaker, and A. M. Reinhom. 2003b. "Performance Characterization of Suspended

Ceiling Systems," Proceedings, ATC-29-1 Seminar on Seismic Design, Performance, and Retrofit of

Nonstmctural Components in critical facilities. Applied Technology Council, Redwood City, CA,

October.

Badrocke, M., and B. Gunston. 1998. Boeing Aircraft Cutaways, The Histoiy ofBoeing Aircraft

Company, Osprey Aviation. Wellingborough, UK.

Clough. R.W., and J. Penzien. 1993. Dynamics ofStructures, 2"^* ed., McGraw-Hill, NY.

ICBO (International Conference of Building Officials). 2000. Acceptance Criteria for Seismic

Qualification Testing of Nonstructural Components. ICBO-AC156. Whittier, CA.

ICC (Intemational Code Council). 2000. International Building Code. Falls Church, VA.

Kusumastuti, D., H. Badillo, A. S. Whittaker, and A. M. Reinhom. 2002. "Seismic Qualificafion Tests Of Ceiling Systems," Part II, Report No. UB CSEE/SEESL-2002-02, State University of New York

at Buffalo, Buffalo, NY, May.

McAllister, T., ed. 2002. World Trade Center Building Performance Study: Data Collection,

Preliminaiy Ohsen-ations, and Recommendations. FEMA403. Federal Emergency Management

Agency. Washington, DC, May.

MTS Systems Corp. 1991. STEX-Seismic Test Evaluation Software, MN.

NISTNCSTAR 1-5D, WTC Investigation 55
Chapter 2

Repp J. R., H. Badillo, A. S. Whittaker , and A. M. Reinhom. 2003. "Seismic Qualification of

Armstrong Suspended Ceiling Systems," Part V, Report No. UB CSEE/SEESL-2003-03, State University of New York at Buffalo, Buffalo, NY, September.

Repp J. R., H. Badillo, A. S. Whittaker , and A. M. Reinhom, 2003a. "Seismic Qualification of

Armstrong Suspended Ceiling Systems," Part VI, Report No. UB CSEE/SEESL-2003-04, State University of New York at Buffalo, Buffalo, NY, November.

56 NISTNCSTAR 1-5D, WTC Investigation
Chapter 3

Test Results

3.1 COMPARISON OF PLATFORM SIMULATOR AND FRAME RESPONSES

The excitations described in Section 2.4 were used as the inputs to the earthquake simulator. The

horizontal and vertical responses of the earthquake simulator and the frame were recorded with

accelerometers and linear potentiometers. These responses were recorded for the purpose of comparing

the input to the simulator and the response of the test frame including the ceiling systems.

Accelerometers were placed at locations termed Table (shaking table acceleration control). Abase (on the center of the base of the frame). Afram (on the center of the roof of the frame), AframTS (on the side and

top of the test frame), and Agrid (located toward the center of the suspension system) as noted in Section 2.2.3.

The figures in Appendix A show test results for each ceiling system for tests OSOOhv, lOOOhv, and

1250hv. These figures include acceleration histories and the response spectra for 5 percent damping for the five locations noted above and displacements histories from horizontal displacement transducers

Dbase (at the bottom of the test frame) and Dcntr (at the top middle of the test frame).

As expected, there was virtually no difference between the histories and spectra calculated using the

accelerometers Table and Abase. However, it is evident from comparing the spectra for Afram (the roof

acceleration), AframTS (on the side and top of the test frame), and Agrid (suspension grid) with Abase

(base acceleration), that the flexibility of the test frame amplified the horizontal and vertical excitation

from the simulator platform to the ceiling systems. Such amplification must be placed in the context of

impact characterization. Although characterization of ceiling systems should be established on the basis

of the input histories to the ceiling system, because the spectra for Afram exceed those for Table across

the entire period range, the characterization of the ceiling systems was conservatively based on spectra

generated using the simulator platform histories {Table). Note that ceiling systems with fundamental

periods ranging from 0.0 s through 0.4 s (bracketing the systems tested as part of this study) sustained

demands substantially more severe than those estimated using the Table accelerometers.

3.2 SINGLE IMPULSE TESTS

Following each test, the ceiling suspension grid system was inspected visually. All connections, anchors,

and hanging rods were examined.

Table 3-1 presents summary information of the resonance search tests performed on each ceiling system.

The natural frequencies of each system are given for both directions of the test frame, the horizontal

direction {f^) and the vertical direction if,) using data from the white noise tests. Table 3-2 presents

summary information on each test of each system. Listed are the test name, the test record, and the

maximum accelerations in five different locations in the test fixture. The maximum horizontal response

of the accelerometers at locations termed Table (shaking table acceleration control). Abase (on the center of the base of the frame), Afram (on the middle of the south side of the top of the frame), AframTS (on the

NISTNCSTAR 1-5D. WTC Investigation 57
Chapter 3

top and side of the frame) and ^gr/c/ (located near the center on the suspension system) are identified. Table 3-3 presents summary information of the damage to each ceiling system for each test. Figures 3-1

through 3-12 are photographs of some of the damage obser\'ed during testing.

Table 3-1. Results from resonance search tests.

Ceiling System Test Record Horizontal Frequency (Hz) V^ertical Frequency (Hz)

CSl

Date of test: o/z //J.\jVj

Slwlh /v =11.91 Hz -

S 1 w 1

V

- / = 7.23Hz

Slwlhv /, = 11.72 Hz /. = 7.03 Hz

CS2

Date of test: o/Z //zUUj

S2wlh / = 11.91 Hz -

S2wlv - / = 6.45 Hz

S2wlhv /, = 11.72 Hz A = 6.45 Hz

CS3

Date of test: 8/28/2003

S3wlh /v =11.13 Hz

S3wlv /. = 7.23Hz

S3wlhv /, = 11.33 Hz /. = 7.23Hz

CS4

Date of test: 8/29/2003

S4wlh /, = 11.91 Hz

S4wlv /. = 6.64 Hz

S4wlhv /, = 11.72 Hz f, = 6.45 Hz

58 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Table 3-2. Measured acceleration values.

Ceiling

System Record

Maximum Recorded Horizontal

Acceleration (g)

Maximum Recorded Vertical Acceleration

(g)

Table Abase Afram Agrid

Afram

TSNS Table Abase Afram Agrid

Afram

TSV

CSl

Date of

test: 8/27/03

005 Oh 0 07 0 07 0 1 ^ 0 07 0 1 7 U. 1 z

0085h n 1

0

0 10 0 22 0 07 0 7 1 U.Z i

0150h n 1

7

n 1

7

0 ?Q 0 08 0 78

0150v 0U. 1

1 ^J 0 1 A u. 1 u 0 AA u.zo 0 1 U. 1 o

0150hv D 1 7 0 1 8 0 TO 0VJ.OO f\9. U.Zo 0 1 U. 1 J 0 1 U. 1 J 0 AT. 0u.tu AO 0 7 1 U.Z 1

0300h 0 •ss 0 1 ^ 0U.J J)

0300v 0 "^7 U. jZ 0 T. 1 U.J 1 0U.707/ 0U.JOS8 0 "^8 U.JO

0300hv n id 0 "if^ 0 77 1 .HO 0U.Oo(^9. 0U.jZ^7 0U.jZ^7 11 .U07/

1 ZL7 1 .'4-Z 0U.HoA8

0500h U.O J 0 1 Od 0U.J 7 0U.7Q7/

0500v 0 A 1 U.u 1 0U.DZA7 1 .jy 0U. 78/ o 0 7"! U. / J

0500hv U.J u.ou J.J7 1 .J J U.O 1 u.ou 1 71 1 . / 1 1 84 fl OA

0750h 1 .U_> 11 .Uo 08 1 QQ 11 .U07/

1 87

075 Ov 1 1

1

1.11 1 1 8 1 . 1 o

I 1 7 J. 1 Z11 . 7^/ J

11 . JH^4

0750hv U. 7 J 0 07 7 1 A ^ 7^ 11.7/Q7 1 1 7 1 . 1 z 1 . 1 J Z.70 ^ 08 J^ .70^J 1

1

. 77/ /

lOOOh 11 . J-+ s 4 1 A

1

1 . D 1 7 11 .oU 80 7Z. JU^0

lOOOv 1 8'=;

1 .o J TZ.UJOS J.J J 7 47 z7 .zu 7fi

lOOOhv 1 /I ~) 1 .J.y 1 1 Q Z. 1 7 A 7n 7 (\A 11 . 77/ Z

7 0^^ z.uo J . 1 7S 7'n J . / J

7 7'^ Z . / J

1250h Z._0 J .J J

1 78 1 . / o1 1A

1250v 7 'iA Z. JH 1 0^^ J .UD 0.7700 11.1^ J . JU^0

CS2

Date of

test: 8/27/03

0050h fi no nu.un7/ n 1

4

U. 0U.Uo08 0 1 A

0085h 0.10 0.10 0.20 0.14 0.19

0150h 0.16 0.16 0.29 0.12 0.27

0150v 0.14 0.16 0.39 0.83 0.17

0150hv 0.16 0.17 0.34 0.93 0.32 0.14 0.14 0.41 1.10 0.21

0300h 0.33 0.34 0.57 0.39 0.55

NISTNCSTAR 1-5D, WTC Investigation 59
Chapter 3

Ceiling

System

Test Record

Maximum Recorded Horizontal

Acceleration (g)

Maximum Recorded Vertical Acceleration

(g)

Table Abase Afram Agrid

Afram

TSNS Table Abase Afram Agrid

Afram

TSV

0300v 0.32 0.32 0.80 1.76 0.36

0300hv 0.32 0.34 0.75 2.03 0.70 0.32 0.32 0.82 4.31 0.47

0500h 0.59 0.62 0.62 0.77 0.96

0500v 0.59 0.59 1.72 2.73 0.72

0500hv 0.56 0.58 1.39 5.03 1.30 0.60 0.58 1.75 3.27 0.93

0750h 1.00 1.05 2.05 2.92 1.95

0750v 1.10 1.14 3.08 2.34 1.27

0750hv 0.97 0.91 2.01 6.99 1.84 1.11 1.16 3.05 4.74 1.80

lOOOh 1.51 1.59 2.70 5.34 2.57

lOOOv 1.78 2.06 5.18 4.36 2.19

lOOOhv 1.40 1.25 2 25 2.10 2.10 1.71 1.98 4.79 5.90 2.80

1250h 2.05 2.24 3.47 6.83 3.30

1250v 2.35 2.94 7.03 5.16 3.07

1250hv 2.03 1.81 2.83 9.25 2.68 2.14 2.57 5.76 6.43 3.60

CS3

Date of

test: 8/28/03

0050h 0.06 0.07 0.13 0.24 0.13

0085h 0.10 0.10 0.20 0.29 0.19

0150h 0.19 0.20 0.32 0.26 0.31

0150v 0.15 0.15 0.43 0.36 0.16

0150hv 0.19 0.20 0.35 0.99 0.33 0.15 0.14 0.44 0.60 0.22

0300h 0.35 0.37 0.61 0.54 0.59

0300v 0.32 0.32 0.97 1.70 0.37

0300hv 0.33 0.36 0.73 3.02 0.68 0.32 0.31 1.01 1.54 0.48

0500h 0.60 0.63 1.02 0.70 0.97

0500v 0.59 0.59 1.93 2.27 0.70

OSOOhv 0.57 0.60 1.48 5.47 1.39 0.61 0.59 2.00 3.75 0.93

60 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Maximum Recorded Horizontal

Acceleration (g)

^'^ Maximum Recorded Vertical Acceleration

Ceiling

System

Test Record Table Abase Afram Asrid

Afram

TSNS Table Abase Afram Asrid

Afram

TSV

0750h 1.00 1.05 1.91 1.78 1.82

0750v 1.10 1.20 2.73 3.51 1.31

075 Ohv 0.95 0.92 -1 J

-) 8.63 1.97 1.08 1.13 2.69 3.89 1.73

lOOOh 1.49 1.58 2.71 4.77 2.58

lOOOv 1.71 2.04 3.63 4.69 2.12

lOOOhv 1.40 1.26 2.42 12.35 2.31 1.67 1.96 3.52 6.80 2.72

1250h 2.05 2.23 3.57 3.56 3.45

1250v 2.34 2.99 6.5 4.29 3.12

1250hv 2.03 1.80 2.82 11.07 2.72 2.17 2.68 5.01 4.65 3.64

005 Oh 0.06 0.07 0.14 0.13 0.14

008 5 h 0.10 0.10 0.20 0.18 0.20

0150h 0.14 0.14 0.24 0.31 0.23

0150v 0.14 0.15 0.41 0.87 0.16

0150hv 0.16 0.17 0.30 0.45 0.30 0.15 0.15 0.43 0.89 0.21

0300h 0.33 0.33 0.53 1.12 0.51

CS4 0300v 0.31 0.32 0.86 2.48 0.37

uate 01

test: 0300h\ 0.32 0.34 1.27 0.68 0.32 0.3

1

0.88 2.92 0.47

8/29/03 0500h 0.58 0.61 1.08 1.78 1.04

0500v _ _ _ _ 0.59 0.61 1.75 3.26 0.72

0500hv 0.55 0.59 1.38 2.04 1.37 0.59 0.60 1.74 3.35 0.90

0750h 1.00 1.05 2.08 3.39 1.99

U / jUV 1.10 1.17 3.20 3.93 1.32

0750hv 0.94 0.90 1.94 2.65 1.91 1.06 1.13 2.74 3.12 1.75

lOOOh 1.47 1.56 2.67 5.77 2.57

NISTNCSTAR 1-5D. WTC Investigation 61
Chapter 3

Maximum Recorded Horizontal

Acceleration (g)

Maximum Recorded Vertical Acceleration

(g)

Ceiling

System

Test Record Table Abase Afram Agrid

Afram

TSNS Table Abase Afram Agrid

Afram

TSV

lOOOv - - - - 1.72 2.07 4.98 4.72 2.11

lOOOhv 1.38 1.26 2.05 4.03 2.04 1.68 1.95 4.32 5.21 2.80

1250h 2.05 2.20 3.44 6.37 3.23

1250v 2.38 3.07 7.39 7.05 3.18

1250hv 1.98 1.75 2.31 5.64 2.37 2.19 2.70 5.98 8.47 3.71

a. See Figs. 2-1 1 and 2-12 for accelerometer locations.

b. Unfiltered maximum recorded acceleration.

62 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Table 3-3. Observed ceiling system damage from single impulse tests.

Ceiling System Test Record Summary Remarks on Observed Damages'*

0050h No damage to the suspension system or tiles.

0085h No damage to the suspension system or tiles.

0150h No damage to the suspension system or tiles.

0150v No damage to the suspension system or tiles.

0150hv No damage to the suspension system or tiles.

0300h No damage to the suspension system or tiles.

0300v No damage to the suspension system or tiles.

0300h%- No damage to the suspension system or tiles.

0500h No damage to the suspension system or tiles.

0500v No damage to the suspension system or tiles. CSl

Date of test; 0500hv No damage to the suspension system or tiles.

8/27/03 0750h No damage to the suspension system or tiles.

0750v No damage to the suspension system or tiles.

0750hv No damage to the suspension system or tiles.

lOOOh No damage to the suspension system or tiles.

lOOOv No damage to the suspension system or tiles.

lOOOhv

One tile was damaged, which was replaced following testing. Two Zbar clips were damaged and replaced following testing. Some

perimeter tiles displaced above the perimeter clips.

1250h No damage to the suspension system or tiles.

1250v

The light fixture on southern side of the ceiling system dislodged

because the light support arm swung inward during testing. Many Zbar clips we re dislodged near the fixtures and center of the ceiling

system. The perimeter tiles displaced above perimeter spring clips

along the northern edge of the ceiling system.

CS2

Date of test' 8/28/03

0050h No damage to the suspension system or tiles.

0085h No damage to the suspension system or tiles.

0150h No damage to the suspension system or tiles.

0150v No damage to the suspension system or tiles.

OlSOhv No damage to the suspension system or tiles.

0300h No damage to the suspension system or tiles.

NISTNCSTAR 1-5D. WTC Investigation 63
Chapter 3

Ceiling System Test Record Summary Remarks on Observed Damages"

0300v No damage to the suspension system or tiles.

0300hv No damage to the suspension system or tiles.

0500h No damage to the suspension system or tiles.

0500v No damage to the suspension system or tiles.

0500hv

One of the four swing arm supports for the south light fixture swung in leaving the comer of the fixture unsupported. No damage to the ^n*snpnmnn ijLtJL'^llOlV./li 'iv^stpm DVOlVlll orKJ I tilp<; lli^D. Thp -lliV *sWinp O W 11 1 £1 ariTi Cll 111 wa<s W Cli5 rpr>o<iitinnpH IWLyWOlllWll^U follnwinrf i^llVJ W 111 LI testing.

0750h

One southern perimeter cross-tee spanning to the wall type molding

LllUlJIJ^VJ L.iClLZtl lliV ilJVJlUlil^. 1 11^ ^IVJoO VA ClCy 1 L/VJoi llUlJ^U Xv/llV W 111 tl testing.

0750v

One tile dislodged up between the cross-tees and onto the grid but did

llVJl not fVill Iclll. \!n i^U H^impiCTp LiCllllClLiW tn\.\J ihp Lllw Qii^npn^sinn 3lJ.OlJWllOlv^ll QVQtpm OVOl&ill nr\Jl. tilp^ LllVO< Thp ±11^ HiqIoHctpH Uldl^JU^WU

tiles were repositioned following testing.

One tile dislodged up between the cross-tees and onto the grid but did not JJv/l 'Ffill lUJl. T\]n iN\J rljiTTififTp VJCllllCl^C toV\J ttip lilt QiiQnpTTSion L>LlL!>lJtlloHJll <;vQtpm ^yolWlli or\Jy tilpQ THp 1 llV HiqIoHctpH Ulc>lv/U^WVJ tiles were repositioned following testing.

One southern perimeter cross-tee spanning to the wall molding

HroT^t^f^H Ulv/L/UCiJ r*nct IJClol InP lilt molnincT lllL/lUlll hi. T~'np lilt r*rocc-tpp tl Uc>o Itt W do rpnocition(=*n 1 1 IJVJol lHJlltLI Tollow/Tncr HJllLfWlllU, testing.

1 \J\J\J V

Five tiles dislodged up between the cross-tees and onto the grid but did

not TCill Mo H^im^ifTP to tnp ci i cr^pncion c\/ctpm or tilpc "Tnf* HicloriCTPri llUl iall. INU LJalI]ciL;t lU lilt ftU olJtllc) JUli oySltlll UJ lllto. 1 lit UlolUU^tU

tiles were repositioned following testing.

lOOOhv

Seven tiles dislodged up between the cross-tees and onto the grid but

did not fall. No damage to the suspension system or tiles. The

niclonopri UlolUUUtU tilpc IJXto w/pvp Wtit rpnocitionpH Tollo\A/i'no' tpctincr 1 1 UUoi llUlltU iUlIUWlllt^ Itollil^.

1250h

Cross-tee connections located at the southern light fixture were

disconnected and reconnected following testing. Five southern

perimeter cross-tees spanning to the wall molding dropped past the

lllUHJillii. lilt dUoj-ltt?> WtlC JtUitittU lUllUWillL^ ItolJllj^.

1250v

Ten tiles dislodged up between the cross-tees and onto the grid but did

not fall. The comer of northern light fixture fell through the grid. No

damage to the suspension system or tiles. The dislodged tiles were

repositioned following testing.

1250hv

Seven tiles dislodged up between the cross-tees and onto the grid but

did not fall. The cross-tee connections located at the southern and

northern light fixtures were disconnected. The connection tabs at these connections were bent inward. Four southem perimeter cross-tees spanning to the wall molding dropped past the molding.

Date of test: 8/28/03

0050h No damage to the suspension system or tiles.

0085h No damage to the suspension system or tiles.

0150h No damage to the suspension system or tiles.

0150v No damage to the suspension system or tiles.

64 NISTNCSTAR 1-5D, WTC Investigation
Test Results

oUllllIlarV IxcillarKS Oil \JDScr\t:U Uallld^cs

0150hv No damage to the suspension system or tiles.

0300h No damage to the suspension system or tiles.

0300v No damage to the suspension system or tiles.

0300hv No damage to the suspension system or tiles.

0500h No damage to the suspension system or tiles.

0500v No damage to the suspension system or tiles.

0500hv No damage to the suspension system or tiles.

0750h No damage to the suspension system or tiles.

0750v No damage to the suspension system or tiles.

0750hv No damage to the suspension system or tiles.

lOOOh No damage to the suspension system or tiles.

lOOOv No damage to the suspension system or tiles.

lOOOhv

Three Z-bar clips were bent disconnecting the Z-bars and channel

sections in the center of the ceiling system. This failure caused the middle of the ceiling system to sag between the runners. The Z-bar

clips were replaced following testing.

1250h

One Z-bar clip was disconnected in the center of the ceiling system.

One southern perimeter cross-tee spanning to the wall molding

dropped past the molding. The system was repositioned after testing.

1250v

Fi\ e Z-bar clips were bent disconnecting the Z-bars and channel

sections in the center of the ceilmg system. These failures caused the middle of the ceiling system to sag between the runners. The Z-bar w ith the five disconnected Z-bar clips had a damaged and disconnected

splice. The Z-bar splice was fixed and the five Z-bar clips were

replaced after testing. Four Z-bar clips were bent disconnecting the Z-bars and channel

sections in the center of the ceiling system. These failures caused the miHHlp ci'f tVif* ppilincT (;\/Qtf*m tn <i^(y Hptwppn tHf* rnnTipr*\ THp 7-b^ir with the four disconnected Z-bar clips had a damaged and

disconnected splice.

CS4

Date of test: 8/20/01

0050h No damage to the suspension system or tiles.

0085h No damage to the suspension system or tiles.

0150h No damage to the suspension system or tiles.

0150v No damage to the suspension system or tiles.

0150hv No damage to the suspension system or tiles.

0300h No damage to the suspension system or tiles.

NISTNCSTAR 1-5D. WTC Investigation 65
Chapter 3

Ceiling System Test Record Summary Remarks on Observed Damages"

0300v No damage to the suspension system or tiles.

0300hv No damage to the suspension system or tiles.

0500h No damage to the suspension system or tiles.

0500v No damage to the suspension system or tiles.

OSOOhv No damage to the suspension system or tiles.

0750h No damage to the suspension system or tiles.

0750v

One tile dislodged up between the cross-tees and onto the grid but did

not fall No Hnrn^iP'p In thp siisnpnsion ^vstpm or tilp^i Thp di*\]odppd

tiles were repositioned following testing.

0750hv

Six tiles dislodged up between the cross-tees and onto the grid but did not fall. No damage to the suspension system or tiles. The dislodged

tiles were repositioned following testing.

lOOOh No damage to the suspension system or tiles.

lOOOv

Five tiles dislodged up between the cross-tees and onto the grid but did not fall. No damage to the suspension system or tiles. The dislodged

tiles were repositioned following testing.

lOOOhv

Nineteen tiles dislodged up between the cross-tees and onto the grid but did not fall. One of the four swing arm supports for the south light fixture rotated in leaving the comer of the fixture unsupported. No

HjiTiiJicTP fn tVip ^ii<;npn*iinn Qv^tptn r\v tilp*i Trip <sWin(T ?irm Jinn niQlnncTpn

tiles were repositioned following testing.

1250h

The cross-tee connections located at the northern light fixture were

Hi<;rnnnpr*tprl THp rnnnprtinn t?ih^ at thp^iP ronnprtiniTs wptp Hpnt

inward. The connection tabs were realigned following testing.

1250v

Nine tiles dislodged up between the cross-tees and onto the grid but did

not fall. No damage to the suspension system or tiles. The dislodged

tiles were repositioned following testing.

1250hv

Ten tiles dislodged up between the cross-tees and onto the grid but did

not fall. Five northern perimeter cross-tees spanning to the wall molding dropped down past the wall-type molding. The grid

connections on the northern perimeter of the ceiling systems between

the light fixtures and ceiling system perimeter failed. One tile fell.

a. See Figs. 3-1 through 3-12 for photographs of representative damage to the ceiling system.

66 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Source: NIST. Figure 3-1 . Displacement of perimeter tiles over perimeter spring clips

following Test 20 for ceiling system CS1.

Source: NIST

Figure 3-2. Bottom view of damage to ceiling system CS1 following Test 20.

NISTNCSTAR 1-5D, WTC Investigation 67
Chapter 3

Source: NIST. Figure 3-3. Bottom view of damage to ceiling system CS1 following Test 20.

.-2'-~i-2'-

L 1 1

18"

111 I 1 7ii I ^lii _] ziii 1 ') 3 II J ')5ii J 1 1 II _j 111 I 8 ^8 ^2 -^8 ^16 -^8 ^2 16

Figure 3-4. Permanent vertical displacements of Z-bars in the east-west direction

following Test 20 for ceiling system CS1.

Source: NIST.

Dislodged light

fixture swing arm

support

Figure 3-5. Light fixture swing arm support dislodged following Test 21 for ceiling

system CS1.

68 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Source: NIST. Figure 3-6. Dislodged Z-bar clip in ceiling system CS1 following Test 21.

Source: NIST. Figure 3-7. Dislodged southern light fixture corner in ceiling system CS2

following Test 14.

NISTNCSTAR 1-5D. WTC Investigation 69
Source: NIST. Figure 3-8. Stretching of Z-bar clips located at northern light fixture corner

in ceiling system CS3 following Test 20.

Source: NIST. Figure 3-9. Damage to the center of ceiling system CS3 following Test 20.

70 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Source: NIST. Figure 3-10. Damage to the center of ceiling system CS3 following Test 23.

Source: NIST. Figure 3-1 1 . Damage to the northern perimeter of ceiling system CS4

following Test 23.

NISTNCSTAR 1-5D, WTC Investigation 71
Chapter 3

Source: NIST. Figure 3-12. Damage to the northern perimeter of celling system CS4

following Test 23.

72 NISTNCSTAR 1-5D, WTC Investigation
Test Results

3.3 EARTHQUAKE TESTS

Earthquake testing was conducted for Ceiling Systems 2, 3, and 4. The earthquake response data are presented in Table 3^. No tests were undertaken for Ceiling 1.

Table 3-4. Observed ceiling system damage from earthquake tests.

Ceiling System

Nominal

Acceleration (g) Summary Remarks on Observed Damages'*

CS2

Date of test: 8/28/03

0.25 No damage to the suspension system or tiles.

0.50 No damage to the suspension system or tiles.

0. / J No damage to the suspension system or tiles.

1 AM 1 .00 Tiles jumped and border tees dropped.

1 .Id Tiles jumped and border tees dropped.

1 C A

1 .50 Tiles jumped and border tees dropped.

1 . /5 Tiles jumped and border tees dropped.

OCA Z.50 Three tiles fell and three were displaced upward. Tees were down at the light fixture.

CS3

Date of test: 8/28/03

0.25 No damage to the suspension system or tiles.

0.50 X T J 4 4.1- A " 1 No damage to the suspension system or tiles.

0. /5 No damage to the suspension system or tiles.

1.00 No damage to the suspension system or tiles.

1.25 Cut border came loose.

1.50 No residual damage to the suspension system or tiles.

Tlirf*A 7 Inline Hiclr\HfTf^H in tni=* C'f^ni f^r r\T ir\f^ Pf^^ilmtr Tr^itnp i^nri tnf* 1 nice K^lly^ UlolUULiCU Jll UiC CCIJLCI Ul IIIC LCllllXt, ildlllC allU lllC center of the frame was sagging.

2.50 Major collapse of the system. See Fig. 3-13.

CS4

Date of test: 8/29/03

0.25 No damage to the suspension system or tiles.

0.50 No damage to the suspension system or tiles.

0.75 No damage to the suspension system or tiles.

1.00 No damage to the suspension system or tiles.

1.25 No damage to the suspension system or tiles.

1.50 The north and south perimeters fell.

1.75 Entire north perimeter fell. Significant damage to south perimeter.

See Figs. 3-14 and 3-15.

a. See Figs. 3-13 through 3-15 for photographs of representative damage to the ceiling system.

NIST NCSTAR 1-5D, WTC Investigation 73
Chapter 3

Source: NIST. Figure 3-14. Damage to north perimeter of ceiling system CS4 after 1.75g

earthquake excitation.

74 NISTNCSTAR 1-5D, WTC Investigation
Test Results

Source: NIST

Figure 3-15. Damage to south perimeter of ceiling system CS4 after 1.75g

earthquake excitation.

NISTNCSTAR 1-5D, WTC Investigation 75
Chapter 3

This page intentionally left blank.

76 NISTNCSTAR 1-5D, WTC Investigation
Chapter 4

Summary

4.1 SUMMARY OF TEST RESULTS

The motion of the test frame and suspension systems was considerably larger than the motion at the base

of the test frame in the period range between 0.0 s and 0.5 s. The ratio of the spectral response of the

ceiling system calculated using the frame (A/ram) and simulator (Abase) acceleration histories, averaged

over a frequency range of 5 Hz to 15 Hz, ranged between 1.5 and 3.0 for horizontal (H) shaking, and

2.3 and 3.2 for vertical (V) shaking.

The performance of the different types of ceiling systems is summarized in Table 4-1, where the

performance for the two limit states of Section 3.2.2 is given in terais of target peak acceleration of the

simulator.

Table 4-1. Performance of ceiling systems.

Testing

Series

Ceiling

System

ID System Description Impulse

Qualification Level (g)

Limit State T Limit State 2''

TSl CSl System with cold rolled sections spanning east-west direction. Tiles were 12 in. (305 mm) square.H >1.25 >1.25

V >1.25 >1.25

H&V >1.00 > 1.00 EQ

TS2 CS2 System with cold rolled sections spanning east-west direction. Tiles were 24 in. (610 mm) square.H >1.25 >1.00

V >1.25 >1.25

H&V >1.25 1.00 EQ 1.75 1.75 TS3 CSS System with cold rolled sections spanning north-south direction. Tiles were 12 in. (305 mm) square.

H >1.25 >1.00

V >1.25 1.00 H&V >1.25 0.75 EQ 1.75 1.50 TS4 CS4 System with cold rolled sections spanning north-south direction. Tiles were 24 in. (610 mm) square.

H >1.25 >1.25

V >1.25 >1.25

H&V 1.25 1.25 EQ 1.25 12.0

a. Limit stale 1 is the loss of one or more tiies. b. Limit state 2 is sufficient damage to one or more components of the suspension system such that repair or replacement of part or all of the suspension system would be required.

Key: EQ, earthquake; H, horizontal; V, vertical.

NISTNCSTAR 1-5D, WTC Investigation 77
Chapter 4

4.2 IMPLICATIONS OF TEST RESULTS

All four combinations of impulse direction and ceiling system resisted significant damage up to about Ig

applied to the test platform, about 2.5g to 3g at the ceihng frame. Tile motion intensified with increasing

impulse strength, and significant damage occurred (or began to occur) for relatively modest further

increments in impulse strength. From analysis of this ascending effect for all systems under all the

impulses suggests that their total failure would occur at values near the 1.75g to 2.5g (at the test platform)

observed for the earthquake impulses. Qualitatively, this corresponds to about 4g to 5g at the ceiling

frame.

Comparison of this magnitude with the results of the impact calculations must take into account that these

tests are not exact replications of the initiating events on September 1 1, 2001:

• The installed ceiling tile systems had been in service for up to 30 years. During that time, the

buildings had been subjected to wind forces that swayed the towers, and several occupants

have reported that high winds resulted in falling ceiling tiles. Thus, the frames were not in the new condition of the systems tested here.

• The boundary conditions in the test frame were not identical to the service boundary

conditions in the towers at the times of the aircraft impact. The tower frames were different

from the test frame and the dimensions of the ceiling system were far larger.

78 NISTNCSTAR 1-5D, WTC Investigation
Appendix A

Test Histories

4.00 3 2.00 5

I

0.00

:j -2.00 <

-4.00

1 1 1

4.00 n 3 2.00 - o

2 0.00 -

§ -2.00 - <

-4.00 -

1 1

1 1

1 1

i r T

I

-

1 1

1 1

1

1 T

1 1

1

1 1

1

1 0 0.2 0.4 0.6 0.8 Time (s)

a) horizontal acceleration (Table)

0.2 0.4 0.6 Time (s

)

0.8

b) horizontal acceleration {Abase)

-4.00 -4.00 0 0.2 0.4 0.6 0.8 Time (s)

c) horizontal acceleration {Afram)

0.2 0.4 0.6 Time (s)

0.8

d) horizontal acceleration (AframTS)

4.00 -

2.00 -

0.00 o

-2.00 <

^.00 -

0 0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6

e) horizontal acceleration (Agrid)

Figure A-1. Horizontal displacement and acceleration histories for Test 14 on ceiling system CS1.

NISTNCSTAR 1-5D, WTC Investigation 79
Appendix A

2.00

0.00

-2.00

2.00

0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase)

-2.00

0.2 0.4 0.6 Time (s)

0.8

g) horizontal displacement (Dcntr)

Figure A-1. Horizontal displacement and acceleration histories for Test 14 on ceiling

system CS1 (continued).

80 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

-4.00

4.00 3 2.00

0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table)

-4.00 ^

0

4.00

0.2 0.4 0.6 0.8 Time (s)

b) vertical acceleration (Abase)

-4.00 -4.00 0 0.: 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

c) vertical acceleration (Afram)

4.00

d) vertical acceleration (AfiamTS)

e) vertical acceleration (Agrid)

Figure A-2. Vertical acceleration histories for Test 14 on ceiling system CS1.

NISTNCSTAR 1-5D. WTC Investigation 81
Appendix A

<

Simulator control (Table)

-Q- - - Simulator plalfonn (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Period (s) a) horizontal response spectra

10.00

8.00

6.00

4.00

2.00

0.00

Simulator control (Table)

-Q- - - Simulator plalfomi (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) -X—Roof frame side (AframTS)

0.1 1 10 Frequency (Hz)

b) horizontal response spectra

100

o<

~i

I—I—II—I—I—

r

Simulator control (Table)

- - - Simulator platfomi (Abase)

- - Roo f fra me (A fram)

Suspension grid (Agrid) ^—Roof frame side (AframTS)

I I I I I I I I I I rT-i-|-nrT--|-r

0.2 0.4 0.6

iB 'BWff ' B 'B 'B'B*

0.8 1 1.2 1.4 Period (s) c) vertical response spectra

niB B BBBBBB

1.6 1.8 2

10.00

8.00 ^

6.00

4.00

2.00

0.00

Simulator control (Table)

-Q- - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) -X—Roof frame side (AframTS)

0.1 1 10 100 Frequency (Hz)

d) vertical response spectra

Figure A-3. Response spectra for Test 14 on ceiling system CS1.

82 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

5.4. ^3. ^ 2. 5 1. ^ 0.

8-2,

<

-4.

-5.

i i

1 1

1

J— —

-L - - - _ u

i 1 !

-! 1 1 \

1

1 3.00 - - 2.00 - 0 1.00 - 1 0.00 - ^-1.00 - 8 -2.00 " ^ -3.00 - -4.00 - -5.00 -

1 __

1

1 r

1 1 r

L

1

-1 L L

1 r

1

1

; \

'

1

1 \

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s

)

0.8

a) horizontal acceleration {Table) b) horizontal acceleration (Abase)

5.00 -

4.00 -

3.00 -

2.00 -

1.00 - 0.00 -

_o -1.00 - o

o -2.00 -

o< -3.00 -

-4.00 '

-5.00 -

0 0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)0.8

c) horizontal acceleration (Afram)

5.00

3.00

d) horizontal acceleration (AframTS)

2.00

e) horizontal acceleration (Agrid)

2.00

-2.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-4. Horizontal displacement and acceleration histories for Test 20 on ceiling

system CS1.

NISTNCSTAR 1-5D. WTC Investigation 83
Appendix A

6.00 - 5.00 - ^ 4.00 - 3 3.00 - = 2.00 -

1 _i

1 I 1

1 1 1

1 1 < 1

1 1 .2 1.00

T= 0.00 o -1.00 o -2.00 - y -3.00 ' < -4.00 ^ -5.00 - -6.00 -

-1 r

L - — r

1 -L

1 1 ' 1 T

\ "J

1

6.00

5.00 4.00

3.00

2.00

1.00 0.00

1.00 2.00

3.00 4.00

5.00 6.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s

)

0.8

a) vertical acceleration {Table) b) vertical acceleration {Abase)

6.00

5.00 _ 4.00 3 3.00

r- 2.00

.2 1.00

1= 0.00 u -1.00 o -2.00 o -3.00 < -4.00 -5.00

-6.00

<

0.2 0.4 0.6 Time (s)0.8

6.00

5.00 4.00 +

3.00 2.00

1.00 0.00

-1.00

-2.00 -3.00

-4.00

-5.00 -6.00 0 0.2 0.4 0.6 Time (s)

0.8

c) vertical acceleration {Afram) d) vertical acceleration {AframTS)

6.00 - 5.00 - ^ 4.00 - 3 3.00 ^ E 2.00 - .2 1.00 -

. 1 1 1 1 -1

) 1] 1 1 1 1

' 1 Ml 1 1 1 1 1

J J J (_ j1 ^ 0.00 G -1.00 ^ o -2.00 - y -3.00 - < -4.00 ~

\ 1

1 1 1 1 1

~

1 11 1 1 1 1 -5.00 - -6.00 \

1 1

1

0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6

e) vertical acceleration {Agrid)

Figure A-5. Vertical acceleration histories for Test 20 on ceiling system CS1.

84 NIST NCSTAR 1-5D. WTC Investigation
Test Histories

<

Simulator control (Table)

Simulator platform (Abase)

Roof frame (Afram)

Suspension grid (Agrid) ^—Roof frame side (AframTS)

0.2 0.4 0.6 0.8 Period (s) a) horizontal response spectra

1 1.2 1.4 1.6 1.8 2

<

12.00

10.00

8.00

6.00

4.00

2.00

0.00

0.1

to

<

12.00

10.00

8.00

6.00

4.00 -

2.00

0.00

Simulator control (Table)

-Q- - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Rooffi^me side (AframTS)

1 10 Frequency (Hz)

b) horizontal response spectra

100

T

I—\—I—I—I—I

\—1

I—I—I I—II—I—I—I—I—

r

Simulator control (Table)

Q - - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) ^—Roof frame side (AframTS)

0.2 0.4 0.6 0.8 Period (s) c) vertical response spectra1 1.2 1.4 1.6

"1—I—I

r-T — Simulator control (Table)

- Simulator platform (Abase)

— Roof frame (Afram) — Suspension grid (Agrid) —Roof frame side (AframTS)

0.1 1 10 Frequency (Hz)

d) vertical response spectra

Figure A-6. Response spectra for Test 20 on ceiling system CS1.

100

NISTNCSTAR 1-5D, WTC Investigation 85
Appendix A

6.00 ^ 4.00 ^ 2.00 oi 0.00

-2.00 - < -4.00 -

-6.00 -

0

6.00 _ 4.00 -

c 2.00 oI

0.00

-2.00 o< -4.00

-6.00

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

a) horizontal acceleration {Table) b) horizontal acceleration (Abase)

6.00 _ 4.00

to ^ 2.00 -

o1 0.00 o -2.00 J

< -4.00 T

-6.00 0 0.2

h0.4 0.6 Time (s)

-6.00

0.8 0.2 0.4 0.6 Time (s)

0.8

c) horizontal acceleration {Afram)

6.00 r- _ 4.00 +

d) horizontal acceleration (AframTS)

2.00 -

< ^.00 -

-6.00 \-

1 0.00— ^..^^^.^ .

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

2.00

0.00

-2.00

Time (s)

e) horizontal acceleration (Agrid)

2.00

-2.00

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-7. Horizontal displacement and acceleration histories for Test 14 on ceiling

system CS2.

86 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

4.00

2.00 -

5

0.00 - _oo

o -2.00 - <

-4.00 -

0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table)

-4.00

0.2 0.4 0.6 0.^ Time (s)

c) vertical acceleration (Afram)

4.00

4.00 3 2.00 5

1 0.00

§ -2.00

-4.00

0.2 0.4 0.6 0.8 Time (s)

b) vertical acceleration (Abase)

-4.00

0.2 0.4 0.6 Time (s)

0.8

d) vertical acceleration (AframTS)

3 2.00

I 0.00

-4.00

1

1

i

1

1

1

1

0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6

e) vertical acceleration (Agrid)

Figure A-8. Vertical acceleration histories for Test 14 on ceiling system CS2.

NISTNCSTAR 1-5D, WTC Investigation 87
Appendix A

<

Simulator control (Table)

Q' - - Simulator platfomi (Abase)

' - -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

0 0.2 0.4 0.6

a H B B B H p p a to B H a H Ih B B

0.8 1 1.2 1.4 1.6 1.8 2

Period (s) a) horizontal response spectra

25.00

20.00 c

_o 15.00

(U 10.00

CJ < 5.00

Simulator control (Table)

- - - Simulator platfomi (Abase

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

0.00

0.] Frequency (Hz)

b) horizontal response spectra

10 100

Simulator control (Table)

Simulator platform (Abase)

Roof frame (Afram)

Suspension grid (Agrid)

Roof frame side (AframTS)

BBBBBPBBW-

' B B pa BB

0.2 0.4 0.6 0.8 1 1.2 Period (s) c) vertical response spectra

1.4 1.6

60

10.00

8.00

6.00

4.00

2.00

0.00

Simulator control (Table)

-Q- - ' Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) -X—Roof frame side (AframTS)

L _ U

1 I

. 1- J- J.

I

I I

0.1 1 10 Frequency (Hz)

d) vertical response spectra

Figure A-9. Response spectra for Test 14 on ceiling system CS2.

100

88 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

6.00 _ 4.00

I

0.00

•S -2.00 ^

<-4.00 +

-6.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

a) horizontal acceleration (Table) b) horizontal acceleration (Abase)

6.00 ^ 4.00 ^ 2.00 o

"I 0.00 §-2.00

<-4.00

-6.00 0 0.:

-n h0.4 0.6 Time (s)

-6.00

0.8 0.2 0.4 0.6 Time (s)

0.8

c) horizontal acceleration (Afram)

6.00

d) horizontal acceleration (AframTS)

4.00

til o

2 0.00 3 -2.00 < -4.00

-6.00

1

1

1

1

1 a J. L J

1

1

1

r 1 1

1

\

r

1

\

1 1

i

\

0.2 0.4 0.6 0.8 1 1.2 Time (s

)

1.4 1.6 1.8

2.00

e) horizontal acceleration (Agrid)

2.00

-2.00 -2.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-10. Horizontal displacement and acceleration histories for Test 20 on celling

system CS2.

NISTNCSTAR 1-5D, WTC Investigation 89
Appendix A

6.00 _ 4.00 ^ 2.00 oi 0.00 u-2.00 o< -4.00

-6.00 0 0.2 0.4 0.6 0.8 Time (s

)

a) vertical acceleration (Table)

-6.00

0.2 0.4 0.6 0.8 Time (s)

c) vertical acceleration (Afram)

6.00

6.00

4.00 -

2.00 -- 5

re 0.00 - S

(Uu

-2.00 "

u< -4.00 --

-6.00 --

0.2 0.4 0.6 Time (s)

0.8

b) vertical acceleration {Abase)

0.2 0.4 0.6 Time (s)

0.8

d) vertical acceleration (AframTS)

5

4.00

0.00 o -2.00 ^ < ^.00

-6.00

! 1 1

1

1

I

I 11 1

1 (V" 'n :

:

1 1 1

1 1 1

1

1

1

1

1

1 T 1

1

1

1

1

1 1 1 1

0 0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6 1.8

e) vertical acceleration (Agrid)

Figure A-11. Vertical acceleration histories for Test 20 on ceiling system CS2.

90 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

Simulator control (Table)

- - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roofframe side (AframTS)

IjlH B B 'W I

0.2 0.4 0.6 0.8 1 1.2 Period (s) a) horizontal response spectra

1.4

! ^ta'BB ^IB B'B B

1.6 1.8 2

<

8.00 7.00

6.00

5.00 4.00

3.00

2.00

1.00 0.00

Simulator control (Table)

-C3 - - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roofframe side (AframTS)

0.1 1 10 Frequency (Hz)

b) horizontal response spectra

100

14.00 Simulator control (Table)

-Q - - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

I I

I I

I I

I I

B B'B B i WB>

0.2 0.4 0.6 0.8 1 1.2 Period (s) c) vertical response spectra

1.4 1.6

14.00 —

12.00 - f 10.00

8.00 -

6.00

4.00 -

2.00 -

0.00 —

Simulator gontrol (Table)

Simulator platform (Abase)

'Roof frame (Afram)

•Suspension grid (Agrid)

Roof frame side (AframTS)

0.1 10 100 Frequency (Hz)

d) vertical response spectra

Figure A-12. Response spectra for Test 20 on ceiling system CS2.

NISTNCSTAR 1-5D, WTC Investigation 91
Appendix A

10.00

8.00 T

AA 1 D.UO y

4.00 -r o O AA

A AA 0.00 -

QJ ^ AA -2.00 —

"uO -4.00 +

o< -6.00 -

-8.00 J

-10.00 -

1 (\ f\f\ JU.UU

0 f\f\ D.UU

c: 4.UU o z.uu

I' n f\r\ v.yjyj - 1 nn -- -Z.uu

"oo -4.00 -- < -6.00 -- -8.00 -

-10.00 +

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

a) horizontal acceleration (Table) b) horizontal acceleration (Abase)

10.00 ^ 8.00 i

6.00 t

4.00 +

2.00 I

0.00 —

-2.00 "

-4.00 -

-6.00 -

-8.00 i

-10.00 ^

0

10.00 1 8.00 - - 6.00 - 4.00 - 5 2.00 - a 0.00 - o -2.00 ^ 8 -4.00 - < -6.00 - -8.00 - -10.00 -

1

1

_ 1

1 i

1 T

1

1

1

4-

1 T

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

c) horizontal acceleration (Afram) d) horizontal acceleration (AframTS)

0.2 0.4 0.6 0.8

3.00

1 1.2 Time (s)

e) horizontal acceleration (Agrid)

3.00 ^ 2.00 ^ I.OO

1.4 1.6 1.8 2

0.2 0.4 0.6 Time (s)

0.8 0 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-13. Horizontal displacement and acceleration histories for Test 23 on ceiling

system CS2.

92 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

8.00 6.00 3 4.00 5 2.00 i 0.00 1-2.00

u-4.00

^-6.00

-8.00

6 3 4 i 2

-6.'

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table) b) vertical acceleration (Abase)

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

c) vertical acceleration (A/ram) d) vertical acceleration (AframTS)

10.00 -

8.00 - 6.00 - 4.00 - 2.00

0.00 -

o -2.00 ^.00

<

-6.00 - -8.00 -

-10.00 -

0 0.2 0.4 0.6 0.8 1 1.2 Time (s

)

1.4 1.6

e) vertical acceleration (Agrid)

Figure A-14. Vertical acceleration histories for Test 23 on ceiling system CS2.

NISTNCSTAR 1-5D, WTC Investigation 93
Appendix A

25.00 ^ 20.00

o

o

cj

CJ <

"T—I—Ii—i—I—I

'—I—

r

Simulator control (Table)

- - -Q' - - Simulator platfonn (Abase)

- - - -Roof frame (Afram)

Suspension grid (Agrid) —X—Roof frame side (AframTS)

0.2 0.4 0.6 0.8 1 1.2 Period (s) a) horizontal response spectra

1.4 1.6 1.

25.00 I

;S 20.00 T

.| 15.00 -

I 10.00 - < 5.00 -r

0.00 -

I I r I r; Simulator control (Table)

Simulator platfonn (Abase)

- - -Roof frame (Afram)

—Suspension grid (Agrid) —Roof frame side (AframTS)

0.1 10 100 Frequency (Hz)

b) horizontal response spectra

20.00 r 1" rT^T" ~i—I

I—I—I—1—I—I—i—I—

r

Simulator control (Table) a- Simulator platform (Abase)

- ' -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

I - I- ^ + H ^ -I - 1- I- 1- ^ -I

-

0.00

20.00 S 15.00 5

S 10.00

(U

OJ

CJ < 5.00

0.00

0.2 0.4 0.6 0.8 1 1.2 Period (s) c) vertical response spectra1.4 1.6 1.8 2

Simulator control (Table)

Simulator platfomi (Abase)

'Roof frame (Afram)

•Suspension grid (Agrid) -X—Roof frame side (AframTS)

0.1 1 10 100 Frequency (Hz)

d) vertical response spectra

Figure A-15. Response spectra for Test 23 on ceiling system CS2.

94 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

6.00 ^ 4.00 ^ 2.00 oI

0.00 -3-2.00 <-4.00

-6.00 0 0.2 0.4 0.6 0.8 Time (s)

a) horizontal acceleration (Table)

6,00 ^ 4.00 ^ 2.00

"I 0.00

-2.00 T

<-4.00

-6.00

0.2 0.4 0.6 Time (s)0.8

b) horizontal acceleration (Abase)

6.00 _ 4.00 -

so

=' 2-00 -

I

0.00 3-2.00

J<-4.00

-6.00 0 0.2 0.4 0.6 0.8 Time (s)

c) horizontal acceleration (Afram)

0.2 0.4 0.6 Time (s)0.8

d) horizontal acceleration (Afram TS)

6.00

0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6 1.8

2.00

e) horizontal acceleration (Agrid)

2.00

-2.00 -2.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-16. Horizontal displacement and acceleration histories for Test 14 on ceiling

system CSS.

NISTNCSTAR 1-5D. WTC Investigation 95
Appendix A

4.00 5 2.00 c

oi 0.00

4.00

<

-2.00

-4.00 -4.00

0.2 0.4 0.6 0.: Time (s)

a) vertical acceleration (Table)

0.2 0.4 0.6 0.8 Time (s

)

b) vertical acceleration (Abase)

4.00 4.00

-4.00 -4.00

0.2 0.4 0.6 0.: Time (s )

c) vertical acceleration (Afram)

0.2 0.4 0.6 Time (s)0.8

d) vertical acceleration (AframTS)

4.00

e) vertical acceleration (Agrid)

Figure A-17. Vertical acceleration histories for Test 14 on ceiling system CSS.

96 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

Simulator control (Table)

- - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roofframe side (AframTS)

0.00

20.00

15.00

10.00

5.00

0.00

0.2 0.4 0.6 0.8 1 Period (s) a) horizontal response spectra

JHMHHIIIMHIlHIIillMMH Bn

1.2 1.4 1.6 1.8 2

Simulator control (Table)

-Q - • - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid)

-)i—Roof frame side (AframTS)

0.1 1 10 Frequency (Hz)

b) horizontal response spectra

100

Simulator control (Table)

'Q- - - Simulator platfonn (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

B B B B B M B'B

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Period (s) c) vertical response spectra

1.8

8.00

7.00

6.00

5.00 4.00

3.00

2.00

1.00 0.00

Simulator control (Table)

-Q- - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) -X—Roof frame side (AframTS)

0.1 1 Frequency (Hz)

d) vertical response spectra

10 100

Figure A-18. Response spectra for Test 14 on ceiling system CSS.

NISTNCSTAR 1-5D, WTC Investigation 97
Appendix A

1 < f\f\

1 j.UU

10.00 --

5.00 "

5

0.00 -

-5.00 < -10.00 --

-15.00 -

1 ^ nn I J.UU

1 0 no - - CO 5.00 o

0.00

-5.00 - < -10.00 -

-15.00 --

0.2 0.4 0.6 Time (s

)

0.8 0.2 0.4 0.6 Time (s )

0.8

a) horizontal acceleration (Table) b) horizontal acceleration (Abase)

15.00 15.00

10.00 c 5.00 Oi 0.00

"5 -5.00 < -10.00

-15.00 0 0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

c) horizontal acceleration (Afram)

15.00 _ 10.00

d) horizontal acceleration (AframTS)

-59 5

< -

2.00

g 0.00

CO Q

-2.00

0.2 0.4 0.6 0.8 1 1.2 Time (s)

e) horizontal acceleration (Agrid)

2.00

1.4 1.6

-2.00

0.2 0.4 0.6 Time (s

)

0.8 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-19. Horizontal displacement and acceleration histories for Test 20 on ceiling

system CS3.

98 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

8.00 —

6.00 - 3 4.00 -

5 2.00 - i 0.00 I

-2.00 -

B -4.00 - ^ -6.00 -

-8.00 —

8.00 6.00 5 4.00 5 2.00 I

0.00 i

-2.00 8 -4.00 ^ -6.00

-8.00

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table) b) vertical acceleration (Abase)

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s )

0.8

c) vertical acceleration (Afram) d) vertical acceleration (AframTS)

8.00 -

6.00 -

4.00 -

_s 2.00 -

0.00 - _oo

-2.00 - ^.00 - < -6.00 -

-8.00 -

0.2 0.4 0.6 0.8 1 Time (s)

1.2 1.4 1.6

e) vertical acceleration (Agrid)

Figure A-20. Vertical acceleration histories for Test 20 on ceiling system CSS.

NISTNCSTAR 1-5D, WTC Investigation 99
Appendix A

35.00 -

, , 30.00 ~

39 25.00 Q

20.00 -

15.00 o ^

o

o 10.00 t

<

5.00

0.00 -

Simulator control (Table)

Simulator platform (Abase)

Roof frame (Afram)

Suspension grid (Agrid)

Roof frame side (AframTS)

0.6 0.8 1 1.2 Period (s) a) horizontal response spectra

35.00

30.00

25.00

20.00

15.00

10.00 -

5.00 ^

0.00

0.1

Simulator control (Table)

Simulator platform (Abase)

•Roof frame (Afram)

Suspension grid (Agrid)

•Roof frame side (AframTS)

1 10 Frequency (Hz)

b) horizontal response spectra

100

o<

Simulator control (Table)

- - Simulator platform (Abase)

- - -Roof frame (Afram)

——Suspension grid (Agrid) —Roof frame side (AframTS)

0.2 0.8 1 1.2 1.4 1.6 1.8 2

Period (s)

0.4 0.6

c) vertical response spectra

20.00 3 15.00

2 10.00 o< 5.00

0.00

Simulator control (Table)

-o- - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (A —Roofframe side (Afr;rid) amTS)

0.1 1 10 Frequency (Hz)

d) vertical response spectra

Figure A-21. Response spectra for Test 20 on ceiling system CSS.

100

100 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

o

oJ<

15.00

10.00

5.00

0.00

-5.00 -

10.00 -

15.00 —

15.00

10.00

5.00

0.00

-5.00 < -10.00

-15.00 0 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

a) horizontal acceleration (Table) b) horizontal acceleration (Abase)

15.00

10.00

5.00

0.00

-5.00 ^

10.00 \

15.00 ^

0

15.00 - _ 10.00 - 60 ^ 5.00 - oi 0.00 - I

-5.00 - < -10.00 -

1

1 n 1

-15.00 -

1

1

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s

)

0.8

c) horizontal acceleration (A/ram)

15.00 - _ 10.00 -

60 T 5.00 I

0.00 Z -5.00 - < -10.00 -

-15.00

d) horizontal acceleration (AframTS)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Time (s

)

e) horizontal acceleration (Agrid)

3.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-22. Horizontal displacement and acceleration histories for Test 23 on ceiling

system CSS.

NISTNCSTAR 1-5D, WTC Investigation 101
Appendix A

6.00 ^ 4.00

tJO ^ 2.00 +

o

'I 0.00 I

-2.00 <-4.00

-6.00

0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table)

0.2 0.4 0.6 Time (s)

0.8

c) vertical acceleration (Afram)

6.00

, 4.00

6.00 _ 4.00 ^ 2.00 -

oI

0.00 o -2.00 +

<-4.00

-6.00

0.2 0.4 0.6 Time (s)0.8

b) vertical acceleration (Abase)

6.00 _ 4.00 -- ^ 2.00 +

oI

0.00 o -2.00 < -4.00

-6.00

0.2 0.4 0.6 Time (s)

0.8

d) vertical acceleration (AframTS)

-6.00

0.2 0.4 0.6 0.8 1 1.2 1.4 Time (s)

1.6

e) vertical acceleration {Agrid)

Figure A-23. Vertical acceleration histories for Test 23 on celling system CSS.

102 NISTNCSTAR 1-5D. WTC Investigation
Test Histories

— Simulator control (Table)

• - Simulator platform (Abase)

-Roof frame (Afram) — Suspension grid (Agrid) —Roof frame side (AframTS)

MMHHHHIHHHHHHmuiUIIIIUIUlBBBI CBBI IB

2 3 4 5 Period (s) a) horizontal response spectra

30.00

25.00

20.00

15.00

10.00

5.00

0.00

Simulator control (Table)

Simulator platform (Abase)

"Roof frame (Afram)

•Suspension grid (Agrid)

• Roof frame side (AframTS)

0.1 Frequency (Hz)

b) horizontal response spectra

10 100

Simulator control (Table)

-Q - - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid) —Roof frame side (AframTS)

2 3 Period (s) c) vertical response spectra

14.00

12.00

10.00 5

8.00 D 6.00 D

'•J 4.00 <

2.00

0.00

-Q. . Simulator control (Table)

Simulator platform (Abase)

'Roof frame (Afram)

•Suspension grid (Agrid)

• Roof frame side (AframTS)

0.1 1 10 Frequency (Hz)

d) vertical response spectra

Figure A-24. Response spectra for Test 23 on ceiling system CSS.

100

NISTNCSTAR 1-5D. WTC Investigation 103
Appendix A

u

u

3.00

2.00

1.00

0.00

1.00

2.00

3.00

3.00

2.00

1.00

0.00

-1.00 < -2.00 -

-3.00

0 0.2 0.4 0.6 0.8 Time (s)

a) horizontal acceleration (Table)

\

\ \ K

0 0.2 0,4 0.6 0.8 Time (s)

b) horizontal acceleration (Abase)

3.00 J

2.00 -

1.00 - 5

re 0.00 -

CJ

CJ -1.00 -

CJ < -2.00 -

-3.00 0 0.2 0.4 0.6 Time (s)

0.8

c) horizontal acceleration (Afram)

3.00

.0 0.2 0.4 0.6 0.8 Time (s)

d) horizontal acceleration (AframTS)

2.00

I

0.00

CO

-2.00

e) horizontal acceleration (Agrid)

2.00

£ 0.00

-2.00 0 0.2 0.4 0.6 0.8 Time (s)

f) horizontal displacement (Dbase)

0 0.2 0.4 0.6 0.8 Time (s

)

g) horizontal displacement (Dcntr)

Figure A-25. Horizontal displacement and acceleration histories for Test 14 on ceiling

system CS4.

104 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

4.00

3.00 3 2.00 3 1.00 i 0.00 1-1.00

'd -2.00 ^ -3.00

-4.00

4.00

3.00 2.00

1.00 0.00

-1.00

-2.00

-3.00 -4.00

0.2 0.4 0.6 Time (s)0.8 0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table) b) vertical acceleration {Abase)

0.2 0.4 0.6 0.: Time (s)

c) vertical acceleration (A/ram)

0.2 0.4 0.6 Time (s)

0.8

d) vertical acceleration {AframTS)

-4.00

0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6

e) vertical acceleration {Agrid)

Figure A-26. Vertical acceleration histories for Test 14 on ceiling system CS4.

NISTNCSTAR 1-5D. WTC Investigation 105
Appendix A

6.00 T

5.00

4.00 -

Q

"cO 3.00 O

o

CJ 2.00 t( <

1.00

0.00 1

Simulator control (Table)

Simulator platform (Abase)

Roof frame (Afram)

•Suspension grid (Agrid)

Roof frame side (AframTS)

0.2 0.4

mWWIt I>1 B B 111 H 'H'BI

' B 'I»

0.6 0.8 1 1.2 1.4 Period (s) a) horizontal response spectra

B B Bl B

1.6

B B lil B BiB 4i

1.8 2

6.00 r

5.00

4.00

_o 3.00 --

O 2.00 <

1.00 -

0.00 --

Simulator control (Table)

Simulator platform (Abase)

•Roof frame (Afram)

•Suspension grid (Agrid)

Roof frame side (AframTS)

1 Frequency (Hz)

b) horizontal response spectra

10 100

Simulator control (Table)

- - - Simulator platfonn (Abase)

- - -Roof frame (Afram)

—-Suspension grid (Agrid) —Roof frame side (AframTS)

0.2 0.4 0.6

»IBBBBBBBB B B B fH B B

0.8 1 1.2 1.4 1.6 Period (s) c) vertical response spectra

0.1 1 10 100 Frequency (Hz)

d) vertical response spectra

Figure A-27. Response spectra for Test 14 on ceiling system CS4.

106 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

-6.00

6.00 - ^ 4.00 -

to ^ 2.00 -

o

"I 0.00 S -2.00 o

<-4.00

-6.00 0 0.2 0.4 0.6 0.8 Time (s)

a) horizontal acceleration (Table)

0.2 0.4 0.6 Time (s)

0.8

b) horizontal acceleration (Abase)

6.00 ^ 4.00 ^ 2.00 oI 0.00 ^-2.00

< AOO

-6.00

6.00 ^ 4.00 ^ 2.00 -- oi 0.00 I

-2.00 <-4.00

-6.00 0 0.2 0.4 0.6 0.8 Time (s)

c) horizontal acceleration (Afram)

0.2 0.4 0.6 Time (s)

0.8

d) horizontal acceleration (AframTS)

6.00

2.00

0.2 0.4 0.6 0.8 1 1.2 Time (s)

e) horizontal acceleration (Agrid)

2.00

1.4 1.6

-2.00 -2.00

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)

0.8

f) horizontal displacement (Dbase) g) horizontal displacement (Dcntr)

Figure A-28. Horizontal displacement and acceleration histories for Test 20 on ceiling

system CS4.

NISTNCSTAR 1-5D. WTC Investigation 107
Appendix A

^ -2.00 < -4.00

-6.00

0.2 0.4 0.6 Time (s)

0.8

a) vertical acceleration (Table)

0.2 0.4 0.6 Time (s)0.8

c) vertical acceleration (A/ram)

6. _ 4. ^ 2. 5

i

0- o -7

00

00

<-4

00 -

00 -

00

00

6.00 0 0.2 0.4 0.6 0.8 Time(s)

b) vertical acceleration (Abase)

0 - 0.2 0.4 0.6 0.8 Time(s)

d) vertical acceleration (AframTS)

6.00 T

4.00

c 2.00 -- o

2

0.00 -

o

SJ -2.00 "

o

CJ < -4.00 -

-6.00 --

0 0.2 0.4 0.6 0.8 1.2 1.4 1.6 Time (s)

e) vertical acceleration (Agrid)

Figure A-29. Vertical acceleration histories for Test 20 on celling system CS4.

108 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

Simulator control (Table)

a - Simulator platfomi (Abase)

- - -Roof frame (Afram)

Suspension gnd (Agrid) —Roof frame side (AframTS)

0.2 0.8 1 1.2 1.4 1.6 1.8 2 Period (s)0.4 0.6

a) horizontal response spectra

0.1 1 10 Frequency (Hz)

b) horizontal response spectra

100

<

"T—I

I—I—

r

~i—I—i—I—

r

Simulator control (Table)

-Q - - - Simulator platform (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid)

-)<—Roof frame side (AframTS)

I I 1 J

.

I I

I I 1 i

,

I I

0.2 BBBB BB BBBBBBBBBWBB

0.8 1 1.2 1.4 1.6 1.8 2 Period (s)

0.4 0.6

c) vertical response spectra

12.00 T

10.00

8.00 -

6.00 - o

'J 4.00 - <

2.00 -

0.00 -

0.1 10 100 Frequency (Hz)

d) vertical response spectra

Figure A-30. Response spectra for Test 20 on ceiling system CS4.

NISTNCSTAR 1-5D, WTC Investigation 109
Appendix A

6.00

4.00

2.00

_5

1= 0.00 5

-2.00 u< -4.00

-6.00

6.00 ^ 4.00 T ^ 2.00 oI 0.00 o -2.00 o< -4.00

-6.00 0 0.2 0.4 0.6 0.8 Time (s)

a) horizontal acceleration {Table)

0 0.2 0.4 0.6 0.8 Time(s)

b) horizontal acceleration {Abase)

6.00

0 0.2 0.4 0.6 0.8 Time (s

)

c) horizontal acceleration {Afram)

6.00

0.2 0.4 0.6 Time (s)0.8

d) horizontal acceleration {AframTS)

0.2 0.4 0.6 0.8 1 1.2 1.4 Time (s) e) horizontal acceleration {Agrid)

3.00

1.6

0.2 0.4 0.6 Time (s)

0.8 0.2 0.4 0.6 Time (s)0.8

f) horizontal displacement {Dbase) g) horizontal displacement {Dcntr)

Figure A-31. Horizontal displacement and acceleration histories for Test 23 on celling

system CS4.

110 NISTNCSTAR 1-5D, WTC Investigation
Test Histories

10.00

5.00

0.00

-5.00

-10.00

) 0.2 0.4 0.6 0.: Time (s)

a) vertical acceleration (Table)

10.00

0 0.2 0.4 0.6 Time (s)

0.8

c) vertical acceleration {Afram)

10.00

10.00

-10.00

0.2 0.4 0.6 Time (s)

0.8

b) vertical acceleration (Abase)

10.00

-10.00

0.2 0.4 0.6 Time (s)0.8

d) vertical acceleration (AframTS)

SB 5.00

I

0.00

d -5.00 <

-10.00

0.2 0.4 0.6 0.8 1 1.2 Time (s)

1.4 1.6 1.8

e) vertical acceleration (Agrid)

Figure A-32. Vertical acceleration histories for Test 23 on ceiling system CS4.

NISTNCSTAR 1-5D, WTC Investigation 111
Appendix A

I I —I—I—i—

r

Simulator control (Table)

-Q - - - Simulator platfonn (Abase)

- - -Roof frame (Afram)

Suspension grid (Agrid)

-><—Roof frame side (AframTS)

0.2 0.4 0.6

mil mi l lU MM lU B BP BBBHB H BBBBHBa

0.8 1 1.2 1.4 1.6 1.8 2 Period (s) a) horizontal response spectra

10.00

8.00

6.00

4.00

2.00

0.00

16.00

Simulator control (Table)

- - - Simulator platform (Abase)

" - - Roo f frame { A fram)

Suspension grid (Agrid) -X—Roof frame side (AframTS)

1 Frequency (Hz)

b) horizontal response spectra

10 100

Simulator control (Table)

SiiTiulator platform (Abase)

Roof frame (Afram)

Suspension grid (Agrid) ^—Roof frame side (AframTS)

. 4- J. -I -I - I- k

I I i I I I L 1 J _l_t_ L B WBBBBBBB BIBIB IL

0.2 0.4 0.6 0.8 1 1.2 Period (s) c) vertical response spectra

1.4 1.6

0.1 1 10 Frequency (Hz)

d) vertical response spectra

Figure A-33. Response spectra for Test 23 on ceiling system CS4.

100

112 NISTNCSTAR 1-5D, WTC Investigation