NISTNCSTAR1-1C

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Maintenance and Modifications to

Structural Systems

David A. Fanella

Arnaldo T. Derecho

S. K. Ghosh

National Institute of Standards and Technology Technology AdministroJion • U.S. Department of Comi

NISTNCSTAR1-1C

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Maintenance and Modifications to

Structural Systems

David A. Fanella

Arnaldo T. Derecho

S. K. Ghosh

S. K. Ghosh Associates, Inc.

September 2005

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary

Technology Administration

Michelle O'Neill, Acting Under Secretary for Technology

National Institute of Standards and Technology

William Jeffrey, Director
Disclaimer No. 1

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

Disclaimer No. 2 The policy of NIST is to use the International System of Units (metric units) in all publications. In this document,

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

Disclaimer No. 3

Pursuant to section 7 of the National Construction Safety Team Act, the NIST Director has determined that certain evidence received by NIST in the course of this Investigation is "voluntarily provided safety-related information" that is "not directly related to the building failure being investigated" and that "disclosure of that information would inhibit the voluntary provision of that type of information" (15 USC 7306c).

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

provided to NIST under nondisclosure agreements.

Disclaimer No. 4 NIST takes no position as to whether the design or construction of a WTC building was compliant with any code

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

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

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

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

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

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

Use in Legal Proceedings

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

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

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

Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-1C, 392 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

This report documents maintenance and modifications that were made to the structural systems of World

Trade Center (WTC) 1, 2, and 7. Included are the Port Authority of New York and New Jersey

(PANYNJ or Port Authority) guidelines for inspection, repair, and modifications to the structural systems

of WTC 1, 2, and 7. Discussed are the guidelines that governed the inspection and strengthening of

existing structural members.

Also contained in this report is a summary of the structural inspection programs that were undertaken

during the occupancy of WTC 1, 2, and 7. Included are summaries of the facility condition survey reports

that were produced for WTC 1, 2, and 7 and descriptions of the structural integrity inspection programs

that were undertaken for WTC 1 and WTC 2.

The significant modifications and repairs that were made to the structural systems of WTC 1, 2, and 7 from initial occupancy to September 11, 2001, are also documented. A discussion on the repairs that were made after the February 1993 bombing of WTC 1 is also included.

Appendixes to this report include copies of referenced documents, including the Tenant Construction

Review Manuals; the Standards for Structural Integrity Inspection of the WTC towers; and the Architectural and Structural Design Guidelines, Specifications, and Standard Details, which were all issued by the Port Authority regarding inspection, repair, and modifications to the structural systems of

WTC 1,2, and 7.

Keywords: Bombing, construction, facility condition survey report, guidelines, inspection, modifications,

repair, strengthening, structural integrity inspection program, structural systems, World Trade Center.

NISTNCSTAR 1-1 C, WTC Investigation iii
Abstract

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IV NISTNCSTAR 1-1C, WTC Investigation
Table of Contents

Abstract iii

Table of Contents v

List of Figures ix

List of Tables xi

List of Acronyms and Abbreviations xiii

Metric Conversion Table xv

Preface xix

Executive Summary xxix

Chapter 1 Introduction 1

Chapter 2 Guidelines for Inspection, Repair, and Modifications to Structural Systems 3

2. 1 Tenant Construction Review Manuals 3

2.1.1 1971 Edition 4

2.1.2 1979 Edition 9

2.1.3 March 1984 Edition, Revised March 1990 14

2.1.4 March 1997 Edition 17

2.2 Standards for Structural Integrity Inspection of the World Trade Center Towers A & B 18

2.2.1 Overview 18

2.2.2 Inspection Program 20

2.2.3 In-House Inspection Personnel 24

2.2.4 Outside Consultants and Suppliers of Special Services 25

2.2.5 Record Keeping and Follow-up Procedure 26

2.2.6 Excluded Work 28

2.3 Architectural and Structural Design Guidehnes, Specifications and Standard Details 28

2.3.1 Structural Design Guidelines 28

2.3.2 Structural Specifications 30

2.4 References 31

Chapters Structural Inspection Programs During the Occupancy of WTC 1, 2, and 7 33

3.1 Facility Condition Survey Reports 33

3.1.1 Port Authority Facility Condition Survey Program - WTC 2 33

NISTNCSTAR 1-1 C, WTC Investigation v
Table of Contents

3.1.2 Port Authority Facility Condition Survey Program - WTC 1 43

3.1.3 Port Authority Facility Condition Survey Program - WTC 7 53

3.1.4 Due Diligence Physical Condition Survey - WTC 1 and WTC 2 58

3.2 Structural Integrity Inspection Program 59

3.2.1 Overview 59

3.2.2 Summary of Structural Integrity Inspection Program Reports 61

3.3 Summary of Structural Inspection Programs 80

3.3.1 Inspection Programs 80

3.3.2 Findings from Inspection Programs 81

3.4 References 93

Chapter 4 Significant Modifications and Repairs to the Structural Framing Systems of

WTC 1, 2, and 7 95

4.1 Overview ....95

4.2 Modifications and Repairs Made to WTC 1 95

4.2.1 Openings Made in Floor Slabs 95

4.2.2 Openings in Floor Slabs That Were Subsequently Closed 95

4.2.3 Structural Members That Were Reinforced 97

4.2.4 Repair Work Following the February 26, 1993 Explosion 97

4.2.5 Other Modifications 1 14

4.3 Modifications and Repairs Made to WTC 2 114

4.3. 1 Openings Made in Floor Slabs 114

4.3.2 Openings in Floor Slabs That Were Subsequently Closed 115

4.3.3 Structural Members That Were Reinforced 1 16

4.3.4 Other Modifications 116

4.4 Modifications and Repairs Made to WTC 7 1 1

6

4.4. 1 Modifications Made due to New Loading Requirements 1 16

4.4.2 Openings Made in Floor Slabs 119

4.4.3 Modifications Made to Beam Webs and Flanges 119

4.4.4 Other Modifications 120

4.5 References 121

vi NISTNCSTAR 1-1C. WTC Investigation
Table of Contents

Appendix A

Tenant Construction Review IVIanual - 1971 123

Appendix B

Tenant Construction Review Manual - 1979 139

Appendix C

Tenant Construction Review Manual - 1990 157

Appendix D

Tenant Construction Review Manual - 1997 177

Appendix E Standards for Structural Integrity Inspection of WTC Towers A & B 199

Appendix F Architectural and Structural Design Guidelines, Specifications, and

Standard Details 255

Appendix G

Supporting Documents 299

NISTNCSTAR 1-1C, WTC Investigation \ ii
Table of Contents

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Vlll NISTNCSTAR 1-1C, WTC Investigation
List of Figures

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

disaster xxi

Figure 3-1. Typical inspection locations of exterior wall per 1990 Condition Survey Report of

WTC 2 36

Figure 3-2. Splice details at typical inspection locations of exterior wall per the 1990 Condition

Survey Report of WTC 2 38

Figure 3-3. Typical inspection locations of floor framing per the 1990 Condition Survey Report of

WTC 2 41

Figure 3-4. Recommendations made in the 1997 Facility Condition Survey Report for WTC 7 57

Figure 3-5. Estimated manpower and cost estimates for structural integrity inspections for WTC 1 and WTC 2 63

Figure 4-1 . Damage assessment for WTC 1 at Level B 1 99

Figure 4-2. Damage assessment for WTC 1 at Level B2 100

Figure 4-3. Bracing on south face of WTC 1 damaged by blast 101

Figure 4-4. Repair of damaged bracing in levels Bl and B2 of WTC 1 103

Figure 4-5. Repair of damaged spandrel beam in level Bl of WTC 1 104

Figure 4-6. Repair of cracked weld on spandrel beam in level Bl of WTC 1 104

Figure 4-7. Repair of damaged floor beams at Level Bl in WTC 1 105

Figure 4-8. Repair of damaged floor beam at Level B3 in WTC 1 106

Figure 4-9. Repair of damaged floor beam at Level B3 in WTC 1 107

Figure 4-10. Repair of damaged reinforced concrete spandrel beam at Level B3 in WTC 1 108

Figure 4-11. Repair of damaged reinforced concrete spandrel beam at Level B4 in WTC 1 109

Figure 4-12. Concrete masonry encasement of columns at subgrade levels in WTC 1 1 10

Figure 4-13. Reconstruction details for existing encased steel beams in WTC 1 1 1

1

Figure 4-14. Repair of encased steel spandrel beam at Level B5 in WTC 1 112

Figure 4-15. Repair of beam connection at Concourse Level in WTC 1 113

NISTNCSTAR 1-1C, WTC Investigation ix
List of Figures

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X NISTNCSTAR 1-1 C, WTC Investigation
List of Tables

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

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

Table 2-1. Checklist for Structural Review in the 1971 Edition of the Tenant

Construction Manual 5

Table 2-2. Inspection requirements in the 1971 edition of the Tenant Construction Manual 8

Table 2-3. Checklist for structural review in the 1979 edition of the Tenant Construction Manual 1

1

Table 2—4. Checklist for items subject to controlled inspection in the 1979 edition of the Tenant

Construction Manual 13

Table 2-5. Details of structural review in the 1990 edition of the Tenant Construction Manual 16

Table 2-6. Checklist for items subject to controlled inspection in the 1990 edition of the Tenant

Construction Manual 17

Table 2-7. Checklist for items subject to controlled inspection in the 1997 edition of the Tenant

Construction Manual 19

Table 2-8. Defects and signs of distress to be recorded during inspection of WTC 1 and WTC 2 26

Table 2-9. Minimum loads specified for tenant alterations in PANYNJ Architectural and

Structural Design Guidehnes, Specifications, and Standard Details 29

Table 3-1 . Percentage of structural elements inspected per office floor and for the entire tower per

the 1990 Facility Condition Survey Report for WTC 2 35

Table 3-2. Number of structural elements inspected per office floor per the 1991 Facility

Condition Survey Report for WTC 1 44

Table 3-3. Findings from inspection of exterior wall column splices in WTC 1 46

Table 3^. Visual inspection of elevator core framing in WTC 1 47

Table 3-5. Locations of holes in gypsum wallboard around elevators in WTC 1 48

Table 3-6. Core column connection inspection in WTC 1 49

Table 3-7. Floor framing and slab inspection results for WTC 1 51

Table 3-8. Core framing inspection results for WTC 1 52

Table 3-9. Column splice inspection points in WTC 7. 54

Table 3-10. Wind inspection points, columns, in WTC 7 55

Table 3-11. Wind inspection points, girders, in WTC 7 55

Table 3-12. Interior beam connection inspection points in WTC 7 56

Table 3-13. Summary of findings from space usage reports 65

Table 3-14. Summary of findings from accessible columns reports 66

NIST NCSTAR 1-1C, WTC Investigation xi
List of Tables

Table 3-15. Summary of findings from Plaza Level box column report 68

Table 3-16. Summary of findings from bracing reports 69

Table 3-17. Summary of findings from hat truss reports 70

Table 3-18. Summary of findings from reports on floor framing over mechanical areas 72

Table 3-19. Summary of findings from reports on floor framing over tenant areas 75

Table 3-20. Reports on natural frequency measurements 76

Table 3-21 . Measured first mode natural frequencies for WTC 1 76

Table 3-22. Summary of natural frequency test results for floors of WTC 1, March 1971 77

Table 3-23. Summary of natural frequency test results for floors of WTC 1 and WTC 2, March 1995 77

Table 3-24. Summary of inspections performed on WTC 1 after the terrorist bombing on

February 16, 1993 79

Table 3-25. Summary of locations where fireproofing was found missing during structural inspections of WTC 1, 2, and 7 82

Table 4-1 . Openings made in floor slabs in WTC 1 96

Table 4-2. Openings in floor slabs that were closed in WTC 1 97

Table 4-3. Structural members that were reinforced in WTC 1 98

Table 4-4. Openings made in floor slabs in WTC 2 1 1

5

Table 4-5. Openings in floor slabs that were closed in WTC 2 1 15

Table 4-6. Structural members that were reinforced in WTC 2 116

Table 4-7. Modifications made due to new loading requirements in WTC 7 1 17

Table 4-8. Openings made in floor slabs of WTC 7 120

Table 4-9. Modifications made to beam webs and flanges in WTC 7 121

Xll NISTNCSTAR 1-1C, WTC Investigation
List of Acronyms and Abbreviations

Acronyms

AISC American Institute of Steel Construction

ASTM American Society for Testing and Materials

BSA Board of Standards and Appeals, New York City

BOCA Building Officials & Code Administrators International, Inc. BPS Building Performance Study

CMU concrete masonry unit EQAD Engineering Quality Assurance Division

FEMA Federal Emergency Management Agency

HVAC heating, ventilation, and air conditioning

LERA Leslie E. Robertson Associates

MEA Materials and Equipment Acceptance Division of the Office of the Commissioner of the Buildings Department of New York City

MER mechanical equipment room NIST National Institute of Standards and Technology

NYC New York City

PANYNJ Port Authority of New York and New Jersey

PONYA Port of New York Authority

SHCR Skilling, Helle, Christiansen, Robertson

SII Structural Integrity Inspection

WSHJ Worthington, Skilling, Helle, and Jackson

WTC World Trade Center

WTC 1 World Trade Center tower 1 (North Tower)

WTC 2 World Trade Center tower 2 (South Tower)

WTC 7 World Trade Center building 7

Abbreviations

ft feet

g acceleration due to gravity = 32.2 ft/s~

NISTNCSTAR 1-1C, WTC Investigation Xlll
List of Acronyms and Abbreviations

Hz Hertz

in. inch

lb pounds

milli 1/1000

min minute

mph miles per hour

pcf pounds per cubic foot

psf pounds per square foot

s second

sq ft square foot

XIV NISTNCSTAR 1-1C, WTC Investigation
Metric Conversion Table

To convert from to Multiply by

AREA AND SECOND MOMENT OF AREA

square foot (ft")

square inch (in.")

square inch (in.")

square yard (yd")

square meter (m )

square meter (m")

square centimeter (cm"

square meter (m")

9.290 304 E-02

6.4516 E-04

6.451 6 E+00

8.361 274 E-01

ENERGY (includes WORK)

kilowatt hour (kW • h)

quad (1015 BtuIT)

therm (U.S.)

ton of TNT (energy equivalent)

watt hour (W • h)

watt second (W s)

joule (.T)

joule (.T)

joule (J)

joule (J)

joule (J)

joule (J)

3.6E+06

1.055 056E+18

1 .054 804 E+08

4.184 E+09

3.6E+03

1.0 E+00

FORCE

dyne (dyn)

kilogram-force (kgf)

kilopond (kilogram-force) (kp)

kip(l kip=l,000 Ibf)

kip(l kip= 1,000 Ibf)

pound-force (Ibf)

newton (N)

newton (N)

newton (N)

newton (N)

kilonewton (kN)

newton (N)

1 .0 E-05

9.806 65 E+00

9.806 65 E+00

4.448 222 E+03

4.448 222 E+00

4.448 222 E+00

FORCE DIVIDED BY LENGTH

pound-force per foot (Ibf/ft)

pound-force per inch (Ibf/in.)

newton per meter (N/m)

newton per meter (N/m)

1.459 390 E+01

1.751 268 E+02

HEAT FLOW RATE

calorieth per minute (calth/min)

calorieth per second (calth/s)

kilocalorieth per minute (kcalth/min)

kilocalorieth per second (kcalth/s)

watt (W)

watt (W)

watt (W)

watt (W)

6.973 333 E-02

4.184 E+00

6.973 333 E+01

4.184 E+03

NISTNCSTAR 1-1 C,, WTC Investigation XV
Metric Conversion Table

To convert from to Multiply by

LENGTH

foot (ft) meter (m) 3.048 E-Ol

inch (in) meter (m) 2.54 E-02

inch (in.) centimeter (cm) 2.54 E+00

micron (m) meter (m) l.OE-06

varH i vH

vdiu \ y \i f meter ivr\^ 9.144 E-Ol

MASS and MOMFNT OF INERTIA

M m till J I Ul LC jCLVJilU ^LjLldldJ per meter (kgf s"/m) kilogram (kg) 9.806 65 E+00

pound foot squared (lb ft") kilogram meter squared (kg • m") 4.214 01 1 E-02

pound mch squared (lb • in.") kilogram meter squared (kg m") 2.926 397 E-04

ton, metnc (t) kilogram (kg) 1 .0 E+03

ton. short (2.000 lb) kilogram (kg) 9.071 847 E+02

MASS DIVIDED BY AREA

pound per square foot (lb/ft") kilogram per square meter (kg/m") 4.562 426 t+00

pound per square inch

(not 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-Ol

PRESSURE or STRESS (FORCE DIVIDED BY AREA)

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

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

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/ff) 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 1-1 C, WTC Investigation
Metric Conversion Table

To convert from to Multiply by

TEMPERATURE

degree Celsius (°C)

degree centigrade

degree Fahrenheit (°F)

degree Fahrenheit {°F)

kelvin (K)

kelvin (K)

degree Celsius (°C)

degree Celsius (°C)

kelvin (K)

degree Celsius (°C)

T/K = t/°C + 273.15

t/°C = t /deg. cent.

t/°C = {t/°F- 32)/1.8 T/K = (t/°F + 459.67)/1.8

t/°C = T/K 2 273.15

TEMPERATURE INTERVAL

degree Celsius (°C)

degree centigrade

degree Fahrenheit (°F)

degree Fahrenheit (°F)

degree Rankine (°R)

kelvin (K)

degree Celsius (°C)

degree Celsius (°C)

kelvin (K)

kelvin (K)

1 .0 E+00

1 .0 E+00

5.555 556 E-01

5.555 556 E-01

5.555 556 E-01

VELOCITY (includes SPEED)

foot per second (ft/s)

inch per second (in./s)

kilometer per hour (km/h)

mile per hour (mi/h)

mile per minute (mi/min)

meter per second (m/s)

meter per second (m/s)

meter per second (m/s)

kilometer per hour (km/h)

meter per second (m/s)

3.048 E-01

2.54 E-02

2.777 778 E-01

1.609 344 E+00

2.682 24 E+01

VOLUME (includes CAPACITY)

cubic foot (ft') cubic meter (m')

cubic inch (in.'' ) cubic meter (m')

cubic yard (yd') cubic meter (m')

gallon (U.S.) (gal) cubic meter (m')

gallon (U.S.) (gal) liter (L)

liter (L) cubic meter (m')

ounce (U.S. fluid) (fl oz) _ cubic meter (m')

ounce (U.S. fluid) (fl oz) milliliter (mL)

2.831 685 E-02

1.638 706 E-05

7.645 549 E-01

3.785 412 E-03

3.785 412 E+00

1 .0 E-03

2.957 353 E-05

2.957 353 E+01

NISTNCSTAR 1-1C, WTC Investigation XVI

1
Metric Conversion Table

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xviii NISTNCSTAR 1-1C, WTC Investigation
Preface

Genesis of This Investigation

Immediately following the terrorist attack on the World Trade Center (WTC) on September 11, 2001, the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers began

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

search efforts ceased, the Building Perfonnance 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 detennine probable failure mechanisms and to identify areas of

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

against such unforeseen events."

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

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

disaster. On October 1, 2002, the National Construction Safety Team Act (Public Law 107-23 1), was

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

Construction Safety Team Act.

The goals of the investigation of the WTC disaster were:

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

• To serve as the basis for: - Improvements in the way buildings are designed, constructed, maintained, and used; - Improved tools and guidance for industi^ and safety officials; - Recommended revisions to cuirent 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. Deteraiine 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. Detennine 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 1-1C, WTC Investigation XIX
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

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

does not have the statutory authority to make findings of fault nor negligence by individuals or organizations. Further, no part of any report resulting from a NIST investigation into a building failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action

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

Law 107-231).

Organization of the Investigation

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

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

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

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

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

Document and analyze the code provisions, procedures, and

practices used in the design, construction, operation, and

maintenance of the structural, passive fire protection, and

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

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

Analyze the baseline performance of WTC 1 and WTC 2 under

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

the structural, fire protection, and egress systems.

Mechanical and Metallurgical Analysis of

Structural Steel; Project Leader: Dr. Frank

W. Gayle

Determine and analyze the mechanical and metallurgical properties

and quality of steel, weldments, and connections from steel recovered from WTC 1. 2, and 7. Investigation of Active Fire Protection Systems; Project Leader: Dr. David

D. Evans; Dr. William Grosshandler

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

Reconstruction of Thermal and Tenability

Environment; Project Leader: Dr. Richard

G. Gann

Reconstruct the time-evolving temperature, thermal environment,

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

structural performance of the buildings and behavior and fate of

occupants and responders.

Structural Fire Response and Collapse

Analysis; Project Leaders: Dr. John

L. Gross and Dr. Therese P. McAllister

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

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

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

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

Communications; Project Leader: Mr. Jason D. 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.

XX NISTNCSTAR 1-1 C, WTC Investigation
Preface

NIST WTC Investigation Projects

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 1-1 C, WTC Investigation XXI
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

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

Diego

This National Construction Safety Team Advisory Committee provided technical advice during the Investigation and commentary on drafts of the Investigation reports prior to their public release. NIST

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

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

however, are solely the responsibility of NIST.

Public Outreach

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

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

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

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

NIST's WTC Public-Private Response Plan

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

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

and teiTorist attacks. Reflecting the enhanced interest in effecting necessaiy 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.

xxn NISTNCSTAR 1-1 WTC Investigation
Preface

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

Date Location Principal Ajjcnda

June ''4 ''00'' New York Citv NY Piiblir mpptino' Piihlir rnmmpnfv; on ihp f^r/jfi f^hni tor tHp pending WTC Investigation.

Au2ust 21 2002 r^aithprshiirp MO MpHi?i hripflriQ nnnounnnp the formal (;tart of the Invp'stiP^f ion December 9 2002 Wrmhiiipton TV UOl 1 1 1 1 I V^l 1^ DCM-^ Mpdia Hripflno on rplpa^p of tViP PuhJir' J Jnrlntp anH NIST rpmipt^t for photographs and videos. Anril 8 ''003 New York Citv NY Jloint k-' 1111 niiHlir LJLIL'IIW foriim Iv^lUill with W 1111 (^ohimhifi V„ VJlUlllL'lCX 1vJInivpr^iitv IJIV^lOllV onV.'li fir<st-nprt^on lllol l^^loVyll interviews.

/\pi Anril11 ''Q-^OJU, ^OD^ VJallllCI dUUl^, iyiVJ INV_ol /AUVIaUiy V_ UIilIUI IICC IllCCUIlg UII piall lUI aiiU JJIU^lC?>h UII WTC Investigation with a public comment session. Mav iviu y 7/ Tin^

,

New York Titv NY iVlCUIa UllClIll^ Uli iClCaoC Ul JVJUy ^\/\JJ J / (Vl^/ c.j.i rxLlJUi I. August 26^27, 2003 Gaithersburg, MD NCST Advisory Committee meeting on status of the WTC

investigation with a public comment session. September 1 7, 2003 New York City, NY Media and public bneiing on initiation oi iirst-person data

r'Allf^r^tiAn nt*a

i

/^r'tc LUllCCliUil piU|CClo.

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

comments on issues to be considered in formulating final

fi^r* Ammf^na n ti An c

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

preliminary findings from the WTC Investigation with a public

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

set of preliminary iindings with a public comment session. November 22, 2004 Gaithersburg, MD NCST Advisory Committee discussion on draft annual report to Congress, a public comment session, and a closed session to discuss pre-draft recommendations for WTC Investigation.

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

codes and practices, evacuation, and emergency response. June li, _UUj IN ew Y orK c ity , in Y Media and public briefing on release of all draft reports for the WTC towers and draft recommendations for public comment.

September 12-13,

2005

Gaithersburg, MD NCST Advisory Committee meeting on disposition of public

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

2005

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

and opportunity for public to make technical comments.

• A dissemination and technical assistance program (DTAP) to (a) engage leaders of the construction and building community in ensuring timely adoption and widespread use of

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

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

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

NISTNCSTAR 1-1C, WTC Investigation xxiii
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 lA. The present report is one of a set that provides more detailed documentation of the Investigation findings and the means by which these technical results were achieved. As such, it is part of the archival record of this Investigation. The titles of the full set of Investigation publications are:

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

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

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

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

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

Lew, H. S., R. W. Bukowski, and N. J. Carino. 2005. Federal Building and Fire Safetx' 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 Safet)'

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

NIST NCSTAR 1-1 A. Nafional Insfitute 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 Safet}' 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 Safet}' Investigation ofthe World

Trade Center Disaster: Comparison of Codes, Standards, and Practices in Use at the Time of the Design and Construction of World Trade Center I, 2, and 7. NIST NCSTAR 1-IE. National

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

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

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

xxiv NIST NCSTAR 1-1 C, WTC Investigation
Preface

York Cit}' 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 Cit}' Building Code by Local Laws Adopted While World Trade Center 1, 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-Construction Modifications to Fire Protection and Life Safety Systems

of World Trade Center 1 and 2. NIST NCSTAR 1-lH. 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-lJ. National Institute of Standards and Technology.

Gaithersburg, MD, September.

Sadek, F. 2005. Federal Building and Fire Safet}' Investigation of the World Trade Center Disaster:

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

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

September.

Faschan, W. J., and R. B. Garlock. 2005. Federal Building and Fire Safet\> Investigation ofthe World Trade Center Disaster: Reference Structural Models and Baseline Performance Analysis of

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

Technology. Gaithersburg, MD, September.

Kirkpatrick, S. W., R. T. Bocchieri, F. Sadek, R. A. MacNeiU, S. Holmes, B. D. Peterson, R. W. Cilke, C. Navarro. 2005. Federal Building and Fire Safety Investigation of the 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 of the World Trade Center Disaster: Contemporaneous Structural Steel

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

Gaithersburg, MD, September.

NIST NCSTAR 1-1 C, WTC Investigation XXV
Preface

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

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

and Technology. Gaithersburg, MD, September.

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

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

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

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

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

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

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

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

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

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

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

Building and Fire Safet}' 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 of the World Trade Center Disaster: Post-Construction Fires Prior to September II, 2001. NIST NCSTAR 1-4A. National Institute of Standards and Technology. Gaithersburg, MD,

September.

Hopkins, M., J. Schoenrock, and E. Budnick. 2005. Federal Building and Fire Safet}' Investigation

of the 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 of the World

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

and Technology. Gaithersburg, MD, September.

Ferreira, M. J., and S. M. Strege. 2005. Federal Building and Fire Safety Investigation ofthe World Trade Center Disaster: Smoke Management Systems. NIST NCSTAR 1-4D. National

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

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

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

Center Disaster: Reconstruction of the 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.

xxvi NIST NCSTAR 1-1C. WTC Investigation
Preface

Hamins, A., A. Maranghides, K. B. McGrattan, E. Johnsson, T. J. Ohlcmillcr, 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. Rcinhom, 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 Safet}' Investigation of the 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 Safet}'

Investigation ofthe 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 Safet}' Investigation ofthe World

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

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

MD, September.

Gross, J. L., and T. McAllister. 2005. Federal Building and Fire Safety Investigation of the 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 Safet}' 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 Safet}' 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 1-1 C, WTC Investigation xxvu
Preface

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

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

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

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

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

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

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

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

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

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

Center?. (Provisional). NIST NCSTAR I-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 II. 2001, Seismogram Data. (Provisional). NIST NCSTAR 1-6G.

National Institute of Standards and Technology. Gaithersburg, MD.

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

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

National Institute of Standards and Technology. Gaithersburg, MD.

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

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

Occupant Behavior, Egress, and Emergencv 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 Documentationfor Survey Administration. NIST NCSTAR 1-7B. National

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

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

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

Standards and Technology. Gaithersburg, MD, September.

xxvin NIST NCSTAR 1-1 C, WTC Investigation
Executive Summary

E.1 OVERVIEW

This report contains a summary of the Port Authority of New York and New Jersey (PANYNJ or Port Authority) guidehnes for inspection, repair, and modifications to the structural systems of World Trade

Center (WTC) 1, 2, and 7. Included are the guidelines governing the inspection and strengthening of

existing structural members and systems for modifications made by tenants of the buildings.

A summary of the (1) structural inspection programs, (2) significant observations, (3) procedures for implementation, and (4) actions taken during the occupancy of WTC 1, 2, and 7 is also documented. In addition to having established guidelines for any type of modifications that were to be made to any of

their facilities, including the WTC, the PANYNJ established programs for inspection and repair. Facility

condition surveys were commissioned for WTC 1, 2, and 7. These surveys reported on the condition of

the buildings, including the structural systems, and contained recommendations for any necessary repairs or upgrading. Periodic inspections of the structural systems were also perfonned under the Structural

Integrity Inspection (SlI) Program for WTC I and WTC 2.

Also contained in this report is a summary of the significant modifications and repairs that were made to the structural framing systems of WTC 1, 2, and 7 from initial occupancy to September 11, 2001. A

discussion is also included on the repairs that were made after the February 1 993 bombing of WTC 1

.

Apart from the repairs following the 1993 bombing of WTC 1, most of the structural modifications in WTC 1 and WTC 2 were perfonned to accommodate tenant requirements. Openings were cut in existing

floors to construct new stairways linking two or more floors, and floor systems were reconstructed over

previously cut openings. In a number of cases, floor trusses outside of the core area and steel beams in the core area had to be reinforced due to heavy loads imposed by tenant requirements.

Similar to WTC 1 and WTC 2, most of the structural modifications in WTC 7 were done to accommodate

tenant requirements. Horizontal members of the floor framing system were strengthened due to increased

loading from high-density files. Strengthening of these beams and girders was achieved by welding cover

plates to the bottom flanges, the underside of the top flanges, or both. In some cases new beams were

introduced to carry a portion of the new load. Floor slabs were completely removed on the east side of the building to accommodate trading floors for Salomon Brothers Inc., one of the major tenants of the building. Columns in this area, which had twice the unsupported length after the slab removal, were

reinforced. Other openings were cut into a few floor levels to accommodate new stairways connecting

adjoining floors. Web openings were cut through some beams and girders to allow passage of ductwork.

In some cases, the beams or girders had to be reinforced in order to increase their capacity.

The information contained in this report is based on documents and structural drawings that were

primarily acquired from the the offices of the PANYNJ in Newark, New Jersey, and New York City, New

York. Paper, microfilm, and electronic versions of these documents were obtained from these sources. Appendixes to this report include copies of referenced documents, including the Tenant Construction

Review Manuals, the Standards for Structural Integrity Inspection of the WTC towers, and the

NISTNCSTAR 1-1C, WTC Investigation xxix
Executive Summary

Architectural and Structural Design Guidelines, Specifications, and Standard Details, which were all issued by the Port Authority regarding inspection, repair, and modifications to the structural systems of

WTC1,2, and?.

E.2 GUIDELINES FOR INSPECTION, REPAIR, AND MODIFICATIONS TO

STRUCTURAL SYSTEMS

E.2.1 Tenant Construction Review Manuals

The first edition of the Tenant Construction Review Manual was issued by Port of New York Authority

(PONYA or Port Authority) in 1971. Subsequent editions appeared in 1979, 1984, 1990, and 1997.

The purpose of these manuals was to present the technical criteria, standards, and requirements that were

to be followed by tenants that were planning construction work in any Port Authority facility. Included in the manuals were the criteria that were used by the Engineering Department of the Port Authority when

reviewing proposed construction or alterations. Requirements were given for alterations and

modifications to architectural, structural, geotechnical, civil, mechanical, plumbing, and fire protection

systems.

The General Requirements section of the manual required that all tenants submit an application form to the Port Authority outlining the scope of work, the design criteria, and the plans prior to construction. The

design was to be performed by a registered architect or licensed professional engineer. Contractors were

required to comply with all applicable provisions of federal, state, municipal, local and departmental laws,

ordinances, rules, regulations, and orders, except where stricter requirements were contained in the project specifications. Except for some editorial changes, the requirements in this section remained

virtually the same in all editions of the manual. In the revised March 1990 edition, requirements were

added concerning the role of consultants working on the project who were not the architect or engineer of

record.

The scope of structural review of the alterations and/or modifications consisted of compliance with the applicable codes, standards, and design criteria given in the Structural Review section of the manual.

In particular, the provisions of the then applicable New York City Building Code were to be satisfied for work performed in New York City. Structural calculations were to be submitted by the registered design

professional for review by the Port Authority'. The checklist for structural review included provisions for

loads, structural work, various structural materials, and foundations. The requirements in this section of

the manual were modified and expanded over the years, most notably the section containing Port Authority design criteria, which was significantly expanded in the revised March 1990 edition of the manual. Included in that edition was a requirement that all structures were to be designed for earthquake zone 2 forces in accordance with the Building Officials Conference of America Basic Building Code.

The Materials, Operations, and Equipment Subject to Controlled Inspection section of the manual

contained a comprehensive inspection program that was to be implemented for all construction. The

inspection that was required during various phases of construction was mainly to be performed in accordance with the applicable sections of the New York City Building Code that governed at the time.

Specific inspection requirements were outlined for concrete and steel. The inspection requirements were

significantly reorganized and modified in the revised March 1990 edition of the manual. Requirements for

xxx NISTNCSTAR 1-1C, WTC Investigation
Executive Summary

approval/acceptance of materials and controlled inspections were abstracted from the applicable sections

of the New York City Building Code.

E.2.2 Standards for Structural Integrity Inspection of the WTC Towers A & B

The Infrastructure Engineering Design Division of the Engineering Department of PANYNJ issued the Standards for Structural Integrit}' Inspection of the World Trade Center Towers A & B in March of 1986.

These standards were to assist the PANYNJ in the evaluation of the structural integrity of WTC 1 and

WTC 2.

Three methods were used to evaluate the structural integrity of the towers: (1) statistical inspections, (2)

reports, and (3) continued measurements. In the first method, periodic visual inspection of selected

structural components in "higher-potential trouble areas" was to be made initially by qualified outside

consultants under PANYNJ management. It was anticipated in the future that PANYNJ in-house

personnel could perfomi such inspections. Periodic inspection of the following components was to be

performed:

1 . TV antenna mast on the top of WTC 1 (every year);

2. Exterior roof and wall elements (every year);

3. Room occupancies (every year);

4. Accessible column envelopes, including fireproofing (every second year);

5. Fireproofing and masonry partitions enclosing the diagonal bracing on exterior column lines

in both towers below the Service Level Floor and the transfer trusses below floor 1 in WTC 2

under exterior and core columns (every second year);

6. Hat truss members between floor 107 and the roof (every second year);

7. Exterior box columns and spandrel plates under column trees below Floor 7 (every fourth

year);

8. Steel floor framing over mechanical spaces (every fourth year); and,

9. Concrete slabs, partitions, and finishes (every fourth year).

Inspections were also to be made when general repair or remodeling was done that involved removing

ceilings, partitions, finishes, or other coverings. Tools and procedures that were to be used to perfonn the inspections were also included in this method. After inspection was complete, it was required that any

spray-on fireproofing that was removed for inspection purposes be properly replaced.

In the second method, various reports were to be examined, which could possibly shed light on

underlying structural problems. Maintenance reports of non-stmctural repairs, water leakage, and tenant complaints about unusual building movements, vibration, or noise are examples of such reports.

NISTNCSTAR 1-1C, WTC Investigation xxxi
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In the third method, the perfonnance of systems within the buildings was to be evaluated through

measurement of movement or defonnation. Measurements of the following were to be performed on a

periodic basis:

1. Natural frequency of the towers;

2. Natural frequency of the TV mast on WTC 1

;

3. Natural frequency of the floor constmction;

4. Viscoelastic dampers; and,

5. Plumbness and level.

This document also contained a list of duties, responsibilities, and minimum qualifications of the inspection supervisor, inspection crew leader, and inspection crewmembers from the PANYNJ. Other

requirements were given for outside consultants and suppliers who were to can'y out periodic inspections

and other special tasks.

During inspections, defects and signs of distress were to be noted and recorded for:

1. Structural steel (rust; cracks; buckles and kinks; connection and joint defects; alignment,

excessive deflection, or bowing; and paint); and,

2. Reinforced concrete (scaling, cracking, and spalling).

General requirements were given on how to identify an inspected member, how to describe the defect or

distress, and how to categorize the urgency of the required repair.

It was noted in the last section of the document that these standards were applicable to only structural

steel and reinforced concrete members in WTC 1 and WTC 2. Glass and glazing, facade panels, ceilings,

partitions, elevators, stairs, and mechanical equipment were listed as components outside the scope of the document.

E.2.3 Architectural and Structural Design Guidelines, Specifications and

Standard Details

Issued by the Port Authority in February of 1998, this document contained architectural and structural design requirements for tenant alterations that were to be made specifically at WTC 1 and WTC 2.

Prior to any design work, the tenant's consultants were required to perform a field inspection of the area where alterations/modifications were to take place. It was required that all calculations and construction

drawings be submitted to the Port Authority for review and approval, and that all documents be sealed by

a professional engineer or registered architect licensed to practice in the state of New York.

Proposed floor loads were to be compared with the allowable floor design loads contained in the Architectural and Structural Design Guidelines, Specifications and Standard Details document. Existing

structural members that would be overstressed by the proposed loads were required to be reinforced to

XXXll NISTNCSTAR 1-1C, WTC Investigation
Executive Summary

carry the additional loads. It was required that the weight of any equipment exceeding 500 lbs and the weight of all files and shelves be shown on the construction drawings. Minimum loads to be used in the designs were also specified in the document.

All proposed penetrations or drilling of cores in tower slabs were required to meet the criteria for location,

spacing, and repair that were specified in this document. Some areas were denoted as "prohibited"' (no

penetrations or cores were allowed) and some were denoted as "restricted" (advisable not to locate penetrations or cores).

Additional criteria were provided for (1) supports for hung ceilings in the two-way truss areas of the towers, (2) weight, dimensions, and location of heating, ventilation, and air conditioning equipment, (3)

walls over an opening, (4) holes in existing steel, (5) coring at power/telephone cells and under induction

units, and (5) concrete anchors that were to be used for any connections made to concrete.

E.3 STRUCTURAL INSPECTION PROGRAMS DURING THE OCCUPANCY OF

WTC 1,2, AND 7

E.3.1 Facility Condition Survey Reports

Port Authority Facility Condition Survey Program - WTC 2

The Engineering Quality Assurance Division of PANYNJ performed a facility condition survey for WTC 2 in 1990. The scope of the survey was based on Standards for Structural Integrity Inspection of

World Trade Center Towers A & B, which was published by PANYNJ in 1986. This document contained

the minimum requirements of periodic and occasional inspection programs that were implemented for WTC 1 and WTC 2.

The scope of work, which was designed to minimize impact on tenant and facility operations, included

inspection of the (1) exterior wall system (columns, spandrel plates, and splices), (2) core columns

(including column splices and lateral bracing below the 7th floor). (3) space frame (hat truss). (4) floor systems (floor slabs and decks, trusses, rolled beams, bridging, and connections), and (5) damping

system. Thirty floors throughout WTC 2 were selected for inspection, including all four of the two-story

mechanical equipment rooms (MER).

Exterior Walls (Columns and Spandrels)

Exterior columns and spandrels were inspected at (1) column field splice connections, (2) spandrel field splice connections, and (3) the inside of the spandrel plate face at the column/ floor truss seat connections.

According to the report, a total of 59 column splices were inspected and all were found to be in good

condition. On two of the floor levels, the columns had only three bolts at the splice location, although the design called for four. According to the report, this had no effect on structural integrity.

Spandrel plates, splice plates, and spandrel bolted connections were also found to be in good condition.

Scattered rust stains were observed on the spandrel fireproofing as well as on the inside of some of the

steel box columns.

NISTNCSTAR 1-1 C, WTC Investigation xxxin
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No priority recommendations were made in the report. It was recommended, however, that a long-temi

maintenance program be developed and implemented to clean and paint the inside surfaces of the exterior

box columns to prevent further corrosion of the structural steel.

Core Columns

Core columns were inspected from elevator shafts and from office area floors. Twenty-five elevator shafts were randomly selected for inspection, and the elevator core framing was primarily inspected with

fireproofing materials in place. In general, some defects were found in the fireproofmg material. In most

of the shafts, several small regions and a few large areas of fireproofmg were found to be missing from

core framing members. In the worst case, 1 00 percent of the fireproofmg was found to be missing from

the south face of column 908 between floors 27 and 29 in elevator shaft number 1. Exposed steel members exhibited only isolated locations of light surface corrosion.

Gypsum wallboards surrounding the elevator shafts were also found to be in good condition, although

isolated holes were detected at various locations.

Inspection of column splices and eccentric-braced column connections with fireproofing removed showed

that all bolts, welds, and structural steel were in good condition.

No priority recommendations for repair were made in the 1 990 report. It was recommended that the

fireproofing that was missing from the framing members in the elevator shaft be replaced, including those

regions where the fireproofing was removed for inspection. It was also recommended that the holes in the gypsum wallboards sunounding the elevators be repaired.

Floor Framing

In the main lobby, beams and connections that were inspected within the core area were found to be in good condition. Fireproofing was missing at various locations, exposing light surface corrosion on these

elements.

On floors 9 through 41, the floor framing that was inspected was also found to be in good condition.

Light corrosion was observed on all core beams and beam connections, and on floor truss connections.

The most significant deficiencies were found at the damping units, where a number of such units were

missing from one to four fasteners in the connections to the framing members.

Floor framing on floors 43 though 75 was found to be in good condition. The most significant

deficiencies were found on floors 64 and 75. A deformed bottom chord was found on the main truss along

column 343 on floor 64; no signs of distress were observed. On the 75th floor, untightened bolts were

found at truss seat connections at several locations, which, according to the report, had no significant

affect on the structural integrity of the framing, since they served erection purposes.

The floor framing on floors 77 through 1 07 was found to be in good condition with light surface

corrosion observed on all core framing beams and connections. The most significant deficiencies were

concrete slabs that had separated from the metal deck at floors 93 and 108. According to the report, structural integrity was not comprised, since the metal deck served as only formwork for the concrete.

xxxiv NISTNCSTAR 1-1C. WTC Investigation
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Hairline cracks were found in concrete beam encasement at various locations on all four mechanical

equipment room levels. Other than that, floor framing and slabs were found to be in good condition.

Selected elements of the hat truss were also found to be in good condition, with light surface corrosion on exposed truss elements and connections.

No priority recommendations for repair were made in the report. All of the deficiencies noted above were

considered to have no significant effect on structural integrity.

Port Authority Facility Condition Survey Program - WTC 1

The Office of Irwin G. Cantor, Consulting Engineers, performed a condition survey of WTC 1 in 1991 for the Engineering Quality Assurance Division of PANYNJ. The scope of the survey was based on

experience gained from the survey of WTC 2 in 1990. As in the case of WTC 2, the scope of work was

designed to minimize impact on tenant and facility operations. The floor framing, damping system,

exterior wall system, core columns, space frame (hat truss), MER, and roof were inspected.

Exterior Walls (Columns and Spandrels)

A total of 28 exterior column splices were inspected throughout 14 office floors on floors 9 through 106. Nondestructive testing was perfonned on the plate splice welds, and ultrasonic testing was performed to verify plate thickness at 26 of these locations. All inspected columns splices were found to be in good

condition.

The inside faces of the steel box column plates exhibited scattered areas of light to moderate corrosion

and peeling paint. Ultrasonic thickness testing on these outer column plates above and below the splice

location indicated no cross-section loss.

Spandrel plates, splice plates, and bolted connections were also found to be in good condition. Scattered

rust stains were observed on the spandrel fireproofing.

In the floors above 106, only the joints at floor 108 were inspected. No structurally significant

deterioration was found.

No priority recommendations for repair were made in the report. It was noted that missing fireproofing

should be replaced on the spandrel plates and splices.

Core Columns

Core columns were inspected from 1 3 elevator shafts with fireproofing left in place. Comer core column

splices were inspected from two office area floors. Core floor beam to column connections were also inspected at 25 of 56 locations on 14 floors.

The exterior wall column splices were found to be in good condition. Results from nondestructive testing

of the splice plate welds were acceptable, and resuhs from ultrasonic thickness testing showed no

significant loss in member thickness.

NISTNCSTAR 1-1 C, WTC Investigation XXXV
Executive Summary

Several small areas and a few large areas of fireproofing were missing from some of the steel beams and

columns in the express elevator shafts. According to the report, the probable cause of missing fireproofing on the columns was the high speed of the elevators moving up and down the shafts. All exposed steel was

found to be in good condition with light to medium surface rust.

Gypsum wallboards were found to be in good condition, except for two isolated holes in two elevator

shafts at the 58th and 69th floors.

Similar to the case of the express elevator shafts, fireproofing was found to be missing on some of the

steel columns and beams, and some isolated holes were found in some of the gypsum wallboards in the

local elevator shafts.

'

Inspection of core comer column splices and floor beam to column connections showed all of the elements to be in good condition.

No priority recommendations were made in the report. It was recommended that missing fireproofing

from the framing members in the elevator shafts be replaced, including those regions where the fireproofing was removed for inspection during the condition survey. It was also recommended that the holes in the gypsum wallboards be repaired.

Floor Framing

Two typical conditions were observed during inspection of the floor trusses: (1) small areas of

fireproofing were missing at scattered locations throughout the floor framing and (2) the underside of the

floor trusses exhibited light rust. Welds were tested at various connections and were found to be in good

condition. In some cases, the connection of the truss to the exterior spandrel plate had one bolt and a weld

instead of the typical two-bolt connection. These field welds were also tested and were found to be in good condition.

At all of the locations that were inspected, the damping units did not have fireproofing covering them.

Light rust was observed on the surfaces of the units. A non-structural bolt was missing on one of the damping units under the 30th floor.

The metal deck and concrete slabs that were inspected were also found to be in good condition, except for the slab in the southeast comer of the 60th floor where cracks were found on the top surface.

No priority recommendations for repair were made in the report. Routine recommendations were made to patch spalls and cracks in the concrete slab. MER and Space Frame

All four mechanical equipment room floor levels (floors 7-8, 41-42, 75-76, and 108-109) were

inspected. Floor slabs at these levels were found to be in good condition with scattered cracks found on

the slab surfaces. Scattered patches of fireproofing were found missing from the underside of the metal

decks outside the core area. A concrete encased beam on the 1 10th floor was subjected to steam from a leaking steam valve. Moderate

msting was found on the member, but no significant section loss was found.

xxxvi NISTNCSTAR 1-1 C, WTC Investigation
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Hangers supporting ducts, piping, etc. were visually inspected, and some were found to be subject to excessive vibration. Loose hanger rods and fatigue of pipe supports were also found at various locations. Beams that supported the duct hangers had fireproofing missing where the hangers were mounted.

A total of 199 members were inspected in the space frame (hat truss). Light rust was found on diagonal

braces, beams, and connections where fireproofing was missing.

A priority recommendation was made in the report to replace the leaking valve under the 1 10th floor that caused the floor beam to rust. Routine recommendations were made to repair cracks in the concrete slabs and to repair hangers that were found to be vibrating, bowed, sagged, and/or defonned.

Roof

No significant structural deficiencies were found at the roof level. Cracking and spalling of the concrete

slab was found in localized areas of the roof.

No priority recommendations were made in the report. Routine recommendations included removing and

replacing existing patches in the roof slab and patching spalled areas in the concrete slabs.

Port Authority Facility Condition Survey Program - WTC 7

Ammann & Whitney performed a condition survey of WTC 7 in 1997 for the Engineering Quality

Assurance Division of PANYNJ. The scope of work was designed to minimize impact on tenant and

facility operations and was limited to unoccupied floors and floors which had vacant space. The

foundation, column splices, wind bracing system, interior beam connections, floor slabs, and the Con

Edison Substation were all inspected.

According to the report, no problems or deterioration were found on the column splices, wind bracing, or

the interior beam connections at any of the locations that were inspected. Rust buildup was found between

the flanges of members that rested on top of one another at the main roof level where the steel framing was exposed. It was recommended that the steel be cleaned and painted to prevent further deterioration, even though this was not considered to be a structural problem.

Fireproofing was found to be missing from the steel framing at various locations where utility supports were installed on all of the floors that were inspected. Missing fireproofing was most prominent on the 5th floor framing above the main lobby and the 2nd floor framing above the loading dock area. It was recommended in the report that the fireproofing be replaced.

Loose concrete was found on the north face of column 51 on the 46th floor of the cooling tower area. Silverstein Properties personnel immediately removed the loose concrete.

Floor slabs were found to be in good condition. No deficiencies were found, except for some shrinkage

cracks on the top of some of the exposed slabs and some damage to the metal deck.

The Con Edison station was found to be in very good condition, and no action was required at that time.

NISTNCSTAR 1-1 C, WTC Investigation xxxvii
Executive Summary

Due Diligence Physical Condition Survey - WTC 1 and WTC 2

Merritt & Harris, Inc., perfomied a condition sui-vey for WTC 1 and WTC 2 in 2000 for PANYNJ. The

on-site evaluations were carried out to assess the general physical condition of the property at that time.

WTC 4, WTC 5, the retail mall and plaza, central services, and the subgrade were inspected in addition to WTC 1 and WTC 2.

Observations were limited to those portions of the buildings that were visible during walk-through. No

material samples were taken, and no tests were perfonned on the building materials or systems.

According to the report, the building structure appeared to be in good overall condition, based on

observations of the structural members that were not concealed by building finishes. The interior slabs were reported to be in good condition, and no apparent movement or settlement of foundations was

observed.

The report notes that Leslie E. Robertson Associates (LERA) and other engineering firms had performed

Structural Integrity Inspections of various structural systems and had pointed out the following

deficiencies: (1) rusting of steel columns in the elevator shafts, (2) missing fireproofing on structural members, and (3) floor coring damage. The report goes on to discuss the damping units, including

LERA's strong recommendation to continue wind acceleration measurements.

E.3.2 Structural Integrity Inspection Program

In 1986, PANYNJ implemented an inspection program to detect, record, and correct any signs of distress,

deterioration, or defonnation that could signal structural problems. This structural integrity inspection

program, which was based on an inspection and testing plan prepared by LERA, contained detailed

guidelines on inspection, record-keeping, and follow-up procedures.

In regard to the follow-up procedure, a description was to be provided of the defect or indication of

distress. Measurements, sketches, and photographs were to be provided in those cases where a written

description was not adequate. The use of a tape recorder was also pemiitted.

If the Supervisor or the inspection team uncovered defects or indications of distress that appeared to require more than routine attention, a separate report of such findings was to be submitted to the Port Authority's Engineer of Design, Infrastructure. For conditions of a serious nature, immediate notification was to be made to the Engineer of Design, Infrastructure in person.

Inspection findings under this program were to be categorized as "Immediate," "Priority," or "Routine."

Repairs falling into the "immediate" category included possible closure of the area and/or structure affected until interim remedial action (such as shoring or removal of a potentially unsafe element or

structure) could be implemented. Such action was to be undertaken immediately after discovery, and a

description of the action taken and recommendations for pennanent repair were to be included in the inspection report. The "priority" category was for those conditions where no immediate action was

required, or for which immediate action had been completed, but for which further investigation, design,

and implementation of interim or long-tenn repairs should be undertaken on a priority basis (i.e., taking

precedence over all other scheduled work). Repairs falling into the "routine" or "non-priority" category

xxxviu NISTNCSTAR 1-1C, WTC Investigation
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could be undertaken as part of a scheduled major work program or other scheduled project, or when

routine facility maintenance was to be perfonned, depending on the type of repair that was required.

An important requirement in the inspection program was that where inspection procedures involved the removal of fireproofing, such fireproofing was to be properly replaced on completion of inspection.

LERA submitted a proposal to PANYNJ in 1990 to monitor the structural integrity of the WTC Complex,

which included WTC 1, WTC 2, WTC 4, WTC 5, WTC 6, the Vista Hotel, and the subgrade. The

proposal called for inspection/monitoring of the following items in WTC 1 and WTC 2:

• TV mast (WTC 1 only)

• Roof water tightness and curtain wall

• Space usage

• Accessible columns, including exterior box columns at locations of spandrel intersections and

"tree' junctions below floor 7 and above floor 1 (Plaza Level)

• Bracing at exterior column line below elevation 294 ft-0 in., and in WTC 2 only, the transfer trusses below floor 1 under exterior columns

• Hat truss between floor 1 07 and the roof

• Floor framing over mechanical spaces

• Concrete slabs, partitions, and finishes

• Steel framing, slabs, and the like where exposed for general repairs or tenant remodeling

• Measurement of natural frequency of tower and TV mast

• Floor natural frequency

• Damping units

• Plaster ceilings in main lobby

• Marble wall panel supports

• Review of maintenance reports

• Fire stairs

Inspection and monitoring of these items were to occur at regular intervals, which were proposed by

LERA.

LERA and other engineering finns conducted periodic inspections of the towers under the WTC

Structural Integrity Inspection Program, which was based on the proposal originally submitted to

NISTNCSTAR 1-1C. WTC Investigation xxxix
Executive Summary

PANYNJ by LERA in 1990. A summaiy of the structural integrity inspection programs and their corresponding dates is given in Table E-1.

Table E-1. Summary of Structural Integrity Inspection programs

for WTC 1 and WTC 2. Inspection Program Date(s) of Inspection Reports

Space Usage Suwey 1995, 1996, 1997. 1998. 1999

Accessible Columns 1993, 1995, 1996, 1997, 1998

Plaza Level Box Columns 1998

Bracing Below Elevation 294 ft- 0 in. 1991,1995

Hat Trusses 1992, 1995

Floor Framing Over Mechanical Areas 1992, 1996, 1999

Floor Framing Over Tenant Areas 1992, 1995, 1997, 1999

Natural Frequency Measurements 1993, 1995, 2000

Natural Frequencies of Floors 1995

Viscoelastic Damping Units 1996

Space Usage Surveys ^

The purpose of the space usage surveys was to identify possible structural overloading of the slabs and

floor framing due to changes in occupancies and uses and/or due to additions of heavy equipment or

furniture. Surveys were conducted annually over a 5 year period starting in 1995, with two surveys

conducted in 1996. The only priority recommendation was made in the 1995 report, which advised

PANYNJ to distribute the load of the granite slabs on floor 106 of WTC 1 over a larger area. A summary

of the findings from the space usage reports can be found in Table 3-13 of this report.

Accessible Columns

Surveys of the accessible columns (columns in the core area that were not enclosed by an architectural

finish, which can be visually inspected) in the elevator shafts of WTC 1 and WTC 2 were performed to:

• Ascertain the condition of the accessible columns with respect to rusting, cracking, bowing,

and deviation from plumb;

• Identify specific locations of structural distress or damage;

• Identify locations of damage to the fireproofing;

• Identify lateral displacement or rotation of the column about a vertical axis where the column was directly braced on only one axis by connecting beams or concrete slabs; and

• Identify deformations of the slabs-on-ground surrounding each column at the sublevel.

Accessible column surveys were performed approximately every 2 years, starting in 1993 and ending in 1998. Priority recommendations were made in the 1996 report and the second report in 1998. The later

xl NISTNCSTAR 1-1C. WTC Investigation
Executive Summary

report recommended that missing fireproofing be replaced on columns at various locations in WTC 1 and

WTC 2. A summai7 of the findings from the accessible columns reports can be found in Table 3-14 of

this report.

Plaza Level Box Columns

The purpose of the inspection of the Plaza Level box columns was to assess their overall structural

integrity, including the condition of the fireproofing. The proposed inspection interval was 4 years.

Fireproofing was found to be missing from approximately 2 to 3 percent of the Plaza Level box columns

and seated beam connections in WTC 1 and about 1 to 2 percent in WTC 2. A summary of the findings

from the Plaza Level box columns report is given in Table 3-15 of this report.

Bracing Below Elevation 294 ft 0 in.

Below Elevation 294 ft 0 in. (Sublevel 1) in both WTC 1 and WTC 2, diagonal bracing was used in place

of deep spandrels between the exterior columns to resist lateral loads from the towers above.

The purpose of the inspection of the bracing system below elevation 294 ft 0 in. in the perimeter walls of

the towers was to:

• Assess the overall perfonnance and structural integrity of the bracing (and, in 1991 only, the

transfer trusses below elevation 310 ft 0 in. in WTC 2);

• Identify specific locations of structural distress or damage;

• Identify locations of damage to the structural fireproofing systems; and

• Provide recommendations for remedial work for both structural and fireproofing damage.

Bracing surveys were performed in 1991 and 1995, and a summary of the findings from these reports can be found in Table 3-16 of this report. No priority recommendations were made in these reports.

It is evident from Table 3-16 that the PANYNJ did not act on a number of recommendations priority and

routine repairs from earlier reports. In particular, draining of flooded areas due to water leaks was not

fUlly accomplished, and repairs to the connections between the braces and the columns were not made.

Fireproofing was not applied to the transfer truss between columns 242 and 248 at the Bl Level in WTC 2. Also, fireproofing was not repaired on some of the bracing members at Level B6 and at other

levels. It appears that all of the damaged concrete masoniy unit (CMU) walls acting as fireproofing,

which were identified in the 1991 Structural Integrity Inspection report, were repaired; many additional

CMU walls were noted for repair in the 1995 Structural Integrity Inspection report.

Hat Trusses

The purpose of the inspection of the hat trusses between floor 107 and the roof was to:

• Assess the overall performance and structural integrity of the hat trusses;

NISTNCSTAR 1-1C. WTC Investigation xli
Executive Summary

• Identify specific locations of stmctural distress or damage;

• Identify locations of damage to the structural fireproofing systems; and

• Provide recommendations for remedial work for both structural and fireproofing damage.

Hat truss surveys were performed in 1992 and 1995. A summary of the findings from these reports can be

found in Table 3-17 of this report. Although no priority recommendations were made in these reports,

routine recomjnendations were made to repair fireproofing and gypsum wallboard at various locations in WTC 1 and WTC 2. No follow-up actions were stated in the report.

Floor Framing over Mechanical Areas

The inspection program for the floor framing supporting the MER consisted of the following:

• Assess the overall perfonnance and structural integrity of the steel and concrete framing.

• Identify locations of defects and signs of distress in slabs, partitions, column enclosures, and

concrete supports for mechanical equipment.

• Identify locations of damaged fireproofing.

• Compare the findings with those of previous inspections.

• Provide recommendations and procedures for remedial work for both structural and

fireproofing damages and/or inadequacies.

Surveys were conducted in 1992, 1996, and 1999. Priority recommendations were made in the 1996 and

1999 reports. The 1996 recommendation called for reapplication of fireproofing at various locations in WTC 1 and WTC 2. The 1999 recommendation called for repair of a water leak in an overhead pipe on

floor 75 of WTC 1 . A summary of the findings from these reports can be found in Table 3-18 of this report.

Floor Framing over Tenant Areas

The inspection program for the floor framing supporting the tenant areas consisted of the following:

• Assess the overall performance and integrity of the steel and concrete framing.

• Identify locations and signs of distress in slabs, partitions, column enclosures, and steel framing.

• Identify locations of inadequate fireproofing.

• Provide recommendations and procedures for remedial work for both structural and

fireproofing damages and/or inadequacies.

xlii NISTNCSTAR 1-1C, WTC Investigation
Executive Summary

Surveys for floor framing supporting tenant areas occurred in 1992, 1995, 1997, and 1999. Priority

recommendations were made in the 1 999 report concerning restoration of fircproofing on a truss on

floor 89 in WTC 2, repair of spalled concrete on floor 89 of WTC 2 and floors 33 and 91 in WTC 1, and

repair of damaged reinforcement on floor 91 of WTC 1. A summary of the findings from these reports can be found in Table 3-19 of this report.

Natural Frequency Measurements

The purpose of this inspection program was to detennine the natural frequencies of oscillation of WTC 1 due to wind excitation. Only WTC 1 was instrumented with accelerometers at six locations on floor 108,

which measured the accelerations in both principal directions of the building with respect to time due to wind. These natural frequencies were to be compared with corresponding values that were determined in the past. A significant change in the tower's dynamic behavior was considered to be a possible indication

of diminishing structural integrity. According to the reports, characteristics that may have been observed

or inferred by review of the recorded acceleration data were:

• Integrity of the lateral-load-resisting system;

• Condition of the viscoelastic damping system;

• Condition of other sources of inherent structural damping; and

• Other changes that affect fundamental characteristics of the lateral-load-resisting system.

Reports were prepared by LERA in 1993, 1995, and 2000. The main conclusion from the 1993 and 1995

reports was that the measured and computed first mode frequencies compared well, especially for the

large wind speeds. The 1995 report also concluded that the February 1993 bombing had no permanent

measurable effect on the dynamic response of WTC 1 . Both reports recommended that WTC 2 be

instrumented similarly to WTC 1

.

The 2000 report pointed out that data acquired since 1998 could not be analyzed due to the dismantling of

the PANYNJ facilities that performed the analysis. The report recommended that the capability to assess the data be re-established as soon as possible.

Natural Frequencies of Floors

The purpose of this inspection program was to determine the natural frequencies of the floor systems in WTC 1 and WTC 2. These natural frequencies were to be compared with corresponding values that were

detennined in the past. A significant change in the vibration characteristics of the floor system was

considered to be a possible indication of diminishing structural integrity. Summaries of the natural frequencies of the floors in WTC 1 and WTC 2 are given in Tables 3-22 and 3-23 of this report.

The report produced by LERA in 1995 summarized the analytical and experimental results to date. The

report concluded that there was no significant measurable change in the performance of the typical floors systems of WTC 1 and WTC 2.

NISTNCSTAR 1-1C, WTC Investigation
Executive Summary

Viscoelastic Damping Units

A summary of the integrity of the viscoelastic damping units in WTC 1 and WTC 2 was given in a report

by LEJIA in 1996. Also given in the report is a historical review related to the perforaiance of the damping units.

The report concluded that based on the then available studies, the integrity of the damping units was

good, and that no action was required at that time beyond the routine testing of the damping units.

Inspections Related to Explosion of February 16, 1993

Six different inspections were perfomied before and after repairs were made to WTC 1 in the aftennath of

the teiTorist attack in Febmary of 1993. A summai^ of these inspections can be found in Table 3-24 of

this report. No anomalies were detected in the welds used to repair structural members.

E.3.2 Summary of Structural Inspection Programs

In general, the structural integrity inspections found that the structural systems of WTC 1, 2, and 7 were

in good condition. The inspection consultants made numerous routine and some priority

recommendations for repairs to the PANYNJ, as outlined in the appropriate sections of this report. Unless

there were scheduled maintenance programs, the PANYNJ did not act expeditiously on some of these

repair recommendations, including not replacing or repairing fireproofmg on structural steel members that was found to be missing from the inspections. According to the PANYNJ, all of the construction records on repairs following the inspections were lost on September 1 1, 2001. Thus, it cannot be determined

whether all of the recommended repairs were perfonned.

Table 3-25 of this report gives a chronological summary of the locations where fireproofmg was reported

to be missing, based on the findings from the applicable inspection programs.

E.4 SIGNIFICANT MODIFICATIONS AND REPAIRS MADE TO THE

STRUCTURAL FRAMING SYSTEMS OF WTC 1, 2, AND 7

Most of the modifications to the structural systems of WTC 1, 2, and 7 were done to accommodate tenant requirements. These generally involved cutting holes in existing floor slabs to construct new stairways

linking two or more floors or reconstructing the floor system over previously cut openings. In other cases

floor or column members were reinforced to accommodate new floor loadings imposed by tenant requirements.

Modifications to the structural systems were to follow the guidelines set forth by the PANYNJ, which are summarized in Sec. E.2 and Chapter 2 of this report.

xliv NISTNCSTAR 1-1C, WTC Investigation
Executive Summary

E.4.1 Modifications and Repairs IVIade to WTC 1

Openings Made in Floor Slabs

Slab openings were made in the floor slabs on the following floors during the following years:

1. Floors 93-95, 1978 (openings were made in floors 93, 94 and 95 between columns 901, 902,

1001, and 1002 in core)

2. Floors 99-101, 1979 (openings were made in floors 100 and 101 between columns 707, 708,

806, and 807 in core, and in floor 99 between columns 701, 702, 801, and 802)

3. Floors 89 and 90, 1985 (opening was made in floors 89 and 90 between columns 901, 902,

1001, and 1002)

4. Floor 107, 1995 (opening was made in floor 107; location could not be determined)

5. Floors 105-roof, 1997 (opening was made in floor 105 near columns 704 and 804A in the core)

6. Floors 93-100, 1999 (openings were made on all floors; location could not be detennined)

Most openings were made to accommodate new stairs and elevators.

Openings in Floor Slabs that Were Closed

Openings that had been cut primarily for stairways were subsequently closed on the following floors during the following years:

1. Floor 95, 1972 and 1985 (new beams and floor deck were added near column lines 124 and

239)

2. Floors 91 and 92, 1987 (new beams and floor deck were added between colunms 901, 902,

1001, and 1002 in the core)

3. Floors 96 and 100, 1998 (new beams and floor deck were added between columns 1 19 and

123 on floor 96 outside of the core and near columns 707, 708, 806, and 807 on floor 100)

Structural Members that were Reinforced

Various floor members were reinforced to accommodate floor loads that were greater than the original

design loads. Members were reinforced on the following floors during the following years:

1. Floors 98 and 99, 1979 (cover plates were added on existing beams on floor 98 between

columns 601 and 602 and between 701 and 702; on floor 98, diagonals were added to existing

floor trusses on the east side of the core between columns 218 and 221; on floor 99, floor

trusses along lines 309, 3 1 1

, 3 1 3, 3 1 5, 3 1 7, 3 1 9, 32 1 , 323, 325, 327, and 329 were reinforced;

and, on floor 99, core perimeter columns were reinforced)

NISTNCSTAR 1-1 C, WTC Investigation xlv
Executive Summary

2. Floor 86, 1996 (floor trusses were reinforced in the northwest comer of the building)

3. Floor 85, 1998 (cover plates were added to existing beams and existing floor trusses were

reinforced)

4. Floors 47 and 48, 2001 (floor trusses were reinforced)

Repair Work Following the February 26, 1993, Explosion

Damagefrom the Explosion

The explosion of February 26, 1993, occurred on Level B2 near the center of the south wall of WTC 1 and adjacent to the Vista Hotel. Structural steel columns, diagonal braces, and spandrel beams in the

vicinity of the blast were damaged. Concrete floor slabs at Levels Bl and B2 and unreinforced masonry

walls were also damaged over a large area.

The explosion tore out the diagonal brace between column 324 at Level B2 and column 327 at Level Bl

and severely bent the diagonal brace between column 324 at Level B2 and column 321 at Level Bl.

Spandrel beams at Level Bl from column 321 to column 324 and from column 324 to column 327 were

also damaged by the blast. Spandrels were bowed and cracked, and some had missing bolts.

The inspection teams observed a crack along the field splice in column 324. Ultrasonic testing determined

that the crack extended across the full width of the weld on the south face of the column and at each end

of the weld on the north face. Magnetic-particle testing procedures detemiined that the crack extended

across the east face of the column and the majority of the weld on the west face as well.

The explosion also damaged floor beams framing into the tower side of column 324 at Levels Bl and B2.

Concrete spandrel beams at Level B3 between columns 318 and 330 also sustained damage. Masonry

walls in WTC 1 were breached over distances of approximately 50 ft to the east and 120 ft to the west of

the blast origin.

Repair Work

The diagonal bracing members between levels B 1 and B2 that were damaged by the explosion were removed and replaced with new members.

New plates were added to the damaged spandrel beam at level Bl between columns 324 and 327 and

between columns 321 and 324. Also, the cracked weld on the south face of the spandrel beam at level Bl

near column 324 was removed and replaced.

An eight-step procedure was prescribed for repair of the crack in column 324 immediately adjacent to the

field weld at the column splice above level B2. No documentation was found to confirm that this crack was repaired according to that procedure.

xlvi NISTNCSTAR 1-1C, WTC Investigation
Executive Summary

Repairs were made to the floor beams framing into columns 321, 324, and 327. Repairs were also made to connections between floor beams and columns on Levels B3 and B4. Along the south face of WTC 1, the damaged concrete spandrel beams were demolished and replaced.

Other Modifications

An FM transmitter was installed on the 1 10th floor in 1997. In June of 2000, structural calculations were

submitted by LERA for the WABC Control Room on floor 110. A new transmitter and ductwork were

suspended from the existing floor system at this level.

E.4.2 IVIodlfications and Repairs Made to WTC 2

Openings Made in Floor Slabs

Slab openings were made in the floor slabs on the following floors during the following years:

1. Floor 77, 1979 (openings were made at nine locations in the northeast quadrant of the building)

2. Floor 96, 1987 (opening was made near columns 901 and 902 in the southeast quadrant of the building)

3. Floors 94 and 95, 1993 (opening was made between columns 507, 508, 607 and 608)

4. Floors 99-101, 1997 (openings were made; locations could not be determined)

5. Floor 99, 1998 (opening was made between columns 601, 602, 701, and 702 in the core on

Floor 99)

6. Floors 25 and 26, 1999 (opening was made near column 901 in the core)

7. Floors 88 and 89, 1999 (openings were made; locations could not be deteraiined)

Most openings were made to accommodate new stairs.

Openings in Floor Slabs that were Closed

Openings that had been cut were subsequently closed on the following floors during the following years:

1 . Floors 37 and 38, 1997 (new framing and floor deck was added near column 608)

2. Floors 95 and 96, 2000 (new beams and floor deck were added between columns 901, 902,

1001, and 1002)

NISTNCSTAR 1-1C, WTC Investigation xlvii
Executive Summary

Structural Members that were Reinforced

Members were reinforced on the following floors during the following years:

1. Floor 96, 1993 (a number of floor trusses and their connections were reinforced in the northeast quadrant of the building)

2. Floor 81, 1991 (two-way floor trusses were reinforced in area occupied by UPS)

Other Modifications

In 1994, the slab in the elevator lobby on floor 90 (bounded by columns 702, 703, 902, and 903) was

repaired for Fiduciary Trust for an unknown reason. The existing slab was demolished and was replaced

with a 5 in. thick lightweight aggregate concrete slab.

E.4.3 Modifications and Repairs Made to WTC 7

Modifications Made due to New Loading Requirements

Members were reinforced primarily to accommodate floor loads that were greater than the loads for which these members were originally designed. Members were reinforced on the following floors during

the following years:

1 . Floor 38, 1988 (cover plates were added to existing beams along column lines 30, 35, 37 and

40)

2. Floor 24, 1989 (cover plates were added to existing beam on column line 45 and to two

adjacent beams)

3. Floor 47, 1989 (cover plates were added to existing beams on column line 25 and to the

existing girder on column line 56)

4. Floors 1 1 and 12, 1990 (cover plates were added to eight existing beams and girders in the northwest comer of the building on floor 1 1 , and to three existing beams between lines 48

and 49 and to the girder between columns 70 and 73 on floor 12)

5. Floor 19, 1991 (cover plates were added to existing beams; location could not be detennined)

6. Floor 12, 1992 (cover plates were added to eleven existing beams in the northwest comer of

the building and a new beam was added between existing beams)

7. Floors 18 and 19, 1992 (cover plates were added to existing beams on lines 31, 32, and 33)

8. Floor 28, 1993 (additional shear studs were added to existing beams located in the mechanical/electrical room)

9. Floors 7 and 8, 1993 (a new beam was added between column lines 7 and 8)

xlviii NISTNCSTAR 1-1 C, WTC Investigation
Executive Summary

10. Floors 7-29, 1994 (cover plates were added to 22 existing beams between lines 5 and 25 on

the south side of the building and on each floor between levels 7 and 29, and to 8 existing

beams on the east side of the building between lines 3 1 and 37)

11. Floor 20, 1995 (cover plates were added to existing beams along lines 23 and 25, and WT

sections and cover plates were added to existing beams east of column line 19)

12. Floor 37, 1999 (a new beam was added between two existing beams along column lines 76

and 77)

13. Floor 13, 1999 (additional shear studs were added to an existing beam; location could not be

detemiined)

14. Floor 40, 1999 (four new beams were added near column 76, and WT sections were welded

to the bottom of two existing beams)

15. Floor 3 1 , 2000 (cover plates were added to an existing beam between columns 77 and 80)

16. Floor 38, 2000 (cover plates were added on existing beams between columns 76 and 77 and

between columns 77 and 78, and to existing girders between columns 76 and 79, 77 and 80,

and 78 and 81)

17. Floor 39, 2000 (new beams were added between columns 76 and 77)

Openings Made in Floor Slabs

The floor slabs on floors 41 and 43 were completely removed on the east side of the building to accommodate the trading floors for Salomon Brothers Inc. Also, columns 76, 78, 79, 80, and 81 were

reinforced with plates that ran from the top of the 39th floor to the underside of the 49th floor due to the removal of the floor slab at the 39th floor. Similarly, column 74 was reinforced with plates that ran from

the top of the 43rd floor to the underside of the of the 44th floor due to the removal of the floor slab at the 43rd floor.

Other slab openings were made in the floor slabs on the following floors during the following years:

1. Floors 3 and 4, 1989 (openings were made on the 3rd floor on the west, north, and east sides

of the building; on the 4th floor, openings were made on the north side of the building)

2. Floor 3, 1 989 (openings were made near columns 24 and 25)

3. Floor 1 1, 1990 (opening was made between columns 77, 78, 80, and 81)

4. Floor 43, 1994 (opening was made near column 71 in the core area)

NISTNCSTAR 1-1C, WTC Investigation xlix
Executive Summary

Modifications Made to Beam Webs and Flanges

Modifications were made to beam webs and flanges on the following floors during the following years:

1. Floor 28, 1993 (openings were cut in the web of an existing beam; location could not be

determined)

2. Floors 4-7, 16, 21, 29, 38, and 45, 1993 (notches were cut in the bottom flanges of various

beams, and plates were welded to the upper side of the bottom flanges)

3. Floor 1 , 1998 (notch was cut into the top flange of an existing beam, and two plates were welded under the top flange; location could not be detennined)

4. Floors 36-44, 1999 (openings were cut in the web of existing beams framing into column 75 on all floor levels; the beams were reinforced with web plates and a WT section welded to its bottom flange)

5. Floors 42 and 44, 1999 (openings were cut in the webs of numerous beams along the north

and east sides of the building)

Other Modifications

A list of structural modifications that were made to WTC 7 prior to April of 1997 is given in Chapter IV,

Section A(5) of the Facility Condition Survey Report for WTC 7. The following is a summary of the modifications that are noted in that report:

1. In the Convention Area on the 3rd floor between column numbers 45 and 48A, steel plates were installed around the perimeter of the room between the slab and the floor surface

(behind the wall coverings and above the suspended ceiling). According to the PANYNJ

report, these plates were installed to protect attendees of the Convention Center from the magnetic field generated from the ConEd Substation beneath the conference rooms. No

documentation was located that provides any additional details on this modification.

2. On the north side of the 5th floor generator room, masonry block walls were added to partition the eight transformer vaults installed for Salomon Brothers. The vaults were

between columns 46 and 53. No documentation was located that provides any additional

details on this modification.

3. A penthouse was constructed on the 47th floor roof to house the chiller plant and the cooling towers for Salomon Brothers. The chiller plant was an enclosed steel-framed structure with

corrugated steel walls. It was approximately 25 ft in height and took up about one-third of the square footage of the 47th floor roof The cooling towers were supported on a steel frame and

were enclosed by louvered walls on the north and south sides and by the chiller plant and the bulkhouse on the east and west sides, respectively. No documentation was located that provides any additional details on this modification.

1 NISTNCSTAR 1-1 C. WTC Investigation
Executive Summary

The list of modifications in the PANYNJ report also include the removal of the floor slabs on floors 41 and 43 to accommodate the trading floors for Salomon Brothers, as noted above.

NISTNCSTAR 1-1 C, WTC Investigation li
Executive Summary

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lii NISTNCSTAR 1-1C, WTC Investigation
Chapter 1 Introduction

This report contains a summary of the maintenance and modifications that were made to the structural systems of World Trade Center (WTC) 1, 2, and 7. Documented in Chapter 2 of this report are the guidelines that were established by the Port Authority of New York and New Jersey (PANYNJ or Port Authority) for inspection, repair, and modifications to the structural systems of WTC 1, 2, and 7. Included

are the guidelines governing the inspection and strengthening of the existing structural systems for modifications made by tenants of the buildings.

Chapter 3 of this report contains a summary of the structural inspection programs that were undertaken

during the occupancy of WTC 1, 2, and 7. Included are summaries of the facility condition survey reports

that were produced for WTC 1, 2, and 7. These surveys reported on the condition of the buildings,

including the structural systems, and contained recommendations for any necessary repairs or upgrading.

This chapter of the report also contains a description of the structural integrity inspection program that was undertaken for WTC 1 and WTC 2. In addition to the structural integrity inspection programs,

significant observations, procedures for implementation, and actions taken are summarized.

The significant modifications and repairs that were made to the structural systems of WTC 1, 2, and 7 from initial occupancy to September 1 1, 2001 are documented in Chapter 4 of this report. A discussion on

the repairs that were made after the February 1993 bombing of WTC 1 is also included. Other than the

repairs following the 1993 bombing of WTC 1, most of the structural modifications in WTC 1 and

WTC 2 were performed to accommodate tenant requirements. Openings were cut in existing floors to construct new stairways linking two or more floors, and floor systems were reconstructed over previously

cut openings. In a number of cases, floor trusses outside of the core area and steel beams in the core area had to be reinforced due to heavy loads imposed by tenant requirements.

As in WTC 1 and WTC 2, most of the structural modifications in WTC 7 were made to accommodate

tenant requirements. Horizontal members of the floor framing system were strengthened due to increased

loading from high-density files. Strengthening of these beams and girders was achieved by welding cover

plates to the bottom flanges, the underside of the top flanges, or both. In some cases new beams were

introduced to carry a portion of the new load. Floor slabs were completely removed on the east side of the building to accommodate trading floors for Salomon Brothers Inc., one of the major tenants of the building. Columns in this area, which had twice the unsupported length after the slab removal, were

reinforced. Other openings were cut into a few floor levels to accommodate new stairways connecting

adjoining floors. Web openings were cut through some beams and girders to allow passage of ductility

work. In some cases, the beams or girders had to be reinforced in order to increase their capacity.

The information contained in this report is based on documents and structural drawings that were

primarily acquired from the following locations: (1) the offices of the PANYNJ in Newark, New Jersey,

and New York City, New York, and (2) the National Institute of Standards and Technology in Gaithersburg, Maryland, where Port Authority documents were sent. Paper, microfikn, and electronic

versions of these documents were obtained from these sources.

NISTNCSTAR 1-1C, WTC Investigation 1
Chapter 1

Appendixes to this report include copies of referenced documents, including the Tenant Construction

Review Manuals; the Standards for Structural Integrity Inspection of the World Trade Center Towers; and

the Architectural and Structural Design Guidelines, Specifications, and Standard Details, which were all issued by the Port Authority regarding inspection, repair, and modifications to the structural systems of

WTC 1,2, and?.

2 NISTNCSTAR 1-1C, WTC Investigation
Chapter 2

Guidelines for Inspection, Repair, and Modifications to

Structural Systems

In 1971, the Port of New York Authority (PONYA or Port Authority), which was later renamed The Port Authority of New York and New Jersey (PANYNJ or Port Authority), established guidelines for all types

of modifications that were to be made to any of their facilities, including the World Trade Center (WTC).

As shown in Sec. 2.1 of this chapter, these guidelines evolved through the years. Standards for structural

integrity inspection and architectural and structural design guidelines and specifications were also issued

by PANYNJ and are discussed in Sees. 2.2 and 2.3, respectively. In addition, the PANYNJ

commissioned facility condition surveys at regular intervals for WTC 1, 2, and 7. These surveys reported on the condition of the buildings, including the structural systems, and included recommendations for any

necessary repairs or upgrading. Discussion on these reports can be found in Chapter 3 of this report.

Periodic inspections of the structural systems were also performed under the Stmctural Integrity

Inspection (SII) Program for WTC 1 and WTC 2, the details of which can also be found in Chapter 3. The

following discussion focuses on the guidelines for inspection, repair, and modifications to the structural systems for WTC 1,2, and 7.

2.1 TENANT CONSTRUCTION REVIEW MANUALS

PONYA issued the first edition of the Tenant Construction Review Manual in 1971, shortly after the first tenants occupied WTC 1 in December of 1970 and prior to initial occupancy of WTC 2 in January 1972.

Other editions of the manual followed. As stated in its Introduction, the manual was published to present

the technical criteria to be used by tenants of Port Authority facilities who were planning construction

work in such facilities. In particular, the manuals set forth the applicable standards and requirements to be

used by tenants and their agents. The manuals also included the review criteria of the design documents

that were used by the Engineering Department of the Port Authority in connection with proposed

construction or alterations. Also covered in the manuals were requirements for alterations and

modifications to architectural, structural, geotechnical, civil, electrical, mechanical, plumbing, and fire protection systems in any Port Authority facility, including the WTC.

General requirements and specifications evolved over the years. The following discussion summarizes the

structural provisions contained in the Tenant Construction Review Manual from the 1971 edition through

the 1997 edition.

NISTNCSTAR 1-1C, WTC Investigation
Chapter 2

2.1.1 1971 Edition^

General Requirements

Prior to construction, all applicants were required to submit a completed application form to PONYA that included, among other things, the scope of work to be perfonned, design criteria, and plans. It was

required that design was perfonned by a registered architect or licensed professional engineer and that the drawings produced by the design professionals were consistent with criteria set forth in the manual. At the

tentiination of construction, a complete set of as-built drawings, sealed and signed by the design

professional, was to be submitted to PONYA.

Contractors were required to comply with all applicable provisions of federal, state, municipal, local, and

departmental laws, ordinances, rules, regulations, and orders, except where stricter requirements were

contained in the project specifications based on the criteria in the manual. In such cases, the latter requirements would govern. It was also necessary for contractors to obtain PONYA permits for any

welding or hot work, in addition to being licensed by the state or municipality. Finally, contractors were

not pennitted to apply for any variance, license, waiver, or permit of any kind in the name of or on behalf

of the Port Authority.

Structural Requirements ^

The scope of structural review of the alterations and/or modifications consisted of compliance with the applicable codes, standards, and design criteria set forth in the Structural Requirements section of the manual.

For work perfonned in New York City, the New York City (NYC) Building Code was to be used. Both

the 1938 edition and the December 6, 1968 edition were listed. Also, the laws, rules, and regulations

adopted by federal, state, and local municipal agencies were to be satisfied, where applicable.

Structural calculations were to be submitted by the registered design professional for review by PONYA.

The PONYA structural reviewer was responsible for the structural integrity of all walls and partitions.

Building frames were checked for stability and sidesway, including the effects of these on the columns.

Once the review of the superstructure was complete, the structural reviewer was to submit all applicable

materials to the Chief Structural Engineer of PONYA for review and comment.

All structural modifications were required to confonn to the provisions contained in Table 2-1. This

checklist, which was utilized during the review process by PONYA, is based on the 1968 edition of the NYC Buildmg Code.

Controlled Inspection of Materials, Operations, and Equipment

A comprehensive inspection program was implemented for all construction. Inspection was required

during various phases of construction, and was mainly to be perfonned in accordance with NYC Building

Code Section C26-106.3 (Materials, Assemblies, Fonns and Methods of Construction; Inspection

See Appendix A for the general and structural requirements in the 1971 edition of the Tenant Construction Review Manual

(PONYA 1971).

4 NISTNCSTAR 1-1C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

Requirements) and Section C26- 107.3 (Service Equipment; Inspection Requirements). Table 2-2 contains a summary of these requirements as they appeared in the 1971 edition of the manual. For brevity, only

general requirements and items related to concrete and steel are contained in the table.

According to Chapter 5, Section VllI of the Tenant Construction Review Manual, tests prescribed by the NYC Building Code were to be made under the supervision of an architect, engineer, or testing service

acceptable to the PONYA Resident Engineer. Also, inspections during the progress of work could be

perfonned without verification by PONYA department inspectors. The architect, engineer, or other

person who supervised the work was required to be present at final inspection by PONYA.

Table 2-1. Checklist for Structural Review in the 1971 Edition of the Tenant

Construction Manual.

Provision Code Reference"

General

Materials, Assemblies, Forms & Methods of Construction C26- 106.0 General Requirements C26-106.1

Acceptance Requirements C26-106.2

Inspection Requirements C26- 106.3

Plan Required C26-n0.2

Structural Plans C26-1 10.2(b)

Loads

Dead Loads 901.0

Floor Live Loads C26-902.2 & RS9-2

Live Loads for Sidewalks, Driveways, and Railings C26-902.3

Roof Loads C26-902.6

Moving Loads C26-902.7

Partial Loading Conditions C26-902.8

Floor Live Load Reduction C26-903.2

Contributory Floor Areas C26-903.3

Wind Loads 904.0 & RS 9-5 Thermal Forces C26-905.7

Shrinkage C26-905.8

Distribution of Loads 906.0

Structural Work

General Requirements C26-1000.6

Materials and Methods of Construction C26-1000.7

Inspection of Materials and Assemblies Table 10-1

Inspection of Methods of Construction C26-1000.9 Use of Used and Unidentified Materials C26-1000.10

Equivalent Systems of Design C26- 1000.1

Deferred Detailing C26-1001.4

NISTNCSTAR 1-1C, WTC Investigation 5
Chapter 2

Table 2-1. Checklist for Structural Review in the 1971 Edition of the Tenant

Construction Manual (continued).

Provision Code Reference"

Structural Work (continued)

Combination of Loads C26-1001.4

Load Tests C26-1002.4

Masonry 1003.0 Unreinforced Masonry RS 10-1 General Section 1

Definitions Section 2

Materials Section 3 Design Section 4

Lateral Support Section 5 Thickness and Height of Masonry Empirical Provisions Section 6 Bonding Section 7 Grouted and Filled Cell Masonry Section 8 Anchorage Section 9 Miscellaneous Requirements Section 10 Veneer Section 1

1

Miscellaneous Structures and Systems Section 12 Reinforced Masonry

Concrete 1004.0

Concrete Mixes C26- 1004.3

Short Span Concrete Floor and Roof Construction

Supported on Steel Beams

Reinforced Concrete RS 10-3 ACI 318-63, Building Code Requirement; modified as specified in RS 10-3

Structural Steel RS 10-5 AISC 1969 Specifications for the Design, Fabrication, and

Erection of Structural Steel for Buildings; modified as specified in RS 10-5

Light Gauge Cold Formed Steel RS 10-6 AISI Specification or the Design of Light Gauge Cold

Formed Steel; modified as specified in RS 10-6 Open Web Steel Joists RS 10-7

Wood 1004.0, Table RS 10-8 and

RS 10-9

Aluminum 1007.0, Table RS 10-10

and RS 10-11

Glass 1011.0

6 NISTNCSTAR 1-1 C. WTC Investigation
Guidelines for Inspection, Repair, and Mod. to Structural Sys.

Table 2-1. Checklist for Structural Review in the 1971 Edition of the Tenant

Construction Manual (continued).

Provision Code Reference"

Soil and Foundations

Depths of Foundations C26- 1100.7 Foundations at Different Levels C26-1 100.8 Borings C26-1 101.2 Probings and Geophysical Explorations C26-1101.5

Foundation Loads 1102.0

Classification of Soil Materials C26-1 103.1 Allowable Soil Bearing Pressures C26-1 103.4 Bearing Capacity of Nominally Unsatisfactory Bearing

Materials C26-1103.5

Soil Load Bearing Tests 1104.0

Footings C26-1 105.2 Foundation Piers C26-1 105.3 Foundation Walls C26-1105.4

Pile Foundations

Administrative Requirements C26-1 106.1 Minimum Pile Penetrations C26-1 106.2 Minimum Spacing of Piles C26-1 106.5 Capping and Bracing of Piles C26-1 106.7 General Requirements for Installation of Piles C26-1106.9

Allowable Axial Loads on Piles C26-1 107.1 Allowable Lateral Load C26-1 107.2

Pile Driving Operations

Equipment C26-1 108.1

Procedures C26-1 108.2

Pile Types

Timber Piles C26-1 109.2

Precast Concrete Piles C26-1 109.3

Cast-in-place Concrete Piles C26-1109.4

Compacted Concrete Piles C26-1 109.5

Steel "H" Sections C26- 1109.6

Concrete Filled Pipe Piles C26-1 109.7

Caisson Piles C26-1 109.8 Composite Piles C26-1109.9

Underpinning 1110.0

Stability 1111.0

NISTNCSTAR 1-10, WTC Investigation 7
Chapter 2

Table 2-1 . Checklist for Structural Review in the 1971 Edition of the Tenant

Construction Manual (continued).

Provision Code Reference"

Inspection

Boring Operations C26-1112.2

Piling C26-1 112.3 Subgrade for Footings, Foundation Piers, and Walls C26-1112.5

Support of Adjacent Properties or Building C26-1 112.6

a. 1968 NYC Building Code.

Table 2-2. Inspection requirements in the 1971 edition of the Tenant

Construction Manual.

Item Code Reference

Concrete

Inspection of materials for all structural elements proportioned on the basis of

calculated stresses 70 percent or greater of basic allowable values Table 10-1, Article 10

Preliminary tests of concrete C26-1004.3(a)(3)

Quality control and inspection at the batch plant

C26-1 004.3(a)(5) except as provided in C26-1004.3(b)(6)

Preparation of cylinders for strength tests C26-1004.5(a)(l)

Checking of all samples recovered for the purpose of strength tests for slump,

air content, unit weight, and temperature

RS 10-3, C26-1 004.5(a)(2)

Measurement of forms for size and dimension of members C26-1004.5(a)(3)

Checking of sizes and position of reinforcement C26-1004.5(a)(3)

Inspection of placement of concrete and the recording of and compliance with Building Code

provisions associated with/to:

Temperature

Protection against excessive temperature

Curing

Erection and connection

of precast members

Amount of water added

in field Tensioning of prestressed elements C26-1004.5(a)(3)

Pre-placed aggregate C26-1 104.1 1(c)

Steel

Inspection of welding operations where stresses in welds are 50 percent or more of basic allowable values Table 1 0-2

Check of welders' licenses or qualifications C26-1005.3(2), C26-1005.3(4)

Inspection of the tensioning of high strength bolts where stresses in bolts are 50 percent or more of basic allowable values Table 1 0-2

Inspection of the connection of fittings to wire cables, except where proofloading to not less than 55 percent ultimate capacity

Table 10-2

8 NISTNCSTAR 1-1C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

Table 2-2. Inspection requirements in the 1971 edition of the Tenant

Construction Manual (continued).

Item Code Reference

Materials, Assemblies, Forms and Methods of Construction

Code test method - whenever the Building Code prescribes a method of

testing, such tests shall be made under the supervision of an architect or an engineer or by a testing service or laboratory acceptable to the PONYA

Resident Engineer.

C26-] 06.2(a)(1)

Inspections During Progress of Work

The commissioner may accept signed statements by architects and engineers

and supporting inspection and test reports without verifying inspection or test by department inspectors.C26-120.5

Final Inspection

The architect, engineer, or other person who supervised or superintended the work is required to be present at final inspection by department.

C26- 120,6

2.1.2 1979 Edition^

General Requirements

Except for some minor editorial changes, the general structural requirements in Section 2 of the 1979

edition of the manual were essentially the same as those outhned in the 1971 edition.

Structural Requirements

As was required in the 1971 edition of the manual, the NYC Building Code was to be used for work

performed in New York City. As before, both the 1938 edition and the December 6, 1968 edition of the code were referenced.

Structural requirements were inodified and expanded in Section 5 of the 1979 edition of the manual. A list of notable differences between the 1971 and 1979 editions follows.

1. New Section A, Plans Notes, Schedules. This section contained the same requirements as in the 1971 edition, except for the following:

a. Requirements for signing and sealing the structural plans and the information required on

the structural plans were directly referenced to code sections C26-1 10.2 and C26-

1 10.2(b), respectively.

b. The requirement that the structural reviewer be responsible for the structural integrity of

all walls and partitions was deleted.

c. New rules and regulations listed in Section C of the Structural chapter that were

applicable to construction in New York City were to be considered. The list is as follows:

See Appendix B for the general and structural requirements in the 1979 edition of the Tenant Construction Review Manual

(PANYNJ 1979).

NISTNCSTAR 1-1C, WTC Investigation 9
Chapter 2

( 1 ) Rules and Regulations Relating to Resistance to Progressive Collapse Under

Extreme Local Loads (Building Department)

(2) Rules and Regulations for the Design of Composite Construction with Metal Decks

or Lightweight Concrete (Building Department)

(3) Rules Related to Structural Design Based on Electronic Computer Computations

(Building Department)

(4) Rules and Regulations Relating to the Design and Installation of Curtain Wall

Systems (Building Department)

(5) Rules for Application and Protection of Sprayed-on Fireproofmg (BSA

Cal. #118-68-GR)-'

(6) Rules and Regulations for Masonry Parapet Walls (Building Department)

(7) Rules for Arc and Gas Welding and Oxygen Cutting of Steel Covering the Specifications for Design, Fabrication, and Inspection of Arc and Gas Welded Steel Structures and the Qualification of Welders and Supervisors (BSA Cal. #l-38-SR)

(8) Rules for Governing the Marking of Transparent Glass Doors and Fixed Adjacent

Glass Sidelights (BSA Cal. #50r-68-SR)

(9) Rules for the Manufacture, Testing, and Use of Concrete Masonry Units (BSA

Cal. #639-40-SR)

d. A new section was introduced requiring that all required schedules for structural and

foundation elements be on the plans.

2. Checklist for structural review (Section B in the 1979 manual). Some items in the checklist were modified and some were deleted. Table 2-3 contains the items in the 1979 checklist. References to code sections were no longer provided.

3. New Section C, Additional Port Authority Criteria. This section required that buildings

designed and/or constructed by PANYNJ that were being ahered needed to be coordinated

with the particular PANYNJ facility design group, especially for foundation requirements.

^ Denotes number of the New York City Board of Standards and Appeals (BSA) document.

10 NISTNCSTAR1-1C,WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

Table 2-3. Checklist for structural review in the

1 979 edition of the Tenant Construction Manual. Provision

Loads

Dead Loads

Floor Live Loads

Live Loads for Sidewalks, Driveways, and Railings

Roof Loads

Moving Loads

Partial Loading Conditions

Floor Live Load Reduction

Contributory Floor Areas Wind Loads

Thennal Forces Shrinkage

Distribution of Loads

Structural Work

General Requirements

Materials and Methods of Construction

Inspection of Materials and Assemblies

Inspection of Methods of Construction

Use of Used and Unidentified Materials

Equivalent Systems of Design

Deferred Detailing

Combination of Loads

Load Tests

Fire Protection Requirements

Soils and Foundations

Depths of Foundations

Foundations at Different Levels

Slabs on Grades Construction

Borings

Probings and Geophysical Explorations

Foundation Loads

Classification of Soil Materials Allowable Soil Bearing Pressures Bearing Capacity of Nominally Unsatisfactory

Bearing Materials

Soil Load Bearing Tests

Footings

NISTNCSTAR 1-1C, WTC Investigation
Table 2-3. Checklist for structural review in the

1979 ed ition of the Tenant Construction Manual (continued).

Provision

Foundation Piers Foundation Walls

Pile Foundations

Administrative Requirements

Minimum Pile Penetrations Minimum Spacing of Piles Capping and Bracing of Piles

General Requirements for Installation of Piles Allowable Axial Loads on Piles Allowable Lateral Load

Pile Driving Operations

Equipment

Procedures

PHe Types

Timber Piles

Precast Concrete Piles

Cast-in-place Concrete Piles Compacted Concrete Piles

Steel "H" Sections Concrete Filled Pipe Piles Caisson Piles Composite Piles Underpinning

Stability

Inspection

Controlled Fills Boring Operations

Piling; Installation and Testing

Subgrade for Footings, Foundation Piers, and Walls

Support of Adjacent Properties or Building

Reports Required

Verification - Stabilized Overburden

Bearing Capacity of Nominally Unsatisfactory

Bearing Material

Alternate or Similitude Method for Pile Load

Verification

Substantiation of Higher Allowable Pile Loads

NISTNCSTAR 1-1 C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

Controlled Inspection of Materials, Operations, and Equipment

The revised introduction to the section on controlled inspection of materials, operations, and equipment in the 1979 manual provided a better explanation of the relevance of this section. The purpose of this section was to list some of the materials, operations, and equipment that normally required the services of a licensed professional engineer in order to assure compliance with the inspection procedures contained in 106.0 and 107.0 of the 1968 NYC Building Code.

The inspection requirements for concrete and steel in the 1979 manual are essentially the same as those in the 1971 manual, with some minor editorial changes (see Table 2-2). For concrete, an inspection

requirement for proper use of admixtures was added. For steel, the requirement for checking welders'

licenses or qualifications was dropped, as this item was covered in the new rules and regulations relating to structural items given in Section 5 of the manual.

In lieu of the general inspection requirements related to ( 1 ) materials, assemblies, fonns and methods of

construction, and (2) inspections during progress of work, and (3) final inspection, requirements were

given for structural materials and assemblies subject to and not subject to controlled inspection, which are defined in C26- 106.3 of the 1968 NYC Building Code. The checklist for items subject to controlled inspections is given in Table 2^. Mill, manufacturers', and suppliers' inspection and test reports were

accepted as evidence of compliance with the provisions of the code for all structural materials and

assemblies not subject to controlled inspection. Spray-on fireproofing was added to the list of items

requiring controlled inspection in this edition of the manual, since such inspection was added for the first time in C26-502.2(l) of the 1968 NYC Building Code in 1976 (Local Law 55). This new paragraph

required that the installation of all sprayed-on fire protection of structural members, except those encased

in concrete, be subject to the controlled inspection requirements of C26-106.3. According to C26-106.3,

all materials designated for controlled inspection were to be inspected and/or tested to verify compliance

with code requirements. All required inspections and tests were to be made and witnessed by or under the

direct supervision of an architect or engineer who the owner retained and who was acceptable to the

architect or engineer who prepared the plans. The architect or engineer was to file with the NYC Building

Department signed copies of all inspection and test reports, together with a signed statement that the material and its use or incorporation into the building complied with code requirements.

Table 2-4. Checklist for items subject to

controlled inspection in the 1979 edition

of the Tenant Construction Manual.

Borings or Test Pits

Piles

Soil

Controlled Fill Underpinning

Welding

Aluminum

Laminated Wood

NISTNCSTAR 1-1C. WTC Investigation 13
Chapter 2

Table 2-4. Checklist for items subject to

controlled inspection in the 1979 edition of the

Tenant Construction Manual (continued). High Strength Bohs

Fire Stops

Heating System

Ventilation System

Refrigeration System

High Pressure System

Prestressed Concrete

Precast Concrete Chimney Smoke Vent

Cable Fittings

Spray-on Fireproofmg

2.1.3 March 1984 Edition, Revised March 1990'*

General Requirements

The general requirements were moved from Section 2 to Section 3 of the 1990 edition of the manual and

contained essentially the same requirements as those in previous editions. Additional requireinents were

included concerning the role of consultants working on the project who are not the architect or engineer

of record. The requirement that the tenant comply with the provisions of all federal, state, municipal,

local, and departmental laws, ordinances, rules, regulations, and orders was moved to a more prominent

location in this section. This requirement was in accordance with the policy of the PANYNJ at that time.

Structural Requirements

The structural requirements section was moved from Section 5 to Section 6 in the 1 990 edition. As in previous editions of the manual, the NYC Building Code was to be used for work perfonned in New York

City. However, unlike the previous editions, no specific editions of the code were listed.

In regard to the rules and regulations of the New York City Department of Buildings, the section title in the 1990 edition of the manual reads as follows: "Rules and Regulations of the Department of Buildings,

such as:" This implies that the list of rules and regulations listed in the 1990 edition is not necessarily

exhaustive. As noted in the previous section, nine rules and regulations first appeared in the 1979 edition

of the manual. In the 1990 edition, only five rules are listed. The following rules and regulations, which

appeared in the 1979 edition, are not explicitly listed in the 1990 edition: (1) application of spray-on

fireproofing, (2) arc and gas welding, (3) transparent glass doors and fixed adjacent glass sidelights, and

(4) manufacture, testing, and use of concrete masonry units.

^ See Appendix C for the general and structural requirements in the March 1984. Revised March 1 990 edition of the Tenant

Construction Review Manual (PANYNJ 1990). Also included is Amendment #1 to the manual, dated October 23, 1990.

14 NISTNCSTAR 1-1 C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

A new subsection on Standards was added to the 1990 edition. The organizations whose standards arc

cited are: (1) American Association of State Highway and Transportation Officials and (2) American

Railway Engineering Association.

The section containing Port Authority design criteria was significantly expanded. Most notably, all structures were required to be designed for earthquake zone 2 forces in accordance with the Building

Officials Conference of America (BOCA) code. Local laws that contained seismic provisions more

stringent than those in the BOCA code were to take precedence. Also, reference was made to American

Society for Testing Materials (ASTM) E 580, Standard Practice for Application of Ceiling Suspension

Systems for Acoustical Tile and Lay-in Panels in Areas Requiring Moderate Seismic Restraint for lightweight ceilings to resist seismic forces.

The checklist for structural review that appeared in earlier editions of the manual (see Table 2-1 and

Table 2-3) was replaced; the 1990 edition of this list is summarized in Table 2-5.

Controlled Inspection of Materials, Operations, and Equipment

The inspection requirements, in Section 14 of the 1990 edition of the manual, were significantly

reorganized and modified compared with those in the earlier editions of the manual. Like earlier editions

of the manual, the NYC Building Code and its referenced standards were specifically referenced for the following requirements: (1) acceptance (approval) of materials, assemblies, fonns, methods of

construction, and (2) inspection of materials, assemblies, and construction.

Requirements for approval/acceptance of materials were abstracted directly from NYC Building Code

Sections C26-106.1, 106.2, 107.1, and 107.2. No materials, assemblies, forms, method of construction,

equipment, machinery, or devices were acceptable unless approved by the Code Test Method of the Materials and Equipment Acceptance (MEA) Division of the Office of the Commissioner of the Buildings

Department of New York City or approved by the New York City Board of Standards and Appeals

(BSA).

Controlled inspections requirements were abstracted from NYC Building Code Sections C26- 106.3 and

107.3. All materials, equipment, and construction designated by the Code for controlled inspection were

required to be inspected and/or tested to verify compliance with the Code. Controlled inspection was

required to be made and witnessed by or under the direct supers ision of a registered architect or

professional engineer retained by the tenant and acceptable to the architect or engineer responsible for the plans. The inspecting design professional was to be independent of the design professional responsible for the work. The hst of items subject to controlled inspection was essentially the same as the list in the 1979

edition (see Table 2-4). with the following exceptions: (1) steel (welding, high-strength bolts, and cable

fittings) and formwork were added, (2) structural integrity during construction operations was added, and

(3) Code section numbers and references to other resource documents were added for all items. Table 2-6

contains the list as it appeared in the 1 990 edition of the manual.

NISTNCSTAR 1-1C. WTC Investigation 15
Chapter 2

Table 2-5. Details of structural review in the 1990 edition of the Tenant

Construction Manual.

Provision

Design Calculations

Design criteria and applicable codes

Reference standards

Materials Type of construction and foundation

Design loads, including wind and other existing forces Machinery and equipment loads in excess of 1000 lbs., including an evaluation of any potential vibration Allowable soil bearing capacity

Design analysis and drawings of all connections other than AISC standard framed or seated beam connections

Analysis and sketches of expansion joints

Design of bracing systems and rigid joints

Wind drift and deflections Ponding

Computer printouts and users' manuals

Investigation of superimposed loads from adjacent construction on structure and foundation

Investigation of existing structural system and foundation under additional loads due to alterations Where it has been established that post-construction settlements of foundations are to be monitored, the monitoring program, the limits of such settlement that the structure can tolerate, and the necessary adjustments

shall be submitted for review

Drawings

Design code and reference standards

Materials Design live loads, wind, and other forces Machinery and equipment loads in excess of 1000 lbs., including footprints or support layout(s) plus technical

details of vibration isolators Allowable soil bearing capacity

Pile type, capacity, and minimum tip elevation Column schedule showing accumulated design load at each level for dead and live loads

Stress diagram(s) for trusses Datum and ground water elevations

Typical moment connection details

Details of non-standard connections

Lists of materials subject to controlled inspection

Construction sequence

Specifications

Shall clearly define the scope of work and materials required for the contract

Shall include limitations, restrictions, or conditions due to existing environs and/or requirements for the methods of construction or staging

16 NIST NCSTAR 1-1 C, WTC Investigation
Guidelines for Inspection. Repair, and Mod, to Structural Sys.

Table 2-6. Checklist for items subject to controlled inspection in the 1990 edition of the

Tenant Construction Manual.

Item Code Section or Resource Document

Borings or Test Pits C26-1 112.2

Piles C26-1 112.3

Soil -

Subgrade for foundation C26-1 112.5

Controlled Fill Underpinning C26-1 112.6 Concrete Tables 10-1 and 10-2

Prestressed concrete -

Precast concrete - Formwork C26- 1904.3(b)

Steel - welding, high strength

bohs, and cable fittings

Table 10-2

Aluminum - welding Table 10-2 Laminated wood Table 10-2

Firestops C26-504.7(g)

Spray-on fireproofmg C26-502.2(f)

Heating systems C26-1401.1(a) and 1401.2(b)

Ventilation System C26-1301.2 and 1301.3

Refrigeration System C26-1301.4

High Pressure System

Chimney Smoke Vent C26-1501.1(e) and 1504.1(b)

Exterior walls C26- 150.1

Structural integrity during

construction operations

Department of Buildings. Rules

2.1.4 March 1997 Edition^

General Requirements

The general requirements are essentially the same as those in previous editions of the manual.

Structural Requirements

The most notable change was made to the Port Authority design criteria section. The NYC Building Code

was mandated to be used for earthquake design, subject to the modifications contained in Attachment S3. The modifications contained in this section pertain to Table 23-P, Horizontal Force Factor Cp of

referenced standard RS 9-6, Earthquake Loads. The manual added horizontal force factors for overhead

See Appendix D for the general and structural requirements in the March 1997 edition of the Tenant Construction Rev iew Manual (PANYNJ 1997).

NISTNCSTAR 1-1 C, WTC Investigation 17
Chapter 2

signs, anchorage for suspended ceilings weighing more than 4 psf without the weight of light fixtures, elevator and counterweight guardrails and supports, sprinkler piping, gas and high hazard piping, other

piping, and heating, ventilation, and air conditioning (HVAC) ducts, along with new notes pertaining to sprinkler piping, other piping, and HVAC ducts. These requirements, which were originally outlined in a Port Authority Memorandum'' and which were included with other such requirements in the document

Port Authority Standards Exceeding Code - Qualit}> Assurance dated April 26, 1999 (PANYNJ 1999), were added to the manual to ensure that potential overhead hazards would not fall on building occupants

during a seismic event.

The details of structural review in the 1997 edition were the same as those in the 1990 edition (see

Table 2-5), except that the hst of materials subject to controlled inspections was deleted.

Controlled Inspection of Materials, Operations, and Equipment

Some additions and modifications were made to the inspection requirements in the 1990 edition of the manual. The checklist for items subject to controlled inspection was also updated to include the updated

NYC Building Code section numbers (see Table 2-7).

2.2 STANDARDS FOR STRUCTURAL INTEGRITY INSPECTION OF THE

WORLD TRADE CENTER TOWERS A & B

2.2.1 Overview

In March of 1986, the Infrastructure Engineering Design Division of the Engineering Department of

PANYNJ issued the Standards for Structural Integrity Inspection ofthe World Trade Center Towers A &

B (PANYNJ 1986).^ These standards were to assist the PANYNJ in the evaluation of the structural

integrity of WTC 1 and WTC 2 and were designed to anticipate structural degradation. If such

degradation were to occur, the standards also contained provisions for repair.

Three methods were used to evaluate the structural integrity of the towers: (1) statistical inspections,

(2) reports, and (3) continued measurements. In the first method, qualified outside consultants under

PANYNJ management were to perfonn periodic visual inspection of selected structural components in "higher-potential trouble areas." It was anticipated that PANYNJ in-house personnel would be able to perform such inspections in the future. The periodic inspections were to be supplemented by occasional

visual inspections when the structure was exposed during tenant remodeling or general maintenance

work.

In the second method, the evaluation would be based on problems identified in various reports. These

reports may include maintenance reports of non-stnictural repairs, water leakage, and tenant complaints

about unusual building movements, vibration, or noise.

^ PANYNJ Memorandum dated August 8, 1995 from Oscar Suros, Manager of the Engineering Department Quality Assurance

Division to Eugene J. Fasullo, Director and Chief Engineer (see Appendix G of this report).

' See Appendix E for the complete document.

18 NISTNCSTAR 1-1 C, WTC Investigation
Guidelines for Inspection, Repair, and Mod. to Structural Sys.

In the third method, the evaluation would be based on mcasureinents of building movements or deformation using appropriate tests and instruments. Measurements were to be performed on individual

components in the towers as well as on the entire towers themselves.

The periodic inspection program outlined in PANYNJ (1986) is adapted from "Standards for In-dcpth

Structural Integrity Inspection of Buildings," which was issued by the Engineering Department of

PANYNJ in October of 1984 and which was relevant to any building owned and operated by the PANYNJ. The other sections in PANYNJ (1986) pertain exclusively to WTC 1 and WTC 2.

Table 2-7. Checklist for items subject to controlled inspection in the 1997

edition of the Tenant Construction Manual.

Item Code Section or Resource Document

Borings or Test Pits 27-720

Piles 27-721 Subgrade for foundation 27-723

Controlled Fill 27-679(a)

Underpinning 27-724

Concrete Tables 10-1 and 10-2 Fomiwork 27- 1035(b)

Steel - welding, high strength

bolts, and cable fittings

Table 10-2

Aluminum - welding Table 10-2 Laminated wood Table 10-2

Firestopping 27-345(h)

Masonry Table 10-2

Exterior Wall Insulation and

Finish Systems

27-335. l(c)13

Spray-on fireproofing 27-324(f)

Heating and combustion

equipment

27-793(a), 27-794(b)

Ventilation System 27-779,27-780

Refrigeration System 27-781 High Pressure System Department of Buildings, Rules Section 20-

02(b)(2)(i)

Welding of gas distribution piping

RS-16, PI 15.8(h)

Chimney Smoke Vent 27-856(e), 27-879(b)

Curtain/Panel Wall Rules of the City of New York, Title 1, Department of Buildings. Chapter 32

Structural integrity during

construction operations

Rules of the City of New York, Tide 1, Department of Buildings, Chapter 16

NISTNCSTAR 1-1C, WTC Investigation 19
Chapter 2

2.2.2 Inspection Program

Visual Inspections

The PANYNJ recognized that the visual inspection of the entire structure, or even a major portion of it, in WTC 1 or WTC 2 was not practical, as stated in PANYNJ (1986). Thus, a statistical inspection program was implemented. This approach involved sampling those components and systems that were important

to structural integrity at locations with "a relatively higher potential for occurrence of defects or problems."

The inspection team was required to carry with them the following items: (1) a set of reduced drawings of

the building(s), (2) field notebooks, (3) a camera, and (4) a tape recorder. Equipment, clothing, methods,

and procedures were to conform strictly to PANYNJ safety regulations and to any applicable federal,

state, or local regulations.

Visual inspection was to be supplemented by the use of simple hand tools, measurements, and recording

techniques, as required. Loose, cracked, or rust-stained spray-on fireproofing and concrete or masonry

encasement covering structural steel members and connections was to be removed prior to examining the

steel. After inspection, any removed fire proofing was required to be properly replaced. Also, where it was necessary to drill a hole through a structural steel element to provide access for a borescope or any

other device for inspection, the access hole was to be sealed with weld metal, body putty, or caulking, as appropriate.

Periodic inspection in WTC 1 and WTC 2 was to be perforaied by PANYNJ or its consultants on the following components at various time intervals, as noted below:

1 . TV antenna mast on the top of WTC 1

.

This program, the details of which are given in Appendix A of PANYNJ (1986), consisted of

four parts: (a) inspection of the structural steel elements in the antenna, (b) inspection of the high tensile bolts and studs, (c) inspection of the weatherproof enclosure, and (4) inspection

of the radomes. Inspection of these components was to be performed on a "continuing basis," as weather and operational restrictions pennitted. A complete inspection of the mast structure within the weatherproof enclosure was to be performed at least once a year; the other

components were to be inspected at least once every 3 years.

The elements of the inspection program for the antenna mast, the high tensile bolts and studs, the weatherproof enclosure, and the radomes are given in Chapters II, III, IV, and V,

respectively, of Appendix A (see Appendix E of this report).

2. Exterior roof and wall elements.

Every year, the exterior roof and wall elements were to be inspected for signs of water

intrusion. Roof leakage was to be ascertained from an examination of the spaces immediately

below the roof areas. Wall leakage was to be detennined from signs of water staining of

interior finishes.

20 NISTNCSTAR 1-1 C. WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

3. Room occupancies.

An inspection of room occupancies and uses throughout both towers was to be performed on

an annual basis to verify that design live load was not exceeded. A schedule of allowable live loads was to be maintained and updated as structural modifications were made. According to PANYNJ (1986), no such schedule existed at that time.

4. Accessible column envelopes, including fireproofing.

Every second year, accessible columns were to be inspected for bowing or deviation from

plumb. Also, fireproofing was to be examined for signs of rust or cracking. Inspection for

lateral displacement or rotation of columns in elevator shafts where the columns were braced on only one axis by connecting beams or concrete slabs was required. The location of these columns is given in Appendix C of PANYNJ (1986).

At Sublevel 5, the slabs on ground surrounding each column were to be examined for signs of

rust or defonnation.

5. Fireproofing and masonry partitions on diagonal bracing and transfer trusses.

Fireproofing and masonry partitions enclosing the diagonal bracing on exterior column lines in both towers below the Service Level Floor and the transfer trusses below floor 1 in WTC 2 under exterior and core columns were to be inspected every second year for cracking, stains,

and other possible signs of structural distress.

6. Hat truss members.

Every second year, the hat truss members between floor 107 and the roof in the core area were to be inspected. Locations of these members are given in Appendix C of PANYNJ

(1986).

7. Exterior box columns and spandrel plates.

Exterior box columns and spandrel plates under column trees below floor 7 were to be

inspected every fourth year. Exterior aluminum covers and spray-on fireproofing were to be

removed to gain access to the exterior surfaces of the box columns and spandrel plates. Both

the columns and plates were to be visually inspected for bowing or distortion, cracking, and

corrosion. Visual inspection was also required for accessible welds. Ultrasonic testing of full or partial penetration welds and adjacent base metal was to be performed where base metal

thickness exceeded 1.5 in.

The interior of the box columns was to be examined by a borescope for the presence of water and the existence of rust on the interior plate surface. This was to be accomplished by drilling an access hole in the column or the spandrel plate at the locations noted in PANYNJ (1986).

The "tree" junction where the three superstructure columns merged was also to be inspected.

The top surface of the horizontal diaphragm plate that capped the tapered box column just

NISTNCSTAR 1-1C, WTC Investigation 21
Chapter 2

below the point where the three separate columns merged was to be examined, as was the

exterior column plate between this location and the column splice at elevation +372 ft 4 in.

8. Steel floor framing over mechanical spaces.

Every fourth year, the steel floor framing over mechanical spaces and other areas without

suspended ceilings was to be inspected. No other details are given in the document.

9. Concrete slabs, partitions, and finishes.

Concrete slabs, partitions, and finishes were to be inspected every fourth year for signs of

distress, which could indicate excessive structural defonnation.

Occasional inspections were also to be made of the structural steel framing, connections, and the concrete

slabs when general repairs or remodeling was done that involved removing ceilings, partitions, finishes, or other coverings. In particular, the top of the concrete slab was to be examined for cracking, spalling,

and exposed or corroded top reinforcement. Where reinforcing bars were corroded and where concrete had spalled, repairs were to be made as tenant relocation pennitted.

General maintenance reports and complaints from tenants were to be used to search for possible problems

related to underlying structural defects. Water damage caused by leaks at the roof level or at the exterior

walls, broken plumbing, and cracks in partitions or the concrete floor slab were to be reviewed to detennine whether such events were caused by structural defonnations. Records were to be kept of tenant complaints of building sway, floor vibration, sagging ceilings, unusual noise, and other items. Visual

inspection of the appropriate area of the building was to be perfonned where a reasonable assessment of

the data in the reports or logs was tied to a specific structural element or system. Reports and log data were to be cortelated with testing and measurements described in Section B of Chapter IV in PANYNJ

(1986), which is discussed in the next section of this report.

Periodic Measurements

Periodic measurements of various types of defonnation and vibration were to be made for the purposes of

monitoring changes in certain important characteristics of the buildings. Adverse changes in such

measurements were assumed to reflect possible structural deterioration.

Measurements of the following items were to be perfonned on a periodic basis:

1 . Natural frequency of the towers.

Accelerometers were to be installed on Mechanical floor 75 in WTC 2, one at each exterior

wall near its midpoint (oriented to respond to horizontal displacements parallel to the wall)

and two near the geometric center of the floor (to respond to displacements along the N-S and

E-W axes of the building). Figure 1 in Appendix C of PANYNJ (1986) shows the location of

the accelerometers (see Appendix E of this report).

11 NISTNCSTAR 1-1C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

The accelerometers in WTC 2, along with those already installed in WTC 1, were to be used

to measure natural frequencies of the towers on a monthly basis. Wind speed and direction were also to be recorded at that time.

No documents reviewed indicate that accelerometers were installed in WTC 2.

2. Natural frequency of the TV mast on WTC 1.

Accelerometers and amplifiers were to be installed within the heated enclosure of the TV

mast on the top of WTC 1 at a level of about two-thirds of the height of the mast above its base. One accelerometer was to be oriented to measure N-S displacements, and one was to be

oriented to measure E-W displacements. Displacement measurements, as well as wind speed

and direction, were to be recorded once a month.

No documents reviewed indicate that accelerometers were installed on the TV mast.

3. Natural frequency of the floor construction.

The natural frequency of the floor construction was to be measured when floor space had

been emptied due to tenant change or remodehng. Figure 2 in Appendix C of PANYNJ

(1986) shows the three zones outside of the core area on a typical floor (see Appendix E of

this report): (1) comer zone (two-way floor trusses), (2) short-span zone (short-span floor

trusses), and (3) long-span zone (long-span floor trusses).

In each tower. Mechanical floors 7, 41, and 75, and Tenant floors 9, 43, and 77, directly

above the Mechanical Floors, were not included in the floor frequency measurement

program, because they were framed with wide-flange steel beams and not trusses. However,

these floors were to be inspected visually. It was also noted that Telephone Equipment Floors

10 through 13 in WTC 2, which were framed with floor trusses similar to typical tenant floors but were more heavily loaded than such floors, would have different dynamic characteristics

in the three zones than would the corresponding zones in the tenant floors.

The natural frequency and damping values of the floor structure within a zone was to be

measured by perfomiing a "heel drop" test. In such tests, vibrations induced in the floor structure by a vertical impact are recorded using an accelerometer attached to the floor. Measurements were taken for an impact load of 100 lbs dropped from approximately 6 in. above the floor slab on to a 1 in. thick neoprene pad.

4. Viscoelastic dampers.

It was noted in PANYNJ (1986) that the testing program for the viscoelastic dampers should

continue. This program consisted of continuously measuring and recording the movements of

WTC 1 that were 3 in. or more. Wind speed and direction were also to be measured. It was

anticipated that such measurements would continue until the end of 1985 or longer,

depending on available funds.

NISTNCSTAR 1-1 C, WTC Investigation 23
Chapter 2

Twelve viscoelastic damping units (four units from each of three floors) were to be removed

from WTC 1 annually and were to be tested by the Minnesota Mining and Manufacturing

Company, who were the manufacturers of the damping units. Temperature effects and shear

strength were to be tested. See Chapter 3 of this report and the report titled Design and

Construction of Structural Systems of WTC 1, 2, and 7 (NIST Special Publication 1000-6A)

for more infonnation on these tests. A log of tenant complaints on noise and building sway was to be maintained on a continuous

basis.

5. Plumbness and level.

Building plumbness and floor level checks were to be performed semiannually for each

tower, preferably in the early morning hours in August when wind velocity was low and

outside air temperatures were moderate.

Building plumbness was to be detemiined by measuring the offsets from a vertical laser beam, which was to be projected up from the bottom of freight elevator shaft 50, to the shaft walls. Offset measurements were to be taken at 20-story intervals.

Floor levelness was to be determined by measuring the relative elevation of sixteen

benchmarks on the floor slab at floor 70 of each tower.

2.2.3 In-House Inspection Personnel

A list of duties, responsibilities, and minimum qualifications of the inspection supervisor, inspection crew

leader, and inspection crew members from the PANYNJ is given in Chapter V of PANYNJ (1986).

The Supervisor of the Structural Integrity Inspection of the Buildings, who reported to the Engineer of

Design, Infrastructure, was responsible for planning and directing the inspection, as well as preparing the inspection report. The Supei"visor was required to have the following minimum qualifications:

• Professional Engineering License in New York or New Jersey specializing in structural engineering

• Five years of experience in responsible charge in structural design of buildings and 5 years experience in responsible charge in inspection of building construction, inspection of existing

buildings, or maintenance of building structures.

The Supervisor did not have to conduct the inspection nor be present at the site at all times during the

inspection. Rather, the Supervisor was to be familiar with the scope of the project and was expected to provide leadership and guidance. That person was also responsible for setting up and supervising any

required training programs for inspection team members.

In addition to the general qualifications listed below for team members, crew leaders of the Inspection

Team were required to have three years experience in responsible charge in inspection of building

construction, inspection of existing buildings, or maintenance of building structures.

24 NISTNCSTAR 1-1C. WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

Field inspection crew members were expected to perform the required inspections without continuous

supervision after initially receiving "moderate" guidance from the crew leader. The following

qualifications were listed:

• Acute observation skills

• Common sense

• Strong motivation and persistence in carrying out any necessary follow-up procedures

As a minimum, an inspector should:

• Be able to climb steel and function comfortably at great heights and in difficult positions;

• Be a high school graduate or equivalent, with commensurate reading, verbal, and written

communication skills;

• Be able to read and understand construction drawings and other documents;

• Be able to letter legibly and sketch technical details;

• Be able to operate a camera;

• Have a working knowledge of the use of measuring devices, such as rulers, tapes, gauges,

protractors, and calipers; and

• Exhibit a proper concern for safety while inspecting.

PANYNJ (1986) also states that it was desirable, but not mandatory, that inspectors have some prior

experience in related work, such as high steel construction, structural maintenance or inspection, or

surveying.

2.2.4 Outside Consultants and Suppliers of Special Services

This section contains the requirements for outside consulting finns hired by the PANYNJ to perform

periodic visual inspections or to accomplish tasks requiring special skills. The consulting firm was to assign a Supervisor who was a Professional Engineer licensed in New York or New Jersey and who

possessed at least 5 years of experience in the design and field supervision of projects of comparable size and complexity. Field inspectors from the consulting finn were to have as a minimum the qualifications

that were required for in-house inspectors, as outlined in Sec. 2.2.3 of this report.

The consulting fimi was required to submit to the PANYNJ a list and description of comparable projects

that were previously undertaken, and a list of the personnel, along with their qualifications and

experience, who would be assigned to the inspection project.

NISTNCSTAR 1-1C, WTC Investigation 25
Chapter 2

2.2.5 Record Keeping and Follow-up Procedure

Defects and Signs of Distress

Chapter VII of PANYNJ (1986) lists the defects and signs of distress that were to be noted and recorded

during inspection of the structural steel and the reinforced concrete. A summary is provided in Table 2-8.

Table 2-8. Defects and signs of distress to be recorded during inspection of WTC 1 and WTC 2.

Material

Defect/Sign

of Distress Description

Structural Steel Rust Rust was to be classified as follows:

• Light — light, loose formation pitting the paint surface

• Moderate - a looser formation with scales or flakes that have

formed

• Severe - heavy, stratified rust or scale with pitting of the metal

surface. Net metal thickness and size of penetration, if any, was to be

measured where pitting had occurred. Cracks Cracks were to be classified as follows:

• Fine

• Medium

• Open

The length, size, and location of any crack were to be recorded. Any

crack was deemed to be potentially serious, and was required to be

reported immediately.

Buckles and

kinks

The type, location, and extent, and amount of deformation were to be

recorded. Connection

and joint

Fine cracks in the paint at joints were deemed an indication of large

strains due to stress concentrations. Records were to be made of the following:

• Sheared, missing, deformed, or loose bolts

• Gusset plate deformations

• Cracks in welds or in adjacent base metal Alignment,

excessive

deflection, or bowing

Records were to be made of any floor truss, beam, or column that was misaligned, deflected, or bowing.

Paint Paint was to be examined for cracking, chipping, rust pitting, and

chalking.

Reinforced Concrete^ Scaling Scaling was to be classified as light, medium, heavy, or severe. Records were to be made of the depth, extent, and location of the - scaling.

Cracking Cracks were to be classified as follows:

• Partial or through the member

• Direction relative to framing or column lines • Horizontal, vertical, or diagonal

• D-, map, or random

Records were to be made of the location, width, depth, and length of

the cracking.

26 NISTNCSTAR 1-1C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

Spalling Spalls were to be classified as small, large, hollow area, joint spall. pop-out, or mudball. Records were to be made of the depth, size or extent, and location of the spalling.

a. Definitions of the defects and classifications as to degree of severity are referenced for reinforced concrete in the F'ANYNJ

document Standards for In-depth Siruclural Inlegrily Inspection ofBuildings, October 1 984. Source: PANYNJ 1986.

Inspection Records

Each component that was inspected was to be identified as follows:

• General location - building number and floor or floors

• Description label - column, beam, floor truss, viscoelastic damper, slab, etc.

• Piece mark and column designations at each end as applicable

• Type and location of affected part

The inspection record should include the description of the defect or distress. Measurements, sketches,

and photographs were to be included in the record in those cases where a written description was not adequate. A tape recorder may also be used in addition to the written record.

If the Supervisor or the inspection team uncovered defects or indications of distress that appeared to require more than routine attention, a separate report of such findings was to be submitted to the Engineer

of Design was to be immediately notified in person.

Three categories of urgency were established for repairs. Repairs falling into the "immediate" category

included possible closure of the area and/or structure affected until interim remedial action (such as shoring or removal of a potentially unsafe element or structure) could be implemented. Such action was to be undertaken immediately after discovery, and a description of the action taken and recommendations

for permanent repair were to be included in the inspection report.

The "priority" category was for those conditions where no immediate action was required, or for which

immediate action had been completed, but for which further investigation, design, and implementation of

interim or long-tenn repairs should be undertaken on a priority basis (i.e., taking precedence over all other

scheduled work).

Repairs falling into the "routine" or "non-priority" category could be undertaken as part of a scheduled

major work program or other scheduled project, or when routine facility maintenance was to be

performed, depending on the type of repair that was required.

Measurements and Test Records

The measurements and test records section of PANYNJ (1986) outlines the various measurements and

test data that were to be recorded during the inspection process for the items listed in Sec. 2.2.2 of this

NISTNCSTAR 1-1C, IVTC Investigation 27
Chapter 2

report. Also given are the criteria that determine whether a possible problem may exist, based on the recorded measurements.

2.2.6 Excluded Work

^

In the last chapter of PANYNJ (1986) it was noted that the standards for structural inspection were

applicable to only structural steel and reinforced concrete members in WTC 1 and WTC 2. Glass and

glazing, facade panels, ceilings, partitions, elevators, stairs, and mechanical equipment were listed as components outside the scope of the document.

2.3 ARCHITECTURAL AND STRUCTURAL DESIGN GUIDELINES,

SPECIFICATIONS AND STANDARD DETAILS

The document entitled Architectural and Structural Design Guidelines, Specifications and Standard

Details was issued on February 27, 1998 by PANYNJ and contained architectural and structural design

requirements for tenant alterations that were to be made specifically at WTC 1 and WTC 2 (PANYNJ 1998).** The following discussion focuses on the structural requirements contained in this document.

2.3.1 Structural Design Guidelines

~

General

Prior to any design work, the tenant's consultants were required to perfonn a field inspection of all areas

that would be affected by the alterations so that the latest infonnation was available for all structural elements, including, but not limited to truss reinforcement, stair openings in slabs, and core-hole

locations.

The tenant's consultants were required to submit calculations and construction drawings to PANYNJ for review and approval. All construction documents were required to be signed and sealed by a professional

engineer or registered architect licensed to practice in the state of New York.

Calculations, Loads, and Design Parameters

For tenant alteration project, proposed floor loads were to be compared with the allowable design loads

contained in Drawing STR-01 (see Appendix E). If the proposed floor loads would overstress the existing

structural members, the floor system was allowed to be reinforced to carry the additional loads.

Calculations to compare the proposed loading with the allowable loads were required to conform to the

latest edition of the NYC Building Code. Both allowable stress design and load-and-resistance-factor

design were acceptable design methods.

The document recognized that portions of the corner floor areas would be able to cany greater loads than

those shown in Drawing STR-01, due to the existing two-way truss system. Higher loads were allowed in

This document is contained in Appendix F of this report.

28 NISTNCSTAR 1-1C, WTC Investigation
Guidelines for Inspection, Repair, and Mod, to Structural Sys.

non-critical corner areas if it could be shown by analysis that such loads could be safely carried by the

floor system.

The document required to show and locate on the construction drawings the weight of any equipment or

cluster of equipment exceeding 500 lb and all files and shelves. In the latter case, a legend was to be

shown on the drawings to indicate each type of file or shelving unit and the size and number of tiers for

files and the height for shelves. Examples that show such weights on the construction documents can be

found in Chapter 4 of this report.

Minimum loads to be used in the calculations were also specified. These loads are summarized in Table 2-9.

Table 2-9. Minimum loads specified for tenant alterations in PANYNJ Architectural and

Structural Design Guidelines, Specifications, and Standard Details.

Item or Use Minimum Load

File cabinets 33 psf per tier, including the weight of the cabinet Open shelves for paper storage 46 pcf of the net volume plus the weight of the shelves Mechanized file storage Use manufacturer's indicated fully loaded weight,

or the net weight of the storage unit plus 46 pcf

for contents

Libraries Aisle loading for aisle width less than or equal to 30 in.30 psf

Aisle loading for aisle width greater than 30 in.60 psf

Reading areas 60 psf

Open shelves 46 pcf of the net volume plus the weight of the shelves

File rooms aisle loadingAisle width less than

or equal to 30 in.

30 psf

Aisle width greater than 30 in.50 psf

Core Holes and Other Slab Penetrations

All proposed penetrations or drilling of cores in tower slabs were required to meet the criteria for location,

spacing, and repair as specified in Drawings STR-02 through STR-08 (see Appendix F), and the section

titled Structural Design Specifications, which is discussed below. As shown in the figures, there were some areas that were denoted as "prohibited" where no penetrations or cores were allowed, and there were some areas denoted as "restricted" where it was advisable not to locate penetrations or cores.

Hung Ceilings

For ceilings in the two-way truss areas of the towers, the size of the carrying channels and caddy clips were required to be larger than those required by the NYC Building Code, due to the long spans between

NISTNCSTAR 1-1C, WTC Investigation 29
Chapter 2

the trusses. The details in Drawings STR-09 through STR-14 (see Appendix F) were required to be

provided on the construction drawings.

HVAC Equipment

The weight, dimensions, and location of all HVAC equipment were required on the drawings, including

whether such units were floor mounted or hung from the framing above. Details for hanging ducts are in drawings HVAC-21 through HVAC-28. Calculations were required for all floor-mounted units showing

that the existing framing would not be overstressed due to the weight of the equipment.

Walls

For walls over an opening, such as a door or other non-supportive materials, a lintel was required, or the wall was allowed to be suspended by studs from the framing above. In such cases, all connections were to be adequately designed for the loads.

Existing Steel

Holes were not allowed to be made in existing steel (beams, floor trusses, and columns) for hanging

purposes, and welds were not allowed to be made to the trusses. Clamps approved by either the MEA

Division of the Office of the Commissioner of the Buildings Department of New York City or by the New York City BSA were allowed.

2.3.2 Structural Specifications

Coring Criteria at Tower Power/Telephone Cells and Under Induction Units

The specifications given in the section on coring criteria were meant to supplement those given in the guidelines section, and were applicable to only those holes cored into the power/telephone cells and under

induction units and only in the following typical tenant floors: (1) in WTC 1: floors 10 to 40, 45 to 74,

and 78 to 105, and (2) in WTC 2: floors 14 to 40, 45 to 74, and 78 to 106.

The maximum core size allowed was 4 in. in diameter. The minimum average center-to-center spacing

along a power/telephone cell for any 4 consecutive cored holes (including abandoned and filled holes) was 1 ft 4 in. Spacing criteria along power/telephone cells adjacent to holes offset from cells was

provided in Drawing STR-05 (see Appendix F).

This section recommended avoiding cutting No. 4, No. 5, and No. 6 reinforcing bars in restricted zones. If such bars were to be cut, the bar repair details in Drawings STR-06 through STR-08 were to be followed

(see Appendix F). As noted previously, coring was not allowed in prohibited zones, except within the induction units at the power/telephone cells only, which was considered a restricted area.

Rust, grease, and other contaminants were to be removed from structural steel and reinforcing bars prior

to welding. All welders were to be qualified in accordance with the NYC Building Code and with other

applicable laws and requirements.

30 NISTNCSTAR 1-1C, WTC Investigation
Guidelines for Inspection. Repair, and Mod. to Structural Sys.

This section required that all work confonn to the latest edition of the NYC Building Code, including any

revisions. Provisions in the latest editions of the following codes took precedence over those in the NYC

Building Code whenever they were more stringent:

• American Institute of Steel Construction, Specification for the Design, Fabrication and

Erection of Structural Steel for Buildings. Supplement 1 is specifically excluded.

• American Concrete Institute, Standard Building Code Requirements for Reinforced Concrete,

ACI 318.

• American Welding Society (AWS), Structural Welding Code - Structural Steel (AWS D 1 . 1

)

and Reinforcing Steel (AWS D1.4).

Any steel plates that were added to reinforce existing framing or for other reasons were required to confonn to ASTM A36, and any reinforcing bars that were added were required to conform to ASTM A615 Grade 60.

Welding materials for structural steel and reinforcing steel were required to be E7018 confonning to AWS A5.1 Specifications for Covered Carbon Steel Arc Welding Electrodes. Specifications for nonshrink grout were also specified.

Lightweight Ceiling Support System for Floors with Double Trusses

Specific proprietary concrete anchors were specified for any connections made to concrete. Other

requirements were given for the type and sizes for clip angles, hangers, channels, and clamps. The

contractor was to keep removal of fireproofing to a minimum and was to replaced removed fireproofing

as "directed" by the Port Authority.

2.4 REFERENCES

PANYNJ (The Port Authority of New York and New Jersey). 1979. Tenant Construction Review

Manual. (WTCI-134-P).

PANYNJ (The Port Authority of New York and New Jersey). 1 986. Standards for Structural Integrity

Inspection of the World Trade Center Towers A & B. Infrastructure Engineering Design Division,

Engineering Department, The Port Authority of New York and New Jersey, (part of WTCI-66-P).

PANYNJ (The Port Authority of New York and New Jersey). 1990. Tenant Construction Review

Manual. Engineering Quality Assurance Division, Engineering Department, The Port Authority of

New York and New Jersey. (WTCI-132-P).

PANYNJ (The Port Authority of New York and New Jersey). 1 997. Tenant Construction Review

Manual. Engineering Quality Assurance Division, Engineering Department, The Port Authority of

New York and New Jersey. ( WTCl- 1 3 1 -P).

NISTNCSTAR 1-1 C, WTC Investigation 31
Chapter 2

PANYNJ (The Port Authority of New York and New Jersey). 1998. Architectural and Structural Design

Guidelines, Specifications, and Standard Details - Architectural, Structural. February.

(WTCI-125-P).

PANYNJ (The Port Authority of New York and New Jersey). 1999. Port Authority Standards Exceeding

Code - Qualit}' Assurance. April. (WTCI-163-P).

PONYA (The Port ofNew York Authority). 1971. Tenant Construction Review. (WTC1-135-P).

32 NISTNCSTAR 1-1C. WTC Investigation
Chapter 3

Structural Inspection Programs During the Occupancy of

WTC1,2,and7

3.1 FACILITY CONDITION SURVEY REPORTS

The following facility condition survey reports, which include summaries on the condition of the

structural systems in World Trade Center (WTC) 1, 2, and 7, were issued from 1990 to 2000 and are presented in chronological order.

3.1.1 Port Authority Facility Condition Survey Program - WTC 2

This section contains the findings of the condition survey of WTC 2 (Tower B), which was performed by

the Engineering Quality Assurance Division (EQAD) of PANYNJ in 1990 (PANYNJ 1990).

Scope

The scope of the survey was based on recommendations made in Standards for Structural Integrity

Inspection of World Trade Center ToM'ers A & B (PANYNJ 1986). This document contains the minimum

requirements of the periodic and occasional inspection programs that were to be implemented for WTC 1 and WTC 2. See Sec. 2.2 of this report for details on this document.

According to the facihty condition survey report, the scope of work was designed to minimize impact on

tenant and facility operations. Upon detennination of minimum sampling sizes and inspection methods,

EQAD perfonned a condition survey of structural and architectural elements. The following is a list of the

structural elements that were inspected:

• Exterior wall system (including columns, spandrel plates, and connections)

• Core columns (including column splices and lateral bracing below the 7th floor; this part of

the condition survey was primarily performed by the consulting finn Corddiy, Carpenter,

Dietz and Zack)

• Space frame (i.e., hat truss, including framing members and connections)

• Floor systems (including floor slabs and decks, trusses, rolled beams, bridging, and

connections)

• Damping system (including damping units and connections)

NISTNCSTAR 1-1 C, WTC Investigation
Chapter 3

Inspection Procedures and Methodology

To assess the condition of the structural system in the tower, EQAD perfomied both visual inspection and

nondestructive testing methods. The thickness of steel members was checked using an ultrasonic

thickness gauge. Fillet welds were tested for cracks and discontinuities using magnetic particle or dye

penetration test methods, and groove welds were tested using the ultrasonic method.

Office Area Floors

The EQAD selected 30 office floors throughout the tower for inspection: 17, 18, 21, 27, 28, 29, 33, 34,

36, 37, 44, 45, 50, 55, 56, 62, 63, 64, 65, 74, 77, 82, 83, 90, 91, 92, 98, 100, 101, and 107. The following

steps were taken when inspecting the structural elements at these levels:

1 . Walk-through inspection with tenant representatives was perfonned to assess floor layout,

detemiine operational areas that were important to the tenant, and select inspection locations.

2. A ceiling tile removal location plan was prepared for concealed spline ceilings.

3. Ceiling tiles were removed (perfonned by World Trade Department's structural contractor).

4. Floor framing and steel decking, inside faces of steel spandrel plates, spandrel splices, ceiling

components, utility supports, and window seals were visually inspected. Structural steel members covered with fireproofmg were examined for signs of deformation or coiTosion.

5. Approximately seven floor framing locations were selected for fireproofing removal and a removal location plan was prepared. In order to inspect column splices, two exterior columns

were selected for plaster removal, both above and below the splice.

6. Fireproofing was removed at designated locations (perfomied by World Trade Department's

structural contractor).

7. An up-close inspection of exposed floor framing and column splices was performed for signs

of cracking, deformation, or corrosion. Scrapers, wire brushes, and mirrors were used to accomplish this task.

8. Nondestructive testing was performed on column splice welds and welded floor framing

connections (perfonned by the Materials and Research Division of PANYNJ, as directed by

the Quality Assurance Division of PANYNJ).

9. Fireproofing and ceiling tiles were replaced, and plaster openings were repaired (perfonned

by World Trade Department's structural contractor).

Table 3-1 contains the percentage of structural elements inspected per office floor and for the entire tower.

34 NISTNCSTAR 1-1 C, WTC Investigation
Draft for Public Comment Structural Insp. Prog. During tfie Occupancy of WTC 1, 2, and 7

Table 3-1. Percentage of structural elements inspected per office floor and for the entire

Element Type of Inspection

Percentage per

Floor

Percentafje

Total Tower

Floor framing trusses Visual 10 3 Fireproofmg removal 4 1

Nondestructive testing 2 0.5

Exterior column spandrel Visual 8 3 plate splices Fireproofmg removal 3 1

Exterior column splices Visual and nondestructive

testing

8 2

Mechanical Equipment Room (MER) and Space Frame

All four two-story MERs were visually inspected from the lower floor, which included inspection of floor framing and slab, interior columns, utility hangers and pads, and exterior setbacks. Concrete fireproofmg

for covering the steel floor framing was examined for delaminations and underlying corrosion.

Inspection of the space frame (hat truss) coincided with the 108th floor MER inspection. Fireproofing was removed from structural steel members and connections at several locations.

Core Columns

Core columns were inspected from the elevator shafts. This included visual inspection of ( 1) floor framing, columns, connections, and splices in 25 elevator shafts with fireproofing in place,

(2) 10 eccentrically-braced column connections with fireproofing removed, and (3) 15 column splices

with fireproofing removed.

Also, the core column lateral bracing at the first six floors was examined at two connection locations by

removing the gypsum board firewall from the floor side. Nondestructive testing was also performed at some of the column splices.

Roof

The roof and appurtenant structures along with the Observation Deck were visually inspected. The roof

framing and underside of the concrete roof slab were visually inspected from the 1 10th floor, and the top

surface of the concrete roof slab and the roof parapet were visually inspected at random locations.

Findings of Inspection

The following sections summarize the findings and recommendations from the 1990 survey report.

Exterior Walls (Columns and Spandrels)

Inspection of the exterior walls was made from inside the building. Inspection locations are indicated in

Fig. 3-1, which is Drawing 5 from the report (PANYNJ 1990).

NISTNCSTAR 1-1 C, WTC Investigation 35
Chapter 3

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36 NISTNCSTAR 1-1C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Floors 9 through 106—The exterior columns and spandrels were inspected on 30 floors at three areas of

the wall panel: (1) column field splice connections, (2) spandrel field splice connections, and (3) inside

spandrel plate face at the column/floor truss seat connections. Details of the splices at these locations are provided in Drawing 4 in the report, which is reproduced here in Fig. 3-2.

According to the report, exterior column splices were found to be in good condition.' A total of 59

splices were inspected throughout 30 floors. At 49 of these locations, nondestructive testing was

perfonned on the plate splice welds (see Sections a-a and b-b in Fig. 3-2 for location of welds), and

ultrasonic testing was performed to verify plate thickness. Bolt tightness was also checked, and no loose

bolts were found. However, on floors 74 and 77 (above and below an MER floor), the column splices had

only three bolts, although the design detail called for four. According to the report, since the column

splices at MER floors are groove welded, the missing bolts have no structural significance.

The inside faces of the steel box column plates were found to have scattered areas of light corrosion and

peeling paint, as did splice bolts, welds, cap and base plates, and column stiffeners. Ultrasonic thickness

testing on these outer column plates above and below the splice location indicated no section loss.

Fillet shop welds connecting the cap and base plates to the interior of the box columns were visually

inspected at all open splice locations, and most of the welds were tested using the magnetic particle

method. No cracking or significant discontinuities were detected at any location. According to the

report, overlaps and undercuts were observed at several locations, but they were not significant enough to affect the performance of the connection.

Groove weld splices were tested on the 74th floor using the dye penetrant method and on the 77th floor using the magnetic particle method. No discontinuities or cracks were detected.

Spandrel plates, splice plates, and spandrel bolted connections were also found to be in good condition.

Scattered rust stains were observed on the spandrel fireproofing, typically at the splice plates. All splice

plate bolts were observed to be tight. Fillet welds at the tioiss seat connections to the spandrels were also found to be in good condition.

Floors 107 through 110—Inspection was limited to the joints at the 108th floor. No structurally

significant deterioration was found.

Recommendations—No priority recommendations for repair were made in the report. It was

recommended, however, that a long-term maintenance program be developed and implemented to clean

and paint the inside surfaces of the exterior box columns to prevent further corrosion of the structural

steel.

In this report, a structural member that receives a "good" condition rating requires no repairs. The structural member is defined to be in "original condition" (see page 1 1 of PANYNJ (1990) for this and other definitions).

NISTNCSTAR 1-1C, WTC Investigation 37
Chapter 3

COLUMN-'

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C

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1. WELDS AND INTERIOR SURFACES OF

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SECTION

^SPANDREL IE. B-B

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DETAIL C

SPANDREL SPLICE

THE WORLD TRADE CENTER

TOWER "B"

CONDITION SURVEY

EXTERIOR COLUMNS AND SPANORELi

SPLICE DETAILS

Drawing Number:

Source: PANYNJ 1990. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 3-2. Splice details at typical inspection locations of exterior v\^all per the 1990

Condition Survey Report of WTC 2.

38 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Core Columns

Inspection of the core columns was performed in two phases. In one phase, staff from the consuhing firm

of Corddry, Carpenter, Dietz and Zack inspected core columns from the elevator shafts. In the other

phase, PANYNJ Quality Assurance Division staff inspected selected core comer columns from office area floors. They also inspected lateral core bracing at two locations from an elevator lobby on the 4th floor.

Core columns inspectedfrom elevator shafts—The consultant randomly selected a total of 25 elevator

shafts for inspection. Table Bl in the survey report contains a list of the elevator shafts that were visually

inspected. Lateral bracing members, columns, and floor framing between the 2nd and 7th floors were

inspected from eight other express elevator shafts.

Elevator core framing was inspected primarily with fireproofmg materials in place. Only in elevator shaft number 52 between the 44th and 55th floors was the fireproofmg removed at the column splices.

According to the report, no defects were found in the existing fireproofing material. In most of the shafts, several small regions and a few large areas of fireproofing were found to be missing from core framing

members, which, according to the report, was probably due to the high-speed elevators moving up and

down the shafts. In particular, an 8 in. wide by I ft 6 in. long area of fireproofing was found to be missing on the top flange of the beam between shaft numbers 30 and 31 on floor 22. Also, 100 percent of the fireproofing was found to be missing from the south face of column 908 between floors 27 and 29 in shaft number 1 . All exposed steel members were found to be in good condition with only isolated locations of

light surface corrosion on the steel. Some minor shrinkage cracks were reported in the troweled-on

fireproofing materials on the columns.

Gypsum wallboards surrounding the elevator shafts were also found to be in good condition, although

isolated holes were detected at various locations as outlined in Table B2 of the survey report. At shaft number 4, a piece of wallboard was found to be loose in the southeast comer of the shaft; facility

personnel repaired this piece.

Close-up inspection of column splices and eccentric-braced column connections with fireproofing

removed at the locations designated in Tables B3 and B4 showed that all bolts, welds, and stmctural steel were in good condition. No defects in the welds were found after EQAD personnel perfonned ultrasonic

tests on the butt welds at the column splices and magnetic particle tests on the fillet welds at the eccentrically-braced column cormections.

Column splices and eccentrically-braced column connections in the express elevator shafts were not

tested due to restricted access.

Quality Assurance personnel inspected the lateral bracing of the core columns at two locations (one

between columns 606 and 607 and one between columns 907 and 908) on the 4th floor. Light surface

corrosion was found on the bracing, splice plates, and bolts. The welds were tested using the magnetic

particle method and were found to be in good condition, and no cracks were observed.

Core columns inspectedfrom office area floors—Quality Assurance personnel inspected core comer

columns at eight splice locations (see Table B6 in the survey report for locations). Seven of the splices were welded, and the welds were tested using the ultrasonic and magnetic particle methods. The eighth

NISTNCSTAR 1-1C, WTC Investigation 39
Chapter 3

location was a bolted splice connection. No defects were found in any of the welded splices. Steel columns exhibited light surface corrosion, as did the bolted splice on the bohs and splice plates.

Recommendations—No priority recommendations for repair were made in the report. It was recommended that the fireproofmg that was missing from the elevator shaft framing members be

replaced, including those regions where the fireproofmg was removed for up-close inspection during the condition sui'vey. This report also reconunended that the holes in the gypsum wallboards surrounding the

elevators, which are listed in Table B2 of the survey report, be repaired.

Floor Framing

Inspection locations for the floor framing at typical floors are shown in Drawing 9 of the report, which is reproduced here as Fig. 3-3. Findings for specific zones are reported below.

Main Lobby (floors 1 through 6)—Beams and connections that were inspected within the core in this zone were found to be in good condition. At various locations, fireproofmg was missing, exposing light

surface corrosion on the beams and connections.

Floors 9 through 41—Floor framing inspected in this zone was found to be in good condition. Light

corrosion was observed on all core beams and beam cormections, and on main truss connections on

floors 28 and 37.

According to the report, the most significant deficiencies in this zone were found at the damping units

(see Table C-1 in the survey report). Damping units on floors 18 and 37 were observed to be missing one

fastener at each unit. Two fasteners were found to be missing in one damping unit on floor 29, as well as on floor 38. Also, at floor 38, a damping unit was observed to be missing four fasteners. According to the

structural drawings (WSHJ 1967a), four fasteners were required to connect the damping unit to the member attached to the bottom chord of the floor truss, and two fasteners were required to connect the damping unit to the exterior column.

40 NISTNCSTAR 1-1 C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

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NISTNCSTAR 1-1C, WTC Investigation 41
Chapter 3

Floors 43 through 75—The floor framing in this zone was also found to be in good condition. Light

corrosion was observed on the same members as in the previous zone.

Minor deficiencies were found at floor 64 and floor 75. A defonned bottom chord was found on the main

truss along column 343 on the 64th floor. According to the report, "No signs of distress were observed."

The entire floor framing was visually inspected on the 75th floor, since the fireproofmg was being

replaced on this level. Most of the exposed structural components and connections were found to be in good condition. Untightened bolts were found at truss seat connections at several locations, which,

according to the report, did not significantly affect the structural integrity of the framing.

Hairline cracks were observed in the 2 in. thick concrete topping slab near the south exterior wall on the 44th floor. According to the report, these cracks were due to shrinkage and did not affect the structural

integrity of the floor slab.

Floors 77 through 107—The floor framing in this zone was found to be in good condition, with light

surface con'osion observed on all core framing beams and connections.

Minor deficiencies were found in floor slabs, where separation of the concrete slab from the metal deck

forms was found at floors 93 and 108. According to the report, this condition did not affect the structural integrity of the slab, since decking served as fonnwork for the concrete and had no structural function.

Mechanical Equipment Rooms (Floors 7-8, 41-42, 75-76, 108-109)—The floor framing and slab inspected on the MER floors were found to be in good condition. On all MER floors, most of the

structural framing was inaccessible due to heating, ventilation, and air conditioning (HVAC) ducts, fans, electrical equipment, or plumbing. No nondestructive testing was perfonned on these levels.

Hairline cracks were found in concrete beam encasement at various locations on all four MER floors. Exposed steel exhibited light surface corrosion, and no deterioration was found at the underside of floor

slabs.

Selected elements of the space frame at various locations on the 107th through 1 10th floors were

inspected and were found to be in good condition. Exposed truss elements and connections both

exhibited light surface corrosion. Bolted and welded connections were also found to be in good condition.

Recommendations—No priority recommendations for repair were made in the report. As mentioned

above, all the deficiencies found were considered to have no significant effect on structural integrity. It was recommended that utility supports found to be bowed or vibrating be replaced as part of the facility's

regular maintenance program.

Roof

Roof framing, which consisted of rolled steel wide flange beams supporting a structural concrete slab, was found to be in good condition. Hairline cracks in the fireproofing and in the underside of the concrete slab were found at various locations.

Recommendations—No priority recommendations for repair were made in the report. Recommendations

that were made were not structural in nature.

42 NISTNCSTAR 1-1 C. WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

3.1.2 Port Authority Facility Condition Survey Program - WTC 1

This section contains the findings of the condition survey of WTC 1 (Tower A), which was performed in 1991 by the Office of Irwin G. Cantor, Consulting Engineers, for the EQAD of PANYNJ

(PANYNJ 1991).

Scope

The scope of the survey was detennined based on experience gained from the condition survey of WTC 2

in 1990, which was discussed in Sec. 3.1.1 of this report.

The scope of work was designed to minimize impact on tenant and facility operations, and was limited to vacant floors and tenant areas and partially occupied floors. The following is a list of the structural elements that were inspected:

1 . Floor framing (long, short, and transverse trusses, rolled beams, concrete encased beams,

bridging, and connections)

2. Damping system (damping units from bottom of trusses to exterior walls and connections)

3. Exterior wall system (columns, column splices, spandrel plates, splices, and bolted

connections of spandrel beams)

4. Core columns (columns within elevator shafts, including visible floor beams)

5. Space frame (framing members and connections)

6. Mechanical equipment room (framing, machinery bases and utility supports, and exterior

offsets)

7. Roof (slab, window washer rails, top fa9ade, antenna bases, and window wash concrete

walls)

Inspection Procedures and Methodology

To assess the condition of the structural system in the tower, both visual inspection and nondestructive

testing methods were employed. The thickness of steel members was checked using an ultrasonic

thickness gauge. Welds were tested using magnetic particle and/or dye penetration test methods.

Office Floor Areas

Fourteen office floors (11, 13, 22, 30, 35, 52, 54, 61, 65, 78, 84, 86, 90, and 93) throughout WTC 1 were

selected for inspection. Inspection of the structural elements at these levels followed the following

sequence:

1 . Six long-span trusses and two short-span trusses were selected from the plans for even, random distribution of inspection locations throughout the floor area.

NISTNCSTAR 1-1C, WTC Investigation 43
Chapter 3

2. Floor framing, damping unit, utility supports, steel decking, inside faces of steel spandrel

plates, spandrel splices, and core concrete or rolled steel members were visually inspected.

Structural steel members were examined for signs of defonnation or corrosion with

fireproofmg still in place.

3. The following locations for fireproof removal were selected and submitted: (a) six truss locations, (b) one core floor beam, (c) two spandrel plate sphces, and (d) two exterior

columns (plaster removal).

4. The 1 1 locations listed above were inspected up close, using lights, scrapers, wire brushes,

and mirrors for signs of cracking, deformation, or corrosion. Photographs were taken of

typical conditions and "Remarks'" were documented.

5. Nondestructive testing was perfonned on column splice welds and welded floor framing

comiections. Testing was perfonned by either the Port Authority's Materials and Research

Division or by Lucius Pitkin, Inc.

On 2 of the 14 floors inspected, column splices on seven core columns were inspected after removal of

the gypsum board firewalls. Top sides of exposed concrete floor slabs were also inspected where

carpeting or floor tiles had previously been removed.

Table 3-2 contains the number of structural elements inspected per office floor.

Table 3-2. Number of structural elements inspected per office

loor per the 1991 Facility Condition Survey Report for WTC 1. Element Type of Inspection Quantit\'

Floor framing trusses Visual 22 Fireproofmg removal 6

Nondestructive testing 4.3 (avg.)

Exterior column spandrel Visual 6

plate splices Fireproofmg removal 2

Exterior column splices Visual and Nondestructive testing

2

MER and Space Frame

All four two-story MERs were visually inspected from the lower floor and accessible upper floor levels. Floor framing, slabs, interior columns, and utility hangers and pads were inspected. Concrete fireproofmg

for covering the steel floor framing was examined for delaminations and underlying conosion.

At the 107th and 108th floors, fireproofmg was removed at nine locations. Of these, seven were welded

connections that were tested by the magnetic particle method.

Core Columns

Core columns were inspected from the elevator shafts in addition to the comer core column splices that were inspected from the two office area floors. The elevator shaft inspections included visual inspection

44 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

of floor framing, columns, connections, and splices in 13 elevator shafts with fireproofmg in place. Core

column connections to floor beams in the core were also examined.

Roof

The roof concrete slab top surface and parapet were visually inspected, along with the roof framing and

underside of the concrete roof slab.

Findings of Inspection

The following sections summarize the findings and recommendations from the WTC 1 survey report.

Exterior Walls (Columns and Spandrels)

Floors 9 through 106—Exterior coluinn splices were found to be in good condition." A total of

28 column splices were inspected throughout the 14 office floors. At 26 of these locations,

nondestructive testing was performed on all of the splice welds and the box column plates; each test showed that the welds were in good condition. Ultrasonic testing was perfonned to verify thickness of

the spandrel plates. These tests showed no loss of thickness. Tightness of the bolts in the spandrel beam

splices was also checked, and no loose or missing bohs were found.

The inside faces of the steel box column plates exhibited scattered areas of light to moderate corrosion^

and peeling paint. Light coiTosion was also found at splice bolts, welds, cap and base plates, and

diaphragms. Ultrasonic thickness testing on these outer column plates above and below the splice

location indicated no section loss.

Fillet shop welds connecting the cap and base plates to the interior of the box coluinns were visually

inspected at all open splice locations. No cracking or significant discontinuities were detected at any

location.

Spandrel plates, splice plates, and bolted connections were also found to be in good condition. Scattered

corrosion stains were observed on the spandrel fireproofing, typically at the splice plates and along the lower edges of the floor slabs. All splice plate bolts were observed to be tight. Fillet welds at the truss seat connections to the spandrels were also found to be in good condition.

A summary of the findings is contained in Table A-2 in the survey report, which is reproduced here as Table 3-3.

Floors 107 through 110—Inspection of the exterior walls was limited to the joints at the 108th floor. No

structurally significant deterioration was found. Joint sealer in the column cladding was missing at nearly

all of the 59 column seals.

^ In this survey report, a structural member that receives a "good" condition rating requires no repairs. The structural member is in "original condition" (see page 14 of PANYNJ (1991) for this and other definitions).

^ In this survey report, "corrosion" and "rust" are used interchangeably. See page 15 of PANYNJ (1991) for a definition of

corrosion.

NISTNCSTAR 1-1C, WTC Investigation 45
Chapter 3

Table 3-3. Findings from inspection of exterior wall column splices in WTC 1

Floor

Col. No.

Condition of Column Splice Plate Welds

Upper Lower Bolts Remarks

NDT - Magnetic

Particle NDT - Dye Penetrant Upper Lower Upper Lower

10-11 403 M T

1 A A T 1 1 trfl CAM 1 f thickness shows no

significant

loss

212 M L T A A

12-13 215 L L T A A

324 TL

TL 1 A A

2 1 -22 N

XT

1 A A

TLTL X A A

T TL X1 A A yj III aSUIllC thickness shows no

significant

loss

318 Ti_. T T A A

34-35 121 L L T

112 M L T

51-52 227 L L T A A

308 L L T A A

53-54 203 L L T A A

329 L L T A A

60-61 327 L L T A A

251 L L T A A

64-65 324 L L T A A

236 L L T A A

77-78 332 L L T A A Ultrasonic

attempted: 123 L L T A A reading erratic

83-84 106 L L T A A

454 L L T A A

85-86 133 TL

TL X1 A A Upper column

rotated 3/16 in. during

construction 209 L L T A A

89-90 315 L L T A A

136 L L T A A

92-93 124 L L T A A Ultrasonic attempted;

reading erratic 336 L L T A A

Key: A, acceptable (no loss of metal); L. light corrosion; M. moderate corrosion; N. no deterioration/defects; T, tight.

46 NISTNCSTAR 1-1C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Recommendations—No priority recommendations for repair were made in the report. It was noted,

however, that missing fireproofmg should be replaced on the spandrel plates and splices, and that the

joints in the aluminum cladding should be resealed where the seals were removed.

Core Columns

Inspection of the core columns was perfonned in three phases:

• Core columns were inspected from the elevator shafts.

• Seven core column splices were inspected from unoccupied office areas.

• Core floor beam to column connections were inspected at 25 of 56 locations on 14 floors.

Core columns inspectedfrom elevator shafts—Inspection of the core columns in an elevator shaft was

perfonned from the top of the elevator cab.

Thirteen elevator shafts (four express elevator shafts and nine local elevator shafts) were randomly

selected for inspection with the concurrence of Port Authority personnel. The shafts that were selected

for inspection can be found in Table B-1 of the report, which is reproduced here as Table 3-4.

Table 3-4. Visual inspection of elevator core framing in WTC 1. Elevator Shaft

Number Floors Inspected Adjacent Column Number Remarks

2 1 -44 907. 1007 No fireproofing

11 1 -44 901, 1001 removed

12 1 -78 501, 601

15 1-78 503. 603

26 9-16 708. 807

35 17-24 706. 805

43 33-40 702, 802

52 46-54 708. 807

62 55-61 706, 805 67 62-67 702. 802

77 80-87 708. 807

80 79-87 806, 907

90 93-101 703. 803

In the express elevator shafts, beams framing in the north-south direction were typically encased in concrete. Steel in the other direction consisted of built-up welded box girders and columns with sprayed- on fireproofmg. According to the report, no defects were found in the fireproofing that would suggest a problem with the steel columns, bracing, and floor framing. However, several small areas and a few large areas of fireproofing were missing from the steel girders and columns. It was suggested in the report that the small areas of exposure were caused by (1) the mounting of brackets and other hardware to support

conduit and guide cables and (2) the movement of hoist cables that were rubbing the shaft girder.

NISTNCSTAR 1-1C, WTC Investigation 47
Chapter 3

According to the report, the probable cause of missing fireproofing on box columns was thought to be the forces induced by the high speed of the elevators moving up and down the shafts. All exposed steel was

found to be in good condition with light to medium surface rust. Gypsum closure wallboards were found

to be in good condition, except for isolated holes in two elevator shafts at the 58th and 69th floors (see

Table B-2 in the survey report, which is reproduced here as Table 3-5). The report states that these

openings represent a fire safety hazard that should be corrected.

Table 3-5. Locations of holes in gypsum

wallboard around elevators in WTC 1. Elevator Shaft Number Floor Number

62 58

12 69

12 58

Local elevator shafts typically had wide-flange columns and girders with sprayed-on fireproofing.

Fireproofing was found to be missing on some of the steel members where there was contact with hoist

cables and where the steel served as staging support for maintenance workers servicing electrical conduits. The exposed steel was found to be in good condition with light surface rust. Steel beams

supporting the elevator door saddles were encased in concrete, except for a few beams that were found to be partially encased (for example, in one case, concrete was missing from the bottom flange of one of the

steel beams). The report states that the fireproofing should be replaced in these cases. The gypsum

closure walls were also found to be in good condition except for a few isolated holes and/or projections

into the shaft (see Table 3-5).

Core corner columns inspectedfrom ojfice area floors—Core comer columns were inspected at all four comers of the 92nd to 93rd floors and at three comers at the 77th to 78th floors. All seven locations were

inspected by removing the five or more layers of gypsum wallboard around the splice locations, which were 3 ft 0 in. above the finished floor level.

On the 92nd to 93rd floors, all four splices were bolted connections. No defects were found at any of the bolted splices. Welded splices were found at all three locations on the 77th to 78th floors, and were tested using the dye penetrant method. Results from the tests showed that there were no surface cracks in the welds. Steel plates, bolts, and welds that were visible were found to have only light surface corrosion.

Core column to floor beam connections inspectedfrom office floors—Twenty-five floor beam to column connections were visually inspected, and seven connections were inspected up-close throughout

the tower (see Table B-3 in the report for locations, which is reproduced here as Table 3-6). No

deformations were found in any of the connections that could be inspected. No inspection occurred

where firewalls obstructed vision or where heavy beams supported minor beams. Either no or light

corrosion was found on the exposed steel.

48 NISTNCSTAR 1-1 C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-6. Core column connection inspection in WTC 1. Number of Beam to Column

Connections Inspected

Floor Number Visually

Up close with

fireproofing removed Corrosion Deformation

10-1

1

3 1 L N

12-13 4 4 N N

21-22 0 0 - -

29-30 4 0 N N

34-35 3 0 L N

51-52 0 0 - -

53-54 1 0 L N

60-61 2 0 L N

64-65 0 0 - -

77-78 0 0 - -

83-84 0 0 85-86 2 0 L N

89-90 4 1 L N

92-93 2 1 L N

Totals 25 7 Key: L, light; N, none.

Recommendations—No priority recommendations for repair were made in the report. It was recommended that the fireproofing that was missing fi'om the elevator shaft framing members be

replaced, including those regions where the fireproofing was removed for up-close inspection during the condition survey. It was also recommended that the holes in the gypsum wallboards surrounding the

elevators, which are listed in Table B-2 of the survey report be repaired.

Floor Framing

Inspection locations for the floor framing were divided into three elevator zones: (1) Zone 1 (floors 9 through 41), (2) Zone 2 (floors 43 through 75), and (3) Zone 3 (floors 77 through 107).

Office floors, trusses—Typical floor framing was inspected from below at five locations in Zone 1 , four

locations in Zone 2, and five locations in Zone 3. Fireproofing was removed at various locations on each

floor that was inspected to provide up-close examination of the framing components and connections.

Welds were tested at most of these locations using either the magnetic particle method or dye penetrant.

Two typical conditions were observed during inspection. First, small areas of fireproofing were missing

at scattered locations throughout the floor framing. Second, the underside of the bottom plates of the seated connections of the trusses exhibited hght rust. According to the report, this was the result of the welding process that had occurred above the plate, which heated the paint, causing it to fall off No

structural deficiency was noted due to this condition.

NISTNCSTAR 1-1C, WTC Investigation 49
Chapter 3

At all locations that were examined, the damping units were not covered with fireproofmg. Small

amounts of light rust were observed throughout. Also, the damping unit under the 30th floor was missing

a non-structural bolt.

In some cases, the connection of the truss to the exterior spandrel plate did not have the typical two-bolt

connection. Instead, the seat had one bolt and a weld. It is suggested in the report that the bolt holes may

not have lined up during erection, so welding was used instead. These field welds were tested by either the magnetic particle or dye penetrant method, and were "found to be functioning properly."

On the 10th and 6 1st floors, diagonal members of bridging trusses were removed in order to allow 2 ft wide by 1 ft deep HVAC ducts to pass through parallel to the floor trusses. According to the report, the bottom chords of the bridging trusses were attached to the adjacent trusses "so that there was no decrease

of structural integrity." No details are provided in the report on how these connections were made.

Officefloors, metal deck—The metal deck was inspected from below at 22 locations per floor. No

significant rust was observed because, according to the report, the metal deck was galvanized. However,

in an area of approximately 500 ft" on the underside of the 84th floor, a scattering of light rust was

observed through the fireproofing.

Of/icefloors, concrete slab—In the core areas, the underside of the cast-in-place concrete slab was

observed to be in good condition. A 4 in. by 4 in. area was spalled under the 1 1th floor, and a 6 in. by

6 in. by 2 in. deep spall was noted under the 54th floor. Also, a construction joint was found to be open

south of columns 505 and 504 under the 13th floor.

Concrete slabs were also inspected from above at locations where floor tiles or carpeting were previously

removed. In general, the slabs in the office floors were found to be in good condition, except for the slab

at the southeast comer of the 60th floor. In this area, cracks were found, which formed at a 45 degree

angle with the comer. Over a period of 4 months, the cracks did not open any further than originally

measured. It was also observed that concrete slabs in the office areas were damaged by constmction and

removal of office partitions. Spalls resulting from nails being removed from the slab were noted on floors without tile or carpeting.

Table C-1 and C-2 in the survey report, which are reproduced here as Table 3-7 and Table 3-8,

respectively, provide a summai-y of the locations and observations of the inspection for the trusses, connections, welds, secondary members and connections, damping units, and metal deck.

Recommendations—No priority recommendations for repair were made in the report for any of the floor framing members. Routine recommendations were made as follows: (1 ) patch elastomeric sealer at the constmction joint south of columns 504 and 505 under the 1 3th floor, (2) even though the modifications

made to the bridging trusses at the 10th and 61st floors did not meet the original design, no further modifications were needed, (3) patch spalls that were created in concrete slabs when partition rails were

removed, and (4) patch cracks on the 60th floor with elastomeric sealer.

50 NISTNCSTAR 1-1C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-7. Floor framing and slab inspection results for WTC 1.

Floor

Level

Outer

Framing

- Main

Trusses,

Beams Connections

Weld Test

Secondary

Members and

Connections

Damping

Units

Metal

Deck

Underside

Column

Line

Test Condition

ZO^E I

11 G G

155, 303,

443

G G L G

13 G G

305,353,

421 G G L G

22 G G

123, 131,

331.335

G G L G

30 G G, L 141,423 G G L G

35 G G, L 121, 133 G G L G

ZONE 2

52 G. L G. L G, L G

54 G. L G. L

151, 351,

353,421

G G

61 G, L G, L

243,331,

305

G G L G

65 G, L L

157,319,

423

G G L G

ZONE 3

78 G. L L 131, 243 G G, L L G

84 G, L G, L

103, 107,

113, 121 G G L G

86 G, L G, L

131, 151,

217

G G L G

90 G, L G, L

135, 243,

319

G G L G

93 G, L G, L

1 17, 307,

443

G G L G

Key: G. good condition; L, light corrosion. MER and Space Frame

A 100 percent visual inspection was perfonned on all four mechanical equipment rooms (floors 7-8,

41-42, 75-76, and 108-109). According to the report, most floor framing was inaccessible due to the presence of HVAC ducts, fans, electrical piping, and plumbing equipment.

Mechanical Equipment Rooms—According to the report, the floor slabs at these levels were detennined

to be in good condition. Scattered cracks ranging in width from 1/16 in. to 1/8 in. were found on the slab

surfaces. The report suggests that previously repaired cracks were found to be deteriorated due to load

and vibration. Cracks were also found in equipment pedestal supports and column encasement.

NISTNCSTAR 1-1C, WTC Investigation 51
Chapter 3

Table 3-8. Core framing inspection results for WTC 1. Floor Level Beams Beam Connection Underside of Slab

ZONE 1

11 G, L G, L G

13 G, L G, L G

22 G G. L G

30 G, L G, L G

35 L L G. L

ZONE 2

52 L L G, L

54 L G. L G

61 G, L G. L G

65 L L G

ZONE 3

78 G. L G G

84 G, L G G

86 L G, L G

90 L G. L G

93 L L G

Key: G, good condilion; L, light corrosion.

Scattered patches of spray-on fireproofmg were found to be missing from the metal decks, which were

used in the perimeter areas (i.e., areas outside the core area). These areas had hght rust visible on the underside of the metal deck. Concrete encasement on the steel beams in the core area was found to be in good condition with hairline cracks at scattered locations. In a few places, the encasement had spalled off

of the steel beams, which exposed the welded wire fabric in the encasement and portions of the steel beams. The exposed steel was found to have a light coating of rust.

Visual inspection of the beam to column connections found them to be in good condition, according to the report. Exposed steel members exhibited only light surface conosion where fireproofmg was removed

on floors 108 through 109. A concrete encased beam at the 1 10th floor was subjected to steam from a leaking steam valve. Moderate

rusting was confirmed on the member, and, according to the report, no discernible section loss was found.

Hangers supporting ducts, piping, etc., were also visually inspected. Hangers subject to excessive

vibration, loose hanger rods, and the fatigue of pipe supports were found at various locations. According

to the report, beams that supported the duct hangers had fireproofmg missing where the hangers were

mounted.

Detailed findings on the MER levels are shown in the four floor plans on pages 41 through 44 of the 1991

Facility Condition Survey Report for WTC 1

.

52 NISTNCSTAR 1-1C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2. and 7

Space Frame—Selected elements of the space frame (hat truss) were inspected at various locations on the 107th to 1 10th floors. A total of 75 diagonal bracing members were visually inspected without removing

fireproofmg. A total of 199 members were inspected in the space frame. Light rust was found on diagonal

braces, beams, and connections where fireproofmg was missing.

Recommendations—A priority recommendation was made in the report to replace the leaking valve

under the 1 10th floor that rusted the floor beam. Routine recommendations were made as follows:

(1) Repair the surface cracks in the MER concrete floor slabs with a surface sealer, (2) Repair the cracks

in the concrete at the base of the columns, (3) Repair the cracks in the concrete pads supporting

mechanical equipment, (4) Patch and repair the spalled concrete encasement of all appropriate structural members, and (5) Repair hangers that were found to be vibrating, bowed, sagged, and/or deformed.

Roof

A visual inspection of the top surface of the concrete roof deck and concrete wall at the inner perimeter of

window washing rails was performed, and no significant structural deficiencies were found. Cracking and

spalling was found at localized areas of the roof. Some of the spalled areas that had been previously

patched with grout were found to be in poor condition due to exposure to weather.

Horizontal cracks and efflorescence, spalled concrete, and exposed reinforcing bars with minor corrosion were found at the exterior walls of the access stairway located at the roof. The report suggests that the spalling of the concrete was due to inadequate concrete cover over the reinforcing bars.

The helicopter pad at the southeast comer of the roof was visually inspected and was found to be in good

condition. No deficiencies were found in the bases of the antennas, all of which were visually inspected.

Recommendations—No priority recommendations were made for the roof Routine recommendations were made as follows: (1) Remove and replace the existing patches in the roof slab using a bonding agent

and non-shrink grout as a replacement and (2) Patch spalled areas of exterior concrete curb of the access stairway located at the roof. Other routine recommendations in the report were not structural in nature.

3.1.3 Port Authority Facility Condition Survey Program - WTC 7

The Port Authority Facility Condition Survey Program - WTC 7 report contains the findings of the condition survey of WTC 7, which was perfomied by Ammann & Whitney in 1997 for the EQAD of

PANYNJ (PANYNJ 1997).

Scope

The scope of work was designed to minimize impact on tenant and facility operations, and was limited to

(1) unoccupied floors, which were the mechanical/electrical and general service floors (floors 3 through 6), and (2) floors that had vacant space (floors 7, 10, 18, 23, and 25). The following is a list of the

structural elements that were inspected:

1 . Foundation

2. Framing (column splices, wind bracing systems, and interior beam connections)

NISTNCSTAR 1-1 C, WTC Investigation 53
Chapter 3

3. Floor slabs

4. Con Edison Substation

Inspection Procedures and Methodology

The inspection was primarily a visual inspection, with "hands-on" inspection"* of approximately 5 percent

of the "critical connections." A field inspection team visually inspected the structural elements noted in the previous section. Inspections were perfonned from the floor level and from ladders. A manlift was

required to inspect the lobby and trading floor ceilings. -

,

"

Column Splices -

Table IIl-l in the report, which is reproduced here as Table 3-9, contains the inspection point locations

for the column splices in interior and exterior columns.

Table 3-9. Column splice inspection points in WTC 7.

Floor

Number of Inspection

Points Column Numbers

Location of Connection

INTERIOR COLUMNS

5

-> 58C(H), E3,& 79 See Drawing S-3

23 6 58(H), 59. 63(H), & 79-81 See Drawing S-8 EXTERIOR COLUMNS

10 46-55 North side

9 19-27 South side

5 5 26, 7(H), 39-41 East side

5 2, 3,& 12-14 West side

2 Hangers 25A & 26 South side

23 1 25 West side Key: (H), hands-on inspection perfonned at these locations.

fVind Bracing System

Tables II1-2 and II1-3 in the report, which are reproduced here as Tables 3-10 and 3-11, respectively,

contain the inspection point locations for columns and girders that were part of the lateral-force-resisting

system.

Interior Beam Connections

Table 111-4 in the report, which is reproduced here as Table 3-12, contains the inspection point locations

for the interior beam connections.

What constituted hands-on inspection is not described in the report (PANYNJ 1997).

54 NISTNCSTAR 1-1 C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-10. Wind inspection points, columns, in WTC 7.

Floor

Number of

Inspection

Points Column Numbers

Location of Connection

CORE

1 4 64-73 North side

2 4 64-73 North side LOH ER EXTERIOR

5 10 43, 46-54 North side

4 25, 26, 27(H), 28(H) South side

3 28(H), 29, 30 East side

4 12- 14A West side

6 2 28-29 East side

3 6-8 West side UPPER EXTERIOR

23 1 29 East side

1 12 West side Key: (H). hands-on inspection perfonried at these locations.

Table 3- 1. Wind inspection points, girders, in WTC 7.

Floor

Number of Inspection

Points Column Numbers

Location of Connection

5 3 16-19A South side

6 8 46-54 North side

1 55-56(H) North side

8 19-27 South side

1 27-28(H) South side

5 28-30, & 38^1 East side

4 2-3 & 12-1 4A West side

8 23-25 South side

2 28-30 East side

19 5 21-26 South side

1 26-27(H) South side

24 4 44-46 & 53-55 North side

3 25-28(H) South side

1 35-36(H) East side

2 5-6 & 9-10 West side 44 1 42-43(H) North side

3 32-33. & 37-39 East side

1 41-42 East side

1 5-6 West side Main Roof 1 57-l(H) North side

1 4-5 West side Key: (H), hands-on inspection perfomied at these locations.

NISTNCSTAR 1-1 C, WTC Investigation 55
Chapter 3

Table 3-12. Interior beam connection

inspection points in WTC 7. Number of Inspection

Floor Points

5 5

/rD 4

O

fS 6

1 1

1 1 D

19 5 24 10 26 7 44 2 Main roof 5

Findings of Inspection

According to the report, the structural framing was found to be in good condition."^ No problems or

deterioration were found on the column splices, wind bracing, or the interior beam connections.

Rust buildup was found between the flanges of members that rested on top of one another at the main roof

level where the steel framing was exposed. Although this was not considered to be a structural problem, it was recommended that the steel should be cleaned and painted to prevent further deterioration.

Throughout the building, fireproofing was found to be missing from the steel framing at locations where

utility supports were installed. This condition was found on all of the floors that were inspected, but it was most prominent on the 5th floor framing above the main lobby and the 2nd floor framing above the loading dock area. The report recommended in the report that the fireproofing be replaced.

Loose concrete was found on the north face of column number 5 1 on the 46th floor of the cooling tower

area.^' Due to the potential hazard immediate action was recommended. Silverstein Properties personnel

irmnediately removed the loose concrete.

Floor slabs were found to be in good condition. Some of the exposed floor slabs exhibited shrinkage

cracks on the top sides, and some had the composite metal deck damaged during construction. Neither of

these conditions was considered to pose a structural problem. The report also recommended that delaminated concrete be removed at the concrete patch in the 6th floor slab. A complete list of the recommendations made in the report for iiTunediate action, safety items, and routine

repairs is reproduced in Fig. 3-4.

In this report (PANYNJ 1997), "good condition" means that the element is sound and performing its functions although it shows signs of use and may require some minor repairs, mostly routine.

* No information is given in PANYNJ (1997) on the size or exact location of this loose concrete.

56 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

The report also noted that the Con Edison station was in very good condition and that no action was

required at that time.

IMMEDIATE ACTION

ITEM FLOOR LOCATION DESCRIPTION PHOTO

1 46th Cooling Loose concrete on the ovitside face of Column No. 5 Tower area 5 1 , on the 46rh floor, in tlie cooling tower area was (eiiio> ed by bmldmg manaaemem personnel

SAFETY ITEMS

ITEM FLOOR ; LO CATION DESCRIPTION PHOTO

1 2nd Ceiling above Loading Docl<

area

Several widths of planking and maintenance equipment are resting on top of the ceiling and

should be removed as soon as possible.

5 th 5th floor steam room adjacent

to column no. 77

Ladder in steam room is offset from the landing

beyond the niaximum required. Provide a now

platfonn which confonns to OSH.'X standards.

1 1

6th 5 th tl trans fr mi

SE corner of

bid. adj to Col No. 30

E.xcess concrete around perimeter of patch in the 6th

floor deck slab is not bonded properly and could

loosen and fall. P,emove the e.xcess concrete

10

5th &

43 id

5th floor steam room and 43rd

floor East MER.

Loose anchor bolts were found on some of the suppons for the ladders. Tighten the anchoi bolts as soon as possible.

5 25th Just west of Column No, 54 A motorized projection screen is supported from the ceiling main carrying channels Either remove the

, screen and repair the ceiling or properly suppon it from its ov^m hangers

9

6 46th Cooling tower

framing

4 cooling tower ladders are not secured at the bases. Provide anchoring system and seal properly to prevent moisture from entering the roof membrane.

-! 48th West side of

cooling tower

Ladder is fitted with a substandard fall protection cage, has loose bolts at the splice and is not secured

properly at the base. Replace the existing cage with one that conforms to OSHA standards. Tighten all

: bolts as necessary and secure the base of the ladder

as performed in item 6 above.

13 & 15

8 48ih ; Northeast

corner

1 of Penthouse

' The hatch on the 48th floor roof opens to the wrong

side of the ladder. Replace the existing hatch cover

! with one that conforms to OSHA standards.

12

Source: PANYNJ 1997. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 3-4. Recommendations made in the 1997 Facility Condition Survey

Report for WTC 7.

NISTNCSTAR 1-1C, WTC Investigation 57
Chapter 3

RorrrNK rkpaiv^s

ITFM FLOOR LOCATION

! '-r! .in mail; roof

46(h &

4-th

4"'Ui Maiii Roof

Koof

Nor:h side of

buikiiag iis Ccuilin^: Tou Cl- are a

Xonh side of

building in Cooling Ti.n^ci'

ai oa

Cooung TcA\ er aiea

Inside face of

Tlu'oa^hoLjt

Sec B.ick

locations

Soucli Geuerritor

Floor framing

DF.SrUirilON I'llOTO

ReitKivc riic vvfre ropes rVc>sn Jhe .siec! sVaHurij.' rio 'j ihc roof. lTO\idc .idequaie support for ihc tcn^porarv se:itToldiiiii usinj; iho existing licdxick system

Clca5\ Uiui puiiU ihf exposed •;ieei Inimsai; and h

coolitsa low^r catwalks oti llie 4<iili i?;. llnors.

hfa! all cracks iii ihe exk-i !oi- buck v. a I!-. uT th,e 4tiih tloor eooltiig tuwer nrea^

Secure and seai ciecrrsc;!! rlxtures ot\ niof

parapets.

Repair root areas wl^erc membrane i.s worn and

or peeline.

Clean the window \'.-ashiiiy support hrackei.

paint, atid provide a cap o\er the crevice lo prevent moisture and debris rr>->in bmldinu inside

Repair and or replace all ir.ijsini: and bruken pipe

supports for die fuel lines

Fireprootlng has been removed from the steel framing to install utiHty suppoits. partilinn walls

or special equipmetu. Provide fireproof coating

where applicable

14

J

This comuHoii wa.s found ihroughoui the floors which wcr<j inspecied^

Source: PANYNJ 1997. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 3-4. Recommendations made in the 1997 Facility Condition Survey Report for

WTC 7 (continued).

3.1.4 Due Diligence Physical Condition Survey - WTC 1 and WTC 2

The Due Dilligence Physical Condition Survey - WTC 1 and WTC 2 report contains the findings of the

condition survey of WTC 1 and WTC 2, which was perfonned by Merritt & Harris, Inc. in 2000 for PANYNJ (Merritt & Harris 2000).

58 NISTNCSTAR 1-1 C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Scope

On-site evaluations were perfomied to assess the general physical condition of the property, as it existed

at that time. In particular, WTC 1, WTC 2, WTC 4, WTC 5, the retail mall and plaza, central services, and

the subgrade were inspected. The following discussion focuses on the findings for WTC 1 and WTC 2.

Inspection Procedures and Methodology

Observations were limited to those portions of the project that were visible during walk-through. In many

areas, building finishes concealed structural components from view. The consultant neither took material

samples nor performed tests on the building materials or systems.

Findings of Inspection

The following findings and recommendations were reported for both WTC 1 and WTC 2.

According to the report, the building structure appeared to be in good overall condition, based on

observations of portions of the structure that were not concealed by building finishes. No apparent

movement or settlement of foundations was observed, and interior slabs were reported to be in good

condition.

The report notes that Leslie E. Robertson Associates (LERA) and other engineering firms had performed, on a regular basis. Structural Integrity Inspections (Sll) of various structural systems and that those

studies have indicated the following deficiencies: (1 ) rusting of steel columns in the elevator shafts, (2)

missing fireproofing, and (3) floor coring damage. The due diligence condition survey report goes on to note that the most recent Sll recommended repairs were underway at the time the report was written.

Damping units had been tested every 5 years, most recently in 1996. The report notes that approximately

two-dozen damping units were kept in stock for replacement. The report also states that LERA strongly

recommended that the analysis of wind acceleration measurements be continued.

The report notes that an ongoing program of re-fireproofing structural steel members was in place at the time of the inspection. Re-fireproofing the structural steel was supposed to provide a two-hour fire rating

for those members. Such work was perfonned on an entire floor when the space was being built-out for new occupancy. At the time of inspection by Merritt & Harris, Inc., approximately 30 floors had been

completed in the two towers.

3.2 STRUCTURAL INTEGRITY INSPECTION PROGRAM

3.2.1 Overview

In 1986, the PANYNJ implemented an inspection program to detect, record, and correct any signs of

distress, deterioration, or defonnation that could signal structural problems for WTC 1 and WTC 2 (PANYNJ 1986). This program for structural integrity, which was based on an inspection and testing plan

prepared by LERA, contained detailed guidelines on inspection, record-keeping, and follow-up

procedures. It included periodic inspection intervals for the TV antenna mast, exterior roof and wall

elements, room occupancies and uses, accessible columns, fireproofing envelopes, bracing truss members

NISTNCSTAR 1-1 C, WTC Investigation 59
Chapter 3

between floor 107 and the roof (hat truss), steel floor framing, and concrete slabs. Details of the SIl program are presented in Sec. 2.2 of this report, including the required follow-up procedures, which are outlined in Sec. 2.2.5.

Inspection findings under the SII program were to be categorized as "Immediate," "Priority," or "Routine." Findings requiring "immediate action" would include possible closure of the area and/or stmcture until interim remedial measures (such as shoring or removal of a potentially unsafe element or

structural member or members) could be implemented. "Priority" findings addressed those conditions for which no immediate action was required or for which immediate action has been completed, but for which further investigation, design, or implementation of interim or long-terai repairs should be

undertaken on a priority basis, i.e., taking precedence over all other scheduled work. For "routine" or nonpriority cases, further investigation and/or remedial work could be undertaken as part of a scheduled

major work program or routine facility maintenance. Where inspection procedures involved the removal

of fireproofing, such fireproofing was to be properly replaced on completion of inspection.

In January of 1990, LERA submitted a proposal to the PANYNJ for monitoring the structural integrity of

the World Trade Center Complex. The proposal contained the scope of testing and inspection services

for WTC 1, WTC 2, WTC 4, WTC 5, WTC 6, the Vista Hotel, and the subgrade and was based on a modified and expanded version of the 1986 action plan that was previously submitted to PANYNJ.

The scope of services presented in the proposal included three separate approaches to identifying potential

component and/or system degradation:

1 . Statistical Inspections - Periodic statistical testing and inspection of structural components in areas that had a higher potential for trouble.

2. Review of Reports - Examination of maintenance reports (e.g., nonstructural repairs, water

leakage, and tenant complaints about building movements and/or vibration) for indications of

possible structural degradation.

3. Continued Measurements - Evaluation of the perfonnance of structural systems through

continued measurement of movement and deformations using appropriate tests and

instruments.

The program called for inspection or monitoring of the following items, among other things, in WTC 1 and WTC 2:

1. TV mast (WTC 1 only) ;

2. Roof water tightness and curtain wall

3. Space usage

' Letter dated January 12, 1990 from Saw-Teen See of Leslie E. Robertson Associates to Suren Batra of the Port Authority of New York and New Jersey (WTCI-123-P; see Appendix G of this report).

60 NISTNCSTAR 1-1C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

4. Accessible columns, including exterior box coluinns at locations of spandrel intersections and

"tree" junctions below floor 7 and above floor 1 (Plaza Level)

5. Bracing at exterior column line below elevation 294 ft 0 in., and in WTC 2 only, the transfer trusses below floor 1 under exterior columns

6. Hat truss between floor 1 07 and the roof

7. Floor framing over mechanical spaces

8. Concrete slabs, partitions, and finishes

9. Steel framing, slabs, and the like where exposed for general repairs or tenant remodeling

10. Measurement of natural frequency of tower and TV mast

1 1 . Floor natural frequency

12. Damping units

13. Plaster ceilings in main lobby

14. Marble wall panel supports

15. Review of maintenance reports

16. Fire stairs

Inspection and monitoring of these items were proposed to occur at regular intervals. Estimated

manpower and cost estimates based on proposed inspection intervals were also given, and are shown here

in Fig. 3-5. A detailed inspection program outlining the steps required for visual inspections and periodic

measurements was also contained in the proposal.

3.2.2 Summary of Structural Integrity Inspection Program Reports

LERA and other engineering firms conducted periodic inspections of the towers under the WTC

Structural Integrity Inspection Program, which was based on the proposal originally submitted to PANYNJ by LERA in 1990. The following sections of this report summarize the findings from the SII Program reports related to the structural aspects of the towers.

The PANYNJ has reported that the construction records on repairs following the SII reports were

destroyed when the towers collapsed on September 11, 2001. In addition, the PANYNJ has reported that any missing fireproofing that was identified in the SII reports to be repaired was done so on a routine

basis.

NISTNCSTAR 1-1 C, WTC Investigation 61
Chapter 3

Space Usage Surveys

The purpose of the space usage surveys was to identify possible structural overloading of the slabs and

floor framing due to changes in occupancies and uses and/or due to additions of heavy equipment or

furniture. The inspections were conducted by a walk-through by LERA personnel on predetermined floors within WTC 1 and WTC 2. Such usage surveys were initially proposed to be conducted annually on an ongoing basis (see Fig. 3-5). Surveys actually were conducted annually over a five-year period starting in 1995 (two surveys were conducted in 1996). A summary of the findings from the space usage reports is contained in Table 3-13.

Accessible Columns

Surveys of the accessible columns (columns in the core area that were not enclosed by an architectural

finish, which can be visually inspected) in the elevator shafts of WTC 1 and WTC 2 were perforaied to:

• Ascertain the condition of the accessible columns with respect to rusting, cracking, bowing,

and deviation from plumb

• Identify specific locations of structural distress or damage

• Identify locations of damage to the fireproofing

• Identify lateral displacement or rotation of the column about a vertical axis where the column was directly braced on only one axis by connecting beams or concrete slabs

• Identify defonnations of the slabs-on-ground suiTounding each column at the sublevel.

Accessible column surveys were proposed to be perfonned every two years on an ongoing basis (see

Fig. 3-5). As seen in Table 3-14, which contains a summary of the findings from the accessible columns

reports, the proposed inspection schedule was not followed exactly. See Appendix G of this report for the exact locations where the columns were inspected over the height of both towers in all of the SII reports.

62 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2. and 7

MANPOWER/COST ESTIMATE

ONE-TIME STARTUP COSTS

lor STRUCTURAL INTEGRITY MONITORING PROGRAM

for THE WORLD TRADE CENTER

MAf^pQWfci^ ESTilytATE C05t ESTIMATE

Building/lnspGctlon Hours/Inspection By Skill Labor/Ccst Estimated Total OnePartner Engineef Technician ConsullanI Inspection Expenses Time Ccsl

One World Trade Cenler

1. TV Mast 0 0 0 0 0 0 0

One and Two World Trade Center

2 Curtainwall A Root ^ 15 60 40 0 5,960 596 6,556

3. Space Usage Survey '

' 30 120 50 0 10,550 1,055 11,605

4. Accessible Columns 0 0 Q 0 0 0 0 S Bracing below El, 294 0 0 0 0 0 0 0 & Hal Truss 0 0 c 0 0 0 0

7. Plaza level box columns 10 20 0 0 1,850 185 2,035 a MER floor framing

9. Slabs, partitions S finishes

0 0 0 0 0 0 0

10 40 0 0 2,850 285 3,135

10. Root framing 10 40 0 0 2,850 285 3,135,

11. Natural frequency measurements 40 leo 20 '80 19,000 1,900 20,900

12. Natural frequency ol doors 50 300 0 •lo) 26,050 2,605 28,655

13. Damper testing 0 0 0 0 0 0 0

14, Lobt^ ceilings 0 0 0 0 0 0 0

15. Marble wall panel supports 0 0 0 0 0 0 0

16. Review of maintenance reports 6 20 0 0 1,680 168 1,848

17. Fke Stairs 10 40 10 0 3.250 325 3,575

Sub-ToUli &2^C 1^ 120 160 i74,o40 i7,464 iii,444

Four, Five & Six World Trade Center

Vista Hotel & Sub-Grade

ia Curtain walls & roofs 16 50 30 0 5,060 506 5,566

19. Space usage survey 16 60 30 0 5,560 556 6,116

20. Cantilever tmsses 10 20 0 0 1,850 185 2,035

21. MER floor franmig 0 0 0 0 0 0 0

22 Slabs, partiSons & finisfies 10 40 0 0 2,850 285 3,135

23. Floor framing 10 40 0 0 2,850 285 3,135

24. Plaster ceilings 20 40 0 0 3,700 370 4,070

25. Marble wall panel supports 0 0 0 0 0 0 0

26. Plaza slabs 16 40 40 0 4,960 496 5,456

27. Accessible columns 16 30 30 0 4,060 406 4,466 2a Pailung garage slabs 20 100 40 0 8,300 830 9,130 '

29. Slur7 walls 20 100 40 40 11,700 1,170 12,870

30. Fire Stairs 10 40 10 0 3,250 325 3,575

Sub-Total 4,5 A 6 WTC, 1^ 560 220 40 $54,140 $5,4l4 $59,554

Vlsla Hole) t Sub-Grade

Total WorU Trade Centef Inspection 348 1,360 340 200 $128,180 $12,818 $140,998

Source: PANYNJ 1990. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 3-5. Estimated manpower and cost estimates for structural integrity inspections

for WTC 1 and WTC 2.

NISTNCSTAR 1-1C, WTC Investigation 63
Chapter 3

MANPOWER/COST ESTIMATE

• ONGOING SERVICES

lor STRUCTURAL INTEGRITY TESTING AND INSFECTJON PROGRAM

tor THE WORLD TRADE CENTER

Inspedon MANPOWER ESTIMATE COST ESTIMATE

Building/Inspection Inlervai hour&'Inspeclia'i By Skill Labor/Cosi Estimaiea Annualized (Yrs) Pariner Engineet Technician ConsuHa.n' Inspection Expenses Cos!/Yr

One Www Track Center

1, TV Mast 2 30 240 60 10 17,800 1,780 9,^

One and Two Wortd Trade Center

1 CurtainwatI & Roof 1 20 40 300 0 15.700 1.570 17.270 3 Space Usage Survey 1 2C 40 300 c 15,705 1,570 i7,2ro

A. Accessible Co!jmns 2 10 40 160 0 9.250 925 5.088 5 BraangbetowEl,294 2 4 16 40 0 2,740 274 1.507 & Hat Truss 2 4 16 40 0 2.740 274 1.507 7 Plaza level box columns 4 20 60 0 €0 9.830 980 2695 a MER (loor traming 4 10 16 80 0 4,£50 485 1,334

9. Slats, parttions S fimhei 0 0 40 0 1,500 160 1,750

10. Floor framing 1 20 60 0 0 4,700 470 5,170

11, Natural frequency measurements 1 20 20 150 0 6,700 3.000 11.700

12. Natural frequency of Roc's 1 20 40 0 0 3,700 370 4,070

13. Damper testing 1 20 0 0 0 i,rao 170 1,670

14, Lobby ceilings 2 25 200 0 c 12,125 1,213 f

C;PO

15. Ivlarbiie wall panel supports 2 30 80 90 0 10,150 1,015 5,583

16. Review of maintenance reports 1 20 80 0 0 5,700 570 6.270

17. Fire Stairs 4 5 15 50 0 3,175 318 £73

Sub-Total 1 & 2 WTC i7« »63 1,310 70 $130,130 $15,143 $100,425

Four, Five & Six Worid Trade Center

Vista Hotel & Sub-Grade

18 Curtain walls & roofs 1 16 25 200 0 10,610 1,061 11,671

19. Space usage survey 1 16 25 200 0 10,610 1,061 11.671 2D Cantitev» trusses 4

23' 40 0 0 3,700 370 1.018

21. MER floor framing 4 10 16 80 0 4,650 485 1,334

22. Slats, partitions S finisties 1 0 0 40 0 1,600 160 1,760 23 Floor framing 1 20 60 0 0 4,700 470 5,170

24, Plaster cetBngs 2 30 300 0 0 17,K0 1,755 9,653 25 Marble wall pane! supports 2 30 80 90 0 10,150 1^15 5,563

2£t. Plaza slabs 4 16 20 80 0 5,560 556 1,529

27, Accessible columns 2 16 40 200 0 11,360 1,136 6,248

26. Parking garage slabs 1 30 80 200 0 14,550 t,455 16.0C6

2S. Slurry walls 1 25 80 200 20 15,825 1,583 17.406

30. Fire Stairs 4 5 15 50 0 3,175 318 873

Sub-Tola! 4,5 & 6 WTC, 234 781 1,340 20 iii4,24A $11,424 $89,921

Vlsts Hotel & Sub-Grad«

Total World Trade Center lr\spectlon 512 1,744 2,650 90 $244,370 $26,567 $190,346 Source: PANYNJ 1 990. Reproduced w/ith permission of The Port Authority of New York and New Jersey.

Figure 3-5. Estimated manpower and cost estimates for structural integrity inspections

for WTC 1 and WTC 2 (continued).

64 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-13. Summary of findings from space usage reports.

Date of ReportFloors

Inspected

Recommendations" LERA/WTCI

Reference

Immediate Priority Routine Numbers

12/31/95 85-110 None PANYNJ to distribute load of

granite slabs on

floor 106 of

WTC 1 over

larger area.

Re-inspect floors with

heavy file storage cabinets. R2753/67-L

05/20/96 85-110 None None PANYNJ to inform tenant of allowable safe loads

(safe was found on floor 91 of WTC 1 that could not be

confirmed on approved

drawings).

4105/66-L

09/20/96 66-84 None None PANYNJ to review

adequacy of floor framing

system on floor 79 of

WTC 2 where file storage

and lateral file cabinets where found that were not on the approved drawings.

PANYNJ to infomi tenant

to remove file storage

blocking aisles on fioor 80

of WTC 1.

4010/66-L

07/31/97 44-65 None None PANYNJ to inform tenants on floors 47 and 53 of

WTC 1 of allowable safe loads (safes were found

that could not be confirmed on approved drawings).

PANYNT to inform tenant

to remove file storage

blocking aisles on floor 61 of WTC 1.

69-L

06/15/98 25-43 None None None 4049/66-L

05/31/99 1-24 None None PANYNJ to repair spalling concrete floor slab on

floor 10 of WTC 2.

4040/66-L

a. Immediate - Action includes possible closure of the area and/or structure affected until remedial actions are implemented.

Priority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures

since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" category. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine

facility maintenance. This action also refers to all non-priority items.

NISTNCSTAR 1-1 C, WTC Investigation 65
Chapter 3

Table 3-14. Summary of findings from accessible columns reports.

Date of Recommendations" LERA/WTCI

Report Immediate Priority Routine Reference Numbers

01/29/93 None None PANYNJ to repair all spalled and

missing fireproofmg on the columns.

4078/66-L

04/14/95 None None PANYNJ to properly clean and

repair fireproofmg on all exposed

steel (columns and connecting

beams) at many or all of the floor

levels that were inspected.

PANYNJ to clean and repair all corroded steel in elevator pits due

to water damage.

4079/66-L

05/17/96 None PANYNJ to test damaged (cause

unknown) beam webs in elevator shaft 34B in WTC 2 below floors 9 and 10. PANYNJ to add new web stiffeners to these beams as a minimum.

PANYNJ to repair deteriorated fireproofmg on columns and

connecting beams throughout all of

the shafts inspected in accordance

with Appendix E of the SII report. PANYNJ to repair drywall in elevator shaft 95A, floor 100 in WTC 1. PANYNJ to repair fireproofmg at base of columns in elevator pits in

all of the shafts that were

inspected.

PANYNJ to reduce cable sway

using a cable damping system in

all of the shafts that were

inspected.

PANYNJ to investigate fire rating

of damaged shaft wall in elevator

nit R in W/TC T of flr>nr Al pii DiiDinwiv^zai iioor hz.

4004/66-L

None PANYNJ to repair deteriorated fireproofmg on column 905 between

floors 35-41 in WTC 2

in accordance with

Appendix E of the SII report.

PANYNJ to repair deteriorated fireproofmg on all of the columns,

connecting beams, and elevator

pits throughout all of the shafts that were inspected in accordance with

Appendix E of the Sll report.

4r)04a/^ifi-l

66 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-14. Summary of findings from accessible columns reports (continued).

Date of Recommendations" LERA/W ICI

Report Immediate Priority Routine Reference Numbers

05/30/98 None PANYNJ to repair deteriorated fireproofing on columns on

floors 2-1 7 and 29-40 in WTC 1 in accordance

with Appendix D of the

SII report. PANYNJ to replace

fireproofing that is missing over the entire height of floor 48 in elevator shaft 68A in WTC 1. PANYNJ to replace

missing fireproofing on column 902 in elevator

shaft 9B at floors 10, 18, and 34; on column 803

in elevator shaft 47B at floors 4 and 3 1 ; and, on column 805 in elevator

shaft 94B at floor 77 in WTC 2.

PANYNJ to repair deteriorated fireproofing on columns and

connecting beams throughout all of

the shafts that were inspected in accordance with Appendix E of the

Sll report. PANYNJ to reduce cable sway

using a cable damping system in

all of the shafts that were

inspected.

PANYNJ to repair fireproofing at base of columns in elevator pits that were inspected per Appendix D in the Sll report.

4050/66-L

a. Immediate - Action includes possible closure of the area and/or structure affected until reinedial actions are implemented.

Priority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures

since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" category. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine facility maintenance. This action also refers to all non-priority items.

Plaza Level Box Columns

The puipose of the inspection of the Plaza Level box columns was to assess their overall structural

integrity, including the condition of the fireproofing. As can be seen from Fig. 3-5, the proposed

inspection interval was four years. One such inspection was performed in April of 1998. The east face of

WTC 1 and the north face of WTC 2 were visually inspected between the Concourse Level ceiling and

the underside of the Plaza Level slab. The columns between the Concourse floor level and ceiling level were inaccessible due to their enclosures.

A summary of the findings from the Plaza Level box columns report is given in Table 3-15. The report notes that fireproofing was missing from approximately 2-3 percent of the Plaza Level box columns and

seated beam connections in WTC 1 and about 1-2 percent in WTC 2.

NISTNCSTAR 1-1C, WTC Investigation 67
Chapter 3

Table 3-15. Summary of findings from Plaza Level box column report.

Date of Report

Recommendations" LERA/WTCl

Immediate Priority Routine Reference Numbers

05/08/98 None None PANYNJ to clean all exposed steel on Plaza Level columns 236, 242,

and 248 in WTC 1 and repair

damaged fireproofmg on columns

and seated beam connections in both towers.

4002/66-L

a. Immediate - Action includes possible closure of the area and/or structure affected until remedial actions are implemented.

Priority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" category. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine facility maintenance. This action also refers to all non-pnority items.

Bracing below Elevation 294 ft 0 in.

Below Elevation 294 ft 0 in. (Sublevel 1) in both WTC 1 and WTC 2, diagonal bracing was used in place

of deep spandrels between the exterior columns to resist lateral loads from the tower above. The purpose

of the inspection of the bracing system in the perimeter walls of the towers was to:

• Assess the overall performance and structural integrity of the bracing (and, in 1991 only, the

transfer trusses below elevation 310 ft 0 in. in WTC 2);

• Identify specific locations of structural distress or damage;

• Identify locations of damage to the structural fireproofing systems; and

• Provide recoiTnnendations for reinedial work for both structural and fireproofmg damage.

As can be seen from Fig. 3-5, the proposed inspection interval was two years, which is less than the actual inspection interval shown in Table 3-16. The 1995 SII report notes that the only prior inspection

of the bracing was done on October 31, 1991. Also, the 1995 Sll report recommended that future inspections should be performed every two years, with particular attention given to coirosion and

fireproofmg. In both the 1991 and 1995 Sll reports, it is noted that the observed thickness of the fireproofmg on the bracing members was between 0.25 in. and 1 in.

It is evident from Table 3-16 that the PANYNJ did not complete action on a number of "routine"

category recommendations from the 1991 report. Remedial work for these recommendations was to be

earned out as part of a scheduled maintenance program. Such recommendations include draining of

flooded areas due to water leaks was not fully accomplished, and repairs to the connections between the braces and the columns were not made. Fireproofing was not applied to the transfer truss between

coluirms 242 and 248 at the Bl Level in WTC 2. Also, fireproofing was not repaired on some of the bracing members at Level B6 and at other levels. It appears that all of the damaged concrete masonry

unit (CMU) walls acting as fireproofing, which were identified in the 1991 SII report, were repaired;

many additional CMU walls were noted for repair in the 1995 SII report.

68 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-16. Summary of findings from bracing reports.

Date of Report

Recommendations" LERA/WICI

Immediate Priority Routine Reference Numbers

10/31/91 None None PANYNJ to drain flooded areas due to water leaks in Level B6 of WTC 1 and

WTC 2. PANYNJ also to repair any

corroded steel and welds at the connections of the bracing members to the columns due to flooding and to reapply fireproofmg after painting all steel with a zinc-rich paint.

PANYNJ to clean, repair, and reinstall fireproofing on structural members at Level B6 in the Mechanical Equipment

Rooms of both towers. PANYNJ to repair CMU walls that serve as fireproofmg at various

locations in WTC 1 and WTC 2 as noted in the report. PANYNJ to repair all spray fireproofmg on the braces in WTC 1 and WTC 2 and the transfer truss in WTC 2 between columns 242 and 248

at the Bl Level.

4096/66-L

03/01/95 None None PANYNJ to drain flooded areas due to water leaks in Level B6 of WTC 1 and

WTC 2. PANYNJ also to repair any

corroded steel and welds at the connections of the bracing members to the columns due to flooding and to reapply fireproofmg after painting all steel with a zinc-rich paint.

PANYNJ to clean, repair, and reinstall fireproofmg on structural members at Level B6 in the Mechanical Equipment

Rooms of both towers. PANYNJ to repair CMU walls that serve as fireproofmg at various

locations in WTC 1 and WTC 2 as noted in the report. PANYNJ to repair all spray fireproofmg on the braces in WTC 1 and WTC 2 and the transfer truss in WTC 2 between columns 242 and 248

at the Bl Level.

4066/66-L

a. Immediate - Action includes possible closure of the area and/or structure affected until remedial actions are implemented.

Priority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures

since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" categor\'. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine facilit>' maintenance. This action also refers to all non-priority items.

The 1995 SlI report notes that large areas of fireproofmg on the structural steel meinbers were remo\ ed or damaged due to the February 1993 bombing of WTC 1. During reconstruction of this area, fireproofmg

NISTNCSTAR 1-1C, WTC Investigation 69
Chapter 3

was reapplied to the structural steel members. LERA was asked by the PANYNJ to inspect this fireproofmg as part of the 1 995 structural integrity inspection of the bracing members, and LERA

". . .found no place where these refireproofmg efforts were incomplete."

Hat Trusses <

The purpose of the inspection of the hat trusses between floor 107 and the roof was to:

• Assess the overall perforaiance and structural integrity of the hat trusses;

• Identify specific locations of structural distress or damage;

• Identify locations of damage to the structural fireproofmg systems; and

• Provide recommendations for remedial work for both stinctural and fireproofmg damage.

During the inspections, access to some of the bracing members was either not possible or not practical. A

summary of the findings from the hat truss reports is contained in Table 3-17. Note that the actual inspection interval is greater than the proposed interval of two years (see Fig. 3-5). Fireproofmg that was

intentionally removed during the Facility Condition Survey inspections performed by the PANYNJ in 1990 and 1991 for WTCl and WTC 2, respectively, was found not to be repaired.

Table 3-17. Summary of findings from hat truss reports.

Date of Report

Recommendations" LERAAVTCI

Immediate Priority Routine Reference Numbers

10/21/92 None None PANYNJ to repair exposed area of steel with

either spray-on or troweled-on fireproofmg.

PANYNJ to repair existing cracks in the topping slabs on floor 108 of both towers. PANYNJ to apply fireproofmg and

reconstruct column enclosures on columns

903 and 904 on floor 1 10 in WTC 2. PANYNJ to replace damaged portions of

gypsum wallboard that serves as fireproofmg

around columns 707 and 708 on floor 108 of

WTC 1.

R2579/67-L

02/21/95 None None PANYNJ to repair exposed area of steel with

either spray-on or troweled-on fireproofmg.

PANYNJ to repair existing cracks in the topping slabs on floor 108 of both towers. PANYNJ to replace or repair damaged

portions of gypsum wallboard that serves as fireproofmg around columns identified in report.

4014/66-L

a Immediate - Action includes possible closure of the area and/or structure affected until remedial actions are implemented.

Priority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" category. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine facility maintenance. This action also refers to all non-priority items.

70 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Floor Framing over Mechanical Areas

The purpose of the inspection program for the floor framing supporting the MER was to:

• Assess the overall performance and structural integrity of the steel and concrete framing;

• Identify locations of defects and signs of distress in slabs, partitions, column enclosures, and

concrete supports for mechanical equipment;

• Identify locations of damaged fireproofmg;

• Compare the findings with those of previous inspection; and

• Provide recommendations and procedures for remedial work for both structural and

fireproofing damages and/or inadequacies.

Table 3-18 contains a summary of the reports for the floor framing over mechanical areas and shows that the proposed inspection interval of 4 years (see Fig. 3-5) was followed or exceeded.

The reports indicate that damaged CMU walls in Level B6 of WTC 1 and WTC 2 still existed in 1996.

Such damages were found inhially during the structural integrity inspection of the diagonal bracing in 1991 and again in 1995 (see Table 3-16). Similarly, damaged fireproofing on the perimeter diagonal

bracing members at this level in WTC 1 and WTC 2, which was initially found in 1991 and 1995, still existed in 1999. The 1999 SII floor framing over mechanical areas report lists the following items for which repairs were not completed from previous inspections: (1) cracks in slabs on all MER floors in both

towers; (2) spalled concrete on Level B6 in WTC 1; (3) fireproofing hanging from the underside of the metal deck on floor 107 in WTC 2; (4) Damaged fireproofing to the beam on floor 107 in WTC 1 ; (5) A

3 ft by 3 ft hole in the gypsum wallboard on floor 41 in WTC 1 ; and (6) damaged CMU walls at Level B6

in both towers.

Floor Framing over Tenant Areas

The purpose of the inspection program for the floor framing supporting the tenant areas was to:

• Assess the overall performance and integrity of the steel and concrete framing;

• Identify locations and signs of distress in slabs, partitions, column enclosures, and steel framing;

• Identify locafions of inadequate fireproofing; and

• Provide recommendations and procedures for remedial work for both structural and

fireproofing damage and/or inadequacies.

Table 3-19 contains a summary of the reports for the floor framing over tenant areas. The proposed

inspecfion interval of 2 years (see Fig. 3-5) was followed, with one deviation.

NISTNCSTAR 1-1C, WTC Investigation 71
Chapter 3

Table 3-18. Summary of findings from reports on floor framing over mechanical areas.

Date of Recommendations" LERA/WTCl

Report Immediate Priority Routine Reference Numbers

11/03/92 None None PANYNJ to replace missing

fireproofing.

R2582/67-L

04/12/96 None PANYNJ to re- apply fireproofing to deck on floor 108 in WTC 2. PANYNJ to patch

fireproofing on beam supporting

floor 107 in wfc 1 in accordance with

procedure in Appendix D of the

SII report.

PANYNJ to repair cracks throughout

all MER floors. PANYNJ to repair spalled concrete at 3 locations at level B6 in WTC 1 using methods given in Appendix C

of the Sll report. PANYNJ to repair damaged

fireproofing to framing supporting

floor 74 in WTC 1 in accordance with

procedure in Appendix D of the SII

report. PANYNJ to replace damaged drywall on floor 42 in WTC 1. PANYNJ to patch fireproofing on

perimeter bracing at locations indicated in the report on level B6 in WTC 1 and WTC 2 in accordance

with procedure in Appendix D of the

SII report. PANYNJ to replace damaged CMU

walls in level B6 in WTC 1 and

WTC 2 in accordance with procedure

in Appendix D of the SII report. PANYNJ to patch damaged

fireproofing on hat trusses at floor 108 in WTC 2 in accordance with

procedure in Appendix D of the SII

report.

R2776/67-L

72 NISTNCSTAR 1-1 C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-1 8. Summary of findings from reports on floor framing over mechanical areas

(continued).

Date of Recommendations" LERA/WTCI

Reference

Report Immediate Priority Routine Numbers

05/99 None PANYNJ to stop

leak in overhead

pipe on floor 75 in WTC 1. Condition of

inadequate

fireproofing

reported in 1996

study could not be

verified since a drop

ceiling was

subsequently

installed in the area

in question.

PANYNJ to repair spalled concrete at Level B6 in both towers in accordance

with procedure in Appendix C of the Sll report. PANYNJ to patch cracking (new and

from previous repair) in slabs on all MERs in both towers in accordance

with procedure in Appendix C of the Sll report. PANYNJ to remove debris on perimeter areaways on all MERs in both towers. PANYNJ to patch spalled concrete in perimeter areaways on floor 1 08 in WTC 1 towers in accordance with

procedure in Appendix C of the Sll report. PANYNJ to repair spalled concrete at parapet wall on floor 108 in WTC 1 towers in accordance with procedure in Appendix C of the SII report. PANYNJ to repair cracked column

pedestal on floor 41 in WTC 1 towers in accordance with procedure in Appendix

C of the SII report. PANYNJ to verify if newly constructed

cantilevered deck on all MERs in both towers was engineered.

PANYNJ to verify if existing floor framing was evaluated for additional loads due to new construction of

enclosed mechanical rooms on all MERs in both towers. PANYNJ to patch fireproofing to perimeter bracing at Level B6 in WTC

2 towers in accordance with procedure

in Appendix D of the SII report. PANYNJ to replace damaged CMU

walls in level B6 in WTC 1 and WTC 2

in accordance with procedure in Appendix D of the SII report. PANYNJ to patch damaged

fireproofing on hat trusses at floor 108

in WTC 1 in accordance with procedure

in Appendix D of the SII report.

4041/66-1.

a. Immediate - Action includes possible closure of the area and/or structure affected until remedial actions are implemented.

Priority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" category'. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine facility' maintenance. This action also refers to all non-priority items.

NISTNCSTAR 1-1C. WTC Investigation 73
Chapter 3

Natural Frequency Measurements

The purpose of the inspection program was to determine the natural frequencies of oscillation of WTC 1 due to wind excitation. Only WTC 1 was instrumented with accelerometers which were located at six locations on floor 108. The accelerometers measured the accelerations in both principal directions of the building with respect to time due to wind. Data were recorded on tape whenever the acceleration of

floor 108 exceeded approximately 0.003g. A spectral analysis of the recorded accelerations was made;

peaks on this spectrum corresponded to the natural frequencies of various modes of vibration of the towers. The computed natural frequencies were to be compared with corresponding values that had been

determined in the past. A significant change in the tower's dynamic behavior was considered to be a

possible indication of diminishing structural integrity. According to the reports, characteristics that may

be observed or inferred by review of the recorded acceleration data were:

• Integrity of the lateral-load-resisting system;

• Condition of the viscoelastic damping system;

• Condition of other sources of inherent structural damping; and

• Other changes that affect fundamental characteristics of the lateral-load-resisting system.

Three reports were prepared by LERA. Dates and references for the reports are contained in Table 3-20.

The 1993 and 1995 reports compare the then available measured first mode natural frequencies of WTC 1 to those detennined by the structural engineer in 1966, which were 0.084 Hz in the north-south direction

and 0.096 in the east-west direction (WSHJ 1966). A summary of the measured first mode natural frequencies from the 1995 report, which contained the most current data, is given in Table 3-21.

74 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-19. Summary of findings from reports on floor framing over tenant areas.

Date of Recommendations" LEK.\/V\ I( I Report Immediate Priority Routine Reference Numbers

11/03/92 None None PANYNJ to replace fireproofing on steel members and repair or replace damaged

CMU walls on floors noted in report. PAN\'1^IJ to perform survey of core holes, especially in prohibited areas.

R2582/67-L

04/01/95 None None PANYNJ to replace fireproofing on steel members and repair or replace damaged

CMU walls on floors noted in report. PANYNJ to perform survey of core holes, especially in prohibited areas. PANYNJ to patch spalled concrete at locations noted in report.

R2582/67-L

12/10/97 None None PANYNJ to replace fireproofing on steel members and repair or replace damaged

CMU walls on floors noted in report. PANYNJ to perform survey of core holes, especially in prohibited areas. PANYNJ to patch spalled concrete with exposed reinforcement at locations noted

in report. PANYNJ to fill cores/holes in slab at locations noted in report.

4012/66-L

11/29/99 None PANYNJ to restore fireproofing on truss at floor 89 of WTC 2. PANYNJ to repair spalled concrete on

floor 89 of WTC 2 in accordance with repair procedures given in Appendix D of the SII

report. PANYNJ to repair spalled concrete on

floors 33 and 91 of WTC 1 in accordance

with repair procedures

given in Appendix D

of the SII report. PANYNJ to fill in cores with damaged

reinforcement on floor 91 of WTC 1.

None 4023/66-L

a. Immediate - Action mcludes possible closure of the area and/or structure affected until remedial actions are implemented.

Pnority - This action takes precedence over all other scheduled work. This work should not wait for routine repair procedures since waiting may make the damaged area less accessible or allow the damage to quickly worsen to an "immediate" category. Routine - Further investigation and/or remedial work can be undertaken as a part of a scheduled work program or routine facility maintenance. This action also refers to all non-priority items.

NISTNCSTAR 1-1C, WTC Investigation 75
Chapter 3

Table 3-20. Reports on natural frequency measurements. Date of Report LERA/WTCI Reference Numbers

02/01/93 4073/66-L

04/12/95 4056/66-L

07/11/00 4094/66-L

Table 3-21. Measured first mode natural frequencies for WTC 1.

Event Date

Wind Speed (mph) and

Direction

Measured Frequency (Hz)

N-S E-W

10/11/78 11.5, E/SE 0.098 0.105 01/24/79 33.0, E/SE 0.089 0.093 03/21/80 41.0, E/SE 0.085 0.092

12/11/92 49.0 0.087 0.092

02/02/93 20.0. NW 0.085 0.095

03/13/93 32.0. NW 0.085 0.094 03/10/94 14.0. W 0.094 0.094

12/25/94 37.0, W 0.081 0.091

Both the 1993 and 1995 reports conclude that the measured and computed first mode frequencies

compare well, especially for the greater wind speeds. The 1995 report also concluded that the February 1 993 bombing had no permanent measurable effect on the dynamic response of WTC 1 . Both

reports recommended that WTC 2 be instrumented similarly to WTC 1

.

The 2000 SII report pointed out that PANYNJ had not been able to analyze the data acquired from the instrumentation of WTC 1 since 1998 because the PANYNJ laboratory that contained playback and

analytical equipment necessary to assess the recorded data was dismantled in the fall of 1998. The report

recommended that the capability to assess and analyze the accelerometer data be re-established promptly.

The report further recommended that WTC 1 be additionally instrumented at a mid-level floor, and that WTC 2 be instrumented at its top floor and at a mid-level floor. The final recommendation from the 2000 report was that the responsibility for data collection and processing be transferred to a university or

a similar academic research institution. Note that the proposed inspection interval of one year (see

Fig. 3-5) was not followed.

Natural Frequencies of Floors

The purpose of this inspection program was to determine the natural frequencies of the floor systems in WTC 1 and WTC 2 and to compare them with corresponding values that were determined in the past. A

significant change in the vibration characteristics of the floor system was considered to be a possible

indication of diminishing structural integrity. The proposed inspection schedule (see Fig. 3-5) included

measurement of the natural frequencies of floors every year on an ongoing basis, the proposed inspection

schedule was not followed.

76 NISTNCSTAR 1-1 WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

For purposes of determining the natural frequencies of the floor construction, a typical tower floor was

divided into three zones, which corresponded to the type of floor truss that was utilized in that zone:

short-span zone, long-span zone, and two-way zone.

Vibration characteristics of the floor systems were studied both analytically and experimentally. In 1971,

Teledyne Geotronics of Long Beach, CA made field measurements of vertical vibration on floors 13, 27,

and 32 of WTC 1 using seismometers. These field measurements were obtained under the direction of

Skilling, Helle, Christiansen, Robertson (SHCR). SHCR also made analytical estimates of the natural frequencies of the floor systems at that time (SHCR 1971). They detennined that the natural frequencies

of the long-span and short-span trusses, considering viscoelastic damping, were 4.6 Hz and 7.9 Hz,

respectively. A summary of the natural frequency test results for WTC 1 is contained in Table 3-22.

Table 3-22. Summary of natural frequency test

results for floors o1FWTC 1, March 1971.

Floor Zone Frequency Range (Hz)

Long-span 4.6 to 5.1 Two-way 4.6 to 5.7 7.0 to 7.9

Short-span 7.9

In March of 1995, Cerami and Associates, of New York, NY, made field measurements on floors 17, 22,

26, 38, and 88 of WTC 1 and floors 23, 24, an 58 of WTC 2 using the following equipment: piezo-electric

accelerometer, vibration meter, peak band pass filter, and strip chart recorder (Cerami 1996). The floors were subjected to a standard heel-drop test or by jumping in place. All field work was perfonned under

the direction of LERA. A summary of the test results for WTC 1 and WTC 2 is given in Table 3-23.

The SII report produced by LERA in April of 1995 summarized the analytical and experimental results to date (LERA 1995). Based on the available data, the report concluded that there had been no significant

measurable change in the performance of the typical floor systems in WTC 1 and WTC 2.

Table 3-23. Summary of natural frequency test results for floors of WTC 1 and WTC 2, March 1995.

Floor Zone Frequency Range (Hz)

WTCl

Long-span 4.5 to 5.3 Two-way 4.6 to 4.9

6.6 to 7.6

Short-span 7.8 to 8.8 WTC 2 Long-span 4.8 to 5.6 Two-way 4.9 to 5.4

7.5 to 7.8

Short-span 7.9 to 8.0

NISTNCSTAR 1-1C, WTC Investigation 77
Chapter 3

Viscoelastic Damping Units

The report by LERA in May of 1996 provided a summary of the integrity of the viscoelastic damping

units in WTC 1 and WTC 2 (LERA 1996). The integrity assessment represented a continuation of the on- going monitoring program for the damping units. A historical review related to the damping units is given in Appendix A of the SII report, which can be found in Appendix G of this report.

The report was based on information in the following studies:

• Laboratory testing of four in-service dampers taken from the towers (two per tower)

perfonned by the Minnesota Mining and Manufacturing Company (Appendix A in LERA

report)

• Analysis of measured dynamic response of WTC 1 to actual wind events conducted by the

University of Western Ontario (Appendix B in LERA report)

• Investigation ofAging Effects - World Trade Center Dampers, Robert Fowler & Associates

P.C., October 1, 1984 (Appendix C in LERA report).

Details of each study can be found in the applicable appendices cited above.

To assess the integrity of the damping units, the following characteristics were examined:

• Average loss tangent

• The mechanical behavior of the viscoelastic material used in the damping units was modeled

by a linear viscoelastic law, where the stress-strain characteristics of the material are dependent on time and on the temperature of the material (WSHJ 1967b). When subjected to a unifonn shear strain, which is a sinusoidal function of time, the stress-strain diagram of the

viscoelastic material is elliptical. The area within the ellipse represents the work done per

cycle of strain, which is dissipated as heat.

• The loss tangent, which is the ratio of the loss shear modulus of the viscoelastic material to the storage (elastic) shear modulus of the viscoelastic material, is directly proportional to the energy that can be dissipated per cycle of oscillation in the damping unit. Thus, to achieve

maximum damping for a given material, the loss tangent should be made as great as possible.

Over time, it was possible for the loss tangent to decrease.

• Average stiffness

• The stiffness of a damping unit was defined as the force it would take to produce a deformation of 0.020 in. in the viscoelastic material. The loss tangent is also directly

proportional to the stiffness. Over time, it was possible for the stiffness to decrease.

• Mean damping ratios of WTC 1

• Damping of building sway motion in WTC 1 was achieved primarily from two sources:

(1) intrinsic damping by the building structure and (2) damping from the viscoelastic

78 NISTNCSTAR 1-1 C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

damping units. In the design of the damping units, the intrinsic damping was assumed to be

approximately 2 percent of critical damping.

• Contribution of damping units to total damping

• In the design, the contribution of the damping units to the total damping was assumed to be

about 0.6 to 0.7 percent of critical damping.

• Mean natural frequency of oscillation of WTC 1

• A discussion on the natural frequency measurements of WTC 1 is give above.

The report concluded that based on the then available studies, the integrity of the damping units was

good, and that no action was required at that time beyond the routine testing of the damping units.

Inspections Related to Explosion of February 16, 1993

The inspections listed in Table 3-24 were performed on WTC 1 after the terrorist bombing on

February 16, 1993. The reports on each of these inspections can be found in WTCI-67-L.^

Table 3-24, Summary of inspections performed on WTC 1 after the terrorist bombing on

Date Company Inspection

05/14/93 LERA Level B2 and surrounding area. Bowed column 324

above Level B2; missing and bowed diagonals

between Column 324 (Level B2) and Column 327

(Level Bl); Crack at column 324 splice; bent

spandrels and damaged floor beam connections.

Sept. 1993 U.S. Army Corps of Engineers Overall observ ation of damage due to explosion.

10/20/93 Wiss, Janney. Elstner Associates Investigation of plaza level cracks.

11/22/93 Proto Mfg. Ltd. Stress measurements of Level B2 columns.

12/08/93 Lucius Pitkin Inc. Examination of box column and diagonal beam repair.

10/10/94 LERA Memo on repair of concrete masonr>' unit wall.

A summary of the damage observations and a detailed discussion of the repairs made due to damage from

the 1 993 bombing is given in Chapter 4 of this report, which discusses the significant modifications and

repairs that were made to WTC 1,2, and 7.

After the repairs were completed on WTC 1, Lucius Pitkin, Inc. was requested to perform an ultrasonic

thickness survey of box columns and an ultrasonic flaw detection survey of the diagonal and beam weld

repairs that were made (Lucius Pitkin 1993). On level Bl, thickness measurements were made on

existing columns 345, 348, and 351 on a 2 in. grid pattern at areas along all four column faces and at various elevations as specified by LERA. Ultrasonic flaw detection surveys were performed on fiill penetration butt welds of newly erected diagonal bracing repairs at colimins 321, 324, and 327 betw een

NIST WTC investigation catalog number.

NISTNCSTAR 1-1C, WTC Investigation 79
Chapter 3

levels Bl and B2 and on butt and fillet welds of beam repairs at columns 321 and 327 between levels Bl

and B2. Ultrasonic flaw detection included scans of base metal on both sides of the weld for a distance of

1 ft for the full width of the plate. No indication of laminations was found on any of the new welds.

3.3 SUMMARY OF STRUCTURAL INSPECTION PROGRAMS

3.3.1 Inspection Programs

The PANYNJ commissioned various inspection programs during the occupancy of WTC 1, 2, and 7. The

goal of these programs was to determine the condition of the structural systems in these buildings.

Facility Condition Survey Reports

Facility Condition Survey Programs were perfonned from 1990 through 2000 for WTC 1, 2, and 7. The

following is a list of the structural elements that were inspected in WTC 1 and WTC 2:

• Exterior wall system (including columns, spandrel plates, and connections)

• Core columns (including column splices and lateral bracing below the 7th floor)

• Space frame (i.e., hat truss, including framing members and connections)

• Floor systems (including floor slabs and decks, trusses, rolled beams, bridging, and

connections)

• Damping system (including damping units and connections)

The following is a list of the structural elements that were inspected in WTC 7:

• Foundation

• Framing (column splices, wind bracing systems, and interior beam connections)

• Floor slabs

• Con Edison Substation ; A Due Diligence Physical Condition Survey was commissioned by the PANYNJ for WTC 1 and WTC 2

in 2000. On-site evaluations were perfonned during this survey to assess the general physical condition of

the property, as it existed at that time.

Structural Integrity Inspection Programs

An inspection program to detect, record, and correct any signs of distress, deterioration, or deformation

that could signal structural problems was implemented by PANYNJ in 1986 for WTC 1 and WTC 2. This

program for structural integrity contained detailed guidelines on inspection, record-keeping, and followup procedures.

80 NISTNCSTAR 1-1 C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

The program included inspection or monitoring of the following items, among other things, in WTC 1 and WTC 2:

• TV mast (WTC 1 only)

• Roof water tightness and curtain wall

• Space usage

• Accessible columns, including exterior box columns at locations of spandrel intersections and

"tree" junctions below floor 7 and above floor 1 (Plaza Level)

• Bracing at exterior column line below elevation 294 ft 0 in., and in WTC 2 only, the transfer

trusses below floor 1 under exterior columns

• Hat truss between floor 107 and the roof

• Floor framing over mechanical spaces

• Concrete slabs, partitions, and finishes

• Steel framing, slabs, and the like where exposed for general repairs or tenant remodeling

• Measurement of natural frequency of tower and TV mast

• Floor natural frequency

• Damping units

• Plaster ceilings in main lobby

• Marble wall panel supports

• Review of maintenance reports

• Fire stairs

3.3.2 Findings from Inspection Programs

In general, the structural integrity inspections found that the structural systems of WTC 1, 2, and 7 were

in good condition. The inspection consultants made numerous routine and some priority

recommendations for repairs to the PANYNJ, as outlined in the above sections of this report. As noted

above, it is evident that the PANYNJ did not complete action on some of these recommendations. Also,

according to the PANYNJ, all of the construction records on repairs following the inspections were lost on September 11, 2001 . Thus, it cannot be determined whether all of the recommended repairs were

perfonned.

NISTNCSTAR 1-1C, WTC Investigation 81
Chapter 3

Table 3-25 gives a chronological summary of the locations where fireproofmg was reported to be missing

in WTC 1, 2, and 7, based on the findings from the applicable inspection programs.

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections of WTC 1, 2, and 7.

Date

Inspection

Program Building(s) Location/Description

April

1990

Port Authority

Facility Condition

Survey Program - WTC 2

WTC 2 • Several small regions and a few large areas of fireproofmg was

found missing in elevator shafts 1^, 8-13, 16, 18-21, 23, 24,

31, 35, 40, 42, 47, 52, and 58 (see Table Bl in the inspection

report for floor levels that were inspected in these shafts).

• 8 in. wide by 1 ft-6 in. long area of fireproofmg was found

missing on top flange of beam between shafts 30 and 31 on

floor 22.

• 100% of fireproofmg was found missing on south face of

Column 908 between floors 27 and 29 in Shaft 1.

• On floors 1-6, fireproofmg was found missing on the floor framing at various locations.

• Hairline cracks were found in the concrete beam encasement

(fireproofmg) at scattered locations on all four mechanical

equipment room levels. October

1991

Port Authority

Facility Condition

Survey Program - WTC 1

WTC 1 • Missing fireproofmg was found at various locations on the

exterior wall columns and spandrel plates (exact locations were

not given in the report).

• Several small areas and a few large areas of fireproofing was

found missing from steel beams and columns in elevator shafts

2, 1 1, 12, 15, 26, 35, 43, 52, 62, 67, 77, 80, and 90 (see Table B-1 in the inspection report for floor levels that were

inspected in these shafts).

• Fireproofing was found missing on a connection between a core column and a floor beam on floor 30 (exact location was not given in the report).

• Small areas of fireproofing were found missing from the floor iraming at scdiiereu locaiions on iioors y inrougn lu/ (^exaci locations were not given in the report).

• Fireproofing was found missing on many damping units on

floors 9 through 107 (exact locations were not given in the

report).

• On 43rd floor, fireproofing was found missing on an area of

25 ft by 60 ft on the underside of metal deck between column

lines 351 to 359 and 41 1 to 428. Fireproofing was also found

missing on the floor beams in this area.

• On the 77th floor, fireproofing was found missing on an

approximately 100 sq ft area of metal deck.

82 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o fWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

October

1991

SII Report on Bracing

Below Elevation 294 ft 0 in.

WTC 1 and

WTC 2

• Between columns 1 48 and 1 5 1 of WTC 2 at the underside of Level Bl, CMU wall acting as fireproofing was removed to allow pipes to pass through.

• Between columns 154 and 157 of WTC 2 at Level B2,

CMU wall acting as fireproofing was removed for a doorway opening.

• Between columns 1 33 and 1 36 of WTC 2 at the underside of Level Bl, CMU wall acting as fireproofing was removed for a doorway opening.

• Between columns 154 and 157 of WTC 2 between

LevelsB5 and B6, CMU wall acting as fireproofing was

removed for a doorway opening.

• Some degree of damage was found on all of the spray-on

fireproofing on the diagonal bracing members between

Levels B4 and B5 in both WTC 1 and WTC 2.

• Fireproofing (CMU and spray-on) was found missing at the intersection of diagonal bracing members G120B,

G121B, and column 139 on Level B6 in WTC 2.

• CMU fireproofing was found missing at the intersection of diagonal bracing member Gl 19B and column 130 on LevelSe in WTC 2.

• Fireproofing (CMU and spray-on) was found missing at the intersection of diagonal bracing member G418B and

column 421 on Level 1B5 in WTC 2.

• At the base of column 357 on Level B6 in WTC 1 , CMU

lliCpiUUlHl^ Wao lUUIlU lliloolll^.

• Damaged fireproofing due to flooding was found at the

intersection of diagonal bracing member G320A and

column 324 on Level B6 in WTC 1

.

• Fireproofing was found missing on the transfer truss members located between column 242 and 248 on

Level Bl in WTC 2.

NISTNCSTAR 1-1 C, WTC Investigation 83
Chapter 3

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o FWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

October

1992

SII Report on Hat

Trusses WTC 1 andWTC2

• Fireproofing that was removed during the Facility

Condition Survey inspections performed in 1990 and

1991 was not repaired.

• Fireproofing was found missing on two columns of the elevator machine room on floor 1 10 of WTC 2.

• Considerable damage was found-to gypsum wallboard

acting as fireproofing between column lines 806 and 807

on floor 107 m WTC 2.

• Gypsum wallboard acting as fireproofing was found

missing around columns 903 and 904 on floor 1 10 in WTC 2.

• Damaged gypsum wallboard acting as fireproofing was

found around columns 707 and 708 on floor 108 in WTC 1.

• Fireproofing was found missing or damaged on the steel members: (a) between columns 804 and 905 on floor 108 m WTC 1; (b) between columns 701 and 801 on

floor 108 in WTC 1; (c) between columns 707 and 708

on floor 110 in WTC 2; (d) between columns 903 and

904 on floor 1 10 in WTC 2; (e) between columns 702

and 703 on floor 108 in WTC 1 ; (f) between columns

802 and 803 on floor 109 in WTC 1; (g) between

columns 704 and 804A on floor 1 10 of WTC 1; (h) between columns 807 and 908 on floor 108 of WTC 1;

(i ) between columns 608 and 708 on floorl08 of WTC

between columns 1004 and 1005 on floor 108 of

WTC 1 ; (k) between columns 603 and 606 on floor 107 of WTC 2; (1) between columns 331 and 1004 on floor

1 10 of WTC 2; (m) between columns 605 and 705 on

flnnr 108 nf WTC 1 (n\ hptwpen rnliimns 80'' and 803

on floor 109 of WTC 1; and, (o) between columns 704

and 804A on floor 1 1 0 of WTC 1

.

• Extensive gypsum wallboard damage was found

between columns 904 and 1004 on floor 1 10 in WTC 1. Other gypsum wallboard damage was found at scattered

locations on floors 108-1 10 in WTC 1 and WTC 2. November

1992

Sll Report on Floor Framing Over

Tenant/Mechanical Areas

WTC 1 and

WTC 2

• Fireproofing was found missing on some steel members

in WTC 2 (exact locations were not specified in the

report).

84 NISTNCSTAR 1-1C, WTC Investigation
Structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o PWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

November

1992

SII Report on Floor Framing Over

Tenant/Mechanical Areas

WTC 1 and

WTC 2

• CMU fireproofmg was found missing on Levels B2 and

B4 of WTC 2 next to the central corridor.

• Fireproofmg was found not be reapplied after asbestos removal on floors 9, 10, and 12 (see Appendix A of SII report for exact locations).

• Fireproofing was found missing on some beams in the core area on floors 15 and 48 in WTC 2. Fireproofing was also found missing on the undersides of metal deck

and top chords of floor trusses (exact locations were not

specified in the report). January

1993

Sll Report on

Accessible Columns

WTC 1 and

WTC 2

• Spalling and missing fireproofing was found on the steel members in the express elevator shafts in both towers (members and locations were not specified in the report).

• Large areas of fireproofing were found missing on the faces of columns 606 and 607 in WTC 1

.

• Fireproofing was found missing at the splice location of

column 701 in WTC 1.

• Isolated areas of spalled fireproofing were found on members in the local elevator shafts (members and

locations were not specified in the report).

February

1995

Sll Report on Hat

Trusses WTC 1 andWTC 2

• Fireproofing that was removed during the Facility

Condition Survey inspections performed in 1990 and

1991 was not repaired.

• Damaged gypsum wallboard was found at column 704

on floor 109 in WTC 1.

• L/aTua^cu gypsuiTi wdiiDOaru wds luunu uciwccn

columns 904 and 1 004 on floor 1 1 0 of WTC 1

.

• Fireproofing was found missing at the following

connections: (a) column 904 on floor 108 of WTC 2; (b) between columns 804 and 904 on floor 108 of WTC 2; and (c) Between columns 604 and 704 on floor 108 of

WTC 2.

NISTNCSTAR 1-1 WTC Investigation 85
Chapter 3

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o1fWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

February

1995

(continued)

SII Report on Hat

Trusses WTC 1 and

WTC 2

• Fireproofing was found missing or damaged on the steel members: (a) between columns 503 and 504 on floor 109 in WTC 1; (b) between columns 702 and 703 on

floor 109 in WTC 1; (c) between columns 705 and 706

on floor 1 10 in WTC 1; (d) between columns 707 and

709 on floor 108 in WTC 1; (e) between columns 702

and 703 on floor 108 in WTC 1; (f) between columns

801 and 802 on floor 108 in WTC 1; (g) between

columns 802 and 803 on floor 109 in WTC 1; (h) between columns 803 and 805 on floor 1 10 in WTC 1;

(i) between columns 701 and 801 on floor 108 of WTC

1; 0) between columns 329-1005, 332-1004, and 903-

1003 on floor 1 10 in WTC 1; (k) between columns 804

and 904 on floor 108 in WTC 1; (1) between columns

504-604, and 704-804 on floor 109 in WTC 1; (m)

between columns 704 and 804A on floor 1 10 in WTC 1

;

(n) between columns 604-704 and 604-705 on floor 109

in WTC 1 ; (o) between columns 805 and 905 on floor 109 m WTC 1; (p) between columns 608-708, 305-310,

234-238, and 149-508 on floor 108 m WTC 1; (q)

between columns 504 and 506 on floor 109 in WTC 2;

(r) between columns 603 and 606 on floor 107 in WTC

2; (s) between columns 706 and 707 on floors 108 and

1 10 in WTC 2; (t) between columns 802-803 and 805- 806 on floor 108 in WTC 2; (u) between columns 1004

and 1005 on floor 1 10 in WTC 2; (v) between columns

1005 and 1006 on floor 108 in WTC 2; (w) between

columns 331-1 104, 804-904, and 904-1004 on floor 1 10

in WTC 2; and (x) between columns 903 and 904 on

floor 110 of WTC 2.

86 NISTNCSTAR 1-1 C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o WTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

March 1995 SIl Report on Bracing

Below Elevation

294 ft 0 in.

WTC 1 and

WTC 2

• Fireproofing (CMU and spray-on) was found missing or damaged on the steel members in WTC 1 : (a) between

columns 101-103, 121-124, 131-136, 133-139, 148-151,

224-227, 236-239, 245-248, 248-251, 257-259, and 401-

403 on Levels B5-B6; (b) between columns 1 2 1 - 1 24,

127-130, 148-151, 142-145, 139-142, 136-139, 145-151. 151-154, and 251-254 on Levels B2-B3; (c) between

columns 254-257, 303-306, 306-309, and 445-448 on

Levels B4-B5; (d) between columns 251-254, 348-351,

401-406, 406-409, and 434-454 on Levels B1-B2; and,

(e) between columns 454-457 on Levels B3-B4.

• CMU fireproofing was found removed at column 409

between Levels B5 and B6 in WTC 1.

• CMU fireproofing was removed between columns 433

and 436 between Levels B4 and B6 in WTC 1

.

• Fireproofing was found missing at column 421 between

Levels B4 and B5 and at column 427 between Levels B5

and B6 in WTC 1

.

• Fireproofing (CMU and spray-on) was found missing or damaged on the steel members in WTC 2: (a) between

columns 115-118, 139-142, 142-145, 145-148, and 212-

2 1 8 on Levels B5-B6; (b) between columns 2 1 8-22 1

,

330-333, and 342-345 on Levels B4-B5; (c) between

columns 227-230 on Levels B3-B4; (d) between

columns 133-136, 218-221, 227-230, 436-439, and 439-

442, and at column 101 on Levels B1-B2; (e) between

columns 242-248 between level Bl and floor 1; (f) between columns 139-148 and 327-330 on Levels B2-

B3; (g) between columns 412-415, 415-421, and 421- 424 on Levels B4-B6; and, (h) between columns 321-

324, 439-442, 448-451, and 451-454 on Levels B4-B5.

• CMU fireproofing was removed at column 252 between

Level Bl and floor 1 in WTC 2.

• CMU fireproofing was removed between columns 418

and 421 and between columns 433 and 436 between

Levels B3 and B4 in WTC 2. • r^KylT T fir*=>nmnfino rpmnvpH hptwppn rnllimns 4^4

and 457 between Levels B2 and B3 in WTC 2.

• CMU fireproofing was removed between columns 4 1

2

and 4 1 5 and between column 1 1 5 and 1 1 8 between

Levels Bl and B2 in WTC 2.

• CMU fireproofing was removed between columns 1 54

and 157 between Levels B5 and B6 in WTC 2.

April 1995 SII Report on Framing

Over Tenant Areas WTC 1 and

WTC 2

• Fireproofing was found not be reapplied after asbestos removal on floors 17 and 22.

• Fireproofing was found missing on floor members at muhiple locations in WTC 1 and WTC 2.

• Large areas of fireproofing were found missing on the underside of the floor trusses on floor 38 in WTC 1

NISTNCSTAR 1-1C, WTC Investigation 87
Chapter 3

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o1FWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

April 1995 SII Report on

Accessible Columns

WTC 1 and

WTC 2

• Large areas of fireproofmg were found missing in service elevators 49A, 49 B, 50A, and 50 B in both

towers.

• Fireproofmg was found missing or damaged on the following columns in WTC 1: (a) column 901 between

floors 2-44; (b) column 907 at Level B2 and floors 9, 16-20, 28-31, 34, and 36-38; (c) column 906 at Level B2; (d) column 903 at floors 31, 33, 34, 38, and 39; (e) column 902 at Level B2 and floors 39, 41, and 43; (f) column 601 between floors 2-78; (g) column 605

between floors 3-5; (h) colunm 606 at floors 8, 1 1, 19, 25-30, and 43-45; (i) column 607 between floors 2-78;

(j) column 608 between floors 2-78; (k) column 704

between Level Bl and floor 78; (1) column 603and 606

at Level B2; (m) column 704 at Levels B1-B3; and, (n) columns 802 and 905 at Level B3.

• Fireproofing was found missing or damaged on the following columns in WTC 2: (a) column 908 on floors 27-31 and 33-36; (b) column 907 at floor 21 ; (c) column

902 at floors 7, 20, 22, 25, 34-36, 39, and 40; (d) column

901 at floors 15 and 31; (e) column 601 at floors 25 and

35-37; (f) column 602 at floors 7, 10, 12, 14,15, 27, 42,

48, 63, 66, and 75; (g) column 603 at floors 3 and 25;

(h) columns 605 and 606 at Level B2; (i) column 607 at floors 29, 30, 47, 57, 59, 64, and 74; (j) column 608 at floors 41, 45, and 80; (k) column 703 at Level B6 and at floors 5, 17, and 48; (1) column 704 at Level B6 and at floors 48 and 74; and, (m) column 903 at Level B2.

April 1996 Sll Report on Framing

Over Mechanical Areas

WTC 1 and

WTC 2

• Fireproofing was found tearing away from the underside

of the metal deck on F08 in WTC 2.

• Damaged fireproofing was found on a beam in the southwest comer of the core on floor 107 in WTC 1

.

• Fireproofing was found missing or damaged at many

locations on the floor members supporting floor 75 in WTC 1.

• A 3 ft by 3 ft hole was found in the gypsum wallboard in the core area on floor 41 in WTC 1

.

• Damaged CMU fireproofing for the perimeter diagonal

bracing at Level B6 was found at 5 locations in WTC 1 and 3 locations in WTC 2.

• Damaged CMU fireproofing was found on 2 columns in WTC 1 and WTC 2 columns in WTC 2 at Level B6.

• Fireproofing was found missing at 3 locations in the hat

truss on floor 108 in WTC 2.

88 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o1f WTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

May 1996 SlI Report on

Accessible Columns

WTC 1 and

WTC 2

• Fireproofing was found missing at the column bases that were inspected in the elevator pits in both towers.

• Fireproofing was found missing or damaged on columns

in the following elevator shafts of WTC 1 : (a) Shaft 6A,

floor 77, column 904; (b) Shaft 17A, floor 1, column

604; (c) Shaft 34A, floor 1 5, column 706; (d) Shaft 35A,

floors 6-7, column 805; (e) Shafts 69A and 70A,

throughout entire shaft, columns 802 and 702; (f) Shaft 88A, floor 91, column 802; and (g) Shaft 95 A, floors 98-100, column 706.

• Fireproofing was found missing or damaged on columns

in the following elevator shafts of WTC 2: (a) Shaft 18B, floor 3, column 605; (b) Shaft 19B, floors 2, 5, 46,

55, and 73, column 606; (c) Shaft 20B, floors 22, 47, 49,

57, and 64, column 606; (d) Shaft 2 1 B, floor 2 1

, column

607; (e) Shafts 34B and 35 B, throughout entire shafts, columns 706 and 805; (f) Shaft 34B, floor 23, column

702; (g) Shaft 43 B, floor 6, column 702; (h) Shaft 62B,

floor 57, column 805; (i) Shaft 70B, floors 69 and 72. column 702; (j) Shaft 88B, throughout entire shaft, column 802; and, (k) Shaft 96B, floor 101, column 706. May 1996

(continued)

SI I Report on

Accessible Columns

WTC 1 and

WTC 2

• Fireproofing was found missing or damaged on

connecting steel beams to columns in the following

elevator shafts of WTC 1: (a) Shaft 34A, floors 22-23,

column 706; (b) Shaft 35 A, floors 1 1 and 17, column

805; (c) Shafts 42A and 43A, throughout entire shaft, columns 702 and 802; (d) Shafts 61 A and 62A,

throughout entire shaft, columns 706 and 805; (e) Shafts 69A and 70A, throughout entire shaft, columns 702 and

802; (f) Shafts 78A and 79A, floor 76, column 707; (g) Shaft 89A, Levels B1-B3, column 702; and, (h) Shafts 96A and 97A, throughout entire shafts, columns 707 and

806.

• Fireproofing was found missing or damaged on

connecting steel beams to columns in the following

elevator shafts of WTC 2: (a) Shaft 7B. throughout

entire shaft, column 903; (b) Shaft 18B, floors 3 and 13, column 605; (c) Shaft 19B, throughout entire shaft, column 606; (d) Shaft 20B, floors^ 12, 13, 55, 57, 62, 67. 70, 74, and 77, column 606; (e) Shaft 34B, floor 24,

column 706; (f) Shaft 42B, floor 32, column 702; (g) Shaft 43B, throughout entire shaft, column 702; (h) Shafts 61 B and 62B, throughout entire shafts, columns

706 and 805; (i) Shaft 88B, throughout entire shaft, column 802; (j) Shaft 89B, floors, 82, 91, 96 and up. (k) column 702; Shaft 89B, throughout entire shaft, column

802; and, (1) Shaft 96B, floor 77, column 706.

NISTNCSTAR 1-1C, WTC Investigation 89
Chapter 3

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o fWTC 1, 2, and 7 (continued).

Date Inspection Program Building($) Location/Description

April 1997 Port Authority Facility

Condition Survey

Program - WTC 7

WTC 7 • Fireproofing was found missing on steel framing at floors 1, 2, 5, 6, 8, 1 1, 19, 23, 24, 26, and 44. Largest

areas of missing fireproofing were found on floor 5 above the Main Lobby and floor 2 above the Loading

Dock area. May 1997 SII Report on

Accessible Columns

WTC 1 and

WTC 2

• Fireproofing was found missing at the column bases that were inspected in the elevator pits in both towers.

• Fireproofing was found missing or damaged on columns

in the following elevator shafts of WTC 1 : (a) Shaft lOA, floors 3. 9, 10, 22, and 27, column 902; (b) Shaft

1 lA, floors 8 and 30-33, column 901; (c) Shaft 24A,

floor 4, column 807; (d) Shaft 40A, floors 3 and 33,

column 702; (e) Shaft 51 A, floor 45, column 807; (f) Shaft 52A, floors 45 and 53, column 708; (g) Shaft 57A,

floors 44, 45, and 61 , column 806; (h) Shaft 58A, floors 60 and 61, column 707; (i) Shaft 84A, floors 82 and 91,

column 702; (j) Shaft 90A, floors 79, 91, and 95,

column 703; and (k) Shaft 91 A, floor 100, column 803.

• Fireproofing was found missing or damaged on columns

in the following elevator shafts of WTC 2: (a) Shaft 24B, floor 16, column 807; (b) Shaft 25B, floors 2, 1 1, and 14, column 708; (c) Shaft 30B, floor 23, column

806; (d) Shaft 3 IB, floors 2-4, 6, 15, 25, column 707; (e) Shaft 36B, floors 8 and 15, column 801; (f) Shaft 37B,

floor 32, column 701 ; (g) Shaft 48B, floors 35-41

,

column 905; (h) Shaft 52B, floors 45 and 51, column

708; (i) Shaft 57B, floor 52, column 806; (j) Shaft 58B,

floors 57 and 60, column 707; (k) Shaft 67B, floor 47,

column 702; (1) Shaft 68B, floor 44, column 802; (m)

Shaft 90B, floors 94, 96, 98, and 99, column 703; and,

(n) Shaft 91B, floors 84, 96, and 98, column 803.

• Fireproofing was found missing or damaged on

connecting steel beams to columns in the following

elevator shafts of WTC 1: (a) Shaft lOA, floors 16 and

22, column 902; (b) Shaft 24A, floors 2, 3, and 9, columns 708 and 807; (c) Shaft 41 A, floors 19-24,

column 802; and, (d) Shaft 84A, floor 81, column 702.

• Fireproofing was found missing or damaged on

connecting steel beams to columns in the following

elevator shafts of WTC 2: (a) Shaft 248, floors 2, 5, and

12, column 807; (b) Shaft 48B, throughout entire shaft, column 905; (c) Shaft 57B, floors 44 and 55, column

806; (d) Shaft 64B, floor 49, column 701; (e) Shaft 68B,

floors 44, 47, and 56, column 802; (f) Shaft 88B, floors 82 and 84,column 802; and (g) Shaft 90B, floor 98,

column 703.

90 NISTNCSTAR 1-1C, WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o fWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

December

1997

SII Report on Floor Framing Over Tenant

Areas

WTC 1 and

WTC 2

• Fireproofmg was found missing or damaged on the floor framing on the following floors in WTC 1:15, 20, 28,

92, 95, 96, and 97. On floors 95-97, the fireproofmg was

found to be less than 0.25 in. thick. On the other floors, the fireproofmg appeared to be fairly new, and was

found to be approximately 1 .5 to 2.0 in. thick.

• Fireproofmg was found missing or damaged on the floor framing on the following floors in WTC 2: 35, 37. 38,

57, 77, 78, 86, 87, 92, and 93. On floors 77, 86, 87, 92,and 93, the fireproofmg was found to be less than

0.25 in. thick. On floors 35 and 57, the fireproofmg

appeared to be fairly new, and was found to be

approximately 1.5 to 2.0 in. thick. May 1998 SII Report on Plaza

T pvpI Roy ("'oliimnQ

WTC 1 and

WTC 2

• In WTC 1 , approximately 2 to 3% of the fireproofmg on

the plaza level columns was found to be deteriorated

• Fireproofmg was found to be deteriorated and/or missing on the column and seated beam connections at columns

236, 242, and 248 in WTC 1.

• In WTC 2, approximately 1 to 2% of the fireproofmg on

the plaza level columns was found to be deteriorated and/or missing.

May 1998 SII Report on

Accessible Columns

WTC 1 and

WTC 2

• Fireproofing was found missing at the column bases that were inspected in the elevator pits in both towers.

• Fireproofmg was found missing or damaged on columns

in the following elevator shafts of WTC 1: (a) Shaft 5 A,

floor 7, column 906; (b) Shaft 29A, floor 11, column

806; (c) Shaft 30A, floors 8 and 24, column 806; (d) Shaft 46A, floors 32 and 40, column 703; (e) Shaft 47A.

floors 19, 23, 26, and 32, column 803; (f) Shaft 48A,

floors 2-17, 18, and 29-40, column 905; (g) Shaft 56A,

floors 45 and 46, column 806; (h) Shaft 67A. floor 48. column 702; (i) Shaft 68A, floors, 48, 66, and 67,

column 802; (j) Shaft 73A, floor 43, column 703; and

(k) Shaft 78A. floors 77, 78, and 86. column 707.

NISTNCSTAR 1-1C, WTC Investigation 91
Chapter 3

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o1fWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

May 1998

(continued)

SII Report on

Accessible Columns

WTC 1 and

WTC2

• Fireproofing was found missing or damaged on columns

in the following elevator shafts of WTC 2: (a) Shaft 3B,

floors 7 and 39, column 907; (b) Shaft 4B, floors 3, 5 and 23, column 906; (c) Shaft 8B, floor 14, column 903;

(d) Shaft 9B, floors 10, 18, 23, and 34, column 902; (e) Shaft 16B, throughout entire shaft, column 603; (f) Shaft 17B, floors 28. 3l, 38, 45. 52, 58, 59, 66, 69, and 73,

column 604; (g) Shaft 28B, Level Bl, column 707; (h) Shaft 40B, Level Bl, column 702; (i) Shaft 41 B, floor 2, column 802; (j) Shaft 46B, Level Bl and floors 2, 8, 13,

17, 20, and 35, column 705; (k) Shaft 47B, floors 4, 7, 17, 31, and 40. column 803; (1) Shaft 74B, floor 66,

column 803; (m) Shaft 83B, floor 89, column 701; (n) Shaft 85B, floors 83, 89, and 93, column 802; and, (o) Shaft 94B, floors 77, 101, 104, and 106.

• Fireproofing was found missing or damaged on

connecting steel beams to columns in the following

elevator shafts of WTC 1 : (a) Shaft 28A, throughout

entire shaft, column 707; (b) Shaft 29A, floors 9 and 12, column 806; (c) Shaft 30A, floors 10 and 25, column

806; (d) Shaft 31 A, throughout entire shaft, column 707;

(e) Shaft 46A, throughout entire shaft, column 703; (f) Shaft 47A. floors 16, 17, 32, and 34, column 803; (g) Shaft 55A, floors 44-49 and 56, column 707; (h) Shaft 56A, floor 48, column 806; (i) Shaft 67A, throughout

entire shaft, column 802; (j) Shaft 68A, floor 61, column

802; (k) Shaft 78A, floor 82, column 707; and (1) Shaft 79A, throughout entire shaft, column 806.

• Fireproofing was found missing or damaged on

connecting steel beams to columns in the following

elevator shafts of WTC 1: (a) Shaft 4B, floors 7, 15, 23,

31, 39, and 40, column 906; (b) Shaft 8B, floors 14, 20,

and 45, column 903; (c) Shaft 9B, floor 34, column 902;

(d) Shaft 16B, floors 2-48, column 603; (e) Shaft 17B,

floors 28, 40, 48, and 69, column 604; (f) Shaft 40B,

throughout entire shaft, column 702; (g) Shaft 46B,

throughout entire shaft, column /03; (h) Shait 4/B,

floors^ 9, 13, 15, 27, 31, 33. and 34. column 803; (i) Shaft 82B, floors 86 and 87, column 801 ; (j) Shaft 83B,

floor 86, column 701; (1) Shaft 84B, floor 94, column

702; (m) Shaft 85B, floors 78, 79, and 86-88, column

802; (n) Shaft 94B, floors 89 and 101, column 805; and

(p) Shaft 95B. floors 81. 87. 94, and 101. column 706.

92 NISTNCSTAR 1-1C. WTC Investigation
structural Insp. Prog. During the Occupancy of WTC 1, 2, and 7

Table 3-25. Summary of locations where fireproofing was found missing during

structural inspections o1fWTC 1, 2, and 7 (continued).

Date Inspection Program Building(s) Location/Description

May 1999 SlI Report on Floor Framing Over

Mechanical Areas

WTC 1 and

WTC 2

• Fireproofing was found missing on four perimeter braces

in Level B6 of WTC 2. Most of other fireproofing on

perimeter braces as reported in 1996 report was found to be repaired.

• A 3 ft by 3 ft hole was found in the gypsum wailboard in the core area on floor 41 in WTC 1

.

• Damaged CMU fireproofing for the perimeter diagonal

bracing at Level B6 was found at 5 locations in WTC 1

• Damaged CMU fireproofing was found on 2 columns in WTC 1 and WTC 2 columns in WTC 2 at Level B6.

• Fireproofing was found damaged on one of the hat truss members on floor 1 08 in WTC 1 . Most missing

fireproofing on hat truss members as reported in the 1996 was found to be repaired in WTC 2. November

1999

SII Report on Floor Framing Over Tenant Areas

WTC 1 and

WTC 2

• A 6 ft length of fireproofing was found to be missing on

the bottom chord of one of the long-span floor trusses spanning from the core to the west wall on floor 89 in WTC 2 (see Appendix B of Sll report for exact location of floor truss).

3.4 REFERENCES

Cerami and Associates, Inc. 1 996. World Trade Center Tower I and II Floor System Natural Frequency

Test. LERA Report No. 4076. March, (part of WTCI-66-L).

LERA (Leslie E. Robertson Associates). 1 995. One and Two World Trade Center Floor Frequency

Measurements. LERA Report No. 4055. ApriL (part of WTC1-66-L).

LERA (Leslie E. Robertson Associates). 1996. One and Two World Trade Center Damper Testing.

May. (WTC1-230-L).

Lucius Pitkin, Inc. 1993. Examination ofBox Columns and Diagonal Beam Repairs - World Trade

Center, NY. Report No. ME-4525 SI. December, (part of WTC1-66-L).

Merritt & Harris, Inc. 2000. Report ofDue Diligence Physical Condition Swvey - World Trade Center. December. (WTCI-6-P).

PANYNJ (Port Authority of New York and New Jersey). 1 986. Standards for Structural Integrity'

Inspection ofthe World Trade Center Towers A and B. Infrastructure Engineering Design Division,

Engineering Department. March, (part ofWTCI-66-L).

PANYNJ (Port Authority of New York and New Jersey). 1990. Port Authority Facility Condition

Swvey Program, World Trade Center Tower "B." Engineering Quality Assurance Division,

Engineering Department. (WTCI-120-P).

NISTNCSTAR 1-1C, WTC Investigation 93
Chapter 3

PANYNJ (Port Authority of New York and New Jersey). 1991. Port Authority Facility Condition

Sur\>ey Program - World Trade Center Tower A Structure Elements. Engineering Quality Assurance

Division, Engineering Department. October. (WTCI-118-P).

PANYNJ (Port Authority of New York and New Jersey). 1 997. Port Authority Facility Condition

Sun>ey Program — 7 World Trade Center. Engineering Quality Assurance Division, Engineering

Department. April. (WTCI-122-P).

SHCR (Skilling, Helle, Christiansen, Robertson). 1971. Vibration Characteristics ofthe Floors in the World Trade Center Towers. LERA Report No. 1012. September, (part of WTC1-66-L).

WSHJ (Worthington, Skilling, Helle, «fe Jackson). 1966. Part I Final Chapter, WSHJ Wind Report.

June. (partofWTCl-68-L).

WSHJ (Worthington, Skilling, Helle, & Jackson). 1967a. Structural drawings of WTC 1 and 2. (WTCI50-L).

WSHJ (Worthington, Skilling, Helle, & Jackson). 1967b. The World Trade Center Report No. DU-1,

Viscoelastic Damping Units. July, (part of WTCI-67-L).

94 NISTNCSTAR 1-1C, WTC Investigation
Chapter 4

Significant Modifications and Repairs to the Structural

Framing Systems of WTC 1 , 2, and 7

4.1 overview

This chapter contains a summary of the significant modifications and repairs that were made to the

structural framing systems of World Trade Center (WTC) 1, 2, and 7 from initial occupancy to September 11, 2001, including a discussion of the repairs that were made after the February 1993

bombing of WTC 1.

4.2 modifications AND REPAIRS MADE TO WTC 1

4.2.1 Openings Made in Floor Slabs

Structural modifications involving openings made in the floor slabs are hsted in Table 4-1, along with a brief description of the work that was perfonned with respect to the modifications.

In all of the cases cited in Table 4-1, except for the 1995 case, documents included general notes and

drawings that listed the codes, design criteria, and materials that were used in the design, and the proposed sequence of construction. Structural calculations on the design of new structural members and on the check of the capacities of existing structural members were included for the modifications made in 1995 and 1997. The documents for the 1999 modifications include comments made by the Tenant

Construction Review Unit of the Port Authority of New York and New Jersey (PANYNJ or Port Authority) in regard to the project submittal. The Tenant Alteration Application Request Fonn, submitted

to the Port Authority on behalf of the tenant, is also included.

Smaller floor penetrations, also made in the floor slabs, are not included in Table 4-1 . In 1995, a number

of openings were made in the floor slabs on levels 106 and 107 (Windows on the World Restaurant) to allow installation of equipment (W95-1 1 14, PANYNJ, Newark).' The maximum opening size was

5 ft 0 in. by 2 ft 6 in., and new beams were introduced to support the beams added around the openings.

The structural engineer for this project was Leslie E. Robertson Associates (LERA). LERA was also the

structural engineer for the chiller and condenser pipe penetrations on floors 94 through 100 that were made in 1998 for the tenant J&H Marsh & McLennan (W98-1 197-02, PANYNJ, Newark). Openings

ranged in size from 6 in. diameter core holes to 1 ft 6 in. by 6 in. slab openings.

4.2.2 Openings in Floor Slabs That Were Subsequently Closed

Openings in floor slabs that were subsequently closed are listed in Table 4-2. These openings were cut primarily for stairways.

The Port Authonty document number is given in brackets; document was obtained from PANM^IJ office in Newark, NJ.

NISTNCSTAR 1-1C, WTC Investigation 95
Chapter 4

General notes and drawings were provided for the 1985 and 1987 modifications listed in the table. These

included the codes, design criteria, and materials that were used in the design, and the proposed sequence

of construction. Design of the new structural members and checks of the capacities of existing structural members are contained in the documents for the modifications made in 1998.

Table 4-1 . Openings made in floor slabs in WTC 1

.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1978 93-95 The

HeywardRobinson

Co. Inc.

SHCR Slab openings were cut in floors 94 and

95 between columns 90 1 . 902, 1 00 1 , and

1002 in core to accommodate new stair linking floors 93 through 95. Portions of

existing beams on floors 94 and 95 were

removed, and new beams were added to frame new openings. Support framing for

3 hour fire door was also provided.

LERA Box 8

1979 99-101 Deloitte Haskins &

Sells

SHCR Slab openings were cut in floors 100 and

lui Derween columns /u/, /Uo, suo, ana 807 in core to accommodate new stair between these levels. Slab opening was

also cut in floor 99 between columns 701

,

702 801 and 802 to accommodate new

stair. Existing framing was removed and new structural members were added.

LERA Box 8

1985 89, 90 Swiss Bank

International

Robertson

Fowler &

Associates

Slab opening was cut on floor 90 between

columns 901, 902, 1001, and 1002 in core

to accommodate new stair connecting

floors 89 and 90. Existing framing was

removed on floor 90 and new structural members were added on both floors.

LERA Box 8

1995 107 Windows on

the World

Restaurant

LERA Slab openings were cut in floor 107 for grease arrestors (exact location of

openings could not be determined from

drawings).

W95-1114

PANYNJ

(Newark)

1997 105-Roof Unknown LERA Slab openings were cut for new elevator 99A near columns 704 and 804A in the

core. Existing structural members were

checked on floor 105 (support of pit beams), floor 110 (support of machine

beams) and the penthouse roof (support

Ul ClcVdlUI } lUI Ulc appiupilalc lUaUo. 11 was determined that some of the beams

on floor 1 05 and the roof were

overstressed (not more than 4%) due to the increased loads. These members were

not reinforced (calculations state that beams are O.K. since overstress < 5%).

WTCI-66-L

1999 93-100 J&H Marsh &

McClennan

Gensler Several openings were cut in the floor slabs for stairs linking the different floors occupied by the tenant (exact location of

openings could not be determined from

drawings). Mention is also made to new

framing supporting the Skyfold Partition.

W98-11 97-03 PANYNJ

(Newark)

96 NISTNCSTAR 1-1 C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1,2, & 7

Table 4-2. Openings in floor s abs that were closed in WTC 1

.

UaVx. r luu I \^} Xcii3n t

Structural

Enjjinccr Description ol Modification Reference

1972 95 Fiduciary

Trust Co. SHCR New beams and floor deck were added

to frame existing openings near column

Mnes 124 and Zjy.

LERA

Box 8

1985 95 Deloitte Haskins &

Sells

Robertson

Fowler &

Associates

New beam and floor deck were added to frame existing opening between columns

901, 902, 1001, and 1002 in the core.

LERA

Box 8

1987 91,92 ADT LERA New beams and deck were added to frame existing stair opening in core near columns 603 and 702.

LERA

Box 8

1998 96, 100 Unknown LERA New beams and deck were added to frame existing stair openings between

columns 1 19 and 123 on floor 96

(outside of core) and near columns 707,

708, 806, and 807 on floor 100 (inside

core)

W98-1192

PANYNJ

(Newark)

4.2.3 Structural Members That Were Reinforced

Various floor members were reinforced to accommodate floor loads that were greater than the original

design loads. A summary of reinforced members is contained in Table 4-3. In the introduction to documents submitted for the 1998 modifications, it is stated that the existing structural elements were

checked using the PANYNJ Design Guidelines and Specifications. Calculations show that the Port Authority criteria were used for the existing loads on the floor system. The Tenant Alteration Application

Review Request Fonn that was submitted to the Port Authority on behalf of the tenant was also included

in the submittal package.

4.2.4 Repair Work Following the February 26, 1993 Explosion

Damage from the Explosion

The explosion of February 26, 1993 occurred on the second basement level (Level B2) near the center of

the south wall of WTC 1 and adjacent to the Vista Hotel. Structural steel columns, diagonal braces, and

spandrel beams in the immediate vicinity of the blast were damaged. Concrete floor slabs at Levels Bl

and B2 in the parking garage and unreinforced masonry walls were also damaged over a large area. A

discussion on the structural damage in WTC 1 caused by the blast is given below. A summary of the damage assessment in WTC 1 at Level Bl and Level B2 can be found in the floor plans in Figs. 4-1 and

4—2, respectively.

The explosion tore out the diagonal brace between Column 324 at Level B2 and Column 327 at Level Bl

and severely bent the brace between Column 324 at Level B2 and Column 321 at Level Bl (see Figs. 4-1

and 4-2) (LERA 1993a). The braces on the south face of WTC 1 that were damaged by the blast are shown in Fig. 4—3.

Spandrel beams at Level Bl from Column 321 to 324 and from Column 324 to 327 were also damaged by

the blast. Spandrels were bowed and cracked, and some had missing bohs (LERA 1 993b).

NISTNCSTAR 1-1C, WTC Investigation 97
Chapter 4

Table 4-3. Structural members that were reinforced In WTC 1.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1979 97-100 Deloitte Haskins &

Sells

SHCR On floor 98, beams between columns 601 and 602 and between 701 and 702 were

reinforced with bottom cover plates to support mechanical files that were hung

from framing at this level. On floor 98, bridging trusses on the east

side of the core between columns 218 and

221 were reinforced with new diagonals.

No information is given on why the bridging trusses needed to be reinforced. On floor 99, 32 in. deep floor trusses along

column lines 309, 31 1, 313, 315, 317, 319,

321, 323, 325, 327, and 329 were

reinforced by welding additional rods and

angles to the web members near the

supports. Double angles were also welded

to the bottom chords near midspan and to the top chords near the supports. No

information was found on the reason why

the trusses needed to be reinforced. On floor 99, core perimeter columns were

reinforced with 3 new plates. No

infomiation was found on why the columns

h?iH to Hp rpinfnrrpH

On floor 100, supports for a moveable wall were installed.

LERA

Box 8

1996 86 WTC

Planning

LERA Floor trusses were reinforced in the northwest comer of the building to accommodate new loads due to various

types of filing systems.

LERA

Box 9

1998 85 Ohrenstein &. jjiownGilsanz

IVlUITay Steficek

Steel beams and cover plates on existing Deanis were duueu lo suppon lodu irom new filing system. Also, existing floor

trusses were reinforced by welding plates to the bottom chords.

WC98-

1 1 oO PANYNJ

(Newark)

2001 47, 48 First Union

Capital

Management

LERA Floor trusses were reinforced to accommodate loads from new safes and

filing cabinets.

WOl-1115

PANYNJ

(Newark)

98 NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1,2, & 7

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NISTNCSTAR 1-1C, WTCInvestigation 99
Chapter 4

100 NISTNCSTAR 1-1 C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1.2, & 7

REV.

Cracked

weld

LERA '^^''^ ROBERTSON ASSOCIATES

aXJUlTlhO nflUCTUIAl tWilNfCOS WTC • STRUCTURAL INTEGRITY INfVESTlGATION MAjnCTiC 'ARTICLE resTifMOf

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Source: Part of WTCI-167-STB. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 4-3. Bracing on south face of WTC 1 damaged by blast.

LERA observed a crack along the edge of the field splice in Column 324, located 3 ft above Level B2,

that extended across most of the four faces of the column. Lucius Pitkin, Inc., a testing company that was

hired to perform detailed examinations of the structural steel members and welds, confirmed the crack in Column 324. Ultrasonic testing was used to determine that the crack extended across the full width of the weld on the south face of the column and at each end of the weld on the north face. Magnetic-particle

testing procedures were used to determine that the crack extended across the weld on the east face of the column and the majority of the weld on the west face as well. A small inward bow above Level B2 was

also observed on the south face of this column. LEHA noted that the braces and cracked column should

be repaired, but they were not critical to the structural integrity of the building (LERA 1993a).

The explosion damaged the floor beams framing into the tower side of Column 324 (see Figs. 4-1

and 4-2) (Woodson 1993). The floor beam that framed into Column 324 at Level Bl sustained a

NISTNCSTAR 1-1 C, IVTC Investigation 101
Chapter 4

horizontal displacement of about 2.5 in., and the beam at Level B2 had a displacement of about 1 in. The

bolted end connections of these beams also failed. Damage to floor beam connections also occurred at Columns 321 and 324 at Levels B3 and B4.

The concrete spandrel beam at Level B3 between Columns 318 and 330 sustained damage as a result of

the blast. Similar damage occurred to the spandrel beam at Level B4 between the same columns.

The masonry walls in WTC 1 were also damaged by the explosion (Woodson 1993). The 6 in. thick walls on the south side of WTC 1 were breached over distances of approximately 50 ft to the east and 120 ft to the west of the blast origin. The 20 ft long masonry wall that fonned part of the mechanical plenum that was located 10 ft inside of WTC 1 (near columns 321, 324, and 327) was completely destroyed. The

masonry walls of the elevator shafts located approximately 60 ft inside of WTC 1 were also damaged.

Other masonry walls inside of WTC 1 were damaged at distances of up to 90 ft from the blast origin.

None of the damaged walls were load bearing, and none were supported at the top. The walls were built to 1 in. below the structure above; the joint was subsequently caulked. Many of the damaged walls

deflected as though they were free at the top.

Repair Work

The diagonal bracing members between Levels B 1 and B2 that were damaged by the explosion were removed and replaced with new members, which consisted of plates that were welded together (see

Fig. 4^). Also, new plates were added on the flanges of the diagonal between Column 312 at Level B2

and Column 315 at Level Bl (see Fig. 4^).

New plates were added to the damaged spandrel beam at Level Bl between Columns 324 and 327 (see

Fig. and Fig. 4-5) and between Columns 321 and 324. Also, the cracked weld on the south face of

the spandrel beam at Level Bl near Column 324 was removed and replaced (see Fig. 4-6).

LERA prescribed an eight-step procedure for repair to the crack in Column 324 immediately adjacent to the field weld at the column splice above Level B2 (LERA 1993a). No documentation was found to confirm that this crack was repaired according to that procedure.

The Level Bl floor beams framing into Columns 321, 324, and 327 that were damaged during the explosion were repaired by welding new short segments of W12x53 to the existing beams (see Fig. 4—7).

New welded connections between the new beam segments and existing columns were provided.

Connections between floor beams and columns on Levels B3 and B4 were also repaired. As shown in Fig. 4-8, the damaged connection at Level B3 was removed, and a new beam seat and clip angle were

installed at the connection between the W12x72 beam framing into Column 324. New web connection

angles were installed for the beam framing into the same column at Level B4. At Level B3, repairs were made to the damaged bolts and to the gouge in the weld in the connection between the existing W12x72

floor beam and Column 321 (see Fig. 4-9).

Along the south face of WTC 1 , the damaged concrete spandrel beams were demolished and replaced.

Figures 4-10 and 4-1 1 show the details of the repair between Columns 318 and 330 at Levels B3 and B4,

respectively. Similar repairs were made to the concrete spandrel between Coluinns 333 and 345 at Level B3.

102 NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys of WTC 1.2. & 7

Columns 321, 324, and 327 were encased in 4 in. thick concrete masonry units (CMU) at the subgrade

levels after the explosion, as depicted in Fig. 4-12. According to the drawings, existing spray-on fireproofmg on spandrels and diagonals was to be repaired or patched after the columns were encased.

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 4-4. Repair of damaged bracing in levels B1 and B2 of WTC 1.

NISTNCSTAR 1-1C. WTC Investigation 103
Chapter 4

REV. 1 CD A tESLIE e. ROBEFrrSON ASSOCIATES

p /^^//^ DRAVVING NO. gg-TI5W

2-2.3 DlA<S-OMA-U REPA^f^

Source: LERA 1993b. Reproduced with permission of The Port Authority

of New York and New Jersey.

Figure 4-5. Repair of damaged spandrel beam in level B1 of WTC 1.

REV, 1 PDA ISSUE E- ROBERTSON ASSOaATES

i->L»fllA^ «»*3v;J"«<l *r*«u<m^*ut IwatMTCM P I0C5II8 DSAIV1N3 Wl

3-Z

Y/rc- exPupsioM

at sfAN PEEL eEP>ne COLUMN la^TDCOUJHN 32?

'

1

' '

Source: Reproduced with permission of The Port Authority

of New York and New Jersey.

Figure 4-6. Repair of cracked weld on spandrel beam in level B1 of WTC 1.

104 NISTNCSTAR 1-1 C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1,2, & 7

REV. 1 PR A LESLIE E. ROBEFTTSON ASSOCIATES

I— t— CONSUUIHC STRUCTURAL ENGINEERS DRAWING Na

/Ft-5-A/

s-n-n

T

UL

I

1

(0"

T

Ir

vn

C I

1

(0 -J ^

J d5> J

4.

Source: Reproduced with permission of The Port Authority of New York and

New Jersey.

Figure 4-7. Repair of damaged floor beams at Level B1 in WTC 1.

NISTNCSTAR 1-1C, WTC Investigation 105
HERA • '^-J-S^^^'^^'T'Sr^^'^i/^^

\1

!

Exist.

12. WF 72

Mirff.;

Source: Part of WTCI-167-STB. Reproduced with permission of The Port

Authority of New York and New Jersey. ure 4-8. Repair of damaged floor beam at Level B3 In WTC 1.

NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1, 2, &7

REV. 1 PnA LESLIE E. ROBERTSON ASSOCIATES

I— I— 1 1/A CONSULTIhKS STRUCrURAl. ENGINEERS DRAWING NO.

CHtCK

7" Posrs erwAy,

Source: Part of WTCI-303-STB. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 4-9. Repair of damaged floor beam at Level B3 in WTC 1.

NISTNCSTAR 1-1C, WTC Investigation 107
Chapter 4

m

>

REV. 1 PRA I-ESLIE E. ROBERTSON ASSOCIATES »-trir^ CONSUOING STOUCTURW. ENGINEEnS

53 SF>!vP£fi_ KEcc-a/STkucTipa^ 2^t>:;lS

DESSON C«CK 21 Dza 7^

Source: Part of WTCI-303-STB. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 4-10. Repair of damaged reinforced concrete spandrel beam at Level B3 in WTC 1.

108 NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys of WTC 1.2, & 7

-5- 36"C

REV.

1 'IP PA?5^'l-^SUE .E.i ROBERTSON ASSOCIATES i, 1— I— nr\ coNsum>«3 sTsucnwu. 'engineers DRAWING no;

OflAFT OG*

CMtO 27 Cet

-J*-

Cwr. TIE ~

4 Ar

I - * G CoK/T r tB

OJoTS. b)

I

f ' ; -7

Source: Part of WTCI-303-STB. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 4-11. Repair of damaged reinforced concrete spandrel beam at Level B4 in WTC 1.

NISTNCSTAR 1-1C, WTC Investigation 109
Chapter 4

RsV,

1 CD A LESUE E. ROBERTSON ASSOCIATES

DHAVflNG NO. WTC- eiploifari «<«r»

2< Jio. 1*

^I ;<»aug~^ sixgnnv. twi««>» I ^\»aV<t \ DB*wtM5>«)

4 T><iS CMW

TT77T7777

Source: Part of WTCI-303-STB. Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 4-12. Concrete masonry encasement of columns at subgrade levels in WTC 1.

110 NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys of WTC 1, 2, &7

Damaged concrete encasement around existing steel beams was also repaired as required. Figure 4—1

3

shows a typical reconstruction detail for a beam located at Level B2. The extent of concrete encasement

reconstruction at Levels B 1 and B2 is shown in the drawings that were prepared by LERA

(LERA 1993c).

Other repairs were made to spandrel beams at Level B5 and to the connection between the floor beam and

Column 357 at the Concourse Level (see Figs. 4-14 and 4-15, respectively).

Lucius Pitkin, Inc. was hired to perform a thickness survey of box columns by the ultrasonic method and

an ultrasonic flaw detection survey of diagonal and beam weld repairs made at WTC 1 (Lucius Pitkin 1993). Ultrasonic thickness measurements were made at Columns 345, 348, and 351 on

Level Bl. Ultrasonic tlaw detection measurements were made on full penetration butt welds of new

diagonal bracing repairs at Columns 321, 324, and 327 at Levels Bl and B2. Additional measurements were made on butt and fillet welds of beam repairs at Columns 321 and 327 between Levels Bl and B2.

Results of the thickness survey are given in Table 1 and Fig. 1 of the Lucius Pitkin report

(Lucius Pitkin 1993). Results of the ultrasonic flaw survey are given in Figs. 2 through 4 of the same

report. No conclusions were made in the report on the adequacy of the test results.

[^5 ris SPA<-GP 4' B2- i_Ev;?u

/v'Ek^j w k;. r. ~1

i:

-TDp L^-f •> Z" M-i^

EL Z24'

1

_^—_^

Coot.

Source: Part of WTCI-158-STB. Reproduced with permission of The Port Authority of New York and New

Jersey.

Figure 4-13. Reconstruction details for existing encased steel beams in WTC 1.

NISTNCSTAR 1-1 C, WTC Investigation 111
Chapter 4

REV.

1 CD A LESLIE E. ROBERTSON ASSOCIATES

I— I— ri<r\ CONSUUING STRUCTURAL ENGINEERS DRAWING NO.

06SK3N '>JJ 1^

CHECK 27 ^'A>J 94-

«® ® (S> ^ ^ &

n ^ n

UMEgfc-PLA^E, THE- 47XVCrL;E.AL 44A6r

'^£^riM AA

Source: Part of WTCI-303-STB. Reproduced with permission of The Port Authority of New Yorl< and New Jersey.

Figure 4-14. Repair of encased steel spandrel beam at Level B5 in WTC 1.

112 NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys of WTC 1, 2, & 7

REV. 1 PQA LESUE E. ROBERTSON ASSOCIATES

I— tn/A CONSULTING STRUCTURAL ENGINEERS P iooSilB DRAWING NO.

OtSiON

CHECK

A/

\

fS- 4^

A

Source: Part of WTCI-303-STB. Reproduced with permission of The Port Authority of New Yorl< and

New Jersey.

Figure 4-15. Repair of beam connection at Concourse Level in WTC 1.

NIST NCSTAR 1-1 C. WTC Investigation 113
Chapter 4

4.2.5 Other Modifications

An FM transmitter station was installed on the 11 0th floor in 1997 for WNYC-FM (W96-1 171, PANYNJ,

Newark). The structural engineer for this project was J. C. Westrick & Associates. The documentation for

this modification includes: (1) the Tenant Alteration Apphcation Review Request Form submitted to the Port Authority on behalf of the tenant, (2) Port Authority comments made on the project submittal, (3)

J. C. Westrick & Associates comments in response to Port Authority comments, and (4) a letter dated

January 14, 1997 from the Supervisor of the Tenant Aheration Application Unit of the Port Authority to the Vice President of Operations and Engineering at WNYC-FM stating that review on the project was

complete.

In June of 2000, structural calculations were submitted by LERA for the WABC Control Room on

floor 1 10 (WOO- 1 180, PANYNJ, Newark). A new transmitter and ductwork were suspended from the existing floor system at this level. The documentation for this modification includes: (1) the Tenant

Alteration Application Review Request Fonn submitted to the Port Authority on behalf of the tenant, (2) Port Authority comments made on the project submittal, (3) LERA comments in response to Port Authority comments, and (4) a letter of approval from the Port Authority dated May 30, 2001.

Although no major modifications were made to the existing structural members because of the two

projects cited above, they illustrate that the guidelines set forth by the Port Authority for alterations to the

structural systems of the WTC buildings were followed (see Chapter 2 of this report for information on

the Port Authority guidelines for inspection, repair, and modifications).

Structural modifications involving openings made in the floor slabs are listed in Table 4-4,which includes

a brief description of the work that was perforaied with respect to the modifications.

In all of the cases cited in Table except for the 1987 case, general notes and drawings in the documents listed the codes, design criteria, and materials that were used in the design and the proposed

sequence of construction. Structural calculations were included for the modifications made in 1993, 1998,

and 1999 (floors 25 and 26). The design of the new structural members and a check of the capacities of

existing structural members were included in the calculations.

For the modifications perfonned in 1997, the documentation includes the Tenant Alterations Application

Review Request Fonn and comments from the Port Authority in regard to the submittal. Similar

documents are included in the submittal package for the modifications perfonned in 1998 and 1999 (work

done on 88th and 89th floors).

Smaller floor penetrations, the largest of which was 17 in. in diameter, were made on floor 1 10 in 1979

for Sage Gray Todd & Sims (LERA Box 8). The structural engineer was LERA.

4.3 MODIFICATIONS AND REPAIRS MADE TO WTC 2

4.3.1 Openings Made in Floor Slabs

114 NISTNCSTAR 1-1C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1,2, & 7

4.3.2 Openings in Floor Slabs That Were Subsequently Closed

Openings in floor slabs that were subsequently closed are listed in Table 4—5. The design of the new

structural members and a check of the adequacy of existing structural members were included in calculations in all cases.

Table 4-4. Openings made in floor slabs in WTC 2.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1979 77 Ebasco Inc. SHCR Slab openings were cut at nine

locations in the northeast quadrant of

the building along the north and east races or floor 77. Framing channels were also installed.

LERA Box 8

1987 96 Yamaichi

International LERA Slab opening was cut near columns 901 and 902 in the southeast quadrant near

the core. New structural members were

added.

LERA Box

10

1993 94-95 Fiduciary

Trust LERA Slab opening was cut between columns

507, 508, 607, and 608 in the core for

stair linking floors 94 and 95. New

structural members were added.

W93-2179

PANYNJ

(Newark)

1997 99-101 AON Risk

Services

Gensler Slab openings were cut for stairs linking floors 99, 100. and 101. No

Other intormation is provided.

WC97-2185-

001 PANYNJ

(Newark)

1998 99 AON Risk

Services The Office of James Ruderman

Slab opening was cut between columns

601 , 602, 701 , and 702 in the core on

floor 99 for stairs leading down to floor

98. New structural members were

added.

WC98-2212

PANYNJ

(Newark)

1999 25,26 Sun

Microsystems

LERA Slab opening was cut near column 901

in the core for new stair between floors 25 and 26. New structural members

were added.

WTC1-69-L,

SA0279,

0006

1999 88, 89 Keefe,

Bruyette &

Woods, Inc.

Cetra/Ruddy

Inc.

Slab opening was cut for stairs linking

floors 88 and 89. No other information

is provided.

WC99-2114

PANYNJ

(Newark)

Table A Openings in floor slabs that were closed in WTC 2.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1997 37,38 Unknown LERA An escalator was removed between

floors 37 and 38 near column 608. New

floor deck and framing were added to close the opening.

WTCI-66-L

2000 95, 96 Fiduciary

Trust LERA New beams and deck were added to frame existing opening between

columns 901, 902, 1001, and 1002 in the core on floor 96. Existing framing was checked for new loads.

WTC1-66-L

NISTNCSTAR 1-1C, WTC Investigation 115
Chapter 4

4.3.3 Structural Members That Were Reinforced

A summary of the structural members that were reinforced in WTC 2 is given in Table 4-6. The Tenant

Alteration Application Review Request Fonn is included in the documentation for the modifications

perfomied in 1999.

Table A -6. Structural members that were reinforced in WTC 2.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1993 96 Fiduciary

Trust LERA A number of long-span floor trusses and their connections in the northeast quadrant of the building were

reinforced due to additional loads from

high-density mobile filing cabinets.

W93-2179

PANYNJ

(Newark)

1999 81 Fuji Bank

Limited

LERA Documents reference adding

reinforcement to existing two-way floor trusses to accommodate new UPS

workspace. Documents do not specify

the required amounts of reinforcement

due to the new superimposed loads.

W99-2125

PANYNJ

(Newark)

4.3.4 Other Modifications

In 1994, the slab in the elevator lobby on floor 90 (bounded by core columns 702, 703, 902, and 903) was

repaired for Fiduciary Trust for some unknown reason (WTCI-66-L). LERA was the structural engineer

for this repair, which consisted of demolishing and replacing a 5 in. lightweight aggregate concrete slab in

this area.

4.4 MODIFICATIONS AND REPAIRS MADE TO WTC 7

A summary of the major modifications and repairs made to WTC 7 is given below. All modifications were to be made in accordance with the PANYNJ Tenant Construction Review Manual (see Chapter 2 of

this report).

4.4.1 Modifications Made due to New Loading Requirements

Structural modifications due to new loading requirements are listed in Table 4—7. Included is a brief

description of the work that was performed with respect to the modifications. In most cases, members

were reinforced to accommodate floor loads that were greater than the loads for which these members

were originally designed.

In all of the cases cited in Table 4-7, structural calculations were included on the check of the existing

structural members and on the design of new structural members. The documents related to the 1988

modifications include comments made by the Tenant Construction Review Unit of the Port Authority in regard to the project submittal and responses from the structural engineer to the Port Authority on these

comments. Similar documents are available for the modifications made in 1999 on the 40th floor, which

116 NISTNCSTAR 1-1 C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1.2. & 7

include a copy of the Tenant Construction or Alteration Application that was submitted to the Port Authority on behalf of the tenant.

fable 4-7. U odifications made due to new loading requirements in WTC 7.

Date Floor(s) Tenant

Structural Engineer Description of Modification Reference

1988 38 Salomon

Brothers Inc.

Office of

Irwin G. Cantor

Bottom and top cover plates were added to the existing W24x55 beams along column

lines 37 and 40, and bottom cover plates were added to the existing W24x55 beams

Jilr»nri iXl\Jll\L poliitnn L-UlLlIllll 1111^^ linf*c ^fi <X\\\X ^ttm tn\.\J c>\X\}Vj\jI ciinnnrtV new hanger loads.

W-7()04

PANYNJ

(Newark)

1989 24 Genera]

Auditing

Office

Office of

Irwin G. Cantor

Bottom cover plates were added to the existing W21x44 beam on column line 45 and the two adjacent W2 1 x44 beams to the west of column line 45 to support

additional load due to new file storage. The existing W36xl35 girder framing

between columns 76 and 79, which

reinforced with a bottom cover plate.

W-8003

PANYNJ

(Newark)

1989 47 Salomon

Brothers Inc.

Office of

Irwin G. Cantor

Bottom cover plates were added to the existing W 16x31 beam along column line

2, the W16x26 beam along column line 3, and the W14x22 beams along column lines 4 and 5 to support additional mechanical

equipment. The W33x 1 30 girder on

cuiuiiiii line wiii^ii dujjuui icu iiic^c beams, was reinforced with bottom and top cover plates.

W-7004

PANYNJ

(Newark)

1990 11, 12 Spicer &

Oppenheimer

Office of

Irwin G. Csntor

Bottom cover plates were added to eight

existing beams and girders in the

llUlLIIW^^ol L'L'IIIWI \J I Lilt L/UllUlll^ Ull lilt

1 1th floor to support larger live loads. Similarly, bottom cover plates were added

to three existing beams between column

lines 48 and 49 and the girder between columns 70 and 73 on the 12th floor.

W-8005

PANYNJ

1991 19 ITT Hartford Office of James Ruderman

Bottom cover plates were added to existing W24x55 and W24x76 beams to support new files and shelves. Exact

location of these beams could not be

determined from the documentation.

W-8010

PANYNJ

(Newark)

1992 12 Securities Exchange

Commission

Office of

Irwin G. Cantor

Bottom cover plates were added to eleven

existing beams in the northwest comer of

the building to support legal flies. A new W12x1 9 beam was also added between two of the existing beams.

W92-7056

PANYNJ

(Newark)

1992 18, 19 Equal

Employment

Opportunity

Commission

Office of

Irwin G. Cantor

Bottom cover plates were added to existing W24 beams on the 1 8th floor on column lines 31, 32, and 33 to support

larger live loads.

WTCI-166-

P Disk 3 W92-7150

NISTNCSTAR 1-1 C, WTC Investigation 117
Chapter 4

Table 4-7. Modifications made due to new loading requirements in WTC 7 (continued)

Date Floor(s) Tenant

Structural Engineer Description of Modification Reference

1993 28 Salomon

Brothers Inc.

Office of

Irwin G. Cantor

Eight additional shear studs were added to an existing W16x26 beam located in the mechanical/electrical room to support new

equipment loads.

W93-7I38

PANYNJ

(Newark)

1993 7, 8 American

Express Bank

Office of James Ruderman

A new W12x1 4 beam located on the west

side of the building between column lines 7 and 8 was added on the 8th floor to support a new CMU wall.

W93-7233

PANYNJ

(Newark)

1994 7 through 29 Salomon

Brothers Inc.

Office of

Irw'in G. Cantor

Bottom cover plates were added to twenty- two existing beams between columns 5 and 25 on the south side of the building on

each floor between levels 7 and 29 to support larger live loads. Similarly, bottom

cover plates were added to eight beams on

the east side of the building between

column lines 31 and 37 on each of these

floors.

WTCI-166-

P Disk 4 W93-7232

1995 20 ITT Hartford The Cantor Seinuk

Group

Bottom cover plates were added to the existing W16x26 beams along column

lines 23 and 25 to support new filing cabinets. Similarly, WT sections were

welded to the bottom of the existing

W16x26 beams that framed in between the above-mentioned beams. WT sections were welded to the bottom of

the existing W16x26 beam east of column

line 18 and the W16x26 beam on column

line 19 to support new filing cabinets. Similarly, a bottom cover plate was added

to the existing W16x26 beam east of column line 19.

W95-7153

WTCI-I97-

P

1999 37 Salomon

Smith Barney

Gilsanz Murray

Steficek

A new W16x40 beam was added between two existing W1 4x22 beams along column

lines 76 and 77 to support a new highdensity filing system.

W99-7134

PANYNJ

(Newark)

1999 13 The Standard

Chartered Bank

The Cantor

Seinuk

Group

Ten additional shear studs were added to an existing W4x55 beam to support

additional loads from a new file room and

a new UPS/LAN room. Exact location of

this beam could not be determined from

the documentation.

W99-7137-

02PANYNJ

(Newark)

1999 40 Salomon

Smith Barney

Gilsanz Murray

Steficek

Four new W18x3 5 beams were added to support the new high-density files near column 76. WT4x20 sections were welded

to the bottom of two existing W14x22 beams that supported the files. New

W 16x50 beams were connected below to the existing W36xl35 girders that supported the beams in this area.

W99-7I72

PANYNJ

(Newark)

118 NISTNCSTAR 1-1 C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1,2. & 7

Table 4-7. Modifications made due to new loading requirements in WTC 7 (continued)

Date Floor(s) Tenant

Structural

Enjjineer Description of Modification Rflcrcncc 2000 31 Salomon

Smith Barney

Gilsanz Murray

Steficek

Top and bottom cover plates were added to an existing W27x94 beam between

columns 77 and 80 to support a new highdensity filing system. The existing beam

connections were also reinforced with

stiffened seat connections.

WOO-7122

PANYNJ

(Newark

)

2000 38 Salomon

Smith Barney

Gilsanz Murray

Steficek

Bottom cover plates were added to existing W 14x22 beams between columns

76 and 77 and between columns 77 and 78

to support a new high-density filing system. Also, the following existing

girders were reinforced with bottom cover

plates: (1) W36xl35 between columns 76 and 79, (2) W27x94 between columns 77 and 80, and (3) W27x84 between columns

78 and 81.

WOO-7224

PANYNJ

(Newark)

2000 39 Salomon

Smith Barney

Gilsanz Murray

Stetlcek

New W14x53 beams were added under

each rail of a new high-density filing system in lieu of reinforcing existing

W 14x22 beams between columns 76 and 77.

WOO-7202

PANYNJ

(Newark)

4.4.2 Openings Made in Floor Slabs

It is stated in PANYNJ (1997) that the 41st and 43rd floor slabs were completely removed on the east side of the building to accommodate the trading floors for Salomon Brothers Inc.

According to The Office of Irwin G. Cantor P.C. (1989), columns 76, 78, 79, 80, and 81 were reinforced

with plates that ran from the top of the 39th floor to the underside of the 40th floor due to the removal of

the floor slab at the 39th floor. Similarly, column 74 was reinforced with plates that ran from the top of

the 43rd floor to the underside of the 44th floor due to the removal of the floor slab at the 43rd floor.

Structural modifications involving openings made in the floor slabs are listed in Table 4-8, including a brief description of the work that was performed with respect to the modifications.

Structural calculations on the design of new structural members and on the check of the existing structural members were included for the inodification made in 1989 (3rd floor) and 1990.

4.4.3 Modifications Made to Beam Webs and Flanges

Modifications made to beam webs and flanges are summarized in Table 4-9 including a brief description

of the work that was perfomied with respect to the modifications.

NISTNCSTAR 1-1C, WTC Investigation 119
Chapter 4

Table 4-8. Openings made in floor slabs of WTC 7.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1989 3, 4 Salomon

Brothers Inc.

Skidmore

Owings &

Merrill

On the 3rd floor, openings were cut on

the west, north, and east sides of the

building. New framing was introduced

around these openings. On the 4th

floor, new openings and framing were

introduced on the north side of the

building.

WTCI-166-

P, Disk 2

1989 3 Salomon

Brothers Inc. The Office of Irwin G. Cantor

Two 2 ft-6 in. by 3 ft-6 in. openings were cut near columns 24 and 25. New

C8xl 1.5 framing members were added

around the openings.

W-7005

PANYNJ

(Newark)

1990 11 Spicer &

Oppenheimer

Office of

Irwin G. Cantor

A new stair opening was made between

columns 77, 78, 80, and 81. New

W12x1 6 beams were added around the opening.

W-8005

PANYNJ

(Newark)

1994 43 Salomon

Brothers Inc.

Skidmore

Owings &

Merrill

A new slab opening was made near column 71 in the core area. New beams

were added around the opening.

W94-7746,

WTCI-166-

P, Disk 4

4.4.4 Other Modifications

A list of structural modifications that were made to WTC 7 prior to April of 1997 is given in Chapter IV,

Section A(5) of the Facility Condition Survey Report for WTC 7 (PANYNJ 1997). The following is a summary of the modifications that are noted in that report:

• In the Convention Area on the 3rd floor between column numbers 45 and 48A, steel plates

have bee installed around the perimeter of the room between the slab and the floor surface

(behind the wall coverings and above the suspended ceiling). According to the PANYNJ

report, these plates were installed to protect attendees at the Convention Center from the magnetic field generated from the ConEd Substation beneath the conference rooms. No

documentation was located that provides any additional details on this modification.

• On the north side of the 5th floor generator room, masonry block walls were added to partition the eight transformer vaults installed for Salomon Brothers. The vaults were between columns 46 and 53. No documentation was located that provides any additional

details on this modification.

• A penthouse was constructed on the 47th floor roof to house the chiller plant and the cooling towers for Salomon Brothers. The chiller plant was an enclosed steel-framed structure with

corrugated steel walls. It was approximately 25 ft in height and took up about one-third of the square footage of the 47th floor roof The cooling towers were supported on a steel frame and were enclosed by louvered walls on the north and south sides and by the chiller plant and the buUchouse on the east and west sides, respectively. No documentation was located that provides any additional details on this modification.

120 NISTNCSTAR 1-1 C, WTC Investigation
Sig. Mod. & Repairs to the Struc. Framing Sys. of WTC 1.2. & 7

The list of modifications in the PANYNJ report also included the removal of the floor slabs on floors 41 and 43 to accommodate the trading floors for Salomon Brothers, as noted in Sec. 4.4.2 of this report.

Table 4-9. Modifications made to beam webs and flanges in WTC 7.

Date Floor(s) Tenant

Structural

Engineer Description of Modification Reference

1993 28 Salomon

Brothers Inc.

Office of

Irwin G. Cantor

Two 1 in. by 36 in. openings, located

3 ft apart, were cut into the web of an

existing W24x55 beam (unknown

location). Plates were welded on each

side of the web along the upper and

lower edges of the openings.

W93-7138

PANYNJ

(Newark)

1993 4-7, 16, 21,

29,38,45

Salomon

Brothers Inc.

Office of

Irwin G. Cantor

Notches were cut in the bottom flanges

of various beams on these floors to accommodate ductwork. Plates were

welded to the upper side of the bottom

flanges.

W93-

7221,

WTCl166-P,

Disk 2 1998 1 Mayor's

Office of

Emergency

Management

The Cantor Seinuk

Group

A notch was cut into the top flange of

an existing beam (unknown location). Two plates, one on each side of the web, were welded under the top flange.

W98-

1734. WTCl166-P,

Disk 5 1999 36-44 Salomon

Smith Barney

The Cantor Seinuk

Group

Two new openings (68 in. by 22 in. and

76 in. by 22 in.) spaced 3 ft- 10 in. apart were cut into the web of the existing

W24x62 beam framing into column 75. Horizontal and vertical stiffener plates were added on all sides of the openings.

Also, a new WT15x74 section was

welded to the bottom of the beam. The

same size openings were made in an

existing W27x94 beam on the 43rd

floor, which was reinforced in a similar manner.

W99-7127

PANYNJ

(Newark)

1999 42, 44 Salomon

Smith Barney

Gensler New web openings were cut in numerous beams along the north and

east sides of the building.

W99-

7127,

WTCl166-P,

Disk 6

4.5 REFERENCES

LERA (Leslie E. Robertson Associates). 1993a. The World Trade Center - The Explosion of26

February 1993, Inspection Program, South Wall of Tower 1. May. (WTCI-69-L).

LERA (Leslie E. Robertson Associates). 1993b. "WTC Structural Integrity Investigation, Visual

Inspection - Spandrel Damage Assessment." July, (part of WTCI-160-STB).

LERA (Leslie E. Robertson Associates). 1993c. "Reconstruction of Tower A, El. 294-0 and 284-0,"

structural drawing RE-TA-1." December. (WTCI-456-STB).

NISTNCSTAR 1-1 C, K/TC Investigation
Chapter 4

Lucius Pitkin, Inc. 1993. Examination ofBox Columns and Diagonal Beam Repairs - World Trade

Center, New York, Report No. ME-4525 SI. December, (part of WTC1-67-L).

PANYNJ (Port Authority of New York and New Jersey). 1997. Port Authority Facility Condition

Sun'ey Program - 7 World Trade Center. Engineering Quality Assurance Division, Engineering

Department. April. (WTCI-122-P).

The Office of Irwin G. Cantor P.C., "Salomon Brothers Inc. Base Building Modifications - 7 World

Trade Center Structural Computations," January 1989 (W-7004, Port Authority, Newark).

Woodson, S.C., Davis, J.L., and Walton, B.A., 1993. Ohsen'ations of World Trade Center Damage,

Technical Report SL-93, US Army Corps of Engineers Waterways Experiment Station. September,

(part ofWTCI-67-L).

122 NISTNCSTAR 1-1C, WTC Investigation