NISTNCSTAR1-2A

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Reference Structural Models and

Baseline Performance Analysis of the

World Trade Center Towers

William J. Fasclian

Ridiard B. Garlocl<

National Institute of Standards and Technology Technology Administrofion • U.S. Deportment of Commerce

NIST NCSTAR 1-2A

Federal Building and Fire Safety Investigation of the

World Trade Center Disaster

Reference Structural Models and

Baseline Performance Analysis of the

World Trade Center Towers

William J. Faschan

Richard B. Garlock

Leslie E. Robertson Associates. R.L.L.P.

September 2005

i

%

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
Abstract

• Development of estimates of design gravity and wmd loads on the towers for implementation

into the reference structural models and use in the baseline perfonnance analysis. Various

wind load cases were considered in this study, including wind loads used in the original

WTC design, wind loads based on two recent wind tunnel studies conducted in 2002 by

Cennak Peterka Peterson, Inc. (CPP) and Rowan Williams Davies and Irwin, Inc. (RWDl)

for insurance litigation concerning the towers, and refined wind load estimates developed by

NIST from critical assessment of infonnation obtained from the CPP and RWDl reports and

state-of-the-art considerations. The following three loading cases were considered for the baseline perfonnance analysis:

- Original WTC design loads case. Loads included dead and live loads as in original

WTC design in conjunction with original WTC design wind loads.

- Slate-of-the-practice case. Loads included dead loads; cuirent New York City Building

Code (NYCBC 2001) live loads; and wind loads from the RWDl wind tunnel study,

scaled in accordance with NYCBC 2001 wind speed.

- Refined NIST estimate case. Loads included dead loads; live loads from the current American Society of Civil Engineers Standard Minimum Design Loads for Buildings and

Other Structures (ASCE 7-02); and the refined wind load estimates developed by NIST.

The global tower models were analyzed using the various gravity and wind loading cases, and the baseline performance results were obtained. The results included:

• Total and inter-story drift under wind loads

• Demand/capacity ratios for the primary structural components of the towers

• Axial forces in the exterior columns, including shear lag effects and presence of tensile forces

• Perfonnance of splice cormections at the exterior walls

• Towers' resistance to shear sliding and oveituniing under wind loads.

Similarly, the typical floor models were analyzed under gravity loading conditions, and the baseline

perfonnance results were obtained. The results included:

• Floor mid-span deflections

• Demand/capacity ratios for the primary structural components of the floors.

Keywords: Columns, floor system, gravity load, load, model, structural, truss, wind load. World Trade

Center.

iv NISTNCSTAR 1-2A, WTC Investigation
Table of Contents

Abstract iii

Table of Contents v

List of Figures ix

List of Tables xiii

List of Acronyms and Abbreviations xv

Preface xvii

Executive Summary xxvii

Chapter 1 Introduction 1

1 . 1 Description of WTC Structural System 1

1.1.1 Global Structural System 1

1.1.2 Floor Structural System 4

Chapter 2 Development of Structural Databases for the WTC Towers 1

1

2.1 Introduction 1

1

2.2 Description of the WTC Structural Documents 1

1

2.3 Over\ iew of the WTC Structural Database (WTC-DB) 1

3

2.4 Methodology for the WTC-DB Development 14

2.4.1 Data Entry 14

2.4.2 Quality Control 15

2.4.3 Cross Section Property Calculations 15

2.4.4 Relational Database Development 16

2.5 Modifications to Database Elements 16

2.5.1 Core Column Reinforcing at Floors 98 to 106 16

2.5.2 Core Column Reinforcing Due to Construction of Fiduciary Trust Vault 17

2.5.3 Repair Due to the Bombing of February 26, 1993 18

2.5.4 Tenant Alteration for an Interoffice Stair 18

2.5.5 Drawing Book Data Discrepancies 1

8

2.6 Section Property Calculations 20

2.6. 1 Member Designations 20

2.6.2 Column Member Multiple Section Property Calculation 21

NIST NCSTAR 1-2A. WTC Investigation v
Table of Contents

2.6.3 Spandrel Member Multiple Section Property Calculation 23

2.6.4 Section Property Calculation Comparisons 24

2.6.5 Rolled Shape Database 25

2.7 Summary 26

Chapter 3 Development of Reference Structural Models for the WTC Towers 27

3.1 Introduction 27

3.2 Global Models of the Towers 27

3.2.1 Components and Systems in the Towers' Global Models 28

3.2.2 Coordinate System, Nomenclature, and Models Assembly Overview 28

3.2.3 Core Columns Modeling 32

3.2.4 Exterior Wall, Foundation to Floor 4 Modeling 35

3.2.5 Exterior Wall Trees (Floor 4 to 9) Modeling 36

3.2.6 Exterior Wall (Floor 9 to 106) Modeling 38

3.2.7 Exterior Wall (Floor 107 to 1 10) Modeling 41

3.2.8 Hat Truss Modeling ; 41

3.2.9 Flexible and Rigid Floor Diaphragm Modeling 43

3.2.10 Verification of Global Models 43

3.2.11 Results of Modal Analysis 44

3.3 Typical Truss-Framed Floor Model—Floor 96A 46

3.3.1 Primary Trusses 48

3.3.2 Bridging Trusses 49

3.3.3 Truss Member Cover Plates 51

3.3.4 Viscoelastic Dampers 5

1

3.3.5 Strap Anchors 51

3.3.6 Concrete Slab and Metal Deck 52

3.3.7 Verification of the 96th Floor Model 52

3.4 Typical Beam-Framed Floor Model—Floor 75B 53

3.4.1 Composite Beams 55

3.4.2 Horizontal Trusses 55

3.4.3 Concrete Slab and Metal Deck 55

3.4.4 Viscoelastic Dampers 56

3.4.5 Verification of the 75th Floor Model 56

3.5 Parametric Studies 56

VI NISTNCSTAR 1-2A. WTC Investigation
Table of Contents

3.5.1 Exterior Wall Columns/Spandrel Typical Panels (Floors 9 to 106) 57

3.5.2 Exterior Wall Columns/Spandrel Comer Panels (Floors 9 to 106) 59

3.5.3 Flexible Floor Diaphragm 61

3.6 Summary 64

Chapter 4 Gravity and Wind Loads on the WTC Global Models 67

4.1 Introduction 67

4.2 Gravity Loads 68

4.2.1 Gravity Loads from Areas Outside of Core 69

4.2.2 Gravity Loads from Areas Inside of Core 70

4.2.3 Construction Sequence Loading Effects 74

4.3 Wind Loads 74

4.3.1 Original WTC Design Wind Loads 74

4.3.2 State-of-the-Practice Wind Loads 78

4.3.3 Refined NIST Estimates 79

4.3.4 Comparisons of Wind Loads 79

4.4 References 81

Chapter 5 Baseline Performance Analysis of the WTC Global Models 83

5.1 Introduction 83

5.2 Calculation of Demand/Capacity Ratios 83

5.2. 1 Selection of Global Models Design Parameters 85

5.3 Baseline Performance Analysis of WTC 1 87

5.3.1 Original WTC Design Load Case 87

5.3.2 State-of-the-Practice Case 105

5.3.3 The Refined NIST Estimate Case 107

5.4 Baseline Performance Analysis of WTC 2 109

5.4. 1 Original WTC Design Load Case 1 1

0

5.4.2 State-of-the-Practice Case 128

5.4.3 The Refined NIST Estimate Case 1 30

5.5 Summary 132

5.6 References 134

NIST NCSTAR 1-2A, WTC Investigation vii
Table of Contents

Chapters

Baseline Performance Analysis of Typical Floor Models 135

6.1 Introduction 135

6.2 Typical Truss-Framed Floor 1 36

6.2. 1 Gravity Loads 1 36

6.2.2 Results of Baseline Analysis 137

6.3 Typical Beam-Framed Floor 140

6.3.1 Gravity Loads 140

6.3.2 Results of Baseline Analysis 141

Chapter?

Summary 145

Appendix A

WTC Tower Structural Drawings Index for Large-Size Sheets 149

Appendix B

Drawing Book 19 Modifications for Structural Elements Not Included in the

Database 167

Appendix C

WTC Drawing Book Flowcharts 169

Appendix D

Excel File List and Description 179

Appendix E Relational Database File List and Description 185

Appendix F Relational Database Tutorial 187

Appendix G

Categorization of Floor Construction Types for Areas Outside of Core 191

vin NISTNCSTAR 1-2A, WTC Investigation
List OF Figures

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

disaster xix

Figure 1-1 . Typical WTC tower architectural floor plan (floor 26, WTC 2) 2

Figure 1-2. Typical WTC exterior wall, foundation to floor 9 3

Figure 1-3. Typical WTC tower hat truss elevation (Drawing SA 401) 4

Figure 1-4. Typical WTC floor truss framing zones 5

Figure 1-5. Part plan of floor 96 of WTC 1 (Drawing SA-104), components of typical truss framing system 6

Figure 1-6. Typical WTC floor panel layout plan 7

Figure 1-7. Typical WTC floor truss elevation 8

Figure 1-8. Part section t\'pical truss floor panel 8

Figure 1-9. Floor truss with exterior wall end detail 9

Figure 1-10. Details of the damping unit used in the tmss-framed floors 9

Figure 1-1 1. Damping unit used in the beam-framed floors 10

Figure 2-1 . Drawing Book 3 flowchart: WTC 1 and WTC 2 core columns, foundation to floor 106 14

Figure 2-2. Core column reinforcement 17

Figure 2-3. Column section at original column strap detail (taken from drawing book 18,

page 18-AB2-12) 19

Figure 2-4. Core column series 300 19

Figure 2-5. Exterior column type 300. floor 9 to floor 106 (taken from drawing book 4,

page4-AB2-18) 22

Figure 2-6. Column type 6000 with tapered spandrel (taken from drawing book 1, pages 1-A2-27 and 28) 23

Figure 2-7. Box section and a built-up column 24

Figure 3-1 . Global model coordinate axis location 29

Figure 3-2. Typical exterior panel nomenclature 30

Figure 3-3. Rendered isometric views of the WTC 1 model 33

Figure 3—^. Frame v iew of the WTC 2 model: exterior wall elevation and interior section

illustrating the core columns, core bracing, and hat truss 34

Figure 3-5. Frame view and rendered view of the WTC 1 model (foundation to floor 9) 36

NISTNCSTAR 1-2A. WTC Investigation ix
List of Figures

Figure 3-6. Exterior wall tree panel (taken from Drawing Book 2, page 2-AB2-2) 37

Figure 3-7. Exterior wall tree: as-built cross sections for level E (taken from Drawing Book 2, page 2-AB2-13) ^ 39

Figure 3-8. Frame view and rendered view of an exterior wall tree 39

Figure 3-9. Typical WTC tower exterior wall panel 40

Figure 3-10. As-modeled plan of the WTC 1 hat truss 42

Figure 3-1 1. Rendered 3-D model of the WTC 1 hat tmss (prior to assembly in the unified global

model) 42

Figure 3-12. Mode shapes of WTC 1 (exaggerated): (a) first mode shape (E-W), (b) second mode

shape (N-S), (c) Third mode shape (torsion) 45

Figure 3-13. Typical truss-framed floor panels arrangement 47

Figure 3-14. Typical truss-framed floor model (floor 96A), slab not shown 48

Figure 3-15. Typical primary truss cross-section, as-built and as-modeled transfonned truss work

points 49

Figure 3-16. Typical bridging truss cross-section, as-built and as-modeled transformed truss work

points 50

Figure 3-1 7. Connection between bottom chords of primary and bridging trusses 5

1

Figure 3-18. Strap anchors modeling 52

Figure 3-19. Typical beam-framed floor arrangement 54

Figure 3-20. Typical beam-framed floor model (floor 75B) 54

Figure 3-21 . Horizontal truss modehng, slab not shown 55

Figure 3-22. Shell element and frame models of typical exterior wall panel 57

Figure 3-23. Selection of column and spandrel rigidity of typical exterior wall panel 58

Figure 3-24. Shell element and frame models of typical exterior wall comer panel 60

Figure 3-25. Selection of column and spandrel rigidity of typical exterior wall comer panel 60

Figure 3-26. Detailed and simplified model of the exterior wall comer panel 61

Figure 3-27. Deflection of typical beam-framed floor model due to lateral loading 63

Figure 3-28. Deflection of equivalent floor model due to lateral loading 63

Figure 3-29. Deflections of the north and south faces of the floor for the detailed and equivalent

floor models 64

Figure 4-1 . Partition groups A, B, C, D, and E 71

Figure 4-2. Partition groups G and F 72

Figure 4-3. Windward and leeward distribution for (a) orthogonal and (b) diagonal

wind directions 78

X NISTNCSTAR 1-2A, WTC Investigation
List of Figures

Figure 5-1. Drift diagrams of WTC 1 due to original WTC wind loads, (a) AON-E- and

(b) A75N+E- ^ 88

Figure 5-2. Demand/capacity ratios for WTC 1 under original design loads, (a) north elevation

and (b) east elevation 90

Figure 5-3. Demand' capacity ratios for WTC 1 under original design loads, (a) north elevation

below floor 9 ^ 92

Figure 5—4. Demand/capacity ratios for WTC 1 core columns under original design loads, (a) 500

line and (b) 600 line 96

Figure 5-5. Shear lag diagrams of WTC 1 due to original WTC wind loads at (a) floor B6,

(b) floor"'39. and (c) floor 73 100

Figure 5-6. Tension force distribution (kip) in the exterior wall columns of WTC 1 under original

design dead and wind loads, (a) 100 face (north) and (b) 200 face (east) 103

Figure 5-7. Drift diagrams of WTC 1 due to the lower estimate, state-of-the-practice loads,

(a) 1R14PDN and (b) 1R8PDN 106

Figure 5-8. Drift diagrams of WTC 1 due to refined NIST estimate wind loads, (a) 1R14PD and

(b) 1R8PD 108

Figure 5-9. Drift diagrams of WTC 2 due to original WTC wind loads, (a) B180N+E- and

(b) B90N-E+ 1 1

1

Figure 5-10. Demand''capacity ratios for WTC 2 under original design loads, (a) west elevation

and (b) north ele\ ation 1 13

Figure 5-1 1 . Demand/capacity ratios for WTC 2 under original design load case, (a) west

elevation below floor 9 1 15

Figure 5-12. Demand capacity ratios for WTC 2 core columns under original design loads, (a) 500

line and (b) 600 line 119

Figure 5-13. Shear lag diagrams of WTC 2 due to original WTC wind loads at (a) floor B6,

(b) floor 39, and (c) floor 73 ^ 123

Figure 5-14. Tension force distribution (kip) in the exterior wall columns of WTC 2 under original

design dead and wind loads, (a) 100 face (west) and (b) 200 face (north) 126

Figure 5-15. Drift diagrams of WTC 2 due to the lower estimate, state-of-the-practice case,

(a) 2R4PbN and (b) 2R1 IPDN 129

Figure 5-1 6. Drift diagrams of WTC 2 due to refined NIST estimate wind loads, (a) 2R4PD and

(b) 2R11PD 131

Figure 6-1 . Summary of WTC-design criteria reduced live loads for floor design: design load of

100 psf - partition load is included in LL allowance 136

Figure 6-2. Unbraced length of truss diagonal 138

Figure 6-3. Connection detail for beam 30WF1 16, floor 75 of WTC 2 142

Figure 6-4. Demand/capacity ratios for floor 75, WTC 2: original WTC design criteria loading 143

Figure 6-5. Beam-framed floor member groups 143

NISTNCSTAR 1-2A. WTC Investigation xi
List of Figures

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Xll NISTNCSTAR 1-2A. WTC Investigation
List of Tables

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

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

Table 2-1 . Modifications to members of the WTC database (WTC-DB) 13

Table 3-1. Approximate size of the reference structural models (rounded) 35

Table 3-2. Calculated first six periods and frequencies without P-A effects for the WTC towers 44

Table 3-3. Calculated first six periods and frequencies with P-A effects for the WTC towers 44

Table 3^. Comparison of measured and calculated first two natural frequencies and periods for WTC 1 46

Table 3-5. Lateral displacement (in.) for the shell and frame models of typical exterior wall

panel with varied column and spandrel rigidities 59

Table 3-6. Lateral displacement (in.) for the shell and frame models of typical exterior wall comer panel with varied column and spandrel rigidities 61

Table 4—1 . Original WTC design criteria loads for floor 96A model for the design of columns

(typical truss floor).^ 69

Table 4-2. Grouping of the wind directions 77

Table 4-3. A comparison of wind load estimates for WTC 1 from various sources 80

Table Comparison of wind load estimates for WTC 2 from various sources 80

Table 4-5. Base shears and base moments due to wind loads from different building codes 81

Table 5-1 . Statistics of demand/capacity ratios for WTC 1 under original design load case 89

Table 5-2. Maximum calculated demand/capacity ratios (DCRs) for exterior wall column splices for WTC 1 under original design dead and wind load case 105

Table 5-3. Statistics of demand/capacity ratios (DCRs) for WTC 1 under the lower estimate,

state-of-the practice case 107

Table 5—4. Statistics of demand/capacity ratios (DCRs) for WTC 1 under the refined NIST

estimate case 109

Table 5-5. Statistics of demand/capacity ratios (DCRs) for WTC 2 under original design load case 112

Table 5-6. Maximum calculated demand/capacity ratios (DCRs) for exterior wall column splices

for WTC 2 under original design dead and wind load case 128

NISTNCSTAR 1-2A. WTC Investigation xiii
List of Tables

Table 5-7. Statistics of demand/capacity ratios (DCRs) for WTC 2 under the lower estimate,

state-of-the practice case 130

Table 5-8. Statistics of demand/capacity ratios (DCRs) for WTC 2 under the refined

NIST estimate case 132

Table 6-1 . Summary of typical truss-framed floor live loads and (reduced live loads) for areas outside of core 137

Table 6-2. Area inside core: loading floor 96, WTC 1 137

Table 6-3. Summary of maximum deflections for typical truss-framed floor under DL -i- LL for areas outside of core 137

Table 6^. Statistics of demand/capacity ratios for floor 96 under original design load case 139

Table 6-5. Statistics of demand/capacity ratios (DCRs) for floor 96 under the ASCE 7-02

loading case 140

Table 6-6. Beam-framed core area: loading floor 75, WTC 2 141

Table 6-7. Statistics of demand/capacity ratios for floor 75 under the original design loading

case 144

XIV NISTNCSTAR 1-2A, WTC Investigation
List of Acronyms and Abbreviations

Acronyms

American Institute of Steel Construction

/\rntricdn irun dnu oieei insiiiuie

/Vol-' /\iiowdDic oucss ucsign

no/"' A /RRr^ Building Officials and Code Administrators Basic Building Code

construction dead load

Lrr Cermak Peterka Peterson, Inc.

database

ULK demand-'capacity ratio

(JcdU lUaU

F-W n vv

T- Qct W' f=*ct ri 1 r*=*r*ti r\n £Lcljl — vv Col LlilCLLiUll Or 1 Government Furnished Information

LtKA I CD A Leslie E. Robertson Associates, R.L.L.P.

T I LL live ludu

LrvT U i^udu dnu iveaioidncc rdcior uesign

iviiir mecndnicdi, ciecincdi, dnu piumuing

IVlIliN. mccnanicdi ccjuipmeni ruoin

NIST l^CLUKJllal JlllolllUlv \Jl OLu.llLlu.lUo uiiLI 1 ^L-iiliUlUg Y

IN -o l>iUllIl — OUUllI Llll CCLIUIJ

IN I V^DV^ iNevv I urK v^iiy Duiiuing i_uue

i^piicdi \„fidrdcicr ivecugnuiun

PANYNJ Port Authority of New York and New Jersey

RWDI Rowan Williams Davies and Irwin, Inc. SDL superimposed dead load

SQL Structured Query Language

WL wind load

WSHJ Worthington, Skilling, Helle & Jackson

WTC World Trade Center

NISTNCSTAR 1-2A. WTC Investigation XV
List of Acronyms and Abbreviations

WTC 1 World Trade Center 1 (North Tower)

WTC 2 World Trade Center 2 (South Tower)

WTC 7 World Trade Center 7

Abbreviations

2D two dimensional

3D three dimensional

ft foot

ft^ square foot

Fy yield strength

h hour

in. inch

kip a force unit equal to 1,000 pounds

ksi 1 ,000 pounds per square inch

lb pound

min minute

pcf pounds per cubic foot

psf pounds per square foot

psi pounds per square inch

XVI NISTNCSTAR 1-2A, WTC Investigation
Preface

Genesis of This Investigation

Immediately following the terrorist attack on the World Trade Center (WTC) on September 1 1, 2001, the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers began

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

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

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

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

future in\ estigation that could lead to practical measures for improving the damage resistance of buildings

against such unforeseen e\'ents."

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

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

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

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

Construction Safety Team Act.

The goals of the investigation of the WTC disaster were:

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

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

The specific objectives were:

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

aircraft and why and how WTC 7 collapsed;

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

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

emergency response;

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

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

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

practices that warrant revision.

NISTNCSTAR 1-2A, WTC Investigation xvii
Preface

NIST is a nonregulatoiy agency of the U.S. Department of CoiTunerce's Technology Administration. The

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

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

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

does not have the statutoiy 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 menfioned in such report (15 USC 281a, as amended by PubUc

Law 107-231).

Organization of the Investigation

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

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

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

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

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

.

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

Technical Area and Project Leader Project Purpose

Analysis of Building and Fire Codes and

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

and Mr. Richard W. Bukowski

Document and analyze the code provisions, procedures, and

practices used in the design, construction, operation, and

maintenance of the structural, passive fire protection, and

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

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

Analyze the baseline performance of WTC 1 and WTC 2 under

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

the structural, fire protection, and egress systems.

Mechanical and Metallurgical Analysis of

Structural Steel; Project Leader: Dr. Frank

W. Gayle

Determine and analyze the mechanical and metallurgical properties

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

D. Evans; Dr. William Grosshandler

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

Reconstruction of Thermal and Tenability

Environment; Project Leader: Dr. Richard

G. Gann

Reconstruct the time-evolving temperature, thermal environment,

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

structural performance of the buildings and behavior and fate of

occupants and responders.

Structural Fire Response and Collapse

Analysis; Project Leaders: Dr. John

L. Gross and Dr Therese P. McAllister

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

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

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

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

Communications; Project Leader: Mr. Jason

D. 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.

XVlIl NISTNCSTAR 1-2A, WTC Investigation
Preface

NIST WTC Investigation Projects

Analysis of Steel

Stoictural Collapse

Nisr

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

investigation of the WTC disaster.

National Construction Safety Team Advisory Committee

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

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

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

Team Advisory Committee Chair

• John Barsom. President. Barsom Consulting, Ltd.

• John Bryan, Professor Emeritus, University of Maryland

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

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

• Philip DiNenno, President, Hughes Associates, Inc.

NISTNCSTAR 1-2A. WTC Investigation XIX
Preface

• Robert Hanson, Professor Emeritus, University of Michigan

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

Inc.

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

University of Colorado at Boulder

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

Diego

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

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

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

however, are solely the responsibility of NIST.

Public Outreach

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

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

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

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

NIST's WTC Public-Private Response Plan

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

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

and terrorist attacks. Reflecting the enhanced interest in effecting 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 NlST-led public-private response program that includes:

• A federal building and fire safety investigation to study the most probable factors that contributed to post-aircraft impact collapse of the WTC towers and the 47-story WTC 7 building, and the associated evacuation and emergency response experience.

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

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

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

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

XX NISTNCSTAR 1-2A, WTC Investigation
Preface

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

Date 1 Locarion Principal Agenda

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

iiQ 1 1 n f^rc ni 1 m V'lTi VJ al Lilt 1 5UUl li. iML/ Media briefing announcing the formal start of the Investisation. December 9. 2002 Washington. DC Media briefing on release of the Public Update and NIST request

for photographs and videos. April 8. 2003 New York City. NY Joint public forum with Columbia University on first-person

inter\iews.

Apnl 29-30. 2003 Gaithersburg. MD NCST Ad\'isorv Committee meetino on nlan for and nropre*;*; on WTC Investigation with a public comment session. May -. 2003 Ne\\' York C)X\ . NY Media briefing on release of A4av 2003 Pvo^vess Report.

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

investigation with a public comment session. September 1 7. 2003 New York Citv'. NY Media and public briefing on initiation of first-person data

collection projects.

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

comments on issues to be considered m formulating final recommpndatinns

June 18. 2004 New York Cit}-. NY Media public briefing on release of June 2004 Progress Report. June 22-23, 2004 Gaithersburg, MD NCST Ad\'isory Committee meeting on the status of and

preliminary findings fi^om the WTC Investigation with a public

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

set of preliminary findings with a public comment session. 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 of the probable collapse sequence for the WTC towers and draft reports for the projects on

codes and practices, evacuation, and emergency response. June 23. 2005 New York City, NY iviculd allU pUDIlC ullclirig Oil ICICaSC Ui all UlalL 1 CpUI IS lUI lllc WTC towers and draft recommendations for public comment.

September 12-13,

2005

Gaithersburg. .MD NCST Advisorv' 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 1-2A, WTC Investigation XXI
Preface

National Construction Safety Team Reports on the WTC Investigation

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

report on the collapse of WTC 7 is being issued as NIST NCSTAR 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 ofthe 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 Safety Investigation of

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

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

September.

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

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

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

September.

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

Trade Center Disaster: Comparison ofBuilding Code Structural Requirements. NIST

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

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

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

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

MD, September.

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

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

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

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

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

xxu NIST NCSTAR 1-2A, WTC Investigation
Preface

York CiTy- Building Code Provisions. NIST NCSTAR 1-lF. National Institute of Standards and

Technology. Gaithersburg, MD, September.

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

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

York City- Building Code by Local Lmvs 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 I 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-Consti'uction Modifications to Fire Protection, Life

Safety, and Stiiictural Systems of World Trade Center 7. NIST NCSTAR I-II. National Institute of

Standards and Technology. Gaithersburg, MD. September.

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

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

Gaithersburg, MD, September.

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

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

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

September.

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

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

Technology. Gaithersburg, MD, September.

Kirkpatrick. S. W.. R. T. Bocchieri, F. Sadek, R. A. MacNeill, S. Holmes, B. D. Peterson, R. W. Cilke. C. Navarro. 2005. Federal Building and Fire Safety Investigation ofthe World Trade

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

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

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

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

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

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

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

Investigation ofthe World Trade Center Disaster: Contemporaneous Structural Steel

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

Gaithersburg, MD, September.

NIST NCSTAR 1-2A, WTC Investigation xxiii
Preface

Banovic, S. W. 2005. Federal Building and Fire Safet}' Investigation ofthe World Trade Center

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

and Technology. Gaithersburg, MD, September.

Banovic, S. W., and T. Foecke. 2005. Federal Building and Fire Safet}' Investigation ofthe World

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

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

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

T. A. Siewert, and F. W. Gayle. 2005. Federal Building and Fire Safet}' Investigation ofthe World

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

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

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

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

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

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

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

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

September.

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

Investigation of the World Trade Center Disaster: Post-Construction Fires Prior to September II, 2001. NIST NCSTAR I -4A. National Institute of Standards and Technology. Gaithersburg, MD,

September.

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

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

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

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

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

and Technology. Gaithersburg, MD, September.

Ferreira, M. J., and S. M. Strege. 2005. Federal Building and Fire Safet}' 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 Safet}' Investigation ofthe World Trade

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

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

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

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

September.

XXIV NIST NCSTAR 1-2A, WTC Investigation
Preface

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

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

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

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

Standards and Technology. Gaithersburg, MD, September.

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

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

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

Gaithersburg, MD. September.

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

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

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

Technology. Gaithersburg. MD, September.

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

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

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

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

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

Investigation 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 Safety Investigation ofthe World

Trade Center Disaster: Fire Structure Interface and Thermal Response of the World Trade Center

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

MD, September.

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

Center Disaster: Structural Fire Response and Probable Collapse Sequence of the 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. Herx'ey, M. Izydorek, J. Mammoser, and J. Treadway. 2005. Federal Building and

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

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

MD. September.

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

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

NIST NCSTAR 1-2A. WTC Investigation XXV
Preface

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

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

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

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

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

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

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

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

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

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

Center 7. (Provisional). NIST NCSTAR 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 of the World Trade Center

Disaster: Analysis ofSeptember 11, 2001, Seismogram Data. (Provisional). NIST NCSTAR 1-6G.

National Institute of Standards and Technology. Gaithersburg, MD.

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

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

National Institute of Standards and Technology. Gaithersburg, MD.

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

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

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

Standards and Technology. Gaithersburg, MD, September.

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

Center Disaster: Analysis ofPublished Accounts of the World Trade Center Evacuation. NIST

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

Zmud, J. 2005. Federal Building and Fire Safet}' Investigation ofthe World Trade Center

Disaster: Technical Documentation for 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.

XXVI NIST NCSTAR 1-2A, WTC Investigation
Executive Summary

E.1 INTRODUCTION

This report presents the work conducted to estabhsh the basehne performance of the North and South

World Trade Center Towers (WTC 1 and WTC 2) under design gravity and wind loading conditions.

Baseline performance results include basic infomiation about the behavior of the towers, such as total and

inter-story drift under wind loads, floor deflections under gravity loads, demand/capacity ratios for primary structural components, exterior columns response (shear lag effects and presence of tensile forces), performance of connections, and the towers' resistance to shear sliding and overturning.

The primary tasks that were undertaken to establish the baseline performance included the following:

• To develop structural databases for the primary structural components of the WTC 1 and

WTC 2 towers from the original computer printouts of the structural documents.

• To de\ elop reference structural analysis models that capture the intended behavior of each of

the rvvo towers using the generated databases. These reference models were used to establish the baseline performance of the towers and also served as a reference for more detailed

models for other phases of the National Institute of Standards and Technology (NIST)

investigation.

• To develop estimates of design gravity (dead and live loads) and wind loads on each of the two towers for implementation into the reference structural models.

• To perform linear, static structural analyses to establish the baseline performance of each of

the two towers under design gravity and wind loads.

E.2 DEVELOPMENT OF STRUCTURAL DATABASES FOR THE

WTC TOWERS

This task included the dev elopment of structural databases of the primary components of the WTC 1 and

WTC 2 towers. The electronic databases were developed from original computer printouts of the

structural design documents, including modifications made after construction. The databases were

generated for use in the development of the reference structural models of the towers.

The structural databases contained the computer and hand-tabulated data for the primary structural components of the towers from the original Drawing Books 1 through 5, including exterior walls, core columns, and beam schedule. In addition, some information from Drawing Book 6 (core bracing

schedule) and Drawing Book 9 (beams in the hat truss region) were included in the database files as it was utilized in the modeling of the towers. Some modifications that were made to the towers were implemented in the databases, including strengthening of a number of core columns at floors 98 to 106 of

both towers and reinforcing of two comer core column at floors 45 to 97 of WTC 2 due to the construction of a concrete vault at floor 97.

NISTNCSTAR 1-2A. WTC Investigation xxvii
Executive Summary

The task included the scanning and digitization of the original drawing books, a four-step quality control

procedure, cross section property calculations, and development of the relational databases to link the generated database files into a fonnat suitable for the development of the structural models.

E.3 DEVELOPMENT OF REFERENCE STRUCTURAL MODELS FOR THE

WTC TOWERS

This task included the development of reference structural analysis models that capture the intended

behavior of each of the two towers using the generated databases. These reference models were used to establish the baseline perfonnance of the towers and also served as a reference for more detailed models

for aircraft impact damage analysis and thermal -structural response and collapse initiation analysis. The

main types of models developed were:

• Two global models of the major structural components and systems for the towers, one each

for WTC 1 and WTC 2. The models included all primary structural components in the towers, including exterior walls (columns and spandrel beams), core columns, exterior wall

bracing in the basement floors, core bracing at the mechanical floors, core bracing at the main

lobby atrium levels, hat trusses, and rigid and flexible diaphragms representing the floor systems. To validate the global models, the calculated natural frequencies of WTC 1 were compared with those measured on the tower, and good agreement between the calculated and

measured values was obtained.

• One model each of the typical tioiss-framed floor (floor 96 of WTC 1) and typical beamframed floor (floor 75 of WTC 2). The models included all major structural components in the floor system, including primai7 and bridging tmsses, beams, strap anchors and horizontal

trusses, concrete slabs, and viscoelastic dampers. To validate the floor models, several

studies were canied out to compare stresses and deflections estimated from the model with

hand calculations for representative composite sections. Good agreement was obtained

between the model results and hand calculations.

Parametric studies were perfonned to evaluate the behavior of typical portions of the structure and to develop simplified models for implementation into the global models. These parametric studies included

detailed and simplified models of typical exterior and comer wall panels and floor systems.

E.4 GRAVITY AND WIND LOADS ON THE WTC GLOBAL MODELS

This task included the development of estimates of design gravity and wind loads on the towers for implementation into the reference structural models and use in the baseline performance analysis.

Various wind loads were considered in this study, including wind loads used in the original WTC design,

wind loads based on two recent wind tunnel studies conducted in 2002 by Cermak Peterka Peterson, Inc. (CPP) and Rowan Williams Davis and Irwin, Inc. (RWDI) for insurance litigation concerning the towers,

and wind load estimates developed by NIST from critical assessment of information obtained from the CPP and RWDI reports and state-of-the-art considerations. The following three loading cases were

considered for the baseline perfonnance analysis:

xxvui NISTNCSTAR 1-2A, WTC Investigation
Executive Summary

• Original WTC design loads case. Loads included dead and live loads as in original

WTC design in conjunction with original WTC design wind loads.

• State-of-the-practice case. Loads included dead loads; cun'ent New York City Building Code

(NYCBC 2001) live loads; and wind loads from the RWDl wind tunnel study, scaled in accordance with NYCBC 2001 wind speed.

• Refined NIST estimate case. Loads included dead loads; live loads from the American

Society of Civil Engineers (ASCE 7-02) Standard (a national standard); and wind loads

developed by NIST.

The purpose of using the original WTC design loads was to evaluate the performance of the towers under

original design loading conditions and ascertain whether those loads and the corresponding design were

adequate given the knowledge available at the time of the design. The pui"pose of considering the state- of-the-practice and the refined NIST estimate cases was to better understand and assess the effects of

successive changes in standards, codes, and practices on wind design practices for tall buildings.

The study indicated that the original WTC design wind load estimates exceeded those established by the NYCBC prior to 1968. when the WTC towers were designed, and up to and including 2001. The design

values were also higher than those required by other prescriptive building codes of the time.

The two orthogonal base shear and base moment components used in the original design were in general

smaller than the CPP, RWDl, and NIST estimates. However, the most unfavorable combined peaks from

the original design were larger than, or smaller by at most 1 5 percent than, estimates based on the CPP,

RWDl. and NIST estimates. This is due to the conservative procedure used to combine the loads in the

original design.

The estimated wind-induced loads on the towers vary by as much as 40 percent between the wind

tunnel/climatological studies conducted by CPP and RWDl in 2002. with CPP being the larger.

Considering the differences between RWDl and CPP results, the RWDl loads may be viewed as a "lowerestimate, state-of-the-practice case."

E.5 BASELINE PERFORMANCE ANALYSIS OF THE WTC GLOBAL MODELS

The WTC 1 and WTC 2 global models were each analyzed under the three loading cases described above

to establish their baseline performance. The following is a summary of the results:

• Under the original WTC design loads, the cumulative drifts at the top of the WTC 1 tower were about 56.6 in. (H/304) and 55.7 in. (H/309) in the E-W and N-S directions,

respectively. These drifts were about 51.2 in. (H/335) in the E-W direction and 65.3 in. (H/263) in the N-S direction for WTC 2. For the lower estimate, state-of-the-practice case, the drifts for WTC 1 were larger than those from the original design case by about 0.5 percent

and 22 percent for the E-W and N-S directions, respectively. For the lower estimate, state- of-the-practice case for WTC 2, the E-W drift was larger than that of the original design case by about 16 percent, and the N-S drift was smaller by about 15 percent. The drifts obtained

from the refined NIST estimate case were about 25 percent larger than those from the stateNISTNCSTAR 1-2A. WTC Investigation xxix
Executive Summary

of-the practice case. These differences are consistent with the differences between the base

shears for the three loading cases.

• The demand/capacity ratios (DCR) were based on the allowable stress design procedure and were estimated using the AISC Specifications (1989). The results indicated that DCRs

estimated from the original WTC design load case were, in general, close to those obtained

for the lower estimate, state-of-the practice case. For both cases, a small fraction of structural components had DCRs larger than 1.0. These were mainly observed in both towers at (1) the

exterior walls at the columns around the comers, where the hat truss connected to the exterior

walls, and below floor 9; and (2) the core columns on the 600 line between floors 80 and 106

and at core perimeter columns 901 and 908 for much of their height.

• The refined NIST case estimated DCRs were higher than those of the original WTC design

estimates and the lower state-of-the-practice estimates for the following reasons: The NIST

estimated wind loads were about 25 percent higher than those used in the lower state-of-the- practice estimate, and mixed, some higher and others lower than the original WTC design

wind loads. It is noted that the NIST estimated wind loads are about 20 percent smaller than

those estimated by CPP (an upper estimate, state-of-the practice case). In addition, the

original WTC design and the state-of-the-practice cases used NYCBC load combinations,

which result in lower DCRs than the ASCE 7-02 load combinations used for the refined NIST

case.

• Under a combination of the original WTC design dead and wind loads, tension forces were

observed in the exterior walls of both towers. The forces were largest at the base of the building and at the comers. These tensile column loads were transferred from one panel to another through the column splices. The DCR ratios for the exterior wall splice cormections

under the effect of the tensile forces for the two towers were shown to be less than 1.0.

• For the towers' resistance to shear sliding and overturning due to wind, the dead loads that acted on the perimeter walls of the towers provided resistance to shear sliding and

overtuming at the foundation level. Considering the resistance to shear sliding under wind

load, the factor of safety was calculated to be between 10 and 1 1.5, while the factor of safety

against overtuming ranged from 1 .9 to 2.7 for both towers.

E.6 BASELINE PERFORMANCE ANALYSIS OF THE TYPICAL FLOOR

MODELS

The typical floor models were both analyzed under gravity loads. The following is a summary of theresults:

• For the typical tmss-framed floor (floor 96 of WTC 1), the DCRs for all floor trusses were

less than 1.14 for the original WTC Design Criteria loads and less than 0.86 for the ASCE 7-02 loading. Under the original WTC Design Criteria loading, the DCR was less than

1.00 for 99.4 percent of the floor truss components. For the area outside the core, the average

ratio of the DCRs under the ASCE 7-02 loading to the DCRs under the original WTC Design

Criteria loading for all floor tmsses was about 0.80. For the core area, the DCRs for all floor beams inside the core were less than 1 .08, and more than 99 percent had a DCR of less than

XXX NISTNCSTAR 1-2A, WTC Investigation
Executive Summary

1 .0. Under the original WTC Design Criteria loading, the maximum floor deflections were

1.79 in., 0.57 in., and 1.44 in. for the long span one-way trusses, short span one-way trusses, and the two-way zone, respectively.

• For the typical beam-framed floor (floor 75 of WTC 2) under the original WTC Design

Criteria loading, the DCRs for all floor beams were less than 1 .0 except for two core beams

where the shear DCRs were 1.125 and 1.09. The maximum mid-span deflections of the long

span and short span zones under the original WTC Design Criteria loads were about 1.55 in. and 0.70 in., respectively.

NISTNCSTAR 1-2A, WTC Investigation xxxi
Executive Summary

This page intentionally left blank.

xxxn NISTNCSTAR 1-2A, WTC Investigation
Chapter 1 Introduction

The objective of this analysis was to establish the baseline performance of the North and South World

Trade Center Towers (WTC 1 and WTC 2) under design gravity and wind loading conditions. Baseline

perfonnance results pro\ ide basic information about the towers" behavior under design loading

conditions, including total and inter-story drift under wind loads, floor deflections under gravity loads,

demand/'capacit\' ratios for the primary structural components of the towers, exterior columns response

(shear lag effects and presence of tensile forces), performance of connections, and the towers" resistance

to shear sliding and overturning. The primary tasks that were undertaken to establish the baseline

performance include the following:

• To de\ elop structural databases for the primary structural components of the WTC 1 and

WTC 2 towers from the original computer printouts of the structural documents.

• To develop reference structural analysis models that capture the intended behavior of each of

the two tov\ ers using the generated databases. These reference models were used to establish the baseline performance of the towers and also served as a reference for more detailed

models for aircraft impact damage analysis and thermal-structural response and collapse

initiation analysis.

• To dex elop estimates of design gravity (dead and live loads) and wind loads on each of the tu o towers for implementation into the reference structural models.

• To perform linear, static structural analyses to establish the baseline performance of each of

the tv\'o towers under design gravity and wind loads.

Chapter 1 of this report presents an introduction and a brief description of the structural system of the towers. Chapter 2 presents an outline and description of the methodology used for the development of the

structural databases for both towers, along with the relational databases that are used to link the generated

databases for use in the de\ elopment of the reference structural models. Chapter 3 presents the development of the reference structural analysis models for WTC 1 and WTC 2, including global tower

models, typical floor models, and parametric studies conducted for the development of the global models.

Chapter 4 pro\ ides a discussion on the loading cases used in the baseline performance analysis and

outlines the dex elopment of the gravity and wind loads on the global tower models. Chapters 5 and 6

outline the results of the baseline perfonnance analysis for the global tower models and floors models,

respectively. A summary of the report is presented in Chapter 7.

WTC 1 and WTC 2 each consisted of a 1 1 0-story above grade structure and a 6-story below grade

structure. The buildings, which were each approximately 207 ft by 207 ft square in plan and with story

1.1 DESCRIPTION OF WTC STRUCTURAL SYSTEM

1.1.1 Global Structural System

NISTNCSTAR 1-2A. WTC Investigation 1
Chapter 1

heights of typically 12 ft, rose to heights of 1,368 ft (WTC 1) and 1,362 ft (WTC 2) above ground. The

exterior walls of the towers supported part of the gravity loads and all lateral loads, and were constructed

of steel, closely spaced built-up columns and deep spandrels. The core contained coIuituis that supported

the remainder of the gravity loads of the towers. The core area was approximately 135 ft by 87 ft in plan

(Fig. 1-1). The distances between the rectangular core and the square exterior wall were approximately

36 ft and 60 ft. The areas outside of the core were free of columns, and the floors were supported by

truss-framing in the tenant areas and beam-framing in the mechanical rooms and other areas.

<* -S; ..^/jt-p-e-tt^im B no a g a a-*ni-o-ii.a-a-^anBa n na mn na n a n n o g B aff anai a aa ann g a n a a a-ti-g-aSource: Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 1-1. Typical WTC tower architectural floor plan (floor 26, WTC 2).

The primary structural systems for the towers included exterior columns, spandrel beams, and bracing in the basement floors, core columns, core bracing at the mechanical floors, core bracing at the main lobby

atrium levels, hat trusses, and the floor systems.

The exterior wall columns from the foundation level up to elevation 363 ft were spaced 10 ft 0 in. on

center. They were built-up of steel plates and connected by deep spandrels. Bracings existed in the plane

of the exterior wall between the Concourse level and the foundation (Fig. 1-2). Between elevation 363 ft

2 NISTNCSTAR 1-2A, WTC Investigation
Introduction

and floor 7, the single exterior wall columns spaced 10 ft 0 in. on center transitioned to three columns

spaced at 3 ft 4 in. on center as shown in Fig. 1-2 (see also Fig. 3-6).

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 1-2. Typical WTC exterior wall, foundation to floor 9.

The exterior wall columns above floor 7 that were spaced 3 ft 4 in. on center, were built-up of steel plates,

and were connected to each other by spandrel plates, typically 52 in. deep. The exterior columns and

spandrels were pre-assembled into exterior wall panels, typically 3 -columns wide by 3 -stories tall (refer to Fig. 3-9).

The core columns were typically built-up box members at the lower floors and transitioned into rolled

structural steel shapes at the upper floors. The core columns were typically spliced at three-story intervals

at 3 ft above floor level. Diagonal bracing of the core columns existed at the lobby atrium levels, the mechanical levels, and in the area of the hat truss.

At the top of each tower, hat trusses interconnected the core columns with the exterior wall panels and

provided a base for the antennae. The vertical members of the hat trusses were wide flange core columns.

NISTNCSTAR 1-2A, WTC Investigation 3
Chapter 1

The diagonals were primarily wide flange rolled sections, with the exception of the end diagonals

connecting the core to the exterior walls, which consisted of built-up box sections. The majority of the horizontal members in the hat truss system were wide flange and built-up box section floor beams. The

members of the hat trusses were shown in the structural drawings SA/B-400 series elevations (see

Fig. 1-3).

Source: Reproduced with permission of The Port Authority of New Yorl< and New Jersey.

Figure 1-3. Typical WTC tower hat truss elevation (Drawing SA 401).

1.1.2 Floor Structural System

In the typical WTC tower floor plan, the area inside the core was framed with rolled structural steel shapes acting in a composite fashion with formed concrete slabs. The area outside the core was framed

either in trusses (typical on tenant floors) or in rolled structural steel shapes (typical on mechanical

floors).

Truss-Framed Floors—The majority of the floors of the WTC towers were tenant floors where the areas outside of the core were constructed of steel trusses acting in a composite fashion with concrete slabs cast over metal deck. The trusses consisted of double angle top and bottom chords with round bar webs and were designed to act in a composite fashion with the concrete slab. Composite action was achieved by

the shear connection provided by the web bar extending above the top chord and into the slab. Two

trusses were placed at every other exterior column line, resulting in a 6 ft 8 in. spacing between truss

pairs. The typical floor consisted of three truss zones: a long span zone, a short span zone, and a two-way

zone (see Fig. 1-4).

The floor trusses were pre-assembled into floor panels as defined in the contract drawings. The span" of

the primary trusses was about 36 ft in the short direction and 60 ft in the long direction. The floor panels

included prmiary trusses, bridging trusses, deck support angles, metal deck, and strap anchors, all of

which were defined by the contract drawings and specifications. The two-way zone included trusses in the long-span direction (primary trusses) as well the bridging trusses (secondary trusses). The secondary

trusses had additional strength and connectivity to enable them to act in tandem with the long spanning

tmsses to form a two-way spanning truss grid as shown in zones labeled two-way area in Fig. 1-4. Also;

the short span truss at the comer of the core was heavier than the typical ones because it did support the long span trusses that framed to it.

4 NISTNCSTAR 1-2A, WTC Investigation
Introduction

Since the relative stiffness of the bridging trusses was significant in the two-way zone compared to that of

the short span trusses, and since the comer of the floor was supported on two sides and the comer of the

core, tw 0 directional structural behavior was developed, in the one-way zones, the bridging trusses were

lighter and the floor was supported on only two sides (exterior wall spandrels and core perimeter beams),

so only one-way behavior was dominant.

- H ] ^ M M: - '

"

1 ' M 5

Figure 1-4. Typical WTC floor truss framing zones.

The floor truss panel types were indicated in the stmctural plans (Fig. 1-5). The plans refer in turn to Drawing Book 7 for information regarding the components of the floor truss panels, and to Drawing

Book D for damper information (see Chapter 2 for more details). Drawing Book 7 provided panel by

panel layout plans (Fig. 1-6) and elevations (Fig. 1-7) of each referenced tmss. The section through a

floor panel after the concrete was placed is illustrated in Fig. 1-8. Note that the dashed lines in Fig. 1-5

indicate power and telephone cells within the metal deck constmction.

NISTNCSTAR 1-2A. WTC Investigation 5
Chapter 1

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by

NIST. Figure 1-5. Part plan of floor 96 of WTC 1 (Drawing SA-104), components of typical truss

framing system.

6 NISTNCSTAR 1-2A, WTC Investigation
Introduction

3>!

cpcxpcpoocpo cpcpcpooocpo

/=^/a/7 Stee/ Deck j Oof ig oaf ^iTi. L -\see schedule y- ^d3-2

hc^e d*'m. M - \ see schedule 7-^sS-2

I

II ^ Extfirior colc/mn

'

" reference line

T

C327 7 Ci2T7 »

CZ2T3

C22 Tl'

£4lA

\ £4:4

* —

w

<

(

<

o

O

o

o

o

7 .4B^-2a P/o/? Top Chord 5^ 7434-22./

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 1-6. Typical WTC floor panel layout plan.

NISTNCSTAR 1-2A. WTC Investigation
Chapter 1 o o o

Soft- bole- dirmzrision -M - sea? spherule _ ''i.^jSg

?

! \l4® S>'-4' - ^G'-S" \ """\

IJ^I } tfi) cjiy mj t/iji r/?j r-fi /

1

r

Bxh&rior coUmn

Floor f/ne

\ f!

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 1-7. Typical WTC floor truss elevation.

4 in. Slab on 1-1/2 in. Metal

Deck

! r n

] r T^pxq/ \J \j \J \J \J \l

^

\

^:

/ \—xj-

// \

-

fi

;

!

f 1 rcrj >.-Lao ; C3E^i-^ara

Primary Truss Members Bridging Truss

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 1-8. Part section typical truss floor panel.

8 NISTNCSTAR 1-2A. WTC Investigation
Introduction

Viscoelastic damping units were used in the floor system to reduce the wind-induced vibrations of the towers. As the towers oscillated during wind excitations, part of the energy of oscillation was dissipated

through shear deformations in the viscoelastic part of the damping unit. The dampers were located

between the bottom chords of the floor trusses and the exterior wall columns as shown in Fig. 1-9 and the associated detail in Fig. 1-10. The figures show the construction of the dampers along with the plates,

bolts, and viscoelastic material dimensions. The dampers were defined in Drawing Book D. For further

details on the dampers design, construction, and testing, refer to NIST NCSTAR 1-1.'

Gusset plate

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Enhanced by NIST. Figure 1-9. Floor truss with exterior wall end detail. ^ Holes lor 01 high tensile bolls ~.

0.05" X 4' X 10' Section a-a Source: Reproduced with permission of The Port

Authority of New York and New Jersey. Enhanced

by NIST. Figure 1-10. Details of the damping unit used in the truss-framed floors.

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

to this report.

NIST NCSTAR 1-2A, WTC Investigation 9
Chapter 1

Beam-Framed Floors—The typical locations of the beam-framed floors were the mechanical floors, the mechanical mezzanines, and the floors above the mezzanines (e.g., floors 41, 42, and 43). These floors were constructed using rolled structural steel shapes. The beam framing for the typical floor system

consisted of W27 beams in the long span region and W16 beams in the short span region. Typical beam

spacing was 6 ft 8 in. The steel beams acted in composite fashion with the nonnal weight concrete slab on metal deck.

The mechanical floors were 5 in. concrete slabs on 1 Yi in. metal deck outside the core. The deck

spanned in the direction of the primary beams and was supported typically at 6 ft 8 in. intervals by a 4C5.4 deck support channel. A 2 in. concrete topping slab was placed on top of the stmctural slab. The

core area was framed similarly to the core of the truss-framed floors, but the steel beams were typically

larger, and the concrete slab was 6 in. deep. The beam-framed floors above the mechanical mezzanine

had a 7 3/4 in. normal weight concrete slab on 1 1/2 in. metal deck, while the core slab was 8 in. nornial

weight concrete. The floor slabs were omitted from much of the mechanical mezzanines outside the core

to provide double height space for the mechanical equipment.

Similar to the truss-framed floors, viscoelastic damping units were used in the beam-framed floors to reduce wind-induced vibrations. The dampers were located between the bottom flanges of the floor beams and the exterior wall columns as shown in Fig. 1-11. The dampers that were used in the beamframed floors were slightly longer than those used in the truss-frames floors. Also the connections

between the damping units and the floor trusses were different than those between the damping units and

floor beams as can be seen from Fig. 1-9 and Fig. 1-1 1. —Exterior column

reference line

Two 1

" 0 bolts- (A490)

Reference floor line z:

Wide-flange beam

Two %" 0 bolts

o o

Two 1 Va" 0 bolts (A490)

-Damping unit

Vs" Pt-^ Type B

2'- 6"

43/4'

Figure 1-11. Damping unit used in the beam-framed floors.

Beam-framing was added to truss-framed floors at levels which supported escalators or stairs in the areas outside of the core. The escalator floors occurred typically in the two levels directly above the mechanical rooms.

10 NISTNCSTAR 1-2A, WTC Investigation
Chapter 2

Development of Structural Databases for the WTC Towers

2.1 introduction

The objective of this chapter is to describe the development of electronic structural databases for the primary structural components of the World Trade Center towers (WTC 1 and WTC 2) from the original

computer printouts of the structural documents. These databases were generated for use in the development of the reference structural models of the towers (see Chapter 3).

Section 2.2 briefly describes the structural design documents of the towers. Section 2.3 presents an overview of the database development and contents, while Sec. 2.4 outlines the methodology used to develop the structural databases from the original computer printouts, and the relational databases used

for the subsequent development of the reference structural analysis models of the towers (see Chapter 3). Section 2.5 describes the modifications made to elements of the database based on changes made to the primar\' structural components of the towers after construction. The calculation of cross section

properties is presented in Sec. 2.6. Section 2.7 provides a summary of the chapter.

The WTC structural drawings were issued in two main fonnats: large-sized sheets containing plan and

elevation information and smaller book-sized drawings containing details and tabulated infonnation.

Throughout the WTC drawings, Tower A or WTCA denotes WTC 1 (North Tower) and Tower B or WTCB denotes WTC 2 (South Tower). For WTC 1 and WTC 2, the large-size sheets are listed in Appendix A. These large-sized drawings always make reference to the structural drawing books in their notes, sections, and details. The structural drawing books for WTC 1 and WTC 2 contain the following

• Book 1 contains exterior wall information to elevation 363 ft. (Dates: 02/1967 to 12/1968,

Approx. 213 pages.)

• Book 2 contains exterior wall information elevation 363 ft to floor 9. (Dates: 04/1967 to 12/1967, Approx. 62 pages.)

• Book 3 contains core column information. (Dates: 03/1967 to 09/1969, Approx. 137 pages.)

• Book 4 contains exterior wall information floor 9 to floor 110. (Dates: 04/1967 to 10/1972,

Approx. 1.080 pages.)

• Book 5 contains the beam schedule. (Dates: 05/1 967 to 08/1 969, Approx. 292 pages.)

• Book 6 contains connection details and core bracing. (Dates: 08/1967 to 05/1969,

Approx. 1,060 pages.)

NIST NCSTAR 1-2A. WTC Investigation 1

1

2.2 description of the WTC STRUCTURAL DOCUMENTS

materials:
Chapter 2

• Book 7 contains truss floor panel information. (Dates: 10/1967 to 07/1969, Approx. 345

; , . pages.)

• Book 8 contains concrete notes and details. (Dates: 03/1968 to 07/1974, Approx. 926 pages.)

• Book 9 contains roof area column splice details. (Dates: 05/1 970 to 04/1971, Approx.

440 pages.)

• Book 18 contains strap anchor and core truss seat information. (Dates: 10/1968 to 1 1/1969,

Approx. 219 pages.)

• Book 19 contains revisions after fabrication. (Dates: 08/1968 to 05/1975. Approx. 374

pages.)

• Book 20 contains structural steel details. (Dates: 07/1968 to 03/1971, Approx. 41 pages.)

• Book D contains damper details. (Dates: 03/1969 to 09/1971, Approx. 43 pages.)

Books 10, 11, 12, and 13 contain infomiation on the sub-grade structure. Books 14, 15, 16, and 17 were

never used in the original design documents.

Until fabrication was begun, the drawings and drawing books listed above (with the exception of

Book 19) were modified in keeping with requests for changes by contractor(s) and early tenant modifications. The drawings were modified up until such time as the fabrication of elements

commenced. At that time, Book 19 was introduced. It contained the information regarding 'revisions

after fabrication'.

Leslie E. Robertson Associates, R.L.L.P. (LERA) believes that the original structural drawings represent

significantly accurate 'as-builf drawings for the towers. As tenant modification requests became large in scope, they became separate projects (e.g.. the Fiduciary Trust Vault Project, see Sec. 2.5.2). Tenant

structural modifications designed by LERA were then documented in a single book of quarter-size plans, referred to as the 'WTC Tenant Structural Modifications Book.' Later tenant modifications were mostly

archived on a job-by-job basis without a central accounting for all the changes. In some instances (e.g., additions to the mechanical levels) modifications were made by The Port Authority of New York and

New Jersey (PANYNJ) Engineering. In other instances, tenant modifications, such as adding floor openings, were made by other engineers. In these instances, LERA does not have record of the work

completed. These modifications were considered to not significantly affect the member properties

pertaining to the reference structural models and were not included in the WTC structural databases. •

The few modifications made by LERA to the components compiled in the WTC structural databases that have an effect on the global behavior of the towers are listed in Table 2-1

.

Drawing Book 1 9 has records of other modifications to structural elements of the WTC towers that were viewed as non-essential for the development of the reference models of the towers and as such were not included in the structural databases. These modifications are outlined in Appendix B.

12 NISTNCSTAR 1-2A, WTC Investigation
Development of Structural Databases for the WTC Towers

Table 2-1. Modifications to members of the WTC database (WTC-DB).

Item Description Tower Element Floor Element Effected WTC-DB

Modified Archi\ ed

1 Core column

reinforcing

WTC 1 and

WTC 2

Numerous 98-106 Core columns Book 3 Book 19

Fiduciary Bank

Vault WTC 2 Col. 508B and

Col. 1008B

45-97 Core columns Book 3 LERA P209

1.J DLrillUlUU, Ul February 1993

repair

WTP VV 1 1 V_ *^01. JZH, bracing

G313Aand

G304A

D-z level Permieter column and

bracing

IN A I P R A P10031 18

4 EXCO stair WTC 1 Col. 901

A

26 Core column NA LERA

P 1003249

2.3 OVERVIEW OF THE WTC STRUCTURAL DATABASE (WTC-DB)

The original WTC design documents were devised to limit the need for repetition in documenting the data

shared between different elements with similar characteristics. The drawing book schedules refer to subsequent tables for infonnation common to several lines of the same schedule. In an effort to minimize

the amount of repeated infomiation, and thereby, the data checking of the digital WTC-DB, the drawing

book data within the databases were linked in a similar manner. In order to accurately follow the original

flow of the drawing book links, flowcharts of the drawing books to be digitized were developed. These

flowcharts were used to organize the links of the digitized data within the relational database. The

flowcharts are illustrated in Appendix C. An exainple of such flowcharts for Drawing Book 3 (core

coluinns) is shown in Fig. 2-1.

The WTC-DB contained the computer and hand-tabulated data for the major structural components from

original Drawing Books 1 through 5, including exterior walls, core columns, and beam schedule for the towers. Where infonnation from Drawing Books 1 through 5 was modified by Drawing Book 1 9 and

would affect the towers" modeling, the information was included in the database. In addition, some

infonnation from Drawing Book 6 (core bracing schedule) and Drawing Book 9 (beams in the hat truss region) was included in the database files as it was utilized in the finite element modeling of the towers.

The drawing book tables were first digitized and stored in Microsoft Excel format files. The Excel files included several worksheets that described the evolution of the data from the drawing book to the final database format, as well as additional infonnation and notes for interpreting the data. Refer to Appendix D for the list of Excel fonnat files.

The WTC relational database linked the Excel files and allowed users to view and select data through

query commands. The primai7 benefit of the relational database fonnat was the ability to programmatically query the database for data required in assembling the structural models of the towers. The query routine allowed multiple users the ability to review, extract, and export the basic data in any

required fonn. The data can be manipulated using Structured Query Language (SQL) according to the desired output, for example the structure of the user's finite element model input file.

NISTNCSTAR 1-2A, WTC Investigation 13
Chapter 2

Core Column Number/Location

and Elevation

Base Details

((15))

3-AB2-20, 2! [2D]

Core Column Schedule

3-Al-2>48 [47TC]

3-B1-2 >48 [47TC]

WTCA-Ukl-t iircri.liiiAdala.ji Is I A_C«rcC.il)

ttTCH-likJ-CorcColii.Hiiala xls (U_r.>rcCol>

Splice Details

((15))

3-AB2-4,7,8>i3, 15>!6 [lOTH]

3-AB2-3.1>19[18D]

Splice Location

((!))

3-AB2-22 [ID]

Floor 106 Splice Details

((15))

3-AB2-3 [ID]

IB.CI

Shape Property Table

Shape Property Table.xls

lAB^ShapcPropI

Reference Floor Elevation

((2. 3))

3-A2-23[lTC]

3-B2-23[lTC]

\\TCA-Bk3-Corer(>liiiAfloorelcv,xlslA_RcffilcvlJPR/LWR| «TCb-Bk.1-CorcColinBtk>orclov-xls(B RctElcvlU'RyLXTOl

NOTES:

1 . 4-AB-* Denotes Drawing Book 4, Tower A , B or AB, and page number

2. [*TC] Number of pages and type, where page types include; TC - Computer generated tables; TH - Hand wntlen tables; D - Diagrams

3. *.xls Excel spreadsheet file name; (AB_*'**) database heading

4. ((*)) Reference note key from original Drawing Book infonnation table.

5. 1*1 Relational database link (i.e. Excel column number) from previous *.xls file.

6. Figures of columns and panels are shown from inside of building looking out, unless otherwise noted.

Figure 2-1, Drawing Book 3 flowchart: WTC 1 and WTC 2 core columns, foundation to

floor 106.

2.4 METHODOLOGY FOR THE WTC-DB DEVELOPMENT

2.4.1 Data Entry

The tabulated portions of WTC Drawing Books 1, 2. 3, 4, 5, 6, and 9 were first scanned and stored in Tagged Image File Format (TIFF) image files. The image files containing the tabulated information were

then opened in an Optical Character Recognition (OCR) program that converted the infonnation into a

text file. The OCR program was modified to allow for the filtration of unnecessary characters during the document conversion process. In other words, the user could direct the program to block specific characters that were not on the actual page. As an example, if after reviewing a table, one recognizes that

14 NISTNCSTAR 1-2A, WTC Investigation
Development of Structural Databases for the WTC Towers

it uniformly contains numbers and only the characters "A, B, and 'V" then the remaining characters can

be frozen out by the software. This reduced the misinterpretation, as an example, of a 'Z' for a '2,' or an

'O' for a 'zero.'

The raw text file was then opened in a word processing program, where it was compared with the original

hardcopy drawing books. As needed, data columns were adjusted, and obvious errors were individually

corrected. The 'cleaned' text file was then imported into a Microsoft Excel spreadsheet with column

headings and proper ahgnment. When importing into Excel, "texf was the cell format used for handling

of the scanned information to avoid the misinterpretation of fractions as dates (e.g., 3/8 as March 8). An

Excel macro was written at this stage to convert the text fractions into number fractions. The final product of this stage was an Excel file that contains the information from the drawing book table.

2.4.2 Quality Control

Checking began during the OCR data entry process, where the files being entered and the OCR software

interpretation were viewed simultaneously. This was considered a first check. Once the Excel file was

complete, the file entered the 'second check* process.

The 'Second Check'—An engineer not involved during the OCR process performed a second, sample

checking of the database in a random but methodical manner. For approximately once in four pages, every cell of data in the page was compared with the original drawing books. Discrepancies of the files were then either re-entered using OCR or were individually corrected to agree with the original books.

The 'Cross-Check Rectify' Check—After completing the 'second check,' the files were compared with

the database provided by a consultant for the leaseholder of the WTC towers as part of insurance

litigation concerning the towers (provided by NIST as Government Furnished Infonnation [GFI]) using a cross-check macro formula worksheet. Once compared, conflicting information appeared in a yellow

highlighted cell displaying both sets of compared information in the "Calculation" macro formula

worksheet. The cell was then reviewed and confirmed with the WTC drawing books. If errors were from

the developed worksheet, data were rectified, and the yellow highlight in the 'Calculation' worksheet was

then removed by comparing the files again. If errors were from the GFI worksheet, raw GFI data were

not modified, but the cell was highlighted in blue to note that it had been reviewed. The files were then

compared again, and the cell color in the 'Calculation' worksheet changed to blue. The process was

repeated to remove all the yellow cells so that only blue highlighted cells remained. The worksheet

'ComparisonORlGINAL' was retained for the record of the original comparison, and the updated

worksheet 'ComparisonFINAL' was retained for the record of the final comparison.

Final Revien —Finally, the files were reviewed for completeness, formatting, and data units. A final check \A as made to find any numbers that may have been input as text letters. Following this review, the worksheet was used to develop the member section properties.

2.4.3 Cross Section Property Calculations

The next step was to calculate the cross section properties for the members included in the database. The

section properties calculated included cross sectional area (A), moment of inertia (7), section modulus (S),

plastic section modulus (Z), radius of gyration (r), and torsional constant (J) for both the major and minor

NISTNCSTAR 1-2A, WTC Investigation 15
Chapter 2

axes, where applicable. The Section Designer function of SAP2000 Version 8 (SAP2000 2002) was used

to calculate the cross section properties since it streamlines the development of the models and enables

the program to perform more precise code checks, as the dimensions of each plate element that was part

of the section would be input into the finite element model.

The current rolled shape database in SAP2000 represents the modem day rolling practices. The rolled shapes used in the constmction of the WTC towers were from a different era and, thus, had different properties in comparison to present day shapes. Therefore, a rolled shape database consistent with the time of construction was developed. See Sec. 2.6.5 for further discussion about the rolled shape database.

2.4.4 Relational Database Development

As discussed earlier, the original WTC drawing books were designed to avoid repeating identical infonnation. The drawing book schedules, therefore, refer to other tables for infomiation common to several lines of the same schedule. In keeping with the nature of the original drawing books and to minimize the data in the digital WTC-DB, the drawing book and section property data were linked using

Microsoft Access.

The assembly of the relational database began with the mapping of the original WTC drawing book into flowcharts (see Fig. 2-1). The digitized drawing book data with the coiresponding cross sectional

member properties from the Excel-fonnat files were then imported into the Microsoft Access database

program and partitioned into tables. The tables were then joined using the links cataloged in the flowcharts. These tables were developed to provide the input files for the finite element modeling of the towers as illustrated in Chapter 3. The generated Microsoft Access database files are listed in Appendix E. The relational database is described in the tutorial included in Appendix F.

2.5 MODIFICATIONS TO DATABASE ELEMENTS

Most original members and elements defined within the WTC-DB could be fully defined by the original

data in the drawing books. As outlined in Table 2-1, however, some modifications were made, and these

are described in the following sections. Of the items outhned in Table 2-1, items 1 and 2 were included

within the database.

2.5.1 Core Column Reinforcing at Floors 98 to 106

A number of core columns in both WTC 1 and WTC 2 were reinforced at floors 98 to 106. Book 19,

pages 19-AB-974.1 through 4, shows that core columns 501, 508, 703, 803, 904. 1002, 1006, and 1007

from floors 98 to 106 in both towers were reinforced with steel plates. Three methods were used to attach the reinforcing plates to the wide flange columns: (1) the plates were welded to the flanges; (2) the plates were welded to the webs; and (3) the plates, which were parallel to the web, were welded to the flange

ends. The plate infonnation (width, thickness, length, and yield strength) was incoiporated into the database tables of Book 3. Since the plates varied from floor to floor, the original column (defined over a three-story height) was split into typically three floor-by-floor sections, and the designation of the column was appended to include either U (upper), M (middle), or L (lower) designation (refer to Fig. 2-2). For

floors 104 and 106, the columns were two-stories high. Hence, the columns at these floors had only U

and L designations. The section property calculations included the contributions of the reinforcing plate

16 NISTNCSTAR 1-2A, WTC Investigation
Development of Structural Databases for the WTC Towers

at each lev el. For the built-up section property data, the reinforcing plate was considered to be applied to the column for its floor-to-floor height.

Col. Splice

FL 101

CC703A101U

CC703A101M

CC703A101L

Col. Splice

44-

FL 100

FL99

Reinforcing Plate

FL98

Figure 2-2. Core column reinforcement.

2.5.2 Core Column Reinforcing Due to Construction of Fiduciary Trust Vault

The Fiduciary Trust Company added a concrete vault at floor 97 of WTC 2, which required reinforcing

two comer core columns at the north end of the core (columns 508 and 1008). This work was included in the WTC Towers A and B Structural Renovation Drawings Reference Manual. The Fiduciary Trust

Structural Drawing 765-S-A^ indicated that WTC 2 core columns 508 and 1008 were reinforced with

steel plates from floors 45 to 97. The reinforcement consisted of plates welded to the flanges of the built- up box columns (floors 45 to 83) and the flanges of the rolled shape columns (floors 83 to 97). These

reinforcing plate modifications and the reinforcing plates' yield strength, F,,, were added to the original

Book 3 data contained in the WTC-DB. The database included plates that were long enough to substantially affect the member properties of the column, that is, the added plates increased the capacity

of the columns. Where the plates appeared to reinforce only the column splice, they were not included in the database. For the reinforced columns, no specific information is available about the fireproofing of

these elements. It is presumed that these elements were fireproofed in the same way and using the same

materials as other parts of the structure.

NISTNCSTAR 1-2A, WTC Investigation 17
Chapter 2

The reinforcing plate data were tabulated and incorporated into the database in the same manner as the

plates discussed in the previous section, except that a second length designation was added to differentiate the length of the plates on the north and south faces of the columns, i.e., the column designation "LN"

refers to the length of the plates on the north face of the column. Again, when calculating the built-up

column properties, the plate was assumed to be continuous along the floor-to-floor height of the column.

When the length of the reinforcing plate shown in the drawing was greater than the floor height, the plate was attributed to the two column segments. Where the plate extended over the entire height of the segment, the length was tabulated as the height of the column segment. The remaining length of plate was attributed to the other column segment.

2.5.3 Repair Due to the Bombing of February 26, 1993

The 1993 bombing resulted in structural damage to WTC 1, centered at exterior column 324 (south wall),

B-2 level. The face of the column toward the explosion was slightly bowed, and the splice in the column

developed a hairline crack. The column was reinforced locally to account for the loss of steel area. The

bracing on either side was replaced with equivalent sections and attached in a similar manner as the

originals. No modification to the WTC-DB was made for this repair.

2.5.4 Tenant Alteration for an Interoffice Stair

A tenant alteration was provided for an interoffice stair between floors 25 and 26 in WTC 1. This work,

adjacent to core column 901 A, was perfonned by an engineering finn (other than LERA) and

unknowingly resulted in the loss of a core column bracing strap (refer to Fig. 2-3), leaving the column

unbraced about its minor axis for two stories. The PANYNJ alerted LERA to the issue, and asked LERA

for a review. LERA found the column stability to be adequate. No modification to the WTC-DB has

been made for this modification. The effect of removing the strap is accounted for in the global model of

WTC 1; see Sec. 3.2.3.

2.5.5 Drawing Book Data Discrepancies

In the original WTC drawing book data, the following discrepancies were discovered by LERA:

• Book 1, page l-B-15. For member number G31 lA, the inch portion of the length is listed as 3-1/18. Based on the comparison with similar bracing types in the area, this dimension was

modified to be 3-1/8 in. in the WTC-DB.

• Book 3, page 3-Al-lO. For core column 601 A between floors 86 to 89 and 89 to 92, the column type is hsted as 213. Type 213 is a column type which by definition has reinforcing

plates, but for this location no plate data were provided in the schedule. This, in combination

with comparisons with similar columns in plan, led to modifying the column type to 111. This also applies to column 60 IB, page 3-Bl-lO between floors 86 to 89 and 89 to 92.

• Book 3, page 3-B1^8. For column 1008B between floors 63 to 66, the yield strength, F,,, is

listed as 6 ksi in the table. Based on the yield strength of the columns above and below these

floors, the yield strength was modified to be 36 ksi. For the same column number and floor segments, the lower sphce detail number is listed as " OIG." Based on the lower splice detail

18 NISTNCSTAR 1-2A. WTC Investigation
Development of Structural Databases for tfie WTC Towers

number of the columns above and below these floors, the number was modified to be

"301G."

STRAP

PLATE

"CORE

COLUMN

PU\N

— CORE

COLUMN

— I 1/2" DECK

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 2-3. Column section at original column strap detail (taken from drawing

book 1 8, page 1 8-AB2-1 2).

• Book 3, page 3-B1-9. For core column 508B between floors 21 to 24, the length of plate 1, W], is tabulated as 1 1 .25 in. However, length B for this column is 22 in. and thickness t2 is 5.5 in. W] equals B minus two times t2 (see Fig. 2-A). Hence, assuming t2 was listed correctly in the table, WJ was modified to be 1 1 in.

CO

-4 &2

\/y ////////Y/r<A

Source: Reproduced with permission of The Port Authority of New

York and New Jersey. Enhanced by NIST. Figure 2-4. Core column series 300.

NISTNCSTAR 1-2A, WTC Investigation 19
Chapter 2

• Book 1, page l-B-23 and 1-B2-19. The details for column types 1024, 1025, 5024, and

6025 listed in the tables are not explicitly shown in the drawing book. For these members,

column shapes were assumed to be as shown in the typical details in page l-B-19 for the 1000 series columns, l-B-24 for the 5000 series column, and the l-B-27 for the 6000 series column.

• Book 3, page 3-AB2-6. The column type 216 does not appear to be assigned to any member

in the drawing book.

2.6 SECTION PROPERTY CALCULATIONS

SAP2000 Section Designer was typically used to calculate section properties for built-up sections. The

sections were "built-up" within SAP2000 by defining plate dimensions and offsets from 0-0 location. Section orientations were defined with the X-X axis horizontal to the bottom of the original drawing book

page as the detail is shown in the drawing book.

^

During the process of calculating properties there was an exception to this orientation rule. Core column

members CC1007A104L, CC1002A104L, CC703A106L, CC1007B104L, CC1002B104L, and

CC703B106L consist of a wide flange shape and web reinforcing plates. These members were input into SAP2000 rotated 90 degrees from the orientation shown in the details to utilize the default orientation of

the wide flange section in Section Designer. Once the properties were calculated, the sections were

placed in the WTC-DB following the orientation of the detail (i.e., the axis was shifted back 90 degrees).

When rolled shapes were used to create built-up sections, the rolled shapes database developed for this analysis was used to build the sections in SAP2000 Section Designer as explained in Section 2.6.5. The

200 series core columns (wide flange rolled columns reinforced with plates) are examples of members

whose properties were calculated in this manner.

2.6.1 Member Designations

For member section property calculations and assembly of the finite element models, the members were named using the following general member designations. The member designations are listed in the Microsoft Excel files.

First character:

• Book 1 —below tree-B

• Book 2—exterior wall tree-T

• Book 3—core columns-C

• Book 4—exterior columns and spandrels-E

20 NISTNCSTAR 1-2A, WTC Investigation
Development of Structural Databases for the WTC Towers

Second character:

• C—column

• S—spandrel and below grade exterior wall spandrel, strut, or bracing

Third to fifth character: (third to sixth character for 4 digit column e.g., 1004)

• Column number

Sixth character:

• A—WTC 1

• B—WTC 2

Seventh character and above:

• Upper splice level—for core columns

• U (upper), M (middle), or L (lower)—column segment where reinforcing plates are added

• T or B—top or bottom of nonprismatic columns

• Detailletter (lowercase)—(where more than one section is calculated)

• f or C—face or center of nonprismatic spandrel

• Elevation—below tree spandrel elevations

2.6.2 Column Member Multiple Section Property Calculation

In the database, the following three types of column members had different cross sections along the

length of the members:

• Exterior u all tree at level C in Drawing Book 2 (two different cross sections)

• Exterior wall tree at level E in Drawing Book 2 (three different cross sections)

• Exterior column type 300 (floor 9 to 106) in Drawing Book 4 (two different cross sections)

For these three member types, the section properties of the different cross sections were calculated and

listed in the database tables. In an effort to minimize repeated information, the raw input data for all sections were only shown in the rows that corresponded to the first cross section. For the second and

third (if any) cross sections, the calculated data followed in the rows below. The constant raw data such

as the column number were not repeated in these rows of the table, and thus, the corresponding cells were

left blank. Since the column number was used as a link for the development of the relational database,

only the row containing the raw input data and the first cross section properties were returned in a query.

NISTNCSTAR 1-2A. WTC Investigation 21
Chapter 2

and thus, the user must refer back to the Microsoft Access 'Tables' for the remaining section property

information. The section names of the different cross sections along the member length were

distinguished by the last one to two characters, which identified the cross sections where the section

properties were calculated.

For example, exterior column EC339 (mechanical floors) tapers over a portion of the length of the member (refer to Fig. 2-5). The section properties above and below the spandrel were calculated. The

column section above the spandrel was called EC339, while the column section below the spandrel was

called EC339cc. The suffix 'cc' denoted the section below the spandrel. Note that the raw dimensional

data for EC339cc were not shown in the table, as the inforaiation was the same as for EC339.

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Enhanced by NIST. Figure 2-5. Exterior column type 300, floor 9 to floor 106 (taken from

drawing book 4, page 4-AB2-18).

22 NISTNCSTAR 1-2A, WTC Investigation
Development of Structural Databases for the WTC Towers

2.6.3 Spandrel Member Multiple Section Property Calculation

In the database, the exterior columns below elevation 363 ft in column series 5000, 6000, and 7000 in Drawing Book 1 had corresponding spandrels shown in the details in Book 1 . There were two types of

spandrels for these members, tapered built-up box shapes and built-up I shapes. For the tapered built-up

box shapes, the section properties of the different cross sections were calculated and listed in the database

tables. The data were listed in the database files as described for columns with multiple cross sections. The section names of the different spandrel cross sections along the member length were distinguished by

the last three to four characters, which identified the cross sections where the section properties were

calculated.

For these exterior columns, there were spandrels at two elevations, 332 ft and 350 ft (see Fig. 2-6). At

elevation 350 ft, the spandrels tapered, and as a result two cross section properties were calculated. The

first section was at the face of the exterior column, and the corresponding section name had a Suffix F

(face). The second section was at the center of the spandrel between two exterior columns, and the corresponding section name had a Suffix C (center). The elevations and locations of the cross sections of

the spandrels were shown in the figures in the "Cross Section" worksheets in the database Excel files.

El. 363' -0

EL 350'

EL 332--0'

EL. 318--0"

SECTION F (FACE)

a-0

1

SECTION ( (CENTER)

ELEVATION

Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Enhanced by NIST. Figure 2-6. Column type 6000 with tapered spandrel (taken from drawing book 1, pages 1-A2-27 and 28).

For example, four different section properties were calculated for exterior column 6009 in WTC 1. The

first section was the exterior column itself, and the section name was BC6009A. The other three sections,

BS6009AB332, BS6009AT350C, and BS6009AT350F were for the spandrel sections. The suffix B332

in BS6009AB332 denoted the bottom spandrel at elevation 332 ft. Suffixes T350C and T350F in

NISTNCSTAR 1-2A. WTC Investigation 23
Chapter 2

BS6009AT350C and BS6009AT350F, respectively, denoted the top spandrel at elevation 350 ft, and the "C" or "F" identified the location where the section properties were calculated, see Fig. 2-6.

2.6.4 Section Property Calculation Comparisons

For all the members whose section properties were included in the GFl database, the cross sectional

properties in the GFI data were compared with the data contained within the WTC-DB. Most section

property results differed between the GFI and the WTC-DB by no more than 1 percent. It was found that results from the calculations of the torsional constant, J, however, did vary. LERA in-house programs were then used to confirm the accuracy of the J calculation. For core columns in WTC 1 , SAP2000

generated values used in the WTC-DB were on average 8 percent larger than J values calculated using the LERA in-house program, while the results provided by the GFI database were on average 13 percent

greater than LERA in-house program J calculations.

The approximate equation used to calculate J values by the LERA in-house program for a built-up

column or box section as shown in Fig. 2-7 is as follows:

2{bhy

b h — +

(Eq. 2-1)

It was found that for box sections, J values calculated by the above equation matched the J values given

by SAP2000 Tube Section. However, for the same tube section, the J values given by SAP2000 Section

Designer were greater than J given by SAP2000 Tube Section, even while all other properties were

equivalent. According to Computers and Structures, Inc., the developer of SAP2000; the J values given

by SAP2000 Section Designer are more accurate as SAP2000 Section Designer uses a finite element

method to calculate the J values, while an approximate equation is used in SAP2000 Tube Section.

// Ay //

\ 4 \

tw \

\ f

(a) (b)

Figure 2-7. Box section and a built-up column.

In order to minimize the complexity of the model, where the member cross-section was of the type

illustrated in Fig. 2-7 (a), box column members were defined in SAP2000 Tube Section. The remaining

built-up box columns (similar to Fig. 2-7 b) were defined in SAP2000 Section Designer.

24 NISTNCSTAR 1-2A, WTC Investigation
Development of Structural Databases for the WTC Towers

For members whose properties were not given in the GFI database, hand calculations or calculations by

LERA in-house program were carried out to verify the results from SAP2000 Section Designer for at least one section for each member type.

La summary, it was found that SAP2000 Section Designer provided section properties in close agreement

with calculated properties. In most cases these properties also closely matched with the properties listed

in the GFI database. In the cases where SAP2000 results disagreed with the GFI database, the resuhs were reviewed, and it was concluded that the SAP2000 calculation provided the correct properties.

Therefore, the section property results calculated using SAP2000 were used in the WTC-DB and the development of the finite element models of the towers.

2.6.5 Rolled Shape Database

While the majorit\' of the primary members of the WTC towers' super-stiucture were built-up members,

rolled shapes were also used. The rolled shapes specified in the drawings in a number of cases are no

longer produced and, consequently, are not included in the rolled shape database embedded within

SAP2000. Therefore, a rolled shape database was developed using the old nomenclature and section

properties. The result was a file named 'Shape Property Table.xls.' The file contains three worksheets:

'Database,' 'Excel Format.' and 'WF Shape Properties from SAP.' The following is a discussion of their contents.

Data contained in 'Database' and 'Excel Format'—Drawing Books 3, 4, and 5 include reference to specific rolled shapes. The referenced shape names were extracted from these books and assembled into a single reference database for rolled shapes. Most of the section properties were obtained from the Manual of Steel Construction, American Institute of Steel Construction (AISC), Sixth Edition, 1963

(AISC 6th Edition) with few exceptions where cross sections were not included in this edition. Examples

of these exceptions include the following:

• Section properties of 14WF455 to 14WF730 were obtained from the Manual of Steel Construction-Load and Resistance Factor Design, American Institute of Steel Construction,

Third Edition, 2001 (AISC-LRFD 3rd Edition).

• Section properties of 6CH12, 6CH15.1, 12CH40, 12CH45, and 12CH50 were obtained from

the MC-shapes table in the AISC-LRFD 3rd Edition.

• Section properties of 18WF69 were obtained from the Iron and Steel Beams 1873 to 1952,

the American Institute of Steel Construction, 1 968. 1 6WF342 was assumed to have the same

section properties of 16H342 tabulated in Iron and Steel Beams 1873 to 1952, the American

Institute of Steel Construction, 1968.

• For 7x5 tube, Z^, Z, . and J were obtained from the AISC- Allowable Stress Design (ASD),

1989, 9th Edition.

• For 2L 3 1/2 in. x 3 in. x 1/2 in. long leg back to back, the combined properties were taken

from SAP's embedded rolled shape database.

NISTNCSTAR 1-2A. WTC Investigation 25
Chapter 2

Data contained in 'WF Shape Properties from SAP'—For the rolled wide flange shapes, an additional

database was created in SAP2000 based on the tabulated shape dimensions from the AISC Manuals as discussed above. Computers and Structures, Inc. provided an Microsoft Excel file named 'Proper.xls'

with a macro that allowed the accurate calculation of the section properties for use within SAP2000. This

infonnation was then used by SAP2000 Section Designer to calculate section properties for built-up

members comprised of wide flange sections and added plates.

For calculation of the properties with Troper.xls,' dimensions of the webs and flanges, as well as the size of the fillet, were input into the spreadsheet. The macro then calculated the section properties based on

the input infonnation. The results were shown to be in good agreement with the original tabulated

properties.

2.7 SUMMARY

This chapter described the development of the electronic structural databases for the primary structural components of the WTC towers. These databases were developed from original computer printouts of the

structural design documents, including modifications made after construction. The databases were

generated for use in the development of the reference structural models of the towers.

The structural databases contained the computer and hand-tabulated data for the primary structural components of the towers from the original Drawing Books 1 through 5, including exterior walls, core columns, and beam schedule. In addition, some information from Drawing Book 6 (core bracing

schedule) and Drawing Book 9 (beams in the hat truss region) were included in the database files as they were utilized in the modeling of the towers. Modifications to the towers that were implemented in the databases included strengthening of a number of core columns at floors 98 to 106 of both towers and

reinforcing of two comer core columns at floors 45 to 97 of WTC 2 due to the construction of a concrete

vault at floor 97.

The steps that were undertaken to develop the structural databases included: (1) the scanning and

digitization of the original drawing books, (2) a four-step quality control procedure, (3) cross section

property calculations, and (4) the development of the relational databases to link the generated database

files into a format suitable for the development of the structural models.

26 NISTNCSTAR 1-2A, WTC Investigation
Chapter 3

Development of Reference Structural Models for the

WTC Towers

3.1 INTRODUCTION

The objective of this chapter is to outHne the development of the reference structural analysis models that capture the intended behavior of each of the two towers. The models were used to establish the baseline

performance of the towers under gravity and wind loads. They also served as a reference for more

detailed models used for other phases of the National Institute of Standards and Technology (NIST)

Investigation, including aircraft impact analysis and thennal-structural response and collapse initiation analysis.

Included in this chapter are descriptions of the reference structural models, the modehng techniques, the parametric studies utilized in the development of the models, and the methodology used to export to the models the requisite data from the relational database (see Chapter 2). The main types of models

developed are as follows:

• Two global models of the major structural components and systems for the towers, one each

for World Trade Center (WTC) 1 and WTC 2.

• One model each of the typical truss-framed floor and typical beam-framed floor (mechanical

level) within the impact and fire regions.

All models are linearly elastic and three-dimensional, and were developed using the Computers and

Structures, Inc. SAP2000 Software, Version 8 (SAP2000 2002).

Section 3.2 describes the dev elopment, contents, and verification of the global models of WTC 1 and

WTC 2. Sections 3.3 and 3.4 present the models for the typical truss-framed floor and beam-framed

floor, respectively. Section 3.5 describes the parametric studies that were undertaken to facilitate the development of the global models. Section 3.6 presents a summary of the chapter.

3.2 GLOBAL MODELS OF THE TOWERS

A three-dimensional structural analysis computer model of the 1 10-story above-grade structure and

6-story below-grade structure for each of the two towers was developed. The global models for the towers consisted of the major structural components and systems required to establish the baseline

performance of the towers under gravity and wind loads. In establishing the modeling techniques for the global models, parametric studies were performed to evaluate the behavior of typical portions of the

structure and develop simplified models that could be implemented in the global models (see Sec. 3.5).

NISTNCSTAR 1-2A. WTC Investigation 27
Chapter 3

3.2.1 Components and Systems in the Towers' Global Models

The models included all primary structural elements in the towers, including exterior columns, interior (core) columns, exterior wall bracing in the basement floors, core bracing at the mechanical floors, core bracing at the main lobby atrium levels, spandrel beams, hat trusses, and rigid and flexible diaphragms

representing the floor systems, as developed in Sec. 3.5 of this report. While the global models did not

include the structural dampers in floor systems (see Sees. 3.3 and 3.4), the effect of the dampers on the wind load stresses is accounted for in the determination of equivalent static wind loads using a total damping ratio of 2.5 percent (see Chapter 4).

3.2.2 Coordinate System, Nomenclature, and Models Assembly Overview

The large amount of data required to assemble the tower models dictated that the relational database

capability of the WTC-DB be used (see Sec. 2.4.4). The methodology for the development of the models

using the relational database is described in this section.

Coordinate System—The coordinate system for the model geometiy was based on the column layout

from the original drawings. Figure 3-1 shows the location of the X and Y axes for the global models and

the floor models. The Z coordinates were based on actual elevations of the towers. The original column

numbers were used throughout the models for member identification.

Nomenclature—A standard nomenclature for joints, frame names, and section names for use in the models was established. The nomenclature enables the user to know quickly where in the building a section is located by viewing any given piece of the model. Joint names generally included the column

number, tower letter, and floor level. Frame element names generally included the joint name at the 'j' end (second node). Section names were based on the section as described in the drawing book, and were

repeated for each steel yield strength assigned for that section. Alternatively, where the section was

unique to a particular member in the building, sections were named based on the frame member.

As an example, most nodes (or joints) in the tower models were named according to the following format:

• Column number

• Tower letter (A for WTC 1 and B for WTC 2)

• Floor level

• S for column splice nodes only

• J for spandrel splice nodes only

28 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

i noT) (3*2)

ir

ir

. - i

" f

.

,

CORE

60±

>^-H>rK>ocM>rK -c ->c>oooo-i:K>o-c-e - T»0 WAY LDKC SPAN 6T-r

Source: Reproduced with permission from The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 3-1. Global model coordinate axis location.

Figure 3-2 illustrates the detailed frame and joint nomenclature for a t\pical exterior wall panel.

Model Assembly Oven ien —.\n overv iew of the assembly of the data into the tower model is described

herein along w ith an expanded section on the programmatic assembly of the models.

Following a basic study of modeling techniques and testing of S.AP2000. Version 8 input fonnat and

capabilities, it was detennined that the best approach w as to di\ ide the model into six main parts and then

assemble them into a unified model. Manipulation of these individual parts was more efficient than

attempting to build the whole model simultaneously.

NISTNCSTAR 1-2A. WTC Investigation 29
Chapter 3

LSL -

USL-l -

lJSL-2

PANEL

COL 1 +USLtS COL2H/SL iS C(>L3tUSl.rS

COLl iUSL

COLl-^diSL-I)

COLlnLiSL.-2)

COL2HJSI

C0L2+iUSL-h

COL2nUSL-2)

C0I..3+IJS!..+J fOLJtUSL

C0L3+(USL-i)-fJ

C0L3-HijSL-l)

COL3+{USL-2)+J

(;-OL3t(USL-2j

USL: Upper Splice Level COLl ,2 J+USL.i-J ).!-2 w Joint name EC+JOiNT ABOVE: Column name

ES^.IOINT RIC5HT: Spandrel name

: Defined hy adjacent panel TYPICAL PANEL NOMENCLATURE

Figure 3-2. Typical exterior panel nomenclature.

30 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for tfie WTC Towers

The six initial models were:

Core columns

• Exterior wall, foundation to floor 4

• Exterior wall trees (floors 4 to 9)

• Exterior wall, floors 9 to 1 06

• Exterior wall floors 107 to 110

• Hat truss

For the core columns and exterior walls at floors 9 to 106, most of the analysis input files were generated

from queries of the WTC-DB. The other four parts of the model were assembled primarily in a more

con\ entional manner.

Core columns and exterior wall panels (floors 9 to 106) were the greatest data-intensive challenges in the model development. Both parts included a large number of frame members and section and material

property \ ariations. The quer\' files were used to gather the necessary data, and then simple computer

programming was used to convert the data into the SAP2000 input file format. Four main input tables for the SAP2000 input file were developed programmatically:

• Joint coordinates table

• Connectivity-frame/cable table

• Frame section properties tables

- Frame section properties 1 —general

- Frame section properties 5—non-prismatic

- Section designer properties 04—shape 1/wide flange

- Section designer properties 05—shape channel

- Section designer properties 1 1 —shape plate

• Frame assignments table

• Gravity and wind load assignments

The remaining data were added directly in the SAP2000 model;

• Material properties

• Frame local axis

NISTNCSTAR 1-2A. WTC Investigation 31
Chapter 3

• Joint restraint

• Insertion point

• Constraint

After the joint coordinates, connectivity, frame section properties, and frame assignments were complete

for the six parts, the individual models were combined into a unified model. Rigid floor diaphragms,

flexible floor diaphragms, core bracings, gravity loads, wind loads, and masses were then added to the unified model. After assembly of the model, the assignment of properties for selected model elements was spot-checked, and the model was executed to verify its perfonnance.

The development of the WTC 1 and WTC 2 models were separate and consecutive endeavors. The

lessons learned in the assembly of the WTC 1 model were applied to the development of the WTC 2 model. While there were only minor differences in the basic structural systems of the two towers, there were significant differences in section and material properties, and additional column transfers at the lower levels in WTC 2.

Isometric views of the complete WTC 1 model are shown in Fig. 3-3. Elevations of the complete WTC 2

model are shown in Fig. 3^. A summary of the size of the global models of WTC 1 and WTC 2 is presented in Table 3-1. The following presents the details of each of the six parts used in the development of the unified global models for WTC 1 and WTC 2.

3.2.3 Core Columns Modeling

Core column coordinates were tabulated based on the structural drawings. Column locations were

typically referenced at their centerlines. Columns on lines 500 and 1000, however, were located in plan

drawings along most of their height according to the face of the column to which the floor trusses frame

(i.e., WTC 1 north face for 500 columns and south face for 1000 columns). The centerline of these

columns was based on their dimensions given in the drawing books. Where these column centerlines

varied along the height of the towers (typically 1 1/2 in. between three-story pieces), a representative

location was chosen to define the column node. Thus, the column coordinate at floor 106 was used as a constant along the tower height because at this level, these columns aligned with the hat truss above.

Offsets were not used to shift the column locations because the floor framing needed to equilibrate such

offsets was not included in the model.

The spandrel centerline elevation was selected as the representative floor elevation for exterior columns

and used also for core columns. If there were no spandrels in exterior panels, reference elevations were

used for the core columns. The reference elevations were defined in the original drawings and

corresponded to the elevations of the top of the concrete floor.

There were over 5,000 nodes in the core column model. This amount of data required that the Interactive

Database input table of SAP2000 be set up using a macro. These data were converted to text file format

and later imported into SAP. Built-up sections were defined as Section Designer sections, and wide

flange shapes were defined directly from "SectionWFl.pro" file (see Sec. 2.6.5). All section names were

identical to those in the database. Around 1,280 Section Designer sections were defined in this model and

imported through the Interactive Database function of SAP2000 to the model.

32 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers
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ure 3-4. Frame view of the WTC 2 model: exterior wall elevation and interior

section illustrating the core columns, core bracing, and hat truss.

NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

Table 3-1. Approximate size of the reference structural models (rounded).

Model

Number of

Joints Degrees of Freedom

Number of Frame ElementsNumber of

Shell Elements

Total Number

of Elements

WTC 1 global model' 53.700 218,700 73.900 10.000 83,900

WTC 2 global moder 51.200 200,000 73.700 4.800 78,500

Txpical truss-framed model 28.100 166,000 27.700 14.800 42,500

TNjjical beam-framed model 6.500 35.700 7.500 4,600 12,100

a. Model does not include floors except for flexible diaphragms at 17 floors as explained later.

The core columns were defined as frame members spanning from node to node at the representative floor elevations. Splices in core columns occurred typically 3 ft above the floor level. In the models, however,

the splice was considered to occur at the floor level, and nodes were only defined at these levels

(i.e., typically at spandrel centerlines). Most three-story column pieces were unique, as tabulated in the WTC-DB (Drawing Book 3). A section for each three-story piece was defined and then assigned to each

of the three frame members that made up that column. Using the SAP2000 shading feature to graphically

show the section on the model, each frame was rotated to its proper orientation based on the structural drawings.

In the as-designed drawings, there were strap anchors connecting the core columns to the concrete floor

slab to provide lateral bracing for the column. At floor 26 of WTC 1, the straps at column 901 were removed during a renovation project that was engineered by a finn other than Leslie E. Robertson

Associates, R.L.L.P. (see Sec. 2.5.4). The loss of the straps at this location was included in the model by

releasing the column from the diaphragm in the direction of the straps.

3.2.4 Exterior Wall, Foundation to Floor 4 Modeling

The models of the exterior wall up to elevation 363 ft were developed manually, assigning joints and

members connectivity as shown in the drawings. The elevation drawings show that below elevation

363 ft, columns were typically spaced at 10 ft and braced with spandrels and diagonals. Joints were

defined at all locations where diagonals braced the columns. However, when coordinates were not given

in the drawings, joint coordinates were determined based on the geometry of the diagonal. Details in WTC Drawing Book 1 show that the column-diagonal intersections had continuity. Joints at elevation

253 ft (level B-5) were defined only where the diagonals connect to the columns, since the tower floor did

not frame into the exterior spandrels at that floor.

W'here noted in elevation drawings, spandrel centerline elevations were used to define joint coordinates.

Additionally, joints were defined at the spandrel splice midway between two columns at elevation 350 ft 3 in. (floor 3) and at elevation 329 ft 3 in. (floor 2) to allow for section type transitions.

The majority of the elements at these levels were defined as Section Designer sections, except for box

shapes, which were defined as "Box/Tube." Channel shapes were defined directly from the "SectionWFl.pro" file (see Sec. 2.6.5). All section names were identical to those in the database. Around 200 sections were defined in this model using the Interactive Database function of SAP2000,

which was used to import data into the model.

NISTNCSTAR 1-2A, WTC Investigation 35
Chapter 3

Typical columns were connected from bottom to top, and typical spandrels were connected from left to

right. The SAP2000 program allows assignment of rigid zone factors to frame end offsets to account for the overlap of cross sections. At the intersection of columns and spandrels, 100 percent rigidity for the column and the spandrels were assigned due to the large size of both columns and spandrels. Using the SAP2000 shading feature to graphically show the section on the model, each frame was rotated to its proper orientation based on the structural drawings.

Refer to Fig. 3-5 for a frame view and rendered view of the exterior wall (foundation to floor 9) of the WTC 1 model. The figure also shows the core columns and core bracings.

Figure 3-5. Frame view and rendered view of the WTC 1 model (foundation to floor 9).

3.2.5 Exterior Wall Trees (Floor 4 to 9) Modeling

The panels of the exterior wall between elevation 363 ft and elevation 41 8 ft 1 1 1/2 in. were called

exterior wall trees. At the exterior wall trees, the typical exterior wall columns transitioned from a spacing of 10 ft to a spacing of 3 ft 4 in. A typical exterior wall tree panel is shown in Fig. 3—6, which

indicates that each panel was divided into five different levels: B, C, D, E, and F. For each panel in the model, the three exterior columns from above elevation 418 ft 11 1/2 in. continued down to level D. At

that level, the three columns were connected by a horizontal rigid element to become one member, which

extended down to elevation 363 ft.

In the model, the tree was also the location where the column insertion point transitioned from the inside

face (at the spandrel) of the upper column to the centerline of the lower column. Between levels B and D

(see Fig. 3-6), the location of the spandrel transitioned from 6 1/2 in. offset from the exterior column

reference line to the center of this reference line. Within the floor 9 spandrel, the exterior columns

tapered; however, in the model, the tapering of the columns was not included because frame end length

offsets were assigned to the columns to account for the rigidity of the spandrels.

Through the height of level C, the box-shaped columns tapered (Fig. 3-6). In the model, non-prismatic

members were used to model the tapering columns. The columns started to taper at the bottom of the spandrel at level B, and ceased to taper at the top of the spandrel at level D. The dimensions of the

36 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

columns at the spandrel edges were defined in the drawing book. In the model, the column extended from

the centerline of the spandrel at level B to 1 ft below the top of the spandrel at level D (see discussion for level D below). Therefore, in order to obtain the correct section properties along the length, the dimensions of the section at the joints were interpolated based on the dimensions of the section at the spandrel edges shown in the drawing book. The section properties of the tapering column were assumed

to vary linearly between the two sections. Frame end length offsets were assigned to the columns to account for the rigidit>' of the spandrel at level B and the one foot dimension at level D.

WORTHINGTON 5K1LLING, HELLE & JACKSON Civil & SfJUCtura! Engineers

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Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 3-6. Exterior wall tree panel (taken from Drawing Book 2, page 2-AB2-2).

At level D, two transitions occurred in the model. The first transition was for the exterior columns, where

the three columns coming down from level C were connected by a horizontal rigid element to become one member at the bottom of the tree. This frame member consisted of the three exterior columns and the spandrel plate. Another horizontal member of the same section properties with the spandrel plate was

also defined and connected between the neighboring exterior wall trees. This member connected the neighboring exterior wall trees and provided lateral bracing for the columns. Frame end length offsets

NISTNCSTAR 1-2A. WTC Investigation 37
Chapter 3

were assigned to the spandrel to account for the overlap of the spandrel plate with the frame member,

which also included the spandrel plate. The transition of the three members into one member was

assumed to occur at one foot below the top of the spandrel at level D to account for the fact that the spandrel becomes engaged with the exterior columns after being connected to the exterior columns for a

certain distance. Hence, the joints were defined at one foot below the top of the spandrel at level D.

There was a second transition at level D (Fig. 3-6). The nodes for the exterior wall columns were

typically defined at 6 1/2 in. offset from the exterior column reference line, but for the joints at and below

level D in the exterior wall tree, the joint coordinates were defined along the exterior column reference

line. As a result, for the column member that framed between the nodes at levels B and D, a rigid joint

offset of 6 1/2 in. was assigned at the top of the member using a rigid body constraint, while no offset was

assigned at the bottom. Therefore, the column remained a vertically straight element while being

connected to nodes that were not aligned vertically.

At level E, the exterior columns tapered and had two different types of cross section (Fig. 3-7). For each

panel, the exterior column transitioned from Section b-b in Fig. 3-7 into a box-shaped column (Sec. c-c

in Fig. 3-7). The location of the transition between the different types of cross section varied for different column types from 5 ft 8 in. to 6 ft 4 in. measured from the bottom of level E. In the model, the transition was assumed to be at 6 ft measured from the bottom of level E. For each panel, the exterior column at level E was modeled as two non-prismatic members. The top section of the first non-prismatic member

consisted of three box-shaped columns and a middle plate, while the bottom section was a box-shaped

column (Sec. c-c in Fig. 3-7). The properties were assumed to vai"y linearly between the two sections. The second non-prismatic member was a tapering box shaped column (Sec. c-c in Fig. 3-7), and again, the properties were assumed to vary linearly between the two sections. At level F, the exterior wall tree columns were prismatic box-shaped columns.

The final model of a typical tree is illustrated in Fig. 3-8.

3.2.6 Exterior Wall (Floor 9 to 106) Modeling

In plan, column and spandrel members connected at nodes located at the outside face of the spandrel,

6 1/2 in. from the exterior column reference line (see Fig. 3-9). The columns were offset horizontally, or

'inserted,' at this node using an insertion point located at the centerline of plate 3. Insertion points were

not adjusted for spandrel thickness. With this modeling, gravity and wind loads could be applied at the spandrel location.

In elevation, the columns and spandrel members connected at the spandrel centerline, typically 12 1/2 in. below the reference floor elevation (Fig. 3-9). The spandrels were then located coirectly without the need for offsets to be defined. The effect of applying loads at both the spandrel centerlines and the reference floor elevations was studied, and it was found that it resulted in a negligible difference in spandrel stresses.

For typical exterior wall panels (i.e., three columns wide by three stories high), nodes at five elevations were defined. The models included nodes at the three representative floor levels (defined at the spandrel

centerlines) as well as the upper and lower column splices. Diaphragms were assigned to all nodes at floor levels where concrete slabs existed to represent the high in-plane stiffness of the concrete floor

slabs.

38 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

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Source: Reproduced with permission of The Port Authority of New York and New Jersey.

Figure 3-7. Exterior wall tree: as-built cross sections for level E (taken from

Drawing Book 2, page 2-AB2-13).

Figure 3-8. Frame view and rendered view of an exterior wall tree.

NISTNCSTAR 1-2A. WTC Investigation 39
Chapter 3

Cp Cp Cp

Spandrel

Column

j,, JSLiSl i-^i- See Eel.

i [^varies ^'^ Varies Fl 107 4-AB2-iS \Tyclcal

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(See t-AB2-ll)

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••c-c'

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 3-9. Typical WTC tower exterior wall panel.

The SAP2000 program allows assignment of rigid zone factors to frame end offsets to account for the overlap of cross-sections. In the global model, 50 percent rigidity for the column and 100 percent rigidity for the spandrels were assigned for the typical exterior wall panels to match the lateral deflection of the

detailed shell model of the panel based on the parametric study resuhs (see Sec. 3.5.1 ). It was also found

that, due to the relatively large depth of the spandrels and the close spacing between the columns, the spandrels contributed to the axial stiffness of the columns in the panels. This contribution was estimated

to range from 20 percent to 28 percent increase in the vertical stiffness of the panels. Therefore, a frame

property multiplier for the exterior wall column's cross-sectional area was used to provide a 25 percent

increase in columns' axial stiffness (see Sec. 3.5.1).

For exterior wall comer panels, 25 percent rigidity for the columns and 50 percent rigidity for the spandrels were assigned based on the parametric study results (see Sec. 3.5.2). Also, an area modifier

40 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

was used to provide a 25 percent increase in the axial stiffness of the two continuous columns of the comer panels (Sec. 3.5.2). No modifier was used for the 100, 200, 300, and 400 series intennittent

columns.

Exterior column t>'pes were defined in Drawing Book 4. A few types (100 series typical, 300 series at mechanical floors, and 400 to 500 series at corners) repeated extensively throughout the towers, with steel yield strengths that varied from 36 ksi to 100 ksi. Since SAP2000 does not allow for the assignment of

material properties at the member assignment stage, the number of different steel strengths was

determined for each exterior column type, and sections were defined for each. The section name included

the section number and the yield strength as tabulated in the drawing books.

Typical spandrels and comer panels were defined as rectangular shape and Section Designer section with

stiffener, respectively. The top and bottom stiffener of each comer spandrel were included in both the parametric study and the global models. The detail shows that the stiffeners were 6 in. plates of thickness

matching plate 2 in the comer column.

3.2.7 Exterior Wall (Floor 107 to 110) Modeling

Spandrel depths varied at floors 108 and 110. A weighted average of spandrel depth was detennined in order to define the average centerline elevation of the spandrels and therefore, the node elevation for the

entire floor.

For the 7 X 5 structural tube sections that were used in these floors, sections from the current American

Institute of Steel Construction (AISC) Manual were assigned, and modification factors of 1.04 were

applied to the section properties. The modifiers were used to match the section properties from the 6th Edition AISC Manual.

The exterior wall members from floors 107 to 1 10 were typically rolled shapes with F,.=42 ksi or Fy =50 ksi. Where not shown in the drawings as F, =50 ksi, Fy =42 ksi was used.

3.2.8 Hat Truss Modeling

In both WTC 1 and WTC 2, a tmss system referred to as a 'hat tmss' was constmcted between floor 107

and the roof The hat tmss system was intended to support the load of the antenna on top of the tower and

to interconnect the exterior walls to the core. The hat truss was made up of four trusses spanning

perpendicularly to the long direction of the core and four tmsses spanning perpendicularly to the short- direction of the core (refer to Figs. 3-10 and 3-1 1).

Frame members between floors 107 and 1 10 were assigned to the model according to plan and elevation

drawings of the hat tmss. Node locations were set to coincide with the centerline of spandrels at the

exterior wall. Columns, diagonals, and beams were included in the model. All columns and diagonals

shown in drawings SA/B-^00 through SA/B-404 were included in the model. Floor beams that did not

participate in the hat truss system were not included in the model, unless they were used to transfer truss chords or core columns. Flexible floor diaphragms were used in this area.

NISTNCSTAR 1-2A, WTC Investigation 41
Chapter 3

Coordinates were generally not given at floor 109, as this level did not contain a complete concrete floor

slab. The geometi-y of the diagonals, columns, and beams was used to detennine the location of the node

where the diagonal would intersect floor 109. Unless othewise noted in the drawings, diagonals and

/

-

— y X

\

//

/

- I

\ X\ /

\ X / X

Figure 3-10. As-modeled plan of the WTC 1 hat truss.

Figure 3-1 1 . Rendered 3-D model of the WTC 1 hat truss (prior to assembly in the

unified global model).

42 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

columns were assumed to be non-composite, and floor beams were assumed to be composite. Hat truss diagonals, main chords, and main columns were modeled with continuous joints. Hat truss beams,

however, had pinned ends.

3.2.9 Flexible and Rigid Floor Diaphragm Modeling

For most floors, rigid diaphragms provide for a sufficiently accurate representation of the flow of forces

and defomiations for global structural response. This is a customary engineering practice for lateral force

analyses. In cases where the flow of forces and deformations would be affected significantly by the use of rigid diaphragms, the floors were modeled as flexible diaphragms.

The floor models described in Sees. 3.3 and 3.4 were used to develop the flexible diaphragm stiffness utilized within the global models. Section 3.5.3 outlines the study for the detennination of the in-plane

diaphragm stiffness of the detailed floor models, using that in-plane stiffness to aixive at an equivalent

shell element floor model. The equivalent shell element floor was used to represent the in-plane floor

stiffness in the global model. The shell elements attached to all exterior wall columns and core columns.

Flexible diaphragms were used at the floors of the towers in the core of the atrium area, in the mechanical

floors, and in the floors of the hat trusses. The floors modeled using flexible diaphragms were floors 3, 4,

5, 6, 7, 9 (atrium levels); 41, 42, 43, 75, 76, 77 (mechanical levels); 107, 108, 109, 110, and roof (hat truss region) of both towers. For the floors of the hat trusses, the stiffness of the flexible diaphragms was

reduced by a factor of twenty, which resulted in diaphragm forces that were consistent with the diaphragm strength. This was done to achieve a reasonable agreement between the as-modeled stiffness of the floor diaphragm and the strength of the diaphragm to resist the forces it attracts. In the case of

concrete floor slabs at the top and bottom chords of outrigger trusses or hat trusses, it has been found

consistently that floor slabs modeled at nominal uncracked stiffness attract forces completely out of scale with the strength of the slabs. Based on parametric studies for a series of major high rise buildings, it became a customary engineering practice to reduce the stiffness of such floor slabs. This reduction factor was found, based on the parametric studies, to be about twenty. This reduction accounts for cracking and

other factors that are consistent with the expected behavior of the floor diaphragms.

3.2.10 Verification of Global Models

Several steps were taken to verify the model input. SAP2000 Version 8 offers a 'shading' option once a model has been buih with frame section assignments. This allows the user to view the members as the program interpreted their input. The shading option was helpful for using section-designed shapes, and

for verifying the orientation (i.e., local axes) of members. Note that shading is not correct when two

Section Designer sections are used in non-prismatic members, so orientations for these sections were

verified by reviewing their local axis member properties. The work was independently reviewed by

engineers not associated with the initial model development.

Once the models were completed, checks for gravity and wind loads were performed. The overall performance of the tower models under these loads was found to be reasonable by checking deforaiations,

stresses, reactions, etc.

NISTNCSTAR 1-2A, WTC Investigation 43
Chapter 3

3.2.11 Results of Modal Analysis

Verification of the global models also included comparing the calculated natural frequencies with

frequencies measured from accelerometers placed atop WTC 1. The natural frequencies for WTC 1 and

WTC 2 global models were estimated using modal analysis. The mass of the towers was estimated from

the construction and superimposed dead loads only (see Chapter 4 for further details). No live loads were

used in estimating the floor masses for the modal analysis. The calculated first six periods and

frequencies for WTC 1 and WTC 2 are presented in Table 3-2 without P-A effects and in Table 3-3 with

P-A effects. The first three mode shapes are presented in Fig. 3-12.

Table 3-2. Calculated first six periods and frequencies without P-A effects for the

WTC towers.

Direction

of Motion

WTC 1 WTC 2

Mode

Frequency

(Hz) Period (s) Mode

Frequency

(Hz) Period (s) N-S 1 0.088 11.4 2 0.093 10.7 E-W 2 0.093 10.7 1 0.088 11.4

Torsion 3 0.192 5.2 3 0.192 5.2 N-S 4 0.233 4.3 5 0.263 3.8 E-W 5 0,263 3.8 4 0.238 4.2

Torsion 6 0.417 2.4 6 0.417 2.4

Table 3-3. Calculated first six periods and frequencies with P-A effects for the

WTC towers.

Direction

of Motion

WTC 1 WTC 2

Mode

Frequency

(Hz) Period (s) Mode

Frequency

(Hz) Period (s) N-S 1 0.083 12.1 2 0.089 11.2 E-W 2 0.088 11.3 1 0.083 12.1

Torsion 3 0.189 5.3 3 0.192 5.2 N-S 4 0.227 4.4 5 0.250 4 E-W 5 0.250 4 4 0.227 4.4

Torsion 8 0.455 2.2 8 0.455 2.2

44 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

(a) (b) (c)

Figure 3-12. Mode shapes of WTC 1 (exaggerated): (a) first mode shape (E-W),

(b) second mode shape (N-S), (c) Third mode shape (torsion).

NISTNCSTAR 1-2A, WTC Investigation 45
Chapter 3

Table 3^ presents a comparison of the calculated first three natural frequencies and periods (N-S

direction, E-W direction, and torsion) against measured frequencies and periods obtained from WTC 1 based on analyzing acceleration records obtained from accelerometers installed on the top of WTC 1. The table also includes the values of the natural periods and frequencies predicted in the original design.

The table shows good agreement between the calculated and measured periods, especially for the periods

estimated without P-A effects, thus indicating that the reference global model is a reasonable

representation of the actual structure. No measured periods or frequencies were available for WTC 2.

Table 3-4. Comparison of measured and calculated first two natural frequencies and

periods for WTC 1.

Data Source/ Event Date Wind Speed &

Direction

Frequency (HZ) Period (s)

Direction of Motion Direction of Motion

N-S E-W Torsion N-S E-W 1 Torsion

Historical Data

October 11, 1978 11.5 mph, E/SE 0.098 0.105 0.211 10.2 9.5 4.7 January 24, 1979 33 mph, E/SE 0.089 0.093 0.203 11.2 10.8 4.9 March 21, 1980 41 mph, E/SE 0.085 0.092 0.201 11.8 10.9 5.0 Deem be!- 11, 1992 0.087 0.092 11.5 10.9

February 2, 1993^ 20 mph, NW 0.085 0.093 0.204 11.8 10.8 4.9 March 13, 1993^ 32 mph, NW 0.085 0.094 0.199 11.8 10.6 5.0 March 10, 1994^ 14 mph, W 0.094 0.094 0.196 10.6 10.6 5.1 December 25, 1994^ N 0.081 0.091 12.3 11.0 Average of Measured Data

Average 0.088 0.094 0.202 11.4 10.6 4.9 Orginal Design - Predicted Values

Theoretical Value 0.084 0.096 11.9 10.4 Reference Global Model

LERA/NIST - WTC 1 without P-Delta 0.088 0.093 0.192 11.4 10.7 5.2 LERA/NIST - WTC 1 with P-Delta 0.083 0.088 0.189 12.1 11.3 5.3

Notes: ^Reported frequency value is the average of the SW corner, NE corner and center core frequency measurements.

^Reported frequency is based on center core data only.

3.3 TYPICAL TRUSS-FRAMED FLOOR MODEL—FLOOR 96A

In order to select the typical truss-framed floor within the expanded impact and fire zones of both towers,

the drawings for floors 80 to 100 were reviewed to identify structural similarities. The summary of this review is provided in Appendix G, which shows a summary of the construction type and space usage for each floor, along with a categorization and description of floor types for both towers. It was found that floor 96 of WTC 1 (96A) represented the typical truss-framed floor in the expanded impact and fire

46 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

region for WTC 1 (floors 89A to 103 A). The only exception in this region of WTC 1 was floor 92. which

had an increased dead load capacity required for the support of secondary water lines.

Floor 96A was also representati\ e of the typical truss-framed floor in the expanded region for WTC 2

(floors 74B-88B). Specifically, floor 96A was similar to the truss framing at floor 74B and floors 84B

through 88B. Floors 78B and 79B were sky lobby and upper escalator floors, respectively. Both

contained long span trusses, which were similar to floor 96A, but also contained beam-framed floor construction in the entire short span area (where the escalators were located). Floors 80B through 83B

had beam framing in place of a single truss panel in the short span area, while the remaining area contained trusses which were similar to floor 96A.

Based on the abo\ e analysis, floor 96 of WTC 1 was selected as the overall representative truss-framed

floor for the majority of the expanded impact and fire zone in both towers and is described in the following sections (see Fig. 3-13). An isometric view of the typical truss-framed floor model is shown in Fig. 3-14. Table 3-1 includes a summary of the size of the 96A floor model. The following presents the major structural systems and components of the truss-framed floor model.

Type 1 - WTC Typical Truss Floor Panel Plan Tower A Floors: 1 0 - 24 60 -66

26 - 40 68 - 74

50 - 58 84 - 91 93 - 105

Note; All panel types within 1" length tolerance, except floors 10.1 1 . 39, 40. 70. & 71 which are within 6"-10"- Floors 72-74 vary 18"-26".

Tower B Floors; 14-24 60 -74

26 - 40 84 - 91 50-58 93-106

Note: HI = H6

Note: HR1 = HR6

FR1 ER1

G1

HI

J1

HR1

GR1

F1 El

DR1 CR1 BR1 A1 B1 C1 D1

CORE

D1 CI B1 A1 BR1 CR1 DR1

El F1

GR1

HR1

J1

H1

G1

ER1 FR1

Note: J1 =K1 = KR1

Note: HI =M1 = MR1

(all C32T5 Trusses)

Figure 3-13. Typical truss-framed floor panels arrangement.

NISTNCSTAR 1-2A, WTC Investigation 47
Chapter 3

Figure 3-14. Typical truss-framed floor model (floor 96A), slab not shown.

3.3.1 Primary Trusses

The primary trusses consisted of double angle top and bottom chords, which were 29 in. out-to-out of the chords. The trusses acted compositely with a 4 in. concrete slab on 1 1/2 in. metal deck. For a typical

long-span truss, C32T1, the top chord consisted of two angles 2 in. by 1.5 in. by 0.25 in., short legs backto-back (SLB), and the bottom chord consisted of two angles 3 in. by 2 in. by 0.37 in., SLB. The distance

between the centroid of the two chords was calculated to be 28.05 in. The distance from the centroid of

the top chord to the neutral axis of the transfonned composite slab with top chord was calculated to be

1.93 in. The sum of the distances, thus, was 28.05 + 1.93 = 29.98 in. (Fig. 3-15). Dimensions for the short-span trusses were essentially identical to those for the long-span trusses. Therefore, in the model,

30.0 in. was taken as the typical distance between the top and bottom chords for both short- and long-span

primary trusses.

In the long-span truss zone, the two individual primary trusses, which were part of the same floor panel

and attached to the same column, were separated (typically) by a distance of 7 1/8 in. At the joint

between panels, the distance between the abutting long-span trusses was 7 1/2 in. Therefore, in the model, 7 1/2 in. was used as the spacing between all long-span primary trusses. In the short-span truss zone, two individual trusses which attached to the same column were separated by a distance that varied

between 4 7/8 in., 5 in., and 5 1/4 in. In the model, the typical spacing between all short-span double

48 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

trusses was 5 in. The long span trusses in the two-way zone had an as-modeled length of 58 ft 10 in., while the long span trusses in the one-way zone had an as-modeled length of 59 ft 8 in.

C32T1 (Primary Truss Section)

^ / inio siao 4 t/— V-A

4" Slab

Web member extension

into slab 2.48"

L2 X 1.5 X 0.25

13x2x0.37

If,

i0.414"

28.05"

29.98" = 30"

N.A. Combined Slab +

Primary Truss Double L

0.537"

ACTUAL

^-^]-L^

(Note: 2"" Truss of Pair Not Shown)

IVIODEL

Figure 3-15. Typical primary truss cross-section, as-built and as-modeled

transformed truss work points.

The diagonal web bars for the primary trusses were most often 1 .09 in. diameter bars. Therefore, for double angle shapes in the primary trusses, 1 .09 in. was taken as the distance between the two angles.

This holds true for primarv' trusses v\ here bar diameters varied between 0.92 in. and 1 . 1 4 in.

The as-built truss diagonals had end fixitv'. but were considered pinned for the analysis. Pinning the diagonals is conserv ative and pro\ ides an upper bound of the gravity' load stresses. To mitigate the effect of the pinned member approach, end length offsets were used for the truss diagonals to compensate for the difference in the as-built diagonal unbraced length and the model unbraced length. The as-built unbraced length for a typical diagonal in a primary' truss was 32.4 in., while the modeled member length was 36.05 in., and therefore, an end offset of 1 .8 in. was used at both ends. Similarly, for the bridging

trusses, the actual unbraced length for a typical diagonal of a bridging truss was 29 in., while the modeled

length was 30.66 in. Therefore, an end offset of 0.83 in. was used at both ends. A rigid zone factor of

100 percent was used for all offset zones.

In the model, the deck support angles, typically 3 in. by 2 in. by 0.75 in. were located in the same plane as

the combined truss top chord and composhe slab centroid.

3.3.2 Bridging Trusses

The bridging trusses were 24 in. deep, edge-to-edge, with double angle chords. For a typical bridging

truss, 24T1 1, the top and bottom chords consisted of two angles 1.5 in. by 1.25 in. by 0.23 in., SLB. The

distance between the centroid of the two chords was 23.26 in. The distance used as the offset between the top and bottom chords for all bridging trusses was taken as 23.25 in. (Fig. 3-16). The distance between

the work points of the top chord of the bridging truss and the top chord of the primary trusses and

equivalent slab plate for truss 24T1 1 was calculated to be 3.39 in. This distance was selected for all

NISTNCSTAR 1-2A. WTC Investigation 49
Chapter 3

bridging trusses to be 3.375 in. As in the as-built structure, the bridging truss was not connected along its length to the slab shell elements in the model. At the intersection of the top chords of the primary and the bridging trusses, the intersection was modeled using vertical rigid links, connected in turn to the slab shell elements representing the concrete slab.

Figure 3-16. Typical bridging truss cross-section, as-built and as-modeled

transformed truss work points.

The original contract drawings indicated that the bottom chord of the primary trusses was connected to the bottom chord of the bridging trusses along the length of the primary trusses only on column lines 111,

149, 311, and 349. The connection consisted of double angles 2 in. by 1 1/2 in. by 0.25 in. welded to both

primary and bridging truss lower chord members as shown in Fig. 3-17. These connection angles were

included in the model. The Laclede (the manufacturer of the floor truss panels) shop drawings indicated

that the bottom chords of the primary trusses were similarly connected to the bottom chords of the bridging trusses at all their intersections for construction purposes. These were conservatively not included in the models.

50 NISTNCSTAR 1-2A. WTC Investigation

24T11 (Bridging Truss Section)

N.A. Combined Slab +

Primary Truss Double L

0.368" ACTUAL MODEL
Development of Reference Structural Models for the WTC Towers

\

I k'rc72!.o6y—r

^ Priman tmss lower chord

/4 V 3€G

ecr. side

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 3-17. Connection between bottom chords of primary and bridging trusses.

For bridging trusses in the model, a 0.75 in. angle gap was used for trusses with web bar diameters that varied between 0.75 in. and 0.98 in.

3.3.3 Truss Member Cover Plates

In 30 percent of the floor area, truss members were supplemented with cover plates. The members with

additional plates included top chords, web members, and most typically bottom chords. Section

properties were calculated with SAP2000 Section Designer. The primary truss top chords were

reinforced with an additional set of double angles at truss end connections. At these locations, the work

points for the section were located at the centroid of the composite double angle and concrete slab.

The Laclede shop drawings indicated plates 3/8 in. by 3 in. connecting the bottom chord of the primary

truss pairs together at each end and where intersected by a bridging truss. These plates were included in the model.

3.3.4 Viscoelastic Dampers

Viscoelastic dampers were located where the bottom chords of the long span, short span, and bridging

trusses intersected the exterior columns (see Chapter 1 for description and details). The dampers resisted

static and quasi-static loads (such as gravity loads) at the time of load application. Immediately following

load application, the dampers shed load until the stress in the dampers was dissipated. A placeholder

element was located in the model at the damper location.

3.3.5 Strap Anchors

Exterior columns not supporting a truss or truss pair were anchored to the floor diaphragm by strap

anchors. TTiese strap anchors were connected to the columns by complete penetration welds. The strap

anchors were then connected to the slab with shear stud connectors and to the top chords of the trusses by

fillet welds. The straps were included in the model and located in the plane of the centroid of the

NISTNCSTAR 1-2A. WTC Investigation 51
Chapter 3

composite top chord. Also, in the model the work points intersected with the centerline of the column and

used a rigid link to attach back to the spandrel (see Fig. 3-1 8).

i —1 * Trusses

/

/

/ / /

/

/ /

/

/

\

) Deck Support / / Straps

.

Y \. /

'\ /

\ / \ //

Rigid Link /

Frame Elements /

\

\\

Columns

\

Spandrel PL

•

1' Attachment PL to Slab f ^—Attachment PL to Slab Key: PL, Plate. Note: Slab not shown.

Figure 3-18. Strap anchors modeling.

3.3.6 Concrete Slab and Metal Deck

Outside the core, the priinary trusses acted compositely with the 4 in. concrete slab on 1 1/2 in. metal

deck. In the inodel, the average depth of the slab plus deck was modeled as 4.35 in. The concrete slab consisted of lightweight concrete with a self-weight of 100 pcf and a design compressive strength,

f'c= 3,000 psi. The concrete modulus of elasticity, Ec, used for modeling was 1,810 ksi, and the calculated modular ratio, n=E/E,; was taken as 16, where is the steel modulus of elasticity. These

values are consistent with those included in the WTC Structural Design Criteria Book.

Typically, inside the core, the beams acted compositely with a 4 1/2 in. fonned concrete slab. The

concrete slab consisted of normal weight concrete with a self-weight of 150 pcf and a design compressive

strength, /V= 3000 psi. The concrete modulus of elasticity, £(. used for modehng was 3,320 ksi, and the calculated n ratio. EJE, , was taken as 8.7.

The floors of the WTC towers had an in-floor electrical distribution system of electrified metal deck and

trench headers. The effects of the in-slab trench headers were accoirmiodated in the inodel by reducing

the slab shell element thickness. A 1 ft 8 in. wide shell panel (the typical truss-floor shell mesh size) was

reduced in thickness from 4.35 in. to 2.35 in. or 1.35 in. at the trench header locations per drawing

SCA-109 (Floor 96A Structural Concrete Floor Plan).

3.3.7 Verification of the 96th Floor Model

Several steps were taken to verify the model input. SAP2000 Version 8 offers a 'shading' option once a model has been built with frame section assignments. This allows the user to view the members as the program has interpreted their input. The shading option was helpful for using section designed shapes,

52 NISTNCSTAR 1-2A. WTC Investigation
Development of Reference Structural Models for tfie WTC Towers

and for verifying the orientation (i.e.. local axes) of members. The work was independently reviewed by

engineers not associated with the initial model development.

Once the model was completed, checks were performed for gravity loads. All superimposed dead loads

and live loads included in the model were based on WTC Design Criteria; self weight was m accounted

for by SAP2000. To justify the modeling assumptions, several studies were performed to compare stress results to hand calculations for representative composite sections. Hand calculations were used to estimate deflections and member stresses for a simply supported composite truss under gravity loading.

For the composite truss sections, the steel stress resuhs were within 4 percent of those calculated by

SAP2000 for the long-span truss and 3 percent for the short-span truss. Deflections for the beams and

trusses matched hand calculations within 5 percent to 1 5 percent.

3.4 TYPICAL BEAM-FRAMED FLOOR MODEL—FLOOR 75B

As described in Section 3.3 for truss-framed floors, the structural drawings were reviewed to identify

structural similarities between the beam-framed floors within the expanded impact and fire zones of both

towers (see Appendix G). It was found that floor 75 of WTC 2 (75B) represented the typical beamframed floor in the expanded impact zone for WTC 2 (floors 74B to 88B). There were no beam-framed

floors within the expanded impact zone of WTC 1

.

Floors 75 and 76 of WTC 2, lower and upper mechanical equipment room (MER) floors, respectively, were typical of the lower three MER floor pairs in both towers (floors 7 and 8, 41 and 42, and 75 and 76

for both WTC 1 and WTC 2). Floor 77 of WTC 2, a lower escalator floor, was a beam-framed floor similar to the lower floor of the MER floor pairs, i.e., floor 75B.

Based on the above analysis, floor 75 of WTC 2 was selected as the overall representative beam-framed

floor for the expanded impact and fire zone in both towers and is described in the following sections (see

Fig. 3-19). An isometric view of the typical beam-framed floor model is illustrated in Fig. 3-20.

Table 3-1 includes a summary of the size of the 75B floor model. The following presents the major

structural systems and components of the beam-framed floor model.

NISTNCSTAR 1-2A. WTC Investigation 53
Chapter 3

Type 12 - WTC Beam Framed Floor Floor Plan

Towers A& B MER Floors: 7,41,75,108 Towers A & B Near MER Floors: 9,43,77,107,110,Roof

Beams

Beams CORE Beams

Beams

Figure 3-19. Typical beam-framed floor arrangement.

54

Figure 3-20. Typical beam-framed floor model (floor 75B).

NISTNCSTAR 1-2A. WTC Investigation
Development of Reference Structural Models for the WTC Towers

3.4.1 Composite Beams

The beams in the model were located at the elevation of the centerline of the concrete slab. The insertion point for the beams was set at the beam top flange, and then the beam was offset down by one-half the thickness of the slab. The beam was rigidly linked with the slab to simulate the composite action. This

option provided for accurate estimation of the composite stiffness of the floor.

For beams with cover plates, the properties were calculated by SAP2000 Section Designer, and the slab,

beam, and reinforcing plates were rigidly linked.

3.4.2 Horizontal Trusses

Exterior columns which did not support a beam were connected to the floor for bracing puiposes by

horizontal trusses. These exterior horizontal trusses were anchored to the columns with complete joint

penetration welds. The horizontal trusses were then connected with shear stud connectors to the slab. The truss angles (typically 4 in. by 4 in. by 5/16 in.) were then field welded to the top flange of the beams.

In the model, the work points intersected with the centerline of the column and used a rigid link to attach back to the spandrel. The truss members were located in the plane of the centroid of the composite top

chord (see Fig. 3-21).

* Spandrel Plate *

Figure 3-21. Horizontal truss modeling, slab not shown.

3.4.3 Concrete Slab and Metal Deck

Outside the core on the mechanical floors, the beams acted compositely with a 5 3/4 in. concrete slab on

1 1/2 in. metal deck. The average cross-sectional depth of the slab in the model was taken as 6.1 in. The

NISTNCSTAR 1-2A. WTC Investigation 55
Chapter 3

deck spanned between channels that, in turn, spanned between the floor beams. The concrete slab consisted of nonnal weight concrete with a self-weight of 150 pcf and a design compressive strength of

typically /V= 3,000 psi. The concrete modulus of elasticity, Ec, used for modeling was 3,320 ksi and the calculated modular ratio, /?, was taken as 8.7.

Typically, inside the core, the beams acted compositely with a 6 in. fonned concrete slab. The concrete

slab consisted of nonnal weight concrete with the same properties as concrete outside the core.

The mechanical floors had a 2 in. maximum depth topping slab both inside and outside the core. The

topping slab stiffness was not included in the models, but the weight was accounted for in the baseline

perfonnance analysis.

3.4.4 Viscoelastic Dampers

Viscoelastic dampers were located below the bottom flange of the beams where the beams intersected the

exterior columns (see Chapter 1 for description). Similar to floor 96A model, a placeholder element was

located in the model at the damper location.

3.4.5 Verification of the 75th Floor Model

Similar to the 96th floor model, the 'shading" option in SAP2000 was used to view the members as the program interpreted their input. The shading option was helpful for using section designed shapes, and

for verifying the orientation (i.e., local axes) of members. The work was independently reviewed by

engineers not associated with the initial model development.

Once the model was completed, checks were perfonned for gravity loads. All superimposed dead loads

and live loads included in the model were based on WTC Design Criteria; self-weight is accounted for by

SAP2000. To justify the modeling assumptions, several studies were perfonned to compare stress results

to hand calculations for representative composite sections. Hand calculations were used to estimate

deflections and member stresses for a simply supported composite beam under gravity loading. The

model yielded accurate steel stress results compared to hand calculations—around 1 percent for both

short- and long-span beams. Where the beams were built-up with reinforcing plates, it was found that SAP2000 Section Designer shapes were not calculating the stresses conectly, so instead, separate beam

and plate elements drawn over each other were inserted. This method yielded very accurate steel stress results—between 1 percent and 2 percent for both short- and long-span beams.

3.5 PARAMETRIC STUDIES

Modeling techniques employed in the development of the global models of WTC 1 and WTC 2 were

consistent with, but often more advanced than, the techniques typically employed in the analysis and

design of high-rise buildings. As such, building components were idealized so that overall perfonnance was replicated while appropriately reducing the computational requirements. The following describes the

studies undertaken to establish the idealizations used in the models, including typical exterior wall panels,

exterior comer panels, and flexible floor diaphragms.

56 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for tfie WTC Towers

3.5.1 Exterior Wall Columns/Spandrel Typical Panels (Floors 9 to 106)

A parametric study of typical three-column, three-spandrel exterior wall panels from the faces of the towers (floors 9 to 106) was perfonned using two modeling methods (see Fig. 3-22). The first model was

a detailed shell model, where each plate of each column or spandrel was specifically modeled, and the second was a simplified frame model. Internal column stiffeners were included in the shell model. The

parametric study assumed that the shell model best represented the as-built panel performance, and

therefore, it was used to tune the perfonnance of the frame model, which was used throughout the global

model (see Sec. 3.2.6). The objectives of the study were to (1) match the axial stiffness of the frame

model with the detailed shell model under gravity load and (2) match the inter-story drift of the two

models by modifying the rigidity of the column/spandrel intersections in the frame model.

Figure 3-22. Shell element and frame models of typical exterior wall panel.

For comparing the axial stiffness of the simplified frame model of the panel with the detailed shell model,

both models were loaded vertically while pin-supported at the bottom of the columns. The results indicated that the shell model was stiffer than the equivalent beam model due to the contribution of the spandrel beams to the columns' axial stiffness. This was due to the rigidity of the spandrel beams and the proximity between the columns. The parametric study on a wide range of panels over the height of the

NISTNCSTAR 1-2A. WTC Investigation 57
Chapter 3

towers showed that the vertical stiffness of the columns in the bottom third of the towers should be

increased by a factor in the range of 25 percent to 28 percent, and the columns in the middle and upper

thirds of towers should be increased by a factor in the range of 20 percent to 28 percent. Based on these

results, 25 percent increase of the axial stiffness of exterior columns was selected as a reasonable

representation for the panel vertical stiffness over the height of the towers between floors 9 and 106 (see Sec. 3.2.6).

For studying the lateral deformation of the exterior panels, panel properties were taken from three

different areas of the building. These included floors 79 to 82, 53 to 56, and 23 to 26. The defonnations

at points A, B, I, and II (see Fig. 3-23) were studied for three different panel locations and their respective spandrel and column thickness. The topmost columns were connected via a rigid link and

loaded in the plane of the panel and peipendicular to the column with a 100 kip-load. The boundary

conditions were as shown in Fig. 3-22.

Column

I

Spandrel

1

Figure 3-23. Selection of column and spandrel rigidity of typical exterior wall panel.

The lateral displacements found for the shell and frame models of typical exterior wall panels with varied

column and spandrel intersection rigidities are reported in Table 3-5. The study found that 50 percent

column rigidity and 1 00 percent spandrel rigidity in the frame model produced deflection results consistent with the shell model.

58 NISTNCSTAR 1-2A. WTC Investigation
Development of Reference Structural Models for the WTC Towers

Table 3-5. Lateral displacement (in.) for the shell and frame models of typical

exterior wall panel with varied column and spandrel rigidities.

Lateral displacement (in) Floor 79-82

Shell model

Frame model (Rigidity)

No rigidity C:50%, S:100% C:100%, S:100%

A 0.60 1.04 0.59 0.35 B 0.28 0.52 0.29 0.18

1 0.45 0.78 0.44 0.26

II 0.45 0.78 0.44 0.26

Floor 53-56

Shell model

Frame model (Rigidity)

No ngidity C:50%, S:100% C:100%, S;100%

A 0.26 0.43 0.27 0.18 B 0.12 0.22 0.14 0.11

1 0.19 0.32 0.2 0.15

II 0.19 0.32 0.2 0.15

Floor 23-26

Shell model

Frame model (Rigidity)

No rigidity C;50%, S:100% C:100%, 8:100%

A 0.21 0.37 0.21 0.12 B 0.1 0.18 0.1 0.06

1 0.16 0.28 0.16 0.09

II 0.16 0.28 0.16 0.09

3.5.2 Exterior Wall Columns/Spandrel Corner Panels (Floors 9 to 106)

A parametric study was performed of an exterior wall comer panel typical over each comer of the towers from floors 9 to 106. Similar to the exterior typical panels, to account for the contribution of the spandrels into the axial stiffness of the columns, it was found that an area modifier to provide a 25 percent

increase in the axial stiffness of the two continuous columns of the comer panels was suitable for modeling the columns' axial stiffness. No modifiers were needed for the intermittent columns.

The panel from floor 53 to 56 was selected to be representative, with two additional columns attached on

either side. The objective of the study was to match the inter-story drift of a detailed shell model and a simplified frame model of the comer panel by modifying the rigidity of the column/spandrel intersections

in the frame model. For this parametric study, the panel was straightened to simplify the study and to isolate the behavior of interest (see Fig. 3-24). The deformations at points Tl, T2, Bl, B2, and M2

(Fig. 3-25) were studied for representative column and spandrel plate dimensions. The topmost columns were connected via a rigid link and loaded in the plane of the panel and perpendicular to the column with

a 100 kip load.

The lateral displacements calculated for the shell and frame models of the typical exterior wall comer

panel with varied column and spandrel rigidities are reported in Table 3-6. The study indicated that 25 percent column rigidity and 50 percent spandrel rigidity in the frame model produced deflection results consistent with the shell model.

NISTNCSTAR 1-2A. WTC Investigation 59
Chapter 3

Figure 3-24. Shell element and frame models of typical exterior wall corner panel.

Typclal exterior column C:50%, S:100%

T1

Ml

Column

-Spandrel

Corner panel

Rigidity

Figure 3-25. Selection of column and spandrel rigidity of typical exterior wal

corner panel.

60 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

Table 3-6. Lateral displacement (in.) for the shell and frame models of typical exterior

wall corner panel with varied column and spandrel rigidities.

Floor 53-56

Shell model

Corner panel rigidity No rigidity C:25%, S:50% C:100%, S:100%

T1 0.227 0.236 0.222 0.152

12 0.227 0.236 0.222 0.152

Ml 0.149 0.154 0.149 0.102

B1 0.084 0.072 0.077 0.053

B2 0.084 0.072 0.077 0.053

As part of the in-house NIST review of the reference structural models (see NIST NCSTAR 1-2), a detailed shell element model of original comer panel (not straightened) was analyzed under lateral loads

to test the accuracy of the simplified frame model with 25 percent column rigidity and 50 percent

spandrel rigidity calculated above. Both the detailed and simplified models were loaded as shown in Fig. 3-26. The deflections calculated from the frame model were consistent with those estimated from

the shell model, indicating that the rigidities estimated using the straight model (Fig. 3-25) accurately

represented the actual comer panel behavior.

Figure 3-26. Detailed and simplified model of the exterior wall corner panel.

3.5.3 Flexible Floor Diaphragm

The floor models developed as described in Sees. 3.3 and 3.4 were used to develop the flexible diaphragm

stiffness used within the WTC 1 and WTC 2 global models. The in-plane diaphragm stiffness of the

NIST NCSTAR 1-2A. WTC Investigation 61
Chapter 3

detailed floor models was detemiined and used to arrive at an equivalent shell element floor model. This

flexible shell element floor model was then inserted in the global models at specific floors to capture the in-plane flow of forces and defomiations. These flexible diaphragms were not used throughout, as the

rigid diaphragms in the majority of floors provided for a sufficiently accurate representation of the flow of

forces and defonnations while keeping manageable the model's computational requirements. In the global models, flexible diaphragms were used at the beam-framed floors 3, 4, 5, 6, 7, 9, 41, 42, 43, 75, 76,

77, 107, 108, 109, 1 10, and roof of both towers. For floors 107, 108, 109, 110. and roof, the stiffness of

the flexible diaphragms was reduced to prevent these diaphragms from attracting large forces incompatible with the strength of the slabs (see Sec. 3.2.9).

Parametric studies were performed to compare the diaphragm stiffness of two different floor models for both the typical truss-framed floor and the beam-framed floor. The typical floor models were compared

with simplified equivalent models that duplicated the representation of the exterior wall columns, exterior

wall spandrels, core columns, and their boundary conditions. The floor framing, both inside and outside

the core, was replaced by shell elements. The material properties of the shell model matched the

properties of the concrete floor outside the core in the respective floor model.

The comparative floor models were loaded in the plane of the floors with a lateral load of 180 lb/ft (equivalent to 15 psf over the 12 ft story height) on both the windward and leeward faces. The column

base supports were released for the exterior wall columns along the loaded faces and for all core columns

to allow lateral translation only in the direction of loading.

The comparative models were executed to assess the horizontal deflection of the floor on both the windward and leeward sides of the model and for the case where the lateral loads were applied nonconcurrently along the 100 face and 200 face of the tower. Both the total horizontal deflection of the slab and the relative displacement between the windward and leeward sides were compared between the models. The shell thickness was modified to match the in-plane stiffness detennined by the detailed floor models.

The defonnations from the lateral load case using the 75th floor model of WTC 2 are illustrated in Fig. 3-27, while Fig. 3-28 shows the deformations of the simplified floor model. Fig. 3-29 shows the

lateral deflection of the north and south sides of the floor model under lateral load applied in the north

direction using the detailed and equivalent floor models.

62 NISTNCSTAR 1-2A, WTC Investigation
Development of Reference Structural Models for the WTC Towers

Note: Exaggerated scale. Figure 3-27. Deflection of typical beam-framed floor model due to lateral loading.

3

' /K\ /

-1^ I

"TTT W 'Vv /VX ,-

Note: Exaggerated scale. Figure 3-28. Deflection of equivalent floor model due to lateral loading.

NISTNCSTAR 1-2A. WTC Investigation 63
Chapter 3

0.008

3.6 SUMMARY

This chapter described the development of the reference structural models for the WTC towers. These

reference models were used to establish the baseline performance of the towers and also served as a reference for more detailed models for aircraft impact damage analysis and thermal-structural response

and collapse initiation analysis. The main types of models developed were:

• Two global models of the towers, one each for WTC 1 and WTC 2. The models included all primary structural components in the towers, including exterior walls (columns and spandrel

beams), core columns, exterior wall bracing in the basement floors, core bracing at the mechanical floors, core bracing at the main lobby atrium levels, hat trusses, and rigid and

flexible diaphragms representing the floor systems. The models were developed using the

electronic databases described in Chapter 2. To validate the global models, the calculated

natural frequencies of WTC 1 were compared with those measured on the tower and good

agreement between the calculated and measured values was obtained.

• One model each of a typical truss-framed floor (floor 96 of WTC 1 ) and a typical beamframed floor (floor 75 of WTC 2) in the impact and fire zones in the two towers. The models

included all primary structural components in the floor system, including primary and

bridging trusses, beams, strap anchors and horizontal trusses, concrete slabs, and viscoelastic

dampers. To validate the floor models, several studies were carried out to compare stresses

64 NISTNCSTAR 1-2A. WTC Investigation
Development of Reference Structural Models for the WTC Towers

and deflections estimated from the model with hand calculations for representative composite

sections. Good agreement was obtained between the model results and hand calculations.

Parametric studies were performed to evaluate the behavior of typical portions of the structure and to develop simplified models that could be implemented in the global models. These parametric studies

included detailed and simplified models of typical exterior and comer wall panels, and floor systems.

NISTNCSTAR 1-2A. WTC Investigation 65
Chapter 3

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66 NIST NCSTAR 1-2A, WTC Investigation
Chapter 4

Gravity AND Wind Loads on the WTC Global Models

4.1 INTRODUCTION

This chapter outlines the estimation of the gravity and wind loads applied to the global models of the World Trade Center (WTC) towers to establish their baseline perfonnance. The following sources were

used to develop the loads for the various loading cases considered in this study:

• Design Criteria document of the WTC towers, prepared by Worthington, Skilling, Helle &

Jackson (henceforth referred to as Design Criteria).

• WTC architectural and structural drawings (henceforth WTC Dwgs.).

• Wind reports prepared by Worthington, Skilling, Helle & Jackson, describing the development of design wind loads for the WTC towers (henceforth WSHJ Wind Reports).

• Reports from two independent wind turmel studies concerning the WTC towers, conducted in 2002 for insurance litigation by Cermak Peterka Peterson, Inc. (henceforth CPP) and Rowan

Williams Davies and Iru'in, Inc. (henceforth RWDI).

• Current New York City Building Code (henceforth NYCBC 2001).

• Current American Society of Civil Engineers (ASCE 7) Standard (henceforth ASCE 7-02).

Three loading cases were considered for the baseline performance analysis. They included:

• Original WTC design loads case. Loads were as follows: Dead and live loads as in original

WTC design in accordance with Design Criteria, used in conjunction with original

WTC design wind loads from WSHJ Wind Reports.

• Stafe-of-the-practice case. Loads were as follows: Dead loads as in original design; NYCBC

2001 live loads; and wind loads from RWDI wind tunnel study, scaled in accordance with

NYCBC 2001 wind speed. This wind load is considered as a lower estimate state of the practice since, as will be explained later, the CPP wind tunnel study produced larger wind

loads on the towers and is considered as an upper estimate state-of-the-practice case.

• Refined NIST estimate case. Loads were as follows: Dead loads as in original design; live loads from ASCE 7-02 (a national standard); and wind loads developed by National Institute Standards and Technology (NIST) from critical assessment of infonnation obtained from the RWDI and CPP reports and state-of-the-art considerations.

The purpose of using the original WTC design loads was to evaluate the performance of the towers under

original design loading conditions, and ascertain whether those loads and the corresponding design were

adequate given the knowledge available at the time of the design. The purpose of considering the stateNISTNCSTAR 1-2A, WTC Investigation 67
Chapter 4

of-the-practice case and the refined NIST estimate case was to better understand and assess the effects of

successive changes in standards, codes, and practices on wind design practices for tall buildings.

Section 4.2 of this chapter presents the gravity loads on the towers, including: dead loads and live loads

used in the original design, and in accordance with NYCBC 2001 and ASCE 7-02. Section 4.3 presents

and compares the wind loads used in the original design, state-of-the-practice wind loads, and wind load

estimates developed by NIST.

4.2 GRAVITY LOADS

The gravity loads applied to the global WTC models consisted of dead loads (DL) and live loads (LL),

appropriately combined as stipulated in the Design Criteria. Dead loads were applied to the global system

computer models in two parts: construction dead loads (CDL) and superimposed dead loads (SDL), based on the WTC Dwgs and the Design Criteria.

• CDL is defined as the self-weight of the structural system, including floor slabs, beams, truss members, columns, spandrel beams, etc.

• SDL is defined as the added dead load associated with architectural, mechanical, electrical,

and plumbing systems; such as curtain walls, ceilings, partitions, floor finishes, mechanical

equipment and ducts, transfonners, etc.

Three independent sets of live loads were combined with the dead loads:

• The first set was taken from the Design Criteria and was used with the original WTC design

loads case.

• The second set was taken from NYCBC 2001 and was used for the state-of-the-practice case.

• The third set was taken from ASCE 7-02 and was used for the refined NIST estimates case. The Hve loads given in ASCE 7-02 are essentially identical to the NYCBC 2001 live loads.

For each live load set, live load reductions for column design were taken from their respective source. The live load reductions in NYCBC 2001 are essentially identical to those of the Design Criteria.

Gravity loads were applied to the global system computer models using three methods:

• The self-weight of the structural steel frame for the exterior wall, core columns, and hat truss was applied using the SAP2000 self-weight feature.

• The loads from areas outside the core of the typical truss-framed and beam-framed floors were taken from the reactions of the typical floor computer models (see Sec. 4.2.1 ) and were

applied to the global models as concentrated loads on the columns.

• Since the occupancy, opening layout, and floor framing in the core area varied among floors, the loads within the core area, from floor B5 to the roof, were calculated using a spreadsheet

(see Sec. 4.2.2) and were applied to the global models as concentrated loads on the columns.

68 NISTNCSTAR 1-2A, WTC Investigation
Gravity and Wind Loads on the WTC Global Models

4.2.1 Gravity Loads from Areas Outside of Core

The loads from areas outside the core area of the typical truss-framed floor were based on the reactions

from the typical floor computer model (floor 96 of WTC 1). The Design Criteria live load for areas outside of core was 100 psf The reduced applied loads for the typical tmss-framed floor for use in the global system computer models are summarized in Table 4-1, which shows the original WTC design

criteria for gravity loads. The partition allowance from the original WTC Design Criteria was also used

as the partition allowance for the NYCBC 2001 and the ASCE 7-02. The live load of 50 psf is the same

for the original design criteria, the NYCBC 2001, and ASCE 7-02.

Table 4-1. Original WTC design criteria loads for floor 96A model for the

design of columns (typical truss floor).^

Floor Area

CDL" SDL' Total DL LL

(psf) (psf) (psf) (psO

Long Span 3.5 14 17.5 50

Short Span 3.5 14 17.5 50

Two-Way Zone 3.5 16 19.5 50 Core None None None None

a. The self-weight of interior and e.xterior columns, e.xterior spandrels, core frame members, and core floor slabs is not included in the tabulated loads and is not applied to the floor computer model.

b. The self-weight of the concrete slab and of the structural steel members in the floor system, as computed by

SAP2000. is added to these loads.

c. Includes a 6 psf allowance for partitions.

d. Since the loads inside the core are applied separately to the global system computer models, the live loads, superimposed dead loads on the core area, and core frame members are reduced to zero in the floor computer

models.

Live load reductions for columns for the original WTC design live loads were taken from the Design

Criteria and were identical to those specified in NYCBC 2001 . Live load reductions for the ASCE 7-02

live loads follow the ASCE 7-02 tributary area provisions. For the ASCE 7-02 loads, at the exterior walls

live load reductions were calculated using an influence factor coefficient of two as defined in ASCE 7-02. The influence area for exterior wall columns was calculated using a 45 degree spread for the distribution

of loads among the columns located below the loading point.

In the floor model, the self-weights of the exterior columns and spandrels, the interior core columns, and

interior core beams (not including those of the core perimeter) were not included in the analysis, since

these weights were already accounted for in the global models. For this purpose, the zero self-weight

frame property modifier in SAP2000 was used. Appropriate portions of the core slab section definition were also modified by using a zero self-weight property modifier. In addition, since the loads inside the core were applied separately to the global models, the live loads and superimposed dead loads on the core

area elements and core frame members were reduced to zero in the floor computer models.

For calculating the loads outside the core, three typical floors (floor 96, 75, and 43) were selected to be

representative of all of the floors in the tower except for the roof, the floors at and below floor 2, and the mezzanine floors. Models of floors 75 and 96 were developed as discussed previously in Chapter 3, and

floor 43 was used as a representative of the beam-framed floors that were not mechanical floors (floor 75

model with modified loads was used to simulate this floor). Based on the column reactions from the

typical floor computer models, gravity loads on columns at other floors were generated by applying

NISTNCSTAR 1-2A, WTC Investigation 69
Chapter 4

conversion factors to the results from these floor computer models. The conversion factors were based on

unit area loading differences between floors. These calculations were perforaied in a spreadsheet.

The conversion factors were calculated for CDL, SDL, and LL. For CDL and SDL, the conversion

factors were calculated for any given floor by dividing the overall floor CDL and SDL by their counteiparts at the representative typical floor. For LL, the conversion factors were similarly calculated,

except that the factors included also the appropriate live load reduction factor. The overall floor CDL and

SDL were compiled using a weighted average based on the floor area for each of the floor zones: longspan, short-span, and two-way zone.

Loads on columns outside of the core at the roof, floors at and below floor 2, and the mezzanine floors were calculated by spreadsheet.

4.2.2 Gravity Loads from Areas Inside of Core

For the floor areas inside the core from floor B5 to the roof, gravity loads were calculated for individual

columns on the basis of tributaiy areas using a spreadsheet. The calculations were based on the WTC Dwgs and the original Design Criteria.

The floor framing infomiation was obtained from the structural drawings. Occupancies and opening

layouts (elevator and shaft layout) for each floor inside the core were obtained from the architectural

drawings. Floors with similar occupancy, opening layout, and floor framing were grouped together and were represented by a typical floor in the group. Floors with special occupancies, opening layouts, or

floor framing were calculated individually.

The core column loads for each of the typical floors and special floors below floor 107 were calculated in spreadsheets. The NYCBC 2001 loads are essentially identical to, and were used for the ASCE 7-02

loads. In the worksheet, the tributary area of a core column was divided into four regions. For each

region, the area was calculated from the coordinates of the core columns in the computer models, then

modified for each type of floor according to the opening layout specific to that floor.

For each region, the dominant occupancy specified in the architectural plan was used. For the loads

corresponding to each occupancy, the floor worksheet referenced the Load worksheet in the same Excel

file. For each occupancy, the Load worksheet tabulated the CDL of the concrete slab, the SDL, and

the LL.

Dead loads

In addition to the weight of the concrete slab (including reinforcing steel and metal deck), the CDL of the

floor framing consisted of the weight of the structural steel beams. The floor computer models were used

to calculate the weight of the steel floor framing averaged over the floor area. The weight of the steel floor framing was calculated to be 6 psf and 7 psf at floors 96 and 75, respectively.

The floor framing CDL calculated for floor 96 was applied to all floors except the mechanical floors,

where the floor 75 CDL was applied. For typical occupancies inside the core, such as coixidors and

elevator lobbies, the concrete slab CDL was based on the structural drawings and was listed in the Load

worksheet. For special floors, the concrete slab CDL for these typical occupancies was overwritten in the Floor worksheet to reflect the actual thickness of the concrete slab specified in the stmctural drawings.

70 NISTNCSTAR 1-2A, WTC Investigation
Gravity and Wind Loads on tlie WTC Global Models

Where a load was not listed in the Load worksheet, the concrete slab CDL was included in the Floor

worksheet.

The SDL includes the weights of partitions, beam fireproofing, ductwork, electrical conduit and piping,

floor finish, ceiling, and mechanical equipment. The types of floor finish and ceiling applied to each

occupancy were obtained from the architectural plans and from the finish schedule in the architectural

drawings. The weight of finishes was obtained from the Design Criteria (Sheet BC-1-7). In accordance

with the original WTC Design Criteria, for equipment rooms on the mechanical floors an SDL of 75 psf was used.

Partition layouts and types were obtained from the architectural drawings, and the partition weights were

taken from the Design Criteria (Sheets BC-1-7 and BC-1-8). As shown in Figs. 4-1 and 4-2. partition

loads per gross area were calculated for seven typical opening/occupancy configurations. A partition

weight of 20 psf per gross area was assumed for the return plenums and for areas where the occupancy was not specified in the architectural drawings. A partition weight of 6 psf, taken over the gross area, was

used for tenant space. For occupancies that included an additional 75 psf in SDL for equipment weight, a partition weight was not added.

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by

NIST. Figure 4-1. Partition groups A, B, C, D, and E.

NISTNCSTAR 1-2A, WTC Investigation 71
Chapter 4

Source: Reproduced with permission of Tine Port Authority of New York and New

Jersey. Enhanced by NIST. Figure 4-2. Partition groups G and F.

Weights of concrete beam encasements were taken from the structural drawings and the Design Criteria. At floors 77, 43, 9 to B3, and B5, most of the core beams were concrete-encased. For the entire core, a 20 psf uniformly distributed load taken on the gross tributary area was added to the dead load. See below

for the concrete encasement weights assumed for floors in the hat truss region. For all other floors, the concrete beam encasement loads were applied directly to the columns to which concrete-encased beams

were connected.

The loads due to the construction of the Fiduciary Trust vault in WTC 2 (see Sec. 2.5.2) were added to the dead loads of the original construction.

Live Loads

The original WTC live loads for occupancies inside the core were taken from the Design Criteria (Sheets

CC-1-2 and CC-1-3). For a few occupancies not explicitly listed in the Design Criteria, the live load

listed for the most similar occupancy was used.

ASCE7-02 live loads were taken from Table 4-1 of the standard. Where a WTC occupancy was not

listed in ASCE7-02, the Design Criteria live load was used. NYCBC 2001 hve loads are essentially

identical to the ASCE 7-02 live loads and were not tabulated separately.

Live Load Reduction

For use with the corresponding live loads, live load reductions for column design were based on the

original WTC Design Criteria and on ASCE 7-02.

The live load reduction factors in the original WTC design were taken from sheets DC 1-3 of the Design

Criteria. NYCBC 2001 live load reductions are essentially identical to the original WTC Design Criteria and were not tabulated separately.

72 NISTNCSTAR 1-2A, WTC Investigation
Gravity and Wind Loads on the WTC Global Models

For the core columns, the ASCE7-02 hve load reductions were calculated in accordance with the tributary area provisions of ASCE7-02. Core columns were divided into three column groups based on their

tributary' areas:

• Columns 704, 705, 805, and 904

• Columns at the perimeter of the core

• All other core columns

A single set of live load reduction factors was applied to all the columns within the same column group.

Hat Truss Floors

Except for floor 107. for the floor areas tributary to the hat truss framing, gross tributaiy areas were

calculated by hand. Openings were subtracted from gross tributary areas, and the resulting net areas were

entered into an Excel spreadsheet. Except for columns 704B106Z, 704B107, 705B106Z, 803B107,

804AB107, and 804B106Z. where gross and net areas were calculated directly, for floor 107, the net areas were taken from floor 106.

CDL, SDL, and LL were based on the Design Criteria sheets BFl-1 lA, BFl-12, BFl-13, and BFl-14.

These sheets assign uniform loads throughout entire floors (both outside and inside the core). For floor 109 (mechanical floor), sheet BCl-3 indicates LL = 150 psf However, for consistency with the design

criteria for other mechanical floors, this live load was applied in two parts, as LL = 75 psf and additional

SDL = 75 psf.

For some occupancies in the core for floors 107 to the roof, the occupancy-specific live load given

elsewhere in the WTC Design Criteria exceeded the unifonn live load specified for the entire floor. For

these occupancies, the higher live load was applied to the computer model. These occupancies are summarized below;

• Stair: LL=1 00 psf (instead of the uniform LL=75 psf)

• Corridors: LL= 100 psf per WTC Design Criteria or 80 psf per ASCE 7-02 (instead of the uniform LL=75 psf)

• Ser\ ice room: LL= 1 00 psf (instead of the uniform LL=75 psf)

• Window washer storage LL= 1 25 psf (instead of 75 psf)

Note that beams, girders, and diagonals that were part of the hat truss system were included in the global

models and that their self weights were calculated by SAP2000 and added to the CDL. In addition, a 20 psf uniform load at every level (floor 107 to roof) was used to account for the weight of structural steel that was not modeled and the weight of concrete encasement. The ASCE 7-02 loads were essentially identical to and were used for the NYCBC 2001 loads.

The antenna gravity loads were also considered in the WTC 1 global model.

NISTNCSTAR 1-2A, WTC Investigation 73
Chapter 4

4.2.3 Construction Sequence Loading Effects

Located between floor 107 and the roof in both towers, the hat truss interconnected the core columns and

the columns of the exterior walls. The hat truss system distributed both gravity loads and wind loads

between the core and the exterior walls. However, the CDL and SDL put in place prior to the completion

of the hat truss system were not distributed through the hat truss. In order reasonably to differentiate between those loads distributed through the hat truss system and those that were not, the construction

sequence was considered in the computer models.

The effects of construction sequence on the distribution of gravity loads was modeled using the nonlinear

staged construction analysis function in SAP2000. The primary puipose of this step in the analysis was to provide, at the top of the towers, a reasonably accurate distribution of construction and superimposed

dead loads between the core columns and the exterior wall. Accordingly, the global system computer

model was subdivided into two portions: floor 106 and below, and the area above floor 106. In the first stage, the lower portion of the full computer model was loaded with all of the CDL and SDL associated

with floor 106 and below. In the second stage, the portion of the full model above floor 106 was

activated, and the CDL and SDL associated with the upper floors were placed on the full computer model.

Live loads on the whole model were applied to the full building with the hat truss engaged in the second

stage. This methodology approximates well the way in which the towers were built.

4.3 WIND LOADS ^

The investigation of wind loads and wind effects presented in this report has two objectives. The first is to ascertain the adequacy of the original wind loads and the con esponding structural design given the knowledge available at the time of the design. The second objective is better to understand and assess the

effects on design practices of successive changes in standards, codes, and practices, with a view to helping improve standard provisions for wind loads in the future. This case study provides an opportunity

to achieve this objective with unique effectiveness.

To achieve these objectives, three independent sets of wind loads were applied to the global tower models

as explained in Sec. 4.1. These sets are further described as follows:

4.3.1 Original WTC Design Wind Loads

Wind loads were detennined for the original design of the WTC towers through the development and

implementation of a boundaiy-layer wind-tunnel study which simulated the mean and fluctuating

(turbulence) properties of the wind from ground to gradient height by using the knowledge and techniques

available in the 1960s. The original WTC wind loads were taken from summaries given in Part IV of the WSHJ Wind Reports. From among the loading cases, the most severe were determined by comparisons

of diagrams of wind-induced shear and overturning moment.

In the original WTC wind tunnel studies, wind tunnel data were collected for each tower for wind

approaching from 24 wind directions, a, in 15 degree increments. Part IV of the WSHJ Wind Reports

provides equations for the wind-induced shears and overturning moments in the towers at 21 elevations, z, along the building height, //, at increments of 0.05//. For each wind direction, the reports provided sets of coefficients to be used in these equations to obtain the static and the dynamic components of shear and

74 NISTNCSTAR 1-2A, WTC Investigation
Gravity and Wind Loads on the WTC Global Models

overturning moment in the N-S and E-W directions. Coefficients were also provided for calculating

torsional moments. The torsional moments are associated with eccentricity of the global wind excitation

of the building with respect to the building center of rigidity. Based on these equations, shears and

torsions were calculated for each wind direction for the two orthogonal directions. The equivalent

effectiv e static shear forces, 5, and overturning moments, M, at each level were comprised of static and

dynamic components:

S^S + S' M^M + M'

^^^"^

where the first and second terms indicate, respectively, the mean or steady-state components and dynamic

components. The static components of the shears and moments were calculated from the following

equations:

S{z)^^pV;DHC,{z) _ . _ (4-2)

M{z)^-pV:-DHC^{z)

where:

p = design air density = 0.0023 slug/ft^

= mean (or equivalent) design wind speed, determined to be 98 mph averaged over 20 min at a height of 1,500 ft above ground.

and C^/ = shear force and overturning moment coefficients, respectively, obtained from

wind tunnel tests and provided in tabular form

D and H = dimension in plan and height of the tower

The dynamic components of the shear forces and overturning moments at any height z were obtained

from the following equations:

H

S'(z) - An'nlA |w(z)/u{z)dz

(4-3) H M\z) = \s\z)dz

NISTNCSTAR 1-2A. WTC Investigation 75
Chapter 4

where: = natural frequency of oscillation of the tower

A = amplitude of oscillation at the top of the tower coiresponding to the mean design wind speed

m{z) = mass per unit height of the tower

/j(z) = amplitude of fundamental vibration mode at height r for unit amplitude at the top of the tower.

The wind loads were calculated on the basis of 2.5 percent total damping. This value includes the

intrinsic damping of the structural systems plus the supplemental damping provided by the dampers.

The differential static and dynamic shears between successive levels were calculated and distributed using

two different methods:

• The static wind load to be applied to each floor was determined from the shear diagram.

• The dynamic wind load to be applied to each floor was based on the distribution of mass over

the tower height, the fundamental mode shape, and the dynamic component of the lateral wind-induced sway at the roof

Note that for a = 90 degrees, coefficients were not found in the microfilm of the WSHJ Wind Reports for calculating the static component of the wind forces for WTC 1. Accordingly, the static coefficients were

deduced from data for the a = 270 degrees, for WTC 2. By observation of the static coefficient data, it was detennined that the basic data for the two towers is shifted by 180 degrees.

Considering the 24 different wind directions and the four combinations of the static and dynamic

components of the N-S and E-W components of the building forces listed below, there were 96 different wind load cases for each tower.

N-S (Static + Dynamic) and E-W (Static + Dynamic)

N-S (Static + Dynamic) and E-W (Static - Dynamic)

N-S (Static - Dynamic) and E-W (Static + Dynamic)

N-S (Static - Dynamic) and E-W (Static - Dynamic)

The static and dynamic shears in the N-S and E-W directions were calculated for all 96 loading cases, and

the overturning moments were calculated from the shears. In order to determine the most severe of the 96 loading cases for each tower, the wind-induced shears and overturning moments were compared, for each direction, at heights z/H = 0.75, 0.50, 0.25 and 0. The wind loading cases producing the maximum

shears in either of the two orthogonal directions were identified for application to the global models.

To compare overturning moments for each loading case, the moments in the two orthogonal directions were combined vectorially (i.e., the magnitude of the resultant is equal to the square root of the sum of the squares of the components, and the direction P of the resultant moment is the arctangent of the ratio of the

76 NISTNCSTAR 1-2A. WTC Investigation
Gravity and Wind Loads on the WTC Global Models

V- and .Y-components). The load cases were grouped by the angle p using an increment of 45 degrees,

resulting in 8 groups of load cases. For each P group, at z/H = 0.75, 0.50, 0.25 and 0, the wind load cases

that generated the maximum resultant moment were identified for application to the computer global

system models. Eight groups of maximum moment plus four directions of maximum shear at four heights

in the towers would result in 48 different loading cases. However, some individual wind load cases produced a maximum resultant moment and/or a maximum shear at more than one elevation in the towers. As a result, for WTC 1,16 loading cases were identified, and for WTC 2, 17 loading cases were

identified.

For cases where an intermediate floor did not provide lateral support for the exterior wall, the wind load was distributed to the floors above and below, omitting the intermediate floor wind load.

For the floors modeled in the global model by rigid diaphragms, the wind forces in the N-S and E-W

directions were applied as concentrated loads at the geometric center of the building. The torsional

moments were also taken into account. For the floors with flexible diaphragms (see Chapter 3), the

forces, based on tributary' areas, were resolved into point loads at the perimeter columns. Both windward

and leeward forces were applied. At these floors, the torsional moment was represented by four identical concentrated forces applied parallel to the four faces of the tower at the center columns of each face. The

simplified method used for applying the torsional loads at floors with flexible diaphragms did not have

any noticeable effects on the analysis results. For each loading case, the orthogonal wind forces were

subdivided into windward and leeward forces based on the direction of the wind. For this purpose, the 24 wind directions a (discussed previously) were divided into 8 groups as given in Table 4-2. The wind

direction for a = 0 is for wind blowing from north to south.

Table 4-2. Grouping of the wind directions.

Group a

1 337.5 <a<22.5

2 22.5 <a<67.5

67.5 <a< 112.5 4 112.5 <a< 157.5

5 157.5 <a<202.5

6 202.5 <a< 247.5

7 247.5 <a<292.5

8 292.5 <a< 337.5

For groups 1 , 3, 5, and 7 (orthogonal or near-orthogonal wind directions), the wind forces were

distributed in accordance with Fig. 4-3a. For groups 2, 4, 6, and 8 (diagonal or near-diagonal wind

directions), the wind forces were distributed in accordance with Fig. 4-3b. The factors shown in Fig. 4-3 were based on Figure 6-6 of ASCE 7-02 Standard.

NISTNCSTAR 1-2A. WTC Investigation 77
Chapter 4

0.5/1.3 Fy

Leeward

0.8/1.3 Fy

Windward

A

wind Direction

Wind Direction

0.5/1.3 Fy

Leeward

0.5/1.0 Fx 0.5/1.0 Fx 0.8/1.3 Fx

y, Side

X

Side Windward

X

0.5/1.3 Fx

Leeward

0.8/1.3 Fy

Windward

a) (b)

Figure 4-3. Windward and leeward distribution for (a) orthogonal and (b) diagonal

wind directions.

4.3.2 State-of-the-Practice Wind Loads

For the WTC towers, two wind tunnel tests and wind engineering studies based thereon were conducted

in 2002 by independent laboratories as part of insurance litigation unrelated to the NIST investigation.

The tests and studies were conducted by Cermak Peterka Peterson, Inc. (CPP) and by RWDI. The results of both studies were made available to NIST; see NIST NCSTAR 1-2 for more details.

For the purpose of the baseline analysis, the state-of-the-practice wind load case consisted of the wind

load estimates provided by RWDI, scaled in accordance with a wind speed equivalent to the NYCBC 2001 wind speed (interpreted to be the 80 mph fastest-mile wind speed at 30 ft elevation over open ten"ain). These wind loads were applied to the global models using the directional and torsional load

combination factors presented in the RWDI reports.

The wind loads from RWDI are smaller than those obtained from CPP for WTC 2 (see Sec. 4.3.4).

Considering the differences between RWDI and CPP results, RWDI practice may be viewed as a "lowerestimate, state-of-the-practice case."

The state-of-the-practice wind loads were distributed in the global system computer models in a manner

similar to that described in connection with the original design wind loads.

78 NIST NCSTAR 1-2A, WTC Investigation
Gravity and Wind Loads on the WTC Global Models

4.3.3 Refined NIST Estimates

NIST completed an independent analysis to estimate the wind loads that would be appropriate for use in designing the towers based on state-of-the-art considerations. The analysis was based on results provided

by CPP and RWDI. with modifications that draw on recently developed knowledge in M'ind engineering.

The objective of this analysis was not to assess the adequacy of the original design wind loads, but rather

to better understand and assess the effects of successive changes in standards, codes, and practices.

Wind loads based on recently developed knowledge and consistent with the design wind speed in ASCE

7-98 Standard (which is the same as in the ASCE 7-02 Standard) were estimated by NIST using the RW'DI results scaled in accordance with a wind speed equivalent to the ASCE 7-02 Standard wind speed

and then muhiplied by a factor of 1.15. This number was recommended by NIST for the refined NIST

baseline analysis. For details on how these wind loads were obtained see NIST NCSTAR 1-2.

The lateral wind loads on the towers, consistent with the ASCE 7-98 and ASCE 7-02 design wind speed

requirements, were estimated by using the effective static floor-by-floor wind loads presented in Table 5a

(without P-A effects) or Table 5b (with P-A effects) of the RWDI report (north tower) for WTC 1 and

Table 3a (without P-A effects) or Table 3b (with P-A effects) of the RWDI report (south tower) for WTC 2.' These effective static floor-by-floor wind loads were multiplied by the factor 1.15 and by the

factors indicated in note (3) provided at the bottom of Tables 3 and 5 in RWDI. The loads so obtained were applied to the global model of each tower using the load combinations presented in Table 6a of

RWDI (north tower) and Table 4a of RWDI (south tower).

4.3.4 Comparisons of Wind Loads

Tables 4-3 and 4-4 provide a summary of the wind-induced base shears and base moments on WTC I and WTC 2. respectively. The values in Tables 4—3 and 4-4 are based on the 1938 and 1968 versions of

the NYCBC. the RWDI study, the CPP study, the refined NIST estimates, and the original design. The

wind loads are expressed in terms of two orthogonal components and of measures of the most unfavorable

combined peaks obtained by various methods, as follows:

• RWDI: Most unfavorable peak is calculated as vector sum of weighted .v and v peaks, with

weighting factors approximately consistent with the "principle of companion loads," the approximations being based on engineering judgment and in-house experience.

• CPP: Most unfavorable peak is calculated as vector sum of x peak and companion point-intime v-response, or 3; peak and companion point-in-time x-response, whichever is larger.

• Original WTC design: Most unfavorable peak is calculated as vector sum ofx and v peaks

corresponding to most unfavorable wind direction. These x and/or 7 peaks may be smaller

for that most unfavorable direction than the x peaks and j' peaks corresponding to wind

normal to a building face (see Sec. 4.3.1).

" For the WTC 2 tower Tables 3b and 3c in the RUT)I report (South Tower) were inadvertently switched. The loads accounting

for P-A effects are in fact given in Table 3c of the report.

NIST NCSTAR 1-2A. WTC Investigation 79
Chapter 4

Table 4-3. A comparison of wind load estimates for WTC 1 from various sources.

Source

Base Shear 103 kip Base Moment 106kip ft

IT \\l

Most

unfavorable

combined

peak

About About

Most

unfavorable

combined

peak

1

1 Q^S yj o 5.3 5.3 4.2 4.2 NYC Building Code 1968 to date

9.3 9.3 7.7 7.7

R\X/ni / MVP RiiilHino Code

zuuz 1 1.4 10.5 13.0 10.1 10.5 12.2

RWni / A QPP 7 OS zuuz 1 Z.J 1 1 1 1 1 .J 1 A n 1 't.U 1 n 8 1 1 A 1 1 .4 1 ^ 1

1 J. 1 rPP \_ 1 1 // NYr i N 1 \^ RiiilHinP jL> Ul lU 11 J ci, Code

NA NA NA NA NA NA

CPP / ASCE 7-98 2002 NA NA NA NA NA NA

NIST/ third-party SOM

review

2004 14.1 13.0 16.1 12.4 13.1 15.1

Original WTC Design 1960"s 9.8 10.6 14.0 10.3 9.1 13.7

Table 4-4. Comparison of wind load estimates for WTC 2 from various sources.

Source Year

Base Shear 103 kip Base Moment 106kip ft

N-S E-W

Most

unfavorable

combined

peak

About

N-S

About

E-W

Most

unfavorable

combined

peak

NYC Building Code 1938 5.3 5.3 4.2 4.2 NYC Building Code

1968 to date

9.3 9.3 7.6 7.6 RWDI/NYC Building

Code

2002 9.7 11.1 12.3 10.1 9.2 11.3 RWDl / ASCE 7-98 2002 10.6 12.2 13.5 11.1 10.1 12.4 CPP / NYC Building

Code

2002 NA NA NA NA NA NA

CPP / ASCE 7-98' 2002 15,1 15.3 17.1 15.5 14.0 17.0 NIST /third-party SOM

review

2004 1 2.2 14.0 15.5 12.8 11.6 14.3

Original WTC Design 1960-s 13.1 10.1 16.5 8.8 12.6 15.2

a. Using ASCE 7-98 Sections 6.5.4.1 and 6.6.

Table 4-5 presents a summary of design base shears and base moments based on various building codes

at the time of the design. Note that the base moments presented in Tables 4-3 to 4-5 are calculated at the foundation level (rather than at the street level).

80 NISTNCSTAR 1-2A, WTC Investigation
Gravity and Wind Loads on the WTC Global Models

Table 4-5. Base shears and base moments due to wind loads from different

building codes.

Building Code

1938

NYC

Building Code

1968 to Date NYC

Building Code

1964

NY

State Code

1965

BOCA/BBC

1967

Chicago

Municipal Code

Base Shear

(10^ kip)

5.3 9.3 9.5 9.8 8.7

Base Moment

(10^ kip ft)

4.2 7.7 7.6 8.5 7.5

Tables 4-3 and 4-4 indicate that the original design wind load estimates exceed in all cases those

established by the NYCBC (a prescriptive minimum requirements code) prior to 1968, when the WTC towers were designed, and up to and including 2001. Table 4-5 shows that the design values are also higher than those required by other prescriptive building codes of the time, including the 1964 New

York State Code, the 1965 Building Officials and Code Administrators Basic Building Code

(BOCA BBC), and the 1967 Chicago Municipal Code. It is noted also that wind effects obtained from

various wind-tunnel-based studies are in all cases higher than wind effects based on prescriptive codes

and standards.

The two orthogonal base shear and base moment components used in the original design are in general

smaller than the CPP. RWDl, and refined NIST estimates. However, the most unfavorable combined

peaks from the original design are larger than, or smaller, by at most 1 5 percent than estimates based on

the CPP. RWDI, and NIST estimates. This is due to the consei"vative procedure used to combine the loads in the original design. (For example. NIST estimates are higher by about 15 percent than the most

unfavorable original design wind loads for WTC 1, and lower by about 5 percent than the most

unfavorable original design loads for WTC 2.)

Tables 4-3 and 4~4 indicate that the estimated wind-induced loads on the towers vary by as much as 40 percent between the wind tunnel/climatological studies conducted in 2002 by CPP and RWDl, with

CPP being the larger. Thus, CPP loads are considered as an upper estimate, state of the-practice, while

RWDl loads are considered as a lower estimate, state of the-practice.

4.4 REFERENCES

ASCE 7-02: American Society of Civil Engineers, ASCE 7 Standard Minimum Design Loads for Buildings and Other Structures, Reston, VA, 2002.

CPP report: Data Report, Wind-Tunnel Tests - World Trade Center, Cermak Peterka Petersen, Inc. August 2002.

Design Criteria: Design Criteria document for the WTC towers developed by Worthington, Skilling, Helle

& Jackson.

NYCBC 2001: Building Code of the City of New York, 2001 Edition, Gould Publications, Binghamton,

NY.

NIST NCSTAR 1-2A. WTC Investigation 81
Chapter 4

RWDI report: (north tower) Final Report, Wind-Induced Structural Responses, World Trade Center

Tower 1, Rowan Williams Davies and Irwin, Inc., October 4, 2002.

(south tower) Final Report, Wind-Induced Structural Responses, World Trade Center - Tower 2, Rowan

Williams Davies and h-win. Inc., October 4, 2002.

SAP2000 (2002), Linear and Nonlinear Static and Dynamic Analysis and Design of Three-Dimensional

Structures Basic Analysis Reference, Computers & Structures Inc., Berkeley, CA.

WSHJ Wind Reports: A series of wind reports developed by Worthington, Skilling, Helle & Jackson,

outlining the development of design wind loads for the WTC towers (see NIST NCSTAR 1-1 ). WTC Dwgs: WTC architectural and structural drawings.

82 NIST NCSTAR 1-2A, WTC Investigation
Chapter 5

Baseline Performance Analysis of the WTC Global Models

5.1 INTRODUCTION

This chapter presents the resuks of the basehne perfonnance analysis for the World Trade Center

(WTC) 1 and WTC 2 global models under the three gravity and wind loading cases described in Chapter 4. These cases include the original WTC design load case, the lower-estimate state-of-the- practice case, and the refined National Institute of Standards and Technology (NIST) estimate case. Baseline performance results include basic information about the behavior of the towers under design

loading conditions, pertaining to total and inter-story drift, demand/capacitv' ratios of primary structural components, exterior columns response (shear lag effects and presence of tensile forces), perfonnance of

connections, and the towers' resistance to shear sliding and overturning.

Section 5.2 describes the estimation of the demand/capacit\ ratios and the selection of the design

parameters for their estimation. Section 5.3 presents the results of the baseline pertonnance analysis for WTC 1 under the three loading cases. Similarly. Sec. 5.4 presents the results for WTC 2. Section 5.5 presents a summary- of the results. For both towers, detailed baseline perfonnance results are provided for the original WTC design loading case, while a brief summary of the results is provided for the state-of- the-practice and refined NIST estimate cases.

For all anah sis cases, the demand capacity ratios (DCRs) for structural components were estimated using

the Allowable Stress Design (ASD) procedure as specified in the American Institute of Steel Constmction

(AISC) Specification for Stiiictural Steel Buildings - Allowable Stress Design and Plastic Design - 9"'

Edition, 1989. The DCRs were calculated by dividing component demands by component capacities,

taken at unfactored (working) loads and at working stresses, not at ultimate loads or yield stresses. These

DCRs for the structural components were determined as follows:

1 . The component demands were obtained from the results of the baseline performance analysis

using the reference global models (see Sec. 3.2) and working loads based on the following

load combinations:

5.2 calculation of demand/capacity ratios

• For the original WTC design loading case and for the state-of-the-practice case, the load

combinations were those specified by the AISC Specificafion (1989) and the New York

City Building Code (NYCBC) 2001:

Dead Load

Dead Load - Live Load

Dead Load - Live Load ^ Wind Load

NISTNCSTAR 1-2A. WTC Investigation 83
Chapter 5

Dead Load + Wind Load

• For the refined NIST estimate case, the load combinations were those specified by the American Society of Civil Engineers (ASCE 7-02) Standard:

Dead Load

Dead Load + Live Load

Dead Load + Wind Load

Dead Load + 0.75 x (Live Load + Wind Load)

0.6 X Dead Load + Wind Load

2. The component capacities were based on the nominal steel strength as specified in the

original design documents and using the AISC Specification (1989):

For the original design loading case and for the state-of-the-practice case (consistent with

NYCBC 2001), a one-third increase in the allowable stress was considered for load cases

that included wind, as specified at the time of the design and as is currently specified in NYCBC 2001 and AISC Specification (1989).

• For the refined NIST estimate case, where loads were based on the ASCE 7-02 Standard,

load combinations were taken from the ASCE 7-02 Standard, which does not allow the one-third increase in allowable stress.

The interaction equation in AISC Specifications (1989) estimates the DCR as the larger of the following

two equations for members subjected to both axial compression and bending stresses:

f r f C f

£)(^J^ — •'

_j_ m.\.l lx\ _|_ "'1 ' hy

(Eq. 5-1)

Z)Ci? = — + ^+

0.60F, F,^ F,„

For the case when f^,IF^ < 0. 1 5 , the following equation is pennitted in lieu of the previous two . equations:

where the subscripts x and v indicate the axis of bending about which a particular stress or design property

applies, and

84 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

and are the axial compressive stress and compressive bending stress, respectively, that would be permitted if axial force alone or if bending moment alone existed.

and are the computed axial stress and compressive bending stress at a given point,

respectively.

F'^ is the Euler buckling stress divided by a factor of safety.

C„j is a coefficient that depends on column curvature caused by applied moment.

A re\'iew of the basic design equations and allowable stresses for combined axial load and bending for the 6th Edition of the AISC Specifications (1963), which was in effect at the time of the design, indicates that they are essentially identical to those of the 9th Edition (1989) design equations and allowable stresses. There are. however, some variations between the 6th and 9th Editions of the specification. The 1963

Specification did not specifically address biaxial bending in the combined stress equations. In addition, the allow able stress fonnulations for bending with lateral torsional buckling are somewhat different between the two design specifications.

For the original design loading case, the SAP2000 program was used directly to estimate the DCRs using

the above equations. For the lower-estimate state-of-the-practice case and the refined NIST estimate case,

a second order analysis that accounted for P-A effects was used to estimate member demands under the applied gravity and wind loads. The P-A analysis results in a moment magnification in the components of

the global models; as a result, the terms C,,, and (1 — I F^) were assigned a unit value in the above

equations to estimate component DCRs. For these cases, DCRs were calculated in Excel spreadsheets,

using results obtained by the SAP2000 computer program. The calculations were spot-checked for accuracy and to verify that the correct design infonnation was being applied. For most of the component

calculations that were checked, the SAP2000/Microsoft Excel spreadsheet calculations were found to be

acceptable. When errors were detected, the design parameters were corrected to provide for an acceptable

calculation.

5.2.1 Selection of Global Models Design Parameters

For estimating the DCRs of the structural components under the various loading conditions, the following

design parameters were used in the global models of WTC 1 and WTC 2 to yield accurate results:

• The effective length factors, K factors, for ASD coluinn design were selected by comparing

the actual column end conditions with the theoretical end conditions depicted in Table C-C2.1 m the Commentary of the 9th Edition of the AISC ASD Manual.

• Virtually all core columns were designed originally as axially loaded members without

significant eccentric loads and without continuity of framing that would generate significant

P-A moments. The details of construction are consistent with this design approach.

Accordingly, in order to eliminate erroneous bending stresses in the interaction equations,

allowable bending stresses for core columns were increased sufficiently to reduce the bending

term in the interaction equation to less than 0.01.

NISTNCSTAR 1-2A, WTC Investigation 85
Chapter 5

• The cross-section of the intennittent comer columns of the tower included a web plate that extended beyond the flanges. The web plate extensions effectively, but inappropriately,

reduced the section modulus of the cross-section by significantly limiting the allowable stress

in the flange. To correct for this inappropriate reduction, the allowable bending stress for in- plane bending was increased.

• For the floor 107, 108, and 1 10 spandrel beams, for bending in the plane of the slab, the slab would resist the tendency for the spandrels to bend preventing significant bending stresses from developing in the spandrels. To achieve this behavior in the model, the spandrels'

allowable bending stress was increased sufficiently to limit the bending tenn in the

interaction equation to less than 0.01, ehminating erroneous bending stresses.

• For the floor 7 spandrels, the actual span length was insignificant due to the actual geometry

of the spandrel plate construction. Since the as-modeled spandrels had a significant span and

would otherwise develop erroneous bending stresses, the allowable bending stress was

increased sufficiently to limit the bending tenn in the interaction equation to less than 0.01.

• At the exterior wall between floors 1 and 10, the unbraced lengths and the properties of the

exterior columns varied significantly along the height. These variations, particularly

pronounced in the out-of-plane direction, had a notable effect on the buckling strength of the columns. The effects of variation in unbraced lengths and non-prismatic coluinns are only

obliquely addressed in the equations in the AISC specifications for column capacities. To

study the influence of unequal unbraced lengths in consecutive floors on the buckling

strength of the exterior columns, an elastic buckling (eigenvalue) analysis was earned out for a typical column tree using SAP2000. Since the columns buckle in the inelastic range, the

elastic buckling capacities obtained from the SAP2000 buckling analysis were converted into allowable inelastic buckling capacities using the procedure in Appendix E3 of the AISC Load

and Resistance Factor Design (LRFD) Specification (1986). The study showed that, in the

out-of-plane direction, for the typical exterior column unsupported between floors 2 and 7, consideration of the shorter unbraced lengths above and below increased the inelastic out-of- plane buckling capacity by about 25 percent. The default allowable buckling stress calculated by the SAP2000 computer program was, therefore, overwritten to reflect this increase.

Beyond the influence of unequal unbraced lengths in consecutive floors on the columns buckling

capacity, the elastic buckling analysis was also used to study the buckling capacity of the non-prismatic

columns located between floors 7 and 9. Again, the procedure in Appendix E3 of the AISC LRFD

Specification (1986) was used to convert the elastic buckling capacities of the non-prismatic members

into allowable inelastic buckling capacities. The average area along the non-prismatic member was used

in the conversion equations. Based on the inelastic buckling capacities of the non-prismatic members, the allowable buckling stress at the minimum section of the non-prismatic members was used in the global

systems computer models. The resulting modifications to the design parameters were as follows:

• Floors 9 to 10: upper coluiTins - Modified F, = Calculated SAP2000 defauh F x 0.89

• Floors 9 to 10: bottom columns - Modified F = Calculated SAP2000 default F, x 1 .08

86 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

Floors 7 to 9: Modified F

axes)

Calculated SAP2000 default (based on K=1.0 about both

X 1.43.

Floors 2 to 7: Modified F Calculated SAP2000 default F x ] .26 a

Floors 2 to 10: C,„ = 1 .0 for out of plane bending and = 0.85 for in plane bending

5.3 BASELINE PERFORMANCE ANALYSIS OF WTC 1

The baseline performance analysis of the global model of WTC 1 was perfonned on a Pentium 4 personal

computer with a CPU speed of 3.06 GHz and 1.0 GB of RAM. The duration of the analysis was about

15 h. The following summarizes the results under the three loading cases.

The analysis reported in this section used the gravity and wind loads used in the original design of the towers, as explained in Chapter 4.

The results of the analysis indicated that for the dead and live loads used in the original WTC design, the core columns and the exterior walls carried approximately 53 percent and 47 percent, respectively, of the

total gravity load at the basement (B6) level.

The calculated total maximum drift of WTC 1 induced by the original WTC design wind loads was

approximately 56.6 in. (4 ft 8.6 in.) in the E-W direction and 55.7 in. (4 ft 7.7 in.) in the N-S direction. These drifts are equivalent to about H/304 and H/309 in the E-W and N-S directions, respectively, where

H is the height of the tower from the foundation level to the roof. Limitation of total building drift under

wind loads was not part of the original WTC design criteria. Instead, inter-story drifts were determined

and compared to the capability of the architectural building systems such as the partitions and the exterior

cladding, to accommodate these inter-story drifts. Accordingly, there is no historical project-specific data

available to which the total drifts may be compared. Figure 5-1 presents the deflected shape (cumulative

drift) and the inter-story drifts normalized by the stoiy height for WTC 1 under the original design loads. The plots are presented for the E-W and N-S directions for the cases producing the maximum cumulative

drift (wind azimuth 0 and 75 degrees for the E-W and N-S directions, respectively, where azimuth 0

indicates tower north).

DCRs were calculated using the SAP2000 computer program. The calculations were spot-checked for accuracy and to verify that the correct design information was being applied. For most of the component

calculations checked, the SAP2000 calculations were found to be acceptable. The DCR statistics for WTC 1 global systems components under the original WTC design loading are summarized in Table 5-1

.

The statistics include, for each member category, the number of members, the mean value of the DCR,

their coefficient of variation (C.O.V.), the percentage of components with DCR greater than 1.0 and

greater than 1 .05, the number of members with DCR greater than 1 .05, and the maximum calculated DCR. Figure 5-2 shows the distribution of DCRs for the four exterior walls of WTC 1 under the original

design loads. Close-up views are provided for the exterior walls below floor 9 in Fig. 5-3. DCRs for the core columns are provided in Fig. 5-4.

NISTNCSTAR 1-2A. WTC Investigation 87

5.3.1 Original WTC Design Load Case
Chapter 5

Interstory Drif/Story Height for Original Wind Load (E-W)

1600 T

0.00 0.20 0.40 0.60

Interstory Drift/Story Height [%]

(a)

Figure 5-1. Drift diagrams of V

(a) AON-EInterstory Drif/Story Height for Original Wind Load (N-S)

1600

0.00 0.20 0.40 0.60

Interstory Drift/Story Height [%]

(b)

1 due to original WTC wind loads,

(b) A75N+E-.

88 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

Table 5-1. Statistics of demand/capacity ratios for WTC 1 under original design

load case.

Percentage Percentage

of of Number of Number Mean c.o.v. Components Components Components Maximum

of Calculated of with DCR with DCR with DCR Calculated

Member Type Members DCR DCR > 1.0 > 1.05 > 1.05 DCR

Exterior \\ all Columns

Below floor 1 628 0.77 0.19 4.3 2.7 17 1.36 Floor 1 to 9 1,122 0.74 0.25 3.3 0.5 6 1.27 Floor 9 to 106 31.086 0.76 0.12 1.1 0.4 121 1.31 Above floor 1 06 578 0.73 0.31 12.3 10.0 58 1.46

Exterior Wall

Sniinrlrpl^

Rplnw flonr 1 4zU U.44 0.4o 0. / A 1

0. / i

1 IV 1 .Z(S Flnnr 1 tn 9 61U 0.34 0.45 1 .

1

1 A

1 .U 6

1 1

A

Floor 9 to 1 06 ^1 1 AO U.J 1 n 'X(\ u. ju AU

A

U

A

U Above floor 1 06 836 0.35 0.69 1 .9 1 .7 14 1 .55 Core Columns 5.219 0.86 0.14 10 5.3 278 1.36 Hat Truss System

Columns 2j9 0.47 0.45 0.4 A A 0.4 1 1 .26 Beams 499 0.24 0.87 0.4 0.2 1 1.07 Braces 279 0.47 0.53 2.5 0.7 2 1.06

Exterior \\ all Bracing

Below floor 1 200 0.72 0.16 2 1 2 1.16 Above floor 1 06 12 0.40 0.52 0 0 0 0.75

NISTNCSTAR 1-2A. WTC Investigation 89
Chapter 5

(a) (b)

0 .00 0 .50 0 .75 1 .00 1 .08

Figure 5-2. Demand/capacity ratios for WTC 1 under original design loads,

(a) north elevation and (b) east elevation.

90 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

0 .00 0 .50 0 .75 1 .00 1 .08

Figure 5-2. (c) south elevation and (d) west elevation (continued).

NISTNCSTAR 1-2A, WTC Investigation 91
Chapter 5

Figure 5-3. Demand/capacity ratios for WTC 1 under original design loads,

(a) north elevation below floor 9.

92 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

i

1

i

i ; i . .

; .

:

r ]

1

i i 1

1

1 !

:

' L ;

A4VK /K/KAAA/1\AAAAA/1\AAAAA

0 .00 0 .50 0 .75 1 .00 1 .OK

(b)

Figure 5-3. Demand/capacity ratios for WTC 1 under original design loads,

(b) east elevation below floor 9 (continued).

NISTNCSTAR 1-2A, WTC Investigation 93
Chapter 5

'TT

H li ! J.J.J.

''1

r

i :i.

/ ! A A A A A Azt\zl\zl\ Azl\ A A A A AA A/tv4\

0.00 0.50 0.75 1.00 1.08

(c)

Figure 5-3. Demand/capacity ratios for WTC 1 under original design loads

(c) south elevation below floor 9 (continued).

94 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

0 .00 0 .50 0 .75 1 .00 1 .08

(d)

Figure 5-3. Demand/capacity ratios for WTC 1 under original design loads, (d) west

elevation below floor 9 (continued).

NISTNCSTAR 1-2A, WTC Investigation 95
Chapter 5

TOWER A, DCR of CORE COLUMN

500's COLUMN NUMBER

501 502 503 504 505 506 507 508

0

(a)

TOWER A. DCR of CORE COLUMN

600's COLUMN NUMBER

601 602 603 604 60S 606 607 608

(b)

"^ti" 0 80

1 10 1 11 1^ 1.T3 0 92

.,...,,.^„. 'T-ii' 0 M

1 M t la n 93

1.Q6 1-25 1.1S Ki 1.09

1 10 i.iO i.ie 1.16 "Vi tt,,

" 1 20 127' "m ' '"HW

"vi'f"

1 ii

'

1,13 —TTi

1 1* ' ' '

'

(1 hf 0 0 8^ 1 !! 1,17 •TIT [J b9 11^ . t.1 9/ [' 9^

1 ,1.. 1.1 'J, yi. .1 97

.. --J 1,10 -r

"

'' "

^'

1 o&

;

"ToT"

1 11- i 1. . V, , 1 ,

1

'

1 Of ' n. 1 OEt 0 97

1 1)^ r^W r. l.fW 0 88

1 01:. 0 9^' 0 yt. ... H' 1.12 0 9i- 1 05 0 76 rci: ( (;.. 085

n.7fi 0 67 ( 7. 0.86 -~- — 1 0(1

n 8/

;i 0 8^ "oeT" 0,99

1 ua-: I) (it. „ 3^ 0 iJ.a O.Bt 1 o:

1 085 uyi.i 0 85 0 bfc 0 ef. 088

u»o 0 70 Ob^ OIW 083 UB3 086

0.84 0 81 0 65 0 W 088 087 0 87 0 91 U83 OO'i 0 85 0 87 0 86 {'tit (IP? ue: OR'. oaf ifiy P.W (ib: (1 m oa^' fl gy 0 9:' UBi 0 'Jo 0 91' 090 0 91

(J SO 0«1 0 89 Otifc t<87 08*^ 0,99 091 0 8:i OM 0 8*) 088 0 89 1.01 0 9:^ 06^ 0 yr 0 91 089 0 91 1 03

Oltj 081 f. 8P 0 87 0 87 S7 1 05

0 91 0 8? CiB7 0 84 OflF, 0 BS 1 07

0.93 0S^^ 0 8^1 0 8" 090 081 Obi, uet. (.

1 07 ——^

. ~ 1 —tr~ —o7~

1 lU

D.BB 0 fi7 ogi 0.92 0 87 0 8fl 1 Of.

0 87 081 0 83

0 8<) 0 P.2 ( H7 1.. 'n 0 87 0 8T 1 05

0 9t' 088 1 07

08ft 0,81 O.Sfl r 8 1 05

0 87 Sl^ 0 "1 I 05

0.9R

..M7,7,,., ..^'^?... 0.92

0,95

II W (1 fir f>l " O70

0 72

0.65 0 91' 0 8- 0 81 092

0.65 0 7fi 0 6,^ 0 W 084 0 81 0 6J 0 77 0 88 08^ 0 80 090 — 0 90 0 91 ^r0.93

0 92

^ J

^' " 9J

0 92 orj --— ^ 0.92 O&l

^.^

".. 0 95

f^<0 0 90 09i

0 95

. ^, ~77

0S£

0 95

OSti —

0.97

-rp ~08{i~

'„ 1^ "TTm— "iJao"

0 79 0 83 0 95

CJB1 0 77 0.80

0 7a 0 9'J 060 094

0 8i 0 82 094 Lj9;i 0G2 0 81 095

0 78 og-i 0 8/ 0 79 0.9a 0P3 0 78 0 82 095

0.8^ 0 80 0 95 096

U9j 0 76 0 90 097 0 67 0^2 0 87

0 5-' 0 55 0 61 0 5v U62

(. S^. 0 62

0 57 U 60

P.6fi Oftl

Oft<( 0 6:

o.eo 0 71^ 088

0 7y 0 78 0 87 0 79 0 88 oei 0 If 0 82 0 90 0 75 08t 0 87 0 87 0 78 064

0 79 0.H3 0 97 O.Bf. 095

O.fK* O.M U9t. 0.96

0 .00 0 .50 0 .75 1 .00 1 .08

Figure 5-4. Demand/capacity ratios for WTC 1 core columns under original design loads,

(a) 500 line and (b) 600 line.

96 NISTNCSTAR 1-2A. WTC Investigation
Baseline Performance Analysis of the WTC Global Models

TOWER A. DCR of CORE COLUMN

700's COLUMN NUMBER

701 702 703 704 705 706 707 708

TOWER A, DCR of CORE COLUMN

800's COLUMN NUMBER

801 1 802 803 1 804 1 805 | 806 | 807

lUe FL 07* Hit, F"L 0.86 —jTqT— ^'S7 0 5^- ,1

"

106 FL 065 10r, FL 0.93 1 0. uii

FL i.cn . -T, Ilk: FL 082 O.SQ o.-w

' ;^ 0 90

103 Fl UJ.i FL C.B7 0 95 066 0 56 0 62 0 97

102 FL 1 ul' F L 047 OtyJ 1Q1 FL 101 FL 0 73 0 79 0.49 ~o"Iq'~ "'o~E,'~ ^

'

100 FL lOLiFL 0 77 0 55 0.55 *^ FL .1 Wl •i'rl FL 0.8S 0 58 0.60 067 OM —Toi

9*^ FL 0 Si "-h FL 0.85 0.S5 0 62 0 71

S7 FL 0.89 0,83 U 58 068 0 55 0 76

96 FL •Ir, FL 0 73 95 FL 0 5c J~ •4'-. FL 0 71 Uti9 0,57 077 0 74 9i FL FL 0 7j

9i FL ii~ 9;-. FL 0.76 ______0.62 0 8?, 0.81 92 FL

51 FL

O.SC'

, 7^

9:' FL

^1 FL

71

Ij 72' —;\.,7 0 7li 0 57 0 75

0 78 0 77 0 80

9<:f. 0 E"" - 0 7;. Fl J 7h r 1 ftTl 11 V r. n 7-1 Dili at FL 0 ei 7i tiK Fl 0 7^ 0 1.7 -

1

0 7f 0 76

&T FL O.H^ SI ^7 FL 0 75 0 6f> iinli ii6F 0 79 0 78

8<e F,. 0 77 ' B-^FL 0 7-1 0 71 0.70 0 76 0 73 0.72 0 73

85 Fl 0 7S ....^ .'^ — 85 FL 0.76 0 7:i 0.72 0 79 0.76 0 74 0.75 FL JD. . H1 tW FL 0 78 0.75 0 75 O 62 0 78 0.76 0 78

B3 FL 0 7if (vs_FL 0 7d 0 70 n71 11 7l.i 0 7ft 0 72 t) 7x1 — _0-Pl_ —IL. ^ifi ^ ''•^ —-.I*:'-..

:^ ^~

'

',' —iTF

—mTt— ^^ " — 078

tTfl— . ^- —?Tfl— — '[

7bT- : I*

'

tTfT— —0 q<i — —0

6^"" 0 »y ^ q-j 0 83 ~"o'b5"" T7FL 77 f.-|_ ~~t75e~ 0 62 11 ?w 0 50 0 68

7*5 FL 7h FL 0 70 0 49 0 58 (ifcS 0 01 0 57 0 71 75 FL 7^. FL OS? 0 91 0 90

Ta FL ^1 7^ FL 0 9IL' o 7^ U7^ uyi 0 91 73 FL - c~ 'J yi 7 1 M r 9: if7|. 0 7f, n 0 72 FL J -J.

,, L,t 7. Kl 0 fi'J (1 7. (1 H'-. (1 87

71 FL 7 1 F-l 0 91 11 7.; 0 7', 0 88 0 89 7VfL '- 7(1 y\_ O^i 0 76 (1 77 U 90 0 91 6^FL u 76 ''I 0 7? 0 7,' II 7- "8'- Q 76 6SFL or; f. T=. FL 0 76 0 77 Li 7h l"4. 0 79 67 FL 0 71 I- 7S r.7 FL 0 7b 0 75 1.1 7H 1.1 SLi 0 92 0 79 66 FL 0.87 0^' 077 (IHIi 0 in 0 aj (1 93

65 Fl OM ' ! 0 91 077 Mhl (.1 8t. 094

6^ FL 0 9t> r,. 1 L 09j osri Utt4 U9'.t 0 67 0 97

Fl 087 ' 1 0 87 1185 0 82 0 92

62 Fl OK -.•^ FL 0 89 0 7f. ri 1186 U 9.1 61 Fl oai - ^ '- " '' t.1 FL 0 91 077 LI 88 0 95

60 FL OS' hi) FL Oftt. n T" nhl 0 H.' tl 9J

58 Fl OS? " '* FL U9>' nsn II 8' 0 95

5* FL 0£9 - ':.F. n r. II H. 11 H', " 0 17 ST FL Q8"

56 FL 0 89 0 95

55 FL 0 .1 '^^ Fl 0 !il 11 7« u 0;) U 89 0 97 Si FL Ofci -_ FL 0 fi7 0 9? 53 FL 0!n; 'i 1 F

1

( sa 11 H1 0 R"". 0 94 52 FL OP- OtL LI 83 0 95

51 Fl "oei~ 9; 0 m 0 76 0 fiF 0<t1 0 85 — —ill_L

^ — —— 0 86

—

u7o _

"TTq—

zZl^ -Sff — —iZJil

_0H1

—2.?*".- 0 7H __0_87

'^'^'^

1

45 FL OS? FL 0 75 11 73 FL i-: Fl || 7 .1 0 81,1 (18/ ii 76 4J FL 42 Fl 0 •>' :. 1 L ( r, . 1) 7.1 0 68

41 Fl 09' U 87

Fl —

Ci 97

35- Fl f I 0 Bi> 0 77 0 87 0 90 — 0 7C 0 85 0 91 Ptl— — —^ItTI— "oTT" Li76 0.90 0 86 0,92 0 89 —STi

—^"yi" —(Tr— —^,

' ,1 ^,

(1 7H 0 90 —STfl— —t~7T

"'

0 sw —jtTl— ,

^ .-^^ —TTi;; ^v- - —iTfi— ^^^ ' " ^" - —

,1^' — — —^TTl— —

0 H7 —iTT—

'

yj'^^

' —iTTi

jj'^-" " — o'as"

TTfT— OflT !^ on"' —rrn

fit,'- —n 87 0 90

U 88

15 FL oef= Oftfi 0 86 0 89

1-1 FL OS"' 1.187 0 33 1)87 0,36 0 90 nFL Ofii- 0.90 0 88 0 87 090

1?FL 08- UFL 0 79

11 Fl 0 8JI uaa nfl6

10 FL oa?. -.90 1i>Fl 0 69 a9» 0 90

0 97 oe? W. FL uas 0 97 0.91 07H 0 88

07 FL (i7 FL 0 7u 0 55 06 FL 07t nh FL 0,50 0 0 71 05 FL 071 0 72 U57 0 58 0 72

fti FL Urt FL 0 70

03 Fl 0 7i >j 79 oao 0 80

02 FL 0 8.T 01 FL Ofci JiS7 0*1 II 92 B1 FL OiU o.ae (1 9J 62 FL Oftf U/ FL 089 0 92 &3 FL &P 1 b! FL n78 0 87

fr: Fl 0(f- b.-. FL 0.37 0 fs? 0 87 0 97 85 FL ObA 8C FL 0-83 0,86

(c) (d)

0 .00 0 .50 0 .75 1 .00 1 ,08

6-

Figure 5-4. Demand/capacity ratios for WTC 1 core columns under original design loads,

(c) 700 line and (d) 800 line (continued).

NISTNCSTAR 1-2A. WTC Investigation 97
Chapter 5

TOWER A, DCR of CORE COLUMN

900's COLUMN NUMBER

901 902 903 904 905 906 907 908

TOWER A, DCR of CORE COLUMN

1000's COLUMN NUMBER

1001 1002 1003 1001 1005 1006 1007 1008 m

1 13

1 >! IJ Hm

ri q(. n 84

0 94

"iM" 96 i:w.

64

0 6"

96 0 97

n 7fl n flji f>90 0 fi"^

r, pr. 1, U.I

4 1,D9 —

\

111 t«

-iT'

., (J,,

,

i 09

• ^ 0 S.,.' 09U U8b

0.81 0 81 0 76 0 51 U 82 084 088

0.88 0 87 0B2 096 0 82 086 0 89 0 95

0,86 0 85 IJ fi? 11 9F, 0 87 ti 92

r. ah n fl't

"~~o

' Aj

099 1. H.'

1 03 0 93 086

1 Ot 0,88 0 85 ( HA

- WO 1

... ., . 1 1 — 1

ri 87 ^ _. ---^yr

....Jl. M,„,

lost

1 12 0 87 0 92 111

n fi9 It

0.77

065 083 096 0 63 OBJ

1 00 084 •Pi"

1 02 0E5 fl a-i U til1 01' 0 64 0 85 1.1 0 85 0 67

0 86

O.Bfi n fl7

.1 096

1

17.' n 8'. fl 87 "TW 0 K7 n ay 0 9fl

108

•TW oav 87 ..m.-

0 an 0.91

111 o.afl 0 91 t t 0 8S 0 86 b&y

oyi 095

06i 0 6: ObS 0 62 0 63

0.7?

1 ot I,S6

,1S„

lU,. 1 ..r

(e)

ii P-i 1 13 fl =1) 1 n- 1 . ).! 1.11 1 03

0 90

0 9.1 1 1'" 0 91 1- 1^1. 'lis" 0 95 iAi

0 83

II Hh 1 II. 0 9t 11 u 1 !.i y . !,Cl8 0 89

(1 7.1 1 . p,l

.

II HP 1 7J U.74 0 78

0 r:' (1 1: 47 1 ,-i<-i 11 >-h 1 Hi 0 82

0 6^ II 11 t; 1.1 yi 1' (it. ,. 7.-1 0 07 0 70

0 73

0 69

II H 11 r,r, 0 Hli (1 77 fl fl-l 0 72

U 71 .1 (. 7^ li .1 fiRIi u 8t. 0 74

n f. 1 I. — I. 61-. 1. 7P ri 77 081 «M 11 (T-i g m L. 7.. 11811 0.84 _Olj_ — ''I' _ua£_ " _U_|iJ_ 0 87 JlH— "TTT

I"! ~- -~- TT^^

TTT" •~"7f "TTT"" 'Y,

1, a'- fl cvl H

' fl96 0 93

0 4r. n t|7 0 7P, ii HI i.hm 0 9*1 0 96 09) 1 IM . : 71 1 .|. i h!7 Ii an 091

( 7. ' 0 94

1.09 ' ^' 0 9b

'' " J

"

'J

1 -Li±_ " .. -liiiL.

'\' '

. —77;—

'

, , ^.-^ j

' ^ 'J:;--

1. Hj< I, c,: i.M. 0.96 0 02

'

1 H 1 I. P-1 iri^l fl n-< (.P7 0 87

,1 .-1 1, H--. oa4 0 91 11 a'-' 0 93 0 69

0 91 0 9.1 0,87 1-1% 0 9T 0.91 0 96 0 91

0,84 0 67 OfW 0 9? 068 084 0 8S 0.84

0,87 0 9{.i 0 87 0.96 0 91 0 87 0 9^ 0 67

0 87 0 91 0 87 096 0 91 0 88 0 92 0 86 yyT 1

1

118'. V yy 11 (.1 90 oyS 091

us. n V. f 11 (17 fjyt. 0.93 0 94 II ) .1 1. yu 0 98 094

0 -n |"i 91 1 fi-i fl 95 n R9 o9.^ 0.91 09 ' ,. y

=

f' Kt 1 0 9r. 0 91 119'. 0 93 094 ,, .p (-EJ- 11 U 92 fii:- 0 95 091 u 9.1 iiM . 1 111 0 0 8y nq-i 0.91 0 92 {1 9.1 ij HA 1 (1 (ice, 0 91 0 95 0 92 094 0 9b I et 1 Or U97 0 92 0 97 0.94 0 92 o.9:< U8J 1 0; 1194 0 89 0 93 0 92

0 95 0 95 0 93

0 95 ii m. " 8^ 1 ij'-. 11 '^7 0 9.' 0 97 0 95 — '1^^ .. —L!iL_ -—

0 4, >.i ^1 1' H. 1 I.L U 95 (1 a9 11 9^1 0.92 0

9'- 0 96 0.93

n.8<t U 9i< 0 iHj I 01 0 9f. u 85 0 89 0 89

0,90 0 92 0 81 0.91 oaf. 090 0 90

0.91 0.93 062 0 93 0 87 0 92 0 91

' ' ' " """rp~

" '' '''' ,," . " ^''^ "

0 68

0 »iH o.eo II 97 0 88 0 8? 1187 0 89

(f B6 0 8(1 0 96 0 89 0 83 088 0 90

0 87 0 87 088 0S9

0 R"-! fl 8H 0 p.? 1 0! 0 88 0 84 0 87 0 90

0 fl9 11 R7 11 SI n 97 fl R7 0 85 0 90

11 84 0 91 0 9^ ,, y^. ., a 1 1 Oi.t fl ec. 11 MS 088 0 92

u as 0,89

0 3. (1 bb OB''- 0 87 0 90

fl <i| 11 8^1 1 11 a"' 088 0 91

11 r. pi fl H" Oflh II fj-. i| 9?

II 1411 0 ao bi 1 '1] 0 a-j li 85 118'. 0 9lJ 0 HO

08tt 'J 85 fl64 0 88 uas 0 89

fl qfi 11 87 ,

, y._ y ti 87 1) 8fo o6<(

(1 P.I- „, 1 '11 I '81^ n 85 0 85 0.86

fl 36 lift*. 0 flT n flS II R1 ) (11 0 8', 0 84 (187

1115^. U *i 1 0 aj [1 84 1185 0 88

0 89

0 87 0 87

0 88 U 87 fl 85

0 85 0 88

0 flfi 0 69

fl 86 fl 87 0 an 096 0 98 0 87 our

0 79 0 79

0 81

0 Bfi 0 79

0.7(4 0 94 f>81 0 86

OBfi (1 BO Oft"l 0 82 0 83 0 79 0 95 0,83 061 0 8.1 0.83 0 82 0,911 0 82

0,84 0 83 0 7<J 0 95 084 oei 084

0 82 0 67

0 92 085 0.86 0 83 0.88 0 85 1 00 f).86 0 63 086 0.88

(f)

0 .00 0 .50 0 .75 1 .00 1 c08

Figure 5-4. Demand/capacity ratios for WTC 1 core columns under original design loads,

(e) 900 line and (f) 1000 line (continued).

98 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

The npes of members in the exterior wall that had DCRs larger than 1 were calculated for a combination

of axial load and bending under a combination of gravity and wind loads and were generally found in three types of location:

1 . Columns at the comers;

2. Where the hat truss connects to the exterior wall; and

3. Below floor 9.

The members in these locations would be expected to experience large forces. The comer columns had some of the highest calculated forces under wind loads. The hat truss-to-exterior wall connections

interconnected two major stmctural systems with large concentrated load ti-ansfers. The exterior wall

below floor 9 was a highly x ariable and articulated structural system that had large calculated forces. Given the extraordinary difficulty of replicating with precision a set of engineering calculations

perforaied almost forty years ago with relatively mdimentai^y computational tools, DCRs in excess of one were observed in the analysis at locations of highest forces and at locations where there was significant

complexity of system behavior.

The core columns that had DCRs larger than 1 were calculated for axial stresses due to gravity loads and were generally located on the 600 column line between floors 80 and 106 and at core perimeter columns

901 and 908 for much of their height. The gravity loads on these columns were affected significantly by

assumptions about tributary areas, unit construction dead loads and superimposed dead loads, and the sequence of construction of the hat tmss. The high degree of stress calculated at these core columns is likely associated with differences in these assumptions between the original and cunent computations.

Figure 5-5 presents the distribution of the normal stresses due to axial loads (axial coluinn load divided

by columns cross sectional area) in the columns of the four exterior walls due to wind loads only (gravity

loads are not included in these plots). The axial stresses are presented at three levels along the height of

the tower: B6, 39, and 73. The plots show both the tensile and compressive stresses on the columns

induced by wind loading, where shear lag effects can be observed. For comer columns 101, 159, 301,

and 359 at floor 73, Fig. 5-5(c) indicates that their stresses are smaller than their neighboring columns.

This is likely due to the influence of the special comer framing at that floor, i.e., the discontinuous

columns and chamfered plan layout of the exterior wall framing.

The results of the baseline performance analyses indicated that tension forces were developed in the

exterior walls of WTC 1 under the original WTC design dead and wind loads. The tension forces from

the combination of dead and wind loads for all faces are illustrated in Fig. 5-6. The figure indicates that tensile forces are largest at the base of the building and at the comers.

These axial tensile column loads were transferred from one panel to another through the column splices.

The exterior wall column splice capacities were calculated from the original details and compared to the tension forces for all four faces of WTC 1 . The DCR ratios for the exterior wall splice connections for WTC 1 are summarized in Table 5-2.

For the tower resistance to shear sliding and overtuming due to wind, the dead loads that acted on the perimeter walls of the tower provided resistance to shear sliding and overtuming at the foundation level.

NISTNCSTAR 1-2A. WTC Investigation 99
Chapter 5

Considering the resistance to shear sliding under wind load, the factor of safety was estimated to be

approximately 11. 5. This was calculated by dividing the resisting force due to dead load on the perimeter

wall (a coefficient of friction of 0.7 was used) by the wind shear at the foundation level. Considering

resistance to overturning due to wind load, the factors of safety were estimated to be approximately 2.3 and 2.6 for overturning about a north-south axis and for an east-west axis, respectively. This was

calculated by dividing the resisting moment due to dead load on the perimeter wall by the overturning

moment due to wind load taken at the foundation level.

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

-30

300 Face (South Columns) - FL B6

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

459 401

400 Face (West Columns) - FL B6

(a)

Figure 5-5. Shear lag diagrams of WTC 1 due to original WTC wind loads at

(a) floor B6, (b) floor 39, and (c) floor 73.

100 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

30

20

10

0

-10

-20

-30

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

100 Face (North Columns) - FL 39

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

259 201

200 Face (East Columns) - FL 39

Tower A: West to East Wind (AON-E-)

(Gravity Loads not Included) 30

20

-30

300 Face (South Columns) - FL 39

(b)

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

459 401

400 Face (West Columns) - FL 39

Figure 5-5. Shear lag diagrams of WTC 1 due to original WTC wind loads at

(a) floor B6, (b) floor 39, and (c) floor 73 (continued).

NISTNCSTAR 1-2A. WTC Investigation 101
Chapter 5

30

20

10

0} U

ra -10 X<

-20

-30

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

100 Face (North Columns) - FL 73

30

20

10

0

-10

-20

-30

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

259 201

200 Face (East Columns) - FL 73

30

20

« 10

(AS 0 1 -10 X<

-20

-30

Tower A: West to East Wind (AON-E-)

(Gravity Loads not included)

301

359

300 Face (South Columns) - FL 73

Tower A: West to East Wind (AON-E-

(Gravity Loads not included) 30

20

10

-10 -

-20

-30

459 401

400 Face (West Columns) - FL 73

(C)

Figure 5-5. Shear lag diagrams of WTC 1 due to original WTC wind loads at

(a) floor B6, (b) floor 39, and (c) floor 73 (continued).

102 NISTNCSTAR 1-2A. WTC Investigation
Baseline Performance Analysis of the WTC Global Models

240-249 2 50-259

(a) (b)

0 100 500 lood

Figure 5-6. Tension force distribution (kip) in the exterior wall columns of WTC 1 under

original design dead and wind loads, (a) 100 face (north) and (b) 200 face (east).

NISTNCSTAR 1-2A. WTC Investigation 103
Chapter 5

300-309 310-319 320-329

1 330-339| 340-349{ 350-359 400-419 410-419 420-429 430439 440-449 450-459

{

V

(C) (d)

100 500 100(1

Figure 5-6. (c) 300 face (south) and (d) 400 face (west) (continued).

104 NISTNCSTAR 1-2A. WTC Investigation
Baseline Performance Analysis of the WTC Global Models

Table 5-2. Maximum calculated demand/capacity ratios (OCRs) for exterior wall column

Exterior Exterior \\ all Maximum

^^ all Fac6 Column Splices caicuiatefl ui_K

Below floor 1 0.64 100 Face Floor 1 to 9 0.31

( iNortn

)

rloor lU to 41 0.96 Abo\'e floor 42 0.26 Below floor 1 0.53 200 Face Floor 1 to 9 0.32

(East) rloor 1 U to 41 0.6j

Abo^e floor 42 U. 14 Below floor 1 0.54 JUU race Moor 1 to 9 0.26 (South) Floor 10 to 41 0.77 Above floor 42 0.15 Below floor 1 0.59 400 Face Floor 1 to 9 0.36 (West) Floor 10 to 41 0.84 Above floor 42 0.26

5.3.2 State-of-the-Practice Case

The WTC 1 global model was analyzed using the lower estimate, state-of-the-practice loading case, as described in Chapter 4 (see also NIST NCST.AR 1-2). This loading case included dead loads, live loads

according to the NYCBC 2001. and wind loads from the Rowan Williams Da\ ies and Irwin. Inc. (R\\'DI)

wind tunnel study, scaled in accordance with NYCBC 2001 wind speed.

The calculated total drift of WTC 1 induced by the lower estimate, state-of-the-practice case was

approximately 56.8 in. (4 ft 8.8 in.) in the E-W direction and 68.1 in. (5 ft 8.1 in.) in the N-S direction. The drifts are equi\ alent to about H/303 and K''253 in the E-W and N-S directions, respectively.

Figure 5-7 presents the deflected shape (cumulati\ e drift) and the inter-storv' drifts normalized by the

storv' height for WTC 1 under the state-of-the-practice case. The plots are presented for the E-W and N-S

directions for the load combinations producing the maximum cumulative drift. DCR statistics for WTC 1 global system components under the lower estimate, state-of-the-practice

loading case are summarized in Table 5-3. A comparison of the mean values of the DCRs estimated

from the original design case (Table 5-1) with those from the state-of-the-practice case (Table 5-3)

indicated that the results are very similar. Also, the distribution of the DCRs and the locations of

members with DCRs greater than 1 .0 were very similar betv\'een the original design case and the state-of- the-practice case.

NISTNCSTAR 1-2A. WTC Investigation 105
Chapter 5

Interstory Drif/Story Height for RWDI/NYCBC Wind Load (E-W)

1600

0.00 0.20 0.40 0.60 Interstory Drift/Story Height [%]

Interstory Drif/Story Height for RWDI/NYCBC Wind Load (N-S)

1600

(a)

0.00 0.20 0.40 0.60 0.80 Interstory Drift/Story Height [%] (b)

Figure 5-7. Drift diagrams of WTC 1 due to the lower estimate, state-of-the-practice

loads, (a) 1R14PDN and (b) 1R8PDN.

106 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

Table 5-3. Statistics of demand/capacity ratios (OCRs) for WTC 1 under the lower

estimate, state-of-the practice case.

Percentage Percentage

of of Number of Number Mean Components Components Components Maximum

of Calculated c.o.v. with DCR with DCR with DCR Calculated

Member Type Members UCK 01 UCK > l.U > 1.05 > 1.05 DCR

Exterior Wall

Columns

Below floor 1 628 0.77 0.19 6.1 4.0 25 1.30 Floor 1 to 9 1,122 0.78 0.26 13.1 5.2 58 1.15 Floor 9 to 106 31.086 0.78 0.13 2 0.9 281 1.44 /\UUVC liUUl J UU 578 0.71 0.31 10.7 7.6 44 1.36 Exterior W all Spandrels

Below floor 1 4_U n AQ U.40 A 1 nlU Floor 1 to 9 A 1 n 0 I u U.J / 1 .J

1 1 1 .

1

7 1 T)

Floor 9 to 106 31.160 0.32 0

''9 A nu u.ou Above floor 1 06 836 0.35 0.70 1.9 1 .7 14 1.57 Core Columns 5.219 0.86 0.14 9.9 5.3 278 1.36 Hat Truss System

Columns 239 0.45 0.50 0.4 0.4 1 1.26 Beams 499 0.23 0.93 0.2 0.2 1 1.07 Braces 279 0.41 0.60 1.1 0 0 1.03 Exterior WaW

Bracing

Below floor 1 200 0.76 0.16 2.5 2 4 1.18 Above floor 1 06 12 0.35 0.47 0 0 0 0.64

5.3.3 The Refined NIST Estimate Case

The WTC 1 global model was analyzed using the refined NIST estimate case, as described in Chapter 4

(see also NIST NCSTAR 1-2). This loading case included dead loads, live loads in accordance with the ASCE 7-02 Standard, and w ind loads developed by NIST based on critical assessment of information

obtained from RWDl and GPP reports and state-of-the-art considerations in wind engineering.

The calculated total drift of WTC 1 induced by the refined NIST estimate case was approximately 70.6 in.

(5 ft 10.6 in.) in the E-W direction and 83.9 in. (6 ft 1 1.9 in.) in the N-S direction. These drifts are equivalent to about H/244 and H'205 in the E-W and N-S directions, respectively. Figure 5-8 presents

the deflected shape (cumulative drift) and the inter-story drifts normalized by the story height for WTC 1 under the refined NIST wind loads. The plots are presented for the E-W and N-S directions for the load

combination producing the maximum cumulative drift.

NIST NCSTAR 1-2A. WTC Investigation 107
Chapter 5

Interstory Drif/Story Height for NISTWind Load (E-W)

0.00 0.20 0.40 0.60 0.80

Interstory Drift/Story Height [%]

(a)

interstory Drif/Story IHeight for NiSTWind Load (N-S)

0.00 0.20 0.40 0.60 0.80

Interstory Drift/Story Height [%]

(b)

Figure 5-8. Drift diagrams of WTC 1 due to refined NIST estimate wind loads,

(a) 1R14PD and (b) 1R8PD.

108 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

DCR statistics for WTC 1 global systems components under the refined NIST estimate case are summarized in Table 5—4. The DCRs for the core columns and hat truss members estimated from the

original design and the state-of-the-practice cases (Tables 5-1 and 5-3, respectively) are generally close

to those estimated from the refined NIST estimate case (Table 5^). This is due to the fact that core columns and hat truss members do not significantly contribute to wind load resistance. The DCRs for the

exterior walls, including columns, spandrels, and bracings calculated from the refined NIST estimate case

are larger than those estimated from the original design and the state-of-the-practice cases. For example,

for the exterior walls, the ratio of the mean DCRs from the refined NIST estimate case to the mean DCRs

from the original design case ranged from 1 .84 to 1.11. The ratio of the mean DCRs from the refined

NIST estimate case to the mean DCRs from the lower estimate, state-of-the-practice case ranged from

1.65 to 1.14.

Table 5-4. Statistics of demand/capacity ratios (DCRs) for WTC 1 under the refined NIST

estimate case.

Percentage Percentage

of of Number of Number Mean rf^ \7 co.v. Components Components ^ „ „ ^^^^ Components Maximum

of f^alnilafpfl of with DCR with DCR with DCR Calculated

Member Type .Members DCR DCR > 1.0 > 1.05 > 1.05 DCR

CAICI lUI TT ^11 Columns

Below floor 1 628 1.04 0.24 52.5 47.3 297 1.95 Floor 1 to 9 1,122 1.11 0.27 69.0 63.6 714 1.69 Floor 9 to 106 31,086 1.10 0.14 72.1 59.7 18572 2.05 Above floor 106 578 0.81 0.28 19.7 14.2 82 1.57

Exterior Wall

Spandrels

Below floor 1 420 0.81 0.46 22.

1

21.4 90 2.05 Floor 1 to 9 610 0.61 0.45 8.0 4.3 26 2.03 Floor 9 to 106 31,160 0.52 0.29 0.5 0.3 109 1.32 Above floor 1 06 836 0.41 0.68 2.4 1.9 16 1.82 Core Columns 5.219 0.84 0.15 8.9 5.2 270 1.40 Hat Truss System

Columns 239 0.53 0.49 3.8 0.8 2 1.26 Beams 499 0.26 0.93 1.8 1.4 7 1.30 Braces 279 0.49 0.55 6.1 2.5 7 1.10

Exterior Wall

Bracing

Below floor 1 200 1.11 0.18 73.0 62.0 124 1.76 Above floor 106 12 0.52 0.42 0 0 0 0.90

5.4 BASELINE PERFORMANCE ANALYSIS OF WTC 2

The baseline performance analysis of the global model of WTC 2 was perfonned on a Pentium 4 personal

computer with a CPU speed of 3.06 GHz and 1 .0 GB of RAM. The duration of the analysis was about

15 h. The following summarizes the results under the three loading cases.

NISTNCSTAR 1-2A, WTC Investigation 109
Chapter 5

5.4.1 Original WTC Design Load Case

The analysis reported in this section used the gravity and wind loads used in the original design of the towers, as explained in Chapter 4.

The results of the analysis indicated that for the dead and live loads used in the original WTC design, the core coluinns and the exterior walls of WTC 2 earned approximately 53 percent and 47 percent,

respectively, of the total gravity load at the basement (B6) level.

The calculated total drift of WTC 2 induced by the original WTC design wind loads was approximately

51.2 in. (4 ft 3.2 in.) in the E-W direction and 65.3 in. (5 ft 5.3 in.) in the N-S direction. These drifts are equivalent to about H/335 and H/263 in the E-W and N-S directions, respectively. Similar to WTC 1, building drift under wind loads was not a design criterion and accordingly, no historical project-specific

data is available to which the total drifts may be compared. Fig. 5-9 presents the deflected shape

(cumulative drift) and the inter-story drifts normalized by the stoiy height for WTC 2 under the original

design loads. The plots are presented for the E-W and N-S directions for the cases producing the maximum cumulative drift (wind azimuth 180 and 90 degrees for the E-W and N-S directions,

respectively, where azimuth 0 indicates tower north).

DCRs were calculated using the SAP2000 computer program. As was done for WTC 1, the calculations were spot checked for accuracy and to verify that the conect design information was being applied, and

the calculations were found to be acceptable. The DCR statistics for WTC 2 global systems components

under the original WTC design loading are summarized in Table 5-5. Figure 5-10 shows the distribution of the DCRs for the four exterior walls of WTC 2 under the original design loads. Close-up views are provided for the exterior walls below floor 9 in Fig. 5-1 1 . DCRs for the core columns are illustrated in Fig. 5-12.

The types of members in the exterior wall that had DCRs larger than 1 were calculated for a combination

of axial load and bending under a combination of gravity and wind loads and were generally found in three types of location:

1 . Columns at the comers;

2. Where the hat tmss connects to the exterior wall; and

3. Below floor 9.

The members in these locations would be expected to experience large forces. The comer columns had some of the highest calculated forces under wind loads. The hat tmss-to-exterior wall connections

interconnected two major structural systems with large concentrated load transfers. The exterior wall

below floor 9 was a highly variable and articulated structural system that had large calculated forces. Given the extraordinary difficulty of replicating with precision a set of engineering calculations

performed almost 40 years ago with relatively rudimentary computational tools, DCRs in excess of one were observed in the analysis at locations of highest forces and at locations where there was significant

complexity of system behavior.

110 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of ttie WTC Global Models

Interstory Drift/Story Height for Original Wind Load (E-W)

1600

0.00 0.20 0.40 0.60

Interstory Drift/Story Height [%]

(a)

Interstory Drift/Story Height for Original Wind Load (N-S)

1600

1400 — 1200 ^ 1000

800

600

o) 400

200

0.00 0.20 0.40 0.60

Interstory Drift/Story Height [%]

(b)

Figure 5-9. Drift diagrams of WTC 2 due to original WTC wind loads,

(a) B180N+E- and (b) B90N-E+.

NISTNCSTAR 1-2A. WTC Investigation 111
Chapter 5

Table 5-5. Statistics of demand/capacity ratios (OCRs) for WTC 2 under original design

load case.

Percentage Percentage

of of Number of Number Mean Components Components Components Maximum

of Calculated c.o.v. with DCR with DCR with DCR Calculated

iTiiiriiiuci 1 > ijc \'1 pin hpt*c ncR > 1 fi^ 1 / V IX

Exterior Wall

V UIUII1II3 Rplnw flnnr 1 5 / / 0. /4 0,22 4.2 ^ n 1 T

1

7

1 C"?

1 .53 rFlnor luui 11 tnlu Q" 1,122 0.73 0,25 2.3 0.7 8 1.19 Flnnr Q tn 1 (\f\ 31,086 0.81 0,12 4.1 2.9 91

1

1.37 Above floor 106 J / o U. / J Qy.yQ J / 1 .J J Exterior Wall

Spandrels

Below floor 1 408 0,47 0.47 2.2 1.7 7 1.37 Floor 1 to 9 594 0.38 0.47 1 .3 1 .3 8 1 .47 Floor 9 to 106 31.160 0.34 0.30 0 0 0 0.86 Above floor 106 836 0.34 0.71 1.7 1.4 12 1.59 Core Columns J. J4 J U.OO 1 A 0

1 U.o O.O J .JO Hat Truss System

Columns 238 0.50 0.58 4.6 3.4 o8

1 AO

1 ,48 Beams 504 0.24 0.80 0.2 0 0 1,01 Braces 283 0.44 0.57 3.5 1.1 3 1,09

Exterior Wall

Bracing

Below floor 1 227 0,70 0.16 1,3 0 0 1,04

Above floor 106 12 0.31 0.41 0 0 0 0,52

112 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

j

i

i!

fa) (b)

0 .00 0 .50 0 .75 1 .00 1

Figure 5-10. Demand/capacity ratios for WTC 2 under original design loads, (a) west

elevation and (b) north elevation.

NISTNCSTAR 1-2A. WTC Investigation 113
Chapter 5

1

0 .00 0 .50 0 .75 1 .00 1 .08

114

Figure 5-10. (c) east elevation and (d) south elevation (continued).

NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

0 .00 0 .50 0 .75 1 .00 1 .08

(a)

Figure 5-11. Demand/capacity ratios for WTC 2 under original design load case,

(a) west elevation below floor 9.

NISTNCSTAR 1-2A, WTC Investigation 115
Chapter 5

i. . . j } j j

; J

1 M i i ! i ; I

0 .00 0 .50 0 .75 1 .00 1 .08

(b)

Figure 5-11. Demand/capacity ratios for WTC 2 under original design load case,

(b) north elevation below floor 9 (continued).

116 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

0 .00 0 ,50 0 .75 1 .00 1 .08

(c)

Figure 5-11. Demand/capacity ratios for WTC 2 under original design load case,

(c) east elevation below floor 9 (continued).

NISTNCSTAR 1-2A, WTC Investigation 117
Chapter 5

i

I

it

..t-J....|...t.,.|.. l-.i- mini

0 .00 0 .50 0 .75 1 .00 1 .ON

(d)

Figure 5-11. Demand/capacity ratios for WTC 2 under original design load case,

(d) south elevation below floor 9 (continued).

118 NISTNCSTAR 1-2A. WTC Investigation
Baseline Performance Analysis of the WTC Global Models

TOWER B. DCR of CORE COLUMN

500's COLUMN NUMBER

501 I 502 I 503 I 504 I 505 I 506 U I

TOWER B, DCR of CORE COLUMN

600's COLUMN NUMBER

601 I 602 I 603 I 604 I 605 { 606 I 607 I 608

(a)

i.ni"' 133 ( <-ii. 1.1s (1 fi7

1 II- 1 11- 1 i.

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0«7 0 87 0.98 094 0.99

0.87 0.87 098 0.94 0.84 0.99

(b)

0 .00 0 .50 0 .75 1 .00 1 .08

Figure 5-12. Demand/capacity ratios for WTC 2 core columns under original design

loads, (a) 500 line and (b) 600 line.

NISTNCSTAR 1-2A, WTC Investigation 119
Chapter 5

TOWER B. DCR of CORE COLUMN TOWER B, DCR of CORE COLUMN

LEVEL 700's COLUMN NUMBER LEVEL 800's COLUMN NUMBER

701 702 703 705 706 707 708 801 802 803 804 805 806 807

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BJ FL 0 93 B4 Fl 0.97 B5 FL 0.93 85 FL 0 98 0 87 0 97

(c) (d)

0 .00 0 ,50 0 .75 1 ,00 1 .08

Figure 5-12. Demand/capacity ratios for WIG 2 core columns under original design

loads, (c) 700 line and (d) 800 line (continued).

120 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

TOWER B. DCR of CORE COLUMN

9O0's COLUMN NUMBER

901 I 902 I 903 I 904 I 905 I 906 I 907 { 908

TOWER B, DCR of CORE COLUMN

lOOO's COLUMN NUMBER

1001 1002 1003 1004 1005 1006^

^°

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FL

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2fiFi- 27 fL 'y ^^"i n~ 27Tl T- —7T~ "'0'TM

2eFL

35 FL -~a7- 2^Tl ~0H PC ^ 24 FL —

23 FL

22 FL

2' FL '"i'Vj"' \ 'ui' —JTfl— ;

; ^- , '^^)'^gy^

?r.' Fl —uTfl—

ITFL "TTT" —~h-^ 1 tt 17 FL O.BP 0 ftl 1 (k. (. Hf' Oh ; 0 97 ItFL 1 w L-^ (

a

16 FL 0 89 n U7 IfFL 1,11 If. FL 0 87 095

14 FL I a 1

«

!! FL 08"

13 FL 1 re. o.eb 0 84 0 97

1? FL 1 ti 1^ FL 094

11 FL I ii 1.10 11 FL 0 et 0 flS 095

1f.FL 1 rz 10 FL o.eB 0 87 086 ^— OaFL 0.96 0.90 89

Ofc FL — 08 FL 0,96 0.91 1,13 0 89

D7 Fl — 07 FL 0,72 74 0 85 OcFl « FL 0 79 0 73 0.75 0.66

Of. Fl

1

05 FL 0 79 0 73 0.75 0 75 04 FL 0 7? 084

1 —

1—

-

] --- 03 FL 0 92

02 Fl OZFL 093

01 FL .» 01 FL

Bl FL Bl FL oao 0 88 B2 FL ... B2 FL y 78 099 0.88 Bi FL —rB3 FL 0 87 0 79 0,79 &4 FL

-

B-: FL 0 93 DfW 1 07 064 0.87 1 00 B5FL 1 B5 FL 0-87 0,M 1.07 0.64 1 01

(e) (f)

0 .00 0 ,50 0 .75 1 .00 1 .08

Figure 5-12. Demand/capacity ratios for WTC 2 core columns under original des

loads, (e) 900 line and (f) 1000 line (continued).

NISTNCSTAR 1-2A. WTC Investigation
Chapter 5

The core columns that have DCRs>l were calculated for axial stresses due to gravity loads and were

generally located on the 600 column line between floors 80 and 106 and at columns 901 and 908 for much of their height. The gravity loads on these columns were affected significantly by assumptions

about tributary areas, unit construction dead loads and superimposed dead loads, and the sequence of

constmction of the hat truss. The high degree of stress calculated at these core columns is likely

associated with differences in these assumptions between the original and current computations.

Figure 5-13 presents the distribution of the nonnal stresses due to axial loads (axial column load divided

by columns cross sectional area) in the columns of the four exterior walls due to wind loads only (gravity

loads are not included in these plots). The axial stresses are presented at three levels along the height of

the tower: B6, 39, and 73. The plots show both the tensile and compressive stresses on the columns

induced by wind loading, where shear lag effects can be observed. For corner columns 101, 159, 301,

and 359 at floor 73, Fig. 5-1 3(c) indicates that their stresses are smaller than their neighboring columns.

This is likely due to the influence of the special comer framing at that floor, i.e. the discontinuous

columns and chamfered plan layout of the exterior wall framing.

The results of the baseline performance analysis indicated that tension forces were developed in the

exterior walls of WTC 2 under the original WTC design dead and wind loads. The tension forces from

the combination of dead and wind loads for all faces are illustrated in Fig. 5-14. The figure indicates that forces are largest at the base of the building and at the comers.

These axial tensile column loads were transfeiTed from one panel to another through the column splices.

The exterior wall column splice capacities were calculated from the original details and compared to the tension forces for all four faces of WTC 2. The DCR ratios for the exterior wall splice connections for WTC 2 are summarized in Table 5-6.

For the tower resistance to shear sliding and overtuming due to wind, the dead loads that acted on the perimeter walls of the tower provided resistance to shear sliding and overturning at the foundation level. Considering the resistance to shear sliding under wind load, the factor of safety was calculated to be

approximately 10. Considering resistance to overturning due to wind load, the factors of safety were

calculated to be approximately 1.9 and 2.7 for overturning about a north-south axis and for an east-west

axis, respectively.

122 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included) 20

15

tn i. 5

.159

5 -10

-15

-20

100 Face (West Columns) - FL B6

20

15

10

5

0

-5

-10

-15

-20

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included)

201

259

200 Face (North Columns) - FL B6

Figure 5-13. Shear lag diagrams of WTC 2 due to original WTC wind loads at

(a) floor B6, (b) floor 39, and (c) floor 73.

NISTNCSTAR 1-2A. WTC Investigation ]23
Chapter 5

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included)

159 101

100 Face (West Columns) - FL 39

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included)

201

200 Face (North Columns) - FL 39

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included) 20

15

10

5

0

-5

-10

-15

-20

359 301

300 Face (East Columns) - FL 39

Tower B: West to East Wind {BON+E+)

(Gravity Loads not included)

400 Face (South Columns) - FL 39

(b)

Figure 5-13. Shear lag diagrams of WTC 2 due to original WTC wind loads at

(a) floor B6, (b) floor 39, and (c) floor 73 (continued).

124 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

20

15

10

(0 JC 5

la

(fl o 0

-5 *5

Axi -10

-15

-20

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included)

159 101

100 Face (West Columns) - FL 73

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included)

259

201

200 Face (North Columns) - FL 73

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included) 20

15

10 ^- i 5 359 _ -5

-10

-15

-20

300 Face (East Columns) • FL 73

301

20

15 „ 10

'«i, 5 w

^ 0 ? -5

.2< -10

-15

-20

Tower B: West to East Wind (BON+E+)

(Gravity Loads not included)

400 Face (South Columns) - FL 73

(C)

Figure 5-13. Shear lag diagrams of WTC 2 due to original WTC wind loads at

(a) floor B6, (b) floor 39, and (c) floor 73 (continued).

NISTNCSTAR 1-2A, WTC Investigation 125
Chapter 5

100-109 110-119 120-129 130-139 140-149 1 50-159 200-209 210-219 220-229 230-239 240-249 250-259

m

(a) (b)

0 100 500 lood

Figure 5-14. Tension force distribution (kip) in the exterior wall columns of WTC 2 under

original design dead and wind loads, (a) 100 face (west) and (b) 200 face (north).

126 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

300-305 310-319 I 320-329 330-339 340-349 350-359 400-419 410-419 420429 430-439 440-449 450-459

(c)

0 100 500 1000

(d)

Figure 5-14. (c) 300 face (east) and (d) 400 face (south) (continued).

NISTNCSTAR 1-2A. WTC Investigation 127
Chapter 5

Table 5-6. Maximum calculated demand/capacity ratios (OCRs) for exterior wall column

iLAicrior iLAicrior >> dii i>i<i\iniuiii Wall Face Column Splice Calculated DCR

Below floor 1 U.04

1 no Fcirp rF1r\r\r joor 1

1 tn10 Q7 (West) Floor 10 to 41 0.83 Above floor 42 0.10 Below floor 1 u. /u Finnr rioor 1

J tnlo Q7 U.J)D (Norths Floor 10 to 41 0.99 Above floor 42 0.13 Below floor 1 A "7 C mo Fare Flnnr 1 tn Q 0 3^

(East) Floor 10 to 41 0.96 Above floor 42 0.16 Below floor 1 0.60 400 Face Floor 1 to 9 0.33 (South) Floor 10 to 41 0.84 Above floor 42 0.21

5.4.2 State-of-the-Practice Case

The WTC 2 global model was analyzed using the lower estimate, state-of-the-practice loading case, as described in Chapter 4 (see also NIST NCSTAR 1-2). This loading case included dead loads, live loads

according to the NYCBC 2001, and wind loads from RWDl wind tunnel study, scaled in accordance with

the NYCBC 2001 wind speed.

The calculated total drift of WTC 2 induced by the lower estimate, state-of-the-practice case was

approximately 59.7 in. (4 ft 1 1.7 in.) in the E-W direction and 55.9 in. (4 ft 8.1 in.) in the N-S direction. These drifts are equivalent to about H/287 and H/307 in the E-W and N-S directions, respectively.

Figure 5-15 presents the deflected shape (cumulative drift) and the inter-story drifts nonnalized by the

story height for WTC 2 under the lower estimate, state-of-the-practice case. The plots are presented for the E-W and N-S directions for the load combinations producing the maximum cumulative drift. DCR statistics for WTC 2 global systems components under the lower estimate, state-of-the-practice

loading case are summarized in Table 5-7. A comparison of the mean values of the DCRs estimated

from the original design case (Table 5-5) with those from the state-of-the-practice case (Table 5-7)

indicated that the results are very similar. Also the distribution of the DCRs and the locations of members

with DCRs greater than 1.0 were very similar between the original design case and the state-of-the- practice case.

128 NIST NCSTAR 1-2A. WTC Investigation
Baseline Performance Analysis of the WTC Global Models

Figure 5-15. Drift diagrams of WTC 2 due to the lower estimate, state-of-the-practice

case, (a) 2R4PDN and (b) 2R11PDN.

NISTNCSTAR 1-2A. WTC Investigation 129
Chapter 5

Table 5-7. Statistics of demand/capacity ratios (DCRs) for WTC 2 under the lower

estimate, state-of-the practice case.

Percentage Percentage

of of Number of Mean Components Components Components Maximum

Number of Calculated c.o.v. with DCR with DCR with DCR Calculated

i> li. Ill Ui. I 3 nr"R 1 7 V I\

Exterior Wall

Columns

Dclow iioor 1 577 0.70 0.20 3.1 1.4 8 1 .30 Flonr 1 tn Q 1,122 0.72 0.26 1.1 12 1.16

F1/^nr Q tn 1 HA r loor y 10 1 UD 31,086 0.77 0.13 1.8 0.6 189 1.21 Above floor 106 J / o U. / 1 U.jU C 7 o. / J 1 Exterior Wall

Spandrels

Below floor 1 408 0.45 0.47 1 .7 0.7 3 1.15 Floor 1 to 9 594 0.37 0.44 0.7 0.7 4 1.19 Floor 9 to 106 31,160 0.31 0.27 0 0 0 0.73 Above floor 1 06 836 0.33 0.70 1.7 1.4 12 1.47 Core Columns U.86 0. 1 5 J 0.8 6.6 345 1 .36 Hat Truss System

Columns 238 0.48 0.57 3.8 2.5 6 1 .35 Beams 504 0.23 0.82 0.2 0 0 1.01 Braces 283 0.40 0.57 0.7 0 0 1.04

Exterior Wall

Bracing

Below floor 1 227 0.69 0.17 0.9 0.4 1 1.13 Above floor 106 12 0.27 0.31 0 0 0 0.41

5.4.3 The Refined NIST Estimate Case

The WTC 2 global model was analyzed using the refined NIST estimate case as described in Chapter 4

(see also NIST NCSTAR 1-2). This loading case included dead loads, live loads in accordance with the cun-ent ASCE 7-02 Standard, and wind loads developed by NIST based on critical assessment of

infonnation obtained from RWDl and CPP reports and state-of-the-art considerations in wind

engineering.

The calculated total drift of WTC 2 induced by the refined NIST estimate case was approximately 75.6 in. (6 ft 3.6 in.) in the E-W direction and 70.8 in. (5 ft 1 1 in.) in the N-S direction. These drifts are equivalent to about H/227 and H/242 in the E-W and N-S directions, respectively. Fig. 5-16 presents the deflected shape (cumulative drift) and the inter-story drifts normalized by the story height for WTC 2 under the refined NIST wind loads. The plots are presented for the E-W and N-S directions for the load

combinations producing the maximum cumulative drift.

130 NIST NCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of ttie WTC Global Models

Interstory Drift/Story Height for NISTWind Load (E-W)

1600

1400 -

1200 >

» 1000 -

tom 800 - >

o

600 - £ 400

'<i> X 200 -

00.00 0.20 0.40 0.60 0.80

Interstory Drift/Story Height [%]

(a)

Interstory Drift/Story Height for NISTWind Load (N-S)

1600

1400 -

[ft.] 1200

> 1000 - —I

UDm 800 - >

O

600

TO 400 - .2" 'SX 200

00.00 0.20 0.40 0.60

Interstory Drift/Story Height [%]

(b)

Figure 5-16. Drift diagrams of WTC 2 due to refined NIST estimate wind loads,

(a) 2R4PD and (b) 2R11PD.

NISTNCSTAR 1-2A. WTC Investigation 131
Chapter 5

DCR statistics for WTC 2 global systems components under the refined NIST estimate case are summarized in Table 5-8. The DCRs for the core columns and hat truss members estimated from the

original design and the state-of-the-practice cases (Tables 5-5 and 5-7, respectively) are generally close

to those estimated from the refined NIST estimate case (Table 5-8). This is due to the fact that core columns and hat truss members do not significantly contribute to wind load resistance. The DCRs for the

exterior walls, including columns, spandrels, and bracings estimated from the refined NIST estimate case

are larger than those estimated from the original design and the state-of-the-practice cases. For example,

for the exterior wall, the ratio of the mean DCRs from the refined NIST estimate case to the mean DCRs

from the original design case ranged between 1 .60 and 1.11. The ratio of the mean DCRs from the refined NIST estimate case to the mean DCRs from the lower estimate, state-of-the-practice case ranged

between 1.65 and 1.17. •

Table 5-8. Statistics of demand/capacity ratios (DCRs) for WTC 2 under the refined

NIST estimate case.

Percentage Percentage

of of Number of Number Mean Components Components Components Maximum

of Calculated c.o.v. with DCR with DCR with DCR Calculated

Member Type Members DCR of DCR > 1.0 > 1.05 > 1.05 DCR

Exterior Wall

Columns

Below floor 1 577 0.96 0.25 42 41.1 229 1.95 Floor 1 to 9 1,122 1.04 0.27 63.7 58.0 651 1.69 Floor 9 to 106 31,086 1.09 0.14 73.5 60.9 18,941 1.78 Above floor 106 578 0.83 0.28 19.6 15.1 87 1.66

Exterior Wall

Spandrels

Below floor 1 408 0.73 0.46 15.9 13.7 56 1.78 Floor 1 to 9 594 0.61 0.44 7.7 5.2 31 2.02 Floor 9 to 106 31,160 0.51 0.28 0.4 0.2 61 1.21 Above floor 1 06 836 0.39 0.68 2.0 1.9 16 1.73 Core Columns 5,245 0.83 0.16 10.6 6.0 315 1,42 Hat Truss System

Columns 238 0.59 0.59 14.3 10.5 25 1.95 Beams 504 0.28 0.82 1.0 0.8 4 1.12 Braces 283 0.49 0.52 3.9 2.8 8 1.09

Exterior Wall

Bracing

Below floor 1 227 1.01 0.18 48.0 38.8 88 1.04 Above floor 1 06 12 0.43 0.31 0 0 0 0.64

5.5 SUMMARY

This chapter presented the results of the baseline performance analysis for the WTC 1 and WTC 2 global

models under three gravity and wind loading cases: (1) the original WTC design load case, (2) the lowerestimate, state-of-the-practices case, and (3) the refined NIST estimate case. The baseline perforaiance

132 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of the WTC Global Models

results included total and inter-stoi^ drift, demand/capacity ratios, exterior columns behavior (shear lag

effects and presence of tensile forces), behavior of exterior wall splice connections, and the towers'

resistance to shear sliding and overturning.

Under the original WTC design loads, the cumulative drifts at the top of the WTC 1 tower were about

56.6 in. (H 304) and 55.7 in. (H/309) in the E-W and N-S direction, respectively. These drifts were

about 51.2 in. (H/SSS) in the E-W direction and 65.3 in. (Hy263) in the N-S direction for WTC 2. For the lower estimate, state-of-the-practice case, the drifts for WTC 1 were larger than those from the original

design case by about 0.5 percent and 22 percent for the E-W and N-S directions, respectively. For the lower estimate, state-of-the-practice case for WTC 2, the E-W drift was larger than that from the original

design case by about 16 percent, while the N-S drift was smaller by about 15 percent. These differences

are consistent with the differences between the base shears for the two cases (see Tables 4-3 and 4-4 of

Chapter 4). The drifts obtained from the refmed NIST estimate case were about 25 percent larger than

those from the state-of-the practice case.

The demand capaciry ratios (DCR) were based on the allowable stress design procedure and were

estimated using the AISC Specifications (1989). The results indicated that DCRs estimated from the

original WTC design load case were, in general, close to those obtained for the lower estimate, state-of- the practice case. For both cases, a small fraction of structural components had DCRs larger than 1.0. These were mainly observ ed in both towers at (1) the exterior walls: at the columns around the comers, where the hat truss connected to the exterior walls, and below floor 9; and (2) the core columns on the 600 line between floors 80 and 106 and at core perimeter columns 901 and 908 for much of their height.

The DCRs obtained for the refmed NIST estimate case were higher than those from the original

WTC design and the lower estimate, state-of-the-practice load cases, owing to the following reasons:

• The NIST estimated wind loads were higher than those used in the lower estimate, state-of- the-practice case by about 25 percent (about 10 percent difference between the RWDl loads

scaled to the NYCBC 2001 wind speed and RWDI loads scaled to the ASCE 7-02 wind

speed, in addition to the 15 percent increase estimated by NIST, see Sec. 4.4.3). It is noted

that the NIST estimated wind loads were about 20 percent smaller than those estimated by

CPP (an upper estimate state-of-the practice case, see Chapter 4).

• The original WTC design and the state-of-the-practice cases used NYCBC load

combinations, which resuh in lower DCRs than the ASCE 7-02 load combinations used for the refmed NIST case.

Under a combination of the original WTC design dead and wind loads, tension forces were developed in the exterior walls of WTC 1 and WTC 2. The forces were largest at the base of the building and at the comers. These tensile column loads were transferred from one panel to another through the coluinn

splices. The DCR ratios for the exterior wall splice connections under these tensile forces for both towers were shown to be less than 1.0.

For the towers' resistance to shear sliding and overturning due to wind, the dead loads that acted on the perimeter walls of the towers provided resistance to shear sliding and overtuming at the foundation level. Considering the resistance to shear sliding under wind load, the factor of safety was calculated to be

NISTNCSTAR 1-2A. WTC Investigation 133
Chapter 5

between 10 and 1 1.5, while the factor of safety against overturning ranged from 1.9 to 2.7 for both

towers.

5.6 REFERENCES

AISC Specification 1989: American Institute of Steel Construction, Specification for Structural Steel Buildings - Allowable Stress Design and Plastic Design - 9* Edition, Chicago, IL, 1989.

ASCE 7-02: American Society of Civil Engineers, ASCE 7 Standard Minimum Design Loads for Buildings and Other Structures, Reston, VA, 2002.

NYCBC 2001 : Building Code of the City of New York, 2001 Edition, Gould Pubhcations,

Binghamton, NY.

134 NISTNCSTAR 1-2A, WTC Investigation
Chapter 6

Baseline Performance Analysis of Typical Floor Models

6.1 INTRODUCTION

This chapter presents the resuhs of the baseline perfoiTnance analysis for the typical floor models

discussed in Chapter 3. These models included the typical truss-framed floor (floor 96 of World Trade

Center [WTC] 1. see Sec. 3.3) and the typical beam-framed floor (floor 75 of WTC 2, see Sec. 3.4).

For application to the floor models, gravity loads were separated into three categories: construction dead

loads (CDL), superimposed dead loads (SDL), and live loads (LL). CDL is defined as the self-weight of

the structural system. The self-weight of the floor trusses, floor beams, and concrete slabs were

automatically generated in SAP2000. SDL is defined as the added dead load associated with architectural and mechanical electrical plumbing systems (curtain wall, floor finishes, mechanical equipment and

ducts, transformers, etc.) The CDL and SDL were based on the WTC architectural and structural drawings and on the original WTC Design Criteria.

Two independent sets of live loads were applied in combination with the dead loads. The first was taken

from the original WTC Design Criteria and the second from the American Society of Civil Engineers

(ASCE 7-02) Standard. The live loads in the New York City Building Code (NYCBC 2001) are

essentially identical to the American Society of Civil Engineers (ASCE) 7-02 live loads. Live load

reductions were taken from the original WTC Design Criteria and from the ASCE 7-02 Standard, each for use with its respective live loads.

For the baseline performance analysis for the floor systems, demand/capacity ratios (DCRs) for structural components were estimated using the Allowable Stress Design (ASD) procedure as specified in the American Institute of Steel Construction (AISC) Specification (1989), see Chapter 5. The DCRs were

calculated by dividing component demands by component capacities, taken at unfactored (working) loads

and at working stresses, not at ultimate loads or yield stresses. These DCRs for the structural components

were determined as follows:

1 . The component demands were taken from the results of the baseline performance analysis

using the reference floor models, making use of working loads.

2. The component capacities were determined based on the nominal steel strength as specified

in the original design documents and using the AISC Specification (1989).

This chapter reports on the results of the baseline performance analysis for the floor systems under gravity

loading. Sections 6.2 and 6.3 present the loading and baseline performance analysis results for the truss- framed floor and the beam-framed floor, respectively.

NISTNCSTAR 1-2A, WTC Investigation 135
Chapter 6

6.2 TYPICAL TRUSS-FRAMED FLOOR

The analysis of the typical truss-framed floor was perfonned on the computer model of floor 96 of

WTC 1 (see Sec. 3.3). This section describes the gravity loads applied to the model along with the results of the baseline perforaiance analysis.

6.2.1 Gravity Loads

Areas Outside Core

The CDL was calculated based on the member's geometiy and material properties. The SDL allowance was typically 1 1.5 psf to 13.5 psf outside the core. Figure 6-1 shows the WTC Design Criteria reduced

live load for the floor design. Table 6-1 provides a comparison between the live loads from the WTC Design Criteria, NYCBC 2001, and the ASCE 7-02 Standard.

cm. i

1 n.KK.M'KVrV

i I

t

•Wi'-Jl"

Two-\\ ay

55 psf

a.

D. 00 ^ 6X) *- s

Two-Way

55 psf

tip ' Op

Long Span

VV/ Bridging

70 psf

CORE

Long Span

W/ Bridging

70 psf

V I T»0 wit I

Two-Way

55 psf

T

T

B. 9C » e

O CD

Two-Way

55 psf

LONG ^AN

Cms) 61©

WTC TYPiCAL TOWER FLOOR PLAN

Source: Reproduced with permission of The Port Authority of New York and New Jersey. Enhanced by NIST. Figure 6-1. Summary of WTC-design criteria reduced live loads for floor design: design

load of 100 psf - partition load is included in LL allowance.

136 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of Typical Floor Models

Table 6-1. Summary of typical truss-framed floor live loads and (reduced live loads) for areas outside of core.

Criteria Design 1 T\vo-\\ ay Zone Long Span Short Span Partition NVTC Design Criteria Floor 100 psf (55psf) 100 psf (70 psf) 100 psf (82.5 psf) Included in LL

NYC Building Code Floor 50psf (25 psf) 50 psf (39 psf) 50 psf (47 psf) 6 psf

ASCE 7-02 Floor 50 psf (25 psf) 50 psf (39 psf) 50 psf (47 psf) 6 psf

Areas Inside Core

Table 6-2 shows the CDL and SDL used inside the core area along with the live loads from the WTC Design Criteria. NYCBC 2001. and the ASCE 7-02 Standard. Loads are shown for the various

occupancies within the core area.

Table 6-2. Area inside core: loading floor 96, WTC 1

.

Area

Loading (psf)

CDL SDL

Live Load for Floor Design

WTC Design

Criteria

ASCE

7-02 NYCBC 2001

Tenant Space

Varies See Original

Structural Drawings

33 100 50 50

Toilets 49 40 40 40

Stair. Serv ice. Closet 29 100 100 100

Ele\ ator Lobby. Corridor 41 75 80 80

Telephone. Electric Closet 29 75 75 75

6.2.2 Results of Baseline Analysis

The maximum mid-span deflections for each of the long-span, short-span, and two-way zones for the

original WTC Design Criteria and ASCE 7-02 total loads are provided in Table 6-3.

Table 6-3. Summary of maximum deflections for typical truss-framed floor under

DL + LL for areas outside of core.

Criteria T\\o-\\ ay Zone Long Span Short Span

WTC Design Criteria 1.44 in. 1.79 in. 0.57 in. NYCBC ASCE 7-02 1.14 in. 1.43 in. 0.44 in.

For the components of the truss-framed floors, DCRs were calculated using the SAP2000 program.

Calculations were made for the top and bottom chords, the diagonals and the verticals of the primary and

bridging trusses, and for the beams and girders of the core. Since the top chords consisted of a pair of

steel angles plus the concrete slab, the capacity of the concrete slab predominated and was much greater

than the capacity of the top chord; therefore, a calculation of the stress in the slab seemed irrelevant and

would have required significant inter\'ention to SAP's post-processor to establish a proper design

calculation.

NISTNCSTAR 1-2A. WTC Investigation 137
Chapter 6

DCRs were not calculated for the following elements in this computer model:

• Strap elements .. _

• Damper elements

• Frame connections assigned as "plate" elements and similar connectors

• Rigid links

• Core columns, spandrels, and exterior columns

• Deck support angles

• Core perimeter channel members within close proximity to supports

The calculations were spot checked for accuracy and to verify that the correct design infoiTnation was

applied. For most of the component calculations checked, the standard SAP2000-generated calculations were found to be acceptable; however, for some components, the computer model did not accurately

represent the actual construction, and for other components, the standard SAP2000 calculations yielded

eiToneous results. As a result, for estimating the DCRs of the structural components, the following

adjustments to the design parameters were applied to the floor model to yield accurate results:

• Length factors were assigned to tmss web members to reflect the length of the actual constructed member. For example, in the model, to account for the participation of the composite slab, the distance between the top and bottom chord of the primary floor trusses was taken as 30 in. However, this distance was actually 28 in. Therefore, a length modifier was applied to the primary truss diagonals to account for the actual length of the diagonal. In general, the length modifier was determined by measuring the diagonal distance from the underside of the top chord to the centerline of the bottom chord (see Fig. 6-2).

Theoretical unbraced length = 30.1 inches,

measured from the face of top chord to the

centerline of the bottom chord. The unbraced length is adjusted in the SAP2000 computer model by a factor of

30.1"/ 36.0" = 0.84

Figure 6-2. Unbraced length of truss diagonal.

• Significant out-of-plane bending is not expected in the members of planar trusses subjected to concentric vertical loading. However, due to the complexity of the floor model, significant

out-of-plane (i.e., minor axis) bending moments were observed in some truss diagonals and

bottom chord members. As a result, the allowable minor axis bending stress was

substantially increased to effectively eliminate these bending moments from the DCR

calculation.

138 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of Typical Floor Models

• The allowable shear stress for truss diagonals with additional bar reinforcement was

substantially increased since for these members, the SAP2000 program computed an

erroneous shear area.

For the area outside the core, the DCRs for all floor trusses were less than 1.14 for the original

WTC Design Criteria and less than 0.86 for the ASCE 7-02 loading and (by comparison) for the NYCBC

2001 loading. Under the original WTC Design Criteria loading, the DCR was less than 1.00 for 99.4 percent of the floor truss components. For the core area, the DCRs for all floor beams inside the core were less than 1 .08 and more than 99 percent had a DCR of less than 1 .0. DCR statistics for the truss-framed floor model are summarized in Table 6^ for the original design

loading case and in Table 6-5 for the ASCE 7-02 loading case. For the area outside the core, the average

ratio of the DCRs estimated from the ASCE 7-02 loading to the DCRs from the original WTC Design

Criteria loading for all floor trusses was about 0.80.

Table 6-4. Statistics of demand/capacity ratios for floor 96 under original design

load case.

Member T}-pe

Number of Members

Mean

Calculated

DCR

C.O.V. of

DCR

Percentage of Components

with DCR

> 1.0

Percentage of Components

with DCR

> 1.05

Number of Components

with DCR

> 1.05

Maximum

Calculated

DCR

One-\\ ay Long

Span Zone

W eb members 1,792 0.44 0.61 3.7 1.28 23 1.14 Bottom chord 1.038 0.74 0.26 0 0 0 0.99 members

One-W ay Short

Span Zone

Web members 640 0.33 0.61 0 0 0 0.92 Bottom chord 288 0.37 0.32 0 0 0 0.55 members

Two-\\ ay Zone

Web members 3,086 0.30 0.80 0.3 0.26 8 1.06 Bottom chord 2,035 0.48 0.54 0 0 0 0.94 members

Bridging Trusses

within One-\\ ay Span Zones

Web members 692 0.16 1.25 1 0 0 1.02 Bottom chord 327 0.12 1.33 0 0 0 0.95 members

Core Beams

Beams within core Core perimeter channels

1.361 686

0.33 0.360.67

0.58

0.9

1.0

0.3 0.6

4

4

1.07

1.08

NISTNCSTAR 1-2A. WTC Investigation 139
Chapter 6

Table 6-5. Statistics of demand/capacity ratios (DCRs) for floor 96 under the ASCE 7-02

loading case.

Percentage Percentage

of of Number Mean Components Components Maximum

of Calculated C.O.V. of with DCR with DCR Calculated

Member Type Members DCR DCR > 1.0 > 1.05 DCR

One-Way Long Span

Zone

Web members 1,792 0.35 0.60 0 0 0.86 Bottom chord members 1.038 0.59 0.25 0 0 0.80 wiie-vvd\ oiiuri opaii

Zone

Web members C+U V./.0 U.O J u

A

u U.07 Bottom chord members .108 A in U.jU U.J J nu A

u

A A1 U.4J Two-Way Zone

Web members j.Uou U. /y Au

A

u A 78 U. / 0 Bottom chord members U.Jo U.J J A

u

A

u

A lA U. /4 Bridging Trusses within

One-Way Span Zones

Web members 692 0.11 1.55 0 0 0.95 Bottom chord members 327 0.09 1.44 0 0 0.81 Core Beams

Beams within core 1.361 0.28 0.64 0.1 0.1 1.05 Core perimeter chamiels 686 0.28 0.61 0 0 0.86

6.3 TYPICAL BEAM-FRAMED FLOOR

The analysis of the typical beam-framed floor was perfonned on the model of floor 75 of WTC 2 (see Sec. 3.4). This section describes the gravity loads applied to the model along with the results of the baseline performance analysis.

6.3.1 Gravity Loads

Comparing the live loads from the original WTC design criteria, NYCBC 2001, and the ASC E7-02

Standard for this floor, it was found that the three sets of loads were nearly identical. The only difference was that the live load for the corridor within the core was 100 psf in the original WTC design criteria. 75 psf in NYCBC 2001, and 80 psf in ASCE 7-02. As a resuh, only the original WTC design criteria loads were applied to the computer model.

In the areas outside of the core, the superimposed dead load was taken from the original design criteria as 141 psf, including 75 psf for equipment loads, and the live load was 75 psf.

Table 6-6 shows the CDL and SDL used inside the core area along with the live loads from the WTC Design Criteria, NYCBC 2001, and the ASCE 7-02 Standard. Loads are shown for the various

occupancies within the core area.

140 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of Typical Floor Models

Table 6-6. Beam-framed core area: loading floor 75, WTC 2.

Area

Loading (psf)

CDL SDL

Live Load for Floor Design

WTC-DC ASCE 7-02 NYCBC 2001

Return Air Plenum

Varies See Original

Structural Drawings

66 75 75 75

Toilets 66 40 40 40

Stair, Serv ice. Closet 25 100 100 100

Corridor 66 100 80 75 Motor Generator Room 141 75 75 75 Pump Platform 141 75 75 75

Electric Sub-Station 141 75 75 75 Mail Room 141 75 75 75 Secondary Motor Room 141 75 75 75 Unassigned Space 66 75 75 75

6.3.2 Results of Baseline Analysis

The maximum mid-span deflections of the long-span and short-span zones under the original

WTC Design Criteria loads were approximately 1.55 in. and 0.70 in., respectively.

Using the SAP2000 computer program. DCRs were calculated for the components of the floor framing.

The calculations were spot checked for accuracy and to verify that the correct design information was

being applied. For most of the component calculations checked, the SAP2000 calculations were found to be acceptable.

DCRs were not calculated for the bridging members and anchor straps as they were not a part of the primary floor framing system. Also, DCRs were not calculated for the spandrels and columns as their DCRs were calculated in the global systems computer models.

Except for the tw o 30WF1 1 6 beams running in the east-west direction and cantilevering from the core columns 501 and 508 (see Fig. 6-3), the DCRs for all beam-framed floor components were less than 1.0 for the original WTC design criteria loading. For the two beams cited above, the DCRs from the axial load and moment interaction equation were less than 1.0, while the shear DCRs were 1.125 and 1.09. These shear DCRs occurred in the section of the 30WF1 16 beams located near the support between beam

30x 10 V2 WF^ and the centerline of the column.

This beam designation was used in original contract drawings to indicate a 30 in. deep wide flange beam with cover plates and

is used here for consistency.

NISTNCSTAR 141 1-2A. WTC Investigation
Chapter 6

30x10 V2 WF

SKILLING - HELLE - CHRISTIANSEN - ROBERTSON Slruclutal & Civil En ='TW;r WOJ?LD TRAOE CENTBRX CONNBCTION DETAIL SiSA

Source: Drawing reproduced with permission of The Port Authority of New York and New Jersey.

Enhanced by NIST. Figure 6-3. Connection detail for beam 30WF116, floor 75 of WTC 2.

Figure 6^ shows the distribution of DCRs for the floor framing. The figure shows the location of the two beams with DCR greater than 1 .0. DCR statistics for the beam-framed floor model are summarized

in Table 6-7 for the original design loading case. The statistics are provided for member groups that are shown in Fig. 6-5.

142 NISTNCSTAR 1-2A, WTC Investigation
Baseline Performance Analysis of Typical Floor Models

0 .00 0 .50 0 .75 1 .00 1 .08

Figure 6-4. Demand/capacity ratios for floor 75, WTC 2: original WTC design criteria

loading.

Core

Figure 6-5. Beam-framed floor member groups.

NISTNCSTAR 1-2A. WTC Investigation
Chapter 6

Table 6-7. Statistics of demand/capacity ratios for floor 75 under the original design

Member Type

Number

of

Members

Mean

Calculated

DCR

C.O.V. of DCR

Maximum

Calculated

DCR

Long Span Beams 156 0.64 0.16 0.83 Short Span Beams 84 0.65 0.12 0.89 Core Beams 156 0.31 0.77 1.13 Corner Beams 32 0.49 0.35 0.90

144 NISTNCSTAR 1-2A, WTC Investigation
Chapter 7

Summary

This report presented the work conducted to estabhsh the baseline performance of the North and South

World Trade Center Towers (WTC 1 and WTC 2) under design gravity and wind loading conditions.

Baseline perfonnance results include basic information about the behavior of the towers, such as total and

inter-story drift under wind loads, floor deflections under gravity loads, demand/capacity ratios for primary structural components, exterior columns response (shear lag effects and presence of tensile forces

under a combination of dead and wind loads), performance of connections, and the towers' resistance to shear sliding and overturning.

The follow ing tasks were undertaken to allow performing the baseline performance analyses of the towers:

• De\ elopment of structural databases of the primary components of the WTC 1 and WTC 2 towers. The electronic databases were developed from original computer printouts of the

structural design documents, including modifications made after construction. The task included the scanning and digitization of the original drawing books, a four-step quality control procedure, cross-section property calculations, and development of the relational databases to link the generated database files into a format suitable for the development of the

structural models.

• Development of reference structural analysis models that captured the intended behavior of

each of the two towers using the generated databases. These reference models were used to establish the baseline perfonnance of the towers and also served as a reference for more

detailed models for aircraft impact damage analysis and thermal-structural response and

collapse initiation analysis. The main types of models developed were:

- Two global models of the major structural components and systems for the towers, one

each for WTC 1 and WTC 2. The models included all primary structural components in the towers, including exterior walls (coluinns and spandrel beams), core coluinns,

exterior wall bracing in the basement floors, core bracing at the main lobby atrium levels, hat trusses, and rigid and flexible diaphragms representing the floor systems. To validate

the global models, the calculated natural frequencies of WTC 1 were compared with

those measured on the tower, and good agreement between the calculated and measured

values was obtamed.

- One model each of the typical truss-framed floor (floor 96 of WTC 1 ) and typical beamframed floor (floor 75 of WTC 2) in the impact and fire zone of the towers. The models

included all major structural components in the floor system, including primary and

bridging trusses, beams, strap anchors and horizontal trusses, concrete slabs, and

viscoelastic dampers. To validate the floor models, several studies were carried out to compare stresses and deflections estimated Irom the model with hand calculations for

NISTNCSTAR 1-2A. WTC Investigation 145
Chapter 7

representative composite sections. Good agreement was obtained between the model

results and hand calculations.

Parametric studies were perfonned to evaluate the behavior of typical portions of the structure and to develop simplified models for implementation into the global models. These parametric studies included

detailed and simphfied models of typical exterior and comer wall panels and floor systems.

• Development of estimates of design gravity and wind loads on the towers for implementation

into the reference structural models and use in the baseline perfonnance analysis. Various

wind load cases were considered in this study, including wind loads used in the original

WTC design, wind loads based on two recent wind tunnel studies conducted in 2002 by

Cermak Peterka Peterson, Inc. (CPP) and Rowan Williams Davies and Iru in, Inc. (RWDI)

for insurance litigation concerning the towers, and wind load estimates developed by NIST

from critical assessment of infonnation obtained from the CPP and RWDI reports and state- of-the-art considerations. The following three loading cases were considered for the baseline

performance analysis:

- Original WTC design loads case. Loads included dead and live loads as in original

WTC design, in conjunction with original WTC design wind loads.

- State-of-the-practice case. Loads included dead loads; New York City Building Code

(NYCBC) 2001 live loads; and wind loads from the RWDI wind tunnel study, scaled in accordance with NYCBC 2001 wind speed.

- Refined NIST estimate case. Loads included dead loads; live loads from the American

Society of Civil Engineers (ASCE 7-02) Standard; and wind loads developed by NIST.

The purpose of using the original WTC design loads was to evaluate the performance of the towers under original design loading conditions and ascertain whether those loads and the corresponding design were adequate given the knowledge available at the time of the design.

The purpose of considering the state-of-the-practice case and the refined NIST estimate case was to better understand and assess the effects of successive changes in standards, codes, and

practices on wind design practices for tall buildings.

The study indicated that the original WTC design wind load estimates exceeded those

established by the NYCBC prior to 1968, when the WTC towers were designed, and up to and including 2001 . The design values were also higher than those required by other

prescriptive building codes of the time.

The two orthogonal base shear and base moment components used in the original design were, in general, smaller than the CPP, RWDI, and NIST estimates. However, the most

unfavorable combined peaks from the original design were larger, or smaller by at most 1

5

percent, than estimates based on the CPP, RWDI, and NIST estimates. This is due to the conservative procedure used to combine the loads in the original design.

The estimated wind-induced loads on the towers varied by as much as 40 percent between the wind tunnel/climatological studies conducted by CPP and RWDI in 2002.

146 NISTNCSTAR 1-2A, WTC Investigation
Summary

The WTC 1 and WTC 2 global models were each analyzed under the three loading cases described above

to establish their baseline performance. The following is a summary of the results:

• Under the original WTC design loads, the cumulative drifts at the top of the WTC 1 tower were about 56.6 in. (H/304) and 55.7 in. (H/309) in the E-W and N-S direction, respectively.

These drifts were about 51.2 in. (H/335) in the E-W direction and 65.3 in. (H/263) in the N-S

direction for WTC 2. For the lower estimate, state-of-the-practice case, the drifts for WTC 1 were larger than those from the original design case by about 0.5 percent and 22 percent for the E-W and N-S directions, respecti\ ely. For the lower estimate, state-of-the-practice case

for WTC 2. the E-W drift was larger than that from the original design case by about 16

percent, and the N-S drift was smaller by about 15 percent. The drifts obtained from the refined NIST estimate case were about 25 percent larger than those from the state-of-the practice case. These differences are consistent with the differences among the base shears for the three loading cases.

• The demand capacity ratios (DCRs) were based on the allowable stress design procedure and were estimated using the American Institute of Steel Construction (AISC) Specifications

( 1 989). The results indicated that DCRs estimated from the original WTC design load case were, in general, close to those obtained for the lower estimate, state-of-the practice case. For

both cases, a small fraction of structural components had DCRs larger than 1.0. These were

mainly observ ed in both towers at (1) the exterior walls: at the columns around the comers, where the hat truss connected to the exterior walls, and below floor 9; and (2) the core columns on the 600 line between floors 80 and 106 and at core perimeter columns 901 and

908 for much of their height.

• The refined National Institute of Standards and Technology (NIST) case estimated DCRs

were higher than those of the original WTC design estimates and the lower state-of-the- practice estimates for the following reasons: The NIST estimated wind loads were about 25

percent higher than those used in the lower state-of-the-practice estimate, and mixed, some

higher and others lower than the original WTC design wind loads. It is noted that the NIST

estimated wind loads are about 20 percent smaller than those estimated by CPP (an upper

estimate, state-of-the practice case). In addition, the original WTC design and the state-of- the-practice cases used NYCBC load combinations, which result in lower DCRs than the ASCE 7-02 load combinations used for the refined NIST case.

• Under a combination of the original WTC design dead and wind loads, tension forces were

developed in the exterior walls of WTC 1 and WTC 2. The forces were largest at the base of

the building and at the comers. These tensile column loads were transferred from one panel

to another through the column splices. The DCR ratios for the exterior wall splice

connections under the effect of the tensile forces for the two towers were shown to be less than 1.0.

• For the towers" resistance to shear sliding and overturning due to wind, the dead loads that acted on the perimeter walls of the tower provided resistance to shear sliding and overturning

at the foundation level. Considering the resistance to shear sliding under wind load, the

factor of safety was calculated to be between 10 and 1 1.5, while the factor of safety against

overturning ranged from 1.9 to 2.7 for both towers.

NISTNCSTAR 1-2A. WTC Investigation 147
Chapter 7

Two typical floor models were each analyzed under gravity loads. The following is a sununaiy of the

results:

• For the typical truss-framed floor (floor 96 of WTC 1), the DCRs for all floor trusses were

less than 1.14 for the original WTC Design Criteria loads and less than 0.86 for the ASCE 7-02 loading. Under the original WTC Design Criteria loading, the DCR was less than

1.00 for 99.4 percent of the floor truss components. For the area outside the core, the average

ratio of the DCRs under the ASCE 7-02 loading to the DCRs under the original WTC Design

Criteria loading for all floor trusses was about 0.80. For the core area, the DCRs for all floor beams inside the core were less than 1 .08, and more than 99 percent had a DCR of less than

1 .0. Under the original WTC Design Criteria loading, the maximum floor deflections were

1.79 in., 0.57 in., and 1.44 in. for the long-span one-way trusses, short-span one-way trusses, and the two-way zone, respectively.

• For the typical beam-framed floor (floor 75 of WTC 2) under the original WTC Design

Criteria loading, the DCRs for all floor beams were less than 1.0 except for two core beams

where the shear DCRs were 1.125 and 1.09. The maximum mid-span deflections of the longspan and short-span zones under the original WTC Design Criteria loads were about 1.55 in. and 0.70 in., respectively.

148 NISTNCSTAR 1-2A, WTC Investigation
Appendix A

WTC Tower Structural Drawings Index for

Large-Size Sheets

WTC Tower A Structural Steel Drawing Index - (18-May-73)

Drawing Title Latest Revision

Date

LA-1 Foundation loading plan 27-Apr-67

SA-1 Foundation plan 29-Aug-68

SA-2 Plan sub-level 5 EL.242 09-Apr-69

SA-3 Framing plan sub-level 4 09-Apr-69

SA-4 Framing plan sub-level 3 EL.264 07-Oct-68

SA-5 Framing plan sub-level 2 EL.274 17-Jul-68

SA-6 Framing plan sub-level 1 EL.284 07-Oct-68

SA-7 Framing plan service level EL. 294 17-Jul-68

SA-8 Framing plan floor 1 17-Jul-68

SA-9 Framing plan intennediate level 17-Jul-68

SA-10 Framing plan floor 2 17-Jul-68

SA-11 Framing plan floor 3 17-Jul-68

SA-12 Framing plan floor 4 17-Jul-68

SA-1

3

Framing plan floor 5 17-Jul-68

SA-1

4

Framing plan floor 6 17-Jul-68

SA-15 Framing plan floor 7 17-Jul-68

SA-16 Framing plan floor 8 17-Jul-68

SA-1

7

Framing plan floor 9 17-Jul-68

SA-18 Framing plan floors 10-11 09-Oct-68

SA-19 Not used

SA-20 Framing plan floors 12-16 09-Oct-68

SA-21 Not used

SA-22 Not used

SA-23 Not used

SA-24 Not used

SA-25 Framing plan floor 17 09-Oct-68

SA-26 Framing plan floor 18 09-Oct-68

SA-27 Framing plan floor 19 09-Oct-68

SA-28 Framing plan floor 20 09-Oct-68

SA-29 Framing plan floors 21-23 09-Oct-68

SA-30 Not used

NISTNCSTAR 1-2A, WTC Investigation 149
Appendix A

r, • n -r .L, Latest Revision Drawing^ No. Drawing*

Title ^

Date

S A-^ 1 Not iiQpH

1Pt'JiiTiino 1 uliilil^ nlan IJldii floor llLUJl ^4

1 laLLllH^ ijiuil iiVJiJl 75

S A-^4 Pr^irnino" r\lan floor

SA-^'S Fr^immcT r^lnn floor 11 yjy wvi vjo SA-^fi P'r^imincr nl^in floor*; \jy I uo SA-^7 Mot iicpH

<sO/AA-^S_> o tsJot iicpH

MrQiTnr^O" nl^in flr*r\r jridilillig Uiaii iiUUl Vw/ci-oo SA-41 Pr^nTuno r^lnn floor

\ OQ-nrt-68

r" r rn incr r\l^in fJooi' ^4 OQ-Ort-fiR

S A-4^ f lallllll^ Uld.ll llUwl OO-Ort-f^R v_/Cl UO

^A 44 riallllilg piall ilUUIb JO-JO OQ Opt 68

^A 4S

IMwl UoCU.

*s A-47 HrdminfT nlon flrir^f FlclllllllU Ulall llUUl jy OQ-Ort-^iR

•sA 48 riallllll^ pidil llUUl 40 HQ Opt ftR

<sA 40 n allllll^ piali IIUUI 41 11 fl-Tan w-Jdii-u" ftp

rrdiiiing piaii iiuur 47 1 fl Inn ftQ

riaiiiiny piaii iiuur J 1 n Tnn fsQ 1 U Jdll-vJ" 'sA ST Ih t*Q Tn 1 n rr l q ti t1 /~\fw ri aiiiiiig pidii iiuur 44 01 *\pn 70

QA rrdiTiing pidn iiuur 4'^ ^J 01 <sf>r> 70

<s A '^4 rrdminii pidii iiour 4ft 1 0 Inn f\Q

ridiriiny pidn iiuor 47 1 0 Inn ftQ

rrdiriiiiy pidii iiuur 48 77 Nnv ft8

<sA S7 ridiiiiiij^ pidii iiuur 4Q 77 Nn\/ 68

<iA S8 Ih i"Q m1 n rr t\ Ion t 1 r\r\f ridxiiiiig pidii iiuui JU ZZ-INU 77 Nnvv-uo68

<sA Fidllllll^ pidll ilUUIs J 11 Jt- S4 77 Nnv-68

<\A ^0 M lie

<\A ^^1

<sA f«? INUl UbCU

^A Ih i"Q m1 n fT T\ Ion Tl/^r^v Frdiiiiiig pi^Ai iioul J J 77 Kln\/ 68

SA-64 Framing plan floor 56 22-NOV-68

SA-65 Framing plan floor 57 22-NOV-68

SA-66 Framing plan floor 58 22-NOV-68

SA-67 Framing plan floor 59 22-NOV-68

SA-68 Framing plan floor 60 22-NOV-68

SA-69 Framing plan floor 61 22-NOV-68

150 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

Drawing No. Draw ing Title Latest Revision

Date

SA-70 Framinc nlan floor 62 22-N0V-68

SA-71 Framincr nlan floor 63 22-NOV-68

SA-72 Pramino' nlan flnnr 64 ?2-Nov-68

Framincr nlan floor 65 2?-Nov-68

SA-74 ±Pramincr 1 Ui 1 1111 nlan Lf 1 U.11 floor 1 Wl 66 12-Dec-69

Oil. / XPramincr IClllllll^ nlan IJlCLll floor llWVJl 67 12-Dec-69

LPramincT iCllillll^ nlan L71C111 floor llVJWl 68 12-Dec-69

SA-77 Framincr 1. 1 CLllllll^ nlan L/lClll floor llv/V^l 69 22-NOV-68

Oil / o 1Pramino" 1 dXllllJ^ nlan L'lU.ll floor ilVJWl 70 22-NOV-68

S A-7Q l-ramino" nlan floor 71 22-Nov-68

SA-RO ±Framincr 1 Cllllll 1 im, nlan L/lCtll floor i.lX-'V/l 72 22-NOV-68

SA-Rl OAV O 1 1Framing icHiillliC nlan LJiClil floor liWv'l 73 22-NOV-68

FraiTiino nlan floor 74 22-NOV-68

O/A O J XFramino I dlXllll^ nlan L/XCXXX floor XX^J^-fX 75 25-Sep-68

9 A-R4 FramincT nlan floor 76 25-Sep-68

SA-R'S 1Framin0 XCXXlXlll^ nlan LfluXl floor XXlk-l^-fX 77 25-Sep-68

O/T ou XFramincT 1 CXI. iXlXlw. nlan LJi clX 1 floor X 1 VJ W

1

78 18-Aug-69

o/\ o / 1FramintT 1 dXl 1111 iL, nlan IJlClll floor ilVJWl 79 Ol-Aug-69

O/A. OO XFramino 1 CXlllllll^ nlan L/lclll floor XXWWX 80 Ol-Aug-69

9A-RQ XFramino ICXllllllC^ nlan IJlull floor XlWVJl 81 27-NOV-68

^o-'A A-QOy\j Framincy 1 lullllXlc^ nlan L/ldli floor XlWWl 82 Ol-Aug-69

9 A-Q1 XFramino idixiiii^ nlan |jiaii floor iivjvji 83 Ol-Aug-69

XFramincT Idllllllw, nlan IJldll floor Ilwwl 84 -86 Ol-Aug-69

Mnt iiQprl

Tslot I iispH i '* V,/ I LX^^vl

1Framino i dilllll^ nlan jJldll floor llVJVJl 87 Ol-Aug-69

SA-96 XFraming 1 UlllllJ^ nlan ^Idll floor XiWWl 88 Ol-Aug-69

•s A-Q7 XFramino idllllll^ jjldil nlan floor ilUUl 89 Ol-Aug-69

XFramin<T Idllllll^ nlan IJldll floor llWWl 90,91 Ol-Aug-69

SA-99 Not used

s A-1 no XFramincT IdllllllL^ nlan IJldll floor llWVJl 92 Ol-Aug-69

SA-101 Framing plan floor 93 Ol-Aug-69

SA-107 XFrammf XdiXXlli^ nlan L/ldXX floor XXWV^l 94 Ol-Aug-69

XFramincJ XdlllXXJ^ nlan L/ldXl floor xxvwx 95 Ol-Aug-69

Framing plan floor Ol-Au0-69

SA-105 Framing plan floor 97-100 Ol-Aug-69

SA-106 Not used

SA-107 Not used

SA-106 Not used

NISTNCSTAR 1-2A. WTC Investigation 151
Appendix A

„ . rv . rr'^. Latest Revision Drawing^ No. Drawing^

Title ^

Date

SA-107 TSJot h^pH

SA-108 Not nspd

SA-109 FraiTiinff nlan floor 1 01 Ol-Aug-69

SA-110 Framins? nlan floor 102 01-Au2-69

SA-1 11 Framinp nlan floor 1 0^ 01 -Aup-69

SA-1 12 FraiTiinp nl?in floor 104- 01 -Auo-69

SA-1 1 ^ Fr^imincT nlan floor 1 OS 07-Tan-71 \j 1 J aij / 1 SA-1 14 Framinp 1. X %A,XXXXX M iL,, nlan XJ XtmXXX floor 1. l\J\JX 106 X \J \J 16-Jun-77 X V J \AXX 1 ^ SA-1 Oil 11^1 'S 1Frjimino' 1 dllllll^ nlan Uidil floor iivJUl 11 07\J / 11 fS-Tiin-7'' U J Ull / ^ SA-1 16 Framing plan floor 107 upper Void

SA-1 1

7

FmrnincT nlan floor 1 OR 70-Ort-70

SA-1 kjii. 1 11 8O FramincT nlan floor 1 00 7n-Ort-70

SA-1 1 Q FrarntnO" nlan floor 110 07-Inl-71 V/Z. J 111 / 1 SA-1 90 Kr^minCT r\lan r\ n rr\r\T 1 lailliJl^ Ulail U.ll. iVJvJi 07-Mav-71

SA-Hl

S A-H'' Klr\or r\ani^l Tirf*nrooTinfT r\lan 1 lU^Jl pailV^l 111 t-jUHJUilll^ UldlX Hold

SA-1 7^

SA-1 74 Floor nanf*l cr*Vif*Hiilp 1 iKjKJl UdllCl dLllCLlUlC WU Jail U"

SA-1 7S Fvt L^Al. A\/all VVdll toIVJ QtVi "111 - i=»lp\/ation CltVCllUJll \x/all VVdll 100 i\J\J 07-Anr-67

S A-1 7f> 1_-Al. r-vt Wall fr\ IKJ Qt>'llln _ (=»1(=>\/Qti ClCVaLUJlJ r\n \x/q1I Wall ^\J\J /mO wo ivia^-u / SA-1 ''7

i_,Ai. Pvt Wall iniKj Qt^Llln _ (=*lf^\/Qti cicvaiivjll r\n w/qII^MO Wall 07-Anr-67 \J 1 ~/\ui ~u / SA-1 ''8 Pvt \x/q11 fn Qt n _ (^l/^\/iiti r\Y\ n ' o 1 1 A MM 1_^AL. Wall lU "111 ClCVallxJll Wall t-UU 08-Mav-67

S A-1 7Q 1L^y'^Q thrn nil u 1ijyy not iivji iwpH lioCli Fvt LAI. \x/all Wall aUVJVC at^o\/f* QtVi "ill - plp\/ation ClCVaLlUll \x/all Wall 100 i\J\J ^A-141 Pvt cir\/~\\7i=» Qt ri — f=»lf*\/otir\n \x/cill /(lO J_/Al. Wall aUUv'C 7L11 ClCVallUll Wall ^\J\J 0R-'spn-6Q Pvt LZ-Al. Wall aUUVC a r\r\\/f^ Qtn "111 _ f=»l/=»\/Qti ClCVallUli r\r\ Wall D\J\J \ OO n8-*spn-6Q WOoupU"

SA-143 Ext. wall above 9th - elevation wall 300 08-Sep-69

SA-1 44 144 thru 150 not used

SA-1 51 Grillage details 29-Aug-68

SA-1 52 Grillage details 15-NOV-67

SA-153 Not used

SA-154 Not used

SA-155 Not used

^-156 and above see Tower A & B Index

SA-401 T/V mast suppoit el. lines 500, 600 & 700 . 12-Oct-70

SA-402 T/V mast support el. Imes 800, 900 & 1000 12-Oct-70

SA-403 T/V mast support el. lines 001, 002, 003 &004 lO-Jul-70

SA-404 T/V mast support el. lines 005, 006, 007 &008 lO-Jul-70

152 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

WTC Tower A Structural Concrete Drawing Index - (18-May-73)

SCA-l Concrete plan sub level 5 el. 242 18-Dec-68

SCA-2 Concrete plan sub level 4 el. 253 lO-Dec-68

SCA-3 Concrete plan sub level 3 el. 264 - core 17-Jan-69

SCA-4 Concrete plan sub level 3 el. 264 - floor 23-Jan-69

SCA-5 Concrete plan sub level 2 el. 274 - core 22-Jan-69

SCA-6 Concrete plan sub level 2 el. 274 - floor 22-Jan-69

SCA-7 Concrete plan sub level 1 el.284 - core 28-Jan-69

SCA-8 Concrete plan sub level 1 el.284 - floor 28-Jan-69

SCA-9 Concrete plan service level el. 294 - core 03-Feb-69

SCA-10 Concrete plan service level el. 294 - floor 03-Feb-69

SCA-l 1 Concrete plan floor 1 el.310-core lO-Dec-68

SCA-l 2 Concrete plan floor 1 el.310 - floor 19-Mar-69

SCA-l 3 Concrete plan intermediate level 02-Dec-69

SCA-14 Concrete plan floor 2 - core 17-Jan-69

SCA-l 5 Concrete plan floor 2 - floor 04-Oct-71

SCA-l 6 Concrete plan floor 3-6 - floor 02-Dec-69

SCA-l 7 Concrete plan floor 7 - core 02-Dec-69

SCA-l 8 Concrete plan floor 7 - floor 26-May-69

SCA-l 9 Concrete plan floor 8 - core ; 16-Mar-70

SCA-20 Concrete plan floor 9 - core 16-Mar-70

SCA-2

1

Concrete plan floor 9 - floor ll-Feb-69

SCA-22 Not used

SCA-23 Concrete plan floors 10-40 - floor 19-Mar-70

SCA-24 Concrete plan floors 10-16 - core 19-Mar-70

SCA-25 Not used

SCA-26 Not used

SCA-27 Not used

SCA-28 Not used

SCA-29 Not used

SCA-30 Concrete plan floor 17 - core 15-Apr-70

SCA-3

1

Concrete plan floor 1 8 - core 15-Apr-70

SCA-32 Concrete plan floor 19 - core 15-Apr-70

SCA-33 Concrete plan floor 20 - core 15-Apr-70

SCA-34 Concrete plan floors 21-23 - core 15-Apr-70

SCA-35 Not used

SCA-36 Not used

SCA-37 Concrete plan floor 24 - core 12-Mar-69

SCA-38 Concrete plan floor 25 - core 15-Apr-70

SCA-39 Concrete plan floor 26 - core 15-Apr-70

NISTNCSTAR 1-2A, WTC Investigation 153
Appendix A

SrA-40 1 S-Anr-70

SrA-41 r^nnPTPfp nlan floors '^R-^l - potp 1 S-Anr-7n

SrA-42 Not ii^iPfl SCA-43 Not 1I<spH SCA-44 Nlnt h^pH

r^nnrrpfp nlan flnnr - pnrp 1 7-Mar-fi9

1 onprpfp niJin Tlnot* - pnvp Sr A-47 i^r\Tiprptp r\lj^n flnAr ^4 - povp 1 S-Anr-7n

f^nnprptp "nlrin flnm' "^S - pnrp

("nnprptp V^VJlICldt r^lnn Ulu.ll TlnnrQ llVJVJlo -JvJ "^fs-^CS - porp ^VJlt 11 J'S.Anr-7n AVpi 1 \J

XJi^t iicpn INVJl UoCU

^lot 1 1 cpn

iiQpn

\ sr A-S^ sr A-Sd V-UIILICIC Uiail llOUI HI V^Ui C sr A-ss v^Ull^lClC Uiall llUUl 1 llUUl IV/ r\U^ /w sr A-'^f^ 1 0- Aiia-7n sr A-^i? V-UIICICIC Uld.ll llUUl LUIC lA-Opt-^^Q sr A-S8 V^UIICICIC UlalJ llUUl llUUl > ^wr^cu/w ^O-FpH-TO sr A-SQ V_UljvlClC Ulall llVJUl - CUIC *i.*-r v-'c I uy sr A-fio V_UllLlwlC Ulall llVJUl '-tH - llUUl z. v 1 cu / V sr A-f>i 1\„UlldClC nnr*rf*t(=* t^lsin Tlr\r\t* A.S _ pm"f^ Ulall llUUl *-r^ ^UlC lO-AiiP-VO sr A-^i'' 1\„UlldClC r\r\r-r(^ff^ nlcxn Tlr\rw id.^ _ Tlr\r\T" Ulall llUUl llUUl 1 0- Aiia-7n sr A-^s'^ 1 r\nr'r(=*t/^ 'rtlciTi Tlr\r\r zl^^ _ r/mt* V_U11L1CIC Ulall llUOl HU CVJl C 1 O-AiicT-TO sr A-64 1 r^nr*T*(^ff» nlciTi flr^OT'c A.f\ A/i AX _ flr^rxt* V„ unci CIC Ulall llUUl L> T-U^H / ^HO llUVJl 1 0-AiiP-TO sr A-^ss V^UIICICIC Ulall llUUl '-r 1 - CUIC 1 o ocp / \J sr A-f>6 \^U11L1CIC Ulall llUUl T-O CUIC 1 O-AiiP-70

srA ^7 INUl UdCU

srA/A f^A UO V^UIICICIC piall ilUUlo /H- - llUUl 11 n-Aiia_7n W /t.U^ / \) sr A-68 Alt n cwvcYf^i nlQn Tlr\rwc AS^-TIA. -.\\r\cw /All ^^UIILICIC Ulall llUUlji *T-_7 /'-+ llUUl sr A-^SQ V_ unci CIC Ulall llUUlo J/, JO CUIC sr A-7n sr A-71 NI c\\ 1 1 c f*ri sr A-77 sr A-7^ TsJnt iiQpH

srA -74. 1\^UlldClC c\x\C'Tf^\e^ nlcin Tlr\r\v ^zl (wp* Ulall llUUl CUl C srA 7'> ^^UllLlClC piall llUUl JJ LUIC SCA-76 Concrete plan floor 56 - core lO-Aug-70

SCA-77 Concrete plan floors 57,58 -core lO-Aug-70

SCA-78 Not used

SCA-79 Concrete plan floor 59 - core 03-NOV-69

154 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

IsL A-oU Concrete plan floor 60 - core lO-Aug-70

cr^ A CI Concrete plan floor 61 - core A"? XT ^. , /Z A 03-NOV-69

C/^ JjL A-oz A o Concrete plan floor 62 - core 1 A A . . « T A lU-Aug-7(J

cr^ A cj oL. A-oj Concrete plan floor 63 - core 1 A A nr\ lU-Aug-/U

o<^A-o4 Concrete plan floor 64 - core 1 A A TM TA lU-Aug-/U

bLA-oj Concrete plan floor 65 - core lO-Aug-70

C/^ A C^i A-00 Concrete plan floor 66 - core 01 -May-70

cr^ A bLA-0 / Concrete plan floor 67 - core 15-May-70

bLA-oo Concrete plan floor 68 - core 15-May-70

C/"' A OO tjLA-oy Concrete plan floor 69 - core 24-Aug-70

c/^ A on Concrete plan floors 70-73 - core z4-Aug-/U

bCA-yi Not used

c/^ A no Not used

C/^ A n'3 Not used

c/"' A n/1 !:5L,A-y4 Concrete plan floor 74 - core z4-Aug- /U

c/^ A nc Concrete plan floor 75 - coreA1 A4«-., '7A Ul-May-/U

c/"* A n/i ISLA-yo Concrete plan floor 75 - floor O^ A '7A zj-Aug- /U

c/^ bCA-y A m/ Concrete plan floor 76 - core0 C A iirr TA ZJ-AUg- /U

c/^ A no Concrete plan floor 77 - core O^ A ..^ TA zj-Aug- /U

bLA-yy Concrete plan floor 77 - floor ZJ-Aug- /U C A 1 AA Concrete plan floor 78 - core

0 ^ A TA zj-Aug- /U C A 1 A 1 Concrete plan floor 78 - floor O^ A 1.^^ "TA ZJ-AUg- /U C A 1 AO Concrete plan floor 79 - core zj-AUg- /U

Concrete plan floor 79 - floor 1 1 Till TA 1 3-JUl- /U

C/^ A 1 A/1 Concrete plan floor 80 - core OC A iirr 7n ZJ-AUg- /U

SCA-105 Concrete plan floors 80,81,82 - floor 10 T..1 OA 13-Jul-70

SCA-106 Concrete plan floor 81 - core 25-Aug-70

bCA-lU/ Concrete plan floor 82 - core 0^ Ann 7n zj-Aug- /U

Concrete plan floor 106 A - floor 1 A Inn 71 1 D-Jun- /z

r^^^^^*^ -H^z-x^r. 1 f\1 A Q1 1 A/I'D -fl/^/-v*- Loncrete plan tloors o3-lUiA- oi-lU4r>-iloor A1 7n ui -oep- /u A-1 OQ Alt Cnnrrptp nlan flnnrQ 8^-1 n4R-flnnr 04-Mav-70

C A 1 1 A Concrete plan tloors lU4-JUjA-lUj-lUDA-lloor A1 C on 7n

C/^ A 111 Concrete plan floor 83-core 0^ A iirr 7A Zj-AUg- /U

Concrete plan floors 84-86 - core

')'^ Aiirr 70 ZJ-AUg- /u

A 1 1 T Not used

C/"* A 11/1 bCA-l 14 Concrete plan floor s7 - core 7^ AufT 70 ZJ-AUg- /U C A lie Concrete plan floor 88 - core Z

o^;J-/\Ug- Alio 70/U

SCA-116 Concrete plan floors 89,90,91 - core 25-Aug-70

SCA-117 Not used

SCA-118 Not used

SCA-119 Concrete plan floor 92 - core 25-Aug-70

NISTNCSTAR 1-2A, WTC Investigation 155
Appendix A

SrA-1 20 1 1 -AiiP-70

r^ntiPTPtp nl^in floor Q4 - pnrp 11 S-lVIar-71 iVldl /I SCA-l 22 (^nnrrpfp nl^in flnnr - porp 11 »^5-Mar-71 IVldl / i Concrete nlan floors 96-99A-96-1 008-core 1 5-Mar-71

SrA-1 24 \lnt lI<ipH SrA-1 2'S T\fnt iiQpH ' Not uqpH

SrA-1 27 r^nnprptp nlan flnnr 100 - pnrp \J i IV lay / u SrA-128 r^ntiprptp nliin flnnr 101 - pnrp lS-Mar-71 1 ^ IVldl / i SrA-1 2Q 1 nnprpfp nlun flnnr 1 0'7 - pnrp 1 '^-Mar-71 SrA-HO (^nnprpfp nlan flnnr 1 0^ - pnrp 01W i -npr-70 l_-/tt / u srA-1 l3V_ r\ 1 J^11 r^nnprpfp nlan flnnr 1 04 - cnrp Ol-Mar-71 \J 1 IVl di / i

1 nnprpfp nlan flnnrc 1 OS - pnrp 11 S-Ma^-7'> iVld\ / ^ A-1 1 nTir*vf^tp nli^n Tlr\Mt"c 1 \ \f\ - ccwp* U / J Ul / z. sr A-1 "^4 \ c\wcvf^\f^ T\lcin flr\r\f* 1 0 / — 11/^/^1* V^UIICICIC Ulail ilUUl IW/ IHJVJI 1 ^>-Iiin-72 sr A-1 ^5 v_ c\x\cxf^\f* unci wit nlan Uldil flnnr llUVJl 107 1 U / - pnrp tVJl t 1 U J Llil / ^

\ r\T\c^v(^\(^ nlcin flr*r\T" 108 . c^cwf^ \^ Ulltl CIC Uidll ilUUl i V/O tui C 1 S-Mav-7?

SCA-l 37 r^nnrrpfp nlan flnnr lOR - flnnr 01\J 1 -Mar-71 IVldl / 1 i^nnprptp v^uiidciv nlan Uidll flnnr iiuui 1wjyOQ - pnrp cult JU30-Tiil-71 J Ui / 1 srA-i 3Q \c\x\c^vf^\f^ \^UlltltLt v\\c\x\ \\c\r\Y 1 1 0 - r*r\i*(^ Uidll liUUl 1 iW tUl t

1 S-Mav-72 sr A-i4n \v,Ulltitlt c\x\c*vf^\f^ nlc^Ti flr\Mi" 1 1 0 - Tlr\/^t* Uldil iiUUl 1 IW llUUi ^ O J Ul / 1 SrA-141 \V^Uiltivlt c\x\c*vf^\p' v\\'AX\ Uldil r\pntnr\iicp UtilliiUUot vc\c\\ iUUi — crwp tUit 02-"NPn-71 QrA-14'' (^r\-nr*fptp \^uiivitit r\lanc uidiio cppnnHar\/ &ttuiiiJ.diy 1p\/p1c itvti?> 01\J 1 -r)pr-70 i_/ct / u ^Ulldtlt pidll aUU oLdLlUllo, totalalUl pil5> 01W i -Dpp-TO i-/tt / w

1 r^nr*t*f*1"f* nlcin f*l /r\A^ r\r\cf fp*r\c\r\Y\ \^UiltlClC Uidll ti.Z^UT", UU?»L ItllSlUll V UlLl

l^UllLltlt pidli ptillllUU^t luUl lUWtl ItVtl 11 Z"J 7-Tiil-71 Ul~ / 1 SCA-147 Concrete plan penthouse roof upper level Ol-Oct-71

SCA-l 48 Concrete plan raised floor 107 - core 07-Jul-72

SCA-149 Concrete plan raised floor 107 -floor 1 6-Jun-72

SCA-150 Concrete plan raised floor 106 - floor 16-Jun-72

156 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

WTC Tower B Structural Steel Drawing Index - (18-May-73)

SB-Ll Tower B foundation loading plan 21-Mar-68

SB-1 Foundation plan 06-Sep-68

SB-2 Plan sub-level 5 el.242 25-Sep-68

SB-3 Framing plan sub-level 4 el.253 25-Sep-68

SB-4 Framing plan sub-level 3 el. 264 07-Oct-68

SB-5 Framing plan sub-level 2 el. 2 74 17-Jul-68

SB-6 Framing plan sub-level 1 el. 284 07-Oct-68

SB-7 Framing plan service level el. 294 28-May-69

SB-8 Framing plan floor 1 17-Jul-68

SB-9 Framing plan intermediate level 17-Jul-68

SB-10 Framing plan floor 2 17-Jul-68

SB-11 Framing plan floor 3 17-Jul-68

SB-12 Framing plan floor 4 . 17-Jul-68

SB- 13 Framing plan floor 5 17-Jul-68

SB- 14 Framing plan floor 6 17-Jul-68

SB-15 Framing plan floor 7 13-Mar-69

SB-16 Framing plan floor 8 17-Jul-68

SB-17 Framing plan floor 9 17-Aug-68

SB- 18 Framing plan floor 10 19-Mar-69

SB-19 Framing plan floor 11 19-Mar-69

SB-20 Framing plan floor 12 19-Mar-69

SB-21 Framing plan floor 13 19-Mar-69

*SB-22 Framing plan floors 14-16 09-Oct-68

SB-23 Not used

SB-24 Not used

*SB-25 Framing plan floor 17 09-Oct-68

*SB-26 Framing plan floor 18 09-Oct-68

*SB-27 Framing plan floor 19 09-Oct-68

*SB-28 Framing plan floor 20 09-Oct-68

*SB-29 Framing plan floors 21-23 09-Oct-68

SB-30 Not used

SB-31 Not used

SB-32 Framing plan floor 24 09-Oct-68

*SB-33 Framing plan floor 25 09-Oct-68

*SB-34 Framing plan floor 26 09-Oct-68

*SB-35 Framing plan floor 27 09-Oct-68

*SB-36 Framing plan floors 28-31 09-Oct-68

SB-37 Not used

SB-38 Not used

NISTNCSTAR 1-2A, WTC Investigation 157
Appendix A

Wt"o fvi 1 n c\ ir\ \ '\ r\ t1 ridiiiing pidn iiuur jZ no Cinf AS

rrdrning pidn iiuor DO no O/^f AS

rrarning piaii iioor 14 r»o Or.t AS

r raining pidn iioor 1'^ no 0/-t AS

rrduiing pidn iioors 1A IS no Of-t AS

iNUi UbcU

<;r INOl UScU

*CD An rrdining pidn iioor 10 no r\ni AS

oD-fo ridining pidn iiuur 40 no Hr-t AS

*CR 40 rrdining pidn iiuur 41^ 1

1 n Tcin AO

*QR Framing plan floor 474Z 1 n Ton AO

rrdiiiiiig pidii iiuur 41 11 nvj-jdn-D7 AO

QR SO Framing plan floor AA m Ce.T\ 7n

*CR '^'J Framing plan floor A'^ 77 "Mr->A/ AS ZZ-lNOV-Oo

*CR S4 Framing plan floor A(^ 77 AS ZZ-INOV-Oo

*CR ^ ^ Framing plan floor A 1 77 Ma-.i7 as ZZ-JNOV-Oo

*CR '^(^ Framing plan floor A fi 77 XTrA-«r AS ZZ-lNOV-Do

*CR 'n7 Framing plan floor /IQ 77 XTrM/ AS ZZ-InOV-Do

*CR ';c Framing plan floor sn 77 XT/->i; AS ZZ-lNOV-Oo

5>r>-jy Framing plan floors 'n 1 ^A 77 M/->»; AS ZZ-lNOV-Oo

CR AO Not used

CR ^1 Not used

CR Not used

*CR Framing plan floor J J 77 "VT^i/ AS ZZ-iNOV-OO

*CR A/I Framing plan floor JO 77 AS ZZ-i\0V-06

*CR A^ Framing plan floor ^7 77 XT/->\; AS ZZ-iNOV-Do

*CR AA Framing plan floor JO 77 "^Tr^^; AS ZZ-lNOV-Oo

*CR A7 Framing plan floor 'sO jy 77 AS ZZ-lNOV-Oo

*CR Afi Framing plan floor AHDU ZZ-lNOV-Do 77 ^Tr^^/ AS

*CR AO Framing plan floor 77 M<->i; AS ZZ-iNOV-Oo

*CR 1C\ oJt5- /U Framing plan floor A7OZ ZZ-lNOV-Do 77 Mz-ii; AS

*CR 71 ridming pidn iiour ^^1 77 Nnx/ AS

*CR 77 Framing plan floor A/I 04 77 "M/->\; AS ZZ-iNOV-Do

*CR 71 Framing plan floors A'^ AA 0J,OD ZZ-IMOV-Oo 77 Mr>A7 AS

CR 7/1 Not used

CR 7'v Framing plan floor A70 / 77 XT/->\7 AS ZZ-rNOV-Oo

SB-76 Framing plan floor 68 22-NOV-68

SB-77 Framing plan floor 69 22-N0V-68

*SB-78 Framing plan floor 70 22-N0V-68

*SB-79 Framing plan floor 71 22-N0V-68

158 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

Framing plan floor 72 22-NOV-68

*CD CI Framing plan floor 15 22-Nov-68

Framing plan floor n A /4 22-N0V-68

Framing plan floor /j 27-Nov-68

or>-o4 Framing plan floor lb Ol-Aug-69

brJ-oj Framing plan floor 1

1

27-Nov-68

Framing plan floor no75 18-Mar-69

brJ-0 / Framing plan floor ncx ly Ol-Aug-69

* C TD O O Framing plan floor OA Ol-Aug-69

rrammg plan floor O 1 81 27-NOV-68

rrammg plan floor O82 27-Nov-68

*CD n 1 Framing plan floor O 1 8j Ol-Aug-69

Framing plan floor 84-86 27-Nov-68

bB-yj Not used

CT3 O/l D£>-y4 Not used

*bB-y5 rrammg plan floor o n 87 Ol-Aug-69

bB-yo rrammg plan floor O O 60 Ol-Aug-69

**bB-y7 c D m rrammg plan floor O A <^ 1 A /TV Ol-Aug-69

*CD no bB-ys rrammg plan floor AA AT AT Ol-Sep-70

c D nn bB-yy Not used

* C D 1 Arv bB-lUU rrammg plan floor A'^ 27-NOV-68

CD 1 A 1 bB-lUl Not used

*bB-lU2 17 1 IT rrammg plan floor A /I 94 Ol-Aug-69

rrammg plan floor ys Ol-Aug-69

Frammg plan floor A^

yo Ol-Aug-69

*CD 1 AC Framing plan floors A^ 1 AA y7-iuu /~v 1 A /"A Ol-Aug-69

SB-lUo Not used

CD 1 r\n bB-lU7 Not used

CD 1 AO Not used

* C D 1 An rrammg plan floor 1 A 1 JUl A1 A^.^ /CA Ul-Aug-6y

sie C D 1 1 A rrammg plan floor 1 A'^ 102 A1 A..~ ZTA Ol-Aug-69

* C D 111 bo- 1 1 1 Framing plan floor 1 A*? 1U3 A 1 A . . n /I A Ol-Aug-69

* C D 1 1 rrammg plan floor 104 01-Aug-6y

bo- J 1 J rrammg plan floor 1(J5 iu-ijec-6y

* C D 111 rrammg plan floor 106 iu-ijec-6y

* C D TIC ^bB-1 1

5

17 1 rrammg plan floor 1 AT 107 AC n 1 Oj-Mar- /

1

*bB- J 1

6

Framing plan floor 1 07 upper void

*SB-n7 Framing plan floor 108 05-Mar-71

*SB-118 Framing plan floor 109 05-Mar-71

*SB-119 Framing plan floor 110 02-Jul-71

SB-120 Framing plan p.h. roof upper level 27-Sep-71

NISTNCSTAR 1-2A, WTC Investigation 159
Appendix A

SR-1 21 Fri^mincT r>l^in n H ronf lowpr IpvpI 27-Sen-71

SR-1 21 1KrJimino iuiilliJ^ nlfin Uldll tfiipK 11 r^mrn lulllLJ V UlU

SR-1 24 T^lnnr naDipl qpHpHiiIp .^o 78.Mar-6Q ividi \jy SR-1 2*^ LPvtA. I . wall W till to\.\J QtVi 7 111 -p1dL.VclllUll pvjiti oTi wjill Wdll 100 l\J\J 1 5-Fph-68

SR-1 ''6

LJ J_> J PvtI. \\/iill w <xii tn Otli y 111 -plpvatinn dw V U.11VJ11 wall v\ dii 900 1 5-Feh-68

SR-1 27 Pvt l_.Al. \A/all Wdll \C\ Wj Qtrl "111 -plp\/atlOn tlCVClLlVJll \A/ail Wdll -JtOO 1 5-Fph-68 1 c u uo SR-12X LAI. Fvt wall Wdll tn\.\J Qth ^111 -plpvatinn V-l C V d 11 VJll wall Wdll 400 "V/W 1 5-Feh-68

SR-1 '>Q

1 z. 7 1111 ti iivji u^tu

SR-1 40 Pvt l^Al. \x/all wdll dL/VJVv. aKo\/p QtVi 7111 -plpvation dCVdLUJll wall Wdll 100 1 WV 08-Spn-6Q

SR-141 Pvt L<Al. wall Wdll <X\J\J\\, ahovp QtH y 111 -plpvatinn ClCVdlUJll wall Wdll ^\J\J 900 08-Sen-69

SR-142 LjAI. Pvt \\/all Wdll aV*OA/p dU\JVC Otn "111 -plpx/ation CltVdllVJll \A/all Wdll ^00

SR-141 i_/Al. Pvt w/all Wdll dUUVC anr^\/p QtVi !7lll -plp\/atir^n tlCVdlUJll \x/all Wdll 400 08-Spr)-6Q

SAR-144 1 4.4 tlirn 1 SO r»nt ii^prl SR-1 ^1 ItVJlllld^C VI ll^ltTpHptQllc UCLdllo 08-Spn-6Q

SR-1 SI 1 JT-lldlVJl AnpVior Rnlt L>\Jll X-/tldllo OptailQ 08-Spn-6Q

SR-1 S

1

AnplioT Rolf P^pfailc . /A-liCllVJl iJOll J_/Cldll& 08-Spr>-6Q

SR-1 SI 1 /Ali^llVJl AtipVioi" OUll Rolf P^pfailc J_/CLdllo 08-Spr)-6Q

SR-1 S2 |-rT"l VJlllld^C 1 1 ;3 (T(^ Hpf UCldllo CI 1 1 C OQ-Fph-68

SR-1 SI livi llrifTPriPtciilc vJlllidJJ.C UvLdllo 1 5-Nnv-67

SR-1 S4 IrvilliirTf^ vJlllldtI,C riptmlc UCldllo 1 3-npr-67

SR 1 SS

SB-401 TV mast support elev. Lines 500,600,700 05-Mar-71

SB-402 TV mast support elev. Lines 800,900,1000 05-Mar-71

SB-403 TV mast support elev. Lines 001,002,003,004 05-Mar-71

SB-404 TV mast support elev. Lines 005,006,007,008 14-Dec-70

* formerly included with tower A

160 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

\\ TC Tower B Structural Concrete Drawing Index - (18-May-73)

SCB-l Concrete plan sub level 5 el. 242 02-Jan-70

SCB-2 Concrete plan sub level 4 el. 253 ll-Apr-69

SCB-3 Concrete plan sub level 3 el. 264 - core 05-Aug-69

SCB-4 Concrete plan sub level 3 el. 264 - floor 05-Aug-69

SCB-5 Concrete plan sub level 2 el. 274 - core 05-Aug-69

SCB-6 Concrete plan sub level 2 el. 274 - floor 05-Aug-69

SCB-7 Concrete plan sub level 1 el. 284 - core 05-Aug-69

SCB-8 Concrete plan sub level 1 el. 284 - floor 05-Aug-69

SCB-9 Concrete plan service level el.294 - core lO-Jul-69

SCB-10 Concrete plan service level el.294 - floor lO-Jul-69

SCB-l 1 Concrete plan floor 1 el. 3 1 0 - core ll-Jul-69

SCB-12 Concrete plan floor 1 el.3 1 0 - floor ll-Jul-69

SCB-13 Concrete plan intermediate level see SCA-13

*SCB-14 Concrete plan floor 2 - core 06-Dec-69

SCB-l 5 Concrete plan floor 2 - floor see SCA-15

SCB-l 6 Concrete plan floors 3-6 - core see SCA-16

SCB-17 Concrete plan floor 7 - core see SCA-17

SCB-18 Concrete plan floor 7 - floor 02-Dec-69

SCB-19 Concrete plan floor 8 - core see SCA-19

SCB-20 Concrete plan floor 9 - core see SCA-20

SCB-2

1

Concrete plan floor 9 - floor 16-Mar-70

SCB-22 Concrete plan floor 10 - floor 19-Mar-70

*SCB-23 Concrete plan floor 10 - core 19-Mar-70

*SCB-24 Concrete plan floor 1 1 - core 19-Mar-70

SCB-25 Concrete plan floor 1 1 - floor 19-Mar-70

SCB-26 Concrete plan floor 12 - floor 19-Mar-70

SCB-27 Concrete plan floor 12 - core 19-Mar-70

SCB-28 Concrete plan floor 13 - floor 19-Mar-70

SCB-29 Not used

SCB-30 Concrete plan floor 17 - core see SCA-30

SCB-3

1

Concrete plan floor 1 8 - core see SCA-31

SCB-32 Concrete plan floor 1 9 - core see SCA-32

SCB-33 Concrete plan floor 20 - core see SCA-33

SCB-34 Concrete plan floor 21-23 - core see SCA-34

SCB-35 Not used

SCB-36 Not used

SCB-37 Concrete plan floor 24 - core 15-Apr-70

SCB-38 Concrete plan floor 25 - core see SCA-38

SCB-39 Concrete plan floor 26 - core see SCA-39

NISTNCSTAR 1-2A, WTC Investigation 161
Appendix A

SrR-40 r^nnrrpfp nl;^n flnnr 77 - porp cee SrA-4n

r^onrrptp nl?in floor 9^-^l - rorp see SrA-41

SrB-42 T^ot ii<ipH Mot iiQpH

QrR-44 XJot iiQpH

r^OTiPfptp r\l?in flooT" ^7 - porp 1S-Anr-70 1 /T.pi 1 \J

1 onprpfp nlj^Ti floor '^'^ _ povp

(^onprpfp nlnn floor ^4 - porp ope QrA-47

SrR-48 1 otiprpfp tilan floor - Porp cpp srA-48

SrR-4Q 1 onprpfp nljin floor "^f^-^C) - porp dec LJV^/A T"!/ srR-^o Mot iicpn

srR-si Mot iiQpn

SrR-57 Mot iicpn

Mot iicpH

(^onprptp r^lan floor 41 - porp cpp QrA-'i4

f^onprpfp r\lan floor 41 - floor SrR-S6 f^onprptp r\lan floor 47 ~ porp cpp srA-'>6

OV, D J /

tV^UIILICLC r\nr^v(^fi^ rilan T\r%r\r A.^ — r^i^rt^ Ulall llUUl CUIC 10-Aiia-7n I u /\U^ / u

f rxTxr^vf^tf^ r\\ an florw A.^ — flr\r\T" V^UllCiCLC Ulall llUUl llUUl

t r\r\r*r(^ff* ntavi flrvrw A.A. _ r^rwf^ V_ unci CIC Ulall llUUl T-H CUIC ocp / u

I^MTii^ri^^tf^* V^UIICICIC nlcin flrxrw AA. _ flr^i^t* Ulall llUUl 'T'T' llUUl OCp / U

1 r^nr^ff^^ti^* nl^in fli^r^r 4 t _ rrw/^* \^U11C1CIC Ulall llUUl C^UIC Qpp <sPA Al

I rMnr'Vf^ff^ r\\aY\ T\r\r\v 4S _ ilr^rxt" \_^U11L1CIC Ulall llUUl - llUUl cpp QPA-fS7

tf^ ^UULICLC r\T\r*irf^\f^ t\\'ay\ TXc^fw A.r\ r*fwf^ piall ilUUX H\j CUIC QPP QpA-A*^

V^UllCldC Ulall llUUlo 'tU *tO lJUUl opp srA-M

^PR V^UllCICLC Ulall llUUl H- / CUl C opp srA-fS^

V_ UllL^l CIC Ulall llUUl HO CUIC

IMUl U^CU

V^UIICICIC Ulall ilUUl^ / ^ ilUUl opp <srA-68

V^UIILICIC Ulall lliJUla H"-^'T- CUIC cpp srA-6Q

Mr\t iiCi^H Mr\t lie

Mr\t iicf=»H

V^UIICICIC Ulall ilUUl ~}~J CUIC cpp <srA-7^

^rR ov„ Xj- 7^/ O ^UllCltlC piall llUUI JO LUlC «pp ^rA-7rS

SCB-77 Concrete plan floors 57-58 - core see SCA-77

SCB-78 Not used

SCB-79 Concrete plan floor 59 - core see SCA-79

SCB-80 Concrete plan floor 60 - core see SCA-80

162 NISTNCSTAR 1-2A. WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

v^uiiLitit pidii iiuur Di - Lurc in A iirr 7n lU-AUg- /u

v^uiiLicic pidn iiuur d-_ - core see POO C/^ j)UA-oz A O

SCB-83 Concrete plan floor 63 - core see SCA- 83

i-^uuLrcLC pidn iiuur oh- - core coo A 8/1 see bv^A-o^

<;rR 8^ 1 r\n r^ff^ff^ t> Ion t1 f~\f~\ v r\r(^ V^UIlLltlt pidU iiUUi DJ - Lurc coo A fi*; see o^^A-oj

<JPR 86 V-Uncrcic pidn iiour do - cure 7/1 Ann 7n Z4-AUg- /U

QPR 87 Concrete plan floor 67 - core 7/1 A iirr 7n z4-Aug- /U

Qr"R as Concrete plan floor 68 - core 7/1 Ann 7n 24-Aug- /U

cpR on Concrete plan floor 69 - core coo cr' A CO see j>LA-oy

v^oncreie pidn iioors /u-/ j - core coo Qr^ A on see L5L,A-yu

CPR Q1 Not used

M1^^" lie* ^/"i CPR Q"? Not used

Concrete plan floor 74 - core coo Cr^ A QA see b^_A-y4

Concrete plan floor 75 - core see 2>CA-95

SCB-96 Concrete plan floor 75 - floor see SCA-96

SCB-97 Concrete plan floor 76 - core see SCA-97

SCB-98 Concrete plan floor 77 - core see SCA-98

SCB-99 i 1 in in Concrete plan floor 77 - floor see SCA-99

<C("R inn Concrete plan floor 78 - core coo Qr^ A 1 nn see ov^A-iuu

QPR ini Concrete plan floor 78 - floor coo cr^ A 1 n 1 see oCA-iui

cpR in") Concrete plan floor 79 - core coo cr" A 1 n7 see L>i_ A1

VI Qr"R in'? Concrete plan floor 79 - floor coo A 1 ni see oi-^A-iuj

cr^R 1 n 'I Concrete plan floor 80 - core coo A 1 r\A see A- 1 U4

Qr"R in*; Concrete plan floor 80-82 - floor coo Qr^ A 1 n'^ see oca-iuj

CPR 1 nA Concrete plan floor 8 1 - core coo A 1 C\f^ see A- 1 UD

v^oncreic pian iioor oz - core see coo <;p Liv„A-iu A 1 n7/ Qr^R 1 nfi IN 01 useo cpR.i HQ \_^U1JLJCIC Uldll iiUUlo 0-) 1 WU llUOl qpp SrA-1 09

srR-1 1

0

OV— ID I I yj ^r\t llCf*H Qr"R 1 1 1 oL. D- 1 1 1 Concrete plan floor 83 - core coo Qr^ A 111 see ov^A-i 1

1

D- 11.: Concrete plan floor 84-86 - core cop CP A 117 see A- 1 1 z

iNoi used

SCB-1 14

/"* i 1 in o ^ Concrete plan floor 87 - core

C/"' A 11/1 see SCA-1 14

cop A 1 1 sec ov^A-i 1

J

v^oncreie pian iioors o7,7U,v i - core QPP cr A .1 1

A

QPR 1 1

7

od5-l 1 / Not used

SCB-1 18 Not used

SCB-1 19 Concrete plan floor 92 - core see SCA- 11

9

SCB-120 Concrete plan floor 93 - core 15-Mar-71

SCB-1 21 Concrete plan floor 94 - core see SCA-121

NISTNCSTAR 1-2A, WTC Investigation 163
Appendix A

SCB- 122 Concrete plan floor 95 - core see SCA-122

SCB- 123 Concrete plan floors 96-100 - core see SCA-123

SCB- 124 Not used

SCB- 125 Not used

SCB- 126 Not used

SCB- 127 Not used

SCB- 128 Concrete plan floor 101 - core seeSCA-128

SCB- 129 Concrete plan floor 1 02 - core see SCA-129

SCB- 130 Concrete plan floor 103 - core see SCA-130

SCB- 131 Concrete plan floor 104 - core 15-Mar-71

SCB- 132 Concrete plan floor 105 - core 18-Jun-71

SCB-133 Concrete plan floor 1 06 - core 18-Jun-71

SCB-134 Concrete plan floor 107 - floor 30-Jul-71

SCB-135 Concrete plan floor 107 - core 30-Jul-71

SCB- 136 Concrete plan floor 108 - core 30-Jul-71

SCB-137 Concrete plan floor 108 - floor Ol-Dec-71

SCB-138 Concrete plan floor 109 - core see SCA-138

SCB- 139 Concrete plan floor 1 10 - core 03-Sep-71

SCB- 140 Concrete plan floor 1 10 - floor 03-Sep-71

SCB-141 Concrete plan penthouse roof - core lO-Apr-72

SCB-142 Concrete plans secondary levels see SCA- 142

SCB-143 Concrete plan sub stations, escalator pits see SCA-143

SCB-•144 Sections truck ramn el 284 ll-Jul-69

SCB-•145 Concrete plan el. 264, post tension Void

SCB-146 Concrete plan penthouse low roof - floor 26-Mar-73

SCB-147 Concrete plan penthouse high roof - floor 22-Sep-72

SCB-148 Core plan obsei'vation deck 08-Mar-73

* Formerly included with Tower A

Note- Tower B Concrete plan floors 14-40 - floor see SCA-23

Tower B Concrete plans floors 13-16 - core see SCA-24

164 NISTNCSTAR 1-2A, WTC Investigation
WTC Tower Structural Drawings Index for Large-Size Sheets

WTC Tower A & B Structural STEEL DECK Drawing Index - (18-May-73)

SA-156 Steel deck plan floor 7 28-Mar-69

SA-157 Steel deck plan floor 9 28-Mar-69

SA-158 Steel deck plan floors 19-40 28-Mar-69

SA-159 Steel deck plan floor 41 17-Jun-68

SA-160 Steel deck plan floor 43 27-Aug-69

SB-160 Steel deck plan floor 43 27-Aug-69

SAB-161 Steel deck plan floor 45 17-Jun-68

SA-162 Steel deck plan floor 44 27-Aug-69

SB-162 Steel deck plan floor 44 27-Aug-69

SAB- 163 Steel deck plan floors 46-49

11-6-67, 6-17-

68

SAB- 164 Steel deck plan floors 50-58 17-Jun-68

SAB-165 Steel deck plan floors 59-62 17-Jun-68

SAB- 166 Steel deck plan floors 63-66 12-Dec-69

SAB-167 Steel deck plan floors 67-70 12-Dec-69

SAB-168 Steel deck plan floors 71-74 17-Jun-68

SAB- 169 Steel deck plan floors 65-69 17-Jun-68

SB-169

SAB- 170 Steel deck plan floor 75 17-Jun-68

SAB-171 Steel deck plan floor 77 17-Jun-68

SAB- 172 Steel deck plan floors 78-79 18-Mar-69

SAB- 173 Steel deck plan floors 80-81 17-Jun-68

SAB- 174 Steel deck plan floors 82-83 17-Jun-68

SAB- 175 Steel deck plan floors 84-89 17-Jun-68

SAB- 176 Steel deck plan floors 90-94 17-Jun-68

SAB-177 Steel deck plan floors 95-101 17-Jun-68

SAB- 178 Steel deck plan floors 102-106 02-Jul-71

SA-179 Steel deck plan floor 107 08-Sep-70

SB-179 Steel deck plan floor 107 Ol-Oct-70

SA-180 Steel deck plan floor 108 08-Sep-70

SB-180 Steel deck plan floor 108 Ol-Oct-70

SA-181 Steel deck plan floor 110 08-Sep-70

SB-181 Steel deck plan floor 110 29-Jan-72

SB-182 Steel deck plan floor 7 28-Mar-69

SB-183 Steel deck plan floor 9 28-Mar-69

SB-184 Steel deck plan floor 10 28-Mar-69

SB-185 Steel deck plan floor 11 28-Mar-69

SB-186 Steel deck plan floor 12 28-Mar-69

SB-187 Steel deck plan floor 13 07-NOV-69

NISTNCSTAR 1-2A. WTC Investigation 165
Appendix A

Miscellaneous

SX-105 Framing plan-typical office floor 21-Dec-70

SX-144 Sewer ejector & sump pits 20-Mar-69

SX-146 Closure tieback anchorage perimeter 24-Jun-68

7SAB-240 Floor plan el. 229 ^(original print missing) 12-Sep-66

166 NISTNCSTAR 1-2A, WTC Investigation
Appendix B

Drawing Book 19 Modifications for Structural Elements

Not Included in the Database

The following is a table of Drawing Book 19 (Revisions After Fabrication) changes not included in the database because they were considered to not significantly affect the member properties pertaining to the reference structural models. The hsted modifications only pertain to tower modifications. Modifications

outside of the towers are not included.

Drawing Number(s) Title Date Description

19-B-913 Detail 913 10/9/68 '/2 in. by 1 in. shim plates for p/t cells. 19-A-914 Detail 914 11/20/68 Clip angle location changed for seated connection. 19-A-918 Detail 918 1/15/69 Additional studs and flange plates for beam in beam framed between core and

exterior wall in WTC 1, elevation 274 ft. 19-A-921 Detail 921 1/27/69 Additional flange plate for beam in core framing in WTC 1, elevation 284 ft. 19-B-975 Beam repair det. Floor 59

and 92

10/28/70 Beam reinforcing for conduits passing

through core channel. 19-A-982.1, 982.2 Floor 106 beam cover

plate

1/17/71 Beam cover plates Floor 106.

1 9-B-994 Column splice repair Floor 1073/15/71 Column Splice Repair Floor 107

19-A-lOOl.

19-AB-1002. 1003

245 A 12-9

Seat detail

6/5/69 Truss seat modifications Floor 10-12,

Column 246, WTC 1 and seat detail dimensional modifications Floor 10-107,

WTC 1 and WTC 2. 19-AB- 1004.1. 1004.2 Column splice repair

procedure

6/20/69 Additional weld for exterior wall column

splice connections. 19-B-2 100.1 -

2100.4

Modification to pent house

roof framing plan

9/27/71 Raised girder using stubs on roof level framing.

NISTNCSTAR 1-2A, WTC Investigation 167
Appendix B

This page intentionally left blank.

168 NISTNCSTAR 1-2A. WTC Investigation
Appendix C

WTC Drawing Book Flowcharts

This Appendix presents the drawing books flowcharts that illustrate the flow of the drawing book links. These flow chans were used to organize the links of the electronic databases within the relational database. For the flowcharts presented in Figs. C-1 through C-9, the following notes are common:

• "4-AB-*" denotes Drawing Book 4, Tower A , B or AB, and page number

• [*TC] denotes number of pages and type, where page types include:

• TC: computer generated tables; TH: hand written tables; and D: diagrams

• *.xls denotes Microsoft Excel spreadsheet file name; and (AB_***) denotes database heading

• ((*)) denotes reference note key from original Drawing Book information table.

• {*} denotes relational database hnk (i.e. Microsoft Excel column number) from

previous *.xls file.

• Figures of columns and panels are shown from inside of building looking out, unless

otherwise noted.

NISTNCSTAR 1-2A. WTC Investigation 169
Appendix C

Exterior Column

Number and Elevation

Member Number

Column Schedule

Seat Details

1 -A2-2 > 5 [4TC]

l-B2-2>5 [4TC]

Column Types

((4)) Seat Details

((4, 14)) Spandrels

1-A2-18.23 [ITC]

T-A2-19>22, 24>33 [4D]

1-B2-19. 24.27 [3TC]

-B2-20>25, 25, 26, 28>38 16D] WH A-Bkl-t iilimniTy|iod.il.j ^Is lAJ. olT>iu'l WTC B-Bkl-C..lumnTyiKid.itjAls IB_tolTyixl

Column Schedule

Spandrels

1-A2-7, 8 [2TC]

1-B2-7, 8 [2TC]

\VI CA-Bk I -C.>ln)SohcdulcSpandrcl.xl> ( A_Spaiidrol I WTCH-Hkl-CiilmSchedulcSpjndrcl xls (B Spjrida-li

id;

Splice Details

{(7, 8))

1-A2-34>37[4D]

1-B2-41>46[4D]

Tower Details

((10))

1-AB3-1>18 [20D]

Plaza BIdg Details

((11))

]-AB3-50>66

[9TH] [20D]

Truss Schedule

-B2-I8 [ITC]

Bracing, Spandrel, and

Strut Schedule

1-A2-1017 [8TC] 1-B2-10>17 [8TC]

1D|

Truss Type

1-B2-68 [ITH]

WTCB-Bkl-Tnis.,T>TK- xls (B_TnissTypc)

Spandrel Details

((12, 13, 18, 19))

l-A2-38>40 [3D] l-B2-47>50 [3D]

|D|

Member Type

((3))

1-A2-45>57PD][6TH]

l-B2-55>67, 100>I02 []6D3[7TH]

WTC A-Bkl-MemhciTypc xls (A_McmhciTyiic)

WTtB-Bkl-Mi;inbi;rTypi;,xls(BJVlemb>:iTyiu-)

Connection Details

{(6,7))

l-A2-60>66 [7D3 l-B2-69>99 [3 ID]

Figure C-1. Drawing Book 1 - WTC 1 and WTC 2 exterior wall to elevation 363 ft.

170 NISTNCSTAR 1-2A, WTC Investigation
WTC Drawing Book Flowcharts

Exterior Column iNumber and

Elevation

Exterior Wall Tree Schedule

(Panel # = Center Column #)

2-A1-2 > 13 [12TC]

2-B1-2 > 13 [12TC] 2-AB2-2 [ID]

V.TCA-Bt2.

^^TC&-Bk2•

ftTCA-Blt2 \\TCB-BieWTCB-BL2- WTCA-Bk2

WTCB-Bk2- WTCA-Bk2

WTCB-BICExtWallTtec.

Extttairrrc3:_

-ExtWallTree' -ExiW aimer'

ExlWallTtecj

ExittallTicc. EvWallTrcc. ExiWjUTrec ExlWainror"

ColmLttBAJs (A_Coll^Bl

C olniLc\ B.xlM B_ColLc\ B) ColraL<:\CJd>(A ColLevO

ColmLe\-C.x]s lBj:"olLc\0

ColraLc\D.xk lA_ColLc\D)

"ColmLc%D.xb lB_ColLc^ D) 'ColmLc\E.xhlA_ColU\E) WTC

"ColmL^Ej^b (B ColL« E) WTCtt-Bk: CdmLe%F.xl>lA_CoILi:vF) WTCA-Bk

"ColmLc\Fxl>lB C»!L<r.R WTCB-BkJ

rcc_SpaiidLcvB \1> )A_SpandLi:\ Bl Exl\Sjinree_SpandLc%B \l^ (B_SpandLcvBI

-ExtWain rcc'spandLcvD.xIs i A~SpaiidLt:\D) bxiU jUTro:_SrwnJU-\D x]< I B_SpandLc\ D

I

Exterior Wall Tree Corner Panels

(Panel # = Center Column #) 2-AB2-22 [ITH]

2-AB2-17>2i [5D]

WTC-A-Bk:-Lxi\V.illTicc_i: (.nicrP.inSdiud.xls (A ComPan) WTC B-Bk2 -ExtW allTrcc'_t onKTPaiiSclicd.xls ( Bit ornPan)

Column Splice Details

2-AB2-25 > 30 [4D]

iB. G. l: ib,e.h: IB. H. M} {Bl

Column Type

Level B

((2))

2-AB2-5 [ITH] 2-AB2-4>6 [3D]

MTCAB - B>:i-ExcwTret_TH- LevE.XlB iAB_Ccl87ypeBi

Column Type

Level C

{(7))

2-AB2-7 [ITH] 2-AB2-7 [ID]

Column Type

Level D

((8)) :-AB2-8 [ITH]

2-AB2-8, 9,10,11 [4D]

UH AB-Bk:-fc\iU'lrct-_"l H- LcvD.\l> IAB_Col'nypcD)

Column Type

Level E

((10))

2-AB2-14 [ITH]

2-AB2-12>13, 15 m ttTrAB-Bk2-Exl\VTrec TH-LcvE.xk

Column Type

Level F

((12))

2-AB2-16 [ITH]

2-AB2-16[lD]

(. AB-Bk2-Ii\l\\Trcc_TH-U-vp xls (AB_Ty]n;F)

Splice Details

((15, 16))

2-AB2-23 [ITH] 2-AB2-23 [ID]

Seat Details

((17))

2-AB2-31>36 [7D]

Splice Details ((20,21))

2-AB2-24[lTH]

2-AB2-24[lD]

Figure C-2. Drawing Book 2 - WTC 1 and WTC 2 exterior wall tree, elevation 363 ft to floor 9.

NISTNCSTAR 1-2A. WTC Investigation 171
Appendix C

Core Column Number/Location

and Elevation

I Core Column Schedule

3-Al-2>48 [47TC]

3-B1-2 >48 [47TC]

WTCA-Bk3-CorcColmAdau.xls (A CorcCol) WTCB-Uk3-CorcCalmBdala.xls lU CorcCol)

S IG]

Base Details

((15))

3-AB2-20,21

[2D]

Splice Details

((15))

3-AB2-4,7,8>13. 15>16 [lOTH] 3-AB2-3.1>19 [18D]

Floor 106 Splice Details

((15))

3-AB2-3 [ID]

Shape Property Table

Sliape Property Table.xls (AB ShapcPropI

{B,C! ~

Splice Location

((!»

3-AB2-22 [ID]

Reference Floor Elevation

((2,3))

3-A2-23 [ITC]

3-B2-23 [ITC]

\\TCA-Bk1-CoreColmAnoorclev,xls ( A RcfElcvUPR/LWR)

WTrB-Bk3-CorcColmBnrniri-lev.\ls (U Rcltk-vUPR/LWR)

Figure C-3. Drawing Book 3 - WTC 1 and WTC 2 core columns, foundations to floor 106.

172 NISTNCSTAR 1-2A, WTC Investigation
WJC Drawing Book Flowcharts

Core Column Number/Location

and Elevation

Core Column Truss Schedule

3-B1-49 [ITC]

\\TCB-Bk3-CoreColinBdataforTruss.xls (B_Truss)

Truss Elevations

3-B3-2 > 7 [8D]

Truss DetaOs

3-B3-9>16[8D]

Weld Schedules

3-B3-12,15 [2TH]

Figure C-4. Drawing Book 3 - WTC 1 and WTC 2 core column trusses.

NISTNCSTAR 1-2A. WTC Investigation 173
Appendix C

Exterior Column Nixmber and

Elevation

Panel Schedule

(Panel # = Center Column #)

4-A1-2 > 299 (BOOK 2 OF 5) [298TC]

4-A 1-300 > 508 (BOOK 3 OF 5) [209TC]

4-B1-2 >299 (BOOK4 0F5) [298TC]

4-B1-300 > 508 (BOOK 5 OF 5) [209TC]

WTCA-Dk4-ExtW;illPanAdaUi.xls(A_Panel) WTCB-Bk4-ExtWdllPanBdala.xls (B_Panel)\VTCA-Bk4-SpandrelPlatcAdaIa.xlb Partsl. 2 (A Spandrel) WTCB-Bk4-SpaiidrelPlateBdata.xls Pans 1,2 (B Spandrel)

IDl |E,J,0|

Panel Type

((4))'

4-AB2-7 [ITC]

I-AB2-2 > 6 [5D]

WTCAB-Bk4-PandTypcdatj xls lAB PanclTypc)

I no link! Weld Electrodes

4-AB2-17 [ITC]

WTCAB-Bk4-WeldElectuidesdata.xls (AB WfldElcct)

|HJ,M,N,R,S|

Column Tvpe

((5))

"

4-AB2-8>10 [3TC]

4-AB2-8 > 10 [3D]

WTt AB-BkJ-C olamnTN-pcdala \1; lAB CiiltType)

Column Splice

((8.9)) 4-AB2-15 [ITC] 4-AB2-J2>14, 1614DJ

WTCAB-Bk4-ColumnSplicedata.xls (AB_UPR/LWRCoWSplice)

1G,HI |S,T| |AE,AF|

Spandrel Conn.

((13, 14)) 4-AB2-30 [ITC] 4-AB2-26>29 [411

WTCAB-Bk4-SpandreIConnecliondala.xls (AB_LFT/RGTSpn#Con)

!M,N,01

lY.Z.AAl

|AK,AL,AM)

Seat Details

((19))

4-AB2-35 > 37 [3TC]

4-AB2-31,32, 34 [3TH]

4-AB2-31 >34 [5D]

WTCAB-Bk4-ScalDctailsdata.xls lAB Spn#Col#ScaII

Figure C-5. Drawing Book 4 - WTC 1 and WTC 2 exterior wall, floors 9 to 106.

174 NISTNCSTAR 1-2A, WTC Investigation
WTC Drawing Book Flowcharts

Exterior Column Number

and Elevation

Column and Spandrel Schedule

(Panel # = Center Column #)

4-A3-2.1 >2.4 [4TH]

4-B3-2.1 >2.4 [4TH]

WTCA-Bk4-ExtWalll07-l 10ColSpanSched.xls (A_107-l lOSched) WTCB-Bk4-ExtWall 107-1 10ColSpanSched.xls (B_107-l lOSched)

!B,C}

Column Type

4-AB3-5.2 [2TH]

4-AB3-5.2[lD]

\\TCAB-Bk4.ExtWall_ 1 07to 1 1 0 TH-ColmTypcs.xls

I AB *ColT\iic)

Shape Property Table

Column Conn.

4-AB3-7.1, 7.2, 8 [3D]

{D,F}

Spandrel Type

4-AB3-6 [ITH]

4-AB3-6, 9 [2pJ

WTCAB-Bk4-ExtWall_ 1 07to 1 1 0_TH-SpandTypes.xls (AB_RGT#SpnType)

Wall Section

4-AB3-4[lD]

Column Base Splice

4-AB3-11 [2TH]

4-AB3-11 [ID]

Figure C-6. Drawing Book 4- WTC 1 and WTC 2 exterior wall, floors 107 to 110.

NISTNCSTAR 1-2A, WTC Investigation 175
Appendix C

Beam Number and Location

Beam Schedule

5-ABl-l >243 [244TC]

WTCAB-Bk5-BeamSched.xls

(ABBeam)

{E}

Shape Property

Table

Shape Property Table.xls

(AB_ShapcProp)

Beam Type

((3))

5-AB2-l>40 [40D]

Support Detail

((12))

SEE BOOK 6

Figure C-7. Drawing Book 5 - WTC 1 and WTC 2 beam schedule and types.

176 NISTNCSTAR 1-2A, WTC Investigation
WTC Drawing Book Flowcharts

Core Column Number/Location

and Elevation

Core Bracing Schedule

6-AB5-2>4 [4D]

6-AB5-96> 101 [7D]

WTCAB-BK6-CoreBracingScheduleData.xls

(AB_CoreBrace)

{F}

Core Bracing Members

6-AB5-5 [ID]

WTCAB-Bk6-CoreBracingMember.xls

(ABCoreBraceMember)

Figure C-8. Drawing Book 6 - WTC 1 and WTC 2 core bracing schedule and types.

NISTNCSTAR 1-2A. WTC Investigation 177
Appendix C

Beam Number and Location

Member Types - Built Up

9-AB4-l>3 [2D], [3TH]

WTCAB-Bk9-BeamFL107-PH.xls / BU

(AB_107-PH_BUBeains)

Member Types - Rolled Shapes

9-AB5-2 [ITH]

WTCAB-Bk9-BeamFL107-PH.xls /WF (AB_107-

PH WFBeams)

{B}

i

Shape Property

Table

Shape Property Table.xls

(ABShapeProp)

Figure C-9. Drawing Book 9 - WTC 1 and WTC 2 floor 107 to penthouse beam schedule.

178 NISTNCSTAR 1-2A, WTC Investigation
Appendix D

Excel File List and Description

Files with (*) include section property calculations

Files with (*) include multiple section properties calculations for some members

Drawing Book 1 WTCA-Bkl-ColumnTypesdata.xls* A

WTC Drawing Book 1: Tower A Exterior Wall to EL 363 ' Column Types

WTCA-Bk 1 -BracingScheduleData.xls

WTC Dram'ing Book I: Tower A Exterior Wall to EL 363 ' Bracing, Spandrel and Strut Schedule

WTCA-Bkl-CohTiScheduleSeatDet.xls

WTC Drawing Book 1: Tower A Exterior Wall to EL 363' Column Schedule - Seat Details

WTCA-Bkl-ColmScheduleSpandrel.xls

WTC Drawing Book 1: Tower A Exterior Wall to EL 363 ' Column Schedule - Spandrels

WTCA-Bkl-MemberTypes.xls*

WTC Drawing Book 1: Tower A Exterior Wall to EL 363 ' Member Type

WTCB-Bkl-ColumnTypesdata.xls* A

WTC Drcrwing Book 1: Tower B Exterior Wall to EL 363 ' Column Types

WTCB-Bk 1 -BracingScheduledata.xls

WTC Drawing Book 1: Tower B Exterior Wall to EL 363 ' Bracing, Spandrel and Strut Schedule

WTCB-Bkl-ColmScheduleSeatDet.xls

WTC Drawing Book 1: Tower B Exterior Wall to EL 363' Column Schedule - Seat Details

WTCB-Bkl-ColmScheduleSpandrel.xls

WTC Drawing Book 1: Tower B Exterior Wall to EL 363 ' Column Schedule - Spandrels

WTCB-Bkl-MemberTypes.xls*

WTC Drawing Book 1: Tower B Exterior Wall to EL 363 ' Member Type

WTCB-Bkl-TrussScheduledata.xls*

WTC Drawing Book 1: Tower B Exterior Wall to EL 363 ' Truss Schedule

WTCB-Bk ] -TrussType.xls

WTC Drawing Book 1: Tower B Exterior Wall to EL 363' Truss Type

NISTNCSTAR 1-2A, WTC Investigation 179
Appendix D

Drawing Book 2 WTCAB-Bk2-ExtWTree_TH-LevB.xls*

WTC Drawing Book 2: Tower A and B Exterior Wall Tree EL 363 ' to Floor 9 - Column Type at Level B .

WTCAB-Bk2-ExtWTree_TH-LevC.xls*

WTC Drawing Book 2: Tower A and B Exterior Wall Tree EL 363' to Floor 9 - Column Type at Level C

WTCAB-Bk2-ExtWTree_TH-LevD.xls*

WTC Drawing Book 2: Tower A and B Exterior Wall Tree EL 363 ' to Floor 9 - Column Type at Level D

WTCAB-Bk2-ExtWTree_TH-LevE.xls* A

WTC Drawing Book 2: Tower A and B Exterior Wall Tree EL 363 ' to Floor 9 - Column Type at Level E

WTCAB-Bk2-ExtWTree_TH-LevF.xls*

WTC Drawing Book 2: Tower A and B Exterior Wall Tree EL 363 ' to Floor 9 - Column Type at Level F

WTCA-Bk2-ExtWallTree_ColmLevB.xls

WTC Drawing Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level B

WTCA-Bk2-ExtWallTree_ColmLevC.xls

WTC Drawing Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level C

WTCA-Bk2-ExtWallTree_ColmLevD.xls

WTC Drawing Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level D

WTCA-Bk2-ExtWallTree_ColmLevE.xls

WTC DroM'ing Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level E

WTCA-Bk2-ExtWallTree_ColmLevF.xls

WTC Drawing Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level F

WTCA-Bk2-ExtWallTree_ComerPanSched.xls*

WTC Drcnving Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Corner Panel Schedule

WTCA-Bk2-ExtWallTree_SpandLevB.xls

WTC Drawing Book 2: ToM>er A Exterior Wall Tree EL 363' to Floor 9 - Exterior Wall Tree Spandrel Schedule at Level B

WTCA-Bk2-ExtWallTree_SpandLevD.xls

180 NISTNCSTAR 1-2A, WTC Investigation
Excel File List and Description

WTC Drawing Book 2: Tower A Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Spandrel Schedule at Level D

WTCB-Bk2-ExtWallTree_ColmLevB.xls

WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level B

WTCB-Bk2-ExtWallTree_ColmLevC.xls

WTC Dravt ing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level C

WTCB-Bk2-ExtWallTree_ColmLevD.xls

WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level D

WTCB-Bk2-ExtWallTree_ColmLevE.xls

WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level E

WTCB-Bk2-ExtWallTree_ColmLevF.xls

WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Schedule at Level F

WTCB-Bk2-ExtWallTree_ComerPanSched.xls* * WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Corner Panel Schedule

WTCB-Bk2-ExtWallTree_SpandLevB.xls

WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Spandrel Schedule at Level B

WTCB-Bk2-ExtWallTree_SpandLevD.xls

WTC Drawing Book 2: Tower B Exterior Wall Tree EL 363 ' to Floor 9 - Exterior Wall Tree Spandrel Schedule at Level D

Drawing Book 3

WTCA-Bk3-CoreColmAdata.xls*

WTC Drawing Book 3: Tower A Core Columns Foundation to Floor 106 - Core Column

Schedule

WTCA-Bk3-CoreColmAfloorelev.xls

WTC Drawing Book 3: Tower A Core Columns Foundation to Floor 106 Reference Floor

Elevation

WTCB-Bk3-CoreColmBdata.xls*

WTC Drcm'ing Book 3: Tower B Core Columns Foundation to Floor 106 - Core Column

Schedule

NISTNCSTAR 1-2A, WTC Investigation 181
Appendix D

WTCB-Bk3-CoreColmBdataforTruss.xls*

WTC Drawing Book 3: Tower B Core Columns Foundation to Floor 106 - Core Column Truss Schedule

WTCB-Bk3-CoreColi-nBfloorelev.xls

WTC Drawing Book 3: Tower B Core Columns Foundation to Floor 106 Reference Floor

Elevation

Drawing Book 4

WTCAB-Bk4-Colui-nnTypedata.xls* A

WTC Drawing Book 4: Tower A and B Exterior Wall above 9''' Floor (To 106''' Floor) Column

Type

WTCAB-Bk4-PanelTypedata.xls

WTC Drawing Book 4: Tower A and B Exterior Wall above 9''' Floor (To 106''' Floor) Panel Type

WTCAB-Bk4-SeatDetailsdata.xls

WTC Drawing Book 4: Tower A and B Exterior Wall above 9''' Floor (To 106"' Floor) Seat

Details

WTCAB-Bk4-SpandrelConnectiondata.xls

WTC Drawing Book 4: Tower A and B Exterior Wall above 9''' Floor (To 106''' Floor) Spandrel

Connection

WTCAB-Bk4-WeldElectrodesdata.xls

WTC Drawing Book 4: Tower A and B Exterior Wall above 9"' Floor (To 106"' Floor) Weld

Electrodes

WTCAB-Bk4-ColumnSplicedata.xls

WTC Drawing Book 4: Tower A and B Exterior Wall above 9''' Floor (To 106''' Floor) Column

Spice

WTCA-Bk4-ExtWallPaiiAdata.xls

WTC Drawing Book 4: Tower A Exterior Wall above 9''' Floor (To 106"' Floor) Panel Schedule

WTCA-Bk4-SpandrelPlateAdata_pai-t 1 .xls WTC Drawing Book 4: Tower A Exterior Wall above 9"' Floor (To 106"' Floor) Spandrel

Schedule Part 1

WTCA-Bk4-SpandrelPlateAdata_part2.xls

WTC Drawing Book 4: Tower A Exterior Wall above 9'^ Floor (To 106'^ Floor) Spandrel

Schedule Part 2

WTCB-Bk4-ExtWallPanBdata.xls

WTC Drawing Book 4: Tower B Exterior Wall above 9"' Floor (To 106"' Floor) Panel Schedule

WTCB-Bk4-SpandrelPlateBdata_partl .xls WTC Drawing Book 4: Tower B Exterior Wall above 9''' Floor (To 106''' Floor) Spandrel

Schedule Part 1

182 NISTNCSTAR 1-2A. WTC Investigation
Excel File List and Description

WTCB-Bk4-SpandrelPlateBdata_part2.xls

WTC Drawing Book 4: Tower B Exterior Wall above P"' Floor (To 1

06'^' Floor) Spandrel

Schedule Part 2

WTCAB-Bk4-ExtWall_l 07to 1 1 0_TH-ColinTypes.xls*

WTC Drawing Book 4: Tower A and B Exterior Wall Floors 107 to 110 Column Type

WTCAB-Bk4-ExtWall_l 07to 1 1 0_TH-SpandTypes.xls*

WTC Dra\ving Book 4: Tower A and B Exterior Wall Floors 107 to 110 Spandrel Type

WTCA-Bk4-ExtWalll07-110ColSpanSched.xls

WTC Drawing Book 4: Tower A Exterior Wall Floors 107 to 1 10 Column and Spandrel Schedule

WTCB-Bk4-ExtWalll07-110ColSpanSched.xls

WTC Drawing Book 4: Tower B Exterior Wall Floors 107 to 110 Column and Spandrel Schedule

Drawing Book 5 WTCAB-Bk5-BeamSched.xls

WTC Drawing Book 5: Tower A and B Beam Schedule

Drawing Book 6

WTCAB-Bk6-CoreBracingMember.xls*

WTC Drawing Book 6: Tower A and B Core Bracing Members

WTCAB-Bk6-CoreBracingScheduleData.xls

WTC Drawing Book 6: Tower A and B Core Bracing Schedule

Drawing Book 9

WTCAB-Bk9-BeamFL107-PH.xls*

WTC Drawing Book 9: Tower A and B Floors 107 to Penthouse Beam Member Types

Included outside of the Drawing Book folders:

Shape Property Table.xls

Shape Property Table

NISTNCSTAR 1-2A, WTC Investigation 183
Appendix D

This page intentionally left blank.

184

NISTNCSTAR 1-2A, WTC Investigation
Appendix E

Relational Database File List and Description

(Files with (*) include section property calculations)

(Files with (A) include multiple section properties calculations for some members)

WTCA_DBkl.mdb*

WTC Drawing Book 1: Tower A Exterior Wall to EL. 363

'

WTCB_DBkl.mdb*

WTC Drawing Book 1: Tower B Exterior Wall to EL. 363

'

WTCA_DBk2.mdb* A

WTC Drawing Book 2: Tower A Exterior Wall Tree EL. 363 ' to Floor 9

WTCB_DBk2.mdb*

WTC Drawing Book 2: Tower B Exterior Wall Tree EL. 363 ' to Floor 9

WTCA_DBk3_col_foundation.mdb*

WTC Drmving Book 3: Tower A Core Columns Foundations to Floor 106

WTCB_DBk3_col_foundation.mdb*

WTC Drawing Book 3: Tower B Core Columns Foundations to Floor 106

WTCB_DBk3_col_truss.mdb*

WTC Drawing Book 3: Tower B Core Column Trusses

WTCA_DBk4_9-106.mdb* A

WTC Drawing Book 4: Tower A Exterior Wall above 9'^ Floor (To 106"' Fir)

WTCB_DBk4_9-106.mdb* * WTC Drawing Book 4: Tower B Exterior Wall above 9''' Floor (To 106''' Fir)

WTCA_DBk4_107-l lO.mdb*

WTC Drawing Book 4: Tower A Exterior Wall Floor 107 to Floor 110

WTCB_DBk4_107-l lO.mdb*

WTC Drawing Book 4: Tower B Exterior Wall Floor 107 to Floor 110

WTCAB_DBk5.mdb

WTC Drawing Book 5: Tower A and B Beam Schedules and Types

WTCAB_DBk6.mdb*

WTC Drawing Book 6: Tower A and B Core Bracing Schedules and Types

NISTNCSTAR 1-2A. WTC Investigation 185
Appendix E

WTCAB_DBk9.mdb*

WTC DraM'ing Book 9: Tower A and B Floor 107 to Penthouse Beam Schedules

186 NISTNCSTAR 1-2A, WTC Investigation
Appendix F

Relational Database Tutorial

Database Structure:

The relational database was developed using Microsoft Access 2002. Each database was set up based on

the WTC Drawing Book flowcharts (refer to Appendix C). Each flowchart has a separate database for WTC 1 and WTC 2. The arrows in the flowcharts depict the links or common threads between tables. The relational database allows the data to be viewed and exported based on the user's preferences and

communicated to the database via a query (a type of filter). Note: All screen views and examples below

are based on the Drawing Book 2, WTC 1 database (WTC_DBk2_TWRA.mdb).

Viewing Tables:

To view a database table, first make sure that the

tables are listed in the database window. To do

this, chck on "Tables" under Objects in the upper

left box. The list of database tables should

appear in the right hand box. (Fig. F-1) Note

that the table names are listed in the flowcharts of

Appendix C.

Double-click on the desired table to open it. The

table will look similar to an Excel spreadsheet

with columns and rows of data.

^WTC_DBk2_TWRA : Database

^ j Create query iri Design view J Create query by using wizard §1 B)(2_TV/RA_LevB Bk2_TWRfl_Leve_colarea_example

BK2_TV.yRA_LevC

[51 BK2_TWRA_LevD

[§1 BK2_TV«A_LevE

[§) BK2_TV./RA_LevF

lgiWTC_DBk2_TWRA Database li|ji'.jaixj

a

J Create table in Design view

j Create table by using wizard ^ J Create table by entering data m AB_TypeB EE AE_TvpeC

1 Jst of

Database

Tables

Figure F-1. List of database tables.

Running Queries:

To run a query, open up the query view from the main Database window by clicking on "Queries"

under the Objects title in the upper left comer of

the window. (Fig. F-2) A list of queries will be

displayed in the box on the right.

Double-click on the desired query to run the query.

Figure F-2. List of database queries.

NISTNCSTAR 1-2A, WTC Investigation 187
Appendix F

Note: All of the resident queries contain the established links between different tables. These queries list

all data from all linked tables. To include only desired data in a query, see "Creating Custom Queries"

below.

Creating Custom Queries:

Note: All custom queries must be created from

one of the original queries as the links between

tables have already been established in these

queries. Any new query would not contain these

links and would require these links to be created

manually.

Start by saving a new version of the query to be

edited. Right-click on the query to be edited and

select "Save As. . ." from the sub-menu that appears. (Fig. F-3)

ipWTC_DBk2_TWRA : Database

^Ofieri ^Design cf]New X

111

Ohiects H

Groups

Jj

_i

Ej Create query in Design view Ej Create query by using wizard

[P Bl;2_TVi'RA_LevB 1^ Qpen

[§3 BK2_TWRA_LevcM Besl^Viev^

[§3 BK2_TWRA_LevcS Print...

[§0 BK2_TWRA_LevE B. P^nt Preview gl BK2_TWRA_LevF

jjf^"^^

;i=l £opy

Export,.. Send To *

I Add to Group >

1: Create Shortcut... X Delete Rename

Properties

Figure F-3. Copying a query.

In the pop-up window, type in a name for the new query. Make sure that "Query" is selected in the "As" select-box.

(Fig. F^)

Figure F-4. Naming new query.

To edit the query, select the newly copied query and

click on the "Design" button on the upper left comer of

the database window (Fig. F-5). The queiy will appear

in design (edit) view.

3

GrCHjps

[§3 BK2_TWRA_LevE

[§3 Bt:2_TWRA_LevF

|lB WTC_DBk2_TWRA : Database .|n|x| ^Qpen ^Design fgiriew X *a

1^ 1 Lteate query in Design view

tf^

1 'Irea', query by using wizard

-:_T'vVRA_LevE: # \miimmm\

[§3 BH'_T'*RA_LevL [P BK2_TWRA_LevD

Figure F-5. Selecting design view

for a query.

188 NISTNCSTAR 1-2A, WTC Investigation
Relational Database Tutorial

The design view shows all table associations (depicted by arrows) for this query. The first box (from left) shows the main table. The tables to the right are the ones that are linked from the main table. The arrows show where the association is made. For example, "Coll Type" in the main table (table A ColLevB) links

to "Column" in the AB_CollTypeB table. The lower part of the view shows the query selections that will be displayed when the query is run. (Fig. F-6)

I? BK2_TWRA_LevB : Selec* Queqp MM

ID

Coll Type

CollFyBl CollF/e2

CollFyBe

CollweltC CoEType

CotZFyBl Col2FyB2

Col2FyB6

Col2weld3 Col3Type

ColSFyBl CotSFyBZ CoQFyBo

Col3we!d3 CollSpDet

IDColumn

PItB-IN PHB2-IN

PltB3-IN

PItBI PItBS PltB6-IN

PltB7

PItBS weldl-IN

i'ield2-IN

I'. -eldS-IN

ll.•ld^-II^I

inks

i

Section Name

Ar&a-IN2

I«-IN4

ID ID Column Column

PItB-IN PltB-lN PItBC-IN PltBC-IW

PltB3-IN PltB3-IN

PltB4 PltB4

PltB5 PItBS PltBo-IN PltB6-iN

PltB7 PltB7

PItBB PItBS «eldl-IN weldl-IN

weldC-IN weld2-IN

weld3-IN iveldS-IN weld4-IN ,wld4-IN weld5-m •.-veld5-IN »eld6-m .A«ld6-IN

weld7-INI ,veld7-IN weld8-IN weld8-IN

Section Name Section Name

Area-IN2 Aiea-m2

IJ-IM4 zi I.-IN4

6

Figure F-6. Query design view.

First delete all the present query selections by

clicking on the top row of each query selection (Fig.

F-7) and pressing the delete key on the keyboard.

Do this until all text is deleted from the query

selections (the boxes themselves will not disappear)

Field: Table:

Sort; Show;

Criteria;

or:

A ColLevB * A ColLevB

El AB CollTypeB,

"U ABjCollTypeB

Figure F-7. Selecting query selection.

NISTNCSTAR 1-2A, WTC Investigation 189
Appendix F

Double-click on the data to be included in your query (see example below).

Note: Selecting the asterisk (*) at the top of each table will list all fields in that table.

Example: How to include the panel, the three column types, as well as their associated areas in one table.

Note: This example is an example queiy called "Bk2_TWRA_LevB_colarea_example" in the WTC Book 2 Tower A database.

Once the original query selections are deleted, select the "Panel" field from the main table (table A ColLevB) by

double-clicking on it. It should appear as a query

selection below (Fig. F-8).

oil Type

'Bl

Doubleclick

"Panel"

Fieid: TaUe:

Sort;

Crfteria

j

Panel A ColLevB

r! 1

New Qoery

Selection

Figure F-8. Select panel field.

Select "CollType" from the main table. Then, select the "Area-IN2" field from the AB_CollTypeB

table. For the second column, select "Col2Type" from the main table and "Area-IN2" from the AB_Col2TypeB table. Repeat this for the third column, choosing the last table for the area of the column.

There should now be 7 fields displaying in the Query Selection.

<l File Edit View Insert i^uery Tools Window Help

1 S All

ID

Panel CollType .

PltB6-IN

PitB?

PitBS i«rIH1-TM

To run this query, click on

the exclamation mark - Run button - on the middle

top bar of the MS Access

window. (Fig. F-9).

Note: To save the query,

either click on the save

button, or go to File Menu

- Save.

Figure F-9. Run query button.

Exporting Data:

Data can be exported from any query or table into a number of formats, including text and Excel formats.

To export a query, open the query and select File Menu - Export. Select the location, name, and the type

to save as (from the drop-down menu) and click "Save All".

190 NISTNCSTAR 1-2A, WTC Investigation
Appendix G

Categorization of Floor Construction Types for Areas

Outside of Core

The structural drawings for the floors in both towers were reviewed to identify structural similarities within the areas outside the core. Table G-1 summarizes the construction types and space usage for each

floor for both towers. Information regarding the categorization and description of floor construction types

are pro\ ided in Figs. G-1 through G—4. Based on this review, the typical truss-framed and beam-framed

floors were selected for modeling.

NISTNCSTAR 1-2A, WTC Investigation 191
Appendix G

Table G-1. Representative categorizations of floor construction types outside of core. Tower A Floor Framing Tower B Floor Framing

Floor Space Usage Const. Type PH Roof Roof Type 12 110 TV/Storage Type 12 109 Upper f\^ech Fl Type 1

3

108 Lower fylech Fl Type 12 107 Restaurant Tvoe 12

:JJ:S.J.t 106 Tenant Type 10 105 Tenant Tvoe 1 104 Tenant Type 1 103 Tenant Type 1 102 Tenant Type 1 101 Tenant Tvoe 1 100 Tenant Type 1 99 Tenant Tvoe 1 98 Tenant Tvoe 1 97 Tenant Tvoe 1 96 Tenant Tvoe 1 95 Tenant Tvnp 1 94 Tenant Tvoe ypc 1 93 Tenant Type 1 92 Tenant Tvoe 2 91 Tenant Tvoe 1 y^c 11 90 Tenant Tvnp 1 89 Tenant Tvoe 1 88 Tenant

87 Tenant Tvnp 1 ype 11 86 Tenant Tvoe ypc 1 85 Tenant Type 1 84 Tenant Tune 1 83 Tenant Tvnp 9 82 Tenant Type 9

81 Tenant Type 9 80 Tenant Type 9 79 Upper Escalator Type 8 78 Sky Lobby Tvnp 7 77 Lower Escalator Type 12 76 Upper Mech Fl Type 13 75 Lower Mech Fl Type 1

2

74 Tenant Tvnp 1 73 Tenant 72 Tenant Type 1 71 Tenant Tvoe 1 70 Tenant Tvoe 1 69 Tenant Type 1 68 Tenant Type ypc 1 67 Tenant Type 6 60-66 Tenant Type 1 59 Tenant Type2

50-58 Tenant Type 1 49 Tenant Type 3 48 Tenant Type 3 47 Tenant Type 3 46 Tenant Type 3 45 Upper Escalator Type 5 44 Sky Lobby TvDe 4

43 Lower Escalator T^e 12 42 Upper Mecti Type 1

3

41 Lower Mecfi Type 12 27-40 Tenant Tvnp 1 26 Tenant Tvnp 1 25 Tenant Tune 2 14-24 Tenant Tvnp 1

' iry

13 Tenant Tvnp 1 12 Tenant Tvoe 1 11 Tenant Type 1 10 Tenant Type 1 9 Tenant Type 12 8 Upper Mech Type 13

7 Lower Mech Type 12

3-6 Core Only (Storage) NA

2 Plaza - Lobby Type 15

1 Concourse Type 14 B1 EL. 294 Type 14

Floor Space Usage Const. Type PH Roof Observation Type 12 110 Storage Type 12 109 Upper Mech Fl Type 13 ' 108 Lower Mech Fl Type 12 107 Observation Type 12 106 Tenant Tvoe 1 105 Tenant Tvoe 1 104 Tenant Type 1 103 Tenant Tvoe 1 102 Tenant Type 1 101 Tenant Tvoe 1 100 Tenant Tvoe 1 99 Tenant Tvoe 1 y^c 11 98 Tenant Tvoe 1 97 Tenant Tvnp 1 96 Tenant Tvoe 1 yf^c 11 95 Tenant Tvnp 1 ypt; 11 94 Tenant Tune 1 93 Tenant Type 1 92 Tenant Tvoe 2

91 Tenant Type 1 90 Tenant Tvnp 1 ype 11 89 Tenant Tvnp 1 ype 11 88 Tenant Tvnp 1 87 Tenant Tvnp 1 ypc 11 86 Tenant Tvnp 1 85 Tenant Type 1 84 Tenant Tvoe 1 83 Tenant Type 9 82 Tenant Tvnp 1 ype Q=7 8180 Tenant Type 9 79 Upp6r Escslstor Type 8 78 Sky Lobby Tvnp 7 77 Lower Escalator Type 1 2 76 UppGr Mech Fl Type 1

3

75 Lower Mech Fl Type 1

2

74 Tenant Type 1 73 Tensnt Tvnp 1 ype 1i 72 Tertsnt Tvoe 1 71 Tenant Tvoe 1 70 Tensnt Tvoe 1 69 Tenant Type 1 68 Tenant Type 1 67 Tenant Tvoe 1 60-66 Tenant Type 1 59 Tenant Type 2

50-58 Tenant Type 1 49 Tenant Type 3 48 Tenant Type 3 47 Tenant Type 3 46 Tenant Type 3

45 Upper Escalator Type 5 44 Sky Lobby TvDe * 4

/r^ ^ ,1 II 43 Lower Escalator Type 12 42 I Innpr Mpr'h Type 13

41 Lower Mec^ Type 12

27-40 Tenant 26 Tenant Tvoe 1 25 Tenant Tvnp 2

14-24 Tenant Type 1 13 Tenant Type 1

1

12 Tenant Type 1

1

11 Tenant Type 1 10 Tenant Type 11 9 Tenant Type 12 8 Upper Mech Type 13 7 Lower Mech Type 12

3-6 Core Only (Storage) NA

2 Plaza ' Lobby Type 15

1 Concourse Type 14 ^ B1 EL 294 Type 14 |

Expanded Zone

Impact Zone

I I Combined Zones

Refer to Fig. G-1

through G-4 for description of floor system categories

192 NISTNCSTAR 1-2A, WTC Investigation
Categorization of Floor Construction Types

R Roors; 10 - 2A 26-40

50-58

WTC Typicar Truss Roor Panel Plan Tower 6 Ftoore:

Noie: Aa panel n

14-24 60-74

26 - 40 84 - 91 50 • S« 93-106

Type 3 - WTC Beam/Truss Floor Panel Plan

5 A & B Floorsi 46 - 49

)' ftoor; 10 11. 39 40 70 & 71 \.vhich are wimm 6'-1Q" Floors 72-74 vary ie*-26".

FR1 ERl 0R1 CR1 BRl A1 B1 CI D1 El F1 FR1 ERl DR1 CR1 BRl Al B1 CI D1 El F1

G1 GR1 G1 GR1

Note; HI = H6

Hi HR1 HI HR1

J1 CORE J1

Note: J1 =K1 = KRl

Kl CORE KRl

Note: HR1 = HR6 HR1 H1

Note: HI =M1 = MRl M1 MR1

GR1 G1 (all C32T5 Trusses) BEAMS BEAMS

FT E- D1 CI 81 Al BRl CR1 DR1 ERl FRl F5 E5 D5 C1 B1 Al BRl CR1 DR5 ER5 FR5

Type 2 . WTC Non-Typical Truss Floor Panel Plan Towers A&B Roots: 25.59.92

d capacity tor secondary walsr lin«s.

Type 4 - WTC BeamfTruss Sky Lobby Floor Panel Plan ersA& B Floor:

w CO CO FR3 ER3 DR3 CR6 BEAN BEAN BEAN C6 D3 E3 F3

BEAMS BEAMS , BEAMS SEAMS \ BEAMS CORE BEAMS

BEAMS BEAMS

BEAMS BEAMS :

F8 E8 D8 C8 B8 AS BR8 CR8 DR8 ER8 FR8

Figure G-1. Floor construction types 1 through 4.

NISTNCSTAR 1-2A, WTC Investigation 193
Appendix G

Type 5 • WTC Beam/Tmss Upper Escalator Floor Panel Plan Typp 7 WTC Beam/Tr^ss Sky Lobby Floor Panel Plan

Towers A a B Floor: 45 Towers A & B Floor: 78

FR1 ER1 ORI CR6 BEAMS BEAMS BEAMS C6 01 El F1 FR3 ER3 0R3 CR3 BR3 A3 B3 C3 03 E3 F3

G1

CORE

BEAMS BEAMS

CORE

BEAMS

HI BEAMS BEAMS BEAMS

K1 BEAMS BEAMS BEAMS

M1 BEAMS BEAMS BEAMS BEAMS BEAMS BEAMS BEAMS

F5 E5 D5 CI B1 A1 BR1 CR1 DR5 ER5 FR5 F3 E3 D3 C3 B3 A3 BR3 CR3 DR3 ER3 FR3

Type 6 - WTC Non-Typical Truss Floor Panel Plai Tower A Floor 67

FR4 ER4 DR4 CR4 BR4 A4 B4 C4 04 E4

GR4

CORE

HR8 H4

F4 E4 04 C4 BR4 CR4 DR4 ER4 FR4

Type 6 - WTC Beamn'mss Uppar Escalator Floor Panel Plan Towers A & 6 Floor 79

FR5 ER5 0R5 CR1 BR1 CI 05 E5 F5

BEAMS BEAMS

MR1 BEAMS

CORE

BEAMS

GR1 BEAMS

El D1 C1 CR1 DR5

Figure G-2. Floor construction types 5 through 8.

194 NISTNCSTAR 1-2A, WTC Investigation
Categorization of Floor Construction Types

Type 9 - WTC Beam Floor Above MER Floor Panel Plan

Note; Same as Type 3. with opposite onentatic Towers A & B Floors; 80 - 83

F5 E5 D5 CI DR5 ER5 FR5

BEAMS BEAMS

MR1

HR6

CORE

GR1 G1

FR1 ER1 DR1 CR1 BR1 CI D1 El

Typejp - WTC Reinforced Type 1 Rtior Panel Plan Towef A Floor: 106

Note: Same panel plan as typical floor (Type 1) but with reinforced trusses

DR1 D1

CORE

GR1

FR1

Type 1 1

- WTC Heavy Angle Truss Floor Panel Plan

Towers B Floors; 10-13

Figure G-3. Floor construction types 9 through 11.

NISTNCSTAR 1-2A, WTC Investigation 195
Appendix G

Type 12 • WTC Beam Framed Floor Floor Plan

Towers A & B MER Floors: 7.41,75.108 Towers A & B Near MER Floors: 9.43.77.107.1 10. Roof

Beams CORE Beams

Type 14 - WTC Shon Beam Framed Floor Floor Plan

Towers AS B Floors- Cone. B1.B2.B3.B4.B5

E

raQJ 00

Beams

Beams CORE Beams

Beam;

Beams

Figure G-4. Floor construction types 12 through 15.

196 NISTNCSTAR 1-2A, WTC Investigation