NIST NCSTAR 1-1 Federal Building and Fire Safety Investigation of the World Trade Center Disaster Design, Construction, and IVIaintenance of Structural and Life Safety Systems H. S. Lew Richard W. Bukowski Nicholas J. Carino National institute of Standards and Technology Technology Administration • U.S. Deparimeni of Commerce NIST NCSTAR 1-1 Federal Building and Fire Safety Investigation of the World Trade Center Disaster Design, Construction, and IVIaintenance of Structural and Life Safety Systems H. S. Lew Richard W. Bukowski Nicholas J. Carino, retired Building and Fire Researcli Laboratory National Institute of Standards and Technology September 2005 U.S. Department of Commerce Carlos M. Gutierrez, Secretary Technology Administration Mictielle O'Neill. Acting Under Secretary for Technology National Institute of Standards and Technology William Jeffrey, Director Disclaimer No. 1 Certain commercial entities, equipment, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication that the entities, products, materials, or equipment are necessarily the best available for the purpose. Nor does such identification imply a finding of fault or negligence by the National Institute of Standards and Technology. Disclaimer No. 2 The policy of NIST is to use the International System of Units (metric units) in all publications. In this document, however, units are presented in metric units or the inch-pound system, whichever is prevalent in the discipline. Disclaimer No. 3 Pursuant to section 7 of the National Construction Safety Team Act, the NIST Director has determined that certain evidence received by NIST in the course of this Investigation is "voluntarily provided safety-related information" that is "not directly related to the building failure being investigated" and that "disclosure of that information would inhibit the voluntary provision of that type of information" (15 (JSC 7306c). In addition, a substantial portion of the evidence collected by NIST in the course of the Investigation has been provided to NIST under nondisclosure agreements. Disclaimer No. 4 NIST takes no position as to whether the design or construction of a WTC building was compliant with any code since, due to the destruction of the WTC buildings, NIST could not verify the actual (or as-built) construction, the properties and condition of the materials used, or changes to the original construction made over the life of the buildings. In addition, NIST could not verify the interpretations of codes used by applicable authorities in determining compliance when implementing building codes. Where an Investigation report states whether a system was designed or installed as required by a code provision, NIST has documentary or anecdotal evidence indicating whether the requirement was met, or NIST has independently conducted tests or analyses indicating whether the requirement was met. Use in Leqal Proceedings No part of any report resulting from a NIST investigation into a structural failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action for damages arising out of any matter mentioned in such report (15 USC 281a; as amended by P.L. 107-231). National Institute of Standards and Technology National Construction Safety Team Act Report 1-1 Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-1, 278 pages (September 2005) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2005 For sale by the Superintendent of Documents, U.S. Government Printing Office Internet: bookstore.gpo.gov — Phone: (202) 512-1800 — Fax: (202) 512-2250 Mail: Stop SSOP, Washington, DC 20402-0001 Abstract The collapse of World Trade Center (WTC) 1, 2, and 7 resulted from structural damage from direct and indirect effects of aircraft impact and the ensuing fires. Thus, for collapse analyses of these buildings, knowledge of the physical state of the structural and fire safety systems prior to the aircraft impact is essential. To obtain infonnation for the collapse analysis of the buildings. National Institute of Standards and Technology reviewed design and construction documents, correspondence, and memoranda related to the building projects; interv iewed individuals involved in the design, construction, and maintenance of the buildings; obtained information from regulatory and emergency services agencies of New York City; and reviewed books and published journal and magazine articles related to the WTC building projects, hiformation obtained from various sources are synthesized and summarized in this report. Specifically, this report presents ( 1 ) provisions used to design and construct the structural, fire protection and egress systems of the buildings; (2) tests performed to support the design of these systems; (3) criteria that governed the design of the structural and fire protection systems; (4) methods used to proportion structural members and other components of the buildings; (5) innovative features, technologies and materials that are incorporated in design and construction of the structural and fire protection systems; (6) details of deviations to the contract documents granted by Port Authority of New York and New Jersey; (7) fabrication and inspection requirements at the fabrication yard; and (8) inspection protocols during construction. This report also documents the fuel system for the diesel generators that supplied emergency power to many of the tenants in WTC 7. Findings from the synthesis of the information collected and resulting issues are presented. Keywords: Buildings, codes, construction, design, egress, elevators, fire, loads, maintenance, regulations, standards, World Trade Center. NISTNCSTAR 1-1, WTC Investigation iii Abstract This page intentionally left blank. IV NISTNCSTAR 1-1, WTC Investigation Table of Contents Abstract iii List of Figures xi List of Tables xiii List of Acronyms and Abbreviations xv Metric Conversion Table xix Preface xxiii Acknowledgments xxxiii Executive Summary „ xxxv Chapter 1 Introduction 1 1 . 1 Background 1 1 .2 Scope of Report 1 1 .3 Design and Construction Requirements for WTC 1 , 2, and 7 4 1 .4 Organization of Report 5 Chapter 2 Description of WTC 1 2, and 7 , 7 2.1 Site Plan of WTC Complex 7 2.2 Description of WTC 1 and WTC 2 7 2.2. 1 Building Description 7 2.2.2 Structural Description 9 2.3 Description of WTC 7 13 2.3.1 Building Description 13 2.3.2 Structural Description 14 Chapter 3 Development of Building Codes 37 3.1 Building Code Development in the United States 37 3.2 New York City Building Code 38 3.3 Port Authority Policies for Design and Modifications to Buildings 40 3.3.1 Procedures for PANYNJ Owned Projects 40 3.3.2 Review of Tower Plans by New York City Department of Buildings 41 NISTNCSTAR 1-1, WTC Investigation v 1 Table of Contents 3.3.3 Procedures for Tenant Alteration Projects 42 Chapter 4 Code Provisions for Structural Design 43 4. 1 Contemporaneous Codes 43 4.2 Loads 44 4.2.1 Dead Loads 44 4.2.2 Live Loads 45 4.2.3 Wind Load 47 4.2.4 Earthquake Load 49 4.2.5 Other Loads 50 4.2.6 Distribution of Loads 5 4.3 Design Standards 52 4.3.1 Design Standards 52 4.3.2 Load Combinations 53 4.4 Alteration of Existing Buildings 55 4.5 Materials and Methods of Construction 56 4.6 Stability, Bracing, and Secondary Stresses 58 4.7 Deflection Limitations 59 4.8 Load Tests 59 Chapter 5 Structural Design of WTC 1, 2, and 7 63 5.1 Design Criteria 63 5.1.1 Loads 63 5.1.2 Live Load Reduction 66 5.1.3 Wind Load 68 5.1.4 Aircraft Impact 70 5.2 Structural Design Requirements 71 5.2. 1 Concrete Requirements 72 5.2.2 Steel Requirements 72 5.2.3 Methods Used to Proportion Structural Members 73 Chapter 6 Innovative Features Incorporated in Structural Design 87 6. 1 Irmovative Features 87 6.2 Lateral-Load-Resisting System 87 vi NIST NCSTAR 1-1, WTC Investigation 1 Table of Contents 6.3 Composite Floor System 88 6.4 Viscoelastic Damping Units 89 6.5 Wind Tunnel Tests 90 6.5.1 Tests Conducted at CSU 91 6.5.2 Tests Conducted at NPL 93 Chapter 7 Fabrication and Construction Inspections and Deviations 97 7.1 Introduction 97 7.2 Fabrication Inspection Requirements for WTC 1 and WTC 2 97 7.2.1 Floor Trusses 98 7.2.2 Box Core Columns and Built-Up Beams 98 7.2.3 Exterior Columns from Elevation 363 ft to the 9th Floor Splice 100 7.2.4 Exterior Columns Above the 9th floor Splice 100 7.2.5 Rolled Columns and Beams 101 7.2.6 Other Requirements 101 7.3 Fabrication Inspection Requirements for WTC 7 102 7.4 Inspection During Construction 102 7.4.1 Erection Marks and Marking System WTC 1 and WTC 2 103 7.4.2 Quality Control and Inspection Program for WTC 1 and WTC 2 104 7.5 Deviations Granted 104 7.5.1 Deviations Relating to Fabrication and Erection Tolerances 105 7.5.2 Deviations Relating to Defective Components 105 7.5.3 Deviations Relating to Alternate Fabrication and Erection Procedures 106 7.5.4 Deviations Relating to Product Substitutions 106 7.5.5 Deviations Relating to Inspection Practice 107 Chapter 8 Structural Maintenance and Modifications During Occupancy 109 8.1 Introduction 109 8.2 Tenant Construction Review Manuals 109 8.2.1 1971 Edition 110 8.2.2 1979 Edition 110 8.2.3 1 984 Edition, Revised 1 990 1 1 8.2.4 1997 Edition 112 8.3 Standards for Structural Integrity Inspection of the WTC Towers 112 NIST NCSTAR 1-1, WTC Investigation vii 8 Table of Contents 8.3.1 Visual Inspections