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NIST NCSTAR1-3D Federal Building and Fire Safety Investigation of the World Trade Center Disaster Mechanical Properties of Structural Steels William E. Luecke J. David McColskey Christopher N. McCowan Stephen W. Banovic^ Richard J. Fields Timothy Foecke Thomas A. Siewert Frank W. Gayle National Institute of Standards and Technology • TechnologyAdminisiralion • U S. DeparlmenI ofComm NISTNCSTAR1-3D Federal Building and Fire Safety Investigation of the World Trade Center Disaster Mechanical Properties of Structural Steels William E. Luecke J. David McColskey Christopher N. McCowan Stephen W. Banovic Richard J. Fields* Timothy Foecke Thomas A. Siewert Frank W. Gayle Materials Science and Engineering Laboratory National Institute ofStandards and Technology *Retired September 2005 U.S. DepartmentofCommerce Carlos M. Gutierrez, Secretary TechnologyAdministration Michelle O'Neill, Acting UnderSecretaryfor 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 orderto describe a procedure or concept adequately orto trace the history ofthe procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication thatthe entities, products, materials, or equipment are necessarily the best available forthe purpose. Nor does such identification imply a finding offaultor negligence bythe National Institute ofStandards 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 orthe inch-pound system, whichever is prevalent in the discipline. Disclaimer No. 3 Pursuant to section 7 ofthe National Construction SafetyTeam Act, the NIST Director has determined that certain evidence received by NIST in the course ofthis Investigation is "voluntarily provided safety-related information" that is "not directly related to the building failure being investigated" and that "disclosure ofthat information would inhibitthe voluntary provision ofthat type ofinformation" (15 USC 7306c). In addition, a substantial portion ofthe evidence collected by NIST in the course ofthe Investigation has been provided to NIST under nondisclosure agreements. Disclaimer No. 4 NISTtakes no position as to whetherthe design or construction ofa WTC building was compliant with any code since, due tothe destruction ofthe WTC buildings, NIST could not verifythe actual (or as-built) construction, the properties and condition ofthe materials used, orchanges to the original construction made overthe life ofthe buildings. In addition, NIST could not verifythe interpretations ofcodes 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 oranecdotal evidence indicating whetherthe requirement was met, or NIST has independently conducted tests oranalyses indicating whetherthe requirementwas met. Use in Legal Proceedings No part ofany report resulting from a NIST investigation into a structural failure orfrom an investigation underthe National Construction Safety Team Act may be used in any suit or action fordamages arising out ofany matter mentioned in such report (15 USC 281a; as amended by P.L. 107-231). National Institute ofStandards and Technology National Construction SafetyTeam Act Report 1-3D Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-3D, 322 pages (September2005) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2005 Forsale by the Superintende—nt of Documents, U.S. Gov—ernment Printing Office internet: bookstore.gpo.gov Phone: (202) 512-1800 Fax: (202) 512-2250 Mail: Stop SSOP, Washington, DC 20402-0001 Abstract This report provides five types ofmechanical properties for steels fromthe World Trade Center (WTC): elastic, room-temperature tensile, room-temperature high strain rate, impact, and elevated-temperature tensile. Specimens of29 different steels representing the 12 identified strength levels in the building as built were characterized. Elastic properties include modulus, E, and Poisson's ratio, v, for temperatures up to 900 °C. The expression forE{T) for T < 723 °C is based on measurements ofWTC perimeter column steels. Behavior forT > 723 °C is estimated from literature data. Room temperature tensile properties include yield and tensile strength and total elongation for samples ofall grades ofsteel used in the towers. The report provides model stress-strain curves for each type ofsteel, estimated from the measured stress- strain curves, surviving mill test reports, and historically expected values. With a few exceptions, the recovered steels, bolts, and welds met the specifications they were supplied to. In a few cases, the measured yield strengths ofrecovered steels were slightly lowerthan specified, probably because ofa combination ofmechanical damage, natural variability, and differences in testing methodology. High- strain-rate properties for selected perimeter and core column steels include yield and tensile strength, total elongation and strain rate sensitivity forrates up to 400 s"'. Measured properties were consistent with literamre reports on other structural steels. Impact properties were evaluated with Charpy testing. Properties forperimeterand core column steels were consistent with other structural steels ofthe era. The impact toughness at room temperature ofnearly all WTC steels tested exceeded 15 ft lbfat room temperamre. Elevated-temperature stress-strain curves were collected for selected perimeter and core column and truss steels. The report presents a methodology for estimating high-temperature stress-strain curves forthe steels not characterized based on room-temperature behavior and behavior ofother WTC structural steels from the literature. The measured elevated-temperature stress-strain behavior of steels is consistent with other structural steels from that era. Forthe truss steels, the report presents a complete constitutive law for creep deformation based on experimental measurements. For the steels not characterized, the report presents a methodology for estimating the creep deformation law. Keywords: Creep, high strain rate, high temperature, impact, modulus, tensile strength, yield strength. World Trade Center. NISTNCSTAR 1-3D, WTC Investigation ill Abstract This page intentionally left blank. NISTNCSTAR WTC IV 1-3D, Investigation 11 Table of Contents Abstract iii List ofFigures ix List ofTables xv List ofAcronyms and Abbreviations xvii Preface xix Acknowledgments xxix Executive Summary xxxi Chapter 1 Introduction 1 1.1 Overview ofReport 1 1.1.1 Elastic Properties (Chapter 2) 1 1.1.2 Room Temperature Tensile Properties (Chapter 3) 1 1.1.3 High-Strain-Rate Properties (Chapter4) 3 1.1.4 Impact Properties (Chapter 5) 3 1.1.5 Ele\ated-Temperature Properties (Chapter 6) 3 1.2 Description ofthe Major Building Components 4 1.2.1 Perimeter Columns 4 1.2.2 Core Columns 6 1.2.3 Flooring System 6 1.3 Specimen Nomenclature 7 1.4 Symbols and Abbreviations 8 Chapter2 Elastic Properties 11 2.1 Introduction 1 2.2 Experimental Procedure 11 2.3 Elastic Properties (E, v, G) for 0<T<723 °C 1 2.4 Elastic Properties (E, v, G) for T>910 °C 13 2.5 Elastic Properties (E, v, G) for 723 °C<T<910 °C 13 2.6 Uncertainties 14 2.7 References 14 NISTNCSTAR 1-3D. WTC Investigation v 1 Table ofContents Chapters Room-Temperature Tensile Properties 19 3.1 Introduction 19 3.2 Test Procedures 19 3.2.1 Steel 19 3.2.2 Bolts 20 3.2.3 Welds 26 3.3 Results 28 3.3.1 Steel 28 3.3.2 Bolts 28 3.3.3 Welds 28 3.4 Comparison with Engineering Specifications 33 3.4.1 Steel 33 3.4.2 Bolts 60 3.4.3 Welds 60 3.5 Recommended Values 63 3.5.1 Steel 63 3.5.2 Bolts 67 3.5.3 Welds 74 3.6 Summary 75 3.7 References 75 3.7.1 References Available from Publicly Available Sources 75 3.7.2 References Available from Nonpublic Sources 76 Chapter4 High-Strain-Rate Properties 79 4.1 Introduction 79 4.2 Test Procedures 79 4.2.1 High Strain-Rate Tension Tests 79 4.2.2 Analysis ofHigh-Strain-Rate Tension Test Data 8 4.2.3 Kolsky BarTests 82 4.2.4 Quasi-Static Compression Tests 84 4.3 Results 84 4.3.1 High Strain-Rate Tension Tests 84 4.3.2 High Strain-Rate Kolsky Bar Tests 86 4.3.3 Quasi-Static Compression Tests 88 vi NISTNCSTAR 1-3D, WTC Investigation 11 Table ofContents 4.4 Discussion 90 4.4.1 Calculation ofStrain-Rate Sensitivity for Tension Tests 91 4.4.2 Calculation ofStrain-Rate Sensitivity forKolsky Tests 92 4.5 High-Strain-Rate Data Provided to the Investigation 94 4.6 Comparison with Literature Data 95 4.7 Summary 97 4.8 References 99 Chapter 5 Impact Properties 103 5.1 Introduction 103 5.2 Procedures 103 5.3 Results 105 5.3.1 Perimeter Columns 105 5.3.2 HAZ Materials from Perimeter Columns 106 5.3.3 Core Columns 106 5.3.4 Trusses 107 5.3.5 Truss Seats 107 5.3.6 Bolts 107 5.4 Discussion 107 5.4.1 Perimeter Columns 107 5.4.2 HAZ Materials from Perimeter Columns 109 5.4.3 Core Colunms 109 5.4.4 Trusses 109 5.4.5 Truss Seats 110 5.4.6 Expected Values ofImpact Toughness 1 10 5.5 Summary 1 1 5.6 References 1 1 Chapter 6 Elevated Temperature Properties 129 6.1 Introduction 129 6.2 Test procedures 129 6.2.1 Tensile Tests 129 6.2.2 Creep Tests 130 6.3 Results 130 NISTNCSTAR 1-3D. WTC Investigation vii Table ofContents 6.3.1 Tensile Tests 130 6.3.2 Creep Tests 130 6.4 Recommended values for steels 134 6.4.1 A Universal Curve for Elevated-Temperature Tensile Properties 134 6.4.2 Analysis ofTensile Data 136 6.4.3 Estimating Elevated-Temperature Stress-Strain Curves 137 6.4.4 Analysis ofCreep Data 149 6.4.5 Recommended Values for Bolts 155 6.5 Summary 157 6.6 References 158 Chapter? Summary and Findings 161 7.1 Summary 161 7.2 Findings 162 Appendix A Data Tables and Supplemental Figures 163 Appendix B Effects of Deformation ofWide-Flange Core Columns on Measured Yield Strength 253 Appendix C Provisional Analysis of High-Rate Data 263 Appendix D Deformation of Steels Used in WTC 7 273 Appendix E Specimen Geometry Effects on High-Rate Tensile Properties 279 vni NISTNCSTAR 1-3D, WTC Investigation