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Mechanical Properties of Structural Steels

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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 • Technology Adminisiralion • U S. DeparlmenI of Comm 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 of Standards and Technology *Retired September 2005 U.S. Department of Commerce Carlos M. Gutierrez, Secretary Technology Administration Michelle O'Neill, Acting Under Secretary for Technology National Institute of Standards and Technology William Jeffrey, Director Disclaimer No. 1 Certain commercial entities, equipment, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication that the entities, products, materials, or equipment are necessarily the best available for the purpose. Nor does such identification imply a finding of fault or negligence by the National Institute of Standards and Technology. Disclaimer No. 2 The policy of NIST is to use the International System of Units (metric units) in all publications. In this document, however, units are presented in metric units or the inch-pound system, whichever is prevalent in the discipline. Disclaimer No. 3 Pursuant to section 7 of the National Construction Safety Team Act, the NIST Director has determined that certain evidence received by NIST in the course of this Investigation is "voluntarily provided safety-related information" that is "not directly related to the building failure being investigated" and that "disclosure of that information would inhibit the voluntary provision of that type of information" (15 USC 7306c). In addition, a substantial portion of the evidence collected by NIST in the course of the Investigation has been provided to NIST under nondisclosure agreements. Disclaimer No. 4 NIST takes no position as to whether the design or construction of a WTC building was compliant with any code since, due to the destruction of the WTC buildings, NIST could not verify the actual (or as-built) construction, the properties and condition of the materials used, or changes to the original construction made over the life of the buildings. In addition, NIST could not verify the interpretations of codes used by applicable authorities in determining compliance when implementing building codes. Where an Investigation report states whether a system was designed or installed as required by a code provision, NIST has documentary or anecdotal evidence indicating whether the requirement was met, or NIST has independently conducted tests or analyses indicating whether the requirement was met. Use in Legal Proceedings No part of any report resulting from a NIST investigation into a structural failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action for damages arising out of any matter mentioned in such report (15 USC 281a; as amended by P.L. 107-231). National Institute of Standards and Technology National Construction Safety Team Act Report 1-3D Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-3D, 322 pages (September 2005) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2005 For sale by the Superintendent of Documents, U.S. Government Printing Office internet: bookstore.gpo.gov — Phone: (202) 512-1800 — Fax: (202) 512-2250 Mail: Stop SSOP, Washington, DC 20402-0001 Abstract This report provides five types of mechanical properties for steels from the World Trade Center (WTC): elastic, room-temperature tensile, room-temperature high strain rate, impact, and elevated-temperature tensile. Specimens of 29 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 for E{T) for T < 723 °C is based on measurements of WTC perimeter column steels. Behavior for T > 723 °C is estimated from literature data. Room temperature tensile properties include yield and tensile strength and total elongation for samples of all grades of steel used in the towers. The report provides model stress-strain curves for each type of steel, estimated from the measured stress- strain curves, surv iving 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 of recovered steels were slightly lower than specified, probably because of a combination of mechanical 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 for rates up to 400 s"'. Measured properties were consistent with literamre reports on other structural steels. Impact properties were evaluated with Charpy testing. Properties for perimeter and core column steels were consistent with other structural steels of the era. The impact toughness at room temperature of nearly all WTC steels tested exceeded 15 ft lbf at 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 for the steels not characterized based on room-temperature behavior and behavior of other structural steels from the literature. The measured elevated-temperature stress-strain behavior of WTC steels is consistent with other structural steels from that era. For the 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. IV NISTNCSTAR 1-3D, WTC Investigation 1 Table of Contents Abstract iii List of Figures ix List of Tables xv List of Acronyms and Abbreviations xvii Preface xix Acknowledgments xxix Executive Summary xxxi Chapter 1 Introduction 1 1 . 1 Overview of Report 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 (Chapter 4) 3 1 . 1 .4 Impact Properties (Chapter 5) 3 1.1.5 Ele\ ated-Temperature Properties (Chapter 6) 3 1 .2 Description of the 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 Chapter 2 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 NIST NCSTAR 1-3D. WTC Investigation v 1 Table of Contents 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 Chapter 4 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 of High-Strain-Rate Tension Test Data 8 4.2.3 Kolsky Bar Tests 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 1 Table of Contents 4.4 Discussion 90 4.4. 1 Calculation of Strain-Rate Sensitivity for Tension Tests 91 4.4.2 Calculation of Strain-Rate Sensitivity for Kolsky 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 of Impact 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.
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