Mechanical properties of structural steel

2005·18.7 MB·English

by  Luecke, William E.

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
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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
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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
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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