ANSIAISC 36010 An American National Standard

(This Preface is not part of ANSIAISC 36010, Specification for Structural Steel Buildings, but is included for informational purposes only.) This Specification is based upon past successful usage, advances in the state of knowledge, and changes in design practice. The 2010 American Institute of Steel Construction’s Specification for Structural Steel Buildings provides an integrated treatment of allowable stress design (ASD) and load and resistance factor design (LRFD), and replaces earlier Specifications. As indicated in Chapter B of the Specification, designs can be made accord ing to either ASD or LRFD provisions. This Specification has been developed as a consensus document to provide a uniform practice in the design of steelframed buildings and other structures. The intention is to pro vide design criteria for routine use and not to provide specific criteria for infrequently encountered problems, which occur in the full range of structural design. This Specification is the result of the consensus deliberations of a committee of structural engineers with wide experience and high professional standing, representing a wide geo graphical distribution throughout the United States. The committee includes approximately equal numbers of engineers in private practice and code agencies, engineers involved in research and teaching, and engineers employed by steel fabricating and producing compa nies. The contributions and assistance of more than 50 additional professional volunteers working in ten task committees are also hereby acknowledged. The Symbols, Glossary and Appendices to this Specification are an integral part of the Specification. A nonmandatory Commentary has been prepared to provide background for the Specification provisions and the user is encouraged to consult it. Additionally, non mandatory User Notes are interspersed throughout the Specification to provide concise and practical guidance in the application of the provisions. The reader is cautioned that professional judgment must be exercised when data or rec ommendations in the Specification are applied, as described more fully in the disclaimer notice preceding this Preface

Seismic Applications

The Seismic Provisions for Structural Steel Buildings (ANSI/AISC 341) are essential for designing seismic force-resisting systems in structural steel or composite structures with reinforced concrete, unless the relevant building code provides specific exemptions.

ASCE/SEI 7 (Table 12.2-1, Item H) exempts structural steel systems from seismic design requirements in categories B and C when designed per specifications and using a seismic response modification factor, R, of 3 In contrast, for seismic design category A, lateral forces are specified as seismic loads without the R factor, meaning there is no need to define a seismic force resisting system that meets special requirements.

Provisions for Structural Steel Buildingsdo not apply.

The provisions of Appendix 1 of this Specification shall not apply to the seismic design of buildings and other structures.

Nuclear Applications

The design, fabrication and erection of nuclear structures shall comply with the requirements of the Specification for Safety-Related Steel Structures for Nuclear

Facilities (ANSI/AISC N690), in addition to the provisions of this Specification.

A2 REFERENCED SPECIFICATIONS, CODES AND STANDARDS

The following specifications, codes and standards are referenced in this Specification: ACI International (ACI)

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary ACI 318M-08 Metric Building Code Requirements for Structural Concrete and

ACI 349-06 Code Requirements for Nuclear Safety-Related Concrete Structures and

American Institute of Steel Construction (AISC)

AISC 303-10Code of Standard Practice for Steel Buildings and Bridges

ANSI/AISC 341-10 Seismic Provisions for Structural Steel Buildings

ANSI/AISC N690-06 Specification for Safety-Related Steel Structures for Nuclear

American Society of Civil Engineers (ASCE)

ASCE/SEI 7-10 Minimum Design Loads for Buildings and Other Structures ASCE/SEI/SFPE 29-05 Standard Calculation Methods for Structural Fire Protection American Society of Mechanical Engineers (ASME)

ASME B18.2.6-06 Fasteners for Use in Structural Applications

ASME B46.1-02 Surface Texture, Surface Roughness, Waviness, and Lay

American Society for Nondestructive Testing (ASNT)

ANSI/ASNT CP-189-2006 Standard for Qualification and Certification of

Recommended Practice No SNT-TC-1A-2006 Personnel Qualification and

A6/A6M-09 Standard Specification for General Requirements for Rolled Structural

Steel Bars, Plates, Shapes, and Sheet Piling

A36/A36M-08 Standard Specification for Carbon Structural Steel

A53/A53M-07Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc- Coated, Welded and Seamless

A193/A193M-08b Standard Specification for Alloy-Steel and Stainless Steel Bolting

Materials for High Temperature or High Pressure Service and Other Special Purpose Applications

A194/A194M-09 Standard Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature Service, or Both

A216/A216M-08 Standard Specification for Steel Castings, Carbon, Suitable for

Fusion Welding, for High Temperature Service

A242/A242M-04(2009) Standard Specification for High-Strength Low-Alloy Structural Steel

A283/A283M-03(2007) Standard Specification for Low and Intermediate Tensile Strength Carbon Steel Plates

A307-07bStandard Specification for Carbon Steel Bolts and Studs, 60,000 PSI Tensile Strength

A325-09 Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength

A325M-09Standard Specification for Structural Bolts, Steel, Heat Treated 830 MPa Minimum Tensile Strength (Metric)

A354-07a Standard Specification for Quenched and Tempered Alloy Steel Bolts,

Studs, and Other Externally Threaded Fasteners

A370-09Standard Test Methods and Definitions for Mechanical Testing of Steel Products

A449-07bStandard Specification for Hex Cap Screws, Bolts and Studs, Steel, Heat Treated, 120/105/90 ksi Minimum Tensile Strength, General Use

A490-08b Standard Specification for Heat-Treated Steel Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength

A490M-08Standard Specification for High-Strength Steel Bolts, Classes 10.9 and10.9.3, for Structural Steel Joints (Metric)

A500/A500M-07 Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes

A501-07Standard Specification for Hot-Formed Welded and Seamless Carbon Steel Structural Tubing

A502-03 Standard Specification for Steel Structural Rivets, Steel, Structural A514/A514M-05 Standard Specification for High-Yield Strength, Quenched and Tempered Alloy Steel Plate, Suitable for Welding

A529/A529M-05 Standard Specification for High-Strength Carbon-Manganese Steel of Structural Quality

A563-07aStandard Specification for Carbon and Alloy Steel Nuts

A563M-07 Standard Specification for Carbon and Alloy Steel Nuts [Metric] A568/A568M-09 Standard Specification for Steel, Sheet, Carbon, Structural, and High-Strength, Low-Alloy, Hot-Rolled and Cold-Rolled, General Requirements for

A572/A572M-07Standard Specification for High-Strength Low-Alloy Columbium- Vanadium Structural Steel

A588/A588M-05Standard Specification for High-Strength Low-Alloy Structural Steel, up to 50 ksi [345 MPa] Minimum Yield Point, with Atmospheric Corrosion Resistance

A606/A606M-09Standard Specification for Steel, Sheet and Strip, High-Strength, Low-Alloy, Hot-Rolled and Cold-Rolled, with Improved Atmospheric Corrosion Resistance

A618/A618M-04 Standard Specification for Hot-Formed Welded and Seamless High-Strength Low-Alloy Structural Tubing

A668/A668M-04 Standard Specification for Steel Forgings, Carbon and Alloy, for

A673/A673M-04Standard Specification for Sampling Procedure for Impact Testing of Structural Steel

A709/A709M-09 Standard Specification for Structural Steel for Bridges

A751-08 Standard Test Methods, Practices, and Terminology for Chemical Analysis of Steel Products

A847/A847M-05 Standard Specification for Cold-Formed Welded and Seamless High-Strength, Low-Alloy Structural Tubing with Improved Atmospheric Corrosion Resistance

A852/A852M-03(2007)Standard Specification for Quenched and Tempered Low- Alloy Structural Steel Plate with 70 ksi [485 MPa] Minimum Yield Strength to 4 in [100 mm] Thick

A913/A913M-07Standard Specification for High-Strength Low-Alloy Steel Shapes of Structural Quality, Produced by Quenching and Self-Tempering Process (QST)

A992/A992M-06aStandard Specification for Structural Steel Shapes

User Note: ASTM A992 is the most commonly referenced specification for W-shapes.

A1011/A1011M-09aStandard Specification for Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High-Strength Low-Alloy, High-Strength Low-Alloy with Improved Formability, and Ultra-High Strength

A1043/A1043M-05 Standard Specification for Structural Steel with Low Yield to

16.1–4 REFERENCED SPECIFICATIONS, CODES AND STANDARDS [Sect A2.

C567-05a Standard Test Method for Determining Density of Structural Lightweight

E119-08a Standard Test Methods for Fire Tests of Building Construction and Materials E165-02 Standard Test Method for Liquid Penetrant Examination

E709-08Standard Guide for Magnetic Particle Examination

F436-09Standard Specification for Hardened Steel Washers

F436M-09 Standard Specification for Hardened Steel Washers (Metric)

F606-07 Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets

F606M-07 Standard Test Methods for Determining the Mechanical Properties of

Externally and Internally Threaded Fasteners, Washers, and Rivets (Metric)

F844-07a Standard Specification for Washers, Steel, Plain (Flat), Unhardened for

F959-09 Standard Specification for Compressible-Washer-Type Direct Tension Indicators for Use with Structural Fasteners

F959M-07 Standard Specification for Compressible-Washer-Type Direct Tension Indicators for Use with Structural Fasteners (Metric)

F1554-07aStandard Specification for Anchor Bolts, Steel, 36, 55, and 105 ksi Yield Strength

User Note:ASTM F1554 is the most commonly referenced specification for anchor rods Grade and weldability must be specified.

F1852-08Standard Specification for “Twist-Off” Type Tension Control Structural Bolt/Nut/Washer Assemblies, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength

F2280-08 Standard Specification for “Twist Off” Type Tension Control Structural Bolt/

Nut/Washer Assemblies, Steel, Heat Treated, 150 ksi Minimum Tensile Strength

AWS A5.1/A5.1M-2004 Specification for Carbon Steel Electrodes for Shielded

AWS A5.5/A5.5M-2004 Specification for Low-Alloy Steel Electrodes for Shielded

AWS A5.17/A5.17M-1997 (R2007) Specification for Carbon Steel Electrodes and

Fluxes for Submerged Arc Welding

AWS A5.18/A5.18M-2005 Specification for Carbon Steel Electrodes and Rods for

AWS A5.20/A5.20M-2005 Specification for Carbon Steel Electrodes for Flux Cored

AWS A5.23/A5.23M-2007 Specification for Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding

AWS A5.25/A5.25M-1997 (R2009) Specification for Carbon and Low-Alloy Steel

Electrodes and Fluxes for Electroslag Welding

AWS A5.26/A5.26M-1997 (R2009) Specification for Carbon and Low-Alloy Steel

AWS A5.28/A5.28M-2005 Specification for Low-Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding

AWS A5.29/A5.29M-2005 Specification for Low-Alloy Steel Electrodes for Flux

AWS A5.32/A5.32M-1997 (R2007) Specification for Welding Shielding Gases AWS B5.1-2003 Specification for the Qualification of Welding Inspectors

AWS D1.1/D1.1M-2010 Structural Welding Code—Steel

AWS D1.3 -2008 Structural Welding Code—Sheet Steel

Research Council on Structural Connections (RCSC)

Specification for Structural Joints Using High-Strength Bolts, 2009

Structural Steel Materials

Material test reports from fabricators or testing laboratories serve as adequate proof of compliance with the ASTM standards specified in Section A3.1a For hot-rolled structural shapes, plates, and bars, testing must adhere to ASTM A6/A6M, while sheets require compliance with ASTM A568/A568M Additionally, tubing and pipe tests must follow the relevant ASTM standards applicable to those product forms.

Structural steelmaterial conforming to one of the following ASTMspecificationsis approved for use under this Specification:

16.1–6 REFERENCED SPECIFICATIONS, CODES AND STANDARDS [Sect A2.

ASTM A606/A606M ASTM A1011/A1011M SS, HSLAS, AND HSLAS-F

Unidentified steel, devoid of harmful defects, may be utilized solely for structural components where failure will not compromise the overall or local strength of the structure This application requires the approval of the engineer of record.

Unidentified steel is often suitable for components where specific mechanical properties and weldability are not critical, such as curb plates, shims, and similar items.

ASTM A6/A6M defines hot-rolled shapes with a flange thickness greater than 2 inches (50 mm) as rolled heavy shapes These heavy shapes, utilized in structural applications subject to primary tensile forces from tension or flexure, must be spliced or connected using complete-joint-penetration groove welds that penetrate through the flange's thickness or both the flange and web Structural design documents should mandate the supply of such shapes accordingly.

Charpy V-notch (CVN) impact test results in accordance with ASTM A6/A6M, Supplementary Requirement S30, Charpy V-Notch Impact Test for Structural Shapes

– Alternate Core Location The impact test shall meet a minimum average value of

20 ft-lb (27 J) absorbed energy at a maximum temperature of +70 °F (+21 °C).

Bolting splices and connections are exempt from the aforementioned requirements However, when a rolled heavy shape is welded to another shape using groove welds, the requirements only pertain to the shape that has weld metal fused throughout its cross section.

User Note:Additional requirements for joints in heavy rolled members are given in Sections J1.5, J1.6, J2.6 and M2.2.

Built-up heavy shapes, defined as cross sections with plates thicker than 2 inches (50 mm), are utilized in structural applications where they experience primary tensile forces from tension or flexure When these shapes are spliced or connected using complete-joint-penetration groove welds, they must adhere to specific requirements The structural design documents should mandate that the steel used comes with Charpy V-notch impact test results as per ASTM A6/A6M, Supplementary Requirement S5 Furthermore, the impact tests must follow ASTM A673/A673M, Frequency P, ensuring a minimum average absorbed energy of 20 ft-lb (27 J) at a maximum temperature of +70 °F (+21 °C).

When welding a built-up heavy shape to another member with groove welds, the requirement is applicable solely to the shape that has weld metal fused throughout its cross section.

User Note:Additional requirements for joints in heavy built-up members are given in Sections J1.5, J1.6, J2.6 and M2.2.

Steel Castings and Forgings

Steel castings must meet ASTM A216/A216M, Grade WCB, along with Supplementary Requirement S11, while steel forgings should comply with ASTM A668/A668M Test reports generated according to these standards will serve as adequate proof of conformity.

Bolts, Washers and Nuts

Bolt, washer and nut material conforming to one of the following ASTMspecifica- tionsis approved for use under this Specification:

(4) Compressible-Washer-Type Direct Tension Indicators

Manufacturer’s certification shall constitute sufficient evidence of conformity with the standards.

Anchor Rods and Threaded Rods

Anchor rod and threaded rod material conforming to one of the following ASTM specificationsis approved for use under this Specification:

A449 material is acceptable for high-strength anchor rods and threaded rods of any diameter.

Threads on anchor rods and threaded rods shall conform to the Unified Standard Series of ASME B18.2.6 and shall have Class 2A tolerances

Manufacturer’s certification shall constitute sufficient evidence of conformity with the standards.

Consumables for Welding

Filler metalsand fluxes shall conform to one of the following specificationsof the American Welding Society:

Manufacturer’s certification shall constitute sufficient evidence of conformity with the standards Filler metals and fluxes that are suitable for the intended application shall be selected.

Headed Stud Anchors

Steel headed stud anchors shall conform to the requirements of the Structural

Manufacturer’s certification shall constitute sufficient evidence of conformity with AWS D1.1/D1.1M.

A4 STRUCTURAL DESIGN DRAWINGS AND SPECIFICATIONS

The structural design drawingsand specificationsshall meet the requirements in the

User Note: Provisions in this Specification contain information that is to be shown on design drawings These include:

In sections A3.1c and A3.1d, the specifications for rolled and built-up heavy shapes necessitate alternate core Charpy V-notch toughness (CVN) requirements Additionally, section J3.1 highlights the designated locations for connections utilizing pretensioned bolts It is crucial for fabricators and erectors to have comprehensive information displayed on design drawings to ensure clarity and compliance during the construction process.

Fatigue details requiring nondestructive testing(Appendix 3; e.g., Table A3.1, Cases 5.1 to 5.4)

Risk category (Chapter N)Indication of complete-joint-penetration (CJP) welds subject to tension (Chapter N)

DESIGN REQUIREMENTS

Required Strength

The required strengthof structural members and connectionsshall be determined by structural analysisfor the appropriate loadcombinations as stipulated in Section B2.

Design by elastic, inelastic or plastic analysisis permitted Provisions for inelastic and plastic analysis are as stipulated in Appendix 1, Design by Inelastic Analysis.

Limit States

Design shall be based on the principle that no applicable strength or serviceability limit stateshall be exceeded when the structure is subjected to all appropriate load combinations.

Designing for structural integrity in accordance with applicable building codes should prioritize nominal strength over design strength (LRFD) or allowable strength (ASD), unless the building code specifies otherwise Additionally, when addressing structural integrity requirements, it is not necessary to account for limit states related to the deformation or yielding of connection components.

To comply with building code requirements for structural integrity, bearing bolts in connections featuring short-slotted holes aligned with the tension load direction are allowed and should be considered positioned at the end of the slot.

Design for Strength Using Load and Resistance Factor Design (LRFD)

Designing in accordance with load and resistance factor design (LRFD) ensures compliance with this Specification, provided that the design strength of each structural component meets or surpasses the required strength based on LRFD load combinations All aspects of this Specification are applicable, with the exception of Section B3.4.

Design shall be performed in accordance with Equation B3-1:

R u =required strength using LRFD load combinations

R n =nominal strength, specified in Chapters B through K φ =resistance factor, specified in Chapters B through K φR n ign strength

Design for Strength Using Allowable Strength Design (ASD)

Designing in accordance with allowable strength design (ASD) meets the criteria outlined in this Specification when the allowable strength of each structural component is equal to or greater than the required strength calculated based on the design parameters.

ASD load combinations All provisions of this Specification, except those of Section

Design shall be performed in accordance with Equation B3-2:

R a =required strength using ASD load combinations

R n =nominal strength, specified in Chapters B through K Ω =safety factor, specified in Chapters B through K

Design for Stability

Stabilityof the structure and its elements shall be determined in accordance withChapter C.

Design of Connections

Connectionelements shall be designed in accordance with the provisions of Chapters

In the design of connections, the forces and deformations must align with the expected performance and the assumptions made during structural analysis Self-limiting inelastic deformations are allowable in connections Additionally, beams, girders, and trusses must be secured against rotation around their longitudinal axis at support points, unless analysis demonstrates that such restraint is unnecessary.

User Note:Section 3.1.2 of the Code of Standard Practiceaddresses communi- cation of necessary information for the design of connections.

A simple connection transmits minimal moments and is analyzed by allowing unrestricted relative rotation between connected framing elements It is essential for a simple connection to possess adequate rotation capacity to accommodate the required rotations identified in the structural analysis.

Two types of moment connections, fully restrained and partially restrained, are permitted, as specified below.

(a) Fully Restrained (FR) Moment Connections

A fully restrained (FR) moment connection effectively transfers moments while allowing minimal rotation between the connected members In structural analysis, this type of connection is treated as having no relative rotation To ensure stability at strength limit states, an FR connection must possess adequate strength and stiffness to maintain the angle between the connected components.

(b) Partially Restrained (PR) Moment Connections

Partially restrained (PR) moment connections effectively transfer moments while allowing for some rotation between connected members, making it essential to consider their force-deformation response characteristics in structural analysis The response traits of PR connections should be well-documented in technical literature or determined through analytical and experimental methods Moreover, the individual components of a PR connection must possess adequate strength, stiffness, and deformation capacity to meet the required strength limit states.

Moment Redistribution in Beams

The required flexural strengthof beamscomposed of compact sections, as defined in Section B4.1, and satisfying the unbraced lengthrequirements of Section F13.5

The design basis outlined in Section B3 states that nine-tenths of the negative moments at support points, resulting from gravity loading and confirmed by an elastic analysis in accordance with Chapter C, may be utilized Additionally, the maximum positive moment should be increased by one-tenth of the average negative moment from the elastic analysis However, this reduction is not applicable for members with a yield strength (F y) greater than 65 ksi (450 MPa), moments from cantilever loading, partially restrained (PR) moment connections, or inelastic analysis as per Appendix 1 It is allowed for designs following Section B3.3 (LRFD) and Section B3.4 (ASD) Furthermore, the required axial strength must not exceed 0.15φ c F y A g for LRFD or 0.15F y A g /Ωc for ASD, where φ c and Ω c are defined in Section E1, A g is the gross area of the member, and F y is the specified minimum yield stress.

Diaphragms and Collectors

Diaphragmsand collectorsshall be designed for forces that result from loadsas stipulated in Section B2 They shall be designed in conformance with the provisions ofChapters C through K, as applicable.

Design for Serviceability

The overall structure and the individual members and connections shall be checked for serviceability Requirements for serviceability design are given in Chapter L.

Design for Ponding

To ensure the roof system's strength and stability under ponding conditions, a structural analysis must be conducted This is unnecessary if the roof surface has a slope of at least 1/4 inch per foot (20 mm per meter) directing water toward drainage points or if an effective drainage system is in place to prevent water accumulation.

Methods of checking ponding are provided in Appendix 2, Design for Ponding.

Design for Fatigue

Fatigue must be evaluated as outlined in Appendix 3, Design for Fatigue, for structural members and connections experiencing repeated loads However, fatigue does not need to be assessed for seismic impacts or wind loading effects on standard lateral force-resisting systems and building enclosure components.

Design for Fire Conditions

Appendix 4 outlines two design methods for fire conditions: Analysis and Qualification Testing Adhering to the fire protection standards in the relevant building code will fulfill the requirements set forth in this section and Appendix 4.

Nothing in this section is intended to create or imply a contractual requirement for the engineer of recordresponsible for the structural design or any other member of the design team.

Design by qualification testing is the standard method outlined in building codes, where architects typically oversee fire protection specifications In contrast, design by analysis represents an innovative engineering strategy for fire safety It is essential to clearly define the responsible parties for fire condition design in the contractual agreements for each project.

Design for Corrosion Effects

Where corrosion may impair the strength or serviceability of a structure, structural components shall be designed to tolerate corrosion or shall be protected against corrosion.

Anchorage to Concrete

Anchorage between steel and concrete acting compositely shall be designed in accordance with Chapter I The design of column bases and anchor rods shall be in accordance with Chapter J.

Classification of Sections for Local Buckling

In structural design, sections are categorized into nonslender and slender-element sections based on their compression characteristics Nonslender element sections must adhere to specific width-to-thickness ratios, not exceeding λ r as outlined in Table B4.1a If any compression element's width-to-thickness ratio surpasses this limit, the section is classified as a slender-element section.

In flexural design, sections are categorized into three types: compact, noncompact, and slender-element sections A section is deemed compact if its flanges are continuously connected to the web and the width-to-thickness ratios of its compression elements do not surpass the limiting ratios, λ p, specified in Table B4.1b If the width-to-thickness ratio of any compression element exceeds λ p but remains within λ r, the section is classified as noncompact Conversely, if any compression element's width-to-thickness ratio exceeds λ r, the section is identified as a slender-element section.

For unstiffened elementssupported along only one edge parallel to the direction of the compression force, the width shall be taken as follows:

(a) For flanges of I-shaped members and tees, the width, b, is one-half the full-flange width, b f

(b) For legs of angles and flanges of channels and zees, the width, b, is the full nominal dimension.

(c) For plates, the width, b, is the distance from the free edge to the first row of fas- tenersor line of welds.

(d) For stems of tees, d is taken as the full nominal depth of the section.

User Note:Refer to Table B4.1 for the graphic representation of unstiffened element dimensions.

For stiffened elementssupported along two edges parallel to the direction of the compression force, the width shall be taken as follows:

In the context of rolled or formed section webs, "h" refers to the clear distance between the flanges, excluding the fillet or corner radius at each flange Additionally, "h c" is defined as twice the distance from the center of gravity to the inside face of the compression flange, also subtracting the fillet or corner radius.

In built-up sections, the distance between adjacent lines of fasteners, or the clear distance between flanges when welds are utilized, is denoted as h The term h c represents twice the distance from the center of gravity to the nearest line of fasteners at the compression flange or its inside face, also considering the use of welds Additionally, h p indicates twice the distance from the plastic neutral axis to the nearest line of fasteners at the compression flange or its inside face, again in the context of welded connections.

(c) For flange or diaphragm platesin built-up sections, the width, b, is the distance between adjacent lines of fasteners or lines of welds.

For rectangular hollow structural sections (HSS), the flange width (b) is calculated as the clear distance between the webs, minus the inside corner radius on each side The web height (h) is determined by the clear distance between the flanges, also reduced by the inside corner radius If the corner radius is unknown, h should be taken as the outside dimension minus three times the thickness (t), which refers to the design wall thickness as specified in Section B4.2 In the case of perforated cover plates, b represents the transverse distance to the nearest line of fasteners, and the net area of the plate is measured at the widest hole.

User Note:Refer to Table B4.1 for the graphic representation of stiffened element dimensions.

For tapered flanges of rolled sections, the thickness is the nominal value halfway between the free edge and the corresponding face of the web.

Design Wall Thickness for HSS

The design wall thickness, denoted as t, is essential for calculations related to hollow structural sections (HSS) For electric-resistance-welded (ERW) HSS, the design wall thickness is calculated as 0.93 times the nominal wall thickness, while for submerged-arc-welded (SAW) HSS, it is equal to the nominal thickness.

TABLE B4.1a Width-to-Thickness Ratios: Compression Elements

Members Subject to Axial Compression

Limiting Width-to-Thickness Ratio ␭ r

I-shaped sections, plates projecting from rolled I-shaped sections; outstanding legs of pairs of angles connected with continuous contact, flanges of channels, and flanges of tees

I-shaped sections and plates or angle legs projecting from built-up I-shaped sections

Legs of single angles, legs of double angles with separators, and all other unstiffened elements

Webs of doubly- symmetric I-shaped sections and channels

HSS and boxes of uniform thickness

Flange cover plates and diaphragm plates between lines of fasteners or welds

TABLE B4.1b Width-to-Thickness Ratios: Compression Elements

Limiting Width-to-Thickness Ratio

I-shaped sections, channels, and tees

Flanges of doubly and singly symmetric I-shaped built-up sections

I-shaped sections and channels in flexure about the weak axis

Webs of doubly- symmetric I-shaped sections and channels

Webs of singly- symmetric I-shaped sections

Flanges of rectangular HSS and boxes of uniform thickness

Flange cover plates and diaphragm plates between lines of fasteners or welds

[a] k c = 4 兾 but shall not be taken less than 0.35 nor greater than 0.76 for calculation purposes

[b] F L = 0.7F y for major axis bending of compact and noncompact web built-up I-shaped members with S xt /S xc ≥ 0.7;

For major-axis bending of compact and noncompact web built-up I-shaped members with a shear ratio of S xt /S xc less than 0.7, the formula F L = F y S xt /S xc indicates that the load factor must be at least 0.5 times the yield strength (F y) The moment at yielding of the extreme fiber is represented by M y, while M p denotes the plastic bending moment, measured in kip-in (N-mm).

E = modulus of elasticity of steel = 29,000 ksi (200 000 MPa) h t / w

A pipe can be designed according to the guidelines outlined in the Specification for round HSS sections, provided it meets the requirements of ASTM A53 Class B and adheres to the relevant limitations specified.

ASTM A500 HSS and ASTM A53 Grade B pipe are produced by an ERW process An SAW process is used for cross sections that are larger than those permitted by ASTM A500.

Gross and Net Area Determination

The gross area, A g , of a member is the total cross-sectional area.

The net area, A n , of a member is the sum of the products of the thickness and the net width of each element computed as follows:

In computing net area for tension and shear, the width of a bolt hole shall be taken as 1 /16in (2 mm) greater than the nominal dimensionof the hole.

To determine the net width of a part with a series of holes arranged in a diagonal or zigzag pattern, subtract the total diameters or slot dimensions of all holes from the gross width Additionally, for each gage space in the chain, add the value of s²/4g, where 's' represents the longitudinal center-to-center spacing (pitch) between consecutive holes in inches (or mm), and 'g' denotes the transverse center-to-center spacing (gage) between fastener gage lines in inches (or mm).

For angles, the gage for holes in opposite adjacent legs shall be the sum of the gages from the back of the angles less the thickness.

When calculating the net area (A n) for slotted HSS welded to a gusset plate, it is essential to determine the gross area first The net area is then derived by subtracting the product of the thickness and the total width of the material removed to create the slot from the gross area.

In determining the net area across plug or slot welds, the weld metalshall not be considered as adding to the net area.

For members without holes, the net area, A n , is equal to the gross area, A g

User Note:Section J4.1(b) limits A n to a maximum of 0.85A g for spliceplates with holes.

Shop drawings, fabrication, shop painting and erection shall satisfy the requirements stipulated in Chapter M, Fabrication and Erection

B6 QUALITY CONTROL AND QUALITY ASSURANCE

Quality controland quality assuranceactivities shall satisfy the requirements stipulated in Chapter N, Quality Control and Quality Assurance.

The evaluation of existing structures shall satisfy the requirements stipulated inAppendix 5, Evaluation of Existing Structures.

DESIGN FOR STABILITY

Direct Analysis Method of Design

The direct analysis method of design is applicable to all structures, involving the calculation of required strengths as outlined in Section C2 and the assessment of available strengths as specified in Section C3.

Alternative Methods of Design

The effective length method and the first-order analysis method, defined in Appendix

7, are permitted as alternatives to the direct analysis methodfor structures that sat-

The direct analysis method for design requires determining the necessary strengths of structural components through an analysis that adheres to Section C2.1 This analysis must account for initial imperfections as outlined in Section C2.2 and incorporate adjustments to stiffness in accordance with Section C2.3.

General Analysis Requirements

The analysis of the structure shall conform to the following requirements:

The analysis must account for flexural, shear, and axial deformations of members, along with all component and connection deformations that affect structural displacements Additionally, it should include reductions in stiffnesses that impact the stability of the structure, as outlined in Section C2.3.

The analysis must be a second-order evaluation that accounts for both P-Δ and P-δ effects However, the P-δ effect can be disregarded if specific conditions are met: the structure primarily supports gravity loads through vertical columns, walls, or frames; the maximum second-order drift to maximum first-order drift ratio does not exceed 1.7 for all stories, calculated using LRFD load combinations or 1.6 times ASD load combinations with adjusted stiffnesses; and no more than one-third of the total gravity load is carried by columns in moment-resisting frames in the direction of consideration It is essential to consider these factors in all scenarios.

P-δeffects in the evaluation of individual members subject to compression and flexure

User Note:A P-Δ-only second-order analysis (one that neglects the effects of

P-δon the response of the structure) is permitted under the conditions listed. The requirement for considering P-δ effects in the evaluation of individual members can be satisfied by applying the B 1multiplier defined in Appendix 8.

Use of the approximate method of second-order analysis provided in Appendix 8 is permitted as an alternative to a rigorous second-order analysis

(3) The analysis shall consider all gravity and other applied loadsthat may influence the stability of the structure

When conducting an analysis, it is crucial to account for all gravity loads, including those on leaning columns and other structural elements that are not part of the lateral force-resisting system.

In LRFD design, second-order analysis must be conducted using LRFD load combinations Conversely, for ASD design, second-order analysis should be performed with 1.6 times the ASD load combinations, and the resulting strengths of components are obtained by dividing the results by 1.6.

16.1–22 CALCULATION OF REQUIRED STRENGTHS [Sect C2.

Consideration of Initial Imperfections

The stability of a structure must consider the impact of initial imperfections, which can be addressed through either the direct modeling of these imperfections in the analysis, as outlined in Section C2.2a, or by applying notional loads as detailed in Section C2.2b.

This section focuses on imperfections related to the intersection points of structural members, particularly highlighting the significance of column out-of-plumbness in typical building structures While the initial out-of-straightness of individual members is not discussed here, it is addressed within the compression member design guidelines in Chapter E As long as these imperfections remain within the limits set by the AISC Code of Standard Practice, they do not need to be explicitly considered in the analysis.

In structural analysis, it is essential to account for initial imperfections by incorporating them directly into the model This involves analyzing the structure with members positioned away from their intended locations, considering the maximum initial displacements in the design The initial displacement pattern should be optimized to create the most significant destabilizing effect on the structure.

When modeling imperfections, it is essential to consider initial displacements that resemble both loading effects and expected buckling modes The size of these initial displacements should align with allowable construction tolerances outlined in the AISC Code of Standard Practice or other relevant standards, or be based on actual known imperfections.

In the analysis of gravity load-supporting structures, which utilize vertical columns, walls, or frames, if the ratio of maximum second-order drift to maximum first-order drift across all stories is 1.7 or less (calculated using LRFD load combinations or 1.6 times ASD load combinations with specified stiffness adjustments), initial imperfections may be considered solely in gravity-only load analysis, excluding scenarios that involve applied lateral loads.

2b Use of Notional Loads to Represent Imperfections

In structures that primarily support gravity loads through vertical columns, walls, or frames, it is acceptable to utilize notional loads to account for initial imperfections as specified in this section These notional loads should be applied to a model of the structure that reflects its nominal geometry.

The notional load concept applies universally to various structures, but the specific criteria outlined in Sections C2.2b(1) to C2.2b(4) are exclusively relevant to the designated class of structure mentioned.

Notional loads must be applied as lateral loads at every level and are additive to other lateral loads in all load combinations, with specific exceptions noted The magnitude of these notional loads is specified in the guidelines.

N i =notional load applied at level i, kips (N)

Y i =gravity load applied at level ifrom the LRFD load combinationor ASD load combination, as applicable, kips (N)

Notional loads can generate small fictitious base shears within a structure, necessitating the application of an additional horizontal force at the foundation This force should be equal and opposite to the total notional loads and distributed among the vertical load-carrying elements in proportion to their respective gravity loads Additionally, notional loads can cause real overturning effects that must be considered in structural design.

The notional load at each level, denoted as N i, must be distributed similarly to the gravity load at that level These notional loads should be applied in a direction that maximizes their destabilizing impact.

For most building structures, notional load direction requirements can be met by considering two orthogonal directions of load application—both positive and negative—in cases without lateral loading In scenarios that include lateral loading, it is essential to apply all notional loads in the direction of the resultant of all lateral loads in the combination.

The notional load coefficient of 0.002 in Equation C2-1 is derived from a nominal initial story out-of-plumbness ratio of 1/500 If a different maximum out-of-plumbness is warranted, it is acceptable to proportionally adjust the notional load coefficient accordingly.

According to the AISC Code of Standard Practice, the maximum allowable out-of-plumbness for columns is 1/500 However, in certain situations, other specified tolerances, particularly those related to the plan location of columns, may necessitate a stricter plumbness tolerance.

In structures where the ratio of maximum second-order drift to maximum first-order drift is 1.7 or less, as determined by LRFD load combinations or 1.6 times ASD load combinations with stiffness adjustments per Section C2.3, the notional load, Ni, may only be applied in gravity-only load combinations, excluding those that incorporate additional lateral loads.

Adjustments to Stiffness

The analysis of the structure to determine the required strengthsof components shall use reduced stiffnesses,as follows:

A reduction factor of 0.80 will be applied to all stiffnesses that contribute to the stability of the structure This factor can be utilized for all stiffnesses within the structure.

Applying stiffness reduction uniformly across all structural members is crucial, as selectively reducing stiffness in some members may lead to artificial distortion and unintended force redistribution under load To prevent these issues, it is recommended to implement the reduction on all members, regardless of their contribution to the structure's stability.

(2) An additional factor, τ b , shall be applied to the flexural stiffnesses of all members whose flexural stiffnesses are considered to contribute to the stability of the structure.

P r =required axial compressive strength using LRFD or ASD load combinations, kips (N)

User Note: Taken together, sections (1) and (2) require the use of 0.8τ b times the nominal elastic flexural stiffness and 0.8 times other nominal elastic stiffnesses for structural steelmembers in the analysis

In structures governed by Section C2.2b, it is allowed to set τ b = 1.0 for all members instead of τ b < 1.0 when αP r /P y > 0.5, provided that a notional load of 0.001αY i is applied at every level in the specified direction across all load combinations This notional load must be included alongside any existing loads used for imperfections and is exempt from the stipulations of Section C2.2b(4).

Components made from materials other than structural steel that enhance the stability of a structure must adhere to the governing codes and specifications, which may necessitate greater reductions in stiffness Consequently, these increased stiffness reductions will be applied to those specific components.

16.1–24 CALCULATION OF REQUIRED STRENGTHS [Sect C2.

For the direct analysis method of design, the available strengths of members and connections shall be calculated in accordance with the provisions of Chapters D, E,

F, G, H, I, J and K, as applicable, with no further consideration of overall structure stability The effective length factor, K, of all members shall be taken as unity unless a smaller value can be justified by rational analysis

Bracingintended to define the unbraced lengthsof members shall have sufficient stiffnessand strength to control member movement at the braced points

Appendix 6 outlines various methods for meeting bracing requirements for individual columns, beams, and beam-columns However, it is important to note that these requirements do not apply to bracing incorporated within the overall force-resisting system.

DESIGN OF MEMBERS FOR TENSION

This chapter applies to members subject to axial tension caused by static forces acting through the centroidal axis

The chapter is organized as follows:

User Note:For cases not included in this chapter the following sections apply:

• Chapter H Members subject to combined axial tension and flexure

• J4.3 Block shear rupturestrength at end connections of tension members

There is no maximum slenderness limit for members in tension.

User Note:For members designed on the basis of tension, the slenderness ratio

L /r preferably should not exceed 300 This suggestion does not apply to rods or hangers in tension.

The design tensile strength (φ t P n ) and allowable tensile strength (P n /Ω t ) of tension members must be determined by the lower value derived from the limit states of tensile yielding in the gross section and tensile rupture in the net section.

(a) For tensile yielding in the gross section:

P n =F y A g (D2-1) φ t =0.90 (LRFD) Ω t =1.67 (ASD) (b) For tensile rupture in the net section:

A e =effective net area, in 2 (mm 2 )

A g =gross area of member, in 2 (mm 2 )

F y =specified minimum yield stress, ksi (MPa)

F u =specified minimum tensile strength, ksi (MPa)

When members are completely connected by welds without holes, the effective net area is defined in Section D3 and used in Equation D2-2 Conversely, if holes exist in a member with welded end connections or at the welded connection for plug or slot welds, the effective net area through those holes must be applied in Equation D2-2.

The gross area, A g , and net area, A n , of tension members shall be determined in accordance with the provisions of Section B4.3

The effective net areaof tension members shall be determined as follows:

A e =A n U (D3-1) where U, the shear lagfactor, is determined as shown in Table D3.1.

In open cross sections like W, M, S, C, or HP shapes, as well as WTs, STs, and single and double angles, the shear lag factor, U, should not be lower than the ratio of the gross area of the connected elements to the overall gross area of the member However, this guideline is not applicable to closed sections, such as HSS sections, or to plates.

User Note:For bolted splice plates A e =A n ≤0.85A g , according to Section J4.1.

For limitations on the longitudinal spacing of connectors between elements in continuous contact consisting of a plate and a shape or two plates, see Section J3.5.

Perforated cover plates or tie plates without lacing are allowed on the open sides of built-up tension members Tie plates must measure at least two-thirds the distance between the weld or fastener lines connecting them to the member's components, with a thickness of no less than one-fiftieth of that distance Additionally, the longitudinal spacing of intermittent welds or fasteners on tie plates should not exceed 6 inches (150 mm).

User Note:The longitudinal spacing of connectors between components should preferably limit the slenderness ratio in any component between the connectors to300.

TABLE D3.1 Shear Lag Factors for Connections to Tension Members

Case Shear Lag Factor, U Example

All tension members where the tension load is transmitted directly to each of the cross-sectional elements by fasteners or welds (except as in Cases 4, 5 and 6).

Tension members, excluding plates and hollow structural sections (HSS), transmit tension loads through fasteners or longitudinal welds, affecting some, but not all, cross-sectional elements For wide flange shapes (W, M, S, and HP), Case 7 may be applicable, while Case 8 can be used for angle sections.

All tension members where the tension load is transmitted only by transverse welds to some but not all of the cross-sectional elements.

Plates where the tension load is transmitted by longitudinal welds only.

Round HSS with a single concentric gusset plate

Rectangular HSS with a single concentric gusset plate with two side gusset plates

Shapes or Tees cut from these shapes.

(If U is calculated per Case 2, the larger value is permitted to be used.)

Single and double angles (If U is calculated per

Case 2, the larger value is permitted to be used.)

A n = area of the directly connected elements

Flanges should be connected using three or more fasteners per line in the direction of loading, while the web requires a minimum of four fasteners per line in the same direction If there are fewer than three fasteners per line in the direction of loading, refer to Case 2 for guidance.

DESIGN OF MEMBERS FOR TENSION

Tensile Strength

The design tensile strength, φ t P n, and the allowable tensile strength, P n /Ω t, for pin-connected members must be based on the lower value derived from the limit states of tensile rupture, shear rupture, bearing, and yielding.

(a) For tensile rupture on the net effective area:

P n =F u (2tb e ) (D5-1) φ t =0.75 (LRFD) Ω t =2.00 (ASD) (b) For shear rupture on the effective area:

P n =0.6F u A sf (D5-2) φ sf =0.75 (LRFD) Ω sf =2.00 (ASD) where

The shear failure area (A_sf) is calculated as A_sf = 2t(a + d/2), where 'a' represents the shortest distance from the edge of the pinhole to the edge of the member, measured parallel to the force direction The effective width (b_e) is determined by the formula b_e = 2t + 0.63, but it must not exceed the actual distance from the edge of the hole to the edge of the part, measured perpendicular to the applied force Additionally, 'd' denotes the diameter of the pin, and 't' indicates the thickness of the plate For bearing on the projected area of the pin, refer to Section J7.

(d) For yielding on the gross section, use Section D2(a).

Dimensional Requirements

The pin hole must be positioned at the midpoint between the edges of the member, perpendicular to the direction of the applied force If the pin is intended to allow relative movement between connected components while under maximum load, the diameter of the pin hole should not exceed 1/32 inch (1 mm) greater than the pin's diameter.

The plate width at the pin hole must be at least 2b e + d, and the minimum extension, a, beyond the bearing end of the pin hole, parallel to the member's axis, should not be less than 1.33b e.

Corners beyond the pinhole may be cut at a 45° angle to the member's axis, as long as the net area beyond the pinhole on a plane perpendicular to the cut meets or exceeds the area required beyond the pinhole parallel to the member's axis.

The available tensile strength of eyebars shall be determined in accordance withSection D2, with A taken as the cross-sectional area of the body.

For calculation purposes, the width of the body of the eyebars shall not exceed eight times its thickness.

Eyebarsshall be of uniform thickness, without reinforcement at the pin holes, and have circular heads with the periphery concentric with the pin hole.

The radius of transition between the circular head and the eyebar body shall not be less than the head diameter.

The pin diameter must be at least 0.875 times the width of the eyebar body, and the diameter of the pin hole should not exceed 1/32 inch (1 mm) more than the pin diameter.

For steels having F y greater than 70 ksi (485 MPa), the hole diameter shall not exceed five times the plate thickness, and the width of the eyebar body shall be reduced accordingly.

Thicknesses under 1/2 inch (13 mm) are allowed only when external nuts are used to secure pin plates and filler plates tightly together Additionally, the distance from the edge of the hole to the edge of the plate, measured perpendicular to the applied load, must exceed two-thirds and not exceed three-fourths of the eyebar body width for calculation purposes.

DESIGN OF MEMBERS FOR COMPRESSION

This chapter addresses members subject to axial compression through the centroidal axis The chapter is organized as follows:

E3 Flexural Buckling of Members without Slender Elements

E4 Torsional and Flexural-Torsional Buckling of Members without Slender Elements

• H1 – H2 Members subject to combined axial compression and flexure

• H3 Members subject to axial compression and torsion

• J4.4 Compressive strength of connecting elements

The design compressive strength, φ c P n , and the allowable compressive strength,

The nominal compressive strength, P n , shall be the lowest value obtained based on the applicable limit statesof flexural buckling, torsional buckling, and flexural- torsional buckling. φ c =0.90 (LRFD) Ω c =1.67 (ASD)

TABLE USER NOTE E1.1 Selection Table for the Application of

Sections in Limit Sections in Limit Chapter E States Chapter E States

Unsymmetrical shapes other than single angles

Without Slender Elements With Slender Elements

The effective length factor, K,for calculation of member slenderness, KL /r,shall be determined in accordance with Chapter C or Appendix 7, where

L=laterally unbraced lengthof the member, in (mm) r =radius of gyration, in (mm)

User Note:For members designed on the basis of compression, the effective slenderness ratio KL/rpreferably should not exceed 200.

E3 FLEXURAL BUCKLING OF MEMBERS WITHOUT SLENDER

This section applies to nonslender element compression members as defined in Section B4.1 for elements in uniform compression.

User Note:When the torsional unbraced lengthis larger than the lateral unbraced length, Section E4 may control the design of wide flange and similarly shaped columns.

The nominal compressive strength, P n , shall be determined based on the limit stateof flexural buckling

The critical stress, F cr , is determined as follows:

F e =elastic bucklingstress determined according to Equation E3-4, as specified in Appendix 7, Section 7.2.3(b), or through an elastic buckling analysis, as applicable, ksi (MPa)

16.1–34 FLEXURAL BUCKLING OF MEMBERS WITHOUT SLENDER ELEMENTS [Sect E3.

User Note:The two inequalities for calculating the limits and applicability of Sections E3(a) and E3(b), one based on KL/r and one based on F y /F e , provide the same result.

E4 TORSIONAL AND FLEXURAL-TORSIONAL BUCKLING OF

This section pertains to singly symmetric, unsymmetric, and specific doubly symmetric members, including cruciform or built-up columns devoid of slender elements, as outlined in Section B4.1 for components under uniform compression Furthermore, it encompasses all doubly symmetric members without slender elements when the torsional unbraced length surpasses the lateral unbraced length These guidelines are essential for single angles with a b/t ratio greater than 20.

The nominal compressive strength, P n , shall be determined based on the limit states oftorsionaland flexural-torsional buckling, as follows:

The critical stress, F cr , is determined as follows:

(a) For double angle and tee-shaped compression members:

In the context of flexural buckling about the y-axis of symmetry, the critical buckling force (F cry) is derived from Equation E3-2 or E3-3 For tee-shaped compression members, this value is obtained from Section E6, which also applies to double angle compression members.

(b) For all other cases, F cr shall be determined according to Equation E3-2 or E3-3, using the torsional or flexural-torsional elastic bucklingstress, F e , determined as follows:

(E4-4) (ii) For singly symmetric members where yis the axis of symmetry:

F F cr cry crz cry crz cry cr

(E4-5) (iii) For unsymmetric members, F e is the lowest root of the cubic equation:

A g =gross cross-sectional area of member, in 2 (mm 2 )

G =shear modulus of elasticity of steel = 11,200 ksi (77 200 MPa)

I x , I y =moment of inertia about the principal axes, in 4 (mm 4 )

K x =effective length factorfor flexural buckling about x-axis

K y ective length factor for flexural buckling about y-axis

K z ective length factor for torsional buckling

⫺r o =polar radius of gyration about the shear center, in (mm)

⫺r o 2 = (E4-11) r x =radius of gyration about x-axis, in (mm) r y =radius of gyration about y-axis, in (mm) x o , y o =coordinates of the shear center with respect to the centroid, in (mm)

For doubly symmetric I-shaped sections, the warping constant \( C_w \) can be approximated as \( \frac{I_y h_o^2}{4} \), where \( h_o \) represents the distance between the flange centroids In the case of tees and double angles, it is advisable to exclude the \( C_w \) term when calculating \( F_{ez} \) and to set \( x_o \) to 0.

F F e ey ez ey ez ey ez

16.1–36 SINGLE ANGLE COMPRESSION MEMBERS [Sect E5.

The nominal compressive strength (P n) of single angle members must be calculated following Section E3 or E7 for axially loaded members For single angles where the width-to-thickness ratio (b/t) exceeds 20, Section E4 applies Additionally, members that fulfill the criteria in Section E5(a) or E5(b) can be designed as axially loaded members by utilizing the specified effective slenderness ratio (KL/r).

Eccentricity effects on single angle members can be disregarded when assessing them as axially loaded compression members, utilizing the effective slenderness ratios outlined in Section E5(a) or E5(b), under certain conditions.

(1) members are loaded at the ends in compression through the same one leg;

(2) members are attached by welding or by connectionswith a minimum of two bolts; and

(3) there are no intermediate transverseloads.

Single angle members that have end conditions differing from those outlined in Section E5(a) or (b), and possess a long leg width to short leg width ratio exceeding 1.7 or are subjected to transverse loading, must be assessed for combined axial load and flexure according to the guidelines provided in Chapter H.

For both equal-leg and unequal-leg angles connected via the longer leg, whether as individual members or web members of planar trusses, it is essential that adjacent web members are attached to the same side of the gusset plate or chord.

For unequal-leg angles with leg length ratios under 1.7, and when connected through the shorter leg, the value of KL/r should be adjusted by adding 4[(b l /b s )² - 1] However, KL/r must not be considered less than 0.95L/r z for the members involved.

When considering equal-leg or unequal-leg angles connected via the longer leg in box or space trusses, it is essential to note that adjacent web members must be affixed to the same side of the gusset plate or chord for optimal structural integrity.

DESIGN OF MEMBERS FOR COMPRESSION

Compressive Strength

This section pertains to built-up members that feature two configurations: (a) those interconnected by bolts or welds, and (b) those with at least one open side connected by perforated cover plates or lacing with tie plates The end connections must be either welded or secured using pretensioned bolts with Class A or B faying surfaces.

When designing bolted end connections for built-up compression members, it is crucial to account for the full compressive load, utilizing bolts in bearing and based on shear strength, with the requirement that bolts are pretensioned In structures like double-angle struts within trusses, even minor relative slip at end connections can effectively lengthen the combined cross-section, leading to a notable decrease in the strut's compressive strength Therefore, it is essential to design the connections at the ends of built-up members to effectively resist slip.

The nominal compressive strength of built-up members, formed by two interconnected shapes through bolts or welds, should be assessed according to Sections E3, E4, or E7, with specific modifications Instead of a more precise analysis, when the buckling mode leads to relative deformations causing shear forces in the connectors between the shapes, the term KL/r is substituted with (KL/r)m, calculated as outlined.

(a) For intermediate connectors that are bolted snug-tight:

(b) For intermediate connectors that are welded or are connected by means of pretensioned bolts:

= modified slenderness ratio of built-up member

= slenderness ratio of built-up member acting as a unit in the buckling direction being considered

K i = 0.50 for angles back-to-back

= 0.75 for channels back-to-back

= 0.86 for all other cases a = distance between connectors, in (mm) r i = minimum radius of gyration of individual component, in (mm)

When connecting individual components of compression members made up of multiple shapes, it is essential to maintain intervals, denoted as 'a', ensuring that the effective slenderness ratio (Ka/r i) of each component between fasteners remains below 75% of the governing slenderness ratio of the built-up member In calculating the slenderness ratio for each component, the smallest radius of gyration (r i) must be utilized.

At the ends of compression members resting on base plates or finished surfaces, all contacting components must be connected either by a weld that is at least as long as the member's maximum width or by bolts that are spaced no more than four diameters apart, extending for a distance of 1.5 times the member's maximum width.

For built-up compression members, the longitudinal spacing of intermittent welds or bolts must be sufficient to ensure the transfer of required strength between end connections Refer to Section J3.5 for guidelines on the spacing of fasteners in continuous contact between elements, such as a plate and a shape or two plates When an outside plate is part of a built-up compression member, the maximum spacing should not surpass 12 inches (305 mm) or the thickness of the thinner outside plate multiplied by a specified factor, particularly when intermittent welds or fasteners are utilized along all gage lines Additionally, if fasteners are staggered, their maximum spacing on each gage line must not exceed a defined limit.

Compression members constructed from plates or shapes with open sides must include continuous cover plates that feature a series of access holes The unsupported width of these plates at the access holes can be considered in the calculation of available strength, provided that specific requirements outlined in Section B4.1 are satisfied.

(1) The width-to-thickness ratio shall conform to the limitations of Section B4.1.

User Note:It is conservative to use the limiting width-to-thickness ratio for Case

In Table B4.1a, the width (b) is defined as the transverse distance between the closest fastener lines, and the net area of the plate is measured at the widest hole Alternatively, the limiting width-to-thickness ratio can be established through analytical methods.

(2) The ratio of length (in direction of stress) to width of hole shall not exceed 2.

(3) The clear distance between holes in the direction of stress shall be not less than the transverse distance between nearest lines of connecting fasteners or welds.

(4) The periphery of the holes at all points shall have a minimum radius of 1 1 /2in

Lacing with tie plates is an acceptable alternative to perforated cover plates, with tie plates positioned at the ends and at intermediate points if lacing is interrupted End tie plates should be as close to the ends as possible and must be at least as long as the distance between the fasteners or welds connecting them to the member components Intermediate tie plates should be no shorter than half of this distance The thickness of tie plates should not be less than one-fiftieth of the distance between the welds or fasteners In welded constructions, the total welding on each line connecting a tie plate must be at least one-third of the plate's length For bolted constructions, the spacing of tie plates in the direction of stress should not exceed six diameters, and each segment must be connected by a minimum of three fasteners.

Lacing elements, such as flat bars, angles, and channels, must be spaced to ensure that the L/r ratio of the flange element between connections does not exceed 0.75 times the governing slenderness ratio of the entire member Additionally, the lacing must be designed to deliver a shearing strength normal to the member's axis that is equal to 2% of the member's available compressive strength.

The lacing bars in single systems must maintain an L/r ratio not exceeding 140, while for double lacing, this ratio should not surpass 200 It is essential that double lacing bars are connected at their intersections When considering lacing bars under compression, the unsupported length between welds or fasteners is used for single lacing, while for double lacing, it is limited to 70% of that length.

For optimal structural integrity, the angle of lacing bars should ideally be at least 60 degrees for single lacing and 45 degrees for double lacing Additionally, when the distance between the lines of welds or fasteners in the flanges exceeds 15 inches, careful consideration must be given to the design to ensure stability and performance.

(380 mm), the lacing shall preferably be double or be made of angles.

For additional spacing requirements, see Section J3.5.

This section applies to slender-element compression members, as defined in Section B4.1 for elements in uniform compression.

The nominal compressive strength, P n , shall be the lowest value based on the applicable limit statesof flexural buckling, torsional buckling, and flexural-torsional buckling.

The critical stress, F cr , shall be determined as follows:

The elastic buckling stress (F e) is determined using specific equations based on the symmetry of the structural members For doubly symmetric members, apply Equations E3-4 and E4-4; for singly symmetric members, use Equations E3-4 and E4-5; and for unsymmetric members, refer to Equation E4-6 However, for single angles with a width-to-thickness ratio (b/t) of 20 or less, F e is calculated using Equation E3-4, measured in ksi (MPa).

Q =net reduction factor accounting for all slender compression elements;

=1.0 for members without slender elements, as defined in Section B4.1, for elements in uniform compression

=Q s Q a for members with slender-element sections, as defined in Section B4.1, for elements in uniform compression.

User Note:For cross sections composed of only unstiffened slender elements, Q

=Q s (Q a =1.0) For cross sections composed of only stiffened slender elements,

For cross sections featuring both stiffened and unstiffened slender elements, the equation Q = Qs Qa applies, with Qs set at 1.0 for pure compression scenarios When dealing with multiple unstiffened slender elements, it is advisable to use the lower Qs value from the slenderest element to ensure a conservative approach in assessing member strength.

Slender Unstiffened Elements, Q s

The reduction factor, Q s , for slender unstiffened elementsis defined as follows:

(a) For flanges, angles and plates projecting from rolled columnsor other compression members:

(b) For flanges, angles and plates projecting from built-up I-shaped columns or other compression members:

(E7-9) where b =width of unstiffened compression element, as defined in Section B4.1, in. (mm)

, and shall not be taken less than 0.35 nor greater than 0.76 for calculation purposes t =thickness of element, in (mm) b t

(E7-12) where b=full width of longest leg, in (mm) (d) For stems of tees

(E7-15) where d=full nominal depth of tee, in (mm)

16.1–42 MEMBERS WITH SLENDER ELEMENTS [Sect E7.

Slender Stiffened Elements, Q a

The reduction factor, Q a , for slender stiffened elementsis defined as follows:

A g = gross cross-sectional area of member, in 2 (mm 2 )

A e = summation of the effective areas of the cross section based on the reduced effective width, b e , in 2 (mm 2 )

The reduced effective width, b e , is determined as follows:

(a) For uniformly compressed slender elements, with , except flanges of square and rectangular sections of uniform thickness:

(E7-17) where fis taken as F cr with F cr calculated based on Q =1.0 (b) For flanges of square and rectangular slender-element sectionsof uniform thickness with

User Note:In lieu of calculating f = P n /A e , which requires iteration, fmay be taken equal to F y This will result in a slightly conservative estimate of column available strength.

(c) For axially loaded circular sections:

D=outside diameter of round HSS, in (mm) t =thickness of wall, in (mm)

DESIGN OF MEMBERS FOR FLEXURE

This chapter focuses on members experiencing simple bending around a principal axis In simple bending scenarios, the member is subjected to loads in a plane that aligns with a principal axis, which either intersects the shear center or is fixed against twisting at the load points and supports The structure of this chapter is outlined for clarity.

F2 Doubly Symmetric Compact I-Shaped Members and Channels Bent About Their Major Axis

Doubly symmetric I-shaped members with compact webs and noncompact or slender flanges are designed to bend about their major axis, providing structural integrity and efficiency Additionally, other I-shaped members, whether featuring compact or noncompact webs, are also engineered to bend about their major axis, ensuring versatility in various construction applications.

F5 Doubly Symmetric and Singly Symmetric I-Shaped Members With Slender Webs Bent About Their Major Axis

F6 I-Shaped Members and Channels Bent About Their Minor Axis

F7 Square and Rectangular HSS and Box-Shaped Members

F9 Tees and Double Angles Loaded in the Plane of Symmetry

F13 Proportions of Beams and Girders

• Chapter G Design provisions for shear

• H1–H3 Members subject to biaxial flexure or to combined flexure and axial force

• H3 Members subject to flexure and torsion

• Appendix 3 Members subject to fatigue

For guidance in determining the appropriate sections of this chapter to apply, Table User Note F1.1 may be used.

Section in Cross Flange Web Limit

Chapter F Section Slenderness Slenderness States

F12 Unsymmetrical shapes, All limit other than single angles N/A N/A states

Y = yielding, LTB = lateral-torsional buckling, FLB = flange local buckling, WLB = web local buckling, TFY = tension flange yielding, LLB = leg local buckling, LB = local buckling, C = compact, NC = noncompact,

TABLE USER NOTE F1.1 Selection Table for the Application of Chapter F Sections

The design flexural strength, φ b M n,and the allowable flexural strength, M n /Ω b ,shall be determined as follows:

(1) For all provisions in this chapter φ b =0.90 (LRFD) Ω b =1.67 (ASD) and the nominal flexural strength, M n , shall be determined according to Sections F2 through F13.

(2) The provisions in this chapter are based on the assumption that points of support for beamsand girders are restrained against rotation about their longitudinal axis.

(3) For singly symmetric members in single curvatureand all doubly symmetric members:

C b , the lateral-torsional bucklingmodification factor for nonuniform moment diagrams when both ends of the segment are braced is determined as follows:

M max solute value of maximum moment in the unbraced segment, kip-in. (N-mm)

M A solute value of moment at quarter point of the unbraced segment, kip-in (N-mm)

M B solute value of moment at centerline of the unbraced segment, kip- in (N-mm)

M C solute value of moment at three-quarter point of the unbraced segment, kip-in (N-mm)

For cantilevers or overhangs where the free end is unbraced, C b = 1.0

For doubly symmetric members without transverse loading between brace points, Equation F1-1 simplifies to specific values based on end moment conditions: it equals 1.0 for equal end moments of opposite signs (uniform moment), 2.27 for equal end moments of the same sign (reverse curvature bending), and 1.67 when one end moment is zero A more comprehensive analysis for Cb in singly symmetric members is provided in the Commentary.

In singly symmetric members experiencing reverse curvature bending, it is essential to verify the lateral-torsional buckling strength for both flanges The flexural strength must be equal to or exceed the maximum moment that induces compression in the flange being evaluated.

DESIGN OF MEMBERS FOR FLEXURE

Yielding

F y =specified minimum yield stressof the type of steel being used, ksi (MPa)

Z x =plastic section modulus about the x-axis, in 3 (mm 3 )

Lateral-Torsional Buckling

(a) When L b ≤L p , the limit stateof lateral-torsional bucklingdoes not apply. (b) When L p 6.0. where

A fc = area of compression flange, in 2 (mm 2 )

A ft = area of tension flange, in 2 (mm 2 ) b fc = width of compression flange, in (mm) b ft = width of tension flange, in (mm)

In these cases, the nominal shear strength, V n , shall be determined according to the provisions of Section G2.

Shear Strength With Tension Field Action

When tension field actionis permitted according to Section G3.1, the nominal shear strength, V n , with tension field action, according to the limit state of tension field yielding, shall be

(G3-2) where k v and C v are as defined in Section G2.1

Transverse Stiffeners

Transverse stiffenerssubject to tension field actionshall meet the requirements of Section G2.2 and the following limitations:

冇b兾t冈 st =width-to-thickness ratio of the stiffener

F yst =specified minimum yield stressof the stiffener material, ksi (MPa)

The moment of inertia (I_st) of transverse stiffeners is calculated about the axis at the web center for pairs of stiffeners, or about the contact face with the web plate for individual stiffeners, measured in inches to the fourth power (in.⁴) or millimeters to the fourth power (mm⁴).

I st1 =minimum moment of inertia of the transverse stiffeners required for development of the web shear bucklingresistance in Section G2.2, in 4 (mm 4 )

I st2 =minimum moment of inertia of the transverse stiffeners required for development of the full web shear buckling plus the web tension field resistance, V r = V c2 ,in 4 (mm 4 )

V r =larger of therequired shear strengths in the adjacent web panels using

LRFDor ASD load combinations, kips (N)

V c1 =smaller of the available shear strengths in the adjacent web panels with

V n as defined in Section G2.1, kips (N)

V c2 =smaller of the available shear strengthsin the adjacent web panels with

V n as defined in Section G3.2, kips (N) ρ st =the larger of F yw /F yst and 1.0

F yw =specified minimum yield stress of the web material, ksi (MPa)

The nominal shear strength (Vn) of a single angle leg is calculated using Equation G2-1 and Section G2.1(b), where the area (Aw) is defined as the product of the leg width (b) and thickness (t) In this context, 'b' represents the width of the leg that resists the shear force, measured in inches (or millimeters), and 't' denotes the thickness of the angle leg, also measured in inches (or millimeters) The ratio of height to thickness (h/t) is expressed as b/t, with a value of kv set at 1.2.

G5 RECTANGULAR HSS AND BOX-SHAPED MEMBERS

The nominal shear strength (Vn) of rectangular hollow structural sections (HSS) and box members is calculated according to Section G2.1, where the area (Aw) is defined as 2ht Here, 'h' represents the width resisting the shear force, measured as the clear distance between the flanges minus the inside corner radius on each side The design wall thickness (t) is determined as 0.93 times the nominal wall thickness for electric-resistance-welded (ERW) HSS and equals the nominal thickness for submerged-arc-welded (SAW) HSS Additionally, the formula incorporates a factor (kv) defined as 5hF.

If the corner radius is not known, h shall be taken as the corresponding outside dimension minus 3 times the thickness

The nominal shear strength, V n , of round HSS, according to the limit statesof shear yieldingand shear buckling, shall be determined as:

F cr shall be the larger of

A g =gross cross-sectional area of member, in 2 (mm 2 )

L v =distance from maximum to zero shear force, in (mm) t =design wall thickness, equal to 0.93 times the nominal wall thickness for

ERW HSS and equal to the nominal thickness for SAW HSS, in (mm)

User Note:The shear buckling equations, Equations G6-2a and G6-2b, will control for D/tover 100, high-strength steels, and long lengths For standard sections, shear yielding will usually control.

G7 WEAK AXIS SHEAR IN DOUBLY SYMMETRIC AND SINGLY

For doubly and singly symmetric shapes subjected to weak-axis loading without torsion, the nominal shear strength (Vn) of each shear-resisting element is calculated using Equation G2-1 and Section G2.1(b) In this calculation, the area (Aw) is defined as bf tf, the height-to-thickness ratio (h/tw) is expressed as b/tf, and the shear strength coefficient (kv) is set to 1.2 Additionally, for I-shaped members, the width (b) for flanges is half of the full-flange width (bf), while for channel flanges, it is the full nominal dimension of the flange.

User Note:For all ASTM A6 W, S, M and HP shapes, when F y ≤ 50 ksi (345 MPa), C v =1.0

G8 BEAMS AND GIRDERS WITH WEB OPENINGS

The effect of all web openings on the shear strength of steel and composite beams

16.1–72 RECTANGULAR HSS AND BOX-SHAPED MEMBERS [Sect G5.

DESIGN OF MEMBERS FOR COMBINED FORCES

Doubly and Singly Symmetric Members Subject to Flexure

The interaction of flexure and compression in both doubly symmetric and singly symmetric members, with a ratio of moment of inertia (0.1 ≤ I yc / I y ≤ 0.9), must adhere to the constraints of bending about a geometric axis (x and/or y) This is governed by Equations H1-1a and H1-1b, where I yc represents the moment of inertia of the compression flange about the y-axis, measured in inches to the fourth power (in.⁴) or millimeters to the fourth power (mm⁴).

User Note:Section H2 is permitted to be used in lieu of the provisions of this section.

P r =required axial strength using LRFDor ASD load combinations, kips (N)

16.1–74 DOUBLY AND SINGLY SYMMETRIC MEMBERS [Sect H1.

M r =required flexural strengthusing LRFD or ASD load combinations, kip-in. (N-mm)

M c =available flexural strength, kip-in (N-mm) x =subscript relating symbol to strong axisbending y =subscript relating symbol to weak axisbending

For design according to Section B3.3 (LRFD):

P r =required axial strength using LRFD load combinations, kips (N)

P c = φ c P n =design axial strength, determined in accordance with Chapter E, kips (N)

M r =required flexural strength using LRFD load coMbinations, kip-in (N-mm)

M c = φ b M n =design flexural strengthdetermined in accordance with Chapter F, kip-in (N-mm) φ c =resistance factorfor compression =0.90 φ b =resistance factor for flexure =0.90

For design according to Section B3.4 (ASD):

P r =required axial strength using ASD load combinations, kips (N)

P c =P n /Ω c =allowable axial strength, determined in accordance with Chapter

M r =required flexural strength using ASD load combinations, kip-in (N-mm)

M c =M n /Ω b = allowable flexural strength determined in accordance with Chapter F, kip-in (N-mm) Ω c =safety factorfor compression =1.67 Ω b =safety factor for flexure =1.67

Doubly and Singly Symmetric Members Subject to Flexure

The interaction of flexure and tension in doubly symmetric and singly symmetric members, constrained to bend about a geometric axis (x and/or y), must adhere to the limitations set forth by Equations H1-1a and H1-1b.

P c = φ t P n =design axial strength, determined in accordance with Section D2, kips (N)

M r =required flexural strength using LRFD load combinations, kip-in (N-mm)

M c = φ b M n ign flexural strength determined in accordance with Chapter F, kip-in (N-mm) φ t =resistance factorfor tension (see Section D2) φ b =resistance factor for flexure =0.90

P c =P n /Ω t = allowable axial strength, determined in accordance with Section

M c =M n /Ω b =allowable flexural strengthdetermined in accordance with Chapter F, kip-in (N-mm) Ω t =safety factorfor tension (see Section D2) Ω b =safety factor for flexure =1.67

For doubly symmetric members, C b in Chapter F may be multiplied by for axial tension that acts concurrently with flexure where and α =1.0 (LRFD); α =1.6 (ASD)

A more detailed analysis of the interaction of flexure and tension is permitted in lieu of Equations H1-1a and H1-1b.

3 Doubly Symmetric Rolled Compact Members Subject to Single Axis Flexure and Compression

For doubly symmetric rolled compact members with a ratio of 共KL兲 z ≤ 共KL兲 y, subjected to flexure and compression with moments mainly about their major axis, it is acceptable to evaluate the two independent limit states—namely, in-plane instability and out-of-plane buckling or lateral-torsional buckling—separately, rather than using the combined approach outlined in Section H1.1.

For members with M ry 兾M cy ≥0.05, the provisions of Section H1.1 shall be followed

(a) For the limit state of in-plane instability, Equations H1-1 shall be used with P c ,

M rx and M cx determined in the plane of bending.

(b) For the limit state of out-of-plane buckling and lateral-torsional buckling:

P cy =available compressive strengthout of the plane of bending, kips (N)

C b =lateral-torsional buckling modification factor determined from Section F1

M cx =available lateral-torsional strengthfor strong axisflexure determined in accordance with Chapter F using C b = 1.0, kip-in (N-mm)

User Note: In Equation H1-2, C b M cx may be larger than φ b M px in LRFD or

M px /Ω b in ASD The yielding resistance of the beam-column is captured by Equations H1-1.

H2 UNSYMMETRIC AND OTHER MEMBERS SUBJECT TO FLEXURE AND AXIAL FORCE

This section discusses the relationship between flexure and axial stress for shapes not included in Section H1 It allows the use of the guidelines provided here for any shape instead of those specified in Section H1.

(H2-1) where f ra =required axial stress at the point of consideration using LRFD or ASD load combinations, ksi (MPa)

F ca =available axial stressat the point of consideration, ksi (MPa) f rbw , f rbz =required flexural stress at the point of consideration using LRFD or ASD load combinations, ksi (MPa)

F cbw ,F cbz =available flexural stressat the point of consideration, ksi (MPa) w =subscript relating symbol to major principal axis bending z =subscript relating symbol to minor principal axis bending

For design according to Section B3.3 (LRFD): f ra =required axial stress at the point of consideration using LRFD load combinations, ksi (MPa)

F ca = φ c F cr =design axial stress, determined in accordance with Chapter

E for compression or Section D2 for tension, ksi (MPa) f rbw , f rbz =required flexural stress at the point of consideration using LRFD or

ASD load combinations, ksi (MPa)

F cbw , F cbz = =design flexural stressdetermined in accordance with

In Chapter F, the stress values are expressed in ksi (MPa), utilizing the section modulus specific to the cross-section's location while accounting for the stress sign The resistance factor for compression (φc) is set at 0.90, while the resistance factor for tension (φt) is detailed in Section D2 Additionally, the resistance factor for flexure (φb) is also established at 0.90.

For design according to Section B3.4 (ASD): f ra =required axial stress at the point of consideration using ASD load combinations, ksi (MPa)

F ca = =allowable axial stressdetermined in accordance with Chapter E for compression, or Section D2 for tension, ksi (MPa) f rbw , f rbz =required flexural stress at the point of consideration using LRFD or

ASD load combinations, ksi (MPa)

F cbw , F cbz = =allowable flexural stressdetermined in accordance with

Chapter F, ksi (MPa) Use the section modulus for the specific location in the cross section and consider the sign of the stress.

16.1–76 UNSYMMETRIC AND OTHER MEMBERS [Sect H2. f F f F f F ra ca rbw cbw rbz cbz

F cr Ω c Ω t =safety factor for tension (see Section D2) Ω b =safety factor for flexure =1.67

Equation H2-1 is assessed using the principal bending axes, taking into account the direction of flexural stresses at critical cross-section points The flexural components are appropriately combined with the axial term, either by addition or subtraction In cases where the axial force is compressive, second-order effects must be incorporated as outlined in Chapter C.

A more detailed analysis of the interaction of flexure and tension is permitted in lieu of Equation H2-1.

H3 MEMBERS SUBJECT TO TORSION AND COMBINED TORSION,FLEXURE, SHEAR AND/OR AXIAL FORCE

Round and Rectangular HSS Subject to Torsion

The design torsional strength, φ T T n , and the allowable torsional strength, T n /Ω T , for round and rectangular HSSaccording to the limit statesof torsional yieldingand torsional bucklingshall be determined as follows: φ T =0.90 (LRFD) Ω T =1.67 (ASD)

C is the HSS torsional constant

The critical stress, F cr , shall be determined as follows:

(a) For round HSS, F cr shall be the larger of

(ii) (H3-2b) but shall not exceed 0.6F y , where

L =length of the member, in (mm)

D=outside diameter, in (mm) (b) For rectangular HSS

(H3-5) where h=flat widthof longer side as defined in Section B4.1b(d), in (mm) t =design wall thicknessdefined in Section B4.2, in (mm)

User Note:The torsional constant, C, may be conservatively taken as:

For rectangular HSS: C =2共B⫺t兲共H⫺t兲t⫺4.5共4⫺π兲t 3

HSS Subject to Combined Torsion, Shear, Flexure

When the required torsional strength (T r) is 20% or less of the available torsional strength (T c), the interaction of torsion, shear, flexure, and axial force in hollow structural sections (HSS) can be assessed according to Section H1, with torsional effects disregarded However, if T r exceeds 20% of T c, the interactions of torsion, shear, flexure, and axial force must be constrained at the point of consideration.

P r =required axial strengthusing LRFD load combinations, kips (N)

P c = φP n =design tensile or compressive strengthin accordance with Chapter

M r =required flexural strengthusing LRFD load combinations, kip-in (N-mm)

M c = φ b M n = design flexural strength in accordance with Chapter F, kip-in (N-mm)

16.1–78 MEMBERS SUBJECT TO TORSION AND COMBINED TORSION [Sect H3.

V c = φ v V n =design shear strengthin accordance with Chapter G, kips (N)

T r =required torsional strength using LRFD load combinations, kip-in (N-mm)

T c = φ T T n =design torsional strengthin accordance with Section H3.1, kip-in. (N-mm)

P c =P n /Ω = allowable tensile or compressive strength in accordance with Chapter D or E, kips (N)

M c =M n /Ω b =allowable flexural strengthin accordance with Chapter F, kip-in. (N-mm)

V r =required shear strength using ASD load combinations, kips (N)

V c =V n /Ω v =allowable shear strengthin accordance with Chapter G, kips (N)

T r =required torsional strength using ASD load combinations, kip-in (N-mm)

T c =T n /Ω T =allowable torsional strength in accordance with Section H3.1,kip-in (N-mm)

Non-HSS Members Subject to Torsion and Combined Stress

The torsional strength for non-HSS members is determined by the lowest value from the limit states of yielding under normal stress, shear yielding under shear stress, or buckling For the limit state of yielding under normal stress, the design strength is calculated using φ T = 0.90 for Load and Resistance Factor Design (LRFD) and Ω T = 1.67 for Allowable Stress Design (ASD).

(b) For the limit state of shear yielding under shear stress

(c) For the limit state of buckling

F cr =buckling stress for the section as determined by analysis, ksi (MPa) Some constrained local yieldingis permitted adjacent to areas that remain elastic.

H4 RUPTURE OF FLANGES WITH HOLES SUBJECT TO TENSION

When assessing bolt holes in flanges that experience tension from combined axial forces and major axis flexure, the tensile rupture strength of the flange must adhere to Equation H4-1 It is essential to evaluate each flange individually for tension caused by axial forces and flexural stresses.

16.1–80 RUPTURE OF FLANGES WITH HOLES SUBJECT TO TENSION [Sect H4. where

P r =required axial strength of the member at the location of the bolt holes, positive in tension, negative in compression, kips (N)

P c =available axial strength for the limit stateof tensile rupture of the net section at the location of bolt holes, kips (N)

M rx =required flexural strength at the location of the bolt holes; positive for tension in the flange under consideration, negative for compression, kip-in. (N-mm)

The available flexural strength about the x-axis for the limit state of tensile rupture of the flange, denoted as M cx, is determined in accordance with Section F13.1 If the limit state of tensile rupture in flexure is not applicable, the plastic bending moment should be utilized instead.

M p , determined with bolt holes not taken into consideration, kip-in (N-mm)

P c = φ t P n ign axial strength for the limit state of tensile rupture, determined in accordance with Section D2(b), kips (N)

M rx =required flexural strength using LRFD load combinations, kip-in (N- mm)

The flexural strength, M cx, is calculated using the formula φ b M n, which follows Section F13.1, or by determining the plastic bending moment, M p, without accounting for bolt holes, expressed in kip-in (N-mm) The resistance factor for tensile rupture, φ t, is set at 0.75, while the resistance factor for flexure, φ b, is established at 0.90.

P c = =allowable axial strength for the limit state of tensile rupture, determined in accordance with Section D2(b), kips (N)

M rx =required flexural strength using ASD load combinations, kip-in (N-mm)

M cx = =allowable flexural strength determined in accordance with Section

F13.1, or the plastic bending moment, M p , determined with bolt holes not taken into consideration, as applicable, kip-in (N-mm) Ω t =safety factorfor tensile rupture =2.00 Ω b =safety factor for flexure =1.67

DESIGN OF COMPOSITE MEMBERS

This chapter focuses on composite members made of rolled or built-up structural steel shapes, hollow structural sections (HSS), and structural concrete working in unison, particularly steel beams that support reinforced concrete slabs to collectively resist bending It encompasses simple and continuous composite beams featuring steel-headed stud anchors, as well as concrete-encased and concrete-filled beams, whether constructed with or without temporary shores The organization of the chapter is clearly outlined for ease of reference.

I5 Combined Axial Force and Flexure

I7 Composite Diaphragms and Collector Beams

In determining load effectsin members and connectionsof a structure that includes compositemembers, consideration shall be given to the effective sections at the time each increment of loadis applied.

The design and material properties of concrete and reinforcing steel in composite construction must adhere to the reinforced concrete and reinforcing bar specifications outlined in the relevant building code Furthermore, the guidelines set forth in ACI 318 are applicable, subject to specific exceptions and limitations.

(1) ACI 318 Sections 7.8.2 and 10.13, and Chapter 21 shall be excluded in their entirety.

(2) Concrete and steel reinforcement material limitations shall be as specified in Section I1.3

(3)Transverse reinforcementlimitations shall be as specified in Section I2.1a(2), in addition to those specified in ACI 318.

(4) The minimum longitudinal reinforcing ratio for encased composite members shall be as specified in Section I2.1a(3)

Concrete and steel reinforcement components designed in accordance with ACI 318 shall be based on a level of loading corresponding to LRFD load combinations.

The Specification aims for the detailing of concrete and reinforcing steel in composite concrete members to follow the non-composite provisions of ACI 318, with modifications specified in the document All unique requirements pertaining to composite members are addressed within the Specification.

Note that the design basis for ACI 318 is strength design Designers using ASD for steel must be conscious of the different load factors

2 Nominal Strength of Composite Sections

The nominal strengthof composite sections shall be determined in accordance with the plastic stress distribution methodor the strain compatibility methodas defined in this section.

The tensile strengthof the concrete shall be neglected in the determination of the nominal strength of composite members

Local bucklingeffects shall be considered for filled composite members as defined in Section I1.4 Local buckling effects need not be considered for encased composite members

In the plastic stress distribution method, the nominal strength is calculated by assuming that steel components achieve a stress of F y in tension or compression, while concrete components under axial force and/or flexure reach a compression stress of 0.85f′ c For round hollow structural sections (HSS) filled with concrete, a higher stress of 0.95f′ c is allowed for concrete in compression, reflecting the benefits of concrete confinement.

The strain compatibility method assumes a linear strain distribution across the section, with the maximum concrete compressive strain set at 0.003 in./in (mm/mm) To establish the stress-strain relationships for steel and concrete, data should be derived from testing or referenced from published results for comparable materials.

The strain compatibility method is essential for assessing nominal strength in irregular sections and when steel does not display elasto-plastic behavior For encased members under axial load, flexure, or both, refer to the general guidelines outlined in AISC Design Guide 6 and ACI 318.

For concrete, structural steel, and steel reinforcing bars in composite systems, the following limitations shall be met, unless justified by testing or analysis:

To determine the available strength of concrete, it is essential to consider its compressive strength, denoted as f′c For normal weight concrete, the compressive strength should fall within a specific range, not less than 3 ksi (21 MPa) and not more than 10 ksi (70 MPa) However, for other types of concrete, the upper limit is lower, at 6 ksi (70 MPa is not applicable here, only 6 ksi or 42 MPa), with the same lower limit of 3 ksi (21 MPa).

User Note:Higher strength concrete material properties may be used for stiff- nesscalculations but may not be relied upon for strength calculations unless justified by testing or analysis

(2) The specified minimum yield stressof structural steel and reinforcing bars used in calculating the strength of composite members shall not exceed 75 ksi (525 MPa).

4 Classification of Filled Composite Sections for Local Buckling

Filled composite sections are categorized into three types based on their compression characteristics: compact, noncompact, and slender A section is deemed compact if the maximum width-to-thickness ratio of its compression steel elements does not exceed the limiting ratio, λ p, outlined in Table I1.1a If this ratio is exceeded by one or more elements but remains within λ r, the section is classified as noncompact Conversely, if any compression steel element surpasses λ r, the section is considered slender The maximum allowable width-to-thickness ratios are specified in the referenced table.

Filled composite sections for flexure are categorized into three types: compact, noncompact, and slender A section is deemed compact if the maximum width-to-thickness ratio of its compression steel elements does not surpass the limiting ratio, λ p, as outlined in Table I1.1b If this ratio exceeds λ p but remains within λ r, the section is classified as noncompact Conversely, if any steel element's width-to-thickness ratio exceeds λ r, the section is considered slender The maximum allowable width-to-thickness ratios are specified in the referenced table.

Refer to Table B4.1a and Table B4.1b for definitions of width (band D) and thickness (t) for rectangular and round HSSsections.

All ASTM A500 Grade B square hollow structural sections (HSS) are classified as compact, according to the specifications outlined in Table I1.1a and Table I1.1b, with the exception of HSS7×7×1/8, HSS8×8×1/8, HSS9×9×1/8, and HSS12×12×3/16, which are considered noncompact for both axial compression and flexural applications.

All ASTM A500 Grade B round hollow structural sections (HSS) comply with the compactness criteria outlined in Tables I1.1a and I1.1b for axial compression and flexure, except for the HSS16.0×0.25, which is classified as noncompact in flexure.

TABLE I1.1A Limiting Width-to-Thickness Ratios for Compression Steel Elements in Composite Members Subject to Axial Compression

Description of Thickness Compact/ Noncompact/ Maximum

Element Ratio Noncompact Slender Permitted

Walls of Rectangular HSS and Boxes of Uniform

TABLE I1.1B Limiting Width-to-Thickness Ratios for Compression Steel Elements in Composite

Members Subject to Flexure For Use with Section I3.4

Description of Thickness Compact/ Noncompact/ Maximum

Element Ratio Noncompact Slender Permitted

Webs of Rectangular HSS and Boxes of Uniform

This section applies to two types of composite members subject to axial force: encased composite membersand filled composite members

For encased composite members, the following limitations shall be met:

(1) The cross-sectional area of the steel core shall comprise at least 1% of the total composite cross section.

(2) Concrete encasement of the steel core shall be reinforced with continuous longitudinal bars and lateral ties or spirals

When utilizing lateral ties, it is essential to use at least a No 3 (10 mm) bar spaced a maximum of 12 inches (305 mm) apart, or a No 4 (13 mm) bar or larger spaced a maximum of 16 inches (406 mm) apart Additionally, deformed wire or welded wire reinforcement with equivalent area is also acceptable.

Maximum spacing of lateral ties shall not exceed 0.5 times the least column dimension.

(3) The minimum reinforcement ratio for continuous longitudinal reinforcing, ρ sr , shall be 0.004, where ρ sr is given by:

A g =gross area of composite member, in 2 (mm 2 )

A sr =area of continuous reinforcing bars, in 2 (mm 2 )

User Note: Refer to Sections 7.10 and 10.9.3 of ACI 318 for additional tie and spiral reinforcing provisions.

The design compressive strength (φ c P n) and allowable compressive strength (P n /Ω c) of doubly symmetric axially loaded encased composite members are determined for the limit state of flexural buckling based on member slenderness For Load and Resistance Factor Design (LRFD), the design compressive strength is φ c = 0.75, while for Allowable Stress Design (ASD), the allowable compressive strength is Ω c = 2.00.

P e =elastic critical buckling loaddetermined in accordance with Chapter C or Appendix 7, kips (N)

A c =area of concrete, in 2 (mm 2 )

A s =area of the steel section, in 2 (mm 2 )

E c =modulus of elasticity of concrete

EI eff ective stiffnessof composite section, kip-in 2 (N-mm 2 )

C 1 =coefficient for calculation of effective rigidity of an encased composite compression member

E s =modulus of elasticity of steel

F y =specified minimum yield stressof steel section, ksi (MPa)

F ysr =specified minimum yield stress of reinforcing bars, ksi (MPa)

I c =moment of inertia of the concrete section about the elastic neutral axis of the composite section, in 4 (mm 4 )

I s =moment of inertia of steel shape about the elastic neutral axis of the composite section, in 4 (mm 4 )

I sr =moment of inertia of reinforcing bars about the elastic neutral axis of the composite section, in 4 (mm 4 )

L =laterally unbraced lengthof the member, in (mm) f c ′ =specified compressive strength of concrete, ksi (MPa) w c =weight of concrete per unit volume (90 ≤w c ≤155 lbs /ft 3 or 1500 ≤w c ≤

The available compressive strength need not be less than that specified for the bare steel member as required by Chapter E.

The available tensile strength of axially loaded encased composite membersshall be determined for the limit state of yieldingas follows:

Loadtransfer requirements for encased composite membersshall be determined in accordance with Section I6.

Clear spacing between the steel core and longitudinal reinforcing shall be a minimum of 1.5 reinforcing bar diameters, but not less than 1.5 in (38 mm).

To prevent buckling of individual encased steel shapes in a composite cross section before the concrete hardens, it is essential to interconnect these shapes using lacing, tie plates, batten plates, or similar components.

For filled composite members, the cross-sectional area of the steel section shall comprise at least 1% of the total composite cross section.

Filled composite members shall be classified for local bucklingaccording to Section I1.4.

The compressive strength of axially loaded doubly symmetric filled composite members must be assessed for the limit state of flexural buckling, following the guidelines outlined in Section I2.1b, with specified modifications.

C 2 =0.85 for rectangular sections and 0.95 for round sections (b) For noncompact sections

(I2-9c) where λ, λ p and λ r are slenderness ratios determined from Table I1.1a

0 7 ⎠⎟ where (i) For rectangular filled sections

(ii) For round filled sections

The effective stiffness of the composite section, EI eff , for all sections shall be:

C 3 = coefficient for calculation of effective rigidity of filled composite compression member

The available compressivestrengthneed not be less than specified for the bare steel member as required by Chapter E.

The available tensile strengthof axially loaded filled composite members shall be determined for the limit state of yieldingas follows:

Load transfer requirements for filled composite members shall be determined in accordance with Section I6.

DESIGN OF CONNECTIONS

Design Basis

The design strength, φR n , and the allowable strength R n /Ω, of connectionsshall be determined in accordance with the provisions of this chapter and the provisions of Chapter B.

The strength of connections must be established through structural analysis based on the designated design loads, in line with the specified construction type, or as a percentage of the required strength of the connected members when indicated.

Where the gravity axes of intersecting axially loaded members do not intersect at one point, the effects of eccentricity shall be considered.

Simple Connections

Simple connections for beams, girders, and trusses should be designed as flexible and can be sized based solely on the reaction shears, unless specified otherwise in the design documents These flexible beam connections must allow for end rotations of simple beams, and some inelastic yet self-limiting deformation in the connection is acceptable to facilitate this end rotation.

Moment Connections

End connections of restrained beams, girders, and trusses must be engineered to accommodate the combined forces from moment and shear due to connection rigidity For specific guidelines on moment connections, refer to Section B3.6b.

User Note:See Chapter C and Appendix 7 for analysis requirements to establish the required strengthfor the design of connections.

Compression Members With Bearing Joints

Compression members relying on bearingfor loadtransfer shall meet the following requirements:

(1) When columnsbear on bearing plates or are finished to bear at splices, there shall be sufficient connectors to hold all parts securely in place

When compression members, excluding columns, are prepared to bear loads, the splice material and connectors must be aligned to maintain the integrity of all components Their strength requirements will be determined by the lesser of the specified criteria.

(i) An axial tensile force of 50% of the required compressive strength of the member; or

When a transverse load is applied at the splice location of a member, it should equal 2% of the member's required compressive strength This load must be considered independently of any other loads acting on the member For the analysis of shear and moment at the splice, the member is assumed to be pinned.

User Note:All compression joints should also be proportioned to resist any tension developed by theload combinations stipulated in Section B2.

When transmitting tensile forces through splices in heavy sections using complete-joint-penetration groove (CJP) welds, specific provisions must be followed, including material notch-toughness requirements, weld access hole details, filler metal specifications, and thermal cut surface preparation and inspection criteria However, these provisions do not apply to splices of built-up shapes that are welded before assembly.

CJP groove welded splices in heavy sections can lead to harmful effects due to weld shrinkage Compression members experiencing tensile forces may be less prone to shrinkage damage when using partial-joint-penetration (PJP) groove welds on flanges, fillet-welded web plates, or bolts for part or all of the splice.

Weld Access Holes

Weld access holes must be designed to accommodate necessary weld backing, ensuring they are appropriately sized for effective welding operations The length of the access hole should be at least 1.5 times the thickness of the material or a minimum of 1.5 inches (38 mm) Additionally, the height of the access hole must be no less than the thickness of the material itself.

3/4in (19 mm), nor does it need to exceed 2 in (50 mm).

When preparing sections that are rolled or welded before cutting, the web's edge must be sloped or curved from the flange surface to the access hole's reentrant surface For hot-rolled and built-up shapes featuring complete joint penetration (CJP) groove welds connecting the web to the flange, it is crucial that weld access holes remain free of notches and sharp reentrant corners.

No arc of the weld access hole shall have a radius less than 3 /8in (10 mm).

In built-up shapes featuring fillet or partial-joint-penetration groove welds connecting the web to the flange, it is essential that weld access holes are devoid of notches and sharp reentrant corners Additionally, these access holes may end perpendicular to the flange, as long as the weld is terminated at a distance at least equal to the size of the weld away from the access hole.

For heavy sections as outlined in Sections A3.1c and A3.1d, it is essential to grind the thermally cut surfaces of weld access holes to bright metal and inspect them using magnetic particle or dye penetrant methods before applying splice welds However, if the curved transition of the weld access holes is created from predrilled or sawed holes, grinding is not required for that section Additionally, weld access holes of different shapes do not need to be ground or inspected using dye penetrant or magnetic particle methods.

Placement of Welds and Bolts

When designing connections for structural members, it is essential that groups of welds or bolts transmitting axial force are sized to ensure their center of gravity aligns with that of the member This alignment is crucial unless specific measures are taken to account for any eccentricity However, this requirement does not apply to the end connections of single angle, double angle, or similar structural members.

Bolts in Combination With Welds

Bolts are not typically regarded as load-sharing components alongside welds, with the exception of shear connections using any grade of bolts allowed by Section A3.3 These bolts must be installed in standard holes or short slots that are perpendicular to the load direction and can share the load with longitudinally loaded fillet welds However, in these connections, the strength of the bolts should not exceed 50% of the strength of bearing-type bolts in the connection.

When making welded modifications to structures, it is acceptable to use existing rivets and high-strength bolts that meet slip-critical connection standards to support the loads present during the alteration The welding performed should only provide the additional strength necessary for the changes being made.

High-Strength Bolts in Combination With Rivets

In both new constructions and modifications, slip-critical connections that comply with Section J3 allow for high-strength bolts to be recognized as load-sharing components alongside existing rivets.

Limitations on Bolted and Welded Connections

Joints with pretensioned boltsor welds shall be used for the following connections:

(1)Column splicesin all multi-story structures over 125 ft (38 m) in height

(2) Connections of all beamsand girdersto columns and any other beams and girders on which the bracingof columns is dependent in structures over 125 ft (38 m) in height

(3) In all structures carrying cranes of over 5 ton (50 kN) capacity: roof truss splices and connections of trusses to columns; column splices; column bracing; knee braces; and crane supports

(4) Connections for the support of machinery and other live loads that produce impact or reversal of load

Snug-tightened jointsor joints with ASTM A307 bolts shall be permitted except where otherwise specified.

This Specification adheres to all provisions of AWS D1.1/D1.1M, except where specific AISC Specification Sections are referenced, which take precedence over the corresponding AWS provisions.

(1) Section J1.6 in lieu of AWS D1.1/D1.1M, Section 5.17.1

(2) Section J2.2a in lieu of AWS D1.1/D1.1M, Section 2.4.2.10

(3) Table J2.2 in lieu of AWS D1.1/D1.1M, Table 2.1

(4) Table J2.5 in lieu of AWS D1.1/D1.1M, Table 2.3

(5) Appendix 3, Table A-3.1 in lieu of AWS D1.1/D1.1M, Table 2.5

(6) Section B3.11 and Appendix 3 in lieu of AWS D1.1/D1.1M, Section 2, Part C

(7) Section M2.2 in lieu of AWS D1.1/D1.1M, Sections 5.15.4.3 and 5.15.4.4

Groove Welds

The effective area of groove weldsshall be considered as the length of the weld times the effective throat.

The effective throat of a complete-joint-penetration (CJP) groove weldshall be the thickness of the thinner part joined.

The effective throat of a partial-joint-penetration (PJP) groove weld shall be as shown in Table J2.1.

TABLE J2.1 Effective Throat of Partial-Joint-Penetration Groove Welds

V (vertical), (AWS D1.1/D1.1M, Welding Process OH (overhead) Figure 3.3) Effective Throat

Shielded metal arc (SMAW) J or U groove

Gas metal arc (GMAW) All

Shielded metal arc (SMAW) All

45 ° bevel Gas metal arc (GMAW)

Flux cored arc (FCAW) V, OH depth of groove depth of groove depth of groove minus 1 / 8 in.

The effective throat of a partial-joint-penetration groove weld is influenced by the welding process and position Design drawings must specify either the required effective throat or the necessary weld strength Additionally, the fabricator should provide detailed joint specifications based on the chosen welding process and position.

The effective weld throat for flare groove welds, when filled flush to the surface of a round bar or a 90° bend in a formed section or rectangular HSS, is specified in Table J2.2, unless alternative effective throats are validated through testing For flare groove welds that are not filled flush, the effective throat is determined by referencing Table J2.2 and subtracting the maximum perpendicular dimension from a line that is flush to the base metal surface to the weld surface.

Larger effective throats than specified in Table J2.2 are allowed for a welding procedure specification (WPS) if the fabricator can demonstrate consistent production through qualification This qualification involves sectioning the weld perpendicular to its axis at both mid-length and terminal ends The sectioning must be conducted on various combinations of material sizes that represent the range intended for fabrication.

TABLE J2.2 Effective Weld Throats of Flare

Welding Process Flare Bevel Groove [a] Flare V-Groove

For flare bevel grooves with a radius (R) less than 3/8 inch (10 mm), it is essential to utilize only reinforcing fillet welds on filled flush joints Note that the radius of the joint surface can typically be assumed to be twice the thickness (2t) for hollow structural sections (HSS).

TABLE J2.3 Minimum Effective Throat of Partial-Joint-Penetration Groove Welds

Material Thickness of Minimum Effective Thinner Part Joined, in (mm) Throat, [a] in (mm)

Over 1 / 4 (6) to 1 / 2 (13) 3 / 16 (5) Over 1 / 2 (13) to 3 / 4 (19) 1 / 4 (6) Over 3 / 4 (19) to 1 1 / 2 (38) 5 / 16 (8) Over 1 1 / 2 (38) to 2 1 / 4 (57) 3 / 8 (10)

The minimum effective throat of a partial-joint-penetration groove weld must meet or exceed the size necessary to transmit calculated forces, as well as the dimensions specified in Table J2.3 Additionally, the minimum weld size is determined by the thinner of the two components being joined.

Fillet Welds

The effective area of a fillet weld is calculated by multiplying the effective length by the effective throat The effective throat is defined as the shortest distance from the root to the face of the weld If tests demonstrate consistent penetration beyond the root, an increase in the effective throat is allowed based on the production process and procedure variables.

For fillet welds in holes and slots, the effective length is determined by the centerline of the weld along the throat's center plane In instances of overlapping fillets, the effective area must not surpass the nominal cross-sectional area of the hole or slot at the faying surface.

Fillet welds must have a minimum size that meets the calculated force requirements or adheres to the specifications outlined in Table J2.4 However, these requirements do not extend to fillet weld reinforcements for partial- or complete-joint-penetration groove welds Additionally, there are maximum size limits for fillet welds on connected parts.

(a) Along edges of material less than 1 /4-in (6 mm) thick; not greater than the thickness of the material.

Welding along the edges of materials with a thickness of 1/4 inch (6 mm) or more should not exceed the material's thickness minus 1/16 inch (2 mm), unless specified otherwise in the drawings for full-throat thickness In the as-welded state, the gap between the base metal edge and the weld toe may be less than 1/16 inch (2 mm) as long as the weld size is clearly verifiable.

The minimum length of fillet welds, based on strength requirements, must be at least four times the nominal weld size; otherwise, the effective size will be limited to a maximum of one quarter of its length In cases where longitudinal fillet welds are solely used for end connections of flat-bar tension members, each weld's length must equal or exceed the perpendicular distance between them For further details on the impact of longitudinal fillet weld length in end connections on the effective area of the connected member, refer to Section D3.

TABLE J2.4 Minimum Size of Fillet Welds

Material Thickness of Minimum Size of

Thinner Part Joined, in (mm) Fillet Weld, [a] in (mm)

[a] Leg dimension of fillet welds Single pass welds must be used.

Note: See Section J2.2b for maximum size of fillet welds.

For end-loaded fillet welds measuring up to 100 times the weld size, the effective length can be considered equal to the actual length However, if the length of the end-loaded fillet weld exceeds this limit, the effective length must be calculated by applying a reduction factor, β This factor is determined using the formula β = 1.2 - 0.002(l/w), where 'l' represents the actual length of the weld in inches (or mm), and 'w' denotes the size of the weld leg in inches (or mm) It is important to note that β cannot exceed 1.0.

When the length of the weld exceeds 300 times the leg size, w, the effective length shall be taken as 180w.

Intermittent fillet welds are allowed for transferring calculated stress across joints and faying surfaces, as well as for connecting components in built-up members Each segment of intermittent fillet welding must be at least four times the size of the weld, with a minimum length of 1.5 inches (38 mm).

Inlap joints must have a minimum lap length of five times the thickness of the thinner joined part, with a minimum requirement of 1 inch (25 mm) When joining plates or bars under axial stress using only transverse fillet welds, both ends of the lapped parts should be fillet welded, unless the deflection is adequately restrained to prevent joint opening under maximum load.

Fillet weld terminations are permitted to be stopped short or extend to the ends or sides of parts or be boxed except as limited by the following:

For overlapping member elements where one connected part extends beyond the edge of another under tensile stress, fillet welds must terminate at least the size of the weld away from that edge.

For connections that require flexibility in outstanding elements, the length of end returns should not exceed four times the nominal size of the weld or half the width of the part.

Fillet welds that connect transverse stiffeners to plate girder webs with a thickness of 3/4 inch (19 mm) or less must terminate between four to six times the web thickness from the toe of the web-to-flange welds, unless the stiffeners are directly welded to the flange.

(4) Fillet welds that occur on opposite sides of a common plane shall be interrupted at the corner common to both welds.

Fillet weld terminations should be positioned about one weld size away from the connection edge to reduce notching in the base metal Terminating fillet welds at the joint's end, except for those linking stiffeners to girder webs, does not require correction.

Fillet welds in holes or slots are allowed to transmit shear and prevent separation of lapped parts, as well as to connect components of built-up members These fillet welds may overlap, provided they adhere to the guidelines outlined in Section J2 However, it is important to note that fillet welds in holes or slots should not be classified as plug or slot welds.

Plug and Slot Welds

The effective shearing area of plugand slot weldsshall be considered as the nominal cross-sectional area of the hole or slot in the plane of the faying surface.

Plug or slot welds are allowed for transmitting shear in lap joints, preventing buckling or separation of lapped components, and joining parts of built-up members.

The diameter of plug weld holes must be at least the thickness of the part plus 5/16 inch (8 mm), rounded up to the nearest larger odd 1/16 inch (or even mm) Additionally, the diameter should not exceed the minimum diameter plus 1/8 inch (3 mm) or 2.25 times the thickness of the weld.

The minimum center-to-center spacing of plug welds shall be four times the diameter of the hole.

The maximum length of a slot weld should not surpass 10 times the thickness of the weld itself Additionally, the width of the slot must be at least equal to the thickness of the part it is incorporated into, ensuring structural integrity and compliance with welding standards.

The slot dimensions must be 5/16 inch (8 mm) rounded to the next larger odd 1/16 inch (or even mm), and should not exceed 2 1/4 times the thickness of the weld Additionally, the ends of the slot should be semicircular or have corners rounded to a radius that is at least equal to the thickness of the part, except for the ends that reach the edge of the part.

For optimal slot weld performance, ensure that the minimum spacing between lines of slot welds, measured transversely, is four times the width of the slot Additionally, maintain a minimum center-to-center spacing in the longitudinal direction of two times the length of the slot.

For materials with a thickness of 5/8 inch (16 mm) or less, the thickness of plug or slot welds must match the material thickness For materials exceeding 5/8 inch (16 mm) in thickness, the weld thickness should be at least half of the material thickness, with a minimum requirement of 5/8 inch (16 mm).

Strength

The design strength (φR n) and allowable strength (R n /Ω) of welded joints must be based on the lower value between the base material strength, evaluated under the limit states of tensile and shear rupture, and the weld metal strength, assessed according to the limit state of rupture.

The nominal effective stress area is crucial for understanding load types and their relationship to metal strength in welding applications It is essential to consider the direction relative to the weld axis, as well as the required filler metal specifications The effective stress area is expressed in terms of load (F nBM or A BM) and is measured in ksi (MPa) per square inch (in² or mm²), which directly impacts the integrity and performance of welded joints Proper assessment of these factors ensures optimal welding outcomes and structural reliability.

COMPLETE-JOINT-PENETRATION GROOVE WELDS

Matching filler metal shall be used For T- and

Tension corner joints with backing

When welding, it is essential to use a notch-tough filler metal, particularly when the weld axis is oriented normally According to Section J2.6, the filler metal should possess a strength level that is either equal to or one level lower than that of the compression strength It is acceptable to use a filler metal that is less strong than the matching filler metal, provided it meets these criteria.

Tension or Filler metal with a compression strength level equal to

Parallel to weld axis or less than matching filler metal is permitted.

Shear Strength of the joint is controlled Matching filler metal by the base metal shall be used [c]

PARTIAL-JOINT-PENETRATION GROOVE WELDS INCLUDING FLARE V-GROOVE

AND FLARE BEVEL GROOVE WELDS φ = 0.75

Base Ω = 2.00 F u See J4 φ = 0.80 Weld Ω = 1.88 0.60F EXX See J2.1a Compression

Column to base plate and column splices designed per

Base Ω = 1.67 F y See J4 φ = 0.80 Weld Ω = 1.88 0.60F EXX See J2.1a φ = 0.90

Base Ω = 1.67 F y See J4 φ = 0.80 Weld Ω = 1.88 0.90F EXX See J2.1a

TABLE J2.5 Available Strength of Welded Joints, ksi (MPa)

Filler metal with a strength level equal to or less than matching filler metal is permitted.

Strength of the joint is controlled by the base metal

Tension or compression in parts joined parallel to a weld need not be considered in design of welds joining the parts.

Compressive stress need not be considered in design of welds joining the parts.

Connections of members designed to bear other than columns as described in Section J1.4(2)

Connections not finished-to-bear

The nominal effective stress area is crucial for understanding load types and their relation to metal strength in welding applications It is essential to consider the required filler direction relative to the weld axis, as this impacts the effective load and the metal's strength, measured in ksi (MPa) per square inch (mm²) Proper assessment of these factors ensures optimal welding performance and structural integrity.

FILLET WELDS INCLUDING FILLETS IN HOLES AND SLOTS AND SKEWED T–JOINTS

Base Governed by J4 φ = 0.75 Weld Ω = 2.00 0.60F EXX [d] See J2.2a

Base Governed by J4 φ = 0.75 Weld Ω = 2.00 0.60F EXX See J2.3a

Shear Parallel to faying surface on the effective area

TABLE J2.5 (continued) Available Strength of Welded Joints, ksi (MPa)

Filler metal with a strength level equal to or less than matching filler metal is permitted.

[a] For matching weld metal see AWS D1.1/D1.1M, Section 3.3.

[b] Filler metal with a strength level one strength level greater than matching is permitted.

Filler metals with lower strength levels can be utilized for groove welds in built-up sections that transfer shear loads or in situations with significant restraint In such cases, it is essential to detail the weld joint properly and design the weld based on the material thickness as the effective throat, applying φ = 0.80, Ω = 1.88, and 0.60F EXX as the nominal strength.

Section J2.4(a) allows for certain provisions as long as the deformation compatibility of the weld elements is taken into account Additionally, Sections J2.4(b) and (c) serve as specific applications of Section J2.4(a), ensuring the consideration of deformation compatibility in these contexts.

F nBM = nominal stressof the base metal, ksi (MPa)

F nw = nominal stress of the weld metal, ksi (MPa)

A BM = cross-sectional area of the base metal, in 2 (mm 2 )

A we = effective area of the weld, in 2 (mm 2 ) The values of φ, Ω, F nBM and F nw and limitations thereon are given in Table J2.5.

Alternatively, for fillet weldsthe available strengthis permitted to be determined as follows: φ =0.75 (LRFD) Ω =2.00 (ASD)

(a) For a linear weld group with a uniform leg size, loaded through the center of gravity

F nw =0.60F EXX 共1.0 +0.50 sin 1.5 θ兲 (J2-5)

F EXX =filler metalclassification strength, ksi (MPa) θ =angle of loading measured from the weld longitudinal axis, degrees

User Note:A linear weld group is one in which all elements are in a line or are parallel.

In the analysis of weld elements within a weld group using the instantaneous center of rotation method, the nominal strength components, R nx and R ny, along with the nominal moment capacity, M n, can be determined through specific calculations.

M n = ∑关 F nwiy A wei (x i )⫺F nwix A wei (y i )兴 (J2-7) where

A wei ective area of weld throat of the ith weld element, in 2 (mm 2 )

F nwi =0.60F EXX 共1.0 +0.50sin 1.5 θ i 兲f共p i 兲 (J2-8) f共p i 兲 =关p i 共1.9⫺0.9p i )兴 0.3 (J2-9)

F nwi =nominal stress in the ith weld element, ksi (MPa)

F nwix =x-component of nominal stress, F nwi , ksi (MPa)

The nominal stress's y-component, denoted as F nwiy (ksi or MPa), is critical for understanding deformation in weld elements The ratio of deformation for element i, p i, is defined as Δ i /Δ mi, linking its deformation to maximum stress The distance from the instantaneous center of rotation to the weld element with the minimum Δ ui /r i ratio is represented by r cr, while r i indicates the distance to the ith weld element Deformations are expressed as Δ i = r i Δ ucr / r cr, showing how the ith weld element deforms at an intermediate stress level, proportional to critical deformation based on r i Maximum stress deformation for element i is given by Δ mi = 0.209(θ i + 2) - 0.32w The ultimate stress deformation, Δ ui, is defined as 1.087(θ i + 6) - 0.65w, capped at 0.17w, and typically occurs in the element farthest from the instantaneous center of rotation The angle θ i represents the angle between the longitudinal axis of the ith weld element and the direction of the resultant force acting on it.

For fillet weld groups that are concentrically loaded and feature elements with a uniform leg size, oriented both longitudinally and transversely to the applied load, the combined strength, denoted as Rn, must be calculated accordingly.

Base Metal Matching Filler Metal

A36 ≤ 3 / 4 in thick 60 & 70 ksi filler metal

A1011 A992 Other processes: 70 ksi filler metal

*For corrosion resistance and color similar to the base metal, see AWS D1.1/D1.1M, subclause 3.7.3.

Filler metals shall meet the requirements of AWS A5.1, A5.5, A5.17, A5.18, A5.20, A5.23, A5.28 or A5.29

When welding joints with base metals of varying strengths, it's essential to choose a filler metal that either matches the strength of the stronger base metal or corresponds to the weaker base metal, ensuring a low hydrogen deposit.

The User Note Table provides a summary of the AWS D1.1/D1.1M guidelines regarding the matching of filler metals It is important to be aware that additional restrictions may apply For a comprehensive list of base metals and their corresponding prequalified matching filler metals, please refer to Table 3.1 in the AWS D1.1/D1.1M document.

R nwl =total nominal strength of longitudinally loaded fillet welds, as determined in accordance with Table J2.5, kips (N)

R nwt =total nominal strength of transversely loaded fillet welds, as determined in accordance with Table J2.5 without the alternate in Section J2.4(a),kips (N)

Combination of Welds

When combining different types of welds, such as groove, fillet, plug, and slot welds, within a single joint, it is essential to calculate the strength of each weld type individually This calculation should be based on the axis of the group to accurately assess the overall strength of the combined weld joint.

Filler Metal Requirements

When selecting filler metal for complete-joint-penetration groove welds subjected to tension normal to the effective area, it is essential to adhere to the matching filler metal requirements outlined in AWS D1.1/D1.1M.

Filler metal with a specified minimum Charpy V-notch toughnessof 20 ft-lb (27 J) at 40 °F (4 °C) or lower shall be used in the following joints:

Complete joint penetration groove welded T- and corner joints, with steel backing left in place, are subjected to tension normal to the effective area This is unless the joints are designed using the nominal strength and resistance factor or safety factor applicable for a partial joint penetration groove weld.

(2) Complete-joint-penetration groove welded splicessubject to tension normal to the effective area in heavy sections as defined in Sections A3.1c and A3.1d

The manufacturer’s Certificate of Conformance shall be sufficient evidence of compliance.

Mixed Weld Metal

To ensure Charpy V-notch toughness, it is essential that all welding consumables used for weld metal, tack welds, root passes, and subsequent passes are compatible, resulting in a notch-tough composite weld metal.

High-Strength Bolts

Use of high-strength boltsshall conform to the provisions of the Specification for

The RCSC Specification, endorsed by the Research Council on Structural Connections, outlines the use of high-strength bolts in structural joints, categorizing them based on material strength, unless specified otherwise in the document.

Group A—ASTM A325, A325M, F1852, A354 Grade BC, and A449

Group B—ASTM A490, A490M, F2280, and A354 Grade BD

When assembled, all joint surfaces, including those adjacent to the washers, shall be free of scale, except tight mill scale

Bolts are permitted to be installed to the snug-tight condition when used in:

(a) bearing-type connections except as noted in Section E6 or Section J1.10

(b) tension or combined shear and tension applications, for Group A bolts only, where loosening or fatiguedue to vibration or loadfluctuations are not design considerations

The snug-tight condition refers to the necessary tightness that ensures the connected plies are in firm contact Any bolts that need to be tightened beyond this snug-tight condition must be clearly marked on the design drawings.

High-strength bolts designated in design drawings for pretensioned or slip-critical joints must be tightened to a minimum tension specified in Table J3.1 or J3.1M Acceptable installation methods include the turn-of-nut method, direct-tension indicators, twist-off-type tension-control bolts, calibrated wrenches, or alternative design bolts.

When it comes to snug-tight bolts, there are no defined minimum or maximum tension requirements Fully pretensioned bolts, like ASTM F1852 or F2280, are allowed unless the design drawings explicitly prohibit their use.

TABLE J3.1 Minimum Bolt Pretension, kips*

Bolt Size, in Group A (e.g., A325 Bolts) Group B ( e.g., A490 Bolts)

*Equal to 0.70 times the minimum tensile strength of bolts, rounded off to nearest kip, as specified in ASTM specifications for A325 and A490 bolts with UNC threads.

TABLE J3.1M Minimum Bolt Pretension, kN*

Bolt Size, mm Group A ( e.g., A325M Bolts) Group B ( e.g., A490M Bolts)

*Equal to 0.70 times the minimum tensile strength of bolts, rounded off to nearest kN, as specified in ASTM specifications for A325M and A490M bolts with UNC threads.

When bolt specifications exceed the limitations set by the RCSC, such as lengths greater than 12 diameters or diameters larger than 1 1/2 inches (38 mm), it is essential to utilize bolts or threaded rods that meet the standards of Group A or Group B.

B materials are permitted to be used in accordance with the provisions for threaded parts in Table J3.2.

When utilizing ASTM A354 Grade BC, A354 Grade BD, or A449 bolts and threaded rods in slip-critical connections, it is essential that the bolt geometry—including thread pitch, thread length, head, and nut—meets or is proportionally larger than the specifications outlined in the RCSC Specification Additionally, installation must adhere to all relevant RCSC requirements, with necessary adjustments made for any increases in diameter and/or length to ensure proper design pretension.

Size and Use of Holes

The maximum allowable hole sizes for bolts are specified in Table J3.3 or Table J3.3M However, larger holes are permitted in column base details to accommodate the tolerance required for the positioning of anchor rods in concrete foundations.

According to the specifications, standard holes or short-slotted holes should be placed transversely to the load direction, unless there is approval for oversized holes, short-slotted holes aligned with the load, or long-slotted holes.

16.1–120 BOLTS AND THREADED PARTS [Sect J3.

TABLE J3.2 Nominal Strength of Fasteners and Threaded Parts, ksi (MPa)

Nominal Shear Strength in Nominal Tensile Strength, Bearing-Type Connections, Description of Fasteners F nt , ksi (MPa) [a] F nv , ksi (MPa) [b]

Group A (e.g., A325) bolts, when threads are not excluded 90 (620) 54 (372) from shear planes

Group A (e.g., A325) bolts, when threads are excluded 90 (620) 68 (469) from shear planes

Group B (e.g., A490) bolts, when threads are not excluded 113 (780) 68 (469) from shear planes

Group B (e.g., A490) bolts, when threads are excluded 113 (780) 84 (579) from shear planes

Threaded parts meeting the requirements of Section A3.4, when threads are not excluded 0.75F u 0.450F u from shear planes

Threaded parts meeting the requirements of Section A3.4, when threads are excluded 0.75F u 0.563F u from shear planes

[a] For high-strength bolts subject to tensile fatigue loading, see Appendix 3.

For end-loaded connections where the fastener pattern length exceeds 38 inches (965 mm), the value of F nv must be adjusted to 83.3% of the listed values The fastener pattern length refers to the maximum distance, aligned with the line of force, between the centers of bolts that join two components sharing a single faying surface.

[c] For A307 bolts the tabulated values shall be reduced by 1% for each 1 / 16 in (2 mm) over 5 diameters of length in the grip.

[d] Threads permitted in shear planes.

Standard Oversize Short-Slot Long-Slot

(Dia.) (Dia.) (Width ⴛ Length) (Width ⴛ Length)

TABLE J3.3 Nominal Hole Dimensions, in

Standard Oversize Short-Slot Long-Slot (Dia.) (Dia.) (Width ⴛ Length) (Width ⴛ Length)

[a] Clearance provided allows the use of a 1-in bolt if desirable.

TABLE J3.3M Nominal Hole Dimensions, mm

The engineer of record specifies the diameter in millimeters, allowing for finger shims up to 1/4 inch (6 mm) in slip-critical connections These connections, designed with standard holes, must maintain the nominal shear strength of the fastener as outlined for slotted holes.

Oversized holes are allowed in slip-critical connections across any or all plies, but their use is prohibited in bearing-type connections To ensure proper performance, hardened washers must be placed over oversized holes in the outer ply.

Short-slotted holes are allowed in all layers of slip-critical or bearing-type connections, regardless of loading direction in slip-critical connections However, in bearing-type connections, the slot length must be perpendicular to the load direction Additionally, when using high-strength bolts, hardened washers that meet ASTM F436 standards must be installed over short-slotted holes in the outer layer.

For Group B bolts exceeding 1 inch (25 mm) in diameter used in slotted or oversized holes in external plies, it is essential to utilize a single hardened washer that meets ASTM F436 standards, with a minimum thickness of 5/16 inch (8 mm), instead of the standard washer.

User Note: Washer requirements are provided in the RCSC Specification, Section 6.

Long-slotted holes are allowed in only one part of either slip-critical or bearing-type connections at a faying surface, with specific orientation requirements; they can be unrestricted in slip-critical connections but must align with the load direction in bearing-type connections When used in an outer ply, these slots must be covered by plate washers or continuous bars with standard holes that fully encompass the slot after installation For high-strength bolted connections, these washers or bars must be at least 5/16 inches (8 mm) thick and made of structural grade material, though they do not need to be hardened If hardened washers are necessary for high-strength bolts, they should be placed over the outer surface of the plate washer or bar.

Minimum Spacing

The distance between centers of standard, oversized or slotted holes shall not be less than 2 2 /3times the nominal diameter, d, of the fastener; a distance of 3d is preferred.

Minimum Edge Distance

The distance from the center of a standard hole to the edge of a connected part must meet or exceed the values specified in Table J3.4 or Table J3.4M, or adhere to the requirements outlined in Section J3.10 For oversized or slotted holes, this distance should not be less than the standard hole's requirement plus the applicable increment, C2, as indicated in Table J3.5 or Table J3.5M.

The minimum edge distances specified in Tables J3.4 and J3.4M are determined by standard fabrication practices and workmanship tolerances It is essential to adhere to the relevant provisions outlined in Sections J3.10 and J4.

Maximum Spacing and Edge Distance

The maximum allowable distance from the center of any bolt to the nearest edge of connected parts is limited to 12 times the thickness of the connected part, with a maximum cap of 6 inches (150 mm) Additionally, the longitudinal spacing of fasteners between elements, such as a plate and a shape or two continuously contacting plates, must adhere to specified guidelines.

For structural members, the spacing guidelines vary based on the type of finish and material Painted or unpainted members that are not prone to corrosion should have a maximum spacing of 24 times the thickness of the thinner section or 12 inches (305 mm) Conversely, unpainted weathering steel members that may experience atmospheric corrosion must adhere to a spacing limit of 14 times the thickness of the thinner section or 7 inches.

Bolt Diameter, in Minimum Edge Distance

Lesser edge distances may be allowed if the requirements of Sections J3.10 and J4 are met; however, edge distances that fall below one bolt diameter require approval from the engineer of record.

[b] For oversized or slotted holes, see Table J3.5.

TABLE J3.4 Minimum Edge Distance [a] from Center of Standard Hole [b] to Edge of

Bolt Diameter, mm Minimum Edge Distance

Lesser edge distances may be allowed if the requirements outlined in Sections J3.10 and J4 are met; however, edge distances that fall below one bolt diameter require explicit approval from the engineer of record.

[b] For oversized or slotted holes, see Table J3.5M.

TABLE J3.4M Minimum Edge Distance [a] from Center of Standard Hole [b] to Edge of

Slotted Holes Long Axis Perpendicular to Edge Short Slots Long Slots [a]

[a] When length of slot is less than maximum allowable (see Table J3.3), C 2 is permitted to be reduced by one-half the difference between the maximum and actual slot lengths.

TABLE J3.5 Values of Edge Distance Increment C 2 , in

Long Axis Parallel to Edge

Slotted Holes Long Axis Perpendicular to Edge Short Slots Long Slots [a]

[a] When length of slot is less than maximum allowable (see Table J3.3M), C 2 is permitted to be reduced by one-half the difference between the maximum and actual slot lengths.

TABLE J3.5M Values of Edge Distance Increment C 2 , mm

Long Axis Parallel to Edge

User Note: Dimensions in (a) and (b) do not apply to elements consisting of two shapes in continuous contact.

Tensile and Shear Strength of Bolts and Threaded Parts

The design tensile or shear strength (φR n) and the allowable tensile or shear strength (R n /Ω) of snug-tightened or pretensioned high-strength bolts or threaded components must be calculated based on the limit states of tension rupture and shear rupture.

A b = nominal unthreaded body area of bolt or threaded part, in 2 (mm 2 )

F n = nominal tensile stress, F nt , or shear stress, F nv , from Table J3.2, ksi (MPa)

The required tensile strengthshall include any tension resulting from prying action produced by deformation of the connected parts.

The resistance of a snug-tightened or pretensioned high-strength bolt or threaded component is constrained by the bearing strength at the bolt hole, as outlined in Section J3.10 The effective strength of each fastener is determined by the lower value between its shear strength, specified in Section J3.6, and the bearing strength at the bolt hole Additionally, the overall strength of the bolt group is calculated by summing the effective strengths of the individual fasteners.

Combined Tension and Shear in Bearing-Type Connections

The available tensile strengthof a bolt subjected to combined tension and shear shall be determined according to the limit statesof tension and shear ruptureas follows:

F nt ′ = nominal tensile stressmodified to include the effects of shear stress, ksi (MPa)

F nt = nominal tensile stress from Table J3.2, ksi (MPa)

F nv = nominal shear stress from Table J3.2, ksi (MPa) f rv = required shear stress using LRFD or ASD load combinations, ksi (MPa)

The available shear stress of the fastenershall equal or exceed the required shear stress, f rv

When the required stress, f, in shear or tension is at or below 30% of the available stress, there is no need to analyze the effects of combined stress Additionally, Equations J3-3a and J3-3b can be reformulated to determine a nominal shear stress, F′ nv, based on the required tensile stress, f t.

F f F nt nt nv rv nt

High-Strength Bolts in Slip-Critical Connections

Slip-critical connections must be designed to prevent slip and to meet the limit states of bearing-type connections It is essential that when slip-critical bolts are used with fillers, all surfaces exposed to potential slip are properly prepared to ensure the required design slip resistance is achieved.

The available slip resistance for the limit state of slip shall be determined as follows:

For standard size and short-slotted holes that are perpendicular to the load direction, the resistance factor φ is 1.00 (LRFD) and the safety factor Ω is 1.50 (ASD) In contrast, for oversized and short-slotted holes aligned with the load direction, φ is 0.85 (LRFD) and Ω is 1.76 (ASD) For long-slotted holes, φ is 0.70 (LRFD) and Ω is 2.14 (ASD) The mean slip coefficient μ is applicable for Class A or B surfaces and can be determined through established methods or testing.

(i) For Class A surfaces (unpainted clean mill scalesteel surfaces or surfaces with Class A coatings on blast-cleaned steel or hot-dipped galvanized and roughened surfaces) μ =0.30

(ii) For Class B surfaces (unpainted blast-cleaned steel surfaces or surfaces with Class B coatings on blast-cleaned steel) μ =0.50

D u = 1.13 is a crucial multiplier representing the ratio of the average installed bolt pretension to the minimum specified bolt pretension Alternative values may be permitted upon approval from the engineer of record.

T b =minimum fastenertension given in Table J3.1, kips, or Table J3.1M, kN h f tor for fillers, determined as follows:

(i) Where there are no fillers or where bolts have been added to distribute loads in the filler h f =1.0

(ii) Where bolts have not been added to distribute the loadin the filler: (a) For one filler between connected parts h f =1.0 (b) For two or more fillers between connected parts h f =0.85

Combined Tension and Shear in Slip-Critical Connections

In slip-critical connections, when an applied tension decreases the net clamping force, the slip resistance per bolt, as outlined in Section J3.8, must be multiplied by the factor k_sc.

T a =required tension force using ASD load combinations, kips (kN)

T u =required tension force using LRFD load combinations, kips (kN) n b =number of bolts carrying the applied tension

Bearing Strength at Bolt Holes

The available bearing strength, φR n and R n /Ω, at bolt holes shall be determined for the limit state ofbearingas follows: φ =0.75 (LRFD) Ω =2.00 (ASD)

The nominal bearing strength of the connected material, R n , is determined as follows:

For a bolt in a connection featuring standard, oversized, and short-slotted holes, the performance remains consistent regardless of the loading direction This also applies to long-slotted holes when the slot is aligned parallel to the bearing force direction.

(i) When deformation at the bolt hole at service loadis a design consideration

(ii) When deformation at the bolt hole at service load is not a design consideration

(b) For a bolt in a connection with long-slotted holes with the slot perpendicular to the direction of force

(c) For connections made using bolts that pass completely through an unstiffened box member or HSS, see Section J7 and Equation J7-1; where

The specified minimum tensile strength of the connected material, denoted as F u, is measured in ksi (MPa) The nominal bolt diameter is represented by d, indicated in inches (mm) The clear distance, l c, refers to the space in the direction of the force between the edge of the hole and the edge of the adjacent hole or the material's edge, also measured in inches (mm) Lastly, t signifies the thickness of the connected material, expressed in inches (mm).

For connections, the bearing resistance shall be taken as the sum of the bearing resist- ances of the individual bolts.

Bearing strength must be verified for both bearing-type and slip-critical connections According to Section J3.2, the use of oversized holes, as well as short and long slotted holes aligned with the force direction, is limited to slip-critical connections.

The effective strength of a fastener is determined by the lower value between its shear strength, as outlined in Section J3.6, and the bearing strength at the bolt hole, according to Section J3.10 Additionally, the overall strength of the bolt group is calculated by summing the effective strengths of each individual fastener.

Special Fasteners

The nominal strengthof special fasteners other than the bolts presented in Table J3.2 shall be verified by tests.

Tension Fasteners

When bolts or other fastenersin tension are attached to an unstiffened box or HSS wall, the strength of the wall shall be determined by rational analysis.

J4 AFFECTED ELEMENTS OF MEMBERS AND CONNECTING

This section applies to elements of members at connectionsand connecting elements,such as plates, gussets, angles and brackets.

Strength of Elements in Tension

The design strength (φR n) and allowable strength (R n /Ω) for elements subjected to tensile loads must be determined by the lower value derived from the limit states of tensile yielding and tensile rupture.

(a) For tensile yielding of connecting elements

R n =F y A g (J4-1) φ =0.90 (LRFD) Ω =1.67 (ASD) (b) For tensile rupture of connecting elements

A e =effective net areaas defined in Section D3, in 2 (mm 2 ); for bolted splice plates, A e =A n ≤0.85A g

User Note: The effective net area of the connection plate may be limited due to stressdistribution as calculated by methods such as the Whitmore section.

Strength of Elements in Shear

The available shear strength of affected and connecting elements in shear shall be the lower value obtained according to the limit statesof shear yieldingand shear rupture:

(a) For shear yielding of the element:

A gv =gross area subject to shear, in 2 (mm 2 ) (b) For shear rupture of the element:

A nv =net areasubject to shear, in 2 (mm 2 )

Block Shear Strength

The available strengthfor the limit stateof block shear rupturealong a shear failure path or paths and a perpendicular tension failure path shall be taken as

R n =0.60F u A nv +U bs F u A nt ≤0.60F y A gv +U bs F u A nt (J4-5) φ =0.75 (LRFD) Ω =2.00 (ASD) where

A nt =net areasubject to tension, in 2 (mm 2 )

Where the tension stressis uniform, U bs =1; where the tension stress is nonuniform,

User Note:Typical cases where U bs should be taken equal to 0.5 are illustrated in the Commentary.

Strength of Elements in Compression

The available strengthof connecting elements in compression for the limit statesof yieldingand bucklingshall be determined as follows:

P n =F y A g (J4-6) φ =0.90 (LRFD) Ω =1.67 (ASD)(b) When KL/r >25, the provisions of Chapter E apply.

Strength of Elements in Flexure

The flexural strength of affected elements is determined by the lowest value assessed through the limit states of flexural yielding, local buckling, flexural lateral-torsional buckling, and flexural rupture.

Fillers in Welded Connections

When using fillers in joints that need to transfer applied force, it is essential that both the fillers and the connecting welds meet the standards outlined in Section J5.1a or Section J5.1b, depending on the specific requirements.

Fillers with a thickness of less than 1/4 inch (6 mm) should not be utilized for stress transfer If the filler is either less than 1/4 inch (6 mm) thick or at least 1/4 inch (6 mm) but insufficient to effectively transfer the applied force between connected components, it must be flush with the edge of the outer connected part Additionally, the size of the weld must be increased by an amount equal to the thickness of the filler to ensure proper strength and integrity.

To ensure effective force transfer between connected components, the thickness of the filler must be sufficient and extend beyond the edges of the outer connected base metal Welds that connect the outer base metal to the filler must be robust enough to transmit the applied force, while the filler area must be designed to prevent overstressing Additionally, welds linking the filler to the inner connected base metal should also adequately transmit the applied force.

Fillers in Bolted Connections

When a load-bearing bolt passes through fillers that are 1/4 inch (6 mm) thick or thinner, the shear strength remains unchanged However, if the fillers exceed 1/4 inch (6 mm) in thickness, specific requirements must be met.

(a) The shear strength of the bolts shall be multiplied by the factor

1 ⫺0.4(t ⫺0.25) [S.I.: 1 ⫺0.0154(t ⫺6)] but not less than 0.85, where t is the total thickness of the fillers;

To ensure proper distribution of force in connected elements, the fillers must extend beyond the joint and be secured with sufficient bolts Additionally, the joint size should be increased to accommodate the total number of bolts required for effective load distribution.

16.1–130 AFFECTED ELEMENTS OF MEMBERS AND CONNECTING ELEMENTS [Sect J4.

(d) The joint shall be designed to prevent slipin accordance with Section J3.8 using either Class B surfaces or Class A surfaces with turn-of-nut tightening.

Groove-welded splices in plate girders and beams must achieve the nominal strength of the smaller spliced section Additionally, other splice types in the cross sections of plate girders and beams are required to develop the strength necessary to withstand the forces at the splice location.

The design bearing strength, φR n , and the allowable bearing strength, R n /Ω, of surfaces in contact shall be determined for the limit stateof bearing (local compressive yielding) as follows: φ =0.75 (LRFD) Ω =2.00 (ASD)

The nominal bearing strength, R n , shall be determined as follows:

(a) For finished surfaces, pins in reamed, drilled, or bored holes, and ends of fitted bearing stiffeners

A pb =projected area in bearing, in 2 (mm 2 )

F y =specified minimum yield stress, ksi (MPa)

(J7-3M) where d =diameter, in (mm) l b =length of bearing, in (mm)

J8 COLUMN BASES AND BEARING ON CONCRETE

Proper provision shall be made to transfer the column loadsand moments to the foot- ings and foundations.

16.1–132 COLUMN BASES AND BEARING ON CONCRETE [Sect J8.

In the absence of code regulations, the design bearing strength (φ c P p) and the allowable bearing strength (P p /Ω c) for the limit state of concrete crushing can be taken as φ c = 0.65 for LRFD and Ω c = 2.31 for ASD The nominal bearing strength (P p) is determined accordingly.

(a) On the full area of a concrete support:

(b) On less than the full area of a concrete support:

A 1 = area of steel concentrically bearing on a concrete support, in 2 (mm 2 )

A 2 = maximum area of the portion of the supporting surface that is geometrically similar to and concentric with the loaded area, in 2 (mm 2 ) f′ c = specified compressive strength of concrete, ksi (MPa)

Anchor rods must be engineered to resist the loads acting on the structure's column bases, including the net tensile forces from any bending moments as specified in Section B2 Additionally, the design of the anchor rods should comply with the threaded parts standards outlined in Table J3.2.

ASTM F1554 anchor rods can be provided with a body diameter smaller than the nominal size, as specified in product guidelines It is essential to calculate load effects, including bending and elongation, using the minimum diameters allowed by these specifications For detailed information, refer to ASTM F1554 and the table titled "Applicable ASTM Specifications for Various Types of Structural Fasteners" found in Part 2 of the AISC Steel Construction Manual.

The design of column bases and anchor rods must effectively transfer forces to the concrete foundation while ensuring proper bearing against the concrete elements This design should comply with the standards set forth in ACI 318 or ACI 349.

User Note: When columns are required to resist a horizontal force at the base plate, bearing against the concrete elements should be considered

When anchor rods are used to resist horizontal forces, hole size, anchor rod setting tolerance, and the horizontal movement of the column shall be considered in the design.

Oversized and slotted holes in base plates are acceptable as long as sufficient bearing is ensured for the nut This can be achieved by utilizing ASTM F844 washers or plate washers to effectively bridge the hole.

User Note: The permitted hole sizes, corresponding washer dimensions and nuts are given in the AISC Steel Construction Manualand ASTM F1554.

User Note: See ACI 318 for embedment design and for shear friction design See

OSHA for special erection requirements for anchor rods.

J10 FLANGES AND WEBS WITH CONCENTRATED FORCES

This section addresses the effects of single and double concentrated forces applied perpendicular to the flanges of wide flange sections and similar built-up shapes A single concentrated force can be either tensile or compressive, while double concentrated forces consist of one tensile and one compressive force, creating a couple on the same side of the loaded member.

When the required strength surpasses the available strength for the specified limit states, it is essential to incorporate stiffeners and/or doublers These reinforcements must be appropriately sized to address the difference between the required and available strengths for the relevant limit state Additionally, stiffeners must comply with the design criteria outlined in Section J10.8, while doublers must adhere to the requirements specified in Section J10.9.

User Note: See Appendix 6.3 for requirements for the ends of cantilever members.

Stiffeners are required at unframed endsof beamsin accordance with the requirements of Section J10.7.

Flange Local Bending

This section applies to tensile single-concentrated forcesand the tensile component of double-concentrated forces.

The design strength, φR n , and the allowable strength, R n /Ω, for the limit state of flange local bendingshall be determined as follows:

F yf =specified minimum yield stressof the flange, ksi (MPa) t f =thickness of the loaded flange, in (mm)

If the length of loading across the member flange is less than 0.15b f , where b f is the member flange width, Equation J10-1 need not be checked.

When the concentrated force to be resisted is applied at a distance from the member end that is less than 10t f , R n shall be reduced by 50%.

When required, a pair of transverse stiffenersshall be provided.

Web Local Yielding

This section applies to single-concentrated forcesand both components of double- concentrated forces.

The available strengthfor the limit stateof web local yieldingshall be determined as follows: φ =1.00 (LRFD) Ω =1.50 (ASD)

The nominal strength, R n , shall be determined as follows:

(a) When the concentrated forceto be resisted is applied at a distance from the member end that is greater than the depth of the member, d,

(b) When the concentrated force to be resisted is applied at a distance from the member end that is less than or equal to the depth of the member, d,

The specified minimum yield stress of the web material (F yw) is measured in ksi (MPa) The distance from the outer face of the flange to the web toe of the fillet is denoted as k, measured in inches (mm) The length of bearing (l b) must be no less than k for end beam reactions, also measured in inches (mm) Additionally, the thickness of the web (t w) is specified in inches (mm) When necessary, a pair of transverse stiffeners or a doubler plate should be provided to enhance structural integrity.

Web Local Crippling

This section applies to compressive single-concentrated forcesor the compressive component of double-concentrated forces.

The available strength for the limit stateof web local cripplingshall be determined as follows: φ =0.75 (LRFD) Ω =2.00 (ASD)

The nominal strength, R n , shall be determined as follows:

(a) When the concentrated compressive forceto be resisted is applied at a distance from the member end that is greater than or equal to d/2:

(b) When the concentrated compressive force to be resisted is applied at a distance from the member end that is less than d/2:

16.1–134 FLANGES AND WEBS WITH CONCENTRATED FORCES [Sect J10.

(J10-5b) where d =full nominal depth of the section, in (mm)

When required, a transverse stiffener, a pair of transverse stiffeners, or a doubler plate extending at least one-half the depth of the web shall be provided.

Web Sidesway Buckling

This section pertains exclusively to compressive single-concentrated forces acting on members, where there is no restriction on the relative lateral movement between the loaded compression flange and the tension flange at the point where the concentrated force is applied.

The available strengthof the web for the limit stateof sidesway bucklingshall be determined as follows: φ =0.85 (LRFD) Ω =1.76 (ASD) The nominal strength, R n , shall be determined as follows:

(a) If the compression flange is restrained against rotation

(ii) When (h /t w )/(L b /b f ) >2.3, the limit state of web sidesway bucklingdoes not apply.

When the web's required strength surpasses its available strength, it is essential to implement local lateral bracing at the tension flange Alternatively, one can utilize a pair of transverse stiffeners or a doubler plate to enhance structural integrity.

(b) If the compression flange is not restrained against rotation

(ii) When (h /t w )/(L b /b f ) >1.7, the limit state of web sidesway buckling does not apply.

When the web's required strength surpasses its available strength, it is essential to install local lateral bracing at both flanges where concentrated forces are applied.

In Equations J10-6 and J10-7, the following definitions apply:

C r 0,000 ksi (6.62 ⫻10 6 MPa) when M u

Tiêu đề	Specification for Structural Steel Buildings
Trường học	American Institute of Steel Construction
Chuyên ngành	Structural Steel Buildings
Thể loại	Specification
Năm xuất bản	2010
Thành phố	Chicago

Định dạng
Số trang	609
Dung lượng	8,79 MB