SOURCE 2 AISI SPECIFICATION

INTRODUCTION Housed in the construction group of the American Iron and Steel Institute (www.steel.org) ANSI approved specification for the design of cold-formed steel structural members Serves 4 primary industries: Metal buildings (www.mbma.com) Steel studs (www.ssma.com) Racks (www.rmi.com) Metal decks (www.sdi.org)

AISI SPECIFICATION EDITIONS In primary use today Basis for current LSF manual 1999 Supplement New web crippling and shear capacity calculations for C-sections with holes Changes to Base Test 2001 North American Edition Combination of Canada, Mexico, and U.S.

2001 NORTH AMERICAN SPECIFICATION Broad philosophical changes U.S., Canada &Mexico (ASD, LRFD, LSD) Load combinations removed from the Specs. Rational analysis clause when outside scope Detailed changes of interest Effective width changes webs revised based on h/b ratio flanges with multiple intermediate stiffeners revised (decks) flanges with one edge stiffener cleaned up a bit Web crippling completely revised Fastener edge distances = 1.5d (vs. 3d before) Fatigue provisions provided full list at www.umr.edu/~ccfss

2001 NORTH AMERICAN SPECIFICATION (from Section A1.1)

AISI SPECIFICATION COMPLICATION REASONS: Typical sections are not doubly-symmetric (Torsional-flexural buckling possible) Local buckling & post-buckling strength Effective width effective width = f(stress,geometry) stress = f(effective properties: e.g., Aeff, Ieff) iteration results Web crippling calculations

AISI SPECIFICATION PRESENTATION Basic overview of behavior (focusing on C Sections)

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

A. GENERAL PROVISIONS MATERIAL DESIGN BASIS TYPICAL APPROVED STEELS OTHER STEEL AND DUCTILITY REQUIREMENTS DESIGN BASIS ASD LRFD LOAD FACTORS AND LOAD COMBINATIONS STRENGTH INCREASE DUE TO COLD FORMING Complete and detailed listing of ASTM grades that are applicable for cold-formed construction are given in the AISI Specification, Section A3.1. Many of the grades are equally useable for cold-formed and hot-rolled construction. Differences appear in the products. It is possible to use other steels than those listed in A3.1. However, these have to comply with the requirements of Sections A3.2 and 3.3, especially as far as ductility is concerned. Overall, the intent is for the materials and the structural elements to display sufficient strength and ductility. ASTM A847 and A875 have been added.

REQUIRED DUCTILITY (Section A2.3.1) Fu/Fy 1.08 A. GENERAL PROVISIONS REQUIRED DUCTILITY (Section A2.3.1) Fu/Fy 1.08 Elongation 10% (two-inch gage) 7% (eight-inch gage) The criteria are applicable for steels used for members and connections. Additional ductility provisions are given for low ductility steels.

A. GENERAL PROVISIONS MATERIAL DESIGN BASIS TYPICAL APPROVED STEELS OTHER STEEL AND DUCTILITY REQUIREMENTS DESIGN BASIS ASD LRFD LOAD FACTORS AND LOAD COMBINATIONS STRENGTH INCREASE DUE TO COLD FORMING Complete and detailed listing of ASTM grades that are applicable for cold-formed construction are given in the AISI Specification, Section A3.1. Many of the grades are equally useable for cold-formed and hot-rolled construction. Differences appear in the products. It is possible to use other steels than those listed in A3.1. However, these have to comply with the requirements of Sections A3.2 and 3.3, especially as far as ductility is concerned. Overall, the intent is for the materials and the structural elements to display sufficient strength and ductility. ASTM A847 and A875 have been added.

Ru Rn A. GENERAL PROVISIONS ASD STRENGTH REQUIREMENTS (Section A4.1.1) R Rn/ LRFD STRENGTH REQUIREMENTS (Section A5.1.1) Ru Rn The required strength, R, is the load effect based on nominal loads using structural analysis and appropriate critical load combinations. The nominal strength, Rn, comes from the nominal strength equations. The Specification tabulates all factors of safety, .

A. GENERAL PROVISIONS MATERIAL DESIGN BASIS TYPICAL APPROVED STEELS OTHER STEEL AND DUCTILITY REQUIREMENTS DESIGN BASIS ASD LRFD LOAD FACTORS AND LOAD COMBINATIONS (More on this later) STRENGTH INCREASE DUE TO COLD FORMING Complete and detailed listing of ASTM grades that are applicable for cold-formed construction are given in the AISI Specification, Section A3.1. Many of the grades are equally useable for cold-formed and hot-rolled construction. Differences appear in the products. It is possible to use other steels than those listed in A3.1. However, these have to comply with the requirements of Sections A3.2 and 3.3, especially as far as ductility is concerned. Overall, the intent is for the materials and the structural elements to display sufficient strength and ductility. ASTM A847 and A875 have been added.

A. GENERAL PROVISIONS MATERIAL DESIGN BASIS TYPICAL APPROVED STEELS OTHER STEEL AND DUCTILITY REQUIREMENTS DESIGN BASIS ASD LRFD LOAD FACTORS AND LOAD COMBINATIONS STRENGTH INCREASE DUE TO COLD FORMING Complete and detailed listing of ASTM grades that are applicable for cold-formed construction are given in the AISI Specification, Section A3.1. Many of the grades are equally useable for cold-formed and hot-rolled construction. Differences appear in the products. It is possible to use other steels than those listed in A3.1. However, these have to comply with the requirements of Sections A3.2 and 3.3, especially as far as ductility is concerned. Overall, the intent is for the materials and the structural elements to display sufficient strength and ductility. ASTM A847 and A875 have been added.

A. GENERAL PROVISIONS Increase in yield and ultimate strength due to cold-work

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

LOCAL BUCKLING PLATE BUCKLING BUCKLING OF COMPONENT PLATE ELEMENTS

POST LOCAL BUCKLING STRENGTH Photo shows post buckling behavior and interaction of local and overall buckling P= 0.07 k 3.2 k 3.8 k 4.9 k 7.2 k 7.6 k Pult= 7.9 k

EFFECTIVE WIDTH CONCEPT The effective width, b, shall be determined from the following equations: where w = Flat width is a slenderness factor determined as follows:

EFFECTIVE SECTION FOR COLUMNS Actual Stresses

EFFECTIVE SECTION FOR BEAMS Actual Stresses Effective Section

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

AXIALLY LOADED COLUMNS MODES OF BUCKLING AXIALLY LOADED COLUMNS Flexural Buckling Torsional-flexural buckling Column just bends during buckling Column twists and bends during buckling

BEAMS LOCAL DISTORTIONAL LATERAL

INTERACTION OF LOCAL AND OVERALL BUCKLING Find long column elastic buckling stress Fe based on full section, Fe = min (flexural and flexural-torsional) Find nominal column buckling stress Fn using Fe Find effective column area Ae at stress Fn Column strength considering local buckling is AeFn

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

STRUCTURAL ASSEMBLIES

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

Bolted connections Welded connections Screw connections CONNECTIONS AND JOINTS Bolted connections Welded connections Screw connections (more on these topics during the numeric examples)

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

TESTS FOR SPECIAL CASES - Tests for Determining Structural Performance LRFD (Calculation of resistance factors) ASD (Calculation of factors of safety) - Tests for Confirming Structural Performance - Tests for Determining Mechanical Properties

DESIGN OF COLD-FORMED STEEL STRUCTURES USING THE 2001 AISI SPECIFICATION A. GENERAL PROVISIONS B. ELEMENTS C. MEMBERS D. STRUCTURAL ASSEMBLIES E. CONNECTIONS AND JOINTS F. TESTS FOR SPECIAL CASES G. CYCLIC LOADING (FATIGUE)

FATIGUE DESIGN Resistance to be evaluated for: Cold-formed corners and sheared edges of sections Longitudinal and transverse fillet welds Spot welds Bolt and screw connections Evaluation of fatigue resistance is not required for wind and seismic loads

An excellent reference for hand calculations. (Available from the AISI) Similar document is in preparation for Europe using Eurocode

COLD-FORMED STEEL PROVIDES OPTIMUM SOLUTIONS COLD-ROLLED (efficient and elegant solutions) HOT-ROLLED (heavy) (comparison for European sections)

AISI SPECIFICATION EXAMPLE “Simple” axially loaded column

Problem Geometry: 800S163-54, 50ksi h = 8 in. b = 1.625 in. d = 0.500 in. t = 0.0566 in. r = 0.0625 in. r d h t

Lx = 96 in. (8 ft.) Ly = 48 in. Lt = 48 in. Kx = Ky = Kt = 1 Column & support conditions: Lx = 96 in. (8 ft.) Ly = 48 in. Lt = 48 in. Kx = Ky = Kt = 1 A A AA

AISI Procedure Find gross properties Find long column elastic buckling stress (Fe) Fe = min (flexural and flexural-torsional) Find nominal column buckling stress (Fn) launder Fe through AISC column curve →Fn Find effective column area Ae at stress Fn effective width of web, heff effective width of flange, beff effective width of lip, deff Ae=t(heff+2beff+2deff) Column strength is AeFn

Centerline approximation: A centerline approximation of the geometry, ignoring corners, is allowed (centerline approximations tend to overestimate flexural and flexural-torsional buckling but are conservative on local buckling (Ae)) 800S163-54, 50ksi hCL= h - t = 8 - 0.0566 in. bCL = b - t = 1.625 - 0.0566 in. dCL = d - t/2 = 0.500 - 0.0566/2 in. t = 0.0566 in.

example completed in Mathcad®

Gross Properties

Long Column Buckling

Nominal Buckling Stress AISC column curve

Effective Area at Fn: Effective width of each element of the cross-section must be determined. The steps are find appropriate plate buckling coefficient, k determine local plate buckling slenderness, l calculate effectiveness ratio r effective width = r x full width To find k, we must know what kind of element we have (and what kind of loading – in this case pure compression) web = stiffened element flange = edge stiffened element lip = unstiffened element

Elements edge stiffened element, supported on one edge fully, other edge by a stiffener, 0.43 < k < 4, depending on stiffener size and slenderness of flange itself unstiffened element, supported on only one edge, k =0.43, assumes element is simply supported on 3 sides for local buckling consideration stiffened element, supported on both edges, k = 4 used, assumes element is simply supported on all 4 sides for local buckling consideration

Effective Width Web:

Edge Stiffened Elements (fun):

as low as it goes (unstiffened) adequate stiffener size sensitivity to stiffener ratio stiffener adequacy ratio lip/flange interaction reduction final reduction to get k

Flange:

Lip:

Ae=t(heff+2beff+2deff) Ae=0.409 in2 Ag=0.684 in2 Effective Area: Determined at Fn heff = 3.089 in. beff = 1.596 in. deff = 0.472 in. Ae=t(heff+2beff+2deff) Ae=0.409 in2 Ag=0.684 in2 Fn

Capacity Pn = AeFn = (0.409)(29.35) = 12 kips ASD Pallowable = Pn/W = (12)/(1.8) = 6.7 kips compare vs. unfactored load combinations LRFD Pnominal = fPn = (0.85)(12) = 10.2 kips compare vs. factored load combinations

How is a beam different Mn=SeffFn Fn = nominal lateral-torsional buckling stress Seff = effective section modulus Seff determination (iteration) Seff = Ieff / ycg-eff web heff = function of stress gradient stress gradient = function of ycg-eff Even symmetric sections become unsymmetric when effective width of compression flange is less than full width… iteration… Calculations become quite tiresome