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SOURCE 2

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 )

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SOURCE 2

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  1. SOURCE 2 AISI SPECIFICATION

  2. 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)

  3. AISI SPECIFICATION EDITIONS • 1996 Edition • 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.

  4. 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 atwww.umr.edu/~ccfss

  5. 2001 NORTH AMERICAN SPECIFICATION (from Section A1.1)

  6. AISI SPECIFICATION COMPLICATIONREASONS: • 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

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

  8. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

  9. A. GENERAL PROVISIONS • MATERIAL • TYPICAL APPROVED STEELS • OTHER STEEL AND DUCTILITY REQUIREMENTS • DESIGN BASIS • ASD • LRFD • LOAD FACTORS AND LOAD COMBINATIONS • STRENGTH INCREASE DUE TO COLD FORMING

  10. A. GENERAL PROVISIONS • REQUIRED DUCTILITY(Section A2.3.1) • Fu/Fy 1.08 • Elongation 10% (two-inch gage) 7% (eight-inch gage)

  11. A. GENERAL PROVISIONS • MATERIAL • TYPICAL APPROVED STEELS • OTHER STEEL AND DUCTILITY REQUIREMENTS • DESIGN BASIS • ASD • LRFD • LOAD FACTORS AND LOAD COMBINATIONS • STRENGTH INCREASE DUE TO COLD FORMING

  12. A. GENERAL PROVISIONS • ASD STRENGTH REQUIREMENTS (Section A4.1.1)R Rn/ • LRFD STRENGTH REQUIREMENTS (Section A5.1.1) RuRn

  13. A. GENERAL PROVISIONS • MATERIAL • 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

  14. A. GENERAL PROVISIONS • MATERIAL • TYPICAL APPROVED STEELS • OTHER STEEL AND DUCTILITY REQUIREMENTS • DESIGN BASIS • ASD • LRFD • LOAD FACTORS AND LOAD COMBINATIONS • STRENGTH INCREASE DUE TO COLD FORMING

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

  16. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

  17. LOCAL BUCKLING PLATE BUCKLING BUCKLING OF COMPONENT PLATE ELEMENTS

  18. 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

  19. 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:

  20. EFFECTIVE SECTION FOR COLUMNS Effective Section Actual Stresses

  21. EFFECTIVE SECTION FOR BEAMS Actual Stresses Effective Section

  22. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

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

  24. BEAMS LOCAL DISTORTIONAL LATERAL

  25. 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

  26. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

  27. STRUCTURAL ASSEMBLIES

  28. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

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

  30. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

  31. 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

  32. DESIGN OF COLD-FORMEDSTEEL STRUCTURESUSING 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)

  33. 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

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

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

  36. AISI SPECIFICATION EXAMPLE “Simple” axially loaded column

  37. Problem Geometry: b 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

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

  39. 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

  40. 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.

  41. example completed in Mathcad®

  42. Gross Properties

  43. Long Column Buckling

  44. AISC column curve Nominal Buckling Stress

  45. 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 = rx 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

  46. 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 Elements

  47. Effective Width Web:

  48. Edge Stiffened Elements (fun):

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