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
• 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.
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.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
CYCLIC LOADING (FATIGUE)
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
A.
GENERAL PROVISIONS
• REQUIRED DUCTILITY
(Section A2.3.1)
• Fu/Fy  1.08
• Elongation  10% (two-inch gage)
 7% (eight-inch gage)
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
A.
GENERAL PROVISIONS
• ASD STRENGTH REQUIREMENTS
(Section A4.1.1)
R Rn/
• LRFD STRENGTH REQUIREMENTS
(Section A5.1.1)
Ru Rn
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
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
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.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
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:
b  w for   0.673
b  w for   0.673
where
w = Flat width
  (1  0.22/  ) / 
 is a slenderness factor
determined as follows:
  Fy / Fcr
EFFECTIVE SECTION FOR COLUMNS
Actual Stresses
Effective Section
EFFECTIVE SECTION FOR BEAMS
Actual Stresses
Effective Section
DESIGN OF COLD-FORMED STEEL
STRUCTURES
USING THE 2001 AISI SPECIFICATION
A.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
CYCLIC LOADING (FATIGUE)
MODES OF BUCKLING
AXIALLY LOADED COLUMNS
Flexural
Buckling
Column just bends
during buckling
Torsional-flexural 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.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
CYCLIC LOADING (FATIGUE)
STRUCTURAL ASSEMBLIES
DESIGN OF COLD-FORMED STEEL
STRUCTURES
USING THE 2001 AISI SPECIFICATION
A.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
CYCLIC LOADING (FATIGUE)
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.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
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.
B.
C.
D.
E.
F.
G.
GENERAL PROVISIONS
ELEMENTS
MEMBERS
STRUCTURAL ASSEMBLIES
CONNECTIONS AND JOINTS
TESTS FOR SPECIAL CASES
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
HOT-ROLLED
COLD-ROLLED
(heavy)
(efficient and
elegant solutions)
(comparison for European
sections)
AISI SPECIFICATION
EXAMPLE
“Simple” axially loaded column
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
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 flexuraltorsional 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, 
• calculate effectiveness ratio 
• effective width =  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
stiffened element,
supported on both
edges, k = 4 used,
assumes element is
simply supported on all
4 sides for local
buckling consideration
unstiffened element,
supported on only one edge,
k =0.43, assumes element is
simply supported on 3 sides
for local buckling
consideration
Web:
Effective Width
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
k aisi  3.772
Flange:
Lip:
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/ = (12)/(1.8) = 6.7 kips
compare vs. unfactored load combinations
• LRFD
Pnominal = Pn = (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