2012.02.08 - cold-formed steel design - design standards (part 1)

Cold-Formed Steel Light-

Frame Construction

AISI S100 Section D4by

SE University, February 2012

by

Roger LaBoube

1

AISI Standards Development

AISI Secretariat

Committee on

Framing StandardsCommittee on

Specifications


Standards for Cold-

Formed Steel Framing

General Provisions

Design Methods

Prescriptive Methods

Specifications

Specification for the

Design of Cold-Formed

Steel Structural Members

Design Manual

Test Procedures

Design Guides 2

COFS Mission

• To eliminate regulatory barriers and

increase the reliability and cost

competitiveness of cold-formed steel


competitiveness of cold-formed steel

framing in residential and light

commercial building construction

through improved design and

installation standards.

3

Member versus System Design


4

Requirements for

Specification

General Provisions

AISI Standards Hierarchy


Design Standards


Requirements for

engineered or

prescriptive designSpecification

5

2001 Standards2003 Code Adoptions


6

2007 Standards

• Update Existing Standards:– AISI S200-07: General Provisions *

– AISI S211-07: Wall Stud Design *

– AISI S212-07: Header Design *


– AISI S213-07: Lateral Design *

– AISI S214-07: Truss Design *

– AISI S230-07: Prescriptive Method for One and Two Family Dwellings

• New Standards:– AISI S201-07: Product Standard *

– AISI S210-07: Floor and Roof System Design *

7

* North American Standards

• Intended for adoption and use in the United States, Canada and Mexico

• Integrated treatment of ASD, LRFD and LSD– Accomplished by including the appropriate


– Accomplished by including the appropriate resistance factors (φ) for use with LRFD and LSD, and the appropriate factors of safety (Ω) for use with ASD.

• LSD is limited to Canada

• LRFD and ASD are limited to Mexico and the United States

8

AISI Framing Standards

• General:– AISI S200-07: General Provisions

– AISI S201-07: Product Standard

– Code of Standard Practice, 2006 Edition

• Design Standards:– AISI S210-07: Floor and Roof System Design


– AISI S210-07: Floor and Roof System Design

– AISI S211-07: Wall Stud Design

– AISI S212-07: Header Design

– AISI S213-07: Lateral Design

– AISI S214-07: Truss Design

• Prescriptive Methods:– AISI S230-07: Prescriptive Method for One and Two Family

Dwellings

9

Specification

General Provisions



Design Standards

Specification


10

AISI S200: General Provisions

A. GENERAL

B. MEMBER DESIGN

C. INSTALLATION


C. INSTALLATION

D. CONNECTIONS

E. MISCELLANEOUS

11

AISI S200: General Provisions

• A. GENERAL– A1 Scope

– A2 Definitions

– A3 Material

– A4 Corrosion Protection

• C. INSTALLATION– C1 In-Line Framing

– C2 Non-Structural Wall Framing

– C3 Installation


– A4 Corrosion Protection

– A5 Products

– A6 Referenced Documents

• B. MEMBER DESIGN– B1 Members

– B2 Member Condition

– C3 Installation Tolerances

• D. CONNECTIONS– D1 Screw Connections

– D2 Welded Connections

– D3 Other Connections

• E. MISCELLANEOUS– E1 Utilities

– E2 Insulation12

Member Design

• Member design is to be in accordance with

AISI S100: Specification

• Members shall be in good condition


• Damaged members to be replaced/repaired

• Not permitted without approved design:

– Web holes

– Cutting or notching of flanges or lips

– Splicing

13

Installation Tolerances

• Foundation:

– Uniform bearing surface with maximum 1/4” gap

between the track and foundation


• Ground Contact:

– Avoid direct contact with the ground and provide

sufficient height above ground

• Framing:

– Install plumb and level, spacing not to exceed

span capacity of sheathing, bearing requirements

14


• Floor joist web must not be in contact

with rim joist web to prevent squeaks


15


• Wall stud must be seated in track with

maximum gap of 1/8”


16

Installation Tolerance


17

Screw Connections

• Installation:

– Minimum of 3 exposed threads

– No permanent separation between plies


Minimum 3 exposed

threads shall protrude

through steel18

Screw Connections

• Stripped Screws:

– Stripped screw fasteners in direct tension

are considered ineffective


are considered ineffective

– Stripped screw fasteners in shear may be

considered effective (not more than 25%

of the total number considered effective)

19

Screw Connections

• Spacing:

– Provides for an allowance if the spacing is

less than 3 times screw diameter, as


less than 3 times screw diameter, as

specified by AISI S100: Specification

– If spacing is greater than 2 times screw

diameter, screws can be considered

80% effective

20

Screw Connections

• Pattern:

- Distinct pattern vs. shotgun blast


21

Corrosion Protection

• “Additional corrosion protection is not required on edges of metallic-coated steel framing members, shop or field cut, punched or drilled.”


or drilled.”

• Recognizes zinc's ability to galvanically protect steel, and

• Exposure of the underlying steel at a cut edge will not result in corrosion of the steel away from the cut edge

22

In-Line Framing

• No restriction

existed that

specifically

addresses the case


addresses the case

where the bearing

stiffener is attached

to the back side of

the floor joist

23

In-Line Framing


24

AISI S201: Product Data

A. GENERAL

B. MATERIALS

C. PRODUCTS


C. PRODUCTS

D. QUALITY

ASSURANCE

25

AISI S201: Product Data

• Scope:

– Materials, Coatings and Thickness

– Shapes and Dimensions


– Designators and Marking

– Tolerances and Quality Assurance

• Purpose:

– Simplify process for specifiers

– Simplify process for inspectors

– Enable development of load-span tables

26

Materials

• Referenced Standard:

– ASTM A1003: Standard Specification for Steel

Sheet, Carbon, Metallic- and Nonmetallic-Coated

for Cold-Formed Framing Members


for Cold-Formed Framing Members

• Requirements:

– Type H (high ductility), Structural Grade 33 or 50

– Type L (low ductility), Structural Grade 33 or 50

– Type NS, Nonstructural Grade 33

27

Thickness


28

Coatings

• Referenced Standard:

– ASTM A1003: Standard Specification for

Steel Sheet, Carbon, Metallic- and


Steel Sheet, Carbon, Metallic- and

Nonmetallic-Coated for Cold-Formed

Framing Members

• Requirements:

– Structural: G60 or equivalent

– Non-structural: G40 or equivalent

29

Shapes


30

S = C-shaped stud or joist

T = Track

Shapes


T = Track

U = Cold rolled channel

F = Furring (hat) channel

L = Angle or L-header

31

600 S 162 - 54

Product Designator


2 or 3 digit numeral indicating base metal

thickness in 1/1000 inch (mils) (0.054”)

3 digit numeral indicating flange width in 1/100

inches (1-5/8”), followed by a dash

Letter indicating the type of product (C-shape section)

3 or 4 digit numeral indicating web depth in 1/100 inches (6”)

32

Dimensions


33

Dimensions


34

Punchouts


35

Punchouts


36

Product Marking

• Structural members shall be marked legibly to

indicate conformance with the following

minimum characteristics:

– manufacturer (name, logo or initials)


– manufacturer (name, logo or initials)

– steel designation thickness exclusive of coatings

– minimum coating designation if other than G60

– minimum yield strength if other than Grade 33

• Color coding of members or bundles

37

Manufacturing Tolerances

• Referenced Standards:– Structural: ASTM C955

– Non-Structural: ASTM C645

• Requirements:


• Requirements:– Length

– Web Depth

– Flare and Over-bend

– Hole Center Width and Length

– Crown, Camber, Bow and Twist

38

Quality Assurance

• Documented quality control program

• Filing methods that document the

proper application of quality assurance


proper application of quality assurance

procedures

39

Code of Standard Practice

A. GENERAL

B. CLASSIFICATION OF MATERIALS

C. CONTRACT DOCUMENTS


DOCUMENTS

D. INSTALLATION DRAWINGS

E. MATERIALS

F. INSTALLATION

G. QUALITY CONTROL

H. CONTRACTUAL RELATIONS

40

Scope

• Defines and sets forth accepted norms of good practice for fabrication and installation of cold-formed steel structural framing


structural framing

• Supplement to legal building regulation

• Would be used unless differing instructions in the contract documents

• Voluntary document

41

Model Documents

• AISC - Code of Standard Practice for

Steel Buildings and Bridges

• SJI – Code of Standard Practice for


• SJI – Code of Standard Practice for

Steel Joists and Joist Girders

42

Other Related Documents

• CASE (Council of American Structural Engineers)– National Practice Guidelines for Specialty Structural

Engineers

– National Practice Guidelines for the Structural Engineer of Record


Engineer of Record

– A Guideline Addressing Coordination and Completeness of Structural Construction Documents

• STCA Standard Practices and Recommended Guidelines on Responsibilities for Construction Using Cold-Formed Steel Trusses and Components

43

Example 2

• Responsibilities for

field modifications

and repairs must be

clearly defined and


clearly defined and

communicated

44

Summary

• Addresses “Who is responsible for

what?”


45

Specification

General Provisions



Design Standards

Specification


46

AISI S210: Floor and Roof

System Design

• Load Combinations

• Member Design:

– Discretely Braced Design


– Discretely Braced Design

– Continuously Braced Design

• Connection Design:

– Bearing Stiffeners

• Bracing Design

47

Member Design

• Discretely braced design:

– Neglect attached sheathings

– Discrete braces provided along member length


length

• Continuously braced design:

– Sheathing or deck attached to compression side

– Continuous or discrete bracing attached to tension side

48

Connection Design


49

Bracing Design

• Provides a “prescriptive” approach for

compression side bracing:

– 3/8 inch wood structural sheathing or 9/16” x

0.0269” thickness steel deck


0.0269” thickness steel deck

– attached with No. 8 screws at 12 inches o.c.

• Adapts requirements for tension side bracing

from AISI S100 (Specification) requirements

for members where neither flange is attached

to sheathing

50

Neither Flange Restrained and the load acts

through the plane of the web:

MEMBER BRACING(AISI S100 Section D3.2.1)

51SE University, February 2012

• Design brace force, PL:

• Uniform load, PL = 1.5 K'W

• Concentrated load, PL = 1.0 K'P + 1.4K'P(1- l/a)

MEMBER BRACING


C-SECTION BRACING FORCES

F

P


For a uniform

load per unit

length, P:

PL = 1.5K’aP

MEMBER BRACING

d

Pm = F

’KP =

F

P

P

F


’KP =

F

P

F

AISI S211: Wall Stud Design

• Load Combinations

• Sheathing Braced Design

• Stud-to-Track Connection


• Stud-to-Track Connection

• Deflection Track Connection

55

Load Combinations

• Combined Bending and Axial Strength:

– MWFRS wind loads

• Bending Strength:


• Bending Strength:

– C&C wind loads

• Deflection Limits:

– 70% of C&C wind loads with no axial loads

56

Wall Stud Design

• All-steel design:

– Neglect attached sheathings

• Sheathing braced design:


• Sheathing braced design:

– Identical sheathing attached to both sides

– Unbraced length (strong axis) taken as distance between member ends

– Unbraced length (weak axis and torsion) taken as twice the distance between sheathing connectors

57

Wall Stud Design


58

Wall Stud Design

• Special load combination for evaluation

of the stud without sheathing in the

event the sheathing has been removed


event the sheathing has been removed

or has accidentally become ineffective

1.2D + (0.5L or 0.2S) + 0.2W

59

Stud-to-Track Connection


−

+

−=

t

hC1

t

NC1

t

RC1FCtP hNRy

2

nst

60

D110-07: Example 1 – Curtain Wall

• Height = 13 ft

• Spacing = 16 in. o.c.

• Nominal Wind Load = 28 psf


• Nominal Wind Load = 28 psf

w = 28(16/12) = 37.33 lbs/ft

• Deflection Limit = L/360

• Check 600S162-43, Fy = 33 ksi

(based on two rows of bridging).

Check 600S162-43 (Fy = 33 ksi)(Per AISI Specification)

Applied Moment = wL2/8 = 37.33(13)2/8

= 789 ft-lbs = 9.46 in.-kips

Using CFS software to compute the effective


Using CFS software to compute the effective section modulus, Sxe;

Ma = 15.2 in.-kips (without punch-out)

= 15.1 in.-kips (with 1.5 in. punch-out)

OK for bending check!

Sxe and Post-Buckling Stress Distribution


AISC E7

Check 600S162-43 (Fy = 33 ksi)

Deflection, δδδδ = 5wL4/(384EIx) = 0.351 in.

Ix = full moment of inertia = 2.316 in.4

w = 37.33 lbs/ft

(Section A3.1 of Wall Stud Standard - may use


(Section A3.1 of Wall Stud Standard - may use

70% of Components & Cladding wind load)

δδδδ = 0.246 in.

L = 13x12 = 156 in. ; E = 29500 ksi

Permissible Deflection = 156/360 = 0.433 in.

OK for serviceability check!

Check Shear(Per AISI Specification)

Applied End Shear:

V = 0.5wL

= 0.5(37.33)(13) = 243 lbs = 0.243 kips


Using Section C3.2 and CFS software:

Va = 1.42 kips (without punch-out)

= 1.24 kips (with 1.5 in. punch-out)

OK for shear!

Check Web Crippling

Applied End Reaction:

P = 0.5wL


= 0.5(37.33)(13) = 243 lbs = 0.243 kips

Web Crippling(Per AISI Specification)

−

+

−=

t

hC1

t

NC1

t

RC1sinFCtP hNRy

2n θ

Using Section C3.4: Check web crippling at bottom

track

Eq.C3.4.1-1


Eq.C3.4.1-1

C = 4, CR = 0.14, CN = 0.35, Ch = 0.02,

Ω = 1.75

Note: the above value is for a web without a web

opening near the support. See AISI Section

C3.4.2 if a web opening is near the support.


Assume a 600T125-43 track

Section A2.4 stipulates the requirement of .95tdesign

Design thickness = 0.043/0.95 = 0.0451 in.


Design thickness = 0.043/0.95 = 0.0451 in.

R/t = 0.0712/0.0451 = 1.58

h/t = 5.767/0.0451 = 128

Assume N = 1 in. with a ¼ in. gap

N/t = 1/0.0451 = 22.2

Web Crippling(Per Wall Stud Standard)

If a 600T125-43 is specified and N = 1 in., the

stud to track gap is 0.25 in. Note: track

thickness does not have to match stud

thickness.


thickness.

Section C1 of the Wall Stud Standard

stipulates that for curtain walls the ends of the

wall studs shall be seated squarely in the

track with no more than 1/4 in. gap between

the end of the stud and the track.


Eq.C3.4.1-1


Eq.C3.4.1-1

Pa = Pn/Ω = 0.453 kips/1.75 = 0.259 kips,

which is greater than 0.243 kips - OK





Section C3.4.2 for a web opening near the support.

[EOF], assume x = 9 in.:

Rc = 1.01 – 0.325(do/h) + 0.083(x/h) ≤ 1.0 Eq.C3.4.2-1


Eq.C3.4.2-1

= 1.01 – 0.325(2.5/5.767) + 0.083(9/5.767)

= 0.999 ~ 1.0

No reduction is required for a punch-out located 10

in. from the end of the member to the near edge of

the web punch-out (per industry standard).


Eq.C4.2-1

C = 3.7, C = 0.19, C = 0.74, C = 0.019,


C = 3.7, CR = 0.19, CN = 0.74, Ch = 0.019,

Ω = 1.70

Why the increase? Consider the load path!





Eq.C4.2-1


Pa = Pnst/Ω = 0.666 kips/1.70 = 0.392 kips

Note: Using the Wall Stud Standard results in a 51%

increase in web crippling design strength.

Single Deflection Track


75

Deflection Track Connection

wdt

Track

D

eθθ


bstud

Stud

Figure C4.3-1 Deflection Track Connection

76

Deflection Track Design(Per Wall Stud Standard)

Assume single deflection track:

Gap, e = 1.5 in.; D = 1.0 in.

Try 600T250-97


Try 600T250-97

tdesign = 0.097/0.95 = 0.102 in.

Studs must have a line of bridging

12 in. from the end.



wdt = effective track width

wdt = 0.11(e0.5/t1.5) + 5.5 ≤ S

= 9.64 in. ≤ 16 in., Use 9.64 in.


Pnst(e) = ZFy ; Z = wdt t2/4

Pnst = wdt t2Fy/(4e)


= 9.64(0.102)2(50)/(4x1.5) = 0.836 kips

Pa = Pnst/Ω = 0.836/2.8 = 0.298 kips

End reaction from before = 0.243 kips

Since 0.298 kips > 0.243 kips

600T250-97OK!

Deflection Track Design(Per AISI Specification)

• Web crippling of stud at the top track location

must still be

checked.


N = D = 1 in.

• Use unfastened coefficients for EOF Loading in

Table C3.4.1-2 of the AISI Specification.

• Pa = 0.255 kips, which is greater than 0.243 kips

OK

AISI Framing Standards

• General:– AISI S200-07: General Provisions

– AISI S201-07: Product Standard

– Code of Standard Practice, 2006 Edition

• Design Standards:– AISI S210-07: Floor and Roof System Design


– AISI S210-07: Floor and Roof System Design

– AISI S211-07: Wall Stud Design

– AISI S212-07: Header Design

– AISI S213-07: Lateral Design

– AISI S214-07: Truss Design

• Prescriptive Methods:– AISI S230-07: Prescriptive Method for One and Two

Family Dwellings

Cold-Formed Steel Design, 4th Edition

The book has been thoroughly updated and

expanded to reflect:

2007 North American Specification

2007 North American Framing Standards


and other newly published standards

and documents.

Ordering information:

www.ccfssonline.org

Price: $110 plus shipping

Wei-Wen Yu

Center for Cold-Formed Steel Structure


Center for Cold-Formed Steel Structure

[email protected], 573-341-4481

QUESTIONS?


QUESTIONS?

85

2012.02.08 - cold-formed steel design - design standards (part 1)

Documents

design of cold

aisi s210

edition design standards

lateral design aisi

header design aisi s213

aisi s230

improved design

roof system design aisi