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. Appendix A: AISI standard updates

. Appendix A: AISI standard updates

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Recent code development and design standards for cold-formed steel structures



Designation



Title



Published editions



AISI S212



North American Cold-Formed Steel

FramingdHeader Design



Reaffirmed in 2012 and

integrated into AISI

S240-15



AISI S213



North American Cold-Formed Steel

FramingdLateral Design



Reaffirmed in 2012 and

integrated into AISI

S240-15



AISI S214



North American Cold-Formed Steel

FramingdTruss Design



Updated in 2012 and

integrated into AISI

S240-15



AISI S220



North American Cold-Formed Steel

FramingdNonstructural Members



Published in 2011 and

updated in 2015



AISI S230



North American Cold-Formed Steel

FramingdPrescriptive Method



Reaffirmed in 2012 and

updated in 2015



AISI S240



North American Standard for Cold-Formed

Steel Structural Framing



Published in 2015



AISI S400



North American Standard for Seismic Design

of Cold-Formed Steel Structural Systems



Published in 2015



51



AISI design procedures and

practical examples for

cold-formed steel structures



3



W. Zhang 1 , C. Yu 2

1

Tongji University, Shanghai, China; 2University of North Texas, Denton, TX, United States



3.1



Introduction



In 1949 the American Iron and Steel Institute (AISI) published the first edition of its

“Light Gage Steel Design Manual,” which was intended to supplement the design

specification and facilitate its application to ordinary design problems (Kaehler and

Seaburg, 1996). Since then AISI has been developing and updating the manual, which

was later renamed the “Cold-Formed Steel Design Manual” (AISI, 1968). Today, the

manual provides the latest design information and examples for conformance with

S100 North American Specification for the Design of Cold-Formed Steel Structural

Members (AISI, 2012). The 2013 edition of the “Cold-Formed Steel Design Manual”

(AISI, 2013) consisted of two volumes with eight parts.





















Part I: Dimensions and Properties. Contains information regarding the availability and properties of steels referenced in the specification; tables of section properties; and formulas and

examples of calculations of section properties.

Part II: Beam Design. Contains tables and charts to aid in beam design, and beam design

example problems.

Part III: Column Design. Contains tables to aid in column design, and column design

example problems.

Part IV: Connections. Contains tables to aid in connection design, and connection example

problems.

Part V: Supplementary Information. Contains a table of specification cross-references to the

examples provided in the design manual; design procedures of a specification nature which

are not included in the specification itself, either because they are infrequently used or are

regarded as too complex for routine design; and other information intended to assist users

of cold-formed steel (CFS).

Part VI: Test Procedures. Contains a bibliography of other pertinent test methods, and test

calibration example problems.

Part VII: North American Specification. Contains the 2012 edition of the North American

Specification for the Design of Cold-Formed Steel Structural Members.

Part VIII: Commentary on the North American Specification. Contains the 2012 edition of

the Commentary on the North American Specification for the Design of Cold-Formed Steel

Structural Members.



Recent Trends in Cold-Formed Steel Construction. http://dx.doi.org/10.1016/B978-0-08-100160-8.00003-7

Copyright © 2016 Elsevier Ltd. All rights reserved.



54



Recent Trends in Cold-Formed Steel Construction



Up-to-date design examples were added in the AISI Design Manual (2013) to illustrate new design provisions in AISI S100 (2012).

Round and rectangular tubular section member design in Parts II and III.

C-section members subjected to combined bending and torsional loading in Part II.

Distortional buckling of C-section members in Parts II and III.

Sigma-shaped flexural and compression member design by the direct strength method in

Parts II and III.

5. Web crippling strength of beam webs with bearing stiffeners in Part II.

6. Frame design with consideration of second-order analysis in Part III.

1.

2.

3.

4.



AISI’s “Cold-Formed Steel Design Manual” is focused on member or connection

design. For framing or system design, the Cold-Formed Steel Engineers Institute

(CFSEI) has published a series of technical notes to address specific topics related

to CFS framing for residential and commercial construction. Currently the CFSEI technical notes series consists of 10 categories.























Durability and corrosion protection.

Fasteners and connection hardware.

Component assemblies (trusses and wall panels).

General topics.

Floor and joist systems.

Wall systems.

Roof and ceiling systems.

Thermal, fire, and acoustic.

Lateral systems.

Other technical documents.



In addition to the technical notes, the CFSEI also periodically releases research reports, design guides, and technical papers to promote the use of CFS in the construction industry.

In recent years CFS framing has become an attractive and competitive structural

system for midrise residential and office buildings due to its light weight, fast installation, low waste and noise during construction, and noncombustibility. Among the

three sheathing materials for shear walls approved in AISI S213 North American

Standard for Cold-Formed Steel FramingdLateral Design (AISI, 2012) and the International Building Code (IBC, 2015), flat steel is the only noncombustible material for Types I and II construction and other building types such as medical care

facilities, etc., which require noncombustible materials for their load-bearing structures. Fig. 3.1 shows the failure mechanism of CFS shear walls sheathed by flat steel

sheet: the tension field action dominated the load-bearing behavior of these shear

walls.

The existing design methods in AISI S213 and the IBC for CFS-sheathed shear

walls are solely based on experimental data with limited options in sheathing and

framing configurations. To improve the situation, an analytical model and closedform design equations for steel-sheet-sheathed CFS shear walls were developed by

Yanagi and Yu (2014). Named the effective strip method, it offers an alternative



AISI design procedures and practical examples for cold-formed steel structures



AR = 4



AR = 2



55



AR = 1.33



Figure 3.1 Failure mechanism of steel-sheet-sheathed shear walls.

Yanagi, N., Yu, C., 2013. Effective strip model for cold-formed steel shear wall using steel sheet

sheathing. In: Proceedings of the 21st International Specialty Conference on Cold-Formed Steel

Structures, St. Louis, MO, April 2013.



approach for engineers to predict the normal strength of CFS shear walls. The method

was approved by the AISI Committee on Steel Framing and will be included in AISI

S240 and AISI S400. A design example for the effective strip method is provided in

this chapter.

In any structural system, the connection method and its details are always the critical elements to achieve the desired structural behavior and ensure the minimum safety

level defined by building codes and design specifications. The connections in CFS

structures are no different to those in any other structural system, and are even more

critical as fasteners are most commonly used and sometimes have dual responsibilities:

load bearing and energy dissipation. Among the various connections and connectors, a

thin-walled CFS clip angle is a common method used in CFS framing. Fig. 3.2 shows

applications of CFS clip angles to connect the stud to the track in CFS framing, and

attach the curtain wall framing member to the main structure. As illustrated in

Fig. 3.2, a CFS clip angle can be subjected to shear, axial, bending, and a combination

of those three. However, CFS clip angle design has not been developed in the major

design specificationsdAISI S100, the Australian/New Zealand Standard AS/NZS

4600 Cold-Formed Steel Structures (AS/NZS 4600, 2005), and Eurocode 3 Design

of Steel Structures (2006). To address the knowledge gap in the behavior and strength

of CFS clip angles, a research project was conducted by Yu et al. (2015) at the

University of North Texas to develop design methods for clip angles subjected to

shear, compression, and tension forces. This chapter gives examples of shear and

compression designs of CFS clip angles.



56



Recent Trends in Cold-Formed Steel Construction



(a)



(b)



Figure 3.2 Examples of applications of CFS clip angles: (a) CFS framing; (b) curtain wall

framing.



3.2



Sheet steel shear wall designdeffective

strip method



3.2.1



The effective strip method



The effective strip method for determining the nominal shear strength (resistance) for

Type I shear walls with steel sheet sheathing is based on research by Yanagi and Yu

(2014). The method assumes a sheathing strip carries the lateral load via a tension field

action, as illustrated in Fig. 3.3. The shear strength of the shear wall is controlled by the

tensile strength of the effective sheathing strip, which is determined as the lesser of

the fasteners’ tensile strength and the yield strength of the effective sheathing strip.

The statistical analysis in Yanagi and Yu (2014) yielded a load and resistance factor

design (LFRD) resistance factor of 0.79 for the effective strip method. To be consistent

with the resistance factors (0.60 for LRFD) specified in AISI S213 (2012) Section

E2.3.2, the original design equation in Yanagi and Yu (2014) was adjusted accordingly.

The nominal shear strength (resistance) per unit length for a Type I shear wall with

steel sheet sheathing can be determined in accordance with the effective strip method as:

Vn ¼ minimumð1:33Pn cos a; 1:33We tFy cos aị



[3.1]



where

Pn ẳ nominal shear strength (resistance) of screw connections within the effective strip

width, We, on the steel sheet sheathing



a ẳ Arctanh=wị

h ẳ shear wall height

w ẳ shear wall length

t ¼ design thickness of steel sheet sheathing

Fy ¼ yield stress of steel sheet sheathing



[3.2]



AISI design procedures and practical examples for cold-formed steel structures



57



We



Va



α



T

1W

e

2



h



1W

e

2



α



W



Figure 3.3 Effective strip model for steel sheet sheathing.

Yanagi, N., Yu, C., 2013. Effective strip model for cold-formed steel shear wall using steel sheet

sheathing. In: Proceedings of the 21st International Specialty Conference on Cold-Formed Steel

Structures, St. Louis, MO, April 2013.



We ¼ Wmax ;

¼ rWmax ;



when l



0:0819



when l > 0:0819



[3.3]

[3.4]



where

Wmax ¼ w=sin a





1 À 0:55ðl À 0:08ị0:12

l0:12



[3.5]

[3.6]



58



Recent Trends in Cold-Formed Steel Construction



l ẳ 1:736



a1 a2

b1 b2 b23 a



[3.7]



where

a1 ẳ Fush =310:3

ẳ Fush =45



for Fush in ksiị



a2 ¼ Fuf =310:3

¼ Fuf =45

b1 ¼ tsh =0:457

¼ tsh =0:018

b2 ¼ tf =0:457

¼ tf =0:018



ðfor Fush in MPaÞ



ðfor Fuf in MPaÞ



ðfor Fuf in ksiÞ

ðfor tsh in mmÞ

ðfor tsh in inchesÞ

ðfor tf in mmị

for tf in inchesị



b3 ẳ s=152:4 for s in mmị

ẳ s=6 for s in inchesị

Fush ẳ tensile strength of steel sheet sheathing

Fuf ¼ minimum tensile strength of framing materials

tsh ¼ design thickness of steel sheet sheathing

tf ¼ minimum design thicknesses of framing members

s ¼ screw spacing on the panel edges

a ¼ wall aspect ratio (h:w).



The effective strip method is valid within the following range of parameters.

1.

2.

3.

4.

5.

6.



Designation thickness of stud, track, and stud blocking: 0.838e1.37 mm (0.033e0.054 in.).

Designation thickness of steel sheet sheathing: 0.457e0.838 mm (0.018 e0.033 in.).

Screw spacing at panel edges: 50.8e152 mm (2e6 in.).

Height to length aspect ratio (h:w): 1:1e4:1.

Sheathing screw shall be minimum No. 8.

Yield stress of steel sheet sheathing shall not be greater than 345 MPa (50 ksi).



3.2.2



Design example



In this section, a design example of 1220  2440 mm (4 ft  8 ft) CFS shear walls using 1.092 mm (43 mil) framing and 0.838 mm (33 mil) sheet steel sheathing is provided. The nominal yield stress is 230 MPa (33 ksi) for the framing and 345 MPa



AISI design procedures and practical examples for cold-formed steel structures



59



(50 ksi) for the sheathing. Sheathing-to-framing fasteners at the perimeter are No. 8

self-drilling tapping screws spaced at 76 mm (3 in.).

Step 1: Estimating the effective strip width.

Fush ¼ 448:2 MPa

Fuf ¼ 310:3 MPa

tsh ¼ 0:879 mm

tf ¼ 1:146 mm

a ¼ ð2440 mmÞ=ð1220 mmÞ ¼ 2:0

a ¼ tanÀ1 a ¼ tan1 2:0ị ẳ 63:43 degrees

Maximum effective width of the steel sheet sheathing

Wmax ẳ



W

W

1220 mm





ẳ 1363 mm

sin a sin63:43 degreeị sin63:43 degreeị



a1 ẳ Fush =310:3 MPaị ẳ 448:2 MPaị=310:3 MPaị ẳ 1:444

a2 ẳ Fuf =310:3 MPaị ẳ 310:3 MPaị=310:3 MPaị ẳ 1:0

b1 ẳ tsh =0:457 mmị ẳ 0:879ị=0:457 mmị ẳ 1:923

b2 ¼ tf =ð0:457 mmÞ ¼ ð1:146Þ=ð0:457 mmÞ ¼ 2:508

b3 ¼ s=152:4 mmị ẳ 76 mmị=152:4 mmị ẳ 0:499

l ẳ 1:736



a1 a2

1:444 Â 1:0

¼ 0:601

¼ 1:736 Â

2

b1 b2 b3 a

1:923 Â 2:508 0:499ị2 2:0



l ẳ 0:601 > 0:0819

Effective strip width of the steel sheet sheathing

1 À 0:55ðl À 0:08Þ0:12

Wmax

l0:12

1 0:55 0:601 0:08ị0:12



1363 mmị ẳ 712:0 mm

0:601ị0:12



We ẳ rWmax ẳ



60



Recent Trends in Cold-Formed Steel Construction



Step 2: Determining the nominal shear capacity of individual connections.

Connection shear limited by tilting and bearing

t1 ¼ 0:879 mm

t2 ¼ 1:146 mm

d ¼ 4:166 mm

Fu1 ¼ 448:2 MPa

Fu2 ¼ 310:3 MPa

t2 =t1 ¼ ð1:146 mmÞ=ð0:879 mmÞ ¼ 1:304

1:0 < t2 =t1 < 2:5

For t2/t1



Pns



1.0,



8

n

o1=2

3 1=2

>

>

Fu2 ẳ 4:2 1:146 mmị3 4:166 mmị

310:3 MPaị ẳ 3:263 kN

> 4:2 t2 d

<

ẳ min

2:7t1 dFu1 ẳ 2:7 0:879 mmị 4:166 mmị 448:2 MPaị ẳ 4:431 kN

>

>

>

:

2:7t2 dFu2 ẳ 2:7 1:146 mmị 4:166 mmị 310:3 MPaị ẳ 4:000 kN



For t2/t1 ! 2.5,

(

Pns ¼ min



2:7t1 dFu1 ¼ 2:7 Â 0:879 mmị 4:166 mmị 448:2 MPaị ẳ 4:431 kN

2:7t2 dFu2 ẳ 2:7 1:146 mmị 4:166 mmị 310:3 MPaị ẳ 4:000 kN



By linear interpolation of the smallest of the above two cases

Pns ¼ 3:412 kN

Connection shear limited by end distance

t ¼ 0:879 mm

a ¼ tanÀ1 a ¼ tanÀ1 ð2Þ ¼ 63:4 degrees

wf ¼ flange width of stud ¼ 41:2 mm

wf

41:2 mm

e ¼ 2 cos

a ¼ 2Âðcos 63:4 degreesị ẳ 46:0 mm (assume the screws are installed at the



center of the flange of the outer stud)



AISI design procedures and practical examples for cold-formed steel structures



61



Fu ¼ 448:2 MPa

Pns ẳ teFu ẳ 0:879 mmị 46:0 mmị 448:2 MPaị ẳ 18:114 kN

Connection shear limited by shear in screw.

The nominal shear strength of the screw is provided by the manufacturer. It is

assumed that a No. 8e18 Phillips truss head screw by HILTI is used. The screw shear

strength can be found in a HILTI self-drilling screws report (ESR-2196, 2013).

Pss ¼ 5:204 kN

Pns;s ¼ minf3:412 kN; 18:114 kN; 5:204 kNg ¼ 3:412 kN

Similarly,

Pns;t ¼ 3:412 kN ðsheathing to track connectionÞ

Pns;ts ¼ 3:412 kN ðsheathing to track and stud connectionÞ

Step 3: Determining the nominal shear strength of the shear wall.

tsh ¼ 0:879 mm

Fy ẳ 344:7 MPa

&

Vn ẳ minimum



'



We

We

Pns;t ỵ

Pns;s ỵ Pns;ts cos a; We tFy cos a

2s sin a

2s cos a



Limited by connection capacity







We

We

Pns;t ỵ

Pns;s ỵ Pns;ts cos a

2s sin a

2s cos a









712:0 mm

3:412 kNị

2 76 mmị sin63:43 degreeị









712:0 mm

3:412 kNị ỵ 3:412 kN

2 76 mmị cos63:43 degreesị



cos63:43 degreeị

ẳ 25:50 kN



62



Recent Trends in Cold-Formed Steel Construction



Limited by sheathing yield capacity

À



Á

We tsh Fy cos a ¼ ð712:0 mmÞ Â ð0:879 mmÞ Â 0:3447 kN mm2

 cos63:43 degreesị

ẳ 96:49 kN

Vn ẳ minimumf25:50 kN; 96:49 kNg ẳ 25:50 kN

Nominal shear strength of the shear wall

Vn ¼ 25:50 kNð20:90 kN=mÞ



3.3



Shear design of load-bearing clip angle connectors



3.3.1



Shear strength without consideration of clip

angle deformation



The nominal shear strength (resistance), Vn, of the cantilevered leg of a clip angle is

calculated as follows:

Vn ¼ 0:17lÀ0:8 Fy Bt



0:35Fy Bt



[3.8]



where

rffiffiffiffiffiffi

Fy



Fcr



[3.9]



 2

kp2 E

t

Fcr ¼

2

12ð1 À m Þ B



[3.10]



 À2:202

L

k ¼ 2:569

B



[3.11]



B ¼ width of cantilevered leg measured parallel to the applied shear force

L ¼ flat length of cantilevered leg measured from the center of the first line of fasteners to the

bend line.



These equations are valid within the following range of parameters and boundary

conditions.

Clip angle design thickness: 0.838e2.464 mm (0.033e0.097 in.).

Clip angle design yield strength: 228e345 MPa (33e50 ksi.).

L/B ratio: 0.18e1.40.

The fastener pattern allows full engagement of the cantilevered leg in bearing the shear load.



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