FATIGUE OF WELDED CONNECTIONS - A PRIMER, PART I (4).pdf

AISC Live Webinar Webinar May 23, 2013

Fatigue of Welded Connections A Primer, Part I

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Course Description

May 23, 2013 – Fatigue of Welded Welded Connections: Connections: A Primer, Part I Using AISC 360 Appendix 3, this live webinar examines the basic concepts behind fatigue including the definition, application and causation; as well as welded connections and variables affecting fatigue. The presentation then reviews the aspects of the design model including fatigue testing, categories of connection details and predictive model.

© The American Institute of Steel Construction 2013

Learning Objectives

• To learn and understand understand the the provisions provisions included included in Appendix 3 of the 201 AISC Specification for Structural Steel Buildings. • To learn and understand understand the the concepts concepts behind behind the fatigue design design requirements. • Become familiar with with fatigue fatigue testing, testing, categories categories of connection connection details and predictive models.

Fatigue of Welded Connections: A Primer, Primer, Part I written and presented by Duane K. Miller, Sc. D., P.E. Manager, Engineering Services, The Lincoln Electric Company, Cleveland, OH.

• To understa understand nd the implemen implementati tation on of the fatigue fatigue design design requirements for welded connections.

8




Fatigue of Welded Connections: A Primer


This session is specifically geared toward Engineers and Contractors involved with bridge construction, but is equally applicable to individuals involved with the design and fabrication of crane girders and supports, and other weldments subject to cyclic loading.

The basic concepts behind fatigue-resistant steel structures are considered, explaining the interrelated variables of stress range, connection geometry and the expected life of the welded connection. The role of dead load stress versus live load stress are discussed, as are the variable of weld quality and steel strength.



Using AISC 360 Appendix 3, weld geometries are considered considered in detail w ith a practical focus on how to increase the fatigue resistance of welded connections.


Fatigue enhancement methods are presented. The role of material toughness on fatigue life is discussed. Case studies, including the bad and ugly, are presented.



AISC 360-10 SPECIFICATION

AISC 360-10 SPECIFICATION For Structural Steel Buildings

APPENDIX 3 DESIGN FOR FATIGUE

14



1. Backgr Backgroun ound d and and Theory Theory

1. Backgr Backgroun ound d and and Theory Theory

2. Desi Design gn Mode Modell

• Definition

3. Design Design and Constructi Construction on Details Details

• Applications

4. Fatigu Fatigue e Enhanc Enhanceme ement nt

• Causation

5. Exampl Examples: es: Good Good,, Bad and Ugly Ugly

• Weld Welded ed Conn Connec ecti tion ons s • Varia ariable bles s Aff Affec ectin ting g Fati Fatigu gue e


AISC Live Webinar May 23, 2013



GLOSSARY

Fatigue. Limit state of crack initiation and growth resulting from repeated application of live loads.

17

18


FRACTURE and FATIGUE CONTROL in STRUCTURES

APPENDIX 3 “Fatigue is the process of cumulative damage in a benign environment that is caused by repeated fluctuating loads and, in the presence of an aggressive environment, is known as corrosion fatigue .”

DESIGN FOR FATIGUE This appendix applies to members and connections subject to high cycle loading within the elastic range of stresses of frequency and magnitude sufficient to initiate cracking and progressive failure, which defines the limit state of fatigue . User Note: See AISC Seismic Provisions for Structural Steel Buildings for structures subject to seismic loads .

Barsom and Rolfe

19

American Institute of Steel Construction

Elastic, high cycle loading

20





APPENDIX 3

APPENDIX 3 Commentary

DESIGN FOR FATIGUE 3.1. GENERAL PROVISIONS 3.1. GENERAL PROVISIONS (cont’d)

In general, members or connections subject to less than a few thousand cycles of loading will not constitute a fatigue condition except possibly for cases involving full reversal of loading and particularly sensitive categories of details. This is because the applicable cyclic allowable stress range will be limited by the static allowable stress.

No evaluation of fatigue resistance of members consisting of shapes or plate is required if the number of cycles of application of live load is less than 20,000.

21


Not for low cycle loading

22


APPENDIX 3


DESIGN FOR FATIGUE ….Issues of fatigue are not normally encountered in building design; however, when encountered and if the severity is great enough, fatigue is of concern and all provisions of Appendix 3 must be satisfied.

This appendix applies to members and connections subject to high cycle loading within the elastic range of stresses of frequency and magnitude sufficient to initiate cracking and progressive failure, which defines the limit state of fatigue. User Note: See AISC Seismic Provisions for Structural Steel Buildings for structures subject to seismic loads. Not for seismic loading


23

Not for typical building design

24



Crane Supports

Reciprocating Machinery Supports

25


26

Bridges

CHAPTER J DESIGN OF CONNECTIONS J1.10 Limitations on Bolted and Welded Connections Joints with pretensioned bolts or welds shall be used for the following connections: (3) In all structures carrying cranes of over 5 ton (50 kN) capacity; ....and crane supports (4) Connections for the support of machinery and other live loads that produce impact or reversal of load. 27


28


Fatigue of Welde

Bridges

What is fatigue?


Fatigue


Fatigue is the result of repeated plastic deformation.

3.1. GENERAL PROVISIONS (cont’d) The provisions of this Appendix apply to stresses calculated on the basis of service loads. The maximum permitted stress due to service loads is 0.66F y.



DEFORMATION AND FRACTURE MECHANICS OF ENGINEERING MATERIALS


“Fatigue damage of components subjected to normally elastic stress fluctuations occurs at regions of stress (strain) raisers where the localized stress exceeds the yield stress of the material. After a certain number of load fluctuations, the accumulated damage causes the initiation and subsequent propagation of a crack, or cracks, in the plastically damaged regions.”

“It is important to recognize that fatigue damage will occur only when cyclic plastic strains are generated. This basic rule should not be construed as a “security blanket” whenever nominal applied stresses are below the material yield strength, since stress concentrations readily elevate local stresses and associated strains into the plastic range.”

Barsom and Rolfe

Richard W. Hertzberg

33

34

75

Plastic ) i s k (

s s e r t S

50

30 kips 1”

25

Elastic

1”

0

nominal

Strain American Institute of Steel Construction

35

= P/A = 30 kips/1 in 2 = 30 ksi 36



75

Stress Concentrator (kt) ) i s k (

50

s s e r t S

kt = 2

30 kips Nominal Design Stress: 30 ksi (60% of yield)

25

1”

1”

0

kt = Strain

maximum/

nominal

=

max/

nom

37

38

75

Stress Concentrator (kt) ) i s k (

kt = 2

30 kips

1”

s s e r t S

50

25

max

= 60 ksi

Nominal Design Stress: 30 ksi (60% of yield)

1”

kt = 2 =

max

/ 30

max

0

= 60 ksi 39


Strain

40



Residual Stresses


“Welding technology is complex and fabrication by welding encompasses characteristics that should be understood to different levels by the design engineer, the fabricator, and the welder. Some of these characteristics pertinent to the present discussion are residual stresses, imperfections, and stress concentrations.” Barsom and Rolfe

41

Residual Stresses


Residual Stresses



Residual Stresses

Residual Stresses

Residual Stresses


MPa

36 Ksi, 250 MPa

50 Ksi, 350 MPa

100 Ksi, 690 MPa

690

350

0

47 From “Economical and Fatigue Resistant Steel Bridge Details, National Highway Institute Course No. 13049



48



Imperfections

Imperfections

Crack in Weld

Crack in Heat Affected Zone (HAZ)

49

50

Imperfections

Imperfections

Incomplete Joint Penetration in CJP

Incomplete Joint Penetration in CJP

51


52



Imperfections

Imperfections

Incomplete Fusion

Porosity

53

54

Imperfections

Imperfections

Slag Inclusions

Undercut

55


56



Stress Concentrations


Weld Toes “Welding technology is complex and fabrication by welding encompasses characteristics that should be understood to different levels by the design engineer, the fabricator, and the welder. Some of these characteristics pertinent to the present discussion are residual stresses, imperfections, and stress concentrations.” Barsom and Rolfe

57

58



Unfused Root of Single Sided PJP Groove Weld

Unfused Root of Double Sided PJP Groove Weld

59


60





Weld Toes and Weld Roots in Cruciform Joints

tp

Width Transitions in Butt Joints

2a 62 61



Ends of Intermittent Fillet Welds

Ends of Fillet Welds at Partial Length Cover Plates

63


64





APPENDIX 3


DESIGN FOR FATIGUE 3.5. GENERAL PROVISIONS 3.1. GENERAL PROVISIONS (cont’d)

Extensive test programs using full-size specimens, substantiated by theoretical stress analysis, have confirmed the following general conclusions (Fisher et al., 1970; Fisher et al., 1974):

Stress range is defined as the magnitude of the change in stress due to the application or removal of the service live load.

(1) Stress range and notch severity are the dominant stress variables for welded details and beams; 65

66

Stress Range

max

-

s s e r t S d e i l p p A

min

total load

max. stress, σmax

Stress range, min. stress, σmin “live” load

“dead” load

Time 67


68


15


Complete Reversal

) i s 10 k ( s s 5 e r t S d 0 e i l p p A- 5

20

max. stress, σmax

Stress range, min. stress, σmin

-10

=

max –

min

max. stress, σmax


=

= 5 – (-5) = 10 ksi 69

Time

Tensile to Full Tensile

) i s 20 k ( s s 15 e r t S d10 e i l p p A 5

-10

max. stress, σmax


max –

min

= 10 – 0 = 10 ksi 70

Time

10

0

-5

) i s 15 k ( s s 10 e r t S d 5 e i l p p A 0 -5

-15

25

Zero to Full Tensile

Compression Only

) i s 5 k ( s s 0 e r t S d- 5 e i l p p A-10

max. stress, σmax


-15

=

max –

min

= 15 – 5 = 10 ksi

Time


71

= -20

max –

Time

min

= 0 – (-10) = 10 ksi 72



5 0

AISC 360-10 SPECIFICATION Stress range,

= 10 ksi

-5

APPENDIX 3 Commentary 10 5

Stress range,

= 10 ksi

3.5. GENERAL PROVISIONS

0

Extensive test programs using full-size specimens, substantiated by theoretical stress analysis, have confirmed the following general conclusions (Fisher et al., 1970; Fisher et al., 1974):

15 10

Stress range,

= 10 ksi

5 0

(1) Stress range and notch severity are the dominant stress variables for welded details and beams;

0 -5

Stress range,

= 10 ksi

-10

74

Residual Stresses: Before Welding



75




Residual Stresses: After Welding

Residual Stresses: Tensile Load Applied

Residual Stresses: Tensile Load Removed—Some Stress Reduction

Residual Stresses: After Welding




Residual Stresses: Compressive Load Applied

Residual Stresses: Compressive Load Removed—No Reduction

Complete Reversal

Zero to Full Tensile

y

y

s s e r t S

s s e r t S

0

0 Time

Time 83


84



Tensile to Full Tensile

Compression Only

y

y

s s e r t S

s s e r t S

0

0 Time

Time 85

86


APPENDIX 3 Commentary 3.5. GENERAL PROVISIONS Extensive test programs using full-size specimens, substantiated by theoretical stress analysis, have confirmed the following general conclusions (Fisher et al., 1970; Fisher et al., 1974): (1) Stress range and notch severity are the dominant stress variables for welded details and beams; 87


88




Effect of Minimum Stress, Maximum Stress

APPENDIX 3 Commentary a P M100 e g n a R s s e r t S

2) Other variables such as minimum stress, mean stress and maximum stresses are not significant for design purposes; and 3) Structural steels with a specified minimum yield stress of 36 to 100 ksi (250 to 690 MPa) do not exhibit significantly different fatigue strengths for given welded details fabricated in the same manner.

i

10

e g n a R s s e r t S

s 14.5 k

Minimum Stress ksi [MPa]

Welded

Rolled

Maximum Stress

5

(at 14.5 ksi [100 MPa])

- 6 [-41.4]

+8.5 [58.6]

2 [13.8]

+16.5 [113.8]

10 [68.9]

+24.5 [168.9]

10

1.4

0.1

89

20

1.0

Cycles x


10 6

10 Adapted from “A Fatigue Primer for Structural Engineers” by Fisher, Kulak, Smith, published by NSBA

Effect of Base Metal Strength

APPENDIX 3 Commentary a P M100 e g n a R s s e r t S

2) Other variables such as minimum stress, mean stress and maximum stresses are not significant for design purposes; and 3) Structural steels with a specified minimum yield stress of 36 to 100 ksi (250 to 690 MPa) do not exhibit significantly different fatigue strengths for given welded details fabricated in the same manner.


i

10


s 14.5 k

Steel

5

A 36

36 ksi [250 MPa]

A441

50 ksi [350 MPa]

A514

100 ksi [690 Mpa]

10 91

20

1.4

0.1

1.0

Cycles x

10 6

10 Adapted from “A Fatigue Primer for Structural Engineers” by Fisher, Kulak, Smith, published by NSBA



Lower Yield Steel

Higher Yield Steel y

y

s s e r t S

s s e r t S

0

0 Time

Time 93

s s e r t S d e i l p p A


Higher strength steel will not allow for greater “live loads”

1. Background and Theory: SUMMARY

total load

max. stress, σmax

Stress range, min. stress, σmin “live” load

“dead” load

Time

94

Higher strength steel will allow for greater 95 “dead loads”






“Fatigue damage of components subjected to normally elastic stress fluctuations occurs at regions of stress (strain) raisers where the localized stress exceeds the yield stress of the material. After a certain number of load fluctuations, the accumulated damage causes the initiation and subsequent propagation of a crack, or cracks, in the plastically damaged regions.”


Barsom and Rolfe

97





2) Other variables such as minimum stress, mean stress and maximum stresses are not significant for design purposes; and

3.5. GENERAL PROVISIONS Extensive test programs using full-size specimens, substantiated by theoretical stress analysis, have confirmed the following general conclusions (Fisher et al., 1970; Fisher et al., 1974):

3) Structural steels with a specified minimum yield stress of 36 to 100 ksi (250 to 690 MPa) do not exhibit significantly different fatigue strengths for given welded details fabricated in the same manner.

(1) Stress range and notch severity are the dominant stress variables for welded details and beams; 99


98

100





1. Background and Theory

2. Design Model

2. Design Model

• Fatigue Testing

3. Design and Construction Details

• Categories of Connection Details

4. Fatigue Enhancement

• Predictive Model

5. Examples: Good, Bad and Ugly

• Special Categories: C’ and C”

Full Scale Fatigue Tests

103


104



90o

45o

22 1/2o 11 1/4o

Number of Cycles to Failure 105

106

Two standard deviations e g n a R s s e r t S g o L

Mean Regression Line

e g n a R s s e r t S g o L

(95% confidence intervals)

97.5% above this line Threshold value

Log Number of Cycles to Failure

Log Number of Cycles to Failure 107


108



Effect of Details

e g n a R s s e r t S g o L

a P M100 e g n a R s s e r t S

Design Curve

20

i

10


s 14.5 k

Detail

5

Welded Beams Welded beams with end welded cover plates

Log Number of Cycles to Failure

10

1.4

0.1

109

1.0

Cycles x

10

10 6

Adapted from “A Fatigue Primer for Structural Engineers” by Fisher, Kulak, Smith, published by NSBA

UNWELDED STEEL

A

B

C

D

E

F

111


A

B

C

D

E

F

112



Category B Details

CJP Flange Splice Longitudinal Fillet Longitudinal CJP

A

B

C

D

113

E

F

114

Category C Details

A

B

C

D

E

F

115


116



Category E Details

C o v e r p l a t e d B e a m

T r a n s v e r s e S t i f f e n e r

A

B

D

C

E

117

118

) i100 s k ,

) i100 s k ,

R S

( e g n a R10 s s e r t S g o L 1

3 1

R S


Category A Category B

Category F

Category C Category D Category E

20x103

105

106

107

108

Log Number of Cycles (N)

Category A Category B

Category F

1

Category C

6

Category D Category E

20x103

105

106

107

108

Log Number of Cycles (N) 119


F

120



) i100 s k , R S


Category B Category B’ Category C

Category F Category G

Category D Category E Category E’

A 20x103

105

106

107

C o v e r p l a t e d B e a m

T r a n s v e r s e S t i f f e n e r

Category A

B

C

D

E

F

108


122


APPENDIX 3 DESIGN FOR FATIGUE 3.3. PLAIN MATERIAL AND WELDED JOINTS

A

B

B’

C

D

E

E’

F

G

123


In plain material and welded joints the range of stress at service loads shall not exceed the allowable stress range computed as follows:

124




AISC 360-10 SPECIFICATION where

(a) For stress categories A, B, B ′ , C, D, E and E ′ the allowable stress range, F SR , shall be determined by Equation A-3-1 or A-3-1M, as follows:

 C f   F SR =  n  SR 

C f = constant from Table A-3.1 for the fatigue category F SR = allowable stress range, ksi (MPa)

0.333

≥ F TH

 C f x 329   F SR =   nSR 

(A-3.1)

F TH = threshold allowable stress range, maximum stress range for indefinite design life from Table A-3.1, ksi (MPa)

0.333

≥ F TH

(S.I.)

nSR = number of stress range fluctuations in design life = number of stress range fluctuations per day × 365 × years of design life

(A-3.1M)

125


) i100 s k ,

0.333

≥ F TH

 C f x 329   F SR =   nSR 

(A-3.1)

0.333

≥ F TH

(S.I.)

(A-3.1M)

1


Category A Category B Category B’ Category C

Category F Category G


20x103

105

106

107

108



3

R S


 C f   F SR =  n  SR 

126

128




) i100 s k , R S

(b) For stress category F, the allowable stress range, F SR , shall be determined by Equation A-3-2 or A-3-2M, as follows:

 C f   F SR =  n  SR 

0.167

≥ F TH

 C f (11 x 10 4 )   F SR =    n SR  

(A-3.2)

0.167

≥ F TH

(S.I.) (A-3.2M)


Category A Category B Category F

1

Category B’ Category C

6 Category G


20x103

105

106

107



130


(c) For tension-loaded plate elements connected at their end by cruciform, T or corner details with complete-jointpenetration (CJP) groove welds or partial joint-penetration (PJP) groove welds, fillet welds, or combinations of the preceding, transverse to the direction of stress, the allowable stress range on the cross section of the tensionloaded plate element at the toe of the weld shall be determined as follows:


 C f   F SR =  n  SR 

0.333

≥ F TH

 C f x 329   F SR =   nSR  131


108

(A-3.1)

0.333

≥ F TH

(S.I.)

(A-3.1M)

132





SECTION 1—PLAIN MATERIAL AWAY FROM ANY WELDING

SECTION 2—CONNECTED MATERIAL IN MECHANICALLLY FASTENED JOINTS 133

134

SECTION 1

SECTION 2

PLAIN MATERIAL AWAY FROM ANY WELDING

CONNECTED MATERIAL IN MECHANICALLY FASTENED JOINTS

135


136



SECTION 3

SECTION 4

WELDED JOINTS JOINING COMPONENTS OF BUILT-UP MEMBERS

LONGITUDINAL FILLET WELDED END CONNECTIONS

137

138

SECTION 5

SECTION 6

WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS

BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS

139


140



SECTION 7

SECTION 8

BASE METAL AT SHORT ATTACHMENTS

MISCELLANEOUS

141

142


SECTION 1

A

1.1

PLAIN MATERIAL AWAY FROM ANY WELDING

Description: Base metal, except noncoated weathering steel, with rolled or cleaned surface. Flame-cut edges with surface roughness value of 1,000 μin. (25 μm) or less, but without re-entrant corners.

Potential Crack Initiation Point: Away from all welds or structural connections. 143


144





B

1.2

B

1.3

Description: Noncoated weathering steel base metal with rolled or cleaned surface. Flame-cut edges with surface roughness value of 1,000 μin. (25 μm) or less, but without re-entrant corners.

Description: Member with drilled or reamed holes. Member with re-entrant corners at copes, cuts, block-outs or other geometrical discontinuities made to requirements of Appendix 3, Section 3.5, except weld access holes.

Potential Crack Initiation Point: Away from all welds or structural connections.

Potential Crack Initiation Point: At any external edge or at hole perimeter. 145

146


SECTION 2 C

1.4

CONNECTED MATERIAL IN MECHANICALLY FASTENED JOINTS

Description: Rolled cross sections with weld access holes made to requirements of Section J1.6 and Appendix 3, Section 3.5. Members with drilled or reamed holes containing bolts for attachment of light bracing where there is a small longitudinal component of brace force.

Potential Crack Initiation Point: At reentrant corner of weld access hole or at any small hole (may contain bolt for minor connections).


147

148



SECTION 2—CONNECT ED MATERIAL IN MECHANICALLY FASTENED JOINTS

SECTION 2—CONNECTE D MATERIAL IN MECHANICALLY FASTENED JOINTS

B

2.1

D

2.3

Description: Gross area of base metal in lap joints connected by high-strength bolts in joints satisfying all requirements for slipcritical connections.

Description: Base metal at the net section of other mechanically fastened joints except eye bars and pin plates.

Potential Crack Initiation Point: Through gross section near hole.

Potential Crack Initiation Point: In net section originating at side of hole. 149

150

SECTION 2—CONNECT ED MATERIAL IN MECHANICALLY FASTENED JOINTS

SECTION 3 E

2.4

WELDED JOINTS JOINING COMPONENTS OF BUILT-UP MEMBERS

Description: Base metal at net section of eyebar head or pin plate.

Potential Crack Initiation Point: In net section originating at side of hole. 151


152



SECTION 3—WELDED JOINTS JOINING COMPONENTS OF BUILT-UP MEMBERS


B

3.1

B’

3.2

Description: Base metal and weld metal in members without attachments, built up of plates or shapes connected by continuous longitudinal CJP groove welds, back gouged and welded from second side, or by continuous fillet welds.

Description: Base metal and weld metal in members without attachments, built up of plates or shapes, connected by continuous longitudinal CJP groove welds with backing bars not removed, or by continuous PJP groove welds.

Potential Crack Initiation Point: From surface or internal discontinuities in weld away from end of weld.

Potential Crack Initiation Point: From surface or internal discontinuities in weld, including weld attaching backing bars. 153

154



D

3.3

E

3.4

Description: Base metal at weld metal terminations of longitudinal welds at weld access holes in connected built-up members.

Description: Base metal at ends of longitudinal intermittent fillet weld segments.

Potential Crack Initiation Point: From the weld termination into the web or flange.

Potential Crack Initiation Point: In connected materials at start and stop locations of any weld deposit.

155


156





E

3.5a

E’

3.5b

Description: Base metal at ends of partial length welded coverplates narrower than the flange having square or tapered ends, with or without welds across the ends. Coverplates wider than the flange with welds across the ends.

Description: Base metal at ends of partial length welded coverplates narrower than the flange having square or tapered ends, with or without welds across the ends. Coverplates wider than the flange with welds across the ends.

Flange thickness (t f ) < 0.8 in. (20 mm).

Flange thickness (t f ) > 0.8 in. (20 mm).

Potential Crack Initiation Point: In flange at toe of end weld or in flange at termination of longitudinal weld or in edge of flange 157 with wide coverplates.

Potential Crack Initiation Point: In flange at toe of end weld or in flange at termination of longitudinal weld or in edge of flange 158 with wide coverplates.


SECTION 4 E’

3.6

LONGITUDINAL FILLET WELDED END CONNECTIONS

Description: Base metal at ends of partial length welded coverplates wider than the flange without welds across the ends.

Potential Crack Initiation Point: In edge of flange at end of coverplate weld. 159


160



SECTION 4—LONGITUDINAL FILLET WELDED END CONNECTIONS

SECTION 4—LONGITUDINAL FILLET WELDED END CONNECTIONS

E

4.1a

E’

4.1b

Description: Base metal at junction of axially loaded members with longitudinally welded end connections. Welds shall be on each side of the axis of the member to balance weld stresses.

Description: Base metal at junction of axially loaded members with longitudinally welded end connections. Welds shall be on each side of the axis of the member to balance weld stresses.

Thickness t < 0.5 in. (12 mm).

Thickness t > 0.5 in. (12 mm).

Potential Crack Initiation Point: Initiating from end of any weld termination extending into the base metal.

Potential Crack Initiation Point: Initiating from end of any weld termination extending into the base metal.

161

162

SECTION 5—WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS

SECTION 5

B

5.1

WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS

Description: Weld metal and base metal in or adjacent to CJP groove welded splices in rolled or welded cross sections with welds ground essentially parallel to the direction of stress and with soundness established by RT or UT.

Potential Crack Initiation Point: From internal discontinuities in weld metal or along the fusion boundary. 163


164





B

5.2a

B’

5.2b

Description: Weld metal and base metal in or adjacent to CJP groove welded splices with welds ground essentially parallel to the direction of stress at transitions in thickness or width made on a slope no greater than 1:2 1/2 and with weld soundness established by RT or UT. Fy < 90 ksi (620 MPa)

Description: Weld metal and base metal in or adjacent to CJP groove welded splices with welds ground essentially parallel to the direction of stress at transitions in thickness or width made on a slope no greater than 1:2 1/2 and with weld soundness established by RT or UT. Fy ≥ 90 ksi (620 MPa).

Potential Crack Initiation Point: From internal discontinuities in weld metal or along fusion boundary.

Potential Crack Initiation Point: From internal discontinuities in weld metal or along fusion boundary or at start of transition when 166 Fy ≥ 90 ksi (620 MPa).

165



B’

5.2b

B

5.3

C

5.4

Description: Weld metal and base metal in or adjacent to the toe of CJP groove welds in T or corner joints or splices, with or without transitions in thickness having slopes no greater than 1:2 1/2. Weld reinforcement is not removed. Weld soundness established by RT or UT.

Potential Crack Initiation Point: From surface discontinuity at toe of weld extending into base metal or into weld metal. 167


168




SECTION 6 C

5.5a

BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS

Description: Base metal and weld metal at transverse end connections of tension-loaded plate elements using PJP groove welds in butt or T- or corner joints, with reinforcing or contouring fillets. F SR shall be the smaller of the toe crack or root crack allowable stress range. Crack initiating from weld toe. Potential Crack Initiation Point: Initiating from geometrical discontinuity at toe of weld extending into base metal. 169

170

SECTION 6—BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS


B

6.1a

C

6.1b

Description: Base metal at details attached by CJP groove welds subject to longitudinal loading only when the detail embodies a transition radius, R, with the weld termination ground smooth and with weld soundness established by RT or UT.


R ≥ 24 in. (600 mm).

24 in. > R ≥ 6 in. (600 mm > R ≥ 150 mm)

Potential Crack Initiation Point: Near point of tangency of radius at edge of member.

Potential Crack Initiation Point: Near point of tangency of radius at edge of member. 171


172





D

6.1c

E

6.1d



6 in. > R ≥ 2 in. (150 mm > R ≥ 50 mm)

R < 2 in. (50 mm)

Potential Crack Initiation Point: Near point of tangency of radius at edge of member.

Potential Crack Initiation Point: Near point of tangency of radius at edge of member. 173


6.1

174


B

6.2a

R ≥ 24 in. (600 mm).

B

24 in. > R ≥ 6 in. (600 mm > R ≥ 150 mm)

C

6 in. > R ≥ 2 in. (150 mm > R ≥ 50 mm)

D

R < 2 in. (50 mm)

E 175


Description: Base metal at details of equal thickness attached by CJP groove welds subject to transverse loading with or without longitudinal loading when the detail embodies a transition radius, R, with the weld termination ground smooth and with weld soundness established by RT or UT. Weld reinforcement is removed. R ≥ 24 in. (600 mm) Potential Crack Initiation Point: Near points of tangency of radius or in the weld or at fusion boundary or member or attachment.

176





C

6.2e

D

6.3a

Description: Base metal at details of equal thickness attached by CJP groove welds subject to transverse loading with or without longitudinal loading when the detail embodies a transition radius, R, with the weld termination ground smooth and with weld soundness established by RT or UT. Weld reinforcement is not removed. R ≥ 24 in. (600 mm)

Description: Base metal at details of unequal thickness attached by CJP groove welds subject to transverse loading with or without longitudinal loading when the detail embodies a transition radius, R, with the weld termination ground smooth and with weld soundness established by RT or UT. Weld reinforcement is removed. R > 2 in. (50 mm).

Potential Crack Initiation Point: At toe of the weld either along edge of member or the attachment.

Potential Crack Initiation Point: At toe of weld along edge of thinner material.

177

178


6.4a

SECTION 7 D

BASE METAL AT SHORT ATTACHMENTS

Description: Base metal subject to longitudinal stress at transverse members, with or without transverse stress, attached by fillet or partial-joint-penetration groove welds parallel to direction of stress when the detail embodies a transition radius, R, with weld termination ground smooth. R > 2 in. (50 mm). Potential Crack Initiation Point: Initiating in base metal at the weld termination or at the toe of the weld extending into the base 179 metal.


180



SECTION 7—BASE METAL AT SHORT ATTACHMENTS

SECTION 7—BASE ME TAL AT SHORT ATTACHMENTS

C

7.1a

D

7.1b

Description: Base metal subject to longitudinal loading at details with welds parallel or transverse to the direction of stress where the detail embodies no transition radius and with detail length in direction of stress, a, and thickness of the attachment, b.


a < 2 in. (50 mm)

2 in. (50 mm) ≤ a ≤ 12b or 4 in. (100 mm)

Potential Crack Initiation Point: Initiating in base metal at the weld termination or at the toe of the weld extending into the base 181 metal.



7.1c


E

7.1d



a > 4 in. (100 mm) when b > 0.8 in. (20 mm)

a > 12b or 4 in. (100 mm) when b ≤ 0.8 in. (20 mm)




E’




No attachments

A

7.1

a < 2 in. a < 50mm a < 2 in. (50 mm)

C

2 in. (50 mm) ≤ a ≤ 12b or 4 in. (100 mm)

D

a > 4 in. (100 mm) when b > 0.8 in. (20 mm)

E

a > 12b or 4 in. (100 mm) when b ≤ 0.8 in. (20 mm)

a > 4 in. a > 100mm

a C

a E’

E’ 185

186



D

7.2a

E

7.2b

Description: Base metal subject to longitudinal stress at details attached by fillet or partial-joint-penetration groove welds, with or without transverse load on detail, when the detail embodies a transition radius, R, with weld termination ground smooth.

Description: Base metal subject to longitudinal stress at details attached by fillet or partial-joint-penetration groove welds, with or without transverse load on detail, when the detail embodies a transition radius, R, with weld termination ground smooth.

R > 2 in. (50 mm)

R ≤ 2 in. (50 mm)

Potential Crack Initiation Point: Initiating in base metal at the weld termination, extending into the base metal.

Potential Crack Initiation Point: Initiating in base metal at the weld termination, extending into the base metal. 187


188



SECTION 8—MISCELLANEOUS

SECTION 8

C

8.1

MISCELLANEOUS

Description: Base metal at steel headed stud anchors attached by fillet or automatic stud welding.

Potential Crack Initiation Point: At toe of weld in base metal. 189

190



F

8.2

Description: Shear on throat of continuous or intermittent longitudinal or transverse fillet welds.

Description: Base metal at plug or slot welds.

Potential Crack Initiation Point: Initiating at the root of the fillet weld, extending into the weld.

Potential Crack Initiation Point: Initiating in the base metal at the end of the plug or slot weld, extending into the base metal.

191


E

8.3

192





F

8.4

G

8.5

Description: Shear on plug or slot welds.

Description: Snug-tightened high-strength bolts, common bolts, threaded anchor rods, and hanger rods with cut, ground or rolled threads. Stress range on tensile stress area due to live load plus prying action when applicable.

Potential Crack Initiation Point: Initiating in the weld at the faying surface, extending into the weld.

Potential Crack Initiation Point: Initiating at the root of the threads, extending into the fastener. 193



 C f   F SR =  n  SR 

0.333

≥ F TH

 C f x 329    nSR 

F SR = 

(A-3.1)

0.333

≥ F TH

(S.I.)

(A-3.1M)

195


194

Stress Category

Coefficient Cf

Threshold FTH

A

250 x 108

24

B

108

16

B’

61 x

108

12

C

44 x 108

10

D

22 x 108

7

E

11 x

108

4.5

E’

3.9 x 108

2.6

F

150 x 1010

8

G

108

7

120 x

3.9 x

For Imperial Units (ksi)

196



DESIGN PROCEDURE

DESIGN PROCEDURE

1. Determine the number of cycles the connection must endure (n sr ). 1, 2 2. Determine the forces on the connection due to live and dead loads.

Note 1:

For n sr < 20,000 cycles, fatigue need not be considered if maximum stress < 0.66 F y.

3. Determine fatigue category from illustration. Find C f coefficient for the fatigue detail.

Note 2:

For n sr = infinite, F SR < FTH

4. Calculate FSR. 5. For all Categories except Category F, for a given live load, select a member geometry that results in a stress range less than F SR. For Category F, modify weld size. 6. Consider alternative connection details with increased fatigue resistance and recalculate F SR.

197

198

DESIGN EXAMPLE 100,000 cycles

1. Determine the number of cycles the connection must endure (n sr ). 1, 2 100,000 cycles

Grade 50

2. Determine the forces on the connection due to live and dead loads. Fdead = - 20 K, Flive = + 80 K

CJP, reinforcement left in place, UT

3. Determine fatigue category from illustration. Find C f coefficient for the fatigue detail. 4. Calculate FSR. Fdead = - 20K

5. For all Categories except Category F, for a given live load, select a member geometry that results in a stress range less than F SR. For Category F, modify weld size. 6. Consider alternative connection details with increased fatigue resistance and recalculate F SR.


R = 1”

Flive = + 80 K

t = 1” W

199

Fmin = - 20 K, Fmax = + 60 K 200



E

6.2h

t = 1” Grade 50 R = 1”

Fmax = 60 kips tension

Reinforcement left in place

Fmin = 20 kips compression

Weld receives UT

100,000 cycles required

 C f   F SR =  n  SR 

0.333

≥ F TH 201

202

E

6.2h

Fmax = 60 kips tension Fmin = 20 kips compression

100,000 cycles

 11x108   F SR =  3  100x10  

t = 1” Grade 50 R = 1” Reinforcement left in place Weld receives UT

100,000 cycles required 0.333

 11x108   F SR =  3  100x10  

≥ 4.5 203


0.333

≥ 4.5 204



E

6.2h

Fmax = 60 kips tension Fmin = 20 kips compression 100,000 cycles required

t = 1” Grade 50 R = 1”

t = 1” Grade 50 R = 1”


Reinforcement Reinforceme nt left in place

Reinforcement Reinforcement left in place place


Weld receives UT

8  Fmax − Fmin   11x10    F SR =  = 3  A 100x10    

E

6.2h

Weld receives UT


0.333

8  60 − - 20   11x10    F SR =  = 3  A 100x10    

≥ 4.5

0.333

≥ 4.5

205

206

E

6.2h

Fmax = 60 kips tension Fmin = 20 kips compression 100,000 cycles required

t = 1” Grade 50 R = 1” Reinforcement Reinforceme nt left in place Weld receives UT

t = 1” Grade 50 R = 1”




Weld receives UT


 80   = 22.17  A 

F SR = 

 80  3 0.333 ≥ 4.5  = (11x10 )  A 

F SR = 

Amin = 3.6 in2 207


E

4” wide

6.2h

Use 4 in2

208



Category D

E

4” wide

6.2h

6” > R > 2” Cf = 22 x 10 8 FTH = 7 ksi [48 MPa] t = 1” Grade 50 R = 1”




Weld receives UT

100,000 cycles required Static Strength Check:

 60   = 15 < 0.66Fy = 0.66(50) = 33  4 

F = 

OK 209

210

D

6.2h

t = 1” Grade 50 R = 2”




Weld receives UT


 22x10   F SR =  3  100x10   8

D

6.2h

t = 1” Grade 50 R = 2”




Weld receives UT


 80   = 27.93  A 

F SR = 

0.333

≥7

Amin = 2.9 in2 211 211


Use 3 in2

212



Category C

D

3” wide

6.2h

24” 24” > R > 6” Cf = 44 x 10 8 FTH = 10 ksi [69 MPa] t = 1” Grade 50 R = 2”




Weld receives UT


 60   = 20 < 0.66Fy = 0.66(50) = 33  3 

F = 

OK 213

214

C

6.2h

t = 1” Grade 50 R = 6”




Weld receives UT


 44x10   F SR =  3  100x10   8

C

2.5” wide

6.2h

t = 1” Grade 50 R = 6”




Weld receives UT


 80  35. 18  =35.  A 

F SR = 

0.333

≥ 10

Amin = 2.27 in2 215


Use 2.5 in2

216



Category E C

2.5” wide

6.2h

t = 1” Grade 50 R = 6”




R = 1”

Weld receives UT


 60   = 24 < 0.66Fy = 0.66(50) = 33  2.5 

F = 

W = 4”

OK 217

Category D

218

Category C

R = 2”

W = 3”

W = 2.5” 219


R = 6” 220



Width of Required Material = 2R + W Category E

Category E 2” > R

Category D

Cf = 11 x 10 8 FTH = 4.5 ksi [31 MPa] 6” = 2(1) + 4

7” CategoryC

= 2(2) + 3

14.5” = 2(6) + 2.5

222

Category E

DESIGN PROCEDURE 1. Determine the number of cycles the connection must endure (n sr ). 1, 2 2. Determine the forces on the connection due to live and dead loads. 3. Determine fatigue category from illustration. Find C f coefficient for the fatigue detail.

R=0

4. Calculate FSR.

The best answer, despite the “poor” Category E detail

5. For all Categories except Category F, for a given live load, select a member geometry that results in a stress range less than F SR. For Category F, modify weld size. W = 4” 223


6. Consider alternative connection details with increased fatigue resistance and recalculate F SR.

224



Category A

Base metal (except weathering) Maximum roughness of 1000 µin No re-entrant corners

A

B

C

D

E

F

225

226

Category B

Category B

Noncoated weathering base metal

Base metal

Maximum roughness of 1000 µin

Reamed or drilled holes

No re-entrant corners

Copes, cuts, blockouts with large, smooth radius

227


228



Category B

Category B

CJPs with no reinforcement, no backing, no tabs Slip critical bolted connections

UT or RT inspected

Same as above but with width or thickness transitions of 2.5:1 Continuous longitudinal CJPs and fillets 229

Category B

Category C

Weld access hole in rolled section CJPs with no reinforcement, no backing, no tabs UT or RT inspected R > 24”

CJPs with reinforcement, no backing, no tabs 231


UT or RT inspected

232



Category C

Category C

Transverse fillet welds—cracking at toes

Short attachments a < 2”

CJPs with no reinforcement, no backing, no tabs UT or RT inspected 24” > R > 6”

Welded shear studs 233

Category D

234

Category E

Eye bars

235


236



Category E

Category E

Ends of axially loaded members with longitudinal fillet welds

Intermittent fillet welds

CJPs with no reinforcement, no backing, no tabs UT or RT inspected

Ends of partial length coverplates 237

Category E

R < 2”

238

Category F

Shear on continuous PJP or fillet weld throat Base metal at plug or slot welds

Shear on plug or slot weld 239


240



Category D

Category D

CJPs with no reinforcement, no backing, no tabs Snug tightened bolts, rivets

UT or RT inspected 6” > R > 2”

Weld access holes in build-up sections

Intermediate length attachments: 2” < a < 4”

241

242



243


Category

Residual Stress

Major Imperfections

Stress Concentration

A

Low

None

None

B

High

Low

None

C

High

Low-Medium

Low

D

High

Medium

Medium

E

High

Medium

High

F

High

Medium

Low 244



Category B’

Continuous longitudinal CJPs with backing Continuous longitudinal PJPs

A

B

C

D

E

F

245

Category E’

Transverse CJPs with Fy > 90 ksi, straight width taper

Category G

In general, Category E’ are Category E details but with thicker materials involved.

Threaded fasteners subject to stress range

Coverplates wider than the beam flange. 248





APPENDIX 3 DESIGN FOR FATIGUE 3.3. PLAIN MATERIAL AND WELDED JOINTS

A

B

B’

C

D

E

E’

F

G

In plain material and welded joints the range of stress at service loads shall not exceed the allowable stress range computed as follows:

249

250


AISC 360-10 SPECIFICATION where


 C f   F SR =  n  SR 

C f = constant from Table A-3.1 for the fatigue category F SR = allowable stress range, ksi (MPa)

0.333

≥ F TH

 C f x 329   F SR =   nSR 

(A-3.1)

0.333

≥ F TH

(S.I.)

(A-3.1M)

251


F TH = threshold allowable stress range, maximum stress range for indefinite design life from Table A-3.1, ksi (MPa) nSR = number of stress range fluctuations in design life = number of stress range fluctuations per day × 365 × years of design life 252






 C f   F SR =  n  SR 

0.167

≥ F TH

 C f (11 x 10 4 )   F SR =    n SR  

(A-3.2)


0.167

≥ F TH

(S.I.) (A-3.2M)

253

Cruciform

Inside Corner

T (tee)


254

with CJPs



with PJPs

with fillets

CJPs with fillets

PJPs with fillets







(i) Based upon crack initiation from the toe of the weld on the tension loaded plate element the allowable stress range, F SR , shall be determined by Equation A-3-3 or A-33M, for stress category C as follows:

 44 x 10 8   F SR =  n SR  

Three options follow, labeled i, ii, and iii .

0.333

 14.4 x 1011   F SR =  n SR  

261

≥ 10

(A-3.3)

0.333

≥ 68.9

(S.I.) (A-3.3M) 262


Stress Category

Coefficient Cf

Threshold FTH

A

250 x 108

24

B

108

16

B’

61 x

108

12

C

44 x 108

10

D

22 x 108

7

E

11 x

108

4.5

E’

3.9 x 108

2.6

F

150 x 1010

8

G

108

7

120 x

3.9 x



C

5.4

Description: Weld metal and base metal in or adjacent to the toe of CJP groove welds in T or corner joints or splices, with or without transitions in thickness having slopes no greater than 1:2 1/2. Weld reinforcement is not removed. Weld soundness established by RT or UT.

Potential Crack Initiation Point: From surface discontinuity at toe of weld extending into base metal or into weld metal. 263

264



AISC 360-10 SPECIFICATION with CJPs Category C

(i) Based upon crack initiation from the toe of the weld on the tension loaded plate element the allowable stress range, F SR , shall be determined by Equation A-3-3 or A-33M, for stress category C as follows: 8  44 C  x 10 f  F SR =  n SR  

Condition i

0.333

 14.4 Cf xx329 1011   F SR =  n SR  

FTH ≥ 10

(A-3.3)

0.333

Toe Cracks

68.9 ≥F TH

(S.I.) (A-3.3M) 265



 44 x 108   F SR = R PJP  n SR  

0.333

 14.4 x 1011   F SR = R PJP  n SR  

C

5.5a

(ii) Based upon crack initiation from the root of the weld the allowable stress range, F SR , on the tension loaded plate element using transverse PJP groove welds, with or without reinforcing or contouring fillet welds, the allowable stress range on the cross section at the toe of the weld shall be determined by Equation A-3-4 or A-3-4M, for stress category C ′ as follows: (A-3.4)

Description: Base metal and weld metal at transverse end connections of tension-loaded plate elements using PJP groove welds in butt or T- or corner joints, with reinforcing or contouring fillets. F SR shall be the smaller of the toe crack or root crack allowable stress range. Crack initiating from weld toe.

0.333


(S.I.) (A-3.4M) 267

Potential Crack Initiation Point: Initiating from geometrical discontinuity at toe of weld extending into base metal. 268



with PJPs

PJPs with fillets

Category C’

Category C'

Condition ii

Condition ii

Root Cracks

Root Cracks



(ii) Based upon crack initiation from the root of the weld the allowable stress range, F SR , on the tension loaded plate element using transverse PJP groove welds, with or without reinforcing or contouring fillet welds, the allowable stress range on the cross section at the toe of the weld shall be determined by Equation A-3-4 or A-3-4M, for stress category C ′ as follows: 8  44 C  x 10 f   F SR = R PJP  n SR  

where R PJP , the reduction factor for reinforced or non-reinforced transverse PJP groove welds, is determined as follows:

0.333

 14.4 Cf xx329 1011    F SR = R PJP  n SR  

(A-3.4) Note: no value for F TH

0.333


(S.I.) (A-3.4M) 271

       0.65 − 0.59 2a  + 0.72 w    t   t     p   p  ≤ 1.0 R PJP =   0.167 t p              1.12 − 1.01 2a  + 1.24 w    t   t     p   p  ≤ 1.0 R PJP =   0.167 t p      

(A-3.5)

(S.I.) (A-3.5M) 272



AISC 360-10 SPECIFICATION PJPs with fillets Category C Condition i

If R PJP = 1.0, use stress category C. 2a = length of the nonwelded root face in the direction of the thickness of the tension-loaded plate, in. (mm) w = leg size of the reinforcing or contouring fillet, if any, in the direction of the thickness of the tensionloaded plate, in. (mm) t p = thickness of tension loaded plate, in. (mm)

Toe Cracks

273

w

1.0

) P tp 2a R PJP increases as • 2a decreases (i.e., as E increases)

      0. 65 −0. 59  2a  +0. 72  w   •  t   t     p   p  ≤1. 0 R PJP =   0. 167 t   p    

w increases


Domain of practical solutions

J 0.8 P

R ( r o 0.6 t c a F n o 0.4 i t c u d e 0.2 R

w

tp    0.65 −0.59  2a  +0.72  t    p  R PJP =  0.167 t p   

 w      t    p  ≤1.0    

2a

Tp = 1”

0 0

275

1/8”

1/4” 3/8” 1/2” 5/8” 3/4” 7/8” 5/16” Fillet Weld Leg Size (w)

1”

Minimum fillet size for 1” steel (AWS) Minimum contouring fillet size (AISC)

1-1/8”

276




AISC 360-10 SPECIFICATION where R PJP , the reduction factor for reinforced or non-reinforced transverse PJP groove welds, is determined as follows:


DK Miller Commentary 3.5. SPECIAL FABRICATION AND ERECTION REQUIREMENTS

The term “reduction factor” may be non-intuitive. A “large reduction factor” (a high number) is good in this case; a “small reduction factor” is bad.

In transverse complete-joint-penetration T and corner joints, a reinforcing fillet weld, not less than 1/4 in. (6 mm) in size shall be added at re-entrant corners.

277


REVIEW

278


APPENDIX 3 (a) For stress categories A, B, B ′ , C, D, E and E ′ the allowable stress range, F SR , shall be determined by Equation A-3-1 or A-3-1M, as follows:

DESIGN FOR FATIGUE

 C f   F SR =  n  SR 

3.3. PLAIN MATERIAL AND WELDED JOINTS In plain material and welded joints the range of stress at service loads shall not exceed the allowable stress range computed as follows:

≥ F TH

 C f x 329   F SR =   nSR 

Three options follow, labeled a, b, and c . 279


0.333

(A-3.1)

0.333

≥ F TH

(S.I.)

(A-3.1M)

280






 C f   F SR =  n  SR 

0.167

≥ F TH

 C f (11 x 10 4 )   F SR =    n SR  

(A-3.2)

(c) For tension-loaded plate elements connected at their end by cruciform, T or corner details with complete-jointpenetration (CJP) groove welds or partial joint-penetration (PJP) groove welds, fillet welds, or combinations of the preceding, transverse to the direction of stress, the allowable stress range on the cross section of the tensionloaded plate element at the toe of the weld shall be determined as follows: Three options follow, labeled i, ii, and iii .

0.167

≥ F TH

(S.I.) (A-3.2M)

281


AISC 360-10 SPECIFICATION (ii) Based upon crack initiation from the root of the weld the allowable stress range, F SR , on the tension loaded plate element using transverse PJP groove welds, with or without reinforcing or contouring fillet welds, the allowable stress range on the cross section at the toe of the weld shall be determined by Equation A-3-4 or A-3-4M, for stress category C ′ as follows:


 44 x 10 8   F SR =  n SR  

0.333

 14.4 x 1011   F SR =  n SR  

≥ 10

(A-3.3)

0.333

≥ 68.9


282

(S.I.) (A-3.3M) 283

 44 x 10 8   F SR = R PJP  n SR  

0.333

 14.4 x 1011   F SR = R PJP  n SR  

(A-3.4)

0.333

(S.I.) (A-3.4M) 284





(iii) Based upon crack initiation from the roots of a pair of transverse fillet welds on opposite sides of the tension loaded plate element, the allowable stress range, F SR , on the cross section at the toe of the welds shall be determined by Equation A-3-6 or A-3-6M, for stress category C ′′ as follows:

 44 x 10   n SR   8

F SR = R FIL 

where R FIL is the reduction factor for joints using a pair of transverse fillet welds only.

R FIL

0.333

 14.4 x 1011   n SR  

(A-3.6) Note: no value for F TH

0.333

F SR = R FIL 

R FIL

(S.I.) (A-3.6M) 285

     0.06 + 0.72 w    t p      ≤ 1.0 =  0.167 t   p          0.10 − 0.72 w    t p      ≤ 1.0 =  0.167 t   p    

(A-3.7)

(S.I.) (A-3.7M)

286

If R FIL = 1.0, use stress category C.

AISC 360-10 SPECIFICATION w

For fillet welds, 2a = t p.

tp

0.06

1

       0.65 − 0.59 2a  + 0.72 w      t p     t p    ≤ 1.0 R PJP =   0.167 t p              1.12 − 1.01 2a  + 1.24 w      t p     t p    ≤ 1.0 R PJP =   0.167 t p      


where R FIL is the reduction factor for joints using a pair of transverse fillet welds only.

2a

R FIL (A-3.5)

R FIL (S.I.) (A-3.5M) 287

     0.06 + 0.72 w    t p      ≤ 1.0 =  0.167 t   p          0.10 − 0.72 w    t p      ≤ 1.0 =  0.167 t   p    

If R FIL = 1.0, use stress category C.

(A-3.7)

(S.I.) (A-3.7M)

288



Fillets only

AISC 360-10 SPECIFICATION 1.0 I F 0.8

R ( r o t c 0.6 a F n o 0.4 i t c u d e 0.2 R

Three options follow, labeled i, ii, and iii . i.

RFIL = 1.0 when w = 1.31”

) L


CJP groove welds

w tp

R FIL

0 0

ii. PJPs without or with fillet welds iii. Fillet welds

1/8”

r o t c a F n o i t c u d e R

(2a = t p)

• Select w to obtain RFIL = 1

w

2a

1

1-1/8”

290

w

• Divide w by t p to obtain multiplier

0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0

1”

Fillets

tp

R

Tp = 1”

Minimum fillet size for 1” steel (AWS) Minimum contouring fillet size (AISC)

289

• RFIL > 0.50 for t p < 3” L I F

2a

1/4” 3/8” 1/2” 5/8” 3/4” 7/8” 5/16” Fillet Weld Leg Size (w)

Fillets • w = (3/4) t p

     0.06 + 0.72 w    t p      ≤ 1.0 =  0.167 t p      

2

3

Steel Thickness (in.)


4

tp

• Results in very large fillets 2a

2 r e i l p i t l 1.5 u M d 1 l e W t e 0.5 l l i F 0 5 291

0

1

2

3


4

5 292



PJPs with contouring fillets


• Let E = w and 2t w = tp, i.e. “Full Strength” for static (c) For tension-loaded plate elements connected at their end by cruciform, T or corner details with complete-jointpenetration (CJP) groove welds or partial joint-penetration (PJP) groove welds, fillet welds, or combinations of the preceding, transverse to the direction of stress, the allowable stress range on the cross section of the tensionloaded plate element at the toe of the weld shall be determined as follows: Three options follow, labeled i, ii, and iii . i.

CJP groove welds

ii. PJPs without or with fillet welds iii. Fillet welds

293

294

PJPs with contouring fillets

PJPs with contouring fillets • Let E = w and 2t w = tp, i.e. “Full Strength” for static

W = 0.35 t p

• RPJP > 0.5 for t w up to 4” tp

P J P

R

2a

r o t c a F n o i t c u d e R

E = 0.35 t p

PJP effective throat (E) = fillet weld leg size (w) 2a = t p – 2E = 0.3 tp

w = E =0.35 t p

tw = effective throat of combined PJP/fillet 2tw = tp


1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

t p

2 a

0 295

W = 0.35 tp

1

2

3


E = 0.35 tp

4

5 296





C

5.5a

C

5.5a mod

Description: Base metal and weld metal at transverse end connections of tension-loaded plate elements using PJP groove welds in butt or T- or corner joints, with reinforcing or contouring fillets. FSR shall be the smaller of the toe crack or root crack allowable stress range. Crack initiating from weld toe.

Description: Base metal and weld metal at transverse end connections of tension-loaded plate elements using PJP groove welds in butt or T- or corner joints, with reinforcing or contouring fillets. FSR shall be the smaller of the toe crack or root crack allowable stress range. Crack initiating from weld toe.

Potential Crack Initiation Point: Initiating from geometrical discontinuity at toe of weld extending into base metal.

Potential Crack Initiation Point: Initiating from geometrical discontinuity at toe of weld extending into base metal. 297

298



C’

5.5b mod

C

5.6a

Description: Base metal and weld metal at transverse end connections of tension-loaded plate elements using PJP groove welds in butt or T- or corner joints, with reinforcing or contouring fillets. FSR shall be the smaller of the toe crack or root crack allowable stress range. Crack initiating from weld root.

Description: Base metal and weld metal at transverse end connections of tension loaded plate elements using a pair of fillet welds on opposite sides of the plate. FSR shall be the smaller of the toe crack or root crack allowable stress range.

Potential Crack Initiation Point: Initiating at weld root subject to tension extending into and through weld.

Potential Crack Initiation Point: Initiating from geometrical discontinuity at toe of weld extending into base metal.

299


Crack initiating from weld toe.

300





C”

5.6b

Description: Base metal and weld metal at transverse end connections of tension loaded plate elements using a pair of fillet welds on opposite sides of the plate. F SR shall be the smaller of the toe crack or root crack allowable stress range.

C

5.7

Description: Base metal of tension loaded plate elements and on girders and rolled beam webs or flanges at toe of transverse fillet welds adjacent to welded transverse stiffeners.

Crack initiating from weld root. Potential Crack Initiation Point: Initiating at weld root subject to tension extending into and through weld.

Potential Crack Initiation Point: From geometrical discontinuity at toe of fillet extending into base metal.

301

302


Fatigue of Welded Connections: A Primer 2. Design Model--SUMMARY

APPENDIX 3 DESIGN FOR FATIGUE 3.3. PLAIN MATERIAL AND WELDED JOINTS In plain material and welded joints the range of stress at service loads shall not exceed the allowable stress range computed as follows:

304







 C f   F SR =  n  SR 


0.333

≥ F TH

 C f x 329   F SR =   nSR 

(A-3.1)

(A-3.1M)

 C f (11 x 10 4 )   F SR =    n SR  

0.333

≥ F TH

(S.I.)

0.167

 C f   F SR =  n  SR 

≥ F TH

(A-3.2)

0.167

≥ F TH

(S.I.) (A-3.2M)

305





 44 x 10 8   F SR =  n SR  

307


306

0.333

 14.4 x 1011   F SR =  n SR  

≥ 10

(A-3.3)

0.333

≥ 68.9

(S.I.) (A-3.3M) 308





(ii) Based upon crack initiation from the root of the weld the allowable stress range, F SR , on the tension loaded plate element using transverse PJP groove welds, with or without reinforcing or contouring fillet welds, the allowable stress range on the cross section at the toe of the weld shall be determined by Equation A-3-4 or A-3-4M, for stress category C ′ as follows:

 44 x 108   n SR  

 44 x 10 8   F SR = R FIL  n SR  

0.333

F SR = R PJP 

 14.4 x 10   n SR  

F SR = R PJP 

(iii) Based upon crack initiation from the roots of a pair of transverse fillet welds on opposite sides of the tension loaded plate element, the allowable stress range, F SR , on the cross section at the toe of the welds shall be determined by Equation A-3-6 or A-3-6M, for stress category C ′′ as follows:

11

(A-3.4)

0.333

(A-3.6) Note: no value for FTH

 14.4 x 1011   n SR  

F SR = R FIL 

0.333

(S.I.) (A-3.4M)

0.333

(S.I.) (A-3.6M)

309


310

) i100 s k ,

APPENDIX 3

R S


DESIGN FOR FATIGUE 3.1. GENERAL PROVISIONS (cont’d) No evaluation of fatigue resistance is required if the live load stress range is less than the threshold allowable stress range, F TH . See Table A-3.1.

Category A Category B Category B’ Category C

Category F


20x103

105

106

107

108



312



Stress Category

Coefficient Cf

Threshold FTH

A

250 x 108

24

B

120 x

108

16

B’

61 x 108

12

C

44 x 108

10

D

22 x 108

7

E

11 x 108

4.5

E’

108

2.6

3.9 x

F

150 x 1010

8

G

3.9 x 108

7


Fatigue of Welded Connections: A Primer Thank You!

313

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