NS32 - Session 8 - Handouts - 2 Per

Industrial Structure Design
AISC Night School Session 8: Fatigue, Inspections, and

September 26, 2023 Maintenance for Industrial Structures
Night School 32:

Industrial Structure
Design
Thank you for joining our live

webinar. We will begin shortly.
Please standby.

Session 8: Fatigue, Inspections, and Maintenance for Industrial
Structures
September 26, 2023 | Josh Buckholt, PE, SE
Today’s live webinar will begin shortly. Please stand by.
© Copyright 2023 1
American Institute of Steel Construction
Today’s live webinar will begin shortly. Please stand by.
Today’s audio will be broadcast through the internet. Please be sure to turn
up the volume on your speakers.
Please type any questions or comments in the Q&A window.

Session 8: Fatigue, Inspections, and Maintenance for
Industrial Structures
September 26, 2023 | Josh Buckholt, PE, SE
© Copyright 2023 2
Night School 32: Industrial Structure Design

Session 8: Fatigue, Inspections, and Maintenance for
Industrial Structures
September 26, 2023
Joshua Buckholt, PE, SE

Vice President
CSD Structural Engineers
Milwaukee, WI
Session Description
32.8 Fatigue, Inspections, and Maintenance for Industrial
Structures
September 26, 2023
This session will provide an overview of fatigue design,

inspection, and maintenance for industrial structures. Attendees
will be introduced to the fatigue design provisions of the AISC
Specification focusing on portions commonly used in crane
runway structures.
© Copyright 2023 3
Learning Objectives
• Participants will gain a general understanding of what fatigue design

is and factors that influence fatigue performance.
• Participants will understand the role that the AISC Specification
performs in design for fatigue.
Session 8 Outline
1. What is fatigue and why is it relevant to industrial structures?

2. Theory and factors influencing fatigue performance
3. Design for fatigue per the AISC Specification with crane girder
example.
4. Review of selected design details and level of expected fatigue
performance.
5. The role of inspections and maintenance in structures designed for
fatigue.
© Copyright 2023 4
Session 8 Outline

example.
performance.
fatigue.
What is Fatigue? ANSI/AISC 360-16
Fatigue: Limit state of crack initiation and

growth resulting from repeated application of
live loads.
https://www.aisc.org/publications/
steel-standards/aisc-360/
6
© Copyright 2023 5
Fatigue: Limit state of crack initiation and

growth resulting from repeated application
of live loads.
7
1. Limit state:
• Exceeding the limit state can result
in structural failure.
• A criteria in the design of
structures.
2. Crack initiation
• Conditions are present such that a
crack can form.
3. Growth resulting from repeated
application of live loads.
• Cycling of loading.
8
© Copyright 2023 6
What is Fatigue?
Pervasive cyclic inelastic stresses -> Low cycle fatigue

(beyond scope of the AISC Specification)
Image by Stefan Schweihofer

from Pixabay
What is Fatigue?
High Cycle Fatigue

(covered by AISC Specification, Appendix 3) 10
© Copyright 2023 7
Why is it Relevant to Industrial Structures?

1. Limit state:
• Failure would result in risk to life safety.
• Failure would result in economic losses.
2. Crack initiation
• Industrial structures many times contain
details which have discontinuities (see
AISC Specification Table A-3.1) that are
subjected to tension stress.
3. Growth resulting from repeated application of
live loads.
• Overhead cranes resulting in cyclic
loads.
Reciprocating Equipment Support
• Other moving equipment.
• Stationary equipment with moving parts.
11
Why is it Relevant to Industrial Structures?
Fatigue is relevant to industrial

buildings because steel is commonly
used in high-cycle applications
12
© Copyright 2023 8
Session 8 Outline

example.
performance.
fatigue.
13
Theory of Fatigue – Behavior
“Fatigue is the process of cumulative damage…that is caused by

repeated fluctuating 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.”
-Barsom and Rolfe as quoted in AISC DG 21.
14
© Copyright 2023 9
“Fatigue is the process of cumulative damage…that is caused by

repeated fluctuating 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.”
-Barsom and Rolfe as quoted in AISC DG 21.
Fatigue damage will only occur in regions that deform plastically

(local stress exceeding the yield stress) under repeated fluctuating
loads.
15
Causes of inelastic local stresses in an element designed to be elastic?
Stress Concentration
From AISC Specification Table A-3.1
16
© Copyright 2023 10
Other sources of stress concentrations can be derived from:
1. Surface discontinuity
2. Weld flaws
3. Changes in Shape or Geometry
17
Stress Concentration
Area of local
plastic stress
18
Cyclic Loading Propagating the Crack
19
Factors Influencing Fatigue Performance
1. Type of stress concentration or riser.

2. Number of cycles.
3. Magnitude of the stress range.
20
From AISC Specification 21
29.3 ksi
1,000,000 cycles
24 ksi
Factors With Less Influence on Fatigue Performance
1. Minimum applied stress

2. Mean applied stress
3. Maximum stress (<0.66Fy)
4. Specified yield stress of the material (36 ksi ≤ Fy ≤ 100 ksi)
5. Elevated temperature (as long as T < 300°F)
6. Lower temperature (brittle fracture concerns may govern)
24
Session 8 Outline

example.
performance.
fatigue.
25
Fatigue Design in the AISC Specification Appendix 3
AISC Specification Section B3.11:
26
Appendix 3 – Fatigue
3.1 – General Provisions
3.2 – Calculation of Maximum Stresses and Stress Ranges
3.3 – Plain Material and Welded Joints
3.4 – Bolts and Threaded Parts
3.5 – Fabrication and Erection Requirements for Fatigue
3.6 – Nondestructive Examination Requirements for Fatigue
27
3.1 General Provisions

• Applies to members and connections subjected to high-
cycle loading within the elastic range of stresses of
frequency and magnitude sufficient to initiate cracking and
progressive failure.
• Applies to items subjected to more than 20,000 cycles.
• No further evaluation required when the applied cyclic
stress range is less than the threshold allowable stress
range, FTH.
28
3.1 General Provisions

• Engineer of Record (EOR) must provide full details for all
elements subjected to fatigue or provide planned cycle life
and maximum force ranges.
• Maximum stress must be kept less than 0.66Fy.
• Adequate corrosion protection must be provided, if
applicable.
• Only applicable when the temperature is less than 300 °F.
29
3.2 Determining Maximum Stresses and Stress Range

• Use elastic analysis:
P
fa =
A
M
fb =
S
From AISC Specification
30

• No need to include stress concentration factors (already
accounted for in the AISC Specification Equations)
31

P
Mmax=PL/4, fb,max = Mmax/S 32

P
b
M=Pb/2, fb = M/S
33
Maximum Stress
Stress range
One cycle 34
Stress from constant

dead load (if fb/fb,max Maximum Stress
from dead load is 20%)
Stress range
One cycle 35
= −
= 20 − −20 = 40
Tension
Compression
Additional examples from AISC Design Guide 21 on

Stress range
Welded Connections (Miller, 2017)
36
3.3 Plain Material and Welded Joints
37

For stress categories A, B, B’, C, D, E, and E’
.
= 1,000 ≥ (Spec. Eq. A-3-1)
where:
=constant from Table A-3.1 for the fatigue category
= allowable stress range (ksi)
= threshold allowable stress range, maximum stress
range for indefinite design life from Table A-3.1, ksi
= number of stress range fluctuations in design life
39
.
= 1,000 ≥ (Spec. Eq. A-3-1)
10
≈

For stress category F (Shear on fillet weld throat, plug weld, or slot welds)
.
1.5
= 100 ≥8 (Spec. Eq. A-3-2)
where:
1.5 × 10
≈
41
3.3 Plain Material and Welded Joints – Tension Loaded Plate Elements
with transverse PJP or fillet welds.
PJP Fillet

42
2
0.65 − 0.59 + 0.72
(Spec. Eq. A-3-4) = . ≤ 1.0
where:
= weld reduction factor for reinforced or nonreinforced
transverse PJP groove welds.
= thickness of tension loaded plate
2 = length of nonwelded root face in the direction of the
thickness of the tension-loaded plate.
= leg size of reinforcing or contouring fillet, if any, in the
direction of the thickness of the tension loaded plate 43
with transverse PJP welds.
RPJP Per Eq. A-3-4 RPJP = 1.0 RPJP < 1.0
Crack Initiation Toe of Weld Root of Weld

Point
Stress Category C C’
. .
FSR 4.4 4.4
1,000 ≥ 10 1,000
(Spec. Eq. A-3-3)

(from Spec. Eq. A-3-1)
(No threshold stress) 44
0.06 + 0.72 ⁄
(Spec. Eq. A-3-6) = . ≤ 1.0
where:
= reduction factor for joints using a pair of transverse fillet
welds only
= thickness of tension loaded plate
= leg size of fillet weld in the direction of the thickness of the
tension loaded plate
45
RFIL Per Eq.A-3-6 RFIL = 1.0 RFIL < 1.0
Crack Initiation Toe of Weld Root of Weld

Point
Stress Category C C’’

. .
FSR 4.4 4.4
1,000 ≥ 10 1,000
(Spec. Eq. A-3-5)

(from Spec. Eq. A-3-1)
(No threshold stress) 46

47
3.4 Bolts and Threaded Parts

Mechanically fastened connections in shear (similar to previous):
.
= 1,000 ≥ (Spec. Eq. A-3-1)
where:
=constant from Table A-3.1 for the fatigue category
= threshold allowable stress range, maximum stress
range for indefinite design life from Table A-3.1, ksi
48
3.4 Bolts and Threaded Parts

Bolts and Threaded Parts in Tension (Spec. Eq. A-3-7)
0.9743
1. Stress range must include = −
4
applicable tension effects from
prying. where:
2. Tensile stress area, At, must be =nominal bolt diameter
used (See Equation A-3-7 or = threads per inch
Manual Table 7-17).
3. Stress category G is applicable
(Cf = 0.39, FTH = 7 ksi).
49
RCSC Additional Requirements for Joints Subject to Fatigue:
Section 4.3 - Slip Critical

• Joints subject to shear or combined shear and tension
fatigue (with reversal of the loading direction)
Section 4.2 - Pretensioned but not Slip Critical
• All other joints subject to fatigue (tension only or shear
force with no reversal of load)
50
RCSC Section 5.5 - Additional Requirements for Joints Subject to

Fatigue:
1. The portion of the force from prying cannot exceed 30% of the
externally applied load.
2. The maximum bolt stress is limited based on values contained in
Table 5.2 of the RCSC Specification.
51
RCSC Additional Requirements for Joints Subject to Fatigue:

Table 5.2 – Maximum tensile stress for fatigue loading
Maximum Bolt Stress for Designa, ksi
Number of Cycles
ASTM A325 or F1852 ASTM A490 or F2280
Not more than 20,000 45 57
From 20,000 to
40 49
500,000
More than 500,000 31 38
a Including the effects of prying action, if any, but excluding the pretension.
*Calculated stress is based on the nominal diameter.
52
3.5 Fabrication and Erection Requirements for Fatigue

1. Requirements for longitudinal steel backing.
2. Requirements for the addition of reinforcing fillets in transverse
CJP groove welded joints at reentrant corners.
3. Requirements for surface roughness of thermally cut edges.
4. Requirements for radii for reentrant corners at cuts, copes and
weld access holes.
5. Requirements for welding at transverse butt joints in regions of
tensile stress.
6. Requirements for end returns when fillet welds are used at
outstanding legs of angles or end plates.
53
3.6 Nondestructive Examination Requirements for Fatigue
CJP welds must meet the acceptance criteria of AWS D1.1 Clause
8.12.2 or Clause 8.13.2 through ultrasonic or radiographic testing in
order to use the allowable stress ranges in AISC Specification
Appendix 3.
54
Crane Girder Example

Given: Crane Information
• Crane Capacity = 65 tons = 130 kips
• Wheel Spacing = 5’-9”, 5’-11”, 5’-9”
• Impact Factor (Not relevant for fatigue)
• Lateral Load = PL = 6.5 kips /wheel
• Maximum Wheel Load = P = 62 kips (without impact)
• Minimum Wheel Load = Pmin = 22 kips (without impact)
• 1,000,000 cycles (whole crane passing past the point of interest)
55

Given: Crane girder information
(Session 4)
• Span = 40’ (simple span)
• W Beam – W36x441,
weight = 441 plf
• Angles – L6x6x3/4,
weight = 28.7 plf/angle
• Superimposed dead load (rail, rail
clips, electrification) = 108.3 plf
• Total Dead Load = 606.7 plf
56

Design Section Combined Properties (using section analysis software):
A = 146.9 in2 d = 38.9 in rx = 15.62 in

Ix = 35,830 in4 tw = 1.36 in ry = 5.11 in
Iyc = 2,828 in4 bf = 17.0 in rt = 6.54 in
Iyt = 999 in4 tf = 2.44 in kdes = 3.39 in
Sxc = 2,025 in3 Zx = 2,077.4 y1 = 21.21 in
in3
Sxt = 1,690 in3 Zyc = 301 in3 Qx = 114.2 in3 (per angle)
Syc = 236 in3 Zyt = 176 in3 Qy = 86.6 in3 (per angle)
Syt = 118 in3
57

Determine: 3
1. If the applied stress range at the

bottom flange is acceptable per 2
AISC Specification Appendix 3.

2. If net tension stress exists at the
top flange, and if so, if the applied
tensile stress range is acceptable
per AISC Specification Appendix 3.
3. If the stress range is acceptable in
the weld between the reinforcing
1
angles and the wide-flange girder
58

General Procedure
1. Determine internal forces from the applied loading differentiating
between permanent and cyclical forces.
2. Confirm the peak stress from the applied loading does not exceed
the limit from AISC Specification Appendix 3 of 0.66Fy.
3. Determine the applicable stress category based on the detailing of
the member and its allowable stress range and compare to the
applied cyclical loading.
59

Determination of the effects of the crane actions at service load level
using AIST Technical Report No. 13 Guide for the Design and
Construction of Mill Buildings.
Cds: Crane dead load for a single crane with crane trolley positioned to produce the
maximum load effect for the element under consideration (Crane bridge, end
trucks, and trolley.)
Cvs: Crane lifted load for a single crane with crane trolley positioned to produce the
maximum load effect for the element in consideration.
Css: Crane side thrust from a single crane
60

• Crane girder self-weight and similar items such as crane rail or
electrification system do not vary with time and therefore do not
contribute to the stress range amplitude. However, they should be
considered when checking to see if an element is subjected to
tension stress at any time during its life.
• Cds,max + Cvs,max = maximum wheel load, P = 62 kips/wheel
• Cds,min + Cvs,min = minimum wheel load, Pmin = 22 kips/wheel
• Css = PL = 6.5 kips/wheel
• Combination for fatigue -> Cds + Cvs + ½ Css (without impact)
• Combination for net tensile stress -> D + Cds + Cvs + ½ Css (without
impact)
61

• Determine location of maximum stress.
• AISC Manual Table 3-23:
– General Rules for Simple Beams Carrying Moving Concentrated Loads
– “The maximum bending moment produced by moving concentrated loads occurs
under one of the loads when that load is as far from one support as the center of
gravity of all the moving loads on the beam is from the other support.”
AISC Manual Table 3-23 62

18.52 ft 2.96 ft 18.52 ft
12.77 ft 5.75 ft 2.96 ft 2.96 ft 5.75 ft 9.81 ft
Maximum moment location CG of load group
40 ft
63

• AISC Manual Table 3-23, Case 10:
– Use superposition for each pair of wheel loads.
AISC Manual Table 3-23 64

• For the left pair, a = 12.77 ft., b = 21.48 ft., l = 40 ft
M PL  R2b
P 
  l  b  a  b
l 
 P
  40 ft.  21.48 ft.  12.77 ft.  21.48 ft.
 40 ft. 
 P 16.8 ft.
65

• For the right pair, a = 24.44 ft., b = 9.81 ft., l = 40 ft, x = 18.52 ft
M PR  R1x
P 
  l  a  b  x
l 
 P
  40 ft.  24.44 ft.  9.81 ft. 18.52 ft.
 40 ft. 
 P 11.7 ft.
66

• AISC Manual Table 3-23, Case 10:
– Use superposition for each pair of wheel loads.
M P  M PL  M PR
 P 16.8 ft.  P 11.7 ft.
 P  28.5 ft.
Case P (kip) MP (kip-ft)

Cds,max + Cvs,max 62.0 1,770
Cds,min + Cvs,min 22.0 627
Css 6.5 185
67
Crane Lateral – Consider amplification for vertical rail eccentricity

P
e
e+h e
Peff, Top = P Peff, Top
h Peff, Top
(6+2.44/2) + (38.9−2.44) hf
Peff, Top = P hf
(38.9 − 2.44)
Peff, Top = P (1.198) Peff, Bott Peff, Bott
Peff, Bott = P (0.198)

68

• Design Moments adjusted for rail eccentricity
Case P MP (kip-ft)
Cds,max + Cvs,max 62.0 kip 1,770
Cds,min + Cvs,min 22.0 kip 627
Css (top flange) 6.5 kip x 1.198 = 222
7.79 kip
Css (bottom 6.5 kip x 0.198 = 36.8
flange) 1.29 kip
69
One cycle
Stress range
70
wD = 0.607 klf
From AISC Manual Table 3-23, Case 1:
0.607 40
= = = 12.1
2 2
0.607 40
= = = 121 −
8 8
0.607 18.52
= − = 40 − 18.52 = 121 −
2 2
71

Applied forces (See Session 4):
Load
Vx Vy Mx Myc Myt P
Case
D 12.1 k 121.3 k*ft
Cds 83.6 k 762.3 k*ft
Cvs 110.4 k 1,007.9 k*ft
Ci 48.5 k 442.6 k*ft
Css 24.3 k (t) 222.4 k*ft 36.7 k*ft
4.0 k (c)
Cls 2.3 k 92.8 k*ft 24.8 k (T or
C)
Cbs 19.4 k 775.1 k*ft 135 k (T)
72

Determine:
bottom flange is acceptable per
1
73
Effective sections for resisting forces at the bottom flange
= 35,830 .
35,830 .
= = = 1,690 .
21.21 .
Strong Axis Moments

74
Effective sections for resisting forces at the bottom flange
= ⁄6
= 2.44 . 17 . ⁄6
= 118 .
Weak Axis Moments

75
Check maximum stress under cyclic loading < 0.66Fy.

Mx = D + Cds,max + Cvs,max + ½ Css = 121 kip-ft + 1,770 kip-ft = 1,890 kip-ft =
22,700 kip-in.
My = D + Cds,max + Cvs,max + ½ Css = (1/2)(36.8 kip-ft) = 18.4 kip-ft = 221 kip-in.
Sxt = 1,690 in.3 (at bottom flange, from previous)
Syt = 118 in.3 (at bottom flange, from previous)
22,700 − . 221 − .
= + = + = 15.3
1,690 . 118 .
0.66 = 0.66 50 = 33 > 15.3 . .
76
Mx = Cds,max + Cvs,max + ½ Css = 1,770 kip-ft = 21,200 kip-in.

My = Cds,max + Cvs,max + ½ Css = (1/2)(36.8 kip-ft) = 18.4 kip-ft = 221 kip-
in.
Sxt = 1,690 in.3 (at bottom flange, from section analysis software)
Syt = 118 in.3 (at bottom flange, from section analysis software)
21,200 − . 221 − .
= + = + = 14.4
1,690 . 118 .
77
Stress Category A
= 14.4 < = 24 o.k.
78
Stress Category A
= 25, = 1,000,000
.
= 1,000 ≥ (Eq. A-3-1)
.
25
= 1,000 ≥ 24
1,000,000
= 29.3 79

Determine:

top flange, and if so, if the
applied tensile stress range is
acceptable per AISC
Specification Appendix 3.
per AISC Specification Appendix 3. 80
Determine forces producing largest potential tension at top flange

allowing for benefit of dead load.
Mx,min = D + Cds,min + Cvs,min + ½ Css = 121 kip-ft + 627 kip-ft = 748 kip-ft = 8,980 kip-in.
My = D + Cds,max + Cvs,max + ½ Css = (1/2)(222 kip-ft) = 111 kip-ft = 1,330 kip-in.
81
Effective sections for resisting forces at the top flange
Strong Axis Moments Weak Axis Moments

= 35,830 . = 2,828 .
82
E
Potential governing stress points
D
C
B
A
Strong Axis Moments

Weak Axis Moments
= 35,830 . = 2,828 .
83
Stress under D + Cds,min + Cvs,min + 1/2Css
Point y (in.) fbx (ksi) x (in.) fby (ksi) fb (ksi)

A 9.25 -2.32 12.0 5.64 3.33
B 15.25 -3.82 12.0 5.64 1.82
C 15.25 -3.82 8.50 4.00 0.175
D 15.25 -3.82 6.00 2.82 -1.00
E 17.69 -4.43 8.50 4.00 -0.436
= 35,830 . = 2,828 .
Mx,min = 8,980 kip-in. My = 1,330 kip-in.
84
Determine forces producing largest potential stress at top flange including

dead load.
Mx,max = D + Cds,max + Cvs,max + ½ Css = 121 kip-ft + 1,770 kip-ft = 1,890 kip-ft = 22,700 kip-in.
My = D + Cds,max + Cvs,max + ½ Css = (1/2)(222 kip-ft) = 111 kip-ft = 1,330 kip-in.
85
Stress under D + Cds,max + Cvs,max + 1/2Css

Point y (in.) fbx (ksi) x (in.) fby (ksi) fb (ksi)
A 9.25 -5.86 12.0 -5.64 -11.5
≤ 0.66 = 33
B 15.25 -9.66 12.0 -5.64 -15.3 o.k.
C 15.25 -9.66 8.50 -4.00 -13.7
D Not subject to net tension during service life
E Not subject to net tension during service life
= 35,830 . = 2,828 .
Mx,max = 22,700 kip-in. My = 1,330 kip-in.
86
Determine forces producing largest potential extreme stress range at top

flange (not including dead load).
Mx,max = Cds,max + Cvs,max + ½ Css = 1,770 kip-ft = 21,200 kip-in. (maximum compression case)
Mx,min = Cds,max + Cvs,max + ½ Css = 627 kip-ft = 7,520 kip-in. (maximum tension case)
My = Cds,max + Cvs,max + ½ Css = (1/2)(222 kip-ft) = 111 kip-ft = 1,330 kip-in.
87
Stress under Cds,max + Cvs,max + 1/2Css

Point y (in.) fbx (ksi) x (in.) fby (ksi) fmin (ksi)
A 9.25 -5.47 12.0 -5.64 -11.1
B 15.25 -9.02 12.0 -5.64 -14.7
C 15.25 -9.02 8.50 -4.00 -13.0
= 35,830 . = 2,828 .
88
Stress under Cds,min + Cvs,min + 1/2Css

Point y (in.) fbx (ksi) x (in.) fby (ksi) fmax (ksi)
A 9.25 -1.94 12.0 5.64 3.70
B 15.25 -3.20 12.0 5.64 2.44
C 15.25 -3.20 8.50 4.00 0.797
= 35,830 . = 2,828 .
89
Stress Range from Maximum to Minimum Stress

Point fmin (ksi) fmax (ksi) fSR (ksi) Stress Threshold
Category Stress,
FTH
(ksi)
A -11.1 3.70 14.8 ? ?
B -14.7 2.44 17.1 ? ?
C -13.0 0.797 13.8 ? ?
= − 90
Stress category assignment

E
D
C
B
A
91

E
D
C
B
A
92

E
D
C
B
A
93

E
D
C
B
A
94

E
D
C
B
A
95
In all cases, predicted stress range is

Crane Girder Example less than the threshold limit at points
where net tension may occur during
service life.
Top Flange Fatigue Summary
Point fmin (ksi) fmax (ksi) fSR (ksi) Stress Threshold
Category Stress,
FTH
(ksi)
A -11.1 3.70 14.8 A 24
B -14.7 2.44 17.1 A 24
C -13.0 0.797 13.8 B 16
96

Determine: 3

bottom flange is acceptable per
3. If the stress range is acceptable
in the weld between the
reinforcing angles and the wide-
flange girder per AISC
Specification Appendix 3. 97

Critical Wheel Location to produce largest shears
5.75 ft 5.92 ft 5.75 ft 22.58 ft
40 ft
98

Applied forces (See Session 4):
Load
Vx Vy Mx Myc Myt P
Case
D 12.1 k 121.3 k*ft
Cds 83.6 k 762.3 k*ft
Cvs 110.4 k 1,007.9 k*ft
Ci 48.5 k 442.6 k*ft
Css 24.3 k (c) 222.4 k*ft 36.7 k*ft
4.0 k (t)
Cls 2.3 k 92.8 k*ft 24.8 k (T or
C)
Cbs 19.4 k 775.1 k*ft 135 k (T)
99
Determine forces producing largest potential extreme stress range at top

flange welds (not including dead load).
Vx,max = Cds,max + Cvs,max + ½ Css = 194 kips (shear in vertical direction)

Vy = Cds,max + Cvs,max + ½ Css = (1/2)(24.3 kips) = 12.2 kips (shear in
horizontal direction)
Vx stress range will be based on no crane present to Vx,max

Vy stress range will be based on ±Vy since it can work in either direction
100

• Check welds for shear flow forces due to vertical and lateral shear
similar to process in session 4.
VQ (194 k)(114.2 in ) k
q = = = 0.62
I 35,830 in in
VQ (12.2 k)(86.6 in ) k
q = = = 0.37
I 2,828 in in
Conservative stress range envelope:
q = 0.62 + 2(0.37 ) = 1.36 k/in.
101

Stress range envelope:
q = 0.62 + 2(0.37 ) = 1.36 k/in.
1.36 .
= = 5.13
1.5 0.707 ∗ 0.25 .
102

103

.
1.5
= 100 ≥ 8 ksi
. .
= 100 = 10.7 ksi > 8 ksi
Eq. A-3-2 , ,
= 10.7 ksi
= 5.13 < = 10.7 ksi
o.k.
104
Additional Comments:
1. Basis of stress range in this example enveloped the condition with the
trolley at far girder in combination with lateral portion to the trolley at the
near girder in combination with the lateral portion in the opposite direction at
the worst location on the girder for 1,000,000 cycles.
2. This is an envelope of the possible stress ranges.
3. Further refinement may be possible with close examination of the actual
behavior of the expected crane cycles and foresight into how the crane
operations may change over time.
4. Based on judgment, using an envelope may be prudent to account for
uncertainty in crane operations over time or for girders with concentrated
operations.
105
Example of a concentrated crane operation

106

Summary: 3
1. The applied stress range at the


2. Net tension stress exists at the top
flange; however, the stress range is
acceptable per AISC Specification
Appendix 3.
3. The stress range is acceptable in
1
107
• Max Stress = 28 ksi

• Total Cycles = 1,265,000
108
• 28 ksi: 5,000 cycles; maintenance function

twice per week (0.4%)
• 18 ksi: 420,000 cycles; full ladle
once per hour (33.2%)
• 14 ksi: 420,000 cycles; empty ladle
• 10 ksi: 420,000 cycles; no load
109
• Miner’s Rule
• ni = number of cycles at stress range i
• Ni = Constant amplitude fatigue life at stress range i
110
• Miner’s Rule
• ni = number of cycles at stress range i
• Ni = Constant amplitude fatigue life at stress range i
• Equivalent Stress Range – FHWA

• Sre = Equivalent Stress Range
• Sri = Stress Range of an Individual Cycle
• gi = Percentage of whole corresponding to each stress range
111
• 28 ksi: 5,000 cycles; maintenance function twice per week

• 18 ksi: 420,000 cycles; full ladle once per hour
• 14 ksi: 420,000 cycles; empty ladle once per hour
• 10 ksi: 420,000 cycles; no load once per hour
112
• Equivalent Stress Range  Sre = 14.8 ksi

• Sre is less than FSR = 21.3 ksi
• Design meets requirements of Appendix 3
• Sre is less than FTH = 16 ksi
• Design does not have infinite life because some cycles are above FTH
113

.
10
= 1,000 ≥ ≈
(Spec. Eq. A-3-1)
114

.
10
= 1,000 ≥ ≈
(Spec. Eq. A-3-1)
115

.
10
= 1,000 ≥ ≈
(Spec. Eq. A-3-1)
=
=
10
116
Total number of cycles = ∑ = 1,265,000

Equivalent Stress Range = = 14.837
1,265,000 14.837
= = = 34.4%
10 10 12
34.4% of fatigue life is utilized

meaning that 65.6% remains
117
Total number of cycles = ∑ = 1,265,000

Maximum Stress Range = = 28
1,265,000 28
= = = 231%
10 10 12
231% of fatigue life is utilized
118
=
10
Operation Stress Range, Number of Cumulative % of total

FSR, ksi cycles, ni Damage ∑ cycles
Maintenance 28 5,000 0.915% 0.395%

Full Ladle 18 420,000 20.4% 33.2%
Empty Ladle 14 420,000 9.60% 33.2%
No Lifted 10 420,000 3.50% 33.2%
Load
Total 1,265,000 34.4% < 1.0 100%
119
28 ksi
28 ksi
Cycles 1%
1% 18 ksi
20%
10 ksi 18 ksi
33% 33%
14 ksi
10%
Unused 10 ksi
66% 3%
14 ksi
33%
/
120
Session 8 Outline

example.
performance.
fatigue.
121
Fatigue Performance of Selected Details
122
123
124
125
= 14.4 > = 10
.
Stress Category C = 1,000 ≥ (Eq. A-3-1)
= 4.4, = 1,000,000 .
4.4
= 1,000 ≥ 10
1,000,000
= 16.6 > = 14.4 ok.
126

Stress category C
14.4 ksi
10
≈
10 4.4
≈
14.4
1.47 million cycles
≈ 1.47
127
128
1. Additional cyclic
stresses from
local bending in
the top flange
(or weld of built-
up section).
2. Additional cyclic
stresses from
torsion.
129

See Session 3 for discussions on:
1. Details for accommodating girder end movement at crane

beam to cap plate connections.
2. Details for accommodating girder end movement at crane
beam tie back connections.
130
Session 8 Outline

example.
performance.
5. The role of inspections and maintenance in structures
designed for fatigue.
131
Role of Inspections in Structures Designed for Fatigue
1. Inspections during fabrication

1. Quality control/Quality assurance
2. NDE Specific to Fatigue (AISC Specification Appendix 3, Section
3.6)
2. Inspections during erection
1. Structural Observations (general conformance with design intent)
2. Special Inspection (Quality control/Quality Assurance)
132
Role of Inspections in Structures Designed for Fatigue
Inspections during service

1. Performance of an initial inspection of the runway structure for a
baseline.
2. Developing a plan for periodic general inspection.
3. Special-Purpose Inspections
1. For high-use areas or historically problematic areas.
2. Before upgrades or major changes in manufacturing process.
133
Role of Maintenance in Structures Designed for Fatigue
Documentation of • Goal is to identify and repair

Remedial Work Inspection
fatigue damage in a timely
manner to maintain a safe
building and serviceable
runway structure.
Documentation
Remedial
of Damage and
Work
Wear
Evaluation
of
Inspection
Results
134
Summary
1. Fatigue is a limit state of crack initiation and growth resulting
from repeated applications of live loads and can be especially
relevant in the design of industrial structures.
2. Stress range, detailing (stress category), and number of cycles
have the more significant effect on fatigue performance.
3. The AISC Specification Appendix 3 provides allowable stress
ranges that can be used to design for fatigue.
4. Ongoing inspections and maintenance are beneficial to prevent
and mitigate potential fatigue damage in industrial structures.
135
Learning Objectives
• Participants will gain a general understanding of what fatigue design

is and factors that influence fatigue performance.
• Participants will understand the role that the AISC Specification
performs in design for fatigue.
136
AISC | Questions?
Group Registrants – 8 session package

PDH Certificates
•Register all attendees before the webinar, register coworkers to give them access to their own webinar
connection and certificate (e.g. work-from-home).
•All registrants must be pre-registered and participate from their own connection. For Night School, we no
longer offer the option to register attendees (report attendance) after the webinar.
•All group participants have the option to watch live sessions on Tuesday evenings. Or watch the recordings
and take/pass a quiz for PDH credit. Access the quiz and recording 48 hours after the live session at
learning.aisc.org. Log in to your account, then access your course.
•One certificate will be issued at the conclusion of all 8 sessions.
Individual Registrants: 8 session package

PDH Certificates
•All individual registrants have the option to watch live sessions on Tuesday evenings. Or watch the
recordings and take/pass a quiz for PDH credit. Access the quiz and recording 48 hours after the live session
at learning.aisc.org. Log in to your account, then access your course.
•One certificate will be issued at the conclusion of all 8 sessions.
All Registrants
Access to the recording | Access to the quiz | Access to attendance
records
Go to learning.aisc.org.
- Click on the session drop-down menu, then choose recording, quiz, or credits.
All Registrants
Access to the recording | Access to the quiz | Access to attendance
records
Go to learning.aisc.org.
- Click on the session drop-down menu, then choose recording, quiz, or credits.
All Registrants
Reasons for quiz

• Certificate of Completion – You must pass 7 of 8 quizzes and the final exam to receive certificate of
completion.
• PDHs – If you watch a recorded session or did not watch at your own connection, you must pass quiz for
PDHs.
• REINFORCEMENT – Reinforce what you learn tonight. Get more out of the course.
Note: If you attend the live presentation at your own connection, you do not
have to take the quizzes to receive PDHs
All Registrants
PDHs via recording
If you watch a recorded session or watched at someone else’s connection, you must take and pass the quiz
for PDHs.
8-Session Registrants
Night School Resources
Find all your handouts, quizzes and quiz scores, recording access, and
attendance information all in one place!
learning.aisc.org
AISC | Thank you

NS32 - Session 8 - Handouts - 2 Per

Uploaded by

Copyright:

Available Formats

NS32 - Session 8 - Handouts - 2 Per

Uploaded by

Document Information

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

NS32 - Session 8 - Handouts - 2 Per

Uploaded by

Copyright:

Available Formats

Industrial Structure Design

AISC Night School Session 8: Fatigue, Inspections, and

Night School 32:

Thank you for joining our live

Industrial Structure Design

Today’s live webinar will begin shortly. Please stand by.

Today’s live webinar will begin shortly. Please stand by.

Please type any questions or comments in the Q&A window.

Industrial Structure Design

Night School 32: Industrial Structure Design

Joshua Buckholt, PE, SE

This session will provide an overview of fatigue design,

• Participants will gain a general understanding of what fatigue design

1. What is fatigue and why is it relevant to industrial structures?

1. What is fatigue and why is it relevant to industrial structures?

What is Fatigue? ANSI/AISC 360-16

Fatigue: Limit state of crack initiation and

What is Fatigue? ANSI/AISC 360-16

Fatigue: Limit state of crack initiation and

What is Fatigue? ANSI/AISC 360-16

Pervasive cyclic inelastic stresses -> Low cycle fatigue

Image by Stefan Schweihofer

High Cycle Fatigue

Why is it Relevant to Industrial Structures?

Why is it Relevant to Industrial Structures?

Fatigue is relevant to industrial

1. What is fatigue and why is it relevant to industrial structures?

Theory of Fatigue – Behavior

“Fatigue is the process of cumulative damage…that is caused by

-Barsom and Rolfe as quoted in AISC DG 21.

Theory of Fatigue – Behavior

“Fatigue is the process of cumulative damage…that is caused by

-Barsom and Rolfe as quoted in AISC DG 21.

Fatigue damage will only occur in regions that deform plastically

Theory of Fatigue – Behavior

Causes of inelastic local stresses in an element designed to be elastic?

From AISC Specification Table A-3.1

Theory of Fatigue – Behavior

Other sources of stress concentrations can be derived from:

Theory of Fatigue – Behavior

From AISC Specification Table A-3.1

Theory of Fatigue – Behavior

Cyclic Loading Propagating the Crack

Factors Influencing Fatigue Performance

1. Type of stress concentration or riser.

Factors Influencing Fatigue Performance

From AISC Specification 21

Factors Influencing Fatigue Performance

From AISC Specification 22

Factors Influencing Fatigue Performance

From AISC Specification 23

Factors With Less Influence on Fatigue Performance

1. Minimum applied stress

1. What is fatigue and why is it relevant to industrial structures?

Fatigue Design in the AISC Specification Appendix 3

AISC Specification Section B3.11:

Fatigue Design in the AISC Specification Appendix 3

Fatigue Design in the AISC Specification Appendix 3

3.1 General Provisions