Class 6 Local Stress Based Fin

8/6/2019 Class 6 Local Stress Based Fin

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Local (Structural) Stress BasedFatigue Design

Chitoshi Miki

Department of Civil Engineering

Tokyo Institute of Technology

Retrofit Engineering for Urban Infrastructures, Lecture #6

ContentsContents

Brief Review of Nominal Stress BasedBrief Review of Nominal Stress BasedFatigue DesignFatigue Design

Structural Stress Based Fatigue DesignStructural Stress Based Fatigue Design

--Fatigue Assessment of Welded JointsFatigue Assessment of Welded Joints--

>Cope Hole Joints>Cope Hole Joints

>High Strength Steel Steels>High Strength Steel Steels

Stress Analysis Method for Root CracksStress Analysis Method for Root Cracks

--Effective Notch StressEffective Notch Stress--

Fatigue Design

Nominal Stress Based Fatigue Design (Review)

Butt Welded Joints:

JSSC-Category D

Non-Load Carrying

Cruciform Joints:

JSSC-Category E

Load CarryingCruciform Joints:JSSC-Category H

StrengthCategoryJoint Types

Structural Hot-spot Stress Approach

Structural Stress Based Fatigue Design

Fatigue Design

Define the fatigue strengths directly

By the local stress at crack initiation points

Stress Distribution

Stress Concentration

Structural Stress (Hot Spot Stress)Structural Stress (Hot Spot Stress)

approachapproach

Local Stresses

control the fatigue phenomenon

in any types of joints.

The Types of Joints dont affectthe Fatigue Strengths Definedby Structural Hot-Spot Stress Approach

Importance of The StructuralImportance of The Structural

HotHot--Spot Stress ApproachSpot Stress Approach

The Structural Hot-Spot Stress Approach isApplicable to Complicated Stress Conditions

due to complicated geometry

due to structural discontinuities

due to complicated plate deformation


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Complicated Geometry of JointsComplicated Geometry of Joints

Weld Bead Sizes, Angle, Finishing, Plate Thickness,

Symmetry, Complicated Stress Transferring

Influential Factors

Structural Discontinuities

Complicated Plate DeformationComplicated Plate Deformation

For Example,In case of Steel Orthotropic DeckBridges

Axle Load

FEM Analysis Result

HotHot SpotsSpots

2 Types: a and b

Definition of The StructuralDefinition of The Structural

HotHot--Spot StressSpot Stress

2

2

11

1 =HotSpot

1

< 45

Dependency of Structural Stress on the Angle (1)


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2

2

11

normalHotSpot =

normal

> 45

Dependency of Structural Stress on the Angle (2)Definition of The StructuralDefinition of The Structural

HotHot--Spot StressSpot Stress

The Estimation Method ofThe Estimation Method of

The Structural HotThe Structural Hot--Spot StressSpot Stress

by Measuring Strainby Measuring Strain

Linear Extrapolation

Hot Spot SHot Spot S--N CurvesN Curves

Hot Spot SHot Spot S--N CurvesN CurvesHot Spot Stresses in ComplexHot Spot Stresses in Complex

Welded StructuresWelded StructuresTypes of Weld Toes

Type a) : On the Plate Surface at the End of an AttachmentType b) : At the Plate Edge at the End of an AttachmentType c) : Along the Weld of an Attachment


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The Estimation Method ofThe Estimation Method of

The Structural HotThe Structural Hot--Spot StressSpot Stress

by FEM Analysisby FEM Analysis

FEM Modeling for StructuralFEM Modeling for Structural

HotHot--Spot Stress Evaluation(1)Spot Stress Evaluation(1)

Solid Elements

Extrapolation pointsAt Nodes

FEM Modeling for StructuralFEM Modeling for Structural

HotHot--Spot Stress Evaluation(2)Spot Stress Evaluation(2)

Shell Elements

Extrapolationpoints

Modeling of Offsets in Shell ModelsModeling of Offsets in Shell Models

Doubling Plates Hopper Corner

Round Robin StudyRound Robin Study

for Hopper Corner Modelfor Hopper Corner Model

Recommended Techniques forRecommended Techniques for

Modeling of WeldsModeling of Welds

Shell Elements

Method I:Inclined Shell Elements

Method II:Thickness Changes

International Institute of Welding (IIW)


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Fatigue Assessment of CopeFatigue Assessment of Cope

Hole Details in Steel BridgesHole Details in Steel Bridges Fatigue Test Results

FEM Analysis Results

R=35(Tension)

R=35(Compression)

FEM Analysis ResultsR=35

R=45

Cope Hole Located 250mmaway from the Loading Point

Cope Hole Located directlybelow the Loading Point

Definition of Hot Spot Stress Influence of Shear Force (Specimen 1)


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Stress Distribution (FEM) Comparison between Analyzedand Estimated SCF Values

Crack Length: 10mm Crack Length: 20mm

S-N Diagram Arrangedon Hot Spot Stress Range

Fatigue Assessment of Welded Jointsmade of High Strength Steels

Out-of-Plane GussetsCruciform JointsLongitudinal Joints

Fatigue Test Data

-Out-of-Plane Gusset Joints-Effects of Strength of Steels

900MPa Class SteelJIS SM570

Fatigue Test Data

-Out-of-Plane Gusset Joints-

Girder SpecimensJoint Specimens


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SYMGusset

Uniform Uni-Axial Loading

SYM

Stress Distribution around a Gusset Plate (FEM Results)

Joint Specimens

Girder Specimens

A Proposed Definition of Hot Spot Stress

Principal Stress Distribution around the Gussets

Location of MaximumPrincipal Stress

Stress Distribution

Crack Initiated from the toelocated in the front

Joint Specimens

Principal Stress Distribution around the Gussets

Girder Specimens

Pure BendingShear Bending

4 Point Bending Tests

1.667

1.645

1.829

3.115

1.784

3.110

2.245

1.704 1.667

2.263

1.876

1.682

1.879

1.781

1.675 1.639

1.775

1.720

1.670 1.644

1.746

1.769

1.725

1.675 1.648

1.809

1.990

1.698 1.666

2.097

2.564

1.793 1.755

2.730

2.261

1.753

2.010

2.513

1.856

1.687

1.723

1.670 1.653

1.692

1.777

1.667 1.651

1.735

1.658

1.681 1.679

1.658

1.665

1.697 1.697

1.665

1.749

1.676

1.748

1.682

1.706

1.8401.824

1.691

Pure BendingShear Bending

A:X=1300 B:X=1100A:X=900 B:X=700

A:X=500 B:X=300A:X=-350 B:X=-550

H=50

H=91

H=158

H=200

Dependent

on the Location of the Gussets

Change of Stress

With Increase of the RatioBetween Principal Stress and

Nominal Stress


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The Target Cracks of StructuralThe Target Cracks of Structural

HotHot--Spot Stress ApproachSpot Stress Approach

AB

B

A: Cracks Initiated from the Weld Toe

B: Cracks Initiated from the Roots

Structural Stress ApproachCannot be Applied

Structural Stress ApproachCan be Applied

Different Approach is Needed

Stress Evaluation by theStress Evaluation by the

Effective Notch StressEffective Notch Stress

Limited to the thickness t >= 5mm

If the Toe is Finished, the radius = 2mm

An Example of Application of theAn Example of Application of the

Effective Notch StressEffective Notch Stress

BeamBeam--toto--Column ConnectionsColumn Connections--

Analysis CodeAnalysis Code ABAQUSABAQUS

Min Element SizeMin Element Size 11.5mm (T/2)11.5mm (T/2)

Number of NodesNumber of Nodes 91,27891,278

Number of ElementNumber of Element 90,20090,200

170

79

10690

111

5500

2500

4750

2500

Load

Fixed

Beam Element

Full Scaled Structures

Detailed Solid ModelsDetailed Solid Models

FEM Mesh

No. of Nodes: 294966No. of Elements: 191382

The Analysis ResultThe Analysis Result

0 20 40 60 80 1000

50

100

150

60mm

Column

Beam

Weld toe

Top of the notch

Stress(MPa)

distance from the edge (mm)

x

Region of Delta zone

Distant Location

Documents

Class 6 Local Stress Based Fin