Delegation of Japan

IIW-DOCUMENT XIII–2386-11

2011 REPORT OF WORK IN PROGRESS

ON FATIGUE STRENGTH OF WELDED JOINTS IN JAPAN

by Chitoshi MIKI

Department of Civil Engineering, Tokyo Institute of Technology 2-12-1, Ookayama, Meguro-ku, Tokyo, Japan

Takeshi MORI

Department of Civil and Environmental Engineering, Hosei University 3-7-2, Kajino-cho, Koganei-shi, Tokyo, Japan

Shozo NAKAMURA

Department of Civil Engineering, Nagasaki University 1-14, Bunkyo-machi, Nagasaki, Japan

Abstract A survey of works in progress on the fatigue strength of welded joints in Japan was conducted on the basis of replies to a questionnaire distributed to the researchers majoring in fatigue of welded joints as well as the members of Commission XIII of the Japanese Institute of Welding and Fatigue Strength Committee of the Japan Welding Society. Three researches on low cycle fatigue, five on high cycle fatigue, three on fatigue crack propagation, and five on fatigue strength improvement and repair are included in this report.

Paper presented at Commission XIII International Institute of Welding

17 July – 22 July 2011, Chennai, India

1

1. LOW CYCLE FATIGUE (1) Fatigue Strength Assessment of Load Carrying Cruciform Joints Based on Effective Notch Strain

Approach

C. Miki, S. Kawin and T. Hanji (Tokyo Institute of Technology) (Contact Address: Chitoshi MIKI / E-mail miki@cv.titech.ac.jp)

Keywords: Load carrying cruciform joints, incomplete penetration, strength mis-matching, local strain approach

The incomplete penetration and strength mis-matching are important issues to assess low and high cycle fatigue resistance of load carrying cruciform joints. This research is aimed to evaluate the fatigue strength focusing on the governing parameters, incomplete penetration and strength mis- matching, using elasto-plastic analysis and effective notch concept. Low and high cycle fatigue test have been carried out for load carrying cruciform joints. Elasto-plastic analysis has been performed on analysis models which were built based on geometry of joint specimens. Effective notch concept is assigned in the analysis models. Local strains along the notch of the failure location were selected and plot against fatigue life. Unique curve can be obtained from the local strain-fatigue life data.

Fig.1 Load-carrying cruciform joint containing incomplete penetration.

Cyclic load-i

Incomplete penetration

Beam Load-carrying cruciform welded joint

Column

101 102 103 104 105 106 10710-4

10-3

10-2

10-1

IidaMiki

Δεef

f

Fatigue life

Toe failure specimen

P100-O45P100-O25-aP100-O25-bP100-O25-cP100-U10P100-U20P100-U25

P60-O45P60-O25-bP60-O25-cP50-O25-aP50-U25P25-O25-aP25-U25

P50-O25-aP25-O25-a

Fig.2 Relation between local strain and fatigue life

2

(2) Improvement in Low Cycle Fatigue Strength of Steel Bridge Piers by Weld Toe Grinding

T. Hanji, N. Nagamatsu and K. Tateishi (Nagoya University) (Contact Address: Takeshi HANJI / E-mail hanji@civil.nagoya-u.ac.jp)

Keywords: low cycle fatigue, weld toe treatment, fatigue strength improvement

This study investigated the effect of the weld toe grinding technique on the low cycle fatigue strength of the steel bridge pier. The steel pier specimens, of which weld toe at the connection between column and base plate was finished by grinding, were tested by applying large cyclic displacement. After comparing the fatigue strength of the specimen in the condition of as-welded and finished toe, it was revealed that the weld toe grinding can improve the fatigue strength of the steel pier even in low cycle fatigue region. Then, local strains around finished weld toe were analyzed by finite element method. The analysis results demonstrated that the local strain at as-welded toe was significantly reduced by grinding.

Testing system

Low cycle fatigue test results

1 100.001

0.01

0.1

Number of Cycles

Nom

inal

Stra

in A

mpl

itude

As–welded specimen: P1I: P1C6: P1C3: P2C6

Finished specimen: P1I: P1C6: P1C3: P2C6

Specimen

Cyclic large displacement

3

(3) Influences of Plate Thickness on Low Cycle Fatigue Strength at Weld Toes of Cruciform Welded Joints

K. Kinoshita and K. Ueda (Gifu University) (Contact Address: Koji KINOSHITA/E-mail kinosita@gifu-u.ac.jp)

Keywords: low cycle fatigue strength, influences of plate thickness, cruciform welded joints

The influences of plate thickness ranging from 25mm to 40mm on low cycle fatigue strength at weld toes of cruciform welded joints were investigated by bending fatigue tests under large plastic strain, and its elasto-plastic FEM analysis. It was found that low cycle fatigue strength decrease with increasing of plate thickness due to increases of local strain at weld toes by increasing plate thickness. Moreover, the decreases of low cycle fatigue strength were evaluated based on increases of local strain at weld toes obtained from elasto-plastic FEM analyses.

Cruciform welded joint specimen

and its set-up

FEM model

Low cycle fatigue strength

Evaluation of decreases of low cycle fatigue strength based on local strain

JackJig

Specimen

450mm

Roller Roller

JackJig

Specimen

450mm

Roller Roller

Cyclic loading

0 1 2（ｍｍ）0 50 100（mm）

0.05mm0.05mm

Minimum mesh size

0.01

0.1

1 10 100

Nom

inal

stra

in a

mpl

itude

Number of cycles

25A-5%-1 25A-5%-2 25A-5%-325A-5%-4 40A-5%-1 40A-5%-240A-5%-3 40A-5%-4

Average 10.50Average 6.50

decrease by 40%

0.5

0.6

0.7

0.8

0.9

1

25 30 35 40 45

Nt/N

t25

Plate thickness (mm)

Fatigue test resultsEvaluation based on local strain

Influence of plate thickness in high cycle fatigue region

4

2. HIGH CYCLE FATIGUE (1) Fatigue Strength Evaluation Method for Out-of-Plane Gusset Welded Joints Failing from Weld

Root

T. Mori (Hosei University) (Contact Address: Takeshi MORI /Email mori@hosei.ac.jp)

Keywords: Out-of-Plane Gusset Welded Joint, Root Failure, Fatigue Strength, Hot Spot Stress

Fatigue crack origin of out-of-plane gusset welded joints is usually weld toe with high stress concen-tration caused by geometrical discontinuities. However, in the case of finishing weld with small weld leg length，the stress concentration at weld root becomes higher compared with that at the toe, and weld root may be an originating point of a fatigue failure. The fatigue strength evaluation method for the out-of-plane gusset welded joints failing from weld root has not been made clear. In this study, fatigue strength evaluation method for out-of-plane welded joints failing from the weld root has been proposed using hot spot stress range through arrangement of existing fatigue test data and FEM ana-lyses.

105 106 1075060708090

100

200

300

400

500

Nom

inal

Stre

ss R

ange

on

Mai

n P

late

⊿σ

(N/m

m2 )

Fatigue Life (cycles)

12−14−912−10.8−8.230−16−412−12−10

12−13−9

10−13−1010−18−12

JSSC−GJSSC−E

12−12−10

JSSC−F

A-B-C A: main plate thickness B: weld leg length on main plate side C: weld leg length on gusset plate side

Root Failure

Hot spot

Hot spot

How to obtain hot spot stress

Finite element model

105 106 1075060708090

100

200

300

400

500

Hot

Spo

t Stre

ss R

ange

at W

eld

Roo

t (N

/mm2 )

Fatigue Life (cycles)

12−17−812−14−9

12−10.8−8.212−12−10 30−16−412−13−9

5−13−105−18−12

JSSC−E

5

(2) Fatigue Test of Misaligned Butt Welded Joints in the Bottom Flange of a Plate Girder Bridge

M. Sakano, D. Yamaoka and K. Funayama (Kansai University) (Contact Address: Masahiro SAKANO / E-mail: peg03032@kansai-u.ac.jp)

Keywords: misalignment, butt weld, fatigue test, fatigue strength, taper, toe grinding

In the case of the plate thickness is 50mm or less, Japanese specifications for highway and railway bridges stipulate that the misalignment of plate thickness of butt welded joints should be 10% or less of the thinner plate thickness. In this study, we investigated the fatigue strength of butt welded joints with 10% or more misalignment of the plate thickness, through fatigue tests using 3 steel girder spe-cimens that have 0mm (0%), 2mm (18%) and 4mm (36%) misaligned butt welded joints in the 11mm thick bottom flange. In addition, the effects of taper grinding and toe grinding are investigated against those misaligned butt welded joints.

(3) Fatigue Test of Floor Beam and Stringers in an Old Deck Truss Bridge Repaired by Welded Steel Plates

M. Sakano, T. Mizuno (Kansai University), Y. Natsuaki (Japan Bridge Association) And K. Masuda (Ministry of Land, Infrastructure and Transport) (Contact Address: Masahiro SAKANO / E-mail: peg03032@kansai-u.ac.jp)

Keywords: deck truss bridge，floor beam，stringer，fillet weld，fatigue strength

An 85 year old deck truss bridge has a lot of bullet wounded members repaired by welded steel plates. In this study, their fatigue strength and cracking behaviour is investigated by fatigue tests using I beam specimens modeled on their stringers and a floor beam wounded and repaired by welded steel plates.

Figure 1．The configurations and dimensions of the specimen

Figure.1 Configurations and dimensions of the specimen

6

(4) Evaluation of Scatter in Fatigue Life of Welded Joints by Fracture Mechanics

K. Tateishi, M. Yoshida and T. Hanji (Nagoya University) (Contact Address: Kazuo TATEISHI / E-mail tateishi@civil.nagoya-u.ac.jp

Keywords: fatigue strength, fracture mechanics, welded joints, Monte-Carlo simulation

In this study, an evaluation method for the scatter in fatigue life of welded joints was developed by applying linear elastic fracture mechanics and Monte-Carlo simulation technique. Fatigue crack prop-agation analysis, of which initial conditions were determined by the Monte-Carlo simulation, was performed on non-load-carrying cruciform welded joints and out-of-plane gusset welded joints. It is demonstrated that the estimated fatigue life by the proposed method distributes around the similar re-gion as the fatigue test data. Consequently, the results indicate the possibility that the fatigue strength curves of welded joints can be established by incorporating a small number of fatigue test data with the proposed method.

Non-load-carrying cruciform welded joints Out-of-plane gusset welded joints

Simulation results and fatigue test data

10

100

1000

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09

Fatigue Life　N

Str

ess

Ran

ge　

⊿σ

1000

Fatigue Life (cycles)105

100

Test Data

106 107 108 109104103

Fatigue crack

(Failure)

MedianSimulation

2.5% 2.5%

meanmean-2s.d.

JSSC-G

Stre

ss R

ange

Δσ

(MPa

)

1010

100

1000

1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09

Fatigue Life　N

Str

ess

Ran

ge　

⊿σ

1000

100

Stre

ss R

ange

Δσ

(MP

a) Median

Simulation

2.5%

Fatigue crack

105 106 107 108 109104

Test Data(Failure)

2.5%

JSSC-E

mean-2s.d. mean

Fatigue Life (cycles)

10

7

(5) Fatigue Strength Evaluation Method for Welded Joints by New Local Stress Concept

K. Tateishi, W. Naruse, T. Hanji and I. Itoh (Nagoya University) (Contact Address: Kazuo TATEISHI / E-mail tateishi@civil.nagoya-u.ac.jp

Keywords: local stress approach, stress concentration, weld toe geometry, fatigue assessment

This study proposed a simple method for estimating local stresses in as-welded joints and established a fatigue assessment method by using the estimated local stress. In this method, the local stress at the as-welded toe is calculated from the stress at the weld toe finished by the grinding technique, where the stress can be measured by strain gauges. Fatigue tests and finite element analyses were conducted with out-of-plane gusset welded joints under the as-welded and the finished condition. Based on the results, the correlation of the local stress in the as-welded and finished joints was established. The proposed local stress estimation formula for out-of-plane gusset welded joints is given as follows. It was concluded that the fatigue strength of the as-welded joints can be evaluated by using the local stress estimated by the proposed method with the stress measured at the finished toe.

σl,aw= Kt,awKt,g

×σl,g.

. .

.. . . ×σl,g where,

.

.

σl,aw is the local stress at the as-welded toe, σl,g is the stress at the finished toe, Kt,aw and Kt,g are the stress concentration factors in the as-welded and the finished joints, raw and θ are toe radius and flank angle in the as-welded joint, rg and d are groove radius and groove depth in the finished joint, t is main plate thickness, h is weld size, and W is the sum of the plate thickness and weld size (=t+h).

Fatigue test results

104 105 106 107

100

1000

Number of Cycles

Loca

l Stre

ss R

ange

(M

Pa)

JSSC–A

: As–welded joint

500

2000

50

: Finished joint

BC

D

E

F

G

8

3. FATIGUE CRACK PROPAGATION (1) Fatigue Crack Growth Behaviour of A5083 Series Aluminium Alloys and Their Welded Joints

K. Gotoh, K. Murakami and Y. Noda (Kyushu University) (Contact address: Koji GOTOH / E-mail: gotoh@nams.kyushu-u.ac.jp)

Keywords: Fatigue, Aluminium alloy A5083, RPG stress, Numerical simulation of fatigue crack growth

We investigated the difference in fatigue behaviour between the aluminium alloys A5083-O and A5083-H321 because they are used as structural components in ships and high speed craft. We ob-tained S-N curves for the base materials and the welded joints made of A5083-O. The relationship between the fatigue crack propagation rates and the stress intensity factor ranges ΔK, ΔKeff and ΔKRPG was determined by applying the centre cracked tensile specimens. Additionally, the evolution of fatigue crack growth for the base materials and the welded joints (cru-ciform joints) made of A5083-O was measured. We also carried out numerical simulations of fatigue crack growth for both base metals and their welded joints made of A5083-O. The difference in fatigue crack growth behaviour for each alloy and the validity of the numerical simulations of fatigue crack growth based on the RPG stress criterion proposed by Toyosada et al. in the base materials and their welded joints was investigated.

Figure 1 Relationship between ΔK/E, ΔKeff /E and ΔKRPG /E as well as the fatigue crack propagation rate for the A5083-O and A5083-H321 materials.

Figure 2 Comparison between the estimated fati-

gue crack growth curves and the measured curves.

10-6 10-5 10-4 10-3 10-210-11

10-10

10-9

10-8

10-7

10-6

Fatig

ue c

rack

pro

paga

tion

rate

: da/

dN [

m/c

ycle

]

: O1: O2: O3 : H4

: H3: H2: H1

ΔKRPG / E [m1/2 ]

: R=0.05: R=0.3: R=0.5

: R=0.05 (ΔKth test)

A5083-O, H321

Mild steel (SM400B)

0 2 4 6 8 100

0.1

0.2

0.3

Number of cycles: N [x105]

Dim

ensi

onle

ss c

rack

leng

th: a

/t

Specimen N1

Maximum load: 94.1 kNMinimum load: 47.1 kN

Curve: EstimationMark: Measurements

Fatigue crack initiation

9

(2) Fatigue Crack Propagation Behaviour of Through-Thickness Crack Subjected to Out-of-Plane Bending

K. Tateishi and X. Ju (Nagoya University) (Contact Address: Kazuo TATEISHI / E-mail tateishi@civil.nagoya-u.ac.jp)

Keywords: through-thickness crack, out-of-plane bending, crack growth rate, stress intensity factor

Experimental and numerical studies were performed on a through-thickness cracked plate to clarify the fatigue crack propagation behaviour under out-of-plane bending. In the test, alternating loads were applied to the specimen. It was found that the crack propagates ununiformly in the thickness direction, forming the symmetric V shape in the fracture surface. The stress intensity factor along the crack front was calculated by finite element analysis and correlated with the fatigue crack growth rate measured on the specimen surfaces. Based on the results, the relationship between the stress intensity factor and the crack growth rate under out-of-plane bending was obtained.

Specimen and loading device Crack growth rate versus stress intensity factor range

Fracture surface

1.0E

-05

1.0E

-04

10 100

Cra

ck g

row

th ra

te o

n su

rfac

e:

da/d

N (m

m/c

ycle

)

Stress intensity factor range: (MPa·m1/2)

Notch

BoltRoller Cyclic bending

Specimen

t=15

110 110

150

160

8

0.2

Unit: mm

Fix

10

(3) Retardation of Fatigue Crack Propagation in Welded Joints under Plate Bending by Hardening Material Injection

K. Tateishi, R. Tsuboi and T. Hanji (Nagoya University) (Contact Address: Kazuo TATEISHI / E-mail tateishi@civil.nagoya-u.ac.jp)

Keywords: fatigue crack, crack growth retardation, hardening material injection, crack opening dis-placement

A simple repair method for fatigue cracks in steel bridge members was proposed in this study. This method can retard or arrest the crack growth by injecting hardening material into the crack to restrain its closure. To verify the applicability of the proposed method, fatigue tests under plate bending were conducted on out-of-plane gusset welded joints. It was indicated that the effect of the crack growth retardation depends on when injecting the hardening material into the crack, and that the proposed method can extend the fatigue life of the cracked welded joints regardless of the stress ratio.

Crack length versus number of cycles Nominal stress range versus fatigue life

0 1 2 3 4 50

50

100

150

Number of Cycles after Initiation ( ×10 )

Cra

ck L

engt

h (m

m)

: No injection

6

Min. stress : 0MPa

: Injection at 80MPa: Injection at 0MPa

Injecting hardening material

Injecting hardening material

Stress ratio : 0

Max. stress : 80MPa

105 106 10710

100

Number of Cycles

Nom

inal

Stre

ss R

ange

(M

Pa)

JSSC–C

: R=0

50

Repaired joint: R=0

Non–repaired joint

D

E

F

G

H

: R=–1: R=–∞ : R=–∞

: R=–1

11

4. FATIGUE STRENGTH IMPROVEMENT AND REPAIR (1) Fatigue Strength Improvement by Hammer Peening Treatment under Variable Amplitude Load-

ing

C. Miki, M. Tai and K. Suzuki (Tokyo Institute of Technology) (Contact Address: Chitoshi MIKI / E-mail miki@cv.titech.ac.jp)

Keywords: variable amplitude loading, peening, compressive residual stress, fatigue strength improvement

Hammer peening treatment which introduces compressive residual stresses has been studied. The purpose of this research is to clarify the improvement effect of fatigue strength under variable amplitude loading (hereafter VAL). The joint specimen with out-of-plane gusset plate is used. VAL follows the weibull distribution which simulates the actual loading amplitude distribution. In this research, two stress patterns, where one has constant maximum stress, called “Down”, and another has constant minimum stress, called “Up”, are applied. Toe conditions are as-weld, cleaning and CP. Cleaning is the pre-treatment for peening using small radius burr grinder (r=3mm) to remove undercut, and CP is the combined treatment of cleaning and peening. When using modified Miner’s rule for evaluating equivalent stress range, for as-weld and cleaning, both fatigue lives under VAL are longer than those under constant amplitude loading (hereafter CAL). However, in the case of CP, fatigue life is extremely short compared to CAL. In other words, the improvement effect under VAL is much less than that under CAL.

(a) Down (b) Up

Fig.2 Examples of stress pattern

Fig.1 Test Specimen

Fig.3 Test results

12

(2) Influence of Steel Static Strength on Fatigue Strength Improvement of Out-of Plane Gusset Welded Joints by UIT

T. Mori (Hosei University), H. Shimanuki and M. Tanaka (Nippon Steel) (Contact Address: Takeshi MORI / Email mori@hosei.ac.jp)

Keywords: Fatigue Strength, Out-of-Plane Gusset welded Joint, UIT, Static Strength of Steel

It has been confirmed through a lot of experimental researches that UIT (Ultrasonic Impact Treatment) gives excellent improving effect on fatigue strength of welded joints. Main factor to increase the fati-gue strength is considered to be introduction of compressive residual stress. It is expected to be able to introduce higher compressive residual stress and realize further improvement of fatigue strength by increasing the static strength of steel used. The purpose of the present study is to clarify the influence of static strength on the fatigue strength of out-of-plane gusset welded joints with UIT. For this purpose, the fatigue tests on SBHS700 steel (yield stress higher than 700N/mm2) specimens have been performed under constant amplitude stress and maximum stress being constant, and their results are compared with test results of SBHS500 steel (yield stress higher than 500N/mm2) specimens.

Appearances of Weld Beads

x

0 2 4 6 8 10−800

−600

−400

−200

0

200

400

AW（SBHS700）UIT（SBHS700）

Distance from weld toe x (mm)

Rsi

dual

stre

ss (N

/mm

2 )

AW（SBHS500）UIT（SBHS500）

Specimen

Residual Stress Distribution

Fatigue Tests Results

105 106 107

40

5060708090

100

200

300

400

500

SBHS700SBHS500

Fatigue Life N (cycles)

Sres

s R

ange

⊿σ

(N/m

m2 )

As−Welded Specimens(AW Specimens)

105 106 107

40

5060708090

100

200

300

400

500

UIT (SBHS700)UIT (SBHS500)

Fatigue Life N (cycles)

Stre

ss R

ange

⊿σ

(Nm

m2)

AW試験体

UIT Specimens（maximum stress：352N/mm2

）

105 106 107

40

5060708090

100

200

300

400

500

UIT (SBHS700)UIT (SBHS500)

Fatigue Life N (cycle)

Stre

ss R

ange

⊿σ

(Nm

m2)

AW試験体

UIT Specimens （maximum stress ： 300N/mm2

）

13

(3) Influence of Grinding Depth on Fatigue Strength of Out-of-Plane Gusset Welded Joints

T. Mori (Hosei University) (Contact Address: Takeshi MORI / Email mori@hosei.ac.jp)

Keywords: Fatigue Strength, Out-of-Plane Gusset welded Joint, Finishing Weld Toe, Grinding Depth

Finishing the weld toe by burr grinder is usually used for improving the fatigue strength of welded joints because it makes weld toe profile smooth and decreases stress concentration there. In order to get the certain effect by this method, the toe must be finished so that as-welded toe line does not remain. In this case, weld toe is prone to be grinded to some depth. When the depth is large, the fatigue strength is considered to be low, so the limit of depth is specified to 1mm in the IIW Recommendations and 0.5mm in the Japanese Specifications. In this study, aiming to clarify the influence of grinding depth on fatigue strength of out-of-plane gusset welded joints with finished weld toe by burr grinder, fatigue tests on model specimens and FEM analyses have been performed.

Specimen Weld toe radius Grinding depth SCF AW (as-welded) 1.1mm ‐ 4.13

3RS 3.4mm 0.14mm 2.77 3RD 3.9mm 0.48mm 2.73 5RS 5.2mm 0.14mm 2.40 5RD 5.2mm 0.49mm 2.49

SCF : Stress Concentration Factor

Specimen

Steel: SM40YA Yield strength : 418 – 438 N/mm2 Tensile strength : 529-560 N/mm2

Elongation : 21 – 27 %

Type of Specimen

105 106 10750

100

200

Stre

ss R

ange

Δσ

(N/m

m2 )

Fatigue Life N(cycles)

3RS3RD

AW

105 106 10750

100

200

Stre

ss R

ange

Δσ

(N/m

m2 )

Fatigue Life N(cycles)

5RS5RD

AW

3RS

3RD

Fatigue Test Results

14

(4) Fatigue Test of Orthotropic Steel Deck Specimen with Trough Ribs Retrofitted by TIG Welding

M. Sakano, D. Yamaoka, K. Asane (Kansai University), N. Kanjo, H. Sugiyama(Hanshin Expressway Co.) H. Sakoda, Y. Tanba (Hanshin Expressway Management Technology Center) (Contact Address: Masahiro SAKANO / E-mail anami@sic.shibaura-it.ac.jp)

Keywords: orthotropic steel deck, trough rib, fatigue crack, fillet weld, TIG welding

In the orthotropic steel deck with trough ribs, deck plate and ribs are usually connected by the fillet weld from the only outside of trough ribs. Most of existing structures have those outside fillet welds with so poor penetration that a number of fatigue cracks developed at the root of fillet welds. In this study, we try to reproduce bead-propagating cracks, and investigate the effect of repair TIG welding through fatigue tests using an actual size specimen.

Figure 1. Specimen and Loading position

15

0

50

100

150

200

-80 -60 -40 -20 0 20 40

SM490(EBW無し）SM490(B=13mm)SM490(B=4mm)

(5) Fracture Toughness Test with Stop-Hole-Size Core

K. Ono (Osaka University), K. Anami and M. Oikawa (Shibaura Institute of Technology) (Contact Address: Kengo ANAMI / E-mail )

Keywords: repair and retrofit, fracture toughness, Charpy Test

In order to consider maintenance methods, repair and retrofit, for existing fatigue damaged steel bridge structures, it is also necessary to obtain information of mechanical and chemical properties of steel of damaged members or joints. However, for the aging bridges, it is sometimes difficult to obtain such kinds of information from design articles. For such case, a sample material might be taken from the structures, but the sample should be as small as possible. This study examines the use of a core, which is taken from stop-hole (for prevention of crack propagation) or bolt-hole (for retrofit with splice plate), for tests of material properties, especially fracture toughness tests (e.g. charpy test). Figure 1 explains the fabrication process of charpy test specimens. Materials tested in this study are 1920~30’s steel taken from a displaced bridge structure and present steel (JIS-SM490), and present steels (JIS-SM490 and SM570) are laser welded to test materials to fabricate charpy test specimens. The parameter of this series of charpy test is the width of test material, B. An example of charpy test results is shown in Fig.2, and the results indicate the influences of heat input and constraint of plastic deformation around the notch tip can be eliminated when the width, B is larger than 13mm. The observation of heat-affected area, measurement of hardness change and a series of FEM analyses regarding to the constraint effect are also carried out in this study.

Core from stop hole

Fig.1 Fabrication of Charpy Test Specimen

Test material

One side (B=13)

Another side (B=13)

One side laser welding is conducted

Temperature (℃)

□ No weld▲ B=13mm◆ B=4mm

Fig.2 Result of Charpy Test (JIS-SM490)

B

B=4, 9, 13mm Test-material

laser weld laser weld