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Ⅷ-12 Maintenance of Steel Bridges

Mr. Jun MURAKOSHI Team Leader, Bridge Structure Team, Structures Research Group, Public Works Research Institute

Maintenance of Steel Bridges

Jun MURAKOSHI Bridge Team, PWRI

Contents of presentation ■Major Damage of Steel bridges and Countermeasures - Corrosion of Steel member - Fatigue） of RC deck - Fatigue crack of steel member ■Current R/D at PWRI

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Bridge type Recent trend of steel bridges

Others 4% (5,461)

Others 13% (47) Steel Bridge Prestressed 39% (56,136) Concrete Bridge 39% (55,222)

Box-girder 36% (131)

Reinforced Concrete Bridge 18% (25,702)

I-girder Steel Bridge 51% (1,242)

Fewer plate girder 9% (223) （Length >30m as in 2000 ～ 2003）

Bridge number by bridge type （Length >15m as of 2002.4）

http://www.jasbc.or.jp/kyoryodb/index.cgi

Number of bridge by year of construction 30,000 The others

25,000

RC bridges

15,000

Steel bridges

10,000

1996～2000

1991～95

1986～90

1981～85

1976～80

1971～75

1966～70

1961～65

1956～60

1951～55

1946～50

1941～45

1936～40

0

1931～35

5,000

1926～30

Number of bridges

PC bridges 20,000

Length >15m as of 2002.4

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Major causes of replacement of steel bridges (1986-1995) ・Most are functional problem so far. ・About 12% is Deterioration of superstructure. ⇒ Deterioration of concrete deck, Corrosion of steel members (Importance of preventive maintenance) Others EQ resistance （2.8%） （1.7%）

Damage of superstructure （12.1%）

Damage of substructure （1.5%）

Others （6.8%）

Corrosion （26.0%）

Load capacity （67.2%）

Improving Road Alignment（45.9%）

Improving Road Width （31.5%）

603 bridges

Fatigue of Concrete Decks （67.2%）

73 bridges

Deterioration factor -Corrosive environmentSevere geographical feature ・Long & slender country, coastal area, mountainous area ・Much rain, Seasonal wind in winter, Typhoon ・About 60% area is snowy and cold etc.

Splashed in Winter Airborne salts

De-icing salts use

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Deterioration factor -Traffic ConditionsHeavy traffic in urban area

Heavy truck

Corrosion of steel bridge Corrosion of girders

Corrosion protection

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Corrosion prevention method Measures

Mechanism

In case of deterioration

Painting

Protection by paint

Repainting

Weathering steel

Protective rust layer

Repair with painting

Hot dip galvanizing

Protective layers by zinc and alloys, and Sacrificial protection

Repair with painting

Metal spray

Spray deposit and Repair with painting Sacrificial protection by zinc-aluminum pseudoalloys

Weathering steel highway bridge

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Classification of environment for weathering steel bridge Area category Japan Sea Coast

Area where W/S can be used (Minor effect of airborne salt) Ⅰ

Areas over 20 km from coast

Ⅱ

Areas over 5 km

Pacific Ocean Coast

Areas over 2 km

Seto Inland Sea Coast

Areas over 1 km

Okinawa Island

NA

Japan Sea Coast Ⅰ

(where the amount of airborne salt is less than 0.05 mg/dm2/day） Japan Sea Coast Ⅱ

Pacific Ocean Coast

Seto Inland Sea Okinawa

Prevention of corrosion Manual for painting and corrosion protections for steel highway bridges ・Revised in 2005 to reduce LCC for prevention of corrosion ・Contents of the revised manual Part 1: General Part 2: Painting Part 3: Weathering steels Part 4: Hot dip galvanizing Part 5: Metal spray

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Corrosion of girder end Stiffener

・Rain water leakage from road surface through expansion joint ・Corrosive environment (Humid, stuffy )

Web Loss of thickness

Deformation 33 mm

Buckling caused by section loss

Corrosion of girder end

Corroded area was cut and replaced with new steel members.

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Corrosion of through truss Corrosion in upper chord

Upside down

Corrosion in lower chord

Corrosion of inside of box girder

Accumulation of dropping of birds

Corrosion by stagnant water

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Current research theme ■Repair method for prevention system of corrosion (New material Team) ・Repair methods for -corroded weathering steel bridges, -hot dip galvanized bridges, -metal sprayed bridges

■Retrofit method of severe corrosion at girder ends of steel bridge (Bridge Team) ・Selection of repair methods ・Effectiveness of repair method by bolted connection plate for corrosion members

Damage of reinforced concrete deck

Transverse direction crack

Cracks in a grid pattern

Falling of concrete portions

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Damage of road surface

Fatigue of concrete deck „Concrete deck is subjected to traffic load ⇒Cracks, Dropping of concrete portion ・Improvement of durability (Revision of design code several times) ・Increase of thickness ・Increase of design moment ・Increase of amount of rebars ・Waterproofing of deck surface, etc.

・Fatigue Evaluation by wheel running test

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Wheel Running Machine Load Deck Deformation

Cracking on the bottom

Deck 床 版

主 桁 Girider

Major Research Issues: - To establish evaluation method for durability of concrete decks - To evaluate effectiveness of repair methods for concrete decks - To evaluate durability of newly developed bridge decks

Loading / Static punching shear resistance

S-N curve by wheel running test Dry

1973 Spec

1964 Spec

103

104

Wet

105 106 Cycles to failure

107

Provided by Prof S. Matsui et al., Osaka Univ.

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Deterioration process of RC deck ①Initial cracks due to shrinkage causes tranvese cracks

②Formation of grid cracks due to truck wheel loading

⇒Improvement of flexure ③Increase of grid crack density. Occurrence of penetrating cracks (Water leak and free lime) ④Decrease of punching shear strength

⑤Punching shear failure (concrete dropping)

⇒Improvement of shear resistance

Increase of thickness of deck from upper and/or lower side, etc.

CFRP Sheet bonding, Steel plate bonding, etc.

⇒Reconstruction

Bridge deck strengthened by CF sheets

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Bridge deck strengthened by CF sheets

Crack monitoring is available.

Draining leakage water out to prevent the sheets from disbonding

Bridge deck strengthened by increasing deck thickness with SFRC

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Bridge deck strengthened by increasing deck thickness with SFRCSFRC

Before repair

After repair Deck was overlaid by SFRC.

Asphalt and upper concrete cover was removed.

SFRC Existing concrete

Replacing concrete deck by using steel forms

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Replacing concrete deck by using precast composite panels Next lane was already replaced. Old deck was removed. One of new panel

After replacing

Fatigue of steel bridge Major factors of fatigue damage ・Heavy truck traffic ・Design -Improper structural detail (Low fatigue resistance) -Secondary stress (Analytical model vs. Actual bridge) ・Fabrication -Welding quality, welding defects

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Fatigue crack at hinges of cantilever through truss

Strengthened by bolted stiffened steel member

Fatigue crack at weld of sole plate

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Fatigue crack at weld of sole plate

・Replace bearing ・Replace with extended sole plate ・Strengthened by bolted stiffened steel member

Fatigue cracks of steel piers at beam to column connection

Crack

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Fatigue cracks of steel piers at beam to column connection

Cracks

脚上面溶接部 60 30

用 賀

用賀側

5 1

■Intersection of 3 Weld line : prone to weld defect (Internal un-welded zone, Weld crack in high constraint region) ■Beam to column connection (Geometrical stress concentration)

Retrofit -plate stiffening• Reduction of Live load stress • Support the beam in case of brittle failure • Compensation for section loss due to stiffening plate

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Fatigue cracks of orthotropic steel deck cross girder trough rib transverse rib

Welded thin(12mm) steel plate Direct wheel load Complicated plate bending Stress concentration Fatigue damage

Fatigue cracks of orthotropic steel deck

U-rib

Transverse rib

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Current Research Theme

„ Retrofit method for fatigue damage of orthotropic steel deck ・Replace asphalt pavement with SFRC ・Strengthened by bolted splice plate

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