Sozuka-Ohhashi (at member connection) のバックアップ(No.1)

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- 1 (2013-08-22 (木) 14:37:55)

Deck-type Arch bridge on Tomei Expressway †

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1.Field of application †

Deck-type Arch bridge, opened in 1969, on Tomei Expressway, Japan.

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2.Circumstances of Repair †

Fatigue cracks were found at the joints of a vertical member and a stiffening girder and arch rib.

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3.Types of structure †

Deck-type Langer bridge that the bridge length is 121m (Fig.1).

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Fig.1 Deck-type Langer bridge.

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4.Details of loading †

Fluctuating loads due to highway live load.

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5.Description of damage †

Fatigue cracks occurred in the boxing joint at the vertical member connection with the stiffening girder (Fig.2). The cracks were classified in two type, one propagated into the stiffening girder bottom flange in a direction perpendicular to the bridge axis and the other propagated into the bottom flange of the vertical member in a direction parallel to the bridge axis. Both types propagated through the flange plate. The degree of damage was more prominent at the middle part of the bridge, that is, at joints where lengths of vertical members are short.

Cause of fatigue crack was thought as follows.

Relative difference in displacement which occurs in the horizontal direction between stiffening girder and arch rib.

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Fig.2 Crack at the vertical column connection detail of deck type arch bridge.

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6.Repair method applied †

To reduce the secondary stress due to relative displacement, repair and strengthening were performed as follows (Fig.3).

Emergency repair

All the boxing joints at the vertical member connection with the stiffening girder bottom flange were finished by grinding. The cracks which propagated through the girder bottom flange were arrested by drilling holes at each crack tip.

Permanent repair

1. L-type plates were installed at all the corner joints of the stiffening girder bottom flange and vertical member.

2. Replacement to the connection plate with 14mm thickness from the original plate of 10mm thickness.

3. The reinforcing plate was covered on the outside flange surface of the vertical members.

4. Replacement from the rivet to the high strength bolt (M22 or M24).

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Fig.3 Retrofit work.