Sozuka-Ohhashi (at member connection) †

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1.Field of application †

Sozuka-Ohhashi over dam lake which is located between Ohtsu, Shiga prefecture, and Uji, Kyoto metropolitan prefecture, Japan.

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2.Circumstances of Repair †

Fatigue cracks were found at the joints of the arch rib and the cross beam and at the cross beam-stringer connection in 1981 after 15 years of service. Immediately the reinforcing members were installed. However, the cracks reinitiated at the repaired members. Therefore, a whole strengthening of the bridge structure was required.

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3.Types of structure †

This bridge is the 2-hinge rib arch through bridge of which arch span length is 106m long. Bridge view is shown in figure 1. Elevation, framing and cross section are shown in figure 2. The reinforced concrete deck had 16cm thickness.


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Fig.1 Sozuka-Ohhashi side view.


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Fig.2 Plan and cross section.


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4.Details of loading †

Fluctuating loads due to vehicles live load.

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5.Description of damage †

Fatigue cracks occurred in the joint of the arch rib and the cross beam and at the cross beam-stringer connection (Fig.3).

In the joint of the arch rib and cross beam, the cracks initiated from the boxing weld at the >joints and propagated into the web of the arch rib (Fig.4).

In the cross beam-stringer connection, the cracks initiated from the weld bead (Fig.5).

Cause of fatigue cracks is as follows.

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6.Repair method applied †

For damage of the joint of the arch rib and the cross beam and of the cross beam-stringer connection, re-welding, drilling-holes and reinforcing members ( brackets, branching members ) were firstly installed as shown in figure 6. However, the cracks reinitiated in the repaired members after 5 years from the repair completion. Therefore, the whole strengthening of the bridge structure were recommended in order to lessen the relative displacement. The strengthening procedure was to add the diagonal members in the arch span by bolting and improve the original slot-holes of the arch ribs to the hinge connections (Fig.7,8).

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Fig.6 First localized repair.


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Fig.7 Complete view.


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Fig.8 Addition of the diagonal members.


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