Shindenpo Bridge of Route 43 のバックアップ(No.1)

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- 1 (2013-07-20 (土) 12:09:57)

Shindenpo Bridge of Route 43 : Replacement and Bolt connecting †

1.Field of application †

Shindenpo Bridge of Route 43, Osaka.

2.Circumstances of Repair †

Fatigue cracks were found in the sol plate welds at the girder support locations in 1990 after 24 years of service. Inspection of the support indicated that repair was required.

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3.Types of structure †

The outline of the bridge structure is as follows.

Bridge length : 860.3m

Span length : 4@66.6m+5@65.5m+4@66.6m (13 spans)

Structure : Simple composite two-box girder bridge

Deck : Reinforced concrete deck

Structural steel : Corresponding SM 50 (steel proof against climate)

Plan and cross section were shown in figure 1. The interior of the box girders contains the diaphragms. Two pin supports are constructed per a box girder.

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Fig.1 Framing plan and cross section.

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4.Details of loading †

Fluctuating loads due to highway live load.

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5.Description of damage †

Fatigue cracking were found in the weld toes of the connection plate end at the transverse lateral locations (Fig.2).

Cause of fatigue cracks was as follows:

Out-of-plane distortion which resulted from the differential deflection between the girders.

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Fig.2 Crack location.

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6.Repair method applied †

Repair of parts subjected to cracking was performed by crack-removing, re-welding and weld toe finishing (Grinding or TIG dressing) in order to improve the weld bead and reduce the localized stress concentration at the weld toe, because most of cracks occurred in the fillet weld toe. This repair method is effective in case the occurring stress is not severe.

However the occurring stress is high in this bridge, crack reinitiated.

Therefore, strengthening was performed by addition of the transverse cross bracing or addition of the reinforced concrete deck. It was verified that these strengthening were enough effective to reduce the stress.

Periodic inspection of the strengthened procedures will be continued.