Analysis of Soundness of Bridges Affected By Environmental Factors

Abstract eng:
In recent years extending the service life of the bridges has come to be studied. Many bridges are built in the period of high economic growth, and they reached their service life. Consideration of rebuilding and extending the service life must be carried out. But implementation of replacement or maintenance works for those bridges will be difficult in terms of both labor and cost. Moreover, possible events of bridge closure may probably bring significant negative effects on the road traffic networks. Under such circumstances, the bridges in the Ishikawa Prefecture has been placed under the harsh environment. For example, flying salt due to the weather characteristics of winter, the influence of the water from pipe buried under a road with nozzles that spray liquid to melt snow, sprinkling salt for antifreeze, the damage of alkali silica reaction that peculiar to Hokuriku region, seismic risk occurred by active fault . Therefore, each bridge is inspected once every five years and the priority of each bridge is determined and recorded depending on health of respective components and importance of the bridge. However, in and around Ishikawa Prefecture there are a number of active faults including the Morimoto-Togashi Active Fault posing a high risk of bridge damages caused by earthquakes, and the existing methods to determine bridge maintenance priorities with no consideration of the seismic risks are expected to result in significant damages in the event of a major earthquake disaster. In this study, we propose a repair priority determination method taken into account the seismic risk by using the principal component analysis. For the principal component analysis, importance and vulnerability of bridges against earthquake were used as variables. For importance of bridges, the potential impact of bridge destruction on transportation was considered from perspectives of emergency transportation, crossing, daily traffic volume and bridge length. As for vulnerability of bridges against earthquake, health scores in regular inspections that indicate possibilities of destruction in the event of an earthquake (main girder, bearing apparatus, expansion devices) and seismic risks were considered. Seismic risk-based priorities obtained in this research were compared with priorities calculated by the conventional calculation method. As a result, when the seismic risk was considered, the priority of the bridges was changed. It have become clear that the new method of calculation bridge repair priority using the principal component analysis considered importance of bridges and vulnerability of bridges against earthquake is suited to consider both the existing damage and seismic risk.

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