Vibration Monitoring of a Real Steel Plate Girder Bridge Under Artificial Local Damage and Varying Temperature

Abstract

This study is intended to investigate how the local damage and varying temperature affect changes in modal frequencies of a steel plate girder bridge. A damage experiment on a real bridge was conducted. Artificial cracks were applied to the lower flange and web plate near base plate of shoe, which models fatigue cracks observed in actual steel plate girder bridges. The longitudinal displacement of the bridge at supports were also monitored to investigate structural behaviors of supports under local damage and varying temperature. Observations showed that frequency of the 1st bending mode increased due to artificial damage even though frequencies of the 2nd bending mode and 3rd bending mode decreased. For a finite element model, changes in stiffness of spring which models the cantilever steel pivot bearings at support due to the damage as well as temperature change are considered to examine the reason why the frequency of the 1st bending mode increased while those of the 2nd and the 3rd bending modes decreased. FE analysis demonstrated that the 1st bending mode was more sensitive to changes in the boundary condition than changes in stiffness of girder. Seasonal changes in longitudinal displacement of each support are also examined. In addition, FE analysis also showed that the boundary condition was changed by not only the stiffness reduction of girder due to the damage but also thermal expansion due to varying temperature.KeywordsDamage experimentSteel plate girder bridgeTemperatureVibration measurement