Field verification of the damage index method in a concrete box-girder bridge via visual inspection

The structural condition of a concrete box-girder bridge is monitored twice by detecting and localizing potential damage in the bridge superstructure. Experimental field data were collected on the bridge in December 1997 and 9 months later in September 1998. Modal parameters for the structure are extracted from the measured frequency-response functions, and the resulting resonant frequencies and modeshapes are fed into a proven systems identification procedure. Modal parameters from the identified baseline structure and the modal parameters determined in the field are used as input to a field-rested nondestructive damage-evaluation method (the damage index method) to localize damage in the bridge superstructure. To provide some evidence of the veracity of the predictions of the possible damage locations, a visual inspection was performed on the bridge in Map 1999 and surface cracks on the deck were recorded. A comparison of the predicted damage locations on the superstructure with the surface cracks documented via visual inspection is provided. The results indicate that a strong correlation exists between the predicted damage locations and the observed surface crack pattern.