Documentation of changes in modal properties of a concrete box-girder bridge due to environmental and internal conditions

The results of two modal tests preformed on a concrete box-girder bridge are presented. The two modal tests were performed on the bridge sequentially with a 9-month rime interval between tests. This sequence of tests form the initial phase of a modal-based level IV nondestructive damage-evaluation process implemented to establish the rate of structural deterioration and remaining service life of the rested structure. A level IV process detects, locates, and sizes damage and determines the impact of the damage on the performance of the structure. A novel feature of the field testing is the execution of an incremental and minimally intrusive (to existing traffic flow) modal test procedure. The instrumentation, experimental test plan, and resulting modal analyses are discussed. In addition, the changes in the two modal data sets are discussed.