A damage evaluation method for bridge substructures using longitudinal impact dynamic responses

The soundness index (SI) of the substructure is defined as:

When SI is below 0.90, it indicates that damage exists in the structure (Zhan 2004).

The signature assurance criterion (SAC) is usually used to describe the similarity of the FRFs of different points:

Damage Index (DI) based on SAC value is defined as:

The following evaluation criteria for bridge substructures are suggested.