Experimental Methods to Identify Modal Parameters of Bridges, Viaducts, and Other Civil Structures

Identification of modal parameters of a structure is useful for verification, validation, and improvement of Finite Element Analysis (FEA) models, identifying structural degradation and damping appropriate to anticipated structural response levels. Accurate identification of actual modal properties consequently leads to more accurate structural analysis and response prediction. Modal properties are defined as resonant frequencies, mode shapes, and modal damping. The effective values of these modal properties may vary depending on the excitation levels. The effective modal property variations with amplitude are gradual but shed light on the nature of these non-linearities and their relation to structural damage. These experimental studies focus on various experimental techniques to identify modal properties of bridges, viaducts, and other civil structures. These techniques include ambient vibration surveys, impulse excitors, eccentric mass vibrators producing sinusoidal forcing, and servo hydraulic vibrators producing impulsive, random, or sinusoidal forcing. Example results and applications are presented with emphasis on railway bridges and viaducts, but also dams and nuclear power plant structures. Many of the test and structural model identification techniques were developed at the University of California Los Angeles following the 1971 San Fernando Earthquake.