Identification of Modal Properties of Bridges

Abstract

Modal stiffness and damping are determined from experimental test data for a single‐span laboratory bridge model and a full‐scale three‐span highway bridge. Steady‐state vibration tests are conducted on both structures using an electro‐hydraulic actuator. Accelerations are recorded at selected locations on the structures. For the laboratory model, the modal properties are calculated from experimental data for the as‐built model and after one flange is cut. Modal properties for the highway bridge are determined during a 40,000‐cycle fatigue test of the in situ structure. Changes in stiffness and mode shapes are related to the observed deterioration of the structures. Mode shapes are the best indicators of the deterioration.