Abstract: With a train of high arch dams built in Southwest China, the health of dam structures and their anti-seismic properties have become a hot issue in recent years. Modal parameters reflect the dynamic characteristics of dam structures and are applicable to evaluating dam health status and updating the finite element models for arch dam anti-seismic analysis. This paper presents a study on the identification of modal parameters for Xiluodu arch dam using the ARX, SSI and FDD procedures separately, based on two earthquake recorders located in Yongshan County and ambient vibration test data. The results show the modal parameters identified using ambient vibration tests agree with those identified using the recorded data. When the reservoir stage varies from 566 m to 598 m, the fundamental vibration frequency of this dam is lowered from 1.63 Hz to 1.51 Hz. And similar frequencies identified before and after the earthquakes indicate that the dam is in the normal operation condition.

Key words: modal parameter identification, Xiluodu arch dam, earthquake recorders, ambient vibration test