Hassan Hosseinian - Tehrani - Electric Power Research Center ( EPRC)

The Ambient Vibration Survey (AVS) is performed for identification of damping ratio of a natural draught latticed welded steel cooling tower. There is no analytical approach to measure the damping ratio of structures. AVS is a simple nondestructive test for 1 a-lntiivlny dynamic properties of structures. The test was performed to measure the damping ratio, then only one single -directional seismometer was used, which was connected to a solid state recorder. The seismometer was located at the height about fifty meters above the ground. The data was recorded in two orthogonal horizontal directions, tangential and perpendicular to the surface of structure body. At testing time the unit was out of service, and a mild wind was blowing. The data was processed by fast Fourier transform technique and the damping ratio was derived from half power method. The is mean value of both directions tests, and shows the value of %1.05 of critical camping .it is obovious that value of damping may be used only for small amplitude excitation analysis.