AMBIENT VIBRATION TESTING OF WATER TOWERS

Abstract

The ambient vibration testing of structures is a direct and practical method of determining the dynamic characteristics of structures such as natural frequencies, mode shapes and damping. In this testing, structure is excited by natural microtremors, wind, traffic load and machine or man made blast. This technique can be used to verify the mathematical models and to investigate changes in resonant frequency before and after earthquake. This thesis presents the results of ambient vibration test of two water towers (i) near the G.F.Hostel and (ii) near the Sarojini Bhawan. The vibrations produced by wind were picked upby a Ranger Seismometers (SS-1) and recorded in a Solid State Recorder (SSR-1). The recorded data were then transferred to Note-Book computer and analyzed by using Seismic Workstation Software (SWS). The experimentally measured fundamental time periods were compared with the values obtained from mathematical model for the two water towers. A reasonably close agreement in fundamental time period between theoretically and experimentally measured values has been observed for the tank near G.P, Hostel, while for the tank near Sarojini Bhawan difference has been observed between experimental and theoretical time periods. The possible reason for the difference in the time period could be attributed to the fact that high frequency was picked up by seismometers due to weak wind velocity.