International Institute of Earthquake Engineering and Seismology

M. Davoodi

Abstract

Based on previous investigations in IIEES, there were some problems in evaluating dynamic characteristics (including resonant frequencies, mode shapes and modal damping values) of embankment dams. These experiences indicate that the identification of dynamic characteristics becomes difficult and cumbersome not only when non-stationary signals are recorded on dam body but also if PSD functions include closely spaced or overlapped peeks. In-fact, the classical signal processing methods provided reasonable results as long as the amplitude and frequency contents of the recorded signal didn't vary with time and natural frequencies of the structure were well separated and well defined. To overcome this problem, the main purpose of this experimental research is to introduce the advanced TFD (Time Frequency Distribution) method. In-fact, The TFD method maps a one-dimensional signal into a two-dimensional function of time and frequency and describes how the spectral content of the signal changes with time. The basic concept in this experimental study was to excite the dynamic response of the two highest embankment dams in Iran namely Masjed Soleiman and Marun by detonating explosive charges. The recorded signals were processed by classical 4-spectra and modern TFD methods and the obtained modal frequencies of the dam body were compared. Differences between the two methods were described and the benefits of the modern signal processing method were discussed. Overall results indicated that non-stationary in-situ tests on embankment dams such as explosion tests are an excellent method of exciting the dam-foundation system, and that it is possible to evaluate the dynamic characteristics of this kind of dams more accurately by using modern TFD method. Besides the in situ dynamic tests on embankment dams, the non-stationary recorded signals on the machinery foundations were also analyzed by classical and modern signal processing methods and then compared with permissible vibrations. Totally, the results indicated that it is possible to evaluate the amplitude of the non-stationary vibrations in the interest frequency more rapidly and accurately by using TFD method.

Keywords:

signal processing; Time Frequency Distribution; seismic behavior; embankment dam; machinery foundation