_Speaker:

_{Sami F. Masri
Professor
University of Southern California, Los Angeles, California, USA}

_{Time: 2016-03-17 15:30-17:00
Venue: Civil Engineering B504     Chair: Zheng Lu}

_{Outline :
A relatively simple and straightforward procedure is presented for representing nonstationary  random process data in a compact probabilistic format which can be used as excitation input in multi-degree-of-freedom analytical random vibration studies. The method involves two main stages of compaction. The first stage is based on the spectral decomposition of the covariance matrix by the orthogonal Karhunen-Loeve expansion. The dominant eigenvectors are subsequently least-squares fitted with orthogonal polynomials to yield an analytical approximation. This compact analytical representation of the random process is then used to derive an exact closed-form solution for the nonstationary response of general linear multi-degree-of-freedom dynamic systems. The approach is illustrated by the use of an ensemble of free-field acceleration records from the 1994 Northridge earthquake to analytically determine the covariance kernels of the response of a two-degree-of-freedom system resembling a commonly encountered problem in the structural control field. Spectral plots of the extreme values of the rms response of representative multi-degree-of-freedom systems under the action of the subject earthquake are also presented. It is shown that the proposed random data-processing method is not only a useful data-archiving and earthquake feature-extraction tool, but also provides a probabilistic measure of the average statistical characteristics of earthquake ground motion corresponding to a spatially distributed region. Such a representation could be a valuable tool in risk management studies to quantify the average seismic risk over a spatially extended area.
About the Speaker :
Sami F Masri is a Professor of Civil and Environmental Engineering, and a Professor of Aerospace and Mechanical Engineering, in the Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA. He received a BS and MS degrees in Aerospace Engineering, from the University of Texas, and an MS and PhD in Mechanical Engineering from the California Institute of Technology. He has been on the faculty of USC since 1966.}