A. Sarkar et Cs. Manohar, CRITICAL SEISMIC VECTOR RANDOM EXCITATIONS FOR MULTIPLY SUPPORTED STRUCTURES, Journal of sound and vibration, 212(3), 1998, pp. 525-546
A method for determining critical power spectral density matrix models
for earthquake excitations which maximize steady response variance of
linear multiply supported extended structures and which also satisfy
constraints on input variance, zero crossing rates, frequency content
and transmission time lag has been developed. The optimization problem
is shown to be non-linear in nature and solutions are obtained by usi
ng an iterative technique which is based on linear programming method.
A constraint on entropy rate as a measure of uncertainty which can be
expected in realistic earthquake ground motions is proposed which mak
es the critical excitations more realistic. Two special cases are also
considered. Firstly, when knowledge of autospectral densities is avai
lable, the critical response is shown to be produced by fully coherent
excitations which are neither in-phase nor out-of-phase. The critical
phase between the excitation components depends on structural paramet
ers, but independent of the auto-spectral densities of the excitations
. Secondly, when the knowledge of autospectral densities and phase spe
ctrum of the excitations is available, the critical response is shown
to be produced by a system dependent coherence function representing n
either fully coherent nor fully incoherent ground motions. The applica
tions of these special cases are discussed in the context of land-base
d extended structures and secondary systems such as nuclear piping ass
embly. Illustrative examples on critical inputs and response of sdof a
nd a long-span suspended cable which demonstrated the various features
of the approach developed are presented. (C) 1998 Academic Press Limi
ted.