  Our interest itself of this paper is strongly inspired from an open problem
in the paper [1] published by D'Abbicco. In this article, we would like to
study the Cauchy problem for a weakly coupled system of semi-linear
structurally damped wave equations. Main goal is to find the threshold, which
classifies the global (in time) existence of small data solutions or the
nonexistence of global solutions under the growth condition of the
nonlinearities.
