# Can dynamic equivalent stiffness matrix sigularity??

Dear all, I have two questions boring me.
1. In finite element dynamic analysis. The structrural equivalent
stiffness matrix, Ke=K+2/h*C+4/h^2*M, can become sigularity?? I kown
that in static analysis the structrural stiffness matrix can be
sigularity with Det(K) = 0.
2.In finite element dynamic analysis (note: not in static). If a beam
is no any restraints, I can directly analyse it under a force using
the Newmark method?? I try this, I think it can be work, am I wrong??
Many thanks.
For an unrestrained structure, K is singular, but Ke will not be singular, in general, if you have a physically reasonable distribution of mass. Thus, there is no problem, in principle, with doing dynamic analysis of unrestrained structures.
Good! I want to get a more definied answer.
This means that the Ke is always positive-definite matrix, and never become a negative definite matrix??
And so the so-called Arc-Lengh method which to overcame load limit point to negative stiffness region can be only useful in static analysis (because K can become singular)??
I think it right??

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