For the short range of
natural period 0 < T < 0.2 sec, the C value contains various uncertainties in relation
to the ground motion as well as to the ductility of the SDOF system considered.
Therefore, in this range the C value should be taken equal to A m . It can then be stated
that for T < T c the response spectrum is associated with a constant maximum
response acceleration, while for T > T c it is associated with a constant maximum
response velocity, as a consequence of the hyperbolic function in this range.