In july 1990 mechanical engg news this is the statement : The total force on the element producing stress throughout the element is kx or mx’’. The force at the end of the element should be kx not kx + mx’’.

In november 1994 mechanical engg news, this is the statement: The DLF response spectrum for a given load is generated by solving the dynamic equation of motion for a single degree of freedom system:
Ma(t) + Cv(t) + Kx(t) = F(t)

The force acting on a node in a DYNAMIC problem is whether kx or mx’’ or kx+mx’’ ???