The use of constrained viscoelastic materials has been regarded as a convenient strategy to reduce noise and vibrations in many types of industrial applications. The presence of local nonlinearities in the system or the implementation of a hyper-visco-elastic behaviour law, cannot be appropriately dealt with in the frequency domain and require the analysis to be performed in the time domain. This work aims at presenting a general framework for the computation of time responses of viscoelastically damped systems, by using two-step recurrence formulas involving internal variables into an unconditionally stable Newmark time discretization scheme. After validating the implementation of the methods on a sandwich beam, a numerical analysis of the modified Newmark algorithms is carried out. The methodology is then applied to a structure with more complex geometry to assess memory and CPU requirements.