This paper deals with control strategies for the mitigation of unwanted vibrations in typical medium and long-span cable-supported bridges, aiming to underline general observations and side effects related to the adoption of different control strategies. Two finite-element models of medium and long-span bridges, namely a suspension and a cable-stayed bridge, are developed for simulating the structural response under wind and earthquake excitation. Passive and semi-active control strategies are then implemented in the models for mitigating dynamic effects. Such control schemes have been designed for wind excitation on the suspension bridge, and seismic excitation on the cable-stayed bridge. Attention is initially focused on high-intensity loading conditions, having a low probability of occurrence. The same control strategies and arrangements have then been re-assessed by changing the input intensity; in addition, a cross-check has been performed by addressing earthquake actions on the suspension bridge and wind forces on the cable-stayed bridge. The results have been also analysed in terms of indirect effects, such as fatigue damage.