An energy-based criterion is introduced in order to investigate the nonlinear dynamic response of RC beams subject to rapid and unexpected damages. Since only static pushover analysis is necessary, the structural behavior of the damaged members can be evaluated with a new simplified procedure. It is firstly applied to the case of elastic–perfectly plastic continuous beam, when one of the supports is quickly removed. In such a situation, the proposed procedure gives satisfactory results if compared to those of a more rigorous dynamic analysis. By means of a nonlinear static analysis, which encompasses also the post-peak response, the energy-based approach is also applied to concrete beams. More specifically, it is used to predict the bearing capacities of reinforced concrete beams, having different steel rebars, when they suddenly lose a single support.