An improved numerical model that can simulate the nonlinear behavior of RC beams subjected to blast loadings is introduced in this paper. The model is based on the moment-curvature relationship of a RC section, and a dynamic increase factor (DIF) defined with the curvature rate is newly designed to be used in the moment-curvature relationship. The plastic hinge length is considered in the finite-element (FE) idealization of RC beams to accurately reflect the effects of the plastic deformation concentrated at the midspan or beam-column joint after yielding of the main reinforcement. A modification of the moment-curvature relationship is also proposed to take into account the fixed-end rotation accompanied by large bond-slip at the yielding stage of the main reinforcement. The advantages of the proposed model, compared with the layered-section approach, are reduced calculation time and memory space in application to large-frame structures with many degrees of freedom. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model, and the effect of the finite-element mesh size is also discussed in connection with the importance of considering the fixed-end rotation. The results are also compared with those obtained from the single-degree-of-freedom (SDOF) model to demonstrate the better prediction capability of the proposed method.