A simplified mechanics-based model for unified ductility estimation of RC beams under static and dynamic loading

One of the most important performance parameters that control the ability of reinforced concrete (RC) members to support inelastic deformation and energy dissipation without catastrophic failure, especially under extreme loading circumstances, is ductility. The accurate prediction of the ductility of curvature is crucial for reliable structural design and seismic performance assessment. However, the majority of current analytical models have been designed for quasi-static loading and are usually employed separately for static and dynamic loading. This separation does not consider the strain-rate sensitivity of concrete and reinforcing steel which results in conservative predictions of concrete ductility, and in a limited applicability to structures exposed to dynamic actions like earthquakes, impact or blast loads. Thus, a unified mechanics-based model is proposed in this study to predict the yielding curvature ductility and ultimate curvature ductility of RC beams under static and dynamic loadings. The proposed formulation combines depth of the concrete compression block, curvature relationships, reinforcement characteristics, and the effect of strain rate in one analytical formulation that is consistent with the provisions of ACI 318 − 19. Dynamic increase factors (DIFs) have been introduced to account for the rate-dependent response of concrete and reinforcing steel, allowing for simultaneous consideration of curvature ductility, moment capacity and failure response as a function of loading rate. The predictive performance of the model was evaluated using statistical analysis and comparing the model. The results indicate good correlation with an R 2 of 0.992 and a CoV of 18.1% between the predicted and observed ductility responses. Based on the results of parametric analysis, it is observed that the most significant factors affecting the curvature ductility are the concrete compressive strength (26.18%), reinforcement area, section geometry and ratio of transverse reinforcement, with the steel yield strength and strain-rate effects having moderate influence. The proposed unified framework provides a reliable tool for ductility assessment of RC beams under combined loading regimes and supports more consistent performance-based design of concrete structures exposed to dynamic actions. The findings contribute to improving structural safety assessment and may assist in refining design recommendations for RC members in seismically demanding environments.