ABSTRACT
This paper investigates the vulnerability of reinforced concrete (RC) frame structures under extreme loading conditions such as blast and high-velocity impact events, emphasizing complex responses and secondary failure mechanisms. Explosions in close proximity generate intense shock waves that damage vertical load-bearing elements, particularly columns, leading to loss of load path continuity and potential progressive collapse. The study focuses on catenary mechanisms that temporarily redistribute loads but induce excessive tensile forces, accelerating failure. Traditional design approaches based on predefined threat scenarios are critically compared with more general, threat-independent frameworks such as dynamic column removal, which promote robustness through redundancy and alternative load paths. While threat-dependent methods provide accuracy for specific cases, they may overlook unforeseen failure modes, whereas threat-independent approaches aim to ensure resilience against a wider range of hazards. A numerical case study of a short RC frame using the Applied Element Method quantifies structural response under different damage scenarios, including sudden column loss and blast loading. The comparison of results highlights differences between threat-dependent and threat-independent frameworks, emphasizing the role of initial damage characteristics and secondary mechanisms in collapse progression. The findings underline the need for robustness-oriented design methodologies that address uncertainties in loading scenarios and enhance the capacity of RC frames to resist and adapt to extreme events while preventing progressive collapse.
