This paper explores methods of simulating the behaviour of building structures under progressive collapse conditions through alternative models of different levels of structural idealization. Such models have been applied in many previous studies, but there is insufficient information regarding their reliability and their ability to represent actual structural behaviour as the level of idealization is reduced. To address this, the study adopts the alternative load path method through the well-established concept of notional column removal, performed via nonlinear static analyses of models with different levels of structural idealization. The focus is on the interaction between the directly affected structural members and the surrounding structure, which is shown to significantly influence the overall response under progressive collapse. The results demonstrate that this interaction depends on multiple factors and cannot be reliably captured when the surrounding structure is not explicitly modelled. Building on this finding, the study systematically evaluates how reduced models can be enhanced to better represent these interactions and proposes strategies for defining boundary conditions that preserve global structural behaviour. Overall, the study advances understanding of model idealization effects and provides practical guidance for developing efficient reduced models for progressive collapse simulations without compromising essential aspects of structural response.

This paper explores methods of simulating the behaviour of building structures under progressive collapse conditions through alternative models of different levels of structural idealization. Such alternative simulation models have been applied in many previous studies of the problem, but there is insufficient information regarding the degree of reliability and appropriate representation of the actual structural behaviour as the model is simplified by reducing the level of structural idealization. To investigate the problem, the study adopts the alternative load path method through the well-established concept of notional column removal. The study focuses on the interaction of the directly affected structural members with their neighboring structural components. The results demonstrate the significant influence of this parameter on the overall structural response under progressive collapse conditions. Most importantly, it is demonstrated that this parameter depends on many factors and is difficult to quantify without explicitly analyzing the behaviour of the surrounding structure. As a conclusion, a local failure that can potentially lead to progressive collapse should be analyzed in the context of the global behaviour of the structure. Alternatively, effective methods for simulating the boundary conditions of individual structural members should be studied and developed to enable the application of reduced analysis models.