Robustness interpretation of intact and damaged framed structures

This paper explores the concept of structural robustness in buildings, focusing on progressive collapse—a failure mechanism where localised damage leads to widespread structural failure. Resilient structures are expected to perform adequately under extraordinary events such as explosions, impacts, or earthquakes, yet defining ‘adequate’ performance remains challenging. Design codes often emphasise the disproportion between accidental events and their consequences, underscoring the need for a deeper understanding of collapse mechanisms. Progressive collapse involves the sequential failure of structural elements, triggering dynamic load redistribution and potential catastrophic outcomes. While strengthening all components improves damage tolerance, it is economically impractical. Strategies such as redundancy and compartmentalisation are commonly adopted, although their effectiveness is debated. Anti-seismic design contributes to robustness but is not optimal for collapse resistance. This study introduces a simulation method based on the discrete-element method to analyse collapse mechanisms and derive simplified formulas for calculating collapse loads and robustness. The methodology extends the P-Δ method to both intact and damaged structures and is applied to two-dimensional reinforced concrete frames subjected to sudden removal of beams and columns. Results highlight the importance of ductility and load redistribution in preventing fragile failure and improving structural resilience.