Fragility-based robustness assessment of steel modular building systems: Connection and building height

Robustness is an important factor in determining structures' ability to withstand accidental extreme events. However, assessment of structural safety typically does not take probabilistic factors into account, which results in disregarding uncertainties even when extreme conditions are considered. The are limited studies in the literature, highlighting the need for fragility risk assessment of the impact of inter-module connections (IMCs) and building height of steel modular building systems (MBSs) subjected to progressive collapse scenario. This paper investigates the robustness of steel modular building systems (MBSs) under progressive collapse scenarios that vary in connection type and building height. A nonlinear static pushdown analysis was carried out on 5-, 10-, and 15-story MBSs with bolted and post-tensioned rod IMCs, focusing on column removal during the analysis using OpenSees software. Results showed that taller structures are more robust due to their increased redundancy while they exhibit greater resistance to collapse than lower structures. Fragility analysis can be utilised to predict the probability of progressive collapse in the case of local damage. With the derived fragility functions, the probability of progressive collapse is quantified for different IMCs and building heights. By optimising connection types and building configurations, the results provide new insights into designing safer modular steel buildings.