AbstractThis paper investigates the robustness of a 6‐storey corner‐supported Modular Steel Building (MSB) under notional ground floor corner column removal (i.e. alternate path method). The robustness assessment investigates the following structural effects that were frequently ignored for the sake of simplicity in existing numerical modelling approaches: (1) semi‐rigidity in the beam‐to‐column connections, and (2) initial out‐of‐straightness (geometric imperfection) in the compression members. Commonly, the welded connections between the beams and square hollow section columns are modelled as fully rigid, however, this may overestimate the actual robustness of MSBs as fully rigid connections often have a higher energy absorption capacity. Similarly, modelling a perfectly straight column could overestimate the actual robustness of MSBs. Comparing the model with semi‐rigid connections to that with fully rigid connections, an additional 30% vertical displacement was observed at the point of removal. However, geometric imperfections in the columns and diagonal braces did not cause any increase in building displacement/drift after removal. This highlights the importance of modelling the semi‐rigidity in the connections especially when the connections involve joining hollow sections.