Elastic stability of unbraced plate-type modular steel frames with semi-rigid corner connections

Assembled modular buildings can improve on-site construction efficiency and reduce environmental pollution and resource waste. As an innovative structural form, a steel building with semi-rigid corner connections composed of plate modular units to form a double-beam and multi-column structure is proposed. This self-load-bearing modular plate-type structure, without an additional internal lateral resistance system forms a low multi-story building with fewer than six stories. To calculate the elastic stability of this structure, based on the assumptions of equal story drifts (case 1) and unequal story drifts (case 2), two different three-column sub-assemblage models were established using effective-length methods to calculate the effective lengths of columns (K-factors). According to the theoretical models, the governing equations and simplified formulas for case 1 and case 2 were obtained, respectively. The governing equations of Li et al.(2018), cases 1 and 2 and the finite element model (FEM) were adopted to analyze the influencing factors of the K-factors. The results showed that the governing equation and simplified formulas in case 2 possess a higher accuracy compared with that reported in existing literature. The variation trends of the curves in case 2 were completely consistent with those evaluated by FEM, and the errors between them were small.