Structural and Fire Performance of Cold-Formed Steel Columns Subjected to Cavity Fire in Modular Buildings

Fire safety is one of the critical concerns for the design and construction of modular structures. The lack of understanding of cavity fire spread in modular construction could create variations in the fire performance of structural members. This study aimed to assess the impact of cavity fire spread in modular buildings initiated by a room fire using validated fire dynamics and structural numerical models. A comprehensive parametric study was conducted to identify critical thermal conditions affecting adjacent structural members under plausible cavity fire scenarios. The identified critical cavity fire thermal conditions were used to examine the structural performance of cold-formed steel intermediate column specimens while varying geometric configurations, material properties, and boundary conditions. The results highlighted two distinct phases of restrained thermal expansion and lateral deformations under material yielding and buckling, resulting in the loss of structural integrity. The restrained thermal expansion significantly increased axial/restraint forces, reaching up to 155% of the initial load. This behavior decreased axial load capacity by 2.4% to 35% of the ambient capacity. Further, the study identifies a requirement for designing the intermediate columns and the connected intermodular connections for increased design action equivalent to 56% of the service load.