Experimental and Analytical Study on Fire Resistance Performance of Mid-High Rise Modular Rectangular Steel Tube Columns Using a 3 h Fireproof Cladding Method

To ensure the fire resistance performance of modular construction, various methods such as spray-applied fire resistive material (SFRM), intumescent paint, and gypsum board can be used. Rectangular steel tube columns, commonly used in modular construction units, are fireproofed by attaching fireproofing boards. The required thickness of the fireproof board increases with the duration of fire exposure, which in turn increases the self-weight. To address these issues, this study proposes two conditions for improving fire resistance: (1) SFRM application, and (2) mortar filling or finishing on both the inside and outside of small-sized rectangular steel tube columns in modular units. Experimental and analytical approaches were employed to evaluate the behavior of these columns over time under fire exposure and to analyze the required sheathing thickness according to the fire-resistant sheathing method. The results indicated that mortar filling suppressed the temperature rise due to its thermal storage effect. The application of fireproofing spray after mortar filling extended the fire resistance time by approximately 143 to 146% compared to the unfilled specimen. It was also found that SFRM provided a 149% higher fireproofing performance compared to finishing mortar.