Fire performance of superabsorbent polymers protecting cold-formed steel walls with high load ratios

Abstract

Superabsorbent polymers (SAPs) have great potential in the fire protection of steel structures due to their high absorbency and water-holding capacity. In this paper, SAP is applied to the full-scale cold-formed steel (CFS) wall studs to investigation the fire performance of the CFS walls. An axial compression experiment of CFS wall specimen at ambient temperature and three experiments at elevated temperature were conducted. Meanwhile, considering the effect of thermal expansion load, the actual load of CFS walls may increase significantly under fire condition. Hence, the load ratio of the specimens was 0.85 in the fire experiments. The specimens use an autoclaved lightweight concrete (ALC) board and calcium-silicate (CS) board as the face and base layers of sheathings, respectively. The effect of SAP insulation material, high load ratios and thermal expansion load on the fire resistance of walls are discussed. The results indicate that SAP insulation materials can improve the structural and insulation performance of CFS walls under fire exposure. This is because the dehydration and heat absorption process of the SAP insulation material removes the heat inside the wall cavity, maintaining the maximum temperature of the wall studs below 140 °C. Hence, the fire resistance time (FRT) is extended by 41 min after using the SAP insulation material. In addition, neither a high load ratio nor SAP insulation material changes the failure mode of the wall studs. For the present specimens at ambient and elevated temperature, local buckling was identified on the whole section of stud ends. However, the SAP insulation material will change the fire-induced failure position of wall studs. Specimen W3 with SAP insulation material fails at the top of the studs. Furthermore, a thermal expansion load will significantly speed up the fire-induced structural failure of CFS walls with a high load ratio. The FRT of specimen W4 decreases by 79 min after considering the effect of thermal expansion load.