Improvement in fire resistance of glulam beams containing modified laminae by thermal treatment, inorganic impregnation and compression in the fire-side tension zone

Fast-growing wood species are unsuitable for direct use in load-bearing structures due to their loose fiber structure, low mechanical strength, and inadequate combustion performance. Traditional impregnation using low-molecular-weight resin may enhance certain characteristics but also poses environmental pollution risks. This study explores an alternative approach: subjecting Chinese fir lumbers to thermal treatment, impregnation with an inorganic solution, compression, and utilization as exposed side laminas for glulam beams. The fire performance of full-scale beams was evaluated under three-side fire exposure conditions. Results revealed that addressing the mechanical deficiencies of thermally treated wood could be achieved through 2.0 mol/L inorganic solution impregnation combined with a 20% compression ratio. The modifier weight percent gains in specimens after thermal treatment increased by 24.8% under identical conditions. Composite modification notably enhanced both mechanical and combustion properties, manifesting promising flame-retardant effects. Building upon these findings, fire-resistant laminas were created and applied to the tensile zone of the glulam beam to investigate residual bearing capacity post three-side fire exposure. After 60 min, the modified laminas-containing beam in the fire-exposed tension zone showed a 31.4% increase in residual bearing capacity over the untreated beam. This study underscores that the combined modification methods are not only cost-effective and environmentally friendly but also establish a vital theoretical foundation for safeguarding the structural safety of rapidly cultivated fast-growing wood in fire scenarios.