Fire performance and post-fire axial capacity of composite columns composed of parallel strand bamboo and laminated bamboo lumber

Parallel strand bamboo (PSB)-laminated bamboo lumber (LBL) composite columns were tested under ISO 834 standard fire exposure and post-fire axial compression to investigate their charring behavior and residual axial capacity. Results showed that charring depth increased bilinearly with exposure time, with nominal rates of 0.42 mm/min for the outer PSB layer and 0.86 mm/min for the inner LBL core. An area-equivalent charring-depth model was developed to account for corner rounding and nonuniform cross-sectional loss, yielding depths approximately 1.04 times the measured values. As fire exposure increased, failure shifted from local crushing under the combined action of the outer PSB layer and LBL core to coupled crushing–lateral buckling dominated by the residual LBL cross-section. Over 0–105 min, the post-fire slenderness ratio increased from 20.78 to 59.95, residual axial capacity decreased by 93.6% from 2620.12 to 166.71 kN, and ultimate axial displacement decreased from 25.60 to 9.05 mm. A post-fire residual axial capacity assessment method was also developed by combining the effective residual cross-section method with stability coefficients from timber design codes. Zonal design recommendations based on the post-fire slenderness ratio were proposed: GB 50005–2017 is recommended when λ ≤ 38, whereas EN 1995–1–1 is recommended when λ > 38. The findings provide guidance for the fire resistance design and post-fire safety assessment of PSB–LBL composite columns.