Long-term creep behaviour of cross-laminated bamboo and timber under axial compression: Experimental and probabilistic modelling

Creep in Cross-Laminated Timber (CLT) and Cross-Laminated Bamboo-Timber (CLBT) panels governs long-term serviceability and reliability, yet its coupling with hygrothermal actions remains insufficiently quantified. This study combines experiments and modelling to characterize the compressive creep behaviour of three panel types: conventional CLT, CLBT with thick-strip GluBam (CLBT1), and CLBT with thin-strip GluBam (CLBT2). Short-term compression tests established baseline mechanical properties, followed by 180-day sustained-loading tests under controlled stress levels. Ambient Temperature and Relative Humidity were continuously monitored to assess mechano-sorptive contributions to time-dependent strains. Both CLBT variants exhibited higher load-bearing capacity and greater resistance to retarded viscoelastic deformation than CLT, but showed increased sensitivity to humidity-driven effects. Deterministic viscoelastic models and probabilistic formulations incorporating hygrothermal covariates were developed and calibrated against the full experimental dataset. The probabilistic models reproduced the dispersion of creep strains more accurately and yielded realistic long-term creep coefficients with predictive intervals, enabling risk-informed assessment. A finite element application demonstrates how the proposed framework can be integrated into structural analyses to predict the long-term response of bio-based laminated components. The results demonstrate that accurate prediction of creep in laminated bamboo-timber systems requires explicit treatment of hygrothermal effects and material variability. The proposed methodology supports performance-based design and the broader adoption of sustainable, bio-based laminated construction products.