Experimental testing on the creep behavior of laminated veneer lumber (LVL) under various compression directions

As an engineered wood product (EWP), laminated veneer lumber (LVL) exhibits two inherent wood characteristics: anisotropic mechanical properties and time-dependent creep behavior. Understanding the creep behavior of LVL is crucial for its applications. This paper presents an experimental investigation into the creep behavior of LVL under three compression directions: compression parallel to grain, edgewise compression perpendicular to grain, and flatwise compression perpendicular to grain. Short-term compression tests were first conducted on LVL along the three directions, providing basic data to determine the stress magnitude for long-term compression tests. The long-term tests were performed for 220 days in an uncontrolled indoor environment, considering the three compression directions and different stress levels. The long-term behavior of the LVL specimens was assessed across time-dependent moisture contents, strain, and creep. Creep models were then calibrated against the experimental data, further characterizing the compressive creep behavior of LVL. The experimental results show that the moisture content and environmental strain exhibited a strong but slightly lagged correlation with relative humidity. The maximum creep coefficients at 77.9 % average humidity were 1.87–3.25 times as large as those at 61.7 % humidity. Creep effect in LVL under parallel-to-grain compression was significantly lower than that subjected to compression perpendicular to grain. The flatwise-compression-perpendicular-to-grain LVL exhibited larger creep coefficients compared to that in edgewise compression configuration. The low-stress LVL had lower creep coefficients compared to that in high-stress scenarios.