Effects of specimen longitudinal dimensions on the compressive mechanical properties of timber: Experimental investigation and quantitative analysis

Wood is recognized as a sustainable, low-carbon construction material, yet a comprehensive theoretical model explaining length-dependent size effects on its longitudinal compressive properties is lacking. Although previous studies have highlighted the importance of longitudinal compressive performance, the impact of wood species variation on this property has not been fully explored. Critically, quantitative relationships between longitudinal compressive behavior and specimen length across various species remain undefined, hindering the application of laboratory results to engineering practice. This study addresses existing knowledge gaps by examining three wood species: Pinus sylvestris var. mongolica (conifer), Elm (broadleaved) and Paulownia (broadleaved). Specimens with varying lengths were subjected to systematic longitudinal compression tests. The analysis focused on compression characteristics across different sizes and a thorough investigation of failure mechanisms. Load-displacement and stress-strain curves were used to elucidate the relationship between mechanical properties and specimen size. Longitudinal compressive strength size effect coefficients were determined using Weibull's weakest-link theory, while finite element simulations modeled axial compression behavior based on experimental data. Key findings include: (1) A significant negative correlation between longitudinal compressive strength and specimen length, with size effect coefficients of 0.08 for Pinus sylvestris var. mongolica, 0.16 for elm, and 0.18 for paulownia. (2) The elastic modulus decreased with increasing specimen length, whereas Poisson's ratio remained unaffected by size variations. (3) Finite element models accurately replicated axial compression failure patterns but required strength reduction factors to account for length-dependent size effects. The proposed model for length-dependent size effect coefficients offers a new framework for characterizing the multiscale mechanical behavior of wood. • Height-based size effect coefficients established for compressive strength of pine, elm, and paulownia woods. • A robust strength conversion model validated by experiment and FE simulation bridges lab tests to real-world engineering. • A practical methodology converts compressive strength across specimen sizes, informing code and restoration practices. • Validating the conversion model with large-scale test specimens, which is critical for practical engineering use.