Characterization and strength modeling of parallel-strand lumber

The current work expands on a three-dimensional, non-linear, stochastic finite-element model previously developed by the author. The model predicts a materially non-linear stress-strain curve for tension, compression and bending scenarios. It is based on the non-linear constitutive properties of the individual strands, which are characterized within the framework of orthotropic elastoplasticity. The constitutive model employs the Tsai-Wu yield criterion and an associated flow rule. Failure is marked by an upper bound surface whereupon either perfect plasticity or an abrupt loss of strength and stiffness ensues. The finite element code has also extended the capacity to perform Monte Carlo simulations. The model was further developed to predict the mechanical behavior of parallel-strand lumber (PSL) made from Douglas fir. The physical features of PSL were measured and incorporated into the finite element model and the mechanical behavior of PSL was simulated. Statistical distributions for macroporosity and grain angle variation in PSL were created and included in the model as individual random variables in a stochastic and probabilistic manner. Constitutive curves for PSL were numerically generated under tensile, compressive and three-point bending conditions. Comparison of the computed and experimental data sets demonstrates the validity of the proposed modeling technique.