Composite behavior of laminated strand lumber

The mechanical properties of laminated strand lumber are dependent on the orientation of strands and on the variability of strand alignment in the production process. A model is proposed to predict the in-plane properties and their statistical distributions to allow manufacturers to set target reliability levels for their products. The model is based on the theory of mechanics of composites and assumes homogeneity in each panel layer to allow for multiple-layer panels to be simulated. To verify the model, five types of panels are fabricated using aspen strands with the following stacking sequences: (a) fully-oriented (0° throughout); (b) fully-random (R throughout); (c) random core/oriented surfaces (0°/R/R/0°); (d) random surfaces/oriented core (R/0°/0°/R); and (e) eight oriented layers (0°/+45°/−45°/0°/0°/−45°/+45°/0°). In-plane elastic moduli and ultimate strengths (in tension, compression, and shear) are determined for each panel type. Model predictions match well with experimental results. Properties are shown to be dependent on the degree of strand alignment in each panel type. Using the first-order reliability method, statistical distributions on the properties were predicted and found to compare well with experimental results. A method is proposed for dealing with misalignment of strands based on the von Mises distribution of strand angles to assist manufacturers with production process optimization.