FINITE-ELEMENT ANALYSIS OF WOOD JOINTS

A finite-element program to evaluate the stresses found in finger-join ted lumber subjected to uniaxial tension has been developed and verifi ed. This program exploits a unique contact element useful in modeling a thin, isotropic boundary (glueline) between two anisotropic adherent s, A parameter study was conducted using the aforementioned model to e valuate the influences of certain key finger-joint properties on the s tress distributions induced in the lumber. Three joint geometries (ste p, scarf, and finger), three combinations of adherents (isotropic mate rials on both sides, orthotropic materials on both sides, and an isotr opic material on one side and an orthotropic material on the other), a nd two glueline thicknesses (0.01 and 0.001 times the joint length) we re studied. Glueline thickness is directly related to glueline stiffne ss, which is known to influence the stresses in the glueline, and cons equently, in the adherents. The results showed that maximum adherent s tresses were developed at the interface with the glueline. For isotrop ic materials with constant ratios of the elastic parameters between ad herent and adhesive (e.g., E(adherent)/E(adhesive)), stress distributi ons are identical, as expected. Stiff gluelines, relative to the adher ent stiffness, tend to increase stress concentrations at the edges of all three types of joints. In step joints, the large fingertip width w as the most influential factor in accounting for the high stress conce ntrations. In contrast to the step joint, stress concentrations in sca rf joints were highly sensitive to differences in material properties between adherents. It was concluded in this study that the development of a finger-joint manufacturing process that produces fingertips of n ear-zero width is desirable.