Stress analysis of a pinned wood joint by grey-field photoelasticity

Pinned (bolted) joints/connections are a widely used, but difficult to analyze, component. Their bolt/hole interface stresses are typically unknown a priori. Structural failures often initiate at connections and their contact stresses can be the “Achilles’ heel”. Although such connections are extremely prevalent in wood structures, ability to determine the individual stresses in mechanical wood joints is aggravated by the material’s orthotropy. Solutions to such non-linear problems that account for finite geometry, pin/hole friction and clearance are non-trivial. Many mechanical-joint analyses ignore friction for simplicity, but some contact friction is virtually always present. By applying a thin birefringent coating to the wood, the individual stresses and strains in the coating (and hence in the wood) are determined by synergizing grey-field photoelasticity, a stress function and boundary information. Full-field individual stresses are obtained in the wood, including at the contact boundary. Predicted strength based on the determined stresses is compatible with the connection failure.