Volume 20, Issue 6 (November 1992)
Superposition Theory Applied to Nail/Glue Joints in Wood: Part II—Stiffness Behavior
A model based on concepts involving nonlinear superposition of nail and glue joint characteristics was examined to predict the load-slip (P-Δ) behavior of nail joints with elastomeric construction adhesives (nail/glue) in wood subjected to lateral loading. Four combinations of two wood species (lodgepole pine and hard maple) and two nail sizes (6d and 8d) were explored. One brand of commercially-available elastomeric construction adhesive was used. One-hundred-sixty-nine nail, glue, and nail/glue joints were tested to evaluate the P-Δ curve from the origin to 0.08125 in. (2.1 mm) slip. Theoretical predictions based on nail and glue joint stiffness were compared with experimental data from nail/glue joint tests. The results showed that the presence of glue used in conjunction with nails proved to substantially increase joint stiffness. Increases in joint stiffness from 25 to 100% per square inch (645 mm2) of bonded surface over the stiffness of joints without glue were realized. The superposition model proved to be a reasonable predictor of nail/glue joint stiffness at levels of slip not exceeding 0.03 in. (0.762 mm). For slip levels greater than 0.03 in., superposition consistently underpredicted (conservatively) joint stiffness for all four combinations of nail size and wood species studied. Therefore, superposition has been shown to be an accurate predictor of joint stiffness in the range of slip values from which allowable loads are determined in the allowable stress and draft reliability-based design codes.