Influence of Bolt Threads on the Net Section Tensile Rupture Strength of Single-Bolt Connections in Pultruded Structures

In this article, we examine the influence of bolt threads on the tensile rupture strength of the net section corresponding to single-bolt double-lap connections in pultruded materials made of dicyclopentadiene-based unsaturated polyester resin reinforced with E-glass fibers in the forms of roving, continuous-strand mats and triaxial fabrics that incorporate chopped strand mats and plies oriented in the ${45}^{\circ }$, ${90}^{\circ }$, and ${-45}^{\circ }$ directions with respect to the longitudinal direction (i.e., roving direction). Thirty-six single-bolt double-lap connection tests were carried out on plates in which the bolt-hole diameter to plate width ratios were 0.5, 0.6, and 0.75. All these connection tests incorporated finger-tight A307 zinc-coated bolts fully threaded in one case and partially threaded in another case. The results from these experiments revealed that bolt threads in contact with the bolt-hole surface influence the tensile resistance of the net section. This influence is evident as the bolt-hole diameter to plate width ratio decreases. Analysis of our findings highlights a notable discrepancy: current design guidelines in both the United States and Europe can considerably underestimate the net section tensile rupture strength of single-bolt connections made from pultruded materials with an offaxis reinforcement scheme. Recommended design guidelines that can be adopted by practicing engineers are proposed.