Ductile Timber Beam to Steel Column Connection with Replaceable Fuses

Despite its low energy and carbon footprint, timber has inherent disadvantages like limited strength and stiffness, as well as low damping and ductility in tension. To alleviate these issues, hybridizing timber members/joints with more ductile materials such as steel has been explored. Among different methods for developing moment-resisting connections, the application of glued-in rods with and without post-tensioning tendons has received a lot of attention in the past two decades. However, these solutions come with additional costs and drawbacks such as the need to reinforce the timber column (joint zone) and replace damaged structural components, e.g., beams and columns. This is primarily due to the timber's (column) low strength perpendicular to the grain direction and the permanent nature of the glued-in rods used as energy dissipators. A replaceable hybrid timber beam-to-steel column connection that takes advantage of high-strength (8.8 Grade) glued-in rods and replaceable mild steel (4.6 Grade) fuses is introduced. The timber beams were Radiata Pine GL17, with 3 and 2 layers of glued-in steel rods, and the steel columns used were stiffened 250UC72.9. Four full-scale hybrid timber beam-to-steel column subassemblies were built and subjected to monotonic and cyclic loads. The subassemblies were tested up to three times, in each direction, after fuse replacement, to determine the reusability of the hybrid connections and loss of strength and stiffness after each use. The subassemblies exhibited failure due to the yielding and fracturing of the mild steel fuses, with no damage observed in the timber, accompanied by moderate ductility and stable energy dissipation capacity.