Experimental investigation of the splitting behavior of tensile-bolted joints in timber structures

Tensile-bolted joints in timber structures, such as beam–column and column–base connections, can exhibit splitting failure—a brittle mode where timber beneath the washer cracks due to lateral tensile stress. This failure mechanism remains insufficiently understood, and no established evaluation method exists. This study experimentally investigates the splitting failure and proposes a new evaluation method along with a reinforcement technique using self-tapping screws. The tensile tests revealed that the splitting failure, typically characterized by three cracks under the washer, occurred in most specimens. Screw reinforcement effectively suppressed central cracks and increased load-bearing capacity, shifting the failure mode from splitting to shearing. Key influencing factors include washer area, timber length under the washer, and minimum edge distance. Specimens with larger washers, shorter timber lengths, and smaller edge distances were more susceptible to splitting. A central crack (Mode I) may initiate and lead to edge cracking (Mode II). The proposed evaluation method assumes that the strain energy stored in timber equals the product of crack area and fracture toughness. This approach, incorporating edge distance effects, showed strong correlation (R² = 0.7) between calculated and experimental values, enabling safe prediction of the splitting failure capacity. • Splitting at the column butt end is caused by lateral tensile stress near bolt holes. • Washer area, timber length under washer, and edge distance affect load capacity. • Proposed method shows strong correlation (R² = 0.7) with experimental results.